Lead-acid battery and charge / discharge control system

Abstract

This invention provides a lead-acid battery that can maintain a long lifespan even under operating conditions where acceleration-assisted discharge is performed in small mobility vehicles. Furthermore, it provides a charge / discharge control system suitable for charge / discharge control, including acceleration-assisted discharge, using this lead-acid battery. [Solution] A valve-regulated lead-acid battery for use in small mobility devices, comprising at least one cell having a positive electrode plate 3, a negative electrode plate 2, and an electrolyte. The positive electrode plate comprises a positive electrode current collector having a mesh portion and a positive electrode material supported on the positive electrode current collector. In the thickness direction of the positive electrode plate, the density S in the overpaste portion of the positive electrode material that extends beyond the mesh portion of the positive electrode current collector is greater than the density T located inside the mesh portion of the positive electrode current collector, and is 4.1 g / cm³. 3 That's all.

Description

Technical Field

[0001] The present invention relates to a lead storage battery and a charge / discharge control system using the same.

Background Art

[0002] Lead storage batteries are used in various applications, including in-vehicle and industrial applications. A lead storage battery includes a negative electrode plate, a positive electrode plate, a separator (or mat), and an electrolyte. Each electrode plate includes a current collector and an electrode material.

[0003] There are liquid-type lead storage batteries and control valve-type lead storage batteries. A liquid-type lead storage battery is an open-type lead storage battery including a battery case, a group of electrode plates housed in the battery case, and an electrolyte. On the other hand, a control valve-type lead storage battery is a sealed-type lead storage battery including a group of electrode plates including a positive electrode plate, a negative electrode plate, and a fine glass mat separator (retainer mat) interposed between the positive electrode plate and the negative electrode plate, and an electrolyte. In the control valve-type lead storage battery, the electrolyte is held by the separator, and the so-called oxygen cycle principle is utilized, in which oxygen gas generated at the positive electrode plate is reduced to water at the negative electrode plate.

[0004] Conventionally, lead storage batteries have been used for starting and driving an internal combustion engine mounted on a vehicle.

[0005] On the other hand, in recent years, in consideration of suppressing CO2 emissions, the use of secondary batteries (storage batteries) in vehicles has been promoted. As an example, an electric vehicle (BEV) that does not use an internal combustion engine and drives a motor connected to the rotation shaft of a wheel with a high-output storage battery and runs only with the output of the motor, and a hybrid vehicle (HEV) that combines the output of an engine and the output of a motor to improve fuel efficiency are being improved. The secondary battery (storage battery) directly supplies power to the motor and also supplies power necessary for starting and driving the engine in a hybrid vehicle. A lithium-ion battery is used for driving the motor.

[0006] [[ID=二十七]] Patent Document 1 provides a cell comprising an electrode group and an electrolyte, wherein the electrode group comprises a negative electrode plate, a positive electrode plate, and a separator interposed between the negative electrode plate and the positive electrode plate, the negative electrode plate comprises a negative electrode material, and the negative electrode material is measured using deuterated chloroform as a solvent. 1 The polymer compound has a peak in the chemical shift of the H-NMR spectrum between 3.2 ppm and 3.8 ppm. The positive electrode plate is equipped with the positive electrode material, and the density of the positive electrode material is 3.70 g / cm³. 3 More than 4.65g / cm 3 We propose a valve-regulated lead-acid battery characterized by the following:

[0007] Patent Document 2 describes a lead-acid battery comprising a group of electrode plates stacked with a positive electrode plate, a negative electrode plate, and a separator, and a sulfuric acid electrolyte, wherein the density of the positive electrode active material after chemical formation is 4.5 g / cm³. 3 More than 4.7g / cm 3 The following is a proposed lead-acid battery characterized by having an average pore diameter of 0.10 μm or more and 0.30 μm or less in the positive electrode active material after chemical formation, a positive electrode plate thickness of 1.30 mm or more and 1.50 mm or less, and containing 20 mmol / L or more and 200 mmol / L or less of aluminum ions in the sulfuric acid electrolyte. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2022-113635 [Patent Document 2] Japanese Patent Publication No. 2011-57108 [Overview of the project] [Problems that the invention aims to solve]

[0009] In small mobility vehicles such as motorcycles, a method called mild hybrid is being explored, in which a secondary battery (storage battery) is used to start and drive the engine during normal driving, and the output of a motor is used to assist acceleration when starting. Lithium-ion batteries are generally used to drive the motor. However, in mild hybrids, the use of lead-acid batteries as secondary batteries for motor-assisted acceleration is also being considered.

[0010] However, when realizing a mild hybrid for small mobility vehicles using lead-acid batteries, a large current (e.g., 20-25 CA) needs to be supplied by the discharge of the lead-acid battery to drive the motor during acceleration assist, and the lead-acid battery needs to perform high-rate discharge with an extremely large discharge current.

[0011] Conventional lead-acid batteries for small mobility vehicles are not designed for use in acceleration-assisted discharge as described above. Therefore, designs suitable for acceleration-assisted discharge in such small mobility vehicles have never been considered. Thus, we investigated lead-acid batteries that can maintain high lifespan characteristics even in environments where acceleration-assisted discharge occurs in small mobility vehicles. [Means for solving the problem]

[0012] In view of the above, a first aspect of the present invention is a valve-regulated lead-acid battery comprising at least one cell having a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector having a mesh portion and a positive electrode material supported on the positive electrode current collector, and in the thickness direction of the positive electrode plate, the density S of the overpaste portion of the positive electrode material that extends beyond the mesh portion of the positive electrode current collector is greater than the density T of the positive electrode material located inside the mesh portion of the positive electrode current collector, and is 4.1 g / cm³. 3 The above concerns lead-acid batteries used in small mobility vehicles.

[0013] In view of the above, a second aspect of the present invention is a valve-regulated lead-acid battery, a small mobility device that receives power from the lead-acid battery, and a control unit that controls the charging and discharging of the lead-acid battery, wherein the small mobility device includes an engine and motor coupled to an axle, the lead-acid battery includes at least one cell comprising a positive electrode plate, a negative electrode plate, and an electrolyte, the positive electrode plate comprises a positive electrode current collector having a mesh portion, and a positive electrode material supported on the positive electrode current collector, wherein in the thickness direction of the positive electrode plate, the density S of the overpaste portion of the positive electrode material that protrudes from the mesh portion of the positive electrode current collector is greater than the density T of the positive electrode material located inside the mesh portion of the positive electrode current collector, and is 4.1 g / cm³. 3 The above relates to a charge / discharge control system in which the control unit starts the engine based on a first discharge current supplied from the lead-acid battery, and then controls the motor to drive based on a second discharge current that is greater than the first discharge current supplied from the lead-acid battery. [Effects of the Invention]

[0014] This technology enables the creation of a lead-acid battery that maintains a long lifespan even under operating conditions involving acceleration-assisted discharge in small mobility vehicles. Furthermore, this lead-acid battery can be used to realize a charge-discharge control system suitable for charge-discharge control, including acceleration-assisted discharge. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view showing the structure of a valve-regulated lead-acid battery according to one embodiment. [Figure 2] This is a block diagram showing a schematic configuration of a charge / discharge control system according to one embodiment for driving a small mobility device using a lead-acid battery. [Figure 3] This is a schematic diagram showing a cross-section of a positive electrode plate with the positive electrode material overlaid. [Modes for carrying out the invention]

[0016] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0017] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0018] A lead-acid battery comprises a positive electrode plate, a negative electrode plate, a separator interposed between the positive and negative electrode plates, and an electrolyte. The electrolyte contains sulfuric acid. Charging and discharging proceed through the movement of sulfate ions between the positive and negative electrode plates and the electrolyte. During discharge, sulfate ions move to the positive and negative electrode plates, causing the density of the electrolyte to decrease. During charging, sulfate ions move from the positive and negative electrode plates into the electrolyte, causing the density of the electrolyte to increase.

