Hierarchical Doping Engineering with Active/Inert Dual Elements Stabilizes LiCoO2 to 4.6 V

作者：Qin, Ning; Gan, Qingmeng; Zhuang, Zhaofeng; Wang, Yanfang; Li, Yingzhi; Li, Zhiqiang; Iftikhar, Hussain; Zeng, Chun; Liu, Guiyu; Bai, Yunfei; Zhang, Kaili^*; Lu, Zhouguang^*

来源：Advanced Energy Materials, 2022, 12(31): 2201549.

DOI：10.1002/aenm.202201549

• hierarchical doping
• high voltage cathodes
• lithium cobalt oxide
• lithium-ion batteries
• metastable structure stabilization

It is highly desirable to raise the charge cutoff voltage to realize the potential of LiCoO2 (LCO) with its ultra-high theoretical capacity of 275 mAh g(-1). However, rapid fading due to structure collapse caused by the formation of the H1-3 metastable phase and the release of surface lattice oxygen has largely hindered the operation of LCO under voltages of higher than 4.55 V. Here, stable cycling of LCO at 4.6 V through hierarchical doping engineering with inert P-outside and active Ni-inside dual doping is achieved. This ingenious outside-in structure design enables Ni2+ occupation in the Li layer in the bulk layered phase and P gradient doping at the superficial lattice. Compared with the conventional inert element substitution strategy, the doped active Ni2+ can not only serve as a "pillar" to restrain the formation of the metastable H1-3 phase, but also regulate the electronic structure of LCO and trigger the superexchange interaction of Ni2+-O-Co4+, together with strong P-O coordination to substantially suppress the lattice oxygen escape from the surface. Therefore, it considerably reduces the risk of layer structure collapse and consequently achieves stable and high-capacity operation over 4.6 V. This hierarchical outside-in doping strategy may serve as inspiration for stabilizing high energy electrode materials working under high voltages.