Battery module

Abstract

To prevent deviation between cells while preventing an increase in volume.SOLUTION: A battery module includes: a laminated cell in which a plurality of unit cells each having a resin current collector of a first electrode including a first surface and a resin current collector of a second electrode including a second surface are laminated; and an exterior body covering the laminated cell. The laminated cell is laminated such that the first surface and the second surface of a pair of adjacent unit cells are adjacent to each other, each of the adjacent resin current collectors has a static friction coefficient measured by a measurement method in accordance with JIS K 7125 of 0.30 or more and 1.30 or less, the laminated cell is laminated in a state where the adjacent unit cells are not connected to each other, and the laminated cell is accommodated in the exterior body in a state of being constrained under reduced pressure at a pressure of 100 [kN / m2] or more in the laminating direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a battery module. [Background technology]

[0002] Lithium-ion batteries are high-capacity secondary batteries that have been used in a variety of applications in recent years. A lithium-ion battery is composed of a combination of multiple unit cells. Specifically, lithium-ion batteries are used in the form of a battery module (battery assembly) in which unit cells each consisting of an active material layer, a current collector layer, etc. are stacked and modularized, or in the form of a battery pack in which multiple such battery modules are combined to adjust the voltage and capacity.

[0003] Here, a force may be applied to a lithium-ion battery in a direction parallel to the stacking surface of the stacked cells. The causes of the force being applied in a direction parallel to the stacking surface vary depending on the application of the lithium-ion battery. For example, in the case of a lithium-ion battery mounted in an automobile, such a force may be applied when a collision or sudden braking occurs. Even when a force is applied in a direction parallel to the stacking surface, it is preferable to prevent displacement between the stacked cells. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5660619 [Patent Document 2] Patent No. 6303729 Summary of the Invention [Problem to be solved by the invention]

[0005] To prevent misalignment between stacked cells, it is conceivable to provide a fixing member to prevent misalignment. For example, Patent Document 1 describes filling the space between the exterior material and the battery element with resin. Furthermore, Patent Document 2 describes integrating the battery module and the lid by sandwiching an elastic body. However, since the fixing member itself has a volume, preventing misalignment using the fixing member is not preferable from the perspective of the volumetric capacity of the lithium-ion battery.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a battery module that can prevent misalignment between unit cells while preventing an increase in volume. [Means for solving the problem]

[0007] In order to achieve the above object, the battery module of the present invention comprises a stacked cell formed by stacking a plurality of unit cells, each unit cell having a resin current collector of a first electrode including a first surface and a resin current collector of a second electrode including a second surface, and an exterior body covering the stacked cell, wherein the stacked cells are stacked so that the first surfaces and second surfaces of adjacent pairs of unit cells are adjacent, and each of the adjacent resin current collectors has a static friction coefficient measured by a measurement method in accordance with JIS K 7125 of 0.30 or more and 1.30 or less, and the stacked cell is stacked such that adjacent unit cells are not connected to each other, and is housed within the exterior body in a state where they are restrained under a reduced pressure of 100 kN / m2 or more in the stacking direction. [Effects of the Invention]

[0008] According to the battery module of the present invention, it is possible to prevent an increase in volume and also to prevent misalignment between the unit cells. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a cell according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the battery module of the first embodiment. [Figure 3] FIG. 3 is a diagram showing forces applied to the unit cell of the first embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between the number of stacked cells and the acceleration at which the unit cells are displaced in the first embodiment. [Figure 5] FIG. 5 is a graph showing the measurement results of the friction force in the resin current collector of the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view of the battery module of the first embodiment. [Figure 7] FIG. 7 is a perspective view showing electrodes of a battery module according to the second embodiment.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for the purpose of emphasizing the characteristic portions, and the dimensional ratios of the components may not be the same as in reality. Also, for the same purpose, some parts may be omitted in the drawings.

[0011] (First embodiment) The battery module 1 according to the first embodiment includes a stacked cell formed by stacking a plurality of unit cells 10, and an exterior body that covers the stacked cell. First, an example of the configuration of the unit cell 10 will be described with reference to FIG.

[0012] <Single cell (battery cell)> 1 is a schematic cross-sectional view of a cell 10. The cell 10 has, for example, two electrodes 20 (battery electrodes), a positive electrode 20a and a negative electrode 20b, and a separator 30.

[0013] The separator 30 is disposed between the positive electrode 20a and the negative electrode 20b. In the battery module, the plurality of cells 10 are stacked with the positive electrode 20a and the negative electrode 20b facing in the same direction.

[0014] The separator 30 holds an electrolyte. As a result, the separator 30 functions as an electrolyte layer. The separator 30 is disposed between the electrode active material layers 22 of the positive electrode 20a and the negative electrode 20b, and prevents them from contacting each other. As a result, the separator 30 functions as a partition wall between the positive electrode 20a and the negative electrode 20b.

