Positive electrode for lead-acid storage battery

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

Positive electrodes for lead-acid batteries

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

[0002] Lead-acid batteries, with their stable quality and economical efficiency, are primarily used as automotive batteries, accounting for nearly 30% of Japan's secondary battery production. High-performance lead-acid batteries are essential for hybrid cars and idle-stop vehicles, which have recently come into practical use, and demand for lead-acid batteries is rapidly increasing. Furthermore, research into their use in energy storage has become active in recent years. Although lead-acid batteries have a long history since their development, many unknowns remain regarding the reactions within the battery.

[0003] If a lead-acid battery is discharged too much, it becomes difficult to charge it again, so it must be charged before it is completely discharged. As a result, the theoretical capacity of the lead-acid battery is not being used effectively.

[0004] In the lead-acid battery described above, the positive electrode usually has a layer of lead oxide as a positive electrode active material formed on a lead current collector as a positive electrode, and the reaction formula during charging and discharging is as follows: Positive electrode: PbO ２ + 4H ＋ + SO ４ ２－ + 2e － ⇔ PbSO ４ + 2H ２ O negative electrode: Pb + SO ４ ２－ ⇔ PbSO ４ + 2e － It is expressed as follows.

[0005] PbO used as the positive electrode active material ２ is α-type PbO ２ and β-type PbO ２ In the low pH region (acidic region), β-type PbO ２ In the high pH range (alkaline range), it exists as α-type PbO ２ It is known that lead-acid batteries exist as β-type PbO because lead acid batteries usually use an aqueous sulfuric acid solution as the electrolyte and charge / discharge is carried out at a low pH. ２is expected to exist, but in reality, α-type PbO ２ and β-type PbO ２ However, α-type PbO ２ and β-type PbO ２ The relationship between the mixture of these two and the inability to fully utilize the theoretical capacity is still unclear.

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

[0007] As a result of extensive research, the inventors have discovered that when a lead-acid battery is in an open circuit state (when not in use), the positive electrode active material PbO ２ (Especially β-type PbO ２ They found that a local cell reaction occurs between the β-type PbO ２ is the positive electrode and lead is the negative electrode, and a battery reaction occurs, resulting in α-type PbO ２ The inventors have found that the formation of a carbon-containing layer, which is a layer different from the positive electrode current collector and contains a conductive carbon material and a phenolic resin, between the positive electrode current collector and the positive electrode active material layer suppresses local battery reactions during an open circuit, 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 conducted further research and have completed the present invention. That is, the present invention includes the following configurations.

[0008] Item 1. A positive electrode for a lead-acid battery, comprising a positive electrode current collector, a carbon-containing layer, and a positive electrode active material layer arranged in this order, wherein the carbon-containing layer contains a conductive carbon material and a phenolic resin.

[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. The positive electrode for a lead acid battery according to Item 1 or 2, wherein the carbon-containing layer contains 5 to 20% by mass of carbon black, with the total amount of the carbon-containing layer being 100% by mass.

[0011] Item 4. The positive electrode for a lead acid battery according to any one of Items 1 to 3, wherein the carbon-containing layer contains 10 to 65 mass% of graphite, with the total amount of the carbon-containing layer being 100 mass%.

[0012] Item 5. The positive electrode for a lead acid battery according to any one of Items 1 to 4, wherein the phenolic resin is contained in an amount of 30 to 70% by mass, with the total amount of the carbon-containing layer being 100% 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 comprising the lead-acid battery positive electrode according to any one of Items 1 to 6.

[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 cell reactions during an open circuit are suppressed, so that the battery can be recharged even after being fully discharged and stopped for a long period of time, and the battery has high durability. Because of the adoption of such a configuration, it is also possible to recharge the battery even after being fully discharged and stopped for a long period of time, while using lead oxide, which is commonly used as the positive electrode current collector for the positive electrode active material layer.

