Low-temperature crystal structures of the solvent dimethyl carbonate

Abstract

Dimethyl carbonate (DMC) is an important industrial solvent but is additionally a common component of liquid lithium-ion battery electrolytes. Pure DMC has a melting point of 277 K, so encountering solidification under outdoor climatic conditions is very likely in many locations around the globe. Even eutectic, ethylene carbonate:dimethyl carbonate commercial LiPF6 salt electrolyte formulations can start to solidify at temperatures around 260 K with obvious consequences for their performance. No structures for crystalline DMC are currently available which could be a hindrance for in situ battery studies at reduced temperatures. A time-of-flight neutron powder diffraction study of the phase behavior and crystal structures of deuterated DMC was undertaken to help fill this knowledge gap. Three different orthorhombic crystalline phases were found with a previously unreported low-temperature phase transition around 50–55 K. The progression of Pbca → Pbcm → Ibam space groups follow a sequence of group–subgroup relationships with the final Ibam structure being disordered around the central carbon atom.