Preparation And Properties Of New PVdF-HFP Polymer Composite Membrane

Lithium-ion batteries have assumed an increasingly important role as high energy density energy storage devices.As one of the most important components in lithium-ion batteries,separators have attracted more and more attention.In particular,the gel polymer electrolyte separator(GPEs)is considered as a promising candidate because of its advantages such as good electrochemical stability and favorable safety.However,the poor mechanical strength and the poor dimensional stability restricts its development.In this paper,PVd F-HFP based polymer membranes were modified by inorganic porosity agent,acrylate cross-linking and intermediate layers made by electrospinning.The purpose was to improve the electrochemical properties,mechanical strength and dimensional stability of the separators.This paper can be divided into three parts:(1)Attempted to modify PVd F-HFP-based polymer membranes using nano-ZnO as a pore-forming agent.The modified membrane was tested for elution rate,scanning electron microscopy(SEM),porosity and liquid uptake,mechanical properties,and a series of electrochemical performance tests.The test results showed that 30 nm was the appropriate particle size of ZnO,and 18% was the suitable amount.The ionic conductivity of the CR18 separator was about 1.2 m S cm-1,and the tensile strength reached 11.5 MPa.The cells assembled by the separator also showed good cycle performance and rate discharge performance.(2)A new porous cross-linked membrane was prepared and applied as the separator for rechargeable lithium-ion batteries.The inorganic ZnO nanoparticle(nano-ZnO)was added as a pore-forming agent and filler to the preparing process of membranes made of the poly(vinylidene fluoride-co-hexafluoropropylene)(PVd F-HFP)and a cross-linked polymer by the copolymerization from poly(ethylene glycol methyl ether methacrylate)(PEGMEMA),methyl methacrylate(MMA)and octavinyl-T8-silsesquioxane(POSS).Firstly,the prepared membrane was swollen by propylene carbonate(PC),Secondly,nanoZnO was eluted by hydrochloric acid to form the microporous structure.The effects of different particle sizes of nano-ZnO and addition on the mechanical and electrochemical properties of the microporous membrane were studied.The SEM images showed that 30 nm nano-ZnO was the suitable diameter for microporous membrane structure.It was comprehensively considered that ionic conductivity and mechanical strength were two related factors negatively,18% addition of nano-ZnO was a suitable usage for the preparation of a microporous membrane(CRZ18)with an ionic conductivity of 1.4 m S cm-1 and tensile strength of 16 MPa.Meanwhile,the Li Fe PO4/Li half-cell assembled with CRZ18 membrane as a separator showed the best C-rate capacity and cyclability,indicating that the CRZ18 membrane is a kind of promising separator for the high-performance lithium-ion batteries.(3)A sandwich-like composite membrane was prepared with cellulose electrospun membrane as an intermediate layer,linear poly(vinylidene fluoride-co-hexafluoropropylene)(PVd F-HFP)as the membrane substrate,poly(ethylene glycol)methyl ether methacrylate(PEGMEMA)and methyl methacrylate(MMA)as monomers,trimethylolpropane triacrylate(TMPTA)as the crosslinking agent.The experimental results illustrate that the ion conductivity and mechanical strength of the modified membrane are significantly improved,which reach 1.8 m S cm-1 and 12.5 MPa,respectively.The modified membrane also has good dimensional stability at 180 oC compared with commercial PE membrane.In the battery tests,the cell assembled by composite membrane shows favorable cycle performance and C-rate capability,with the discharge capacity reaching 137 m A h g-1 under the 0.5 C/0.5 C test.