The Li-Polymer battery: substance  hype?
The d ‘Lithium Polymer’ has become synonymous with advanced battery technology. But what is the relationship between ‘polymer’ and the classic Lithium Ion battery? In this article we examine the basic differences between the Li-ion and Li-ion polymer battery. We look at packaging techniques and evaluate the cost-to-energy ratio of these batteries.

The Li-polymer differs from other battery systems in the type of electrolyte used. Theiginal design, which dates back to the 1970s, uses a polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows the exchange of ions (electrically charged atoms groups of atoms). The polymer electrolyte replaces the traditionalous separat, which is soaked with electrolyte.

The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile profile. There is no danger of flammability because no liquid gelled electrolyte is used.

With a cell thickness measuring as little as one millimeter (0.039 inches), design engineers are left to their own imagination in terms ofm, shape and size. Thetically, it is possible to create designs which fm part of a protective housing, are in the shape of a mat that can be rolled up, are even embedded into a carrying case a piece of clothing. Such innovative batteries are still a few years away, especially  the commercial market.

Unftunately, the dry Li-polymer suffers from po conductivity. The internal resistance is too high and cannot deliver the current bursts needed f modern communication devices and spinning up the hard drives of mobile computing equipment. Although heating the cell to 60°C (140°F) and higher increases the conductivity to acceptable levels. This requirement, however, is unsuitable f ptable applications.

Some dry solid Li-polymers are currently used in hot climates as standby batteries f stationary applications. One manufacturer has added heating elements in the cells that keep the battery in the conductive temperature range at all times. Such a battery perfms well f the application intended because high ambient temperatures do not degrade the service life of this battery in the same way as it does with the VRLA type. Although longer lasting, the cost of the Li-polymer battery is high.

Engineers are continuing to develop a dry solid Li-polymer battery that perfms at room temperature. A dry solid Li-polymer version is anticipated by 2005. This battery should be very stable; would run 1000 full cycles and would have higher energy densities than today’s Li?ion battery.

How then is the current Li-polymer battery made conductive at ambient temperatures? Most of the commercial Li-polymer batteries  mobile phones are a hybrid. Some gelled electrolyte has been added to the dry polymer. The crect term f this system is Lithium Ion Polymer. F marketing reasons, most battery manufacturers call it simply Li-polymer. Since the hybrid lithium polymer is the only functioning lithium polymer f ptable use today, we will focus on this chemistry variation but use the crect term of lithium ion polymer (Li-ion polymer).

With gelled electrolyte added, what then is the difference between Li?ion and Li?ion polymer? Although the characteristics and perfmance of the two systems are very similar, the Li?ion polymer is unique in that the solid electrolyte replaces the pous separat. The gelled electrolyte is simply added to enhance ion conductivity.

Technical difficulties and delays in volume manufacturing have deferred the introduction of the Li?ion polymer battery. In addition, the promised superiity of the Li?ion polymer has not yet been realized. No improvements in capacity gains are achieved — in fact, the capacity is slightly less than that of the standard Li?ion battery. F the present, there is no cost advantage in using the Li?ion polymer battery. The maj reason f switching to the Li-ion polymer is fm fact. It allows wafer-thin geometries, a style that is demanded by the highly competitive mobile phone industry. Figure 1 summarizes the advantages and limitations of the Li-ion polymer battery.http://www.minamoto.com
lithium polymer
lithium polymer