Degradation behavior analysis of High Energy Hybrid Lithium-ion capacitors in stand-alone PV applications

This paper presents the capacity fade of hybrid Lithium-ion capacitor (LiC) as supercapacitor storage integrated into a PV system for self-consumption and the effect of the operating and environmental conditions. An aging model was developed from the results obtained from aging tests performed on LiC supercapacitor cells. The tests were performed at a 3x3 test matrix with two axes representing temperature and C-rate. An aging function is derived through lab testing of 5 cases and then extrapolation of the capacity fade coefficient for a given current and temperature inputs. Test results show that the tested cells at 50°C and 7C of charging and discharging cycles were degraded the most in terms of lower capacity and higher equivalent series resistance (ESR). Cycling at a low C-rate and high temperature was seen to have a higher degradation than the cells at lower temperature and higher C-rate which is due to the calendar aging in higher temperatures. An aging model as a function of temperature, Current, and the number of cycles was built and used in a PV with a storage system to predict the capacity fade of the storage in a duration of 3 years; the capacity reduction was 0.5% and 1.1% in two simulated cases.