Theoretical evaluation of multivalent cation diffusion in the 1T-δ-MnO2 electrode via potential energy surface

Polymorphs of MnO2 have been studied extensively for their potential application in rechargeable batteries which provide attractive structures as the host for the cation insertion. In this study, the simplest form of δ-MnO2 has been taken as the representative of layered MnO2 and the ion diffusion performance is carefully examined. The potential energy surfaces of Li+, Na+, K+, NH4 +, Mg2+, Zn2+, Ca2+ and Al3+ ion diffusing in the 1T-δ-MnO2 are firstly obtained within the density functional theory framework, which give a comprehensive and detailed view of the diffusing process. We not only assess the 1T-δ-MnO2 as candidate electrode material quantitatively but also elucidate the influence of the cooperative Jahn–Teller effect which governs multivalent diffusion in the intuitive and clear view. Our findings are well matched with the reported results and lead to practical and implementable guidelines to find MnO2-based fast-diffusion multivalent ion conductors.