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Enhanced lithium storage capability in Li-ion batteries via porous 3D Co3O4 nanofiber anode Lei Fan, Wei-Dong Zhang, Shoupu Zhu, and Yingying Lu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00222 • Publication Date (Web): 31 Jan 2017 Downloaded from http://pubs.acs.org on February 2, 2017

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Industrial & Engineering Chemistry Research

Enhanced lithium storage capability in Li-ion batteries via porous 3D Co3O4 nanofiber anode Lei Fan, Weidong Zhang, Shoupu Zhu, Yingying Lu* State Key Laboratory of Chemical Engineering, Institute of Pharmaceutical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China ABSTRACT Transition metal oxides have been considered as one of the most promising alternative anode materials for high performance lithium ion batteries. Here, we fabricated porous Co3O4 nanofibers by electrospinning, and used as the anode material to improve the energy density of lithium-ion batteries (LIBs). Each nanofiber consists of nanoparticles and nanopores, and the nanopores among the Co3O4 nanoparticles and the interlayer empty space between the 3D nanofibers are created to accommodate the volume expansion during the charge/discharge process. We compared the cycling performance of three types of Co3O4 anode: Co3O4 nanoparticles, Co3O4 microparticles and Co3O4 nanofibers, and found that cells with Co3O4 nanofibers show outstanding electrochemical performance with a high capacity of 1227.9 mAh g-1 at a current density of 100 mA g-1. We suspect that the unique structure of the fabricated Co3O4 nanofibers could enhance the accessibility of Li ion intercalation while reducing possible side reactions as the specific surface area increases. The reversible capacity of cells with Co3O4 nanofibers can reach as high as 1000 mAh g-1 after 60 cycles at a current density of 100 mA g-1, which is even higher than the theoretical capacity of Co3O4 anode. This is related to the formation of polymer/gel like film at the electrolyte/electrode interface. INTRODUCTION Lithium-ion batteries (LIBs) have been widely used in grid energy storage and hybrid electrical vehicles, but commercial LIBs with graphite anode can hardly meet the demands for high-density energy storage.1-3 Alternative anode materials with high theoretical capacities have been fabricated, such as silicon/carbon composites, porous carbon materials, transition metal chalcogenides and transition metal oxides.4-8 Silicon provide a high theoretical specific capacity of 4212 mAh g-1, but its large volume expansion (>400 %) could cause rapid capacity decline. Compared with traditional graphite, porous carbon shows excellent electrochemical properties due to its high surface area. However, the increased surface area would cause electrolyte decomposition and irreversible capacity loss. Transition metal chalcogenides such as MoS2 exhibit excellent lithium ion storage ability due to their layer crystal structure, but the formation of Li2S during the electrochemical reaction could reduce the rate capability and cyclic stability. Transition metal oxides (such as CuO, NiO, Fe3O4, TiO2, and Co3O4) have long been used as electrode materials for LIBs due to their high specific capacities, which are owing to the conversion reaction between lithium and transition metal oxides. The reaction can be described as equation (1).9-14 + 2y + 2y ↔ x + y O (M = transition metals)

(1)

As the most stable phase of cobalt oxide, Co3O4 has received intensive attentions due to its high

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reversible capacities, excellent cycling performance and cost effectiveness. Co3O4 is a mixed valance oxide containing both Co2+ and Co3+. The theoretical capacity of Co3O4 is 892 mAh g-1, much higher than the conventional anode material graphite (theoretical capacity of 372 mAh g-1). The overall reaction for Co3O4 anode during charge-discharge is shown in equation (2). Per mole Co3O4 can react with 8 moles Li+.7,15,16 !"# $ + 8 + 8 ↔ 3Co + 4 O

(2)

