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-NH4) and poly(acrylic acid-co-maleic acid) (PAMA), on the dispersion and electrochemical properties of carbon-coated lithium iron phosphate (LiFePO4) cathodes are studied. The influence of the addition of dispersants on the dispersion behaviors of carbon-coated LiFePO4 and conductive agents in aqueous suspensions is explored by analyses of zeta-potential and rheology. The homogeneity of the composition in the LiFePO4 cathode is assessed by scanning electron microscopy observation. The result shows that both PSSA and PAMA can interact with the carbon-coated LiFePO4 and they are efficient dispersants for LiFePO4 cathodes. PAA-NH4, however, is unfavorable to interact with carbon materials, and thus has a restricted efficiency for the dispersion of carbon-coated LiFePO4 cathodes. In addition to the dispersion property, the effect of the addition of dispersants on the rate capability of LiFePO4 cathodes is also examined. Although PSSA improves the dispersion homogeneity of the LiFePO4 electrodes, it is detrimental to the electrochemical property due to its high average molecular weight ((M-n) over bar) of 70,000 g/mol. On the contrary, the PAMA used has a low (M-n) over bar 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. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592158] All rights reserved.