Secondary batteries

Abstract

To improve an inspection accuracy of short circuit failures generated between electrodes caused by contamination of metal foreign matters.SOLUTION: A secondary battery 1 comprises positive and negative electrode sheets 35P and 35N laminated so as to sandwich a separator 5 therebetween. Electrode sheet 35P, 35N are respectively formed by coating electrode mixtures 60P, 60N including an electrode active material, on base materials 36P, 36N that are to be a current collector 31. The electrode sheet 35P that configures a positive electrode 3 has at a peripheral edge part 65 a positive electrode uncoated part 70 with no electrode mixture 60P. A gap 75 is formed between an uncoated surface 70s of the positive electrode uncoated part 70 and an opposed surface 5s of the separator 5. Further, the electrode sheet 35N configuring a negative electrode 4 has a negative electrode mixture layer 62N abutting on the separator 5 at a position where the separator 5 is sandwiched between the positive electrode uncoated part 70 and itself. The secondary battery 1 comprises a liquid-holding structure 80 that secures an electrolyte 43 at the gap 75 between the uncoated surface 70s of the positive electrode uncoated part 70 and the opposed surface 5s of the separator 5.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, as shown in Patent Document 1, for example, in secondary batteries such as lithium-ion secondary batteries, there is a possibility that metallic foreign matter such as copper (Cu) may be mixed into the positive electrode during manufacturing. Furthermore, in such cases, there is a phenomenon in which the metallic foreign matter dissolves in the electrolyte and migrates to the negative electrode side during charging. Then, the metallic foreign matter that has migrated to the negative electrode side may locally precipitate, causing a short circuit between the negative electrode and the positive electrode.

[0003] In consideration of this, in the manufacture of secondary batteries, assembled secondary batteries are typically stored under a certain environment for a so-called aging process, after which their voltages are measured, and then manufacturing defects in the secondary batteries, including short circuits between electrodes due to the inclusion of metallic foreign matter, are inspected based on the voltage drop detected after aging. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 121563 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even in secondary batteries containing metallic foreign matter, a voltage drop may not be detected in post-aging tests. That is, if the metallic foreign matter in the positive electrode does not dissolve during charging before aging, the manufacturing defect cannot be detected in post-aging tests. In such cases, the metallic foreign matter may dissolve in the electrolyte after shipping the secondary battery, potentially causing a short circuit between the electrodes. [Means for solving the problem]

[0006] A secondary battery that solves the above-mentioned problems comprises positive and negative electrode sheets stacked with a separator sandwiched therebetween, and each of the electrode sheets is formed by coating an electrode mixture containing an electrode active material on a substrate that serves as a current collector, the electrode sheet that constitutes the positive electrode has a positive electrode uncoated portion at its periphery that is not coated with the electrode mixture, and a gap is formed between the uncoated surface of the positive electrode uncoated portion and the opposing surface of the separator that faces the uncoated surface, and the electrode sheet that constitutes the negative electrode has a negative electrode mixture layer that abuts against the separator at a position where the separator is sandwiched between the electrode sheet and the positive electrode uncoated portion, and the secondary battery has a liquid retention structure that secures an electrolyte in the gap.

[0007] According to the above configuration, sufficient electrolyte can be secured in the gap between the uncoated surface of the positive electrode uncoated portion and the opposing surface of the separator, facilitating the dissolution of metallic foreign matter that has entered the uncoated positive electrode portion. As a result, if there is a possibility that the metallic foreign matter may migrate to the negative electrode side and locally deposit, causing a short circuit, the dissolution and local deposition of the metallic foreign matter that leads to the short circuit can be promoted during the initial charging process performed after assembly of the secondary battery. In other words, manufacturing defects can be detected in post-aging inspections based on voltage drop measurements. This improves the accuracy of inspections for short circuits that occur between positive and negative electrodes due to the inclusion of metallic foreign matter.

[0008] In the secondary battery that solves the above-described problems, the liquid retention structure preferably has a thickness set to be greater at a portion of the separator having the opposing surface than at a portion of the separator that contacts a positive electrode composite layer formed on the substrate in the electrode sheet that constitutes the positive electrode.

[0009] According to the above configuration, the opposing surface of the separator approaches the uncoated surface of the positive electrode uncoated portion, which makes it easier for metal foreign matter located in the gap to come into contact with the opposing surface of the separator impregnated with the electrolyte. In addition, the gap itself is also expected to have improved liquid retention capacity based on its surface tension. As a result, the electrolyte can be more effectively retained in the gap.

[0010] In the secondary battery that solves the above problems, the liquid retaining structure is preferably formed by applying a liquid retaining material to the opposing surface. According to the above configuration, the metallic foreign matter mixed in the uncoated portion of the positive electrode comes into contact with the liquid-retaining material impregnated with the electrolyte, and the electrolyte can be secured in the gap between the uncoated surface of the uncoated portion of the positive electrode and the opposing surface of the separator.

[0011] In the secondary battery that solves the above-described problems, the liquid-retaining structure preferably has a gap between the uncoated surface and the opposing surface that is narrower than a thickness of a positive electrode composite layer formed on the base material of the electrode sheet that constitutes the positive electrode.

[0012] This configuration allows metal particles located in the gap between the uncoated surface and the opposing surface to easily come into contact with the opposing surface of the separator, which is impregnated with electrolyte. Furthermore, the gap itself is expected to have improved liquid retention capacity due to its surface tension. This effectively ensures that electrolyte is retained in the gap.

