JPH11162517A - Rechargeable battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve energy density and safety by providing a negative elec trode having an interlayer compound formed from multiple cations containing metal ions that belong to group 1A of the periodic table and metal ions that belong to group 2A of the periodic table, an electrolyte, and a positive electrode having a positive electrode active material. SOLUTION: By including at least two kinds of cations to enter and exit from a negative electrode, the insertion in between layers, in which monoatoms can hardly be inserted further more due to being filled to capacity, of interlayer compounds is made possible because of different kinds of atoms so that the energy density can be enhanced. More specifically, a combination of such as a lithium ion and a calcium ion, a potassium ion and a barium ion, and the like can be adopted as the combination of the multiple cations inserted into the interlayer compound host. Any material that can form the interlayer compound, that is, any interlayer compound host can be adopted for the material used for the negative electrode, but carbon is preferable in particular and graphitic carbon is more preferable in terms of the battery performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery, and more particularly, to a secondary battery having a high energy density and capable of being repeatedly used for a long period of time.

[0002]

2. Description of the Related Art A lithium ion secondary battery has been developed as a high energy battery having a high voltage and a large discharge capacity, and is used for portable equipment and the like.

[0003] Originally, a lithium secondary battery using lithium as a metal or alloy for the negative electrode is considered to be a high energy battery, but if used repeatedly over a long period of time, lithium is deposited in a dendritic manner. Then, the dendritic lithium damages the separator (porous polymer film) separating the positive electrode and the negative electrode, or the debris generated by the fragmentation of the dendritic lithium is suspended in the electrolyte. In addition, there is a problem in that the positive electrode and the negative electrode are short-circuited to cause a burst flame of the battery.

[0004] Lithium ion secondary batteries use carbon,
In particular, the use of a lithium intercalation compound such as graphite improves safety and has been put to practical use.

[0005] However, the lithium-carbon intercalation compound also has a problem in chemical stability, and has not yet completely prevented the bursting flame of the battery.

[0006] Further, since the lithium ion secondary battery uses a lithium intercalation compound composed of lithium ions and carbon, particularly graphite, etc. for the negative electrode, the energy density is lower than that of a lithium secondary battery using lithium metal itself.
As described above, the lithium ion secondary battery uses the lithium intercalation compound for the negative electrode, and the lithium secondary battery uses lithium metal or a lithium alloy for the negative electrode.

So far, attempts have been made to use carbon as a host in a secondary battery and to use K, which is the same alkali metal element as Li, instead of Li.
In this case, there is a problem that the energy density is reduced, and the safety is not improved. At present, it is difficult to convert Na into a battery, and information on a battery using Na has not been obtained.

An object of the present invention is to provide a secondary battery having high energy density and high safety. An object of the present invention is not to use lithium alone as a metal ion, but to use lithium, even if lithium is used, to reduce the amount of lithium used by combining other metals, and furthermore, compared to the case of using only lithium. It is to provide a secondary battery having high energy and high discharge capacity.

[0009]

The present invention for solving the above-mentioned problems comprises a plurality of cations including a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table. A secondary battery having a negative electrode having an interlayer compound to be formed, an electrolytic solution, and a positive electrode having a positive electrode active material. In one embodiment of the present invention, the interlayer compound has a host compound. Carbon,
In one embodiment of the present invention, the plurality of cations are each a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table with respect to all ions inserted into and released from the negative electrode. In an embodiment of the present invention, the positive electrode active material contains an inorganic material containing a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table. A salt, wherein the electrolytic solution contains ions of an element or an atomic group belonging to a group different from the metal in the positive electrode active material, and in one embodiment of the present invention, the positive electrode active material includes An inorganic salt containing a metal ion belonging to Group 1A, wherein the electrolytic solution is a metal ion belonging to Group 2A of the periodic table or a group different from the metal ion belonging to Group 2A of the periodic table and the metal in the positive electrode active material. In one embodiment of the present invention, the positive electrode active material is an inorganic salt containing a metal ion belonging to Group 2A of the periodic table, and the electrolytic solution is Rate table 1A
In the positive electrode active material, a metal ion belonging to Group 1A or a metal ion belonging to Group 1A of the periodic table and an ion of an element belonging to a different group or an ion of an atomic group are included. The electrolyte has a boiling point of 60 ° C
The above-described non-aqueous organic solvent is contained. In one embodiment of the present invention, the positive electrode and the negative electrode are separated by a porous membrane.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.

