Secondary battery

Abstract

The present invention improves charge / discharge characteristics. This secondary battery comprises: a positive electrode active material layer; a negative electrode active material layer; a current collector assembly which is provided between the positive electrode active material layer and the negative electrode active material layer; and a separator which is provided on the opposite side of the positive electrode active material layer and / or the negative electrode active material layer from the current collector assembly. The current collector assembly is provided with: a positive electrode current collector that is in contact with the positive electrode active material layer; a negative electrode current collector that is in contact with the negative electrode active material layer; and an insulating film that is sandwiched between the positive electrode current collector and the negative electrode current collector. The insulating film is a porous body. The positive electrode current collector is a porous body or a porous plate. The negative electrode current collector is a porous body or a porous plate. When ε1 is the porosity of the insulating film, L1 is the thickness of the insulating film, ε2 is the porosity of the separator, and L2 is the thickness of the separator, ε1 ≤ ε2 is satisfied.

Description

secondary battery

[0001] This invention relates to a secondary battery.

[0002] Non-patent document 1 describes a secondary battery having an electrode body in which a positive electrode active material layer is laminated on one side of a porous current collector and a negative electrode active material layer is laminated on the other side.

[0003] Ye, Y., Xu, R., Huang, W. et al. Quadruple the rate capability of high-energy batteries through a porous current collector design. Nat Energy 9, 643-653 (2024).

[0004] When a secondary battery was manufactured using the electrode body described in Non-Patent Document 1, dendrites were generated on the negative electrode during the charge-discharge reaction, and there was a possibility that safety would be reduced because short circuits could not be suppressed.

[0005] In view of the above problems, the present invention aims to provide a secondary battery that improves safety.

[0006] A secondary battery according to one aspect of the present disclosure comprises a positive electrode active material layer, a negative electrode active material layer, a current collector assembly provided between the positive electrode active material layer and the negative electrode active material layer, and a separator provided on at least one of the positive electrode active material layer and the negative electrode active material layer opposite the current collector assembly, wherein the current collector assembly comprises a positive electrode current collector in contact with the positive electrode active material layer, a negative electrode current collector in contact with the negative electrode active material layer, and an insulating film sandwiched between the positive electrode current collector and the negative electrode current collector, wherein the insulating film is a porous material, the positive electrode current collector is a porous material or a porous plate, the negative electrode current collector is a porous material or a porous plate, and the porosity of the insulating film is ε １ The thickness of the insulating film is L １ , the porosity of the separator is ε ２ The thickness of the separator is L ２ In that case, ε １ ≤ε ２ It satisfies the condition.

[0007] According to the present invention, a secondary battery with improved safety can be provided.

[0008] Figure 1 is a 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 diagram showing the manufacturing process of the current collector assembly of the secondary battery according to the first embodiment. Figure 5 is a cross-sectional view showing an example of an electrode body of a secondary battery according to a third modification. Figure 6 is a diagram showing an enlarged view of the positive electrode current collector according to the third modification. Figure 7 is a cross-sectional view showing an example of an electrode body of a secondary battery according to a fourth modification.

[0009] Embodiments relating to this disclosure are described below. These embodiments do not limit the disclosure. The embodiments described in this disclosure are illustrative, and partial substitution or combination of configurations is possible between different embodiments. In the modifications, descriptions of aspects common to the first embodiment are omitted, and only the differences are described. In particular, similar effects due to similar configurations are not mentioned sequentially for each embodiment. Also, numerical values ​​in this disclosure include rounding.

[0010] (Secondary Battery) Figure 1 is a 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.

[0011] The battery element 20 is provided inside the outer casing member 30. As shown in Figure 1, 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. Details of the electrode body 200 will be described later.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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 a part of two sets of positive and negative electrodes of the electrode body 200. As shown in Figure 2, the electrode body 200 comprises a current collector assembly 210, a positive electrode active material layer 220, a negative electrode active material layer 230, and a separator 240. The positive electrode active material layer 220 and the negative electrode active material layer 230 contained in the electrode body 200 are layered members for the charge and discharge reaction of the secondary battery 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.

