ARULEPP, Mati (Riia 185, Tartu, EE-51014, EE)
MADIBERK, Vello (Riia 181A, Tartu, EE-51014, EE)
LEIS, Jaan (Riia 185, Tartu, EE-51014, EE)
ARULEPP, Mati (Riia 185, Tartu, EE-51014, EE)
MADIBERK, Vello (Riia 181A, Tartu, EE-51014, EE)
| Claims 1. A multi-cell super capacitor of high operating voltage comprising at least two electrochemical cells (2) connected in series and placed into the external housing of the capacitor, whereas neighbouring cells are provided with a common current terminal, which is minus-terminal with regard to one cell and plus-terminal with regard to the other, with ends of the housing (1) being closed with covers (3, 4), onto which external current terminals (5, 6) have been installed and electrochemical cells have been separated from each other by a partition wall made of metal (7), whereas the maximum operating voltage of the super capacitor is approximately equal to the sum of the maximum operating voltage applied to the electrochemical cells being components of said super capacitor. 2. The super capacitor according to claim 1 , characterised by that the electrochemical cell consists of two or more pairs of electrodes that are separated from each other by ionic conductors and that contain at least 85% of carbon material of high specific surface area. 3. The super capacitor according to claim 1 , characterised by that the dimensions and energy specific characteristics of electrochemical cells are similar. 4. The super capacitor according to claim 1 , characterised by that there can be two or more electrochemical cells (2) connected in series into a common housing (1 ). 5. The super capacitor according to claim 1 , characterised by that the external housing of the super capacitor (1 ) is of cylindrical profile. 6. The super capacitor according to claim 1 , characterised by that the external housing of the super capacitor is of prismatic profile. 7. The super capacitor according to claim 1 , characterised by that the partition wall (7) is insulated from the super capacitor housing and electrochemical cells (2) are hermetically separated from each other by O-ring seals (11), placed between the partition wall (7) and super capacitor housing (1). 8. The super capacitor according to claim 1 , characterised by that current terminals (5, 6) are insulated from the super capacitor covers (3, 4) by an internal insulation washer 8 and insulation washer 15; and that current terminals (5, 6) are insulated from the super capacitor housing (1 ) by an external insulation washer (13), which has been placed around the base part of the current terminal (5, 6), located inside the super capacitor and between the internal wall of the super capacitor external housing (1 ). 9. The super capacitor according to claim 1 , characterised by that the external current terminals (5, 6) are electrically connected with electrochemical cells (2). |
TECHNICAL FIELD
The present invention is related with the electrical double-layer capacitor with high operating voltage and special characteristics. The invention is also related to preparing the double-layer capacitor with high operating voltage, by employing a novel structural solution for the capacitor housing.
BACKGROUND ART
It is known from prior art that the voltage of one single element of the capacitors, based on the electrical double-layer mechanism, from using the non-aqueous electrolyte is 2.5-2.7V (Maxwell, Nesscap, Asachi Glass, Panasonic). In rare cases, e.g. by using carbon nanotubes, the operating voltage of up to 3.3 V of the electrical double-layer capacitor has been reportedly achieved [Kenji Hata, Hiroaki Hatori, Osamu Tanaike. Electrochemical capacitor and electrode material for use therein]. Also, a 3.3 V operating voltage has been reported for a low specific surface area KOH-activated capacitor element with graphite carbon electrodes [Kobayashi Kotaro et al. EP1860673A1].
For achieving the operating voltage required by the customer, separate cells of capacitors are connected in series into a capacitor battery. Necessary energy and capacity level is achieved by connecting in series several individual elements having electric capacity. In order to increase the capacity of the entire capacitor battery, the parallel connection of separate elements in the entire series of chain has been employed [Maxwell 2000], The deficiency of existing connections lies in the necessity of employing bulky connection cables and screw terminals and significant extra mass and volume of the capacitor battery [R. Kotz, M. Bartschi, F. Buchi, R. Gallay, Ph. Dietrich. HY. POWER - A Fuel Cell Car Boosted with Supercapacitors. Florida, Dec. 2002].
The specific energy of single elements of capacitors based entirely on the electrical double-layer mechanism, manufactured today, is on a level of 4-5 Wh/kg with energy density of 5-7 Wh/L, which is achieved within the voltage range of .3 to 2.7 V as is disclosed in the article [A,Burke Electrochimica Acta 53 (2007) 1083-109].
