An electric battery unit with a highly efficient temperature-regulating system

Abstract

In an electric battery unit (1), comprising an array of battery cells (2) immersed in a temperature-regulating fluid within a container (4), the battery cells (2) are kept spaced apart from each other by spacer walls (8). Each spacer wall (8) occupies only a lower part of the space (7) between one cell and another, adjacent to the inlet collector chamber (5) for the temperature-regulating fluid. At least some of the spacer walls (8) have a plurality of passage slits (9) for the temperature-regulating fluid, each configured with a lower inlet port (9A) communicating with an inlet collector chamber (5) of the temperature-regulating fluid, an upper outlet port (9B), having a passage section significantly larger than that of the inlet port (9A), and a passage that connects the inlet port (9A) with the outlet port (9B), having two lateral walls (9C) diverging from each other in the direction of the outlet port (9B). In this way, the space between each cell (2) and another is traversed by a plurality of flows of temperature-regulating fluid exiting from said passage slits (9), so as to substantially and uniformly cover the entire surface of the wall of the cell (2) facing the passage (7) for the temperature-regulating fluid.

Description

[0001] An electric battery unit with a highly efficient temperature-regulating system

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the invention

[0004] This invention relates to an electric battery unit equipped with a highly efficient temperature-regulating system.

[0005] The invention relates in particular to an electric battery unit of the type comprising an array of battery cells immersed in a temperature-regulating fluid within a container of the battery unit, wherein the container includes an inlet opening for the temperature-regulating fluid, communicating with an inlet collector chamber, arranged below the array of battery cells, an outlet opening for the temperature-regulating fluid, communicating with an outlet collector chamber, arranged above the array of battery cells, wherein the inlet collector chamber and the outlet collector chamber communicate with each other via a plurality of passages for the temperature-regulating fluid formed between one battery cell and another, and wherein the battery cells are kept spaced apart from each other by spacer walls, so as to define said passages for the temperature-regulating fluid between one battery cell and another.

[0006] Prior art

[0007] Electric battery units having a temperature-regulating system of the type indicated above are known and used for a long time.

[0008] Figure 1 of the attached drawings shows an example of an electric battery module 1 , comprising an array of aligned battery cells 2 of the prismatic type illustrated in figure 2. This type of battery cell includes a casing with an upper wall 2A, from which the positive and negative poles 3P and 3N of the cell 2 protrude, two main walls 2B (only one of which is visible in figure 2), two end walls 2C (only one of which is visible in figure 2) and a lower wall 2D.

[0009] According to the prior art described above, the battery cells 2 are arranged within a hermetic container 4 and are immersed in a dielectric temperature-regulating fluid (for example an oil). The container 4 defines within it an inlet collector chamber 5 (schematically illustrated in figure 3) arranged below the cells 2, and an outlet collector chamber 6 (also schematically illustrated in figure 3) arranged above the cells 2. The container 4 has an inlet 5A and an outlet 6A for the temperature-regulating fluid, communicating respectively with the inlet collector chamber 5 and with the outlet collector chamber 6. P and N indicate the positive pole and the negative pole of the battery module 1 of figure 1

[0010] Generally, the inlet 5A is always arranged below the cells 2, while the outlet 6A is arranged above the cells 2, to allow any air bubbles formed within the fluid to be collected in the upper collector chamber. However, this layout is not the only possible one. Inlet and outlet can be inverted when it is possible to guarantee an inlet pressure suitable to avoid any form of evaporation of the liquid.

[0011] Battery modules of the type illustrated in figure 1 are used to make battery units intended to power electric traction motors of electric and hybrid vehicles. In use, the temperature-regulating fluid enters the inlet collector chamber 5, arranged below the battery cells 2, and reaches the outlet collector chamber 6, arranged above the battery cells 2, passing through a plurality of passages 7, arranged between the battery cells 2 (in figure 3, the dimensions of the passages 7 have been exaggerated for clarity). In general, it is of fundamental importance to ensure that during use of the electric vehicle, the battery cells are always at a temperature contained within a specified range, typically between a minimum threshold of 20°C and a maximum threshold of 55°C.

[0012] This requirement exists both for batteries using battery cells of the prismatic type illustrated in figure 2, and for batteries using battery cells of the cylindrical type, and for batteries using battery cells of the so-called “pouch” type.

