Binder Distributions in Water-Based and Organic-Based LiCoO2 Electrode Sheets and Their Effects on Cell Performance

The concentration distributions of binders in dried water-based and organic-based LiCoO2 electrode sheets are studied, and the effects of binder distributions on the physical, electrical and electrochemical properties of electrodes are also discussed. When the LiCoO2 slurry is prepared with an organic-based process, the non-uniform distributions of the binder, poly(vinylidene fluoride), and a conductive agent, graphite, are markedly observed in the dried electrode sheet. Nevertheless, these non-uniform distributions of constituents are less significant for the electrode sheet prepared by a water-based process that uses a blend of styrene butadiene rubber and sodium carboxymethyl cellulose as the binder. Beside the experimental results, the binder distributions in the dried electrodes can be accurately predicted via a theoretical calculation based on a migration-controlled drying kinetics. The calculated results show that the organic-based electrode sheet has much higher non-uniformity of binder distribution than the water-based one. Because of the higher non-uniform distributions of binder, the organic-based electrode sheet displays properties of weaker adhesion and higher electrical resistance. Moreover, the electrochemical performance shows that the IR-drop of the organic-based electrode is larger than the water-based one, which has to be reduced by the compression process of electrode sheets. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.107112jes] All rights reserved.