Secondary battery

Abstract

This secondary battery comprises: an insulating film that is a porous body and that has a first main surface and a second main surface on the reverse side from the first main surface; a positive electrode current collector that is a porous body and is provided on the first main surface of the insulating film; a positive electrode active material layer that is provided on the positive electrode current collector; a negative electrode current collector that is a porous body and is provided on the second main surface of the insulating film; and a negative electrode active material layer that is provided on the negative electrode current collector. The negative electrode current collector has a first side surface, a second side surface positioned on the opposite side of the first side surface in a first direction parallel to the second main surface of the insulating film, and a third side surface and a fourth side surface positioned between the first side surface and the second side surface. The negative electrode active material layer covers at least one of the first side surface, the second side surface, the third side surface, and the fourth side surface of the negative electrode current collector.

Description

secondary battery

[0001] This invention relates to a secondary battery.

[0002] Non-patent documents 1 and 2 describe that increasing the thickness of the electrodes of a secondary battery increases the proportion of active material in the battery, thereby improving battery capacity and energy density.

[0003] Yudi Kuang, Chaoji Chen, Dylan Kirsch, Liangbing Hu, Thick Electrode Batteries: Principles, Opportunities, and Challenges, Advanced Energy Materials 9, 1901457 (2019).Christian Heubner, Michael Schneider, Alexander Michaelis, Diffusion-Limited C-Rate: A Fundamental Principle Quantifying the Intrinsic Limits of Li-Ion Batteries, Advanced Energy Materials 10, 1902523 (2020).

[0004] Increasing the thickness of the electrodes in a secondary battery can increase the diffusion distance of carrier ions, potentially making it difficult to pass large currents. This could also lead to a decrease in charge-discharge characteristics at high current rates.

[0005] On the other hand, thinning the electrodes of a secondary battery can cause current concentration at specific points on the current collector, potentially degrading its performance.

[0006] The present invention aims to provide a secondary battery that can suppress current concentration in the current collector.

[0007] A secondary battery according to one embodiment comprises an insulating film which is a porous material and has a first main surface and a second main surface opposite to the first main surface; a positive electrode current collector which is a porous material and is provided on the first main surface of the insulating film; a positive electrode active material layer provided on the positive electrode current collector; a negative electrode current collector which is a porous material and is provided on the second main surface of the insulating film; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode current collector has a first side surface, a second side surface located opposite to the first side surface in a first direction parallel to the second main surface of the insulating film, and a third side surface and a fourth side surface located between the first side surface and the second side surface, and the negative electrode active material layer covers at least one of the first side surface, second side surface, third side surface and fourth side surface of the negative electrode current collector.

[0008] According to the secondary battery of the present invention, current concentration in the current collector can be suppressed.

[0009] Figure 1 is an exploded perspective view showing an example of a secondary battery according to the first embodiment. Figure 2 is an enlarged cross-sectional view showing a part of the cross-section of the electrode body according to Figure 1. Figure 3 is an enlarged cross-sectional view showing the current collector assembly according to Figure 2. Figure 4 is a schematic plan view showing the configuration of a unit electrode body of the secondary battery according to the first embodiment. Figure 5 is a cross-sectional view taken along V-V' of Figure 4. Figure 6 is a schematic plan view showing the configuration of a unit electrode body of the secondary battery according to the second embodiment. Figure 7 is a cross-sectional view taken along VII-VII' of Figure 6. Figure 8 is a cross-sectional view showing an example of a secondary battery according to the third embodiment. Figure 9 is a cross-sectional view taken along IX-IX' of Figure 8. Figure 10 is a schematic plan view showing the configuration of the unit electrode body of the secondary battery according to the third embodiment when unfolded. Figure 11 is a cross-sectional view taken along XI-XI' of Figure 10.

[0010] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure. Each embodiment described in this disclosure is illustrative, and partial substitution or combination of configurations is possible between different embodiments. In modifications and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects and benefits due to similar configurations will not be mentioned sequentially for each embodiment.

[0011] (First Embodiment) Figure 1 is an exploded perspective view showing an example of a secondary battery according to the first embodiment. The secondary battery 1 shown in Figure 1 is a laminate-type lithium-ion secondary battery. As shown in Figure 1, the secondary battery 1 comprises a battery element 20, an outer casing member 30, and an adhesive material 32.

[0012] The battery element 20 is provided inside the outer casing member 30. The battery element 20 comprises an electrode body 200, a positive electrode lead 21, and a negative electrode lead 22. The positive electrode lead 21 is a terminal drawn out from the positive electrode current collector 212 (described later) to the outside of the outer casing member 30. In other words, the positive electrode lead 21 is the terminal that becomes the positive electrode of the secondary battery 1. In Figure 1, the positive electrode lead 21 is provided on the end face of the electrode body 200. The negative electrode lead 22 is a terminal drawn out from the inside of the negative electrode current collector 213 (described later) to the outside of the outer casing member 30. In other words, the negative electrode lead 22 is the terminal that becomes the negative electrode of the secondary battery 1. In Figure 1, the negative electrode lead 22 is provided on the end face of the electrode body 200 opposite to the positive electrode lead 21. Details of the electrode body 200 will be described later.

[0013] The exterior member 30 is a case in which the battery element 20 is housed. The exterior member 30 includes two exterior sheets 30a and 30b. The exterior sheets 30a and 30b comprise an insulating layer, a metal layer, and an outermost layer. In the example shown in Figure 1, the exterior sheet 30a is provided with a recess 31. By housing the battery element 20 in the recess 31 and bonding the peripheral edges of the exterior sheets 30a and 30b, the battery element 20 is housed within the exterior member 30.

[0014] The outer sheets 30a and 30b are constructed by laminating an insulating layer, a metal layer, and an outermost layer in that order, starting from the inside, i.e., the side where the battery element 20 is installed, and then bonding them together by lamination or the like. The insulating layer of the outer sheets 30a and 30b is made of a resin such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or a polyolefin resin containing ethylene or propylene as a monomer. This allows the outer sheets 30a and 30b to reduce the moisture permeability of the secondary battery 1 and improve airtightness. The metal layer of the outer sheets 30a and 30b is made of a metal sheet or foil such as aluminum, stainless steel, nickel, or iron. The outermost layer may be made of any material, but it is preferable to make it of a material with high strength against tearing and punctures, such as a resin similar to the insulating layer or nylon.

[0015] The adhesive material 32 is a component for making the outer casing member 30 airtight. The adhesive material 32 is provided between the outer casing member 30 and the positive electrode lead 21 and the negative electrode lead 22. The material of the adhesive material 32 preferably has good adhesion to the positive electrode lead 21 and the negative electrode lead 22. For example, if the positive electrode lead 21 and the negative electrode lead 22 are made of metal, the adhesive material 32 can be made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. As a result, the adhesive material 32 can seal the gap between the outer casing member 30 and the positive electrode lead 21 and the negative electrode lead 22, thereby making the inside of the outer casing member 30 airtight.

