Method of synthesis for a material made of particles having a core and a coating and/or being connected to each other by carbon cross-linking, the core of these particles containing at least one compound of formula LixM1-yM′y(XO4)n, in which x, y and n are numbers such as 0≦x≦2, 0≦y≦0.6 and 1≦n≦1.5, M is a transition metal, M′ is an element with fixed valency, and the synthesis is carried out by reaction and bringing into equilibrium the mixture of precursors, with a reducing gaseous atmosphere, in such a way as to bring the transition metal or metals to the desired valency level, the synthesis being carried out in the presence of a source of carbon called carbon conductor, which is subjected to pyrolysis. The materials obtained have excellent electrical conductivity, as well as very improved chemical activity.