Lithium ion secondary battery

Abstract

A secondary battery includes: a positive electrode that intercalates and deintercalates lithium ions; a negative electrode that contains a negative electrode active material that intercalates and deintercalates the lithium ions; and an electrolyte that contains an aqueous solvent. The negative electrode active material contains a titanium-containing compound, and the electrolyte has a pH of 11 or more. When a surface of the negative electrode is analyzed by X-ray photoelectron spectroscopy, a proportion of a sum of detection amounts of each of lithium, titanium, tin, zirconium, bismuth, and indium with respect to a sum of detection amounts of all metal elements is 99 atomic % or more.

Description

Technical Field

[0001] This technology relates to lithium-ion secondary batteries. Background Technology

[0002] With the widespread adoption of mobile phones and other electronic devices, lithium-ion secondary batteries are being developed as small, lightweight power sources that can simultaneously achieve high energy density. As such, lithium-ion secondary batteries with an electrolyte containing an aqueous solvent (so-called aqueous electrolyte) have been developed, and various studies have been conducted regarding the structure of these lithium-ion secondary batteries.

[0003] Specifically, to suppress electrolysis of the aqueous electrolyte during charging and discharging, an aqueous electrolyte containing lithium ions, imine anions, and metal cations, and simultaneously having a pH of 3 to 12, is used (e.g., see Patent Document 1). To achieve a self-standing electrode without binders or current collectors, a composite material containing electrode active material particles in a three-dimensional cross-linked network structure of carbon nanotubes is used, and battery tabs are fixed on a body containing this composite material (e.g., see Patent Document 2). To obtain excellent charge / discharge efficiency and storage performance, a negative electrode active material containing a Ti-containing composite oxide is used, and Hg or the like is present on the surface of the negative electrode containing this negative electrode active material (e.g., see Patent Document 3).

[0004] To realize a flexible battery chemical cell, a nonwoven fabric formed from a fibrous active electrode material is used as the electrode (e.g., see Patent Document 4). To ensure cycle stability, a carbon coating is formed on the surface of the negative electrode active material containing titanium oxide (e.g., see Patent Document 5). To obtain excellent rate characteristics, lithium titanate with macropores is used as the electrode active material of the energy storage device (e.g., see Patent Document 6).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-121537

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-075367

[0009] Patent Document 3: Japanese Patent Application Publication No. 2019-169458

[0010] Patent Document 4: Japanese Patent Application Publication No. 2014-107276

[0011] Patent Document 5: Japanese Patent Application Publication No. 2019-053931

[0012] Patent Document 6: International Publication No. 2010 / 137582 Summary of the Invention

[0013] Various studies have been conducted on the battery characteristics of lithium-ion secondary batteries with aqueous electrolytes, but since the charge and discharge characteristics of these lithium-ion secondary batteries are not yet fully developed, there is room for improvement.

[0014] Therefore, a lithium-ion secondary battery with excellent charge-discharge characteristics is desired.

[0015] One embodiment of this technology provides a lithium-ion secondary battery comprising: a positive electrode for inserting and deintercalating lithium ions; a negative electrode containing a negative electrode active material for inserting and deintercalating the lithium ions; and an electrolyte containing an aqueous solvent. The negative electrode active material contains a titanium-containing compound, and the electrolyte has a pH of 11 or higher. When the surface of the negative electrode is analyzed using X-ray photoelectron spectroscopy, the sum of the detected amounts of each of lithium, titanium, tin, zirconium, bismuth, and indium relative to the sum of the detected amounts of all metal elements is 99 atomic percent or higher.

[0016] Another embodiment of this technology provides a lithium-ion secondary battery comprising: a separator disposed between a positive electrode space and a negative electrode space, allowing lithium ions to pass through; a positive electrode disposed inside the positive electrode space, containing intercalated and deintercalated lithium ions; a negative electrode disposed inside the negative electrode space, comprising a negative electrode active material containing intercalated and deintercalated lithium ions; a positive electrode electrolyte contained inside the positive electrode space, comprising an aqueous solvent; and a negative electrode electrolyte contained inside the negative electrode space, comprising an aqueous solvent. The negative electrode active material contains a titanium-containing compound, the positive electrode electrolyte has a pH less than 11, and the negative electrode electrolyte has a pH greater than 11. When the surface of the negative electrode is analyzed using X-ray photoelectron spectroscopy, the sum of the detected amounts of each of lithium, titanium, tin, zirconium, bismuth, and indium relative to the sum of the detected amounts of all metal elements is 99 atomic percent or more.

[0017] Here, "all metallic elements" refers to all metallic elements that can be analyzed (detected) using X-ray photoelectron spectroscopy. More specifically, it refers to all metallic elements (including lithium) belonging to Groups 1 to 17 of the long-period periodic table.

[0018] Furthermore, to calculate the aforementioned proportions, when analyzing the surface of the negative electrode using X-ray photoelectron spectroscopy, any 10 locations on the surface of the negative electrode are analyzed. Therefore, the proportion is the average of 10 proportions calculated for each of these 10 locations. It should be noted that details regarding the analytical steps using X-ray photoelectron spectroscopy and the steps for calculating the proportions will be described later.

[0019] According to one embodiment of the present technology, the negative electrode active material of the negative electrode contains a titanium-containing compound, the electrolyte containing an aqueous solvent has a pH of 11 or higher, and the proportions of the negative electrode surface analyzed by X-ray photoelectron spectroscopy are within the above range, thus achieving excellent charge and discharge characteristics.

[0020] In addition, according to another embodiment of the present technology, the negative electrode active material of the negative electrode contains a titanium-containing compound, the positive electrode electrolyte containing an aqueous solvent has a pH of less than 11, the negative electrode electrolyte containing an aqueous solvent has a pH of more than 11, and the proportions of the negative electrode surface analyzed by X-ray photoelectron spectroscopy are within the above range, so excellent charge and discharge characteristics can be obtained.

[0021] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of a series of effects associated with this technology as described below. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view showing the structure of a lithium-ion secondary battery according to the first embodiment of this technology.

[0023] Figure 2 This is a cross-sectional view showing the structure of a lithium-ion secondary battery according to the second embodiment of this technology.

[0024] Figure 3 This is a cross-sectional view showing the structure of the lithium-ion secondary battery in Modified Example 1.

[0025] Figure 4 This is a cross-sectional view showing the structure of the lithium-ion secondary battery in Modified Example 2. Detailed Implementation

[0026] Hereinafter, an embodiment of the present technology will be described in detail with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0027] 1. First Embodiment (Lithium-ion Secondary Battery)

[0028] 1-1. Structure

[0029] 1-2.Physical properties

[0030] 1-3. Actions

[0031] 1-4. Manufacturing Method

[0032] 1-5. Functions and Effects

[0033] 2. Second Implementation Method (Lithium-ion Secondary Battery)

[0034] 2-1. Structure

[0035] 2-2.Physical properties

[0036] 2-3. Actions

[0037] 2-4. Manufacturing Method

[0038] 2-5. Functions and Effects

[0039] 3. Variations

[0040] 4. Applications of lithium-ion secondary batteries

[0041] <1. First Embodiment (Lithium-ion Secondary Battery)>

[0042] First, the lithium-ion secondary battery of the first embodiment of this technology will be described.

[0043] The lithium-ion secondary battery described herein is a secondary battery that utilizes the insertion and extraction of lithium ions. It includes a positive electrode, a negative electrode, and an electrolyte (aqueous electrolyte) that is a liquid electrolyte containing an aqueous solvent. In this lithium-ion secondary battery, since the charging and discharging reaction is carried out by the insertion and extraction of lithium ions, the battery capacity can be obtained.

[0044] <1-1. Structure>

[0045] Figure 1 The cross-sectional structure of the lithium-ion secondary battery according to the first embodiment is shown. Figure 1 As shown, the lithium-ion secondary battery includes an outer packaging component 11, a positive electrode 12, a negative electrode 13, and an electrolyte 14. Figure 1 In the image, a light shade is marked on electrolyte 14.

[0046] In the following explanation, Figure 1 The upper side serves as the upper side of the lithium-ion secondary battery, while also... Figure 1 The lower side serves as the lower side of the lithium-ion secondary battery.

[0047] [Outer Packaging Components]

[0048] The outer packaging component 11 is a generally box-shaped component with an internal space S for accommodating the positive electrode 12, the negative electrode 13, and the electrolyte 14.

[0049] The outer packaging component 11 comprises any one or more of the following materials: metal, glass, and polymer compounds. Specifically, the outer packaging component 11 can be a rigid metal can, glass shell, or plastic shell, or it can be a flexible (or pliable) metal foil or polymer film.

[0050] [positive electrode]

[0051] The positive electrode 12 is disposed in the internal space S, where lithium ions are inserted and extracted. Here, the positive electrode 12 includes a positive current collector 12A having one side facing each other and a positive active material layer 12B formed on both sides of the positive current collector 12A. Alternatively, the positive active material layer 12B may be formed only on one side of the positive current collector 12A on the side opposite the negative electrode 13.

