Hydrothermally synthesized nanostructured LiMnxFe1−xPO4 (x = 0–0.3) cathode materials with enhanced properties for lithium-ion batteries

Abstract

Nanostructured cathode materials based on Mn-doped olivine LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) were successfully synthesized via a hydrothermal route. The field-emission scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyzed results indicated that the synthesized LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) samples possessed a sphere-like nanostructure and a relatively homogeneous size distribution in the range of 100–200 nm. Electrochemical experiments and analysis showed that the Mn doping increased the redox potential and boosted the capacity. While the undoped olivine (LiFePO4) had a capacity of 169 mAh g−1 with a slight reduction (10%) in the initial capacity after 50 cycles (150 mAh g−1), the Mn-doped olivine samples (LiMnxFe1−xPO4) demonstrated reliable cycling tests with negligible capacity loss, reaching 151, 147, and 157 mAh g−1 for x = 0.1, 0.2, and 0.3, respectively. The results from electrochemical impedance spectroscopy (EIS) accompanied by the galvanostatic intermittent titration technique (GITT) have resulted that the Mn substitution for Fe promoted the charge transfer process and hence the rapid Li transport. These findings indicate that the LiMnxFe1−xPO4 nanostructures are promising cathode materials for lithium ion battery applications.