Secondary battery

Abstract

The present disclosure provides a secondary battery comprising: a negative electrode that occludes and releases metal ions; a positive electrode that occludes and releases metal ions; a negative electrode electrolyte that contains an aqueous solvent; a positive electrode electrolyte that contains an aqueous solvent; a negative electrode chamber that accommodates the negative electrode and the negative electrode electrolyte; and a positive electrode chamber that accommodates the positive electrode and the positive electrode electrolyte. The negative electrode chamber and the positive electrode chamber are separated by a partition that is disposed between the negative electrode chamber and the positive electrode chamber and allows metal ions to pass therethrough. The negative electrode electrolyte has a pH greater than the pH of the positive electrode electrolyte. The partition has a structure obtained by stacking two or more layers including at least a first layer and a second layer that contain different cation exchange groups from one other. The first layer contains a polymer compound containing at least one cation exchange group selected from the group consisting of carboxylic acid groups, hydroxycarboxylic acid groups, phosphonic acid groups, phosphinic acid groups, and xanthic acid groups, and is in contact with at least one of the negative electrode electrolyte and the positive electrode electrolyte.

Description

secondary battery

[0001] This disclosure relates to secondary batteries.

[0002] Rechargeable batteries, which can be repeatedly charged and discharged, have long been used in a variety of applications. For example, rechargeable batteries are used as power sources for electronic devices such as smartphones and laptop computers.

[0003] In such secondary batteries, a configuration has been proposed in which an aqueous electrolyte containing an aqueous solvent is used instead of a flammable organic solvent to improve safety (Patent Document 1).

[0004] International Publication No. 2020 / 218456, Japanese Patent Publication No. 2002-249604, Japanese Patent Publication No. 2016-031832

[0005] The secondary battery described in Patent Document 1 has a structure in which the negative electrode electrolyte and the positive electrode electrolyte, which contain an aqueous solvent, are separated from each other by a partition wall. Furthermore, Patent Documents 2 and 3 describe the use of a cation exchange membrane having a predetermined functional group as the partition wall for separating the two types of aqueous solvents.

[0006] Secondary batteries using aqueous electrolytes, as described above, may experience a gradual decrease in battery performance due to repeated charging and discharging. Therefore, there is a need for secondary batteries that suppress this deterioration and offer superior long-term reliability. The inventors have newly discovered that the decrease in battery performance that occurs when secondary batteries containing an aqueous solvent-based electrolyte undergo repeated charging and discharging is due to the deterioration of the partition wall separating the electrolyte. Furthermore, the inventors have newly discovered that the deterioration of the partition wall may be caused by the interaction between the partition wall and the electrolyte.

[0007] This disclosure has been made in view of the above-mentioned issues. Specifically, the primary purpose of this disclosure is to provide a secondary battery with excellent long-term reliability.

[0008] As a result of diligent research to resolve the above-mentioned problems, the inventor has arrived at the invention of a secondary battery that achieves the above-mentioned main objective.

[0009] A secondary battery according to one embodiment of the present disclosure comprises: a negative electrode that intercepts and releases metal ions; a positive electrode that intercepts and releases metal ions; a negative electrode electrolyte containing an aqueous solvent; a positive electrode electrolyte containing an aqueous solvent; a negative electrode chamber containing the negative electrode and the negative electrode electrolyte; and a positive electrode chamber containing the positive electrode and the positive electrode electrolyte, wherein the negative electrode chamber and the positive electrode chamber are separated by a partition wall disposed between them and permeable to metal ions; the negative electrode electrolyte has a pH greater than that of the positive electrode electrolyte; the partition wall has a structure in which two or more layers are stacked, each containing at least a first layer and a second layer containing different cation exchange groups; the first layer contains a polymer compound containing at least one cation exchange group selected from the group consisting of carboxylic acid groups, hydroxycarboxylic acid groups, phosphonic acid groups, phosphinic acid groups, and xanthogenic acid groups, and is in contact with at least one of the negative electrode electrolyte and the positive electrode electrolyte.

[0010] According to one embodiment of the present disclosure, a secondary battery with excellent long-term reliability is provided.

[0011] Figure 1A is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. Figure 1B is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. Figure 2A is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. Figure 2B is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. Figure 3 is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. Figure 4 is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure.

[0012] The embodiments of this disclosure will be described in detail below. It should be noted that the applicant provides the following descriptions and examples to enable those skilled in the art to fully understand this disclosure, and is not intended to limit the subject matter described in the claims. In other words, the present invention is not particularly limited to the preferred embodiments described below, and can be implemented with appropriate modifications within the scope of its purpose. For convenience, the descriptions may be divided into embodiments and examples, considering the ease of explaining the key points or understanding them, but partial substitution and / or combination of configurations shown in different embodiments is possible. In descriptions of such embodiments, redundant explanations of substantially identical matters may be omitted, and only the differences may be described. In particular, similar effects and benefits from similar configurations may not be mentioned sequentially in each embodiment.

[0013] The various numerical ranges referred to herein are intended to include the lower and upper limits themselves, unless otherwise specified. The term "approximately" means that a variation or difference of a few percent, for example, ±10%, may be included.

[0014] The features of this disclosure relate to the partitions and electrolyte contained in the secondary battery. Below, in order to understand the overall structure of the secondary battery, the basic configuration of the secondary battery will be described. However, the configuration of the secondary battery described here is merely an example for understanding the invention and does not limit the invention. In addition, although the explanation will be given with reference to the drawings as necessary, the contents shown in the drawings are merely schematic and illustrative for understanding this disclosure, and the appearance and dimensional ratios may differ from the actual product.

[0015] [Basic Configuration of a Secondary Battery] Figures 1A and 1B are schematic cross-sectional views showing a secondary battery according to one embodiment of the present disclosure. In this specification, a secondary battery is a secondary battery that utilizes the intercalation and release of metal ions. The secondary battery comprises, as its main components, a negative electrode electrolyte 15, a positive electrode electrolyte 16, a negative electrode 13 immersed in the negative electrode electrolyte 15, a positive electrode 14 immersed in the positive electrode electrolyte 16, and a partition wall 12 separating the negative electrode electrolyte 15 and the positive electrode electrolyte 16. The negative electrode 13 and the positive electrode 14 may be arranged facing each other via the partition wall 12.

[0016] The negative electrode 13 and the negative electrode electrolyte 15 may be housed in the negative electrode chamber S1. The positive electrode 14 and the positive electrode electrolyte 16 may be housed in the positive electrode chamber S2. The negative electrode chamber S1 and the positive electrode chamber S2 may be separated by a partition wall 12. In other words, the negative electrode chamber S1 and the positive electrode chamber S2 may be adjacent to each other via the partition wall 12. With this configuration, the negative electrode electrolyte 15 in the negative electrode chamber S1 and the positive electrode electrolyte 16 in the positive electrode chamber S2 may be separated via the partition wall 12. The negative electrode chamber S1 and the positive electrode chamber S2 may be spaces defined by the partition wall 12 and the exterior member 11, and may be referred to as the negative electrode space and the positive electrode space, respectively.

[0017] (Electrolyte) The negative electrode electrolyte 15 and the positive electrode electrolyte 16 are aqueous electrolytes containing an aqueous solvent. More specifically, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are solutions in which an ionic substance that can be ionized in an aqueous solvent is dissolved or dispersed. Such a secondary battery can also be called an aqueous secondary battery. The secondary battery is charged and discharged by moving metal ions between the negative electrode 13 and the positive electrode 14 through the intercalation and release of metal ions in the negative electrode 13 and the positive electrode 14, which are immersed in the aqueous electrolyte.

[0018] (Negative electrode) The negative electrode 13 is an electrode located inside the negative electrode chamber S1 and capable of intercalating and releasing metal ions. The negative electrode 13 may include a negative electrode current collector 13A and a negative electrode active material layer 13B positioned on the surface of the negative electrode current collector 13A. The negative electrode active material layer 13B may be formed only in a portion of the negative electrode current collector 13A (for example, a single-sided region facing the positive electrode chamber S2). Alternatively, the negative electrode active material layer 13B may be formed over the entire region of the negative electrode current collector 13A that is immersed in the negative electrode electrolyte 15. The negative electrode 13 does not necessarily have to include a negative electrode current collector 13A. For example, the negative electrode 13 may be composed of a negative electrode active material layer 13B.

[0019] The negative electrode current collector 13A may include at least one conductive material, such as a metallic material, a carbon material, and a conductive ceramic material. While not particularly limited, examples of metallic materials include stainless steel (SUS), titanium, zinc, tin, lead, and their alloys. Examples of stainless steel include highly corrosion-resistant stainless steel to which at least one additive element, such as niobium and molybdenum, is added. Specifically, SUS444 with added molybdenum may be used as the stainless steel. Examples of conductive ceramic materials include indium tin oxide (ITO).

[0020] The negative electrode current collector 13A is preferably insoluble or sparingly soluble in the negative electrode electrolyte 15. Furthermore, the negative electrode current collector 13A is preferably corrosion-resistant to the negative electrode electrolyte 15 and has low reactivity with the negative electrode active material described later. In this specification, "low reactivity" refers to the property that unintended chemical reactions, decomposition, and / or alteration do not occur, or occur only to a very limited extent, in a secondary battery. That is, the negative electrode current collector 13A is preferably a material that does not undergo unintended chemical reactions, decomposition, and / or alteration, or occurs only to a very limited extent, upon contact with the negative electrode active material. By having such properties, the deterioration of the negative electrode current collector 13A during use of the secondary battery can be suppressed. From this viewpoint as well, it is preferable that the negative electrode current collector 13A contains the above-mentioned metal material.

[0021] The negative electrode current collector 13A may be a conductor whose surface is coated with one or more of the conductive materials described above. The material of this conductor is not particularly limited as long as it is conductive. For example, if the conductive material contains a metallic material, the surface of the conductor may be plated with that metallic material. Also, as shown in Figure 1A, the negative electrode current collector 13A may have a negative electrode side connection terminal portion 13AT which is formed by leading out a part of it to the outside of the outer casing member 11.

[0022] The negative electrode active material layer 13B contains one or more negative electrode active materials that intercept and release metal ions. However, the negative electrode active material layer 13B may further contain other materials such as a negative electrode binder and a negative electrode conductive agent.

[0023] The negative electrode active material may be, for example, a titanium-containing compound, a niobium-containing compound, a vanadium-containing compound, an iron-containing compound, or a molybdenum-containing compound. By using the above-mentioned materials, the charge-discharge reaction can proceed smoothly and stably even when two types of aqueous electrolytes (negative electrode electrolyte 15 and positive electrode electrolyte 16) are used.

[0024] Examples of titanium-containing compounds include titanium oxides, alkali metal titanium composite oxides, titanium phosphates, alkali metal titanium phosphate compounds, and hydrogen titanium compounds.

