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Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes for high rate and long cycle life Li-ion batteries
Accepted Manuscript Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes for high rate and long cycle life Li-ion batteries Jian-Gan Wang, Huanyan Liu, Hongzhen Liu, Xu Li, Ding Nan, Feiyu Kang PII:
S0925-8388(17)33152-3
DOI:
10.1016/j.jallcom.2017.09.112
Reference:
JALCOM 43168
To appear in:
Journal of Alloys and Compounds
Received Date: 13 May 2017 Revised Date:
8 September 2017
Accepted Date: 11 September 2017
Please cite this article as: J.-G. Wang, H. Liu, H. Liu, X. Li, D. Nan, F. Kang, Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes for high rate and long cycle life Li-ion batteries, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.09.112. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes
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for high rate and long cycle life Li-ion batteries
Jian-Gan Wang a *, Huanyan Liu a, Hongzhen Liu a, Xu Li b, Ding Nan c *, Feiyu Kang b State Key Laboratory of Solidification Processing, Center for Nano Energy Materials, School
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a
of Materials Science and Engineering, Northwestern Polytechnical University and Shaanxi Joint
b
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Lab of Graphene (NPU), Xi’an 710072, China
Institute of Advanced Materials Research, Graduate School at Shenzhen, Tsinghua University,
Shenzhen 518055, China
School of Materials Science and Engineering, Inner Mongolia University of
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c
Technology, Aimin Street 49, Hohhot 010051, China
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*Email: [email protected], [email protected]
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Abstract
High-voltage LiMn1.5Ni0.5O4 spinel with one-dimensional (1D) hollow and porous architecture is
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fabricated via a facile single-spinneret electrospinning technique. The hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers possess ~200 nm in diameter and tens of micrometers in length, as well as a specific surface area as high as 43.2 m2 g-1. When served as Li-ion battery
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cathodes, the as-fabricated material delivers high specific capacities of 135 and 98 mAh g-1 at 0.68 C and 20.4 C, respectively. Under a long-term cycling operation at 6.8 C, the cathode
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sustains good capacity retention of 90% after 1000 cycles. The outstanding electrochemical performance can be attributed to the porous 1D hollow nanostructure that can enlarge effective electrode/electrolyte contact areas, shorten electron/ion transport distance and accommodate
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volume change.
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Keywords: LiMn1.5Ni0.5O4; hollow structure; Li-ion battery; electrospinning; cathode
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1. Introduction
Nanomaterials and nanotechnology have been considered as an advanced and promising strategy
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to boost the development of high-efficient energy storage systems, such as rechargeable Li-ion batteries (LIBs) [1-3] Among various nanostructures, one-dimensional (1D) nanomaterials, including nanorods, nanowires, nanofibers, and nanotubes, are of significant interest in LIB
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community due to their intriguing architecture [4-7]. Particularly, 1D tubular (hollow) nanostructures not only provide short solid-state transport pathways along the confined
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dimension but also buffer the structural strains caused by the repeated Li-ion insertion/extraction processes [8-10]. In addition, the 1D and nanotubular materials could form an interconnected and porous network to permit fast electrolyte diffusion and ensure the effective contact area. Spinel LiMn1.5Ni0.5O4 is a promising cathode candidate for the next-generation high-power
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LIBs owing to its fast three-dimensional (3D) Li+ diffusion channels, high operating voltage of ~4.7 V, low cost and eco-friendliness [11, 12]. The high-voltage spinel LiNi0.5Mn1.5O4 cathode can deliver an energy density as high as 658 Wh kg-1, which is much higher than those of
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LiMn2O4 (440 Wh kg-1) and LiFePO4 (500 Wh kg-1) [13]. Up to now, many kinds of synthesis
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methods, such as solid-state reactions, co-precipitation, sol-gel and spray pyrolysis, has been reported for the preparation of LiMn1.5Ni0.5O4 [11, 14]. However, it is still a challenge to achieve a LiMn1.5Ni0.5O4 material with excellent rate capacity and cyclability because of (i) the difficulty to control uniform distribution, stoichiometric composition, and good crystallinity of the LiMn1.5Ni0.5O4 and (ii) the unstable electrode/electrolyte interfaces under high potential operation [11, 15]. To improve the electrochemical performance, a variety of strategies, such as cation doping, nanostructuring and surface modification, were developed to stabilize the cathode
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structure [15-22]. Among them, nanostructuring is a simple and effective approach. Nevertheless, there are a few studies focusing on the morphology-controlled synthesis of LiMn1.5Ni0.5O4 nanostructures (e.g., nanoparticle, nanorod, and nanofiber) probably owing to
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undesirable particle growth during the high-temperature calcination process [13-15, 23-25] As particularly mentioned earlier, 1D tubular (hollow) nanostructure is rather attractive, however, to
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the best of our knowledge, study on this fantastic topic has rarely been reported.
In this work, we report a 1D porous LiMn1.5Ni0.5O4 hollow nanofiber (LMNO HNF) via a
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facile single-spinneret electrospinning in combination with heat treatment. The as-electrospun polymer nanofibers function as a structure-directing template to confine nanoscaled particle growth along the 1D dimension. The heating rate is crucial to the formation of hollow structure. Benefiting from the unique architecture features, the LMNO HNF cathode exhibits outstanding
2. Experimental 2.1. Materials synthesis
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Li-ion storage performance with high-rate capability and long cycle life.
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All chemical reagents were of analytical grade and used as received. Electrospinning technique
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was employed to fabricate 1D LMNO HNF. In a typical fabrication procedure, 1.5 g of polyacrylonitrile (PAN, Mw=150000) was first dissolved into 15 ml of N,N-Dimethylformamide (DMF) to obtain a homogeneous polymer solution. Subsequently, lithium acetate dihydrate, manganese acetate tetrahydrate, manganese acetate tetrahydrate with a molar ratio of 2:3:1.02 were added to the solution under stirring. The mixture solution was then loaded into a 30 ml syringe. The electrospinning was carried out on Tongli TL-01 setup at room temperature. The distance between the needle and Al-foil collector was controlled to be about 15 cm with an
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applied voltage of 15 kV. The feeding rate of the solution from syringe was about 1.0 ml h-1. The as-fabricated nanofibrous mat was then transferred to a Muffle furnace for calcination. The furnace was heated to 750 °C at a slow heating rate of 0.5 °C min-1 and then subjected to
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calcination for 6 h under air atmosphere to yield the final products. For comparison, solid LMNO nanofibers (NF) were obtained at a high heating rate of 5 °C min-1 and bulk LMNO particles
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were prepared by conventional solid state sintering without electrospinning process. 2.2. Materials Characterization
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The crystallographic structure was identified by powder X-ray diffraction (XRD, X’Pert PRO MPD, Philips). The as-collected XRD data were analyzed using the Rietveld refinement method in the FullProf software package suite. Field emission scanning electron microscope (FE-SEM, FEI NanoSEM 450) and transmission electron microscope (TEM, FEI Tecnai F30G2) were used
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to observe the morphology. Brunauer-Emmet-Teller (BET) specific surface area was determined using N2 adsorption/desorption measurement (Mike ASAP 2020). The pore size distribution was analyzed by Barrett-Joyner-Halenda (BJH) model. The chemical composition of the LMNO
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sample was analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES, IRIS Intrepid II, Thermo Fisher).
