First-principles evaluation of MnO2 polymorphs as cathode material in lithium-ion batteries

Abstract

Polymorphic materials, e.g. manganese dioxide (MnO₂) exhibit promise in energy storage applications, such as serving as cathode material for Li-ion batteries (LIBs). The flexibility to arrange the polyhedral building blocks within their lattice structures allows tunable properties for enhanced performance. In this work, we carried out first-principles simulations to scrutinize the structural, thermodynamic and kinetic properties of polymorphic MnO₂ during Li-ion intercalation. We explored polymorph-specific metrics in dictating its overall performance as cathode material in LIBs, such as thermal and mechanical stability during reversible Li-ion intercalation, achievable energy density, volumetric storage capacity, and Li-ion mobility. Our comprehensive analyses reveal that there are inherent trade-offs among the evaluated properties for optimal performance. For instance, tunneled polymorphs such as α and β phases of MnO₂ allow fast Li-ion diffusion, yet suffer from limited capacity and strain-induced structural vulnerabilities. On the other hand, the spinel (λ) phase of MnO₂ offers a higher voltage window but shows significantly more sluggish Li-ion transport behavior. Overall, the findings and insights presented in this study will provide practical guidelines for materials selection and structural engineering of MnO₂ polymorphs for advanced battery applications.