Lattice Modulation by Ca/P Dual-Doping for Fast and Stable Li<sup>+</sup> Intercalation/Extraction in High-Voltage LiCoO<sub>2</sub>
Yanan Yu, Weijin Kong, Wenyun Yang, Jinbo Yang, Yujun Chai, Xiangfeng Liu
Abstract
LiCoO2 can deliver more capacity under a high voltage but it suffers from a serious capacity decay due to the irreversible structure transition during Li+ intercalation/extraction. Herein, we propose to mitigate the irreversible structural changes through modulating the crystal lattice by Ca-P dual-doping with Ca3(PO4)2. Both the cycling stability and high-rate capacity have been largely enhanced. At 5C and 10C, the capacity retention rate after 500 cycles is significantly enhanced from 4 and 2% (bare samples) to 70 and 73%, respectively. The enhancement can be mainly attributed to the synergy of Ca and P dual-doping. Ca doped in the Li site can act as a “pillar” to prevent the lithium layer from collapsing when Li extracts and inserts during the charging/discharging process. The doped P in the transition metal site can synergize with Ca to further stabilize the crystal structure of LiCoO2 under a high voltage. This study offers some insights on modulating the lattice structure through dual-doping, which can also be extended to other layered structures of cathode materials.