JP2018098172A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkali earth metal secondary battery capable of preventing decomposition of electrolyte.SOLUTION: The secondary battery includes: a first electrode; a second electrode; a first solid electrolyte containing an alkali earth metal which covers the first electrode; and an electrolyte containing a nonaqueous solvent and salt of the alkali earth metal dissolved in the nonaqueous solvent, which is filled in a space between the first electrode and the second electrode.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a secondary battery. The present disclosure particularly relates to alkaline earth metal secondary batteries.

  In recent years, practical use of alkaline earth metal secondary batteries is expected. For example, a magnesium secondary battery has a higher theoretical capacity density than a conventional lithium ion battery.

Patent Document 1 discloses a magnesium secondary battery having, as a positive electrode active material, a magnesium compound represented by the general formula: MgMSiO ₄ (wherein M is at least one of Fe, Cr, Mn, Co, and Ni). Is disclosed.

International Publication No. 2014/017461

  The present disclosure provides a technique capable of suppressing decomposition of an electrolytic solution in an alkaline earth metal secondary battery.

  A secondary battery according to one embodiment of the present disclosure includes a first electrode, a second electrode, a first solid electrolyte that covers the first electrode and contains an alkaline earth metal, and the first electrode. An electrolytic solution that fills a space between the electrode and the second electrode and contains a nonaqueous solvent and the alkaline earth metal salt dissolved in the nonaqueous solvent.

  According to one embodiment of the present disclosure, in an alkaline earth metal secondary battery, decomposition of the electrolytic solution can be suppressed.

FIG. 1 is a schematic cross-sectional view illustrating a configuration example of the secondary battery according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing a configuration of Modification 1 of the secondary battery according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing a configuration of Modification 2 of the secondary battery according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing a configuration of Modification Example 3 of the secondary battery according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing a configuration of Modification 4 of the secondary battery according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing a configuration of Modification Example 5 of the secondary battery according to the first embodiment. FIG. 7 is a schematic cross-sectional view illustrating a configuration example of the secondary battery according to the second embodiment. FIG. 8 is a schematic cross-sectional view showing the configuration of Modification 1 of the secondary battery according to the second embodiment. FIG. 9 is a schematic cross-sectional view showing a configuration of Modification 2 of the secondary battery according to the second embodiment. FIG. 10 is a diagram showing potential-current curves obtained by CV measurement in samples 1 to 4.

(Knowledge that became the basis of this disclosure)
Various positive electrode materials have been reported as one technique for improving the energy density of a magnesium secondary battery. For example, Patent Document 1 discloses a magnesium compound represented by MgMSiO ₄ (wherein M is at least one of Fe, Cr, Mn, Co, and Ni) as a positive electrode material.

  The standard electrode potential of magnesium is -2.36V. This value is more noble than the standard electrode potential of lithium -3.05V. Therefore, higher oxidation resistance is required for the electrolyte solution of the magnesium secondary battery than the electrolyte solution of the conventional lithium ion secondary battery. For example, a charge potential of 4.00 V on a magnesium basis corresponds to a charge potential of 4.69 V on a lithium basis. In the case of a conventional lithium ion secondary battery, this charging potential is high enough that the electrolytic solution is oxidatively decomposed. Therefore, when the charge potential of the positive electrode on a magnesium basis exceeds 4 V, higher oxidation resistance is required that exceeds the range that can be assumed for a conventional lithium ion secondary battery. However, there are few electrolyte solutions that satisfy such requirements in magnesium secondary batteries. In particular, when the potential of the positive electrode exceeds 4 V during charging, no electrolytic solution that satisfies such a requirement has been reported.

  The inventors focused on the fact that the electrolytic solution is decomposed by the exchange of electrons between the positive electrode and the electrolytic solution and / or between the negative electrode and the electrolytic solution, and studied means for suppressing the exchange of electrons. Until now, the present inventors have succeeded in developing a solid electrolyte thin film having ion conductivity of magnesium ions, which has not been reported in the past (for example, Japanese Patent Application Nos. 2006-161513 and 2017-139362). Japanese Patent Application No. 2017-139363). The present inventors have found that these solid electrolyte thin films have the property of blocking the movement of electrons while allowing the movement of magnesium ions, and have come up with the secondary battery described below.

  In addition, the above description does not limit the secondary battery which concerns on this indication to a magnesium secondary battery. Since the standard electrode potential of other alkaline earth metals (for example, Ca, Sr, or Ba) is also slightly more noble than the standard electrode potential of lithium, the present disclosure can be applied to alkaline earth metal secondary batteries. . For example, in various materials exemplified below, magnesium can be appropriately replaced with another alkaline earth metal. In addition, since the standard electrode potential of aluminum is more noble than the standard electrode potential of lithium ions, the present disclosure can be applied to an aluminum secondary battery.

(Definition of drawings and terms)
The present disclosure will be described with respect to particular embodiments and with reference to the drawings but the disclosure is not limited thereto but only by the claims. The drawings are only schematic and non-limiting. In the drawings, the size and shape of some of the components may be exaggerated for illustrative purposes and not drawn to scale. The dimensions and relative dimensions do not necessarily correspond to the actual implementation of the present disclosure.

  In this disclosure, the terms “first” and “second” are used to distinguish similar components, not to describe temporal or spatial order. Therefore, “first” and “second” can be exchanged as appropriate.

  In this disclosure, the terms “top”, “bottom”, etc. are used for illustrative purposes and do not necessarily describe relative positions. These terms are interchangeable under appropriate circumstances, and the various embodiments can operate in other orientations than those described or illustrated herein.

  In the present disclosure, the term “X disposed on Y” means that X is in a position in contact with Y, and the relative positional relationship between X and Y is expressed as follows. It is not limited to a specific orientation.

