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 cathodematerials is well understood, our knowledge of the phonon (heat) transport is still in itsinfancy. We present a first-principles theoretical investigation of the chemical trendsin the phonon frequency dispersion, mode lifetimes, and thermal conductivity in theseries of layered lithium transition-metal oxides Li(NixMnyCoz)O2 (x+y+z = 1). Theoxidation and spin states of the transition metal cations are found to strongly influencethe structural dynamics. Calculations of the thermal conductivity show that LiCoO2has highest average conductivity of 45.9W m−1 K−1 at T = 300 K and the largestanisotropy, followed by LiMnO2 with 8.9W m−1 K−1, and LiNiO2 with 6.0W m−1 K−1The 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/Mncontent. The thermal conductivity of commercial NMC622 (LiNi0.6Mn0.2Co0.2O2) and NMC111 (LiNi0.33Mn0.33Co0.33O2) compositions are substantially larger than NMC811LiNi0.8Mn0.1Co0.1O2). These results serve as a guide to ongoing work on the designof multi-component battery electrodes with more effective thermal management.