The central idea is deceptively straightforward. Nickel sulfate hexahydrate, an inexpensive and widely available salt, is dissolved and spray-coated onto nickel foam, a porous metallic scaffold commonly used as a current collector in aqueous electrochemistry. Once the precursor layer is in place, a CO₂ laser operating at its familiar wavelength of 10.6 micrometers is scanned over the surface. The laser rapidly heats the coated foam, decomposing the sulfate salt and oxidizing the nickel locally, so that a crystalline NiO layer forms directly on the metallic substrate within seconds of exposure. Because the oxide grows in place, it is electrically wired to the underlying foam without any polymer binder, the insulating additive that conventional paste-based electrodes require and that adds dead weight, blocks pores, and degrades over repeated cycling.

Binder-free construction matters more than it might first appear. In a typical slurry-cast electrode, active material particles are glued to a metal foil with a polymer such as polyvinylidene fluoride, along with conductive carbon additives. Every interface introduced by these extra phases adds resistance and a potential failure point. Growing the active material directly on a conductive scaffold eliminates the binder entirely, ensuring that every bit of electrochemically active NiO is in intimate contact with the current collector. It also preserves the open pore structure of the foam, allowing electrolyte ions to flood the interior and reach active sites efficiently. The King Faisal team’s laser route achieves this architecture in a single rapid step, which is precisely what makes it attractive for scale-up.

To tune the electrode, the researchers varied the number of spray passes, which controls how much precursor, and therefore how much final NiO, is loaded onto each square centimeter of foam. Three versions were fabricated with 5, 10, and 20 spray passes. Structural and compositional analyses confirmed that the laser treatment produced crystalline NiO in all cases, but the electrochemical results revealed a clear optimum. The 10-pass electrode, with an intermediate mass loading, consistently outperformed both the lighter and heavier coatings, striking the best balance between having enough active material to store charge and keeping the layer thin enough for ions to access it all.

Tested in a concentrated 5 molar potassium hydroxide electrolyte, the optimized 10-pass electrode reached an areal capacitance of 5838 millifarads per square centimeter at a scan rate of 2 millivolts per second, and 6907 millifarads per square centimeter when driven at a current density of 10 milliamperes per square centimeter. Those figures translate into an areal capacity of 0.94 milliampere-hours per square centimeter, or a specific capacity of 249.9 milliampere-hours per gram. Areal metrics are the ones that matter for practical devices, because they measure how much charge a given footprint of electrode can store, and the reported values place this laser-written NiO among the competitive performers for nickel oxide-based supercapacitor electrodes.

Just as important as the headline numbers is how the electrode behaves under stress. The 10-pass coating maintained high capacitance even when the current density was pushed higher, a sign that ions and electrons can move through the structure without choking. In many electrode materials, capacitance collapses at high rates because the innermost active material becomes inaccessible on the timescale of the charge-discharge cycle. The laser-formed layer on nickel foam apparently avoids that pitfall, indicating efficient ion transport and fast charge transfer, likely a consequence of the direct electronic connection to the metal scaffold and the open porosity that the spray-and-laser process leaves intact.

The team then went a step further and assembled the optimized cathode into a full aqueous nickel–zinc battery, pairing it with a zinc anode in alkaline electrolyte. Nickel–zinc chemistry has attracted renewed attention as a safer, cheaper alternative to lithium-ion systems, using water-based electrolyte and abundant materials, but its performance depends heavily on the quality of the nickel-based positive electrode. The laser-fabricated NiO cathode retained its charge-storage functionality in the full-cell configuration, confirming that the material works beyond the idealized three-electrode setup used for single-electrode screening. The assembled battery delivered an areal capacity of 0.31 milliampere-hours per square centimeter, equivalent to 81.57 milliampere-hours per gram, at a current density of 0.44 milliamperes per square centimeter.

Cycling stability, the perennial challenge for oxide-based aqueous electrodes, was moderate rather than spectacular: the Ni–Zn cell retained roughly 70 percent of its capacitance after 1000 cycles. That figure leaves room for improvement, and the authors are candid that their work is a proof of concept. The demonstration was carried out on 9 square centimeter electrodes, with a preliminary extension to a 16 square centimeter full-cell electrode, showing that the laser process is not confined to tiny laboratory coupons. The researchers identify large-area coating uniformity as the key target for further optimization, since consistent precursor loading across a wide foam sheet will be essential if the technique is to move toward practical device fabrication.

