As shown, charging is accomplished at a constant voltage in about two hours at 2.0 volts per cell. Both slower and faster charging is feasible. Discharging voltage varies with the power demand, in a manner similar to most battery systems. The voltage variation during discharge time, however, is shown to be relatively flat, until nearly full discharge is reached. This flat characteristic is an operational advantage since essentially the same power level is available throughout the discharge cycle-a feature due to the clean surface situation achieved with the circulating electrolyte.

ENERGY DENSITY VERSUS BATTERY SIZE

Present estimates of the energy density, i.e., watt-hours per pound of battery, are shown in Figure 4 for the operational design of the battery. As indicated, a size effect exists for the system, due primarily to the accessory subsystems, which do not scale in proportion to the cell stack. Thus, in large sized batteries over approximately 200 cells of the present cell size, which would be typical for a delivery van, energy densities of over 60 watt-hours per pound appear to be practical based on design studies for operational batteries. This means that the battery would be able to provide a range of 80-120 miles for a delivery vehicle with reasonable battery weights.

ZINC-AIR BATTERY ENERGY DENSITY

AS A FUNCTION OF SIZE

You might be interested in the order of magnitude of the monies which have been invested in order to bring the zinc-air battery development to this succesful stage. The joint funding between the Edison Electric Institute and our own company through 1968 will amount to approximately $3 million, of which about half has already been spent to date, I am pleased to report that we have achieved and are continuing to achieve substantial technical results from this program. The history of the program is shown in Figure 5. Our early studies and experiments started in 1960. Early experimentation with small single cells determined air electrode and zinc deposition characteristics for rechargeable battery operation. Scaling up to more practical cell sizes in 1963 and 1964 led to the design and fabrication of the first "breadboard size" cell stack experiments in 1964 and 1965. This model (shown in Figure 6) was 1 kwh capacity.

Following cell stack experiments, two types of experimental zinc-air battery prototypes with design energy storage capacities of 7 and 14 kilowatt hours, respectively, were built and successfully operated during 1966 at the General Atomic laboratories. These experimental prototypes contain all the elements of a complete battery system, including pump, reservoir, air supply, and zinc oxide separator, as well as the cell bank. The 14 kwh prototype is a smaller capacity unit than is envisioned for economical operational systems, but is a convenient size for experimental purposes. It is also bulkier and heavier than an operational version would be because it is configured for ready modification of plumbing and components. The complete prototype, including all hardware, electrolyte,and reactants, weighs a little under 300 lbs.

The program in 1967 and 1968 will continue the testing of single cells, cellstacks, prototypes, and support a broad series of advanced cell experiments, battery design studies, and vehicle system requirement definitions. From this, a "full size" prototype, suitable for installation is an initial test vehicle, will be designed. This prototype will be constructed in 1968 and will be more nearly representative of an "operational" battery suitable for fleet applications in delivery vans, industrial trucks, and buses.

The period of time between 1968 and the early 1970's is to be spent in extensive testing and refinement of the system to try to achieve trouble-free operation. It is anticipated that during this period, small fleets of vehicles will be run in several locations to determine the suitability of the batteries to such tasks as buses and delivery vans.

We are expecting commercial availability of these zinc-air batteries in the early 1970's. We think the first applications will be in fleet-type operations, such as urban delivery vans and transit school buses. Application to private vehicles would follow that.

I would like to say that we are enthusiastic about our progress of the zincair battery to date and are confident of the contributions it will make to electrical propulsion and the reduction of air contamination in the years to come. Thank you for the opportunity to testify on this development before your committee today.

STATEMENT OF DR. STEWART M. CHODOSH, BATTERY MANAGER, LEESONA MOOS LABORATORIES DIVISION OF LEESONA CORP., GREAT NECK, N.Y.

Mr. CHODOSH. I think the timing has been excellent because we have heard some comments in reference to the small company. We feel that we can act as a representative of this area of industry.

