Mixing duration and performance in NMC electrodes: Insights from 3D imaging and electrochemical simulation

In lithium-ion batteries, energy and power densities depend heavily on the electrode microstructure. Because their structure is determined during the manufacturing process, manufacturing steps must be understood in great detail to tailor the electrodes to the specific needs of the application. The present work investigates the influence of wet mixing time on the conductive networks and consequently on electrode performance. FIB-SEM tomography coupled with 3D-resolved simulations unveils an increased homogeneity of the carbonaceous network inside a NMC622 electrode for longer dispersion times. Quantitative structural analysis is used to correlate microstructure and electrochemical performance using rate capability tests and electrochemical impedance spectroscopy. Longer mixing increases both active material particle coverage in the carbon binder domain (CBD) and homogeneity of the CBD, leading to higher electronic conductivity and reduced contact resistance. Conversely, the more homogeneous CBD negatively affects ionic transport inside the electrolyte due to pore blockage and lowers available surface area of the active material. This leads to a 21% increase in solid diffusion length and a reduction in surface area of 21% after doubling the wet mixing time from 30 to 60 min. Overall, this contribution untangles the complex interaction between wet mixing duration, microstructural evolution, and electrode performance.