How lithium-ion batteries work


Lithium-ion batteries are what make modern electric vehicles possible. This Engineering Explained video shows how they work, and how they’re manufactured.

The video is sponsored by LG Energy Solution, which invited Engineering Explained host Jason Fenske to tour its battery plant in Holland, Michigan. One of the biggest EV battery suppliers, LG is involved in, among other things, the Ultium Cells LLC joint venture with General Motors that aims to build four U.S. battery plants to supply GM EVs.

A lithium-ion battery is made up of four main components. The cathode and anode are positive and negative terminals, respectively. The electrolyte is the medium through which lithium ions and electrons between the cathode and anode flow during charging and discharging. The separator keeps the cathode and anode from touching—preventing short circuits.

The cathode is often the most expensive part of a battery, which in turn is the most expensive part of an EV. Its material composition can vary, with nickel manganese cobalt (NMC) being among the most common. Some automakers have begun shifting to lithium iron phosphate (LFP), which is viewed as a more affordable option and uses fewer scarce raw materials.

Anodes are usually made from graphite because it can store large amounts of lithium. Silicon is being touted an alternative because it can potentially store even more lithium. Battery firm Sila Nanotechnologies has claimed it can boost EV range up to 20% with its silicon anode tech. But silicon can also expand and contract significantly as it absorbs and dissipates lithium.

In current lithium-ion batteries, the electrolyte is a liquid made from lithium salts and a solvent, with some additives. This allows lithium ions to move freely, doesn’t react with the other materials in the battery, and has relatively low freezing and high ignition points. Automakers and battery firms have been investigating solid-state batteries—in which the electrolyte is a solid material—for some time, but liquid electrolyte is likely to remain the default for now.

Finally, the separator is a porous material that allows lithium ions to pass through. Its pores can also close at high temperatures as a safeguard against overheating. With the separator in place to stop short circuits, lithium ions can travel from the anode to the cathode, a process that releases electrons which power the motors. For charging the process is reversed, with lithium ions migrating from the cathode to the anode.

Manufacturing lithium-ion batteries starts by mixing up slurries of cathode and anode material, which are then smeared onto foil (generally aluminum for the cathode and copper for the anode). The coated pieces of foil are then cut into battery-cell sized pieces, laminated with the separator in between, and stacked in multiple layers. Electrolyte is then injected, and the assembly is taken through an aging process. Completed cells are then assembled into modules, with multiple modules making up a battery pack.