Simultaneous modification of dual-substitution with CeO₂ coating boosting high performance sodium ion batteries

Na₃V₂(PO₄)₃ (NVP) is highly valued based on the stable construction among the polyanionic compounds. Nevertheless, the drawback of low intrinsic conductivity has been impeded its further application. In this paper, the internal channels of the crystal structure are extended by the introduction of larger radius Ce³⁺, which increases the transport rate of Na⁺. The introduction of Mo⁶⁺ replacing the V site leads to a beneficial n-type doping effect and facilitates the transportation of electrons. Besides, CeO₂ cladding is introduced to further enhance the electronic conductivity of NVP system. Initially, CeO₂ serves as an n-type semiconductor and functions as a conductive additive to significantly enhance the electronic conductivity of the electrode, thereby improving the electrochemical characteristics. Moreover, CeO₂ functions as an oxygen buffer, aiding in the maintenance of active metal dispersion during operation and enabling efficient electron transfer between CeO₂ and [VO₆] octahedra in NVP, thus fostering outstanding electrical connectivity between the oxides. CeO₂ cladding can be effectively integrated with the carbon layer to stabilize the NVP system. Comprehensively, the modified Na₃V_1.79Ce_0.07Mo_0.07(PO₄)₃/C@8wt.%CeO₂ (CeMo0.07@8wt.%CeO₂) composite exhibits excellent rate and cycling properties. It delivers a capacity of 113.4 mAh/g at 1C with a capacity retention rate of 80.3 % after 150 cycles. Even at 10C and 40C, it also submits high capacities of 84.7 mAh/g and 76 mAh/g, respectively. Furthermore, the CHC//CeMo0.07@8wt.%CeO₂ asymmetric full cell possesses excellent sodium storage property, indicating its prospective application potentials.