TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Powder: The maximum particle size of the powder is less than or equal to 300 (preferably 200) nm. The particle size distribution is mono-modal and in that the ratio (d90-d10)/d50 is less than 0.8 (preferably less than 0.65, more preferably less than 0.5). The crystalline LiMnPO4 powder contains (wt.%): conductive additive (less than 10, preferably less than 9) wt.% The crystalline LiMnPO4 powder is used in the manufacture of a lithium insertion-type electrode, by mixing the powder with a conductive carbon-bearing additive. Preferred Process: The process, followed by a step of post-treatment of the LiMnPO4 powder by heating it in non-oxidizing conditions. The production of the crystalline LiMnPO4 powder or the post-treatment by heating in non oxidizing atmosphere takes place in the presence of at least one further component, in particular a carbon containing or electron conducting substance, or the precursor of an electron conducting substance. In the process, where at least part of the Li(I) is introduced as lithium hydroxide (LiOH); and at least part of the P (V) is introduced as phosphoric acid (H3PO4). The pH of the water-based mixture is obtained by adjusting the ratio of LiOH to H3PO4. The atmospheric boiling point of the water-based mixture is 100-150 (preferably 100-120) degrees C. The aprotic dipolar additive contained in the water-based mixture is dimethylsulfoxide. The water-based mixture contains 5-50 (preferably 10-30) mol.% of dimethylsulfoxide. The step of post treatment of the LiMnPO4 is performed at a temperature of up to 650 (preferably of at least 300) degrees C.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The electron conducting substance is carbon (preferably conductive carbon or carbon fibers). The precursor of an electron conducting substance is a carbon conducting substance (preferably polymer or sugar-type macromolecule). EXAMPLE - In a first step, dimethylsulfoxide (DMSO) was added to an equimolar solution of 0.1 M manganese (II) in manganese sulfate monohydrate (MnSO4-H2O) and 0.1 M phosphorus (V) in phosphoric acid (H3PO4), dissolved in water under stirring. The amount of DMSO was adjusted in order to reach a global composition of water (50 vol.%) and DMSO (50 vol.%) corresponding to respectively 80 mol.% and 20 mol.%. In a second step, an aqueous solution of 0.3 M lithium hydroxide monohydrate (LiOH-H2O) was added to the solution at 25 degrees C; in order to increase the pH up to a value between 6.5 and 7.5. Hence, the final lithium:manganese:phosphorus (Li:Mn:P) ratio was close to 3:1:1. In a third step, the temperature of the solution was increased up to the solvent boiling point, which was 108-110 degrees C. After 6 hours, the obtained precipitate was filtered and washed thoroughly with water, to obtained pure crystalline crystalline manganese phosphate (LiMnPO4). In a fourth step, the dried LiMnPO4 precipitate was poured into a 30 wt.% aqueous solution of sucrose (100 g LiMnPO4 for 140 g sucrose solution) and stirred for 2 hours. The mixture was dried at 150 degrees C under air during 12 hours and, after deagglomeration, heat treated at 600 degrees C for 5 hours under a slightly reducing nitrogen/hydrogen 90/10 flow to obtained crystallized LiMnPO4 powder containing 7.5 wt.% carbon coating.