Micro-batteries made possible

The micro-battery created at University of Illinois can be embedded in sensors enabling new health care possibilities. Credit: University of Illinois

Microbattery schematic illustrating lighting an LED with a 0.5 mA current which corresponds to a 600 C discharge. Credit: University of Illinois

Powering micro devices, like tiny sensors for implanting in the body, remains a challenge. Technology evolution has helped by reducing the power needs of electronics into the micro and nanoWatts range and scavenging approaches can now use ambient energy like thermal differentials, glucose, movements to power a micro device. However, these energy sources are not providing a continuous flow of energy so no matter what you still need a battery where you can store energy and tap it when needed.

The problem is that miniaturisation of batteries is not easy and one of the trickiest part is the miniaturisation of electrodes. As you shrink the size the shape of the electrodes plays an ever important role in the flow of electrons. If the electrodes are big enough the micro variations on their surface compensate one another and you don't have particular problems. However, as you shrink them their surface and 3D structures is affecting the flow of electrons to the point of decreasing the power capacity of the battery to a point where it becomes useless.

Here is where the approach to create electrodes perfected by researchers at the University of Illinois at Urbana-Champaigne comes handy.

The researchers have first determined through experiment and simulation the best structure for a specific electrode dimension and then have been able to manufacture that structure using industrial processes (a crucial requirements if you want to move into industrial production). 

Basically, they have used both 3D holographic lithography and 2D photolithography, the former to create the internal structure of the electrode, the second to shape its surface.

Normally a 3D holographic lithography involves many laser beams whose interference stimulates a photoresist to change its characteristics, i.e. its structure, practically hardening certain parts that will form the electrode and leaving the other "soft" so that they can be removed. This mechanisms is quite complex and if it works in a lab environment is no good for industrial production. The researchers have been able to achieve the same results by using special optics and a single laser beam. 

With this approach the researchers have been able to create a micro-battery (see it in the first figure) that can be used to power sensors and drug dispensers chips injected in the body, as well as applications like autonomous micro-actuators and distributed wireless sensors and transmitters.

The micro battery can be based on lithium as well as on tin, providing it a bigger bang for the buck.

Author - Roberto Saracco

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