Positive electrode for lead-acid batteries

Abstract

Provided is a positive electrode for a lead-acid storage battery, wherein a positive electrode current collector, a carbon-containing layer, and a positive electrode active material layer are arranged in this order; the carbon-containing layer contains a conductive carbon material and a phenolic resin; the positive electrode for a lead-acid storage battery can be charged again even after sufficient discharge followed by a long period of downtime, and has high durability.

Description

Technical Field

[0001] The present invention relates to a positive electrode for lead-acid batteries. Background Art

[0002] Lead-acid batteries have stable quality and economic efficiency, are mainly used as automotive batteries, and account for nearly 30% of the production value of secondary batteries in Japan. In particular, high-performance lead-acid batteries are indispensable for hybrid cars and idling stop vehicles, which have been put into practical use in recent years, and the demand for lead-acid batteries is increasing rapidly. In addition, research on lead-acid batteries for power storage has become active in recent years. Although lead-acid batteries have a long history from their development to the present, unclear points still remain regarding reactions inside the batteries.

[0003] If a lead-acid battery is over-discharged, subsequent charging becomes difficult, so it is necessary to charge the battery before it is completely discharged. For this reason, the theoretical capacity of lead-acid batteries cannot be effectively utilized.

[0004] In the lead-acid battery as described above, as the positive electrode, a layer of lead oxide as a positive electrode active material is usually formed on lead serving as a positive electrode current collector, and the reaction formula during charge and discharge is as follows: Positive electrode: PbO2 + 4H + + SO4 2- + 2e - ⇔ PbSO4 + 2H2O Negative electrode: Pb + SO4 2- ⇔ PbSO4 + 2e - represented as above.

[0005] PbO2, used as a positive electrode active material, exists in two forms: α-PbO2 and β-PbO2. It is known that β-PbO2 exists in low pH regions (acidic regions) and α-PbO2 exists in high pH regions (alkaline regions). Since sulfuric acid aqueous solution is usually used as the electrolyte in lead-acid batteries, charging and discharging occur at low pH levels, so the presence of β-PbO2 is expected. However, in reality, it is known that α-PbO2 and β-PbO2 coexist. Nevertheless, the relationship between the coexistence of α-PbO2 and β-PbO2 and the inability to fully utilize the theoretical capacity remains unclear. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As described above, in lead-acid batteries, it is difficult to say that the theoretical capacity is being fully utilized. Therefore, if the battery can be recharged even after being fully discharged, it is expected that the usable capacity will be increased. Furthermore, when considering repeated charging and discharging of lead-acid batteries, it is necessary to adopt a structure that has excellent adhesion between the positive electrode current collector and the positive electrode active material. From this viewpoint, the present invention aims to provide a positive electrode for lead-acid batteries that can be recharged even after being fully discharged and stopped for a long period of time, and that has high durability. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have discovered that a localized galvanic reaction occurs between PbO2 (particularly β-type PbO2), the positive electrode active material, and lead, the positive electrode current collector, when a lead-acid battery is open-circuited (not in use). Specifically, they found that β-type PbO2 acts as the positive electrode and lead as the negative electrode, and the galvanic reaction generates α-type PbO2, which adversely affects the performance of the lead-acid battery. The inventors have found that by interposing a carbon-containing layer containing a conductive carbon material and phenolic resin as a layer different from the positive electrode current collector between the positive electrode current collector and the positive electrode active material layer, the localized galvanic reaction when the circuit is open is suppressed, allowing the battery to be recharged even after being fully discharged and stopped for a long period of time, and also resulting in high durability. The inventors have further researched and completed the present invention. That is, the present invention encompasses the following configuration.

[0008] Item 1. A positive electrode for a lead-acid battery in which a positive electrode current collector, a carbon-containing layer, and a positive electrode active material layer are arranged in this order, The carbon-containing layer comprises a conductive carbon material and a phenolic resin, and is a positive electrode for a lead-acid battery.

[0009] Item 2. The positive electrode for a lead-acid battery according to Item 1, wherein the conductive carbon material contains graphite and / or carbon black.

