JP7490622B2 - Secondary batteries, battery packs, vehicle and stationary power sources - Google Patents

Description

Embodiments of the present invention relate to secondary batteries, battery packs, vehicles, and stationary power sources.

Non-aqueous electrolyte batteries, particularly lithium secondary batteries, using carbon materials or lithium titanium oxide as the negative electrode active material and layered oxides containing nickel, cobalt, manganese, etc. as the positive electrode active material have already been put to practical use as power sources in a wide range of fields. Such non-aqueous electrolyte batteries come in a wide variety of forms, from small ones for use in various electronic devices to large ones for use in electric vehicles. Unlike nickel-metal hydride batteries or lead-acid batteries, the electrolyte in these lithium secondary batteries uses a non-aqueous organic solvent containing ethylene carbonate, methyl ethyl carbonate, etc. mixed therein. Electrolytes using these solvents have higher oxidation resistance and reduction resistance than aqueous electrolytes, and are less susceptible to electrolysis of the solvent. Therefore, non-aqueous lithium secondary batteries can achieve a high electromotive force of 2V to 4.5V.

On the other hand, since most organic solvents are flammable, the safety of secondary batteries using organic solvents is, in principle, inferior to secondary batteries using aqueous solutions. Although various measures have been taken to improve the safety of lithium secondary batteries using electrolytes containing organic solvents, they are not necessarily sufficient. In addition, non-aqueous lithium secondary batteries require a dry environment in the manufacturing process, which inevitably increases the manufacturing cost. In addition, electrolytes containing organic solvents have poor conductivity, so the internal resistance of non-aqueous lithium secondary batteries is likely to be high. Such issues are a major drawback in electric vehicles or hybrid electric vehicles, where battery safety and battery cost are important, and in large-scale storage batteries for power storage.

To solve these problems, the conversion of the electrolyte into an aqueous solution has been studied. One of the problems with converting the electrolyte into an aqueous solution is the generation of gas at the positive and negative electrodes. The generation of hydrogen at the negative electrode and the generation of oxygen at the positive electrode due to the reduction reaction of water are examples of undesirable gas generation. In addition, chlorine gas may be generated when an aqueous solution in which an electrolyte salt containing chlorine is dissolved is in contact with the positive electrode.

Patent No. 4972862 JP 2020-053385 A

S. Liu et al. "Rechargeable Aqueous Lithium-Ion Battery of TiO2/LiMn2O4 with a High Voltage" Journal of the Electrochemical Society, 158(12) A1490-A1497 (2011) This paper relates to the aqueous LIB.

The problem that the present invention aims to solve is to provide a secondary battery that can achieve high safety by suppressing gas generation.

According to an embodiment, a secondary battery is provided. The secondary battery includes an electrode group, a resin portion , and an exterior member that covers at least a part of the resin portion . The electrode group includes a positive electrode, a negative electrode, and a porous separator that holds an aqueous electrolyte. The positive electrode includes a positive electrode current collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode current collector, and an ion conductive layer. The ion conductive layer covers the main surface and side surface of the positive electrode active material-containing layer, and an end of the ion conductive layer is in contact with the main surface of the positive electrode current collector. The positive electrode current collector has a positive electrode tab portion on which the positive electrode active material-containing layer is not supported. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode current collector. The negative electrode current collector has a negative electrode tab portion on which the negative electrode active material-containing layer is not supported. The positive electrode active material-containing layer is located in a space formed between the positive electrode current collector and the ion conductive layer. The ion-conducting layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via a porous separator. The electrode group is directly covered with a resin portion except for a part of the positive electrode tab portion and a part of the negative electrode tab portion.

According to another embodiment, a battery pack is provided. The battery pack includes a secondary battery according to an embodiment.

According to another embodiment, a vehicle is provided. The vehicle includes a battery pack according to an embodiment.

According to another embodiment, a stationary power source is provided. The stationary power source includes a battery pack according to an embodiment.

FIG. 1 is a perspective view illustrating an example of a secondary battery according to an embodiment. FIG. 2 is a cross-sectional view that illustrates a cross section along line II-II of the secondary battery illustrated in FIG. 1 . FIG. 2 is a two-sided view showing a plan view and a cross-sectional view of a positive electrode according to an example. FIG. 2 is a two-sided view showing a plan view and a cross-sectional view of a negative electrode according to an example. FIG. 4 is a cross-sectional view illustrating another example of a secondary battery according to an embodiment of the present invention. FIG. 11 is a cross-sectional view illustrating a schematic configuration of still another example of a secondary battery according to an embodiment. 3A to 3C are cross-sectional views each showing a schematic process for manufacturing a secondary battery according to an embodiment. 3A to 3C are cross-sectional views each showing a schematic process for manufacturing a secondary battery according to an embodiment. 3A to 3C are cross-sectional views each showing a schematic process for manufacturing a secondary battery according to an embodiment. FIG. 1 is an exploded perspective view illustrating an example of a battery pack according to an embodiment. FIG. 11 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 10 . 1 is a cross-sectional view illustrating an example of a vehicle according to an embodiment. FIG. 1 is a block diagram showing an example of a system including a stationary power supply according to an embodiment.

The following describes the embodiments with reference to the drawings as appropriate. Note that common components throughout the embodiments are given the same reference numerals, and duplicate explanations will be omitted. Also, each figure is a schematic diagram to explain the embodiments and facilitate their understanding, and the shapes, dimensions, ratios, etc. may differ from the actual devices in some places, but these can be appropriately modified in design by taking into account the following explanations and known technologies.

As mentioned above, secondary batteries using aqueous electrolytes containing water as a solvent have the problem that gas is easily generated due to the electrolysis of water. When an electrolysis reaction of water occurs at the positive and negative electrodes, the coulombic efficiency of the secondary battery decreases. In addition, when an aqueous electrolyte containing an electrolyte salt containing chlorine is used, chlorine gas may be generated, for example, at the positive electrode. The generation of chlorine gas is undesirable from the viewpoint of safety. The generation of chlorine gas tends to be promoted when the positive electrode is in an overcharged or overdischarged state.

One way to suppress gas generation in the positive and negative electrodes is to reduce the amount of aqueous electrolyte in contact with the positive or negative electrodes. This suppresses side reactions between the positive and negative electrodes and the aqueous electrolyte, thereby reducing the amount of gas generated in the secondary battery.

First Embodiment
According to a first embodiment, a secondary battery is provided. The secondary battery includes an electrode group and a resin part. The electrode group includes a positive electrode, a negative electrode, and a porous separator holding an aqueous electrolyte. The positive electrode includes a positive electrode current collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode current collector, and an ion conductive layer. The ion conductive layer covers the main surface and side surface of the positive electrode active material-containing layer, and an end of the ion conductive layer is in contact with the main surface of the positive electrode current collector. The positive electrode current collector has a positive electrode tab part on which the positive electrode active material-containing layer is not supported. The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode current collector. The negative electrode current collector has a negative electrode tab part on which the negative electrode active material-containing layer is not supported. The positive electrode active material-containing layer is located in a space formed between the positive electrode current collector and the ion conductive layer. The ion-conducting layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via a porous separator. The electrode group is directly covered with a resin portion except for a part of the positive electrode tab portion and a part of the negative electrode tab portion.

The electrode group according to the embodiment will be described with reference to the drawings.

FIG. 1 is a perspective view that shows an example of a secondary battery 100 according to an embodiment. FIG. 2 is a cross-sectional view that shows an example of the secondary battery 100 taken along line II-II in FIG. 1. FIG. 3 is a two-sided view that shows a plan view and a cross-sectional view of a positive electrode 6 according to an embodiment. FIG. 4 is a two-sided view that shows a plan view and a cross-sectional view of a negative electrode 7 according to an embodiment. The secondary battery according to the embodiment may be an alkali metal ion secondary battery such as a lithium ion secondary battery or a sodium ion secondary battery.

In the following description, the X-axis direction and the Y-axis direction are parallel to the main surface of the electrode group 10 and are perpendicular to each other. The Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction. In other words, the Z-axis direction is the thickness direction.

The secondary battery 100 includes an electrode group 10 and a resin part 9. As shown in FIG. 1, the exterior of the secondary battery 100 exposes, for example, the resin part 9 and a positive electrode tab part 6c and a negative electrode tab part 7c, which will be described later. Here, as an example, the resin part 9 has a rectangular parallelepiped outer shape, but there is no particular restriction on the outer shape of the resin part 9. The outer shape of the resin part 9 may be, for example, a cube, a cylindrical shape, or a cone shape.

The electrode group 10 includes a positive electrode 6, a negative electrode 7, and a porous separator 8. The electrode group 10 shown in FIG. 1 is a laminated electrode group formed by stacking a positive electrode 6, a negative electrode 7, and a porous separator 8, each of which has a sheet shape. The sheet shape is a shape in which the area of the main surface extending in an in-plane direction perpendicular to the thickness direction (Z-axis direction) is larger than the area of the side surfaces.

As described later with reference to FIG. 4, the electrode group 10 may include a plurality of positive electrodes 6, a plurality of negative electrodes 7, and a plurality of porous separators 8. That is, the electrode group 10 according to the embodiment is formed by stacking at least one positive electrode 6, at least one porous separator 8, and at least one negative electrode 7. The electrode group 10 may be a wound electrode group in which these are wound in a stacked state.

The positive electrode 6 includes a positive electrode collector 6a, a positive electrode active material-containing layer 6b provided on a part of both sides of the positive electrode collector 6a, and an ion conduction layer 11. The positive electrode active material-containing layer 6b is provided on at least one of the two surfaces of the positive electrode collector 6a that faces the negative electrode. As shown in FIG. 2 and FIG. 3, the ion conduction layer 11 covers the entire positive electrode active material-containing layer 6b directly. In other words, the ion conduction layer 11 covers the main surface and side surface of the positive electrode active material-containing layer 6b, and the end surface is in contact with the main surface of the positive electrode collector 6a. In other words, the end of the ion conduction layer 11 is in contact with the main surface of the positive electrode collector 6a, forming a space 130 between the positive electrode collector 6a and the ion conduction layer 11. The positive electrode active material-containing layer 6b is located in the space 130. The shape of the space 130 corresponds to, for example, the shape of the positive electrode active material-containing layer 6b. An example of the shape of the space 130 is a substantially rectangular parallelepiped. A gap may be provided between the main surface and/or side surface of the positive electrode active material-containing layer 6b and the ion conductive layer 11.

