porous-carbon anode for high performance lithium ion battery

Journal Pre-proofs A hybrid ZnO/Si/porous-carbon anode for high performance lithium ion battery Xiaochen Sun, Jinling Gao, Chen Wang, Xuan Gao, Junsong Liu, Nan Gao, Hongdong Li, Yu Wang, Kaifeng Yu PII: DOI: Reference:

S1385-8947(19)32610-5 https://doi.org/10.1016/j.cej.2019.123198 CEJ 123198

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

11 June 2019 14 October 2019 15 October 2019

Please cite this article as: X. Sun, J. Gao, C. Wang, X. Gao, J. Liu, N. Gao, H. Li, Y. Wang, K. Yu, A hybrid ZnO/ Si/porous-carbon anode for high performance lithium ion battery, Chemical Engineering Journal (2019), doi: https:// doi.org/10.1016/j.cej.2019.123198

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A hybrid ZnO/Si/porous-carbon anode for high performance lithium ion battery Xiaochen Sun,1 Jinling Gao,1 Chen Wang,1 Xuan Gao,1 Junsong Liu,1 Nan Gao,1Hongdong Li,*1 Yu Wang,2 Kaifeng Yu2 1

State Key Lab of Superhard Materials, College of Physics, Jilin University, Changchun 130012, PR China

2

College of Materials Science and Engineering, Jilin University, Changchun 130025, PR China

Abstract In this work, we report an anode material consisting of three-dimensional porous-carbon, nanometer-sized ZnO and Si nanoparticles to realize the high-performance lithium ion batteries. The composite powders are prepared following the processes of fabricating ZnO precusor by co-precipitation, hydrothermal reaction of mixed ZnO/SiO/porous-carbon powders, and subsequent neutralization and roast treatments. Using the hybrid anode material, the enhanced capacity performance (more than 900 mA h g-1 at 0.2 C after 300 cycles) and remarkable long-term cycle stability (more than 500 mA h g-1 at 2 C after 300 cycles) are achieved, which are significantly higher than that of using ZnO or graphite alone as anode. The improvement is ascribed to the synergistic effect of the highly conductive and large surface area porous-carbon, three-dimensional ZnO nanorods, and high adsorption of Li+ of Si particles.

*Corresponding Author Email address: [email protected]

1. Introduction With the expanding requirements in developing green technologies to power high efficiency, lithium ion batteries (LIBs) with high energy density and long cycle life have become one of the most crucial devices for highly efficient energy storage and conversion [1]. For LIBs, the choice of a novel anode with high capacity to replace conventional graphite (theoretical capacity of 372 mA h g-1) is essential to enhance the electrochemical performance [2, 3]. Zinc oxide (ZnO) has been widely used as catalysts, luminescence, photovoltaic devices [4, 5],owing to its advantages of low-cost, non-toxic, moderate band gap (~3.3 eV), as well as a higher absorption efficiency across the large fraction of the solar spectrum [6-8]. Meanwhile, it has drawn much attention for its high theoretical capacity (978 mA h g-1) [9], as well as a larger lithium ion (Li+) diffusion coefficient compared with other transition metal oxides [10, 11]. However, the serious volume change during the charge-discharge process, and the low electronic conductivity, lead to the inferior cycling stability and reduced rate capacity [12, 13], which are unfavorable for its practical applications in LIBs. Lots of attempts have been made to overcome the shortcomes of ZnO anode in LIBs [14-17]. It is demonstrated that the nanostructure design of ZnO (including zero-dimensional nanoparticles [18], one-dimensional nanowires [19], two-dimensional nanosheets [16], and three-dimensional flower structures [20]) effectively relieve the volume expansion to enhance its cycling capability, and the path of electron transfer could be shorten to enhance rate performance [21]. Moreover, various carbon materials such as graphene [22], carbon nanotube [23] and porous-carbon (PC) [24] have been combined with ZnO to increase the charge/discharge efficiency and the conductivity of hybrid anode. Among them, the PC is regarded as an ideal matrix to support the metal-oxides-based anodes for LIBs, since its pore-rich structure can provide excellent electron transport and buffer the volume expansion of nanoparticles upon cycling, and prevent the electrodes from aggregation and pulverization 1

