Battery module including expansion buffer unit

Abstract

The present invention provides a battery module including an expansion-relief unit, which includes a cell stack in which one or more battery cells are stacked, and a module case that houses the cell stack, and further includes an expansion-relief unit having a protrusion that can apply pressure to at least a portion of the outermost battery cell that is disposed on the outermost side of the cell stack.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 2021-0003604 dated January 11, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a battery module including an expansion relief unit, particularly to a battery module including an expansion relief unit capable of pressurizing a battery cell, the expansion relief unit being disposed in or / and inside a case of the battery module to relieve lithium plating behavior and prevent shortening of the lifespan of the battery cell. [Background technology]

[0003] As the demand for mobile devices such as smartphones increases, the demand for secondary batteries used as their energy sources is also increasing. Secondary batteries are also applied to electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (P-HEVs), energy storage devices (ESSs), and the like.

[0004] Among secondary batteries, the demand for lithium secondary batteries is overwhelmingly high. Lithium secondary batteries function by repeatedly inserting and extracting lithium ions between the negative and positive electrodes. Between these electrodes is an electrolyte containing lithium salt, through which lithium ions can move but electrons cannot.

[0005] The deposition of lithium, so-called lithium plating, can cause side reactions with the electrolyte and changes in the kinetic balance of the secondary battery. This reduces the capacity and cycle life of the battery, and also causes safety issues such as the loss of overcharge regulation function. During repeated charging and discharging, lithium metal is deposited in a dendritic form on the electrode surface, seriously threatening the safety of the battery. If the lithium metal deposited in a dendritic form penetrates the separator and contacts the opposite electrode, it can cause an internal short circuit and induce a temperature rise due to a rapid chemical reaction. As a result, the cell or module can ignite and explode. Lithium plating occurs relatively frequently in the vicinity of the protruding electrode tab of the battery cell, and the cell expands at this location as the number of charging / discharging and cycles increases. This phenomenon occurs more frequently in battery modules in which many battery cells are stacked than in unit battery cells. The cycle life of the battery cells that make up the battery module is shorter than that of unit battery cells, and the scale of accidents can also be greater due to the large number of battery cells.

[0006] 1 to 3 show a battery module 100 according to the related art. Referring to FIG. 1 to FIG. 3, the battery module 100 includes a cell stack 200 in which a plurality of battery cells 21, 22, ..., n-1, n are stacked, and the cell stack 200 is housed in a module case (reference numerals omitted). The outer wide surfaces of the two battery cells 21, n arranged at the outermost positions of the cell stack 200 face the first side cover 130 and the second side cover 140 of the module case, respectively, an expansion control pad 180 is positioned between the battery cells arranged at the outermost positions and the side covers of the module case, and a resin layer 400 for fixing the cell stack 200 may be interposed between the cell stack 200 and the lower cover 120. For stability of the battery cells 21, 22, ..., n-1, n constituting the cell stack 200, an adhesive 300 may be interposed at a predetermined position between the battery cells facing each other.

[0007] The battery cells 21, 22, ..., n-1, n in the battery module 100 according to the related art repeatedly expand and contract during charging and discharging, and the deformation causes the electrode active material to fall off or deteriorate, and also triggers side reactions, which reduces the performance of the battery. To solve these problems, an expansion control pad 180 is generally provided between the module case and the outermost battery cell or between the battery cells, and it is compressed to act as a buffer when the battery cell expands, thereby controlling cell swelling.

[0008] As shown in Figure 3, the volume of the battery cell increases differently between the center and the edge when the battery cell expands. That is, the center expands more like a pot than the edge when the battery cell expands. When the entire surface of the expanding battery cell is supported uniformly, the gas generated inside the battery cell and the lithium plating that can be generated by the gas will cause the cell shape to change.