[0013] A secondary battery that solves the above-described problems preferably includes, in the liquid retention structure, a pressing member that bends the positive electrode uncoated portion based on the application of a pressing force that compresses the electrode sheets and the separator in a thickness direction, such that the uncoated surface of the electrode sheet constituting the positive electrode approaches the opposing surface at a position toward the periphery away from a positive electrode composite coated portion having a positive electrode composite layer formed on the substrate.

[0014] According to the above configuration, the gap formed by bending the uncoated portion of the positive electrode into a closed shape with a substantially triangular cross section can be used as a liquid reservoir, thereby preventing the electrolyte impregnated in the electrode body formed by the positive and negative electrode sheets and the separator from leaking out.

[0015] That is, by retaining the electrolyte in the gap created by the deformation caused by the bending of the uncoated positive electrode portion, a condition is created in which metallic foreign matter located in the gap can easily come into contact with the electrolyte. Furthermore, by bringing the uncoated surface of the bent uncoated positive electrode portion closer to the opposing surface of the separator, metallic foreign matter located in the gap can easily come into contact with the opposing surface of the separator, which is impregnated with the electrolyte. This allows the electrolyte to be secured in the gap between the uncoated surface of the uncoated positive electrode portion and the opposing surface of the separator.

[0016] A secondary battery that solves the above-described problems preferably includes a film material provided at a position where the electrode sheets and the separator are compressed based on the pressing force, and the liquid-retaining structure is configured by setting a thickness shape of the film material that serves as the pressing member such that the thickness of the film material at the position where the film material compresses the positive electrode uncoated portion is greater than the thickness of the film material at the position where the film material compresses the positive electrode composite coated portion.

[0017] According to the above configuration, the difference in thickness between the film material and the uncoated positive electrode portion can be utilized to fold the uncoated positive electrode portion into the gap formed between the uncoated positive electrode portion and the opposing surface of the separator, thereby ensuring electrolyte in the gap between the uncoated surface of the uncoated positive electrode portion and the opposing surface of the separator, while maintaining the uncoated positive electrode portion in a closed shape with a substantially triangular cross section that is deformed by bending the uncoated positive electrode portion.

[0018] Furthermore, due to the thickness profile set for the film material, the force compressing the positive and negative electrode sheets and separator in the thickness direction based on the applied pressure is weaker at the center than at the peripheral edge where the positive electrode composite coating portion is located, which makes it possible to prevent the electrolyte impregnated in the electrode body formed by the positive and negative electrode sheets and separator from migrating from the center to the peripheral edge and leaking out based on the applied pressure to the electrode body. [Effects of the Invention]

[0019] According to the present invention, it is possible to improve the accuracy of inspection for short-circuit defects that occur between electrodes due to the inclusion of metallic foreign matter. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of a secondary battery. [Figure 2] FIG. [Figure 3] FIG. 2 is a side view of the secondary battery. [Figure 4] FIG. 2 is a perspective view of a battery stack. [Figure 5] 1 is a cross-sectional view of a secondary battery showing a liquid retention structure of a first embodiment. [Figure 6] FIG. 1 is a cross-sectional view of a secondary battery according to a conventional example. [Figure 7] FIG. 4 is a cross-sectional view of a secondary battery showing a liquid retention structure of a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a secondary battery showing a liquid retention structure of a third embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a secondary battery showing a liquid retention structure of a third embodiment. [Figure 10] FIG. 10 is an explanatory diagram of a liquid retention structure according to a third embodiment. [Figure 11] FIG. 10 is a cross-sectional view of a secondary battery showing a liquid retention structure according to another example. DETAILED DESCRIPTION OF THE INVENTION

[0021] [First embodiment] A first embodiment of a secondary battery will be described below with reference to the drawings. 1, the secondary battery 1 includes an electrode assembly 10 in which a positive electrode 3, a negative electrode 4, and a separator 5 are integrated, and a case 20 that houses the electrode assembly 10. The secondary battery 1 of this embodiment has a configuration as a lithium ion secondary battery in which the electrode assembly 10 inside the case 20 is impregnated with a non-aqueous electrolyte solution (not shown).

[0022] More specifically, in the secondary battery 1 of this embodiment, the positive electrode 3, the negative electrode 4, and the separator 5 are stacked in a sheet-like outer shape. Then, by winding up the stack of the positive electrode 3, the negative electrode 4, and the separator 5, an electrode assembly 10 is formed in which the positive and negative electrodes and the separators 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4.

[0023] The case 20 of this embodiment includes a case body 21 in the shape of a flat, generally rectangular box, and a lid member 22 that closes an open end 21x of the case body 21. The electrode body 10 of this embodiment has a flat outer shape that corresponds to the box shape of the case 20.

[0024] More specifically, as shown in FIG. 2, in the secondary battery 1 of this embodiment, the positive electrode 3 and the negative electrode 4 each have a configuration as an electrode sheet 35 including a current collector 31 having a sheet-like outer shape and an electrode active material layer 32 laminated on this current collector 31.

