Abstract
Abstract This research intends to investigate the utilization of porous polymer for Li-ion second battery. Using phase separation method to control the porous condition. Various solvents were used to generate phase separation when epoxy was cured. The cured sample was heated in a vacuum oven to remove solvent, and formed porous polymer. In this research, various kinds of solvent、various concentrations of solvent and curing conditions were utilized to prepare porous polymer. Different chemical and physical properties of solvents, compatibility between epoxy and solvents, the curing mechanism are the parameters affect the porous structure of polymer. Scanning electron microscope (SEM) was utilized to observe the void distribution of porous polymer,and to study the effect of porosity of polymer on the density and specific surface of polymer. The thermal degradation kinetics of porous polymer was investigated by thermogravimetric analyzer (TGA). Furthermore, the porous adhesive was applied to the Li-ion battery. The effect of adhesive on the capacity and cycle life of Li-ion battery was investigated.Results indicate that low boiling point solvent should be used, since which can be removed easily. It is an efficient way to find the solvents which are compatible with epoxy by the solubility parameters between the polymer and solvent. Homogeneous mixture of cured epoxy will form uniform porosity.In order to obtain uniform porosity of adhesive, the curing temperature is very critical. Results show the temperature must be moderate. The higher the temperature, the bigger the pores and the lower the degree of porosity . However, when the temperature is lower,the pores become smaller and the degree of porosity will be increased. In this study, 75℃ was selected as the curing temperature for epoxy. In the post-cured step, the porous adhesive must be dried to dispel the solvent to obtain the open pores .The post-cured temperature must be higher than the glass transition temperature (Tg) of the polymer to dispel the solvents.Results also show that the diameter of pores is 10μm mainly, which can be controlled by the concentration of the solvents and the curing temperature. The porous structures may be changed with different solvents, namely, THF, cyclohexane and hexane.The battery properties such as the capacity, cycle life, charge, discharge and the 1st irrev % are affected significantly by the porous adhesive.The 1st irrev%≒10%, and the ratio of discharge to charge is over 90% in the coin-cell. While the capacity of battery decreased slightly (about 6.91%(23mAh/g)) as the coating area of adhesive reached 20%(1cm2 ). The electrical property of Uni-cell shows that 1C/0.2C＞95%, 2C/0.2C＞90%which, meets with the standards of the commercial grade Uni-cell..