Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as

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Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as High Power Cathodes for Lithium-Ion Batteries Yu Wu, Chuanbao Cao, Junting Zhang, Lin Wang, Xilan Ma, and Xingyan Xu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b06820 • Publication Date (Web): 11 Jul 2016 Downloaded from http://pubs.acs.org on July 13, 2016

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ACS Applied Materials & Interfaces

Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as High Power Cathodes for LithiumIon Batteries Yu Wu, Chuanbao Cao,* Junting Zhang, Lin Wang, Xilan Ma and Xingyan Xu Research Center of Materials Science, Beijing Key Laboratory of Construction Tailorable Advanced Functional Materials and Green Applications, Beijing Institute of Technology, Beijing 100081, China KEYWORDS: hierarchical, hollow cubes, LiMn2O4, exposed {111} planes, superior electrochemical performance, lithium-ion batteries

ABSTRACT: Hierarchical LiMn2O4 hollow cubes with exposed {111} planes have been synthesized using cube-shaped MnCO3 precursors, which are fabricated through a facile coprecipitation reaction. Without surface modification, the as-prepared LiMn2O4 exhibits excellent cyclability and superior rate capability. Surprisingly, even over 70% of primal discharge capacity can be maintained for up to 1000 cycles at 50 C and with only about 72 s of discharge time the as-prepared materials can deliver initial discharge capacity of 96.5 mAh g-1. What is more, the materials retain 98.4% and 90.7% capacity retentions for up to 100 cycles at 5 C under the temperature of 25 oC and 60 oC, respectively. The superior electrochemical performance can be

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attributed to the unique hierarchical and interior hollow structure, exposed {111} planes and high-quality crystallinity.

1. INTRODUCTION Lithium ion battery (LIB) is being intensively pursued for high-power applications such as electric vehicles (EVs) and hybrid electric vehicles (HEVs).1,2 Lithium manganese oxide (LiMn2O4), owing to low material cost, nontoxicity, the abundance of sources, and low safety hazard, has been regarded as one of the most hopeful cathode for LIB.3-6 However, the application of LiMn2O4 is hindered by capacity degradation, particularly at high current densities and elevated temperatures, caused by the dissolution of Mn3+ through the disproportionation reaction.7-10 To effectively mitigate the dissolution of Mn3+ and structural degradation, many researchers have adopted a series of approaches, such as surface coating and cation doping. In detail, surface coating can hold back direct contact between the electrolyte and the active spinel material, thus has been generally employed to restrain manganese dissolution.9-14 However, the coating layer generally is not uniform. Moreover, the high resistance resulting from surface coating layer can obstruct lithium ions and electrons diffusion pathways on the surface of spinel material, resulting in a obvious sacrifice in specific capacity. What is more, surface coating often needs complex and time-consuming procedures.15,16 Another approach to confine Mn dissolution is cation doping, which benefits to the crystal structure stability.17,18 The replacement of Mn by Al3+ and Ti4+, has been successfully employed to alleviate capacity degradation, but the strategy simultaneously sacrifice capacity because of the electrochemical inertia of doping ions.19,20 In view of above problems, the present research seeks alternative routes to restrain the manganese dissolution. Surprisingly, it was reported that the lattice orientation of the surface


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affect the dissolution of Mn3+ closed associated with the stabilization of solid electrolyte interphase layers and the compactness of crystal lattice of manganese, and the {111} plane has the lower Mn dissolution and more stable reconstructed surface structure than other planes such as {110} and {100}.21 Based on the stabilization of solid electrolyte interphase, previous study reveals that the exposed {111} facet develops stable solid electrolyte interphase which can relieve manganese dissolution.22 On the contrary, the {110} facet develops less stable solid electrolyte interphase. For another outlook, manganese atoms are denser arranged at the {111} facet than the {110} and {100} facets. It is expected that the denser crystal lattice of manganese has less interaction with electrolyte and hence alleviates manganese dissolution.21 For instance, Qian et al. prepared interconnected LiMn2O4 fibers with exposed {111} facet, which can deliver a capacity retention ratio of 78.9% after 1000 cycles at 5 C.23 Meanwhile, Sun et al. synthesized porous LiMn2O4 nanosheets with exposed {111} facet, which exhibit a good cyclability, with a capacity retention of 86% after 500 cycles.24 The improved cycle performance is attributed to the exposed {111}, which has the lower Mn dissolution and more stable reconstructed surface structure than other planes. In addition to the cyclability, rate capability is also rather important to the practical application. Recently, hollow hierarchical structures have captured considerable attention because the nanosized subunits can significantly reduce the diffusion distance of Li+, and the microsized structure can guarantee toilless fabrication and steadiness, leading to improved rate capability and cyclability.25-28 In our previously reported studies, hierarchical electrode materials have showed excellent rate capability and ameliorative cycle performance.29-32 Furthermore, the hollow structure provide interior void space to timely buffer the volume change resulted from the repeated Li+ intercalation/deintercalation, resulting in enhanced cyclability and rate capability.


