Preparation,Optimization And Interface Control Of High Performance Silicon-based Anode Material Of Lithium Ion Batteries

The silicon anode is expected to play an important role in high-energy LIB s because it provides an extremely high capacity and low electrode potential.Since then a great deal of research has been focused on silicon-based anode materials and silicon-carbon composites.Silicon anode has been a popular topic for nearly 20 years,but it have not yet been applied to practical battery systems on a large scale.This is due to some issues that have not yet been well solved with silicon anode:Si particle expands and contracts,it easily cracks,breaks off and forms fluffy debris.Regrowth and rearrangement of the SEI on Si anode are accompanied by the continuous consumption of the active lithium and the electrolyte within the cells,resulting in the low coulombic efficiency of the electrodes during the charge-discharge cycle.Based on the investigation of the growth mechanism of SEI film on the surface of silicon electrode in literature,several methods for preparation and controlling the surface of silicon electrode are studied in this paper.According to the above problems,the selection of silicon anode materials,the optimization of silicon-carbon composite materials and electrode auxiliary materials are studied in this paper.Specific research contents are as follows:1.Selection and optimization of raw materials for silicon anode.Silicon particles obtained from different major suppliers were characterized by using different spectroscopic techniques and by electrochemical studies as the anode of lithium ion batteries.Correlations between the key physical parameters and electrochemical properties of the silicon particles were summarized.Silicon particle size,surface oxygen content,-OH content and physical appearance have strong influence on the electrochemical properties consist of the first coulombic efficiency,discharge capacity,rate performance and cycling stability.The particle size of 100nm is of great promise for the industrial application of Si nano-particles in lithium ion battery industry.An inverse correlation between the oxygen content and the reversible capacity or first coulombic efficiency is obtained.The-OH content by surface treatment contributes to an enhancement of the cycling stability by the improved affinity between the Si particle and the water soluble binder.By comparison,spherical Si particle performs well compared to the irregular particles and agglomeration dramatically bring down the electrochemical performances of the Si anode.Among these investigated Si products,a sample exhibits the first coulombic efficiency 89%,more than 2500 mAh g-1 capacity with excellent cycle performance,which is of great potential for use in the battery industry.2.Carbon nanotubes were used to modify silicon anode.An in-situ developed neuron like Si-CNT composite is realized with a modified chemical vapor deposition method.The neuron like Si-CNT composite not only contributes to a high conductivity and mechanics of the silicon anode,but also effectively offsets the large volume change of the Si particles.The rate capability and cycling stability of the Si anode are significantly enhanced compared to that of the physical Si+CNT mixture.3.The silicon anode was modified by surface coating strategy.A soft carbon and silicon suboxide modification strategy is presented to create homogeneous and multilayer core-shell structure silicon-based nanomaterials(Si@SiOx@C).The silicon suboxide layer thickness is homogeneous and can be effectively controlled from 2 nm to 15 nm through calcining the mesophase pitch-coated silicon nanoparticles at different temperatures.The optimized silicon suboxide thickness of 13.5 nm allows for good protection of silicon nanoparticles.4.Optimizing of electrode auxiliary materials.Dimethylacrylamide was selected as a new electrolyte additive for silicon anode material.The solid electrolyte interface formed in the electrolyte of silicon negative electrodes without and without DMAA additives was studied by electrochemistry and spectroscopy.It is found that the remarkable improvement of the electrochemical performance of silicon anode can be attributed to the effective passivation of DMAA on silicon anode.The addition of DMAA helps to form a uniform SEI layer,thus preventing side effects at the interface between silicon and electrolyte.Optimize the modification of binder.In this work,water dispersant is modified with different amounts of glycerol(Gly).The effect of dispersant modification on the mechanical and electrochemical properties of the Si anode is evident.It contributes to an improvement of the ductility and flexibility of the binder,which effectively alleviates the severe mechanical crack of the Si electrode laminate upon long-term cycles.At the optimum Alg/Gly ratio of 2:1,silicon anode displays much improved electrochemical performances in terms of the cycling stability and rate capability.