Oxidation-Resistant Metallic Bismuth Nanoparticles for Electrically Conductive Adhesives

Bismuth (Bi) metallic material is one of the most widely used heavy metals because of its low cost, excellent light conversion efficiency, and high X-ray attenuation coefficient. However, large-scale synthesis of highly processable and oxidation-resistant Bi nanoparticles remains challenging. Based on the above concerns, we report a facile, scalable, polyol-mediated synthesis of high-quality Bi nanoparticles using citrate as a capping agent and polyvinylpyrrolidone (PVP) as a dispersant. The presence of citrate and PVP improved Bi nanoparticle's oxidation resistance and processability. These nanoparticles can maintain excellent oxidation resistance in an ambient atmosphere for more than 120 days and form high-quality suspensions in various commonly used solvents. Moreover, large-scale and rapid synthesis of the nanoparticles was achieved by simply using the green reagent stannous citrate [tin (II) citrate] as a reducing agent. These properties make them promising as complementary conductive fillers in electrically conductive adhesives (ECAs). The Bi nanoparticles could be effectively combined with silver flakes in epoxy resins to enhance the conductivity of ECAs significantly. With the addition of only 5 wt % Bi nanoparticles, the resistivity of ECAs could be reduced to 1/3000 of that of ECAs with the same silver content, showing great promise in next-generation ECA products.