One stone two birds: K2CO3 promoting the in-situ synthesis of K3PO4 coated Na3V2(PO4)3 attached on the porous carbon skeleton for superior sodium storage performance

Abstract

Na₃V₂(PO₄)₃ (NVP) has attracted much attention because of its open 3D channel, high voltage platform and capacity, but its inherent low ionic and electronic conductivity limits further development. In this work, we successfully achieve the double modification effect by adding K₂CO₃ in situ for the first time. Firstly, the addition of K₂CO₃ induces the formation of porous carbon substrate, which can reduce the accumulation of Na₃V₂(PO₄)₃ particles, thus making the sample particles more dispersed and uniform. Meanwhile, NVP active particles can be uniformly attached to the porous carbon substrate, effectively promoting the electronic conductivity. Secondly, K₂CO₃ can be decomposed and react to produce K₃PO₄ in the sintering process, which is evenly coated on the periphery of NVP grains to form a double-layer conductive interface with excess amorphous carbon. This unique double-interface not only boost specific conductance but also play a protective role to prevent the side reaction in the electrolyte from destroying the cathode material. Moreover, the ex-situ XRD/XPS/SEM/TEM after cycling further demonstrate the stabilized porous skeleton and the existence of K₃PO₄ coatings. Comprehensively, the optimized NVP/C@1%K₃PO₄ sample behaves outstanding electrochemistry capability and cyclic performance. With a high capacity of 122.3 mAh g⁻¹ at 0.1C, this material exhibits excellent cycling stability. At 60C, it delivers a high capacity of 85.1 mAh g⁻¹ and retains 69.1 mAh g⁻¹ after 7000 cycles. Even at 180C, it demonstrates a remarkable capacity of 79.97 mAh g⁻¹ and maintains 49.8 mAh g⁻¹ after 14,000 cycles. When integrated into a full battery, the assembled NVP/C@1%K₃PO₄//CHC battery exhibits a reversible capacity of 112.2 mAh g⁻¹ at 0.1C and retains 70 mAh g⁻¹ at 2C, highlighting its promising potential for commercial applications.