Designing Electrolytes for Stable Operation of High-Voltage LiCoO₂ in Lithium-Ion Batteries

High-voltage lithium cobalt oxide (LiCoO2) can be used to implement high-energy-density lithium-ion batteries (LIBs). However, the detrimental rock-salt phase-induced poor reversibility, lattice oxygen loss, Co leaching, and construction of a resistive cathode-electrolyte interface (CEI) by uncontrolled electrolyte decomposition at high voltages restrict the use of LiCoO2. Here, we discuss the rational design of an electrolyte for use in LIBs. We obtained this electrolyte using an ester-based solvent, without any severe evolution of CO2. The combined use of fluoroethylene carbonate and lithium fluoromalonato(difluoro)borate (LiFMDFB) constructs a LiF-rich solid-electrolyte interphase. Further, a 1,3,6-hexanetricarbonitrile (HTCN) and LiFMDFB-driven CEI prevent the structural collapse and improve the reversibility of the LiCoO2. Moreover, PF5 stabilization and HF scavenging by HTCN and tris(trimethylsilyl) phosphite limit the damage to interfacial layers and Co leaching. Our method for a rational electrolyte design may help in formulating more advanced electrolytes for practical application in high-voltage cell operations.