FR2893449A1 - Electrode stack compressing method for automobile field, involves compressing stack of electrodes using U-shaped compression clamps which are not supported on can of storage battery for exerting elastic compression force on stack - Google Patents

Abstract

The method involves placing a stack (48) of electrodes (24, 28) inside compartments of a can (40) of a storage battery. The stack is compressed using U-shaped compression clamps (440) which are not supported on the can for exerting an elastic compression force on the stack, where each clamp includes arms and a base. The stack is compressed before placing the stack inside the can, where the clamp is made of metallic material e.g. stainless steel. The clamp is covered with a protection cover. An independent claim is also included for a storage battery.

Description

GENERAL TECHNICAL FIELD The present invention relates to a method of

  compression of an electrode stack of an accumulator, comprising a step of placing the stack inside a tank of the accumulator. The invention also relates to a corresponding accumulator. STATE OF THE ART It is known to exert a compressive force on an electrode stack of an accumulator, used for example in the automotive field, to improve the performance of the accumulator, particularly its endurance in cycling. Such a method and such an accumulator are known from WO 95/15584 for example. They are taken schematically in FIG. 1. FIG. 1 represents a known accumulator comprising a tank 40 containing a stack 48 of a plurality of electrodes 24 and 28. Each pair of electrodes 24 and 28 is included in a cell, and the stack 48 consists of a plurality of cells. The accumulator further comprises two terminals, each terminal being located at one end of the electrode stack 24 and 28.

  FIG. 2 schematically represents an example of a cell of the stack 48 of an accumulator. Each cell comprises a bipolar plate 20 on which is supported a positive electrode 28, a separator 30, a negative electrode 24 and again a bipolar plate 20.

  The separator can generally be composed of a layer of microporous polyethylene (PE) for so-called open batteries, or be composed of a layer of glass wool felt (glass mat according to the English terminology) or be a corrugated spacer perforated polyvinyl chloride (PVC) for so-called sealed recombination batteries. There are also less generally combinations of separators combining several of these materials; for example PE sheets combined with layers of glass wool, or a combination according to Figure 2. In Figure 2, the separator 30 is composed of a layer 31 consisting of a flat sheet of microporous polyethylene on which is The corrugated spacer 32 in turn supports a layer 33 of glass wool. The separator 30 mechanically separates the positive electrodes 28 and negative 24 while allowing an electrolytic junction. FIG. 1 illustrates a method of arranging the stack of electrodes 48 in the tank 40, to exert a constant and uniform compressive force between the bipolar plates 20 and separators 30 constituting the stack 48.

  The electrode stack 48 is bonded to a first end plate 41 forming a current collector and a second end plate 42 also forming a current collector. The first plate 41 is fixed relative to the tray 40. The second end plate 42 is supported by a plurality of springs 44 which provide a compressive force of the stack 48. The springs 44 can exert a compressive force , in particular on the separators 30. In the known embodiment of Figure 1, the terminal connected to the plate 42 urged by the springs 44 slides in sealing means 47 of the tray. The compression device comprising springs 44 according to Figure 1 has drawbacks. Such a device is bulky, and its placement in a tray of an accumulator is at the expense of the number of cells in the stack. It is particularly difficult to set up such a compression device in a traditional non-bipolar battery comprising a tray 40 divided into several compartments and having a stack 48 in each compartment, as shown schematically in FIG. 3. Indeed, a space 5 between a stack 48 and side walls 3 or internal 6 delimiting the compartments of the tray 40 is often less than 5 mm. The space 5 is not sufficient to allow the installation of the compression device of FIG. 1 or it is necessary to remove cells from the stack. In addition, the establishment of a device according to Figure 1 in a tray 40 according to Figure 3 causes insertion difficulties. Said insertion is restrictive and expensive for industrial manufacture. An adaptation of the tray is necessary for mounting a sealing device 47 visible in Figure 1. The device 47 is difficult to achieve technically, and is therefore expensive. Finally, a pressure is applied to the wall 41 of the tray, and the tray can undergo deformation. PRESENTATION OF THE INVENTION The invention proposes to overcome at least one of the disadvantages mentioned above. For this purpose, there is provided according to the invention a method of compressing an electrode stack of an accumulator, comprising a step of placing the stack inside a tank of the accumulator, characterized in that it comprises a step of compressing the stack with at least one compression clamp, so that the compression clamp does not support the pan to exert an elastic compressive force. The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination: the stack is compressed before the stack is placed inside the tank; the stack is compressed by means of at least one U-shaped clamp comprising arms, the stack being placed between the arms of the U; - The clip is spread by a spacer to place the stack between the arms of the U; At least one shim is placed between the clamp and the stack; separators are placed between the electrodes of the stack, the separators being composed of a superposition of a layer of felt glued on a ribbed layer.

  The invention also relates to a corresponding accumulator. The invention has many advantages. It allows in particular the easy and inexpensive mounting of a compression device in a tank of a battery.

