JP7018562B2 - Secondary battery - Google Patents

Description

The present disclosure relates to a secondary battery. The present disclosure relates, in particular, to alkaline earth metal secondary batteries.

In recent years, practical application 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 describes a magnesium secondary battery having a magnesium compound represented by the general formula: MgMSiO ₄ (where M is at least one of Fe, Cr, Mn, Co, and Ni) as a positive electrode active material. 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.

The secondary battery according to one aspect 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 solid electrolyte. The space between the electrode and the second electrode is filled with an electrolytic solution containing a non-aqueous solvent and a salt of the alkaline earth metal dissolved in the non-aqueous solvent.

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

FIG. 1 is a schematic cross-sectional view showing a configuration example of a secondary battery according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of a modification 1 of the secondary battery according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing the configuration of the second modification of the secondary battery according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing the configuration of a modification 3 of the secondary battery according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing the configuration of the modified example 4 of the secondary battery according to the first embodiment. FIG. 6 is a schematic cross-sectional view showing the configuration of the modified example 5 of the secondary battery according to the first embodiment. FIG. 7 is a schematic cross-sectional view showing a configuration example of the secondary battery according to the second embodiment. FIG. 8 is a schematic cross-sectional view showing the configuration of the modified example 1 of the secondary battery according to the second embodiment. FIG. 9 is a schematic cross-sectional view showing the configuration of the second modification 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.

(Findings underlying this disclosure)
Various positive electrode materials have been reported as one of the techniques for improving the energy density of magnesium secondary batteries. For example, Patent Document 1 discloses a magnesium compound represented by MgMSiO ₄ (where 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 noble than the standard electrode potential of lithium-3.05V. Therefore, the electrolytic solution of the magnesium secondary battery is required to have higher oxidation resistance than the electrolytic 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. This charging potential is so high that the electrolytic solution is oxidatively decomposed in the case of a conventional lithium ion secondary battery. Therefore, when the charging potential of the positive electrode exceeds 4 V in the magnesium standard, higher oxidation resistance is required, which exceeds the range that can be assumed in the conventional lithium ion secondary battery. However, in magnesium secondary batteries, there are few electrolytic solutions that satisfy such requirements. In particular, no electrolytic solution satisfying such a requirement has been reported when the potential of the positive electrode exceeds 4 V during charging.

The present inventors have focused on the fact that the electrolytic solution is decomposed by the transfer of electrons between the positive electrode and the electrolytic solution and / or between the negative electrode and the electrolytic solution, and examined means for suppressing the transfer of electrons. So far, the present inventors have succeeded in developing a solid electrolyte thin film having ionic conductivity of magnesium ions, which has not been reported in the past (for example, Japanese Patent Application No. 2016-161513, Japanese Patent Application No. 2017-139362). , Japanese Patent Application No. 2017-139363). Here, the present inventors have found that these solid electrolyte thin films have a property of being able to block the movement of electrons while allowing the movement of magnesium ions, and have arrived at the secondary battery described below.

The above description does not limit the secondary battery according to the present disclosure to a magnesium secondary battery. Since the standard electrode potentials of other alkaline earth metals (eg, Ca, Sr, or Ba) are also slightly noble than the standard electrode potentials of lithium, the present disclosure may apply to alkaline earth metal secondary batteries. .. For example, in the various materials exemplified below, magnesium can be appropriately replaced with other alkaline earth metals. Also, since the standard electrode potential of aluminum is noble than the standard electrode potential of lithium ion, the present disclosure can also be applied to an aluminum secondary battery.

(Definition of drawings and terms)
The present disclosure is described with reference to the drawings for a particular embodiment, but the present disclosure is not limited thereto and is limited only by claim. The drawings are only schematic and non-limiting. In the drawings, the size and shape of some components may be exaggerated or not depicted to scale for explanatory purposes. Dimensions and relative dimensions do not necessarily correspond to the actual reification of the present disclosure.

In the present disclosure, the terms "first" and "second" are used to distinguish similar components, not to describe temporal or spatial order. Therefore, the "first" and "second" are interchangeable as appropriate.

In the present disclosure, the terms "top", "bottom", etc. are used for explanatory purposes and do not necessarily describe relative positions. These terms are interchangeable under the appropriate circumstances and the various embodiments are operable in other orientations than described or illustrated herein.

In the present disclosure, the term "X disposed on Y" means that X is in contact with Y, and refers to the relative positional relationship between X and Y. It is not limited to a specific direction.

