Preparation And Application Of High Performance Polybenzimidazole Lithium-ion Battery Separator

With the continuous progress of global technology,the contradiction between the increasing energy demand and the gradual depletion of traditional energy is increasingly prominent.Lithium-ion batteries have become an integral part of daily life due to their excellent reusability,high efficiency,high energy density and long life.However,with the continuous deepening and rapid development of the research on anode and cathode materials in lithium-ion battery,the relatively backward research on the separator has become the short board of lithium-ion battery technology and the current"neck clamp"technology in the field of lithium-ion battery research,which has seriously affected the development of lithium-ion battery.Traditional polyolefin separator due to the low porosity,no polar groups,poor heat resistance and other disadvantages have caused a certain impact on the electrochemical performance and safety of the battery,so it is of great significance to develop a lithium-ion battery separator with high heat resistance,high liquid absorption rate and high electrochemical performance.Polybenzimidazole(PBI)is an aromatic polymer with excellent thermal stability,high mechanical strength,good chemical stability and excellent flame retardancy.Due to the strong interaction between the polar nitrogen atoms on the molecular chain and the electrolyte,the wettability and ionic conductivity of the electrolyte are improved.As a simple and feasible pore forming method,volatilize induced phase separation(VIPS)has a good improvement on the porosity and pore diameter distribution.In this study,polyvinylidene fluoride(PVDF)and polyether imide(PEI)were blended with PBI respectively,and a lithium-ion battery separator with relatively uniform pore size and high porosity was prepared by VIPS method.Meanwhile,safety performance and battery performance of lithium-ion battery was improved.Furthermore,the pseudo-boehmite nanometer layer is"in-situ growth"on the surface of the PBI-PEI separator to improve the ionic conductivity and safety performance of the separator.The structure and physical and chemical properties of the membrane were characterized by infrared,SEM,ionic conductivity,liquid absorption rate,mechanical properties and thermal analysis,and the prepared membrane was assembled into a button battery to evaluate its battery performance.The results are as follows:1.The advantages of PBI heat resistance and excellent wettability of electrolyte are used to improve the insufficiency of PVDF used as separator alone.PBI and PVDF were mixed in different proportions,and the lithium-ion battery separator with high porosity and good penetration was prepared by VIPS method.Compared with the pure PVDF membrane,when the PBI content was10wt%,the absorbency of the PBF-4 membrane was 374.7%,increasing by 162.5%.The ionic conductivity was 0.552 m S cm^-1,which was increased by 0.201 m S cm^-1,and the resistance decreased.After 30 minutes at 160?,the shrinkage rate was 10.7%,which decreased by 11.6%,and the thermal stability was greatly improved.After the button battery is assembled,the discharge capacity of PBF-4 separator is higher than that of PVDF separator under the same current density.The discharge capacity of 0.5C current density is 135.9 m Ah g^-1,which has been improved by 4.5m Ah g^-1 and 0.5C current density after 50 cycles,the capacity retention rate is 97.5%,which has been increased by 5.2%.The composite properties of the PBF-4 separator were significantly enhanced.2.In order to give full play to the coordination role of PBI and PEI,PBI and PEI were blended to prepare the PBI-PEI separator in different proportions.The results showed that when the PBI-PEI ratio was 4:6(mass ratio),the PBI-PEI separator had the best performance.Compared with pure PEI separator,the fluid absorption rate of PBEI-4 separator was 391.84%,which was increased by172.20%.The porosity was 78.92%,up by 17.26%.The ionic conductivity was 1.943 m S cm^-1,which was improved by 1.460 m S cm^-1,and the resistance decreased.After 30 minutes at 160?,the shrinkage rate was 2.6%,an increase of 1.6%,with almost no thermal shrinkage.The discharge capacity of PBEI-4 separator is higher than that of PEI separator under the same current density.The discharge capacity of 0.5C current density is 141.2 m Ah g^-1,which improves 9.7 m Ah g^-1 and0.5C current density after 50 cycles,the capacity retention rate is 92.7%,reducing by 2.4%.The electrochemical and heat resistance properties of the separator were significantly enhanced.3.The pseudo-boehmite with nano-sheet structure is introduced into the surface of PBEI-4separator through"in-situ growth"to prepare organic-inorganic hybrid membranes(APBEI)with gradient aperture to improve the ionic conductivity and safety of the separator.Compared with the PBEI membrane,the absorbency of the APBEI membrane was 339.44%,which decreased by52.40%.The porosity was 76.02%,decreasing by 2.90%.The ionic conductivity was 2.897 m S cm^-1,which was improved by 0.954 m S cm-1,and the resistance decreased.After 30 minutes at 160?,the shrinkage rate was 2%,decreasing by 0.6%,with almost no thermal shrinkage.This indicates that the introduction of pseudo-boehmite nanometer layer can not only improve the ionic conductivity,but also prevent the puncture of lithium dendrites due to its small pore size,effectively improving the safety performance of the separator.After the button battery is assembled,the lithium-ion battery assembled by the APBEI separator has a discharge specific capacity of 158 m Ah g^-1 at0.2C current density,and 143.7 m Ah g^-1at 0.5C current density.The APBEI separator exhibits excellent battery performance under low current density,which provides a new idea for the preparation of lithium-ion battery separator.