Optimization Of High-temperature Aqueous Zn-V₆O₁₃ Battery Electrolyte And Its Zinc Storage Mechanism

Due to the depletion of fossil fuels and extreme environmental problems such as global warming,there is an urgent need for human society to develop safe and reliable electrochemical energy storage devices.Zinc ion batteries have received widespread attention due to their low cost,high capacity and environmental benefits.In recent years,high-efficiency zinc ion batteries with high specific energy and long cycle life,including cathode materials with excellent Zn²⁺storage capacity,ultra-durable zinc metal anodes,and various hybrid electrolyte have been developed and studied.However,their cycling stability remains challenging due to dissolution of the cathode material and dendritic/corrosion of the metal anode caused by strong water activity in the zinc metal anode,which is particularly prominent in high temperature environments,limiting their wide range of applications.This thesis explores the energy storage mechanism as well as the failure mechanism of Zn-ion batteries in different thermal environments,and adopts a battery electrolyte additive strategy to introduce an acetonitrile（ACN）additive into the electrolyte to improve the embedding and detachment of zinc ions in the anode of Zn-V₆O₁₃ batteries in high temperature environments and the dissolution and dendritic crystals arising from the plating and stripping process of zinc ions in the anode,achieving an aqueous Zn-V₆O₁₃ battery with high-temperature stability’s possible.The main studies are as follows:1.The specific mechanisms by which temperature affects the dissolution of the positive electrode and the corrosion/dendrite of the negative electrode of aqueous Zn-ion batteries were analysed by studying the performance of the batteries in different thermal environments and the failure of the batteries at extreme temperatures.It is shown that the overall cycling performance of V₆O₁₃-Mn@Mn/Zn（Otf）₂//Zn batteries decreases with increasing temperature in high temperature environments（>40°C）.When the ambient temperature increases,the positive nanoribbon structure accelerates the collapse of clusters to nanosheets and the negative dendrite growth size becomes larger.The degradation of cell capacity is attributed to the dissolution of the positive electrode and the short circuiting of the cell is attributed to the overgrowth of negative dendrites piercing the diaphragm.As the temperature increases from 25°C to 80°C,the cell first turn capacity increases from 210 m A h g^-1 at 1 A g^-1 current density to 330 m A h g^-1,with an exponential decrease in cycle life.2.The problem of capacity decay of zinc ion battery cathodes in high temperature environments was enhanced by adding different levels of acetonitrile additives to the zinc trifluoromethanesulfonate electrolyte.With the addition of acetonitrile solvent,the molecular structure of the inner Helmholtz layer（IHP）in the cathode surface double electron layer（EDL）was reconfigured,reducing the lattice changes in the cathode due to zinc ion embedding and detachment while inhibiting the formation of the cathode by-product zinc alkali vanadate and inhibiting cathode dissolution from both physical and chemical perspectives.First principles calculations also show that the addition of acetonitrile molecules improves the free water content in the double electron layer of the cathode surface,thereby alleviating the structural collapse of the cathode under high temperature conditions.The Zn//MVO battery was achieved with stable long cycle performance under high temperature conditions:the capacity retention rate was up to101.7%after 500 cycles of low current 1 A g^-1 at 40°C and 83.6%after 500 cycles of high current density(10 A g^-1)at 60°C.3.The problem of accelerated corrosion and rapid dendrite growth at high temperatures in the anode of zinc ion batteries was improved by adding different levels of acetonitrile additives to the aqueous electrolyte.The addition of acetonitrile molecules results in a change in the structure of the solvent shell of zinc ions in the electrolyte.Molecular dynamics simulations（MD）calculations show that acetonitrile molecules participate in the coordination of zinc ions,effectively weakening the strength of hydrogen bonds in the electrolyte and achieving highly stable and reversible electroplating stripping while inheriting the excellent kinetics of the aqueous cell.The Zn-Zn symmetric cell based on the ACN additive electrolyte was smoothly electroplated and stripped at 60°C and 0.1 m A h cm^-2 current density for>200 h without significant dendrite formation on the negative surface.This thesis provides a promising strategy for the design of safe and reliable high temperature zinc ion battery electrolytes,broadening their application and laying some theoretical groundwork for zinc ion batteries to move towards industrialisation.