JP7207348B2 - storage device - Google Patents

Description

Disclosed herein is an electrical storage device.

Conventionally, as a power storage device, the material of the current collector part is devised in order to improve the current collection efficiency (Patent Documents 1 to 3), and the current collection structure that fixes a plurality of current collector plates and conducting wires (Patent Document 1) References 4-6), etc. are known. Further, as an electricity storage device with high energy density, a plurality of columnar negative electrodes, separation films provided so as to surround the periphery of each columnar negative electrode, and positive electrodes provided so as to fill the spaces between adjacent separation films. There is also known one provided (Patent Document 7). This secondary battery has a structure in which a columnar negative electrode surrounded by a separation membrane is arranged in a positive electrode. The positive electrode of this secondary battery is obtained by filling a space with a columnar positive electrode composed of regular hexagonal columns, and the columnar negative electrode surrounded by a separation film is arranged in the central hole of the columnar positive electrode. A secondary battery having an undercoat layer on the surface of a current collector has also been proposed (Patent Document 8). It is stated that in this secondary battery, the undercoat layer can suppress the flow of a large current in response to an instantaneous temperature rise.

JP 2019-32966 A JP 2019-33066 A JP 2018-116910 A Japanese Patent No. 6159719 JP 2014-154272 A JP 2015-103318 A JP 2018-152229 A JP 2019-36490 A

However, in Patent Documents 1 to 3, although the material of the current collector is devised, this alone causes resistance due to the current collection structure from the electrode and the current collector plate, and the current collection efficiency of the entire battery is improved. Therefore, it was necessary to devise a current collecting structure. Further, Patent Documents 4 to 6 make proposals to attempt to fix current collecting plates and conducting wires, but there are problems from the viewpoint of obtaining batteries with high weight-volume energy. In addition, in Patent Document 7, the negative electrode current collecting structure is such that one end surface of the columnar negative electrode is connected to a metal current collecting plate, so current collection cannot be performed efficiently, and weight energy density and volume The energy density was not sufficiently high. In addition, Patent Document 8 proposes to suppress the flow of a large current, but there is a drawback that current collection efficiency is reduced by introducing an undercoat layer between the electrode layer and the current collection layer. . Thus, there has been a demand for a current collecting structure capable of dealing with an increase in energy density due to efficient current collection and an internal short circuit of electrodes.

The present disclosure has been made in view of such problems, and in an electricity storage device in which a columnar negative electrode surrounded by a separation film is arranged in a positive electrode, it is possible to efficiently collect current and when an internal short circuit occurs. A main object of the present invention is to provide an electricity storage device capable of achieving both the slow discharge mechanism of (1) and (2).

As a result of intensive research to achieve the above-described object, the present inventors provided a current collecting layer with high volume resistivity on the end side of the columnar negative electrode, and provided a current collecting layer with low volume resistivity on the current collecting layer. If a current collecting layer is provided, it is possible to efficiently collect current in an electricity storage device in which a columnar negative electrode surrounded by a separation film is arranged in the positive electrode, and a slow discharge mechanism can be achieved at the time of an internal short circuit. We have found that it is possible to do so, and have completed the invention disclosed in this specification.

That is, the electricity storage device disclosed in this specification is
a plurality of columnar negative electrodes containing a negative electrode active material;
a separation film provided so as to surround each columnar negative electrode;
a positive electrode that contains a positive electrode active material and is provided so as to fill between the adjacent separation membranes;
A negative electrode current collector comprising: a layered first current collector connected to end faces of the plurality of columnar negative electrodes exposed from the positive electrode; and a layered second current collector connected to the first current collector. and
The first current collector has a higher volume resistivity than the second current collector.

INDUSTRIAL APPLICABILITY According to the present disclosure, in an electricity storage device in which a columnar negative electrode surrounded by a separation film is arranged in a positive electrode, current can be efficiently collected and a slow discharge mechanism during an internal short circuit can be compatible. The reason why such an effect is obtained is presumed as follows. For example, by providing a layered first current collector on the end face side of the columnar negative electrode exposed from the positive electrode, it is possible to connect a large number of columnar negative electrodes in parallel. In this case, the resistance of the layered first current collector can be easily controlled by controlling the film thickness. In addition, if only the first current collector with high volume resistivity has high resistance, current from all the columnar negative electrodes cannot flow within a practical voltage drop range. Therefore, it is possible to design a current collecting structure in which a second current collector having a lower resistance is arranged on the first current collector. That is, by setting the resistance between the columnar negative electrode and the second current collector so that the first current collector has a higher volume resistivity than the second current collector, the resistance is reduced by connecting the columnar negative electrodes in parallel. can be achieved. In addition, by increasing the resistance of the first current collector, it is possible to suppress the inflow of current from the peripheral electrodes and, in turn, heat generation when a short circuit occurs in any of the single cells. Therefore, in this electricity storage device, it is possible to achieve both high energy density due to efficient current collection and a slow discharge mechanism during an internal short circuit.

