An experimental study on the failure behaviors of hybrid supercapacitors under overdischarge conditions

Abstract

Abstract Hybrid supercapacitors (HSCs) have higher energy density which can meet more working conditions. However, the improved energy density also brings safety hazards. Thereinto, overdischarge is a common abuse situation that can lead to performance degradation and safety issues. Herein, we fabricated a large-format pouch cell HSC with a composite cathode including activated carbon (AC) and lithium nickel cobalt manganate oxide (NCM), hard carbon (HC) anode, and ceramic polyethylene terephthalate (PET) nonwoven separator. The failure behaviors of cyclic overdischarge and external short circuit were compared, and it is found that the performance failure of HSCs caused by external short circuit is more serious than cyclic overdischarge. After 250 cycles of discharge at 0 V and 0.5 V, copper (Cu) was found on both the anode and separator, but not found at the voltage of 1.0V, 1.5V and 2.0V after 500 cycles. After external short circuit for 24 h, the electrochemical performance decreased significantly, and the energy decayed to less than 80%. 5.62 wt% Cu was found on the anode after charge and discharge once. The gas composition after external short circuit is mainly methane (CH4) and ethylene (C2H4).