Study On Basic Application Of Ammonium Vanadate And Biomass Derived Carbon Materials In Zinc-based Energy Storage Devices

In recent years,the global environmental problems caused by the excessive use of fossil fuels have greatly promoted the development of efficient energy storage devices.Among many kinds of energy storage devices,aqueous zinc-based energy storage devices with the advantages of low cost,high safety,high theoretical capacity,and low redox potential have attracted wild attention.Among them,the electrode materials are the key factor determining their comprehensive performance.As one of the important electrode materials in aqueous zinc-based energy storage devices,ammonium vanadate(NH₄V₄O₁₀,NVO)has been widely studied due to its active-rich layered structure.However,the poor capacity performance,rate capability,and cycle performance of NVO hinder their further commercial application.Therefore,in this paper,ammonium vanadate material with high capacity and high rate performance was first prepared by mild heat treatment and used in the cathode of zinc-ion batteries.Subsequently,we adopted polydopamine coating to improve the cycle stability of ammonium vanadate cathode.Finally,a zinc-ion hybrid supercapacitor was assembled with ammonium vanadate as cathode and bamboo-derived carbon as anode,which further improved the rate capability and cycle performance of the ammonium vanadate material.The specific research contents of the thesis are as follows:（1）Ammonium vanadate with the synergistic effect of ammonium removal and enhancement of oxygen vacancies（NVO-300）was prepared by a two-step method of hydrothermal and mild thermal treatment.Specifically,by removing partial ammonium cations,NVO can receive more space for the（de）intercalation of Zn²⁺ions,thereby increasing its specific capacity.Increasing oxygen vacancies can weaken the strong electrostatic interaction between the V-O layer and Zn²⁺to reduce the energy barrier of the Zn²⁺diffusion process,and improve the electronic conductivity to accelerate the reaction kinetics,thereby giving rise to outstanding rate performance.As a result,the as-prepared NVO-300 with the above dual characteristic displays a much higher specific capacity(355 m Ah g^-1 at 0.3 A g^-1)and better rate capability（59%retention after a 33-fold current increase）compared to NVO without dual characteristic.In addition,our NVO-300//Zn quasi-solid-state battery output a specific capacity of 307 m Ah g^-1 at 0.5 A g^-1,exhibiting its superior potential as a portable electrochemical energy storage device.（2）Based on the NVO-300 prepared in the previous work,the polydopamine-coated ammonium vanadate material（PNVO-300）was prepared by soaking it in a polydopamine（PDA）solution,which was used to construct a highly stable zinc-ion battery.The effects of PDA self-polymerization time and soaking time on the electrochemical performance of PNVO-300 were systematically investigated.The optimized sample（PNVO-300/16-1min）was prepared by PDA self-polymerization for 16 h and soaking for 1 min.The results have proved that an appropriate amount of polydopamine coating protects the NVO-300cathode during the charge-discharge process,and improves its cycle performance.PNVO-300/16-1min cathode can maintain 88.5%of the initial capacity after 1300 cycles,which is better than uncoated NVO-300（72.0%）.In addition,PNVO-300/16-1min cathode still maintains acceptable capacity performance,reaching 306 m Ah g^-1 at 0.3 A g^-1.（3）Compared with the above-mentioned zinc-ion batteries,the zinc-ion hybrid supercapacitors exhibit better rate performance and cycle stability.To this end,N,O co-doped porous carbon（BC-CNa）was prepared by a one-step combustion method using bamboo powder,sodium nitrate,and dimethylimidazole as the raw materials.The zinc-ion hybrid supercapacitor based on BC-CNa cathode（BC-CNa//Zn）demonstrates a high specific capacity of 51.4 m Ah g^-1 at 0.2 A g^-1,and only 4%capacity reduction after 90000 cycles,showing excellent cycle stability.Furthermore,two kinds of zinc-ion hybrid supercapacitors were assembled with BC-CNa as the anodes,and the ammonium vanadate materials prepared in the previous two work as the cathodes.Both of these two zinc-ion hybrid supercapacitors（NVO-300//BC-CNa and PNVO-300/16-1min//BC-CNa）exhibit superior electrochemical performance,showing high specific capacities of 98.9 m Ah g^-1 and 64.9 m Ah g^-1 at 0.3 A g^-1,respectively.In addition,PNVO-300/16-1min//BC-CNa also demonstrates excellent rate performance（72.9%retention after a 15-fold current increase）and cycle capacity retention（only 10.7%capacity reduction after 2000 cycles）.The above results show that the application of ammonium vanadate in the field of zinc-ion hybrid capacitors can further improve its rate performance and cycle performance.