FIG. 2 is a schematic diagram showing an example of an electricity storage device 10; FIG. 2 is a schematic diagram showing a cross-sectional view of the electricity storage device 10. FIG. FIG. 4 is a diagram showing the relationship between the thickness of a first current collector, the area of a columnar negative electrode end face, and the resistance. FIG. 2 is an explanatory diagram of the power storage device 10 of Examples 1 and 2;

(storage device)
A power storage device of the present disclosure described in an embodiment includes a plurality of columnar negative electrodes, a separation membrane, a positive electrode, and a negative electrode collector. This electricity storage device may include a positive electrode current collector electrically connected to the positive electrode. This electricity storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo electric double layer capacitor, an alkali metal secondary battery, an alkali metal ion battery, or the like. Examples of carrier ions in an electric storage device include alkali metal ions such as lithium ions, sodium ions, and potassium ions, group 2 ions such as magnesium ions, strontium ions, and calcium ions. Moreover, the positive electrode may be present around the columnar negative electrodes, or may be filled in the space between the columnar negative electrodes. In addition, the electric storage device may have a structure in which a plurality of columnar negative electrodes are bound together while being adjacent to the positive electrode with a separation film interposed therebetween. Furthermore, in this electricity storage device, one or more of the columnar negative electrode, the positive electrode, and the separation membrane may contain an electrolytic solution. A current collecting member such as a collecting wire may be embedded in the positive electrode and the columnar negative electrode, or the current collecting member may not be provided. Here, for convenience of description, a lithium ion secondary battery using lithium ions as a carrier will be described below as a main example.

Here, the power storage device disclosed in this embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an electricity storage device 10. As shown in FIG. FIG. 2 is a schematic diagram showing a cross-sectional view of the electricity storage device 10. As shown in FIG. The electricity storage device 10 includes a columnar negative electrode 12 , a separation membrane 15 , a positive electrode 16 , a positive electrode collector 17 and a negative electrode collector 20 . A single cell 11 is composed of a columnar negative electrode 12 , a separation film 15 and a positive electrode 16 . This electricity storage device 10 includes a columnar negative electrode 12 containing a negative electrode active material, and a positive electrode 16 containing a positive electrode active material formed around the columnar negative electrode 12 with a separation film 15 interposed therebetween. The power storage device 10 may have a structure in which a plurality of unit cells 11 each including a columnar negative electrode 12 with a separation film 15 and a positive electrode 16 formed thereon are bundled together. Further, the electricity storage device 10 may have a structure in which 500 or more columnar negative electrodes 12 are bound together. Alternatively, the electricity storage device 10 may have a structure in which the columnar negative electrode 12, the separation film 15 formed on the surface of the columnar negative electrode 12, and the positive electrode 16 are filled between the columnar negative electrode 12 with the separation film 15 interposed therebetween. good.

The columnar negative electrode 12 is a member containing a negative electrode active material. Here, the term "columnar" includes not only a non-bendable thickness but also a bendable fibrous thickness. The columnar negative electrode 12 may have a columnar shape, and its cross section may be circular or polygonal. In the electricity storage device 10, a plurality of columnar negative electrodes 12 are arranged in a predetermined direction. The columnar negative electrodes 12 may be arranged in a direction different from the direction of the shortest side of the electricity storage device 10 . The columnar negative electrode 12 is covered with the separation film 15 except for the end connected to the negative electrode collector 20 . For example, the columnar negative electrode 12 may have a capacity of 1/n of the negative electrode capacity of the entire power storage device 10 , and n pieces may be connected in parallel to the negative electrode current collector 20 . The columnar negative electrode 12 preferably has a diameter D of a cross section perpendicular to the longitudinal direction of 10 μm or more, more preferably 15 μm or more, and may be 30 μm or more. The diameter D of the columnar negative electrode 12 is preferably 800 μm or less, more preferably 500 μm or less, and may be 400 μm or less. When the diameter D is 10 μm or more, the strength of the electrode structure can be ensured and stable charging and discharging can be performed. Further, when the diameter D is 800 μm or less, the moving distance of carrier ions does not become too long, and high output performance can be obtained. Moreover, when the diameter D is in the range of 10 to 500 μm, the energy density per unit volume can be further increased. Alternatively, within this range, the migration distance of carrier ions can be shortened, and charging and discharging can be performed with a larger current. The length of the columnar body in the longitudinal direction can be appropriately determined according to the use of the electricity storage device, and may be, for example, in the range of 20 mm or more and 200 mm or less. When the length of the columnar body is 20 mm or more, the battery capacity can be further increased, and when it is 200 mm or less, the electrical resistance of the negative electrode can be further reduced, which is preferable.

The columnar negative electrode 12 preferably contains a carbon material as a negative electrode active material, and may be one or more of a bundle of carbon fibers 14 and an integrated carbon material as the negative electrode active material. A carbon material has high conductivity and is preferable for the columnar negative electrode 12 . Carbon materials include, for example, one or more of graphites, cokes, vitreous carbons, non-graphitizable carbons, and pyrolytic carbons. Among these, graphites such as artificial graphite and natural graphite are preferred. Alternatively, the carbon fibers 14 having a graphite structure may be used. Such carbon fibers 14 preferably have crystals oriented in the longitudinal direction, which is the fiber direction, for example. Moreover, it is preferable that the crystals are oriented radially from the center to the outer peripheral surface side when viewed in cross section in a direction orthogonal to the longitudinal direction (fiber direction). The diameter d of the carbon fibers 14 may be, for example, 5 μm or more, 7.5 μm or more, or 10 μm or more. Also, the diameter d of the carbon fibers 11 may be in the range of 50 μm or less, 25 μm or less, or 20 μm or less. The columnar negative electrode 12 may be obtained by twisting a plurality of carbon fibers 14, or may be obtained by binding a plurality of carbon fibers 14 with a binder. The binder preferably has carrier ion conductivity, for example, polyvinylidene fluoride (PVdF), a copolymer of PVdF and hexafluoropropylene (PVdF-HFP), polymethyl methacrylate (PMMA), and copolymers of PMMA and acrylic polymers. Further, the columnar negative electrode 12 may be an integral body obtained by carbonizing a carbon material raw material formed into a columnar shape, or may be obtained by solidifying a carbonized carbon material with a binder or the like.

