Battery pack configured to block heat transfer between battery cells

Abstract

The present invention relates to a battery pack comprising: a battery cell assembly including several cells; a cooling element for cooling said assembly; a deformation element for dissipating heat from the cells to the cooling element; and a housing that contains the cell assembly, the cooling element, and the deformation element. The latter includes a first deformation element interposed between the cells and a coolant inside. The temperature of the cells can be set to a predetermined level when it is below or equal to a hazardous temperature, and heat transfer between them can be blocked when it exceeds that temperature.

Description

Battery pack configured to block heat transfer between battery cells. Technical sector This application claims the benefit of Korean patent application no. 20210179442, filed on December 15, 2021. The present invention relates to a battery pack configured to block heat transfer between battery cells. More specifically, the present invention relates to a battery pack configured to block heat transfer between battery cells, wherein the battery pack includes a structure capable of preventing heat conduction to an adjacent battery cell when the temperature of a battery cell reaches a dangerous level or higher. Background of the invention Lithium secondary batteries have been used as a power source for wireless mobile devices, which are small, multifunctional products, or wearable devices worn on the body, and have also been used as a power source for electric vehicles and hybrid electric vehicles, presented as alternatives to existing gasoline and diesel vehicles that cause air pollution, or as an energy storage system (ESS). Since lithium-ion batteries are used as high-capacity, high-performance power sources, as described above, ensuring their safety has become crucial. The temperature of lithium-ion batteries increases during charging and discharging, and high temperatures in a battery cell reduce its performance. Furthermore, user safety can become a problem if a fire or explosion occurs due to the increased temperature of the battery cell.To prevent the battery cell temperature from rising to a dangerous temperature, at which the battery cell could catch fire and explode, or higher, a heat transfer element made of a material with high thermal conductivity is included in a battery pack, so that the thermal energy of the battery cell is discharged through the heat transfer element. However, if the battery cells are arranged in close contact with each other to make a battery pack that has a high energy density, thermal propagation to adjacent battery cells can easily occur, instead of the thermal energy being discharged through the heat transfer element. Likewise, if the heat transfer element acts as a heat transfer path between the battery cells, the rate of thermal propagation between the battery cells can increase rapidly. Therefore, when the temperature of a particular battery cell increases rapidly in a state where a plurality of battery cells are arranged in close contact with each other, there is a need for a technology capable of preventing heat transfer to the other battery cells. In connection therewith, patent document 1 discloses a battery pack configured to have a structure in which a heat transfer plate is added to the outer surface of a battery cell, a heat conduction element is fixed to the inner surface of a housing, and an end of the heat transfer plate can come into contact with the heat conduction element, wherein the shape of a connector of the heat transfer plate that comes into contact with the heat conduction element varies depending on the temperature of the battery cell.Specifically, the connector is made up of metal layers with different coefficients of thermal expansion. The connector deforms in such a way that it flexes further when the battery cell temperature is low, increasing the distance between the connector and the heat conduction element. Conversely, when the battery cell temperature is high, this distance decreases. Therefore, when the battery cell temperature rises, heat conduction through the heat conduction element is achieved. As described above, patent document 1 presents a structure in which a flexed insulating plate is arranged in each battery cell and the flexed insulating plate is made up of metallic layers that have different coefficients of thermal expansion, so that the heat from the battery cell is transferred to the heat conduction element. However, patent document 1 does not propose a structure capable of preventing heat conduction between battery cells. In patent document 2, a filler is provided between a module housing and a battery cell, as well as between a plurality of battery cells. The filler is configured so that its volume increases to prevent battery cell swelling when the temperature in the battery module is low, and its volume decreases to ensure a cooling channel between the module housing and the battery cell, as well as between the plurality of battery cells, when the temperature in the battery module is high. The filler material in patent document 2 is made of a shape-change material that is deformable with temperature. Therefore, when the temperature increases, the filler material contracts, thus ensuring the cooling channel and consequently cooling the battery cells. However, in patent document 2, the expanded filler is arranged between the battery cells, and therefore it is difficult to apply the filler to a battery pack that has high energy density. Therefore, there is a need for a technology capable of preventing heat transfer to adjacent battery cells when a thermal runaway phenomenon occurs in a particular battery cell of a battery pack configured so that a plurality of cells are arranged in close contact with each other. State of the art documents (Patent Document 1) Japanese Patent Application Publication No. 201841582 (March 15, 2018) (Patent Document 2) Korean Patent Application Publication No. 20190084775 (July 17, 2019) US2019181515A1 discloses an energy storage module that includes a plurality of cooling elements configured to discharge heat from a plurality of energy storage elements to a heat dissipation element. Explanation of the invention Technical problem The present invention has been conceived taking into account the above problems, and an object of the present invention is to provide a