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Zhou et al. have reported binary spinel LiNi0.5Mn1.5O4 hollow microstructure cathodes with superior rate capability and cycle stability.33 Therefore, hollow nano/micro hierarchical structure of LiMn2O4 with exposed {111} planes can be expected to enhance the cycling stability and simultaneously improve the rate capability. Unfortunately, hollow nano/micro hierarchical structure of LiMn2O4 with exposed {111} planes has not been reported until now. In this work, we report a facile co-precipitation method, coupled with lithiation reaction, to synthesize hierarchical LiMn2O4 hollow cubes with exposed {111} planes for the first time. The co-precipitation reaction is a facile chemical method, in which cube-like MnCO3 precursors were first fabricated after that lithiation reaction was implemented to obtain LiMn2O4 at 750 oC. The obtained hierarchical hollow cubes exhibited superior rate capability and excellent cycling stability, retaining 98.4% and 90.7% capacity retentions for up to 100 cycles at 5 C under the temperature of 25 oC and 60 oC, respectively. These capacity retentions are among the highest values obtained reported for the spinel LiMn2O4 materials at 5 C rate after 100 cycles. What is more, the materials present a capacity retention ratio of even over 70% after 1000 cycles at 50 C rate. More surprisingly, with only about 72 s of discharge time the as-prepared materials yield initial discharge capacity of 96.5 mAh g-1 (10.8 min to full charge). It is to be noted that, such outstanding performances of 50 C rate are reported for the first time to the best of our knowledge. 2. EXPERIMENTAL SECTION 2.1 Preparation of LiMn2O4 Firstly, the submicron cubic MnCO3 was fabricated through the method reported by our group.29 Specifically, 3 mmol MnSO4 was dissolved in 210 mL distilled water to form the A solution and 30 mmol NH4HCO3 dissolved in 210 mL distilled water to form the B solution.


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Then 1050 mL ethanol was added to the above A solution under stirring, after its complete dispersion, the prepared B solution was added to the solution mentioned above. After vigorous stirring for 15 min, the MnCO3 cubes were filtered, washed with distilled water and ethanol to remove impurities. Then, the synthesized submicron MnCO3 cubes were sintered at 400 oC for 5 h to prepare MnO2 cubes. After that, the MnO2 cubes were dispersed along with LiOH·H2O in stoichiometric ratio of 2.00: 1.05 in ethanol to form suspension. The suspension was then evaporated at room temperature. Afterwards, the mixture was ground manually for 15 min and calcined at 750 oC for 8 h in air. 2.2 Characterization The chemical elements of the products were identified by inductively coupled plasma atomic emission spectrometry (ICP-AES, ICAP-6300). The products were analyzed using X-ray diffraction (PANalytical, Netherlands) with Cu Ka radiation, Hitachi field-emission scanning electron microscopy (FESEMS, Hitachi S-4800), transmission electron microscopy (TEM) (HRTEM, FEI Tecnai G2 F20, 200 kV). 2.3 Electrochemical measurements Electrochemical measurements were performed with CR2025 coin-type cells. The cathode electrodes were prepared by mixing 80 wt% product, 10 wt% carbon black, and 10 wt% polyvinylidene fluoride binder, dissolved in N-methyl-2-pyrrolidone to form a slurry. The slurry was spread on an aluminium foil and dried at 110 oC in vacuum for 10 hours. 1 M LiPF6 dissolved in ethyl carbonate/dimethyl carbonate/diethyl carbonate (1 : 1 : 1 v/v) was used as an electrolyte. Charge–discharge tests were conducted on a CT2001A Land battery test instrument between 3 and 4.3 V at different C rates. Cyclic voltammetry (CV; 3-4.3 V, 0.1 mV s-1) was carried out by an IM6e electrochemical workstation (Zahner, Germany).


