We report the transport properties and mechanical behaviors of carbon inks as a conductive component in semi-solid electrodes. Commonly, the suspensions show a gel-like behavior implying the percolation of the solid network. Our work shows the dependency of rheological and conductivities properties on the carbon concentration, morphology, as a function of shear rate. Different percolating thresholds are found as a function of pH and ionic strength that act on the surface charge of the particles and their coulombic interaction. Under shear flow, the suspensions commonly exhibit a three-regime flow curve: shear-thinning at low and high shear rates separated by a small increasing-viscosity region over intermediate rates. These results are strongly dependent of the nature of the carbon slurry and measurement conditions. The highest conductivity can be obtained by tuning these parameters. The rheo-electrical behavior of aqueous carbon suspension shows the possibilities and limitations of semi-solid aqueous inks as flowable electrodes for two different technological applications such as redox flow batteries and electrowinning.

            First, semi-solid aqueous redox flow batteries are discussed in this work for safety, toxicity, cost and reliability. Such as flow-cell concept was recently described by Yet-Ming Chiang’s group at MIT in 2010 [1]. They proposed using typical intercalation electrode materials as active materials for a lithium rechargeable battery, but providing the active material in a slurry that can be mechanically pumped into and out of a reaction chamber. A redox flow batteries (RFBs) using intercalation electrode materials as active materials for a lithium rechargeable battery (such as “MIT suspension redox flow” batteries).

            Second, we discuss the use of such conductive pastes for extraction of various metals such as copper from various mineral ores. The conductive inks can be mixed with powdered ores and permit an electrical percolation that allow electrochemical dissolution of the materials. We analyze the electrochemical yield as a function of the copper concentration and formulation of the carbon paste before we discuss the applications.

[1] M. Duduta, B. Ho, V.C. Wood, P. Limthongkul, V.E. Brunini, W.C. Carter, Y. Chiang, Semi- Solid lithium rechargeable flow battery, Advanced Energy Materials 1 (4) (2011) 511.