Electrolyte barrier film

Abstract

To provide an electrolyte barrier film presenting a barrier property to an electrolyte.SOLUTION: The present invention relates to an electrolyte barrier film 1 presenting a barrier property to an electrolyte. The electrolyte barrier film 1 has a barrier layer 11 and a thermal fusion layer 13 of resin formed in both surfaces of the barrier layer 11. The barrier layer 11 is formed of an ethylene-vinyl alcohol copolymer.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an electrolyte barrier film used, for example, in a power storage device or the like.

Background Art

[0002] A laminated (pouch-type) lithium-ion secondary battery as a power storage device has an exterior material as a casing composed of a laminate film (laminate material). Generally, an electrode assembly such as a positive electrode, a separator, and a negative electrode, and an electrolyte are enclosed inside the exterior material.

[0003] On the other hand, in recent years, a configuration in which a barrier film for preventing the permeation of an electrolyte is disposed in the electrolyte inside a lithium-ion secondary battery has been studied. For example, in the lithium-ion secondary battery shown in Patent Document 1 below, the inside of the exterior body is partitioned by a partition plate (barrier film) to form two independent cavities, and an electrode assembly and an electrolyte are enclosed in each cavity. By thus forming battery cells for each cavity, two battery cells are formed inside one exterior material (battery).

[0004] In such a lithium-ion secondary battery, as a partition wall for partitioning between cavities, a barrier film in which heat-sealing layers made of resin are laminated on both sides of a barrier layer (intermediate layer) having barrier properties is used. As the barrier layer in this barrier film, a polymer material such as polyethylene terephthalate (PET) resin is used, and as the heat-sealing layer, a polymer material such as a thermoplastic resin is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] However, in the barrier film used inside the conventional lithium-ion secondary battery, there has been a problem that it may not be able to exhibit sufficient barrier properties against the electrolytic solution.

[0007] This invention has been made in view of the above problems, and an object thereof is to provide an electrolytic solution barrier film having sufficient barrier properties against the electrolytic solution.

Means for Solving the Problems

[0008] To achieve the above object, the present invention comprises the following means.

[0009] [1] An electrolytic solution barrier film having barrier properties against the electrolytic solution, comprising a barrier layer and resin-made heat-sealing layers provided on both surfaces of the barrier layer, wherein the barrier layer is composed of an ethylene-vinyl alcohol copolymer, characterized electrolytic solution barrier film.

[0010] [2] The electrolytic solution barrier film according to item 1 above, wherein the heat-sealing layer is composed of an olefin resin.

[0011] [3] The electrolytic solution barrier film according to item 1 or 2 above, wherein an adhesive layer is provided between the barrier layer and the heat-sealing layer, and the adhesive layer is composed of an adhesive resin.

[0012] [4] The electrolytic solution barrier film according to item 1 or 2 above, wherein an adhesive layer is provided between the barrier layer and the heat-sealing layer, and the adhesive layer is composed of a two-component curable olefin-based adhesive.

[0013] [5] The electrolytic solution barrier film according to any one of items 1 to 4 above, wherein the electrolytic solution transmittance after 3 days in the barrier layer is 10% or less.

[0014] [6] The electrolytic solution barrier film according to any one of the preceding items 1 to 5, having a total thickness of 80 μm or less.

[0015] [7] A partition plate for a power storage device for partitioning the inside of an exterior material of a power storage device into a plurality of cavities filled with an electrolytic solution, The partition plate for a power storage device, characterized in that it is composed of the electrolytic solution barrier film according to any one of the preceding items 1 to 6.

[0016] [8] A power storage device including an exterior material and a partition plate for partitioning the inside of the exterior material into a plurality of cavities filled with an electrolytic solution, The power storage device, characterized in that the partition plate is composed of the electrolytic solution barrier film according to any one of the preceding items 1 to 6.

Advantages of the Invention

[0017] According to the electrolytic solution barrier film of Invention [1], since the barrier layer is composed of an ethylene-vinyl alcohol copolymer, it has sufficient barrier properties against the electrolytic solution and can prevent the permeation of the electrolytic solution.

