38 Lightweight Electric Hybrid Vehicle Design 233 Newconcept Aluminium Ba Ttery

The cell invented by Rainer Partanen, Fig. 2.8, is an attempt to defeat the disadvantages of the aluminium-air cell. It is a secondary battery which uses coated aluminium for the anode and pure aluminium for the cathode. The electrolyte is a mixture of two elements: (a) an anion/ cation solution currently consisting in proportion of 68 g of 25% ammonia water mixed with 208 g of aluminium hydroxide, and made up with water to give 1 litre of solution; (b) a semi-organic additive consisting of metal amines.

The exact formulation of the additive is a commercial secret. The inventor claims that this electrolyte achieves a large increase in charge carrier mobility and this results in figures of up to 1246 Wh/kg and 2100 Wh/litre, which have been achieved in many prototype cells that have been constructed. The figures relate to active materials, without casing. It is suggested that the technology is suitable for the construction of plate (wet cell) and foil (sealed) cells, with no limitations on capacity. The test cells have achieved a life of up to 3000 cycles, the main degradation mechanism being corrosion of the coating on the anode during recharging. One remaining hurdle to be overcome is the identification of a better coating material to reduce the corrosion.

The battery has some unusual characteristics in that it operates over a very wide temperature range, -40 to +70° C. This is in stark contrast to most batteries whose low temperature/high temperature performance is poor. The cell voltage is a nominal 1.5 V. Some interesting consequences arise if one assumes that the claims are true. The most significant is packaging. If we take the D cell which is 32 mm diameter x 58 mm long, as used by Panasonic/Toyota in the PRIUS battery pack, a battery with 150 g active mass stores 6.8 Ah and has a peak discharge current of around 100 amps. If we build a D Cell at a value of 1246 Wh/kg, this leads to a figure of 150 Ah. Polaron understand that very high levels of discharge current are possible - the inventor claims up to 20 times more power than existing cells in the market - but finding methods of supporting these currents in such a small space is a major challenge to achieve low terminal resistance, lead-outs and sealing, Fig. 2.9. It is claimed that the new technology uses environmentally safe materials which are fully recyclable.

Other developments which lend support to this invention9 are the emergence of ultracapacitors and electrolytic capacitors, both using aluminium electrodes with biological

Leclanch

Alkaline

Lead-acid

Ni-Cad

Ni-Mh

Lithium-ion

Aluminium

Amp. hrs (20)

4.5

18

2.5

4.0

6.5

18

150 (75 Dem)

Cell voltage

1.5

1.5

2.0

1.2

1.2

3.6

1.5

Max C rate

2C

2C

40C

25C

11C

40C

3C

AH/25° C

Not possible

0.5

3.0

5.0

14

Not possible at

present

IR limited 2

Package IR limits

current to 500 A

Aluminium metal in anode/cathode 486 g 180 cm3

Anion/cation reactant solution 1199 g 820 cm3

Aluminium metal in anode/cathode 486 g 180 cm3

Anion/cation reactant solution 1199 g 820 cm3

Theoretical maximum energy and current capacity

2100 Wh/litre 1 448 Ah/litre

1246 Wh/kg 859 Ah/kg

Practical cells in a package should achieve 70-80% of the above values when package mass is included.

Fig. 2.8 Characteristics of D cell (32 X 62 mm) against those of a 1 litre Partanen cell.

electrolytes. Very significantly, ultracapacitors operate well at low temperatures. In Russia 24 V modules, 150 mm diameter x 600 mm long store 20 000 joules and are used for starting diesel engines at -40° C.

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