The new technique for evaluating carbon slurry dispersibility uses a combination of viscosity and electrochemical impedance measurements. Image: Isao Shitanda from TUS, Japan.
The new technique for evaluating carbon slurry dispersibility uses a combination of viscosity and electrochemical impedance measurements. Image: Isao Shitanda from TUS, Japan.

Lithium-ion batteries are the powerhouse of modern-day electronics, and fuel cells are a promising candidate for sustainable energy devices. An important factor affecting the performance of both lithium-ion batteries and fuel cells is the dispersibility of carbon slurries, suspensions made of conductive carbon particles dispersed in a solvent. Such slurries can be easily coated on a metal collector to mass-produce electrodes, but the carbon particles in the slurry must be homogenously dispersed to ensure reliable performance.

Unfortunately, evaluating the dispersibility of thick slurries with high particle concentrations is remarkably difficult. The large number of particles prevents scientists from peering into the internal structure of the slurries using direct spectroscopic techniques. Moreover, there are no methods for evaluating the dispersibility and conductive properties of slurries in response to the shear stress they experience during the coating process.

Against this backdrop, a research team led by Isao Shitanda, an associate professor at Tokyo University of Science (TUS) in Japan, developed a novel technique for estimating the dispersibility of carbon slurries. The researchers report this technique in a paper in ACS Applied Electronic Materials.

The technique involves combining a rheometer – a scientific instrument for measuring the flow/deformation behavior of fluids in response to applied stress – with a spectroscopy setup to measure. Using this approach, the researchers measured the electrochemical impedance of acetylene black slurries, with methylcellulose (a cellulose-derived compound used as a thickener and emulsifier in food and cosmetic products, as a bulk-forming laxative and as eye/ear drops) as a dispersant.

They conducted experiments under the influence of shear stress at various frequencies to obtain the rheo-impedance spectra, which provided information about the internal structure of the carbon particles in a slurry. Interestingly, they noticed that the impedance spectra did not change considerably under applied shear stress for a carbon slurry with good dispersibility.

Additionally, the team developed an equivalent circuit model consisting of three types of contact resistances and capacitances: those between the acetylene black particles, those of the particle bulk and those arising from the design of the measurement setup. The bulk resistance of acetylene black showed no dependence on shear rate but decreased as the methylcellulose concentration increased. Further, the resistance measured at each methylcellulose concentration increased with the shear rate, an observation that was attributed to a partial breakdown of the carbon–carbon network and the decreasing conductivity with rising shear rate.

Together, these results show that it is possible to evaluate the dispersibility of electrode slurries based on a combination of viscosity (measured with the rheometer) and electrochemical-impedance measurements.

Shitanda is excited about the potential of this new technique. “The insights from this study could prove useful for improving the efficiency of large-scale electrode manufacturing processes in which the internal structure of the slurry must be carefully controlled,” he says.

Preparing slurries with higher dispersibility could also lead to improved lithium-ion battery performance and enhanced functional materials. These would be significant contributions toward building a sustainable carbon-neutral society by fostering applications in solar panels, fuel cells and electric vehicles.

“The proposed method can be used to evaluate the dispersibility of not just carbon dispersions, but a wide variety of slurries,” says Shitanda. “In future studies, we plan to conduct further measurements and equivalent circuit verifications by changing the particle type and binder combinations.”

This story is adapted from material from Tokyo University of Science, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.