Assessment of the impact of cathode protection layers on the performance of NMC/Li batteries in electrolytes containing FEC and LiBOB

Achieving stable cycling of high-voltage lithium-ion batteries (LIBs) requires co-design of electrolyte composition and electrode interphases. Here we investigate the combined effects of electrolyte composition and artificial cathode coatings on NMC622 cathodes. Initially, we present an in-depth examination of the commercial electrolyte designed to form LiF/BOB-rich interphases. The electrolyte is based on a quaternary carbonate solvent - dimethyl carbonate/ethyl methyl carbonate/fluoroethylene carbonate/propylene carbonate (DMC/EMC/FEC/PC, 3:3:3:1, v/v), and contains 0.95 M lithium hexafluorophosphate (LiPF₆) and 0.05M lithium bis(oxalato)borate (LiBOB). This system is compared against a standard binary EC:EMC electrolyte containing 1 M LiPF₆. The coatings are applied via electrophoretic deposition (EPD). The study evaluates whether cathode protective coatings in the quaternary electrolyte further improve long-term cycleability, beyond the enhancement provided by the standard electrolyte. Molecular dynamics (MD) simulations reveal distinct Li-ion solvation structures in the formulated electrolytes, demonstrating the formation of LiF/BOB-rich interphases. Electrochemical testing shows that electrolyte composition plays a dominant role in determining cycling performance and interfacial resistance, while artificial coatings provide additional stability. The optimized combination achieves over 80 % capacity retention after 300 cycles at 2.8–4.5V voltage cut-offs. These results highlight the importance of integrating solvation chemistry and surface engineering to stabilize electrode-electrolyte interfaces in advanced LIBs.