LiCoO2 is the prototypical cathode in lithium-ion batteries. Its crystal structure consists of Li+ and CoO2- layers that alternate along the hexagonal «0001»axis. It is well established that the ionic and electronic conduction are anisotropic, but little is known regarding the heat transport. We analyze the phonon dispersion and lifetimes 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. An upper limit to the average thermal conductivity at T = 300 K of 38.5 W m-1 K-1 is set by short phonon lifetimes associated with anharmonic interactions within the octahedral face-sharing CoO2- network. Observations of conductivity <10 W m-1 K-1 can be understood by additional scattering channels including grain boundaries in polycrystalline samples. The impact on thermal processes in lithium-ion batteries is discussed.
Bibliographical noteFunding Information:
This work was carried out with funding from the Faraday Institution ( faraday.ac.uk ; EP/S003053/1) grant number FIRG003 and used the MICHAEL computing cluster. We are also grateful for computer resources from RWTH Aachen. J.Y. is supported by Shandong University (Qilu Young Scholar 89963031). A.W. and B.J.M. are supported by Royal Society University Research Fellowships (Nos. UF100278 and UF130329). J.M.S. is supported by a Presidential Fellowship from the University of Manchester. Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service ( http://www.archer.ac.uk ).
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