According to the authors, this is the first reported case of direct CO₂ laser fabrication of NiO on nickel foam from a nickel sulfate hexahydrate precursor. That distinction matters because CO₂ lasers are among the most mature, affordable, and widely deployed industrial laser systems, already commonplace in cutting, engraving, and marking lines. Building an electrode fabrication step on top of such hardware means the barrier to adoption is low: no vacuum chambers, no electrodeposition baths, no multi-hour hydrothermal reactions in pressurized autoclaves. A spray gun and a laser scanner, in principle, could pattern active electrode material onto metal scaffolds at production speeds, and the precursor is a commodity chemical rather than a specialized organometallic reagent.

The broader significance lies in what the approach represents for energy storage manufacturing. Supercapacitors and aqueous batteries both depend on electrodes that pack a large amount of electrochemically active material into a small footprint while keeping ion and electron pathways short. Laser conversion of a sprayed precursor achieves both goals in one motion, and the identification of precursor loading as the single most important control parameter gives engineers a simple dial to tune performance. If the uniformity challenges on large areas can be solved, the same spray-and-laser recipe could plausibly be extended to other metal salts and substrates, opening a general route to binder-free oxide electrodes written directly onto current collectors. For now, the King Faisal team’s nickel oxide electrodes stand as a compelling demonstration that a tool as ordinary as a CO₂ laser can help build the next generation of energy storage hardware.

Subject of Research: CO₂ laser-assisted fabrication of binder-free NiO electrodes on nickel foam for supercapacitors and Ni–Zn batteries

Article Title: Toward scalable and direct CO₂ laser-assisted fabrication of binder-free NiO/Ni foam electrodes with high areal capacitance for supercapacitor and Ni–Zn battery applications

Article References: Shaalan, N. M., Ahmad, M. M., Aljaafari, A., Kumar, S., & El-Lateef, H. M. A. (2026). Toward scalable and direct CO₂ laser-assisted fabrication of binder-free NiO/Ni foam electrodes with high areal capacitance for supercapacitor and Ni–Zn battery applications. Ionics. https://doi.org/10.1007/s11581-026-07585-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07585-x

Keywords: nickel oxide, nickel foam, CO₂ laser, binder-free electrode, supercapacitor, Ni–Zn battery, areal capacitance, energy storage, electrochemistry, nickel sulfate precursor, aqueous battery, laser processing

The work addresses a persistent headache in battery materials chemistry. Conversion-type anodes such as metal phosphides store sodium through a multi-step reaction in which sodium ions infiltrate the lattice, break metal–phosphorus bonds, and form sodium phosphide alongside metallic nanodomains. This mechanism unlocks capacities well beyond graphite intercalation chemistry, but it also subjects the electrode to enormous volume swings—often several hundred percent—that pulverize particles, sever electrical pathways, and delaminate conventional slurry-cast coatings from their current collectors. Metal phosphides also tend to have sluggish sodium-ion solid-state diffusion and moderate electronic conductivity, making the choice of crystal phase, morphology, and electrode architecture as important as the raw chemistry itself.

The Chinese team’s architecture attacks the structural fragility head-on. They grew the active material directly onto carbon cloth, a flexible woven carbon substrate that acts simultaneously as a binder-free support and an efficient current collector. Eliminating polymer binders and metal foils removes the interfaces where most conversion anodes fail, while the porous three-dimensional fabric gives the active phase room to breathe as it expands and contracts during cycling. But the truly novel element lies upstream of the electrochemistry, in the synthesis pretreatment itself. The authors loaded a nickel-based precursor onto the carbon cloth from either ethanol or water solution, then subjected both samples to an identical phosphating process driven by sodium hypophosphite (NaH₂PO₂), a common phosphorus source that decomposes to deliver reactive phosphorus species at moderate temperatures.

The divergence in results is striking. When ethanol served as the loading solvent, the phosphating reaction yielded hexagonal Ni₅P₄ (space group P6₃mc), a phosphorus-rich nickel phosphide considered attractive for alkali-ion storage. When water was the solvent, the same hypophosphite treatment predominantly produced Ni₂P₄O₁₂, a nickel phosphate containing oxygen retained from the aqueous processing environment. The researchers attribute this solvent-driven phase selection to the distinct chemical microenvironments created during precursor deposition. Ethanol’s reducing, less hydrolytic character appears to shift the local phosphorus chemical potential and steer intermediate formation pathways toward full phosphidation, whereas water promotes hydrolysis and oxidation pathways that trap oxygen in the final product. In effect, a decision made in the wet-chemistry stage—long before any electrochemical testing—determines which crystal structure emerges, which morphology forms, and ultimately how the electrode performs.

