Microstructure-Controlled Ni-Rich Cathode Material by Microscale Compositional Partition for Next-Generation Electric Vehicles

Abstract

A multicompositional particulate Li[Ni0.9Co0.05Mn0.05]O-2 cathode in which Li[Ni0.94Co0.038Mn0.022]O-2 at the particle center is encapsulated by a 1.5 mu m thick concentration gradient (CG) shell with the outermost surface composition Li[Ni0.841Co0.077Mn0.082]O-2 is synthesized using a differential coprecipitation process. The microscale compositional partitioning at the particle level combined with the radial texturing of the refined primary particles in the CG shell layer protracts the detrimental H2 -> H3 phase transition, causing sharp changes in the unit cell dimensions. This protraction, confirmed by in situ X-ray diffraction and transmission electron microscopy, allows effective dissipation of the internal strain generated upon the H2 -> H3 phase transition, markedly improving cycling performance and thermochemical stability as compared to those of the conventional single-composition Li[Ni0.9Co0.05Mn0.05]O-2 cathodes. The compositionally partitioned cathode delivers a discharge capacity of 229 mAh g(-1) and exhibits capacity retention of 88% after 1000 cycles in a pouch-type full cell (compared to 68% for the conventional cathode). Thus, the proposed cathode material provides an opportunity for the rational design and development of a wide range of multifunctional cathodes, especially for Ni-rich Li[NixCoyMn1-x-y]O-2 cathodes, by compositionally partitioning the cathode particles and thus optimizing the microstructural response to the internal strain produced in the deeply charged state.