Enhanced Electrochemical Performance of Li2Mn0.25Co0.75SiO4/C Cathode Materials for Li-Ion Batteries through Reduced Graphene Oxide Addition

Abstract

Lithium transition metal orthosilicates (Li2MSiO4, where M=Fe, Mn, Co, or Ni)1 are promising cathode materials for Li-ion batteries with their high capacity (>300 mAh g−1) and high safety. Particularly, Li2MnSiO4 is expected to have a higher discharge capacity than Li2FeSiO4 and Li2CoSiO4, owing to the extraction of two lithium ions at lower voltage (4.1 and 4.5V) relative to them.1 However, practical energy density of Li2MnSiO4 is much less than the theoretical one due to its lower average discharge voltage (~3 V).2 One strategy to improve discharge voltage of Li2MnSiO4 is to substitute Co into Mn. Because Li2CoSiO4 practically exhibits a well-defined plateau near 4.25 V,3 and this is higher than that of Li2MnSiO4. On the other hand, recently, many researchers have focused their work on reduced graphene oxide (RGO) addition for cathode materials to improve their electrochemical performance.4 In this work, various content of RGO addition for Li2Mn0.25Co0.75SiO4/C (LMCS/RGO/C) were investigated to improve its electrochemical performance. LMCS/RGO/C was synthesized by hydrothermal method followed by carbon coating. In addition, Li2Mn0.25Co0.75SiO4/C (LMCS/C) was also synthesized for comparison. Furthermore, crystallographical and morphological data by x-ray diffraction and transmission electron microscope as well as galvanostatic cycling and rate performance were also collected. Fig. 1 shows the first galvanostatic charge-discharge curves for LMCS/RGO/C and LMCS/C at a current rate of 330 mA g−1 in a voltage range of 1.5–4.5 V at 30 °C. The first discharge capacities of LMCS/RGO/C and LMCS/C were 160 and 143 mAh g−1, respectively, and the corresponding coulombic efficiencies were 78.2 and 71.9 %. This indicates that RGO addition for LMCS/C enhances the electrochemical performance. Detailed data of our investigation will be presented in the meeting.