Revealing the role of spinel phase on Li-rich layered oxides: A review

Li-rich Layered Oxides (LLOs), considered as the most promising cathode material with high theoretical specific capacity (>250 mAh g(-1)) in Lithium-Ion Batteries (LIBs), still suffer from severe intrinsic weaknesses such as low initial coulombic efficiency, poor rate capability, limited cycle life and severe voltage decay. These drawbacks are believed to originate from Transition Metal (TM) ion migration, irreversible oxygen release and cathode-electrolyte interfacial reactions etc. Owing to similar cubic close-packed oxygen arrays with LLOs, spinel phase, which greatly facilitates the transport of Li-ion, protection from organic electrolyte, the suppression of structural collapse and pre-extraction combining with the accommodation of Li-ion at low voltage, is widely applied to ameliorate electrochemical performance. In this article, we systematically review recent progresses of spinel phase on LLOs and comprehensively summarize the effectiveness of proposed strategies in improving the electrochemical performance of LLOs, including surface coating, spinel-layered coherent component, in-situ spinel-layered integration and synergistic effects of spinel with other components. Finally, we discuss the main barrier to the commercialization of LLOs and give advice for future development of LLOs for high-energy-density LIBs.