Despite these attractive properties, Co3O4 as the anode suffer from at least two limitations that hinder their applications in LIBs. First, the solid electrolyte interface (SEI) between Co3O4 anode surface and the electrolyte could grow continuously, irreversibly consuming the electrolyte and the active anode material. Second, the volume change that occurs during the redox reactions could destroy the integrity of the anode, cause serious side reactions, and eventually impair the overall cycling performance. As a result, cells with Co3O4 anode often exhibit capacity fading and battery failure after extensive cycling. The severity of these two effects is dependent on the particle size, shape, texture, and porosity of the Co3O4 material.17-19 Accordingly, researchers have developed several strategies to solve these problems, including synthesize composite materials, carbon or nitrogen doped materials and change the morphology of Co3O4.9 Among these strategies, the morphology of Co3O4 anode has been extensively studied, mainly because it could significantly influence the battery performance.20-22 Nano-sized materials have been developed to solve these problems, by their high surface areas, good conductivities, mechanical stiffness and short diffusion path.23-25 Various nanostructured Co3O4 anode materials have been fabricated, including nanosheet, nanowire, nanoneedle, nanofibers, and nanocapsules, in an attempt to mitigate the SEI growth and volume expansion.26-30 But unfortunately, nanomaterials could, on the other hand, lead to challenges when they used as electrode materials in lithium batteries, such as high inter-particle resistance, serious side reactions and high cost in material manufacture.23 Here, we fabricated free-standing Co3O4 nanofibers via co-electrospinning of Polyacrylonitrile (PAN) and Polyvinylpyrrolidone (PVP) solutions. Compared with other methods, electrospinning shows the advantages of high efficiency, high production rate, simplicity, low cost and industry-viability.31,32 The compete oxidation process of the electrospun nanofibers could create appropriate grain and pore size, and the pores among the nanoparticles are large enough to justify the volume expansion, but not too large in order to maintain the mechanical strength of the nanofibers. The three-dimensional (3D) nanofiber electrode can not only accommodate the volume expansion, but also shorten the Li-ion diffusion length, resulting in fast reaction kinetics and high specific capacity. From impedance measurement, Co3O4 nanofibers show lower inter-particle resistance compared with bare Co3O4 nanoparticles. Besides, the large specific surface area and high surface-to-volume ration of the 3D porous Co3O4 nanofibers could provide numerous active sites, increasing the accessibility of Li ion intercalation. In addition, due to the formation of polymer/gel like film, the side reactions are effectively undermined. The unique structure of Co3O4 nanofiber electrode could simultaneously enhance the redox reaction kinetics and reduce the side reactions, leading to the improved electrochemical cycling performance of


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Co3O4 anode. EXPERIMENTAL SECTION 2.1 Synthesis of Porous Nanofibers. Co3O4 nanofibers were fabricated by electrospinning. 1.5g Cobalt (II) acetate tetrahydrate (Co(CH3COO)2·4H2O), 0.6 g Polyacrylonitrile (PAN, M.W. = 150,000) and 0.2 g Polyvinylpyrrolidone (PVP, M.W. = 1,300,000) were dissolved in 10 mL N, N-Dimethylformamide (DMF) with magnetic stirring for 12 h at 60 °C. The resultant solution was electrospun by a conventional electrospinning machine at 15 kV. Conductive carbon paper was used as the collector, the distance between the needle and collector was 15 cm and the solution flow rate was 80 µL min-1. The obtained electrospun nanofibers were pre-oxidized at 250 °C for 2 h in air and then completely oxidized at 310 °C for 2 h in air. 2.2 Material Characterization. The surface morphologies and microstructures of Co3O4 nanofibers and Co3O4 nanoparticles were analyzed using SEM (SU-8010, Hitachi) and TEM (200 kV-2100F, JEOL). The crystalline structures of Co3O4 nanofibers and Co3O4 nanoparticles were characterized by powder X-ray diffraction (XRD, Shimadzu). The Nitrogen adsorption-desorption isotherms were recorded using an automatic surface area and porosity analyzer (Micromeritics) at 77 K. The specific surface area and the pore size distribution of the carbon aerogels were estimated using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods. Mass loss was tested by Thermogravimetric analysis (TGA, TA-Q500). XPS (ESCALAB250) was employed to analyze the surface chemical compositions of the nanofiber after pre-oxidation and complete oxidation. The scan range was set from 0 to 800 eV and high-resolution scanning was applied near the binding energies of carbon, oxygen and cobalt. 2.3 Electrochemical Characterization. The working electrode consisted of 80 wt% of Co3O4 nanofibers, 10 wt% of conductive agent (carbon Super P) and 10 wt% of binder (polyvinylidede difluoride, PVDF). N-methylpyrrolidone (NMP) was added as the solvent. The slurry was coated on a copper foil to obtain the working electrode. The active material (Co3O4 nanofibers) of the electrode was between 1.0 to 2.0 mg cm-2. Co3O4 microparticle electrode and nanoparticle electrode were fabricated by the same methods. Pure lithium foil was used as the reference and counting electrodes. The electrolyte was 1 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC) and diemethyl carbonate (DMC) (volume ratio = 1:1). 2032 type coin cells were assembled in an argon-filled glovebox. Cyclic voltammograms (CV) and impedance measurements were conducted in an electrochemical workstation (AMETEK). The scan rate of cyclic voltammograms was 0.1 mV s-1 with voltage ranging from 0.01 to 3.0 V (vs. Li+/Li). The frequency range for impedance spectra was from 100 kHz to 0.1 Hz. The galvanostatic measurements were tested by eight-channel LAND battery tester and the voltage range was from 0.01 to 3 V (vs. Li+/Li). 1. RESULTS AND DISCUSSION To incorporate Co3O4 nanofiber electrode into practical Li-ion batteries, we fabricated free-standing Co3O4 nanofibers by electrospinning technique and the details of the preparation procedure are shown in Figure 1. PAN, PVP and Co(CH3COO)2·4H2O were used as the precursors,