[0015] Examples of the electrolyte held in the separator 30 include an electrolytic solution or a gel polymer electrolyte. The use of these electrolytes ensures high lithium ion conductivity. Examples of the separator form include a porous sheet separator made of a polymer or fiber that absorbs and holds the electrolyte, and a nonwoven fabric separator.

[0016] The positive electrode 20a and the negative electrode 20b each have a current collector layer 21, an electrode active material layer 22, and a frame 35. The electrode active material layer 22 and the current collector layer 21 are arranged in this order from the separator 30 side. The frame 35 is frame-shaped (annular). The frame 35 surrounds the periphery of the electrode active material layer 22. The frame 35 of the positive electrode 20a and the frame 35 of the negative electrode 20b are welded to each other and integrated. Alternatively, the frame 35 of the positive electrode 20a and the frame 35 of the negative electrode 20b may be integrally fabricated from the beginning. That is, the frame 35 of the positive electrode 20a and the frame 35 of the negative electrode 20b may be fabricated separately and then integrated, or may be fabricated as a single member. In the following description, when it is necessary to distinguish between the electrode active material layers 22 of the positive electrode 20a and the negative electrode 20b, they will be referred to as the positive electrode active material layer 22a and the negative electrode active material layer 22b, respectively.

[0017] <Specific examples of positive electrode current collectors> The positive electrode current collector constituting the positive electrode current collector layer 21a can be a current collector used in known lithium-ion cells, such as a known metal current collector or a resin current collector composed of a conductive material and a resin (such as the resin current collectors described in JP 2012-150905 A and WO 2015 / 005116 A). From the viewpoint of battery characteristics, etc., the positive electrode current collector constituting the positive electrode current collector layer 21a is preferably a resin current collector.

[0018] Examples of metal current collectors include one or more metal materials selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, alloys containing one or more of these metals, and stainless steel alloys. These metal materials may be used in the form of a thin plate, metal foil, or the like. Alternatively, the metal current collector may be formed by forming the above-mentioned metal material on the surface of a substrate made of a metal other than the above-mentioned metal materials by a method such as sputtering, electrodeposition, or coating.

[0019] The resin current collector preferably contains a conductive filler and a matrix resin (resin composition). Examples of the matrix resin include, but are not limited to, polyethylene (PE), polypropylene (PP), and polymethylpentene (PMP). The conductive filler is not particularly limited as long as it is selected from materials having electrical conductivity. The conductive filler may be in the form of a fibrous conductive fiber.

[0020] The resin current collector may contain, in addition to the matrix resin and the conductive filler, other components (such as a dispersant, a crosslinking accelerator, a crosslinking agent, a colorant, an ultraviolet absorber, and a plasticizer). Furthermore, a plurality of resin current collectors may be stacked, or a resin current collector and a metal foil may be stacked.

[0021] The thickness of the positive electrode current collector layer 21a is not particularly limited, but is preferably 5 to 150 μm. When a plurality of resin current collectors are stacked to form the positive electrode current collector layer 21a, the total thickness after stacking is preferably 5 to 150 μm. The positive electrode current collector layer 21a can be obtained, for example, by melt-kneading a matrix resin, a conductive filler, and an optional filler dispersant to obtain a conductive resin composition, and then molding the resulting composition into a film using a known method.

[0022] <Specific examples of positive electrode active materials> The positive electrode active material layer 22a is preferably a non-binding mixture containing a positive electrode active material. Here, "non-binding" means that the positions of the positive electrode active materials in the positive electrode active material layer are not fixed, and the positive electrode active materials are not irreversibly fixed to each other. When the positive electrode active material layer 22a is a non-binding layer, the positive electrode active materials are not irreversibly fixed to each other, allowing separation without mechanical destruction of the interfaces between the positive electrode active materials. Even when stress is applied to the positive electrode active material layer 22a, the positive electrode active material moves, preventing destruction of the positive electrode active material layer 22a. The non-binding positive electrode active material layer 22a can be obtained by, for example, converting the positive electrode active material layer 22a into a positive electrode active material layer 22a containing a positive electrode active material and an electrolyte solution but not containing a binder. In this specification, "binder" refers to an agent that cannot reversibly fix the positive electrode active materials to each other or to the current collector. Such binders are used by dissolving or dispersing them in a solvent, and when the solvent is evaporated or distilled away, the surface solidifies without exhibiting any adhesiveness, and therefore cannot reversibly fix the positive electrode active materials together or the positive electrode active material to the current collector.

[0023] Examples of the positive electrode active material include, but are not limited to, composite oxides of lithium and transition metals, composite oxides containing two types of transition metal elements, and composite oxides containing three or more types of metal elements.

[0024] The positive electrode active material may be a coated positive electrode active material in which at least a portion of the surface thereof is coated with a coating material containing a polymer compound. When the periphery of the positive electrode active material is coated with a coating material, volume change of the positive electrode is alleviated, and expansion of the positive electrode can be suppressed.

