Electrochemical Synthesis And Lithium Storage Performance Of Three-Dimensional Tin-based Alloys And Co₃O₄Anode Materials

As the lithium-ion battery anode materials, tin-based alloys and the transition metaloxides possess a high theoretical specific capacity, which is more than twice that of thecommercial graphite. However, they all suffer serious volume changes duringcharging/discharging, in addition, transition metal oxides have low electrical conductivity,they deliver poor cycleability and low rate capacities. In this work, the three-dimensionalporous structure is introduced to tin-based alloys and transition metal oxide Co3O4, andcarbon nanotubes(CNTs) networks are introduced into tin-based alloys to reduce theenormous stress generated during the charging/discharging and improve the cycleability andrate capabilities of them. The main research works are given in the following:The three-dimensional porous copper(Cu) film was prepared by electroless plating, andthe relationship between reaction time and the porous structure was also studied. Three porousstructures were synthesized by controlling the reaction time for15min、30min、1h,respectively. The results indicate that the porous structure for1h has the thickest pore wallsand the biggest pore size, and that of the15min has the thinnest pore walls and the smallestpore size.Using the porous copper film as a substrate, the porous Sn-Co alloy and Sn-Co-CNTcomposite were prepared by an electrodepositon process. The porous Sn-Co alloy showsbetter cycleability than the dense Sn-Co alloy, and the porous Sn-Co-CNT composite exhibitsa superior rate capability compared with the porous Sn-Co alloy. The charge capacity of theporous Sn-Co-CNT composite is490mAh/g at100mA/g in the1st cycle and319mAh/g at3200mA/g in the50th cycle, and remains90%after60cycles at different current densities. Inaddition, the Sn-Cu-CNT composite was prepared by the same method, and exhibits superiorelectrochemical performance, compared with the dense Sn-Cu and porous Sn-Cu alloys. TheSn-Cu-CNT composite’s specific capacity remains77.1%after50cycles tested at differentcurrent densities, even at the current density of1,600mA/g, the reversible specific capacityremains257.5mAh/g, which is45.4%of the first specific capacity cycled at the currentdensity of100mA/g. The porous Co3O4electrode was produced by annealing the porous as-prepared Co(OH)2electrode grown on the porous copper substrate. The results reveal that the porous Co3O4electrode displays excellent electrochemical performance, such as excellent cycleability of nosignificantly decay after500cycles at1A/g and remains larger than800mAh/g, and largehigh rate capacity of the reversible capacity at20A/g remains337.1mAh/g, which is muchbetter than that of the Co3O4electrode grown on the copper sheet. The reversible capacity ofCo3O4electrode grown on the copper sheet begin to rapidly decrease after200cycles andremains only125.8mAh/g at20A/g. The results can be attributed to the porous structure cannot only provide rapid electron and ion transfer channels, but also buffer the volume changesduring charging/discharging.