[0052] It should be noted that the positive current collector 12A can be omitted. Therefore, the positive electrode 12 can be simply the positive active material layer 12B.

[0053] (Positive current collector)

[0054] The positive current collector 12A supports the positive active material layer 12B, which comprises one or more conductive materials such as metals, carbon materials, and conductive ceramic materials. Specific examples of metal materials include titanium, aluminum, and their alloys. Specific examples of conductive ceramic materials include indium tin oxide (ITO). Here, the positive active material layer 12B is not formed on a portion of the positive current collector 12A (connection terminal portion 12AT), which is led out to the outside of the outer packaging component 11.

[0055] The material forming the positive current collector 12A is preferably insoluble, poorly soluble, and corrosion-resistant to the electrolyte 14, and also exhibits low reactivity to the positive electrode active material. Therefore, the positive current collector 12A preferably comprises the aforementioned metallic materials, i.e., preferably titanium, aluminum, and their alloys. This is because the positive current collector 12A is less prone to degradation even when using a lithium-ion secondary battery.

[0056] It should be noted that the positive current collector 12A can be a conductive body coated with any one or more of the aforementioned metallic materials, carbon materials, and conductive ceramic materials to cover its surface. The material of the conductive body only needs to be conductive; there are no particular limitations.

[0057] (Positive electrode active material layer)

[0058] The positive electrode active material layer 12B contains any one or more positive electrode active materials that can be intercalated or deintercalated into lithium ions. Furthermore, the positive electrode active material layer 12B may further contain a positive electrode binder and a positive electrode conductive agent, etc.

[0059] Positive electrode active materials include lithium-containing compounds. The types of lithium-containing compounds are not particularly limited; specifically, they include lithium complex oxides and lithium phosphate compounds. Lithium complex oxides are oxides containing lithium and one or more transition metal elements as constituent elements, while lithium phosphate compounds are phosphate compounds containing lithium and one or more transition metal elements as constituent elements. The types of transition metal elements are not particularly limited; specifically, they include nickel, cobalt, manganese, and iron.

[0060] Specific examples of lithium composite oxides with a layered rock salt-type crystal structure are LiNiO2, LiCoO2, and LiCo. 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 Lithium complex oxides with spinel-type crystal structures include LiMn₂O₄, etc. Specific examples of lithium phosphate compounds with olivine-type crystal structures include LiFePO₄, LiMnPO₄, and LiMn₂O₄. 0.5 Fe 0.5 PO4, LiMn 0.7 Fe 0.3 PO4 and LiMn 0.75 Fe 0.25 PO4, etc.

[0061] The positive electrode binder comprises one or more of the following: synthetic rubber and polymeric compounds. Specific examples of synthetic rubber include styrene-butadiene rubber. Specific examples of polymeric compounds include polyvinylidene fluoride and polyimide.

[0062] The positive electrode conductive agent includes one or more conductive materials such as carbon materials. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjen black. In addition, conductive materials can also be metallic materials, conductive ceramic materials, and conductive polymers.

[0063] [negative electrode]

[0064] The negative electrode 13 is disposed in the internal space S in a manner isolated from the positive electrode 12, and is used for lithium ion insertion and extraction. Here, the negative electrode 13 includes a negative electrode current collector 13A having one side facing each other and a negative electrode active material layer 13B formed on both sides of the negative electrode current collector 13A. Alternatively, the negative electrode active material layer 13B may be formed only on one side of the negative electrode current collector 13A on the side of the negative electrode 13 opposite to the positive electrode 12.

[0065] One or both of the negative electrode current collector 13A and the negative electrode active material layer 13B constituting the negative electrode 13 have a specific metallic material on their surface. Therefore, the negative electrode 13 exhibits properties that make it difficult to react with and dissolve in the strongly alkaline electrolyte 14, as described later. This specific metallic material is a material containing a specific type of metallic element as a constituent element; more specifically, it is a material containing one or more of titanium, tin, zirconium, bismuth, and indium as constituent elements. The specific metallic material can be of only one type or two or more types.

[0066] Furthermore, a specific metallic material can be a monomer (metal monomer), an alloy, an oxide (metal oxide acting as a conductor), or two or more of these. Specific examples of oxides are oxides containing one or more of the aforementioned metallic elements such as titanium as constituent elements; more specifically, titanium oxide, etc.

[0067] In contrast, when one or both of the negative electrode current collector 13A and the negative electrode active material layer 13B constituting the negative electrode 13 have a non-specific metallic material on their surfaces, the negative electrode 13 exhibits properties of readily reacting with and dissolving in the strongly alkaline electrolyte 14. This non-specific metallic material is a material containing metallic elements other than the aforementioned specific metallic elements as constituent elements; more specifically, it is a material containing any one or more of aluminum, copper, lead, zinc, magnesium, and iron as constituent elements.

[0068] The reason why one or both of the negative electrode current collector 13A and the negative electrode active material layer 13B have a specific metallic material on their surfaces is that, when the appropriate conditions regarding the element ratio A (described later) are met, the negative electrode 13 is less likely to react with and dissolve in the strongly alkaline electrolyte 14, and therefore the constituent atoms of the negative electrode 13 are less likely to dissolve in the electrolyte 14. Consequently, the electrolyte 14 is less likely to deteriorate or decompose, and therefore the charge-discharge characteristics of the lithium-ion secondary battery are less likely to decrease. It should be noted that details regarding the element ratio A will be described later.

[0069] Preferably, one or both of the negative electrode current collector 13A and the negative electrode active material layer 13B have a material containing titanium as a constituent element on their surface as a specific metallic material. This is because the negative electrode 13 is sufficiently resistant to reaction and dissolution with the strongly alkaline electrolyte 14, thus the electrolyte 14 is sufficiently resistant to degradation and decomposition.

[0070] In particular, both the negative electrode current collector 13A and the negative electrode active material layer 13B preferably have a specific metallic material on their surfaces, and more preferably have a material containing titanium as a constituent element on their surfaces. This is because the negative electrode 13 is less likely to react with and dissolve in the strongly alkaline electrolyte 14, and therefore the electrolyte 14 is less likely to deteriorate and decompose.

[0071] Furthermore, if only one of the negative electrode current collector 13A and the negative electrode active material layer 13B has a specific metallic material on its surface, it is preferable that the negative electrode current collector 13A has a specific metallic material on its surface, and more preferably that it has a material containing titanium as a constituent element. This is because the negative electrode current collector 13A has a high affinity for the negative electrode active material (the titanium-containing compound described later), so the negative electrode active material layer 13B can easily and stably adhere to the negative electrode current collector 13A, and at the same time, the charge and discharge reaction can easily and stably occur in the negative electrode active material layer 13B.

[0072] It should be noted that the surface of one or both of the negative current collector 13A and the negative active material layer 13B can be covered with a specific metal material. In this case, the surface of one or both of the negative current collector 13A and the negative active material layer 13B can be plated with a specific metal material.

[0073] In addition, one or both of the negative electrode current collector 13A and the negative electrode active material layer 13B may further include non-specific metal materials, or may include other materials other than the non-specific metal materials, as long as one or both have a specific metal material on their surface.

[0074] (Negative current collector)

[0075] The negative electrode current collector 13A supports the negative electrode active material layer 13B, which contains any one or more conductive materials. These conductive materials are metallic materials, carbon materials, and conductive ceramic materials, etc. Specific examples of metallic materials include stainless steel (SUS), titanium, zinc, tin, lead, and alloys of two or more of them.

[0076] Here, the negative electrode active material layer 13B is not formed on a portion of the negative electrode current collector 13A (connection terminal portion 13AT), and the connection terminal portion 13AT extends to the outside of the outer packaging component 11. The lead-out direction of the connection terminal portion 13AT is not particularly limited; specifically, it is the same as the lead-out direction of the connection terminal portion 12AT.

[0077] (Negative electrode active material layer)

[0078] The negative electrode active material layer 13B comprises any one or more negative electrode active materials capable of intercalating and deintercalating lithium ions. Furthermore, the negative electrode active material layer 13B may further comprise a negative electrode binder and a negative electrode conductive agent. Details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and similarly, details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent. It should be noted that when the negative electrode conductive agent is a metallic material, this metallic material preferably has the aforementioned specific metallic material on its surface.

[0079] The negative electrode active material contains any one or more titanium-containing compounds. This is because the charge-discharge reaction proceeds smoothly and stably even when using a strongly alkaline electrolyte 14. Preferably, the negative electrode active material has the aforementioned specific metallic material on its surface.

[0080] Titanium-containing compounds refer to the general term for compounds that contain titanium as a constituent element. Specifically, they include titanium oxides, lithium titanium composite oxides, titanium phosphates, lithium titanium phosphates, and hydrogen titanium compounds.

[0081] Titanium oxide is a compound represented by formula (1) (so-called titanium oxide), such as bronze-type titanium oxide.