[0019] A positive electrode plate, a negative electrode plate, and a separator constitute an electrode group. The electrode group, together with the electrolyte, constitutes a cell. One electrode group constitutes one cell. A lead-acid battery comprises one or more cells by comprising one or more electrode groups. There is no particular limit to the number of positive and negative electrode plates included in one electrode group. An electrode group comprising a lead-acid battery according to this disclosure may, for example, include a total of 12 or more positive and negative electrode plates. Multiple electrode groups are typically housed in separate cell chambers and connected in series with one another.

[0020] The positive electrode plate includes a positive electrode material. The positive electrode material includes lead dioxide. More specifically, the positive electrode material, as a positive electrode active material that exhibits capacity through a redox reaction, contains at least lead dioxide during charging and at least lead sulfate during discharging.

[0021] The negative electrode plate includes a negative electrode material. The negative electrode material includes lead. More specifically, the negative electrode material, as a negative electrode active material that exhibits capacity through oxidation-reduction reactions, contains at least lead during charging and at least lead sulfate during discharging. The negative electrode material may further contain barium sulfate (BaSO4) as an additive to suppress shrinkage of the negative electrode material.

[0022] In this specification, 1CA refers to the current value (A) that is the same as the value in Ah indicated in the rated capacity. For example, for a battery with a rated capacity of 5Ah, 1CA is 5A, 1mCA is 5mA, and 20CA is 100A.

[0023] In lead-acid batteries, high-rate discharge conditions typically refer to discharge currents of approximately 8-10 CA or higher. For example, in lead-acid batteries used in IS vehicles with idle stop (also called Idle Reduction or Start-Stop) control, the discharge current flowing during engine restart falls under typical high-rate discharge conditions. In this case, based on the inventors' past knowledge regarding lead-acid batteries for IS vehicles, cycle life tests involving discharge currents of around 10 CA generally result in failure due to the accumulation of lead sulfate on the negative electrode plate, and failure is almost always due to factors on the negative electrode side.

[0024] In response to this, a life test of lead-acid batteries was conducted using a charge-discharge cycle that included high-rate discharges with large discharge currents of approximately 20 CA or more, simulating acceleration assist discharge in small mobility vehicles. When lead-acid batteries that reached the end of their life in the above life test were discharged again and the limiting electrode was determined, it was found that the potential of the positive electrode had dropped significantly, indicating that the battery's lifespan was due to factors on the positive electrode side. Furthermore, analysis of the cross-section of the positive electrode plate using an electron beam microanalyzer (EPMA) and mapping of S element revealed a large accumulation of lead sulfate on the surface of the positive electrode plate.

[0025] Based on the inventors' past knowledge, possible reasons for the failure of the positive electrode due to positive electrode factors include (A) depletion of the positive electrode active material (PbO2) in the region where high-rate discharge mainly occurs, or (B) depletion of sulfate ions retained within the positive electrode plate or diffusing into the positive electrode plate from the electrolyte outside the positive electrode plate.

[0026] (B) As a countermeasure to improve the case where the depletion of sulfate ions is the cause of the lifespan, we attempted to increase the pore size in the positive electrode material by adjusting the amount of additive contained in the positive electrode material, thereby increasing the amount of sulfate ions (electrolyte) held in the positive electrode plate and promoting the reaction inside the positive electrode plate by making it easier for sulfate ions to diffuse into the positive electrode plate, but no effect was obtained. When the cross section of the positive electrode plate to which this improvement measure was applied was analyzed by mapping of S element using EPMA in the same way, a large accumulation of lead sulfate remained on the surface of the positive electrode plate. From this, it was considered that (A) the depletion of the positive electrode active material (PbO2) is the cause of the lifespan, and that the lead sulfate remaining on the surface of the positive electrode active material is causing pore blockage. The present invention is based on these findings.

[0027] This disclosure includes the following technologies: (1) A lead-acid battery according to an embodiment of the present disclosure is a controlled valve type lead-acid battery, and includes at least one cell including a positive electrode plate, a negative electrode plate, and an electrolyte. The positive electrode plate includes a positive electrode current collector having a mesh portion and a positive electrode electrode material supported on the positive electrode current collector. The positive electrode current collector may be an expanded lattice or a punched current collector. In the thickness direction of the positive electrode plate, the density S in the overpaste portion where the positive electrode electrode material protrudes from the mesh portion of the positive electrode current collector is greater than the density T located inside the mesh portion of the positive electrode current collector of the positive electrode electrode material, and 4.1 g / cm 3 or more, and is a lead-acid battery used for small mobility.

[0028] In the lead-acid battery described in (1) above, the density S in the overpaste portion of the positive electrode electrode material is made greater than the density T located inside the mesh portion of the positive electrode current collector of the positive electrode electrode material, and the density S is 4.1 g / cm 3 or more, whereby depletion of the positive electrode active material in the above-described accelerated assist discharge in which an extremely large current flows is suppressed, and a long life can be maintained even under usage conditions where charge and discharge are performed in a charge-discharge cycle including the accelerated assist discharge.

[0029] Under discharge conditions where an extremely large discharge current (for example, 20 CA or more) flows, such as in accelerated assist discharge, a large amount of lead sulfate is generated in a short time. The sulfate is mainly generated on the surface of the positive electrode. In accelerated assist discharge, the utilization rate of the active material inside the positive electrode plate is low, and the discharge reaction proceeds biased near the surface. Therefore, if accelerated assist discharge is repeated, lead sulfate accumulates on the surface of the positive electrode plate. As a result, the active material near the surface available for accelerated assist discharge is depleted, and it is considered that discharge stops or the battery reaches its life.

[0030] On the other hand, according to the lead-acid battery described in (1) above, the density S of the positive electrode electrode material in the overpaste portion corresponding to the surface layer portion of the positive electrode plate is greater than the density T of the positive electrode electrode material inside the positive electrode plate, and 4.1 g / cm 3By doing so, the amount of positive electrode active material available for accelerated-assisted discharge can be increased, thereby suppressing the depletion of the positive electrode active material. As a result, high cycle life performance can be maintained in accelerated-assisted discharge.

[0031] To improve the performance of accelerated-assisted discharge, the density S in the overpaste portion may be increased, the density T in the interior may be increased, or both densities may be increased. However, as mentioned above, in accelerated-assisted discharge, the discharge reaction is concentrated in the surface layer of the electrode plate, so increasing the density S in the overpaste portion, including the surface layer, is effective.

[0032] In general lead-acid batteries, the utilization rate of the active material in the positive electrode is low, at around 50% or less. In valve-regulated lead-acid batteries, the utilization rate of the active material in the positive electrode is even lower than in liquid-type lead-acid batteries, sometimes reaching around 40%. For this reason, depletion of the positive electrode active material is particularly likely to occur in valve-regulated lead-acid batteries, and the aforementioned problems caused by the depletion of the positive electrode active material are likely to occur when accelerated-assisted discharge is performed. Therefore, this disclosure is particularly effective in valve-regulated lead-acid batteries.