[0025] For example, the titanium oxide may be a compound represented by formula (3), that is, bronze-type titanium oxide.

[0026] TiO ｗ ... (3) (where w satisfies 1.85 ≤ w ≤ 2.15).

[0027] Specific examples of titanium oxides include anatase-type, rutile-type, or brookite-type titanium oxide (TiO ２ ). However, the titanium oxide may also be a composite oxide containing, as constituent elements, any one or two or more of phosphorus, vanadium, tin, copper, nickel, iron, and cobalt together with titanium. Specific examples of the composite oxide include TiO ２ -P ２ O ５ , TiO ２ -V ２ O ５ , TiO ２ -P ２ O ５ -SnO ２ and TiO ２ -P ２ O ５ -MeO and the like. Here, Me may be at least one selected from the group consisting of copper, nickel, iron, and cobalt.

[0028] Among the alkali metal titanium composite oxides, lithium titanium composite oxide may be a compound represented by each of formula (4) to formula (6), that is, lithium titanate of the ramsdellite type. M2 shown in formula (4) is a metal element that can become a divalent ion. M3 shown in formula (5) is a metal element that can become a trivalent ion. M4 shown in formula (6) is a metal element that can become a tetravalent ion.

[0029] Li[Li ｘ M2 （１－３ｘ）／２ Ti （３＋ｘ）／２ O ４... (4) (wherein M2 may be at least one selected from the group consisting of Mg, Ca, Cu, Zn, and Sr. x satisfies 0 ≤ x ≤ 1 / 3.)

[0030] Li[Li ｙ M3 １－３ｙ Ti １＋２ｙ ]O ４ ... (5) (In the formula, M3 may be at least one selected from the group consisting of Al, Sc, Cr, Mn, Fe, Ge, and Y. y satisfies 0 ≤ y ≤ 1 / 3.)

[0031] Li[Li １／３ M4 ｚ Ti （５／３）－ｚ ]O ４ ... (6) (wherein M4 may be at least one selected from the group consisting of V, Zr, and Nb. z satisfies 0 ≤ z ≤ 2 / 3.)

[0032] A specific example of the lithium titanium composite oxide shown in formula (4) is Li ３．７５ Ti ４．８７５ Mg ０．３７５ O １２ Examples include LiCrTiO2. ４ Examples include Li ４ Ti ５ O １２ and Li ４ Ti ４．９５ Nb ０．０５ O １２ These are some examples.

[0033] A specific example of potassium titanium composite oxide among alkali metal titanium composite oxides is K ２ Ti ３ O ７ and K ４ Ti ５ O １２ These are some examples.

[0034] A specific example of titanium phosphorus is titanium phosphate (TiP). ２ O ７Examples include LiTi. ２ (PO ４ ) ３ Examples include sodium titanium phosphate compounds among alkali metal titanium phosphate compounds, such as NaTi. ２ (PO ４ ) ３ Examples include H ２ Ti ３ O ７ (3TiO ２ ・1H ２ O), H ６ Ti １２ O ２７ (3TiO ２ 0.75H ２ O), H ２ Ti ６ O １３ (3TiO ２ 0.5H ２ O), H ２ Ti ７ O １５ (3TiO ２ 0.43H ２ O) and H ２ Ti １２ O ２５ (3TiO ２ 0.25H ２ O) and so on.

[0035] Examples of niobium-containing compounds include alkali metal niobium composite oxides, hydrogen niobium compounds, and titanium niobium composite oxides. Note that materials that fall under the category of niobium-containing compounds are excluded from the category of titanium-containing compounds.

[0036] A specific example of an alkali metal niobium composite oxide is LiNbO ２ Examples include H ４ Nb ６ O １７ Examples include TiNb. ２ O ７ and Ti ２ Nb １０ O２９ Examples thereof include etc. Note that in the titanium niobium composite oxide, an alkali metal may be intercalated.

[0037] The vanadium-containing compound may be, for example, vanadium oxide and alkali metal vanadium composite oxide, etc. However, the material corresponding to the vanadium-containing compound is excluded from each of the titanium-containing compound and the niobium-containing compound.

[0038] Specific examples of the vanadium oxide include vanadium dioxide (VO ２ ), etc. Specific examples of the alkali metal vanadium composite oxide include LiV ２ O ４ and LiV ３ O ８ , etc.

[0039] The iron-containing compound may be, for example, iron hydroxide, etc. However, the material corresponding to the iron-containing compound is excluded from each of the titanium-containing compound, the niobium-containing compound, and the vanadium-containing compound.

[0040] Specific examples of the iron hydroxide are iron oxyhydroxide (FeOOH), etc. However, the iron oxyhydroxide may be α-iron oxyhydroxide, β-iron oxyhydroxide, γ-iron oxyhydroxide, δ-iron oxyhydroxide, or any two or more of them.

[0041] The molybdenum-containing compound may be, for example, molybdenum oxide and cobalt molybdenum composite oxide, etc. However, the material corresponding to the molybdenum-containing compound is excluded from each of the titanium-containing compound, the niobium-containing compound, the vanadium-containing compound, and the iron-containing compound.

[0042] Specific examples of the molybdenum oxide may be molybdenum dioxide (MoO ２ ), etc. Specific examples of the cobalt molybdenum composite oxide may be CoMoO ４ , etc.

[0043] The negative electrode binder may contain one or more materials such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber. Specific examples of polymer compounds include polyvinylidene fluoride and polyimide.

[0044] The negative electrode conductive agent may contain one or more conductive materials, such as carbon materials, metallic materials, conductive ceramic materials, and conductive polymers. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjenblack.

[0045] (Positive electrode) The positive electrode 14 is capable of intercepting and releasing metal ions that permeate through the partition wall 12. The positive electrode 14 is located inside the positive electrode chamber S2, and at least a portion of it is immersed in the positive electrode electrolyte 16.

[0046] The positive electrode 14 may include a positive electrode current collector 14A and a positive electrode active material layer 14B. However, the positive electrode current collector 14A may be omitted.

[0047] The positive electrode current collector 14A is a conductive support member that supports the positive electrode active material layer 14B, and may have, for example, a pair of surfaces on which the positive electrode active material layer 14B is provided. The positive electrode current collector 14A may contain one or more conductive materials such as metal materials, carbon materials, and conductive ceramic materials. As shown in Figure 1A, the positive electrode current collector 14A may include a positive electrode side connection terminal portion 14AT at one end. The positive electrode side connection terminal portion 14AT may be led out to the outside of the exterior member 11. The direction of lead-out of the positive electrode side connection terminal portion 14AT may be the same as the direction of lead-out of the negative electrode side connection terminal portion 13AT, or they may be led out in different directions.

[0048] Specific examples of metallic materials include titanium, aluminum, and their alloys. Details regarding conductive ceramic materials are as described above.

[0049] The positive electrode current collector 14A is preferably insoluble or sparingly soluble in the positive electrode electrolyte 16. Furthermore, it is preferable that the positive electrode current collector 14A has corrosion resistance to the positive electrode electrolyte 16 and low reactivity to the positive electrode active material described later. By having such properties, the deterioration of the positive electrode current collector 14A during use of the secondary battery can be suppressed. From this viewpoint as well, it is preferable that the positive electrode current collector 14A contains the above-mentioned metal material.

[0050] The positive electrode current collector 14A may be a conductor whose surface is coated with one or more of the conductive materials described above. The material of this conductor is not particularly limited as long as it is conductive. If the conductive material contains a metallic material, the surface of the conductor may be plated with that metallic material.

[0051] The positive electrode active material layer 14B may be formed only in a portion of the positive electrode current collector 14A (for example, a single-sided region facing the negative electrode chamber S1). Alternatively, the positive electrode active material layer 14B may be formed over the entire region of the positive electrode current collector 14A that is immersed in the positive electrode electrolyte 16.

[0052] The positive electrode active material layer 14B contains one or more positive electrode active materials that intercept and release metal ions. However, the positive electrode active material layer 14B may further contain other materials such as a positive electrode binder and a positive electrode conductive agent.

[0053] The positive electrode active material that intercepts and releases lithium ions as metal ions may contain lithium-containing compounds. The type of lithium-containing compound is not particularly limited, but may include, for example, lithium composite oxides and lithium phosphate compounds. A lithium composite oxide is an oxide that contains lithium and one or more transition metal elements as constituent elements. A lithium phosphate compound is a phosphate compound that contains lithium and one or more transition metal elements as constituent elements. The type of transition metal element is not particularly limited, but may include nickel, cobalt, manganese, and iron.

[0054] Specific examples of the layered rock salt-type lithium composite oxide include LiNiO ２ , LiCoO ２ , LiCo ０．９８ Al ０．０１ Mg ０．０１ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , Li １．２ Mn ０．５２ Co ０．１７５ Ni ０．１ O ２ and Li １．１５ (Mn ０．６５ Ni ０．２２ Co ０．１３ )O ２ etc. Specific examples of the spinel-type lithium composite oxide include LiMnO ２ O ４ etc. Specific examples of the olivine-type lithium phosphate compound include LiFePO ４ , LiMnPO ４ , LiMn ０．５ Fe ０．５ PO ４ , LiMn ０．７ Fe<> ０．３ PO ４ and LiMn ０．７５ Fe ０．２５ PO ４ etc.

[0055] The positive electrode active material that occludes and releases sodium ions as metal ions may contain a sodium-containing compound or the like. The type of the sodium-containing compound is not particularly limited, and for example, it may be a Prussian blue analog represented by the formula (7).

[0056] Na ｘ K ｙ M5 ｚ Fe(CN) ６ ・aH ２O...(7) (wherein M5 may be at least one of Mn and Zn. x, y, and z satisfy 0.5 < x ≤ 2, 0 ≤ y ≤ 0.5, and 0 ≤ z ≤ 2, respectively. a is any value, except that y may satisfy 0.05 ≤ y ≤ 0.2.)

[0057] Specific examples of Prussian blue analogs shown in formula (7) include Na ２ MnFe(CN ６ ), Na １．４２ K ０．０９ Mn １．１３ Fe(CN) ６ 3H ２ O and Na ０．８３ K ０．１２ Zn １．４９ Fe(CN) ６ 3.2H ２ Examples include O.

