LIKE most technological discoveries and their innovated incarnations, power-supplying batteries are a necessary evil. While
modern life cannot be envisaged without them, the environmental toll they take is fearsome. Hence, scientists are hot in
pursuit of an environmentally benign cell. Researchers looking for new dry batteries, are working on finding chemical
reactions that employ cheap, light-weight materials, which can
be made in large numbers and results in a reliable as well as
environment friendly product. And the news is that lithium,
the lightest metal known, is providing a weighty solution.
Heavy demands have been made on the battery being
developed. Its unique two-way system is intended to make it
more efficient: the charge reaction should store electricity,
while discharge reaction should make power available to the
consumer. The battery should run at normal temperatures,
and would be quickly rechargeable -
without hazardous gases being emitted. High longevity has to be achieved
by using material which will not break
down even after 300-400 charge-discharge cycles. And finally, it should not
damage the environment when disposed off and buried in landfills.
In 1800, Alexander Volta produced
the first battery called the voltaic cell,
the forerunner of all modern batteries.
(The common usage of the word battery is a bit of a misnomer, rooted in
the fact that some systems of stored
power supply - such as those used in
car - are, in fact, batteries (groups) of
single cells.) Electric current is produced in a battery cell by the reaction
of two electrodes with an electrolyte.
Each electrode is connected to one of
the cell's metal terminals.
A major improvement on the earlier versions was made in 1866 by a
French engineer, George Leclanche,
which forms the basis of today's zinc
carbon dry batteries. In the 1860's
another Frenchman, Plante, innovated
on the battery to make it rechargeable.
This eventually became the immediate
forerunner of today's rechargeable
batteries.
Dry batteries are of two main 3
types: primary and secondary. In a primary battery the electrochemical reaction
is unidirectional. But in a secondary system, the electro-chemical reaction is reversible, so that the battery can be
recharged by using an external electrical supply to reverse the
flow of current. The cylindrical, single-cell battery used in a
torch is called "dry" because the electrolyte contains no liquid
chemical, and needs no refilling. The metal casing of a zinc-
carbon battery is a zinc container that forms one electrode. It
holds a mixture of ammonium chloride, which is the electrolyte, and manganese dioxide which in effect is the second
electrode.
Zinc-carbon batteries, for decades the workhorse for battery-operated gadgets, are steadily losing out to the zinc-alkaline batteries. In this battery the alkaline electrolyte is mixed with powdered zinc. A porous sleeve separates the mixture from a manganese- dioxide lining. A metal 'nail' collects electric current from the zinc and takes it to the negative terminal. In recent years, the capacity of alkaline batteries has been improved by more than 30 per cent.
BPL, a well known player in the surprisingly diverse fields of entertainment and medical electronics, is setting up a Rs 500-crore battery manufacturing plant near Bangalore in collaboration with Sanyo of Japan, another internationally known name in electronics. The plant will initially manufacture alkaline batteries, like the
imported Duracell and Wonder batteries available in the market today.
But the billions of zinc-carbon and
alkaline batteries used the world over
each year all end up in landfills. India
alone dumps about 1,500 million of
these in her landfills each year. And
almost all the elements used for producing these cells are extremely toxic
and, therefore, environmental tyrants.
Production of primary batteries, in
fact, can easily be done away with. There's little justification, especially because they are horribly
expensive to manufacture. Battery research today is, thus,
directed primarily at developing improved varieties of secondary batteries.
One type of secondary batteries, or rechargeable, as they
are also called, is made with nickel and cadmium. The nickel-
cadmium cell consists of a negative electrode of cadmium, a
positive electrode of nickel hydroxide and as the electrolyte, it
has an aqueous solution of potassium or sodium hydroxide.
Its nominal output is 1.2 volts. These cells are made in the
same sizes as zinc-carbon or alkaline batteries. They are less
efficient when compared to zinc-carbon batteries, and can
only hold 35 WH/kg but, the fact that they can be recharged
and reused makes them attractive for the consumer as well as
the environmentalist. As of today, nickel-cadmium batteries,
called Nicads, are the most widely used rechargeable batteries.
But they require cylindrical steel cans to contain the hazardous
liquid electrolyte - caustic soda or potash.
These rechargeables last a long time, but not for ever.
Environmentally speaking they are potential threats, and if
dumped carelessly, they may reach the seas and endanger
marine life. Cadmium -contaminated fish can
cause serious kidney malfunctions in people
who eat them. And as concerns with the health
and environmental impact of Nicads grow, there
are chances that they may come a cropper in the
near future.
The nickel metal hydride (MH) rechargeable
batteries work well but they constitute certain
rare and relatively scarce materials. These can
hold up to twice as much electricity as a Nicad,
but its self-discharge rate is twice as much. It is
more expensive than the Nicads. Also, they have
a slower power delivery speed than the Nicads,
and are thus unsuited for portable power supply,
because the batteries drain out rapidly. This is
the advantage the Nicads retain, despite being
more hazardous.
In 1958, W S Harris, working at the University of
California, Berkeley, USA, demonstrated the possibility of
using lithium and organic compounds (polymers) as likely
candidates in battery technology. Today, lithium occupies an
important place in battery technology.
Lithium batteries, with capacities
ranging from as low as a few milliwatt hours to a million WH, have now been
developed. The efficiency of lithium batteries is about 300 WH/hr. They are made
in both primary and secondary types.
They have a very long shelf-life, and the
discharge life is an estimated 10 to 20 years.
Two research teams in the us are
working on a Lithium-polymer battery,
the size of a credit card, that would run a
lap top computer, while the larger ones,
layered or rolled, would run electric cars.
Lithium-polymer batteries offer several
advantages. Lithium is the lightest metal
in the periodic table. The other components of these lithium-polymer batteries, like plastics and
hydrocarbons, are also generally light. The electrolyte used in
these lithium-polymer batteries is a solid, which means it cannot leak, corrode parts or give off hazardous gases.
Today, small lithium-polymer batteries are used in devices
like miniature hearing aids, but large sizes suitable for electric
cars are yet to be manufactured. The presently manufactured
small lithium polymer cells store about 140 WH/kg. Lithium
polymer watch batteries store 120 WH/kg.
One of the research teams believes that they can build a
375 kg battery of about a 181 litres volume that would give a
small electric car a range of 600 kilometres.The calculations
assume an energy efficiency of 125 watt hours per kilometer
which is much less than the batteries used in a two-seat electric
car made by General Motors of America. The life of Lithium
battery would be about 177,000 kilometers.
The long-term target is to make a battery that stores 400
WH/kg. This is several times better than lead-acid batteries. It
should cost no more than us $100 for each kilowatt-hour of
electricity stored. The lead-acid batteries cost around us $150-
200 every kilowatt-hour of capacity.
With the introduction of digital and analog quartz watches, new types of primary batteries were designed
and manufactured in large numbers. These measure up to the size of or smaller than a 50-paise
coin, and are called button cells. They use silver
and mercuric oxide as cathodes. However, mercury is a toxic metal, proven to be extremely hazardous to humans and animals when ingested or
inhaled. Today, lithium batteries are fast replacing the mercury ones.
Crompton Greaves was reportedly setting
up a lithium battery plant near Panaji, Goa.
The Rs 5-crore project was expected to be
commissioned by April, 1992. The general
opinion is that the government should not
permit the manufacture of Nicads in India.
Rather, only lithium battery production should
be encouraged.
Scientists working at the Central Electrochemical
Research Institute in Karaikudi, Tamil Nadu, have carried
out extensive research work on lithium batteries. It is
time they take up research to develop lithium polymer
batteries in India.
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