[0016] The electrode body 200 of the secondary battery 1 has a laminate in which a positive electrode active material layer 220, a current collector assembly 210, a negative electrode active material layer 230, and a separator 240 are stacked in that order. In the example of Figure 2, the electrode body 200 of the secondary battery 1 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 stacked in that order, but this is merely one example. The electrode body 200 of the secondary battery 1 may also be a structure in which multiple laminates are stacked in which a positive electrode active material layer 220, a current collector assembly 210, a negative electrode active material layer 230, and a separator 240 are stacked in that order.

[0017] Figure 3 is an enlarged cross-sectional view showing the current collector assembly according to Figure 2. As shown in Figure 3, the current collector assembly 210 comprises an insulating film 211, a positive electrode current collector 212, and a negative electrode current collector 213.

[0018] The insulating film 211 is an insulating film. In this disclosure, insulating means that the electrical conductivity is 10 －６ This refers to the material being made of a material with a density of S / m or less. This suppresses short circuits between the positive electrode current collector 212 and the negative electrode current collector 213.

[0019] The insulating film 211 is porous. In this disclosure, a porous material refers to a material with a porosity of 10% or more. This allows carrier ions of the secondary battery 1, such as lithium ions, to pass through the insulating film 211 in the thickness direction. Preferably, the porosity of the insulating film 211 is 40% or more. This increases the strength of the insulating film 211, enabling both electrochemical stability and good mechanical properties of the secondary battery 1.

[0020] In this disclosure, porosity refers to the ratio of the total pore volume V to the bulk volume, and can be calculated as follows: porosity (%) = total pore volume V / bulk volume × 100. Bulk volume can be calculated based on dimensions such as thickness or area.

[0021] The average pore size of the insulating film 211 is preferably 10 nm to 50 μm, and more preferably a nanoporous material. Here, a nanoporous material refers to a material in which the average pore size is in the mesopore range, i.e., in the range of 10 nm to 50 nm. This results in excellent lithium ion permeability. The insulating film 211 includes, for example, a polymer material.

[0022] In this disclosure, the average pore diameter refers to 4V / S, which is the value obtained by dividing the total pore volume V, calculated by the BJH method from pore analysis obtained by the gas adsorption method, by the specific surface area S and multiplying by four.

[0023] The insulating film 211 preferably contains at least one of polyolefins, polyimides, polyamides, polyesters, cellulose, glass, and metal oxides, and is particularly preferably poly(p-phenylene terephthalamide). Here, an example of an insulating film 211 containing glass is glass filter paper such as ADVANTEC's GC-50. Another example of an insulating film 211 containing metal oxide is a porous alumina film. This makes it possible to increase the strength of the insulating film 211 and achieve both electrochemical stability and good mechanical properties of the secondary battery 1.

[0024] The positive electrode current collector 212 is laminated on the first main surface 211a, which is the surface in the Z1 direction of the insulating film 211. The positive electrode current collector 212 is a porous material. The positive electrode current collector 212 has a positive electrode porous material 212a and a positive electrode conductive layer 212b.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 Z2 direction of the insulating film 211.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 of 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.

[0034] Here, in the current collector assembly 210, the thickness of the positive electrode current collector 212 is preferably smaller than the thickness of the negative electrode current collector 213. Thereby, the resistance of the negative electrode current collector 213 increases, and the dendritic crystal growth reaction in the negative electrode current collector 213 can be suppressed.

[0035] Here, in the current collector assembly 210, the porosity of the positive electrode current collector 212 is preferably larger than the porosity of the negative electrode current collector 213. Thereby, the area where the dendritic crystal growth reaction occurs in the negative electrode current collector 213 is reduced, so safety can be improved.

[0036] The positive electrode active material layer 220 contains one or more types of positive electrode active materials that can occlude and release 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 may be a coating method or the like.

