Effects of Surface-coated Carbon on the Chemical Selectivity for Water-Soluble Dispersants of LiFePO4

The effects of additions of dispersants, poly(4-styrene sulfonic acid) (PSSA), poly(ammonium acrylate) (PAA-NH 4 ) and poly(acrylic acid- co -maleic acid) (PAMA), on the dispersion and electrochemical properties of carbon-coated lithium iron phosphate (LiFePO 4 ) cathodes are studied. The influence of the addition of dispersants on the dispersion behaviors of carbon-coated LiFePO 4 and conductive agents in aqueous suspensions is explored by analyses of zeta-potential and rheology. The homogeneity of the composition in the LiFePO 4 cathode is assessed by scanning electron microscopy observation. The result shows that both PSSA and PAMA can interact with the carbon-coated LiFePO 4 and they are efficient dispersants for LiFePO 4 cathodes. PAA-NH 4 , however, is unfavorable to interact with carbon materials, and thus has a restricted efficiency for the dispersion of carbon-coated LiFePO 4 cathodes. In addition to the dispersion property, the effect of the addition of dispersants on the rate capability of LiFePO 4 cathodes is also examined. Although PSSA improves the dispersion homogeneity of the LiFePO 4 electrodes, it is detrimental to the electrochemical property due to its high average molecular weight ( M n − ) of 70,000 g/mol. On the contrary, the PAMA used has a low M n − of 3,000 g/mol, and hence only the positive influence of the improved dispersion of the cathode in terms of an increase in rate capability is observed.