Simultaneous zirconium substitution and polypyrrole interconnection of Na3V2(PO4)3/C nanoparticles for superior sodium storage performance

The intrinsic poor conductivity resulted from the phosphate-based framework is seriously hindered the development of Na3V2(PO4)3 (NVP). Herein, we propose a simultaneous strategy of Zr4+ doping and polypyrrole (ppy) decorating to synergistically improve the electronic and ionic conductivities of NVP. The introduced Zr4+ can expand the channel for the facilitated Na+ migration and enhance the structural stability due to the pillar effect. The conductive ppy nanotubes can bridge sufficient channels for rapid electronic transportation among the active particles. The performance of half cell in an aqueous electrolyte is evaluated, and the optimized Na2.9V1.9Zr0.1(PO4)3/[email protected] (Zr0.1-NVP/[email protected]) exhibits a capacity of 114.2 mAh g−1 at 0.1 C. It performs an initial capacity of 94.6 mAh g−1 at 20 C, retaining 74.8% after 2000 cycles. Even at 300 C, it still exhibits a capacity of 74.3 mAh g−1, and the retention of 76.4% is obtained after 2000 cycles, corresponding to a capacity decay of 0.038% per cycle. The symmetric full cell fabricated by Zr0.1-NVP/[email protected] delivers a capacity of 76 and 46.4 mAh g−1 at 0.5 and 60 C. Retention of 80.47% is achieved at 5 C after 165 cycles. The kinetic characteristics of Zr0.1-NVP/[email protected] are explored by galvanostatic intermittent titration technique, indicating the minimum diffusion coefficient of Na+ appears at 3.4 V due to the intense interactions from the phase transfer reactions.