Phase Diagram Approach to Control of Ionic Conductivity and Electrochemical Stability of Solid Polymer Electrolyte Membrane for Li-ion Battery Application

Résumé du livre

Binary and ternary phase diagram of poly(ethylene glycol) dimethacrylate (PEGDMA), bis(trifluoromethane)sulfonimide (LiTFSI), and succinonitrile (SCN) blends have been established by means of differential scanning calorimetry and polarized optical microscopy. The binary phase diagram of PEGDMA/SCN mixture is of typical eutectic type, whereas the binary phase diagram of PEGDMA/LiTFSI mixture exhibits a wide single-phase region at the intermediate compositions. The ternary phase diagram of PEGDMA/SCN/LiTFSI mixture shows a wide isotropic region. The polymer electrolyte membrane (PEM), which is formed by ternary blends in this region after UV-crosslinking, remains in the isotropic phase and performs. The room temperature ion conductivity as evidenced in AC impedance measurement, was found to be extremely high (i.e., 10−3 S/cm). This ionic conductivity increases to 10−2 S/cm at 60 °C that continues to improve further up to 135 °C investigated. More importantly, the high ionic conductivity behavior is reproducible in repeated heating/cooling cycles. Those PEM are solid-state, stretchable, nonflammable, and light weight, which may be applicable to lithium ion battery as a replacement of commercial liquid electrolyte. SCN in ternary blends affords not only dissociation of the lithium salt, but also plasticization to the cross-linked PEGDMA network. Last not least, thermal and electrochemical stability of these membranes were examined for further application probability.