A low cost and scalable processes for producing nanostructured LiFe.sub.xM.sub.1-xPO.sub.4 and nanostructured LiFe.sub.xM.sub.1-xPO.sub.4/C composite powders, where 1.ltoreq.x.ltoreq.0.1 and M is a metal cation, such as Mn, Co, Ni, and V. Electronics made of either nanostructured LiFe.sub.xM.sub.1-xPO.sub.4 powders or nanostructured LiFe.sub.xM.sub.1-xPO.sub.4/C composite powders exhibit good electrochemical properties. The electronic conductivity of nanostructured LiFe.sub.xM.sub.1-xPO.sub.4 powders is enhanced by intimately mixing them with ultrafine carbon particles. Thus, the use of nanostructured LiFe.sub.xM.sub.1-xPO.sub.4/C composite powders will lead to high power density, low cost and environmentally friendly rechargeable Li-ion batteries.