WO1994002969A1

WO1994002969A1 - Electrical accumulator battery with a cooling system, and assembly comprising same

Info

Publication number: WO1994002969A1
Application number: PCT/FR1993/000767
Authority: WO
Inventors: Jean Leveque; Michel Vigarie; Michel Lapautre
Original assignee: Bertin & Cie; Societe De Recherche Et D'applications Electrochimiques Sorapec
Priority date: 1992-07-27
Filing date: 1993-07-27
Publication date: 1994-02-03
Also published as: FR2694136B1; FR2694136A1

Abstract

A battery with a stack of series-connected bipolar flat accumulator cells (11-1n), and at least one heat radiator element (91, 92, 93) adjacent to at least one accumulator cell of the stack, and defining flow passage for an electrically non-conductive cooling fluid for extracting from the battery the heat released by the accumulator cells (11-1n), said radiator element (91, 92, 93) being made of an electrically conductive material in electrical contact with the adjacent accumulator element(s) in such a way that it does not disrupt the series connection of the accumulator cells in the stack.

Description

ELECTRIC ACCUMULATOR BATTERY EQUIPPED WITH COOLING MEANS AND SET OF SUCH BATTERIES

The present invention relates to an electric storage battery equipped with cooling means and, more particularly, to a set of such batteries designed in particular for the power supply of a motor vehicle with electric propulsion.

There is known an electric accumulator element called "cadmium-nickel" constituted by a planar positive electrode provided with a layer of nickel hydroxide, a planar negative electrode provided with a layer of cadmium oxide, the whole being impregnated of potash constituting the electrolyte. Such bipolar elements are each capable of delivering a potential difference of 1.2 volts for example. They can be stacked on top of each other so as to be electrically connected in series so that the potential differences established by each element are added to each other. It is thus possible to constitute very robust, leaktight storage batteries, supporting without damage high intensities of charging and discharging. We are therefore currently considering the use of such batteries for powering vehicles powered by one or more electric motors.

When charging or discharging a battery made up of several tens of elements as described above, there is a significant release of heat in the mass of the battery. This release is due both to exothermic electrochemical reactions which develop in the elements and to a Joule effect, resulting from the passage of electric current, in the various layers of the elements. It was thus possible to evaluate a few tens of W / dm ³ this release of heat, in particular at the end of charging, in the case of a battery with a capacity of 50 Ah at 48 Volts, for example. This is too important to be able to dissipate by natural thermal conduction and convection without excessive rise in the temperature of the battery. It therefore causes differential heating of the active material of the battery cells, consisting of nickel hydroxide, cadmium oxide and the electrolyte. The active material then no longer delivers a constant current density over the entire surface of an accumulator element. It has been observed that Current density gradients that are noted on this surface can cause long deformations of the accumulator elements and therefore a deterioration of the battery.

The present invention therefore aims to achieve a battery of electric accumulators of the type described above, equipped with means for dissipating the heat energy released by the operation of the battery in particular in the charging phase, this by controlling the evolution of the temperature of the active material of the elements and maintaining a practically uniform temperature in each element of accumulator in order to avoid the appearance of gradients of current density on the surface of any element.

These objects of the invention are achieved, as well as others which will appear on reading the description which follows, with an electric accumulator battery, comprising a stack of flat bipolar and electrically connected accumulator elements. , this battery being remarkable in that it comprises at least one heat radiator element attached to at least one accumulator element of the stack, this radiator element delimiting a circulation passage for a non-conductive cooling fluid of electricity and capable of extracting heat from the battery from the accumulator elements, the radiator element itself being made of an electrically conductive material in electrical contact with the element (s) adjacent accumulator so as not to disturb the series connection of the accumulator elements of the stack.

Thanks to the radiator elements incorporated in the stack of accumulator elements, it is possible to maintain the battery at a homogeneous temperature everywhere below a predetermined temperature making it possible to avoid degradation of the structure of the battery and of its performance.

According to the invention, the accumulator elements are rectangular in shape and each radiator element generally conforms to the accumulator elements and consists of two parallel flat metal sheets separated by means for directing the circulation of the cooling fluid between these two. leaves, parallel to the short sides of these sheets, the coolant entering and leaving the element between large sides opposite them.

According to a preferred embodiment of the invention, the orientation means are constituted by a metal sheet folded along a surface with parallel generatrices resting on a director with periodic waveform of amplitude equal to the distance separating the two flat metal sheets of the radiator element, with which the folded metal sheet is in electrical contact.

