Rational design of three-dimensional pomegranate-shaped double-layer carbon-shell-coated Si nanoparticles as an excellent anode material for lithium-ion batteries

Abstract

Silicon is considered a promising anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity and relatively low discharge potential. However, due to its low conductivity and large volume change during cycling, its practical commercial application is hindered. In this study, we prepared pomegranate-shaped Si coated with a double-carbon-shell spherical (Si@DCSS) material. Firstly, a composite material made of thin carbon shells coated with several Si nanoparticles (Si@C) was obtained via a hydrothermal reaction followed by a magnesium thermal reduction process. In the structure of the obtained material, each Si particle was tightly coated in the carbon shell, similar to pomegranate seeds and membranes, forming a 3D network structure. This structure increased the rapid transfer of electrons and Li⁺ ions between Si particles and promoted electrode reaction kinetics. Secondly, a thick carbon shell was coated on the outer layer of Si@C via a chemical vapor deposition (CVD) method, forming a double-carbon-shell structure. The thick carbon layer could effectively alleviate a serious volume change in Si nanoparticles, thus maintaining structural integrity and increasing cyclic stability. The obtained Si@DCSS material showed good electrochemical performance when used as an anode material for a lithium-ion battery. At a current density of 1 A g⁻¹, Si@DCSS could maintain a capacity of 525 mA h g⁻¹ after 300 cycles.