Effect of crystal morphology of nickel-rich cathode materials on electrochemical stability and ion transport kinetics of sulfide-based all-solid-state batteries

Nickel-rich layered oxides are considered highly promising cathode materials for all-solid-state batteries (ASSBs) due to their high theoretical specific capacity and energy density. In this study, a comparison between polycrystalline and single-crystalline cathode materials was conducted. It was found that, during the charging process, ion transport at the interface of polycrystalline cathodes is significantly influenced by phase transitions and side reactions with the electrolyte, resulting in an irreversible increase in impedance after cycling. Furthermore, the structural stability of the cathode material affects internal ion diffusion kinetics, thereby influencing its electrochemical performance. Unlike single-crystalline materials, ion migration in polycrystalline materials must traverse anisotropic grain boundaries, which, due to anisotropic lattice contraction, evolve into intergranular cracks, leading to reduced ion diffusion kinetics and degraded electrochemical performance. In contrast, single-crystalline cathodes exhibit more stable interfacial resistance and uniform ion transport during charging, ensuring structural stability over long-term cycling. Consequently, at a 0.5 C rate, the single-crystalline cathode maintains a specific capacity of 143 mAh/g after 500 cycles, with a capacity retention of 89.2 %, while preserving its intact single-crystal morphology. This study provides valuable new insights into the localized lithium-ion transport behavior in single-crystalline and polycrystalline cathode materials for sulfide-based all-solid-state batteries.