Batteries and Fuel Cells

A battery is a device that stores energy chemically and converts it into electricity through electrochemical reactions. Each cell contains two electrodes — a negative anode and a positive cathode — separated by an electrolyte that allows ions to move between them. When the cell is connected to a circuit, a chemical reaction drives electrons through the external wire, producing a current. Primary batteries are used once and discarded, while secondary, or rechargeable, batteries can be restored by passing current through them in reverse.

Several rechargeable chemistries are in common use. Lithium-ion batteries offer high energy density and low self-discharge and are widely used in portable electronics and electric vehicles. Nickel-metal hydride and nickel-cadmium cells are older rechargeable types, with nickel-cadmium now restricted in many applications because of its toxic cadmium content. Sealed lead-acid batteries, descendants of the traditional car battery, remain common for backup power and standby systems because they are robust and inexpensive. Reusable alkaline cells were developed as a rechargeable alternative to disposable alkaline batteries.

A fuel cell also produces electricity from a chemical reaction, but unlike a battery it is supplied with fuel continuously rather than storing it internally. A common type combines hydrogen and oxygen to generate electricity, with water as the main by-product. Solid oxide fuel cells operate at high temperatures and can run on a range of fuels. Both batteries and fuel cells are central to efforts to store and use renewable energy, which is often generated intermittently.

Frequently asked questions

What is the difference between a battery and a fuel cell?

A battery stores its chemical energy internally and is depleted as it discharges, whereas a fuel cell generates electricity continuously as long as fuel and oxygen are supplied to it.

Why are lithium-ion batteries so widely used?

They store a large amount of energy for their weight, can be recharged many times, and lose charge slowly when idle, which suits phones, laptops, and electric vehicles.

What comes out of a hydrogen fuel cell?

When hydrogen reacts with oxygen in the cell, the main by-product is water, along with heat and electricity.