Secondary battery

Abstract

The secondary battery is provided with: a partition wall that partitions a first space and a second space from each other and that transmits metal ions between the first space and the second space; a negative electrode that is disposed inside the first space and that occludes and releases metal ions; a positive electrode that is disposed inside the second space and that absorbs and releases metal ions; a first aqueous electrolyte solution that is housed inside the first space and that contains metal ions that are occluded and released in the negative electrode and the positive electrode, respectively; and a second aqueous electrolyte solution which is housed inside the second space, contains metal ions that are occluded and released in the negative electrode and the positive electrode, and has a pH lower than the pH of the first aqueous electrolyte solution, and the partition wall contains an ion exchange membrane.

Description

[0001] This application is a divisional application of a patent application with an application date of April 23, 2020, application number 202080023579.7, and invention name “Secondary Battery”, and all contents are incorporated herein by reference. Technical Field

[0002] The present technology relates to a secondary battery having a positive electrode, a negative electrode and an aqueous electrolyte. Background Art

[0003] As various electronic devices such as mobile phones are becoming more common, secondary batteries are being developed as power sources that are small, lightweight, and have high energy density. As such secondary batteries, those having aqueous electrolytes have been developed.

[0004] The structure of a secondary battery with an aqueous electrolyte affects the battery characteristics, so various studies have been conducted on the structure of the secondary battery. Specifically, in order to obtain excellent charge and discharge efficiency, in a lithium storage and release type secondary battery, the lithium ion concentration of the second aqueous electrolyte on the negative electrode side is set to be higher than the lithium ion concentration of the first aqueous electrolyte on the positive electrode side (for example, refer to patent document 1.). In order to achieve high voltage and high output, in a flow-type secondary battery, the pH of the negative electrode electrolyte is set to be higher than the pH of the positive electrode electrolyte (for example, refer to patent document 2.). In order to obtain excellent charge and discharge cycle characteristics, in a lithium storage and release type secondary battery, an aqueous electrolyte with a pH of 6 to 10 is used (for example, refer to patent document 3.).

[0005] In order to realize a high-performance secondary battery, an acidic electrolyte is used as the positive electrode electrolyte, and an alkaline electrolyte is used as the negative electrode electrolyte (for example, refer to Patent Document 4). In order to ensure cycle safety, a titanium oxide provided with a carbon coating is used as the negative electrode active material, and the charging potential of the negative electrode active material is set to a potential higher than the reduction decomposition potential of carbon and lower than the reduction decomposition potential of the negative electrode collector (for example, refer to Patent Document 5). In order to suppress the electrolysis of the aqueous electrolyte on the surface of the negative electrode during charging and discharging, an aqueous electrolyte containing imide anions such as lithium ions and TFSI anions and metal cations such as aluminum ions is used, and the pH of the aqueous electrolyte is 3 to 12 (for example, refer to Patent Document 6).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-156837

[0009] Patent Document 2: Japanese Patent Application Publication No. 2017-123222

[0010] Patent Document 3: Japanese Patent Application Publication No. 2005-251586

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 04-101358

[0012] Patent Document 5: Japanese Patent Application Publication No. 2019-053931

[0013] Patent Document 6: Japanese Patent Application Publication No. 2019-121537

[0014] Electronic devices equipped with secondary batteries are becoming increasingly high-performance and multifunctional. As a result, the frequency of use of electronic devices has increased, and the use environment of electronic devices has expanded. Therefore, there is still room for improvement in the battery characteristics of secondary batteries.

[0015] The present technology has been developed in view of the above-mentioned problems, and an object of the present technology is to provide a secondary battery capable of obtaining excellent battery characteristics. Summary of the invention

[0016] A secondary battery according to one embodiment of the present technology comprises: a partition wall that separates a first space and a second space from each other and allows metal ions to pass between the first space and the second space; a negative electrode that is arranged inside the first space and absorbs and releases metal ions; a positive electrode that is arranged inside the second space and absorbs and releases metal ions; a first aqueous electrolyte that is contained inside the first space and contains metal ions absorbed and released in the negative electrode and the positive electrode, respectively; and a second aqueous electrolyte that is contained inside the second space and contains metal ions absorbed and released in the negative electrode and the positive electrode, respectively, and has a pH lower than the pH of the first aqueous electrolyte.

[0017] According to a secondary battery of one embodiment of the present technology, the negative electrode that absorbs and releases metal ions is arranged inside the first space, and the first aqueous electrolyte is accommodated inside the first space. The positive electrode that absorbs and releases metal ions is arranged inside the second space, and the second aqueous electrolyte is accommodated inside the second space. The first aqueous electrolyte and the second aqueous electrolyte each contain metal ions absorbed and released in the negative electrode and the positive electrode, respectively, and the second aqueous electrolyte has a pH lower than the pH of the first aqueous electrolyte. Therefore, excellent battery characteristics can be obtained.

[0018] It should be noted that the effects of the present technology are not necessarily limited to the effects described here, and may be any effect among a series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cross-sectional view showing the structure of a secondary battery according to one embodiment of the present technology.

[0020] Figure 2 It is a cross-sectional view showing the structure of a secondary battery according to Modification 2. DETAILED DESCRIPTION

[0021] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. It should be noted that the order of description is as follows.

[0022] 1. Secondary battery

[0023] 1-1. Structure

[0024] 1-2. Action

[0025] 1-3. Manufacturing method

[0026] 1-4. Function and effect

[0027] 2. Modifications

[0028] 3. Uses of secondary batteries

[0029] <1. Secondary batteries>

[0030] First, a secondary battery according to an embodiment of the present technology will be described.

[0031] The secondary battery described herein is a secondary battery utilizing the occlusion and release of metal ions, and comprises a positive electrode, a negative electrode, and an electrolyte (aqueous electrolyte), wherein the electrolyte is a liquid electrolyte containing an aqueous solvent. In this secondary battery, since the charge and discharge reaction is performed utilizing the occlusion and release of metal ions, the battery capacity can be obtained.

[0032] The type of metal ions absorbed and released in the secondary battery is not particularly limited. For example, the metal ions include light metal ions such as alkali metal ions and alkaline earth metal ions. Among them, the metal ions preferably include alkali metal ions. This is because the charge and discharge reactions can be stably carried out while obtaining a high voltage. The alkali metal ions are, for example, lithium ions, sodium ions, and potassium ions.

[0033] <1-1. Structure>

[0034] Figure 1 The cross-sectional structure of a secondary battery is shown. Figure 1As shown, the secondary battery comprises a partition wall 12, a negative electrode 13, a positive electrode 14, a negative electrode electrolyte 15 as a first aqueous electrolyte, and a positive electrode electrolyte 16 as a second aqueous electrolyte inside an outer packaging member 11. The negative electrode electrolyte 15 and the positive electrode electrolyte 16 are respectively the above-mentioned aqueous electrolytes. That is, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are respectively electrolytes using an aqueous solvent, and more specifically, are solutions in which ionizable ionic substances are dissolved or dispersed in the aqueous solvent. It should be noted that in Figure 1 In FIG. 1 , the negative electrode electrolyte 15 is dark shaded, and the positive electrode electrolyte 16 is light shaded.

[0035] Hereinafter, for example, the case where the metal ions stored and released in the negative electrode 13 and the positive electrode 14 include alkali metal ions is taken as an example. That is, in the secondary battery described below, the battery capacity is obtained by utilizing the storage and release of the alkali metal ions.

[0036] [Outer packaging parts]

[0037] The outer packaging member 11 has an internal space for accommodating the partition wall 12, the negative electrode 13, the positive electrode 14, the negative electrode electrolyte 15, and the positive electrode electrolyte 16. The outer packaging member 11 includes, for example, any one or more of a metal material, a glass material, and a polymer compound. Specifically, the outer packaging member 11 can be, for example, a rigid metal can, a glass shell, a plastic shell, etc., or a soft (or flexible) metal foil and a polymer film.

