Advanced Cell Technology for High Performance Li-Al/FeS2 Secondary Batteries

In early 1993, Argonne National Laboratory (ANL) initiated a major R&D effort to develop bipolar Li-Al/LiCl-LiBr-KBr/FeS2 batteries for electric vehicles, targeting the USABC Long-Term Goals. Significant advancements were achieved in the areas of (i) chemical purity, (ii) electrode and electrolyte additives, and (iii) peripheral seals. It was determined that key chemical constituents contained undesirable impurities. ANL developed new chemical processes for preparing Li2S, FeS, and CoS2 that were >98.5% pure. We evaluated a large variety of electrode and electrolyte additives for reducing cell area specific impedance (ASI). Candidate positive electrode additives offered increased electronic conductivity, enhanced reaction kinetics, and/or improved porous electrode morphology. CoS2, CuFeS2, MgO, and graphite (fibers) were identified as the most beneficial impedance-reducing positive electrode additives. Although electronically conductive carbon and graphite additives produced measurable ASI reductions in the negative electrode, they degraded its structural integrity and were deemed impractical. Lil and LiF were identified as beneficial electrolyte additives, that enhance positive electrode kinetics. ANL refined its baseline metal/ceramic peripheral seal and increased its strength by a factor of three (achieving a safety factor >10). In parallel, ANL developed a high-strength advanced metal/ceramic seal that offers appreciable cost reductions.