Core-shell structure and 3D CNTs networks promote Si@Cu nanoparticle anodes with enhanced reversible capacity and cyclic performance for Li-ion batteries

Abstract

With the rapid growth of demand for energy storage technology in various industries, it is particularly urgent to develop battery systems with higher energy density. Among the candidates, silicon (Si) has a high lithium storage capacity as anode material, but its large volume variation and low electron and ion conductivity prevent it from being diffusely used in multiple fields, such as large-scale energy storage systems. In this work, we complement the advantages of Si, metal copper (Cu), and carbon nanotubes (CNTs) to synthesize Si@Cu nanoparticles with core-shell structures encapsulated in a 3D CNTs network (Si@Cu/CNTs). The coating of Cu and the 3D CNTs network help to slow down the volumetric expansion of Si during the cycle and the exfoliation and pulverization which are caused by volume expansion. Meanwhile, the synergy of the highly conductive metal Cu and 3D CNTs network provides fast migration channels for ions/electrons, which is advantageous for the capacity at high current densities. The synergy of Cu and 3D CNTs network also avoids the immediate between the electrolyte and the Si nanoparticles, which is beneficial to maintaining the integrity of the SEI film, thus enhancing the electrochemical performance of the material. Si@Cu/CNTs exhibit a capacity of 2107.5 mAh g−1 after 50 cycles at a current density of 100 mA g−1, with a capacity retention rate of 74.06%. Si@Cu/CNTs also have favourable rate capability, with a capacity of 2338.6 mAh g−1 and a capacity retention rate close to 80% when the current density drops to 100 mA g−1. This work presents a novel idea for the modification of Si materials.