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 condensation section (12), characterized in that the battery cell (3) is surrounded by 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).

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, wherein the heat pipe has an evaporator section and a condensation section.

[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] A cooling device is known from DE 10 2009 057 163 A1, wherein the device comprises at least one heat pipe that can be used as an evaporator or part of an evaporator of a cooling circuit, wherein the at least one heat pipe can be connected to the cooling circuit and separated from the cooling circuit. Thermal energy of at least one battery cell can preferably be absorbed by means of at least a part of a heat absorption surface of the at least one heat pipe and transferred to a cooling medium and / or cooling element by means of at least a part of a heat dissipation surface of the at least one heat pipe. The battery cells are arranged in a motor vehicle, wherein at least a part of the heat dissipation surface is arranged outside the motor vehicle, wherein at least a part of the heat dissipation surface is arranged thermally opposite the cooling medium and / or cooling element. Insulation is preferably provided by a movable insulating cap.

[0004] From DE 23 21 087 A1, a fuel cell unit is known in which thermal insulation is provided to enable proper operation at low outside temperatures, whereby the thermal insulation must be removed at outside temperatures of more than 25°C.

[0005] DE 10 2009 058 842 A1 discloses a temperature control device for a vehicle comprising at least one phase-change material that can be brought into thermal contact with a passenger compartment of the vehicle and with a battery of the vehicle. The thermal contact can be established, for example, by means of a heat pipe.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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 an internal combustion engine, for example. This can cause the battery module to reach temperatures that limit performance despite cooling.

[0010] The invention is based on the object of creating a battery module which reduces external heat input while providing good heat dissipation.

[0011] The solution to this technical problem according to the invention results from the subject matter having the features of claim 1. Further advantageous embodiments of the invention result from the subclaims.

[0012] 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 heat pipe and the battery cell are preferably in mechanical contact in order to achieve the best possible heat transfer. It should also be noted that the cross-section of the heat pipe does not have to be circular. Rather, other cross-sections, such as rectangular ones, are also possible. If multiple battery cells are present, not every battery cell has to be assigned a heat pipe. On the other hand, multiple heat pipes can also be assigned to one battery cell. The battery cell or the battery cells are surrounded by thermal insulation. The thermal insulation can, for example, be a fleece or a housing.The thermal insulation has low thermal conductivity, which prevents or reduces heat input from outside into the battery cell. At least one heat pipe is routed through the thermal insulation, so that the evaporator section is located within the thermal insulation and the condensation section is located outside the thermal insulation. This means that heat can still be dissipated from the battery cells, but heat input from outside is greatly reduced. Heat can only be introduced from outside into the space surrounded by the thermal insulation via the heat pipe tube. However, since the area through which heat is passed through the thermal insulation is small compared to the total surface area of ​​the thermal insulation, this heat input is extremely low.

[0013] In principle, the heat pipe(s) can be designed as gravity heat pipes. It is also possible to use controlled heat pipes, where, for example, the flow can be controlled via a valve. Other forms of heat pipe control or combinations of heat pipes are also known and, in principle, applicable.

[0014] 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 control system, 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.

[0015] In a further embodiment, the tube of the heat pipe is composed of at least two sections, one section having a lower thermal conductivity than the other, with the section with the lower thermal conductivity being arranged in the region of the passage through the thermal insulation. This further minimizes heat input from the outside. For example, the section with the higher thermal conductivity is made of copper, and the section with the lower thermal conductivity is made of plastic. However, it is also possible to use the same base material, which is doped in sections with additives that change the thermal conductivity.

[0016] Further preferably, the tube is formed from at least three sections, with the middle section having a lower thermal conductivity than the other sections and being arranged at the passage through the thermal insulation. This allows for good heat input into and heat output from the heat pipe while simultaneously providing good thermal insulation against heat input from outside the thermal insulation.

[0017] In a further embodiment, surface-enlarging elements are arranged on the evaporator section and / or the condensation section, which improve the heat input and / or heat output from the heat pipe. The shape of the elements on the evaporator section is adapted, for example, to the shape of the battery cell.

[0018] 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.

[0019] 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 promotes heat transfer from bottom to top, which supports circulation within the battery cell, which is particularly advantageous for lead-acid batteries.

