JP2022143728A - Aqueous electrolyte bipolar secondary battery, battery pack, vehicle and stationary power source - Google Patents

Abstract

To provide an aqueous electrolyte battery superior in life characteristic, and including a bipolar electrode having a current collector that exhibits high endurance.SOLUTION: Provided is an aqueous electrolyte bipolar secondary battery 500. The aqueous electrolyte bipolar secondary battery 500 comprises: an anode 3; a cathode 5; a bipolar electrode having a bipolar electrode collector 502; and an aqueous electrolyte. The bipolar electrode collector 502 has a metal layer a 502a and a metal layer b 502b. The metal layer a contains at least one element selected from a group consisting of Cr, Ni, Fe, Ti and Al. The metal layer b contains either Zn or Sn, which is 10 wt% or more and 100 wt% or less to a weight per unit layer of the metal layer b. The metal layer a and the metal layer b are electrically connected. The bipolar electrode has a cathode active material-containing layer 5b2 on a face of the metal layer a, and an anode active material-containing layer 3b2 on a face of the metal layer b.SELECTED DRAWING: Figure 1

Description

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

Non-aqueous electrolyte batteries such as lithium ion batteries are used as power sources in a wide range of fields. Non-aqueous electrolyte batteries have a wide variety of forms, from small ones for various electronic devices to large ones for electric vehicles and the like. Non-aqueous electrolyte batteries use a non-aqueous electrolyte containing a combustible substance such as ethylene carbonate, and thus require safety measures.

Development of an aqueous electrolyte battery using an aqueous electrolyte containing a non-flammable aqueous solvent instead of a non-aqueous electrolyte is underway.

Since bipolar electrodes can be connected in series within a single cell, high voltage is possible without external connection. However, in an aqueous electrolyte battery using an aqueous electrolyte, different aqueous electrolytes may be used on each electrode side in order to achieve high performance. When a bipolar electrode is used in this water-based electrolyte battery, there is a problem with the durability of the current collector of the bipolar electrode.

JP 2020-53385 A

To provide a water-based electrolyte bipolar secondary battery and a battery pack having excellent life characteristics by providing a bipolar electrode having a current collector exhibiting high durability, and to provide a vehicle and a stationary power source equipped with the battery pack. With the goal.

According to embodiments, an aqueous electrolyte bipolar secondary battery is provided. This aqueous electrolyte bipolar secondary battery has a negative electrode provided on at least one surface of a negative electrode current collector as a first negative electrode active material containing layer, and a first positive electrode active material containing layer provided on at least one surface of a positive electrode current collector. A bipolar electrode current collector having a positive electrode provided on one surface, a second positive electrode active material-containing layer provided on one surface, and a second negative electrode active material-containing layer provided on the opposite surface. and an aqueous electrolyte. The bipolar electrode current collector has a metal layer a and a metal layer b, the metal layer a containing at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al, and the metal layer b , 10 wt. % or more 100 wt. % or less of any one element of Zn and Sn. The metal layer a and the metal layer b are electrically connected, have a second positive electrode active material containing layer on the surface of the metal layer a, and have a second negative electrode active material containing layer on the surface of the metal layer b. have

1 is a schematic diagram of a water-based electrolyte bipolar secondary battery according to an embodiment; FIG. Schematic diagram of a bipolar electrode current collector provided in a water-based electrolyte bipolar secondary battery according to an embodiment. BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing which shows schematically an example of the secondary battery which concerns on embodiment. FIG. 4 is a cross-sectional view along the IV-IV line of the secondary battery shown in FIG. 3; FIG. 4 is a partially cutaway perspective view schematically showing another example of the secondary battery according to the embodiment; FIG. 6 is an enlarged cross-sectional view of the B portion of the secondary battery shown in FIG. 5; The perspective view which shows roughly an example of the assembled battery which concerns on embodiment. 1 is a perspective view schematically showing an example of a battery pack according to an embodiment; FIG. FIG. 4 is an exploded perspective view schematically showing another example of the battery pack according to the embodiment; FIG. 10 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 9; FIG. 1 is a partially transparent view schematically showing 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; FIG.

Embodiments will be described below. Unless otherwise specified, values given for pH and other measurements are values measured at atmospheric pressure and 25°C.

(First embodiment)
The aqueous electrolyte bipolar secondary battery according to the first embodiment includes a negative electrode provided with a first negative electrode active material containing layer on at least one surface of a negative electrode current collector, and a first positive electrode active material containing layer. A positive electrode provided on at least one surface of a positive electrode current collector, a second positive electrode active material-containing layer provided on one surface, and a second negative electrode active material-containing layer provided on the other opposite surface. An aqueous electrolyte bipolar secondary battery comprising a bipolar electrode having a bipolar electrode current collector and an aqueous electrolyte, wherein the bipolar electrode current collector has a metal layer a and a metal layer b, and the metal layer a is The metal layer b contains at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al, and the metal layer b contains 10 wt. % or more 100 wt. % or less of any one of Zn and Sn, the metal layer a and the metal layer b are electrically connected, and the metal layer a has a second positive electrode active material-containing layer on the surface of the metal layer a , has a second negative electrode active material-containing layer on the surface of the metal layer b.

FIG. 1 is a schematic diagram of a water-based electrolyte bipolar secondary battery according to the first embodiment. An aqueous electrolyte bipolar secondary battery 500 includes a negative electrode 3 , a positive electrode 5 and a bipolar electrode 501 . The negative electrode 3 is provided with a first negative electrode active material containing layer 3b1 on at least one surface of the negative electrode current collector 3a. The positive electrode 5 is provided with a first positive electrode active material containing layer 5b1 on at least one surface of the positive electrode current collector 5a. The bipolar electrode 501 includes a second positive electrode active material containing layer 5b2 facing the first negative electrode active material containing layer 3b1 with the first separator 4a interposed therebetween, a first positive electrode active material containing layer 5a1 and a second separator. A bipolar electrode current collector 502 is provided in contact with the second negative electrode active material containing layer 3b2 facing across 4b. The first separator 4a and the second separator 4b may be porous or non-porous. The first separator 4a and the second separator 4b may be of the same type or of different types. The bipolar electrode current collector 502 has a metal layer a502a and a metal layer b502b, the metal layer a502a is in contact with the positive electrode active material containing layer 5b2, and the metal layer b502b is in contact with the negative electrode active material containing layer 3b2. The aqueous electrolyte provided in the aqueous electrolyte bipolar secondary battery 500 is retained in the positive electrode active material containing layer and the negative electrode active material containing layer. In FIG. 1, the negative electrode side aqueous electrolyte 504 and the positive electrode side aqueous electrolyte 505 are shown for convenience. There is a positive electrode side aqueous electrolyte 505 in contact with the metal layer a 502a and a negative electrode side aqueous electrolyte 504 in contact with the metal layer b 502b, and the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte are different. The same type of aqueous electrolyte can be used as the aqueous electrolyte contained in the first positive electrode active material-containing layer and the second positive electrode active material-containing layer, or different types can be used. Similarly, the aqueous electrolyte contained in the first negative electrode active material-containing layer and the second negative electrode active material-containing layer may be of the same type or may be different.

If the first and second separators are porous, the aqueous electrolyte is also retained in the separators.

The types of the first negative electrode active material and the second negative electrode active material may be different or the same. The types of the first positive electrode active material and the second positive electrode active material may be different or the same.

Unless otherwise specified, the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte are collectively referred to simply as "aqueous electrolyte".

By using a bipolar for the aqueous electrolyte battery, it is possible to connect in series within a single cell, so it is possible to increase the voltage without external connection. In particular, by using an aqueous electrolyte that matches the active materials used for the positive electrode and the negative electrode, it is possible to further improve the battery characteristics. However, suitable current collectors should be used for the positive and negative electrodes, respectively, but these current collectors tend to corrode depending on the type of water-based electrolyte. Therefore, by using a bipolar electrode current collector that matches the aqueous electrolyte and electrodes, it is possible to suppress corrosion of the current collector, improve the capacity retention rate and initial discharge capacity of the secondary battery, and improve the self-discharge rate. Such battery characteristics can be improved.

Here, constituent members of the water-based electrolyte bipolar secondary battery according to this embodiment will be described.

(positive electrode)
The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer provided on at least one surface of the positive electrode current collector. The first positive electrode active material-containing layer and the second positive electrode active material-containing layer are collectively referred to as positive electrode active material-containing layers. The positive electrode active material-containing layer contains a positive electrode active material and optionally a conductive agent and a binder.

Positive electrode current collectors include, for example, metals such as stainless steel, aluminum (Al), and titanium (Ti). The positive electrode current collector has, for example, the shape of foil, porous body or mesh. In order to prevent corrosion due to 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 made of, for example, a Ti foil having excellent corrosion resistance and oxidation resistance. When Li ₂ SO ₄ is used as the aqueous electrolyte, corrosion does not progress, so Al may be used as the positive electrode current collector.

In addition, the positive electrode current collector can include a portion on the surface of which the positive electrode active material-containing layer is not provided. This portion can serve as a positive current collecting tab.

The positive electrode active material containing layer contains a positive electrode active material. The positive electrode active material-containing layer may be carried on both the front and back surfaces of the positive electrode current collector.

As the positive electrode active material, a compound having a lithium ion insertion-desorption potential of 2.5 V or more and 5.5 V or less with respect to the oxidation-reduction potential of lithium (vs. Li/Li ⁺ ) can be used. The positive electrode may contain one compound alone as a positive electrode active material, or may contain two or more compounds as a positive electrode active material.

Examples of compounds that can be used as positive electrode active materials include lithium-manganese composite oxides, lithium-nickel composite oxides, lithium-cobalt-aluminum composite oxides, lithium-nickel-cobalt-manganese composite oxides, spinel-type lithium-manganese-nickel composite oxides, Lithium manganese cobalt composite oxides, lithium iron oxides, lithium fluorinated iron sulfates, phosphoric acid compounds with an olivine crystal structure (for example, compounds represented by Li _k FePO ₄ where 0 < k ≤ 1, Li _k MnPO ₄ and 0<k≦1). Phosphate compounds with an olivine crystal structure are excellent in thermal stability.

Examples of the compound capable of obtaining a high positive electrode potential include, for example, a compound represented by Li _k Mn ₂ O ₄ having a spinel structure and satisfying 0<k≦1, and a compound represented by Li _k MnO ₂ satisfying 0<k≦1. Lithium-manganese composite oxides such as; Lithium-nickel-aluminum composite oxides such as compounds represented by Li _k Ni _1-i Al _i O ₂ where 0 < k ≤ 1 and 0 < i <1; For example Li _k CoO Lithium cobalt composite oxides such as compounds represented by ₂ and ₀ <k≦1; for example Li _k Ni _{1-i-t Co i} Mnt O lithium-nickel-cobalt composite oxides such as compounds where _{0 ≦ t} <₁; Composite oxides; for example, spinel-type lithium manganese nickel composite oxides such as compounds represented by Li _k Mn _1-i Ni _i O ₄ where 0 < _k ≤ ₁ and 0 < i <1; a compound represented by _{LikFe1 - yMnyPO4} with 0< _k≤1 and _0≤y≤1 ; a compound represented by _LikCoPO4 with 0<k≤1 and fluorinated iron sulfate (for example, a compound represented by Li _k FeSO ₄ F where 0<k≦1).

The positive electrode active material preferably contains one or more selected from the group consisting of lithium cobalt composite oxides, lithium manganese composite oxides, and lithium phosphorous oxides having an olivine structure. The action potentials of these compounds are 3.5 V (vs. Li/Li ⁺ ) or more and 4.2 V (vs. Li/Li ⁺ ) or less. That is, the action potential of these compounds as active materials is relatively high. A high battery voltage can be obtained by using these compounds in combination with the aforementioned negative electrode active materials such as spinel-type lithium titanate and anatase-type titanium oxide.

