Cyclic Production of Biocompatible Graphene Ink with In-Line Shear-Mixing for Inkjet-Printed Electrodes, Li-Ion Energy Storage and Sensors

The scalable production of two-dimensional (2D) materials is needed to accelerate their adoption to industry. [1] Here 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 <i>Y</i>_w ~ 100% yield by weight and throughput of ~ 8.3 g/h. [2] The in-line process minimises basal plane defects compared to traditional beaker-based shear mixing which we attribute to a reduced Reynolds number, <i>Re </i>~ 10⁵. We demonstrate highly conductive graphene material with conductivities as high as <i>σ</i> ∼ 1.5 × 10⁴ S/m leading to sheet-resistances as low as <i>R_s </i>∼ 2.6 <i>Ω/sq</i> (thickness<i> </i>∼ 25 μm). The process is ideal for formulating non-toxic, biocompatible and highly concentrated (<i>c</i> ∼ 100 mg/ml) inks for use in the printed/flexible electronics industry. [3] We utilise the graphene inks for inkjet printable conductive interconnects and blade coated lithium-ion battery anode composites that demonstrate a low-rate lithium storage capability of 370 mAh/g, close to the theoretical capacity of graphite. The use of the graphene ink for screen printed capacitive textile sensors will also be discussed. Finally, we demonstrate the biocompatibility of the graphene inks with human colon cells and human umbilical vein endothelial cells at high <i>c</i> ∼ 1 mg/ml facilitating a route for the use of the graphene inks in applications that require biocompatibility at high <i>c</i> such as electronic textiles. [4]<br/>[1] Paton, K.R.<i> et al.</i> Scalable production of large quantities of defect-free few-layer graphene by shear exfoliation in liquids. <i>Nature Materials</i> <b>13</b>, 624-630 (2014).<br/>[2] Carey, T. <i>et al.</i> Cyclic Production of Biocompatible Few-layer Graphene Ink with In-line Shear-Mixing for Inkjet-Printed Electrodes and Li-ion Energy Storage. (<i>Submitted</i>)<br/>[3] Torrisi, F. & Carey, T. Graphene, related two-dimensional crystals and hybrid systems for printed and wearable electronics. <i>Nano Today</i> 23, 73-96 (2018).<br/>[4] Seyedin, S. <i>et al.</i> Fibre electronics: towards scaled-up manufacturing of integrated e-textile systems. <i>Nanoscale</i> 13, 12818-12847 (2021).