Battery module and method for operating a battery module

Abstract

Battery module (1) comprising at least one battery cell (3) and at least one heat pipe (4) which is in thermal contact with the at least one battery cell (3), wherein the heat pipe (4) has an evaporator section (10) and a condenser section (12), wherein at least one surface-enhancing element (13, 26) is arranged on the evaporator section (10) and / or the condenser section (12), wherein the battery module (1) has at least one actuator (20), wherein the at least one surface-enhancing element (13, 26) is displaceable relative to the heat pipe (4) by means of the at least one actuator (20), wherein the at least one surface-enhancing element (13, 26) is made of a material with good heat conductivity.

Description

[0001] The invention relates to a battery module comprising at least one battery cell and at least one heat pipe which is in thermal contact with the at least one battery cell, as well as a method for operating a battery module.

[0002] The temperature control or cooling of battery modules has been a known problem for a long time, and heat pipes, among other solutions, have been proposed. Heat pipes are essentially gas-tight tubes that are partially filled with a liquid with a defined boiling point. In the range from 0°C to approximately 400°C, water, for example, can be used, with the boiling point being adjusted by the internal pressure of the tube. The heat pipe has an evaporator section and a condensation section. In the simplest design, also known as a gravitational heat pipe, the liquid collects at the bottom of the tube (evaporator section) and absorbs heat through evaporation. The vapor then rises into the cold zone (condensation section), where it condenses and releases the enthalpy of vaporization to the environment. The condensate then flows back down to the heat source, completing the cycle.The processes are essentially isothermal, which is why the temperatures at the ends of the heat pipe differ only minimally during heat transfer. By utilizing the heat transfer heat from the medium's latent heat, heat pipes can dissipate many times more energy than solid heat conductors. Another advantage is that heat pipes are lighter.

[0003] From WO 2013 / 056 877 A1, a generic battery module is known, comprising a plurality of lithium-ion cells and a temperature control unit for regulating the temperature of the lithium-ion cells, wherein the temperature control unit comprises one or more heat pipes.

[0004] DE 197 24 020 A1 discloses a battery module comprising battery cells in a housing. The housing rests on a thermally conductive plate in which a heat pipe is arranged. The heat from the battery cells is transferred through the housing base into the plate and from there dissipated via the heat pipe.

[0005] EP 2 370 280 B1 discloses a device for cooling the battery of a motor vehicle, which includes an air conditioning system whose evaporator is suitable for cooling the interior of the vehicle and is contained in a closed space, the battery being located in a container. The evaporator space is connected to a duct whose outlet is directed toward a heat exchange zone provided on at least one outer side of the container, the heat exchange zone having a region outside the container, located opposite the outlet of the duct, and a region located opposite the interior of the container. The heat exchange zone consists of a radiator having a metallic base plate, which has, on one of its sides, a first row of fins directed toward the outlet of the duct, and, on the opposite side, a second row of fins directed toward the interior of the container.The cooler is tightly connected to an outer wall of the tank, located opposite the outlet of the channel. The device includes means for conduction heat exchange between the fins of the cooler and the battery, which means comprise a metallic structure or heat pipes.

[0006] A problem with all known solutions is that, while they describe heat dissipation, they do not prevent heat from entering the battery from outside. One such heat source is a combustion engine, for example. This can cause the battery module to reach temperatures that limit performance, despite cooling.

[0007] Another problem with the use of heat pipes is that heat transport is difficult or impossible to control.

[0008] DE 10 2009 057 163 A1 discloses a cooling device, wherein the device comprises at least one heat pipe, wherein the at least one heat pipe can be used as an evaporator or as part of an evaporator of a cooling circuit. The at least one heat pipe can be connected to the cooling circuit or separated from the cooling circuit. Furthermore, the device is designed such that thermal energy of at least one battery cell can be absorbed by means of at least a portion of a heat absorption surface of the at least one heat pipe and can be transferred to a cooling medium and / or cooling element by means of at least a portion of a heat dissipation surface of the at least one heat pipe. At least a portion of the heat dissipation surface can be thermally insulated from the cooling medium and / or cooling element by means of an insulating cap, wherein the insulating cap can be moved by an electric motor.

[0009] A fuel cell unit is known from DE 23 21 087 A1.

[0010] The invention is therefore based on the object of creating a battery module with at least one heat pipe in which the heat transport can be controlled, and of providing a method for operating such a battery module.

[0011] The solution to this problem according to the invention results from the objects having the features of claims 1 and 8. Further advantageous embodiments of the invention result from the subclaims.

