Cell manufacturers are generally in the business of building high-performance batteries for high-volume applications. They can recoup their development and factory tooling costs in applications like cell phones, notebooks, and PDAs, which have the greatest potential demand.
When Li-ion and Li-polymer cells initially go into production, their availability will likely be limited to these big applications. To some extent the product descriptions included in this article may be viewed more as benchmarks for the current state-of-the-art, rather than listings of off-the-shelf standard products. The general availability of these products may come in six months, a year, or perhaps further down the road, depending on the specific vendor, product, application, and customer.
Many of these cells are only available from the manufacturer, reflecting economic considerations and practical safety concerns. In general, the cell vendors don't want to sell bare cells to OEM customers. They prefer to offer these cells within application-specific battery packs that include the necessary active and passive cell protection.
The cell manufacturer may choose to produce the packs internally, or work with third-party assembly houses that are well versed in Li-ion requirements for safe handling, packaging, and charging. Of course, there are exceptions. Cell vendors may supply bare cells to OEM customers with whom they previously established a working relationship. Cell makers may then be inclined to develop battery packs for projects that don't involve high volumes.
Another mitigating factor is the cell maker's level of automation. Cell vendors that rely more on manual assembly might be more willing to work with customers seeking lower volume production.
If either pricing or availability for the latest, thinnest prismatic cells presents a problem, designers may have better luck obtaining some of the larger cells, which are currently in widespread use. For example, Michael Shu, sales engineer at BYD America, says that among cell phones—the largest market for Li-ion cells—the 6- by 30- by 48-mm prismatic is the most popular size (see the table).
Designers should take notice of emerging trends that may seem at odds with the overall industry trends. For instance, Doug Magnuson of Gold Peak Industries observes that many laptop designs are migrating from 18650 cylindricals to 10-mm prismatics.
So, despite the increased development of thin cells, there may be renewed interest in the larger and older prismatic sizes. Moreover, these sizes will supply the highest capacities available. Among the new 10-mm prismatics are two from Gold Peak—a 19- by 41-mm cell rated for 600 mAh, and a 34- by 48-mm cell rated for 1650 mAh. Both are expected to begin sampling in May.
Panasonic also recently introduced a 10.5- by 34- by 50-mm cell that's currently in production. The CGA103450 offers a typical capacity of 1800 mAh.
For designers who can live with a cylindrical battery, the industry-standard 18650 offers both availability and highest performance. As noted previously, this cell is now being available with capacities of greater than 2000 mAh.