Secondary batteries

Abstract

In a secondary battery 1 having a laminated structure in which a positive electrode active material layer 3 coated on a current collector 2 and a negative electrode active material layer 5 coated on a current collector 4 face each other with a separator 6 in between, the present invention provides a structure that prevents the active material layers from being compressed even when expansion / contraction of each part occurs due to heat, and prevents contact between the positive electrode and negative electrode current collectors and short circuits caused by the intrusion of foreign matter. [Solution] The secondary battery is configured such that a sealing portion welded to either the positive electrode current collector or the negative electrode current collector is interposed between the uncoated area of ​​the positive electrode active material layer on the positive electrode current collector and the uncoated area of ​​the negative electrode active material layer on the negative electrode current collector, with an outer seal 7 surrounding the periphery of the positive electrode current collector and maintaining the distance between them.

Description

Technical Field

[0001] The present invention relates to secondary batteries, and more particularly to the structure of secondary batteries.

Background Art

[0002] Briefly stated, a secondary battery such as a lithium-ion secondary battery has a laminated structure in which a positive electrode active material layer coated on a current collector that may be a metal foil and a negative electrode active material layer coated on a current collector that may be a metal foil face each other with a separator interposed therebetween, an electrolytic solution is injected therebetween, and the peripheries of the current collector and the separator are sealed by a sealing member. Various configurations have been proposed for various problems that can occur in such secondary batteries. For example, in Patent Document 1, in order to suppress the progress of electrolyte leakage (alkali creep) from the negative electrode that occurs in a battery using an alkaline aqueous solution, it is proposed to form an insulating portion containing a metal in the composition at the edge of the current collector. In Patent Document 2, in order to suppress deformation of the current collector, a spacer thicker than each sealing portion is sandwiched between the sealing portion welded to the current collector on the positive electrode side and the sealing portion welded to the current collector on the negative electrode side.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the laminated structure of the secondary battery described above, where a positive electrode active material layer coated on the current collector and a negative electrode active material layer coated on the current collector face each other with a separator in between, foreign matter may enter between the current collectors as the electrolyte is injected. If there is only a separator between the areas of the current collector where the positive electrode active material layer and the negative electrode active material layer are not coated, and the foreign matter comes into contact with both the positive and negative electrode current collectors, it can cause a short circuit between the current collectors. Also, if the current collectors come into contact with each other for any reason, an electrical short circuit will occur. In this regard, it has been proposed to insert an insulator made of silicone resin or the like between current collectors to prevent electrical short circuits between them. However, in this case, the insulator cannot be heat-welded to the electrode foil, which is the current collector. Therefore, when temperature changes occur, the electrode foil and the insulator expand / contract with their respective different coefficients of thermal expansion. This can cause the insulator to compress or become embedded in the active material layer, potentially inducing delamination of the active material or a decrease in capacity. Thus, in a secondary battery having the above-described laminated structure, it would be advantageous to have a structure that prevents short circuits between the positive and negative electrode current collectors, and that does not cause compression or other effects on the active material layer even when expansion / contraction occurs in each part due to temperature changes.

[0005] In view of the above circumstances, the main object of the present invention is to provide a structure for a secondary battery having a laminated structure in which a positive electrode active material layer coated on a current collector and a negative electrode active material layer coated on a current collector face each other with a separator in between, that prevents contact between the positive electrode and negative electrode current collectors and prevents short circuits caused by foreign matter, even when thermal expansion / contraction occurs in each part. [Means for solving the problem]

[0006] According to the present invention, the above problems are solved by a secondary battery having a laminated structure in which a positive electrode active material layer coated on a positive electrode current collector and a negative electrode active material layer coated on a negative electrode current collector face each other with a separator in between, and an electrolyte is injected between the positive electrode current collector and the negative electrode current collector, wherein an outer seal surrounding the periphery of the positive electrode current collector and the negative electrode current collector maintains the distance between them, and a seal portion is welded to the positive electrode active material layer and the negative electrode active material layer on the respective surfaces of the positive electrode current collector and the negative electrode current collector, and the seal portion welded to the surface of either the positive electrode current collector or the negative electrode current collector is interposed between the area of ​​the positive electrode active material layer on the positive electrode current collector and the area of ​​the negative electrode active material layer on the negative electrode current collector.

