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

Abstract

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.

Reduced Drying Time of Anodes for Lithium‐Ion Batteries through Simultaneous Multilayer Coating

“…A possible explanation for the different adsorption behaviors of the CMC on the spherical and the nonspherical graphite can be derived from Raman measurements (Figure 4). In the case of the spherical graphite, a pronounced D-peak in the Raman spectrum was measured, indicating a disordered crystal structure that is prone to provide OH groups at its surface, as described by Chang et al [13] In addition to the increasing number of bonding sites with the carboxyl groups of the CMC, these OH groups are also capable of establishing strong ester bonds, which might further promote fixation of the polymer on the graphite surface. A larger amount of the binder could therefore adhere on the surface of the graphite, whereas the mobile fraction in the interstices between the graphite particles would be smaller.…”

“…The binding mechanism between CMC, SBR, and the active material has been investigated for various systems. [10][11][12][13][14][15][16] CMC was found to form a network at contents of around 2 wt% CMC in the dry composite. [17] It was further found that the bonding mechanism between CMC and the active material depends on the surface properties of the active material.…”

“…Formation of ester bonds was shown with these -OH groups, leading to a strong crosslinking between binder and active material and a suppressed binder migration. [13] A difference between the distribution of the SBR binder and that of the CMC was found using time of flightÀsecondary-ion mass spectrometry (TOFÀSIMS) mapping depending on the surface properties of the graphite. [13] Different networking behaviors of CMC and graphite particles were observed by Lim et al depending on the mass fraction of CMC.…”

“…[13] A difference between the distribution of the SBR binder and that of the CMC was found using time of flightÀsecondary-ion mass spectrometry (TOFÀSIMS) mapping depending on the surface properties of the graphite. [13] Different networking behaviors of CMC and graphite particles were observed by Lim et al depending on the mass fraction of CMC. Furthermore, it was shown that SBR only is adsorbed on graphite particles at very low concentrations of CMC in the slurry by means of rheological investigations as well as by cryoÀSEM.…”

Process‐Structure‐Formulation Interactions for Enhanced Sodium Ion Battery Development: A Review

“…Adhesion loss from binder migration leads to delamination of electrodes from current collectors during battery operation, therefore drying rates should be minimized when fabrication time is not restricted. This was shown in both NMP‐based and aqueous slurries, though differences in solvent evaporation and binder chemistry should be considered when selecting drying parameters [157,158] …”