  Among the constituent elements described in the present disclosure, constituent elements that are not described in the independent claims indicating the highest concept are described as optional constituent elements.

(First embodiment)
[1. Configuration of secondary battery]
FIG. 1 is a schematic cross-sectional view showing the configuration of the secondary battery 100 according to the first embodiment.

  The secondary battery 100 includes a positive electrode 10, a negative electrode 20, an electrolytic solution 30, and a solid electrolyte layer 40. The negative electrode 20 is opposed to the positive electrode 10 at a distance. The solid electrolyte layer 40 covers the positive electrode 10. The electrolytic solution 30 is filled in a space between the positive electrode 10 and the negative electrode 20. The secondary battery 100 is charged and discharged as alkaline earth metal ions move between the positive electrode 10 and the negative electrode 20.

  The secondary battery 100 may further include, for example, a separator (not shown) that separates the solid electrolyte layer 40 and the negative electrode 20. In this case, the electrolytic solution 30 may be impregnated inside the separator.

  The shape of the secondary battery 100 is not limited to the example illustrated in FIG. 1, and may be, for example, a sheet type, a coin type, a button type, a stacked type, a cylindrical type, a flat type, or a square type.

[2. Positive electrode]
The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 is disposed on the positive electrode current collector 11 and includes a plurality of positive electrode active material particles 13. In other words, the plurality of positive electrode active material particles 13 are arranged on the positive electrode current collector 11. The upper surface of the positive electrode active material layer 12 is an uneven surface defined by the plurality of positive electrode active material particles 13.

The positive electrode current collector 11 is, for example, a metal sheet or a metal film. The positive electrode current collector 11 may be porous or non-porous. Examples of the metal material include aluminum, aluminum alloy, stainless steel, titanium, and titanium alloy. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 11. Alternatively, the positive electrode current collector 11 may be a transparent conductive film. Examples of transparent conductive films include indium tin oxide (ITO), indium zinc oxide (IZO), fluorine doped tin oxide (FTO), antimony doped tin oxide (ATO), and indium oxide (In ₂ O ₃ ). , Tin oxide (SnO ₂ ), and zinc oxide containing Al.

  The positive electrode active material particles 13 include, for example, a metal oxide containing an alkaline earth metal and a transition metal, a metal sulfide containing an alkaline earth metal and a transition metal, and a polyanion containing an alkaline earth metal and a transition metal. Including at least one selected from a salt compound and a fluorinated polyanion salt compound containing an alkaline earth metal and a transition metal, and the alkaline earth metal is, for example, at least selected from Mg, Ca, Sr and Ba The transition metal is selected from, for example, Mn, Co, Cr, V, Ni, and Fe. These materials can occlude and release alkaline earth metal ions.

When the secondary battery 100 is a magnesium secondary battery, examples of the material of the positive electrode active material particles 13 include MgM ₂ O ₄ (where M is at least one selected from Mn, Co, Cr, Ni, and Fe). MgMO ₂ (wherein M is at least one selected from Mn, Co, Cr, Ni and Al), MgMSiO ₄ (wherein M is selected from Mn, Co, Ni and Fe) that is at least one), and _{Mg x M y AO z F w} ( however, M is a transition metal, Sn, Sb or an in, a is P, Si or S, 0 <x ≦ 2 0.5 ≦ y ≦ 1.5, z is 3 or 4, 0.5 ≦ w ≦ 1.5).

When the secondary battery 100 is a calcium secondary battery, examples of the material of the positive electrode active material particles 13 include CaM ₂ O ₄ and CaMO ₂ (where M is at least one selected from Mn, Co, Ni, and Al). Species).

The positive electrode active material particles 13 are not limited to the above materials, and may not contain an alkaline earth metal, for example. For example, the positive electrode active material particles 13 may be graphite fluoride, metal oxide, or metal halide. The metal oxide and metal halide may contain at least one selected from, for example, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. For example, the positive electrode active material particles 13 may be a sulfide such as Mo ₆ S ₈ or a chalcogenide compound such as Mo ₉ Se ₁₁ .

The positive electrode active material particles 13 may be a material whose electrode potential with respect to an alkaline earth metal is greater than + 4V, for example. In this case, the secondary battery 100 can achieve a capacity of more than 4V while suppressing oxidative decomposition of the electrolyte solution 30 as will be described later. Examples of such a material include MgNiSiO ₄ and MgCoSiO ₄ when the secondary battery 100 is a magnesium secondary battery.

  In addition to the above materials, the positive electrode active material layer 12 may contain a conductive material and / or a binder as necessary.

  Examples of the conductive material include a carbon material, a metal, and a conductive polymer. Examples of the carbon material include graphite such as natural graphite (eg, lump graphite, flake graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, and carbon fiber. Examples of metals include copper, nickel, aluminum, silver, and gold. These materials may be used alone, or a plurality of types may be mixed and used.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resins such as fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfone. EPDM rubber, and natural butyl rubber (NBR). These materials may be used alone, or a plurality of types may be mixed and used. The binder may be, for example, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR).

  Examples of the solvent for dispersing the positive electrode active material particles 13, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N -Dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. For example, a thickener may be added to the dispersant. Examples of the thickener include carboxymethyl cellulose and methyl cellulose.

  The positive electrode 10 is formed as follows, for example. First, the positive electrode active material particles 13, the conductive material, and the binder are mixed. Next, an appropriate solvent is added to the mixture, whereby a paste-like positive electrode mixture is obtained. Next, the positive electrode mixture is applied to the surface of the positive electrode current collector 11 and dried. Thereby, the positive electrode 10 is obtained. The dried positive electrode mixture may be rolled together with the positive electrode current collector 11 in order to increase the electrode density.

  The positive electrode 10 may be a thin film. The film thickness of the positive electrode 10 may be 500 nanometers or more and 20 micrometers or less, for example.

