Secondary battery

Abstract

To provide a secondary battery capable of suppressing a reduction in battery performance due to gas generation without adding a new gas diffusion layer.SOLUTION: The secondary battery includes at least one power generating element having a negative electrode current collector, a negative electrode composition layer, a separator, a positive electrode composition layer, and a positive electrode current collector in this order. The negative electrode current collector includes a first inclined part that is inclined and covers a first peripheral part of the negative electrode composition layer. The positive electrode collector includes a second inclined part that is inclined and covers a second peripheral part of the positive electrode composition layer. The negative electrode current collector and the positive electrode current collector transmit gas generated inside the power generation element through the first inclined part and the second inclined part.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Secondary batteries such as lithium ion secondary batteries that can be repeatedly charged and discharged are widely used in various technical fields such as mobile phones, personal computers, electric vehicles, hybrid vehicles, stationary power storage applications, etc. For example, a lithium ion secondary battery has a power generating element including a positive electrode, a negative electrode, and a separator, and an exterior body, and the power generating element is housed inside the exterior body.

[0003] It is known that such secondary batteries generate gases such as hydrogen, hydrocarbons, and carbon oxides inside the batteries due to the initial charging or due to changes over time, and that such gases inhibit the battery reaction and reduce the battery performance.

[0004] Patent Document 1 discloses a technology that can prevent a decrease in performance of a bipolar battery due to gas generated during initial charging by forming a seal portion and a gas diffusion layer to surround the outer periphery of the single cell layer.

[0005] However, in the secondary battery of Patent Document 1, a new gas diffusion layer must be provided, which may complicate the structure of the secondary battery. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-192587 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the problems of the prior art as described above. That is, one of the objects of the present invention is to provide a secondary battery capable of suppressing a decrease in battery performance due to gas generation without newly providing a gas diffusion layer.

Means for Solving the Problems

[0008] As a result of intensive studies based on the above findings, the inventor of the present invention has arrived at the following aspects of the invention. A secondary battery including at least one power generation element having, in order, a negative electrode current collector, a negative electrode composition layer, a separator, a positive electrode composition layer, and a positive electrode current collector, wherein the negative electrode current collector covers a first peripheral edge portion of the negative electrode composition layer and includes a first inclined portion that is inclined, the positive electrode current collector covers a second peripheral edge portion of the positive electrode composition layer and includes a second inclined portion that is inclined, and the negative electrode current collector and the positive electrode current collector allow gas generated inside the power generation element to permeate through the first inclined portion and the second inclined portion.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a secondary battery capable of suppressing a decrease in battery performance due to gas generation without newly providing a gas diffusion layer.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same members are denoted by the same reference numerals. Note that the dimensional ratios in the drawings may be exaggerated for convenience of explanation and may be different from the actual ratios. In this specification, when referring to a lithium-ion battery, it is intended to include the concept of a lithium-ion secondary battery.

[0012] First, the secondary battery of this embodiment will be described. The secondary battery is used in the form of an assembled battery in which a plurality of power generation elements are combined and modularized. The secondary battery is, for example, a lithium-ion battery. Hereinafter, an example in which the secondary battery according to this embodiment is configured as a lithium-ion battery will be described.

[0013] <First Embodiment> First, with reference to FIG. 1, the lithium-ion battery according to the first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing the lithium-ion battery 100.

[0014] As shown in FIG. 1, the lithium-ion battery 100 has a power generation element 5 including a positive electrode 1, a negative electrode 2, and a separator 30. The positive electrode 1 includes a flat positive electrode current collector 10 and a flat positive electrode composition layer 11 disposed on the upper surface of the positive electrode current collector 10 in the figure. The negative electrode 2 includes a flat negative electrode current collector 20 and a flat negative electrode composition layer 21 disposed on the upper surface of the negative electrode current collector 20 in the figure. The power generation element 5 is arranged such that the positive electrode composition layer 11 and the negative electrode composition layer 21 face each other with the separator 30 interposed therebetween, and includes the positive electrode 1, the separator 30, and the negative electrode 2 in this order. Note that FIG. 1 illustrates a case where a plurality (here, four layers) of power generation elements 5 are stacked, but the number of stacked power generation elements 5 may be a single number and is appropriately determined in consideration of battery performance such as the required battery capacity.

[0015] The positive current collector 10 and the negative current collector 20 are each a resin current collector containing a conductive resin which is a conductive polymer material. As the conductive polymer material of the resin current collector, for example, a material obtained by adding a conductive agent to a matrix resin as needed can be used. As the conductive agent constituting the conductive polymer material, the same materials as the conductive aids contained in the coated positive electrode active material described later can be preferably used. Note that the surface of the resin current collector may be appropriately metal-plated. Hereinafter, the positive current collector 10 and the negative current collector 20 are also simply referred to as current collectors.

