Method for synthesis of carbon-coated redox materials with controlled size

A method for the synthesis of compounds of the formula C—LixM1−yM′y(XO4)n, wherein C represents carbon cross-linked with the compound of formula LixM1−yM′y(XO4)n, wherein 0≦x≦2, ≦y≦0.6, and 1≦n≦1.5, M is at least one transition metal selected from the first line of the periodic table, M′ is an element with a fixed valency selected from the group consisting of Mg2+, Ca2+, Al3+, Zn2+ and combinations thereof and X is S, P or Si, said method comprising:

• bringing into equilibrium in the required proportions, for a duration of less than 5 hours, a mixture comprising the following precursors:
• a) a source of M comprising at least one transition metal or at least one salt thereof;
• b) a source of the element M′ that is a salt of M′;
• c) a source of lithium that is a salt of lithium;
• d) a compound that is a source of X;
• and
• e) a source of a carbon conductor that is an organic substance,
• wherein the source of M and the source of M′, if any, is in the form of precursor particles having a size of between 0.1 micrometer to 6 micrometer, wherein the precursor particles are made up of agglomerates of nanoparticles on the order of 50 nm to 100 nm,
• wherein the sources of the elements M, M′, Li and X are introduced, in whole or in part, in at least one step, in the form of compounds having more than one source element,
• wherein the precursors a) to d) are mixed intimately, and
• wherein a synthesis reaction is carried out by thermodynamic or kinetic reaction and bringing into equilibrium, in the required proportions, the mixture of the precursors a) to d), with a gaseous reducing atmosphere to provide an oxidation state of the transition metal of the desired valency for the formation of LixM1−yM′y(XO4)n, by controlling the composition of said gaseous atmosphere, the temperature of the synthesis reaction step, and the amount of precursor c) relative to the amount of precursors a), b) and d);
• the method further comprising at least one pyrolysis step of the source compound e) so as to obtain a carbon conductor with an electronic conductivity greater than 10−8 S·cm−1, when measured on a sample of powder compressed at a pressure greater than or equal to 3000 Kg·cm−2, wherein the synthesis reaction between the precursors a) to d) is carried out simultaneously with the pyrolysis reaction of the precursor e).