[0009] FIG. 4 is a schematic diagram illustrating the state before and after deformation of a battery cell, taking as an example one of the battery cells 21 arranged at the outermost position among the battery cells 21, 22, ..., n-1, n according to the related art. Such expansion may occur in all battery cells, including the battery cell arranged at the outermost position. Referring to FIG. 4, the portion adjacent to the electrode tab and electrode lead 2 of the battery cell 21 expands relatively more. As the expansion of the central portion is suppressed, gas generated inside expands the left and right outer portions where the electrode tabs are located. As charging and discharging continues, such deformation becomes more significant. Each battery cell expands, and deformation becomes more significant in the cell stack 200 in which many battery cells are joined together. This shortens the life of the battery module 100 and may also lead to accidents such as fires.

[0010] It is necessary to extend the life of the battery cells in the battery module 100 and improve the safety of the battery module by reducing the expansion caused by lithium plating of the battery cells 21, 22, ..., n-1, n in the battery module 100. However, there is a limit to how much the lithium plating phenomenon can be suppressed by the electrochemical mechanism of the battery cells.

[0011] Patent Document 1 discloses a lithium secondary battery for making lithium safe, in which microcapsules containing a stabilizing substance that stabilizes lithium that precipitates from the negative electrode when the secondary battery is overcharged are formed between the negative electrode and a separator, and the surface of the microcapsules is formed of a thermoplastic resin layer so that the stabilizing substance will leak when the secondary battery is overcharged due to the collapse of the microcapsules.

[0012] Patent Document 2 discloses a method for detecting lithium deposition in a negative electrode in real time by observing a change in battery voltage according to SOC during charging of a secondary battery, and is characterized in that the point at which the rate of increase in battery voltage slows down is determined to be the starting point of lithium deposition.

[0013] Patent documents 1 and 2 disclose technologies for ensuring safety against lithium precipitation in lithium secondary batteries, but do not disclose a battery module equipped with an expansion mitigation unit for mitigating the expansion of battery cells arranged in the battery module during charging and discharging.

[0014] As described above, an effective means for solving the problem caused by deformation of battery cells in a battery module including a cell stack in which a large number of battery cells are stacked has not yet been presented. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Korean Patent Publication No. 2017-0111566 [Patent Document 2] Korean Patent Publication No. 2017-0023583 Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention is intended to solve the above problems, and aims to provide a battery module including an expansion relief unit that can prevent shortening of the lifespan of battery cells in a battery module while using existing battery modules and battery cells as they are.

[0017] Another object of the present invention is to provide a battery module including an expansion relief unit that allows gas generated during use of the battery module to quickly move to the outer periphery without being retained in an electrode assembly of a battery cell. [Means for solving the problem]

[0018] In order to achieve the above-mentioned objectives, the battery module of the present invention includes a cell stack in which one or more battery cells are stacked, and a module case that houses the cell stack, and an expansion relief unit having a protrusion that is capable of applying pressure to at least a portion of an outermost battery cell that is arranged on the outermost side of the cell stack may be arranged facing the outermost battery cell of the cell stack.

[0019] The expansion buffer unit may be disposed between an outermost battery cell disposed at the outermost position of the cell stack and the module case.

[0020] The expansion buffer unit may be disposed for all of the outermost battery cells disposed on the outermost side of the cell stack.

[0021] The protrusion of the expansion relief unit may be located only at a predetermined position in the center of the outermost battery cell.

[0022] The protrusions of the expansion relief units may be made of an elastic material.

[0023] The convex portion of the expansion relief unit may be deformed into a concave shape when a certain pressure or more is applied.

[0024] The surfaces of the battery cells that face each other may be bonded together with an adhesive layer.

[0025] The adhesive layer may be applied to the entire surface facing the battery cells.

[0026] The expansion cushioning unit may be integrally formed with a side cover of the module case.

[0027] The present invention can also provide a battery pack including the battery module, and a device including the battery pack.

[0028] The present invention can select and combine one or more of the above-mentioned configurations that are not contradictory to each other. Effect of the Invention

[0029] The battery module of the present invention has an expansion relief unit disposed in the outermost battery cell, thereby suppressing abnormal expansion of the battery cells and battery module caused by the number of charge / discharge cycles, preventing a reduction in the service life of the battery cells and improving stability.

