In Situ Surface Protection for Enhancing Stability and Performance of LiNi_0.5Mn_0.3Co_0.2O₂ at 4.8 V: The Working Mechanisms

Layered metal oxide cathodes suffer from a low specific capacity (below 200 mAh g–1), while long-term capacity retention is limited by electrolyte decomposition at high voltage (>4.5 V), decohesion, and fracture in primary grains upon cycling. Here, LiNi0.5Co0.2Mn0.3O2 (NCM523) at 4.8 V, employing p-toluenesulfonyl isocyanate (PTSI) as an electrolyte additive, has been investigated, which shows much improved cycling capabilities and rate performances for long-term cycling when a cell voltage of 4.8 V is applied. On the basis of the electrochemical analysis results and the first-principles calculation, the product CH3C6H4NCO from PTSI can be polymerized to produce a polymer (CH3C6H4NCO)2 to generate a stable solid electrolyte interphase film on the NCM523 cathode, which inhibits the decomposition of the electrolyte upon cycling at 4.8 V and offers a long-term cycling performance over 680 cycles. This work emphasizes that in situ surface protection induced by electrolyte additives can drive stable cycling of layered metal oxide cathodes at 4.8 V in advanced Li-ion batteries.