Controllable Preparation And Electrochemical Properties Of Li_xNa_yV₂?PO₄?₃/C?x+y=3? Cathode Materials

With the increasing demand for energy,it is obvious that the reserves of traditional fossil energy can't keep up with the demand,the development of new energy is a good breakthrough,the utilization of wind and solar energy has gradually increased for decades.But the biggest problem with these energies is limited by region and time,so the development of energy storage devices is a good way to resolve the limitations of new energy applications.Among many energy storage devices,lithium-ion batteries have become a better choice because of their high energy density and low self-discharge rate.However,with the expansion of the application range of lithium-ion batteries,lithium resources are constantly consumed,and sodium-ion batteries with sufficient sodium resources,simple extraction,and similar to lithium-ion batteries working principle,become a hot alternative to lithium-ion batteries.In lithium/sodium ion batteries,cathode materials play a key role in battery performance.Which Li₃V₂?PO₄?₃materials and Na₃V₂?PO₄?₃ materials with NASICON structure have great research value due to their high specific capacity and high potential platform.Therefore,this paper focuses on the synthesis and electrochemical properties of Li₃V₂?PO₄?₃/C materials,Na₃V₂?PO₄?₃/C materials and Li_3-xNa_xV₂?PO₄?₃/C?0<x<3?of lithium sodium co-deposition systems.1:Li₃V₂?PO₄?₃/C material is synthesized by sol-gel method.In the process of synthesis,the optimum cauterization temperature is determined by controlling the change of temperature.After the optimum cauterization temperature is determined,to control the different holding time to find the best holding time,finally the optimum synthesis scheme is determined to be 750?for 8 h.Li₃V₂?PO₄?₃/C material obtained under this condition has the best crystal crystallinity,without other heterogeneous peaks,uniform particle size and excellent cycling and rate capability.The first cycle charge specific capacity of the battery is 131.6mAh/g at 0.2C current density,the first cycle discharge specific capacity is 129mAh/g,the first cycle coulomb efficiency is 98%.2:Na₃V₂?PO₄?₃/C material is synthesized by sol-gel method,the same method is used to determine the optimal synthesis conditions,the optimum temperature is 750?and the optimum time is 8h.Na₃V₂?PO₄?₃/C material obtained under this condition,the surface of the material is honeycomb-like,which is beneficial to electrolyte penetration,the cycling performance and rate performance of the material are superior.In charge and discharge at different rates,the initial discharge specific capacity of the material reaches111.5mAh/g at the rate of 0.1C,the first cycle discharge specific capacity of the material reaches 89.9mAh/g at the rate of 5C,and the discharge specific capacity reaches110.5mAh/g when the material returns to the rate 0.1C from 5C,and the capacity recovery rate reaches 99.1%.3:The Li_3-xNa_xV₂?PO₄?₃/C?0<x<3?series materials of lithium-sodium co-deposition system is synthesized by sol-gel method.The synthesis scheme adopts the optimum synthesis conditions of Li₃V₂?PO₄?₃/C materials and Na₃V₂?PO₄?₃/C materials.Of the obtained series of Li_3-xNa_xV₂?PO₄?₃/C?x=2.5,2,1.5,1,0.5?materials,Li_2.5Na_0.5V₂?PO₄?₃/C has better electrochemical performance.At the rate of 0.2C,the first cycle discharge specific capacity of the material reaches 126.9mAh/g,after 100cycles of cycling,the discharge capacity can still reaches 117.5mAh/g,the capacity retention rate is 92.6%,and the material rate performance is also very superior,which has good application prospects.