Thin, Uniform, and Highly Packed Multifunctional Structural Carbon Fiber Composite Battery Lamina Informed by Solid Polymer Electrolyte Cure Kinetics

Multifunctional structural batteries promise advancements in structural energy storage technologies by seamlessly integrating load-bearing and energy-storage functions within a single material, reducing weight, and enhancing safety. Yet, commercialization faces challenges in materials processing, assembly, and design optimization. Here, we report a systematic approach to develop a carbon fiber (CF)-based structural battery impregnated with epoxy-based solid polymer electrolyte (SPE) via robust vacuum-assisted compression molding (VACM). Informed by cure kinetics, SPE processing enhances the multifunctional performance with no fillers or additives. The thin flexible CF-based laminae impregnated under high pressure achieved a substantial enhancement of ∼160% in the fiber volume fraction (FVF) as although thin and strip-shaped, the fibers were optimally packed with low void. A CF/SPE-based battery was fabricated, with a hybrid layered ionic liquid (IL)/ carbonate electrolyte (CE) showing enhanced safety and multifunctional performance. Enhanced by thin, uniform, and stiff CF-based composites, this study propels the development of advanced multifunctional structures, thereby expediting sustainable commercialization.

Design and Characterization of Poly(ethylene oxide)-Based Multifunctional Composites with Succinonitrile Fillers for Ambient-Temperature Structural Sodium-Ion Batteries

A new approach to developing structural sodium batteries capable of operating in ambient-temperature conditions has been successfully achieved. The developed multifunctional structural electrolyte (SE) using poly(ethylene oxide) (PEO) as a matrix integrated with succinonitrile (SN) plasticizers and glass-fiber (GF) reinforcements identified as GF_PEO-SN-NaClO4 showed a tensile strength of 32.1 MPa and an ionic conductivity of 1.01 × 10-4 S cm-1 at room temperature. It displayed a wide electrochemical stability window of 0 to 4.9 V and a high sodium-ion transference number of 0.51 at room temperature. The structural electrode (CF|SE) was fabricated by pressing the structural electrolyte with carbon fibers (CFs), and it showed a tensile strength of 72.3 MPa. The fabricated structural battery half-cell (CF||SE||Na) demonstrated good cycling stability and an energy density of 14.2 Wh kg-1, and it retained 80% capacity at the end of the 200th cycle. The cycled electrodes were observed using scanning electron microscopy, which revealed small dendrite formation and dense albeit uniform deposition of the sodium metal, helping to avoid a short-circuit of the cell and providing more cycling stability. The developed multifunctional matrix composites demonstrate promising potential for developing ambient-temperature sodium structural batteries.

Unveiling the Multifunctional Carbon Fiber Structural Battery

Structural batteries refer to the multifunctional device capable of both storing electrical energy and bearing mechanical loads concurrently. In this context, carbon fibers emerge as a compelling choice of material and serve dual purpose by storing energy and providing stiffness and strength to the battery. Previous investigation has demonstrated proof-of-concept of functional positive electrodes against metallic lithium in structural battery electrolyte. Here, an all-carbon fiber-based structural battery is demonstrated utilizing the pristine carbon fiber as negative electrode, lithium iron phosphate (LFP)-coated carbon fiber as positive electrode, and a thin cellulose separator. All components are embedded in structural battery electrolyte and cured to provide rigidity to the battery. The energy density of structural battery is enhanced by use of the thin separator. The structural battery composite demonstrates an energy density of 30 Wh kg-1 and cyclic stability up to 1000 cycles with ≈100% of Coulombic efficiency. Remarkably, the elastic modulus of the all-fiber structural battery exceeds 76 GPa when tested in parallel to the fiber direction - by far highest till date reported in the literature. Structural batteries have immediate implication in replacing structural parts of electric vehicles while reducing the number of conventional batteries. Thus, offering mass savings to future electric vehicles.

