WO2023188062A1

WO2023188062A1 - Electrode group, secondary battery and battery pack

Info

Publication number: WO2023188062A1
Application number: PCT/JP2022/015801
Authority: WO
Inventors: 佑磨菊地; 龍之介宍戸; 祐輝渡邉; 智裕望月
Original assignee: 株式会社東芝
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2023-10-05

Abstract

One embodiment of the present invention provides an electrode group that comprises a first electrode structure and a second electrode structure, at least a part of which faces the first electrode structure. The first electrode structure is provided with: a first collector; a first active material-containing layer which is provided on at least one surface of the first collector; and a first film which contains inorganic particles and is provided on the first active material-containing layer. The second electrode structure is provided with: a second collector; a second active material-containing layer which is provided on at least one surface of the second collector; and a second film which contains an organic material and is provided on the second active material-containing layer. With respect to the first film, the volume-based frequency distribution chart as obtained by a laser diffraction/scattering method has two peaks.

Description

Electrode group, secondary battery and battery pack

Embodiments of the present invention relate to an electrode group, a secondary battery, and a battery pack.

In a secondary battery such as a lithium secondary battery, a porous separator is placed between the positive electrode and the negative electrode to avoid contact between the positive electrode and the negative electrode. A self-supporting membrane separate from the positive and negative electrodes is used as the separator. An example of this is a microporous membrane made of polyolefin resin. Such a separator is produced, for example, by extruding a melt containing a polyolefin resin composition into a sheet, extracting and removing substances other than the polyolefin resin, and then stretching the sheet.

Separators made of resin films need to have mechanical strength so as not to break during battery production, so it is difficult to make them thinner than a certain point. Since the positive electrode and the negative electrode are stacked or wound with a separator interposed therebetween, if the separator is thick, the number of layers of the positive electrode and negative electrode that can be stored per unit volume of the battery is limited. As a result, battery capacity decreases. In addition, separators made of resin films have poor durability, and when used in secondary batteries, the separators deteriorate due to repeated charging and discharging, resulting in a decrease in battery cycleability.

In order to reduce the thickness of the separator, it is being considered to integrate a nanofiber membrane into either the positive electrode or the negative electrode. This electrode-integrated separator has a problem in that self-discharge of the secondary battery tends to progress as the separator becomes thinner.

Japanese Patent Application Publication No. 2019-153431

The present invention was made in view of the above circumstances, and provides an electrode group having excellent insulation, a secondary battery including this electrode group, and a battery pack including this secondary battery.

According to an embodiment, an electrode group is provided that includes a first electrode structure and a second electrode structure at least partially facing the first electrode structure. The first electrode structure includes a first current collector, a first active material-containing layer provided on at least one surface of the first current collector, and inorganic particles. and a first film provided in the first film. The second electrode structure includes a second current collector, a second active material-containing layer provided on at least one surface of the second current collector, and an organic material; and a second film provided on. Regarding the first film, a volume-based frequency distribution chart obtained by laser diffraction scattering has two peaks.

According to another embodiment, a secondary battery is provided that includes the electrode group according to the embodiment and an electrolyte.

According to another embodiment, a battery pack including the secondary battery according to the embodiment is provided.

1 is a cross-sectional view showing an example of an electrode group according to an embodiment. FIG. 2 is a perspective view showing a first electrode structure included in the electrode group shown in FIG. 1; FIG. 2 is a perspective view showing a second electrode structure included in the electrode group shown in FIG. 1; FIG. 7 is a perspective view showing another example of the first electrode structure. FIG. 3 is a cross-sectional view showing another example of the electrode group according to the embodiment. FIG. 6 is a perspective view showing the first electrode structure of the electrode group shown in FIG. 5; FIG. 7 is a perspective view showing another example of the first electrode structure. FIG. 3 is a cross-sectional view showing another example of the electrode group according to the embodiment. FIG. 1 is a schematic diagram showing one step in a method for manufacturing an electrode group according to an embodiment. FIG. 10 is a perspective view showing the coating apparatus shown in FIG. 9; FIG. 1 is a schematic diagram of one step in a method for manufacturing a laminate according to an embodiment. FIG. 1 is a partially cutaway perspective view showing an example of a secondary battery according to an embodiment. FIG. 6 is an exploded view of another example of the secondary battery according to the embodiment. FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. 15 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 14. FIG. 3 is a particle size distribution chart related to the first film included in the electrode group manufactured in Example 1.

Embodiments will be described below with reference to the drawings. Note that common components throughout the embodiments are denoted by the same reference numerals, and redundant explanations will be omitted. In addition, each figure is a schematic diagram for explaining the embodiment and promoting understanding thereof, and the shape, dimensions, ratio, etc. may differ from the actual device, but these are in accordance with the following explanation and known technology. The design can be changed as appropriate by taking into consideration.

(First embodiment)
According to the first embodiment, an electrode group is provided that includes a first electrode structure and a second electrode structure at least partially facing the first electrode structure. The first electrode structure includes a first current collector, a first active material-containing layer provided on at least one surface of the first current collector, and inorganic particles. and a first film provided in the first film. The second electrode structure includes a second current collector, a second active material-containing layer provided on at least one surface of the second current collector, and an organic material; and a second film provided on. Regarding the first film, a volume-based frequency distribution chart obtained by laser diffraction scattering has two peaks.

As separators become thinner, insulation performance tends to decline. By appropriately controlling the particle size distribution of the inorganic particle layer (first film) provided between the positive electrode and the negative electrode, the present inventors have achieved excellent insulation properties even with a thin inorganic particle layer. I found out that it shows.

Hereinafter, electrode groups according to embodiments will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing an example of an electrode group according to an embodiment. FIG. 2 is a perspective view showing the first electrode structure 1 included in the electrode group 10 shown in FIG. FIG. 3 is a perspective view showing the second electrode structure 2 included in the electrode group shown in FIG.

The electrode group shown in FIG. 1 includes a first electrode structure 1 and a second electrode structure 2.

The first electrode structure 1 includes a first current collector 1a, a first active material-containing layer 1b provided on at least one surface of the first current collector 1a, and inorganic particles. and a first film 4 provided on the substance-containing layer 1b. The first current collector 1a and the first active material-containing layer 1b may constitute a first electrode. The first current collector 1a is a conductive sheet. A part of the first current collector 1a may be a first current collecting tab 1c on which the first active material-containing layer 1b is not supported. The first current collector tab 1c is formed, for example, on one side of the first current collector 1a to have a substantially constant width along a direction parallel to the side.

For the electrode group 10 according to this embodiment, an XYZ orthogonal coordinate system is adopted as shown in the drawings. The Z axis in the drawing is a direction parallel to the lamination direction of the first electrode structure 1 and the second electrode structure 2. The X axis is a direction parallel to the direction in which the first current collecting tab 1c projects from the first electrode structure 1. The Y-axis is a direction perpendicular to the X-axis and the Z-axis.

The first active material-containing layer 1b may be formed, for example, on at least a portion of at least one surface of the first current collector 1a. The first active material-containing layer 1b has, for example, a sheet shape having a first surface 40 and a first back surface 41. The first surface 40 and the first back surface 41 may be main surfaces of the first active material-containing layer 1b. The first back surface 41 is in contact with the first current collector 1a. The first surface 40 is in contact with the first membrane 4 .

The first film 4 may be formed, for example, on at least a portion of the main surface (first surface 40) of the first active material-containing layer 1b. The first film 4 may be formed over the entire main surface of the first active material-containing layer 1b. The first film 4 may have a sheet shape having a front surface A and a back surface B. The back surface B of the first film 4 covers the first surface 40 of the first active material-containing layer 1b. Although there are no particular limitations on how the first film 4 is fixed to the first active material-containing layer 1b, examples include adhesion and thermal fusion.

The second electrode structure 2 includes a second current collector 2a, a second active material-containing layer 2b provided on at least one surface of the second current collector 2a, and an organic material. and a second film 5 provided on the substance-containing layer 2b. The second current collector 2a and the second active material-containing layer 2b may constitute a second electrode. The second current collector 2a is a conductive sheet. A part of the second current collector 2a may be a second current collecting tab 2c on which the second active material-containing layer 2b is not supported. The second current collector tab 2c is formed, for example, on one side of the second current collector 2a with a substantially constant width along a direction parallel to the side.

The second active material-containing layer 2b may be formed, for example, on at least a portion of at least one surface of the second current collector 2a. The second active material-containing layer 2b has, for example, a sheet shape having a second surface 42 and a second back surface 43. The second surface 42 and the second back surface 43 may be the main surfaces of the second active material-containing layer 2b. The second back surface 43 is in contact with the second current collector 2a. The second surface 42 is in contact with the second film 5.

As shown in FIG. 3, the second film 5 includes a second surface 42 of the second active material-containing layer 2b, four side surfaces 44 orthogonal to the second surface 42, and one of the four side surfaces of the second current collector 2a. , covering the three end surfaces 45 exposed on the surface of the second electrode structure 2 and the portion 46 including the boundary with the second active material-containing layer 2b on both main surfaces of the second current collecting tab 2c. There is. The second film 5 has a front surface C and a back surface D. The back surface D of the second film 5 is in contact with the second active material containing layer 2b.

As shown in FIGS. 1 and 3, the second film 5 includes a boundary between the end surface 45 of the second current collector 2a and the second active material-containing layer 2b on the surface of the second current collector tab 2c. When the portion 46 is covered, internal short circuits due to contact between the first electrode structure and the second electrode structure 2 are reduced.

