Graphene-Anchored Bismuth-Antimony Sulfide Nanorods Boost Lithium and Sodium Battery Anodes

Researchers at the National Institute of Technology Rourkela and the Indian Institute of Technology Kharagpur have unveiled a binder-free battery anode that could reshape how next-generation lithium- and sodium-ion batteries are built. The team, led by Love Dashairya, Debasish Das, and Partha Saha, grew clusters of bismuth-antimony sulfide nanorods on sheets of reduced graphene oxide and then deposited the hybrid material directly onto copper foil using a rapid electrophoretic deposition technique. The resulting electrode, described in the journal Discover Electrochemistry, delivered stable capacities of roughly 379 mAh per gram over 100 cycles in lithium-ion cells and about 334 mAh per gram over 30 cycles in sodium-ion cells, with Coulombic efficiencies of approximately 98.6 percent and 96.7 percent respectively. The work addresses one of the most stubborn problems in alloy-type anode chemistry: the catastrophic physical breakdown that occurs when these materials swell and shrink during charging and discharging.

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