[0030] When the convex portion of the expansion mitigation unit is subjected to a certain pressure or more, it deforms into a concave shape, reducing the pressure on the center of the battery cell and the battery module, preventing the periphery of the electrode tab from expanding, thereby mitigating the occurrence of lithium plating and preventing accidents such as a rise in temperature inside the battery cell and a fire in the battery module.

[0031] The expansion buffer unit of the present invention can be easily installed in an existing battery module without modifying it, so there is no need to change the battery module production process, which is economically advantageous.

[0032] An adhesive layer is applied to the entire surfaces of adjacent battery cells facing each other within a battery module to bond them together, so that gas generated inside the battery cells during charging and discharging can be quickly moved to the outer periphery of the battery cells, preventing uneven deterioration of the battery cells. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a schematic diagram of a battery module according to the prior art. [Diagram 2] 2 is a cross-sectional view taken along line AA' in FIG. [Diagram 3] FIG. 2 is an exploded perspective view of the battery module shown in FIG. [Figure 4] 1A and 1B are schematic diagrams illustrating a battery cell according to a conventional technique before and after deformation. [Diagram 5] 1 is an exploded perspective view of a battery module according to a first embodiment of the present invention; [Figure 6] 6 is a cross-sectional view taken along line AA' in FIG. 5. [Figure 7] FIG. 4 is an exploded perspective view of a battery module according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In this application, terms such as "comprise", "have" or "comprise" are intended to specify the presence of features, numbers, steps, components, parts or combinations thereof described in the specification, but are to be understood as not precluding the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0035] In addition, the same reference numerals are used in the drawings for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection, but also an indirect connection with another element interposed therebetween. Furthermore, unless otherwise specified, the inclusion of a certain component does not mean the exclusion of other components, but means that other components may also be included.

[0036] Hereinafter, a battery module according to the present invention will be described with reference to the accompanying drawings.

[0037] FIG. 5 is an exploded perspective view of a battery module according to a first embodiment of the present invention, and FIG. 6 is a cross-sectional view taken along line AA' in FIG.

[0038] 5 and 6, the battery module 1000 according to the first embodiment of the present invention may be configured to include a cell stack 1200 in which a plurality of battery cells (drawing number omitted) are stacked inside a module case (drawing number omitted) having an approximately rectangular parallelepiped outer shape, and an expansion relief unit 1500.

[0039] The module case may be composed of an upper cover 1110, a lower cover 1120, a first side cover 1130 and a second side cover 1140 facing each other so as to be positioned toward the side surface which is the wide surface of the cell stack 1200, and a front cover 1150 and a rear cover 1160 located on the surface on which the electrode tabs are arranged.

[0040] Here, the front cover 1150 and the rear cover 1160 are arranged facing the direction in which the electrode leads of the battery cells are located to protect the electrode leads and bus bars 1170, etc., and a pair of side covers 1130, 1140 protect the sides (XZ plane) of the cell stack 1200 housed inside the module case.

[0041] Top cover 1110 and bottom cover 1120 provide protection for the top and bottom of cell stack 1200 .

[0042] The above-mentioned upper cover 1110, lower cover 1120, pair of side covers 1130, 1140, front cover 1150 and rear cover 1160 can be manufactured separately and configured to be assembled together, or, if necessary, some components can be manufactured as a single unit.

[0043] The battery cell having the above-mentioned configuration is arranged inside the module case in close contact with the first side cover 1130 and the second side cover 1140 of the module case with their sides (XZ plane) standing parallel to the side covers.

[0044] The cell stack 1200 housed in the internal space of the module case is composed of a plurality of battery cells stacked together with their wide surfaces in close contact, and the battery cell includes a cell case (not shown) that houses an electrode assembly (not shown) and electrode leads (not shown).

[0045] The cell case is a pouch-type (laminate sheet) cell case, in which at least one electrode assembly is accommodated in a storage portion, the edges are fused to seal the storage portion, and a pair of electrode leads are connected to both sides or one side of the electrode assembly and protrude outside the cell case. Of course, a positive electrode tab and a negative electrode tab of the electrode assembly may be exposed to the outside of the cell case after being electrically connected to each other, or the tabs may be omitted and the cell assembly and the electrode leads may be directly connected to each other.

