One of the biggest hurdles with electrification is the batteries. Despite advances in battery technology that allow for ever-greater storage capacity and faster charging speeds, batteries’ considerable weight and volume represent challenges for designers. For example, electric vehicle batteries typically weigh between 1,000 and 2,000 pounds. Based on their singular function, batteries are add-ons rather than fundamental elements, inhibiting the shift to a renewable economy.
Multifunctional Materials: Batteries That Bear Load
One of the most compelling ways to make batteries multifunctional is to impart them with structural properties. For example, scientists at Chalmers University of Technology in Gothenburg, Sweden, have developed a structural battery—a power source that supports loads. Made of carbon fiber, the load-bearing battery is considered a form of “mass-less energy storage” since its weight is associated entirely with structure.
Beyond Devices: The Architectural Potential of Structural Batteries
While vehicles and mobile electronics are obvious applications for structural batteries, buildings can also benefit from this technology. Buildings have long functioned as batteries in the broad sense of storing and releasing energy, and thermal mass is one of the most effective methods of coupling energy storage with structure. However, the marriage of lithium-ion (or other) electrochemical storage media and structure is relatively new.
Two Paths to Structural Energy Storage
Structural battery technology originated in 2007 when the US Army Research Laboratory (ARL) first attempted to create a laminated structural battery composite. Since then, two primary approaches have emerged: embedded batteries, in which lithium-ion cells are incorporated within a composite, and laminated structural electrodes, such as the above example.
Chalmers University’s Carbon Fiber Breakthrough
The Chalmers technology comprises a carbon fiber negative electrode, fiberglass textile, and aluminum foil positive electrode with a lithium iron phosphate coating. The structural battery exhibits an energy density of 24 Wh/kg, roughly 20% of the capacity of today’s typical lithium-ion batteries, and a stiffness of 25 GPa. Despite this suboptimal performance, the team predicts that its next version, which will substitute the aluminum foil with carbon fiber, will boast an energy density of 75 Wh/kg and a stiffness of 75 GPa. (For reference, the elastic modulus of concrete ranges from 30 to 50 GPa.) While carbon fiber composites are prohibitively expensive for most building applications, other structural composites employing conductive materials are being developed for construction.
Power in the Foundation: Electrified Cement
One promising development is electrified cement. Civil engineer Franz-Josef Ulm and his research team at MIT have developed a cement-based battery, known as a supercapacitor, that incorporates two electrically charged plates with an interstitial electrolyte and membrane. Because cement is not a good conductor, Ulm added highly conductive carbon black, which forms interconnected strands within the cement mixture. According to the MIT team, if this conductive cement were used in the concrete foundation of an average home (roughly 45 m3 in volume), it could supply enough power for one day’s needs (approximately 10 kWh).
Benefits of a Dual-Function Building Material
Adding electrochemical storage capabilities to a load-bearing construction material in this way offers many advantages. This multifunctional approach can reduce overall physical resources, assuming the material performs adequately in both functions. As massless storage, the battery adds no additional dead load and does not occupy additional area or volume. Meanwhile, a necessary building element provides an added energy storage benefit.
Barriers to Adoption: Safety, Scale, and Performance
However, many concerns must be addressed before Building-Integrated Structural Batteries (BISBs) are ready for architectural applications. The optimal balance of mechanical strength and storage capacity can be challenging to achieve. (The MIT team claims that up to 10% carbon black may be added to a cement mixture before its structural integrity is compromised.) The structural battery’s scale and form also affect its effectiveness as a storage medium. Safety is also a concern, as an electrified structure could be vulnerable to damage or fire and must be thoroughly evaluated for potential human health effects.
A Market Poised for Growth
Despite these cautions, structural batteries are predicted to be in considerable demand based on their impressive potential. A recent report by Credence Research indicates that the global structural battery market will grow more than 20% by 2032. The study predicts that the emphasis on low-carbon construction will motivate the rapid adoption of structural batteries in buildings. Electrified building structures could take full advantage of the proliferation of renewable energy systems, provide more reliable energy in remote or vulnerable areas, and accelerate society’s shift toward a net-zero carbon future.
