High-voltage operation of Li4Ti5O12/AC hybrid supercapacitor cell in carbonate and sulfone electrolytes: Gas generation and its characterization. (1st April 2019)

• Record Type: Journal Article
• Authors: Iwama, Etsuro; Ueda, Tsukasa; Ishihara, Yoko; Ohshima, Kenji; Naoi, Wako; Reid, McMahon Thomas Homer; Naoi, Katsuhiko
• Is Part Of: Electrochimica acta. Volume 301(2019)
• Page Start: 312
• Page End: 318
• Publication Date: 2019-04-01
• Subjects: Hybrid supercapacitors -- High-voltage operation -- Electrolyte -- Gas generation -- Li4Ti5O12-interface stability; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2019.01.088
• Languages: English
• ISSNs: 0013-4686

Abstract

Abstract: Designing a hybrid supercapacitor, composed of Li4 Ti5 O12 (LTO)/activated carbon (AC), is one of promising routes to enhance the energy density of supercapacitors (SCs) using symmetrical AC electrodes. At high-voltage operations (>3.0 V), however, the failure mode or gas generation is critical for the system, which is greatly dependent on the type of electrolyte. In this study, we investigated the voltage dependence of the interfacial phenomena of LTO/1 M lithium tetrafluoroborate (LiBF4 ) in propylene carbonate (PC)/AC. The results reveal that the interface between the negative LTO electrode and the electrolyte becomes unstable at cell voltages above 3.0 V, corresponding to potentials above 4.5 V vs . Li/Li + for the AC positive electrode. The destabilization of the LTO/electrolyte interface appears to be initiated by an irreversible reaction occurring at the AC positive electrode, accompanied by a release of absorbed H2 O. This hypothesis is further confirmed by replacing PC with a hydrolysis-resistant solvent, ethyl isopropyl sulfone (EiPS); the EiPS-based electrolyte successfully realizes a high-voltage operation at 3.3 V without LTO degradation, regardless of the oxidative reaction at the AC positive electrode, with a 95% capacity retention after 1000 cycles. Highlights: Voltage dependence of the interfacial phenomena of LTO/AC system was investigated. H2 evolution on LTO electrode is the main factor for the degradation of cell performance at voltages above 3.0 V. H2 gas originated from the PC reduction, which is accelerated by the release of absorbed H2 O from the AC electrode. Using hydrolysis-resistant EiPS, the system supports 3.3 V operation over 1000 cycles.