[0038] [Partition wall]

[0039] The partition wall 12 is disposed between the negative electrode 13 and the positive electrode 14, and separates the internal space of the outer packaging member 11 into two spaces (the negative electrode chamber S1 as the first space and the positive electrode chamber S2 as the second space). Thus, the partition wall 12 separates the negative electrode chamber S1 and the positive electrode chamber S2 from each other inside the outer packaging member 11, so that the negative electrode 13 and the positive electrode 14 are separated from each other by the partition wall 12.

[0040] The partition wall 12, for example, includes a material that prevents anions from passing through between the negative electrode chamber S1 and the positive electrode chamber S2, and allows substances (excluding anions) such as alkali metal ions (cations) absorbed and released in the negative electrode 13 and the positive electrode 14 to pass through. This is because the negative electrode electrolyte 15 and the positive electrode electrolyte 16 can be prevented from mixing with each other. That is, the partition wall 12 allows cations to pass from the negative electrode chamber S1 to the positive electrode chamber S2, and allows cations to pass from the positive electrode chamber S2 to the negative electrode chamber S1.

[0041] Specifically, the partition wall 12 includes, for example, any one or more of an ion exchange membrane and a solid electrolyte membrane. The ion exchange membrane is a porous membrane (cation exchange membrane) that allows cations to pass through. The solid electrolyte membrane has conductivity of alkali metal ions. This is because the permeability of cations in the partition wall 12 is improved.

[0042] Partition wall 12 preferably includes an ion exchange membrane rather than a solid electrolyte membrane because the aqueous solvent in negative electrode electrolyte 15 and the aqueous solvent in positive electrode electrolyte 16 easily penetrate into partition wall 12 , thereby improving the ion conductivity inside partition wall 12 .

[0043] [negative electrode]

[0044] The negative electrode 13 is arranged inside the negative electrode chamber S1, and can absorb and release alkali metal ions. The negative electrode 13 includes, for example, a negative electrode collector 13A and a negative electrode active material layer 13B formed on both sides of the negative electrode collector 13A. In addition, the negative electrode active material layer 13B may also be formed on only one side of the negative electrode collector 13A. It should be noted that the negative electrode collector 13A may be omitted, so the negative electrode 13 may include, for example, only the negative electrode active material layer 13B.

[0045] The negative electrode current collector 13A, for example, includes any one or more of conductive materials such as metal materials, carbon materials, and conductive ceramic materials. Metal materials include stainless steel (SUS), titanium, zinc, tin, lead, and alloys thereof. The stainless steel, for example, can be highly corrosion-resistant stainless steel to which any one or more of additional elements such as niobium and molybdenum are added. Specifically, stainless steel is, for example, SUS444 to which molybdenum is added. Conductive ceramic materials include, for example, indium tin oxide (ITO). It should be noted that a portion of the negative electrode current collector 13A (connection terminal portion 13AT) is, for example, derived from the inside of the outer packaging member 11 to the outside.

[0046] Among them, the material forming the negative electrode collector 13A is preferably insoluble, poorly soluble and corrosion-resistant to the negative electrode electrolyte 15, and has low reactivity to the negative electrode active material described later. Therefore, the negative electrode collector 13A preferably includes the above-mentioned metal material, that is, preferably includes stainless steel, titanium, zinc, tin, lead and their alloys. This is because the negative electrode collector 13A is not easy to deteriorate even if a secondary battery is used.

[0047] It should be noted that the negative electrode current collector 13A may be a conductor plated with one or more of the above-mentioned metal materials, carbon materials, and conductive ceramic materials to cover the surface. The material of the conductor is not particularly limited as long as it has conductivity.

[0048] The negative electrode active material layer 13B contains any one or more of the negative electrode materials capable of absorbing and releasing alkali metal ions as negative electrode active materials. The negative electrode material is, for example, a titanium-containing compound, a niobium-containing compound, a vanadium-containing compound, an iron-containing compound, and a molybdenum-containing compound. This is because, even when an aqueous electrolyte (negative electrode electrolyte 15 and positive electrode electrolyte 16) is used, the charge and discharge reaction proceeds smoothly and stably. In addition, the negative electrode active material layer 13B may also contain other materials such as a negative electrode binder and a negative electrode conductive agent.

[0049] The titanium-containing compound is exemplified by titanium oxide, alkali metal titanium composite oxide, titanium phosphorus oxide, alkali metal titanium phosphate compound, and hydrogen titanium compound.

[0050] The titanium oxide is, for example, a compound represented by the following formula (1), that is, bronze-type titanium oxide.

[0051] TiO w …(1)

[0052] (w satisfies 1.85≤w≤2.15.)

[0053] The titanium oxide is, for example, anatase, rutile or brookite titanium oxide (TiO2). In addition, the titanium oxide may also be a composite oxide containing titanium and any one or more of phosphorus, vanadium, tin, copper, nickel, iron and cobalt as constituent elements. The composite oxide is, for example, TiO2-P2O5, TiO2-V2O5, TiO2-P2O5-SnO2 and TiO2-P2O5-MeO. In addition, Me is, for example, any one or more of copper, nickel, iron and cobalt.

[0054] The lithium titanium composite oxide in the alkali metal titanium composite oxide is, for example, a compound represented by the following formula (2) to formula (4), i.e., ramsdellite-type lithium titanate, etc. M2 represented by formula (2) is a metal element that can become a divalent ion. M3 represented by formula (3) is a metal element that can become a trivalent ion. M4 represented by formula (4) is a metal element that can become a tetravalent ion.

[0055] Li[Li x M2 (1-3x) / 2 Ti (3+x) / 2 ]O4…(2)

[0056] (M2 is at least one of magnesium (Mg), calcium (Ca), copper (Cu), zinc (Zn) and strontium (Sr). x satisfies 0≤x≤1 / 3.)

[0057] Li[Li y M3 1-3y Ti 1+2y ]O4…(3)

[0058] (M3 is at least one of aluminum (Al), scandium (Sc), chromium (Cr), manganese (Mn), iron (Fe), germanium (Ga) and yttrium (Y). y satisfies 0≤y≤1 / 3.)

[0059] Li[Li 1 / 3 M4 z Ti (5 / 3)-z ]O4…(4)

[0060] (M4 is at least one of vanadium (V), zirconium (Zr) and niobium (Nb). z satisfies 0≤z≤2 / 3.)

[0061] Specifically, the lithium titanium composite oxide represented by formula (2) is, for example, Li 3.75 Ti 4.875 Mg 0.375 O 12 The lithium titanium composite oxide represented by formula (3) is, for example, LiCrTiO4. The lithium titanium composite oxide represented by formula (4) is, for example, Li4Ti5O 12 and Li4Ti 4.95 Nb 0.05 O 12 wait.

[0062] Among the alkali metal titanium composite oxides, potassium titanium composite oxides are, for example, K2Ti3O7 and K4Ti5O 12 wait.

[0063] Examples of titanium phosphorus oxides include titanium phosphate (TiP2O7). Examples of lithium titanium phosphate compounds among alkali metal titanium phosphate compounds include LiTi2(PO4)3. Examples of sodium titanium phosphate compounds among alkali metal titanium phosphate compounds include NaTi2(PO4)3. Examples of hydrogen titanium compounds include H2Ti3O7(3TiO2·1H2O), H6Ti 12 O 27 (3TiO2·0.75H2O), H2Ti6O 13 (3TiO2·0.5H2O), H2Ti7O 15 (3TiO2·0.43H2O) and H2Ti 12 O 25 (3TiO2·0.25H2O), etc.

[0064] Examples of the niobium-containing compound include alkali metal niobium composite oxides, hydrogen niobium compounds, and titanium niobium composite oxides. In addition, materials corresponding to the niobium-containing compound are excluded from the titanium-containing compound.