[3. Negative electrode]
The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 is disposed on the negative electrode current collector 21 and includes a plurality of negative electrode active material particles 23. In other words, the plurality of negative electrode active material particles 23 are arranged on the negative electrode current collector 21. The lower surface of the negative electrode active material layer 22 is an uneven surface defined by the plurality of negative electrode active material particles 23.

  The negative electrode current collector 21 is, for example, a metal sheet or a metal film. The negative electrode current collector 21 may be porous or non-porous. Examples of the metal material include aluminum, aluminum alloy, stainless steel, titanium, and titanium alloy. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 21.

  Examples of the negative electrode active material particles 23 include metals, carbon, metal oxides, carbon intercalation compounds, and sulfides. The negative electrode active material particles 23 contain, for example, an alkaline earth metal or an alloy containing an alkaline earth metal. Alternatively, the negative electrode active material particles 23 may be a material that can occlude and release alkaline earth metal ions.

  When the secondary battery 100 is a magnesium secondary battery, examples of the material of the negative electrode active material particles 23 include magnesium, tin, bismuth, antimony, and magnesium alloy. The magnesium alloy contains, for example, magnesium and at least one selected from tin, bismuth, titanium, manganese, lead, antimony, aluminum, silicon, gallium, and zinc.

  When the secondary battery 100 is a calcium secondary battery, examples of the material of the negative electrode active material particles 23 include calcium and a calcium alloy.

  In addition to the above materials, the negative electrode active material layer 22 may include a conductive material and / or a binder as necessary. As the conductive material, the binder, the solvent, and the thickener in the negative electrode active material layer 22, the materials described for the positive electrode active material layer 12 can be appropriately used.

  The negative electrode 20 can be formed by a method similar to the method for forming the positive electrode 10 described above.

  The negative electrode 20 may be a thin film. The film thickness of the negative electrode 20 may be, for example, 500 nanometers or more and 20 micrometers or less.

[4. Solid electrolyte layer]
The solid electrolyte layer 40 is a single layer disposed on the positive electrode active material layer 12 and collectively covers the plurality of positive electrode active material particles 13. The solid electrolyte layer 40 is formed along an uneven surface defined by the plurality of positive electrode active material particles 13.

  The solid electrolyte layer 40 contains an alkaline earth metal, and can move alkaline earth metal ions according to an electric field. On the other hand, the solid electrolyte layer 40 blocks the movement of electrons between the positive electrode active material particles 13 and the electrolytic solution 30.

  The solid electrolyte layer 40 is composed of an inorganic solid electrolyte. The solid electrolyte layer 40 may contain a polyanion composed of at least one of oxygen and nitrogen and at least one of phosphorus and silicon, in addition to the alkaline earth metal.

When the secondary battery 100 is a magnesium secondary battery, examples of the material of the solid electrolyte layer 40 include magnesium nitride phosphate, Mg _x SiO _y N _z (where 1 <x <2, 3 <y <5, 0 _{≦ z <1), Mg x} M y SiO z ( however, M is at least one selected Ti, Zr, Hf, Ca, from the group consisting of Sr and Ba, 0 <x <2,0 < y <2, 3 <z <6), Mg _2-1.5x Al _x SiO ₄ (where 0.1 ≦ x ≦ 1), Mg _2-1.5x-0.5y Al _xy Zn _y SiO ₄ (where 0. 5 ≦ x ≦ 1, 0.5 ≦ y ≦ 0.9, xy ≧ 0, x + y ≦ 1), MgZr ₄ (PO ₄ ) ₆ , MgMPO ₄ (where M is selected from Zr, Nb and Hf) Mg _1-x A _x M (M′O ₄ ) ₃ (where A is selected from Ca, Sr, Ba, and Ra). At least one, M is at least one selected from Ze and Hf, M ′ is at least one selected from W and Mo, 0 ≦ x <1), and Mg (BH ₄ ) (NH ₂ ).

The solid electrolyte layer 40 is, for example, magnesium phosphate nitride acid _{or,, Mg x M y SiO z} ( however, M is at least one selected Ti, Zr, Hf, Ca, from the group consisting of Sr and Ba, You may contain 0 <x <2, 0 <y <2, 3 <z <6). Since these materials exhibit a relatively high conductivity, decomposition of the electrolytic solution 30 can be suppressed without limiting the charge / discharge reaction. In order to further increase the conductivity, the solid electrolyte layer 40 contains, for example, magnesium nitride phosphate or Mg _x Ca _y SiO _z (0 <x <2, 0 <y <2, 3 <z <6). May be. Alternatively, from the viewpoint of low activation energy, the solid electrolyte layer 40 is, for example, Mg _x M _y SiO _z (however, M is Zr or Ca, 0 <x <2,0 < y <2,3 <z <6) may be contained.

  As a detailed description of each material, Japanese Patent Application No. 16-161513, Japanese Patent Application No. 2017-139362, and Japanese Patent Application No. 2017-139363 are incorporated by reference into the present disclosure.

When the secondary battery 100 is another alkaline earth metal secondary battery, examples of the material of the solid electrolyte layer 40 include AM (M′O ₄ ) ₃ (where A is Ca, Sr, Ba, and Ra). And M is at least one selected from Ze and Hf, and M ′ is at least one selected from W and Mo).

  The solid electrolyte layer 40 can be formed by, for example, a physical deposition method or a chemical deposition method. Examples of physical deposition methods include sputtering, vacuum evaporation, ion plating, and pulsed laser deposition (PLD). Examples of chemical deposition methods include atomic layer deposition (ALD), chemical vapor deposition (CVD), liquid phase deposition, sol-gel, metal organic compound decomposition (MOD), and spray pyrolysis (SPD). ) Method, doctor blade method, spin coating method, and printing technique. Examples of the CVD method include a plasma CVD method, a thermal CVD method, and a laser CVD method. The liquid phase film forming method is, for example, wet plating, and examples of wet plating include electrolytic plating, immersion plating, and electroless plating. Examples of printing techniques include inkjet methods and screen printing.

