| As the most appealing candidate of anode materials for lithium ion battery,Silicon has high theoretical capacity of 4200 mAh/g, relatively abundant resources and environmentally friendly. However, Silicon anodes have limited applications because of the large volume expansion in the process of Li+ inserted, which leads to material pulverization and a dramatic drop in capacity as well as cycle performance.As reported, Si-containing composite which is electrochemically inactive with lithium can minimize the volume expansion during the insertion process of Lithium-ion, and then improve its cycle performance. Especially, Si-Ni binary alloys as Silicon-based anode material have good conductivity and cycle performance. In order to investigate the phase change order, microstructure evolution and related physical properties during Li+insert into Si-Ni alloy anode, it is necessary to study the thermodynamic properties of the Li-Si-Ni ternary system, which can provided a theoretical reference of the insertion/extraction of Li+ in the Si-Ni binary alloy anode materials.The equilibrium alloy method has been used in this work. The samples of equilibrium alloy of the Li-Si-Ni ternary system have been observed by scanning electron microscope(SEM) and detected by X-ray diffraction analysis(XRD), and the isothermal section of the Li-Si-Ni ternary system at 150 °C has been measured. The existence of six ternary compounds, i.e. Ï„1(Li Ni2Si), Ï„2(Li13Ni40Si31), Ï„3(LiNi6Si6), Ï„4(Li13Ni9Si18), Ï„5(Li0.6Ni5.4Si6) and Ï„6(Li75Ni20Si128) is conformed. Fourteen three-phase regions and four two phase regions have been detected, i.e. Li13Si4 + Ï„1+Li22Si5, Li13Si4 + Ï„1 + Ï„2, γ + Ï„1 + Ï„2, Li7Si3 + Ï„4 + Ï„2, Li7Si3 + Ï„4 + Li12Si7, Ï„6 + Ï„4 +Li12Si7, γ + Ï„1 +β1, γ + δ + Ï„2, Ï„3 + δ + Ï„5, ε + δ + Ï„5, NiSi2 +(Si) + Ï„5,(Si) + Ï„5 + Ï„4, Ï„2 +Ï„3 + Ï„4, Ï„5 + NiSi + NiSi2, Ï„2 + Ï„4, Ï„2 + Ï„4ã€Ï„3 + Ï„5 and Ï„4 + Ï„5.Based on the available experimental, the Li-Ni binary has been calculated by using the Thermo-Calc software. A self-consistent thermodynamic parameters are obtained. Furthermore, thermodynamic description of Li-Si-Ni ternary system has been carried out with the CALPHAD approach on the basis of three binary systems,the present experimental results and the first-principle calculation of the formation enthalpies for Ï„1 and Ï„3 ternary compounds. Reasonable agreement of the phase equilibria in the Li-Si-Ni ternary system between the experiment and thermodynamic calculation is achieved. By using the present thermodynamic database, the 150 °Cisothermal section and liquidus projection of Li-Si-Ni ternary system were calculated. |
PDF Full Text Request