[24, 25]. As summarized in Table I, although the most reported capacities of hybrid ZnO/carbon anodes are in the region of 450850 mA h g-1 [13, 14, 16, 24, 26-28], it is still a challenge to approach the theoretical capacity of ZnO. Recently, a complex structure of ZnO/ZnFe2O4/N-doped-carbon micro-polyhedrons was reported to achieve a high capacity of 1000 mA h g-1 (at 200 mA h g-1 after 100cycles) [29]. However, the preparation process of this anode structure is relatively complex and unfavorable for industrialization. It is accepted that silicon (Si) is another attractive anode material having high theoretical specific capacity of 4200 mA h g-1 [3, 30], but its cycling stability is poor due to the destructive volumetric expansion-contraction in charge-discharge process [31-33]. The other suitable anode material of SiO with unique microstructure is generally mixed with Si, as the thermodynamically unstable SiO could transform into nanocrystallite Si and amorphous Si-oxide matrix (SiO2) during high-temperature treatment [34-37]. It is thus speculated that introducing the Si and/or silicon oxide nanoparticles into ZnO/PC (ZPC) hybrids anode might be favorable for increasing capacity and stability of the ZnO-anode related LIBs. In this work, we synthesize a hybrid ZnO/Si/PC (ZSPC) nanocomposite consisting of PC matrix and ZnO nanorods with Si nanoparticles embedded. Based on the anode, the LIBs exhibit significant high rate performances (934 mA h g-1 at 0.2 C after 300 cycles) and superior long-term cyclic stability (with a capacity of 547mA h g-1 at 2 C after 300 cycles), which are significantly higher than those of using ZnO and/or graphite as anode. The enhancement mechanisms are discussed.

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Table I Comparison of electrochemical performances of the ZnO and carbon hybrids anodes for LIBs.

Anode Material

Electrochemical performances

Ref.

ZnO@Graphene

850 mA h g-1 (at 97.8 mA h g-1 after 50 cycles)

[13]

ZnO-loaded/porous carbon

653 mA h g-1 (at 195.6 mA h g-1 after 100 cycles)

[24]

C-ZnO porous nanosheet

851 mA h g-1 (at 100 mA h g-1 after 50 cycles)

[16]

CNT@ZnO

709.2 mA h g-1 (at 100 mA h g-1after 50 cycles)

[27]

ZnO/C hierarchical porous nanorods

623.9 mA h g-1 (at 978 mA h g-1 after 1500 cycles)

[26]

ZnO/ZnFe2O4/N-doped-carbon micro-polyhedrons

1000 mA h g-1 (at 200 mA h g-1 after 100 cycles)

[20]

ZnO/mesoporous carbon

610 mA h g-1 (at 100 mA h g-1 after 50 cycles)

[28]

ZnO/Three dimensionally ordered macroporous carbon

673 mA h g-1 (at 97.8 mA h g-1 after 300 cycles)

[14]

ZnO/porous-carbon

453 mA h g-1 (at 195.6 mA h g-1 after 300 cycles)

ZnO/Si/porous-carbon

934 mA h g-1 (at 195.6 mA h g-1 after 300 cycles)

