Key experiments and challenging thermodynamic modeling of the Li-Si-C system

Abstract

The phase equilibria and thermodynamic properties of the ternary Li-Si-C system are crucial for developing new anode materials containing Si and/or C for Li-ion batteries. We carried out the long time annealing experiments and confirmed the key three-phase equilibrium of βLi2C2+SiC + Li7Si3 at 630 °C–650 °C. A consistent thermodynamic description of the Li-Si-C ternary system has been constructed based on the recently published Li-Si system, and the Li-C and Si-C binary systems that we revised in this work. The revision requires a more negative Gibbs energy for the αLi2C2 and βLi2C2 phases in the Li-C system, and a more positive Gibbs energy for the SiC phase in the Si-C system. The more negative Gibbs energy of the βLi2C2 phase requires an associate solution model to be introduced for the liquid phase. Calculated partial pressures from the revised thermodynamic description of the Li-C binary system show better agreement with the experimental data. The calculated phase diagram sections of the Li-Si-C ternary system are not only in good agreement with the key annealing experiment results, but also with differential scanning calorimetry results.