Interfacial Origin of Performance Improvement and Fade for 4.6 V LiNi0.5Co0.2Mn0.3O2 Battery Cathodes

The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi0.5Co0.2Mn0.3O2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0–4.6 V versus Li/Li+ results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205–182 mAhg–1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi0.5Co0.2Mn0.3O2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes.