A new solid-state rechargeable lithium battery based on polymer-polyacrylonitrile

Recently, the development of electric vehicles (EV) and popularity of portable equipments have driven the rechargeable battery industry to develop a battery with a light weight, low self- discharge rate, high energy density and long cycle life. In order to achieve these requirements for a rechargeable battery, the electrolyte in the cell has a very important role. PAN-based polymer electrolytes are one of the promising nonconventional electrolytes for application in rechargeable lithium batteries.; PAN-based polymer electrolytes are gel-like electrolytes which are composed of lithium salt and a mixed organic solvent in a PAN polymer matrix. This type of gel electrolyte has a high conductivity of 10 -3 S cm-1 at room temperature which is one order less than those of organic electrolytes. However, the ion migration mechanism for this type of polymer electrolyte has not yet been proposed. In this study, it was found that the conductivity values of PAN-based polymer electrolytes were dependent not only on the content of PAN but also on the concentration of lithium salt. The result indicates that the content of PAN in the electrolyte dominates the conduction property of electrolytes and the concentration of LiClO4 is a secondary effect on the conduction properties. The investigation of conductivity of LiClO₄!PC+EC systems has been studied by AC impedance. The conduction properties strongly depend on the concentration of LiClO₄. The optimized composition of liquid electrolytes is when the EC/PC molar ratio equals to one and the concentration of LiClO ₄ is 1 M. Also, AC impedance technique was used to characterize the ion migration mechanism of the polymer electrolytes and the microstructure of electrolytes (equivalent circuit). According to the AC impedance results, three equivalent circuit models were simulated and thus used to interpret the ion migration mechanisms of electrolytes. These models based on the theories of the brick model, the easy path model and the modified easy path model can successfully interpret the ion migration in the electrolytes.; The FTIR and Raman spectra study on liquid and solid polymer electrolyte systems have been done. Both results reveal that Li ions interact with both molecules in the mixed solvent in liquid electrolyte systems and also with both the PAN polymer and the mixed solvent molecules in polymer electrolyte systems. A double glass transition temperature (T_g) for each polymer electrolyte was observed by DMTA studies. This observation indicates that polymer electrolytes have inhomogeneous structure. The first T_g of polymer electrolytes is just slightly lower than that of pure PAN due to a region containing no solvent. The second T_g at 175°C is due to the region with solvent, salt, and PAN.