battery pack configured such that a deformation element disposed between a plurality of battery cells arranged in close contact with each other deforms when the battery cell temperature increases, thereby blocking heat transfer between adjacent battery cells. Technical solution The invention is set forth in the appended set of claims. A battery pack according to the present invention for achieving the foregoing objective is defined in claim 1 and includes a battery cell stack comprising a plurality of battery cells, a cooling element configured to cool the battery cell stack, a deformation element configured to discharge heat from the plurality of battery cells to the cooling element, and a pack housing configured to receive the battery cell stack, the cooling element, and the deformation element therein, wherein the deformation element comprises a plurality of first deformation elements interposed between the plurality of battery cells, and each of the first deformation elements contains a coolant therein. The deformation element also includes a second deformation element arranged between the battery cell stack and the cooling element. The deformation element can be in a vacuum state in which the remaining part of the deformation element, excluding the coolant contained within it, is an empty space. The coolant can undergo a phase transition and evaporate due to the heat from the battery cells and condense through the cooling element, and heat transfer from the battery cells to the cooling element can occur through the phase transition of the coolant. When the temperature of the deformation element reaches the boiling point of the coolant or higher, the deformation element deforms in such a way that the volume of the deformation element expands, and when the entire coolant passes into the gaseous phase, the transfer of heat from the plurality of battery cells to the cooling element is blocked. A deformation element housing can be made of a shape memory alloy. The refrigerant can undergo a phase transition between evaporation and condensation depending on the temperature of the battery cell. The housing may include a first surface and a second surface, each configured to face the battery cell or cooling element. Each of the first and second surfaces may be flat at a temperature below the deformation temperature of the shape memory alloy, and each of the first and second surfaces may deform into a curved shape at a temperature above the deformation temperature. Heat transfer from the plurality of battery cells to the cooling element can be blocked when all of the coolant in the deformation element evaporates into a gaseous state, as a result of each of the first and second surfaces expanding and deforming into a curved shape. The first deformation element or a thermal insulation element may be arranged between the plurality of battery cells. The thermal insulation element may include an elastic material. The deformation element can be configured to have a flat shape. The coolant can be selected from the group consisting of ethanol, methanol, and water. The present invention provides a device that includes the battery pack as a power source. Furthermore, the present invention can provide various combinations of the aforementioned solution means. Advantageous effects As can be seen from the above description, a battery pack according to the present invention includes a deformation element configured to discharge heat from a plurality of battery cells to a cooling element, so that it is possible to avoid a rapid increase in the temperature of the battery cells. Furthermore, the thermal conductivity of the deformation element is significantly reduced when the temperature of each of the battery cells rises to a dangerous level, making it possible to block heat transfer between the battery cells. Brief description of the drawings FIG.1 is a perspective view of a battery pack according to the present invention. FIG.2 is a partial perspective view of a battery pack according to a first embodiment. FIG.3 is a cross-sectional view along line AA of FIG.2. FIG.4 is a vertical sectional view of a deformation element before and after deformation. FIG. 5 is a partial perspective view of a battery pack according to a second embodiment. Preferred embodiment of the invention The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that a person with ordinary technical knowledge in the field to which the present invention pertains can readily implement them. However, when describing in detail the operating principle of the preferred embodiments of the present invention, detailed descriptions of known functions and configurations incorporated herein will be omitted where doing so might obscure the object of the present invention. Furthermore, the same reference numbers will be used on all drawings to refer to parts that perform similar functions or operations. If a part is described as being connected to another part in the description, the part may be connected not only directly, but also indirectly through an additional component. Additionally, the inclusion of a particular element does not exclude other elements; it simply means that such elements may be included unless otherwise specified. Likewise, in the description of the invention and in the claims of this application, the singular forms include the plural forms, unless otherwise indicated. Furthermore, in the description of the invention and in the claims of this application, "or" includes "and", unless otherwise indicated. Therefore, "which includes A or B" means three cases, namely, the case which includes A, the case which includes B, and the case which includes both A and B. The embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view of a battery pack according to the present invention. With reference to FIG. 1, the battery pack according to the present invention includes a battery cell stack 100 comprising a plurality of battery cells 110, a cooling element 200 configured to cool the battery cell stack 100, a deformation element 300 configured to discharge heat from the plurality of battery cells 110 to the cooling element 200, and a pack housing 400 configured to receive the battery cell stack 100, the cooling element 200, and the deformation element 300 therein, wherein the deformation element 300 includes a first deformation element 310 interposed between one battery cell 110 and another battery cell 110. In addition, the deformation element 