Capillary suspensions as beneficial formulation concept for high energy density Li-ion battery electrodes

Bitsch B, Gallasch T, Schroeder M, Börner M, Winter M, Willenbacher N

Abstract

We introduce a novel formulation concept to prepare high capacity graphite electrodes for lithium ionbatteries. The concept is based on the capillary suspension phenomenon: graphite and conductive agentare dispersed in an aqueous binder solution and the organic solvent octanol is added as immiscible,secondary fluid providing the formation of a sample-spanning network resulting in unique stability andcoating properties. No additional processing steps compared to conventional slurry preparation arerequired. The resulting ultra-thick electrodes comprise mass loadings of about 16.5 mg cm 2, uniformlayer thickness, and superior edge contours. The adjustment of mechanical energy input ensures uniformdistribution of the conductive agent and sufficient electronic conductivity of the final dry compositeelectrode. The resulting pore structure is due to the stable network provided by the secondary fluidwhich evaporates residue-free during drying. Constant current-constant potential (CC-CP) cycling clearlyindicates that the corresponding microstructure significantly improves the kinetics of reversible Liþ (de-)intercalation. A double layer electrode combining a conventionally prepared layer coated directly ontothe Cu current collector with an upper layer stabilized with octanol was prepared applying wet-on-wetcoating. CC-CP cycling data confirms that staged porosity within the electrode cross section results insuperior electrochemical performance.