3-cyano-5-fluorobenzenzboronic acid as an electrolyte additive for enhancing the cycling stability of Li1.2Mn0.54Ni0.13Co0.13O2 cathode at high voltage

Abstract

Layered lithium/manganese-rich oxides (LMR) receive much attention due to its high specific capacity (∼300 mAh g-1). However, the serious capacity degradation during cycling hinders the commercial application of the LMR. Herein, 3-cyano-5-fluorophenylboronic acid (CFBA) was applied as an electrolyte additive for enhancing the cycling stability of LMR at high voltage. Linear sweep voltammetry (LSV), density function theory (DFT) calculations and the initial charge dQ/dV profiles indicate that the preferential oxidation of CFBA can improve the oxidative stability of electrolyte. By adding 0.7 wt% CFBA into standard (STD) electrolyte (1 M LiPF6 in EC:EMC:DMC = 1:1:1, by weight), the LMR/Li half-cell delivered a discharge capacity of 245 mAh g-1 with a capacity retention of 88.4% after 200 cycles at 0.5C, while only 68 mAh g-1 with 25.2% retention in STD electrolyte. Further characterizations and theoretical calculation illustrate that CFBA can effectively eliminate the harmful HF, which improve the electrochemical performance. More importantly, the CFBA participates in the formation of a thin and uniform protective cathode-electrolyte interface (CEI) film on the surface of LMR, which effectively suppresses electrolyte decomposition and protects the structural integrity of LMR.