WO2014168218A1

WO2014168218A1 - Polyvalent metal secondary battery

Info

Publication number: WO2014168218A1
Application number: PCT/JP2014/060435
Authority: WO
Inventors: 哲市坪; 松原　英一郎; 貴之土井
Original assignee: 国立大学法人京都大学
Priority date: 2013-04-11
Filing date: 2014-04-10
Publication date: 2014-10-16
Also published as: JPWO2014168218A1; CN105103360A; KR20150143535A

Abstract

The present invention provides a polyvalent metal secondary battery provided with a negative electrode which contains a negative electrode active material comprising a polyvalent metal and which has a standard electrode potential of -0.7V or less, a positive electrode, and an electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode contains a positive electrode active material comprising a lithium compound.

Description

Multivalent metal secondary battery

The present invention relates to a polyvalent metal secondary battery including a negative electrode containing a polyvalent metal. More specifically, the present invention relates to a multivalent metal secondary battery that can be suitably used for power storage, a power source of a hybrid vehicle or an electric vehicle, a power source of a mobile device having high functions, and a positive electrode active material used therefor About.
The multivalent metal secondary battery of the present invention has a high operating voltage and high energy density, and is excellent in safety. Therefore, the multivalent metal secondary battery is used for a secondary battery for storing electric power, a hybrid vehicle, an electric vehicle, etc. It is expected to be suitably used as a secondary battery, a secondary battery for mobile devices, and the like.

In recent years, demand for secondary batteries has been increasing due to demands for optimizing energy supply and demand and reducing environmental impact. In addition, since miniaturization and high performance of mobile devices are required, miniaturization and high capacity of secondary batteries are desired. Currently, lithium ion secondary batteries are used as secondary batteries for storing electric power, secondary batteries for vehicles, secondary batteries for mobile devices, and the like. However, the lithium ion secondary battery may generate heat due to overcharge or the like.

Thus, a magnesium secondary battery has been proposed that includes a positive electrode containing a chevrel compound as a positive electrode active material, and an electrolytic solution made of a solution obtained by dissolving a Grignard reagent and aluminum chloride in tetrahydrofuran (for example, see Non-Patent Document 1). ).

However, since the magnesium secondary battery described in Non-Patent Document 1 has a low operating voltage and a small charge capacity per unit mass, a higher operating voltage and energy density can be ensured, and the safety is further improved. There is a need for secondary batteries.

The present invention has been made in view of the above-described prior art, can ensure a higher operating voltage and energy density, and is more excellent in safety, and a positive electrode active material used therefor The issue is to provide substances.

The present invention
(1) A negative electrode including a negative electrode active material made of a polyvalent metal having a standard electrode potential of −0.7 V or less, a positive electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode,
A multivalent metal secondary battery, wherein the positive electrode is a positive electrode containing a positive electrode active material comprising a lithium compound;
(2) The polyvalent metal secondary battery according to (1), wherein the electrolytic solution is an electrolytic solution containing a solution containing a lithium cation and a cation of the polyvalent metal.
(3) The multivalent metal secondary battery according to (1) or (2), wherein the polyvalent metal is a metal selected from the group consisting of metal calcium, metal magnesium, metal aluminum, and metal zinc; 4) The multivalent metal secondary battery according to (3), wherein the polyvalent metal is magnesium metal.
About.

According to the multivalent metal secondary battery and the positive electrode active material of the present invention, it is possible to ensure a higher operating voltage and energy density, and to achieve an excellent effect of being superior in safety.

(A) is schematic explanatory drawing which shows the state at the time of the discharge reaction of the polyvalent metal secondary battery which concerns on one Embodiment of this invention, (B) is the charge of the polyvalent metal secondary battery which concerns on one Embodiment of this invention It is a schematic explanatory drawing which shows the state at the time of reaction. It is a schematic explanatory drawing of the multivalent metal secondary battery which concerns on other embodiment of this invention. In Example 1, a working electrode for a lithium compound iron phosphate (LiFePO ₄₎ lithium cations from the desorbed (FePO ₄₎ as a host compound, and a reference electrode made of polished metal magnesium, consisting polished metal magnesium It is a figure which shows the cyclic voltammogram at the time of using a counter electrode. In Example 2, it is a figure which shows the cyclic voltammogram at the time of using the electrolyte solution with which lithium salt and magnesium salt were mix | blended. In Example 3, it is a graph of the charging / discharging curve which shows the result of having investigated the charging / discharging characteristic at the time of using the electrolyte solution with which lithium salt and magnesium salt were mix | blended. In Example 4, it is a figure which shows the cyclic voltammogram at the time of using the electrolyte solution with which lithium salt and magnesium salt were mix | blended. In Example 4, it is a graph of the charging / discharging curve which shows the result of having investigated the charging / discharging characteristic at the time of setting the cutoff potential to 1.3V and using the electrolyte solution with which lithium salt and magnesium salt were mix | blended. In Example 5, it is an X-ray diffraction diagram which shows the result of having performed the X-ray diffraction analysis of the positive electrode active material after charge and after discharge. In Example 6, a diagram illustrating the cyclic voltammograms when using a positive electrode containing a positive electrode active material composed of Chevrel compound _{_{_{(Mg 2 Mo 2 Cr 4 S}}} 8). (A) is schematic explanatory drawing which shows the charge process in the polyvalent metal secondary battery which has precipitation saturated electrolyte solution as electrolyte solution, (B) is the discharge process in the polyvalent metal secondary battery which has precipitation saturated electrolyte solution as electrolyte solution The schematic explanatory drawing which shows is shown.