[0025] As the polymer compound constituting the coating material, those described as resins for coating active materials in JP 2017-054703 A and WO 2015 / 005117 A, etc., can be suitably used.

[0026] The coating material may contain a conductive agent, which may be the same as the conductive filler contained in the positive electrode current collector layer 21a.

[0027] The positive electrode active material layer 22a may contain an adhesive resin. Examples of suitable adhesive resins include those described in JP 2017-054703 A, in which a small amount of organic solvent is mixed with a nonaqueous secondary battery active material coating resin to adjust its glass transition temperature below room temperature, and those described in JP 10-255805 A as adhesives. The adhesive resin refers to a resin that remains tacky even after drying by volatilizing the solvent components and remains tacky (i.e., adheres by application of slight pressure without using water, solvents, heat, etc.). On the other hand, a solution-drying electrode binder used as a binder refers to a material that dries and solidifies by volatilizing the solvent components, thereby firmly adhering and fixing active materials together. Therefore, the binder (solution-drying electrode binder) and the adhesive resin are different materials.

[0028] The positive electrode active material layer 22a may contain an electrolytic solution containing an electrolyte and a non-aqueous solvent. The electrolyte may be any of those used in known electrolytic solutions. The non-aqueous solvent may be any of those used in known electrolytic solutions. For example, a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC), or a mixed solution of ethylene carbonate (EC) and propylene carbonate (PC) may be used.

[0029] The positive electrode active material layer 22a may contain a conductive additive, which may be a conductive material similar to the conductive filler contained in the positive electrode current collector layer 21a.

[0030] The thickness of the positive electrode active material layer 22a is not particularly limited, but from the viewpoint of battery performance, it is preferably 100 to 700 μm, and more preferably 200 to 500 μm.

[0031] In this embodiment, the positive electrode composition supplied to form the positive electrode active material layer 22a is a wet powder containing a positive electrode active material and a nonaqueous electrolyte. The wet powder is preferably in a pendular or funicular state. Alternatively, the positive electrode composition may be a clay-like (semi-solid) positive electrode active material kneaded with an electrolyte.

[0032] The proportion of the non-aqueous electrolyte in the wet powder is not particularly limited, but in order to achieve a pendular or funicular state, in the case of a positive electrode, it is desirable that the proportion of the non-aqueous electrolyte be 0.20 to 50% by weight of the entire wet powder.

[0033] <Specific examples of negative electrode current collectors> The negative electrode current collector constituting the negative electrode current collector layer 21b can be appropriately selected from the same configuration as that described for the positive electrode current collector and can be obtained by the same method. From the viewpoint of battery characteristics, the negative electrode current collector layer 21b is preferably a resin current collector. The thickness of the negative electrode current collector layer 21b is not particularly limited, but is preferably 5 to 150 μm.

[0034] <Specific examples of negative electrode active materials> The negative electrode active material layer 22b is preferably a non-binding mixture containing a negative electrode active material. The reasons why the negative electrode active material layer is preferably a non-binding material and the method for obtaining the non-binding negative electrode active material layer 22b are the same as the reasons why the positive electrode active material layer 22a is preferably a non-binding material and the method for obtaining the non-binding positive electrode active material layer 22a.

[0035] The negative electrode active material may be, for example, a carbon-based material, a silicon-based material, or a mixture thereof, but is not particularly limited thereto.

[0036] The negative electrode active material may be a coated negative electrode active material in which at least a portion of the surface thereof is coated with a coating material containing a polymer compound. When the periphery of the negative electrode active material is coated with the coating material, volume change of the negative electrode is alleviated, and expansion of the negative electrode can be suppressed.

[0037] As the coating material, the same coating material as that constituting the coated positive electrode active material can be suitably used.

[0038] The negative electrode active material layer 22b contains an electrolytic solution containing an electrolyte and a non-aqueous solvent. The composition of the electrolytic solution can be the same as that of the electrolytic solution contained in the positive electrode active material layer 22a.

[0039] The negative electrode active material layer 22b may contain a conductive additive, which may suitably be the same conductive material as that contained in the positive electrode active material layer 22a.

[0040] The negative electrode active material layer 22b may contain an adhesive resin, which may be the same as the adhesive resin that is an optional component of the positive electrode active material layer 22a.

[0041] The thickness of the negative electrode active material layer 22b is not particularly limited, but from the viewpoint of battery performance, it is preferably 100 to 700 μm, and more preferably 200 to 500 μm.

[0042] In this embodiment, the negative electrode composition supplied to form the negative electrode active material layer 22b is a wet powder containing a negative electrode active material and a nonaqueous electrolyte. The wet powder is preferably in a pendular or funicular state. Alternatively, the negative electrode composition may be a clay-like (semi-solid) negative electrode active material kneaded with an electrolyte.

[0043] The proportion of the non-aqueous electrolyte in the wet powder is not particularly limited, but in order to achieve a pendular or funicular state, in the case of a negative electrode, it is desirable that the proportion of the non-aqueous electrolyte be 0.20 to 50% by weight of the entire wet powder.