[0010] Item 3. A positive electrode for a lead-acid battery according to item 1 or 2, wherein the total amount of the carbon-containing layer is 100% by mass, and the positive electrode contains 5 to 20% by mass of carbon black.

[0011] Item 4. A positive electrode for a lead-acid battery according to any one of items 1 to 3, wherein the total amount of the carbon-containing layer is 100% by mass, and graphite is contained in an amount of 10 to 65% by mass.

[0012] Item 5. A positive electrode for a lead-acid battery according to any one of items 1 to 4, wherein the total amount of the carbon-containing layer is 100% by mass, and the phenolic resin is contained in an amount of 30 to 70% by mass.

[0013] Item 6. The positive electrode for a lead-acid battery according to any one of items 1 to 5, wherein the positive electrode active material layer contains lead oxide.

[0014] Item 7. A lead-acid battery having a positive electrode for a lead-acid battery as described in any one of items 1 to 6. [Effects of the Invention]

[0015] According to the present invention, by interposing a carbon-containing layer containing a conductive carbon material and a phenolic resin between the positive electrode current collector and the positive electrode active material layer, as a layer different from the positive electrode current collector, local battery reactions during open-circuit operation are suppressed. As a result, the battery can be recharged even after being fully discharged and stopped for a long period of time, and its durability is high. Because of this configuration, it is also possible to recharge the battery even after being fully discharged and stopped for a long period of time, even when using lead oxide, which is commonly used as the positive electrode current collector in the positive electrode active material layer. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view of the evaluation test cell. [Figure 2] This shows the results of a charge-discharge test on the evaluation test cell using the positive electrode of Comparative Example 1, when it was deeply discharged to 0V and left standing in an open circuit. [Figure 3] This shows the charge and discharge waveforms of the evaluation test cell using the positive electrode of Comparative Example 2. [Figure 4] This shows the results of a charge-discharge test on the evaluation test cell using the positive electrode of Comparative Example 3, when it was deeply discharged to 0.2V and left standing in an open circuit. [Figure 5] This shows the results of a charge-discharge test on the evaluation test cell using the positive electrode of Comparative Example 4, when it was deeply discharged to 0.2V and left standing in an open circuit. [Figure 6] This shows the results of a charge-discharge test on the evaluation test cell using the positive electrode of Example 1, where the cell was deeply discharged to 0V and left to stand in an open circuit twice. [Figure 7] This shows the results of a charge-discharge test on the evaluation test cell using the positive electrode of Example 2, where the cell was repeatedly discharged to 0.2V and left to stand in an open circuit. [Figure 8]These are the results of a charge-discharge test performed on an evaluation test cell using the positive electrode of Example 3, in which the cell was deeply discharged to 0.2 V and left standing in an open circuit repeatedly. [Figure 9] These are the results of a charge-discharge test performed on an evaluation test cell using the positive electrode of Example 4, in which the cell was deeply discharged to 0 V and left standing in an open circuit twice. [Figure 10] These are the results of a charge-discharge test performed on an evaluation test cell using the positive electrode of Example 5, in which the cell was deeply discharged to 0 V and left standing in an open circuit twice. [Figure 11] These are the results of a charge-discharge test performed on an evaluation test cell using the positive electrode of Example 6, in which the cell was deeply discharged to 0 V and left standing in an open circuit twice. MODE FOR CARRYING OUT THE INVENTION

[0017] As used herein, the term "contain" is a concept that includes all of "comprise", "consist essentially of", and "consist of".

[0018] As used herein, when a numerical range is expressed as A to B, it indicates a range from A to B inclusive.

[0019] 1. Positive electrode for lead-acid batteries The positive electrode of the lead-acid storage battery of the present invention is a positive electrode for a lead-acid storage battery in which a positive electrode current collector, a carbon-containing layer and a positive electrode active material layer are arranged in this order, and the carbon-containing layer contains a conductive carbon material and a phenol resin.

[0020] (1-1) Positive electrode current collector There are no particular restrictions on the positive electrode current collector, and a wide variety of materials can be used. However, it is preferable to use a material that is inert to sulfuric acid, which is the electrolyte of lead-acid batteries. Specifically, lead, gold, palladium, platinum, etc., can be used. Considering corrosion resistance to sulfuric acid, an alloy of lead and at least one of the following can also be used: tin, silver, antimony, calcium, etc. It is also possible to use a carbon sheet as the positive electrode current collector.