A multivalent metal secondary battery according to an embodiment of the present invention (hereinafter also referred to as “Embodiment 1”) includes a negative electrode including a negative electrode active material composed of a polyvalent metal having a standard electrode potential of −0.7 V or less. A multivalent metal secondary battery comprising: a positive electrode; and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive electrode active material made of a lithium compound.

In the multivalent metal secondary battery according to the first embodiment, a negative electrode including a negative electrode active material composed of a polyvalent metal having a standard electrode potential of −0.7 V or less and a positive electrode including a positive electrode active material composed of a lithium compound are used. Therefore, a high operating voltage can be secured and a large charge / discharge rate can be obtained. Moreover, since the negative electrode which consists of the said polyvalent metal is used for the polyvalent metal secondary battery which concerns on this Embodiment 1, a high energy density can be ensured, and also it is excellent in safety | security.

FIG. 1A shows a state during a discharge reaction of a multivalent metal secondary battery according to one embodiment of the present invention, and FIG. 1 shows a state during a charge reaction of the multivalent metal secondary battery according to one embodiment of the present invention. Shown in (B). In the figure, “LiR ¹ ” is a lithium compound, “M” is a polyvalent metal having a standard electrode potential of −0.7 V or less, “M ^{n +} ” is an n-valent polyvalent metal cation, “e” is an electron, “ne” represents n electrons, and “n” represents an integer of 2 to 4.

During the discharge reaction, the reaction of “M → M ^{n +} + ne” proceeds in the negative electrode 20 of the multivalent metal secondary battery 1, and the cation M ^{n + of the} polyvalent metal is desorbed from the negative electrode 20. The polyvalent metal cation M ^{n +} desorbed from the negative electrode active material of the negative electrode 20 of the multivalent metal secondary battery 1 is the same as the positive electrode active material (lithium compound LiR ¹ ) of the positive electrode 10 of the multivalent metal secondary battery 1. The cation M ^{n +} has a crystal structure that does not have a gap into which the cation M ^{n +} can be inserted, so that it is not substantially inserted into the positive electrode 10, but the lithium cation in the electrolytic solution 30 is inserted into the positive electrode 10 to generate a lithium compound. [Refer FIG. 1 (A)]. Therefore, during the discharge reaction, the positive electrode active material of the positive electrode 20 of the multivalent metal secondary battery 1 also functions as a separator. On the other hand, during the charging reaction, lithium is a base metal rather than the polyvalent metal that is the negative electrode active material of the negative electrode 20 of the multivalent metal secondary battery 1. When the lithium cation desorbed from the positive electrode active material 20 receives electrons from the negative electrode 20, the polyvalent metal cation in the electrolytic solution 30 receives electrons from the negative electrode 20 at a potential higher than the potential at which metallic lithium is deposited. Multivalent metals are deposited (see FIG. 1B). At this time, the reaction of “M ^{n ++} + ne → M” proceeds in the negative electrode 20 of the multivalent metal secondary battery 1, and the multivalent metal is deposited in the negative electrode 20. As described above, the multivalent metal secondary battery according to Embodiment 1 can satisfactorily perform the charge / discharge reaction even when the diaphragm (separator) is not provided between the positive electrode 10 and the negative electrode 20. Therefore, the multivalent metal secondary battery according to the present embodiment can be easily manufactured as compared with a secondary battery having a diaphragm (separator).

The multivalent metal secondary battery of Embodiment 1 is manufactured by, for example, housing a positive electrode and a negative electrode in a battery container, filling the battery container with an electrolyte, and then sealing the battery container body. can do. Since the material, size, and shape of the battery container vary depending on the use of the polyvalent metal secondary battery and the like, it is preferable to determine appropriately according to the use of the polyvalent metal secondary battery and the like.

The positive electrode is an electrode including a positive electrode active material made of the lithium compound. Such a positive electrode is an electrode in which a positive electrode material containing the positive electrode active material is supported on a current collector. The positive electrode can be manufactured, for example, by applying the positive electrode material to a current collector.

In the present specification, the “lithium compound” refers to a lithium compound having a crystal structure having no gap or position into which the cation of the polyvalent metal is inserted. Examples of the lithium compound include lithium transition metal oxides such as LiCoO ₂ , LiNiO ₂ , Li ₂ MnO ₃ , and LiMn ₂ O ₂ ; and olivine type crystal structures such as LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , and LiNiPO _4. Lithium transition metal phosphates; fluorine-containing lithium transition metal phosphates having an olivine crystal structure such as Li ₂ FePO ₄ F, Li ₂ MnPO ₄ F, Li ₂ CoPO ₄ F, Li ₂ NiPO ₄ F, etc. However, the present invention is not limited to such examples. These lithium compounds can be appropriately selected according to the use of the multivalent metal secondary battery, the width of the potential window of the electrolyte, the magnitude of the desired electromotive force, and the like.

