Enhanced Energy Density of Li₂MnSiO₄/C Cathode Materials for Lithium-ion Batteries through Mn/Co Substitution

抄録

The crystal structure, morphology, and galvanostatic cycling and rate performances of cobalt-substituted Li₂MnSiO₄/C compounds, Li₂Mn_1−xCo_xSiO₄/C (x = 0.25, 0.5, and 0.75), were evaluated and compared with those of Li₂MnSiO₄/C and Li₂CoSiO₄/C. Li₂Mn_1−xCo_xSiO₄/C (x = 0.25, 0.5, and 0.75) compositions comprising uniform nanosized primary particles and no impurities were successfully synthesized using a hydrothermal method, followed by carbon coating. In addition, Li₂MnSiO₄/C and Li₂CoSiO₄/C were synthesized for comparison. The synthesized Li₂Mn_1−xCo_xSiO₄/C (x = 0.25, 0.5, and 0.75) were solid solutions and were identified using an orthorhombic unit cell with Pmn2₁ space group symmetry. Although the capacity fades for Li₂Mn_1−xCo_xSiO₄/C were similar to those for Li₂MnSiO₄/C, the discharge capacity, average discharge voltage and rate capability of Li₂MnSiO₄/C improved when Co was substituted for Mn. Li₂Mn_0.25Co_0.75SiO₄/C exhibited the best electrochemical performance with first energy density of 659.7 Wh kg⁻¹ which was greater than that of LiMn₂O₄ (500 Wh kg⁻¹) and LiNi_1/3Co_1/3Mn_1/3O₂ (600 Wh kg⁻¹). The good electrochemical performance of Li₂Mn_0.25Co_0.75SiO₄/C is attributed to its lower charge transfer resistance relative to that of Li₂MnSiO₄/C.