Ion-Transport Processes in Dual-Ion Cells Utilizing a Pyr1,4TFSI/LiTFSI Mixture as the Electrolyte

In dual-ion cells, the extraction of ions from the electrolyte during charging leads to the formation of ion concentration gradients and to ion transport processes. In order to obtain information about these processes, we examine changes in the electrolyte resistance in an exemplary dual-ion cell utilizing a Pyr(1,4)TFSI/LiTFSI mixture as electrolyte. The negative and the positive electrode are metallic lithium and graphite, respectively. The individual changes in the electrolyte resistance in both half-cells are monitored insitu by means of three-electrode electrochemical impedance spectroscopy. The results are compared to finite element simulations, for which concentration-dependent diffusion and conductivity data of Pyr(1,4)TFSI/LiTFSI mixtures are used as input parameters. We show that differences in the mobilities of the three types of ions play a decisive role for the time evolution of the ion concentration gradients and the resulting resistance changes in the two half-cells.