As petroleum fuels continue to dwindle and alternate energy sources continue to develop, the demand for economic, high performance batteries will continue to grow. The applications for these batteries will be varied and include utility load leveling, military and commercial standby power, and energy storage for electric vehicles. Although the present state-of-art batteries and those presently under development (such as the bipolar lead-acid) should meet most of the demands of these applications, one application will be sorely lacking. An energy storage system for a "first" or only electric vehicle family is not under development. The characteristics of such a system are a large energy density and a rapid, easily accomplished recharge. These qualities will enable the electric vehicle to free itself from its range limitations and compete directly with the internal combustion engine (ICE) powered vehicle. Thus far, no battery design has overcome this range limitation economically.
One design, the aluminum-air battery, can provide the range but is uneconomical and so physically voluminous that it is impractical for a vehicle. On the other hand, the lead-acid design is economical but suffers from a low energy density and impractical fast recharges due to the high electrical power levels needed. Other battery types are unacceptable since they suffer from poor economics or the high power levels during fast recharge or both.
The iron-air battery has the potential to overcome both the economic and recharge problems. The iron-air battery, as it is presently configured, is constructed of materials found readily, easily, and cheaply in the U.S. In particular, the air electrode design has been constrained to be economic. It does not use platinum as do most air electrodes (such as that found in the aluminum-air battery), but uses only small amounts of silver. The battery has a relatively high energy density (.about.100 Wh/kg), moderate power density (.about.90 Wh/kg) when compared to other near-term and advanced batteries. Its cells have achieved 300 cycles at 80% DOD. However, this battery has fairly low electrical charge efficiency (55%) and, as in all electrically recharged batteries, a long recharge time.
In order to satisfy the need for a single family vehicle, the vehicle must be capable of both short distance and long distance uses. Iron-air batteries can provide energy for local driving and for moderate highway trips up to 150 miles. To travel farther, one must perform a slow electrical recharge of about eight hours, a rapid one hour electrical recharge or replace the iron plates. The slow electrical charge is the standard procedure utilized to recharge iron-air batteries but results in unacceptably slow average trip speed. The rapid one hour electrical recharge requires enormous electrical power levels. Replacement of the plates has not been demonstrated and would require about 300 kg of iron to be exchanged in the battery and stored. This would require a vast network of stations storing the plates and it is not a practical system.