[0082] TiO w …(1)

[0083] (w satisfies 1.85≤w≤2.15.)

[0084] The titanium oxide is any one or more of anatase, rutile, and brookite titanium oxide (TiO2). Alternatively, the titanium oxide can also be a composite oxide containing any one or more of phosphorus, vanadium, tin, copper, nickel, iron, and cobalt as constituent elements along with titanium. Specific examples of such composite oxides are TiO2-P2O5, TiO2-V2O5, TiO2-P2O5-SnO2, and TiO2-P2O5-MeO, etc. Where Me is any one or more of Cu, Ni, Fe, and Co.

[0085] Among them, anatase titanium oxide is preferred. This is because anatase titanium oxide is stable in the strongly alkaline electrolyte 14, thus ensuring stable operation (charge and discharge) of the lithium-ion secondary battery.

[0086] Lithium-titanium composite oxides are any one or more compounds represented by formulas (2) to (4), such as orthorhombic manganese oxide type lithium titanate, etc. M1 shown in formula (2) is a metal element that can become a divalent ion. M2 shown in formula (3) is a metal element that can become a trivalent ion. M3 shown in formula (4) is a metal element that can become a tetravalent ion.

[0087] Li[Li x M1 (1-3x) / 2 Ti (3+x) / 2 ]O4…(2)

[0088] (M1 is at least one of Mg, Ca, Cu, Zn, and Sr. x satisfies 0 ≤ x ≤ 1 / 3.)

[0089] Li[Li y M2 1-3y Ti 1+2y ]O4…(3)

[0090] (M2 is at least one of Al, Sc, Cr, Mn, Fe, Ge, and Y. y satisfies 0 ≤ y ≤ 1 / 3.)

[0091] Li[Li 1 / 3 M3 z Ti (5 / 3)-z ]O4…(4)

[0092] (M3 is at least one of V, Zr, and Nb. z satisfies 0 ≤ z ≤ 2 / 3.)

[0093] A specific example of the compound shown in formula (2) is Li 3.75 Ti 4.875 Mg 0.375 O 12 Specific examples of compounds represented by formula (3) are LiCrTiO4, etc. Specific examples of compounds represented by formula (4) are Li4Ti5O 12 and Li4Ti 4.95 Nb 0.05 O 12 wait.

[0094] Specific examples of titanium phosphate oxides include titanium phosphate (TiP₂O₇). Specific examples of lithium titanium phosphate compounds include LiTi₂(PO₄)₃. Specific examples of hydrogen titanium compounds include H₂Ti₃O₇ (3TiO₂·1H₂O) and H₆Ti. 12 O 27(3TiO2·0.75H2O), H2Ti6O 13 (3TiO2·0.5H2O), H2Ti7O 15 (3TiO2·0.43H2O) and H2Ti 12 O 25 (3TiO2·0.25H2O), etc.

[0095] The titanium-containing compound is preferably one or both of titanium oxide and lithium-titanium composite oxide, more preferably titanium oxide. This is because the charge-discharge reaction proceeds fully even when a strongly alkaline electrolyte 14 is used.

[0096] It should be noted that, in addition to the titanium-containing compounds mentioned above, the negative electrode active material may further include any one or more compounds that do not contain titanium as a constituent element. The types of other compounds are not particularly limited, and include alkali metal titanium composite oxides (excluding the lithium titanium composite oxides mentioned above), alkali metal titanium phosphate compounds (excluding the lithium titanium composite oxides mentioned above), niobium-containing compounds, vanadium-containing compounds, iron-containing compounds, and molybdenum-containing compounds, etc.

[0097] Niobium-containing compounds include lithium-niobium composite oxides, hydrogen-niobium compounds, and titanium-niobium composite oxides. Additionally, materials equivalent to niobium compounds are not included in titanium-containing compounds. Specific examples of lithium-niobium composite oxides include LiNbO2. Specific examples of hydrogen-niobium compounds include H4Nb6O. 17 Specific examples of titanium-niobium composite oxides are TiNb₂O₇ and Ti₂Nb₂. 10 O 29 Alternatively, lithium can be inserted into titanium-niobium composite oxides.

[0098] Vanadium-containing compounds include vanadium oxides and alkali metal vanadium composite oxides. However, materials equivalent to vanadium compounds are not included in each of the categories of titanium-containing compounds and niobium-containing compounds. Specific examples of vanadium oxides are vanadium dioxide (VO2), etc. Specific examples of lithium vanadium composite oxides, which are alkali metal vanadium composite oxides, are LiV2O4 and LiV3O8, etc.

[0099] Iron-containing compounds include iron hydroxides, etc. However, materials equivalent to iron-containing compounds are not included in each of the categories of titanium-containing compounds, niobium-containing compounds, and vanadium-containing compounds. Specific examples of iron hydroxides include iron hydroxyl oxide (FeOOH), etc. Furthermore, iron hydroxyl oxide can be α-iron hydroxyl oxide, β-iron hydroxyl oxide, γ-iron hydroxyl oxide, δ-iron hydroxyl oxide, or any two or more of these.

[0100] Molybdenum-containing compounds include molybdenum oxides and cobalt-molybdenum composite oxides. However, materials equivalent to molybdenum compounds are not included in each of the categories of titanium-containing compounds, niobium-containing compounds, vanadium-containing compounds, and iron-containing compounds. Specific examples of molybdenum oxides are molybdenum dioxide (MoO2), etc. Specific examples of cobalt-molybdenum composite oxides are CoMoO4, etc.

[0101] (Presence or absence of carbon materials)

[0102] It should be noted that the negative electrode 13 may or may not contain carbon materials. The cases where the negative electrode 13 contains carbon materials as described here refer to the following: the negative electrode current collector 13A contains carbon as a constituent element; the negative electrode current collector 13A contains a carbon capping layer; the negative electrode active material layer 13B contains carbon materials as a negative electrode conductive agent; the negative electrode active material layer 13B contains a carbon capping layer; and the negative electrode active material contains a carbon capping layer.

[0103] Alternatively, the carbon coating layer may cover the entire surface of the negative electrode current collector 13A, or it may only cover a portion of the surface of the negative electrode current collector 13A. In the latter case, multiple mutually isolated carbon coating layers may cover the surface of the negative electrode current collector 13A. The details regarding the coverage area of ​​the carbon coating layer described herein also apply to the cases where the carbon coating layer covers the surface of the negative electrode active material layer 13B and the cases where the carbon coating layer covers the surface of the negative electrode active material layer.

[0104] The negative electrode 13 preferably does not contain carbon material. This is because carbon material has a low hydrogen overvoltage, so when the negative electrode 13 contains carbon material, the aqueous solvent in the electrolyte 14 is easily decomposed on the surface of the negative electrode 13. Therefore, in order to suppress the decomposition reaction of the aqueous solvent, the negative electrode 13 preferably does not contain carbon material.

[0105] On the other hand, when the negative electrode 13 contains carbon material, the content of carbon material in the negative electrode 13 is preferably as small as possible. Specifically, the weight ratio of carbon material relative to the weight of the negative electrode 13 (carbon ratio C (wt%)) is preferably less than 0.1 wt%. This is because aqueous solvents are not easily decomposed on the surface of the negative electrode 13. The carbon ratio C is calculated based on the formula: carbon ratio C (wt%) = (weight of carbon material / weight of negative electrode 13) × 100. The value of the carbon ratio C is rounded to two decimal places.

[0106] Electrolyte

[0107] The electrolyte 14 is contained in the internal space S, and as described above, it is an aqueous electrolyte containing an aqueous solvent. That is, the electrolyte 14 is a solution in which ionizable ionic substances are dissolved or dispersed in an aqueous solvent.

[0108] Specifically, the electrolyte 14 comprises one or more of an aqueous solvent and an ionic substance capable of ionization in the aqueous solvent. More specifically, the electrolyte 14 contains lithium ions that are inserted and extracted in each of the positive electrode 12 and the negative electrode 13.

[0109] There are no particular limitations on the types of aqueous solvents; specifically, it includes pure water, etc. There are no particular limitations on the types of ionic substances; specifically, it includes any one or more of acids, bases, and electrolyte salts. Specific examples of acids include carbonic acid, oxalic acid, nitric acid, sulfuric acid, hydrochloric acid, acetic acid, and citric acid, etc.

[0110] Electrolyte salts are salts containing both cations and anions; more specifically, they are any one or more lithium salts. Specific examples of lithium salts include lithium carbonate, lithium oxalate, lithium nitrate, lithium sulfate, lithium chloride, lithium acetate, lithium citrate, lithium hydroxide, and imine salts. These imine salts include lithium bis(fluorosulfonyl)imine and lithium bis(trifluoromethanesulfonyl)imine, among others.

[0111] In particular, as mentioned above, electrolyte 14 has a pH of 11 or higher, and is therefore strongly alkaline. This is because lithium ions move easily in electrolyte 14, thus facilitating the charge-discharge reaction. This pH value is a value rounded to the nearest decimal place, and the definition of pH value explained here will be the same in the following explanations.

