- Email: [email protected]
graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries
Journal of Alloys and Compounds xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries Ruizi Li a, b, Jianfeng Huang a, *, Jiawen Ren b, Liyun Cao a, Jiayin Li a, Winbin Li c, Guoxing Lu b, Aimin Yu b, ** a School of Materials Science & Engineering, Xi’an Key Laboratory of Green Processing for Ceramic materials, Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science and Technology, Xi’an, 710021, China b Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia c Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an, Shaanxi, 710048, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 September 2019 Received in revised form 28 October 2019 Accepted 28 October 2019 Available online xxx
Hard carbon becomes a candidate for anode materials due to its rich resources and abundant lithium storage sites. However, amorphous carbon with poor stability and electronic conductivity limits its electrochemical performance. In response, this work synthesizes a sandwich-like porous hard carbon/ graphene hybrid (HC/G) with graphene sandwiching the hard carbon via a KOH-assisted one-step pyrolysis process from rapeseed shuck. The highly ordered graphene layers constitute conductive multidimensional paths for fast electronic transport and supply sufficient electrons for redox reactions. Moreover, the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the whole structure. The porous hard carbon with numerous defects and C]O groups could provide more adsorption sites and redox reactions for lithium storage. When serving as anode material, HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and exhibits a superior rate performance that of 381 and 308 mAhg1 even at a higher rate of 2000 and 5000 mAg1, respectively. This work sheds a light on the high-value use of waste rapeseed shuck for eco-friendly and low cost lithium-ion batteries anode material. © 2019 Elsevier B.V. All rights reserved.
Keywords: Rapeseed shuck Hard carbon/graphene hybrid Sandwich-like structure Lithium-ion batteries Anode
1. Introduction Owing to the unmatchable combination of long cycling life, high energy density, and no memory effect, lithium-ion batteries (LIBs) have emerged as the first choice for portable electronics, power tools, and electric vehicles since they were successfully commercialized by SONY in 1990s [1e3]. LIBs also received great interests as potential candidates for intermittent renewable energy storage from sources like hydro, solar, and wind, which could mitigate environmental hazards from fossil fuels [4,5]. At this stage, the performance and cost of LIBs are primarily restricted by the electrode materials [6]. Thus, the development of electrode materials with high performance and low cost has been a significant strategy to further promote the LIBs.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Huang), [email protected] (A. Yu).
In the past decades, graphite is usually used as the anode materials for commercial LIBs and the mechanism of lithium-ion (Liþ) storage is the intercalation between long-range ordered graphitic layers. However, since the low theoretical capacity of 372.1 mAh g1, graphite-based LIBs cannot offer enough energy for electric vehicles [7,8]. It is necessary to synthesis a superior carbon material to replace graphite for efficient Liþ storage. Biomass derived hard carbon with the advantages of low cost, environmental friendliness, and wide abundance has become a candidate for anode material [9e15]. Amorphous hard carbon consists mainly of disordered turbostratic nanodomains, which are graphene layers with many defects randomly arranged in disorder [16e21]. This carbon structure usually offers the numerous pores and broad parallel carbon layers for Liþ adsorption and intercalation, thus giving a higher capacity [9,12,22e24]. However, the disordered amorphous hard carbon derived from biomass has low electronic conductivity and constrained electrochemical stability, causing a poor cycling stability and rate performance [8]. Accordingly, introducing graphite domains into hard carbon structure is a valid way to
https://doi.org/10.1016/j.jallcom.2019.152849 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
2
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
enhance electronic conductivity [8,21]. Graphene, a novel class of two-dimensional carbon material, has attracted a great deal of attention since its excellent electrical conductivity, outstanding chemical stability and mechanical flexibility [25e28]. Graphene has been widely used in constructing the conducting networks for LIBs anode material because of the high electronic conductivity with the aim to enhance the rate capability and cycling performance [29e31]. Zhang and co-workers fabricated a mixture of hard carbon with graphene for Li-storage by the pyrolysis of hard carbon and graphene oxide, which exhibits a capacity of 311 mAhg1 after 100 cycles at 80 mAg1 [32]. Disordered hard carbon/graphene hybrid as the anode materials for sodiumion storage was also anode fabricated by the hydrothermal treatment of glucose with graphene oxide and subsequent calcination, achieving a capacity of 300 mAhg1 at 50 mAg1 after 100 cycles [33]. Nevertheless, these hybrids prepared by physically mixing hard carbon and graphene oxide (or graphene) exhibited insatiable cycling and rate performances because of the non-stable structure resulting in the detachment of hard carbon and graphene during the long term charging/discharging process. In this article, to obtain an advanced carbon anode material with both excellent electrical conductivity and abundant storage sites for Liþ, we validated a KOH-assisted one-step pyrolysis process to prepare a sandwich-like porous hard carbon/graphene with porous hard carbon sandwiched in graphene. Benefiting from the stable sandwich-like porous structure and superior synergistic effect between hard carbon and graphene, the obtained HC/G exhibits superior cycling stability and rate performance. HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and displays an outstanding rate performance that of 377 and 313 mAhg1 even at a higher rate of 2000 and 5000 mAg1.
SUPRA X-ray Photoelectron Spectrometer with monochromatic Al Ka radiation at 15 kV. The Fourier transform infrared (FTIR) spectrum was collected on a TENSOR 27 FTIR spectrometer using KBr pellets. The specific surface area, total pore volume and pore size distribution were evaluated via the N2 adsorption/desorption isotherms with ASAP2460 specific surface area instrument at 77 K. The specific surface area was obtained from the Brunauer-Emett-Teller formula. The total pore volume was calculated by determining the amount of the adsorbed nitrogen at a relative pressure of 0.99. The pore size distribution was observed by the Barrett-Joyner-Halenda method. 2.3. Electrochemical test
2. Experimental
The electrochemical performances were conducted on coin cells (CR2032), which were assembled in an argon filled glove box (H2O, O2 < 0.1 ppm) by using lithium metal foil as the counter electrode, and glass fiber as the separators. The electrolyte was a solution of 1 M LiPF6 in a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC), with a volume ratio of EC: EMC: DMC ¼ 1:1:1. Working electrodes were fabricated by mixing the active carbon material, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) binder in a weight ratio of 8:1:1. The obtained slurry was coated onto the surface of a Cu foils current collector, followed by drying in a vacuum oven at 90 C for 10 h. The galvanostatic discharge/charge tests were measured by a Neware battery tester at various current densities over a potential range of 0.01e3.00 V (vs. Li/Liþ). Cyclic voltammetry (CV) with the voltage ranging from 0.01 to 3.00 V (vs. Li/Liþ) at 0.1 mV s1, and electrochemical impedance spectroscopy (EIS) with an AC perturbation signal of 5 mV in the frequency range between 100 kHz and 0.01 Hz were carried out using an CHI660E electrochemical workstation. All the electrochemical measurements were conducted at room temperature.
2.1. Material synthesis
3. Results and discussion
Rapeseed shuck (collected after seed harvest from suburb farmlands of Shaanxi) was firstly pulverized into powder. Then, the powder was mixed and grounded thoroughly with KOH in a weight ratio of 1:3. Afterward, the mixture was pyrolyzed at 700 C or 1000 C with argon flow of 100 sccm/min, and held there for 2 h, and the heating rate was 5 C/min. After cooling, the obtained black powder was thoroughly immersed into 2 M HCl solutions and kept for 2 h to remove the impurities, followed by washing with the distilled water and absolute ethanol until pH close to 7. The final materials were dried at 60 C for 8 h. The rapeseed shuck derived carbon materials pyrolyzed at 700 and 1000 C were respectively marked as HC and HC/G. For comparison, graphene (GN) was synthesized from natural flake graphite powder as reported elsewhere [34].
3.1. Structure characterization
2.2. Materials characterization The morphological characteristics were investigated with a Hitachi S-4800 field-emission scanning electron microscopy (SEM). The transmission electron microscopy (TEM) images were characterized from a JEM-2100 transmission electron microscope and high-resolution transmission electron microscope (HRTEM) was performed on JEOL-2011 at 200 kV. X-ray diffraction (XRD) patterns of all samples were recorded with a Rigaku D/MAX2200PC diffraction instrument with Cu Ka radiation (l ¼ 0.15 418 nm) over the 2q range of 10e70 . Raman spectra were obtained using a Renishaw-invia confocal microprobe Raman system (632.8 nm). Xray Photoelectron Spectrum (XPS) was performed using an AXIS
Fig. 1a exhibits a schematic illustration of the synthesis of HC/G derived from rapeseed shuck. The rapeseed shuck was directly pyrolyzed at a high temperature assisted with KOH. In this way, prepared HC/G in a simple manner, and creatively utilized biomass waste. The morphologies of the as-prepared HC and HC/G were characterized by SEM. As displayed in Fig. 1b, the HC prepared at 700 C shows a highly 3D-porous interconnected structure, and there are numerous cavities on the surface, resulting from the interior etching process of KOH. When the pyrolysis temperature rises to 1000 C, the HC/G exhibits the 3D-porous interconnected structure enveloped with cross-linked ultrathin nanosheets (Fig. 1e). These structures can shorten the diffusion path for Liþ, and offer minimum diffusive resistance to transport on an electrode/ electrolyte interface for charge-transfer reaction [35]. Further, TEM (Fig. 1c) and HRTEM images (Fig. 1d) display the amorphous structure of HC with numerous pores. As for HC/G, TEM (Fig. 1f) presents graphene winkled lamellar morphology with porous hard carbon in the middle like a sandwich structure. And many sharp textures on wrinkled lamellar can be seen, which correspond to the vertical graphene structure and indicate the high crystal quality [36]. HRTEM image (Fig. 1g) of HC/G shows a sandwich-like porous structure with the graphene sandwiching the hard carbon. It is well-established that the graphene with graphite microcrystallites could promote electronic transmission and provide sufficient electrons for redox reactions. Moreover, the sandwiching graphene layers provide mechanical support, which effectively adapts