[0016] Figure 2 is an enlarged cross-sectional view showing a part of the cross-section of the electrode body according to Figure 1. More specifically, Figure 2 is a cross-sectional view showing two sets of unit electrode bodies 10 of the electrode body 200. As shown in Figure 2, each unit electrode body 10 of the electrode body 200 comprises a current collector assembly 210, a positive electrode active material layer 220, and a negative electrode active material layer 230. The electrode body 200 also has a separator 240 provided between the stacked unit electrode bodies 10. The secondary battery 1 of this embodiment is a stacked type secondary battery composed of a plurality of unit electrode bodies 10 stacked together.

[0017] In the secondary battery 1, the electrode body 200 has a structure in which a positive electrode active material layer 220, a current collector assembly 210, a negative electrode active material layer 230, a separator 240, a positive electrode active material layer 220, a current collector assembly 210, and a negative electrode active material layer 230 are laminated in this order. The positive electrode active material layer 220 and the negative electrode active material layer 230 included in the electrode body 200 are layered members for the charge and discharge reaction of the secondary battery 1 according to the first embodiment. In the following description, one of the thickness directions of the electrode body 200 may be described as the Z1 direction, and the other thickness direction of the electrode body 200 may be described as the Z2 direction. Note that the lamination order of the electrode body 200 and the current collector assembly 210 shown in FIGS. 2 and 3 is merely an example, and the lamination order may be reversed up and down.

[0018] Note that the number of unit electrode bodies 10 included in the electrode body 200 is not limited to two sets, and a plurality of three or more unit electrode bodies 10 may be laminated. In a configuration in which a plurality of three or more unit electrode bodies 10 are laminated, separators 240 are respectively disposed between the layers of the plurality of unit electrode bodies 10. Alternatively, the number of unit electrode bodies 10 included in the electrode body 200 is not limited to a plurality, and at least one set of unit electrode bodies 10 may be provided.

[0019] FIG. 3 is an enlarged cross-sectional view showing the current collector assembly according to FIG. 2. As shown in FIG. 3, the current collector assembly 210 includes an insulating film 211, a positive electrode current collector 212, and a negative electrode current collector 213. The current collector assembly 210 is composed of a sandwich-shaped, porous, and hierarchical polymer matrix coated with conductive metals of the cathode and anode having a thickness of about 1.5 μm on both sides.

[0020] The insulating film 211 is an insulating film. In the present disclosure, being insulating means being made of a material having an electric conductivity of 10 －６ S / m or less. Thereby, it is possible to suppress a short circuit between the positive electrode current collector 212 and the negative electrode current collector 213. The insulating film 211 is a porous body. In the present disclosure, being a porous body means a material having a porosity of 10% or more. Thereby, carrier ions of the secondary battery 1 such as lithium ions can pass through the insulating film 211 in the thickness direction.

[0021] The porosity of the insulating film 211 is preferably 30% or more. Thereby, the Li ion conductivity of the insulating film 211 can be improved. The porosity of the insulating film 211 is preferably 70% or less. Thereby, the strength of the insulating film 211 can be increased. The porosity of the insulating film 211 is more preferably 40% or more and 60% or less. Thereby, the Li ion conductivity of the insulating film 211 can be improved and the strength can be increased, and the electrochemical stability and mechanical properties of the secondary battery 1 can be compatible.

[0022] The average pore diameter of the insulating film 211 is preferably 10 nm or more and 50 μm or less, and more preferably a nanoporous material. Here, the nanoporous material refers to a material having an average pore diameter in the range of mesopores, that is, in the range of 10 nm or more and 50 nm or less. Thereby, it has excellent lithium ion permeability.

[0023] The insulating film 211 includes, for example, a polymer material. The insulating film 211 preferably includes at least one of polyolefin, polyimide, polyamide, polyester, cellulose, glass, and metal oxide, and particularly preferably poly(p-phenylene terephthalamide). Here, an example of the insulating film 211 containing glass is a glass filter paper such as GC-50 of ADVANTEC. Also, an example of the insulating film 211 containing metal oxide is a porous alumina film. Thereby, the strength of the insulating film 211 can be increased, and the electrochemical stability and good mechanical properties of the secondary battery 1 can be compatible.

[0024] In the present disclosure, the average pore diameter refers to a value 4V / A obtained by dividing the total pore volume V calculated by the BJH method from the pore analysis obtained by the gas adsorption method by the specific surface area A and multiplying by 4. In the present disclosure, the porosity refers to the ratio of the total pore volume V to the bulk volume, and can be calculated by porosity (%) = total pore volume V / bulk volume × 100. The bulk volume can be calculated based on dimensions such as thickness and area.

[0025] The insulating film 211 has a first main surface 211a and a second main surface 211b opposite to the first main surface 211a. The positive electrode current collector 212 is laminated on the first main surface 211a, which is the surface of the insulating film 211 in the Z2 direction.

[0026] The positive electrode current collector 212 is a porous body. The positive electrode current collector 212 has a positive electrode porous body 212a and a positive electrode conductive layer 212b. The positive electrode porous body 212a is a porous body laminated on the first main surface 211a of the insulating film 211. Preferably, the average pore diameter of the positive electrode porous body 212a is 10 nm or more. This ensures excellent lithium ion permeability even when the positive electrode conductive layer 212b is formed within the pores of the positive electrode porous body 212a. Furthermore, it is more preferable that the average pore diameter of the positive electrode porous body 212a is 1 μm or more. This prevents the pores of the positive electrode porous body 212a from being blocked by the positive electrode conductive layer 212b, even when a positive electrode conductive layer 212b of sufficient thickness is used to obtain sufficient conductivity.

[0027] The positive electrode porous body 212a preferably contains at least one of polyolefins, polyimides, polyamides, polyesters, cellulose, glass, and metal oxides, and includes polymers such as polyimide and poly(vinylidene-co-hexafluoropropene). In this disclosure, polyimide refers to a polymer containing imide bonds. An example of a positive electrode porous body 212a containing glass is, for example, glass filter paper such as ADVANTEC's GC-50. An example of a positive electrode porous body 212a containing a metal oxide is a porous alumina film. This makes it possible to increase the strength of the positive electrode porous body 212a and achieve both electrochemical stability and good mechanical properties of the secondary battery 1.

[0028] The positive electrode conductive layer 212b is a conductive coating that covers the surface of the pores of the positive electrode porous body 212a. In this disclosure, conductivity means that the electrical conductivity is 10 ４ This refers to being made of a material with a density of S / m or greater. The positive electrode conductive layer 212b includes a conductor such as aluminum or stainless steel.

[0029] The thickness of the positive electrode conductive layer 212b is preferably 100 nm or more, and more preferably 1 μm or more. This improves electrical conductivity and reduces the internal resistance of the secondary battery 1. The thickness of the positive electrode conductive layer 212b is preferably 10 μm or less, and more preferably 2 μm or less. This prevents the pores of the positive electrode porous body 212a from being blocked by the positive electrode conductive layer 212b and improves the permeability of the electrolyte. Here, the thickness of the positive electrode conductive layer 212b refers to the average thickness of the positive electrode conductive layer 212b along the normal direction of the surface of the pores of the positive electrode porous body 212a. The thickness of the positive electrode conductive layer 212b can be measured with a scanning electron microscope.