[0044] <Examples of separators> Examples of the electrolyte held in the separator 30 include an electrolytic solution and a gel polymer electrolyte. The use of these electrolytes ensures high lithium ion conductivity in the separator 30. The form of the separator 30 is, for example, a porous film made of polyethylene or polypropylene, but is not particularly limited thereto.

[0045] <Example of frame body> The frame 35 is not particularly limited as long as it is a material that is durable against the electrolyte, but for example, a polymer material is preferred, and a thermoplastic polymer material is more preferred. The material constituting the frame 35 may be any material that has insulating properties, sealing properties (liquid-tightness), heat resistance at battery operating temperatures, electrolyte resistance, etc., and a resin material is preferably used. More specifically, the frame 35 may be made of, for example, a polyolefin resin, a polyurethane resin, or a polyvinylidene fluoride resin, with polyolefin resin being preferred because of its high durability and ease of handling.

[0046] <Battery module (assembled battery)> Next, a configuration example of the battery module 1 will be described with reference to Fig. 2. Lithium-ion batteries are used in the form of a battery module as shown in Fig. 2, or a battery pack in which multiple battery modules are combined to adjust the voltage and capacity. Fig. 2 is a schematic configuration diagram of the battery module 1.

[0047] 2 illustrates five cells 10a to 10e as an example of the cells 10 shown in FIG. 1. The cells 10a to 10e are stacked as shown in FIG. 2 to form a stacked cell. Note that FIG. 2 is merely an example, and the number of cells 10 included in the battery module 1 is not particularly limited.

[0048] As described with reference to FIG. 1, the cell 10 includes a positive electrode current collector layer 21a and a negative electrode current collector layer 21b. Hereinafter, the positive electrode current collector layer 21a will be described as a first electrode current collector, and the negative electrode current collector layer 21b will be described as a second electrode current collector. In this case, in the flat cell 10, a first surface can be defined on the side of the current collector for the first electrode, and a second surface can be defined on the side of the current collector for the second electrode. For example, in the cell 10 of FIG. 1, the surface on the -Y direction side is the first surface, and the surface on the +Y direction side is the second surface. The stacked cell, which is made up of the cells 10a to 10e of FIG. 2, is stacked such that the first and second surfaces of a pair of adjacent cells 10 are adjacent to each other. That is, in the battery module 1, the cells 10 are stacked such that the positive electrodes 20a and negative electrodes 20b face in the same direction. The definitions of the first electrode and the second electrode may be reversed, with the negative electrode current collector layer 21b being the current collector for the first electrode and the positive electrode current collector layer 21a being the current collector for the second electrode.

[0049] The battery module 1 also includes an exterior body 11 that covers the stacked cells. Any flexible insulating material can be used for the exterior body 11. For example, a known laminate film can be used for the exterior body 11. There are no particular limitations on the material or configuration of the laminate film, but one example is a three-layer laminate film that has a nylon film on the outside, aluminum foil in the center, and an adhesive layer such as modified polypropylene on the inside. Note that in the battery module 1, current extraction sections (not shown) are provided on both ends of the cells 10 in the stacking direction, and current is supplied to various electrical appliances via these current extraction sections.

[0050] Here, the behavior of the cells 10 when a force is applied in a direction parallel to the stacking plane of the stacked cells 10 will be described with reference to Fig. 3. Fig. 3 is a diagram showing the force applied to the cells of the first embodiment.

[0051] FIG. 3 illustrates an external force A1 acting in the X direction, which is perpendicular to the stacking direction (Y direction) in which the cells 10 are stacked, as a force parallel to the stacking surface. In the following description, the Y direction corresponds to the vertical direction. That is, the -Y direction corresponds to the direction of gravity. The X and Z directions correspond to horizontal directions. A shear resistance force A2 (static friction force) occurs between adjacent cells 10, and if the external force A1 exceeds the maximum value of the shear resistance force A2 (maximum static friction force), the cells 10 will be misaligned.

[0052] The maximum value of the shear resistance force A2 can be expressed as the product of the static friction coefficient between adjacent cells 10 and the normal force. Here, the inside of the exterior body 11 is depressurized, and a restraining force A3 due to atmospheric pressure is generated. The restraining force A3 is applied equally to all of the stacked cells 10. Furthermore, except for the topmost cell 10, each cell 10 is subjected to a restraining force A4 due to the weight of the cell 10 placed above it. The normal force can be expressed as the sum of the restraining forces A3 and A4.

[0053] Specifically, the restraining force A3 can be expressed by the following formula (1).

[0054]

number

[0055] In equation (1), "P" is the magnitude of the pressure generated due to atmospheric pressure. When the inside of the exterior body 11 is an absolute vacuum, "P" is equal to atmospheric pressure and has a value of approximately "101,325 [N / m2]." While maintaining an absolute vacuum is naturally difficult in reality, it is possible to set "P" to a value of "100,000 [N / m2] = 100 [kN / m2]" or more by reducing the pressure inside the exterior body 11. Also, in equation (1), "A" is the area of ​​the cell 10. More precisely, "A" is the area of ​​the surface of the cell 10 that is in contact with an adjacent cell. In other words, "A" is the area of ​​the first or second surface of the cell 10.

