WO2016045752A1

WO2016045752A1 - Method for packaging and connecting electric storage cells for efficiency and cycle/life expectancy

Info

Publication number: WO2016045752A1
Application number: PCT/EP2014/070684
Authority: WO
Inventors: Peter Coenen; Filip Leemans; Johan De Smet
Original assignee: Vlaamse Instelling Voor Technologisch Onderzoek (Vito) Nv
Priority date: 2014-09-26
Filing date: 2014-09-26
Publication date: 2016-03-31
Also published as: CN105469997A; CN205376309U

Abstract

An energy storage device is described comprising high power energy storage cells in modules, the high power energy storage cells being two-terminal devices. The high power energy storage cells are disposed in a module so that every high power energy storage cell is surrounded on at least a first side by at least a first cooling surface and on at least a second side by at least a second cooling surface, each cooling surface being thermally connected to a different terminal of the high power energy storage cells. The high power energy storage cells are ultracapacitors or supercapacitors or capacitors.

Description

METHOD FOR PACKAGING AND CONNECTING ELECTRIC STORAGE CELLS FOR EFFICIENCY AND CYCLE/LIFE EXPECTANCY

The present invention relates to energy storage devices comprising high power energy storage cells such as ultracapacitors or supercapacitors and methods of constructing and operating these devices. In particular the present invention relates to power/energy sources used to deliver power to drive loads such as to drive vehicles or stationary devices. Technical Background

Ultracapacitors or supercapacitors are electrical storage devices that combine high power density with extended life expectancy. They are therefore particularly well suited for applications allowing frequent recovery of kinetic or potential energy, e.g. city buses, trams, cranes, lifts. Certain types of battery cells, mainly based on Lithium, present the same advantages.

Ultracapacitors are often combined with other energy sources, the energy sources typically being selected to provide different types of power. For example, one source may be designed to provide long-term power (which means it is capable of delivering a large amount of energy over time, and is therefore a high energy source) while another energy source may be designed to provide high short-term power (in which case it is a high power source for a limited time). The high power source may be used to assist the high energy source in providing power to the system during, for example, acceleration of a vehicle or pulsed load events such as a reaction to an emergency situation. The high power source can be provided by ultracapacitors. Combinations of rechargeable energy storage devices such as Lithium batteries and ultracapacitors including balancing circuits are known from WO2009/112069.

One approach to increasing the life time of the ultracapacitors could be to increase their size, i.e. to overdesign them. This could be a possible solution for stationary power sources although the cost and size would be increased and materials would be used unnecessarily. However, for movable objects increasing size typically leads to an increased cost and weight and may be prohibited because of space limitations. For a movable object such as a vehicle this extra weight can also reduce acceleration. Although a major advantage of the ultraca acitor is its high power capability, the duration and total amount of power supply is limited due to heating which is in turn a consequence of the capacitor' s internal resistance, the high currents resulting from high power and the frequent charging and discharging of the capacitor due to the nature of the application cycle. Temperature rise is the main factor decreasing life expectancy of ultracapacitors following Arrhenius' law. According to Arrhenius' law, the life expectancy of a capacitor is halved for every 10°C of temperature rise. As described in WO2012/007290 Al cooling of ultracapacitors can be achieved by a design of casing adding cooling fins and forced ventilation. However, forced ventilation consumes energy and results in a decreased efficiency of the system although improved cooling has an advantage of increased life expectancy, both as calendar life and as cycle life.

Summary of the present invention

An object of the present invention is to provide alternative energy storage devices comprising high power energy storage cells such as ultraca acitors or supercapacitors and/or methods of constructing and operating these devices. In particular an object of the present invention is to provide alternative power/energy sources used to deliver power to drive loads such as to drive vehicles or stationary devices.

Embodiments of the present invention relate to design of a module for high power energy storage cells such as ultracapacitors or supercapacitors. An advantage of embodiments of the present invention is the provision of an energy storage device that has a good lifetime and/or cycle life by keeping the high energy storage cells cool in operation.

The terms "ultracapacitor" "supercapacitor" or "capacitor" are used in this invention and these apply generally to high power energy storage cells.

Accordingly embodiments of the present invention provide an energy storage device comprising high power energy storage cells in modules, wherein there is a limited number of high power energy storage cells such as ultracapacitors or supercapacitors or capacitors per module. The high power energy storage cells such as ultracapacitors or supercapacitors or capacitors are two-terminal devices. The high power energy storage cells such as ultracapacitors or supercapacitors or capacitors are disposed in such a way that every high power energy storage cell such as ultracapacitor or supercapacitor or capacitor is surrounded at least on one side or on at least two sides by a cooling surface. This cooling surface is thermally connected to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors. Each cooling surface can be thermally connected to a different terminal of the high power energy storage cells. The cooling surface can be provided by an extension of bus bars or may be provided by a side or wall of a module casing which is in conductive thermal contact with the extension of the bus bars. In either case, this can have the advantage that heat can be removed from the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors in a plurality of parallel heat paths. Modules according to the present invention may have two or more such cooling surface areas.

A module's dimensions need not be determined by optimal use of space but can be determined by the availability of exterior heat exchanging surface, and hence improved cooling. The high power energy storage cells such as ultracapacitors or supercapacitors or capacitors are arranged in at least one row, each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor has a width "W" and a height "H".

