Researchers at the University of Illinois at Urbana-Champaign have experimentally shown for the first time that the thermal conductivity of lithium cobalt oxide (LixCoO2), a material used in the cathodes of lithium-ion batteries, can be reversibly electrochemically modulated over a significant range.
Many technologies require control over the flow of heat through materials in order to function properly. However, while materials with high and low thermal conductivities are fairly available, materials with variable and reversible thermal conductivities are rare and, other than in specialized experiments, only exhibit very small reversible modulations.
The new research on LixCoO2 represents “the first experimental demonstration of the electrochemical modulation of the thermal conductivity of a material, and, in fact, the only demonstration of large variable and reversible thermal conductivities in any material by any approach, other than very high pressure experiments,” Paul Braun, a professor of materials science and engineering (MatSE) at UIllinois, said.
During the experiment, researchers deposited a LixCoO2 film directly on a metal coated electrode, then immersed it in a common electrolyte. Time-domain thermoreflectance (TDTR) was used to measure the thermal conductivity of the lithium cobalt oxide thin film as a function of lithiation.
“We [performed] both in-situ experiments, which enable direct observation of thermal conductivity as a function of the degree of lithiation, and ex-situ experiments, which provide the thermal conductivity of the lithiated and delithiated state in the absence of electrolyte,” Jiung Cho, first author of the paper, explained.
The study’s findings are expected to significantly impact the field of electrochemical energy storage. While it is critical for designers to understand and control heat evolution and dissipation in rechargeable batteries, prior to this research, it was not even known that the thermal conductivity of materials often used as cathodes changed significantly as a function of the state of charge.
“Our work opens up opportunities for dynamic control of thermal conductivity and additionally, may be important for thermal management in electrochemical energy storage devices which use cathodes based on transition metals oxides such as lithium cobalt oxide,” David Cahill, a MatSE professor and one of the paper’s co-authors, said. In particular, the findings could lead to the design of safer battery electrodes that can be charged more rapidly and deliver more power.
The results of research have been reported in the article, “Electrochemically Tunable Thermal Conductivity of Lithium Cobalt Oxide,” in the journal Nature Communications.