The first film 4 and the second film 5 can constitute a separator. The surface A of the first film 4 and the surface C of the second film 5 can be in contact with each other. The first active material containing layer 1b and the second active material containing layer 2b are opposed to each other, for example, with the first film 4 and the second film 5 interposed therebetween. At least a portion of the first active material-containing layer 1b and the second active material-containing layer may be opposed to each other with the first film 4 and the second film 5 interposed therebetween, and the entire surface thereof may be opposed to the first film 4. and may be opposed to each other with the second film 5 interposed therebetween.

As shown in FIG. 1, when the first active material-containing layer 1b and the second active material-containing layer 2b face each other with a first film 4 containing inorganic particles and a second film 5 containing an organic material interposed therebetween. In other words, when the first electrode structure and the second electrode structure face each other, the thickness of the separator can be reduced in this laminate. Therefore, since the energy density is high and the first film containing inorganic particles has high insulation properties, it is possible to realize a secondary battery with less self-discharge.

Note that the first and second current collector tabs are not limited to one side of the first and second current collectors, respectively, on which no active material-containing layer is supported. For example, a plurality of strips protruding from one side of the first and second current collectors can be used as the first and second current collection tabs. An example of this is shown in FIG. FIG. 4 shows another example of the first electrode structure 1. As shown in FIG. 4, a plurality of strips protruding from one side of the first current collector 1a may be used as the first current collector tab 1c.

Hereinafter, the first electrode structure, the second electrode structure, the first film, and the second film will be explained.

(1) First electrode structure and second electrode structure One of the first electrode structure and the second electrode structure may function as a positive electrode, and the other may function as a negative electrode. The opposite pole of the first electrode structure is the second electrode structure. For example, the first electrode structure is a positive electrode structure, and the second electrode structure is a negative electrode structure. The first electrode structure may be a negative electrode structure, and the second electrode structure may be a positive electrode structure.

The first electrode structure includes a porous first active material-containing layer having a first surface and a first back surface. The second electrode structure includes a porous second active material-containing layer having a second surface and a second back surface. The first electrode structure and the second electrode structure are stacked such that the first active material containing layer and the second active material containing layer thereof face each other. In this case, as described above, the first film 4 and the second film 5 may be interposed between the first active material containing layer and the second active material containing layer.

The first electrode structure may further include a first current collector and a first current collection tab. The second electrode structure may further include a second current collector and a second current collection tab. The first active material-containing layer and the second active material-containing layer may be formed on both the main surfaces of the first current collector and the second current collector, respectively, but they can also be formed on only one surface. be.

A positive electrode active material and a negative electrode active material are used as the active materials contained in the first active material containing layer and the second active material containing layer. The number of types of active materials can be one or more. The active material included in the first active material-containing layer is referred to as a first active material. The active material included in the second active material-containing layer is referred to as a second active material.

As the positive electrode active material, for example, a lithium transition metal composite oxide can be used. Examples of lithium transition metal composite oxides include LiCoO ₂ , LiNi _1-x Co _x O ₂ (0<x<0.3), LiMn _x Ni _y Co _z O ₂ (0<x<0.5, 0<y<0.5,0≦z<0.5), LiMn _2-x M _x O ₄ (M is at least one element selected from the group consisting of Mg, Co, Al and Ni, 0<x< 0.2), LiMPO ₄ (M is at least one element selected from the group consisting of Fe, Co, and Ni), and the like.

As the negative electrode active material, carbon materials such as graphite, tin-silicon alloy materials, etc. can be used, but it is preferable to use lithium titanate. Further, titanium oxide or lithium titanate containing other metals such as (niobium)Nb may also be used as negative electrode active materials. Examples of lithium titanate include Li _4+x Ti ₅ O ₁₂ (0≦x≦3) having a spinel structure and Li _2+y Ti ₃ O ₇ (0≦y≦3) having a ramsteride structure. Can be mentioned.

As the negative electrode active material, carbon materials such as graphite, tin-silicon alloy materials, etc. can be used, but it is preferable to use titanium-containing oxides. As the titanium-containing oxide, lithium titanium composite oxide, niobium titanium composite oxide, sodium niobium titanium composite oxide, etc. can be used.

Examples of lithium titanium oxide include spinel structure lithium titanium oxide (for example, general formula Li _4+x Ti ₅ O ₁₂ (x is -1≦x≦3)), ramsdellite structure lithium titanium oxide (for example, Li _2+x Ti ₃ O ₇ (-1≦x≦3)), Li _1+x Ti ₂ O ₄ (0≦x≦1), Li _1.1+x Ti _1.8 O ₄ (0≦x≦1), Li _1.07+x These include Ti _1.86 O ₄ (0≦x≦1), Li _x TiO ₂ (0<x≦1), and the like. Further, the lithium titanium oxide may be a lithium titanium composite oxide into which a different element is introduced.

Niobium titanium composite oxide is, for example, Li _a TiM _b Nb _2±β O _7±σ (0≦a≦5, 0≦b≦0.3, 0≦β≦0.3, 0≦σ≦0.3 , M is at least one element selected from the group consisting of Fe, V, Mo, and Ta).

The sodium titanium composite oxide has, for example, the general formula Li _2+V Na _2-W M1 _X Ti _6-y-z Nb _y M2 _z O _14+δ (0≦v≦4, 0≦w<2, 0≦x<2, 0≦y<6, 0≦z<3, -0.5≦δ≦0.5, M1 includes at least one selected from Cs, K, Sr, Ba, Ca, M2 includes Zr, Sn, The present invention includes an orthorhombic Na-containing niobium titanium composite oxide represented by V, Ta, Mo, W, Fe, Co, Mn, and Al.

The active material may be a single primary particle, a secondary particle that is an agglomeration of primary particles, or a mixture of primary particles and secondary particles.

The average particle size of the primary particles of the negative electrode active material is preferably within the range of 0.001 or more and 1 μm or less. The average particle size can be determined, for example, by observing the negative electrode active material with a scanning electron microscope (SEM). The particle shape may be either granular or fibrous. When it is fibrous, it is preferable that the fiber diameter is 0.1 μm or less. Specifically, the average particle diameter of the primary particles of the negative electrode active material can be measured from an image observed with a SEM. When lithium titanate having an average particle size of 1 μm or less is used as the negative electrode active material, a negative electrode active material-containing layer with a highly flat surface can be obtained. Furthermore, when lithium titanate is used, the negative electrode potential becomes nobler than that of a lithium ion secondary battery using a general carbon negative electrode, so that lithium metal does not precipitate in principle. Since the negative electrode active material containing lithium titanate has small expansion and contraction due to charge/discharge reactions, it is possible to prevent the crystal structure of the active material from collapsing.

The first active material containing layer and the second active material containing layer may contain a binder and a conductive agent in addition to the active material. Examples of the conductive agent include acetylene black, carbon black, graphite, or mixtures thereof. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene-butadiene rubber, or mixtures thereof. The binder has a function of binding the active material and the conductive agent.

In the positive electrode active material-containing layer, the contents of the active material, conductive agent, and binder are 80% by mass or more and 97% by mass or less, 2% by mass or more and 18% by mass or less, and 1% by mass or more and 17% by mass or less, respectively. It is preferable that there be. In the negative electrode active material-containing layer, the contents of the negative electrode active material, the conductive agent, and the binder are 70% by mass or more and 98% by mass or less, 1% by mass or more and 28% by mass or less, and 1% by mass or more and 28% by mass or less, respectively. It is preferable that there be.

The thickness of the first active material-containing layer and the second active material-containing layer may be 5 μm or more and 100 μm or less, respectively.

The first current collector and the second current collector may be conductive sheets. Examples of conductive sheets include foils made of conductive materials. Examples of conductive materials include aluminum and aluminum alloys. The thickness of the first current collector and the second current collector may be 5 μm or more and 40 μm or less, respectively.

The first current collector tab and the second current collector tab may be made of the same material as each current collector, but a current collector tab made of a different material from each current collector is prepared, This may be connected to a current collector by welding or the like.

(2) First film The first film contains inorganic particles. The form of the inorganic particles may be, for example, granular or fibrous. The first film may further include a binder.

The thickness of the first film (on one side) is, for example, in the range of 1 μm to 5 μm, preferably in the range of 2 μm to 4 μm. If the thickness of the first film is too small, the positive and negative electrodes are likely to short-circuit, and the amount of self-discharge may increase, which is not preferable. On the other hand, if the first film is excessively thick, it is not preferable because there is a possibility that the battery capacity will decrease and the resistance will increase.

The thickness of the first film can be measured by scanning electron microscopy (SEM) observation, which will be described later.

The content of inorganic particles in the first film is preferably in the range of 80% by mass or more and 99.9% by mass or less. Thereby, the insulation properties of the first film can be increased.

Examples of inorganic materials constituting inorganic particles include oxides (e.g., Li ₂ O, BeO, B ₂ O ₃ , Na ₂ O, MgO, Al ₂ O ₃ , SiO ₂ , P ₂ O ₅ , CaO, Cr). ₂ O ₃ , Fe ₂ O ₃ , ZnO, ZrO ₂ , TiO ₂ , magnesium oxide, silicon oxide, aluminum oxide, zirconia, titanium oxide, etc., oxides of IIA to VA groups, transition metals, IIIB, IVB), zeolites ( M _2/n O・Al ₂ O ₃・xSiO ₂・yH ₂ O (in the formula, M is a metal atom such as Na, K, Ca, and Ba, n is a number corresponding to the charge of the metal cation Mn ⁺ , x and y is the number of moles of SiO ₂ and H ₂ O (2≦x≦10, 2≦y), nitrides (e.g. BN, AlN, Si ₃ N ₄ and Ba ₃ N ₂ etc.), silicon carbide (SiC ), zircon (ZrSiO ₄ ), carbonates (e.g., MgCO ₃ and CaCO ₃ , etc.), sulfates (e.g., CaSO ₄ and BaSO _{4 ,} etc.), and complexes thereof (e.g., steatite (MgO -SiO ₂ ), forsterite (2MgO.SiO ₂ ), cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ )), tungsten oxide, or mixtures thereof.