There are "N" high power energy storage cells such as ultracapacitors or supercapacitors or capacitors in a row. The area of the cooling surface thermally connected by thermal conduction to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and provided by an extension of bus bars is equal to at least 30% of (N x W x H). This area may be increased to above 40%, to above 50%, to above 60% to above 70% to above 80% or to above 90% (N x W x H). For cost and space saving reasons the area of the cooling surface is likely to be 200% as a maximum.

If there are "N" such high power energy storage cells such as ultracapacitors or supercapacitors or capacitors in a row each spaced with a spacing "S" from the next capacitor (free space between two capacitors not the pitch), the area of the cooling surface thermally connected by thermal conduction to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and provided by an extension of bus bars is equal to at least 30% of (N x W x H) + ((N-l) x S)). This area may be increased to above 40%, to above 50%, to above 60% to above 70% to above 80% or to above 90% of (N x W x H) + ((N-l) x S). For cost and space saving reasons the area of the cooling surface is likely to be 200% as a maximum. Where there are two rows of different length the longest one can be used for the calculation. The above ratios can be increased greatly by the casing being provided with fins and or heat sinks to improve heat transfer to the air and to provide better cooling. Hence the external design can include cooling fins and/or heat sinks, for example or can include means for liquid cooling, e.g. liquid channels 11 in or on the casing walls.

In accordance with embodiments of the present invention the convection surface can be equal or almost equal to the conduction surface, e.g. the convection surface can be between 30%, or 40% or 50% or 60% or 70% of conduction surface up to 90% thereof. Energy storage devices according to embodiments of the present invention can have an internal and/or external design of the module to make use of cooling by air circulation or a driving wind, which can be often in excess of 3m/s for vehicles such as buses thus making any forced ventilation superfluous. Heat that is produced in operation in the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be conducted at and through terminals of the high power energy storage cells such as ultracapacitors or

supercapacitors or capacitors. The advantage of this is that terminals are connected to conductive layers of the capacitor and hence are directly in contact with the component of the capacitors which generates the heat during operation.

These terminals are preferably connected to bus bars designed as heat conducting elements rather than (e.g. only) as electric current conductors. The thermal bus bars are preferably made of a highly thermally conductive material such as copper or aluminium or are heat pipes. These materials provide efficient heat flow.

The modules preferably have a large heat exchanging surface. In embodiments of the present invention bus bars and casing preferably share the large heat exchanging surface whereby the bus bars are isolated electrically but not thermally from the casing. This has the advantage that there is a large area for heat to escape. The bus bars may be separated electrically from the casing by an electric isolator or may be made of an insulating material. The electrical isolator or the insulating material should support heat flow from the bus bars to the casing or directly to external. These heat transfer components such as bus bars and casing are preferably firmly and permanently connected to each other in order to increase heat transfer.

In some embodiments, the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be mounted onto bus bar - casing assemblies. The design of the bus bars is to increase thermal conduction (i.e. lower thermal resistance) between the terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and the environment via the casing. The casing can have a polygonal cross-section, i.e. having flat sides such as four flat sides of a square or rectangle. In some embodiments, each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor preferably has at least two conductive thermal paths to the casing, e.g. two conductive thermal paths each to one side of the casing, e.g. flat side of the casing. For example if the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors or arranged with the terminals at the top and bottom, then the bus bar from the top terminal can convey heat to an upper surface, e.g. flat surface, of the casing whereas the bus bar connected to the bottom terminal can convey heat to a side surface, e.g. flat surface of the casing. If the casing has four sides then the bus bars connected to each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor can provide conductive paths to three surfaces, e.g. flat surfaces of the casing, e.g. to top and bottom and a side surfaces, e.g. flat surfaces of the casing. The bus bars can be bent and distorted by any means so that the bus bars create a large surface area in thermal contact with the casing on at least two sides, or three sides of the casing in order to increase surface with minimal space requirements. Cooling can be by air flowing inside or outside the modules or liquid cooling of the casing.

If a sealed casing is not required then when the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors or arranged with the terminals at the top and bottom, then the bus bar from the top terminal can have an upper surface to convey heat upwards whereas the bus bar connected to the bottom terminal can be bent around to have a side surface to convey heat away from that side. Additional bus bars surface can be provided between rows of high power energy storage cells such as an ultracapacitors or supercapacitors or capacitors and there can be conductive paths to several radiating surfaces, e.g. three or more surfaces. The bus bars can be bent and distorted by any means so that the bus bars create a large surface area for radiating heat or for thermal conductive contact with the casing on at least two sides, or three sides of the casing in order to increase surface with minimal space requirements. Cooling can be by air flowing inside or outside the modules or liquid cooling of the casing. If the casing has four sides like a box, then each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor can have bus bars having conductive heat paths to the four sides although assembly can be more difficult. Where bolted terminals are used these may need to be left untightened while the bus bars surfaces are fixed to the four sides. Then the bolted terminals are tightened through access holes in the casing. When these heat transfer bus bars and casing sides are firmly connected to each other the terminal access holes can be sealed off.

The completed modules can be sealed or open. Sealing increases the life of the energy storage devices as it prevents ingress by contaminants, vermin, water etc. If open, the casings can be made of mesh to allow free convection of heat.

The modules can be stacked to form a compact system preferably with a spacing in between each other in order to allow for natural convection. The spacing can be for instance at least 20mm.

Means for liquid cooling can be provided, e.g. added to the exterior of the casing, replacing ambient air as a coolant; or can be added to the interior of the casing.

