Lithium doped N-methyl-N-ethylpyrrolidinium bis(trifluoromethanesulfonyl)amide fast-ion conducting plastic crystals

The incorporation of dopant levels of lithium ions (0.5 to 9.3% by mole) in the N-methyl-N-ethylpyrrolidinium bis(trifluoromethanesulfonyl)amide (P(12 )TFSA) plastic crystalline phase results in increases in the solid state io nic conductivity of more than 3 orders of magnitude at 298 K. Conductivitie s as high as 10(-4) S cm(-1) at 323 K have been measured in these doped pla stic crystal phases. These materials can therefore be classified as fast-io n conductors. Higher levels of Li only marginally increase the conductivity , up to around 33 mol%, followed by a slight decrease to 50 mol%. Thermal a nalysis behaviour has allowed the partial development of the binary phase d iagram for the LiTFSA-P(12)TFSA system between 0-50 mol% LiTFSA, which sugg ests the presence of a solid solution single phase at concentrations less t han 9.3 mol% LiTFSA. There is also strong evidence of eutectic behaviour in this system with a eutectic transition temperature around 308 K at 33 mol% LiTFSA. A model relating ionic conduction to phase behaviour in this syste m is presented. The increased conductivity upon doping has been associated with lithium ion motion via Li-7 solid state NMR linewidth measurements.