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
3
Fig. 1. (a) Schematic illustration of the synthesis of HC/G derived from rapeseed shuck. SEM images of the (b) HC and (e) HC/G. TEM of (c) HC and (f) HC/G. HRTEM images of (d) HC, and (g) HC/G. (Red area, graphene layer; yellow area, hard carbon). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
volume change to stabilize the whole structure. The crystalline structures of HC and HC/G were firstly characterized by XRD patterns and Raman spectra. In Fig. 2a, both of the
samples exhibit a broad peak at ~23 , corresponding to the (002) reflection of graphite, which reveals the typical amorphous structure of random packing at c axis. Notably, (100) peak at ~ 43 can be
Fig. 2. (a) XRD patterns, (b) Raman spectra, (c) Survey XPS spectra, (d) FTIR spectra, (e) N2 adsorption-desorption isotherms, and (f) Pore size distribution of HC/G, and HC.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
4
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
obviously observed in the HC/G, indicating it more ordered graphitic structures relative to that of HC. The interlayer spacing (d002) values of the samples were calculated by Bragg’s equation based on the (002) peak. The smaller interlayer distance of HC/G (0.359 nm) than HC (0.384 nm) indicates that constituting stacks of HC/G contains more organized graphene layers [37]. From the Raman spectra in Fig. 2b, it can be observed that both samples exhibit two standard peaks at ~1345 and 1580 cm1, corresponding to the D peak (the defective graphitic or disordered carbon peak) and G peak (the crystalline graphite peak), respectively. The G peak comes from the in-plane E2g vibration mode of sp2 carbon, while the D peak is caused by A1g mode breathing vibrations of hexagonal sp2 carbon, and becomes Raman activity after adjacent sp2 carbon is transformed into sp3 hybrid [38]. In general, the IG/ID integral intensity ratio is used to characterize the average size of the sp2 domains and disorder degree [39]. The calculated IG/ID value of HC/ G is 1.17, very close to GN of 1.22 [26] and higher than 0.81 for HC, further indicating the existence of well-crystallized graphene. It should be noted that there is a strong and narrow 2D peak in HC/G at 2685 cm1. This reveals the existence of few-layer graphene. The 2D peak is associated with the second-order boundary phonon modes of graphene, and the intensity ratio of I2D/IG could be characterized by the number and stacking of graphene layers [40]. The I2D/IG ratio of HC/G is 0.67, this implies that the as-obtained HC/G should be few-layer graphene [41], consistent with the HRTEM. The results of Raman, XRD and TEM confirmed that the HC/G should be a sandwich-like porous hard carbon/graphene hybrid with graphene sandwiching the hard carbon. The presence of hard carbon with many defects in HC/G could provide more adsorption sites for Liþ, while graphene layers serve as a bridge to connect hard carbon, benefiting the transport of electrons. The chemical composition and functional groups of HC/G and HC were further checked by XPS measurement (Fig. 2c). In the survey XPS spectra, two elements including C and O are mainly observed and no N can be detected in all samples. As shown in Table S1, with the pyrolysis temperature rising from 700 to 1000 C, the carbon content gradually increases from 82 to 91 wt%, and the oxygen content evidently decreases from 14 to 7 wt%, suggesting that the oxygen-containing functional groups decreased. The curve fittings of high-resolution C 1s XPS spectra are exhibited in Fig. S3. In detail, three types of carbon including sp2 C, CeO and C]O (OeC]O/C]O) were detected at 284.6, 285.7 and 288.7 eV, respectively. Compared with the HC, CeO and C]O in HC/G are not obvious, which is caused by the rising of pyrolysis temperature. Meanwhile, the sp2 C peak becomes sharper with the temperature increasing, indicating the existence of graphene structure. The residual oxygen atoms can produce some radicals in the surface of HC/G, which would significantly enhance the storage capability of Liþ by forming chemical-bonding [42]. In addition, the surface organic groups of HC and HC/G were checked by FTIR spectra (Fig. 2d). The peak of HC at 3470 cm1 is associated with the stretching vibration of OeH groups, and peeks at 886, 1090, and 1250 cm1 belong to the CeO groups. Moreover, the bands at 1700 cm1 is attributed to the C]O [43]. As for HC/G, these vibrations become weaker and even difficult to be detected, which means that some oxygen-containing groups in HC have been removed, agree well with the XPS observation. Fig. 2e exhibits the N2 adsorption/desorption isotherms of HC and HC/G, while Fig. 2f shows the calculated pore size distributions. At the low pressure, the adsorption curve of HC displays an obvious vertical linear region and a clear hysteresis loop in middle and high region, which belongs to the IV type isotherm. The results suggest that KOH activation produces mesopores and micropores in HC. While, HC/G shows a short vertical linear region of low pressure related to micropore filling, possibly ascribed to the appearance of
graphene structure. Furthermore, the hysteresis loop exhibits a trend of horizontal parallel, which may be related to higher graphitization [44]. This isotherm curve also demonstrates that the HC/G has the obvious hierarchical porous structure at 1000 C. The specific BET surface area and total pore volume of HC are 850.7 m2 g1 and 0.49 cm3 g1, respectively. Owing to formation of the less porous graphene structure from carbon atoms rearrangement, the specific BET surface area and total pore volume of HC/G are reduced significantly to 571.5 m2 g1 and 0.31 cm3 g1. In Fig. 2f, both the HC and HC/G show a broad pore distribution ranging from 1 to 30 nm. After annealing at 1000 C, it is indicated that HC/G has the highest pore volume between 1 and 4 nm, which is well in agreement with SEM and TEM observation. The obtained HC/G with the lower surface area could decrease the formation of solid electrolyte interface (SEI). As can be seen above characterization, HC/G with a stable sandwich-like porous structure has been obtained. The synthesis mechanism of rapeseed shuck derived sandwich-like structure is proposed in Fig. 3. At a low pyrolytic temperature, KOH as a chemical etching agent reacts with the char forming the hard carbon with 3D-porous interconnected structure [45]. When the pyrolysis temperature rising, a large number of active potassium atoms are produced during the reaction (Equation (1)). 6KOH þ 2C / 2K þ 3H2 þ 2K2CO3
(1)
These K atoms intercalate into the outer layers of hard carbon and remove surface functional groups through the strong reducibility. The hard carbon surface produce a lot of dangling bonds. At the pyrolysis temperature of 1000 C, potassium atoms vaporized and speed up the intercalation process as well as the insertion depth. These potassium atoms also repair the carbon dangling bond and promote the rearrangement of carbon atoms into a graphitic structure (catalytic graphitization) and finally exfoliate into fewlayer graphene [46]. Therefore, intercalated and catalyzed by K, the outer layers of hard carbon gradually rearranges and exfoliates into graphene, resulting in HC/G with a stable sandwich-like porous structure. The sandwich-like porous HC/G materials are the desirable anode materials. 3.2. Electrochemical characterization The lithium storage properties and electrochemical performances of the obtained HC/G and HC electrodes were firstly evaluated by CV and charge/discharge profile. Fig. 4a and d shows the CV curves of HC and HC/G electrodes for the first three cycles at a scan rate of 0.1 mV s1 between 0.01 and 3 V. In the first reduction process, the peak at 0.20e0.46 V is associated with the electrolyte decomposition, the SEI layer formation. It disappears in the subsequent scans, suggesting good reversibility in the following cycles [33]. Because of its higher surface area and unstable mechanical support, this peak in HC is obviously stronger than HC/G, indicating a low Coulombic efficiency (CE) in HC. In a lower potential range (0.01e0.20 V), a pair of redox peaks is attributed to Liþ insertion/ extraction in the defects, mesopores, small clusters of hard carbon and the interlayers of graphene [37,47]. In addition, the weak hump of each curve in a wide voltage range from 0.2 V to 1.0 V, implies that the Liþ adsorption/desorption processes occur on the surface of carbon by redox reactions of Liþ with carboxylic groups, carbonyl, and ester (e.g. Liþ þ C]O þ e 4 CeOeLi) [21,48]. Fig. 4b and e presents the first three charge and discharge profiles of HC/G and HC electrodes at 100 mA g1. HC/G electrode has a typical sloping voltage profile with little plateaus, and the capacity contributions mainly focus on 0.2e1.0 V. This indicates that the main Liþ storage mechanism is the surface adsorption/desorption and reversible
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
5
Fig. 3. Schematic diagram displaying the overall evolution of rapeseed shuck to HC/G.
Fig. 4. CV curves of HC/G (a) and HC (d) electrodes from 0.01 V to 3 V at a scan rate of 0.1 mV s1. Galvanostatic charge/discharge profile of HC/G (b) and HC (e) electrodes at 100 mA g1. (c) Cycling performance at a current load of 100 mA g1 and (f) rate performance at variant current loads of HCG, HC and GN electrodes.
redox reactions, which corresponds well to the weak hump in CV curves [48]. In comparison with the Liþ intercalation mechanism, the faster surface adsorption/desorption and redox reactions are beneficial to the little electrode structure change during chargedischarge process and result in the good cycling stability (Fig. 4c) as well as rate performance (Fig. 4f) [11]. Noticeably, closed CV and charge/discharge curves of the second and third cycles indicate outstanding electrochemical reversibility for HC/G after the first cycle. The cycling and rate performances of HC/G, HC and GN electrodes are then evaluated. As shown in Fig. 4c and f, HC/G electrode exhibits the best cycling and rate performances, which are superior
to the most reported hard carbon/graphene electrodes (Fig. S5). When compared with other recently reported carbon electrodes, the HC/G shows better electrochemical performance, especially in rate performance (Table 1). As can be seen, the initial discharge and charge capacities of the HC/G electrode is 731 and 1587 mAhg1 at 100 mAg1, higher than those of HC (433 and 1623 mAhg1) and GN (327 and 961 mAhg1) electrode. The corresponding fist Coulombic efficiency (CE) of HC/G electrode is 46%, whereas that of HC and GN electrode is only 37% and 34%, which is related to the lower surface area for HC/G electrode [11]. The enhanced CE is ascribed to the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
6
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Table 1 Comparison of the performances used HC/G and some other typically carbon materials as anode for lithium-ion batteries. Sample
Reversible capacity (mAg1)
Rate Capacity (mAhg1)
Ref.
