Clarification of the dispersion mechanism of cathode slurry of lithium-ion battery under effects of both poly vinylidene fluoride/carbon black ratio and mixing time

Abstract

This paper presents the effects of both poly vinylidene fluoride (PVDF)/carbon black (CB) ratio (mPVDF:mCB) and mixing time t on the dispersion mechanism of the cathode slurry of lithium-ion battery (LIB). The dispersion mechanism is deduced from the electrochemical, morphological and rheological properties of the cathode slurry by using electrical impedance spectroscopy (EIS), scanning electron microscopy and rheology methods, respectively. From the perspective of EIS method, static simulation models are established in the COMSOL Multiphysics software; meanwhile, the simulated results are used to verify the correctness of the electrochemical properties of the cathode slurry. As a result, the following conclusions are able to be obtained. Firstly, in the case of the mass ratio mPVDF:mCB = 5:10, LiCoO2 particles are completely coated by the mixture of CB and PVDF to form a stable polymer gel structure. Higher or lower mPVDF:mCB leads to the larger impedance and worse dispersion status for the cathode slurry. Secondly, when t = 6 min, a good gel-like conductive network structure is formed by coating the thinner evenly dispersed CB–PVDF double layer around LiCoO2 particles. Finally, a strategy regarding to both mPVDF:mCB and t in experimental scale is proposed, which has the capability of improving the performance of LIB.