[0016] As the matrix resin constituting the conductive polymer material, polyolefin is used. From the viewpoint of electrical stability, it is preferable to apply polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and polycycloolefin (PCO), and it is more preferable to apply polyethylene (PE), polypropylene (PP), and polymethylpentene (PMP).

[0017] When the resin current collector is constituted by adding a conductive agent to the matrix resin, this conductive agent is constituted by a conductive filler. The conductive filler includes metals [such as nickel, aluminum, stainless steel (SUS), silver, copper, and titanium], carbon-based materials [such as graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof, among which carbon-based materials are preferable. If the conductive filler is a carbon-based material, it is possible to prevent the metals derived from the negative current collector 11 and the positive current collector 15 from being mixed into the negative electrode active material and the positive electrode active material. Particularly in the positive electrode active material, it leads to suppression of characteristic deterioration.

[0018] Such a conductive filler may be used alone or in combination of two or more. Further, the conductive filler may be an alloy or metal oxide of the above-described metals. Further, as the conductive filler, a material obtained by coating a particle-based ceramic material or a resin material with a conductive material composed of the above-described metals or the like by plating or the like may also be used.

[0019] The positive electrode composition layer 11 contains a positive electrode active material. Examples of the positive electrode active material contained in the positive electrode composition layer 11 include composite oxides of lithium and transition metals. Examples of this lithium transition metal composite oxide include composite oxides in which the transition metal is one type (LiCoO 2 , LiNiO 2 , LiAlMnO 4 , LiMnO 2 and LiMn 2 O 4 , etc.), composite oxides in which there are two transition metal elements (for example, LiFeMnO 4 , LiNi 1-x Co x O 2 , LiMn 1-y Co y O 2 , LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 ), and composite oxides in which there are three or more metal elements [for example, LiM a M’ b M’’ c O 2 (M, M’ and M’’ are different transition metal elements respectively, and satisfy a + b + c = 1. For example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 ), etc.], lithium-containing transition metal phosphates (for example, LiFePO 4 , LiCoPO 4 , LiMnPO 4 and LiNiPO 4 ), transition metal oxides (for example, MnO 2 and V 2 O 5 ), transition metal sulfides (for example, MoS 2 and TiS 2) and conductive polymers (such as polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinylcarbazole), etc. can be mentioned. As the positive electrode active material 42, two or more of the above-described various lithium transition metal composite oxides, etc. may be used in combination. Note that the lithium-containing transition metal phosphate may be one in which a part of the transition metal sites is substituted with another transition metal. The positive electrode composition layer 11 can contain, in addition to the positive electrode active material, a coating resin, a conductive aid such as a metal or carbon, an electrolytic solution containing an electrolyte salt, etc. The positive electrode active material may be coated with a coating material containing a coating resin and a conductive aid. Further, the positive electrode composition layer 11 may or may not contain conductive fibers such as carbon fibers.

[0020] The negative electrode composition layer 21 contains a negative electrode active material. Examples of the negative electrode active material contained in the negative electrode composition layer 21 include carbon-based materials [graphite, hard carbon (non-graphitizable carbon), amorphous carbon, resin fired bodies (such as those obtained by firing and carbonizing phenol resins and furan resins, etc.), cokes (such as pitch coke, needle coke, and petroleum coke, etc.), and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (those in which the surface of carbon particles is coated with silicon and / or silicon carbide, those in which the surface of silicon particles or silicon oxide particles is coated with carbon and / or silicon carbide, and silicon carbide, etc.), and silicon alloys (such as silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, and silicon-tin alloy, etc.), etc.], conductive polymers (such as polyacetylene and polypyrrole, etc.), metals (such as tin, aluminum, zirconium, and titanium, etc.), metal oxides (such as titanium oxide and lithium-titanium oxide, etc.), and metal alloys (such as lithium-tin alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy, etc.), etc. and mixtures of these with carbon-based materials, etc. The negative electrode composition layer 21 can contain, in addition to the negative electrode active material, a coating resin, a conductive aid such as a metal or carbon, an electrolytic solution containing an electrolyte salt, etc. The negative electrode active material may be coated with a coating material containing a coating resin and a conductive aid. Further, the negative electrode composition layer 21 may or may not contain conductive fibers such as carbon fibers.