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 that are aggregates of primary particles, or mixtures of primary particles and secondary particles. The shape of the particles is not particularly limited, and can be, for example, spherical, elliptical, flattened, 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 measured by the same method as for the negative electrode active material particles.

The positive electrode active material-containing layer may contain a conductive agent, a binder, and the like in addition to the positive electrode active material. The conductive agent is blended as necessary in order to improve the current collection performance and suppress the contact resistance between the active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, ketjen black, graphite and coke. The conductive agent may be of one type or a mixture of two or more types.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, ethylene-butadiene rubber, polypropylene (PP), polyethylene (PE), carboxymethylcellulose (CMC), polyimide ( PI), polyacrylimide (PAI), and the like. One type of binder may be used, or two or more types may be mixed and used.

The compounding ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material-containing layer is 70% by mass or more and 95% by mass or less, 3% by mass or more and 20% by mass or less, and 2% by mass or more and 10% by mass or less. is preferably When the compounding ratio of the conductive agent is 3% by mass or more, the conductivity of the positive electrode can be improved, and when it is 20% by mass or less, decomposition of the aqueous electrolyte on the surface of the conductive agent can be reduced. When the compounding ratio of the binder is 2% by mass or more, sufficient electrode strength can be obtained, and when it is 10% by mass or less, the insulating portion of the electrode can be reduced.

The positive electrode current collector is in contact with the second surface of the positive electrode active material-containing layer. The positive electrode current collector may be in contact with the second surface of one positive electrode active material-containing layer, or may be in contact with the second surfaces of two positive electrode active material-containing layers. For example, one surface of the positive electrode current collector may contact the second surface of one positive electrode active material-containing layer, and the other surface of the positive electrode current collector may contact the second surface of another positive electrode active material-containing layer. can. That is, it can include two positive electrode active material-containing layers with one positive electrode current collector sandwiched therebetween.

A positive electrode can be obtained, for example, by the following method. First, a slurry is prepared by suspending a positive electrode active material, a conductive agent and a binder in an appropriate solvent. This slurry is applied to one side or both sides of the positive electrode current collector. The coating film on the positive electrode current collector is dried to form a positive electrode active material-containing layer. Thereafter, the positive electrode current collector and the positive electrode active material-containing layer formed thereon are pressed. As the positive electrode active material-containing layer, a pellet-shaped mixture of a positive electrode active material, a conductive agent and a binder may be used.

(negative electrode)
The negative electrode can include a negative electrode current collector and a negative electrode active material-containing layer provided on at least one surface of the negative electrode current collector. The first negative electrode active material-containing layer and the second negative electrode active material-containing layer are collectively referred to as negative electrode active material-containing layers. The negative electrode active material-containing layer contains a negative electrode active material and optionally a conductive agent and a binder. When a compound having a lower limit of lithium ion insertion-extraction potential of 1 V or more (vs. Li/Li ⁺ ) is used as the negative electrode active material contained in the negative electrode active material-containing layer, high capacity and excellent stability can be obtained. A secondary battery can be realized.

Examples of compounds having a lithium ion insertion-desorption potential of 1 V or more and 3 V or less (vs. Li/Li ⁺ ) based on the oxidation-reduction potential of lithium include titanium oxides and titanium-containing oxides. mentioned. Titanium-containing oxides include lithium-titanium composite oxides, niobium-titanium composite oxides, sodium-niobium-titanium composite oxides, and the like. The negative electrode active material can include one or more titanium oxides and titanium-containing oxides.

Titanium oxide includes, for example, monoclinic structure titanium oxide, rutile structure titanium oxide, and anatase structure titanium oxide. The titanium oxide of each crystal structure can be represented by TiO ₂ for the composition before charging and by Li _y TiO ₂ (subscript y is 0≦y≦1) after charging. In addition, the pre-charged structure of titanium oxide having a monoclinic structure can be expressed as TiO ₂ (B).

Lithium titanium oxides include, for example, spinel structure lithium titanium oxides (for example, compounds represented by the general formula Li _4+j Ti ₅ O ₁₂ and −1≦j≦3), ramsdellite structure lithium titanium oxides (for example, a compound represented by Li _2+j Ti ₃ O ₇ where −1≦j≦3), a compound represented by Li _1+y Ti ₂ O ₄ where 0≦y≦1, and a compound represented by Li _1.1+y Ti _1.8 O ₄ and 0 ≤ y ≤ 1, a compound represented by Li _{1.07 + y} Ti _1.86 O ₄ and 0 ≤ y ≤ 1, a compound represented by Li _k TiO ₂ with 0 < k ≤ 1, etc. . Also, the lithium-titanium oxide may be a lithium-titanium composite oxide into which a dissimilar element is introduced.

The niobium-titanium composite oxide is represented, for example, by Li _χ TiMe _α Nb _2±β O _7±σ , where 0≦χ≦5, 0≦α≦0.3, 0≦β≦0.3, and 0≦σ≦0. .3, Me includes compounds that are one or more selected from the group consisting of Fe, V, Mo and Ta.

The sodium-niobium-titanium composite oxide is represented, for example, by the general formula Li _2+d Na _2-e Me1 _f Ti _6-g-h Nb _g Me2 _h O _14+δ , where 0≦d≦4, 0≦e<2, 0≦ f < 2, 0 < g < 6, 0 ≤ h < 3, -0.5 ≤ δ ≤ 0.5, Me1 contains one or more selected from Cs, K, Sr, Ba, Ca, Me2 is Zr , Sn, V, Ta, Mo, W, Fe, Co, Mn, and Al.

As the negative electrode active material, it is preferable to use an anatase-structured titanium oxide, a monoclinic-structured titanium oxide, a spinel-structured lithium-titanium oxide, a niobium-titanium composite oxide, or a mixture thereof. On the other hand, when a titanium oxide with an anatase structure, a titanium oxide with a monoclinic structure, or a lithium titanium oxide with a spinel structure is used as a negative electrode active material, for example, a positive electrode using a lithium manganese composite oxide as a positive electrode active material A high electromotive force can be obtained by combining with On the other hand, by using a niobium-titanium composite oxide, a high capacity can be exhibited.

The negative electrode active material may be included in the negative electrode active material-containing layer in the form of particles, for example. The negative electrode active material particles can be primary particles, secondary particles that are aggregates of primary particles, or mixtures of single primary particles and secondary particles. The shape of the particles is not particularly limited, and may be, for example, spherical, elliptical, flattened, or fibrous.

Secondary particles of the negative electrode active material can be obtained, for example, by the following method. First, active material raw materials are reacted and synthesized to prepare an active material precursor having an average particle size of 1 μm or less. After that, the active material precursor is subjected to a calcination treatment, and then subjected to a pulverization treatment using a pulverizer such as a ball mill or a jet mill. Next, in the baking treatment, the active material precursor is aggregated and grown into secondary particles having a large particle size.

The average particle size (diameter) of the secondary particles of the negative electrode active material is preferably 3 μm or more, more preferably 5 μm or more and 20 μm or less. Within this range, since the surface area of the active material is small, decomposition of water can be further suppressed.

The average particle size of the primary particles of the negative electrode active material is desirably 1 μm or less. This shortens the diffusion distance of Li ions inside the active material and increases the specific surface area. Therefore, excellent high input performance (rapid charging) can be obtained. On the other hand, when the average particle diameter of the primary particles of the negative electrode active material is small, aggregation of the particles tends to occur. If the particles of the negative electrode active material aggregate, the aqueous electrolyte tends to be unevenly distributed on the negative electrode in the secondary battery, which may lead to depletion of ionic species in the positive electrode. Therefore, the average particle size of the primary particles of the negative electrode active material is preferably 0.001 μm or more. The average particle size of the primary particles of the negative electrode active material is more preferably 0.1 μm or more and 0.8 μm or less.

The primary particle size and secondary particle size mean the particle size at which the volume integrated value is 50% in the particle size distribution determined by a laser diffraction type particle size distribution analyzer. For example, Shimadzu SALD-300 is used as a laser diffraction particle size distribution analyzer. During the measurement, the light intensity distribution is measured 64 times at intervals of 2 seconds. As a sample for this particle size distribution measurement, a dispersion diluted with N-methyl-2-pyrrolidone so that the concentration of the active material particles is 0.1% by mass to 1% by mass is used. Alternatively, a measurement sample is prepared by dispersing 0.1 g of the active material in 1 to 2 ml of distilled water containing a surfactant.

The negative electrode active material has a specific surface area of, for example, 3 m ² /g or more and 200 m ² /g or less as determined by the BET method by nitrogen (N ₂ ) adsorption. When the specific surface area of the negative electrode active material is within this range, the affinity between the electrode and the aqueous electrolyte can be further increased. This specific surface area can be obtained, for example, by a method similar to the method for measuring the specific surface area of the negative electrode active material-containing layer, which will be described later.

The porosity of the negative electrode active material-containing layer is desirably 20% or more and 50% or less. As a result, it is possible to obtain an electrode having excellent affinity with the aqueous electrolyte and having a high density. More preferably, the porosity of the negative electrode active material-containing layer is 25% or more and 40% or less.

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

More preferably, the specific surface area of the negative electrode active material-containing layer by nitrogen (N ₂ ) adsorption by the BET method is 3 m ² /g or more and 50 m ² /g or less. If the specific surface area of the negative electrode active material-containing layer is less than 3 m ² /g, the affinity between the active material and the aqueous electrolyte will be low. As a result, the interfacial resistance of the electrode increases, and the output performance and charge/discharge cycle performance of the secondary battery may deteriorate. On the other hand, when the specific surface area of the negative electrode active material-containing layer exceeds 50 m ² /g, the distribution of the ion species ionized from the electrolyte salt contained in the aqueous electrolyte is biased toward the negative electrode, leading to a shortage of the ion species at the positive electrode. Performance and charge/discharge cycle performance may be degraded.

This specific surface area can be determined, for example, by the following method. When the negative electrode including the negative electrode active material-containing layer to be measured is incorporated in a secondary battery, the secondary battery is disassembled and part of the negative electrode active material-containing layer is collected. In nitrogen gas at 77K (boiling point of nitrogen), the nitrogen gas pressure P (mmHg) is gradually increased, and the nitrogen gas adsorption amount (mL/g) of the sample is measured for each pressure P. The value obtained by dividing the pressure P (mmHg) by the saturated vapor pressure P0 (mmHg) of nitrogen gas is defined as the relative pressure P/P0, and the adsorption isotherm is obtained by plotting the nitrogen gas adsorption amount against each relative pressure P/P0. A BET plot is calculated from this nitrogen adsorption isotherm and the BET equation, and the specific surface area is obtained using this BET plot. Note that the BET multi-point method is used to calculate the BET plot.

The conductive agent is added as necessary in order to improve the current collection performance and suppress the contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as acetylene black, ketjen black, graphite and coke. The conductive agent may be of one type or a mixture of two or more types.

The binder has a function of binding the active material and the conductive agent. Binders include, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulosic polymers such as carboxymethyl cellulose (CMC), fluororubbers, styrene-butadiene rubbers, acrylic resins or copolymers thereof, At least one selected from the group consisting of polyacrylic acid and polyacrylonitrile can be used, but is not limited thereto. For example, a polymer material contained in the solid electrolyte layer of the separator can be used as the binder. One type of binder may be used, or two or more types may be mixed and used.

The compounding ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode active material-containing layer is 70% by mass or more and 95% by mass or less, 3% by mass or more and 20% by mass or less, and 2% by mass or more and 10% by mass or less. is preferably in the range of When the compounding ratio of the conductive agent is 3% by mass or more, the conductivity of the negative electrode active material-containing layer can be improved, and when it is 20% by mass or less, decomposition of the aqueous electrolyte on the surface of the conductive agent can be reduced. When the compounding ratio of the binder is 2% by mass or more, sufficient electrode strength can be obtained, and when it is 10% by mass or less, the insulating portion of the electrode can be reduced.

