Effect of annealing temperature on the continuity and conductivity of coal-based carbon films prepared by ball milling

Abstract A simple solution-based method was used to prepare high value-added, coal-based carbon films, which were prepared by spin coating a centrifugal ball-milled coal suspension. The prepared carbon films retained abundant carbon chemical properties from the raw coal and did not change the order and bonding mode of the carbon atoms. By annealing the prepared carbon films, an appropriate annealing temperature was able to reduce the surface voids of the carbon films and improve the surface smoothness. XPS and Raman testing showed that the annealing treatment increased the sp2 content and disorder of carbon films, resulting in changing lattice and grain size of the material. As a result, the number of out-of-domain electrons increased and electronic conduction at grain boundaries was reduced. Meanwhile, with an increase in annealing temperatures, the proportion of film cracks increased. The film cracks ratios are 3.84, 4.36 and 9.75% at 400, 600 and 800 °C, which correspond to film conductivities of 6.25 × 10−6, 1.67 and 136.28 S/m, respectively. The change in film conductivity was more than 7 orders of magnitude, which indicates that increases in film conductivity are much greater as a result of changes in the annealing temperature than by cracking.