[0021] The separator 30 is formed of a porous sheet made of a polymer or fiber that absorbs and holds an electrolytic solution or a gel polymer electrolyte or the like. A nonwoven separator or the like may be used.

[0022] Regarding the power generation element 5 of the above-described form, it may be replaced with a power generation element of a so-called all-solid-state lithium-ion battery using a solid electrolyte instead of the liquid electrolytic solution. In this power generation element, the separator 30 is unnecessary, and the space from the positive electrode 1 to the negative electrode 2 is filled with the solid electrolyte. In the positive electrode composition layer 11, the positive electrode active material is interposed in the solid electrolyte. In the negative electrode composition layer 21, the negative electrode active material is interposed in the solid electrolyte. Details and materials of each component member constituting this power generation element are the same as those of each component element constituting the power generation element 5.

[0023] The power generation element 5 further includes an annular frame-like member 40 disposed so as to surround its side surface. The frame-like member 40 supports the separator 30 by embedding the end portion of the separator 30 therein, and the peripheral portion of the positive electrode current collector 10 and the peripheral portion of the negative electrode current collector 20 are brought into surface contact with the upper surface and the lower surface of the frame-like member 40 and then fixed respectively. By fixing the negative electrode current collector 20, the separator 30, and the positive electrode current collector 10 via the frame-like member 40, it becomes possible to firmly seal the positive electrode composition layer 11 and the negative electrode composition layer 21 without leakage to the outside. The frame-like member 40 may be made of a material having durability against the electrolytic solution, and a thermosetting polymer material is preferable. Examples of the thermosetting polymer material include epoxy resins having high durability and easy handling. Although not shown in the cross-sectional view of FIG. 1, the frame-like member 40 also extends in the front-rear direction of FIG. 1.

[0024] The high-power tab 50 is a substantially plate-shaped metal member (for example, copper), is in surface contact with a part of the current collectors of the power generation elements located in the lowermost layer and the uppermost layer, and is used to extract current from the stacked power generation elements. The current collector with which the high-power tab 50 is in surface contact is also the outermost current collector.

[0025] Further, the lithium-ion battery 100 has an exterior body 60 for housing the power generation element 5 therein. The exterior body 60 is configured to prevent liquid such as water existing outside the exterior body 60 from entering, and is a laminate film or a laminate sheet formed by coating a metal material such as aluminum with an insulating material. It is formed by covering with a laminate film or a laminate sheet and sealing under vacuum.

[0026] Note that the materials of the respective constituent members of the lithium-ion battery 100 are not limited to the above materials, and various materials are used.

[0027] In the present embodiment, the positive electrode current collector 10 and the negative electrode current collector 20 are each a resin current collector containing a conductive resin which is a conductive polymer material. The resin used for the positive electrode current collector 10 and the negative electrode current collector 20 has innumerable fine voids at the molecular level and actually allows gas to permeate. By using a resin current collector as the positive electrode current collector 10 and the negative electrode current collector 20, when gas is generated inside the power generation element 5 due to the first charge or aging, etc., the gas is released to the outside of the power generation element 5 through the surfaces of the positive electrode current collector 10 and the negative electrode current collector 20. In the present embodiment, the case of using a resin current collector as a current collector through which gas generated inside the power generation element 5 can permeate is exemplified, but any conductive material having fine voids that allow gas to permeate to a certain extent can be applied as the current collector of the present embodiment.

[0028] As described above, since the exterior body 60 is a laminate film, a laminate sheet, etc., liquid such as water existing outside the lithium-ion battery 100 does not enter the interior of the exterior body 60. Since the power generation element 5 is housed inside the exterior body 60 and the exterior body 60 is sealed, the power generation element 5 is prevented from being affected by the liquid existing outside the lithium-ion battery 100.

[0029] [First charge] Here, a case where gas is generated inside the power generation element 5 due to the first charging of the lithium-ion battery 100 will be described. The lithium-ion battery 100 is subjected to the first charging. As described above, the lithium-ion battery 100 is composed of a positive electrode containing lithium and a negative electrode that occludes lithium, and charging (discharging) occurs when lithium moves from the positive electrode to the negative electrode (or from the negative electrode to the positive electrode) through the electrolyte. During the process of the first charging, a film called an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode due to the decomposition of the electrolyte or the like.

[0030] Due to a chemical reaction such as when the SEI film is formed, gas is generated inside the power generation element 5. It is known that the amount of this gas generated increases when a predetermined voltage is applied. Even in such a case, in this embodiment, as described above, the positive electrode current collector 10 and the negative electrode current collector 20 of the power generation element 5 allow the gas generated inside the power generation element 5 to permeate. Thereby, the inhibition of the battery reaction caused by the gas generated inside the power generation element 5 is suppressed, and the battery performance is maintained.

