Battery pack

Abstract

To improve a short-circuit resistance of a single cell.SOLUTION: A battery pack includes: a single cell; and a restraint member. The single cell includes an electrode laminate. The electrode laminate includes a positive electrode, a separator, and a negative electrode. The separator is interposed between the positive electrode and the negative electrode. The restraint member applies a restraint weight to the electrode laminate. The restraint weight is applied to a thickness direction of the electrode laminate. A breaking elongation, the restraint weight, and an opposite area of the separator satisfy a specific relationship.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a battery pack. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2019-029097 (Patent Document 1) discloses that initial charging of a cell is started in a restrained state in which a restraint load is applied to the cell along the stacking direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-029097 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for battery packs with high energy density. Battery packs are equipped with single batteries (single cells). The energy density of a battery pack depends on how efficiently the single cells can be installed within the specified pack volume.

[0005] For example, by making each cell have a large capacity, the number of cells mounted in a battery pack can be reduced. By reducing the number of cells mounted, for example, the dead space between the cells in the battery pack can be reduced. The reduction in the dead space is expected to improve the energy density of the battery pack.

[0006] The unit cell includes a positive electrode, a separator, and a negative electrode. The separator is interposed between the positive electrode and the negative electrode. The separator is an insulating film. The separator insulates the positive electrode from the negative electrode.

[0007] For example, it is expected that conductive foreign matter (such as small metal pieces) may become mixed between the positive and negative electrodes during the manufacturing process of a single cell. The conductive foreign matter may cause a micro-short circuit. In other words, the conductive foreign matter applies a local load to the separator. The separator may stretch locally, causing it to break locally. The local breakage of the separator may cause a micro-short circuit. When a micro-short circuit occurs in a large-capacity single cell, the amount of heat generated may increase. In battery packs incorporating large-capacity single cells, it is desirable to improve the short-circuit resistance of the single cells.

[0008] An object of the present disclosure is to improve the short circuit resistance of a cell. [Means for solving the problem]

[0009] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[0010] The battery pack includes a single cell and a restraining material. The single cell includes an electrode stack. The electrode stack includes a positive electrode, a separator, and a negative electrode. The separator is interposed between the positive electrode and the negative electrode. The restraining material applies a restraining load to the electrode stack. The restraining load is applied in the thickness direction of the electrode stack. The battery pack satisfies the following formula (1).

[0011]

number

[0012] In the battery pack, the cells are subjected to a restraining load. According to the new findings of the present disclosure, when the restraining load, the facing area, and the rupture elongation of the separator satisfy a specific relationship, it is expected that a micro-short circuit will not occur even when a conductive foreign object of the maximum size that can be expected is mixed in during the manufacturing process of the cells. In other words, the battery pack satisfies the above formula (1).

[0013] FIG. 1 shows the results of measuring the breaking elongation. 1, the numerical values ​​in each cell indicate the breaking elongation of the separator corresponding to various restraining loads (η) and various opposing areas (S). The method of measuring the breaking elongation will be described later.

[0014] FIG. 2 is a graph showing the relationship between the restraint load, the facing area, and the breaking elongation. The curved surface in FIG. 2 is obtained by plotting the measurement results in FIG. 1. The breaking elongation (Z Rup. ( η ,S) ) is expressed as a function of the constraint load (η) and the facing area (S) as variables. For example, the right-hand side of the above formula (1) can be derived by surface fitting.

[0015] In the curved surface of FIG. 2, as the restraint load (η) and the facing area (S) increase, the breaking elongation (Z Rup. ( η ,S) ) can converge to a constant value. In the right-hand side of the above formula (1), (Z Rup. ( η ,S) The limit value (η, S → ∞) of the constraint load (η) and the opposing area (S) on the curved surface in Figure 2 is obtained by extrapolating to infinity (∞).

