WO2025093976A1

WO2025093976A1 - An electric battery unit with cells having internal passages for a temperature-regulating fluid, an electric vehicle comprising the battery unit and a control method

Info

Publication number: WO2025093976A1
Application number: PCT/IB2024/060127
Authority: WO
Inventors: Raffaele Ricco
Original assignee: Centro Ricerche Fiat SCpA
Current assignee: Centro Ricerche Fiat SCpA
Priority date: 2023-10-30
Filing date: 2024-10-16
Publication date: 2025-05-08
Anticipated expiration: 2026-04-30

Abstract

An electric battery unit (1 ) comprises an array of battery cells (2) immersed in a temperature-regulating fluid within a container (4). The 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). The container (4) further comprises an outlet opening (6) for the temperature-regulating fluid, communicating with an outlet collector chamber (6), arranged above the array of battery cells (2). The inlet collector chamber (5) and the outlet collector chamber (6) communicate with each other through a plurality of external passages (7) on the outside of the battery cells (2), formed between one battery cell (2) and another, and also through a plurality of internal passages (8), each formed through the body of a respective battery cell (2), within the battery cell (2). In one example, all internal passages (8) and/or all external passages (7) include respective restricted sections (R) configured and sized to create a given pressure drop in the flow of the temperature-regulating fluid through the restricted section (R).

Description

An electric battery unit with cells having internal passages for a temperature-regulating fluid, an electric vehicle comprising the battery unit and a control method

TEXT OF THE DESCRIPTION

Field of the invention

The present invention relates to an electric battery unit equipped with an improved temperature regulating system, an electric vehicle using such an electric battery unit and a control method.

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, for maintaining the battery unit within a specified temperature range, wherein said 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 external passages on the outside of the battery cells, formed between one battery cell and another.

Prior art

Electric battery units having a temperature regulating system of the type indicated above have been known and used for some time.

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. Of course, the cell of Figure 2 is only an example. In other examples, the cell has the face bearing the poles 3P and 3N oriented vertically on one side with respect to the case of figure 2.

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. Figure 1 shows an example in which an inlet 5A for the temperature-regulating fluid communicating with the inlet collector chamber 5 and an outlet 6A communicating with the outlet collector chamber 6 are provided. P and N indicate the positive and negative poles of the battery module.

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. In this case, the upper collector chamber receives fluid at a higher pressure.

Battery modules of the type illustrated in figure 1 are used to make battery units intended to power electric traction motors of electric 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, in particular the electrolyte contained therein, 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.

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.

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.

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.

It should also be noted that the invention applies both to the case of a liquid temperature-regulating fluid and to the case of a temperatureregulating fluid in the form of a gas, for example forced-movement air.

With reference to the configuration illustrated as an example in figure 3, the experiments 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.

Numerous studies have shown that:

- 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

- to avoid a phenomenon of “thermal runaway”, which is destructive for the battery, it is necessary to keep the entire battery assembly at an average temperature below 55°C. 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.

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.

Furthermore, it is desirable that the flow field in each space separating two adjacent cells is relatively homogeneous and similar for all spaces between cells.

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 vehicle, equipped with a temperature regulating system configured to maintain the temperature of the battery unit within a specified temperature range with a higher level of efficiency than known solutions.

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.

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

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

A further object is to obtain a substantially similar flow field of the temperature-regulating fluid in all the passages.

Summary of the invention

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 said inlet collector chamber and said outlet collector chamber also communicate with each other through a plurality of internal passages, each formed through the body of a respective battery cell, within the battery cell.

According to the invention, said internal passages are formed in at least some of the battery cells that are at a position farthest from said inlet opening for the temperature-regulating fluid.

In the preferred embodiment, the battery unit is further characterized in that:

- said inlet opening of the container is a first inlet opening,

- said container has a second inlet opening for the temperatureregulating fluid which does not communicate with the first inlet opening,

- said container has said inlet collector chamber constituting a first inlet collector chamber, communicating with said first inlet opening,

- said container also has a second inlet collector chamber, which does not communicate with the first inlet collector chamber and which communicates with said second inlet opening,

- said first inlet collector chamber communicates with said outlet collector chamber solely through said internal passages, formed within respective battery cells,

- said second inlet collector chamber communicates with the outlet collector chamber solely through said external passages on the outside of the battery cells.

