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.
Structural battery composites offer mass‐less energy storage for electrical vehicles and devices. Structural batteries are enabled by the recently discovered multifunctional properties of carbon fibers and the development of a structural electrolyte matrix material. The emergent multifunctional properties reach a level that allows lightweight vehicles and innovations across and beyond all transport modes.
Multifunctional materials facilitate lightweight and slender structural solutions for numerous applications. In transportation, construction materials that can act as a battery, and store electrical ...energy, will contribute to realization of highly energy efficient vehicles and aircraft. Herein, a multicell structural battery composite laminate, with three state‐of‐the‐art structural battery composite cells connected in series is demonstrated. The experimental results show that the capacity of the structural battery composite cells is only moderately affected by tensile loading up to 0.36% strain. The multicell structural battery laminate is made embedding the three connected structural battery composite cells between carbon fiber/glass fiber composite face sheets. Electrochemical performance of the multicell structural battery is demonstrated experimentally. High charge transfer resistance for the pack as well as the individual cells is reported. Mechanical performance of the structural battery laminate is estimated by classical laminate theory. Computed engineering in‐plane moduli for the multicell structural battery laminate are on par with conventional glass fiber composite multiaxial laminates.
Structural batteries offer lightweight solutions for electrical systems. With these materials, energy efficiency can be improved across transport modes. Herein, multifunctional durability of structural battery composite cells is proven for alternating electrochemical and tensile mechanical loads. Furthermore, a multicell structural battery laminate operating at 10.5 V is manufactured and its multifunctional performance characterized, experimentally and theoretically.
In this paper propagation of matrix cracks and debonds at the coating/matrix interface in the 90°-layer of a cross-ply structural composite battery are studied numerically. The structural composite ...battery consists of micro-battery units, made of a solid electrolyte coated carbon fiber embedded in an electrochemically active polymer matrix. During charging the fiber swells and the matrix shrinks leading to high stresses on the fiber/matrix scale and to anisotropic free expansion of the composite ply. Two load cases are considered, pure electrochemical load (intercalation) and combined electrochemical and thermomechanical load. Energy release rates (ERR) of radial matrix cracks along two potential propagation paths are calculated using 2-D finite element models of the transverse plane in a cross-ply laminate with a square packing of fibers in the 90°-ply and using homogenized 0°-ply. Results show that the matrix crack growth towards the nearest fiber is unstable, and that the debond crack growth is in mixed mode. For a cross-ply structural battery composite the sequence of macro-scale crack forming events differs from a conventional cross-ply composite, as well as for a UD composite battery laminate. The most likely course of failure events in a cross-ply laminate are: 1) vertical radial matrix crack initiation and unstable growth; 2) debond is initiated at certain length of the matrix crack.
Multifunctional materials offer a possibility to create lighter and more resource‐efficient products and thereby improve energy efficiency. Structural battery composites are one type of such a ...multifunctional material with potential to offer massless energy storage for electric vehicles and aircraft. Although such materials have been demonstrated, their performance level and consistency must be improved. Also, the cell dimensions need to be increased. Herein, a robust manufacturing procedure is developed and structural battery composite cells are repeatedly manufactured with double the multifunctional performance and size compared to state‐of‐the‐art structural battery cells. Furthermore, six structural battery cells are selected and laminated into a structural battery composite multicell demonstrator to showcase the technology. The multicell demonstrator performance is characterized for two different electrical configurations. The low variability in the multifunctional properties of the cells verifies the potential for upscaling offered by the proposed manufacture technique.
In this paper, the propagation of radial matrix cracks and debond cracks at the coating/matrix interface in unidirectional carbon fiber structural micro-battery composite are studied numerically. The ...micro battery consists of a solid electrolyte-coated carbon fiber embedded in an electrochemically active polymer matrix. Stress analysis shows that high hoop stress in the matrix during charging may initiate radial matrix cracks at the coating/matrix interface. Several 2-D finite element models of the transverse plane with different arrangements of fibers and other matrix cracks were used to analyze the radial matrix crack growth from the coating/matrix interface of the central fiber in a composite with a square packing of fibers. Energy release rates of radial cracks along two potential propagation paths are calculated under pure electrochemical loading. The presence of a radial matrix crack imposes changes in the stress distribution along the coating/matrix interface, making debonding relevant for consideration. Results for energy release rates show that the debond crack growth is governed by mode II.