[0037] The type of the positive electrode active material is not particularly limited, and specific examples thereof include lithium-containing compounds. A lithium-containing compound is a compound that contains 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 lithium and transition metal elements, and specific examples are elements belonging to any of Groups 2 to 15 in the long-form periodic table.

[0038] The type of the lithium-containing compound is not particularly limited, and specific examples of the lithium-containing compound include oxides, phosphate compounds, silicate compounds, borate compounds, and the like. Specific examples of oxides include 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 O２ LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ Li １．２ Mn ０．５２ Co ０．１７５ Ni ０．１ O ２ Li １．１５ Mn ０．６５ Ni ０．２２ Co ０．１３ O ２ and LiMn ２ O ４ These are some examples. A specific example of a phosphorylated compound is 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 type of negative electrode active material is not particularly limited and specifically includes 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 provided on the side opposite to the current collector assembly 210 of at least one of the positive electrode active material layer 220 and the negative electrode active material layer 230. In the first embodiment, 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, thereby insulating the positive electrode active material layer 220 and the negative electrode active material layer 230. 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] 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.

[0047] 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 ).

[0048] 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.

[0049] 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.

[0050] The relationship between the porosity and thickness of the insulating film 211 and the separator 240 will be explained in detail below. In the following explanation, the porosity of the insulating film 211 will be ε １ The thickness of the insulating film 211 is L １ The void ratio of separator 240 is ε ２ The thickness of separator 240 is L ２ Let's assume that.

[0051] In this embodiment, the void ratio ε of the insulating film 211 １ The void ratio ε of the separator 240 ２ The following applies to the relationship between the porosity of the insulating film 211 and the separator 240, ε １ ≤ε ２ This satisfies the following condition. As a result, the charging ion current of the current collector assembly 210 can be set to be less than or equal to the charging ion current of the separator 240, thereby reducing resistance with the current collector assembly 210 while suppressing the dendrite formation reaction in the negative electrode current collector 213.

[0052] In this embodiment, the relationship between the void ratio and thickness of the insulating film 211 and the separator 240 is as follows: １ / ε １ > L ２ / ε ２It is preferable that the following conditions are met. As a result, the diffusion resistance of the insulating film 211 becomes greater than the diffusion resistance of the separator 240, so that the current collector assembly 210 can reduce resistance while suppressing the dendrite formation reaction in the negative electrode current collector 213. In this disclosure, diffusion resistance is the resistance value represented by the following formula (1). In equation (1), R ｅｌ κ, τ, ε, L, and A are the diffusion resistance of the porous material, the ionic conductivity of the electrolyte, the curvature ratio, the porosity, the thickness of the porous material, and the surface area of ​​each electrode, respectively. Furthermore, the curvature ratio τ can be approximated as 0.5. Incidentally, on page 59 of Andreas Josef Ehrl, Determination of Transport Parameters of Binary Electrolyte Solutions for the Use in Numerical Simulations, Technical University of Munich (2017), the diffusion resistance R is given. ｅｌ The definition of diffusion resistance R is described in this disclosure. ｅｌ The definition of [this] is used.

[0053] In equation (1), the ionic conductivity κ of the electrolyte and the surface area A of the electrode are the same for the insulating film 211 and the separator 240 contained in the electrode body 200. Therefore, the diffusion resistance of the porous material is proportional to L / ε, and L １ / ε １ > L ２ / ε ２ By satisfying this condition, the diffusion resistance of the insulating film 211 becomes greater than that of the separator 240, making it more difficult for ions to flow through the insulating film 211 than through the separator 240. This suppresses the accumulation of carrier ions on the negative electrode current collector 213, thereby suppressing the generation of dendrites and improving safety.

[0054] Also, the thickness L of the insulating film 211 １ The thickness L of the separator 240 ２ Smaller, that is, L １ <L ２it is preferable to further satisfy the following condition. This allows the current collector assembly 210 to be reduced in size, so that the current collector assembly 210 can reduce resistance while increasing energy density.