[0016] 1 is a schematic cross-sectional view of an evaluation test cell. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Comparative Example 1, where the cell was deeply discharged to 0 V and left stationary at an open circuit. It shows the charge / discharge waveforms of an evaluation test cell using the positive electrode of Comparative Example 2. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Comparative Example 3, where the cell was deeply discharged to 0.2 V and left stationary at an open circuit. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Comparative Example 4, where the cell was deeply discharged to 0.2 V and left stationary at an open circuit. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Example 1, where the cell was deeply discharged to 0 V and left stationary at an open circuit twice. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Example 2, where the cell was deeply discharged to 0.2 V and left stationary at an open circuit repeatedly. It shows the results of a charge / discharge test for an evaluation test cell using the positive electrode of Example 3, where the cell was deeply discharged to 0.2 V and left stationary at an open circuit repeatedly. 1 shows the results of a charge-discharge test for an evaluation test cell using the positive electrode of Example 4, where the cell was deeply discharged to 0 V and left stationary at an open circuit twice. 2 shows the results of a charge-discharge test for an evaluation test cell using the positive electrode of Example 5, where the cell was deeply discharged to 0 V and left stationary at an open circuit twice. 3 shows the results of a charge-discharge test for an evaluation test cell using the positive electrode of Example 6, where the cell was deeply discharged to 0 V and left stationary at an open circuit twice.

[0017] In this specification, the term "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist only of."

[0018] In this specification, when a numerical range is expressed as A to B, it means A or more and B or less.

[0019] 1. Positive electrode for lead-acid battery The positive electrode for a lead-acid battery of the present invention is 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, 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 limitations 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 inactive to sulfuric acid, which is the electrolyte of lead-acid batteries. Specifically, lead, gold, palladium, platinum, etc. can be used. In consideration of corrosion resistance to sulfuric acid, an alloy of lead and at least one of tin, silver, antimony, calcium, etc. can also be used. Furthermore, a carbon sheet can also be used as the positive electrode current collector.

[0021] The shape of the positive electrode current collector is not particularly limited, and any shape such as a lattice shape or a thin plate shape can be used.

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

[0023] The above-described positive electrode current collector can be used alone or can be laminated on another substrate. In particular, even if the thickness of the positive electrode current collector is thinner than the above-described range, it can be laminated on another substrate for use. For example, when the thickness of the positive electrode current collector is thin (about 1 μm to 0.1 mm) and it is difficult for it to stand alone as a support for the positive electrode active material layer described below, it is preferable to laminate it on another substrate. Examples of such other substrates include ceramics such as alumina; polymers such as polyethersulfone resin; and the like. 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 a conductive carbon material and a phenolic resin.

[0025] Conductive carbon materials are inert to sulfuric acid, which is typically used as an electrolyte, and do not undergo local cell reactions with the positive electrode current collector (described later) or lead dioxide, the positive electrode active material. Therefore, by incorporating a conductive carbon material into the carbon-containing layer, local cell reactions during an open circuit can be suppressed, allowing the battery to be recharged even after sufficient discharge and long-term cessation. Such conductive carbon materials are not particularly limited, and preferred examples include 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 sheet, isotropic graphite, flake graphite, etc.); activated carbon; and amorphous carbon. These conductive carbon materials can be used alone or in combination of two or more.

[0026] The content of the conductive carbon material is not particularly limited. From the viewpoint of more easily suppressing a local cell reaction during an open circuit and more easily improving conductivity, the content of the conductive carbon material is preferably 30 to 70 mass%, more preferably 40 to 60 mass%, when the total amount of the carbon-containing layer is taken as 100 mass%. When multiple conductive carbon materials are contained, it is preferable to adjust their total amount to be within the above range. Note that when carbon black is contained as the conductive carbon material, from the viewpoint of more easily suppressing a local cell reaction during an open circuit and more easily improving conductivity, the content is preferably 5 to 20 mass%, more preferably 7 to 15 mass%, when the total amount of the carbon-containing layer is taken as 100 mass%. Furthermore, when graphite is contained as the conductive carbon material, from the viewpoint of more easily suppressing a local cell reaction during an open circuit and more easily improving conductivity, the content is preferably 10 to 65 mass%, more preferably 25 to 55 mass%, when the total amount of the carbon-containing layer is taken as 100 mass%.

