Spherical LiMn0.7Fe0.3PO4/C Cathode Materials for Lithium-Ion Batteries

Lithium manganese iron phosphates (LiMn x Fe 1-x PO 4 ) [1] are attractive as next-generation cathode materials for lithium-ion batteries because they are safer than conventional lithium transition metal oxides (e.g. LiCoO 2 ) [2] and are Co- and Ni-free. However, due to their low electronic conductivity [3], they can deliver much lower electrochemical properties than theoretically expected one. Therefore, many researchers have focused on chemical composition, reducing primary particle size, and carbon coating. On the other hand, granulation of LiMn x Fe 1-x PO 4 primary nanoparticles is effective in improving poor handling of LiMn x Fe 1-x PO 4 primary nanoparticles during cathode slurry preparation. However, electrochemical properties of granulated LiMn x Fe 1-x PO 4 have not been well studied in previous reports. In this study, the electrochemical properties of the spherical LiMn 0.7 Fe 0.3 PO 4 /C composed of primary nanoparticles are reported. Spherical LiMn 0.7 Fe 0.3 PO 4 /C was synthesized by hydrothermal method followed by granulation and carbon coating. The synthesized spherical LiMn 0.7 Fe 0.3 PO 4 /C was characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Electrochemical properties of spherical LiMn 0.7 Fe 0.3 PO 4 /C were examined using CR2032 coin-type cells. Fig. 1 (a) shows the SEM images of spherical LiMn 0.7 Fe 0.3 PO 4 /C. As shown in Fig. 1 (a), spherical particle 10 μm in diameter composed of homogeneously sized primary nanoparticles were observed. Fig. 1 (b) shows the galvanostatic charge-discharge curves for spherical LiMn 0.7 Fe 0.3 PO 4 /C at discharge current rates of 0.2, 1, 5, and 10 C in a voltage range of 1.5–4.5 V at 30 °C. Spherical LiMn 0.7 Fe 0.3 PO 4 /C delivered a 0.2 C discharge capacity of 153 mAh g −1 . At the 10C rate, spherical LiMn 0.7 Fe 0.3 PO 4 /C also delivered a high discharge capacity of 137 mAh g −1 , which was 89 % of the 0.2C discharge capacity. Detailed data of our study including blended cathode of LiNi a Mn b Co c O 2 and spherical LiMn 0.7 Fe 0.3 PO 4 /C will be presented in the meeting. References: A.K. Padhi, J. Electrochem.Soc. 144 (1997) 1188. C. Delmas et al., Nat.Mater. 7 (2008) 665. A. Yamada et al., J. Electrochem. Soc. 148 (2001) A224. Figure 1