Advantages are that by adding a liquid cooling to the exterior of the casing, the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be cooled to temperatures lower than ambient without compromising safety and ease of handing which would be the case if the liquid coolant were to be routed inside the module's casing. Circulating cooling gas may be provided in the modules, e.g. air or hydrogen. Embodiments of the present invention provide a method of constructing an energy storage device comprising high power energy storage cells in modules, wherein there can be a limited number of high power energy storage cells such as ultracapacitors or supercapacitors or capacitors per module and these can be disposed in such a way that every high power energy storage cell such as ultracapacitor or supercapacitor or capacitor is surrounded at least on one side by heat radiating surface provided by a bus bar or by a module casing.

Terminals of the high power energy storage cells such as ultracapacitors or

supercapacitors or capacitors are preferably connected to bus bars designed as heat conducting elements rather than as electric current conductors. The bus bars are preferably made of a highly thermally conductive material such as copper or aluminium or aluminium oxide or nitride or are heat pipes. These materials provide efficient heat flow. In cases with high requirements on cooling and a complicated form factor, e.g. due to space limitations, the bus bars 14 may be preferably constructed as heat pipes transporting heat away from the cell terminals 24, 26 towards external or towards the module casing.

The bus bars and casing preferably share a large heat exchanging surface whereby the thermal bus bars are isolated electrically but not thermally from the casing. The bus bars may be separated electrically from the casing by an electric isolator. The electrical isolator should support heat flow from the thermal bus bars to the casing. During assembly the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be mounted within the casings of the modules on bus bars - casing assemblies. The bus bars are preferably made of a highly thermally conductive material such as copper or aluminium or are heat pipes. These materials provide efficient heat flow. These can be assembled to a closed module. These heat transfer components such as bus bars and casing are preferably firmly and permanently connected to each other in order to increase heat transfer.

Modules can be stacked to form a system with spacing in between each other in order to allow natural convection.

Liquid cooling can be added to the exterior or interior of the casing, replacing ambient air as a coolant. Advantages are that by adding a liquid cooling system on the exterior of the casing, the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be cooled to temperatures lower than ambient without compromising safety and ease of handing which would be the case if the liquid coolant were to be routed inside the module's casing.

In constructing a module its dimensions need not be determined by optimal use of space but can be determined by the availability of exterior heat exchanging surface, and hence improved cooling. Energy storage devices according to embodiments of the present invention can have an external design of the casing to make use of cooling by a driving wind, which can be often in excess of 3m/s for vehicles such as buses thus making any forced ventilation superfluous. The area of the cooling surface thermally connected by thermal conduction to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and provided by an extension of bus bars is equal to at least 30% of (N x W x H) or of (N x W x H) + ((N-l) x S) . This area may be increased to above 40%, to above 50%, to above 60% to above 70% to above 80% or to above 90% (N x W x H) or of as defined above. For cost and space saving reasons the area of the cooling surface is likely to be 200% as a maximum. In accordance with embodiments of the present invention the convection surface can be equal or almost equal to the conduction surface, e.g. the convection surface can be between 30%, or 40% or 50% or 60% or 70% of conduction surface up to 90% thereof.

Embodiments of the present invention provide a method of operating an energy storage device comprising high power energy storage cells in modules, wherein heat that is produced in operation in the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors is conducted through terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and through bus bars connected to the terminals, the bus bars being designed as heat conducting elements rather than as electric current conductors.

The bus bars and casing preferably share a large heat exchanging surface whereby the thermal bus bars are isolated electrically but not thermally from the casing. This has the advantage that there is a large area for heat to escape. The bus bars may be separated electrically from the casing by an electric isolator. The electrical isolator should support heat flow from the thermal bus bars to the casing. These heat transfer components such as bus bars and casing are preferably firmly and permanently connected to each other in order to increase heat transfer. Each heat exchanging surface can be thermally connected to a different terminal of the high power energy storage cells.

In operation for a mobile application, e.g. on a vehicle, the energy storage devices according to embodiments of the present invention can be cooled with the driving wind, often in excess of 3m/s thus making any forced ventilation superfluous. However, means for liquid cooling can be used in operation, e.g. added to the exterior of the casing, replacing ambient air as a coolant or can be added to the interior of the casing. Additional cooling may be required in a traffic jam where there will be many short stop/start actions with low velocity. Especially in high temperature environments (e.g. summer months) when there is no wind, overheating of vehicles is common. An advantage of adding a liquid cooling to the exterior of the casing, is that the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors can be cooled to temperatures lower than ambient without compromising safety and ease of handing which would be the case if the liquid coolant were to be routed inside the module's casing. In operation the method for delivering power to a load can comprise collecting charge from an energy source; charging the high power energy storage cells such as

ultracapacitors or supercapacitors or capacitors with the collected charge, charging a high energy source such as one or more batteries from the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors. Power to the load can be provide by the the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors, or by the high energy source or a combination of both.

Brief description of the drawings FIG. 1 to FIG. 4 show an energy storage device in accordance with an embodiment of the present invention having cylindrical cells.

FIG. 5 and FIG. 6 show modules in accordance with embodiments the present invention having lids, a frame and a control unit.

FIG. 7 AND FIG. 8 shows an energy storage device in accordance with another embodiment of the present invention having prismatic cells.

FIG. 9 and FIG. 10 show an energy storage device in accordance with an embodiment of the present invention having a spacer between modules. Definitions

As used in this document high power energy storage cells are referred to as

ultracapacitors or supercapacitors or capacitors. "Heat conduction" or "thermal conduction" as used in this document and as understood by the skilled person is the transfer of internal energy by microscopic diffusion and collisions of particles or quasi-particles within a body due to a temperature gradient. The microscopically diffusing and colliding objects include molecules, electrons, atoms, and phonons. They transfer disorganized microscopic kinetic and potential energy, which are jointly known as internal energy. Conduction can only take place within an object or material, or between two objects that are in direct or indirect contact with each other. As used in this document, conduction takes place in solids or liquids, gases.

