Tailored coating method for the spontaneous formation of Li2MoO4 nanolayer from residual lithium on single crystal Ni-rich cathode in lithium-ion batteries

Ni-rich single-crystal materials are next-generation cathode materials for achieving a high specific energy density in lithium-ion batteries and solving intergranular cracking in polycrystal cathodes. However, residual lithium compounds generated on the cathode surface by high-temperature calcination can hamper its rate capability. In this study, a Mo-based Li+-ion conductor Li2MoO4 coating layer was generated from the residual lithium compounds on the Ni-rich single-crystal cathode surface using (NH4)6Mo7O24∙4H2O via melt decomposition. The process of Li2MoO4 coating involves heat treatment, which promotes the diffusion of Mo ions from the coating layer into the surface region of single-crystal LiNi0.9Co0.07Mn0.03O2(SC NCM90) and it leads to the formation of a Mo6+-doped phase. The Mo-based Li+ conductor coating layer facilitated lithium-ion transport and suppressed side reaction of SC NCM90 at the electrode/electrolyte interface. At an 8 C rate, the discharge capacity of the Li2MoO4-coated SC NCM90 cathode was 128.1 mAh g−1, whereas pristine SC NCM90 exhibited a lower capacity of 62 mAh g−1. In addition, the Li2MoO4-coated SC NCM90 demonstrated superior cyclability and a notable capacity retention during the cycling test after undergoing twice for 3 days of storage tests at 60 °C while fully charged.