[0021] There are no particular restrictions on the shape of the positive electrode current collector; grid-like, thin plate-like, or other shapes can be used.

[0022] The thickness of such a positive electrode current collector is preferably 0.1 to 1.5 mm, and more preferably 0.2 to 1.0 mm, from the viewpoint of allowing it to function as a support for the positive electrode active material layer described later.

[0023] The positive electrode current collector described above can be used alone or laminated on other substrates. In particular, even if the thickness of the positive electrode current collector is thinner than the range described above, it can still be used laminated on other substrates. For example, if the thickness of the positive electrode current collector is thin (approximately 1 μm to 0.1 mm) and it is difficult for it to stand on its own as a support for the positive electrode active material layer described later, it is preferable to laminate it on other substrates. Examples of such other substrates include ceramics such as alumina and polymers such as polyethersulfone resin. The thickness of such other substrates is preferably about 0.1 mm to 10 mm.

[0024] (1-2) Carbon-containing layer The carbon-containing layer contains conductive carbon material and phenolic resin.

[0025] Conductive carbon materials are inert to sulfuric acid, which is typically used as an electrolyte, and do not undergo localized galvanic reactions with the positive electrode current collector or lead dioxide, which is the positive electrode active material, as described later. Therefore, by incorporating conductive carbon material into the carbon-containing layer, localized galvanic reactions during open-circuit operation can be suppressed, and the battery can be recharged even after being fully discharged and stopped for a long period of time. There are no particular restrictions on such conductive carbon materials, but preferably, carbon blacks such as channel black, furnace black, Ketjen black, acetylene black, and lamp black; graphites such as natural graphite, artificial graphite, and expanded graphite (expanded graphite sheets, isotropic graphite, flake graphite, etc.); activated carbon; and amorphous carbon can be used. These conductive carbon materials can be used individually or in combination of two or more types.

[0026] The content of the conductive carbon material is not particularly limited. From the viewpoint of more easily suppressing local galvanic reactions when the circuit is open and more easily improving conductivity, the content of the conductive carbon material when the total amount of the carbon-containing layer is 100% by mass is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass. When multiple conductive carbon materials are included, it is preferable to adjust the total amount so that it falls within the above range. When carbon black is included as the conductive carbon material, from the viewpoint of more easily suppressing local galvanic reactions when the circuit is open and more easily improving conductivity, the content is preferably 5 to 20% by mass, and more preferably 7 to 15% by mass, when the total amount of the carbon-containing layer is 100% by mass. When graphite is included as the conductive carbon material, from the viewpoint of more easily suppressing local galvanic reactions when the circuit is open and more easily improving conductivity, the content is preferably 10 to 65% by mass, and more preferably 25 to 55% by mass, when the total amount of the carbon-containing layer is 100% by mass.

[0027] The phenolic resin is preferably a polymer compound that is inert to lead oxide, which is the positive electrode active material, and sulfuric acid, which is the electrolyte. The phenolic resin is included to function as a binder and improve the adhesion between the positive electrode current collector and the positive electrode active material layer. By using a phenolic resin that is inert to lead oxide, which is the positive electrode active material, and sulfuric acid, a carbon-containing layer that is non-wetting to sulfuric acid and inert to lead oxide is formed, which further helps to suppress the degradation of the lead-acid battery.

[0028] There are no particular restrictions on the phenolic resin, but examples include novolac-type phenolic resins, resol-type phenolic resins, xylene-modified resol-type resins, and rosin-modified phenolic resins. These phenolic resins can be used individually or in combination of two or more types.

[0029] The content of phenolic resin is not particularly limited. From the viewpoint of improving adhesion between the positive electrode current collector and the positive electrode active material layer, suppressing local battery reactions during open circuits, and improving conductivity, the content of phenolic resin is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass, based on 100% by mass of the total amount of the carbon-containing layer. When multiple types of phenolic resin are included, it is preferable to adjust their total amount so that it falls within the above range.