[0030] In a more desirable embodiment, the thickness of the positive electrode conductive layer 212b is 100 nm or more and 10 μm or less. The thickness of the negative electrode conductive layer 213b is 100 nm or more and 10 μm or less. This improves electrical conductivity, reduces the internal resistance of the secondary battery 1, and prevents the pores of the positive electrode porous body 212a and the negative electrode porous body 213a from being blocked by the positive electrode conductive layer 212b and the negative electrode conductive layer 213b, thereby improving the permeability of the electrolyte.

[0031] The positive electrode conductive layer 212b is less than 1 / 5 the thickness of the positive electrode active material layer 220, and the negative electrode conductive layer 213b is less than 1 / 5 the thickness of the negative electrode active material layer 230. Since the active material layer is more than five times thicker than the conductive layer, a large amount of the active material layer that can provide capacity can be created in the battery.

[0032] The negative electrode current collector 213 is a porous material. The negative electrode current collector 213 has a negative electrode porous material 213a and a negative electrode conductive layer 213b. The negative electrode current collector 213 is laminated on the second main surface 211b, which is the surface in the Z1 direction of the insulating film 211.

[0033] The negative electrode porous body 213a is a porous body laminated on the second main surface 211b of the insulating film 211. Preferably, the average pore diameter of the negative electrode porous body 213a is 10 nm or more. This ensures excellent lithium ion permeability even when the negative electrode conductive layer 213b is formed within the pores of the negative electrode porous body 213a. Furthermore, preferably, the average pore diameter of the negative electrode porous body 213a is 1 μm or more. This prevents the pores of the negative electrode porous body 213a from being blocked by the negative electrode conductive layer 213b, even when a negative electrode conductive layer 213b of sufficient thickness is used to obtain sufficient conductivity.

[0034] The negative electrode porous body 213a preferably contains at least one of polyolefins, polyimides, polyamides, polyesters, cellulose, glass, and metal oxides, and for example, it contains polymers such as polyimide and poly(vinylidene-co-hexafluoropropene). Here, an example of a negative electrode porous body 213a containing glass is glass filter paper such as ADVANTEC's GC-50. An example of a negative electrode porous body 213a containing a metal oxide is a porous alumina film. This makes it possible to increase the strength of the negative electrode porous body 213a and achieve both electrochemical stability and good mechanical properties of the secondary battery 1.

[0035] The negative electrode conductive layer 213b is a conductive coating that covers the surface of the pores of the negative electrode porous body 213a. The negative electrode conductive layer 213b contains a conductor such as copper or stainless steel. The thickness of the negative electrode conductive layer 213b is preferably 100 nm or more, and more preferably 1 μm or more. This improves electrical conductivity and reduces the internal resistance of the secondary battery 1. The thickness of the negative electrode conductive layer 213b is preferably 10 μm or less, and more preferably 2 μm or less. This prevents the pores of the negative electrode porous body 213a from being blocked by the negative electrode conductive layer 213b and improves the permeability of the electrolyte. Here, the thickness of the negative electrode conductive layer 213b refers to the average thickness of the negative electrode conductive layer 213b along the normal direction to the surface of the pores of the negative electrode porous body 213a. The thickness of the negative electrode porous body 213a can be measured with a scanning electron microscope.

[0036] As shown in FIG. 2, the positive electrode active material layer 220 contains one or more positive electrode active materials capable of occluding and releasing lithium. However, the positive electrode active material layer 220 may further contain one or more other materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 220 is not particularly limited, and specifically, it may be a coating method or the like. The thickness of the positive electrode active material layer 220 is 70 μm. The thickness of the positive electrode active material layer 220 may be 60 μm or more and 80 μm or less. Here, the N / P ratio is 1.1. The N / P ratio (N / P ratio) and the negative electrode / positive electrode capacity ratio (negative / cathode capacity ratio) refer to the ratio of the capacity of the negative electrode to the capacity of the positive electrode.

[0037] The type of the positive electrode active material is not particularly limited, and specifically, it is a lithium-containing compound or the like. A lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements. The lithium-containing compound may further contain one or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than each of the lithium and transition metal elements, and specific examples include elements belonging to any of Groups 2 to 15 in the long-period type periodic table.

[0038] The type of the lithium-containing compound is not particularly limited, and specific examples include lithium-containing compounds such as oxides, phosphate compounds, silicate compounds, and borate compounds. Specific examples of the oxide are LiNiO ２ , LiCoO ２ , LiCo ０．９８ Al ０．０１ Mg ０．０１ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , Li １．２ Mn ０．５２ Co ０．１７５ Ni ０．１ O２ Li １．１５ Mn ０．６５ Ni ０．２２ Co ０．１３ O ２ and LiMn ２ O ４ Examples include LiFePO4. ４ LiMnPO ４ LiFe ０．５ Mn ０．５ PO ４ and LiFe ０．３ Mn ０．７ PO ４ And so on.

[0039] The positive electrode binder contains one or more types of synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene-propylenediene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, and carboxymethylcellulose.

[0040] The positive electrode conductive agent contains one or more conductive materials, such as carbon materials. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjenblack. However, the conductive material may also be a metallic material or a polymer compound.

[0041] The negative electrode active material layer 230 contains one or more negative electrode active materials capable of intercalating and deintercalating lithium. However, the negative electrode active material layer 230 may further contain one or more other materials such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 230 is not particularly limited and may be one or more of the following: coating, gas phase, liquid phase, thermal spraying, and firing (sintering).

[0042] The negative electrode active material contains lithium metal. The type of negative electrode active material is not particularly limited and may include one or both of carbon materials and metallic materials. This allows for a high energy density to be obtained. Specific examples of carbon materials include easily graphitizable carbon, poorly graphitizable carbon, and graphite such as natural graphite and artificial graphite. Metallic materials are materials that contain elements capable of forming alloys with lithium, and which are either metallic elements or metalloid elements, with specific examples being silicon and tin. Metallic materials may be one or more of elements, alloys, and compounds, or they may be mixtures or materials containing two or more phases. A specific example of a metallic material is TiSi ２ and SiO ｘ (e.g., 0 < x ≤ 2).

[0043] The negative electrode binder can be made from the same material as the positive electrode binder. Similarly, the negative electrode conductive agent can be made from the same material as the positive electrode conductive agent.

[0044] The separator 240 is a film that insulates the positive electrode active material layer 220 and the negative electrode active material layer 230. The separator 240 is provided between the main surface of the positive electrode active material layer 220 and the main surface of the negative electrode active material layer 230 so that the positive electrode active material layer 220 and the negative electrode active material layer 230 do not come into direct contact with each other. In the example shown in Figure 1, the shape of the separator 240 is a rectangular sheet when viewed in plan in the thickness direction.

[0045] The material of the separator 240 is preferably electrically stable, chemically stable with respect to the positive electrode active material, negative electrode active material, and electrolyte, and is insulating. The separator 240 can be, for example, a layer containing at least one of a polymer nonwoven fabric, a porous film, and glass and ceramic fibers. The material of the separator 240 is more preferably a porous polyolefin film. This can improve the safety of the battery by providing short-circuit prevention and shutdown effects.

