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

Olivine compounds LiFe_1-xMn_xPO₄ (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-xMn_xPO₄ under test, LiFe_0.8Mn_0.2PO₄ 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 LiFe_0.8Mn_0.2PO₄ 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 LiFe_0.8Mn_0.2PO₄ is electrochemically utilizable correspondingly. For a comparison, they are only 65% and 15% for the pristine LiFePO₄ prepared by a similar process. LiFe_1-xMn_xPO₄ 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.