General synthesis of nano-M embedded Li4Ti5O12/C composites (M = Sn, Sb and Bi) with high capacity and good cycle stability

Abstract

Nano-metal embedded Li4Ti5O12/C composites (Li4Ti5O12/M/C samples labeled as Li4Ti5O12/Sn/C-L, Li4Ti5O12/Sn/C-H, Li4Ti5O12/Sb/C-L, Li4Ti5O12/Sb/C-H, Li4Ti5O12/Bi/C-L and Li4Ti5O12/Bi/C-H, respectively) as high capacity anode were synthesized by sol-gel and high temperature solid state reaction methods. The physical properties of Li4Ti5O12/M/C were detected by X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM) and elemental analysis. All composites were completely coated by a thin carbon layer. Besides the Li4Ti5O12/Bi/C-L, other Li4Ti5O12/M/C samples were composed of spherical-like aggregate particles. Nano-M was embedded between inner Li4Ti5O12 and outer carbon layer. Their electrochemical performances were studied by galvanostatic cycle and cyclic voltammograms (CVs). These analyses show that Li4Ti5O12/Sn/C-L, Li4Ti5O12/Sn/C-H, Li4Ti5O12/Sb/C-H, Li4Ti5O12/Bi/C-H delivered a reversible capacity of 231.9, 308.1, 235.9 and 213.5mAhg−1 at 500th cycle on current density of 200mAg−1, respectively, while Li4Ti5O12/C composite only delivered a capacity of 197.6mAhg−1 at the same conditions. The results demonstrated that metal M can play an important role on high capacity performance of Li4Ti5O12-based anode when it was embedded between inner “zero-strain” Li4Ti5O12 and outer carbon coating layer. Their stable cycle performance owning to the co-effect of Li4Ti5O12 as the structural stabilizer and carbon layer as the volume change buffer for preventing the volume change caused by M during cycling. This work provides an effective way to improve the discharge capacity of Li4Ti5O12-based anodes.