Method of fabricating structured particles composed of silicon or silicon-based material and their use in lithium rechargeable batteries

A method of treating silicon to form elongate structures on a treated surface, the method comprising a nucleation step in which metal is deposited on the silicon surface and an etching step in which silicon underlying the deposited metal is etched, wherein

• a. the nucleation step comprises exposing a silicon containing material to a solution comprising HF at a concentration of less than 5M and
• 0.002 to 0.2M of metal ions capable of nucleating on and forming a porous layer comprising regions of elemental metal on the silicon surface;
• and
• b. the etching step comprises
• i. exposing the silicon surface comprising regions of elemental metal to a solution comprising HF at a concentration of greater than 5M and 0.001 to 0.70M of an oxidant selected from the group comprising O2, O3, H2O2, the acid, ammonium or alkali metal salt of NO3−, S2O82−, B4O72− and ClO4− or a mixture thereof;
• and
• ii. adding oxidant to the solution during etching to maintain the concentration of oxidant within the above range.