Both electrodes proved remarkably durable, belying the reputation of conversion materials for rapid fade. The Ni₅P₄@CC anode sustained a discharge-specific capacity exceeding 100 mAh g⁻¹ after 1000 cycles at a current density of 100 mA g⁻¹, and it recovered 92.8% of its capacity when rate-performance testing swung the current density from 50 up to 2000 mA g⁻¹ and back. The Ni₂P₄O₁₂@CC anode performed comparably, retaining 121.1 mAh g⁻¹ after 1000 cycles with a 92.2% rate recovery. While neither figure sets records in absolute capacity, the combination of four-figure cycle life, binder-free construction, and near-complete rate recovery signals electrodes engineered for stability rather than one-shot headline numbers—a trait that matters enormously for real-world grid storage, where sodium-ion chemistry is expected to make its commercial debut.

The deeper contribution of the study lies in its electrochemical kinetics analysis, which dissects why each phase behaves as it does. Using temperature-dependent measurements, the team extracted activation energies for the two competing steps that govern sodium storage: charge transfer across the electrode–electrolyte interface and solid-state diffusion of sodium ions through the crystal. Ni₅P₄ emerged as the kinetically more agile interactor at its surface, exhibiting a lower charge-transfer activation energy of 48.63 kJ mol⁻¹, meaning sodium ions face a smaller barrier when passing from the electrolyte into the electrode. That advantage comes at a price: Ni₅P₄ carries a higher solid-state diffusion barrier of 67.19 kJ mol⁻¹, so sodium atoms move more reluctantly once inside the bulk crystal.

What rescues Ni₅P₄ from its own diffusion penalty is a structural quirk. The compound offers interstitial sodium storage sites—voids in the lattice between the nickel and phosphorus sublattices—into which sodium ions can slip without needing to displace host atoms. Interstitial storage typically proceeds faster and with less lattice strain than substitutional insertion, effectively providing a kinetic bypass that compensates for the material’s elevated diffusion barrier. This interplay between interfacial kinetics, bulk transport, and storage-site geometry illustrates a broader lesson for the field: phase selection is not merely about capacity numbers but about the entire sodium-transport landscape, and small synthesis choices can reshape that landscape in measurable ways.

The transferability of the solvent-control principle may prove to be its most valuable feature. Hypophosphite phosphating is a workhorse technique across transition metal phosphide synthesis, used for cobalt, iron, tin, molybdenum, and copper phosphide electrodes in lithium, sodium, and even potassium-ion systems. If the same ethanol-versus-water logic applies across that family—and the authors position solvent selection as an effective and transferable strategy—it gives battery chemists a cheap, scalable dial for tuning phase purity, oxygen incorporation, and morphology without reformulating precursor chemistry or investing in exotic equipment. Because the pretreatment happens before phosphating, it slots neatly into existing synthesis workflows, and carbon cloth electrodes grown this way could suit flexible or structurally integrated battery formats where binder-free architecture is especially valuable.

The timing is favorable. Sodium-ion batteries are attracting renewed industrial investment because sodium is abundant, geopolitically unconstrained, and compatible with aluminum current collectors on both electrodes, trimming cost and weight. Nonaqueous liquid electrolytes for the technology have matured rapidly, and recent reviews of metal phosphide anodes highlight the family’s combination of high theoretical capacity and reasonable operating voltage as a key asset for next-generation cells. What has been missing is precise synthetic control over which phosphide phase forms and how it is anchored to the current collector—precisely the gap this study targets. By demonstrating that a solvent swap in a pretreatment step can dictate phase composition, morphology, and sodium-storage kinetics end to end, the Shenyang-based researchers have added a deceptively simple tool to the battery engineer’s kit, one that turns an ordinary bottle of ethanol into an instrument of crystal engineering.

The work, funded by the Basic Research Projects of the Liaoning Provincial Department of Education and the Doctoral Research Start-up Project of the Liaoning Provincial Natural Science Fund, was received in June 2026 and published on 13 October 2026. Its conclusions stop short of commercial claims—capacities of around 100 to 120 mAh g⁻¹ after 1000 cycles are modest by anode standards—but the study’s real legacy may be conceptual. It shows that in conversion-type battery materials, the boundary between synthesis chemistry and electrochemical performance is thinner than often assumed. Choose the right solvent at the pretreatment stage, and the crystal lattice, the diffusion pathways, the interfacial charge transfer, and the long-term cycling stability all follow. For a technology racing to displace lithium from the grid, that kind of upstream control could be worth far more than any single record-breaking electrode.