[0033] (2) In the lead-acid battery described in (1) above, the density S of the positive electrode material is 4.42 g / cm³ 3 It is preferable that the above conditions are met. This allows for even longer lifespan in charge-discharge cycles that include accelerated discharge.

[0034] On the other hand, as the density of the positive electrode material increases, the space available to hold electrolyte (sulfate ions) within the positive electrode plate decreases, which tends to reduce the high-rate discharge duration, especially at low temperatures. In terms of suppressing the decrease in high-rate discharge duration at low temperatures, a density S of, for example, 4.8 g / cm³ is desirable. 3 The following is the value: 4.7 g / cm³ 3 The following is also acceptable.

[0035] (3) In the lead-acid battery described in (1) or (2) above, the density T of the positive electrode material is 4.16 g / cm³. 3The following is preferable. In this case, there is sufficient space inside the positive electrode plate to hold the electrolyte (sulfate ions), which suppresses the decrease in high-rate discharge duration at low temperatures. Therefore, under operating conditions in which charging and discharging are performed in charge-discharge cycles including accelerated-assisted discharge, it is possible to achieve a long lifespan while suppressing the decrease in high-rate discharge duration in low-temperature environments.

[0036] (4) In the lead-acid battery described in any one of (1) to (3) above, the ratio of density S to density T, S / T, may be 1.06 or greater.

[0037] (5) A charge / discharge control system according to one embodiment of the present disclosure comprises a valve-regulated lead-acid battery, a small mobility device that receives power from the lead-acid battery, and a control unit that controls the charging and discharging of the lead-acid battery. The small mobility device comprises an engine and a motor coupled to an axle. The lead-acid battery comprises at least one cell comprising a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector having a mesh portion and a positive electrode material supported on the positive electrode current collector, and in the thickness direction of the positive electrode plate, the density S in the overpaste portion of the positive electrode material that extends beyond the mesh portion of the positive electrode current collector is greater than the density T located inside the mesh portion of the positive electrode current collector, and is 4.1 g / cm³. 3 That concludes the explanation. The control unit starts the engine based on a first discharge current supplied from the lead-acid battery, and then controls the motor to drive based on a second discharge current that is greater than the first discharge current supplied from the lead-acid battery.

[0038] In the charge / discharge control system described in (5) above, the lead-acid battery has a density S in the overpaste portion of the positive electrode material greater than the density T located inside the mesh portion of the positive electrode current collector, and the density S is 4.1 g / cm³. 3This is the result. As a result, depletion of the positive electrode active material under accelerated-assisted discharge conditions is suppressed, and a long lifespan can be maintained even under operating conditions in which charging and discharging are performed in charge-discharge cycles that include accelerated-assisted discharge. Therefore, a charge-discharge control system that includes accelerated-assisted discharge conditions can be realized using this lead-acid battery.

[0039] The lead-acid battery relating to this disclosure may be a liquid-type battery (vented battery), but is more suitable for a valve-regulated lead-acid battery (VRLA type battery). Furthermore, the lead-acid battery used in the charge / discharge control system relating to this disclosure may be a liquid-type battery (vented battery), but is more suitable for a valve-regulated lead-acid battery (VRLA type battery). Valve-regulated lead-acid batteries are sometimes called sealed lead-acid batteries.

[0040] (Explanation of terms) (electrode material) The negative electrode material and the positive electrode material are usually held by the current collector. The electrode material is the portion of the electrode plate excluding the current collector. The electrode plate may have components such as mats or pasting paper attached to it. Such components (also called attached components) are used integrally with the electrode plate and are therefore included in the electrode plate. When the electrode plate includes attached components (mats, pasting paper, etc.), the electrode material is the portion of the electrode plate excluding the current collector and attached components.

[0041] In a clad positive electrode plate, the 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 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.

[0042] (Density of positive electrode material) The density of the positive electrode material is determined by dividing the mass of the positive electrode material by the bulk volume obtained by the mercury intrusion method (g / cm³). 3The density is determined for a sample of positive electrode material taken from a positive electrode plate removed from a fully charged lead-acid battery. Unground samples are taken from the top or bottom of the positive electrode plate in the planar direction.

[0043] The density S in the overpaste portion of the positive electrode material and the density T inside the mesh portion of the positive electrode current collector are determined by selecting a position in the planar direction of the positive electrode plate that does not overlap with the mesh portion (the position of the mesh center), measuring the density of the positive electrode material at multiple depths in the thickness direction of the positive electrode plate, and taking the average value.

[0044] Figure 3 shows a cross-sectional view of a positive electrode plate in which the positive electrode material is held by the positive electrode current collector. The positive electrode plate 3 comprises a positive electrode current collector 31 and a positive electrode material 32 supported on the positive electrode current collector 31. The positive electrode current collector 31 has multiple bones (mesh parts), which form a mesh or lattice. Figure 3 shows one bone part 31A of the positive electrode current collector 31.

[0045] The cross-sectional shape of the bone portion can be any shape. If the distance from the surface of the bone portion to the outer surface of the positive electrode material is not constant, the shortest distance from the surface of the bone portion to the outer surface of the positive electrode material is defined as the thickness of the overpaste portion. In the example in Figure 3, the distance D from point X on the contour of the bone portion 31A to one of the outer surfaces of the positive electrode material 32 is defined. X , and the distance D from location Y on the contour of bone portion 31A to the other outer surface of the positive electrode material. Y However, this is the thickness of the overpaste portion. The density S in the overpaste portion of the positive electrode material is measured from one outer surface 41 of the positive electrode material 32 to a depth D. X The density of the positive electrode material in the region up to, or the depth D from the other outer surface 42 of the positive electrode material 32. Y This is the average density of the positive electrode material in the region up to a certain point, in the thickness direction. The density T located inside the mesh portion of the positive electrode material is the density at a depth of D from one outer surface 41 of the positive electrode material 32. X The depth is greater, and the depth from the other outer surface 42 of the positive electrode material 32 is D YThis is the average density of the positive electrode material in the deeper regions, calculated in the thickness direction. The density S in the overpaste portion has two densities corresponding to both sides of the positive electrode plate: density S1 on one outer surface 41 of the positive electrode material 32 and density S2 on the other outer surface 42 of the positive electrode material 32. One of densities S1 and S2 is 4.1 g / cm³. 3 The above conditions may be met, and the density may be greater than T, and both conditions must be 4.1 g / cm³. 3 Preferably, the density is greater than or equal to T.

[0046] In the thickness direction of the positive electrode plate, the positive electrode material may have a density distribution in which the density of the positive electrode material increases from the inside of the positive electrode plate toward the surface. However, the density distribution in the thickness direction of the positive electrode material is not particularly limited, as long as the density does not increase gradually from the inside of the positive electrode plate toward the surface, or increases in steps toward the inside of the positive electrode plate toward the surface, and the density S and density T calculated based on the above definition satisfy the aforementioned relationship. For example, in the thickness direction of the positive electrode plate, the positive electrode material may have a first region including the surface layer of the positive electrode plate and a second region located inside the positive electrode plate from the first region, and the density of the positive electrode material in the first region may be higher than the density of the positive electrode material in the second region. The depth of the boundary between the first region and the second region does not have to coincide with the thickness of the overpaste portion, and it is not necessarily required that the density of the positive electrode material changes at the boundary between the overpaste portion and the portion inside it (inside the mesh portion).