300 includes a second deformation element 320 arranged between the battery cell stack 100 and the cooling element 200. The deformation element 300 contains a coolant, and a housing designed to receive the coolant is made of a material with excellent thermal conductivity. Consequently, cooling of the battery cells and heat transfer between the battery cells are achieved through the deformation element 300; temperature variation between the battery cells can be prevented by the first deformation element 310, and the heat generated by the battery cells 110 can be discharged to the cooling element 200 via the second deformation element 320. Specifically, the cooling element 200, configured to cool the battery cells 110, is positioned below the battery cell stack 100, which comprises the plurality of battery cells 110, and the second deformation element 320 is positioned between the battery cell stack 100 and the cooling element 200. Consequently, heat from the battery cell stack 100 can be discharged to the cooling element 200 via the second deformation element 320, thus maintaining the temperatures of the battery cells 110 within a predetermined range. The battery cell stack 100, the deformation element 300, and the cooling element 200 can be received in the pack housing 400. An open top surface of the pack housing 400 can be covered with a top plate 410, and the pack housing 400 can be hermetically sealed, so that the battery pack can be assembled. However, unlike what is shown in FIG.1, the 400 pack housing may be in the form of a unique frame configured so that the end plates are assembled in the directions in which the electrode terminals protrude, or a U-frame, and a method of hermetically sealing the battery pack may vary depending on the shape of the pack housing. The cooling element 200 can be configured so that the coolant flows through the housing, and the cooling element 200 can be provided with an inlet and an outlet through which the coolant is introduced and discharged, respectively. The coolant can be supplied from outside the package housing 400, and the coolant can be discharged to the outside of the package housing 400. The battery cell can be a pouch-type battery cell, configured so that an assembly of electrodes is received in a pouch-type battery casing made of a laminated sheet that includes a metal layer and a resin layer, a prismatic battery cell, configured so that an assembly of electrodes is received in a prismatic metal can, or a cylindrical battery cell, configured so that an assembly of electrodes is received in a cylindrical metal can. Furthermore, FIG. 1 shows a bidirectional pouch-type battery cell configured so that a conductor 111 from the positive electrode and a conductor 112 from the negative electrode protrude in opposite directions. However, in contrast, a unidirectional pouch-type battery cell can be used, configured so that the conductor 111 from the positive electrode and the conductor 112 from the negative electrode protrude in the same direction. FIG.2 is a partial perspective view of a battery pack according to a first embodiment, and FIG.3 is a cross-sectional view along line AA of FIG.2. With reference to FIGS.2 and 3, the state is shown in which the package casing of FIG.1 is omitted. Each of the first deformation element 310 and the second deformation element 320 is planar. The length in the y-direction and the length in the z-direction of the first deformation element 310 can be greater than or equal to the length in the y-direction and the length in the z-direction of each of the corresponding battery cells 110, respectively. Consequently, the contact surface between the battery cells 110 and the first deformation element 310 can be maximized, thus enabling rapid heat transfer. The length in the xy direction and the length in the z direction of the second strain element 320, on which the battery cell stack is arranged, may be greater than or equal to the length in the x direction and the length in the z direction of a structure in which the battery cells 110 and the second strain element 320 are arranged in close contact with each other, respectively. Consequently, the second strain element 320 presents a large heat transfer area between the battery cells 110 and the first strain element 310 and the cooling element 200. In a specific example, assuming the temperature at which thermal runaway can occur due to the heat generated by a battery cell is approximately 150°C, the state in which the battery cell temperature is below 150°C can be called the safe temperature range, and the state in which the battery cell temperature is equal to or greater than 150°C can be called the hazardous temperature range. The first 310 deformation element and the second 320 deformation element remain flat, and the contact area with the battery cells can be maximized within the safe temperature range, allowing the battery cells to cool gently and thus preventing overheating. FIG.4 is a vertical cross-sectional view of the deformation element before and after deformation. FIG. 4 is a vertical sectional view of the first deformation element 310 that constitutes the deformation element, and the following description of the first deformation element will apply equally to the second deformation element. The first deformation element 310 contains refrigerant 313 and can be in a vacuum state, where the remaining portion of the first deformation element, excluding the refrigerant 313, is empty space. In this vacuum, the refrigerant 313 can evaporate and condense depending on the battery cell temperature. Specifically, a phase transition of the refrigerant occurs, in which the refrigerant evaporates due to the heat from the battery cell and condenses due to the cooling element 200. As a result of this phase transition, heat from the plurality of battery cells 110 can be transferred to the cooling element 200 via the first deformation element 310 and the second deformation element 320. In Figure 4, the lower portion of the first deformation element 310, which contains the coolant, is arranged to come into contact with the second deformation element 320, and the second deformation element 320 is arranged to come into contact with the cooling element. As a result, the temperature of the second deformation element 320 is lower than that of the first deformation element 310. Consequently, a process can be carried out in which the coolant condenses in a lower portion of the