A composite cathode material for lithium-ion batteries: synthesis and electrochemical properties of xNa 3 V 2 (PO 4 ) 2 F 3 ·(1-x)Na 2 MnPO 4 F@C

In order to improve the electrochemical properties of Na 2 MnPO 4 F (NMPF), low-cost biomass cane bagasse was used as a carbon source for coating, Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) was used as a doped phase to prepare different ratios of xNa 3 V 2 (PO 4 ) 2 F 3 ·(1-x)Na 2 MnPO 4 F@C (NVPF/NMPF@C) composite materials via a sol–gel method. The results including analysis of XRD, SEM, EDS, and XPS methods showed that NVPF/NMPF@C (x = 0.2) composite material had good crystallinity, and NVPF can be uniformly doped in NMPF@C. The rate performance of NVPF/NMPF@C composite was tested at 0.1, 0.2, 0.5, 1, and 2 C. The first discharge specific capacity of NVPF/NMPF@C composite electrode material reached 193 mAh/g and increased by approximately 20 times when compared to only 9 mAh/g of NMPF@C. The coulombic efficiency of NVPF/NMPF@C material remained 95% after 35 cycles at 0.1 C. The introduction of NVPF can improve charge transfer and Li + diffusion, and enhance the electrochemical behavior of the lithium-ion battery cathodes.