Interfacial Architectures Derived by Lithium Difluoro(bisoxalato) Phosphate for Lithium-Rich Cathodes with Superior Cycling Stability and Rate Capability

Abstract

Lithium-ion batteries (LIBs) have been recently gained recognition as one of the most reliable energy storage devices for using portable appliances. The scale of LIBs market has been gradually expanded, especially the large-scale batteries for electric vehicles (EVs) and energy storage systems (ESSs). To develop LIBs with high energy density, many research groups have focused on Li-rich cathodes (xLi2MO3-(1-x)LiMO2 (M = Co, Mn, Ni)). However, there are severe challenges to apply Li-rich cathodes to LIBs; considerable voltage decay and capacity fading during cycling, serious oxidative decomposition of electrolytes at high voltage conditions. To overcome these various drawbacks of Li-rich cathodes, we focus on the use of electrolyte additives forming a stable solid electrolyte interphase (SEI) layer on the Li-rich cathode. Lithium difluoro(oxalato)phosphate (LiDFBP) is utilized as a lithium salt-type electrolyte additive for Li-rich cathodes of LIBs. Our investigation reveals that a durable and uniform protective surface film on the Li-rich cathode was produced by the LiDFBP additive. It is found that the LiDFBP-derived SEI layer effectively inhibits undesirable electrolyte decomposition and mitigates the voltage decay of Li-rich cathodes caused by phase transformation from layered to spinel-like during cycling. Remarkably, much improved cycling performance of Li-rich cathodes was achieved in the LiDFBP-added electrolyte.