Structural Positive Electrodes Engineered for Multifunctionality

Multifunctional structural batteries are of high and emerging interest in a wide variety of high-strength and lightweight applications. Structural batteries typically use pristine carbon fiber as the negative electrode, functionalized carbon fiber as the positive electrode, and a mechanically robust lithium-ion transporting electrolyte. However, electrochemical cycling of carbon fibre-based positive electrodes is still limited to tests in liquid electrolytes, which does not allow for to introduction of multifunctionality in real terms. To overcome these limitations, structural batteries with a structural battery electrolyte (SBE) are developed. This approach offers massless energy storage. The electrodes are manufactured using economically friendly, abundant, cheap, and non-toxic iron-based materials like olivine LiFePO4. Reduced graphene oxide, renowned for its high surface area and electrical conductivity, is incorporated to enhance the ion transport mechanism. Furthermore, a vacuum-infused solid-liquid electrolyte is cured to bolster the mechanical strength of the carbon fibers and provide a medium for lithium-ion migration. Electrophoretic deposition is selected as a green process to manufacture the structural positive electrodes with homogeneous mass loading. A specific capacity of 112 mAh g-1 can be reached at C/20, allowing the smooth transport of Li-ion in the presence of SBE. The modulus of positive electrodes exceeded 80 GPa. Structural battery-positive half-cells are demonstrated across various mass-loadings, enabling them to be tailored for a diverse array of applications in consumer technology, electric vehicles, and aerospace sectors.

Nanostructured Transition Metal Oxides on Carbon Fibers for Supercapacitor and Li-Ion Battery Electrodes: An Overview

Nowadays, owing to the new technological and industrial requirements for equipment, such as flexibility or multifunctionally, the development of all-solid-state supercapacitors and Li-ion batteries has become a goal for researchers. For these purposes, the composite material approach has been widely proposed due to the promising features of woven carbon fiber as a substrate material for this type of material. Carbon fiber displays excellent mechanical properties, flexibility, and high electrical conductivity, allowing it to act as a substrate and a collector at the same time. However, carbon fiber's energy-storage capability is limited. Several coatings have been proposed for this, with nanostructured transition metal oxides being one of the most popular due to their high theoretical capacity and surface area. In this overview, the main techniques used to achieve these coatings-such as solvothermal synthesis, MOF-derived obtention, and electrochemical deposition-are summarized, as well as the main strategies for alleviating the low electrical conductivity of transition metal oxides, which is the main drawback of these materials.

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

Stereolithography 3D Printed Carbon Microlattices with Hierarchical Porosity for Structural and Functional Applications

Hierarchically porous carbon microlattices (HPCMLs) fabricated by using a composite photoresin and stereolithography (SLA) 3D printing is reported. Containing magnesium oxide nanoparticles (MgO NPs) as porogens and multilayer graphene nanosheets as UV-scattering inhibitors, the composite photoresin is formed to simple cubic microlattices with digitally designed porosity of 50%. After carbonization in vacuum at 1000 °C and chemical removal of MgO NPs, it is realized that carbon microlattices possessing hierarchical porosity are composed of the lattice architecture (≈100 µm), macropores (≈5 µm), mesopores (≈50 nm), and micropores (≈1 nm). The linear shrinkage after pyrolysis is as small as 33%. Compressive strength of 7.45 to 10.45 MPa and Young's modulus of 375 to 736 MPa are achieved, proving HPCMLs a robust mechanical component among reported carbon materials with a random pore structure. Having a few millimeters in thickness, the HPCMLs can serve as thick supercapacitor electrodes that demonstrate gravimetric capacitances 105 and 13.8 F g-1 in aqueous and organic electrolyte, reaching footprint areal capacitances beyond 10 and 1 F cm-2 , respectively. The results present that the composite photoresin for SLA can yield carbon microarchitectures that integrate structural and functional properties for structural energy storages .

Structural pseudocapacitors with reinforced interfaces to increase multifunctional efficiency

Structural supercapacitors hold promise to expand the energy capacity of a system by integrating load-bearing and energy-storage functions in a multifunctional structure, resulting in weight savings and safety improvements. Here, we develop strategies based on interfacial engineering to advance multifunctional efficiency. The structural electrodes were reinforced by coating carbon-fiber weaves with a uniquely stable conjugated redox polymer and reduced graphene oxide that raised pseudocapacitive capacitance and tensile strength. The solid polymer electrolyte was tuned to a gradient configuration, where it facilitated high ionic conductivity at the electrode-electrolyte interfaces and transitioned to a composition with high mechanical strength in the bulk for load support. The gradient design enabled the multilayer structural supercapacitors to reach state-of-the-art performance matching the level of monofunctional supercapacitors. In situ electrochemical-mechanical measurements established the device durability under mechanical loads. The structural supercapacitor was made into the hull of a model boat to demonstrate its multifunctionality.