Subject of Research: Solvent-controlled synthesis of nickel phosphide anode materials and sodium-ion storage kinetics in sodium-ion batteries

Article Title: Solvent-controlled hypophosphite phosphating method for pretreatment: Structure and kinetics of nickel phosphide anode in sodium-ion batteries

Article References: Gong, H., Jin, J., Zhang, X., Zhou, L., Cheng, Z., & Du, T. (2026). Solvent-controlled hypophosphite phosphating method for pretreatment: Structure and kinetics of nickel phosphide anode in sodium-ion batteries. Ionics. https://doi.org/10.1007/s11581-026-07576-y

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07576-y

Keywords: sodium-ion batteries, nickel phosphide, Ni5P4, anode materials, hypophosphite phosphating, solvent control, carbon cloth, electrochemical kinetics, activation energy, energy storage, transition metal phosphides, binder-free electrode

The appeal of metal sulfide anodes lies in their chemistry. Compounds containing two electrochemically active metals can undergo multiple redox reactions, and the presence of sulfur helps accommodate some of the volumetric strain that develops when metals alloy with lithium or sodium. Bismuth sulfide, for example, offers a theoretical capacity of about 625 mAh per gram through the formation of Li3Bi or Na3Bi phases. Crucially, bismuth sulfide and antimony sulfide form a complete solid solution across the entire compositional range, meaning researchers can tune the bismuth-to-antimony ratio freely to optimize performance. Previous studies of related compositions, such as Bi0.94Sb1.06S3 nanorod clusters, had already shown improved cycling stability compared with single-metal sulfide anodes, but the fabrication method itself remained a limiting factor in how uniformly the active material adhered to the current collector.

The Indian team’s solution was to eliminate the polymer binder altogether. Conventional electrodes are made by mixing active material with conductive additives and a glue-like binder, then coating the slurry onto metal foil. Binders add dead weight, can impede electron transport, and may fail mechanically over time. Instead, the researchers used electrophoretic deposition, a technique in which charged particles suspended in a liquid migrate toward and deposit onto an oppositely charged electrode under an electric field. By applying a constant DC voltage of around 300 volts in an isopropanol-based bath containing nickel nitrate, poly(acrylic acid), and carbon black, they fabricated complete electrodes on copper foil in roughly three minutes. The method is inherently scalable and produces a film whose adhesion, porosity, and uniformity can be controlled through deposition parameters rather than through binder chemistry.

Synthesis of the active material itself relied on a one-step hydrothermal process. Graphene oxide, prepared by a modified Hummer’s method from graphite powder, was dispersed in water and sonicated to achieve partial exfoliation. Bismuth nitrate and antimony trichloride precursors were dissolved separately and combined, then thioacetamide was added as the sulfur source. The negatively charged graphene oxide sheets electrostatically attracted the positively ionized Bi3+ and Sb3+ species, promoting a uniform distribution of metal ions across the carbon surface. Under hydrothermal conditions of 200 degrees Celsius for 24 hours in a Teflon-lined autoclave, the amorphous bismuth-antimony-sulfur complex nucleated and grew into crystalline nanorods anchored on the reduced graphene oxide sheets. Prolonged treatment favored unidirectional growth along the (011) crystallographic plane, producing the one-dimensional nanorod clusters that give the material its distinctive morphology.

Characterization confirmed the composite’s structure in detail. X-ray diffraction revealed an orthorhombic Bi1.09Sb0.91S3 phase matching the standard reference pattern, with crystallite sizes of approximately 22 nanometers in the composite compared with about 30 nanometers for the pristine sulfide. Raman spectroscopy showed the characteristic D-band and G-band of reduced graphene oxide, and thermogravimetric analysis quantified the composition at roughly 94 weight percent sulfide and 6 weight percent graphene. Electron microscopy showed nanorod clusters with average diameters near 35 to 40 nanometers and lengths around 0.35 micrometers, well anchored to the graphene sheets without phase segregation. Nitrogen adsorption measurements revealed that adding graphene increased the surface area from about 11 square meters per gram to roughly 48 square meters per gram, providing more electrochemically active reaction sites and shorter ion diffusion pathways.

