Abstract
To achieve higher energy density in lithium-ion batteries, increasing the operating voltage is essential, but it challenges electrolyte stability, especially with catalytic cathodes like NCM811. We suggest adding aluminum metaphosphate (Al(PO3)3) and fluoroethylene carbonate (FEC) to the electrolyte to stabilize the NCM811 interface. This modified electrolyte improves cycling stability (96.5% capacity retention after 100 cycles at 0.5 C under 4.5 V), rate capability, and high-temperature endurance (60 °C) of NCM811 cells. Analysis shows that Al(PO3)3 decomposes on the cathode surface, forming a stable cathode electrolyte interphase (CEI) with inorganic components like AlF3 and Al2O3. This CEI efficiently neutralizes hydrofluoric acid (HF) and physically separates the cathode from the electrolyte, reducing transition metal dissolution, minimizing Li+/Ni2+ disorder, and maintaining the structural integrity of NCM811 with a CEI thickness of ~3.91 nm. This study offers a solution to interfacial degradation in high-voltage batteries by regulating the cathode interface.