[0055] As explained above, the secondary battery according to the first embodiment includes: a positive electrode active material layer; a negative electrode active material layer; a current collector assembly provided between the positive electrode active material layer and the negative electrode active material layer; and a separator provided on the opposite side of at least one of the positive electrode active material layer and the negative electrode active material layer from the current collector assembly. The current collector assembly includes a positive electrode current collector in contact with the positive electrode active material layer, a negative electrode current collector in contact with the negative electrode active material layer, and an insulating film sandwiched between the positive electrode current collector and the negative electrode current collector. The insulating film is a porous body. The positive electrode current collector is a porous body or a porous plate. The negative electrode current collector is a porous body or a porous plate. Let ε be the porosity of the insulating film １ , L be the thickness of the insulating film １ , ε be the porosity of the separator ２ , L be the thickness of the separator ２ , then ε １ ≦ε ２ is satisfied. Further, L １ / ε １ >L ２ / ε ２ it is preferable to further satisfy . Further, L １ / ε １ >L ２ / ε ２ it is preferable to further satisfy .

[0056] This allows carrier ions such as lithium ions to pass through the stacking direction of the current collector assembly 210. Furthermore, during charging and discharging of the secondary battery 1, the ion current in the path through the current collector assembly 210 can be made smaller than the ion current in the path through the separator 240. Therefore, the diffusion distance of carrier ions in the charge-discharge reaction can be shortened, the current that can flow under diffusion resistance-limited rate can be increased, and the accumulation of carrier ions on the negative electrode current collector 213 can be suppressed. 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 dendrites. Thus, the secondary battery according to the first embodiment can improve safety while improving the charge-discharge characteristics at high rates.

[0057] The following describes a method for manufacturing a current collector assembly according to the first embodiment. Figure 4 is a diagram showing the manufacturing process of a current collector assembly for a secondary battery according to the first embodiment. As shown in Figure 4, the manufacturing process of the current collector assembly according to the first embodiment includes a step of preparing an insulating film 211 (step S1), a step of forming a positive electrode porous body 212a and a negative electrode porous body 213a (step S2), and a step of forming a positive electrode conductive layer 212b and a negative electrode conductive layer 213b (step S3).

[0058] In the step of preparing the insulating film 211 (step S1), the insulating film 211 is prepared by cutting out a sheet of insulating material.

[0059] In the step of forming the positive electrode porous body 212a and the negative electrode porous body 213a (step S2), the positive electrode porous body 212a and the negative electrode porous body 213a are formed on the first main surface 211a and the second main surface 211b of the insulating film 211, respectively. Specifically, for example, pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) are stirred and reacted to obtain a slurry of microporous polyimide precursor. The obtained slurry is then coated onto the first main surface 211a and the second main surface 211b of the insulating film, immersed in a mixed solution of ethanol and water, and then dried at room temperature to obtain a composite. After that, the obtained composite is heated in a box furnace. This allows the porous polyimide layers to be formed on the insulating film 211 as the positive electrode porous body 212a and the negative electrode porous body 213a.

[0060] In the step of forming the positive electrode conductive layer 212b and the negative electrode conductive layer 213b (step S3), the positive electrode conductive layer 212b and the negative electrode conductive layer 213b are formed on the surfaces of the pores of the positive electrode porous body 212a and the negative electrode porous body 213a, respectively. Specifically, for example, the positive electrode conductive layer 212b can be formed on the surface of the pores of the positive electrode porous body 212a by performing pulsed DC magnetron sputtering on the positive electrode porous body 212a using the material for the positive electrode conductive layer 212b as a target. Similarly, the negative electrode conductive layer 213b can be formed on the surface of the pores of the negative electrode porous body 213a by performing pulsed DC magnetron sputtering on the negative electrode porous body 213a using the material for the negative electrode conductive layer 213b as a target.

