Owing to their high theoretical specific capacity and low cost,lithium-and manganese-rich layered oxide(LMR)cathode materials are receiving increasing attention for application in lithium-ion batteries.However,poor lithium ion and electron transport kinetics plus side effects of anion and cation redox reac-tions hamper power performance and stability of the LMRs.In this study,LMR Li1.2Mn0.6Ni0.2O2 was mod-ified by phosphorus(P)-doping to increase Li+ conductivity in the bulk material.This was achieved by increasing the interlayer spacing of the lithium layer,electron transport and structural stability,resulting in improvement of the rate and safety performance.P5+doping increased the distance between the(003)crystal planes from～0.474 nm to 0.488 nm and enhanced the structural stability by forming strong cova-lent bonds with oxygen atoms,resulting in an improved rate performance(capacity retention from 38％to 50％at 0.05 C to 5 C)and thermal stability(50％heat release compared with pristine material).First-principles calculations showed the P-doping makes the transfer of excited electrons from the valence band to conduction band easier and P can form a strong covalent bond helping to stabilize material struc-ture.Furthermore,the solid-state electrolyte modified P5+doped LMR showed an improved cycle perfor-mance for up to 200 cycles with capacity retention of 90.5％and enhanced initial coulombic efficiency from 68.5％(pristine)or 81.7％(P-doped LMR)to 88.7％.