The cycle is the discharge and subsequent recharge of a battery.

Cycle Life

The cycle life is the number of cycles that a cell can undergo before failing to meet its efficiency performance criteria.

Calendar Life

The calendar life is the period during which a cell is capable of operating above a specified efficiency performance level measured in years.


The Capacity is the maximum total electrical charge which a battery can deliver to a load under a specific set of conditions.

Energy density

Energy density relates the mass of an energy store to its stored energy (Wh/kg). The higher the energy density, the more energy may be stored or transported for the same amount of mass.

Lead acid Battery

In the charged state each cell contains a lead (Pb) metal anode and a lead(VI) dioxide (PbO2) cathode in a sulphuric acid (H2SO4) electrolyte. In the discharged state both electrodes turn into lead(II) sulfate (PbSO4) and the electrolyte becomes primarily water.

Lithium-ion (Li-ion) Battery

Li-ion batteries typically consist of a graphite cathode, a ‘lithium transition metal oxide’ e.g. LiCoO2, and an electrolyte of lithium hexafluorophosphate dissolved in an organic solvent. The Li ion is shuttled between the electrodes; during charging Li from the cathode is intercalated into the anode and during discharging Li from the anode is intercalated into the cathode.


Nanomaterials are materials with structural features of at least one dimension in the range 1-100 nm.

Nickel-Cadmium (Ni-Cd) Battery

Ni-Cd typically they consist of a nickel oxyhydroxide cathode, a cadmium metal anode and an alkaline electrolyte such as potassium hydroxide.

Nickel-Metal hydride (Ni-MH) Battery

Ni-MH batteries are similar to Ni-Cd batteries but a hydrogen-absorbing alloy is used for the negative electrode instead of toxic Cd.

Polymer-electrolyte membrane (PEM) fuel cells

A PEM fuel cell uses hydrogen fuel (H2) and oxygen (O2) from the air to produce electricity. H2 fuel is channelled through field flow plates to the anode where a platinum catalyst causes the H2 to split into protons and electrons. The membrane allows only the protons to pass through it to the cathode; the electrons must travel along an external circuit to the cathode, creating an electrical current. At the cathode the electrons and protons combine with O2 to form water, which flows out of the cell.

Power density

Power density relates the mass of an energy store to its power stored (W/kg).

Sodium-Sulphur Battery

Na-S cells are cylindrical and consist of an outer layer sulphur cathode and a liquid sodium anode, with a solid electrolyte in between them. The container is sealed at the top with an airtight alumina lid. An essential part of the cell is the presence of a BASE (beta-alumina sodium ion exchange) membrane, which selectively conducts Na+ ions. 

Solid oxide fuel cells (SOFCs)

A SOFC is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. A single SOFC consisting of four layers stacked together is only a few millimeters thick; hundreds of these cells are then connected in series. The cathode is a thin porous layer on the solid oxide electrolyte where the reduction of oxygen into oxygen ions occurs. These ions then diffuse through electrolyte to the ceramic anode layer, where they electrochemically oxidize the fuel. Two electrons, which are given off in this reaction, flow through an external circuit where they can do work. The cycle then repeats as those electrons reenter the cathode.


Supercapacitors are electrochemical double layer capacitors constituted of two activated carbon electrodes, a membrane separator, and an electrolyte. The electrolyte supplies and conducts the ions from one electrode to the other. They have an unusually high energy density compared to normal capacitors and the energy is stored by charge transfer at the boundary between electrode and electrolyte.

Zebra Battery

The technical name for the Zebra battery is the Na-NiCl2 battery. Molten chloroaluminate (NaAlCl4) is used as the electrolyte. The cathode is nickel in the discharged state; nickel chloride in the charged state. The anode is molten sodium.