Direct Observation of Carboxymethyl Cellulose and Styrene-Butadiene Rubber Binder Distribution in Practical Graphite Anodes for Li-Ion Batteries.

Despite the important role of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) binders in graphite electrodes for Li-ion batteries, the direct analysis of these binders remains challenging, particularly at very low concentrations as in practical graphite anodes. In this paper, we report the systematic investigation of the physiochemical behavior of the CMC and SBR binders and direct observations of their distributions in practical graphite electrodes. The key to this unprecedented capability is combining the advantages of several analytic techniques, including laser-ablation laser-induced break-down spectroscopy, time of flight secondary ion mass spectrometry, and a surface and interfacial cutting analysis system. By correlating the vertical distribution with the adsorption behaviors of the CMC, our study reveals that the CMC migration toward the surface during the drying process depends on the degree of cross-linked binder-graphite network generation, which is determined by the surface property of graphite and CMC materials. The suggested analytical techniques enable the independent tracing of CMC and SBR, disclosing the different vertical distribution of SBR from that of the CMC binder in our practical graphite anodes. This achievement provides additional opportunity to analyze the correlation between the binder distribution and mechanical properties of the electrodes.