[0058] The positive electrode active material that intercepts and releases potassium ions as metal ions may contain potassium-containing compounds. Specific examples of potassium-containing compounds include K ０．７ Fe ０．６ Mn ０．６ O ２ _K ０．６ MnO ２ _K ０．３ MnO ２ _K ０．３１ CoO ２ , KCrO ２ _K ０．６ CoO ２ _K ２／３ Mn ２／３ Co １／３ Ni １／３ O ２ _K ２／３ Ni ２／３ Te １／３ O ２ _K ２／３ Ni １／６ Co １／２ Te １／３ O ２ _K ２／３ Ni １／２ Mn １／６ Te １／３ O ２ _K ２／３ Ni １／２ Cu１／６ Te １／３ O ２ _K ２／３ Ni １／３ Zn １／３ Te １／３ O ２ _K ２／３ Ni １／６ Mg １／２ Te １／３ O ２ _K ２／３ Ni １／２ Co １／６ Te １／３ O ２ _K ２／３ Ni １／３ Mg １／３ Te １／３ O ２ and K ２／３ Ni １／３ Co １／３ Te １／３ O ２ These are some examples.

[0059] Details regarding the positive electrode binder may be the same as those regarding the negative electrode binder. The positive electrode binder and the negative electrode binder may be made of the same material, or they may be made of different materials. Furthermore, details regarding the positive electrode conductive agent may be the same as those regarding the negative electrode conductive agent. The positive electrode conductive agent and the negative electrode conductive agent may be made of the same material, or they may be made of different materials.

[0060] (Negative electrode electrolyte) The negative electrode electrolyte 15 is housed in the negative electrode chamber S1. As a result, the negative electrode electrolyte 15 is separated from the positive electrode electrolyte 16 housed in the positive electrode chamber S2 via a partition wall 12.

[0061] The negative electrode electrolyte 15 contains an aqueous solvent and an ionic substance. This ionic substance is a substance that ionizes in the aqueous solvent and contains metal ions.

[0062] (Aqueous solvent) The type of aqueous solvent is not particularly limited. For example, the aqueous solvent may be pure water.

[0063] (Ionic substances) The type of ionic substance is not particularly limited, but may be, for example, one or more of any of the electrolyte salts. The ionic substance may further contain one or more of any of the acids and bases. Specific examples of acids include carbonic acid, oxalic acid, nitric acid, sulfuric acid, hydrochloric acid, acetic acid, and citric acid.

[0064] The electrolyte salt is a salt containing cations and anions. More specifically, since the electrolyte salt contains metal ions that are intercalated and released at the negative electrode 13 and the positive electrode 14 as cations, it may contain one or more types of metal salts that have those metal ions as cations. This allows for the acquisition of a high voltage.

[0065] In the following, the metal ions absorbed and released at the negative electrode 13 and the positive electrode 14 will also be simply referred to as "metal ions."

[0066] In the secondary battery of this disclosure, the type of metal ion involved in charging and discharging is not particularly limited. For example, examples of metal ions involved in charging and discharging include alkali metal ions and light metal ions such as alkaline earth metal ions. When considering the high voltage obtained and the stability of the charge-discharge reaction, it is preferable that the metal ions involved in charging and discharging are alkali metal ions. Examples of suitable alkali metal ions include lithium ions, sodium ions, and potassium ions.

[0067] The metal salts whose cations are intercalated and released at the negative electrode 13 and positive electrode 14 may be, for example, lithium salts, sodium salts, and potassium salts. Specific examples of lithium salts include lithium carbonate, lithium oxalate, lithium nitrate, lithium sulfate, lithium chloride, lithium bisulfate, lithium bicarbonate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, lithium acetate, lithium citrate, lithium hydroxide, and imide salts. Imide salts may include bis(fluorosulfonyl)imidolithium and bis(trifluoromethanesulfonyl)imidolithium. Specific examples of sodium salts include compounds in which the lithium ions from the above-mentioned specific examples of lithium salts are substituted with sodium ions. Specific examples of potassium salts include compounds in which the lithium ions from the above-mentioned specific examples of lithium salts are substituted with potassium ions.

[0068] The electrolyte salt may further contain one or more metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14, respectively. The electrolyte salt may further contain one or more metal salts in which the metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14 are used as cations.

[0069] Specific examples of metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14 are the same as the specific examples of metal ions that are intercepted or released at the negative electrode 13 and the positive electrode 14 described above. However, the types of metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14 are different from the types of metal ions that are intercepted or released at the negative electrode 13 and the positive electrode 14.

[0070] Specific examples of metal salts whose cations are metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14 are the same as the specific examples of metal salts whose cations are metal ions that are intercepted or released at the negative electrode 13 and the positive electrode 14 described above. However, the types of metal salts whose cations are metal ions that are not intercepted or released at the negative electrode 13 and the positive electrode 14 are different from the types of metal salts whose cations are metal ions that are intercepted or released at the negative electrode 13 and the positive electrode 14.

[0071] Furthermore, the electrolyte salt further contains one or more types of other metal ions different from the metal ions that are intercepted and released at the negative electrode 13 and the positive electrode 14, and the metal ions that are not intercepted and released at the negative electrode 13 and the positive electrode 14. Therefore, the electrolyte salt may also contain one or more types of other metal salts in which the other metal ions are cations.

[0072] Other metal ions include, for example, alkaline earth metal ions, transition metal ions, and other metal ions. Specific examples of alkaline earth metal ions include magnesium ions and calcium ions. Specific examples of transition metal ions include titanium ions, vanadium ions, iron ions, manganese ions, nickel ions, cobalt ions, and copper ions. Specific examples of other metal ions include aluminum ions and zinc ions.

[0073] Specific examples of other metal salts with other metal ions as cations include compounds in which the lithium ion in the lithium salt examples mentioned above is substituted with alkaline earth metal ions, transition metal ions, and other metal ions.

[0074] In particular, the electrolyte salt preferably contains metal ions that are not intercepted or released at the negative electrode 13 and positive electrode 14, along with metal ions that are intercepted or released at the negative electrode 13 and positive electrode 14, respectively. For example, the electrolyte salt preferably contains one or more types of metal salts in which alkali metal ions that are intercepted or released at the negative electrode 13 and positive electrode 14 are cations, along with one or more types of alkali metal salts in which alkali metal ions that are not intercepted or released at the negative electrode 13 and positive electrode 14 are cations. This makes it easier to control the pH of the negative electrode electrolyte 15 to be sufficiently higher than the pH of the positive electrode electrolyte 16, as will be described later. It also makes it easier to maintain the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16. This improves the long-term reliability of the secondary battery.

[0075] When prioritizing the high voltage and energy density obtained by the secondary battery, it is preferable that the metal ions intercalated and released at the negative electrode 13 and the positive electrode 14 each contain lithium ions.

[0076] Furthermore, when the metal ions intercepted and released at the negative electrode 13 and the positive electrode 14 include lithium ions, it is preferable that the metal ions not intercepted and released at the negative electrode 13 and the positive electrode 14 include potassium ions. In other words, it is preferable that the electrolyte salt contains potassium ions along with lithium ions as cations. This is because it is easier to maintain the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 as described above.

[0077] Furthermore, the electrolyte salt may also contain one or more non-electrolytes.

[0078] The type of anion is not particularly limited. In particular, it is preferable that the anion contains hydroxide ions. This sufficiently suppresses fluctuations in the pH of the negative electrode electrolyte 15, making it easier to maintain the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16, which will be described later.

[0079] The composition of the negative electrode electrolyte 15 (type of aqueous solvent and type of electrolyte salt) and the composition of the positive electrode electrolyte 16 (type of aqueous solvent and type of electrolyte salt) may be the same or different from each other.

[0080] The content of ionic substances in the negative electrode electrolyte 15, i.e., the concentration (mol / kg) of the negative electrode electrolyte 15, is not particularly limited and can be set arbitrarily.

[0081] (pH) The negative electrode electrolyte 15 has a pH higher than that of the positive electrode electrolyte 16.

[0082] Because the negative electrode electrolyte 15 has a pH higher than that of the positive electrode electrolyte 16, the decomposition potential of the aqueous solvent shifts due to the difference in pH between the two, compared to the case where the negative electrode electrolyte 15 has a pH equal to or lower than that of the positive electrode electrolyte 16. As a result, the decomposition reaction of the aqueous solvent is thermodynamically suppressed during charging and discharging, and the potential window of the aqueous solvent is expanded. Therefore, a high voltage can be obtained, and the charging and discharging reaction utilizing the intercalation and deintercalation of metal ions can proceed sufficiently and stably.

[0083] In particular, it is preferable that the composition of the negative electrode electrolyte 15 (type of electrolyte salt) and the composition of the positive electrode electrolyte 16 (type of electrolyte salt) are different from each other. This is because it becomes easier to control the pH of the negative electrode electrolyte 15 to be higher than the pH of the positive electrode electrolyte 16.

[0084] The pH of the negative electrode electrolyte 15 is not particularly limited, as long as the pH of the negative electrode electrolyte 15 is higher than the pH of the positive electrode electrolyte 16. In particular, the pH of the negative electrode electrolyte 15 is preferably 11 or higher, more preferably 12 or higher, and even more preferably 13 or higher. As a result, the pH of the negative electrode electrolyte 15 becomes sufficiently high, making it easier for the pH of the negative electrode electrolyte 15 to become higher than the pH of the positive electrode electrolyte 16. Furthermore, as the difference between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 becomes sufficiently large, the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16 is more easily maintained.

[0085] Furthermore, it is preferable that the pH of the negative electrode electrolyte 15 is set so as not to corrode the negative electrode current collector 13A and the negative electrode active material layer 13B. This makes it easier for the charge-discharge reaction using the negative electrode 13 to proceed stably and continuously.

[0086] (Preferred configuration) The negative electrode electrolyte 15 preferably contains a saturated solution of an electrolyte salt, that is, it preferably contains a saturated solution of a metal salt in which the metal ions intercepted and released at the negative electrode 13 and the positive electrode 14 are cations. This makes it easier for the intercept and release reaction of metal ions to proceed stably during charging and discharging, thus allowing the charging and discharging reaction to proceed more favorably.

[0087] Whether or not the negative electrode electrolyte 15 is a saturated solution of electrolyte salt can be confirmed by visually inspecting the inside of the negative electrode chamber S1 after disassembling the secondary battery to see if electrolyte salt has precipitated. Specifically, the inside of the negative electrode chamber S1 includes the liquid in the negative electrode electrolyte 15, the surface of the partition wall 12, the surface of the negative electrode 13, and the inner wall surface of the exterior member 11. If electrolyte salt has precipitated, and the negative electrode electrolyte 15 (liquid) and electrolyte salt precipitates (solid) coexist inside the negative electrode chamber S1, then it can be determined that the negative electrode electrolyte 15 is a saturated solution of electrolyte salt. To investigate the composition of the precipitates, surface analysis methods such as X-ray photoelectron spectroscopy (XPS) may be used, or compositional analysis methods such as inductively coupled plasma (ICP) emission spectroscopy may be used.

[0088] The negative electrode electrolyte 15 may also be a pH buffer. This pH buffer may be an aqueous solution of a weak acid and its conjugate base, or an aqueous solution of a weak base and its conjugate acid, or both. This sufficiently suppresses pH fluctuations, making it easier to maintain the pH of the negative electrode electrolyte 15.

