The new design helps develop powerful micro batteries

Translating the electrochemical performance of large-format batteries into microscale power sources has been a long-standing technological challenge, limiting the ability of batteries to power microdevices, microrobots, and implantable medical devices. Researchers at the University of Illinois Urbana-Champaign (UIUC) have created a high-voltage (>9V) microbattery with high energy and power density unmatched by any existing battery design.

Paul Braun Professor of Materials Science and Engineering (Grainger Distinguished Chair in Engineering, Materials research laboratory director), Dr. Sungbong Kim (postdoc, MatSE, current assistant professor at the Korean Military Academy, co-first author), and Arghya Patra (graduate student, MatSE, MRL, co-first author) recently published their paper “Series-Integrated Miniature High-Voltage, High-Power Batteries” in Cell reports. Physical sciences.

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Schematic of the microbattery design.

The team demonstrated hermetically sealed (closed to avoid exposure to ambient air), durable, compact lithium batteries with exceptionally low package mass fraction in single, dual and triple stack configurations with unprecedented operating voltages, high power densities and energy densities.

Braun explains: “We need powerful tiny batteries to unlock the full potential of microscale devices, improving electrode architectures and proposing innovative battery designs.” The problem is that as batteries get smaller, the packaging dominates the volume and mass of the battery while the electrode area gets smaller. This results in dramatic reductions in battery energy and power.

In their unique design of powerful microbatteries, the team developed a new 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 pack mass fraction (10.2%) of batteries. Also, they stacked the electrode cells vertically in series (so the voltage of each cell adds up), which allowed for the battery’s high operating voltage.

Another way these micro batteries are improved is by using very dense electrodes which offer energy density. Normal electrodes are almost 40% by volume occupied by polymers and carbon additives (non-active materials). Braun’s group has developed electrodes using an intermediate temperature direct electrodeposition technique that are completely dense and without polymer and carbon additives. These fully dense electrodes offer higher volumetric energy density than their commercial counterparts. The microbatteries in this research were fabricated using dense DirectPlate LiCoO electroplating2 electrodes manufactured by Xerion Advanced Battery Corporation (XABC, Dayton, Ohio), a Braun research company.

Patra says, “Until now, electrode architectures and cell designs at the micro-nano scale have been limited to high power density designs at the expense of porosity and volumetric energy density. Our work has been successful in creating a microscale power source that exhibits both high power density and volumetric energy density.”

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Size comparison of a US penny (left) and an assembled microbattery (right).

An important application space for these microbatteries includes powering insect-sized microrobots to obtain valuable information during natural disasters, search and rescue missions, and in hazardous environments where direct human access is impossible. Co-author James Pikul (assistant professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania) points out that “high voltage is important for reducing the electronic load a microrobot must carry. 9V can directly power motors and reduce loss of energy associated with increasing the voltage to the hundreds or thousands of volts needed for some actuators.This means that these batteries allow for system-level improvements as well as improved energy density, so that small robots can travel farther or send information more critical of human operators”.

Kim adds, “Our work bridges the knowledge gap at the intersection of materials chemistry, unique material manufacturing requirements for energy-dense planar microbattery configurations, and applied nano-microelectronics that require an on-line power source.” high voltage board to operate microactuators and micromotors”.

Braun, a pioneer in the field of battery miniaturization, concludes: “Our current microbattery design is suitable for high energy, high power, high voltage, single discharge applications. The next step is to translate the design into all solid-state microbattery platforms, batteries that would be inherently safer and more energy-dense than their liquid-cell counterparts.”

Other contributors to this work include Dr. James H. Pikul (Assistant Professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania), Dr. John B. Cook (XABC), Dr. Ryan Kohlmeyer (XABC), Dr. Beniamin Zahiri (Research Assistant Professor, MRL, UIUC) and Dr. Pengcheng Sun (Researcher, MRL, UIUC).

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