[0056] Furthermore, the restraining force A4 applied to the "n"th cell 10 from the top can be expressed by the following formula (2).

[0057]

number

[0058] In equation (2), "m" is the mass of each cell 10. "m" is the product of the mass "d" of the cell 10 per unit area and the area "A." Furthermore, "9.8 [m / s2]" represents the gravitational acceleration "g." As is clear from the form of equation (2), the larger "n" is, i.e., the lower the cell 10, the greater the restraining force A4.

[0059] When an impact with acceleration "α" occurs as an external force A1, the condition for preventing displacement of the "n"th cell 10 from the top can be expressed by the following formula (3).

[0060]

number

[0061] In equation (3), it is assumed that the "n"th cell 10 from the top and the cells 10 above it are integrated. That is, the external force A1 is expressed as the product of the mass "nm" of the integrated multiple cells 10 and the acceleration "α".

[0062] Furthermore, "μ" in Equation (3) represents the static friction coefficient. The static friction coefficient depends on the material and surface roughness of the positive electrode current collector layer 21a and the negative electrode current collector layer 21b. That is, the static friction coefficient depends on the material and surface roughness of the first and second surfaces. For example, polyethylene (PE) or polypropylene (PP) can be selected as the resin composition for the resin current collector. PE alone has a static friction coefficient of approximately 0.36, while PP alone has a static friction coefficient of approximately 0.40. Many materials selected for the resin composition have static friction coefficients of approximately 0.30 to 0.40. However, resin current collectors are not composed solely of a resin composition but also contain conductive fillers and other components. While surface roughness must also be considered, it is difficult to determine the static friction coefficient based solely on the material of the resin composition. In this embodiment, the first and second surfaces are described as not being subjected to any special surface treatment.

[0063] Furthermore, "A3+A4" represents the normal force acting on the "n"th cell 10 from the top. That is, "μ×(A3+A4)" in formula (3) represents the maximum value (maximum frictional force) of the shear resistance force A2.

[0064] By rearranging equation (3), the magnitude of the acceleration "α" at which a deviation occurs between the cells 10 can be calculated. Hereinafter, the acceleration "α" will be calculated using equation (4) and substituting specific numerical values ​​for each of the parameters described above. Note that equation (4) uses specific numerical values ​​for the sake of clarity, and the embodiments are not limited to these numerical values.

[0065]

number

[0066] In equation (4), the coefficient of static friction "μ" is set to "0.40." The mass "d" of the cell 10 per unit area is set to "2.472 [kg / m2]." The product of the mass "d" and the area "A" is the mass "m" of the cell 10. The pressure "P" is set to the atmospheric pressure value of "101,325 [N / m2]." Rewriting equation (4) assuming the standard gravitational acceleration to be "1 G," we obtain the following equation (5).

[0067]

number

[0068] As is clear from the form of equation (5), the magnitude of the acceleration "α" at which misalignment occurs between the cells 10 decreases as "n" increases. In other words, the cell 10 located at the bottom of the stacked cell is most likely to misalign. Also, as shown in FIG. 4, the greater the number of cells 10 included in one stacked cell (i.e., the greater the number of cells stacked), the more likely misalignment will occur. Also, as is clear from the fact that the area "A" has disappeared in the transformed equation, the magnitude of the acceleration "α" at which misalignment occurs does not depend on the area of ​​the cell 10.

[0069] The various values ​​used in equation (4) are merely examples and can be changed as appropriate, but the scale of the changes will not change. For example, it is unlikely that the mass "d" of the cell 10 per unit area will be "10 times" 2.472 kg / m2. From this perspective, it can be said that the restraining force A3 (PA) caused by the decompression of the interior of the exterior body 11 has a greater contribution to the magnitude of the acceleration "α" at which a shift occurs than the restraining force A4 (nmg) caused by the weight of the cell 10.

[0070] Here, in the battery module 1, the acceleration "α" at which displacement occurs can be increased by decompressing and restraining the cells 10 at a pressure of 100 kN / m2 or more in the stacking direction. That is, in the battery module 1, displacement between the cells 10 is unlikely even in the event of a collision or the like. Using the values ​​shown in equations (4) and (5) as an example, in the battery module 1, when the number of stacks is "40", no displacement occurs even when an acceleration of "42 G" occurs. Furthermore, in the battery module 1, when the number of stacks is "100", it is possible to withstand an acceleration of up to "17 G".

[0071] In addition, in the battery module 1, adjacent cells 10 are stacked in a state where they are not connected to each other. That is, in the battery module 1, no fixing members are provided to prevent the cells 10 from shifting, and the static friction coefficient and restraining force are adjusted to prevent the cells 10 from shifting. This reduces the volume of the fixing members, and improves battery performance per unit volume.