As described below, when manufacturing the secondary battery according to the embodiment, the aqueous electrolyte may flow into the space 130 via the ion conductive layer 11. However, the amount of the flow is small. The aqueous electrolyte may or may not be held in the positive electrode active material-containing layer 6b. The space 130 may be a closed space. The closed space does not need to be strictly closed.

For example, as shown in FIG. 3, the positive electrode collector 6a has a positive electrode tab portion 6c that does not support either the positive electrode active material-containing layer 6b or the ion conductive layer 11. The positive electrode tab portion 6c protrudes along the X-axis direction, for example, from a part of one side of the rectangular positive electrode collector 6a that extends in the X-axis direction and the Y-axis direction. The shape of the positive electrode 6 is not particularly limited, but here, the positive electrode 6 has a rectangular sheet shape that extends in the X-axis direction and the Y-axis direction, excluding the positive electrode tab portion 6c.

The negative electrode 7 includes a negative electrode collector 7a and a negative electrode active material-containing layer 7b provided on a portion of both sides of the negative electrode collector 7a. The negative electrode active material-containing layer 7b is provided on at least the surface facing the positive electrode, among the front and back surfaces of the negative electrode collector 7a. The negative electrode active material-containing layer 7b may hold an aqueous electrolyte. As shown in FIG. 2 and FIG. 4, the negative electrode collector 7a has a negative electrode tab portion 7c on which the negative electrode active material-containing layer 7b is not supported. The negative electrode tab portion 7c protrudes along the X-axis direction, for example, from a portion of one side of the rectangular negative electrode collector 7a extending in the X-axis direction and the Y-axis direction. The shape of the negative electrode 7 is not particularly limited, but here, the negative electrode 7 has a rectangular sheet shape extending in the X-axis direction and the Y-axis direction, except for the negative electrode tab portion 7c.

The porous separator 8 is interposed between the positive electrode 6 and the negative electrode 7. The porous separator 8 has a rectangular sheet shape extending in the X-axis direction and the Y-axis direction. Although not shown, an aqueous electrolyte is held in the porous separator 8. When an aqueous electrolyte is held in both the negative electrode active material-containing layer 7b and the positive electrode active material-containing layer 6b, the mass of the aqueous electrolyte held per unit volume of the positive electrode active material-containing layer 6b may be smaller than the mass of the aqueous electrolyte held per unit volume of the negative electrode active material-containing layer 7b.

As shown in FIG. 2, the positive electrode 6, the porous separator 8, and the negative electrode 7 are stacked in this order along the Z-axis direction. The ion conduction layer 11 of the positive electrode 6 and the negative electrode active material-containing layer 7b of the negative electrode 7 face each other via the porous separator 8. Therefore, for example, the ion conduction layer 11 of the positive electrode 6 and the porous separator 8 are in contact. Also, for example, the negative electrode active material-containing layer 7b of the negative electrode 7 and the porous separator 8 are in contact.

As shown in Figures 1 and 2, the positive electrode 6 and the negative electrode 7 are stacked with a porous separator 8 interposed between them so that the direction in which the positive electrode tab portion 6c protrudes and the direction in which the negative electrode tab portion 7c protrudes are opposite to each other. However, the directions in which the positive electrode tab portion 6c and the negative electrode tab portion 7c protrude are not particularly limited, and these directions may be the same as each other.

A portion of the electrode group 10 including the positive electrode 6, the porous separator 8, and the negative electrode 7 is covered with the resin part 9. Specifically, the electrode group 10 is directly covered with the resin part 9, except for a portion of the positive electrode tab part 6c and a portion of the negative electrode tab part 7c. A portion of the positive electrode tab part 6c protrudes outside the resin part 9, while the other portion is covered with the resin part 9. A portion of the negative electrode tab part 7c protrudes outside the resin part 9, while the other portion is covered with the resin part 9.

In this way, in the secondary battery according to the embodiment, the resin part 9 covers almost the entire electrode group 10. The electrode group 10 covered with the resin part 9 is less likely to receive an aqueous electrolyte from the outside, compared to when the electrode group 10 is immersed in an aqueous electrolyte without being covered with the resin part 9. Therefore, gas generation in the positive electrode 6 and the negative electrode 7 can be significantly suppressed, compared to when the electrode group 10 is immersed in an aqueous electrolyte. In particular, since the positive electrode active material-containing layer 6b is present in the space 130, there is no or almost no aqueous electrolyte supply from the outside of the ion conductive layer 11 to the positive electrode active material-containing layer 6b. Therefore, in the positive electrode active material-containing layer 6b, side reactions between the positive electrode active material and the aqueous electrolyte are suppressed, and chlorine gas generation and oxygen gas generation in the positive electrode 6 are suppressed. As a result, the secondary battery according to the embodiment can achieve high safety.

On the other hand, since the porous separator 8 holds an aqueous electrolyte, ionic conduction between the positive and negative electrodes is ensured. The negative electrode active material-containing layer 7b and the porous separator 8 are in direct contact, whereas the positive electrode active material-containing layer 6b and the porous separator 8 are not in direct contact. However, as described above, the positive electrode active material-containing layer 6b is coated with an ion conduction layer 11. The ion conduction layer 11 can conduct alkali metal ions as charge carriers. Therefore, ionic conduction between the positive electrode active material-containing layer 6b and the negative electrode active material-containing layer 7b is ensured.

Figure 5 is a cross-sectional view that shows a schematic diagram of another example of a secondary battery according to an embodiment. The secondary battery 100 shown in Figure 5 has the same configuration as the secondary battery described with reference to Figures 1 to 4, except that it further includes an exterior member 2 that covers at least a part of the resin part 9. In Figure 5, as an example, the entire resin part 9 is covered with the exterior member 2. A part of the part of the positive electrode tab part 6c that protrudes (exposed) from the resin part 9 and a part of the part of the negative electrode tab part 7c that protrudes (exposed) from the resin part 9 are drawn out to the outside of the exterior member 2. For example, the exterior member 2 directly covers the entire surface of the resin part 9. There may be a gap between the exterior member 2 and the resin part 9.

When the secondary battery 100 further includes the exterior member 2, the robustness of the secondary battery 100 is increased, and the secondary battery 100 has high resistance to external impacts. In addition, since the electrode group 10 is covered not only by the resin portion 9 but also by the exterior member 2, high airtightness can be obtained.

As the exterior member 2, a metal container, a container made of laminate film, or a resin container can be used. As the metal container, a metal can made of nickel, iron, stainless steel, or the like, having a rectangular or cylindrical shape can be used. As the resin container, a container made of polyethylene or polypropylene can be used.

The wall surface of the exterior member 2 can have, for example, two or more openings. Each opening preferably has an openable and closable lid or valve. As will be explained in the method for manufacturing a secondary battery described later, the openings can function as an inlet for injecting or discharging the aqueous electrolyte. The openings can also function as an inlet for injecting or discharging the molten resin.

Figure 5 shows a case where the exterior member 2 has two openings 2a and 2b. The positions of the two or more openings are not particularly limited. The two openings 2a and 2b are provided, for example, on the top and bottom surfaces of an exterior member 2 having a substantially rectangular parallelepiped shape, which face each other. Specifically, in Figure 5, one of the two openings (here, 2a) is provided at a position facing the negative electrode 7 via the resin part 9. The other of the two openings (here, 2b) is provided at a position facing the positive electrode 6 via the resin part 9. It is desirable that the positions of the two openings are not too close to each other.

Figure 6 is a cross-sectional view that shows a schematic diagram of yet another example of a secondary battery according to an embodiment. The secondary battery 100 shown in Figure 6 has a structure similar to that of the secondary battery 100 described with reference to Figures 1 and 2, except that the electrode group 10 includes a plurality of positive electrodes 6, a plurality of negative electrodes 7, and a plurality of porous separators 8. In the electrode group 10 shown in Figure 6, the plurality of positive electrodes 6 and the plurality of negative electrodes 7 are stacked with the porous separators 8 interposed between the respective positive electrodes 6 and negative electrodes 7. The plurality of positive electrodes 6 and the plurality of negative electrodes 7 are stacked such that the positive electrode tab portion 6c and the negative electrode tab portion 7c protrude in opposite directions from each other.

Although not shown, the multiple positive electrode tab portions 6c protruding from the resin portion 9 can be bundled together and then welded to the positive electrode lead. Also, the multiple negative electrode tab portions 7c protruding from the resin portion 9 can be bundled together and then welded to the negative electrode lead.

In the secondary battery 100 shown in FIG. 6, the electrode group 10 is also covered with the resin part 9 except for the multiple positive electrode tab parts 6c and the multiple negative electrode tab parts 7c. Therefore, the electrode group 10 is not supplied with aqueous electrolyte from the outside. Therefore, the amount of aqueous electrolyte in contact with the positive electrode 6 and the negative electrode 7 is small. Therefore, gas generation that may occur due to contact between the positive and negative electrodes and the aqueous electrolyte can be significantly suppressed. In particular, the generation of chlorine gas and oxygen gas in the positive electrode 6 tends to be suppressed. As a result, the secondary battery according to the embodiment can achieve high safety.

Next, we will explain the details of each component that makes up the secondary battery according to the embodiment.

(1) Positive electrode The positive electrode includes a positive electrode current collector, a positive electrode active material-containing layer supported on at least one of the main surfaces of the positive electrode current collector, and an ion conductive layer. The positive electrode active material-containing layer includes a positive electrode active material. The positive electrode active material-containing layer may further include a conductive agent and a binder. The conductive agent is mixed as necessary to improve current collection performance and reduce contact resistance between the active material and the current collector. The binder has the function of binding the active material, the conductive agent, and the current collector.

The thickness of the positive electrode active material-containing layer is not particularly limited, but is, for example, in the range of 5 μm to 100 μm. The thickness of the ion-conducting layer is not particularly limited, but is, for example, in the range of 3 μm to 200 μm.

The positive electrode current collector is made of metals such as stainless steel, aluminum (Al) and titanium (Ti). The positive electrode current collector is, for example, in the form of a foil, a porous body or a mesh. In order to prevent corrosion due to the reaction between the positive electrode current collector and the aqueous electrolyte, the surface of the positive electrode current collector may be coated with a different element. The positive electrode current collector is preferably one having excellent corrosion resistance and oxidation resistance, such as Ti foil. In addition, when the aqueous electrolyte contains _{Li2SO4 ,} Al may be used as the positive electrode current collector because corrosion does not progress.

The thickness of the positive electrode current collector is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less.

