Conversion reaction-based transition metal oxides as anode materials for lithium ion batteries: recent progress and future prospects

The rapid increase in demand for high-performance lithium ion batteries (LIBs) has prompted the development of high capacity anode materials that can replace/complement the commercial graphite. Transition metal oxides (TMOs) have attracted great attention as high capacity anode materials because they can store multiple lithium ions (electrons) per unit formula via conversion reaction, resulting in high specific capacity (700-1,200 mAh g-1) and volumetric capacity (4,000-5,500 mAh cm-3). In addition, TMOs are cheap, earth-abundant, non-toxic and environmentally friendly. However, there have been no reports of practical LIBs using conversion-based TMO anodes, because of several major problems such as large voltage hysteresis, low initial Coulombic efficiency (large initial capacity loss), low electrical conductivity, and large volume changes (100~200%). This review summarizes the recent progress, challenges and opportunities for TMO anode materials. The conversion reaction mechanism, problems and solutions of TMO anode materials are discussed. Considering iron oxide as a promising candidate, future research directions and prospects for the practical use of TMO for LIB are presented.