The positive electrode material contains a positive electrode active material made of the lithium compound. Further, the positive electrode material may further contain a conductive additive and a binder as necessary.

Examples of the conductive auxiliary agent include powders of carbon materials such as acetylene black and graphite, but the present invention is not limited to such examples. Since the content rate of the conductive auxiliary agent in the positive electrode material varies depending on the type of conductive auxiliary agent and the like, it is preferable to determine appropriately according to the type of conductive auxiliary agent.

Examples of the binder include polyolefin resins such as polyethylene and polypropylene; fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, but the present invention is not limited to such examples. . Since the content of the binder in the positive electrode material varies depending on the type of the binder and the like, it is preferably determined as appropriate according to the type of the binder and the like.

Examples of the material constituting the current collector include platinum, aluminum, molybdenum, chromium, tungsten, and various amorphous metals, but the present invention is not limited to such examples. Examples of the shape of the current collector include a porous body, a plate, and a roll-shaped thin plate. However, the present invention is not limited to such an example.

Since the amount of the positive electrode material applied to the current collector varies depending on the use of the multivalent metal secondary battery and the like, it is preferably determined as appropriate according to the use of the multivalent metal secondary battery and the like.

The negative electrode is an electrode including a negative electrode active material made of a polyvalent metal having a standard electrode potential of −0.7 V or less. Such a negative electrode may be an electrode made of a polyvalent metal having a standard electrode potential of −0.7 V or less, or may be an electrode in which a negative electrode material containing the negative electrode active material is supported on a current collector. .

In this specification, “polyvalent metal” refers to a metal having a valence of 2 or more. Examples of the polyvalent metal having a standard electrode potential of −0.7 V or less include metallic calcium, metallic magnesium, metallic aluminum, metallic zinc, and the like, but the present invention is not limited to such examples. . Among these polyvalent metals having a standard electrode potential of −0.7 V or less, since there are many charge capacities stored per unit mass and charge capacities stored per unit volume, metallic calcium, metallic magnesium, metallic aluminum And zinc metal is preferred. Especially, since the energy density per unit mass and the energy density per unit volume are high, metallic magnesium is more preferable.

When the negative electrode is an electrode in which a negative electrode material containing the negative electrode active material is supported on a current collector, the negative electrode material may be a material containing a negative electrode active material made of the polyvalent metal. Moreover, the said negative electrode material may further contain the conductive support agent and the binder as needed. The conductive auxiliary agent and the binder in the negative electrode material are the same as the conductive auxiliary agent and the binder in the positive electrode material.

The electrolytic solution is not particularly limited as long as the electrolytic solution contains a solution containing a lithium cation and a cation of the polyvalent metal. The electrolytic solution is preferably a solution having a dielectric constant of 3 to 10 and capable of electrodepositing polyvalent metals. The dielectric constant is preferably 3 or more from the viewpoint of sufficiently dissolving a salt containing lithium cations and a salt containing polyvalent metal cations, and preferably 10 or less from the viewpoint of electrodeposition of polyvalent metals. is there. Moreover, it is preferable that the said electrolyte solution has a wide electric potential window from a viewpoint of suppressing the decomposition | disassembly at the time of charging / discharging reaction. Examples of the electrolytic solution include a lithium salt and a salt containing a polyvalent metal cation used for the negative electrode (hereinafter also referred to as “polyvalent metal salt”) such as tetrahydrofuran, methyltetraglyme, and cyclopentylmethyl ether. Although the electrolyte solution containing the solution dissolved in solvents, such as an organic solvent, is mentioned, this invention is not limited only to this illustration.

Examples of the lithium salt, for _example, those _{_{_{LiClO 4, LiAsF 6, LiPF 6}}} , Li 2 CO 3, LiBF 4, although an inorganic lithium salt such as LiAlF ₄ and the like, and the present invention is to be limited only to those exemplified is not.

Examples of the polyvalent metal salt include calcium salts such as calcium inorganic salts and calcium organic salts; magnesium salts such as magnesium inorganic salts and magnesium organic salts; aluminum salts such as aluminum inorganic salts and aluminum organic salts; Although zinc salts, such as a zinc organic salt, are mentioned, this invention is not limited only to this illustration. Among these polyvalent metal salts, magnesium salts are preferred because of their abundant resources. Specific examples of the magnesium salt include, for example, magnesium inorganic salt compounds such as magnesium chloride, magnesium bromide, magnesium iodide, magnesium perchlorate, magnesium tetrafluoroborate, magnesium hexafluorophosphate; bis (trifluoromethyl) Sulfonyl) imidomagnesium, magnesium benzoate, magnesium salicylate, magnesium phthalate, magnesium acetate, magnesium propionate, formula (x1):
R ₂ MgX (x1)
(Wherein R represents an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 or more carbon atoms, preferably 6 to 12 carbon atoms, and X represents a halogen atom)
Examples include magnesium organic salt compounds such as Grignard reagents represented by the following, but the present invention is not limited to such examples.

Examples of the solvent include water; ethers such as diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, cyclopentylmethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, methyltetraglyme, and dioxane. Compound; carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate; and lactone compounds such as γ-butyrolactone and γ-valerolactone, etc. It is not something.

