A method for preparing a Li.sub.xM.sub.yPO.sub.4 compound having an olivine structure includes: preparing a solution containing transition metal M ions, Li.sup.+ ions and PO.sub.4.sup.3- ions; drying the solution to form particles of a starting material; and forming the particles of the starting material into particles of the Li.sub.xM.sub.yPO.sub.4 compound with an olivine structure, in which 0.8.ltoreq.x.ltoreq.1.2 and 0.8.ltoreq.y.ltoreq.1.2, and coating the particles of the Li.sub.xM.sub.yPO.sub.4 compound with a carbon layer thereon.