Synergistic Co-doping effect of CNTs and PVP in Na4MnCr(PO4)3 cathode as a strategy for improving the electrochemical performance of SIBs

In order to solve the contradiction between the rapidly growing energy demand and the excessive exploitation of fossil fuels, it is urgent to research and develops more environmentally friendly and efficient energy storage technologies. Therefore, the development of high-performance cathode materials to enhance the energy density of SIB is currently one of the most important topics of scientific research. Advanced high-voltage and low-cost cathode material for SIBs, a composite of carbon-coated Na4MnCr(PO4)3 (NASICON-type), polyvinylpyrrolidone (PVP), and modified carbon nanotubes (CNTs) is prepared by sol-gel and freeze-drying method. Due to the high conductivity of CNTs, the conductivity of the composite is significantly improved, and its initial capacity is increased to 114 mAh/g at 0.5 C and 96 mAh/g at 5 C (Mn2+/Mn4+ conversion for voltage windows 1.4-4.3 V). Moreover, the multi-electrons transfer of Cr3+/Cr4+ and Mn2+/Mn4+ can provide a high capacity of 165 mAh/g at 0.1 C and 102 mAh/g at 5 C in the high voltage window of 1.4-4.6 V. Furthermore, PVP can effectively inhibit the Jahn-Teller effect caused by Mn ion, making the composite have more excellent high-rate performance and stability. In addition, GITT, EIS and CV curves were drawn to better reveal the excellent kinetic properties of Na4MnCr(PO4)3@C@PVP@CNT cathode, and the mechanism of its performance improvement is deeply studied and discussed. Accordingly, the co-doping of CNTs and PVP is a simple way to high conductivity and fast charging of cathode materials for SIBs.