The negative electrode current collector is in contact with the second surface of the negative electrode active material-containing layer. The negative electrode current collector may be in contact with the second surface of one negative electrode active material-containing layer, or may be in contact with the second surfaces of two negative electrode active material-containing layers. For example, one surface of the negative electrode current collector may be in contact with the second surface of one negative electrode active material-containing layer, and the other surface of the negative electrode current collector may be in contact with the second surface of another negative electrode active material-containing layer. can. That is, it can include two negative electrode active material-containing layers with one negative electrode current collector sandwiched therebetween.

At least a portion of the negative electrode current collector can include a portion that is not in contact with the negative electrode active material-containing layer on both the front and back surfaces at that location. This portion can act as a current collecting tab. Alternatively, a collector tab separate from the negative electrode collector may be electrically connected to the electrode. Further, when the negative electrode active material-containing layers are arranged on both sides of the negative electrode current collector, at least part of one surface of the negative electrode current collector is in contact with the negative electrode active material-containing layer at that location. It can contain parts that are not For example, a current collecting tab separate from the negative electrode current collector can be connected to this portion.

A material that is electrochemically stable in the electrode potential range when alkali metal ions are intercalated or deintercalated is used as the material of the negative electrode current collector. The negative electrode current collector is, for example, zinc foil, aluminum foil, or magnesium (Mg), titanium (Ti), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu) and silicon (Si). It is preferable that the surface is coated with an aluminum alloy foil containing one or more selected from and with a metal having a large hydrogen overvoltage such as Zn or Sn. 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 20 μm or less. A negative electrode current collector having such a thickness can balance the strength and weight reduction of the electrode.

A negative electrode can be obtained, for example, by the following method. First, a slurry is prepared by suspending a negative electrode active material, a conductive agent, and a binder in an appropriate solvent. This slurry is applied to one side or both sides of the negative electrode current collector. The coating film on the negative electrode current collector is dried to form a negative electrode active material-containing layer. After that, the negative electrode current collector and the negative electrode active material-containing layer formed thereon are pressed. As the negative electrode active material-containing layer, a mixture of a negative electrode active material, a conductive agent and a binder formed into pellets may be used.

(bipolar electrode)
The bipolar electrode has a positive electrode active material containing layer on one surface and a negative electrode active material containing layer on the opposite surface. A positive electrode active material-containing layer and a negative electrode active material-containing layer are provided on two sides of a bipolar electrode current collector.

As the active material-containing layer contained in the positive electrode active material-containing layer and the negative electrode active material-containing layer, the active material-containing layers described above for the positive electrode and the negative electrode can be used, respectively.

One or more bipolar electrodes can be provided in one secondary battery. For example, two or more can be provided.

A bipolar electrode current collector has a metal layer a and a metal layer b. The metal layer a and the metal layer b are electrically connected. It has a positive electrode active material containing layer on the surface of the metal layer a, and has a negative electrode active material containing layer on the surface of the metal layer b. For example, FIG. 2 is a schematic diagram of a bipolar electrode current collector provided in a water-based electrolyte bipolar secondary battery. In FIG. 2a, the metal layer a 502a and the metal layer b 502b of the bipolar electrode current collector 502 are in direct contact. In FIG. 2b, there is a conductive adhesive layer 503 between metal layer a 502a and metal layer b 502b of the bipolar electrode current collector. In FIG. 2c, a conductive adhesive layer a 503a and a conductive adhesive layer b 503b are present between the metal layer a 502a and the metal layer b 502b. In FIG. 2d, a conductive adhesive layer a 503a, a conductive adhesive layer b 503b and a conductive adhesive layer c 503c exist between the metal layer a 502a and the metal layer b 502b. It is sufficient that the metal layer a and the metal layer b of the bipolar electrode current collector are electrically connected.

The metal layer a contains at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al. Since the metal layer a is in contact with the positive electrode active material containing layer, it is in contact with the aqueous electrolyte used on the positive electrode side (positive electrode side aqueous electrolyte). By using the above metal element for the metal layer a, it is possible to have durability against corrosion from the positive electrode side aqueous electrolyte. The positive electrode side aqueous electrolyte will be described later in detail.

Since the metal layer a contains at least one element selected from the group consisting of Cr, Ni, Fe, Ti, and Al, the metal layer a is composed of almost one metal element such as Ni foil and Ti foil. Approximately 100 wt. % of one element selected from the group consisting of Ni, Fe, Ti, and Al may be contained, and alloy foils such as stainless steel foils, Al-Mg alloys and Al-Zn-Mg alloys may be included, and The surface of the substrate may be provided with at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al by plating the material. That is, at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al should be provided in the portion of the metal layer a in contact with the aqueous electrolyte. Therefore, it is preferable that at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al is present on all the surfaces of the metal layer a that are in contact with the aqueous electrolyte. In order to provide the above elements, it is preferable to use a foil shape or a coated state by plating.

The thicknesses of the metal layer a and the metal layer b can be changed depending on the metal species on the surface of the metal layer in contact with the aqueous electrolyte. If the hardness of the metal species used is high, the strength of the electrode can be maintained when it is made into a bipolar electrode. Therefore, when the hardness of the metal used is high, the thickness of the metal layer a and the metal layer b can be made thinner than the thickness of the bipolar electrode current collector.

The strength of the bipolar electrode should be maintained by at least one of the metal layer a and the metal layer b.

Depending on the metal type and thickness used for the metal layer a, pinholes and cracks occurring in the bipolar electrode current collector can be suppressed, and when a battery is made, an electrode group including a negative electrode, a positive electrode, and a bipolar electrode due to external impact can be formed. Bending or the like can also be reduced.

The thickness of the bipolar electrode current collector is preferably 10 μm or more and 100 μm or less. If it is larger than 100 μm, the energy density is lowered, which is not preferable. If the thickness is less than 10 μm, the strength is insufficient, and it is difficult to maintain strength as a bipolar electrode.

When Al is used for the metal layer a, the thickness of the metal layer a is preferably 9% or more and 95% or less of the thickness of the bipolar electrode current collector. The use of Al means the case of using a material composed of almost one kind of metal element, such as Al foil. Since the thicknesses of the metal layer a and the metal layer b are in a trade-off relationship with respect to the thickness of the bipolar electrode current collector, the thickness of the metal layer a is 9% or more and 95% of the thickness of the bipolar electrode current collector. This is because the corrosion resistance as a bipolar electrode current collector can be maintained by satisfying the following. If the thickness of the metal layer a is less than 9% of the thickness of the bipolar electrode current collector, the metal layer b will be exposed if the metal layer a is peeled off due to press working or the like. It is not preferable because it lowers corrosion resistance. If the thickness of the metal layer a exceeds 95% of the thickness of the bipolar electrode current collector, the metal layer a will be exposed if peeling or the like occurs in the metal layer b due to press working or the like. It is not preferable because it lowers corrosion resistance. More preferably, the thickness of the metal layer a is 40% or more and 60% less than the thickness of the bipolar electrode current collector.

When the metal layer a contains Cr, Fe, Ni, Ti, an Al-Mg alloy, or an Al-Mg-Zn alloy, the thickness of the metal layer a is 7% or more and 95% or less of the thickness of the bipolar electrode current collector. Preferably. Cr, Fe, Ni, Ti, Al--Mg alloy, and Al--Mg--Zn alloy may be used as foil or plated. Since the thicknesses of the metal layer a and the metal layer b are in a trade-off relationship with respect to the thickness of the bipolar electrode current collector, the thickness of the metal layer a is 7% or more and 95% of the thickness of the bipolar electrode current collector. This is because the corrosion resistance as a bipolar electrode current collector can be maintained by satisfying the following. If the thickness of the metal layer a is less than 7% of the thickness of the bipolar electrode current collector, the metal layer b will be exposed if the metal layer a is peeled off due to press working or the like. It is not preferable because it lowers corrosion resistance. If the thickness of the metal layer a exceeds 95% of the thickness of the bipolar electrode current collector, the metal layer a will be exposed if peeling or the like occurs in the metal layer b due to press working or the like. This is not preferable because it lowers the corrosion resistance. More preferably, the thickness of the metal layer a is 30% or more and 70% or less of the thickness of the bipolar electrode current collector. Even more preferably, the thickness of the metal layer a is 40% or more and 60% or less of the thickness of the bipolar electrode current collector.

When stainless steel is used for the metal layer a, the thickness of the metal layer a is preferably 5% or more and 95% or less of the thickness of the bipolar electrode current collector. The use of stainless means, for example, the use of stainless steel foil. Since the thicknesses of the metal layer a and the metal layer b are in a trade-off relationship with respect to the thickness of the bipolar electrode current collector, the thickness of the metal layer a is 5% or more and 95% of the thickness of the bipolar electrode current collector. This is because the corrosion resistance as a bipolar electrode current collector can be maintained by satisfying the following. If the thickness of the metal layer a is less than 5% with respect to the thickness of the bipolar electrode current collector, the metal layer b is exposed when the metal layer a is peeled off due to press working or the like. This is not preferable because it lowers the corrosion resistance. If the thickness of the metal layer a exceeds 95% of the thickness of the bipolar electrode current collector, the metal layer a will be exposed if peeling or the like occurs in the metal layer b due to press working or the like. This is not preferable because it lowers the corrosion resistance.

When the metal layer a is plated to contain at least one element selected from the group consisting of Cr, Ni, Fe, Ti, and Al, the thickness of the metal layer a is the thickness of the plating and the thickness of the base material. is the sum of the The thickness of this plating is preferably 5% or more and 95% or less of the thickness of the bipolar electrode current collector. This is because when the thickness of the plating is within the above range, the corrosion resistance as a bipolar electrode current collector can be maintained.

The metal layer b has a weight of 10 wt. % or more 100 wt. % or less of any one element of Zn and Sn. The term "per layer of metal layer b" refers to the metal layer b of a bipolar electrode current collector included in one bipolar electrode. Since the metal layer b is in contact with the negative electrode active material containing layer, it is in contact with the aqueous electrolyte used on the negative electrode side (negative electrode side aqueous electrolyte). The metal layer b has a weight of 10 wt. % or more 100 wt. % or less of any one element of Zn and Sn, it is possible to have durability against corrosion from the negative electrode side aqueous electrolyte. The details of the negative electrode side aqueous electrolyte will be described later. The metal layer b contains at least one of Zn and Sn in an amount of 10 wt. % or more means that the metal layer b is a metal foil or alloy foil such as Zn foil or Sn foil, or that the surface of the base material is provided with either Zn or Sn by plating the base material. You may let When plating is applied, the metal layer b is a combination of the plated portion and the substrate portion. That is, at least one of Zn and Sn is added to the portion of the metal layer b in contact with the water-based electrolyte in an amount of 10 wt. % or more.

More preferably 15 wt. % or more, and more preferably 20 wt. % or more. This is because side reactions can be suppressed within these ranges, and corrosion resistance can be further improved.

More preferably, the metal layer b is a Cu--Zn alloy or a Cu--Sn alloy. Corrosion resistance is further improved by using either a Cu--Zn alloy or a Cu--Sn alloy for the metal layer b.

The thickness of the metal layer b relative to the bipolar electrode current collector can be appropriately changed according to the type and thickness of the metal layer a.

When the metal layer a and the metal layer b of the bipolar electrode current collector are in contact with each other, these two layers may be produced like a clad material, or a laminate obtained by simply stacking the metal layer a and the metal layer b. It's okay.

A bipolar electrode current collector may comprise a conductive adhesive layer. The conductive adhesive layer is present between metal layer a and metal layer b and is in contact with metal layer a and metal layer b. As shown in FIGS. 2c and 2d, the conductive adhesive layer may have two layers, three layers, or a plurality of layers. When there are a plurality of conductive adhesive layers, the materials used for each may be different or the same.

