Aluminum metaphosphate-derived CEI suppresses interfacial degradation of NCM811 at 4.5 V and 60 °C

To enhance the energy density of lithium-ion batteries, increasing the operating voltage is crucial; however, this poses challenges to electrolyte stability, particularly with catalytic cathodes such as NCM811. We propose the incorporation of aluminum metaphosphate and fluoroethylene carbonate into the electrolyte to stabilize the NCM811 interface. This modified electrolyte formulation significantly enhances cycling stability, achieving 96.5% capacity retention after 100 cycles at 0.5C under 4.5 V, as well as improves rate capability and high-temperature endurance at 60 °C for NCM811. Analytical results indicate that Al(PO₃)₃ decomposes on the cathode surface, forming a stable cathode electrolyte interphase (CEI) composed of inorganic constituents such as AlF₃ and Al₂O₃. This CEI effectively neutralizes hydrofluoric acid (HF), physically isolates the cathode from the electrolyte, reduces transition metal dissolution, minimizes Li⁺/Ni²⁺ disorder, and preserves the structural integrity of NCM811 with a CEI thickness of approximately 3.91 nm. This study provides a viable solution to interfacial degradation in high-voltage batteries by regulating the cathode interface.