Mitigating Lattice Distortion of High-Voltage LiCoO2 via Core-Shell Structure Induced by Cationic Heterogeneous Co-Doping for Lithium-Ion Batteries
Zezhou Lin, Ke Fan, Tiancheng Liu, Zhihang Xu, Gao Chen, Honglei Zhang, Hao Li, Xuyun Guo, Xi Zhang, Ye Zhu, Peiyu Hou, Haitao Huang
Abstract
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.