[0112] Therefore, the electrolyte salt is preferably lithium hydroxide, etc. This is because the pH of the electrolyte 14 can easily reach above 11, thus easily and stably achieving a strongly alkaline electrolyte 14.

[0113] The content of ionic substances, i.e., the concentration (mol / kg) of electrolyte 14, is not particularly limited and can therefore be set arbitrarily. Specifically, the concentration of electrolyte 14 is preferably 0.2 mol / kg to 4 mol / kg. This is because a strongly alkaline electrolyte 14 can be easily and stably achieved.

[0114] It should be noted that, in addition to lithium salts mentioned above, electrolyte salts may further include one or more other metal salts. The types of other metal salts are not particularly limited, but specifically include alkali metal salts (excluding lithium salts), alkaline earth metal salts, and transition metal salts. Specific examples of alkali metal salts are sodium and potassium salts. Specific examples of alkaline earth metal salts are calcium and magnesium salts.

[0115] Here, the electrolyte 14 is more preferably a saturated solution of an electrolyte salt. This is because lithium ions can easily and stably insert and extract during charging and discharging, thus the charging and discharging reaction can proceed stably.

[0116] To confirm whether electrolyte 14 is a saturated solution of electrolyte salt, after disassembling the lithium-ion secondary battery, it is necessary to investigate whether electrolyte salt has precipitated in the internal space S. Specifically, the internal space S refers to the liquid electrolyte 14, the surface of the positive electrode 12, and the inner wall of the outer packaging component 11. Since electrolyte salt has precipitated, if electrolyte 14 (liquid) and precipitated electrolyte salt (solid) coexist in the internal space S, electrolyte 14 can be considered a saturated solution of electrolyte salt. It should be noted that to investigate the composition of the precipitated material, surface analysis methods such as X-ray photoelectron spectroscopy (XPS) can be used, as well as compositional analysis methods such as inductively coupled plasma (ICP) emission spectroscopy.

[0117] <1-2.Physical Properties>

[0118] In this lithium-ion secondary battery, the physical properties of the negative electrode 13 are optimized in order to obtain excellent charge and discharge characteristics.

[0119] [Element Ratio A]

[0120] Specifically, when using XPS to analyze the surface of each of the negative electrode active material layer 13B and the negative electrode current collector 13A, the proportion of the detection amount of the second element group relative to the detection amount of the first element group (elemental proportion A (atomic %)) is 99 atomic % or more.

[0121] Here, the first element group refers to a series of metallic elements that can be constituent elements of each of the negative electrode current collector 13A and the negative electrode active material layer 13B. More specifically, as mentioned above, it includes all metallic elements (including lithium) belonging to Groups 1 to 17 of the long-period periodic table. Therefore, the detection quantity of the first element group is the sum of the detection quantities of all metallic elements.

[0122] On the other hand, the second element group refers to a series of metal elements and lithium that constitute the specific metallic material described above, among a series of elements that can be constituent elements of each of the negative electrode current collector 13A and the negative electrode active material layer 13B. As mentioned above, this series of metal elements is any one or more of titanium, tin, zirconium, bismuth, and indium.

[0123] Therefore, the detection amount of the second element group is the sum of the detection amounts of any one or more of titanium, tin, zirconium, bismuth and indium, and the total detection amount of lithium.

[0124] Therefore, the elemental ratio A is calculated based on the formula: Elemental Ratio A (atomic %) = (Detection amount of the second element group / Detection amount of the first element group) × 100. The value of this elemental ratio A is rounded to the nearest whole number.

[0125] It should be noted that the reason why both the first element group and the second element group contain lithium is that in a lithium-ion secondary battery, lithium ions are inserted into the negative electrode 13. Therefore, lithium can be detected when analyzing the surface of the negative electrode active material layer 13B using XPS, and lithium can also be detected when analyzing the surface of the negative electrode current collector 13A using XPS.

[0126] As mentioned above, the elemental ratio A is an average value calculated based on the surface analysis results of the negative electrode 13 using XPS. When analyzing the surface of the negative electrode 13 using XPS, any 10 locations on the surface of the negative electrode 13 are analyzed. Therefore, the elemental ratio A is the average of 10 elemental ratios A calculated for each of the aforementioned 10 locations.

[0127] Here, as described above, the negative electrode 13 includes a negative electrode current collector 13A and a negative electrode active material layer 13B. In this case, the elemental ratio A is calculated through the steps described below.

[0128] Specifically, when using XPS to analyze the surface of each of the negative electrode active material layer 13B and the negative electrode current collector 13A, any nine parts of the surface of the negative electrode active material layer 13B are analyzed, and at the same time, any one part of the surface of the negative electrode current collector 13A is analyzed.

[0129] Any nine locations on the surface of the negative electrode active material layer 13B refer to nine locations on the surface of the negative electrode active material layer 13B that are sufficiently isolated from each other. Furthermore, any one location on the surface of the negative electrode current collector 13A refers to a portion of the negative electrode current collector 13A where the negative electrode active material layer 13B is not formed (such as the connection terminal portion 13AT).

[0130] Therefore, the element ratio A is the average of 10 element ratios A obtained by combining the 9 element ratios A calculated in 9 locations of the negative electrode active material layer 13B and the 1 element ratio A calculated in 1 location of the negative electrode current collector 13A.

[0131] The reason why the elemental ratio A is 99 atomic% or higher is that, regarding the constituent materials (constituent elements) of the surface of the negative electrode 13 (negative electrode current collector 13A and negative electrode active material layer 13B), the amount of metal elements constituting the specific metal material is sufficiently large relative to the amount of metal elements constituting the non-specific metal material. Therefore, the constituent atoms of the negative electrode 13 are not easily dissolved in the strongly alkaline electrolyte 14, thus the electrolyte 14 is not easily degraded or decomposed. Therefore, even when using the strongly alkaline electrolyte 14, the charge-discharge reaction can easily proceed stably, and even with repeated charge-discharge cycles, the discharge capacity is not easily reduced.

[0132] It should be noted that when calculating the elemental proportion A based on the surface analysis results of each of the negative electrode active material layer 13B and the negative electrode current collector 13A using XPS, commercially available analytical software can be used. There is no particular limitation on the type of analytical software; specifically, software such as SpecSurf manufactured by JEOL Ltd., which calculates the atomic fraction based on the peak area of ​​the XPS spectrum related to each constituent element, is suitable.

[0133] [Element Ratio B]

[0134] In particular, when using XPS to analyze the surface of each of the negative electrode active material layer 13B and the negative electrode current collector 13A, the ratio of the detection amount of the third element group to the detection amount of the first element group (element ratio B (atomic %)) is preferably 99 atomic % or more.

[0135] The third element group refers to titanium and lithium, which are among the metallic elements that constitute the specific metallic materials mentioned above. Therefore, the detection quantity of the third element group is the sum of the detection quantities of titanium and lithium.

[0136] Therefore, the elemental ratio B is calculated based on the formula: Elemental Ratio B (atomic %) = (Detection amount of the third element group / Detection amount of the first element group) × 100. This elemental ratio B is the value after rounding to the nearest decimal place.

[0137] In addition, similar to the element ratio A mentioned above, the element ratio B is an average value calculated based on the surface analysis results of the negative electrode 13 (negative electrode current collector 13A and negative electrode active material layer 13B) using XPS.

[0138] The reason why elemental B has a proportion of over 99 atomic percent is that the constituent atoms of the negative electrode 13 are less likely to dissolve in the strongly alkaline electrolyte 14, thus making the electrolyte 14 less prone to deterioration and decomposition. Therefore, even when using the strongly alkaline electrolyte 14, the charge-discharge reaction is more likely to proceed stably, and even with repeated charge-discharge cycles, the discharge capacity is less likely to decrease.

[0139] It should be noted that when calculating the elemental ratio B based on the surface analysis results of each of the negative electrode active material layer 13B and the negative electrode current collector 13A using XPS, the steps are the same as those for calculating the elemental ratio A described above.

[0140] <1-3. Actions>

[0141] During the charging of the lithium-ion secondary battery, when lithium ions are deintercalated from the positive electrode 12, they move to the negative electrode 13 via the electrolyte 14. Thus, lithium ions are intercalated in the negative electrode 13.

[0142] On the other hand, during the discharge of the lithium-ion secondary battery, when lithium ions are deintercalated from the negative electrode 13, they move to the positive electrode 12 via the electrolyte 14. Thus, lithium ions are intercalated in the positive electrode 12.

[0143] <1-4. Manufacturing Method>

[0144] In the case of manufacturing a lithium-ion secondary battery, as described below, each of the positive electrode 12 and the negative electrode 13 is made, and the electrolyte 14 is prepared, and then the lithium-ion secondary battery is manufactured.