Alternatively, the columnar negative electrode 12 may be formed by molding a composite oxide capable of intercalating and deintercalating carrier ions into a columnar body. Examples of composite oxides include lithium-titanium composite oxides and lithium-vanadium composite oxides. The negative electrode made of this composite oxide may have a conductive component formed on at least part of its surface. This conductive component can further increase the conductivity. This conductive component is not particularly limited as long as it is a highly conductive material, and may be, for example, a metal.

The separation film 15 has ion conductivity for carrier ions (for example, lithium ions) and insulates the columnar negative electrode 12 from the positive electrode 16 , and is provided around the columnar negative electrode 12 . The separation film 15 is formed on the entire outer peripheral surface of the columnar negative electrode 12 facing the positive electrode 16 to prevent short-circuiting between the columnar negative electrode 12 and the positive electrode 16 . The separation membrane 15 may be formed, for example, by forming a self-supporting film from a raw material solution containing a resin and coating the surface of the columnar negative electrode 12 with this self-supporting film, or by immersing the columnar negative electrode 12 in the raw material solution. It may also be formed by coating the surface of the material. Examples of the resin for the separation membrane 15 include polyvinylidene fluoride (PVdF), a copolymer of PVdF and hexafluoropropylene (PVdF-HFP), polymethyl methacrylate (PMMA), and a mixture of PMMA and acrylic polymer. A copolymer etc. are mentioned. For example, in the case of a copolymer of PVdF and HFP, part of the electrolytic solution swells and gels the film, forming an ion-conducting film. The thickness of the separation membrane 15 is, for example, preferably 2 μm or more, more preferably 5 μm or more, and may be 8 μm or more. A thickness of 2 μm or more is preferable for ensuring insulation. In particular, if the thickness of the separation membrane 15 is 2 μm or more, it is easy to manufacture. Also, the thickness of the separation membrane 15 is preferably 15 μm or less, more preferably 10 μm or less. A thickness of 15 μm or less is preferable in terms of suppressing a decrease in ionic conductivity and further reducing the volume occupied in the cell. When the thickness of the separation membrane 15 is in the range of 2 to 15 μm, ionic conductivity and insulation are suitable.

Separation membrane 15 may contain an electrolytic solution that conducts ions that are carriers. Examples of the electrolytic solution include non-aqueous solvents. Solvents for the electrolytic solution include, for example, solvents for non-aqueous electrolytic solutions. Examples of the solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used singly or in combination. Specifically, the carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate, ethyl - chain carbonates such as n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate and t-butyl-i-propyl carbonate; cyclic esters such as γ-butyl lactone and γ-valerolactone; Chain esters such as methyl formate, methyl acetate, ethyl acetate and methyl butyrate; ethers such as dimethoxyethane, ethoxymethoxyethane and diethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran. sulfolane such as sulfolane and tetramethylsulfolane; and dioxolane such as 1,3-dioxolane and methyldioxolane. This electrolytic solution may be a solution in which a supporting salt containing ions that are carriers of the electric storage device 10 is dissolved. Examples of supporting salts include _LiPF6 , _LiBF4 , _LiAsF6 , _LiCF3SO3 , LiN( _CF3SO2 ) ₂ , _{LiC ( CF3SO2} ) ₃ , _LiSbF6 , _LiSiF6 , _LiAlF4 , _LiSCN , LiClO ₄ , LiCl, LiF, LiBr, LiI, LiAlCl ₄ and the like. Among them, 1 selected from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ and LiClO ₄ and organic salts such as LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ and LiC(CF ₃ SO ₂ ) ₃ From the viewpoint of electrical properties, it is preferable to use a species or a combination of two or more salts. The concentration of the supporting salt in the electrolytic solution is preferably 0.1 mol/L or more and 5 mol/L or less, more preferably 0.5 mol/L or more and 2 mol/L or less.

The positive electrode 16 contains a positive electrode active material and is provided so as to fill the space between adjacent separation films 15 . The positive electrode 16 may contain a positive electrode active material, and optionally a conductive material and a binder. The positive electrode 16 may include the columnar negative electrode 12 and have a hexagonal cross-sectional shape when the electricity storage device 10 is manufactured (see FIG. 1). With this shape, when the columnar negative electrodes 12 with the positive electrode active material formed on the outer circumference are bound, the positive electrode 16 is easily filled between the columnar negative electrodes 12, which is preferable. The positive electrode 16 may be present between the plurality of columnar negative electrodes 12, and is not limited to a hexagonal outer shape as shown in FIG. The positive electrode 16 may include a conductive material and have conductivity in itself, and may omit a current collecting member. A positive current collector 17 is connected to one of the regions of the positive electrode 16 . The positive electrode 16 may be formed, for example, by forming the separation film 15 on the periphery of the columnar negative electrode 12 and then coating the raw material of the positive electrode 16 on the periphery.

