Modification On The Electrolytes Of Aqueous Zinc Ion Batteries And Investigation On The Mechanism Of Action

Aqueous zinc ion batteries have attracted widespread attention due to their advantages such as low cost,high safety,environmental friendliness,and considerable energy density,thereby exhibiting great promise in the fields of large-scale energy storage systems and wearable electronic devices.However,with the increase of cycle number,side reactions,zinc dendrites,corrosion,passivation,and other problems would occur on the Zn anode,which would lead to irreversible capacity loss of the battery.The main work of this dissertation is to modify aqueous electrolytes and fabricate functional hydrogel electrolytes.The electrochemical performance of the assembled batteries is evaluated,and the effect and mechanism of inhibiting side reactions and zinc dendrites by the modified electrolytes are discussed.（1）The electrolyte is modified and optimized by adding proper amount of sorbitol.With abundant hydroxyl groups,food-grade sorbitol is used as the electrolyte additive,which can interact strongly with both water molecules and Zn anode,thus tailoring the solvation sheath of hydrated Zn²⁺ions,broadening the working potential of electrolyte,enhancing the Zn²⁺ion transfer number,preventing the corrosion issue,and enhancing the freezing-tolerance ability.According to a series of electrochemical tests as well as in-situ and ex-situ measurements,the addition of 10%sorbitol into aqueous electrolyte can effectively inhibit dendritic growth and harmful side reactions at the surface of Zn electrode.Hence,the modified electrolyte enables Zn/Mn O₂ battery to own superior cyclability（89.5%capacity retention after 1000 cycles）and slow self-discharge rate at 20℃.Even at a low temperature of-10℃,the battery can still offer good electrochemical performance,while that without sorbitol additive cannot work normally.（2）A facile and cost-effective method is developed to construct a cellulose hydrogel electrolyte derived from wheat straws by using Ca Cl₂ as the crosslinking agent and sorbitol as the antifreeze agent.The concentrated Zn Cl₂ is utilized in this hydrogel electrolyte to realize“water-in-salt”effect.The obtained hydrogel electrolyte owns superior mechanical properties,rich porosity,ultralow freezing point（-101.5℃）,and large ionic conductivity(35.4 and 19.7m S cm^-1 at 20 and-40℃,respectively).Benefiting from excellent anti-freezing ability,tuned solvation sheath,and facilitated desolvation process within this hydrogel electrolyte,the assembled flexible Zn/polyaniline battery delivers high zinc stripping/plating reversibility from20 to-40℃and superior electrochemical performances even at-40℃.（3）High-concentration kosmotropic ions are introduced to hydrogel electrolyte,taking advantage of the salting-out effect.This significantly improves the mechanical properties of the cellulose hydrogel electrolyte.Additionally,the hydrogel electrolyte is found to own various superior properties（including strong adhesion,large ionic conductivity,wide electrochemical stability window,and good water retaining ability）,facilitate desolvation process,improve Zn deposition kinetics,promote Zn deposition along the（002）plane,and suppress parasitic reactions.Consequently,the Zn/Zn cell exhibits dendrite-free Zn stripping/plating behavior with a long lifespan and can endure ultra-large areal capacity of 25 m Ah cm^-2.The Zn/Cu cell realizes large average Coulombic efficiency of 99.54%over 500 cycles.The assembled pouch-type Zn/polyaniline full battery provides great rate capability,superior cyclability,slow self-discharge rate,and outstanding affordability to external forces.