[0065] Alkali metal niobium composite oxides include LiNbO2 and the like. Hydrogen niobium compounds include H4Nb6O17 Titanium-niobium composite oxides include TiNb2O7 and Ti2Nb 10 O 29 Etc. In addition, for example, an alkali metal may be intercalated into the titanium-niobium composite oxide.

[0066] Examples of the vanadium-containing compound include vanadium oxides and alkali metal vanadium composite oxides, etc. In addition, materials corresponding to the vanadium-containing compound are excluded from the titanium-containing compound and the niobium-containing compound, respectively.

[0067] Examples of vanadium oxides include vanadium dioxide (VO2), etc. Examples of alkali metal vanadium composite oxides include LiV2O4 and LiV3O8.

[0068] The iron-containing compound is, for example, iron hydroxide, etc. In addition, materials corresponding to the iron-containing compound are excluded from the titanium-containing compound, the niobium-containing compound, and the vanadium-containing compound.

[0069] Examples of iron hydroxides include iron oxyhydroxide (FeOOH), etc. The iron oxyhydroxide may be, for example, α-iron oxyhydroxide, β-iron oxyhydroxide, γ-iron oxyhydroxide, δ-iron oxyhydroxide, or any two or more thereof.

[0070] Examples of molybdenum-containing compounds include molybdenum oxides and cobalt-molybdenum composite oxides, etc. In addition, materials corresponding to molybdenum-containing compounds are excluded from titanium-containing compounds, niobium-containing compounds, vanadium-containing compounds, and iron-containing compounds.

[0071] Examples of molybdenum oxides include molybdenum dioxide (MoO2) and cobalt-molybdenum composite oxides include CoMoO4 and the like.

[0072] The negative electrode binder includes, for example, one or more of synthetic rubber and polymer compounds, etc. Synthetic rubber is, for example, styrene-butadiene rubber, etc. Polymer compounds are, for example, polyvinylidene fluoride and polyimide, etc.

[0073] The negative electrode conductive agent includes, for example, any one or more of conductive materials such as carbon materials, such as graphite, carbon black, acetylene black, and Ketjen black, etc. In addition, the conductive material may also be a metal material, a conductive ceramic material, and a conductive polymer.

[0074] [positive electrode]

[0075] The positive electrode 14 is arranged inside the positive electrode chamber S2, and can absorb and release alkali metal ions. The positive electrode 14, for example, includes a positive electrode collector 14A and a positive electrode active material layer 14B formed on both sides of the positive electrode collector 14A. In addition, the positive electrode active material layer 14B, for example, can also be formed only on one side of the positive electrode collector 14A. It should be noted that the positive electrode collector 14A can be omitted, so the positive electrode 14, for example, can only include the positive electrode active material layer 14B.

[0076] The positive electrode current collector 14A includes, for example, any one or more of conductive materials such as metal materials, carbon materials, and conductive ceramic materials. Metal materials are, for example, titanium, aluminum, and alloys thereof. The details of the conductive ceramic material are, for example, as described above. It should be noted that a portion of the positive electrode current collector 14A (connection terminal portion 14AT) is, for example, led out from the inside of the outer packaging member 11 to the outside. The lead-out direction of the connection terminal portion 14AT is, for example, the same as the lead-out direction of the connection terminal portion 13AT.

[0077] Among them, the material forming the positive electrode collector 14A is preferably insoluble, poorly soluble and corrosion-resistant to the positive electrode electrolyte 16, and has low reactivity to the positive electrode active material described later. Therefore, the positive electrode collector 14A preferably includes the above-mentioned metal material, that is, preferably includes titanium, aluminum and their alloys. This is because the positive electrode collector 14A is not easy to deteriorate even if a secondary battery is used.

[0078] It should be noted that the positive electrode current collector 14A may be a conductor plated with one or more of the above-mentioned metal materials, carbon materials, and conductive ceramic materials to cover the surface. The material of the conductor is not particularly limited as long as it has conductivity.

[0079] The positive electrode active material layer 14B contains one or more of positive electrode materials capable of occluding and releasing alkali metal ions as positive electrode active materials. In addition, the positive electrode active material layer 14B may further contain other materials such as a positive electrode binder and a positive electrode conductor.

[0080] Positive electrode materials that can absorb and release lithium ions as alkali metal ions include, for example, lithium-containing compounds. The types of lithium-containing compounds are not particularly limited, and include, for example, lithium composite oxides and lithium phosphate compounds. Lithium composite oxides are oxides containing lithium and one or more transition metal elements, and lithium phosphate compounds are phosphate compounds containing lithium and one or more transition metal elements. The types of transition metal elements are not particularly limited, and include, for example, nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe).

[0081] Specifically, layered rock salt type lithium composite oxides such as LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.33 Co 0.33 Mn 0.33 O2、Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, etc. Spinel-type lithium composite oxides include LiMn2O4, etc. Olivine-type phosphate compounds include LiFePO4, LiMnPO4, LiMn 0.5 Fe 0.5 PO4、LiMn 0.7 Fe 0.3 PO4 and LiMn 0.75 Fe 0.25 PO4, etc.

[0082] The positive electrode material capable of absorbing and releasing sodium ions as alkali metal ions includes, for example, a sodium-containing compound. The type of the sodium-containing compound is not particularly limited, and examples thereof include a Prussian blue analog represented by the following formula (5).

[0083] Na x K y M5 z Fe(CN)6·aH2O…(5)

[0084] (M5 is at least one of manganese (Mn) and zinc (Zn), and x, y, and z satisfy 0.5<x≤2, 0≤y≤0.5, and 0≤z≤2. a is an arbitrary value. In addition, y may satisfy 0.05≤y≤0.2.)

[0085] Specifically, the Prussian blue analogue represented by formula (5) is, for example, Na2MnFe(CN6), Na 1.42 K 0.09 Mn 1.13 Fe(CN)6·3H2O and Na 0.83 K 0.12 Zn 1.49 Fe(CN)6·3.2H2O, etc.

[0086] The positive electrode material capable of absorbing and releasing potassium ions as alkali metal ions includes, for example, a potassium-containing compound. The type of the potassium-containing compound is not particularly limited, and for example, K 0.7 Fe 0.6 Mn 0.6 O2, K 0.6 MnO2、K 0.3 MnO2、K 0.31 CoO2, KCrO2, K 0.6 CoO2, K 2 / 3 Mn 2 / 3 Co 1 / 3 Ni 1 / 3 O2, K 2 / 3 Ni 2 / 3 Te 1 / 3 O2, K 2 / 3 Ni 1 / 6 Co 1 / 2 Te 1 / 3 O2, K 2 / 3 Ni 1 / 2 Mn 1 / 6 Te 1 / 3 O2, K 2 / 3Ni 1 / 2 Cu 1 / 6 Te 1 / 3 O2, K 2 / 3 Ni 1 / 3 Zn 1 / 3 Te 1 / 3 O2, K 2 / 3 Ni 1 / 6 Mg 1 / 2 Te 1 / 3 O2, K 2 / 3 Ni 1 / 2 Co 1 / 6 Te 1 / 3 O2, K 2 / 3 Ni 1 / 3Mg 1 / 3 Te 1 / 3 O2 and K 2 / 3 Ni 1 / 3 Co 1 / 3 Te 1 / 3 O2, etc.

[0087] The details of the positive electrode binder are, for example, the same as those of the negative electrode binder. The details of the positive electrode conductive agent are, for example, the same as those of the negative electrode conductive agent.

[0088] [Negative Electrolyte and Positive Electrolyte]

[0089] The negative electrode electrolyte 15 is stored in the negative electrode chamber S1, and the positive electrode electrolyte 16 is stored in the positive electrode chamber S2. Therefore, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are separated by the partition wall 12 and are not mixed with each other.

[0090] Specifically, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 each contain an aqueous solvent and any one or more ionic substances that can be ionized in the aqueous solvent. In addition, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 each contain alkali metal ions that are absorbed and released in the negative electrode 13 and the positive electrode 14, respectively.