  The battery tray remains standard and needs no adaptation. The bin does not require any reinforcement of its thickness nor any addition of an external system of maintenance of the sides. The invention makes it possible to obtain a constant elastic compression force. The variation of the volume of the stack of electrodes is thus allowed, which limits a creep and allows a better performance in the cycles of the accumulator. PRESENTATION OF THE FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which: FIG. commented, schematically shows a section of a known accumulator having a single stack of electrodes, and a method for applying a compressive force to said stack; FIG. 2, already commented on as well, schematically represents a pair of known electrodes separated by a known separator; - Figure 3, already commented also, represents a known tray of an accumulator having a plurality of compartments, each compartment comprising a stack of electrodes; FIG. 4 schematically represents an accumulator according to FIG. 3 comprising compression clamps according to the invention; - Figure 5 shows a side view of a stack compressed by a pair of clamps according to the invention; - Figures 6a and 6b show diagrammatically views of a clamp 30 according to Figure 5, respectively from behind and profile; and FIG. 7 is a diagrammatic sectional view of a separator which can advantageously be placed in a stack of electrodes.

  In all the figures, similar elements bear identical reference numerals. DETAILED DESCRIPTION FIG. 4 schematically illustrates an example of a compression method implemented in an accumulator comprising at least one stack 48 of electrodes 24 and 28 arranged in cells. In the example of FIG. 4, the accumulator comprises a trough 40 with longitudinal outer walls 3 and transverse outer walls 2. The trough 40 comprises, for example, six compartments, each receiving a stack 48. The compartments are delimited by a medial longitudinal internal wall 6 intersecting transverse internal walls 7. Of course, it is also possible to consider in-line containers, and the example of the tray of the present description is not limiting. 10 and 11 refer to the longitudinal faces of the stacks 48. Frames 8 perpendicular to the faces 10 and 11 make it possible to hold the electrodes 24 and 28 together. The frames 8, which provide the electrical connection between the electrodes 24 and 28, are connected to a part 9 (inter-element welding) which allows the electrical connection between the different elements of the battery. The stacks 48 are supported in each compartment by the frames 8 and 9. As shown in FIG. 4, a method of compressing the electrode stack 24 and 28 includes a step of compressing the stack 48. thanks to at least one compression pliers 440. The compression clamp does not support the tray to exert an elastic compressive force. Very advantageously, two clamps are placed on each stack, one on each small side of the faces 10 and 11. Advantageously, the stack 48 is compressed before placing the stack inside the tray 40. It is easy to placing the stack 48 in the tray 40, because it is compressed by the clamp.

  Advantageously, the stack is compressed by means of at least one U-shaped clamp 440, as shown more precisely in FIGS. 5, 6a and 6b. The U-shaped clamp thus comprises a base 446 and two arms 445, advantageously made of material on the base 446. The base 446 may comprise longitudinal or transverse reinforcements (not shown in the figures). Preferably, the arms 445 are slightly inclined inward with respect to the base 446, so that an internal angle θ between the base 446 and one of the arms 445 is less than 90. The value of this angle makes it possible to exert a compressive force when the stack 48 is placed between the arms 445 of the U, as shown in FIG. 5 in particular. It is understood that other forms are possible, depending on the different criteria related to the size, a coating, the establishment, the mass and the cost of the clamp. The elastic compression force is exerted on the stack, for better performance and better performance of the accumulator, including its endurance in cycling. The invention allows an increase of a factor of between 5 and 10 approximately on the endurance in cycling. The pressure exerted by the clamp 440 corresponds to a pressure of 0.1 to 1 kg / cm 2, ie 0.01 to 0.1 MPa. In order to be able to place the stack between the arms 445 of the U forming the clamp 440, in particular before the placement of the stack 48 in the tray 40, the clip is spread apart by means of a spacer. Advantageously, at least one wedge 12 is placed between the clamp 440 and the stack 48. Such a wedge allows the distribution of forces on all the faces 10 and 11 of the stack. Advantageously, each clamp 440 is made of metallic material. For example, the manufacture of the pliers 440 may be made of stainless steel, preferably austenitic type 301, because this steel is available in a wide range of thicknesses and cold work is possible.

  Of course, the choice of the material for the clamp 440 may be different, depending on the size of the stack 48, the desired mass of the clamp, its desired manufacturing cost, etc. The accumulator is subjected to very variable temperature conditions. Overall, the material of the compression tongs 440 and shims 12, as well as their characteristics, must be stable for a range of temperatures between -20 C and +80 C. The clamps 440 and shims 12 are further immersed in a solution of sulfuric acid whose concentration varies from 0.5 to 5 mol / L.

  The clamps 440 and shims 12 must therefore be stable in sulfuric acid medium. They must also keep all of these properties for a duration equivalent to the calendar life of the accumulator, more than five years for an average temperature of about 25 C.