[0047] (Measurement of the density of the positive electrode material) The following describes a method for measuring the density of the positive electrode material. Prior to measurement or analysis, a fully charged lead-acid battery is disassembled to obtain the positive electrode plate to be analyzed. The obtained positive electrode plate is washed with water and dried to remove the electrolyte from the positive electrode plate. Next, the positive electrode plate is cut so that the center position surrounded by the mesh portion of the positive electrode current collector (the position of the center of the mesh) is included in the cut surface, thereby obtaining a cross-section in the thickness direction of the positive electrode plate. Samples of the positive electrode material are taken from multiple positions with different depths in the thickness direction that are exposed in the cross-section to obtain a sample (sample D).

[0048] The density (bulk density) of sample D is determined using a mercury porosimometer and the mercury intrusion method. More specifically, a predetermined amount of sample D is first taken and its mass is measured. This sample D is placed in the measuring container of the mercury porosimometer, evacuated under reduced pressure, and then filled with mercury at a pressure of 0.5 psia to 0.55 psia (≒ 3.45 kPa to 3.79 kPa). The bulk volume of sample D is measured, and the density of the positive electrode material is determined by dividing the measured mass of sample D by the bulk volume. The bulk volume is defined as the volume of the measuring container minus the volume of mercury injected. As the mercury porosimometer, an automatic porosimometer (Autopore IV9505) manufactured by Shimadzu Corporation is used.

[0049] Let X be the thickness of the positive electrode plate. The region from the surface of the positive electrode plate to a depth of X / 2 is divided into N+1 sections. Positions are selected where the depth from the surface of the positive electrode plate is (n+1)X / 2N (where n=0 to N), and the density of the positive electrode material is determined at N+1 locations with different depths. The number of divisions N is set such that at least 3 locations are included in the overpaste area, and at least 3 locations are inside the overpaste area (inside the mesh area). Density S is the average value of the density of the positive electrode material at the locations belonging to the overpaste area among the N+1 locations. Density T is the average value of the density of the positive electrode material at the remaining locations.

[0050] By observing the cross-section of the positive electrode plate under a microscope, it is possible to estimate the relationship between density S and density T based on the difference in porosity between the interior and surface layers of the positive electrode plate. In the cross-section, if the ratio of the area occupied by voids to the total area (including voids) of the positive electrode material on the surface side (overpaste portion) of the positive electrode plate is greater than the ratio of the area occupied by voids to the total area (including voids) of the positive electrode material in the portion located inside the mesh portion of the positive electrode plate, then it can be estimated that density S is greater than density T. Based on the area occupied by voids, it is also possible to determine the porosity of the positive electrode material in a predetermined region and quantitatively evaluate density S and density T. When observing the cross-section, a fully charged lead-acid battery after chemical formation or during use (preferably in the initial stages of use) is disassembled, the removed electrode plates are washed with water to remove the electrolyte containing sulfuric acid, and then dried. After that, vinyl ester resin or epoxy resin is impregnated into the entire positive electrode plate and cured. In the cured state, a predetermined location is cut, and the cut cross-section is polished.

[0051] (Fully charged) In this specification, a fully charged state means, in the case of a valve-regulated lead-acid battery, a 20-hour rate current of 1 in an air chamber at 25°C ± 2°C. 20 Five times the current 5I 20 (Unit: A) Constant current constant voltage charging is performed at 2.67V / cell (16.00V for a lead-acid battery with a rated voltage of 12V), and charging is terminated when the total charging time reaches 24 hours. Note that the 20-hour rate current I 20 This refers to a current (A) that is 1 / 20th of the Ah value listed in the rated capacity. The value listed as the rated capacity is a value in Ah (ampere-hour). The unit of the current set based on the value listed as the rated capacity is A (ampere).

[0052] A fully charged lead-acid battery is a lead-acid battery that has been charged to its full capacity after chemical formation. The timing for charging a lead-acid battery to its full capacity can be immediately after chemical formation, or after some time has passed since chemical formation (for example, 720 hours or less). For example, a lead-acid battery that has been chemically formed and is in use (preferably in the early stages of use) may be charged. An early-stage battery refers to a battery that has not been in use for very long and has hardly deteriorated (for example, a battery that has not been used for more than 720 hours, including the time since chemical formation).

[0053] (Small mobility vehicles) Small mobility refers to motorcycles and powersports vehicles. Examples of small mobility include motorcycles, motorcycles, buggies (including both three-wheeled and four-wheeled vehicles), water skis, snowmobiles, and all-terrain vehicles. Small mobility vehicles are equipped with engines and lead-acid batteries specifically designed for small mobility. Lead-acid batteries used in or installed in small mobility vehicles (i.e., lead-acid batteries for small mobility) refer to lead-acid batteries that fall within the scope of IEC 60095-7:2019 and JIS D 5302:2004.

[0054] The small mobility vehicle is equipped with an engine and motor coupled to the axle. The lead-acid battery may be configured to start the engine and drive the motor. In other words, the lead-acid battery may be used in a small mobility vehicle controlled by a mild hybrid system.

[0055] In a mild hybrid system, the secondary battery is used to start and drive the engine during normal driving, and the motor is driven along with the engine during acceleration assistance. When supplying the current necessary for acceleration assistance by the motor from a lead-acid battery, it is necessary to supply an extremely large discharge current of about 20 CA or more. The lead-acid battery according to this embodiment can achieve a long lifespan even in applications such as mild hybrids, where charge and discharge control is performed including high-rate discharge conditions that supply an extremely large current of 20 CA or more.

[0056] The lead-acid battery according to an embodiment of the present invention will be described in more detail below with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0057] The following describes examples of components of a lead-acid battery.

[0058] (Positive plate) The positive electrode plates of lead-acid batteries can be classified into paste type, clad type, etc. Either paste type or clad type positive electrode plate may be used. The positive electrode plate comprises a positive electrode current collector and a positive electrode material.

[0059] The positive electrode material is held by the positive electrode current collector. The positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector. Note that adhesive members such as conductive layers, mats, and pasting paper may be attached to the positive electrode plate. Since the adhesive members are used integrally with the positive electrode plate, they are included as components of the positive electrode plate. When the positive electrode plate includes adhesive members, the positive electrode material is the portion of the positive electrode plate excluding the positive electrode current collector and adhesive members.

[0060] 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. Processing methods may include, for example, expansion or punching. Using a grid-like current collector as the positive electrode current collector facilitates the support of the positive electrode material. The positive electrode current collector has a mesh structure.

[0061] As the lead alloy used for the positive electrode current collector, Pb-Ca alloys and Pb-Ca-Sn alloys, which have excellent corrosion resistance and mechanical strength, are preferred. The positive electrode current collector may have metal layers of different compositions, and the metal layers may be one layer or multiple layers. The positive electrode current collector has a surface layer, and the surface layer and the inner layers may have different compositions. The surface layer may be formed on a part of the positive electrode current collector. The surface layer may be formed only on the grid portion, only on the lug portion, or only on the frame portion of the positive electrode current collector.

[0062] (Positive electrode material) The positive electrode material includes a positive electrode active material that exhibits capacity through a redox reaction. The positive electrode active material includes lead dioxide, lead sulfate, etc. The positive electrode material may also include additives as needed. Additives may include reinforcing materials, antimony compounds, etc. Examples of reinforcing materials include inorganic fibers and organic fibers.

[0063] Unformed positive electrode plates are obtained by maturing and drying a positive electrode current collector and a positive electrode paste filled in the positive electrode current collector. The positive electrode paste is prepared by kneading a mixture containing lead powder, water, and sulfuric acid. The positive electrode paste may contain additives as needed. These additives may include reinforcing materials, antimony compounds, etc. Such positive electrode plates are also called paste-type positive electrode plates.

