Preparation And Li-storage Properties Investigation Of A High-capacity Silicon-based Anode Composite Materials For Lithium-Ion Batteries

Silicon has attracted huge attention and become the most promising candidate of the graphite as the lithium ion batteries ?LIBs? anodes in the last decade because of its high theoretical gravimetric and volumetric capacities (about 4198 mAh g^-1 and 9781 mAh cm^-3, respectively). Moreover, Silicon anodes can provide an attractive working potential ?-0.4 V vs Li⁺/Li.? to avoid safety concern of lithium deposition upon cell overcharge. Unfortunately, there are multiple disadvantages associated with its practical performance including the enormous volume change ??300%? during lithiation/delithiation processes, low intrinsic electrical conductivity, and instability of the solid electrolyte interface. These drawbacks will seriously lead to the poor cycle performance and short cycle life when used as anode materials for LIBs. Significant efforts have been undertaken to solve these problems by designing the silicon architecture and introducing the carbonaceous materials. The research contents and results are shown below:The porous silicon has prepared via employing Diatomite mineral as silicon raw material, and enhance the performance of which by making dual-carbon enhanced Si-based composite. Diatomite is not only low cost and rich resources, but also porous and surficial area larger. Through the magnesium thermal reduction reaction, silicon can be obtained with a rich porous structure. With glucose and graphite as carbon sources, the conductivity and cycling performance can be further improved. Electrochemical tests as anode material for lithium ion batteries ?LIBs? demonstrate that the dual-carbon enhanced Si-based composite exhibits much improved Li-storage properties in terms of superior high-rate capabilities and excellent cycle stability compared to the pristine Si material as well as both single-carbon modified composites. It can still deliver a high capacity of 938 mAh g^-1 at current density of 0.1 A g^-1 with excellent capacity retention in the following 300 cycles and exhibit a high specific capacity of about 470 mAh g^-1 at an ultrahigh current density of 5 A g^-1. The significantly enhanced Li-storage properties should be attributed to the co-existence of both highly conductive graphite and amorphous carbon in the Si/C/G composite. While the former can enhance the electrical conductivity of the composite, the latter acts as the adhesives to connect the porous Si particulates and conductive graphite flakes to form robust and stable conductive network.Herein, ultrafine nano-Si has been prepared via a NaCl-assisted magnesiothermic reduction with scalable silicate as silicon source. In the high-temperature procedures of magnesiothermic reduction, as an effective heat scavenger, adjuvant NaCl promote the formation of interconnected silicon grains with ultrasmall size of 5-10 nm. When used as anode materials for lithium-ion batteries, reduced graphene oxide ?rGO? plays another significant roles on enhancing the electrochemical performance due to its high conductivity and flexibility by forming the nano-Si/rGO composite. Electrochemical tests demonstrate that the nano-Si/rGO exhibits much improved Li-storage properties in terms of superior high-rate capabilities and excellent cycle stability compared to the pristine nano-Si and micro-Si prepared without the addition of NaCl. For instance, it can deliver a high specific capacity of up to 1955 mAh g^-1 at 100 mAg^-1 with high initial columbic efficiency of>80%. In addition, nano-Si/rGO also exhibits superior rate capability (891 mAh g^-1 at 5 A g^-1). The significantly enhanced Li-storage properties should be attributed to the synergistic effects of highly conductive rGO and nanosized silicon particles in the nano-Si/rGO. While the former can improve the electrical conductivity, the latter will decrease the Li+ diffusion length, heighten the capacity and optimize the cycling stability.