Mitigating Lattice Distortion of High-Voltage LiCoO2 via Core-Shell Structure Induced by Cationic Heterogeneous Co-Doping for Lithium-Ion BatteriesOACSTPCD

Inactive elemental doping is commonly used to improve the structural stability of high-voltage layered transition-metal oxide cathodes.However,the one-step co-doping strategy usually results in small grain size since the low diffusivity ions such as Ti4+will be concentrated on grain boundaries,which hinders the grain growth.In order to synthesize large single-crystal layered oxide cathodes,considering the different diffusivities of different dopant ions,we propose a simple two-step multi-element co-doping strategy to fabricate core-shell structured LiCoO2(CS-LCO).In the cur-rent work,the high-diffusivity Al3+/Mg2+ ions occupy the core of single-crystal grain while the low diffusivity Ti4+ions enrich the shell layer.The Ti4+-enriched shell layer(～12 nm)with Co/Ti substitution and stronger Ti-O bond gives rise to less oxygen ligand holes.In-situ XRD demonstrates the constrained contraction of c-axis lattice parameter and mitigated structural distortion.Under a high upper cut-off voltage of 4.6 V,the single-crystal CS-LCO maintains a reversible capacity of 159.8 mAh g-1 with a good retention of-89％after 300 cycles,and reaches a high specific capacity of 163.8 mAh g-1 at 5C.The proposed strategy can be extended to other pairs of low-(Zr4+,Ta5+,and W6+,etc.)and high-diffusivity cations(Zn2+,Ni2+,and Fe3+,etc.)for rational design of advanced layered oxide core-shell structured cathodes for lithium-ion batteries.