This work

2. Experimental section 2.1 Preparation of hybrid ZSPC The schematic illustration for the synthesis procedures of ZSPC nanocomposites is presented in Fig. 1.The PC derived from sunflower straw as a host matrix, the detailed preparation process was shown in Supporting Information. The precursors of 0.44 g Zn (AC)2·2H2O, 0.72 g CTAB (cetyltrimethylammoniumbromide), 0.2 g NaOH and 0.268 ml EDA (ethylenediamine) were dissolved separately in 40 ml anhydrous ethanol. Then, the ethanol solutions CTAB, NaOH and EDA were added dropwise into the stirring Zn (AC)2·2H2O ethanol solution in turn, and the time of dropping was 30 min. Subsequently, the 0.15 g composite powders composed with SiO and PC (1:2) were put in the solution having the total volume of 160 ml and stirred for 30 minutes. The suspensions were moved to Teflon-lined autoclaves followed by heating at 180 oC for 8 h. The resulting precipitation was etched with ammonia for 6 h, centrifuged and washed with ethanol until the pH value reached 3

approximately 7. Finally, the washed powders were dried at 60 oC for 24 h, the ZSPC nanocomposites could be obtained by further annealed in argon gas at 500 oC for 3 h at a heating rate of 3 oC min-1. For comparison, the ZPC powder was synthesized and the procedures was described in Supporting Information.

Fig. 1. Schematic illustration for the synthesis procedures of ZnO/Si/porous-carbon (ZSPC) composite powders.

2.2 Material characterizations The elements, morphology, and crystalline structure of the hybrid ZSPC materials were tested by means of X-ray diffractometry (XRD, 6000 AS-3K, NOPC), Raman spectroscopy (Witech CRM200, excitation at 532 nm), X-ray photoelectron spectroscopy (XPS, ESCALAB-250Xi), scanning electron microscopy (SEM, S-4800, Hitachi Limited), and transmission electron microscopy (TEM, JEM-2100F, JEOL). Thermogravimetric analysis (TGA, SDT Q-600, TA Instruments-Waters LLC) was conducted under air atmosphere with a heating rate of 10 °C min-1.The nitrogen adsorption/desorption tests were performed for surface area on Brunauer–Emmett–Teller (BET) measurements (JW-BK132F surface area analyzer).

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2.3 Electrochemical measurements Electrochemical measurements were tested using two electrodes of CR2025 button cells. The electrodes were prepared by coating slurries containing the 80 wt% active material powders, 10wt% carbon black and 10wt% polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone with stirring. The slurry was coated on copper foil by glass rod and then dried at 120 °C for 12 h. Lithium foil was used as the counter and reference electrode, besides Celgard 2300 was used as a separator, and 1 M LiPF6 was used as the electrolyte. A constant current charge/discharge test under a different current density was carried out on Land Battery Measurement System (CT2001 1A), with a cut-off voltage of 0.01‒3V at room temperature. Cyclic voltammograms (CVs) of scanning rate at 0.2 mV s-1and electrochemical impedance spectroscopy (EIS) were carried out at room temperature on CHI660E electrochemical workstation. The galvanostatic titration technique (GITT) was performed by discharging/charging in the potential range of 3.0‒0.01 V for 10 min at 0.2 C rate with a relaxation period of 10 min.

3. Results and discussion The XRD patterns of ZSPC, as well as the ZPC and pure ZnO for comparision, are presented in Fig. 2a. The main peaks indexed are assigned to the corresponding diffractions of wurtzite ZnO (JCPDS No. 1-1336). Because there is only a small amount of crystalline Si in the sample, the weak diffraction patterns from Si are not evident with the strong background from ZnO and carbon matrix. Moreover, the broad peak centered at about 23o appears with a very weak intensity is assigned to the overlap between amorphous carbon and SiO2 [38]. The Raman spectroscopy result of ZSPC sample (in Fig. 2b) shows that the characteristic peak at 438 cm-1 corresponds to the E2 vibration of ZnO [39]. The two broad peaks of D-band (at 1340 cm-1) and G-band (at 1588 cm-1) are presented, demonstrating the 5