In a particularly preferred embodiment, the battery unit comprises at least one electrically actuated valve configured to regulate the flow through one of said first inlet opening and said second inlet opening, said at least one electrically actuated valve being controlled by an electronic controller based on the operating condition of the battery unit.

Thanks to said features, the temperature regulating system of the battery unit according to the invention ensures on the one hand that each battery cell remains within a specified temperature range and on the other hand that the temperature of the different battery cells and the temperature of the different zones of each battery cell is more uniform than what is possible to obtain with known solutions.

The provision of passages for the temperature-regulating fluid within the battery cells ensures greater uniformity of the temperature in the various zones of each cell. At the same time, the provision of said internal passages, together with the external passages, allows to obtain maximum efficiency in the cooling action.

In the embodiment that involves the use of a control valve, it is possible to obtain a regulation, for example, of the flow of temperatureregulating fluid that passes through the external passages. In this way, it is possible, for example, to cancel the flow of fluid through the external passages and to achieve a flow of temperature-regulating fluid only through the internal passages in an initial phase of the battery operation, when it is important to obtain the maximum effectiveness of the cooling action inside the cells. When instead the battery unit reaches a steady state condition, the control valve is opened to obtain the maximum possible effectiveness in obtaining uniform cooling of the different cells.

This process can be applied both during the battery warm-up phase, that is when the cell temperature is below the optimal operating range between 20°C and 55°C, and when the cell temperature increases rapidly tending to exceed the maximum threshold value of the active material temperature of the cells, equal to 55-60°, for example while the vehicle is running or during the charging process.

In particular, during the fast charging process, a cyclic alternation (for example a transition every 3-4 minutes) between the cooling of only the internal part of the cells and the simultaneous cooling of both the internal and external parts could be even more effective.

In order to better quantify the meaning of the term “fast charging”, a parameter called “C-rate” has been introduced and defined as the charging power - in kW- divided by the battery capacity in kWh. So, for example, if the charging system has a power of 300kW and the battery has a nominal capacity of 100kWh, the C-rate is equal to 3 [h^A-1 ] which corresponds to a charging time of 20 minutes. If the charging system had a power of 600kW, the C-rate would be equal to 6, or the charging time would be 10 minutes. It is therefore evident that the higher the C-rate, the greater the heat released by the cells that needs to be removed to avoid exceeding the temperature threshold value of 50-55°C.

Said internal passages are formed in at least some of the battery cells, which are at a position furthest from said inlet opening and/or from said outlet opening for the temperature-regulating fluid and the configuration and dimensions of the internal passages of different cells may be the same or different from each other. In one example, said internal passages are sized to define a heat exchange surface that increases from one cell to another, depending on the distance of each cell from said inlet opening and/or from said outlet opening for the temperature-regulating fluid. In a preferred embodiment, said internal passages are configured and sized such that:

- if S1 is the surface in contact with the temperature-regulating fluid of a cell without the internal passage,

- if V1 is the volume of a cell without the internal passage,

- if R1 [nr¹] is the ratio of S1 to V1 ,

- if S2 is the surface area in contact with the temperature-regulating fluid of a cell with the internal passage,

- if V2 is the volume of a cell with the internal passage,

- if R2 [nr¹] is the ratio of S2 to V2,

- then:

- R2 is equal to at least 1.2 R1 , and preferably is equal to at least 1 .35 R 1 , in the case of a prismatic or pouch cell, and

- R2 is equal to at least R1 -1.1 , and preferably is equal to at least 1 .2 R1 , in the case of a cylindrical cell.

Experiments conducted by the Applicant have shown that thanks to the above values of the R2 ratio, the battery can be recharged with a C-rate of at least 3 and, in the case of the preferred values, with a C-rate higher than 3.

Finally, it should be remembered that the thermal conductivity of the active material of lithium ion cells is of the order of magnitude of a few tens of W/(m*K) (the thermal conductivity of aluminum is equal to 204 W/(m*K), therefore the smaller the heat exchange surface/volume ratio of the cell, the greater the temperature gradient between the innermost points of the cell compared to those on the surface.

