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

Abstract

The crystal structure, morphology, and galvanostatic cycling and rate performances of cobalt-substituted Li2MnSiO4/C compounds, Li2Mn1-xCoxSiO4/C (x = 0.25, 0.5, and 0.75), were evaluated and compared with those of Li2MnSiO4/C and Li2CoSiO4/C. Li2Mn1-xCoxSiO4/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 Li2Mn1-xCoxSiO4/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 Li2Mn1-xCoxSiO4/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. Li2Mn0.25Co0.75SiO4/C exhibited the best electrochemical performance with first energy density of 659.7Whkg-1 which was greater than that of LiMn2O4 (500Whkg-1) and LiNi1/3Co1/3-Mn1/3O2 (600Whkg-1). The good electrochemical performance of Li2Mn0.25Co0.75SiO4/C is attributed to its lower charge transfer resistance relative to that of Li2MnSiO4/C.