Preparation And Properties Of Zinc Ion Conducting Polymer Electrolyte Films Based On PVDF-HFP

With the rapid urbanization and technological expansion,the increasing demand of energy has posed a great challenge which is antagonizing the mankind worldwide.In the report of the 19th CPC National Congress,concerns have been shown to develop more efficient and sustainable energy storage technologies to meet the growing energy demand.The existing energy storage systems have certain limitations such as safety issues,high cost,insufficient power density etc,which hinders their long-term viability.Hence,it is highly desirable to design and fabricate extremely safe and high performance energy storage devices.In this regard,zinc-ion battery has been receiving extensive attention at home and abroad owing to their higher theoretical energy density,low cost,safety potential,environmental friendliness and ease of fabrication.However,the use of organic electrolytes in the conventional batteries poses major risks of leakage,flammability and explosion.In order to curb these problems,the concept of polymer electrolytes emerged as an efficient alternative.Therefore,in the present study,a safe and stable zinc-ion conductive PVDF-HFP-based polymer electrolyte has been developed.The solid polymer electrolyte was prepared by solution casting method using PVDF-HFP polymer and Zn?Tf?₂ zinc salt as raw materials.Further,the surface morphology,crystal structure,thermal stability and electrochemical properties were analyzed by SEM,XRD,TGA,EIS and CV respectively.The results showed that the addition of zinc salt have significantly improved the surface structure of the PVDF-HFP polymer matrix.There was an apparent increase in the number of micropores and reduction in the crystallinity.And,the best comprehensive performance was reported at mass ratio of 40%?zinc salt to polymer matrix?.Moreover,the solid polymer electrolyte showed considerable thermal stability up to 350°C,the Young's modulus was 220 MPa,the tensile strength was 7.69 MPa and the tensile fracture strain was 204%.The ionic conductivity was found to be2.44×10^-5 S/cm with the electrochemical chemical stability window of 3.45 V and the ion transference number of 0.983.Despite exhibiting good comprehensive properties,the solid polymer electrolyte has quite low ionic conductivity,which is hard for its application in batteries.Aiming at the problem of low ion conductivity and narrow electrochemical window of solid polymer electrolytes,[EMIM][OTf]ionic liquid was used as plasticizer to prepare gel polymer electrolyte.The structure and performance of gel polymer electrolyte was analyzed by the same characterization methods as mentioned above.The results showed that the ionic liquid[EMIM][OTf]substantially improved the microporous structure of the polymer electrolyte.The morphology confirmed the appearance of abundant micropores within the polymer matrix and there was a great reduction in the crystallinity too.Albeit,the obtained gel polymer electrolyte has the best overall performance when the mass ratio of 40%?[EMIM][OTf]to polymer matrix?.The thermal stability was up to 305?,Young's modulus was 117 MPa and tensile strength was 5.74 MPa.The ionic conductivity was notably enhanced to 1.44×10^-4 S/cm with ion transference number of 0.999.In addition,a wide electrochemical stability window of 4.14 V was attained.Compared with solid polymer electrolytes,the electrochemical properties are improved significantly.The results are good enough to meet the application in energy storage devices.Therefore,the prepared gel polymer electrolyte was further applied to the supercapacitor.It was found that the supercapacitor had a small internal resistance of only 48.81?,and it was more stable under the voltage range of 0¹ V.The charge and discharge curves were relatively symmetrical and have good capacitance performance.At a current density of 0.045 A/g,the charge and discharge reached88.24 F/g,With the increase of current density,the specific capacitance decreases little and has excellent rate performance.Under the cyclic charge-discharge test,the coulomb efficiency is always around 98%,and the charge-discharge process is stable,nevertheless,the cycle stability needs to be improved.