[0089] Furthermore, the negative electrode electrolyte 15 may also contain one or more types of buffering agents. Specific examples of buffering agents include trishydroxymethylaminomethane and ethylenediaminetetraacetic acid.

[0090] Furthermore, the negative electrode electrolyte 15 may be an isotonic solution that has an isotonic relationship with the positive electrode electrolyte 16. This optimizes the osmotic pressure of the negative electrode electrolyte 15 and makes it easier to maintain the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16.

[0091] (Positive electrode electrolyte) The positive electrode electrolyte 16 is housed in the positive electrode chamber S2. As a result, the positive electrode electrolyte 16 may be separated from the negative electrode electrolyte 15 housed in the negative electrode chamber S1 via a partition wall 12.

[0092] The composition of the positive electrode electrolyte 16 may be the same as that of the negative electrode electrolyte 15 described above, except as described below. That is, the details regarding the aqueous solvent and the ionic substance may be as described above.

[0093] The types of anions contained in the positive electrode electrolyte 16 are not particularly limited. In particular, it is preferable that the anions contain one or more types selected from the group consisting of nitrate ions, sulfate ions, bisulfate ions, carbonate ions, bicarbonate ions, phosphate ions, monohydrogen phosphate ions, dihydrogen phosphate ions, and carboxylate ions. This sufficiently suppresses fluctuations in the pH of the positive electrode electrolyte 16, making it easier to maintain a good relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16, as described later. Specific examples of carboxylate ions include formate ions, acetate ions, propionate ions, tartrate ions, and citrate ions.

[0094] In particular, it is more preferable that the anions include one or more of the following: nitrate ions, sulfate ions, bisulfate ions, carbonate ions, bicarbonate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions. This further suppresses fluctuations in the pH of the positive electrode electrolyte 16, making it easier to maintain the relationship between the pH of the negative electrode electrolyte 15 and the pH of the positive electrode electrolyte 16, as described later.

[0095] The content of ionic substances in the positive electrode electrolyte 16, i.e., the concentration (mol / kg) of the positive electrode electrolyte 16, is not particularly limited and can be set arbitrarily.

[0096] As described above, the negative electrode electrolyte 15 has a pH higher than that of the positive electrode electrolyte 16. In other words, the positive electrode electrolyte 16 has a pH lower than that of the negative electrode electrolyte 15.

[0097] It is preferable that the composition of the positive electrode electrolyte 16 (type of electrolyte salt) and the composition of the negative electrode electrolyte 15 (type of electrolyte salt) are different from each other. This makes it easier to control the pH of the positive electrode electrolyte 16 to be lower than the pH of the negative electrode electrolyte 15.

[0098] The pH of the positive electrode electrolyte 16 is not particularly limited, as long as the pH of the positive electrode electrolyte 16 is lower than the pH of the negative electrode electrolyte 15. In particular, the pH of the positive electrode electrolyte 16 is preferably 3 to 8, more preferably 4 to 8, and even more preferably 4 to 6. This makes it easier to control the pH of the positive electrode electrolyte 16 to a value lower than the pH of the negative electrode electrolyte 15, as the pH of the positive electrode electrolyte 16 becomes sufficiently low. In addition, the difference between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15 becomes sufficiently large, making it easier to maintain the relationship between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15. Furthermore, according to the above pH range, corrosion of the exterior member 11, the negative electrode current collector 13A, and the positive electrode current collector 14A can be suitably suppressed.

[0099] Furthermore, it is preferable that the pH of the positive electrode electrolyte 16 is set so as not to corrode the positive electrode current collector 14A and the positive electrode active material layer 14B. This makes it easier for the charge-discharge reaction using the positive electrode 14 to proceed stably and continuously.

[0100] Furthermore, the positive electrode electrolyte 16 is preferably a saturated solution of an electrolyte salt, specifically a saturated solution of a metal salt in which the metal ions intercepted and released at the negative electrode 13 and the positive electrode 14 are cations. This allows the intercept and release reaction of metal ions to proceed more stably during charging and discharging, thus facilitating the charging and discharging reaction.

[0101] Whether or not the positive electrode electrolyte 16 is a saturated solution of electrolyte salt can be determined in the same manner as the method described above for determining whether or not the negative electrode electrolyte 15 is a saturated solution of electrolyte salt, except that the positive electrode chamber S2 is examined instead of the negative electrode chamber S1.

[0102] Furthermore, the positive electrode electrolyte 16 may be a pH buffer solution. This effectively suppresses pH fluctuations, making it easier to maintain the pH of the positive electrode electrolyte 16.

[0103] Furthermore, the positive electrode electrolyte 16 may also contain one or more types of buffering agents. Details regarding the buffering agents are as described above in relation to the negative electrode electrolyte 15.

[0104] Furthermore, the positive electrode electrolyte 16 may be an isotonic solution that has an isotonic relationship with the negative electrode electrolyte 15. This optimizes the osmotic pressure of the positive electrode electrolyte 16, making it easier to maintain the relationship between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 15.

[0105] (Partition Wall) The partition wall 12 is positioned between the negative electrode electrolyte 15 and the positive electrode electrolyte 16, separating the internal chamber of the outer casing member 11 into two spaces. These two spaces are the negative electrode chamber S1, which houses the negative electrode electrolyte 15, and the positive electrode chamber S2, which houses the positive electrode electrolyte 16.

[0106] Since the partition wall 12 is located between the negative electrode chamber S1 and the positive electrode chamber S2, it separates the negative electrode electrolyte 15 contained in the negative electrode chamber S1 and the positive electrode electrolyte 16 contained in the positive electrode chamber S2. The partition wall 12 may be in contact with each of the negative electrode electrolyte 15 and the positive electrode electrolyte 16. The negative electrode 13 immersed in the negative electrode electrolyte 15 and the positive electrode 14 immersed in the positive electrode electrolyte 16 may face each other through the partition wall 12.

[0107] The partition wall 12, located between the negative electrode electrolyte 15 and the positive electrode electrolyte 16, suppresses the permeation of anions while allowing substances such as metal ions (cations) absorbed and released at the negative electrode 13 and positive electrode 14 to pass through. This prevents the negative electrode electrolyte 15 and the positive electrode electrolyte 16 from mixing with each other, while allowing metal ions to move between the negative electrode 13 and the positive electrode 14. Therefore, the partition wall 12 allows metal ions to pass through from the negative electrode electrolyte 15 to the positive electrode electrolyte 16, and also allows metal ions to pass through from the positive electrode electrolyte 16 to the negative electrode electrolyte 15.

[0108] (Exterior component) The exterior component 11 has an internal space for housing a partition wall 12, a negative electrode 13, a positive electrode 14, a negative electrode electrolyte 15, and a positive electrode electrolyte 16, etc.

[0109] The exterior component 11 may include one or more materials such as metal materials, glass materials, and polymer compounds. For example, the exterior component 11 may be any of the rigid metal cans, glass cases, and plastic cases, or any of the flexible or pliable metal foils and polymer films.

[0110] [Features of the secondary battery of this disclosure] The secondary battery of this disclosure has particular features in the partition wall 12. The features of the secondary battery of this disclosure will be described in detail below.

[0111] In the secondary battery of this disclosure, the partition wall 12 is a membrane comprising a plurality of polymer compound layers. The partition wall 12 may include polymer compound layers containing polymer compounds that include cation exchange groups. More specifically, the partition wall 12 may be a cation exchange membrane comprising a plurality of polymer compound layers stacked on top of each other along the direction in which the negative electrode chamber S1 and the positive electrode chamber S2 are adjacent.

[0112] A cation exchange membrane is a polymer membrane that can selectively permeate cations such as metal ions, and has multiple anionic functional groups (-X － It is a polymer membrane having ). Its multiple anionic groups contain hydrogen ions (H ＋ ) and metal ions (Mn ＋It is neutralized by multiple cations, including one or more of the following: (e.g., -X). Here, n is an integer of 1 or more. Specific examples of metal ions include lithium ions, sodium ions, and potassium ions. As a result, the cation exchange membrane has multiple cation exchange groups (e.g., -X). － H ＋ and -X － M ＋ They may have (etc.).

[0113] The first layer 12A and the second layer 12B each contain at least one different cation exchange group. The first layer 12A and the second layer 12B may be porous layers that can selectively permeate cations such as metal ions, and the partition wall 12 may be a cation exchange membrane in which two or more layers, at least the first layer 12A and the second layer 12B, are laminated. Since such a cation exchange membrane comprises multiple laminated layers, it may also be called a cation exchange laminated membrane or a cation exchange composite membrane.

[0114] Each of the first layer 12A and the second layer 12B has multiple cation exchange groups (-X － ) has, and the plurality of cation exchange groups have hydrogen ions (H ＋ ) and metal ions (Mn ＋ It is neutralized by multiple cations, including one or more of the following: (e.g., -X). Here, n is an integer of 1 or more. The metal ions may be metal ions that are intercepted and released by the negative electrode 13 and the positive electrode 14. Specific examples of metal ions include lithium ions, sodium ions, and potassium ions. As a result, each of the first layer 12A and the second layer 12B has multiple ion exchange groups (e.g., -X － H ＋ and -X － M ＋ They may have (etc.).

[0115] The first layer 12A contained in the partition wall 12 is in contact with at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16. In other words, at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may be arranged to be in contact with the first layer 12A. For example, at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may be in contact with the first layer 12A, but not in direct contact with the second layer 12B. Specifically, the first layer 12A may be in contact with at least the negative electrode electrolyte 15. Alternatively, as shown in Figure 1B, the first layer 12A may be in contact with at least the positive electrode electrolyte 16.

[0116] The first layer 12A may be a layer that excels at suppressing the permeation of anions, and the first layer 12A may be a layer with high cation selectivity. Furthermore, the first layer 12A may be a layer that does not easily contain electrolyte salts. The first layer 12A may have an electrolyte salt concentration lower than at least one of the electrolyte salt concentration contained in the negative electrode electrolyte 15 and the electrolyte salt concentration contained in the positive electrode electrolyte 16. For example, the first layer 12A may contain cation exchange groups having a low acid dissociation constant as cation exchange groups.

