Dual-cation electrolytes for low H2 gas generation in Li4Ti5O12//AC hybrid capacitor system

H2 gas generation with associated swelling using Li4Ti5O12 (LTO)-based hybrid capacitors upon high-voltage operation over 3.0 V has been a major challenge owing to catalytic reductive decomposition of solvent such as propylene carbonate (PC) at the Lewis-acid sites on LTO surface. Herein, we report method suppress gassing behavior by adding spiro(1,1?)-bipyrrolidinium tetrafluoroborate (SBPBF4) lithium-based electrolyte [1 M lithium (LiBF4) in PC]. The dual-cation (Li+/SBP+) electrolyte, which previously reported composition used for rate-capability enhancement, reduced 35–50% volume generated compared that single-cation (Li+) under floating conditions (3.5 V, 60 °C). This was attributed surface passivated Lewis-based layer via Hofmann elimination SBP+. concept passivation site presence SBP+ further confirmed applying alternative quaternary ammonium cations, tetraethylammonium (TEA+) and triethylmethylammonium (TEMA+), resulting same level obtained SBP+-based dual-cation.