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.