Battery packaging - a look at old and new systems(A)
In the 1700 and 1800s, battery cells were encasedin large glass jars. Later, multi-cell batteries were developedusing wooden containers treated with a sealant to preventelectrolyte leakage. With the need for portability, the cylindricalcell was developed. The sealed cylindrical cells became commonafter World War II.Continued downsizing called for smaller and morecompact cell design and in the 1980s the button cell appeared. Theearly 1990s brought the prismatic cell, which was followed by themodern pouch cell. We are now examining the strength and limitationof each packaging system.
The cylindrical cell The cylindrical cell continues to be the mostwidely used packaging. It is easy to manufacture, offers highenergy density and provides good mechanical stability. The cylinderhas the ability to withstand high internal pressures. Typicalapplications are wireless communication, mobile computing,biomedical instruments, power tools and applications that do notdemand ultra-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 the cylindrical cell is poor space utilization.Because of fixed cell size, a battery pack must be designed aroundavailable cell sizes.
The button cell The button cell was developed to reduce packs sizeand improve stacking. Non-rechargeable cells and are found inwatches, hearing aids and memory backup. (Photo courtesy of Sanyo;design courtesy of 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.