One step closer to the battery powered car

Will present battery technology replace the IC engine in future generations of automobiles? Contributing editor Michael Sibley takes a look

The dominance of the IC engine will undoubtedly continue until the twin pressures of fuel cost/availability and environmental concerns catch up with it. But EVs, though not yet coming up on the rails, are at last within sight, as a still rare but no longer only a curious spectacle.

The advantages of cost, acceleration, range and ease of refuelling all still lie with the petrol and diesel engined car. Of these four factors, acceleration is the least concern, as the best battery driven cars are quite lively and compete well with the average family small car.

Range and ease of refuelling are related factors. The range of a typical IC engine car is presently around two to three times that of the best battery vehicles, but the difference is diminishing and the discrepancy is less important for the city or commuting user.

The huge and so far insurmounted problem is the cost factor, both capital cost and running cost. And it is cost, when the technology has matured, which is likely to govern if and when the EV takes over.

A battery driven EV consists of a battery to supply the energy, a motor, or motors, to transmit the energy to the wheels, and electronics to control the system. The limited number of elements in the system should ensure both a high reliability and low maintenance level.

The key to successful EVs lies in developing the battery to rival the IC engine in cost and energy density. Because EVs currently suffer a severe penalty on both counts, attention is focused on reducing the cost, size and weight of the battery. Estimates have shown that batteries cost around three times that of an IC engine drive system.

There are six principal types of batteries vying for leadership to provide the power for EVs. They are the lead acid, two alkaline technologies (nickel-cadmium and nickel-metal hydride), the sodium nickel chloride, lithium-ion and lithium polymer types. The first two are in current production, the second two exist but cannot yet be manufactured economically, and the third two are just laboratory devices.

The familiar lead-acid or `milk-float’ battery is established as a heavy, bulky, but reliable system. It is also relatively cheap to produce compared with any of the other five types. General Motors’ two seater EV1 contains 26 lead acid batteries weighing 535kg (1175lbs).

Chrysler and Ford have both used lead acid for their first generation EVs; Ford after an expensive excursion into sodium sulphur technology which it has now abandoned. The lead acid type called Electrosource, which uses packs of 600 spiral-wound units developed for power tools and provides 100kW output, is being examined by both companies.

Three types of battery are being developed by Saft, the Alcatel-Alsthom subsidiary, which invests Ffr100 million annually on research into the technology.

Production of nickel-cadmium (Ni-Cd) batteries by Saft is running now at mass production rates of 3000units/annum with the capability of being raised very quickly to 15,000units annually. These are now being fitted to a range of EVs.

But Toyota’s new RAV4 EV has broken away from lead acid by using a nickel-metal hydride battery, combined with a permanent magnet motor, to increase its range.

Equipped with regenerative braking, a range of 200km is claimed for the vehicle. Charging the battery takes about ten hours. However, a fast charge can replenish 50% of the battery capacity in 30 minutes.

Of the several types available, the Li-Ion design offers the best mass/energy figure of some 140Wh/kg compared to 50Wh/kg for the Ni-Cd type with the Ni-MH type somewhere in between. Unfortunately, the costs are in inverse proportion, which is why most current EVs use the more established Ni-Cd. This could be set to change in the next few years since the Japanese are now involved in building the Li-Ion type.

The range of the three types is, predictably, in proportion to the mass/energy figures, going from 128km for the Ni-Cd to a claimed 200km for the more exotic Li-Ion, depending on the weight and size of vehicle they are driving. Limited range used to be considered a major drawback, but for the small commuting city car and delivery vans which will be the entry point for EVs, useful ranges can now be obtained and are already on offer. Their acceptance will be fuelled by the use of rapid charging techniques.

Maximum speeds and acceleration show little problem for the types of vehicle envisaged. Weight is a reducing problem, but at 360kg, a Ni-Cd battery constitutes a disproportionate weight for a small city car.

