Electrochemically tunable thermal conductivity of lithium cobalt oxide

Using time-domain thermoreflectance, the thermal conductivity and elastic properties of a sputter deposited LiCoO 2 film, a common lithium-ion cathode material, are measured as a function of the degree of lithiation. Here we report that via in situ measurements during cycling, the thermal conductivity of a LiCoO 2 cathode reversibly decreases from ~5.4 to 3.7 W m −1 K −1 , and its elastic modulus decreases from 325 to 225 GPa, as it is delithiated from Li 1.0 CoO 2 to Li 0.6 CoO 2 . The dependence of the thermal conductivity on lithiation appears correlated with the lithiation-dependent phase behaviour. The oxidation-state-dependent thermal conductivity of electrolytically active transition metal oxides provides opportunities for dynamic control of thermal conductivity and is important to understand for thermal management in electrochemical energy storage devices. Materials with variable and reversible thermal conductivities are important in technologies, and yet such materials are rare. Here, Cho et al . report in situ measurements of thermal conductivity of lithium cobalt oxide, and show how to reversibly modulate thermal conductivities over a considerable range.