  The solid electrolyte layer 40 can be formed, for example, without annealing. Therefore, the manufacturing method can be simplified, the manufacturing cost can be reduced, and the yield can be improved.

  The solid electrolyte layer 40 may be a crystalline body or an amorphous body. The film thickness of the solid electrolyte layer 40 may be, for example, 200 nanometers or less. When the solid electrolyte layer 40 is an amorphous ultrathin film, the film thickness may be, for example, 1 nanometer or more and 3 nanometers or less. In addition, when the solid electrolyte layer 40 is an amorphous body, the solid electrolyte layer 40 can be easily formed along the uneven surface of the positive electrode active material layer 12.

[5. Electrolyte]
The electrolytic solution 30 is filled in a space between the positive electrode 10 and the negative electrode 20. The electrolytic solution 30 may further fill a gap between the plurality of positive electrode active material particles 13 or may fill a gap between the plurality of negative electrode active material particles 23.

  The electrolytic solution 30 is a liquid in which an alkaline earth metal salt is dissolved in a nonaqueous solvent, and can move alkaline earth metal ions according to an electric field.

  Examples of non-aqueous solvent materials include cyclic ethers, chain ethers, cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, pyrocarbonates, phosphate esters, borate esters, sulfuric acid Examples include esters, sulfites, cyclic sulfones, chain sulfones, nitriles, and sultone.

  Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3, Examples include 5-trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether, and derivatives thereof. Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl Phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1, 1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetrae Glycol dimethyl, and derivatives thereof.

  Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,4-trifluoroethylene carbonate, fluoromethylethylene carbonate, trifluoro Examples include methylethylene carbonate, 4-fluoropropylene carbonate, 5-fluoropropylene carbonate, and derivatives thereof. Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, and derivatives thereof.

  Examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone, γ-caprolactone, ε-caprolactone, α-acetolactone, and derivatives thereof. Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and derivatives thereof.

  Examples of pyrocarbonates include diethyl pyrocarbonate, dimethyl pyrocarbonate, di-tert-butyl dicarbonate, and derivatives thereof. Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, hexamethylphosphamide, and derivatives thereof. Examples of boric acid esters include trimethyl borate, triethyl borate, and derivatives thereof. Examples of the sulfate ester include trimethyl sulfate, triethyl sulfate, and derivatives thereof. Examples of sulfites include ethylene sulfite and its derivatives.

  Examples of cyclic sulfones include sulfolane and its derivatives. Examples of chain sulfone include alkyl sulfone and derivatives thereof. Examples of nitriles include acetonitrile, valeronitrile, propionitrile, trimethylacetonitrile, cyclopentanecarbonitrile, adiponitrile, pimelonitrile and derivatives thereof. Examples of sultone include 1,3-propane sultone and its derivatives.

  As the solvent, only one type of the above substances may be used, or two or more types may be used in combination.

When the secondary battery 100 is a magnesium secondary battery, examples of magnesium salts include MgBr ₂ , MgI ₂ , MgCl ₂ , Mg (AsF ₆ ) ₂ , Mg (ClO ₄ ) ₂ , Mg (PF ₆ ) ₂ , Mg (BF ₄ ) ₂ , Mg (CF ₃ SO ₃ ) ₂ , Mg [N (CF ₃ SO ₂ ) ₂ ] ₂ , Mg (SbF ₆ ) ₂ , Mg (SiF ₆ ) ₂ , Mg [C (CF ₃ SO _{2) 3] 2, Mg [} N (FSO 2) 2] 2, Mg [N (C 2 F 5 SO 2) 2] 2, MgB 10 Cl 10, MgB 12 Cl 12, Mg [B (C 6 F 5 ₄ ] ₂ , Mg [B (C ₆ H ₅ ) ₄ ] ₂ , Mg [N (SO ₂ CF ₂ CF ₃ ) ₂ ] ₂ , Mg [BF ₃ C ₂ F ₅ ] ₂ , and Mg [PF ₃ ( CF ₂ CF ₃ ) ₃ ] ₂ . As a magnesium salt, only 1 type may be used among said substance, and 2 or more types may be used in combination.

  When the secondary battery 100 is a calcium secondary battery, an example of the calcium salt is calcium perchlorate.

  For example, the electrolytic solution 30 is filled in a space between the positive electrode 10 and the negative electrode 20 facing each other in an exterior (not shown), and impregnates the positive electrode 10, the solid electrolyte layer 40, and the negative electrode 20.

[6. effect]
In the case of a conventional secondary battery that does not have a solid electrolyte layer, as described above, electrons may be transferred at the contact surface between the positive electrode and the electrolytic solution, and the electrolytic solution may be decomposed. On the other hand, since the secondary battery 100 has the solid electrolyte layer 40 covering the positive electrode 10, while allowing the alkaline earth metal ions to move between the positive electrode 10 and the electrolytic solution 30, Movement can be deterred. Therefore, decomposition of the electrolytic solution 30 can be suppressed while maintaining the electrical characteristics of the secondary battery 100. As a result, the secondary battery 100 can be stabilized and the life can be extended.

  The solid electrolyte layer 40 may not completely prevent the contact between the positive electrode 10 and the electrolytic solution 30. For example, the contact area between the positive electrode 10 and the electrolytic solution 30 may be smaller than that in the configuration without the solid electrolyte layer 40. It only has to be reduced.

