Batteries and electric insulators

Persons in charge: Odile Fichet

Some of the materials developed at the LPPI have been designed to solve certain issues regarding energy storage and conversion. This is why functional materials, such as ionic conductors, were evaluated as fuel cell membranes or for metal-air batteries and structural materials, made from polyimides and/or polysiloxanes, as electrical insulation materials. Tests on devices have made it possible to assess the advantages of using them in place of existing materials, but also their limitations. The synthesis is then reviewed and optimized.

Based on the morphology of Nafion®, the reference membrane for fuel cells, new IPNs were developed combining a network of fluorinated polymers with a protonic conductive polyelectrolytic network. The fluorinated polymer network restricts deformation of the membrane during operation and ensures its mechanical resistance, while, at the same time, the polyanion network allows protonic conduction through the membrane. These materials, depending on their composition, have a swelling rate in water of 22-59% by mass and a protonic conduction of 1-63mS/cm. Additionally, they are 10 times less permeable to oxygen and hydrogen than Nafion®. However, the performance of IPNs as a fuel cell membrane is still slightly lower than that of Nafion®.

In the same way, IPNs that combine a polycation with a neutral polymer protect air electrodes from carbonatation when positioned between the electrode and the electrolyte in an air-metal battery. While the unprotected air electrode only works for 60 hours in LiOH 5M in cycling when fed by untreated air, the same electrode, modified by a fluorinated polymer/PECH IPN, remains stable for more than 1550 hours in operation in the presence of LIOH 5M and more than 6000 hours in the presence of concentrated potash.