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 Li₂Mn_0.25Co_0.75SiO₄/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, Li₂Mn_0.25Co_0.75SiO₄/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.

References:

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2. A. Bhaskar, et al., J. Electrochem. Soc., 2012, 159(12), A1954–A1960.

3. C. Lyness, et al., Chem. Commun., 2007, 4890–4892.

4. L.H. Hu, et al., Nature Communications, 2013, 4, 1687.