Structural multifunctional materials have the potential to transform current technologies by implementing several functions to one material. In a multifunctional structural battery, mass saving and energy efficiency are created by the synergy between the mechanical and electrochemical properties of the material's constituents. Consequently, structural batteries could e.g. mitigate electric vehicle overweight or enable thinner portable electronics. This requires combining the best composite and battery manufacturing practices. In the present work this is achieved through the infusion of a stack of carbon fibre-based electrodes with a hybrid polymer-liquid electrolyte. The realised full cell structural battery is based on carbon fibre electrodes with a lithium iron phosphate (LiFePO4) coating on the positive side. This battery laminate shows a very good balance between energy density, stiffness and strength of 33.4 Wh/kg, 38 GPa and 234 MPa, respectively. To push these performances further, different improvement strategies are discussed, and the results are compared with previously published target performances. Ultimately, we demonstrate the feasibility of designing and manufacturing all-fibre solid-state structural batteries as a material solution for future lightweight electric commodities.

Carbon fibre based electrodes offer the potential to significantly improve the combined electrochemical and mechanical performance of structural batteries in future electrified transport. This review compares carbon fibre based electrodes to existing structural battery electrodes and identifies how both the electrochemical and mechanical performance can be improved. In terms of electrochemical performance achieved to date, carbon fibre based anodes outperform structural anode materials, whilst carbon fibre based cathodes offer similar performance to structural cathode materials. In addition, while the application of coating materials to carbon fibre based electrodes can lead to improved tensile strength compared to that of uncoated carbon fibres, the available mechanical property data are limited; a key future research avenue is to understand the influence of interfaces in carbon fibre based electrodes, which are critical to overall mechanical integrity. This review of carbon fibre based electrode materials, and their assembly strategies, highlights that research should focus on sustainable electrode materials and scalable assembly strategies.

Engineering materials that can store electrical energy in structural load paths can revolutionize lightweight design across transport modes. Stiff and strong batteries that use solid-state electrolytes and resilient electrodes and separators are generally lacking. Herein, a structural battery composite with unprecedented multifunctional performance is demonstrated, featuring an energy density of 24 Wh kg−1 and an elastic modulus of 25 GPa and tensile strength exceeding 300 MPa. The structural battery is made from multifunctional constituents, where reinforcing carbon fibers (CFs) act as electrode and current collector. A structural electrolyte is used for load transfer and ion transport and a glass fiber fabric separates the CF electrode from an aluminum foil-supported lithium–iron–phosphate positive electrode. Equipped with these materials, lighter electrical cars, aircraft, and consumer goods can be pursued.

This study focuses on the fabrication and evaluation of structural batteries, emphasizing their electrochemical performance. LiFePO₄ (LFP)-impregnated carbon fibers (CFs), produced via the powder impregnation method, were employed as positive electrodes. These electrodes underwent infusion with structural battery electrolyte (SBE) and curing to yield positive structural battery electrodes. A structural battery fully based on CFs was constructed and subjected to electrochemical testing, with positive electrodes assembled versus pristine CF of T800S as negative electrodes. The results revealed specific discharge capacities of 123 mAh g^-1_LFP for the structural positive electrode and 178 mAh g^-1_T800S for the structural battery, both at similar current densities. Both the half and full structural cells maintained capacities of 94% and 96%, respectively, during rate capability tests when reverting to their initial current densities. The electrochemical impedance spectroscopy (EIS) results revealed that, the structural battery demonstrated a relatively improved surface impedance, with the values ranging between 186 Ω cm² and 2000 Ω cm². Additionally, similar comparative studies were conducted on full cells in a commercial liquid electrolyte consisting of 1M LiPF₆ in EC: DEC (1:1 vol.%). The research introduces a prototype of laminated composite batteries, showing their potential, especially when utilizing fully carbon fiber-based electrodes.