Battery packaging - a look at old and new systems

In the 1700 and 1800s, battery cells were encased in large glass jars. Later, multi-cell batteries were developed using wooden containers treated with a sealant to prevent electrolyte leakage. With the need for portability, the cylindrical cell was developed. The sealed cylindrical cells became common after World War II.
Continued downsizing called for smaller and more compact cell design and in the 1980s the button cell appeared. The early 1990s brought the prismatic cell, which was followed by the modern pouch cell. We are now examining the strength and limitation of each packaging system.

The cylindrical cell

The cylindrical cell continues to be the most widely used packaging. It is easy to manufacture, offers high energy density and provides good mechanical stability. The cylinder has the ability to withstand high internal pressures. Typical applications are wireless communication, mobile computing, biomedical instruments, power tools and applications that do not demand ultra-small size.

The button cell
The button cell was developed to reduce packs size and improve stacking. Non-rechargeable cells and are found in watches, hearing aids and memory backup.
(Photo courtesy of Sanyo; design courtesy of Panasonic)

The rechargeable button cells are mostly nickel-based and are found in older cordless telephones, biomedical devices and industrial instruments. Although inexpensive to manufacture, the main drawback is charge times of 10-16 hour and swelling if charged too rapidly. New designs claim faster charge capabilities. Button cells have no safety vent.

The prismatic cell
The prismatic cell was developed in the early 1990 to response to consumer demand for thinner geometry. Prismatic cells are commonly reserved for the lithium battery family. The polymer version is exclusively prismatic.

The prismatic cell comes in various sizes with capacities from 400mAh to 2000mAh and higher. No standard cell size exists; rather, prismatic cells are custom-made for cell phones and other high volume items.

The negative attributes of the prismatic cell are slightly lower energy densities and higher manufacturing costs than the cylindrical cell. In addition, the prismatic cell does not provide the same mechanical stability enjoyed by the cylindrical cell.
Prismatic cells have no venting system. To prevent bulging on pressure build up, heavier gauge metal is used for the container. Some degree of bulging must be considered in equipment design.

The pouch cell
The introduction of the pouch cell in 1995 made a profound advancement in cell design. Rather than using expensive metallic enclosures and glass-to-metal electrical feed-troughs, a heat-sealable foil is used. The electrical contacts consist of conductive foil tabs that are welded to the electrode and sealed to the pouch material.

The pouch cell concept allows tailoring to exact cell dimensions. It makes the most efficient use of available space and achieves a packaging efficiency of 90 to 95 percent, the highest among battery packs. Because of the absence of a metal can, the pouch pack is light. The main application is cell phones. No standardized pouch cells exist, each manufacturer builds to a special application.

The pouch cell is exclusively used for lithium-based chemistries. Manufacturing cost is still higher than conventional systems and its reliability has not been fully proven. In addition, the energy density and load current are slightly lower. The cycle life is not well documented but remains less than that of other packaging systems.

A critical issue with the pouch cell is the swelling that occurs when gas is generated during charging or discharging. Allowance must be made for some expansion, even though battery manufacturers insist that the cells do not generate gas if correctly charged. It is best not to stack pouch cells, but lay them side-by-side.

The pouch cell is highly sensitive to twisting. Point pressure must also be avoided. The protective housing must be designed to protect the cell from mechanical stress.

Battery packs for portable devices

Most manufacturers of cell phones, laptops and cameras develop their own battery packs. A model change often results in a redesigned battery. The typical contact arrangements of cell phone and video camera batteries are: battery positive, negative and temperature sensor. Additional contacts, if present, may serve as control switch or battery type identifier. 'Smart' batteries have extra contacts to provide state-of-charge indication and other information.
There are no norms and standards for these batteries. Each manufacturer has its own design.

In the 1990s, the Smart Battery System (SBS) forum made a concerted effort to standardize on battery norms for laptops, survey equipment and medical instruments. Beside physical size, these batteries ran on a standard SMBus protocol. With miniaturizing and securing a lucrative battery replacement market, laptop manufacturers went their own way. The SMBus batteries (type 2020, 1030, 1020, 210, 202, 201, 36, 35, 30, 17 and 15) are still widely used today for specialty instruments. (See also "The 'smart' battery" in Part One and "How to service laptop batteries" in Part Two.)

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Created: April 2003, Last edited: January 2004

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