Effect of mechanical properties on processing behavior and electrochemical performance of aqueous processed graphite anodes for lithium-ion batteries

Abstract

A combination of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) is a well-established binder system in aqueous processed anodes for lithium-ion batteries. The main function of SBR is to increase the adhesive strength between the active anode layer and the current collector, providing a robust connection capable of withstanding mechanical stresses encountered during cell manufacturing and cell cycling. To determine the optimal adhesion level ensuring failure-free processing without compromising the electrochemical performance we variated SBR concentration and investigated the effect on the processability and electrochemical performance of graphite anodes with application relevant mass loadings (5.7 mg cm⁻² and 10.1 mg cm⁻²).

Our results indicate that the inclusion of SBR enhances cohesion of anodes, a vital factor in preserving the mechanical integrity during bending, winding and cutting, particularly at elevated mass loadings. However, our findings reveal that unnecessarily high adhesion does not yield benefits on the processability of anodes. Furthermore, SBR is virtually dispensable for adhesion during cell cycling, and it proves to be counterproductive, primarily due to the rise in internal resistance and, most likely, SBR degradation. For the system investigated here, optimal adhesion was found for 1.5 % SBR in the current collector-free anode.