Lithium-ion battery

Lithium-ion battery (Li-ion battery) is a type of rechargeable battery. It is the most widely used battery in power tools and portable devices, such as smartphones and laptops, and also in electric vehicles.

How do lithium-ion batteries work?

Li-ion batteries consist of a negative electrode (anode), a positive electrode (cathode), a separator between them, electrolyte and current collectors. When using the battery, lithium ions (Li+) move from anode to cathode through the electrolyte creating a flow of electrons in the external circuit. During charging, external electric energy enforces the movement of Li+ ions from the cathode back to the anode and the cycle can begin again.

Materials used in lithium-ion batteries

The cost, safety, exact chemistry and performance depend on the materials used in the lithium-ion battery. 

The cathode is a solid lithium compound, usually lithium cobalt oxide (LiCoO2) or lithium manganese(III,IV) oxide (LiMn2O4). Cobalt-based cathodes are the most common since they offer great performance. But it is the most expensive part of a Li-ion battery. Because of this, manganese cathodes are gaining use and other materials are also actively tested. For example, Tesla is developing batteries that use lithium iron phosphate as a cathode.

The anode is usually graphite. It is cheap and has good energy density but limited capacity. Researchers are testing materials that would offer higher capacity. Possible alternatives include silicon-based anodes with nanowires or -tubes, hard carbon and tin/cobalt alloy.

The electrolyte usually consists of lithium salts (such as lithium hexafluorophosphate – LiPF6 and lithium hexafluoroarsenate – LiAsF6) in an organic solvent (such as ethylene carbonate). Handheld devices mostly use a polymer electrolyte that provides more energy per mass. Also, many car manufacturers are investing in solid electrolyte research. For example, ceramic electrolytes potentially offer higher energy density and faster charging.

Advantages and disadvantages

Lithium-ion batteries have a high energy density, low self-discharge and long life. They have no memory effect. This means that they don’t “remember” a smaller capacity after several partial discharge/charge cycles. They are stable, reliable and efficient.

The main downside is that Li-ion batteries can be a fire hazard because they contain flammable electrolytes. If damaged or incorrectly charged, they can explode and cause fires. This also might happen when the battery short-circuits or is exposed to extreme heat. Fortunately, battery fires are not a common problem because of strict quality controls and research into non-flammable electrolytes. Solid-state and gel polymer electrolytes are promising alternatives to liquid electrolytes.

The environmental impact of lithium-ion batteries also needs improvement. Manufacturing processes of lithium, nickel, cobalt, solvent and mining byproducts have a huge carbon footprint. These metals can be recycled and used again in new batteries but this is rarely done. With the increase of electric cars, car manufacturers are trying to lower the environmental impact of their products. They are actively investing in recycling and research into increasing the efficiency of the process.

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