A compact interphase involving a reversible redox couple stabilizes a 4.6 V LiCoO2 cathode

Abstract

LiCoO₂ (LCO), as a commercialized cathode material for batteries, suffers from severe structural instability and capacity fading when charged to high voltages (>4.5 V) due to oxygen release, Co dissolution, and subsequent crack formation/electrolyte decomposition. Herein, we constructed a compact SO_x-rich cathode electrolyte interphase (CEI) involving a reversible SO₄²⁻/S₂O₃²⁻ redox couple via an additive (bis(4-fluorophenyl) sulfone)-assisted electrolyte, thus improving the electrochemical performance of graphite‖LCO cells at high voltage. Bis(4-fluorophenyl) sulfone was found to adsorb on the LCO cathode and form a reversible SO₄²⁻/S₂O₃²⁻ redox couple, which alleviated oxygen release by continuous reduction/oxidation during the charging/discharging process, thus inhibiting the decomposition of the electrolyte. The designed electrolyte endows a 4.6 V Li‖LCO cell and 4.55 V graphite‖LCO cell with high capacity retention of 88% over 300 cycles and 96% over 150 cycles, respectively. The compact CEI involving a reversible redox couple strategy provides new insights into electrolyte design for high-voltage cathodes and overcomes the limit toward the development of high-energy-density batteries.