Batteries are indispensable energy storage systems for mobile and stationary applications. They are mostly used for portable devices or when electrical lines are impractical or impossible.
Their application fields reach from smaller devices such as MP3 players or smartphones up to high power systems for the automotive market or energy storage systems for power plants, e.g. wind power plants.
Cell reactions in primary batteries (toys, remote controls, flashlights) are irreversible. During use reactants are converted to products, and when the reactants are used up, the battery is “dead.”
Inexpensive “flashlight batteries” sold in retail stores use a design called a Leclanche dry cell. The body of the battery is made of
- Zinc which acts as the anode
- A carbon rod in the center of the cell serves as the cathode
- Surrounded by a moist paste of graphite powder (carbon), manganese dioxide (MnO 2 ), and ammonium chloride (NH 4 Cl)
The anode reaction is the oxidation of the zinc cylinder to zinc ions. The cathode reaction involves the reduction of manganese dioxide.
Alkaline cells are similar, except that the zinc case is porous and the paste around the carbon cathode is moist manganese dioxide and potassium hydroxide. These are more expensive than ordinary zinc-carbon cells, but they maintain a high voltage longer.
Lead-Acid Storage Batteries
Lead-acid storage batteries used in automobiles is a secondary rechargeable battery. The automobile battery operates as a galvanic cell when used to start the engine (or discharging), and as an electrolytic cell when it is charged by the alternator or by an external battery charger.
- The anode consists of porous lead plates in contact with a sulfuric acid (H 2 SO 4 ) solution.
- The cathode consists of lead dioxide (PbO 2 ) plates, also in sulfuric acid.
- Electrons flow from the lead plates to the lead oxide plates.
Nickel-cadmium (Ni-Cad) Batteries
The rechargeable nickel-cadmium (Ni-Cad) batteries are used in a variety of cordless appliances such as telephones, battery operated tools, and portable computers. During discharge, cadmium metal (Cd) acts as the anode, and nickel dioxide (NiO 2 ) as the cathode. Both metals form insoluble hydroxides due to the presence of the potassium hydroxide electrolyte.
Lithium ion Batteries
Lithium ion batteries are currently the focus of research as it is the battery of choice for the automotive market. In order to reach high power and energy densities, highly porous materials are used as electrode materials. For the anode, graphite is attached on copper foil which serves as current collector. Cathodes use mostly lithium transition metal oxides which are attached on aluminum foil.
Gamry Instruments has several available application notes on battery research – Electrochemical Techniques for Energy-storage Devices.