Cathode Performance as a Function of Inactive Material and Void Fractions

Li[Ni(1/3)Co(1/3)Mn(1/3)]O(2)-based laminates of approximately the same loading and of varying levels of poly(vinylidene fluoride) (PVDF) binder and acetylene black (ratio held constant) were fabricated and calendered to different porosities, with the objective to investigate performance on a volume basis. The electronic conductivity of the laminates depends strongly on the inactive material content but not significantly on porosity. Electrochemical impedance spectroscopy studies found that charge-transfer resistance with calendering varied greatly with inactive material content. When the electrode contains low levels of inactive material (2% PVDF and 1.6% carbon), calendering significantly reduced the bulk resistance of the electrode. With high levels of inactive material (8% PVDF and 6.4% carbon), charge-transfer resistance increased with increased calendering. Above a certain level, depending on the overall composition, the inactive material reduces ionic transport to the active material surface. For a plug-in hybrid electric vehicle required to go 40 miles at an average rate of 20 miles/h with a 38 kW 10 s power-pulse capability, the cell chemistry studied is energy-limited. Therefore, based on the results of this study, the cathode should be compressed to 10% porosity with a minimal amount of inactive material. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3459878] All rights reserved.