The guest of the interlayer compound used for the negative electrode in the secondary battery of the present invention is not one kind of cation but a plurality of kinds of cations.

What is important in the present invention is that the plural kinds of metal ions serving as guests of the intercalation compound are selected from the group consisting of metal ions belonging to Group 1A of the periodic table and metal ions belonging to Group 2A of the periodic table. At least two kinds of metal ions. That is, in the present invention, it is important that the plurality of types of metal ions serving as guests of the intercalation compound include one type of metal ion belonging to Group 1A of the periodic table and one type of metal ion belonging to Group 2A of the periodic table. is there.

In the secondary battery according to the present invention, inorganic salts containing these plural kinds of cations (for example, complex oxides, sulfides and intermetallic compounds) are used for the positive electrode, or these plural kinds of cations are used. A material capable of forming the intercalation compound, that is, an intercalation compound host, such as carbon and amorphous tin oxide, using an inorganic salt containing one kind of cation for the positive electrode and using an electrolyte containing another kind. Thus, a negative electrode is formed, and cations are exchanged between the two electrodes, whereby a function as a secondary battery is exhibited.

In this secondary battery, before the first charge, the potentials of the negative electrode and the positive electrode having the interlayer compound host are almost zero.
V.

By charging, a cation is inserted as a guest between the layers of the intercalation compound host in the negative electrode, and takes on a negative potential. On the other hand, in the positive electrode, atoms forming cations are released from the inorganic salts and have a positive potential.
Also, some of the cations of the electrolyte may be inserted into the negative electrode and may decrease.

When the battery charged in this way is connected to a device to be used, guest cations between layers in the interlayer compound are released, move to the positive electrode, are inserted into the inorganic salts, and the electrons when the inorganic salts return to the original state. The transfer of energy releases energy as a discharge reaction. In addition, the cations in the electrolyte that have been partially reduced by being inserted into the negative electrode may be restored. In the present invention, by making at least two types of cations entering and exiting the negative electrode, not only can it be formed with an interlayer compound negative electrode in which atoms that are conventionally difficult to insert are inserted, but also it is full with single atoms and it is difficult to insert it further It is intended to increase the energy density by allowing insertion between different interlayer compounds due to heteroatoms.

In the alkali metal element and the alkaline earth metal element, the potential when a cation receives an electron to become an atom becomes extremely low, that is, becomes negative. For example, alkaline earth metal 2A group elements (Be, Mg, Ca, Sr, B
a, Ra ²⁺ ions Among Ra) of the redox potential when changing from Ra ²⁺ ions Ra of about -2.92V
And the oxidation-reduction potential of Li is about -3.05 V, K
About -2.93V, which is the oxidation-reduction potential of Similarly, the redox potential of Ba is about -2.91 V, the redox potential of Ca is about -2.87 V, the redox potential of Mg is about -2.36 V, and the redox potential of Be is about 2.36 V. −
1.90 V, and therefore the redox potential of the alkaline earth metal is negatively large.

Therefore, in the present invention, when the cations are converted into the ions of the alkali metal element and the ions of the alkaline earth metal element, a battery having a high voltage and a high energy density can be obtained.

The secondary battery of the present invention having the above action will be described in more detail.

The positive electrode in the secondary battery of the present invention is formed having an inorganic salt capable of releasing metal cations when charged in a state of being in contact with the electrolytic solution.

The inorganic salts have a cation source capable of releasing a metal capable of forming an intercalation compound with the material of the negative electrode as a metal cation.

As the cation from the positive electrode and the cation from the electrolytic solution, at least one metal selected from various metals belonging to Group 1A of the periodic table and from various metals belonging to Group 2A of the periodic table. Combinations with at least one selected metal can be mentioned.

As the alkali metal, Li, K, N
a, Rb, and Cs; and alkaline earth metals include Be, Mg, Ca, Sr, Ba, and Ra.

In the present invention, as described above, at least two kinds of the metals are inserted into the intercalation compound host. As a combination of a plurality of cations inserted into the intercalation compound host, the periodic table 1A Combination of a cation of at least one metal selected from various metals belonging to group III and a cation of at least one metal selected from various metals belonging to group IIA of the periodic table, for example, lithium ion As specific examples, embodiments such as a combination of calcium ions, potassium ions and barium ions can be given.

