This article was taken from the October issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content bysubscribing online
Each month Wired’s chemist Dr John Emsley, author of nine books and 110 research papers, deconstructs an everyday product. This month: Energizer lithium batteries
Retouch your face, treat bipolar disorder and create nuclear fusion, while powering an alarm clock
INGREDIENTS
> A positive electrode (anode) made of lithium
> A negative electrode (cathode) made of manganese dioxide and graphite
> An electrolyte of lithium perchlorate in a mixed solvent of propylene carbonate
LithiumThe lightest of all metals, lithium is also used in greases, to treat bipolar disorder and in hydrogen bombs. In a battery, current is generated at the anode and the cathode, and involves a transfer of electrons.
The chemical reaction begins when the battery becomes part of an external circuit through which the electrons flow between electrodes. The lithium atoms release electrons to become positive ions (Li+); the manganese atoms gain them, thereby going from Mn4+ to Mn3+.
Lithium stearate is made from stearic acid, a fatty acid that’s a component of most lubricant greases. It stays soft at temperatures as low as -60˚C and is used on vehicles in the Antarctic. A component in hydrogen bombs is lithium hydride, in which lithium is the lithium-6 isotope and the hydrogen is the hydrogen-2 isotope, also known as deuterium.
The solventsTo dissolve charged ions, in this case Li+ and ClO4 –, a solvent is required; but water reacts too violently. Propylene carbonate (C4H6O3) works but needs diluting with dimethoxyethane (C4H10O2). In other uses C4H6O3 is a base for lipstick, and C4H10O2 is used in pesticides.
The electrolyteThis is the salt lithium perchlorate (LiClO4) dissolved in a solvent and which provides a conducting medium between the anode and cathode.
**Manganese dioxide (MnO2)**This compound solid has always been used in dry-cell batteries. MnO2 occurs naturally, as pyrolusite, which is mined on a large scale but it must be processed to remove impurities before being incorporated into batteries. MnO2 is also the black pigment commonly used in prehistoric cave paintings.
This article was originally published by WIRED UK
