Lithium carbide (${\mathrm{Li}}_2{\mathrm{C}}_2$), a potential electrode material for lithium ion batteries, has recently gained attention as a promising tritium breeding material for magnetic confinement fusion reactor owing to its higher breeding ratio compared to conventional ternary ceramics. Motivated by the reported pressure-induced $Immm\to Pnma$ structural phase transition in ${\mathrm{Li}}_2{\mathrm{C}}_2$ [I. Efthimiopoulos et al., Phys. Rev. B 92, 064111 (2015)], previously we had investigated pressure dependence of structural, dynamical, electronic, and mechanical properties of these two phases. However, for prospective applications in fusion reactors and energy-storage technologies, a comprehensive understanding of its thermal response under extreme thermodynamic conditions is essential. In this work, we present a comprehensive ab initio investigation of the thermophysical behavior of the aforementioned phases over a wide range of temperatures (0–900 K) and hydrostatic pressures (0–25 GPa). Various thermodynamic quantities including thermal expansion coefficient, isothermal and adiabatic bulk moduli, isochoric and isobaric heat capacities, Debye temperature, and ion thermal conductivity are systematically evaluated. The findings highlight significant changes in the thermal response among two allotropes of ${\mathrm{Li}}_2{\mathrm{C}}_2$. A unique class of exponential functions is proposed to describe the temperature dependence of thermophysical parameters for both phases of ${\mathrm{Li}}_2{\mathrm{C}}_2$. Additionally, the pressure dependence of all studied thermophysical parameters is found to conform to a generalized power-law relationship. Study enabled estimating shock Hugoniot parameters, a prerequisite for understanding dynamic response of a material. The volume dependence of Grüneisen parameter is determined and compared with analytical models proposed by Slater, Dugdale and MacDonald, Vaschenko and Zubarev, and scaling law of Meyers. Study reveals that the Vaschenko-Zubarev model and scaling law follow closely with ab initio results, whereas others deviate significantly. The compression-dependent Grüneisen parameter is then utilized to predict melting curve of this compound. Finally, study is extended to construct high-temperature high-pressure equation of state of ${\mathrm{Li}}_2{\mathrm{C}}_2$. This comprehensive analysis provides valuable insights into the behavior of ${\mathrm{Li}}_2{\mathrm{C}}_2$ under different thermodynamic conditions, and supports its potential application as a tritium breeding material in fusion energy systems.

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• Electronic structure
• Equations of state
• Lattice dynamics
• Pressure effects
• Thermal conductivity
• Thermal expansion
• Thermal properties
• Carbides
• First-principles calculations