Patent Application
20130286544
The present invention concerns the general technical field of electrical energy storage assemblies.
In the present invention by “electrical energy storage assembly” is meant a supercapacitor (i.e. a system comprising at least two electrodes whose material is of same type—for example activated carbon—an electrolyte and at least one separator) or a battery (i.e. a system comprising at least two electrodes made in different materials, an electrolyte and at least one separator) or an electrolytic capacitor (i.e. a system comprising at least two electrodes in aluminium, an electrolyte and at least one separator).
Different types of supercapacitors are known. These supercapacitors are intended to be connected to each other to form modules for the following reasons.
Two different unit supercapacitor structures, having a unit voltage generally of less than 3.0 V and operating in an organic medium, are generally used:
In general, the design of cylindrical supercapacitors allows an electrical energy storage assembly to be obtained whose series resistance is lower than that of prismatic supercapacitors: current collection is at times obtained directly by laser welding on the coil as described in document EP1964138, which allows a considerable reduction in contact electrical resistance.
However cylindrical supercapacitors have a disadvantage: the energy density of the modules obtained by electrically connecting several cylindrical supercapacitors is lower than the energy density of the modules obtained with the electrical connecting of several prismatic supercapacitors. Modules with cylindrical supercapacitors are less compact than modules with prismatic supercapacitors due to the presence of a dead volume between two adjacent cylindrical supercapacitors.
Yet a module forms the basic unit of applications. A unit supercapacitor effectively cannot be used alone due to its low voltage (in general 2.7 V or 2.8 V). The advantage of a prismatic supercapacitor is its volumetric energy density.
However the series resistance of prismatic supercapacitors is generally much higher than that of cylindrical supercapacitors on account of the type of current collection which is obtained by a screwed mounting, hence costly in terms of labour and parts.
This strong series resistance is the major drawback of the technology since it involves very strong heating (Joule effect) which leads to accelerated ageing of modules.
Appended Table II gives the values of volumetric and gravimetric energy densities:
It is ascertained in Table I that the series resistance of a module containing prismatic supercapacitors is 25% higher than that of a module containing cylindrical supercapacitors. It is also ascertained that the gravimetric energy density of a module containing prismatic supercapacitors is 25% higher than that of a module containing cylindrical supercapacitors.
Table I also shows that prismatic supercapacitors, on account of their complex mounting, generally have a higher number of parts than a cylindrical supercapacitor.
Problems inherent in the module assembling of prismatic supercapacitors are therefore the additional number of parts (packing, heat sink, . . . ), labour-intensive process, large weight contribution of inactive components (generally at least 50% of total weight). Finally, component assembly requires the use of welding to join components via bars. To withstand vibration tests, it is therefore important to form a robust structure, and hence most generally a solid structure.
Cylindrical and prismatic supercapacitors therefore each have advantages and disadvantages.
Whether cylindrical or prismatic, the voltage of supercapacitors working in an organic electrolytic medium—such as TEABF4 in acetonitrile—is limited to around 6 V for organic electrolytes and in the region of I V for aqueous electrolytes (Ref: “Electrochemical Properties of Organic Liquid Electrolytes Based on Quaternary Onium Salts for Electrical Double-Layer Capacitors” Makoto Ue, Kazuhiko Ida and Schoichiro Mori, J. Electrochem. Soc. Vol. 141, No 11, 1994).
Over and above this voltage total degradation is observed of the electrolyte (solvent and salt). In addition, the higher the operating voltage of a supercapacitor the faster the degradation of the electrolyte, and hence the shorter the lifespan of the supercapacitor.
On this account, manufacturers of supercapacitors produce supercapacitors whose nominal voltage is limited to 2.7 V, even 2.8 V, for organic electrolytes. This voltage is a trade-off between lifetime and energy performance level of the supercapacitor.
The energy of a supercapacitor is directly related to voltage via the formula:
E=½C·U2
A unit supercapacitor therefore has a low operating voltage. This is why a unit supercapacitor cannot be used alone in the vast majority of applications.
As recalled above, supercapacitors are therefore generally assembled to form a module operating at a high voltage—the operating voltage of the module being equal to the sum of the nominal voltages of the supercapacitors when mounted in series. In general, the sizing of applications lays down minimum and maximum operating voltages and required energy. From these parameters is determined the number of necessary components to obtain the voltage and total capacitance of the module. As a result, the unit capacitance of each component is calculated, then each supercapacitor is sized in relation thereto. However, depending upon applications, the parameters of voltage and energy and therefore the sizing of the supercapacitor vary. This raises a major disadvantage for the manufacturer who is unable to use one same supercapacitor irrespective of the application.
