Surface phase stability of high-nickel layered oxides by titanium and sulfur co-modifications

High-nickel layered oxides are promising cathodes for lithium-ion batteries due to relatively high capacity and low cost, which however are still faced with safety issues because of poor stability against cycling. Herein, a facile one-pot solid-state method is employed for preparation of trace Ti/S co-doped LiNiCoO. Ti and S co-doping enhances both rate capability and intrinsic stability greatly in a mutually promoting manner compared with individual Ti and S doping. The co-doped samples show excellent rate capability with 170.9 mAh/g at 5 C and superior intrinsic stability with a capacity retention of 88.6% at 1 C after 200 cycles at room temperature, in sharp contrast with 132.2 mAh/g and 61.6% for the pristine samples. Full cells achieve excellent long-term stability with a retention of 92.7% after 400 cycles at 1 C. The improved performance can be ascribed to the formation of stronger Ti–O bonds and of a thin rock-salt protective layer enabled by sulfur with the stability enhanced by Ti modifications, and the activation of extra redox reactions triggered by sulfur. The mutually promoting enhancement effect by doping different alien elements opens a new and unique design strategy for performance improvement of electrode materials.