Battery options expand
for portable devices

BY THOMAS GEBHARDT
Panasonic Industrial Company
OEM Battery Sales Group
Elgin, IL

The demand for smaller and lighter cellular phones, computers, and cordless tools is driving battery makers to create correspondingly smaller and lighter batteries of many types. Nickel-cadmium (NiCd) is still around, but it is facing stiff competition from nickel-metal-hydride (NiMH) and, more recently, from lithium-ion (Li-ion) and lithium-polymer (Li-polymer).

Long the standard in portable electronic equipment, NiCd batteries have offered high power and reliability for audio and visual communications equipment, motorized devices, and hobby equipment. However, they require frequent and repeated recharging–particularly with the emergence of advanced cell phones and portable computers, which call for longer run times than that previously demanded by portable equipment.

Furthermore, the use of cadmium as an electrode has raised environmental concerns. These issues have all but led to the disappearance of the NiCd battery in cell phones and portable computers.

NiMH replaced NiCd as the industry standard in the early 1990s. With almost twice the energy density of NiCd, NiMH allows battery equipment makers to increase operating size while they decrease the size of the battery unit at a reasonable cost.

For example, a single Panasonic NiMH battery offers up to three times the capacity of a NiCd battery of the same size. Additionally, NiMH carries fewer of the environmental concerns associated with NiCd.

Fewer batteries required

More recently, Li-ion has emerged as a second successor to NiCd. Li-ion batteries are offered in cylindrical sizes, though not in the common C, sub-C, AA, and AAA sizes. They also come in prismatic (rectangular) form, though there are many nonstandard sizes. Rated at 3.7 V, these batteries provide more energy density than both NiCd and NiMH.

Since a product powered by Li-ion requires fewer batteries, the product can be made smaller and lighter. The downside, however, is that Li-ion costs considerably more than NiMH. For this reason, Li-ion is primarily used in higher-end products with a great deal of specialty features while NiMH has become the battery of choice for midrange electronic devices. The Li-ion battery has also become somewhat of a selling point for manufacturers, who use the battery in the hopes of implying that their products are more highly specialized.

The race for a successor to Li-ion is currently in full swing. Battery manufacturers are trying to develop batteries in even smaller size and longer run times. And industries that do not usually pay much attention to this market, such as the automotive electric vehicle industry, are keenly watching to see what will come next.

An entirely new structure

Li-polymer is the leading successor to Li-ion in the rapidly evolving battery marketplace. Li-polymer offers an entirely new structure for batteries, doing away with the common metal-can battery construction. Instead, Li-polymer batteries use solid or gel electrolytes, which are sandwiched between electrodes to create a thinner battery. The battery cells are contained in laminated foil, making them thinner, lighter, and potentially easier to mold to fit the application.

Thus, compared to NiCd, NiMH, and Li-ion, Li-polymer batteries can be made lighter and slimmer–advantages appealing to the makers of cellular phones. In fact, several major cellular phone manufacturers are designing their phones to run on Li-polymer. A typical Li-polymer battery is less than 5 mm thick and is rated at 3.7 V, the same voltage as a Li-ion battery.

Initial quantities of Li-polymer will hit the market this year with a price premium typical of a new technology. However, as more become available, the price will drop. Coupled with efficiency-enhancing chip technologies that reduce power consumption in portable devices, Li-polymer will drive the demand for even smaller, lighter batteries and products.