Investigation of hybrid electrode optimization for energy storage applications with varying energy and power requirements using HPPC cycling

This paper explores hybrid energy storage devices in which an individual electrode is composed of a mixture of the active materials used in lithium-ion batteries and ultracapacitors, allowing them to exhibit characteristics of both device types. In order to explore the breadth of options between a pure battery electrode and a pure ultracapacitor electrode, seven different electrode compositions containing mixtures of lithium iron phosphate (LiFePO
₄
) and activated carbon are studied in this work. The hybrid electrodes have been implemented in an aqueous lithium sulfate electrolyte with single electrode measurements using a reference electrode. To characterize the energy and power capability of each electrode composition, the hybrid pulse power characterization (HPPC) test profile has been employed. An approach for converting single electrode cycling results to full cell predictions suitable for the HPPC analysis procedure is presented. By executing this procedure, battery scale factors representing estimates of the quantity of active material required to achieve a set of energy storage target requirements are calculated. These results show that the required amount of active materials in an energy storage system can be minimized for a given application by using a hybrid electrode and adjusting the constituent fraction of battery and ultracapacitor materials.