The secondary battery of the present invention having a negative electrode formed of an interlayer compound of an interlayer compound host and an alkaline earth metal or an alkali metal has a negative electrode formed of an interlayer compound of an interlayer compound host and an alkali metal. Higher safety than secondary batteries.

In the present invention, the inorganic salts used for the positive electrode need only be capable of releasing alkali metal ions or alkaline earth metal ions when charged in contact with the electrolytic solution. Is preferably used. As this composite oxide, for example, MgAl ₂ O ₄ , Li
CoO ₂ or a mixture of MgAl ₂ O ₄ and LiCoO ₂ , a mixture of MgAl ₂ O ₄ and LiCoO ₂ and calcined, a hydrate containing Mg and / or Li and a carbonate mixed and calcined The composite oxide and the like obtained by the above method can be cited as one specific example.

As the composite oxide, there are various compounds other than those described above as long as the object of the present invention is not impaired. For example, LiNiO ₂ , LiMnO ₂ , LiV ₂ O ₆ , B
aNiO ₃ , BaNiO ₂ , BaCoO ₃ , BaCoO
_2.8 , BaFeO ₃ , SrNiO ₃ , SrCoO _2.5 ,
SrCoO _2.8 , SrCoO ₃ , SrFeO ₄ , SrF
eO _2.5 , SrFeO ₃ , CaCo ₂ O ₅ , Ca ₃ Co
₄ O ₈ , Ca ₂ Co ₂ O ₅ , Ca ₃ Co ₂ O ₆ , CaF
eO ₃ , CaFeO ₂ , MgNiO ₂ , MgCo ₂ O
₄ , MgFe ₂ O ₄ , BaSmO _{5 and the} like.

The positive electrode in the present invention can be formed by forming a composition or mixture obtained by mixing the inorganic salt and a conductive substance, for example, carbon and a binder, on a conductive support. .

As the binder, polyethylene,
Examples include elastomers such as polypropylene, ethylene rubber, ethylene propylene rubber, butylene rubber, polytetrafluoroethylene, and polyvinylidene fluoride.

The content of the inorganic salt in the composition or the mixture is usually at least 85% by weight,
Preferably it is at least 90% by weight. The content of the conductive substance in the composition or mixture is usually 1
-15% by weight, preferably 3-10% by weight. The amount of the binder is an amount necessary for easily performing various operations such as a coating operation when the composition or the mixture is coated on the support, and a drying operation thereof, and is appropriately determined.
Usually, it is 1 to 15% by weight, preferably 3 to 10% by weight.

The support is not particularly required as long as it has self-shape retention and conductivity only with inorganic salts. However, usually, the support is required to have a predetermined shape as a positive electrode. A support is used. Examples of this support include metals such as aluminum foil and titanium mesh.

On the other hand, the electrolytic solution can be selected and determined according to the combination of the cation inserted into and released from the negative electrode and the positive electrode active material. The combinations of the positive electrode active material and the electrolyte are as follows.

(1) The positive electrode active material is an inorganic salt containing a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table, and an element belonging to a different group from the metal in the positive electrode active material. (2) the positive electrode active material is an inorganic salt containing a metal ion belonging to Group 1A of the periodic table, and a metal ion or a periodic table belonging to Group 2A of the periodic table. An electrolyte in which metal ions belonging to group 2A and ions of elements belonging to a group different from the metal in the positive electrode active material or ions of atomic groups are dissolved; (3) the positive electrode active material belongs to group 2A of the periodic table An inorganic salt containing a metal ion, in which a metal ion belonging to Group 1A of the periodic table or a metal ion belonging to Group 1A of the periodic table and an ion or an ion of an atomic group belonging to another group different from the metal in the positive electrode active material are dissolved. Electrolyte It is below.

Specifically, the case where the cations inserted and released from the negative electrode are Li and Ca will be described as an example.

As the positive electrode active material, LiCoO ₂ and Ca (CoO
₂ ) When a mixture of ₂ was used, Li was also Ca
An electrolyte solution containing NH ₄ ClO ₄ or Fe (ClO ₄ ) _3, which does not contain any impurities, is used. When only LiCoO ₂ is used as the positive electrode active material, an electrolytic solution in which Ca (ClO ₄ ) ₂ is dissolved or an electrolytic solution in which Ca (ClO ₄ ) ₂ and NH ₄ ClO ₄ or Fe (ClO ₄ ) ₃ are dissolved Use liquid or C
An electrolytic solution in which NH ₄ ClO ₄ or Fe (ClO ₄ ) ₃ containing no a is dissolved is used.

