Methyl 3,3,3-Trifluoropyruvate Electrolyte Additive Enables High-Voltage Stable Cycling of LiCoO 2

Achieving high-energy-density lithium-ion batteries critically depends on stabilizing the cathode operation at elevated voltages. However, severe interfacial degradation and electrolyte oxidation remain two major challenges that urgently need to be addressed. In this study, methyl 3,3,3-trifluoropyruvate (MTFP) is proposed as an electrolyte additive for high-voltage LiCoO2 (LCO), which stabilizes the cathode–electrolyte interface (CEI) by forming a robust protective layer. Density functional theory calculations indicate that MTFP preferentially adsorbs onto LCO crystal planes and undergoes oxidation reactions, highlighting its function as an interfacial sacrificial precursor. Electrochemical test results show that with the addition of 1 vol % MTFP, LCO maintains a specific capacity of 120.6 mAh g–1 after 700 cycles at a 2 C charge–discharge rate at 4.5 V, corresponding to a 74.3% capacity retention. Surface characterizations (SEM, TEM, and XPS) confirm that MTFP promotes the formation of a dense and uniform CEI layer enriched with LiF and C–F species on the LCO surface. Impedance analyses further demonstrate that this engineered interphase effectively suppresses polarization and enhances Li+ transport kinetics. Collectively, these results prove that MTFP combines the dual advantages of suppressing side reactions and reducing interfacial resistance, providing a promising electrolyte-engineering strategy for high-voltage, long-life LCO-based lithium-ion batteries.