interior of the first deformation element 310, which is at a relatively low temperature due to contact with the second deformation element, and the coolant evaporates in an upper portion of the interior of the first deformation element 310, which is at a relatively high temperature. For example, each of the first deformation element and the second deformation element can be heat pipes, and any of the known heat pipes can be used as a deformation element according to the present invention, regardless of its type. In a specific example, the first deformation element 310 is made of a shape-changing material. When the battery cell temperature reaches 150°C or higher, entering the hazardous temperature range, the first deformation element 310 can deform, expanding its volume as shown in Figure 4. That is, when the temperature of the battery cell reaches the boiling point of refrigerant 313 or higher, the first deformation element 310 can deform in such a way that the volume of the first deformation element expands, and when the entirety of the refrigerant 313 passes into the gaseous phase, heat transfer from the plurality of battery cells to the cooling element can be blocked. When the volume of the first 310 deformation element expands, as described above, all of the coolant transitions to the gaseous phase due to adiabatic expansion, so the thermal conductivity drops rapidly and heat exchange between the battery cells, as well as heat exchange between the battery cells and the cooling element, can be blocked. Furthermore, the contact area with the battery cells is reduced due to the volumetric expansion of the first 310 deformation element, so the heat exchange between the battery cells can be reduced even further. In a volumetric expansion method of the deformation element, a housing made of a material that deforms when activated at a specific temperature or higher may be used. Alternatively, a method may be used to connect a pressurization medium, such as a cylinder, to a deformation element made of a material that is expandable and contractable under pressure, and apply pressure to the deformation element to expand its volume. In a specific example, the deformation element housing may be made of a shape-memory alloy, and the coolant, whose phase transition occurs such that it evaporates and condenses depending on the battery cell temperature, may be incorporated into the deformation element. The housing includes a first surface 311 and a second surface 312, each shaped like a wide rectangle, configured to face the battery cell or the cooling element. Each of the first surface 311 and the second surface 312 is flat at a temperature below the deformation temperature of the shape-memory alloy, and each of the first surface 311 and the second surface 312 deforms into a curved shape at a temperature above the deformation temperature of the shape-memory alloy. When all of the coolant in the deformation element evaporates into the gaseous phase as a result of each of the first surface 311 and the second surface 312 expanding and deforming into a curved shape, as described above, heat transfer between the plurality of battery cells and heat transfer from the plurality of battery cells to the cooling element can be blocked. The refrigerant 313 can be selected based on the temperature required for expansion deformation. For example, the refrigerant can be selected from the group consisting of methanol, ethanol, and water. In the first deformation element 310, the same phase transition can also occur as in the second deformation element 320 in an upward-downward direction. FIG. 5 is a partial perspective view of a battery pack according to a second embodiment. With reference to FIG. 5, the state is shown in which the battery pack casing and cooling element are omitted according to the present invention. A second deformation element 320 is arranged below the plurality of battery cells 110, and a first deformation element 310 or a thermal insulation element 300 is arranged between the plurality of battery cells 110. That is, either of the first deformation element 310 and the thermal insulation element 330 is disposed between one battery cell 110 and another battery cell 110, and each of the battery cells comes into contact with the first deformation element 310 on at least one of its outer surfaces. Consequently, it is possible to block heat exchange between adjacent battery cells by means of the 330 thermal insulation element and discharge heat from the battery cells to the outside through the deformation elements. Furthermore, each of the first and second deformation elements according to the present invention may be made of a material that has a volume that expands when the temperature of the battery cell increases, and, therefore, the external shape of a battery cell stack including the cells may expand when the volume of each of the deformation elements increases. However, it is preferable that the volume of the battery cell stack does not exceed a predetermined space provided in the battery pack, and, therefore, a thermal insulation element made of an elastic material may be provided as a thermal insulation element 330 to reduce the increase in volume of the deformation element. Furthermore, the description of the first deformation element and the second deformation element, set out with reference to FIGS. 2 to 4, can be equally applied to the first deformation element and the second deformation element shown in FIG. 5. The present invention can provide a device that includes the battery pack according to the present invention as a power source. For example, the device can be an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an energy storage system (ESS), an electric cart, or a two-wheeled electric vehicle. Although the battery pack according to the present invention is applied to a device requiring high capacity and high power, as described above, it is possible to prevent a rapid increase in battery cell temperature and block heat conduction between battery cells, and thus provide a battery pack with improved safety. Description of reference numbers 100: Battery cell stack 110: Battery cell 111: Positive electrode conductor 112: Negative electrode conductor 200: Cooling element 300: Deformation element 310: First deformation element 320: Second deformation element 311: First surface 312: Second surface 313: Refrigerant 330: Thermal insulation element 400: Package casing 410: Top plate

