TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The reducing atmosphere may be obtained by partial oxidation with O2 or air of a hydrocarbon and/or carbon(sacrificial carbon), in the presence of water vapor of content 0.1-10 moles of water per C of hydrocarbon, at 400-1200 degreesC to give a mixture of CO and H2.The carbon may be acetylene black or a petroleum coke.The sources (a)-(d) are mixed with a carbon source (conductive carbon) and the process includes a pyrolysis stage, after or preferably at the same time as the preparation of the precursor mixture.The carbon source contains chemically bonded O2 and H2, pyrolysis liberating locally CO and/or CO2 and/or H2 and locally creating a reducing atmosphere.Possible sources include polyethylene, polypropylene, glucose, fructose, sorbose, starch, cellulose, block polymers of ethylene and ethylene oxide and furfuryl alcohol polymers.The content of carbon in the reaction mixture is preferably 0.3-1.5%.The thermal treatment is effected at 500-800 degreesC.Claimed Compound: A specific compound (A) is claimed which is LiMPO4 in which the C content after pyrolysis is 0.1-10%., and more preferably the compound LiFePO4, in which the Fe source compounds are iron phosphates, iron oxy- or hydroxyphosphates, oxides of iron and oxides of iron and lithium, in which part of the iron is in oxidation state (III).preferred Compound: The Li source may be the phosphate, dihydogenophosphate, carbonate, acetate or hydroxide. and the P sources may be ammonium phosphate, ortho-meta, or pyro-phosphoric acid or the pentoxide.The prepared product (A) is in the form of particles of 0.05-15 (preferably 0.1-10) microns, which have a conductivity, as measured on a compacted powder sample at a pressure of 7350 Kg.cm-2 greater than 10 power -8 S.cm-1.The C content is preferably greater than 0.1%, more preferably 0.3%, and is present as a coating of the particles and/or an inter-particular bridging.Claimed Electrochemical Cell: An electrochemical cell is claimed in which the positive electrode contains one of the products (A) described, alone or mixed with a double oxide of Co and Li, and the negative electrode is metallic lithium or a lithium alloy.Preferred Cell: The cell also contains an electrolyte which may be a polyether, polyester, a methyl methacrylate polymer acrylonitrile and/or vinylidine fluoride, and also a solvent such as ethylene or propylene carbonate, a 1-4C alkyl carbonate or a polyglycol.For a cell acting as a supercapacity generator, the positive electrode is a material of the invention and the negative electrode is carbon of surface area greater than 50 m2/g in the form of powder, fibre or a mesoporous composite.For a light modulation system, the optically inactive counter-electrode is a material of the invention spread as a thin layer on a glass or polymer support and covered with a doped tin or indium oxide. EXAMPLE - A sample of triphylite, LiFePO4, was prepared from FePO4.2H2O and Li2CO3 in the presence of H2. This was then impregnated with a solution of cellulose acetate (39.7% acetyl, molecular weight 50000) in acetone, amounting to 5% of the treated triphylite. After drying the mixture was placed in a furnace and heated to 700 degreesC (6 degreesC/ min) under argon, held for 1 h then cooled. The sample contained 1% carbon, corresponding to a carbonization yield of 20%. The surface electronic conductivity was measured on a compacted powder sample under a force of 5 tonnes. The conductivity was 5x10 power -5 S.cm-1.    The two materials, LiFePO4 (treated and untreated) were tested in lithium button batteries of type CR 2032 at 80 degreesC. The cathodes were prepared by mixing the active material with carbon black and poly(ethylene oxide). Acetonitrile was added to dissolve the poly(ethylene oxide) and form a homogeneous suspension. The latter was poured on to a 1 cm2 stainless steel disc. The cathode thus prepared was dried in vacuum and transferred to a glove box under helium. A lithium laminate (27 microns) on a nickel substrate acted as anode, and the electrolyte was a compound of a poly(ethylene oxide) and a lithium salt of bistrifluorisulfoninimide.    Comparative experiments of slow voltammetry were carried out and the results shown from the curves in the figure.