Structural battery
Structural batteries are multifunctional materials or structures, capable of acting as an electrochemical energy storage system (i.e. batteries) while possessing mechanical integrity.<ref>"Concept for a structural battery". ResearchGate. Retrieved 4 August 2020.</ref><ref>Johannisson, Wilhelm; Ihrner, Niklas; Zenkert, Dan; Johansson, Mats; Carlstedt, David; Asp, Leif E.; Sieland, Fabian (10 November 2018). "Multifunctional performance of a carbon fiber UD lamina electrode for structural batteries". Composites Science and Technology. ScienceDirect. 168: 81–87. doi:10.1016/j.compscitech.2018.08.044.</ref>
They help save weight and are useful in transport applications<ref>Bradburn, David (12 February 2014). "Structural Batteries". Materials Today. Retrieved 30 January 2020.</ref><ref>"Study links carbon fibre microstructure to Lithium insertion mechanism in structural batteries". Green Car Congress. 18 October 2018.</ref> such as electric vehicles and drones,<ref>"Structural batteries lighten drones' loads". Chemical & Engineering News. American Chemical Society. Retrieved 4 August 2020.</ref> because of their potential to improve system efficiencies. Two main types of structural batteries can be distinguished: embedded batteries and laminated structural electrodes.<ref>Asp, Leif (21 November 2019). "Structural battery composites: a review". Functional Composites and Structures. 1 (4): 42001. Bibcode:2019FCS.....1d2001A. doi:10.1088/2631-6331/ab5571. S2CID 210257472.</ref>
Embedded batteries
Embedded batteries represent multifunctional structures where lithium-ion battery cells are efficiently embedded into a composite structure, and more often sandwich structures. In a sandwich design, state-of-the-art lithium-ion batteries are embedded forming a core material and bonded in between two thin and strong face sheets (e.g. aluminium). In-plane and bending loads are carried by face sheets while the battery core takes up transverse shear and compression loads as well as storing the electrical energy. The multifunctional structure can then be used as a load-bearing as well as an energy storage material.<ref>Pereira, Tony (29 January 2009). "Energy Storage Structural Composites: a Review". Journal of Composite Materials. 43 (5): 549. Bibcode:2009JCoMa..43..549P. doi:10.1177/0021998308097682. S2CID 13864856.</ref>
Laminated structural electrodes
In laminated structural electrodes the electrode material possesses an intrinsic load-bearing and energy storage function. Such batteries are also called massless batteries, since in theory vehicle body parts could also store energy thus not adding any additional weight to the vehicle as additional batteries would not be needed.<ref>"Massless Energy Storage: The Next Step in Battery Technology". www.azocleantech.com. Archived from the original on 25 October 2021. Retrieved 22 February 2022.</ref> An example for such batteries are those based on a zinc anode, manganeseoxide cathode and a fiber/ polymer composite electrolyte.<ref>Wang, Mingqiang (4 January 2019). "Biomimetic Solid-State Zn2+ Electrolyte for Corrugated Structural Batteries". ACS Nano. 13 (2): 1107–1115. doi:10.1021/acsnano.8b05068. PMID 30608112. S2CID 58589418.</ref> The structural electrolyte enables stable charge and discharge performance. This assembly has been demonstrated in an unmanned aerial vehicle. A commonly proposed structural battery is based on a carbon fiber reinforced polymer (CFRP) concept. Here, carbon fibers serve simultaneously as electrodes and structural reinforcement. The lamina is composed of carbon fibers that are embedded in a matrix material (e.g. a polymer). Multiple layers of carbon fibers are impregnated with a matrix that enables load transfer between the fibers but also lithium-ion transport, unlike commonly used vinylester or epoxy matrices. This type of energy storage system can be based on a nickel<ref>"BAE provides details of 'structural battery' technology". BBC. 8 March 2012. Retrieved 30 January 2020.</ref> or on lithium-ion chemistry.<ref>Asp, Leif (21 November 2019). "Structural battery composites: a review". Functional Composites and Structures. 1 (4): 42001. Bibcode:2019FCS.....1d2001A. doi:10.1088/2631-6331/ab5571. S2CID 210257472.</ref> The laminate is made of the combination of a negative electrode, a separator and a positive electrode, embedded in an ionically conductive and structural electrolyte. In the laminated structural electrodes concept, carbon fibers can be used to intercalate e.g. lithium-ions (structural anode); similarly, to commercially available graphite anodes. The structural cathode consists of carbon fibers coated with electrochemically active species, e.g. lithium oxide particles. An example of a structural battery exploiting a carbon fiber negative electrode and lithium iron phosphate positive electrode was demonstrated to be capable of lighting an LED.<ref>Asp, Leif E.; Bouton, Karl; Carlstedt, David; Duan, Shanghong; Harnden, Ross; Johannisson, Wilhelm; Johansen, Marcus; Johansson, Mats K. G.; Lindbergh, Göran; Liu, Fang; Peuvot, Kevin (2021). "A Structural Battery and its Multifunctional Performance". Advanced Energy and Sustainability Research. 2 (3): 2000093. doi:10.1002/aesr.202000093. ISSN 2699-9412.</ref> Some separator material is used in between the two structural electrodes to prevent short-circuits.<ref>Asp, Leif (21 November 2019). "Structural battery composites: a review". Functional Composites and Structures. 1 (4): 42001. Bibcode:2019FCS.....1d2001A. doi:10.1088/2631-6331/ab5571. S2CID 210257472.</ref><ref>Hurst, Nathan (2 November 2018). "Let's Build Cars Out of Batteries". Smithsonian Magazine. Retrieved 30 January 2020.</ref> However, the CFRC concept described above is still being researched.<ref>Bradburn, David (12 February 2014). "Structural Batteries". Materials Today. Retrieved 30 January 2020.</ref>