Description of the illustrative embodiments

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The present invention provides an energy storage device with good cooling. Such a system may find use in. for example, in stationery equipment or in movable equipment such as lifts, or in the automotive industry. An energy storage device in accordance with embodiments of the present invention may comprise an assembly of similar or different high power energy storage cells such as ultracapacitors or supercapacitors or capacitors. With reference to FIG. 1 - 4 an ultracapacitor module 20 is shown. Such an ultracapacitor module 20 comprises a plurality of ultracapacitors 15 in a casing 22, e.g. a polygonal casing 22 having a number of sides 22a to d. The number of sides is preferably 4 to allow easy and efficient stacking however more sides re included within the scope of the present invention. Cell packs exposed to mechanical stress may be strengthened by adding the casing 22 and further mechanical protection such as frame 12 into which the modules 20 can be fitted and secured - see FIG 5 and FIG 6. The casing 22 may be extruded in one, two or more sections 9 to obtain optimal shape while reducing manufacturing costs. Optionally, the casing 22 may have liquid cooling, e.g. fluid or liquid such as water cooling channels 11. The casing 22 may be formed in such a way that by adding lids 13 on the end surfaces - see FIG 6, it can easily be made water tight. The casing sections 9, and/or the lids 13 may be adapted to interlock in such a way that the modules 20 can easily be stacked into a system in such a way that there is a sufficient gap between modules 20 to allow air to circulate as shown schematically in FIG. 6. The gap can be provided at all surfaces of the module. Storage modules stacked in a matrix using interlocking lids 13. Cooling air can flow over all module surfaces. The lids 13 can have grooves to mount shields or fins that can help direct air flow and increase the surface areas in contact with the moving air if required.

Gaps can be maintained between modules 20 by corner spacers 19 as shown in FIG. 7 and 8, wherein the corner spacers 19 plug into recesses on each module 20.

The casing 22 is preferably made from a heat conductive material such as a metal, e.g. aluminium. In FIG. 1 and 2 one row of ultracapacitors 15 is shown in a module 20 which increases the ratio of surface area of casing 22 to ultracapacitors 15 which can improve cooling. The present invention includes modules 20 with two parallel rows of ultracapacitors 15. The present invention includes modules 20 with more than two parallel rows of ultracapacitors 15. Each ultracapacitor 15 has two terminals 24, 26 - one for connection to the negative and one for the positive electrode of the ultracapacitor 15. These terminals 24, 26 are generally located at opposite ends of a ultracapacitor 15. FIG 1 to 4 shows cylindrical capacitors 15 but cylindrical or prismatic capacitors or pouch cells 15 may be used with any of the described modules.

Embodiments of the present invention include capacitors 15 having bolted/ screw and/or welded type connections (terminals 24, 26) to the electrodes of the ultracapacitors 15 although the invention will be described mainly with reference to screw/bolted connections to the terminals 24, 26. The capacitors 15 can be connected electrically in series, in parallel or in a combination of series and parallel. The configuration depends on the required voltage and capacity and can be adapted to any level.

The ultracapacitors 15 can be positioned in a single layer having a square-form (a matrix with identical parallel rows) to provide more space between them for cooling but a layer with close-packed triangle-form (as shown in Fig. 5 of WO2012/007290) can be used even if less preferred.

Connecting a plurality of at least one of the terminal types (positive or negative) and preferable each of the terminals 24, 26 of the same type of the ultracapacitors 15 together is done by bus bars 14. Each ultracapacitor 15 is surrounded at least on one side by an extended bus bar 14. In accordance with embodiments of the present invention the bus bars 14 can include a first part 14a which is mainly for the conduction of electric current and heat and a second part or extension 14b which is mainly for the conduction of heat. As shown in FIG. 1 a bus bar 14 has the first portion 14a attached to terminals 24 is extended and bent over to make the portion 14b which has a large area surface against side 22a of the casing 22 of the module 20. This is best seen in FIG. 1 where the ultracapacitors 15 and insulating layer 17 have been removed for clarity purposes to expose the bus bar extension portion 14b. The insulating layer 17 is placed between the cells 15 and the second portion 14b of bus bar 14. As this insulating layer 17 can get quite hot is can be made of a ceramic material. The bus bars 14, in particular the extension of bus bar 14 to make the second portion 14b, and the module casing 22 are adapted to remove heat from the ultracapacitors 15, ideally along a plurality of parallel heat paths. To provide this adaption, a module's dimensions and/or the arrangement of the ultracapacitors inside the module need not be determined by optimal use of space but can be determined by the availability of exterior heat exchanging surface, and hence improved cooling. Energy storage devices according to embodiments of the present invention can have an external design of the casing 22 to make use of cooling by a driving wind, which can be often in excess of 3m/s for vehicles such as buses thus making any forced ventilation superfluous.

Each high power energy storage cell 15 such as an ultracapacitor or supercapacitor or capacitor has a width "W" and a height "H" and there are "N" high power energy storage cells 15 such as ultracapacitors or supercapacitors or capacitors in a row. In the case of cylindrical cells, the terminals 24 are connected by heat conduction to a heat sink (e.g. casing 22 with optionally fins attached) via busbar portions 14a and b. In embodiments of the present invention the bus bars 14 are used for heat exchange (e.g. as shown in fig.4) and the heat exchange area is at least N x W x H.

