Aqueous electrolyte secondary batteries

Abstract

SOLUTION: An aqueous electrolyte secondary battery includes an electrode plate group and an aqueous electrolyte. The electrode plate group includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. Chemical oxygen demand in the aqueous electrolyte is 5 mg / L or more and 160 mg / L or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aqueous electrolyte secondary battery.

Background Art

[0002] An aqueous electrolyte secondary battery is a secondary battery that uses an aqueous solution as an electrolyte. Examples of aqueous electrolyte secondary batteries include lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like.

[0003] Patent Document 1 proposes a battery separator for a lead-acid battery to reduce float charging, reduce water electrolysis, and / or reduce the water loss rate, the battery separator containing at least one additive having a density of at least 5.0 g / m 2 and at least one metal salt having a density of at least 1.0 g / m 2 . Patent Document 1 also proposes a lead-acid battery including such a separator.

[0004] Patent Document 2 proposes a lead-acid battery containing 0.5 mg / L or more and 3 mg / L or less of a reducing organic substance in the electrolyte.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In aqueous electrolyte secondary batteries, improving charge acceptance is required. Generally, charge acceptance can be improved by increasing the reaction area of ​​the positive and negative electrodes, raising the temperature of the aqueous electrolyte secondary battery, or lowering the specific gravity of the electrolyte. However, adopting these methods requires significant changes to the battery design, and the challenge has been the need to control various factors in relation to the battery design. [Means for solving the problem]

[0007] One aspect of this disclosure is an aqueous electrolyte secondary battery, The aforementioned aqueous electrolyte secondary battery includes an electrode plate group and an aqueous electrolyte, The electrode plate group includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. This invention relates to an aqueous electrolyte secondary battery, wherein the chemical oxygen demand in the aqueous electrolyte is 5 mg / L or more and 160 mg / L or less. [Effects of the Invention]

[0008] This can improve the charge acceptance of aqueous electrolyte secondary batteries. [Brief explanation of the drawing]

[0009] [Figure 1] This is a partially cutaway perspective view showing the external appearance and internal structure of an aqueous electrolyte secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] In aqueous electrolyte secondary batteries, the electrolyte contains a certain amount of organic components from the initial stage. These organic components are thought to originate from the battery's constituent elements. Examples of battery components that serve as sources of organic components include electrolyte additives, separators, and electrodes. Organic components originating from the separator or electrodes are thought to be included in the electrolyte, for example, when additives contained in the separator or electrodes dissolve, or when components that adhere to the separator or electrodes during the manufacturing process dissolve. Examples of components that adhere to the separator or electrodes during the manufacturing process include cutting oils and mold release agents.

[0011] The inventors have found that in aqueous electrolyte secondary batteries, the presence of a certain amount of organic components in the electrolyte reduces the charge acceptance rate. This reduction in charge acceptance rate is likely due to the following reasons: In aqueous electrolyte secondary batteries, during charging, charging reactions occur at both the positive and negative electrodes, and a charging current flows between the positive and negative electrodes. However, it is presumed that the presence of organic components in the electrolyte causes side reactions such as oxidation of the organic components. As a result, the charging current becomes less able to flow, and the charge acceptance rate decreases.

[0012] In view of the above, (1) an aqueous electrolyte secondary battery according to one aspect of the present invention includes an electrode plate group and an aqueous electrolyte. The electrode plate group includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. The chemical oxygen demand (COD) in the aqueous electrolyte is 5 mg / L or more and 160 mg / L or less.

[0013] COD (Chemical Oxygen Demand) is the amount of oxygen required to oxidize oxidizable substances in water. The COD in an aqueous electrolyte can be considered an indicator of the concentration of organic components in the aqueous electrolyte. In this specification, COD refers to the COD in an aqueous electrolyte secondary battery collected from a fully charged, initially used battery. An "initially used battery" refers to a battery that has not been in use for very long and has shown little degradation.

[0014] In the above aspect of the present invention, the COD in the aqueous electrolyte of the aqueous electrolyte secondary battery is set to 5 mg / L or more and 160 mg / L or less. As a result, the charging current flows more easily between the positive and negative electrodes compared to cases where the COD in the aqueous electrolyte is less than 5 mg / L or more than 160 mg / L, and the charge acceptance is greatly improved. This is thought to be because the concentration of organic components in the aqueous electrolyte is within the above range, which suppresses side reactions, such as the decomposition reaction of organic components. Specifically, when the COD in the aqueous electrolyte is 5 mg / L or more, the decomposition reaction of organic components on the surface of the positive electrode occurs preferentially to the oxidation reaction of the separator, thus reducing oxidative degradation of the separator. As a result, internal short circuits due to oxidative degradation of the separator are suppressed, and higher lifespan performance is obtained. Furthermore, when the COD in the aqueous electrolyte is 160 mg / L or less, it is thought that side reactions in which organic matter in the electrolyte is oxidized or reductively decomposed on the surface of the electrode are suppressed.

[0015] For example, Figure 5 of Patent Document 1 shows that the COD values ​​of batteries A, B, and D are 20,031 mg / L, 5,920 mg / L, and 13,004 mg / L, respectively. While these values ​​cannot be directly compared to the COD of 160 mg / L or less in the aqueous electrolyte in this disclosure, the COD values ​​in the batteries of Patent Document 1 are considerably high.

[0016] (2) In (1) above, the COD in the aqueous electrolyte may be 130 mg / L or less. In this case, higher charge acceptance can be ensured.

