The Preparation Of SiO₂/C Composites Derived From Rice Husks And Electrochemical Performance For Lithium Ion Batteries

As one of the ways of energy storage,batteries are widely available for various fields of daily life.Lithium ion batteries?LIBs?play a prominent role in the production and application of batteries in consideration of high energy density,excellent cycling performance,high working voltage and friendly environment.With the increasing development of technology and living standard,the research and development of LIBs with higher energy density are highly desirable.Silica as one of the richest materials on the earth,with high theoretical specific capacity(1965 mA h g^-1),has become one of the hot topics in the research of anode materials for LIBs.However,SiO₂ electrode materials,associated with poor electrical conductivity and the large volume change during charge-discharge step,can suffer from destruction and then rapid decline of capacity.Therefore,it is usually necessary to combine carbon component with high conductivity and good elasticity to prepare SiO₂/C composites as anode materials for LIBs.Here,based on a fact that the porous SiO₂ nanoparticles and organic carbon in rice husks?RHs?possess natural advantages,SiO₂/C composite anode materials for LIBs,RHs as raw materials,were prepared by calcination,acid treatment and then the crucial ball milling operation.The effects of ball milling time and milling speed on the morphology and electrochemical properties of SiO₂/C composites were studied particularly in this paper.The main results are as follows below:?1?After calcination and acid treatment,the RH-SiO₂/C mixture obtained,was milled at the rotational speed of 800 rpm and different milling times to prepare SiO₂/C composites.With the increase of milling time,the aggregation of SiO₂ particles and sintered carbon blocks of RH-SiO₂/C mixture tended to decrease,meanwhile SiO₂nanoparticles were gradually coated with fine carbon matrix;Average particle size of SiO₂/C-12 composite was measured as the minimum amount with narrow size distribution when the milling time was extended to 12 h,which presented optimal electrochemical properties:a highly reversible capacity of 827 mA h g^-1 after 300cycles at the current density of 100 mA g^-1.Moreover,the specific capacity exhibited above 400 mA h g^-11 at the large current density of 1.0 A g^-1,indicating benign cycling performance and rate performance.?2?SiO₂/C composites,obtained at milling time of 12 h and different milling speeds,were evaluated as anode material for LIBs.SiO₂/C-800 composite obtained at the milling speed of 800 rpm displayed a better initial discharge specific capacity,initial coulombic efficiency and stable capacity,which determined the optimum milling conditions:800 rpm and 12 h.?3?Under the best milling conditions,SiO₂/CB,commercial SiO₂ nanoparticles and carbon black?CB?used the same as mole ratio of silica and carbon of RH-based SiO₂/C composites as raw materials,were prepared and were tested electrochemical performance:the initial specific capacity of 516 mA h g^-1 and only 348 mA h g^-1 after85 cycles,which is inferior to that of RH-SiO₂/C mixture(the first discharge capacity of 631 mA h g^-1 and the capacity of 460 mA h g^-1 over 100 cycles),demonstrating that the rice husks are equipped with natural advantages as silica-based anode materials for LIBs.?4?It is the homogeneous coating between C layer and naturally porous SiO₂nanoparticles and compactly connected network among SiO₂/C composites that can get access to more active sites for Li⁺storage,which is related to high specific capacity.Furthermore,the uniform carbon layer of SiO₂/C composites can effectively buffer volume charge during cycling to maintain the stability electrode materials,which might manifest good cycle life.The smaller particle size of SiO₂/C composite as well as the compact contact among composites facilitates fast ionic diffusion and electronic transportion,ensuring the excellent rate performance.In this paper,biomass RHs were taken full advantage to fabricate SiO₂/C composites as the anode materials for LIBs,which involves easily available raw materials,simple method,friendly environment,and outstanding electrochemical performance.Therefore,it is expected to provide a new idea for the preparation and industrialization of RHs-based anode materials for LIBs.