[0012] For this purpose, the battery module comprises at least one battery cell and at least one heat pipe that is in thermal contact with the at least one battery cell, wherein the heat pipe has an evaporator section and a condensation section. It should be noted that the cross-section of the heat pipe does not have to be circular. Other cross-sections, such as rectangular ones, are also possible. If multiple battery cells are present, it is not necessary for each battery cell to be assigned a heat pipe. At least one surface-enlarging element is arranged on the evaporator section and / or the condensation section. This element is made of a material that dissipates heat well, such as copper. The function of the surface-enlarging element on the evaporator section is to improve heat transport from the battery cell to the heat pipe. This element can therefore also be referred to as a heat collector.The primary function of the surface-enlarging element in the condensation section is to improve heat dissipation from the heat pipe. Therefore, this element can also be referred to as a heat sink.

[0013] The battery module further comprises at least one actuator, wherein at least one surface-enlarging element can be displaced relative to the heat pipe by means of the at least one actuator. This makes it very easy to control the heat transport between the battery cell and the heat pipe. The relative displacement is such that in at least one position there is good thermal coupling between the heat pipe and the surface-enlarging element and in at least one position there is poorer thermal coupling. This displacement can also result in mechanical contact in one position and the heat pipe and surface-enlarging element being spatially separated in the other position. It can be provided that a surface-enlarging element is assigned to both sections of the heat pipe, but only one is displaceable by an actuator.Furthermore, it is also possible for each surface-enlarging element for each section to be assigned an actuator, each operating independently of the other. The actuators can be either active or passive, which will be explained in more detail later. Furthermore, the displacement can be continuous or occur only between two discrete positions. A surface-enlarging element can also be assigned to multiple heat pipes.

[0014] In one embodiment, the battery cell or battery cells are surrounded by thermal insulation. The thermal insulation can be a fleece or a housing, for example. The thermal insulation has low thermal conductivity, which prevents or reduces heat input from the outside into the battery cell. The at least one heat pipe is guided through the thermal insulation so that the evaporator section is arranged within the thermal insulation and the condensation section is arranged outside the thermal insulation. This means that heat can still be dissipated from the battery cells, but the heat input from the outside is greatly reduced. Heat can only be introduced from the outside into the space surrounded by the thermal insulation via the pipe of the heat pipe.However, since the area passing through the thermal insulation is small relative to the total surface area of ​​the thermal insulation, this heat input is extremely low. By shifting the surface-enlarging elements, especially those associated with the condensation sections, the heat input from outside can be further reduced.

[0015] In principle, the heat pipe(s) can be designed as gravitational heat pipes.

[0016] Preferably, however, the heat pipe is designed as a capillary heat pipe. These typically have a central channel made of a large-pore material and a surrounding channel made of a small-pore material, through which the condensed medium can be returned to the evaporation section via capillary force, even against gravity. In addition to the advantage that the heat pipes do not have to be installed with a gradient, a capillary heat pipe also allows the battery module to be heated under certain conditions. For example, if the ambient temperature is higher than the boiling point of the medium in the heat pipe, but the temperature inside the thermal insulation is lower than the boiling point, liquid can flow into the actual condensation section due to capillary force.There, the liquid absorbs heat from the environment, evaporates, and returns as vapor to the evaporation section of the battery cell, where it can condense and release its heat. In this situation, the heat pipe essentially works in reverse. The capillary heat pipe thus allows for effective heat dissipation from the battery cells during normal operation without the need for a separate controller, and even heats the battery cells when the ambient temperature is above and the battery cell temperature is below the boiling point of the medium.

[0017] In a further embodiment, the heat pipe tube has an insulating section between the evaporator section and the condensation section, which has a lower thermal conductivity than the other two sections. The insulating section is arranged in the region where the heat pipe passes through the thermal insulation. This allows for good heat input into and heat output from the heat pipe while simultaneously providing thermal insulation against heat input from outside the thermal insulation. The condensation section and the evaporator section are preferably made of copper, with the insulating section being made of plastic.

[0018] In a further embodiment, the surface-enlarging element at the condensation section is designed as a plate with at least one recess, wherein the heat pipe(s) are aligned with the recesses such that they dip into the recesses. This allows the use of only one surface-enlarging element for all condensation sections of the heat pipes, whereby in principle only one actuator is required for this element. However, this is not mandatory. This makes it possible to move one plate using more than one actuator. This is advantageous, for example, in order to uniform the lifting movement of the plate across the entire width. Furthermore, it is conceivable to divide one plate into several plates. If the heat pipes then dip into the recesses, good thermal coupling is achieved. Accordingly, the thermal coupling is reduced if the heat pipes are pulled out of the recesses and are spaced from the plate.Alternatively, the element can be designed as a cooling grille with holes for the heat pipes.