The positive electrode 16 may be made of, for example, a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and, if necessary, a binder. Examples of the positive electrode active material include materials capable of intercalating and deintercalating lithium, which is a carrier. Examples of positive electrode active materials include compounds containing lithium and a transition metal, such as oxides containing lithium and a transition metal element, and phosphate compounds containing lithium and a transition metal element. Specifically, a lithium-manganese composite oxide having a basic composition formula of Li _(1-x) MnO ₂ (0≦x≦1, etc., hereinafter the same) or Li _(1-x) Mn ₂ O ₄ , etc., basic composition A lithium cobalt composite oxide having a formula such as Li _{( 1} -x)CoO2, a lithium nickel composite oxide having a basic composition formula such as Li( _{1 -x)} NiO2, and a basic composition formula of Li _{(1-x) CoaNibMncO2 (} a>0, _b >0, _c >0, a+b+ _c =1), Li _{(1-x) CoaNibMncO4 (} 0<a<1, 0< _b <1, 1 ≤ c < 2, a + b + c = 2), etc., lithium vanadium composite oxides with a basic composition formula of LiV ₂ O ₃ , etc., basic composition formulas of V ₂ O ₅ , etc. A transition metal oxide or the like can be used. Also, a lithium iron phosphate compound having a basic compositional formula of LiFePO ₄ or the like can be used as the positive electrode active material. Among these, lithium-cobalt-nickel- _manganese composite oxides such as _{LiCo1 / 3Ni1} / _3Mn1 / _3O2 and _{LiNi0.4Co0.3Mn0.3O2 are} preferable. In addition, the "basic composition formula" means that other elements such as Al and Mg may be included.

The conductive material contained in the positive electrode 16 is not particularly limited as long as it is an electronic conductive material that does not adversely affect the battery performance. One or a mixture of two or more of carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, metals (copper, nickel, aluminum, silver, gold, etc.) can be used. The binder plays a role of binding the active material particles and the conductive material particles to keep them in a predetermined shape. Fluororesins, thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubbers, sulfonated EPDM rubbers, natural butyl rubbers (NBR), and the like can be used alone or as a mixture of two or more. Cellulose-based or styrene-butadiene rubber (SBR) aqueous dispersions, which are water-based binders, can also be used.

The content of the positive electrode active material in the positive electrode 16 is preferably larger, preferably 70% by mass or more, more preferably 80% by mass or more, based on the total mass of the positive electrode 16 . The content of the conductive material is preferably in the range of 0% by mass or more and 20% by mass or less, more preferably in the range of 0% by mass or more and 10% by mass or less with respect to the total mass of the positive electrode 16 . Within such a range, a decrease in battery capacity can be suppressed and sufficient conductivity can be imparted. Further, the content of the binder is preferably in the range of 0.1% by mass or more and 5% by mass or less with respect to the entire mass of the positive electrode 16, and is in the range of 0.2% by mass or more and 3% by mass or less. is more preferable.

The positive electrode current collector 17 is a conductive member and is electrically connected to the positive electrode 16 . This positive electrode current collector 17 is arranged on the side surface of the electricity storage device 10 . The positive electrode current collector 17 is made of, for example, carbon paper, aluminum, copper, titanium, stainless steel, nickel, iron, platinum, calcined carbon, conductive polymer, conductive glass, etc., as well as adhesion, conductivity and acid resistance. For the purpose of improving reducibility (reduction) properties, the surface of aluminum, copper, or the like may be treated with carbon, nickel, titanium, silver, platinum, gold, or the like. The shape of the positive electrode current collector 17 is not particularly limited as long as the positive electrode 16 can be connected thereto. Examples thereof include porous bodies, foams, and fiber group forming bodies.

The negative electrode collector 20 is a conductive member that collects current from the columnar negative electrode 12 and is electrically connected to the end surface 12 a of the columnar negative electrode 12 . The negative electrode current collector 20 includes a first current collector 21 and a second current collector 22 . The first current collector 21 is a layered member that is connected to the end faces 12a of the plurality of columnar negative electrodes 12 exposed from the positive electrode 16 and has a flat surface 21a. The second current collector 22 is a layered member having a flat surface 22 a connected to the flat surface 21 a of the first current collector 21 . Here, the term “layered” refers to a flat shape of one layer to which a plurality of columnar negative electrodes 12 can be connected and one or more surfaces of which may or may not be flat. It includes a film shape of 50 μm or less and a plate shape of 1000 μm or less. This first current collector 21 has a higher volume resistivity than the second current collector 22 . Since the first current collector 21 has a higher volume resistivity, for example, when a partial internal short circuit occurs, it acts as a large resistance and exhibits a slow discharge function that further suppresses rapid discharge. Since a large number of columnar negative electrodes 12 are connected in parallel with the first current collector 21, the effect on current collection is reduced during normal charging and discharging. In addition, the second current collector 22 has a lower volume resistivity, thereby realizing efficient current collection.

The first current collector 21 preferably has a volume resistivity higher than that of the second current collector 22, which is 10 times or more, more preferably 100 times or more, or 200 times or more that of the second current collector 22. It may have a volume resistivity twice or more or 500 times or more. The lower the volume resistivity of the second current collector 22 is, the better. The first current collector 21 may have the columnar negative electrodes 12 of which the number N is 500 or more connected in parallel, or may have the columnar negative electrodes 12 of 1,000 or more, or 10,000 or more connected in parallel. It can be assumed that there is Since the resistance applied to one single cell 11 via the first current collector 21 is determined according to the number N of parallel connections, the number of parallel connections of the columnar negative electrodes 12 is determined according to the desired charge/discharge characteristics. N, the volume resistivity of the first current collector 21, and the like may be appropriately set. For example, the first current collector 21 has a volume resistivity of 1.0×10 ⁻⁶ Ωm or more, and the second current collector 22 has a volume resistivity of 1.0×10 ⁻⁷ Ωm or less. may be The first current collector 21 may have a volume resistivity of 1.0×10 ⁻⁵ Ωm or more, or 1.0×10 ⁻⁴ Ωm or more. The second current collector 22 may have a volume resistivity of 5.0×10 ⁻⁸ Ωm or less, or may have a volume resistivity of 2.0×10 ⁻⁸ Ωm or less. .