[0091] The aqueous solvent is, for example, pure water. The ionic substance is, for example, an acid, an alkali, and an electrolyte salt, and may be two or more thereof. The acid is, for example, oxalic acid (H2C2O4), nitric acid (HNO3), sulfuric acid (H2SO4), hydrochloric acid (HCl), acetic acid (CH3COOH), and citric acid (H3C6H5O7).

[0092] The electrolyte salt is a salt containing cations and anions, and more specifically, is any one or more of metal salts. The type of metal salt is not particularly limited, and examples thereof include alkali metal salts, alkaline earth metal salts, transition metal salts, and other metal salts.

[0093] Alkali metal salts include, for example, lithium salts, sodium salts, and potassium salts. The type of lithium salt is not particularly limited, and examples include lithium oxalate (Li2C2O4), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium chloride (LiCl), lithium acetate (CH3COOLi), lithium citrate (Li3C6H5O7), lithium hydroxide (LiOH), and imide salts. Examples of the imide salts include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The type of sodium salt is not particularly limited, and examples include compounds in which the lithium ions in the above-mentioned lithium salts are replaced by sodium ions. The type of potassium salt is not particularly limited, and examples include compounds in which the lithium ions in the above-mentioned lithium salts are replaced by potassium ions.

[0094] The type of alkaline earth metal salt is not particularly limited, and for example, it is a compound obtained by replacing the lithium ions in the above-mentioned lithium salt with cations of alkaline earth metal elements, more specifically, calcium salts, etc. The type of transition metal salt is not particularly limited, and for example, it is a compound obtained by replacing the lithium ions in the above-mentioned lithium salt with cations of transition metal elements, etc. The type of other metal salts is not particularly limited, and for example, it is a compound obtained by replacing the lithium in the above-mentioned lithium salt with cations of other metal elements, etc.

[0095] The content of the ionic substance, that is, the concentration (mol / kg) of each of the negative electrode electrolyte solution 15 and the positive electrode electrolyte solution 16 can be set arbitrarily.

[0096] The composition formula (type of electrolyte salt) of the negative electrode electrolyte 15 may be the same as the composition formula (type of electrolyte salt) of the positive electrode electrolyte 16, or may be different from the composition formula of the positive electrode electrolyte 16. In addition, the pH of the positive electrode electrolyte 16 is less than the pH of the negative electrode electrolyte 15. This is because, compared with the case where the pH of the positive electrode electrolyte 16 is equal to the pH of the negative electrode electrolyte 15, the decomposition potential of the aqueous solvent is offset due to the difference in pH. Thus, during charge and discharge, the decomposition reaction of the aqueous solvent can be thermodynamically suppressed, and the potential window of the aqueous solvent is expanded. Therefore, while obtaining a high voltage, the charge and discharge reaction utilizing the absorption and release of alkali metal ions can be fully and stably carried out.

[0097] The composition formula (type of electrolyte salt) of the negative electrode electrolyte 15 is preferably different from the composition formula (type of electrolyte salt) of the positive electrode electrolyte 16 . This is because the pH of the positive electrode electrolyte 16 can be easily controlled to be lower than that of the negative electrode electrolyte 15 .

[0098] As long as the pH of the positive electrode electrolyte 16 is lower than the pH of the negative electrode electrolyte 15 , the pH values ​​of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are not particularly limited.

[0099] Among them, the pH of the negative electrode electrolyte 15 is preferably 11 or more, more preferably 12 or more, and further preferably 13 or more. This is because, since the pH of the negative electrode electrolyte 15 becomes sufficiently high, the pH of the positive electrode electrolyte 16 easily becomes lower than the pH of the negative electrode electrolyte 15. In addition, since the difference between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15 is sufficiently large, it is easy to maintain the magnitude relationship of the pH of the two.

[0100] In addition, the pH of the positive electrode electrolyte 16 is preferably 3 to 8, more preferably 4 to 8, and further preferably 4 to 6. This is because the difference between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15 becomes sufficiently large, so it is easy to maintain the magnitude relationship of the pH of the two. In addition, since the corrosion of the outer packaging member 11, the negative electrode collector 13A, and the positive electrode collector 14A can be suppressed, their durability (stability) can be improved.

[0101] It should be noted that the electrolyte salt includes, for example, an alkali metal salt, which uses the alkali metal ions absorbed and released in the negative electrode 13 and the positive electrode 14 as cations. In this case, the electrolyte salt may also include any electrolyte salt (excluding alkali metal salts that absorb and release alkali metal ions in the above-mentioned negative electrode 13 and positive electrode 14 as cations) and any one or more of non-electrolytes. The type of the arbitrary electrolyte salt (type of cation and type of anion) is not particularly limited, so it can be selected arbitrarily.

[0102] Here, as described above, one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 contain an alkali metal salt as a cation that occludes and releases alkali metal ions in the negative electrode 13 and the positive electrode 14, respectively. The type of the alkali metal salt is not particularly limited, and may be only one type or two or more types.

[0103] In this case, one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may further include any one or two or more of other metal salts that use other metal ions different from the alkali metal ions occluded and released in the negative electrode 13 and the positive electrode 14 as cations. The other metal ions may be metal ions occluded and released in the negative electrode 13 and the positive electrode 14, respectively, or metal ions that are not occluded and released in the negative electrode 13 and the positive electrode 14, respectively, or both.

[0104] The types of other metal ions as metal ions occluded and released in the negative electrode 13 and the positive electrode 14 are not particularly limited, so there may be only one or more than two metal ions. In this case, for example, other alkali metal ions other than the alkali metal ions occluded and released in the negative electrode 13 and the positive electrode 14, respectively.

[0105] The types of other metal ions that are not occluded and released in the negative electrode 13 and the positive electrode 14 are not particularly limited, so there may be only one type or two or more types. The other metal ions in this case are, for example, any one or more types of any metal ions such as other alkali metal ions, alkaline earth metal ions, transition metal ions, and other metal ions other than the alkali metal ions occluded and released in the negative electrode 13 and the positive electrode 14, respectively.

[0106] More specifically, one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 contain a lithium salt having lithium ions as cations and an alkali metal salt having alkali metal ions as cations which are stored and released in the negative electrode 13 and the positive electrode 14 , respectively.

[0107] In this case, it is preferred that one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 further contain any one or two or more of the other metal salts having other metal ions as cations. This is because, by using two or more metal salts (alkali metal salts and other metal salts) in combination, it is easier to control the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16, respectively, compared with the case of using only one metal salt (alkali metal salt).

[0108] Among them, one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 preferably contain a lithium salt (lithium ion) as an alkali metal salt and one or both of a sodium salt (sodium ion) and a potassium salt (potassium ion) as other metal salts. Since it is easy to control the pH of the positive electrode electrolyte 16 to be sufficiently small relative to the pH of the negative electrode electrolyte 15, it is easy to maintain the magnitude relationship of the pH of the two.

[0109] It should be noted that one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are preferably a saturated solution of an alkali metal salt that uses alkali metal ions absorbed and released in the negative electrode 13 and the positive electrode 14 as cations. Among them, both the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are more preferably saturated solutions of the above-mentioned alkali metal salts. This is because the charge and discharge reaction (absorption and release reaction of alkali metal ions) is stably carried out during charge and discharge.

[0110] In order to confirm whether the negative electrode electrolyte 15 is a saturated solution of an electrolyte salt (alkali metal salt), for example, after disassembling the secondary battery, it is possible to check whether the electrolyte salt is precipitated inside the negative electrode chamber S1. The interior of the negative electrode chamber S1 is, for example, the liquid of the negative electrode electrolyte 15, the surface of the partition wall 12, the surface of the negative electrode 13, and the surface (inner wall surface) of the outer packaging component 11. Due to the precipitation of the electrolyte salt, when the negative electrode electrolyte 15 (liquid) and the precipitate (solid) of the electrolyte salt coexist inside the negative electrode chamber S1, the negative electrode electrolyte 15 can be considered to be a saturated solution of the electrolyte salt. It should be noted that in order to check the composition of the precipitate, for example, surface analysis methods such as X-ray photoelectron spectroscopy (XPS) can be used, and composition analysis methods such as inductively coupled plasma (ICP) emission spectrometry can be used.

