BATTERY MODULE EQUIPPED WITH POUCH CELLS

Description

Title BATTERY MODULE EQUIPPED WITH POUCH CELLS BATTERY MODULE EQUIPPED WITH POUCH CELLS DESCRIPTION Technical field The present invention relates to a battery module, which includes a plurality of pouch-type battery cells and is suitable for forming a battery pack consisting of multiple modules, in particular for the transport sector, for example for electric traction vehicles and hybrid thermal / electric traction vehicles. Context As is known, in electric or hybrid vehicles with battery packs, each battery pack is composed of a plurality of electrical energy storage modules, usually called battery modules, arranged in close proximity to one another within a housing structure. Each battery module, in turn, includes a casing and a plurality of battery cells, arranged side by side within that casing. The terminals of the battery cells, usually called tabs, are then electrically connected to each other to provide the intended electrical voltage at electrical terminals outside their casing. Safety requirements are extremely stringent and require the adoption of appropriate measures to minimize the spread of any thermal instability between battery cells within a single battery module. Specifically, measures must be taken to limit / prevent a temperature increase and possible gas emission from any one battery cell from affecting adjacent battery cells. This prevents a cascade of degeneration, compromising the function and / or integrity of the entire battery module and potentially causing fires. This requirement is particularly acute for pouch-type battery cells (generally referred to as "pouch cells"). In fact, in the event of thermal runaway, pouch cells typically release hot gases along a relatively wide edge, at random locations. This gas release can also cause self-ignition of flames along the same edge. This behavior—the venting of hot gases at random locations—increases the likelihood and speed of thermal propagation to adjacent pouch cells, thus making it more difficult to meet the homologation requirements of current regulations for electric and hybrid vehicles. From this perspective, conventional battery modules are unsatisfactory, as they cannot effectively manage the venting of hot gases. For example, battery module enclosures are closed and sealed at the top, so hot gases tend to remain trapped inside, and therefore tend to spread relatively quickly between all the battery cells inside. The aim of the present invention is therefore to meet the above-mentioned requirement (i.e. to slow down as much as possible the propagation of thermal instabilities between pouch cells) in a relatively simple and economical way, in order to satisfy the requirements of the approval regulations and, more generally, in order to reduce as much as possible the risk of fire in battery packs. Summary According to the present invention, a battery module as defined in claim 1 is provided. The dependent claims relate to specific and preferred embodiments of the present invention. Brief description of the drawings For a better understanding of the present invention, a preferred embodiment thereof is now described, purely by way of non-limiting example, with reference to the attached drawings, in which: Figure 1 is a perspective of the preferred embodiment of the battery module according to the present invention; Figures 2 to 5 are several partial perspective views of the battery module in Figure 1 and show some of its parts in exploded view; Figure 6 illustrates a detail of the battery module of the present invention, on an enlarged scale and in cross-section along a substantially vertical section plane, identified by the line VI-VI in Figure 1; Figure 7 shows a detail of Figure 6, in perspective view from above, on a further enlarged scale, and in cross-section along a section plane parallel to that of Figure 6; and Figures 8 and 9 show, respectively, two opposite longitudinal ends of the battery module, in perspective view, and in cross-section along a substantially horizontal section plane, identified by the trace VIII-VIII in Figure 6. Description of embodiments In Figure 1, the reference number 1 indicates a battery module, which can be used to form a battery pack capable of supplying electrical energy for traction of a vehicle, together with other battery modules (e.g. with the same dimensions, shape and structure) arranged side by side. The teachings reported below apply, in general, not only to the automotive and transport sector, but to any application that needs to store electrical energy, even if this description explicitly refers to the vehicle example. Therefore, the term battery module, here and hereafter, refers to an energy storage element, which is capable of storing electrical energy, of supplying the stored electrical energy, and of being recharged (through appropriate systems, known and not described in detail). The battery module 1 has a substantially parallelepiped