  In particular, when the charging potential of the positive electrode 10 exceeds 4 V when the secondary battery 100 is charged, the action of suppressing the decomposition of the electrolytic solution 30 works more significantly. For example, the designer can use, for the secondary battery 100, an electrolyte material that is considered to be unusable in a region where the charging potential exceeds 4V. For example, a designer can employ a nonaqueous solvent used in a conventional lithium ion secondary battery as a nonaqueous solvent for a high-capacity alkaline earth metal secondary battery. Therefore, the degree of freedom in material selection for the secondary battery 100 is increased.

  In the secondary battery 100, the electrolytic solution 30 and the solid electrolyte layer 40 can function as an electrolyte. For example, the designer can make the electrolytic solution 30 function as a main component of the electrolyte by adjusting the distance between the negative electrode 20 and the solid electrolyte layer 40 and the film thickness of the solid electrolyte layer 40. Thereby, for example, a secondary battery having an electrolyte having excellent electrical characteristics can be realized as compared with a secondary battery in which the electrolyte is all solid (that is, an all-solid secondary battery).

  In the secondary battery 100, the solid electrolyte layer 40 covers the positive electrode active material layer 12 so as to collectively cover the plurality of positive electrode active material particles 13. Therefore, the manufacturing method of the solid electrolyte layer 40 is easier than that of, for example, a solid electrolyte coating 40c described later. Further, for example, when the positive electrode active material layer 12 includes a conductive material, the solid electrolyte layer 40 can cover the conductive material in addition to the plurality of positive electrode active material particles 13. Therefore, the solid electrolyte layer 40 can also suppress a reaction between the conductive material and the electrolytic solution 30.

  In the case where the secondary battery 100 is a magnesium secondary battery, the following new effects can be obtained.

  When the positive electrode and the electrolytic solution are in contact with each other in the magnesium secondary battery, a magnesium compound (for example, magnesium oxide) may be deposited on the contact surface. This deposit is a passive film and inhibits the migration of magnesium ions between the positive electrode and the electrolyte. Therefore, the magnesium secondary battery may not be able to be charged / discharged due to the deposited passive film.

  In addition, it is known that a lithium compound precipitates also in a lithium ion secondary battery. However, since this precipitate has ionic conductivity, it does not inhibit the movement of lithium ions. Therefore, the problem of the passive film is a problem peculiar to the magnesium secondary battery that does not occur in the lithium ion secondary battery.

  Therefore, when the secondary battery 100 is a magnesium secondary battery, the solid electrolyte layer 40 suppresses the generation of a passive film on the positive electrode 10 by covering the positive electrode 10, thereby stabilizing the secondary battery 100. Charge / discharge operation can be guaranteed.

[7. Various modifications]
[7-1. Modification 1]
FIG. 2 is a schematic cross-sectional view showing a configuration of a secondary battery 100a as Modification 1 of the secondary battery according to the first embodiment.

  The secondary battery 100 a includes a positive electrode 10, a negative electrode 20, an electrolytic solution 30, a solid electrolyte layer 40, and a solid electrolyte layer 50. The solid electrolyte layer 50 covers the negative electrode 20. In the secondary battery 100a, each configuration excluding the solid electrolyte layer 50 is the same as the corresponding configuration of the secondary battery 100, and thus description thereof is omitted.

  The solid electrolyte layer 50 is a single layer disposed on the negative electrode active material layer 22 and collectively covers the plurality of negative electrode active material particles 23. The solid electrolyte layer 50 is formed along an uneven surface defined by the plurality of negative electrode active material particles 23.

  The material of the solid electrolyte layer 50 is, for example, the above [4. It can be selected from the various materials listed in [Solid Electrolyte Layer]. The method for forming the solid electrolyte layer 50 is, for example, [4. It can be selected from various forming methods listed in [Solid Electrolyte Layer].

  The solid electrolyte layer 50 may be a crystalline body or an amorphous body. The film thickness of the solid electrolyte layer 40 may be, for example, 20 micrometers or less. The film thickness of the solid electrolyte layer 40 may be, for example, 5 nanometers or more and 200 nanometers or less. When the solid electrolyte layer 40 is an amorphous ultrathin film, the film thickness may be, for example, 1 nanometer or more and 3 nanometers or less. In addition, when the solid electrolyte layer 50 is an amorphous body, the solid electrolyte layer 50 is easily formed along the uneven surface of the negative electrode active material layer 22.

  The secondary battery 100a includes the above-mentioned [6. In addition to the various effects described in [Effect], the effects due to the solid electrolyte layer 50 are exhibited. The effects resulting from the solid electrolyte layer 50 are as described in [6. In the description of [Effect], it can be understood by appropriately replacing “solid electrolyte layer 40” and “positive electrode 10” with “solid electrolyte layer 50” and “negative electrode 20”, respectively. In short, the solid electrolyte layer 50 can suppress reductive decomposition of the electrolyte solution 30 by suppressing contact between the negative electrode 20 and the electrolyte solution 30. Further, when the secondary battery 100 a is a magnesium secondary battery, the solid electrolyte layer 50 can suppress the generation of a passive film on the negative electrode 20.

[7-2. Modification 2]
FIG. 3 is a schematic cross-sectional view showing a configuration of a secondary battery 100b as Modification 2 of the secondary battery according to the first embodiment.

  The secondary battery 100 b includes a positive electrode 10, a negative electrode 20, an electrolytic solution 30, and a solid electrolyte layer 50. That is, the secondary battery 100b has a configuration in which the solid electrolyte layer 40 is removed from the secondary battery 100a. Since each structure of the secondary battery 100b is the same as the corresponding structure of the secondary battery 100, the description thereof is omitted.

  The secondary battery 100b includes the above [7-1. The same effects as the effects caused by the solid electrolyte layer 50 described in the modification 1] are obtained.

[7-3. Modification 3]
FIG. 4 is a schematic cross-sectional view illustrating a configuration of a secondary battery 100c as a third modification of the secondary battery according to the first embodiment.

