Study On Aqueous Rechargeable Lithium-ion Batteries Based On The Li₃V₂（PO₄）₃ Cathode Material

The safety of the lithium ion batteries（LIBs） has been the focus of attention. The effective way to solve this problem is to change flammable organic electrolytes into aqueous electrolyte, namely aqueous rechargeable lithium-ion batteries. For the first time, the paper put forward using the Li₃V₂（PO₄）₃ as the cathode material of aqueous rechargeable lithium-ion batteries. The charge-discharge test was carried out in 0.25 1.35 V（vs SHE） Li NO3 saturated solution, with average discharge voltage of 0.95 V. The initial specific discharge capacity of anode material was about 100 m Ah g-1. The high irreversible capacity of charge and discharge cycles was obtained in 5 C rates, more than 80% after 50 cycles.The study shown that the electrochemical properties of Li₃V₂（PO₄）₃in aqueous electrolytes varied violently corresponding to the differences in the electrolytes, the binders and the mass ratio of smear and electrolyte. Taking Li NO3 solution as the electrolyte, the electrochemical performance Li₃V₂（PO₄）₃ materials was improving with the increase of electrolytes’ concentration（1, 3, 5 mol L-1 and saturated Li NO3）.The electrochemical performance of Li₃V₂（PO₄）₃ in different p H value（p H = 5, 7, 9） of Li NO3 saturated solution was also studied, which illustrated that Li₃V₂（PO₄）₃ had higher cycle performance with p H value of 5. Li₃V₂（PO₄）₃ materials got good electrochemical performance under the following conditions: saturated Li NO3 solution（p H=5） as electrolyte, PVDF as binder, liquid product the mass ratio of smear and electrolytic between 1.0 1.3. After 50 cycles under 5 C rates, its specific discharge capacity was 76.29 m Ah g-1.Two reasons was contributed to the attenuation of Li₃V₂（PO₄）₃ materials in aqueous electrolyte: the dissolution of active materials and secondary reactions. There is a saturation value for active substances dissolved in the aqueous electrolyte, so the less the amount of electrolyte is, the less active substances dissolved. Sealing could reduce the side effects by preventing the existence of dissolved oxygen and eventually improve the cycle performance.In this paper, the different doping ratio of zinc and nickel materials were synthesized and marked Li3V（6-2x）/3Znx（PO4）3 and Li3V（6-2x）/3Nix（PO4）3, in which x was 0.01, 0.05, 0.1, 0.15 respectively. The results shown that the doped Li3V1.97Zn0.05（PO4）3、Li3V1.99Ni0.01（PO4）3 material performed higher, especially Li3V1.99Ni0.01（PO4）3 materials which was suitable for application in aqueous electrolyte with its initial specific discharge capacity in 5C rates reaching 100.7 m Ah g-1, its specific discharge capacity after 50 circles obtaining 90.5 m Ah g-1 and capacity retention ratio keeping 89.92%,.The studies elucidated that Li₃V₂（PO₄）₃ as an anode material of aqueous rechargeable lithium-ion batteries had high discharge capacity and good stability; the cycle performance of doped Li₃V₂（PO₄）₃ materials was more stable. Li₃V₂（PO₄）₃ can be one of the prosperous anode materials for aqueous rechargeable lithium-ion batteries.