The Research On The Effect Of Interface Optimization On The Performance Of Silicon Anode In Lithium Ion Batteries

One of the important ways to deal with the energy crisis is to develop lithium ion batteries(LIBs)with high energy density,silicon(Si)is one of the most promising lithium ion battery anode material to replace the traditional graphite anode and realize the high energy density LIBs due to its theoretical capacity only lower than lithium metal(3572 m Ah g^-1),and abundant storage in earth.However,repeated volume changes(over 300%volume expansion)induced by alloy/dealloy reactions between silicon and lithium resulted in attachment failure in the electrode,which simultaneously causes the morphology changes of the silicon material(agglomeration and pulverization),and distabilizes the solide electrolye interface layer(SEI layer),finally causes the dramaticallt capacity fading of Si anode.Recently,works of designing electrolyte and binder according to the traits of silicon anode greatly stabilized the interfaces in Si anode,some of them were proved to be more efficient than many optimization methods involving complicated structure designing,indicating the important role that interface stability plays in the silicon anode.In order to reveal the mechanism of how the interfaces in the silicon anode affect the battery performance,the electrochemical impedance spectra(EIS)of the silicon anode were tested and transferred to function of distributed relaxation times(DRT)in this research.Precise and detailed information concerning the electrochemical reaction in the silicon anode was attained with the help of DRT functions,and was applied to the analysis of the interface reactions in the electrode.In the meantime,the polymer chitonsan with water solubility was applied as a basic material to optimize the interface in the silicon anode,and investigated the the performance improvement of silicon anode in the lithium ion battery as well as its mechanism through three different interface optimization methods with the help of DRT analysis:1.The chitosan and polyacrylic acide(PAA)formed covalent networks which were applied to silicon anode as binder,it enhanced the mechanical property of the Si anode,and dramatically suppressed the interface deterioration in the silicon anode due to the enhancement of the electrode mechanical property,and the volume change caused pulverization of the silicon material during cycling was also prevented,the structure stability and reversibility of the silicon particle were raised,and improved the stability of silicon anode during cycling.2.On the base of chitosan binder,Si anode surface was decorated by the polyethylene glycol diglycidyl ether(PEGDE).It was found that control the interface character could determine the degradation reaction method preference and the composition of the SEI layer.It greatly enhanced the the interface stability and the lithium ion conductivity in the SEI layer,dramatically improved the cyclability and rate property of silicon anode,and attained capacity of more than 700 m Ah g^-1 at current density of 20 A g^-1.3.Chitosan film was applied as artificial SEI layer and coated on the surface of the Si particle to optimize the interface property of the Si anode.It was found that chitosan layer could not only suppress the continuous SEI layer growth and stabilize the interface,but also function as uniform lithium ion transport layer,and raise the atomic arrangement order in the cycled silicon particle,finally attain a better reversibility of alloy reaction occur in the Si anode,and reduce the diffusion resistance in the active material.All the work comes to the conclusion that interface property is crucial to the performance of silicon anode,either binder with network structure,interface decoration on the surface of the electrode,or appropriate decoration on the surface of the material particle surface could dramatically improve the interface stability.These methods turned out to be easy access,environment friendly,economical,and are compatible with the conventional material synthesis and battery producing technology,are among the important directions to pass the bottle-neck in the high performance Si anode material developing.