Strain regulation of microscopic processes in lithium-rich cathodes: thermodynamics and kinetics

Abstract

Lithium-rich transition metal oxides exhibit nearly twice the capacity of traditional layered materials, positioning them as promising candidates for addressing energy challenges. However, the internal stress induced by uneven delithiation and its relaxation significantly impacts the thermodynamics and kinetics of processes related to the structural evolution during charging, such as vacancy formation and ion migration. These processes interact dynamically, modifying stress distribution and influencing the electrochemical properties. In this work, first-principles calculations are utilized to investigate the impact of strain on the formation energy of lithium and oxygen vacancies, as well as the migration kinetics of oxygen vacancies and transition metal ions. The interactions between them are studied in depth, both directly and as mediated by internal stress. The results reveal that the tensile strain arising from the relaxation of compressive stress accumulated in Li₂MnO₃ plays a crucial role in structural evolution, as it facilitates the formation of oxygen vacancies as well as the migration of oxygen vacancies and Mn ions. We therefore propose stress-engineering strategies to mitigate structural degradation by introducing tensile strain through appropriate doping in order to offset internal compressive stress.