Stability and rheological study of sodium carboxymethyl cellulose and alginate suspensions as binders for lithium ion batteries

Currently, the most widely used binder in batteries is polyvinylidene fluoride (PVDF) with N-methyl-2-pyrrolidone (NMP) used as a solvent. This solvent is flammable and toxic. Here we focus on the suitability of using water soluble sodium alginate (Na-alginate) and sodium carboxymethyl cellulose (Na-CMC) as alternative biobased binder materials for the anodes of lithium ion batteries. It reduces the environmental impact of current manufacturing processes. However, control of the rheological characteristics of the binder whilst containing active and conductive additives is key for optimised processing. Here we perform stability and rheological measurements of Na-alginate and Na-CMC solutions containing varying amounts of graphite and carbon black used as active and conductive materials respectively. Comparing to the benchmark Na-CMC, the degree of flocculation shows that for the same concentration of binder in water, Na-alginate suspensions are more stable. The rheology measurements show that Na-alginate slurries have a higher viscosity than Na-CMC at a shear rate of 50 s-1 with that for a 1.5% of Na-alginate binder being 1.26 Pa·s while for Na-CMC it was for 0.20 Pa·s. The loss factor was lower for Na-Alginate, between 2 and 3 against between 2.9 and 3.3 for Na-CMC, showing a more developed network structure.