Of the components described in the present disclosure, components not described in the independent claims indicating the highest level concept are described as arbitrary components.

(First Embodiment)
[1. Secondary battery configuration]
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 faces the positive electrode 10 at a distance from each other. The solid electrolyte layer 40 covers the positive electrode 10. The electrolytic solution 30 is filled in the space between the positive electrode 10 and the negative electrode 20. The secondary battery 100 is charged and discharged by the movement of alkaline earth metal ions 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 shown in FIG. 1, and may be, for example, a sheet type, a coin type, a button type, a laminated 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 arranged 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 a 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 may be non-porous. Examples of metallic materials include aluminum, aluminum alloys, stainless steels, titanium, and titanium alloys. 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 are, 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. The alkaline earth metal comprises at least one selected from a salt compound and a fluorinated polyanionic salt compound containing an alkaline earth metal and a transition metal, wherein the alkaline earth metal is at least selected from, for example, Mg, Ca, Sr and Ba. It is one kind, and 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, as an example of the material of the positive electrode active material particles 13, MgM ₂ O ₄ (where M is at least one selected from Mn, Co, Cr, Ni and Fe). ), MgMO ₂ (where M is at least one selected from Mn, Co, Cr, Ni and Al), MgMSiO ₄ (where M is selected from Mn, Co, Ni and Fe). (At least one), and Mg _x My AO _z F _w (where _M is a transition metal, Sn, Sb or In, A is P, Si or S and 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 are CaM ₂ O ₄ and Ca MO 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, for example, an alkaline earth metal. For example, the positive electrode active material particles 13 may be graphite fluoride, a metal oxide, or a metal halide. The metal oxide and metal halide may contain, for example, at least one selected from 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, for example, a material having an electrode potential higher than + 4 V with respect to an alkaline earth metal. In this case, the secondary battery 100 can realize a capacity of more than 4 V while suppressing oxidative decomposition of the electrolytic solution 30 as 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, a conductive material and / or a binder may be added to the positive electrode active material layer 12, if necessary.

Examples of conductive materials include carbon materials, metals, and conductive polymers. Examples of carbon materials include graphite such as natural graphite (for example, lump graphite, scaly 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 in admixture of a plurality of types.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluororesin such as fluororubber, thermoplastic resin such as polypropylene and polyethylene, ethylene propylene diene monomer (EPDM) rubber, and sulfone. Examples thereof include polyethylene chemicalized EPDM rubber and natural butyl rubber (NBR). These materials may be used alone or in admixture of a plurality of types. The binder may be, for example, an aqueous dispersion of cellulosic 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, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N. -Includes dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. For example, a thickener may be added to the dispersant. Examples of thickeners include carboxymethyl cellulose and methyl cellulose.

The positive electrode 10 is formed, for example, as follows. First, the positive electrode active material particles 13, the conductive material, and the binder are mixed. Next, a suitable solvent is added to this mixture, whereby a paste-like positive electrode mixture is obtained. Next, this positive electrode mixture is applied to the surface of the positive electrode current collector 11 and dried. As a result, 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 in the form of a thin film. The film thickness of the positive electrode 10 may be, for example, 500 nanometers or more and 20 micrometers or less.

[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 arranged 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 a 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 may be non-porous. Examples of metallic materials include aluminum, aluminum alloys, stainless steels, titanium, and titanium alloys. 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 interlayer 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 capable of occluding and releasing 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 a 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, a conductive material and / or a binder may be added to the negative electrode active material layer 22 as needed. 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 the same method as the above-mentioned method for forming the positive electrode 10.

The negative electrode 20 may be in the form of 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 one layer arranged on the positive electrode active material layer 12, and collectively covers a plurality of positive electrode active material particles 13. The solid electrolyte layer 40 is formed along an uneven surface defined by a 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. In addition to the alkaline earth metal, 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.

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 (however, 1 <x <2, 3 <y <5, 0). ≦ _z <1), Mg _x My SiO _z (where M is at least one selected from the group consisting of Ti, Zr, Hf, Ca, Sr and Ba, and 0 <x <2, 0 <y. <2, 3 <z <6), Mg _2-1.5x Al _x SiO ₄ (however, 0.1 ≤ x ≤ 1), Mg _2-1.5x-0.5y Al _xy Zn _y SiO ₄ (however, 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. Is at least one species), Mg _1-x A _x M (M'O ₄ ) ₃ (where A is at least one species selected from Ca, Sr, Ba and Ra, and M is Ze. And Hf, and M'is at least one selected from W and Mo, and examples thereof include 0 ≦ x <1) and Mg (BH ₄ ) (NH ₂ ).