As the positive electrode active material, a compound having a lithium ion absorption/release potential of 3 V (vs. Li/Li ⁺ ) to 5.5 V (vs. Li/Li ⁺ ) based on metallic lithium can be used. The positive electrode may contain one type of positive electrode active material, or may contain two or more types of positive electrode active materials.

Examples of the positive electrode active material include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, spinel type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium iron oxide, lithium fluorinated iron sulfate, phosphate compounds having an olivine crystal structure (e.g., Li _x FePO ₄ (0<x≦1), Li _x MnPO ₄ (0<x≦1)), etc. Phosphate compounds having an olivine crystal structure have excellent thermal stability.

Examples of positive electrode active materials that can provide a high positive electrode potential include lithium manganese composite oxides such as spinel structure Li _x Mn ₂ O ₄ (0<x≦1) and Li _x MnO ₂ (0<x≦1), lithium nickel aluminum composite oxides such as Li _x Ni _1-y Al _y O ₂ (0<x≦1, 0<y<1), lithium cobalt composite oxides such as Li _x CoO ₂ (0<x≦1), lithium nickel cobalt composite oxides such as Li _x Ni _1-y-z Co _y Mn _z O ₂ (0<x≦1, 0<y<1, 0<z<1), lithium manganese cobalt composite oxides such as Li _x Mn _y Co _1-y O ₂ (0<x≦1, 0<y<1), and lithium manganese cobalt composite oxides such as Li _x Mn _{1-y Ni Examples} of such _lithium phosphate oxides include spinel-type lithium manganese nickel composite oxides such as _LixFePO4 (0<x≦1, 0<y<2, 0<1-y<1), _lithium phosphate oxides having an olivine structure such as _LixFePO4 (0<x≦1), LixFe1 _- yMnyPO4 (0<x≦ ₁ , 0<y≦1), _{and LixCoPO4} (0<x≦1), and fluorinated iron _sulfates (for example, _LixFeSO4F (0<x≦1)).

The positive electrode active material is preferably at least one selected from the group consisting of lithium cobalt composite oxide, lithium manganese composite oxide, and lithium phosphate having an olivine structure. The operating potential of these active materials is 3.5 V (vs. Li/Li ⁺ ) or more and 4.2 V (vs. Li/Li ⁺ ) or less. That is, the operating potential of these active materials is relatively high. By using these positive electrode active materials in combination with the above-mentioned spinel-type lithium titanate and anatase-type titanium oxide or other negative electrode active materials, a high battery voltage can be obtained.

The positive electrode active material is contained in the positive electrode in the form of particles, for example. The positive electrode active material particles can be single primary particles, secondary particles which are aggregates of primary particles, or a mixture of primary particles and secondary particles. The shape of the particles is not particularly limited, and can be, for example, spherical, elliptical, flat, or fibrous.

The average particle size (diameter) of the primary particles of the positive electrode active material is preferably 10 μm or less, more preferably 0.1 μm or more and 5 μm or less. The average particle size (diameter) of the secondary particles of the positive electrode active material is preferably 100 μm or less, more preferably 10 μm or more and 50 μm or less.

The primary particle size and secondary particle size of the positive electrode active material can be determined using a laser diffraction particle size distribution measuring device, similar to the negative electrode active material particles described below.

In the layer containing the positive electrode active material, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass or more and 98% by mass or less and 2% by mass or more and 20% by mass or less, respectively.

By making the amount of binder 2% by mass or more, sufficient electrode strength can be obtained. The binder can also function as an insulator. Therefore, by making the amount of binder 20% by mass or less, the amount of insulator contained in the electrode is reduced, and the internal resistance can be reduced.

When a conductive agent is added, it is preferable to mix the positive electrode active material, binder, and conductive agent in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

By setting the amount of conductive agent to 3 mass% or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15 mass% or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

The ion conductive layer is at least one selected from the group consisting of a solid electrolyte layer and a gel electrolyte layer. The ion conductive layer has alkali metal ion conductivity as a charge carrier. The ion conductive layer may be composed of only a solid electrolyte layer, may be composed of only a gel electrolyte layer, or may be a laminate of a solid electrolyte layer and a gel electrolyte layer. The ion conductive layer has a lithium ion conductivity of 1×10 ⁻¹⁰ S/cm or more at 25° C., for example.

The solid electrolyte layer may include solid electrolyte particles and a polymer material. The solid electrolyte layer may be composed of only solid electrolyte particles. The solid electrolyte layer may include one type of solid electrolyte particles, or may include multiple types of solid electrolyte particles. The solid electrolyte layer may include at least one selected from the group consisting of a plasticizer and an electrolyte salt. When the solid electrolyte layer includes an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further increased. The polymer material may be in the form of, for example, a granular or fibrous form.

The solid electrolyte layer is preferably in sheet form and has few or no pores such as pinholes. The thickness of the solid electrolyte layer is not particularly limited, but is, for example, 150 μm or less, and preferably in the range of 20 μm to 50 μm.

The polymer material (first polymer material) used for the solid electrolyte layer is preferably a polymer material insoluble in aqueous solvents. Examples of polymer materials that meet this condition include polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and fluorine-containing polymer materials. By using a fluorine-containing polymer material, water repellency can be imparted to the separator. In addition, inorganic solid electrolytes have high stability against water and excellent lithium ion conductivity. By forming a complex between a lithium ion conductive inorganic solid electrolyte and a fluorine-containing polymer material, a solid electrolyte layer that is flexible and conductive to alkali metal ions can be realized. A separator made of this solid electrolyte layer can reduce resistance, thereby improving the large current performance of the secondary battery.

Examples of fluorine-containing polymeric materials include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride (PVdF), etc. The type of fluorine-containing polymeric material can be one or two or more types.

When the solid electrolyte layer contains a polymer material, the content of the polymer material in the solid electrolyte layer is preferably 1% by weight or more and 20% by weight or less. In this range, high mechanical strength can be obtained and resistance can be reduced when the thickness of the solid electrolyte layer is in the range of 10 to 100 μm. Furthermore, there is little risk that the solid electrolyte will become a factor that inhibits lithium ion conductivity. A more preferable range for this content is 3% by weight or more and 10% by weight or less.

As the solid electrolyte, it is preferable to use an inorganic solid electrolyte. As the inorganic solid electrolyte, for example, an oxide-based solid electrolyte or a sulfide-based solid electrolyte can be mentioned. As the oxide-based solid electrolyte, it is preferable to use a lithium phosphate solid electrolyte having a NASICON structure and represented by the general formula LiM ₂ (PO ₄ ) _3. In the above general formula, M is preferably at least one element selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), and aluminum (Al). It is more preferable that the element M contains any one of Ge, Zr, and Ti, and Al.

Specific examples of lithium phosphate solid electrolytes having a NASICON structure include LATP (Li1 _{+ xAlxTi2 -x} ( _PO4 ) ₃ ), Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ , and Li1 _{+ xAlxZr2 -x} ( _PO4 ) ₃ . In the above formula, x is in the range of 0<x≦5, and preferably in the range of 0.1≦x≦0.5. It is preferable to use LATP as the solid electrolyte. LATP has excellent water resistance and is less likely to undergo hydrolysis in a secondary battery.

Moreover, as the oxide-based solid electrolyte, amorphous LIPON (Li _2.9 PO _3.3 N _0.46 ) or LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) having a garnet structure may be used.

The solid electrolyte layer preferably has an air permeability coefficient of 1×10 ⁻¹⁹ m ² or more and less than 1×10 ⁻¹⁵ m ^2. When the air permeability coefficient of the solid electrolyte layer is within this range, an effect of easily suppressing the permeation of the aqueous electrolyte into the positive electrode active material-containing layer through the ion conductive layer can be obtained during the production of a secondary battery described later.

The gel electrolyte layer is composed of, for example, a polymer material (second polymer material), an organic solvent, and an alkali metal salt. The polymer chains constituting the polymer material (second polymer material) are three-dimensionally entangled, and an electrolyte solution containing an organic solvent and an alkali metal salt is held inside the polymer chains.

The mass ratio of the second polymer material in the gel electrolyte is, for example, in the range of 0.5% by mass to 10% by mass, and preferably in the range of 1.5% by mass to 8% by mass. If this ratio is too small, the gel electrolyte may not gel properly. If this ratio is too large, the ion conduction resistance increases too much, tending to result in poor input/output characteristics.

The mass ratio of the organic solvent in the gel electrolyte is, for example, in the range of 80% to 97% by mass, and preferably in the range of 80% to 90% by mass. By appropriately adjusting the mass ratio of the organic solvent in the gel electrolyte, it is possible to adjust the concentration (mass ratio) of the polymer material (second polymer material) and the concentration of the alkali metal salt.

The alkali metal salt concentration in the gel electrolyte is, for example, in the range of 0.5 mol/L to 3 mol/L, and preferably in the range of 0.5 mol/L to 2 mol/L. By keeping the alkali metal salt concentration within this range, the viscosity of the electrolyte becomes appropriate and relatively high ionic conductivity can be maintained.

The second polymeric material is preferably at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and polyethylene oxide (PEO). The second polymeric material may be one of these, or a mixture containing two or more of them.

The alkali metal salt contained in the gel electrolyte layer may be, for example, a lithium salt, a sodium salt, or a mixture thereof. The alkali metal salt may be the same as that contained in the aqueous electrolyte described below.

Whether or not the ion conductive layer is a gel electrolyte layer can be confirmed as follows. That is, a pressure of 10 g/ ^cm2 is applied to the ion conductive layer, and the presence or absence of seepage of the organic electrolyte solution is checked. If the organic electrolyte solution seeps out, the layer can be determined to be a gel electrolyte layer.

<Measurement of lithium ion conductivity>
The lithium ion conductivity of the solid electrolyte layer can be measured as follows: The secondary battery is disassembled in a glove box under an argon atmosphere, and the electrode group having the solid electrolyte layer as a separator is taken out. The electrode group is washed and vacuum dried at room temperature.

Next, a part of the solid electrolyte layer is scraped off and molded into a powder compact using a tablet molding machine. Gold (Au) electrodes are deposited on both sides of this powder compact to obtain a measurement sample. Then, the measurement sample is measured using a Solartron Frequency Response Analyzer Model 1260. The measurement frequency range is from 5 Hz to 32 MHz. The measurement is performed in a 25°C environment by placing the measurement sample in a dry argon atmosphere without exposing it to the air. From the measurement results, the AC impedance component Z _Li [ohm] of Li ion conduction is obtained. The ionic conductivity σ _Li [S/cm] of the solid electrolyte layer can be calculated from this Z _Li and the area S [cm ² ] and thickness d [cm] of the measurement sample by the following formula.
σ _Li = (1/Z _Li ) × (d/S)

The lithium ion conductivity of the gel electrolyte layer can be measured by the method described above, except that it is molded into a powder compact.

