Designing Electrolytes for Stable Operation of High-Voltage LiCoO 2 in Lithium-Ion Batteries

High-voltage lithium cobalt oxide (LiCoO 2 ) 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 LiCoO 2 . 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 CO 2 . 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 LiCoO 2 . Moreover, PF 5 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.