Steady‐State Composition Profiles in Mixed Molten Salt Electrochemical Devices: I . Lithium/Sulfur Battery Analogs

Abstract

During charge or discharge of batteries with a binary molten salt mixture as t~he electrolyte, composition gradients are produced by the electrode reactions and the differences in mobilities of the electroactive and nonelectroactive ions. The effects of current density, electrode separatioa, and initial composition of the electrolyte are predicted by an analytical solution of the flux equations derived with transport properties similar to those of LiCI-KC1 mixtures. Numerical solution of the flux equations predicts the composition profiles in lithium sulfur battery analogs with LiC1-KCI mixtures of differing compositions. Either complete depletio,n of the electroactive constituent at one electrode, or precipitation of a solid phase at the electrodes, could result from the predicted composition gradients. Changes in electrolyte composition at the electrodes may also affect J-phase formation at the sulfur electrode during discharge. * Electrochemical Society Active Member. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-02-18 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-02-18 to IP

Effective conductivities of an FeS positive in LiCl-KCl eutectic electrolyte at different states of charge

“…This result appears to support the deposition or freezing of KC1 suggested by several previous investigators [4][5][6]. We have attempted to examine the KCI deposition at the interface of FeS particles where it is expected to freeze due to the consumption of Li +, but this phenomenon has not shown up using the ordinary microscopic method.…”

“…In practice, the resistance increase may not be quite so rapid as calculated because it is possible for the positive to swell. One of the experimental evidences for KC1 deposition may be electrode resistance decrease after interrupting discharge current as predicted by Vallet and Braunstein [4], and Pollard and Newman [5]. Such a resistance decrease was observed as shown in Fig.…”

“…The transference number is assumed to be equal to xi [4]. We used the Cottrell equation [ The other parameters used in the calculation of the effective conductivity are listed in Table 1.…”

Reactions of FeS Electrodes in LiCl ‐ KCl Electrolyte

“…[17]) and E7 (Eq. [19]) E4* (J <-> Li2S) --1333.0 --0.0245T [21] The difference between E4 (Eq. [18] ) and E4* is only 1.7 mV at 400~ In view of the difficulties in establishing the E4 line, we consider the agreement between E4 and E4* to be acceptable.…”

“…[18]) and calculated (Eq. [21]). Of course, the value of 5G~ that would be obtained from the calculated E4(E4*) would agree with the results given in Table II.…”