Lead-acid battery

Abstract

A lead-acid battery 1 according to the present disclosure comprises a positive electrode plate 2P. The positive electrode plate 2P comprises a positive electrode material 33P. The positive electrode material 33P contains short fibers 40 formed from a polymer. The short fibers 40 have a monomer molecular weight M of 42 or more, and the degree of polymerization Gn calculated from the number average molecular weight (Mn) by the formula indicated below is 1040 or less. The content of the short fibers 40 in the positive electrode material 33P is more than 0.01 mass%. Formula: Gn = Mn / M (Gn denotes the degree of polymerization, Mn denotes the number average molecular weight, and M denotes the monomer molecular weight).

Description

lead acid battery

[0001] The present disclosure relates to lead-acid batteries.

[0002] It has been known to use short fibers as a reinforcing material for preventing the softening and shedding of active materials in lead-acid batteries. For example, the short fibers described in International Publication No. 2016 / 158753 (Patent Document 1) are known. Patent Document 1 discloses the use of acrylonitrile-based fibers containing a hydrophilic component as short fibers for electrodes, which have excellent acid resistance and are less susceptible to decomposition even after prolonged use.

[0003] International Publication No. 2016 / 158753

[0004] In Patent Document 1, the objective is to improve the acid resistance of acrylonitrile fibers by using a hydrophilic component. However, the type of monomer is not limited to a monomer having a hydrophilic component, and it is preferable that other monomers can also be used.

[0005] The lead-acid battery according to the present disclosure includes a positive electrode plate, the positive electrode plate including a positive electrode material containing short fibers formed of a polymer, the short fibers having a monomer molecular weight M of 42 or more and a degree of polymerization Gn calculated from the number average molecular weight (Mn) according to the following formula of 1040 or less, and the content of the short fibers in the positive electrode material is greater than 0.01 mass%: Gn = Mn / M (Gn: degree of polymerization, Mn: number average molecular weight, M: monomer molecular weight).

[0006] According to the present disclosure, the high-temperature overcharge life performance of a lead-acid battery can be improved.

[0007] FIG. 1 is a partially cutaway perspective view showing the appearance and internal structure of a lead-acid battery according to an embodiment of the present disclosure. FIG. 2 is a diagram showing a cross section of an electrode plate according to an embodiment of the present disclosure. FIG. 3 is a diagram schematically illustrating repeated charge and discharge in an electrode plate not included in an embodiment of the present disclosure when short fibers are not contained in the positive electrode material. FIG. 4 is a diagram schematically illustrating repeated charge and discharge in an electrode plate according to an embodiment of the present disclosure when short fibers are contained in the positive electrode material. FIG. 5 is a graph showing the correlation between Gn (degree of polymerization of number average molecular weight) and life performance. FIG. 6 is a graph showing the correlation between content and capacity performance. FIG. 7 is a graph showing the correlation between content and life performance. FIG. 8 is a graph showing the correlation between fiber diameter and life performance. FIG. 9 is a graph showing the correlation between fiber length and life performance. FIG. 10 is a graph showing the correlation between monomer molecular weight and life performance. FIG. 11 is a table showing the results of GPC measurement. FIG. 12 is a table showing the results of capacity performance and life performance for each fiber condition. Fig. 13 is a graph showing the correlation between pore volume and life performance, Fig. 14 is a graph showing the correlation between content and life performance, and Fig. 15 is a table showing the results of life performance relative to content and pore volume.

[0008] (Summary of the Present Embodiment) (1) A lead-acid battery according to the present disclosure includes a positive electrode plate, the positive electrode plate including a positive electrode material, the positive electrode material including short fibers formed of a polymer, the short fibers having a monomer molecular weight M of 42 or more and a degree of polymerization Gn calculated from the number average molecular weight (Mn) by the following formula of 1040 or less, the content of the short fibers in the positive electrode material being greater than 0.01% by mass: Gn = Mn / M (Gn: degree of polymerization, Mn: number average molecular weight, M: monomer molecular weight).

[0009] Short fibers are known to function as a reinforcing material for positive electrode materials. According to the lead-acid battery disclosed herein, by setting the degree of polymerization (Gn) of the short fibers to 1040 or less and increasing the short fiber content to more than 0.01% by mass, the life performance of the lead-acid battery can be improved compared to conventional batteries. The mechanism is as follows: By setting the degree of polymerization to 1040 or less, a structure with fewer repeating monomers is obtained, thereby reducing the number of sites where polymerization reactions have occurred. As a result, polarization at the positive electrode is less likely to occur even with repeated charge and discharge, and the short fibers remain in the positive electrode material even at the end of its life, so they continue to function as a reinforcing material for a long time, which is thought to suppress softening and shedding for a long period of time.

