Mechanoactivation-assisted synthesis and electrochemical characterization of manganese lightly doped LiFePO<inf>4</inf>

Abstract

Olivine compounds LiFe1-xMnxPO4 (0.0 = x = 0.3) for cathodes of secondary lithium-ion batteries were synthesized via a mechanoactivation-assisted solid-state reaction. The optimal manganese content and electrochemical performance of the as-synthesized powders were investigated by XRD, EDX mapping, cyclic voltammetry, and charge-discharge characterizations. According to XRD and EDX mapping results, phase-pure compounds with olivine structure were formed after the calcination under nitrogen atmosphere at 700 °C for 20 h. Among the various LiFe1-xMnxPO4 under test, LiFe0.8Mn0.2PO4 showed the highest electrical conductivity, which reached a value of 3.49 × 10-5 S cm-1 at room temperature, more than 5 orders higher than that of pristine LiFePO4 (1.08 × 10-10 S cm-1). Without the carbon coating, pristine LiFe0.8Mn0.2PO4 showed discharge capacity of ~123 and 100 mAh g-1 at 0.1 and 1 C rates, respectively. It means about 91% and 74% of the Fe2+ in LiFe0.8Mn0.2PO4 is electrochemically utilizable correspondingly. For a comparison, they are only 65% and 15% for the pristine LiFePO4 prepared by a similar process. LiFe1-xMnxPO4 also showed stable cycling performance within the 50 cycles under test. It suggests manganese lightly doped LiFePO4 could be practical cathode materials for high-rate lithium-ion batteries. © 2009 Elsevier B.V. All rights reserved.