[0019] In a further embodiment, additional thermal insulation runs around the surface-enlarging elements at the condensation section and the thermal insulation. This additional thermal insulation prevents heat exchange with the environment. Preferably, the additional thermal insulation is designed as a bellows. Preferably, the common plate with recesses or a common cooling grid is used as the surface-enlarging element, as this simplifies sealing.

[0020] In a further embodiment, the surface-enlarging element on the evaporator section is formed as at least one sheet, preferably made of copper. A large amount of heat can be absorbed and dissipated from the battery cell via the large surface area of ​​the sheet. Preferably, such a sheet is arranged on each peripheral wall of the battery cell.

[0021] In a further embodiment, the at least one actuator is designed as a shape memory alloy, an expansion element, or a bimetal. The advantage of these passive actuators is that they do not require a separate control system, additional energy, sensors, or electronics. Rather, there is a pre-set temperature at which the actuator generates a force by changing its shape. Shape memory alloys have the property of changing their lattice structure at a specific, within-limits adjustable temperature. In doing so, they can perform work, for example by shortening (wire actuator) or assuming a specific, previously trained shape. If they are cooled below their transformation temperature, they can be returned to their original position with a fraction of the force they exert as an actuator when heated. An expansion element is an actuator filled with expansion material.The expansion element typically consists of a housing, a working piston, and the expansion material. Temperature changes trigger a material-dependent phase transition. The expansion material undergoes a significant volume change. When the expansion material cools down, the working piston is usually pushed back into the housing by a spring mechanism. In principle, the actuator can also be designed as an active actuator, for example, an electric motor. This allows for more complex and flexible control strategies, but is correspondingly more complex.

[0022] Preferably, the medium of the heat pipe is water, as it can cover a wide range of boiling temperatures by adjusting the pressure, is non-toxic and inexpensive.

[0023] In another embodiment, the heat pipe is arranged along a peripheral surface of the battery cell. In addition to the increased heat absorption area, this causes heat to be transported from bottom to top, which promotes circulation within the battery cell, which is particularly advantageous for lead-acid batteries.

[0024] In a further embodiment, the boiling temperature of the medium is between 20°C and 30°C, so that heat dissipation begins early before a critical temperature for the battery cells is reached.

[0025] A preferred application area for the battery module is as an on-board network, starter or traction battery in a motor vehicle.

[0026] The invention is explained in more detail below using a preferred embodiment. The figures show: Fig. 1 a schematic cross-section through a battery module, Fig. 2 a schematic cross-section through a capillary heat pipe, Fig. 3 a schematic side view of a part of the battery module with a lowered surface-enlarging element, Fig. 4 a schematic side view of a part of the battery module with raised surface-enlarging element, Fig. 5 a schematic front view of an embodiment with a surface-enlarging element on the evaporator section and Fig. 6 a schematic side view showing the movement of the surface enlarging element according to Fig. 5.

[0027] In the Fig. 1 schematically shows a battery module 1 in cross-section, wherein the cut was made such that a front wall of a thermal insulation 2 was cut away without cutting a battery cell 3 located within the thermal insulation 2. In addition to the already mentioned thermal insulation 2 and the battery cell 3, the battery module 1 comprises several heat pipes 4, wherein Fig. 4 shows four heat pipes 4. In this case, one heat pipe 4 is arranged on a left side wall 5 and one heat pipe 4 on the right side wall 6 of the battery cell 3, as well as two heat pipes 4 on a front wall 7. The heat pipes 4 extend over the full height of the battery cell 3. Preferably, further heat pipes are arranged around the entire circumferential surface of the battery cell 3 and are concealed by the heat pipes 4 shown. Air or a vacuum 8 is located between the battery cell 3 and the thermal insulation 2 in order to achieve the lowest possible thermal conductivity between the thermal insulation 2 and the battery cell 3. The heat pipes 4 each comprise a tube 9 which consists of three sections. The lower section forms an evaporator section 10 and the upper section a condensation section 12 of the heat pipe 4. The middle section represents a thermal insulation section 11.The heat pipes 4 are guided through the thermal insulation 2, with the thermal insulation section 11 located in the region of the passage through the thermal insulation 2. The condensation section 12 lies outside the thermal insulation 2, with an element 13 designed as a plate being arranged at its end to increase the surface area. The evaporator section 10 and the condensation section 12 have a high thermal conductivity. For example, these two sections 10, 12 are made of copper. The insulation section 11 has a lower thermal conductivity than sections 10, 12 and is made of plastic, for example. The plate-shaped element 13 has recesses into which at least some of the condensation sections 12 of the heat pipes 4 are immersed.The recesses can be dimensioned such that mechanical contact also occurs between the plate-shaped element 13 and the condensation section 12. However, this is not mandatory. At least in this position, good thermal coupling is ensured between the heat pipe 4 and the plate-shaped element 13. An additional thermal insulation 17, designed, for example, as a bellows, runs around the plate-shaped element 13 and the thermal insulation 2. The function of the additional thermal insulation 17 will be explained below in connection with the . Fig. 3 and Fig. 4. Finally, it should be noted that additional surface-enlarging elements can be arranged between the battery cell 3 and the evaporator sections 10 of the heat pipes 4. These can be, for example, sheets, preferably made of copper. The sheets are preferably arranged on the front wall 7, the rear wall, and the side walls 5, 6 of the battery cell 3.