[0046] Note that the separator 240 is not an essential component. The separator 240 may be replaced, for example, with the current collector assembly 210.

[0047] The electrolyte is impregnated into the insulating film 211 and the separator 240. In the example shown in Figure 1, the electrolyte is filled into the space within the outer casing member 30. The electrolyte is a non-aqueous electrolyte containing an electrolyte salt and a solvent that dissolves this electrolyte salt.

[0048] Electrolyte salts include, for example, lithium perchlorate (LiClO2). ４ ), lithium hexafluoride phosphate (LiPF) ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO) ２ CF ３ ) ２ ), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO) ２ C ２ F ５ ) ２ ), lithium hexafluoroarsenate (LiAsF ６ Contains lithium salts such as ).

[0049] The solvents include, for example, lactone-based solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; carbonate ester-based solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; ether-based solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitrile-based solvents such as acetonitrile; sulforane-based solvents; phosphoric acids; phosphoric acid ester solvents; and non-aqueous solvents including pyrrolidones.

[0050] The electrolyte preferably contains at least one additive from among fluorinated carboxylic acid esters, sulfonic acid esters, sulfonic acid anhydrides, and carboxylic acid anhydrides. This promotes the formation of low-resistance SEI (Solid Electrolyte Interphase), thereby improving the charging load characteristics. Examples of fluorinated carboxylic acid esters include fluoroethylene carbonate (FEC). Examples of sulfonic acid anhydrides include propanedisulfonic acid anhydride (PSAH). Examples of sulfonic acid esters include 1,3-propanesultone. Examples of carboxylic acid anhydrides include 1,4-dioxan-2,6-dione.

[0051] Next, with reference to Figures 4 and 5, the detailed configurations of the positive electrode active material layer 220, positive electrode current collector 212, insulating film 211, negative electrode current collector 213, and negative electrode active material layer 230 constituting the unit electrode body 10 will be described. Figure 4 is a schematic plan view showing the configuration of the unit electrode body of the secondary battery according to the first embodiment. Figure 5 is a cross-sectional view taken along line V-V' in Figure 4.

[0052] As described above, the unit electrode body 10 includes an insulating film 211, a positive electrode current collector 212 which is a porous material provided on the first main surface 211a of the insulating film 211, a positive electrode active material layer 220 provided on the positive electrode current collector 212, a negative electrode current collector 213 which is a porous material provided on the second main surface 211b of the insulating film 211, and a negative electrode active material layer 230 provided on the negative electrode current collector 213.

[0053] As shown in Figure 4, in a plan view, the positive electrode active material layer 220, the positive electrode current collector 212, the insulating film 211, the negative electrode current collector 213, and the negative electrode active material layer 230 are each rectangular in shape.

[0054] In the following explanation, the direction parallel to the second main surface 211b of the insulating film 211 is defined as the X direction. The Y direction is parallel to the second main surface 211b of the insulating film 211 and perpendicular to the X direction. The Z direction is perpendicular to the second main surface 211b of the insulating film 211 and perpendicular to both the X and Y directions. Furthermore, a plan view refers to the arrangement when viewed from a direction perpendicular to the second main surface 211b of the insulating film 211 (the Z direction).

[0055] The negative electrode current collector 213 has a first side surface 213s1, a second side surface 213s2, a third side surface 213s3, and a fourth side surface 213s4. The first side surface 213s1 and the second side surface 213s2 each extend in the Y direction. In the X direction, the second side surface 213s2 is located on the opposite side from the first side surface 213s1. The third side surface 213s3 and the fourth side surface 213s4 each extend in the X direction. The third side surface 213s3 and the fourth side surface 213s4 are located between the first side surface 213s1 and the second side surface 213s2.

[0056] In the external shape of the negative electrode current collector 213 in a plan view, the lengths of the first side surface 213s1 and the second side surface 213s2 are longer than the lengths of the third side surface 213s3 and the fourth side surface 213s4. That is, the first side surface 213s1 and the second side surface 213s2 are the longer sides, and the third side surface 213s3 and the fourth side surface 213s4 are the shorter sides.

[0057] The negative electrode active material layer 230 has a first side surface 230s1, a second side surface 230s2, a third side surface 230s3, and a fourth side surface 230s4. The first side surface 230s1 and the second side surface 230s2 each extend in the Y direction. In the X direction, the second side surface 230s2 is located on the opposite side from the first side surface 230s1. The third side surface 230s3 and the fourth side surface 230s4 each extend in the X direction. The third side surface 230s3 and the fourth side surface 230s4 are located between the first side surface 230s1 and the second side surface 230s2. In the plan view of the external shape of the negative electrode active material layer 230, the first side surface 230s1 and the second side surface 230s2 are the long sides, and the third side surface 230s3 and the fourth side surface 230s4 are the short sides.

[0058] The insulating film 211 has a first side surface 211s1, a second side surface 211s2, a third side surface 211s3, and a fourth side surface 211s4. The positive electrode current collector 212 has a first side surface 212s1, a second side surface 212s2, a third side surface 212s3, and a fourth side surface 212s4. The positive electrode active material layer 220 has a first side surface 220s1, a second side surface 220s2, a third side surface 220s3, and a fourth side surface 220s4. The descriptions of each side surface of the insulating film 211, the positive electrode current collector 212, and the positive electrode active material layer 220 are the same as those of the negative electrode current collector 213 and the negative electrode active material layer 230 described above, and repeated descriptions are omitted.

[0059] In a plan view, the sides of the positive electrode active material layer 220, positive electrode current collector 212, negative electrode current collector 213, and negative electrode active material layer 230 are offset from each other. Furthermore, the sides of the insulating film 211 are located outside the positive electrode active material layer 220, positive electrode current collector 212, negative electrode current collector 213, and negative electrode active material layer 230.

[0060] In other words, the width of the insulating film 211 in the X direction is greater than the width of the positive electrode active material layer 220, the positive electrode current collector 212, the negative electrode current collector 213, and the negative electrode active material layer 230 in the X direction. The width of the insulating film 211 in the Y direction is greater than the width of the positive electrode active material layer 220, the positive electrode current collector 212, the negative electrode current collector 213, and the negative electrode active material layer 230 in the Y direction.

[0061] In Figure 4, the insulating film 211 is shown offset from the first side surface 213s1 of the negative electrode current collector 213 and the second side surface 212s2 of the positive electrode current collector 212 in order to illustrate each side surface of the insulating film 211. However, it is not limited to this, and the first side surface 211s1 of the insulating film 211 may be arranged to coincide with and overlap the first side surface 213s1 of the negative electrode current collector 213. The second side surface 211s2 of the insulating film 211 may be arranged to coincide with and overlap the second side surface 212s2 of the positive electrode current collector 212.

[0062] Next, the arrangement relationship between the negative electrode current collector 213 and the negative electrode active material layer 230 will be described. As shown in Figures 4 and 5, the first side surface 213s1 of the negative electrode current collector 213 is exposed from the negative electrode active material layer 230. The second side surface 213s2, the third side surface 213s3, and the fourth side surface 213s4 of the negative electrode current collector 213 are covered by the negative electrode active material layer 230. In other words, the first side surface 213s1 of the negative electrode current collector 213 is located outside the first side surface 230s1 of the negative electrode active material layer 230. The second side surface 213s2, the third side surface 213s3, and the fourth side surface 213s4 of the negative electrode current collector 213 are located inside the second side surface 230s2, the third side surface 230s3, and the fourth side surface 230s4 of the negative electrode active material layer 230.

