A Shuttle mechanism for molten-electrolyte lithium batteries
Abstract
The lithium-transport rates arising from a lithium shuttle mechanism (LSM) were examined by potentiometric control of a lithium-alloy electrode in a temperature range of 400 to 515 C in three electrolytes: LiCl-KCl, LiCl-LiBr-KBr, and LiF-LiCl-LiBr. Lithium transport in Li/FeS(x) cells by LSM was found to occur by diffusion of reduced lithium species across the separator layer, which was controlled by the Li-activity of the Li-alloy electrode. Solubility of lithium was strongly affected by electrolyte composition, especially K(+) content, which in turn regulated the lithium transport rate. As evidenced by LSM rates, the solubilized lithium would appear to form dimers (e.g. Li2(+) or LiK(+)). The half-cell self-discharge rates, which were measured, correlate well with self-discharge rates in developmental cells ranging from 0.1 to 10 mA/sq cm. Innovative application of the LSM has led to the development of overcharge tolerant Li/FeS(x) cells. A bimodal self-discharge characteristic (a 20-fold increase toward the end of charge) results from a 150-250 mV step increase in lithium activity of a two-phase Li-alloy electrode (Li-Al plus Li-Al 5Fe2). Three versions of the battery cell (100 sq cm separator area) have been demonstrated: LiAl+Li5Al5Fe2 (10% of capacity) /LiCl-LiBr-KBr(MgO)/FeS2, as well as a FeS-type, (both operated at 400 C) and LiAl+Li5Al5Fe2 (10% of capacity) /LiF-LiCl-LiBr(MgO)/FeS (operated at 475C). These cells exhibit a unique combination of overcharge capacity and extended trickle-charge tolerance at 2-5 mA/sq cm. Additionally, Li/FeS2 cells having overcharge tolerance have operated with stable performance for greater than 500 cycles. The overcharge tolerance rates are sufficient for battery cells to exhibit built-in charge/equalization capability by way of full-battery trickle charging.
- Publication:
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Presented at the 184th Meeting of the Electrochemical Society
- Pub Date:
- December 1993
- Bibcode:
- 1993ecs..meet...10K
- Keywords:
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- Diffusion;
- Dimers;
- Electric Batteries;
- Electrical Properties;
- Electrochemistry;
- Electrodes;
- Electrolytes;
- Electrolytic Cells;
- Lithium Chlorides;
- Separators;
- Solubility;
- Bromides;
- Cycles;
- Halides;
- Iron;
- Molten Salts;
- Potassium Bromides;
- Potentiometric Analysis;
- Sulfides;
- Electronics and Electrical Engineering