[0013] The battery cells used in electric vehicles are typically lithium-ion battery cells that tend to develop heat as a result of the chemical reaction that occurs inside the battery cell during operation, and also due to the Joule effect caused by the passage of current inside the battery. The term “battery operation” here refers to both the battery charging process and the discharging process, which typically occurs while the vehicle is running. It should be noted that the most critical battery operating conditions are those related to the fast charging process, i.e. charging the battery in less than an hour.

[0014] During normal operating conditions of the battery unit, the temperature-regulating fluid must perform a cooling action, to counteract the increase in temperature due to the heat that develops in the cells for the reasons indicated above. To this end, the temperature-regulating system comprises a circuit external to the battery module (not shown in figure 1 ) including one or more heat exchangers configured to cool the hot fluid coming from the outlet 6A, before it is fed again, by a pump (not shown) to the inlet 5A. However, in extreme operating conditions, in particular in cold weather conditions, the temperature-regulating fluid must perform a heating function. To this end, the external circuit may comprise a heater exchanger and / or an electrical resistance heating device.

[0015] With reference to the configuration illustrated as an example in figure 3, the experiences conducted on batteries of this type show that the temperature inside the battery module varies considerably both from cell to cell, as the cells 2 that are further away from the inlet 5A of the temperatureregulating fluid are subjected to less cooling, and within each cell, where the temperature distribution tends to be higher where the current lines are denser, for example near the poles.

[0016] Numerous studies have shown that:

[0017] - to reduce the aging process of the individual battery cell, it is advisable to reduce the internal temperature gradient of the cell within 5°C

[0018] - to avoid a phenomenon of “thermal runaway”, which is destructive for the battery, it is necessary to keep the maximum temperature of each individual cell below 55°C

[0019] It is therefore desirable not only to maintain the temperature of the battery cells within a preferred temperature range, but also to try to make the temperature of the different battery cells and the temperature inside each cell as uniform as possible.

[0020] From this perspective, it is also important to try to obtain substantially equal fluid flow rates through the different passages that connect the inlet collector chamber with the outlet collector chamber.

[0021] Object of the invention It is therefore an object of the invention to provide an electric battery unit, in particular an electric battery unit for powering an electric traction motor of an electric or hybrid vehicle, equipped with a temperatureregulating system configured to help maintain the temperature of the battery unit within a specified temperature range.

[0022] A further object of the invention is to provide a temperature-regulating system for a battery unit that promotes greater uniformity of temperature within the battery unit, from cell to cell and within each cell, compared to known solutions.

[0023] A further object of the invention is to achieve said objectives with relatively simple and low-cost means.

[0024] A further specific object of the invention is to promote a flow rate of the temperature-regulating fluid that is substantially equal in all the passages that connect the inlet collector chamber with the outlet collector chamber.

[0025] Summary of the invention

[0026] In order to achieve one or more of said aims, the invention has as its object an electric battery unit having the features that have been indicated at the beginning of this description and further characterized in that:

[0027] - each spacer wall occupies only a lower part of the space between one cell and another, adjacent to the inlet collector chamber,

[0028] - at least some of said spacer walls each have a plurality of passage slits for the temperature-regulating fluid, distributed along the transverse direction with respect to a longitudinal direction of the array of battery cells,

[0029] - each of said passage slits connects the inlet collector chamber below the spacer wall with the space between two adjacent cells above the spacer wall,

[0030] - each of the passage slits of a spacer wall is configured to define:

[0031] - a lower inlet port,

[0032] - an upper outlet port, and

[0033] - a passage connecting the inlet port with the outlet port, and wherein:

[0034] - the upper outlet port of each passage slit has a passage section significantly larger than that of the respective inlet port, - the passage connecting the inlet port with the outlet port of each passage slit has two lateral walls diverging from each other towards the outlet port.

