Charge of the right brigade
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.
Current issues Although convenient, a normal battery wastes a lot of energy. The amount of energy required to make one is about 50 times greater than the energy it produces. The efficiency of a battery is measured in the amount of electricity it can hold per unit weight, that is, watt-hours per kilogram (WH/KG).
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.
Toxic power
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.