Study On Preparation And Performance Of Flame Retardant Separator For Lithium Ion Battery

As one of the most popular energy storage systems,lithium-ion batteries are currently widely used in new fields such as high-end electronic products and new energy vehicles.In the internal structure of lithium-ion batteries,the separator is located between anode and cathode.Its main function is to isolate the physical contact between the two electrodes,and as a storage substrate for the electrolyte,providing a migration path for lithium ions.The thermal stability of the traditional lithium battery seperator is not good,which causes the battery to burn out of control during the charging and discharging process,and then explode.Therefore,the development and application of flame-retardant separators to improve the safety performance of lithium batteries has become a research hotspot.In this paper,polyvinylidene fluoride-hexafluoropropene P(VDF-HFP)was used as polymer matrix material and cellulose acetate was added to prepare P(VDF-HFP)/CA separator.Through scanning electron microscopy,differential thermal scanner,thermo-gravimetric analyzer,electrochemical workstation and blue battery testing system,the different properties of P(VDF-HFP)and CA were studied and compared.Then,the effect of different content of Mg(OH)₂nanoparticles on the composite membrane was studied with fixed proportion of P(VDF-HFP)and CA.the aim was to prepare a composite membrane with high liquid absorption and porosity,good mechanical strength,excellent thermal stability and flame retardancy.The specific research contents are mainly divided into the following two parts:(1)P(VDF-HFP)/CA separators were prepared by physical blending and phase conversion.The effects of the ratio of two materials on the properties of prepared separators and assembled button cells were studied.The results show that:Compared with P(VDF-HFP)separator,the performance of P(VDF-HFP)/CA separator has been effectively improved.When the ratio of P(VDF-HFP)to CA is 9:1,P(VDF-HFP)/CA separator(PC10)has the best overall performance.The tensile strength of the separator can reach 14.2 MPa,the porosity and liquid absorption are25.74%and 77.57%,respectively,and the ion conductivity can reach0.192 m S·cm^-1,The button cell assembled by the PC10 separator shows good charge-discharge cycle performance and rate discharge performance.(2)Based on the optimum mixing ratio of P(VDF-HFP)and CA 9:1,adding different contents of Mg(OH)₂,through the preparation and characterization of P(VDF-HFP)/CA/Mg(OH)₂composite separator,Study the influence of Mg(OH)₂content on the performance of composite membrane.The results showed that proper addition of Mg(OH)₂could effectively improve the performance of the separator,but excessive addition of Mg(OH)₂was not conducive to the improvement of the separator performance.When the addition of Mg(OH)₂was 9%,the PCM9had excellent performance and the liquid absorption rate could reach121.8%,and the liquid absorption rate was increased by nearly 40%,the ionic conductivity was reached 1.025 m S·cm^-1,and the tensile strength was up to 29.27 MPa compared with the P(VDF-HFP)/CA separator.