Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/04—Cells with aqueous electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/54—Electrolytes
  • H01G11/58—Liquid electrolytes
  • H01G11/62—Liquid electrolytes characterised by the solute, e.g. salts, anions or cations therein
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0568—Liquid materials characterised by the solutes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0569—Liquid materials characterised by the solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
  • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
  • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
  • H01M6/164—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by the solvent
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M6/00—Primary cells; Manufacture thereof
  • H01M6/14—Cells with non-aqueous electrolyte
  • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
  • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
  • H01M6/166—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by the solute
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/54—Electrolytes
  • H01G11/58—Liquid electrolytes
  • H01G11/60—Liquid electrolytes characterised by the solvent
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

• the present invention relates generally to non-aqueous electrolytes, and, more specifically, to non-aqueous electrolytes for use in supercapacitors.
• a typical supercapacitor comprises carbon-based electrodes and an electrolyte having charged ions which can be ordered about the electrodes to create a potential between the electrodes. Therefore, critical to the overall performance of a supercapacitor is its electrolyte.
• An electrolyte typically comprises an ionic salt dissolved in a solvent.
• solvents and salts are available for such use, offering specific advantages depending on the application being considered (e.g., low temperature vs. high temperature).
• non- aqueous electrolytes are preferred from the standpoint of electrochemical stability and are considered herein in detail.
• a common non-aqueous electrolyte comprises a salt, e.g., tetraethyl ammonium tetrafluoroborate (TEABF4), dissolved in an organic solvent, e.g., acetonitrile (AN), propylene carbonate (PC) or gamma butyrolactone (GBL).
• a salt e.g., tetraethyl ammonium tetrafluoroborate (TEABF4)
• AN acetonitrile
• PC propylene carbonate
• GBL gamma butyrolactone
• the conductivity of the electrolyte
• a new non-aqueous electrolyte system disclosed in US Patent No. 5,965,054 purportedly addresses this problem by identifying a class of salts which are highly soluble in non-aqueous solvents to provide good conductivity. More specifically, the '054 patent discloses a salt consisting of a cation selected from a number of an alkyl substituted, cyclic delocalized aromatics and their perfluoro derivatives, and a polyatomic perfluorinated anion.
• the '054 patent states that imidazolium, particularly, l-ethyl-3 methyl imidazolium (EMI) and l-methyl-3 methyl imidazolium (MMI) in combination with PF6 are preferred because they are particularly soluble and thus can be added in relatively high concentration to a non-aqueous solvent. It is claimed that this high concentration of salt in the non-aqueous solvent correlates to high conductivity.
• EMI l-ethyl-3 methyl imidazolium
• MMI l-methyl-3 methyl imidazolium
• electrolytes Although the above-mentioned electrolytes have desirable electrochemical properties that make them suitable for electrolytes, they are, unfortunately, expensive. Therefore, there is a need for a less expensive non-aqueous electrolyte having performance which is at least as good as known electrolytes.
• the present invention fulfills this need among others.
• the present invention provides for a relatively inexpensive non-aqueous pyridinium- based electrolyte having electrochemical performance comparable or better than conventional electrolyte systems, even at relatively low concentrations.
• a salt consisting of a cation of pyridinium (PyH) and an anion of a fluorinated non-metal, such as tetrafluoroborate (BF4 )
• BF4 tetrafluoroborate
• PC propylene carbonate
• AN acetonitrile
• GBL gamma butyrolactone
• the '054 patent states that EMI and MMI are particularly soluble and thus can be used in higher concentrations in electrolytes, i.e., over 2M and even greater than 3M. Since they can be used in higher concentrations, the '054 patent purports that they impart greater conductivity to the electrolyte.
• pyridinium has excellent electrochemical properties even at relatively low concentrations.
• the pyridinium cation and a fluorinated anion, such as BF4- form a salt which has unexpectedly good conductivity and electrochemical stability at concentrations below 2M. Therefore, the present invention provides for an effective electrolyte salt which is not only relatively inexpensive, but which can also be used in relatively low concentrations. Since less of the inexpensive pyridinium-based salt can be used with satisfactory results, there is a two-fold savings realized by its use. This is a significant and unexpected advantage over conventional and newly introduced non-aqueous salts.
• one aspect of the present invention is an electrolyte comprising a pyridinium-based salt at a relatively low concentration.
• the electrolyte comprises a salt of pyridinium and a fluorinated anion at a concentration of less than about 2M in a non-aqueous solvent.