When the electrolytic solution is an electrolytic solution containing a solution in which a lithium salt and a polyvalent metal salt are dissolved in a solvent, the amount of the lithium salt per 100 parts by mass of the solvent depends on the use of the polyvalent metal secondary battery, the positive electrode Since it varies depending on the type of lithium compound used as the active material, it is preferable to determine appropriately according to the use of the multivalent metal secondary battery, the type of lithium compound used as the positive electrode active material, and the like. Moreover, when the electrolytic solution is an electrolytic solution made of a solution in which a lithium salt and a polyvalent metal salt are dissolved in a solvent, the blending amount of the polyvalent metal salt per 100 parts by mass of the solvent is that of the polyvalent metal secondary battery. Since it varies depending on the use, the type of polyvalent metal used as the negative electrode active material, etc., it is preferable to determine appropriately according to the use of the polyvalent metal secondary battery, the type of polyvalent metal used as the negative electrode active material, and the like. The compounding ratio of lithium salt and polyvalent metal salt to the solvent (lithium salt / polyvalent metal (molar ratio)) varies depending on the use of the polyvalent metal secondary battery, the type of lithium salt and polyvalent metal salt, etc. It is preferable to determine appropriately according to the use of the polyvalent metal secondary battery, the type of lithium salt and polyvalent metal salt, and the like.

In addition, when the polyvalent metal salt is a magnesium salt, the electrolytic solution preferably contains aluminum chloride from the viewpoint of sufficiently ionizing magnesium ions.

A multivalent metal secondary battery according to another embodiment (hereinafter, also referred to as “embodiment 2”) of the present invention includes a negative electrode including a negative electrode active material made of a polyvalent metal having a standard electrode potential of −0.7 V or less. And an electrolyte solution interposed between the positive electrode and the negative electrode, the polyvalent metal is magnesium metal, and the positive electrode has the formula (I):
Mg ₂ Mo _6-p Cr _p A ₈ (I)
(In the formula, A represents a chalcogen atom, and p represents an integer of 1 to 5)
It is an electrode containing the positive electrode active material which consists of a chevrel compound which has the composition represented by these.

As shown in FIG. 2, the multivalent metal secondary battery according to Embodiment 2 includes a negative electrode including a negative electrode active material made of magnesium metal (see 21 in the figure) and a positive electrode active material made of the chevrel compound. Since the positive electrode (see 11 in the figure) is used, a high operating voltage can be secured and a high charge / discharge rate can be obtained. In addition, since the polyvalent metal secondary battery according to Embodiment 2 uses the negative electrode made of the polyvalent metal, a high energy density can be secured and the safety is excellent. In the multivalent metal secondary battery according to the second embodiment, the electrolytic solution 31 is an electrolytic solution made of a solution containing a lithium cation and a magnesium cation.

The positive electrode is an electrode including a positive electrode active material made of the chevrel compound. Such a positive electrode is an electrode in which a positive electrode material containing the positive electrode active material is supported on a current collector. The positive electrode can be manufactured, for example, by applying the positive electrode material to a current collector.

The positive electrode material contains a positive electrode active material made of the chevrel compound. Further, the positive electrode material may further contain a conductive additive and a binder as necessary.

The conductive auxiliary agent and the binder are the same as the conductive auxiliary agent and the binder in the multivalent metal secondary battery according to the first embodiment. Since the content rate of the conductive auxiliary agent in the positive electrode material varies depending on the type of conductive auxiliary agent and the like, it is preferable to determine appropriately according to the type of conductive auxiliary agent. Moreover, since the content rate of the binder in the positive electrode material varies depending on the type of the binder and the like, it is preferable to appropriately determine the content according to the type of the binder and the like.

The material constituting the current collector is the same as the conductive additive and the binder in the multivalent metal secondary battery according to the first embodiment. Moreover, since the application amount of the positive electrode material to the current collector varies depending on the use of the multivalent metal secondary battery and the like, it is preferable to appropriately determine according to the use of the multivalent metal secondary battery and the like.

In the formula (I), A is a chalcogen atom. As a chalcogen atom, a sulfur atom, a selenium atom, a tellurium atom etc. are mentioned, for example. In the formula (I), p is an integer of 1 to 5. Specific examples of the chevrel compound include Mg ₂ Mo ₅ CrS ₈ , Mg ₂ Mo ₄ Cr ₂ S ₈ , Mg ₂ Mo ₃ Cr ₃ S ₈ , Mg ₂ Mo ₂ Cr ₄ S ₈ , and Mg ₂ Mo ₁ Cr ₅ S. _{_{_{_{8, Mg 2 Mo 5 CrSe 8}}}} , Mg 2 Mo 4 Cr 2 Se 8, Mg 2 Mo 3 Cr 3 Se 8, Mg 2 Mo 2 Cr 4 Se 8, Mg 2 Mo 1 Cr 5 Se 8, Mg 2 Mo 5 CrTe ₈ , Mg ₂ Mo ₄ Cr ₂ Te ₈ , Mg ₂ Mo ₃ Cr ₃ Te ₈ , Mg ₂ Mo ₂ Cr ₄ Te ₈ , Mg ₂ Mo ₁ Cr ₅ Te _8, etc. It is not limited. Since the chevrel compound represented by the formula (I) has a mass smaller than that of Mg ₂ Mo ₆ S ₈ , the polyvalent compound provided with the positive electrode including the positive electrode active material composed of the chevrel compound represented by the formula (I) According to the metal secondary battery, a high energy density can be ensured.

