| Owing to its high power, environmental protection and convenience, Li-ion battery has been widely recognized and it occupies a leading role in the battery market. Although numerous coating experimental investigations are conducted on Li-ion anode material, most of them stop in laboratory step. This paper aims at exploring a new process to enhance the properties of Li-ion anode composite material which can be used in the factury. To achieve this goal, we focus on modifying the spherical graphite with various coating amounts mixed with CNTs and Nano-Si for the sake of improving battery capacitance, cycle performance and electrical conductivity. Moreover, SEM, XRD analysis and IR, charge-discharge cycle, cyclic voltammetry, and impedance tests on composite material were performed.SEM observation show that there are less gullies and concave points on the surface of the coated graphite. It can be discovered from XRD that there are no influences on surface crystal structure of the graphite but a weakening of characteristic peak intensity of the graphite after coating and mixing of CNTs and Nano-Si. Therefore, it can be concluded that there is a substance on the surface of the graphite. IR test show that there presents characteristic peak possessed by pitch and coke after the coating of pitch and coke on the surface of graphite, reducing bonds like C-O and C=O on the surface of graphite and IR absorption of the surface of the composite material.Galvanostatic Charge-Discharge cycling test show that there presents an obvious increase in capacitance of the material with certain pitch coating spherical graphite and there manifests an increase in both capacitance and cycle performance of the composite material with the adding of coating amount. Specifically speaking,pitch-coated sample PC-177 witnesses a capacitance of 506.5mAh/g in initial discharge while initial columbic efficiency(hereinafter referred to as CE) is 81.3%,and there is a capacitance of 368.8mAh/g after 50 times of cycling. After the mixture of CNTs, composite material's capacitance increases along with the increase of CNTs content and there also presents good cycle performance. As for sample 1% CNTs,there presents a capacitance of 549.6mAh/g in initial discharge while initial CE is80.3%, and there is a capacitance of 395.9mAh/g after 50 times of cycling. There presents an increase on both capacitance and cycle performance of the Nano-Si mixed composite material along with the increase of Si content. Sample 2% Si: capacitance of initial discharge is 424.4mAh/g while the initial CE is up to 92.2%, and there is a capacitance of 335.6mAh/g after 50 times of cycling. On the other hand, structure deficiency of the composite material weakens its high rate performance.Cyclic voltammetry test show that the pitch coating and carbon nanotubes doped with reduced voltage embedded, nano Si powder doped lead to composite material can be inserted under high voltage and embedded embedded.The impedance test show that presence of loose and porous coating layer helps to accelerate velocity of Li-ion penetrating SEI membrane and reduce impedance of the composite material.CNTs doped ion diffusion rate of improved material, nano Si powder doped improve the charge transfer rate. |
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