It is one objective of the present invention to propose a prismatic supercapacitor whose operating voltage is higher than that of existing prismatic supercapacitors, to allow the production of modules operating under high voltage.
A further objective of the invention is to propose a prismatic supercapacitor whose series resistance is lower than that of existing prismatic supercapacitors.
For this purpose an electrical energy storage assembly is proposed, comprising:
In the present invention by “stacked complexes” is meant complexes at least partly superimposed over each other. It is noted that complexes wound together in coils to obtain a coiled element are not considered to be stacked complexes in the meaning of the present invention.
For example, each of the complexes located at one end of the stack is connected to or forms one of the connection terminals, each particularly being connected to or forming a separate connection terminal. Said storage assembly in fact comprises at least one separate complex connected to each respective terminal of the assembly, and at least one complex which is not connected to any terminal of the assembly and whose potential is therefore not imposed by one of these terminals.
Said energy storage assembly can withstand a higher voltage than a prior art assembly. In the assembly of the invention only some of the complexes, each forming a terminal of two adjacent unit elements (each unit element being formed by two complexes and forming a capacitor, a supercapacitor or a battery), are connected to an external generator. The other complexes are arranged in “floating” manner i.e. not connected to the outside.
The unit elements of the assembly behave as if they were in series. Therefore, when the complexes electrically connected to the outside of the assembly are well chosen, for example they are positioned at the ends of the stack, the voltage of the external generator is not delivered to each unit element as is the case in the state of the art, but to a set of unit elements in series i.e. those located between the two complexes connected to the outside. The unit voltage applied to each unit element is therefore equal to the voltage applied to the terminals of the assembly divided by the number of unit elements between the two connected complexes.
It is therefore possible to prevent degradation of the electrolyte, irrespective of the voltage applied to the terminals of the assembly, if the number of unit elements is wisely chosen so that the local voltage is sufficiently low to avoid electrolyte degradation. On this account, by means of the invention, it is easy to create an energy storage assembly that operates reliably even if subjected to a high voltage. Said assembly is additionally of simple design, reduced size and obviates the need for interconnects such as bars or balancing circuitry, which allows a reduction in the manufacturing costs of the assembly.
It also allows a module to be obtained of large capacitance and low resistance. Since each assembly operates at the voltage it is desired to apply to the application, it is possible to arrange different assemblies in parallel and not in series, which makes it possible to add together the capacitances of the different assemblies and not to obtain a total capacitance of the assemblies that is lower than the capacitance of each assembly as is the case when the assemblies are connected in series. On the other hand, due to this assembly in parallel, the total resistance of the assemblies is lower than the resistance of each assembly, which is advantageous in particular to prevent over-heating of the module.
Therefore, with the assembly of the invention it is possible to obtain supercapacitors having good electrical properties whilst being low-cost and simple to produce. The electrical energy storage assembly may also comprise a housing intended to receive the stack formed of complexes and of the separator or separators, the housing containing an electrolyte for impregnation of the complexes. This housing is advantageously formed of a single compartment. Therefore the complexes are not each placed in a respective compartment but are placed in one single compartment.
Preferred but non-limiting aspects of the energy storage assembly of the invention are the following:
The invention also concerns a module comprising a casing comprising at least one assembly of the invention.
Preferred but non-limiting aspects of the module of the invention are the following:
Other characteristics, objectives and advantages of the present invention will become apparent from the following description which is purely illustrative and non-limiting and is to be read with reference to the appended drawings in which:
For better understanding of the invention, the operating principle of a supercapacitor will briefly be recalled.
A supercapacitor is conventionally formed of two complexes 1, 2, of a separator 3 between the two complexes 1,2 and of an electrolyte.
The separator 3 is made of electrically insulating material.
The electrolyte may be an aqueous medium or an organic medium. In all cases, the electrolyte comprises ions and is electrically conductive. One pertinent example of an electrolyte is tetraethylammonium difluoromono[1,2-oxalato(2-)-o,o′]borat(1-), (or [TEABF2Ox]).
Each complex 1, 2 comprises a current collector 11, 21 and at least one electrode 12, 13, 22, 23.
