IN A NUTSHELL: Metal-air battery technology is unique because the cathode active material is not stored in the battery, but simply extracted from ambient air and used as needed. Organic solvents are used as electrolytes, and a membrane with low organic permeability is required to keep them from migrating away over an extended period of time. At the same time, high oxygen permeability of the membrane is required to ensure a steady supply of this reactant from ambient air to the cathode. The lithium-air battery is seen by many in the field as the ultimate battery (because of its extremely high specific energy density), so improving it is something that could affect our very way of life. For an example, let’s look at mobile electronics. If we could improve their batteries’ longevity and power, wouldn’t that be something manufacturers and consumers might be interested in? Lithium-air batteries show great promise in terms of energy and power density. Their market potential is in the billions of dollars, and the membrane that we’re developing will help make the lithium-air battery a marketable success.

THE PROBLEM: Early work on lithium-air batteries focused on aqueous electrolyte systems, and these suffered from a number of problems including self-discharge, excessive parasitic corrosion of the lithium anode, and safety concerns due to formation of gaseous hydrogen. The lithium-air battery with a non-aqueous electrolyte was introduced to circumvent these problems. However, the limiting factor for such a system is a suitable membrane that will satisfy all requirements (high oxygen permeabilty, low moisture permeability, low electrolyte permeability and resistance to organic electrolytes).

THE STATE OF TECHNOLOGY: Current lithium-air battery constructions use a double sided cathode, consisting of a carbon sheet impregnated with a slurry of carbon, binder and catalyst. Two of these impregnated mats are laminated around a current collector, and a microporous PTFE layer is added to the side exposed to the environment. However, such a cathode design does not allow sufficient oxygen from the air to diffuse into the battery cathode.

OUR NOVELTY: Our effort focuses on developing a better membrane for use in lithium-air batteries. Our approach is based on unique hyperbranched polymer technology, pairing high oxygen permeability with strong chemical resistance, as well as low moisture permeability. The hyperbranched polymer approach also provides the ability to tune in appropriate levels of crosslink density to optimize the required mechanical properties of the membrane.

Additional applications for these membrane materials include:

1. Membranes for lithium ion batteries
2. Protection from chemical and biological agents in oxygen permeable windows for temporary shelter (tents, etc.)
3. Protective garments for military as well as industrial applications. Such garments will provide protection against toxic organic chemicals while allowing air to pass through
4. High flux gas separation membranes for industrial applications
5. Fuel cell membranes