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

Abstract

Lithium manganese iron phosphates (LiMnxFe1-xPO4) [1] are attractive as next-generation cathode materials for lithium-ion batteries because they are safer than conventional lithium transition metal oxides (e.g. LiCoO2) [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 LiMnxFe1-xPO4 primary nanoparticles is effective in improving poor handling of LiMnxFe1-xPO4 primary nanoparticles during cathode slurry preparation. However, electrochemical properties of granulated LiMnxFe1-xPO4 have not been well studied in previous reports. In this study, the electrochemical properties of the spherical LiMn0.7Fe0.3PO4/C composed of primary nanoparticles are reported. Spherical LiMn0.7Fe0.3PO4/C was synthesized by hydrothermal method followed by granulation and carbon coating. The synthesized spherical LiMn0.7Fe0.3PO4/C was characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Electrochemical properties of spherical LiMn0.7Fe0.3PO4/C were examined using CR2032 coin-type cells. Fig. 1 (a) shows the SEM images of spherical LiMn0.7Fe0.3PO4/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 LiMn0.7Fe0.3PO4/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 LiMn0.7Fe0.3PO4/C delivered a 0.2 C discharge capacity of 153 mAh g−1. At the 10C rate, spherical LiMn0.7Fe0.3PO4/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 LiNiaMnbCocO2 and spherical LiMn0.7Fe0.3PO4/C will be presented in the meeting.