Carbon fibers (CF), commonly used in the structure of airplanes or cars, can also work as conductive electrodes in “structural batteries” for distributed energy storage. To this aim CF should be ...chemically functionalized, which is challenging due to their complex geometry and surface. Here, we describe an “all-electrostatic” approach taking advantage of the intrinsic conductivity of CF to coat them with a cathode material composed of LiFePO4 blended with nanosheets of electrochemically exfoliated graphene oxide (EGO). We first achieve electrostatic self-assembly of the nanometric components at the nanoscale, then use Electrophoretic Deposition (EPD) to obtain a uniform, macroscale coating on the fibers. We achieve a LiFePO4 loading >90 wt% featuring good adhesion on the carbon fibers, low degradation upon battery cycling, low charge transfer resistance. The electrode composite outperforms similar state-of-the-art cathode materials when used in Half-Cell vs. Li. Full battery cells using coated CF as cathode and pristine CF as anode yield specific energy density of 222.14 Wh⋅kg−1 and power density of 0.29 kW⋅kg−1 with 88.1% capacity retention at 1 C over 300 cycles, compatible with industrial applications of this technique in composites production.
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Structural battery composites fall under the category multifunctional materials with the ability to simultaneously store electrical energy and carry mechanical load. While functioning as the negative ...electrode, the carbon fibres also act as mechanical reinforcement. Lithium ion insertion in the carbon fibres is accompanied by a large radial expansion of 6.6% and an axial expansion of 0.85 % of the fibres. Furthermore, the elastic moduli of the carbon fibres are significantly affected by the insertion of lithium. Current structural battery modelling approaches do not consider these features. In this paper, we investigate the effect of lithium insertion in carbon fibres on the structural electrode mechanical properties by developing a computational model considering finite strains and lithium concentration dependent fibre moduli. The computational model enables representation of morphological change, whereby, features such as internal stress state, homogenized tangent stiffness and effective expansion of the electrode caused by carbon fibre lithiation can be predicted. The adopted finite strain formulation allows for consistent consideration of measurement data at varying state of lithiation. The significance of adopting the finite strain formulation is also shown numerically. Finally, by implementing a novel approach to homogenized stress-free expansion, it is shown that the computed expansion of the structural electrode follows a similar trend to what is observed from experiments.
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•Auger electron spectroscopy can distinguish chemical configurations of lithium.•Lithium distribution in carbon fibres is charge rate dependent.•Lithium is first inserted into ...disordered domains of carbon fibres, then ordered.•The solid electrolyte interphase varies between carbon fibres in the same tow.•Lithium plating occurs on some lithiated carbon fibres.
Structural batteries are multifunctional devices that store energy and carry mechanical load, simultaneously. The pivotal constituent is the carbon fibre, which acts as not only structural reinforcement, but also as electrode by reversibly hosting Li ions. Still, little is known about how Li and carbon fibres interact. Here we map Li inserted in polyacrylonitrile based carbon fibres with Auger electron spectroscopy (AES). We show that with slow charge/discharge rates, Li distributes uniformly in the transverse and longitudinal direction of the fibre, and when fully discharged, all Li is virtually expelled. With fast rates, Li tends to be trapped in the core of the fibre. In some fibres, Li plating is found between the solid electrolyte interphase (SEI) and fibre surface. Our findings can guide AES analysis on other carbonaceous electrode materials for Li-ion batteries and be used to improve the performance of structural batteries.
Structural composite materials that simultaneously carry mechanical loads, while storing electrical energy offers the potential of significantly reduced total component weight owing to the ...multifunctionality. In the suggested micro-battery, the carbon fiber is employed as a negative electrode of the battery and also as a composite reinforcement material. It is coated with a solid polymer electrolyte working as an ion conductor and separator while transferring mechanical loads. The coated fiber is surrounded by a conductive positive electrode material matrix. This paper demonstrates a computational methodology for addressing mechanical stresses arising in a conceptualized micro-battery and dimensional changes of the cell during electrochemical cycling, caused by time-dependent gradients in lithium ion concentration distribution.
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