[0063] As shown in Figure 5, the negative electrode current collector 213 includes a negative electrode current collector main portion 213c and a negative electrode current collector exposed portion 213d. The negative electrode current collector main portion 213c is the portion covered by the negative electrode active material layer 230 and is positioned between the second main surface 211b of the insulating film 211 and the negative electrode active material layer 230 in the Z direction. The negative electrode current collector exposed portion 213d is formed continuously with the negative electrode current collector main portion 213c and is exposed from the first side surface 230s1 of the negative electrode active material layer 230. In other words, of the negative electrode current collector 213, the negative electrode current collector main portion 213c is the portion that overlaps with the negative electrode active material layer 230, and the negative electrode current collector exposed portion 213d is the portion that does not overlap with the negative electrode active material layer 230.

[0064] The exposed portion 213d of the negative electrode current collector 213 is electrically connected to the negative electrode lead 22 (see Figure 1), which is an external terminal. More specifically, in a stacked plurality of unit electrode bodies 10, the plurality of exposed portions 213d of the negative electrode current collectors are bundled together via a conductive member (not shown) and electrically connected to a single negative electrode lead 22 (see Figure 1).

[0065] The negative electrode active material layer 230 covers and is in contact with the second side surface 213s2 of the negative electrode current collector 213. The lower end of the second side surface 230s2 of the negative electrode active material layer 230 is in contact with the second main surface 211b of the insulating film 211.

[0066] As a result, the second side surface 213s2 of the negative electrode current collector 213 is in planar contact with the negative electrode active material layer 230, which suppresses the concentration of the current flowing through the negative electrode current collector 213 during charging and discharging of the secondary battery 1 at a predetermined location on the second side surface 213s2 of the negative electrode current collector 213. More specifically, compared to a configuration in which, for example, the second side surface 230s2 of the negative electrode active material layer 230 is arranged to overlap with the second side surface 213s2 of the negative electrode current collector 213, forming the same plane as the second side surface 213s2 of the negative electrode current collector 213, and the second side surface 213s2 of the negative electrode current collector 213 is exposed from the negative electrode active material layer 230, the contact area between the second side surface 213s2 of the negative electrode current collector 213 and the negative electrode active material layer 230 is increased. As a result, in this embodiment, the concentration of current at the second side surface 213s2 of the negative electrode current collector 213 can be suppressed.

[0067] Since the negative electrode active material layer 230 covers the second side surface 213s2, which is the longer side of the negative electrode current collector 213, current concentration can be effectively suppressed.

[0068] Although not shown in Figure 5, similar to the second side surface 213s2, the negative electrode active material layer 230 covers and is in contact with the third side surface 213s3 and the fourth side surface 213s4 of the negative electrode current collector 213. In addition, the lower ends of the third side surface 230s3 and the fourth side surface 230s4 of the negative electrode active material layer 230 are in contact with the second main surface 211b of the insulating film 211. As a result, in this embodiment, current concentration on the second side surface 213s2, the third side surface 213s3 and the fourth side surface 213s4 of the negative electrode current collector 213 can be suppressed during charging and discharging of the secondary battery 1.

[0069] Next, the arrangement relationship between the positive electrode current collector 212 and the positive electrode active material layer 220 will be explained. The second side surface 212s2 of the positive electrode current collector 212 is exposed from the positive electrode active material layer 220. In other words, the second side surface 212s2 of the positive electrode current collector 212 is located outside (to the right in Figure 4) of the second side surface 220s2 of the positive electrode active material layer 220.

[0070] The first side surface 212s1, the third side surface 212s3, and the fourth side surface 212s4 of the positive electrode current collector 212 are arranged to overlap and coincide with the first side surface 220s1, the third side surface 220s3, and the fourth side surface 220s4 of the positive electrode active material layer 220. In Figure 4, in order to illustrate each side surface of the positive electrode current collector 212 and the positive electrode active material layer 220, the first side surface 212s1, the third side surface 212s3, and the fourth side surface 212s4 of the positive electrode current collector 212 are shown offset from the first side surface 220s1, the third side surface 220s3, and the fourth side surface 220s4 of the positive electrode active material layer 220.

[0071] However, the invention is not limited to this, and the first side surface 212s1, the third side surface 212s3, and the fourth side surface 212s4 of the positive electrode current collector 212 may be covered with the positive electrode active material layer 220.

[0072] As shown in Figure 5, the positive electrode current collector 212 includes a positive electrode current collector main portion 212c and a positive electrode current collector exposed portion 212d. The positive electrode current collector main portion 212c is the portion covered by the positive electrode active material layer 220 and is positioned between the first main surface 211a of the insulating film 211 and the positive electrode active material layer 220 in the Z direction. The positive electrode current collector exposed portion 212d is formed continuously with the positive electrode current collector main portion 212c and is exposed from the second side surface 220s2 of the positive electrode active material layer 220. The positive electrode current collector exposed portion 212d is located on the opposite side from the negative electrode current collector exposed portion 213d in the X direction. In other words, of the positive electrode current collector 212, the main part 212c of the positive electrode current collector is the part that overlaps with the positive electrode active material layer 220, and the exposed part 212d of the positive electrode current collector is the part that does not overlap with the positive electrode active material layer 220.

[0073] The exposed portion 212d of the positive electrode current collector 212 is electrically connected to the positive electrode lead 21 (see Figure 1), which is an external terminal. More specifically, in a stacked plurality of unit electrode bodies 10, the plurality of exposed portions 212d of the positive electrode current collectors are bundled together via a conductive member (not shown) and electrically connected to a single positive electrode lead 21 (see Figure 1).

[0074] Focusing on the arrangement of the negative electrode current collector 213 and negative electrode active material layer 230, and the positive electrode current collector 212 and positive electrode active material layer 220, the width of the positive electrode active material layer 220 in the X direction is smaller than the width of the negative electrode active material layer 230 in the X direction. In a plan view, the first side surface 220s1 and the second side surface 220s2 of the positive electrode active material layer 220 are located between the first side surface 230s1 and the second side surface 230s2 of the negative electrode active material layer 230.

[0075] The width of the positive electrode active material layer 220 in the Y direction is smaller than the width of the negative electrode active material layer 230 in the Y direction. In a plan view, the third side surface 220s3 and the fourth side surface 220s4 of the positive electrode active material layer 220 are located between the third side surface 230s3 and the fourth side surface 230s4 of the negative electrode active material layer 230.

[0076] As shown in Figure 5, the positions in the X direction of the first side surface 211s1 and the second side surface 211s2 of the insulating film 211 are denoted as IL and IR, respectively. The positions in the X direction of the first side surface 213s1 and the second side surface 213s2 of the negative electrode current collector 213 are denoted as CuL and CuR, respectively. The positions in the X direction of the first side surface 230s1 and the second side surface 230s2 of the negative electrode active material layer 230 are denoted as AnL and AnR, respectively.