In accordance with embodiments of the present invention, the area of the cooling surface thermally connected by thermal conduction to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and provided by an extension 14b and the first portion 14a of bus bars 14. In case of prismatic cells, the area exposed for convection is a maximum of N x 2 x W x H if all cells are surrounded by air.

In accordance with embodiments of the present invention, the area of the cooling surface thermally connected by thermal conduction to terminals of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and provided by an extension 14b and the first portion 14a of bus bars 14 is equal to at least 30% of (N x W x H) or 30% of (N x W x H) + ((N-l) x S). This area may be increased to above 40%, to above 50%, to above 60% to above 70% to above 80% or to above 90% (N x W x H) or of as defined above. For cost and space saving reasons the area of the cooling surface is likely to be 200% as a maximum. This ratio can be increased greatly by the casing 22 being provided with fins and or heat sinks to improve heat transfer to the air and to provide better cooling. Hence the external design can include cooling fins and/or heat sinks, for example or can include means for liquid cooling, e.g. liquid channels 11 in or on the casing walls.

In accordance with embodiments of the present invention the convection surface can be equal or almost equal to the conduction surface, e.g. the convection surface can be between 30%, or 40% or 50% or 60% or 70% of conduction surface up to 90% thereof. Accordingly, heat that is produced in operation in the ultracapacitors 15 is conducted at and through terminals 24, 26 of the ultracapacitors 15. The advantage of this is that terminals 24, 26 are connected to conductive layers of the capacitor and hence are directly in contact with the component of the capacitors which generates the heat during operation.

These terminals 24, 26 are connected to the bus bars 14 which are designed as heat conducting elements rather than as electric current conductors alone, i.e. the bus bars have a first portion for conducting electricity and heat and a seond portion mainly for the conduction and convection of heat. A bus bar 14 (or at least the first portion 14a) or the bus bar material must be capable of good thermal conduction of heat (transcalent) as well as being electrically conductive. Hence the bus bars 14 may be made of a solid material or may be heat pipes. Whichever is used, the material of the bus bar 14 can be for example copper or aluminum or any of their alloys. These materials provide efficient heat flow. The shape of the bus bar 14 should be chosen such as to allow a large external surface area of the bus bar 14 in the form of busbar portion 14b to be in thermal contact with external e.g. either directly as radiating panels or through the sides 22a to d of the casing 22. The ultracapacitors or supercapacitors 15 are mounted onto bus bar - casing assemblies. The bus bars 14 can comprise electrically conductive heat pipes comprising materials providing efficient heat flow as well as an electrical connection. Hence bus bars 14 may comprise copper or aluminum or any other convenient conductor. Aluminum bus bars may be extruded into optimal shape and cross section. Alternatively separate electrical (14a) and thermal (14b) bus bars can be provided. Hence there can be separate thermally conductive and electrically conductive bus bars.

Thermally conductive bus bars may comprise ceramic materials such as aluminium oxide (AI2O₃) or aluminium nitride. These materials have high mechanical and dielectric strength and high thermal conductivity. These materials come in the form of sheets that can easily be cut to fit to flat bus bars.

The bus bars 14 used for thermally conduction and the casing 22 preferably share a large heat exchanging surface whereby the bus bars 14 can be isolated electrically but not thermally from the casing 22. This has the advantage that there is a large area for heat to escape.

The bus bars 14 may be separated electrically from the casing by an electric isolator 16 while maintaining a conductive thermal path. The electrical isolator 16 should support heat flow from the bus bars 14 to the casing 22. This conductive thermal contact between the bus bars 14 and the outer casing.22 will allow conduction o the developed heat from the ultracapacitors 15 directly to the outside of the module 20 with better cooling as a result. Electrically insulating, and preferably thermally conductive (transcalent) material is used to make the isolator 16 between the bus bars 14 and the casing 22 of the modules. The electric isolator 16 can be an insulating foil such as a polymer foil (typically a thin foil) or can be an insulating coating such as an epoxy or polyester coating.

The bus bars 14 attached to different terminals 24, 26 are preferably isolated one from the other. They can be kept in place by applying (e.g. gluing) an electric isolating foil onto the exterior of the bus bars 14. This foil may be thin for good thermal conductance but must have high electric isolation. An example of such foil is PET. For energy storage devices submitted to moderate mechanical stress, e.g. stationary storage systems, the electric isolating foil may be used as an external skin of a module 20. This reduces the number of thermal interfaces, increasing cooling capacity. The bus bars 14 may be insulated by an outer insulation such as a coating of polymer or varnish or by a layer of polymer film insulation, optionally of two different compositions, to provide a tough, continuous insulating layer. Such coatings can be for example made of, polyvinyl formal, polyurethane, polyamide, polyester, polyester-polyimide, polyamide-polyimide or amide- imide, or polyimide. In case an exterior casing 22 is used, the isolating foil between bus bars 14 and housing may be at least partially replaced by an insulating foil or an insulating coating such as an epoxy or polyester coating either on the bus bars 14 and/or on the interior of the casing 22. The heat transfer components such as bus bars 14 and casing 22 are preferably firmly and permanently connected to each other in order to increase conductive heat transfer.

The design of the bus bars 14 is to increase thermal conduction (i.e. lower thermal resistance) between the terminals 24, 26 of the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors and the environment either directly or via the casing.