The solid electrolyte layer 40 is, for example, magnesium nitride phosphate or at least one selected from the group consisting of Mg _x My SiO _z (where _M is Ti, Zr, Hf, Ca, Sr and Ba). It may contain 0 <x <2, 0 <y <2, 3 <z <6). Since these materials exhibit 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 Cay} 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 may be, for example, Mg _x My SiO _z (where 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. 2016-161513, Japanese Patent Application No. 2017-139362, and Japanese Patent Application No. 2017-139363 are incorporated by reference in this disclosure.

When the secondary battery 100 is another alkaline earth metal secondary battery, as an example of the material of the solid electrolyte layer 40, AM (M'O ₄ ) ₃ (where A is Ca, Sr, Ba and Ra). At least one selected from, 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, for example, by a physical deposition method or a chemical deposition method. Examples of physical deposition methods include sputtering, vacuum deposition, 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 thermal decomposition (SPD). ) Method, doctor blade method, spin coating method, and printing technology. 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, dip 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, it becomes easy to form the solid electrolyte layer 40 along the uneven surface of the positive electrode active material layer 12.

[5. Electrolyte]
The electrolytic solution 30 is filled in the space between the positive electrode 10 and the negative electrode 20. The electrolytic solution 30 may further fill the gaps between the plurality of positive electrode active material particles 13, or may fill the gaps 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 non-aqueous solvent, and alkaline earth metal ions can be transferred according to an electric field.

Examples of non-aqueous solvent materials include cyclic ethers, chain ethers, cyclic carbonate esters, chain carbonate esters, cyclic carboxylic acid esters, chain carboxylic acid esters, pyrocarbon esters, phosphoric acid esters, borate esters, and sulfuric acid. Examples include esters, sulfite esters, cyclic sulfones, chain sulfones, nitriles, and sulton.

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. Included are 5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ethers, 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 and 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, Examples thereof include 1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene 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, and trifluoro. Examples thereof include methylethylene carbonate, 4-fluoropropylene carbonate, 5-fluoropropylene carbonate, and derivatives thereof. Examples of chain carbonates include dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylisopropylcarbonate, and derivatives thereof.

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

Examples of pyrocarbonate esters include diethylpyrocarbonate, dimethylpyrocarbonate, di-tert-butyldicarbonate, and derivatives thereof. Examples of phosphoric acid esters include trimethyl phosphate, triethyl phosphate, hexamethyl phosphate, and derivatives thereof. Examples of borate esters include trimethylborate, triethylborate, and derivatives thereof. Examples of sulfate esters include trimethylsulfate, triethylsulfate, and derivatives thereof. Examples of sulfite esters include ethylene sulphite and its derivatives.

Examples of cyclic sulfones include sulfolanes and their derivatives. Examples of chain sulfones include alkyl sulfones and derivatives thereof. Examples of nitriles include acetonitrile, valeronitrile, propionitrile, trimethylnitrile, cyclopentanecarbonitrile, adiponitrile, pimeronitrile and derivatives thereof. Examples of sultone include 1,3-propane sultone and its derivatives.

As the solvent, only one of the above substances may be used, or two or more of them 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 , and so on. 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 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 can be mentioned. As the magnesium salt, only one of the above substances may be used, or two or more of them may be used in combination.

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

The electrolytic solution 30 is filled, for example, in the space between the positive electrode 10 and the negative electrode 20 facing each other in the 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 having no solid electrolyte layer, as described above, electrons may be transferred to and received from 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 a solid electrolyte layer 40 that covers the positive electrode 10, the electrons of the positive electrode 10 and the electrolytic solution 30 are allowed to move between the positive electrode 10 and the electrolytic solution 30 while allowing the movement of alkaline earth metal ions. Movement can be suppressed. Therefore, it is possible to suppress the decomposition of the electrolytic solution 30 while maintaining the electrical characteristics of the secondary battery 100. As a result, the secondary battery 100 can be stabilized and its life can be extended.

