Preparation And Properties Of PVdF-HFP/Cross-linked PEGMEMA Separators For Lithium-ion Batteries

With the expansion of applications of new-style electric vehicles,portable electronics and energy storage systems,rechargeable lithium-ion batteries(LIBs)with high energy density,lightweight and long lifepan have got a quick development.As an important component of LIBs,the separator not only functions as a physical barrier to prevent short circuit between the anode and cathode,but also serves as the electrolyte reservoir for the transport of ions.Gel polymer electrolyte separators(GPEs)have been regarded as the promising candidate for separator of LIBs due to their high ionic conductivity and good stability.In this paper,the PVdF-HFP/cross-linked PEGMEMA blending membrane is prepared by the blend of PVdF-HFP and crosslinked polymer derived from PEGMEMA and OVPOSS using UV-induced technology.Moreover,the membrane was modified by nonwoven and pore-forming agent to enhance the mechanical strength,electrolyte uptake and stability.The present work can be summarized as follow:(1)PVdF-HFP was first blended with PEGMEMA,cross-linker OVPOSS as well as various pore-forming agents.Subsequentlty,the mixture was initiated by UV-induced technology to fabricate porous GPEs.The physical properties of membranes were investigated by SEM analysis,porosity test and tensile test.The results showed that the membrane without pore-forming agent showed good mechanical strength of 7.0 MPa,but it exhibited poor porosity and electrolyte uptake.The membrane with PEG400 as pore-forming agent(PPFA)possesses abundant uniform microporous structure,high porosity(47%)and electrolyte uptake(156 wt%).The electrochemical properties of the membranes were studied by the electrochemical workstation and land battery test system.The results showed that the ionic conductivity of PPFA membrane was up to 1.22 mS cm-1,and the half-cell assembled with PPFA membrane exhibited better C-rate capability and higher discharge capacity which the coulombic efficiency kept above 99%than others.(2)Based on study above,we prepared porous membranes using polyethylene glycol with different molecular weight as pore-forming agent.Results showed that the microporous membranes all exhibited better electrolyte uptake and higher porosity than pristine membrane.Among the microporous membrane,the membrane using PEG4000 as pore-forming agent(PPFA4T)possessed excellent capability to absorb and store liquid electrolyte,which the pore diameters concentrate into 0.2～0.4 μm and still kept high tensile strength.The half-cell assembled with PPFA4T separator showed high ionic conductivity and interface stability,and displayed good cycle performance and C-rate capacity,which the discharge capacity can reach up to 146 mAh g-1 at 0.5 C/0.5 C.(3)In order to further enhance the electrochemical perporties and tensile strength of PVdF-HFP/cross-linked PEGMEMA membrane(pristine),the cellulose nonwoven was as a support of pristine membrane to prepare the CMs membrane,and PEG4000 pore-forming agent was added in CMs casting solution to prepared PCMs membrane.The results demonstrated that CMs membrane displayed good tensile strength of 10.6 MPa and can still keep excellent dimensional stability under 150 ℃.The tensile strength of PCMs was 9.5 MPa,and the half-cell assembled with this membrane displayed better cycle performance and C-rate capacity,the highest discharge capacity reached 145 mAh g-1 at 0.5 C/0.5 C.In conclusion,the mechanical strength,ionic conductivity and porosity of PVdF-HFP/cross-linked PEGMEMA membrane were clearly improved by the cellulose nonwoven and pore-forming agent.