[0025] Specifically, for the electrode sheet 35P for the positive electrode 3, a composite paste 37P containing a lithium transition metal oxide as the positive electrode active material is applied to a substrate 36P made of aluminum or the like that constitutes the positive electrode current collector 31P. For the electrode sheet 35N for the negative electrode 4, a composite paste 37N containing a carbon-based material that serves as the negative electrode active material is applied to a substrate 36N made of copper or the like that constitutes the negative electrode current collector 31N. Each of these composite pastes 37P and 37N further contains a binder. In the secondary battery 1 of this embodiment, the composite pastes 37P and 37N are dried to form corresponding positive electrode active material layers 32P and negative electrode active material layers 32N on the positive and negative electrode sheets 35P and 35N, respectively.

[0026] Furthermore, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N are each shaped like a strip. The electrode body 10 of this embodiment has a configuration as a wound body 10X in which the positive and negative electrode sheets 35P, 35N, stacked with the separator 5 sandwiched therebetween, are wound around a winding axis L extending in the width direction of the strip shape (the left-right direction in FIG. 2).

[0027] 2, the separator 5 and each electrode sheet 35 are wound in such a way that the electrode sheet 35P constituting the positive electrode 3 is wound on the inside. However, this figure is one example showing the structure of the electrode assembly 10, and the separator 5 and each electrode sheet 35 may also be wound in such a way that the electrode sheet 35N constituting the negative electrode 4 is wound on the inside. This determines whether the electrode sheet 35 arranged on the outermost shell of the electrode assembly 10 is the electrode sheet 35P constituting the positive electrode 3 or the electrode sheet 35N constituting the negative electrode 4.

[0028] 1 to 3, the lid member 22 of the case 20 is provided with a positive electrode terminal 38P and a negative electrode terminal 38N that protrude outside the case 20. Furthermore, each electrode sheet 35 has an uncoated portion 39 where the electrode active material layer 32 is not formed on the current collector 31. The secondary battery 1 of this embodiment is configured such that the electrode sheet 35P constituting the positive electrode 3 and the positive electrode terminal 38P are electrically connected, and the electrode sheet 35N constituting the negative electrode 4 and the negative electrode terminal 38N are electrically connected, using the uncoated portion 39.

[0029] Specifically, the electrode body 10 of this embodiment is housed in the case 20 with its winding axis L aligned along the longitudinal direction (left-right direction in FIG. 1 ) of the lid member 22, which is an elongated, generally rectangular plate. Furthermore, in this state, an uncoated portion 39P of an electrode sheet 35P constituting the positive electrode 3 is connected to a positive electrode terminal 38P via a connecting member 40P. Similarly, an uncoated portion 39N of an electrode sheet 35N constituting the negative electrode 4 is connected to a negative electrode terminal 38N via a connecting member 40N.

[0030] 3, the secondary battery 1 includes an insulating film 41 housed in the case 20 together with the electrode body 10. Furthermore, this insulating film 41 has a bag shape that opens on the side of the opening end 21x of the case body 21 and is housed in the case 20. The secondary battery 1 of this embodiment is configured such that the electrode body 10 is insulated from the case 20 by disposing the electrode body 10 inside the bag shape of the insulating film 41.

[0031] 1 and 3, in the secondary battery 1 of this embodiment, an electrolyte solution 43 is injected into the case 20 through an injection port 42 provided in the lid member 22. That is, the electrolyte solution 43 of the secondary battery 1 configured as a lithium ion secondary battery is one in which a lithium salt serving as a supporting salt is dissolved in an organic solvent. Thus, the secondary battery 1 of this embodiment is configured so that the electrode assembly 10 sealed in the case 20 is impregnated with the electrolyte solution 43.

[0032] In the secondary battery 1 of this embodiment, the filler port 42 is provided near a safety valve 44 formed in the approximate center in the longitudinal direction of the lid member 22, which is a long, approximately rectangular plate. The secondary battery 1 of this embodiment is configured so that the filler port 42 is sealed by, for example, laser welding after the electrolyte solution 43 is poured into the lid member 22.

[0033] In this way, the secondary battery 1 of this embodiment has its constituent unit, that is, one cell 50, formed by sealing the electrode assembly 10 and the electrolyte solution 43 inside the case 20. Furthermore, the secondary battery 1 of this embodiment combines a plurality of such cells 50. As a result, the secondary battery 1 of this embodiment is configured to be used as a power source for an electric vehicle, for example, with its charge / discharge capacity and output voltage increased.

[0034] (battery stack) As shown in FIG. 4, the secondary battery 1 of this embodiment forms a battery stack 51 as a battery collection unit, which is made up of a plurality of cells 50 arranged in a line and bound together.

[0035] More specifically, the battery stack 51 of this embodiment has a predetermined number of cells 50. For ease of explanation, the battery stack 51 in FIG. 4 is depicted with a smaller number of cells than the actual number. In the battery stack 51 of this embodiment, the cases 20 of the cells 50 have the same flat, generally rectangular box-like shape as described above. The battery stack 51 of this embodiment has a configuration in which the cells 50 are arranged in the thickness direction of the case 20 (see FIG. 3 , the direction perpendicular to the paper surface in the figure).

[0036] The battery stack 51 of this embodiment has a substantially flat spacer 52 interposed between each of the cells 50. The battery stack 51 also has a pair of end plates 53, 53 arranged at both ends of the alignment direction of each of the cells 50. The battery stack 51 also has restraining members 54, 54 spanning between the pair of end plates 53, 53. The battery stack 51 of this embodiment is configured such that the aligned cells 50 are integrated together by being sandwiched between the pair of end plates 53, 53 provided at both ends of the alignment direction of each of the cells 50 based on the restraining force of the restraining members 54, 54.