[0017] (3) In (1) or (2) above, the COD in the aqueous electrolyte may be 8 mg / L or more. In this case, higher charge acceptance can be ensured.

[0018] (4) In any one of the above (1) to (3), the aqueous electrolyte secondary battery may be a lead-acid battery. The aqueous electrolyte secondary batteries include lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, and the like. Among the aqueous electrolyte secondary batteries, the lead-acid battery has the highest positive electrode potential. Therefore, organic components are likely to be oxidized and decomposed on the surface of the positive electrode plate, and side reactions are likely to proceed. In the present disclosure, even in such a lead-acid battery, high charge acceptance can be ensured.

[0019] The lead-acid battery may be a controlled valve type battery (also referred to as a sealed battery), but a liquid type battery (also referred to as a vent type battery) is preferred. The controlled valve type lead-acid battery may be called a VRLA (Valve Regulated Lead-Acid Battery).

[0020] (5) In the above (4), the negative electrode plate may contain at least one selected from the group consisting of an organic anti-shrinkage agent and a carbonaceous material. When the negative electrode plate contains at least one selected from the group consisting of an organic anti-shrinkage agent and a carbonaceous material, there is a tendency to obtain high charge acceptance. However, when the negative electrode plate contains at least one selected from the group consisting of an organic anti-shrinkage agent and a carbonaceous material, the COD in the electrolyte may be higher than when the negative electrode plate does not contain any of these substances, and this may affect the charge acceptance. Even in such a case, in the aqueous electrolyte secondary battery according to the above aspect of the present invention, the COD in the electrolyte is within a specific range, and by including at least one selected from the group consisting of an organic anti-shrinkage agent and a carbonaceous material in the negative electrode plate, higher charge acceptance can be ensured.

[0021] (6) In the above (4) or (5), the electrode plate group may include a fiber mat interposed between the positive electrode plate and the negative electrode plate. When the electrode plate group includes a fiber mat, the internal resistance of the battery tends to increase and the charge acceptance tends to decrease compared to when the electrode plate group does not include a fiber mat. Even in such a case, in the aqueous electrolyte secondary battery according to the above aspect of the present invention, high charge acceptance can be ensured by the fact that the COD in the electrolyte is within a specific range.

[0022] In this specification, the fully charged state of a flooded lead-acid battery is defined according to JIS D 5301:2019. More specifically, in a water tank at 25°C ± 2°C, the terminal voltage during charging (unit: V) measured every 15 minutes or the electrolyte density converted to 20°C shows a constant value for three consecutive times with three significant digits. Until then, the lead-acid battery is charged with a current (unit: A) that is 0.2 times the value (unit: Ah) of the rated capacity described as the rated capacity. The state of being charged is defined as the fully charged state. Hereinafter, the value (unit: Ah) described as the rated capacity is simply referred to as the "rated capacity". In the case of a controlled valve type lead-acid battery, the fully charged state means that in an air tank at 25°C ± 2°C, constant current and constant voltage charging is performed at 2.23 V / cell with a current (unit: A) that is 0.2 times the rated capacity, and charging is terminated when the charging current during constant voltage charging reaches a value (unit: A) that is 0.005 times the rated capacity.

[0023] A fully charged lead-acid battery is a lead-acid battery that has been fully charged from a preformed lead-acid battery. The full charge of the lead-acid battery may be immediately after formation if it is after formation, or may be performed after a certain period of time has elapsed since formation. A fully charged lead-acid battery may be, for example, a lead-acid battery that has been fully charged from a lead-acid battery during use, preferably at the initial stage of use, after formation.

[0024] The fully charged state of a nickel-metal hydride battery is a state in which it has been charged in accordance with the "charging procedure before conducting the test" of JIS C 63115-2:2022. First, at an ambient temperature of 20°C ± 5°C, it is discharged at a constant current of 0.2It (unit: A) until 1.0 V per single cell. Thereafter, it is in a state of being charged at a constant current of 0.1It (unit: A) for 10 to 16 hours. It is the reference test current. The reference test current is a current expressed by the formula It (unit: A) = C5 (unit: Ah) / 1 (unit: h) corresponding to a reference time of 5 hours. Here, C5 is the rated capacity, which represents the electrical capacity specified by the manufacturer.

[0025] The fully charged state of a nickel-cadmium battery is defined according to the same criteria as the fully charged state of the above nickel-metal hydride battery.

[0026] The following describes in more detail, according to the main requirements, an aqueous electrolyte secondary battery relating to one aspect of the present invention. However, the present invention is not limited to the constituent elements described below. The components described herein can be combined in any combination. At least one component described herein may be combined with at least one of (1) to (6) above.

[0027] [Aqueous electrolyte secondary battery] A water-based electrolyte secondary battery includes a group of electrode plates and a water-based electrolyte.

[0028] (aqueous electrolyte) The COD in the aqueous electrolyte is between 5 mg / L and 160 mg / L. From the viewpoint of obtaining higher charge acceptance, the upper limit of the COD in the aqueous electrolyte is preferably 130 mg / L or less or 100 mg / L or less, more preferably 50 mg / L or less or 30 mg / L or less, and even more preferably 25 mg / L or less. From the viewpoint of easily obtaining higher charge acceptance, the lower limit of the above range is preferably 8 mg / L or more, and this lower limit may be combined with each of the upper limits mentioned above.