According to a further particularly preferred feature, each of said internal passages formed through the battery cells and/or each of said external passages, formed between one battery cell and another, includes at least one restricted section configured and sized to create a given pressure drop, preferably of at least 35 mbar, in the flow of the temperatureregulating fluid through the restricted section, the sum of the passage areas of the restricted sections associated with all the internal and/or external passages being less than 1/6 of the passage area through the inlet collector chamber, intended as the section of the chamber normal to the X direction (figure 1 ) along which the cells in the module are aligned. Preferably, the same condition is also achieved for the passage area of the outlet collector chamber.

Thanks to this feature, each of the internal passages and each of the external passages offers a resistance to the flow of the temperatureregulating fluid sufficiently high to discourage a tendency of the temperature-regulating fluid to flow at a greater rate in the passages closer to the inlet opening for the fluid. In this way, the flow rate of temperatureregulating fluid through said passages is substantially identical for all passages, regardless of whether a passage is more or less close to the inlet opening.

Studies and experiments of the Applicant have shown that to achieve said result, the value of the ratio of the passage area through the inlet collector chamber, i.e. the section of the chamber in a plane normal to the direction along which the cells are aligned, to the sum of the passage areas of all the restricted sections communicating with the inlet opening is critical. In particular, the Applicant has noted that the sum of the passage areas of all the restricted sections must not exceed 1/6 of the passage area of the inlet collector chamber. Preferably, the same is also achieved for the passage area of the outlet collector chamber, i.e. the passage area of the outlet collector chamber normal to the X direction of alignment of the cells.

The invention also relates to an electric vehicle comprising a battery unit having the above-mentioned features, including said feature relating to the provision of the electrically actuated control valve, wherein the battery unit powers at least one electric traction motor of the electric vehicle. The vehicle according to the invention is characterized in that the battery unit comprises an electrically actuated valve which is arranged and configured to regulate the flow through said second inlet opening and in that said electronic controller is configured to enable the flow of temperatureregulating fluid to the second inlet collector chamber and to said external passages on the outside of the battery cells:

- when the electric traction motor is running and only after a transient phase following an activation of the electric traction motor,

- when the electric traction motor is off, but the vehicle is in battery charging conditions, particularly in fast charging conditions,

- when the electric traction motor is off, the vehicle is in parking mode and the external conditions are extreme, in the sense that the ambient temperature is above or below the range of 20-55°C.

A particular case is that of an extremely cold ambient temperature, for example <-5°C. In this case the electronic controller can be programmed to implement the battery heating process in a predefined time interval before the driver of the vehicle begins to use the vehicle itself.

It should be noted, however, that the present invention is of general application and could therefore be applied to any type of vehicle (car, truck, motorcycle, train, ship) as well as to a unit of lithium ion batteries not part of a vehicle, for example used in a stationary system such as a system for generating energy through solar panels associated with a home.

It is understood that the invention can also be applied in the case in which the temperature-regulating fluid is air or another gas.

It is also understood that the invention also applies to layouts in which, with reference to figure 2, in addition to the faces of the cell 2B, the faces 2C also come into contact with the temperature-regulating fluid: in this case, the passage section defined between the face 2C and the casing 4 must be considered as a further gap crossed by the fluid and must therefore also be associated with one or more restricted sections that regulate the flow rate.

For example, if the size of the cell along the X direction (figure 2) is equal to 1/3 of the size in the Y direction, then it is necessary that the passage area of the restricted sections associated with the face 2B is three times the passage area through the restricted sections associated with the lateral face 2C.

More generally, the ratio of the areas of the restricted sections associated with the faces 2B and 2C must be equal to the ratio of the dimensions of the cell in the Y and X directions.

Finally, the invention also has as its object the method for controlling the battery unit that has been described above. Detailed description of the invention

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:

- figure 1 is a perspective view of an exemplary embodiment of an electric battery module, comprising a plurality of prismatic battery cells,

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

- figure 3 is a schematic view of a cooling system provided in the battery module of figure 1 ,

- figure 4 shows a battery cell according to the present invention, including an internal passage, formed through the body of the battery, for the temperature-regulating fluid,

- figure 5 is a partial schematic view of a battery module including a plurality of cylindrical battery cells, according to the present invention,

- figures 6, 7 are perspective views illustrating the technique for manufacturing a cell of a cylindrical battery and a "Pouch" type battery cell by means of a winding technique,

- figure 8 is a variant of figure 5, corresponding to a preferred embodiment of the present invention,

- figure 9 is a diagram showing the advantages of the cooling system according to the invention,

- figure 10 is a further variant of figure 8 according to a further preferred embodiment,

- figure 11 is a variant of figure 10, showing a further particularly preferred embodiment, and

- figure 12 is a plan diagram of a battery unit including a matrix of cells aligned along two orthogonal directions.

