In this paper* we study hybrid energy storage devices which feature electrodes which are composed of a mixture of the active materials used in lithium-ion batteries and ultracapacitors. This imparts dual battery/capacitor functionality on the electrodes, and in operation they demonstrate behaviors of both devices. The exact composition of the hybrid electrodes can then be tailored to the energy/power demands required from the device based on its intended usage. Naturally, battery-composition electrodes will be suited for high-energy applications while ultracapacitor-composition electrodes for high-power applications, but this paper focuses on the options which exist in between.
In order to demonstrate the spectrum of options between standalone battery and capacitor electrode behavior, seven different combinations of electrode materials have been implemented. Lithium iron phosphate (LiFePO4) has been utilized as the battery material, activated carbon as the ultracapacitor material, implemented in a cell using an aqueous lithium sulfate electrolyte. To study the behavior of the hybrid electrodes in detail, testing has been implemented in a half-cell, three electrode configuration utilizing a reference electrode. The hybrid pulse power characterization (HPPC) testing protocol has been utilized to determine the dynamic energy and power capabilities of each electrode composition. Methods for extrapolating single electrode measurements to full cell performance predictions required by the HPPC protocol are presented.
By applying this test, scaling factors can be determined for each electrode composition which predicts the total amounts of active materials required to achieve the energy/power requirements for various energy storage applications. These results are then used to model full 18650-format energy storage cells, and predict the overall size and mass of the overall energy storage system. As a result, it is shown that the exact composition of the hybrid electrodes can be tailored in order to optimize the overall energy storage system on the basis of quantity of active materials, total mass, or total volume for any given application.
(*) Frankforter, K.J., Tejedor-Tejedor, M.I., Anderson, M.A., Jahns, T.M. Investigation of Hybrid Battery/Ultracapacitor Electrode Customization for Energy Storage Applications with Different Energy and Power Requirements Using HPPC Cycling (2020) IEEE Transactions on Industry Applications, 56 (2), art. no. 8941245, pp. 1714-1728. DOI: 10.1109/TIA.2019.2962109
More information: Marc Anderson, Advisor, Electrochemical Processes Unit. firstname.lastname@example.org