[0035] Thanks to said features, the space provided between each battery cell and another, for the passage of the temperature-regulating fluid, is crossed by multiple flows of temperature-regulating fluid exiting from said outlet ports defined by the spacer wall arranged between one battery cell and another. Furthermore, thanks to the configuration of each of said passage slits, defined through each spacer wall, the flows of the temperature-regulating fluid exiting from such passage slits fan out, so as to cover an enlarged area of the walls of the battery cells that face each other. In this way, the walls of the battery cells facing the passages for the temperature-regulating fluid are covered entirely and in a substantially uniform manner by the temperature-regulating fluid, which allows for a much more uniform distribution of the fluid flow field and consequently of the temperature in the various areas of each battery cell. Furthermore, the arrangement described above also allows for a more efficient cooling of all the battery cells overall, in order to reliably ensure that in no cell and in no part of each cell the temperature reach values outside the permissible range. In order to make the temperature of the different battery cells as uniform as possible among themselves, it is possible to provide that the spacer walls have passage slits in a different number and with a different shape, for example depending on the distance of each spacer wall from the inlet of the temperature-regulating fluid.

[0036] Preferably, according to the invention, the passage slits defined by at least some of the spacer walls are at least three in number and preferably at least five, for each spacer wall.

[0037] According to a further preferred feature of the invention, each passage slit has said two lateral walls diverging from each other towards the outlet port which are configured according to two diverging curved profiles, so that the flow of the temperature-regulating fluid flowing adjacent to one of said curved lateral walls tends, due to the Coanda effect, to exit from the outlet port following a trajectory corresponding to a theoretical extension of said diverging curved wall.

[0038] Thanks to this feature, the flow of the temperature-regulating fluid exiting from each outlet port defined by the spacer wall that is arranged between one battery cell and another tends to further fan out, to cover the maximum possible portion of the surface of the walls of the battery cells facing the passage for the temperature-regulating fluid.

[0039] In a further embodiment, between each battery cell and another, in addition to said lower spacer wall, an auxiliary spacer wall is arranged, located above and at a distance from said lower spacer wall, which defines a plurality of intermediate passages for the temperature-regulating fluid distributed along the transverse dimension of the battery unit.

[0040] Detailed description of the invention

[0041] Further features and advantages of the invention will be apparent from the following description with reference to the attached drawings, provided purely by way of non-limiting example, in which:

[0042] - figure 1 is a perspective view of an exemplary embodiment of an electric battery module, comprising the plurality of prismatic type battery cells,

[0043] - figure 2 is a schematic perspective view of a battery cell of the type used in the battery module of figure 1 ,

[0044] - figure 3 is a schematic view of a temperature-regulating system provided in the battery module of figure 1 ,

[0045] - figure 4 is a prismatic type battery cell forming part of the battery unit according to the invention,

[0046] - figures 5, 6 are a perspective view and a front view of a spacer wall, arranged between one battery cell and another in the battery unit according to the invention,

[0047] - figure 7 is a perspective view of the battery cell of figure 4 illustrating the flows of temperature-regulating fluid at the inlet of the passages defined by the spacer wall visible in figure 4,

[0048] - figure 8 is a front view of a battery cell of the battery unit according to the invention, where the flow field of the temperature-regulating fluid that passes through the passage defined between one battery cell and another is shown, and

[0049] - figure 9 is a variant of figure 8, which refers to the flow field of the temperature-regulating fluid in the case of a second embodiment of the battery unit according to the invention.

[0050] Figures 1-3 relating to the prior art have already been described above.

[0051] Figures 4-9 illustrate the invention with reference to a battery module of the type illustrated in figure 1 , with battery cells 2 of the prismatic type illustrated in figure 2. According to the invention, the passages 7 for the temperature-regulating fluid between each battery cell and another are defined by a plurality of lower spacer walls 8.

[0052] The accompanying drawings do not show the construction details relating to the way in which the battery cells 2 are held in position between them and the way in which the spacer walls 8 are mounted and secured between the battery cells 2. Such details can in fact be made in any known way. In particular, each spacer wall 8 can be secured by adhesive to the main face 2B of a respective battery cell 2, for example.

[0053] According to the invention, each spacer wall 8 occupies only a lower part of the space between one cell and another, adjacent to the inlet collector chamber 5.

[0054] As can be seen in figures 4-6, the spacer wall 8 defines a plurality of passage slits 9 (five in the example) for the temperature-regulating fluid, distributed along the direction X of the cell 2, i.e. along a horizontal direction transverse to the longitudinal direction of the battery module 1.

[0055] Each passage slit 9, defined by the spacer wall 8 interposed between each battery cell and another, connects the inlet collector chamber 5, arranged below the battery cells 2, with the space between two adjacent cells, defined above each spacer wall 8. A particular case is represented by the spacer walls 8 which are connected to the first and last cell of module 1 shown in figure 1 which are not interposed between two cells but between a cell and the container 4.

