Multifunctional Structural Batteries Research Articles

Structural cathodes: Navigating the challenges in fabrication and multifunctional performance analysis

Multifunctional structural batteries have gained interest in recent years due to their capability to simultaneously store electrochemical energy and bear mechanical load. The structural cathode is an integral component to form multifunctional structural batteries, and its electrochemical and mechanical performance are highly dependent on the fabrication process. Thus, this review aims to explore the fabrication techniques for these cathodes via indirect (casting, dip coating and layer-by-layer assembly, electrophoretic deposition, vacuum filtration & use of polymer matrix) and direct (synthesis) methods. Challenges and improvements in fabricating structural cathodes specific to these techniques will also be put forth, and the influence of cathode microstructure on the electrochemical and mechanical performances will also be discussed. This review also aims to introduce a performance metric using multifunctional efficiency as a basis for comparison when evaluating the multifunctional performance of structural cathodes. Future considerations on improving energy storage and load-bearing capability of structural cathodes will also be highlighted in order to develop more robust and efficient structural batteries.

Multiphysics topology optimization of a multifunctional structural battery composite

Multiphysics topology optimization of a multifunctional structural battery composite

Concepts and Emerging Trends for Structural Battery Electrolytes.

The structural battery is a multifunctional energy storage device that aims to address the weight and volume efficiency issues that conventional batteries face, especially in electric transportation. By combining the functions of mechanical load bearing and energy storage, structural batteries can reduce the reliance on, or even eventually replace the main power source in an electric vehicle or a drone. However, one of the key challenges to be addressed before achieving multifunctionality in structural batteries would be the design of a suitable multifunctional structural battery electrolyte. The structural battery electrolyte is the constituent that provides mechanical integrity under flexural loads or impact and hence determines the electrochemical and much of the mechanical performance of a structural battery device. This concept paper aims to cover the key considerations and challenges facing the design of structural battery electrolytes. In addition, the main approaches to surmount these challenges are highlighted, keeping design aspects like sustainability and recyclability in view.

Structural Batteries for Aeronautic Applications—State of the Art, Research Gaps and Technology Development Needs

Radical innovations for all aircraft systems and subsystems are needed for realizing future carbon-neutral aircraft, with hybrid-electric aircraft due to be delivered after 2035, initially in the regional aircraft segment of the industry. Electrical energy storage is one key element here, demanding safe, energy-dense, lightweight technologies. Combining load-bearing with energy storage capabilities to create multifunctional structural batteries is a promising way to minimize the detrimental impact of battery weight on the aircraft. However, despite the various concepts developed in recent years, their viability has been demonstrated mostly at the material or coupon level, leaving many open questions concerning their applicability to structural elements of a relevant size for implementation into the airframe. This review aims at providing an overview of recent approaches for structural batteries, assessing their multifunctional performance, and identifying gaps in technology development toward their introduction for commercial aeronautic applications. The main areas where substantial progress needs to be achieved are materials, for better energy storage capabilities; structural integration and aircraft design, for optimizing the mechanical-electrical performance and lifetime; aeronautically compatible manufacturing techniques; and the testing and monitoring of multifunctional structures. Finally, structural batteries will introduce novel aspects to the certification framework.

Tubular laminated composite structural battery

This paper introduces a polymer-matrix composite-based structural lithium-ion battery system with tubular morphology. Its shape and closed cross-section, fabricated during the autoclave process, allow for high electrochemical performance by controlling the electrode distance and battery environment. To prevent the degradation of the organic liquid electrolyte within this continuous resin polymer system, extra components such as thermoplastic hot melt film, a double glass load-bearing separator, aluminum film, and polydimethylsiloxane were implanted. The electrochemical properties of this manufactured multi-functional structural battery design, named the tubular laminated composite battery (TLCB), were tested with a galvanic cell testing machine. The initial specific capacity of TLCB was found to be approximately 120–130 mAh/g with good cycling performance and steady coulombic efficiency. Furthermore, mechanical load resistance and correlation with electrochemical performance were also assessed under the four-point bending load condition. These results show that the TLCB has the potential to operate as a subsidiary energy storage for future electric vehicle systems with a certain level of structural specific capacity and load-bearing properties.

