Gas phase synthesis of anode materials for Li-ion batteries

Both environmental concerns and advances in consumer electronics place increasing demands on efficient energy storage solutions. Currently lithium ion batteries with their high energy density and long life-time are, perhaps, the best available technology to meet these demands (Hall and Bain, 2008). However, for the widespread utilization of Li-ion batteries in applications such as electric vehicles, several challenges still remain. These include price, safety, specific energy and power, and the cycle life (Du Pasquier et al. 2003, Wen et al. 2008). For Li-ion batteries there is an interest in silicon based high specific energy materials and stable and safe materials such as lithiumtitanate for stationary applications. Gas phase synthesis of these materials is a viable option to produce these materials. First we describes a single-stage gas phase method for the production of doped LTO. The particles were synthesised using a flame spray pyrolysis (FSP) system from a precursor solution containing Li-acetylacetonate (0.22 M) and titanium tetraisopropoxide (0.28 M). Doping with silver and copper was achieved by adding, respectively, silver and copper 2-ethyl hexanoic acid directly into the precursor solution. The resulting particles were found to be high purity, single crystalline nanoparticles with a primary particle size of about 10 nm (BET derived), and a uniform dopant distribution. The silver dopant was found to form ultrafine particles on the surface of the LTO particles. The copper, on the other hand, reacted chemically with the LTO to form what is likely a double spinel structure. Electrochemical testing of the produced material is also presented. The other aim was to produce silicon nanoparticles at temperatures above the limit of resistance heating furnaces. High temperature required in the process is achieved with an induction heating furnace. The source metal is placed in a zirconia crucible embedded in solid graphite or other suitable conductor. The system is enclosed in graphite felt insulation. Argon flow carries silicon vapour outside the insulation, where nitrogen sheath flow rapidly cools the carrier flow and metal vapour forms nanoparticles. The temperature is monitored with a pyrometer above the furnace through a small opening in the insulations. The furnace has been tested to withstand crucible temperature at 2300°C while the temperature of the quenched gas remains below 150°C. The method to produce silicon nanoparticles with an induction heating furnace offers good repeatability in concentration and size distribution. Even with relatively large concentrations the primary particle size is small due to rapid cooling.