Rational design of MoO2−based electrodes via crystal surface engineering control for ultra-stable sodium ion batteries

Crystal structure and composition of electrode materials in sodium ion batteries (SIBs) can directly affect their cell performances. Due to the metallic conductivity and high theoretical capacity, MoO2 has been regarded as a promising candidate material for sodium storage. Herein, a suite of N−doped carbon coated MoO2 materials with tunable crystal structures and compositions are designed, including (−111) plane enriched MoO2/NC (−111), (−211) plane preferred MoO2/NC (−211), and heterostructured MoO2–Mo2N/NC. Effects of crystalline facets and composition of those MoO2−based materials on their electrochemical performances are systematically investigated. Excellent rate performances and ultra-long cycling life are obtained in the MoO2/NC (−111) with almost 100% capacity retention after 10000 cycles at 10 A g−1, and 57.0% reversible capacity reservation when increase the current density from 0.1 A g−1 to 10 A g−1. Kinetic investigations show that the exposure of more MoO2 (−111) facets can create more active sites for Na+ storage, provide more feasible Na+ migration channels, and finally promote higher pseudocapacitive response, which is favorable for faster Na+ storage. Ex-situ XRD analysis indicates that a reversible phase transformation is happened during the sodiation/desodiation processes of MoO2/NC (−111), resulting in the stable cycling life.