Scientists create rice grain size microbatteries to power 'smart dust'

After smartphones and smartwatches, it is time for "smart dust."
Rupendra Brahambhatt
Micro-Swiss roll and a grain of rice.
Micro-Swiss roll and a grain of rice.Advanced Energy Materials
  • Scientists demonstrate microbatteries as tiny as rice grains.
  • Such microbatteries would be used to power microbots, electronic chips, microsensors, and smart dust.
  • Smart dust is a futuristic IoT application that will incorporate a network of millions of autonomous microsystems.

A team of researchers at the Chemnitz University of Technology in Germany has developed microbatteries that could be used in the future to power advanced IoT (Internet of things) applications like smart microsensors and millimeter-scale computing devices.

The fancy fitness bands and smartwatches that we use today are some early applications of IoT (a system of computers and sensors that are connected to one another via the internet). The researchers believe that in the future, we could see a highly advanced version of IoT called “smart dust.” This technology would probably exist in the form of a large network of billions of autonomous microsensors and microcomputing devices.

Such micro and nano-scale devices would be distributed everywhere, including our cities, factories, and forests (just like dust and air), and monitor the different changes happening around us. For instance, a smart dust network in a jungle would be able to predict fire incidents way before they happen by continuously keeping an eye on the moisture levels and heat. The technology might also be able to detect the presence of new viruses in our environment and inform us about the same before they spread.

The researchers suggest that just like contemporary smart home devices, all the components of the smart dust network would use the internet to connect and exchange information with one another. However, a big challenge with smart dust and other micro and nano-scale devices is to provide them with highly efficient and tiny power sources. This is where the microbatteries demonstrated by Chemnitz University researchers could play an important role.

The science behind smart dust microbatteries

Scientists create rice grain size microbatteries to power 'smart dust'
The internal structure of the proposed Swiss roll microbattery.
Zhe Qu et al. 2022/Advanced Energy Materials 

The microbatteries created by researchers can be considered somewhat similar to the Swiss roll batteries used in electric cars produced by Tesla. One of the authors of the study and scientist at Chemnitz University’s Center for Materials, Architectures, and Integration of Nanomembranes (MAIN), Dr. Minshen Zhu told Nanowerk, “the most successful design in the bulky battery world is to comprise many layers of the electrode material into a limited volume. For instance, Tesla is using so-called Swiss roll cylinder batteries for its electric cars."

However, Tesla’s cylindrical Swiss roll batteries can not be used directly for powering a smart dust system because each of them measures 1.8 cms in diameter. Whereas the researchers needed batteries having diameters in micrometers because, unlike a car, a smart dust network is composed of micro-scale devices. Such components require power sources with great energy density and a small footprint.

So the researchers decided to create their own modified on-chip Swiss role batteries. They employed micro origami, a self-assembly technique that involves the use of a thin metal layer (which collects current) surrounded by a stack of flat actuator layers (regulate the movement of current) and swellable hydrogen layers. This complex method resulted in the formation of multiple battery rolls, each having size of less than a grain of rice.

The diameters of each microbattery were 178 µm (178 x 10-6 meters), and therefore they can be easily integrated into any chip-based system that functions as microcomputers or a tiny sensor chip.

Not an ordinary power source

The microbatteries come equipped with an electrode slurry (a mixture of conductive particles and solvent that decides the performance of a battery) has a drying period of one hour. This is a significant achievement because traditional electrode slurries have drying periods of around 10 hours. Longer drying periods are detrimental to the micro-layered structure of the microbatteries and adversely affect their energy densities.

The researchers also linked a 250 micrometer-long zinc wire with the microbatteries to achieve a desirable electrode footprint falling in the sub-millimeter range. "Our work offers a new technology to create on-chip micro batteries and is compatible with both on-chip processes (lithography, etching, etc) and battery fabrication protocols (synthesis of high-performance electrode materials, making electrode slurries and uniform coating on the current collector),” said Dr. Zhu.

Although the technology looks like a great energy solution for smart dust and other micro-scale devices, it is not the first Swiss roll microbattery developed by Dr. Zhu and his team. They previously developed microbatteries of the size of a grain of salt, and now they look forward to making Swiss roll microbatteries commercially available for use in real-world IoT applications.

The study is published in the journal Advanced Energy Materials.

Abstract:

As substantial progress has been made to miniaturize intelligent microsystems to the sub-square-millimeter scale, there is a desperate need to move beyond existing microbattery technologies to offer adequate energy at the same footprint. A micro-origami technology able to wind up a flat layer stack into a Swiss roll presents a promising approach in this regard because it mimics the most successful way to make energy-dense full-sized batteries. Here, an on-chip Swiss-roll current collector made via the micro-origami process is developed and it is infused with a MnO2 slurry comprising a zincophilic binder. The zincophilic binder layer enhances zinc ion transportability and suppresses MnO2 dissolution. The MnO2 Swiss-roll microelectrode is used to create an on-chip microbattery with a small electrode footprint area of 0.75 mm2, which shows a footprint capacity up to 3.3 mAh cm–2. The microbattery demonstrates a reversible capacity of more than 1 mAh cm–2 for 150 cycles. The battery stability can be improved to over 600 cycles at a 50% depth of discharge. An on-chip integration of a microsystem with the microbattery is demonstrated. The microbatteries set foot in the untrodden sub-square-millimeter area providing adequate energy for ever more miniaturized intelligent microsystems.

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