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and core-shell structure nanofibers were obtained according to the different viscosities. As shown in Figure 1a, two phases segregate with higher viscosity PAN- Co(CH3COO)2·4H2O as the core and PVP-Co(CH3COO)2·4H2O precursor as the shell of the nanofiber.33 The resultant free-standing nanofibers were pre-oxidized in a convection furnace and the PVP in the shell would be removed from thermal decomposition due to its low melting temperature and thermoplasticity (Figure 1b). During the pre-oxidation procedure, Co(CH3COO)2·4H2O starts to transform and becomes crystalline, and some Co3O4 nanoparticles would appear after the pre-oxidation. PVP was used as a functional additive to modulate the morphology of the nanofiber in order to keep the uniformity of the nanofiber.33 PVP can also regulate and control the crystallization of Co3O4, preventing its agglomerate.34 The temperature for pre-oxidation and complete oxidation process were determined by the TGA analysis. It can be seen in Figure S1 that there is a slow drop starting from 200 °C and ending at around 305°C. It could be due to the thermal decomposition of PVP and pre-oxidation of PAN, so we choose 250 °C as the pre-oxidation temperature. Short after this process at 305 °C, a sudden drop occurs, which is due to the complete oxidation of PAN and Co(CH3COO)2·4H2O. So we set the oxidation temperature to be 310 °C. After complete oxidizing in an air atmosphere, the nanofiber consists of Co3O4 and carbon, which is confirmed by the XRD analysis and EDX mapping (Figure 3 and 4, will be discussed later).

Figure 1. Scheme of the fabrication procedure of Co3O4 nanofibers. a) Pristine electrospun nanofibers. b) Nanofibers after pre-oxidation with low crystalline Co3O4. c) Nanofibers after complete oxidation with high crystalline Co3O4. The morphologies of the nanofibers were analyzed by SEM and TEM. Figure 2a-c show the pristine core-shell structures of electrospun nanofibers, and the length of the nanofiber can be up to tens of micrometres. SEM images of electrospun nanofibers after pre-oxidation and complete oxidation are shown in Figure 2d-f and Figure 2g-i, respectively. After pre-oxidation, the morphology of the nanofibers keeps almost the same as the pristine electrospun nanofibers, and the diameter of the nanofibers decreases from 200-300 nm to 150-250 nm, which is due to the decomposition and removal of PVP in the shell. And after complete oxidation, the nanofibers become curly and the diameter reduces to 100-150 nm.


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Figure 2. SEM images at different resolutions for pristine electrospun nanofibers (a to c), nanofibers after pre-oxidation (d to f), and nanofibers after complete oxidation (g to i). HR-TEM was also employed to determine the structure of the nanofibers after pre-oxidation and complete oxidation. Seen from Figure 3a and b, some small nanoparticles appear on the surface of the nanofiber after pre-oxidation, and the interplanar spacing is 0.29 nm, corresponding to the interplanar spaces of (220) lattice plane of Co3O4. SAED pattern, shown in the inset of Figure 3b, is consistent with this result. Figure 3c and d show the TEM images of the Co3O4 nanofibers after complete oxidation. Interestingly, after complete oxidation, each nanofiber is composed of Co3O4 nanoparticles with large amount of nanopores. The particle size of Co3O4 is between 7 nm and 17 nm and the pore size is about 7 to 10 nm. The interplanar and SAED pattern in Figure 3d are similar to these in Figure 3b, meaning that the complete oxidation step only changes the morphology of the nanofiber while keeps the chemical composition the same. From the EDX mapping results, we find Co and O signals, and carbon signal. The legacy of trace amounts of carbon (about 1%, Figure S1) may contribute to the electrical conductivity of the nanofibers.