Expanded nanographite Banana peel pseudographite Graphitic carbon nanosheets Hollow Carbon Spheres/Reduced Graphene honeycomb-like porous carbon Hierarchical carbon nanocages Nitrogen-Doped Carbon Nanocages Porous carbons derived from microalgae Carbonaceous photonic crystals N-doped organic porous carbon HC/G
661 of 1st cycle and 401 of 1000th cycle at 1Ag-1 790 of 11th cycle and 717 of 300th cycle at 100 mAg1 502 of 1st cycle and 443.7 of 50th cycle at 37 mAg1 755 of 600th cycle at 2 Ag-1 721 of 200th cycle at 1 Ag-1 970 of 10th cycle at 0.1 Age1 450 of 500th cycle at 1 Age1 445 of 1st cycle and 433 of 100th cycle at 37 mAg1 590 of 10th cycle at 50 mAg1 562.89 of 100th cycle at 0.2 Ag-1 731 of 1st cycle and 623 of 500th cycle at 100 mAg1
251 at 5 Ag-1 243 at 5 Ag-1 161.4 at 3.72 Ag-1 606 at 5 Ag-1 203 at 10 Ag-1 229 at 25 Ag-1 135 at 25 Ag-1 355 at 1 Ag-1 113 at 5 Ag-1 226 at 2 Ag-1 308 at 5 Ag-1
[8] [10] [41] [43] [49] [50] [51] [52] [53] [54] This work
whole structure. After 500 cycles, HC/G electrode still delivers an excellent reversible capacity of 623 mAhg1 with the capacity retention (relative to 5th) of 94%, ~1.9 and ~2.2 times higher than that of HC (332 mAhg1) and GN (284 mAhg1) electrode, respectively. The enhanced lithium storage capacity of HC/G is associated with the superior synergistic effect between hard carbon and graphene. Porous hard carbon with numerous defects and C]O groups could provide more adsorption sites and redox reactions for Liþ storage, while the ordered graphene layer could supply sufficient electrons for redox reactions. The excellent cycling stability of HC/G can be associated with the stable sandwich-like structure prepared by an one-step pyrolysis method from rapeseed shuck. Unlike physical mixture of hard carbon and graphene, there is no detachments (or phase separation) occurring for HC/G during the long-term charge/discharge process. Fig. 4f displays that HC/G electrode delivers outstanding reversible capacities of 753, 649, 579, 521, 442, 381, 308, and 228 mAhg1 at the current densities of 50, 100, 200, 500, 1000, 2000, 5000, and 10 000 mAg1, respectively. These values are obviously higher than those of HC (453, 387, 323, 234 173, 91, 40, and 24 mAhg1) and GN (357, 311, 271, 225, 164, 143, 94, and 67 mAhg1) electrode at the same current density. When the rate finally reduced back to 50 mAg1, a reversible capacity of HC/G electrode still can recover to 714 mAhg1, while the reversible capacity of HC and GN electrode is only 393 and 308 mAhg1. The remarkable rate performance of HC/G should can be attributed to the sandwich-like porous structure, which is conducive to high-speed electronic transmission and allows Liþ to fast access the bulk material. From another point of view, these results also suggest that the presence of graphene layer in HC/G guarantees the adequate electrons for surface redox reactions. EIS measurements (Fig. 5a) of the HC/G and HC electrodes were performed to better understand the excellent electrochemical performance. The Rct (charge-transfer resistance, depending on the semicircle diameter) of HC/G electrode (73 U) is obviously smaller than that of HC (126 U), suggesting HC/G has a superior electrical conductivity and a high-speed charge transfer process for redox reactions. In addition, EIS is also an important tools to investigate the diffusion coefficient of Liþ (Dþ Li) in the electrode materials based on the formula in equation (2):
DLiþ ¼
R2 T2 2A2 n4 F4 C2 s2
Z0 ¼ RD þ RL þ su1=2
(2)
(3)
in the formula, R is the gas constant, T is the test absolute temperature, A is the surface area of the working electrode, n is the number of electrons attending the electronic transfer reaction, F is Faraday constant, C is the molar concentration of Liþ, and s is the Warburg impedance factor [48]. From Fig. 5b, s can be derived from
the slope of the line between Z0 and u1/2 through equation (3). The calculation shows that the s value of HC/G is smaller, reflecting a larger Dþ Li than HC. Thereby, the highly ordered graphene in HC/G can be used as conductive multi-dimensional paths to connect hard carbon, effectively facilitating the electron transfer and Liþ diffusion kinetics. To obtain an in-depth understanding of the superior rate performance and long-time cycling stability of HC/G electrode, the lithium storage mechanisms were studied by CV curves at different scan rates from 0.1 to 1.0 mVs1 (Fig. 5c). The capacities of the carbon anode materials can be divided into the diffusion-controlled capacity (Liþ insertion/extraction in the defects, mesopores, small clusters of hard carbon and the interlayers of graphene) and the surface capacitive-controlled capacity (Liþ adsorption/desorption process occurs on the surface of carbon by redox reactions) [49]. According to the similar CV curves, HC/G electrode can maintain a fast CV response to the quick potential scan, indicating an excellent rate capability for lithium storage, which is correspond to the superior rate performance. The capacitive value is used to calculate and analyse the electrochemical kinetics processes, using equation (4):
I ¼ ayb
(4)
where I is the measured current, ʋ is the scan rate, and a and b are controlled constants. In particular, the b value is the indicator that determines the main Liþ storage behaviour. Normally, when b is close to 0.5, it indicates diffusion-controlled capacity process, while the value of 1 represents surface capacitive-controlled capacity behaviour. The b value could be calculated according to the slop of the linear relationship between log I and log ʋ. The related linear curves of log I and log ʋ are presented in Fig. 5d. The b value of anode material is 0.59, indicating that the capacity of HC/G electrode derived from both the diffusion-controlled and surface capacitive-controlled process. Moreover, the contribution ratios of the diffusion-controlled and capacitive-controlled capacity can be determined by the following equation (5):
IðVÞ ¼ K1 y þ K2 y1=2
(5)
in which I (V) is the total current at a given voltage, and k1ʋ and k2ʋ1/2 represent the current contributions from surface capacitivecontrolled process and diffusion-controlled behaviour, respectively. At a scan rate of 0.5 mVs1, the typical current could be divided into surface capacitive-controlled current and the diffusion-controlled current in Fig. 5e. The surface capacitance-controlled capacity for HC/G accounts for ~57.3% of the total charge storage. This further suggests the structure of HC/G is beneficial for the surface adsorption and redox reaction. As the scanning rate increases to 0.8 and 1 mVs1 (as shown in Fig. 5f), the contribution of surface
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
7
Fig. 5. (a) EIS for HC/G and HC electrodes, inset: the equivalent circuit diagram. (b) Relationship between real parts of the impedance (Z0 ) and reciprocal square root of angular frequency (u1/2) of HC/G and HC in the low frequency region. (c) CV curves of the HC/G electrode at different scan rates. (d) Linear relationship of HC/G electrode between log (peak current) and log (scan rate). (e) Capacitance (red area) and diffusion-controlled (blue area) capacity contribution at 0.5 mV s1 and (f) corresponding capacity contribution ratios of the capacitive and diffusion controlled process at different scan rates for HC/G electrode. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
capacitance increases to 65.7% and 71.3%, which means that the capacitive-controlled storage behaviour plays an important role in total capacity, especially at high density. The high capacitivecontrolled contribution is contributed to the sandwich-like porous structure with a short ion diffusion length, high-speed electron transfer, and abundant storage sites of Liþ, which are key factors resulting in the enhanced Liþ storage kinetics and high-rate capability of the HC/G electrode. Based on structure characterizations and lithium storage properties, the superior electrochemical performance of HC/G electrode is mainly due to the stable sandwich-like porous structure and excellent synergistic effect between porous hard carbon and graphene layer, as shown in Fig. 6. On the one hand, the highly ordered
graphene layer in HC/G can constitute the conductive multidimensional paths to connect hard carbon, effectively facilitating the transport of electrons and supplying sufficient electrons for redox reactions. Meanwhile, the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the whole structure. On the other hand, the porous hard carbon in HC/G with many defects could provide more adsorption sites for Liþ. Moreover, hard carbon has abundant C]O groups, providing more reversible Liþ storage sites by redox reactions with little electrode structure change. Notably, compared with other physically mixed composites, directly synthesized hybrid from biomass-precursor with interweaving hard carbon and graphene structure would be more stable from phase separation
Fig. 6. Schematic representation of Liþ storage and electron transmission in HC/G electrode.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
8
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
during the long-term charge/discharge process. 4. Conclusions In summary, this work proposed a facile and economical method to fabricate a sandwich-like porous hard carbon/graphene hybrid with hard carbon sandwiched in graphene. When served as LIBs anode, the stable sandwich-like porous structure and superior synergistic effect between porous hard carbon and graphene layer render the excellent rate performance, long-time cycling stability, and highly reversible capacity. HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and exhibits an excellent rate performance that of 377 and 313 mAhg1 even at a higher rate of 2000 and 5000 mAg1, respectively. Overall, this work provides a new strategy for highvalue use of rapeseed shuck for low cost and eco-friendly LIBs anodes.
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[19]
[20]
Acknowledgements [21]
This work was supported by the National Natural Science Foundation of China (No. 51672165, 51702198), the China Scholarship Council (No. 201808610232), the Postdoctoral Foundation of China (Special 155660, 2016M592897XB), the Natural Science Foundation of Shaanxi Province (2018JQ5107) and the National Key Research and Development Program of China (2017YFB030830303).
[22] [23]
[24]
Appendix A. Supplementary data
[25]
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.152849.
