Liquid-solid phase diagrams of binary carbonates for lithium batteries

We present the liquid-solid phase diagrams that we mapped with a differential scanning calorimeter (DSC) for the following seven binary carbonates: dimethyl carbonate (DMC)-ethylene carbonate (EC), ethyl methyl carbonate (EMC)-EC, EMC-propylene carbonate (PC), EMC-dimethyl ethylene carbonate (DMEC), EMC-isobutylene carbonate (iBC), PC-EC, and EMC-DMC. Many of these are among the most frequently used solvent systems for making the nonaqueous electrolytes fur lithium batteries. The phase diagrams of these carbonate systems are all of the simple eutectic type but with vastly different particular features. Comparison of these phase diagrams shows that to expand the liquid region of a carbonate system toward low temperature, the two components of the system need to have comparable melting temperatures and compatible molecular structures. These results are consistent with thermodynamic considerations and have significant practical implications. (C) 2000 The Electrochemical Society. S0013-4651(99)08-117-3. All rights reserved.