Special Topic Review: Structural Energy-Storage Composite Materials — Carbon Fiber Transforms from "Load-Bearing Material" to "Energy-Storage Electrode"
Can future electric vehicles, drones, and robots stop treating batteries as an "extra burden" and instead enable the fuselage, body, and skeleton themselves to store energy?
With the rapid development of lightweight equipment such as new-energy vehicles, aircraft, and intelligent robots, the industry has long faced a difficult technical contradiction: traditional structural components and energy-storage devices are independent of each other, making it hard to simultaneously meet the three core requirements of high structural strength, high energy density, and high power output. Against this backdrop, load-bearing and energy-storage integrated composite materials have become a global frontier research track. The core idea is to break down the boundary between structural load-bearing and electrical energy storage, allowing a single material to perform both mechanical and energy-storage functions. With its excellent mechanical properties, carbon fiber is the mainstream reinforcement material for lightweight components and also holds potential for use as an electrode.
Existing structural supercapacitors offer fast power output but limited energy density; structural batteries, while offering higher energy potential, often face issues such as low power density, irreversible capacity loss of carbon fiber, increased interfacial impedance, and reduced structural strength. Carbon fiber accounts for a significant proportion of the total mass of structural energy-storage composites, yet its intrinsic lithium-ion storage capability has not been fully utilized.
Innovative Material System + Integrated Molding Process Creates Thin-Walled Multifunctional Energy-Storage Components
To address existing technical pain points, researchers have developed a novel structural lithium-ion capacitor composite system, along with a complete integrated preparation process. The process consists of four core steps: electrochemical lithium intercalation modification of carbon fiber, multilayer material stacking and arrangement, composite electrolyte infiltration, and high-temperature pressurized integrated curing molding. First, carbon fibers are modified through electrochemical regulation to transform them into stable, reversibly lithium-storing low-potential anodes. Then, the modified carbon fiber anode, specialized separator, and carbon-fiber-based cathode are stacked in layers, injected with a composite electrolyte precursor solution, and hot-pressed and cured to directly form an ultra-thin integrated component.
This material employs a hybrid energy-storage mechanism: high energy storage is achieved through lithium intercalation/deintercalation reactions at the carbon fiber anode, while high-power discharge is enabled by rapid ion adsorption at the carbon fiber cathode, combining the advantages of both batteries and capacitors. On one hand, this approach mitigates the issue of irreversible capacity loss during the first charge/discharge cycle of carbon fibers. On the other hand, it eliminates the heavy active coatings used in traditional structural batteries, preventing coating-induced damage to the mechanical properties of the component, thereby providing a new manufacturing pathway for lightweight thin-walled load-bearing energy-storage components.
Revealing the Mechanism: Lithium-Intercalated Carbon Fibers Combine Reversible Energy Storage with Efficient Load Bearing
Through electrochemical testing, time-of-flight secondary ion mass spectrometry (TOF-SIMS), molecular dynamics simulations, and in-situ X-ray micro-CT/DVC analysis, the distribution, migration, and mechanical response mechanisms of lithium ions within carbon fibers were systematically revealed. The study found that after full lithiation, some lithium ions in the carbon fiber interact weakly with the carbon framework. These ions are favorable for reversible deintercalation and cause minimal disruption to the fiber structure. Meanwhile, deeply bound residual lithium ions maintain a lithium-rich interfacial environment, facilitating subsequent lithium-ion exchange. Impedance tests showed that during the first lithiation/delithiation cycle, the SEI impedance gradually decreases and stabilizes, indicating that the interface forms a relatively stable electrochemical state under controlled conditions.
In terms of mechanics, in-situ 4D digital volume correlation (DVC) analysis revealed that the lithiated carbon fiber layer bears the primary load during loading and maintains a relatively uniform strain evolution. Compared with conventional symmetric activated-carbon-coated carbon fiber structures, SLIC exhibits higher tensile modulus and strength, demonstrating that lithiation regulation does not impair the structural load-bearing capacity of carbon fibers.
Comprehensive Performance Leap: Multi-Dimensional Breakthroughs in Mechanical and Electrochemical Indicators
By optimizing the separator system—using a dense ultra-thin cellulose separator to replace traditional glass fiber separators, thereby enhancing interlayer interfacial bonding and stress transfer—the optimized material achieves the following key performance parameters:
- Mechanical Properties: Modulus 72.2 GPa, Tensile Strength 1084 MPa
- Electrochemical Properties: Energy Density 44.5 Wh/kg, Power Density 789 W/kg, Operating Voltage 3.95 V, Cathode Capacity Utilization close to full utilization
When compared horizontally with various reported structural energy-storage materials domestically and internationally, this material demonstrates comprehensive advantages across five dimensions: structural strength, energy density, power density, operating voltage range, and cathode capacity utilization. Based on combined structural efficiency and electrochemical efficiency calculations, the material's multifunctional efficiency exceeds 150%, significantly reducing overall equipment weight and delivering substantial lightweighting value.
Physical Verification: 0.4 mm Ultra-Thin Sheet Supports 25 Times Its Own Weight While Continuously Supplying Power
To verify practical application value, the research team fabricated an ultra-thin sheet only 0.4 mm thick for physical testing. In the experiment, the sheet withstood bending loads exceeding 25 times its own weight while stably powering small electronic devices such as LED screens, e-ink displays, and micro fans, visually demonstrating the material's practical ability to deliver stable electrical output under load-bearing conditions.
Broad Application Scenarios: Advancing Equipment Toward "Embodied Energy Storage"
This novel structural lithium-ion capacitor composite system provides a complete technical solution and mature preparation process for thin-walled load-bearing and energy-storage integrated components. In the future, it can be applied in multiple fields including lightweight new-energy transportation vehicles, unmanned aerial vehicles, intelligent robots, and aerospace equipment, driving the transformation of industry components from single-function load-bearing structures to dual-function structural and energy-storage components, offering a new solution for the upgrade of high-end lightweight equipment.
This article was compiled and translated by the China Composites Industry Association, with partial data sourced from online materials. This article is not for commercial purposes and is intended solely for industry exchange. Please cite the source when referencing.
