Solid energy

AN AMERICAN company, UltralifeBatteries, has launched the world's firstlightweight rechargeable battery madeentirely from solid materials. The battery, launched a few weeks ago, can berecharged more than 1,000 times withonly a tiny loss of capacity. In comparison, conventional batteries can berecharged a maximum of 200 times(New Scientist, Vol 146, No 197 1).

Being completely solid, Ultralifebatteries can be shaped to suit any sizeto power portable equipment such aslaptop computers, camcorders andmobile telephones, or if currentresearch efforts succeed, even automobiles, according to Colin Newnham, thevice-president of rechargeable productdevelopment at Ultralife. The batteriescan be made thinner than a millimetreand with as large an area as that of anA4 sheet of paper.

Unlike conventional nickel-cadmium, rechargeable batteries, which contain liquid electrolytes, Ultralife batteries contain lightweight lithium-basedelectrodes and a solid polymer electrolyte - whose exact composition is aclosely guarded secret. As it is entirelysolid, there is no danger of any chemicals leaking out. The manufacturersays that the safety factor of the batterieson this account gives them an edgeover Japanese companies, includingSony, Sanyo and Matsushita, whichhave launched rechargeable lithiumion-based batteries, but with liquidelectrolytes.

The new battery is known as "rocking chair" or "shuttle -cock" cell,because it relies on lithium ions passingto and fro as it is charged and discharged. While discharging, lithiumions migrate from the flat carbon anode,cross a layer of polymer electrolyte and combine with the cathode material on the other side to form lithiated manganese oxide. Sheetsof metallic mesh on thetop and the bottom of thecell act as current collectors. Recharging reversesthis process. The cell issealed in laminated aluminium foil to keep themoisture out.

Ultralife will soon besupplying an unnamedmultinational communications company with the first commercial version of the battery, for use in ,d mobile phones. Newnham says that the newbatteries would cost around us $1 perwatt-hour - the same price as energyfrom nickel-cadmium rechargeable batteries. He expects the product to undercut other lithium-based rechargeablebatteries as it uses cheaper lithiatedmanganese oxide cathode material.

The motor industry has taken a keeninterest in lithium battery technologyfor possible use in electric cars.American car manufacturers Ford,General Motors and Chrysler are collaborating with the us government in theirown us $1.5 billion lithium batterydevelopment programmes.