[0064] A positive electrode plate can be obtained by chemically treating an untreated positive electrode plate. Chemical treatment may 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 charging the electrode plate group. Chemical treatment may also be carried out before the assembly of the lead-acid battery or the electrode plate group.

[0065] The density of the positive electrode material is greater on its surface than in its interior. The density S in the overpaste portion of the positive electrode material that extends beyond the mesh of the positive electrode current collector is greater than the density T located inside the mesh of the positive electrode material. The density S is 4.1 g / cm³. 3 This concludes the explanation. As a result, depletion of the positive electrode active material under accelerated-assisted discharge conditions is suppressed, and a long lifespan can be maintained even under operating conditions in which charging and discharging are performed in charge-discharge cycles including accelerated-assisted discharge. The thickness of the overpaste portion is, for example, 0.04 mm or more and 0.4 mm or less, and may be 0.1 mm or more and 0.3 mm or less.

[0066] The density S of the positive electrode material is 4.1 g / cm³. 3 The above is 4.29 g / cm³. 3 (or 4.3 g / cm³) 3 (The above is preferable, and 4.42 cm) 3The above is more preferable. By setting the density S of the positive electrode material within this range, a long lifespan can be maintained under operating conditions in which accelerated-assisted discharge is performed. The density S of the positive electrode material is, for example, 4.8 g / cm³. 3 The following is also acceptable: In order to suppress the decrease in high-rate discharge duration in low-temperature environments, the density S of the positive electrode material should be 4.7 g / cm³. 3 The following or 4.6 g / cm³ 3 The following are preferable.

[0067] The density S of the positive electrode material is 4.1 g / cm³. 3 More than 4.8g / cm 3 The following (or 4.7 g / cm³) 3 below), 4.16g / cm 3 More than 4.8g / cm 3 The following (or 4.7 g / cm³) 3 ), 4.29g / cm 3 More than 4.8g / cm 3 The following (or 4.7 g / cm³) 3 ), 4.42g / cm 3 More than 4.8g / cm 3 The following (or 4.7 g / cm³) 3 below), 4.1g / cm 3 More than 4.6g / cm 3 Below, 4.16g / cm 3 More than 4.6g / cm 3 Below, 4.29g / cm 3 More than 4.6g / cm 3 Below, 4.42g / cm 3 More than 4.6g / cm 3 The following is also acceptable.

[0068] The density T of the positive electrode material is 4.42 g / cm³. 3 It may also be less than 4.16 g / cm³. 3 The following is also acceptable: 4.0 g / cm³ 3 The following or 3.95 g / cm³ 3 The following is also acceptable: The density T of the positive electrode material is 3.5 g / cm³. 3 It may be greater than or equal to 3.52 g / cm³. 3 It may be greater than or equal to 3.61 g / cm³. 3That's fine too.

[0069] The density T of the positive electrode material is 3.5 g / cm³. 3 (or 3.52 g / cm³) 3 or more)4.42g / cm 3 Below 3.5g / cm 3 (or 3.52 g / cm³) 3 or more)4.16g / cm 3 Below 3.5g / cm 3 (or 3.52 g / cm³) 3 or more)4.0g / cm 3 Below 3.5g / cm 3 (or 3.52 g / cm³) 3 or more)3.95g / cm 3 Below, 3.61g / cm 3 More than 4.42g / cm 3 Below, 3.61g / cm 3 More than 4.16g / cm 3 Below, 3.61g / cm 3 More than 4.0g / cm 3 Below, 3.61g / cm 3 More than 3.95g / cm 3 The following is also acceptable.

[0070] The ratio of density S to density T, S / T, may be between 1.04 and 1.26 (or 1.22), between 1.06 and 1.26 (or 1.22), or between 1.12 and 1.26 (or 1.22).

[0071] To increase the amount of positive electrode active material in the positive electrode plate, thereby suppressing the depletion of available positive electrode active material during accelerated-assisted discharge and maintaining high discharge performance even during accelerated-assisted discharge, the theoretical capacity of the positive electrode Cp may be made larger than the theoretical capacity of the negative electrode Cn. The ratio of Cn to Cp, X = Cn / Cp, may be less than 1, for example, 0.7 or more and less than 1.

[0072] The ratio X = Cn / Cp may be 0.7 or greater and less than 1 (or 0.95 or less), 0.78 or greater and less than 1 (or 0.95 or less), 0.85 or greater and less than 1 (or 0.95 or less), 0.8 or greater and less than 1 (or 0.95 or less), 0.7 or greater and 0.91 or less (or 0.9 or less), 0.78 or greater and 0.91 or less (or 0.9 or less), 0.8 or greater and 0.91 or less (or 0.9 or less), or 0.85 or greater and 0.91 or less (or 0.9 or less).

[0073] The theoretical capacity Cp of the positive electrode and the theoretical capacity Cn of the negative electrode are determined based on the mass M obtained by converting the active material contained in each electrode material to lead (Pb). The theoretical capacity Cp of the positive electrode and the theoretical capacity Cn of the negative electrode are calculated using the following formulas, where Mp is the mass of the positive electrode active material (PbO2) contained in the positive electrode material and Mn is the mass of the negative electrode active material (Pb) contained in the negative electrode material. (Theoretical capacity of positive electrode Cp [Ah]) = Mp [g / cell] / 4.463 [g / Ah] (Theoretical capacity of the negative electrode Cn [Ah]) = Mn [g / cell] / 3.866 [g / Ah]

[0074] The theoretical capacity Cp of the positive electrode and the theoretical capacity Cn of the negative electrode are measured in a fully charged battery at the beginning of use. If the cell has multiple positive or negative plates, Mp or Mn is the sum of the masses of the active material contained in each plate.

[0075] (Negative electrode plate) The negative electrode plate comprises a negative electrode current collector and a negative electrode material. The negative electrode material is held by the negative electrode current collector. The negative electrode material is the portion of the negative electrode plate excluding the negative electrode current collector. Note that adhesive members such as conductive layers, mats, and pasting paper may be attached to the negative electrode plate. The adhesive members are included as components of 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.

[0076] The negative electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. The processing method may be expansion or punching. Using a grid-like current collector as the negative electrode current collector makes it easier to support the negative electrode material.

[0077] The lead alloy used for the negative electrode current collector may be any of the following: Pb-Sb alloy, Pb-Ca alloy, or Pb-Ca-Sn alloy. The lead alloy used for the negative electrode current collector may also 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 metal layers of different compositions, and the metal layers may be one layer or multiple layers. The negative electrode current collector has a surface layer, and the surface layer and the inner layers of the negative electrode current collector may have different compositions. The surface layer may be formed on a part of the negative electrode current collector. The surface layer may be formed on the lug portion of the negative electrode current collector. The surface layer of the lug portion may contain Sn or a Sn alloy.

[0078] The negative electrode plate is obtained by chemically converting an unconverted negative electrode plate. The unconverted negative electrode plate is obtained by aging and drying a negative electrode current collector and a negative electrode paste filled in the negative electrode current collector. Cultivation is preferably carried out in an atmosphere with a temperature higher than room temperature and high humidity. The negative electrode paste is prepared by kneading a mixture containing lead or lead oxide powder, barium sulfate particles, water, and sulfuric acid.

[0079] The chemical treatment may be carried out by immersing the electrode plate group, including the untreated negative electrode plate, in the sulfuric acid-containing electrolyte in the lead-acid battery case and charging the electrode plate group. The chemical treatment may also be carried out before the assembly of the lead-acid battery or the electrode plate group. The negative electrode active material in the charged state contains spongy lead. Although the negative electrode active material in the charged state is spongy lead, the untreated negative electrode plate is usually made using lead powder.

