Could Microbatteries Be the Next Step in Li-ion Battery Evolution?
The need for smaller batteries with higher energy and power density has given rise to new technology: the microbattery. What is this technology and what research has been revolving around it?
In many ways, the history of electronics has been a history of scaling devices smaller and smaller. One growing field that is feeling the pressure of this trend is IoT, where engineers are working tirelessly to decrease device area. However, this pursuit of IoT scaling has been hindered mainly by a crucial component: the battery.
A high-level overview of some design challenges facing IoT devices. Image used courtesy of Design Spark
This challenge has inspired the advent of the "microbattery," a new paradigm in battery technology and research. The field's reach can be seen everywhere, from academia to industry, where companies like Connect 2 Cleanrooms (C2C) and Ilika are working together to create the right environment needed to manufacture this specific type of technology.
In this article, let's discuss the technology on a higher level and touch on many of the research developments in the field.
What is a Microbattery?
On a high level, microbatteries are simply batteries that are small enough to be embedded into a device's sensor or processor circuitry.
Batteries have historically been the bottleneck towards scaling electronic devices and systems. This scaling issue is real in almost all "wireless" devices, from electric cars to smartphones; scaling down battery size while maintaining equal or better capacity has been a significant challenge. In general, microbatteries attempt to address this problem by leveraging solid-state techniques to create smaller batteries with a sufficient capacity.
An example of a microbattery that has been fabricated on the backside of a silicon chip. Image used courtesy of UC Berkely
Traditionally, microbatteries use thin-film lithium-ion (Li-ion) technology, which has allowed them to achieve volumes smaller than 10 mm3. These techniques may have helped create batteries with solid power relative to their mass; however, the power output is still too small to support most wireless devices.
Further, conventional thin-film Li-ion technology becomes mostly impractical to manufacture as technology scales below 10 mm3. These issues are mainly because of the thin electrodes used, which allow for fast transport of electrons and ions, but eventually limits storage capacity and manufacturability.
These challenges have prompted scientists to look for new techniques for achieving even better microbatteries.
Fab Process Tackles Power Density Challenges
One university that is working on novel approaches to microbatteries is the University of Illinois Urbana-Champaign.
Earlier this year, researchers at the university introduced a new microbattery fabrication process where thick, 3D electrodes are developed using lithography and electrodeposition and then sealed in a gel electrolyte.
Schematic of the researcher’s proposed microbattery fabrication. Image used courtesy of Sun et al
In their paper, the researchers share that their new microbattery can achieve a power density up to 218 mWcm-2 and also has the ability to be cycled 200 times in the air with 75% capacity retention. According to their estimates, this is the highest peak power reported of any microbattery to date.
Though this new technique hopes to open the doors for future microbattery development, there is still a long way to go, with many other challenges, before this technology can become completely mainstream. Another group of researchers, this time from the University of Pennsylvania, are aiming to tackle another challenge: energy density.
A New Way of Packaging Microbatteries
Another university working at solving microbattery challenges is the University of Pennsylvania.
The new microbattery on a dandelion is shown for scale. Image used courtesy of University of Pennsylvania
Over the summer, these researchers released new data that introduced a new way to build and package microbatteries to maximize energy density per volume.
The key development in the research was to create a new kind of current collector and cathode that doubles as both a conductor and as a protective shell for the battery. This structure aims to remove the need for the non-conductive packaging that usually protects a battery's internals, thus effectively increasing the battery's size and energy density.
The researchers claim that this technique can create microbatteries with energy densities up to 4x that of the current state-of-the-art.
Keeping the Progress Going
As the demand for smaller and more lightweight electronics increases, there will ultimately be a need for smaller and more lightweight batteries. Microbatteries could be a potential step in this direction, and the amount of development occurring in both academia and industry is highly promising. It will be interesting to see where this research goes and if more companies in the industry will start investing in it as well.
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