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3. RESULTS AND DISCUSSION Scheme 1 illustrates the formation process of the hollow LiMn2O4 cubes. The formation of cubic MnCO3 (Supporting Information (SI) Figure S1) via the co-precipitation method and its conversion to the cubic MnO2 after annealing at 400 oC are confirmed by XRD and SEM analysis (Figure S2, Figure S3). Then, stoichiometric amounts of cubic MnO2, LiOH·H2O are added in ethanol to form suspension, which is evaporated under stirring at room temperature until dryness. Lastly, the calcinations is necessary to prepare the hollow LiMn2O4 cubes. Scheme 1. The preparation of hollow LiMn2O4 cubes.

The XRD pattern of hierarchical LiMn2O4 hollow cubes is dispalyed in Figure 1. All peaks can be assigned to cubic LiMn2O4 (JCPDS No. 35-0782).34 The Rietveld refinement shows calculated lattice parameter of a = 8.243 Å that is a little less than the standard value of cubic LiMn2O4 (8.247 Å), indicating that the segmental manganese ions were substituted by lithium ions.5,6 The results are also supported by the ICP-AES, which show that exact ratios of Li: Mn is 0.53, demonstrating the formation of a lithium-rich phase of Li1.03Mn1.97O4, which leads to a decrease of the concentration of Mn3+ and thereby restrains the structural degradation in some degree.


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Figure 1. XRD pattern of hollow LiMn2O4 cubes. Figure 2 demonstrates the typical morphology and structure of the as-synthesized materials. As can be seen from Figure 2a and Figure 2b, the LiMn2O4 cathode material is composed of uniform cubic secondary assemblies with the size of about 500 nm, which guarantees toilless fabrication and steadiness. Moreover, from the magnified SEM image of the as-prepared LiMn2O4 (Figure 2b), we can also clearly observe the highly porous structure and nano-sized subunits, which are further confirmed by the TEM image (Figure 2c). These features can significantly reduce the diffusion distance for Li+. Moreover, the samples are examined by TEM and HRTEM. Figure 2c presents the TEM image for as-synthesized LiMn2O4, and reveals the highly porous and interior hollow structure, which ensures easy penetration of electrolyte into the interior void space of as-prepared cubes, provides internal void space to effectively accommodate the volume change resulted from the repeated Li+ intercalation/deintercalation. The high magnification TEM image of a hollow LiMn2O4 cube in Figure 2d manifests that the cube is made up of nanoparticles with the size about 50 nm. To define the exposed flat face of the rectangle region marked in Figure 2d, a high resolution TEM image is illustrated in Figure 2e, which shows clear lattice fringes, the interplanar spacings of 0.48 nm assigned to the (111) and (111) crystal faces of LiMn2O4, respectively, indicating that the exposed plane is {111} facet,


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which has the lower Mn dissolution and more stable reconstructed surface structure than other planes such as {110} and {100}. And the interplanar spacings of 0.29 nm indexed to (220) planes of LiMn2O4. Moreover, the corresponding FFT patterns (Figure 2f) present clearly spots, which can be assigned to cubic spinel.

Figure 2. (a) and (b) SEM images of hierarchical LiMn2O4 hollow cubes. (c) and (d) TEM images of hierarchical LiMn2O4 hollow cubes. (e) high resolution TEM image of the rectangle region in (d) and (f) the relevant FFT pattern.