[0145] [The production of the positive electrode]

[0146] First, the positive electrode active material, positive electrode binder, and positive electrode conductive agent are mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent to prepare a paste-like positive electrode mixture slurry. This solvent can be an aqueous solvent or an organic solvent. Finally, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 12A (excluding the connecting terminal portion 12AT), and then dried to form a positive electrode active material layer 12B. Thereafter, the positive electrode active material layer 12B can be compressed and molded using a roller press or the like. In this case, the positive electrode active material layer 12B can be heated, or the compression molding process can be repeated multiple times. Thus, the positive electrode 12 is produced.

[0147] [Making the negative electrode]

[0148] Following the same steps as those used in the fabrication of the positive electrode 12, a negative electrode active material layer 13B is formed on both sides of the negative electrode current collector 13A. Specifically, a negative electrode active material containing a titanium compound, a negative electrode binder, and a negative electrode conductive agent are mixed together to prepare a negative electrode mixture. This mixture is then added to a solvent to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 13A (excluding the connecting terminal portion 13AT), and then dried to form the negative electrode active material layer 13B. The negative electrode active material layer 13B can then be compressed and molded. Thus, the negative electrode 13 is manufactured.

[0149] [Preparation of Electrolyte]

[0150] An ionic substance is added to an aqueous solvent. The ionic substance is then dispersed or dissolved in the aqueous solvent to prepare electrolyte 14. In this case, the pH of electrolyte 14 is adjusted to be 11 or higher by adjusting the type and concentration (mol / kg) of the ionic substance.

[0151] [Assembly of lithium-ion secondary batteries]

[0152] First, the positive electrode 12 and the negative electrode 13 are housed in the internal space S of the outer packaging component 11. In this case, each of the connecting terminals 12AT and 13AT is led out to the outside of the outer packaging component 11.

[0153] Next, electrolyte 14 is supplied to the internal space S through an injection port (not shown) that communicates with the internal space S. Thus, the internal space S is filled with electrolyte 14. Afterward, the injection port is sealed.

[0154] Therefore, the electrolyte 14 is housed in the internal space S that houses each of the positive electrode 12 and the negative electrode 13, thereby completing a lithium-ion secondary battery using an aqueous electrolyte (electrolyte 14).

[0155] <1-5. Functions and Effects>

[0156] According to this lithium-ion secondary battery, the negative electrode active material of the negative electrode 13 contains a titanium-containing compound, the electrolyte 14 containing an aqueous solvent has a pH of 11 or higher, and the elemental ratio A is 99 atomic% or higher.

[0157] In this case, as described above, because the elemental ratio A is appropriately adjusted, the constituent atoms of the negative electrode 13 are less likely to dissolve in the strongly alkaline electrolyte 14, thus the electrolyte 14 is less prone to deterioration and decomposition. Therefore, even when using the strongly alkaline electrolyte 14 with a negative electrode 13 containing a titanium compound, the charge-discharge reaction proceeds stably, and the discharge capacity does not easily decrease even with repeated charge-discharge cycles. Therefore, excellent charge-discharge characteristics can be obtained.

[0158] In particular, if the elemental proportion B is 99% or more, the constituent atoms of the negative electrode 13 are less likely to dissolve in the strongly alkaline electrolyte 14, thus achieving a higher effect.

[0159] In addition, if the negative electrode 13 contains carbon material and the carbon ratio C is less than 0.1% by weight, the electrolyte 14 is less prone to degradation and decomposition, thus achieving higher performance.

[0160] In addition, if the concentration of electrolyte 14 is 0.2 mol / kg to 4 mol / kg, a strongly alkaline electrolyte 14 can be easily and stably achieved, thus obtaining higher performance.

[0161] In addition, if the titanium-containing compound includes one or both of titanium oxide and lithium titanium composite oxide, the charge-discharge reaction will proceed fully even when using a strongly alkaline electrolyte 14, thus achieving a higher efficiency.

[0162] In this case, if the titanium oxide contains anatase titanium oxide, a higher voltage can be obtained, thus achieving a higher effect.

[0163] Furthermore, if the negative electrode 13 includes a negative electrode active material layer 13B and the surface of the negative electrode active material layer 13B is analyzed using XPS, the constituent atoms of the negative electrode active material layer 13B are not easily dissolved in the strongly alkaline electrolyte 14, thus achieving a higher efficiency.

[0164] In this case, if the negative electrode 13 further includes a negative electrode current collector 13A and XPS is used to analyze the surface of each of the negative electrode active material layer 13B and the negative electrode current collector 13A, then not only the constituent atoms of the negative electrode active material layer 13B, but also the constituent atoms of the negative electrode current collector 13A are not easily dissolved in the strongly alkaline electrolyte 14, thus achieving a higher effect.

[0165] <2. Second Embodiment (Lithium-ion Secondary Battery)>

[0166] Next, the lithium-ion secondary battery of the second embodiment of this technology will be described.

[0167] <2-1. Structure>

[0168] Figure 2 The cross-sectional structure of a lithium-ion secondary battery according to a second embodiment is shown. This second embodiment of the lithium-ion secondary battery, except as described below, has a structure similar to that of the lithium-ion secondary battery of the first embodiment described above. Figure 1 The same structure.

[0169] like Figure 2 As shown, this lithium-ion secondary battery is newly equipped with a separator 15, and also provides a positive electrolyte 16 and a negative electrolyte 17 to replace the electrolyte 14. Figure 2 In the diagram, the positive electrode electrolyte 16 is marked with a light shade, while the negative electrode electrolyte 17 is marked with a dark shade.

[0170] The outer packaging component 11 has two spaces separated by a partition 15 (positive electrode chamber S1, which serves as the positive electrode space, and negative electrode chamber S2, which serves as the negative electrode space).

[0171] The partition 15 is disposed between the positive electrode 12 and the negative electrode 13, separating the internal space of the outer packaging component 11 into a positive electrode chamber S1 and a negative electrode chamber S2. Thus, the positive electrode 12 and the negative electrode 13 are isolated from each other by the partition 15, and are also opposite to each other by the partition 15.

[0172] The separator 15, located between the positive electrode chamber S1 and the negative electrode chamber S2, prevents anions from passing through while allowing lithium ions (cations) and other substances (excluding anions) that have been inserted or extracted in each of the positive electrode 12 and the negative electrode 13 to pass through. This is because it prevents the mixing of the positive electrode electrolyte 16 and the negative electrode electrolyte 17. In other words, the separator 15 allows lithium ions to pass through from the positive electrode chamber S1 to the negative electrode chamber S2, and simultaneously allows lithium ions to pass through from the negative electrode chamber S2 to the positive electrode chamber S1.

[0173] Specifically, separator 15 comprises one or both of an ion exchange membrane and a solid electrolyte membrane. The ion exchange membrane is a porous membrane (cation exchange membrane) that allows lithium ions to pass through. The solid electrolyte membrane has lithium ion conductivity. This is because lithium ion permeability is increased in separator 15.

[0174] In this design, the separator 15 preferably comprises an ion exchange membrane, compared to a solid electrolyte membrane. This is because each of the aqueous solvents in the positive electrode electrolyte 16 and the negative electrode electrolyte 17 can easily penetrate into the interior of the separator 15, thereby improving the lithium-ion conductivity inside the separator 15.

[0175] A positive electrode 12 is disposed inside the positive electrode chamber S1, where lithium ions are inserted and extracted, while a negative electrode 13 is disposed inside the negative electrode chamber S2, where lithium ions are inserted and extracted. As described above, the negative electrode 13 contains a titanium-containing compound as the negative electrode active material.

[0176] Each of the positive electrode electrolyte 16 and the negative electrode electrolyte 17 is an aqueous electrolyte containing an aqueous solvent. The positive electrode electrolyte 16 is housed inside the positive electrode chamber S1, while the negative electrode electrolyte 17 is housed inside the negative electrode chamber S2. Therefore, the positive electrode electrolyte 16 and the negative electrode electrolyte 17 are separated from each other by a partition 15, preventing them from mixing.

[0177] That is, since the positive electrode electrolyte 16 is contained inside the positive electrode chamber S1, it does not come into contact with the negative electrode 13 but comes into contact with the positive electrode 12. On the other hand, since the negative electrode electrolyte 17 is contained inside the negative electrode chamber S2, it does not come into contact with the positive electrode 12 but comes into contact with the negative electrode 13.

[0178] The pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 17 are different from each other. Specifically, the negative electrode electrolyte 17, which is in contact with the negative electrode 13, has a pH of 11 or higher, similar to the electrolyte 14 in the first embodiment. In contrast, the positive electrode electrolyte 16, which is in contact with the positive electrode 12, has a pH of less than 11. As long as the pH-related magnitude relationship is satisfied, the composition (type of aqueous solvent, type and concentration of ionic substances, etc.) of the positive electrode electrolyte 16 and the negative electrode electrolyte 17 can be arbitrarily set.