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

In figures 4-10, the parts common to those of figures 1 -3 are indicated with the same reference numbers.

A first essential element of the battery unit according to the present invention consists in the provision, inside at least some battery cells, whether they are prismatic battery cells, whether they are cylindrical battery cells, whether they are pouch type battery cells, an internal passage for the temperature-regulating fluid, which passes through the body of the battery cell from its lower end to its upper end (with reference to the condition illustrated in the attached drawings).

Figure 4 shows an example of a prismatic type battery cell 2, entirely similar to that illustrated in figure 2, which however presents the difference consisting in the provision of an internal passage 8 for the temperatureregulating fluid, which passes entirely through the body of the cell 2 from the lower wall to the upper wall. The same concept can also be applied to a cylindrical cell 2 (figure 6) or to a pouch type cell 2.

Figures 6, 7 show a well-known winding technique for manufacturing cylindrical and pouch battery cells. The same technique can also be applied to the manufacture of prismatic battery cells illustrated in figure 4. Thanks to this technique, it is possible to easily obtain the internal passage 8 for the temperature-regulating fluid.

The shape and size of the hole depend on the type of battery and the application; in general, it is desirable that:

- for prismatic and pouch batteries, the internal hole is such as to increase the heat exchange surface/volume ratio of the original cell without a hole by at least 20%,

- for cylindrical batteries, thanks to a more favorable symmetry with respect to the longitudinal axis, the increase can be less marked, for example it can be 10-15% of the heat exchange surface/volume ratio of the original cell.

More precisely:

- if V1 is the volume of a cell without the internal passage,

- if R1 [nr¹] is the ratio of S1 to V1 ,

- if V2 is the volume of a cell with the internal passage,

- if R2 [nr¹] is the ratio of S2 to V2,

- then:

- R2 is equal to at least R1 ■ 1 .1 , and preferably is equal to at least 1 .2 R1 , in the case of a cylindrical cell.

It is understood that if, in the design phase of the battery temperature regulating system, the ability to charge the cell with particularly high C-rate values (>3) is desired, said values must be increased, respectively to 35- 45% for prismatic and pouch cells and 15-25% for cylindrical cells.

Figure 5 presents a first embodiment of a battery unit according to the invention. Figure 5 refers to the case in which the battery unit 1 includes cylindrical type battery cells 2. The drawing illustrates only three battery cells, but it is understood that the battery unit may include one or more rows of battery cells, each composed of any number of battery cells. The cells 2 may therefore be arranged in a matrix, according to two mutually orthogonal alignment directions.

In the solution of figure 5, in accordance with the known solution of figure 3, the unit 1 includes a container 4 that defines an inlet collector chamber 5, arranged below the battery cells 2, which receives the temperature-regulating fluid from an inlet 5. Above the battery cells 2, the container 4 defines an outlet collector chamber 6, communicating with an outlet 6A. As can be seen in figure 5, the inlet collector chamber 5 and the outlet collector chamber 6 communicate with each other both through a plurality of external passages 7, formed outside the battery cells 2, between one cell and another, and through a plurality of internal passages 8, formed through the body of each cell 2, from one end of the cell to the other.

In this way, the temperature regulating system of the battery unit according to the invention is able to achieve a double result: on the one hand, the temperature inside the body of each battery cell is significantly more uniform than in a solution of the type shown in figure 3. This result is achieved thanks to the greater heat exchange surface/volume ratio and therefore to a greater tendency of the cell to release heat rather than trap it inside. On the other hand, a greater uniformity of temperature is also achieved from one cell to another. Finally, the temperature of each cell remains within the specified temperature range. Of course, it doesn’t mean that all the battery cells of the battery unit each have an internal passage 8 and above all that the internal passage 8 is identical for all the cells assembled in the container: for example, cells closer to the inlet or outlet of the container could have less cooling requirements and therefore require smaller heat exchange surface/volume ratios (i.e. smaller hole passage section). For example, it is possible to provide such internal passage only for a part of the battery cells that is located in a more distant position with respect to the inlet opening 5A, so as to promote greater uniformity of temperature from one cell to the other; alternatively, the passage section could be - for example - continuously increasing from the first cell to the last cell present in the container.