The conductive adhesive layer has conductivity, and any type can be used as long as the electrical connection between the metal layer a and the metal layer b can be maintained. Therefore, the conductive adhesive layer may use a conductive resin or metal. Metals are those used, for example, in solders. Specifically, a Pb--Zn alloy or a resin in which conductive carbon is dispersed is preferable. A conductive resin and a metal may be used as one conductive adhesive layer, or if there are multiple conductive adhesive layers, each layer may be provided with a different type of conductive resin, or each layer may be provided with a different type of conductive resin. A conductive adhesive layer may be formed by providing metal to metal. A plurality of conductive adhesive layers may be formed by using a layer provided with a conductive resin and a layer provided with a metal. Also, a plurality of types of materials may be used for one conductive adhesive layer.

Although the thickness of the conductive adhesive layer is not particularly limited, it is preferably 0.1 μm or more and 10 μm or less.

A method for measuring the thicknesses of the metal layer a, the metal layer b, and the conductive adhesive layer and the ratio of elements contained in the metal layer a, the metal layer b, and the conductive adhesive layer will be described.

(Confirmation of conductivity of bipolar electrode)
First, make sure the bipolar electrodes are conductive. If conductive, if there is a layer between metal layer a and metal layer b in later measurements, that layer is a conductive adhesive layer.

(Method for measuring thickness of metal layer a, metal layer b, and conductive adhesive layer)
A section is checked and measured with a scanning electron microscope (SEM). Magnification is, for example, 100 times to 5000 times. Elemental analysis is performed on the cross section by Energy Dispersive X-ray Spectroscopy (EDX) to measure the elements and layer thicknesses contained in the metal layer a, the metal layer b and the conductive adhesive layer.

(separator)
A separator can be installed between the positive electrode and the negative electrode. The first separator and the second separator are collectively called separators.

By configuring the separator with an insulating material, it is possible to prevent electrical contact between the positive electrode and the negative electrode. Moreover, it is desirable to use a separator having a shape in which the electrolyte can move within the separator.

Examples of separators include non-woven fabrics, films, paper, and the like. Examples of constituent materials of the separator include polyolefins such as polyethylene and polypropylene, and cellulose. Examples of preferred separators include nonwoven fabrics containing cellulose fibers, porous films containing polyolefin fibers, and the like.

The separator can be porous or non-porous, preferably non-porous. By using a non-porous material, mixing of the aqueous electrolyte can be prevented.

The fiber diameter of the separator containing fibers is preferably 10 μm or less. By setting the fiber diameter to 10 μm or less, the affinity of the separator to the electrolyte is improved, so that the battery resistance can be reduced. A more preferable range of the fiber diameter is 3 μm or less.

The 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. Within this range, a balance can be achieved between the mechanical strength and the reduction in battery resistance, and a secondary battery with high output and suppressed internal short-circuiting can be provided. Moreover, the heat shrinkage of the separator in a high-temperature environment is small, and good high-temperature storage performance can be obtained.

A solid electrolyte layer containing solid electrolyte particles can also be used as the separator. The solid electrolyte layer may contain one type of solid electrolyte particles, or may contain a plurality of types of solid electrolyte particles. The solid electrolyte layer may be a solid electrolyte composite membrane containing solid electrolyte particles. The solid electrolyte composite membrane is, for example, formed by molding solid electrolyte particles into a membrane using a polymer binder. The solid electrolyte layer may contain at least one selected from the group consisting of a plasticizer and an electrolyte salt. If the solid electrolyte layer contains an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further enhanced.

Examples of inorganic solid particles contained in the solid electrolyte layer include oxide-based ceramics such as alumina, silica, zirconia, yttria, magnesium oxide, calcium oxide, barium oxide, strontium oxide and vanadium oxide, sodium carbonate, potassium carbonate, magnesium carbonate, Carbonates and sulfates such as calcium carbonate, barium carbonate, lanthanum carbonate, cerium carbonate, calcium sulfate, magnesium sulfate, aluminum sulfate, gypsum, barium sulfate, hydroxyapatite, lithium phosphate, zirconium phosphate, titanium phosphate, etc. Nitride-based ceramics such as phosphates, silicon nitride, titanium nitride, and boron nitride are examples. The inorganic particles listed above may be in the form of hydrates.

The inorganic solid particles preferably contain solid electrolyte particles having ion conductivity for alkali metal ions. Specifically, inorganic solid particles having ion conductivity with respect to lithium ions and sodium ions are more preferable.

Examples of inorganic solid particles having lithium ion conductivity include oxide-based solid electrolytes and sulfide-based solid electrolytes. As the oxide-based solid electrolyte, a lithium phosphoric acid solid electrolyte having a NASICON (Sodium (Na) Super Ionic Conductor) structure and represented by the general formula Li _1+x M ₂ (PO ₄ ) ₃ can be used. preferable. M in the above general formula is, for example, selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). is one or more. The subscript x is in the range 0≤x≤2. The ion conductivity of the lithium phosphoric acid solid electrolyte represented by the general formula LiM ₂ (PO ₄ ) ₃ is, for example, 1×10 ⁻⁵ S/cm or more and 1×10 ⁻³ S/cm or less.

A specific example of a lithium phosphate solid electrolyte having a NASICON structure is a LATP compound represented by Li _1+w Al _w Ti _2-w (PO ₄ ) ₃ where 0.1≦w≦0.5; Li _{1 +y} Al _z M1 _2-z (PO ₄ ) ₃ , where M1 is 1 or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and 0 ≤ y ≤ 1 and 0 ≤ z a compound represented by Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ and wherein 0≦x≦2; and Li _1+x Al _x Zr _2-x (PO ₄ ) ₃ represented by Li _1+u+v Al _u Mα _2-u Si _v P _3-v O ₁₂ and Mα is 1 or more selected from the group consisting of Ti and Ge; compounds where 0<u≦2 and 0≦v<3; and compounds represented by Li _1+2t Zr _{1-t Cat} (PO ₄ ) ₃ and where 0≦t<1. Li _1+2t Zr _{1-t Cat} (PO ₄ ) ₃ has high water resistance, low reducibility and low cost, and is therefore preferably used as inorganic solid electrolyte particles.

In addition to the lithium phosphoric acid solid electrolyte described above, the oxide-based solid electrolyte may be represented by Li _p PO _q N _r with 2.6 ≤ p ≤ 3.5, 1.9 ≤ q ≤ 3.8, and an amorphous _LIPON compound ₍ for example, Li _2.9 PO _{3.3 N 0.46} ) where 0.1≦ _r ≦1.3; A compound represented by O ₁₂ , wherein A is 1 or more selected from the group consisting of Ca, Sr, and Ba, Mβ is 1 or more selected from the group consisting of Nb and Ta, and 0 ≤ s ≤ 0.5; A compound represented by Li ₃ Mγ _2-s L ₂ O ₁₂ , wherein Mγ is 1 or more selected from the group consisting of Ta and Nb, L may contain Zr, and 0≦s≦0.5; Li _7-3s a compound represented by Al _s La ₃ Zr ₃ O ₁₂ where 0≦s≦0.5; and Li _5+x La ₃ M2 _2-x Zr _x O ₁₂ where M2 is selected from the group consisting of Nb and Ta. and 0≦x≦2 (for example, Li ₇ La ₃ Zr ₂ O ₁₂ ). One type of solid electrolyte may be used, or two or more types may be mixed and used. The ionic conductivity of LIPON is, for example, 1×10 ⁻⁶ S/cm or more and 5×10 ⁻⁶ S/cm or less. The ion conductivity of LLZ is, for example, 1×10 ⁻⁴ S/cm or more and 5×10 ⁻⁴ S/cm or less.

Moreover, a sodium-containing solid electrolyte may be used as the inorganic solid particles having ion conductivity of sodium ions. Sodium-containing solid electrolytes are excellent in ion conductivity of sodium ions. Examples of sodium-containing solid electrolytes include β-alumina, sodium phosphate sulfide, and sodium phosphate. The sodium ion-containing solid electrolyte is preferably in the form of glass ceramics.

The inorganic solid particles are preferably a solid electrolyte having a lithium ion conductivity of 1×10 ⁻⁵ S/cm or higher at 25°C. Lithium ion conductivity can be measured, for example, by an AC impedance method. Details will be described later.

The shape of the inorganic solid particles is not particularly limited, but may be, for example, spherical, elliptical, flattened, or fibrous.

The average particle size of the inorganic solid particles is preferably 15 μm or less, more preferably 12 μm or less. When the average particle size of the inorganic solid particles is small, the denseness of the solid electrolyte layer can be enhanced.

The average particle size of the inorganic solid particles is preferably 0.01 μm or more, more preferably 0.1 μm or more. If the average particle size of the inorganic solid particles is large, aggregation of the particles tends to be suppressed.

The average particle size of the inorganic solid particles means the particle size at which the volume integrated value is 50% in the particle size distribution determined by a laser diffraction type particle size distribution analyzer. As a sample for this particle size distribution measurement, a dispersion diluted with ethanol so that the concentration of the inorganic solid particles is 0.01% by mass to 5% by mass is used.

Solid electrolyte layer WHEREIN: It is preferable that an inorganic solid particle is a main component. From the viewpoint of increasing the ion conductivity of the solid electrolyte layer, the proportion of the inorganic solid particles in the solid electrolyte layer is preferably 70% by mass or more, more preferably 80% by mass or more, and 85% by mass or more. is more preferable. From the viewpoint of increasing the film strength of the solid electrolyte layer, the proportion of the inorganic solid particles in the solid electrolyte layer is preferably 98% by mass or less, more preferably 95% by mass or less, and 90% by mass or less. It is even more preferable to have The proportion of inorganic solid particles in the solid electrolyte layer can be calculated by thermogravimetric analysis (TG).

The polymer material contained in the solid electrolyte layer enhances the binding properties between the inorganic solid particles. The weight average molecular weight of the polymeric material is, for example, 3000 or more. When the weight average molecular weight of the polymer material is 3000 or more, the binding property of the inorganic solid particles can be further enhanced. The weight average molecular weight of the polymeric material is preferably 3,000 to 5,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. The weight average molecular weight of the polymeric material can be determined by gel permeation chromatography (GPC).

The polymeric material can be a polymer (polymer) consisting of a single monomer unit, a copolymer (copolymer) consisting of multiple monomer units, or a mixture thereof. The polymer material contains monomer units composed of hydrocarbons having functional groups containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). It is preferable to be In the polymer material, it is preferable that the ratio of the portion composed of the monomer unit is 70 mol % or more. Hereinafter, this monomer unit is referred to as the first monomer unit. In addition, in the copolymer, those other than the first monomer units are referred to as second monomer units. A copolymer of the first monomer unit and the second monomer unit may be an alternating copolymer, a random copolymer, or a block copolymer.

In the polymer material, if the proportion of the portion composed of the first monomer units is less than 70 mol %, the water impermeability of the first and second solid electrolyte layers may deteriorate. In the polymer material, it is preferable that the ratio of the portion composed of the first monomer unit is 90 mol % or more. Most preferably, the polymer material has a proportion of 100 mol % of the portion composed of the first monomer units, that is, a polymer composed only of the first monomer units.

The first monomer unit has a functional group containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F) in the side chain, and the main chain may be a compound composed of carbon-carbon bonds. The hydrocarbon may have one or more functional groups containing one or more elements selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). The functional group in the first monomer unit enhances the conductivity of alkali metal ions passing through the solid electrolyte layer.

The hydrocarbon constituting the first monomer unit preferably has a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S) and nitrogen (N). When the first monomer unit has such a functional group, the alkali metal ion conductivity in the solid electrolyte layer is further enhanced, and the internal resistance tends to be lowered.

The functional group contained in the first monomer unit preferably contains one or more selected from the group consisting of formal group, butyral group, carboxymethyl ester group, acetyl group, carbonyl group, hydroxyl group and fluoro group. Moreover, the first monomer unit more preferably contains at least one of a carbonyl group and a hydroxyl group as a functional group, and still more preferably contains both.

The first monomer unit can be represented by the following formula.