[0010] (2) In the lead-acid battery according to (1), the content of short fibers in the positive electrode material may be less than 0.5% by mass.

[0011] When the short fiber content is 0.01% by mass or less, the short fibers cannot fully function as a reinforcing material that anchors the positive electrode active material to the grid of the positive electrode current collector. On the other hand, according to the lead-acid battery described in (2) above, when the short fiber content is less than 0.5% by mass, the positive electrode active material is believed to be anchored to the grid of the positive electrode current collector, and the short fibers can effectively function as a reinforcing material. Therefore, the softening and shedding of the positive electrode active material can be suppressed for a long period of time, improving the life performance in life tests of lead-acid batteries. Note that when the short fiber content is 0.5% by mass or more, the effect of anchoring the positive electrode active material to the grid of the positive electrode current collector remains unchanged, but if the short fiber content is too high, the capacity of the positive electrode active material may decrease relatively, resulting in a risk of overall reduced capacity performance.

[0012] (3) In the lead-acid battery according to (1) or (2), the monomer molecular weight: M may be 180 or more, and the content of short fibers in the positive electrode material may be 0.02 mass% or more and 0.3 mass% or less.

[0013] When the monomer molecular weight: M is 180 or more, if the short fiber content is less than 0.02 mass%, the life performance may decrease, and if the short fiber content is more than 0.3 mass%, the capacity performance may decrease. According to the lead-acid battery described in (3) above, the short fiber content is 0.02 mass% or more and 0.3 mass% or less, so that it is easy to achieve both life performance and capacity performance.

[0014] (4) In the lead-acid battery according to any one of (1) to (3), the short fibers may have a fiber diameter of 0.5 dtex or more and 3.5 dtex or less.

[0015] According to the lead-acid battery described in (4) above, when the fiber diameter of the short fibers is within the range of 0.5 dtex to 3.5 dtex, it is easy to ensure the life performance.

[0016] (5) In the lead-acid battery according to any one of (1) to (4), the short fibers may have a fiber length of 2 mm or more and 6 mm or less.

[0017] According to the lead-acid battery described in (5) above, when the fiber length of the short fibers is in the range of 2 mm to 6 mm, the life performance can be easily ensured.

[0018] (6) In the lead-acid battery according to any one of (1) to (5), a ratio V1 / V0 of a pore volume V1 of the positive electrode material having a pore diameter of 1 μm or more and 10 μm or less to a total pore volume V0 of the positive electrode material may be 0.01 or more and 0.80 or less.

[0019] According to the lead-acid battery described in (6) above, when V1 / V0, which is the ratio of the pore volume V1 to the total pore volume V0, is in the range of 0.01 to 0.80, the life performance is easily ensured.

[0020] <Embodiments> Embodiments of the present disclosure will be described with reference to Figures 1 to 15. The present disclosure is not limited to the embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0021] (Overall Configuration of Lead Acid Battery) The lead acid battery 1 is for use in a vehicle such as an automobile, and is installed, for example, in the engine compartment or luggage space of the vehicle to supply power to an engine starting device and various vehicle loads. The lead acid battery may be either a valve-regulated (sealed) lead acid battery (VRLA type lead acid battery) or a flooded (vented) lead acid battery.

[0022] FIG. 1 shows the external appearance of an example of a lead-acid battery 1 according to an embodiment of the present disclosure. The lead-acid battery 1 includes a battery case 12 and a lid 15 having a pair of terminals 16N, 17P. The battery case 12 contains an electrode plate pack 11 and an electrolyte (not shown). The battery case 12 has four outer walls and a bottom wall, and is box-shaped with an open top. The opening of the battery case 12 is closed by a lid 15 equipped with a negative electrode terminal 16N and a positive electrode terminal 17P. When rehydrating, a vent plug 18 on the lid 15 is removed and rehydration solution is added. The vent plug 18 may have the function of venting gas generated in the cell chamber 14 to the outside of the battery.

[0023] The electrolyte contains sulfuric acid. Charging and discharging proceed as sulfate ions move between the electrolyte and the positive and negative electrode plates 2P and 3N. During discharging, sulfate ions move to the positive and negative electrode plates 2P and 3N, decreasing the density of the electrolyte. During charging, sulfate ions move from the positive and negative electrode plates 2P and 3N into the electrolyte, increasing the density of the electrolyte.

[0024] In the following description, the direction in which the terminals 16N and 17P are arranged is referred to as the Z direction, the direction perpendicular to the direction in which the terminals 16N and 17P are arranged is referred to as the X direction, and the height direction (vertical direction) of the battery case 12 is referred to as the Y direction.