[0031] As described above, according to this embodiment, a lithium-ion battery capable of suppressing a decrease in battery performance due to gas generation is realized.

[0032] <Second Embodiment> Hereinafter, a second embodiment of the present invention will be described. In this embodiment, in the lithium-ion battery disclosed in the first embodiment, the site where the gas generated inside the power generation element is particularly likely to be released will be described in detail.

[0033] As shown in FIG. 1, in the lithium ion battery 100, a plurality of power generation elements 5 (four layers in the illustrated example) are stacked. For example, focusing on the second layer from the top in FIG. 1, the upper surface of the positive electrode current collector 10 of the power generation element 5 is in contact with the lower surface of the negative electrode current collector 20 of the first layer power generation element 5. Similarly, the lower surface of the negative electrode current collector 20 of the power generation element 5 is in contact with the upper surface of the positive electrode current collector 10 of the third layer power generation element 5. Furthermore, these contact portions are pressed by atmospheric pressure. Among the surfaces of the current collectors of each power generation element 5 (the surface of the positive electrode current collector 10 and the surface of the negative electrode current collector 20), it is assumed that smooth gas release may be difficult in the upper and lower surface portions that are in a non-exposed state due to contact and compression.

[0034] As shown in FIG. 1, the end portions (peripheral portions, hereinafter also simply referred to as the peripheral portions of the power generation element 5) of the power generation element 5 in the direction intersecting the thickness direction of each power generation element 5 are in an exposed state without contact and compression. Specifically, the thickness of the peripheral portion of the power generation element 5 is adjusted to be tapered. The peripheral portion of the power generation element 5 is inclined such that the thickness of the power generation element 5 decreases from the center of the power generation element 5 towards the periphery in a cross-sectional view.

[0035] In the example of FIG. 1, the total thickness of the negative electrode current collector 20, the negative electrode composition layer 21, the separator 30, the positive electrode current collector 10, and the positive electrode composition layer 11 is thicker than the total thickness of the positive electrode current collector 10, the frame-like member 40, and the negative electrode current collector 20. Therefore, as shown in FIG. 1, the current collector includes an inclined slope 5a formed based on the difference in these total thicknesses. The slope 5a is an inclined portion that covers the end portion (peripheral portion) of the electrode composition layer in the direction intersecting the thickness direction of the electrode composition layer. In other words, the peripheral portion of the power generation element 5 includes the inclined slope 5a. Note that the inclination may be planar, or may be curved convexly or concavely.

[0036] Since the normal plane 5a is in an exposed state without contact and compression, it can allow gas to permeate smoothly compared to the upper and lower surface portions of the surface of the current collector of the power generation element 5. Further, although the normal plane 5a is narrower than the upper and lower surface portions of the surface of the current collector of the power generation element 5, it is provided at the entire peripheral edge (four sides) of the power generation element 5. Therefore, a sufficiently large area is secured as a gas release site for the normal plane 5a, and gas can permeate smoothly. As a result, inhibition of the battery reaction due to the gas generated inside the power generation element 5 is suppressed, and the battery performance is maintained.

[0037] As described above, according to the lithium ion battery 100 of the present embodiment, even if gas is generated inside the power generation element 5, the gas inside the power generation element 5 can be reliably released particularly at the normal plane 5a on the surface of the current collector of the power generation element 5 without newly forming or providing a mechanism or means.

[0038] [Examples] Hereinafter, examples of the lithium ion battery 100 according to the present embodiment will be described. In this example, various simulations were performed regarding permeating the gas generated inside the power generation element 5 from the peripheral edge portion (normal plane) of the surface of the current collector. Specifically, step (1) of simulating the gas component and the gas generation amount, step (2) of calculating the relationship between the charge-discharge conditions and the gas generation rate, step (3) of simulating the gas permeation rate from the resin current collector, and step (4) of calculating the initial charge conditions where the gas permeation rate > the gas generation rate were sequentially performed.

[0039] [Step (1) of Simulating the Gas Component and the Gas Generation Amount] First, the gas component and the gas generation amount were simulated. The gas components generated during the first charge were identified. When forming the SEI film, the following redox reactions represented by Chemical Formula 1 and Chemical Formula 2 occur. "EC" in Chemical Formula 1 represents ethylene carbonate, and "·" represents a radical.