In the above formula, R1 is preferably selected from the group consisting of hydrogen (H), alkyl groups and amino groups. R2 is selected from the group consisting of hydroxyl group (-OH), -OR1, -COOR1, -OCOR1, -OCH(R1)O-, -CN, -N(R1) ₃ and SO ₂ R1 is preferred.

Examples of the first monomer unit include vinyl formal, vinyl alcohol, vinyl acetate, vinyl acetal, vinyl butyral, acrylic acid and its derivatives, methacrylic acid and its derivatives, acrylonitrile, acrylamide and its derivatives, styrenesulfonic acid, and polyvinylidene fluoride. , and one or more selected from the group consisting of tetrafluoroethylene.

The polymeric material preferably contains one or more selected from the group consisting of polyvinyl formal, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polymethyl methacrylate, polyvinylidene fluoride, and polytetrafluoroethylene.

Examples of structural formulas of compounds that can be used as the polymer material are described below.

The structural formula of polyvinyl formal is as follows. In the following formula, a is preferably 50 or more and 80 or less, b is 0 or more and 5 or less, and c is preferably 15 or more and 50 or less.

The structural formula of polyvinyl butyral is as follows. In the following formula, l is preferably 50 or more and 80 or less, m is 0 or more and 10 or less, and n is preferably 10 or more and 50 or less.

The structural formula of polyvinyl alcohol is as follows. In the following formula, n is preferably 70 or more and 20000 or less.

The structural formula of polymethyl methacrylate is as follows. In the following formula, n is preferably 30 or more and 10,000 or less.

The second monomer unit is a compound other than the first monomer unit, that is, a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N), and fluorine (F). or, if it does have this functional group, it is not a hydrocarbon. Second monomer units can include, for example, ethylene oxide and styrene. Examples of polymers composed of second monomer units include polyethylene oxide (PEO) and polystyrene (PS).

The types of functional groups contained in the first monomer unit and the second monomer unit can be identified by Fourier Transform Infrared Spectroscopy (FT-IR). Moreover, it can be determined by nuclear magnetic resonance (NMR) that the first monomer unit is composed of a hydrocarbon. In the copolymer of the first monomer unit and the second monomer unit, the ratio of the portion composed of the first monomer unit can be calculated by NMR.

A polymeric material may contain an electrolyte. The proportion of electrolyte that can be contained in the polymer material can be grasped from its water absorption rate. Here, the water absorption rate of the polymer material is obtained by subtracting the mass Mp of the polymer material before immersion from the mass Mp′ of the polymer material after being immersed in water at a temperature of 23° C. for 24 hours. This value is divided by the mass Mp of the polymer material before immersion ([Mp'-Mp]/Mp×100). It is believed that the water absorption of polymeric materials is related to the polarity of the polymeric materials.

Examples of polymeric binders also include polyvinyl-based, polyether-based, polyester-based, polyamine-based, polyethylene-based, silicone-based and polysulfide-based.

Using a polymer material with a high water absorption rate tends to increase the alkali metal ion conductivity of the solid electrolyte layer. In addition, when a polymer material having a high water absorption rate is used, the bonding strength between the inorganic solid particles and the polymer material increases, so the flexibility of the solid electrolyte layer can be increased. The water absorption rate of the polymer material is preferably 0.01% or more, more preferably 0.5% or more, and even more preferably 2% or more.

The strength of the solid electrolyte layer can be increased by using a polymer material with a low water absorption rate. That is, if the water absorption rate of the polymeric material is too high, the solid electrolyte layer may swell due to the electrolyte. Moreover, if the water absorption rate of the polymer material is too high, the polymer material in the solid electrolyte layer may flow out into the electrolyte. The water absorption of the polymeric material is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 3% or less.

From the viewpoint of increasing the flexibility of the solid electrolyte layer, the proportion of the polymer material in the solid electrolyte layer is preferably 1% by mass or more, more preferably 3% by mass or more, and more preferably 10% by mass or more. is more preferable. Also, the denser the solid electrolyte layer, the higher the proportion of the polymer material.

In addition, the proportion of the polymer material in the solid electrolyte layer is preferably 20% by mass or less, more preferably 10% by mass or less, from the viewpoint of increasing the lithium ion conductivity of the solid electrolyte layer. % by mass or less is more preferable. The proportion of polymeric material in the solid electrolyte layer can be calculated by thermogravimetric (TG) analysis.

The separator may consist of only the solid electrolyte layer, or may consist of a base layer and a solid electrolyte layer provided with a base layer. The substrate layer can carry a solid electrolyte layer (first solid electrolyte layer) on one surface thereof. Alternatively, the base layer can carry the first solid electrolyte layer and the second solid electrolyte layer on both sides thereof. When the first solid electrolyte layer and the second solid electrolyte layer are provided on both the front and back surfaces of the base material layer, the thickness of each solid electrolyte layer may be the same or different. When the thicknesses are different, it is preferable that the first solid electrolyte layer in contact with the first surface of the negative electrode active material-containing layer is thicker than the other second solid electrolyte layer. Since the first solid electrolyte layer is thicker, the water impermeability can be improved. Moreover, the solid electrolyte layers respectively provided on both the front and back surfaces of the base material layer may have the same configuration, or may have different configurations.

When the first solid electrolyte layer and the second solid electrolyte layer are included, the polymer materials included in each solid electrolyte layer may be the same as each other, or different types may be used. Moreover, a single type of polymeric material may be used, or a plurality of types may be mixed and used.

The thickness of the solid electrolyte layer is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more, from the viewpoint of preventing internal short circuits. The thickness of the solid electrolyte layer is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less, from the viewpoint of increasing ion conductivity and energy density.

Although the above thicknesses are preferable for the first solid electrolyte layer and the second solid electrolyte layer, they are not necessarily required for both solid electrolyte layers.

The substrate layer is, for example, a nonwoven fabric or a self-supporting porous membrane. Materials for the non-woven fabric or self-supporting porous membrane include, for example, polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidenefluoride (PVdF). The base material layer is preferably a cellulose nonwoven fabric.

The substrate layer can contain many pores and can be impregnated with a large amount of electrolyte. The substrate layer typically does not contain inorganic solid particles. For example, the ratio of the area occupied by the inorganic solid particles in the cross section of the substrate layer may be 5% or less.

The thickness of the base layer is, for example, 1 μm or more, preferably 3 μm or more. When the base material layer is thick, the mechanical strength of the separator increases, and the internal short circuit of the secondary battery is less likely to occur. The thickness of the base material layer is, for example, 30 μm or less, preferably 10 μm or less. When the base layer is thin, the internal resistance of the secondary battery tends to decrease and the volume energy density of the secondary battery tends to increase. The thickness of the substrate layer can be measured, for example, with a scanning electron microscope.

As the electrolyte salt to be contained in the solid electrolyte layer, lithium salt and/or sodium salt that can be contained in the aqueous electrolyte can be used.

The proportion of the electrolyte salt in the solid electrolyte layer is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less. The proportion of electrolyte salt in the solid electrolyte layer can be calculated by thermogravimetric (TG) analysis.

Whether the solid electrolyte layer contains an electrolyte salt is confirmed, for example, by the distribution of alkali metal ions obtained from energy dispersive X-ray spectrometry (EDX) on a cross section of the solid electrolyte layer. be able to. That is, when the solid electrolyte layer is made of a material that does not contain an electrolyte salt, most of the alkali metal ions remain in the surface layer of the polymer material in the solid electrolyte layer. A concentration gradient can be observed in which the concentration of alkali metal ions is high in the surface layer of the solid electrolyte layer and the concentration of alkali metal ions is low in the interior of the solid electrolyte layer. On the other hand, when the solid electrolyte layer is made of a material containing an electrolyte salt, it can be confirmed that the alkali metal ions are uniformly present even inside the solid electrolyte layer.

Alternatively, when the electrolyte salt contained in the solid electrolyte layer and the electrolyte salt contained in the aqueous electrolyte are different types, the solid electrolyte layer contains an electrolyte salt different from the aqueous electrolyte due to the difference in the type of ions present. I understand. For example, when lithium chloride (LiCl) is used as the aqueous electrolyte and LiTFSI (lithium bis(fluorosulfonyl)imide) is used as the solid electrolyte layer, the presence of (fluorosulfonyl)imide ions in the solid electrolyte layer can be confirmed. On the other hand, the presence of (fluorosulfonylimide) ions cannot be confirmed in the aqueous electrolyte, or they are present at extremely low concentrations.

The separator can have an air permeability coefficient of 1×10 ⁻¹³ m ² or less. For example, a nonwoven fabric containing cellulose fibers has an air permeability coefficient of the order of 5×10 ⁻¹⁴ m ² . The air permeability coefficient of the solid electrolyte composite membrane can be 1×10 ⁻¹⁶ m ² or less, eg, 1×10 ⁻¹⁷ m ² . By using a separator with a low air permeability coefficient, when different aqueous electrolytes are used on the positive electrode side and the negative electrode side, mixing of these aqueous electrolytes can be further suppressed. Even when the separator includes a base material layer, the air permeability coefficient of the base material layer is larger than that of the solid electrolyte layer, so the air permeability coefficient of the solid electrolyte layer can be measured without separating the solid electrolyte layer and the base material layer. .

The air permeability coefficient KT(m ² ) of the separator can be calculated as follows. In the calculation of the air permeability coefficient KT, for example, when a separator having a thickness L (m) is to be measured, a gas having a dynamic viscosity coefficient σ (Pa s) is allowed to permeate the range of the measurement area A (m ² ). . At this time, the gas is permeated under a plurality of conditions in which the pressure p (Pa) of the introduced gas is different from each other, and the amount of gas Q (m ³ /s) permeated through the separator is measured under each of the plurality of conditions. do. Then, from the measurement results, the amount of gas Q is plotted against the pressure p, and the slope dQ/dp is obtained. Then, from the thickness L, the measured area A, the dynamic viscosity coefficient σ, and the slope dQ/dp, the air permeability coefficient KT is calculated as in Equation (1):
KT = ((σ l)/A) x (dQ/dp) (1)

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 having a hole with a diameter of 10 mm. Then, air is fed at pressure p from the hole of one stainless steel plate. Then, the gas amount Q of the air leaking from the hole of the other stainless steel plate is measured. Therefore, the hole area (25πmm ² ) is used as the measurement area A, and 0.000018 Pa·s is used as the kinematic viscosity coefficient σ. Also, the gas amount Q is calculated by measuring the amount δ (m ³ ) leaked from the hole for 100 seconds and dividing the measured amount δ by 100.

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

In addition, in measuring the air permeability coefficient of the separator, the battery is disassembled and the separator is separated from other parts of the battery. After washing both sides of the separator with pure water, the separator is immersed in pure water and left for 48 hours or longer. After that, both surfaces are rinsed with pure water, dried in a vacuum drying oven at 100° C. for 48 hours or more, and then the air permeability coefficient is measured. In addition, the air permeability coefficient is measured at a plurality of arbitrary points on the separator. Then, the value at the place where the air permeability coefficient is the lowest value among arbitrary plural places is taken as the air permeability coefficient of the separator.

(Method for measuring lithium ion conductivity of inorganic solid particles)
Measurement of lithium ion conductivity of inorganic solid particles by AC impedance method will be described. First, inorganic solid particles are molded using a tablet molding machine to obtain a green compact. Gold (Au) is vapor-deposited on both sides of this green compact to obtain a measurement sample. An impedance measuring device is used to measure the AC impedance of the measurement sample. As a measuring device, for example, a frequency response analyzer Model 1260 manufactured by Solartron can be used. The measurement is performed at a measurement frequency of 5 Hz to 32 MHz, a measurement temperature of 25° C., and an argon atmosphere.

A complex impedance plot is then generated based on the measured AC impedance. The complex impedance plot plots the real component on the horizontal axis and the imaginary component on the vertical axis. The ionic conductivity σLi of the inorganic solid particles is calculated by the following formula (2). In the following formula, ZLi is the resistance value calculated from the diameter of the arc of the complex impedance plot, S is the area, and d is the thickness.
σLi=(1/ZLi)×(d/S) (2)

(Aqueous electrolyte)
The aqueous electrolyte contains an aqueous solvent and an electrolyte salt. The aqueous electrolyte is, for example, liquid. A liquid aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an aqueous solvent.

