Synergistic effects of conformal surface precise nanofilm coating and doping on single-crystal LiNi0.5Co0.2Mn0.3O2 at high voltage

Surface and interfacial instability is a critical issue for nickel-based layered oxides LiNixCoyMn1−x−yO2 (NCM) (x ≥ 0.5) operating at high cut-off voltages (≥4.5 V). In this work, precise nanofilm coating and doping (PNCD), which combines conformal surface coating by atomic layer deposition and Al surface doping by post-annealing, is used to modify the surface structure of NCM523 (P-NCM523). After PNCD, the rate capability of P-NCM523 at 10C is significantly improved to 160.3 mAh/g with a high cut-off voltage (4.55 V). Furthermore, an excellent reversible capacity of 167.5 mAh/g with a capacity retention of 87.4 % is achieved after 800 cycles at 0.5C within 3.0–4.5 V in the pouch cell constructed by P-NCM523 and a commercial graphite anode. Not only does P-NCM523 have a comparable energy density at 4.5 V to that of NCM811 at 4.2 V, but its thermal stability is also much better. Through surface and phase-transition analysis during the electrochemical process, we conclude that PNCD treatment promotes the formation of a LiAlO2-rich surface layer and plays a crucial role in high-voltage cycling and safety. By increasing the cut-off voltages of other cathode materials, the PNCD process achieves high energy density while preserving stability.