Batteries as composites

  • Structural batteries are hybrid and multifunctional composite materials able to carry load and store electrical energy as a lithium ion battery. In such a device, carbon fibres are used as the primary load carrying material, due to their excellent strength and stiffness properties, but also as the active negative electrode providing the battery function. Structural batteries can be made utilising a traditional battery structure similar to a composite laminate in which also the positive electrode is reinforced with carbon fibres coated with lithium oxides particles.

    The research comprises pursuing several research tracks involving studying electrode materials (one being carbon fibres), matrix materials which provide stiffness for the composite while still being ionically conductive (structural battery electrolytes), device development, etc. Possible ground-breaking applications for such innovative material concepts are chassis for mobile phones, laptops or car- and airplane structures that simultaneously carry load and store electrical energy, allowing substantial weight savings.

  • Figure 1. An exploded view of a structural battery.

    Figure 2. Schematic lamina structural battery layup shown with separator for aeronautical applications.

  • Supercapacitors as composites

  • Supercapacitors provide exceptional power density, high dimensional stability, and very long cycle life, making them excellent candidates for new structural energy storage systems. They typically use high surface area carbon electrodes laminated with a separator (Shirshova et al., 2013 and Carlson and Asp, 2013). This architecture maps onto conventional composite laminate designs, if suitable constituents are developed. However, there are several challenges. One is to provide a ‘structural electrode’, a conductive carbon-rich electrode with high electrochemical surface area and maximum mechanical performance, in particular stiffness and strength. Here, we use both intrinsically high strength nanoscale carbons (nanotubes), and combine high strength carbon fibres with nanostructured carbon matrices.

    For example, structural supercapacitor composites can combine carbon fibre fabrics with thin electric double-layer capacitor based on carbon nanotube (CNT) fibre veils as interleaves, (Senokos et al., 2018) as shown in Figure 1. The first step is to produce a thin (100 micron-thick) electrochemical double-layer capacitor (EDLC) by laminating two CNT fibre electrodes with a polymer electrolyte. This material can then be integrated between structural woven CF lamina by a conventional vacuum resin infusion manufacturing process. This strategy produces structural composites with electrochemical properties that are very resilient to mechanical deformations. In-situ galvanostatic charge discharge measurements during bending show almost no changes in capacitance even at very large deformations (Figure 2 a-d). This resilience is due to the high toughness of the CNT fibre fabrics.

    Another strategy uses high surface area carbon aerogels as a monolithic porous ‘matrix’ for conventional structural carbon fibres. The aerogel provides both electrochemical activity and mechanical rigidity (Qian et al., 2013 and Nguyen et al., 2019) schematically shown in Figure 2.

    The second challenge is the development of a ‘structural electrolyte’ that can carry mechanical shear loads whilst providing a high ionic conductivity. Here, we use nanostructured polymer systems that organise to form bicontinuous structural and ionic-conducting phases, though thermally-induced phase segregation (Kerbs et al., 2013)) or self-assembly of block copolymers (Leijonmarck et al., 2013). For example, a fine-tuned mixture of a structural matrix with a lithium salt, segregates upon curing into a bi-continuous microstructure of stiff matrix with channels for ion transport (Shirshova et al., 2013). A more top-down approach, can exploit CNT fibre electrodes: by making macroscopic patterns in the electric double-layer capacitor part of the structural supercapacitor to promote the interconnection of CF plies by epoxy (Figure 3 e-f). This method is not only simple, but also enables the design and fabrication of composites with different balance of mechanical and electrochemical properties.

    Realizing high energy/power densities and excellent mechanical properties simultaneously presents numerous challenges in terms of materials properties, fabrication routes, testing, evaluation, etc. Further details are discussed in specific reviews (Asp and Greenhalgh, 2014; González et al., 2017) on the topic.