The casing 22 can have a polygonal cross-section, i.e. having flat sides such as four flat sides 22a to d of a square or rectangular cross- section. Each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor preferably has at least two conductive thermal paths to external e.g. via the casing, such as two conductive thermal paths each to one side 22a to d or wall of the casing, e.g. flat side of the casing. For example if the high power energy storage cells such as ultracapacitor s or supercapacitor s or capacitors or arranged with the terminals 24, 26 at the top and bottom, then the bus bar 14 from the top terminal 24 can be extended, bent and shaped (not shown) to present a large surface area convey heat to an upper side 22b, e.g. flat surface, of the casing 22 whereas the bus bar 14 connected to the bottom terminal 26 can convey heat to another side 22a or wall surface, e.g. flat surface of the casing 22. If the casing22 has four sides then the bus bars connected to each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor can provide separate conductive paths to two or three of these sides 22a to d, e.g. flat surfaces of the casing, e.g. to top and bottom surfaces (on sides 22b, 22D) and a side surface (on sides 22a or 22c), e.g. flat surfaces of the casing 22. The bus bars 14 can be bent and distorted by any means so that the bus bars 14 create a large surface area in thermal contact with the external or with the casing on at least two sides, or three sides of the module 20, e.g. on at least two sides, or three sides 22a to d of the casing in order to increase surface with minimal space requirements. Cooling can be by air flowing inside or outside the modules either convective or forced or by liquid cooling of the casing. When liquid cooling is used, pipes can be routed as close as possible to the cell terminals but outside the isolation barrier. They may be provided by channels 11 e.g. be part of the casing 22. Liquid cooling may be performed by using an insulating liquid such as an oil, e.g. transformer oil circulated inside the modules. All designs to increase cooling surface of cells exposed to air will work with oil cooling. The oil can be cooled either at the surface of the modules or in a separate radiator. Using oil as an intermediate coolant allows high power to be removed while maintaining a small form factor.

If the casing 22 has four sides 22a to d like a box, then each high power energy storage cell such as an ultracapacitor or supercapacitor or capacitor can have bus bars 14 having conductive heat paths to the four sides although assembly can then be more difficult. The bolted terminals 24, 26 may need to be left untightened while the extended bus bar surfaces are fixed to the four sides. Then the bolted terminals 24, 26 can be tightened through access holes in the casing 22. When these heat transfer bus bars 14 and casing sides are firmly connected to each other the terminal access holes can be closed off.

When the energy storage device is to be used in a protected environment, e.g. indoors with a lift installation no casing is needed or can be an open mesh. The bus bars 14 may be extended and folded to the side of the cells as shown in FIG. 7 and 8 in order to have a portion 14b with increased surface are but minimal space requirements. These extended bus bar surfaces can be cooled by air flowing inside the modules. FIG. 7 shows prismatic high power energy storage cells such as ultracapacitors or supercapacitors or capacitors 15 connected to cooling fins 21 which are separate from the bus bars 14. The cooling fins 21 increase the heat exchange surface of the cells, e.g. by a factor 4. As can be seen from FIG. 7 the fins 21 extend on either side of each cell 15 thus providing two separate heat extraction paths. Cooling can be achieved by circulating a gas such as air over the cooling fins 21 in longitudinal direction.

FIG. 8 shows prismatic high power energy storage cells such as ultracapacitors or supercapacitors or capacitors 15 connected in series/parallel by a single bus bar/cooling fin 14. The bus bar/cooling fin 14b extends down each side of the prismatic cell 15 thus providing two separate heat extraction paths. Also additional fin surfaces are provided at the end of the assembly. The heat exchange surface is increased by a factor 1.9. The cross section of the bus bar/cooling fins 14b is determined by the electrical current. Cooling can be achieved by circulating air transversely (e.g. top down).

The completed modules 20 can be sealed, e.g. against moisture ingress. Sealing increases the life of the energy storage devices as it prevents ingress by contaminants, vermin, water etc. For example, a module 2 may be constructed, for example to a degree of impermeability of IP65, IP66, IP68 and IPX9-k, according to DIN EN 60529 und DIN 40 050 Teil 9 e.g. by appropriate sealing (e.g. 27 in FIG. 1). In case o a water tight module design, air may be replaced for forced cooling by other gases with better thermal performance, e.g. hydrogen. Hydrogen is circulated in order to transport heat from the cooling fins or cells to the module casing making the complete casing surface available for cooling to the outside air. Using hydrogen reduces ventilation losses. On bus bar 14 a connection can be foreseen to connect a wire. When quick connections are desi ed, a rivet can be used. Bolting the wire to bus bar can also be done. The purpose of this wire is to bring the voltages of each ultracapacitor 15 individually to an electronics unit such as a printed circuit board. Some of the functions these electronics can have are: balancing, ovei vol tage protection, and a safety discharge unti l empty.

The outer side of the housing of an ultracapacitor module is, for example a rectangular box comprising casing sections 9 which can be folded, glued, soldered, welded together, screwed or riveted together or a combination of these. On the casing sections 9 or integral with them heat sinks or fins can be located, e.g. finned heat sinks. The casing sections 9 can be assembled together to create a box which is generally rectangular or hexagonal and it is preferred i the side surfaces are larger than the end surfaces. Thi s provides better heat conduction away from the capaci tors in each module. The housi ng can be water- sealed, e.g. by weldi ng, gluing, soldering or by application of sealants (e.g. 27 in FIG. 1). The housing material is preferably a thermally and electrically conductive and light metal such as aluminium or other low weight material.

