Solid-state electrolytes for Li-rich layered oxide cathodes

Li-rich layered oxide (LLO) cathode materials have been known as possible cathode materials for application in the high energy density lithium batteries based on their high specific capacity, high energy density, and relatively low cost. However, there are several problems that limit its commercial applications on a large scale. The main problems include low initial Coulombic efficiency, poor rate performance, significant capacity fading, and voltage decay during charge-discharge cycles. Using solid-state electrolytes (SSEs) to replace current widely used liquid electrolytes (LEs) has been considered as a promising method to improve the electrical performance of the LLO-based lithium batteries and it is worth studying in depth. In this review, we summarize the investigations of SSEs applied in the LLO cathodes and discuss how to improve the performance of LLO-based lithium batteries through SSEs. At the beginning, the current issues of LLO cathode limiting its application have been generalized. Then, the possible strategies to improve LLO cathodes by SSEs are discussed in detail. SSEs can be roughly divided into quasi-solid-state electrolytes (QSSEs) and all-solid-state electrolytes (ASSEs). QSSEs include the electrolytes prepared by in-situ polymerization and swelling effect, while ASSEs contain oxide-based, sulfide-based and halogen-based SSEs. Finally, the review lists challenges for the SSEs applied in LLO cathodes for both QSSEs and ASSEs and provides some potential suggestions for SSEs to overcome the shortcomings when they are applied in the LLO cathodes. The key point is to increase the stability with LLO cathodes at 4.8 V and the compatibility with Li based anode. This review would promote future commercial applications of LLO cathode-based high energy density and high safety lithium batteries.