一步法高效制备纳米Si/C复合材料及其在高性能锂离子电池中的应用

A Highly Efficient One-step Preparation Method of Nano-silicon and Carbon Composite for High-performance Lithium Ion Batteries

开发了一种一步高效合成纳米硅/碳复合材料的新方法,该方法通过球磨SiCl_(4)、Mg_(2)Si和商业碳片,使SiCl4自下而上还原,原位形成的纳米硅均匀生长在碳片上,高效制备了纳米硅与碳片均匀复合物(Nano-Si/C).该Nano-Si/C用作锂离子电池负极材料展现出高的可逆储锂容量(2450 mA·h/g)、良好的倍率性能及优异的长循环稳定性,在2 A/g电流密度下,经过600次循环后,容量仍然稳定在1400 mA·h/g.其突出的电化学性能主要归因于小尺寸纳米硅与碳片均匀复合的纳米结构,在循环嵌锂/脱锂过程中仍能保持结构和电化学性质的稳定性.

Lithium-ion batteries(LIBs)have been widely applied in portable electronic devices and electric vehicles and energy storage industries.However,with the rapid development of our society,it is more and more difficult to meet the increasing demand of people for commercial LIBs because their energy densities are generally lower than 250 W·h/kg.Thus,it is urgent to further develop higher-capacity electrode materials to efficiently increase the energy densities of LIBs.Silicon is a very attractive anode material for LIBs with superhigh theoretical capacity(4200 mA·h/g),suitable working potential and abundant earth reserve.Although the pure Si material suffers from poor cycling performance due to very large volume change during repeated lithiation/delithiation,recent researches have shown that the homogeneous carbon composite for nano-silicon could improve the cycling performance effectively.But the preparation methods of nano-silicon and carbon composite are still very complicated,limiting the large-scale preparation and application.A highly efficient one-step method to synthesize the homogeneous composite between nano-silicon and carbon sheet(nano-Si/C)was developed through mechanically milling SiCl4,Mg2Si and commercial carbon sheets.During the milling process,nano-Si is produced from the bottom-up reduction of SiCl4.The in situ formed nano-Si can directly grow on the carbon sheet,further leading to homogeneous composite between nano-Si and carbon sheet.This method possesses a very high reaction efficiency as reactants convert into nano-Si and MgCl_(2) completely without the gene-ration of any impurities.The scanning electron microscopy(SEM)and transmission electron microscopy(TEM)display that the nano-Si supported on carbon sheet is around 30—80 nm in diameter.As the anode material for LIBs,the nano-Si/C sample shows a very high reversible capacity(2450 mA·h/g at 0.2 A/g),good rate performance(1040 mA·h/g at 4.8 A/g)and excellent long cycling stability(retaining 1400 mA·h/g even after 600 cycles at 2 A/g).The cyclic voltammograms of nano-Si/C at different sweep rates demonstrate the electrochemical kinetics is controlled by both lithium diffusion process and pseudocapacitance effect.The outstan-ding electrochemical performance is mainly attributed to the uniform composite nanostructures between small-sized nano-Si and carbon sheet,which can maintain the structural integrity and stable electrochemical properties after lithiation/delithiation cycles,as suggested by the electrochemical impedance spectroscopy and SEM images tested after cycles.Combining cheap reactants,simple preparation step and homogeneous composite structure,this method is very promising for low-cost and large-scale preparation of high-performance Si and carbon composite anode with good application prospect.