Examples of other inorganic materials include barium titanate, calcium titanate, lead titanate, γ-LiAlO ₂ , LiTiO ₃ , solid electrolytes or mixtures thereof.

Examples of solid electrolytes include solid electrolytes with no or low lithium ion conductivity, and solid electrolytes with lithium ion conductivity. Examples of oxide particles with no or low lithium ion conductivity include lithium aluminum oxide (for example, LiAlO ₂ , Li _x Al ₂ O ₃ where 0<x≦1), lithium silicon oxide, and lithium zirconium oxide. It will be done.

Examples of solid electrolytes having lithium ion conductivity include oxide solid electrolytes with a garnet type structure. Oxide solid electrolytes with a garnet-type structure have the advantage of high reduction resistance and a wide electrochemical window. Examples of oxide solid electrolytes with a garnet-type structure include La _5+x A _x La _3-x M ₂ O ₁₂ (A is at least one element selected from the group consisting of Ca, Sr, and Ba; M is Nb and ₍ M is _Nb and/or Ta, _L is _Zr , x is 0. (preferably a range of .5 or less (including 0)), Li _7-3x Al _x La ₃ Zr ₃ O ₁₂ (x is preferably a range of 0.5 or less (including 0)), Li ₇ La ₃ Zr ₂ Contains _O12 . Among them, Li _6.25 Al _0.25 La ₃ Zr ₃ O ₁₂ , Li _6.4 La ₃ Zr _1.4 Ta _0.6 O _12, Li _6.4 La ₃ Zr _1.6 Ta _0.6 O _{12 ,} Li ₇ La ₃ Zr ₂ O ₁₂ has high ionic conductivity and is electrochemically stable, so it has excellent discharge performance and cycle life performance.

Furthermore, examples of the solid electrolyte having lithium ion conductivity include a lithium phosphate solid electrolyte having a NASICON type structure. An example of a lithium phosphate solid electrolyte with a NASICON type structure includes LiM1 ₂ (PO ₄ ) ₃ , where M1 is one or more elements selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Al. included. Preferred examples include Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ , Li _1+x Al _x Zr _2-x (PO ₄ ) ₃ , and Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ . Here, in each case, x is preferably in the range of 0 or more and 0.5 or less. Further, each of the illustrated solid electrolytes has high ionic conductivity and high electrochemical stability. Both a lithium phosphate solid electrolyte having a NASICON type structure and an oxide solid electrolyte having a garnet type structure may be used as the solid electrolyte having lithium ion conductivity.

The inorganic particles may be made of only one type of the above-mentioned inorganic materials, or may be a mixture of two or more types.

The first film is, for example, a porous film containing inorganic particles and binder particles. Although there are inorganic materials that have lithium ion conductivity, such as solid electrolytes, many of the inorganic materials have low electronic conductivity or have insulating properties. Therefore, the first film can function as a partition wall for electrically insulating the positive electrode and the negative electrode.

Since the first membrane can hold the electrolyte in its porous portion, it does not inhibit the permeation of Li ions. The first film containing the above-described type of inorganic material has high insulating properties while having Li ion permeability. From the viewpoint of achieving high insulation, it is preferable that the inorganic particles contain a substance having an energy bandgap value of 3.0 eV or more. Examples of substances with an energy bandgap value of 3.0 eV or more include aluminum oxide and barium sulfate.

Aluminum oxide and barium sulfate are preferred because they have an energy bandgap value of about 9 eV. The inorganic particles may consist of aluminum oxide or barium sulfate.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, styrene-butadiene rubber, or mixtures thereof. The content of the binder in the first film is preferably in the range of 0.01% by mass to 20% by mass.

Regarding the first film, the volume-based frequency distribution chart obtained by the laser diffraction scattering method has two peaks. The frequency distribution chart may include three or more peaks, but preferably includes two peaks.

When the particles included in the first film include two peaks with different particle diameters, the electrode group including the first film exhibits excellent insulation. One reason for this is thought to be that the density within the layer is improved because two types of particle groups having mutually different particle diameters are present within the layer. It is thought that the density within the layer is increased by particles having a relatively small particle size entering the gaps between particles having a relatively large particle size. Note that the particles included in the first film may include inorganic particles and binder particles.

Another reason why the electrode group according to the embodiment exhibits excellent insulation is that the layer does not contain or substantially does not contain coarse particles. The coarse particles refer to, for example, primary particles having a diameter of 40 μm or more, or secondary particles obtained by agglomerating primary particles. If the first coating film is formed using a slurry containing a large amount of coarse particles, there is a tendency for coating failure to occur due to the coarse particles. Coating failure occurs, for example, when coarse particles are caught in a coating head provided in a coating device. The term "missing coating" refers to the occurrence of uncoated parts in parts of the coating film that should be formed into a uniform film. Since the insulating film (first film) is not formed in the portion where the coating omission has occurred, the insulating property is reduced. The frequency distribution chart of the first film included in the electrode group according to the embodiment includes two peaks with different particle sizes. Therefore, the first film is less likely to have holes due to coating failure. The reason for this will be explained in detail below.

If the volume-based frequency distribution chart obtained by the laser diffraction scattering method for the first film includes two peaks with different particle sizes, the slurry used to form the first film also has a similar particle size distribution. can be shown. That is, a volume-based frequency distribution chart obtained by a laser diffraction scattering method for the slurry for forming the first film may include two peaks having different particle diameters.

Such a slurry includes at least primary particles having a relatively small particle size and primary particles having a relatively large particle size. Here, for convenience, the former will be referred to as first particles, and the latter will be referred to as second particles. Further, the slurry may include secondary particles that are aggregates of first particles and/or second particles. These secondary particles are called third particles. The third particles may be the above coarse particles. Since the first particles have a small particle diameter, they tend to aggregate with each other. Therefore, most of the particles constituting the third particles are the first particles. For example, 50% or more by weight of the third particles can be the first particles.

When the first film is subjected to a dispersion process such as a bead mill using a slurry that develops a frequency distribution chart with two peaks, the third particles, which are mainly composed of aggregates of the first particles, are When the two particles collide, the third particle is likely to be crushed. In other words, the second particles having a relatively large particle size collide with the aggregate, that is, the coarse particles (third particles), which are the aggregates of the first particles having a relatively small particle size, resulting in an aggregate. Easy to crush. Therefore, the number of coarse particles can be reduced by dispersion treatment. In other words, the slurry has excellent dispersibility.

In the slurry for forming the first film that exhibits excellent dispersibility, the probability of the presence of coarse particles is low, so even if the first film is formed using the slurry, coating defects are unlikely to occur. Therefore, by evaluating the number of coarse particles contained in the slurry after the dispersion treatment, it is possible to evaluate the insulation properties of the first film formed using the slurry.

Whether or not the slurry for forming the first film contains coarse particles can be determined using a grind gauge according to Japanese Industrial Standard JIS K 5600. The number of coarse particles contained in 5 mL of slurry is, for example, 15 or less, preferably 10 or less, and more preferably 5 or less. The smaller the number of coarse particles, the lower the probability that coating defects will occur. As a result, the amount of self-discharge can be reduced.

Note that even if the frequency distribution chart for the first film forming slurry does not have two peaks, it is sufficient that the frequency distribution chart for the first film has two peaks. Even in this case, the effect of increasing the density as described above can be obtained, so that an electrode group exhibiting excellent insulation properties can be obtained. It is preferable that the volume-based frequency distribution chart obtained by the laser diffraction scattering method for the first film-forming slurry also includes two peaks having different particle diameters.

Two peaks having different particle diameters in the frequency distribution chart for the first film are defined as a first peak and a second peak, respectively, in order from the peak with the smallest particle diameter. The first peak having a small particle size may be, for example, a peak caused by the first particles. The second peak having a large particle size may be, for example, a peak caused by the second particles. Since the number of third particles contained in the first film is very small, they are hardly detected or not detected in the frequency distribution chart.

The frequency distribution chart is a graph in which the horizontal axis indicates particle diameter [μm] and the vertical axis indicates frequency (frequency distribution) [%].

The particle diameter D1 corresponding to the peak top of the first peak is smaller than the particle diameter D2 corresponding to the peak top of the second peak. The particle diameter D1 is, for example, within the range of 0.4 μm or more and 1.0 μm or less, preferably within the range of 0.5 μm or more and 0.9 μm or less. If the particle size D1 of the first peak is excessively small, agglomerates are likely to be formed, which is not preferable because the frequency of coating failure due to agglomerates (coarse particles) may increase.

The particle diameter D2 is, for example, in the range of more than 1.0 μm and less than 2.0 μm, preferably in the range of 1.1 μm or more and less than 1.8 μm. If the particle diameter D2 of the second peak is excessively large, the number of primary particles having large particle diameters is too large, and the probability of contact between these primary particles increases. As a result, the probability of contact between primary particles having a relatively large particle size and aggregates decreases, and dispersibility tends to be poor. When the dispersibility is poor, coarse particles in the slurry are difficult to crush, and coating omissions may easily occur.

