Radical‐Scavenging Lithium Salt for Stable High‐Voltage Li||LiCoO2 Batteries

A functional lithium salt, 2,2,6,6-tetramethyl-1-piperidinyloxyl-4-sulfate lithium (TEMPO-OSO₃Li), affects the accumulation of TEMPO-OSO₃ ⁻ anion at the cathode under electric field modulation, scavenging free radicals to prevent the continuous oxidative decomposition of the electrolyte, stabilizing the cathode-electrolyte interphase and the structure of lithium cobalt oxide (LiCoO₂). This contributes to the improved electrochemical performance of Li||LiCoO₂ batteries at 4.6 V.

Abstract

High-voltage cathodes improve the energy density of the batteries, which satisfies the pursuit of high-energy-density lithium metal batteries (LMBs). However, layered lithium cobalt oxide (LiCoO₂) cathodes suffer from severe interfacial side reactions under high voltage (4.6 V), which is detrimental for practical applications. Herein, a functional lithium salt, 2,2,6,6-tetramethyl-1-piperidinyloxyl-4-sulfate lithium (TEMPO-OSO₃Li) is developed that possesses radical-scavenging anion TEMPO-OSO₃ ⁻. The anion accumulates at the cathode interface and effectively scavenges free radicals under the electric field at high voltage, thereby, inhibiting the electrolyte decomposition and interfacial side reactions. As a result, the Li||LiCoO₂ batteries with dual-salt (TEMPO-OSO₃Li (0.02 m) and LiPF₆ (1 m)) electrolyte exhibit high capacity retention of 92% after 100 cycles at 4.6 V and maintain 81% after 200 cycles, which is superior to that of the baseline electrolyte (26%). The work demonstrates a promising strategy for designing electrolyte salts to realize the practical application of LiCoO₂ at high voltage.