[0111] The method for confirming whether the positive electrode electrolyte 16 is a saturated solution of the electrolyte salt (alkali metal salt) is the same as the method for confirming whether the negative electrode electrolyte 15 is a saturated solution of the electrolyte salt (alkali metal salt) except that the positive electrode chamber S2 is checked instead of the negative electrode chamber S1.

[0112] In addition, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may also be pH buffer solutions. The pH buffer solution may be, for example, an aqueous solution mixed with a weak acid and its conjugate base, or an aqueous solution mixed with a weak base and its conjugate acid. This is because the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 can be easily maintained, respectively, because the pH change can be fully suppressed.

[0113] Among them, the positive electrode electrolyte 16 preferably contains any one or more of sulfate ion, hydrogen sulfate ion, carbonate ion, hydrogen carbonate ion, phosphate ion, monohydrogen phosphate ion, dihydrogen phosphate ion and carboxylate ion as anions. This is because the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 can be fully maintained, respectively, because the change of the pH of the positive electrode electrolyte 16 can be fully suppressed. Carboxylate ions are, for example, formate ions, acetate ions, propionate ions, tartrate ions and citrate ions.

[0114] It should be noted that the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may each contain one or more of tris(hydroxymethyl)aminomethane and ethylenediaminetetraacetic acid as a buffer.

[0115] More specifically, it is preferred that the negative electrode electrolyte 15 contains hydroxide ions as anions, and the positive electrode electrolyte 16 contains any one or two or more of sulfate ions, hydrogen sulfate ions, carbonate ions, hydrogen carbonate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions as anions. This is because it is easy to control the pH of the negative electrode electrolyte 15 to be sufficiently large, and it is easy to control the pH of the positive electrode electrolyte 16 to be sufficiently small.

[0116] Here, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are preferably isotonic solutions having an isotonic relationship with each other. This is because the osmotic pressures of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are optimized, so that the pH relationship between the two can be easily maintained.

[0117] In particular, as described above, the negative electrode electrolyte 15 contains cations as metal ions (hereinafter referred to as "metal cations"), and the metal cations contain alkali metal ions. In addition, as described above, the positive electrode electrolyte 16 contains metal cations, and the metal cations contain alkali metal ions. The type of metal cations contained in the negative electrode electrolyte 15 may be only one or more than two as described above, and the type of metal cations contained in the positive electrode electrolyte 16 may be only one or more than two as described above. These metal cations do not contain cations such as hydrogen ions as non-metal ions.

[0118] In this case, the difference between the total cation concentration (mol / kg) of metal cations containing alkali metal ions in the negative electrode electrolyte 15 and the total cation concentration (mol / kg) of metal cations containing alkali metal ions in the positive electrode electrolyte 16, that is, the cation concentration difference (the concentration difference of metal cations containing alkali metal ions) of the total cation concentration of the positive electrode electrolyte 16-the total cation concentration of the negative electrode electrolyte 15 is preferably 4 mol / kg or less, and more preferably 2 mol / kg or less. This is because, since the cation concentration difference between the negative electrode electrolyte 15 and the positive electrode electrolyte 16 is appropriated, it is easier to maintain the magnitude relationship of the pH of the two. Although the reason is still uncertain, it can be considered that the metal cations in the negative electrode electrolyte 15 and the metal cations in the positive electrode electrolyte 16 are easy to move through the partition wall 12, respectively, so the charge and discharge reaction is easy to proceed stably.

[0119] The “total cation concentration” described here refers to the concentration of the metal cation when there is only one kind of metal cation, and refers to the total concentration of each metal cation when there are two or more kinds of metal cations.

[0120] That is, when the negative electrode electrolyte 15 contains only alkali metal ions occluded and released in the negative electrode 13 and the positive electrode 14 as metal cations, the total cation concentration is the concentration of metal cations containing only the alkali metal ions. In addition, when the negative electrode electrolyte 15 contains alkali metal ions and other metal ions occluded and released in the negative electrode 13 and the positive electrode 14 as metal cations, the total cation concentration is the concentration of metal cations containing the alkali metal ions and other metal ions. As described above, the other metal ions may be metal ions occluded and released in the negative electrode 13 and the positive electrode 14, respectively, or may be metal ions that are not occluded and released in the negative electrode 13 and the positive electrode 14, respectively, or may be both.

[0121] The definition of the total cation concentration of the negative electrode electrolyte 15 described here is the same as the definition of the total cation concentration of the positive electrode electrolyte 16 .

[0122] It should be noted that, when checking the total cation concentration of the negative electrode electrolyte 15, for example, after the negative electrode electrolyte 15 is recovered by disassembling the secondary battery, a composition analysis method such as ICP emission spectrometry is used to analyze the negative electrode electrolyte 15. The procedure for checking the total cation concentration of the positive electrode electrolyte 16 is the same as the procedure for checking the total cation concentration of the negative electrode electrolyte 15, except that the positive electrode electrolyte 16 is used instead of the negative electrode electrolyte 15.

[0123] In addition, the pH of the negative electrode electrolyte 15 is preferably set so that the negative electrode collector 13A and the negative electrode active material layer 13B are not easily corroded. Similarly, the pH of the positive electrode electrolyte 16 is preferably set so that the positive electrode collector 14A and the positive electrode active material layer 14B are not easily corroded. This is to make the charge and discharge reaction using the negative electrode 13 and the positive electrode 14 easy to be carried out stably and continuously.

[0124] <1-2. Action>

[0125] In this secondary battery, for example, when charging, if alkali metal ions are released from the positive electrode 14, the alkali metal ions move to the negative electrode 13 via the positive electrode electrolyte 16, the partition 12, and the negative electrode electrolyte 15. As a result, the alkali metal ions are stored in the negative electrode 13.

[0126] In the secondary battery, for example, when alkali metal ions are released from the negative electrode 13 during discharge, the alkali metal ions move to the positive electrode 14 via the negative electrode electrolyte 15, the partition wall 12, and the positive electrode electrolyte 16. As a result, the alkali metal ions are stored in the positive electrode 14.

[0127] <1-3. Manufacturing method>

[0128] When manufacturing the secondary battery, for example, as described below, after the negative electrode 13 and the positive electrode 14 are produced and the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are prepared, the secondary battery is assembled.

[0129] [Production of negative electrode]

[0130] First, a negative electrode mixture is prepared by mixing a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. Next, a paste-like negative electrode mixture slurry is prepared by putting the negative electrode mixture into a solvent such as an organic solvent. Finally, the negative electrode mixture slurry is applied to both sides of the negative electrode collector 13A (excluding the connection terminal portion 13AT) to form a negative electrode active material layer 13B. Then, the negative electrode active material layer 13B can be compression molded using a roller press or the like. In this case, the negative electrode active material layer 13B can be heated, or the compression molding can be repeated multiple times.

[0131] [Production of positive electrode]

[0132] The positive electrode active material layer 14B is formed on both sides of the positive electrode collector 14A through the same steps as the above-mentioned production steps of the negative electrode 13. Specifically, after the positive electrode mixture is prepared by mixing the positive electrode active material, the positive electrode binder and the positive electrode conductive agent, a paste-like positive electrode mixture slurry is prepared by putting the positive and negative electrode mixture into a solvent such as an organic solvent. Next, the positive electrode mixture slurry is applied to both sides of the positive electrode collector 14A (excluding the connection terminal portion 14AT) to form the positive electrode active material layer 14B. Then, the positive electrode active material layer 14B can be compression molded.