[0029] COD in an aqueous electrolyte can be adjusted by adjusting the concentration of organic additives in the aqueous electrolyte used in the assembly of an aqueous electrolyte secondary battery, by not adding organic additives to the aqueous electrolyte, or by adjusting the content of organic components in components other than the aqueous electrolyte. For example, the COD in the aqueous electrolyte can be kept low by reducing the amount of relatively low molecular weight organic additives contained in the separator, by removing at least a portion of the cutting oil adhering to the current collector of the electrode plate or the metal plate before it is processed into a current collector through cleaning, or by reducing the content of at least one of the organic components and carbonaceous materials contained in the electrode material. Examples of relatively low molecular weight organic additives include penetrants and oils. The method for adjusting the COD in the aqueous electrolyte may be one of these methods or a combination of several methods. Cleaning of the current collector or metal plate is performed, for example, using an organic solvent. The type of organic solvent is selected according to the type of organic component adhering to the current collector or metal plate. Examples of organic solvents include at least one selected from alcohols, ketones, esters, ethers, amides, and sulfoxides. Examples of alcohols include ethanol. Examples of ketones include acetone and ethyl methyl ketone. Examples of esters include ethyl acetate. Examples of ethers include tetrahydrofuran. Examples of amides include dimethylformamide and N-methyl-2-pyrrolidone. Examples of sulfoxides include dimethyl sulfoxide. To prevent residual organic solvents from increasing the COD in the electrolyte, it is preferable to use organic solvents that are easily removed by rinsing with water after cleaning the current collector or metal plate, or volatile organic solvents. Examples of organic solvents that are easily removed by rinsing with water include organic solvents that are miscible with water. The cleaning time for the current collector or metal plate is preferably 3 seconds or more in an organic solvent that is miscible with water. The upper limit of the cleaning time is not particularly limited and may be, for example, 60 seconds or less. Organic components contained in the electrode material also include organic shrinkage inhibitors.

[0030] Aqueous electrolytes are aqueous solutions in which a solute is dissolved. Aqueous electrolytes may be gelled as needed. The solute is selected, for example, according to the type of aqueous electrolyte secondary battery. The concentration of the solute or the specific gravity of the electrolyte is also determined, for example, according to the type and application of the aqueous electrolyte secondary battery.

[0031] For example, in lead-acid batteries, an aqueous solution containing sulfuric acid is used as the aqueous electrolyte. The aqueous electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions.

[0032] The aqueous electrolyte used in the assembly of lead-acid batteries may contain organic additives. Examples of organic additives include surfactants. However, from the viewpoint of keeping the COD in the aqueous electrolyte contained in lead-acid batteries low, it is preferable that the aqueous electrolyte used in the assembly of lead-acid batteries does not contain organic additives.

[0033] In lead-acid batteries, the specific gravity of the aqueous electrolyte at 20°C is, for example, 1.10 or higher. Alternatively, the specific gravity of the aqueous electrolyte at 20°C may be 1.35 or lower. These specific gravity values ​​are for the electrolyte of a fully charged lead-acid battery.

[0034] Furthermore, in the case of water-based electrolyte secondary batteries, nickel-metal hydride batteries and nickel-cadmium batteries, for example, aqueous solutions containing inorganic bases such as alkali metal hydroxides (such as potassium hydroxide aqueous solution) are used as the water-based electrolyte. However, not limited to this case, aqueous solutions containing known solutes used in nickel-metal hydride batteries or nickel-cadmium batteries can be used as the water-based electrolyte.

[0035] The COD of aqueous electrolytes is measured in accordance with JIS K 0102-1:2021, "17.2 Oxygen consumption by acidic potassium permanganate (CODMn)". COD (CODMn) is calculated using the following formula. In this calculation, CODMn is calculated with 2 significant figures, 1 decimal place, and a lower limit of <0.5. CODMn=(titration value-BL)×F×1000 / V×0.2 Titration value: The volume (mL) of 5 mmol / L potassium permanganate aqueous solution required to titrate the sample prepared from the electrolyte. Blank (BL): The volume (mL) of 5 mmol / L potassium permanganate aqueous solution required for titration in a test using distilled water. F: Factor of potassium permanganate aqueous solution with a concentration of 5 mmol / L V: Volume (mL) of sample prepared from the electrolyte (sample used for titration) Oxygen equivalent (mg) in 1 mL of 0.2:5 mmol / L potassium permanganate aqueous solution

[0036] The titration sample is prepared using the following procedure: First, the electrolyte is taken from an initially fully charged aqueous electrolyte secondary battery into a 300 mL Erlenmeyer flask. The amount of electrolyte taken should be a maximum of 100 mL, and adjusted so that the titration volume is in the range of 3.5 mL to 5.5 mL. If the amount taken is less than 100 mL, the amount is measured and distilled water is added until the diluted volume reaches 100 mL. In this way, the electrolyte sample is prepared. In addition, 100 mL of distilled water is prepared in a separate 300 mL Erlenmeyer flask as a sample for BL (Body Line). BL measurement is performed each time the sample prepared from the electrolyte is titrated.

