Preparation And Properties Of NaTi₂（PO₄）₃-based Anode For Hybrid Aqueous Rechargeable Lithium-ion Batteries

Manganese-based material Li Mn₂O₄ has the advantages of high energy density,low cost,safety,eco-friendliness,and high rate capability,and is considered as a promising cathode candidate for hybrid aqueous rechargeable lithium-ion batteries.Na Ti₂（PO₄）₃/C has the advantages of stable three-dimensional framework structure,low cost,and eco-friendliness,and is considered as a promising anode candidate material for aqueous rechargeable lithium-ion batteries.In view of the problems of poor conductivity,insufficient cycle performance and poor rate performance of Na Ti₂（PO₄）₃/C anode materials,Na Ti₂（PO₄）₃/C anode materials under different conditions were prepared in this paper,and the materials were modified and composited.The relationship between its composition and electrochemical performance and the electrochemical performance of hybrid aqueous full battery assembled by Na Ti₂（PO₄）₃/C anode and Li Mn₂O₄ cathode were investigated.The precursor was synthesized by solvothermal method,and the Na Ti₂（PO₄）₃/C negative electrode was prepared by high temperature calcination.In the process of material synthesis,70%phytic acid solution was used as carbon source and phosphorus source,nickel foam was used as current collector,and the paste ratio was 7:2:1.The precursor was synthesized by co-precipitation method,and Na Ti₂（PO₄）₃/C containing Ti³⁺/oxygen vacancies was prepared by controlling the high temperature calcination gas atmosphere of the precursor.The anode has a specific capacity of 98.46 m Ah·g^-1 in the second discharge at 1 C.The discharge specific capacity is 69 m Ah·g^-1at 7 C.The improvement of material specific capacity and rate capability is attributed to the fact that Ti³⁺/oxygen vacancies can（1）facilitate ion/electron transfer;（2）enhance electrical conductivity and improve Na⁺reaction kinetics.The lithium-sodium hybrid aqueous full battery assembled with the anode and Li Mn₂O₄ can provide a discharge specific capacity of up to 101.07 m Ah·g^-1.Na Ti₂（PO₄）₃/C materials under different conditions were prepared by solvothermal method combined with coprecipitation method and high temperature calcination.The research shows that the discharge capacities of Na Ti₂（PO₄）₃/C anode synthesized at solvothermal time of 12 h,solvothermal temperature of 180℃and calcination temperature of 750℃are 102.73,94.34,89.98,86.60 m Ah·g^-1,respectively,at 1,3,5and 7 C.After 500 cycles at 1 C,the discharge specific capacity is 88.41 m Ah·g^-1,and the capacity retention rate is 86%.The good cycling stability and rate capability of the anode material can be attributed to the more complete reaction process of the material precursor preparation after hydrothermal treatment,and the introduction of more Ti³⁺/oxygen vacancies under the subsequent calcination conditions（750℃,H₂/Ar=10:90）,which endow the material with higher electrical conductivity,with an energy gap of 3.787 e V.The lithium-sodium hybrid aqueous full cell assembled with this anode material and Li Mn₂O₄ has a specific capacity of 50.59 m Ah·g^-1 after 200 cycles at1 C,and the co-existence of Li⁺in anode is confirmed during the reaction process of the full cell.