Organic skin layer with carboxyl and electron-withdrawing nitro groups to chemically bind with residual Li and Ni cations on single-crystal LiNi0.8Co0.1Mn0.1O2

Abstract

Interfacial issue is very critical to the electrochemical properties of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, and it also poses a great challenge for successful commercialization of NCM811 via construction of a desirable surface layer. This work constructs a novel metal-organic interface by grafting organic 4-NBA (4-nitrobenzoic acid) layer onto singe-crystal NCM811 surface. The electron transfer from the interfacial Ni2+ to the electron-withdrawing nitro group of 4-NBA promotes the formation of metal-organic interface, which inhibits Ni dissolution into the organic electrolyte. The neutralization reaction between the carboxyl groups of 4-NBA and residual lithium compounds of NCM811 constructs an interfacial layer with improved Li+ conductivity. The 4-NBA organic layer also helps constructing a thin and stable cathode/electrolyte interphase by alleviating the side reactions of electrolyte. The electrochemical properties of single-crystal NCM811 cathode are remarkably enhanced. At a high discharge rate of 20C, a capacity of 141 mAh g−1 can be delivered, significantly higher than that of 101 mAh g−1 of the pristine cathode. After 200 cycles at 1C, the modified sample exhibits excellent capacity retention of 84.5%.