Mitigating Jahn–Teller effect of MnO2 via charge regulation of Mn-local environment for advanced calcium storage

Manganese dioxide (MnO2) stands out as a prospective cathode material for calcium ion batteries (CIBs) owing to its elevated theoretical capacity and high operating voltage. Nevertheless, MnO2 with Jahn-Teller (J-T) twisted MnO6 octahedra experiences severe Mn dissolution during cycling, leading to the destabilization of the transition metal layer and resulting in poor cycling performance. In this work, Mo-substitution is purposely proposed to suppress the J-T effect in MnO2 for CIBs. The local charge of Mn is regulated by Mo doping, which enhances the electrical conductivity of MnO2 and suppresses the J-T distortion of the MnO6 octahedron. Meanwhile, density-functional theory (DFT) calculations manifest that Mo doping enhances the structural integrity of MnO2, making it difficult for Mn to escape from the MnO6 structure and inhibiting the dissolution of Mn. Accordingly, Mo-MnO2 demonstrates impressive rate capability (112 mAh g−1 at 1 A g−1) and excellent cycling stability, maintaining approximately 93.9% capacity after 900 cycles at 1 A g−1. As a result, the introduction of heteroatoms through doping offers a novel design approach for the advancement of cathode materials for advanced CIBs.