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2.3. Electrochemical Evaluation
The electrochemical properties of the as-prepared products were measured using CR2030 cointype half cells. The working electrodes were prepared by coating a slurry of mixture containing 80 wt.% of active materials, 10 wt.% of acetylene black, and 10 wt.% of poly(vinylidene fluoride) onto a clean aluminum foil. After coating, the foil was dried overnight at 100 °C in a vacuum oven. The mass loading of the active materials was about 2.2±0.2 mg cm-2. Coin cells were
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assembled in an argon-filled glovebox using a metal Li foil as the counter electrode, Celgard 2320 as the separator, and 1 M LiPF6 in a mixture of 1:1 (v/v) ethylene carbonate (EC) /diemethyl carbonate (DMC) as the electrolyte. Cyclic voltammetry (CV) measurement was
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carried out on a Solatron electrochemical workstation (1260+1287) between 3.5 and 5.0 V (vs. Li/Li+). Galvanostatic charge/discharge curves were obtained from a Land Battery Testing
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System. 3. Results and discussion
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XRD analysis was carried out to identify the crystallographic phase. Fig. 1 exhibits the XRD pattern of the as-prepared LMNO HNF, NF and bulk products. All of the diffraction peaks can be readily assigned to the ordered cubic spinel LiNi0.5Mn1.5O4 phase with a space group of Fd3m (JPCDS 80-2162) [13, 15]. No peak of other impurities is observed, indicating high purity of the
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products. In addition, the sharp diffraction peaks reveals a high crystallinity of the structure. The lattice parameters determined by the Retrieved refinement method are 8.1704, 8.1798, and 8.1916 Å for the LMNO HNF, NF and bulk materials, respectively. The Li/Ni/Mn ratio from the
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ICP-AES analysis is determined to be 1.00/0.49/1.51, 1.00/0.53/1.52, and 1.00/0.52/1.52 for the LMNO HNF, NF and bulk sample, respectively, which are close to the chemical composition of
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the LiNi0.5Mn1.5O4.
The precursor fabric is composed of randomly interwoven nanofibers with smooth surface and an average diameter of 400 nm (Fig. S1). After calcination in air, the 1D nanostructure is well preserved (Fig. 2(a-b)), and the nanofibers have tens of microns in length and ~200 nm in diameter. In addition, the surface becomes rough mainly due to the decomposition of polymer and the growth of LMNO nanoparticles confined along the nanofibers. More interesting, a close
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SEM examination manifests unique hollow structure of the nanofibers, as evidenced by the open ends indicated in Fig. 2(c). The thickness of the LMNO nanowall is estimated to be 50 nm. The 1D porous hollow structure is clearly confirmed by TEM imaging (Fig. 2(d)). From the Fig. 2(e),
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the nanofiber wall is constructed by interconnected ultrafine nanograins with diameters of 30-60 nm. The distinct lattice fringes in HRTEM image (Fig. 2(f)) indicate good crystallinity of the products, and the interplanar distance of 0.47 nm agrees well with the d-spacing of (111) plane of
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spinel LMNO.
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The textual characteristics of the LMNO HNF was examined by N2 adsorption/desorption measurements. For comparison, a control sample of bulk LMNO particles with an average diameter of ~200 nm was prepared using conventional solid-state sintering (Fig. S2). Fig. 3 exhibits the resulting isotherms of the two LMNO products, which are typical of IUPAC Type II. The N2 adsorption uptake of the LMNO HNF in the full P/P0 range is much larger than that of
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the LMNO bulk, indicating a much higher specific surface area. Based on the BET calculation, the specific surface area of the LMNO HNF is as high as 43.2 m2 g-1, which is about five times of the control sample (8.6 m2 g-1). In addition, the BJH pore-size distribution (inset) reveals the
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presence of abundant mesopores in the LMNO HNF. The porosity of LMNO HNF is resulting
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from the construction of ultrafine nanoparticles along the 1D direction and the unique hollow structure. Notably, the hierarchical porous architecture could enlarge the electrode/electrolyte interfacial contact area for high energy storage and reduce the solid-state Li-ion diffusion distance in active materials to boost high-rate delivery [24, 26]. Electrospinning is a simple and versatile technique to fabricate 1D nanostructures with different morphologies by controlling spinneret configuration, polymer precursor and posttreatment [27]. There are various solid nanofibers that have been prepared by single-spinneret
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electrospinning [13, 23, 25], but the nanofibers with unique hollow structure are rarely reported, especially for complex metal oxides. It is thus interesting to probe the possible formation mechanism of LMNO HNF, as schematically illustrated in Fig. 4. Generally, the generation of
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nanofibers is resulting from the decomposition of the polymer precursor containing metal salts at high temperatures. In this study, it is revealed that the heating rate plays a crucial role in the microstructure. The key issue is to control the polymer decomposition rate vs. the kinetic
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diffusion rate of metal elements [23, 26]. At a slow heating rate (e.g., 0.5 °C min-1), the polymer nanofiber could serve as a robust structure-directing template for the formation of rigid 1D
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nanostructure. As the PAN is gradually eliminated, the metal species at the outer surface exposing to the air atmosphere would generate Li-metal oxide nucleus while those in the interior part will migrate outward through kinetic diffusion. The Li-metal oxide nucleus will further grow and crystallize into a shell of LMNO phase at high temperature, and a hollow structure is
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obtained after the completely removal of PAN. At a fast heating rate (5 °C min-1), the Li-metal oxide shells will collapse into solid 1D nanofiber (Fig. S3) due to the insufficient kinetic diffusion time of the metal cation and the relatively rapid decomposition of the polymer
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backbone [28-30].
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The electrochemical properties of the as-prepared samples are evaluated in half cells. Fig. 5(a) shows CV curves of the LMNO HNF cathode at a scan rate of 0.1 mV s-1. The pronounced A1/C1 redox couple in the high-voltage region is associated with the two-step oxidation/reduction of Ni2+/Ni3+ and Ni3+/Ni4+. The weak A2/C2 peaks in the low-voltage range can be attributed to the Mn3+/Mn4+ redox couple [11, 17]. It is important to note that the CV curves are well overlapped, indicating excellent electrochemical reversibility and good cycling stability of the cathodic host materials for Li-ion insertion/extraction reactions. The typical
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electrochemical behavior is further confirmed by galvanostatic charge/discharge measurement. As shown in Fig. 5(b), the long and flat plateaus at approximately 4.7 V and the short plateaus at around 4.0 V represent the reversible reactions of Ni and Mn cations, respectively, which
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coincides with the CV results. The narrow charge/discharge potential difference indicates a small electrode polarization. The well-defined charge/discharge plateaus can be ascribed to the high
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crystallinity of the samples.
Fig. 6(a) exhibits a comparison of the cycling performance of the LMNO cathodes at a
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0.68C (100 mA g-1) rate. The hollow-structured LMNO cathode delivers a high reversible discharge capacity of 135 mAh g1 with an initial Coulombic efficiency of 93%. More impressively, the cathode can retain 96% of the initial capacity after 200 cycles, which is much better than that of the LMNO NF (86.8%) and LMNO bulk (76%) cathodes. In addition to the cycling performance, the hollow-structured LMNO cathode also demonstrates superior rate
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capability. As shown in Fig. 6(b), it reveals higher discharge capacity than the bulk counterpart at high current rates. Even at a high rate of 20.4 C, the cathode can still deliver a specific capacity of 98 mAh g-1. The capacity recovers its initial value when the current rate is reduced to
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0.34 C, again indicating the excellent electrochemical reversibility of the LMNO HNF cathode.
