Thin-film lithium-ion batteries used in microdevices such as portable and medical electronics are often unable to provide enough power for many devices due to size limitations.
The new study from University of Illinois Urbana-Champaign outlines how researchers built a prototype with thick 3D electrodes using lithography and electrodeposition, that seals each unit in a gel electrolyte-filled package.
While most microbatteries have space-saving thin, flat anodes and cathodes, researchers said these are not sufficient for the wireless transmission required of today’s technologies.
“The answer might seem to be to use thicker electrodes, which could hold more energy on a confined footprint, but that alone will only increase the pathway that ions and electrons must travel, cutting down on power,” project leader Pengcheng Sun said in a statement.
“Using 3D porous electrodes filled with liquid electrolyte can shorten this pathway, but it is extremely challenging to package such microbatteries.”
According to the team, a previous study that used imprinting lithography to build a 3D microbattery achieved high peak power using a liquid electrolyte, but the performance of that example was measured from an unsealed battery under laboratory conditions.
For the new study, published in Advanced Materials, researchers developed a capillary filling process that could fill gel electrolyte into the 3D porous electrodes, making airtight packaging of the microbattery possible.
Paul Braun, professor of materials science and engineering at Illinois, explained that the thicker gel electrolyte gave the team more control than a liquid would. “The gel nature of the electrolyte gives us more time to seal the battery without the electrolyte spilling out,” he said.
“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 per cent retention of the initial discharge capacity, and new batteries provide an even higher power density of 218mW/cm2 using a liquid electrolyte, the study reported.
Sun added that the microbattery could provide a microscale autonomous power for 132 days, based on the assumption that this type of device draws five microwatts in standby mode and five milliwatts during data transmission, when the standby time is 100 seconds and the transmit time is ten milliseconds.
Fabrication and packaging techniques used in the study could accelerate development of high-performance solid-state microscale storage devices with complex 3D electrode configurations, the team said.