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Figure 3. TEM images of nanofibers after pre-oxidation (a and b), nanofibers after complete oxidation (c and d). The insets of (b) and (d) are SAED patterns of nanofibers after pre-oxidation (b) and complete oxidation (d). (e to h) EDX maps of cobalt (Co), oxygen (O), and carbon (C) signals on Co3O4 nanofiber after complete oxidation. The Brunauer-Emmett-Teller (BET) surface area and porosity were determined by nitrogen adsorption-desorption experiment. The BET surface area of the nanofiber is 29.8 m² g-1 and the pore volume is 0.1 cm³ g-1. The low surface area compared with nanoparticle shaped Co3O4 (36.5 m² g-1) can significantly suppress the electrolyte decomposition and side reactions, and consequently improve the cycling performance and Coulombic efficiency. N2 adsorption-desorption isotherms are shown in Figure 4a, and the isotherms are of type IV, indicating the existence of mesopores. According to the pore size distribution and the isotherms (inset of Figure 4a), the pore size mostly ranges from 7 to 10 nm, which is correlate well with TEM results. The chemical composition of nanofibers after complete oxidation is characterized by powder X-ray diffraction (XRD). The XRD pattern in Figure 4b shows that all the peaks can be perfectly indexed to a cubic spinel phase of Co3O4 (JCPDS Card no. 42-1467), which is consistent with common Co3O4 microparticles (Figure S2). XPS was also employed to analyze the composition of nanofibers after pre-oxidation and complete oxidation (Figure S3). From cobalt signal (Figure S3c), we can ensure the existence of Co3O4 after pre-oxidation, which supports the TEM results in Figure 3a and 3b. The shift of oxygen signal of the nanofiber after pre-oxidation is mostly because of the production of pre-oxidized polymer.


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Figure 4. (a) The nitrogen adsorption-desorption isotherms at 77 K with corresponding pore size distributions of Co3O4 nanofibers (inset). (b) XRD pattern of Co3O4 nanofibers after complete oxidation. Figure 5a shows the CV curves of Co3O4 nanofiber electrode at a scan rate of 0.1 mV s-1 in the voltage range of 0.01-3.00 V vs. Li+/Li at room temperature. There is a sharp peak located around 0.8 V, corresponding to the reduction of Co3O4 to metallic cobalt, the formation of Li2O, and irreversible formation of SEI.35,36 The peak at about 2.1 V can be ascribed to the reversible oxidation of Co to CoO. The main reduction peak shifts to 1 V and the peak intensity decreases in the subsequent cycles. This is due to the irreversible reactions such as SEI formation during the first cycle. The main anodic peak has little difference in the second and third cycle, indicating the high reversibility of Co3O4 nanofibers in lithium storage. CV curves for Co3O4 nanoparticle electrode and Co3O4 microparticle electrode are shown in Figure S5a and S5b, respectively. Compared with Co3O4 nanofibers and microparticles, the main anodic peak for Co3O4 nanoparticle electrode decreases dramatically, indicating serious side reactions for nanoparticle-shaped electrode. Figure 5b exhibits the voltage vs. charge/discharge capacity profiles of Li/Co3O4 nanofiber cells at



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different cycles. The long potential plateau at 1.1 V is attributed to the reduction process from Co3O4 to CoO and then to metallic cobalt. The initial capacity of cells with porous Co3O4 nanofiber electrode is 1345.1 mAh g-1, much higher than cells with Co3O4 microparticles (1112.9 mAh g-1 in Figure S5c) or nanoparticles (1062 mAh g-1 in Figure S5d). At the 10th cycle, the specific discharge capacities for Co3O4 nanofiber electrode, Co3O4 microparticle electrode and Co3O4 nanoparticle electrode are 1187.8 mAh g-1, 843.7 mAh g-1 and 617.7 mAh g-1, respectively. These cycling results indicate that Co3O4 nanofiber electrode outperforms Co3O4 microparticle electrode and Co3O4 nanoparticle electrode.

