| In recent years,the rapid development of lithium ion batteries has promoted the revolution of electronic devices,which is also changing our life.The high power density and energy density are pursued vigorously by the power battery,while the cycling stability and safety of li-ion batteries are also the focus of attention.In lithium ion batteries,the separator as electrical insulators,ionic conductors to prevent short circuit due to physical contact between the positive and negative and ensure that is between the cathode of lithium ion transport has played an important role.Therefore,the development of high temperature resistant separator is an urgent problem to be solved in the performance of high safety and high cycle stability of lithium ion power battery.At present,the polyolefin porous membrane used by power batteries,such as PP,PE,PP/PE composite membrane,still has some non-negligible defects,such as poor thermal stability,which can be easily affected by heat under high temperature.The porosity is low and the pore diameter is uneven.The electrolyte infiltration is poor.In this paper,the electrostatic spinning technology and vacuum suction filter technique was used to prepare different lithium ion battery separator,based on the preparation of the thin film material composition and structure were analyzed,and the thermal stability of separator,strength,porosity,electrolyte invasive control,significantly improve the cycle performance of lithium from the battery,the safety performance and ratio of performance.The details are as follows:1.Using electrostatic spinning technology,a series of SiO2 modified PVdF-PVdF films were prepared by introducing SiO2 nanoparticles with high specific surface area.The results showed that the mechanical strength and thermal stability of SiO2@PVdF/PE/PVdF films were significantly improved compared with commercial PP/PE separator and pure PVdF-PE-PVd F films.In addition,the film of SiO2@PVdF/PE/PVdF also shows high porosity and absorption rate,which is mainly due to the high specific surface area of SiO2 and its good infiltration of electrolyte.2.In order to further improve the SiO2@PVdF/PE/PVdF membrane material porosity and fluid absorption rate,this work by ammonium bicarbonate as the pore-forming agent,continue with the electrostatic spinning technique was used to prepare a series of ultra-thin with porous nanometer fiber structure of SiO2@PVdF/PE/PVdF membrane.Multiple test results show that ammonium bicarbonate of the modified SiO2@PVdF/PE/PVdF composite membrane compared with commercialization and PP/PE and separator,shows the higher porosity and fluid absorption rate,the rich channel structure and good infiltrating to improve lithium ion electrolyte transport,improve cell ratio performance play an important role.The results showed that the introduction of SiO2 nanoparticles not only greatly improved the thermal stability and mechanical properties of the films,but also enhanced the absorption of electrolyte by the composite separator.Study found that SiO2 modify quantity of 15wt%,dosage of ammonium bicarbonate to 10wt%as the best addition amount,the preparation of SiO2@PVdF/PE/PVdF film shows a good mechanical strength and thermal stability（170℃,shrinkage rate 3%）,the electrolyte fluid absorption rate is as high as 380%,ionic conductivity of 2.5 x 10-3s/cm-2 LiFePO4 as the anode assembly of lithium ion battery in the initial discharge capacity of 134.3.After 300cycles remain 129.2 mA hg-1,shows the excellent performance and cycle stability.3.Because of the abundance of celluloses,low cost and easy to process,cellulose has an important prospect in the application of separator.This section work directly with A4 Paper as base,through the vacuum suction filter method,the high strength Kevlar（Kevlar）composite nanofibers and A4 Paper,with the double channel structure was prepared Paper/Kevlar new biomass thin film,and it will be used for lithium ion battery separator.Results show that the introduction of the Kevlar nano fibers significantly enhances the thermal stability of the Paper/Kevlar separator（complete）240℃structure,mechanical strength and puncture strength significantly increased（30 mpa）,is expected to pass to prevent lithium dendrite pierced separator,thus greatly improve the safety performance of the battery.Through the assembly of lithium ion battery test showed that the Paper/Kevlar composite separator overcomes the low intensity of pure cellulose Paper and micron grade channel cause short-circuit phenomenon effectively and avoid the phenomenon of short circuit,the overall performance or even better than commercial PP membrane;The capacity of 1C charge and discharge is 94.3%,and coulomb efficiency is close to 100%,which shows good electrochemical performance.Therefore,based on the Paper/Kevlar biomass composite membrane materials in membrane application has important research value and significance,on the one hand,can reduce the dependence on fossil fuels the preparation of polyolefins separator,protect the environment on the other hand,is conducive to the sustainable development of renewable energy. |
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