existence of disordered carbon and/or defective graphitic. The weak characteristic peak at around 520 cm-1 corresponding to crystalline Si [36, 40] is presented as a shoulder of the peak from ZnO. Therefore, the as-prepared samples mainly consist of crystalline ZnO with a small amount of amorphous carbon/SiO2, and crystalline Si. The thermogravimetric (TG) spectrum for the ZSPC sample is shown in Fig. 2c. It is observed that about 50% weight loss from room temperature to 450 °C, while the weight of the remainder is unchanged until to 800 °C. The weight loss process is divided into two regions, the Region I at 100–200 °C corresponds to the weight loss due to the evaporation of adsorbed water in air [2], and the Region II at 200–450 °C is related to the loss of pyrolysis PC from the composite [41]. The remainder at high temperatures (450–800 oC) mainly consists of the thermally stable oxides of ZnO powder, as well as a small amount of SiO 2, implying that the ZnO content in ZSPC is close to 50%.

Fig. 2. (a) XRD patterns of the as-prepared ZSPC, ZPC, and pure ZnO samples. (b) Raman spectrum and (c) TG curve of ZSPC sample, (d) Nitrogen adsorption/desorption isotherms of ZSPC and ZPC samples. The inset of (d) shows the pore size of ZSPC (ZPC) nanocomposite. 6

The N2 adsorption/desorption isotherm of the ZSPC sample shows a typical IV-type isotherm (Fig. 2d), indicating a mesoporous structure. An indicator of macropore of a sudden N2 adsorption appears at the higher pressure of P/P0 (0.8–1.0) [42]. The N2 adsorption/desorption isotherm of the ZPC sample shows a similar behavior to ZPSC. Interestingly, for the specific surface area of ZSPC with Si nanoparticles is 190 m2 g-1, slightly smaller than that of ZPC (219 m2 g-1), and the pore volume of ZSPC (7.7 cm3 g-1) is larger than that of ZPC (0.3 cm3 g-1), meaning that the ZnO/Si composites is impregnated well into the PC matrix. The large surface area is benefit to the more interfacial contact with the electrolyte, thus it promotes the Li+ transport kinetics and effective volume to buffer the strain during the Li+ insertion and extraction [43]. Based on the Barrett–Joyner–Halenda (BJH) equation, the pore size of ZSPC (ZPC) nanocomposite is mainly distributed in 3−10 nm (1−5 nm), as shown in the inset of Fig. 2d. The pore-rich structure can effectively promote the permeation of the electrolyte, which is beneficial for the electrode reaction and electrochemical cyclic performance [16, 24]. In Fig. S1a, the signals of Zn, Si, C, and O elements are found in the XPS spectrum of ZSPC powder [44]. The spectrum of C 1s (Fig. S1b) exhibits five peaks centered at 283.8, 284.6, 285.3, 285.6, and 286.5 eV, corresponding to the C-Si, C=C, C-C, C-O-Zn, and C-O bonds, in turn [45, 46]. There are three peaks in the spectrum of Si 2p (Fig. S1c), which belong to the Si-C (101.1 eV), Si-O (102.3 eV), and SiO2 bonds (103.5 eV) [44]. Meanwhile, the peaks for the O 1s spectrum (Fig. S1d) at 531.0, 532.5, 532.1, 532.4, 532.9, and 533.2eV are attributed to the Zn-O, C=O, Zn-O-C, Si-O, Zn-C, and SiO2 bonds in turn [47, 48]. The results further prove the interaction between ZnO, PC, Si and SiOx in the samples. The