The solid electrolyte layer 40 does not have to 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 is larger than that in the configuration without the solid electrolyte layer 40. It suffices if it is 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 the material of the electrolytic solution, which was considered to be unusable in the region where the charging potential exceeds 4 V, for the secondary battery 100. For example, the designer can adopt the non-aqueous solvent used in the conventional lithium ion secondary battery as the non-aqueous solvent for the high-capacity alkaline earth metal secondary battery. Therefore, the degree of freedom in selecting the material of 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. The designer can make the electrolytic solution 30 function as the main component of the electrolyte by adjusting, for example, 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 as compared with a secondary battery in which the electrolyte is all solid (that is, an all-solid secondary battery) can be realized.

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 solid electrolyte layer 40 is easier to manufacture than, for example, the solid electrolyte coating 40c described later. Further, for example, when the positive electrode active material layer 12 contains 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 the reaction between the conductive material and the electrolytic solution 30.

When the secondary battery 100 is a magnesium secondary battery, the following new effects are further obtained.

When the positive electrode and the electrolytic solution come into contact with each other in a magnesium secondary battery, a magnesium compound (for example, magnesium oxide) may precipitate on the contact surface thereof. This precipitate is a passivation membrane and inhibits the movement of magnesium ions between the positive electrode and the electrolytic solution. Therefore, the magnesium secondary battery may not be able to perform charge / discharge operation due to the precipitated passivation film.

It is also known that a lithium compound precipitates 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 passivation film is a problem peculiar to the magnesium secondary battery, which 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 dynamic film on the positive electrode 10 by covering the positive electrode 10, thereby stabilizing the secondary battery 100. Charging / discharging operation can be guaranteed.

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

The secondary battery 100a 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. Since each configuration of the secondary battery 100a except for the solid electrolyte layer 50 is the same as the corresponding configuration of the secondary battery 100, the description thereof will be omitted.

The solid electrolyte layer 50 is one layer arranged on the negative electrode active material layer 22, and collectively covers a plurality of negative electrode active material particles 23. The solid electrolyte layer 50 is formed along an uneven surface defined by a 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, the above [4. It can be selected from the 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 thickness of the solid electrolyte layer 40 may be, for example, further 5 nanometers or more and 200 nanometers or less. When the solid electrolyte layer 40 is an amorphous ultra-thin film, the film thickness may be, for example, 1 nanometer or more and 3 nanometer or less. In addition, when the solid electrolyte layer 50 is an amorphous body, it becomes easy to form the solid electrolyte layer 50 along the uneven surface of the negative electrode active material layer 22.

The secondary battery 100a is described in the above [6. In addition to the various effects described in [Effect], the effect caused by the solid electrolyte layer 50 is exhibited. The effect caused by the solid electrolyte layer 50 is described in the above [6. Effect] can be understood by appropriately replacing the “solid electrolyte layer 40” and the “positive electrode 10” with the “solid electrolyte layer 50” and the “negative electrode 20”, respectively. In short, the solid electrolyte layer 50 can suppress the reductive decomposition of the electrolytic solution 30 by suppressing the contact between the negative electrode 20 and the electrolytic solution 30. Further, when the secondary battery 100a is a magnesium secondary battery, the solid electrolyte layer 50 can suppress the generation of a passivation film on the negative electrode 20.

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

The secondary battery 100b 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 configuration of the secondary battery 100b is the same as the corresponding configuration of the secondary battery 100, the description thereof will be omitted.

The secondary battery 100b is described in the above [7-1. It has the same effect as the effect caused by the solid electrolyte layer 50 described in the modified example 1].

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

The secondary battery 100c includes a positive electrode 10, a negative electrode 20a, 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. Since each configuration of the secondary battery 100c except for the negative electrode active material layer 22a is the same as the corresponding configuration of the secondary battery 100, the description thereof will be omitted.

The negative electrode active material layer 22a is a flat plate-like layer arranged on the negative electrode current collector 21. The material of the negative electrode active material layer 22a is, for example, the above [3. It can be selected from various materials listed in [Negative electrode]. The negative electrode active material layer 22a can be formed, for example, by 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 described in the above [6. It has the same effect as the various effects described in [Effect].

[7-4. Modification 4]
FIG. 5 is a schematic cross-sectional view showing the configuration of the secondary battery 100d as a 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. Since each configuration of the secondary battery 100d except for the solid electrolyte layer 50a is the same as the corresponding configuration of the secondary battery 100c, the description thereof will be omitted.

The solid electrolyte layer 50a is a flat plate-like layer arranged on the negative electrode active material layer 22a. The material and forming method of the solid electrolyte layer 50a are described in the above [4. Solid electrolyte layer] as described.