In the multivalent metal secondary battery according to the second embodiment, the negative electrode is the same as the negative electrode in the multivalent metal secondary battery according to the first embodiment.

Examples of the electrolytic solution include an electrolytic solution containing a solution in which a magnesium salt is dissolved in a solvent, but the present invention is not limited to such examples. The magnesium salt and the solvent are the same as the magnesium salt and the solvent in the multivalent metal secondary battery according to the first embodiment. The electrolytic solution may further contain aluminum chloride from the viewpoint of sufficiently dissolving the magnesium salt. Since the compounding amount of the magnesium salt per 100 parts by mass of the solvent varies depending on the use of the polyvalent metal secondary battery, the type of the magnesium salt, etc., it is appropriately determined depending on the use of the polyvalent metal secondary battery, the type of magnesium salt, etc. It is preferable to determine.

The present invention provides a positive electrode active material for use in a multivalent metal secondary battery having a negative electrode made of a negative electrode active material made of metallic magnesium, and comprising a chevrel compound having a composition represented by formula (I). Substances are also included.

A conventional lithium ion battery employs a rocking chair type mechanism in which carrier ions move between both electrodes. On the other hand, in the multivalent metal secondary battery of the present invention, positive carrier ions (lithium ions) do not deposit on the negative electrode, and negative carrier ions (magnesium ions) do not intercalate inside the positive electrode active material. The carrier ions are stored in the electrolytic solution. Therefore, in order to store these carrier ions contained in the entire active material of the positive electrode and the negative electrode in the electrolytic solution, it is desirable that the solvent of the electrolytic solution is large. Therefore, in the multivalent metal secondary battery of the present invention, the electrolyte solution is preferably a precipitation saturated electrolyte solution from the viewpoint of reducing the amount of the electrolyte solution and improving the energy density. In the present specification, the “precipitation-containing saturated electrolyte solution” includes a salt precipitate composed of two types of carrier ions so that the amount of the carrier ions is equivalent to each electrode dose. Refers to electrolyte. Such a precipitation-containing saturated electrolyte includes, for example, a porous body composed of two kinds of salts (for example, MgCl ₂ , LiCl, etc.) as a separator between a positive electrode and a negative electrode, and pores of the porous body It can be obtained by adding a small amount of solvent sufficient to fill the part to the porous body. Here, the amount of the solvent added to the porous body is preferably determined as appropriate according to the type of salt constituting the porous body.

FIG. 10A shows a charging process in a polyvalent metal secondary battery having a precipitated saturated electrolyte as an electrolytic solution, and FIG. 10B shows a discharging process in a polyvalent metal secondary battery having a precipitated saturated electrolyte as an electrolytic solution. Show. In FIG. 10, a description will be given by taking as an example a multivalent metal secondary battery in which LiFePO ₄ (“LFP” in the figure) is used as the positive electrode active material. In the figure, LFP is LiFePO ₄ , Mg is magnesium, Mg ²⁺ is a magnesium cation, A ⁻ is an anion [eg, chloride ion (Cl ⁻ ), borofluoride ion (BF ₄ ⁻ ), hexafluorophosphate ion (PF ₆ ⁻ ) etc.], Li ⁺ represents a lithium cation, MgA ₂ represents a precipitate composed of a magnesium salt, and LiA represents a precipitate composed of a lithium salt.

In the saturated precipitation electrolyte containing two kinds of cations (lithium cation and polyvalent metal cation), the solubility of each cation in the solvent is different from each other, but the cation ratio in the saturated precipitation electrolyte is kept constant in the equilibrium state. It is.

In the charging process, as shown in FIG. 10A, lithium cations are desorbed from LiFePO ₄ (“LFP” in the figure) which is a positive electrode active material [see (1a) in FIG. 10A]. At this time, since the lithium cation is saturated in the precipitation saturated electrolyte, the reaction proceeds in a direction in which a precipitate (LiA) made of a lithium salt is generated (see (2b) in FIG. 10A). Magnesium is electrodeposited on the negative electrode (see (1b) in FIG. 10A). At this time, since the magnesium ion concentration of the saturated precipitation electrolyte decreases, the precipitate (MgA ₂ ) composed of a magnesium salt dissolves (see (2a) in FIG. 10 (A)), whereby magnesium cations and anions ( A) occurs. The lithium ions desorbed from the positive electrode and the anion (A) dissolved from the precipitate (MgA ₂ ) made of a magnesium salt form a salt and precipitate. On the other hand, in the discharging process, as shown in FIG. 10B, a process opposite to the charging process is performed. As a result, the equilibrium solubility of the two types of carrier ions in a small amount of solvent in the precipitation saturated electrolyte solution is maintained. Therefore, when the precipitation saturated solution is used as the electrolyte solution of the multivalent metal secondary battery of the present invention. Can reduce the amount of electrolyte and improve the energy density.