7

high-resolution XPS spectrum in the Zn 2p region of the ZSPC sample is shown in Fig. S1e. The characteristic peaks at 1022.7 eV and 1045.7 eV correspond to the binding energy of Zn 2p3/2 and Zn 2p1/2, respectively, revealing a normal state of Zn2+ in the samples. Compared with pure ZnO, the Zn 2p peak for ZSPC shifts to a higher binding energy, ascribed to the formation of Zn–O–Si on the interface between the ZnO particles and the pore walls [44], which is beneficial to keep the structure stability. The typical porous feature of the PC materials (Fig. S2a) provide the porous carbonaceous substrate for fabricating ZSPC structure. The EDS spectra (Fig. S2b) reveal the uniform distribution of the C, O and Si elements in the biological PC sample.The ZSPC has a 3-dimensional architecture (Fig. 3a, b), which commonly exhibits more interspace to accommodate volume expansion and more active sites to accelerate Li+ storage, resulting in excellent electrochemical stability and high rate capability. Moreover, there are some spiny ZnO nanorods appreaing in the ZSPC sample (Fig. 3). The SEM image of ZSPC after long cycling for 80 circles (Fig. S3) indicates a slightly bulge, but no distinct variation in morphology occurs with respect to the initial morphology. It suggests that the ZSPC anode material is stable and not easy to be collapsed and degraded after cycles. The EDS elemental mappings in Fig. 3c-g prove the uniform distribution of Zn, O, C and Si elements. Furthermore, it is found that ZnO embedded with Si grows based on carbon matrix, and the SiO2 distributes on the edge of pore is originated from SiO and biological carbon which contains SiO2 (proved in Fig. S2). The content of Si nanoparticles (especially embedded in ZnO nanorods) is low and lower than the content of SiO2 appearing on the edge of pore. The abundant SiO2 on the edge of pore, as well as Si, would play an important role in improving the capacity of the cells.

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Fig. 3. (a, b) SEM micrographs and (c-g) corresponding EDS elemental maps of the ZSPC powders.

Compared with the spiny morphology of ZPC composite in the SEM image (Fig. S4), it is concluded that the formation of three-dimensional flower feature of ZSPC is attribuated to introducing precusor SiO. The SiO could partly be transformed into crystallite Si and SiO X (Si-suboxide and amorphous SiO2) during heating treatment at 500 °C, following the reaction equation:

. The Si particles work as modifiers to alter their

surface properties, induce its growth direction and relieve possible agglomeration. The morphlogies of the nano ZnO nanorods with embeded Si nanoparticles are evident in the TEM images (Figs. 4a, b). The Si nanoparticles are generally embeded in ZnO nanorods. The HRTEM images and selected area electron diffraction (SAED) patterns of ZSPC are presented in Fig. 4 (c) and (d), respectively. Based on the typical lattice spacings of (100), (101), (110), (002) facets of ZnO and (111) facets of Si, the nanosized particles in the PC matrix observed are assigned to crystalline ZnO and Si. The above results support the presence of strong interactions between ZnO, Si, and C, where an excellent pathway for 9

electron transport are provided during charge/discharge cycles [49].

Fig. 4. TEM images of ZSPC powders at (a) low and (b) high magnitude, showing the Si nanoparticles and ZnO nanorods in the PC matrix. (c) HRTEM images and (d) SAED pattern of ZSPX powders.

The electrochemical properties of ZSPC anode in LIBs are examined using a half-cell. The CV curves for ZSPC composite anode at a scan rate of 0.2 mV s-1 in the voltage region of 1−3 V help clarifying the reversible electrochemical reaction between Li+ and anode (Fig. 5). In general, the insertion and extraction of Li+ in electrode can be represented by the reaction equation [50]: 2Li+ + ZnO +2e- → Li2O + Zn

(2)

Zn +xLi+ + xe- ↔ LiZn

(3)

The electrochemical performance of the ZSPC anode is examined by the 10

Discharge/Charge profiles over the potential window of 0.01−3V at 0.2 C (Fig. 5a). The discharge and charge capacities in the first cycle are 2406 and 1493 mA h g-1, respectively, presenting the initial coulombic efficiency is 63%. The columbic efficiency is higher than 97% in the following cycles, indicating the outstanding cycling performance. During the first cycle, the irreversible capacity loss is due to the formation of solid electrolyte interface (SEI) film and the LiZn alloying [51]. This feature vanishes at the subsequent cycles, confirming that the SEI formation is completed during the first cycle. Upon the further cycling the potential curves overlap with each other, demonstrating the enhanced electrochemical stability and reversibility of the ZSPC electrode.

