Mechanical characterization of a composite structural battery laminate

Recently, ambitious targets have been set out in various branches of transportation sector to restrict pollutant emissions and to combat climate change and environmental degradation. In this frame, with specific reference to the aeronautic field, new designs including electric or hybrid-electric powertrains propulsion systems penalize battery characteristics, especially in terms of limited energy and power density performances, in turn imposing an increase of the machine weight. Structural batteries (SB) constitute an interesting technology, with the potential to alleviate such problems. In the literature, structural batteries can be classified into different categories depending on their degree of structural integration. Starting from a side-by-side combination of a structural element and a conventional battery (zero degree of integration) in a fully integrated system, in which the structural element also acts as an energy accumulator, a common classification of structural batteries is based on the integration parameter structural. The class including the integrated thin-film energy storages is not fully considered, as this approach is not expected to yield high enough energy densities for a meaningful contribution to the overall energy needs of an aeronautical vehicle. Furthermore, structural batteries are further divided into two categories: multifunctional structures (or decoupled systems) and multifunctional materials (or coupled systems). In the first case different materials within the structural battery perform a single function (either energy storage or load bearing), however the overall composite is multifunctional, whereas in the latter all materials adopt multiple functions (i.e. energy storage and load bearing). Multifunctional structures are best known as type-I and type-II, whereas multifunctional materials are usually named type-III and type-IV structural batteries. Although higher mass savings are predicted for high degrees of structural integration (i.e. type-III and -IV), current research efforts show that structural batteries with low degree of multifunctionality, (i.e. type-I and -II) exhibit better overall performances. The purpose of this work is to describe the process used to manufacture a type-III structural battery. Basing on the state of the art, to maximize the mechanical properties of the final product, carbon fiber with twill architecture is used to get the electrodes. The separator between them is made by glass fiber. The matrix is chosen to have both a high adhesion with carbon fibers and a compaction cycle compatible with the battery materials maximum allowable temperature and pressure. As it regards the binders material, carbon-coated copper foils are used to avoid galvanic corrosion. The mechanical properties of the obtained SB are assessed via three-point bending tests.