Mitigating Lattice Distortion of High-Voltage LiCoO ₂ via Core-Shell Structure Induced by Cationic Heterogeneous Co-Doping for Lithium-Ion Batteries

Highlights

• A simple two-step multi-element co-doping strategy is proposed to fabricate core-shell structured LiCoO ₂ based on the different diffusivities of dopant ions.

• The high diffusivity Al ³⁺/Mg ²⁺ ions occupy the core of single-crystal grain while the low diffusivity Ti ⁴⁺ ions enrich the shell layer.

• In-situ XRD demonstrates the mitigated structural distortion under a high cut-off voltage of 4.6 V, resulting in a significantly improved cycling stability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-023-01269-1.

Abstract

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 Ti ⁴⁺ 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 LiCoO ₂ (CS-LCO). In the current work, the high-diffusivity Al ³⁺/Mg ²⁺ ions occupy the core of single-crystal grain while the low diffusivity Ti ⁴⁺ ions enrich the shell layer. The Ti ⁴⁺-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- (Zr ⁴⁺, Ta ⁵⁺, and W ⁶⁺, etc.) and high-diffusivity cations (Zn ²⁺, Ni ²⁺, and Fe ³⁺, etc.) for rational design of advanced layered oxide core–shell structured cathodes for lithium-ion batteries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40820-023-01269-1.