Fig. 5. Charge and Discharge profiles of the cells made of (a) ZSPC and (c) ZPC anodes at 0.2 C. Cyclic voltammogram curves of (b) ZSPC and (d) ZPC anodes with a scan rate of 0.1 mv s-1.

In Fig. 5b, the CV spectra with a scan rate of 0.1 mv s-1 between 0.01 and 3 V of ZSPC at the 1st, 2nd and 3rd cycles show the redox reaction in the battery in the processes of charge 11

and discharge. During the first cathodic scan, a peak at around 0.1 V vs. Li+/Li corresponds to the insertion of Li+ into the material. A reduction peak at ~0.3 V is associated with the reduction of Zn2+ to Zn and its further alloying to LiZn, and formation of a SEI layer. In the first anode scan, two obvious peaks at ~0.6 V and ~1.3 V are related to multi-step dealloying reactions of LiZn [22]. In the subsequent cathodic scans, the peak at 0.3 V shifts to 1 V, indicating that the SEI formation is completed at the initial cycle, and it is no longer reflected in the CV curves. In the further operation, the peak at 0.6 V corresponds to formation of the LiZn alloy [14]. The CV curves of the 2nd and 3rd cycles tend to be coincident, and the new clearly sharp peaks between 0 and 0.5 V after the first cycle signify the reduction of SiOx and reversible lithiation of silicon [52]. For comparison, the discharge/charge profiles over the potential window of 0.01−3V at 0.2 C of the ZPC anode are examined (Fig. 5c). The discharge and charge capacities in the first cycle are 1312 and 837 mA h g-1, respectively, having an initial Coulombic efficiency of 64%. The Columbic efficiency is higher than 92% in the following cycles, indicating a steady cycling performance. The CV spectra of ZPC is performed in Fig. 5d. The peak at ~0.3 V during the first reduction process and the two obvious peaks at ~0.6 V and ~1.3 V in the first anodic scan are similar to ZPSC. Moreover, an irreversible cathodic peak occurs at 0.75 V versus Li/Li+, corresponding to the formation of SEI layer of PC [53]. In the subsequent scans, the curve tends to coincide, confirming that the SEI formation is completed during first two cycles. The relatively poor stability and capacity of ZPC with respect to the case of ZSPC demonstrate the important role of Si in improving the Li+ storage performance.

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Fig. 6. (a) Cycling performance and Coulombic efficiency over 100 cycles at 0.2 C for the cells with ZnO, ZPC and ZSPC anodes. (b) Rate performance at various current densities for the cells with ZPC and ZSPC anodes.

The cyclic performance of the cells with ZSPC, ZPC and ZnO anodes are tested at a rate of 0.2 C after 100 cycles (Fig. 6a). The reversible capacity of the ZSPC anode is 973 mA h g-1 after 100 cycles, which is 4 times the capacity of pristine ZnO (240 mA h g-1), and 2.1 times the data of ZPC anode (453 mA h g-1). Importantly, the value is higher than most previous reports (450−850 mA h g-1) reported in literature [13, 14, 16, 24, 26, 27]. The high specific capacity of the ZSPC anode can be ascribed to the favorable combination of ZnO/Si and PC, which would undergo minimal structural damage upon cycling. From the electrodes at various rates from 0.1 C to 2 C (Fig. 6b), the ZSPC anode exhibits excellent rate performance. The reversible capacity at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C rate are 1734, 1235, 868, 635 and 403 mA h g-1, respectively. When the current density drops to 0.1 C, the reversible capacity of 1410 mA h g-1 is restored, and the capacity retention rate reaches 81%, indicating that the ZSPC composite anode has a favorable capacity retention and excellent stability. However, for the case of the ZPC anode, the specific capacity drops from 719 mA h g-1 to 290 mA h g-1, when the current density increases from 0.1 C to 2 C. It is further demonstrated the introduced Si could significantly improves the capacity performance of ZPC anode in LIBs. To investigate the role of ZnO content in ZSPC anode in electrochemical performance, in 13