[0040] According to Chemical Formula 1, it is found that lithium ethylene dicarbonate (lithium ethylene carbonate) is formed and ethylene is generated. Also, according to Chemical Formula 2, it is found that lithium carbonate and ethylene glycol are formed and carbon dioxide is generated. (Chemical Formula 1) 2EC + 2Li+ + 2e - → 2LiOCO 2 CH 2 CH 2 · → (CH 2 OCO 2 Li) 2 + C 2 H 4 ↑ (Chemical Formula 2) (CH 2 OCO 2 Li) 2 + H 2 O → Li 2 CO 3 ↓ + (CH 2 OH) 2 + CO 2 ↑

[0041] Also, the electrolysis reaction of water (described by combining the anode and cathode reactions) is as shown in Chemical Formula 3 below. According to Chemical Formula 3, it is found that hydrogen and oxygen are generated. (Chemical Formula 3) 2H 2 O → 2H 2 ↑ + O 2 ↑ From these chemical formulas, it is assumed that the gas components generated during the first charge are the four types of C 2 H 4 , CO 2 , H 2 , O 2 .

[0042] The gas generation amount was assumed to be 133.5 cc, converted from that of a lithium-ion battery different from the lithium-ion battery of the present embodiment measured in the past, and used as a reference. Also, the reaction ratio of water was assumed to be 50:50 according to (Chemical formula 2) and (Chemical formula 3). Based on the above assumptions, for each gas component C 2 H 4 , CO 2 , H 2 , O 2 , when the generation amounts of were calculated by a predetermined calculation, for 133.5 cc, H 2 was 30 cc, O 2 was 15 cc, CO 2 was 30 cc, C 2 H 4 was calculated to be 58.5 cc.

[0043] [Step (2) of estimating the relationship between charge / discharge conditions and gas generation rate] Next, the relationship between charge / discharge conditions and gas generation rate was estimated. The reaction voltage during SEI film formation was assumed to gradually react in the range of 0 V or more of the negative electrode and was set to 3.9 V or less. Also, the reaction voltage during water electrolysis was calculated with reference to the data described in "Special Feature 1 Aqueous Lithium-Ion Secondary Battery with Improved Safety by Using Aqueous Solution as Electrolyte (Toshiba Review, Vol. 75, No. 4 (July 2020))". According to that, since the potential window of water is 0 V to 1.23 V vs. SHE and the redox potential of Li is -3.04 V vs. SHE, the potential window of water with respect to Li is 3.04 V to 4.27 V vs. Li / Li+, so the reaction voltage during water electrolysis was set to 3.04 V or less.

[0044] The gas generation rate during SEI film formation was calculated as follows. CO 2 's generation rate, assuming that CO 2 generated 30 cc when reacting in the range of SOC from 0 to 75%, was 30 cc / (100 h×75%) = 0.4 cc / h when the charge rate was 0.01C, and 30 cc / (3.33 h×75%) = 12 cc / h when the charge rate was 0.3C. Also, C 2H 4 The generation rate of 2 H 4 is assumed to be 58.5 cc when the SOC reacts in the range of 0 to 75%. When the charging rate is 0.01C, it becomes 58.5 cc / (100 h × 75%) = 0.8 cc / h, and when the charging rate is 0.3C, it becomes 58.5 cc / (3.33 h × 75%) = 24 cc / h.

[0045] The gas generation rate during the electrolysis reaction of water was calculated. H 2 The generation rate of 2 H 2 is assumed to be 30 cc when the SOC reacts in the range of 0 to 20%. When the charging rate is 0.01C, it becomes 30 cc / (100 h × 20%) = 1.5 cc / h, and when the charging rate is 0.3C, it becomes 30 cc / (3.33 h × 20%) = 45 cc / h. Also, for the generation rate of 2 O 2 2 4 From the above, regarding the gas generation rate during SEI film formation and the electrolysis reaction of water, when the SOC reacts in the range of 0 to 20% and the charging rate is 0.01C, CO 2 is 0.4 cc / h, C 2 H 2 is 0.8 cc / h, H 2 is 1.5 cc / h, and O 4 is 0.75 cc / h. Summing them up, it becomes 3.45 cc / h. When the SOC reacts in the range of 20 to 75% and the charging rate is 0.01C, CO 2 is 0.4 cc / h, C 2 H 4Since it is 0.8 cc / h, the total is 1.2 cc / h when added together. When the reaction occurred in the range of SOC from 75% to 100% and the charging rate was 0.01C, it was 0 cc / h. Similarly, when the reaction occurred in the range of SOC from 0% to 20% and the charging rate was 0.3C, CO 2 was 12 cc / h, C 2 H 4 was 24 cc / h, H 2 was 45 cc / h, O 2 was 22.5 cc / h. The total was 103.5 cc / h when added together. When the reaction occurred in the range of SOC from 20% to 75% and the charging rate was 0.3C, CO 2 was 12 cc / h, C 2 H 4 was 24 cc / h. The total was 36 cc / h when added together. When the reaction occurred in the range of SOC from 75% to 100% and the charging rate was 0.3C, it was 0 cc / h.

