| Mar 16, 2026 |
Spray-dried graphite CNT silicon composite anodes improve battery cycling stability
A scalable spray-drying method produces graphite, carbon nanotube, and silicon composite anodes that retain 95% capacity after 100 cycles in lithium-ion batteries.
(Nanowerk News) A team of researchers has developed a scalable spray-drying method to produce graphite, carbon nanotube, and silicon composite microspheres that significantly improve the cycling stability of lithium-ion battery anodes. The work, published in Energy Materials ("Scalable spray-dried graphite/CNT/silicon composites with enhanced cycling stability for Li-ion battery anodes"), addresses one of the central obstacles to using silicon in next-generation batteries: the material's tendency to expand, crack, and lose capacity during repeated charging and discharging.
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Key Findings
- A spray-dried composite containing 15% nano-silicon and just 1% single-walled carbon nanotubes retained 95.3% of its capacity after 100 charge-discharge cycles, compared with 68% for a carbon nanotube-free equivalent.
- The carbon nanotube network reduced charge-transfer resistance by more than half relative to composites without carbon nanotubes, as confirmed by impedance spectroscopy.
- The process uses low-cost graphite fines, a by-product of natural graphite spheroidization, combined with minimal carbon nanotube content, offering clear economic and environmental advantages for industrial scale-up.
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Silicon can theoretically store roughly ten times more lithium than graphite, the material used in most commercial battery anodes today. But silicon swells by up to 300% each time it absorbs lithium ions, and this repeated expansion and contraction fractures particles, disrupts electrical connections, and causes the electrode to lose capacity rapidly. These problems have kept silicon from replacing graphite in mainstream lithium-ion cells despite years of research.
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The researchers used a spray-drying process to embed nano-silicon particles and single-walled carbon nanotubes within a matrix of graphite flakes. During spray drying, a slurry of these materials is atomized into micron-sized droplets. As the water evaporates, capillary forces pull the solid components together, forming dense, spherical secondary particles where the silicon and carbon nanotubes are uniformly distributed throughout the graphite framework. Heat treatment at 1,000°C under argon then carbonizes the binder and locks the structure in place.
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Cross-sectional imaging with focused ion beam scanning electron microscopy confirmed that the nano-silicon and carbon nanotubes were embedded within the porous graphite agglomerates rather than merely sitting on the surface. Some carbon nanotubes bridged silicon aggregates and graphite surfaces, creating conductive links between the components. The resulting particles measured roughly 14 micrometers in diameter, within the range used in commercial battery production.
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In electrochemical testing, the optimized composite, containing 15% nano-silicon and 1% carbon nanotubes, delivered a discharge capacity of 630 milliampere-hours per gram after 100 cycles at a rate of C/9, corresponding to an areal capacity of 3.15 milliampere-hours per square centimeter. By contrast, the same formulation without carbon nanotubes retained only 68% of its third-cycle capacity over the same period, declining to roughly 436 milliampere-hours per gram.
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The researchers traced the improvement to two complementary effects. First, carbon nanotubes formed a conductive network that maintained electrical pathways even as silicon particles expanded and contracted. Second, the mechanical strength and flexibility of the nanotubes reinforced the agglomerate structure, limiting particle fracture and the progressive electrical isolation that normally degrades silicon anodes. Analysis of irreversible capacity losses showed that mechanical disconnection was the dominant failure mechanism in composites without carbon nanotubes, while in the carbon nanotube-containing material, this contribution was suppressed almost entirely.
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Carbon nanotubes did introduce a trade-off. Because they increased the composite's specific surface area from 7.3 to 11.9 square meters per gram, more electrode surface was exposed to the electrolyte, leading to greater formation of the solid electrolyte interphase layer and slightly lower initial coulombic efficiency of 78.3% compared with 79.7% for the carbon nanotube-free version. The researchers noted that this side effect could be mitigated through electrolyte optimization or the use of appropriate additives.
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Rate performance testing further highlighted the advantage of carbon nanotube incorporation. At a charge rate of 1C, the composite with carbon nanotubes retained 97.2% of its capacity, while the version without nanotubes dropped to approximately 62%. When the rate was returned to 0.1C after being pushed to 4C, the carbon nanotube composite recovered 93% of its original capacity, demonstrating strong electrochemical reversibility.
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Impedance spectroscopy using a three-electrode configuration revealed that the carbon nanotube composite had significantly lower resistance at every level. Bulk resistance fell from 12.0 to 5.2 ohms, solid electrolyte interphase resistance from 19.1 to 2.1 ohms, and charge-transfer resistance from 11.7 to 4.7 ohms. These reductions confirm that the conductive nanotube network improves electronic contact throughout the electrode and stabilizes the interfaces involved in lithium-ion transfer.
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Post-mortem examination of cycled electrodes provided a visual record of these effects. After 20 cycles, the composite without carbon nanotubes showed evidence of electrochemical sintering, where originally distinct nano-silicon particles had fused into larger, less effective agglomerates. The carbon nanotube-containing composite, by contrast, maintained its layered graphite structure with nano-silicon still interspersed between flakes, and porosity reduction in dense silicon regions was less than 1% compared with roughly 20% in the carbon nanotube-free version.
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Separately, X-ray nano-holo-tomography performed at the European Synchrotron Radiation Facility on a related composite containing 9% nano-silicon without carbon nanotubes provided three-dimensional images of electrode microstructure before and after calendering. This analysis, conducted on the 9% formulation due to limited beam time, is considered representative of the structural changes expected in higher silicon-loading composites. Calendering compressed the agglomerates from spherical particles averaging 25 by 20 by 20 micrometers into flattened shapes of 9 by 9 by 3 micrometers, reducing internal porosity from 31% to 9.5%. Despite this compression, the porous network remained nearly fully interconnected at 98.9%, ensuring electrolyte could still reach the active material throughout the electrode.
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An important practical consideration is that the graphite used in these composites is not a premium raw material but rather the fine particles generated as waste during the spheroidization of natural graphite for commercial anode production. Repurposing this by-product reduces both material cost and environmental impact. Combined with the low carbon nanotube loading of just 1% by weight, the process avoids the expense associated with high nanotube content or complex synthesis methods such as chemical vapor deposition that have been used in earlier studies.
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The tapped density of the carbon nanotube composite reached 0.49 grams per cubic centimeter, higher than the 0.40 grams per cubic centimeter measured for the equivalent material without nanotubes. While still below the 1.0 grams per cubic centimeter typical of commercial graphite anodes, this represents a meaningful improvement that the researchers suggested could be further optimized by adjusting spray-drying and coating parameters.
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This work establishes a practical, one-step manufacturing route for integrating silicon into graphite-based anodes at industrially relevant mass loadings and areal capacities. By demonstrating that a minimal addition of carbon nanotubes can suppress the mechanical degradation that limits silicon anode lifetime, the study offers a pathway toward higher-energy lithium-ion batteries for electric vehicles, portable electronics, and grid-scale energy storage.
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