[0016] In the curved surface of FIG. 2, the larger the opposing area (S) and the smaller the restraining load (η), the greater the breaking elongation (Z Rup. ( η ,S) The breaking elongation (Z Rup. ( η ,S) If the thickness exceeds 1.41 mm, it is expected that the separator will not break even if a conductive foreign object of the largest possible size is mixed in during the manufacturing process of the unit cell. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows the results of measuring the breaking elongation. [Diagram 2] FIG. 2 is a graph showing the relationship between the restraint load, the facing area, and the breaking elongation. [Diagram 3] FIG. 3 is a schematic diagram of the battery pack in this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a method for measuring breaking elongation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present disclosure (which may be abbreviated as "the present embodiment") will be described. However, the present embodiment does not limit the technical scope of the present disclosure.

[0019] In this specification, the words "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. The open-ended form may or may not include additional elements in addition to the required elements. The word "consisting of" is closed-ended. However, even in the closed form, additional elements that are normally associated impurities or unrelated to the disclosed technology are not excluded. The word "consisting essentially of..." is semi-closed. In the semi-closed form, the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology is permitted.

[0020] In this specification, unless otherwise specified, a numerical range such as "m to n%" includes the upper and lower limits. In other words, "m to n%" indicates a numerical range of "m% or more and n% or less." In addition, "m% or more and n% or less" includes "more than m% and less than n%."

[0021] <Battery pack> FIG. 3 is a schematic diagram of the battery pack in this embodiment. Hereinafter, “the battery pack in this embodiment” may be abbreviated to “the present battery pack.” The present battery pack 100 includes a cell 110 and a restraining member 120.

[0022] 《Single battery》 The battery pack 100 includes one or more cells 110. The battery pack 100 may include, for example, 1 to 50 cells 110. The cells 110 may be arranged in a predetermined direction. The cells 110 may form a parallel circuit or a series circuit. The cells 110 may have a large capacity. The cells 110 may have a rated capacity of, for example, 100 to 300 Ah.

[0023] The unit cell 110 may include, for example, a case 119. The case 119 may be, for example, a metal container or a pouch made of a metal foil laminate film. The case 119 houses the electrode stack 115 and an electrolyte (not shown).

[0024] <Electrode laminate> The electrode laminate 115 is a power generating element. The electrode laminate 115 includes a positive electrode 111, a separator 113, and a negative electrode 112. The separator 113 is interposed between the positive electrode 111 and the negative electrode 112. The electrode laminate 115 can be formed by alternately stacking the positive electrodes 111 and the negative electrodes 112 with the separator 113 sandwiched therebetween.

[0025] 《Positive electrode》 The positive electrode 111 may include, for example, a positive electrode substrate and a positive electrode active material layer. The positive electrode substrate may include, for example, aluminum (Al) foil or the like. The positive electrode active material layer may be disposed on the surface of the positive electrode substrate. The positive electrode active material layer may be disposed on only one side of the positive electrode substrate. The positive electrode active material layer may be disposed on both the front and back sides of the positive electrode substrate. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material may include, for example, lithium nickel cobalt manganate (NCM), lithium nickel cobalt aluminate (NCA), etc. NCM and NCA may expand during charging. The positive electrode active material may not include, for example, spinel type lithium manganate. Spinel type lithium manganate may contract during charging.

[0026] The positive electrode active material layer may further include, for example, a conductive material, a binder, and the like. The conductive material may include any component. The conductive material may include, for example, acetylene black (AB), vapor grown carbon fiber (VGCF), and the like. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The binder may include any component. The binder may include, for example, polyvinylidene fluoride (PVDF), and the like. PVDF is suitable from the viewpoints of withstand voltage, adhesive strength, battery resistance, and the like. The amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0027] 《Negative electrode》 The negative electrode 112 may include, for example, a negative electrode substrate and a negative electrode active material layer. The negative electrode substrate may include, for example, copper (Cu) foil or the like. The negative electrode active material layer may be disposed on the surface of the negative electrode substrate. The negative electrode active material layer may be disposed on only one side of the negative electrode substrate. The negative electrode active material layer may be disposed on both the front and back sides of the negative electrode substrate. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material may be, for example, graphite, hard carbon, soft carbon, silicon oxide (SiO x ) or the like. The graphite may be natural graphite or artificial graphite. The negative electrode active material may contain, for example, a mixture of a carbon-based material (such as graphite) and silicon oxide. When the negative electrode active material contains a mixture of a carbon-based material and silicon oxide, the mass fraction of the carbon-based material in the negative electrode active material layer may be, for example, 50 to 99.5%.