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The electrochemical properties of the LMNO HNF are superior or comparable to the recent reported LMNO materials [13-15, 19, 21, 24, 25, 31-37], as summarized in Table 1. Fig. 6(c) further presents the cycling performance of the cathode operated at a high 6.8 C rate. The specific capacity increases to a maximum value of 109 mAh g-1 during the first ten cycles probably due to the activation process. Notably, the cathode retains almost 90% (94.3% and 97.8%) of the maximum capacity after 1000 (500 and 200) extended cycles. The long-term cycling performance is superior or at least comparable to the LMNO materials reported in
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literature, such as porous LMNO nanorods (91% after 500 cycles) [15], LMNO/carbon nanofiber nanocomposites (88% after 500 cycles) [21], Cr-doped LMNO microparticles (90% after 500
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cycles) [36] and hollow LMNO spheres (96.6% after 200 cycles) [24]. The outstanding Li-ion storage performance of the LMNO HNF cathode can be rationalized by its unique hierarchical architecture. First, the porous hollow structure with large surface area
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enables efficient electrolyte ingress and diffusion throughout the electrode, thereby affording enlarged electrode/electrolyte contact area and more active sites for high Li-ion storage. Second,
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the nanofiber walls are constructed by nano-grains, which offer a reduced solid-state distance for fast Li-ion/electron transport. Combing the 3D Li-ion diffusion pathways in the spinel structure, the cathode possesses enhanced electrode kinetics and thus high-rate capability. Third, the 1D porous nanostructure could accommodate the structural strains caused by the Li-ion insertion/extraction and the maintenance of the structure integrity leads to long cycling stability.
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Moreover, it is worth noting that one possible reason for the capacity degradation of LMNO is the Mn disproportiontive dissolution and Jahn-Teller structural distortion caused by Mn3+ [14, 15]. The LMNO HNF cathode exhibits a much shorter plateau of Mn3+/Mn4+ redox couple than
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that of LMNO bulk counterpart (Fig. S4), indicating a smaller amount of Mn3+ generation during
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the cycling test. Meanwhile, the fast electrode kinetics of the LMNO HNF helps to mitigate the accumulation of Mn3+ in the spinel structure. A low concentration of Mn3+ in the LMNO HNF cathode would minimize the Jahn-Teller effect and further promote the remarkable cycling stability [14, 38]. 4. Conclusions
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Hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers have been successfully fabricated via a facile single-spinneret electrospinning method. The novel architecture provides large specific surface area for more electrode/electrolyte contact sites, short electron/ion transport distance for
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enhanced electrode kinetics and good structural strain relaxation for maintenance of electrode integrity. The electrochemical evaluations indicate that the as-fabricated LiMn1.5Ni0.5O4 spinel cathode can deliver a stable specific capacity of 135 mAh g-1 at 0.68 C and a 20.4 C reversible
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capacity of 98 mAh g-1. More remarkably, the cathode sustains capacity retention up to 90% after 1000 cycles. The outstanding Li-ion storage performance demonstrates the great potential
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of LiMn1.5Ni0.5O4 hollow structures as advanced cathodes for high-rate and long cycle life LIBs. Acknowledgments
The authors acknowledge the financial supports of this work by the National Natural Science
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Foundation of China (51772249, 51402236), the Research Fund of the State Key Laboratory of Solidification Processing (NWPU), China (Grant No.: 123-QZ-2015), the Key Laboratory of New Ceramic and Fine Processing and State Key Laboratory of Control and Simulation of Power
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System and Generation Equipment (Tsinghua University, KF201607, SKLD17KM02), the Fundamental Research Funds for the Central Universities (G2017KY0308) and the Program of
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Introducing Talents of Discipline to Universities (B08040). Supporting Information
SEM images of precursor fabric and LMNO samples. Charge/discharge curves of LMNO samples. References
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[1] P.G. Bruce, B. Scrosati, J.M. Tarascon, Angew. Chem. Int. Ed 47 (2008) 2930-2946. [2] K. Amine, R. Kanno, Y. Tzeng, MRS Bull. 39 (2014) 395-401.
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[3] J. Jiang, Y. Li, J. Liu, X. Huang, C. Yuan, X.W.D. Lou, Adv. Mater. 24 (2012) 5166–5180. [4] J.-G. Wang, C. Zhang, D. Jin, K. Xie, B. Wei, J. Mater. Chem. A 3 (2015) 13699–13705.
SC
[5] L. Mai, X. Tian, X. Xu, L. Chang, L. Xu, Chem. Rev. 114 (2014) 11828–11862.
3852–3856.
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[6] H.-W. Lee, P. Muralidharan, R. Ruffo, C.M. Mari, Y. Cui, D.K. Kim, Nano Lett. 10 (2010)
[7] J.-G. Wang, D. Jin, R. Zhou, X. Li, X.-r. Liu, C. Shen, K. Xie, B. Li, F. Kang, B. Wei, ACS Nano, 10 (2016) 6227–6234.
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[8] W. Tang, Y. Hou, F. Wang, L. Liu, Y. Wu, K. Zhu, Nano Lett. 13 (2013) 2036–2040. [9] J.-G. Wang, Z. Zhang, X. Zhang, X. Yin, X. Li, X. Liu, F. Kang, B. Wei, Nano Energy 39 (2017) 647-653.
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[10] S. Jayaraman, V. Aravindan, P.S. Kumar, W.C. Ling, S. Ramakrishna, S. Madhavi, Chem.
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Commun. 49 (2013) 6677-6679.
[11] A. Manthiram, K. Chemelewski, E.-S. Lee, Energy Environ. Sci. 7 (2014) 1339-1350. [12] B. Xu, D. Qian, Z. Wang, Y.S. Meng, Mater. Sci. Eng.: R 73 (2012) 51–65. [13] J. Liu, W. Liu, S. Ji, Y. Zhou, P. Hodgson, Y. Li, ChemPlusChem 78 (2013) 636–641. [14] C.J. Jafta, M.K. Mathe, N. Manyala, W.D. Roos, K.I. Ozoemena, ACS Appl. Mater. Interfaces 5 (2013) 7592–7598.
12
ACCEPTED MANUSCRIPT
[15] X. Zhang, F. Cheng, J. Yang, J. Chen, Nano Lett. 13 (2013) 2822–2825. [16] J. Liu, A. Manthiram, J. Phys. Chem. C 113 (2009) 15073–15079.
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[17] T.-F. Yi, Y. Xie, Y.-R. Zhu, R.-S. Zhu, M.-F. Ye, J. Power Sources 211 (2012) 59–65. [18] K.R. Chemelewski, D.W. Shin, W. Li, A. Manthiram, J. Mater. Chem. A 1 (2013) 3347.
SC
[19] Z.-H. Xiao, Q.-Q. Cui, X.-L. Li, H.-L. Wang, Q. Zhou, Ionics 21 (2015) 1261–1267. [20] S.-X. Zhao, X.-F. Fan, Y.-F. Deng, C.-W. Nan, Electrochim. Acta 65 (2012) 7–12.
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[21] X. Fang, M. Ge, J. Rong, C. Zhou, ACS Nano 8 (2014) 4876–4882.
[22] Z. Lu, X. Rui, H. Tan, W. Zhang, H.H. Hng, Q. Yan, ChemPlusChem 78 (2013) 218–221. [23] R. Xu, X. Zhang, R. Chamoun, J. Shui, J.C.M. Li, J. Lu, K. Amine, I. Belharouak, Nano
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Energy 15 (2015) 616–624.
[24] L. Zhou, D. Zhao, X.D. Lou, Angrew Chem. Int. Ed. 124 (2012) 243–245.