[0037] (liquid retention structure) Next, a liquid retention structure implemented in the secondary battery 1 of this embodiment will be described. As shown in FIG. 5, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N form the electrode body 10 described above with the separator 5 sandwiched between the positive electrode active material layer 32P and the negative electrode active material layer 32N.

[0038] That is, these electrode sheets 35P, 35N are formed by applying composite pastes 37P, 37N as electrode composite materials 60P, 60N, respectively, onto base materials 36P, 36N that will become current collectors 31 (see FIG. 2). Therefore, in these electrode sheets 35P, 35N, the base materials 36P, 36N are referred to as a positive electrode core material 61P and a negative electrode core material 61N, respectively. Furthermore, the positive electrode active material layer 32P and the negative electrode active material layer 32N formed on these base materials 36P, 36N are referred to as a positive electrode composite layer 62P and a negative electrode composite layer 62N, respectively. In the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N form an electrode body 10, with a separator 5 sandwiched between the positive electrode composite layer 62P and the negative electrode composite layer 62N.

[0039] As described above, the electrode assembly 10 of this embodiment has a configuration as a wound assembly 10X in which the electrode sheets 35P, 35N and the separator 5 are wound (see FIG. 2). Therefore, the secondary battery 1 of this embodiment has a configuration in which the stacked positive electrode core material 61P, positive electrode composite layer 62P, separator 5, negative electrode composite layer 62N, and negative electrode core material 61N are arranged in multiple stages in the radial direction of the wound assembly 10X. However, for ease of explanation, only one stage, which is a structural unit, is shown in FIG. 5 and the following figures.

[0040] In the secondary battery 1 of this embodiment, an uncoated portion 39P of the electrode sheet 35P constituting the positive electrode 3 is disposed at the axial end 10e of the electrode assembly 10 configured as such a wound body 10X. In other words, the electrode sheet 35P on the positive electrode 3 side is wound in a state in which the uncoated portion 39P formed at the widthwise end of the strip shape is disposed at one axial end of the winding axis L (see FIG. 2). In the secondary battery 1 of this embodiment, a gap 75 is thereby formed between the uncoated surface 70s of the positive electrode uncoated portion 70 formed at the peripheral edge 65 of the electrode sheet 35P and the opposing surface 5s of the separator 5 opposing the uncoated surface 70s. Furthermore, the electrode sheet 35N constituting the negative electrode 4 has a negative electrode composite layer 62N in contact with the separator 5 at a position where the separator 5 is sandwiched between the electrode sheet 35N and the positive electrode uncoated portion 70. The secondary battery 1 of this embodiment is provided with a liquid retention structure 80 that secures the electrolyte 43 in the gap 75 between the uncoated surface 70s of the uncoated positive electrode portion 70 and the opposing surface 5s of the separator 5.

[0041] Specifically, in the secondary battery 1 of this embodiment, the liquid retention structure 80 is composed of a binder 82 as a liquid retention material 81 applied to the opposing surface 5s of the separator 5 that faces the uncoated surface 70s. That is, the binder 82 is made of a resin material that has a high affinity with the electrolyte 43, such as SBR (styrene butadiene rubber), PVDF (polyvinylidene fluoride), or acrylic acid ester. The secondary battery 1 of this embodiment is configured so that the electrolyte 43 is retained in the gap 75 formed by the uncoated surface 70s of the positive electrode uncoated portion 70 by impregnating the binder 82 applied to the opposing surface 5s of the separator 5 with the electrolyte 43.

[0042] 6, in a conventional secondary battery 85 that does not have a liquid retention structure 80, it is difficult to ensure a sufficient amount of electrolyte 43 to be retained in the gap 75 between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5. For this reason, even if a metallic foreign matter M such as copper (Cu) is mixed into the positive electrode uncoated portion 70 during manufacturing, a manufacturing defect caused by the mixing of this metallic foreign matter M may not be detected by a general inspection after aging.

[0043] That is, metallic foreign matter M1 mixed into positive electrode composite coating portion 90 having positive electrode composite layer 62P formed on positive electrode core material 61P dissolves in electrolyte 43 during the first charging process performed after secondary battery 85 is assembled. Furthermore, metallic foreign matter M1 dissolved in electrolyte 43 moves toward negative electrode 4 and precipitates on the surface of electrode sheet 35N constituting negative electrode 4. Furthermore, locally precipitated metallic foreign matter M1 short-circuits electrode sheet 35N constituting negative electrode 4 and electrode sheet 35P constituting positive electrode 3. Then, based on the resulting voltage drop, a manufacturing defect in secondary battery 85 is detected by inspection after aging.

[0044] However, with respect to metallic foreign matter M2 mixed in positive electrode uncoated portion 70 not including positive electrode composite layer 62P, dissolution tends to be difficult due to a lack of electrolyte 43 in contact with metallic foreign matter M2. For this reason, during the initial charging process performed after assembly of secondary battery 85, the above-described deposition of metallic foreign matter M2 that has migrated through electrolyte 43 to the negative electrode 4 side and a short-circuit failure due to the locally deposited metallic foreign matter M2 may not occur. As a result, even if metallic foreign matter M2 that could actually cause such a short-circuit failure is present, there is a risk that the battery may pass the post-aging inspection based on the measurement of the voltage drop.