The module 20 is equipped with all necessary electrical and mechanical connectors, e.g. . power, signal, control and cooling connections as required. Wateiproof sealing can be provided around the connectors. A pressure compensation element can provide an equal pressure inside and outside the module. This to compensate the pressure rising caused by a temperature changes (rising/fal l ing ) of the working ul tracapaci tors. Pressure compensation elements serve for the aeration and de-aeration of components in the housing. This prevents damage to built-in components caused by condensation that occurs because of variations in temperature/pressure peaks. Such a pressure

compensation element can allow a h igh air flow rate combi ned with high water retention capacity. The internal pressure of the closed housing is adapted to the ambient pressure, and at the same time, water penetration is prevented. A membrane can be integrated into the pressure compensation element, which is permeable to air on both sides and

permeable to water from only the side towards the inner of the housing. This means that air is free to flow from inside the module to the outside or from the outside to the inside. Water ca only flow from the inside to the outside. This way water in the module can be removed automatically. Hence the housing can have a pressure compensation element which is mounted in the module for equalizing the pressure inside an outside while draining water to the outside. In a less preferred embodiment an air cushion can be located in each water sealed module which assists in equalising the pressure.

As shown schematically in FIG. 5 and 6 an energy storage device according to embodiments of the present invention comprises a connection module 7 to combine the different ultracapacitor modules 20 and a frame 12 to keep the modules mechanically together. The frame 12 can be adapted to hold and secure ultracapacitor modules 2 and any connection modules 7.

When operated, the ultracapacitor modules 2 produce heat. Passive cooling of the modules 2 is often only acceptable at low current applications. When higher currents are required, e.g. hybrid vehicles, active or forced cooling is preferable. Active cooling can be performed by fans and/or water cooling. Fans can be attached to frame 12 or directly onto the ultracapacitor modules 20. Preferably the modules 20 are provided with heat sinks such as finned heat sinks on any of the surfaces of each module 20.

To control and monitor the working of the ultracapacitor system, an electronic controller can be provided. Relays or other switches can be used to switch the power connections on or off, both on the positive and negative cable. Additionally a pre-charge relay and pre- charge resistors can be provided. An electronic isolation detection system can be used to monitor the system for isolation faults. Temperature sensors can be provided to monitor the temperature on different places in the ultracapacitor modules 20. A fuse can be used to protect against high currents. A current sensor can be provided for measuring the current flowing in the system. The voltage of the system can be measured using sensors at one or more places. One place is before the fuse and a second is after. This means that the working of the fuse can be measured by comparing the two voltages. Alternatively, the place of first measurement can be after the fuse and the second after the relay. This way, the working of the fuse can be checked with the first voltage measurement and the voltage from a CAN bus, for example. This way also the voltage can be controlled for switching the relays from pre-charge to normal operation. Hardware is foreseen to control fans in speed. All the electronics can be placed in a different module that slide into the frame like an ultracapacitor module. Another possibility is placing the electronics into a connection module. An electric storage device in accordance with any of the embodiments of the present invention can be mounted on a vehicle such as an aircraft, a boat, an automobile, a bus, a truck, a milk float or any other electric vehicle to provide an electrical energy supply. For example it can be an emergency energy supply or it may be a primary energy supply for the vehicle. Alternatively, an energy storage device in accordance with embodiments of the present invention can be mounted on a stationary electrically powered device. An electric storage device in accordance with any of the embodiments of the present invention can be combined with a source designed to provide long-term power (which means it is capable of delivering a large amount of energy over time). The high power source may be used to assist the high energy source in providing power to a system during, for example, acceleration of a vehicle or pulsed load events such as a reaction to an emergency situation. The high energy source can be a rechargeable energy storage such as a lead- acid or lithium battery.

In operation the method for delivering power to a load can comprise collecting charge from an energy source; charging the high power energy storage cells such as

ultracapacitors or supercapacitors or capacitors according to any of the embodiments of the present invention with the collected charge, charging a high energy source such as one or more batteries from the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors. Power to the load can be provide by the the high power energy storage cells such as ultracapacitors or supercapacitors or capacitors, or by the high energy source or a combination of both.

Results obtained with assemblies according to embodiments of the present invention are shown in the table below. The comparison is an assembly according to WO2012/007920. Standard is according to embodiments of the present invention where the cells 15 are in parallel rows. Compact is according to embodiments of the present invention where the cells 15 are in rows of the compact type shown in FIG. 5 of WO2012/007920. casing design comparison standard compact heat exchange surface 2.6 m² 0.4 m² 0.25 m² cooling power by natural 12 W/m²K 12 W/m²K convection 4.8 W/K 3 W/K

cooling power at 3 m/s air speed 8.5 W/m²K 23 W/m²K 31 W/m²K

22 W/K 9.2 W/K 7.7 W/K losses at 150A RMS 384 W 137 W 124 W

end temperature rise with natural 29 K 44.5 K

convection

test series length

180 min 165 min* end temperature rise at 3 m/s air 17,5 K 15.3 K 16 K

speed

test series length

180 min 188 min

Table 1 : air cooling for different box designs.

test interrupted due to over temperature

In order to estimate the cooling potential of a system according to embodiments of the present invention, the ratio of the heat exchange area divided by the losses of a system can be used as a reference. These can be expressed as :

P = R * I² where R = internal electrical resistance of a string of cells (in ohms), P = losses (in watts) and I = the current through the cells (in amps)

