Synthesis routes and formation rule of Ni-rich single crystal material based on the regulation of process lithium content

Single crystallization is an effective approach to address the structural degradation of agglomerated polycrystalline layered cathode materials. Conventional methods of preparing single-crystal layered materials predominantly rely on long periods of calcination with elevated temperatures. However, the thermodynamic instability of Ni3+ leads to the structural instability of Ni-rich (LiNixCoyMnzO2, x ≥ 0.8, x + y + z = 1) layered materials at high temperatures, which severely degrades the electrochemical properties of the cathodes. The formation mechanism and synthesis method of single-crystal Ni-rich materials need to be systematically re-explored. In this work, the formation process of single crystal morphologies and crystal structures of Ni-rich materials based on the different lithium contents during the period of calcination are investigated in detail. After evaluating the feasibility of inducing a phase transition to obtain a single crystal morphology in the lithium-deficient state, the critical conditions for the formation of single-crystals in the shortest possible time at elevated temperatures are explored. Simultaneously, the method of preparing single crystals using molten salts formed from an excess of mixed lithium sources is also extended to Ni-rich materials.