Other characteristics and advantages of the present invention will appear on reading the description which follows and on examining the appended drawing in which:

FIG. 1 is a schematic perspective view of the storage battery according to the present invention,

FIGS. 2, 3 and 4 are partial sectional views of three embodiments of radiator elements which can be incorporated into the battery of FIG. 1,

FIG. 5 is a sectional diagram of the battery of FIG. 1, showing its connection to means for supplying cooling fluid, and

- Figure 6 is a layout diagram of a set of batteries according to the invention, allowing their connection to a single source of cooling fluid.

In Figure 1 of the accompanying drawing, it appears that the battery according to the invention is constituted by a stack of accumulator elements (1 .. 1 „.. 1 _n ) which, by way of illustrative and nonlimiting example , can be of the "cadmium-nickel" type. It is known that such an accumulator element then comprises an active material consisting of a layer of nickel hydroxide deposited on a metal sheet 2 (see element 1,) to form a positive electrode, of a layer d cadmium oxide deposited on a metal sheet 3 placed opposite the sheet 2 to form a negative electrode, the two layers immersed in an electrolyte consisting of potassium hydroxide.

According to the invention, the metal sheets and the element are given a rectangular flat shape enabling batteries to be formed parallelepiped that can be grouped into compact sets, as we will see later.

According to a characteristic of the accumulator elements of the battery according to the invention, the active material consists of an assembly comprising two coplanar layers 4.5 rectangular 4.5 spaced from one another and a textile carrying the electrolyte. Seals close the space between the two sheets 2,3, following the superimposed contours of these two sheets (in Figure 1 only the seals 6,7 along the short sides of the contours are shown for clarity of drawing). The active material has a total thickness equal to the distance from the facing faces of the sheets 2,3. The two layers 4,5 are dimensioned and spaced from one another so as to provide around each, in element 1, for example, a volume or retention space 8 for oxygen which is released from the active material during the charging of the element. This space makes it possible to limit the rise in pressure of the element during this release of oxygen. In addition, the presence of a central channel between the two layers facilitates the release of oxygen by reducing the distance that the oxygen has to travel to reach the retention volume.

Such an element gives off heat, both during the charging of the battery and during its discharge. The release of heat at the end of charging is particularly important and experience shows that one cannot count on a cooling by natural conduction and convection of the battery to maintain the temperature of this one, in all points, at a value allowing to avoid the appearance of gradients in the density of the current which passes from an element of accumulator to an adjacent element in the stack. Such gradients cause deformations of the structure of the battery and a degradation of its performance. Studies have shown that, to prevent such degradation in a battery with cadmium-nickel storage cells, the temperature in this battery must be kept as uniform as possible and in any case lower than 65 ° C.

According to the present invention, these conditions are satisfied by incorporating one or more radiator elements such as 9 9 ₂ , 9 ₃ into the battery, allowing to establish a convecîiαn (force at at least one side of battery cell. Danseun embodiment of the invention provided by way of example, disposte ^'Λ .s radiator elements 9, and 9 ₂ at the top and bottom of the stack, respectively ^~ i point of view of Figure 1). When the number of accumulator elements is large, for example of the order of 40 in which case heating of the battery at the end of charging is particularly important, there is an additional radiator element such as 9 ₃ at mid-height of the stacking.

Each radiator element is advantageously substantially in accordance with the accumulator elements of the stack. This is how a stacking end radiator element is constituted, such as% with rectangular metal sheets 10 and 11 and means 12 for orienting a cooling fluid put into forced circulation between these leaves. Note that the sheet 11 is common to the radiator element 9. and to an accumulator element 1, adjacent. The orientation means comprise a plurality of partitions 12, parallel and adjacent, disposed between the sheets 10 and 11 parallel to the short sides of the rectangular radiator element 9 It is understood that a cooling fluid put into forced circulation between the sheets 10 and 11, between two large opposite sides of these leaves spring, heated by the calories received from the adjacent accumulator elements, between the two other opposite large sides of these leaves, the partitions 12 _j advantageously causing a unidirectional flow of fluid in the radiator element, favorable to the performance of this element.

According to the present invention, this efficiency is further improved by preventing any heat loss from the side faces of the battery. To this end, all of the elements of this battery are placed inside an envelope 13 shown schematically in broken lines in FIG. 1, an envelope made of a thermally insulating material or provided with thermal insulation means (not shown ) on its side faces. This promotes the transfer of heat in the battery in a direction normal to the plane of the rectangular metal sheets and therefore to the coolant / air flows for example, circulated in the elements of radiator. This orthogonality is very favorable for improving the efficiency of these radiator elements and therefore for cooling the battery.