• the solvent is an organic solvent, such as a linear ether, cyclic ether, ester, carbonate, formate, lactone, nitrile, dinitrile, amide, sulfone or sulfolane, and, more preferably, an alkyl carbonate, alkyl nitrile or alkyl lactone.
• the solvent is propylene carbonate (PC), acetonitrile (AN), or gamma butyrolactone (GBL).
• the non-aqueous electrolytes of the present invention may be used in any traditional device or apparatus using an electrolyte. Of particular interest herein is their use in electrical energy storage devices, especially electrochemical capacitors/supercapacitors.
• the electrolytes can also be used in potentiometric and voltametric electrochemical sensors, photovoltaic devices, fuel cells, and in primary and secondary batteries employing alkali and alkaline earth anode materials so long as the electrolyte contains the cation of the alkali or alkaline earth anode material. Further, the electrolytes of the invention may be used as media for catalysis or electro catalysis.
• another aspect of the present invention is a device containing a pyridinium- based electrolyte.
• the device is an energy storage device, and, more preferably, a supercapacitor having carbon-based electrode and an electrolyte comprising a pyridinium-based salt at a concentration of less than about 2M in a non-aqueous solvent.
• Figs. 1-3 show the electrochemical stability for various concentrations of PyHBF4 in PC
• Figs. 4-7 show the electrochemical stability for various concentrations of PyHBF4 in AN.
• Figs. 8 & 9 show the electrochemical stability for various concentrations of PyHBF4 in GBL. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• non-aqueous electrolytes of the invention are superior to conventional electrolytes in a number of respects that serve to make them particularly useful in electrical energy storage devices.
• pyridinium (PyH + ) based salts can be dissolved in an organic solvent to provide an electrolyte having excellent electrochemical properties.
• Such electrolytes can be used in a host of electrochemical applications and are particularly useful in carbon-based electrode supercapacitors.
• the salt of the present invention comprises the cation pyridinium and an anion.
• the ions are selected to complement one another such that when the ionic compound is dissolved in an organic solvent, the ions readily dissociate and have good mobility in the organic solvent to align with their respective electrodes. To this end, the ions are small enough to promote mobility through the solvent, but are not so small as to be solvated excessively to become, in effect, larger compounds with compromised mobility.
• the cation pyridinium in combination with a perfluorinated non-metal anion is preferred.
• Preferred non-metal ions include boron, phosphorous, sulfur, arsenic and antimony.
• the cation pyridinium in combination with the anion tetrafluoroborate was found to have unexpectedly good ionic properties including excellent mobility, conductivity and electrochemical stability. Furthermore, given the relatively low cost of pyridinium, the PyHBF4 salt is substantially less expensive than traditional salts such as tetraethyl ammonium tetrafluoroborate and EMIPF6.
• Pyridinium tetrafluoroborate is a known material and can be prepared very economically using known techniques. For example, it can be prepared using the procedures and techniques disclosed in (Polyhedron Vol. 4,pp 787-789 (1985).
• the pyridinium tetrafluoroborate should be relatively pure, preferably high purity grade with low water and oxygen content ( ⁇ 30 ppm). It is important that water and oxygen impurities be minimized as they have a particularly detrimental effect on the electrochemical performance of the salt.
• PyHBF4 is the preferred salt in the electrolyte of the present invention, it may be preferable to augment the electrolyte with a conventional conductive salt, e.g., tetraalkylammonium or tetraalkylphosphonium salt, to customize it for a particular application.
• a conventional conductive salt e.g., tetraalkylammonium or tetraalkylphosphonium salt
• the solvent is important and affects directly the performance of the electrolyte.
• the non-aqueous solvent is an organic solvent.
• the organic solvent is a linear ether, cyclic ether, ester, carbonate, formate, lactone, nitrile, dinitrile, amide, sulfone or sulfolane, and, even more preferably, is an alkyl carbonate, alkyl nitrile or alkyl lactone.
• the solvent is propylene carbonate (PC), acetonitrile (AN), or gamma butyrolactone (GBL).
• Suitable electrolytes must have high conductivity and good electrochemical stability.
• the power output capability of an energy storage device depends on the working voltage and the maximum current output capability of the electrolyte in combination with the electrodes.
• the working voltage is directly related to the electrolyte's electrochemical stability while the maximum current output (at least in the double layer type supercapacitors) is mainly dictated by the electrolyte's conductivity.
• the electrolyte is subjected to cyclic voltammetry to determine its "voltage window."