The particle diameter D1 corresponding to the peak top of the first peak is 0.4 μm or more and 1.0 μm or less, and the particle diameter D2 corresponding to the peak top of the second peak is more than 1.0 μm and 2.0 μm or less. It is preferable that there be. When the particle diameters D1 and D2 are within these ranges, it can be considered that the primary particles contained in the first film have a small particle diameter as a whole. Therefore, in this case, since the thickness of the first film can be made sufficiently thin, a high battery capacity can be achieved.

The ratio D1/D2 of the particle diameter D1 corresponding to the peak top of the first peak to the particle diameter D2 corresponding to the peak top of the second peak is, for example, in the range of 1.0 or more and 5.0 or less, preferably It is in the range of 1.50 or more and 3.0 or less, more preferably 2.0 or more and 2.5 or less. If the ratio D1/D2 is too high, the number of particles having a large primary particle diameter to collide with the aggregates is insufficient, so that the dispersibility tends to deteriorate. If the ratio D1/D2 is too low, the number of particles having a large primary particle diameter will be too large, reducing the collision probability (frequency) during dispersion and deteriorating the dispersibility. As a result, coarse particles tend to exist in the slurry or in the first film, which tends to cause coating failure.

Note that a method for manufacturing the first film included in the first electrode structure according to the embodiment will be described later.

<Particle size distribution measurement of first film>
The frequency distribution chart for the first film according to the embodiment is obtained by measuring according to the following procedure.

First, the electrode group is taken out from the battery, and the electrode structure (positive electrode or negative electrode) including the first film containing an inorganic material is taken out. The taken-out electrode structure is immersed in ethyl methyl carbonate to remove Li salt, and then dried. After drying, only the first film of the electrode structure is peeled off with a spatula and immersed in NMP (N-methyl-2-pyrrolidone) solvent. Thereafter, while immersed in the NMP solvent, the first film is dispersed in the NMP solvent using ultrasound to obtain a dispersion solution as a sample. Regarding this dispersion solution, the particle size distribution of the constituent particles is measured using a laser diffraction type distribution measuring device. The dispersion solution may further contain not only the inorganic particles contained in the first film but also a binder component such as PVdF that may be contained in the first film. Since the particle size of the binder component is very small compared to the particle size of the inorganic particles, it is not detected. As a measuring device, for example, Microtrac MT3100II manufactured by Microtrac Bell Co., Ltd. can be used.

Note that the ultrasonic treatment when obtaining the above-mentioned dispersion solvent is performed using a sample supply system attached to a laser diffraction type distribution measuring device. Ultrasonication is carried out at a power of 40W for 300 seconds.

The first peak and the second peak can be determined from the frequency distribution chart obtained by the above measurement. Furthermore, D10, D50, and D90 of the particles constituting the first film can be determined from this frequency distribution chart. D10, D50, and D90 are particle diameters of particles whose integrated value of particle diameter distribution corresponds to 10%, 50%, and 90%, respectively. D50 is also called the median diameter.

The average particle diameter D50 of the inorganic particles can be, for example, within the range of 0.60 μm to 2.0 μm. It is preferable that D50 is within this range because the thickness of the first film can be reduced. The D50 of the inorganic particles may preferably be within the range of 0.80 μm to 1.20 μm.

D10 in the frequency distribution chart above is, for example, 0.10 μm or more. A high value of D10 means less fine powder. D10 may be 0.20 μm or more, or 0.30 μm or more. According to one example, D10 may be 0.60 μm or less. When D10 is 0.10 μm or more, the proportion of primary particles in the first film is low, so that agglomeration of fine powder can be suppressed. In this case, coarse particles are reduced and high insulation properties can be exhibited.

D90 in the above frequency distribution chart is, for example, within the range of 1.50 μm to 3.0 μm, although it is not particularly limited.

(3) Second film The second film contains organic fibers. The second membrane may be a porous membrane in which organic fibers are deposited in the plane direction and the thickness direction. The second film has a front surface and a back surface. One main surface of the second film corresponds to the front surface, and the other main surface corresponds to the back surface.

The organic fiber comprises, for example, at least one organic material selected from the group consisting of polyamideimide, polyamide, polyolefin, polyether, polyimide, polyketone, polysulfone, cellulose, polyvinyl alcohol (PVA) and polyvinylidene fluoride (PVdF). . Examples of polyolefins include polypropylene (PP) and polyethylene (PE). The number of types of organic fibers can be one or more. Preferred is at least one selected from the group consisting of polyimide, polyamide, polyamideimide, cellulose, PVdF, and PVA, and more preferred is at least one selected from the group consisting of polyimide, polyamide, polyamideimide, cellulose, and PVdF. At least one type of

Since polyimide is insoluble, infusible, and does not decompose even at 250 to 400°C, it is possible to obtain a second film with excellent heat resistance.

The organic fiber preferably has a length of 1 mm or more and an average diameter of 2 μm or less, more preferably an average diameter of 1 μm or less. Since such a second film has sufficient strength, porosity, air permeability, pore size, electrolyte resistance, oxidation-reduction resistance, etc., it functions well as a separator. The average diameter of organic fibers can be measured by observation with a focused ion beam (FIB) device. Further, the length of the organic fiber is obtained based on length measurement during observation with an FIB device.

Since it is necessary to ensure ion permeability and electrolyte retention, 30% or more of the total volume of the fibers forming the second membrane is preferably organic fibers with an average diameter of 1 μm or less, and organic fibers with an average diameter of 350 nm or less. It is more preferable that it is an organic fiber, and even more preferable that it is an organic fiber of 50 nm or less.

Further, it is more preferable that the volume of the organic fibers having an average diameter of 1 μm or less (more preferably 350 nm or less, still more preferably 50 nm or less) accounts for 80% or more of the volume of the entire fibers forming the second film. Such a state can be confirmed by observing the second film using a scanning ion microscope (SIM). More preferably, the organic fibers having a thickness of 40 nm or less occupy 40% or more of the total volume of the fibers forming the second film. The smaller the diameter of the organic fiber, the less the effect of interfering with the movement of ions.

It is preferable that cation exchange groups exist on at least a portion of the entire surface of the organic fiber, including the front and back surfaces. Cation exchange groups promote the movement of ions, such as lithium ions, through the separator, thereby enhancing battery performance. Specifically, it becomes possible to perform rapid charging and rapid discharging over a long period of time. The cation exchange group is not particularly limited, but includes, for example, a sulfonic acid group and a carboxylic acid group. Fibers having cation exchange groups on their surfaces can be formed, for example, by electrospinning using a sulfonated organic material.

The second film preferably has pores, and the average pore diameter of the pores is preferably 5 nm or more and 10 μm or less. Further, the porosity is preferably 30% or more and 90% or less. If such pores are provided, a separator with excellent ion permeability and good electrolyte impregnation properties can be obtained. More preferably, the porosity is 40% or more. The average pore diameter and porosity of the pores can be confirmed by mercury intrusion method, calculation from volume and density, SEM observation, SIM observation, and gas desorption method. It is desirable that the porosity be calculated from the volume and density of the second film. Further, the average pore diameter is preferably measured by a mercury intrusion method or a gas adsorption method. A large porosity in the second film means that the effect of interfering with the movement of ions is small.

The thickness of the second film is preferably in the range of 12 μm or less. The lower limit of the thickness is not particularly limited, but may be 1 μm.

In the second film, the porosity can be increased by making the organic fibers contained in a sparse state, so it is not difficult to obtain a layer with a porosity of about 90%, for example. It is extremely difficult to form a layer with such a high porosity using particles.

The second film is more advantageous than the inorganic particle deposit in terms of roughness, breakability, electrolyte content, adhesion, bending properties, porosity, and ion permeability.

The second film may contain particles of an organic compound. The particles are made of the same material as the organic fibers, for example. The particles may be formed integrally with the organic fiber.

The second film may be formed on the second active material-containing layer, or may be formed on the first film. Alternatively, the second film may be formed on both surfaces of the second active material-containing layer and the first film. In either case, one of the front and back surfaces of the second film can be in contact with the front surface of the first film.

<Cross-sectional SEM observation>
The thickness of the first film and the second film, and the thickness of the first active material-containing layer and the second active material-containing layer can be measured by performing SEM observation on the cross section of the electrode.

First, the target electrode group is cut using an ion milling device. When cutting the electrode group, the electrode group is cut along the thickness direction. The cross section of the electrode group after cutting is pasted on the SEM sample stage. At this time, conductive tape or the like is used to prevent the electrode group from peeling off or floating from the sample stage. Observe the electrode group attached to the SEM sample stage using SEM. Note that when introducing the electrode group into the sample chamber, it is preferable to maintain an inert atmosphere.

If the electrode group to be measured is incorporated into a battery, first, the secondary battery to be analyzed is brought into a discharge state. For example, in a 25° C. environment, the secondary battery can be brought into a discharge state by discharging it to the rated final voltage with a 0.1 C current. The discharged secondary battery is disassembled in a glove box filled with argon. Remove the electrode group to be measured from the disassembled battery. This electrode group is washed with a suitable solvent. As the solvent used for washing, for example, ethyl methyl carbonate can be used. Thereafter, SEM observation is performed according to the above-described procedure.

The second film is formed, for example, by electrospinning. In the electrospinning method, the first electrode structure or the second electrode structure on which the second film is to be formed is grounded to serve as a ground electrode. When forming the first electrode structure, the first electrode structure on which the first film is already formed is prepared.