[0030] The thickness of such a carbon-containing layer is not particularly limited, but from the viewpoint of further suppressing the degradation of the positive electrode due to localized battery reactions, thereby improving durability and capacity, and further improving adhesion between the positive electrode current collector and the positive electrode active material (lead oxide), a thickness of 5 nm to 10 mm is preferred, and 10 nm to 1 mm is more preferred.

[0031] The method for forming the carbon-containing layer is not particularly limited. For example, coating methods can be employed. When a coating method is employed, it can be applied using means such as roller coating with an applicator roll, screen coating, doctor blade method, spin coating, bar coating, or dip coating. Specifically, it can be obtained by coating a paint containing a conductive carbon material, a phenolic resin, and an organic solvent onto, for example, a positive electrode current collector and drying it by a conventional method. The organic solvent that can be used in this case is not particularly limited, and a wide range of common organic solvents (for example, butyl carbitol, diisopropyl ether, butyl cellosolve, tetrahydrofuran, dioxane, and other ether solvents) can be used.

[0032] While paints containing conductive carbon material, phenolic resin, and organic solvent can be manufactured by mixing each component separately, it is also possible to use commercially available paints containing conductive carbon material, phenolic resin, and organic solvent. Specific examples of such commercially available products include Everohm T-30PLB-UL(BC) and Everohm T-30PLB-U, both manufactured by Nippon Graphite Industries Co., Ltd.

[0033] (1-3) Positive electrode active material layer The positive electrode for a lead-acid battery of the present invention has a positive electrode active material layer formed on top of the carbon-containing layer. As described above, the carbonaceous material contained in the carbon-containing layer can suppress local galvanic reactions (especially local galvanic reactions when the circuit is open) with the positive electrode active material layer. Therefore, the generation of α-type PbO2 by local galvanic reactions when the circuit is open can be suppressed, and the battery can be recharged and discharged even after being fully discharged and stopped for a long period of time (open circuit), thus improving durability.

[0034] In the positive electrode for lead-acid batteries of the present invention, it is preferable to use conventionally used lead oxide (lead monoxide (PbO), lead dioxide (PbO2), etc.) as the positive electrode active material contained in the positive electrode active material layer. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited and can be set to the extent that has been conventionally applied to the positive electrode of lead-acid batteries. With the total amount of the positive electrode active material layer as 100% by mass, 50 to 95% by mass is preferred, and 70 to 90% by mass is more preferred.

[0035] In the present invention, the positive electrode active material layer may also contain a conductive additive. Preferably, the conductive additive is an electronically conductive material that is less prone to localized galvanic reactions (a substance electrochemically inert to lead oxide and sulfuric acid). Specifically, it may contain one or a mixture thereof of conductive materials such as graphite (isotropic graphite, etc.), natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon whiskers, carbon fibers, or vapor-grown carbon. The content of the conductive additive in the positive electrode active material layer is not particularly limited and can be similar to that conventionally applied to the positive electrode of lead-acid batteries. Based on 100% by mass of the total amount of the positive electrode active material layer, 5 to 35% by mass is preferred, and 10 to 20% by mass is more preferred.

[0036] In addition to the components mentioned above, the positive electrode active material layer can also contain binders, thickeners, and other additives.

[0037] Typically, thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, and polypropylene; or rubber-elastic polymers such as ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber can be used as binders, either individually or as a mixture of two or more.

[0038] As a thickening agent, polysaccharides such as carboxymethylcellulose and methylcellulose can usually be used as one or a mixture of two or more.

[0039] The content of binders and thickeners in the positive electrode active material layer is not particularly limited and can be the same as that conventionally applied to the positive electrode of lead-acid batteries. With the total amount of the positive electrode active material layer being 100% by mass, the total amount of binders and thickeners is preferably 2 to 15% by mass, and more preferably 3 to 10% by mass.

[0040] The mixing method for these components is physical mixing, and uniform mixing is preferred. Therefore, powder mixers such as V-type mixers, S-type mixers, grinders, ball mills, and planetary ball mills can be used in a dry or wet manner.