(2) Negative Electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer supported on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer contains a negative electrode active material. The negative electrode active material-containing layer is disposed on at least one surface of the negative electrode current collector. For example, the negative electrode active material-containing layer may be disposed on one surface of the negative electrode current collector, or the negative electrode active material-containing layer may be disposed on one surface of the negative electrode current collector and on the back surface thereof.

The thickness of the negative electrode active material-containing layer is not particularly limited, but is, for example, in the range of 5 μm to 100 μm.

The material of the negative electrode current collector is a substance that is electrochemically stable in the negative electrode potential range when the alkali metal ions are inserted or removed. The negative electrode current collector is preferably a metal foil selected from the group consisting of aluminum (Al), magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), tin (Sn) and silicon (Si), or an alloy foil containing at least one of these metal elements. The negative electrode current collector may be in other forms such as a porous body or a mesh. The thickness of the negative electrode current collector is preferably 5 μm or more and 50 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

It is desirable for the porosity of the negative electrode active material-containing layer to be 20% or more and 50% or less. This makes it possible to obtain a high-density negative electrode that has excellent affinity with the aqueous electrolyte. It is more preferable for the porosity of the negative electrode active material-containing layer to be 25% or more and 40% or less.

The porosity of the negative electrode active material-containing layer can be obtained, for example, by mercury intrusion porosimetry. Specifically, first, the pore distribution of the active material-containing layer is obtained by mercury intrusion porosimetry. Next, the total pore volume is calculated from this pore distribution. Next, the porosity can be calculated from the ratio of the total pore volume to the volume of the active material-containing layer.

As the negative electrode active material, a compound having a lithium ion absorption/release potential of 1 V (vs. Li/Li ⁺ ) to 3 V (vs. Li/Li ⁺ ) based on metallic lithium can be used.

Specific examples of such compounds include titanium oxide and titanium-containing oxide. Examples of titanium-containing oxides that can be used include lithium titanium composite oxide, niobium titanium composite oxide, and sodium niobium titanium composite oxide. The negative electrode active material can contain one or more types of titanium oxide and titanium-containing oxide.

Titanium oxide includes, for example, titanium oxide with a monoclinic structure, titanium oxide with a rutile structure, and titanium oxide with an anatase structure. The composition of titanium oxide with each crystal structure before charging can be expressed _{as TiO2} , and the composition after charging can be expressed as _LixTiO2 (x is 0≦x≦1). The structure of titanium oxide with a monoclinic structure before charging can be expressed as _TiO2 (B).

Examples of the lithium titanium oxide include lithium titanium oxide having a spinel structure (e.g., general formula _{Li4 + xTi5O12} (x is -1≦x≦3)), lithium titanium oxide having a ramsdellite structure (e.g., Li2 _{+ xTi3O7} (-1≦x≦3) ₎ , Li1 _+xTi2O4 (0≦x≦1 ₎ , _Li1.1 +xTi1.8O4 (0≦x≦1 _{) , Li1.07+ xTi1.86O4 (} 0≦x≦ _{1 )} , _LixTiO2 (0<x≦1), etc. The lithium titanium oxide may also be a lithium titanium composite oxide having a different element introduced therein.

Niobium titanium composite oxides include, for example, those represented by 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 includes, for example, an _orthorhombic Na-containing niobium titanium composite oxide represented by the general formula Li2 _{+VNa2 -} WM1XTi6 _{- y} - _{zNb yM2zO14+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, and Ca, and M2 includes at least one selected from Zr, Sn, V, Ta, Mo, W, Fe, Co, Mn, and Al).

As the negative electrode active material, it is preferable to use titanium oxide with an anatase structure, titanium oxide with a monoclinic structure, lithium titanium oxide with a spinel structure, or a mixture of these. When these oxides are used as the negative electrode active material, for example, in combination with a lithium manganese composite oxide as the positive electrode active material, a high electromotive force can be obtained.

The negative electrode active material is contained in the negative electrode active material-containing layer, for example, in the form of particles. The negative electrode active material particles can be primary particles, secondary particles which are aggregates of primary particles, or a mixture of a single primary particle and a secondary particle. The shape of the particles is not particularly limited, and can be, for example, spherical, elliptical, flat, fibrous, etc.

The average particle size (diameter) of the primary particles of the negative electrode active material is preferably 3 μm or less, more preferably 0.01 μm or more and 1 μm or less. The average particle size (diameter) of the secondary particles of the negative electrode active material is preferably 30 μm or less, more preferably 5 μm or more and 20 μm or less.

The primary particle size and secondary particle size refer to the particle size at which the volume cumulative value is 50% in the particle size distribution determined by a laser diffraction particle size distribution measuring device. For example, a Shimadzu SALD-300 is used as a laser diffraction particle size distribution measuring device. During the measurement, the luminous intensity distribution is measured 64 times at 2-second intervals. The sample used for this particle size distribution measurement is a dispersion diluted with N-methyl-2-pyrrolidone so that the concentration of the negative electrode active material particles is 0.1% to 1% by weight. Alternatively, the measurement sample is one in which 0.1 g of negative electrode active material is dispersed in 1 to 2 ml of distilled water containing a surfactant.

The negative electrode active material-containing layer may contain a conductive agent and a binder in addition to the negative electrode active material. The conductive agent is mixed as necessary to improve current collection performance and reduce contact resistance between the active material and the current collector. The binder has the function of binding the active material, conductive agent, and current collector.

Examples of conductive agents include carbonaceous materials such as acetylene black, ketjen black, graphite, and coke. The conductive agent may be one type or a mixture of two or more types.

The binder is blended to fill the gaps between the dispersed active material and to bind the active material to the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVdF), fluorine-based rubber, styrene butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethylcellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

The compounding ratio of the conductive agent and the binder in the negative electrode active material-containing layer is preferably in the range of 1 part by weight to 20 parts by weight and 0.1 parts by weight to 10 parts by weight, respectively, per 100 parts by weight of the active material. When the compounding ratio of the conductive agent is 1 part by weight or more, the conductivity of the negative electrode can be improved, and when it is 20 parts by weight or less, the decomposition of the aqueous electrolyte on the conductive agent surface can be reduced. When the compounding ratio of the binder is 0.1 parts by weight or more, sufficient electrode strength can be obtained, and when it is 10 parts by weight or less, the insulating part of the electrode can be reduced.

The crystal structure and elemental composition of the positive and negative electrode active materials can be confirmed by powder X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy.

(3) Aqueous Electrolyte The aqueous electrolyte contains an aqueous solvent and an electrolyte salt. The aqueous electrolyte is, for example, liquid. The liquid aqueous electrolyte is an aqueous solution prepared by dissolving an electrolyte salt as a solute in an aqueous solvent. When the aqueous electrolyte is held in both the negative electrode active material-containing layer and the positive electrode active material-containing layer, the types of the aqueous electrolytes may be the same or different.

The aqueous solution preferably contains 1 mol or more of aqueous solvent per 1 mol of solute salt, and more preferably 3.5 mol or more.

As the aqueous solvent, a solution containing water can be used. The aqueous solution may be pure water or a mixed solvent of water and an organic solvent. The aqueous solvent contains, for example, 50% or more by volume of water.

The presence of water in aqueous electrolytes can be confirmed by GC-MS (Gas Chromatography - Mass Spectrometry) measurements. The salt concentration and water content in aqueous electrolytes can be measured, for example, by ICP (Inductively Coupled Plasma) emission spectrometry. The molar concentration (mol/L) can be calculated by weighing a specified amount of aqueous electrolyte and calculating the salt concentration contained therein. The number of moles of solute and solvent can also be calculated by measuring the specific gravity of the aqueous electrolyte.

The aqueous electrolyte may be a gel electrolyte. The gel electrolyte is prepared by mixing the above-mentioned liquid aqueous electrolyte with a polymer compound to form a composite. Examples of the polymer compound include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

As the electrolyte salt, for example, a lithium salt, a sodium salt, or a mixture thereof can be used. One type or two or more types of electrolyte salt can be used.

Examples of lithium salts that can be used include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide ( _{LiOH), lithium sulfate (Li2SO4 ) ,} lithium nitrate ( _LiNO3 ), lithium acetate ( _CH3COOLi ), lithium oxalate ( _Li2C2O4 ) _{, lithium carbonate (Li2CO3 )} , lithium bis( _{trifluoromethanesulfonyl} )imide (LiTFSI; LiN( _SO2CF3 ) ₂ ), lithium bis( _{fluorosulfonyl} )imide (LiFSI; LiN( _SO2F ) ₂ ), and lithium bisoxalate borate (LiBOB: LiB[(OCO) ₂ ] ₂ ).

The lithium salt preferably contains LiCl. The use of LiCl can increase the lithium ion concentration of the aqueous electrolyte. The lithium salt preferably contains at least one of _LiSO4 and LiOH in addition to LiCl.

As the sodium salt, sodium chloride (NaCl), sodium sulfate (Na ₂ SO ₄ ), sodium hydroxide (NaOH), sodium nitrate (NaNO ₃ ), sodium trifluoromethanesulfonylamide (NaTFSA), and the like can be used.

The molar concentration of alkali metal ions (e.g., lithium ions) in the aqueous electrolyte may be 3 mol/L or more, 6 mol/L or more, or 12 mol/L or more. In one example, the molar concentration of alkali metal ions in the aqueous electrolyte is 14 mol/L or less. If the concentration of alkali metal ions in the aqueous electrolyte is high, electrolysis of the aqueous solvent at the negative electrode is likely to be suppressed, and hydrogen generation from the negative electrode tends to be reduced.

The aqueous electrolyte preferably contains, as an anion species, at least one selected from the group consisting of chloride ions (Cl ⁻ ), hydroxide ions (OH ⁻ ), sulfate ions (SO ₄ ²⁻ ) and nitrate ions (NO ₃ ⁻ ).

The pH of the aqueous electrolyte is preferably 3 or more and 14 or less, and more preferably 4 or more and 13 or less. When separate electrolytes are used for the negative electrode side electrolyte and the positive electrode side electrolyte, the pH of the negative electrode side electrolyte is preferably in the range of 3 or more and 14 or less, and the pH of the positive electrode side electrolyte is preferably in the range of 1 or more and 8 or less.