  Therefore, the clamp 440 is advantageously coated with a protective coating of the metallic material against corrosion and / or acid attack. The coating must be stable in a sulfuric acid solution with a concentration ranging from 0.5 to 5 mol / L.

  The method of application of the coating on the clamp should not change the mechanical properties of the clamp, knowing that some clamps undergo heat treatments - for example, the stainless steel 301 undergoes heat treatment at 400 C. When setting in place of the clamp on the stack, and during the cycling of the battery (charge / discharge), the clamp undergoes significant mechanical stresses. The coating must therefore have sufficient elastic properties to follow the deformations of the clamp without changing its hiding power. For example when placing the clamp on the stack, the coating is subjected to stresses of the type friction and / or crushing which should not damage it. Advantageously, the coating is of the polymer type. The polymer is, for example, a polypropylene / polytetrafluoroethylene polymer sprayed on the hot or fluidized-bed clamp. The thickness of the coating is preferably of the order of 0.5 mm. Advantageously, the shims 12 are made of hard plastic, for example of the polycarbonate type, or of glass.

  As for the clamps, other materials are of course possible for the coating and shims 12. FIG. 7 shows advantageous separators placed between the electrodes 24 and 28 of the stack different from those of FIG. 2. Each separator 30 is composed of a superposition of a felt layer 301 bonded to a rib layer 302. Advantageously, the felt layer 301 is glass wool and the rib layer 302 is made of polyethylene. The rib layer 302 includes a plate 304 having regularly spaced ribs 303. The distance 306 between each rib is preferably between 3.5 and 4 mm. The plate 304 has a thickness 305 of the order of 0.5 mm. The total height of the ribs 303 with respect to the base of the plate 304 is a height 308 of the order of 1.5 to 1.75 mm. The thickness 309 of the layer 301 of felt is of the order of 0.7 mm. The total thickness 307 of the separator 30 is of the order of 2.2 to 2.45 mm. Of course, the preceding dimensions are given by way of non-limiting examples. Figures 5, 6a and 6b show a preferred embodiment of the invention. In this embodiment, the stack 48 comprises seven positive electrodes 28 and eight negative electrodes 24, for faces 10 and 11 having a length of 153 mm and a width of 86 mm. The height of the stack 48, with the separators and before compression, is about 74 mm. The height 443 of the arms 445 is approximately equal to half the width 442 of the base 446. The maximum value for the dimension 442 is of the order of 74 mm, and therefore the dimension 443 has a value of the order 35 mm. The spacing 441 between the arms 445 may be variable depending on the compression force to be exerted. The length 447 of the clamp 440 is equal to 86 mm. The thickness 444 of the clamp 440 is equal to about 1.2 mm. The shims 12 have thicknesses of between 1 mm and 3 mm, for example 2 mm.

  Under these conditions, the stack at a height of 62.5 mm for a compressive force of 0.7 kg / cm 2 (0.07 MPa). Figure 4 shows an example of a battery with six compartments, but the number of compartments can be any.

Claims (13)

  A method of compressing a stack (48) of electrodes (24, 28) of an accumulator, comprising a step of placing the stack inside a tank (40) of the accumulator, characterized in that it comprises a step of compressing the stack (48) with at least one compression pliers (440) so that the compression pliers do not support the bin to exert a compressive force elastic.   2. Method according to the preceding claim, wherein the stack (48) is compressed before placing the stack inside the tray (40).   3. Method according to one of the preceding claims, wherein the stack is compressed by at least one U-shaped clamp (440) having arms (445), the stack being placed between the arms (445) of the U.   4. Method according to the preceding claim, wherein the clip is spread through a spacer to place the stack between the arms of the U.   5. Method according to one of the preceding claims, wherein is placed at least one wedge (12) between the clamp (440) and the stack (48).   6. Method according to one of the preceding claims, wherein separators (30) are placed between the electrodes (24, 28) of the stack, the separators being composed of a superposition of a felt layer (301). stuck on a ribbed layer (302).   7. Accumulator comprising a tray (40) and at least one stack (48) of electrodes (24, 28), the stack being placed inside the tray, characterized in that it comprises at least one clamp of compression (440) compresses the stack (48), so that the clamp (440) exerts an elastic compressive force on the stack (48) by taking no support on the tray (40).   8. Accumulator according to the preceding claim, wherein the clamp is U-shaped having arms (445), the stack being placed between the arms (445) of the U.   9. Accumulator according to the preceding claim, wherein the arms 10 (445) of the U are inclined inwardly.   10. Accumulator according to one of the three preceding claims, wherein the clamp (440) is of metal material. 15   11. Accumulator according to the preceding claim, wherein the clip is covered with a protective coating of the metallic material against corrosion and / or attack by an acid.   12. Accumulator according to one of the five preceding claims, 20 comprising at least one shim (12) between the clamp (440) and the stack (48).   Accumulator according to one of the six preceding claims, wherein the stack comprises separators (30) between the electrodes (24, 28), the separators being composed of a superposition of a felt layer (301). stuck on a ribbed layer (302).