Olivine LiMnPO4 has been produced using a new synthetic method. Reversible extraction and insertion of lithium into olivine LiMnPO4 at 4.1 V vs. lithium demonstrated that this material is a promising candidate for the cathode in lithium-ion batteries. When charged to 4.5 V, ca. 0.94 Li per formula unit can be extracted during the first charge. When charged to 4.8 V, 152 mAh/g was delivered in the first discharge. An overall reversible capacity of 140 mAh/g has been attained at room temperature. A flat two-phase region with open-circuit voltage similar to4.1 V was identified. The thermal stability of the charged cathode was evaluated by thermogravimetric analysis and differential scanning calorimetry. (C) 2002 The Electrochemical Society.