Multifunctional Structural Battery Combines Energy Storage and Load-bearing CapacityMultifunctional Structural Battery Combines Energy Storage and Load-bearing Capacity

Batteries are at the core of green and clean technologies that propel forward the automotive, mobility, and aerospace segments. All these markets demand both high energy density for energy storage and high load-bearing capacity. Whereas conventional structural battery technology has struggled to enhance both functions concurrently, KAIST researchers have succeeded in developing foundational technology to address this issue.

The KAIST team, led by Professor Seong Su Kim from the Department of Mechanical Engineering, has developed a thin, uniform, high-density, multifunctional structural carbon-fiber-composite battery capable of supporting loads that is reportedly safe from fire risks. A multifunctional structural battery refers to the ability of each material in the composite to simultaneously serve as a load-bearing structure and an energy-storage element.

Energy-storing composite materials

Early structural batteries involved embedding commercial lithium-ion batteries into layered composite materials. These batteries suffered from low integration of their mechanical and electrochemical properties, leading to challenges in material processing, assembly, and design optimization that made commercialization difficult.

To overcome these challenges, Professor Kim's team explored the concept of "energy-storing composite materials," focusing on interface and curing properties, which are critical in traditional composite design. This led to the development of high-density multifunctional structural carbon-fiber-composite batteries that maximize multifunctionality.

Related:The Limits of Lithium in Meeting Future Battery Demand

Energy-storing carbon-fiber epoxy composites also function as structural members in a new battery design concept. Image courtesy of KAIST.

The team analyzed the curing mechanisms of epoxy resin, known for its strong mechanical properties, combined with ionic liquid and carbonate electrolyte-based solid-polymer electrolytes. By controlling temperature and pressure, they were able to optimize the curing process.

Enhanced current density

The newly developed structural battery was manufactured through vacuum compression molding, increasing the volume fraction of carbon fibers — serving as both electrodes and current collectors — by over 160% compared to previous carbon-fiber-based batteries. 

This greatly increased the contact area between electrodes and electrolytes, resulting in a high-density structural battery with improved electrochemical performance. Furthermore, the team effectively controlled air bubbles within the structural battery during the curing process, simultaneously enhancing the battery's mechanical properties.

 “We proposed a framework for designing solid-polymer electrolytes, a core material for high-stiffness, ultra-thin structural batteries, from both material and structural perspectives,” explained Kim. “These material-based structural batteries can serve as internal components in cars, drones, airplanes, and robots, significantly extending their operating time with a single charge. This represents a foundational technology for next-generation multifunctional energy.”

This research was supported by the National Research Foundation of Korea’s Mid-Career Researcher Program and the National Semiconductor Research Laboratory Development Program.