[0117] Specifically, the first layer 12A is a carboxylic acid group (-C(=O)-O － ), hydroxycarboxylic acid group, phosphonic acid group (-P(=O)OH(O) － )), phosphinic acid group (-P(=O)H(O － )) and xanthogenic acid group (-O-C(=S)-S － The polymer layer may contain at least one cation exchange group selected from the group consisting of ). Therefore, the ion exchange group contained in the first layer 12A is a carboxylate ion group (-C(=O)-O-H ＋ ), or carboxylate metal complex (-C(=O)-O － M ＋ ) (so-called carboxylic acid metal base), hydroxycarboxylic acid ion group, hydroxycarboxylic acid metal complex, phosphonate ion group (-P(=O)OH(O) － H ＋ )), phosphonic acid metal complex (-P(=O)OH(O － M ＋ )), phosphinate ion group (-P(=O)H(O－ H ＋ )), phosphinate metal complex (-P(=O)H(O － M ＋ )), xanthogenic acid ion group (-OC(=S)-S － H ＋ ), xanthogenic metal complex (-O-C(=S)-S － M ＋ ) and so on. By including the functional groups described above, the penetration of electrolyte salts into the membrane is suppressed. Therefore, as will be described in detail below, it is thought that the deterioration of the membrane is suppressed and a rechargeable secondary battery that can be stably charged and discharged is realized. The rechargeable battery of this disclosure has a cation exchange layer in the first layer 12A that is in contact with at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16, which is particularly excellent at suppressing the penetration of electrolyte salts.

[0118] In particular, the first layer 12A preferably contains a carboxylic acid group, a phosphonic acid group, a phosphinic acid group, and / or a hydroxycarboxylic acid group. When the first layer 12A is in contact with a negative electrode electrolyte 15 having a pH higher than that of the positive electrode electrolyte 16, it is preferable that the first layer 12A contains a carboxylic acid group. Furthermore, when the first layer 12A is in contact with a positive electrode electrolyte 16 having a pH lower than that of the negative electrode electrolyte 15, it is preferable that the first layer 12A contains a phosphonic acid group, a phosphinic acid group, and / or a hydroxycarboxylic acid group, and more preferably a phosphonic acid group. By containing the above-mentioned functional groups in the first layer 12A, the acid dissociation of the functional groups is optimized with respect to the pH of the electrolyte, and the selectivity of cations can be further enhanced.

[0119] The inventors have newly discovered that the long-term reliability of a secondary battery can be improved by providing a first layer 12A in which the partition wall 12 is arranged to be in contact with at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16. As a result of diligent research, the inventors have found that the deterioration of the partition wall 12 over time is caused by electrolyte salts that have penetrated the partition wall 12. Specifically, a reaction occurs inside or on the surface of the partition wall 12 due to electrolyte salts contained in at least one of the positive electrode electrolyte and the negative electrode electrolyte, changing the structure or composition of the film constituting the partition wall 12, and as a result the resistance of the partition wall 12 increases, which can degrade the performance of the secondary battery. In contrast, with the secondary battery of this disclosure, the presence of the first layer 12A can suppress the penetration of electrolyte salts from the negative electrode electrolyte 15 and / or positive electrode electrolyte 16 into the partition wall 12, which are in contact with the first layer 12A. Therefore, deterioration of the partition wall 12 caused by the reaction of electrolyte salts that have penetrated into the partition wall 12 and / or electrolyte salts that have permeated through the partition wall 12 is suppressed, and a secondary battery with excellent long-term reliability can be obtained.

[0120] The type of skeleton to which multiple cation exchange groups are bonded is not particularly limited, as long as it is a polymer compound to which those multiple cation exchange groups can be bonded. Specific examples of polymer compounds that form this skeleton include perfluorohydrocarbons, polymer compounds obtained by polymerizing monomers having ethylene-based unsaturated double bonds, polyethylene oxide, polyamide, polyimide, polysulfone, polyphenylene sulfide, polyether ketone, polyether ether ketone, polyetherimide, polyphenylene oxide, polyethersulfone, polybenzimidazole, polystyrene-poly(ethylene-butylene)-polystyrene triblock copolymer, polystyrene-poly(ethylene-propylene)-polystyrene triblock copolymer, and styrene-based elastomers. Polymer compounds obtained by polymerizing monomers having ethylene-based unsaturated double bonds include vinyl-based, styrene-based, or acrylic-based polymer compounds. Examples of styrene-based elastomers include polystyrene-polyisoprene block copolymer and hydrogenated polystyrene-polyisoprene block copolymers.

[0121] Figure 2A is a schematic cross-sectional view showing the configuration of a secondary battery according to one embodiment of the present disclosure. As shown in the figure, the partition wall 12 may be a film made up of three or more layers, including a third layer 12C which is another polymer compound layer, in addition to the polymer layers containing cation exchange groups of the first layer 12A and the second layer 12B described above. The third layer 12C may be, for example, a solid electrolyte layer and / or a porous polymer layer that does not contain cation exchange groups. The partition wall 12 may contain a plurality of third layers 12C. The plurality of third layers 12C may be made of the same material or may be made of different materials. For example, the partition wall 12 may contain two or more layers as the third layer 12C, including a solid electrolyte layer and a porous polymer layer that does not contain cation exchange groups. Alternatively, the partition wall 12 may contain two or more layers as the third layer 12C, which are either a solid electrolyte layer or a porous polymer layer that does not contain cation exchange groups.

[0122] As shown in Figure 2A, the partition wall 12 may comprise, for example, a first layer 12A in contact with the negative electrode electrolyte 15, a second layer 12B in contact with the positive electrode electrolyte 16, and a third layer 12C positioned between the first layer 12A and the second layer 12B, connected to the first layer 12A and the third layer 12C, and containing a solid electrolyte. In this case, the contact of the first layer 12A with the negative electrode electrolyte 15 can suppress the intrusion of electrolyte salts from the negative electrode electrolyte 15 into the partition wall 12. Therefore, deterioration of the partition wall 12 caused by reactions of electrolyte salts that have entered the partition wall 12 and / or electrolyte salts that have permeated through the partition wall 12 is suppressed, and a secondary battery with excellent long-term reliability can be obtained.

[0123] Alternatively, the partition wall 12 may comprise, for example, a first layer 12A in contact with the positive electrode electrolyte 16, a second layer 12B in contact with the negative electrode electrolyte 15, and a third layer 12C positioned between the first layer 12A and the second layer 12B, connected to the first layer 12A and the third layer 12C, and containing a solid electrolyte. In this case, the contact of the first layer 12A with the positive electrode electrolyte 16 can suppress the intrusion of electrolyte salts from the positive electrode electrolyte 16 in contact with the first layer 12A into the partition wall 12. Therefore, deterioration of the partition wall 12 caused by reactions of electrolyte salts that have entered the partition wall 12 and / or electrolyte salts that have permeated through the partition wall 12 is suppressed, and a secondary battery with excellent long-term reliability can be obtained.

[0124] Furthermore, as shown in Figure 2B, the partition wall 12 may comprise, for example, a first layer 12A in contact with the negative electrode electrolyte 15, a third layer 12C in contact with the positive electrode electrolyte 16 and containing a solid electrolyte, and a second layer 12B positioned between the first layer 12A and the third layer 12C and connecting to the first layer 12A and the third layer 12C. In this case, the first layer 12A in contact with the negative electrode electrolyte 15 can suppress the intrusion of electrolyte salts from the negative electrode electrolyte 15 in contact with the first layer 12A into the partition wall 12. Therefore, deterioration of the partition wall 12 caused by the reaction of electrolyte salts that have intruded into the partition wall 12 and / or electrolyte salts that have permeated through the partition wall 12 is suppressed, and a secondary battery with excellent long-term reliability can be obtained.

[0125] Alternatively, the partition wall 12 may comprise, for example, a first layer 12A in contact with the positive electrode electrolyte 16, a third layer 12C containing a solid electrolyte in contact with the negative electrode electrolyte 15, and a second layer 12B positioned between the first layer 12A and the third layer 12C and connecting to the first layer 12A and the third layer 12C. In this case, the first layer 12A in contact with the positive electrode electrolyte 16 can suppress the intrusion of electrolyte salts from the positive electrode electrolyte 16 in contact with the first layer 12A into the partition wall 12. Therefore, deterioration of the partition wall 12 caused by reactions of electrolyte salts that have entered the partition wall 12 and / or electrolyte salts that have permeated through the partition wall 12 is suppressed, and a secondary battery with excellent long-term reliability can be obtained.

[0126] As the solid electrolyte, an inorganic solid electrolyte is preferred, for example, an oxide-based solid electrolyte or a sulfide-based solid electrolyte. The oxide-based solid electrolyte has a NASICON-type structure and the general formula is LiM ２ (PO ４ ) ３ It is preferable to use a lithium phosphate solid electrolyte represented by the above general formula. In the above general formula, M is preferably at least one element selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), and aluminum (Al). It is more preferable that element M includes one of Ge, Zr, and Ti, and Al.

[0127] A specific example of a lithium phosphate solid electrolyte having a NASICON-type structure is LATP (Li １＋ｘ Al ｘ Ti ２－ｘ (PO ４ ) ３ ), Li １＋ｘ Al ｘ Ge ２－ｘ (PO ４ ) ３ Li １＋ｘ Al ｘ Zr ２－ｘ (PO ４ ) ３ The following can be cited. In the above formula, x is preferably in the range of 0 < x ≤ 5 and in the range of 0.1 ≤ x ≤ 0.5. LATP has excellent water resistance and is less prone to hydrolysis in secondary batteries. It is preferable to use LATP as the solid electrolyte.

[0128] Furthermore, as an oxide-based solid electrolyte, amorphous LIPON (Li ２．９ PO ３．３ N ０．４６ ), or LLZ (Li ７ La ３ Zr ２ O １２ ) may also be used.

[0129] Examples of porous polymer layers include polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), ethylene tetrafluoroethylene copolymer, and polyvinylidene fluoride (PVdF).

[0130] Furthermore, the third layer 12C may be, for example, a porous composite membrane comprising a solid electrolyte layer and a polymer compound layer. The porous composite membrane may be a composite solid electrolyte membrane having a solid electrolyte layer on at least one main surface of the porous polymer layer described above. The composite solid electrolyte membrane has a density of 1 × 10⁻¹⁶ at 25°C. －１０ It is preferable to include a solid electrolyte layer containing a solid electrolyte having a lithium ion conductivity of S / cm or higher. The permeability coefficient of the porous composite membrane is not particularly limited, but is 1 × 10⁻⁶. －１９ I understand ２ The above 1 x 10 －１５ I understand ２ It is preferable that it be within the range of less than

[0131] The first layer 12A is in contact with at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16. As described above, the negative electrode electrolyte 15 has a higher pH than the positive electrode electrolyte 16. Furthermore, if we are concerned with maintaining the relative pH of the negative electrode electrolyte 15 and the positive electrode electrolyte 16, it is preferable that the positive electrode electrolyte 16 contains at least one selected from the group consisting of nitrate ions, sulfate ions, bisulfate ions, carbonate ions, bicarbonate ions, phosphate ions, monohydrogen phosphate ions, and dihydrogen phosphate ions. On the other hand, it is preferable that the negative electrode electrolyte 15 contains hydroxide ions.

