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(NixMnyCoz)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 45.9W m−1 K−1 at T = 300 K and the largest
anisotropy, followed by LiMnO2 with 8.9W m−1 K−1, and LiNiO2 with 6.0W 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 (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.