The voltage applied to the spinning nozzle charges the liquid raw material (for example, the raw material solution), and the amount of charge per unit volume of the raw material solution increases due to the volatilization of the solvent from the raw material solution. Due to the continuous volatilization of the solvent and the accompanying increase in the amount of charge per unit volume, the raw material solution discharged from the spinning nozzle extends in the longitudinal direction and forms nano-sized organic fibers at the first electrode, which is the ground electrode. or a second electrode structure. Coulomb force is generated between the organic fiber and the earth electrode due to the potential difference between the nozzle and the earth electrode. Therefore, the contact area with the first film can be increased by the nano-sized organic fibers, and the organic fibers can be deposited on the first electrode structure or the second electrode structure by Coulomb force. It becomes possible to increase the peel strength of the two films from the electrode (second active material-containing layer). The peel strength can be controlled, for example, by adjusting the solution concentration, the sample-nozzle distance, and the like.

By using the electrospinning method, the second film can be easily formed on the electrode surface. In principle, the electrospinning method forms one continuous fiber, so it is possible to ensure a thin film with resistance to breakage due to bending and cracking of the film. If the organic fibers constituting the second film are seamless and continuous, the probability of fraying or partial loss of the second film is low, which is advantageous in terms of suppressing self-discharge.

As the liquid raw material used for electrospinning, for example, a raw material solution prepared by dissolving an organic material in a solvent is used. Examples of the organic material include the same materials as those mentioned for the organic materials constituting the organic fibers. The organic material is used by being dissolved in a solvent at a concentration of, for example, about 5 to 60% by mass. The solvent for dissolving the organic material is not particularly limited, and any solvent such as dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), N,N'dimethylformamide (DMF), N-methylpyrrolidone (NMP), water, alcohols, etc. A solvent can be used. For organic materials with low solubility, electrospinning is performed while melting the sheet-like organic material using a laser or the like. In addition, it is also permissible to mix high boiling point organic solvents and low melting point solvents.

The second film is formed by discharging the raw material from the spinning nozzle over the surface of a predetermined electrode while applying voltage to the spinning nozzle using a high voltage generator. The applied voltage is appropriately determined depending on the solvent/solute species, boiling point/vapor pressure curve of the solvent, solution concentration, temperature, nozzle shape, sample-nozzle distance, etc. It can be set to 100kV. The feed rate of the raw material is also appropriately determined depending on the solution concentration, solution viscosity, temperature, pressure, applied voltage, nozzle shape, etc. In the case of a syringe type, the flow rate can be, for example, about 0.1 to 500 μl/min per nozzle. Furthermore, in the case of multiple nozzles or slits, the supply rate may be determined depending on the opening area.

Since the organic fibers are formed directly on the surface of the electrode in a dry state, it is substantially possible to prevent the solvent contained in the raw material from penetrating into the electrode. The amount of solvent remaining inside the electrode is extremely low, below the ppm level. The residual solvent inside the electrode causes an oxidation-reduction reaction, causing battery loss, leading to a decrease in battery performance. According to the second film containing an organic material, the possibility of such inconvenience occurring is reduced as much as possible, so that battery performance can be improved.

The first film may be formed only on at least one main surface of the first active material-containing layer, but it is also possible to further cover at least a portion of the surface of the first current collecting tab with the first film. good. An example of this is shown in FIGS. 5 and 6. For each of the two first active material-containing layers 1b, four side surfaces 47 perpendicular to the main surface are covered with the first film 6. The first film 6 also covers the portions adjacent to the first active material-containing layer 1b (including the boundary with the first active material-containing layer 1b) on both main surfaces of the first current collecting tab 1c. . The location where the first film 6 is provided is close to the end surface of the second electrode structure opposite to the side from which the second current collecting tab 2c extends. By providing the first film 6, it is possible to reduce internal short circuits caused by contact between the first current collecting tab 1c of the first electrode structure and the end surface of the second electrode structure. In addition, when using a plurality of strips protruding from one side of the first current collector 1a as the first current collecting tab 1c as shown in FIG. It is desirable that the first film 6 covers a portion 48 adjacent to the current collector 1a and an end surface 49 of the first current collector 1a located between the first current collector tabs 1c. This configuration is effective in reducing internal short circuits.

The second film may be formed on the second electrode structure, but instead of being formed on the second electrode structure, it may be formed on the surface of the first electrode structure. An example of this is shown in FIG. The second film 7 covers the surface of the first film 4 and all end faces of the first electrode structure. Further, the second film 7 also covers portions of both main surfaces of the first current collecting tab 1c, including the boundary with the first active material containing layer 1b.

The second electrode structure is arranged such that the second active material containing layer 2b faces the first active material containing layer 1b with a separator 3 formed of the first film 4 and the second film 7 interposed therebetween. A portion of the main surface of the first current collecting tab 1c adjacent to the first active material containing layer 1b is covered with the second film 7, and the side opposite to the side of the first electrode structure from which the first current collecting tab 1c protrudes The end face located at is covered with the second film 7. This configuration suppresses self-discharge and internal short circuits.

<Method for manufacturing electrode group>
The electrode group according to the embodiment can be manufactured by, for example, the first or second manufacturing method described below.

<First manufacturing method>
A slurry containing the first active material (hereinafter referred to as slurry I) and a slurry containing inorganic particles (hereinafter referred to as slurry II) are simultaneously applied to at least one main surface of the first current collector. An example of the coating process is shown in FIGS. 9 and 10. The coating device 60 includes a tank 62 containing slurry I and a tank 63 containing slurry II. The coating device 60 is configured to be able to simultaneously coat slurry I and slurry II onto the base material.

The elongated first current collector 1a before being cut into a predetermined size is conveyed to the slurry discharge port of the coating device 60 by the conveyance roller 61. In FIG. 10, the slurry I outlet 62a is located upstream of the current collector than the slurry II outlet 63a. Therefore, slurry I is discharged onto the current collector before slurry II. Slurry I is applied from the coating device 60 onto the first current collector 1a except for both ends in the short side direction. Next, before slurry I dries, slurry II is overcoated so as to protrude from the area coated with slurry I. Since Slurry II is coated over Slurry I, Slurry II can easily follow the surface shape of Slurry I. After drying slurries I and II, the dried slurries are roll pressed. The first active material-containing layer can be formed by drying and pressing slurry I. On the other hand, the first film can be formed by drying and pressing slurry II. In this way, a first electrode structure can be obtained. The first electrode structure may be cut to a desired size.

The first film-forming slurry II can be obtained, for example, by obtaining a dispersion liquid in which inorganic particles and a binder are suspended in a suitable solvent, and then performing a dispersion treatment using a bead mill or the like. One method for making the frequency distribution chart for the first film have two peaks is, for example, a method of mixing two types of inorganic particles with different D50s.

As the inorganic particles contained in the slurry for forming the first film, for example, two powders having a D50 of 0.4 μm to 0.7 μm and a powder having a D50 of 1.4 μm to 1.8 μm are used. : Use a mixture at a ratio of 8 to 8:2. These inorganic particles may be of the same type or different types. As described above, the particle size may be adjusted by further performing a dispersion treatment on the dispersion containing the inorganic particles.

When performing dispersion using a bead mill, it is possible to control the particle size of the material constituting the first film by adjusting the bead material, bead diameter, bead filling rate, blade rotation speed, and processing time. be. That is, by adjusting these conditions in a complex manner, the particle size and frequency of the first peak and second peak can be adjusted.

The diameter of the beads used is, for example, within the range of 1 mm to 2 mm. The filling rate is, for example, within the range of 40% to 70%. The rotation speed is, for example, within the range of 500 rpm to 3000 rpm. The processing time is, for example, 3 to 10 minutes.

In order to increase the frequency F1 of the first peak, it is effective to crush secondary particles of inorganic particles in order to increase the abundance ratio of inorganic particles existing in the form of primary particles. Therefore, in order to increase the frequency F1 of the first peak, it is preferable to perform bead mill dispersion using a sand grinder or the like using large collision energy.

For example, if the dispersion solution is strongly dispersed by compositely adjusting the bead material, bead diameter, bead filling rate, impeller rotation speed, and processing time described above, the first peak position D1 (particle diameter) will become smaller. As a result, the ratio D1/D2 tends to become smaller. For example, if the dispersion solution is dispersed too strongly by extending the treatment time, D10 becomes too small and aggregates are likely to be formed, which is not preferable.

On the other hand, if the dispersion solution is weakly dispersed by compositely adjusting the bead material, bead diameter, bead filling rate, impeller rotation speed, and processing time, the second peak position D2 (particle diameter) becomes larger. Therefore, the ratio D1/D2 tends to increase.

The second electrode structure can be manufactured as follows. After applying the slurry containing the second active material onto the second current collector, the slurry is dried, and the dried slurry is roll pressed to obtain a laminate. The obtained laminate may be a second electrode including a second active material-containing layer on at least one main surface of the second current collector. After cutting the laminate as the second electrode into a predetermined size as necessary, a second film is formed on the laminate by electrospinning. Then, pressing may be performed. Examples of the pressing method include roll pressing.