Claims

1. A battery pack comprising: a battery cell stack (100) comprising a plurality of battery cells (110); a cooling element (200) configured to cool the battery cell stack; a deformation element (300) configured to discharge heat from the plurality of battery cells to the cooling element; and a pack housing (400) configured to receive the battery cell stack, the cooling element, and the deformation element therein, wherein the deformation element comprises a plurality of first deformation elements (310) interposed between the plurality of battery cells, and wherein the deformation element comprises a second deformation element (320) disposed between the battery cell stack and the cooling element, wherein each of the plurality of first deformation elements comprises a coolant (313) therein,wherein the coolant is configured to condense in a lower portion of the interior of the first deformation element due to contact with the second deformation element and can be configured to evaporate in an upper portion of the interior of the first deformation element, wherein, when the temperature of the deformation element reaches or exceeds the boiling point of the coolant, the deformation element deforms such that its volume expands, and wherein, when all of the coolant transitions to the gaseous phase, heat transfer from the plurality of battery cells to the cooling element is blocked.

2. The battery pack according to claim 1, wherein the deformation element is in a vacuum state, wherein the remaining portion of the deformation element, excluding the coolant contained therein,is an empty space.

3. The battery pack according to claim 1, wherein: the coolant undergoes a phase transition and evaporates due to the heat of the battery cell and condenses due to the cooling element, and heat transfer from the plurality of battery cells to the cooling element occurs through the phase transition of the coolant.

4. The battery pack according to claim 1, wherein a housing of the deformation element is made of a shape-memory alloy.

5. The battery pack according to claim 1, wherein the coolant undergoes a phase transition between evaporation and condensation depending on the temperature of each of the plurality of battery cells.

6. The battery pack according to claim 4, wherein: the housing comprises a first surface (311) and a second surface (312),each configured to face either the battery cell or the cooling element, each of the first and second surfaces being flat at a temperature below the deformation temperature of the shape-memory alloy, and each of the first and second surfaces deforming into a curved shape at a temperature above the deformation temperature.

7. The battery pack according to claim 6, wherein heat transfer from the plurality of battery cells to the cooling element is blocked when all the coolant in the deformation element evaporates into a gaseous state as a result of each of the first and second surfaces expanding and deforming into the curved shape.

8. The battery pack according to claim 1,wherein the first deformation element or a thermal insulation element (330) is arranged between the plurality of battery cells.

9. The battery pack according to claim 8, wherein the thermal insulation element comprises an elastic material.

10. The battery pack according to claim 1, wherein the deformation element is configured to have a flat shape.

11. The battery pack according to claim 1, wherein the coolant is selected from a group consisting of ethanol, methanol, and water.

12. A device comprising the battery pack according to any one of claims 1 to 11 as a power source.

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