Preparation And Study Of PVDF/PVC/PMMA Gel Polymer Electrolyte For Lithium Ion Battery

Because of the high working voltage,high energy density,long cycle life,lightweight,small size,non-toxic,pollution-free etc.lithium-ion batteries have become the preferred power source for new energy vehicles.However,there are safety bottlenecks due to the utilization of liquid organic electrolyte.When the gel polymer electrolyte is dissolved in the polymer matrix as solvent,the polymer solution gel is formed and the gel polymer is no longer mobile.As a result,the gel is neither solid nor liquid,and its properties are also between the solid state and liquid state.Because of its special structure,the gel polymer has the advantage of either diffusion and conduction of liquid or cohesive property of solid.Therefore,gel polymer electrolyte has become the primary priority of the research.In this paper,polymethyl methacrylate?PMMA?with high conductivity,low interfacial impedance and good interfacial stability was adopted,but its mechanical properties were low.For the good mechanical properties,the polyvinyl chloride?PVC?was added into the PMMA to ensure the absorption of electrolyte and improve the transmission efficiency of lithium ions.Polyvinylidene fluoride?PVDF?has good thermal stability,excellent electrochemical properties,high dielectric constant,but its crystallinity is high.With the addition of PVC and PMMA,its crystallinity became lower.In order to get the ternary PVDF/PVC/PMMA based gel polymer electrolytes?GPEs?with excellent properties,they were blend,and the procedure was as follows:?1?The electrospun membranes were prepared by electrospinning technology based on PVC/PMMA,PVDF/PMMA and PVDF/PVC/PMMA,respectively.The physical and electrochemical properties,such as SEM,mechanical properties,ionic conductivity,first charge and discharge etc.were measured after vacuum drying.The results showed that the electrospun membrane based on PVDF/PVC/PMMA had the best comprehensive properties.?2?Four solutions of PVDF/PVC/PMMA in different concentrations were prepared.Films were prepared by electrospinning,morphology,thermal stability and porosity were measured after vacuum drying,and electrochemical properties were measured after the batteries assembled.The results showed that the electrospun membrane with 11%concentration had the best morphology,the largest porosity and the best thermal stability.Its first charge-discharge reached 164.7 mAh.g^-1,163.8mAh.g^-1.After 50 cycles,the discharge capacity was 155.7 mAh.g^-1 and the capacity retention rate was 94.5%.It showed excellent electrochemical performance.?3?On the basis of the above,PVDF/PVC/PMMA blend spinning solutions with different mass ratios were prepared,and four kinds of electrospinning membranes with different mass ratios were prepared by electrospinning.After drying,the morphology,liquid absorption rate,mechanical properties,ionic conductivity and electrochemical stability window etc.were examined.The results showed that the electrospun membrane with 4:4:1 mass ratio had the highest liquid absorption rate,the largest tensile strength,excellent physical properties,and the highest ionic conductivity.The electrochemical stability window reached 5.6V,showing excellent electrochemical performance,which was suitable for lithium-ion batteries.