[0077] Let AlL and AlR be the positions in the X direction of the first side surface 212s1 and the second side surface 212s2 of the positive electrode current collector 212, respectively. Let CaL and CaR be the positions in the X direction of the first side surface 220s1 and the second side surface 220s2 of the positive electrode active material layer 220, respectively.

[0078] The second side surface 213s2 of the negative electrode current collector 213, the second side surface 230s2 of the negative electrode active material layer 230, and the second side surface 211s2 of the insulating film 211 satisfy the relationship given by equation (1): CuR < AnR ≤ IR ... (1)

[0079] The second side surface 220s2 of the positive electrode active material layer 220 and the second side surface 213s2 of the negative electrode current collector 213 satisfy the relationship in equation (2): CaR ≤ CuR ... (2)

[0080] The second side surface 220s2 of the positive electrode active material layer 220 and the second side surface 212s2 of the positive electrode current collector 212 satisfy the relationship in equation (3): CaR ≤ AlR ... (3)

[0081] The first side surface 213s1 of the negative electrode current collector 213, the first side surface 230s1 of the negative electrode active material layer 230, and the first side surface 220s1 of the positive electrode active material layer 220 satisfy the relationship in equation (4): CuL < AnL < CaL ... (4)

[0082] The first side surface 211s1 of the insulating film 211 and the first side surface 230s1 of the negative electrode active material layer 230 satisfy the relationship in equation (5): IL ≤ AnL ... (5)

[0083] The first side surface 212s1 of the positive electrode current collector 212 and the first side surface 220s1 of the positive electrode active material layer 220 satisfy the relationship in equation (6): AlL ≤ CaL ... (6)

[0084] As described above, in the secondary battery 1 of this embodiment, the insulating film 211, positive electrode current collector 212, and negative electrode current collector 213 of the current collector assembly 210 are porous materials. This allows carrier ions such as lithium ions to pass through the stacking direction of the current collector assembly 210. In other words, during charging and discharging of the secondary battery 1, carrier ions can move between the positive electrode active material layer 220 and the negative electrode active material layer 230 not only through the separator 240 but also through the current collector assembly 210.

[0085] Therefore, the secondary battery 1 of this embodiment can shorten the diffusion distance of carrier ions in the charge-discharge reaction, and the current that can flow under diffusion resistance-limited rate is increased. As a result, even when charging and discharging is performed at a high rate with a large current, the uneven distribution of lithium ion concentration between the positive and negative electrodes can be suppressed, thereby suppressing the generation of irreversible capacity due to the generation of metallic lithium, etc. Therefore, the secondary battery 1 having the current collector assembly 210 according to the first embodiment can improve the charge-discharge characteristics at high rates.

[0086] Furthermore, the insulating film 211, positive electrode current collector 212, positive electrode active material layer 220, negative electrode current collector 213, and negative electrode active material layer 230 are arranged to satisfy the relationships of equations (1) to (6) described above. In a plan view, the negative electrode active material layer 230 and the negative electrode current collector 213 each have a region that overlaps with the positive electrode active material layer 220 and a region that does not overlap. This makes it possible to suppress the concentration of current at a predetermined location (for example, the second side surface 213s2) of the negative electrode current collector 213 during charging and discharging of the secondary battery 1.

[0087] The configurations of the secondary battery 1 and electrode body 200 described above are merely examples and can be modified as appropriate. For example, although the configuration described above covers the second side surface 213s2, the third side surface 213s3, and the fourth side surface 213s4 of the negative electrode current collector 213, it is not limited to this configuration. The negative electrode active material layer 230 may cover at least one of the sides of the negative electrode current collector 213.

[0088] (Second Embodiment) Figure 6 is a schematic plan view showing the configuration of a unit electrode body of a secondary battery according to the second embodiment. Figure 7 is a cross-sectional view taken along line VII-VII' of Figure 6. As shown in Figures 6 and 7, the secondary battery 1A according to the second embodiment differs from the first embodiment in that the exposed portion 212Ad of the positive electrode current collector is located on the same side as the exposed portion 213Ad of the negative electrode current collector.

[0089] As shown in Figure 6, the exposed portion 213Ad of the negative electrode current collector is formed such that a part of the first side surface 213As1 of the negative electrode current collector 213A protrudes in a direction away from the first side surface 230As1 of the negative electrode active material layer 230A (to the left in Figure 6). The portion of the first side surface 213As1 of the negative electrode current collector 213A on which the exposed portion 213Ad is not formed coincides with and overlaps with the first side surface 230As1 of the negative electrode active material layer 230A.

[0090] The exposed portion 212Ad of the positive electrode current collector is formed such that a part of the first side surface 212As1 of the positive electrode current collector 212A protrudes away from the first side surface 220As1 of the positive electrode active material layer 220A. The portion of the first side surface 212As1 of the positive electrode current collector 212A on which the exposed portion 212Ad is not formed coincides with and overlaps with the first side surface 220As1 of the positive electrode active material layer 220A.

[0091] The exposed portion 213Ad of the negative electrode current collector and the exposed portion 212Ad of the positive electrode current collector are positioned on the same side with respect to the negative electrode active material layer 230A and the positive electrode active material layer 220A. In a plan view, the exposed portion 212Ad of the positive electrode current collector and the exposed portion 213Ad of the negative electrode current collector are positioned so as not to overlap with each other and are adjacent to each other in the Y direction.

[0092] In this embodiment, since the exposed portion 213Ad of the negative electrode current collector and the exposed portion 212Ad of the positive electrode current collector are provided on the same side, the overall length in the X direction of the negative electrode current collector 213A and the positive electrode current collector 212A, including the exposed portion 213Ad and the exposed portion 212Ad, can be shortened compared to the first embodiment. In other words, the overall volume of the unit electrode body 10A, that is, the volume in the region where the negative electrode active material layer 230A, the negative electrode current collector 213A, the positive electrode current collector 212A, and the positive electrode active material layer 220A overlap, can be reduced. Therefore, the secondary battery 1A of this embodiment can improve the volumetric energy density.

[0093] As shown in Figures 6 and 7, in this embodiment as well, the negative electrode active material layer 230A covers and is in contact with the second side surface 213As2, the third side surface 213As3, and the fourth side surface 213As4 of the negative electrode current collector 213A. In addition, the lower ends of the second side surface 230As2, the third side surface 230As3, and the fourth side surface 230As4 of the negative electrode active material layer 230A are in contact with the second main surface 211Ab of the insulating film 211A.

[0094] This makes it possible to suppress current concentration on the second side surface 213As2, the third side surface 213As3, and the fourth side surface 213As4 of the negative electrode current collector 213A during charging and discharging of the secondary battery 1A.

[0095] Furthermore, in this embodiment as well, the width and arrangement relationship of the insulating film 211A, positive electrode active material layer 220A, positive electrode current collector 212A, negative electrode current collector 213A, and negative electrode active material layer 230A in the X direction are the same as in the first embodiment described above. That is, the insulating film 211A, positive electrode active material layer 220A, positive electrode current collector 212A, negative electrode current collector 213A, and negative electrode active material layer 230A satisfy the relationships of equations (1) to (6) described above.