[0028] The negative electrode active material layer may further contain, for example, a conductive material, a binder, and the like. The conductive material may contain any component. The conductive material may contain, for example, AB, VGCF, and the like. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. The binder may contain any component. The binder may contain, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and the like. CMC and SBR are suitable from the viewpoints of withstand voltage, adhesive strength, battery resistance, and the like. The amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

[0029] <Facing area> In the above formula (1), the facing area (S) indicates the facing area of ​​the positive electrode 111 and the negative electrode 112. That is, the facing area indicates the area of ​​the portion where the positive electrode active material layer (one side) and the negative electrode active material layer (one side) face each other. Usually, the positive electrode active material layer can have an area smaller than that of the negative electrode active material layer. When the area of ​​the positive electrode active material layer is smaller than that of the negative electrode active material layer, the entire surface of the positive electrode active material layer can face the negative electrode active material layer. That is, the area of ​​the positive electrode active material layer can be equal to the facing area. The separator 113 has an area larger than that of the positive electrode active material layer and the negative electrode active material layer. In the separator 113, a restraining load is applied to a portion corresponding to the facing area. The facing area is one of the governing factors of the breaking elongation of the separator 113. The facing area is, for example, 3.8×10 to 2.0×10 6 cm 2 The facing area may be, for example, 5×10 3 cm 2 The facing area may be, for example, 1.6×10 4 ~1.8×10 5 cm 2 may be also possible.

[0030] <Separator> The separator 113 is electrically insulating. The separator 113 is a porous film. The electrolyte can penetrate into the pores of the separator 113. The separator 113 may contain, for example, polyolefin. Polyolefin is suitable from the viewpoints of affinity with the electrolyte, oxidation resistance, reduction resistance, and the like. The separator 113 may contain, for example, polyethylene (PE), polypropylene (PP), and the like. PE and PP are suitable from the viewpoints of material cost, and the like. The separator 113 may be manufactured by any method. The separator 113 may be manufactured by, for example, a biaxial stretching method. A biaxially stretched film is suitable from the viewpoints of crack area at the time of breakage, and the like. The separator 113 may have, for example, a single layer structure or a multilayer structure. The separator 113 may be made of, for example, a PE layer. The separator 113 may be formed by, for example, stacking a PP layer, a PE layer, and a PP layer in this order. A ceramic particle layer may be formed on the surface (one side or both sides) of the separator 113. The ceramic particle layer may contain, for example, alumina. The ceramic particle layer can impart heat resistance to the surface of the separator 113.

[0031] 《Electrolyte》 The electrolyte includes a solvent and a lithium salt. The lithium salt is dissolved in the solvent. The lithium salt may include any component. The lithium salt is, for example, LiPF 6 The solvent may include, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. The solvent is aprotic. The solvent may include any component. The solvent may include, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc.

[0032] 《Restraint material》 The restraining material 120 restrains the periphery of the battery pack 100. The restraining material 120 applies a restraining load (η) to each of the single cells 110. The restraining load is applied in the thickness direction of the electrode stack 115. The thickness direction of the electrode stack 115 can be said to be the stacking direction of the electrodes. The restraining material 120 can have any shape. The restraining material 120 may be composed of, for example, one member, or may be composed of multiple members.

[0033] Restraint Load The restraint load is also applied to the electrode laminate 115 in the cell 110. The restraint load is also applied to the separator 113. The restraint load is applied in the thickness direction of the separator 113. The restraint load is one of the governing factors of the breaking elongation of the separator 113. The restraint load may be, for example, 1 to 6.7 kPa, or 3.1 to 5.6 kPa.

[0034] <Separator breaking elongation> FIG. 4 is a schematic diagram showing a method for measuring breaking elongation. A positive electrode 11, a negative electrode 12, a separator 13a, and a separator 13b are prepared. The positive electrode 11, the separator 13a, the negative electrode 12, and the separator 13b are stacked in this order to form an electrode stack 15. The measurement target is the uppermost separator 13b. In this embodiment, the area of ​​the separator 13b is regarded as the facing area. The facing area is "S" in the above formula (1).

