Battery packaging - a look at old and new systems`(A)
In the 1700 and 1800s, battery cells were encased in large glassjars. Later, multi-cell batteries were developed using woodencontainers 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 WarII.Continued downsizing called for smaller and more compact celldesign and in the 1980s the button cell appeared. The early 1990sbrought the prismatic cell, which was followed by the modern pouchcell. We are now examining the strength and limitation of eachpackaging system.
The cylindrical cell
The cylindrical cell continues to be the most widely usedpackaging. It is easy to manufacture, offers high energy densityand provides good mechanical stability. The cylinder has theability to withstand high internal pressures. Typical applicationsare wireless communication, mobile computing, biomedicalinstruments, power tools and applications that do not demandultra-small size.
Most nickel cadmium systems come in cylindrical cells. Otherchemistries also make use of the cylindrical design. The 18650 isamong the most popular lithium-ion cells ('18' denotes the diameterand '650' the length in millimeters). Lead-based systems are alsoavailable in cylindrical design of which the Cyclone by Hawker isthe most common.Cylindrical cells are equipped with a resealableventing mechanism to release pressure under extreme conditions suchas excessive overcharge. nickel-based cells can sustain a pressureof about 13.5 Bar or 200 pounds per square inch (psi). Ventingoccurs between 10-13.5 Bar or 150-200 psi.The drawback of thecylindrical cell is poor space utilization. Because of fixed cellsize, a battery pack must be designed around available cellsizes.
The button cell
The button cell was developed to reduce packs size and improvestacking. Non-rechargeable cells and are found in watches, hearingaids and memory backup. (Photo courtesy of Sanyo; design courtesyof Panasonic)
The rechargeable button cells are mostly nickel-based and are foundin older cordless telephones, biomedical devices and industrialinstruments. Although inexpensive to manufacture, the main drawbackis charge times of 10-16 hour and swelling if charged too rapidly.New designs claim faster charge capabilities. Button cells have nosafety vent.