| With the rapid increase in demand for portable electronic devices and flexible wearable medical devices,commercial graphite lithium-ion batteries with lower energy density are far from being able to meet the rapidly growing market demand.Among the emerging anode materials,silicon anode material with alloy lithium intercalation mechanism is considered as the best candidate material for lithium-ion battery anode due to its highest energy density,but the unavoidable volume change of silicon material during lithiation/delithiation process and lower conductivity than graphite hinder its widespread application in the field of large-scale energy storage.Based on this,this study designed composite materials with stable structures by introducing high conductivity copper and carbon materials with good mechanical properties,significantly improve the conductivity of silicon electrode and largely buffer mechanical strain,which provides a new solution for the low coulomb efficiency and rapid capacity decay of the silicon anode.Firstly,we prepared core-shell Si@Cu nanoparticles by chemical precipitation and hydrogen thermal reduction.Subsequently,Si@Cu was combined with carboxylated CNT by electrostatic self-assembly to obtain Si@Cu nanoparticles/carbon nanotubes composites（Si@Cu/CNT）with three-dimensional conductive framework matrix.The core-shell structure effectively buffers the huge volume change caused by Li-Si alloy formation.In addition,the interlaced carbon nanotubes provide more charge contact sites,significantly enhancing the electronic conductivity of the composites.The Si@Cu/CNT electrode still maintained high lithium storage capacities of2107.5 m Ah g-1（50 cycles）and 1676.1 m Ah g-1（100 cycles）after charging and discharging at current densities of 0.1 A g-1and 1 A g-1,respectively.In addition,after 70 times of charging and discharging at different current densities,the Si@Cu/CNT electrode still had a lithium storage capacity of2196.6 m Ah g-1and a capacity retention rate close to 80%,which is much higher than those of Si electrode and Si@Cu electrode.Secondly,we introduced flexible graphene as carbon source,and prepared core-shell structure Si@Cu nanoparticles/graphene composites（Si@Cu@rGO）through simple electrostatic attraction and high temperature thermal reduction.The double-layered structure of graphene and copper shells greatly enhance the structural stability and electrical conductivity of the composites,and a large number of voids remained in the middle effectively alleviate the volume change during the lithiation of silicon.The results show that the Si@Cu@rGO composite electrode exhibited initial discharge specific capacities of 4280.3 m Ah g-1and 4027.2 m Ah g-1at current densities of 0.1 A g-1and 1 A g-1,respectively,and still maintained high lithium storage capacities of 2147.4 m Ah g-1（130 cycles）and 1518.3 m Ah g-1（200 cycles）after long cycling.In addition,after of charging and discharging at different current densities,the lithium storage capacity of the Si@Cu@rGO composite electrode increased to 2401.5 m Ah g-1,which is much higher than the 1366.2m Ah g-1of the silicon electrode.Finally,we introduced one-dimensional high-strength carbon nanotubes and two-dimensional flexible graphene into the zero-dimensional Si@Cu C2O4nanoparticles,and synthesized core-shell Si@Cu nanoparticles/carbon nanotubes/graphene composites（Si@Cu/CNT/rGO）by one-step reduction method.The bidirectional constrained conductive network composed of carbon nanotubes and graphene significantly improves the volume expansion and conductivity of electrode materials.The Si@Cu/CNT/rGO composites maintained high lithium storage capacities of 1915.5 m Ah g-1（130 cycles）and1486.7 m Ah g-1（200 cycles）after being charged and discharged at 0.1 A g-1and 1 A g-1,respectively.In addition,after charging and discharging at different current densities,the specific discharge capacity can be recovered to2293.8 m Ah g-1,and the capacity retention rate was as high as 87.1%. |
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