How a Battery Works
The Chemical Machines Powering Our Lives
A battery consists of three active components, an anode, a cathode and an electrolyte that sits between them.
In the most basic sense, a battery is a chemical machine which separates atoms into electrons and ions. It pushes the electrons out through the device circuit, powering it, while the ions travel internally from the anode to the cathode, where they are re-united with their lost electrons arriving from the device. When the chemical processes that drive this flow are exhausted, the battery is depleted.
If the chemical reaction is reversible, the battery can then be recharged by applying an electric current in the opposite direction. This process is illustrated below.
Figure 1: Lithium-ion Battery Componentry and Function
How a Lithium-ion Battery Works
In a lithium-ion battery the anode is usually made of carbon (graphite), and the cathode is a heavy metal compound such as lithium cobalt oxide. When a lithium-ion battery is charged, the applied charging current forces the lithium cobalt oxide in the cathode to release positively charged lithium ions. The lithium ions travel through the electrolyte to the anode where they insert (intercalate) into the anode’s carbon layers.
During discharge the reverse happens. The anode releases its lithium ions which travel back through the electrolyte to the cathode. At the same time electrons are pushed out from the anode and travel through the device circuits (powering the device) before arriving back at the cathode. Further information on the components of a lithium-ion battery and an illustration of how it works during charge and discharge are provided in Figure 1 above.
Figure 2: Lithium-sulphur Battery Componentry and Function
How a Lithium-sulphur Battery Works
In a lithium-sulphur battery (shown above), the anode consists of pure lithium metal, and the cathode consists of sulphur mixed with carbon.
During discharge, the lithium metal anode “dissolves” and releases lithium ions. These travel to the cathode where they combine with sulphur to create a number of lithium polysulphides, in a series of progressive chemical reactions at each stage absorbing more lithium ions. At the same time the reaction causes the anode to push electrons out to the circuit powering the connected device.
During charging, the charging current forces the cathode to release its lithium ions by dissociating the lithium polysulphides, to form lithium ions and sulphur. The ions travel back to the anode, combining with electrons from the charger current to form pure lithium metal, which then deposits back onto the lithium anode.
To achieve the increased cycle life performance of the new Li-S Energy Battery, BNNT is added to the cathode to help stabilise and protect it and Li-Nanomesh is added to the anode to reduce dendrite formation.