The smallest quaternary ammonium salts with ether groups for high-performance electrochemical double layer capacitors

Electrochemical double layer capacitors (EDLCs) are energy storage devices that have been used for a wide range of electronic applications. In particular, the electrolyte is one of the important components, directly related to the capacitance and stability. Herein, we first report a series of the smallest quaternary ammonium salts (QASs), with ether groups on tails and tetrafluoroborate (BF4) as an anion, for use in EDLCs. To find the optimal structure, various QASs with different sized head groups and ether-containing tail groups were systematically compared. Comparing two nearly identical structures with and without ether groups, QASs with oxygen atoms showed improved capacitance, proving that ions with oxygen atoms move more easily than their counterparts at lower electric fields. Moreover, the ether containing QASs showed low activation energy values of conductivities, leading to smaller IR drops during the charge and discharge processes, resulting in an overall higher capacitance

DOE STI Product/Final Report Number 3 Electrochemical Investigation of Novel Electrolytes for Ambient Temperature Sodium Batteries

The need for low-cost, high-energy density, durable, secondary batteries continues to rise with the demands of the electronics and automobile industries. A room-temperature version of the (high-temperature) ''Zebra Cell'' may provide an interesting technology for portable electronics and transportation. Sodium-based batteries have received attention as an alternative to the lithium-based batteries due to several factors including the absence of dendrite formation during sodium deposition and the abundance of sodium. This work focused on (1) the development of room-temperature ionic liquids (IL) for use in electrochemical devices, including batteries, (2) development and evaluation of secondary sodium batteries using room-temperature ILs, and (3) advancing the fundamental understanding of the electrochemical processes involving ILs and battery technology. Several objectives were accomplished during this program

Electrochemical and thermal properties of 2,4,6-tris (trifluoromethyl)-1,3,5-triazine as a flame retardant additive in Li-ion batteries

Triazines are well known as flame retardants, however, their properties for battery applications have not been much explored. Flame retardants can play an important role in preventing dangerous situations that may occur when battery packs malfunction or are misused. However, the addition of flame retardants to batteries can degrade their performance due to the non-ionic properties of the additives. In order to overcome this drawback of additives, fluorinated material has been investigated, because fluorination frequently prevents deterioration of performance. A fluoride-rich triazine used as an additive to the electrolyte, 2,4,6-tris(trifluoromethyl)-1,3,5-triazine (TTFMT), showed excellent thermal stability with charged cathodes and anodes. Addition of 5 wt.% TTFMT to the electrolyte reduced the exothermic heat from the oxygen release reaction in the cathode by 54%. Surface film formation on the cathode is discussed with reference to cyclic voltammetry combined with impedance spectroscopy and differential scanning calorimetry. The properties of the film were influenced by the additive so as to markedly reduce the charge-transfer resistance, which enhanced the charge retention during cycle life, the capacity, and the high-rate discharge capacity of the battery

Studies on film formation on cathodes using pyrazole derivatives as electrolyte additives in the Li-ion battery

Pyrazole derivatives are flame retardants and provide thermal protection on cathodes, as they help to form a thick protective film. A thicker film provides more protection and delays the thermal decomposition of the cathode. Among the tested pyrazoles, bis(trifluoromethyl)pyrazole (BFTMP) serves as the best flame retardant additive. Additionally, a cell with BFTMP shows better capacity retention than a cell with no additive in full-cell cycle life tests

Allyl-substituted triazines as additives for enhancing the thermal stability of Li-ion batteries

Triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC) are new electrolytic additives for the Li-ion battery. Both additives are structural isomers, and are found to be flame retardant. So TAC has a triallyl structure, and TAIC a triamine structure. Both molecules include unsaturated C–C bonds, which can be good building blocks for a protective film on cathode. Flame retardants that have double bonds are able to improve both the flame retardancy of the electrolyte and the thermal protection for the cathode. The unsaturated carbon materials form a good protective film, by which the exothermic oxygen evolution reaction at the cathode is suppressed very effectively. TAC is the better thermal protector. Addition of 3 wt.% TAC delays the exothermic reaction by 52 °C, i.e., from 275 to 327 °C. A 5 wt.% TAC solution suppresses 75.1% of exothermic energy from the oxygen evolution reaction

Lithium-induced supramolecular hydrogel

We describe a novel anisotropic supramolecular gel made of cyclodextrin-dye, in which physical gelation is completed by lithium salt. Rheological experiment reveals the elastic behaviors of the hydrogel, and high ionic conductivity represents a good mobility of ions inside the gel matrix.close171