[0045] In consideration of this, as shown in FIG. 5 , in the secondary battery 1 of this embodiment, the liquid retention structure 80 ensures that the electrolyte 43 is stored in the gap 75 between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5. That is, by ensuring sufficient electrolyte 43 in this gap 75, dissolution of metallic foreign matter M mixed in the positive electrode uncoated portion 70 is promoted. As a result, if the metallic foreign matter M migrates to the negative electrode 4 and locally deposits, potentially causing a short circuit, the local deposition leading to the short circuit will progress during the first charging process performed after assembly of the secondary battery 1. The secondary battery 1 of this embodiment is thus configured to detect manufacturing defects in post-aging inspections based on measurement of the voltage drop, thereby improving the accuracy of inspections for short circuits caused by the inclusion of metallic foreign matter M between the positive and negative electrodes.

[0046] More specifically, in secondary battery 1 of the present embodiment, thickness d2 of binder 82 applied to opposing surface 5s of separator 5 as liquid retaining material 81 constituting liquid retaining structure 80 is set to, for example, 60% or more and 100% or less of thickness d0 of positive electrode composite layer 62P. That is, thickness d0 of positive electrode composite layer 62P is the width α of gap 75 formed between uncoated surface 70s of positive electrode uncoated portion 70 and opposing surface 5s of separator 5 in a state where binder 82 serving as liquid retaining material 81 is not applied. In this case, thicknesses d0 and d2 are values ​​in a swollen state impregnated with electrolyte solution 43.

[0047] That is, by applying the binder 82 to the opposing surface 5s of the separator 5, the effective thickness d1' of the opposing portion 91 of the separator 5 having this opposing surface 5s becomes thicker than the original thickness d1 by the thickness d2 of the applied binder 82 (d1' > d1). This also causes the new opposing surface 5s' formed by the applied binder 82 to approach the uncoated surface 70s of the positive electrode uncoated portion 70. In other words, the gap α between the opposing surface 5s' and the uncoated surface 70s is narrower than the thickness d0 of the positive electrode composite layer 62P (α' < α), so that the metallic foreign matter M located in the gap 75 is more likely to come into contact with the binder 82 impregnated with the electrolyte solution 43. Thus, the secondary battery 1 of this embodiment is configured such that the liquid-retaining structure 80 formed by the binder 82 as the liquid-retaining material 81 secures the electrolyte solution 43 in the gap 75.

[0048] (action) Next, the operation of this embodiment will be described. For example, assuming that the thickness d0 of the positive electrode mixture layer 62P is 22.5 μm and the particle size (thickness direction) of the metallic foreign matter M mixed in the positive electrode uncoated portion 70 is 10 μm, the thickness d2 of the binder 82 to be applied to the opposing surface 5s of the separator 5 is 13.5 μm or more. Furthermore, as a result, the distance α' between the new opposing surface 5s' formed by the binder 82 and the uncoated surface 70s of the positive electrode uncoated portion 70 is 9.0 μm or less, which is smaller than the particle size of the metallic foreign matter M mixed in the positive electrode uncoated portion 70. Note that even if the thickness d0 of the positive electrode mixture layer 62P is, for example, 24.9 μm, the distance α' can be set smaller than the particle size of the metallic foreign matter M by similarly calculating the thickness d2 of the binder 82. This makes it possible to secure the electrolyte 43 in the gap 75 formed between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5, in a manner that the binder 82 as the liquid-retaining material 81 impregnated with the electrolyte 43 comes into contact with the metal foreign matter M.

[0049] Next, the effects of this embodiment will be described. (1) The secondary battery 1 includes positive and negative electrode sheets 35P, 35N stacked with a separator 5 sandwiched therebetween. These electrode sheets 35P, 35N are formed by coating electrode composites 60P, 60N containing an electrode active material onto substrates 36P, 36N, which serve as current collectors 31, respectively. The electrode sheet 35P constituting the positive electrode 3 has a positive electrode uncoated portion 70 at its peripheral edge 65, which is not coated with the electrode composite 60P. A gap 75 is formed between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5 facing the uncoated surface 70s. Furthermore, the electrode sheet 35N constituting the negative electrode 4 has a negative electrode composite layer 62N abutting against the separator 5 at a position where the separator 5 is sandwiched between the positive electrode uncoated portion 70 and the electrode sheet 35N. The secondary battery 1 is provided with a liquid retention structure 80 that secures the electrolyte 43 in the gap 75 between the uncoated surface 70s of the uncoated positive electrode portion 70 and the opposing surface 5s of the separator 5.

[0050] According to the above configuration, sufficient electrolyte 43 can be secured in the gap 75 between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5, thereby facilitating the dissolution of metallic foreign matter M mixed in the positive electrode uncoated portion 70. As a result, if there is a possibility that the metallic foreign matter M may migrate to the negative electrode 4 side and locally deposit, causing a short circuit, the localized deposition leading to the occurrence of the short circuit can be accelerated during the first charging process performed after assembly of the secondary battery 1. In other words, manufacturing defects can be detected in post-aging inspections based on voltage drop measurements. This improves the accuracy of inspections for short circuits occurring between positive and negative electrodes due to the inclusion of metallic foreign matter M.

[0051] (2) The liquid-retaining structure 80 is formed by applying a binder 82, which serves as a liquid-retaining material 81, to the opposing surface 5s of the separator 5. According to the above configuration, the metal foreign matter M mixed in the positive electrode uncoated portion 70 comes into contact with the binder 82 impregnated with the electrolyte 43, and the electrolyte 43 can be secured in the gap 75 between the uncoated surface 70s of the positive electrode uncoated portion 70 and the opposing surface 5s of the separator 5.