Macroscale Fabrication of Lightweight and Strong Porous Carbon Foams through Template-Coating Pair Design

Manufacturing of low-density-high-strength carbon foams can benefit the construction, transportation, and packaging industries. One successful route to lightweight and mechanically strong carbon foams involves pyrolysis of polymeric architectures, which is inevitably accompanied by drastic volumetric shrinkage (usually >98%). As such, a challenge of these materials lies in maintaining bulk dimensions of building struts that span orders of magnitude difference in length scale from centimeters to nanometers. This work demonstrates fabrication of macroscale low-density-high-strength carbon foams that feature exceptional dimensional stability through pyrolysis of robust template-coating pairs. The template serves as the architectural blueprint and contains strength-imparting properties (e.g., high node density and small strut dimensions); it is composed of a low char-yielding porous polystyrene backbone with a high carbonization-onset temperature. The coating serves to imprint and transcribe the template architecture into pyrolytic carbon; it is composed of a high char-yielding conjugated polymer with a relatively low carbonization-onset temperature. The designed carbonization mismatch enables structural inheritance, while the decomposition mismatch affords hollow struts, minimizing density. The carbons synthesized through this new framework exhibit remarkable dimensional stability (≈80% dimension retention; ≈50% volume retention) and some of the highest specific strengths (≈0.13 GPa g^-1 cm³ ) among reported carbon foams derived from porous polymer templates.

Multifunctional Quasi-Solid-State Zinc-Sulfur Battery

The introduction of structural energy storage devices into emerging markets, such as electric vehicles, is predominately hindered by weak energy density, safety concerns, and immaturity of the field in materials. Herein, fabrication and testing of a freeze-resistant, multifunctional quasi-solid-state zinc-sulfur battery (ZnS) are reported. To this end, an electrostatic spray coating technique was used to deposit a thin layer of sulfur on the highly porous, unidirectional activated carbon nanofibers (A-CNFs) as a load-bearing cathode. This technique could fill micro- and mesopores, and microsized channels with sulfur, achieving an extensive sulfur loading of 60 wt %. Several drawbacks of structural energy storage devices (applicability under varied climate conditions, poor electrochemical performance and mechanical properties) are addressed by initiating an antifreezing hydrogel electrolyte with a failure strain of over 200%. This electrolyte possesses ethylene glycol and an I2 additive as an antifreezing agent and redox mediator, respectively. The as-assembled ZnS battery offers a high energy density of 283 Wh/kg based on the CNF-S cathode (149 Wh/kg based on the ZnS cell) and mechanical properties beyond state-of-the-art structural energy storage devices with a tensile strength of 377 MPa, Young's modulus of 16.7 GPa, and energy-to-failure of 4.5 MJ/m3. The electrochemomechanical properties of the ZnS battery were also investigated to elucidate the effects of electrochemical energy storage on mechanical properties and vice versa. Overall, the ZnS battery outperforms state-of-the-art structural energy storage devices in terms of energy storage and load-bearing capabilities.

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.

Chemomechanics of Rechargeable Batteries: Status, Theories, and Perspectives

Chemomechanics is an old subject, yet its importance has been revived in rechargeable batteries where the mechanical energy and damage associated with redox reactions can significantly affect both the thermodynamics and rates of key electrochemical processes. Thanks to the push for clean energy and advances in characterization capabilities, significant research efforts in the last two decades have brought about a leap forward in understanding the intricate chemomechanical interactions regulating battery performance. Going forward, it is necessary to consolidate scattered ideas in the literature into a structured framework for future efforts across multidisciplinary fields. This review sets out to distill and structure what the authors consider to be significant recent developments on the study of chemomechanics of rechargeable batteries in a concise and accessible format to the audiences of different backgrounds in electrochemistry, materials, and mechanics. Importantly, we review the significance of chemomechanics in the context of battery performance, as well as its mechanistic understanding by combining electrochemical, materials, and mechanical perspectives. We discuss the coupling between the elements of electrochemistry and mechanics, key experimental and modeling tools from the small to large scales, and design considerations. Lastly, we provide our perspective on ongoing challenges and opportunities ranging from quantifying mechanical degradation in batteries to manufacturing battery materials and developing cyclic protocols to improve the mechanical resilience.

