Page 301 - Battery Reference Book

26/4 Metal - air batteries
discharge cycle. A clamping mechanism on one side McGraw Edison supply 1100-3300A h versions of
of the battery is desirable to maintain proper pressure these batteries with voltages between 6 and 22.5 V.
on the cells once the anodes are inserted into the cells.
Such zinc-air batteries are capable of giving energy Dry electrolyte zinc-air cells
densities up to 220 W hkg, which is much higher than
for the magnesium-manganese dioxide systems. In dry electrolyte zinc-air cells the gelled electrolyte
thickened with cellulose derivatives is used. These
cells are spill-proof. The dry cell has a much greater
Button cells energy density output in terms of electrolyte cells.
Button cells with solid cathodes are designed as anode Much of the success of this type of cell is related to
limited, Le. 5- 10% more cathode capacity than anode the plastic bonded carbon cathode design.
capacity. The anode is amalgamated powdered or Hydrogen peroxide is produced by a secondary
gelled zinc and contains a gelling agent, and is housed energy wasting reaction in the cell. This reaction is
in a triclad metal (nickel-stainless steel-copper) top avoided by incorporating manganese dioxide into the
with the copper in direct contact with the zinc. The cathode which removes the hydrogen peroxide by the
anode is separated from the air cathode by a diffusion following cyclic reactions:
pad between the air cathode and an air hole at the base MnOz + H202 + 2H+ = Mn2+ + 2Hz0 + 02 (26.5 j
of the positive can.
A constructional diagram of the Berec zinc-air Mn2' + 2H20 = Mn (OHjz + 2Hf (26.6)
button cell is given in Figure 26.l(b).
McGraw Edison supply a range of Carbonaire Mn (OH12 + H20 = MnO2 + 2H20 (26.7)
zinc-air cells and batteries. These batteries use a car-
bon-zinc couple and a caustic potash and lime elec-
trolyte, and are activated by the addition of water. The 26.2 Metal-air secondary batteries
lime combines with, and thereby removes, the zinc
reaction products, thus extending the useful life of the See Chapter 12, Sections 12.1-12.3.
electrolyte. A rechargeable zinc battery with an e.m.f of 1.65 V
is being developed by AER Energy Resources Ltd,
Electric Fuel Ltd (Israel) and CGE Ltd (France).
McGraw Edison Carbonaire wet caustic potash-lime Electric vehicle applications of this battery are
zinc-air cells being considered.
In these wet electrolyte cells containing 5 M potassium Reported energy densities:
hydroxide, zincate ions (Zn (OH):-) diffuse away AER Energy Reserves Inc. (USA), 98 W h kg-'(C/S rate)
from the anode and migrate to a limed bed to pro-
duce calcium zincate. This has a low solubility in the Electric Fuels Ltd (Israel), 200 W h kg-'
electrolyte and releases hydroxyl ions into the bulk of
the electrolyte: CGE Ltd. (France), 90 W h kg-'
CGE report cyclic lives of 500 to over 1000 cycles
Ca (OH)2 + Zn (OH):- = CaZn (OH), + 20H- (26.4) depending on type and battery layout.
This process continues so long as oxygen is supplied to Matsushita Battery Industry Co. (Japan) and
the cathode and there is sufficient lime left to remove Swedish International Development Co. are devel-
oping rechargeable iron-air cells which achieve an
the zincate. When the lime is exhausted, the zinc
consumes the alkali, decreasing electrolyte alkalinity energy density of about 80 Whplcg-' at the Ci5 rate
and passivating the zinc. The performance of the cell and 200 charge-discharge cycles at 60% depth of
then starts to deteriorate. discharge; Westinghouse (US) and Siemens (Ger-
McGraw Edison supply a range of batteries for use many) are also working on the development of
in navigational aids, railway lamps, etc. The batter- iron - air batteries.
ies as supplied are contained in plastic bags to pre-
vent deterioration of the zinc anode during storage by 26.3 Aluminium-air secondary reserve
ingress of air and moisture. The batteries are activated batteries
simply by topping up with water. Individual cells can
be connected in series or in parallel with external con- To date the only supplier of this type of battery is
nections. Normally these batteries require no routine Alcon Aluminium Ltd. Applications have been limited
maintenance or inspection for the first year. Should the to the development of a telecommunications battery,
service period run well over a year, an annual visual although further applications are expected over the
inspection of battery solution levels is desirable. The next few years. Although some work has been done
transparent case permits the user to see when each on the development of an electric vehicle battery this
battery is ready for replacement. has not, so far, reached fruition.