The article reveals as one of the significant examples the measured data of capacitor batteries by many major manufacturers (Maxwell, NessCap, Power System, Asahi, Epcos), which confirm that specific energy values from capacitor batteries decrease 50-77% when compared with initial level per weight and 36- 70% per volume, depending on the capacitor connection diagram and dimensions. This factor is called packing density [A.F. Burke. Supercapacitor Technology - Present and Future. Advanced Capacitor World Summit 2006. San Diego, CA. July 17-19].
The manufacturers of super capacitor cells with best weight average and volume average specific parameters include Power Systems Inc. that uses housings made of lightweight materials (laminated aluminium and plastics) in manufacturing its capacitors. Using lightweight housings will guarantee higher weight and volume specific parameters for an individual cell, however when putting it into practice, the entire system still needs to be encased in the capacitor battery with an additional housing of reasonable material, which in turn will increase the weight and volume of the apparatus ([http://www.powersystems.co.jp ). For example, the packing density of a 59-volt capacitor battery, packed in this manner by so-called L4-cells in series connection, is 0.642 and 0.413, respectively, either per mass or volume [A. Burke, San Diego 2006].
DISCLOSURE OF INVENTION
Current invention describes an electric double-layer capacitor or super capacitor, which has two or more electrochemical cells formed into its prismatic or cylindrical housing, connected in series, so that neighbouring cells are hermetically separated with a partition wall, which is a minus-terminal with regard to one cell and plus-terminal with regard to the other. The maximum operating voltage of the electrical double-layer capacitor according to the invention is approximately equal to the sum of the maximum operating voltage applied to the electrochemical cells being components of said super capacitor, whereas the total volume and mass of a given capacitor is smaller than that of two conventional capacitor batteries with the same operating voltage, connected in series and having equal gross electrical capacity.
BRIEF DESCRIPTION OF DRAWINGS
The structure of a super capacitor according to the invention is described in more detail in the following embodiment with references to drawings in which
Fig 1 is the simplified sectional view of the super capacitor according to the invention,
Fig 2 is a potential embodiment of the super capacitor according to the invention,
Fig 3 displays a partition wall separating the electrochemical cells of the super capacitor together with O-ring rubber seals, which have been placed between the partition wall and super capacitor housing.
BEST MODE FOR CARRYING OUT THE INVENTION
Fig 1 displays the simplified cross-section of the super capacitor according to the invention in which 1 is the housing and 2 are capacitor cells, 3 and 4 are covers and 5 and 6 are current terminals.
Fig 3 displays the partition wall separating the cells of the super capacitor in which 1 is the super capacitor housing, 7 is the partition wall isolating the individual cells of the super capacitor and 10 is O-ring rubber seals between the super capacitor housing 1 and partition wall 7 for separating the partition wall from the super capacitor housing.
Current invention describes a super capacitor that has two or more electrochemical cells (henceforth capacitors) connected in series formed into its housing, whereas neighbouring cells are provided with a common current terminal, which is minus-terminal with regard to one cell and plus-terminal with regard to the other. The maximum operating voltage of the super capacitor according to the invention is approximately equal to the sum of maximum operating voltages applied to the electrochemical cells that are its components, whereas the total volume and mass of a given capacitor is smaller than that of two conventional capacitor batteries with the same operating voltage, connected in series and having equal gross electrical capacity.
Electrochemical cell consists of two or more pairs of electrodes that are separated from each other by ionic conductors and that contain at least 85% of carbon material of high specific surface area and the dimensions and energy specific characteristics of two or more electrochemical cells are similar.
One of the potential exemplary embodiments of the super capacitor according to the invention is displayed schematically on Fig 2.
Serial connection of super capacitors is normally used to achieve the necessary operating voltage, whereas individual cells are connected into a common capacitor battery. Also, electrical connections of cells require significant volume and these connections must endure great loads (up to 1000A), which is why bulky metal connectors are normally used for these connections.
Super capacitor according to current invention includes the capacitor housing 1 (Fig 2), with at least two electrochemical cells 2 fitted into it, whereas the housing 1 has been closed by covers 3 and 4 on both ends, onto which the external current terminals 5 and 6, respectively, have been installed. Electrochemical cells 2 have been electrically connected by a partition wall made of metal 7. The partition wall 7 (Fig 2, Fig 3) is surrounded by an O-ring type of rubber seal 1 1 , which hermetically seals the electrochemical cells 2 from each other. The partition wall 7 constitutes the aforementioned common current terminal between the adjacent electrochemical cells. The external current terminals 5 and 6 of the capacitor are electrically connected correspondingly with electrochemical cells 2. External current terminals 5 and 6 have been separated from the common super capacitor housing 1 for example by plastic washers, which are made up of the internal insulating washer 8, insulating washer 15 and external insulating washer 13. Internal insulating washer 8 and insulating washer 15 have been placed one on each side of the capacitor Cover 3, 4, insulating the external current terminals 5, 6 from capacitor covers 3, 4. External insulating washer 13 has been placed around the base part of the external current terminal 5, 6, located inside the super capacitor, so as to insulate the current terminal 5, 6 from the super capacitor housing 1. Also, the external current terminal and cover are tightened against each other for example by an O-ring rubber seal 9, which is located also between the two insulating washers - the internal insulating washer 8 and insulating washer 15.