• the term "voltage window” refers to the voltage range which the electrolyte can tolerate without substantially reacting (i.e., undergoing reduction or oxidation).
• an electrolyte is placed in a cell having a working electrode, a counter electrode, and a test electrode, which is immediately adjacent but not touching the working electrode.
• the electrodes in the cell are connected to a cyclic voltammetry apparatus, called a potentiostat, which is configured to adjust the current between the working and counter electrodes to maintain a "desired voltage" between the working electrode and the reference electrode.
• the voltage between the reference electrode and the working electrode can be varied as a function of time in a programmed manner (for example, suitable results have been obtained using a linear change rate of 20 mV/s).
• the voltage window is determined by progressively increasing the desired voltage (in both the positive and negative directions) until there is a precipitous increase in the current required to drive the working and counter electrodes to maintain the desired voltage.
• the sharp rise in current at the end voltages generally indicates the breakdown voltage of the electrolyte, meaning that the salt or the solvent is undergoing a reduction reaction at the negative end voltage or an oxidation reaction at the positive end voltage.
• Such reactions could include gas evolution or simple oxidation/reduction reactions.
• the voltage window of pyridinium-based electrolytes is considerably higher than one would expect.
• an electrolyte of PyHBF4 in PC at a concentration of 1.02M has a voltage window of 4 volts
• an electrolyte of PyHBF4 in AN at a concentration of 0.59 M solution has a voltage window of 3.5 V
• an electrolyte of PyHBF4 in GBL at a concentration of 1.62M solution has a voltage window of 4 volts.
• the electrolyte of the present invention has a voltage window preferably of at least 3.5 V and, more preferably, of at least
• the conductivity for pyridinium-based electrolytes is comparable to prior art electrolyte systems, and is particularly good for PyHBF4 in AN and GBL, even at low concentrations.
• an electrolyte of PyHBF4 in PC at a concentration of 1.02M solution has a conductivity of 10.53 mS/cm
• an electrolyte of PyHBF4 in AN at a concentration of 0.59 M solution has a conductivity of 32 mS/cm
• an electrolyte of PyHBF4 in GBL at a concentration of 1.62m/l has a conductivity of 20.2 mS/cm.
• EMIPF6/PC has a maximum conductivity of 15.3 mS/cm at 2M concentration ('054 patent, Table 2), and the maximum conductivity for 1M TEABF4/PC is 13 mS/cm (Ue et al., J. Electrochem. Soc. 141:2989, 1994).
• the conductivities of the pyridinium-based electrolytes compare favorably with these electrolyte systems, and, the PyHBF4/AN and PyHBF4/GBL systems, in particular, compare favorably with these maximum conductivities of conventional electrolytes, even at lower concentrations.
• the concentration of the PyHBF4 in the solvent can be tailored to the application's particular needs.
• the preferred concentration of the electrolyte for the supercapacitor application is one at which the conductivity and the electrochemical window are maximum. Since the voltage window is generally constant for the various concentrations, optimization will typically be a function of optimizing conductivity. Furthermore, since the high surface area activated carbon electrodes are standard for non-aqueous systems, the power output capability depends mainly on the electrolyte conductivity. Higher electrolyte conductivity leads to lower internal voltage drop in the capacitor. Generally, increasing the concentration of the salt in the solvent will improve the electrolyte's conductivity which, in turn, improves its performance as an electrolyte.
• the concentration of pyridinium-based salt be less than 2M. More preferably, the concentration is less than 1.75M and, still more preferably, around 1.0M.
• PC it has been found that suitable results have been obtained with a concentration of PyHBF4 below 1.02 M.
• AN suitable results have been obtained with a concentration of PyHBF4 of less than 1.1M.
• GBL suitable results have been obtained with a concentration of PyHBF4 less than about 1.62 M.
• Example 1 Solutions of varying concentrations of PyHBF4 in PC were prepared by mixing high purity propylene carbonate solvent (Honeywell's high purity PC used in Digirena® electrolyte) and high purity PyHBF4 (Sigma Aldrich Co,).
• the PyHBF4 was transferred from its sealed original container to a glove box.
• the moisture level and the oxygen level in the glove box was maintained below 1 and 2 ppm, respectively. Such limitations are preferred, however, moisture and oxygen levels below 10 ppm may be adequate.
• a known quantity of the high purity propylene carbonate solvent was transferred to a glass container with a cap or lid.
• the voltage window was determined using an electrochemical microcell.