  • Figure 1. Structural supercapacitor a) produced by stamping a CNT fibre-based electric double-layer capacitor (EDLC) interleaf, embedding it between carbon fibre (CF) plies and infusion/curing of epoxy resin. b) Photograph of a CF/EDLC/CF lay-up during vacuum assisted resin infusion. c) Optical micrograph of the composite cross-section (top) showing successful integration of EDLC/CF/epoxy in the laminate and scanning electron micrograph (bottom) of integrated EDLC interleaf.(Image source Senokos et al., 2018)

    Figure 2. Schematic illustration of the concept of multifunctional structural supercapacitor device based on CAG-modified structural carbon fiber fabrics as the electrodes, structural glass fabric separator, in a polymer-based electrolyte. (Image source Qian et al., 2013)

    Figure 3. In situ electrochemical characterization during four point bending flexural test of the structural supercapacitor composite. (a) Photographs of the flexural test setup at the initial and bent states. (b) Comparison of stress-strain curves obtained for the structural composite containing three embedded EDLC interleaves and a reference composite produced without interleaves. (c) Relative energy and (d) equivalent series resistance obtained from charge-discharge at 5 mA/cm2 measured during bending, for the interleaves under compression (SC_1C), neutral (SC_2N) and tensile (SC_3T) stress states. (e) Schematic of the envisaged structure. (f) 3D tomography image confirming penetration of epoxy resin through channels in the interleaf. (Image source Senokos et al., 2018)

  • References

    Structural composite supercapacitors
    N Shirshova, H Qian, MSP Shaffer, JHG Steinke, ES Greenhalgh, PT Curtis, ARJ Kucernak, A Bismarck
    Composites Part A: Applied Science and Manufacturing, Volume: 46, Pages: 96-107 (2013)

    Structural carbon fibre composite/PET capacitors – Effects of dielectric separator thickness
    T Carlson, LE Asp
    Composites Part B: Engineering, Volume 49, Pages 16-21 (2013)

    Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves
    EA Senokos, Y Ou, JJ Torres, F Sket, C González, R Marcilla, JJ Vilatela
    Scientific Reports, Volume: 8, Article Number: 3407 (2018)

    Multifunctional structural supercapacitor composites based on carbon aerogel modified high performance carbon fiber fabric
    H Qian, ARJ Kucernak, ES Greenhalgh, A Bismarck, MSP Shaffer
    ACS Applied Materials & Interfaces, Volume: 5, Issue: 13, Pages: 6113-6122 (2013)

    Mechanical and physical performance of carbon aerogel reinforced carbon fibre hierarchical composites
    SN Nguyen, DB Anthony, H Qian, C Yue, A Singh, A Bismarck, MSP Shaffer, ES Greenhalgh
    Composites Science and Technology, Volume: 182, Article: 107720 (2019)

    Reactive and Functional Polymers
    H Krebs, L Yang, N Shirshova, JHG Steinke
    Reactive and Functional Polymers, Volume: 72, Issue: 12, Pages: 931-938 (2012)

    Solid polymer electrolyte-coated carbon fibres for structural and novel micro batteries
    S Leijonmarck, T Carlson, G Lindbergh, LE Asp, H Maples, A Bismarck
    Composites Science and Technology, Volume: 89, Pages: 149-157 (2013)

    Structural supercapacitor electrolytes based on bicontinuous ionic liquid–epoxy resin systems
    N Shirshova, A Bismarck, S Carreyette, QPV Fontana, ES Greenhalgh, P Jacobsson, P Johansson, MJ Marczewski, G Kalinka, ARJ Kucernak, J Scheers, MSP Shaffer, JHG Steinke, M Wienriche
    Journal of Materials Chemistry A, Volume: 1, Issue: 48, Pages: 15300–15309 (2013)

    Multifunctionality of Polymer Composites
    Chapter 20 - Multifunctional structural battery and supercapacitor composites
    LE Asp, ES Greenhalgh
    Challenges and New Solutions, Pages: 619-611 (2015)

    Structural composites for multifunctional applications: Current challenges and future trends
    C González, JJ Vilatela, JM Molina-Aldareguía, CS Lopes, J LLorca
    Progress in Materials Science, Volume: 89, Pages: 194-251 (2017)

    International Landscape

  • There is a growing field of structural power composites with a strong European basis of which the SORCERER Project is instrumental.

    Organizational networks for journal articles were populated from keywords "Multifunctional Structures" or "Structural Batteries", between 2000-2018 using the KTH Bibmet database based on the Core Collection from Web of Science (Thomas Routers) which was used in conjunction with VOSviewer, a tool developed by the Centre for Science and Technology Studies at Leiden University.

    Dot size in the networks relate to the number of publications by country, or institute, and their position relates to their interconnectivity. To view in full screen please click on the network thumbnail.

    SORCERER would like to acknowledge Tobias Jeppsson from the KTH library for compiling and processing the distribution network maps.