Mitigating Diffusion-Induced Intragranular Cracking in Single-Crystal LiNi_0.5Mn_1.5O₄ via Extended Solid-Solution Behavior

Single-crystal cathodes have been investigated for their inherent resistance to intergranular cracking due to the absence of grain boundaries. However, these materials exhibit significant intragranular cracking, and the underlying mechanisms remain unclear. In this study, we examined the impact of extended solid-solution reactions on mitigating crack formation in magnesium-doped single-crystal LiNi_0.5Mn_1.5O₄ (Mg-SC-LNMO) cathodes. With Mg acting as a structural pillar, the overall volume change was reduced by nearly 50 %, the two-phase reaction was effectively suppressed, and the Li-ion diffusion coefficient was doubled. Continuum modeling based on experimental observations demonstrates that Mg doping significantly reduces the internal stress induced by lithium diffusion, thereby preserving the mechanical integrity of single-crystal LNMO. This improvement leads to enhanced electrochemical performance and durability. Our study provides new insights into mechanically robust single-crystal cathodes and proposes a design strategy to improve the durability of next-generation Li-ion batteries.