Preparation And Investigation Of Electrochemical Properties Of Rice Husk Amorphous Carbon And Si/C Composite Material

Lithium-ion batteries(LIBs) are widely used in all kinds of electronic devices owing to their advantages of high operation voltage, long cycle life, environment friendly and so on.But the low theoretical capacity and poor rate capability of commercialized graphite anode materials cannot meet the ever-increasing energy demands. It is necessary to develop a kind of anode material with higher energy density to substitute commercialized graphite. Due to the good cycling stability and high specific capacity, disordered carbons have been widely used as anode materials for LIBs. Silicon has been considered as a promising anode material for LIBs due to its much higher specific capacity(4200 mAh g-1). Nevertheless, a large volume change will repeatedly occur during lithiation/delithiation process, which eventually leads to the electrode pulverization and capacity fading. At present, the preparation of silicon-carbon composites is one of the most effective methods to improve the cycling performance of silicon anode materials.Rice husk(RH) was employed as a precursor for the preparation of porous lamellar disordered carbon and silicon which used for preparing Si/C composite with epoxy resin as carbon precursor. Meanwhile, the morphology and electrochemical properties of disordered carbon and Si/C composites were tested. In this paper, the main research contents and results are as follows:(1) The RH was pyrolyzed at 500 ℃ in a nitrogen atmosphere for 3 h, followed by hydrothermal treatment for 3 h with 2 mol L-1 NaOH solution at 150 ℃, obtained disordered carbon with porous lamellar structure. The electrochemical test results indicate that the carbon has a high initial discharge capacity of 1647 mAh g-1 at 0.2 C, and a reversible capacity of 502 mAh g-1 after 100 cycles, the coulombic efficiency is above 100%.(2) The RH was pyrolyzed at 600 ℃ or 700 ℃ in a nitrogen atmosphere for 3 h,followed by hydrothermal treatment for 3 h with 2 mol L-1 NaOH solution at 150 ℃, The electrochemical test results show that the carbon obtained at 500 ℃ has a higher capacity than that obtained at 600 ℃ or 700 ℃.(3) The silicon derived from RH by magnesium reduction was used for preparing Si/C composite material through carbonation with epoxy resin as carbon precursor. The SEM and TEM results show that the pyrolytic carbon and the silicon with a size less than 10 nm form secondary particle. The electrochemical test results show that the Si/C composite material has a first discharge capacity of 1042 mAh g-1 at the current density of 100 mA g-1, and a reversible capacity of 575 mAh g-1 after 50 cycles, the coulombic efficiency is 98.4%.