[0037] Samples for titration are prepared from 100 mL of electrolyte and distilled water samples for BL using the following procedure. First, 47% by mass aqueous sulfuric acid solution is added to each sample using an autoburette until acidic. However, in the case of lead-acid battery electrolyte, this step of adding the aqueous sulfuric acid solution is skipped. To the resulting mixture or the above sample, 10 mL of 5 mmol / L aqueous potassium permanganate solution is added using a volumetric pipette and stirred. Next, each Erlenmeyer flask is placed in a boiling water bath and heated for 30 minutes. During this time, the water in the water bath is kept boiling at all times, and the liquid level in the water bath is kept above the liquid level in the Erlenmeyer flask. After 30 minutes of heating, the Erlenmeyer flask is removed and immediately 10 mL of 12.5 mmol / L aqueous sodium oxalate solution is added to the liquid in the Erlenmeyer flask using a volumetric pipette. The samples for titration are prepared by cooling the liquid until the temperature is within the range of 50°C to 60°C. If the sample contains chloride ions, add 2 mL of 500 g / L silver nitrate aqueous solution using a measuring pipette and stir the resulting mixture thoroughly until the precipitate disappears and the liquid becomes clear. If the turbidity persists, continue stirring while gradually adding more silver nitrate aqueous solution until the turbidity disappears. The amount of silver nitrate aqueous solution added should be such that the total amount of silver nitrate is 1 g in excess of the equivalent amount of chloride ions contained in each sample. The silver nitrate aqueous solution is added to the sample or the mixture to which the sulfuric acid aqueous solution has been added.

[0038] Each prepared sample for titration is titrated with a 5 mmol / L potassium permanganate aqueous solution. During titration, stop the titration when the liquid in the Erlenmeyer flask turns slightly red, and allow it to stand for about 30 seconds to check if the red color has disappeared. If the red color disappears, repeat the titration and standing process until the red color disappears. For samples prepared from the electrolyte and samples prepared from distilled water, the amount of potassium permanganate aqueous solution (mL) required for titration is used as the titration value and BL in the above formula to determine the COD of the electrolyte. If the electrolyte is diluted with distilled water during sample preparation, the COD of the electrolyte before dilution is calculated taking the dilution into account.

[0039] (electrode group) The electrode group includes, for example, a positive electrode plate, a negative electrode plate, and a separator interposed between them. Each component is selected according to the type of aqueous electrolyte secondary battery.

[0040] (Positive plate) The positive electrode plate includes, for example, a positive electrode material and a positive electrode current collector that holds the positive electrode material.

[0041] In nickel-metal hydride batteries and nickel-cadmium batteries, a nickel substrate is used as the positive electrode current collector. Examples of nickel substrates include sintered substrates and foamed substrates. The positive electrode material includes, for example, nickel oxide and may optionally include a binder, a conductive agent, etc. An example of nickel oxide is nickel oxyhydroxide.

[0042] In lead-acid batteries, either a paste-type or clad-type positive electrode plate may be used.

[0043] In a paste-type positive electrode plate, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector. Note that the positive electrode plate may have components such as mats or pasting paper attached to it. Such components (hereinafter also referred to as "attached components") are used integrally with the positive electrode plate and are therefore included in the positive electrode plate. If the positive electrode plate includes attached components, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector and attached components.

[0044] A clad positive electrode plate comprises multiple porous tubes, a core inserted into each tube, a current collector connecting the multiple cores, a positive electrode material filled into the tubes into which the cores are inserted, and a connecting seat connecting the multiple tubes. In a clad positive electrode plate, the positive electrode material is the portion of the positive electrode plate excluding the tubes, cores, current collector, and connecting seat. In a clad positive electrode plate, the cores and current collector together are sometimes referred to as the positive electrode current collector.

[0045] The positive electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. Examples of processing methods include expansion or punching. Using a grid-like current collector as the positive electrode current collector is preferable because it facilitates the support of the positive electrode material.

[0046] As the lead alloy used for the positive electrode current collector, Pb-Ca alloys and Pb-Ca-Sn alloys are preferred in terms of corrosion resistance and mechanical strength. The positive electrode current collector may have lead alloy layers of different compositions, and the alloy layers may be one layer or multiple layers.

[0047] The positive electrode material contained in the positive electrode plate includes a positive electrode active material that exhibits capacity through a redox reaction. Examples of positive electrode active materials include lead dioxide or lead sulfate. The positive electrode material may also contain other additives as needed. Examples of other additives include reinforcing materials and carbonaceous materials.

[0048] Examples of reinforcing materials include fibers. Examples of fibers include inorganic fibers and organic fibers. Examples of inorganic fibers include glass fibers and carbon fibers. Examples of resins or polymers constituting organic fibers include at least one selected from the group consisting of acrylic resins, polyolefin resins, polyester resins, and cellulose compounds. An example of a polyester resin is polyethylene terephthalate. Examples of cellulose compounds include cellulose and cellulose derivatives. Examples of cellulose derivatives include cellulose ethers and cellulose esters. Rayon is also included among cellulose compounds.

[0049] The reinforcing material content in the positive electrode material is, for example, 0.03% by mass or more. Alternatively, the reinforcing material content in the positive electrode material is, for example, 0.5% by mass or less.

[0050] Unformed paste-type positive electrode plates are obtained by filling a positive electrode current collector with positive electrode paste, followed by maturation and drying. The positive electrode paste is prepared by kneading lead powder, antimony compounds, and other additives such as reinforcing materials and carbonaceous materials as needed, with water and sulfuric acid.

[0051] A positive electrode plate can be obtained by chemically treating an untreated positive electrode plate. Chemical treatment can be carried out by immersing the electrode plate group, including the untreated positive electrode plate, in an electrolyte containing sulfuric acid in the battery case of a lead-acid battery, and then charging the electrode plate group. However, chemical treatment may also be carried out before the assembly of the lead-acid battery or the electrode plate group.

[0052] (Negative electrode plate) The negative electrode plate includes, for example, a negative electrode material and a negative electrode current collector that holds the negative electrode material.

