Highly Anisotropic Thermal Transport in LiCoO2

LiCoO₂ is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li⁺ and CoO₂^- layers along the hexagonal <0001> axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO₂ using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm^-1K^-1) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO₂^- networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.