As described above, the multivalent metal secondary battery of the present invention has a high operating voltage and a high energy density, and is excellent in safety. Therefore, the multivalent metal secondary battery of the present invention can optimize energy supply and demand and develop an energy supply and demand system that can reduce environmental load, hybrid vehicles and electric vehicles that are more fuel efficient. It is useful for development, development of smaller and higher performance mobile devices.

Next, the present invention will be described in more detail based on examples. However, the present invention is not limited to such examples.

Example 1
Working electrode made of a platinum plate coated with 3 mg / cm ^{2 of} iron phosphate (FePO ₄ ) from which lithium cations are desorbed from a lithium compound (LiFePO ₄ ) in a glove box maintained in an argon gas atmosphere Electrode using a polished reference electrode made of metallic magnesium, a counter electrode made of polished metallic magnesium, and an electrolytic solution (a tetrahydrofuran solution containing 0.5M phenylmagnesium chloride and 0.25M aluminum chloride) Built. Cyclic voltammetry measurement was performed at a scanning speed of 0.1 mV / s using the obtained three-electrode cell and an electrochemical measurement device (trade name: SP-300, manufactured by BioLogic).

In Example 1, a working electrode for a lithium compound iron phosphate (LiFePO ₄₎ lithium cations from the desorbed (FePO ₄₎ as a host compound, and a reference electrode made of polished metal magnesium, consisting polished metal magnesium A cyclic voltammogram in the case of using a counter electrode is shown in FIG.

From the results shown in FIG. 3, since no cathode peak is observed, a magnesium cation is inserted into the working electrode made of a lithium compound (LiFePO ₄ ) containing iron phosphate (FePO ₄ ) as a host compound during the discharge reaction. I understand that it is not done.

Example 2
In a glove box maintained in an argon gas atmosphere, a working electrode made of platinum, a reference electrode made of polished metal magnesium, a counter electrode made of polished metal magnesium, an electrolyte [1M phenylmagnesium chloride (magnesium salt), A beaker cell using 0.2M aluminum chloride and a tetrahydrofuran solution containing 0.2M lithium tetrafluoroborate (LiBF ₄ ) (lithium salt) was constructed. Using the obtained beaker cell and an electrochemical measurement device (trade name: SP-300, manufactured by BioLogic), cyclic voltammetry measurement was performed at a scanning speed of 10 mV / s.

FIG. 4 shows a cyclic voltammogram when an electrolytic solution containing a lithium salt and a magnesium salt is used in Example 2.

From the results shown in FIG. 4, lithium dissolution [(A) in the figure], magnesium dissolution [(B)], magnesium precipitation [(C)], and lithium precipitation [FIG. It can be seen that (D)] occurs. Therefore, these results suggest that metal magnesium can be dissolved and deposited by charge / discharge reaction even when an electrolyte containing a lithium salt and a magnesium salt is used.

Example 3
A working electrode made of a platinum plate coated with a charged lithium compound (LiFePO ₄ ) at 3 mg / cm ² in a glove box kept in an argon gas atmosphere, and a reference electrode made of polished metallic magnesium , A counter electrode made of polished metal magnesium, and an electrolytic solution [a tetrahydrofuran solution containing 1M phenylmagnesium chloride (magnesium salt), 0.2M aluminum chloride, and 0.2M lithium tetrafluoroborate (LiBF ₄ ) (lithium salt)] And a beaker cell was constructed. Using the obtained beaker cell and an electrochemical measurement device (trade name: SP-300, manufactured by BioLogic), cyclic voltammetry measurement was performed at a scanning speed of 10 mV / s.

FIG. 5 shows a cyclic voltammogram when an electrolytic solution containing a lithium salt and a magnesium salt in Example 3 is used. In the figure, LFP represents the potential at the working electrode made of a platinum plate coated with a lithium compound (LiFePO ₄ ), and Mg represents the potential at the counter electrode.

From the results shown in FIG. 5, it can be seen that a plateau potential is observed near 2.3 V in the working electrode during the discharge reaction, and lithium cations are inserted into the host compound (FePO ₄ ) constituting the working electrode. . In addition, the change in the potential of the counter electrode indicates that the metal magnesium is dissolved and precipitated in the charge / discharge process, which indicates that the charge / discharge reaction is well performed. Therefore, from these results, during the discharge reaction, the cation of magnesium, which is a polyvalent metal, is not substantially inserted into the host compound (FePO ₄ ) constituting the working electrode, but the lithium cation is the host constituting the working electrode. While being inserted into the compound (FePO ₄ ), a lithium compound (LiFePO ₄ ) is generated, and during the charging reaction, it is suggested that metal magnesium, which is a polyvalent metal, is deposited before metal lithium is deposited. .

Example 4
A working electrode made of a platinum plate coated with a charged lithium compound (LiFePO ₄ ) at 3 mg / cm ² in a glove box kept in an argon gas atmosphere, and a reference electrode made of polished metallic magnesium , A counter electrode made of polished metal magnesium, and an electrolytic solution [a tetrahydrofuran solution containing 1M phenylmagnesium chloride (magnesium salt), 0.2M aluminum chloride, and 0.4M lithium tetrafluoroborate (LiBF ₄ ) (lithium salt)] And a beaker cell was constructed. Using the obtained beaker cell and an electrochemical measurement device (trade name: SP-300, manufactured by BioLogic), cyclic voltammetry measurement was performed at a scanning speed of 10 mV / s. Further, the cut-off potential was set to 1.3 V, and the charge / discharge characteristics were examined.