[0056] With particular reference to figures 5, 6, the inlet 9 has a lower inlet port 9A, an upper outlet port 9B having a passage section significantly larger than that of the inlet port 9A, and a passage that connects the inlet port 9A to the outlet port 9B, defined by two lateral walls 9C diverging from each other towards the outlet port 9B.

[0057] In the illustrated example, the lower spacer wall 8 is in the form of a strip with an upper longitudinal edge 80, a lower longitudinal edge 81 and two end edges 82. Again, in the case of the illustrated example, the passage slits 9 are defined by recesses configured substantially in a V-shape, with the sides of the V-shape defining said divergent side walls 9C and with the apex of each V-shaped recess defining the inlet port 9A. The apex of each V-shaped recess defining the inlet port 9A protrudes below the level 50 (figure 6) of the temperature-regulating fluid within the inlet collector chamber 5, so that the inlet port 9A of each opening 9 is in fluid communication with the inlet collector chamber 5, as exemplified in figure 7, where the arrows 51 indicate the flows of temperature-regulating fluid entering the inlet ports 9 of the passage slits 9 defined by each spacer wall 8. Substantially, figure 7 shows how the fluid enters the passage slit 9, with a direction normal to the spacer wall 8.

[0058] As visible in figures 5, 6, in the preferred embodiments, the two side walls 9C of each passage slit 9, defined by the spacer wall 8, have curved profiles diverging from each other in the direction of the outlet port 9B. Thanks to this feature, the flow of temperature-regulating fluid that flows adjacent to each of said curved side walls 9C tends, due to the Coanda effect, to exit from the outlet port 9B, following a trajectory corresponding to a theoretical extension of said curved wall 9C. If one wishes to increase the Coanda effect, a connection could be provided between the terminal part of the curved wall 9C and the upper horizontal section of the spacer wall.

[0059] Said phenomenon is illustrated in figure 8, which shows a front view of the main wall 2C of a battery cell 2, with the spacer wall 8 in the lower part of the cell, defining the passage slits 9 for the temperature-regulating fluid. In figure 8, the flows of the temperature-regulating fluid have been shown with areas having different hatching corresponding to different fluid rates and correspond to what was found in tests carried out by the Applicant.

[0060] As can be seen, thanks to the provision of a relatively high number (preferably greater than 3 and even more preferably equal to at least 5) of openings 9 distributed along the direction X of each spacer wall 8, and thanks to the configuration of the openings 9, the result is obtained of causing the temperature-regulating fluid to uniformly lap substantially the entire surface of the wall of the battery cell facing the passage for the temperature-regulating fluid.

[0061] Figure 9 is similar to figure 8 and shows the results of tests conducted by the Applicant in the case of a further embodiment, in which, between each battery cell and another, in addition to the lower spacer wall 8 described above, an auxiliary spacer wall 10 is interposed, arranged above and at a distance from the lower spacer wall 8 and defining a plurality of narrow passages 11 , each defined by two walls parallel to each other. The auxiliary spacer wall 10 is arranged substantially at least at an elevation greater than half the height of the cell 2 and has the dual purpose of obtaining an increase in the rate of the temperature-regulating fluid exiting from each of the passages 11 as well as making the flow field in the upper part of the auxiliary spacer wall 10 more uniform. Preferably, the passages 11 , also distributed along the direction X, are relatively numerous, preferably greater than 10.

[0062] The studies and experiences conducted by the Applicant have shown that the features provided for in the battery unit according to the invention allow a drastic increase in the temperature-regulating efficiency of the entire battery unit and above all drastically better results in uniforming the temperature of the various areas of each battery cell. Of course, the same advantages are also obtained in operating conditions in which the fluid performs a heating function of the battery module, when it is operating in a cold weather.

[0063] According to a further teaching forming part of this invention, each of the inlet ports 9A of the passage slits 9 defines a restricted section configured and sized to create a given pressure drop, preferably of at least 35 mbar, in the flow of the temperature-regulating fluid.