The common super capacitor housing 1 can, in an alternative embodiment of the invention, be in electrical contact with the partition wall 7, which in that instance will readily provide an electrical control over each individual electrochemical cell 2.
The above described structure and design shall provide the super capacitor according to the invention a substantial advantage in terms of volume and mass when compared with arranging the electrical connections of separate individual cells by external connections. The housing with live partition wall enables, in addition to observing and controlling the voltage of individual electrochemical cells 2, also to perform electronic stabilisation of voltages, in order to protect electrochemical cells form potential overvoltage and counter polarity.
Taking as a basis a super capacitor cell with the external dimensions of the aluminium housing being 47*47mm and the height being 45mm, it would result in a capacity of 766F for an individual cell with covers, which would give a calculated energy per volume of 21 .4J/cm 3 at the voltage of 2.7V according to the formula
E=CU 2 /2V, in which E is the capacitor energy [JJ, C-capacity [F], U-cell operating voltage [V] and V is the capacitor cell volume [cm 3 ]. By extending the super capacitor cell aluminium housing dimensions to 170mm (see example 6 in table 1) the cell total capacity would be 4760F, whereas specific capacity would reach to 42.7J/cm 3 .
By applying the embodiment according to present invention as described above, the energy per volume of the super capacitor can be increased by at least 10%, when compared with a standard single-cell capacitor by using electrochemical cells of similar dimensions. By using for example a double 45 mm long capacitor design (see example 7 in table 2), or in other words, by accommodating into 92 mm long aluminium housing (2*45 mm without terminals) two electrochemical cells separated by a partition wall, the calculated specific capacity of the entire system would be 23.8J/cm 3 . In addition to the aforementioned energy the super capacitor also needs to guarantee certain power output properties. The capacity output characteristics are based on the capacitor internal resistance R, from which the specific output is derived according to the following formula: P=U 2 /4RV. In case of a capacitor with 45 mm long housing (example 1 in table 1), specific capacity of 39kW/L is achieved for the corresponding cell. By employing the capacitor structure according to the invention, the two-cell super capacitor of that kind (example 7 in table 2) achieves a specific capacity value of 43.7kW/L, which is -1 1% higher when compared with a single cell. By extending the single cell dimensions to 155mm (example 2 in table 1), the specific capacity of 41 .6kW/L is achieved. By employing idea according to the example 8 in table 2 of current invention, the specific capacity achieves a value of 44.8kW/L, which exceeds the special characteristics of the corresponding single cell by 8 %.
Table 1. Calculated parameters of super capacitors with one electrochemical cell of prior art.
EXAMPLE 1 2 3 4 5 6
Capacity F 766 1565 2363 3161 3960 4758
Total volume cm 3 99 155 210 265 320 376
Specific capacity F/cm 3 , 5.9 8.4 9.8 10.7 11.3 11 .7
Dimensions (w*l*h) mm 47x47x45 47x47x70 47x47x95 47x47x120 47x47x145 47x47x170
Height with terminals mm 59 84 109 134 159 184
Total volume* cm 3 130 186 241 296 351 406
Specific energy* J/cm 3 21.4 30.7 35.8 38.9 41.1 42.7
Specific output * kW/L 39.3 41.6 36.6 30.9 25.8 21 .8 calculated with terminals fable 2. Calculated parameters of super capacitors with two electrochemical cells according to the invention.
EXAMPLE 7 8 9 10 11 12
Capacity F 383 782.5 1 181.5 1580.5 1980 2379
Total volume* cm 3 130 186 241 296 351 406
Dimensions (w*l*h) mm 47x47x92 47x47x142 47x47x192 47x47x242 47x47x292 47x47x342
Height with terminals mm 106 156 206 256 306 356
Total volume cm 3 234 345 455 566 676 786
Specific energy * J/cm 3 , 23.8 33.1 37.9 40.7 42.7 44.1
Specific output * kW/L 43.7 44.8 38.7 32.4 26.8 22.5
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