  The secondary battery 100 c includes a positive electrode 10, a negative electrode 20 a, an electrolytic solution 30, and a solid electrolyte layer 40. The negative electrode 20a includes a negative electrode current collector 21 and a negative electrode active material layer 22a. In the secondary battery 100c, each configuration excluding the negative electrode active material layer 22a is the same as the corresponding configuration of the secondary battery 100, and thus description thereof is omitted.

  The negative electrode active material layer 22 a is a flat layer disposed on the negative electrode current collector 21. The material of the negative electrode active material layer 22a is, for example, [3. It can be selected from various materials listed in [Negative Electrode]. The negative electrode active material layer 22a can be formed by, for example, a physical deposition method or a chemical deposition method. The negative electrode active material layer 22a may be, for example, a metal layer or an alloy layer.

  The secondary battery 100c is the same as the above [6. The same effects as the various effects described in [Effect] are produced.

[7-4. Modification 4]
FIG. 5 is a schematic cross-sectional view showing a configuration of a secondary battery 100d as Modification 4 of the secondary battery according to the first embodiment.

  The secondary battery 100d includes a positive electrode 10, a negative electrode 20a, an electrolytic solution 30, a solid electrolyte layer 40, and a solid electrolyte layer 50a. Each configuration of the secondary battery 100d excluding the solid electrolyte layer 50a is the same as the corresponding configuration of the secondary battery 100c, and thus the description thereof is omitted.

  The solid electrolyte layer 50a is a flat layer disposed on the negative electrode active material layer 22a. The material and the formation method of the solid electrolyte layer 50a are described in [4. As described in [Solid electrolyte layer].

  The secondary battery 100d has the above [7-1. The same effects as the various effects described in the first modification are obtained.

[7-5. Modification 5]
FIG. 6 is a schematic cross-sectional view showing a configuration of a secondary battery 100e as Modification 5 of the secondary battery according to the first embodiment.

  The secondary battery 100e includes a positive electrode 10, a negative electrode 20a, an electrolytic solution 30, and a solid electrolyte layer 50a. That is, the secondary battery 100e has a configuration in which the solid electrolyte layer 40 is removed from the secondary battery 100d. Since each structure of the secondary battery 100e is the same as the corresponding structure of the secondary battery 100d, description thereof is omitted.

  The secondary battery 100e includes the above [7-1. The same effects as the effects caused by the solid electrolyte layer 50 described in the modification 1] are obtained.

[8. Experiment]
The experiment described below confirmed that the electrode on which the solid electrolyte was formed can suppress decomposition of the electrolytic solution.

[8-1. Sample preparation]
[8-1-1. Sample 1]
As Sample 1, a cell provided with a working electrode having a solid electrolyte membrane formed on its surface, a counter electrode, and a reference electrode was prepared.

A working electrode and a solid electrolyte membrane were produced as follows. First, a 200 nm thick V ₂ O ₅ film was formed on a Pt / Ti / SiO ₂ substrate by a pulse laser deposition (PLD) method. Regarding the film forming conditions, the substrate temperature was 350 degrees, the laser intensity was 100 mJ, the repetition frequency was 20 Hz, and the oxygen partial pressure was 18 Pa. Thereafter, a solid electrolyte film having a thickness of 2.5 nm was formed on the V ₂ O ₅ film by high-frequency magnetron sputtering using Mg ₂ SiO ₄ and ZrSiO ₄ as targets. The substrate temperature was room temperature. The sputtering gas was an argon-oxygen mixed gas in which 5% oxygen gas was mixed with argon gas, and the gas pressure was 0.67 Pa. The sputtering powers of Mg ₂ SiO ₄ and ZrSiO ₄ were 50 W (RF) and 200 W (RF), respectively. The composition of the formed solid electrolyte was Mg _0.67 Zr _1.25 SiO _5.22 .

  As the counter electrode, Mg foil (manufactured by Niraco) having a thickness of 0.25 mm, a width of 3 mm, and a length of 30 mm was used.

  As the reference electrode, an Ag / AgCl double junction reference electrode (manufactured by EC Frontier, model number RE-10A) was used. As an internal solution of the reference electrode, an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which 0.01 mol / L of silver bis (trifluoromethanesulfonyl) imide (Ag (TFSI)) was dissolved in acetonitrile was used.

As the cell, a micro analysis cell (manufactured by EC Frontier, model number VB7) was used. As an electrolytic solution filling the cell, an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which 0.5 mol / L magnesium bis (trifluoromethanesulfonyl) imide (Mg (TFSI) ₂ ) was dissolved in triethylene glycol dimethyl ether was used.

[8-1-2. Sample 2]
Sample 2 was the same as Sample 1 except that the thickness of the solid electrolyte membrane was 1 nm.

[8-1-3. Sample 3]
Sample 3 was the same as Sample 1 except that no solid electrolyte membrane was formed.

[8-1-4. Sample 4]
Sample 4 was the same as Sample 1 except that the V ₂ O ₅ film and the solid electrolyte film were not formed.

[8-2. CV measurement]
Samples 1 to 4 were placed in a glove box having a dew point of less than −80 ° C. and an oxygen concentration of less than 1 ppm, and an electrochemical analyzer (model number ALS660E manufactured by BAS Co., Ltd.) was used. Cyclic voltammetry (CV) measurement was performed at 1 mV / sec.

  FIG. 10 shows the results of CV measurement in samples 1 to 4. The horizontal axis represents the potential of the working electrode with reference to the reference electrode, and the vertical axis represents the current flowing through the working electrode. As shown in FIG. 10, the electrolytes of Samples 3 and 4 were oxidatively decomposed at around 3.3V, whereas the electrolytes of Samples 1 and 2 were not oxidatively decomposed at around 3.7V. This indicates that the solid electrolyte provided on the working electrode in Samples 1 and 2 suppressed the oxidative decomposition of the electrolytic solution. Further, in Sample 1, the electrolytic solution was not oxidatively decomposed even when the voltage exceeded 4.0V.