[0052] (3) In particular, for the opposing portion 91 of the separator 5 whose opposing surface 5s is coated with the binder 82, its effective thickness d1' is greater than the original thickness d1 by the thickness d2 of the coated binder 82. This causes the new opposing surface 5s' formed by the coated binder 82 to approach the uncoated surface 70s of the positive electrode uncoated portion 70. In other words, the gap α between the opposing surface 5s' and the uncoated surface 70s is narrower than the thickness d0 of the positive electrode composite layer 62P, making it easier for the metallic foreign matter M located in the gap 75 to come into contact with the binder 82 impregnated with the electrolyte 43. Additionally, the liquid retention capacity of the gap 75 itself can be expected to be improved based on its surface tension. As a result, the electrolyte 43 can be more effectively retained in the gap 75.

[0053] (4) Thickness d2 of binder 82 applied to opposing surface 5s of separator 5 as liquid-retaining material 81 constituting liquid-retaining structure 80 is set to be 60% or more and 100% or less of thickness d0 of positive electrode mixture layer 62P. This makes it possible to set a suitable distance α that allows metallic foreign matter M located in gap 75 to easily come into contact with binder 82 as liquid-retaining material 81.

[0054] [Second embodiment] Hereinafter, a second embodiment of the secondary battery will be described with reference to the drawings. For the sake of convenience, the same components as those in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

[0055] As shown in FIG. 7, a secondary battery 1B of this embodiment differs from that of the first embodiment in the configuration of a liquid retention structure 80B. More specifically, in secondary battery 1B of this embodiment, separator 5B has thickness d4 of facing portion 91B having facing surface 5s which is thicker than thickness d3 of positive electrode composite abutting portion 92 which abuts positive electrode composite layer 62P formed on positive electrode core material 61P (d4>d3). As a result, secondary battery 1B of this embodiment is configured such that liquid retention structure 80B that retains electrolyte 43 is formed in gap 75B between uncoated surface 70s of positive electrode uncoated portion 70 and facing surface 5s of separator 5B.

[0056] That is, by adopting this configuration, the opposing surface 5s of the separator 5B is brought closer to the uncoated surface 70s of the positive electrode uncoated portion 70. In other words, the gap α between the opposing surface 5s and the uncoated surface 70s can be narrowed below the thickness d0 of the positive electrode composite layer 62P. As a result, the metallic foreign matter M located in the gap 75B is more likely to come into contact with the opposing surface 5s of the separator 5B, which is impregnated with the electrolyte 43. Furthermore, the liquid retention capacity of the gap 75B itself can be expected to be improved based on its surface tension. This effectively ensures that the electrolyte 43 is retained in the gap 75B formed by the positive electrode uncoated portion 70.

[0057] Therefore, similar to the secondary battery 1 in the first embodiment, the secondary battery 1B in this embodiment can also improve the accuracy of inspection for short-circuit defects that occur between the positive and negative electrodes due to the inclusion of metallic foreign matter M. In addition, there is an advantage that a step of coating the binder 82 that becomes the liquid-retaining material 81 on the opposing surface 5s of the separator 5, as in the first embodiment, is not required.

[0058] [Third embodiment] Hereinafter, a third embodiment of the secondary battery will be described with reference to the drawings. For the sake of convenience, the same components as those in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

[0059] As shown in FIGS. 8 and 9, a secondary battery 1C of this embodiment also differs from the first embodiment in the configuration of a liquid retention structure 80C. More specifically, similar to the secondary battery 1 of the first embodiment, the secondary battery 1C of this embodiment also forms a battery stack 51 in which multiple cells 50 are constrained (see FIG. 4). That is, in this secondary battery 1C, a constraining pressure F0 is applied to the electrode assembly 10, which is configured as a wound body 10X flattened to fit the shape of a flat, generally rectangular box-shaped case 20, from the outside of the case 20 in the thickness direction (a direction perpendicular to the paper surface in FIG. 3). Furthermore, in the secondary battery 1C of this embodiment, this constraining pressure F0 acts as a pressing force F that compresses the positive and negative electrode sheets 35P, 35N and separator 5 that form the electrode assembly 10 in the thickness direction (the vertical direction in FIG. 9). The secondary battery 1C of this embodiment also includes a pressing member 100 that folds the positive electrode uncoated portion 70C based on the application of this pressing force F.

[0060] Specifically, in the secondary battery 1C of this embodiment, the insulating film 41 housed in the case 20 together with the electrode assembly 10 as described above functions as the pressing member 100 (see FIG. 3). That is, the insulating film 41 has a bag shape and is housed in the case 20, thereby placing the electrode assembly 10 inside the bag shape. In the secondary battery 1C of this embodiment, a portion of the insulating film 41 located near the axial end 10e of the electrode assembly 10 constitutes a film material 101 provided in a position that compresses the positive and negative electrode sheets 35P, 35N and the separator 5 when the pressing force F is applied.

[0061] More specifically, in secondary battery 1C of this embodiment, film material 101 serving as pressing member 100 is disposed in a position (lower side in FIGS. 8 and 9 ) along positive electrode core material 61P of electrode sheet 35P constituting positive electrode 3. Film material 101 of this embodiment has a thickness shape set so that thickness d6 at a position where film material 101 compresses positive electrode uncoated portion 70C is greater than thickness d5 at a position where film material 101 compresses positive electrode composite coated portion 90.