When only Ca (CoO ₂ ) ₂ is used as the positive electrode active material, an electrolytic solution in which LiClO ₄ is dissolved is used, or LiClO ₄ and NH ₄ ClO ₄ or Fe (ClO ₄₎ is used.
₄ ) Use an electrolyte solution in which ₃ is dissolved.

Usually, metal ions belonging to Group 1A of the periodic table are easier to insert and release at the positive and negative electrodes.
An inorganic salt containing a metal ion belonging to Group 1A of the periodic table is used for the positive electrode active material, an electrolytic solution in which a metal ion belonging to Group 2A of the periodic table is dissolved is used for the electrolyte, or the positive electrode active material is a periodic table. In the case of an inorganic salt containing a metal ion belonging to Group 1A and a metal ion belonging to Group 2A in the periodic table, the ion of an element or an atom of an atomic group belonging to a different group from the group to which the metal belongs in the positive electrode active material is also used. A suitable amount of metal ions belonging to Group 2A of the periodic table may be dissolved and used in the dissolved electrolyte.

In the electrolytic solution, a plurality of types of anions with respect to the cations may be used, or a single type of anion may be used.

[0039] Of the anions only such as chlorine and bromine, also be capable of dissolving in a non-aqueous solvent is not preferable in view of it can cause the gas during the cell reaction, for example, ClO ₄ ^- and PF ₆ ^- anion is a good group of atoms consisting of a plurality of elements such as.

Suitable solutes include those which are easily dissolved in a solvent, have good conductivity of a solvent in which the solute is dissolved, ie, an electrolytic solution, are unlikely to be decomposed, are stable, and have little risk of explosion or toxicity. Examples thereof include LiPF ₆ , NH ₄ ClO ₄ , and Mg (ClO ₄ ).
₂ , CaSi, Ba (PF ₆ ) ₂ , Zn (ClO
₄ ) ₂ , Al (PF ₆ ) ₃ , Fe [CH (COCH ₃ ) _2
3 etc. can be mentioned.

In addition to these, for example, LiClO
₄ , alkali metal salts such as LiBF ₄ and LiAsO ₆ , C
a (BF ₄ ) ₂ , Ca (CF ₃ SO ₃ ), Ca (PF
₆ ) ₂ , Ca (ClO ₄ ) ₂ , Ca (As) ₂ , Ca
(Sb) ₂ , Mg (BF ₄ ) ₂ , Mg (CF ₃ SO ₃ )
₂ , Mg (PF ₆ ) ₂ , Mg (ClO ₄ ) ₂ , Mg (A
s) ₂ , Mg (Sb) ₂ , Ba (BF ₄ ) ₂ , Ba (C
F ₃ SO ₃ ) ₂ , Bs (PF ₆ ) ₂ , Ba (ClO ₄ )
₂ , Ba (As) ₂ , Ba (Sb) ₂ , Sr (BF ₄ )
₂ , Sr (CF ₃ SO ₃ ) ₂ , Sr (PF ₆ ) ₂ , Sr
Alkaline earth metal salts such as (ClO ₄ ) ₂ , Sr (As) ₂ , Sr (Sb) ₂ , Zn (PF ₅ ) ₂ , Zn (BF
₄ ) ₂ , Mn (CF ₃ SO ₃ ) ₄ , Pb (ClO ₄ )
₂ , salts of ions of another group or ions of atomic groups such as NH ₄ ClO ₄ can be mentioned as the solute.

The preferred solute concentration in the electrolyte is 0.5 to 2
M, a more preferred solute concentration is 1-1.5M. However, this solute concentration is appropriately determined according to the conductivity and viscosity of the electrolytic solution.

The solvent used in the present invention has a boiling point of 60 ° C.
From the above organic compounds, a solvent appropriately selected in consideration of the solubility of the solute, conductivity, withstand voltage and the like can be used. As the solvent, for example, ethylene carbonate, diethyl carbonate, propylene carbonate,
Non-aqueous solvents such as dimethyl carbonate, vinylene carbonate, dimethoxyethane, tetrahydrofuran and the like can be mentioned. Among the non-aqueous solvents, a mixed solvent based on ethylene carbonate with dimethyl carbonate, diethyl carbonate or the like is preferable.

