Substituted phosphonium cation based electrolytes for nonaqueous electrical double-layer capacitors

Abstract

Tetrakis(diethylamino)phosphonium tetrafluoroborate (TDENPBF 4 ), tetrakis (diethylamino)phosphonium hexafluorophosphate (TDENPPF 6 ), and tetrakis (dimethylamino)phosphonium tetrafluoroborate (TDMNPBF 4 ) in acetonitrile (AN) have been studied as electrical double-layer capacitor electrolytes in a two-electrode test cell using titanium carbide derived carbon, C(TiC), as an electrode material. Electrochemical characteristics for C(TiC)j1 M TDENPBF 4 þ AN, C(TiC)j1 M TDENPPF 6 þ AN, and C(TiC)j1 M TDMNPBF 4 þ AN interfaces have been obtained by cyclic voltammetry, constant current charging/discharging, and electrochemical impedance spectroscopy. High-capacitance (85 F/g) and gravimetric power (269 kW/kg) have been achieved at cell voltage 3.2 V. Data obtained have been compared with results published previously.

A review of electrolyte materials and compositions for electrochemical supercapacitors

“…In addition, Kurig et al 226 tested a series of substituted phosphonium cation based electrolytes for EDLCs with titanium carbide derived carbon (C(TiC)) as the electrodes. The C(TiC) electrodes were found to be ideally polarizable in a 1 M tetrakis(diethylamino)-phosphonium hexafluorophosphate (TDENPPF 6 )/ ACN electrolyte up to 3.2 V. The EDLC with a 1 M TDENPPF 6 /ACN electrolyte showed a gravimetric capacitance of 85 F g À1 , a characteristic relaxation time of 0.9 s, and a gravimetric energy density of 27 W h kg À1 when the cell voltage was 3.2 V. No visible loss in the discharging capacitance could be observed after 10 000 chargingdischarging cycles.…”

Electrolytes for electrochemical energy storage

“…69 Furthermore, the salt also plays an important role in affecting the electrochemical window of organic electrolytes. 63,72,73 The ionic liquid, N-butyl-Nmethylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI) was used to formulate the electrolyte, and EDLCs containing PYR14TFSI in PC exhibited a high operating voltage (up to 3.5 V) and excellent cycling stability. A small capacitance loss of only 5 % was also achieved after 100,000 cycles carried out at 3.5 V. 74,75 Additionally, the spiro-(1,1')-bipyrolidinium tetrafluoroborate (SBP-BF4) salt was also tested, confirming that the novel SBP-BF4/PC electrolyte in activated carbon based EDLCs had a high withstand voltage of up to 3.2 V and good capacitor behaviour.…”

Electrochemical studies of acetonitrile based supercapacitor electrolytes containing alkali and alkaline earth metal cations

“…Quaternary ammonium and quaternary phosphonium cations are the most reductively stable organic cations available, they typically undergo gross reduction at or beyond À2.8 V (vs. SHE) [7], and in some situations the stability may be extended to nearly À3 V (vs. SHE) such as when the materials are of exceptional purity or when large alkyl groups are used. Although phosphonium cations have been studied as potential electrolyte salts [4,8,9], and have even been proven to be of equal stability to quaternary ammonium cations in some cases [4], to the best of our knowledge phosphonium cations are not being used in commercial supercapacitors, instead quaternary ammonium cations are preferred. The reduction potentials of alkali metal cations in organic solvents are expected to be similar or even better than that of a quaternary ammonium cation, however metal cation reduction potentials for any system will depend on both the solvent type [10] and the anion.…”