comparison to the 50% ZnO in ZSPC discussed in the text, two groups of ZnO content of 64%, (named as ZSPC-1) and 37% (named as ZSPC-2) are tested (Fig. S5). The cycling performance and coulombic efficiency reveal that there is a suitable content of ZnO (~50%) for realizing optimized anode. Fig. 7 shows the cycling performance of ZSPC composite electrodes after 300 cycles at 0.2 C, which is cycled between 0.01 and 3 V. The discharge and charge capacities at the first cycle are 2406 mA h g-1 and 1493 mA h g-1, respectively, with a low initial coulombic efficiency of 63%, due to the formation of a SEI film related to electrolyte decomposition and the irreversible conversion from ZnO to Zn/Li2O mixtures. The low Coulombic efficiency is limited to the first cycle, after which the coulombic efficiency is above 97%, suggesting most side reactions occur only in the initial cycle. A high reversible capacity (934 mA h g-1 at 0.2 C and 547 mA h g-1 at 2 C) can continuously maintains after 300 cycles.

Fig.7. Discharge/Charge cycling performance and coulombic efficiency over 300 cycles at 0.2 C and 2 C of the cell with ZSPC anode.

To further study the performance enhancement mechanism of the ZSPC anode for LIBs, the EIS and measurements were carried out. The EIS curves of ZSPC before and after 10th cycles have been performed in the frequency range of 100 kHz to 0.01 Hz (Fig. S6). The 14

ZSPC shows a lower charge-transfer impedances and interface layer resistance after charge–discharge cycles, due to the activation of the electrode and more sufficient contact between the active material and the electrolyte [54]. Fig. S7a shows the GITT curves of ZSPC composite electrode during discharge/charge cycle as a function of time, and the inset shows the single step of GITT curve during discharge. The calculated DLi+ of the ZSPC anode dependent on the voltage applied are presented in Fig. S7b, the data are in the range of 10−13 to 10-11 cm2 s−1, which exhibits a higher diffusion coefficient compared with the GeOx/ZnO/C anodes (10−13 to 10-10 cm2 s−1) [17]. The fast Li+ diffusion observed for ZSPC is ascribed not only to its unique three-dimensional porous structure, but also the presence of PC, Si, and SiOX in the hybrid matrix. Therefore, the EIS and GITT results suggest that the low charge transfer resistance and higher Li+ diffusivity can effectively improve the charge transfer of the hybrid ZSPC electrode. 4. Conclusions In summary, the hybrid ZSPC anode is synthesized for realizing high-performance LIBs by hydrothermal method. The PC material derived from sunflower straw is used as the growth matrix with the Si nanoparticles embedded in ZnO. The hybrid anode exhibits the high reversible capacity (934 mA h g-1 at 0.2 C after 300 cycles) and long-term cyclic stability (547 mA h g-1 at 2 C after 300 cycles), which benefits from the high adsorption of Li+ of Si particles, large surface area of PC and three-dimensional flower-like structure of ZnO. This work opens new ideas for the design and manufacture of a class of anodes consisting of metallic oxide and silica-based materials to realize high performance LIBs in practical application fields.

Acknowledgements This work was supported by National Natural Science Foundation of China (No. 51672102 and No. 51972135). 15

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Highlights 1. Three dimensional nanosized ZnO/Si/porous-carbon were fabricated as anode material. 2. The anodes lead to improving the performances of corresponding lithium ion battery. 3. The mechanism of the novel anode for increasing the battery performances is studied.

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