• the microcell comprised electrodes mounted to its top. Specifically, a 3mm diameter polished glassy carbon rod was used as a working electrode. This rod was covered on the cylindrical surface with a plastic sheath. A silver wire was used as a reference electrode. The tip of the silver wire is placed as close to the working electrode as possible without touching it (i.e., approximately 1mm). A platinum foil was used as a counter electrode. The electrodes are connected to an electrochemical microcell.
• the microcell comprised electrodes mounted to its top. Specifically, a 3mm diameter polished glassy carbon rod was used as a working electrode. This rod was covered on the cylindrical surface with a plastic sheath. A silver wire was used as a reference electrode. The tip of the silver wire is placed as close to the working electrode as possible without touching it (i.e., approximately 1mm). A platinum foil was used as a counter electrode. The electrodes are connected to an electrochemical microcell.
• the microcell comprised electrodes mounted to its top.
• the figures and the table provide evidence to the electrochemical performance of this electrolyte at different concentrations. Even at relatively low concentrations, for example, below 1M, the electrochemical performance of the pyridinium-based salt is relatively good compared to prior art.
• the preferred concentration of the electrolyte for the supercapacitor application is one at which the conductivity and the electrochemical voltage window are maximum. Since the voltage window remains fairly constant at all concentrations, selecting a preferred concentration becomes a function of desired conductivity. Higher concentrations equate to higher conductivities.
• the voltage window was determined using the same apparatus and procedure as described above with respect to Example 1.
• the graph produced by this technique is presented in Figures 4-7 for the concentrations 0.33 m/1 and 0.22 m/1 of pyridinium tetrafluoroborate in acetonitrile.
• there will be current peaks on the top half or the bottom half of the graph if there are electrochemical reduction or oxidation processes occurring at any potential in this voltage window.
• the PyHBF4/AN there are no such electrochemical reactions observed other than at the end voltages.
• Example 1 The conductivity as a function of the electrolyte concentration is shown in Table 2. Thus, the figures and the table provide evidence to this capability of the herein disclosed new electrolyte.
• the figures and the table provide evidence to the electrochemical performance of this electrolyte at different concentrations. Even at relatively low concentrations, for example, below 1M, the electrochemical performance of the pyridinium-based salt is relatively good compared to prior art.
• the preferred concentration of the electrolyte for the supercapacitor application is one at which the conductivity and the electrochemical voltage window are maximum. Since the voltage window remains fairly constant at all concentrations, selecting a preferred concentration becomes a function of desired conductivity. Higher concentrations equate to higher conductivities.
• Solutions of varying concentrations of PyHBF4 in gamma butyrolactone solvent were prepared by mixing high purity gamma butyrolactone solvent (Honeywell's high purity gamma butyrolactone solvent used in Digirena® electrolyte) and high purity PyHBF4 (supplied by
• the voltage window was determined using the same apparatus and procedure as described above with respect to Example 1.
• the graph produced by this technique for the PyHBF4/PC electrolyte solution is presented in Figs. 8 & 9 for various concentrations up to the saturation limit of 1.62 m/1.
• a current peak on the top half or the bottom half of the graph indicates respectively an electrochemical reduction or oxidation process taking place at the potential corresponding to the peak location.
• this electrolyte and electrode system there is no oxidation or reduction peak. It means that this electrolyte is stable through the voltage window indicated by the sharp rise in the current level at the end voltages. In this case we see an electrochemical window of nearly 4 V. This is comparable to or higher than any known state of the art electrolyte system.
• the figures and the table provide evidence to the electrochemical performance of this electrolyte at different concentrations. Even at relatively low concentrations, for example, below 1M, the electrochemical performance of the pyridinium-based salt is relatively good compared to prior art.
• the preferred concentration of the electrolyte for the supercapacitor application is one at which the conductivity and the electrochemical voltage window are maximum. Since the voltage window remains fairly constant at all concentrations, selecting a preferred concentration becomes a function of desired conductivity. Higher concentrations equate to higher conductivities.

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• 2003
  • 2003-12-19 AU AU2003300357A patent/AU2003300357A1/en not_active Abandoned
  • 2003-12-19 EP EP03814953A patent/EP1611629A1/en not_active Withdrawn
  • 2003-12-19 JP JP2004565690A patent/JP2006512773A/ja not_active Withdrawn
  • 2003-12-19 KR KR1020057012475A patent/KR20050092032A/ko not_active Application Discontinuation
  • 2003-12-19 WO PCT/US2003/041210 patent/WO2004062007A1/en not_active Application Discontinuation
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