[0041] In the present invention, the method for forming the positive electrode active material layer is not particularly limited. For example, one method involves mixing various components such as positive electrode active material with water to prepare a paste composition for forming the positive electrode active material layer, and then impregnating or coating the carbon-containing layer with the paste composition and drying it.

[0042] Regarding the coating method, for example, it can be applied using roller coating such as an applicator roll; screen coating; doctor blade method; spin coating; bar coater; dip coating, etc. Furthermore, there are no particular restrictions on drying conditions, and they can be used within the range typically employed in lead-acid batteries.

[0043] 2.Lead acid battery The lead-acid battery of the present invention is equipped with the positive electrode for the lead-acid battery of the present invention.

[0044] Other components besides the positive electrode include the negative electrode for lead-acid batteries, the electrolyte for lead-acid batteries, and the separator for lead-acid batteries. These can be manufactured as needed, or they can be commercially available products; known components and materials for lead-acid batteries can be used. [Examples]

[0045] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0046] Example 1 Lead grid, which is the positive electrode current collector ( made in china The structure was prepared in a grid pattern, with the grid bones finished to a thickness of 1.2 mm ± 0.1 mm.

[0047] As raw materials for forming the carbon-containing layer, conductive paint Everohm T-30PLB-UL(BC) manufactured by Nippon Graphite Industries Co., Ltd. was used (50% by mass of flake graphite and acetylene black, 50% by mass of resol-type phenolic resin, and 300% by mass of butyl carbitol; viscosity 109.5 mPa·s; electrical resistance value 40.8 Ω / sq). The lead grid described above was immersed in this conductive paint for several seconds, dried at 150°C for 30 minutes, and the carbon-containing layer was dip-coated onto the lead, which served as the positive electrode current collector, to a thickness of 0.1 to 0.2 mm after drying.

[0048] The active material was lead dioxide, and a slurry containing lead dioxide, carbon black, and polyvinylidene fluoride (PVDF) was used. Specifically, first, β-type PbO2 (lead dioxide manufactured by Johnson Matthey), acetylene black, and PVDF were added in a ratio of β-type PbO2:acetylene black:PVDF of 90:5:5 (mass%), pre-mixed, then dispersed in the solvent N-methylpyrrolidone (NMP) to form a slurry, and stirred and mixed for 5 minutes using a self-rotating agitator (Mazelstar KK-250S manufactured by Kurabo Industries Ltd.) to prepare a slurry for forming the positive electrode active material layer. The lead grid with the carbon-containing layer formed above was immersed in this conductive paint for several seconds and dried at 100°C for 1 hour. The positive electrode active material layer was then dip-coated on top of the carbon-containing layer to a thickness of 0.1 to 0.2 mm after drying. In this way, the positive electrode for the lead-acid battery of Example 1 was obtained.

[0049] Example 2 In forming the carbon-containing layer, the lead grid was immersed for several seconds in conductive paint Everohm T-30PLB-UL(BC) manufactured by Nippon Graphite Industries Co., Ltd., and dried at 150°C for 30 minutes. This process was repeated twice, and the carbon-containing layer was dip-coated to a thickness of 0.2 to 0.4 mm after drying. Otherwise, the positive electrode for the lead-acid battery of Example 2 was obtained in the same manner as in Example 1.

[0050] Example 3 In forming the carbon-containing layer, the lead grid was immersed for several seconds in the conductive paint Everohm T-30PLB-UL(BC) manufactured by Nippon Graphite Industries Co., Ltd., and dried at 150°C for 30 minutes. This process was repeated three times to dip-coat the carbon-containing layer so that its thickness after drying was 0.3 to 0.6 mm. Otherwise, the positive electrode for the lead-acid battery of Example 3 was obtained in the same manner as in Example 1.

[0051] Comparative Example 1 A positive electrode for a lead-acid battery of Comparative Example 1 was obtained in the same manner as in Example 1, except that a carbon-containing layer was not formed.

[0052] Comparative Example 2 A positive electrode for a lead-acid battery, Comparative Example 2, was obtained in the same manner as in Example 1, except that PF-50 (0.5 mm thick) manufactured by Toyo Tanso Co., Ltd. was used as the positive electrode current collector, and a carbon-containing layer was not formed.