When the pH of the negative electrode electrolyte is within the above range, the hydrogen generation potential at the negative electrode is reduced, thereby suppressing hydrogen generation at the negative electrode. This improves the storage performance and cycle life performance of the battery. When the pH of the positive electrode electrolyte is within the above range, the oxygen generation potential at the positive electrode is increased, thereby reducing oxygen generation at the positive electrode. This improves the storage performance and cycle life performance of the battery. It is more preferable that the pH of the positive electrode electrolyte is within the range of 3 or more and 7.5 or less.

The aqueous electrolyte may contain a surfactant. Examples of the surfactant include non-ionic surfactants such as polyoxyalkylene alkyl ether, polyethylene glycol, polyvinyl alcohol, thiourea, disodium 3,3'-dithiobis(1-propanephosphoric acid), dimercaptothiadiazole, boric acid, oxalic acid, malonic acid, saccharin, sodium naphthalenesulfonate, gelatin, potassium nitrate, aromatic aldehydes, and heterocyclic aldehydes. The surfactants may be used alone or in combination of two or more.

(4) Porous separator A porous separator is interposed between the positive electrode and the negative electrode. The porous separator is interposed, for example, in at least a part of the opposing parts of the positive electrode and the negative electrode. By forming the porous separator from an insulating material, it is possible to suppress electrical contact between the positive electrode and the negative electrode. In the present specification and claims, the porous separator refers to a separator having an air permeability coefficient of 1×10 ⁻¹⁹ m ² or more and 1×10 ⁻¹⁴ m ² or less. If the air permeability coefficient is too low, the electrolyte is unlikely to permeate into the separator, and the charge/discharge capacity may decrease. On the other hand, if the air permeability coefficient is too high, the filled resin (molten resin) may permeate into the separator during the production of the secondary battery described later, which is not preferable because the charge/discharge capacity may decrease.

Examples of porous separators include nonwoven fabrics, films, and papers. Examples of materials constituting porous separators that make up nonwoven fabrics, films, and papers include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferred porous separators include nonwoven fabrics containing cellulose fibers and porous films containing polyolefin fibers.

The air permeability coefficient of the porous separator is preferably 1×10 ⁻¹⁹ m2 ^or more and less than 1×10 ^{−14 m2} . When the air permeability coefficient of the porous separator is 1×10 ^{−19 m2} or more, the electrolyte is easily impregnated into the porous separator. Therefore, there is an advantage that the alkali ion conductivity of the porous separator is increased and the resistance can be reduced.

The porosity of the porous separator is preferably 60% or more. The fiber diameter is preferably 10 μm or less. By making the fiber diameter 10 μm or less, the affinity of the porous separator to the electrolyte is improved, thereby reducing the battery resistance. A more preferable range for the fiber diameter is 3 μm or less. A cellulose fiber-containing nonwoven fabric with a porosity of 60% or more has good electrolyte impregnation and can provide high output performance from low to high temperatures. A more preferable range for the porosity is 62% to 80%.

The porous separator preferably has a thickness of 20 μm or more and 100 μm or less and a density of 0.2 g/cm ³ or more and 0.9 g/cm ³ or less. In this range, a balance between mechanical strength and reduction in battery resistance can be achieved, and a secondary battery with high output and suppressed internal short circuit can be provided. In addition, the separator suffers little thermal shrinkage in a high-temperature environment, and good high-temperature storage performance can be achieved.

<Air permeability coefficient measurement>
The air permeability coefficient (m ² ) of the porous separator is calculated as follows. In calculating the air permeability coefficient KT, for example, when a separator with a thickness L (m) is the measurement target, a gas with a viscosity coefficient σ (Pa·s) is allowed to permeate within a range of a measurement area A (m ² ). At this time, the gas is allowed to permeate under a plurality of conditions in which the pressure p (Pa) of the gas introduced is different from one another, and the amount of gas Q (m ³ /s) that permeates the separator is measured under each of the plurality of conditions. Then, from the measurement results, the amount of gas Q against the pressure p is plotted, and the slope dQ/dp is obtained. Then, the air permeability coefficient KT is calculated from the thickness L, the measurement area A, the viscosity coefficient σ, and the slope dQ/dp as shown in formula (5).

In one example of a method for calculating the air permeability coefficient KT, a separator is sandwiched between a pair of stainless steel plates, each with a hole of 10 mm in diameter. Air is then pumped in through the hole in one of the stainless steel plates at a pressure p. The amount of air Q leaking through the hole in the other stainless steel plate is then measured. The area of the hole (25πmm ² ) is used as the measurement area A, and 0.000018 Pa·s is used as the viscosity coefficient σ. The amount of air Q is calculated by measuring the amount δ (m ³ ) leaking through the hole in 100 seconds and dividing the measured amount δ by 100.

Then, the amount of gas Q with respect to pressure p is measured as described above at four points where the pressure p is at least 1000 Pa apart from each other. For example, the amount of gas Q with respect to pressure p is measured at each of four points where the pressure p is 1000 Pa, 2500 Pa, 4000 Pa, and 6000 Pa. Then, the amount of gas Q with respect to pressure p is plotted for the four measured points, and the slope (dQ/dp) of the amount of gas Q with respect to pressure p is calculated by linear fitting (the least squares method). The calculated slope (dQ/dp) is then multiplied by (σ·L)/A to calculate the air permeability coefficient KT.

When measuring the air permeability coefficient of the separator, first, the battery is disassembled and the separator is separated from the other components of the battery. After rinsing both sides of the separator with pure water, it is immersed in pure water and left to stand for 48 hours or more. After that, both sides of the separator are further rinsed with pure water and dried in a vacuum drying oven at 100°C for 48 hours or more, after which the air permeability coefficient is measured. The value at the point where the air permeability coefficient is the lowest among the four points measured is regarded as the air permeability coefficient of the separator.

(5) Resin Part The resin part includes at least one of a thermosetting resin and a thermoplastic resin. The resin part preferably includes a thermosetting resin, and more preferably includes a thermosetting resin. According to another aspect, the resin part may include a thermoplastic resin that is soluble in acetone or alcohol. If a thermoplastic resin is used as the resin part, there is a risk that the inside of the exterior member will become hot during the manufacture of the secondary battery described below. For this reason, there is a possibility that the organic solvent that may be contained in the porous separator will bump. In contrast, when the resin part includes a thermosetting resin, it can be melted at room temperature, and when cured, it can be cured by heating at a relatively low temperature for a short time. In this way, when the resin part includes a thermosetting resin, it is preferable because it has the advantage of being easy to handle during the manufacture of the secondary battery.

It is preferable that the resin constituting the resin portion has a melt viscosity suitable for flowing into the storage space of the exterior member during the manufacture of the secondary battery described below. The melt viscosity of the resin is, for example, in the range of 3000 Pa·s to 15000 Pa·s at atmospheric pressure and in a 25°C environment. If the melt viscosity is less than 3000 Pa·s, there is a risk that the molten resin will over-impregnate the porous separator during the manufacture of the secondary battery. If the melt viscosity is higher than 15000 Pa·s, the resin will have poor fluidity, making it difficult to inject the resin into the exterior member.

The type of thermosetting resin may be, for example, at least one selected from the group consisting of epoxy resin, silicon resin, silicone, propylene rubber, butadiene rubber, and olefin rubber. The epoxy resin may be a mixture of a base agent and a curing agent in a desired ratio. There are no particular limitations on the types of base agent and curing agent used.

The type of thermoplastic resin is not particularly limited, but may be, for example, at least one selected from the group consisting of polyolefin resins, polyvinyl chloride resins, polyamide resins, polyester resins, polyacetal resins, polyvinyl acetal resins, polycarbonate resins, polyaromatic ether or thioether resins, polyaromatic ester resins, polysulfone resins, styrene resins, and acrylate resins. According to one embodiment, the resin portion preferably contains polyvinyl butyral. In this case, the temperature required to melt the resin during the manufacture of the secondary battery described below is low, so that deterioration of the various materials contained in the electrode group can be suppressed.

When the secondary battery does not have an exterior member, in order to increase the robustness of the resin part, it is preferable that the resin part contains ABS resin. The resin part may be made of ABS resin. ABS resin is a copolymer resin containing acrylonitrile, butadiene, and styrene.

The type of resin that makes up the resin part can be inferred using techniques such as Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC-MS), and X-ray fluorescence analysis (XRF).

(6) Exterior Member As described above, the exterior member may be a metal container, a laminate film container, or a resin container.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

As the laminate film, a multilayer film containing multiple resin layers and metal layers interposed between these resin layers is used. The resin layers contain polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior member by sealing it by heat fusion.

The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably 100 ppm by mass or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the application of the battery.

The secondary battery according to the embodiment can be used in various forms, such as a rectangular, cylindrical, flat, thin, or coin-shaped battery. The secondary battery may be a secondary battery having a bipolar structure. For example, the electrode group may have a bipolar structure in which a positive electrode active material-containing layer and an ion-conducting layer are provided on one side of a single current collector, and a negative electrode active material-containing layer is provided on the other side. In this case, there is an advantage that multiple serially connected cells can be produced from a single cell.

<Secondary Battery Manufacturing Method>
Next, an example of a method for manufacturing a secondary battery according to this embodiment will be described with reference to FIGS.

(Preparation of Positive Electrode)
The active material, the conductive agent, and the binder are suspended in a suitable solvent to prepare a first slurry. The first slurry is then applied to one or both sides of a positive electrode current collector. The coating of the first slurry applied to the positive electrode current collector is dried to form a positive electrode active material-containing layer. The positive electrode current collector and the positive electrode active material-containing layer formed thereon are then pressed.

Next, an ion-conducting layer is formed on the positive electrode active material-containing layer by the method described below. A second slurry for forming a solid electrolyte layer or a gel electrolyte is prepared. The second slurry can be prepared, for example, by suspending solid electrolyte particles and a polymer material in a suitable solvent.
Examples of a method for applying the second slurry or the gel electrolyte onto the positive electrode active material-containing layer include a gravure method, a gravure offset method, and a kiss coat method.

The second slurry or gel electrolyte is applied so as to cover the entire main surface of the positive electrode active material-containing layer formed on the positive electrode current collector, as well as the side surface of the positive electrode active material-containing layer. At this time, the applied second slurry or gel electrolyte also comes into contact with the positive electrode current collector so as to cover the entire positive electrode active material-containing layer. Therefore, the positive electrode active material-containing layer is contained within the space formed between the second slurry or gel electrolyte and the positive electrode current collector. The second slurry or gel electrolyte is then subjected to a predetermined drying process, and these coating films form an ion-conducting layer.

