in our ink formulation.

The high viscosity of our ink means that a suitable processing method is required to sufficiently disperse the agglomerates and aggregates of the graphene flakes into primary particles [@Ng2019e]. Hence, three-roll milling is selected as the main method of dispersion. A three-roll mill consists of a feed roll, a center roll and an apron roll that rotate in opposing directions and at different speeds. It is commonly used in ink, paint and coating industries to disperse pigment particles within high viscosity liquids [@Goldschmidt2003]. As a dispersion method, it utilises the internal shear and impact forces generated from the movement of the three rollers to break down agglomerates and aggregates into primary particles.

In our formulation, the EC is first mixed with graphene powder (CamGraph G3, Cambridge Nanosystems, avg. flake thickness $\sim$12.4 nm, avg. flake size $\sim$94.5 nm) until the premix becomes a coarse slurry; Fig. \[panel1\]a. We note that the dimensions of the graphene powder fall out of the scope of nomenclature postulated by academic literatures which define 2D graphitic materials with a thickness and/or lateral dimension less than 100 nm as “Graphite nanoplates”, “graphite nanosheets” or “graphite nano-flakes” [@Bianco2013]. This is to distinguish from finely 