[0080] The negative electrode material of the negative electrode plate after chemical formation contains a negative electrode active material that exhibits capacity through an oxidation-reduction reaction. The negative electrode active material includes lead, lead sulfate, etc. The negative electrode material may also contain at least one selected from the group consisting of organic shrinkage inhibitors, carbonaceous materials, and other additives. Examples of additives include, but are not limited to, barium sulfate and fibers (such as resin fibers).

[0081] (Organic shrinkage inhibitor) Organic shrinkage inhibitors are organic compounds that have the function of suppressing the shrinkage of lead, the negative electrode active material, when lead-acid batteries are repeatedly charged and discharged. Organic shrinkage inhibitors are generally broadly classified into lignin compounds and synthetic organic shrinkage inhibitors. Synthetic organic shrinkage inhibitors can also be said to be organic shrinkage inhibitors other than lignin compounds. Examples of organic shrinkage inhibitors contained in negative electrode materials include lignin compounds and synthetic organic shrinkage inhibitors. The negative electrode material may contain one type of organic shrinkage inhibitor, or two or more types.

[0082] Examples of lignin compounds include lignin and lignin derivatives. Examples of lignin derivatives include lignin sulfonic acid or its salts (such as alkali metal salts (sodium salts)).

[0083] Synthetic organic shrinkage inhibitors are, for example, organic polymers containing sulfur, and generally contain multiple aromatic rings within the molecule, as well as sulfur as a sulfur-containing group. Among sulfur-containing groups, stable forms such as sulfonic acid groups or sulfonyl groups are preferred. Sulfonic acid groups may exist in acid form or in salt form, such as a sodium salt.

[0084] The synthetic organic shrinkage inhibitor may be a condensate containing aromatic compound units, for example, a formaldehyde condensate of a phenol compound.

[0085] Organic shrinkage inhibitors may be used individually or in combination of two or more. From the viewpoint of further reducing self-discharge, at least a lignin compound may be used as the organic shrinkage inhibitor.

[0086] The content of the organic shrinkage inhibitor in the negative electrode material is, for example, 0.005% by mass or more, and may be 0.01% by mass or more, or 0.1% by mass or more. When the content of the organic shrinkage inhibitor is within this range, higher low-temperature HR discharge performance is easily obtained. The content of the organic shrinkage inhibitor is, for example, 1.0% by mass or less, and may be 0.5% by mass or less.

[0087] (carbonaceous material) As carbonaceous materials, carbon black, graphite, hard carbon, soft carbon, etc., can be used. Examples of carbon black include acetylene black, furnace black, and lamp black. Furnace black also includes Ketjenblack (trade name). Graphite can be any carbonaceous material containing a graphite-type crystal structure, and may be either artificial graphite or natural graphite. Carbonaceous materials may be used individually or in combination of two or more.

[0088] The carbonaceous material content in the negative electrode material is, for example, 0.1% by mass or more and 3% by mass or less. From the viewpoint of reducing self-discharge, the carbonaceous material content in the negative electrode material may be 1.2% by mass or less.

[0089] (Separator) Lead-acid batteries typically include a separator between the negative and positive electrodes. The separator is made of nonwoven fabric. Nonwoven fabric is a mat in which fibers are intertwined without weaving, and is primarily composed of fibers. For example, the nonwoven fabric is formed of fibers by 60% or more by mass. The nonwoven fabric may also contain components other than fibers, such as acid-resistant inorganic powders (e.g., silica powder, glass powder, diatomaceous earth) and polymers as binders.

[0090] As for the fibers, glass fibers, organic fibers, etc., can be used. As for organic fibers, fiber materials that are insoluble in the electrolyte are used. Examples of organic fibers include polymer fibers (polyolefin fibers, acrylic fibers, polyester fibers (polyethylene terephthalate fibers, etc.)), pulp fibers, etc.

[0091] The nonwoven fabric preferably contains at least glass fibers. A nonwoven fabric containing glass fibers is also called an AGM (Absorbed Glass Mat) separator. The nonwoven fabric may contain both glass fibers and organic fibers. The proportion of glass fibers in the total fibers constituting the nonwoven fabric is preferably 60% by mass or more.

[0092] The separator may consist solely of nonwoven fabric. The separator may also be a laminate of nonwoven fabric and a microporous membrane, a nonwoven fabric bonded to a different or similar material, or a nonwoven fabric bonded to a different or similar material with interlocking protrusions and indentations, as needed.

[0093] A microporous membrane is a porous sheet mainly composed of materials other than fibrous components. For example, it can be obtained by extruding a composition containing a pore-forming agent into a sheet, and then removing the pore-forming agent to form pores. Microporous membranes are preferably made of acid-resistant materials, and microporous membranes mainly composed of polymer components are preferred. As the polymer component, polyolefins (polyethylene, polypropylene, etc.) are preferred. As the pore-forming agent, at least one selected from the group consisting of polymer powders and oils can be used.

[0094] The thickness of the separator placed between the negative and positive electrodes should be selected according to the distance between the electrodes. The number of separators should be selected according to the number of electrodes.

[0095] (electrolyte) The electrolyte is an aqueous solution containing sulfuric acid, and may be gelled if necessary. The electrolyte may contain the above-mentioned polymer compounds.

[0096] The electrolyte may optionally contain cations (e.g., metal cations) and / or anions (e.g., anions other than sulfate anions, such as phosphate ions). Examples of metal cations include at least one selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions.

[0097] The specific gravity of the electrolyte in a fully charged lead-acid battery at 20°C is, for example, 1.20 or higher, and may be 1.25 or higher. The specific gravity of the electrolyte at 20°C is 1.35 or lower, and preferably 1.32 or lower.

[0098] The specific gravity of the electrolyte at 20°C may be 1.20 or more and 1.35 or less, 1.20 or more and 1.32 or less, 1.25 or more and 1.35 or less, or 1.25 or more and 1.32 or less.

[0099] (others) A lead-acid battery can be obtained 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 the lead-acid battery comprises a group of electrodes and an electrolyte housed in each cell chamber. Prior to housing the electrode group in the cell chamber, the electrode group is assembled by stacking a positive electrode, a negative electrode, and a separator, with the separator interposed between the positive and negative electrodes. The positive electrode, negative electrode, electrolyte, and separator are each prepared prior to the assembly of the electrode group. After housing the electrode group and the electrolyte in the cell chamber, the manufacturing method of the lead-acid battery may optionally include a step of chemically transforming at least one of the positive electrode and the negative electrode.

[0100] Each electrode in a group of electrodes contained in a single cell may consist of one or two or more electrodes. When a group of electrodes in a single cell comprises two or more positive electrodes, at least one positive electrode must have a density S of the positive electrode material (density of the overpaste portion on the surface facing the negative electrode) of 4.1 g / cm³. 3The above is sufficient, and the density S should be greater than the density T of the positive electrode material inside the positive electrode plate. In this case, the depletion of the positive electrode active material in accelerated-assisted discharge is suppressed, and the effect of maintaining a long lifespan even in charge-discharge cycles including accelerated-assisted discharge is obtained. From the viewpoint of achieving an even longer lifespan in charge-discharge cycles including accelerated-assisted discharge, the density S should be 4.1 g / cm³ in 50% or more (more preferably 80% or more or 90% or more) of the number of positive electrode plates in the electrode plate group contained in one cell. 3 Preferably, the density S is greater than T. All positive electrodes in the electrode plate group contained within a single cell have a density S of 4.1 g / cm³. 3 The above conditions may be greater than or equal to the density T.