The aqueous electrolyte includes a positive electrode side aqueous electrolyte in contact with the metal layer a and a negative electrode side aqueous electrolyte in contact with the metal layer b, and the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte are different. "Different" means that the electrolyte salt contained in the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte, the electrolyte salt concentration, and the pH are different. Unless otherwise specified, the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte are collectively referred to simply as "aqueous electrolyte".

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

Examples of lithium salts include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium acetate ( _CH3COOLi ), lithium oxalate (Li2 C ₂ O ₄ ), lithium carbonate (Li ₂ CO ₃ ), 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).

Sodium salts include sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium hydroxide (NaOH), sodium nitrate (NaNO3) and sodium trifluoromethanesulfonylamide (NaTFSA).

LiCl is preferably included as the lithium salt. LiCl can be used to increase the lithium ion concentration of the aqueous electrolyte. Also, the lithium salt preferably contains at least one of LiSO4 and LiOH in addition to LiCl.

Besides the lithium salt, a zinc salt such as zinc chloride or zinc sulfate may be added to the aqueous electrolyte. By adding such a compound to the aqueous electrolyte solution, a zinc-containing coating layer and/or a zinc oxide-containing region can be formed on the negative electrode.

The molar concentration of lithium ions in the aqueous electrolyte is preferably 3 mol/L or more, preferably 6 mol/L or more, and preferably 12 mol/L or more. When the concentration of lithium ions in the aqueous electrolyte is high, electrolysis of the aqueous solvent at the negative electrode tends to be suppressed, and hydrogen generation from the negative electrode tends to be small.

The water-based electrolyte preferably contains 1 mol or more of the water-based solvent per 1 mol of the salt serving as the solute. A more preferred form is that the amount of the aqueous solvent is 3.5 mol or more per 1 mol of the salt as the solute. The aqueous solvent contains, for example, water at a rate of 50% by volume or more. The aqueous electrolyte contains, as an anion species, at least one selected from chloride ions (Cl ⁻ ), hydroxide ions (OH ⁻ ), sulfate ions (SO ₄ ²⁻ ), and nitrate ions (NO ₃ ⁻ ). is preferred.

The pH of the aqueous electrolyte is preferably 3 or more and 14 or less, more preferably 4 or more and 13 or less.

When the pH of the aqueous electrolyte differs between the negative electrode side and the positive electrode side after the initial charge, the pH of the negative electrode side aqueous electrolyte in the secondary battery after the initial charge is preferably 3 or more. It is more preferably 7 or more, and still more preferably 7 or more. In the secondary battery after the initial charge, the pH of the positive electrode side aqueous electrolyte is preferably in the range of 0 to 7, more preferably in the range of 0 to 6.

The pH of the aqueous electrolyte on the negative electrode side and the positive electrode side can be obtained, for example, by disassembling the secondary battery and measuring the pH of the aqueous electrolyte present between the separator and the negative electrode and the positive electrode.

A solution containing water can be used as the aqueous solvent. The solution containing water may be pure water or a mixed solvent of water and an organic solvent.

The aqueous electrolyte may be a gel electrolyte. The gel electrolyte is prepared by mixing the above liquid aqueous electrolyte and a polymer compound to form a composite. Examples of polymer compounds include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO). The aqueous electrolyte contained in the first positive electrode active material-containing layer and the second positive electrode active material-containing layer, and the aqueous electrolyte contained in the first negative electrode active material-containing layer and the second negative electrode active material-containing layer are Either a liquid electrolyte or a gel electrolyte can be selected as appropriate.

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

(Method for measuring pH of aqueous electrolyte)
The method for measuring the pH of the aqueous electrolyte is as follows.

The secondary battery is dismantled and the aqueous electrolyte contained in the electrodes and separators taken out is extracted, and after the liquid volume is measured, the pH value is measured with a pH meter. Measurement of pH measurement is performed, for example, as follows. For this measurement, for example, F-74 manufactured by HORIBA, Ltd. is used, and the measurement is carried out in an environment of 25±2°C. First, standard solutions of pH 4.0, 7.0 and 9.0 are prepared. Next, these standard solutions are used to calibrate the F-74. An appropriate amount of the aqueous electrolyte (aqueous electrolytic solution) to be measured is prepared and placed in a container, and the pH is measured. After measuring the pH, the sensor part of the F-74 is washed. When measuring another object to be measured, the procedures described above, namely calibration, measurement and cleaning, are carried out each time.

The secondary battery according to the first embodiment can further include an electrode group including a negative electrode, a positive electrode, and a bipolar electrode, and an outer layer member containing an aqueous electrolyte.

(Outer layer member)
A metal container, a laminate film container, or a resin container can be used for the outer layer member in which the electrode group and the aqueous electrolyte are accommodated.

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

The plate thickness of each of the resin container and the metal container is preferably in the range of 0.05 mm or more and 1 mm or less. The plate thickness is more preferably 0.5 mm or less, still more preferably 0.3 mm or less.

Examples of laminate films include multilayer films in which a metal layer is coated with a resin layer. Examples of metal layers include stainless steel foil, aluminum foil, and aluminum alloy foil. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used for the resin layer. The thickness of the laminate film is preferably in the range of 0.01 mm or more and 0.5 mm or less. The thickness of the laminate film is more preferably 0.2 mm or less.

Secondary batteries can be used in various forms such as prismatic, cylindrical, flat, thin, and coin-shaped.

(Terminal)
The negative electrode terminal may be made of a material that is electrochemically stable and conductive in a potential range of 1 V or more and 3 V or less (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium, for example. can. Specifically, the material of the negative electrode terminal is zinc, copper, nickel, stainless steel, aluminum, or at least one selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum alloys containing elements are mentioned. Zinc or a zinc alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce the contact resistance with the negative electrode current collector (for example, the current collecting layer included in the negative electrode structure).

The positive electrode terminal is, for example, electrically stable in a potential range of 2.5 V or more and 4.5 V or less (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium, and is made of a conductive material. be able to. Materials for the positive electrode terminal include titanium, aluminum, and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. In order to reduce contact resistance with the positive electrode current collector, the positive electrode terminal is preferably made of the same material as the positive electrode current collector.

Details of the secondary battery according to the embodiment will be described below with reference to FIGS. 3 and 4. FIG. FIG. 3 is a cross-sectional view schematically showing an example of the secondary battery according to the embodiment. FIG. 4 is a cross-sectional view of the secondary battery shown in FIG. 3 taken along line IV-IV.

The electrode group 1 is housed in an exterior member 2 that is a rectangular tubular metal container. The electrode group 1 includes a negative electrode 3, a positive electrode 5 and a bipolar electrode. The electrode group 1 has a structure in which a positive electrode 5, a negative electrode 3, and a bipolar electrode are arranged with a separator 4 interposed therebetween, and spirally wound into a flat shape. A water-based electrolyte (not shown) is held in the electrode group 1 . As shown in FIG. 3 , strip-shaped negative electrode current collecting tabs 16 are electrically connected to a plurality of positions on the end of the negative electrode 3 positioned on the end face of the electrode group 1 . A band-shaped positive electrode current collecting tab 17 is electrically connected to each of a plurality of locations on the end portion of the positive electrode 5 located on this end face. The plurality of negative electrode current collecting tabs 16 are bundled together and connected to the negative electrode terminal 6 as shown in FIG. Similarly, although not shown, the positive electrode current collecting tabs 17 are also bundled together and electrically connected to the positive electrode terminal 7 .

The sealing plate 10 made of metal is fixed to the opening of the exterior member 2 made of metal by welding or the like. The negative electrode terminal 6 and the positive electrode terminal 7 are drawn out from extraction holes provided in the sealing plate 10, respectively. A negative electrode gasket 8 and a positive electrode gasket 9 are arranged on the inner peripheral surface of each extraction hole of the sealing plate 10 in order to avoid a short circuit due to contact with the negative electrode terminal 6 and the positive electrode terminal 7, respectively. By disposing the negative electrode gasket 8 and the positive electrode gasket 9, the airtightness of the secondary battery 100 can be maintained.

A control valve 11 (safety valve) is arranged on the sealing plate 10 . When the internal pressure in the battery cell increases due to the gas generated by the electrolysis of the aqueous solvent, the generated gas can be released to the outside through the control valve 11 . As the control valve 11, for example, a return type valve that operates when the internal pressure exceeds a set value and functions as a sealing plug when the internal pressure drops can be used. Alternatively, a non-returnable control valve may be used that does not restore its function as a sealing plug once it is actuated. Although the control valve 11 is arranged in the center of the sealing plate 10 in FIG. Control valve 11 may be omitted.

In addition, the sealing plate 10 is provided with a liquid injection port 12 . An aqueous electrolyte can be injected through this injection port 12 . The injection port 12 can be closed with a sealing plug 13 after the aqueous electrolyte is injected. The injection port 12 and the sealing plug 13 may be omitted.

FIG. 5 is a partially cutaway perspective view schematically showing another example of the secondary battery according to the embodiment. FIG. 6 is an enlarged cross-sectional view of the B portion of the secondary battery shown in FIG. FIGS. 5 and 6 show an example of a secondary battery 100 using a laminated film exterior member as a container.

A secondary battery 100 shown in FIGS. 5 and 6 includes an electrode group 1 shown in FIGS. 5 and 6, an exterior member 2 shown in FIG. 5, and an aqueous electrolyte (not shown). The electrode group 1 and the water-based electrolyte are housed inside the exterior member 2 . A water-based electrolyte is held in the electrode group 1 .

The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed therebetween.

FIG. 6 is a schematic diagram of an aqueous electrolyte bipolar secondary battery in which a plurality of bipolar electrodes are laminated.

A water-based electrolyte bipolar secondary battery in which a plurality of bipolar electrodes are laminated includes a bipolar electrode 501 having a structure in which a negative electrode active material-containing layer 3b2, a bipolar electrode current collector 502, and a positive electrode active material-containing layer 5b2 are laminated in this order. , a plurality of separators 4 arranged to face the negative electrode active material containing layer 3b2 and the positive electrode active material containing layer 5b2 of the bipolar electrode 501, and the outermost layer is the positive electrode active material supported on the positive electrode current collector 5a The negative electrode active material containing layer 3b1 carried on the negative electrode current collector 3a and the negative electrode active material containing layer 5b1 are provided.

The positive electrode current collector and the negative electrode current collector, which are the outermost layers when laminated, are not in contact with the positive electrode active material-containing layer and the negative electrode active material-containing layer, and have portions that are pulled out. This part is the lead. Although not shown, the lead is electrically connected to the strip-shaped negative terminal 6 and the strip-shaped positive terminal 7 . The tip of the strip-shaped negative electrode terminal 6 is drawn out of the exterior member 2 . The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side of the negative electrode terminal 6 and is drawn out of the exterior member 2 .

The aqueous electrolyte bipolar secondary battery according to the first embodiment includes a negative electrode provided with a first negative electrode active material containing layer on at least one surface of a negative electrode current collector, and a first positive electrode active material containing layer. A positive electrode provided on at least one surface of a positive electrode current collector, a second positive electrode active material-containing layer provided on one surface, and a second negative electrode active material-containing layer provided on the other opposite surface. An aqueous electrolyte bipolar secondary battery comprising a bipolar electrode having a bipolar electrode current collector and an aqueous electrolyte, wherein the bipolar electrode current collector has a metal layer a and a metal layer b, and the metal layer a is The metal layer b contains at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al, and the metal layer b contains 10 wt. % or more 100 wt. % or less of any one of Zn and Sn, the metal layer a and the metal layer b are electrically connected, and the metal layer a has a second positive electrode active material-containing layer on the surface of the metal layer a , has a second negative electrode active material-containing layer on the surface of the metal layer b. Therefore, since the bipolar electrode current collector can be matched to the types of the positive electrode side aqueous electrolyte and the negative electrode side aqueous electrolyte, the secondary battery has excellent life characteristics.