[0018] According to the electrolytic solution barrier films of Inventions [2] to [4], they are excellent in the adhesive strength between the barrier layer and the heat fusion, and can surely prevent delamination between layers.

[0019] According to the electrolytic solution barrier film of Invention [5], the permeation of the electrolytic solution can be more surely prevented.

[0020] According to the electrolytic solution barrier film of Invention [6], thinning can be achieved.

[0021] According to the partition plate for a power storage device of Invention [7], similarly to the above, it has sufficient barrier properties against the electrolytic solution and can prevent the permeation of the electrolytic solution.

[0022] According to the invention [8], it is possible to provide an energy storage device including a partition plate having sufficient barrier properties against an electrolytic solution and capable of preventing permeation of the electrolytic solution.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0024] FIG. 1 is a perspective view showing a lithium ion secondary battery as an energy storage device which is an embodiment of this invention, FIG. 2 is a cross-sectional view, and FIG. 3 is an exploded perspective view. As shown in these figures, the energy storage device of the present embodiment includes, as will be described in detail later, two cavities 25 (see FIG. 2) whose interiors are partitioned by a partition plate (separator) 10, and the partition plate 10 is constituted by an electrolytic solution barrier film 1 related to this invention.

[0025] As shown in FIG. 4, in the present embodiment, the barrier film 1 includes a barrier layer 11 as an intermediate layer, and heat-sealing layers 13 laminated on both the upper and lower surfaces of the barrier layer 11 via adhesive layers 12, respectively.

[0026] The barrier layer 11 is constituted by a synthetic resin made of ethylene-vinyl alcohol copolymer (EVOH).

[0027] The thickness of the barrier layer 11 is preferably set to 5 μm to 20 μm, more preferably 7 μm to 15 μm. That is, if the thickness of the barrier layer 11 is too thin, it may be difficult to sufficiently ensure the barrier property, which is not preferable. Conversely, if the thickness of the barrier layer 11 is too thick, it may be difficult to reduce the thickness of the barrier film 1 and thus the thickness of the entire power storage device, which is not preferable.

[0028] The heat-sealing layer 13 is composed of a resin capable of heat-sealing (heat-bonding). Specifically, the heat-sealing layer 13 is preferably composed of an olefin-based resin in consideration of the adhesiveness with the barrier layer 11. Among them, in particular, it is preferably composed of polypropylene (PP) or a polypropylene-olefin copolymer.

[0029] In addition, in the present embodiment, a resin having a lower melting point than the resin constituting the barrier layer 11 is used for the resin constituting the heat-sealing layer 13.

[0030] The thickness of the heat-sealing layer 13 is preferably set to 12 μm to 30 μm, more preferably 15 μm to 25 μm.

[0031] The adhesive layer 12 is preferably an olefin-based one in order to improve the adhesiveness with the barrier layer 11 and the heat-sealing layer 13. For example, when the heat-sealing layer 13 is laminated on the barrier layer 11 by dry lamination, it is preferable to use a two-component curable olefin-based adhesive as the adhesive layer 12. When the heat-sealing layer 13 is laminated on the barrier layer 11 by heat lamination, it is preferable to use an adhesive resin such as acid-modified polypropylene as the adhesive layer 12.

[0032] The barrier film 1 may also be manufactured by co-extruding and laminating a resin for the heat-sealing layer and a resin for the adhesive layer on the barrier layer film.

[0033] The barrier film 1 is more likely to have a thinner thickness when manufactured by dry lamination than by heat lamination.

[0034] In this embodiment, the total thickness of the barrier film 1 is preferably adjusted to 80 μm or less in order to reduce the thickness of the power storage device.

[0035] Next, the configuration of the power storage device of this embodiment using the barrier film 1 will be described.

[0036] As shown in FIGS. 1 to 3, the power storage device of this embodiment is composed of an exterior material that constitutes the casing, which is composed of an upper exterior material 21 and a lower exterior material 22. The upper exterior material 21 and the lower exterior material 22 have the same shape, and the upper exterior material 21 is in a state where it is upside-down with respect to the lower exterior material 22.