[0096] (Third Embodiment) Figure 8 is a cross-sectional view showing an example of a secondary battery according to the third embodiment. Figure 9 is a cross-sectional view taken along IX-IX' in Figure 8. As shown in Figures 8 and 9, the secondary battery 1B according to the third embodiment comprises a unit electrode body 10B, conductive members 114, 115 and a housing 120. The secondary battery 1B is a wound type, constructed by winding the unit electrode body 10B. The unit electrode body 10B is wound to form the electrode body 200B of this embodiment. The unit electrode body 10B is stacked in the following order from the inner circumference to the outer circumference: positive electrode active material layer 220B, current collector assembly 210B (positive electrode current collector 212, insulating film 211, negative electrode current collector 213), and negative electrode active material layer 230B.

[0097] The housing 120 comprises a main body portion 121 and a lid portion 122. The materials of the main body portion 121 and the lid portion 122 are conductive. Examples of materials for the main body portion 121 and the lid portion 122 include iron, stainless steel, and aluminum.

[0098] The main body portion 121 is cylindrical with an opening 121a at one end. A conductive member 115 is electrically connected to the inner surface of the main body portion 121.

[0099] The lid portion 122 covers the opening 121a of the main body portion 121. The lid portion 122 is placed on the main body portion 121 in a state of electrical insulation from the main body portion 121. A conductive member 114 is electrically connected to the lid portion 122.

[0100] Note that the stacking order of the unit electrode body 10B shown in Figures 8 and 9 is merely an example, and the stacking order may be from the inner circumference to the outer circumference in the following order: negative electrode active material layer 230B, current collector assembly 210B (negative electrode current collector 213, insulating film 211, positive electrode current collector 212), and positive electrode active material layer 220B. Also, the configuration of the current collector assembly 210B is the same as in the first embodiment (see Figure 3), so a repeated explanation will be omitted.

[0101] In the following explanation, the direction along the winding center axis will be referred to as the axial direction C, the direction along the winding direction of the unit electrode body 10B with respect to the winding center axis will be referred to as the circumferential direction D1, and the direction perpendicular to the axial direction C will be referred to as the radial direction D2.

[0102] Figure 10 is a schematic plan view showing the configuration of the secondary battery according to the third embodiment when the unit electrode is unfolded. Figure 11 is a cross-sectional view taken along line XI-XI' in Figure 10.

[0103] As shown in Figure 10, the first side surface 213Bs1 and the second side surface 213Bs2 of the negative electrode current collector 213B each extend in the circumferential direction D1. In the axial direction C, the second side surface 213Bs2 is located on the opposite side from the first side surface 213Bs1. The third side surface 213Bs3 and the fourth side surface 213Bs4 each extend in the axial direction C. The third side surface 213Bs3 and the fourth side surface 213Bs4 are located between the first side surface 213Bs1 and the second side surface 213Bs2.

[0104] Compared to the first and second embodiments described above, when the unit electrode body 10B is unfolded, the axial direction C in this embodiment corresponds to the X direction (first direction), the circumferential direction D1 corresponds to the Y direction, and the radial direction D2 corresponds to the Z direction.

[0105] Each side of the negative electrode active material layer 230B (first side 230Bs1, second side 230Bs2, third side 230Bs3, fourth side 230Bs4) is arranged in correspondence with each side of the negative electrode current collector 213B. Each side of the insulating film 211B (first side 211Bs1, second side 211Bs2, third side 211Bs3, fourth side 211Bs4), each side of the positive electrode current collector 212B (first side 212Bs1, second side 212Bs2, third side 212Bs3, fourth side 212Bs4), and each side of the positive electrode active material layer 220B (first side 220Bs1, second side 220Bs2, third side 220Bs3, fourth side 220Bs4) are also arranged in correspondence with each side of the negative electrode current collector 213B.

[0106] In this embodiment as well, the first side surface 213Bs1 of the negative electrode current collector 213B, located in one axial direction C, is exposed from the negative electrode active material layer 230B. The second side surface 213Bs2 of the negative electrode current collector 213B, located in the other axial direction C, is covered by the negative electrode active material layer 230. In other words, the first side surface 213Bs1 of the negative electrode current collector 213B is located outside the first side surface 230Bs1 of the negative electrode active material layer 230B in the axial direction C. The second side surface 213Bs2 of the negative electrode current collector 213B is located inside the second side surface 230Bs2 of the negative electrode active material layer 230B.

[0107] In Figure 10, the positions of the sides are shifted to illustrate each side on the outer edge side in the circumferential direction D1. However, the third side 213Bs3 and the fourth side 213Bs4 of the negative electrode current collector 213B coincide with and overlap the third side 230Bs3 and the fourth side 230Bs4 of the negative electrode active material layer 230B, respectively.

[0108] Of the sides of the negative electrode current collector 213B, the first side 213Bs1 and the second side 213Bs2, which extend along the circumferential direction D1, are sufficiently longer than the third side 213Bs3 and the fourth side 213Bs4, which extend along the axial direction C. In this embodiment, the negative electrode active material layer 230B covers and contacts the longer second side 213Bs2 of the negative electrode current collector 213B in a planar manner. This prevents the current flowing through the negative electrode current collector 213B during charging and discharging of the secondary battery 1B from concentrating at a predetermined location on the second side 213Bs2 of the negative electrode current collector 213B.

[0109] The second side surface 212Bs2 of the positive electrode current collector 212B is exposed from the positive electrode active material layer 220B. In other words, the second side surface 212Bs2 of the positive electrode current collector 212B is located outward in the axial direction C (upward in Figure 10) compared to the second side surface 220Bs2 of the positive electrode active material layer 220B.

[0110] The first side surface 212Bs1, the third side surface 212Bs3, and the fourth side surface 212Bs4 of the positive electrode current collector 212B are arranged to overlap and coincide with the first side surface 220Bs1, the third side surface 220Bs3, and the fourth side surface 220Bs4 of the positive electrode active material layer 220B. Furthermore, on the outer edge side of the circumferential direction D1 of the unit electrode body 10B, the third side surface 212Bs3 of the positive electrode current collector 212B and the third side surface 220Bs3 of the positive electrode active material layer 220B are arranged to overlap and coincide with the third side surface 213Bs3 of the negative electrode current collector 213B and the third side surface 230Bs3 of the negative electrode active material layer 230B. The fourth side surface 212Bs4 of the positive electrode current collector 212B and the fourth side surface 220Bs4 of the positive electrode active material layer 220B are arranged to coincide with and overlap the fourth side surface 213Bs4 of the negative electrode current collector 213B and the fourth side surface 230Bs4 of the negative electrode active material layer 230B.

[0111] The third side surface 211Bs3 and the fourth side surface 211Bs4 of the insulating film 211B may also be arranged to overlap with the sides of the positive electrode current collector 212B, the positive electrode active material layer 220B, the negative electrode current collector 213B, and the negative electrode active material layer 230B.