The advantages of the invention are shown in figure 9, relating to the results of tests carried out by the Applicant on a battery unit of the type in figure 5. In this figure, diagram A refers to the temperature distribution inside a battery cell along the vertical dimension of the battery cell. As can be seen, diagram A is a Gaussian bell that shows a relatively high average temperature (approximately 330°K) and a relatively wide temperature variability range (from 315°K to 345°K). Diagram B refers to the same battery cell in the case where the internal passage to the battery cell for the temperature-regulating fluid is provided. As can be seen, the average temperature is lower (about 310°K) and the temperature variability range is narrower (from 300° K to 320° K).

Figure 8 illustrates a preferred embodiment that provides for the provision of two separate inlet collector chambers. A first inlet collector chamber 5 communicates only with the internal passages 8, formed through the body of each battery cell 2, while a second collector chamber 50, communicating with a second inlet opening 50A, communicates only with the external passages 7, formed between one cell and another. The internal passages 8 and the external passages 7 then all communicate with a single outlet collector chamber 6 and with the outlet opening 6A.

In the solution of figure 8, preferably, in the second inlet opening 50A communicating with the external passages 7 there is a flow control valve 9, electrically actuated, of any known type, configured to be controlled by an electronic controller E. In a simplified embodiment, the valve 9 can be of the on/off type. In a more advanced embodiment, the valve 9 can be of any known type capable of allowing the flow of the temperature-regulating fluid to be controlled progressively between a zero value and a maximum value. The electronic controller E can be configured in such a way that, for example during the fast battery charging phase, when the need to dispose of the heat produced by the losses due to the Joule effect is particularly high, the temperature-regulating fluid is conveyed only into the internal passages 8, after closing the control valve 9, so as to obtain greater efficiency in the internal cooling of the battery cells, in a phase in which the cooling determined by the external passages would be less effective. Once a steady-state condition is reached, valve 9 is opened to allow the flow of element fluid also through the external passages 7.

Of course, nothing excludes the possibility of providing a control system operating differently, for example by giving priority to the flow through the external passages 7 and only allowing the arrival of the temperature-regulating fluid to the internal passages in a subsequent phase. This solution would imply the provision of a control valve at inlet 5A, communicating with internal passages 8. It is also possible to provide for the provision of two control valves, one at inlet 5A and the other at inlet 50A. Furthermore, the electronic controller E can be configured in any other way to open and close the communication of the internal passages 8 and the external passages 7 with the respective inlet openings 5A and 50A depending on certain operating parameters of the battery unit and/or the electric vehicle.

For example, the electronic controller could be programmed to cyclically alternate cooling/heating of the internal part of the cells only with cooling/heating of both the external and internal parts. As already indicated above, in case of external temperatures below the range of 25°C - 55°C, particularly for external temperatures below -5°C, it is necessary to heat the cells: in this case the warmer fluid could be heated externally to the battery container by means of an electrical resistance and initially directed only to the internal part of the cells via the passages 8.

Figure 10 illustrates a further embodiment that substantially coincides with that of figure 8, except that in this case the first inlet collector chamber 5 communicates with the internal passages 8, formed through the body of the battery cells 2, by means of tubular fittings 10 that engage within the lower ends of the internal cavities of the battery cells 2, defining the internal passages 8. In this way, the tubular fittings 10 also serve as supports for retaining the battery cells 2 on the base structure in which the inlet collector chambers 5 and 50 are formed: in this way it is not necessary to provide external supports for the cells, which makes it easier fixing the cells themselves inside the container 4. Furthermore, the elimination of external fixings increases the external exchange surface, with obvious benefits on the capacity to release heat.

