Investigation of Hybrid Battery/Ultracapacitor Electrodes with Adjustable Energy Storage Properties

摘要

This research investigates the integration of active materials from batteries and ultracapacitors into a hybrid electrode. The battery material lithium iron phosphate (LiFePO4) and an ultracapacitor-grade activated carbon are utilized to study the performance of hybrid electrodes in an aqueous electrolyte. Residing in the same electrode, the materials are electrically in parallel, and current passed through the electrode is shared. Being implemented in this manner, the materials work together to exhibit a fusion of their individual performance characteristics. By changing the relative proportions of the two materials in the electrode, the energy and power capabilities of an energy storage device can be tailored to the requirements of a particular application.;Results from constant-current cycling are provided, demonstrating the variation in charge storage and rate capabilities of the hybrid electrodes as the proportion of materials are adjusted. Pulsed-current cycling highlights the dynamic response characteristics of the hybrid electrodes under transient cycling conditions. The hybrid pulse power characterization (HPPC) test has been used to characterize the energy and power capabilities of each hybrid electrode composition. These results are used to determine the mass of the energy storage device required to fulfill the energy/power requirements of different energy storage applications. Over a range of such requirements, the optimal electrode composition has been identified. Full cell performance has been projected for the hybrid LiFePO4/activated carbon electrodes paired with graphite, Li4Ti5O12, and LiTi2(PO4)3 negative electrode materials to implement a full cell, coupled to a discussion of electrolyte options for a full device containing hybrid electrodes. Additionally, the round-trip efficiency has been characterized using a variety of test cycles, including dynamic drive cycles.;The performance of each hybrid electrode composition has been modeled as a full device in the 18650-cell format with estimates of the inert mass required for each composition. This provides a projection of specific energy, specific power, energy density, and power density capabilities of full hybrid electrode devices.;This research program highlights the advantages hybrid electrodes offer over traditional batteries and ultracapacitors in terms of reduced system size and improved performance, particularly for applications with a demanding combination of energy and power requirements.