For developing durable high-energy cathodes in lithium-ion batteries, Ni-rich layered oxides, i.e. Li-Ni-Mn-Co-O system, are particularly interesting for their high capacities and low costs, but suffer from poor cycling stabilities. Herein, we report on developing new high-capacity Ni-rich cathodes with enhanced cyclability via tuning the stoichiometry and structure of the materials. Systemic investigation is made to the phase evolution of Ni-rich LiNi1-x-yMnxCoyO2 (x+y ≤ 0.2) under different annealing temperatures by ex-situ and in-situ synchrotron X-ray diffraction (XRD) measurements, coupled with quantitative structural analysis through refinements. Structural characterization indicates an intriguing phase transition of LiNi1-x-yMnxCoyO2 from a rock-salt structure at low annealing temperatures directly to a layered α-NaFeO2-type structure with a R-3m space group at high temperatures. The in-situ XRD studies gain us access to the phase diagram in the confined Ni-rich region of the Ni-Mn-Co space (x+y ≤ 0.2), thereby enabling the design of synthetic protocols for preparing high-capacity LiNi1-x-yMnxCoyO2 cathodes with stabilized structure and reasonable cycling stability. Furthermore, preheating process and Li2TiO3 coating layer have been introduced during the synthesis of LiNi1-x-yMnxCoyO2 cathode materials, in order to achieve higher specific lithium storage capacity and excellent cycling stability. This work sheds light on the fundamental relationship between crystal structure and electrochemical performance of Ni-rich cathodes for high-energy lithium-ion batteries.

Synthetic control and structural stabilization of Ni-rich layered oxides as high-energy cathodes for lithium-ion batteries

255th National Meeting (2018)

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