Figure 11 shows, purely by way of example, the application of a further teaching forming part of the present invention, to the embodiment of figure 10. In the case of this example, each of the internal passages 8 formed through the battery cells 2 and each of the external passages 7, formed between one battery cell and another, includes a restricted section R configured and sized to create a given pressure drop, preferably of at least 35 mbar, in the flow of the temperature-regulating fluid through the restricted section R. The sum of the passage areas of the restricted sections R associated with all the internal passages 8 and the sum of the passage areas of the restricted sections R associated with all the external passages 7 is chosen to be less than 1/6 of the passage area of the inlet collector chamber, as already illustrated above.

Studies and experiences of the Applicant have shown that to achieve the above result, the value of the ratio of the passage area through the inlet collector chamber, i.e. the section of the chamber in a plane normal to the X direction along which the cells are aligned, to the sum of the passage areas of all the restricted sections communicating with the inlet opening is critical. In particular, the Applicant has noted that the sum of the passage areas of all the restricted sections must not exceed 1/6 of the passage area of the inlet collector chamber. Preferably, the same applies to the passage area of the outlet collector chamber, i.e. the passage section of the outlet collector chamber normal to the X direction of alignment of the cells.

Thanks to this feature, each of the internal passages and each of the external passages offers a resistance to the flow of the temperatureregulating fluid sufficiently high to discourage a tendency for the temperature-regulating fluid to flow with a greater flow rate in the passages closest to the inlet opening for the fluid. In this way, the flow rate of the temperature-regulating fluid through said passages is substantially identical for all the passages, regardless of whether a passage is more or less close to the inlet opening.

Figure 11 shows an example in which the restricted sections R are provided for both the internal passages 8 and the external passages 7. However, it would be possible to provide the restricted sections R only for the external passages 7, or only for the internal passages 8. Furthermore, the restricted sections R are also applicable to embodiments such as those in figure 5, in which a single inlet collector chamber is provided, communicating with both the internal passages 8 and the external passages 7. In this case, the passage area of the inlet collector chamber must be at least six times the sum of all the passage areas of the restricted sections R of the internal passages 8 and the external passages 7. Preferably, this condition is also applied to the outlet collector chamber.

Figure 12 shows a plan view of a battery unit including a matrix of prismatic cells 2 aligned along two mutually orthogonal directions X, Y.

In this case, internal passages and external passages to the cells with respective restricted sections can also be provided. In this case, too, the overall passage area through the restricted sections must not exceed a given limit with respect to the passage area of the inlet collector chamber and preferably also of the outlet collector chamber. In this specific case, for greater safety, the limit case is considered in which the temperatureregulating fluid passes, with reference to figure 12, from inlet 5A, located in the lower collector chamber, to outlet 6A, located in the upper collector chamber (therefore 5A and 6A are arranged at different heights) following the longest path F, i.e. first along the Y direction and then along the X direction, thus travelling along the two sides of the matrix. The condition always applies that the total passage area (Atot) of all the restricted sections located along the path F of the fluid must not exceed 1/6 of the area (A1 ) of the passage section of the fluid in the inlet collector chamber. In analogy with what was seen in the case of a single module, in the case illustrated in figure 12, the passage area in the inlet collector chamber is taken to be equal to the product D x H, where D is the largest horizontal dimension of the single cell 2, while H is the height of the inlet collector chamber. The total sampling area Atot associated with the restricted sections R is taken to be equal to the product R1 x N, where R1 is the passage area of each restricted section R and N is the number of restricted sections associated with the cells that are located along the path F (10 cells in the example in figure 12; restrictions associated with a cell mean the sum of those for the external path 7 and the internal path 8).

Unlike what is shown in figure 8 and figure 11 , the restricted sections R can be of the distributed type rather than concentrated, that is, they can be made up of bodies of porous material, which generate a distributed flow resistance RD. For example, the distributed resistance RD could consist of a predefined volume of porous material having a known hydraulic resistance per unit length of fluid passage. The hydraulic resistance can vary significantly depending on the porous material chosen. In this case, all the considerations previously made are valid, provided that the development of the resistance RD along the direction of the flow introduces the same pressure drop as the restricted section R.

Another possible case consists of combinations of concentrated resistances R and distributed resistances RD: for example, for an internal passage 8 of a given cell, it could be possible to introduce both a concentrated restricted section R’ that introduces a pressure drop equal to half the pressure drop corresponding to the restricted section R of figures 8 and 11 , and, connected in series, a volume of porous material RD’, whose length in the direction of the flow is characterized by the introduction of a pressure drop equal to half the pressure drop corresponding to the restricted section R.