[0061] The manufacturing method described above is merely an example and is not limited thereto. For example, the step of forming the positive electrode porous body 212a and the negative electrode porous body 213a (step S2) may be the following: A precursor slurry is prepared by dissolving poly(vinylidene-co-hexafluoropropene) (PVDF-HFP) with a molecular weight of about 455,000 in acetone and adding water. Next, the slurry is applied to the first main surface 211a and the second main surface 211b of the insulating film at room temperature and dried in a vacuum oven to form the positive electrode porous body 212a and the negative electrode porous body 213a.

[0062] Hereinafter, specific examples of the combination of the insulating film 211 and the separator 240 will be described. Table 1 shows the porosity ε of the insulating film 211 and the separator 240 according to Examples 1 to 4 １ , ε ２ and thickness L １ , L ２ in this table. Here, in Table 1, "Y" means that the relationship of the formula is satisfied, and "N" means that the relationship of the formula is not satisfied.

[0063]

[0064] (Example 1) In Example 1, PVDF-HFP / Kevlar (registered trademark) (thickness: 25 μm, porosity: 0.65) is used as the insulating film 211, and Celgard (registered trademark) 2325 (thickness: 25 μm, porosity: 0.55) is used as the separator 240.

[0065] (Example 2) In Example 2, a porous polymer film (thickness: 9 μm, porosity: 0.40) is used as the insulating film 211, and a porous separator (thickness: 12 μm, porosity: 0.50) is used as the separator 240. Example 2 is an example showing the combination of the insulating film 211 and the separator 240 used in the secondary battery according to the first embodiment.

[0066] (Example 3) In Example 3, a porous polyethylene polymer film (thickness: 38 μm, porosity: 0.41) is used as the insulating film 211, and a porous polyethylene separator (thickness: 19 μm, porosity: 0.41) is used as the separator 240. Example 3 is an example showing the combination of the insulating film 211 and the separator 240 used in the secondary battery according to the first embodiment.

[0067] (Example 4) In Example 4, Celgard 2500 (thickness: 25 μm, porosity: 0.39) is used as the insulating film 211, and Celgard 2325 (thickness: 25 μm, porosity: 0.55) is used as the separator 240. Example 4 is an example showing the combination of the insulating film 211 and the separator 240 used in the secondary battery according to the first embodiment.

[0068] As shown in Table 1, ε １ ≦ε ２In examples 2, 3, and 4 that satisfy this condition, ε １ ≤ε ２ Compared to Example 1, which does not satisfy the condition, carrier ions flow less easily at the interface between the negative electrode active material layer 230A and the insulating film 211 than at the interface between the negative electrode active material layer 230A and the separator 240. As a result, in Examples 2, 3, and 4, compared to Example 1, the accumulation of carrier ions on the negative electrode current collector 213 can be suppressed, thereby suppressing the generation of dendrites and improving safety.

[0069] Also, in examples 3 and 4 of Table 1, L １ / ε １ > L ２ / ε ２ By achieving this, the diffusion resistance of the insulating film 211 becomes greater than that of the separator 240, making it more difficult for ions to flow through the insulating film 211 than through the separator 240. This suppresses the accumulation of carrier ions on the negative electrode current collector 213, thereby suppressing the generation of dendrites and improving safety.

[0070] Furthermore, in examples 2 and 4 of Table 1, L １ <L ２ By achieving this, the volume of the current collector assembly 210 is reduced, thereby improving the energy density.

[0071] The secondary battery according to the first embodiment is not limited to those described above, but may also relate to the modified examples described below.

[0072] In the secondary battery according to the first modification, the current collector assembly differs from the current collector assembly 210 in Figure 3 in that it does not have a positive electrode porous body 212a and a negative electrode porous body 213a. In the first modification, the positive electrode current collector is a positive electrode conductive layer provided on the surface of the pores on the first main surface 211a of the insulating film 211. In the first modification, the negative electrode current collector is a negative electrode conductive layer provided on the surface of the pores on the second main surface 211b of the insulating film 211. Even in this case, carrier ions such as lithium ions can pass through in the stacking direction of the current collector assembly, so the charge and discharge characteristics at high rates can be improved.

