Process for preparing electroactive materials for use in metal-ion batteries

A process for preparing Si-containing composite particles in a fluidized bed comprises (i) providing porous conductive particles having mesopores and/or micropores, a D50 particle diameter between 1-30 µm, a PD50 pore diameter ≤ 10 nm, and a total pore volume of micropores and mesopores in the range 0.4-2.2 cm3/g, (ii) combining the porous conductive particles with a particulate additive having a D50 particle diameter between 40-300 µm, a particle density between 1.3-6 g/cm3 and a BET surface area ≤ 200 m2/g, wherein the mass ratio of the porous conductive particles to the particulate additive is from 95:5 to 70:30, and (iii) passing a fluidizing gas including a Si precursor gas through the combined particles at a gas velocity to cause fluidization of the combined particles and at a temperature effective to cause deposition of Si in the pores of the porous conductive particles (Chemical Vapour Infiltration; CVI). The properties of the particulate additive are chosen to allow easier separation of the particles afterwards while still enabling effective fluidization of the combined particles during the CVI process. The porous conductive particles are preferably carbon, but may comprise porous metal oxides (e.g. titanium oxide) instead. The composite particles are preferably used as an anode material in a rechargeable metal-ion battery.