New method evaluating currents keeping the voltage constant for fast and highly resolved measurement of Arrhenius relation and capacity fade

摘要

The evaluation of floating currents is a powerful method to characterize capacity fade induced by calendaric aging and enables a highly resolved representation of the Arrhenius relation. The test arrangement is simple and could constitute a cheap alternative to state-of-the-art calendaric aging tests including check-up tests. Therefore the currents to maintain a constant voltage are evaluated. This method is validated by analyzing nine cylindrical 8 Ah LiFePO4 broken vertical bar Graphite battery cells during calendaric aging at 25 degrees C, 40 degrees C and 60 degrees C at 3.6 V (100% SOC). The 3.6 V are kept by applying constant voltage while the floating currents are logged. The floating currents correlate with the rate of capacity loss measured during capacity tests. The floating currents reveal to be rather constant at 25 degrees C, linearly increasing at 40 degrees C and decreasing from a higher level at 60 degrees C. Additional tests with three test cells, with the temperature rising from 40 to 60 degrees C in steps of 5 K, exhibit non-constant currents starting from 50 degrees C on with high variations amongst the tested cells. Once stored above 50 degrees C, the cells exhibit increased floating currents compared to the measurement at the same temperature before exceeding 50 degrees C. (C) 2017 Elsevier B.V. All rights reserved.