Dual-Cation Electrolytes for High-Power and High-Energy LTO//AC Hybrid Capacitors

Dual-cation electrolyte systems, which contain two cations [Li+ and spiro-1,1′-bipyrrolidinium (SBP+), are proposed to enhance the power capability of hybrid capacitors composed of thick Li4Ti5O12 (LTO) negative (200 μm) and activated carbon (AC) positive electrodes (400 μm), which thus reduces the resistive overvoltage in the system. Detailed studies of the mass transport properties based on the combination of spectroscopy and electrochemical analysis have shown that the presence of SBP+, despite slower Li+ transport in the electrolyte bulk, further reduces overvoltage associated with migration limitation in the thick LTO electrode macropores. This study on the dual-cation electrolyte quantifies the influence of the addition of a supporting electrolyte and shows interest in SBPBF4 addition for increasing the output power density of hybrid capacitors with a thick electrode configuration.