How Does A Lithium-Ion Battery Work?

Louise Smyth

Rechargeable lithium-ion batteries are utilised within a range of modern technologies, from phones and laptops through to car batteries. Tesla has been working with lithium-ion batteries to extend the lifespan of their electric car batteries whilst simultaneously reducing consumer costs.

Electrochemical potential

While fewer lithium particles are used within the battery than other molecules, it is the electrochemical potential of lithium that is the driving force behind the battery.

Lithium only has one electron per molecule and the highest tendency to lose its electron. Separating the two (creating an electron and a lithium-ion) is crucial to the battery charging process, which is what makes lithium-ion batteries essential to modern technology.

The charging process

Lithium-ion cells consist of a metal oxide, a liquid electrolyte and graphite. The graphite is constructed of loosely-bonded layers so that lithium-ions and separated electrons can be safely stored.

The aim is to separate the electrons from the lithium by passing the lithium from the metal oxide, through the electrolyte, to the graphite. The liquid electrolyte only allows lithium-ions to pass through, separating the lithium from its electron. The electrons will reach the graphite through a circuit so that both can be stored separately.

This process is achieved when a power source (a battery) is added to the process, the electrons are attracted to the positive side of the battery and travel through a separate circuit to reach the graphite.

Whereas the lithium-ions are attracted to the negative side, travelling through the electrolyte and into the graphite. When the detached electrons and the lithium-ions are fully stored within the graphite, the cell is charged.

The discharging process

The discharging process involves the electrons and the lithium-ions being naturally attracted back to the metal oxide once the power source is removed. Essentially, the process is reversed. The lithium-ions travel back through the electrolyte and the electrons travel back to the metal oxide via the separate pathway.

The process of charging and discharging lithium-ion batteries allows our phones, laptops and even electric car batteries to have a longer lifespan.

Tesla’s use of lithium-ion batteries

Tesla utilises multiple compact lithium-ion battery cells rather than one large cell to improve product performance. In this instance, the graphite is coded onto copper foil and the metal oxide onto aluminium foil, both of which work as current collectors. An organic salt of lithium acts as an electrolyte and is coded onto a separator sheet (preventing short-circuiting if overheating occurs). All three layers are then wound around a steel core.

Tesla electric car battery packs consist of 16 modules (multiple lithium-ion battery cells connected in a series). To reduce overheating that would cause cell decay, a battery management system (BMS) is implemented to monitor the health of the cells, manage the state of charge and ensure voltage protection. Glycol-based cooling technology is adjusted by the BMS to ensure overheating does not take place.

Not only does the size and cooling system mean that Tesla car batteries perform better than their competitors, but the chances of the lithium-ion battery decaying prematurely are also reduced.