[0072] The measurement results of the static friction coefficient of the resin current collector are shown in Figure 5. The measurements shown in Figure 5 were carried out in accordance with "JIS K 7175 (Plastics - Films and sheets - Test method for coefficient of friction)" of the Japanese Industrial Standards (JIS).

[0073] More specifically, the measurements shown in Figure 5 were performed using the horizontal method. The specific procedure for the horizontal method involves first fixing a first test piece on a horizontal plate and then attaching a second test piece to a weight. In the measurements shown in Figure 5, the first and second test pieces are resin current collectors. Next, one end of a metal wire is connected to the weight, and the other end of the metal wire is connected to a load cell. The frictional force (static frictional force and kinetic frictional force) between the first and second test pieces is measured based on the output from the load cell when the horizontal plate is moved. More specific measurement conditions include a resin current collector test piece size of 80 mm × 200 mm, a weight size of 63 mm × 63 mm, and a weight mass of 200 ± 2 g. The measurement environment was 23 ± 2 °C and 50 ± 6% RH. The sliding speed of the test piece was set to 100 mm / min, and the test time was set to 15 seconds.

[0074] FIG. 5 shows three graphs. These graphs are the results of measurements of friction force using the horizontal method on different test pieces (resin current collector 21c, resin current collector 21d, and resin current collector 21e). In each graph, the friction force initially increases over time. This indicates a gradual increase in the force applied to the test piece in a stationary state. The friction force then peaks and decreases. The peaks in the friction force correspond to the maximum static friction force of each test piece, and the decrease in friction force after the peak corresponds to the kinetic friction force. In FIG. 5, peak P1 indicates the maximum static friction force for resin current collector 21c, peak P2 indicates the maximum static friction force for resin current collector 21d, and peak P3 indicates the maximum static friction force for resin current collector 21e.

[0075] The resin current collector 21c, the resin current collector 21d, and the resin current collector 21e were produced according to the first specification, the second specification, and the third specification, respectively, which will be described below.

[0076] In the first specification, the resin that makes up the resin current collector has a three-layer structure. The three-layer structure is broken down as follows: the first layer is polypropylene, the second layer is polypropylene or polyethylene, and the third layer is polypropylene. Carbon black is used as the conductive filler. The filler concentration is expected to be "20 to 30 [mass%]" or a wider range than this.

[0077] In the second specification, the resin that makes up the resin current collector is a three-layer structure. The first, second, and third layers of the three-layer structure are all polypropylene. Furthermore, nickel is used as the conductive filler in the first layer, nickel in the second layer, and carbon black in the third layer. Furthermore, a copper (Cu) vapor-deposited film is applied to the surface of the nickel layer as a surface treatment. Furthermore, the filler concentration is expected to be approximately 70-80 (mass%) for nickel, and 20-30 (mass%) for carbon black, or a wider range.

[0078] In the third specification, the resin current collector is made of polyolefins such as polypropylene and polyethylene, or engineering plastics such as polyvinylidene fluoride. The conductive filler is made of metal fillers such as nickel, aluminum, stainless steel (SUS), silver, copper, titanium, platinum, gold, and mixtures thereof. Alternatively, the conductive filler may be a non-conductive material such as a particulate ceramic material or a resin material coated with a conductive metal material by plating or other methods. Alternatively, the conductive filler may be a conductive carbon filler such as graphite, carbon black, carbon nanotubes, or mixtures thereof. The shape and average particle size of the conductive filler are not particularly limited and may be set as needed. A metal layer or a carbon coating layer is applied as a surface treatment. The filler concentration is expected to be approximately 5-40 mass% for carbon black, 70-80 mass% for nickel powder, and 0.5-30 mass% for nickel-plated resin powder.

[0079] As shown in Figure 5, the peak of the friction force can be identified as the maximum static friction force. In reality, it is difficult to reduce the measurement error to "0," so it is preferable to obtain multiple actual measurement values ​​by performing measurements on multiple test pieces under the same conditions, or by performing multiple measurements on a single test piece, and then use a statistical value based on these multiple actual measurement values ​​as the test result.

[0080] Although not shown in FIG. 5, multiple test pieces with the same material, dimensions, and other conditions were prepared as resin current collector 21c, and the actual measured value of maximum static friction force was obtained for each test piece. Furthermore, the maximum static friction force was repeatedly measured for each test piece to obtain multiple actual measured values ​​of maximum static friction force. The average of the multiple measured values ​​of maximum static friction force obtained in this manner for resin current collector 21c was 1.06 [N]. Similarly, the average of the multiple measured values ​​of maximum static friction force obtained for resin current collector 21d was 2.03 [N]. Similarly, the average of the multiple measured values ​​of maximum static friction force obtained for resin current collector 21e was 0.90 [N].