[0073] In the secondary battery according to the second modification, the current collector assembly differs from the current collector assembly 210 in Figure 3 in that the positive electrode conductive layer and the negative electrode conductive layer are provided in a portion of the pores of the positive electrode porous body 212a and the negative electrode porous body 213a, respectively. In the second modification, the positive electrode conductive layer and the negative electrode conductive layer are formed, for example, to form a mesh when viewed in plan in the Z direction. In this case, even if the pore diameter of the positive electrode porous body 212a and the negative electrode porous body 213a is made smaller, the pores are not blocked by the positive electrode conductive layer or the negative electrode conductive layer, so the strength can be improved.

[0074] (Third Modification) Figure 5 is a cross-sectional view showing an example of an electrode body of a secondary battery according to the third modification. As shown in Figure 5, the secondary battery according to the third modification differs from the first embodiment in that the current collector (positive electrode active material layer 220A and negative electrode active material layer 230A) is a porous plate. In this disclosure, a current collector being a porous plate means that a plate-shaped member of metal such as stainless steel or copper has a large number of holes, and the porosity is 10% or more. In the example of Figure 5, the positive electrode current collector 212A and the negative electrode current collector 213A are provided on the insulating film 211 side of the positive electrode active material layer 220A and the negative electrode active material layer 230A, respectively. That is, the electrode body 200A has a structure in which the positive electrode active material layer 220A, positive electrode current collector 212A, insulating film 211, negative electrode current collector 213A, and negative electrode active material layer 230A are stacked in that order.

[0075] Figure 6 shows an enlarged view of the positive electrode current collector according to the third modification. In the third modification, the positive electrode current collector 212A is a porous plate laminated on the positive electrode active material layer 220A. The positive electrode current collector 212A contains a porous conductive material, such as a perforated stainless steel (SS) foil. More specifically, as shown in Figure 6, the positive electrode current collector 212A has multiple holes 212h that penetrate in the thickness direction (Z direction). This allows carrier ions of a secondary battery, such as lithium ions, to move in the thickness direction of the positive electrode current collector 212A, thereby improving high-rate charge and discharge characteristics. In the example in Figure 6, the positive electrode current collector 212A has circular holes with a diameter of 80 μm spaced 80 μm apart, but the shape, diameter, spacing, and arrangement of the holes 212h of the positive electrode current collector 212A are merely examples and are not limited thereto. This allows carrier ions such as lithium ions to pass through the positive electrode current collector 212A in the thickness direction.

[0076] In the third modification, the negative electrode current collector 213A is a porous plate laminated on the negative electrode active material layer 230A. The negative electrode current collector 213A contains a porous conductive material, such as a perforated copper foil. More specifically, the negative electrode current collector 213A has multiple holes 213h that penetrate in the thickness direction (Z direction), as in Figure 6. The shape, diameter, spacing, arrangement, etc., of the holes in the negative electrode current collector 213A are not limited to those shown in Figure 6, and may differ from those of the positive electrode current collector 212A.

[0077] In the example shown in Figure 6, the positive electrode active material layer 220A and the negative electrode active material layer 230A are porous and have multiple holes penetrating in the thickness direction (Z direction), similar to Figure 6.

[0078] As explained above, in the secondary battery according to the third modification, the positive electrode current collector 212A is a porous plate provided on the insulating film 211 side of the positive electrode active material layer 220A. The negative electrode current collector 213A is a porous plate provided on the insulating film 211 side of the negative electrode active material layer 230A. Even in this case, the charge and discharge characteristics at high rates can be improved.

[0079] Furthermore, in the secondary battery according to the third modified example, the positive electrode current collector 212A is a porous plate provided on the side of the positive electrode active material layer 220A opposite to the insulating film 211. The negative electrode current collector 213A may be a porous plate provided on the side of the negative electrode active material layer 230A opposite to the insulating film 211. This further improves the charge and discharge characteristics at high rates.

