Synthesis of crystalline nanometric LiFeMPO4 The invention relates to a crystalline nanometric LiFe1-xMxPO4 (LFMP) powder with small particle size and narrow particle size distribution for use as positive electrode material in Li batteries. It also describes a preferred manufacturing method by precipitation at low temperature and atmospheric pressure of the crystalline nanometric powder. Since the original work of Padhi et al. (JES, 144 (1997), 1188), phospho-olivines LiMPO4 (with M = Fe, Ni, Co, Mn, ...) have appeared to be potential candidates to be used as cathode materials for Li batteries. Among all these isostructural compositions, LiFePO4 was the most investigated and its commercialization is now a reality thanks to very high performances in term of reversible capacity, rate properties and cycle life (International Publication Number WO2004/001881 A2). LiCoPO4 (Amine et al., ESSL, 3, (2000), 178) and LiMnPO4 (Okada et al., J. Power Sources, 97-98 (2001) 430), due to their higher redox potential values oft 4.8 V and 4.1 V vs. Li respect., are of particular interest because of the higher energy density they offer compared to LiFePO4 (3.5V vs. Li, Chen et al., JES, 149 (2002) Al 184). However, it is now well known that these phospho-olivines materials suffer from poor electronic and ionic conductivity (Delacourt et al., JES, 152 (2005) A913) so that the need for optimising the microstructure of these compounds is essential. Striebel et al. (JES, 152, (2005), A664) insisted on the fact that, even if the matrix conductivity has been improved by conductive coating, the battery developer would welcome so-far inexistent compounds having a primary particle size in the 50 to 100 nm range and, overall, attempts should be made to minimise the particle size distribution, in order to yield better power efficiency. Most promising results on mixed metal phosphates such as LiFe1-xMnxPO4 materials were obtained on C/LiFe0.4Mno.6P04 composites, in which C acts as a sintering inhibitor. This approach leads to mixed C/LiFeMnPO4 composites with particles in the 100 to 200 rim range (Mi et al., Mater. Sci. Eng., 129 (2006) 8). Similar results were obtained by Lloris et al. (ESSL, 5 (2002) A234), on pure LiCoPO4 with small particles in the 200 to 300nm range. No data were published on LiFe1-xCoxPO4 materials so far. In addition to the small particle size, emphasis must be put on narrowing the particle size distribution in order to ensure a homogeneous current distribution in the electrode and thus achieve better battery performances, in particular high power efficiency and long cycle life. The present invention therefore aims at providing a crystalline LFMP powder with small particle size and narrow particle size distribution. To this end, a process is disclosed yielding metal phosphate powders offering essential improvements over the materials cited above. The invented process for the synthesis of crystalline LiFe1-XMxPO4 powder where M is one or both of Co and Mn, and 04 powder, and up to 10 %wt of conductive additive. A further embodiment concerns the electrode mix that can be prepared using this composite powder. Conductive carbons, carbon fibres, amorphous carbons resulting from decomposition of organic carbon containing substances, electron conducting polymers, metallic powders, and metallic fibres are particularly well suited as conductive additives. Another embodyment of this invention concerns the use of the composite powder for the manufacture of a lithium insertion-type electrode, by mixing said powder with a conductive carbon-bearing additive. The invention also pertains to a crystalline LiFe-1-XoxPO4 powder with 0