Dual-Laser Writing Creates Binder-Free Graphene Electrodes for Powerful Supercapacitors

Researchers at Qingdao Agricultural University in China have unveiled a strikingly simple yet powerful fabrication strategy that could reshape how flexible energy storage devices are made. In a study published in the Journal of Materials Science, a team led by Hanqing Gao and corresponding author Xinzhi Sun demonstrated that firing two laser passes in sequence over metal-ion-loaded polymer films produces self-supporting graphene composite electrodes with electrochemical performance far beyond what a single laser pass can achieve. The work addresses one of the most persistent bottlenecks in next-generation electronics: how to manufacture high-performance supercapacitor electrodes quickly, cleanly, and without the binders and additives that bog down conventional methods.

The technique, known as sequential dual-laser direct writing, builds on the well-established phenomenon of laser-induced graphene, or LIG. First reported in 2014, LIG formation relies on the fact that certain polymers, when swept by a focused infrared laser beam, do not simply burn away. Instead, their carbon backbone undergoes rapid localized photothermal conversion, reorganizing into a porous, conductive network of graphene sheets directly on the substrate. The process is one-step, mask-free, and can be carried out in ambient air, which is precisely why it has attracted so much attention for wearable sensors, micro-supercapacitors, and printed electronics.

What the Qingdao team recognized is that a single laser pass has inherent limitations. The energy distribution within a moving laser spot is Gaussian, hottest at the center and cooler at the edges, which produces uneven graphitization: some regions become well-formed conductive graphene while others remain partially carbonized or over-burned. By splitting the transformation into two sequential irradiation steps, the researchers allowed the material to graphitize more gradually and uniformly. The result, confirmed through microscopy and Raman spectroscopy, was a denser, more homogeneous graphene architecture with improved electrical continuity throughout the electrode.

The starting material is equally central to the story. The team used polyethersulfone, a robust engineering polymer rich in aromatic carbon and sulfur, as the precursor film. Crucially, they incorporated transition metal ions—cobalt and iron—into the polymer before laser writing. During laser exposure, these ions are simultaneously converted in situ into electrochemically active metal oxide species embedded within the growing graphene matrix. This one-step co-conversion eliminates the need for separate synthesis of active materials, current collector coatings, or conductive additives. The finished electrode is freestanding and binder-free: there is no polymer glue diluting conductivity, no metal foil current collector adding weight, and no slurry-casting step generating solvent waste.

The electrochemical payoff was substantial. The optimized cobalt-containing electrode, designated Co@PES-LIG, delivered an areal specific capacitance of 3800 millifarads per square centimeter at a current density of 1 milliampere per square centimeter, while its iron-based counterpart, Fe@PES-LIG, reached 1980 millifarads per square centimeter under the same conditions. Areal capacitance is the figure of merit that matters most for flexible and miniaturized devices, where the footprint rather than the mass of the electrode sets the design limit. Values in this range place the dual-laser electrodes among the more competitive LIG-based systems reported to date, and the improvement over single-pass processing underscores how much performance had been left on the table by conventional laser writing.

To demonstrate practical relevance, the researchers paired the two materials in an asymmetric supercapacitor, using the cobalt-based electrode as the cathode and the iron-based electrode as the anode. Asymmetric configurations exploit the different stable voltage windows of the two electrodes to extend the overall operating voltage of the cell beyond what either electrode could sustain alone. The assembled device operated at 1.8 volts in aqueous electrolyte—an unusually wide window for a water-based system, where most cells are limited to roughly 1.0 to 1.6 volts before water splitting consumes current and degrades performance.

The full device metrics are impressive for a fabrication method this simple. The asymmetric supercapacitor achieved an areal capacitance of 855 millifarads per square centimeter and an energy density of 125 microwatt-hours per square centimeter at a power density of 800 microwatts per square centimeter. Energy density has long been the Achilles heel of supercapacitors relative to batteries, so every improvement matters. Equally important for real-world use, the device retained 89.4 percent of its capacitance after 10,000 charge-discharge cycles, demonstrating that the in-situ-formed metal oxide phases and the surrounding graphene network can withstand repeated electrochemical cycling without rapid degradation.

The environmental and manufacturing implications are as compelling as the numbers. Because the entire electrode is written directly from a polymer film with two laser scans, the process requires no toxic solvents, no high-temperature furnaces, no vacuum deposition, and no multi-step materials synthesis. Laser direct writing is also digitally programmable: electrode geometry, interdigitated patterns for micro-supercapacitors, and device layouts can simply be drawn in software and written on demand. For flexible and wearable electronics—where devices must bend, stretch, and conform to skin or fabric—the freestanding nature of the electrodes is a particular advantage, since rigid current collectors and brittle binder networks are common points of mechanical failure.

The researchers point out that the strategy is efficient, simple, and environmentally benign, offering a general route for designing high-performance flexible energy storage. Because the dual-laser principle is not tied to any single metal ion, the approach could plausibly extend to other transition metal systems, opening paths to tailored pseudocapacitive chemistries written directly onto polymer substrates in a single integrated step. The work was supported by the Natural Science Foundation of Shandong Province, the Natural Science Foundation of Qingdao, and the Shandong Province Higher Educational Program for Young Innovation Talents. As demand grows for power sources that can be manufactured as easily as they are designed, sequential dual-laser writing of metal-ion-loaded polymers offers a persuasive glimpse of that future—one in which the electrode of a supercapacitor is not assembled at all, but simply drawn.

Subject of Research: Sequential dual-laser direct writing of binder-free laser-induced graphene composite electrodes for high-performance asymmetric supercapacitors

Article Title: Sequential dual-laser direct writing of binder-free electrodes for high-performance supercapacitors

Article References: Gao, H., Yang, L., Han, X., Peng, Z., Ge, L., & Sun, X. (2026). Sequential dual-laser direct writing of binder-free electrodes for high-performance supercapacitors. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13724-6

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13724-6

Keywords: laser-induced graphene, supercapacitors, dual-laser direct writing, binder-free electrodes, polyethersulfone, asymmetric supercapacitor, energy density, flexible electronics, transition metal oxides, energy storage, cobalt electrode, iron electrode