[0133] [Preparation of negative electrode electrolyte and positive electrode electrolyte]

[0134] Negative electrode electrolyte 15 and positive electrode electrolyte 16 are prepared by adding an ionic substance to an aqueous solvent. In this case, the pH of positive electrode electrolyte 16 is made lower than that of negative electrode electrolyte 15 by adjusting conditions such as the type and concentration (mol / kg) of the ionic substance.

[0135] [Assembly of secondary battery]

[0136] First, prepare an outer package member 11 provided with a partition wall 12. The outer package member 11 has, for example, a negative electrode opening (not shown) communicating with the negative electrode chamber S1, and a positive electrode opening (not shown) communicating with the positive electrode chamber S2. Next, the negative electrode 13 is stored from the negative electrode opening to the inside of the negative electrode chamber S1, and the positive electrode 14 is stored from the positive electrode opening to the inside of the positive electrode chamber S2. In this case, a portion of the negative electrode collector 13A (connection terminal portion 13AT) is led out from the inside of the outer package member 11 to the outside, and a portion of the positive electrode collector 14A (connection terminal portion 14AT) is led out from the inside of the outer package member 11 to the outside. Finally, the negative electrode electrolyte 15 is supplied from the negative electrode opening to the inside of the negative electrode chamber S1, and the positive electrode electrolyte 16 is supplied from the positive electrode opening to the inside of the positive electrode chamber S2. Then, the negative electrode opening and the positive electrode opening can be sealed separately using welding or the like. Thus, the negative electrode electrolyte 15 is stored in the negative electrode chamber S1 where the negative electrode 13 is arranged, and the positive electrode electrolyte 16 is stored in the positive electrode chamber S2 where the positive electrode 14 is arranged, thereby completing the secondary battery.

[0137] <1-4. Functions and Effects>

[0138] According to this secondary battery, the negative electrode 13 capable of absorbing and releasing metal ions is arranged inside the negative electrode chamber S1, and the negative electrode electrolyte 15 is stored inside the negative electrode chamber S1. The positive electrode 14 capable of absorbing and releasing metal ions is arranged inside the positive electrode chamber S2, and the positive electrode electrolyte 16 is stored inside the positive electrode chamber S2. The negative electrode electrolyte 15 and the positive electrode electrolyte 16 each contain metal ions absorbed and released in the negative electrode 13 and the positive electrode 14, respectively, and the positive electrode electrolyte 16 has a pH lower than the pH of the negative electrode electrolyte 15.

[0139] In this case, as described above, during charge and discharge, the decomposition reaction of the aqueous solvent can be thermodynamically suppressed, and the potential window of the aqueous solvent is expanded, so that the charge and discharge reaction utilizing the occlusion and release of metal ions can be fully and stably carried out while obtaining a high voltage. Therefore, a high voltage can be obtained, and a higher discharge capacity and a higher charge and discharge efficiency can be obtained, thereby obtaining excellent battery characteristics.

[0140] In particular, in the case where one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 contain alkali metal ions (for example, lithium ions) absorbed and released in the negative electrode 13 and the positive electrode 14, respectively, if one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 also contain other metal ions, the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15 can be easily controlled, respectively, and the relationship between the pH values ​​of the two can be easily maintained, thereby achieving a higher effect.

[0141] In this case, if one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 contain one or both of sodium ions and potassium ions as other metal ions, it is easier to control the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15 respectively, and it is easier to maintain the relationship between the pH values ​​of the two, so that a higher effect can be obtained.

[0142] Furthermore, when negative electrode 13 contains a titanium-containing compound or the like, even when an aqueous electrolyte (negative electrode electrolyte 15 and positive electrode electrolyte 16) is used, the charge and discharge reactions tend to proceed smoothly and stably, and thus a higher effect can be obtained.

[0143] Furthermore, when the pH of the negative electrode electrolyte 15 is 11 or more, the pH of the positive electrode electrolyte 16 tends to be lower than the pH of the negative electrode electrolyte 15. Therefore, the charge and discharge reaction proceeds more stably, and thus a higher effect can be obtained.

[0144] Furthermore, when the pH of the positive electrode electrolyte 16 is 4 to 8, the pH of the positive electrode electrolyte 16 tends to be lower than the pH of the negative electrode electrolyte 15 , so that a higher effect can be obtained.

[0145] Furthermore, if the positive electrode electrolyte 16 contains sulfate ions or the like as anions, it is easy to stably control the pH of the positive electrode electrolyte 16 and to maintain the magnitude relationship between the pH values ​​of the two, thereby achieving a higher effect.

[0146] In addition, if the negative electrode electrolyte 15 contains hydroxide ions as anions and the positive electrode electrolyte 16 contains sulfate ions or the like as anions, it is easy to control the pH of the negative electrode electrolyte 15 to be sufficiently high, and it is easy to stably control the pH of the positive electrode electrolyte 16, so that a higher effect can be obtained.

[0147] Furthermore, if the cation concentration difference between the total cation concentration of the negative electrode electrolyte 15 and the total cation concentration of the positive electrode electrolyte 16 is 2 mol / kg or less, the magnitude relationship of the pHs of both can be easily maintained, and thus a higher effect can be obtained.

[0148] In addition, if one or both of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 is a saturated solution of an alkali metal salt that uses the alkali metal ions absorbed and released in the negative electrode 13 and the positive electrode 14 as cations, a higher voltage can be obtained while making the charge and discharge reactions easier to carry out, thereby achieving a higher effect.

[0149] Furthermore, when the partition wall 12 includes one or both of an ion exchange membrane and a solid electrolyte membrane, the permeability of metal ions (cations) is improved, so that a higher effect can be obtained.

[0150] <2. Modifications>

[0151] As described below, the structure of the secondary battery described above can be appropriately changed. In addition, any two or more of the series of modified examples described below can be combined with each other.

[0152] [Modification 1]

[0153] As the negative electrode active material (negative electrode material), titanium-containing compounds, niobium-containing compounds, vanadium-containing compounds, iron-containing compounds and molybdenum-containing compounds are exemplified. However, as long as the charge and discharge reaction is easy to proceed smoothly and stably when an aqueous electrolyte (negative electrode electrolyte 15 and positive electrode electrolyte 16) is used, the negative electrode active material may also be other compounds other than the above-mentioned titanium-containing compounds.

[0154] [Modification 2]

[0155] exist Figure 1 In the present invention, an electrolyte solution (negative electrode electrolyte solution 15 and positive electrode electrolyte solution 16) is used as a liquid electrolyte. However, for example, Figure 1 Corresponding Figure 2As shown, electrolyte layers 17 and 18 which are gel-like electrolytes may be used instead of the electrolytic solution.

[0156] When the electrolyte layers 17 and 18 are used, for example, Figure 2 As shown, the electrolyte layer 17 is interposed between the partition wall 12 and the negative electrode 13, and the electrolyte layer 18 is interposed between the partition wall 12 and the positive electrode 14. That is, the electrolyte layer 17 is adjacent to the partition wall 12 and the negative electrode 13, and the electrolyte layer 18 is adjacent to the partition wall 12 and the positive electrode 14, respectively.

[0157] Specifically, the electrolyte layer 17 includes a negative electrode electrolyte 15 and a polymer compound. In the electrolyte layer 17, the negative electrode electrolyte 15 is retained by the polymer compound. The electrolyte layer 18 includes a positive electrode electrolyte 16 and a polymer compound. In the electrolyte layer 18, the positive electrode electrolyte 16 is retained by the polymer compound. The polymer compound is, for example, any one or more of polyvinylidene fluoride and polyethylene oxide. It should be noted that in Figure 2 In the figure, the electrolyte layer 17 including the negative electrode electrolyte 15 is dark shaded, and the electrolyte layer 18 including the positive electrode electrolyte 16 is light shaded.