[0037] In this embodiment, the exterior materials 21 and 22 are composed of a laminate material or the like. As the laminate material for the exterior material, for example, a resin heat-sealing layer is laminated on the inner surface side of the metal foil layer via an adhesive layer, and a resin protective layer is laminated on the outer surface side via an adhesive layer. As the heat-sealing layer of the exterior material, it is preferable to use a resin such as an olefin-based resin in consideration of the adhesiveness with the heat-sealing layer 13 of the barrier film 1 (partition plate 10).

[0038] The exterior materials 21 and 22 of this embodiment are formed by the molded product of this laminate material. In this embodiment, the exterior material is not limited to being formed by a laminate material, and may be formed using a resin sheet (resin film) or the like.

[0039] The upper exterior material 21 has a recess 23 formed to be recessed upward in the middle part, and a flange 24 is formed on the outer peripheral edge of the recess 23. The lower exterior material 21 has a recess 23 formed to be recessed downward in the middle part, and a flange 24 is formed on the outer peripheral edge of the recess 23.

[0040] Inside the power storage device, the electrode assembly 3 is accommodated vertically. The electrode assembly 3 includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In the present embodiment, the electrode assembly 3 is, for example, a laminated type in which a positive electrode sheet and a negative electrode sheet are laminated via a separator sheet, a folded type in which a positive electrode sheet and a negative electrode sheet disposed via a separator sheet are folded and laminated, or a jelly roll type formed by winding a positive electrode sheet and a negative electrode sheet disposed via a separator sheet. Further, two tab leads 31 respectively connected to the positive electrode and the negative electrode are provided so as to protrude from the end face of the electrode assembly 3.

[0041] In the present embodiment, the lower electrode assembly 3 is accommodated in the recess 23 of the lower exterior member 22, and the partition plate 10 which is a barrier film 1 is disposed so as to close the opening of the recess 23. In this case, the outer peripheral edge of the partition plate 10 is disposed so as to overlap the flange 24 of the lower exterior member 22, and the two tab leads 31 of the electrode assembly 3 are disposed so as to be drawn out to the outside through between the flange 24 of the lower exterior member 22 and the outer peripheral edge of the partition plate 10.

[0042] Further, the upper electrode assembly 3 is disposed on the intermediate portion of the partition plate 10, and the upper exterior member 21 is disposed so as to cover the electrode assembly 3, and the upper electrode assembly 3 is accommodated in the recess 23 of the upper exterior member 21. In this case, the flange 24 of the upper exterior member 21 is disposed so as to overlap the outer peripheral edge of the partition plate 10, and the two tab leads of the upper electrode assembly 3 are disposed so as to be drawn out to the outside through between the outer peripheral edge of the partition plate 10 and the flange 24 of the upper exterior member 21.

[0043] In this way, the exterior members 21 and 22, the electrode assembly 3, and the partition plate 10 are disposed to form a power storage device provisional assembly.

[0044] Furthermore, the heat-sealing layer of the flange 24 of the exterior materials 21 and 22 in the temporary assembly is heat-sealed to the heat-sealing layer 13 at the outer peripheral edge of the partition plate 10. As a result, the recess 23 of the upper exterior material 21 and the partition plate 10 form an upper sealed space (cavity) 25, and the recess 23 of the lower exterior material 22 and the partition plate 10 form a lower sealed space (cavity) 25 independent of the upper cavity 25.

[0045] Note that an electrolytic solution (not shown) is enclosed in each of the upper and lower cavities 25 together with the electrode structure 3.

[0046] In this embodiment, the upper battery cell is formed by the upper cavity 25, the electrode structure 3, and the electrolytic solution, and the lower battery cell is formed by the lower cavity 25, the electrode structure 3, and the electrolytic solution. Thus, the power storage device of this embodiment having two battery cells in one casing (exterior materials 21, 22) is formed.