[0020] 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.

[0021] A preferred application area for the battery module is as an on-board power supply, starter or traction battery in a motor vehicle.

[0022] 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 and Fig. 2 a schematic cross-section through a capillary heat pipe.

[0023] 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. 1 shows four heat pipes 4. In each 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 routed through the thermal insulation 2, with the thermal insulation section 11 located in the area of ​​the passage through the thermal insulation 2. The condensation section 12 lies outside the thermal insulation 2, with rib-shaped elements 13 arranged at its end to increase the surface area. The evaporator section 10 and the condensation section 12 have 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.

[0024] 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.

[0025] The functionality of the battery module 1 will now be explained in more detail, considering four constellations, namely: 1) Ti, Ta < Ts 2) Ti > Ts > Ta 3) Ti, Ta > Ts 4) Ta > Ts > Ti To 1)

[0026] The medium of the heat pipe 4 is completely liquefied and no heat transfer takes place. 2)

[0027] Due to the heat from the battery cell 3, the medium evaporates in the heat pipe 4 in the evaporation section 10. The vapor rises in the channel with the large-pore material 14 and condenses at the condensation section 12. Heat is released in the process, particularly via the elements 13. The condensed medium flows back down into the evaporator section 10 via the channel with the small-pore material 15. This cools the battery cell 3. This cooling allows the battery cell 3 to remain within a permissible operating range of, for example, 0°C to 55°C for longer. To 3)

[0028] The medium in the heat pipe 4 is completely in the form of steam and no heat transfer takes place. To 4)

[0029] The medium is initially present as a liquid. Due to capillary action, the liquid flows through the channel with the small-pore material 15 from the evaporator section 10 to the condensation section 12. Since the temperature Ta there is greater than the boiling point Ts, the liquid medium evaporates, and the vapor flows through the channel with the large-pore material 14 to the battery cell 3. The battery cell 3 is heated.

[0030] This is advantageous, for example, in winter when the battery cell 3 is still very cold after the vehicle has started, but the environment around the condensation section 12 is already warmer (e.g., due to engine waste heat). When using a gravity heat pipe, however, the liquefied medium remains in the evaporator section 10, and no heat transfer occurs.

[0031] It should be noted that in the case of 4), the heat pipe 4 works in reverse, i.e. evaporates at the condensation section 12 and condenses at the evaporator section 10.

[0032] In operating situations where Ta > Ti, the thermal insulation 2 prevents heat from entering from the outside, preventing the battery cell 3 from heating up further. The insulation section 11 prevents a thermal bridge at the passage of the heat pipes 4 through the thermal insulation 2.

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), characterized by that the battery cell (3) is surrounded by 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). [2] Battery module (1) according to claim 1, characterized by that the heat pipe (4) is designed as a capillary heat pipe (4). [3] Battery module (1) according to claim 1 or 2, characterized bythat a tube (9) of the heat pipe (4) is composed of at least two sections, one section having a lower thermal conductivity than the other section, the section with the lower thermal conductivity being arranged in the region of the passage through the thermal insulation (2). [4] Battery module (1) according to claim 3, characterized by that the tube (9) of the heat pipe (4) is composed of at least three sections, wherein a middle insulation section (11) has a lower thermal conductivity than the other two sections (10, 12), wherein the insulation section (11) with the lower thermal conductivity is arranged in the region of the passage through the thermal insulation (2). [5] Battery module (1) according to one of the preceding claims, characterized by that surface-enlarging elements (13) are arranged on the evaporator section (10) and / or the condensation section (12). [6] Battery module (1) according to one of the preceding claims, characterized by that there is a medium in the heat pipe (4), the medium being water. [7] Battery module (1) according to one of the preceding claims, characterized by that the heat pipe (4) is arranged along a circumferential surface of the battery cell (3). [8] Battery module (1) according to one of the preceding claims, characterized by that the battery cell (3) is designed as a lead-acid battery. [9] Battery module (1) according to one of the preceding claims 6 to 8, characterized by that the boiling temperature Ts of the medium is between 20°C and 30°C. [10] Battery module (1) according to one of the preceding claims, characterized by that the battery module (1) is a starter, on-board network or traction battery of a motor vehicle.

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