Information workplace | ILLINOIS
CHAMPAIGN, Fig – The thin-film lithium-ion batteries used in micro-devices such as portable and medical electronics may perform well for their mass, but their limited size does not provide enough power for many devices. Researchers have introduced a manufacturing process that uses lithography and electrodeposition to make micro-batteries with thick 3D electrodes – and each unit is sealed in a gel-filled package. The new prototype shows the highest peak power density of any reported microbattery, the researchers said.
The new study, led by postdoctoral fellow Pengcheng Sun of the University of Illinois Urbana-Champaign and professor of materials science and engineering Paul Braun, was published in the journal Advanced Materials.
Most micro-batteries have very thin, flat anodes and cathodes that are space efficient but do not provide the breakdown necessary for the wireless transmission needs of today’s technologies, the researchers said.
“The answer seems to be to use thicker electrodes that could hold more energy in a confined space, but that alone only increases the distance ions and electrons travel and reduces power,” Sun said. “Using porous 3D electrodes filled with liquid electrolyte can shorten this path, but it is extremely difficult to package such microbatteries.”
The team said there was a study in which embossed lithography was used to create a 3-D microbattery that had high peak performance using a liquid electrolyte. However, the performance of this example was measured under laboratory conditions with an unsealed battery.
In the new study, the team developed a unique capillary filling process that allows gel electrolyte to be poured into the porous 3D electrodes, allowing the microbattery to be packaged airtight.
“Using the thicker gel electrolyte instead of a liquid gives us a lot more control,” said Braun. “The gel nature of the electrolyte gives us more time to seal the battery without the electrolyte leaking. By default, the gel also makes for a safer lithium-ion battery as it is less likely to leak, which can be a problem with lithium-ion batteries filled with liquid electrolyte. “
The new packaged battery cells have high energy and power densities of 1.24 joules per square centimeter and 75.5 milliwatts per square centimeter, respectively, which is about ten times better than what is currently available, the researchers said. The batteries can be changed 200 times under normal conditions, whereby the initial discharge capacity is retained at 75%. and using a liquid electrolyte, new batteries offer an even higher power density of 218 milliwatts per square centimeter, the study reports, and show the potential for further improvement.
“Our micro-battery could provide micro-scale autonomous power for 132 days,” Sun said. “This is based on the reasonable assumption that this type of device consumes 5 microwatts in standby mode and 5 milliwatts during data transmission if the standby time is 100 seconds and the transmission time is 10 milliseconds.”
The team said the manufacturing and packaging techniques used in this study could accelerate the development of high-performance, microscale solid-state storage devices with complex 3D electrode configurations.
The US Department of Defense, the National Science Foundation, and the National Natural Science Foundation of China supported the study.
Braun is director of the Materials Research Laboratory and also a member of the Beckman Institute for Advanced Science and Technology, the Holonyak Micro & Nanotechnology Lab, and the chemistry and engineering departments in Illinois.