Gradient-morph LiCoO2single crystals with stabilized energy density above 3400 W h L-1

The cycling stability of LiCoO(2)under high voltages (>4.5 V) was plagued by hybrid anion- and cation-redox (HACR) induced oxygen escape and uncontrolled phase collapse. With DEMS andin situXANES mapping at the NSLS-II, we demonstrate that oxygen escape triggers irreversible transformations into bad surface phases that rapidly propagate inward. Enabling HACR but stopping global oxygen migration is key to a stable high-energy cathode. Therefore, we developed similar to 10 mu m single crystals with LiCoO(2)in the bulk smoothly transitioning to Co-free LiMn(0.75)Ni(0.25)O(2)at the surface. By means of initial electrochemical formation, a semi-coherent LiMn(1.5)Ni(0.5)O(4)spinel-like shell was establishedin operandowith little oxygen loss to integrally wrap the LiCoO(2)bulk. Then we obtained gradient-morph LiCoO(2)single crystals to prevent the percolating migration of oxygen out of the particle and achieved enhanced HACR reversibility at high voltages. The gradient-morph HACR cathode undergoes substantially stabilized cycling when charged to above 4.6 V, and hence a stable cyclic volumetric energy density of >3400 W h L(-1)has been achieved in a pouch full-cell coupled with a commercial graphite anode and lean electrolyte (2 g A h(-1)), exhibiting up to 2906 W h L(-1)even after 300 cycles.