Chemical Batteries. How Do They Work?

Chemical batteries are those used to power devices that are provided with slots for batteries. You have already heard about Li-ion, alkaline, carbon-zinc and NiMH batteries and you probably wonder how they work and why they have different chemical properties.

General principles

Chemical batteries work by converting chemical energy into electrical one. Their construction represents an energy cell or a group of cells stacked in series (higher voltage) or in parallel (higher output current). Electrochemical cells are those containers filled with chemicals used for the reaction and create voltage.

After chemical reaction has occurred, electrons which are captured at different ends of a conductor are released. In other words a chemical reaction between its anode, cathode and electrolyte materials takes place.

Each cell is conventionally divided in halves -- one of which is losing electrons and the other one is gaining them. A 1.5 Volt battery is a great example of an electrochemical cell.

So, how electrochemical cells work?

Most batteries are composed of one or more voltaic cells. Each cell has two half-cells. The battery has two ends which do not contact - one positive (cathode), and one negative (anode). Both are immersed in a liquid or solid electrolyte. The electrolyte is a conductive material to help ions pass between.

Chemicals used for reaction

Batteries use different chemicals to create reactions. The type of materials and their quantity, primarily determine the battery's output capacity. The capacity is expressed in ampere-hours (Ah) or watt-hours (Wh). For example, 1.5 volts alkaline and carbon-zinc batteries produce less energy comparing with 3 volts Lithium and Li-ion batteries.

Batteries classification

A basic classification would divide batteries in primary (non-rechargeable) and secondary (rechargeable). Non-rechargeable batteries irreversibly convert the chemical energy into electrical energy. At their turn rechargeable batteries, are able to reverse the chemical reaction when being recharged.

Primary batteries are usually used where minimal current is necessary for long-term operation. These are low-cost, consumer-type primary batteries used with the most of the devices we deal with daily. Some of the relevant examples include remote control devices, portable hand-held multi-meters, remote or emergency signaling devices, etc. The standard AA, C and D-size dry-cell batteries are used in radios, flashlights, toys, etc.

Lithium and alkaline batteries are the widest spread primary batteries.

Secondary batteries are wider used and have the advantage of being recharged. They are parts of complex applications such as battery backup in an ac-powered system (mainframe computers or emergency lighting systems). Portable devices are provided mainly with rechargeable batteries.

Secondary batteries can be continuously charged by the system, or use specific device to be recharged from the socket. Among the most used secondary batteries you will find Lead-acid (PbO2), Nickel-Cadmium (Ni-Cd), and Nickel Metal-Hydride (NiMH) batteries.

You had also heard about reserve batteries. These are designed for very long term storage, and cannot provide any output until a key chemical element (usually the electrolyte) is added. A relevant example of a reserve battery is car's 12 volt battery on the automotive dealer's shelf.

Besides, batteries are distinguished by their sizes:

• standard AA
• C
• D-size dry-cell