[0053] In nickel-metal hydride and nickel-cadmium batteries, the negative electrode current collector is made of, for example, stainless steel, nickel, or a nickel alloy. The negative electrode material of a nickel-metal hydride battery includes, for example, a hydrogen-containing hydrogen storage alloy or hydrogen compound, and may optionally include a conductive agent, a binder, etc. The negative electrode material of a nickel-cadmium battery includes a cadmium compound, and may optionally include a conductive agent, a binder, etc.

[0054] In lead-acid batteries, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector. Note that the negative electrode plate may have adhesive members attached as described above. In this case, the adhesive members are included in the negative electrode plate. When the negative electrode plate includes adhesive members, the negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector and the adhesive members.

[0055] The negative electrode current collector can be formed in the same manner as the positive electrode current collector.

[0056] The lead alloy used for the negative electrode current collector may be any of the following: a Pb-Sb alloy, a Pb-Ca alloy, or a Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one additive element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, Cu, etc. The negative electrode current collector may have lead alloy layers of different compositions, and the alloy layers may be one layer or multiple layers.

[0057] The negative electrode material contained in the negative electrode plate includes a negative electrode active material that exhibits capacity through oxidation-reduction reactions, and may also contain organic shrinkage inhibitors, carbonaceous materials, barium sulfate, etc. Lead or lead sulfate is used as the negative electrode active material. The negative electrode material may also contain other additives such as reinforcing materials as needed.

[0058] Examples of organic shrinkage inhibitors include lignin, ligninsulfonic acid, and synthetic organic shrinkage inhibitors. Examples of synthetic organic shrinkage inhibitors include formaldehyde condensates of phenolic compounds. The negative electrode material may contain one organic shrinkage inhibitor or two or more.

[0059] The content of the organic shrinkage inhibitor in the negative electrode material is, for example, 0.01% by mass or more. The content of the organic shrinkage inhibitor is, for example, 1% by mass or less.

[0060] Examples of carbonaceous materials included in the negative electrode material include carbon black, graphite (artificial graphite, natural graphite, etc.), hard carbon, and soft carbon. The negative electrode material may contain one type of carbonaceous material, or two or more types.

[0061] The carbonaceous material content in the negative electrode material is, for example, 0.1% by mass or more. The carbonaceous material content may also be, for example, 3% by mass or less.

[0062] The barium sulfate content in the negative electrode material is, for example, 0.1% by mass or more. Alternatively, the barium sulfate content may be, for example, 3% by mass or less.

[0063] Examples of reinforcing materials include fibers. The fibers can be selected from the materials exemplified for the positive electrode plate.

[0064] The reinforcing material content in the negative electrode material is, for example, 0.03% by mass or more. Alternatively, the reinforcing material content in the negative electrode material is, for example, 0.5% by mass or less.

[0065] The negative electrode active material in the charged state is spongy lead, but the unformed negative electrode plate is usually made using lead powder.

[0066] The negative electrode plate can be formed by filling a negative electrode current collector with negative electrode paste, aging and drying it to produce an unformed negative electrode plate, and then forming the unformed negative electrode plate. The negative electrode paste is prepared by kneading lead powder, an organic shrinkage inhibitor, and various additives as needed, with water and sulfuric acid. In the aging process, it is preferable to age the unformed negative electrode plate at a temperature higher than room temperature and at high humidity.

[0067] The chemical conversion can be carried out by immersing the electrode plate group, including the unconverted negative electrode plate, in the sulfuric acid-containing electrolyte in the lead-acid battery case and then charging the electrode plate group. However, the chemical conversion may also be performed before the assembly of the lead-acid battery or the electrode plate group. Spongy lead is produced by the chemical conversion.

[0068] (Separator) Microporous membranes and nonwoven fabrics can be used as separators. These may be combined as needed. Nonwoven fabrics are mats in which fibers are intertwined without weaving, and are primarily composed of fibers. For example, more than 60% by mass of the separator is made up of fibers. Hydrophilization treatment may be applied to the separator as needed.

[0069] In nickel-metal hydride batteries and nickel-cadmium batteries, examples of materials for the microporous membrane used as a separator or the fibers constituting the separator include polyolefin resin, fluororesin, and polyamide resin. Examples of polyolefin resins include polyethylene and polypropylene, but are not limited to these. The thickness of the separator may be, for example, 10 μm or more. Alternatively, the thickness of the separator may be 300 μm or less.

[0070] In lead-acid batteries, examples of fibers constituting the nonwoven fabric include glass fibers, polymer fibers, and pulp fibers. The nonwoven fabric may also contain components other than fibers, such as acid-resistant inorganic powders and polymers as binders. A microporous membrane is a porous sheet mainly composed of components other than fibers. A microporous membrane can be obtained, for example, by forming a resin composition containing a base polymer, a pore-forming agent, and a penetrating agent (surfactant) into a sheet, stretching it, and then removing at least a portion of the pore-forming agent to form pores in the polymer matrix. The resin composition may also contain inorganic particles. Polyolefins such as polyethylene and polypropylene are preferred as the base polymer.

[0071] Examples of pore-forming agents include liquid pore-forming agents and solid pore-forming agents. From the viewpoint of easily suppressing oxidative degradation of the separator, it is preferable that the pore-forming agent contains at least oil. One type of pore-forming agent may be used alone, or two or more types may be used in combination. Oil may be used in combination with other pore-forming agents. Liquid pore-forming agents and solid pore-forming agents may be used in combination. At room temperature (temperature between 20°C and 35°C), liquid pore-forming agents are classified as liquid pore-forming agents, and solid pore-forming agents are classified as solid pore-forming agents. As a liquid pore-forming agent, the above-mentioned oil is preferred. As a solid pore-forming agent, for example, polymer powder is an example.

