Research On The Silicon Composite Anode And Characteristics Of Its Electrochemical Interphase

Lithium-ion batteries?LIBs?have been widely used as power source for electric vehicles?EVs?because of their high energy density and long cycle life.In order to extend the travel distance of EVs,the development of LIBs with higher energy density becomes more and more urgent recently.The energy density of LIBs is largely dependent on anode.Silicon has been regarded as one of the promising anode materials due to its high theoretical specific capacity and low charge/discharge potential.However,the tremendous volume change during the lithiation/delithation reactions causes pulverization of silicon particles,disintegration of electrode and excessive growth of solid electrolyte interface?SEI?,leading to low Coulombic efficiency and capacity fading during cycling.Hollow structured silicon can effectively accommodate the volume expanison of lithiation reaction and prohibit the excessive growth of SEI,which has high practical application prospect.However,the lithiation/delithiation behavior of hollow structured silicon is not clear.Besides,to meet the demands of next generation anode materials for LIBs,Coulombic efficiency and volumetric specific capacity of hollow structured silicon still need to be enhanced.Focus on the challenges of hollow structured silicon,our work are shown as below:One-dimension silicon-carbon nanotube is prepared and used as model to study the lithiation/delithiation behavior of hollow structured silicon,which reveal that lithiated silicon tend to expand inward to the hollow structure,and shrink to its original morphology when delithiation,thus can prohibit the excessive growth of SEI.Based on the experimental results,we extablished a model of the relationship between surface energy and expansion tendency.The as-prepared material exhibited high reversible capacity of 1200mAh g^-1 after 300 cycles,with Coulombic efficiency of more than 99.95%.A method of filling solid polymer electrolyte into hollow structured silicon is developed to occupy the space of SEI growth.The SPE filled hollow structured silicon delivered a long term cycle stability of 1350 mAh g^-1 over 500 cycles with Coulombic efficiency of more than 99.99%.We combined electrochemical impedance spectroscopy and differential scanning calorimetry to investigate the growing behavior of SEI,which confirmed that the internal space occupation method is effective to prevent the excessive growth of SEI.A novel design of hollow structured SnO₂@Si nanospheres are synthesized,which not only deamonstrates high volumetric capacity as anode of LIBs,but also prevents aggregation of Sn and confines solid electrolyte interphase thickening.The influence of silicon layer thickness to the morphology of composite was investigated.The as-prepared material exhibited a high initial volumetric specific capacity of 1600mAh cm^-3,and demonstrated a capacity retention of 1000 mAh cm^-3 over 500 cycles,which is twice of commercialized graphite anode.Considering the facile preparation and low cost,the hollow structured SnO₂@Si nanospheres has great potential to be applied in real batteries.