Nanoconfined carbon-coated Na₃V₂(PO₄)₃ particles in mesoporous carbon enabling ultralong cycle life for sodium-ion batteries

Na₃V₂(PO₄)₃ (denoted as NVP) has been considered as a promising cathode material for room temperature sodium ion batteries. Nevertheless, NVP suffers from poor rate capability resulting from the low electronic conductivity. Here, the feasibility to approach high rate capability by designing carbon-coated NVP nanoparticles confined into highly ordered mesoporous carbon CMK-3 matrix (NVP@C@CMK-3) is reported. The NVP@C@CMK-3 is prepared by a simple nanocasting technique. The electrode exhibits superior rate capability and ultralong cyclability (78 mA h g^-1 at 5 C after 2000 cycles) compared to carbon-coated NVP and pure NVP cathode. The improved electrochemical performance is attributed to double carbon coating design that combines a variety of advantages: very short diffusion length of Na⁺/e^- in NVP, easy access of electrolyte, and short transport path of Na⁺ through carbon toward the NVP nanoparticle, high conductivity transport of electrons through the 3D interconnected channels of carbon host. The optimum design of the core-shell nanostructures with double carbon coating permits fast kinetics for both transported Na⁺ ions and electrons, enabling high-power performance. Nanoconfined carbon-coated Na₃V₂(PO₄)₃ particles in mesoporous carbon are prepared using a simple nanocasting technique. The optimum design of the core-shell nanostructures with double carbon coating permits fast kinetics for both transported Na⁺ ions and electrons, enabling excellent rate capability of the Na₃V₂(PO₄)₃ electrode.