Lightweight Electric/Hybrid Vehicle Design

38 Lightweight Electric/Hybrid Vehicle Design
2.3.3 NEW-CONCEPT ALUMINIUM BATTERY
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 semiorganic
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 × 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 cm 3
Anion/cation reactant solution 1199 g 820 cm 3
Theoretical maximum energy and current capacity
2100 Wh/litre 1448 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 × 62 mm) against those of a 1 litre Partanen cell.