[0047] As described above, according to the power storage device of this embodiment, as the partition plate 10 that partitions the two cavities 25 filled with the electrolytic solution, the barrier film 1 excellent in barrier properties against the electrolytic solution is used. Therefore, it is possible to surely prevent the problem that the electrolytic solution in one cavity 25 permeates through the partition plate 10 and leaks into the other cavity 25, and it is possible to surely prevent the deterioration of battery performance due to the leakage of the electrolytic solution.

[0048] In addition, the barrier film 1 of this embodiment is a unique laminated structure in which olefin-based heat-sealing layers 13 are formed on both sides of a barrier layer 11 made of an ethylene-vinyl alcohol copolymer via olefin-based adhesive layers 12. Therefore, the adhesive strength (interlayer strength) between the barrier layer 11 and the heat-sealing layer 13 can be improved. For this reason, even in an environment where both sides of the barrier film 1 (partition plate 10) are exposed to the electrolytic solution, delamination between the barrier layer 11 and the heat-sealing layer 13 can be surely prevented, a stable structure can be maintained for a long time, and high performance can be maintained as a power storage device (secondary battery).

[0049] In addition, since the barrier film 1 of the present embodiment has heat-sealing layers 13 laminated on both sides, when it is used in a power storage device such as a laminate type, it can be surely heat-sealed to the resin layer (heat-sealing layer) on the inner surface side of the exterior material, and has excellent versatility.

[0050] In the above embodiment, the case where the electrolyte barrier film of the present invention is used as a partition plate for partitioning the inside of the power storage device has been described as an example. However, the present invention is not limited thereto, and the electrolyte barrier film of the present invention can be applied to any structure as long as at least one side is exposed to the electrolyte.

[0051] In the above embodiment, the case where the present invention is applied to a lithium-ion secondary battery has been described as an example. However, the present invention is not limited thereto, and the electrolyte barrier film of the present invention can be applied to any power storage device as long as it is a power storage device (battery) in which the electrolyte is enclosed.

Example

[0052] Next, examples and comparative examples related to the electrolyte barrier film used in the power storage device of the above embodiment will be described.

[0053]

Table 1

[0054] <Example 1> As shown in Table 1, on both sides of a resin film of ethylene-vinyl alcohol copolymer (EVOH) with a thickness of 8 μm as a barrier layer, a layer of polypropylene (PP) with a thickness of 25 μm as a heat-sealing layer was formed via an acid-modified polypropylene (acid-modified PP) with a thickness of 4 μm as an adhesive layer, and a barrier film of Example 1 with a total thickness (Total thickness) of 66 μm was produced.

[0055] This barrier film was cut to form two barrier film pieces with a size of 75 mm square.

[0056] Then, two barrier film pieces were overlapped, and three sides of the periphery were sealed by heat fusion to form a three-sided bag. From the open side of the three-sided bag, 3 ml of dimethyl carbonate (DMC) used as a solvent for the electrolytic solution was injected, and then the open side was sealed by heat fusion, thereby producing a pouch-type simulated battery sample of Example 1 in which DMC was encapsulated.

[0057] <Example 2> As shown in Table 1, a simulated battery sample of Example 2 with a total thickness of 76 μm was produced in the same manner as in Example 1, except that the thickness of the heat-sealing layer was 30 μm.

[0058] <Example 3> As shown in Table 1, a simulated battery sample of Example 3 with a total thickness of 73 μm was produced in the same manner as in Example 1, except that the thickness of the barrier layer was 15 μm.

[0059] <Example 4> As shown in Table 1, a simulated battery sample of Example 4 with a total thickness of 83 μm was produced in the same manner as in Example 3, except that the thickness of the heat-sealing layer was 30 μm.

[0060] <Example 5> As shown in Table 1, a simulated battery sample of Example 5 with a total thickness of 64 μm was produced in the same manner as in Example 1, except that a two-component curable olefin-based adhesive (two-component curable adhesive) with a thickness of 3 μm was used as the adhesive layer.

[0061] <Example 6> As shown in Table 1, a simulated battery sample of Example 6 with a total thickness of 74 μm was produced in the same manner as in Example 5, except that the thickness of the heat-sealing layer was 30 μm.