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[25] S. Zhong, P. Hu, X. Luo, X. Zhang, L. Wu, 22 Ionics (2016) 2037–2044. [26] C. Niu, J. Meng, X. Wang, C. Han, M. Yan, K. Zhao, X. Xu, W. Ren, Y. Zhao, L. Xu, Q.
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Zhang, D. Zhao, L. Mai1, Nat. Commun. 6 (2015) 7402. [27] J.-W. Jung, C.-L. Lee, S. Yu, I.-D. Kim, J. Mater. Chem. A 4 (2016) 703-750. [28] S.M. Hwang, Y.-G. Lim, J.-G. Kim, Y.-U. Heoc, J.H. Limd, Y. Yamauchi, M.-S. Park, Y.-J. Kim, S.X. Dou, J.H. Kim, Nano Energy 10 (2014) 53-62.
13
ACCEPTED MANUSCRIPT
[29] J.-G. Kim, M.-S. Park, S.M. Hwang, Y.-U. Heo, T. Liao, Z. Sun, J.H. Park, K.J. Kim, G. Jeong, Y.-J. Kim, J.H. Kim, S.X. Dou, ChemSusChem 7 (2014) 1451-1457.
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[30] S.M. Hwang, S.Y. Kim, J.-G. Kim, K.J. Kim, J.-W. Lee, M.-S. Park, Y.-J. Kim, M. Shahabuddin, Y. Yamauchi, J.H. Kim, Nanoscale 7 (2015) 8351-8355.
[31] J. Xiao, X. Chen, P.V. Sushko, M.L. Sushko, L. Kovarik, J. Feng, Z. Deng, J. Zheng, G.L.
SC
Graff, Z. Nie, D. Choi, J. Liu, J.-G. Zhang, M.S. Whittingham, Adv. Mater. 24 (2012) 2109– 2116.
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[32] J.C. Arrebola, A. Caballero, M. Cruz, Hernán, M. L., J., E.R. Castellón, Adv. Funct. Mater. 16 (2006) 1904-1912.
[33] X. Huang, Q. Zhang, J. Gan, H. Chang, Y. Yang, J. Electrochem. Soc. 158 (2011) A139-
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A145.
[34] J. Gao, J. Li, C. Jiang, C. Wan, J. Electrochem. Soc. 157 (2010) A899-A902.
127-133.
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[35] H. Luo, P. Nie, L. Shen, H. Li, H. Deng, Y. Zhu, X. Zhang, ChemElectroChem 2 (2015)
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[36] J. Mao, K. Dai, M. Xuan, G. Shao, R. Qiao, W. Yang, V.S. Battaglia, G. Liu, ACS Appl. Mater. Interfaces 8 (2016) 9116–9124. [37] W. Luo, J. Alloys Compd. 636 (2015) 24-28. [38] H. Wang, T.A. Tan, P. Yang, M.O. Lai, L. Lu, J. Phys. Chem. C 115 (2011) 6102–6110.
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Figure captions Fig. 1. XRD patterns of the LMNO HNF, NF, and bulk samples.
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Fig. 2. (a-c) SEM, (d-e) TEM and (f) HRTEM images of the LMNO HNF. Fig. 3. N2 adsorption/desorption isotherms and BJH pore size distribution (inset) of the LMNO
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products.
Fig. 4. Schematic illustration for the formation process of the LMNO HNF.
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Fig. 5. (a) CV (0.1 mV s-1) and (b) charge/discharge curves (0.34 C) of the LMNO HNF cathode. Fig. 6. (a) Cycling stability and (b) rate capability of the LMNO sample cathodes. (c) High-rate
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cycling performance of the LMNO HNF cathode at 6.8 C.
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(533) (622)
(440) (531)
(511)
(331)
(400)
Intensity (a.u.)
(311) (222)
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LMNO HNF
LMNO NF
10
20
30
40
50
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LMNO bulk
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80
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2 theta (deg.)
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Fig. 1. XRD patterns of the LMNO HNF, NF, and bulk samples.
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(c)
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(a)
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Fig. 2. (a-c) SEM, (d-e) TEM and (f) HRTEM images of the LMNO HNF.
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0.015
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Adsorp amount (cm3 g-1, STP)
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Relative Pressure (P/P0)
Fig. 3. N2 adsorption/desorption isotherms and BJH pore size distribution (inset) of the LMNO
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products.
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Fig. 4. Schematic illustration for the formation process of the LMNO HNF.
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4.85 V
1st cycle 2nd cycle 3rd cycle
A1
0.2
4.08 V
A2
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Cuurent (mA)
(a)0.4
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C2 3.96 V -0.2
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Voltage (V vs. Li/Li+)
(b)5.0 Voltage (V vs. Li /Li)
4.4
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4.57 V
4.0
1st cycle 2nd cycle 3rd cycle
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3.5
0
20
40
60
80
100
120
140
-1
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Specific capacity (mAh g )
Fig. 5. (a) CV (0.1 mV s-1) and (b) charge/discharge curves (0.34 C) of the LMNO HNF cathode.
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120 90
@0.68C
60
LMNO HNF LMNO NF LMNO bulk
30 0
0
50
100
150
200
0.34C 0.68C
120
0.34C 3.4C
6.8C 13.6C 20.4C
80
40
LMNO HNF LMNO bulk
0
0
20
40
60
Cycle number
80
100
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Cycle number
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(c) 120 100 80 60
20 0
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40
200
400
600
800
1000
Cycle number
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Specific capacity (mAh g-1)
1.4C
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Specific capacity (mAh g-1)
150
Specific capacity (mAh g-1)
(b)160
(a)
Fig. 6. (a) Cycling stability and (b) rate capability of the LMNO sample cathodes. (c) High-rate
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cycling performance of the LMNO HNF cathode at 6.8 C.
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Table 1 Comparison of the electrochemical properties of LMNO materials. Specific capacity (mAh g-1)
C-rate
Retention (Cycle number)
Rate capacity (mAh g-1)
Ref.
Nanofiber
133
0.5 C
95.4% (30)
80 (15 C)
13
Porous particle
125
0.1 C
108% (50)
Nanorod
128
5C
91% (500)
Particle
132
0.1 C
96.9% (100)
Nanoparticle
135
0.5 C
98.3% (100)
99.3 (20 C)
21
Hollow sphere
115
2C
97.6 (200)
104 (20 C)
24
Nanofiber
130.3
0.1 C
97.1% (50)
97 (3 C)
25
Particle
124
0.1 C
~100% (40)
100 (10 C)
31
Nanoparticle
120
0.25 C
~92% (30)
100 (10 C)
32
Nanoparticle
96
1C
-
73 (20 C)
33
Sphere
136.7
0.2 C
91.1% (200)
108.8 (5 C)
34
Hollow sphere
137.3
0.1 C
96.5% (200)
~45 (20 C)
35
Nanowire
130.1
0.2 C
90% (500)
90.7 (5 C)
36
Nanoparticle
130.4
0.17 C
98% (50)
104.4 (10 C)
37
135
0.68 C
96% (200)
98 (20.4 C)
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109 (20 C)
15
105.3 (10 C)
19
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~75 (10 C)
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Hollow nanofiber
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Morphology
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ACCEPTED MANUSCRIPT Highlights: Hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers are prepared via electrospinning.
The LiMn1.5Ni0.5O4 hollow nanofibers deliver a high-rate capacity of 98mAh g-1 at 20.4 C.
The LiMn1.5Ni0.5O4 cathode exhibits a ultrastable cycling performance up to 1000 cycles.