[0027] The phenolic resin is preferably a polymer compound that is inactive to lead oxide, which is the positive electrode active material, and sulfuric acid, which is the electrolyte. The phenolic resin is contained for the purpose of functioning as a binder and improving the adhesion between the positive electrode current collector and the positive electrode active material layer, but by using a phenolic resin that is inactive to lead oxide, which is the positive electrode active material, and sulfuric acid, which is the electrolyte, a carbon-containing layer is formed that is non-wettable by sulfuric acid and inactive to lead oxide, which makes it easier to further suppress deterioration of the lead-acid battery.

[0028] The phenolic resin is not particularly limited, and examples thereof include novolac-type phenolic resins, resole-type phenolic resins, xylene-resin-modified resole-type resins, and rosin-modified phenolic resins. These phenolic resins can be used alone or in combination of two or more.

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

[0030] The thickness of such a carbon-containing layer is not particularly limited, and is preferably 5 nm to 10 mm, and more preferably 10 nm to 1 mm, from the viewpoints of more easily suppressing deterioration of the positive electrode due to a local cell reaction, more easily improving durability and capacity, and more easily improving adhesion between the positive electrode current collector and the positive electrode active material (lead oxide).

[0031] The method for forming the carbon-containing layer is not particularly limited. For example, a coating method can be used. When a coating method is used, the carbon-containing layer can be formed using means such as roller coating (e.g., applicator roll), screen coating, doctor blade method, spin coating, bar coater, or dip coating. Specifically, the carbon-containing layer can be obtained by applying a coating material 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 variety of common organic solvents (e.g., ether solvents such as butyl carbitol, diisopropyl ether, butyl cellosolve, tetrahydrofuran, and dioxane) can be used.

[0032] The paint containing the conductive carbon material, phenolic resin, and organic solvent can be produced by mixing the respective components, but it is also possible to use a commercially available paint containing the conductive carbon material, phenolic resin, and organic solvent. Specific examples of such commercially available products include Ebriohm T-30PLB-UL(BC) and Ebriohm T-30PLB-U, both manufactured by Nippon Graphite Industries Co., Ltd.

[0033] (1-3) Positive Electrode Active Material Layer In the positive electrode for a lead acid battery of the present invention, a positive electrode active material layer is formed on the carbon-containing layer. As described above, the carbonaceous material contained in the carbon-containing layer can suppress a local cell reaction (particularly a local cell reaction during an open circuit) between the positive electrode active material layer and α-type PbO due to the local cell reaction during an open circuit. ２ Therefore, the battery can be charged and discharged again even after being fully discharged and stopped for a long period of time (open circuit), and durability can also be improved.

[0034] In the positive electrode for a lead acid battery of the present invention, the positive electrode active material contained in the positive electrode active material layer is lead oxide (lead monoxide (PbO)), lead dioxide (lead dioxide (PbO)) which has been conventionally used. ２The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, and can be set to a level conventionally applied to the positive electrode of a lead-acid battery, and is preferably 50 to 95 mass %, more preferably 70 to 90 mass %, where the total amount of the positive electrode active material layer is 100 mass %.

[0035] In the present invention, the positive electrode active material layer may also contain a conductive additive. It is preferable to use a conductive additive that is an electronically conductive material and that is unlikely to cause a local cell reaction (a material that is electrochemically inactive with lead oxide and sulfuric acid). Specifically, the conductive additive may contain one or a mixture of conductive materials such as graphite (isotropic graphite, etc.) such as natural graphite or artificial graphite; carbon black; acetylene black; ketjen black; carbon whiskers; carbon fiber; and vapor-grown carbon. The content of the conductive additive in the positive electrode active material layer is not particularly limited and may be at a level conventionally applied to the positive electrode of a lead-acid battery. The content is preferably 5 to 35% by mass, and more preferably 10 to 20% by mass, of the total amount of the positive electrode active material layer taken as 100% by mass.

[0036] In addition to the above components, the positive electrode active material layer may also contain a binder, a thickener, and the like.

[0037] As the binder, typically, one or a mixture of two or more of thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, and polypropylene; and polymers having rubber elasticity such as ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber can be used.

