Abstract
We develop a model based on concentrated solution theory for predicting the cycling characteristics of a lithium-polymer-lithium symmetric cell containing an electrolyte with known transport properties. The electrolytes used in this study are mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, prepared over a wide range of salt concentrations. The transport properties of PEO/LiTFSI previously reported in the literature are used as inputs for our model. We calculate salt concentration and potential profiles, which develop in these electrolytes under a constant dc polarization, as a function of current density, electrolyte thickness, and salt concentration. These profiles are nonlinear at steady-state due to the strong concentration dependence of the transport properties of this electrolyte. The effect of this nonlinearity on limiting current is demonstrated. Cycling characteristics of a series of lithium symmetric cells were measured to test the validity of our model, without resorting to any adjustable parameters. The time-dependence and steady-state value of the potential measured during cycling experiments were in excellent agreement with model predictions.
Highlights
29nonlinear at steady-state due to the strong concentration dependence of the 30transport properties of this electrolyte
We use rav to denote 72the average salt concentration of the electrolyte, where rav is defined as the 73molar ratio of lithium ions to ether oxygens in the system: rav = [Li+]/[O]. 74Although both cells in Figure 1 were cycled at the same current density of iss 75= ± 0.02 mA/cm[2], the cell containing an electrolyte with a lower salt
Concentration gradients in polyethylene oxide (PEO)/LiTFSI electrolytes predicted by the 343model at steady-state
Summary
10b Materials Sciences Division, Lawrence Berkeley National Laboratory, 11Berkeley, California 94720, USA. 12c Argonne Collaborative Center for Energy Storage Science, Argonne National 13Laboratory, Lemont, Illinois 60439, USA. 14d Joint Center for Energy Storage Research (JCESR), Lawrence Berkeley 15National Laboratory, Berkeley, California 94720, USA. 16e Energy Storage and Distributed Resources Division, Lawrence Berkeley 17National Laboratory, Berkeley, California 94720, USA
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