Electrochemical testing in lithium-ion coin cells highlighted the graphene’s contribution. The composite anode delivered an initial discharge capacity of about 1269 mAh per gram, with the substantial first-cycle irreversibility attributed to electrolyte decomposition and solid electrolyte interphase formation, a familiar feature of nanostructured metal sulfide anodes. From the second cycle onward the electrode stabilized, and over 100 cycles at 0.5 amperes per gram it maintained average capacities near 506 mAh per gram, substantially outperforming the pristine sulfide electrode, which managed about 331 mAh per gram. Rate capability testing told a similar story: at 4 amperes per gram the composite still delivered about 128 mAh per gram, more than double the 58 mAh per gram of the bare material, and when the current was lowered back to 0.5 amperes per gram the composite recovered roughly 353 mAh per gram, evidence of excellent structural reversibility.

Sodium-ion performance followed the same pattern. Cyclic voltammetry identified the expected sequence of reactions: conversion of the sulfide into metallic bismuth, antimony, and sodium sulfide, followed by alloying of the metals into Na3Bi and Na3Sb, with the reverse reactions on charge. Over 33 cycles at 0.1 amperes per gram, the composite averaged about 413 mAh per gram with a Coulombic efficiency near 95 percent, compared with roughly 257 mAh per gram for the pristine electrode. Impedance spectroscopy revealed the underlying kinetics: the composite’s charge transfer resistance after cycling measured just 12.5 ohms in lithium cells and 21.7 ohms in sodium cells, dramatically lower than the pristine material’s values, and calculated diffusion coefficients confirmed faster ion transport through the graphene-supported structure. The team noted that sodium-ion gains were more modest than lithium-ion gains because the larger sodium ion is intrinsically slower and more constrained by the crystal lattice.

Perhaps the most compelling evidence came from postmortem analysis using synchrotron X-ray absorption spectroscopy and electron microscopy. Ex situ XANES measurements at the Bi L3-edge and Sb K-edge showed the reduction of trivalent bismuth and antimony to their metallic states during discharge, with irreversible edge shifts consistent with the formation of pseudo-crystalline Li3Bi, Na3Bi, Li3Sb, and Na3Sb phases. Cross-sectional electron microscopy quantified the mechanical toll of cycling: the pristine electrode swelled from about 10.9 micrometers to 29 to 34 micrometers, nearly a threefold increase, while the graphene composite expanded only to about 20.4 micrometers in lithium cells and 18.2 micrometers in sodium cells. The pristine electrode’s nanorods fragmented and agglomerated into dense aggregates riddled with voids, whereas the composite largely retained its nanorod morphology, with the graphene sheets acting as a mechanical buffer that absorbed volume fluctuations and prevented active material from detaching from the copper collector.

The study demonstrates that combining a tunable bimetallic sulfide solid solution with a conductive, flexible graphene scaffold and a fast, binder-free deposition process can produce an anode that works effectively in both lithium and sodium chemistries. Because sodium-ion batteries rely on abundant, inexpensive materials and are viewed as a complement to lithium technology for grid-scale storage, an anode strategy that serves both systems is particularly valuable. The electrophoretic deposition step, completed in minutes at ambient conditions, avoids the energy-intensive drying and calendering complexities of slurry coating while producing electrodes with a practical mass loading of about 1.3 milligrams per square centimeter. As the authors conclude, the Bi1.09Sb0.91S3/reduced graphene oxide composite represents a promising dual-functional anode candidate, and the scalable fabrication route suggests a plausible path from laboratory coin cells toward practical electrode manufacturing.

Subject of Research: Binder-free bismuth-antimony sulfide nanorod anodes on reduced graphene oxide for lithium-ion and sodium-ion battery storage

Article Title: Binder-free Bi₁.₀₉Sb₀.₉₁S₃ nanorod clusters anchored on reduced graphene oxide via electrophoretic deposition for enhanced lithium and sodium-ion storage

Article References: Dashairya, L., Das, D., & Saha, P. (2026). Binder-free Bi₁.₀₉Sb₀.₉₁S₃ nanorod clusters anchored on reduced graphene oxide via electrophoretic deposition for enhanced lithium and sodium-ion storage. Discover Electrochemistry, 3(1), Article 28. https://doi.org/10.1007/s44373-026-00116-3

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00116-3

Keywords: lithium-ion batteries, sodium-ion batteries, bismuth sulfide, antimony sulfide, reduced graphene oxide, electrophoretic deposition, binder-free electrode, anode materials, nanorods, solid solution, XANES, energy storage