Spreading monoclinic boundary network between hexagonal primary grains for high performance Ni-rich cathode materials

Knowledge of structure-performance relationship is a fundamental issue in the field of material design and engineering. Functional-directed fine tune of the crystal structure has always been inspiring but rarely implemented in energy storage materials. Here we develop an approach to improve the performance of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), a typical Ni-rich layered cathode material, through building monoclinic surfaces onto hexagonal primary grains, simply accomplished by oxidizing the flake-like primary precursors with KMnO₄. In this way, the local octahedral ligand field has been engineered by inducing Jahn-Teller distortion of low spin Ni³⁺ state, resulting in a three-dimensional monoclinic functional network spreading over a secondary particle. Such an elaborate monoclinic architecture stabilizes the hexagonal structure of primary grains from phase transitions, and also offers an interconnected highway for both ionic and electronic transportations. Accordingly, an enhanced cycling stability and an outstanding rate capability have been achieved in our designed NCM811 material. Our approach starts a prospective way of designing Ni-rich cathode material with local electronic and structural engineering, which could be expanded to widespread battery researches.