Preparation And Performance Of SiO-based-graphene Nanocomposite Lithium Storage Material

Graphite has been considered as the commercial anode material because of its flat and low insertion potential of Li+, low cost and preferable cycling performance. However, it suffers from safety issues, low theoretical capacity (leding to the low power density of batteries). SiO-based materials have been considered as promising Li-ion battery anode material among Si-based material owing to their high volume capacity and weight capacity, low cost and environmentally friendly properties. Nevertheless, the application of SiO-based has been limited due to the fast capacity fading, which arises from the large volume variation during the Li+insertion/deinsertion process and its low electrical conductivity. In this work, SiO material has been used as active material and graphene has been utilized as the buffered carrier to prepare binary composite material-nano-SiO-graphene composites, electrode system-nano-3D SiO-graphene multilayered electrode, ternary composite material-nano-SiOx@C/RGO composites and the ternary composite material-nano-SiO@NC/NG composites. The preparation strategy, physical properties, electrochemistry lithium storage properties and lithium storage mechanism of SiO-based-graphene composite material have been researched deeply. Graphene oxide was synthesized by a modified Hummers’ method, microngraphite was used as the starting material. The reduced graphene oxide(RGO) and high temperature treated graphene(TG) were prepared though the “the approach combinated chemical reduction method and thermal reduction method” and “method of heat treatment”. By comparison, RGO was founded as a more suitable buffering carrier in the preparation of SiO-based-graphene composite material. Nano-size SiO particles were prepared using the high speed grinding method which caused a higher specific surface area and better cycling performance than the commercial SiO particles. But the nano-SiO particles also have showed rapid capacity fading, and the specific capacity was reduced to0after20cycles, so it is not suitable for using nano-SiO particles independently as anode material for lithium-ion batteries. The SiO/RGO composites and SiO+RGO compounds were prepared though the “the approach combinated chemical reduction method and thermal reduction method” and “method of heat treatment”. The electrochemical properties of SiO/RGO composites were superior to SiO+RGO compounds according to the result of comparative experiment. The as-prepared composites exhibited a reversible capacity of774.3mAh g-1after100cycles at a current density of100mA g-1. Rate capability tests indicated that the composites exhibited weak high rate properties, and the reversible capacity was as low as191.5mAh g-1at800mA g-1, and the rate performance needs to be improved. By compared studying the effect of different content of graphene on cycling performance, we could get the best cycling performance through adjusting SiO and graphene oxide in accordance with mass ratio of1:2. The mechanism of the enhanced lithium storage performance of SiO-graphene compared with SiO was investigated by density functional theory.3D porous nickel foam current collector was used to replace traditional copper collector, an “alternating conglutination” method was developed to fabricate electrode system-nano-3D SiO-graphene multilayered electrode by loading nano-SiO paticles and graphene. The specific capacity of nano-3D SiO-graphene multilayered electrode were much better than the counterpart of nano-3D SiO electrode according to the results of comparative experiment. The reversible capacity of nano-3D SiO-graphene multilayered electrode was1369.5mAh g-1after100cycles at the current density of100mA g-1. After400cycles at the same current density, the reversible capacity was1349.1mAh g-1, which could realize a better cycling performance and the average reversible capacity was as high as519.5mAh g-1even at3200mA g-1.Ternary composite material-nano-SiOx@C/RGO composites was designed and prepared via a co-modification strategy. The physical properties and electrochemistry lithium storage properties of the composites were also investigated. SiOx@C shows nanosized particle size distributions, and SiOx@C/RGO typically shows the properties of enormous specific surface area and porous structure. The electrochemical performance of SiOx@C/RGO was better than the counterpart of SiOx@C according to the results of comparative experiment. Specifically, SiOx/C@RGO anode delivers a capacity of2402.9mAh g-1in the first discharge and1225.5mAh g-1in the first charge process, exhibiting an initial coulombic efficiency of51%. The reversible capacity of SiOx/C@RGO after400cycles is observed to be1264mAh g-1, which is only20mAh g-1less than that after100cycles and realizing a better cycling performance. The synergistic lithium storage mechanism between carbon coating layer and graphene was investigated by electrochemical impedance spectroscopy and FESEM, and mechanism of carbon coating layer and RGO on SiO-based composite materials was also proposed.Based on the co-modification strategy, a further modification action was operated to improve the double modification layer. Ternary composite material-nano-SiO@NC/NG composites was prepared. The physical properties and electrochemistry lithium storage properties of the composites were also investigated. The electrochemical performance of nano-SiO@NC/NG composites was better than the counterpart of SiOx@C/RGO. Nano-SiO@NC/NG anode delivers a capacity of2465mAh g-1in the first discharge and1372mAh g-1in the first charge process at the current density of100mA g-1, exhibiting an initial coulombic efficiency of55.66%. The reversible capacity of nano-SiO@NC/NG after500cycles is observed to be1790mAh g-1and the average reversible capacity was as high as580mAh g-1even at3200mA g-1. At last, mechanism of improved cycling performance of electrode of nano-SiO@NC/NG was investigated by electrochemical impedance spectroscopy and FESEM.