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 Li.sub.xM.sub.1-yM'.sub.y(XO.sub.4).sub.n, in which x, y and n are numbers such as 0.ltoreq.x.ltoreq.2, 0.ltoreq.y.ltoreq.0.6 and 1.ltoreq.n.ltoreq.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.