Batteries for EVs have fewer similarities with the familiar car battery with two terminals connecting six cells. The package consists of a case holding the modules and a cooling system. In batteries using the Ni-MH and Li-Ion technology, it includes an electronic management system for cell charging and discharging which also acts as an interface with the vehicle’s electronics.

Saft’s Ni-Cd batteries, in its STM series, are currently being fitted to the Citroen AX, Peugeot 106 and Renault’s Clio and Express electric versions of these models. PSA and Renault have been partners in the development. A range of 90km (60miles) is claimed making them suitable for city and second car use.

In a second version, Saft’s STH-STX Ni-Cd battery is designed for hybrid vehicles which use a combination of a powerful battery and a small IC engine. Cars built with these hybrid system are designed for a longer range than just a city car. The company also manufactures Ni-MH batteries on demand which include control electronics for cell-balancing.

A typical battery for an EV is a precision product comprising 3000 plates, none of which can tolerate a single defect or the whole unit is rendered useless. Production stages include coating, drying, sintering, spiralling, impregnation and welding. Cost reduction which will be essential for the future of electric vehicles lies in automating this complex process.

In a joint development between Nissan and Sony, a Li-Ion battery is planned for a new Nissan electric vehicle for California in 1998. The vehicle will seat four adults and will have a range of around 190km (120miles) with road performance claimed to be similar to IC engine vehicles.

In the UK, a battery dubbed the Zebra (Zero Emission Research Activity) also uses sodium-nickel chloride. It is claimed to have four times the storage capacity of lead acid for the same weight. The raw material in the Zebra electrodes is nickel and sodium chloride separated by a ceramic electrolyte. Charging combines the nickel and sodium chloride to form sodium and nickel chloride. Discharging reverses the reaction.

The core of the cell is an ionically conducting beta alumina tube and a thermocompression bond seal. The battery operates at an internal temperature of up to 350 degreesC and needs external air or liquid cooling. Each battery is a closed system with its own cooling and control unit.

A 200kg Zebra battery delivers 30kW, the figure looked for by EV carmakers. Both BMW and Mercedes-Benz have used Zebras for early trials and a 365 cell unit has been tested in a Mercedes 190 series. Several trials will be conducted this year with Zebra powered buses, both direct drive and in hybrid form.

Carmakers and the battery industry are waiting for a lead from governments before they will redouble their efforts to provide a viable electric solution. Nevertheless, battery costs and weights will have to be cut drastically and their makers will have to demonstrate that they are safe, reliable and durable before the electric revolution takes off.

{{Toyota (GB) LtdTel: Redhill (01737) 768585Enter 560

Panasonic (UK)Tel: Bracknell (01344) 862444Enter 561

Beta R & DTel: Derby (01332) 770500Enter 562

Mercedes BenzTel: Milton Keynes (01908) 245000Enter 563

Saft NifeTel: 0181-979 7755Enter 564

ChryslerTel: +1 (810) 512 2694Enter 565

Ford Motor CompanyTel: Brentwood (01277) 253000Enter 566

PivcoTel: +47 22 25 20 50Enter 567

Peugeot Talbot Motor CompanyTel: Coventry (01203) 694444Enter 568

Renault UKTel: Swindon (01793) 486001Enter 569}}

Figure 1: Unlike other EVs that run on conventional lead acid batteries, the RAV4 EV is powered by a NiH battery and permanent magnet motor

Figure 2: Comparing the technologies: Saft produces a range of batteries including Ni-Cd, Ni-MH and Li-Ion

Figure 3: Saft’s vision of a future city EV

Figure 4: Each Zebra battery comprises individual cells. The chemical reaction in the Zebra battery converts common salt and nickel to nickel chloride and sodium during the charging process. As it is discharged, the reaction is reversed

{{SAFT SOLUTIONS AND THEIR PERFORMANCES Ni-Cd Ni-MH Li-Ion

Battery weight (kg) 360 260 180Mass energy (Wh/kg) 50 70 140Energy (kWh) 18 18.2 25Range (km) 128 145 205Maximum speed (km/h) 95 110 120}}