[0046] The electrode assembly may be, but is not limited to, a jelly roll type assembly having a structure in which a separator is interposed between long sheet-like positive and negative electrodes and then wound up, a stack type assembly having a structure in which rectangular positive and negative electrodes are stacked with a separator sandwiched between them, a stack-folding type assembly in which unit cells are wound up with a long separator film, or a lamination-stack type assembly in which battery cells are stacked with a separator sandwiched between them and attached to each other.

[0047] As a matter of course, the electrolyte in the battery cell may be a solid electrolyte or a quasi-solid electrolyte in a gel form that is an intermediate form between a liquid and a solid, in addition to the commonly used liquid electrolyte.

[0048] The electrode assembly is housed in a cell case, and the cell case generally has a laminated sheet structure of an inner layer / metal layer / outer layer. The inner layer must have insulating properties and electrolyte resistance at the point where it directly contacts the electrode assembly, and must have sealing properties for sealing from the outside, i.e., the sealing portion where the inner layers are thermally bonded to each other must have excellent thermal bonding strength. The material of the inner layer may be selected from polyolefin resins such as polypropylene, polyethylene, polyethylene acrylic acid, and polybutylene, which have excellent chemical resistance and good sealing properties, polyurethane resins, and polyimide resins, but is not limited thereto, and polypropylene, which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, and impact strength, and excellent chemical resistance, is the most preferred.

[0049] The metal layer in contact with the internal layer corresponds to a barrier layer that prevents moisture and various gases from penetrating into the battery from the outside. A preferred material for such a metal layer is an aluminum thin film, which is lightweight yet has excellent formability.

[0050] An outer layer is provided on the other side of the metal layer. The outer layer may be made of a heat-resistant polymer having excellent tensile strength, moisture permeability, and air permeability so as to protect the electrode assembly while ensuring heat resistance and chemical resistance. For example, nylon or polyethylene terephthalate may be used, but is not limited thereto.

[0051] The expansion buffer unit 1500 according to the first embodiment of the present invention may be located between the pair of side covers 1130 and 1140 of the module case and the cell stack 1200.

[0052] The expansion relief unit 1500 as described above may be composed of a substantially flat plate portion 1520 and a protruding portion 1510 formed to protrude toward the cell stack 1200 based on the broad surface (XZ plane) of the flat plate portion 1520. In particular, the protruding portion 1510 may be located at the center side in the longitudinal direction (X-axis direction) of the flat plate portion 1520, and the protruding portion 1510 may be located in close contact with the center side of the outermost side surface (X-axis direction in the XZ plane) of the battery cell located at the outermost side of the cell stack 1200. In addition, the portion of the protruding portion 1510 in close contact with the outermost side surface of the outermost battery cell of the cell stack 1200 may be flat or arc-shaped.

[0053] Since expansion occurs at the center of the battery cell in the initial stage of charging and discharging, as described above, the convex portion 1510 of the expansion mitigating unit 1500 is in close contact with a predetermined portion of the center of the battery cell and mitigates the expansion limit by deformation at a predetermined pressure, which is advantageous for extending the lifespan. In the present invention, the convex portion 1510 of the expansion mitigating unit 1500 is located in close contact or close proximity to the outermost battery cell of the cell stack 1200. When the battery cell expands during charging and reaches a predetermined pressure or higher, the convex surface of the convex portion 1510 is deformed toward the side covers 1130 and 1140 of the module case, and when it contracts during discharging, the deformed convex portion 1510 regains its shape toward the corresponding outermost battery cell. At this time, the flat portion 1520 remains in its initial shape and is not deformed.