[Second embodiment]
According to a second embodiment, an assembled battery is provided. The assembled battery includes a plurality of secondary batteries according to the first embodiment.

In the assembled battery according to the embodiment, each unit cell may be electrically connected in series or parallel and arranged, or may be arranged by combining series connection and parallel connection.

Next, an example of the assembled battery will be described with reference to the drawings.

FIG. 7 is a perspective view schematically showing an example of the assembled battery according to the embodiment. The assembled battery 200 shown in FIG. 7 includes five single cells 100a to 100e, four bus bars 21, a positive lead 22, and a negative lead 23. As shown in FIG. Each of the five cells 100a to 100e is the secondary battery according to the first embodiment.

The bus bar 21 connects, for example, the negative terminal 6 of one cell 100a and the positive terminal 7 of the adjacent cell 100b. In this manner, five cells 100 are connected in series by four busbars 21 . That is, the assembled battery 200 in FIG. 7 is a five-series assembled battery. Although an example is not shown, in an assembled battery including a plurality of cells electrically connected in parallel, for example, a plurality of negative terminals are connected to each other by a bus bar and a plurality of positive terminals are connected to each other by a bus bar. Thus, a plurality of cells can be electrically connected.

The positive terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive lead 22 for external connection. The negative terminal 6 of at least one of the five cells 100a to 100e is electrically connected to the negative lead 23 for external connection.

The assembled battery according to the embodiment includes the secondary battery according to the embodiment. Therefore, the assembled battery can exhibit excellent life characteristics.

[Third embodiment]
According to a third embodiment, a battery pack including the secondary battery according to the first embodiment is provided. This battery pack can comprise the assembled battery according to the second embodiment. This battery pack may include a single secondary battery according to the first embodiment instead of the assembled battery according to the second embodiment.

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

In addition, the battery pack may further include an external terminal for energization. The external terminal for energization 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 terminals for power supply. Also, when charging the battery pack, a charging current (including regenerated energy from the power of an automobile or the like) is supplied to the battery pack through an external terminal for power supply.

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

FIG. 8 is a perspective view schematically showing an example of the battery pack according to the embodiment.

The battery pack 300 includes, for example, an assembled battery made up of secondary batteries shown in FIGS. Battery pack 300 includes housing 310 and assembled battery 200 housed in housing 310 . The assembled battery 200 is formed by electrically connecting a plurality of (for example, five) secondary batteries 100 in series. The secondary battery 100 is stacked in the thickness direction. The housing 310 has openings 320 on each of the top and four sides. The side surface from which the negative terminal 6 and the positive terminal 7 of the secondary battery 100 protrude is exposed to the opening 320 of the housing 310 . The output positive electrode terminal 332 of the assembled battery 200 has a strip shape, one end of which is electrically connected to any positive electrode terminal 7 of the secondary battery 100, and the other end of which protrudes from an opening 320 of the housing 310 and extends into the housing. It protrudes from the top of body 310 . On the other hand, the output negative electrode terminal 333 of the assembled battery 200 has a strip shape, one end of which is electrically connected to the negative electrode terminal 6 of one of the secondary batteries 100, and the other end of which protrudes from the opening 320 of the housing 310. It protrudes from the top of housing 310 .

Another example of such a battery pack will be described in detail with reference to FIGS. 9 and 10. FIG. FIG. 9 is an exploded perspective view schematically showing another example of the battery pack according to the embodiment. 10 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 9. FIG.

A battery pack 300 shown in FIGS. 9 and 10 includes a container 31, a lid 32, a protective sheet 33, an assembled battery 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown). .

A storage container 31 shown in FIG. 9 is a bottomed rectangular container having a rectangular bottom surface. The storage container 31 is configured to be able to store the protective sheet 33 , the assembled battery 200 , the printed wiring board 34 , and the wiring 35 . Lid 32 has a rectangular shape. The lid 32 accommodates the assembled battery 200 and the like by covering the container 31 . Although not shown, the storage container 31 and the lid 32 are provided with openings, connection terminals, or the like for connection to an external device or the like.

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

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

The adhesive tape 24 fastens the plurality of unit cells 100 . Instead of the adhesive tape 24, heat-shrinkable tape may be used to fix the plurality of unit cells 100. FIG. In this case, the protection sheets 33 are placed on both sides of the assembled battery 200 , the heat-shrinkable tape is wrapped around, and then the heat-shrinkable tape is heat-shrunk to bind the plurality of unit cells 100 together.

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

The printed wiring board 34 is installed along one short-side surface of the inner surface of the container 31 . The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wirings 342a and 343a, an external terminal 350 for conducting electricity, and a positive wiring (positive wiring) 348a. and a negative wiring (negative wiring) 348b. One surface of the printed wiring board 34 faces one side surface of the assembled battery 200 . An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200 .

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

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

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

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

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

The protection circuit 346 controls charging and discharging of the plurality of cells 100 . In addition, based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from each unit cell 100 or the assembled battery 200, the protection circuit 346 and an external terminal for energizing the external device. 350 (positive terminal 352, negative terminal 353) is cut off.

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

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

The battery pack 300 also has the external terminals 350 for power supply as described above. 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 350 for power supply. In other words, when the battery pack 300 is used as a power source, current from the assembled battery 200 is supplied to the external device through the external terminals 350 for power supply. Also, when charging the battery pack 300 , a charging current from an external device is supplied to the battery pack 300 through the external terminal 350 for power supply. When this battery pack 300 is used as an on-vehicle battery, the regenerated energy of the motive power of the vehicle can be used as the charging current from the external device.

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

Such battery packs are used in applications that require excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power supply for electronic equipment, a stationary battery, and a vehicle battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as a vehicle battery.

A battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the assembled battery according to the second embodiment. Therefore, the battery pack can exhibit excellent life characteristics.

[Fourth embodiment]
According to a fourth embodiment, a vehicle is provided that includes the battery pack according to the third embodiment.

In such a vehicle, the battery pack, for example, recovers regenerative energy of the power of the vehicle. The vehicle may include a mechanism (regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

Examples of vehicles according to embodiments include, for example, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, assisted bicycles, and railroad vehicles.

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

A vehicle according to an embodiment may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, may be electrically connected in parallel, or may be electrically connected by combining series connection and parallel connection. good too. For example, when each battery pack includes an assembled battery, the assembled batteries may be electrically connected in series or may be electrically connected in parallel. may be connected to Alternatively, if each battery pack contains a single battery, the respective batteries may be electrically connected in series, electrically in parallel, or a combination of series and parallel connections. may be electrically connected.

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

FIG. 11 is a partially transparent view schematically showing an example of the vehicle according to the embodiment.
A vehicle 400 shown in FIG. 11 includes a vehicle body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in FIG. 11, vehicle 400 is a four-wheeled automobile.

This vehicle 400 may be equipped with a plurality of battery packs 300 . In this case, the batteries (eg, cells or assembled batteries) included in the battery pack 300 may be connected in series, may be connected in parallel, or may be connected in a combination of series connection and parallel connection.

FIG. 11 shows an example in which the battery pack 300 is installed in the engine room located in front of the vehicle body 40 . As described above, battery pack 300 may be mounted, for example, in the rear of vehicle body 40 or under the seat. This battery pack 300 can be used as a power source for vehicle 400 . Also, this battery pack 300 can recover the regenerated energy of the power of the vehicle 400 .

A vehicle according to the fourth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, the vehicle is excellent in running performance and reliability.

[Fifth embodiment]
According to a fifth embodiment, there is provided a stationary power supply including the battery pack according to the fourth embodiment.

Such stationary power supply may be equipped with the assembled battery according to the second embodiment or the secondary battery according to the first embodiment instead of the battery pack according to the fourth embodiment. The stationary power supply according to the embodiment can achieve a long life.

FIG. 12 is a block diagram showing an example of a system including the stationary power supply according to the embodiment. FIG. 12 is a diagram showing an example of application of the battery packs 300A and 300B according to the embodiment to stationary power supplies 112 and 123. As shown in FIG. The example shown in FIG. 12 shows a system 110 in which stationary power supplies 112 and 123 are used. The system 110 includes a power plant 111 , a stationary power supply 112 , a consumer side power system 113 and an energy management system (EMS) 115 . A power network 116 and a communication network 117 are formed in the system 110 , and the power plant 111 , the stationary power supply 112 , the consumer-side power system 113 and the EMS 115 are connected via the power network 116 and the communication network 117 . The EMS 115 utilizes the power network 116 and the communication network 117 to perform control to stabilize the entire system 110 .

The power plant 111 generates large amounts of electric power from fuel sources such as thermal power and nuclear power. Power is supplied from the power plant 111 through the power network 116 or the like. Also, the stationary power supply 112 is equipped with a battery pack 300A. The battery pack 300A can store electric power supplied from the power plant 111 and the like. Also, the stationary power supply 112 can supply the power stored in the battery pack 300A through the power network 116 or the like. System 110 is provided with power converter 118 . The power conversion device 118 includes converters, inverters, transformers, and the like. Therefore, the power conversion device 118 can perform conversion between direct current and alternating current, conversion between alternating currents with different frequencies, transformation (step-up and step-down), and the like. Therefore, the power conversion device 118 can convert the power from the power plant 111 into power that can be stored in the battery pack 300A.

The consumer-side power system 113 includes a factory power system, a building power system, a home power system, and the like. 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 supply 123 is equipped with a battery pack 300B. The consumer side EMS 121 performs control to stabilize the consumer side power system 113 .

Power from the power plant 111 and power from the battery pack 300A are supplied to the consumer side power system 113 through the power network 116 . The battery pack 300B can store the power supplied to the power grid 113 on the consumer side. Also, the power conversion device 122 includes a converter, an inverter, a transformer, and the like, like the power conversion device 118 . Therefore, the power conversion device 122 can perform conversion between direct current and alternating current, conversion between alternating currents with different frequencies, transformation (step-up and step-down), and the like. Therefore, the power conversion device 122 can convert the power supplied to the consumer-side power system 113 into power that can be stored in the battery pack 300B.

The electric power stored in the battery pack 300B can be used, for example, for charging a vehicle such as an electric vehicle. System 110 may also be provided with a natural energy source. In this case, the renewable energy source generates electricity by means of natural energy such as wind and solar. Power is then supplied through power grid 116 from renewable energy sources in addition to power plant 111 .

[Example]
(Example 1)
<Production of aqueous electrolyte bipolar secondary battery>
An aqueous electrolyte bipolar secondary battery was manufactured by the following method.

(Preparation of bipolar electrode)
Preparation of Positive Electrode Active Material Slurry A positive electrode active material slurry is prepared in order to form a positive electrode active material containing layer. A mixture of LiMn ₂ O ₄ as a positive electrode active material, acetylene black as a conductive agent, and PVDF as a binder in a ratio of 100:5:5 was used for the positive electrode active material slurry.

Preparation of Negative Electrode Active Material Slurry In order to form the negative electrode active material containing layer, a negative electrode active material slurry is prepared. Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, graphite as a conductive aid, and PVDF as a binder were mixed at a ratio of 100:5:1 for the negative electrode active material slurry.

100 wt. % Ti, 100 wt. % Zn is used. A laminate of the metal layer a and the metal layer b was used as a bipolar electrode current collector. A positive electrode active material slurry is applied to one side of a Ti foil, and a negative electrode active material slurry is applied to one side of a Zn foil so that an uncoated portion remains, and dried at 120° C. for 12 hours to form a positive electrode active material-containing layer and a negative electrode active material-containing layer. formed. After applying a PVdF solution in which acetylene black is dispersed to the other side of the metal layer Ti foil that is not coated with the positive electrode active material slurry, and bonding the surface of the Zn foil that is not coated with the negative electrode active material slurry. , and vacuum-dried at 120° C. for 12 hours to prepare a bipolar electrode having a positive electrode surface on one side and a negative electrode surface on the other side.

