Li–Si phase diagram: Enthalpy of mixing, thermodynamic stability, and coherent assessment

Abstract

Silicon has been recently used as negative electrode in Li-ion batteries which makes the Li–Si system the focus of numerous studies. In this work, the Li–Si system was studied by means of drop calorimetry, differential scanning calorimetry, first principles calculations and the CALPHAD method. The enthalpies of mixing of the liquid phase were determined for the first time. The optimization started by the liquid phase and was performed using the experimental data. The following steps of the optimization of the thermodynamic properties and assessment of the phase diagram were conducted using the CALPHAD method. According to very recent studies in the literature and with our calculations, Li17Si4, Li21Si5 and Li4.13Si phases were considered as the Li-rich phases instead of Li22Si5. The LiSi phase was also considered for the first time in the assessment. The Li13Si4, Li7Si3 and Li12Si7 phases were also taken into account. Additionally, the crystal structure of the Li–Si phases was established by optimization of the electronic structure of each phase and phonon calculations were performed to attain the thermodynamic data at T>0K. The first principles thermodynamic data was compared with experimental and CALPHAD results.