Mr. Chairman and members of the committee, my name is Stewart Chodosh. I am battery manager of the Leesona Moos Laboratories Division of Leesona Corp. The laboratories are located in Great Neck, N.Y. Since 1956, Leesona has carried out extensive research and development in fuel cells and other electrochemical power devices. It was our research, for example, that was instrumental in the development by United Aircraft Corp. of the hydrogen-oxygen fuel cell which will be employed in the Apollo spacecraft. More recently we have developed and are delivering mechanically rechargeable high-performance zincair batteries to the U.S. Army Electronic Command and the U.S. Marine Corps I have this type of battery here and zinc-oxygen batteries for the National Aeronautics and Space Administration.

Although these batteries are not applicable for practical electric propulsion, they would be useful immediately for electric car testing and demonstration. In addition, we believe the work we are now carrying out on rechargeable batteries for industrial uses could lead to the development within 2 years of Leesona zinc-air batteries that would make the electric car feasible.

Previous electric vehicles have been limited by the capabilities of batteries employed for their propulsion. This has usually resulted in poor acceleration and low operating ranges. To overcome these drawbacks, it is clearly important to utilize the best available energy conversion technology. We must also keep in mind that the most urgent need for electric vehicles is in urban areas where pollution is at its worst. The primary goal therefore should be to fulfill the requirements of the present city driving patterns rather than the more severe requirements of high-speed, long-range travel. Nonetheless, we believe that the latter problem is also soluble and I will elaborate on this later.

FUEL CELLS

It has been speculated for many years that fuel cells would ultimately provide the power for electric cars. The major characteristic in support of this viewpoint is that the fuels for the fuel cell are contained outside the device itself so that the operating range is, in principle. virtually unlimited and restricted only by the capacity of the fuel tanks. Since, in addition, fuel cells are generally highly efficient devices, very competitive operating ranges would be expected. Unfortunately, however, in practice the present complexity, cost, and size of fuel cells able to operate on practical fuels appears to preclude their use, at least in the immediate future.

BATTERIES

Turning now to batteries. Evaluation of any battery as a potential power source for electric vehicles must be made, I believe, in the context of the triple requirement of performance, cost, and safety. Although some compromises are possible, there will be minimum standards of each of these factors which any prospective battery must reach. As an example, the lead-acid battery though relatively economically feasible and certainly perfectly safe, is unable to meet the high performance necessary to give satisfactory mileage. On the other hand, while some of the other advanced battery systems offer the promise of the necessary high performance and possibly the prospect of acceptable cost levels, one must have definite reservations about their ultimate safety. With the performance, cost, and safety requirement in mind, therefore, Leesona Corp. considers that the best prospects for practical electric vehicle propulsion can be obtained with zinc-air batteries.

ZINC-AIR BATTERIES

I would like at this point to describe the Leesona zinc-air battery. This device is a hybrid battery/fuel cell. One active half of this battery. namely the zinc, is gradually consumed as energy is withdrawn. The

surrounding air, or more exactly the oxygen in it, is the other active half of the battery and is consumed at catalytic electrodes. The air, of course, is free, giving good economics, and has no weight, giving good performance. The charts I am submitting show both the construction of our prospective rechargeable zinc-air batteries and the performance we project will be available from them.

Figure 1 shows a cross section of a typical single cell. Figure 2 is a cutaway drawing of our proposed complete rechargeable zinc-air battery which appears suitable for use in an electric car. Figure 3 shows how the voltage of our existing cells varies as the current drawn by the motor increases. This is important since it indicates that the battery will handle the acceleration required in normal driving. In figure 4, the energy density which is the factor determining operating range or mileage has been drawn for a series of commercially available batteries and our projected internal and external rechargeable zinc-air batteries, with the zinc-air giving the best performance by far. The source of all curves except the Leesona batteries is a paper that was presented at the U.S. Army Electronic Command 18th Power Sources Conference. We have calculated, based on the performance levels of our existing zinc

FIGURE 1. CROSS SECTION OF A SINGLE ZINC/AIR CELL