Figure 5. (a) Cyclic voltammograms of cells with Co3O4 nanofiber electrode at a scan rate of 0.1 mV s-1 in the voltage range of 0.01-3.00 V vs. Li+/Li. (b) The 1st, 10th and 20th charge/discharge capacities of Li/Co3O4 nanofiber cells at a current density of 100 mA g-1. (c) Impedance spectra of cells with Co3O4 nanofibers (black), Co3O4 nanoparticles (blue) and Co3O4 microparticles (red). Electrochemical impedance spectroscopy (EIS) was employed to characterize the charge-transfer kinetics of different electrodes, and the impedance spectra for cells with Co3O4 nanofibers, nanoparticles or microparticles are presented in Figure 5c. The semicircle at intermediate


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frequency is related to the charge-transfer resistance.37 It can be clearly observed that Co3O4 nanofiber electrode owns the smallest charge-transfer impedance while Co3O4 microparticle electrode has the largest charge-transfer impedance among the three electrodes. The small impedance of Co3O4 nanofiber electrode could be due to the unique structure of the nanofiber electrode containing nanoparticles and nanopores in each nanofiber and interlayer 3D mesopores among the nanofibers. The trace amount of conductive carbon in the nanofibers may also contribute to this improvement.38



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Figure 6. (a) Cycling performance of Li/Co3O4 cells using Co3O4 nanofibers, microparticles or nanoparticles at current density of 100 mA g-1. (b) Long-term cycling performance of cells with Co3O4 nanofibers, microparticles or nanoparticles at current density of 500 mA g-1. (c) Rate capabilities of cells with Co3O4 nanofibers, microparticles or nanoparticles at different current densities.


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Cycling performance of the three type Co3O4 electrodes at different current densities are shown in Figure 6a, 6b and S6. Cells with Co3O4 nanofibers show an enhanced specific capacity at a current density of 100 mA g-1, much higher than cells with Co3O4 microparticles or nanoparticles, and even higher than the theoretical capacity of Co3O4 electrode. This phenomenon is mostly because of the polymer/gel like film formation at the electrode/electrolyte interface.29 The high catalytic activity of Co3O4 would electrochemically facilitate the ring-opening polymerization of the electrolyte, and cause the formation of a polymer/gel-like film. Besides, the structure of the Co3O4 nanofibers could be another reason. The small particle size and increased amount of mesopores provide more Li-ion insertion sites, similar to previous reported literatures in ref. 39 and 40. Compared with cells using Co3O4 nanoparticles and Co3O4 microparticles, cells with Co3O4 nanofibers have higher Coulombic efficiency at the first cycle. The low Coulombic efﬁciency of the ﬁrst cycle can be attributed to the formation of SEI. From the second cycle, the Coulombic efficiency of cells with Co3O4 nanofiber can reach about 99%. It is also interesting to notice that the specific capacity of Co3O4 nanofiber electrode increases initially, decreases after 20 cycles and increases again after 40 cycles. During the initial 20 cycles, the increment in capacity is associated with the activation/lithiation process of the electrode, the polymer/gel-like film formation and the electrode lithiation. The drastic fading from 20 to 40 cycles is due to the decomposition of the unstable polymer/gel-like film. Then the capacity increases again, which could be explained by the lithiation-induced reactivation.29,41 When the current density increasing to 1000 mA g-1, this phenomenon is more obvious (Figure 6S). We also measured the discharge capacities of cells with Co3O4 nanofibers, microparticles or nanoparticles at different current densities (Figure 6c). Cells with Co3O4 nanofibers show an outstanding electrochemical performance at all current densities. These results suggest that the unique structure of Co3O4 nanofiber electrode could enhance the lithium storage capability of Li/Co3O4 cells.