The above also applies to the case in which the passage 8 inside a single cell is divided into n passages, which are however configured and sized to satisfy the relationships indicated above relating to the ratio R2.

In embodiments that use prismatic cells, in the space between one battery cell and another, several parallel and spaced vertical partitions can be provided, 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 embodiments and construction details may vary widely from those described and illustrated by way of example, without thereby departing from the scope of the invention, as defined in the attached claims.

Claims

1. An electric battery unit (1 ), 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 external passages (7), on the outside of the battery cells (2), formed between one battery cell (2) and another, said battery unit (1 ) being characterized in that said inlet collector chamber (5) and said outlet collector chamber (6) also communicate with each other via a plurality of internal passages (8), each formed through the body of a respective battery cell (2), within the battery cell (2).

2. The battery unit according to claim 1 , characterized in that said internal passages (8) are formed in at least some of the battery cells (2), which are at a position furthest from said inlet opening (5A) and/or from said outlet opening (6A) for the temperature-regulating fluid and in that the configuration and dimensions of the internal passages of different cells may be the same or different from each other.

3. The battery unit according to claim 2, characterized in that said internal passages (8) are sized to define an increasing heat exchange surface from one cell (2) to the other, depending on the distance of each cell from said inlet opening (5A) and/or from said outlet opening (6A) for the temperature-regulating fluid.

4. The battery unit according to claim 1 , characterized in that said cells (2) are prismatic cells or pouch cells or cylindrical cells, and said internal passages (8) are configured and sized such that: - if S1 is the surface in contact with the temperature-regulating fluid of a cell without the internal passage,

- if V1 is the volume of a cell without the internal passage,

- if R1 [nr¹] is the ratio of S1 to V1 ,

- if V2 is the volume of a cell with the internal passage,

- if R2 [nr¹] is the ratio of S2 to V2,

- then:

5. The battery unit according to claim 1 , characterized in that:

- said inlet opening (5A) of the container (4) is a first inlet opening,

- said container (4) has a second inlet opening (50A) for the temperature-regulating fluid, which does not communicate with the first inlet opening (5A),

- said container (4) has said inlet collector chamber (5) constituting a first inlet collector chamber, communicating with said first inlet opening (5A),

- said container (4) also has a second inlet collector chamber (50) which does not communicate with the first inlet collector chamber (5), and which communicates with said second inlet opening (50A),

- said first inlet collector chamber (5) communicates with said outlet collector chamber (6) solely through said internal passages (8) formed within respective battery cells (2),

- said second inlet collector chamber (50) communicates with the outlet collector chamber (6) solely through said external passages (7) on the outside of the battery cells (2).

6. The battery unit according to claim 1 , characterized in that it comprises at least one electrically actuated control valve (9), configured to regulate the flow through one of said first inlet opening (5A) and said second inlet opening (50A) and in that said at least one electrically actuated control valve (9) is controlled by an electronic controller (E) based on the operating condition of the battery.

7. The battery unit according to claim 6, characterized in that it comprises two electrically actuated control valves, configured to regulate the flow through said first inlet opening (5A) and said second inlet opening (50A), respectively, and in that said electrically actuated control valves (9) are controlled by an electronic controller (E) based on the operating condition of the battery, preferably in such a way as to periodically alternate, for example every 3-4 minutes, an operating phase in which the temperature-regulating fluid flows only through the internal passages (8) and an operating phase in which the temperature-regulating fluid flows only through the external passages (7) or an operating phase in which, by partially opening the two electrically actuated control valves, the temperature-regulating fluid flows through both the internal passages (8) and the external passages (7).

8. The battery unit according to claim 5, characterized in that said first inlet collector chamber (5) communicates with said internal passages (8) by means of tubular fittings (10) formed in the container base structure (4) and each engaged within a lower portion of a cavity defining the respective internal passage (8), such that said tubular fittings (10) also serve as supports for retaining said battery cells on said container base structure (4).

