Researchers have developed a new, non-aqueous electrolyte system for lithium-ion batteries that is chemically and electrochemically stable with respect to the anode, cathode and separator materials. The system has excellent energy capacity, capacity retention, and maintains stability and safety at extended temperature ranges without sacrificing performance. The invention is based upon an available lithium salt, lithium hexafluorophosphate (LiPF6), dissolved in a solvent system consisting of a mixture of available lactams and esters. The ARL electrolyte is comparable in cost to existing formulations and does not require changes to existing state of the art manufacturing processes for lithium-ion batteries. The patented electrolyte system is intended for rechargeable energy storage devices comprised of a carbonaceous anode and is compatible with a wide variety of cathode materials.
The ARL invention provides improved battery cycling at very low temperatures, where standard carbonate electrolytes would shut down or function so poorly as to produce only a tiny fraction of rated capacity. In addition, the electrolyte offers performance improvements at higher temperatures, with tests demonstrating insignificant capacity loss and excellent cycling stability in a graphite/lithiated transition metal cell at 60º C. The ARL electrolyte system is compatible with cells operating in the range of 3.7 V to 4.2 V, and likely could reach to 3.5 V. Applicability extends to any electrochemical storage device based on non-aqueous electrolytes, including ultra-capacitors and hybrid capacitors.