[0158] When the electrolyte layer 17 is formed, for example, a precursor solution containing the negative electrode electrolyte 15, a polymer compound, an organic solvent, etc. is prepared, and then the precursor solution is applied to the negative electrode 13. When the electrolyte layer 18 is formed, for example, a precursor solution containing the positive electrode electrolyte 16, a polymer compound, an organic solvent, etc. is prepared, and then the precursor solution is applied to the positive electrode 14.

[0159] In this case, since metal ions such as alkali metal ions can move between the negative electrode 13 and the positive electrode 14 via the electrolyte layers 17 and 18 , the same effect can be obtained.

[0160] <3. Application of secondary batteries>

[0161] The use of secondary batteries is not particularly limited as long as the secondary batteries can be used as a driving power source and a power storage source for power accumulation, etc., for machinery, equipment, appliances, devices and systems (a collection of multiple devices, etc.). The secondary battery used as a power source can be a main power source or an auxiliary power source. The main power source is the power source that is used preferentially, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source used instead of the main power source, or it can be a power source switched from the main power source as needed. When using a secondary battery as an auxiliary power source, the type of the main power source is not limited to a secondary battery.

[0162] Specifically, the uses of secondary batteries are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals (including portable electronic devices). Portable living appliances such as electric shavers. Storage devices such as backup power supplies and memory cards. Power tools such as electric drills and electric saws. Battery packs mounted on laptop computers, etc. as removable power sources. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric vehicles (including hybrid vehicles). Power storage systems such as home battery systems that store electricity in advance in case of emergencies. Of course, the uses of secondary batteries can also be other uses besides the series of uses exemplified here.

[0163] Example

[0164] Examples of the present technology will be described.

[0165] (Examples 1 to 20)

[0166] As described below, after a secondary battery using alkali metal ions as metal ions for occlusion and release was produced, the battery characteristics of the secondary battery were evaluated. Here, a secondary battery using a glass container (glass case) as the outer casing 11 was produced.

[0167] [Manufacturing of Secondary Batteries]

[0168] When preparing the negative electrode 13, first, 89 parts by mass of a negative electrode active material, 10 parts by mass of a negative electrode binder (polyvinylidene fluoride), and 1 part by mass of a negative electrode conductive agent (graphite) are mixed together to prepare a negative electrode mixture. As the negative electrode active material, TiO2 and Li4Ti5O as titanium-containing compounds are used. 12 (LTO) and NaTi2(PO4)3(NTP) as a titanium phosphate compound. Next, the negative electrode mixture is put into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent is stirred to prepare a paste-like negative electrode mixture slurry. Next, using a coating device, the negative electrode mixture slurry is applied to both sides of the negative electrode collector 13A (thickness = 10μm) except for the connecting terminal portion 13AT, and then the negative electrode mixture slurry is dried to form a negative electrode active material layer 13B. Here, stainless steel (SUS444), tin (Sn), and titanium (Ti) are used as materials for forming the negative electrode collector 13A.

[0169] When preparing the positive electrode 14, first, 91 parts by mass of a positive electrode active material, 3 parts by mass of a positive electrode binder (polyvinylidene fluoride) and 6 parts by mass of a positive electrode conductive agent (graphite) are mixed together to prepare a positive electrode mixture. As the positive electrode active material, LiFePO4 (LFP) as a lithium phosphate compound, LiCoO2 (LCO), LiMn2O4 (LMO) as a lithium composite oxide, and LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA), Na2MnFe (CN6) (NMHCF) as a sodium-containing compound. Next, the positive electrode mixture is put into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent is stirred to prepare a paste-like positive electrode mixture slurry. Next, using a coating device, the positive electrode mixture slurry is applied to both sides of the positive electrode collector 14A (thickness = 10μm) except for the connecting terminal portion 14AT, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer 14B. Here, aluminum (Al) and titanium (Ti) are used as materials for forming the positive electrode collector 14A.

[0170] When preparing the negative electrode electrolyte 15 and the positive electrode electrolyte 16 separately, an ionic substance is added to an aqueous solvent (pure water), and then the aqueous solvent is stirred. The type of ionic substance, the concentration (mol / kg) of the negative electrode electrolyte 15 and the positive electrode electrolyte 16, and the pH are shown in Tables 1 and 2. Here, as the ionic substance, lithium hydroxide (LiOH), potassium hydroxide (KOH), lithium citrate (Li3Cit), lithium nitrate (LiNO3), sodium hydroxide (NaOH), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium chloride (LiCl), potassium nitrate (KNO3), lithium sulfate (Li2SO4), dilithium hydrogen phosphate (Li2HPO4), dipotassium hydrogen phosphate (K2HPO4) and lithium dihydrogen phosphate (LiH2PO4) are used as electrolyte salts (lithium salts, sodium salts and potassium salts as alkali metal salts).

[0171] Saturated solutions of electrolyte salts were used as negative electrode electrolyte 15 and positive electrode electrolyte 16 by adjusting the concentrations as needed. The brackets (sat) shown in the concentration column in Tables 1 and 2 indicate that negative electrode electrolyte 15 or positive electrode electrolyte 16 is a saturated solution of electrolyte salt.

[0172] In addition, as the negative electrode electrolyte 15 and the positive electrode electrolyte 16 , pH buffer solutions containing citrate ions, sulfate ions, and phosphate ions as anions were used, respectively, as necessary.

[0173] When the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are prepared separately, the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 are adjusted by using two alkali metal salts (lithium salt and potassium salt) as necessary.

[0174] When assembling a secondary battery, first, a glass container equipped with a partition wall 12 is prepared as the outer casing 11. Inside the glass container, the negative electrode chamber S1 and the positive electrode chamber S2 are partitioned from each other by the partition wall 12 in advance.

[0175] As the partition wall 12, an ion exchange membrane (cation exchange membrane Nafion115 (registered trademark) purchased from Sigma Aldrich Japan Contract Co., Ltd.) and a solid electrolyte membrane (solid electrolyte LICGC (registered trademark) AG-01 manufactured by OHARA Co., Ltd.) were used. The solid electrolyte membrane contains a solid electrolyte of the Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 system. In the column of "partition wall" shown in Table 1 and Table 2, it is marked as "exchange membrane" when an ion exchange membrane is used, and it is marked as "electrolyte" when a solid electrolyte membrane is used.

[0176] Next, the negative electrode 13 is arranged inside the negative electrode chamber S1, and then the negative electrode electrolyte 15 is supplied to the inside of the negative electrode chamber S1. In this case, a part of the negative electrode 13 (connection terminal portion 13AT) is led out of the outer packaging member 11. Finally, the positive electrode 14 is arranged inside the positive electrode chamber S2, and then the positive electrode electrolyte 16 is supplied to the inside of the positive electrode chamber S2. In this case, a part of the positive electrode 14 (connection terminal portion 14AT) is led out of the outer packaging member 11. Thus, the negative electrode electrolyte 15 is accommodated inside the negative electrode chamber S1, and the positive electrode electrolyte 16 is accommodated inside the positive electrode chamber S2, thereby completing the secondary battery for the test.

[0177] It should be noted that the concentration (mol / kg) and pH of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are shown in Tables 1 and 2. In this case, the total cation concentration (mol / kg) of the negative electrode electrolyte 15 and the total cation concentration (mol / kg) of the positive electrode electrolyte 16 were checked, and the results shown in Table 3 were obtained.

[0178] [Evaluation of battery characteristics]

[0179] As battery characteristics of the secondary battery, charge and discharge characteristics (charge and discharge capability, charge and discharge efficiency at the 10th cycle, and charge and discharge efficiency at the charge and discharge cycle after storage) were evaluated, and the results shown in Tables 1 to 3 were obtained.

[0180] When charging the secondary battery, the secondary battery is charged at a constant current of 2C in a normal temperature environment (temperature = 25°C) until the charging end voltage (V) shown in Table 1 and Table 2 is reached. In this case, the charging end voltage is set according to the type of negative electrode active material and the type of positive electrode active material. It should be noted that 2C refers to the current value at which the battery capacity (theoretical capacity) is completely discharged within 0.5 hours.

