Pressure-Induced Polymerization of CO2 in Lithium-Carbon Dioxide Phases.

We report the discovery of novel CO2-based networks stabilized by Li+ cations in solid-state phases. Our exploration of the energy landscape of the Li-CO2 binary phase diagram using ab initio evolutionary structure searches revealed that in addition to the well-characterized C2O42- oxalate in Li2C2O4 viable covalent CO2-based nets emerge upon compression within the 0-100 GPa pressure range. Novel molecular units are described, such as ethene-like C2O44- in C2/m Li2(CO2), finite C4O86- chains in P1̅ Li3(CO2)2, one-dimensional polymeric forms based on 1,4-dioxane rings in P2/c LiCO2, and the C(O-)2 moieties in Pnma Li2CO2. This investigation shows the oxalate motif is maintained when the concentration of lithium increases from 1 to 2 in LixCO2; this interesting property may have potential in the development of renewable Li-ion batteries. Moreover, a variety of metastable phases were predicted, such as the covalent CO2-based layer in P1̅ Li(CO2)2.