Molten salts assisted synthesis of single crystalline NCM811 with surface modification for high energy density lithium-ion batteries

Abstract

Single crystalline nickel rich Li [Ni_xCo_yMn_1-x–y]O₂ (SCNCM) layered oxide cathodes show higher ionic conductivity and better structure integrity than polycrystalline NCM (PCNCM) cathodes by eliminating grain boundaries. However, it remains challenges in the controlled synthesis process and restricted cycling stability of SCNCM. Herein, take single crystalline nickel rich Li [Ni_0.8Co_0.1Mn_0.1]O₂ (SC811) as an example, a dual molten salts (LiOH and Li₂SO₄) assisted secondary calcination method is proposed, for which LiOH salt improves primary crystal size and Li₂SO₄ prevents the aggravation of NCM nanocrystals. To further reduce the interfacial side reactions, Mg-doping and B-coating surface modification was carried out, which effectively suppress anisotropic lattice changes and Li/Ni disorder. In addition, a thin and uniform H₃BO₃ coating effectively prevents direct contact between the electrode and electrolyte, thus reducing harmful parasitic reactions. The single crystal structure engineering and surface modification strategy of oxide layered cathodes significantly improve the cycling stability of the modified SC811 cathode. For example, during a long-term cycling of 470 cycles, a high-capacity retention of 74.2% obtained at 1C rate. Our work provides a new strategy for engineering high energy nickel rich layered oxide NCM cathodes.

Graphical abstract