Battery Cell Types

Alkaline

The alkaline cell gets its name from the alkaline aqueous solution used as the electrolyte. First introduced in the 1960s, the cell has grown in popularity. The overall chemical reaction in this cell is:

Popular in toys and radios, these non rechargeable batteries operate at high discharge rates over a wide temperature range.

Nickel / Cadmium

In this cell, the cathode is nickel-plated woven mesh and the anode is a cadmium-plated net. The electrolyte is KOH and acts as an ion conductor. Since little electrolyte is needed in this cell, it is lighter. The overall chemical reaction is:

Popular in many electronic devices, they have a distinct advantage in high-discharge applications, have a long shelf life, and use life. The best-known limitation is the "memory effect" – the cell retains the characteristics of the previous cycle. This temporary loss of cell capacity occurs when the cell is recharged without being fully discharged.

Nickel / Metal Hydride

This sealed cell is a hybrid of the NiCd cell. Modern NiMH batteries have an anode that consists of many metal alloys including Vanadium, Titanium, Zirconium, Nickel, Carbon, Cobalt, and Iron. The overall reaction in this cell is:

The NiMH cell does cost more and has half the service life of NiCd, but it also has 30% more capacity and increased power density. It is also susceptible to the memory effect. This cell is preferred over the NiCd cell when capacity is the more crucial design specification.

Lithium Ion

Lithium ion battery chemistry comprises a number of cell designs that use lithium ion as the anode. This metal has gained much popularity because it is the lightest, has the highest standard electrical potential, and has the highest energy-density.

Lithium ion cells have just recently become commercially viable, due to their violent reaction when encountered with water as well as with the nitrogen found in the air. This requires the lithium ion cells be sealed. High-rate lithium ion cells can build up pressure if they short circuit and cause the temperature and pressure in the cell to rise. The cell design needs to include safety vents that will rupture to help prevent explosion.

The advantage is that they have no memory effect and a slow loss of charge when not in use. Capacity loss is approximately 5% per month compared to over 30% per month for NiMH and 20% per month for NiCd. These batteries are often lighter than equivalent chemistries. A typical chemical reaction of a Lithium Ion battery is:

Lithium Ion cells require a protection circuit to maintain safe operation. This circuit protection limits peak voltage of each cell during charge and helps prevent the cell voltage from dropping too low on discharge.

Lithium Polymer

The lithium polymer battery is differentiated by the electrolyte used. Commercial cells use a separator / electrolyte membrane filled with a polymer that gels when filled with liquid electrolyte. The net result is that wafer thin cell profiles can be created for unique geometric requirements.