A pre-fatigue training strategy to stabilize LiCoO2 at high voltage

Layered cathodes are among the most promising cathodes for high-energy-density Li-ion batteries, yet hindered by the structural degradation from both bulk strain and surface oxygen loss at high voltage (above 4.5 V). Herein, we report a pre-fatigue training strategy on layered LiCoO2 through plasma to reconstruct a coherent, soft, fatigued rock-salt layer to enable high voltage capability. The reconstructed surface layer shows a typical rocksalt structure with good lattice coherency with the bulk phase, which provides an intimate physical pinning effect with the bulk phase. Furthermore, the surface layer is mechanically soft, which provides an adhesive force to prevent the surface layer from peeling off from the bulk fatigued phase during cycling. Moreover, the interface shows a typical cation disorder, which would block the oxygen ion transport from the bulk phase. In this way, the bulk strain is suppressed as evidenced by the greatly suppressed adverse phase transition of O3 -> H1-3 and the gas evolution is blocked by the cation disorder interface. As a result, the pre-fatigued surface with a soft and coherent interface enabled outstanding cycling performance over 1000 cycles at a high voltage of 4.6 V with minimum voltage decay, which is superior to the state-of-the-art LiCoO2 performance. Our strategy on pre-fatigued training on a LiCoO2 electrode could be expanded to other layered structures with anion redox reaction, which would boost the development of high energy lithium ion batteries.