Each electrode 12, 13, 22, 23 is made from activated carbon, a conductive additive and one (or more) polymers to bind the two preceding constituents. This electrode 12, 13, 22, 23 is then coated or extruded on the current collector 11, 21. It forms the active material of the complex 1, 2.
The constituent material of the current collector 11, 21 is aluminium, nickel, copper or stainless steel for example. The material of the current collector 11, 21 is chosen for its chemical and electrochemical inertia against the constituents of the electrode 12, 13, 22 and 23 of the electrolyte.
The distance between the electrodes 12, 22, 13, 23 is generally in the order of a few tens of micrometres (in general between 15 and 45 μm) i.e. more than 10,000 times greater than the size of the ions. This can guarantee that an ion is therefore unable to be in contact simultaneously with the two electrodes 12, 22, 13, 23.
In a supercapacitor, electrical energy storage is obtained by movement of ions within the porosity of the activated carbon forming the electrodes. The size of the ions is in the order of 0.3 to 0.7 nm ([B. E. Conway, R. E. Verall, J. E. Desnoyers, Trans. Faraday Soc. 62, pp 2738-2744, 1966]-[R. A. Robinson, R. H. Stokes, Electrolyte Solutions, 2nd Edition, Butterworths, London, 1965]-[W. G. Pell, B. E. Conway, N. Marincic, J. Electroanal. Chemistry 491, pp 9-21, 2000]-[M. Endo, Y. J. Kim, H. Ohta, K. Ishii, T. Inoue, T. Hayashi, Y. Nishimura, T. Maeda, M. S. Dresselhaus, Carbon 40, pp 2613-2626, 2002]).
When a voltage is applied to the terminals of a supercapacitor it generates an electric field. Under the effect of this electric and electrostatic field, the positive ions (e.g. TEA+) will preferably move towards the negative electrode and the negative ions (e.g. BF4−) will move towards the positive electrode.
Therefore, the total equivalent capacitance of the component is (C+×C−)/(C++C−). If C+ and C− are of same order, the total equivalent capacitance is C/2.
Total degradation of the electrolyte only occurs as from the time the voltage between the two electrodes of opposite signs is in the order of 6 V for organic electrolytes and in the order of 1 V for aqueous electrolytes. By strongly limiting the voltage between the electrodes of opposite signs, the ageing of the supercapacitor is limited.
It is one objective of the invention to allow an increase in voltage at the terminals of a supercapacitor without accelerating the ageing thereof.
One solution to this problem is to form a supercapacitor comprising a stack of electrodes 12, 22, 13, 23 of opposite signs, of which only the electrodes positioned at the ends of the stack are electrically connected to the outside of the supercapacitor. The other electrodes of the supercapacitor are therefore in “floating” position i.e. not connected to the outside.
A description will now be given of different embodiments of the storage assembly according to the invention with reference to the Figures. In these different Figures, equivalent parts of the storage assembly carry the same reference numbers.
With reference to
The separator 3 is in electrically insulating material. The separator 3 extends between the first and second complexes 1, 2. It ensures electrical insulation between the first complexes 1 and second complexes 2.
In the embodiment illustrated in
The structure of the supercapacitor in
The separator 3 extends accordion-wise: it comprises at least three sections 34, two adjacent sections being connected at a fold-line 35 to form a fold having a concave side and a convex side.
Each first complex 1 extends chevron-wise: it comprises two single sections 14 connected along a fold-line 15 to form a complex fold having a concave side and a convex side. The concave side of each first complex 1 is intended to come and lie opposite a respective convex side of the first face 31 of the separator 3.
Similarly, each second complex 2 extends chevron-wise and has a concave side and a convex side. Here again, the concave side of each second complex 2 is intended to come and lie opposite a respective convex side of the second face 32 of the separator 3.
Each first complex 1 faces a second complex 2 to form a unit element 4. The first and second complexes of a unit element 4 are offset from each other by a section 34 of separator 3. In other words, each first complex 1 is folded along a fold-line 15 and is arranged on a respective convex side of the first face 31 of the separator 3 so that the fold-line 15 of each first complex 1 coincides with a respective fold-line 35 of the separator 3. Similarly, each second complex 2 is folded along a fold-line 25 and is arranged on a respective convex side of the second face 32 of the separator 3 so that the fold-line 25 of each second complex 2 coincides with a respective fold-line 35 of the separator.
The final supercapacitor may be formed of several unit elements 4 arranged in series and separated two by two by a separator section to form a stack 5.