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S0925-8388(17)33152-3
DOI:
10.1016/j.jallcom.2017.09.112
Reference:
JALCOM 43168
To appear in:
Journal of Alloys and Compounds
Received Date: 13 May 2017 Revised Date:
8 September 2017
Accepted Date: 11 September 2017
Please cite this article as: J.-G. Wang, H. Liu, H. Liu, X. Li, D. Nan, F. Kang, Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes for high rate and long cycle life Li-ion batteries, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.09.112. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Electrospun LiMn1.5Ni0.5O4 hollow nanofibers as advanced cathodes
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for high rate and long cycle life Li-ion batteries
Jian-Gan Wang a *, Huanyan Liu a, Hongzhen Liu a, Xu Li b, Ding Nan c *, Feiyu Kang b State Key Laboratory of Solidification Processing, Center for Nano Energy Materials, School
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a
of Materials Science and Engineering, Northwestern Polytechnical University and Shaanxi Joint
b
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Lab of Graphene (NPU), Xi’an 710072, China
Institute of Advanced Materials Research, Graduate School at Shenzhen, Tsinghua University,
Shenzhen 518055, China
School of Materials Science and Engineering, Inner Mongolia University of
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c
Technology, Aimin Street 49, Hohhot 010051, China
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*Email: [email protected], [email protected]
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Abstract
High-voltage LiMn1.5Ni0.5O4 spinel with one-dimensional (1D) hollow and porous architecture is
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fabricated via a facile single-spinneret electrospinning technique. The hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers possess ~200 nm in diameter and tens of micrometers in length, as well as a specific surface area as high as 43.2 m2 g-1. When served as Li-ion battery
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cathodes, the as-fabricated material delivers high specific capacities of 135 and 98 mAh g-1 at 0.68 C and 20.4 C, respectively. Under a long-term cycling operation at 6.8 C, the cathode
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sustains good capacity retention of 90% after 1000 cycles. The outstanding electrochemical performance can be attributed to the porous 1D hollow nanostructure that can enlarge effective electrode/electrolyte contact areas, shorten electron/ion transport distance and accommodate
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volume change.
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Keywords: LiMn1.5Ni0.5O4; hollow structure; Li-ion battery; electrospinning; cathode
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1. Introduction
Nanomaterials and nanotechnology have been considered as an advanced and promising strategy
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to boost the development of high-efficient energy storage systems, such as rechargeable Li-ion batteries (LIBs) [1-3] Among various nanostructures, one-dimensional (1D) nanomaterials, including nanorods, nanowires, nanofibers, and nanotubes, are of significant interest in LIB
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community due to their intriguing architecture [4-7]. Particularly, 1D tubular (hollow) nanostructures not only provide short solid-state transport pathways along the confined
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dimension but also buffer the structural strains caused by the repeated Li-ion insertion/extraction processes [8-10]. In addition, the 1D and nanotubular materials could form an interconnected and porous network to permit fast electrolyte diffusion and ensure the effective contact area. Spinel LiMn1.5Ni0.5O4 is a promising cathode candidate for the next-generation high-power
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LIBs owing to its fast three-dimensional (3D) Li+ diffusion channels, high operating voltage of ~4.7 V, low cost and eco-friendliness [11, 12]. The high-voltage spinel LiNi0.5Mn1.5O4 cathode can deliver an energy density as high as 658 Wh kg-1, which is much higher than those of
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LiMn2O4 (440 Wh kg-1) and LiFePO4 (500 Wh kg-1) [13]. Up to now, many kinds of synthesis
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methods, such as solid-state reactions, co-precipitation, sol-gel and spray pyrolysis, has been reported for the preparation of LiMn1.5Ni0.5O4 [11, 14]. However, it is still a challenge to achieve a LiMn1.5Ni0.5O4 material with excellent rate capacity and cyclability because of (i) the difficulty to control uniform distribution, stoichiometric composition, and good crystallinity of the LiMn1.5Ni0.5O4 and (ii) the unstable electrode/electrolyte interfaces under high potential operation [11, 15]. To improve the electrochemical performance, a variety of strategies, such as cation doping, nanostructuring and surface modification, were developed to stabilize the cathode
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structure [15-22]. Among them, nanostructuring is a simple and effective approach. Nevertheless, there are a few studies focusing on the morphology-controlled synthesis of LiMn1.5Ni0.5O4 nanostructures (e.g., nanoparticle, nanorod, and nanofiber) probably owing to
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undesirable particle growth during the high-temperature calcination process [13-15, 23-25] As particularly mentioned earlier, 1D tubular (hollow) nanostructure is rather attractive, however, to
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the best of our knowledge, study on this fantastic topic has rarely been reported.
In this work, we report a 1D porous LiMn1.5Ni0.5O4 hollow nanofiber (LMNO HNF) via a
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facile single-spinneret electrospinning in combination with heat treatment. The as-electrospun polymer nanofibers function as a structure-directing template to confine nanoscaled particle growth along the 1D dimension. The heating rate is crucial to the formation of hollow structure. Benefiting from the unique architecture features, the LMNO HNF cathode exhibits outstanding
2. Experimental 2.1. Materials synthesis
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Li-ion storage performance with high-rate capability and long cycle life.
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All chemical reagents were of analytical grade and used as received. Electrospinning technique
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was employed to fabricate 1D LMNO HNF. In a typical fabrication procedure, 1.5 g of polyacrylonitrile (PAN, Mw=150000) was first dissolved into 15 ml of N,N-Dimethylformamide (DMF) to obtain a homogeneous polymer solution. Subsequently, lithium acetate dihydrate, manganese acetate tetrahydrate, manganese acetate tetrahydrate with a molar ratio of 2:3:1.02 were added to the solution under stirring. The mixture solution was then loaded into a 30 ml syringe. The electrospinning was carried out on Tongli TL-01 setup at room temperature. The distance between the needle and Al-foil collector was controlled to be about 15 cm with an
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applied voltage of 15 kV. The feeding rate of the solution from syringe was about 1.0 ml h-1. The as-fabricated nanofibrous mat was then transferred to a Muffle furnace for calcination. The furnace was heated to 750 °C at a slow heating rate of 0.5 °C min-1 and then subjected to
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calcination for 6 h under air atmosphere to yield the final products. For comparison, solid LMNO nanofibers (NF) were obtained at a high heating rate of 5 °C min-1 and bulk LMNO particles
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were prepared by conventional solid state sintering without electrospinning process. 2.2. Materials Characterization
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The crystallographic structure was identified by powder X-ray diffraction (XRD, X’Pert PRO MPD, Philips). The as-collected XRD data were analyzed using the Rietveld refinement method in the FullProf software package suite. Field emission scanning electron microscope (FE-SEM, FEI NanoSEM 450) and transmission electron microscope (TEM, FEI Tecnai F30G2) were used
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to observe the morphology. Brunauer-Emmet-Teller (BET) specific surface area was determined using N2 adsorption/desorption measurement (Mike ASAP 2020). The pore size distribution was analyzed by Barrett-Joyner-Halenda (BJH) model. The chemical composition of the LMNO
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sample was analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES, IRIS Intrepid II, Thermo Fisher).