Multifunctional Carbon Fiber Composites: A Structural, Energy Harvesting, Strain-Sensing Material

Multifunctional structural materials are capable of reducing system level mass and increasing efficiency in load-carrying structures. Materials that are capable of harvesting energy from the surrounding environment are advantageous for autonomous electrically powered systems. However, most energy harvesting materials are non-structural and add parasitic mass, reducing structural efficiency. Here, we show a structural energy harvesting composite material consisting of two carbon fiber (CF) layers embedded in a structural battery electrolyte (SBE) with a longitudinal modulus of 100 GPa─almost on par with commercial CF pre-pregs. Energy is harvested through mechanical deformations using the piezo-electrochemical transducer (PECT) effect in lithiated CFs. The PECT effect creates a voltage difference between the two CF layers, driving a current when deformed. A specific power output of 18 nW/g is achieved. The PECT effect in the lithiated CFs is observed in tension and compression and can be used for strain sensing, enabling structural health monitoring with low added mass. The same material has previously been shown capable of shape morphing. The two additional functionalities presented here result in a material capable of four functions, further demonstrating the diverse possibilities for CF/SBE composites in multifunctional applications in the future.

Production and Characterisation of Fibre-Reinforced All-Solid-State Electrodes and Separator for the Application in Structural Batteries

The electrification of the air transport sector demands for an energy storage that adds as little volume and weight to the overall system as possible. Regarding this so-called structural battery, composites enable the storage of electrical energy in commonly used load bearing fibre composite structures. A structural battery composite can store electrical energy while bearing mechanical loads, thus reducing parasitic mass and volume. In this study, structural cathodes were prepared by slurry coating carbon fibres with lithium iron phosphate (LFP), polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and carbon black. For the structural anodes, the carbon fibres were utilised as active material and slurry coated with PEO and LiTFSI. These structural electrodes as well as a structural separator were characterised by electrochemical cycling. With 139 mAhgAM−1, the structural cathodes demonstrated good utilisation of the active material. The carbon fibres used in the anode exhibited capacities of up to 92 mAhgAM−1. High irreversible lithium losses were observed, which are attributed to the poor electrolyte wetting behaviour of the carbon fibres. A structural battery demonstrator with a lithium metal anode was realised and reached a maximum specific energy of 64 Whkg−1 with respect to electrode and separator weight.

An efficient computational approach for three-dimensional modeling and simulation of fibrous battery electrodes

Fibrous electrodes are a promising alternative to conventional particle-based lithium-ion battery electrodes. In this contribution, we propose an efficient computational approach for the modeling and simulation of electrochemical phenomena taking place in fibrous electrodes during battery charge/discharge processes. Since each fiber is explicitly modeled by means of a dimensionally reduced embedded fiber model, the framework enables simulations in a three-dimensional setting with relatively modest discretization and computational requirements compared to simulations with fully resolved fiber discretizations. The approach is applied to electrodes with high volume fractions of high aspect ratio fibers. Various local and global quantities are analyzed and results are compared to those obtained with the standard finite element method and the pseudo-2D model.

Energized Composites for Electric Vehicles: A Dual Function Energy-Storing Supercapacitor-Based Carbon Fiber Composite for the Body Panels

The current electric vehicles (EVs) face many challenges like limited charge capacity, low miles/charge, and long charging times. Herein, these issues are addressed by developing a dual-function supercapacitor-based energy-storing carbon fiber reinforced polymer (e-CFRP) that can store electrical energy and function as the structural component for the EV's body shell. This is achieved by developing a unique design, vertically aligned graphene sheets attached to carbon fiber electrodes on which different metal oxides are deposited to obtain high-energy density electrodes. A high-strength multilayer e-CFRP assembly is fabricated using an alternate layer patterning configuration of epoxy and polyacrylamide gel electrolyte. The e-CFRP so developed delivers a high areal energy density of 0.31 mWh cm^-2 at 0.3 mm thickness and a high tensile strength of 518 MPa, bending strength of 477 MPa, and impact strength of 2666 J m^-1 . To show its application in EVs, a toy car's body panel is fabricated with e-CFRP and the toy car is able to operate using the energy stored in its frame. Moreover, when integrated with a solar cell, this composite powers an Internet of Things device, showing its feasibility in communication satellites.