2. CONCLUSIONS In summary, we have successfully created porous Co3O4 nanofibers via electrospinning technique, and used it to improve the lithium storage capability in Li-ion batteries. The as-prepared Co3O4 nanofiber has a diameter of about 100-150 nm and consists of small nanoparticles with the size of 7-17 nm and nanopores with the size of 7-10 nm. The nanopores in each nanofiber and the interlayer space among the nanofibers are used to accommodate the volume expansion during cell cycling. As a result, the cycling behavior of cells with Co3O4 nanofiber electrode outperforms cells with either Co3O4 nanoparticle electrode or Co3O4 microparticle electrode. Besides, the specific capacity (1200 mAh g-1) of cells with Co3O4 nanofiber electrode is even higher than the theoretical capacity of Co3O4 electrode, which is due to the formation of the polymer-gel like film at the electrode/electrolyte interface and the increased active sites in the nanofibers. Moreover, Co3O4 nanofiber electrode shows lower charge-transfer impedance compared with common Co3O4 electrodes, which is mainly attributed to the unique nanostructure of Co3O4 nanofiber and the trace amount of conductive carbon. We believe that the facile method could be applied to other transition metal oxides, such as CuO and NiO, for better anodes in Li-ion batteries ASSOCIATED CONTENT Supporting Information TGA analysis of pristine electrospun nanofibers (Figure S1); XRD pattern of Co3O4 microparticles



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(Figure S2); XPS spectra of C, O, Co signals of nanofiber after pre-oxidation, Co3O4 nanofibers and Co3O4 microparticles (Figure S3); SEM images of Co3O4 microparticles and nanoparticles (Figure S4); Electrochemical test of Co3O4 microparticle electrode and Co3O4 nanoparticle electrode (Figure S5); Cycling performance of Li/Co3O4 nanofiber cells at current density of 1000 mA g-1. (Figure S6).

AUTHOR INFORMATION Corresponding Author Tel: +86-0571-87953906. E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGE We acknowledge the financial support from Ministry of Science and Technology of the People’s Republic of China (MOST, 2016YFA0202900), and from the Natural Science Foundation of China (NSFC, general program: 21676242), and from Chinese government under the “Thousand Youth Talents Program”. We thank Prof. Xiaokun Ding, Prof. Qiaohong He and Prof. Fang Chen from Department of Chemistry, Zhejiang University for TEM and SEM analyses. REFERENCES (1) Wang, C.; Zhang, G.; Ge, S.; Xu, T.; Ji, Y.; Yang, X.; Leng, Y. Lithium-ion battery structure that self-heats at low temperatures. Nature 2016, 529, 515-518. (2) Lee, J.; Urban, A.; Li, X.; Su, D.; Hautier, G.; Ceder, G. Unlocking the potential of cation-disordered oxides for rechargeable lithium batteries. Science 2016, 343, 519-522. (3) Tarascon, J.-M.; Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 2001, 414, 359-367. (4) Liu, N.; Lu, Z.; Zhao, J.; McDowell, M. T.; Lee, H.; Zhao, W.; Cui, Y. A pomegranate-inspired nanoscale design for large-volume-change lithium battery anodes. Nature Nanotech. 2014, 9, 187-192. (5) Zhu, Z.; Wang, S.; Du, J.; Jin, Q.; Zhang, T.; Cheng, F.; Chen, J. Ultrasmall Sn nanoparticles embedded in nitrogen-doped porous carbon as high-performance anode for lithium-ion batteries. Nano Lett. 2014, 14, 153-157. (6) Chen, Y. M.; Yu, X. Y.; Li, Z.; Paik, U.; Lou, X. W. Hierarchical MoS2 tubular structures internally wired by carbon nanotubes as a highly stable anode material for lithium-ion batteries. Sci. Adv. 2016, 2, e1600021. (7) Roy, P.; Srivastava, S. K. Nanostructured anode materials for lithium ion batteries. J. Mater. Chem. A 2015, 3, 2454-2484. (8) Jiang, J.; Li, Y.; Liu, J.; Huang, X.; Yuan, C.; Lou, X. W. Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage. Adv. Mater. 2012, 24, 5166-5180. (9) Yu, S.; Lee, S. H.; Lee, D. J.; Sung, Y.; Hyeon, T. Conversion reaction-based oxide nanomaterials for lithium ion battery anodes. Small 2016, 12, 2146-2172. (10) Wu, R.; Qian, X.; Yu, F.; Liu, H.; Zhou, K.; Wei, J.; Huang, Y. MOF-templated formation of porous CuO hollow octahedra for lithium-ion battery anode materials. J. Mater. Chem. A 2013,


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Enhanced Lithium Storage Capability in Li-Ion ... - ACS Publications

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