In the present invention, the material used for the negative electrode may be any material as long as it is a material capable of forming an interlayer compound, that is, an interlayer compound host, but carbon is particularly preferable. Examples of the carbon include low-crystalline carbon having low crystallinity, for example, low-crystalline carbon having a graphite mesh spacing d ₀₀₂ by X-ray diffraction of at least 0.37 nm and graphitic carbon having high crystallinity, for example, X-ray Any of the graphitic carbons having a graphite net spacing d ₀₀₂ of at most 0.34 nm by diffraction can be used, and the graphitic carbon is particularly good in battery performance. The carbon having the intermediate crystallinity may result in a battery having lower performance than the former two. However, depending on the type of cation, it is also possible to use carbon having intermediate crystallinity between the two, and a mixture of low crystalline carbon and graphitic carbon.

Examples of the graphite include natural graphite powder, artificial graphite powder, spherical mesophase pitch graphite, fibrous mesophase pitch graphite, graphitized vapor grown carbon fiber, and among them, graphitized vapor grown carbon fiber is particularly preferable. This is because the graphitized vapor-grown carbon fiber has a hexagonal carbon network plane superimposed in an annual ring shape, and a metal atom is inserted between the annual rings to easily form an intercalation compound. When the graphitized vapor-grown carbon fiber is used as a host for an intercalation compound, (1) an almost perfect intercalation compound can be formed, so that a negative electrode having a large discharge capacity can be formed. Since the surface edge is limited to both ends of the fiber and is small, there is little reduction in charge and discharge efficiency due to irreversible reaction at the edge,
Because it has an annual ring structure, it does not break down due to guest ions entering and exiting, and has good cycle characteristics. (4) Since ions can enter and exit at high speed, short-time charging and high load use are possible. And the like.

The negative electrode of the present invention can be formed of a material capable of forming the above-mentioned intercalation compound, ie, an intercalation compound host itself, or a mixture of the intercalation compound host and a conductive material such as carbon and a binder. The composition may be formed in a layered form on a conductive support.

In the secondary battery according to the present invention, the positive electrode and the negative electrode are separated from each other by a porous film, as in the conventional secondary battery.

The porous membrane is permeable to an electrolytic solution, in other words, has ion permeability, does not allow passage of particles and the like, and can be made of either an organic substance or an inorganic substance if it does not deteriorate during a battery reaction. For example, a sheet-like porous film formed of polyethylene, polypropylene, or the like may be used. The secondary battery according to the present invention can be formed in any of a button battery and a can battery.

[0049]

EXAMPLES (Example _{1) Li Co O 2 · Ca} (Co O
₂ ) Graphitized vapor-grown carbon fiber is coated with PVDF using a positive electrode obtained by applying the sintered powder of ₂ together with graphite powder and polyvinylidene fluoride (PVDF) on an aluminum foil.
In addition, a negative cell coated on a copper foil was used, and a flat cell opposed to each other via a polyethylene porous film was assembled. As an electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in which NH ₄ Cl O ₄ is dissolved at a concentration of 1.3 M (volume ratio; EC /
(DEC = 1 / 1.5).

The battery was subjected to a charge / discharge test, and was subjected to 550 mAh /
g of negative electrode graphite discharge capacity was obtained.

[0051] (Comparative Example 1) Li Co O ₂ powder and graphite powder · P
A positive electrode coated on an aluminum foil with VDF;
A flat cell in which an artificial graphite powder was applied to a copper foil together with PVDF on a copper foil and opposed through a polyethylene porous film was assembled. LiClO ₄ as electrolyte
Is a mixed solvent of ethylene carbonate and diethyl carbonate dissolved at a concentration of 1.0 M (volume ratio; EC /
(DEC = 1 / 1.5). The negative electrode graphite discharge capacity when the battery was subjected to a charge / discharge test was 290 mAh / g.

[0052] (Example _{2) Li Co O 2 · Ca} (Co O
Positive electrode and a negative electrode made of graphitized vapor grown carbon fiber was applied to a copper foil both sides with the PVDF _{2) 2} sintered pulverized powder formed by applying an aluminum foil both sides with graphite powder, polyvinylidene fluoride (PVDF) Are wound through a polyethylene porous film, and Ca (Cl O ₄ ) is added to the electrolytic solution.
₂ is a mixed solvent of ethylene carbonate and diethyl carbonate in a concentration of 1.0 M (volume ratio; EC
/ DEC = 1/1) was manufactured.

