Effect of carboxymethyl cellulose on the flow behavior of lithium-ion battery anode slurries and the electrical as well as mechanical properties of corresponding dry layers

Abstract

We present a holistic view on the role of polymeric binders in waterborne LiB anodes, including preparation and processing of wet slurries as well as microstructure, electrical conductivity and mechanical integrity of dry electrode layers. We focus on carboxymethyl cellulose (CMC), with respect to technical application the influence of soft, nano-particulate styrene–butadiene rubber (SBR) as secondary binder is also addressed. We discuss the influence of CMC concentration, molecular weight (Mw) and degree of substitution (DS) on flow behavior of anode slurries. Rheological data are not only relevant for processing, here we use them to characterize the adsorption of CMC on active material particles and dispersion of these particles in the slurry at technically relevant concentrations. The fraction of CMC adsorbed onto graphite particles increases with increasing Mw and decreasing DS. Electrical conductivity increases with Mw, i.e. with decreasing free polymer deteriorating conductive carbon black pathways. CMC does not contribute to the adhesion of electrode layers, irrespective of Mw or DS, technically feasible adhesion is inferred by SBR. Cohesive strength of anode layers, determined here for the first time under well-defined mechanical load, increases with increasing Mw and decreasing DS, i.e. with increasing fraction of adsorbed CMC and corresponding improved particle dispersion. Strong cohesion and high electrical conductivity are correlated to an alignment of graphite particles as revealed by electron microscopy, presumably enabled by higher particle mobility in well-dispersed slurries. Accordingly, targeted choice of CMC is a valuable means to control processing, electrical conductivity and mechanical strength of LiB electrodes.

Advances of polymer binders for silicon‐based anodes in high energy density lithium‐ion batteries

“…For linear polymer binders, the binding ability is largely decided by their molecular weight ( M w ) and side groups 28,42,52‐54 . By means of copolymerization, blending or post‐modification, the binding ability can be further improved.…”

“…For linear polymer binders, the binding ability is largely decided by their molecular weight (M w ) and side groups. 28,42,[52][53][54] By means of copolymerization, blending or post-modification, the binding ability can be further improved. Natural derived polymers including CMC, Alg, CS, and so forth, and synthetic polymers including PAA, PVA, and so forth, are the typical linear polymer binders for Si-based anodes.…”

Solvent Properties Influence the Rheology and Pinching Dynamics of Polyelectrolyte Solutions: Thickening the Pot with Glycerol and Cellulose Gum

“…Cellulose gum (NaCMC) is widely used as an additive or a rheology modifier (as a thickener) in consumer products, including food, 79 pharmaceuticals, 80,81 paper, cosmetics, and batteries. 82 The shear rheological response of aqueous NaCMC solutions, with and without salt, is relatively well characterized. 5−7,19,25−28,83−97 In a recent publication, 19 we characterized the role of cellulose gum of M w = 250 kg/mol or M w = 250 kDa as a shear and extensional rheology modifier in both the presence and absence of salt.…”

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

“…[14] The choice of CMC in terms of substitution degree (DS) and molecular weight is another factor that has to be taken into account regarding the adsorption behavior of CMC onto graphite. [18] While the binder system and especially the choice and the mass fraction of CMC influence the networking behavior and thus the properties of the slurry, another important impact factor on that matter is the conductive agent carbon black. It was shown that the mass fraction as well as the bound fraction in contrast to the free fraction of DOI: 10.1002/ente.202100367…”