Mechanically-robust structural lithium-sulfur battery with high energy density

The development of structural batteries has been obstructed by the intrinsically low mechanical strength of battery materials inside. Here, we propose a multifunctional structural battery platform by deploying electrodeposition-like reactions to prepare for conformally-coated electrodes, together with carbon fabrics as the skeleton to endow them with mechanical robustness. As a proof of concept, the Li/S battery system based on the electrodeposition-like mechanism was introduced into the structural batteries for the first time. The Young's modulus of optimized sulfur and lithium electrodes reach 9.2 ± 1.2 GPa and 4.5 ± 0.6 GPa, respectively, 5–20 times higher than conventional electrodes. Additionally, a thermally stable composite separator combining boron nitride nanofiller with PVdF polymer (BN/PVdF) is rationally designed, which possesses high compressive strength over 180 MPa. The structural cell integrated with these structural components delivered an excellent lifespan under compression up to 20 MPa for 20 cycles at 0.2 C. Moreover, the structural Li/S cell in pouch configuration displays better resistance to mechanical deformation when compared to the regular Li/S cell. This work provides valuable insight into structural batteries with high energy density.

Graphitic microstructure and performance of carbon fibre Li-ion structural battery electrodes

Carbon fibres (CFs), originally made for use in structural composites, have also been demonstrated as high capacity Li-ion battery negative electrodes. Consequently, CFs can be used as structural electrodes; simultaneously carrying mechanical load and storing electrical energy in multifunctional structural batteries. To date, all CF microstructural designs have been generated to realise a targeted mechanical property, e.g. high strength or stiffness, based on a profound understanding of the relationship between the graphitic microstructure and the mechanical performance. Here we further advance this understanding by linking CF microstructure to the lithium insertion mechanism and the resulting electrochemical capacity. Different PAN-based CFs ranging from intermediate- to high-modulus types with distinct differences in microstructure are characterised in detail by SEM and HR-TEM and electrochemical methods. Furthermore, the mechanism of Li-ion intercalation during charge/discharge is studied by in situ confocal Raman spectroscopy on individual CFs. Raman G band analysis reveals a Li-ion intercalation mechanism in the high-modulus fibre reminiscent of that in crystalline graphite. Also, the combination of a relatively low capacity of the high-modulus CFs (ca. 150 mAh g−1) is shown to be due to that the formation of a staged structure is frustrated by an obstructive turbostratic disorder. In contrast, intermediate-modulus CFs, which have significantly higher capacities (ca. 300 mAh g−1), have Raman spectra indicating a Li-ion insertion mechanism closer to that of partly disordered carbons. Based on these findings, CFs with improved multifunctional performance can be realised by tailoring the graphitic order and crystallite sizes.

Multifunctional structural lithium ion batteries for electrical energy storage applications

Multifunctional structural batteries based on carbon fiber-reinforced polymer composites are fabricated that can bear mechanical loads and act as electrochemical energy storage devices simultaneously. Structural batteries, containing woven carbon fabric anode; lithium cobalt oxide/graphene nanoplatelets coated aluminum cathode; filter paper separator and cross-linked polymer electrolyte, were fabricated through resin infusion under flexible tooling (RIFT) technique. Compression tests, dynamic mechanical thermal analysis, thermogravimetric analysis and impedance spectroscopy were done on the cross-linked polymer electrolytes while cyclic voltammetry, impedance spectroscopy, dynamic mechanical thermal analysis and in-plane shear tests were conducted on the fabricated structural batteries. A range of solid polymer electrolytes with increasing concentrations of lithium perchlorate salt in crosslinked polymer epoxies were formulated. Increased concentrations of electrolyte salt in cross-linked epoxy increased the ionic conductivity, although the compressive properties were compromised. A structural battery, exhibiting simultaneously a capacity of 0.16 mAh L−1, an energy density of 0.32 Wh L−1 and a shear modulus of 0.75 GPa have been reported.