[0112] As shown in Figure 11, the negative electrode current collector 213B includes a negative electrode current collector main portion 213Bc and a negative electrode current collector exposed portion 213Bd. In the wound unit electrode body 10B, the negative electrode current collector exposed portion 213d is electrically connected to one conductive member 114 (see Figure 8) at multiple points.

[0113] The positive electrode current collector 212B includes a positive electrode current collector main portion 212Bc and a positive electrode current collector exposed portion 212Bd. In the wound unit electrode body 10B, the positive electrode current collector exposed portion 212Bd is electrically connected to one conductive member 115 (see Figure 1) at multiple locations.

[0114] In this embodiment as well, the width and arrangement relationship of the insulating film 211B, positive electrode active material layer 220B, positive electrode current collector 212B, negative electrode current collector 213B, and negative electrode active material layer 230B in the axial direction C are the same as in the first embodiment described above. That is, the insulating film 211B, positive electrode active material layer 220B, positive electrode current collector 212B, negative electrode current collector 213B, and negative electrode active material layer 230B satisfy the relationships of equations (1) to (6) described above.

[0115] More specifically, the width of the insulating film 211B in the axial direction C is greater than the width of the positive electrode active material layer 220B, the positive electrode current collector 212B, the negative electrode current collector 213B, and the negative electrode active material layer 230B in the axial direction C. Also, the width of the insulating film 211B in the circumferential direction D1 is substantially equal to the width of the positive electrode active material layer 220B, the positive electrode current collector 212B, the negative electrode current collector 213B, and the negative electrode active material layer 230B in the circumferential direction D1.

[0116] The width of the positive electrode active material layer 220B in the axial direction C is smaller than the width of the negative electrode active material layer 230B in the axial direction C. In a plan view, the first side surface 220Bs1 and the second side surface 220Bs2 of the positive electrode active material layer 220B are located between the first side surface 230Bs1 and the second side surface 230Bs2 of the negative electrode active material layer 230B.

[0117] This makes it possible to suppress the concentration of current at a predetermined location (for example, the second side surface 213Bs2) of the negative electrode current collector 213B during charging and discharging of the secondary battery 1B.

[0118] Furthermore, the secondary battery 1B in this embodiment has a tabless structure. Specifically, the positive electrode current collector 212B and the negative electrode current collector 213B do not have tabs at their respective circumferential ends D1 that are used for connecting to external terminals. However, the secondary battery 1B is not limited to this, and may have a configuration that includes tabs for electrically connecting to external terminals.

[0119] (Example) In the secondary battery according to the example, the thickness of the negative electrode conductive layer 213b and the positive electrode conductive layer 212b is 1.5 μm. The thickness of the positive electrode porous body 212a and the negative electrode porous body 213a is 5 μm. The thickness of the insulating film 211 is 15 μm.

[0120] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0121] 1, 1A, 1B Secondary battery 10, 10A, 10B Unit electrode body 20 Battery element 21 Positive electrode lead 22 Negative electrode lead 114, 115 Conductive member 30 Outer material 30a, 30b Outer sheet 31 Recess 32 Adhesive material 200, 200B Electrode body 210, 210B Current collector assembly 211, 211A, 211B Insulating film 211a First main surface 211b, 211Ab Second main surface 212, 212A, 212B Positive electrode current collector 212a Positive electrode porous body 212b Positive electrode conductive layer 212c, 212Bc Main part of positive electrode current collector 212d, 212Ad, 212Bd Exposed part of positive electrode current collector 213, 213A, 213B Negative electrode current collector 213a Negative electrode porous body 213b Negative electrode conductive layer 213c, 213Bc Main part of negative electrode current collector 213d, 213Ad, 213Bd Exposed part of negative electrode current collector 220, 220A, 220B Positive electrode active material layer 230, 230A, 230B Negative electrode active material layer 240 Separator

Claims

1. A secondary battery comprising: an insulating film which is a porous material and has a first main surface and a second main surface opposite to the first main surface; a positive electrode current collector which is a porous material and is provided on the first main surface of the insulating film; a positive electrode active material layer provided on the positive electrode current collector; a negative electrode current collector which is a porous material and is provided on the second main surface of the insulating film; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode current collector has a first side surface, a second side surface located opposite to the first side surface in a first direction parallel to the second main surface of the insulating film, and a third side surface and a fourth side surface located between the first side surface and the second side surface, and the negative electrode active material layer covers at least one of the first side surface, the second side surface, the third side surface and the fourth side surface of the negative electrode current collector.

2. The secondary battery according to claim 1, wherein the first side surface of the negative electrode current collector is exposed from the negative electrode active material layer, and the second side surface of the negative electrode current collector is covered by the negative electrode active material layer.

3. The secondary battery according to claim 1 or claim 2, wherein the width of the positive electrode active material layer in the first direction is smaller than the width of the negative electrode active material layer in the first direction.

4. The secondary battery according to any one of claims 1 to 3, wherein the width of the insulating film in the first direction is greater than the width of the negative electrode active material layer in the first direction.

5. The secondary battery according to any one of claims 1 to 4, wherein the negative electrode active material layer covers the second side, third side, and fourth side of the negative electrode current collector.

6. A secondary battery according to any one of claims 1 to 4, having a unit electrode body formed by laminating the negative electrode active material layer, the negative electrode current collector, the insulating film, the positive electrode current collector, and the positive electrode active material layer, wherein a plurality of the unit electrode bodies are laminated.

7. A secondary battery according to any one of claims 1 to 6, wherein, in a plan view, the lengths of the first side surface and the second side surface of the negative electrode current collector are longer than the lengths of the third side surface and the fourth side surface, and the negative electrode active material layer covers at least one of the first side surface and the second side surface among the first side surface, second side surface, third side surface and fourth side surface of the negative electrode current collector.

8. A secondary battery according to any one of claims 1 to 7, wherein, in a plan view, the negative electrode active material layer and the negative electrode current collector each have a region that overlaps with the positive electrode active material layer and a region that does not overlap with it.

9. A secondary battery according to any one of claims 1 to 4, having a unit electrode body in which the negative electrode active material layer, the negative electrode current collector, the insulating film, the positive electrode current collector, and the positive electrode active material layer are laminated, wherein the unit electrode body is wound to form a wound electrode body.

10. The secondary battery according to claim 9, wherein the first direction is the direction along the winding central axis around which the unit electrode body is wound, and when the unit electrode body is unfolded, the lengths of the first side surface and the second side surface of the negative electrode current collector are longer than the lengths of the third side surface and the fourth side surface, and the negative electrode active material layer covers the first side surface or the second side surface among the first side surface, second side surface, third side surface and fourth side surface of the negative electrode current collector.

11. The secondary battery according to any one of claims 1 to 10, wherein the positive electrode current collector comprises a positive electrode porous body and a positive electrode conductive layer provided on the surface of the pores of the positive electrode porous body, the negative electrode current collector comprises a negative electrode porous body and a negative electrode conductive layer provided on the surface of the pores of the negative electrode porous body, the positive electrode conductive layer has a thickness of 1 / 5 or less of the positive electrode active material layer, and the negative electrode conductive layer has a thickness of 1 / 5 or less of the negative electrode active material layer.

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