[0101] If a lead-acid battery has two or more cells, it is sufficient that the positive and negative plates included in the plate group within at least one cell satisfy the above relationship. From the viewpoint of achieving a longer lifespan in charge-discharge cycles including accelerated discharge, it is preferable that the positive and negative plates included in the plate group satisfy the above relationship in 50% or more (more preferably 80% or more or 90% or more) of the number of cells in the lead-acid battery. The ratio of cells in the lead-acid battery in which the positive and negative plates included in the plate group satisfy the above relationship is 100% or less. It is more preferable that the positive and negative plates included in the plate group satisfy the above relationship in all cells in the lead-acid battery.

[0102] [Evaluation Method] (1) Accelerated discharge performance A fully charged test battery is subjected to multiple cycles, with each cycle consisting of (a) and (b) below. However, the temperature conditions are changed every 1000 cycles, and (A) and (B) below are repeated.

[0103] (a) Discharge: Discharge for 0.2 seconds at a current (A) 30 times the Ah value indicated in the rated capacity. (b) Charging: Charge for 50 seconds at a constant voltage of 14.5V (2.42V / cell) (however, the maximum current is 5.4A).

[0104] (A): Place the test battery in an environment with temperature T (room temperature: 40-50°C), and repeat steps (a) and (b) above for 1000 cycles, with each cycle being considered one cycle. (B): After (A), place the test battery in an environment with a temperature of T-40°C, and repeat (a) and (b) above for 1000 cycles, with each cycle being considered one cycle. Then, return to (A) and repeat the cycle.

[0105] During the discharge described in (a) above, the test is terminated when the terminal voltage falls below 1.0V / cell, indicating that the battery has reached the end of its lifespan.

[0106] (2) Low temperature HR discharge performance In accordance with the cold cranking current (CCA) test described in JIS D 5302:2022, the device is discharged for 30 seconds at -18°C ± 1°C using the rated cold cranking current, and the terminal voltage after discharge (voltage at 30 seconds of low-temperature HR discharge) (V) is determined. The low-temperature HR discharge performance is evaluated based on this low-temperature HR discharge voltage at 30 seconds.

[0107] Figure 1 is a schematic cross-sectional view showing the structure of an example of a valve-regulated lead-acid battery. In Figure 1, the lead-acid battery 1 comprises a battery case 10 that houses an electrode plate group 11 and an electrolyte (not shown). The upper opening of the battery case 10 is closed with a lid 12. The electrode plate group 11 is composed of multiple negative electrode plates 2 and positive electrode plates 3 stacked with separators 4 in between.

[0108] In the positive electrode plate 3, the density S of the positive electrode material in the overpaste portion is greater than the density T of the positive electrode material inside the positive electrode plate, which is 4.1 g / cm³. 3 That's all.

[0109] Each of the multiple negative electrode plates 2 has an upward-projecting current-collecting tab (not shown) on its upper part. Each of the multiple positive electrode plates 3 also has an upward-projecting current-collecting tab (not shown) on its upper part. The tabs of the negative electrode plates 2 are connected and integrated by negative electrode straps (not shown). Similarly, the tabs of the positive electrode plates 3 are connected and integrated by positive electrode straps (not shown). The negative electrode straps are connected to negative electrode posts (not shown) which serve as external terminals, and the positive electrode straps are connected to positive electrode posts (not shown) which serve as external terminals.

[0110] The battery case 10 is divided into multiple (three in the illustrated example) independent cell chambers 10R, and one electrode plate group 11 is housed in each cell chamber 10R. The lid 12 is equipped with an independent exhaust valve 13 for each cell chamber 10R. When the internal pressure of a cell chamber 10R exceeds a predetermined upper limit, the exhaust valve 13 opens, and gas is directly released from the cell chamber 10R to the outside. When the internal pressure of a cell chamber 10R is below the upper limit, the oxygen generated on the positive electrode plate 3 is reduced on the negative electrode plate 2 in the same cell chamber 10R to produce water.

[0111] The structure of a valve-regulated lead-acid battery is not limited to the above. For example, although Figure 1 shows a case with individual cell exhaust, a single exhaust type may also exist in which the lid has a central exhaust chamber that communicates with each cell chamber, and the central exhaust chamber has fewer exhaust valves than the number of cell chambers (for example, one).

[0112] Figure 2 shows an example of a charge / discharge control system configured to drive a small mobility device using the valve-regulated lead-acid battery 1 shown in Figure 1. Figure 2 is a block diagram showing an example of a schematic configuration of the charge / discharge control system 100.

[0113] The charge / discharge control system 100 comprises a valve-regulated lead-acid battery 1, a small mobility device 110 that receives power from the lead-acid battery 1, and a control unit 120. The control unit 120 controls the charging and discharging of the lead-acid battery 1, as well as the driving of the engine 112 and the motor 114.

[0114] The small mobility vehicle 110 is equipped with an engine 112 and a motor 114. The engine 112 and the motor 114 are each coupled to the axle (drive shaft) 116 of the small mobility vehicle, and the power necessary for driving is supplied from the lead-acid battery 1. Tires (not shown) are attached to the axle 116. When the small mobility vehicle 110 is in motion, the axle rotates due to the drive of the engine 112 and / or the motor 114, and the tires attached to the axle rotate.

[0115] The lead-acid battery 1 is controlled by the control unit 120 so that its charge and discharge cycle is controlled by a charge-discharge cycle comprising a first discharge step in which it discharges with a first discharge current I1, a second discharge step in which it discharges with a second discharge current I2 that is greater than the first discharge current I1, and a charge step. The first discharge step is, for example, the step of starting the engine 112. The second discharge step is, for example, the step of driving the motor 114.

[0116] In the first discharge process, the control unit 120 controls the discharge of the lead-acid battery 1 based on the first discharge current I1. The first discharge current I1 is supplied to the engine 112, which drives the starter motor attached to the engine 112. This starts the engine 112 and starts the small mobility device 110 from running. The first discharge current I1 at this time is usually 10CA (10 times the current (A) value, which is the numerical value in Ah as indicated on the rated capacity of the lead-acid battery 1).

[0117] In the second discharge process, the control unit 120 controls the discharge of the lead-acid battery 1 based on the second discharge current I2. The second discharge current I2 is supplied to the motor 114, driving the motor 114. This causes the small mobility device 110 to accelerate. The second discharge current I2 at this time may be 20CA or more (20 times the current (A) value, expressed in Ah as the unit of the rated capacity of the lead-acid battery 1).

[0118] Once the small mobility device 110 has completed its acceleration and is moving at a constant speed, the lead-acid battery 1 is charged using the rotation of the engine 112. At this time, the regenerative force of the motor 114 may also be used to charge the lead-acid battery.

[0119] [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.

[0120] 《Lead acid batteries E1, E2, C1~C6》 (1) Fabrication of the negative electrode plate A negative electrode paste was prepared by mixing lead powder, an organic shrinkage inhibitor, a carbonaceous material (carbon black), and barium sulfate with an appropriate amount of sulfuric acid aqueous solution. The negative electrode paste was filled into the mesh of an expanded grid made of Pb-Ca-Sn alloy, and aged and dried to obtain an unformed negative electrode plate.

[0121] (2) Fabrication of the positive electrode plate Lead powder was mixed with an aqueous sulfuric acid solution to prepare a first positive electrode paste. The first positive electrode paste was filled into the mesh of an expanded grid made of Pb-Ca-Sn alloy.

