Design And Electrochemical Performance Study Of Electrolyte For Zinc-ion Hybrid Capacitors

With the rapid development of portable electronic products and electric vehicles,people have higher and higher performance requirements for high-performance energy storage devices,which should have high working voltage and energy density while satisfying fast charging and discharging and safety.Compared with traditional secondary batteries,supercapacitors have the characteristics of high power density,fast charge-discharge rate and good cycle stability,but their operating voltage and energy are relatively low,which limits their popularization and application.Therefore,how to further improve the working voltage and energy density of supercapacitors while maintaining the above advantages is one of the research hotspots in this field in recent years.In this paper,aiming at the above problems,we start with the selection of electrolytes for Zinc-ion hybrid capacitors（ZIHCs）,and design different electrolyte systems to effectively improve the working voltage and energy density of ZIHCs,and conduct preliminary research on the corresponding mechanisms.The specific research contents are as follows:（1）A Using Zn（Cl O₄）₂as electrolyte,PEG 400 as molecular crowding agent and AN as diluent,a new Zn（Cl O₄）₂/PEG/AN/H₂O mixed electrolyte system was obtained.The ZIHC constructed with this electrolyte has an operating voltage of 2.0 V and exhibits a high specific capacity of 110 m Ah g^-1at a current density of 0.3 A g^-1.The mechanism of action was studied by Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy.It was found that the addition of acetonitrile not only preserved the interaction between PEG and H₂O,but also decreased the viscosity and expanded the operating temperature range while improving the conductivity of the mixed electrolyte.Further research found that the electrolyte obtained by using Zn（TFSI）₂,Zn（BF₄）₂and Zn（OTF）₂instead of Zn（Cl O₄）₂also has the characteristics of wide operating voltage when applied to aqueous ZIHCs,indicating that the electrolyte solvent universality of configuration policies.（2）The application of tetrapropylammonium bromide（TPABr）in the conventional aqueous ZIHCs electrolyte successfully improved the electrochemical performance of the device.The operating voltage of the device was extended from 1.3 V to 2.0 V,and the Zn-Br battery exhibited ultra-long cycle stability（capacity remained at 80%after 10000cycles）and a Coulombic efficiency close to 100%.In the mechanism analysis,it was found that the addition of TPABr introduced a new chemical reduction active species,and also formed a solid complex with the oxidation product Br₃^-,which was bound in its mesopores by the mesoporous carbon CMK-3 on the electrode.In the structure,the redox reversibility of the device is further improved.In addition,we also found that TPABr has obvious protective effect on the zinc anode.（3）Using CH₃COOK and Zn（CH₃COO）₂to construct a"water-in-bisalt"electrolyte,which was applied to ZIHCs,it was found that the operating voltage of the device could be extended to 0-2.0 V.On this basis,TPABr was introduced to form a"water-in-trisalt"（WITS）electrolyte,and the operating voltage of the device was greatly expanded to 2.6V after being applied to the Zn-Br battery.The introduction of redox couples and the conditions of high-concentration CH₃COOK alkaline electrolyte,thus changing the deposition and stripping mode of zinc ions in the electrolyte,played a key role in broadening the electrochemical stable window.According to this strategy,"water-in-bisalt"and"water-in-trisalt"were successfully constructed based on Na Cl O₄,and the electrochemical performance of the device was also significantly improved after being applied to ZIHCs（the electrochemical window was 0-2.0 V,and the capacity was basically no attenuation after 9000 cycles）.