[26]
References [27] [1] J.B. Goodenough, K.-S. Park, The Li-ion rechargeable battery: a perspective, J. Am. Chem. Soc. 135 (2013) 1167e1176. [2] Z. Huang, H. Lu, K. Qian, Y. Fang, Q. Du, Y. He, T. Masese, X. Yang, Y. Ma, W. Huang, Interfacial engineering enables Bi@ C-TiOx microspheres as superpower and long life anode for lithium-ion batteries, Nano Energy 51 (2018) 137e145. [3] B. Huang, Z. Pan, X. Su, L. An, Recycling of lithium-ion batteries: recent advances and perspectives, J. Power Sources 399 (2018) 274e286. [4] M.M. Thackeray, C. Wolverton, E.D. Isaacs, Electrical energy storage for transportationdapproaching the limits of, and going beyond, lithium-ion batteries, Energy Environ. Sci. 5 (2012) 7854e7863. [5] X. Su, Q. Wu, J. Li, X. Xiao, A. Lott, W. Lu, B.W. Sheldon, J. Wu, Silicon-based nanomaterials for lithium-ion batteries: a review, Adv. Energy Mater. 4 (2014) 1300882. [6] F. Zhang, L. Wan, J. Chen, X. Li, X. Yan, Crossed carbon skeleton enhances the electrochemical performance of porous silicon nanowires for lithium ion battery anode, Electrochim. Acta 280 (2018) 86e93. [7] F.A. Soto, P. Yan, M.H. Engelhard, A. Marzouk, C. Wang, G. Xu, Z. Chen, K. Amine, J. Liu, V.L. Sprenkle, F. El-Mellouhi, P.B. Balbuena, X. Li, Tuning the solid electrolyte interphase for selective Li- and Na-ion storage in hard carbon, Adv. Mater. 18 (2017) 1606860. [8] Z. Yu, S. Xin, Y. You, L. Yu, Y. Lin, D. Xu, C. Qiao, Z. Huang, N. Yang, S. Yu, J.B. Goodenough, Ion-catalyzed synthesis of microporous hard carbon embedded with expanded nanographite for enhanced lithium/sodium storage, J. Am. Chem. Soc. 45 (2016) 14915e14922. [9] Y. Yao, F. Wu, Naturally derived nanostructured materials from biomass for rechargeable lithium/sodium batteries [J], Nano Energy 17 (2015) 91e103. [10] X. Ma, F. Ouyang, Adsorption properties of biomass-based activated carbon prepared with spent coffee grounds and pomelo skin by phosphoric acid activation, Appl. Surf. Sci. 268 (2013) 566e570. [11] R. Li, J. Huang, W. Li, J. Li, L. Cao, Z. Xu, Y. He, A. Yu, G. Lu, Controlling carbon-
[28]
[29] [30]
[31]
[32] [33]
[34]
[35]
[36]
[37]
oxygen double bond and pseudographic structure in shaddock peel derived hard carbon for enhanced sodium storage properties, Electrochim. Acta 313 (2019) 109e115. E.M. Lotfabad, J. Ding, K. Cui, A. Kohandehghan, W.P. Kalisvaart, M. Hazelton, D. Mitlin, High-density sodium and lithium ion battery anodes from banana peels [J], ACS Nano 8 (2014) 7115e7129. J. Ding, Huanlei Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Lotfabad, B.C. Olsen, D. Mitlin, Carbon nanosheet frameworks derived from peat moss as high performance sodium ion battery anodes, ACS Nano 7 (2013) 11004e11015. Z. Zhu, L. Feng, Z. Zhou, X. Zeng, D. Wang, P. Dong, J. Zhao, S. Sun, Y. Zhang, X. Li, Expanded biomass-derived hard carbon with ultra-stable performance in sodium-ion batteries, J. Mater. Chem. A 6 (2018) 1513e1522. W. Cao, E. Zhang, J. Wang, Z. Liu, J. Ge, X. Yu, H. Yang, B. Lu, Potato derived biomass porous carbon as anode for potassium ion batteries, Electrochim. Acta 293 (2019) 364e370. Y. Bai, Z. Wang, C. Wu, R. Xu, F. Wu, Y. Liu, H. Li, Y. Li, J. Lu, K. Amine, Hard carbon originated from polyvinyl chloride nanofibers as high-performance anode material for Na-ion battery, ACS Appl. Mater. Interfaces 7 (2015) 5598e5604. Z. Jian, Z. Xing, C. Bommier, Z. Li, X. Ji, Anode materials: hard carbon microspheres: potassium-ion anode versus Sodium Ion anode, Adv. Energy Mater. 6 (2016) 1501874. rez, C. Bommier, X. Ji, Hard carbon Z. Li, Z. Jian, X. Wang, I.A. Rodríguez-Pe anodes of sodium-ion batteries: undervalued rate capability, Chem. Commun. 53 (2017) 2610e2613. Z. Jian, C. Bommier, L. Luo, Z. Li, W. Wang, C. Wang, P.A. Greaney, X. Ji, Insights on the mechanism of Na-ion storage in soft carbon anode, Chem. Mater. 29 (2017) 2314e2320. L. Xiao, Y. Cao, W.A. Henderson, M.L. Sushko, Y. Shao, J. Xiao, W. Wang, M.H. Engelhard, Z. Nie, J. Liu, Hard carbon nanoparticles as high-capacity, high-stability anodic materials for Na-ion batteries, Nano Energy 19 (2015) 279e288. R. Li, J. Huang, Z. Xu, H. Qi, L. Cao, Y. Liu, W. Li, J. Li, Controlling the thickness of disordered turbostratic nanodomains in hard carbon with enhanced sodium storage performance, Energy Technol. 6 (2018) 1080e1087. D.A. Stevens, J.R. Dahn, High capacity anode materials for rechargeable sodium-ion batteries, J. Electrochem. Soc. 147 (2000) 1271e1273. K. Gotoh, T. Ishikawa, S. Shimadzu, N. Yabuuchi, S. Komaba, K. Takeda, A. Goto, K. Deguchi, S. Ohki, K. Hashi, T. Shimizu, H. Ishida, NMR study for electrochemically inserted Na in hard carbon electrode of sodium ion battery, J. Power Sources 225 (2013) 137e140. J. Xu, M. Wang, N.P. Wickramaratne, M. Jaroniec, S. Dou, L. Dai, High-performance sodium ion batteries based on a 3D anode from nitrogen-doped graphene foams, Adv. Mater. 27 (2015) 2042. X. Wang, G. Li, F.M. Hassan, J. Li, X. Fan, R. Batmaz, X. Xiao, Z. Chen, Sulfur covalently bonded graphene with large capacity and high rate for high performance sodium-ion batteries anodes, Nanomater. Energy 15 (2015) 746e754. N. Sun, Y. Guan, Y. Liu, Q. Zhu, J. Shen, H. Liu, S. Zhou, B. Xu, Facile synthesis of free-standing, flexible hard carbon anode for high-performance sodium ion batteries using graphene as a multi-functional binder, Carbon 137 (2018) 475e483. Z.L. Wang, D. Xu, H.G. Wang, Z. Wu, X.B. Zhang, In situ fabrication of porous graphene electrodes for high-performance energy storage, ACS Nano 7 (2013) 2422e2430. X.L. Huang, R.Z. Wang, D. Xu, Z.L. Wang, H.G. Wang, J.J. Xu, Z. Wu, Q.C. Liu, Y. Zhang, X.B. Zhang, Homogeneous CoO on graphene for binder-free and ultralong-life lithium ion batteries, Adv. Funct. Mater. 23 (2013) 4345e4353. S. Xin, Y.G. Guo, L.J. Wan, Nanocarbon networks for advanced rechargeable lithium batteries, Acc. Chem. Res. 45 (2012) 1759e1769. I.H. Son, J.H. Park, S. Kwon, S. Park, M.H. Rümmeli, A. Bachmatiuk, H.J. Song, J. Ku, J.W. Choi, J.M. Choi, S.G. Doo, Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density, Nat. Commun. 6 (2015) 7393. J. Han, P. Liu, Y. Ito, X. Guo, A. Hirata, T. Fujita, M. Chen, Bilayered nanoporous graphene/molybdenum oxide for high rate lithium ion batteries, Nano Energy 45 (2018) 273e279. X. Zhang, S. Han, C. Fan, L. Li, W. Zhang, Hard carbon enveloped with graphene networks as lithium ion battery anode, Mater. Lett. 138 (2015) 259e261. L. Yin, Y. Wang, C. Han, Y. Kang, X. Ma, H. Xie, M. Wu, Self-assembly of disordered hard carbon/graphene hybrid for sodium-ion batteries, J. Power Sources 305 (2016) 156e160. C. Shi, L. Hu, J. Hou, K. Guo, T. Zhai, H. Li, Alkali metal boosted atom rearrangement in amorphous carbon towards crystalline graphitic belt skeleton for high performance supercapacitors, Energy Storage Mater. 15 (2018) 82e90. H. Liu, M. Jia, B. Cao, R. Chen, X. Lv, R. Tang, F. Wu, B. Xu, Nitrogen-doped carbon/graphene hybrid anode material for sodium-ion batteries with excellent rate capability, J. Power Sources 319 (2016) 195e201. N.G. Shang, P. Papakonstantinou, M. McMullan, M. Chu, A. Stamboulis, A. Potenza, S.S. Dhesi, H. Marchetto, Catalyst-free efficient growth, orientation and biosensing properties of multilayer graphene nanoflake films with sharp edge planes, Adv. Funct. Mater. 18 (2008) 3506e3514. X. Zhang, S. Han, P. Xiao, C. Fan, W. Zhang, Thermal reduction of graphene
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
[38]
[39]
[40] [41]
[42]
[43]
[44]
[45]
[46]
oxide mixed with hard carbon and their high performance as lithium ion battery anode, Carbon 100 (2016) 600e607. D.H. Seo, A.E. Rider, Z.J. Han, S. Kumar, K. Ostrikov, Plasma break-down and Re-build: same functional vertical graphenes from diverse natural precursors, Adv. Mater. 25 (2013) 5638e5642. S. Niyogi, E. Bekyarova, M.E. Itkis, H. Zhang, K. Shepperd, J. Hicks, M. Sprinkle, Spectroscopy of covalently functionalized graphene, Nano Lett. 10 (2010) 4061e4066. L.M. Malard, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene, Phys. Rep. 473 (2009) 51e87. X. Zhou, F. Chen, T. Bai, B. Long, Q. Liao, Y. Ren, J. Yang, Interconnected highly graphitic carbon nanosheets derived from wheat stalk as high performance anode materials for lithium ion batteries, Green Chem. 18 (2016) 2078e2088. S. Lee, N. Yabuuchi, B.M. Gallant, S. Chen, B.-S. Kim, P.T. Hammond, Y. ShaoHorn, High-power lithium batteries from functionalized carbon-nanotube electrodes, Nat. Nanotechnol. 5 (2010) 531e537. Y. Zhang, Q. Ma, S. Wang, X. Liu, L. Li, Poly (vinyl alcohol)-assisted fabrication of hollow carbon spheres/reduced graphene oxide nanocomposites for highperformance lithium-ion battery anodes, ACS Nano 12 (2018) 4824e4834. C. Wang, D. Li, T. Zhai, H. Wang, Q. Sun, H. Li, Direct conversion of waste tires into three-dimensional graphene, Energy Storage Mater. (2019), https:// doi.org/10.1016/j.ensm.2019.04.014. Z. Wu, W. Ren, L. Gao, B. Liu, C. Jiang, H. Cheng, Synthesis of high-quality graphene with a pre-determined number of layers, Carbon 47 (2009) 493e499. T. Liu, X. Li, Biomass-derived nanostructured porous carbons for sodium ion
9
batteries: a review, Mater. Technol. 34 (2018) 232e245. [47] Y. Liu, L. Fan, L. Jiao, Graphene highly scattered in porous carbon nanofibers: a binder-free and high-performance anode for sodium-ion batteries, J. Mater. Chem. A 5 (2017) 1698e1705. [48] H.R. Byon, B.M. Gallant, S.W. Lee, Y.S. Horn, Role of oxygen functional groups in carbon nanotube/graphene freestanding electrodes for high performance lithium batteries, Adv. Funct. Mater. 23 (2013) 1037e1045. [49] L. Su, L. Kong, S. Hao, Y. Zhao, Z. Ma, X. Qin, G. Shao, Honeycomb-like porous carbon with nano-graphitic domains, supported on graphene layers: applicability for lithium/sodium storage, ACS Sustain. Chem. Eng. 7 (2019) 10986e10994. [50] Z. Lyu, L. Yang, D. Xu, J. Zhao, H. Lai, Y. Jiang, Q. Wu, Y. Li, X. Wang, Z. Hu, Hierarchical carbon nanocages as high-rate anodes for Li-and Na-ion batteries, Nano Res. 8 (2015) 3535e3543. [51] Z. Lyu, R. Feng, J. Zhao, H. Fan, D. Xu, Q. Wu, L. Yang, Q. Chen, X. Wang, Z. Hu, Nitrogen-Doped carbon nanocages as high-rate anode for lithium ion batteries, Acta Chim. Sin. 73 (2015) 1013e1017. [52] H. Ru, N. Bai, K. Xiang, W. Zhou, H. Chen, X.S. Zhao, Porous carbons derived from microalgae with enhanced electrochemical performance for lithium-ion batteries, Electrochim. Acta 194 (2016) 10e16. [53] W. Lv, J. Zhao, F. Wen, J. Xiang, L. Li, L. Wang, Z. Liu, Y. Tian, Carbonaceous photonic crystals as ultralong cycling anodes for lithium and sodium batteries, J. Mater. Chem. A 3 (2015) 13786e13793. [54] H. Sun, H. Xiao, W. Song, J. Wang, W. Zhang, S. Ru, Z. Ai, C. Wang, A novel Ndoped organic porous carbon derive from water-based alkyd resin for lithium ion battery anode materials, J. Alloy. Comp. 805 (2019) 984e990.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries Ruizi Li a, b, Jianfeng Huang a, *, Jiawen Ren b, Liyun Cao a, Jiayin Li a, Winbin Li c, Guoxing Lu b, Aimin Yu b, ** a School of Materials Science & Engineering, Xi’an Key Laboratory of Green Processing for Ceramic materials, Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science and Technology, Xi’an, 710021, China b Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia c Institute of Advanced Electrochemical Energy & School of Materials Science and Engineering, Xi’an University of Technology, Xi’an, Shaanxi, 710048, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 September 2019 Received in revised form 28 October 2019 Accepted 28 October 2019 Available online xxx
Hard carbon becomes a candidate for anode materials due to its rich resources and abundant lithium storage sites. However, amorphous carbon with poor stability and electronic conductivity limits its electrochemical performance. In response, this work synthesizes a sandwich-like porous hard carbon/ graphene hybrid (HC/G) with graphene sandwiching the hard carbon via a KOH-assisted one-step pyrolysis process from rapeseed shuck. The highly ordered graphene layers constitute conductive multidimensional paths for fast electronic transport and supply sufficient electrons for redox reactions. Moreover, the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the whole structure. The porous hard carbon with numerous defects and C]O groups could provide more adsorption sites and redox reactions for lithium storage. When serving as anode material, HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and exhibits a superior rate performance that of 381 and 308 mAhg1 even at a higher rate of 2000 and 5000 mAg1, respectively. This work sheds a light on the high-value use of waste rapeseed shuck for eco-friendly and low cost lithium-ion batteries anode material. © 2019 Elsevier B.V. All rights reserved.
