Gradient-morph LiCoO2 single crystals with stabilized energy density above 3400 W h L−1

• Main Authors: Zhu, Zhi (Author), Yu, Daiwei (Author), Shi, Zhe (Author), Gao, Rui (Author), Xiao, Xianghui (Author), Waluyo, Iradwikanari (Author), Ge, Mingyuan (Author), Dong, Yanhao (Author), Xue, Weijiang (Author), Xu, Guiyin (Author), Lee, Wah-Keat (Author), Hunt, Adrian (Author), Li, Ju (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Nuclear Science and Engineering (Contributor), Massachusetts Institute of Technology. Department of Materials Science and Engineering (Contributor), Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science (Contributor)
• Format: Article
• Language: English
• Published: Royal Society of Chemistry (RSC), 2021-09-22T14:21:19Z.
• Subjects: Article
• Online Access: Get fulltext

 The cycling stability of LiCoO[subscript 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 and in situ XANES 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 ∼10 μm single crystals with LiCoO[subscript 2] in the bulk smoothly transitioning to Co-free LiMn[subscript 0.75]Ni[subscript0.25]O[subscript 2] at the surface. By means of initial electrochemical formation, a semi-coherent LiMn[subscript 1.5]Ni[subscript 0.5]O[subscript 4] spinel-like shell was established in operando with little oxygen loss to integrally wrap the LiCoO[subscript 2] bulk. Then we obtained gradient-morph LiCoO[[subscript 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.