Note that when the second film is not formed on the second current collection tab, the second film can be formed after masking the second current collection tab. An example of this is shown in FIG. FIG. 11 is a perspective view showing an example of the process of forming a second film on the second electrode. As shown in FIG. 11, the second film 5 is directly formed by depositing the raw material solution discharged from the nozzle N on the second active material-containing layer 2b and the second current collecting tab 2c as organic fibers. One side of the second current collecting tab 2c and its vicinity are covered with a mask M. Therefore, the second film 5 includes organic fibers deposited across the surface of the second active material-containing layer 2b and the portion of the surface of the second current collecting tab 2c adjacent to the second active material-containing layer 2b. It becomes a porous membrane containing

The electrode group of the embodiment can be obtained by stacking the first electrode structure and the second electrode structure so that they face each other with the first film and the second film interposed in between.

<Second manufacturing method>
A second film is formed by electrospinning on the first electrode structure produced by the first manufacturing method. Then, pressing may be performed. In this way, a first electrode structure further having a second film on the first film can be obtained.

Next, after applying a slurry containing the second active material onto at least one surface of the second current collector, the slurry is dried, and the dried material is roll pressed and cut into a predetermined size. Obtain 2 electrodes.

The electrode group of the embodiment can be obtained by stacking a first electrode structure having a second film and a second electrode so that they face each other with the first film and the second film interposed in between.

The electrode group obtained by the first or second manufacturing method may be used as a single electrode group, or a plurality of electrode groups may be stacked and used. Furthermore, one or more electrode groups may be spirally wound. Note that the electrode group may be further pressed.

According to the first embodiment, an electrode group is provided that includes a first electrode structure and a second electrode structure at least partially facing the first electrode structure. The first electrode structure includes a first current collector, a first active material-containing layer provided on at least one surface of the first current collector, and inorganic particles. and a first film provided in the first film. The second electrode structure includes a second current collector, a second active material-containing layer provided on at least one surface of the second current collector, and an organic material; and a second film provided on. Regarding the first film, a volume-based frequency distribution chart obtained by laser diffraction scattering has two peaks.

In the first film, particles having a relatively small particle size enter gaps between particles having a relatively large particle size, thereby increasing the density of the layer, so that the electrode group according to the embodiment Shows excellent insulation properties. Further, the frequency distribution chart regarding the first film forming slurry for forming the first film, which shows a frequency distribution chart having two peaks, also has the same chart shape as the frequency distribution chart for the first film. Since such a slurry for forming the first film has excellent dispersibility, the number of coarse particles contained after dispersion treatment using a bead mill or the like is small. As a result, in the coating process using the slurry, coating omission can be suppressed, so that the resulting electrode group including the first film can achieve high insulation.

(Second embodiment)
The secondary battery according to the second embodiment includes the electrode group according to the first embodiment and an electrolyte. The secondary battery may further include an exterior member capable of accommodating the electrode group and the electrolyte.

One or more electrode groups can be used in a laminated type, or in a spirally or flat spirally wound manner. The plurality of electrode groups are stacked, for example, so that first electrode structures and second electrode structures are alternately arranged.

The secondary battery may further include a first electrode terminal electrically connected to the first current collecting tab, and a second electrode terminal electrically connected to the second current collecting tab.

As the electrolyte, for example, a non-aqueous electrolyte is used. Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel-like non-aqueous electrolyte made of a composite of a liquid electrolyte and a polymer material, and the like. The liquid non-aqueous electrolyte can be prepared, for example, by dissolving the electrolyte in an organic solvent at a concentration of 0.5 mol/L or more and 2.5 mol/L or less.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), and trifluoromethane. Examples include lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN(CF ₃ SO ₂ ) ₂ ], or mixtures thereof. It is preferable that it is resistant to oxidation even at high potentials, and LiPF ₆ is most preferable.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate, and chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC). , cyclic ethers such as tetrahydrofuran (THF), 2methyltetrahydrofuran (2MeTHF), dioxolane (DOX), chain ethers such as dimethoxyethane (DME), diethoxyethane (DEE), γ-butyrolactone (GBL), Examples include acetonitrile (AN) and sulfolane (SL). These organic solvents may be used alone or as a mixture of two or more.

Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (P1N), and polyethylene oxide (PEO).

Note that as the non-aqueous electrolyte, a room temperature molten salt (ionic melt) containing lithium ions, a polymer solid electrolyte, an inorganic solid electrolyte, etc. may be used.

As the exterior member, for example, a metal container or a laminated film container can be used.

The shape of the secondary battery is not particularly limited, and can be in various shapes, such as cylindrical, flat, thin, square, coin-shaped, etc.

FIG. 12 is a partially cutaway perspective view showing an example of the secondary battery according to the embodiment. FIG. 12 is a diagram showing an example of a secondary battery using a laminate film as an exterior member. The secondary battery 100 shown in FIG. 12 includes an exterior member 110 made of a laminate film, an electrode group 120, a first electrode terminal 130, a second electrode terminal 140, and a nonaqueous electrolyte (not shown). The electrode group 120 includes a plurality of electrode groups according to the embodiment. These electrode groups are stacked such that the first electrode structures and the second electrode structures are alternately arranged. A non-aqueous electrolyte (not shown) is held or impregnated in the electrode group 120. A first current collection tab of the first electrode structure is electrically connected to the first electrode terminal 130 . A second current collection tab of the second electrode structure is electrically connected to the second electrode terminal 140 . As shown in FIG. 12, the first electrode terminal 130 and the second electrode terminal 140 are spaced apart from each other, and their tips protrude outward from one side of the exterior member 110.

FIG. 13 is an exploded perspective view showing another example of the secondary battery according to the embodiment. FIG. 13 is a diagram showing an example of a secondary battery using a square metal container as an exterior member. The secondary battery shown in FIG. 13 includes an exterior member 20, a wound electrode group 51, a lid 52, a first electrode terminal 53, a second electrode terminal 54, and a non-aqueous electrolyte (not shown). . The wound electrode group 51 has a structure in which the electrode group according to the embodiment is wound in a flat spiral shape. In the wound electrode group 51, the first current collecting tab 25 wound in a flat spiral shape is located on one end surface of the winding shaft, and the first current collecting tab 25 wound in a flat spiral shape is located on one end surface of the winding shaft. Two current collection tabs 26 are located on the other end surface of the winding shaft. A non-aqueous electrolyte (not shown) is held or impregnated in the electrode group 51.

The first electrode lead 27 is electrically connected to the first current collecting tab 25 and also to the first electrode terminal 53. Further, the second electrode lead 28 is electrically connected to the second current collecting tab 26 and also to the second electrode terminal 54 . The electrode group 51 is arranged within the exterior member 20 such that the first electrode lead 27 and the second electrode lead 28 face the main surface side of the exterior member 20 . The lid 52 is fixed to the opening 20a of the exterior member 20 by welding or the like. The first electrode terminal 53 and the second electrode terminal 54 are each attached to the lid 52 via an insulating hermetic seal member (not shown).

The secondary battery of the second embodiment described above includes the electrode group according to the first embodiment, and thus exhibits excellent insulation properties.

(Third embodiment)
According to a third embodiment, a battery pack is provided. This battery pack includes the secondary battery according to the second embodiment or an assembled battery including a plurality of secondary batteries.

The battery pack according to the second embodiment can further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses a battery pack as a power source may be used as a protection circuit for the battery pack.

Furthermore, the battery pack according to the third embodiment may further include an external terminal for power supply. The external terminal for energization is for outputting current from the secondary battery to the outside and/or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for energization. Furthermore, when charging the battery pack, charging current (including regenerated energy from the motive power of an automobile, etc.) is supplied to the battery pack through an external terminal for energization.

Next, an example of the battery pack according to the third embodiment will be described with reference to the drawings.

FIG. 14 is an exploded perspective view schematically showing an example of a battery pack according to the third embodiment. FIG. 15 is a block diagram showing an example of the electric circuit of the battery pack shown in FIG. 14.

The battery pack 300 shown in FIGS. 14 and 15 includes a storage container 31, a lid 32, a protective sheet 33, an assembled battery 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown). .

The storage container 31 shown in FIG. 14 is a bottomed square container with a rectangular bottom surface. The storage container 31 is configured to be able to accommodate the protective sheet 33, the assembled battery 200, the printed wiring board 34, and the wiring 35. The lid 32 has a rectangular shape. The lid 32 accommodates the assembled battery 200 and the like by covering the accommodation container 31. Although not shown, the container 31 and the lid 32 are provided with an opening or a connection terminal for connection to an external device or the like.

The assembled battery 200 includes a plurality of single cells 100, a positive lead 22, a negative lead 23, and an adhesive tape 24.

At least one of the plurality of single cells 100 is a secondary battery according to the second embodiment. Each of the plurality of unit cells 100 is electrically connected in series as shown in FIG. 15. The plurality of unit cells 100 may be electrically connected in parallel, or may be connected in a combination of series connection and parallel connection. When a plurality of single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

The adhesive tape 24 fastens the plurality of unit cells 100 together. Instead of the adhesive tape 24, a heat shrink tape may be used to fix the plurality of cells 100. In this case, the protective sheets 33 are arranged on both sides of the assembled battery 200, and after a heat-shrinkable tape is made to go around, the heat-shrinkable tape is heat-shrinked to bundle the plurality of unit cells 100.

One end of the positive electrode side lead 22 is connected to the assembled battery 200. One end of the positive electrode side lead 22 is electrically connected to the positive electrode of one or more unit cells 100. One end of the negative electrode side lead 23 is connected to the assembled battery 200. One end of the negative electrode side lead 23 is electrically connected to the negative electrode of one or more unit cells 100.

The printed wiring board 34 is installed along one of the inner surfaces of the container 31 in the short side direction. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346,

wiring

342a and 343a, an external terminal 350 for energization, and a positive wiring (positive wiring) 348a. and a negative side wiring (negative side wiring) 348b. One main surface of the printed wiring board 34 faces one side of the assembled battery 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200.