[0038] As the thickener, polysaccharides such as carboxymethyl cellulose and methyl cellulose can usually be used alone or in a mixture of two or more kinds.

[0039] The contents of the binder and thickener in the positive electrode active material layer are not particularly limited and can be set to the same extent as conventionally applied to the positive electrode of a lead-acid battery. The total amount of the binder and thickener is preferably 2 to 15 mass%, more preferably 3 to 10 mass%, where the total amount of the positive electrode active material layer is 100 mass%.

[0040] The components are mixed by physical mixing, preferably uniform mixing, using a powder mixer such as a V-type mixer, S-type mixer, mortar, ball mill, or planetary ball mill in either 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, a method may be used in which various components such as the positive electrode active material are mixed with water to prepare a paste composition for forming the positive electrode active material layer, and then the paste composition is impregnated into or applied to the carbon-containing layer, followed by drying.

[0042] The coating method can be, for example, roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, dip coating, etc. The drying conditions are not particularly limited, and can be within the range usually used for lead-acid batteries.

[0043] 2. Lead Acid Battery The lead acid battery of the present invention includes the positive electrode for a lead acid battery of the present invention.

[0044] Examples of components other than the positive electrode include a negative electrode for a lead-acid battery, an electrolyte for a lead-acid battery, a separator for a lead-acid battery, etc. These may be appropriately manufactured or commercially available products, and known components and materials for lead-acid batteries can be used.

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

[0046] Example 1 A lead grid (made in China) serving as a positive electrode current collector was prepared in a lattice shape with a lattice frame thickness of 1.2 mm±0.1 mm.

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

[0048] The active material was lead dioxide, and a slurry containing lead dioxide, carbon black, and polyvinylidene fluoride (PVDF) was used. ２ (lead dioxide manufactured by Johnson Matthey), acetylene black, and PVDF were mixed with β-type PbO ２ The materials were premixed in a ratio of 90:5:5 (by mass), and then dispersed in N-methylpyrrolidone (NMP) to form a slurry. The mixture was stirred and mixed for 5 minutes using a planetary stirring device (Mazerustar KK-250S, manufactured by Kurabo Industries, Ltd.) to prepare a slurry for forming a positive electrode active material layer. The lead grid on which the carbon-containing layer had been formed was immersed in the conductive paint for several seconds and dried at 100°C for 1 hour. A positive electrode active material layer was then dip-coated onto the carbon-containing layer to a thickness of 0.1 to 0.2 mm after drying. In this way, the lead-acid battery positive electrode of Example 1 was obtained.

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

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

[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 the carbon-containing layer was not formed.

[0052] Comparative Example 2 A positive electrode for a lead acid battery of Comparative Example 2 was obtained in the same manner as in Example 1, except that PF-50 (thickness: 0.5 mm) manufactured by Toyo Tanso Co., Ltd. was used as the positive electrode current collector and no carbon-containing layer was formed.

[0053] Comparative Example 3 A lead-acid battery positive electrode of Comparative Example 3 was obtained in the same manner as in Example 1, except that conductive paint Bunny Height UCC-2 (58% by mass of flake 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 as a raw material for forming the carbon-containing layer, and the drying conditions were 100°C and 20 minutes.

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

[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 mass% in total of flake natural graphite and acetylene black, 50 mass% novolac phenolic resin, 300 mass% 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 A 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 mass% in total of flake natural graphite and acetylene black, 50 mass% of xylene resin-modified phenolic resin, and 300 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.

[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 mass% in total of flake natural graphite and acetylene black, 50 mass% of rosin resin-modified phenolic resin, and 300 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] Production Example 1: Cell for Evaluation Test A bipolar glass cell was used as the cell for the following evaluation test. The positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 4 described above were used as the positive electrodes, and a lead alloy grid filled with lead powder was used as the negative electrode removed from a ready-made lead-acid battery. A 35% by mass aqueous sulfuric acid solution was used as the electrolyte, to produce the cell shown in FIG. 1 .