(Production of aqueous electrolyte bipolar secondary battery)
A Ti foil was welded to the non-coated portion of the Ti foil surface of the bipolar electrode, and this was used as a lead. A 12M-LiCl electrolyte solution was applied to the negative electrode surface of the bipolar electrode, and a solid electrolyte sheet containing Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was placed as a solid electrolyte from above. A -Li ₂ SO ₄ electrolyte was applied, and another bipolar electrode prepared in the same manner as described above was placed facing the positive surface. At that time, the bipolar electrodes were placed so that the directions of the leads were the same. This operation was repeated to stack three bipolar electrodes.

After placing the stacked bipolar electrodes in a polyethylene container and taking the lead out of the container, the space between the bipolar electrodes and the container was filled with silicon sealant, covered with a lid, and an aqueous electrolyte bipolar secondary battery was created. did.

In order to evaluate the number of cycles and the self-discharge characteristics, the following tests were conducted.

<Number of cycles>
After waiting for 12 hours after assembling the secondary battery, the secondary battery was charged at a constant current of 2.55 V at a rate of 0.2 C in an environment of 25 ° C. (converted to the negative electrode active material). Discharge at 0.2 C to 0.8 V was performed to measure the initial discharge capacity.

<Self-discharge characteristics>
(initial discharge capacity)
After waiting for 12 hours after assembling the secondary battery, the secondary battery was charged at a constant current of 2.6 V at a rate of 0.1 C in an environment of 25 ° C. (converted to the negative electrode active material). The battery was discharged at 0.1 C to 0.2 V, and the initial discharge capacity (mAh/g (per weight of negative electrode active material)) was measured.

(Self-discharge rate)
After measuring the initial discharge capacity, after repeating the charge-discharge measurement for a predetermined number of cycles at a rate of 0.25C, the battery was charged to 2.6V at a constant current of 0.1C rate (in terms of negative electrode active material), and left for 24 hours. A discharge at 0.1C to 2.2V is then carried out. As an index of storage performance, the self-discharge rate (%) was calculated from the following formula.
(Self-discharge rate) = 100 - (discharge capacity after 24 hours / initial discharge capacity) x 100

(Example 2)
100 wt. % of Sn was used, and evaluation was performed in the same manner as described in Example 1 except that Sn foil was used.

(Example 3)
100 wt. % of Sn was used, and evaluation was performed in the same manner as described in Example 1 except that Sn foil was used.

(Example 4)
100 wt. % of Ti, and a Zn—Sn plated copper foil containing 15 wt. It was produced by the method and evaluated.

(Example 5)
100 wt. % of Ti, and a Cu—Zn alloy foil containing 30 wt. was produced and evaluated.

(Example 6)
100 wt. % of Ti, and Sn-plated copper foil containing 15 wt. It was produced and evaluated.

(Comparative example 1)
A stainless steel foil was used for the metal layer a, and a stainless steel foil was used for the metal layer b.

(Comparative example 2)
100 wt. % Al, the same Al foil as that used for the metal layer a was used for the metal layer b, and 12M-LiCl was used as the electrolyte in contact with the positive electrode surface. It was produced by the method and evaluated. The Al foil is 100 wt. %.

(Comparative Example 3)
100 wt. % of Ti, and stainless steel foil was used for the metal layer b.

(Comparative Example 4)
3 wt. Aqueous electrolyte bipolar secondary batteries were fabricated and evaluated in the same manner as in Example 1, except that a Cu—Sn alloy foil containing 10% Sn was used.

From the above results, it was confirmed that the first negative electrode active material-containing layer was provided on at least one surface of the negative electrode current collector, and the first positive electrode active material-containing layer was provided on at least one surface of the positive electrode current collector. and a bipolar electrode current collector provided with a second positive electrode active material-containing layer on one surface and a second negative electrode active material-containing layer on the opposite surface, respectively. and an aqueous electrolyte, wherein the bipolar electrode current collector has a metal layer a and a metal layer b, the metal layer a comprising Cr, Ni, Fe, Ti and Al The metal layer b contains at least one element selected from the group consisting of 10 wt. % or more 100 wt. % or less of any one of Zn and Sn, the metal layer a and the metal layer b are electrically connected, and the metal layer a has a second positive electrode active material-containing layer on the surface of the metal layer a , Since corrosion of the bipolar electrode current collector can be suppressed by being an aqueous electrolyte bipolar secondary battery having a second negative electrode active material-containing layer on the surface of the metal layer b, the capacity retention rate and the initial The discharge capacity was improved and the self-discharge was improved. It can be seen that the life performance is excellent even when the aqueous electrolyte is used.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1... Electrode group 2... Exterior member 3... Negative electrode 3a... Negative electrode current collector 3b... Negative electrode active material containing layer 3b1... First negative electrode active material containing layer 3b2... Second negative electrode active material containing layer , 4... Separator 4a... First separator 4b... Second separator 5... Positive electrode 5a... Positive electrode current collector 5b... Positive electrode active material containing layer 5b1... First positive electrode active material containing layer 5b2 Second cathode active material-containing layer 6 Negative electrode terminal 7 Positive electrode terminal 8 Negative electrode gasket 9 Positive electrode gasket 10 Sealing plate 11 Control valve 12 Filling port 13 Sealing Plug 16 Negative collector tab 17 Positive collector tab 21 Bus bar 22 Positive lead 23 Negative lead 24 Adhesive tape 31 Container 32 Lid 33 Protective sheet , 34... Printed wiring board, 35... Wiring, 40... Vehicle body, 100... Secondary battery, 110... System, 111... Power plant, 112... Stationary power supply, 113... Consumer side power system, 115... Energy management system , 116 power network 117 communication network 118 power converter 121 consumer side EMS 122 power converter 123 stationary power supply 200 assembled battery 300 battery pack 300A battery pack 300B Battery pack 310 Housing 320 Opening 332 Positive output terminal 333 Negative output terminal 342 Positive connector 343 Negative connector 345 Thermistor 346 Protection circuit 342a...Wiring 343a...Wiring 350...External terminal for energization 352...Positive side terminal 353...Negative side terminal 348a...Plus side wiring 348b...Minus side wiring 400...Vehicle 500...Water-based electrolyte bipolar Secondary battery 501 Bipolar electrode 502 Bipolar electrode current collector 502a Metal layer a 502b Metal layer b 503 Conductive adhesive layer 504 Negative electrode side aqueous electrolyte 505 Positive electrode side aqueous electrolyte.

Claims (22)

a negative electrode provided with a first negative electrode active material-containing layer on at least one surface of a negative electrode current collector;
A positive electrode provided with a first positive electrode active material-containing layer on at least one surface of a positive electrode current collector;
a bipolar electrode having a bipolar electrode current collector provided with a second positive electrode active material-containing layer on one surface and a second negative electrode active material-containing layer on the opposite surface;
An aqueous electrolyte bipolar secondary battery comprising an aqueous electrolyte,
The bipolar electrode current collector has a metal layer a and a metal layer b,
The metal layer a contains at least one element selected from the group consisting of Cr, Ni, Fe, Ti and Al,
The metal layer b has a weight of 10 wt. % or more 100 wt. % or less of any one element of Zn and Sn,
The metal layer a and the metal layer b are electrically connected,
Having the second positive electrode active material-containing layer on the surface of the metal layer a,
A water-based electrolyte bipolar secondary battery having the second negative electrode active material-containing layer on the surface of the metal layer b. Having a conductive adhesive layer between the metal layer a and the metal layer b;
The conductive adhesive layer is a conductive resin or metal,
The water-based electrolyte bipolar secondary battery according to claim 1. 2. The water-based electrolyte bipolar secondary battery in accordance with claim 1, wherein said metal layer a and said metal layer b are in direct contact with each other. The water-based electrolyte bipolar secondary battery according to any one of claims 1 to 3, wherein the metal layer b is a Cu-Zn alloy or a Cu-Sn alloy. The bipolar electrode current collector is
The water-based electrolyte according to any one of claims 1 to 4, wherein when Al is used for the metal layer a, the thickness of the metal layer a is 9% or more and 95% or less of the thickness of the bipolar electrode current collector. Bipolar secondary battery. The bipolar electrode current collector is
When the metal layer a contains Cr, Fe, Ni, Ti, an Al-Mg alloy, or an Al-Mg-Zn alloy, the thickness of the metal layer a is 7% or more of the thickness of the bipolar electrode current collector and 95%. % or less, the aqueous electrolyte bipolar secondary battery according to any one of claims 1 to 5. The bipolar electrode current collector is
7. The water-based electrolyte according to any one of claims 1 to 6, wherein when stainless steel is used for the metal layer a, the thickness of the metal layer a is 5% or more and 95% or less of the thickness of the bipolar electrode current collector. Bipolar secondary battery. The water-based electrolyte bipolar secondary battery according to any one of claims 1 to 7, wherein the water-based electrolyte in contact with the metal layer a and the water-based electrolyte in contact with the metal layer b are different. The water-based electrolyte bipolar secondary battery according to any one of claims 1 to 8, wherein the water-based electrolyte in contact with the metal layer a and the water-based electrolyte in contact with the metal layer b are liquid or gel. The aqueous electrolyte bipolar secondary battery according to any one of claims 1 to 9, wherein the aqueous electrolyte bipolar secondary battery comprises a separator, and the separator contains inorganic solid particles. The aqueous electrolyte bipolar secondary battery according to any one of claims 1 to 10, wherein said separator has an air permeability coefficient of 1 x ^{10-13 m2} or less. 11. The aqueous electrolyte bipolar secondary battery in accordance with claim 10, wherein said inorganic solid particles include solid electrolyte particles having ion conductivity for alkali metal ions. The inorganic solid particles are Li1 ₊ yAlzM12 _{-z (} PO4), a compound represented by Li1 _{+ wAlwTi2 -w (} PO4) ₃ and satisfying _{0.1≤w≤0.5} . ) ₃ , and M1 is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and 0 ≤ y ≤ 1 and 0 ≤ z ≤ 1, and Li5+xLa3M2 10. Represented by _{2 - xZrxO12} , wherein M2 is one or more selected from the group consisting of Nb and Ta, and includes at least one selected from the group consisting of compounds where 0≤x≤2. 13. The water-based electrolyte bipolar secondary battery according to 12. The separator includes a polymer material, and the polymer material is carbonized with a functional group containing one or more selected from the group consisting of oxygen (O), sulfur (S), nitrogen (N) and fluorine (F). 14. The water-based electrolyte bipolar secondary battery according to any one of claims 10 to 13, comprising a monomer unit composed of hydrogen, wherein the proportion of said monomer unit in said polymer material is 70 mol% or more. The first negative electrode active material-containing layer or the second negative electrode active material-containing layer has a lithium ion insertion-extraction potential of 1 V or more and 3 V or less (vs. Li/Li ⁺ ) with respect to the oxidation-reduction potential of lithium. The water-based electrolyte bipolar secondary battery according to any one of claims 1 to 14, comprising a negative electrode active material containing a certain compound. The first positive electrode active material-containing layer or the second positive electrode active material-containing layer has a lithium ion insertion-extraction potential with respect to the oxidation-reduction potential of lithium of 2.5 V or more and 5.5 V or less (vs. Li/ The aqueous electrolyte bipolar secondary battery according to any one of claims 1 to 15, comprising a positive electrode active material containing a compound that is Li ⁺ ). A battery pack comprising the secondary battery according to any one of claims 1 to 16. 18. The battery pack according to claim 17, further comprising an external terminal for power supply and a protection circuit. The battery pack according to claim 17 or 18, comprising a plurality of said secondary batteries, wherein said plurality of secondary batteries are 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 17 to 19. 21. The vehicle of claim 20, including a mechanism for converting kinetic energy of the vehicle into regenerative energy. A stationary power supply comprising the battery pack according to any one of claims 17 to 19.

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