Grain size effect of nanocrystalline-Si embedded in buffering alloy-matrix as anode for Li-ion batteries

Abstract Silicon is the anode material of choice to fulfill the ever-growing demand for high energy density lithium-ion batteries when the intrinsic low conductivity and volume expansion of silicon-based electrodes are well addressed. Herein, we report Si-alloys with nano-Si grains embedded in a rigid buffering matrix and attempted to determine the effect of Si grain size on the microstructural stability of the matrix. A simple and mass-producible melt-spinning process was used to synthesize two quinary alloys of Si70MZr5 and Si70MNi5, as well as one senary alloy of Si70MZr5Ni5 (M = Al19–14, Fe5, Cu1). Microscopic analysis techniques reveal that alloy composition has a significant impact on the final microstructure. In particular, the quinary alloys comprising Zr or Ni elements have well-developed Si grains ranging in size from tens to several hundreds of nanometers. While the senary Si-alloy comprising Zr and Ni elements features a fine microstructure with Si grain sizes of less than 50 nm. Comparative analysis of microstructure and electrochemical properties reveal that the senary Si-alloy with the fine microstructure exhibits a high initial Coulombic efficiency of 90% and stable capacity retention over 50 cycles, guiding us further to design practical Si-alloy compositions with grain size and homogeneity controlled microstructures.