How long can a battery smaller than a grain of salt provide power?

Batteries are an essential part of our lives. They come in all sizes, from large batteries that power electric cars to button batteries that fit into watches.

How small is the smallest battery you have ever seen?

Recently, research teams from Chemnitz University of Technology in Germany and the Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences have collaborated to develop the smallest microbattery to date, which is smaller than a grain of salt. It can power the world's smallest computer chip for about 10 hours and can be recharged repeatedly.

The world's smallest micro battery (Image source: References)

How do batteries work?

We can think of a battery as a multi-layer sandwich, with two electrodes storing electrical energy in the form of chemical energy. Between the two electrodes, an electrolyte guides the flow of charge, and two metal collectors on the electrodes lead the current to the external circuit. The smaller the electrode, the less charge it can hold, and cracks and other defects can also prevent the flow of charge. The twisted channels of ions and electrons in thick layers of material will also increase resistance, causing power loss.

Button battery structure (Image source: self-translated by the author)

There are two key points in the development of micro batteries: small and fine. Small refers to small size; fine refers to the battery having sufficient energy density, which requires a particularly high manufacturing process.

The production technology of micro batteries is completely different from the battery manufacturing technology used in everyday use.

Button cells with high energy density are manufactured using wet chemistry, where the battery's electrode materials and additives are coated on metal foil, and the electrolyte membrane is sandwiched between the electrodes, with an electrode thickness of up to 100 µm. The battery electrodes produced by this manufacturing method are too thick, while the chip allows for an electrode thickness of several microns, and the amount of charge that can be accommodated is also limited. This poses a huge challenge to the process and performance of micro batteries.

In order to achieve the goal of making microbatteries small and precise, the team used the "Swiss roll" process. As the name suggests, the battery is rolled up layer by layer like a Swiss roll.

The appearance of Swiss roll (Image source: Veer Gallery, References)

The "Swiss roll" process creates a layered system with tension by coating different films. This tension is like the energy brought by the spring inside a steel tape measure. The tension will be released by the film automatically rolling into a Swiss roll structure. Therefore, no external force is required to build this spontaneously winding cylindrical microbattery.

The standard "Swiss roll" microbattery has at least five layers: two collector layers, a cathode film, an anode film and an electrolyte film. Such a complex stacking requires extremely high production technology. In addition, the "Swiss roll process" has very high requirements for the toughness of the film, and it is also necessary to avoid problems such as battery short circuits caused by the rolling process.

Swiss roll (Image source: self-translated by the author)

Microbatteries have great potential and are expected to be used in areas such as the Internet of Things and micro medical implants.

Produced by: China Science Expo

Author:Sasha

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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