Synthesis of SiO nanoparticles for Li-ion batteries

Induction nucleation is a very well suited technique for large scale synthesis of various nanomaterials (Auvinen et. al, 2010) Using induction materials can efficiently be heated to a very high temperature thus enabling high production rates. At the same time the gas flow can be kept cool, which induces extremely high temperature gradients needed for formation of nanoparticles. The synthesis can be carried out at normal pressure, which significantly decreases the facility costs as well as the pumping power. At the outlet of the furnace also the temperature of the inert gas flow is close to ambient enabling the use of common structural materials, rubber seals and inexpensive bag filters. Typically the precursors can be relatively low-cost and yet high purity bulk materials. Induction nucleation process is also environmentally sound as it uses no water, produces no liquid waste and releases only filtered nitrogen from the reactor. The induction nucleation method was initially developed for production of metallic nanoparticles. The source materials are vaporised from tungsten or graphite crucibles to nitrogen or argon carrier gas flow. Graphite felt insulation separates the hot carrier gas from cool nitrogen flow. When the gas flows are mixed turbulently, rapid cooling induces formation of nanoparticles. In this work the same method was applied for production of SiO nanoparticles applied in Li-ion battery anodes. SiO is well suited for material for induction nucleation synthesis as it has significantly higher vapour pressure than either Si or SiO2. It is also far less reactive in high temperatures than pure silicon. SiO particles were produced by heating silicon in contact with oxides in temperature varying between 1 600°C to 1 790°C. The highest mass concentration reached in the tests was 2 600mg/m3 at 1 790°C. The produced particles were amorphous with primary diameter of about 15 nm. In the gas phase the primary particles formed larger agglomerates with mobility diameter of about 150 nm. Also production of SiO-Cu composite particles was tested by placing the source materials either in the same or in separate crucibles. With single crucible set-up the copper content of the produced powder ranged from 2 wt-% to 4 wt-% depending on the test parameters. A two-crucible set-up allowed more freedom in tuning the copper content of the particles. This study belongs to Active Nanocomposite Materials project funded by Tekes under Functional Materials Program.