[0028] The heat pipes 4 are designed as capillary heat pipes 4 (see also Fig. 2). For this purpose, the heat pipe 4 has, inside the closed tube 9, a core with large-pore material 14 and a jacket with small-pore material 15. A medium with a defined boiling point Ts of, for example, 25°C is located within the heat pipe 4. The medium is, for example, water, with the boiling point Ts being adjusted by a corresponding negative pressure in the heat pipe 4. The temperature of the battery cell 3 is designated Ti, and the ambient temperature at the condensation section 12 is designated Ta.

[0029] In the Fig. 3 and Fig. Figure 4 shows a front view of a portion of the battery module 1. A toggle lever 18 is shown on the left and right, with one leg 19 of the toggle lever 18 being connected to the thermal insulation 2, and the other leg of the toggle lever 18 being connected to the plate-shaped element 13. A rod 21 or wire made of a shape memory alloy is arranged between the toggle lever 18. The toggle lever 18 and the rod 21 form an actuator 20.

[0030] In the Fig. 3 shows that the ambient temperature Ta is below the ambient temperature of the shape memory alloy. The plate-shaped element 13 is lowered, and the heat pipes 4 are thermally coupled to the element 13. The heat of the battery cell 3 can thus be dissipated to the outside via the heat pipes 4 and the element 13. When the ambient temperature reaches the transition temperature of the rod 21, the rod contracts and lifts the element 13 via the toggle levers 18, so that the thermal coupling is interrupted or reduced (see Fig. 4). This interrupts the heat transfer. While no more heat can be dissipated from the battery cell 3, no more heat can be coupled into the battery cell 3 from the outside. The additional thermal insulation 17, designed as a bellows, now prevents the loss of heat directly from the now free condensation sections 12 of the heat pipes 4 through convection to the outside. At the same time, the thermal insulation 17 also prevents heat from entering from the outside.

[0031] If the rod 21 then cools below its transition temperature, it loses a large part of its tension, and the element 13 lowers itself under its weight back onto the heat pipes 4, more precisely, the condensation sections 12. This can also be assisted by spring elements (not shown), which tense up during the lifting process. The transition temperature of the rod 21 thus represents a predetermined limit temperature Tg, depending on which the movement occurs. For reasons of symmetry, two actuators (one at the front and one at the back) are preferably provided to raise and lower the element evenly.

[0032] Applications are also conceivable where the actuator 20 is to operate in reverse. Through a correspondingly adapted deflection, the element 13 can then be raised when a certain temperature is undershot. Conversely, in warm environments, the element is then pressed against the heat pipes 4 by the actuator 20 against the force of spring elements.

[0033] It should also be noted that the element 13 can also be designed as a cooling grid 24 instead of as a plate (see also Fig. 5). Furthermore, it should be noted that in the illustrated embodiment, the movement by the actuator 20 is vertically up and down. However, embodiments are also conceivable in which a horizontal movement is generated by the actuator 20. For example, the heat pipes 4 are positioned in the recesses such that they are spaced from the element in a first position and touch the element in a second position.

[0034] Alternatively or additionally, the heat transport can also be interrupted or established by displacing a surface-enlarging element, which is assigned to the evaporator section 10 of the heat pipe 4, relative to the heat pipe 4. This will now be explained with reference to the Fig. 5 and Fig. 6 will be explained in more detail.

[0035] In the Fig. 5 shows two heat pipes 4, each having a horizontal section 22 and a vertical section 23. The vertical sections 23 correspond to the condensation sections 12, and the horizontal sections 22 correspond to the evaporator sections 10. The vertical sections 23 are guided by a cooling grid 24 as element 13, which dissipates the heat at the condensation section 12. The horizontal sections 22 are connected, for example, by soldering, to a sheet metal strip 25. Arranged below the sheet metal strip 25 is a surface-enlarging element 26 in the form of a sheet metal, which is designed, for example, as a copper sheet. By means of at least one actuator 20, the element 26 can now be displaced relative to the sheet metal strip 25 so that they either touch one another or are separated from one another.

