Recent developments in the ENEA lithium metal battery project

Abstract

Solvent-free P(EO) 20LiTFSI + PYR 14TFSI polymer electrolyte films with PYR 14 +/Li + mole ratios ranging from 0.96 to 3.22 were prepared by hot-pressing mixtures composed of PEO, LiTFSI and PYR 14TFSI of selected stoichiometries. The PYR 14TFSI room temperature ionic liquid (RTIL) is homogeneously incorporated into the P(EO) 20LiTFSI membrane without phase separation. For a PYR 14 +/Li + mole ratio of 3.22, the ionic conductivity was about 2 × 10 −4 S/cm at 20 °C, i.e., more than one order of magnitude higher than that of the RTIL-free electrolyte. The electrochemical stability window of the polymer electrolyte containing the RTIL was about 6 V (versus Ag/Ag +). Li/V 2O 5 cells with the polymer electrolyte (PYR 14 +/Li + = 1.92) showed a 60% capacity retention after 80 cycles at 40 °C (the initial capacity was 210 mA h/g). Li/V 2O 5 cells (PYR 14 +/Li + = 1.28) held at 30 °C delivered about 93 mA h/g (at 0.057 mA/cm 2), which corresponds to approximately 34% utilization of the active material. These results suggest that the incorporation of the RTILs into PEO-based polymer electrolytes is very promising for the future realization of solid-state lithium metal polymer batteries operating near ambient temperatures.