The secondary battery 100d is described in the above [7-1. It has the same effects as the various effects described in the modified example 1].

[7-5. Modification 5]
FIG. 6 is a schematic cross-sectional view showing the configuration of the secondary battery 100e as a 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 configuration of the secondary battery 100e is the same as the corresponding configuration of the secondary battery 100d, the description thereof will be omitted.

The secondary battery 100e is described in the above [7-1. It has the same effect as the effect caused by the solid electrolyte layer 50 described in the modified example 1].

[8. experiment]
Through the experiments described below, it was confirmed that the electrode on which the solid electrolyte was formed on the surface could suppress the decomposition of the electrolytic solution.

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

The working electrode and the solid electrolyte membrane were prepared as follows. First, a V ₂ O ₅ film having a thickness of 200 nm was formed on a Pt / Ti / SiO ₂ substrate by a pulsed 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. Then, using Mg ₂ SiO ₄ and ZrSiO ₄ as targets, a solid electrolyte membrane having a thickness of 2.5 nm was formed on the V ₂ O ₅ membrane by high-frequency magnetron sputtering. 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 a counter electrode, an 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 a reference electrode, an Ag / AgCl double junction reference electrode (manufactured by EC Frontier, model number RE-10A) was used. As the internal solution of the reference electrode, an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) in which 0.01 mol / L silver bis (trifluoromethanesulfonyl) imide (Ag (TFSI)) was dissolved in acetonitrile was used.

As the cell, a microanalytical cell (manufactured by EC Frontier, model number VB7) was used. As the electrolytic solution for 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 it did not form a solid electrolyte membrane.

[8-1--4. Sample 4]
Sample 4 was similar to Sample 1 except that it did not form a V ₂ O ₅ membrane and a solid electrolyte membrane.

[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 the potential scanning speed was 0. Cyclic voltammetry (CV) measurements were performed at 1 mV / sec.

FIG. 10 shows the results of CV measurement in Samples 1 to 4. The horizontal axis shows the potential of the working pole with respect to the reference pole, and the vertical axis shows the current flowing through the working pole. As shown in FIG. 10, the electrolytic solutions of Samples 3 and 4 were oxidatively decomposed at around 3.3 V, whereas the electrolytic solutions of Samples 1 and 2 were not oxidatively decomposed at around 3.7 V. This indicates that the solid electrolyte provided at 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 if it exceeded 4.0 V.

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

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

(Second embodiment)
[1. Secondary battery configuration]
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 12c is arranged on the positive electrode current collector 11 and includes a plurality of positive electrode active material particles 13. The surface of each of the plurality of positive electrode active material particles 13 is covered with the 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 of forming the solid electrolyte and the positive electrode, the description thereof will be 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 likely to be formed along the shape of the positive electrode active material particles 13, and the covering property 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, for example, as follows.

First, the surface of the positive electrode active material particles 13 is coated with a solid electrolyte to form a solid electrolyte coating 40c. Then, the coated positive electrode active material particles 13, the conductive material, and the binder are mixed. Next, a suitable solvent is added to this mixture, whereby a paste-like positive electrode mixture is obtained. Next, this positive electrode mixture is applied to the surface of the positive electrode current collector 11 and dried. As a result, the positive electrode 10c is obtained.

The solid electrolyte coating 40c may be formed, for example, by depositing the solid electrolyte material by the above-mentioned 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 above-mentioned liquid phase film forming method.

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

In the secondary battery 200, each of the plurality of positive electrode active material particles 13 is covered with the solid electrolyte coating 40c. Therefore, the surface of the positive electrode active material particles 13 is not exposed or is difficult to be 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 passivation film on the positive electrode 10c. Occurrence can be effectively suppressed.

[4. Various variants]
[4-1. Modification 1]
FIG. 8 is a schematic cross-sectional view showing the configuration of the secondary battery 200a as a 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 22c is arranged on the negative electrode current collector 21 and includes a plurality of negative electrode active material particles 23. The surface of each of the plurality of negative electrode active material particles 23 is covered with the 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 likely to be formed along the shape of the negative electrode active material particles 23, and the covering property 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. It may be the same as the method described in [Positive electrode and solid electrolyte coating].

The secondary battery 200a is described in the above [3. In addition to the various effects described in [Effect], the effect caused by the solid electrolyte coating 50c is exhibited. The effect caused by the solid electrolyte coating 50c is described in [6. Effect] can be understood by appropriately replacing the “solid electrolyte layer 40” and the “positive electrode 10” with the “solid electrolyte coating 50c” and the “negative electrode 20c”, respectively.

