Coating Ni particles to preserve their conductivity during sintering in oxidizing atmospheres

In this study, a new Ni electrode was introduced which was able to preserve its electrical conductivity during sintering in oxidizing atmosphere. The Ni electrode was manufactured from Ni nanoparticles, which were coated by Li salts, namely Li₂CO₃, LiOH, and LiF, with an innovative coating method. The coating process is schematically shown in the graphical abstract. After the confirmation of a successful coating on Ni particles by SEM (Scanning Electron Microcopy) imaging, the Ni particles with Li₂CO₃ coating demonstrated the greatest preservation in conductivity among the other salts. Thus they were selected for further investigation; the effect of Li₂CO₃ percentage, sintering program, and pO₂ on electrode resistance were systematically studied. The results suggest that the coating can reduce the resistance by five orders of magnitude at oxidizing atmosphere (e.g. pO₂ = 2 × 10⁻⁴ atm). The reduced resistances were as low as 1 Ω, suitable to be used as an electrode. SEM and FIB (Focused Ion Beam) cross section imaging were used to document the Ni oxidation, the sintering process of Ni particles, and the Li₂CO₃ decomposition. Finally, two mechanisms were speculated to be the reasons of the conductivity conservation and the importance of this invention in the reducing of oxygen vacancies in electroceramic devices was discussed.