Polymeric solid electrolytes
There is great demand for the development of polymer electrolytes that can be used in lithium batteries in automobile manufacturing. Solid polymer electrolytes have to be developed that have an ionic conductivity greater than 10-5 S/cm in a temperature range of -20 to +60°C. In addition they have to remain mechanically, thermally and electrochemically stable throughout this temperature range. The high conductivity in such systems is based on the considerable amount of organic solution in the gel electrolytes. This creates a major problem in terms of electrochemical stability and their ability to be processed into separators. For safety reasons the gel electrolytes that have so far been developed cannot be used for lithium batteries in the automotive industry. Conventional solid polymer electrolytes suffer from weak conductivity however they are simple in terms of production, robustness and safety. Thus Fraunhofer IAP is developing new, stable solid polymer electrolytes with better performance that can be used in lithium polymer batteries. Work is focusing on the safety aspects and temperature stability of the batteries.
A new synthesis concept for producing solid polymer electrolytes has been developed. New blend components, like a polymerization-capable matrix and new cross-linkable ionic liquids, were synthesized to achieve this. A conducting salt component was added and the blend systems were crosslinked as a film. Their lithium conductivity was investigated using impedance spectroscopy. The blend systems were characterized in terms of their thermo-mechanical stability and processability.