[0062] That is, the liquid retention structure 80C in the secondary battery 1C of this embodiment utilizes the difference in thickness shape set in this film material 101 to fold the positive electrode uncoated portion 70C in a manner that pushes it into the gap 75 formed between the film material 101 and the opposing portion 91 of the separator 5. Specifically, the secondary battery 1C of this embodiment is configured so that the uncoated surface 70s of the positive electrode uncoated portion 70C folded by this film material 101 approaches the opposing surface 5s of the separator 5 toward the peripheral edge side (left side in each figure) away from the positive electrode composite coated portion 90. The liquid retention structure 80C of this embodiment is configured so that the gap 75C deformed into a closed shape with a substantially triangular cross section serves as a liquid reservoir 105, thereby preventing the electrolyte solution 43 impregnated in the electrode assembly 10 from leaking out to the outside.

[0063] That is, the liquid-retaining structure 80C of the present embodiment retains the electrolyte 43 in the gap 75C that is deformed by bending the positive electrode uncoated portion 70C, thereby creating a state in which the metallic foreign matter M located in the gap 75C can easily come into contact with the electrolyte 43. In addition, the uncoated surface 70s of the bent positive electrode uncoated portion 70C approaches the opposing surface 5s of the separator 5, which makes it easier for the metallic foreign matter M located in the gap 75C to come into contact with the opposing surface 5s of the separator 5 that is impregnated with the electrolyte 43.

[0064] 10 , in secondary battery 1C of this embodiment, thickness d6 of film material 101 at the position where film material 101 compresses positive electrode uncoated portion 70C may be set to be equal to or greater than thickness d0 of positive electrode composite layer 62P (d6≧d0), for example. This allows deformed gap 75C to form a sealed shape that effectively functions as liquid pool 105.

[0065] That is, for the extremely thin, foil-like positive electrode core material 61P, the thickness is ignored to simplify the calculation. In this case, the triangular shape δ0 of the gap 75C deformed into the closed shape as described above is similar to the thickness d6 of the film material 101 that presses the positive electrode core material 61P into the gap 75 before deformation, and the triangular shape δ1 whose two sides are the amount of pressing x1 of the positive electrode core material 61P that forms the closed shape. Furthermore, the length x0 of the opposing surface 5s of the separator 5 extending in the direction away from the positive electrode composite coated portion 90 is absolutely greater than the thickness d0 of the positive electrode composite layer 62P that maximizes the distance α between the opposing surface 5s and the uncoated surface 70s. Thus, the thickness d6 of the film material 101 required to ensure the amount of pressing x1 necessary for the deformed gap 75C to form the closed shape can be approximated by the thickness d0 of the positive electrode composite layer 62P.

[0066] As described above, the secondary battery 1C of this embodiment can also effectively secure the electrolyte 43 in the gap 75C formed by the positive electrode uncoated portion 70C. As a result, similar to the secondary battery 1 of the first embodiment, it is possible to improve the accuracy of inspection for short-circuit defects that occur between the positive and negative electrodes due to the inclusion of metallic foreign matter M.

[0067] Furthermore, due to the thickness shape set for the film material 101, the force compressing the positive and negative electrode sheets 35P, 35N and the separator 5 in the thickness direction based on the applied pressing force F is weaker at the center than at the peripheral edge 65 where the positive electrode composite coated portion 90 is located. That is, in the case of an electrode body 10 having the outer shape of a wound body 10X, the compressive force crushing the electrode body 10 is weaker at the axial central portion 10c than at the axial end portions 10e (see FIGS. 2 and 3). Thus, the secondary battery 1C of this embodiment is configured to be able to prevent the electrolyte solution 43 impregnated in the electrode body 10 from migrating from the axial central portion 10c toward the axial end portions 10e and leaking to the outside.

[0068] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0069] In the first embodiment, SBR (styrene butadiene rubber), PVDF (polyvinylidene fluoride), acrylic ester, or the like is used as the binder 82 applied to the opposing surface 5s of the separator 5 as the liquid-retaining material 81. However, the liquid-retaining material 81 is not limited to this, and does not necessarily have to be called a "binder" as long as it is a material that has a high affinity with the electrolyte 43 and has the same retention function as the separator 5.

[0070] In the second embodiment, the thickness d4 of the facing portion 91 having the facing surface 5s of the separator 5B is greater than the thickness d3 of the positive electrode composite contact portion 92 that contacts the positive electrode composite layer 62P formed on the positive electrode core material 61P. This results in a configuration in which the gap α between the facing surface 5s of the separator 5B and the uncoated surface 70s is narrower than the thickness d0 of the positive electrode composite layer 62P. However, this is not limiting, and the gap α between the facing surface 5s of the separator 5B and the uncoated surface 70s may be narrowed by thickening the positive electrode core material 61P at a position that constitutes the positive electrode uncoated portion 70C. Even with this configuration, a liquid retention structure 80 that retains the electrolyte 43 in the gap 75 can be formed.

[0071] In the third embodiment, the film material 101 serving as the pressing member 100 has a stepped thickness shape such that the thickness d6 at the position where the positive electrode uncoated portion 70C is compressed is larger than the thickness d5 at the position where the positive electrode composite coated portion 90 is compressed (see FIG. 8).

