Lithium-Ion Batteries

One look at the location of lithium in the periodic table's upper left-hand corner and the reason for its celebrity status in the battery world becomes apparent. "It's the most electropositive and lightest element to use," says Dan Doughty of Sandia National Laboratories, Albuquerque, where he runs his lab's component of the FreedomCAR battery development initiative. "If you want to get beyond [lithium battery performance], you need to go to nuclear processes."

Prior to 1990, nickel-cadmium batteries were the only rechargeables commercially available, amounting to an annual market of about $1.2 billion, according to data presented last year by Hideo Takeshita, vice president of the Institute of Information Technology, Tokyo, at a battery seminar and exhibit.

In 1990, nickel/metal-hydride batteries, with their slightly higher energy capacity, added diversity to the rechargeables market and are now found in many hybrid electric vehicles. At about the same time, Sony introduced the first commercial lithium-ion battery, packaging it in one of its popular camcorder models. The battery incorporated a lithium cobalt oxide cathode, still the predominant cathode material in lithium-ion batteries, and a graphite-based anode. It was more expensive than the other rechargeables available, but it also was far smaller and lighter, thereby opening up vast new design and product possibilities for portability and for shedding plugs.

Researchers have been trying everything they can think of to eke more performance out of lithium-ion batteries. One approach has been to increase the mobility of lithium ions between the battery's electrodes. Another tack is to replace the graphitic anode materials into which lithium intercalates in most of today's lithium-ion batteries with metallic alloys that can host more ions in the same amount of space and therefore accommodate more of the current-generating electrochemical reaction between the anode and cathode.

Early last year, for example, Sony unveiled its Nexelion line of lithium-ion batteries, which includes an anode made of an amorphous tin-based metal alloyed with cobalt, carbon, and other ingredients.

The quest for practical alloys that can work well as an anode in lithium-ion batteries has been tough because the materials most often expand and contract dramatically as lithium ions move in and out. According to Sony, the material in Nexelion batteries minimizes these shape changes, thereby resulting in a practical anode that can pack 50% more lithium ions in a given volume than can graphite anodes. The battery's so-called multistage composite cathode incorporates the usual lithium cobalt oxide but also includes other components made of cobalt, manganese, and nickel oxides. The new batteries, which the company claims will deliver 30% more capacity than conventional lithium batteries of the same size, are slated to be packaged first in Sony's camcorders.

The marketplace beckons for more innovation in lithium-based batteries. In 2005, Takeshita estimates, lithium batteries accounted for $4 billion of a roughly $6 billion market for rechargeables, and billions more in growth is projected for the coming few years.