New 3D microbatteries offer high levels of power efficiency
A US team claims to have developed a manufacturing process for 3D lithium-ion microbatteries which offer higher peak power than the current industry standard.
The team, based at the University of Illinois Urbana-Champaign, conducted a study that supports to have introduced a prototype for batteries with thick, 3D electrodes manufactured using lithography.
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These kinds of lithium batteries are frequently used in microdevices, such as portable and medical electronics, and generally offer decent power efficiency for their size.
The team hopes to extend the power capacity within a small shell to offer flexibility to power larger devices using smaller batteries.
The researchers claim the new prototype shows the highest peak power density for any reported microbatteries.
Most modern microbatteries contain thin anodes and cathodes which work well for saving space, but the researchers suggest these are not sufficient for the levels of energy needed for wireless transmission required for today's technologies.
Postdoctoral researcher Dr Pengcheng Sun, the project's head, said the initial answer may be to use thicker electrodes, which can hold more energy in the confined footprint.
However, he warned this would only increase the pathway the electrons must travel, limiting the net power gains.
"Using 3D porous electrodes filled with liquid electrolyte can shorten this pathway, but it is extremely challenging to package such microbatteries," he added.
The team pointed to a previous study that developed a 3D microbattery using imprinting lithography and achieved high power using a liquid electrolyte, but the performance of this prototype was measured from an unsealed battery under laboratory conditions.
In their amended study, the team developed a unique capillary filling process that could fill gel electrolyte into the 3D porous electrodes, making airtight packaging of the microbattery possible.
Paul Braum, a material science and engineering professor at the University, said using the gel electrolyte instead of a liquid gives them much more control of the battery's power levels.
He added: “The gel-nature of the electrolyte gives us more time to seal the battery without the electrolyte spilling out. And, by default, the gel also makes for a safer lithium-ion battery because it is less likely to leak, which can be a problem in liquid electrolyte-filled lithium-ion batteries.”
Researchers said the new packaged battery cells have energy and power densities of 1.24J/cm2 and 75.5mW/cm2 respectively.
The batteries can reportedly be cycled 200 times in normal conditions with 75% retention of the initial discharge capacity.
Using a liquid electrolyte, the new batteries provide an even higher power density of 218mW/cm2, with the potential for further improvements, the data suggests.
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Dr Sun added: “Our microbattery could provide a microscale autonomous power for 132 days. This is based on the reasonable assumption that this type of device draws 5 microwatts in standby mode and 5 milliwatts during data transmission, when the standby time is 100 seconds and the transmit time is 10 milliseconds.”
The team claim the fabrication and packaging techniques used in this study could accelerate the development of high-performance solid-state microscale storage devices with complex 3D electrode configurations.
The study itself was further supported by The U.S. Department of Defense, the National Science Foundation and the National Natural Science Foundation of China.
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