There is provided a method of forming a porous particle comprising an electrically conductive continuous shell encapsulating a core, said core comprising an elemental compound that reversibly reduces in the presence of a cation and oxidizes in the absence of said cation, said method comprising the steps of: a) encapsulating an elemental compound precursor with said electrically conductive shell; b) reacting said elemental compound precursor with an oxidation agent to oxidise said elemental compound precursor to form said elemental compound, thereby forming said electrically conductive shell encapsulating said core comprising said elemental compound.