Solid-state exfoliation growth mechanism of single-crystal Li-rich layered cathode materials

Abstract

Single-crystal (SC) Li-rich cathodes have demonstrated superior structural and electrochemical stability compared to their polycrystal (PC) counterparts. However, the principles governing the solid-state synthesis of SC Li-rich oxides remain elusive, and the growth mechanisms of SC cathodes are still poorly understood. Herein, a prototype Li-rich layered oxide, Li_1.2Ni_0.13Co_0.13Mn_0.54O₂, was synthesized with well-dispersed SC morphology through the regulation of Li excess content during solid-state reactions. This approach facilitated a solid-state exfoliation growth process, transforming spherical secondary particles into monodisperse primary SC oxides. Furthermore, two diffusion pathways of Li source—boundary diffusion and grain diffusion—were proposed to elucidate the underlying mechanisms driving SC exfoliation during solid-state reactions. This understanding enables the flexible synthesis of both PC and SC Li-rich cathodes. Compared to traditional PC counterparts, severe irreversible oxygen release, crack formation, and the transition from layered to spinel phases were effectively suppressed within the exfoliated SC cathode, resulting in an extended battery lifespan with a capacity retention of 93.6 % over 500 cycles at 1 C. These findings provide practical methodology and mechanism insights for the synthesis and design of high-energy-density and high-stability Li-rich cathodes.