Experimental Investigation And Thermodynamic Modeling Of The Li-Si-(Zr,V) System

Silicon is one of the most promising anode materials because it has the highestknown theoretical charge capacity and is the second most abundant element on earth.However, silicon anodes have limited applications because of the huge volumechange associated with the insertion and extraction of lithium. This causes crackingand pulverization of the anode, which leads to a loss of electrical contact and eventualfading of capacity. intermetallic compounds that constitute silicon and lithium inertmetal can improve the electrochemical performance and minimize the mechanicalstress caused by the large volume change of Si-based alloy electrodes.For instance,Si-(Zr,V) binary alloys as silicon-based anode material has good conductivity andcycle performance. In order to investigate for the compound and the metastableequilibriums may be generated in the process of insertion and extraction of lithium ofthe Si-(Zr,V) binary alloy anode materials, it is necessary to study thermodynamicproperties of the Li-Si-(Zr,V) ternary system.The samples of equilibrium alloy of the Li-Si-Zr system have been observed byscanning electron microscope (SEM) and detected by X-ray diffractionanalysis(XRD), the isothermal section of the Li-Si-Zr system at470K has beenmeasured. It was found that there were three three-phase regions in the isothermalsection of the Li-Si-Zr system at470K. They are Zr5Si4+ZrSi+Zr4Li1.38Si4three-phaseregion，ZrSi2+ZrSi+Zr4Li1.38Si4three-phase region and (Si)+ZrSi2+ZrLiSi three-phaseregion. And in the Si-rich side the phase equilibrium is (Si)+ZrSi2+ZrLiSi and(Si)+Li12Si7+ZrLiSi three-phase regions, contrary to the earlier erroneously assigned(Si)+Li12Si7+ZrSi2three-phase region.The experimental information and thermodynamic data of Li-Si-(Zr,V) ternarysystem have been collected and studied systematically and Li-Zr, Li-V binary systemwhich lack of thermodynamic parameter in the literature have been optimized withThermo-Calc. The thermodynamic parameter of Li-Zr, Li-V binary system obtainedin this work have been used in building ternary system.The Li-Si-(Zr,V) ternarysystem have been optimized by the means of CALPHAD and the experimental resultof the work and the phase equilibrium in the literature are under consideration in thisassessment. By using the present thermodynamic database, the isothermal section ofthe Li-Si-Zr system at470K, the isothermal section of the Li-Si-Zr system at670K,the isothermal section of the Li-Si-Zr system at870K, the liquidus projection ofLi-Si-Zr system, the isothermal section of the Li-Si-V system at570K and theisothermal section of the Li-Si-V system at870K were calculated. A set ofself-consistent thermodynamic parameters for the ternary system has been obtainedand a thermodynamics reference of the insertion and extraction of lithium in theSi-(Zr,V) binary alloy anode materials has been provided.