Technology Transfer / Zinc-Air Batteries

Technology Transfer

Taking advantage of the know how generated at PSI during a long lasting research and development project, the rechargeable zinc-air battery technology has been successfully transferred to ZOXY AG a German battery manufacturer.

This technology transfer project was completed in 2003. It was just one of the many PSI technology transfer projects.

Last state of PSI's zinc-air battery technology

Electrically rechargeable zinc-air batteries are not yet available commercially at present. As developed, the system has a high specific energy of 100 to 150 Wh/kg, consists of inexpensive components, and promises low environmental impact. Research and development work performed over the last seven years in the PSI Laboratory for Electrochemistry, partly in collaboration with Swiss and foreign partners from institutes and industry, culminated in the demonstration of a multicell electrically rechargeable zinc-air battery exhibiting a specific energy higher than 100 Wh/kg.

It is the special feature of the zinc-air system that only the active component of the negative electrode (zinc) needs to be stored in the battery, while the reagent of the positive electrode (air oxygen) during discharge is drawn from the air, and during charging released back into the air. This is the basis for the system's high specific energy - distinctly higher than that of conventional battery systems (Lead-acid, Ni/Cd, Ni/MeH). For many applications, and particularly so for electric traction, market introduction decisively depends on the cost per kWh and on the specific energy. In view of the low-cost battery components and of the fact that aqueous systems generally can be produced at lower cost than organic ones (such as used in lithium-ion batteries), it should certainly be possible to produce the zinc-air battery at a very favorable cost.
A major difficulty that had been encountered when building electrically rechargeable zinc-air batteries was the stability of the zinc electrodes and of the porous, carbon-based oxygen-diffusion electrodes. At the latter, oxygen is evolved during battery charging, and consumed during battery discharge. The PSI research team succeeded in producing large-surface-area electrodes of both types and assembling them in a modular fashion to a 12-Volt, 20-Ampere-hour demonstration battery. Figure 1 shows the components in the configuration entering the battery. Figure 2 shows the 20-Ampere-hour single cells assembled (without housing) to the final 12-Volt battery.

Significant progress has been made in the development of durable zinc electrodes and bifunctional air electrodes. A cycle life of 600 cycles was measured at our laboratory for bifunctional air electrodes containing optimised carbon substrate and metal-oxide catalyst (Figure 3).

Innovative features of the project

• The electrically rechargeable zinc-air battery is a new European development.
• The electrically rechargeable system constitutes an improvement and extension of the mechanically rechargeable battery, which will facilitate broad consumer market entry of the battery.
  
• The technical development has advanced to the point that knowledge can efficiently be transferred to an industrial-scale production process.
  
• The system has features of economic and of ecologic interest.

The zinc-air battery is distinguished for its high energy storage density and low cost. The innovation contributed by PSI research was that of demonstrating electrical rechargeability. This was the reason for developing full-scale battery components at PSI.

Consumer benefit and practical realization

Great efforts are made worldwide to develop battery systems having high specific energy. The demand for such systems has risen dramatically in recent times, particularly in connection with electric traction, the storage of electrical energy from photovoltaic installations and the operation of portable devices. The particular consumer benefits deriving from high-energy zinc-air batteries are related to their price and ecology. The specific energy of zinc-air batteries is practically twice that of the Ni/Cd storage batteries, and the problem of memory effects exhibited by the latter is practically inexistent in the former. Zinc recycling is feasible on a large scale. Environmental impacts are substantially reduced when zinc and air are used instead of lead, cadmium, and other heavy metals. Relative to the lithium-ion batteries, which in their specific energy are comparable with zinc-air batteries, the latter have the advantage of lower manufacturing cost, estimated to be about 150 CHF/kWh, which is the same order of magnitude as for lead-acid batteries. Low-cost, ecological batteries are indispensable for the commercialisation of electric vehicles.

A potential market for this technology is seen in electric scooters, mobile back-up power for leisure activities, and mobile GPS (Global Positioning Systems). Two important industrial countries, Italy and Taiwan, already passed legislation requiring the introduction of electrically operated two-wheelers (electric scooters) starting in 2000. In the classical scooter nation, Italy, according to a market analysis by LAFET performed at the end of 1998, the market should develop from 12,500 such vehicles in 2000 to as many as 100,000 in 2004. Electric scooters available today are equipped with lead-acid batteries. Refitting with zinc-air batteries would extend the operating range of the scooters by a factor of three to four when maintaining the present weight.

Advantages and disadvantages relative to known technologies

Advantages:

• High specific energy (100 to 150 Wh/kg).
• Low-cost energy vector (CHF 1.60 for 1 kg of zinc) and low-cost battery components.
• The energy vector can be recycled; the battery components have low environmental impact.
• New applications should develop from the feature of rechargeability.

Disadvantages:

• The need to further extend the operating lifetime
• The common time requirements for battery charging.

Prizes and distinctions earned by the team

• Innovation prize of Technology Base Switzerland 1999.
• Venture 2000, Companies for Tomorrow: Award for the business idea. Partners: PSI and chemTEK (Germany).
  

Acknowledgments

We thank the Swiss Federal Office of Energy, the Federal Office of Science and Education (Joule project: JOR3-CT98-0298; Partners: ZSW (D), KTH (S), ChemTek (D), Saft (F)), and the Project and Studies Fund of the Swiss Electric Industry for financial support of the work. Our thanks also go to the companies Electrona S.A., Boudry, und LARAG AG, Wil, Switzerland, for their technical support.

Recent Publications

Contact Point

For further information on this and other technology transfer projects contact Dr. Philipp Dietrich