The economically feasible synthesis of porous silicon for lithium-ion battery anodes via the magnesiothermic reduction of silica at ultra-low temperatures

In the electric vehicle (EV) sector, lithium-ion batteries are the energy device of choice however its energy density still leaves EVs unable to compete with their fossil fuelled counterparts in terms distance travelled on a single refuel event. The search for more energy dense materials has found that the most promising high-energy anode material is silicon, with a theoretical specific capacity 3579 mAh/g, compared to 372 mAh/g for the presently used graphite anode. The capacity of silicon fades quickly due to its anisotropic volumetric expansion of 280% at maximum lithiation capacity, causing the silicon particles to fracture and exfoliate. Creating void space in the silicon allows the dissipation of mechanical stresses, minimising anode degradation. While the existing method of manufacturing silicon is geared towards the transistor and metallurgy sectors, it is not suitable for making porous silicon (p-Si). The method requires temperatures ≥2000°C followed by etching of the silicon in HF to produce p-Si. The magnesiothermic reduction (MgTR) is an alternative, more efficient bulk method of manufacturing p-Si which operates at 650°C. This method has been researched heavily since its first report in 2007, with studies showing that it can reduce commercial precipitated silica, glass, and even rice husks. The cost of producing p-Si via the MgTR using the methods reported in literature were calculated in this thesis. Strategies for lowering the temperature requirement, whilst increasing the yield and capacity of the p-Si are presented in this thesis. This was much lower than the market price of SiO anode materials, which was ~£160/kg.