[0007] In the above configuration, the secondary battery may be a non-aqueous secondary battery, and is typically a lithium-ion secondary battery. The positive electrode current collector and the negative electrode current collector may be current collectors made of metal foil in a conventional manner, and the positive electrode active material layer and the negative electrode active material layer may be coated onto the positive electrode current collector and the negative electrode current collector, respectively, in a conventional manner. The separator and electrolyte may also be a separator and electrolyte in a conventional manner. The outer seal and the seal portion welded to the surfaces of the positive electrode current collector and the negative electrode current collector may be formed of a resin material commonly used in this field, such as polyethylene. Furthermore, in a secondary battery, a structure may be formed in which multiple stacked structures, each sandwiched between a positive electrode current collector and a negative electrode current collector as described above, are stacked on top of each other. The positive electrode current collector and the negative electrode current collector are bonded to the negative electrode current collector and the positive electrode current collector of the adjacent stacked structure, and as a result, except for both ends of the battery, the separator may be sandwiched between two bipolar electrode bodies (electrode bodies stacked in the order of negative electrode active material layer - negative electrode current collector - positive electrode current collector - positive electrode active material layer).

[0008] Furthermore, in the configuration of the present invention described above, between the positive electrode current collector and the negative electrode current collector facing each other with a separator in between in the laminated structure, the areas where the positive electrode active material layer on the positive electrode current collector and the areas where the negative electrode active material layer on the negative electrode current collector are not coated are covered as much as possible (to the extent technically possible), and so that a seal portion welded to the surface of either the positive electrode current collector or the negative electrode current collector is interposed between the areas where the positive electrode active material layer on the positive electrode current collector and the areas where the negative electrode active material layer on the negative electrode current collector is not coated. With this configuration, as can be understood from the diagrams to be explained later, in addition to a separator, there is at least one sealing portion welded to either the positive or negative current collector between the uncoated area of ​​the active material layer on the positive and negative current collectors. This ensures that the entry of foreign matter between the current collectors or short circuits caused by contact between the current collectors can be prevented more reliably. In this case, since the sealing portion is welded to the surface of either the positive or negative current collector, the sealing portion and the current collector expand / contract together during temperature changes, and peeling of the active material or a decrease in capacity due to the sealing portion pressing on the active material layer is not induced.

[0009] Furthermore, the seal portion between the positive electrode current collector and the negative electrode current collector is also welded to the surface of the portion where the electrolyte injection port is formed, which is located in a part of the space between the positive electrode current collector and the negative electrode current collector. This ensures that insulation between the current collectors at the electrolyte injection port is maintained more reliably. [Effects of the Invention]

[0010] Thus, according to the configuration of the present invention, in a secondary battery having a structure in which a positive electrode active material layer coated on a current collector and a negative electrode active material layer coated on a current collector face each other with a separator in between, a structure is provided that prevents electrical short circuits between current collectors by covering as much as possible the areas of the current collector where the active material layer is not coated with the sealing portion, and by interposing a sealing portion in addition to the separator between the areas of the current collector where the active material layer is not coated with the sealing portion. Such a sealing portion is welded to the surface of the current collector, and as a result, it expands / contracts together with the current collector when the temperature changes, which is advantageous in that it does not affect the active material layer. Furthermore, the configuration of the present invention is advantageous in that it can be achieved in substance simply by widening the welding area of ​​the sealing portion for holding the current collector, and there is no increase in the number of parts.

[0011] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view of a part of the stacked structure in a secondary battery to which this embodiment is applied. [Explanation of Symbols]

[0013] 1...Secondary battery, 2...Positive electrode current collector, 3...Positive electrode active material, 4...Negative electrode current collector, 5...Negative electrode active material layer, 6...Separator, 7...Outer seal, 8...Positive electrode seal section, 9...Negative electrode seal section, 10...Electrolyte inlet, v...Electrolyte filling space [Best Mode for Carrying Out the Invention]

[0014] The present invention will be described in detail below with reference to the attached figures, with reference to several preferred embodiments. In the figures, the same reference numerals indicate the same parts.

[0015] As schematically depicted in Figure 1, in the secondary battery 1 to which this embodiment is applied, a single cell C is formed by a laminated structure in which a positive electrode active material layer 3 coated on the surface of a positive electrode current collector 2 and a negative electrode active material layer 5 coated on the surface of a negative electrode current collector 4 are facing each other with a separator 6 in between, and a structure in which multiple such cells C are stacked on top of each other. In this case, the positive electrode current collector 2 of each cell C is bonded to the negative electrode current collector 4 of the cell adjacent to it on the upper side in the figure, and the negative electrode current collector 4 of each cell C is bonded to the positive electrode current collector 2 of the cell adjacent to it on the lower side in the figure, thereby forming a state in which multiple cells are connected in series. Thus, the positive electrode current collector 2 and negative electrode current collector 4 bonded to each other constitute a "bipolar electrode". Here, the positive electrode current collector 2 and the negative electrode current collector 4 may be commonly used metal foils with a thickness of several tens of micrometers, such as aluminum foil and nickel foil, respectively. The positive electrode active material layer 3 may be a mixture of commonly used positive electrode active materials such as NCM (nickel-cobalt-lithium manganese oxide) with a conductive additive such as carbon black and a binder such as PVdF (polyvinylidene fluoride), applied in a layer with a thickness of about 0.1 mm. The negative electrode active material layer 5 may be a mixture of commonly used negative electrode active materials such as natural graphite with a binder such as SBR / CMC (styrene-butadiene rubber / carboxymethylcellulose), applied in a layer with a thickness of about 0.1 mm. The separator 6 may be formed from a three-layer lithium ion permeable resin film of PP-PE-PP (polypropylene-polyethylene-polypropylene) with a thickness of about 20 μm. The space v between the positive electrode current collector 2 and the negative electrode current collector 4 is filled with electrolyte. The electrolyte is selected appropriately depending on the type of battery. For example, in the case of a non-aqueous lithium-ion battery, it may be a non-aqueous solvent in which LiPF6 (lithium hexafluoride phosphate) is dissolved at 1M in a non-aqueous solvent consisting of a 1:1:1 mixture of EC (ethyl carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate).