In this way, a positive electrode having a positive electrode active material-containing layer and an ion conductive layer on at least one surface of the positive electrode current collector can be produced. As an example, Figures 7 to 9 show a positive electrode 6 having a positive electrode active material-containing layer 6b and an ion conductive layer 11 on both surfaces of the positive electrode current collector 6a.

(Preparation of negative electrode)
The negative electrode can be obtained, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in an appropriate solvent to prepare a slurry. Then, this slurry is applied to one or both sides of a current collector. The coating on the current collector is dried to form an active material-containing layer. Then, the current collector and the active material-containing layer formed thereon are pressed. As the active material-containing layer, a mixture of an active material, a conductive agent, and a binder formed into a pellet shape may be used. FIGS. 7 to 9 show, as an example, a negative electrode 7 having a negative electrode active material-containing layer 7b on both sides of a negative electrode current collector 7a.

(Preparation of electrode group and housing in exterior member)
Next, the electrode group 10 is prepared by stacking the positive electrode 6 and the negative electrode 7 prepared as described above with a porous separator 8 interposed therebetween. At this time, the positive electrode 6 and the negative electrode 7 are stacked, for example, so that the direction in which the positive electrode tab portion 6c protrudes and the direction in which the negative electrode tab portion 7c protrudes are opposite to each other. Furthermore, the prepared electrode group 10 is accommodated in the storage space 2c of the exterior member 2. The wall surface of the exterior member 2 is provided with the above-mentioned two openings 2a and 2b. After the electrode group 10 is accommodated in the storage space 2c of the exterior member 2, the exterior member 2 is closed except for the two openings 2a and 2b provided on the exterior member 2. As shown in the figure, for example, the positive electrode tab portion 6c and the negative electrode tab portion 7c are drawn out to the outside of the exterior member 2.

(Injection of aqueous electrolyte)
Next, with the mouth 2b closed, the aqueous electrolyte 26 is injected into the exterior member 2 (the storage space 2c) from the mouth 2a as shown in Fig. 7. Fig. 7 is a cross-sectional view that shows a schematic process of injecting the aqueous electrolyte 26 into the exterior member 2. By this injection, the storage space 2c is filled with the aqueous electrolyte 26. As a result, the aqueous electrolyte 26 is held in a part of the electrode group 10. Specifically, the aqueous electrolyte 26 is impregnated into at least the porous separator 8. The aqueous electrolyte 26 may also be impregnated into the negative electrode active material-containing layer 7b.

However, the positive electrode active material-containing layer 6b is located in a space 130 surrounded by the ion conductive layer 11 and the positive electrode current collector 6a. Therefore, the aqueous electrolyte 26 does not impregnate the positive electrode active material-containing layer 6b, or hardly impregnates it at all. The ion conductive layer 11 may have multiple pores through which the aqueous electrolyte can penetrate. When the aqueous electrolyte 26 is injected, the aqueous electrolyte 26 may impregnate the positive electrode active material-containing layer 6b through these multiple pores. However, the amount of impregnation is thought to be quite small.

(Injection of molten resin)
8, molten resin 27 is then poured into the storage space 2c filled with the aqueous electrolyte 26. At this time, both of the two openings 2a and 2b are in an open state. With the inflow of the molten resin 27, for example, a part of the aqueous electrolyte 26 filled in the storage space 2c is discharged. The other part of the aqueous electrolyte 26 filled in the storage space 2c remains retained in the electrode group 10. When the inflow of the molten resin 27 into the storage space 2c continues, the molten resin 27 covers the entire electrode group 10 except for a part of the positive electrode tab portion 6c and a part of the negative electrode tab portion 7c.

Alternatively, prior to the inflow of the molten resin 27, both of the two openings 2a and 2b may be opened to allow a portion of the aqueous electrolyte 26 to be discharged from the storage space 2c toward the outside of the exterior member 2. After the aqueous electrolyte 26 is discharged from the storage space 2c, the molten resin 27 is, for example, caused to flow from the opening 2a to fill the interior of the exterior member 2. This allows the molten resin 27 to cover the entire electrode group 10, except for a portion of the positive electrode tab portion 6c and a portion of the negative electrode tab portion 7c.

If the melt viscosity of the molten resin 27 is excessively high, it may be difficult to cover the entire electrode group 10 with the molten resin 27. In this case, for example, defects such as pinholes may occur in part of the resin part 9, which is not preferable. If the melt viscosity of the molten resin 27 is excessively low, the molten resin may impregnate the porous separator impregnated with the aqueous electrolyte. Excessive impregnation of the porous separator with the molten resin is not preferable because it increases resistance.

In FIG. 8, the molten resin 27 is shown flowing in through the mouth 2a, but the molten resin 27 may also flow in through the mouth 2b. In this case, the aqueous electrolyte 26 that is filled in the storage space 2c before the molten resin 27 flows in can be discharged from the mouth 2a.

(Hardening of molten resin)
Next, the exterior member 2 in which the molten resin 27 is filled in the storage space 2c is allowed to cool, for example, at room temperature. As a result, the molten resin 27 hardens to form the resin portion 9. When a thermosetting resin is used as the resin, the exterior member 2 in which the molten resin 27 is filled may be heated to harden the resin. The heating temperature can be changed appropriately depending on the type of resin, and is, for example, 23°C to 70°C. The hardening time (the time for which the heating is maintained) is, for example, 1 hour to 24 hours. FIG. 9 is a cross-sectional view that shows a schematic state in which the storage space 2c is filled with the molten resin 27. When the exterior member 2 has a predetermined rigidity, the shape of the resin portion 9 is determined depending on the shape of the storage space 2c that the exterior member 2 has. For example, when the shape of the storage space 2c is an approximately rectangular parallelepiped, the outer shape of the resin portion 9 can be an approximately rectangular parallelepiped. Also, for example, when the shape of the storage space 2c is an approximately cylindrical shape, the outer shape of the resin portion 9 can be an approximately cylindrical shape.

After the resin portion 9 is formed, there are no particular restrictions on the open/closed state of the mouth portions 2a and 2b, but for example, they are in a closed state.

The molten resin 27 shown in FIG. 9 is cured to form the resin portion 9, and the secondary battery 100 described with reference to FIG. 5 can be manufactured. After the molten resin 27 is cured, the exterior member 2 may be removed. For example, a part of the exterior member 2 can be cut open to remove it. By removing the exterior member 2, the secondary battery 100 described with reference to FIGS. 1 and 2 can be manufactured.

As described with reference to Figures 7 to 9, the electrode group 10 without aqueous electrolyte can be accommodated in the storage space 2c of the exterior member 2, and then the aqueous electrolyte can be injected into the storage space 2c to hold the aqueous electrolyte in the electrode group 10. Alternatively, the electrode group 10 with the aqueous electrolyte held in advance can be accommodated in the storage space 2c of the exterior member 2, and the molten resin 27 can be poured into the storage space 2c without injecting the aqueous electrolyte. In this case, for example, the aqueous electrolyte can be held only in the porous separator 8, and the electrode group 10 can be prepared by sandwiching this porous separator 8 between the positive and negative electrodes.

According to a first embodiment, a secondary battery is provided. The secondary battery includes an electrode group and a resin part. The electrode group includes a positive electrode, a negative electrode, and a porous separator that holds an aqueous electrolyte. The positive electrode includes a positive electrode collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode collector, and an ion conductive layer. The ion conductive layer covers the main surface and side surface of the positive electrode active material-containing layer, and an end of the ion conductive layer is in contact with the main surface of the positive electrode collector. The positive electrode collector has a positive electrode tab portion on which the positive electrode active material-containing layer is not supported. The negative electrode includes a negative electrode collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode collector. The negative electrode collector has a negative electrode tab portion on which the negative electrode active material-containing layer is not supported. The positive electrode active material-containing layer is located in a space formed between the positive electrode collector and the ion conductive layer. The ion-conducting layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via a porous separator. The electrode group is directly covered with a resin portion, except for a part of the positive electrode tab portion and a part of the negative electrode tab portion.

In this secondary battery, since the positive electrode active material-containing layer exists in the space, no aqueous electrolyte is supplied to the positive electrode active material-containing layer from outside the ion conductive layer. Therefore, in this secondary battery, the generation of gas such as chlorine at least in the positive electrode can be suppressed. Therefore, the secondary battery according to the embodiment can achieve a high level of safety.

Second Embodiment
According to a second embodiment, a battery pack is provided. The battery pack includes the secondary battery according to the first embodiment. The battery pack may include one secondary battery according to the first embodiment, or may include a battery pack including a plurality of secondary batteries.

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

The battery pack according to the second embodiment may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the secondary battery to the outside and/or for 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 current flow. When charging the battery pack, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current flow.

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

Figure 10 is an exploded perspective view that shows a schematic example of a battery pack according to the second embodiment. Figure 11 is a block diagram that shows an example of an electrical circuit of the battery pack shown in Figure 10.

The battery pack 300 shown in Figures 10 and 11 includes a container 310, a lid 320, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

The storage container 310 shown in FIG. 10 is a bottomed, square container having a rectangular bottom. The storage container 310 is configured to be able to store the protective sheet 33, the battery pack 200, the printed wiring board 34, and the wiring 35. The lid 320 has a rectangular shape. The lid 320 covers the storage container 310 to store the battery pack 200 and the like. Although not shown, the storage container 310 and the lid 320 are provided with openings or connection terminals for connection to external devices and the like.

The battery pack 200 includes a plurality of cells 100, a positive electrode lead 14, a negative electrode lead 17, and an adhesive tape 24.

At least one of the multiple single cells 100 is a secondary battery according to the first embodiment. The multiple single cells 100 are stacked in a manner that aligns them so that the positive electrode terminal 21 and the negative electrode terminal 22 extending outward face the same direction. Each of the multiple single cells 100 is electrically connected in series as shown in FIG. 11. The multiple single cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity is increased compared to when they are connected in series.

The adhesive tape 24 fastens the multiple cells 100 together. Instead of the adhesive tape 24, heat shrink tape may be used to secure the multiple cells 100 together. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat shrink tape is wrapped around the battery pack 200, and the heat shrink tape is then thermally shrunk to bind the multiple cells 100 together.

One end of the positive electrode lead 14 is connected to the positive electrode terminal 21 of the cell 100 located in the top layer of the stack of cells 100. One end of the negative electrode lead 17 is connected to the negative electrode terminal 22 of the cell 100 located in the bottom layer of the stack of cells 100.