Designing Structural Electrochemical Energy Storage Systems: A Perspective on the Role of Device Chemistry

Structural energy storage devices (SESDs), designed to simultaneously store electrical energy and withstand mechanical loads, offer great potential to reduce the overall system weight in applications such as automotive, aircraft, spacecraft, marine and sports equipment. The greatest improvements will come from systems that implement true multifunctional materials as fully as possible. The realization of electrochemical SESDs therefore requires the identification and development of suitable multifunctional structural electrodes, separators, and electrolytes. Different strategies are available depending on the class of electrochemical energy storage device and the specific chemistries selected. Here, we review existing attempts to build SESDs around carbon fiber (CF) composite electrodes, including the use of both organic and inorganic compounds to increase electrochemical performance. We consider some of the key challenges and discuss the implications for the selection of device chemistries.

Designing Versatile Polymers for Lithium-Ion Battery Applications: A Review

Solid-state electrolytes are a promising family of materials for the next generation of high-energy rechargeable lithium batteries. Polymer electrolytes (PEs) have been widely investigated due to their main advantages, which include easy processability, high safety, good mechanical flexibility, and low weight. This review presents recent scientific advances in the design of versatile polymer-based electrolytes and composite electrolytes, underlining the current limitations and remaining challenges while highlighting their technical accomplishments. The recent advances in PEs as a promising application in structural batteries are also emphasized.

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.

Structural ceramic batteries using an earth-abundant inorganic waterglass binder

Sodium trisilicate waterglass is an earth-abundant inorganic adhesive which binds to diverse materials and exhibits extreme chemical and temperature stability. Here we demonstrate the use of this material as an electrode binder in a lay-up based manufacturing system to produce structural batteries. While conventional binders for structural batteries exhibit a trade-off between mechanical and electrochemical performance, the waterglass binder is rigid, adhesive, and facilitates ion transport. The bulk binder maintains a Young's modulus of >50 GPa in the presence of electrolyte solvent while waterglass-based electrodes have high rate capability and stable discharge capacity over hundreds of electrochemical cycles. The temperature stability of the binder enables heat treatment of the full cell stack following lay-up shaping in order to produce a rigid, load-bearing part. The resulting structural batteries exhibit impressive multifunctional performance with a package free cell stack-level energy density of 93.9 Wh/kg greatly surpassing previously published structural battery materials, and a tensile modulus of 1.4 GPa.

Structural Power Performance Targets for Future Electric Aircraft

The development of commercial aviation is being driven by the need to improve efficiency and thereby lower emissions. All-electric aircraft present a route to eliminating direct fuel burning emissions, but their development is stifled by the limitations of current battery energy and power densities. Multifunctional structural power composites, which combine load-bearing and energy-storing functions, offer an alternative to higher-energy-density batteries and will potentially enable lighter and safer electric aircraft. This study investigated the feasibility of integrating structural power composites into future electric aircraft and assessed the impact on emissions. Using the Airbus A320 as a platform, three different electric aircraft configurations were designed conceptually, incorporating structural power composites, slender wings and distributed propulsion. The specific energy and power required for the structural power composites were estimated by determining the aircraft mission performance requirements and weight. Compared to a conventional A320, a parallel hybrid-electric A320 with structural power composites >200 Wh/kg could potentially increase fuel efficiency by 15% for a 1500 km mission. For an all-electric A320, structural power composites >400 Wh/kg could halve the specific energy or mass of batteries needed to power a 1000 km flight.

Structural Batteries: A Review

Structural power composites stand out as a possible solution to the demands of the modern transportation system of more efficient and eco-friendly vehicles. Recent studies demonstrated the possibility to realize these components endowing high-performance composites with electrochemical properties. The aim of this paper is to present a systematic review of the recent developments on this more and more sensitive topic. Two main technologies will be covered here: (1) the integration of commercially available lithium-ion batteries in composite structures, and (2) the fabrication of carbon fiber-based multifunctional materials. The latter will be deeply analyzed, describing how the fibers and the polymeric matrices can be synergistically combined with ionic salts and cathodic materials to manufacture monolithic structural batteries. The main challenges faced by these emerging research fields are also addressed. Among them, the maximum allowable curing cycle for the embedded configuration and the realization that highly conductive structural electrolytes for the monolithic solution are noteworthy. This work also shows an overview of the multiphysics material models developed for these studies and provides a clue for a possible alternative configuration based on solid-state electrolytes.