[0025] The battery case 12 is made of synthetic resin. The interior of the battery case 12 is divided into a plurality of cell chambers 14 by partition walls 13. Six cell chambers 14 are provided in the width direction of the battery case 12 (Z direction in FIG. 1 ), and each cell chamber 14 contains one electrode plate group 11 together with a flowable electrolyte (not shown).

[0026] Each electrode plate assembly 11 includes a plurality of negative electrode plates 3N, a plurality of positive electrode plates 2P, and a plurality of separators 4 separating adjacent electrode plates 2P, 3N. The separators 4 are stacked in the arrangement direction (Z direction) of the cell chambers 14. The separators 4 are made of an electrically insulating material. The separators 4 may be made of a microporous polyolefin sheet. Of the electrode plate assembly 11, the negative electrode plates 3N are housed inside the separators 4. The negative electrode plates 3N and positive electrode plates 2P housed inside the separators 4 are arranged alternately.

[0027] In the cell chamber 14 located at one end of the battery case 12, a negative electrode shelf 6N that connects multiple negative electrode plates 3N in parallel is connected to the feedthrough connector 8. A positive electrode shelf 5P that connects multiple positive electrode plates 2P in parallel is connected to a positive electrode pole 7P. The positive electrode pole 7P is connected to a positive electrode terminal 17P outside the lid 15.

[0028] In the cell chamber 14 located at the other end of the battery case 12, a negative electrode pole 9N is connected to the negative electrode shelf 6N. A feedthrough connector 8 is connected to the positive electrode shelf 5P. The negative electrode pole 9N is connected to a negative electrode terminal 16N outside the lid 15.

[0029] Each of the through-connectors 8 passes through a through-hole provided in the partition wall 13 to connect in series the electrode plate assemblies 11 of adjacent cell chambers 14. The lid 15 and the battery case 12 are molded from resin.

[0030] (Electrode Plate) The negative electrode plate 3N of the lead-acid battery 1 includes a negative electrode current collector (not shown) and a negative electrode material (not shown). The negative electrode material is held by the negative electrode current collector. The negative electrode plate 3N may further include an adhesive member.

[0031] The negative electrode current collector may be formed by casting lead (Pb) or a lead alloy. Alternatively, the negative electrode current collector may be formed by processing a lead sheet or a lead alloy sheet. For example, processing methods include expanding and punching. When a lattice-shaped current collector is used as the negative electrode current collector, it is easy to support the negative electrode material.

[0032] FIG. 2 shows a cross section of a positive electrode plate 2P. The positive electrode plate 2P of the lead-acid battery 1 includes a positive electrode current collector 30P and a positive electrode material 33P. The positive electrode plate 2P may further include an adhesive member. The positive electrode material 33P further includes a positive electrode active material 50 (specifically, lead dioxide 52 or lead sulfate 64). The positive electrode material 33P includes short fibers 40, which are synthetic fibers formed from a polymer. The short fibers 40 function as a reinforcing material. The positive electrode material 33P may further include an antimony compound or a reinforcing material other than the short fibers 40, as necessary.

[0033] The positive electrode material 33P is held by a positive electrode current collector 30P. The positive electrode current collector 30P is formed in a substantially lattice or mesh shape. The positive electrode current collector 30P may be formed by processing a lead sheet or a lead alloy sheet. For example, processing methods include expanding and punching. Using a lattice-shaped current collector as the positive electrode current collector 30P makes it easier to support the positive electrode material 33P.

[0034] The positive electrode current collector 30P is made of a lead alloy. In terms of corrosion resistance and mechanical strength, the lead alloy used for the positive electrode current collector 30P is preferably a Pb—Sb alloy, a Pb—Ca alloy, or a Pb—Ca—Sn alloy.

[0035] (Short Fiber) The short fiber 40 of the present disclosure is included in the positive electrode material 33P as a reinforcing material. The short fiber 40 is formed from a polymer in which a certain number of monomers are polymerized. For example, the short fiber 40 may be made of synthetic fibers such as polyolefin fiber, polyester fiber, or acrylic fiber. Examples of polyolefin fiber include polyethylene fiber and polypropylene fiber. Examples of polyester fiber include polyethylene terephthalate fiber and polyarylate fiber. The short fiber 40 of the present disclosure has a monomer molecular weight (M) of 42 or more and a degree of polymerization of 1040 or less, calculated from the number average molecular weight (Mn) using the formula: Gn = Mn / M (Gn: degree of polymerization, Mn: number average molecular weight, M: monomer molecular weight). The degree of polymerization Gn may be 900 or less, 800 or less, 600 or less, or 200 or less. The monomer molecular weight may be 180 or more or 210 or less. The content of the short fibers 40 in the positive electrode material 33P (the proportion of the mass of the short fibers 40 based on the mass of the positive electrode material 33P) is greater than 0.01 mass%, and may be 0.02 mass% or greater, or 0.03 mass% or greater. The content of the short fibers 40 in the positive electrode material 33P is, for example, less than 0.5 mass% but may be 0.3 mass% or less. The fiber diameter of the short fibers 40 is 0.5 dtex or greater and 3.5 dtex or less. The lower limit of the fiber diameter may be 0.3 dtex or 1 dtex. The upper limit of the fiber diameter may be 3 dtex or 4 dtex. The fiber length of the short fibers 40 is 2 mm or greater and 6 mm or less. The lower limit of the fiber length may be 1 mm or 3 mm. The upper limit of the fiber length may be 5 mm or 7 mm. The mass of the positive electrode material 33P is the mass of the positive electrode material 33P contained in any one positive electrode plate 2P, and the content of short fibers 40 is the ratio of the mass of the short fibers 40 based on the mass of the positive electrode material 33P contained in any one positive electrode plate 2P.