The printed wiring board 34 is installed along one of the short sides of the inner surface of the container 310. The printed wiring board 34 includes a negative connector 341, a positive connector 342, a thermistor 343, a protection circuit 344, wiring 345 and 346, an external terminal 347 for current flow, a negative wiring 348a, and a positive wiring 348b. One main surface of the printed wiring board 34 faces the surface of the battery pack 200 from which the positive terminal 21 and the negative terminal 22 extend. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

The negative electrode connector 341 has a through hole. The other end of the negative electrode lead 17 is inserted into this through hole, so that the negative electrode connector 341 and the negative electrode lead 17 are electrically connected. The positive electrode connector 342 has a through hole. The other end of the positive electrode lead 14 is inserted into this through hole, so that the positive electrode connector 342 and the positive electrode lead 14 are electrically connected.

The thermistor 343 is fixed to one main surface of the printed wiring board 34. The thermistor 343 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 344.

The external terminal 347 for electrical current is fixed to the other main surface of the printed wiring board 34. The external terminal 347 for electrical current is electrically connected to a device that is external to the battery pack 300.

The protection circuit 344 is fixed to the other main surface of the printed wiring board 34. The protection circuit 344 is connected to the external terminal 347 for current supply via the negative side wiring 348a. The protection circuit 344 is connected to the external terminal 347 for current supply via the positive side wiring 348b. The protection circuit 344 is also electrically connected to the negative electrode side connector 341 via wiring 345. The protection circuit 344 is electrically connected to the positive electrode side connector 342 via wiring 346. Furthermore, the protection circuit 344 is electrically connected to each of the multiple single cells 100 via wiring 35.

The protective sheet 33 is disposed on both inner surfaces of the long sides of the container 310 and on the inner surface of the short side that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

The protection circuit 344 controls the charging and discharging of the multiple cells 100. The protection circuit 344 also cuts off the electrical connection between the protection circuit 344 and the external terminal 347 for current flow based on a detection signal transmitted from the thermistor 343 or a detection signal transmitted from each cell 100 or the battery pack 200.

The detection signal transmitted from the thermistor 343 may be, for example, a signal that detects that the temperature of the cell 100 is equal to or higher than a predetermined temperature. The detection signal transmitted from each cell 100 or the battery pack 200 may be, for example, a signal that detects overcharging, overdischarging, or overcurrent of the cell 100. When detecting overcharging or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

The protection circuit 344 may be a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack 300 as a power source.

As described above, the battery pack 300 is provided with an external terminal 347 for current flow. Therefore, the 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 347 for current flow. 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 via the external terminal 347 for current flow. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminal 347 for current flow. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and wiring 35 may be omitted. In this case, the positive electrode lead 14 and the negative electrode lead 17 may be used as external terminals for current flow.

Such battery packs are used in applications that require excellent cycle performance, for example, when drawing large current. Specifically, these battery packs are used as power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

The battery pack according to the second embodiment includes the secondary battery according to the first embodiment. Therefore, the battery pack according to the second embodiment can achieve a high level of safety.

Third Embodiment
According to a third embodiment, a vehicle is provided. The vehicle is equipped with the battery pack according to the second embodiment.

In the vehicle according to the third embodiment, the battery pack, for example, recovers regenerative energy from the vehicle's motive power. The vehicle may include a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

Examples of vehicles include, for example, two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, power-assisted bicycles, and rail vehicles.

The mounting position of the battery pack in the vehicle is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

The vehicle may be equipped with multiple battery packs. In this case, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

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

Figure 12 is a cross-sectional view that shows an example of a vehicle according to the third embodiment.

The vehicle 400 shown in FIG. 12 includes a vehicle body 40 and a battery pack 300 according to the second embodiment. In the example shown in FIG. 10, the vehicle 400 is a four-wheeled automobile.

The vehicle 400 may be equipped with multiple battery packs 300. In this case, the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

Figure 12 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for the power of the vehicle 400.

The vehicle according to the third embodiment is equipped with the battery pack according to the second embodiment. Therefore, according to this embodiment, it is possible to provide a vehicle equipped with a battery pack that can achieve a high level of safety.

Fourth Embodiment
According to the fourth embodiment, a stationary power source is provided. This stationary power source is equipped with the battery pack according to the second embodiment. Note that this stationary power source may be equipped with the secondary battery or battery pack according to the first embodiment, instead of the battery pack according to the second embodiment.

FIG. 13 is a block diagram showing an example of a system including a stationary power source according to the fourth embodiment. FIG. 13 is a diagram showing an example of application to stationary power sources 112 and 123 as an example of use of battery packs 300A and 300B according to the second embodiment. In the example shown in FIG. 13, a system 110 in which stationary power sources 112 and 123 are used is shown. The system 110 includes a power plant 111, a stationary power source 112, a consumer-side power system 113, and an energy management system (EMS) 115. In addition, a power grid 116 and a communication network 117 are formed in the system 110, and the power plant 111, the stationary power source 112, the consumer-side power system 113, and the EMS 115 are connected via the power grid 116 and the communication network 117. The EMS 115 uses the power grid 116 and the communication network 117 to perform control to stabilize the entire system 110.

The power plant 111 generates a large amount of electricity using fuel sources such as thermal power and nuclear power. Electricity is supplied from the power plant 111 through the power grid 116, etc. The stationary power source 112 is equipped with a battery pack 300A. The battery pack 300A can store the electricity supplied from the power plant 111. The stationary power source 112 can supply the electricity stored in the battery pack 300A through the power grid 116, etc. The system 110 is provided with a power conversion device 118. The power conversion device 118 includes a converter, an inverter, a transformer, etc. Therefore, the power conversion device 118 can convert between direct current and alternating current, convert between alternating currents with different frequencies, and perform voltage transformation (boosting and bucking), etc. Therefore, the power conversion device 118 can convert the electricity from the power plant 111 into electricity that can be stored in the battery pack 300A.

The consumer-side power system 113 includes a power system for factories, a power system for buildings, and a power system for homes. The consumer-side power system 113 includes a consumer-side EMS 121, a power conversion device 122, and a stationary power source 123. The stationary power source 123 is equipped with a battery pack 300B. The consumer-side EMS 121 performs control to stabilize the consumer-side power system 113.

The consumer-side power system 113 is supplied with power from the power plant 111 and from the battery pack 300A through the power grid 116. The battery pack 300B can store the power supplied to the consumer-side power system 113. Similarly to the power conversion device 118, the power conversion device 121 includes a converter, an inverter, a transformer, and the like. Therefore, the power conversion device 121 can convert between DC and AC, convert between ACs with different frequencies, and perform voltage transformation (boost and step-down), etc. Therefore, the power conversion device 121 can convert the power supplied to the consumer-side power system 113 into power that can be stored in the battery pack 300B.

The power stored in the battery pack 300B can be used, for example, to charge a vehicle such as an electric car. The system 110 may also be provided with a natural energy source. In this case, the natural energy source generates power using natural energy such as wind power and solar power. Power is supplied from the natural energy source in addition to the power plant 111 through the power grid 116.

The stationary power source according to the fourth embodiment is equipped with the battery pack according to the second embodiment. Therefore, according to this embodiment, it is possible to provide a stationary power source equipped with a battery pack that is highly safe.

[Example]
Examples will be described below, but the embodiments are not limited to the examples described below.

Example 1
<Preparation of Positive Electrode>
The positive electrode was prepared as follows.

5 g of lithium manganese oxide (LiMn ₂ O ₄ ) was prepared as a positive electrode active material, 0.25 g of acetylene black as a conductive agent, and 6.25 g of a PVDF dispersion (NMP solution with a solid content of 8%) as a binder. These were mixed for 3 minutes using a kneader to obtain a first slurry. The first slurry was applied to both sides of a Ti foil. The solvent was then distilled off at 120° C. to obtain a laminate. This laminate was rolled using a roll press to produce positive electrode active material-containing layers on both sides of the positive electrode current collector.

Next, Li ₇ La ₃ Zr ₂ O ₁₂ particles with an average particle diameter D50 of 1 μm and cellulose acetate and polyvinylidene fluoride as polymer materials were prepared as solid electrolyte materials, and dispersed in NMP to obtain a second slurry. The mixing ratio of the above materials in the second slurry was 98:1:1 by weight. The second slurry was applied to the entire main surface of the positive electrode active material-containing layer formed on the positive electrode current collector, and was applied by gravure method so as to cover the side surface of the positive electrode active material-containing layer. That is, the area to which the second slurry was applied was made larger than the area of the main surface of the positive electrode active material-containing layer, and the positive electrode active material-containing layer was covered with the second slurry. As a result, the end of the second slurry was in contact with the positive electrode current collector.

Then, the laminate coated with the second slurry was thoroughly dried in a drying oven to obtain a laminate in which a solid electrolyte layer was formed on the positive electrode active material-containing layer. The obtained laminate was punched using a die into the shape illustrated in FIG. 3 to obtain a positive electrode. In the obtained positive electrode, a positive electrode active material-containing layer and a solid electrolyte layer were formed in this order on both sides of the positive electrode current collector. In addition, the positive electrode current collector had a positive electrode tab portion on which the positive electrode active material-containing layer and the solid electrolyte layer were not supported.

<Preparation of negative electrode>
Li ₄ Ti ₅ O ₁₂ (10 g) as a negative electrode active material, graphite (1 g) as a conductive agent, PTFE dispersion (solid content 40 wt %, 1 g) as a binder, and 8 g of NMP (N-methyl-2-pyrrolidone) were mixed for 3 minutes using a kneader to obtain a slurry. This slurry was applied to both sides of a Zn foil. Then, the solvent was distilled off at 120° C. to obtain a laminate. Next, this laminate was rolled using a roll press and then dried. Then, the obtained laminate was punched into the shape illustrated in FIG. 4 to obtain a negative electrode.

<Adjustment of aqueous electrolyte>
A liquid aqueous electrolyte containing pure water and lithium chloride (LiCl) was prepared as the aqueous electrolyte. The concentration of lithium chloride in this liquid aqueous electrolyte was 12 mol/L.

<Preparation of separator>
As a separator, a polypropylene film with an air permeability coefficient of 1×10 ⁻¹⁶ m ² was prepared.

