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Solvent
Electrolyte ions
Electrolyte solvent categories
- Solid state electrolyte capacitors
- Aqueous electrolyte capacitors (< 1.23 V)
- Organic liquid electrolyte capacitors (typical 2.5V - 3V)
Electrolyte solvent properties
Aqueous for high ionic conductance
- higher ionic mobility
- smaller ESR (10 x)
- higher power capability
- big problems with aluminum
Organic for "high" voltage
- higher energy density capability
- Less cells in series in application
- dry process
Acetonitrile solvent
Equivalent designation for ACETONITRILE:
- Methyl cyanide
- Cyanomethane
- Ethanenitrile
- C2H3N/CH3CN
Physical data
- Molecular weight: 41.06 g/mole
- Appearance: colourless liquid
- Melting point: -41.9°C
- Boiling point: 81.67°C
- Vapor density: 1.42 (air = 1)
- Vapor pressure: 72.8 mm Hg at 20°C
- Specific gravity: 0.787 g/cm3
- Flash point: 5.85°C
- Explosion limits: 4.4 - 16 %
- Autoignition temperature: 524°C
Decomposition in Fire: CO, CO2, CN.
Acetonitrile is toxic and flammable. It is metabolized into hydrogen cyanide (HCN) and thiocyanate.
R-phrases R11, R20/21/22, R36
S-phrases (S1/2), S16, S36/37
Propylene carbonate solvent
Physical data
- Molecular weight: 102.09 g/mole
- Appearance: colourless liquid
- Melting point: -49.2°C
- Boiling point: 240°C
- Vapor density: 3.52 (air = 1)
- Vapor pressure: 0.03 mm at 20°C
- Specific gravity: 1.205
- Flash point: 135°C (closed cup)
- Explosion limits: 1.8 - 14.3 %
- Autoignition temperature: 455°C
Acetonitrile Polypropylene carbonate properties comparison
In the next slides a comparison of capacitance and series resistance as a function of the temperature is given for the the two main solvents used in the supercapacitor industry. It is obvious from the data displayed in the chart from General Motors that the PC has lower capacitance and higher series resistance. At low temperature the resistance in PC is even 10 times bigger.