The total resistance of the negative electrode current collector 20 is preferably lower, for example, preferably 1.0 mΩ or less, more preferably 0.7 mΩ or less, and even more preferably 0.1 mΩ or less. A lower total resistance of the negative electrode current collector 20 is more preferable from the viewpoint of energy density.

In the negative electrode current collector 20, the ratio t/S of the thickness t of the first current collector 21 to the area S of the end face 12a of the columnar negative electrode 12 is preferably 0.01 or less. If this t/S is smaller, the same effect as that of the first current collector 121 (see FIG. 3B described later) having the same shape as the columnar negative electrode 12 can be exhibited more easily, which is preferable. That is, when this t/S is smaller, it is possible to further suppress the resistance applied to the single cell 11 while exhibiting the slow discharge function at the time of a partial short circuit. This t/S is preferably 0.008 or less, more preferably 0.006 or less. In addition, t/S is preferably 0.001 or more or 0.002 or more from the limit of manufacturing the first current collector 21 with the thickness t.

The thickness t of the first current collector 21 is preferably thinner (smaller) than the thickness T of the second current collector 22 . A thinner thickness t of the first current collector 21 is effective in increasing the resistance. Further, a thicker thickness T of the second current collector 22 is effective in reducing the resistance. The thickness t of the first current collector 21 is preferably 1/2 or less, more preferably 1/3 or less, and 1/5 or less of the thickness T of the second current collector 22. good too. The thickness t of the first current collector 21 is, for example, preferably 75 μm or less, more preferably 50 μm or less, even more preferably 25 μm or less, and may be 20 μm or less. The thickness t may be 2 μm or more or 5 μm or more due to manufacturing limitations. Further, the thickness T of the second current collector 22 is, for example, preferably 25 μm or more, more preferably 50 μm or more, and may be 100 μm or more. From the viewpoint of energy density per volume, the thickness T is preferably thinner, and may be 1000 μm or less or 500 μm or less.

The first current collector 21 may be, for example, a solidified ink in which metal particles or carbon particles as a conductive material are dispersed, or a conductive polymer having conductivity. Examples of the metal of the conductive material include noble metals such as silver. Examples of conductive polymers include polymeric materials such as polythiophene, polyacetylene, polyaniline, and polypyrrole.
As for the material and shape of the second current collector 22, for example, any material and shape listed for the positive electrode current collector 17 can be used.

The method for producing the first current collector 21 and the second current collector 22 can be as follows. The first current collector 21 may be, for example, a film formed on the end face 12a of the columnar negative electrode 12 and crimped. Moreover, when ink or a conductive polymer is used, it can be formed by printing on the end face 12a of the columnar negative electrode 12 or the like. At this time, an insulating layer 23 (see later FIG. 4) is formed between the exposed columnar negative electrodes 12 and between the positive electrode 16 and the first current collector 21 so that the columnar negative electrodes 12 and the positive electrodes 16 are not short-circuited. You may The insulating layer 23 may be made of, for example, any of the materials listed for the isolation film 15 . For the second current collector 22, for example, the surface of the first current collector 21 may be a flat surface, and the foil of the second current collector 22 may be arranged and crimped onto the flat surface. Alternatively, the second current collector 22 may be formed by printing the material paste of the second current collector 22 on the flat surface 21 a of the first current collector 21 . If the first current collector 21 and the second current collector 22 are formed in a layered shape including a film shape and a plate shape, the structure in which the first current collector 21 and the second current collector 22 are connected to the end face 12a is compared. It can be produced by a simple and easy process.

In the electricity storage device 10, the slow discharge function of the negative electrode current collector 20 at the time of internal short circuit from the fully charged state is preferably longer from the viewpoint of safety, for example, preferably 20 minutes or more. Minutes or more are more preferable, and one hour or more is even more preferable. If this slow discharge function lasts longer, it is possible to further suppress rapid discharge at the time of a partial short circuit inside the cell, and to ensure safety. This slow discharge function may be performed for 5 hours or less from the viewpoint of energy density, such as an increase in the resistance of the electricity storage device 10 .

In the electricity storage device 10, the volumetric energy density is more preferably higher, for example, preferably 400 Wh/L or more, more preferably 500 Wh/L or more, and further preferably 600 Wh/L or more. preferable. In the electricity storage device 10, the positive/negative electrode capacity ratio (negative electrode capacity/positive electrode capacity), which is the ratio of the capacity of the negative electrode active material to the capacity of the positive electrode active material, is preferably in the range of 1.0 or more and 1.5 or less. More preferably, it is in the range of 1.2 or less. The formation thickness of the positive electrode 16 is appropriately set according to the diameter D of the columnar negative electrode 12 and the positive/negative electrode capacity ratio, and may be, for example, in the range of 5 μm or more and 50 μm or less. The formation thickness of the positive electrode 16 is, for example, the maximum thickness among the portions formed on the columnar negative electrode 12 .

