Deconstructing the Li-ion Battery

Look inside a li-ion battery (based on Panasonic’s battery for Tesla) by clicking on the names of each component.

The li-ion battery was invented by John B. Goodenough in 1980 but was eventually patented and commercialized by the Sony corporation of Japan in the early 1990s. Unfortunately, Goodenough did not get much reward for the commercial success of his invention.

Li-ion is currently the preferred battery for many products because lithium is the lightest metal and has excellent electrochemical properties. Li-ion batteries have high energy density and are considered chemically stable, unlike previous lithium-metal based batteries.

The different types of li-ion battery are determined by their specific chemistries. But they share the same basic structure and components.

The most complex and important component of the battery, the cathode is the positive charge. It contains the most materials and therefore constitutes the bulk of the battery cost. The cathode, usually set on an aluminum current collector, discharges lithium ions to the anode when the battery is being charged. When the battery is fully charged and in use, the ions flow back to the cathode. In addition to lithium, the most common metals in a cathode are cobalt, nickel, and manganese, and the specific choices and proportions of these metals determine the properties and performance of the battery.

As its name suggests, the separator’s main function is to separate the cathode and anode, while still allowing lithium ions to flow back and forth between the two parts. It contains microscopic pores, measured in nanometers, that allow the ions to flow through but can also close up in the event of overheating. The separator is typically made of a material called polyolefin, which contains ethylene that is derived from petrochemical sources. It is a low cost and chemically stable material.

The anode is the negative charge in li-ion batteries and is fairly simple in composition. It is made almost entirely of layers of carbon, in the form of graphite. Japan’s Sony originally used coke for the anode material but then switched to graphite because of its superior long-term stability. In the future, graphene or silicon could increasingly replace graphite as the primary anode material as they are, respectively, more reliable and have better energy density.

The electrolyte functions as a conductive catalyst that promotes the movement of the ions between the cathode and the anode. It is generally composed of soluble lithium salts and other organic compounds in a liquid solution, although sometimes it can be a gel. Different additives are put into the electrolyte solution to increase conductivity, though such additives are usually kept an industry secret. The electrolyte should be stable and is usually contained in the separator part of the battery.