Studies On Preparation And Properties Of The Novel Gel Polymer Electrolyte And Li₂FeSiO₄ Cathode Material

The Li-ion battery is one of the key research fields in chemical power sources in recent decade years,and gel polymer lithium ion battery（GPLB） has become a new developing orientation of lithium ion battery,which solves the possible problem of leakage owing to no free liquid electrolyte and can be easy to be made some special batteries such as super-thin and bending-freely batteries.However,some common problems such as low conductivity and poor mechanical strength are found in gel polymer lithium ion batteries.Besides,the commoditization of cathode material such as LiCoO2 has disadvantages,which it has higher price and is not suitable for high-power charge and discharge.In this paper,modification of the novel gel polymer electrolyte and Li₂FeSiO4 cathode material were studied in details.Firstly,starch and acrylic monomers were fabricated in laboratory by the graft copolymerization method,and high electrolyte-absorbent resins were prepared,then they were blended with polyvinyl alcohol（PVA）,the polymer matrix was prepared by one-step method of preparation of direct volatilizing solvent and the polymerization conditions and reaction ratios were improved and optimized.The structure and performance of polymer membranes were performed by means of FTIR,DSC,TG analysis methods.On the other hand,the novel gel polymer electrolytes were prepared with those polymer electrolyte membranes.The ionic conductivities of polymer electrolyte membrane were tested by AC impedance method.Their surface structures were studied by SEM method.The results showed that the conductivity of the gel polymer electrolyte membrance got to 6.46x10^-4 S/cm,which can be expected to be used in polymer lithium ion batteries.Secondly,Li₂FeSiO₄ is cheaper material than LiFePO₄,so Li₂FeSiO₄ has become the new developing cathode material.However,Li₂FeSiO₄ has the drawbacks of low conductivity and bad electrochemical properties as well as lower lithium ion diffusion rate.In order to overcome disadvantages above,Li₂FeSiO₄ was doped with the pyrolysis carbon from heat-treatment of phenolic resin at different temperatures with different iron resources by the method of solid-state reaction in this paper.The obtained materials were characterized by means of FTIR,TG,XRD, and SEM,and the influence of the heat-treatment temperatures on electrochemical properties was studied here.The results showed that when FeC₂O₄ ? 2H₂O was selected as the iron resource,and the heat-treatment temperature reached 750℃, and the content of the doping carbon was 9%,the capacity reached the maximum, the charge capacity was 127.3 mAh/g,and the discharge capacity was 158.8 mAh/g.