In the electricity storage device 10 described in detail above, in which the columnar negative electrode 12 surrounded by the separation film 15 is arranged in the positive electrode 16, current can be efficiently collected and the slow discharge mechanism at the time of internal short circuit can be realized. can be compatible. The reason why such an effect is obtained is presumed as follows. For example, by providing the layered first current collector 21 on the end surface 12a side of the columnar negative electrode 12 exposed from the positive electrode 16, it is possible to connect a large number of columnar negative electrodes 12 in parallel. In this case, the resistance of the layered first current collector 21 can be easily controlled by controlling the film thickness. Further, if only the first current collector 21 having a high volume resistivity has a high resistance, current from all the columnar negative electrodes 12 cannot flow within a practical voltage drop range. Therefore, it is possible to design a current collecting structure in which the second current collector 22 having a lower resistance is arranged on the first current collector 21 . That is, by setting the resistance between the columnar negative electrode 12 and the second current collector 22 so that the first current collector 21 has a higher volume resistivity than the second current collector 22, the columnar negative electrode 12 Low resistance can be achieved by parallel connection. In addition, by increasing the resistance of the first current collector 21, when a short circuit occurs in any of the single cells 11, it is possible to suppress the inflow of current from the peripheral electrodes and, in turn, the heat generation. Therefore, in the electricity storage device 10, by providing the negative electrode current collecting portion 20 having a two-layer structure with different volume resistivities, it is possible to achieve both high energy density due to efficient current collection and a slow discharge mechanism during an internal short circuit. can be done.

It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

For example, in the above-described embodiment, the carrier of the electricity storage device is lithium ions, but it is not particularly limited to this, and alkali metal ions such as sodium ions and potassium ions, group 2 element ions such as calcium ions and magnesium ions can also be used. good. Moreover, the positive electrode active material may contain carrier ions. Moreover, although the electrolytic solution is a non-aqueous electrolytic solution, it may be an aqueous electrolytic solution.

In the above-described embodiment, the columnar negative electrode 12 has a columnar shape. Moreover, although the positive electrode 16 is shown to have a hexagonal columnar outer diameter, it may have a square columnar shape or a cylindrical columnar shape.

In the above-described embodiments, the positive electrode active material is a transition metal composite oxide, but is not particularly limited, and may be, for example, a carbon material used in capacitors. Examples of carbon materials include, but are not limited to, activated carbons, cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons exhibiting a high specific surface area are preferred. Activated carbon as the carbon material preferably has a specific surface area of 1000 m ² /g or more, more preferably 1500 m ² /g or more. When the specific surface area is 1000 m ² /g or more, the discharge capacity can be further increased. The specific surface area of this activated carbon is preferably 3000 m ² /g or less, more preferably 2000 m ² /g or less, for ease of production. The positive electrode is thought to store electricity by adsorbing and desorbing at least one of the anions and cations contained in the ion-conducting medium. It is also possible to store electricity by

Although not specifically described in the above-described embodiment, a connecting portion having a fuse mechanism may be provided between the first current collector 21 and the second current collector 22 . In the negative electrode current collector 20, since the resistance of the first current collector 21 is larger than the resistance of the second current collector 22, the first current collector 21 itself serves as a fuse. A slow discharge mechanism is ensured without adding a mechanism.

Examples in which the electricity storage device described above was specifically manufactured will be described below as examples.

First, the effectiveness of the layered first current collector, which has a higher resistance than the second current collector, was examined. FIG. 3 is a diagram showing the relationship between the thickness t of the first current collector 21, the area S of the end surface of the columnar negative electrode 12, and the resistance of the first current collector 21. As shown in FIG. FIG. 3A is a diagram showing the relationship of the resistance ratio to thickness t/area S, FIG. 3B is a diagram showing the configuration of an ideal first current collector 121, and FIGS. 2 is a configuration diagram of a current collector 21. FIG. As shown in FIG. 3B, in the electricity storage device 10 having a large number of columnar negative electrodes 12, high-resistance first columnar current collectors 121 are placed between the low-resistance second current collectors 22 and the columnar negative electrodes 12, respectively. , the columnar negative electrodes 12 are normally connected in parallel, so that the current load as a whole is reduced even if the high-resistance first current collector 121 is present. On the other hand, when a short circuit occurs locally, it is expected that the presence of the high-resistance first current collector 121 will produce the effect of slow discharge, in which current concentration at the short-circuited portion is greatly suppressed. However, it is extremely difficult to form the first current collector 121 having the same shape as the columnar negative electrode 12 for each of a large number (hundreds to tens of thousands) of columnar negative electrodes 12 . Therefore, as shown in FIGS. 3C and 3D, when a layered first current collector 21 including a film shape and a plate shape, which is relatively easy to manufacture, is formed, a similar structure to the electricity storage device 110 shown in FIG. 3B is formed. We examined whether it would be effective. Here, the resistance value of the first current collector 121 in FIG. Calculations were conducted to determine whether the behavior of the FIG. 3A is the calculation result. The vertical axis in FIG. 3A represents a normalized value obtained by dividing the resistance value of the layered first current collector 21 by the resistance value of the columnar first current collector 121 . The horizontal axis of FIG. 3A is a value obtained by dividing the thickness t (μm) of the first current collector 21 by the end surface area S (μm ² ) of one columnar negative electrode 12 and normalizing it as a thickness per unit area. and As shown in FIG. 3A, when the thickness t is reduced to the limit, the current flowing in the plane direction (horizontal direction in FIG. 3) of the first current collector 21 is almost eliminated, and the first current collector 121 in FIG. It shows the same resistance "1". On the other hand, as shown in FIG. 3D, as the thickness t increases, the current flowing in the planar direction of the first current collector 21 increases and the effect of the high resistance layer decreases. As shown in FIG. 3A, when t/S is 0.01 or less, the resistance value is 35% or more of that of the first current collector 121, and it is presumed that the effect of the high-resistance first current collector 21 can be obtained. was done.