Keywords: Rapeseed shuck Hard carbon/graphene hybrid Sandwich-like structure Lithium-ion batteries Anode
1. Introduction Owing to the unmatchable combination of long cycling life, high energy density, and no memory effect, lithium-ion batteries (LIBs) have emerged as the first choice for portable electronics, power tools, and electric vehicles since they were successfully commercialized by SONY in 1990s [1e3]. LIBs also received great interests as potential candidates for intermittent renewable energy storage from sources like hydro, solar, and wind, which could mitigate environmental hazards from fossil fuels [4,5]. At this stage, the performance and cost of LIBs are primarily restricted by the electrode materials [6]. Thus, the development of electrode materials with high performance and low cost has been a significant strategy to further promote the LIBs.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Huang), [email protected] (A. Yu).
In the past decades, graphite is usually used as the anode materials for commercial LIBs and the mechanism of lithium-ion (Liþ) storage is the intercalation between long-range ordered graphitic layers. However, since the low theoretical capacity of 372.1 mAh g1, graphite-based LIBs cannot offer enough energy for electric vehicles [7,8]. It is necessary to synthesis a superior carbon material to replace graphite for efficient Liþ storage. Biomass derived hard carbon with the advantages of low cost, environmental friendliness, and wide abundance has become a candidate for anode material [9e15]. Amorphous hard carbon consists mainly of disordered turbostratic nanodomains, which are graphene layers with many defects randomly arranged in disorder [16e21]. This carbon structure usually offers the numerous pores and broad parallel carbon layers for Liþ adsorption and intercalation, thus giving a higher capacity [9,12,22e24]. However, the disordered amorphous hard carbon derived from biomass has low electronic conductivity and constrained electrochemical stability, causing a poor cycling stability and rate performance [8]. Accordingly, introducing graphite domains into hard carbon structure is a valid way to
https://doi.org/10.1016/j.jallcom.2019.152849 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
2
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
enhance electronic conductivity [8,21]. Graphene, a novel class of two-dimensional carbon material, has attracted a great deal of attention since its excellent electrical conductivity, outstanding chemical stability and mechanical flexibility [25e28]. Graphene has been widely used in constructing the conducting networks for LIBs anode material because of the high electronic conductivity with the aim to enhance the rate capability and cycling performance [29e31]. Zhang and co-workers fabricated a mixture of hard carbon with graphene for Li-storage by the pyrolysis of hard carbon and graphene oxide, which exhibits a capacity of 311 mAhg1 after 100 cycles at 80 mAg1 [32]. Disordered hard carbon/graphene hybrid as the anode materials for sodiumion storage was also anode fabricated by the hydrothermal treatment of glucose with graphene oxide and subsequent calcination, achieving a capacity of 300 mAhg1 at 50 mAg1 after 100 cycles [33]. Nevertheless, these hybrids prepared by physically mixing hard carbon and graphene oxide (or graphene) exhibited insatiable cycling and rate performances because of the non-stable structure resulting in the detachment of hard carbon and graphene during the long term charging/discharging process. In this article, to obtain an advanced carbon anode material with both excellent electrical conductivity and abundant storage sites for Liþ, we validated a KOH-assisted one-step pyrolysis process to prepare a sandwich-like porous hard carbon/graphene with porous hard carbon sandwiched in graphene. Benefiting from the stable sandwich-like porous structure and superior synergistic effect between hard carbon and graphene, the obtained HC/G exhibits superior cycling stability and rate performance. HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and displays an outstanding rate performance that of 377 and 313 mAhg1 even at a higher rate of 2000 and 5000 mAg1.
SUPRA X-ray Photoelectron Spectrometer with monochromatic Al Ka radiation at 15 kV. The Fourier transform infrared (FTIR) spectrum was collected on a TENSOR 27 FTIR spectrometer using KBr pellets. The specific surface area, total pore volume and pore size distribution were evaluated via the N2 adsorption/desorption isotherms with ASAP2460 specific surface area instrument at 77 K. The specific surface area was obtained from the Brunauer-Emett-Teller formula. The total pore volume was calculated by determining the amount of the adsorbed nitrogen at a relative pressure of 0.99. The pore size distribution was observed by the Barrett-Joyner-Halenda method. 2.3. Electrochemical test
2. Experimental
The electrochemical performances were conducted on coin cells (CR2032), which were assembled in an argon filled glove box (H2O, O2 < 0.1 ppm) by using lithium metal foil as the counter electrode, and glass fiber as the separators. The electrolyte was a solution of 1 M LiPF6 in a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC), with a volume ratio of EC: EMC: DMC ¼ 1:1:1. Working electrodes were fabricated by mixing the active carbon material, conductive carbon black (Super-P), and polyvinylidene fluoride (PVDF) binder in a weight ratio of 8:1:1. The obtained slurry was coated onto the surface of a Cu foils current collector, followed by drying in a vacuum oven at 90 C for 10 h. The galvanostatic discharge/charge tests were measured by a Neware battery tester at various current densities over a potential range of 0.01e3.00 V (vs. Li/Liþ). Cyclic voltammetry (CV) with the voltage ranging from 0.01 to 3.00 V (vs. Li/Liþ) at 0.1 mV s1, and electrochemical impedance spectroscopy (EIS) with an AC perturbation signal of 5 mV in the frequency range between 100 kHz and 0.01 Hz were carried out using an CHI660E electrochemical workstation. All the electrochemical measurements were conducted at room temperature.
2.1. Material synthesis
3. Results and discussion
Rapeseed shuck (collected after seed harvest from suburb farmlands of Shaanxi) was firstly pulverized into powder. Then, the powder was mixed and grounded thoroughly with KOH in a weight ratio of 1:3. Afterward, the mixture was pyrolyzed at 700 C or 1000 C with argon flow of 100 sccm/min, and held there for 2 h, and the heating rate was 5 C/min. After cooling, the obtained black powder was thoroughly immersed into 2 M HCl solutions and kept for 2 h to remove the impurities, followed by washing with the distilled water and absolute ethanol until pH close to 7. The final materials were dried at 60 C for 8 h. The rapeseed shuck derived carbon materials pyrolyzed at 700 and 1000 C were respectively marked as HC and HC/G. For comparison, graphene (GN) was synthesized from natural flake graphite powder as reported elsewhere [34].
3.1. Structure characterization
2.2. Materials characterization The morphological characteristics were investigated with a Hitachi S-4800 field-emission scanning electron microscopy (SEM). The transmission electron microscopy (TEM) images were characterized from a JEM-2100 transmission electron microscope and high-resolution transmission electron microscope (HRTEM) was performed on JEOL-2011 at 200 kV. X-ray diffraction (XRD) patterns of all samples were recorded with a Rigaku D/MAX2200PC diffraction instrument with Cu Ka radiation (l ¼ 0.15 418 nm) over the 2q range of 10e70 . Raman spectra were obtained using a Renishaw-invia confocal microprobe Raman system (632.8 nm). Xray Photoelectron Spectrum (XPS) was performed using an AXIS
Fig. 1a exhibits a schematic illustration of the synthesis of HC/G derived from rapeseed shuck. The rapeseed shuck was directly pyrolyzed at a high temperature assisted with KOH. In this way, prepared HC/G in a simple manner, and creatively utilized biomass waste. The morphologies of the as-prepared HC and HC/G were characterized by SEM. As displayed in Fig. 1b, the HC prepared at 700 C shows a highly 3D-porous interconnected structure, and there are numerous cavities on the surface, resulting from the interior etching process of KOH. When the pyrolysis temperature rises to 1000 C, the HC/G exhibits the 3D-porous interconnected structure enveloped with cross-linked ultrathin nanosheets (Fig. 1e). These structures can shorten the diffusion path for Liþ, and offer minimum diffusive resistance to transport on an electrode/ electrolyte interface for charge-transfer reaction [35]. Further, TEM (Fig. 1c) and HRTEM images (Fig. 1d) display the amorphous structure of HC with numerous pores. As for HC/G, TEM (Fig. 1f) presents graphene winkled lamellar morphology with porous hard carbon in the middle like a sandwich structure. And many sharp textures on wrinkled lamellar can be seen, which correspond to the vertical graphene structure and indicate the high crystal quality [36]. HRTEM image (Fig. 1g) of HC/G shows a sandwich-like porous structure with the graphene sandwiching the hard carbon. It is well-established that the graphene with graphite microcrystallites could promote electronic transmission and provide sufficient electrons for redox reactions. Moreover, the sandwiching graphene layers provide mechanical support, which effectively adapts
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
3
Fig. 1. (a) Schematic illustration of the synthesis of HC/G derived from rapeseed shuck. SEM images of the (b) HC and (e) HC/G. TEM of (c) HC and (f) HC/G. HRTEM images of (d) HC, and (g) HC/G. (Red area, graphene layer; yellow area, hard carbon). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
volume change to stabilize the whole structure. The crystalline structures of HC and HC/G were firstly characterized by XRD patterns and Raman spectra. In Fig. 2a, both of the
samples exhibit a broad peak at ~23 , corresponding to the (002) reflection of graphite, which reveals the typical amorphous structure of random packing at c axis. Notably, (100) peak at ~ 43 can be