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To further reveal the exposed facet features of as-prepared materials, HRTEM characterization and the FFT pattern of randomly selected LiMn2O4 particles are exhibited in Figure 3. We emphasize the edge of each randomly selected particle in Figure 3a and Figure 3c. The HRTEM images (Figure 3b, Figure 3d) correspond to the rectangle regions marked in Figure 3a and Figure 3c, respectively. In both two regions, the apparent lattice fringes with interplanar distance of 0.48 nm are clearly observed. These fringes are well assigned to the planar distance between (111) crystal faces of spinel LiMn2O4, indicating that the exposed planes are {111} facets. Such characteristics fringes can be continually presented in the investigation of asprepared LiMn2O4 materials. Therefore, we can conclude that the LiMn2O4 with exposed {111} planes has been successfully fabricated. As mentioned previously, the {111} plane has the lower Mn dissolution and more stable reconstructed surface structure than other planes such as {110} and {100} and thereby enhance the cyclability.22 Moreover, the corresponding FFT patterns (inset of Figure 3b and Figure 3d) present well-defined spots, implying the prepared LiMn2O4 is single crystal structure, which shows better steadiness than poly-crystalline structure.24


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Figure 3. (a) and (c) HRTEM images of randomly selected particles in as-prepared LiMn2O4. (b) a magnified HRTEM image and corresponding FFT pattern (inset) taken from the rectangle region in (a). (d) a magnified HRTEM image and corresponding FFT pattern (inset) taken from the rectangle region in (c). The electrochemical performances of LiMn2O4 cathode materials were investigated using Li metal as anodes between 3 and 4.3 V and the charge rate was equal to the discharge rate. Figure 4a presents the cyclability of as-prepared materials at 5 C (1 C = 148 mA g-1) at 25 oC. The initial discharge capacity is 97.7 mAh g-1. After 100 charge and discharge cycles, the discharge capacity of as-prepared LiMn2O4 cathode is maintained at 96.1 mAh g-1 with excellent capacity retention of 98.4% and coulombic efficiencies are almost 100%, which indicate that the cell exhibits extremely superior cycle performance and good electrochemical reversibility. As we know, the Mn dissolution becomes more serious at high temperature, giving rise to the poor cyclability of common LiMn2O4. However, as-prepared LiMn2O4 cathode materials maintain superior cycle stability at elevated temperatures. When the temperature increases to 60 oC, the cycle performance of as-prepared LiMn2O4 at 5 C is shown in Figure 4b. After 100 charge-


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discharge cycles, the corresponding capacity retention ratio is 90.7% even at 60 oC. To the best of our knowledge, these capacity retentions are among the highest values obtained reported for the spinel LiMn2O4 materials at 5 C (1 C = 148 mA g-1) after 100 cycles. More surprisingly, assynthesized LiMn2O4 even shows better cycling stability at 5 C rate than that of state-of-art advanced LiMn2O4 materials at 1 C rate reported in the literatures (Table S1 Supporting Information),5,6,9,11,14,34-37 owing to the exposed {111} planes of as-prepared LiMn2O4 cathode material, which has the lower Mn dissolution associated with the stabilization of solid electrolyte interphase layers and the compactness of crystal lattice of manganese than other facets. Based on the stabilization of solid electrolyte interphase, previous study reveals that the exposed {111} facet develops stable solid electrolyte interphase which can relieve manganese dissolution.22 On the contrary, the {110} facet develops less stable solid electrolyte interphase. For another outlook, manganese atoms are denser arranged at the {111} facet than the {110} and {100} facets. It is expected that the denser crystal lattice of manganese has less interaction with electrolyte and hence alleviates manganese dissolution.21 In order to detect manganese deposited on the anode, XPS measurements were performed on lithium metal collected after 100 cycles. The analysis of XPS spectra show that the anode has little Mn deposited (Supporting Information Figure S4a-b). In addition, XPS were conducted to detect the manganese of separator collected after 100 cycles. On the basis of the XPS spectra (Supporting Information Figure S4c-d), it is clear that we have detected little Mn on separator. From these results above, we conclude that the exposed {111} planes of the hierarchical LiMn2O4 hollow cubes lead to little dissolution of Mn. Moreover, the interior void and porous structure, which can effectively accommodate the structural strain and volume change caused by the repeated Li+ insertion/extraction, improving the cycle performance. Figure 4c shows the galvanostatic charge/discharge curves at 0.5 C at 25


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o

C. Charge and discharge curves present two pseudoplateaus, which are attributed to the two-

phase transformation of λ-MnO2/Li0.5Mn2O4 and Li0.5Mn2O4/LiMn2O4, respectively.5,6 The processes accord with the two pairs of peaks in the CV curves (inset in Figure 4c). Figure S5 displays the Nyquist plot of the as-prepared LiMn2O4 and the corresponding equivalent electrical circuit. The single semicircle appears as a contribution of two different frequency semicircles. One is the high-frequency semicircle resulted from the solid electrolyte interface resistance (RSEI). The other is the intermediate-frequency semicircle which is ascribed to the chargetransfer resistance (Rct). The low-frequency oblique line is attributed to the lithium ion diffusion in the cathode materials, the Warburg impedance (W). To evaluate the rate capability, the asprepared LiMn2O4 was cycled at various charge/discharge rates from 1 to 5 C during 3-4.3 V with 10 cycles per step (Figure 4d). Significantly, the specific capacity can recover to almost initial capacity while current density back to 1 C.