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2.3. Electrochemical Evaluation
The electrochemical properties of the as-prepared products were measured using CR2030 cointype half cells. The working electrodes were prepared by coating a slurry of mixture containing 80 wt.% of active materials, 10 wt.% of acetylene black, and 10 wt.% of poly(vinylidene fluoride) onto a clean aluminum foil. After coating, the foil was dried overnight at 100 °C in a vacuum oven. The mass loading of the active materials was about 2.2±0.2 mg cm-2. Coin cells were
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assembled in an argon-filled glovebox using a metal Li foil as the counter electrode, Celgard 2320 as the separator, and 1 M LiPF6 in a mixture of 1:1 (v/v) ethylene carbonate (EC) /diemethyl carbonate (DMC) as the electrolyte. Cyclic voltammetry (CV) measurement was
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carried out on a Solatron electrochemical workstation (1260+1287) between 3.5 and 5.0 V (vs. Li/Li+). Galvanostatic charge/discharge curves were obtained from a Land Battery Testing
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System. 3. Results and discussion
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XRD analysis was carried out to identify the crystallographic phase. Fig. 1 exhibits the XRD pattern of the as-prepared LMNO HNF, NF and bulk products. All of the diffraction peaks can be readily assigned to the ordered cubic spinel LiNi0.5Mn1.5O4 phase with a space group of Fd3m (JPCDS 80-2162) [13, 15]. No peak of other impurities is observed, indicating high purity of the
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products. In addition, the sharp diffraction peaks reveals a high crystallinity of the structure. The lattice parameters determined by the Retrieved refinement method are 8.1704, 8.1798, and 8.1916 Å for the LMNO HNF, NF and bulk materials, respectively. The Li/Ni/Mn ratio from the
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ICP-AES analysis is determined to be 1.00/0.49/1.51, 1.00/0.53/1.52, and 1.00/0.52/1.52 for the LMNO HNF, NF and bulk sample, respectively, which are close to the chemical composition of
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the LiNi0.5Mn1.5O4.
The precursor fabric is composed of randomly interwoven nanofibers with smooth surface and an average diameter of 400 nm (Fig. S1). After calcination in air, the 1D nanostructure is well preserved (Fig. 2(a-b)), and the nanofibers have tens of microns in length and ~200 nm in diameter. In addition, the surface becomes rough mainly due to the decomposition of polymer and the growth of LMNO nanoparticles confined along the nanofibers. More interesting, a close
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SEM examination manifests unique hollow structure of the nanofibers, as evidenced by the open ends indicated in Fig. 2(c). The thickness of the LMNO nanowall is estimated to be 50 nm. The 1D porous hollow structure is clearly confirmed by TEM imaging (Fig. 2(d)). From the Fig. 2(e),
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the nanofiber wall is constructed by interconnected ultrafine nanograins with diameters of 30-60 nm. The distinct lattice fringes in HRTEM image (Fig. 2(f)) indicate good crystallinity of the products, and the interplanar distance of 0.47 nm agrees well with the d-spacing of (111) plane of
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spinel LMNO.
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The textual characteristics of the LMNO HNF was examined by N2 adsorption/desorption measurements. For comparison, a control sample of bulk LMNO particles with an average diameter of ~200 nm was prepared using conventional solid-state sintering (Fig. S2). Fig. 3 exhibits the resulting isotherms of the two LMNO products, which are typical of IUPAC Type II. The N2 adsorption uptake of the LMNO HNF in the full P/P0 range is much larger than that of
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the LMNO bulk, indicating a much higher specific surface area. Based on the BET calculation, the specific surface area of the LMNO HNF is as high as 43.2 m2 g-1, which is about five times of the control sample (8.6 m2 g-1). In addition, the BJH pore-size distribution (inset) reveals the
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presence of abundant mesopores in the LMNO HNF. The porosity of LMNO HNF is resulting
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from the construction of ultrafine nanoparticles along the 1D direction and the unique hollow structure. Notably, the hierarchical porous architecture could enlarge the electrode/electrolyte interfacial contact area for high energy storage and reduce the solid-state Li-ion diffusion distance in active materials to boost high-rate delivery [24, 26]. Electrospinning is a simple and versatile technique to fabricate 1D nanostructures with different morphologies by controlling spinneret configuration, polymer precursor and posttreatment [27]. There are various solid nanofibers that have been prepared by single-spinneret
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electrospinning [13, 23, 25], but the nanofibers with unique hollow structure are rarely reported, especially for complex metal oxides. It is thus interesting to probe the possible formation mechanism of LMNO HNF, as schematically illustrated in Fig. 4. Generally, the generation of
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nanofibers is resulting from the decomposition of the polymer precursor containing metal salts at high temperatures. In this study, it is revealed that the heating rate plays a crucial role in the microstructure. The key issue is to control the polymer decomposition rate vs. the kinetic
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diffusion rate of metal elements [23, 26]. At a slow heating rate (e.g., 0.5 °C min-1), the polymer nanofiber could serve as a robust structure-directing template for the formation of rigid 1D
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nanostructure. As the PAN is gradually eliminated, the metal species at the outer surface exposing to the air atmosphere would generate Li-metal oxide nucleus while those in the interior part will migrate outward through kinetic diffusion. The Li-metal oxide nucleus will further grow and crystallize into a shell of LMNO phase at high temperature, and a hollow structure is
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obtained after the completely removal of PAN. At a fast heating rate (5 °C min-1), the Li-metal oxide shells will collapse into solid 1D nanofiber (Fig. S3) due to the insufficient kinetic diffusion time of the metal cation and the relatively rapid decomposition of the polymer
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backbone [28-30].
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The electrochemical properties of the as-prepared samples are evaluated in half cells. Fig. 5(a) shows CV curves of the LMNO HNF cathode at a scan rate of 0.1 mV s-1. The pronounced A1/C1 redox couple in the high-voltage region is associated with the two-step oxidation/reduction of Ni2+/Ni3+ and Ni3+/Ni4+. The weak A2/C2 peaks in the low-voltage range can be attributed to the Mn3+/Mn4+ redox couple [11, 17]. It is important to note that the CV curves are well overlapped, indicating excellent electrochemical reversibility and good cycling stability of the cathodic host materials for Li-ion insertion/extraction reactions. The typical
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electrochemical behavior is further confirmed by galvanostatic charge/discharge measurement. As shown in Fig. 5(b), the long and flat plateaus at approximately 4.7 V and the short plateaus at around 4.0 V represent the reversible reactions of Ni and Mn cations, respectively, which
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coincides with the CV results. The narrow charge/discharge potential difference indicates a small electrode polarization. The well-defined charge/discharge plateaus can be ascribed to the high
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crystallinity of the samples.
Fig. 6(a) exhibits a comparison of the cycling performance of the LMNO cathodes at a
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0.68C (100 mA g-1) rate. The hollow-structured LMNO cathode delivers a high reversible discharge capacity of 135 mAh g1 with an initial Coulombic efficiency of 93%. More impressively, the cathode can retain 96% of the initial capacity after 200 cycles, which is much better than that of the LMNO NF (86.8%) and LMNO bulk (76%) cathodes. In addition to the cycling performance, the hollow-structured LMNO cathode also demonstrates superior rate
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capability. As shown in Fig. 6(b), it reveals higher discharge capacity than the bulk counterpart at high current rates. Even at a high rate of 20.4 C, the cathode can still deliver a specific capacity of 98 mAh g-1. The capacity recovers its initial value when the current rate is reduced to
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0.34 C, again indicating the excellent electrochemical reversibility of the LMNO HNF cathode.