Fig. 2. (a) XRD patterns, (b) Raman spectra, (c) Survey XPS spectra, (d) FTIR spectra, (e) N2 adsorption-desorption isotherms, and (f) Pore size distribution of HC/G, and HC.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
4
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
obviously observed in the HC/G, indicating it more ordered graphitic structures relative to that of HC. The interlayer spacing (d002) values of the samples were calculated by Bragg’s equation based on the (002) peak. The smaller interlayer distance of HC/G (0.359 nm) than HC (0.384 nm) indicates that constituting stacks of HC/G contains more organized graphene layers [37]. From the Raman spectra in Fig. 2b, it can be observed that both samples exhibit two standard peaks at ~1345 and 1580 cm1, corresponding to the D peak (the defective graphitic or disordered carbon peak) and G peak (the crystalline graphite peak), respectively. The G peak comes from the in-plane E2g vibration mode of sp2 carbon, while the D peak is caused by A1g mode breathing vibrations of hexagonal sp2 carbon, and becomes Raman activity after adjacent sp2 carbon is transformed into sp3 hybrid [38]. In general, the IG/ID integral intensity ratio is used to characterize the average size of the sp2 domains and disorder degree [39]. The calculated IG/ID value of HC/ G is 1.17, very close to GN of 1.22 [26] and higher than 0.81 for HC, further indicating the existence of well-crystallized graphene. It should be noted that there is a strong and narrow 2D peak in HC/G at 2685 cm1. This reveals the existence of few-layer graphene. The 2D peak is associated with the second-order boundary phonon modes of graphene, and the intensity ratio of I2D/IG could be characterized by the number and stacking of graphene layers [40]. The I2D/IG ratio of HC/G is 0.67, this implies that the as-obtained HC/G should be few-layer graphene [41], consistent with the HRTEM. The results of Raman, XRD and TEM confirmed that the HC/G should be a sandwich-like porous hard carbon/graphene hybrid with graphene sandwiching the hard carbon. The presence of hard carbon with many defects in HC/G could provide more adsorption sites for Liþ, while graphene layers serve as a bridge to connect hard carbon, benefiting the transport of electrons. The chemical composition and functional groups of HC/G and HC were further checked by XPS measurement (Fig. 2c). In the survey XPS spectra, two elements including C and O are mainly observed and no N can be detected in all samples. As shown in Table S1, with the pyrolysis temperature rising from 700 to 1000 C, the carbon content gradually increases from 82 to 91 wt%, and the oxygen content evidently decreases from 14 to 7 wt%, suggesting that the oxygen-containing functional groups decreased. The curve fittings of high-resolution C 1s XPS spectra are exhibited in Fig. S3. In detail, three types of carbon including sp2 C, CeO and C]O (OeC]O/C]O) were detected at 284.6, 285.7 and 288.7 eV, respectively. Compared with the HC, CeO and C]O in HC/G are not obvious, which is caused by the rising of pyrolysis temperature. Meanwhile, the sp2 C peak becomes sharper with the temperature increasing, indicating the existence of graphene structure. The residual oxygen atoms can produce some radicals in the surface of HC/G, which would significantly enhance the storage capability of Liþ by forming chemical-bonding [42]. In addition, the surface organic groups of HC and HC/G were checked by FTIR spectra (Fig. 2d). The peak of HC at 3470 cm1 is associated with the stretching vibration of OeH groups, and peeks at 886, 1090, and 1250 cm1 belong to the CeO groups. Moreover, the bands at 1700 cm1 is attributed to the C]O [43]. As for HC/G, these vibrations become weaker and even difficult to be detected, which means that some oxygen-containing groups in HC have been removed, agree well with the XPS observation. Fig. 2e exhibits the N2 adsorption/desorption isotherms of HC and HC/G, while Fig. 2f shows the calculated pore size distributions. At the low pressure, the adsorption curve of HC displays an obvious vertical linear region and a clear hysteresis loop in middle and high region, which belongs to the IV type isotherm. The results suggest that KOH activation produces mesopores and micropores in HC. While, HC/G shows a short vertical linear region of low pressure related to micropore filling, possibly ascribed to the appearance of
graphene structure. Furthermore, the hysteresis loop exhibits a trend of horizontal parallel, which may be related to higher graphitization [44]. This isotherm curve also demonstrates that the HC/G has the obvious hierarchical porous structure at 1000 C. The specific BET surface area and total pore volume of HC are 850.7 m2 g1 and 0.49 cm3 g1, respectively. Owing to formation of the less porous graphene structure from carbon atoms rearrangement, the specific BET surface area and total pore volume of HC/G are reduced significantly to 571.5 m2 g1 and 0.31 cm3 g1. In Fig. 2f, both the HC and HC/G show a broad pore distribution ranging from 1 to 30 nm. After annealing at 1000 C, it is indicated that HC/G has the highest pore volume between 1 and 4 nm, which is well in agreement with SEM and TEM observation. The obtained HC/G with the lower surface area could decrease the formation of solid electrolyte interface (SEI). As can be seen above characterization, HC/G with a stable sandwich-like porous structure has been obtained. The synthesis mechanism of rapeseed shuck derived sandwich-like structure is proposed in Fig. 3. At a low pyrolytic temperature, KOH as a chemical etching agent reacts with the char forming the hard carbon with 3D-porous interconnected structure [45]. When the pyrolysis temperature rising, a large number of active potassium atoms are produced during the reaction (Equation (1)). 6KOH þ 2C / 2K þ 3H2 þ 2K2CO3
(1)
These K atoms intercalate into the outer layers of hard carbon and remove surface functional groups through the strong reducibility. The hard carbon surface produce a lot of dangling bonds. At the pyrolysis temperature of 1000 C, potassium atoms vaporized and speed up the intercalation process as well as the insertion depth. These potassium atoms also repair the carbon dangling bond and promote the rearrangement of carbon atoms into a graphitic structure (catalytic graphitization) and finally exfoliate into fewlayer graphene [46]. Therefore, intercalated and catalyzed by K, the outer layers of hard carbon gradually rearranges and exfoliates into graphene, resulting in HC/G with a stable sandwich-like porous structure. The sandwich-like porous HC/G materials are the desirable anode materials. 3.2. Electrochemical characterization The lithium storage properties and electrochemical performances of the obtained HC/G and HC electrodes were firstly evaluated by CV and charge/discharge profile. Fig. 4a and d shows the CV curves of HC and HC/G electrodes for the first three cycles at a scan rate of 0.1 mV s1 between 0.01 and 3 V. In the first reduction process, the peak at 0.20e0.46 V is associated with the electrolyte decomposition, the SEI layer formation. It disappears in the subsequent scans, suggesting good reversibility in the following cycles [33]. Because of its higher surface area and unstable mechanical support, this peak in HC is obviously stronger than HC/G, indicating a low Coulombic efficiency (CE) in HC. In a lower potential range (0.01e0.20 V), a pair of redox peaks is attributed to Liþ insertion/ extraction in the defects, mesopores, small clusters of hard carbon and the interlayers of graphene [37,47]. In addition, the weak hump of each curve in a wide voltage range from 0.2 V to 1.0 V, implies that the Liþ adsorption/desorption processes occur on the surface of carbon by redox reactions of Liþ with carboxylic groups, carbonyl, and ester (e.g. Liþ þ C]O þ e 4 CeOeLi) [21,48]. Fig. 4b and e presents the first three charge and discharge profiles of HC/G and HC electrodes at 100 mA g1. HC/G electrode has a typical sloping voltage profile with little plateaus, and the capacity contributions mainly focus on 0.2e1.0 V. This indicates that the main Liþ storage mechanism is the surface adsorption/desorption and reversible
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
5
Fig. 3. Schematic diagram displaying the overall evolution of rapeseed shuck to HC/G.
Fig. 4. CV curves of HC/G (a) and HC (d) electrodes from 0.01 V to 3 V at a scan rate of 0.1 mV s1. Galvanostatic charge/discharge profile of HC/G (b) and HC (e) electrodes at 100 mA g1. (c) Cycling performance at a current load of 100 mA g1 and (f) rate performance at variant current loads of HCG, HC and GN electrodes.
redox reactions, which corresponds well to the weak hump in CV curves [48]. In comparison with the Liþ intercalation mechanism, the faster surface adsorption/desorption and redox reactions are beneficial to the little electrode structure change during chargedischarge process and result in the good cycling stability (Fig. 4c) as well as rate performance (Fig. 4f) [11]. Noticeably, closed CV and charge/discharge curves of the second and third cycles indicate outstanding electrochemical reversibility for HC/G after the first cycle. The cycling and rate performances of HC/G, HC and GN electrodes are then evaluated. As shown in Fig. 4c and f, HC/G electrode exhibits the best cycling and rate performances, which are superior
to the most reported hard carbon/graphene electrodes (Fig. S5). When compared with other recently reported carbon electrodes, the HC/G shows better electrochemical performance, especially in rate performance (Table 1). As can be seen, the initial discharge and charge capacities of the HC/G electrode is 731 and 1587 mAhg1 at 100 mAg1, higher than those of HC (433 and 1623 mAhg1) and GN (327 and 961 mAhg1) electrode. The corresponding fist Coulombic efficiency (CE) of HC/G electrode is 46%, whereas that of HC and GN electrode is only 37% and 34%, which is related to the lower surface area for HC/G electrode [11]. The enhanced CE is ascribed to the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
6
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Table 1 Comparison of the performances used HC/G and some other typically carbon materials as anode for lithium-ion batteries. Sample
Reversible capacity (mAg1)
Rate Capacity (mAhg1)
Ref.