The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23 a of the negative lead 23 is electrically connected to the negative connector 343 .

The thermistor 345 is fixed to one main surface of the printed wiring board 34. Thermistor 345 detects the temperature of each cell 100 and transmits the detection signal to protection circuit 346.

The external terminal 350 for power supply is fixed to the other main surface of the printed wiring board 34. The external terminal 350 for energization is electrically connected to a device existing outside the battery pack 300. External terminal 350 for energization includes a positive terminal 352 and a negative terminal 353.

The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. Furthermore, the protection circuit 346 is electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative electrode side connector 343 via wiring 343a. Further, the protection circuit 346 is electrically connected to each of the plurality of unit cells 100 via the wiring 35.

The protective sheets 33 are disposed on both inner surfaces of the container 31 in the long side direction and on the inner surface of the container 31 in the short side direction facing the printed wiring board 34 with the assembled battery 200 interposed therebetween. The protective sheet 33 is made of resin or rubber, for example.

The protection circuit 346 controls charging and discharging of the plurality of single cells 100. Furthermore, the protection circuit 346 connects the protection circuit 346 to an external terminal for energizing the external device based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from the individual cells 100 or the assembled batteries 200. 350 (positive side terminal 352, negative side terminal 353).

The detection signal transmitted from the thermistor 345 can be, for example, a signal that detects that the temperature of the cell 100 is higher than a predetermined temperature. Examples of the detection signal transmitted from each single cell 100 or assembled battery 200 include signals that detect overcharging, overdischarging, and overcurrent of the single cell 100. When detecting overcharging or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

Note that as the protection circuit 346, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses the battery pack 300 as a power source may be used.

Additionally, this battery pack 300 includes the external terminal 350 for power supply, as described above. Therefore, this battery pack 300 can output current from the assembled battery 200 to an external device and input current from the external device to the assembled battery 200 via the external terminal 350 for energization. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for energization. Further, when charging the battery pack 300, a charging current from an external device is supplied to the battery pack 300 through the external terminal 350 for energization. When this battery pack 300 is used as an on-vehicle battery, regenerated energy from the motive power of the vehicle can be used as the charging current from an external device.

Note that the battery pack 300 may include a plurality of assembled batteries 200. In this case, the plurality of assembled batteries 200 may be connected in series, in parallel, or by a combination of series connection and parallel connection. Further, the printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as a positive terminal and a negative terminal of an external terminal for energization, respectively.

Such a battery pack is used, for example, in applications that require excellent cycle performance when drawing a large current. Specifically, this battery pack is used, for example, as a power source for electronic equipment, a stationary battery, and an in-vehicle battery for various vehicles. An example of the electronic device is a digital camera. This battery pack is particularly suitable for use as a vehicle battery.

The battery pack according to the third embodiment includes the secondary battery according to the second embodiment. Therefore, this battery pack can achieve excellent insulation.

[Example]
(Example 1)
An electrode group including a first electrode structure as a positive electrode and a second electrode structure as a negative electrode, and a secondary battery including this electrode group were manufactured by the method described below.

LiNi _0.33 Co _0.33 Mn _0.33 O ₂ particles were prepared as a positive electrode active material, carbon black was prepared as a conductive agent, and polyvinylidene fluoride was prepared as a binder. These were mixed at a mass ratio of 90:5:5 to obtain a mixture. Next, the obtained mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare slurry I. Slurry I is a slurry for forming a layer containing a positive electrode active material.

Next, slurry II was prepared as the slurry for forming the first film as follows. First, as inorganic particles, alumina particles (material 1) with an average particle diameter D50 of 0.6 μm and alumina particles (material 2) with an average particle diameter D50 of 1.7 μm are prepared, and these are mixed in a 1:1 mass ratio. The mixture was mixed at the same ratio and subjected to a mixing process using a Henschel mixer. Of the two types of materials used as the inorganic particles, the material with a relatively small D50 is called "Material 1", and the material with a relatively large D50 is called "Material 2". Next, 4 parts by mass of PVDF and NMP were mixed with 100 parts by mass of the inorganic particles, stirred with a stirrer, and then dispersed with a bead mill. The dispersion conditions using the bead mill were as shown in Table 1 below. In this way, Slurry II was prepared. Slurry II is a slurry for forming the first layer.

Using the coating apparatus shown in FIGS. 9 and 10, slurry I and slurry II were overcoated in this order on both sides of a 20 μm thick aluminum foil. By setting the coating speed of slurry I to 20 m/min and the coating speed of slurry II to 20 m/min, slurry II was applied onto slurry I before slurry I dried. Thereafter, after drying Slurry I and Slurry II, the dried slurry was subjected to a roll press at a linear pressure of 1 kN/cm and cut into a predetermined size to obtain a positive electrode as a first electrode structure. The thickness of each positive electrode active material containing layer was 20 μm. Note that a portion not supported by the positive electrode active material-containing layer was provided on one long side of the current collector, and this portion was used as a positive electrode current collecting tab. In the obtained first electrode structure, both surfaces (principal surfaces) of the positive electrode active material-containing layer were covered with the first film, as shown in FIGS. 1 and 2. The content of the inorganic material in the first film was 98% by mass.

On the other hand, a negative electrode as a second electrode was produced by the following method. Lithium titanate particles having an average primary particle diameter of 0.5 μm, carbon black as a conductive agent, and polyvinylidene fluoride as a binder were prepared. These were mixed at a mass ratio of 90:5:5 to obtain a mixture. The resulting mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare a slurry. The obtained slurry was applied to a 20 μm thick aluminum foil and dried. Next, the dried coating film was pressed to obtain a negative electrode. The thickness of each negative electrode active material containing layer was 50 μm. Note that a portion not supported by the negative electrode active material-containing layer was provided on one long side of the current collector, and this portion was used as a negative electrode current collection tab.

Next, organic fibers were deposited on this negative electrode by electrospinning to form a second film. Polyimide was used as the organic material. This polyimide was dissolved in DMAc as a solvent at a concentration of 20% by mass to prepare a raw material solution as a liquid raw material. The obtained raw material solution was supplied to the surface of the positive electrode from a spinning nozzle at a supply rate of 5 μl/min using a metering pump. A voltage of 20 kV was applied to the spinning nozzle using a high voltage generator, and a layer of organic fibers was formed on the surface of the positive electrode while moving the spinning nozzle over an area of 100 x 200 mm. In addition, the electrospinning method was performed with the surface of the negative electrode current collecting tab masked except for a 10 mm portion from the boundary with the positive electrode active material-containing layer on both surfaces (principal surfaces) of the negative electrode current collecting tab. A negative electrode (second electrode structure) having the structure shown in was obtained. That is, the second film includes the surface of the negative electrode active material-containing layer, four side surfaces perpendicular to the respective surfaces (principal surfaces) of the negative electrode active material-containing layer, and three end surfaces exposed on the negative electrode surface of the negative electrode current collector. , and the portion including the boundary with the negative electrode active material-containing layer on the surface of the negative electrode current collector tab.

Next, this negative electrode was pressed using a roll press. In the second film, the average diameter of the organic fibers was 700 nm, and 50% or more of the total volume of the fibers forming the second film was occupied by organic fibers with an average diameter of 1 μm or less. The average pore diameter of the second membrane was 10 μm, and the porosity was 45%.

Next, using the produced positive electrode (first electrode structure) and negative electrode (second electrode structure), a secondary battery was produced as follows.

The positive electrode and the negative electrode are arranged so that the positive electrode active material-containing layer and the negative electrode active material-containing layer face each other with the first film and the second film interposed therebetween, and are wound into a flat spiral shape. An electrode group with a shape was obtained. After vacuum drying at room temperature overnight, it was left in a glove box with a dew point of -80°C or lower for one day. This was placed in a metal container together with an electrolyte to obtain a non-aqueous electrolyte battery of Example 1. The electrolytic solution was one in which 1 mol/L of LiPF ₆ was dissolved as an electrolyte in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1).

(Comparative example 1)
When producing the first electrode structure, secondary electrode structure was prepared in the same manner as in Example 1, except that titania particles having only one peak in the particle size distribution chart were used as inorganic particles to be mixed in slurry II. A battery was created. The average particle diameter D50 of the titania particles was 0.40 μm.

<Self-discharge performance evaluation>
The secondary batteries produced in Example 1 and Comparative Example 1 were each charged until the SOC reached 70%, and then left in a 25° C. environment. Then, the voltage drop rate ΔV [mV/d] from the 15th day to the 18th day of standing was measured for each example. As a result, the ΔV of the secondary battery according to Example 1 was 0.5 mV/d, and the ΔV of the secondary battery according to Comparative Example 1 was 1.0 mV/d. From this result, it can be seen that the voltage drop rate in Example 1 was significantly slower. The voltage drop rate is an index for evaluating self-discharge characteristics.

<Particle size distribution measurement>
The secondary batteries produced in Example 1 and Comparative Example 1 were disassembled according to the method described in the first embodiment, and the particle size distribution of particles constituting the first film was measured. FIG. 16 is a particle size distribution chart obtained by a laser diffraction scattering method for the first film according to Example 1. In FIG. 16, the horizontal axis shows particle diameter [μm], the left vertical axis shows frequency [%], and the right vertical axis shows cumulative [%]. When D10 and D50 were calculated based on the chart shown in FIG. 16, they were 0.50 μm and 1.1 μm, respectively. Moreover, as can be read from FIG. 16, the position (particle diameter) of the first peak P1 was 0.6 μm, and its frequency was 4%. The position (particle diameter) of the second peak P2 was 1.3 μm, and its frequency was 5%. The ratio D1/D2 of the first peak position D2 to the second peak position D1 was 2.2.

