Types of Battery Cells
Cylindrical Cell
The cylindrical cell continues to be one of the most widely used packaging styles for primary and secondary batteries. The advantages are ease of manufacture and good mechanical stability. The tubular cylinder can withstand high internal pressures without deforming.
Many lithium and nickel-based cylindrical cells include a positive thermal coefficient (PTC) switch. When exposed to excessive current, the normally conductive polymer heats up and becomes resistive, stopping current flow and acting as short circuit protection. Once the short is removed, the PTC cools down and returns to the conductive state.
Most cylindrical cells also feature a pressure relief mechanism, and the simplest design utilizes a membrane seal that ruptures under high pressure. Leakage and dry-out may occur after the membrane breaks. Re-sealable vents with a spring-loaded valve are the preferred design. Some consumer Li-ion cells include the Charge Interrupt Device (CID) that physically and irreversibly disconnect the cell when activated to an unsafe pressure builds up. Figure 1 shows a cross section of a cylindrical cell.
Many lithium and nickel-based cylindrical cells include a positive thermal coefficient (PTC) switch. When exposed to excessive current, the normally conductive polymer heats up and becomes resistive, stopping current flow and acting as short circuit protection. Once the short is removed, the PTC cools down and returns to the conductive state.
Most cylindrical cells also feature a pressure relief mechanism, and the simplest design utilizes a membrane seal that ruptures under high pressure. Leakage and dry-out may occur after the membrane breaks. Re-sealable vents with a spring-loaded valve are the preferred design. Some consumer Li-ion cells include the Charge Interrupt Device (CID) that physically and irreversibly disconnect the cell when activated to an unsafe pressure builds up. Figure 1 shows a cross section of a cylindrical cell.
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Button Cell
The button cell, also known as coin cell, enabled compact design in portable devices of the 1980s. Higher voltages were achieved by stacking the cells into a tube. Cordless telephones, medical devices and security wands at airports used these batteries.
Although small and inexpensive to build, the stacked button cell fell out of favor and gave way to more conventional battery formats. A drawback of the button cell is swelling if charged too rapidly. Button cells have no safety vent and can only be charged at a 10- to 16-hour charge; however, newer designs claim rapid charge capability.
Most button cells in use today are non-rechargeable and are found in medical implants, watches, hearing aids, car keys and memory backup. Figure 4 illustrates the button cells with a cross section.
Although small and inexpensive to build, the stacked button cell fell out of favor and gave way to more conventional battery formats. A drawback of the button cell is swelling if charged too rapidly. Button cells have no safety vent and can only be charged at a 10- to 16-hour charge; however, newer designs claim rapid charge capability.
Most button cells in use today are non-rechargeable and are found in medical implants, watches, hearing aids, car keys and memory backup. Figure 4 illustrates the button cells with a cross section.
| CAUTION | Keep button cells to out of reach of children. Swallowing a cell can cause serious health problems. |
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