[0072] The amount of pore-forming agent in the separator may vary depending on the type. The amount of pore-forming agent in the separator is, for example, 30 parts by mass or more per 100 parts by mass of base polymer. The amount of pore-forming agent is, for example, 60 parts by mass or less per 100 parts by mass of base polymer.

[0073] The surfactant used as a penetrating agent may be either an ionic surfactant or a nonionic surfactant. The surfactant may be used alone or in combination of two or more types.

[0074] The content of the penetrant in the separator is, for example, 0.01% by mass or more, and may be 0.09% by mass or more. From the viewpoint of easily obtaining high affinity for aqueous electrolytes, the content of the penetrant in the separator may be 0.1% by mass or more. The content of the penetrant in the separator may be 10% by mass or less. From the viewpoint of easily keeping the COD in the aqueous electrolyte low, the content of the penetrant in the separator may be 3% by mass or less or 1% by mass or less, preferably 0.5% by mass or less, and more preferably 0.2% by mass or less.

[0075] The content of the penetrant in the separator is: 0.01 mass% to 10 mass%, 0.1 mass% to 10 mass%, 0.01 mass% to 3 mass%, 0.1 mass% to 3 mass%, 0.01 mass% to 1 mass%, 0.1 mass% to 1 mass%, 0.01 mass% to 0.5 mass%, 0.1 mass% to 0 .5 mass% or less, 0.01 mass% or more and 0.2 mass% or less, 0.1 mass% or more and 0.2 mass% or less, 0.09 mass% or more and 10 mass% or less, 0.09 mass% or more and 3 mass% or less, 0.09 mass% or more and 1 mass% or less, 0.09 mass% or more and 0.5 mass% or less, or 0.09 mass% or more and 0.2 mass% or less.

[0076] The amount of penetrating agent in the separator is preferably, for example, 1 part by mass or less, and more preferably 0.7 parts by mass or less, per 100 parts by mass of the base polymer. By setting the amount of penetrating agent within the above range, it becomes easier to keep the COD in the aqueous electrolyte low and improve the charge acceptance of the aqueous electrolyte secondary battery. The amount of penetrating agent in the separator is, for example, 0.1 parts by mass or more, and may be 0.3 parts by mass or more, per 100 parts by mass of the base polymer.

[0077] The amount of penetrating agent in the separator may be 0.1 parts by mass or more and 1 part by mass or less, 0.1 parts by mass or more and 0.7 parts by mass or less, 0.3 parts by mass or more and 1 part by mass or less, or 0.3 parts by mass or more and 0.7 parts by mass or less per 100 parts by mass of base polymer.

[0078] Examples of inorganic particles include ceramic particles. Examples of ceramic particles include at least one selected from the group consisting of silica, alumina, and titania.

[0079] The separator may or may not have ribs. The ribs are erected in a region of the separator's surface that faces either the positive or negative electrode plate. In such a region, the part of the separator other than the ribs is referred to as the base. The ribs may be provided on only one surface of the separator, or on both surfaces. The separator may be formed in a bag shape, and either the positive or negative electrode plate may be enclosed in the bag-shaped separator.

[0080] In a lead-acid battery, the thickness of the separator may be, for example, 90 μm or more. Alternatively, the thickness of the separator may be 300 μm or less. If the separator comprises a base portion and ribs erected from at least one surface of the base portion, the thickness of the separator is the average thickness of the base portion. If an adhesive material such as a mat or pasting paper is attached to the separator, the thickness of the adhesive material is not included in the thickness of the separator.

[0081] If the separator has ribs, the height of the ribs may be 0.05 mm or more. Alternatively, the height of the ribs may be 1.2 mm or less. The height of the ribs is the height of the portion that protrudes from the surface of the base (protrusion height). The height of the ribs provided in the region of the separator facing the positive electrode plate may be 0.4 mm or more. The height of the ribs provided in the region of the separator facing the positive electrode plate may be 1.2 mm or less.

[0082] (Fiber mat) A lead-acid battery may further include a fiber mat interposed between the positive and negative electrodes. The fiber mat is a component distinct from the separator. The fiber mat comprises a sheet-like fiber aggregate. Such a fiber aggregate may be a sheet in which fibers insoluble in the electrolyte are intertwined. Examples of such sheets include nonwoven fabrics, woven fabrics, and knitted fabrics. For example, 60% or more by mass of the fiber mat is made up of fibers. As fibers, glass fibers, polymer fibers, pulp fibers, etc., can be used. Among polymer fibers, polyolefin fibers are preferred.

[0083] (others) A water-based electrolyte secondary battery may contain one cell or two or more cells. If the water-based electrolyte secondary battery contains multiple cells, in other words, if it contains multiple groups of plates, the multiple groups of plates may be connected in series.