[0054] Meanwhile, when the battery cell expands to a predetermined volume or more during charging and discharging and the pressure applied to the convex portion 1510 is equal to or greater than a certain pressure, the convex portion 1510 is deformed into a generally concave shape. The convex surface of the convex portion 1510 is permanently deformed toward the side covers 1130 and 1140 of the module case as a whole, and the convex portion 1510 is deformed into a concave shape. As a result, the battery cell that expands to a certain volume or more is not subjected to pressure. The convex portion 1510 is deformed into a shape closer to the side covers 1130 and 1140 of the module case than the flat portion 1520. The present invention uses the expansion relaxation unit 1500 whose shape is deformed during charging and discharging, thereby adjusting the degree of pressure applied to the battery cell that is being charged and discharged. The battery expands naturally during charging and discharging, which can provide the most appropriate pressure for improving the safety and life of the battery.

[0055] In the present invention, the expansion mitigating unit 1500 may be made of an elastic material so as to suppress the expansion of the battery cell at an early stage. The convex portion 1510 of the expansion mitigating unit 1500 located in close contact with the battery cell receives the expansion pressure when the battery cell expands. The convex portion 1510, which is bulged toward the side of the battery cell, can be deformed by the expansion of the battery cell. If the convex portion 1510 is not made of an elastic material, it may be broken by the expansion pressure of the battery cell, causing damage to the battery cell and causing an accident such as a fire. Therefore, by making the expansion mitigating unit 1500 of an elastic material, it is easily deformed when the battery cell expands, which is advantageous in preventing accidents. In addition, the flat portion 1520 of the expansion mitigating unit 1500 maintains a flat shape regardless of deformation due to the expansion and / or contraction of the battery cell, which is advantageous in mitigating deformation of the shape of the cell caused by lithium plating generated when gas generated inside the battery cell moves to both ends of the battery cell.

[0056] The protrusions 1510 may be in close contact with the entire or part of the height (Z-axis direction) of the battery cell, and more specifically, may be symmetrically arranged on both sides from the center in the height direction, which is advantageous in mitigating expansion by bringing the protrusions 1510 into close contact with the outside of the cell case at the center of both ends of the battery cell, which is relatively prone to expansion.

[0057] Here, the material of the expansion buffer unit 1500 may be an elastic metal or synthetic resin, and more specifically, may be a material including a soft elastic material such as polyurethane (PU) or EDPM (Ethylene Propylene Diene Monomer). The above elastic material has excellent water absorption and repulsive force against compression against vibration, so that it is possible to provide a battery module 1000 having excellent dimensional stability even if a cell swelling phenomenon occurs in a plurality of battery cells. In the present invention, the material is not particularly limited to the above as long as it can suppress the expansion of the battery cells and at the same time, can maintain its shape up to a certain pressure before deforming.

[0058] Although not shown in FIG. 5, the expansion relief unit 1500 according to the first embodiment of the present invention may have a convex portion 1510 formed in the center of the flat portion 1520, and one or more convex portions 1510 may be formed. The number of convex portions 1510 is not particularly limited as long as it can relieve the expansion caused by lithium plating of the battery cell.

[0059] Meanwhile, as shown in Fig. 6, the battery cells can be bonded to each other by applying an adhesive 1300 between the side surfaces (XZ plane) of adjacent battery cells. The adhesive 1300 is preferably applied to the entire side surfaces of the adjacent battery cells.

[0060] By applying adhesive 1300 to all of the side surfaces where battery cells 121, 122, ..., m constituting cell stack 1200 are in close contact with each other, adjacent battery cells are stably bonded in close contact, forming a more stable structure for cell stack 1200. Therefore, cell stack 1200 can be stably housed in a module case even without interposing resin layer 400 used in battery modules according to conventional technology between lower cover 1120.

[0061] Since a resin layer for fixing the stacked battery cells to the lower surface of the module case in the conventional battery module is not used, gas generated inside the battery cells can move in all directions around the battery cells, which is advantageous in preventing a reduction in the service life of the battery cells since the gas generated inside the battery cells can be quickly and effectively diffused and does not remain in the electrode assembly, thereby reducing the expansion of the battery cells.

[0062] The adhesive 1300 may be made of a polyolefin such as polyethylene (PE), cast polypropylene (cPP) or polypropylene (PP), or a copolymer thereof.

[0063] FIG. 7 is an exploded perspective view of a battery module 2000 according to a second embodiment of the present invention.