[0080] The manufacturing process for the electrode body of the secondary battery according to the third modified example includes the steps of laminating a current collector onto an active material layer, drilling holes in the current collector, and laminating it onto an insulating film 211. In the third modified example, in the step of drilling holes in the current collector, pores as shown in Figure 6 are formed in the current collector by ultraviolet laser cutting. Here, since the current collector is laminated onto the active material layer, holes are also drilled in the active material layer. Here, for example, a diode-pumped solid state (DPSS) laser having an ultraviolet laser with a wavelength of 355 nm can be used.

[0081] Figure 7 is a cross-sectional view showing an example of an electrode body of a secondary battery according to the fourth modification. As shown in Figure 7, in the electrode body 200B of the secondary battery according to the fourth modification, the positive electrode current collector 212A and the negative electrode current collector 213A are porous plates that are mesh-like metal foils. In the fourth modification, for example, a mesh-like SS foil can be used as the positive electrode current collector 212A, and for example, a mesh-like copper foil can be used as the negative electrode current collector 213A. Here, the mesh-like metal foil may be a sheet woven from wire-like metal, or it may be expanded metal. As a result, there is no need to make holes in the manufacture of the electrode body of the secondary battery, so in the fourth modification, no pores are provided in the positive electrode active material layer and the negative electrode active material layer.

[0082] Furthermore, the manufacturing process for the electrode body of the secondary battery according to the fourth modified example includes the steps of laminating a mesh-like current collector onto the active material layer and laminating it onto the insulating film 211. In other words, in the fourth modified example, since there are already gaps in the current collector, it is not necessary to drill holes in the current collector. As a result, in the manufacturing of the secondary battery according to the fourth modified example, no holes are drilled in the active material layer.

[0083] The embodiments described above are provided to facilitate understanding of this disclosure and are not intended to limit it. This disclosure may be modified or improved without departing from its intent, and equivalents thereof are included.

[0084] 1 Secondary battery 20 Battery element 21 Positive electrode lead 22 Negative electrode lead 30 Outer casing 30a, 30b Outer sheet 31 Recess 32 Adhesive material 200, 200A, 200B Electrode body 210 Current collector assembly 211 Insulating film 212, 212A Positive electrode current collector 212a Positive electrode porous body 212b Positive electrode conductive layer 213 Negative electrode current collector 213a Negative electrode porous body 213b Negative electrode conductive layer 220 Positive electrode active material layer 230 Negative electrode active material layer 240 Separator

Claims

1. A positive electrode active material layer, a negative electrode active material layer, a current collector assembly provided between the positive electrode active material layer and the negative electrode active material layer, and a separator provided on at least one of the positive electrode active material layer and the negative electrode active material layer opposite the current collector assembly, wherein the current collector assembly comprises a positive electrode current collector in contact with the positive electrode active material layer, a negative electrode current collector in contact with the negative electrode active material layer, and an insulating film sandwiched between the positive electrode current collector and the negative electrode current collector, wherein the insulating film is a porous material, the positive electrode current collector is a porous material or porous plate, the negative electrode current collector is a porous material or porous plate, and the porosity of the insulating film is ε １ The thickness of the insulating film is L １ , the porosity of the separator is ε ２ The thickness of the separator is L ２ In that case, ε １ ≤ε ２ A secondary battery that satisfies the following conditions.

2. L １ / ε １ > L ２ / ε ２ The secondary battery according to claim 1, which further satisfies 3. L １ <L ２ A secondary battery according to claim 1 or 2, further satisfying the above conditions.

4. The secondary battery according to any one of claims 1 to 3, wherein the thickness of the positive electrode current collector is smaller than the thickness of the negative electrode current collector.

5. The secondary battery according to any one of claims 1 to 4, wherein the void ratio of the positive electrode current collector is greater than the void ratio of the negative electrode current collector.

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