ARTICLES PUBLISHED: 29 APRIL 2016 | ARTICLE NUMBER: 16050 | DOI: 10.1038/NENERGY.2016.50 Multi-shelled metal oxides prepared via an anion-adsorption mechanism for lithium-ion batteries Jiangyan Wang 1,2 , Hongjie Tang 1 , Lijuan Zhang 1 , Hao Ren 3 , Ranbo Yu 3 * , Quan Jin 1 , Jian Qi 1 , Dan Mao 1 , Mei Yang 1 , Yun Wang 4 , Porun Liu 4 , Yu Zhang 5 * , Yuren Wen 6 , Lin Gu 6 , Guanghui Ma 1 , Zhiguo Su 1 , Zhiyong Tang 4 , Huijun Zhao 4 and Dan Wang 1,4 * One of the major problems in the development of lithium-ion batteries is the relatively low capacity of cathode materials compared to anode materials. Owing to its high theoretical capacity, vanadium oxide is widely considered as an attractive cathode candidate. However, the main hindrances for its application in batteries are its poor capacity retention and low rate capability. Here, we report the development of multi-shelled vanadium oxide hollow microspheres and their related electrochemical properties. In contrast to the conventional cation-adsorption process, in which the metal cations adsorb on negatively charged carbonaceous templates, our approach enables the adsorption of metal anions. We demonstrate controlled syntheses of several multi-shelled metal oxide hollow microspheres. In particular, the multi-shelled vanadium oxide hollow microspheres deliver a specific capacity of 447.9 and 402.4 mAh g -1 for the first and 100th cycle at 1,000 mA g -1 , respectively. The significant performance improvement offers the potential to reduce the wide capacity gap often seen between the cathode and anode materials. R echargeable lithium-ion batteries (LIBs) have long been regarded as a promising candidate to meet the energy needs of a sustainable society 1–5 . However, the energy density of LIBs has still fallen short of expectations. The advancement has been mainly limited by the mismatch between the specific capacities of cathode and anode materials 6 . As a typical example, the reversible capacity of LiCoO 2 (<190 mAh g −1 ), a common cathode material, is much lower than that of the widely used anode material (graphite, 372 mAh g −1 ), resulting in an overall low energy density 7–11 . Vanadium oxide (V 2 O 5 ) is an attractive cathode material for next-generation LIBs because of its high theoretical specific capacity (294 or 441 mAh g −1 , based on an insertion of two or three lithium (Li) per formula unit, respectively) and abundance 12 . Unfortunately, the low ionic conductivity as well as its poor structural stability upon deep discharge has greatly limited its application in LIBs (refs 13–15). A potential solution to circumvent these challenges would be to develop hollow micro-/nanostructures, especially three-dimensional (3D) hollow microspheres with porous shells and zero-dimensional (0D) nanoparticles as basic units, to substitute the bulk structures as LIB cathode materials. Such hollow micro-/nanostructures combine the advantages of both low- dimensional and three-dimensional nanostructures, which could enhance the LIB performance 16 . Specifically, the low-dimensional nanostructures can provide a larger specific surface area, a greater number of surface lithium-storage sites, better access for electrolytes and shorter diffusion paths for both ions and electrons. The 3D nanostructures with interior vacancies can also buffer the volume expansion and alleviate the stress and strain induced by the repeated insertion/extraction of lithium ions 17,18 . Furthermore, the self-supporting multi-shelled structures can achieve even larger specific surface areas, faster diffusion kinetics and better volumetric capacities than the single-shelled structures 19–22 . Significant efforts have been devoted to fabricating hollow structured V 2 O 5 in recent years 23–25 . Owing to the restriction of the surface energy minimization principle 26 , however, most studies have dealt with simple nanostructures 27–30 . Although a few papers have reported the synthesis of V 2 O 5 hollow spheres, the methods often involved multiple steps and/or the main products were single- shelled structures 16,31 . More recently, some other metal oxides of multi-shelled hollow microspheres (MO-MS-HMSs) have been fabricated based on the electrostatic attraction between negatively charged carbonaceous microsphere (CMS) templates and metal cations 32–34 . Unfortunately, the approach failed when extended to synthesize multi-shelled V 2 O 5 hollow microspheres (MS-V 2 O 5 - HMSs) because V(v) ions usually exist as anions (such as VO 3 − and V 3 O 9 3− ) when the pH value is over 2 (ref. 35). Although cationic V (VO 2 + ) might form when decreasing the pH value to below 2, the negative charges of carbon templates become too weak to be able to adsorb the V(v) ions 22,34 . As a result, only single-shelled structures could be produced through this approach 1 National Key Laboratory of Biochemical Engineering, CAS Center for Excellence in Nanoscience, Institute of Process Engineering, Chinese Academy of Sciences, 1 North 2nd Street, Zhongguancun, Haidian District, Beijing 100190, China. 2 Institute of Physics, Chinese Academy of Sciences, No. 8, 3rd South Street, Zhongguancun, Beijing 100190, China. 3 University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China. 4 Department of Physical Chemistry, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, 30, Xueyuan Road, Haidian District, Beijing 100083, China. 5 Centre for Clean Environment and Energy, Gold Coast Campus Griffith University, Queensland 4222, Australia. 6 Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environmental, Beihang University, Beijing 100191, China. *e-mail: ranboyu@ustb.edu.cn; jade@buaa.edu.cn; danwang@ipe.ac.cn NATURE ENERGY | www.nature.com/natureenergy 1 © 2016 Macmillan Publishers Limited. 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