Electrolytes Design For Aqueous Zinc Ion Batteries And Their Electrochemical Performances

Aqueous zinc ion batteries（AZIB）are considered as an intense competitive system for the future large scale power storage due to their high security and low cost.Zn metal anode shows rich reserves,high theoretical capacity,and low redox potential.The aqueous electrolytes have intrinsic safety and high ionic conductivity,which can be fast charge and discharge.However,it is easy to form Zn dendrites and further lead to short circuit owing to the disorder diffusion and uneven deposition of Zn²⁺in anode.Meanwhile,the hydrogen evolution reaction occurs during the deposition of Zn²⁺,accompanied by by-products.The above Zn dendrites,hydrogen evolution reaction and by-products mitigate against sufficiently the coulombic efficiency and life span,which impede the practical application of AZIBs.To date,various strategies have been carried out to improve the reversibility and stability of Zn anode,such as artificial interface layer,Zn anode structure design,and electrolyte optimization.However,electrolyte optimization is regarded as one of the most promising methods for its convenience,economic benefits,and high efficiency.Therefore,this topic starts with the electrolyte,and designs the structure of the electrolyte by the introduction electrolyte additives and the selection of appropriate zinc salts,to achieve high-performance AZIB.The specific research work are as follows:（1）The artificial sweetener aspartame was used as the electrolyte additive,and micro addition(1.0 g L^-1)could achieve high-performance,non-dendritic and non-corrosive zinc anode.Aspartame is preferentially adsorbed on the surface of zinc anode.The O atoms and N atoms in the molecular structure of aspartame have high affinity with Zn²⁺,which can provide rich Zn²⁺coordination sites,thus inducing the uniform deposition of Zn²⁺,inhibiting the formation of Zn dendrites,and forming a water-poor double layer,inhibiting the side reaction between water and Zn anode,and improving the electrochemical performance of the cells.The Zn||Zn symmetrical cells operated for 4638 h at 1 m A cm^-2/1 m Ah cm^-2 and 2347 h at 10 m A cm^-2/5 m Ah cm^-2,realizing an ultra-high cumulative plating capacity of 11.735 Ah cm^-1.In addition,the Zn||Zn symmetrical cell operated stably for at least 270 h at 80%depth of discharge.And the Zn||Cu half cells and Zn||NH₄V₄O₁₀ full cells assembled with optimized electrolyte showed extremely excellent performance.（2）The zinc sulfamate（Zn（NH₂SO₃）₂）was used as the electrolyte of AZIB,which not only improved the cycle stability of positive and negative electrodes,but also realized the application in low temperature environment.The N-H in sulfamate anion can build hydrogen bonds with water molecules and form a competitive relationship with the hydrogen bonds between water molecules,thus breaking the original hydrogen bond network in water and reducing the freezing point of the electrolyte.In addition,sulfamate anion can participate in the solvation structure of Zn²⁺,reducing the content of active water molecules,thus restraining the decomposition of water.The electrochemical performance of the cells assembled by the electrolyte was not only excellent at room temperature,but also extremely outstanding at low temperature environment.The corresponding Zn||Zn symmetrical cell operated stably for more than 3750 h at-20℃,the Zn||Cu half cell provided high average coulomb efficiency of 99.63%,and the Zn||KVOH full cell operated stably for more than 2000 cycles at-20℃and 0.5 A g^-1 without capacity decay.