(Example 1)
(Production of power storage device)
A carbon fiber bundle having a diameter D of 156.5 μm obtained by twisting and binding 400 carbon fibers (manufactured by Nippon Graphite Fiber Co., Ltd.) having a diameter d of 7 μm was used as a columnar negative electrode. This columnar negative electrode was coated with a solution of vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) dissolved in N-methylpyrrolidone (NMP) by a dipping method, and dried to obtain a film thickness of 5 μm. A polymer film as a separation film was uniformly coated on the surface of the negative electrode. Next, a positive electrode active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ), acetylene black (HS-100 manufactured by Denka) as a conductive material, and vapor grown carbon fiber (VGCF manufactured by Showa Denko) as a conductive material. , and polyvinylidene fluoride (PVdF7305 manufactured by Kureha Co., Ltd.) as a binder were blended in a mass ratio of 90:4:2:4, and N-methylpyrrolidone was added to prepare a positive electrode mixture paste. The positive electrode slurry was dip-coated on the polymer-coated negative electrode to form a positive electrode mixture layer having a thickness of 35 μm. The single cells of the negative electrode/polymer film/positive electrode mixture layer thus produced were stacked in 107 columns×495 rows (52965 cells) and pressed using a hydrostatic press to obtain a cell of 96.2 mm×24.5 mm. , height 88 mm). This electrode structure was housed in an Al case, and an insulating layer equivalent to a separation film was formed on the tip side of the columnar negative electrode exposed from the positive electrode. A layered first current collector electrically connected to the end surface of the columnar negative electrode was formed by printing so as to obtain the following. After forming the first current collector, it was heat-treated at 120°C. Then, a copper foil (thickness: 100 μm) as a second current collector was attached to the upper surface of the first current collector, and was pressed and fixed. The Al case was electrically connected to the side surface of the electrode structure and used as a positive current collector. A test cell obtained by injecting a non-aqueous electrolyte into this case and sealing the case was designated as Example 1. For the non-aqueous electrolyte, _LiPF6 was dissolved at a concentration of 1 M in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 30/40/30. I used something else. FIG. 4 is an explanatory diagram of the power storage device 10 of Examples 1 and 2. FIG. In this electricity storage device 10 , an insulating layer 23 is formed between the positive electrode 16 and the first current collector 21 .

(Examination of resistance and slow discharge mechanism of Example 1)
In Example 1, the volume resistivity of the first current collector is 1.68×10 ⁻⁴ Ωm, and the volume resistivity of the second current collector is 1.65×10 ⁻⁸ Ωm. The thickness of the first current collector was 15.65 μm, the thickness of the second current collector was 100 μm, and the total resistance of the first current collector was 1.87×10 ⁻⁶ Ω. , the total resistance of the second current collector is estimated to be 6.60×10 ⁻⁴ Ω. The total resistance of the negative electrode current collector is the sum of the total resistance of the first current collector and the total resistance of the second current collector, which is 6.62×10 ⁻⁴ Ω. The total resistance value of the negative electrode current collector satisfies 0.7 mΩ or less. On the other hand, comparing the current collectors in terms of resistance per unit cell, the resistance of the first current collector was 9.91×10 ⁻² Ω, and the total resistance of the second current collector was 6.91×10 −2 Ω. The resistance of each current collector layer was 60×10 ⁻⁴ Ω, and the magnitude of the resistance of each current collector satisfied the first current collector>>second current collector. Here, consider the case where a short circuit occurs near the contact point between the first current collector and the columnar negative electrode. Here, since the resistance of the first current collector is large enough to prevent the inflow of current from the adjacent electrode, the discharge time is different from the discharge current determined by the resistance of each columnar negative electrode of the first current collector. In between, the following relationship holds: first current collector resistance per columnar negative electrode=cell average voltage/discharge current. In Example 1, the resistance per negative electrode is 6.75×10 ⁻² Ω, so if the average cell voltage is 3.7V, the discharge current is 37.3A. Therefore, discharge time=35Ah/discharge current=35/37.3=0.937h. That is, according to the structure of the negative electrode current collector of Example 1, even when a short circuit occurs between the single cells, the presence of the high-resistance first current collector enables slow discharge for about 1 hour. It became clear that the mechanism was established.

(Example 2)
Using a columnar negative electrode made of a carbon rod with a diameter of 40 μm and a length of 88 mm, a unit cell was prepared by covering the columnar negative electrode with a 5 μm-thick separation membrane and then covering it with a 35 μm-thick positive electrode mixture in the same manner as in Example 1. 107 columns in length and 495 rows in width were bound to form an electricity storage device of length 24.5 mm×width 92.6 mm×height 88 mm. As shown in FIG. 4, a conductive polymer (poly3,4-ethylenedioxythiophene-polystyrenesulfonic acid, volume resistivity: 3×10 ⁻⁶ Ωm) was deposited on the upper surface as a first current collector. It was formed to have a thickness of 50 μm. A 100 μm-thick copper foil (volume resistivity: 1.68×10 ⁻⁸ Ωm) was placed as a second current collector on the upper surface of the first current collector, and was pressed and fixed. As in Example 1, Example 2 was an electricity storage device obtained by putting the produced electrode structure in an Al case and injecting an electrolytic solution into it. Table 1 summarizes the calculation results of Examples 1 and 2.