[0047] [Step (3) of simulating the gas permeation rate from the resin current collector] Next, the gas permeation rate from the resin current collector was simulated. The permeation rate of each gas component from the polypropylene (PP) of the resin current collector material was calculated. Here, the data described in "Technical Data Thermo Scientific TM Nalgene TM Plastic Products, Physical Properties of Plastics, P3)" and "Ethylene Permeability of Commercially Available Freshness Preservation Films and Freshness Preservation of Broccoli (Journal of the Japanese Society of Refrigeration and Food Preservation, VOL.17 NO.3 1991 [Article], P2 and P4)" were used as references for the calculation. As a result, the permeation rate [cc-mil / (100 sqin·day·atm)] of each gas component from polypropylene (PP) was that O 2 was 240, N 2 was 48, CO 2 was 800, and as a predicted value, C 2 H 4 was 300.

[0048] From the permeation rates of each gas component from the above polypropylene (PP), the permeation rate of the gas component per 1 mm in terms of the material and thickness of the resin current collector was calculated for 1 h (1 hour) and a pressure difference of 1 atm. 2 As a result, the permeation rate of the gas component per 1 mm in terms of the material and thickness of the resin current collector for 1 h (1 hour) and a pressure difference of 1 atm was [cc - 50 μm / (mm 2 ·h·atm)]. For O 2 , it was 0.18, for N 2 it was 0.04, for CO 2 it was 0.59, and for C 2 H 2 it was 0.22. The sum of these was 1.02. This means that 1.02 cc of gas permeates per 1 h (1 hour) and a pressure difference of 1 atm in 1 mm of the resin current collector. That is, the gas permeation rate per 1 h (1 hour) and a pressure difference of 1 atm in 1 mm of the resin current collector was 1.02 [cc / (mm 4 ·h·atm)]. 2 For the peripheral part (normal plane) of the resin current collector surface, the area (permeation area) was calculated. 2 Figure 2 is an enlarged schematic view of the peripheral part of the power generation element 5 in Fig. 1, that is, the peripheral part (normal plane) of the current collector surface. The peripheral part is the part that becomes the periphery of the power generation element in the direction intersecting the lamination direction of the power generation element. A power generation element with a size of 400 mm in length × 400 mm in width was assumed. In Fig. 2, (10) indicates the total thickness of the positive electrode 1, separator 30, and negative electrode 2, which is 487 + 9 + 620 = 1116 μm. (11) indicates the total thickness of the positive electrode current collector 10, frame-shaped member 40, and negative electrode current collector 20, which is 250 + 400 = 650 μm. (12) indicates one side of the difference between the total thicknesses of (10) and (11), which is (1116 - 650) / 2 = 233 μm. (13) indicates the area of the normal plane, which is 233 × √2 = 330 μm. Therefore, the permeation area of the peripheral part (normal plane) of the resin current collector per one power generation element was 330 μm × 400 mm × 4 × 2 = 1056 mm 2 ².

[0049]

[0050] 2 ². ​​Also, the gas permeation rate in the permeation area of the peripheral part (normal plane) of the resin current collector was calculated. The gas permeation rate is per unit area of 1 mm of the resin current collector 2 or more, the permeation rate of the gas component per 1 h (1 hour) and per 1 atm of pressure difference [cc / (mm 2 ·h·atm)], and the permeation area of the peripheral part (normal plane) of the resin current collector, and can be calculated from 1.02 [cc / (mm 2 ·h·atm)] × 1056 mm 2 = 1077 [cc / (h·atm)]. This means that 1077 cc of gas permeates per 1 h (1 hour) and per 1 atm of pressure difference from the resin current collector of one power generation element. That is, the gas permeation rate per 1 h (1 hour) and per 1 atm of pressure difference in the permeation area of the peripheral part (normal plane) of the resin current collector surface was 1077 [cc / (h·atm)].

