Develop safe, low-cost method of manufacturing rechargeable, high conductivity lithium batteries. Final report

The focus of much of this work is the rechargeable lithium battery, because of its high energy density, and the use of solid polymer electrolytes (SPE`s) for ease of fabrication and lightness of weight. The classical solid polymer electrolyte is based on the use of salts such as lithium triflate dissolved in poly(ethylene oxide) (PEO) or poly(propylene oxide). This specific polymer electrolyte has severe limitations. Poly(ethylene oxide) is a microcrystalline polymer at 25 C, and ion migration occurs only in the 20--30% of the material that is amorphous. Useable conductivities (10{sup {minus}5} S/cm) can be achieved only when the material is heated above 80 C. Two approaches to generate higher electrolyte conductivities at ambient temperatures are being developed. In the first, organic solvents are added to the polymer to plasticize it and dissolve the microcrystallites. This increases the conductivity but raises the possibility of fires if the battery casing ruptures during high charge or discharge conditions or when the device is punctured by impact. The alternative is to design new polymers that are good solid electrolyte media but which are completely amorphous and have low glass transition temperatures. Such a polymer is MEEP (poly[bis(methoxyethoxy)phosphazene]), first synthesized in the author`s laboratories. The main objective was to develop crosslinking methods for MEEP which could be used on a mass production scale to produce thin film rechargeable lithium batteries. A further objective was to assemble working energy storage devices to investigate the feasibility that this system could be developed commercially