[0081] By identifying the maximum static friction force, the static friction coefficient of each test piece can be calculated. That is, the static friction force is expressed as the product of the static friction coefficient, the mass of the weight, and the gravitational acceleration, and since the static friction force, the mass of the weight, and the gravitational acceleration are known values, the static friction coefficient can be calculated. The calculation results of the static friction coefficient are shown in Table (1) below.

[0082] [Table 1]

[0083] In Table 1, the static friction coefficient (Ave.) of resin current collector 21c based on multiple measurements was 0.54. As shown in Table 1 as three actual measurement values ​​(n1, n2, n3), the measurement was performed "three times." Furthermore, the static friction coefficient (Ave.) of resin current collector 21d based on multiple measurements was "1.03." Furthermore, the static friction coefficient (Ave.) of resin current collector 21e based on multiple measurements was "0.46."

[0084] Among all the measured values ​​of the static friction coefficient for resin current collector 21c, resin current collector 21d, and resin current collector 21e, the minimum value was 0.41 and the maximum value was 1.13. Even taking into account various factors such as measurement error, it is believed that the numerical range of the static friction coefficient for resin current collector 21c, resin current collector 21d, and resin current collector 21e is equal to or greater than 0.30 and equal to or less than 1.30.

[0085] Here, assuming that the bottom cell 10 is the most susceptible to displacement as explained using equation (5), and assuming that the magnitude of pressure "P" caused by atmospheric pressure is "100 kN / m2 (= 100,000 N / m2)," the resistance force of the stacked cell to the external force A1 is equal to or greater than "9.8 × 0.30 × (n_max - 1) × m + 100,000 × 0.30 × A [N]," where "9.8 m / s2" is the gravitational acceleration, "n_max" is the number of stacked cells 10, "m [kg]" is the mass of each cell 10, and "A" is the area of ​​the cell 10. That is, the stacked cells are stacked while being pressurized in the stacking direction so that the resistance to impact from a direction perpendicular to the stacking direction of the single cells 10 is equal to or greater than "9.8 x 0.30 x (n_max-1) x m + 100,000 x 0.30 x A [N]".

[0086] The magnitude of the restraining force A3 (PA) caused by reducing the pressure inside the exterior body 11 depends on the degree of vacuum inside the exterior body 11. Here, gas generation from the cells 10 may reduce the degree of vacuum inside the exterior body 11. Therefore, to maintain the degree of vacuum inside the exterior body 11, a gas absorbent material may be provided inside the exterior body 11. For example, as shown in FIG. 6, the battery module 1 may include gas absorbents 13a and 13b. The materials for the gas absorbents 13a and 13b are not particularly limited, but molecular sieves may be used as an example.

[0087] Incidentally, when the above-mentioned formula (3) is transformed while expressing the mass "m" of each cell 10 as the product of the mass "d" of the cell 10 per unit area and the area "A", the following formula (6) is obtained. Furthermore, the area "A" can be deleted from formula (6), resulting in formula (7).

[0088]

number

[0089]

number

[0090] As is clear from equation (7), the smaller the mass "d" of the cell 10 per unit area, the less likely it is to become displaced. Explaining this using the arrows in Figure 3, the smaller "d" is, the smaller the external force A1 becomes, while the restraining force A3 caused by atmospheric pressure remains unchanged, making it less likely that displaced cells will become displaced.

[0091] The mass "d" of the cell 10 per unit area depends on the thickness of the electrode (the dimension in the Y direction shown in FIG. 1) and the material composition of the active material. As an example, the values ​​shown in Table 2 below are obtained for each condition of the electrode thickness and material composition. As shown in Table 2, the mass "d" of the cell 10 per unit area is preferably in the numerical range of "2.6 [kg / m2]" or less and "0.29 [kg / m2]" or more.

[0092] Specifically, there is a trade-off between thicker electrodes: the thicker the electrode, the higher the energy density, but the lower the rate characteristics. The condition that prioritizes energy density while achieving the minimum rate characteristics is "d = 2.6 [kg / m2]." The condition that prioritizes rate characteristics while achieving the minimum energy density is "d = 0.29 [kg / m2]."

[0093] [Table 2]

[0094] (Second embodiment) In the first embodiment, it has been described that no particular surface treatment is performed on the contact surfaces (first surface and second surface) between the cells 10. In the second embodiment, an example will be described in which the surface treatment is performed on the first surface and the second surface.

[0095] By performing a surface treatment on the first and second surfaces to increase the surface roughness, it is possible to increase the static friction coefficient and make it even more difficult for the unit cells 10 to slip. Examples of such surface treatments include embossing and blasting.

[0096] However, performing surface treatment on the first and second surfaces increases the number of manufacturing steps for the cell 10, raising manufacturing costs. Furthermore, surface treatment is also expected to reduce the strength of the positive electrode current collector layer 21 a and the negative electrode current collector layer 21 b. While it is possible to ensure the strength by increasing the thickness of the positive electrode current collector layer 21 a and the negative electrode current collector layer 21 b, this is not desirable from the viewpoint of manufacturing costs and battery performance.

