Cycling stability of LiNi0.80Co0.15Al0.05O2 cathode modified by solid-state electrolyte film

Ni-rich LiNi 0.80 Co 0.15 Al 0.05 (NCA) cathode material with high energy density always suffers from structural degradation during cycles, resulting in rapid capacity fading and severe voltage decay. In this study, a solid-state electrolyte film of Li 1.8 Sc 0.8 Ti 1.2 (PO 4 ) 3 (LSTP) is constructed on the surface of NCA cathode via a chemical route to enhance the cycling stability of NCA cathode. The Ex-situ XRD, EIS, dQ/dV, and SEM analyses show that the structural degradation of NCA derives mainly from the corrosion of electrolyte rather than H2-H3 phase transition, which gives rise to the extremely weak phase transitions of H1-M−H2−H3 after cycles. Besides the isolation role of LSTP film, it is found that Ti 4+ ions in LSTP incorporate into the subsurface structure of NCA, which can accelerate the Li + diffusion, reduce the Li + /Ni 2+ disorder, reinforce the crystal structure, and enlarge the inter-slab spacing of NCA. Consequently, the coated NCA-2 %LSTP cathode reveals well structural integrity and evident phase transition behavior, delivering stable cycling performance with a superior capacity retention of 96.8 % at 1.0C after 100 cycles. This study not only deeply analyzes the mechanism of the structural degradation of NCA, but also demonstrates an efficient improving approach through LSTP modification.