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Figure 4. (a) Cycling performances and corresponding coulombic efficiencies cycled at 5 C at 25 oC. (b) Cycling performances and corresponding coulombic efficiencies at 5 C at 60 oC. (c) The first galvanostatic charge/discharge curves at 0.5 C, inset: CV plot at 0.1 mV s-1. (d) Rate capability at various rates from 1 C to 5 C. Taking practical application into consideration, where rapid charge-discharge capability is in demand, the prepared hierarchical LiMn2O4 hollow cubes were cycled at different charge rates and at ultrahigh current rate of 50 C for discharge (Figure 5a, Figure 5b). As shown in Figure 5a, the hierarchical LiMn2O4 hollow cubes yield high initial discharge capacity of 119.4 mAh g-1 (1 C charge/50 C discharge) and 96.5 mAh g-1 (5 C charge/50 C discharge), respectively, and even retain over 70% at all rates at the completion of 1000 cycles. It is to be noted that, such outstanding performances of 50 C rate are first reported to the best of our knowledge. More surprisingly, with only about 72 s of discharge time the as-prepared materials can achieve initial specific capacity of 96.5 mAh g-1 (10.8 min to full charge) as illustrated in Figure 5b. The excellent performance in terms of high-power capability, cycling stability, and shortened charge/discharge time are what we are looking for in developing the power sources of EVs or HEVs.


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Figure 5. (a) Cycling performances at different charge rates and at ultrahigh current rate of 50 C for discharge. (b) Ultrafast charge/discharge capability of as-prepared materials at 5 C (charge) and 50 C (discharge). In addition, the excellent cycling stability, superior rate capability, and the high specific capacity are mainly originated from the unique hierarchical and interior hollow structure, exposed {111} planes, and high-quality crystallinity. First, the nanosized primary blocks provide the short diffusion distance for lithium ions, leading to superior rate performance.29,38 Second, the structural strain and volume change resulting from the repeated Li+ insertion/extraction could be effectively buffered by the interior hollow structure and porosity, thus enhancing the cyclability.33 Third, the exposed {111} planes have the lower Mn dissolution and more stable reconstructed surface structure than other facets, contributing to the structural stability.22 Fourth, the superior crystallinity can enhance the integrity of structure of LiMn2O4.6 Fifth, better structure integrity is also attributed to lithium-rich phase of the hierarchical LiMn2O4 hollow


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cubes. The substitution of lithium ions for manganese ions (Li1.03Mn1.97O4) leads to a decrease in the concentration of Mn3+, which restrains the structural degradation in some degree and produces better cycling behaviors.5,6 4. CONCLUSIONS In conclusion, we have reported a facile co-precipitation reaction to fabricate MnCO3 precursors, coupled with lithiation reaction, to synthesize hierarchical LiMn2O4 hollow cubes with exposed {111} planes for the first time. When valued as cathode for LIB, the prepared hierarchical hollow cubes presented superior rate performance and excellent cycling stability, which mainly be accredited to their unique hierarchical and interior hollow structure, exposed {111} planes and high-quality crystallinity. These results clearly demonstrate that the hierarchical LiMn2O4 hollow cubes would be hopeful cathode candidate for high power applications in rechargeable lithium-ion batteries. ASSOCIATED CONTENT Supporting Information SEM images of the cubic MnCO3 and MnO2 precursors, XRD patterns of the prepared MnO2 precursors, XPS spectra of the lithium metal and separator and the electrochemical performances for several advanced LiMn2O4 cathode materials, Nyquist plot of the as-prepared LiMn2O4. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].