external shape and extends along a longitudinal axis 2, a transverse axis 3 and a vertical axis 4, which are orthogonal to each other. The battery module 1 comprises a plurality of pouch-type battery cells, commonly referred to in English as pouch cells and identified by the reference 5 in Figures 4-6. The pouch cells 5 are identical to each other (in structure, shape and dimensions) and have an elongated shape, typical of this type of battery cell, with a main dimension, measured parallel to the longitudinal axis 2, greater than the other two dimensions, measured as height and thickness respectively along the vertical axis 4 and the transverse axis 3. In greater detail, with reference to figures 5 and 6, each pouch cell 5 has two external faces 8, which are opposite to each other and orthogonal to the transverse axis 3, and are connected to each other by a perimeter edge region 10, consisting of a lower side 12 and an upper side 13, opposite to each other along the vertical axis 4, and by two end sides 14, opposite to each other along the longitudinal axis 2. The pouch cells 5 are arranged in a row along the transverse axis 3, so that the faces 8 of each pouch cell 5 face the faces 8 of the adjacent pouch cells 5. At the opposite longitudinal ends, each pouch cell 5 ends with respective electrical poles, generally referred to by the English term tabs, and defined by respective tabs 16. The latter are parallel to the vertical axis 4, protrude longitudinally from the respective end sides 14 and are flexed or curved in such a way as to each have a respective terminal portion 17 (figures 8 and 9) which faces transversely and comes into electrical contact with the terminal portion 17 of an adjacent tab 16, to define a series electrical connection.In practice, with this series connection, the pouch cells 5 form a sort of serpentine: at the opposite ends of this serpentine (figure 8), the respective fins 16 are then connected to respective electrical poles of the battery module 1, in a known manner and not described in detail. With reference to figures 1 and 6, the battery module 1 further comprises a casing 19, in turn comprising a base wall 20, on which the lower sides 12 of the pouch cells 5 are arranged, and a perimeter wall, which extends upwards from a rectangular edge of the base wall 20 so as to define the outline of a housing 24, hosting the set of pouch cells 5. This perimeter wall is made up of four plates, coupled in fixed positions to the base wall 20 in a known manner and not described in detail, so as to ensure the sealing of the housing 24 along the perimeter of the base wall 20. These plates are defined by: a front plate 25 and a rear plate 26, opposed to each other along the longitudinal axis 2; and two side plates 27, opposed to each other along the transverse axis 3.The coupling of the plates 25 and 26 to the plates 27 is of a known type and not described in detail, and is configured so as to ensure sealing along the vertical edges of the housing 24. The plates 27 are parallel to each other and orthogonal to the transverse axis 3 and are arranged in such a way as to exert a compressive action on the bag cells 5 along the transverse axis 3, i.e. towards the faces 8. The casing 19 further comprises a cover plate 28, which closes an upper opening of the housing 24 and is coupled to an upper edge of the plates 25, 26, 27, in a known manner and not described in detail (for example, in such a way as to ensure the sealing of the housing 24 along such upper edge). The cover plate 28 is substantially parallel to the base wall 20 and is spaced from the upper sides 13 of the pouch cells 5 along the vertical axis 4, as also visible in the enlargement of figure 7, so as to ensure an empty space, or gap, at an upper end 29 of the housing 24. Preferably, the cover plate 28 has a plurality of openings 30, of the through type, so as to put the upper end 29 of the housing 24 in communication with an external environment, above the battery module 1. This external environment corresponds, in use, to an upper area of ​​the battery pack where the battery module 1 is installed. Preferably, the openings 30 are aligned in directions parallel to the longitudinal axis 2 so as to form a series of longitudinal rows 31 of openings (figure 1). In particular, each longitudinal row 31 of openings is above a respective pair of pouch cells 5. In the specific case illustrated, the two pouch cells 5 are an exception, which are arranged on opposite sides, along the plates 27, as they have respective longitudinal rows 31 of openings dedicated to them. Still referring to Figure 7, the openings 30 are provided to ensure the venting of any hot gases emitted by the bag cells 5, from the upper end 29 of the housing 24 towards the external environment. Preferably, the passage for the hot gases to be vented through each opening 30 is partially blocked, i.e. partially obstructed, or is closed by a respective shutter element 32, which is vertically