Li-ion batteries are essential for next generation electric vehicles as well as energy storage for smart grids. However, the traditional carbon based anode material shows low Li charge densities (372 mAh/g), motivating the search for new materials.
One group of candidate materials for next generation anodes is intermetallic compounds. These can provide up to three times the Li charge densities compared to the carbon based materials. However, the drastic volume expansion of intermetallic anodes during lithiation (~150% for Sb) can result in short cycle lifetimes. One strategy to improve the cyclability is to use intermetallic compounds which go through more complex phase transformations during lithiation which buffer the volume expansions. Sb has been considered an important component and has been studied in various compounds such as Cu2Sb, InSb, SnSb, AlSb etc.
During lithiation / delithiation process, complex phase transformations occur within the anode. Therefore, it is essential to study the phase diagram of the corresponding systems. Moreover, different chemical potentials of Li in each phase region correspond to different open-circuit voltages in the Li-ion battery. Therefore, the thermochemical data of the corresponding Li containing systems are also essential for the development Li-ion batteries.
The Calphad (Calculation of Phase Diagram) approach describes the Gibbs energy of each phase as an analytical function, and phase diagrams can be calculated by minimizing the Gibbs energy at different conditions. However, no Calphad database of the Li-Sb system is available. Therefore, in this work, a self-consistent and reliable thermodynamic description of the Li-Sb system was developed for the first time. During the thermodynamic assessment of the Li-Sb system, we found that there are no heat capacity data available for the Li3Sb and Li2Sb compounds. Therefore, both compounds were synthesized and their heat capacities were measured using differential scanning calorimetry in tian-calvet type calorimeters.