[0097] Therefore, the surface treatment may be performed only on a predetermined number of cells 10 from the bottom in the vertical direction. That is, as explained using equations (4) and (5), the cells 10 located at the bottom are more likely to shift. By performing surface treatment preferentially only on the cells 10 that are more likely to shift, it is possible to increase the acceleration "α" at which shifting occurs for the entire battery module 1 while suppressing increases in manufacturing costs and decreases in battery performance. The surface treatment may be performed on both the first and second surfaces, or on only one of them.

[0098] In a battery module 1 formed by stacking a plurality of cells 10, current flows perpendicular to the surface. At least one of the first and second surfaces may be subjected to a surface treatment, such as a roughening treatment, to increase friction between the current collectors, thereby reducing the contact area between the negative electrode current collector layer 21b and the positive electrode current collector layer 21a. It is preferable to prevent the increase in impedance (resistance) that accompanies the reduction in contact area from impeding the flow of current perpendicular to the surface and thus affecting battery performance.

[0099] Therefore, the surface may be treated only on a portion of the surface so that the flow of current perpendicular to the surface is not obstructed. For example, the central portion may be made smooth to maintain adhesion, and the other portions may be surface treated. That is, the surface may be treated on positions other than the central portions of the first surface and the second surface. In other words, the first surface and the second surface may be surface treated in a frame-like manner. Furthermore, in consideration of manufacturing costs, etc., the surface may be treated only on at least a portion of the first surface and the second surface of a predetermined number of unit cells 10 from the vertically lower side.

[0100] An example of surface treatment will be described with reference to Fig. 7. Fig. 7 is a perspective view showing the electrodes of a battery module. As in the case of the single cell 10, in the battery module, the electrodes are sealed by a frame 35. For example, by applying surface treatment only to the edge portion 20c of the electrode, avoiding the center portion 20d of the electrode, it is possible to increase the static friction coefficient while suppressing a decrease in contact area (increase in impedance) and maintaining battery performance.

[0101] Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configurations are not limited to these embodiments, and modifications, combinations, deletions, etc. of the configurations are also included within the scope of the gist of the present invention. Furthermore, it goes without saying that the configurations shown in each embodiment can be appropriately combined and used. When using the lithium-ion secondary battery exemplified above, the secondary battery includes a battery using a liquid material for the electrolyte and a battery using a solid material for the electrolyte (so-called all-solid-state battery). Furthermore, the battery in this embodiment includes a battery having a metal foil (metal current collector foil) as a current collector, and a battery having a so-called resin current collector made of a resin to which a conductive material has been added instead of the metal foil. [Explanation of symbols]

[0102] 1: Battery module 10, 10a, 10b, 10c, 10d, 10e: Single cell 11: Exterior body 13a, 13b: Gas absorbent material 20: Electrode 20a: Positive electrode 20b: Negative electrode 20c:Edge 20d: Central part 21: Current collector layer 21a: Positive electrode current collector layer 21b: Negative electrode current collector layer 22: Electrode active material layer 22a: Positive electrode active material layer 22b: Negative electrode active material layer 30: Separator 35:Frame body

Claims

1. a stacked cell formed by stacking a plurality of unit cells each having a resin current collector for a first electrode including a first surface and a resin current collector for a second electrode including a second surface; an exterior body that covers the stacked cell, The stacked cells are stacked such that the first surfaces and second surfaces of adjacent pairs of unit cells are adjacent to each other, each of the adjacent resin current collectors has a static friction coefficient of 0.30 or more and 1.30 or less, as measured by a measurement method in accordance with JIS K 7125; The stacked cell is stacked such that adjacent cells are not connected to each other, and is housed inside the exterior body in a state where the cells are decompressed and restrained in the stacking direction at a pressure of 100 kN / m or more. Battery module.

2. 2. The battery module according to claim 1, wherein the stacked cells are stacked while being pressurized in a stacking direction so that a resistance force to an impact from a direction perpendicular to the stacking direction of the cells satisfies (9.8 × 0.30 × (n_max - 1) × m + 100,000 × 0.30 × A) [N] or more, where: gravitational acceleration is defined as 9.8 [m / s2], the number of stacked cells is defined as n_max, the mass per cell is defined as m [kg], the magnitude of pressure generated by atmospheric pressure is defined as 100,000 [N / m2], and the area of ​​a surface of a cell that is in contact with an adjacent cell is defined as A [m2].

3. 2. The battery module according to claim 1, wherein the mass of the unit cells per unit area is 2.6 kg / m<2> or less and 0.29 kg / m<2> or more.

4. The battery module according to claim 1 , further comprising a gas absorbent provided inside the exterior body.

5. 2. The battery module according to claim 1, wherein a surface treatment is applied to at least a portion of at least one of the first surface and the second surface of a predetermined number of the plurality of single cells included in the stacked cell, starting from the vertically lower side.

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