The fold-lines 35 of the separator 3 form the sides 51 of the stack 5. A section 16 of a first complex 1′ is located at a first end of the stack so as to form the top of the stack 5 and a section 26 of a second complex 2′ is located at a second end of the stack so as to form the underside of the stack 5.
The first complex 1′ located at the first end of the stack 5 is intended to be electrically connected to (or to form) a first connection terminal of the storage assembly. The second complex 2′ located at the second end of the stack 5 is intended to be electrically connect to (or to form) a second connection terminal of the storage assembly.
The first complex 1′ forms a first sample of complexes. The second complex 2′ forms a second sample of complexes. In the present invention by “first sample of complexes” (respectively “second sample of complexes”) is meant a group of complexes intended to be electrically connected to (or to form) the first (respectively second) connection terminal of the storage assembly.
In the embodiment illustrated in
The reader will appreciate that the number of complexes belonging to the combining of the two samples is less than the total number of complexes and the intersection of the two samples is a void assembly.
In other words:
This means:
The stack 5 is arranged in a housing 6 illustrated in
This housing 6 may be rigid and of parallelepiped shape for example, as illustrated in
The fact that only two complexes 1′, 2′ of the stacked element 5 project beyond the separator 3 and are electrically connected to the upper and lower lids 7,8, the other complexes “floating”, means that it is possible to reduce the risks of short-circuiting between the different complexes 1, 2 of the stacked element 5, and more especially to apply a high voltage to the terminals of the supercapacitor without degrading the electrolyte however, as explained above.
Advantageously the separator 3 can be designed sufficiently long so that the end portions 36 thereof are folded over such that they overlap the sides of the stack 5 comprising the fold-lines 35, to cover (or hoop wrap) the stacked element 5 as can be seen in
In some embodiments, the section 16 of the first complex 1′ forming the top of the stack 5 does not have any electrode on its surface facing the lid 7. This firstly allows the facilitated electrical connection of the upper lid 7 to the first complex 1′ forming the top of the stacked element 5, and secondly a reduction in the electrical resistance between the lid 7 and the complex 1′. Similarly, the section 26 of the second complex 2′ forming the underside of the stack 5 can be devoid of any electrode on its surface facing the second lid 8.
One advantage of the structure of the supercapacitor illustrated in
The structure of the prismatic supercapacitor of the invention allows the voltage to be varied at the terminals of the supercapacitor in relation to the number of constituent electrodes of the stacked element 5 of the supercapacitor as explained above.
In addition, the structure of the prismatic supercapacitor prevents the creation of any parasitic induced current, since the supercapacitors produced are not coiled contrary to cylindrical supercapacitors.
The use of supercapacitors according to the invention in modules also allows elimination of the balancing circuitry of the module. The working voltage between two unit electrodes of the supercapacitor can be chosen to be sufficiently low to prevent ageing. For example, it can be chosen to maintain a voltage of 2.3 V between two opposite-facing electrodes of the supercapacitor. On this account, gas generation is very strongly limited and the fabrication of the module does not require any very rigid component to withstand an increase in internal pressure.
Since the supercapacitor can be sized so that the voltage between its terminals is equal to the desired voltage in the intended application, it is possible to fabricate modules in which the supercapacitors are mounted in parallel, which is highly advantageous both for the capacitance and total resistance of the module.
a and 4b illustrate another embodiment of the supercapacitor of the invention. In this embodiment, the housing 6 containing the stack 5 is made in a gas-tight and electrolyte-tight flexible material.
For example, the housing 6 may be formed of one (or more) heat-sealable sheets (whether or not with foil laminate) and whether or not folded over. The detailed characteristics of said housing are notably described in document U.S. Pat. No. 4,092,464. Said housing is already given industrial use in particular to receive lithium-ion and lithium-polymer batteries dedicated to portable applications (mobile telephones, PDAs, GPS, etc.).
Advantageously, one portion of the section 16 of the first complex 1′ forming the top of the stacked element 5 projects outside the housing 6. This portion of the section 16 acts as first electrical connection terminal to the supercapacitor. Similarly, one portion of the section 26 of the second complex 2′ forming the underside of the stacked element 5 projects outside the housing 6.
This portion 26 acts as second electrical connection terminal to the supercapacitor. These connection terminals are used for example to connect the supercapacitor electrically to another supercapacitor.