  In FIG. 10, the graph of sample 3 shows the peak of the anode current near 2.8V, while the graphs of sample 1 and 2 show the peaks around 3.0 and 3.1V, respectively. From these results, it is considered that the peak shift amount is caused by the resistance of the solid electrolyte membrane.

  Therefore, in order to reduce the shift amount of the peak of the anode current, the secondary battery according to the present embodiment has a reduced solid electrolyte membrane thickness and / or increased solid electrolyte membrane conductivity. It may be designed as follows. For example, the thickness of the solid electrolyte may be designed to be 10 nm or less, and further 3 nm or less. Alternatively, for example, a material having a relatively high conductivity may be selected as the solid electrolyte material. Thereby, decomposition | disassembly of electrolyte solution can be suppressed, without limiting an electrode reaction.

(Second Embodiment)
[1. Configuration of secondary battery]
FIG. 7 is a schematic cross-sectional view showing the configuration of the secondary battery 200 according to the second embodiment.

  The secondary battery 200 has the same configuration as the secondary battery 100 described in the first embodiment except for the positive electrode 10c and the solid electrolyte coating 40c.

  The positive electrode 10c includes a positive electrode current collector 11 and a positive electrode active material layer 12c. The positive electrode active material layer 12 c is disposed on the positive electrode current collector 11 and includes a plurality of positive electrode active material particles 13. Each surface of the plurality of positive electrode active material particles 13 is covered with a solid electrolyte coating 40c. In other words, the positive electrode 10c is covered with a solid electrolyte composed of a plurality of solid electrolyte coatings 40c.

[2. Positive electrode and solid electrolyte coating]
Since the secondary battery 200 is the same as that described in the first embodiment except for the shape of the solid electrolyte and the method for forming the solid electrolyte and the positive electrode, description thereof is omitted. Specifically, the material of the solid electrolyte coating 40c is, for example, [4. It can be selected from the various materials listed in [Solid Electrolyte Layer].

  The solid electrolyte coating 40c may be a crystalline body or an amorphous body. In the latter case, the solid electrolyte coating 40c is easily formed along the shape of the positive electrode active material particles 13, and the coverage is improved. The film thickness of the solid electrolyte coating 40c may be, for example, 1 nanometer or more and 200 nanometers or less.

  The positive electrode 10c and the solid electrolyte coating 40c are formed as follows, for example.

  First, the surface of the positive electrode active material particles 13 is coated with a solid electrolyte, thereby forming the solid electrolyte coating 40c. Thereafter, the coated positive electrode active material particles 13, the conductive material, and the binder are mixed. Next, an appropriate solvent is added to the mixture, whereby a paste-like positive electrode mixture is obtained. Next, the positive electrode mixture is applied to the surface of the positive electrode current collector 11 and dried. Thereby, the positive electrode 10c is obtained.

  The solid electrolyte coating 40c may be formed, for example, by depositing a solid electrolyte material by the above physical deposition method or chemical deposition method while moving the positive electrode active material particles 13. Alternatively, the solid electrolyte coating 40c may be formed by, for example, a sol-gel method or the liquid phase film forming method described above.

[3. effect]
The secondary battery 200 has the same effects as the various effects described in the first embodiment. Specifically, [6. In the description of [Effect], it can be understood by appropriately replacing “solid electrolyte layer 40” with “solid electrolyte coating 40c”.

  In the secondary battery 200, each of the plurality of positive electrode active material particles 13 is covered with a solid electrolyte coating 40c. Therefore, the surface of the positive electrode active material particles 13 is not exposed or hardly exposed in the gaps between the plurality of positive electrode active material particles 13. Therefore, for example, even when the electrolytic solution 30 fills these gaps, the oxidative decomposition of the electrolytic solution 30 can be more effectively suppressed and / or the passive film on the positive electrode 10c can be prevented. Generation | occurrence | production can be suppressed effectively.

[4. Various modifications]
[4-1. Modification 1]
FIG. 8 is a schematic cross-sectional view showing a configuration of a secondary battery 200a as Modification 1 of the secondary battery according to the second embodiment.

  The secondary battery 200a has the same configuration as the secondary battery 200 except for the negative electrode 20c and the solid electrolyte coating 50c.

  The negative electrode 20c includes a negative electrode current collector 21 and a negative electrode active material layer 22c. The negative electrode active material layer 22 c is disposed on the negative electrode current collector 21 and includes a plurality of negative electrode active material particles 23. Each surface of the plurality of negative electrode active material particles 23 is covered with a solid electrolyte coating 50c. In other words, the negative electrode 20c is covered with a solid electrolyte composed of a plurality of solid electrolyte coatings 50c.

  The material of the solid electrolyte coating 50c is, for example, [4. It can be selected from the various materials listed in [Solid Electrolyte Layer]. The solid electrolyte coating 50c may be a crystalline body or an amorphous body. In the latter case, the solid electrolyte coating 50c is easily formed along the shape of the negative electrode active material particles 23, and the coverage is improved. The film thickness of the solid electrolyte coating 50c may be, for example, 1 nanometer or more and 200 nanometers or less.

  The method for forming the negative electrode 20c and the solid electrolyte coating 50c is, for example, the above [2. The method described in [Positive electrode and solid electrolyte coating] may be the same.

  The secondary battery 200a has the above described [3. In addition to the various effects described in [Effect], the effects due to the solid electrolyte coating 50c are exhibited. The effect resulting from the solid electrolyte coating 50c is the same as that of the first embodiment [6. In the description of [Effect], it can be understood by appropriately replacing “solid electrolyte layer 40” and “positive electrode 10” with “solid electrolyte coating 50c” and “negative electrode 20c”, respectively.