(Examination of resistance and slow discharge mechanism in Example 2)
The thickness of the first current collector is 50 μm, and the thickness of the second current collector is 100 μm. The total resistance of the first current collector was estimated to be 1.27×10 ⁻⁶ Ω, and the total resistance of the second current collector was estimated to be 6.60×10 ⁻⁴ Ω. The magnitude of the total resistance of the negative electrode current collector is the total resistance of the first current collector + the total resistance of the second current collector, so it is 6.61×10 ⁻⁴ Ω, which is relative to the resistance of the entire cell. It was found that the total resistance of the negative electrode current collector satisfies 0.7 mΩ or less. On the other hand, when the resistance per unit cell of each current collector is compared, the resistance of the first current collector is 6.75×10 ⁻² Ω, and the total resistance of the second current collector is 6.60×10 −2 Ω. Since it is 10 ⁻⁴ Ω, it was found that the magnitude of the resistance of each current collector satisfies the relationship of the first current collector>>second current collector. In Example 2, since the resistance per columnar negative electrode was 6.75×10 ⁻² Ω, when the average cell voltage was 3.7 V, the discharge current was 54.8 A, and the discharge time was 35 Ah/discharge. Current = 35/54.8 = 0.639. That is, according to the structure of the negative electrode current collector of Example 2, even when a short circuit occurs between single cells, the presence of the high-resistance first current collector enables a slow discharge time of about 30 minutes or longer. It was clarified that the discharge mechanism was established.

It goes without saying that the present disclosure is by no means limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

10, 110 power storage device 11 unit cell 12 negative electrode 12a end surface 14 carbon fiber 15 separation membrane 16 positive electrode 17 positive electrode current collector 20 negative electrode current collector 21, 121 first current collector 21a, 22a plane, 22 second current collector, 23 insulating layer, d, D diameter, N number, t, T thickness, S area.

Claims (9)

a plurality of columnar negative electrodes containing a negative electrode active material;
a separation film provided so as to surround each columnar negative electrode;
a positive electrode that contains a positive electrode active material and is provided so as to fill between the adjacent separation membranes;
A negative electrode current collector comprising: a layered first current collector connected to end faces of the plurality of columnar negative electrodes exposed from the positive electrode; and a layered second current collector connected to the first current collector. and
The electricity storage device , wherein the first current collector has a volume resistivity higher than that of the second current collector, and has a volume resistivity 100 times or more that of the second current collector . a plurality of columnar negative electrodes containing a negative electrode active material;
a separation film provided so as to surround each columnar negative electrode;
a positive electrode that contains a positive electrode active material and is provided so as to fill between the adjacent separation membranes;
A negative electrode current collector comprising: a layered first current collector connected to end faces of the plurality of columnar negative electrodes exposed from the positive electrode; and a layered second current collector connected to the first current collector. and
The first current collector has a higher volume resistivity than the second current collector,
The first current collector has a volume resistivity of 1.0×10 ⁻⁶ Ωm or more,
The electricity storage device, wherein the second current collector has a volume resistivity of 1.0×10 ⁻⁷ Ωm or less . 3. The electricity storage device according to claim 1 , wherein the total resistance of said negative electrode current collector is 0.7 m[Omega] or less. a plurality of columnar negative electrodes containing a negative electrode active material;
a separation film provided so as to surround each columnar negative electrode;
a positive electrode that contains a positive electrode active material and is provided so as to fill between the adjacent separation membranes;
A negative electrode current collector comprising: a layered first current collector connected to end faces of the plurality of columnar negative electrodes exposed from the positive electrode; and a layered second current collector connected to the first current collector. and
The first current collector has a higher volume resistivity than the second current collector,
An electricity storage device , wherein the negative electrode current collector has a total resistance of 0.7 mΩ or less . 5. The electricity storage device according to claim 3 , wherein a ratio t/S of the thickness t of said first current collector to the area S of the end face of said columnar negative electrode is 0.01 or less. a plurality of columnar negative electrodes containing a negative electrode active material;
a separation film provided so as to surround each columnar negative electrode;
a positive electrode that contains a positive electrode active material and is provided so as to fill between the adjacent separation membranes;
A negative electrode current collector comprising: a layered first current collector connected to end faces of the plurality of columnar negative electrodes exposed from the positive electrode; and a layered second current collector connected to the first current collector. and
The first current collector has a higher volume resistivity than the second current collector,
An electricity storage device , wherein a ratio t/S of the thickness t of the first current collector to the area S of the end face of the columnar negative electrode is 0.01 or less . The electricity storage device according to any one of claims 1 to 6 , wherein the thickness t of the first current collector is smaller than the thickness T of the second current collector. The electricity storage device according to any one of claims 1 to 7 , wherein the thickness t of the first current collector is 1/2 or less of the thickness T of the second current collector. The electricity storage device according to any one of claims 1 to 8 , wherein the first current collector has 500 or more of the columnar negative electrodes connected in parallel.

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