This battery had an average discharge characteristic of 3.4 V and 1.9 Ahr under charge / discharge conditions at a time rate of 1 C. Note that the average discharge voltage and the discharge capacity decrease as the time rate increases.

(Example 3) In the same manner as in Example 2,
A sintered powder of KCo O ₂ · Ba (Co O ₂ ) ₂ was used for the positive electrode, graphitized vapor-grown carbon fiber was used for the negative electrode, and NH ₄ Cl O ₄ was 1.0 M for the electrolyte. Ba (PF
₆ ) An AA cylindrical secondary battery was manufactured using a mixed solvent of ethylene carbonate, diethyl carbonate and propylene carbonate (volume ratio 1: 1: 1) in which ₂ was dissolved at a concentration of 0.5M.

This battery had discharge characteristics of 3.2 V and 1.8 Ahr on average under charge / discharge conditions at a rate of 4 C.

Example 4 As in Example 2, LiCoO ₂ powder was used for the positive electrode, graphitized vapor-grown carbon fiber was used for the negative electrode, and Ca (ClO ₄ ) was used for the electrolytic solution. ₂ is 1.2
An AA cylindrical secondary battery using a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio of 1: 1) dissolved at a concentration of M was manufactured.

This battery had discharge characteristics of 3.1 V and 1.4 Ahr on average under charge and discharge conditions at a rate of 8 C.

[0058] (Example 5) In the same manner as in Example 2, using the Li Co O ₂ powder in the positive electrode, use the graphitized vapor grown carbon fiber as a negative electrode, the electrolytic solution Ba (Cl O _{4) 2} Is 0.8
An AA cylindrical secondary battery was manufactured using a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) in which M and AgClO ₄ were dissolved at a concentration of 0.7M.

This battery had discharge characteristics of 3.4 V and 1.9 Ahr on average under charge and discharge conditions at a rate of 2 C.

[0060]

According to the present invention, a secondary battery with high energy density and high safety can be provided. According to the present invention, instead of using only lithium as a metal ion, even if lithium is used, the amount of lithium used is reduced by combining other metals, and is higher than when only lithium is used. A secondary battery having high discharge capacity with energy can be provided.

Claims (8)

[Claims] 1. A negative electrode having an interlayer compound formed of a cation comprising a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table, a positive electrode having an electrolytic solution and a positive electrode active material. A secondary battery comprising: 2. The secondary battery according to claim 1, wherein the host compound of the intercalation compound is carbon. 3. The cations of metal ions belonging to group 1A of the periodic table and metal ions belonging to group 2A of the periodic table each account for 20% of all ions inserted into and released from the negative electrode.
2. The secondary battery according to claim 1, wherein the content of the secondary battery is in the range of 80% to 80%. 4. The positive electrode active material is an inorganic salt containing a metal ion belonging to Group 1A of the periodic table and a metal ion belonging to Group 2A of the periodic table. The secondary battery according to claim 1, comprising ions of elements belonging to different groups or ions of an atomic group. 5. The positive electrode active material is an inorganic salt containing a metal ion belonging to Group 1A of the periodic table, and the electrolyte is a metal ion belonging to Group 2A of the periodic table or Group 2A of the periodic table. 2. The secondary battery according to claim 1, comprising a metal ion and an ion of an element belonging to a group different from a metal of the positive electrode active material or an ion of an atomic group. 6. The positive electrode active material is an inorganic salt containing a metal ion belonging to Group 2A of the periodic table, and the electrolyte is a metal ion belonging to Group 1A of the periodic table or a metal belonging to Group 1A of the periodic table. 2. The secondary battery according to claim 1, comprising ions and ions of an element or an atomic group belonging to a different group from the metal in the positive electrode active material. 7. The electrolyte according to claim 1, wherein the electrolytic solution according to claim 1 contains a non-aqueous organic solvent having a boiling point of 60 ° C. or higher. Next battery. 8. The secondary battery according to claim 1, wherein the positive electrode and the negative electrode according to any one of claims 1 to 6 are separated by a porous membrane.