The Application And Properties Of Aqueous Liquid And Gel Polymer Electrolyte In Zinc Ion Batteries

With the social development,the world’s resource reserves has decreased as the days go by.It is urgent to solve the problem of traditional fossil fuel energy depletion.China has set a goal of“carbon peaking and carbon neutrality”,and has shifted the development direction of the energy industry to clean energy development.More efficient,safe and environmentally friendly energy storage equipment is needed urgently to solve the volatility and intermittency of traditional clean energy.Batteries are regarded as one of the best energy storage equipments.The most popular battery productions on the market are commercial lithium-ion batteries.However,most lithium-ion batteries have the risk of organic electrolyte leakage,flammable and explosive.The developments of lithium-ion batteries are limited by the above safety concerns.The development of safe and stable batteries has become the focus of research.Aqueous Zinc Ion batteries（AZIBs）are safe intrinsically and burn difficultly compared with lithium-ion organic batteries.At the same time,the cost of battery has been reduced greatly by the high abundance of zinc metal and water solvent.Nonetheless,there are some promblems in zinc-ion aqueous batteries,such as dendrite growth,interface chemical instability,and battery system shutdown at low temperatures.In this paper,to develop batteries with high safety,low cost and environmental friendly of batteries,“water-in-salt,WIS”electrolyte and alginate-based flexible gel polymer electrolyte were prepared to solve the problem of poor dendrite,interface and lowtemperature performance of AZIBs.The phychemical properties of these electrolytes were investigated and their electrochemical performance and practical applications were studied in zinc-lithium hybrid batteries,the main research contents are as follows:1.The bulk energy density and mass energy density of AZIBs were enhanced with WIS electrolyte,and the influence of electrolyte concentration on the performance of zinc-ion batteries was investigated.The bulk energy density and mass energy density of Zn//Li Fe PO₄ full cells assembled with different molar ratios（Zn Cl₂/Li Cl）electrolytes were obtained by theoretical calculation,and the mass energy density and bulk energy density of Zn//Li Fe PO₄ hybrid batteries were improved by reducing the dosage of electrolyte.The full cell exhibited 107.5 Wh kg^-1 of mass energy density and 157.8 Wh L^-1 of bulk energy density.Compared with the different molar ratio electrolyte,WIS electrolyte had good polarization stability and electrochemical stability window.Compared with the low molar ratio electrolyte,the WIS electrolyte enabled the zinc anode to achieve high coulomb efficiency and inhibit dendrite growth effectively,the capacity retention of zinc-lithium hybrid battery assembled with that was 70.1%after 1000 cycles at rate of 3 C.2.SA/PVA/PVP composite gel polymer electrolyte（SPP）was prepared through sol-gel method.The skeleton structure was formed by mixing sodium alginate（SA）,polyvinyl alcohol（PVA）and polyvinylpyrrolidone（PVP）.Sodium alginate in the skeleton structure crosslinked with zinc ions,which provided good mechanical properties for the gel electrolyte.At the same time,the pyrrolidone group of PVP provided a fast ion transport channel,giving SPP high ionic conductivity.The optimized S₅PP exhibited 521.6 k Pa of tensile strength and 9.46×10^-3 S cm^-1 of ionic conductivity.S₅PP flexible gel electrolyte has good polarization stability,rate performance and circulation performance.The information of stable SEI membranes induced uniform deposition of zinc ions on the zinc anode side,and the whole battery showed 68.0%of capacity retention after 1000 cycles at rate of 3 C,and the coulombic efficiency was higher than 98.3%.3.To improve the low temperature resistance of SPP gel electrolyte,the antifreezing gel electrolyte（ASPP）was prepared by soaking the polymer matrix into a salt solution containing high solubility lithium chloride and moderate glycerol without changing the optimal ratio of the polymer matrix.The gel electrolyte exhibited good mechanical strength and ionic conductivity,and kept unfreezing at-50 ^oC.At-20°C,ASPP achieved high polarization stability in the symmetrical cell and 1000 cycles of charge and discharge in the whole battery（1 C）.The flexible battery assembled with ASPP can supply power continuously under the harsh conditions of continuous bending,knocking and shearing,showed ultra-high safety performance.4.To enhance the mechanical properties and interfacial electrochemical stability of SPP gel electrolyte,a graphene oxide-enhanced alginate-based gel polymer electrolyte（SPPG）was constructed by introducing graphene oxide（GO）into the polymer matrix.The abundant functional groups on the GO surface can increase the crosslinking sites of zinc ions,while the esterification reaction in SPPG enhances the interaction force between polymers,which can further improve the mechanical strength of SPP（904.8 k Pa）.Compared with S₅PP,SPPG was less polarized in zinc-symmetric cells,achieving higher coulomb efficiency（>99.5%）in zinc-lithium hybrid cells.SPPG exhibited a capacity retention rate of 70.3%（1 C）after 400 cycles,and more stable sheet zinc deposition was observed on the zinc anode surface compared with S₅PP.