[0132] The first layer 12A is positioned on at least one of the main surfaces of the partition wall 12 on the negative electrode chamber S1 side or the positive electrode chamber S2 side. The first layer 12A does not necessarily have to be provided across the entire surface of the main surface of the partition wall 12. The first layer 12A may be positioned in any region of the main surface as long as it is in contact with at least one of the negative electrode electrolyte 15 or the positive electrode electrolyte 16. This makes it possible to obtain the effect of suppressing the intrusion of electrolyte salts into the partition wall 12 by the first layer 12A.

[0133] Preferably, the first layer 12A extends over the entire wetted area where the partition wall 12 is in contact with at least one of the negative electrode electrolyte 15 or the positive electrode electrolyte 16. Specifically, the partition wall 12 comprises a negative electrode side wetted area in contact with the negative electrode electrolyte 15 and a positive electrode side wetted area in contact with the positive electrode electrolyte 16. It is preferable that the first layer 12A is present over the entire area of ​​at least one of the negative electrode side wetted area or the positive electrode side wetted area. With this configuration, it is possible to suppress the intrusion of electrolyte salts into the interior of the partition wall 12 over the entire wetted area of ​​the partition wall 12, and an effective effect of suppressing the deterioration of the partition wall 12 can be obtained.

[0134] More preferably, the first layer 12A may extend over the entire surface of at least one of the main surfaces of the partition wall 12 on the negative electrode chamber S1 side or the positive electrode chamber S2 side. In other words, at least one of the main surfaces of the partition wall 12 on the negative electrode chamber S1 side or the positive electrode chamber S2 side may be covered by the first layer 12A. With this configuration, the intrusion of electrolyte salts into the interior of the partition wall 12 can be suppressed over the entire main surface of the partition wall 12, and the effect of suppressing the deterioration of the partition wall 12 can be obtained more effectively.

[0135] As described above, the first layer 12A can suitably suppress the intrusion of electrolyte salts into the interior of the partition wall 12. On the other hand, such a first layer 12A may have low ionic conductivity and may have relatively high resistance. It is conceivable to reduce the overall thickness of the partition wall 12 in order to reduce resistance, but this would reduce the mechanical strength of the partition wall 12 and may actually accelerate the deterioration of the partition wall 12. In the secondary battery of this disclosure, by providing at least the first layer 12A and the second layer 12B which contains different functional groups from the first layer 12A, it is possible to improve the mechanical strength of the partition wall while suppressing the increase in resistance compared to the case in which only the first layer 12A is provided. In other words, with the secondary battery of this disclosure, the intrusion of electrolyte salts can be suppressed by providing the first layer 12A, and the mechanical strength of the partition wall can be improved by providing the second layer 12B, thereby improving the long-term reliability of the partition wall 12. As a result, it is possible to obtain a secondary battery with excellent long-term reliability, low resistance and high output.

[0136] The second layer 12B may be a cation exchange polymer layer with excellent ionic conductivity. The material for the second layer 12B may be selected to prioritize lower film resistance compared to the first layer 12A. The functional groups contained in the second layer 12B may have a higher acid dissociation constant than the functional groups contained in the first layer 12A. For example, the second layer 12B may contain sulfonic acid groups (-S(=O) ２ -O － ), aminosulfonic acid group (-CH ｎ (NH ２ )S (=O) ２ -O － ) and sulfate group (-OS (=O) ２ -O － The polymer may contain at least one functional group selected from the group consisting of ). Therefore, the ion exchange group contained in the second layer 12B is a sulfonate ion group (-S (=O) ２ -O － ), or sulfonic acid metal complex (-S (=O) ２ -O － M ＋ ) (so-called sulfonic acid metal base), aminosulfonic acid ion group (-CH ｎ (NH ２ )S (=O) ２ -O － H ＋ ), aminosulfonic acid metal complex (-CH ｎ (NH ２ )S (=O) ２ -O － M ＋ ), sulfate ion group (-OS (=O) ２ -O － H ＋ ), metal sulfate complex (-OS (=O) ２ -O － M ＋ ) and so on. By providing the above-mentioned functional groups, a polymer layer with excellent ionic conductivity can be provided as the second layer 12B. This makes it possible to improve the ionic conductivity of the entire partition wall 12. If low film resistance and excellent strength characteristics are important, it is preferable that the second layer 12B contains sulfonic acid groups.

[0137] The first layer 12A and the second layer 12B may be stacked adjacent to each other. This allows at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 to be in contact with the first layer 12A, but not with the second layer 12B. In other words, the first layer 12A may be interposed between at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16 and the second layer 12B. Specifically, the first layer 12A may be interposed between the negative electrode electrolyte 15 and the second layer 12B. Also, as shown in Figure 1B, the first layer 12A may be interposed between the positive electrode electrolyte 16 and the second layer 12B. With this structure, by providing a first layer 12A in contact with at least one of the negative electrode electrolyte 15 and the positive electrode electrolyte 16, the penetration and permeation of electrolyte salts into the partition wall 12 is suitably suppressed, while by providing a second layer 12B via the first layer 12A, the overall resistance of the partition wall 12 can be reduced. As a result, a secondary battery with excellent long-term reliability and output can be obtained.

[0138] More preferably, as shown in Figure 3, the partition wall 12 may have a structure comprising a second layer 12B sandwiched between two first layers 12A. Figure 3 is a schematic cross-sectional view showing a secondary battery according to another embodiment of the present disclosure. As shown, the first layer 12A may be in contact with both the negative electrode electrolyte 15 and the positive electrode electrolyte 16. The partition wall 12 may comprise two first layers 12A, one on each side of the negative electrode electrolyte 15 side and the other on the positive electrode electrolyte 16 side. In other words, the partition wall 12 may have a multilayer structure in which one or more other layers, including a second layer 12B, are sandwiched between two first layers 12A. In short, the partition wall 12 may have first layers 12A on both side surfaces that are in contact with the electrolyte, while having a second layer 12B inside. Specifically, the partition wall 12 may comprise a first layer 12A1 in contact with the negative electrode electrolyte 15, a first layer 12A2 in contact with the positive electrode electrolyte 16, and a second layer 12B located between the first layers 12A1 and 12A2. With such a structure, the negative electrode electrolyte 15 and the positive electrode electrolyte 16 are in contact with the first layer 12A (12A1, 12A2), but not with the second layer 12B. This effectively suppresses the intrusion of electrolyte salts into the partition wall 12 from the negative electrode electrolyte 15 and positive electrode electrolyte 16 sides, while the ionic conductivity of the partition wall 12 can be increased by providing the second layer 12B between the first layers 12A. Such a structure may be particularly useful in secondary batteries where repeated charging and discharging involves bidirectional movement of cations between the negative electrode chamber S1 and the positive electrode chamber S2, and attraction of anions to the partition wall from both sides. In other words, according to this disclosure, even when charging and discharging are repeated, deterioration of the partition wall 12 can be suppressed, and a secondary battery with high ionic conductivity can be provided.

[0139] In a secondary battery, electrolyte salts are contained on both sides of the partition wall 12 (i.e., both the negative electrode electrolyte 15 side and the positive electrode electrolyte 16 side). During charging and discharging of the secondary battery, the polarity reverses, which can reverse the direction in which cations and anions are electrically attracted to each other. Specifically, during charging, anions in the negative electrode electrolyte 15 are attracted to the positive electrode chamber S2 side (i.e., the partition wall 12 side), while during discharging, anions in the positive electrode electrolyte 16 are attracted to the negative electrode chamber S1 side (i.e., the partition wall 12 side). Furthermore, cations in the negative electrode electrolyte 15 and cations in the positive electrode electrolyte 16 are attracted and moved in the opposite direction to that of the anions. In other words, during charging and discharging of the secondary battery, cations and anions, i.e., electrolyte salts, can move in both directions, either towards the negative electrode chamber S1 side or the positive electrode chamber S2 side. As described above, in one embodiment, the secondary battery of the present disclosure has a first layer 12A provided on each of the two side surfaces of the partition wall 12 so as to be in contact with both the negative electrode electrolyte 15 and the positive electrode electrolyte 16. This makes it possible to suppress the intrusion and permeation of electrolyte salts from both the negative electrode electrolyte 15 side and the positive electrode electrolyte 16 side. Therefore, even when the secondary battery is repeatedly charged and discharged, the deterioration of the partition wall 12 is suitably suppressed, and a secondary battery with better long-term reliability can be obtained.

[0140] The two first layers 12A, provided on both the negative electrode electrolyte 15 side and the positive electrode electrolyte 16 side of the partition wall 12, may contain different functional groups or may contain the same functional groups.

[0141] If the partition wall 12 comprises two first layers 12A1 and 12A2 facing the negative electrode chamber S1 side and the positive electrode chamber S2 side, the two first layers 12A1 and 12A2 may be polymer compound layers containing the same cation exchange groups. Alternatively, the two first layers 12A1 and 12A2 may be polymer compound layers containing different cation exchange groups. For example, one of the two first layers 12A1 and 12A2 may be a polymer compound layer containing carboxylic acid groups, while the other first layer may be a polymer compound layer containing phosphonic acid groups.

[0142] If the focus is on reducing film resistance and improving ionic conductivity, the thickness Ta of the first layer 12A may be smaller than the thickness Tb of the second layer 12B. In other words, the second layer 12B may have a greater thickness Tb than the thickness Ta of the first layer 12A. For example, the thickness Ta of the first layer 12A may be 10% to 95% or 30% to 80% of the thickness Tb of the second layer 12B. By making the thickness Tb of the second layer 12B, which has low film resistance, larger than the thickness Ta of the first layer 12A, which has high film resistance, the overall resistance of the partition wall 12 can be kept lower.

[0143] Furthermore, as shown in Figure 3, when the first layer 12A is provided on both the negative electrode chamber S1 side and the positive electrode chamber S2 side, the first layer 12A1 located on the negative electrode chamber S1 side may have the same thickness as the first layer 12A2 located on the positive electrode chamber S2 side. Alternatively, the first layer 12A1 located on the negative electrode chamber S1 side and the first layer 12A2 located on the positive electrode chamber S2 side may have different thicknesses.

[0144] The configuration of the secondary battery described above can be modified as appropriate, as explained below. However, the series of modification examples described below may be combined with each other.

[0145] For example, the partition wall 12 may be pre-ion-exchanged by metal ions absorbed and released at the negative electrode 13 and the positive electrode 14, respectively. In this case as well, since the metal ions permeate through the partition wall 12, a similar effect can be obtained.

[0146] In this case, in particular, the metal ions absorbed and released at the negative electrode 13 and the positive electrode 14 can more easily permeate the partition wall 12, thus achieving a higher effect.

