Improving the Cycling Stability of NCM811 at High-Voltage 4.5V in Ester-Based Electrolytes with LiDFOB

Nickel-rich layered cathode materials, particularly LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811), have garnered significant attention due to their high energy density and impressive electrochemical performance. However, their cycling stability is compromised at elevated voltages, primarily due to structural instability and interfacial degradation. In this study, lithium difluoro(oxalato)borate (LiDFOB) is introduced into a commercial electrolyte based on lithium hexafluorophosphate (LiPF₆) to elucidate the structural and interfacial changes occurring in NCM811 at a high cut-off voltage of 4.5 V. It is found that the preferential decomposition of LiPF₆ leads to the formation of a protective inert interface. At the same time, violent anisotropic lattice contraction and expansion generate cracks that contribute to the rapid degradation of NCM811. Notably, the incorporation of LiDFOB significantly mitigates these detrimental effects. Consequently, NCM811|Li cells utilizing this optimized electrolyte demonstrate an initial specific capacity of 214 mAh g^-1 and remarkable capacity retention of 83.6% after 400 cycles at a 1C rate (1C = 200 mAh g^-1). The findings pave the way for leveraging higher capacities of NCM811 at elevated cut-off voltages, thereby enhancing its viability for high-end energy applications.