Synthesis And Electrochemical Properties Of Na_1.2Fe₄（PO₄）₃//Na₃V₂（PO₄）₃/C Electrode Material For Lithium/Sodium Hybrid Ion Battery

The huge application of commercial lithium-ion batteries has increasingly increased the consumption of metal lithium resources,but the mining cost and difficulty of metal lithium are high,and the lithium-ion batteries have huge heat when charging and discharging with large current,and their stability is relatively poor.How to replace lithium-ion battery,save the consumption of lithium and ensure that the battery safe becomes a research hotspot.The structure of phosphate is stable and the thermal stability is good.In this paper,Na_1.2Fe₄（PO₄）₃and Na₃V₂（PO4）₃/C containing sodium phosphate electrode materials are studied to solve the above problems,and the construction of phosphate electrode materials for full battery is closer to commercial production.Firstly,the netted single crystal Na_1.2Fe₄（PO₄）₃ material was prepared by sol-gel method and sintering in inert atmosphere.It was used as the anode of lithium-ion battery,and showed good electrochemical performance.After 100 cycles at 0.2 C rate,the reversible capacity was up to 210 mAh g^-1.Even at the high current density of 10 C,Na_1.2Fe₄（PO₄）₃ anode material has an initial reversible capacity of 128.6 mAh g^-1,and the capacity retention rate is 86.72%after 1500 cycles.The diffusion path of lithium ion in Na_1.2Fe₄（PO₄）₃ anode material and the valence state of transition metal during the electrochemical cycle were explained by electrochemical testing technology and first-principles calculationSecondly,the porous spherical Na₃V₂（PO₄）₃/C sodium superion conductor cathode material was successfully synthesized by solvothermal method.The electrochemical properties of the porous spherical Na₃V₂（PO₄）₃/C for sodium storage and lithium storage were tested respectively.The material was applied to the hybrid ion battery to combine the advantages of the two.The discharge performances at 0.1 C,0.2 C,0.5 C,1 C,2 C,5 C,10C,20 C,30 C,50 C and 0.1 C were 108.4 mAh g^-1,109.7 mAh g^-1,111.54 mAh g^-1,109.2mAh g^-1,106.4 mAh g^-1,102.9 mAh g^-1,93.1 mAh g^-1,83.3 mAh g^-1,73.3 mAh g^-1,69.2mAh g^-1 and 102.4 mAh g^-1.The storage of the material of lithium,sodium,and mixed ion diffusion coefficient were analyzed,and found that mixed ion diffusion behavior,and in situ X-ray diffraction（XRD）analysis of the electrode materials with the in-situ X-ray photoelectron spectroscopy of mixed ion battery is embedded and embedding mechanism are analyzed,and found mixed ion in electrode materials with certain synergy.At the same time,the storage mechanism of Na₃V₂（PO₄）₃/C cathode material under different current densities was also analyzed by pseudocapacitance analysis.Based on the above work,three kinds of batteries are constructed in this paper.The reversible capacity of single-crystal reticular Na_1.2Fe₄（PO₄）₃//LiFePO₄ full battery is 202.6mAh g^-1 after the first cycle,and the full battery capacity is stabilized at 101.2 mAh g^-1 after50 cycles.Graphite//Na₃V₂（PO₄）₃/C lithium sodium mixed ion full battery,through Graphite electrode on sodium ion limitation,make lithium sodium mixed ion can better in Na₃V₂（PO₄）₃ positive side of coordination,rate performance and half battery similar,After14000 cycles at 5 C,the battery capacity is still 98 mAh g^-1,and the full battery capacity retention rate reaches an astonishing 96.08%.Na_1.2Fe₄（PO₄）₃//Na₃V₂（PO₄）₃/C full battery,after 35 cycles,the capacity is stable at 94.1 mAh g^-1,coulomb efficiency is 99.1%,but the long cycle performance is poor.