Assessment of the wettability of porous electrodes for lithium-ion batteries

The wettability of lithium cobalt oxide (LiCoO2) and mesocarbon microbead electrodes in nonaqueous electrolyte is analyzed by a mathematical model of capillary liquid movement. Results show that wetting in the LiCoO2 electrodes is difficult as compared with the MCMB electrodes at the same electrolyte composition. Wetting in the porous electrodes is controlled mainly by electrolyte penetration and spreading in pores. Electrolyte penetration is determined by viscosity. On the other hand, electrolyte spreading is controlled by surface tension. Organic solvent composition and lithium salt concentration may influence the wettability of porous electrodes due to changes in the viscosity and surface tension of the electrolyte. Increasing the amount of EC and/or lithium salts can cause poorer electrolyte spreading and penetration. Furthermore, careful pressure control has a positive effect on increasing the surface area of the solid-liquid interface. AC impedance data show that batteries with vacuuming prior to electrolyte filling may reach a maximum wetting in a few hours. If no vacuuming is applied, a few days are required to obtain sufficient wetting.