Double carbon modified Na3V2(PO4)3with dual charge carriers and high performance synthesized in-situ in polypyrrole and chitosan quaternary ammonium hydrogel

Sodium-ion batteries (SIBs) are regarded as the most promising battery to replace lithium-ion batteries (LIBs) in the future. Na3V2(PO4)3(NVP), as an ideal positive electrode material for SIBs, is limited by poor electronic conductivity and low reversible capacity. In this paper, the double carbon resources of chitosan quaternary ammonium hydrogel (CHACC) and Polypyrrole (PPy) were introduced into NVP. Through the construction of double charge carriers, the high conductivity and the high reversible capacity of NVP which broke the theoretical limit were achieved. The introduction of CHACC brings the second charge carrier, ClO4−, in addition to Na+in NVP system. Furthermore, the conductive network and defect-rich carbon coatings formed by CHACC and PPy significantly improve the electronic conductivity and kinetics of the electrode. Comprehensively, the detailed functional mechanism of dual carriers in NVP is deeply investigated by ex-situ FTIR and XPS, revealing that ClO4−utilizes the N+in the carbonized substrate of CHACC and PPy as the binding sites to reversibly inserted/extracted from the carbon layer to provide additional capacities. Notably, the optimized CHACC-PPy-NVP submits superior sodium storage performance. It delivers a capacity of 148.3 and 139.3 mAh g−1at 0.1 and 1C, significantly exceeding the theoretical capacity (117.6 mAh g−1). Even at 140C, it still maintains a capacity value of 88.9 mAh g−1with 75.7 mAh g−1remaining after 2000 cycles, corresponding to a low decay rate of 0.007 % per cycle.