Conformal formation of Carbon-TiO_x matrix encapsulating silicon for high-performance lithium-ion battery anode

摘要

Nanonization strategies are effective in preventing silicon anodes from pulverization and reducing the required diffusion lengths of lithium ions inside silicon structure, and thus obtain improved cycling performance over bulky silicon. However, new problems arise with nano silicon, such as reduced tap density, larger specific surface area, and poorly percolating conductive paths in electrodes. These new issues can result in reduced volumetric energy densities, unstable solid electrolyte interphase, increased irreversible capacities and low Coulombic efficiencies. This study introduces an effective strategy in harvesting the benefits of nano silicon, while eliminating the unfavorable phenomena that arise from nanonization. A novel micron-sized secondary cluster with silicon nanoparticles embedded in an amorphous carbon and TiOx matrix is developed. The matrix is conformally formed on the surface of silicon, which not only uniformly casts a protective layer on silicon, but also integrates nano silicon into micron clusters. The secondary cluster exhibits much improved tap density over silicon nanoparticles. The amorphous and defect-rich nature of the TiOx coating not only exhibits enhanced electronic conductivity over its crystalline counterparts, but also provides better elasticity and stress-release capability that can maintain the structural integrity over lithiation/delithiation of silicon. Direct and repetitive contact between silicon and electrolyte is prevented and thus formation of a stable solid electrolyte interphase is facilitated. Half cell batteries made with the composite exhibit an initial capacity of 1410 mA g(-1) at a current density of 100 mA g(-1), and display stable long-term cycling with similar to 88% capacity retention after 200 cycles at 1 A g(-1).