[0147] Furthermore, titanium-containing compounds, niobium-containing compounds, vanadium-containing compounds, iron-containing compounds, and molybdenum-containing compounds were given as examples of negative electrode active materials. However, the negative electrode active material may be any other compound as long as it facilitates a smooth and stable charge-discharge reaction even when using two types of aqueous electrolytes (negative electrode electrolyte 15 and positive electrode electrolyte 16). In this case as well, the same effect can be obtained.

[0148] In Figure 1A, liquid electrolytes (negative electrode electrolyte 15 and positive electrode electrolyte 16) were used. However, as shown in Figure 4, gel-like electrolytes, the electrolyte layers 17 and 18, may be used instead of liquid electrolytes. The polymer compounds contained in the electrolyte layers 17 and 18 do not have cation exchange groups. The polymer compounds contained in the electrolyte layers 17 and 18 may form a matrix for holding the electrolyte. The electrolyte layers 17 and 18 are gel-like layers formed by swelling by incorporating a solvent into the cross-linked structure of the polymer compounds, and are clearly distinguishable from the partition wall 12, which prevents mixing of the electrolyte layers 17 and 18 with the liquid electrolyte and enables selective ion permeability.

[0149] When electrolyte layers 17 and 18 are used, as shown in Figure 4, electrolyte layer 17 may be interposed between the partition wall 12 and the negative electrode 13, and electrolyte layer 18 may be interposed between the partition wall 12 and the positive electrode 14. In this way, electrolyte layer 17 may be adjacent to both the partition wall 12 and the negative electrode 13, and electrolyte layer 18 may be adjacent to both the partition wall 12 and the positive electrode 14.

[0150] Specifically, the electrolyte layer 17 contains a polymer compound together with the negative electrode electrolyte 15, and the negative electrode electrolyte 15 may be held in place by the polymer compound. This can prevent leakage of the negative electrode electrolyte 15.

[0151] The electrolyte layer 18 contains a polymer compound together with the positive electrode electrolyte 16, and the positive electrode electrolyte 16 may be held in place by the polymer compound. This can prevent leakage of the positive electrode electrolyte 16.

[0152] The type of polymer compound is not particularly limited as long as it does not have a cation exchange group, but specifically, it may be one or more of the following: polyvinylidene fluoride and polyethylene oxide.

[0153] When forming the electrolyte layer 17, a precursor solution containing the negative electrode electrolyte 15, a polymer compound, and an organic solvent may be prepared, and then the precursor solution may be applied to the negative electrode 13. When forming the electrolyte layer 18, a precursor solution containing the positive electrode electrolyte 16, a polymer compound, and an organic solvent may be prepared, and then the precursor solution may be applied to the positive electrode 14.

[0154] In this case as well, metal ions can move between the negative electrode 13 and the positive electrode 14 via the electrolyte layers 17 and 18. Furthermore, by providing the partition wall 12 comprising the first layer 12A and the second layer 12B, a similar effect of improving the long-term reliability of the secondary battery can be obtained.

[0155] [Operation of Rechargeable Batteries] Rechargeable batteries can operate as follows:

[0156] During charging, metal ions are released from the positive electrode 14, and these metal ions move to the negative electrode 13 via the positive electrode electrolyte 16, the partition wall 12, and the negative electrode electrolyte 15, so that metal ions are absorbed at the negative electrode 13.

[0157] During discharge, metal ions are released from the negative electrode 13, and these metal ions move to the positive electrode 14 via the negative electrode electrolyte 15, the partition wall 12, and the positive electrode electrolyte 16, so that metal ions are absorbed at the positive electrode 14.

[0158] [Method for Manufacturing a Secondary Battery] When manufacturing the secondary battery of this disclosure, the partition wall 12, the negative electrode 13, and the positive electrode 14 may be manufactured according to the example procedure described below, and the negative electrode electrolyte 15 and the positive electrode electrolyte 16 may be prepared, after which the secondary battery may be assembled. Note that the method described below is merely an example, and the method for manufacturing a secondary battery according to this disclosure is not limited to the method described below.

[0159] (Preparation of the negative electrode) First, the negative electrode active material, negative electrode binder, and negative electrode conductive agent are mixed together to form a negative electrode mixture. Next, the negative electrode mixture is added to a solvent to prepare a paste-like negative electrode mixture slurry. The solvent may be an aqueous solvent or an organic solvent. Finally, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 13A, excluding the connection terminal portion 13AT, to form a negative electrode active material layer 13B. After this, the negative electrode active material layer 13B may be compressed and molded using a compression device such as a roll press. In this case, the negative electrode active material layer 13B may be heated, or the compression molding may be repeated multiple times. As a result, the negative electrode active material layer 13B is formed on both sides of the negative electrode current collector 13A. The negative electrode 13 may be prepared in this manner.

[0160] (Preparation of the positive electrode) A positive electrode active material layer 14B is formed on both sides of the positive electrode current collector 14A using the same procedure as the preparation of the negative electrode 13 described above. Specifically, the positive electrode active material, positive electrode binder, and positive electrode conductive agent are mixed together to form a positive electrode mixture, and then the positive electrode mixture is added to a solvent to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 14A, excluding the connection terminal portion 14AT, to form the positive electrode active material layer 14B. After this, the positive electrode active material layer 14B may be compression molded. This forms a positive electrode active material layer 14B on both sides of the positive electrode current collector 14A. The positive electrode 14 can be prepared in this manner.

[0161] (Preparation of the partition wall) As described above, a cation exchange membrane is used as the partition wall 12, in which a first layer 12A and a second layer 12B containing predetermined cation exchange groups are laminated. Such a partition wall 12 may be prepared by known polymer membrane preparation methods. For example, the partition wall 12 may be prepared by forming the second layer 12B and then forming the first layer 12A on top of it by coating or the like, or by separately synthesizing the first layer 12A and the second layer 12B, etc., then laminating them in a predetermined order and bonding them together by pressure or the like.

[0162] (Preparation of positive electrode electrolyte) The positive electrode electrolyte 16 may be prepared by adding an ionic substance to an aqueous solvent and dispersing or dissolving the ionic substance in the aqueous solvent.

[0163] (Preparation of negative electrode electrolyte) The negative electrode electrolyte 15 is prepared using the same procedure as the preparation of the positive electrode electrolyte 16 described above, so that it has a pH higher than that of the positive electrode electrolyte 16.

[0164] (Assembly of secondary battery) First, the partition wall 12 is attached to the outer casing member 11 by placing the partition wall 12 inside the outer casing member 11. This may form a negative electrode chamber S1 and a positive electrode chamber S2 that are separated from each other via the partition wall 12.

[0165] Next, the negative electrode 13 and positive electrode 14 are attached to the outer casing member 11 by placing them inside the outer casing member 11. In this case, the negative electrode 13 is placed inside the negative electrode chamber S1, and the connection terminal portion 13AT is led out to the outside of the outer casing member 11. The positive electrode 14 is placed inside the positive electrode chamber S2, and the connection terminal portion 14AT is led out to the outside of the outer casing member 11.

[0166] Next, the negative electrode electrolyte 15 is supplied to the negative electrode chamber S1 from a supply port (not shown) provided in the outer casing member 11, and the positive electrode electrolyte 16 is supplied to the positive electrode chamber S2 from the same supply port (not shown) provided in the outer casing member 11. As a result, the negative electrode electrolyte 15 is contained in the negative electrode chamber S1, and the negative electrode 13 is immersed in the negative electrode electrolyte 15. Similarly, the positive electrode electrolyte 16 is contained in the positive electrode chamber S2, and the positive electrode 14 is immersed in the positive electrode electrolyte 16.

[0167] Finally, the supply port used to supply the negative electrode electrolyte 15 is sealed, and the supply port used to supply the positive electrode electrolyte 16 is also sealed.

[0168] This completes a secondary battery containing two types of aqueous electrolytes (negative electrode electrolyte 15 and positive electrode electrolyte 16).

[0169] The embodiments of the present invention have been described above, but these are merely typical examples. Those skilled in the art will easily understand that the present invention is not limited thereto, and various embodiments are conceivable without altering the essence of the invention.

[0170] One embodiment of the present disclosure described above encompasses the following preferred embodiments: <1> A secondary battery comprising: a negative electrode that intercepts and releases metal ions; a positive electrode that intercepts and releases metal ions; a negative electrode electrolyte containing an aqueous solvent; a positive electrode electrolyte containing an aqueous solvent; a negative electrode chamber containing the negative electrode and the negative electrode electrolyte; and a positive electrode chamber containing the positive electrode and the positive electrode electrolyte, wherein the negative electrode chamber and the positive electrode chamber are separated by a partition wall disposed between them and permeable to metal ions; the negative electrode electrolyte has a pH greater than that of the positive electrode electrolyte; and the partition wall has a structure in which two or more layers are stacked, each containing at least a first layer and a second layer containing different cation exchange groups, wherein the first layer contains a polymer compound containing at least one cation exchange group selected from the group consisting of carboxylic acid groups, hydroxycarboxylic acid groups, phosphonic acid groups, phosphinic acid groups, and xanthogenic acid groups, and is in contact with at least one of the negative electrode electrolyte and the positive electrode electrolyte. <2> The secondary battery according to <1>, wherein the second layer comprises a polymer compound containing at least one cation exchange group selected from the group consisting of sulfonic acid groups, aminosulfonic acid groups, and sulfate groups. <3> The secondary battery according to <1> or <2>, wherein the first layer extends across the entire surface of the partition wall on at least one of the negative electrode chamber side and the positive electrode chamber side. <4> The secondary battery according to any one of <1> to <3>, wherein the first layer is in contact with the negative electrode electrolyte. <5> The secondary battery according to any one of <1> to <4>, wherein the first layer is interposed between the negative electrode electrolyte and the second layer. <6> The secondary battery according to <4> or <5>, wherein the polymer compound contained in the first layer contains a carboxylic acid group as the cation exchange group. <7> The secondary battery according to any one of <1> to <3>, wherein the first layer is in contact with the positive electrode electrolyte. <8> The secondary battery according to any one of <1> to <3> and <7>, wherein the first layer is interposed between the positive electrode electrolyte and the second layer. <9> The secondary battery according to <7> or <8>, wherein the polymer compound contained in the first layer contains a phosphonic acid group as the cation exchange group.<10> The secondary battery according to any one of <1> to <9>, wherein the partition wall comprises two first layers located on the negative electrode chamber side and the positive electrode chamber side, and one of the two first layers is in contact with the negative electrode electrolyte and the other is in contact with the positive electrode electrolyte. <11> The secondary battery according to <10>, wherein the second layer is located between the two first layers. <12> The secondary battery according to any one of <1> to <11>, wherein the partition wall comprises a structure in which three or more layers are laminated, further including a third layer which is a polymer compound layer made of a different material from the first layer and the second layer. <13> The secondary battery according to any one of <1> to <12>, wherein the thickness of the first layer is smaller than the thickness of the second layer.