  In the secondary battery 200a, each of the plurality of negative electrode active material particles 23 is covered with a solid electrolyte coating 50c. Therefore, even when the electrolytic solution 30 fills the gaps between the plurality of negative electrode active material particles 23, the reductive decomposition of the electrolytic solution 30 can be more effectively suppressed and / or the negative electrode Generation | occurrence | production of the passive film on 20c can be suppressed effectively.

[4-2. Modification 2]
FIG. 9 is a schematic cross-sectional view showing a configuration of a secondary battery 200b as Modification 2 of the secondary battery according to the second embodiment.

  The secondary battery 200b has a configuration in which the solid electrolyte film 40c is removed from the secondary battery 200a. Since each configuration of the secondary battery 200b is the same as the corresponding configuration of the secondary battery 200a, the description thereof is omitted.

  The secondary battery 200b has the above [4-1. The same effect as the effect resulting from the solid electrolyte coating 50c described in the first modification example] is achieved.

[4-3. Other variations]
The secondary batteries 200, 200a, and 200b described above may be combined with any one of the secondary batteries 100, 100a, 100b, 100c, 100d, and 100e described in the first embodiment. .

  For example, the negative electrode 20 of the secondary battery 200 is the same as that in the first embodiment [7-3. It may be replaced with the negative electrode 20a described in the modification 3], and further [7-4. The solid electrolyte layer 50a described in the modification 4] may be added.

  The secondary battery of the present disclosure can be used for, for example, a wearable device, a portable device, a hybrid vehicle, or an electric vehicle.

DESCRIPTION OF SYMBOLS 10,10c Positive electrode 11 Positive electrode collector 12,12c Positive electrode active material layer 13 Positive electrode active material particle 20,20a, 20c Negative electrode 21 Negative electrode collector 22,22a, 22c Negative electrode active material layer 23 Negative electrode active material particle 30 Electrolyte 40 , 50, 50a Solid electrolyte layer 40c, 50c Solid electrolyte coating 100, 100a, 100b, 100c, 100d, 100e Secondary battery 200, 200a, 200b Secondary battery

Claims (19)

A first electrode;
A second electrode;
A first solid electrolyte covering the first electrode and containing an alkaline earth metal;
An electrolyte solution filled in a space between the first electrode and the second electrode and containing a non-aqueous solvent and the alkaline earth metal salt dissolved in the non-aqueous solvent,
Secondary battery. The alkaline earth metal is magnesium;
The secondary battery according to claim 1. The first solid electrolyte further contains a polyanion composed of at least one of oxygen and nitrogen and at least one of phosphorus and silicon.
The secondary battery according to claim 1 or 2. The first solid electrolyte, magnesium phosphonitrilic acid _{or,, Mg x M y SiO z} ( however, M is at least one selected Ti, Zr, Hf, Ca, from the group consisting of Sr and Ba, 0 <x <2, 0 <y <2, 3 <z <6),
The secondary battery as described in any one of Claim 1 to 3. The first solid electrolyte contains Mg _x Zr _y SiO _z (where 0 <x <2, 0 <y <2, 3 <z <6).
The secondary battery according to claim 4. The first solid electrolyte is amorphous;
The secondary battery as described in any one of Claim 1 to 5. The first electrode is a positive electrode and the second electrode is a negative electrode;
The secondary battery as described in any one of Claim 1 to 6. The positive electrode is
A positive electrode current collector;
A positive electrode active material layer disposed on the positive electrode current collector and including a plurality of positive electrode active material particles;
The first solid electrolyte is a single layer disposed on the positive electrode active material layer and collectively covering the plurality of positive electrode active material particles.
The secondary battery according to claim 7. The positive electrode active material layer has an uneven surface defined by the plurality of positive electrode active material particles,
The first solid electrolyte is formed along the uneven surface,
The secondary battery according to claim 8. The positive electrode is
A positive electrode current collector;
A positive electrode active material layer disposed on the positive electrode current collector and including a plurality of positive electrode active material particles;
The first solid electrolyte includes a plurality of coatings individually covering the plurality of positive electrode active material particles.
The secondary battery according to claim 7. A second solid electrolyte covering the negative electrode and containing the alkaline earth metal;
The secondary battery as described in any one of Claims 7 to 10. The first electrode is a negative electrode and the second electrode is a positive electrode;
The secondary battery as described in any one of Claim 1 to 5. The negative electrode is
A negative electrode current collector;
A negative electrode active material layer disposed on the negative electrode current collector and including a plurality of negative electrode active material particles,
The first solid electrolyte is a single layer that is disposed on the negative electrode active material layer and collectively covers the plurality of negative electrode active material particles.
The secondary battery according to claim 12. The negative electrode active material layer has an uneven surface defined by the plurality of negative electrode active material particles,
The first solid electrolyte is formed along the uneven surface,
The secondary battery according to claim 13. The negative electrode is
A negative electrode current collector;
A negative electrode active material layer disposed on the negative electrode current collector and including a plurality of negative electrode active material particles,
The first solid electrolyte includes a plurality of films individually covering the plurality of negative electrode active material particles.
The secondary battery according to claim 12. The negative electrode is
A negative electrode current collector;
Including a metal layer or an alloy layer disposed on the negative electrode current collector,
The secondary battery according to claim 12. The standard electrode potential of the metal layer or the alloy layer is noble from -3V,
The secondary battery according to claim 16. The electrode potential of the positive electrode relative to the alkaline earth metal is greater than + 4V;
The secondary battery according to any one of claims 7 to 17. The first solid electrolyte blocks movement of electrons between the first electrode and the electrolytic solution, and allows alkaline earth metal ions to move between the first electrode and the electrolytic solution. To
The secondary battery according to any one of claims 1 to 18.

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