Selenium treatment towards enhanced cyclic stability for single-crystal Ni-rich cathode at ultra-high voltage of 4.7 V

Developing high-voltage (≥4.3 V vs Li/Li+) single-crystal Ni-rich LiNixCoyMn1-x-yO2 offers an enticing strategy to achieve high energy density for lithium-ion batteries. However, at high-voltage operation, the cathode will be vulnerable to induce the intrinsic Oα- (α < 2) migration, triggering the serious structural degradation, notorious parasitic reaction and oxygen loss, which may ultimately result in the battery performance attenuation. Herein, an outside-in oriented nanostructure is well designed and constructed on the single-crystal LiNi0.6Co0.1Mn0.3O2 (SC-NCM) cathode materials, exhibiting an "anti-aging" effect of inhibiting the escape of oxygen from SC-NCM particles during the ultra-high voltage (4.7 V) cycling. Both theoretical calculation and experimental results confirm that the outside-in nanostructure would stabilize the oxygen lattice and suppress O2 release during long-term cycling. Meanwhile, the surface modification of thin Se layer will alleviate the parasitic reactions and improve the electronic conductivity. Under the synergistic strategy of surface modification and interface doping, the obtained SC-NCM exhibits boosted cyclic stability in coin half-cell and pouch full-cell simultaneously. Therefore, the reversible capacity of LiNi0.6Co0.1Mn0.3O2 at high voltage is competitive with comercial LiNixCoyMn1-x-yO2 (x ≥ 0.8), demonstrating more superior safety ability and cyclic property. It provides an effective approach for improving the long-term performance of Ni-rich cathode materials for practical application under ultra-high working voltage.