Battery Types & Chemistries
Battery is a vessel containing various chemicals which produces electricity as a result of reactions taking place between these chemicals. These reactions which produce electrons are called electrochemical reactions. The earliest version of the battery was created by Alessandro Volta. He used alternating layers of Zinc, blotting paper soaked in salt water and Silver, known as a voltaic pile.
Here is an explanation of the chemical reaction taking place in a simple form of Zinc-Carbon battery. A small jar containing Sulphuric Acid (electrolytesolution), a Zinc rod and a Carbon rod (electrodes) are required. When both the rods are placed in the acid, an immediate noticable reaction takes place. The Zinc in the anode (the negative terminal) oxidizes, releasing negatively charged electrons and positively charged metal ions. The electrons travel through the wire (and the electrical load) to the cathode, Carbon (the positive terminal). The electrons combine with the Hydrogen ions at the cathode, releasing Hydrogen gas bubbles. While the Zinc rod dissolves to form Zinc sulphate.
However, this would be impractical as a battery with a highly corrosive liquid in a container and outlet for the gas produced. The Zinc/Carbon batteries which are commonly known as standard battery contains an acidic paste which serves as the electrolyte. Allowing for a more compact size that we use today. Modern batteries use different chemicals, listed below are some of the widely used battery chemistries. These can be grouped into two fundamental types, primary and scondary. Primary cells are meant meant to be used once only and Secondary cells are designed to be recharged over and over (typically several hundreds of times). Energizer's Learning Center have useful information on how batteries work, history and how these are constructed.
- Zinc/Carbon Battery: Used in all inexpensive AA, C and D dry cell batteries. It has Zinc and Carbon as electrodes and an acidic paste as the electrolyte.
- Alkaline Battery: Used in Duracell and Energizer batteries, it uses Zinc and Manganese dioxide in powdered form as the electrodes and an Alkaline, like Potassium hydroxide, as the electrolyte.
- Lithium Cell: Used in cameras, calculators and pacemakers. Different Lithium cells exist because of its stability and low reactivity with a number of cathodes and nonaqueous electrolytes. The most common electrolytes are organic liquids.
- Zinc/Air Cells: Used in pagers, hearing aids. Amalgamated Zinc powder and Oxygen (Air) are the electrodes and Potassium Hydroxide is used as the electrolyte. This cell is lightweight, environmentally friendly and has a relatively low cost.
- Lead Acid Battery: Used in cars. Lead and Lead oxide are used as electrodes with a very strong acidic electrolyte. This is rechargeable. The modern variation is known as Gel Cell, where the electrolyte is in a gelatin form.
- Nickel/Cadmium Cells (NiCd): Used in Digital cameras, laptops, calculators. Cadmium and Nickel are used as electrodes and aqueous Potassium Hydroxide is used as the electrolyte. It is a rechargeable battery, but it is prone to the memory effect, where the cell retains the characteristics of the previous cycle. The image on the right shows the inside of a NiCd battery, showing the actual cells that make up the battery.
- Nickel Metal Hydride (NiMh): Used in laptops, camcorders, mobile phones, power tools. Rare-earth or nickel alloys with many metals are used as the electrodes and Potassium Hydroxide is used as the electrolyte. This is rechargeable and is also prone to the memory effect, but less so than the Ni Cad cells. The image on the right is of a NiMH laptop battery showing the actual cells inside.
- Lithium Ion Cells: Used in laptops and mobile phones. Carbon compound and Lithium Oxide are used as electrodes and organic solvents are used as the electrolyte. Has a very good power to weight ratio and is rechargeable. Check Apple's page on Lithium Ion batteries. The image on the right shows the cells and the microprocessor inside a Lithium Ion battery.
- Lithium Ion Polymer Cells: Used in PDAs, handhelds, micro-models, MP3 players. The electrolyte used is a polymer. It resembles a plastic like film which does not conduct electricity, but allows the exchange of ions. The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile. There is no danger of flammability because no liquid or gelled electrolyte is used.
- Silver/Zinc Cells: Used in aeronautical and defence applications. Has a very good power to weight ratio.
- Sodium/Sulphur Cells: Used in electric vehicles and aerospace applications such as satellites. Uses molten Sodium and Sulphur as electrodes and
ceramic beta alumina as the electrolyte. This has been studied extensively for electric vehicles because of its inexpensive materials, high cycle life, and high specific energy and power. The problems with this cell are that the temperature has to be kept at 350C to keep the Sulphur in liquid form. This is achieved through insulation or heating through the cells own power. This lowers the energy density. The electrolyte is brittle and develops microfissures. Thus the liquid sodium and sulfur come in contactówith explosively violent results.