[0084] Aqueous electrolyte secondary batteries can be obtained, for example, by a manufacturing method that includes the step of housing a group of electrodes and an electrolyte in the cell chambers of a battery case. Each cell of an aqueous electrolyte secondary battery contains a group of electrodes and an electrolyte housed in each cell chamber. The electrode group is assembled, for example, by stacking a positive electrode, a negative electrode, and a separator, with the separator interposed between the positive and negative electrodes, prior to housing them in the cell chambers. Each of the positive electrode, negative electrode, and separator is usually prepared prior to the assembly of the electrode group. The electrolyte is prepared prior to housing it in the cell chambers. If an aqueous electrolyte secondary battery has one group of electrodes, the battery case does not need to be divided into multiple cell chambers, and the electrode group and electrolyte may be housed in the battery case. After the step of housing the electrode group and electrolyte in the cell chambers, the manufacturing method of an aqueous electrolyte secondary battery may optionally include a step of chemically forming at least one of the positive electrode and the negative electrode. For example, lead-acid batteries, nickel-cadmium batteries, or nickel-metal hydride batteries may be manufactured according to such a manufacturing method. In the case of nickel-cadmium batteries and nickel-metal hydride batteries, the battery may be formed by, for example, housing the electrode plate group and electrolyte in a battery case and sealing the opening of the battery case. The assembled aqueous electrolyte secondary battery may undergo break-in charge and discharge as needed.

[0085] The following explains how to evaluate charge acceptance, using a lead-acid battery as an example. The charge acceptance of a lead-acid battery is evaluated based on the charging current Ica2 at 10 minutes after the start of charging, after discharging and charging under the following conditions. 1) After confirming that the electrolyte temperature of one cell near the center of the lead-acid battery is 25±2℃, discharge it for 2.5 hours at a current 3.42 times the 20-hour rate current. 2) Immediately after the discharge described in 1) above, move the lead-acid battery to a cooling chamber at 0±1℃ and leave it there until the electrolyte temperature of one of the cells near the center reaches 0±1℃. 3) After confirming that the electrolyte temperature of any one cell near the center is 0±2℃, charge the lead-acid battery at the same temperature with a constant voltage of 2.4±0.015V / cell and a limiting current of 100A, and measure the charging current Ica2 10 minutes after the start of charging.

[0086] In nickel-metal hydride and nickel-cadmium batteries, the internal resistance of the battery is measured, and the charge acceptance is evaluated based on this measurement. The internal resistance of nickel-metal hydride and nickel-cadmium batteries is measured in accordance with JIS C8708;2019, 7.13.3 "Measurement of DC internal resistance".

[0087] Figure 1 shows the external appearance of a lead-acid battery, which is an example of an aqueous electrolyte secondary battery according to an embodiment of the present invention. If necessary, at least one component of the following embodiments may be combined with any one of (1) to (6) above. The lead-acid battery 1 comprises a battery case 12 that houses an electrode plate group 11 and an electrolyte (not shown). The battery case 12 is divided into multiple cell chambers 14 by a partition wall 13. Each cell chamber 14 houses one electrode plate group 11. The opening of the battery case 12 is closed with a lid 15 equipped with a negative electrode terminal 16 and a positive electrode terminal 17. The lid 15 is provided with a vent plug 18 for each cell chamber. When replenishing with water, the vent plug 18 is removed and the water is supplied. The vent plug 18 may also have a function of venting gas generated in the cell chamber 14 to the outside of the battery.

[0088] Each electrode plate group 11 is constructed by stacking multiple negative electrode plates 2 and positive electrode plates 3 via separators 4. Here, a bag-shaped separator 4 that houses the negative electrode plates 2 is shown, but the shape of the separator is not particularly limited. In the cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6 that connects multiple negative electrode plates 2 in parallel is connected to a through connector 8, and a positive electrode shelf 5 that connects multiple positive electrode plates 3 in parallel is connected to a positive electrode column 7. The positive electrode column 7 is connected to a positive electrode terminal 17 on the outside of the lid 15. In the cell chamber 14 located at the other end of the battery case 12, a negative electrode column 9 is connected to the negative electrode shelf 6, and a through connector 8 is connected to the positive electrode shelf 5. The negative electrode column 9 is connected to a negative electrode terminal 16 on the outside of the lid 15. Each through connector 8 passes through a through hole provided in the partition wall 13 and connects the electrode plate groups 11 of adjacent cell chambers 14 in series.

[0089] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0090] Lead-acid batteries E1-E12 and C1-C5 Each lead-acid battery was manufactured using the following procedure.

[0091] (1) Fabrication of the positive electrode plate A positive electrode paste was prepared by mixing lead oxide, synthetic resin fibers as a reinforcing material, water, and sulfuric acid. The positive electrode paste was filled into the mesh of an expanded grid made of an antimony-free Pb-Ca-Sn alloy, and aged and dried to obtain an unformed positive electrode plate with a width of 100 mm, a height of 110 mm, and a thickness of 1.6 mm.

[0092] (2) Fabrication of the negative electrode plate A negative electrode paste was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, synthetic resin fibers as a reinforcing material, water, and sulfuric acid. The negative electrode paste was filled into the mesh of an expanded grid made of Pb-Ca-Sn alloy that did not contain antimony, and aged and dried to obtain an unformed negative electrode plate with a width of 100 mm, a height of 110 mm, and a thickness of 1.3 mm. The amounts of carbon black, barium sulfate, lignin, and synthetic resin fibers used were adjusted so that the content of each component in the negative electrode plate taken from a fully charged lead-acid battery was 0.3 mass%, 2.1 mass%, 0.1 mass%, and 0.1 mass%, respectively.

[0093] (3) Fabrication of separators A resin composition containing 100 parts by mass of polyethylene, 160 parts by mass of silica particles, 80 parts by mass of paraffin-based oil as a pore-forming agent, and an appropriate amount of penetrating agent was extruded into a sheet, stretched, and then a portion of the pore-forming agent was removed to produce a microporous membrane with ribs on one side. The height of the ribs was 0.6 mm. The average thickness of the base portion of the separator was 0.2 mm. The sheet-like microporous membrane was folded in half so that the ribs were positioned on the outer surface to form a bag, and the overlapping ends were pressed together to obtain a bag-shaped separator.

