Al(s,T) | Li(1-x) CoO2(s,T) | EC, DEC, LiPF6(diss) | Lix CO2(s,T + ΔT) | Al(s,T+ ΔT)
The electrodes are commercial LiCoO2 electrodes on an aluminium current collector, each kept at temperatures; T and T + ΔT. The electrolyte is 1 M lithium hexafluorophosphate (LiPF6) in a EC DEC mixture (1:1, volume wise) soaked in a separator. The cell is assembled as a pouch cell, and the electrodes are thermostatted to the specified temperatures.
We show that there are two significant contributions of opposite sign to the thermoelectric signal relative to the temperature difference; commonly known as the Seebeck coefficient. The contribution from the Peltier heat is obtained from the steady state value after 3-5 days. The second contribution, which manifests itself within hours, is a Soret effect. From these results, we report the transported entropy of Li+ and estimate the heats of transfer for the electrolyte components.
The attached figure shows a cross section of the cell used in these measurements, where one side is heated by hot water and the other cooled by cold water. The pouch cell is sandwiched between these two sides and layers of copper containing thermocouples, so that the actual temperature difference on the surfaces of the pouch cell is known and uniform.
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