Ti/Sr Gradient Doping with SrTiO ₃ Coating for Mitigating Strain and Oxygen Loss in Ni-Rich Cathode

Ni-rich layered oxides are a class of lithium-ion battery cathode materials with great application potential, but their structural instability during cycling can adversely affect the battery performance. Here, we report bulk-to-surface engineering of Ti/Sr gradient-doped and SrTiO 3 -coated LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM90-2TS) cathode materials to circumvent instability. The Ti/Sr gradient-doping reduces the Li + diffusion barrier, alleviates stress-strain accumulation and interlayer slip, and suppresses Li/Ni mixing during long-term cycling. Furthermore, the SrTiO 3 coating suppresses the outward migration of oxygen anions, protecting the highly active surface, stabilizing the electrode−electrolyte interface, and effectively mitigating severe surface side reactions. Impressively, the NCM90-2TS achieves superior cycling stability with capacity retention remaining 96.3% at 4.5 V after 200 cycles. In a pouch cell comprising graphite anodes at 1 C, the capacity retention is nearly 96.3% after 500 cycles at 30 °C within 3.0−4.2 V. To boost the cycling stability of Ni-rich cathodes, the proposed synergistic strategy integrating coating, doping, and microstructural control provides a practical route for optimizing high-energy-density lithium-ion battery systems.