In this embodiment the sections 16, 26 of the first and second complexes 1′, 2′, forming the top and underside of the stacked element 5, comprise a single electrode positioned facing the remainder of the stack, in particular facing the adjacent electrode. In addition the collector of each section 16, 26, is extended so as to project from the housing 6, the portion of the collector projecting from the housing being devoid of any electrode.
In the embodiment illustrated in
As in the embodiment illustrated in
The different separators 3, 3′, 3″, 3′″ and their associated complexes 1, 2 are stacked on each other to form the stack 5. This embodiment with separators of finite length allows a stacked element to be formed irrespective of its desired height.
In a third embodiment, illustrated in
A description will now be given of a method for assembling an assembly according to the third embodiment of the invention.
The fabrication of said assembly can be conducted using the following steps:
A description will now be given of variants of embodiment of the invention.
In this invention, it will be noted that the assembly does not necessarily comprise two-faced complexes (i.e. the complex comprises a current collector and two opposite electrodes either side of the collector). All the complexes of the module can be single-sided on a collector (i.e. the complex comprises a current collector and one electrode on one of the faces of the collector) or more advantageously at least some complexes may be self-supporting (i.e. the complex solely comprises one electrode and does not comprise any current collector) as described for example in patents FR 2871615 and FR2759087. In this case, the stacked complexes and the energy density are increased compared with the component comprising a collector. This solution is also economically advantageous since it allows substantial limitation of the use of a collector, this being an expensive constituent in supercapacitors, and the use of one same complex for supercapacitors operating in an organic medium or aqueous medium for which the collectors usually used are not the same.
The complexes and the separators may evidently be of simpler design than the description given, each being planar.
It will also be noted as shown in
It is then possible as illustrated in
As illustrated more clearly in
Before being placed in the housing 6, the element 47 is folded over along a fold-line 49 extending to the centre thereof so that the first half of the element forms an end complex 46C of a first stack 5C and the second half thereof forms an end complex 46D of an adjacent stack 5D. The region without any electrode then projects outside the housing 6. To ensure the seal of the assembly provided with said complex it is necessary however to add a fusible material 50 between the two halves of the complex, for example when heat sealing the casing. This material is placed on the surface opposite the surface on which the electrode has been deposited.
It will also be noted that a sheet of sealing material 57 such as the one forming the housing can be placed in the housing between two stacks. The presence of such sheet is optional however.
One means of simplifying an assembly comprising several stacks is to form an assembly such as described in
As illustrated in
In one variant of embodiment, the thicknesses of the electrodes deposited on the two faces of the collector are different. If an electrolyte is used whose cation is more voluminous than the anion (diameter of the ion), the negative electrode is preferably chosen to be the thinnest to limit ageing. It is possible however to choose a thicker negative electrode with a view to increasing energy density. This choice is made however to the detriment of ageing.
In another embodiment, the assembly comprises complexes with a collector and battery electrodes, i.e. electrodes made of different materials and respectively forming the cathode and anode of the battery. In this case, the collector is preferably chosen to form an ion barrier. One first face of the collector comprises one type of electrode (e.g. cathode) and a second face comprises the electrode of opposite polarity (anode). The anode may be formed of metal Lithium for example or graphite or a carbon material or insertion compound (tin, antimony, silicon, sulfur, etc.) whereas the cathode can be in LiFePO4 for example. The thicknesses of the two electrodes can also be different. This makes it possible to considerably increase the density of the batteries, as in the case of the previously described supercapacitors.
The results in appended Table II were obtained with a supercapacitor of the following type:
It was found that the mean value of the capacitance obtained was very close to the expected theoretical value.
The time constant remained less than one second, which clearly shows the standard behaviour of the supercapacitor thus obtained.
Fabrication of a Module from Supercapacitors of the Invention:
A description will now be given, with reference to
Each supercapacitor 9 was composed of a stack 5 comprising two connection terminals 16, 26.
The supercapacitors were arranged so that:
These two planes P+, P− extended either side of the supercapacitors 9. All these connection terminals can be mechanically secured together using glue or resin 91 to form a block as illustrated in
The “edges” 92, 93 either side of the module thus formed were then joined together to form only two connection pads of the module. The edges 92, 93 can advantageously be of size equal to the size of the connection terminals 16, 26 of the supercapacitors. This makes it possible for the current to be conducted in uniform manner (identical potential over the entire supercapacitor) and also to form an efficient “radiator” for the supercapacitor.
