| Polymer lithium battery is a high energy-density power source. Because it has many advantages such as high specific capacity, little possibility of electrolyte leakage, flexible packaging and shapes, polymer battery has broad prospects and has received great interest in recent years. This paper aims to prepare a lithium battery-used polymer electrolyte which has excellent properties, and study the A.C impedance and mechanism of energy decline and ionic transmission. The main contents of this dissertation are as follows:The technology of preparing PVDF-HFP-based polymer electrolyte using phase inversion method and its mechanism of producing micro-pores were researched, the modified poly(vinylidene fluoride-hexafluoro-propylene/methyl methacrylate) polymer electrolyte and non-woven fabric reinforced poly(vinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer electrolyte were prepared. By introducing methyl methacrylate, the surface properties of polymer electrolyte are improved, and by using non-woven fabric as supporting medium, the mechanical intensity of PVDF-HFP based polymer electrolyte is enhanced. Both the polymer electrolyte membranes have rich micro-pores. After absorbing electrolyte, their ionic conductivity at room temperature exceeds 1mS·cm-1, and their electrochemical window reaches 5.0V. The interfacial property of polymer battery prepared by non-woven fabric reinforced PVDF-HFP polymer electrolyte is stable. After 50 cycles, its capacity maintenance ratio is up to 97%, when discharging at 1.0 current rate, it can retain 94% of the discharge capacity of 0.1 current rate. So the electrochemical properties of this polymer battery are very good.By directly volatilizing solvent, a new method to prepare micro-porous polymer membrane was put forward, and its mechanism to produce micro-pores was investigated. When using this method to prepare PVDF-HFP/organo-Montmorillonite(OMMT) composite polymer membrane, the reunition of inorganic particles can be restrained. The polymer electrolyte with 5% OMMT has rich micro-pores, its uptake of liquid electrolyte is 290%, and its ionic conductivity at room temperature is up to 1.51mS·cm-1. By using PVDFHFP/OMMT composite polymer electrolyte, the interfacial impedance of polymer battery is reduced, the capacity maintenance ratio after 50 cycles reaches 95.5%, and its rate performance is also improved.The meaning represented by A.C impedance plot of polymer lithium battery was studied, an equivalent circuit of electrode system was put forward, and the polymer lithium battery is simulated by using this equivalent circuit. The result of simulation is consistent to that of the experiment. The capacity declining mechanism of polymer battery was then discussed. It is suggested that during cycling, the increase of interfacial impedance resulting from deterioration of interfacial properties and the increase of electrochemical impedance bring by crystal lattice pulverization of cathode material are the main reason of battery's capacity decline. Based on this investigation, methods to improve the electrochemical properties of polymer battery are educed.A monomer with three arms synthesized by pentaerythritol and methyl acrylic acid was used to prepared gel polymer electrolyte, and by introducing glycol methyl methacrylate to the polymer framework, pliability and viscidity of gel polymer electrolyte were improved. This method has many advantages such as quick polymerizing speed, better capability for polymer to contain liquid electrolyte. The gel with 92% of liquid electrolyte has an ionic conductivity up to 1.89mS·cm-1 at room temperature, and the electrochemical performance of gel polymer battery is as good as that of liquid electrolyte battery. Beside this polymer electrolyte, another gel polymer electrolyte synthesized by polydiethyleneglycol methacrylate with different molecular weight was prepared, and the effect of molecular longness on its electrochemical performance was also discussed. The results show that when the ratio of diglycol to electrolyte is 1:9, the gel polymer electrolyte has optimal electrochemical properties. Compared with other gel electrolytes, polydiethyleneglycol methacrylate based gel polymer electrolyte has many characters such as low cost, simple operation and good electrochemical properties. Relationship of gel polymer electrolyte's ionic conductivity to temperature and the effect of polymer content on the apparent activation energy of lithium ion transmission as well as its transfer number were investigated. It turns out that the relationship of ionic conductivity to temperature is not consistent with Arrhenius equation. Additionally, the results also show that with the increase of polymer content, the apparent activation energy of lithium ion transmission enhances, and its transfer number declines. Based on this research, some methods were put forward to improve the properties of gel polymer electrolyte. If a polymer with network structure and right longness is selected to prepare gel polymer electrolyte, and the content of polymer is apropos, the movement ability of both the liquid electrolyte and the polymer itself can be enhanced, so the electrochemical performance of gel polymer electrolyte can be improved. |
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