Thermodynamics of Li-Si and Li-Si-H phase diagrams applied to hydrogen absorption and Li-ion batteries

A consistent thermodynamic description of the Li-Si system and its extension to the Li-Si-H system is developed based on comprehensive Calphad-type assessment of all pertinent thermodynamic and phase equilibrium data. Key experiments were performed by measuring the equilibrium pressure for the hydrogenation of the lithium silicides at 773 K, 748 K and 723 K. The Gibbs energy functions of the Li-Si compounds developed in this work are validated by direct comparison of the predicted hydrogen pressure with experimental data. The interrelation of the hydrogen absorption pressure with the calculated Li-Si-H ternary phase diagram is also elucidated. The calculated Li-Si phase diagram, both on chemical potential and composition scale, is well supported by the entity of experimental data. In addition to the stable intermetallics Li17Si4, Li16.42Si4 (Li4.11Si), Li13Si4, Li7Si3, Li12Si7, LiSi also metastable Li15Si4 and an approximate for amorphous Si(Li) is included in the thermodynamic modeling. Qualitative prediction of open-circuit voltage curves during metastable lithiation/delithiation of Si as advanced anode material for Li-ion batteries at room temperature is made.