9. The battery unit according to claim 1 , characterized in that each of said internal passages (8) formed through the battery cells (2) and/or each of said external passages (7), formed between one battery cell (2) and another, includes a restricted section (R) configured and sized to create a given pressure drop, preferably of at least 35 mbar, in the flow of the temperature-regulating fluid through the restricted section (R), the sum of the passage areas of the restricted sections (R) associated with all the internal (8) and external (7) passages being less than 1/6 of the passage area of the inlet collector chamber (5) in a plane normal to the direction (X) of alignment of the cells (2).

10. The battery unit according to claim 1 , characterized in that each of said internal passages (8) formed through the battery cells (2) and/or each of said external passages (7), formed between one battery cell (2) and another, includes a restricted section (R) configured and sized to create a given pressure drop in the flow of the temperature-regulating fluid through the restricted section (R), the sum of the passage areas of the restricted sections (R) associated with all the internal (8) and external (7) passages being less than 1/6 of the passage area of the outlet collector chamber (6) in a plane normal to the direction (X) of alignment of the cells (2).

11. The battery unit according to claim 1 , characterized in that each of said internal passages (8) formed through the battery cells (2) and/or each of said external passages (7), formed between one battery cell (2) and another, includes a restricted section (R) configured and sized to create a given pressure drop in the flow of the temperature-regulating fluid through the restricted section (R), in that the battery cells are arranged in a matrix and aligned in two directions (X, Y) orthogonal to each other, and in that:

- the sum (Atot) of the passage areas of the restricted sections (R) associated with all the cells (2) located along two sides of the matrix is not greater than 1/6 of the passage area (A1 ) in the inlet collector chamber (5), wherein:

- the passage area (A1 ) in the inlet collector chamber (5) is taken to be equal to the product D x H, where D is the largest horizontal dimension of each cell and H is the height of the inlet collector chamber (5),

- the sum (Atot) of the passage areas of the restricted sections (R) is taken to be equal to the product R1 x N,

- where R1 is the passage area of each restricted section (R),

- and N is the number of said restricted sections (R) that are associated with the cells located along two sides of the cell matrix.

12. The battery unit according to claim 9, characterized in that:

- the battery cells are prismatic cells having major surfaces (2B) and side surfaces (2C),

- the cells (2) are aligned in a direction (X) orthogonal to the major surfaces,

- said external passages (7) include both first passages defined between facing major surfaces (2B) of adjacent cells, and second passages defined between the side surfaces (2C) of the cells and the container (4),

- one or more restricted sections are associated with each of said first passages, and one or more restricted sections are associated with each of said second passages, the ratio of the total passage areas through the restricted sections of the second passages with respect to the first passages being equal to the ratio of the the dimensions of each cell in the direction (X) of cell alignment and in the horizontal direction (Y) orthogonal thereto.

13. The battery unit according to claim 9, characterized in that said restricted sections comprise concentrated restricted sections or distributed restricted sections, each defined by a body of porous material, or said restricted section comprise both concentrated restricted sections and distributed restricted sections, arranged in series or in parallel with each other.

14. The battery unit according to claim 1 , characterized in that it is configured to receive a temperature-regulating fluid in gaseous form, e.g., air.

15. An electric vehicle, comprising a battery unit according to claim 6, wherein said battery unit (1 ) powers at least one electric traction motor of the electric vehicle, characterized in that:

- said battery unit comprises a single electrically actuated control valve (9) which is arranged and configured to regulate the flow through said second inlet opening (50A),

- said electronic controller (E) is further configured to control said electrically actuated control valve (9) so as to enable the flow of temperature-regulating fluid to the second inlet collector chamber (50) and to said external passages (7) to the battery cells (2), as well as through said internal passages (8) only under given operating conditions.

16. A method for controlling an electric vehicle according to claim 15, comprising controlling the electrically actuated control valve (9), via the electronic controller (E), to enable the flow of temperature-regulating fluid to the second inlet collector chamber (50) and to said external passages (7) on the outside of the battery cells (2), as well as through said internal passages (8)

- when the electric traction motor is running and only after a transient phase following the activation of the electric traction motor,

- or when the electric traction motor is off, but the vehicle is in a battery charging condition, particularly in fast charging, - or when the electric traction motor is off, the vehicle is in a parking mode, and the external climatic conditions are extreme, in the sense that the ambient temperature is above or below the range of 20-55°C, the activation of the flow of temperature-regulating fluid for heating the battery unit being actuated, through said electronic controller (E) also with a given time advance, before the vehicle is used.