[0064] The second embodiment is the same as the first embodiment except that the expansion cushioning unit 2500 is integrally formed with the pair of side covers 2130, 2140 of the module case, and therefore only the expansion cushioning unit 2500 will be described below.

[0065] In the second embodiment of the present invention, the expansion mitigating unit 2500 may be formed in the center of the first side cover 2130 and the second side cover 2140 of the module case in the longitudinal direction (X-axis direction). Here, the flat plate portion of the expansion mitigating unit 2500 may be the side cover, and may be partially bulged and bent from the side cover toward the cell stack 2200.

[0066] 7, the expansion mitigating unit 2500 is located at the center of the height (Z-axis direction) of the side covers 2130, 2140 of the module case, but it may be provided at the entire height (Z-axis direction), and is not particularly limited as long as the side covers 2130, 2140 can be combined with the upper cover 2110 and the lower cover 2120 to form a module case. Also, as shown in FIG 7, the expansion mitigating unit 2500 may be rectangular, or may be polygonal, circular, or elliptical, and the shape is not particularly limited as long as it can be elastically deformed by the expansion of the battery cell.

[0067] As described above, the battery module according to the present invention may be applied to various devices and automobiles such as electric automobiles and hybrid automobiles.

[0068] Although certain parts of the present invention have been described in detail above, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the present invention. Various changes and modifications are possible within the scope of the scope and technical ideas of the present invention, and it is natural that these changes and modifications fall within the scope of the appended claims. [Industrial Applicability]

[0069] The present invention relates to a battery module including a cell stack in which one or more battery cells are stacked, and a module case that houses the cell stack, in which an expansion relief unit having a protrusion that can apply pressure to at least a portion of an outermost battery cell that is arranged on the outermost side of the cell stack is arranged, and is industrially applicable. [Explanation of symbols]

[0070] 1: Battery cell side 2: Electrode lead 21, 22, 121, 122, m, n-1, n: battery cell 100: Battery module according to the prior art 110, 1110, 2110: Top cover 120, 1120, 2120: Lower cover 130, 1130, 2130: 1st side cover 140, 1140, 2140: 2nd side cover 1150, 2150: Front cover 160, 1160, 2160: Rear cover 170, 1170, 2170: Busbar 180: Inflation control pad 200, 1200, 2200: Cell stack 300, 1300: Adhesive 400: Resin layer 1500, 2500: Inflation relief unit 1510: Convex 1520: Flat plate part 1000: Battery module according to a first embodiment of the present invention 2000: Battery module according to a second embodiment of the present invention

Claims

1. A battery module including a cell stack in which one or more battery cells, which are lithium secondary batteries including a pouch-shaped cell case having a storage section that stores an electrode assembly and an electrode lead, are stacked, and a module case that stores the cell stack therein, an expansion relief unit is disposed facing an outermost battery cell disposed on the outermost side of the cell stack and having a protrusion capable of applying pressure to at least a center portion of the battery cell; The protrusion of the expansion-relief unit is deformed into a concave shape when a pressure equal to or greater than a certain pressure is applied to the expansion-relief unit.

2. The battery module according to claim 1 , wherein the expansion buffer unit is disposed between an outermost battery cell disposed at the outermost position of the cell stack and the module case.

3. The battery module according to claim 1 , wherein the expansion buffer units are disposed for all of the outermost battery cells disposed at the outermost positions of the cell stack.

4. 4. The battery module according to claim 1, wherein the protrusion of the expansion buffer unit is located only at a predetermined position in a central portion of the outermost battery cell.

5. The battery module according to claim 1 , wherein the protrusions of the expansion relaxation units are made of an elastic material.

6. The battery module according to claim 1 , wherein surfaces of the battery cells that face each other are bonded to each other by an adhesive layer.

7. The battery module according to claim 6 , wherein the adhesive layer is applied to the entire surfaces of the battery cells that face each other.

8. The battery module according to claim 1 , wherein the expansion-relief unit is integrally formed with a side cover of the module case.

9. A battery pack comprising a battery module according to any one of claims 1 to 8.

10. A device comprising a battery pack according to claim 9.

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