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The electrochemical properties of the LMNO HNF are superior or comparable to the recent reported LMNO materials [13-15, 19, 21, 24, 25, 31-37], as summarized in Table 1. Fig. 6(c) further presents the cycling performance of the cathode operated at a high 6.8 C rate. The specific capacity increases to a maximum value of 109 mAh g-1 during the first ten cycles probably due to the activation process. Notably, the cathode retains almost 90% (94.3% and 97.8%) of the maximum capacity after 1000 (500 and 200) extended cycles. The long-term cycling performance is superior or at least comparable to the LMNO materials reported in
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literature, such as porous LMNO nanorods (91% after 500 cycles) [15], LMNO/carbon nanofiber nanocomposites (88% after 500 cycles) [21], Cr-doped LMNO microparticles (90% after 500
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cycles) [36] and hollow LMNO spheres (96.6% after 200 cycles) [24]. The outstanding Li-ion storage performance of the LMNO HNF cathode can be rationalized by its unique hierarchical architecture. First, the porous hollow structure with large surface area
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enables efficient electrolyte ingress and diffusion throughout the electrode, thereby affording enlarged electrode/electrolyte contact area and more active sites for high Li-ion storage. Second,
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the nanofiber walls are constructed by nano-grains, which offer a reduced solid-state distance for fast Li-ion/electron transport. Combing the 3D Li-ion diffusion pathways in the spinel structure, the cathode possesses enhanced electrode kinetics and thus high-rate capability. Third, the 1D porous nanostructure could accommodate the structural strains caused by the Li-ion insertion/extraction and the maintenance of the structure integrity leads to long cycling stability.
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Moreover, it is worth noting that one possible reason for the capacity degradation of LMNO is the Mn disproportiontive dissolution and Jahn-Teller structural distortion caused by Mn3+ [14, 15]. The LMNO HNF cathode exhibits a much shorter plateau of Mn3+/Mn4+ redox couple than
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that of LMNO bulk counterpart (Fig. S4), indicating a smaller amount of Mn3+ generation during
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the cycling test. Meanwhile, the fast electrode kinetics of the LMNO HNF helps to mitigate the accumulation of Mn3+ in the spinel structure. A low concentration of Mn3+ in the LMNO HNF cathode would minimize the Jahn-Teller effect and further promote the remarkable cycling stability [14, 38]. 4. Conclusions
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Hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers have been successfully fabricated via a facile single-spinneret electrospinning method. The novel architecture provides large specific surface area for more electrode/electrolyte contact sites, short electron/ion transport distance for
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enhanced electrode kinetics and good structural strain relaxation for maintenance of electrode integrity. The electrochemical evaluations indicate that the as-fabricated LiMn1.5Ni0.5O4 spinel cathode can deliver a stable specific capacity of 135 mAh g-1 at 0.68 C and a 20.4 C reversible
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capacity of 98 mAh g-1. More remarkably, the cathode sustains capacity retention up to 90% after 1000 cycles. The outstanding Li-ion storage performance demonstrates the great potential
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of LiMn1.5Ni0.5O4 hollow structures as advanced cathodes for high-rate and long cycle life LIBs. Acknowledgments
The authors acknowledge the financial supports of this work by the National Natural Science
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Foundation of China (51772249, 51402236), the Research Fund of the State Key Laboratory of Solidification Processing (NWPU), China (Grant No.: 123-QZ-2015), the Key Laboratory of New Ceramic and Fine Processing and State Key Laboratory of Control and Simulation of Power
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System and Generation Equipment (Tsinghua University, KF201607, SKLD17KM02), the Fundamental Research Funds for the Central Universities (G2017KY0308) and the Program of
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Introducing Talents of Discipline to Universities (B08040). Supporting Information
SEM images of precursor fabric and LMNO samples. Charge/discharge curves of LMNO samples. References
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[1] P.G. Bruce, B. Scrosati, J.M. Tarascon, Angew. Chem. Int. Ed 47 (2008) 2930-2946. [2] K. Amine, R. Kanno, Y. Tzeng, MRS Bull. 39 (2014) 395-401.
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[3] J. Jiang, Y. Li, J. Liu, X. Huang, C. Yuan, X.W.D. Lou, Adv. Mater. 24 (2012) 5166–5180. [4] J.-G. Wang, C. Zhang, D. Jin, K. Xie, B. Wei, J. Mater. Chem. A 3 (2015) 13699–13705.
SC
[5] L. Mai, X. Tian, X. Xu, L. Chang, L. Xu, Chem. Rev. 114 (2014) 11828–11862.
3852–3856.
M AN U
[6] H.-W. Lee, P. Muralidharan, R. Ruffo, C.M. Mari, Y. Cui, D.K. Kim, Nano Lett. 10 (2010)
[7] J.-G. Wang, D. Jin, R. Zhou, X. Li, X.-r. Liu, C. Shen, K. Xie, B. Li, F. Kang, B. Wei, ACS Nano, 10 (2016) 6227–6234.
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[8] W. Tang, Y. Hou, F. Wang, L. Liu, Y. Wu, K. Zhu, Nano Lett. 13 (2013) 2036–2040. [9] J.-G. Wang, Z. Zhang, X. Zhang, X. Yin, X. Li, X. Liu, F. Kang, B. Wei, Nano Energy 39 (2017) 647-653.
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[10] S. Jayaraman, V. Aravindan, P.S. Kumar, W.C. Ling, S. Ramakrishna, S. Madhavi, Chem.
AC C
Commun. 49 (2013) 6677-6679.
[11] A. Manthiram, K. Chemelewski, E.-S. Lee, Energy Environ. Sci. 7 (2014) 1339-1350. [12] B. Xu, D. Qian, Z. Wang, Y.S. Meng, Mater. Sci. Eng.: R 73 (2012) 51–65. [13] J. Liu, W. Liu, S. Ji, Y. Zhou, P. Hodgson, Y. Li, ChemPlusChem 78 (2013) 636–641. [14] C.J. Jafta, M.K. Mathe, N. Manyala, W.D. Roos, K.I. Ozoemena, ACS Appl. Mater. Interfaces 5 (2013) 7592–7598.
12
ACCEPTED MANUSCRIPT
[15] X. Zhang, F. Cheng, J. Yang, J. Chen, Nano Lett. 13 (2013) 2822–2825. [16] J. Liu, A. Manthiram, J. Phys. Chem. C 113 (2009) 15073–15079.
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[17] T.-F. Yi, Y. Xie, Y.-R. Zhu, R.-S. Zhu, M.-F. Ye, J. Power Sources 211 (2012) 59–65. [18] K.R. Chemelewski, D.W. Shin, W. Li, A. Manthiram, J. Mater. Chem. A 1 (2013) 3347.
SC
[19] Z.-H. Xiao, Q.-Q. Cui, X.-L. Li, H.-L. Wang, Q. Zhou, Ionics 21 (2015) 1261–1267. [20] S.-X. Zhao, X.-F. Fan, Y.-F. Deng, C.-W. Nan, Electrochim. Acta 65 (2012) 7–12.
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[21] X. Fang, M. Ge, J. Rong, C. Zhou, ACS Nano 8 (2014) 4876–4882.
[22] Z. Lu, X. Rui, H. Tan, W. Zhang, H.H. Hng, Q. Yan, ChemPlusChem 78 (2013) 218–221. [23] R. Xu, X. Zhang, R. Chamoun, J. Shui, J.C.M. Li, J. Lu, K. Amine, I. Belharouak, Nano
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Energy 15 (2015) 616–624.
[24] L. Zhou, D. Zhao, X.D. Lou, Angrew Chem. Int. Ed. 124 (2012) 243–245.
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[25] S. Zhong, P. Hu, X. Luo, X. Zhang, L. Wu, 22 Ionics (2016) 2037–2044. [26] C. Niu, J. Meng, X. Wang, C. Han, M. Yan, K. Zhao, X. Xu, W. Ren, Y. Zhao, L. Xu, Q.