aligned, for example coaxial, with the corresponding opening 30. More preferably, each shutter element 32 is defined by a plate parallel to the cover plate 28. In particular, each shutter element 32 is fixedly coupled onto the two bag cells 5 which are arranged below the corresponding opening 30. More specifically, the shutter elements 32 are arranged lower than the cover plate 28; in other words, they are inside the upper end of the housing 24. An annular slit may be present between the peripheral edge 33 of each opening 30 and the peripheral edge 34 of the corresponding shutter element 32, but such annular slit has an insufficient width for the passage of gases which are emitted into the housing 24 when the bag cells 5 reach a condition of thermal instability. At the same time, the shutter elements 32 are coupled to the upper sides 13 of the battery cells 5 in such a way that they automatically detach upon reaching a critical operating condition, defined by design, for example upon reaching a given threshold temperature and / or a given internal pressure (in the upper end 29 of the housing 24), due to gases emitted by the pouch cells 5 under conditions of thermal instability. When this critical operating condition is reached, the shutter elements 32 are configured so as to suddenly detach from the pouch cells 5 and be automatically ejected through the respective openings 30, in order to fully open the openings 30 and thus vent the hot gases to the outside.In particular, this expulsion is due to the combination of high temperature and pressure values, which manage to break the coupling constraint of the shutter elements 32 on the upper side 13 of the bag cells 5: more specifically, the shutter elements 32 are expelled upwards under the thrust of the gases. Therefore, when the operating conditions of one or more bag cells 5 become critical (due to thermal instability), a passage opens for the venting of the hot gases, and this passage is equal to the entire extension of the openings 30 in correspondence with the detachment of the shutter elements 32 (i.e. precisely in correspondence with the bag cells 5 that have become critical). The shape and dimensions of the perimeter edges 33 and 34 must be established in the design in such a way as to ensure this expulsion, without the risk of interference or jamming (for example, the shutter elements 32 must be slightly smaller than the corresponding openings 30). In practice, the set of openings 30 and shutter elements 32 defines a set of valves that, under critical operating conditions (i.e., in the presence of thermal instability), perform a safety function by opening a passage to discharge hot gases in a preferential direction, i.e., upwards. In this way, during use, the hot gases are rapidly vented into the upper area of ​​the battery pack. At the same time, for the bag cells 5 that do not reach the critical operating condition, the corresponding shutter elements 32 remain in their standard position (attached to the upper sides 13 of the bag cells 5) and continue to block the corresponding openings 30, thereby preventing the hot gases already vented to the outside from re-entering the housing 24 (or, in any case, the amount of gas that can re-enter through the annular slot between the edges 33 and 34 is negligible, so that it does not compromise the thermal stability of the other bag cells 5). To achieve relatively simple automatic detachment of the shutter elements 32, the latter are preferably fixed to the upper sides 13 of the bag cells 5 by gluing, i.e., using an adhesive material 35, specifically chosen based on the intervention threshold that must define such detachment. The choice of adhesive material 35, as well as the width of the glued area and any other coupling parameters, can be chosen on the basis of simulations and / or experimental tests in order to achieve detachment at the desired time. With reference to Figure 6, the bag cells 5 are alternated along the transverse axis 3 with a plurality of partitions, defined by flat walls, with a rectangular perimeter, whose faces rest directly against the faces 8 of the bag cells 5. In particular, the partitions are of two different types and are indicated respectively by 40a and 40b in the figures. In turn, the partitions 40a are alternated with the partitions 40b along the transverse axis 3. The partitions 40a preferably have a thermally conductive material, configured so as to transfer heat from the faces 8 of the pouch cells 5 towards the base wall 20. Indeed, in use, at or below the base wall 20, a cooling system will be provided, for example a plate defining internal channels for a cooling liquid. In particular, the partitions 40a comprise respective metal sheets, for example aluminium, in direct contact with the faces 8. More specifically, each partition 40a is made up of a single metal sheet. Partitions 40b, on the other hand, act as a thermal barrier along the transverse axis 3. To this end, with reference to Figures 