Thermal conductivity of intercalation, conversion, and alloying lithium-ion battery electrode materials as function of their state of charge

Upon insertion and extraction of lithium, materials important for electrochemical energy storage can undergo changes in thermal conductivity (Λ) and elastic modulus (M). These changes are attributed to evolution of the intrinsic thermal carrier lifetime and interatomic bonding strength associated with structural transitions of electrode materials with varying degrees of reversibility. Using in situ time-domain thermoreflectance (TDTR) and picosecond acoustics, we systemically study Λ and M of conversion, intercalation and alloying electrode materials during cycling. The intercalation V₂O₅ and TiO₂ exhibit non-monotonic reversible Λ and M switching up to a factor of 1.8 (Λ) and 1.5 (M) as a function of lithium content. The conversion Fe₂O₃ and NiO undergo irreversible decays in Λ and M upon the first lithiation. The alloying Sb shows the largest and partially reversible order of the magnitude switching in Λ between the delithiated (18 W m⁻¹ K⁻¹) and lithiated states (<1 W m⁻¹ K⁻¹). The irreversible Λ is attributed to structural degradation and pulverization resulting from substantial volume changes during cycling. These findings provide new understandings of the thermal and mechanical property evolution of electrode materials during cycling of importance for battery design, and also point to pathways for forming materials with thermally switchable properties.