Chemical Trends in the Lattice Thermal Conductivity of Li(Ni, Mn, Co)O₂ (NMC) Battery Cathodes

While the transport of ions and electrons in conventional Li-ion battery cathode materials is well understood, our knowledge of the phonon (heat) transport is still in its infancy. We present a first-principles theoretical investigation of the chemical trends in the phonon frequency dispersion, mode lifetimes, and thermal conductivity in the series of layered lithium transition-metal oxides Li(Ni_xMn_yCo_z)O₂ (x+y+z = 1). The oxidation and spin states of the transition metal cations are found to strongly influence the structural dynamics. Calculations of the thermal conductivity show that LiCoO₂ has highest average conductivity of 45.9 W m⁻¹ K⁻¹ at T = 300 K and the largest anisotropy, followed by LiMnO₂ with 8.9 W m⁻¹ K⁻¹, and LiNiO₂ with 6.0 W m⁻¹ K⁻¹. The much lower thermal conductivity of LiMnO₂ and LiNiO₂ is found to be due to 1–2 orders of magnitude shorter phonon lifetimes. We further model the properties of binary and ternary transition metal combinations and show that the thermal conductivity of NMC is suppressed with decreasing Co content and increasing Ni/Mn content. The thermal conductivity of commercial NMC622 (LiNi_0.6Mn_0.2Co_0.2O₂) and NMC111 (LiNi_0.33Mn_0.33Co_0.33O₂) compositions are substantially larger than NMC₈₁₁LiNi_0.8Mn_0.1Co_0.1O₂). These results serve as a guide to ongoing work on the design of multi-component battery electrodes with more effective thermal management.