Page 250 - Handbook of Battery Materials

220 8 Metallic Negatives

The most suitable way to organize the different metallic negatives in groups
seems to be a combination of these three classifications, using one as the main
criterion and the others to create subdivisions. Such a system is demonstrated in
the following example:
• First parameter: (A) Element name (in alphabetical order)
• Second parameter: (B) Battery type;
– (AB1) primary;
–(AB11 ... AB1n) cathodes;
– (AB2) storage;
• Third parameter: (C) Method of preparation;
– (AB2C1) introduced in metallic form;
– (AB2C2) introduced as metal oxide or hydroxide;
– (AB2C3) introduced as other metal compound.
The paragraphs AB2C1–AB2C3 may be similarly subdivided by considering the
different cathode materials and thus defining a particular battery system.

8.3
Battery Anodes (‘Negatives’)

8.3.1
Aluminum (Al)

Aluminum is directly applied in its metallic form when it serves as battery anode,
and it contributes significantly to the success of these battery systems by its
−1
outstanding electrochemical equivalent of 2980 Ah kg .
Traditional battery concepts are in general single-use types (primary batteries).
The most developed systems belong to the ‘metal–air’-batteries using the reduction
of atmospheric oxygen as the cathode reaction, for example, (−) Al/KOH/O 2 (+) or
(−) Al/seawater/O 2 (+).
In some cases oxygen may be generated by decomposition of hydrogen per-
oxide [1].
Aluminum/air batteries with their high (theoretical) specific energy of 8.1
−1
kWh kg −1 of Al, energy density of 219 kWh L , and nearly unlimited access to
the cathode active material (sometimes these batteries are called ‘semi-fuel cells’),
found particular applications in the past and will be considered for electric vehicle
propulsion in the near future [2]. The theoretical open-circuit voltage (OCV) of
2.73 V is another argument for the choice of this battery system. A review of the
long history of aluminum as battery anode was given by Li [3].
The main discharge reactions are:
Anode: 4Al → 4Al 3+ + 12e − (8.2)
−
Cathode: 3O 2 + 6H 2 O + 12e → 12OH − (8.3)
Overall cell reaction: 4Al + 3O 2 + 6H 2 O → 4Al(OH ) (8.4)
3