| Layered sodium titanate(Na2Ti3O7)can reversibly intercalated/extracted by sodium-ion at a lowest voltage(ca.0.3V vs.Na+/Na).It is an ideal negative electrode material for sodium-ion batteries(SIBs)with a theoretical capacity of 178mAh·g-1 approximately,when Na2Ti3O7 accommodates additional two Na+ions.However,the traditional synthesis method requires high temperature(>800℃)or long time(>48h),and the products have unsatisfied electrochemical performance,low capacity,and poor cycle stability.Ionic liquids(ILs)has excellent solvating properties and low vapor in the ion-thermal method,which can instead of autoclave overcome the hydrothermal/solvothermal methods high-pressure processes.However,ILs is not only very expensive,but also hard to degrade which could pollute the environment.The deep eutectic solvents(DESs)is a good alternative because of having advantages similar to ILs.What’s more,it is easy to synthesize,low toxicity and inexpensive,which overcomes the limitations of ILs and has a large number of applications in life,such as electrodeposition,metal deposition,nanomaterials,gas adsorption,etc.In this paper, using choline chloride/ethylene glycol as the reaction medium,TBOT and NaOH were used as raw materials to synthesize the negativeelectrodeNa2Ti3O7 under normal pressure and low temperature conditions.which has a good sodium-ion battery performance. The effects of the amount of eutectic solvents, reaction time, reaction temperature, sintering time andsintering temperature on the microscopic appearance and electrochemica properties of the material were also investigated.The mechanism of sodiumstorage of Na2Ti3O7 was analyzed by cyclic voltammetry. At the same time, the effect of carbon nanotubes on the performance of sodium-ion hybrid capacitors assembled with Na2Ti3O7, as anode and activated carbon as anode was investigated.The best synthetic process for the synthesis of Na2Ti3O7, by cholinechloride/ethylene glycol eutectic solvent is: eutectic solvent is 100mL, reaction temperature is 70℃, reaction time is 4h, sintering temperature is 500.℃,sintering time is 7h. The Na2Ti3O7, material synthesized under this process exhibits outstanding electrochemical performance. It can deliver discharge capacities of 122.1mAg-1 after 100 cycles and 72m-1Ahg after 2000 cycles at current density of 1Cand 5C, respectively. The main kinetic behavior of Na2Ti3O7,in the process of sodium ion intercalation and deintercalation is pseudocapacitive behavior, which contributes more than 85% specific capacity. By uniformly dispersing the carbon nanotube material in the DESs,Na2Ti3O7 is grown on the surface to obtain the Na2Ti3O7@CNT electrode material, and the specific surface area and pore diameter of Na2Ti307, are increased to form a sodium ion capacitor assembled with the activated carbon material. It has good performance, the power density reaches 420.8W.kg-1at a current density of 0.1A·g-1, and the energy density reaches 61.7Wh·kg-1; After 600 cycles at a current density of 0.5A·g-1, the capacity retention rate is still above 70%. |
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