Abstract
We compare two experimental approaches for measuring the cation transference number in mixtures of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt: the well-established current-interrupt method proposed by Ma et al. [J. Electrochem. Soc., 142, 1859 (1995)], and a more recent method based on measuring the steady-state current proposed by Balsara and Newman [J. Electrochem. Soc., 162, A2720 (2015)]. In electrolytes comprised of high molecular weight PEO, the data from the two techniques agree, highlighting the equivalence of these two approaches. However, in lower molecular weight PEO electrolytes the values of the two approaches diverge at low salt concentrations. We posit this is because the approach of Ma et al. requires measurements that are sensitive to the nature of the interface between the electrolyte and the electrode. The transference numbers measured by the approach of Balsara and Newman for both low and high molecular weight samples vary from 0.7 to −0.8 and are within experimental error throughout the entire salt concentration window.
Highlights
46cation transference number, t+, in addition to the thermodynamic factor, 47(1+dlnγ±/dlnm).[7]
54the concentration of salt within compartmentalized sections of the 55electrolyte.[8]. This technique is straightforward for liquid electrolytes and has 56been applied to a wide variety of systems.[9]
A polarization is applied across a 69symmetric cell with non-blocking electrodes, and the transference number is 70calculated by the ratio of the steady-state current to the initial current
Summary
9b Materials Sciences Division, Lawrence Berkeley National Laboratory, 10Berkeley, California 94720, USA. 11c Joint Center for Energy Storage Research (JCESR), Lawrence Berkeley 12National Laboratory, Berkeley, California 94720, USA. 13d Energy Storage and Distributed Resources Division, Lawrence Berkeley 14National Laboratory, Berkeley, California 94720, USA
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