[0062] <Example 7> As shown in Table 1, a simulated battery sample of Example 7 with a total thickness of 71 μm was produced in the same manner as in Example 5, except that the thickness of the barrier layer was 15 μm.

[0063] <Comparative Example 1> As shown in Table 1, a simulated battery sample of Comparative Example 1 with a total thickness of 67 μm was prepared in the same manner as in Example 1, except that a polyethylene terephthalate (PET) resin with a thickness of 9 μm was used as the barrier layer.

[0064] <Comparative Example 2> As shown in Table 1, a simulated battery sample of Comparative Example 2 with a total thickness of 65 μm was prepared in the same manner as in Comparative Example 1, except that a two-component curable olefin-based adhesive with a thickness of 3 μm was used as the adhesive layer.

[0065] <Comparative Example 3> As shown in Table 1, a simulated battery sample of Comparative Example 3 with a total thickness of 70 μm was prepared in the same manner as in Comparative Example 1, except that the thickness of the barrier layer was changed to 12 μm.

[0066] <Comparative Example 4> As shown in Table 1, a simulated battery sample of Comparative Example 4 with a total thickness of 68 μm was prepared in the same manner as in Comparative Example 2, except that the thickness of the barrier layer was changed to 12 μm.

[0067] <Comparative Example 5> As shown in Table 1, a simulated battery sample of Comparative Example 5 with a total thickness of 78 μm was prepared in the same manner as in Comparative Example 4, except that the thickness of the heat-sealing layer was changed to 30 μm.

[0068] <Measurement of DMC Permeation Rate> For the simulated battery samples of each example and each comparative example, the weight (mass) immediately after production, the weight (mass) after 1 day, and the weight (mass) after 3 days were measured. Based on the weight loss rate, the DMC permeation rate after 1 day and the DMC permeation rate after 3 days were determined. The results are shown together in Table 1.

[0069] <Evaluation Results> As is clear from Table 1, in the simulated battery samples of Examples 1 to 7 related to the present invention, compared with the simulated battery samples of Comparative Examples 1 to 5, the DMC transmittance after 1 day and 3 days is very low, and it was confirmed that there is no problem of electrolyte leakage and a long-term stable state can be obtained.

Industrial Applicability

[0070] The electrolyte barrier film of this invention can be applied to a power storage device in which an electrolyte is enclosed.

Explanation of Signs

[0071] 1: Electrolyte barrier film 10: Partition plate 11: Barrier layer 12: Adhesive layer 13: Heat-sealing layer 25: Cavity

Claims

1. An electrolyte barrier film having barrier properties against an electrolyte, comprising: a barrier layer and resinous heat-sealing layers provided on both surfaces of the barrier layer, wherein the barrier layer is made of an ethylene-vinyl alcohol copolymer. The electrolyte barrier film is characterized by this.

2. The electrolyte barrier film according to Claim 1, wherein the heat-sealing layer is made of an olefin resin.

3. The electrolyte barrier film according to Claim 1 or 2, wherein an adhesive layer is provided between the barrier layer and the heat-sealing layer, and the adhesive layer is made of an adhesive resin.

4. The electrolyte barrier film according to Claim 1 or 2, wherein an adhesive layer is provided between the barrier layer and the heat-sealing layer, and the adhesive layer is made of a two-component curable olefin-based adhesive.

5. The electrolyte barrier film according to Claim 1 or 2, wherein the electrolyte permeability after 3 days in the barrier layer is 10% or less.

6. The electrolyte barrier film according to Claim 1 or 2, having a total thickness of 80 μm or less.

7. A partition plate for a power storage device for partitioning the inside of an exterior material of the power storage device into a plurality of cavities filled with an electrolyte, characterized by being made of the electrolyte barrier film according to Claim 1 or 2.

8. A power storage device comprising an exterior material and a partition plate for partitioning the inside of the exterior material into a plurality of cavities filled with an electrolyte, wherein the partition plate is made of the electrolyte barrier film according to Claim 1 or 2. The power storage device is characterized by this.

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