[0016] As shown in the figure, the active materials 3 and 5 of the positive and negative electrodes are coated on the central regions of the corresponding current collectors 2 and 4. The outer edges of the current collectors 2 and 4 are in contact with the outer seal 7, and sealing portions 8 and 9 extending inward from the outer seal 7 in the planar direction of the current collectors 2 and 4 are welded to the surfaces of the current collectors 2 and 4, respectively, thereby maintaining the spacing between the current collectors 2 and 4 in the stacking direction. The outer edge of the separator 6 may be fixed to the sealing portion 8 or 9. The outer seal 7 and the sealing portions 8 and 9 may be made of any resin with appropriate rigidity, such as polyethylene. A part of the outer seal 7 between the current collectors 2 and 4 is opened to form an injection port 10 for injecting electrolyte.

[0017] Regarding the sealing portions 8 and 9 welded to the outer surface of the current collectors 2 and 4, normally the sealing portions 8 and 9 are applied to the extent that they maintain the position of the current collectors 2 and 4. However, in this embodiment, the sealing portions 8 and 9 are welded to extend as far inward in the planar direction of the current collectors 2 and 4 as is technically possible. As can be seen from the figure, the sealing portions extend so that they are always interposed in the areas of the current collectors 2 and 4 where the active material is not coated, in addition to the separator 6 (in the figure, the sealing portion 8 extends to area a where the active material is not coated on both current collectors 2 and 4). As a result, it is expected that the sealing portions will ensure insulation between the current collectors 2 and 4 even if conductive foreign matter enters the space v or if the current collectors 2 and 4 come into close proximity due to some factor. Furthermore, since the sealing portion is welded to the current collector, it follows the expansion / contraction of current collectors 2 and 4 due to temperature changes, preventing situations where the sealing portion compresses the active material, and thus preventing peeling of the active material or a decrease in capacity.

[0018] Typically, the negative electrode active material 5 is coated onto the current collector such that its surface area is larger than that of the positive electrode active material 3. Therefore, the sealing portion 8 on the positive electrode side may be welded to extend so that its surface area is larger than that of the sealing portion 9 on the negative electrode side.

[0019] Thus, in the configuration of this embodiment described above, the seal portion welded to the current collector to hold the current collector is also used to ensure insulation between the current collectors. Even if the current collector expands / contracts due to temperature changes, the seal portion expands / contracts in accordance with it, so that it does not compress the active material layer. In the configuration of this embodiment, since the seal portion extends in the direction of the active material, there is no area where the exposed regions of the positive electrode current collector and the negative electrode current collector face each other with only a separator in between. This ensures that short circuits between the positive electrode current collector and the negative electrode current collector are prevented very well and reliably, and is also advantageous because it eliminates the need to prepare a separate insulating material between the current collectors.

[0020] While the above description is made in relation to embodiments of the present invention, many modifications and changes are readily possible for those skilled in the art, and it will be clear that the present invention is not limited to the embodiments illustrated above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A secondary battery having a laminated structure in which a positive electrode active material layer coated on a positive electrode current collector and a negative electrode active material layer coated on a negative electrode current collector are facing each other with a separator in between, and an electrolyte is injected between the positive electrode current collector and the negative electrode current collector, wherein an outer seal surrounds the periphery of the positive electrode current collector and the negative electrode current collector to maintain the distance between them, and a seal portion is welded to the positive electrode active material layer and the negative electrode active material layer on the respective surfaces of the positive electrode current collector and the negative electrode current collector, and the seal portion welded to the surface of either the positive electrode current collector or the negative electrode current collector is interposed between the area of ​​the positive electrode active material layer on the positive electrode current collector and the area of ​​the negative electrode active material layer on the negative electrode current collector that is not coated.

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