[0179] The positive electrode electrolyte 16 has a pH less than 11, while the negative electrode electrolyte 17 has a pH greater than 11. This is because, compared to the case where both have equal pH, the decomposition potential of the aqueous solvent shifts due to the pH difference. Therefore, during charging and discharging, the decomposition reaction of the aqueous solvent can be thermodynamically suppressed while simultaneously expanding its potential window. Thus, a high voltage can be obtained while the charge-discharge reaction utilizing lithium-ion insertion and extraction proceeds fully and stably.

[0180] The composition (type of electrolyte salt) of the negative electrode electrolyte 17 is preferably different from that of the positive electrode electrolyte 16. This is because it is easier to satisfy the pH-related magnitude relationship mentioned above.

[0181] As long as the pH-related magnitude relationship described above is satisfied, the pH value of each of the positive electrode electrolyte 16 and the negative electrode electrolyte 17 is not particularly limited.

[0182] The pH of the negative electrode electrolyte 17 is preferably 12 or higher, and more preferably 13 or higher. This is because, since the pH of the negative electrode electrolyte 17 is sufficiently high, it is easy to satisfy the pH-related relationship described above. Furthermore, since the difference between the pH of the positive electrode electrolyte 16 and the pH of the negative electrode electrolyte 17 becomes sufficiently large, it is easy to maintain the pH relationship between the two.

[0183] Furthermore, 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 is because the pH difference between the positive electrode electrolyte 16 and the negative electrode electrolyte 17 is sufficiently large, making it easy to maintain the pH relationship between the two. Additionally, this is because the outer packaging component 11 is less susceptible to corrosion, and battery structural components such as the positive electrode current collector 12A and the negative electrode current collector 13A are also less susceptible to corrosion, thus improving the electrochemical durability (stability) of the lithium-ion secondary battery.

[0184] It should be noted that, similar to the electrolyte 14 in the first embodiment, one or both of the positive electrode electrolyte 16 and the negative electrode electrolyte 17 are preferably saturated solutions of an electrolyte salt (lithium salt). This is because the charge-discharge reaction (the insertion and extraction reaction of lithium ions) proceeds stably during charge and discharge. The method for confirming whether each of the positive electrode electrolyte 16 and the negative electrode electrolyte 17 is a saturated solution of a lithium salt is the same as the method for confirming whether the electrolyte 14 is a saturated solution of a lithium salt.

[0185] <2-2.Physical Properties>

[0186] In this lithium-ion secondary battery, similar to the lithium-ion secondary battery of the first embodiment described above, the physical properties of the negative electrode 13 are optimized to obtain excellent charge-discharge characteristics. Specifically, the elemental composition A when analyzing the surface of each of the negative electrode active material layer 13B and the negative electrode current collector 13A using XPS is 99 atomic percent or more. In this case, an elemental composition B of 99 atomic percent or more is further preferred.

[0187] <2-3. Actions>

[0188] When a lithium-ion secondary battery is charged, as lithium ions are deintercalated from the positive electrode 12, they move to the negative electrode 13 via the positive electrolyte 16, the separator 15, and the negative electrolyte 17. Thus, lithium ions are intercalated in the negative electrode 13.

[0189] On the other hand, during the discharge of the lithium-ion secondary battery, when lithium ions are deintercalated from the negative electrode 13, they move to the positive electrode 12 via the negative electrode electrolyte 17, the separator 15, and the positive electrode electrolyte 16. Thus, lithium ions are intercalated in the positive electrode 12.

[0190] <2-4. Manufacturing Method>

[0191] Except for the following description, the manufacturing steps of this lithium-ion secondary battery are the same as those of the lithium-ion secondary battery in the first embodiment described above.

[0192] In preparing each of the positive electrode electrolyte 16 and the negative electrode electrolyte 17, an ionic substance is added to the aqueous solvent. In this case, by adjusting the type and concentration (mol / kg) of the ionic substance, the pH of the positive electrode electrolyte 16 is made less than 11, and the pH of the negative electrode electrolyte 17 is made greater than 11.

[0193] In assembling a lithium-ion secondary battery, firstly, an outer packaging component 11 (positive electrode chamber S1 and negative electrode chamber S2) pre-installed with a separator 15 is prepared. Next, the positive electrode 12 is housed inside the positive electrode chamber S1, while the connection terminal 12AT is led out to the outside of the positive electrode chamber S1. Similarly, the negative electrode 13 is housed inside the negative electrode chamber S2, while the connection terminal 13AT is led out to the outside of the negative electrode chamber S2. Finally, positive electrolyte 16 is supplied to the inside of the positive electrode chamber S1 through a positive electrode injection port (not shown) communicating with the positive electrode chamber S1, and negative electrolyte 17 is supplied to the inside of the negative electrode chamber S2 through a negative electrode injection port (not shown) communicating with the negative electrode chamber S2. Afterward, each of the positive and negative electrode injection ports is sealed. Thus, the positive electrolyte 16 is contained inside the positive electrode chamber S1 containing the positive electrode 12, and the negative electrolyte 17 is contained inside the negative electrode chamber S2 containing the negative electrode 13. Thus, a lithium-ion secondary battery using two aqueous electrolytes (positive electrolyte 16 and negative electrolyte 17) was completed.

[0194] <2-5. Functions and Effects>

[0195] According to this lithium-ion secondary battery, the negative electrode active material of the negative electrode 13 contains a titanium-containing compound, the positive electrode electrolyte 16 containing an aqueous solvent has a pH of less than 11, the negative electrode electrolyte 17 containing an aqueous solvent has a pH of 11 or more, and the elemental proportion A is 99 atomic% or more. Therefore, for the same reasons as the lithium-ion secondary battery of the first embodiment described above, excellent charge-discharge characteristics can be obtained.

[0196] The other functions and effects of this lithium-ion secondary battery are the same as those of the lithium-ion secondary battery in the first embodiment.

[0197] <3. Variations>

[0198] As explained below, the structure of a lithium-ion secondary battery can be modified appropriately. Furthermore, any two or more of the variations described below can be combined with each other.

[0199] [Variation Example 1]

[0200] In each of the first and second embodiments, the negative electrode 13 includes a negative electrode active material layer 13B and a negative electrode current collector 13A. However, the negative electrode 13 may also include only the negative electrode active material layer 13B without the negative electrode current collector 13A (except for the connection terminal portion 13AT). In this case, in the surface analysis of the negative electrode 13 using XPS, the elemental ratio A is calculated by analyzing any 10 portions of the surface of the negative electrode active material layer 13B.

[0201] In this case, the element ratio A also meets the above-mentioned appropriate conditions, so the same effect can be obtained.

[0202] [Variation Example 2]

[0203] In each of the first and second embodiments, a negative electrode active material layer 13B is formed using a coating method. That is, in the process of forming the negative electrode active material layer 13B, a paste-like negative electrode slurry containing a negative electrode active material including a titanium compound, a negative electrode binder, and a negative electrode conductive agent is coated on both sides of the negative electrode current collector 13A, and then the negative electrode slurry is dried.

[0204] However, a sintering method can also be used instead of a coating method to form the negative electrode active material layer 13B. That is, in the process of forming the negative electrode active material layer 13B, after coating the negative electrode slurry and simultaneously drying the negative electrode slurry, the negative electrode slurry can be sintered at a high temperature. Thus, the negative electrode active material in the negative electrode slurry is sintered, thereby forming the negative electrode active material layer 13B.

[0205] In detail, a negative electrode active material containing a titanium compound and polyethylene oxide as a negative electrode binder are mixed to prepare a negative electrode mixture. This mixture is then added to a solvent to prepare a paste-like negative electrode slurry. Next, after coating the negative electrode slurry, it is fired in an oxygen atmosphere. The firing temperature is not particularly limited, specifically 500°C to 1200°C. The firing time is not particularly limited and can be set arbitrarily. Thus, the negative electrode active material in the negative electrode slurry is sintered and fixed to the surface of the negative electrode current collector 13A, thereby forming a negative electrode active material layer 13B.

[0206] It should be noted that when the negative electrode active material layer 13B is formed using a sintering method, the negative electrode slurry may not contain one or both of the negative electrode binder and the negative electrode conductive agent. This is because, when using a sintering method, the negative electrode active material is sintered, so even without using a negative electrode binder, the negative electrode active material is fixed on the negative electrode current collector 13A. Furthermore, even without using a negative electrode conductive agent, the electrical conductivity of the negative electrode active material layer 13B can be ensured.

[0207] In this case, the element ratio A also meets the above-mentioned appropriate conditions, so the same effect can be obtained.

[0208] [Variation Example 3]

[0209] In the first embodiment, such as Figure 1 As shown, electrolyte 14 was used as a liquid electrolyte. However, as with Figure 1 corresponding Figure 3 As shown, electrolyte layers 18 and 19, which are gel-like electrolytes, can also be used instead of electrolyte 14. Figure 3 The structure of the lithium-ion secondary battery shown is similar to that described below. Figure 1 The lithium-ion secondary battery shown has the same structure.

