Robust graphene layer modified Na₂MnP₂O₇ as a durable high-rate and high energy cathode for Na-ion batteries

Na₂MnP₂O₇ has been considered as a promising cathode candidate for advanced sodium-ion batteries due to its high potential, low cost and non-toxicity. However, the low initial Coulombic efficiency, poor high-rate and unsatisfactory cycling ability originated from the intrinsic inferior electronic conductivity and manganese dissolution severely hinder its practical application. Herein, we report an approach based on a feasible high energy vibrating activation process to fabricate a robust graphene layers (GL) modified Na₂MnP₂O₇ material (noted as NMP@GL) for the first time. The as-prepared NMP@GL could exhibit an ultrahigh initial Coulombic efficiency of 90%, and a high energy density over 300 Wh kg^-1. In addition, rate performance and cycling stability were also improved, with high capacity retention of 83% after 600 cycles at 2 C. These impressive progresses should be ascribed to the enhanced electron transportation with distinctive framework through graphene layer modifying, and structural stability of triclinic Na₂MnP₂O₇ with spacious 3D ion migration channels. Ex-situ XRD and GITT demonstrate a consecutive multi-phase reaction mechanism with facile sodium diffusion. Our design makes Na₂MnP₂O₇@GL to achieve its potential for practical application.