7-9, partitions 40b comprise respective sheets 67 made of flame-retardant material. The term flame-retardant material refers to a refractory material, specifically a material resistant to temperatures above 900°C and direct contact with flames for a period of time greater than 15 minutes, without interacting with other adjacent materials and maintaining its integrity. For example, to meet these requirements, sheet 67 comprises phlogopite mica. The partitions 40b also comprise respective sheets 68 which cover, at least in part, one face of the sheets 67 and are made of elastically deformable material, of a known type, to keep the bag cells 5 compressed along the transverse axis 3. In other words, each partition 40b is made up of two layers, defined respectively by the sheets 67 and 68. As regards the partitions 40a, they have a lower edge 41a which is arranged on the base wall 20 and is preferably coupled to the latter in a fixed position by means of an adhesive material 42 (figure 4), deposited for example in the form of a continuous layer. In particular, the adhesive material 42 extends longitudinally along the entire lower edge 41a. With reference to Figure 7, the partitions 40a have a height lower than the housing 24, so that they do not engage its upper end 29. Preferably, each partition 40a is vertically aligned with at least one of the openings 30; more preferably, each partition 40a is vertically aligned with a respective longitudinal row 31 of openings. In greater detail, each partition 40a has an upper edge 43a that extends upwards beyond the faces 8 (next to the upper sides 13 of the pouch cells 5), so as to engage the adhesive material 35 and, therefore, perform an additional support function for the gluing of the shutter elements 32. Not only that, but the upper edge 43a also has the function of a mechanical stop or strut, as it prevents the respective shutter element 32 from moving downwards and therefore increasing the passage section of the annular slot between the edges 33 and 34.In other words, since the upper side 13 of the bag cells 5 is relatively soft, a more rigid structure, i.e. the partitions 40a, is used for the correct positioning and operation of the shutter elements 32. The adhesive material 35 advantageously fills two areas on opposite sides of the upper edge 43a. With reference to Figures 9 and 8, along the longitudinal axis 2 each partition 40a ends, towards the plate 25, with an edge 45a and, towards the plate 26, with an edge 46a. The edges 45a and 46a extend longitudinally beyond the faces 8 of the pouch cells 5 and are coupled to respective support elements 47a and 48a which, for example, extend for the entire height of the partitions 40a. With reference to figure 8, each of the support elements 48a defines a respective shoulder 49a, facing longitudinally towards the plate 26; at the same time, the terminal portions 17 of the fins 16 rest longitudinally on the shoulders 49a. The material of the shoulders 49a on the support elements 48a must be such as to support the fins 16 during the welding operations performed for the electrical connection between the end portions 17 and, for example, is defined by metallic material. As regards the plate 26 (fig. 8), the latter is preferably of the multi-layer type and comprises a relatively rigid external wall 55, in particular made of metal (for example aluminium), covered by an intermediate layer 52, made of a relatively flexible material, with mineral fibres to perform a thermal insulation function, and a layer of intumescent material 51, of a spongy or porous type, which in turn covers the layer 52 and defines an internal surface 50 of the plate 26 in the housing 24. More preferably, the plate 26 is shaped so as to have, along the internal surface 50, vertical ribs 53 alternating transversely with vertical recesses 54. At the opposite longitudinal end of the battery module 1, with reference to figure 9, preferably the plate 25 has a structure similar to that just described for the plate 26; in particular, it comprises a relatively rigid external wall 56, for example in thermosetting material. SMC (sheet moulding compound), coated with a relatively flexible intermediate layer 62, with mineral fibres, in turn coated with a layer of intumescent material 57, which defines an internal surface 58 of the plate 25 in the housing 24. In particular, the plate 25 is shaped so as to have, along the internal surface 58, vertical ribs 59 alternating transversely with vertical recesses 60. In particular, the support elements 47a on the edges 45a define respective shoulders 61a, which are longitudinally facing the plate 25 and are arranged in correspondence with the vertical recesses 60. In the attached figures, the parts that are related to partitions 40b, and which correspond to those described above for partitions 40a, are indicated by the same reference numbers, followed by the letter b, instead of the letter a. As shown in figure 9, for each partition 