[0210] Here, the lithium-ion secondary battery further includes a separator 20, which is disposed between electrolyte layers 18 and 19. Electrolyte layer 18 is disposed between the positive electrode 12 and the separator 20, while electrolyte layer 19 is disposed between the negative electrode 13 and the separator 20. That is, electrolyte layer 18 is adjacent to each of the positive electrode 12 and the separator 20, while electrolyte layer 19 is adjacent to each of the negative electrode 13 and the separator 20.

[0211] Specifically, each of the electrolyte layers 18 and 19 contains an electrolyte 14 and a polymer compound, and the electrolyte 14 is held in place by the polymer compound. The type of polymer compound is not particularly limited, but specifically, it is any one or more of polyvinylidene fluoride and polyethylene oxide. Figure 3 In the middle, each of the electrolyte layers 18 and 19 is marked with a light shade.

[0212] The separator 20 is an insulating porous membrane that allows lithium ions to pass through while isolating the electrolyte layers 18 and 19 from each other. It contains polymer compounds such as polyethylene.

[0213] In forming electrolyte layer 18, electrolyte 14 and polymer compound are mixed with solvent to prepare a sol-like precursor solution, which is then coated onto the surface of positive electrode 12. The steps for forming electrolyte layer 19 are the same as those for forming electrolyte layer 18, except that the precursor solution is coated onto the surface of negative electrode 13.

[0214] In this case, since lithium ions can move between the positive electrode 12 and the negative electrode 13 via the electrolyte layers 18 and 19, it is also possible to obtain the same... Figure 1 The same effect is shown.

[0215] [Variation Example 4]

[0216] In the second embodiment, such as Figure 2 As shown, a positive electrode electrolyte 16 and a negative electrode electrolyte 17, both in liquid form, are used. However, as with... Figure 2 corresponding Figure 4 As shown, electrolyte layers 21 and 22, which are gel-like electrolytes, can be used instead of the positive electrolyte 16 and the negative electrolyte 17. Figure 4 The structure of the lithium-ion secondary battery shown is similar to that described below. Figure 2 The lithium-ion secondary battery shown has the same structure.

[0217] Here, electrolyte layer 21 is disposed between positive electrode 12 and separator 15, and electrolyte layer 22 is disposed between negative electrode 13 and separator 15. That is, electrolyte layer 21 is adjacent to each of positive electrode 12 and separator 15, and electrolyte layer 22 is adjacent to each of negative electrode 13 and separator 15.

[0218] Specifically, electrolyte layer 21 comprises a positive electrode electrolyte 16 and a polymer compound, the positive electrode electrolyte 16 being held in place by the polymer compound. Electrolyte layer 22 comprises a negative electrode electrolyte 17 and a polymer compound, the negative electrode electrolyte 17 being held in place by the polymer compound. Details regarding the types of polymer compounds are as described above. Figure 4 In the diagram, a light shade is marked on the electrolyte layer 21 containing the positive electrode electrolyte 16, while a dark shade is marked on the electrolyte layer 22 containing the negative electrode electrolyte 17.

[0219] When forming electrolyte layer 21, a sol-like precursor solution is prepared by mixing positive electrode electrolyte 16, a polymer compound, and a solvent, and then the precursor solution is coated onto the surface of positive electrode 12. When forming electrolyte layer 22, a sol-like precursor solution is prepared by mixing negative electrode electrolyte 17, a polymer compound, and a solvent, and then the precursor solution is coated onto the surface of negative electrode 13.

[0220] In this case, since lithium ions can move between the positive electrode 12 and the negative electrode 13 via the electrolyte layers 21 and 22, it is also possible to obtain the same... Figure 4 The same effect is shown.

[0221] <4. Applications of Lithium-ion Secondary Batteries>

[0222] There are no particular limitations on the applications of lithium-ion rechargeable batteries. Lithium-ion rechargeable batteries used as a power source can be the main power source for electronic devices and electric vehicles, or they can be an auxiliary power source. The main power source is the power source used preferentially, regardless of the availability of other power sources. An auxiliary power source is a power source used in place of the main power source, or a power source switched from the main power source.

[0223] Specific examples of applications for lithium-ion rechargeable batteries are as follows: Electronic devices such as camcorders, digital still cameras, mobile phones, laptops, stereo headphones, portable radios, and portable information terminals. Backup power supplies and storage devices such as memory cards. Power tools such as electric drills and chainsaws. Battery packs integrated into electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as household or industrial battery systems that pre-store power for emergencies. In these applications, one or multiple lithium-ion rechargeable batteries can be used.

[0224] Battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using lithium-ion batteries as their power source, and can also be hybrid vehicles that have a power source other than the lithium-ion battery. In home power storage systems, electricity stored in lithium-ion batteries, which serve as power storage sources, can be used to operate household electrical products, etc.

[0225] Of course, lithium-ion secondary batteries can also be used for purposes other than those exemplified here.

[0226] Example

[0227] Embodiments of this technology will be described.

[0228] <Examples 1-6 and Comparative Examples 1-3>

[0229] As described below, the battery characteristics of the lithium-ion secondary battery were evaluated after its manufacture.

[0230] [Manufacturing of Lithium-ion Secondary Batteries]

[0231] The following steps were used to manufacture [product / equipment]. Figure 1 The lithium-ion secondary battery shown is a type of aqueous electrolyte (electrolyte 14).

[0232] (The production of the positive electrode)

[0233] First, 91 parts by mass of the positive electrode active material (LiFePO4 (LFP) as a lithium phosphate compound), 3 parts by mass of the positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of the positive electrode conductive agent (graphite) are mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent (N-methyl-2-pyrrolidone as an organic solvent), and the solvent is stirred to prepare a paste-like positive electrode mixture slurry. Finally, using a coating apparatus, the positive electrode mixture slurry is coated on both sides of the positive electrode current collector 12A (a titanium foil with a thickness of 10 μm), excluding the connecting terminal portion 12AT, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer 12B. Thus, the positive electrode 12 is produced.

[0234] (Making the negative electrode)

[0235] In Examples 1-5, a negative electrode active material layer 13B was formed using a coating method. In this case, firstly, 89 parts by mass of the negative electrode active material (containing a titanium compound) and 11 parts by mass of the negative electrode binder (polyvinylidene fluoride) were mixed together to prepare a negative electrode mixture. Secondly, 89 parts by mass of the negative electrode active material (containing a titanium compound), 10 parts by mass of the negative electrode binder (polyvinylidene fluoride), and 1 part by mass of the negative electrode conductive agent (carbon black (CB) as a carbon material) were mixed together to prepare a negative electrode mixture.

[0236] As titanium-containing compounds, anatase-type titanium oxide (TiO2) was used as a titanium oxide, and lithium-titanium composite oxide (Li4Ti5O2) was used. 12 (LTO), and lithium-titanium composite oxide (Li4Ti5O) whose surface is covered by a carbon layer (carbon capping layer) as a carbon material. 12 (CLTO)).

[0237] Next, the negative electrode agent is added to a solvent (N-methyl-2-pyrrolidone as the organic solvent), and the solvent is stirred to prepare a paste-like negative electrode agent slurry. Finally, using a coating apparatus, the negative electrode agent slurry is coated onto both sides of the negative electrode current collector 13A (a titanium (Ti) foil with a thickness of 10 μm) except for the connecting terminal portion 13AT, and then the negative electrode agent slurry is dried to form the negative electrode active material layer 13B. Thus, the negative electrode 13 is manufactured.

[0238] In Example 6, a negative electrode active material layer 13B was formed using a sintering method. In this case, firstly, 89 parts by mass of the negative electrode active material (anatase-type titanium oxide containing a titanium compound) and 11 parts by mass of the negative electrode binder (polyethylene oxide) were mixed to prepare a negative electrode binder. Next, a surfactant and the negative electrode binder were added together to a solvent (pure water as an aqueous solvent), and the solvent was stirred to prepare a paste-like negative electrode binder slurry. Next, using a coating apparatus, the negative electrode binder slurry was coated onto both sides of the negative electrode current collector 13A (a titanium foil with a thickness of 10 μm), excluding the connecting terminal portion 13AT, and then the negative electrode binder slurry was dried. Finally, the negative electrode binder slurry was calcined in an oxygen atmosphere (calcination temperature = 700°C, calcination time = 1 hour), thereby forming the negative electrode active material layer 13B. Thus, the negative electrode 13 was produced.

[0239] The carbon percentage C (wt%) of the negative electrode 13 is shown in Table 1. Additionally, surface analysis of the negative electrode 13 (negative electrode current collector 13A and negative electrode active material layer 13B) was performed using XPS. Based on the surface analysis results, the elemental percentages A and B (atomic%) were calculated using the aforementioned analytical software, yielding the results shown in Table 1.