[0181] When discharging the secondary battery, the secondary battery is discharged at a current of 2C until reaching the discharge end voltage (V) shown in Table 1 and Table 2. In this case, the discharge end voltage is set according to the type of the negative electrode active material and the type of the positive electrode active material, as in the case of setting the charge end voltage.

[0182] When evaluating whether or not the secondary battery is chargeable and dischargeable, the secondary battery is charged and discharged under the above-mentioned charge and discharge conditions to check whether or not the secondary battery is chargeable and dischargeable.

[0183] The above-mentioned charge and discharge results are evaluated. If the secondary battery can be charged and discharged, the charge and discharge efficiency of the 10th cycle is further calculated. In this case, the charge capacity of the 10th cycle is measured by charging and discharging the secondary battery for 10 cycles under the above-mentioned charge and discharge conditions, and the discharge capacity of the 10th cycle is measured. Then, the charge and discharge efficiency (%) is calculated as (discharge capacity of the 10th cycle / charge capacity of the 10th cycle) × 100.

[0184] In addition, when the secondary battery is chargeable and dischargeable, the secondary battery is stored in a room temperature environment (storage period = 4 days), and then the charge and discharge efficiency after storage, i.e., the post-storage efficiency (%), is calculated by the same steps as the above-mentioned charge and discharge efficiency calculation steps.

[0185] [Table 1]

[0186]

[0187] [Table 2]

[0188]

[0189] [Table 3]

[0190]

[0191] [Investigation]

[0192] As shown in Tables 1 to 3, the charge and discharge characteristics of the secondary battery vary depending on the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 .

[0193] Specifically, when the pH of the positive electrode electrolyte 16 was equal to the pH of the negative electrode electrolyte 15 (Experimental Examples 8 to 10, 19, and 20), the secondary battery could be charged but not discharged, so the secondary battery could not be charged or discharged. Therefore, the charge and discharge efficiency could not be calculated.

[0194] On the other hand, when the pH of the positive electrode electrolyte 16 is lower than the pH of the negative electrode electrolyte 15 (Experimental Examples 1 to 7, 11 to 18), the secondary battery can be charged and discharged, and thus the secondary battery can be charged and discharged. Therefore, the charge and discharge efficiency can also be calculated.

[0195] In particular, when the pH of the positive electrode electrolyte 16 is lower than the pH of the negative electrode electrolyte 15 , a series of tendencies described below are obtained.

[0196] First, when other metal ions (potassium ions) are used together with alkali metal ions (lithium ions) (Experimental Example 6), the difference between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 increases compared to the case where only the alkali metal salt (lithium ions) is used (Experimental Example 3), so the charge and discharge efficiency increases.

[0197] Second, when saturated solutions of electrolyte salts were used as the negative electrode electrolyte 15 and the positive electrode electrolyte 16 (Experimental Example 2), the charge and discharge efficiency was increased compared to the case where no saturated solution of the electrolyte salt was used (Experimental Example 3).

[0198] Third, when a pH buffer solution was used as the positive electrode electrolyte 16 (Experimental Example 17), the charge and discharge efficiency was increased compared to the case where the pH buffer solution was not used (Experimental Example 1).

[0199] Fourth, alkali metal ions (lithium ions) and other metal ions (potassium ions) are used, and saturated solutions of electrolyte salts are used as the negative electrode electrolyte 15 and the positive electrode electrolyte 16 respectively, and a pH buffer solution is further used as the positive electrode electrolyte 16 (Experimental Example 15). In this case, the charge and discharge efficiency is increased the most.

[0200] Fifth, in the case where the partition wall is an ion exchange membrane (Experimental Example 13), the charge and discharge efficiency is increased compared to the case where the partition wall is a solid electrolyte membrane (Experimental Example 16).

[0201] Sixth, when the cation concentration difference was 4 mol / kg or less (Experimental Examples 13 and 14), the efficiency after storage increased compared to when the cation concentration difference was greater than 4 mol / kg (Experimental Example 1). In this case, if the cation concentration difference was 2 mol / kg or less, the storage efficiency was sufficiently improved.

[0202] [Summarize]

[0203] The results shown in Tables 1 to 3 show that in a metal ion storage and release type secondary battery, the charge and discharge characteristics are improved when the pH of the negative electrode electrolyte 15 is lower than the pH of the positive electrode electrolyte 16. Therefore, excellent battery characteristics can be obtained in the secondary battery.

[0204] In the above, the structure of the secondary battery of the present technology has been described by taking one embodiment and an example. However, the structure of the secondary battery of the present technology is not limited to the structure described in one embodiment and an example, and various modifications are possible.

[0205] The effects described in this specification are merely examples, and therefore the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects related to the present technology can also be obtained.

[0206] Explanation of symbols

[0207] 11 ... outer packaging member, 12 ... partition wall, 13 ... negative electrode, 14 ... positive electrode, 15 ... negative electrode electrolyte, 16 ... positive electrode electrolyte, 17, 18 ... electrolyte layer, S1 ... negative electrode chamber, S2 ... positive electrode chamber.

Claims

1. A secondary battery comprising: a partition wall that separates the first space and the second space from each other and allows metal ions to pass between the first space and the second space; A negative electrode is disposed inside the first space and absorbs and releases the metal ions; A positive electrode is disposed inside the second space and absorbs and releases the metal ions; a first aqueous electrolyte contained in the first space and containing the metal ions absorbed and released in the negative electrode and the positive electrode respectively; as well as a second aqueous electrolyte contained in the second space, containing the metal ions absorbed and released by the negative electrode and the positive electrode, respectively, and having a pH lower than that of the first aqueous electrolyte, The partition wall comprises an ion exchange membrane.

2. The secondary battery according to claim 1, in, At least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution contains alkali metal ions as the metal ions to be stored and released in the negative electrode and the positive electrode, respectively.

3. The secondary battery according to claim 2, in, At least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution contains lithium ions as the alkali metal ions.

4. The secondary battery according to any one of claims 1 to 3, in, At least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution further contains other metal ions different from the metal ions respectively stored and released in the negative electrode and the positive electrode.

5. The secondary battery according to claim 4, in, At least one of the first aqueous electrolyte solution and the second aqueous electrolyte solution contains at least one of sodium ions and potassium ions as the other metal ions.

6. The secondary battery according to any one of claims 1 to 3, in, The negative electrode comprises at least one of a titanium-containing compound, a niobium-containing compound, a vanadium-containing compound, an iron-containing compound, and a molybdenum-containing compound.

7. The secondary battery according to any one of claims 1 to 3, in, The pH of the first aqueous electrolyte is 11 or higher.

8. The secondary battery according to any one of claims 1 to 3, in, The pH of the second aqueous electrolyte solution is 4 or more and 8 or less.

9. The secondary battery according to any one of claims 1 to 3, in, The second aqueous electrolyte contains at least one of sulfate ions, hydrogen sulfate ions, carbonate ions, hydrogen carbonate ions, phosphate ions, monohydrogen phosphate ions, dihydrogen phosphate ions, and carboxylate ions as anions.

10. The secondary battery according to any one of claims 1 to 3, in, The first aqueous electrolyte contains hydroxide ions as anions, The second aqueous electrolyte contains at least one of sulfate ions, hydrogen sulfate ions, carbonate ions, hydrogen carbonate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions as anions.

11. The secondary battery according to any one of claims 1 to 3, in, The difference between the total cation concentration of metal cations containing the metal ions in the first aqueous electrolyte and the total cation concentration of metal cations containing the metal ions in the second aqueous electrolyte, i.e., the total cation concentration of the second aqueous electrolyte minus the total cation concentration of the first aqueous electrolyte, is less than 2 mol / kg, and the unit of the concentration is mol / kg.

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