[0051] Then, based on the pressure difference between the inside and outside of the lithium-ion battery according to this embodiment, the gas permeation rate per 1 h (1 hour) in the permeation area of the peripheral part (normal plane) of the resin current collector surface was calculated. Regarding the pressure difference between the inside and outside of the lithium-ion battery according to this embodiment, the external pressure (outer pressure) is 1 atm which is the standard atmospheric pressure. The internal pressure (inner pressure) is about 0 atm by evacuating the inside of the exterior body and the increase in the internal pressure due to gas generation during the first charge. First, in order to calculate the increase in the internal pressure, Table 1 shows the necessary parameter information and pressure values for each generated gas component.

[0052]

Table 1

[0053] According to Table 1, the pressure values of each generated gas can be obtained from the ideal gas state equation P = mRT / MV (m = mass, R = gas constant, T = temperature, M = molecular weight, V = volume). As a result, C 2 H 4 is 1.100 [atm], CO 2 is 1.098 [atm], H 2 is 1.098 [atm], O 2It became 1.091 [atm]. When calculating their average value, the pressure value of the generated gas at a gas generation amount of 133.5 cc became approximately 1.097 [atm]. The pressure difference, that is, the difference between the internal pressure and the external pressure (internal pressure - external pressure), became (0 [atm] + 1.097 [atm]) - 1 [atm] = 0.097 [atm].

[0054] From the above, based on the pressure difference between the inside and outside of the lithium-ion battery according to this embodiment, when calculating the gas permeation rate per 1 h (1 hour) in the permeation area of the peripheral edge (normal plane) of the resin current collector surface, it became 1077 [cc / (h·atm)] × 0.097 [atm] = 104.5 cc / h. This means that 104.5 cc of gas permeates per 1 h (1 hour) from the resin current collector of one power generation element. That is, the gas permeation rate per 1 h (1 hour) in the permeation area of the peripheral edge (normal plane) of the resin current collector surface became 104.5 cc.

[0055] [Step (4) of calculating the initial charging conditions for which the gas permeation rate > gas generation rate] The initial charging conditions for which the gas permeation rate > gas generation rate were calculated. Figure 3 is a characteristic diagram showing the relationship between the gas generation rate and the gas permeation rate at the SOC and each charging rate during the first charging. In Figure 3, the broken line represents the gas permeation rate of 104.5 cc per 1 h (1 hour) in the permeation area of the peripheral edge (normal plane) of the resin current collector surface. The single-dashed line represents the gas generation rate at a charging rate of 0.01C, the two-dot chain line represents the gas generation rate at a charging rate of 0.1C, the solid line represents the gas generation rate at a charging rate of 0.3C, and the thick line represents the gas generation rate at a charging rate of 0.5C, respectively.

[0056] As described above, regarding the gas generation rate at a charging rate of 0.3C, when the SOC reacts in the range of 0 to 20%, it is 103.5 cc / h, when the SOC reacts in the range of 20 to 75%, it is 36 cc / h, and when the SOC reacts in the range of 75 to 100%, it is 0 cc / h. Also, regarding the gas generation rate at a charging rate of 0.01C, when the SOC reacts in the range of 0 to 20%, it is 3.45 cc / h, when the SOC reacts in the range of 20 to 75%, it is 1.2 cc / h, and when the SOC reacts in the range of 75 to 100%, it is 0 cc / h.

[0057] Regarding the gas permeation rate of 104.5 cc per hour at the peripheral part (normal plane) of the resin current collector surface in terms of the permeation area, when the gas generation rate is at a charging rate of 0.3C, 0.1C, or 0.01C, the initial charging condition where the gas permeation rate > the gas generation rate is satisfied. On the other hand, for the gas generation rate at a charging rate of 0.5C, when the SOC reacts in the range of 0 to 20%, it exceeds the gas permeation rate, so the initial charging condition is not satisfied. From the above, the initial charging condition where the gas permeation rate > the gas generation rate is set when the charging rate is 0.3C or less.

[0058] Therefore, if the charging rate at the first charge is set to 0.3C or less, the relationship of gas permeation rate > gas generation rate is satisfied, and gas permeates from the peripheral part (normal plane) of the resin current collector surface at a rate equal to or higher than the rate at which gas is generated inside the power generation element of the lithium-ion battery of this embodiment. Therefore, charging can be performed without gas accumulating inside the power generation element. In other words, since the permeation rate of gas permeating from the peripheral part (normal plane) of the resin current collector surface is constant, by slowly taking time with a low current value so that the charging rate is 0.3C or less, gas can be gradually generated and gas can be surely permeated from the peripheral part (normal plane) of the resin current collector surface.

[0059] As described above, according to the lithium ion battery 100 of the present embodiment, even if gas is generated inside the power generation element 5 without newly forming or providing a mechanism or means, it has been confirmed that the gas can be reliably released from the resin current collector surface, particularly from the peripheral portion (normal surface).

