Synthesis And Electrochemical Performance Study Of Si-Based Anode Materials Based On Industrial Waste Silicon For Lithium-Ion Batteries

Silicon has the highest theoretical specific capacity among the known anode materials for lithium-ion batteries?LIBs?,which is about ten times that of the graphite anode.It has great potential for large-scale application.However,the volume expansion of silicon during lithium insertion is more than 300%,which leads to large pulverization and hence rapid decline of capacity.In addition,the poor intrinsic conductivity of silicon results in a low kinetic performance of lithium insertion/extraction.The introduction of high electronic conductivity additives to improve the conductivity of silicon-based electrode and the introduction of lithium inert or less active phase to buffer the volume expansion of Si during lithium insertion process are proved to be effective ways to improve the electrochemical performance of silicon-based anode materials.In addition,high-performance silicon-based anode materials are commonly high-cost.In this thesis,silicon-based anode materials with low cost and high performance are prepared by several facile methods with solar silicon wafer cutting waste Si as the main raw material.The results show that the particle size of waste Si is reduced from micron to submicron after sand milling.As the anode material of lithium-ion batteries,it delivers initial discharge and charge capacities of 3114 and 1992 m A h/g,respectively,at a current density of 300 m A/g,which also shows imporved cyclic performance.The crystallinity of Si increases by the heat treatments at temperature range of 350 °C to 950 °C.The initial coulombic efficiency and cyclic stability of the Si anode material increase with the increase of the heat treatment temperature.Composites of micron-sized Si spheres composed of sub-micron Si slices encapsulated in an amorphous carbon doped with rich nitrogen?C-N?is fabricated by a process of sand–milling,spray drying and thermal pyrolysis.With an optimization of the melamine addition,the composite with 14.4 wt% C-N shows excellent electrochemical performance as anode material for LIBs.Its initial reversible capacity at 300 m A/g is 2158 m A h/g.The capacity remains 1461 m A h/g after 200 cycles,corresponding to the capacity retention of 67.7%.Besides,a high electronic conductivity additive of Ti N in differention molar fractionsis introduced to the waste Si by a high-energy ball-milling method.Partial Ti N is reacted with Si forming high electron conductive TiSi₂.In addition,the ball-milling reduces the particle size of Si and favores its amorphization.Ti N and TiSi₂ not only improves the electronic conductivity of the material,but also buffers the volume expansion of Si during lithiation.The Si/Ti N/TiSi₂ composite with optimized composition shows favorable electrochemical performance.The particle sizes of the present silicon-based materials are in submicron and micron level,which are conducive to obtain high tap-density,and hence improve the volume capacity density of the electrodes,which is of great significance to the utilization in commercial batteries.The present work provides a facile and efficient method for the preparation of high-performance Si-based composite anode materials.The raw materials are low-cost and the electrochemical properties of the obtained composites are superior.It is prospect in future applications.