Effect of electrode mixing conditions on the performance of lithium-ion batteries analyzed by fast Fourier transform electrochemical impedance spectroscopy

We have investigated the influence of mixing conditions during the positive electrode fabrication on the discharge performance and internal resistances under high rate discharge of a test lithium-ion battery at 30 °C, employing fast Fourier transform electrochemical impedance spectroscopy in-situ to minimize the change in the state of charge. The internal resistances are assigned to each component in the positive electrode by comparing with cross-sectional scanning electron micrographs. The mixings of the active material and conductive filler with too low rotating speed both before and after the addition of the binder and solvent, pre-mixing and slurry mixing, respectively, give smaller active contact area between agglomerated conductive filler and the active material, leading to larger interfacial resistance. The pre-mixing and slurry mixing under too high rotating speed both result in larger interfacial resistances due to poor contacts of agglomerated active material with the conductive filler and the electrolyte.