[0171] It should be noted that the effects described above are merely illustrative examples. Therefore, the present invention is not limited to the matters described above, and additional effects may also be present.

[0172] After fabricating a secondary battery using the procedure described below, its battery characteristics were evaluated.

[0173] (Fabrication of the negative electrode) First, 89 parts by mass of negative electrode active material (anatase-type titanium oxide, a titanium-containing compound (titanium oxide)), 10 parts by mass of negative electrode binder (polyvinylidene fluoride), and 1 part by mass of negative electrode conductive agent (graphite) were mixed to prepare a negative electrode mixture. Next, the negative electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both sides of a titanium foil negative electrode current collector (thickness = 20 μm), excluding the connection terminals, using a coating apparatus. Then, the negative electrode mixture slurry was dried to form a negative electrode active material layer. This completed the fabrication of the negative electrode.

[0174] (Fabrication of the positive electrode) First, the positive electrode active material (LiMn, which is a lithium composite oxide) ２ O ４A positive electrode mixture was prepared by mixing 91 parts by mass of (a), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (graphite). Subsequently, the positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector (titanium foil with a thickness of 20 μm), excluding the connection terminals, using a coating apparatus, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer. This completed the production of the positive electrode.

[0175] (Preparation of negative electrode electrolyte and positive electrode electrolyte) The negative electrode electrolyte and positive electrode electrolyte were prepared by adding an electrolyte salt to an aqueous solvent (pure water) and then stirring. Specifically, lithium hydroxide (LiOH) was used as the electrolyte salt for the negative electrode electrolyte, and the concentration of LiOH was adjusted to 4 mol / kg. Lithium sulfate (LiOH) was used as the electrolyte salt for the positive electrode electrolyte. ２ SO ４ ) and monopotassium hydrogen phosphate (KH ２ PO ４ ) and Li ２ SO ４ The concentration is 2 mol / kg, KH ２ PO ４ The concentration was adjusted to 0.2 mol / kg. The pH of the negative electrode electrolyte was approximately 14, and the pH of the positive electrode electrolyte was approximately 4.

[0176] (Preparation of the partition wall) A cation exchange membrane (Nafion® NRE212, purchased from Sigma-Aldrich Japan LLC), which is a polymer membrane containing sulfonic acid groups, was used as the second layer of the partition wall. A polymer solution containing carboxylic acid groups or phosphonic acid groups was applied to this cation exchange membrane, and by heating and drying, a polymer layer containing carboxylic acid groups or phosphonic acid groups was formed on the cation exchange membrane, which is a polymer membrane containing sulfonic acid groups. This resulted in a partition wall 12 having a first layer and a second layer.

[0177] As the polymer compound containing a carboxylic acid group, lithium polyacrylate polymer (PAA) was used. Water was added to polyacrylic acid (Wako Pure Chemical Industries, molecular weight 250,000) to prepare an aqueous solution of polyacrylic acid of approximately 7% by weight. 3 mol / kg of LiOH aqueous solution was then gradually added to this solution until the pH of the polyacrylic acid solution reached 5, thereby obtaining an aqueous solution of polyacrylic acid-lithium polyacrylate. 0.15 mL of butanediol glycidyl ether (Tokyo Chemical Industries, Ltd.) was added dropwise to 50 mL of this solution, and a crosslinking reaction was carried out at 80°C to obtain a crosslinked gel of lithium polyacrylate. This crosslinked gel was coated onto one side of a Nafion film and dried at 90°C to obtain a laminated film.

[0178] Similarly, polyvinylphosphonic acid polymer (PVPA) was used as the polymer compound containing phosphonic acid groups. A mixture of approximately 10% by weight was prepared by adding water to polyvinylphosphonic acid (manufactured by Aldrich), and this mixture was applied to one side of the Nafion film and dried at 90°C to obtain a laminated film.

[0179] (Assembly of secondary battery) First, a plastic (vinyl chloride) container was prepared as the outer casing, and then a partition wall was installed inside the outer casing. This formed a negative electrode chamber and a positive electrode chamber inside the outer casing 11. As the secondary battery of Example 1, a partition wall having a polymer layer containing carboxylic acid groups as the first layer was installed so that the first layer faced the negative electrode chamber. As the secondary battery of Example 2, a partition wall having a polymer layer containing phosphonic acid groups as the first layer was installed so that the first layer faced the positive electrode chamber. As the secondary battery of Example 3, a partition wall having a polymer layer containing phosphonic acid groups as the first layer was installed so that the first layer faced the negative electrode chamber. Furthermore, as a comparative example secondary battery, a partition wall consisting only of a second layer and without a first layer was installed.

[0180] Next, in each of Examples 1, 2, 3, and the Comparative Example, a negative electrode was placed inside the negative electrode chamber, and a positive electrode was placed inside the positive electrode chamber. In this case, the negative electrode connection terminal and the positive electrode connection terminal were led out from the negative electrode and positive electrode, respectively, to the outside of the outer casing.

[0181] Finally, the negative electrode electrolyte was supplied to the negative electrode chamber, and the positive electrode electrolyte was supplied to the positive electrode chamber. As a result, the negative electrode was immersed in the negative electrode electrolyte, and the positive electrode was immersed in the positive electrode electrolyte, thus completing the secondary battery.

[0182] (Evaluation of Battery Characteristics) The battery characteristics (charge / discharge characteristics) of the secondary batteries of Example 1, Example 2, Example 3, and the Comparative Example were evaluated. First, the discharge capacity of the first cycle was measured by charging and discharging the secondary batteries in a normal temperature environment (temperature = 23°C). In this case, the batteries were charged with a current of 1C until the voltage reached 2.8V, and then discharged with a current of 1C until the voltage reached 1.5V. Note that 1C is the current value required to discharge the battery capacity (theoretical capacity) in one hour.

[0183] Next, the secondary battery was stored in the same environment for 10 days, and then the discharge capacity of the second cycle was measured. The charge and discharge conditions were the same as those for the first cycle.

[0184] Finally, the capacity ratio, an index for evaluating charge-discharge characteristics, was calculated based on the following formula: Capacity Ratio (%) = (Discharge Capacity in Cycle 2 / Discharge Capacity in Cycle 1) × 100. The results shown in Table 1 were obtained. The values ​​of this capacity ratio are rounded to the first decimal place.

[0185]

[0186] As shown in Table 1, the secondary batteries of Examples 1 to 3 showed a higher capacity ratio after 10 days compared to the secondary battery of the comparative example. This indicates that the capacity degradation of the secondary battery over time is suppressed by providing a partition wall in which the first and second layers are stacked, and by positioning the partition wall so that at least the first layer is in contact with the negative electrode electrolyte or the positive electrode electrolyte. Therefore, the secondary battery of this disclosure provides a secondary battery with excellent long-term reliability.

[0187] The applications of the secondary battery disclosed herein are not particularly limited, as long as it can be used as a power source for driving, a power storage source for power storage, or for other purposes in machines, equipment, devices, apparatus, and systems (assemblies of multiple devices, etc.). The secondary battery used as a power source may be a primary power source or an auxiliary power source. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of a primary power source, or a power source that can be switched from the primary power source as needed. When a secondary battery is used as an auxiliary power source, the type of primary power source is not limited to a secondary battery.

[0188] Specifically, concrete examples of secondary battery applications include electronic devices (including portable electronic devices) such as video cameras, digital still cameras, mobile phones, notebook computers, cordless telephones, headphone stereos, portable radios, portable televisions, and portable information terminals; portable household appliances such as electric shavers; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in notebook computers and other devices as detachable power sources; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household battery systems that store power in preparation for emergencies. Of course, secondary batteries may have applications other than the series of applications exemplified here.

[0189] 11: Outer casing 12: Partition wall 12A, 12A1, 12A2: First layer 12B: Second layer 12C: Third layer 13: Negative electrode 13AT: Negative electrode side connection terminal 14: Positive electrode 14AT: Positive electrode side connection terminal 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 negative electrode that intercepts and releases metal ions; a positive electrode that intercepts and releases metal ions; a negative electrode electrolyte containing an aqueous solvent; a positive electrode electrolyte containing an aqueous solvent; a negative electrode chamber containing the negative electrode and the negative electrode electrolyte; and a positive electrode chamber containing the positive electrode and the positive electrode electrolyte, wherein the negative electrode chamber and the positive electrode chamber are separated by a partition wall positioned between them and permeable to metal ions; the negative electrode electrolyte has a pH greater than that of the positive electrode electrolyte; and the partition wall has a structure in which two or more layers are stacked, each containing at least a first layer and a second layer containing different cation exchange groups; the first layer contains a polymer compound containing at least one cation exchange group selected from the group consisting of carboxylic acid groups, hydroxycarboxylic acid groups, phosphonic acid groups, phosphinic acid groups, and xanthogenic acid groups, and is in contact with at least one of the negative electrode electrolyte and the positive electrode electrolyte.

2. The secondary battery according to claim 1, wherein the second layer comprises a polymer compound containing at least one cation exchange group selected from the group consisting of sulfonic acid groups, aminosulfonic acid groups, and sulfate groups.

3. The secondary battery according to claim 1 or 2, wherein the first layer extends across the entire surface of the partition wall on at least one of the negative electrode chamber side and the positive electrode chamber side.

4. The secondary battery according to any one of claims 1 to 3, wherein the first layer is in contact with the negative electrode electrolyte.

5. The secondary battery according to any one of claims 1 to 4, wherein the first layer is interposed between the negative electrode electrolyte and the second layer.

6. The secondary battery according to claim 4 or 5, wherein the polymer compound contained in the first layer contains a carboxylic acid group as the cation exchange group.

7. The secondary battery according to any one of claims 1 to 3, wherein the first layer is in contact with the positive electrode electrolyte.

8. The secondary battery according to any one of claims 1 to 3 and 7, wherein the first layer is interposed between the positive electrode electrolyte and the second layer.

9. The secondary battery according to claim 7 or 8, wherein the polymer compound contained in the first layer contains a phosphonic acid group as the cation exchange group.

10. The secondary battery according to any one of claims 1 to 9, wherein the partition wall comprises two first layers located on the negative electrode chamber side and the positive electrode chamber side, and one of the two first layers is in contact with the negative electrode electrolyte and the other is in contact with the positive electrode electrolyte.

11. The secondary battery according to claim 10, wherein the second layer is located between the two first layers.

12. The secondary battery according to any one of claims 1 to 11, wherein the partition wall has a structure in which three or more layers are stacked, the third layer being a polymer compound layer composed of a material different from the first layer and the second layer.

13. The secondary battery according to any one of claims 1 to 12, wherein the thickness of the first layer is smaller than the thickness of the second layer.

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