LITHIUM BATTERY ENGINEERING Limited Liability Company — Department of Defense SBIR Phase II: A15-101

Description

Warfare is becoming more dependent on technology; smart munitions require batteries that have to work over a wide temperature range and must be ready on demand. Lithium ion batteries, while providing rechargeability and higher energy density lack low temperature performance and fast charging. Commercial cells have little or no performance below 0oC and even military cells with low temperature electrolytes barely function at -40oC. None can be charged safely below 0oC or at high rate. Phase I examined transport behavior of several new ionic liquids, silicon and carbon anodes and several separators. The neat liquids did cycle well for the viscosity, but were rate limited. These ionic liquids do wet the electrodes and separator. Blending with EC/EMC, EMC and PC showed excellent promise; some of the blends even yielded an increased cell capacity over a standard ARMY -40oC electrolyte indicating a high ion transport rate. Formulations gave better than 70% capacity retention at 0oC. Phase I compared silicon to carbon anodes which performed better at low temperatures plus providing increased energy. Silicon allows using propylene carbonate with a flatter viscosity profile. Anode pretreatment with PEDOT was beneficial. Pulse charging was shown to be beneficial but high voltage charging was not.