| 초록 |
Several research institutes have been developing batteries with solid polymer electrolytes for more than 15 years. Research efforts have been growing each year, resulting in projects such as the United State Advanced Battery Consortium in the United States, and the national program led by NEDO in Japan. The objective has been to identify solid polymer electrolytes (SPE) with a conductivity higher than 10-3S cm-1, and a redox stability window higher than 4V, which is the lower limit in the case of utilization of high-voltage cathodes. Investigating the manufacturing process of lithium polymer battery in common use recently4, there is a pressure imposed on the SPE to improve the degree of contact between electrolyte and electrode. Physical properties of the compressed SPE system would be totally different from those of the incompressed SPE system. Further, when plasticized SPE is used, the effect will be even greater. Smith and Pennings5 showed that, according to the Flory-Huggins theory of melting point depression, an eutectic point may occur in an athermal polymer/diluent system if the melting point of a diluent is not too low in comparison with that of the polymer. Myasnikova et al.7 provided the phase diagram of PEO/resorcinol system in which resorcinol molecules form hydrogen bonds to the polymer chain. However, in previous studies of the phase behavior of SPE, it is hard to find a theoretical prediction that can describe and predict the change of liquidus curves including an eutectic point owing to the compression effect. In this study, we develop a model to describe phase behaviors of compressed polymer/salt systems. We combine two theory to take into account the pressure effect of the given systems: theory of melting point depression15 and the generalized lattice-fluid (GLF) model16. We then compare the proposed model with experimental data for PEO/ZnX2 ( X = Cl, Br ) and PEO/LiCF3SO3 as model systems to show the change of liquidus curve and an eutectic point with various pressure.
|