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Zhang, D. Zhao, L. Mai1, Nat. Commun. 6 (2015) 7402. [27] J.-W. Jung, C.-L. Lee, S. Yu, I.-D. Kim, J. Mater. Chem. A 4 (2016) 703-750. [28] S.M. Hwang, Y.-G. Lim, J.-G. Kim, Y.-U. Heoc, J.H. Limd, Y. Yamauchi, M.-S. Park, Y.-J. Kim, S.X. Dou, J.H. Kim, Nano Energy 10 (2014) 53-62.
13
ACCEPTED MANUSCRIPT
[29] J.-G. Kim, M.-S. Park, S.M. Hwang, Y.-U. Heo, T. Liao, Z. Sun, J.H. Park, K.J. Kim, G. Jeong, Y.-J. Kim, J.H. Kim, S.X. Dou, ChemSusChem 7 (2014) 1451-1457.
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[30] S.M. Hwang, S.Y. Kim, J.-G. Kim, K.J. Kim, J.-W. Lee, M.-S. Park, Y.-J. Kim, M. Shahabuddin, Y. Yamauchi, J.H. Kim, Nanoscale 7 (2015) 8351-8355.
[31] J. Xiao, X. Chen, P.V. Sushko, M.L. Sushko, L. Kovarik, J. Feng, Z. Deng, J. Zheng, G.L.
SC
Graff, Z. Nie, D. Choi, J. Liu, J.-G. Zhang, M.S. Whittingham, Adv. Mater. 24 (2012) 2109– 2116.
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[32] J.C. Arrebola, A. Caballero, M. Cruz, Hernán, M. L., J., E.R. Castellón, Adv. Funct. Mater. 16 (2006) 1904-1912.
[33] X. Huang, Q. Zhang, J. Gan, H. Chang, Y. Yang, J. Electrochem. Soc. 158 (2011) A139-
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A145.
[34] J. Gao, J. Li, C. Jiang, C. Wan, J. Electrochem. Soc. 157 (2010) A899-A902.
127-133.
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[35] H. Luo, P. Nie, L. Shen, H. Li, H. Deng, Y. Zhu, X. Zhang, ChemElectroChem 2 (2015)
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[36] J. Mao, K. Dai, M. Xuan, G. Shao, R. Qiao, W. Yang, V.S. Battaglia, G. Liu, ACS Appl. Mater. Interfaces 8 (2016) 9116–9124. [37] W. Luo, J. Alloys Compd. 636 (2015) 24-28. [38] H. Wang, T.A. Tan, P. Yang, M.O. Lai, L. Lu, J. Phys. Chem. C 115 (2011) 6102–6110.
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Figure captions Fig. 1. XRD patterns of the LMNO HNF, NF, and bulk samples.
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Fig. 2. (a-c) SEM, (d-e) TEM and (f) HRTEM images of the LMNO HNF. Fig. 3. N2 adsorption/desorption isotherms and BJH pore size distribution (inset) of the LMNO
SC
products.
Fig. 4. Schematic illustration for the formation process of the LMNO HNF.
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Fig. 5. (a) CV (0.1 mV s-1) and (b) charge/discharge curves (0.34 C) of the LMNO HNF cathode. Fig. 6. (a) Cycling stability and (b) rate capability of the LMNO sample cathodes. (c) High-rate
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cycling performance of the LMNO HNF cathode at 6.8 C.
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(533) (622)
(440) (531)
(511)
(331)
(400)
Intensity (a.u.)
(311) (222)
(111)
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LMNO HNF
LMNO NF
10
20
30
40
50
SC
LMNO bulk
60
70
80
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2 theta (deg.)
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Fig. 1. XRD patterns of the LMNO HNF, NF, and bulk samples.
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(c)
(d)
TE D
(f )
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(e)
SC
(b)
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(a)
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Fig. 2. (a-c) SEM, (d-e) TEM and (f) HRTEM images of the LMNO HNF.
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0.015
80
0.010
3
-1
-1
dV/dr (cm g nm )
40
0.005
0.000
1
10
100
Pore width (nm)
LMNO HNF LMNO bulk
20
0 0.0
0.2
0.4
0.6
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60
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Adsorp amount (cm3 g-1, STP)
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0.8
1.0
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Relative Pressure (P/P0)
Fig. 3. N2 adsorption/desorption isotherms and BJH pore size distribution (inset) of the LMNO
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products.
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Fig. 4. Schematic illustration for the formation process of the LMNO HNF.
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4.85 V
1st cycle 2nd cycle 3rd cycle
A1
0.2
4.08 V
A2
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Cuurent (mA)
(a)0.4
0.0
C2 3.96 V -0.2
C1 -0.4 3.6
4.0
4.5
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+
4.8
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Voltage (V vs. Li/Li+)
(b)5.0 Voltage (V vs. Li /Li)
4.4
SC
4.57 V
4.0
1st cycle 2nd cycle 3rd cycle
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3.5
0
20
40
60
80
100
120
140
-1
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Specific capacity (mAh g )
Fig. 5. (a) CV (0.1 mV s-1) and (b) charge/discharge curves (0.34 C) of the LMNO HNF cathode.
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120 90
@0.68C
60
LMNO HNF LMNO NF LMNO bulk
30 0
0
50
100
150
200
0.34C 0.68C
120
0.34C 3.4C
6.8C 13.6C 20.4C
80
40
LMNO HNF LMNO bulk
0
0
20
40
60
Cycle number
80
100
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Cycle number
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(c) 120 100 80 60
20 0
TE D
40
200
400
600
800
1000
Cycle number
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Specific capacity (mAh g-1)
1.4C
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Specific capacity (mAh g-1)
150
Specific capacity (mAh g-1)
(b)160
(a)
Fig. 6. (a) Cycling stability and (b) rate capability of the LMNO sample cathodes. (c) High-rate
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cycling performance of the LMNO HNF cathode at 6.8 C.
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Table 1 Comparison of the electrochemical properties of LMNO materials. Specific capacity (mAh g-1)
C-rate
Retention (Cycle number)
Rate capacity (mAh g-1)
Ref.
Nanofiber
133
0.5 C
95.4% (30)
80 (15 C)
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Porous particle
125
0.1 C
108% (50)
Nanorod
128
5C
91% (500)
Particle
132
0.1 C
96.9% (100)
Nanoparticle
135
0.5 C
98.3% (100)
99.3 (20 C)
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Hollow sphere
115
2C
97.6 (200)
104 (20 C)
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Nanofiber
130.3
0.1 C
97.1% (50)
97 (3 C)
25
Particle
124
0.1 C
~100% (40)
100 (10 C)
31
Nanoparticle
120
0.25 C
~92% (30)
100 (10 C)
32
Nanoparticle
96
1C
-
73 (20 C)
33
Sphere
136.7
0.2 C
91.1% (200)
108.8 (5 C)
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Hollow sphere
137.3
0.1 C
96.5% (200)
~45 (20 C)
35
Nanowire
130.1
0.2 C
90% (500)
90.7 (5 C)
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Nanoparticle
130.4
0.17 C
98% (50)
104.4 (10 C)
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135
0.68 C
96% (200)
98 (20.4 C)
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109 (20 C)
15
105.3 (10 C)
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~75 (10 C)
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Hollow nanofiber
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Morphology
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ACCEPTED MANUSCRIPT Highlights: Hierarchical porous LiMn1.5Ni0.5O4 hollow nanofibers are prepared via electrospinning.
The LiMn1.5Ni0.5O4 hollow nanofibers deliver a high-rate capacity of 98mAh g-1 at 20.4 C.
The LiMn1.5Ni0.5O4 cathode exhibits a ultrastable cycling performance up to 1000 cycles.
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