[0059] Test Example 1: Charge / Discharge Test (Deep Discharge Test and Charge / Discharge Waveform) Evaluation test cells using the positive electrodes of Examples 1 to 6 and Comparative Examples 1 to 4 were charged and discharged under the following conditions. For the charge / discharge test, a charge / discharge device (HJ1001SD8) manufactured by Hokuto Denko Corporation was used.

[0060] For Example 1, first, to stabilize the battery reaction, 20 cycles of discharge at 0.1 C to 1.8 V and charge at 0.5 C to 2.3 V were repeated, followed by deep discharge at 0.1 C to 0 V. After that, the battery was left standing for 48 hours in an open circuit state, followed by 20 cycles of shallow charge and discharge (2.3 V to 1.8 V) at 0.5 C, followed by deep discharge at 0.5 C to 0 V. After further leaving the battery standing for 48 hours in an open circuit state, deep charge and discharge (2.3 V to 0 V) ​​at 0.5 C were repeated.

[0061] For Examples 2 to 6 and Comparative Examples 1 to 4, first, to stabilize the battery reaction, 20 charge-discharge cycles were repeated, with one cycle consisting of 30 minutes of discharge at 9 mA / g and 20 minutes of charge at 180 mA / g. Next, at the 20th cycle, the battery was deeply discharged at 9 mA / g to 0.2 V. The battery was then left to stand for 48 hours in an open-circuit state. Thereafter, 10 charge-discharge cycles were repeated, with one cycle consisting of 20 minutes of charge at 180 mA / g and 20 minutes of discharge at 9 mA / g. At the final cycle, the battery was deeply discharged at 9 mA / g to 0.2 V. The battery was then left to stand for 48 hours in an open-circuit state. This charge-discharge pattern was repeated.

[0062] The results of Comparative Example 1 are shown in Figure 2. As a result, even in the charge-discharge cycle before deep discharge, charge-discharge with a stable discharge waveform was not possible at high potential. Furthermore, after deep discharge and open circuit holding, further charge-discharge was not possible, making it unsuitable for practical use.

[0063] The results of Comparative Example 2 are shown in Figure 3. In this case, too, even in the charge-discharge cycle before deep discharge, charge-discharge was not possible at high potential with a stable discharge waveform, and the energy efficiency was also insufficient.

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

[0065] The results of Comparative Example 4 are shown in Figure 5. As a result, although the battery was able to be charged and discharged again after deep discharge and open circuit holding, it was not possible to charge and discharge at a high potential, and the discharge waveform deteriorated, resulting in poor energy efficiency and a durability of just under 600 hours, making it unsuitable for practical use.

[0066] The results of Example 1 are shown in Figure 6. As a result, it can be seen that in the charge-discharge cycle before deep discharge, charge and discharge were possible at high potentials with a stable discharge waveform, and that the energy efficiency was excellent. Furthermore, even when the above charge-discharge pattern, which includes deep discharge and open circuit retention, was repeated, stable charge and discharge was possible at high potentials, the discharge waveform was good, the energy efficiency was excellent, and the durability was such that the battery could operate continuously for more than 1,500 hours, making it suitable for practical use. Furthermore, when the thickness of the carbon-containing layer was increased by repeated dip coating as in Examples 2 and 3, the durability was further improved, and it was possible to operate continuously for more than 2,500 hours, as shown in Figures 7 and 8.

[0067] The results of Examples 4 to 6 are shown in Figures 9 to 11. In all cases, even after deep discharging to 0 V and leaving the battery stationary in an open circuit twice, deep charging and discharging was possible, 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, wherein the carbon-containing layer contains a conductive carbon material and a phenolic resin.

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

3. The positive electrode for a lead-acid battery according to claim 1, containing 5 to 20% by mass of carbon black with the total amount of the carbon-containing layer being 100% by mass.

4. The positive electrode for a lead-acid battery according to claim 1, containing 10 to 65% by mass of graphite with the total amount of the carbon-containing layer being 100% by mass.

5. The positive electrode for a lead-acid battery according to claim 1, containing 30 to 70% by mass of the phenolic resin with the total amount of the carbon-containing layer being 100% by mass.

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

7. A lead-acid battery comprising the positive electrode for a lead-acid battery according to any one of claims 1 to 6.

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