[0072] However, the present invention is not limited to this, and the thickness shape may be set so that the thickness d7 of the film material 101D gradually increases toward the peripheral edge 65 side (toward the left in FIG. 11) of the electrode sheet 35P constituting the positive electrode 3, as in the liquid retention structure 80D of the secondary battery 1D shown in FIG. 11. Even when such a configuration is adopted, the film material 101D can be used as a pressing member 100D to form a sealing shape in which the deformed gap 75D effectively functions as the liquid reservoir 105.

[0073] Thus, the liquid retention structure 80D of the present embodiment also secures the electrolyte 43 in the gap 75D in a manner that the electrolyte 43 retained in the liquid pool 105 formed by the deformed gap 75D comes into contact with the metallic foreign matter M mixed in the positive electrode uncoated portion 70D. In addition, the bending of the positive electrode uncoated portion 70D brings the uncoated surface 70s closer to the opposing surface 5s of the separator 5, thereby making it easier for the metallic foreign matter M located in the gap 75D to come into contact with the opposing surface 5s of the separator 5 impregnated with the electrolyte 43. As a result, the electrolyte 43 can be effectively secured in the gap 75D formed by the positive electrode uncoated portion 70D. As a result, similar to the above-described embodiments, the accuracy of inspection for short-circuit defects occurring between the positive and negative electrodes due to the inclusion of the metallic foreign matter M can be improved.

[0074] In the third embodiment, the insulating film 41 housed in the case 20 together with the electrode body 10 is used as the film material 101 that functions as the pressing member 100. However, this is not limiting, and a film material 101 separate from the insulating film 41 may be used as the pressing member 100. Furthermore, a pressing member 100 other than the film material 101 may be provided.

[0075] The terminal shapes of the positive electrode terminal 38P and the negative electrode terminal 38N are not limited to the shapes shown in Fig. 1 and may be changed as desired. The shape of the case 20, which defines the outer shape of the secondary battery 1, is also not necessarily limited to a flat rectangular box shape and may be changed as desired, for example, to a cylindrical shape.

[0076] In each of the above embodiments, the electrode assembly 10 is configured to form a wound body 10X in which the positive and negative electrode sheets 35P, 35N are stacked with the separator 5 sandwiched between them and wound around a winding axis L extending in the width direction of the strip shape (left and right direction in FIG. 2). However, the present invention is not limited to this, and may be applied to, for example, a configuration including a planar layered electrode assembly 10 in which the positive and negative electrode sheets 35P, 35N stacked with the separator 5 sandwiched between them do not form a wound body 10X.

[0077] In addition, in each of the above embodiments, the secondary battery 1 is configured as a lithium-ion secondary battery. However, the present invention is not limited to this, and may be applied to a secondary battery 1 other than a lithium-ion secondary battery. Furthermore, the battery stack 51 does not necessarily have to be formed by binding a plurality of cells 50. [Explanation of symbols]

[0078] 1…Secondary battery 3...Positive electrode 4...Negative electrode 5...Separator 5s...Opposing surface 31...Current collector 35P, 35N...Electrode sheet 36P,36N…Base material 43...Electrolyte 60P,60N…electrode composite material 62N…Negative electrode composite layer 65...periphery 70...Positive electrode uncoated area 70s...Uncoated surface 75...gap 80…Liquid retention structure

Claims

1. The device is provided with positive and negative electrode sheets stacked with a separator sandwiched therebetween, Each of the electrode sheets is formed by coating an electrode mixture containing an electrode active material on a substrate serving as a current collector, The electrode sheet constituting the positive electrode has a positive electrode uncoated portion on its periphery where the electrode mixture is not coated, and a gap is formed between the uncoated surface of the positive electrode uncoated portion and the opposing surface of the separator that faces the uncoated surface, the electrode sheet constituting the negative electrode has a negative electrode composite layer in contact with the separator at a position where the separator is sandwiched between the electrode sheet and the positive electrode uncoated portion, a liquid retention structure for securing an electrolyte in the gap; the liquid-retaining structure is a secondary battery including a pressing member that, based on application of a pressing force that compresses the electrode sheets and the separator in a thickness direction, bends the positive electrode uncoated portion such that the uncoated surface approaches the opposing surface at a position toward the periphery, away from a positive electrode composite coated portion having a positive electrode composite layer formed on the base material, in the electrode sheet that constitutes the positive electrode.

2. 2. The secondary battery according to claim 1, wherein the liquid-retaining structure is configured such that a thickness of a portion of the separator having the opposing surface is set to be greater than a thickness of a portion of the separator in contact with a positive electrode composite layer formed on the substrate in the electrode sheet constituting the positive electrode.

3. The liquid-retaining structure is formed by applying a liquid-retaining material to the opposing surface. The secondary battery according to claim 1 or 2.

4. The liquid-retaining structure is formed by narrowing the gap between the uncoated surface and the opposing surface of the electrode sheet constituting the positive electrode to a thickness smaller than the thickness of the positive electrode mixture layer formed on the substrate. The secondary battery according to any one of claims 1 to 3.

5. a film material provided at a position where the electrode sheets and the separator are compressed based on the pressing force; The liquid-retaining structure is configured such that the thickness of the film material serving as the pressing member at a position where the film material compresses the positive electrode uncoated portion is greater than the thickness of the film material at a position where the film material compresses the positive electrode composite coated portion. The secondary battery according to claim 1 .

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