[0035] A restraining member 20 is prepared. The restraining member 20 includes a first plate 21, a second plate 22, a bolt 23, and a nut 24. The electrode stack 15 is sandwiched between the first plate 21 and the second plate 22. In a plan view, holes are provided at the four corners of the first plate 21 and the second plate 22. The bolts 23 are inserted into the holes. The nuts 24 are screwed into the bolts 23. When the nuts are tightened, the first plate 21 and the second plate 22 press the electrode stack 15. That is, a restraining load is applied to the electrode stack 15. The magnitude of the restraining load can be adjusted, for example, by the tightening torque of the nuts 24. The restraining load is "η" in the above formula (1).

[0036] A metal needle 40 is prepared. The needle 40 is a simulated conductive foreign body. The needle 40 is conductive. The needle 40 has a hemispherical tip. The tip shape radius of the needle 40 is 100 μm. The needle 40 is connected to a resistance meter 30. The resistance meter 30 is connected to the negative electrode 12 adjacent to the separator 13b (measurement object). In other words, the resistance meter 30 measures the electrical resistance between the needle 40 and the negative electrode 12.

[0037] A hole 25 for passing a needle 40 is provided in the center of the first plate 21. The diameter of the hole 25 is 10 mm. The needle 40 is inserted into the separator 13b through the hole. The amount of displacement (mm) at the point when the resistance meter 30 reading changed from "100 kΩ or more" to "10 Ω or less" was regarded as the breaking elongation. When the resistance meter 30 reading changed from "100 kΩ or more" to "10 Ω or less", it was considered that a micro-short circuit (local breakage) had occurred. The breaking elongation is calculated by subtracting "Z" from "Z" in the above formula (1). Rup. ( η ,S) "

[0038] The data in Figure 1 was measured under the following conditions. Cathode active material: Li(Ni) 0.33 Co 0.33 Mn 0.33 )O 2 Composition of the positive electrode active material layer: positive electrode active material / AB / PVDF=95 / 2.5 / 2.5 (mass ratio) Negative electrode active material: graphite Composition of negative electrode active material layer: negative electrode active material / CMC / SBR=98 / 1 / 1 Separator: Two-layer structure "base layer (PE layer) / surface layer (ceramic particle layer)" Manufacturing method of PE layer: Biaxial stretching Main component of ceramic particle layer: Alumina Electrolyte: LiPF 6 , EC+EMC+DMC

[0039] This embodiment is illustrative in all respects. This embodiment is not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, it is also intended from the beginning that any configuration may be extracted from this embodiment and that they may be arbitrarily combined. [Explanation of symbols]

[0040] 11,111 positive electrode, 12,112 negative electrode, 13,13a,13b,113 separator, 15,115 electrode laminate, 20,120 restraint, 21 first plate, 22 second plate, 23 bolt, 24 nut, 25 hole, 30 resistance meter, 40 needle, 100 battery pack, 110 single cell, 119 case.

Claims

1. A battery cell and a restraining material are included. The cell includes a case and an electrode stack, The case is a pouch made of a metal foil laminate film, The electrode laminate includes a positive electrode, a separator, and a negative electrode, The separator is interposed between the positive electrode and the negative electrode, the electrode stack is formed by stacking two or more layers of the positive electrodes and two or more layers of the negative electrodes alternately with the separator between them, the opposing area of ​​the positive electrode and the negative electrode is 1.4×10 3 cm 2 to 2.0×10 6 cm 2 , The restraining material applies a restraining load to the electrode stack, The restraining load is applied in a thickness direction of the electrode stack, Satisfying the following formula (1): Battery pack. [0010]

2. The opposing area is 5.0×10 3 cm 2 to 1.8×10 5 cm 2 , The restraint load is 3.1 kPa to 6.7 kPa. The battery pack according to claim 1 .

3. The single battery has a rated capacity of 100 Ah to 300 Ah. The battery pack according to claim 1 or 2.

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