In Example 4, the cyclic voltammogram when using an electrolytic solution in which a lithium salt and a magnesium salt are blended is set in FIG. 6, the cutoff potential is set to 1.3 V, and the lithium salt and the magnesium salt are blended. FIG. 7 shows the result of examining the charge / discharge characteristics when the electrolytic solution is used.

From the results shown in FIGS. 6 and 7, the potential of the positive electrode is a potential corresponding to desorption and insertion of lithium cations from the lithium compound (LiFePO ₄ ), and the potential of the negative electrode is related to the dissolution and precipitation of magnesium metal. From the corresponding potential, it can be seen that the charge / discharge reaction is well performed. Further, the result shown in FIG. 6 indicates that the electromotive force can be increased because the potential (arrow in FIG. 6) when the current value changes to − or + is approximately 0V.

Example 5
In Example 3, the positive electrode active material after charging and discharging was collected and analyzed by X-ray diffraction.

FIG. 8 shows the results of X-ray diffraction analysis of the positive electrode active material after charging and discharging in Example 5.

From the results shown in FIG. 8, it can be seen that the X-ray diffraction pattern of the positive electrode active material after charging is the same as the X-ray diffraction pattern of the host compound (FePO ₄ ) constituting the working electrode. Further, the results shown in FIG. 8 show that the X-ray diffraction pattern of the positive electrode active material after discharge is the same as the X-ray diffraction pattern of the lithium compound (LiFePO ₄ ) constituting the working electrode. Therefore, it can be seen from these results that lithium cations are well desorbed and inserted in the working electrode during the charge / discharge reaction, and magnesium cations are not inserted during the discharge reaction.

In addition, theoretical capacity, electromotive force, and energy density were determined when a positive electrode containing a lithium compound (LiCoO ₂ , LiFePO ₄ or LiMn ₂ O ₄ ) and a negative electrode containing metal magnesium were used. As a control, theoretical capacity, electromotive force, and energy density were obtained when a positive electrode containing a lithium compound (LiCoO ₂ , LiFePO ₄ or LiMn ₂ O ₄ ) and a negative electrode containing carbon were used. The results are shown in Table 1.

From the results shown in Table 1, when using a positive electrode containing a lithium compound of any one of LiCoO ₂ , LiFePO ₄ and LiMn ₂ O ₄ and a negative electrode containing metallic magnesium, the energy density is LiCoO ₂ , LiFePO _4. It is expected that the energy density is higher than that when a positive electrode including any lithium compound of LiMn ₂ O ₄ and a negative electrode including carbon is used.

Based on the above results, according to a multivalent metal secondary battery comprising a negative electrode including a negative electrode active material composed of a polyvalent metal having a standard electrode potential of −0.7 V or less and a positive electrode including a positive electrode active material composed of a lithium compound. For example, a high operating voltage and a high energy density can be ensured, and excellent safety can be ensured. Therefore, a secondary battery for power storage, a hybrid vehicle, an electric vehicle, etc. It is suggested that it is suitable as a secondary battery, a secondary battery for mobile devices and the like.

Example 6
And Mg ₂ Mo, the Mo ₆ S ₈ is a Chevrel compound is substituted with _{_{_{_{Cr Mg 2 Mo 2 Cr 4 S}}}} 8 ( positive electrode active material) and carbon black (conductive auxiliary agent) and polyvinylidene fluoride (binder), Mixing was performed so that Mg ₂ Mo ₂ Cr ₄ S ₈ / carbon black / polyvinylidene fluoride (volume ratio) was 8/1/1 to obtain a positive electrode material. Next, in a glove box maintained in an argon gas atmosphere, the working electrode made of a platinum plate coated with the positive electrode material to 3 mg / cm ^2, and a reference electrode made of polished metal magnesium were polished. A three-electrode cell using a counter electrode made of metallic magnesium and an electrolytic solution [tetrahydrofuran solution containing 1M phenylmagnesium chloride (magnesium salt) and 0.2M aluminum chloride] was constructed. Cyclic voltammetry measurement was performed at a scanning speed of 0.1 mV / s or 10 mV / s using the obtained three-electrode cell and an electrochemical measuring device (trade name: SP-300, manufactured by BioLogic). I did it.

FIG. 9 shows a cyclic voltammogram when a positive electrode including a positive electrode active material made of a chevrel compound (Mg ₂ Mo ₂ Cr ₄ S ₈ ) is used in Example 6.

From the results shown in FIG. 9, it can be seen that a potential of about 1 V is the magnesium cation deinsertion potential on a magnesium basis. Therefore, from these results, it is suggested that a working voltage of 1 V can be obtained when a positive electrode including a positive electrode active material made of a chevrel compound (Mg ₂ Mo ₂ Cr ₄ S ₈ ) is used in a magnesium secondary battery. Is done.

