How Do Batteries Store and Release Energy? Chemical Energy Explained

WHAT IS MECHANICAL ENERGY? EXPLAINED

Take a rainwater tank at home connected via a hose to a garden sprinkler; the type that rotates to evenly water the lawn. If the rainwater tank is full the sprinkler spins quite rapidly; less so as the tank empties. What is happening?
The answer is that the potential energy due to the height of the water in the tank is converted into work done, and kinetic energy expended by the rotating water turbine. We say potential or static energy because while the tank is at rest and no water is flowing the water has the potential to do work and expend energy whilst it’s not actually doing any work.

When full the tank has, by virtue of the height if the water, greater potential to do work than when the level falls. The tank stores more potential energy when its full; less when empty.

WHAT IS KINETIC ENERGY? EXPLAINED

Kinetic energy is the energy of motion — it's what potential energy becomes once it is released and doing work. In the water tank example, kinetic energy is the spinning sprinkler. In a battery, kinetic energy is the flow of electrons through a circuit once the battery is connected. A battery at rest stores potential energy; a battery powering a device is producing kinetic energy in the form of electrical current.

WHAT IS POTENTIAL ENERGY? EXPLAINED

The first obvious one is a battery whereby chemical reactions, electrical energy is stored in the chemistry of the battery. Like with the water tank the energy is stored as potential energy or here as chemical potential energy; waiting in the battery to do work by forcing a flow of electrons through an outside element such as a light bulb for that potential energy to be converted electrical energy and then to light energy and heat energy in the light bulb.

Note that the light bulb doesn’t store energy, it dissipates energy and converts energy from one form to another; light and heat.

HOW ARE BATTERY CELLS MANAGED?

The word battery suggests an array or collection of things operating in concert. For example, we speak of a battery of cannons. In an electrical battery we are referring to more than one electrochemical cell connected, usually in series. The individual cell voltages accumulate to give us the total battery voltage. In the domestic renewables world battery nominal voltages range from 48 volts to over 500 volts.

In a lithium-ion cell the nominal or average voltage varies with the chemistry employed. 3.2 volts for lithium ferro phosphate and 3.7 volts for those cells containing nickel, manganese, cobalt. As the cell charges and discharges these voltages rise and fall. There are upper limits over which the cell’s life can be compromised and overheating may occur and lower voltages where permanent damage will occur.

In the battery manufacturing process, cells are chosen to have closely matched characteristics before being joined to form a battery. However, no matter how closely they are matched, during the charging phase individual cell voltages inevitably drift apart and this causes problems. Unchecked, some cells may rise to the dangerous overvoltage region and with some chemistries, catastrophic failure accompanied by fire.