[0036] The principle should be based on Fig. 6, where Fig. 6 is only a schematic diagram and not an exact side view of the illustration according to Fig.5. The actuator 20 consists, for example, of two springs 27, 28 made of a shape memory alloy. The left spring 27, for example, has a transition temperature T1 and the right spring 28 a transition temperature T2, with the springs 27, 28 expanding above the transition temperature T1, T2. In the illustrated case, the temperature Ti of the battery cell 3 is between T1 and T2. The element 26 is separated from the sheet metal strip 25, and heat transfer is interrupted. If the temperature Ti then rises above T2, the spring 28 relaxes and presses the element 26 against the sheet metal strip 25. The spring 27 is compressed by the force of the spring 28. Heat transfer is established. Alternatively, the spring 27 can also be a normal spring. Preferably, the element 26 is firmly connected to the battery cell 3, so that only a part of the element 26 is moved by the actuator 20 to contact the sheet metal strip 25.Instead of the shape memory alloy springs 27, 28, bending beams made of shape memory alloys can also be used. Furthermore, expansion elements or bimetals can also be used as the actuator 20.

Claims

[1] Battery module (1), comprising at least one battery cell (3) and at least one heat pipe (4) which is in thermal contact with the at least one battery cell (3), wherein the heat pipe (4) has an evaporator section (10) and a condensation section (12), wherein at least one surface-enlarging element (13, 26) is arranged on the evaporator section (10) and / or the condensation section (12), wherein the battery module (1) has at least one actuator (20), wherein by means of the at least one actuator (20) the at least one surface-enlarging element (13, 26) is displaceable relative to the heat pipe (4), wherein the at least one surface-enlarging element (13, 26) consists of a material which dissipates heat well. [2] Battery module (1) according to claim 1, characterized bythat the battery cell (3) is surrounded by a thermal insulation (2), wherein the heat pipe (4) is guided through the thermal insulation (2) so that the evaporator section (10) is arranged within the thermal insulation (2) and the condensation section (12) is arranged outside the thermal insulation (2). [3] Battery module (1) according to claim 2, characterized by that a tube (9) of the heat pipe (4) between the evaporator section (10) and the condensation section (12) has an insulation section (11) which has a lower thermal conductivity than the two other sections (10, 12), wherein the insulation section (11) is arranged in the region of the passage of the heat pipe (4) through the thermal insulation (2). [4] Battery module (1) according to one of the preceding claims, characterized bythat the surface-enlarging element (13) on the condensation section (12) is designed as a plate with at least one recess, wherein the heat pipe(s) (4) are arranged relative to the recesses in such a way that they dip into the recesses, or that the surface-enlarging element (13) is designed as a cooling grid (24) with at least one bore. [5] Battery module (1) according to one of claims 2 to 4, characterized by that a further thermal insulation (17) runs around the surface-enlarging elements (13) on the condensation section (12) and around the thermal insulation (2). [6] Battery module (1) according to one of claims 1 to 3, characterized by that the surface-enlarging element (26) on the evaporator section (10) is formed as at least one sheet. [7] Battery module (1) according to one of the preceding claims, characterized bythat the at least one actuator (20) is designed as a shape memory alloy or as an expansion element or as a bi-metal. [8] Method for operating a battery module (1), wherein the battery module (1) has at least one battery cell (3) and at least one heat pipe (4) which is in thermal contact with the at least one battery cell (3), wherein the heat pipe (4) has an evaporator section (10) and a condensation section (12), wherein surface-enlarging elements (13, 26) are arranged on the evaporator section (10) and / or the condensation section (12), and the battery module (1) has at least one actuator (20), wherein by means of the at least one actuator (20) at least one surface-enlarging element (13, 26) is displaced relative to the heat pipe (4), wherein the at least one surface-enlarging element (13, 26) consists of a material which dissipates heat well. [9] Method according to claim 8, characterized bythat the actuators (20) move the surface-enlarging elements (13, 26) relative to the heat pipe (4) as a function of an ambient temperature (Ta) and / or as a function of a battery cell temperature (Ti). [10] Method according to claim 9, characterized by that at an ambient temperature (Ta) above a predetermined limit temperature (Tg), the surface-enlarging element(s) (13) of the condensation section (12) is / are moved away from the heat pipe (4) or the heat pipes (4).

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