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

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 SOx-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.

Automated summary

By using an additive-assisted electrolyte, researchers have improved the stability and capacity retention of LiCoO2 cathode at high voltages. The additive forms a reversible redox couple (SO42-/S2O32-) on the cathode, which reduces oxygen release and electrolyte decomposition, leading to enhanced electrochemical performance.