Further, the _Mg 2 _Mo 4 _Cr 2 _{S 8} or _Mg 2 _Mo 2 _Cr 4 _{S 8} is a Chevrel compound of Mo of the _Mg 2 _Mo 4 _Cr 2 _{S 8} similarly to _Mg 2 _Mo 6 _{S 8} was replaced by Cr The theoretical capacity, electromotive force, and energy density were determined when a positive electrode containing and a negative electrode containing metallic magnesium were used. As a control, theoretical capacity, electromotive force, and energy density were determined when a positive electrode containing Mg ₂ Mo ₆ S ₈ and a negative electrode containing metal magnesium were used. The results are shown in Table 2.

From the results shown in Table _2, Mg 2 _Mo 6 compared with actual capacity of _{S _8,} Mg 2 _Mo 6 Mo, the _{S 8} which is a compound obtained by substituting the _{_{_{_{Cr Mg 2 Mo 4 Cr 2 S}}}} 8 and _Mg 2 Mo ₂ It is expected that the actual capacity of each of Cr ₄ S ₈ is high. From these results, in the multivalent metal secondary battery using metal magnesium as the negative electrode, the formula (I):
Mg ₂ Mo _6-p Cr _p A ₈ (I)
(In the formula, A represents a chalcogen atom, and p represents an integer of 1 to 5)
As a positive electrode active material of a multivalent metal secondary battery using metal magnesium as a negative electrode, a high energy density can be secured when a positive electrode including a positive electrode active material made of a chevrel compound having a composition represented by It is suggested that it can be used suitably.

Example 7
In a glove box kept in an argon gas atmosphere, a porous body composed of two kinds of salts (MgCl ₂ and LiCl) is sandwiched between a positive electrode made of LiFePO ₄ and a negative electrode made of polished metallic magnesium. Install. Next, a small amount of solvent (ether solvent such as tetrahydrofuran and glyme) is added to the porous body to form a saturated precipitation electrolyte solution, thereby obtaining a multivalent metal secondary battery. About the obtained polyvalent metal secondary battery, performance (such as a charge / discharge cycle test) is evaluated. As a result, it can be seen that the multivalent metal secondary battery can ensure high operating voltage and high energy density.

From the above results, according to the multivalent metal secondary battery provided with the negative electrode including the negative electrode active material composed of metallic magnesium and the positive electrode including the positive electrode active material composed of the chevrel compound having the composition represented by the formula (I), Since it is possible to ensure the operating voltage and high energy density and to ensure excellent safety, secondary batteries for power storage, in-vehicle secondary batteries used in hybrid vehicles, electric vehicles, etc. It is suggested that it is suitable as a secondary battery for mobile devices.

The embodiments and examples described above are described for facilitating understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the embodiment and examples is intended to include all design changes and equivalents belonging to the technical scope of the present invention. In addition, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are within the scope of the present invention.

Apart from the following claims, the following aspects are also included in the scope of the present invention.
(1) A negative electrode including a negative electrode active material made of a polyvalent metal having a standard electrode potential of −0.7 V or less, a positive electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode,
The polyvalent metal is magnesium metal;
The positive electrode has the formula (I):
Mg ₂ Mo _6-p Cr _p A ₈ (I)
(In the formula, A represents a chalcogen atom, and p represents an integer of 1 to 5)
A multivalent metal secondary battery comprising a positive electrode active material comprising a chevrel compound having a composition represented by: According to such a polyvalent metal secondary battery, since a negative electrode including a negative electrode active material made of metal magnesium and a positive electrode including a positive electrode active material made of the chevrel compound are used in combination, a high energy density and a high operating voltage are ensured. It is possible to obtain a large charge / discharge rate and is excellent in safety.

(2) A positive electrode active material for use in a polyvalent metal secondary battery including a negative electrode made of a negative electrode active material made of metallic magnesium,
Formula (I):
Mg ₂ Mo _6-p Cr _p A ₈ (I)
(In the formula, A represents a chalcogen atom, and p represents an integer of 1 to 5)
A positive electrode active material comprising a chevrel compound having a composition represented by: According to the positive electrode active material, since it is composed of the chevrel compound represented by the formula (I), a high energy density can be ensured.

DESCRIPTION OF SYMBOLS 1 Multivalent metal secondary battery 2 Multivalent metal secondary battery 10 Positive electrode 11 Positive electrode 20 Negative electrode 21 Positive electrode 30 Electrolytic solution 31 Electrolytic solution

Claims

A negative electrode including a negative electrode active material made of a polyvalent metal having a standard electrode potential of −0.7 V or less, a positive electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode;
The multivalent metal secondary battery, wherein the positive electrode is a positive electrode containing a positive electrode active material made of a lithium compound.
The multivalent metal secondary battery according to claim 1, wherein the electrolytic solution is an electrolytic solution containing a solution containing a lithium cation and a cation of the polyvalent metal.
The multivalent metal secondary battery according to claim 1 or 2, wherein the polyvalent metal is a metal selected from the group consisting of metallic calcium, metallic magnesium, metallic aluminum and metallic zinc.
The multivalent metal secondary battery according to claim 3, wherein the polyvalent metal is magnesium metal.