One can conveniently produce a radiator element, as shown in the cross-sectional view of Figure 2, using a metal sheet 12 'folded so as to have a regulated surface with parallel generators resting on a directrix in the form of a periodic wave, for example in slots as shown in this figure. Weld beads such as 22 make it possible to assemble this folded sheet to two adjacent metallic sheets 2, 3. The whole of the radiator element being made of metal, for example of nickel strip, it is understood that an element ensures perfect electrical conduction between the two accumulator elements which it separates or between an accumulator element and a current collector such as that marked (10, 14, 15) in FIG. 1. The radiator element is thus, from the electrical point of view, "transparent".

According to the invention, the radiator elements are supplied with an electrically non-conductive cooling fluid, such as air for example. Thus the current of cooling air which passes through each radiator element does not cause any shunt effect with respect to the current which passes through the accumulator elements of the battery.

It will be noted that the radiator element constituted as described above makes it possible, at the same time, to direct the passage of air in the element while providing a maximum exchange surface thanks to the partitions 12 _j , to transmit the electric current through these same partitions, homogeneously over the entire surface of the metal sheets without disturbing the desired uniformity of the current density on these sheets thanks to a uniform transverse resistivity opposing the appearance of transverse currents, and to provide the element with sufficient mechanical strength by virtue of the stiffening effect obtained by the partitions 12, or by folding the intermediate sheet. In this regard, it should be noted that the internal pressure in such a battery can reach 3 bars and the radiator element must be able to withstand such pressure. The structure chosen for this element therefore proves to be advantageous from the thermal, electrical and mechanical point of view.

There is shown in Figure 3 of the accompanying drawing a sectional view of a variant of the radiator element of Figure 2. The folding of the intermediate sheet 12 "has a periodic shape in trapezoidal slots rather than rectangular. Of course other known forms of surface regulated with spatial frequency could be envisaged to constitute a radiator element usable in the battery according to the invention.Alternatively still, as represented in FIG. 4, this element can take the form of a group profiles 12 "', arranged parallel to each other in the same plane between two sheets or metal plates to which they are connected by suitable welds 22'.

The battery current is collected at the two ends of the stack by terminals such as terminal 14 visible in FIG. 1. According to the present invention, this terminal is advantageously formed for example on a current collector 15 of elongated shape, arranged in electrical contact with the sheet or end plate 10 or formed in one piece with it so as to constitute a presser for stacking of elements constituting the battery. Connecting means, for example tie rods (not shown) can connect the two end pressers to ensure the cohesion of the stack.

According to an advantageous characteristic of the battery according to the invention, the axis of the collector 15 is perpendicular to the partitions 12,. Thus the current passing through these partitions to arrive on the sheet or plate 10 with a uniform current density, is it concentrated by the collector 15 along current lines which join this collector parallel to the short sides of the sheet or plate 10 before d 'to be collected by the collector on terminal 14. This progresses progressively from the distrioution on the surface of the current to a point concentration of this current without disturbing the desired uniformity of the density of the current on the surface of the sheet 10.

By way of nonlimiting example, a battery according to the invention has been produced consisting of 40 cadmium-nickel accumulator elements arranged in two stacks of 20 elements separated by a radiator element such as element 9 ₃ of FIG. 1, the ends of the assembly being furnished with radiator elements such as 9, and 9 ₂ associated with the means for collecting the current described above. Each accumulator element delivers a voltage of 1.2 volts, the surface of each element being approximately 13 dm ² so that the battery has a charge of 50 Ah, under 48 volts. The thickness of an accumulator element is approximately 2.6 mm, that of a radiator element is approximately 6 mm, which gives the assembly overall dimensions of approximately 620 mm x 280 mm over a height of 122 mm, this space not taking into account that of the necessary means of connection to a source of a non-electrically conductive fluid, such as air.

There is shown schematically in Figure 5 an embodiment of these connection means, by way of illustration and not limitation. The means shown take the form of a connector 16 in "carp tail" establishing a fluid connection between a single inlet 1 7 and the three radiator elements of the battery of Figure 1, through a pressure distributor 18 leading l air directly to the radiator elements without cooling the battery walls. A source of pressurized air (not shown) is connected to the input 1 7, in particular during the battery charging period to cool the latter, in particular at the end of charging when the heat generation inside the battery by reaction electrochemical exothermic and Joule effect can reach a few tens of W / dm ³ . The air loaded with entrained calories is dissipated into the environment.