The edges 92, 93 can be laid flat as described in document FR 2 921 195 for the purpose of welding them together as illustrated in
For the electrical connecting of the edges 92, 93, a metal plate 94 can be welded to (or brazed onto) the edges 92, 93 previously laid flat and assembled, laid flat and non-assembled previously, not laid flat and previously assembled or not previously laid flat and assembled.
By laying the edges 92, 93 flat and assembling the metal plate 94 directly onto the flattened edges it is possible to reduce contact electrical resistance. The metal plate 94 thus assembled also allows heat to be dissipated efficiently towards outside the module. Each plate 94 can be made in aluminium which provides a thermal advantage and may comprise grooves to improve heat dissipation.
The connection to the application can be made via a pin 95 positioned in the centre of the plate 94 to distribute the current uniformly as illustrated in
Verticalisation of the supercapacitors facilitates dissipation of the heat produced during module charging/discharging: vertical supercapacitors therefore act as thermal “radiator”.
The supercapacitors can be placed directly side by side. It is also possible to position interstices 97 between the supercapacitors. These interstices 97 can be formed of a rigid material for mechanical reinforcement of the module. These interstices can also be formed of a polymer material (e.g. of gad pad type) to improve heat dissipation performance.
It is also possible to insert mould the entire module obtained (as is the case for electric motors for example). This makes it possible to provide against leaks whilst rigidifying the module.
The sidewalls 96 of the module can be made in plastic material for electrical insulation of the two poles of the module.
The entire module can also be coated with an insulating cladding only leaving the two connection pins 95 of the module protruding to provide against any user or utilization safety problems. This cladding can be flexible or can be formed by insert moulding (e.g. by immersion). Preferably, the thickness of this cladding is sufficiently thin to facilitate heat dissipation.
It can also be contemplated that the protruding portions of the end complexes project not over the height of the module but over its length. In this case, two opposite sidewalls can be conductive whilst the other walls of the modules are insulating.
In another configuration, all the walls of the modules are insulating: each terminal respectively groups together the complexes respectively forming a positive and negative terminal of each assembly, and passes through one or more walls of the module. In this embodiment, it is then possible to position the terminals of the module on the same side.
It will also be noted that if several stacks are placed in a single housing, an assembly may itself form a module which can be used for one of the applications described below.
To highlight the advantage of the supercapacitor of the invention a comparison will now be made between sizing methods for:
It is recalled that one advantage of the invention is to be able to obtain compact, high voltage supercapacitors.
The problem to be solved for any manufacturer of supercapacitors and modules is, within a given volume, to adapt the assembly of supercapacitors of high unit capacitance (generally higher than 500 F) to a voltage set by the application (generally very high compared to the unit voltage which each supercapacitor is able to withstand) and to minimum useful energy.
Let us assume the following input data:
Umax·application=120V·Umin·application=60 V
The voltage of the application entails a necessary number of supercapacitors:
The problem of choice facing the manufacturer can immediately be seen: the use of 44 cylindrical supercapacitors appears to be more advantageous than the use of a higher number (48 supercapacitors); however, the use of 44 supercapacitors can only correspond to 4 rows of 11 components, which is not advantageous in terms of volumetric sizing. Sizing based on 40 components appears to be more compact (8 rows of 5 components) but is particular harsh in terms of ageing having regard to the higher voltage applied to the terminals of each supercapacitor.
The required energy determines the sizing of each supercapacitor:
200 kJ=½C((Umax)2−(Umin)2)
200 000×2/(1202−602)=37.04 F
If each supercapacitor operates at 2.5 V, a unit capacitance of 1778 F is obtained for each supercapacitor.
If each supercapacitor operates at 2.73 V the capacitance is then 1630 F.
If each supercapacitor operates at 3.0 V the capacitance is then 1482 F.
Similarly this generates the development of lids, casings etc. to fabricate these supercapacitors which do not exist in the manufacturer's range. It can easily be seen that for each application the capacitance of the supercapacitor will be different.
In addition, by causing a supercapacitor to work at 2.5 V or 2.3 V even 3.0 V this leads to a considerable change in the components of the electronic balancing circuitry.
It is therefore not economically advantageous, for each application, to modify the unit voltage of the supercapacitor. This unit voltage is therefore an additional constraint having a direct influence on the sizing of the final module. Also the self-discharging of each supercapacitor will not be the same depending on the unit voltage of the supercapacitor (higher voltage loss AU at a set time if the unit voltage U increases).
The energy is achieved with 50 supercapacitors; this represents a module comprising 5 rows of 10 supercapacitors.