[0064] The sum Atot of the passage areas of the restricted sections defined by the inlet ports 9A of all the passage slits 9 is preferably chosen to be less than 1 / 6 of the passage area A1 in the inlet collector chamber 5, in a plane normal to the direction of alignment of the cells 2 (where A1 is considered equal to the product D x H, where D is the largest horizontal dimension of each cell 2 and H is the height of the inlet collector chamber 5).

[0065] Preferably the same condition applies to the passage area B1 in the outlet collector chamber 6 (where B1 is considered equal to the product D x H1 , where D is the largest horizontal dimension of each cell 2 and H1 is the height of the inlet collector chamber 5. Therefore, the area B1 must be at least six times the value of the area Atot of all the restricted sections 9A. In the case where the auxiliary spacer wall 10 is present, then the condition must be verified that the sum of the passage areas of all the restricted sections of the wall 8 and of the additional wall 10 must be less than 1 / 6 of the passage area A1 in the inlet collector chamber 5 and preferably must also be less than 1 / 6 of the passage area B1 in the outlet collector chamber 6.

[0066] Thanks to this feature, each of the passage slits 9 associated with the different cells 2 offers a resistance to the flow of the temperatureregulating fluid sufficiently high to discourage a tendency of the temperature-regulating fluid to flow with greater flow rate in the passages 7 that are closer to the inlet opening 5A.

[0067] In the case in which, in the module 1 , the cells 2 are oriented with the poles 3P, 3N arranged on the vertical lateral faces of the cells, preferably the spacer plate 8 associated with each cell extends at one end beyond the lateral face of the cell bearing the poles, by a distance at least equal to the measure of the protrusion of the poles from such lateral face.

[0068] It may be preferable to differentiate the distance between the slits 9 of each cell, with the aim of differentiating the intensity of the flow field: for example, in the case in which the faces 2C are also wetted by the fluid, then it is preferable to cool the central part of the cell 2 more, so that the slits 9 will be more densely packed towards the central part.

[0069] In some embodiments, in series with the restricted sections defined by the spacer wall 8, elements capable of introducing a pressure drop distributed along the direction of flow, for example consisting of porous material, may also be provided.

[0070] In other embodiments, as provided for in a co-pending patent application by the same Applicant, additional communication passages may be provided between the inlet and outlet collector chambers 5, 6 formed within the cells, through the cell body. In this case, preferably also such internal passages include restricted sections suitable for providing a certain resistance to the flow of the temperature-regulating fluid. In this case, preferably, the relations A1 > 6Atot and B1 > 6Atot are always observed, but in the Atot value the areas of the restricted sections associated with the internal passages of the cells must also be considered.

[0071] In other embodiments, in the space between one battery cell and another, above said spacer wall adjacent to the lower collector chamber, several vertical partitions are provided, parallel and spaced apart, which define, between one cell and another, a plurality of parallel vertical passages for the temperature-regulating fluid. Of course, notwithstanding the principle of the invention, the construction details and embodiments may vary widely with respect to what is described and illustrated purely by way of example, without thereby departing from the scope of this invention.

Claims

CLAIMS1. An electric battery unit, comprising an array of battery cells (2) immersed in a temperature-regulating fluid within a container (4) of the battery unit (1 ), for maintaining the battery unit within a specified temperature range, wherein said container (4) includes:- an inlet opening (5A) for the temperature-regulating fluid, communicating with an inlet collector chamber (5), arranged below the array of battery cells (2),- an outlet opening (6A) for the temperature-regulating fluid communicating with an outlet collector chamber (6), arranged above the array of battery cells (2),- wherein the inlet collector chamber (5) and the outlet collector chamber (6) communicate with each other via a plurality of passages (7) for the temperature-regulating fluid, formed between one battery cell (2) and another,- wherein the battery cells (2) are kept spaced apart from each other by means of spacer walls (8), so as to define said passages (7) for the temperature-regulating fluid, said battery unit being characterized in that:- each spacer wall (8) occupies only a lower part of the space (7) between one cell (2) and another, adjacent to the inlet collector chamber (5),- at least some of the spacer walls (8) each have a plurality of passage slits (9) for the temperature-regulating fluid, distributed along a transverse direction (X) with respect to a longitudinal direction of the array of battery cells (1 ),- each of said passage slits (9) connects the inlet collector chamber (5), arranged below the spacer wall (8), with the space (7) between two adjacent cells (2) above the spacer wall (8),- each of the passage slits (9) of each spacer wall (8) is configured to define:- a lower inlet port (9A),- an upper outlet port (9B), and- a passage connecting the inlet port (9A) with the outlet port (9B), and wherein:- the upper outlet port (9B) of each passage slit (9) has a passage section significantly larger than that of the respective inlet port (9A),- the passage connecting the inlet port (9A) with the outlet port (9B) of each passage slit (9) has two side walls (9C) diverging from each other towards the outlet port (9B).