40b, the edge 46b, the support element 48b and the shoulder 49b face the plate 25 (figure 9) and are coupled in a gas-tight manner to its internal surface 58, with the interposition of the terminal portions 17 of the fins 16, for the entire height of the partition 40b and of the fins 16 themselves. In detail, the terminal portions 17 remain longitudinally clamped between the shoulders 49b and the internal surface 58 of the plate 25 (in particular, in correspondence with the vertical ribs 59). Specifically, the layer of intumescent material 57, increasing in volume with the temperature during use, further seals the coupling between the plate 25 and the terminal portions 17 of the fins 16. In particular, the edge 46b, on which the support element 48b is mounted, is made only of the sheet 67, i.e. it is not covered by the sheet 68. At the same time, as shown in Figure 8, the edge 45b of the partitions 40b faces the plate 26 and is gas-tightly coupled to the internal surface 50 along the entire height of the partitions 40b (for example, at the vertical recesses 54). Preferably, the edge 45b is coupled directly to the intumescent material layer 51 of the plate 26, so that the intumescent material layer 51, increasing in volume with the temperature during use, seals the coupling between the plate 26 and the edge 45b of the partitions 40b even better. Accordingly, at opposite longitudinal ends (i.e., along edges 45b and 46b) partitions 40b are gas-tightly coupled, directly or indirectly, to internal surfaces 50 and 58 of plates 25 and 26. Preferably, the upper edges 43b of the partitions 40b (Figure 7) are also gas-tightly coupled to the cover plate 28, over the entire length of the housing 24, preferably by means of sealing material 64, deposited on the cover plate 28 itself, for example in the form of longitudinal beads. Finally, the lower edge 41b of the partitions 40b (figure 6) is arranged on the base wall 20 and is coupled to the latter in a gas-tight manner, for example by means of the adhesive material 42, along the entire length of the housing 24. In this way, with reference to figures 6 and 7, any hot gases emitted from each bag cell 5 flow only into the upper end 29 of the housing 24, i.e. upwards, and then vent through the openings 30 as described above. Furthermore, the partitions 40b define between them, along the transverse axis 3, a series of compartments 66, each of which is isolated from the adjacent compartments 66, preferably along the entire perimeter (i.e. in correspondence with the base wall 20, the cover plate 28 and the plates 25 and 26). In particular, each compartment 66 houses a respective pair of bag cells 5 (with the exception of the two opposite sides along the plates 27, where each compartment 66 has only one bag cell 5). Therefore, the hot vent gases emitted into a given compartment 66 are confined, and can only vent in one specific direction, namely upwards, into the upper end 29 of the housing 24. In other words, the propagation of the hot gases into the housing 24 along the transverse axis 3 is prevented. Each compartment 66 then communicates with the outside environment through at least one of the openings 30, and therefore houses at least one corresponding shutter element 32, so as to allow the hot gases to escape to the outside. In particular, each compartment 66 communicates with the outside through a respective longitudinal row 31 of openings. From the above it is evident that the battery module 1 is able to limit the propagation of hot gases in the housing 24 along the transverse direction 3 and define a very precise preferential direction for the venting of such hot gases, i.e. upwards, thanks to the airtight couplings of the partitions 40b along at least part of their perimeter. Thanks to the openings 30, the hot gases are allowed to flow upwards towards the outside environment, as if the battery module 1 were equipped with safety valves. In particular, as mentioned above, the openings 30, with their respective shutter elements 32, help keep the compartments 66 isolated from the hot gases that have already been vented to the outside. At the same time, the partitions 40b are advantageous to prevent heat transfer along the transverse axis 3. Furthermore, partitions 40a are advantageous for dissipating heat towards the base wall 20. The combination of partitions 40a and 40b, in alternating positions with each other, offers an optimal solution. Other advantages are then evident to a technician in the sector based on what is set out above with reference to the attached drawings. Finally, it is clear that modifications and variations can be made to the battery module 1 described and illustrated here without departing from the scope of the present invention, as defined in the attached claims. In particular, each compartment 66 could contain a different number of pouch cells 5, and / or the partitions 40a and / or 40b could be made of materials other than those indicated above by way of example.