<Grind Gauge>
Separately, slurry II, which was used when producing the first film included in the electrode group according to Example 1 and Comparative Example 1, was tested using a grind gauge according to the method described in the first embodiment. In this test, primary particles or secondary particles with a diameter of 40 μm to 60 μm, primary particles or secondary particles with a diameter of 60 μm to 80 μm, and primary particles or The number of each type of secondary particle present was investigated.

The results of particle size distribution measurement, grind gauge measurement, and self-discharge performance evaluation according to Example 1 and Comparative Example 1 are summarized in Tables 1 and 2 below.

(Example 2)
In Example 2, a secondary battery was produced in the same manner as in Example 1, except that alumina particles with a D50 of 1.5 μm were used as material 2 when producing the first film-forming slurry. .

(Example 3)
In Example 3, a secondary battery was produced in the same manner as in Example 1, except that alumina particles with a D50 of 2.0 μm were used as material 2 when producing the first film-forming slurry. .

(Example 4)
In Example 4, when producing the first film forming slurry, alumina particles with a D50 of 0.5 μm were used as material 1, and alumina particles with a D50 of 1.5 μm were used as material 2. A secondary battery was produced in the same manner as in Example 1 except for the following.

(Example 5)
In Example 5, when producing the first film forming slurry, alumina particles with a D50 of 0.4 μm were used as material 1, and alumina particles with a D50 of 1.2 μm were used as material 2. A secondary battery was produced in the same manner as in Example 1 except for the following.

(Example 6)
In Example 6, when producing the first film forming slurry, alumina particles with a D50 of 0.4 μm were used as material 1, and alumina particles with a D50 of 0.6 μm were used as material 2. A secondary battery was produced in the same manner as in Example 1 except for the following.

(Example 7)
In Example 7, when producing the slurry for forming the first film, alumina particles with D50 of 0.4 μm were used as material 1, alumina particles with D50 of 1.2 μm were used as material 2, and a bead mill was used. A secondary battery was produced in the same manner as in Example 1, except that the conditions were changed as shown in Table 3.

<Particle size distribution measurement and grind gauge measurement>
Particle size distribution measurement and grind gauge measurement were performed on the first film forming slurry according to each of Examples 2 to 7. The above results are shown in Tables 3 and 4. In Tables 2 and 4, the column "Ratio of peak positions" shows the ratio D1/D2 of the position D1 of the first peak P1 to the position D2 of the second peak P2.

As shown in Tables 1 and 2, from the comparison between Example 1 and Comparative Example 1, when the volume-based frequency distribution chart obtained by the laser diffraction scattering method for the first film has two peaks, the voltage It can be seen that the descending speed ΔV was able to be significantly lowered. Further, the number of coarse particles contained in the first film forming slurry produced in Example 1 was 0 in any diameter range. In contrast, the first film forming slurry prepared in Comparative Example 1 contained 30 particles with a diameter of 40 μm to 60 μm, and 10 particles with a diameter of 60 μm to 80 μm. It was. From this, it is considered that the first film-forming slurry according to Comparative Example 1 had poor dispersibility because the particle size distribution chart of the inorganic particles contained therein had only one peak. Therefore, it is considered that the number of coarse particles contained in the first film-forming slurry was large, and the frequency of coating omissions increased, resulting in poor self-discharge performance.

In this way, by examining the number of coarse particles contained in the slurry for forming the first film, it is possible to estimate the self-discharge performance of the first film produced using the slurry. Specifically, the greater the number of coarse particles contained in the first film-forming slurry, the lower the self-discharge performance tends to be.

Based on this, the results of Examples 2 to 7 will be discussed.
The particle size distribution charts of the first film forming slurries according to Examples 2 to 7 had two peaks in all examples. Therefore, since the dispersibility of these slurries was excellent, the number of coarse particles contained in the first film forming slurry according to Examples 2 to 7 was lower than that contained in the first film forming slurry according to Comparative Example 1. The number of coarse particles was small compared to the number of coarse particles. From this, it can be inferred that if the first film is produced using the first film forming slurry according to Examples 2 to 7, an electrode group with excellent insulation properties can be obtained.

From the comparison between Example 2 and Example 3, it can be seen that when the peak position ratio D1/D2 is 3.0 or less, the number of coarse particles in the slurry tends to be small.

Furthermore, as shown in Examples 4 and 5, when the particle diameter D1 of the first peak P1 is 1.0 μm or less and the particle diameter D2 of the second peak P2 is 1.0 μm or more, The number of coarse particles was 0. On the other hand, as shown in Example 6, when the particle diameter D1 of the first peak P1 is 1.0 μm or less and the particle diameter D2 of the second peak P2 is also 1.0 μm or less, the number of coarse particles increases. increased slightly. This shows that the slurries according to Examples 4 and 5 had better dispersibility than the slurry according to Example 6.

From a comparison between Example 4 and Example 7, in Example 4 where D10 was 0.20 μm or more, the number of coarse particles in the slurry was smaller than in Example 7 where D10 was 0.10 μm. This is considered to be because in Example 4, the amount of fine powder itself was small, so the number of coarse particles as aggregates was reduced.

According to at least one embodiment and example described above, an electrode group is provided that includes a first electrode structure and a second electrode structure at least partially facing the first electrode structure. The first electrode structure includes a first current collector, a first active material-containing layer provided on at least one surface of the first current collector, and inorganic particles. and a first film provided in the first film. The second electrode structure includes a second current collector, a second active material-containing layer provided on at least one surface of the second current collector, and an organic material; and a second film provided on. Regarding the first film, a volume-based frequency distribution chart obtained by laser diffraction scattering has two peaks. Such an electrode group has excellent insulation properties.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1...1st electrode structure, 1a...1st current collector, 1b...1st active material containing layer, 1c...1st current collection tab, 2...2nd electrode structure, 2a...2nd current collector, 2b ...Second active material containing layer, 2c...Second current collection tab, 3...Separator, 4...First film, 5...Second film, 6...First film, 7...Second film, 10...Electrode group, 20 ... Exterior member, 20a... Opening, 22... Positive electrode side lead, 23... Negative electrode side lead, 24... Adhesive tape, 25... First current collecting tab, 26... Second current collecting tab, 27... First electrode lead, 28 ...Second electrode lead, 31...Accommodation container, 32...Lid, 33...Protection sheet, 34...Printed wiring board, 35...Wiring, 40...First surface, 41...First back surface, 42...Second surface, 43... Second back surface, 44...Four sides, 51...electrode group, 51...wound type electrode group, 52...lid, 53...first electrode terminal, 54...second electrode terminal, 60...coating device, 61...conveying roller , 62...tank, 62a...slurry I discharge port, 63...tank, 63a...slurry II discharge port, 100...secondary battery, 110...exterior member, 120...electrode group, 130...first electrode terminal, 140...second Electrode terminal, 200... Plural assembled batteries, 200... Assembled battery, 300... Battery pack, 342... Positive electrode side connector, 342a... Wiring, 343... Negative electrode side connector, 343a... Wiring, 345... Thermistor, 346... Protection circuit, 348a ...Plus side wiring (positive side wiring), 348a...Plus side wiring, 348b...Minus side wiring (negative side wiring), 348b...Minus side wiring, 350...External terminal, 352...Positive side terminal, 353...Negative side terminal, A...Front side, B...Back side, C...Front side, D...Back side.

Claims

comprising a first electrode structure and a second electrode structure at least partially facing the first electrode structure,
The first electrode structure includes:
a first current collector; a first active material-containing layer provided on at least one surface of the first current collector; and a first active material-containing layer that includes inorganic particles and is provided on the first active material-containing layer. comprising a membrane;
The second electrode structure includes:
a second current collector; a second active material-containing layer provided on at least one surface of the second current collector; and a second active material-containing layer that includes an organic material and is provided on the second active material-containing layer. comprising a membrane;
The volume-based frequency distribution chart obtained by the laser diffraction scattering method for the first film shows an electrode group having two peaks.
The two peaks are a first peak and a second peak,
The particle diameter D1 corresponding to the peak top of the first peak is smaller than the particle diameter D2 corresponding to the peak top of the second peak,
The electrode group according to claim 1, wherein a ratio D1/D2 of the particle diameter D1 to the particle diameter D2 is within a range of 1.0 or more and 3.0 or less.
The two peaks are a first peak and a second peak,
The particle diameter D1 corresponding to the peak top of the first peak is 0.4 μm or more and 1.0 μm or less,
The electrode group according to claim 1 or 2, wherein a particle diameter D2 corresponding to the peak top of the second peak is more than 1.0 μm and 2.0 μm or less.
The electrode group according to any one of claims 1 to 3, wherein D10 in the frequency distribution chart is 0.20 μm or more.
The electrode group according to any one of claims 1 to 4, wherein D50 in the frequency distribution chart is within a range of 0.60 μm to 2.0 μm.
The electrode group according to any one of claims 1 to 5, wherein the inorganic particles include a substance with an energy bandgap value of 3.0 eV or more.
The electrode group according to any one of claims 1 to 6, wherein the first film has a thickness within a range of 1.0 μm to 5.0 μm.
An electrode group according to any one of claims 1 to 7,
A secondary battery comprising an electrolyte.
A battery pack comprising the secondary battery according to claim 8.