[0122] A second positive electrode paste was prepared by mixing lead powder with an aqueous sulfuric acid solution. The second positive electrode paste was filled to cover the first positive electrode paste and the exposed bone structure of the expanded grid, forming an overpaste portion. The positive electrode plate after the overpaste portion was formed was aged and dried to obtain an unformed positive electrode plate. The thickness of the overpaste portion of the positive electrode material was 0.3 mm on each side of the positive electrode after formation.

[0123] Furthermore, for lead-acid batteries fully charged after chemical conversion, the concentration and amount of sulfuric acid aqueous solution used in the preparation of the first and second positive electrode pastes were adjusted so that the densities S and T of the positive electrode material, determined by the procedure described above, were the values ​​shown in Table 1.

[0124] (3) Manufacturing of lead-acid batteries Three positive plates and four negative plates were alternately stacked with separators in between to form an electrode plate group. The electrode plate group was housed in a polypropylene battery case along with an electrolyte (sulfuric acid aqueous solution) and sealed with a lid. A fine glass mat was used as the separator. A valve-regulated lead-acid battery was fabricated by chemical conversion of the electrode plate group within the battery case. The chemical conversion brought the lead-acid battery to a fully charged state. The specific gravity of the electrolyte in the fully charged lead-acid battery at 20°C was set to 1.32. The lead-acid battery has a rated voltage of 12V and a rated 10-hour rate capacity of 5Ah. In this lead-acid battery, the rated capacity is generally determined by the amount of sulfuric acid in the electrolyte, as long as neither the theoretical negative electrode capacity Cn nor the theoretical positive electrode capacity Cp is extremely small. Cn and Cp were adjusted to a range where Cp was 16Ah or more and Cn was 11Ah or more.

[0125] In this manner, several lead-acid batteries E1, E2, and C1-C6 were created with different densities S in the overpaste portion of the positive electrode material on the positive electrode plate, and / or densities T located inside the mesh portion of the positive electrode current collector. The accelerated-assisted discharge performance was evaluated using the method described above. The evaluation results are shown in Table 1. In Table 1, E1 and E2 are examples, and C1-C6 are comparative examples. In Table 1, the accelerated-assisted discharge performance is shown as a relative value with the result of lead-acid battery C6 set to 100. For lead-acid batteries E1, E2, and C1-C6, the density T was 4.42 g / cm³. 3 The density was kept constant, and only the density S was changed.

[0126] [Table 1]

[0127] Table 1 shows that the higher the density S in the overpaste portion of the positive electrode material, the better the acceleration-assisted discharge performance. For a density S of 4.1 g / cm³, the performance improves. 3 The lead-acid batteries E1, E2, and C4-C6 described above have significantly superior acceleration-assisted discharge performance compared to C1-C3.

[0128] 《Lead-acid batteries E3~E6, C7~C10》 For lead-acid batteries fully charged after chemical conversion, the concentration and amount of sulfuric acid aqueous solution used in the preparation of the first and second positive electrode pastes were adjusted so that the densities S and T of the positive electrode material, determined by the procedure described above, were the values ​​shown in Table 2.

[0129] Other than the above, the same procedure as for lead-acid battery C6 was followed. Multiple lead-acid batteries E3-E6 and C7-C10 with different densities S and / or T were created, and their accelerated-assisted discharge performance and low-temperature HR discharge performance were evaluated using the method described above. The evaluation results are shown in Table 2, along with the results for lead-acid batteries C3 and C6 shown in Table 1. In Table 2, E3-E6 are examples, and C7-C10 are comparative examples. In Table 2, the accelerated-assisted discharge performance and low-temperature HR discharge performance are shown as relative values ​​with the result for lead-acid battery C6 set to 100.

[0130] [Table 2]

[0131] Tables 1 and 2 show that the acceleration-assisted discharge performance improves as the density S in the overpaste portion of the positive electrode material increases, and as the density T located inside the mesh portion of the positive electrode current collector increases. However, the improvement in acceleration-assisted discharge performance is more pronounced when density S is increased than when density T is increased.

[0132] On the other hand, as shown in Table 2, there is a tendency for low-temperature HR discharge performance to decrease as density S increases. One possible reason for this is that as the density of the positive electrode material increases, the space available to hold the electrolyte (sulfate ions) within the positive electrode plate decreases, making it more difficult for the electrolyte to diffuse. However, as shown in Table 2, low-temperature HR discharge performance can be improved by reducing density T.

[0133] Therefore, by making density S larger than density T and the ratio S / T smaller than 1, it is possible to suppress the decrease in low-temperature HR discharge performance while maintaining high accelerated assist discharge performance. The density S in the overpasted portion of the positive electrode material is 4.1 g / cm 3 or more. In lead-acid batteries E1 to E6 in which density S is made larger than density T, the decrease in low-temperature HR discharge performance can be suppressed while maintaining high accelerated assist discharge performance.

Industrial Applicability

[0134] The control valve type lead-acid battery is suitable for small mobility, IS vehicle applications, industrial batteries, etc. These applications are merely examples and are not limited to these applications.

Explanation of Symbols

[0135] 1: Control valve type lead-acid battery [[ID=十七]] 2: Negative electrode plate 3: Positive electrode plate 31: Positive electrode current collector 31A: Bone part 32: Positive electrode material 4: Separator 11: Electrode plate group 10: Battery case 10R: Cell chamber 12: Cover 13: Exhaust valve 100: Charge / discharge control system 110: Small mobility 112: Engine 114: Motor 120: Control unit

Claims

1. A valve-regulated lead-acid battery, The device comprises at least one cell having a positive electrode plate, a negative electrode plate, and an electrolyte, The positive electrode plate comprises a positive electrode current collector having a mesh portion and a positive electrode material supported on the positive electrode current collector. In the thickness direction of the positive electrode plate, the density S in the overpaste portion of the positive electrode material that protrudes from the mesh portion of the positive electrode current collector is greater than the density T located inside the mesh portion of the positive electrode material of the positive electrode current collector, and is 4.1 g / cm³. ３ That's all. Lead-acid batteries used in small mobility vehicles.

2. The density S of the positive electrode material is 4.42 g / cm³. ３ The lead-acid battery according to claim 1.

3. The density T of the positive electrode material is 4.16 g / cm³. ３ The lead-acid battery according to claim 1, which is as follows:

4. The lead-acid battery according to claim 1, wherein the ratio S / T of density S to density T is 1.06 or more.

5. A valve-regulated lead-acid battery, A small mobility device that receives power from the aforementioned lead-acid battery, The system comprises a control unit for controlling the charging and discharging of the lead-acid battery, The aforementioned small mobility device is equipped with an engine and motor coupled to the axle, The aforementioned lead-acid battery is The device comprises at least one cell having a positive electrode plate, a negative electrode plate, and an electrolyte, The positive electrode plate comprises a positive electrode current collector having a mesh portion and a positive electrode material supported on the positive electrode current collector. In the thickness direction of the positive electrode plate, the density S in the overpaste portion of the positive electrode material that protrudes from the mesh portion of the positive electrode current collector is greater than the density T located inside the mesh portion of the positive electrode material of the positive electrode current collector, and is 4.1 g / cm³. ３ That's all. The control unit is a charge / discharge control system that starts the engine based on a first discharge current supplied from the lead-acid battery, and then drives the motor based on a second discharge current that is greater than the first discharge current supplied from the lead-acid battery.

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