The diameter of each supercapacitor is 6.2 cm and the height with bar is 11 cm. The capacitance of the electrode is 30 F/cm3. The active layer (layer containing the active material) is 10 cm. The volumetric energy at the supercapacitor (without bar) is 4.4 Wh/L at 2.4 V.
The necessary space between each supercapacitor to prevent short-circuiting problems is 2 mm on each side of a supercapacitor. This space is the same between a supercapacitor and the sidewall of the module. The thickness of the sidewalls is 3 mm. The thickness of the elastomer insulators (upper and lower) is 3 mm each. The thickness of the upper and lower covers is also 3 mm.
The volume of the module is therefore equal to: 328 mm×648 mm×122 mm=25.9 litres. The volumetric energy of this module is 2.15 Wh/L. In the field of automotive vehicles it is sometimes useful for vehicles consuming greater energy to provide a module having higher energy (e.g. up to 500 kJ). Nonetheless, for obvious economic reasons—choice of converter, interconnects and electronic circuit boards—the working voltage will be the same (maximum 120 V). This voltage is generally set by the converter, by associated power electronics and the electric motor used.
Applying the same type of sizing (2.7 V/supercapacitor, Umax=120 V and Umin=60 V), the unit supercapacitance is 4167 F. The diameter of each component is then 6.7 cm and the height of the component is 17.8 cm. The energy density of the component is then 4.2 Wh/L at 2.7 V. The volume of the module is then H×L×W (in dm)=1.9×6.29 (row of 9 components)×3.53 (row of 5 components)=42.2 L. The energy density of the module is then 3.30 Wh/L.
The above calculations are made as explained above, taking into account the characteristics of the module made from the following coiled components of unit capacitance 4167 F:
Organisation: 9 rows of 5 lines of components (total of 45). Intercomponent space: 2 mm.
Thickness of the bar included in the lid.
Thickness of the lids: 3 mm
Thickness of elastomer insulators: 3 mm.
For an application having a peak working amperage of 500 A, the two supercapacitors connected to the terminals of the module are subjected to very high amperage and hence to high over-heating compared with the other supercapacitors of the module, and hence to accelerated ageing.
In addition, the assembling of the supercapacitors into a module has a major disadvantage: the potential of each supercapacitor at the lower (respectively upper) lid is different at every point. This requires the adding of electrically insulating materials able to withstand a high breakdown voltage. However, the materials used must be thermally capable of evacuating heat which also generally entails a major difficulty for the obtaining of a module which performs well. The invention provides most interesting means for overcoming this problem and for strongly limiting the use of these costly materials.
Appended Table III gives the sizing of modules of varying energy (200 kJ and 500 kJ). With the invention it is possible to meet different required energy values but with one same voltage level and one same type of energy storage assembly of which only the number thereof varies. These assemblies, or supercapacitors, are electrically connected in parallel to obtain the aforementioned result.
As shown by the result obtained with the 500 kJ module, for an identical voltage the volume is reduced by 28% compared with the solution proposed using coiled components.
For the 200 kJ module, the gain is 45%.
The invention also shows that it is not necessary to increase voltage to reach a high energy density.
In the prior art, as detailed above, the obtaining of modules with variable energy but with identical voltage cannot be based on an identical unit since the voltage and capacitance parameters vary when the number of supercapacitors of identical capacitance is changed. This is economically detrimental.
In the invention, an identical unit assembly can be adopted to obtain different energy values when the voltage is identical, as shown in Table III, since the voltage of the assembly is the voltage of the application. This strategy strongly simplifies assembling and reduces the manufacturing costs of such assemblies with a view to forming a module.
The supercapacitors of the invention are capable of operating at the application voltage.
Let us assume the following input data, identical to the data used to prepare the prior art module:
Umaxapplication=120 V; Uminapplication=60 V
The voltage of each supercapacitor is a function of the number of sheets stacked in the stacked element.
If drastic limiting of ageing is required, it is possible to cause the opposite-facing electrodes to operate at a maximum voltage of 2.4 V.
With 51 sheets (hence 50 planar capacitors in series) the voltage between electrodes is 2.40 V. It will be noted that the number of sheets is not a limiting factor as regards choice: there is nothing to prevent the use of only 45 sheets operating in pairs at 2.7 V.
The capacitance to be reached is 37.04 F for the final module. By using a prismatic supercapacitor having a unit capacitance of 4.63 F, it is sufficient to mount 8 prismatic supercapacitors (or assemblies) in parallel to obtain the final desired module.