[0094] (4) Manufacturing of lead-acid batteries Untreated negative electrode plates were placed in a bag-shaped separator and stacked with positive electrode plates to form an electrode plate group consisting of seven untreated negative electrode plates and six untreated positive electrode plates.

[0095] The tabs of the positive electrode plate and the tabs of the negative electrode plate were welded to the positive and negative electrode trays, respectively, using a cast-on-strap method. The electrode plates were inserted into a polypropylene battery case, electrolyte was poured in, and a chemical conversion was performed inside the case to assemble a liquid-type lead-acid battery with a rated voltage of 12V and a rated capacity of 30Ah. Six electrode plates are connected in series inside the battery case. Here, the rated capacity is the 5-hour rate capacity. The 5-hour rate capacity is the capacity when discharged at a current (A) of 1 / 5 of the Ah value indicated in the rated capacity.

[0096] A sulfuric acid solution was used as the electrolyte. The specific gravity of the electrolyte after chemical conversion was 1.285 at 20°C.

[0097] In lead-acid battery C1, the amount of penetrant used to prepare the separator was set to 2 parts by mass. Also, in lead-acid battery C1, the expanded grids of the positive and negative electrodes, as well as the plate-like material before forming the expanded grid, were not cleaned before the positive and negative electrodes were formed. In lead-acid batteries E1 to E12, the amount of penetrant used to prepare the separator was reduced compared to that of C1, so that the COD in the electrolyte of the lead-acid battery in its initial fully charged state, as determined by the procedure described above, was the value shown in Table 1.

[0098] (5) Evaluation The charge acceptability of the obtained lead-acid batteries was evaluated using the procedure described above. Charge acceptability was evaluated by the ratio of Ica2 values ​​of each lead-acid battery to Ica2 value of lead-acid battery C1, with Ica2 value set to 100.

[0099] The evaluation results are shown in Table 1. E1 to E12 are examples. C1 to C5 are comparative examples.

[0100] [Table 1]

[0101] As shown in Table 1, comparing C1 with E1 to E12, charge acceptance was significantly improved when the COD in the electrolyte was 160 mg / L or less compared to when it was greater than 160 mg / L. On the other hand, comparing E12 with C2 to C5, charge acceptance was significantly improved when the COD in the electrolyte was 5 mg / L or more compared to when it was less than 5 mg / L. From the above, it became clear that charge acceptance improves when the COD in the electrolyte is between 5 mg / L and 160 mg / L.

[0102] Comparing C1 with E2 or E3 to E12, higher charge acceptance was obtained when the COD in the electrolyte was 130 mg / L or less or 100 mg / L or less. As shown in E4 to E12, even higher charge acceptance was obtained when the COD in the electrolyte was between 5 mg / L and 50 mg / L, and as shown in E5 to E11, particularly high charge acceptance was obtained when it was between 8 mg / L and 30 mg / L.

[0103] The above examples and comparative examples show the results for lead-acid batteries, but in the case of nickel-metal hydride batteries or nickel-cadmium batteries, a similar trend can be observed where the charge acceptance improves by setting the COD in the electrolyte to a specific range. [Industrial applicability]

[0104] In a water-based electrolyte secondary battery according to one aspect of the present invention, high charge acceptance is achieved, and the charge-discharge reaction can be carried out smoothly. Examples of such water-based electrolyte secondary batteries include lead-acid batteries, nickel-metal hydride batteries, and nickel-cadmium batteries. Each battery can be used for a variety of applications. For example, lead-acid batteries are suitable for idling stop (also called start-stop or idle reduction) applications and as starting power sources for various vehicles. Idling stop applications include, for example, lead-acid batteries for vehicles with idling stop systems. Examples of vehicles include automobiles and motorcycles. Lead-acid batteries can also be suitably used as power sources for industrial energy storage devices. Examples of industrial energy storage devices include power sources for electric vehicles such as forklifts. These applications are merely examples. The applications of the water-based electrolyte secondary battery according to the above aspect of the present invention are not limited to these. [Explanation of Symbols]

[0105] 1:Lead acid battery 2: Negative plate 3: Positive plate 4: Separator 5: Positive electrode shelf 6: Negative electrode shelf 7: Positive pole column 8: Through-connector 9: Negative pole column 11: Plate group 12:Battery container 13: Bulkhead 14: Cell Room 15: Lid 16: Negative terminal 17: Positive terminal 18: Liquid outlet stopper

Claims

1. A water-based electrolyte secondary battery, The aforementioned aqueous electrolyte secondary battery is a lead-acid battery comprising an electrode plate group and an aqueous electrolyte. The electrode plate group includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate. A water-based electrolyte secondary battery, wherein the chemical oxygen demand in the aqueous electrolyte is 5 mg / L or more and 160 mg / L or less.

2. The aqueous electrolyte secondary battery according to claim 1, wherein the chemical oxygen demand in the aqueous electrolyte is 130 mg / L or less.

3. The aqueous electrolyte secondary battery according to claim 1 or 2, wherein the chemical oxygen demand in the aqueous electrolyte is 8 mg / L or more.

4. The aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode plate includes at least one selected from the group consisting of an organic shrinkage inhibitor and a carbonaceous material.

5. The aqueous electrolyte secondary battery according to claim 1 or 4, wherein the electrode plate group includes a fiber mat interposed between the positive electrode plate and the negative electrode plate.

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