The above table states losses for different designs. The first column "Comparison" refers to a design known in prior art. As the diameter of the terminal 24 is approximately half that of the cell, the area of busbar 14 involved in the heat transfer from both terminals of each cell and for all cells in a row in conventional designs is 2 x N x (W/2)² x π I 4 or N x W² /8 if H > W. The heat conduction surface for this case is accordinglyW² /8 per cell or in this example 4,5 cm² (W=60mm). The heat convection surface is 460cm² (=2,6m² / 56 cells), or 100 times higher. This shows the limitation of the prior art : there is no advantage in increasing the convection area if the conduction area cannot be increased. The need for a high conduction area is a consequence of the electric isolation that is required between the terminals or their interconnections and the cooling surface common to a number of interconnections. Although the convection area for the prior art system is 2,6m² for 384W of losses , so 68cm²/W, it cannot be cooled without forced ventilation because the conduction area is only 0.7cm²/W. In embodiments of the present invention the convection surface can be made equal or almost equal to the conduction surface : 29cm /W. Cooling is therefore far superior.

Claims

1. An energy storage device comprising high power energy storage cells in modules, the high power energy storage cells being two-terminal devices, the high power energy storage cells being disposed in a module so that every high power energy storage cell is surrounded on at least a first side by at least a first cooling surface and on at least a second side by at least a second cooling surface.

An energy storage device according to claim 1 each cooling surface being thermally connected to a different terminal of the high power energy storage cells.

An energy storage device according to claim 1 or 2, wherein each cooling surface is provided by an extension of a bus bar which is in conductive thermal contact with the relevant terminal.

An energy storage device according to claim 3, wherein each cooling surface provided by a side or wall of a module casing which is in conductive thermal contact with the extension of the bus bars but isolated from the bus bars.

An energy storage device according to any previous claim wherein the high power energy storage cells are arranged in at least one row in the module, the area of at least one of the first and second cooling surfaces thermally connected by thermal conduction to terminals of the high power energy storage cells is equal to at least 30% of (N x W x H), where each high power energy storage cell has a width "W" and a height "H" and and there are "N" high power energy storage cells in the at least one row; or

wherein the high power energy storage cells are arranged in at least one row in the module, the area of at least one of the first and second cooling surfaces thermally connected by thermal conduction to terminals of the high power energy storage cells is equal to at least 30% of (N x W x H) + ((N-l) x S)), where each high power energy storage cell has a width "W" and a height "H" and and there are "N" high power energy storage cells in the at least one row, and the free space between the the high power energy storage cells is "S".

6. An energy storage device according to any previous claim , wherein the area of the area of at least one of the first and second cooling surfaces is above 40%, above 50%, above 60%, above 70%, above 80% or above 90% of (N x W x H).

7. An energy storage device according to claim 5, wherein the area of the area of at least one of the first and second cooling surfaces is above 40%, above 50%, above 60%, above 70%, above 80%, or above 90% of (N x W x H) + ((N-l) x S).

An energy storage device according to any previous claim, wherein a convection surface is provide that is between 30%, or 40% or 50% or 60% or 70% of a surface provided for heat conduction up to 90% thereof.

An energy storage device according to any previous claim 4 to 8, wherein the module casing is provided with fins and/or heat sinks to improve heat transfer to the air and to provide better cooling.

An energy storage device according to any of claims 4 to 9, further comprising means for gas or liquid cooling.

11. An energy storage device according to any of the previous claims wherein the high power energy storage cells are ultracapacitors or supercapacitors or capacitors.

12. A method of constructing an energy storage device comprising high power

energy storage cells in modules, the high power energy storage cells being two- terminal device, the method comprising:

arranging the high power energy storage cells in a module so that every high power energy storage cell is surrounded on at least a first side by at least a first cooling surface and on at least a second side by at least a second cooling surface,

13. A method according to claim 12 further comprising thermally connecting each cooling surface to a different terminal of the high power energy storage cells.

14. A method of operating an energy storage device comprising high power energy storage cells in modules, wherein heat that is produced in operation in the high power energy storage cells is conducted through terminals of the high power energy storage cells and through bus bars connected to the terminals, the bus bars being extended as heat conducting elements so that every high power energy storage cell is surrounded on at least a first side by at least a first cooling surface and on at least a second side by at least a second cooling surface.

15. A method according to claim 14 further comprising thermally connecting each cooling surface to a different terminal of the high power energy storage cells.

16. A method according to any of the claims 12 to 15 wherein the high power energy storage cells are ultracapacitors or supercapacitors or capacitors.

17. A method according to claim 16, wherein each cooling surface is provided by a side or wall of a module casing which is in conductive thermal contact with the extension of the bus bars but isolated from the bus bars.

18. A method according to any of the claims 12 to 17 wherein the high power energy storage cells are arranged in at least one row in the module, the area of at least one of the first and second cooling surfaces thermally connected by thermal conduction to terminals of the high power energy storage cells is equal to at least 30% of (N x W x H), where each high power energy storage cell has a width "W" and a height "H" and and there are "N" high power energy storage cells in the at least one row; or

wherein the high power energy storage cells are arranged in at least one row in the module, the area of at least one of the first and second cooling surfaces thermally connected by thermal conduction to terminals of the high power energy storage cells is equal to at least 30% of (N x W x H) + ((N-l) x S)), where each high power energy storage cell has a width "W" and a height "H" and and there are "N" high power energy storage cells in the at least one row, and the free space between the the high power energy storage cells is "S", or

wherein a convection surface is provide that is between 30%, or 40% or 50% or 60% or 70% of a surface provided for heat conduction up to 90% thereof.