2. The battery unit according to claim 1 , characterized in that the said two side walls (9C) of each passage slit (9) are curved walls diverging from each other in the direction of the outlet port (9B), such that the flow of the temperature-regulating fluid flowing adjacent to each of said diverging curved side walls (9C) tends, due to the Coanda effect, to flow out of the outlet port (9B) following a trajectory corresponding to a theoretical extension of said curved side wall (9C).

3. The electric battery unit according to claim 1 or 2, characterized in that the passage slits (9), defined by at least some of the spacer walls (8), are at least three in number and preferably at least five, for each spacer wall, the passage slits (9) associated with a spacer wall (8) being equidistant from each other or being distributed at different distances, so that they are more densely packed towards the central part of the battery cell (2).

4. The battery unit according to claim 1 , characterized in that it comprises spacer walls (8) associated with different battery cells (2) that differ from each other in the number and / or configuration of the passage slits (9) defined by each spacer wall.

5. The battery unit according to claim 1 , characterized in that between each battery cell (2) and another, an auxiliary spacer wall (10) is arranged above and at a distance from said spacer wall (8), defining a plurality of intermediate passages (11 ) for the temperature-regulating fluid, distributed along the transverse dimension (X) of the respective battery cell (2).

6. The battery unit according to claim 5, characterized in that said intermediate passages (11 ) are arranged substantially at an elevation greater than half the height of the respective battery cell (2) and are each defined by two side surfaces parallel to each other.

7. The battery unit according to claim 6, characterized in that said intermediate passages (11 ) defined by the auxiliary spacer wall (10) are at least ten in number.

8. The battery unit according to claim 1 , characterized in that the battery cells (2) are prismatic type cells each having an upper wall (2A), a lower wall (2D), two main walls (2B) and two end walls (2C), said battery cells (2) being arranged aligned in a direction orthogonal to their main walls (2B), and said spacer walls (8) being each interposed between the facing main walls (2B) of two adjacent cells (2).

9. The battery unit according to claim 8, characterized in that each spacer wall (8) is in the form of a strip with an upper longitudinal edge (80), a lower longitudinal edge (81 ), two end edges (82), and in that the upper longitudinal edge (80) has a plurality of recesses defining said passage slits (9) and configured substantially in a V-shape, with the sides of the V-shape defining said curved side walls (9C) and with the apex portion of the V- shaped recess defining said inlet port (9A) and protruding within the inlet collector chamber (5) for the temperature-regulating fluid, such that the passage defined by each V-shaped recess connects the inlet collector chamber (5) with the space (7) defined between two adjacent cells (2).

10. The battery unit according to claim 1 , characterized in that the inlet port (9A) of each of said passage slits (9) defines a restricted section configured and sized to create a given pressure drop, preferably of at least 35 mbar, in the flow of the temperature-regulating fluid, the sum Atot of the passage areas of the restricted sections defined by the inlet ports (9A) of all said passage slits (9) being less than 116 of the passage area A1 in the inlet collector chamber (5), in a plane normal to the direction of alignment of the cells (2) and preferably being also less than 1 / 6 of the passage area B1 in the outlet collector chamber (6), in a plane normal to the direction of alignment of the cells (2).

11. The battery unit according to claim 1 , characterized in that in series or in parallel to the restricted sections (9A) defined by the spacer wall (8), elements are provided that are capable of introducing a pressure drop distributed along the direction of flow, for example consisting of porous material.

12. The battery unit according to claim 1 , characterized in that itincludes additional communication passages between the inlet and outlet collector chambers (5, 6) formed within the cells (2), through the cell body, and in that such internal passages include restricted sections suitable for providing a certain resistance to the flow of the temperature-regulating fluid, so that the value of the total passage area of all the restricted sections also includes the passage areas of the restricted sections associated with said internal passages.

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