In situ 4D distribution visualization of carbon-black volume fraction in cathode slurry of lithium-ion battery by multi-layered electrical resistance tomography (mlERT)

Abstract

In situ 4D (3D spatial + 1D temporal) distribution of carbon black (CB) volume fraction ϕCB in cathode slurry of lithium-ion battery (LIB) (CB powder and lithium cobalt dioxide (LiCoO2) particles in NMP/PVDF solution) has been visualized by multi-layered electrical resistance tomography (mlERT). The mlERT are composed of 24 electrodes (=8 electrodes/layer × 3 layers) with a newly developed multiplexer unit, which reconstructs the normalized conductivity σ¯ from the measured voltages U. The conditions of ϕCB is observed in the three dispersion states which are initial state, dispersing state, and fully dispersed state, under the mixing time t=0-360s and the mixing speed ω=720,400, and 200rpm. As the results, in the initial state (t=0s), the distribution of ϕCB is clearly visualized by the spatial σ¯ distribution from the high conductivity of ϕCB to the low conductivity of ϕLi which represents the initial position of CB powder and LiCoO2 particles in NMP/PVDF solution. In the dispersing state (t=30-120s), the distribution of ϕCB is dynamically changed as the σ¯ distribution is graduallly increased in the 3D spatial domain of mlERT which represents the dispersing CB powder within LiCoO2 particles in NMP/PVDF solution. In the fully dispersed state (t=120-360s), the ϕCB is in the uniformity as the σ¯ distribution tends to be uniformly dispersed which represents the fully dispersed CB in cathode slurry. In order to evaluate the distribution visualization of ϕCB in the fully dispersed state by mlERT, a qualitatively-scanning electron microscope (SEM) and a quantitatively-invasive two-wire resistance measurement are tested. The qualitatively-SEM images of fully dispersed CB at the height z=5 and 20mm are observed in the distributed formation of CB powder within LiCoO2 particles in NMP/PVDF solution which agrees to the uniformity of the σ¯ distribution by mlERT. Moreover, the comparison of σ¯ distribution by mlERT to the quantitatively-invasive two-wire resistance measurement is resulted in a low root means square error RSME=0.00196% which indicates the high accuracy of the in situ 4D distribution visualization of ϕCB in cathode slurry of LIB by mlERT.