Improvements of dispersion homogeneity and cell performance of aqueous-processed LiCoO2 cathodes by using dispersant of PAA-NH4

The dispersion property of aqueous lithium cobalt oxide (LiCoO2) slurries and their corresponding cell performance with and without addition of dispersant, ammonium polyacrylic acid (PAA-NH4), were investigated. The surface chemical properties of LiCoO2 and graphite powders were characterized by diffuse reflectance using infrared Fourier transform spectrometry. The adsorption effects of PAA-NH4 and latex binder (LA132), respectively, on the dispersion behaviors of LiCoO2 and graphite powders in aqueous suspensions were analyzed by measurements of adsorption behavior, zeta potential, sedimentation property, and rheology. The results showed that the PAA-NH4 can adsorb onto both the LiCoO2 and graphite powders to stabilize them in aqueous suspensions, but LA132 binder only adsorbs onto graphite and showed a competitive adsorption with PAA-NH4 on the graphite surface. By observation of scanning electron microscope, it was shown that the as-prepared LiCoO2 sheet without PAA-NH4 addition had significant agglomeration of powders and accumulation of binder around the powder. These undesired coagulations of powder and binder can be diminished by increasing the PAA-NH4 content. Although the dispersion property of powders was increased with increasing PAA-NH4 content, too much addition of PAA-NH4 is detrimental to the electronic conduction, adhesion strength, and electrochemical properties of LiCoO2 electrode. To simultaneously obtain a well-dispersed and a better electrochemical property of LiCoO2 electrode sheet, the appropriate amount of PAA-NH4 was found to be on the order of 0.01 wt % based upon LiCoO2. (c) 2006 The Electrochemical Society.