Expanded nanographite Banana peel pseudographite Graphitic carbon nanosheets Hollow Carbon Spheres/Reduced Graphene honeycomb-like porous carbon Hierarchical carbon nanocages Nitrogen-Doped Carbon Nanocages Porous carbons derived from microalgae Carbonaceous photonic crystals N-doped organic porous carbon HC/G
661 of 1st cycle and 401 of 1000th cycle at 1Ag-1 790 of 11th cycle and 717 of 300th cycle at 100 mAg1 502 of 1st cycle and 443.7 of 50th cycle at 37 mAg1 755 of 600th cycle at 2 Ag-1 721 of 200th cycle at 1 Ag-1 970 of 10th cycle at 0.1 Age1 450 of 500th cycle at 1 Age1 445 of 1st cycle and 433 of 100th cycle at 37 mAg1 590 of 10th cycle at 50 mAg1 562.89 of 100th cycle at 0.2 Ag-1 731 of 1st cycle and 623 of 500th cycle at 100 mAg1
251 at 5 Ag-1 243 at 5 Ag-1 161.4 at 3.72 Ag-1 606 at 5 Ag-1 203 at 10 Ag-1 229 at 25 Ag-1 135 at 25 Ag-1 355 at 1 Ag-1 113 at 5 Ag-1 226 at 2 Ag-1 308 at 5 Ag-1
[8] [10] [41] [43] [49] [50] [51] [52] [53] [54] This work
whole structure. After 500 cycles, HC/G electrode still delivers an excellent reversible capacity of 623 mAhg1 with the capacity retention (relative to 5th) of 94%, ~1.9 and ~2.2 times higher than that of HC (332 mAhg1) and GN (284 mAhg1) electrode, respectively. The enhanced lithium storage capacity of HC/G is associated with the superior synergistic effect between hard carbon and graphene. Porous hard carbon with numerous defects and C]O groups could provide more adsorption sites and redox reactions for Liþ storage, while the ordered graphene layer could supply sufficient electrons for redox reactions. The excellent cycling stability of HC/G can be associated with the stable sandwich-like structure prepared by an one-step pyrolysis method from rapeseed shuck. Unlike physical mixture of hard carbon and graphene, there is no detachments (or phase separation) occurring for HC/G during the long-term charge/discharge process. Fig. 4f displays that HC/G electrode delivers outstanding reversible capacities of 753, 649, 579, 521, 442, 381, 308, and 228 mAhg1 at the current densities of 50, 100, 200, 500, 1000, 2000, 5000, and 10 000 mAg1, respectively. These values are obviously higher than those of HC (453, 387, 323, 234 173, 91, 40, and 24 mAhg1) and GN (357, 311, 271, 225, 164, 143, 94, and 67 mAhg1) electrode at the same current density. When the rate finally reduced back to 50 mAg1, a reversible capacity of HC/G electrode still can recover to 714 mAhg1, while the reversible capacity of HC and GN electrode is only 393 and 308 mAhg1. The remarkable rate performance of HC/G should can be attributed to the sandwich-like porous structure, which is conducive to high-speed electronic transmission and allows Liþ to fast access the bulk material. From another point of view, these results also suggest that the presence of graphene layer in HC/G guarantees the adequate electrons for surface redox reactions. EIS measurements (Fig. 5a) of the HC/G and HC electrodes were performed to better understand the excellent electrochemical performance. The Rct (charge-transfer resistance, depending on the semicircle diameter) of HC/G electrode (73 U) is obviously smaller than that of HC (126 U), suggesting HC/G has a superior electrical conductivity and a high-speed charge transfer process for redox reactions. In addition, EIS is also an important tools to investigate the diffusion coefficient of Liþ (Dþ Li) in the electrode materials based on the formula in equation (2):
DLiþ ¼
R2 T2 2A2 n4 F4 C2 s2
Z0 ¼ RD þ RL þ su1=2
(2)
(3)
in the formula, R is the gas constant, T is the test absolute temperature, A is the surface area of the working electrode, n is the number of electrons attending the electronic transfer reaction, F is Faraday constant, C is the molar concentration of Liþ, and s is the Warburg impedance factor [48]. From Fig. 5b, s can be derived from
the slope of the line between Z0 and u1/2 through equation (3). The calculation shows that the s value of HC/G is smaller, reflecting a larger Dþ Li than HC. Thereby, the highly ordered graphene in HC/G can be used as conductive multi-dimensional paths to connect hard carbon, effectively facilitating the electron transfer and Liþ diffusion kinetics. To obtain an in-depth understanding of the superior rate performance and long-time cycling stability of HC/G electrode, the lithium storage mechanisms were studied by CV curves at different scan rates from 0.1 to 1.0 mVs1 (Fig. 5c). The capacities of the carbon anode materials can be divided into the diffusion-controlled capacity (Liþ insertion/extraction in the defects, mesopores, small clusters of hard carbon and the interlayers of graphene) and the surface capacitive-controlled capacity (Liþ adsorption/desorption process occurs on the surface of carbon by redox reactions) [49]. According to the similar CV curves, HC/G electrode can maintain a fast CV response to the quick potential scan, indicating an excellent rate capability for lithium storage, which is correspond to the superior rate performance. The capacitive value is used to calculate and analyse the electrochemical kinetics processes, using equation (4):
I ¼ ayb
(4)
where I is the measured current, ʋ is the scan rate, and a and b are controlled constants. In particular, the b value is the indicator that determines the main Liþ storage behaviour. Normally, when b is close to 0.5, it indicates diffusion-controlled capacity process, while the value of 1 represents surface capacitive-controlled capacity behaviour. The b value could be calculated according to the slop of the linear relationship between log I and log ʋ. The related linear curves of log I and log ʋ are presented in Fig. 5d. The b value of anode material is 0.59, indicating that the capacity of HC/G electrode derived from both the diffusion-controlled and surface capacitive-controlled process. Moreover, the contribution ratios of the diffusion-controlled and capacitive-controlled capacity can be determined by the following equation (5):
IðVÞ ¼ K1 y þ K2 y1=2
(5)
in which I (V) is the total current at a given voltage, and k1ʋ and k2ʋ1/2 represent the current contributions from surface capacitivecontrolled process and diffusion-controlled behaviour, respectively. At a scan rate of 0.5 mVs1, the typical current could be divided into surface capacitive-controlled current and the diffusion-controlled current in Fig. 5e. The surface capacitance-controlled capacity for HC/G accounts for ~57.3% of the total charge storage. This further suggests the structure of HC/G is beneficial for the surface adsorption and redox reaction. As the scanning rate increases to 0.8 and 1 mVs1 (as shown in Fig. 5f), the contribution of surface
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
7
Fig. 5. (a) EIS for HC/G and HC electrodes, inset: the equivalent circuit diagram. (b) Relationship between real parts of the impedance (Z0 ) and reciprocal square root of angular frequency (u1/2) of HC/G and HC in the low frequency region. (c) CV curves of the HC/G electrode at different scan rates. (d) Linear relationship of HC/G electrode between log (peak current) and log (scan rate). (e) Capacitance (red area) and diffusion-controlled (blue area) capacity contribution at 0.5 mV s1 and (f) corresponding capacity contribution ratios of the capacitive and diffusion controlled process at different scan rates for HC/G electrode. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
capacitance increases to 65.7% and 71.3%, which means that the capacitive-controlled storage behaviour plays an important role in total capacity, especially at high density. The high capacitivecontrolled contribution is contributed to the sandwich-like porous structure with a short ion diffusion length, high-speed electron transfer, and abundant storage sites of Liþ, which are key factors resulting in the enhanced Liþ storage kinetics and high-rate capability of the HC/G electrode. Based on structure characterizations and lithium storage properties, the superior electrochemical performance of HC/G electrode is mainly due to the stable sandwich-like porous structure and excellent synergistic effect between porous hard carbon and graphene layer, as shown in Fig. 6. On the one hand, the highly ordered
graphene layer in HC/G can constitute the conductive multidimensional paths to connect hard carbon, effectively facilitating the transport of electrons and supplying sufficient electrons for redox reactions. Meanwhile, the sandwiching graphene layers provide mechanical support, which effectively adapts volume change to stabilize the whole structure. On the other hand, the porous hard carbon in HC/G with many defects could provide more adsorption sites for Liþ. Moreover, hard carbon has abundant C]O groups, providing more reversible Liþ storage sites by redox reactions with little electrode structure change. Notably, compared with other physically mixed composites, directly synthesized hybrid from biomass-precursor with interweaving hard carbon and graphene structure would be more stable from phase separation
Fig. 6. Schematic representation of Liþ storage and electron transmission in HC/G electrode.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
8
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
during the long-term charge/discharge process. 4. Conclusions In summary, this work proposed a facile and economical method to fabricate a sandwich-like porous hard carbon/graphene hybrid with hard carbon sandwiched in graphene. When served as LIBs anode, the stable sandwich-like porous structure and superior synergistic effect between porous hard carbon and graphene layer render the excellent rate performance, long-time cycling stability, and highly reversible capacity. HC/G displays a stable lithium storage capacity of 623 mAhg1 at a current density of 100 mAg1 after 500 cycles, and exhibits an excellent rate performance that of 377 and 313 mAhg1 even at a higher rate of 2000 and 5000 mAg1, respectively. Overall, this work provides a new strategy for highvalue use of rapeseed shuck for low cost and eco-friendly LIBs anodes.
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[19]
[20]
Acknowledgements [21]
This work was supported by the National Natural Science Foundation of China (No. 51672165, 51702198), the China Scholarship Council (No. 201808610232), the Postdoctoral Foundation of China (Special 155660, 2016M592897XB), the Natural Science Foundation of Shaanxi Province (2018JQ5107) and the National Key Research and Development Program of China (2017YFB030830303).
[22] [23]
[24]
Appendix A. Supplementary data
[25]
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.152849.
