Scientists develop world’s smallest battery: The size of a grain of sand

A research team from Chemnitz University of Technology (CUT) have developed the world’s smallest battery, which is smaller than a dust mote.

Why is there a sudden demand for a smaller battery?

As computers are getting smaller and smaller, and mobile phones are offering computing power similar to that of a laptop, the trend toward miniaturisation is expanding. Smart dust applications (or tiny microelectronic devices), such as biocompatible sensor systems in the body, demand computers and batteries smaller than a dust mote in order to function.

Unitl now, this development has been hindered by two main factors: lack of on-chip power sources for operation anytime and anywhere, and difficulties in producing integrable microbatteries.

How can these issues be rectified?

In the most recent issue of the prestigious journal: Advanced Energy Materials, several scientists, including Dr Oliver G. Schmidt—head of the Professorship for Material Systems of Nanoelectronics and Scientific Director of the Center for Materials, Architectures, and Integration of Nanomembranes (MAIN) at Chemnitz University of Technology— discuss how a solution can be realised regarding these two factors.

Researchers considered how battery-powered smart dust applications can be realised in the sub-millimetre-scale, and present the world’s smallest battery, as an application-oriented prototype.

“Our results show encouraging energy storage performance at the sub-square-millimetre scale,” said Dr Minshen Zhu, scientist included in the study.

Dr Schmidt added: “There is still a huge optimisation potential for this technology, and we can expect much stronger microbatteries in the future.”

What processes did scientists consider to create theirs?

Scientists have noted that the power to run tiny sub-millimetre-scale computers can be provided by developing appropriate batteries or ‘harvesting’ methods to generate electricity.

In the area of ‘harvesting,’ micro-thermoelectric generators convert heat to electricity, but their output power is too low to drive dust-sized chips. Researchers have discovered that mechanical vibrations are another source of energy for powering tiny-scale devices, and the small photovoltaic cells that convert light into electrical energy on small chips also hold potential.

However, an issue that researchers have faced in developing the world’s smallest battery, is that light and vibrations are not available at all times and in all places, which makes on demand operation impossible in a majority of environments. This is also the case in the human body, where tiny sensors and actuators require a continuous power supply; powerful, tiny batteries would solve this problem.

Additionally, the production of small batteries is significantly different when it comes to the construction of standard batteries. This is because compact batteries with high energy density are manufactured using wet chemistry. This means electrode materials and additives (carbon materials and binders) are processed into a slurry and coated onto a metal foil.

Microbatteries that are produced using such standard technologies can deliver good energy and power density but have a footprint of significantly more than one square millimetre.

Furthermore, stacked thin films, electrode pillars, or interdigitated microelectrodes, are used for on-chip battery manufacturing. However, these designs often suffer from inferior energy storage, and the footprint of these batteries cannot be reduced below one square millimetre.

How was this technology developed?

The goal of Professor Schmidt, Dr Zhu and their research team was to design a battery significantly less than one square millimetre across and integrable on a chip, which still has a minimum energy density of 100 microwatt hours per square centimetre.

To achieve this, the team assembled current collectors and electrode strips at the microscale – a similar process also used by Tesla on the large scale to manufacture the batteries for its e-cars.

The researchers utilised the ‘micro-origami’ process, which is a layered system with inherent tension that is created by consecutively coating thin layers of polymeric, metallic, and dielectric materials onto a wafer surface.

The mechanical tension was released by peeling off the thin layers, which then automatically snapped back to roll up into a ‘swiss-roll’ (micro-origami) architecture. Thus, no external forces were needed to create such a self-wound cylinder microbattery. This method is compatible with established chip manufacturing technologies and is capable of producing high throughput micro-batteries on a wafer surface.

By employing this method, the research team has produced rechargeable microbatteries that could power the world’s smallest batteries for approximately ten hours. The team concluded that this creation is a tiny battery with great potential for future micro- and nanoelectronic sensorics, and actuator technologies in areas such as the Internet of Things, miniaturised medical implants, microrobotic systems and ultra-flexible electronics.

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