In the secondary battery 200a, each of the plurality of negative electrode active material particles 23 is covered with the 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. The generation of the immobile membrane on 20c can be effectively suppressed.

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

The secondary battery 200b has a configuration in which the solid electrolyte coating 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 will be omitted.

The secondary battery 200b is described in the above [4-1. It has the same effect as the effect caused by the solid electrolyte coating 50c described in the modified example 1].

[4-3. Other variants]
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 [7-3. It may be replaced with the negative electrode 20a described in the first embodiment [7-4. The solid electrolyte layer 50a described in the modified example 4] may be added.

The secondary batteries of the present disclosure may be used, for example, in wearable devices, portable devices, hybrid vehicles, or electric vehicles.

10, 10c Positive electrode 11 Positive electrode current collector 12, 12c Positive electrode active material layer 13 Positive electrode active material particles 20, 20a, 20c Negative electrode 21 Negative electrode current collector 22, 22a, 22c Negative electrode active material layer 23 Negative electrode active material particles 30 Electrolyte liquid 40 , 50, 50a Solid Electrode Layer 40c, 50c Solid Electrode Coating 100, 100a, 100b, 100c, 100d, 100e Secondary Battery 200, 200a, 200b Secondary Battery

Claims (15)

With the first electrode
With the second electrode
A solid electrolyte membrane covering the first electrode and having a first solid electrolyte containing an alkaline earth metal,
The space between the first electrode and the second electrode is filled with an electrolytic solution containing a non-aqueous solvent and a salt of the alkaline earth metal dissolved in the non-aqueous solvent.
The first solid electrolyte is amorphous and contains Mg _x Zry SiO _z (where 0 <x <2, 0 <y <2, 3 <z <6) _.
Secondary battery. 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 . The first electrode is a positive electrode and the second electrode is a negative electrode.
The secondary battery according to claim 1 or 2 . The positive electrode is
Positive current collector and
A positive electrode active material layer arranged on the positive electrode current collector and containing a plurality of positive electrode active material particles.
The solid electrolyte membrane is one layer that is arranged on the positive electrode active material layer and collectively covers the plurality of positive electrode active material particles.
The secondary battery according to claim 3 . The positive electrode active material layer has an uneven surface defined by the plurality of positive electrode active material particles, and has an uneven surface.
The solid electrolyte membrane is formed along the uneven surface.
The secondary battery according to claim 4 . The positive electrode is
Positive current collector and
A positive electrode active material layer arranged on the positive electrode current collector and containing a plurality of positive electrode active material particles.
The solid electrolyte membrane comprises a plurality of films individually covering the plurality of positive electrode active material particles.
The secondary battery according to claim 3 . It covers the negative electrode and further comprises a second solid electrolyte containing the alkaline earth metal.
The secondary battery according to any one of claims 3 to 6 . The first electrode is a negative electrode and the second electrode is a positive electrode.
The secondary battery according to claim 1 or 2 . The negative electrode is
Negative electrode current collector and
A negative electrode active material layer arranged on the negative electrode current collector and containing a plurality of negative electrode active material particles.
The solid electrolyte membrane is one layer that is arranged on the negative electrode active material layer and collectively covers the plurality of negative electrode active material particles.
The secondary battery according to claim 8 . The negative electrode active material layer has an uneven surface defined by the plurality of negative electrode active material particles.
The solid electrolyte membrane is formed along the uneven surface.
The secondary battery according to claim 9 . The negative electrode is
Negative electrode current collector and
A negative electrode active material layer arranged on the negative electrode current collector and containing a plurality of negative electrode active material particles.
The solid electrolyte membrane comprises a plurality of films individually covering the plurality of negative electrode active material particles.
The secondary battery according to claim 8 . The negative electrode is
Negative electrode current collector and
A metal layer or an alloy layer arranged on the negative electrode current collector.
The secondary battery according to claim 8 . The standard electrode potential of the metal layer or the alloy layer is noble than -3V.
The secondary battery according to claim 12 . The electrode potential of the positive electrode with respect to the alkaline earth metal is larger than + 4V.
The secondary battery according to any one of claims 3 to 13 . The first solid electrolyte blocks the movement of electrons between the first electrode and the electrolyte and allows the movement of alkaline earth metal ions between the first electrode and the electrolyte. do,
The secondary battery according to any one of claims 1 to 14 .

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