2, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
One of the crucial steps in battery manufacturing is the electrolyte wetting step which typically requires a relatively long time to be completed. It is known that the relationship between polar and dispersive components of the electrolyte surface tension and the electrode surface free energy (SFE) plays a vital role in the extent of wetting and, thus, tuning the SFE can accelerate the wetting step in battery manufacturing.
This work developed and validated a systematic approach to characterize surface free energy of composite electrodes for lithium-ion batteries, which has never been reported in literature. We introduced two main surface parameters, r and f, that represent the surface roughness ratio and surface solid fraction, respectively. These parameters are crucial in determining the so called actual SFE of the electrodes.
The effect of slurry formulation and electrode porosity on the SFE of electrodes were investigated. It is demonstrated that the SFE of LiNi0.5Mn0.3Co0.2O2 cathode was higher than the graphite anode. Replacing the conventional Polyvinylidene fluoride (PVDF) with water soluble binder significantly increased the polar component of the electrodes surface free energy. The increased polar component is expected to enhance the wetting of the electrodes toward different common electrolytes. The results from this work provide insights in slurry formulation for optimal slurry wetting on current collector and electrolyte wetting on dry electrodes.