Preparation Of Solid Electrolyte And Flexible Electrode For Lithium Ion Battery

With the development of society,bendable and foldable flexible electronic devices have gradually entered into people’s life,which has higher requirements on energy storage devices.The traditional energy storage devices mainly use metal as the current collectors of the electrode material,which obviously does not have the property of being bendable and foldable.Therefore,the use of flexible current collectors instead of metal current collectors has become a hot topic of research.At present,the main research direction is to employ carbon materials as current collectors.Because the traditional electrolytes of lithium ion battery use liquid electrolytes containing organic solvents,there will be problems such as easy leakage,poor security and easy formation of lithium dendrites when applied to flexible electronic equipment,which is increasingly not in line with the needs of social development.Compared with liquid electrolyte,solid polymer electrolyte has the advantages of high safety,high temperature performance and high energy density.However,the current research on polyethylene oxide(PEO)-based solid electrolytes has the defect of low ionic conductivity at room temperature,which leads to its poor electrochemical performance.Since the "gel-like"state helps the electrolyte "flow" in the polymer matrix,thereby increasing the ionic conductivity.The gel electrolyte has attracted extensive attention due to its higher room temperature ionic conductivity and lower interfacial resistance between electrolyte and electrode.In this experiment,the gel solid electrolyte was prepared by UV curing method.The effects of different polymer matrix on the electrochemical properties were studied.The highly conductive graphene-based flexible electrode was prepared by continuous suction filtration.The effects of electrode materials with different current collectors on its electrochemical performance were studied.All solid-state batteries with gel electrolytes and flexible electrodes were prepared,and the effects of different temperatures on the performance of all solid-state batteries were discussed.The experimental results of this paper are as follows:(1)The gel electrolyte of the semi-interpenetrating polymer grid substrate prepared by the ultraviolet curing method had excellent electrochemical performance.Infrared test results indicate that the carbon-carbon double bonds in the ethoxylated trimethylolpropane triacrylate had disappeared and formed a cross-linked polymer substrate.The ionic conductivity of the prepared gel electrolyte based on semi-interpenetrating polymer grid was 1.31×10-4 S/cm at room temperature,and the electrochemical stability window reached about 5.09 V,which was suitable for most electrode materials.Compared with a gel electrolyte without PVDF-HFP,the gel electrolyte with a semi-interpenetrating polymer grid substrate had higher discharge specific capacity,better cycle stability and less polarization.The gel electrolyte was applied to the lithium ion battery of aluminum foil-based lithium iron phosphate,the first charge-discharge specific capacity was 144.4 mAh/g and 143 mAh/g at a rate of 0.2 C,and the capacity retention rate was 88.9%after 40 cycles.(2)The flexible electrode was prepared by continuous suction filtration.The X-ray diffraction test proved that the flexible electrode had no impurity phase.The scanning electron microscope test showed that the graphene film had a porous structure,which facilitated ion transport and helped to strengthen the bonding between the electrode material and the current collector.The prepared flexible lithium titanate electrode was applied to the lithium ion battery and found to have excellent cycle stability.The first discharge specific capacity was 170.2 mAh/g at a rate of 0.2 C.After 200 cycles,the discharge specific capacity still reached 163.6 mAh/g.The flexible electrode also had excellent rate performance and had a smaller charge transfer resistance.A full cell prepared from flexible lithium iron phosphate and flexible lithium titanate had a first discharge specific capacity of 156.6 mAh/g at a rate of 0.2 C.(3)The prepared gel polymer electrolyte was applied to a solid state lithium ion battery together with a flexible lithium titanate electrode,and the first discharge specific capacity was 138 mAh/g at 50℃ and 0.2 C rate,and the capacity was 104.8 mAh/g after 30 cycles.