Towards lightweight conductors: Improving the conductivity in graphitic films by transition metal additives

Graphite based conductors are promising low cost and light-weight alternatives to copper but current challenges are among others the improvement of the conductivity of graphite films (GF). Therefore, in this work the influence of copper(II) chloride and nickel(II) chloride on the graphitization of graphene oxide and the electrical conductivity of the resulting GF was studied. The electrical conductivity was measured at different scales by contactless eddy current method and four point probe scanning tunneling microscopy transport measurements. The macroscopic and nanoscopic transport measurements were complemented by network-based simulations, which allowed us to estimate the microscopic material properties of the GF with and without additives. Annealing temperatures between 1600 °C to 2850 °C and varying metal chloride concentrations revealed an optimum at 2850 °C and a concentration of 8.8 mmol/l NiCl2 in the aqueous dispersion. These GFs displayed an electrical conductivity of 609 kS/m, around 30 % higher than the GFs without any metal chloride addition. The graphitization morphology was analyzed by x-ray diffraction and scanning electron microscopy respectively. The precipitation effect of carbon from Ni supports the growth of graphitic structures, whereas the catalytic activity of Cu known from chemical vapor deposition does not promote graphitic structures. Rather, the annealing temperature is the crucial parameter for achieving highly conductive films. Furthermore, the influence of applied pressure during compression was studied. High pressures of at least 250 MPa are needed to obtain compact GFs with an electrical conductivity 3 times larger than before compression.