[0053] Comparative Example 3 As raw materials for forming the carbon-containing layer, a conductive paint Bunny Height UCC-2 (58% by mass of flaky natural graphite, 11% by mass of acetylene black, 31% by mass of rubber-based resin, and 430% by mass of toluene) manufactured by Nippon Graphite Industries Co., Ltd. was used, and the positive electrode for a lead-acid battery of Comparative Example 3 was obtained in the same manner as in Example 1, except that the drying conditions were 100°C and 20 minutes.

[0054] Comparative Example 4 As a raw material for forming the carbon-containing layer, conductive paint Bunny Height T-602U (containing a total of 100% by mass of flake-like natural graphite, acetylene black, and cellulose resin, and 270% by mass of water) manufactured by Nippon Graphite Industries Co., Ltd. was used, and the drying conditions were set to 100°C and 20 minutes, except that the process was the same as in Example 1 to obtain the positive electrode for a lead-acid battery of Comparative Example 4.

[0055] Example 4 A positive electrode for a lead-acid battery of Example 4 was obtained in the same manner as in Example 1, except that a conductive paint (50% by mass of flake-like natural graphite and acetylene black in total, 50% by mass of novolac-type phenolic resin, and 300% by mass of butyl carbitol; viscosity 109.5 mPa·s; electrical resistance value 40.8 Ω / sq) was used as a raw material for forming the carbon-containing layer.

[0056] Example 5 The positive electrode for a lead-acid battery of Example 5 was obtained in the same manner as in Example 1, except that a conductive paint (50% by mass of flake-like natural graphite and acetylene black, 50% by mass of xylene resin-modified phenolic resin, and 300% by mass of butyl carbitol; viscosity 109.5 mPa·s; electrical resistance value 40.8 Ω / sq) was used as the raw material for forming the carbon-containing layer.

[0057] Example 6 A positive electrode for a lead-acid battery of Example 6 was obtained in the same manner as in Example 1, except that a conductive paint (50% by mass of flake-like natural graphite and acetylene black in total, 50% by mass of rosin resin-modified phenolic resin, and 300% by mass of butyl carbitol; viscosity 109.5 mPa·s; electrical resistance value 40.8 Ω / sq) was used as a raw material for forming the carbon-containing layer.

[0058] Manufacturing Example 1: Cell for Evaluation Testing For the following evaluation tests, a two-electrode glass cell was used. The positive electrodes were those of Examples 1-6 and Comparative Examples 1-4 described above, respectively. For the negative electrode, a lead alloy grid filled with lead powder was used, taken from a commercially available lead-acid battery. A 35% by mass sulfuric acid aqueous solution was used as the electrolyte, and the cell shown in Figure 1 was fabricated.

[0059] Test Example 1: Charge / Discharge Test (Deep Discharge Test and Charge / Discharge Waveforms) The evaluation test cells using the positive electrodes of Examples 1-6 and Comparative Examples 1-4 were charged and discharged under the following conditions. A charge / discharge device (HJ1001SD8) manufactured by Hokuto Denko Co., Ltd. was used for the charge / discharge tests.

[0060] In Example 1, to stabilize the battery reaction, the battery was first discharged to 1.8V at 0.1C and charged to 2.3V at 0.5C for 20 cycles, and then deeply discharged at 0.1C until it reached 0V. After that, it was left standing in an open circuit state for 48 hours, and then shallow charge-discharge (2.3V to 1.8V) at 0.5C was repeated for 20 cycles, followed by deep discharge at 0.5C until it reached 0V. Furthermore, after being left standing in an open circuit state for another 48 hours, deep charge-discharge (2.3V to 0V) at 0.5C was repeated.

[0061] For Examples 2-6 and Comparative Examples 1-4, first, to stabilize the battery reaction, a cycle of 30 minutes of discharge at 9 mA / g and 20 minutes of charge at 180 mA / g was repeated for 20 cycles. Then, during the 20th discharge cycle, the battery was deeply discharged to 0.2V at 9 mA / g. After that, it was left standing in an open circuit state for 48 hours. Subsequently, a cycle of 20 minutes of charge at 180 mA / g and 20 minutes of discharge at 9 mA / g was repeated for 10 cycles, with the final discharge cycle being deeply discharged to 0.2V at 9 mA / g, followed by being left standing in an open circuit state for 48 hours. This charge-discharge pattern was repeated.

