Liquid/solid phase diagrams of binary carbonates for lithium batteries part II

With a differential scanning calorimeter, we mapped five liquid/solid phase diagrams of binary carbonates: propylene carbonate (PC)-dimethyl carbonate (DMC), PC-diethyl carbonate (DEC), DEC-ethylene carbonate (EC), DEC-DMC, and DEC-ethyl methyl carbonate (EMC). These phase diagrams, together with the ones we had published earlier, provided a complete representation for all the binary combinations of these five common carbonates: EC, PC, DMC, EMC, DEC. The results showed that ail the combinations formed simple eutectic systems, although details of their phase diagrams greatly varied, that DEC melted at -74.3 degreesC instead of the currently accepted value of -43 degreesC, and that DEC was less effective than either EMC or DMC in bringing down the liquidus temperatures of their binary mixtures with EC. These results followed the trend we had observed earlier that an expansion toward low temperature of the liquid region of a binary system was facilitated by the two components having close melting points and similar molecular structures. (C) 2001 The Electrochemical Society.