There is shown in Figure 6, still by way of example only, a set of 8 batteries as described above. This set generates the energy necessary for the traction chain of a passenger vehicle. The use of a high voltage reduces the masses of the motor and the electrical distribution; therefore the series connection of the batteries will be preferred and will allow to reach 360 Volts in the case of our example. The cooling of the 8 batteries from a single source of air, pressurized in 19 and possibly conditioned in 20, can be effected by fluidly connecting the radiator elements of the batteries, in two parallel series of the four batteries, the batteries of each series being connected by bellows 21 ^ 21 ₆ as shown. The overall size of the assembly in FIG. 6 is approximately 1,500 x 1,400 mm. We could constitute a more compact set by arranging the eight batteries in two bunk beds of four batteries. The overall dimensions are compatible with the space available for the batteries in a passenger motor vehicle. The pressurized air source necessary for cooling the battery can then be installed in the room used as a garage for the electric vehicle, where the batteries are recharged. This source of pressurized air, a fan for example, could just as easily be mounted on the vehicle.

Of course, the present invention is not limited to the embodiments described and shown which have been given only by way of example. Thus the invention makes it possible to constitute the electrical supply of various machines other than a motor vehicle. The accumulator elements incorporated in the battery according to the invention could be of a type other than nickel-cadmium elements. In addition, in certain applications, it is possible to envisage using a cooling fluid other than gaseous, liquid for example. Some non-electrically conductive oils could be used for this purpose.

Claims

1. Electric storage battery, comprising a stack of elements (1 ₇ to 1 _n ) of flat bipolar accumulators electrically connected in series, at least one element (9 _1; 9 ₂ , 9 ₃ ) of heat radiator attached to the least one element for accumulating in the stack, this radiator element (9 9 ₂ , 9 ₃ ) delimiting a circulation passage for a cooling fluid which is not electrically conductive and capable of extracting heat from the battery coming from the accumulator elements (1, to 1 _n ), the radiator element (9 ,, 9 ₂ , 9 ₃ ) itself being made of an electrically conductive material in electrical contact with the one or more adjacent accumulator elements so as not to disturb the series connection of the accumulator elements of the stack, battery characterized in that it comprises an envelope (13) comprising means for thermal insulation of the faces of the stacking of accumulator elements ulator, so as to favor a diffusion of the heat generated in these elements in a direction normal to them.

2. Battery according to claim 1, consisting of accumulator elements of rectangular shape, characterized in that the radiator element generally conforms to the accumulator elements and consisting of two flat metal sheets (10, 1 1) , parallel and separated by means (12, 12 ', 12 ", 12"') to direct the circulation of the coolant between these two sheets, parallel to the short sides of these sheets, the coolant entering and leaving the element between large sides opposite them.

3. Battery according to claim 2, characterized in that said orientation means consist of a folded metal sheet (12 ', 12 ") along a surface with parallel generators resting on a director with a periodic waveform. of amplitude equal to the distance separating the two flat metallic sheets (10, 1 1) from the radiator element with which the folded metallic sheet is in electrical contact.

4. Battery according to claim 3, characterized in that said director has a square wave shape.

5. Battery according to claim 2, characterized in that said orientation means are constituted by tubular sections (12 "') arranged parallel to each other in the same plane between the two flat metal sheets.

6. Battery according to any one of claims 1 to 5, characterized in that it comprises a radiator element (9 _V 9 ₂ ) at each end of the stack of accumulator elements.

7. Battery according to all of claims 3 and 6, characterized in that it comprises a current collector (15) of elongated shape fixed on each of the end radiator elements (9 ₁₇ 9 ₃ ), perpendicular to the generators of the folded sheet of the radiator element.

8. Battery according to claim 6, characterized in that it further comprises at least one radiator element (9 ₃ ) placed between two accumulator elements, substantially in the middle of stacking accumulator elements.

9. Battery according to any one of claims 1 to 8, characterized in that each accumulator element comprises, between two rectangular metal sheets, an active material distributed in at least two layers (4, 5) coplanar and separated l 'from one another so as to provide around the two layers a retention volume (8) for a gas given off by the active material.

10. Battery according to claim 1, characterized in that the active material is distributed in two identical rectangular layers (4, 5) elongated parallel to each other and to the long sides of the accumulator element.

1 1. Battery according to any one of claims 1 to 10, characterized in that it comprises means (16) for connecting the radiator elements (9 9 ₂ , 9 ₃ ) to a source of a cooling fluid.

12. Battery according to any one of the preceding claims, characterized in that the accumulator elements are of the cadmium-nickel type and in that the radiator elements are made of nickel strip.

1 3. Battery assembly according to any one of claims 1 to 12, electrically connected in series, characterized in that the radiator elements of the batteries are connected in a series and / or parallel arrangement to a source of cooling fluid .