Unit dimensions of the sheet:
Electrode capacitance: 30 F/cm3
49 double-sided stacked sheets of thickness 230 μm and 2 single-sided sheets of thickness 130 μm identical to those used in the preceding example (i.e. a total of 51 sheets).
A width of 16 cm is a good compromise to limit resistance with a complex of this thickness. The volume of an electrode is therefore calculated as follows:
Volume of an electrode=L×16×0.01 cm3.
The theoretical capacitance to be attained is 4.63 Farad, as explained above. It is calculated as follows:
Theoretical capacitance to be reached=electrode volume×volumetric capacitance/number of stacked supercapacitors (=number of separators)=electrode volume×30/50.
The volume of an electrode layer is therefore 7.712 cm3.
The length of the unit electrode is therefore L=7.712/(0.01×16) i.e. about 48.2 cm (or 482 mm as indicated in Table III).
As can be seen, the sizing of the electrode is solely limited by the length of the electrode, which amounts to sizing the length of the housing for the final module covering the electrode i.e. not a mechanical part but a film that can be unwound and cut to the desired size. It is therefore easy to adapt the assembly to the desired application.
The final module will therefore have the following minimum dimensions (reference can be made to Table III).
For each assembly:
These electrodes have an active size of 16 cm×48.2 cm and the single-sided electrodes also comprise a collecting extension (forming a connection terminal) of 3 cm, increasing the width of the module.
Casing to form the housing of thickness 2 mm (hence a total of 4 mm as indicated in Table III) and outer dimensions: (16+2) cm×(48.2+2) cm=18 cm×50.2 cm.
Therefore the following dimensions are obtained for the assembly:
Total thickness: 1.7 cm;
Total height: 19 cm (taking into account the collecting extension);
Total length: 50.2 cm.
The total dimensions of the module comprising 8 assemblies of 4.63 F/unit at 120 V such as described above are as follows:
Width of module: 14.5 cm;
Total length: 51.2 cm (taking into account the necessary spacing for assembling the assemblies);
Total height: 19 cm.
This width is reached since, between the assemblies a spacer is added for efficient heat evacuation (heat-conductive material). Each spacer may have a thickness of 1 mm.
Consideration is also given to the thickness of the sidewalls of the final module, which may be 3 mm. These sidewalls are chosen to be insulating or conductive depending on the positioning of the module terminals, so as not to perturb the electrical functioning of the supercapacitor.
The module does not require balancing circuitry since the unit voltages between sheets are low (2.4 V) and the assemblies are mounted in parallel.
A module is therefore obtained having a total volume of: 51.2×14.5×19=14.1 litres.
This therefore represents a savings of 45% in volume compared with a module core made from cylindrical supercapacitors operating at the same voltage.
The volumetric energy density is therefore: 200 kJ/14.1 L=3.9 Wh/L even though the unit working voltage of the electrodes is 2.4 V.
It will be noted that the current of each assembly remains low although the current of the module is high, since the current of each branch is the division of the total current by the number of energy storage assemblies. In the case of the module size here, the application requires a peak current in the order of 500 A on the module. This therefore leads to a unit current of 67.5 A for each assembly which is relatively low. The heating of each supercapacitor is therefore quite limited.
It will be appreciated that one advantage of the invention is to size the module directly via the maximum voltage given by the application.
The desired capacitance level is then determined by the energy to be supplied. The energy is therefore directly dependent upon the capacitance to be provided (by summing) which corresponds to parallel assembling of supercapacitors whose pre-required voltage level is already reached.
Conversely, by fabricating supercapacitors having high capacitance value and low unit voltage, it is generally complex to best meet the constraints of the application on account of the voltage level to be reached: it is therefore simpler to assemble together assemblies of high voltage and low capacitance than the reverse.
A further advantage of a module working at high voltage is the possibility of using a DC/DC converter between the module of supercapacitors and the application (of variable voltage) using lower currents than when operating at low voltage.
To summarize, the advantages of the above-described supercapacitor are the following:
therefore the number of parts used is much lower (optimized fabrication costs);
The reader will appreciate that numerous modifications can be made to the above-described storage assembly and module without departing in substance from the novel teachings and advantages described herein.
Therefore any modifications of this type are to be construed as being incorporated within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1150269 | Jan 2011 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP12/50480 | 1/13/2012 | WO | 00 | 7/11/2013 |
