Mechanoactivation-assisted synthesis and electrochemical characterization of manganese lightly doped LiFePO4

Abstract

Olivine compounds LiFe 1− x Mn x PO 4 (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 LiFe 1− x Mn x PO 4 under test, LiFe 0.8 Mn 0.2 PO 4 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 LiFePO 4 (1.08 × 10 −10 S cm −1 ). Without the carbon coating, pristine LiFe 0.8 Mn 0.2 PO 4 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 Fe 2+ in LiFe 0.8 Mn 0.2 PO 4 is electrochemically utilizable correspondingly. For a comparison, they are only 65% and 15% for the pristine LiFePO 4 prepared by a similar process. LiFe 1− x Mn x PO 4 also showed stable cycling performance within the 50 cycles under test. It suggests manganese lightly doped LiFePO 4 could be practical cathode materials for high-rate lithium-ion batteries.