Preparation Of Bacterial Cellulose-based Composite Hydrogels And Application For The Aqueous Zinc Batteries

With the use of non-renewable resources such as fossil fuels and problems such as environmental pollution,countries around the world are looking for renewable,sustainable and efficient new energy technologies.Water system zn-metal battery has become the most potential new energy storage technology due to its high theoretical volume capacity,low cost,safety and environmental friendliness.However,zinc metal batteries also have some unavoidable problems such as dendrite growth,side reactions and hydrogen evolution,which will lead to the shortening of cycle life and even battery failure during the use of the battery.In order to solve these problems,researchers have modified zinc anode interface,rationally proporated electrolyte and optimized design of gel electrolyte to inhibit the growth of zinc dendrites and the occurrence of side reactions.Gel electrolyte is a very important component in battery devices,which can play the role of liquid electrolyte and diaphragm at the same time.The mechanical properties and ionic conductivity of gel electrolyte have been the key indexes of its research,which directly affect the performance of the battery.However,these two indicators influence and restrict each other,and it is difficult to achieve the ideal balance.Therefore,improving the ionic conductivity while ensuring the good mechanical properties of gel electrolytes is one of the hot issues in the development and research of gel electrolytes.Based on this,bacterial cellulose（BC）was selected as the research object in this paper,and the oxidized bacterial cellulose（TBC）containing carboxyl functional groups on the surface was prepared by TEMPO oxidation modification of bacterial cellulose.Further,using the oxidized modified bacterial cellulose as the matrix,through in situ polymerization and ion cross-linking,A variety of composite gels including oxidized bacterial cellulose/polyacrylamide（TBC-PAM）,oxidized bacterial cellulose/ionic liquid/polyacrylamide（TBC-IL-PAM）and oxidized bacterial cellulose/[EMIM]BF₄/polyacrylamide（TBC-B-PAM）were prepared respectively.Through the comprehensive analysis of the mechanical properties,reabsorption capacity,ionic conductivity,thermal stability and other physical and chemical properties of the prepared composite gel,the composite gel with higher ionic conductivity and better mechanical properties was selected for the assembly of zinc batteries,and its electrochemical properties were discussed and studied.The main research contents and conclusions of this paper are as follows:（1）TBC-PAM composite gel was prepared by adjusting the ratio of acrylamide monomer（AM）and TBC,and its mechanical properties,ionic conductivity and other physical and chemical properties were tested and analyzed.The results show that the mechanical properties of TBC-PAM gel are significantly improved compared with pure TBC gel:when the mass ratio of AM to TBC is 10:1,the ionic conductivity of TBC-PAM-10 gel reached 2.73 m S cm^-1,the breaking strength was 70.63 KPa,and the elongation at break was 111.53%.（2）In order to further improve the ionic conductivity of TBC-PAM gel,TBC-IL-PAM composite gel was prepared by the synergistic interaction of ionic liquid（IL）-[EMIM]BF₄,[EMIM]PF₆ and[EMIM]TFSI.The results show that TBC-IL-PAM gel has better tensile fracture strength and elongation at break than pure TBC hydrogel.Among them,the composite gel prepared by[EMIM]BF₄ ionic liquid has the best mechanical properties:the tensile strength is 175.25 KPa,and the elongation at break is 38.36%,which is about twice that of the composite gel prepared by the other two ionic liquids.At the same time,the ionic conductivity of the composite gel prepared by[EMIM]BF₄ was 20.16 m S cm^-1,which was significantly higher than that of TBC-PAM(3.11 m S cm^-1).（3）TBC-B-PAM composite gel was prepared by[EMIM]BF₄ ionic liquid.By adjusting the content of[EMIM]BF₄,the TBC-B₂-PAM composite gel with better ionic conductivity and mechanical properties（the content of[EMIM]BF₄ is 20%）was prepared and applied to zinc batteries.The results show that the Zn²⁺migration number（0.45）of TBC-B₂-PAM gel electrolyte is significantly increased compared with that of glass fiber membrane（0.27）.Moreover,TBC-B₂-PAM is less corrosive to zinc foil,and after assembling it into Zn//Ti cells,the cells maintain high Coulomb efficiency.Under the test condition of current density of 1 m A cm^-2 and deposition surface capacity of 1m Ah cm^-2,the zinc symmetrical cell assembled by TBC-B₂-PAM gel electrolyte can work for 200 h.Under the test condition of current density of 5m A cm^-2 and deposition surface capacity of 5 m Ah cm^-2,the zinc symmetrical cell assembled by TBC-B₂-PAM gel electrolyte can work for 400 h.The normal working time is much higher than the life of glass fiber assembly battery（50 h）.