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Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (Grant No. 50972017 and 21371023) and Research Fund for the Doctoral Program of Higher Education of China (Grant No.20101101110026). REFERENCES (1) Tarascon, J. M.; Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 2001, 414, 359-367. (2) Armand, M.; Tarascon, J. M. Building better batteries. Nature 2008, 451, 652-657. (3) Park, O. K.; Cho, Y.; Lee, S.; Yoo, H. C.; Song, H. K.; Cho, J. Who will drive electric vehicles, olivine or spinel? Energy Environ. Sci. 2011, 4, 1621-1633. (4) Lee, S.; Oshima, Y.; Hosono, E.; Zhou, H.; Kim, K.; Chang, H. M.; Kanno, R.; Takayanagi, K. Phase Transitions in a LiMn2O4 Nanowire Battery Observed by Operando Electron Microscopy. ACS Nano 2015, 9, 626-632. (5) Cheng, F.; Wang, H.; Zhu, Z.; Wang, Y.; Zhang, T.; Tao, Z. J. Chen, Porous LiMn2O4 nanorods with durable high-rate capability for rechargeable Li-ion batteries. Energy Environ. Sci. 2011, 4, 3668-3675. (6) Ding, Y. L.; Xie, J.; Cao, G. S.; Zhu, T. J.; Yu, H. M.; Zhao, X. B. Single-Crystalline LiMn2O4 Nanotubes Synthesized Via Template-Engaged Reaction as Cathodes for HighPower Lithium Ion Batteries. Adv. Funct. Mater. 2011, 21, 348-355. (7) Huang, R.; Ikuhara, Y. H.; Mizoguchi, T.; Findlay, S. D.; Kuwabara, A.; Fisher, C. A. J.; Moriwake, H.; Oki, H.; Hirayama, T.; Ikuhara, Y. Oxygen-Vacancy Ordering at Surfaces


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of Lithium Manganese(III,IV) Oxide Spinel Nanoparticles. Angew. Chem. Int. Ed. 2011, 50, 3053-3057. (8) Zhan, C.; Lu, J.; Kropf, A. J.; Wu, T.; Jansen, A. N.; Sun, Y. K.; Qiu, X.; Amine, K. Mn(II) deposition on anodes and its effects on capacity fade in spinel lithium manganate– carbon systems. Nat. Commun. 2013, 4, 2437. (9) Lee, S.; Yoon, G.; Jeong, M.; Lee, M. J.; Kang, K.; Cho, J. Hierarchical Surface Atomic Structure of a Manganese-Based Spinel Cathode for Lithium-Ion Batteries. Angew. Chem. Int. Ed. 2015, 54, 1153-1158. (10) Lu, J.; Zhan, C.; Wu, T.; Wen, J.; Lei, Y.; Kropf, A. J.; Wu, H.; Miller, D. J.; Elam, J. W.; Sun, Y. K.; Qiu, X.; Amine, K. Effectively suppressing dissolution of manganese from spinel lithium manganate via a nanoscale surface-doping approach. Nat. Commun. 2014, 5, 5693. (11) Lee, M. J.; Lee, S.; Oh, P.; Kim, Y.; Cho, J. High Performance LiMn2O4 Cathode Materials Grown with Epitaxial Layered Nanostructure for Li-Ion Batteries. Nano Lett. 2014, 14, 993-999. (12) Myung, S. T.; Lee, K. S.; Kim, D. W.; Scrosati, B.; Sun, Y. K. Spherical core-shell Li[(Li0.05Mn0.95)0.8(Ni0.25Mn0.75)0.2]2O4 spinels as high performance cathodes for lithium batteries. Energy Environ. Sci. 2011, 4, 935-939. (13) Lee, S.; Cho, Y.; Song, H. K.; Lee, K. T.; Cho, J. Carbon-Coated Single-Crystal LiMn2O4 Nanoparticle Clusters as Cathode Material for High-Energy and High-Power Lithium-Ion Batteries. Angew. Chem. Int. Ed. 2012, 51, 8748-8752.


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Table of Contents/Abstract Graphic and Synopsis

Hierarchical LiMn2O4 hollow cubes with exposed {111} planes have been fabricated through a facile reaction. As cathode, as-prepared materials exhibit superior cyclability and outstanding rate performance for lithium-ion batteries. The superior performance can be attributed to the unique hierarchical interior hollow structure and exposed {111} planes.


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Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as

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