[26]
References [27] [1] J.B. Goodenough, K.-S. Park, The Li-ion rechargeable battery: a perspective, J. Am. Chem. Soc. 135 (2013) 1167e1176. [2] Z. Huang, H. Lu, K. Qian, Y. Fang, Q. Du, Y. He, T. Masese, X. Yang, Y. Ma, W. Huang, Interfacial engineering enables Bi@ C-TiOx microspheres as superpower and long life anode for lithium-ion batteries, Nano Energy 51 (2018) 137e145. [3] B. Huang, Z. Pan, X. Su, L. An, Recycling of lithium-ion batteries: recent advances and perspectives, J. Power Sources 399 (2018) 274e286. [4] M.M. Thackeray, C. Wolverton, E.D. Isaacs, Electrical energy storage for transportationdapproaching the limits of, and going beyond, lithium-ion batteries, Energy Environ. Sci. 5 (2012) 7854e7863. [5] X. Su, Q. Wu, J. Li, X. Xiao, A. Lott, W. Lu, B.W. Sheldon, J. Wu, Silicon-based nanomaterials for lithium-ion batteries: a review, Adv. Energy Mater. 4 (2014) 1300882. [6] F. Zhang, L. Wan, J. Chen, X. Li, X. Yan, Crossed carbon skeleton enhances the electrochemical performance of porous silicon nanowires for lithium ion battery anode, Electrochim. Acta 280 (2018) 86e93. [7] F.A. Soto, P. Yan, M.H. Engelhard, A. Marzouk, C. Wang, G. Xu, Z. Chen, K. Amine, J. Liu, V.L. Sprenkle, F. El-Mellouhi, P.B. Balbuena, X. Li, Tuning the solid electrolyte interphase for selective Li- and Na-ion storage in hard carbon, Adv. Mater. 18 (2017) 1606860. [8] Z. Yu, S. Xin, Y. You, L. Yu, Y. Lin, D. Xu, C. Qiao, Z. Huang, N. Yang, S. Yu, J.B. Goodenough, Ion-catalyzed synthesis of microporous hard carbon embedded with expanded nanographite for enhanced lithium/sodium storage, J. Am. Chem. Soc. 45 (2016) 14915e14922. [9] Y. Yao, F. Wu, Naturally derived nanostructured materials from biomass for rechargeable lithium/sodium batteries [J], Nano Energy 17 (2015) 91e103. [10] X. Ma, F. Ouyang, Adsorption properties of biomass-based activated carbon prepared with spent coffee grounds and pomelo skin by phosphoric acid activation, Appl. Surf. Sci. 268 (2013) 566e570. [11] R. Li, J. Huang, W. Li, J. Li, L. Cao, Z. Xu, Y. He, A. Yu, G. Lu, Controlling carbon-
[28]
[29] [30]
[31]
[32] [33]
[34]
[35]
[36]
[37]
oxygen double bond and pseudographic structure in shaddock peel derived hard carbon for enhanced sodium storage properties, Electrochim. Acta 313 (2019) 109e115. E.M. Lotfabad, J. Ding, K. Cui, A. Kohandehghan, W.P. Kalisvaart, M. Hazelton, D. Mitlin, High-density sodium and lithium ion battery anodes from banana peels [J], ACS Nano 8 (2014) 7115e7129. J. Ding, Huanlei Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Lotfabad, B.C. Olsen, D. Mitlin, Carbon nanosheet frameworks derived from peat moss as high performance sodium ion battery anodes, ACS Nano 7 (2013) 11004e11015. Z. Zhu, L. Feng, Z. Zhou, X. Zeng, D. Wang, P. Dong, J. Zhao, S. Sun, Y. Zhang, X. Li, Expanded biomass-derived hard carbon with ultra-stable performance in sodium-ion batteries, J. Mater. Chem. A 6 (2018) 1513e1522. W. Cao, E. Zhang, J. Wang, Z. Liu, J. Ge, X. Yu, H. Yang, B. Lu, Potato derived biomass porous carbon as anode for potassium ion batteries, Electrochim. Acta 293 (2019) 364e370. Y. Bai, Z. Wang, C. Wu, R. Xu, F. Wu, Y. Liu, H. Li, Y. Li, J. Lu, K. Amine, Hard carbon originated from polyvinyl chloride nanofibers as high-performance anode material for Na-ion battery, ACS Appl. Mater. Interfaces 7 (2015) 5598e5604. Z. Jian, Z. Xing, C. Bommier, Z. Li, X. Ji, Anode materials: hard carbon microspheres: potassium-ion anode versus Sodium Ion anode, Adv. Energy Mater. 6 (2016) 1501874. rez, C. Bommier, X. Ji, Hard carbon Z. Li, Z. Jian, X. Wang, I.A. Rodríguez-Pe anodes of sodium-ion batteries: undervalued rate capability, Chem. Commun. 53 (2017) 2610e2613. Z. Jian, C. Bommier, L. Luo, Z. Li, W. Wang, C. Wang, P.A. Greaney, X. Ji, Insights on the mechanism of Na-ion storage in soft carbon anode, Chem. Mater. 29 (2017) 2314e2320. L. Xiao, Y. Cao, W.A. Henderson, M.L. Sushko, Y. Shao, J. Xiao, W. Wang, M.H. Engelhard, Z. Nie, J. Liu, Hard carbon nanoparticles as high-capacity, high-stability anodic materials for Na-ion batteries, Nano Energy 19 (2015) 279e288. R. Li, J. Huang, Z. Xu, H. Qi, L. Cao, Y. Liu, W. Li, J. Li, Controlling the thickness of disordered turbostratic nanodomains in hard carbon with enhanced sodium storage performance, Energy Technol. 6 (2018) 1080e1087. D.A. Stevens, J.R. Dahn, High capacity anode materials for rechargeable sodium-ion batteries, J. Electrochem. Soc. 147 (2000) 1271e1273. K. Gotoh, T. Ishikawa, S. Shimadzu, N. Yabuuchi, S. Komaba, K. Takeda, A. Goto, K. Deguchi, S. Ohki, K. Hashi, T. Shimizu, H. Ishida, NMR study for electrochemically inserted Na in hard carbon electrode of sodium ion battery, J. Power Sources 225 (2013) 137e140. J. Xu, M. Wang, N.P. Wickramaratne, M. Jaroniec, S. Dou, L. Dai, High-performance sodium ion batteries based on a 3D anode from nitrogen-doped graphene foams, Adv. Mater. 27 (2015) 2042. X. Wang, G. Li, F.M. Hassan, J. Li, X. Fan, R. Batmaz, X. Xiao, Z. Chen, Sulfur covalently bonded graphene with large capacity and high rate for high performance sodium-ion batteries anodes, Nanomater. Energy 15 (2015) 746e754. N. Sun, Y. Guan, Y. Liu, Q. Zhu, J. Shen, H. Liu, S. Zhou, B. Xu, Facile synthesis of free-standing, flexible hard carbon anode for high-performance sodium ion batteries using graphene as a multi-functional binder, Carbon 137 (2018) 475e483. Z.L. Wang, D. Xu, H.G. Wang, Z. Wu, X.B. Zhang, In situ fabrication of porous graphene electrodes for high-performance energy storage, ACS Nano 7 (2013) 2422e2430. X.L. Huang, R.Z. Wang, D. Xu, Z.L. Wang, H.G. Wang, J.J. Xu, Z. Wu, Q.C. Liu, Y. Zhang, X.B. Zhang, Homogeneous CoO on graphene for binder-free and ultralong-life lithium ion batteries, Adv. Funct. Mater. 23 (2013) 4345e4353. S. Xin, Y.G. Guo, L.J. Wan, Nanocarbon networks for advanced rechargeable lithium batteries, Acc. Chem. Res. 45 (2012) 1759e1769. I.H. Son, J.H. Park, S. Kwon, S. Park, M.H. Rümmeli, A. Bachmatiuk, H.J. Song, J. Ku, J.W. Choi, J.M. Choi, S.G. Doo, Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density, Nat. Commun. 6 (2015) 7393. J. Han, P. Liu, Y. Ito, X. Guo, A. Hirata, T. Fujita, M. Chen, Bilayered nanoporous graphene/molybdenum oxide for high rate lithium ion batteries, Nano Energy 45 (2018) 273e279. X. Zhang, S. Han, C. Fan, L. Li, W. Zhang, Hard carbon enveloped with graphene networks as lithium ion battery anode, Mater. Lett. 138 (2015) 259e261. L. Yin, Y. Wang, C. Han, Y. Kang, X. Ma, H. Xie, M. Wu, Self-assembly of disordered hard carbon/graphene hybrid for sodium-ion batteries, J. Power Sources 305 (2016) 156e160. C. Shi, L. Hu, J. Hou, K. Guo, T. Zhai, H. Li, Alkali metal boosted atom rearrangement in amorphous carbon towards crystalline graphitic belt skeleton for high performance supercapacitors, Energy Storage Mater. 15 (2018) 82e90. H. Liu, M. Jia, B. Cao, R. Chen, X. Lv, R. Tang, F. Wu, B. Xu, Nitrogen-doped carbon/graphene hybrid anode material for sodium-ion batteries with excellent rate capability, J. Power Sources 319 (2016) 195e201. N.G. Shang, P. Papakonstantinou, M. McMullan, M. Chu, A. Stamboulis, A. Potenza, S.S. Dhesi, H. Marchetto, Catalyst-free efficient growth, orientation and biosensing properties of multilayer graphene nanoflake films with sharp edge planes, Adv. Funct. Mater. 18 (2008) 3506e3514. X. Zhang, S. Han, P. Xiao, C. Fan, W. Zhang, Thermal reduction of graphene
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849
R. Li et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
[38]
[39]
[40] [41]
[42]
[43]
[44]
[45]
[46]
oxide mixed with hard carbon and their high performance as lithium ion battery anode, Carbon 100 (2016) 600e607. D.H. Seo, A.E. Rider, Z.J. Han, S. Kumar, K. Ostrikov, Plasma break-down and Re-build: same functional vertical graphenes from diverse natural precursors, Adv. Mater. 25 (2013) 5638e5642. S. Niyogi, E. Bekyarova, M.E. Itkis, H. Zhang, K. Shepperd, J. Hicks, M. Sprinkle, Spectroscopy of covalently functionalized graphene, Nano Lett. 10 (2010) 4061e4066. L.M. Malard, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene, Phys. Rep. 473 (2009) 51e87. X. Zhou, F. Chen, T. Bai, B. Long, Q. Liao, Y. Ren, J. Yang, Interconnected highly graphitic carbon nanosheets derived from wheat stalk as high performance anode materials for lithium ion batteries, Green Chem. 18 (2016) 2078e2088. S. Lee, N. Yabuuchi, B.M. Gallant, S. Chen, B.-S. Kim, P.T. Hammond, Y. ShaoHorn, High-power lithium batteries from functionalized carbon-nanotube electrodes, Nat. Nanotechnol. 5 (2010) 531e537. Y. Zhang, Q. Ma, S. Wang, X. Liu, L. Li, Poly (vinyl alcohol)-assisted fabrication of hollow carbon spheres/reduced graphene oxide nanocomposites for highperformance lithium-ion battery anodes, ACS Nano 12 (2018) 4824e4834. C. Wang, D. Li, T. Zhai, H. Wang, Q. Sun, H. Li, Direct conversion of waste tires into three-dimensional graphene, Energy Storage Mater. (2019), https:// doi.org/10.1016/j.ensm.2019.04.014. Z. Wu, W. Ren, L. Gao, B. Liu, C. Jiang, H. Cheng, Synthesis of high-quality graphene with a pre-determined number of layers, Carbon 47 (2009) 493e499. T. Liu, X. Li, Biomass-derived nanostructured porous carbons for sodium ion
9
batteries: a review, Mater. Technol. 34 (2018) 232e245. [47] Y. Liu, L. Fan, L. Jiao, Graphene highly scattered in porous carbon nanofibers: a binder-free and high-performance anode for sodium-ion batteries, J. Mater. Chem. A 5 (2017) 1698e1705. [48] H.R. Byon, B.M. Gallant, S.W. Lee, Y.S. Horn, Role of oxygen functional groups in carbon nanotube/graphene freestanding electrodes for high performance lithium batteries, Adv. Funct. Mater. 23 (2013) 1037e1045. [49] L. Su, L. Kong, S. Hao, Y. Zhao, Z. Ma, X. Qin, G. Shao, Honeycomb-like porous carbon with nano-graphitic domains, supported on graphene layers: applicability for lithium/sodium storage, ACS Sustain. Chem. Eng. 7 (2019) 10986e10994. [50] Z. Lyu, L. Yang, D. Xu, J. Zhao, H. Lai, Y. Jiang, Q. Wu, Y. Li, X. Wang, Z. Hu, Hierarchical carbon nanocages as high-rate anodes for Li-and Na-ion batteries, Nano Res. 8 (2015) 3535e3543. [51] Z. Lyu, R. Feng, J. Zhao, H. Fan, D. Xu, Q. Wu, L. Yang, Q. Chen, X. Wang, Z. Hu, Nitrogen-Doped carbon nanocages as high-rate anode for lithium ion batteries, Acta Chim. Sin. 73 (2015) 1013e1017. [52] H. Ru, N. Bai, K. Xiang, W. Zhou, H. Chen, X.S. Zhao, Porous carbons derived from microalgae with enhanced electrochemical performance for lithium-ion batteries, Electrochim. Acta 194 (2016) 10e16. [53] W. Lv, J. Zhao, F. Wen, J. Xiang, L. Li, L. Wang, Z. Liu, Y. Tian, Carbonaceous photonic crystals as ultralong cycling anodes for lithium and sodium batteries, J. Mater. Chem. A 3 (2015) 13786e13793. [54] H. Sun, H. Xiao, W. Song, J. Wang, W. Zhang, S. Ru, Z. Ai, C. Wang, A novel Ndoped organic porous carbon derive from water-based alkyd resin for lithium ion battery anode materials, J. Alloy. Comp. 805 (2019) 984e990.
Please cite this article as: R. Li et al., A sandwich-like porous hard carbon/graphene hybrid derived from rapeseed shuck for high-performance lithium-ion batteries, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.152849