[0240] (Preparation of electrolyte)

[0241] An ionic substance was added to an aqueous solvent (pure water), and then the aqueous solvent was stirred to prepare electrolyte 14. The types of ionic substances, the concentration (mol / kg) of electrolyte 14, and the pH are shown in Table 1. In this case, the pH of electrolyte 14 is 11 or higher. Lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were used as ionic substances, serving as electrolyte salts (lithium salts).

[0242] (Assembly of lithium-ion secondary batteries)

[0243] First, each of the positive electrode 12 and the negative electrode 13 is housed within the internal space S of the outer packaging component 11 (glass beaker) made of glass. In this case, each of the connecting terminals 12AT and 13AT is led out to the outside of the outer packaging component 11. Next, a reference electrode (silver-silver chloride electrode) is placed in the internal space S. Finally, electrolyte 14 is supplied to the internal space S. Thus, electrolyte 14 is contained within the internal space S, thereby completing the lithium-ion secondary battery.

[0244] [Manufacturing of lithium-ion secondary batteries for comparison]

[0245] A lithium-ion secondary battery was manufactured using the same steps as the negative electrode current collector 13A, except that aluminum (Al) foil and copper (Cu) foil were used. Additionally, a lithium-ion secondary battery was manufactured using the same steps, except that lithium nitrate (LiNO3) was used as the ionic substance to make the pH of the electrolyte 14 less than 11. The types of ionic substances, the concentration (mol / kg) of the electrolyte 14, and the pH are shown in Table 1.

[0246] [Evaluation of Battery Characteristics]

[0247] As a lithium-ion secondary battery, the battery characteristics (charge and discharge characteristics, charge and discharge capability, and charge and discharge efficiency) were evaluated, and the results are shown in Table 1.

[0248] In investigating whether charging and discharging are possible, the investigation focused on whether lithium-ion secondary batteries can be charged and discharged, i.e., whether both charging capacity and discharging capacity can be obtained.

[0249] Given that a lithium-ion secondary battery can be charged and discharged, its charge and discharge efficiency is calculated based on the formula: charge and discharge efficiency (%) = (discharge capacity / charge capacity) × 100.

[0250] Here, using titanium oxide as the negative electrode active material, the battery is charged at a constant current of 1C until the voltage reaches -1.3V, and then discharged at a constant current of 1C until the voltage reaches -1.0V. Finally, it is discharged at a constant voltage of -1.0V until the current reaches 0.1C. 1C refers to the current value required to fully discharge the battery's theoretical capacity in one hour, while 0.1C refers to the current value required to fully discharge the battery's capacity in 10 hours.

[0251] In addition, when lithium titanium composite oxide is used as the negative electrode active material, it is charged at a constant current of 1C until the voltage reaches -1.65V, and discharged at a constant current of 1C until the voltage reaches -1.35V. Then, it is discharged at a constant voltage of -1.35V until the current reaches 0.1C.

[0252] [Table 1]

[0253]

[0254] [Inspection]

[0255] As shown in Table 1, the charge-discharge efficiency varies with the physical properties of the negative electrode 13 (elemental ratio A) and the physical properties of the electrolyte 14 (pH).

[0256] Specifically, when the pH of the electrolyte 14 is 11 or higher, but the elemental ratio A is less than 99 atomic% because a metal material including metal elements (Al, Cu) constituting non-specific metal materials is used as the forming material of the negative electrode current collector 13A, the lithium-ion secondary battery cannot be charged and discharged, or even if the lithium-ion secondary battery can be charged and discharged, the charge and discharge efficiency is significantly reduced.

[0257] Furthermore, in the case where the elemental proportion A is 99 atomic percent or more, and the pH of the electrolyte 14 is less than 11, the lithium-ion secondary battery cannot be charged and discharged because a metal material including a metal element (Ti) constituting a specific metal material is used as the forming material of the negative electrode current collector 13A.

[0258] In contrast, when a metal material including a metal element (Ti) constituting a specific metal material is used as the forming material of the negative electrode current collector 13A and the element ratio A is 99 atomic% or more, and the pH of the electrolyte 14 is 11 or more (Examples 1 to 6), the lithium-ion secondary battery can be charged and discharged, and the charging and discharging efficiency is increased.

[0259] In this case, in particular, the following tendencies are observed: First, high charge-discharge efficiency is obtained when the elemental proportion B is 99 atomic% or higher. Second, the charge-discharge efficiency further increases when the carbon proportion C is less than 0.1 atomic%. Third, the charge-discharge efficiency further increases when the concentration of electrolyte 14 is between 0.2 mol / kg and 4 mol / kg. Fourth, the charge-discharge efficiency further increases when titanium oxide (anatase-type titanium oxide) is used as the negative electrode active material.

[0260] [Summarize]

[0261] As shown in Table 1, when the negative electrode active material of the negative electrode 13 contains a titanium-containing compound, the electrolyte 14 containing an aqueous solvent has a pH of 11 or higher, and the elemental ratio A is 99 atomic% or higher, the lithium-ion secondary battery can be charged and discharged with high charge and discharge efficiency. Therefore, excellent charge and discharge characteristics are obtained in the lithium-ion secondary battery.

[0262] The above description illustrates the structure of the lithium-ion secondary battery of this technology through one embodiment and example. However, the structure of the lithium-ion secondary battery of this technology is not limited to the structure described in one embodiment and example, and various modifications are possible.

[0263] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described herein. Thus, other effects can also be obtained with this technology.

Claims

1. A lithium-ion secondary battery, comprising: Positive electrode, lithium ion insertion / deintercalation; A negative electrode includes a negative electrode active material layer and a negative electrode current collector, wherein the negative electrode active material layer comprises negative electrode active material into which lithium ions are intercalated or deintercalated, and the negative electrode current collector supports the negative electrode active material layer; and Electrolyte, containing aqueous solvent, The negative electrode active material contains titanium-containing compounds. The electrolyte has a pH of 11 or higher. When analyzing the surface of the negative electrode active material layer using X-ray photoelectron spectroscopy, the sum of the detected amounts of lithium and titanium relative to the sum of the detected amounts of all metal elements is over 99 atomic%. When analyzing the surface of the negative electrode current collector using X-ray photoelectron spectroscopy, the sum of the detected amounts of lithium and titanium relative to the sum of the detected amounts of all metal elements is more than 99 atomic percent. The negative electrode does not contain carbon material, or if it does contain carbon material, the weight ratio of the carbon material to the weight of the negative electrode is less than 0.1 by weight.

2. The lithium-ion secondary battery according to claim 1, wherein, The concentration of the electrolyte is above 0.2 mol / kg and below 4 mol / kg.

3. A lithium-ion secondary battery, comprising: A separator is placed between the positive and negative electrode spaces to allow lithium ions to pass through; A positive electrode is disposed inside the positive electrode space, where lithium ions are inserted and de-intercalated; A negative electrode is disposed inside the negative electrode space and includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer contains negative electrode active materials that are inserted into or extracted from lithium ions, and the negative electrode current collector supports the negative electrode active material layer. The positive electrode electrolyte, contained within the positive electrode space, comprises an aqueous solvent; and The negative electrode electrolyte, contained within the negative electrode space, includes the aqueous solvent. The negative electrode active material contains titanium-containing compounds. The positive electrode electrolyte has a pH less than 11. The negative electrode electrolyte has a pH of 11 or higher. When analyzing the surface of the negative electrode active material layer using X-ray photoelectron spectroscopy, the sum of the detected amounts of lithium and titanium relative to the sum of the detected amounts of all metal elements is over 99 atomic%. When analyzing the surface of the negative electrode current collector using X-ray photoelectron spectroscopy, the sum of the detected amounts of lithium and titanium relative to the sum of the detected amounts of all metal elements is more than 99 atomic percent. The negative electrode does not contain carbon material, or if it does contain carbon material, the weight ratio of the carbon material to the weight of the negative electrode is less than 0.1 by weight.

4. The lithium-ion secondary battery according to claim 3, wherein, The concentration of the negative electrode electrolyte is above 0.2 mol / kg and below 4 mol / kg.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, wherein, The titanium-containing compound comprises at least one of a titanium oxide represented by formula (1) and a lithium-titanium composite oxide represented by formulas (2) to (4), respectively. TiO w …(1), w satisfies 1.85 ≤ w ≤ 2.

15. Li[Li x M1 (1-3x) / 2 You (3+x) / 2 ]O4…(2), M1 is at least one of Mg, Ca, Cu, Zn, and Sr, and x satisfies 0 ≤ x ≤ 1 / 3. Li[Li y M2 1-3y Ti 1+2y ]O4…(3), M2 is at least one of Al, Sc, Cr, Mn, Fe, Ge, and Y, where y satisfies 0 ≤ y ≤ 1 / 3. It[It 1 / 3 M3 z Small (5 / 3)-z ]O4…(4), M3 is at least one of V, Zr, and Nb, and z satisfies 0 ≤ z ≤ 2 / 3.

6. The lithium-ion secondary battery according to claim 5, wherein, The titanium oxide comprises anatase titanium oxide.

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