Claims

CLAIMS 1 .- Battery module (1) comprising: - a casing (19) defining a housing (24) and comprising: a) a base wall (20) and a cover plate (28) opposite each other along a vertical direction (4); b) a front plate (25) and a rear plate (26), opposite each other along a longitudinal direction (2), orthogonal to the vertical direction (4); c) two side plates (27), opposite each other along a transverse direction (3), orthogonal to the longitudinal (2) and vertical (4) directions; - a plurality of pouch cells (5) parallel to the longitudinal direction (2), arranged in a row along the transverse direction (3) and electrically connected in series to each other;wherein said housing (24) is divided, along said transverse direction (3), into a plurality of compartments (28) by means of first partitions (40b) arranged between said bag cells (5), and each said compartment (66) houses at least one respective bag cell (5); characterised in that said compartments (66) are insulated from each other in a gas-tight manner at said base wall (20), said front plate (25) and said rear plate (26).; 2 .- The battery module according to claim 1, wherein said compartments (66) are insulated from each other in a gas-tight manner also at said cover plate (28). 3 .- The battery module according to claim 2, wherein said first partitions (40b) comprise respective upper edges (43b), which are gas-tightly coupled to said cover plate (28) by means of beads of sealing material (64). 4 .- The battery module according to any of the preceding claims, wherein at least some of said compartments (66) each house a respective pair of pouch cells (5). 5 .- The battery module according to any of the preceding claims, wherein said first partitions (40b) each comprise a respective first sheet (67) made of flame-retardant material. 6 .- The battery module according to claim 5, wherein each said first partition (40b) comprises a respective second sheet (68) made of elastically deformable material, arranged at least in part on one face of said first sheet (67). 7 .- The battery module according to any of the preceding claims, wherein said first partitions (40b) comprise respective lateral edges (45b, 46b), which are gas-tightly coupled, directly or indirectly, to said front and rear plates via intumescent material. 8 .- The battery module according to claim 7, wherein said front and rear plates have respective internal surfaces, longitudinally delimiting said housing and defined by respective layers of intumescent material. 9 .- The battery module according to claim 8, wherein said pouch cells (5) terminate with respective fins (16) having terminal portions (17) which are fixed to terminal portions (17) of adjacent fins (16), so as to define the series electrical connection; and wherein said terminal portions (17) are coupled gas-tight against one of said layers of intumescent material. 10.- The battery module according to any of the preceding claims, wherein said casing further comprises second partitions (40a) arranged between said pouch cells (5), comprising respective lower edges coupled to said base wall (20) and having a thermal conductive material arranged in contact with said pouch cells (5) so as to transfer heat from said pouch cells (5) to said base wall (20). 11 .- The battery module according to claim 10, wherein said second partitions (40a) comprise respective metal sheets. 12 .- The battery module according to claim 10 or 11, wherein said first partitions (40b) and second partitions (40a) are alternated with each other along said transverse direction (3). 13.- The battery module according to any of the preceding claims, wherein said cover plate (28) has at least one through opening (30) for each of said compartments (66), to put said compartments (66) in communication with an external environment. 14 .- The battery module according to claim 13, wherein each said through opening (30) is at least partially closed by a respective shutter element (32) coupled to said pouch cells (5) in such a way as to detach upon reaching a critical operating condition and, consequently, to be automatically ejected through the corresponding through opening (30). 15 .- The battery module according to claim 14, wherein said shutter elements (32) are supported by second partitions (40a) arranged between said pouch cells (5).