Dual-cation electrolytes for low H2 gas generation in Li4Ti5O12//AC hybrid capacitor system. (1st February 2021)

• Record Type: Journal Article
• Authors: Chikaoka, Yu; Iwama, Etsuro; Seto, Shinichi; Okuno, Yuta; Shirane, Tomohide; Ueda, Tsukasa; Naoi, Wako; Reid, McMahon Thomas Homer; Naoi, Katsuhiko
• Is Part Of: Electrochimica acta. Volume 368(2021)
• Publication Date: 2021-02-01
• Subjects: Supporting electrolyte -- Hybrid capacitor -- H2 gas suppression -- Li4Ti5O12 -- Lewis-based passivation; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2020.137619
• Languages: English
• ISSNs: 0013-4686

Abstract

Highlights: Dual-cation system (LiBF4 with SBPBF4 ) suppressed H2 gas in LTO//AC hybrid capacitor. 50% reduction of generated H2 volume was achieved by use of dual-cation electrolyte. Generated H2 reduction owing to the suppressed PC/H2 O decomposition on LTO surface. SBP + -derived Lewis-based passivates LTO surface to slow PC/H2 O decomposition. Dual-cation simultaneously achieves high power and low H2 gas generation for LTO//AC. Abstract: H2 gas generation with associated swelling using Li4 Ti5 O12 (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 the LTO surface. Herein, we report a method to suppress gassing behavior by adding spiro(1, 1′)-bipyrrolidinium tetrafluoroborate (SBPBF4 ) to the lithium-based electrolyte [1 M lithium tetrafluoroborate (LiBF4 ) in PC]. The dual-cation (Li + /SBP + ) electrolyte, which has previously been reported as the electrolyte composition used for rate-capability enhancement, reduced 35–50% volume of generated H2 compared to that for the single-cation (Li + ) electrolyte under high-voltage floating conditions (3.5 V, 60 °C). This behavior was attributed to the LTO surface passivated by the Lewis-based layer via Hofmann elimination of SBP + . The concept of passivation of the LTO Lewis-acid site in the presence of SBP + was further confirmed by applying alternative quaternary ammonium cations, such as tetraethylammonium (TEA + ) and triethylmethylammonium (TEMA + ), resulting in reduced H2 generation to the same level as that obtained using the SBP + -based dual-cation. Graphical abstract: Image, graphical abstract