Dual Design of the Surface via an Ion Conductor Coating and In Situ Electrochemical Diffusion Enabling a Long Life for a Ni-Rich Cathode

Ni-rich layered materials are widely regarded as the highly promising cathodes to realize high-energy density and low-cost batteries. However, they still suffer from surface/interface degradation. Herein, Li1.5Al0.5Ge1.5(PO4)3 acts as an effective coating material regarding high Li+ conductivity and excellent stability in air. The Li1.5Al0.5Ge1.5(PO4)3 coating layer can suppress the side reaction in the cathode and the electrolyte interface without deteriorating Li+ transport. More interestingly, we find that Ge ions diffuse into Ni-rich layered oxide during the charge/discharge process, which contributes to reduce the Li/Ni mixing and enhance the structural stability. These advantages endow the Ni-rich cathode with a superior capacity retention of 94.5% after 100 cycles at 0.2C and 83.1% at 1C after 400 cycles.