Researchers at the University of Illinois Urbana-Champaign have created a high-voltage 9V lithium microbattery with a unique packaging design.
The battery is hermetically sealed to prevent exposure to ambient air in single-, double-, and triple-stacked configurations with high operating voltages, high power densities, and energy densities.
“We need powerful tiny batteries to unlock the full potential of microscale devices, by improving the electrode architectures and coming up with innovative battery designs,” said Paul Braun, Material Science and Engineering Professor at the University.
The problem, say the researchers, is that as batteries become smaller, the packaging dominates the battery volume and mass while the electrode area becomes smaller. This results in drastic reductions in energy and power of the battery.
The researchers developed novel packaging technology that used the positive and negative terminal current collectors as part of the packaging itself rather than a separate entity. This allowed for the compact volume (= 0.165 cm3) and low package mass fraction (10.2%) of the batteries. In addition, they vertically stacked the electrode cells in series (so the voltage of each cell adds), which enabled the high operating voltage of the battery.
Another way they improved the microbatteries was by using very dense electrodes, which offers energy density. Normal electrodes are almost 40% by volume occupied by polymers and carbon additives (not active materials). The researchers have grown electrodes by an intermediate temperature direct electrodeposition technique that are fully dense and without polymer and carbon additives.
These fully dense electrodes offer more volumetric energy density than their commercial counterparts. The microbatteries were fabricated using the dense electroplated DirectPlate LiCoO2 electrodes manufactured by Xerion Advanced Battery Corporation (XABC, Dayton, Ohio), a company that spun out of Braun’s research.
“To date,” says Arghya Patra, graduate student, MatSE, MRL, and co-first author of a paper on the research, “electrode architectures and cell designs at the micro-nano scale have been limited to power dense designs that came at the cost of porosity and volumetric energy density. Our work has been successful to create a microscale energy source that exhibits both high power density and volumetric energy density.”
An important application space of these microbatteries, say the researchers, includes powering insect-size microrobots to obtain valuable information during natural disasters, search and rescue missions, and in hazardous environments where direct human access is impossible.
“The high voltage is important for reducing the electronic payload that a microrobot needs to carry,” says co-author James Pikul (Assistant Professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania). “9 V can directly power motors and reduce the energy loss associated with boosting the voltage to the hundreds or thousands of volts needed from some actuators. This means that these batteries enable system level improvements beyond their energy density enhancement so that the small robots can travel farther or send more critical information to human operators.”
Dr. Sungbong Kim (Postdoc, MatSE, current assistant professor at Korea Military Academy, co-first author) adds, “Our work bridges the knowledge gap at the intersection of materials chemistry, unique materials manufacturing requirements for energy dense planar microbattery configurations, and applied nano-microelectronics that require a high-voltage, on-board type power source to drive microactuators and micromotors.”
Their current microbattery design, say the researchers, is well-suited for high-energy, high-power, high-voltage, single-discharge applications. Their next step is to translate the design to all solid-state microbattery platforms, batteries that would inherently be safer and more energy dense than liquid-cell counterparts.