[0060] <Third Embodiment> Hereinafter, a third embodiment of the present invention will be described. FIG. 4 is a cross-sectional view showing a lithium ion battery according to the third embodiment.

[0061] The lithium ion battery 100 of the present embodiment has a foam material 70 made of a hard sponge-like material that fills the remaining space inside the exterior body 60 in addition to the battery configuration disclosed in the second embodiment. The remaining space is the space (gap) between the peripheral portion of each power generation element 5 and the exterior body 60, and the space (gap) between the peripheral portions of each power generation element 5. In other words, the remaining space is the space other than the region occupied by the contents (power generation element 5 and power tab 50) in the internal space covered by the exterior body 60. The lithium ion battery 100 is formed by covering the power generation element 5 with the exterior body 60 and sealing it under vacuum, and since the remaining space is decompressed, there is a risk that the peripheral portion of the power generation element 60 will be deformed due to the adhesion of the exterior body 60 to the peripheral portion. Therefore, in the present embodiment, the foam material 70 made of a hard sponge-like material is filled into the remaining space by a predetermined method.

[0062] In the present embodiment, by filling the remaining space with the foam material 70, it is possible to prevent the deformation of the peripheral portion of the power generation element 5 and to maintain the shape as the remaining space, so that the gas released from the peripheral portion of the power generation element 5 can be accommodated in the foam material 70.

[0063] As described above, in the described embodiment, the lithium ion battery according to the present embodiment has been described. However, it goes without saying that those skilled in the art can appropriately add, modify, and omit within the scope of the technical idea of the present embodiment.

[0064] The secondary battery has been described as a lithium-ion battery. However, other secondary batteries such as lead-acid batteries, all-solid-state batteries, semi-solid-state batteries, nickel-metal hydride batteries, etc. may also be used.

Industrial Applicability

[0065] By using the lithium-ion battery according to this embodiment, for example, in an electric vehicle or a hybrid vehicle, a long driving range per charge and a long life can be achieved.

Explanation of Symbols

[0066] 1 Positive electrode 2 Negative electrode 5 Power generation element 5a Normal plane 10 Positive electrode current collector 11 Positive electrode composition layer 20 Negative electrode current collector 21 Negative electrode composition layer 30 Separator 40 Frame member 50 High-voltage tab 60 Outer package 70 Foam material 100 Secondary battery (lithium-ion battery)

Claims

1. At least one power generation element having, in order, a negative electrode current collector, a negative electrode composition layer, a separator, a positive electrode composition layer, and a positive electrode current collector A secondary battery comprising: The negative electrode current collector covers a first peripheral edge portion of the negative electrode composition layer and includes a first inclined portion that is inclined; The positive electrode current collector covers a second peripheral edge portion of the positive electrode composition layer and includes a second inclined portion that is inclined; The negative electrode current collector and the positive electrode current collector allow gas generated inside the power generation element to permeate through the first inclined portion and the second inclined portion; Secondary battery.

2. Comprising an exterior body that houses the at least one power generation element, A space is provided between the first inclined portion and the exterior body and between the second inclined portion and the exterior body; The secondary battery according to claim 1.

3. The first inclined portion and the second inclined portion are inclined such that the thickness of the power generation element decreases from the center to the periphery of the power generation element; The secondary battery according to claim 1.

4. The power generation element includes a frame-shaped member provided between a peripheral edge portion of the negative electrode current collector and a peripheral edge portion of the positive electrode current collector, The total thickness of the negative electrode current collector, the negative electrode composition layer, the separator, the positive electrode current collector, and the positive electrode composition layer is greater than the total thickness of the positive electrode current collector, the frame-shaped member, and the negative electrode current collector; The secondary battery according to claim 1.

5. The gas permeation rate of the negative electrode current collector corresponding to the first inclined portion and the positive electrode current collector corresponding to the second inclined portion is greater than the gas generation rate inside the at least one power generation element during the first charge; The secondary battery according to claim 1.

6. Having, in order, a negative electrode current collector, a negative electrode composition layer, a separator, a positive electrode composition layer, and a positive electrode current collector, The negative electrode current collector covers a first peripheral edge portion of the negative electrode composition layer and includes a first inclined portion that is inclined; The positive electrode current collector covers a second peripheral edge portion of the positive electrode composition layer and includes a second inclined portion that is inclined; The negative electrode current collector and the positive electrode current collector allow gas generated inside to permeate through the first inclined portion and the second inclined portion; Power generation element.

Images