Cyclic production of biocompatible few-layer graphene ink with in-line shear-mixing for inkjet-printed electrodes and Li-ion energy storage

The scalable production of two-dimensional (2D) materials is needed to accelerate their adoption to industry. In this work, we present a low-cost in-line and enclosed process of exfoliation based on high-shear mixing to create aqueous dispersions of few-layer graphene, on a large scale with a Y_w ~ 100% yield by weight and throughput of ϕ ~ 8.3 g h⁻¹. The in-line process minimises basal plane defects compared to traditional beaker-based shear mixing which we attribute to a reduced Reynolds number, Re ~ 10⁵. We demonstrate highly conductive graphene material with conductivities as high as σ ∼ 1.5 × 10⁴S m⁻¹ leading to sheet-resistances as low as R_s ∼ 2.6 Ω □⁻¹ (t ∼ 25 μm). The process is ideal for formulating non-toxic, biocompatible and highly concentrated (c ∼ 100 mg ml⁻¹) inks. We utilise the graphene inks for inkjet printable conductive interconnects and lithium-ion battery anode composites that demonstrate a low-rate lithium storage capability of 370 mAh g⁻¹, close to the theoretical capacity of graphite. Finally, we demonstrate the biocompatibility of the graphene inks with human colon cells and human umbilical vein endothelial cells at high c ∼ 1 mg ml⁻¹ facilitating a route for the use of the graphene inks in applications that require biocompatibility at high c such as electronic textiles.