Preparation And Properties Of PVDF-HFP/Al₂O₃ Cross-linked PEGMEMA Composite Separators

In recent years,lithium-ion batteries(LIBs)have been widely used in electronic equipment,transportation,aerospace military industry and other fields due to their high energy density,excellent cycling performance,long service life and green environmental protection,etc.However,the performance of LIBs is gradually improved to meet the requirement of rapid charge and dischargeWith the development of the application fields such as rapid charge and discharge,the requirements for various aspects of the performance of LIBs are gradually improved.The membrane acting as one of the important components of LIBs plays an important role in isolating positive and negative electrodes and carrying electrolytes to transport lithium-ion,which has an important effect on the electrochemical performance of the battery.Moreover,the gel polymer electrolyte membrane has become a research hotspot owing to its better absorption of swelling effect,higher ionic conductivity and compatibility with the electrode.In this paper,Al2O3 cross-linker(VTMO@Al2O3)was prepared by using vinyl modification Al2O3,and then PVDF-HFP/Al2O3 cross-linked PEGMEMA composite polymer electrolyte membrane was prepared successfully using thermal initiated radical polymerization,wherein PEGMEMA and VTMO@Al2O3 as reaction monomers.For further improving the porosity and electrolyte uptake,the membrane was modified with PVP,and the effect of the amount of PVP on the performance of the membrane was investigated.On the basis of the above research,in order to overcome the problem of poor mechanical properties of porous membrane due to the addition of porous agent,cellulose nonwoven fabric with better compatibility was used as skeleton material,and then cellulose reinforced Al2O3 cross-linked composite membrane was prepared by coating method.The specific research content is divided into the following three parts(1)Inorganic nanoparticles cross-linker VTMO@Al2O3 was successfully prepared using VTMO.Then PVDF-HFP and Al2O3 cross-linked PEGMEMA composite membrane was prepared by heat initiated free radical polymerization of cross-linker VTMO@Al2O3 and PEGMEMA monomers,with PVDF-HFP as matrix.The physical and electrochemical property of cross-linked composite membrane was further characterized.The results showed that the mechanical properties and thermal stability of the membrane could be effectively enhanced by Al2O3 participating in the formation of cross-linked network structure(no change in size at 180?).The cross-linked membrane PMAv has abundant and uniform porous structure,and its ionic conductivity is up to 0.82 mS cm-1 at room temperature.In addition,the charge-discharge cycle of the battery assembled with the cross-linked membrane PMAv can keep stable,and the discharge specific capacity is kept at 142.9mA hg-1(97.8%)after 100 cycles.(2)On the basis of the Al2O3 cross-linked composite membrane,the porous cross-linked composite membrane was prepared by the addition of different PVP content to control the micro-porous structure,and the effect of different PVP content on the performance of the membrane was further studied.The results showed that the porosity and electrolyte uptake of porous membrane increased with the increase of PVP content.However,the membrane PV10 had the highest ionic conductivity of 1.37 mS cm-1 when the content of PVP increased to 10.The tensile strength of the porous membrane PV10 remains at 30.4 MPa,and the thermal decomposition temperature is up to 200?,the increase of micropore has no effect on the mechanical properties and thermal stability of the membrane..After the half-cell was assembled,the specific discharge capacity was 147 mA h g"1 after 100 cycles,and the specific capacity retention rate was close to 98%,and the specific capacity retention rate was still about 60%at 4C rate.(3)On the basis of the cross-linked composite membrane,the cellulose nonwoven fabric with better compatibility and stability was used to prepare Al2O3 cross-linked cellulose nonwoven composite membrane.The micro-porous structure and mechanical properties of cross-linked composite membrane were further improved.The composite membrane CMAs showed high porosity(?60.8%)and electrolyte uptake(168.6 wt%)The ionic conductivity is up to 1.64 mS cm-1.The tensile strength of the composite membrane is up to 34.5 MPa,and its thermal stability is good.The decomposition temperature is as high as 200?.The composite membrane CMAs has good cyclic stability and charge/discharge performance,the initial discharge specific capacity is up to 148.7 mA h g-1,and the specific capacity of the composite membrane CMAs is still about 52%at 4 C rate discharge.