Multifunctional structural lithium-ion battery for electric vehicles

An innovative concept for a multifunctional structural battery using lithium-ion battery materials as load bearing elements in a sandwich panel construction has been demonstrated. The structural battery prototype has exhibited an initial capacity of 17.85 Ah, an energy density of 248 Wh L−1, a specific energy of 102 Wh kg−1, and a capacity retention of 85.8% after 190 charge–discharge cycles at ~ C/3 rate and eight mechanical loading cycles (upto 1060 N). The mechanical stiffness in three-point bend tests follows expectations based on sandwich beam theory, proving that the battery materials are sharing in the load-carrying function of the sandwich panel. While areas for improvement of the fabrication and performance of the prototype still exist, the results of the current investigation demonstrate the promising potential of the proposed structural battery concept for the efficient use of space and mass in an electric vehicle.

Thermal analysis of multifunctional structural battery for satellite applications

Multifunctional structures combine multiple functionalities in a single structural part in order to increase performance while limiting mass and volume. Conventional satellite batteries are designed separately as a stand-alone subsystem then added to satellite host structure in the last assembly, bringing assistant containers and connectors etc. that often cause undesirable mass loading effects and consume valuable space. Power subsystem and then the whole satellite can benefit from the introduction of multi-functionality as a means of improving overall system efficiency. This paper presents the investigation of a new multifunctional structural battery (MFSB) consisting of energy storage, energy supply, and load bearing ability in a single composite structural panel for satellite applications. Thermal vacuum testing (TVT) was carried out and transient thermal analysis was performed, and the results demonstrated that the current material formula and workmanship are viable in the space. When mounted within satellites as an equipment-panel, the designed MFSB panel can keep itself retaining the required operational temperature without supplementary thermal control approaches.

Design and fabrication of multifunctional structural batteries

A new design of lithium ion batteries with tunable mechanical properties has been developed. Depending on the material design of the battery components, the battery can range from elastic to structurally rigid. Elastic battery electrodes have been fabricated by utilizing elastic polymer binders in the electrode construction. The design of structural batteries capable of carrying load is based on a fiber reinforced polymer composite structure. The first generation structural battery has been fabricated based on a high molecular weight polyvinylidene fluoride (PVDF) matrix achieving a modulus of 3.1 GPa and an energy density of 35 Wh kg −1. Remaining challenges in fully realizing a multifunctional structural battery are outlined.

Electrochemical and Mechanical Behavior in Mechanically Robust Solid Polymer Electrolytes for Use in Multifunctional Structural Batteries

Polymer electrolytes were investigated for potential use in multifunctional structural batteries requiring both mechanical and electrochemical properties. Electrolytes were formulated with a broad range of multifunctional behaviors, spanning continuously from highly conductive and structurally weak materials to poorly conductive and highly structural materials. Solvent-free polymer scaffolds were synthesized from monomers containing poly(ethylene glycol) (PEG) oligomers and one to four vinyl ester groups. The electrolytes were formed by dissolving lithium trifluoromethanesulfonate in the monomers prior to thermal cure. Electrochemical, mechanical, and viscoelastic properties were studied with respect to salt concentration, polymer chemistry, and polymer architecture. The addition of salt was found to have minimal impact on compressive stiffness, whereas it increased Tg and significantly influenced ion conductivity, with a maximum conductivity at 9−12% salt w/w PEG. At a constant salt concentration, the homopolymer electrolytes exhibited close to a 1:1 inverse correlation between conductivity and stiffness as monomer composition was changed.