[0062] The results of Comparative Example 1 are shown in Figure 2. These results show that even in the charge-discharge cycle before deep discharge, stable discharge waveforms were not achieved at high potentials. Furthermore, after deep discharge and open-circuit holding, further charging and discharging was not possible, making it unsuitable for practical use.

[0063] The results for Comparative Example 2 are shown in Figure 3. In this case as well, even in the charge-discharge cycle before deep discharge, charging and discharging with a stable discharge waveform was not possible at high potential, and the energy efficiency was not sufficient.

[0064] The results of Comparative Example 3 are shown in Figure 4. As a result, after deep discharge and open-circuit holding, recharging was not possible. Because charging was not possible, the charge / discharge device automatically switched to 48 hours of open-circuit holding without repeating the 10 charge / discharge cycles. Subsequently, the charge / discharge device automatically switched to charging, but charging was not possible, so it automatically switched back to 48 hours of open-circuit holding, and this process was repeated. Because charging and discharging were not possible, it was unsuitable for practical use.

[0065] The results of Comparative Example 4 are shown in Figure 5. As a result, although charging and discharging were possible again after deep discharge and open circuit holding, charging and discharging at high potential was not possible, the discharge waveform was degraded, the energy efficiency was poor, and the durability was only slightly less than 600 hours, making it unsuitable for practical use.

[0066] The results of Example 1 are shown in Figure 6. These results demonstrate that, in the charge-discharge cycle before deep discharge, charging and discharging are possible at high potential with a stable discharge waveform, resulting in excellent energy efficiency. Furthermore, even when the above charge-discharge pattern, which includes deep discharge and open-circuit holding, is repeated, stable charging and discharging are possible at high potential, the discharge waveform is good, energy efficiency is excellent, and it exhibits durability that allows for continuous operation for over 1500 hours, making it suitable for practical use. Additionally, as shown in Examples 2-3, when the thickness of the carbon-containing layer is increased by repeated dip coating, durability is further improved, allowing for continuous operation for over 2500 hours, as shown in Figures 7-8.

[0067] The results of Examples 4-6 are shown in Figures 9-11. In all cases, deep charging and discharging could be maintained even after two cycles of deep discharge to 0V and standing in an open circuit, demonstrating high durability and practicality.

Claims

1. A positive electrode for a lead-acid battery, in which a positive electrode current collector, a carbon-containing layer, and a positive electrode active material layer are arranged in this order, The carbon-containing layer contains a conductive carbon material and a phenolic resin. The phenolic resin is a polymer compound inert to lead oxide and sulfuric acid, and is at least one selected from the group consisting of novolac-type phenolic resin, resol-type phenolic resin, xylene resin-modified phenolic resin, and rosin-modified phenolic resin, for use as a positive electrode for a lead-acid battery.

2. The positive electrode for a lead-acid battery according to claim 1, wherein the conductive carbon material contains graphite and carbon black.

3. The positive electrode for a lead-acid battery according to claim 2, wherein the graphite is flaky graphite.

4. The positive electrode for a lead-acid battery according to claim 1, wherein the total amount of the carbon-containing layer is 100% by mass, and the positive electrode for a lead-acid battery contains 5 to 20% by mass of carbon black.

5. The positive electrode for a lead-acid battery according to claim 1, wherein the total amount of the carbon-containing layer is 100% by mass, and graphite is contained in an amount of 10 to 65% by mass.

6. The positive electrode for a lead-acid battery according to claim 1, wherein the total amount of the carbon-containing layer is 100% by mass, and the phenolic resin is contained in an amount of 30 to 70% by mass.

7. The positive electrode for a lead-acid battery according to claim 1, wherein the positive electrode active material layer contains lead oxide.

8. A lead-acid battery comprising a positive electrode for a lead-acid battery according to any one of claims 1 to 7.

Images