<Preparation of Electrode Group and Housing in Exterior Member>
The positive and negative electrodes prepared above were laminated with a separator interposed therebetween to prepare a laminated electrode group. Then, a pack consisting of a 0.1 mm thick laminate film composed of an aluminum foil having a thickness of 40 μm and a polypropylene layer formed on both sides of the aluminum foil was prepared, and the obtained electrode group was stored in the storage space of the pack (exterior member), and the pack and the electrode group were subjected to vacuum drying at 120 ° C. for 24 hours. The wall surface of this pack had two mouth parts that could be opened and closed. A part of the positive electrode tab part and a part of the negative electrode tab part were pulled out of the pack. The positions where the positive electrode tab part and the negative electrode tab part were pulled out were different from the two mouth parts.

<Injection of aqueous electrolyte>
With one of the two openings closed, the aqueous electrolyte was poured from the other opening (see FIG. 7 ). As a result, the inside of the exterior member, i.e., the storage space, was filled with the aqueous electrolyte, and the aqueous electrolyte was retained in the electrode group.

<Injection of molten resin and hardening>
Next, both of the two openings of the exterior member were opened, and the molten resin was poured into the storage space from one of the openings. An epoxy resin was used as the molten resin. After confirming that the entire storage space was filled with the molten resin, the inflow of the molten resin was stopped. By inflowing the molten resin, the aqueous electrolyte that had been poured into the storage space in advance was discharged. Thereafter, the exterior member (secondary battery) into which the molten resin had been poured into the storage space was left to stand for one hour in an environment of 50°C to harden the molten resin. In this way, the entire electrode group was covered with the molten resin, except for a part of the positive electrode tab portion and a part of the negative electrode tab portion.

Then, with the two openings of the exterior member closed, the molten resin was allowed to cool at room temperature to harden. Thus, the portion corresponding to the molten resin constituted the resin part. In the obtained secondary battery, the resin part directly covered the electrode group, except for a part of the positive electrode tab part and a part of the negative electrode tab part. In addition, the exterior member directly covered the entire resin part.

(Comparative Example 1)
A secondary battery was fabricated in the same manner as in Example 1, except that no operations were performed after the injection of the molten resin. That is, in the secondary battery according to Comparative Example 1, the storage space of the exterior member was filled with a liquid aqueous electrolyte, and the electrode group was immersed in the liquid aqueous electrolyte.

<Irreversible capacity measurement>
The secondary batteries prepared in Example 1 and Comparative Example 1 were charged and discharged for 5 cycles under the following conditions to compare the amount of side reactions. It can be determined that the greater the amount of side reactions (irreversible capacity) measured here, the greater the amount of gas generated from the secondary battery being measured. The charge and discharge were performed for 5 cycles at a current value of 0.1 C with an upper limit voltage of 2.7 V and a lower limit voltage of 1.8 V. The total amount of irreversible capacity during the 5 cycles was calculated.

As a result, the total irreversible capacity of the secondary battery according to Example 1 was 1.29 mAh. The total irreversible capacity of the secondary battery according to Comparative Example 1 was 2.24 mAh. From these results, it can be seen that in Example 1, in which the electrode group is almost entirely covered with a resin portion, gas generation (side reaction) was significantly suppressed compared to Comparative Example 1, in which the electrode group is almost entirely immersed in a liquid aqueous electrolyte.

According to at least one of the above-described embodiments, a secondary battery is provided. The secondary battery includes an electrode group and a resin portion. The electrode group includes a positive electrode, a negative electrode, and a porous separator that holds an aqueous electrolyte. The positive electrode includes a positive electrode collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode collector, and an ion conductive layer. The ion conductive layer covers the main surface and side surface of the positive electrode active material-containing layer, and an end of the ion conductive layer is in contact with the main surface of the positive electrode collector. The positive electrode collector has a positive electrode tab portion on which the positive electrode active material-containing layer is not supported. The negative electrode includes a negative electrode collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode collector. The negative electrode collector has a negative electrode tab portion on which the negative electrode active material-containing layer is not supported. The positive electrode active material-containing layer is located in a space formed between the positive electrode collector and the ion conductive layer. The ion-conducting layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via a porous separator. The electrode group is directly covered with a resin portion, except for a part of the positive electrode tab portion and a part of the negative electrode tab portion.

In this secondary battery, since the positive electrode active material-containing layer exists in the space, no aqueous electrolyte is supplied to the positive electrode active material-containing layer from outside the ion conductive layer. Therefore, in this secondary battery, the generation of gases such as chlorine at least in the positive electrode can be suppressed.

Although some 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 modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
The invention as described in the claims of the present application as originally filed is set forth below.
[1] An electrode group including a positive electrode, a negative electrode, and a porous separator holding an aqueous electrolyte;
A secondary battery comprising a resin portion,
the positive electrode comprises a positive electrode current collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode current collector, and an ion conductive layer;
the ion conduction layer covers a main surface and a side surface of the positive electrode active material-containing layer, and an end of the ion conduction layer is in contact with a main surface of the positive electrode current collector,
the positive electrode current collector has a positive electrode tab portion on which the positive electrode active material-containing layer and the ion conductive layer are not supported,
the negative electrode comprises a negative electrode current collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode current collector,
the negative electrode current collector has a negative electrode tab portion on which the negative electrode active material-containing layer is not supported,
the positive electrode active material-containing layer is located in a space formed between the positive electrode current collector and the ion conductive layer,
the ion conductive layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via the porous separator;
the electrode group is directly covered with the resin portion except for a portion of the positive electrode tab portion and a portion of the negative electrode tab portion.
[2] The secondary battery according to [1], further comprising an exterior member that covers at least a portion of the resin portion.
[3] The secondary battery according to [1] or [2], wherein the ion conductive layer has a lithium ion conductivity of 1×10 ⁻¹⁰ S/cm or more at 25° C.
[4] The secondary battery according to any one of [1] to [3], wherein the ion conductive layer is at least one of a solid electrolyte layer and a gel electrolyte layer.
[5] The secondary battery according to any one of [1] to [4], wherein the resin portion contains a thermosetting resin.
[6] The negative electrode active material-containing layer contains a negative electrode active material,
The secondary battery according to any one of [1] to [5], wherein the negative electrode active material is a compound having a lithium ion absorption/release potential of 1 V or more and 3 V or less, in terms of a potential relative to metallic lithium.
[7] The positive electrode active material-containing layer contains a positive electrode active material,
The secondary battery according to any one of [1] to [6], wherein the positive electrode active material is a compound having a lithium ion absorption/release potential of 3 V or more and 5.5 V or less, in terms of a potential relative to metallic lithium.
[8] A battery pack comprising the secondary battery according to any one of [1] to [7].
[9] The battery pack according to [8], further comprising an external terminal for current flow and a protection circuit.
[10] The battery pack according to [8] or [9], comprising a plurality of the secondary batteries, the secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel.
[11] A vehicle equipped with the battery pack according to any one of [8] to [10].
[12] A stationary power source comprising the battery pack according to any one of [8] to [10].

2...Exterior member (container), 2a...mouth, 2b...mouth, 2c...storage space, 6...positive electrode, 6a...positive electrode current collector, 6b...positive electrode active material-containing layer, 6c...positive electrode tab portion, 7...negative electrode, 7a...negative electrode current collector, 7b...negative electrode active material-containing layer, 7c...negative electrode tab portion, 8...porous separator, 10...electrode group, 14...positive electrode lead, 17...negative electrode lead, 21...positive electrode terminal, 22...negative electrode terminal, 23...insulating member, 24...adhesive tape, 25...insulating member, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 100...secondary battery, 110...system, 111...power plant, 112...stationary power source, 1 13... Consumer side power system, 115... Energy management system (EMS), 116... Power network, 117... Communication network, 118... Power conversion device, 121... Power conversion device, 122... Power conversion device, 123... Stationary power source, 200... Battery pack, 300... Battery pack, 300A... Battery pack, 300B... Battery pack, 310... Storage container, 320... Lid, 341... Negative connector, 342... Positive connector, 343... Thermistor, 344... Protection circuit, 345... Wiring, 346... Wiring, 347... External terminal for energization, 348a... Negative wiring, 348b... Positive wiring, 400... Vehicle.

Claims (11)

an electrode group including a positive electrode, a negative electrode, and a porous separator holding an aqueous electrolyte;
A resin part ;
a packaging member that covers at least a portion of the resin portion ,
the positive electrode comprises a positive electrode current collector, a positive electrode active material-containing layer supported on at least one surface of the positive electrode current collector, and an ion conductive layer;
the ion conduction layer covers a main surface and a side surface of the positive electrode active material-containing layer, and an end of the ion conduction layer is in contact with a main surface of the positive electrode current collector,
the positive electrode current collector has a positive electrode tab portion on which the positive electrode active material-containing layer and the ion conductive layer are not supported,
the negative electrode comprises a negative electrode current collector and a negative electrode active material-containing layer supported on at least one surface of the negative electrode current collector,
the negative electrode current collector has a negative electrode tab portion on which the negative electrode active material-containing layer is not supported,
the positive electrode active material-containing layer is located in a space formed between the positive electrode current collector and the ion conductive layer,
the ion conductive layer of the positive electrode and the negative electrode active material-containing layer of the negative electrode face each other via the porous separator;
the electrode group is directly covered with the resin portion except for a portion of the positive electrode tab portion and a portion of the negative electrode tab portion. 2. The secondary battery according to claim 1 , wherein the ion conductive layer has a lithium ion conductivity of 1×10 ^-10 S/cm or more at 25° C. 3. The secondary battery according to claim 1 , wherein the ion conductive layer is at least one of a solid electrolyte layer and a gel electrolyte layer. The secondary battery according to claim 1 , wherein the resin portion includes a thermosetting resin. the negative electrode active material-containing layer contains a negative electrode active material,
5. The secondary battery according to claim 1, wherein the negative electrode active material is a compound having a lithium ion absorption/release potential of 1 V or more and 3 V or less , in terms of a potential based on metallic lithium. The positive electrode active material-containing layer contains a positive electrode active material,
6. The secondary battery according to claim 1 , wherein the positive electrode active material is a compound having a lithium ion absorption/release potential of 3 V or more and 5.5 V or less, in terms of a potential based on metallic lithium. A battery pack comprising the secondary battery according to any one of claims 1 to 6 . 8. The battery pack according to claim 7 , further comprising an external terminal for current supply and a protection circuit. 9. The battery pack according to claim 7 , comprising a plurality of the secondary batteries, the secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle comprising the battery pack according to any one of claims 7 to 9 . A stationary power source comprising the battery pack according to any one of claims 7 to 9 .