[0036] An unformed paste-type positive electrode plate is obtained by filling a positive electrode current collector with a positive electrode paste, aging it, and drying it. The positive electrode paste is prepared by adding water and sulfuric acid to lead powder, an antimony compound, and optionally other additives such as a reinforcing material and a carbonaceous material, and kneading them.

[0037] A positive electrode plate can be obtained by chemically forming an unformed positive electrode plate. Chemical formation can be performed by immersing an electrode plate assembly including the unformed positive electrode plate in an electrolyte containing sulfuric acid in a battery container of a lead-acid battery and then charging the electrode plate assembly. However, chemical formation may also be performed before assembling the lead-acid battery or the electrode plate assembly.

[0038] FIG. 3 is a schematic diagram illustrating the state of a lead-acid battery 1 in which the positive electrode material 33P does not contain short fibers 40 after repeated charge and discharge. During discharge of the positive electrode, lead dioxide 52 reacts with sulfuric acid in the electrolyte to produce lead sulfate 64. Because the reacted lead sulfate 64 has a larger volume than lead dioxide 52, the plate expands. During charge, lead sulfate 64 reacts with water in the electrolyte to form lead dioxide 52, which has a smaller volume than lead sulfate 64, causing the plate to shrink. The lead-acid battery 1 of the present disclosure undergoes repeated charge and discharge cycles. As described above, repeated charge and discharge cycles increase the likelihood of stress occurring near the interface between lead dioxide 52 and lead sulfate 64, potentially causing cracks or fissures in the positive electrode plate 2P near the interface. During subsequent repeated charge and discharge cycles, cracks or fissures that have already formed near the interface are more likely to develop, potentially leading to further cracks or fissures, which may cause the plate to fall off the positive electrode current collector 30P.

[0039] 4 is a schematic diagram illustrating the state of a lead-acid battery 1 in which short fibers 40 are contained in the positive electrode material 33P after repeated charging and discharging. When the positive electrode is repeatedly charged and discharged in the same manner as in FIG. 3, cracks and fissures are less likely to occur near the interface between the lead dioxide 52 and the lead sulfate 64 compared to FIG. 3. Reinforcing the positive electrode material 33P with short fibers 40 makes it easier to prevent the positive electrode active material 50 from falling off.

[0040] (Electrolyte) The electrolyte is an aqueous solution containing sulfuric acid. The electrolyte may be gelled as necessary. The electrolyte may further contain at least one metal ion selected from the group consisting of Na ions, Li ions, Mg ions, and Al ions.

[0041] The specific gravity of the electrolyte at 20° C. is, for example, 1.10 or more. The specific gravity of the electrolyte at 20° C. may be 1.35 or less. Note that these specific gravities are values ​​for the electrolyte of a lead-acid battery in a fully charged state.

[0042] Example 1 Hereinafter, Example 1 will be described to confirm the effects of the above embodiment. In Example 1, lead-acid batteries were fabricated using short fibers with various properties, and tests were conducted on their life performance and the like.

[0043] (Number Average Molecular Weight, Weight Average Molecular Weight) The monomer molecular weight (M) of the short fibers may be, for example, 28, 42, 53, 116, 192, or 228. The monomer molecular weight (M) may be 180 or more or 210 or less. In this specification, the number average molecular weight (Mn) and weight average molecular weight (Mw) of the short fibers of the present disclosure are determined by measuring the molecular weight distribution using gel permeation chromatography (GPC) analysis. Furthermore, for each of the short fiber samples (shown as S1 to S9 in FIG. 11 and in Example 1 below) and each of the lead-acid battery samples (shown as S10 to S25, S160 to S163, and S220 to S224 in FIG. 12 and in Example 1 below), the degree of polymerization (Gn) of the number average molecular weight was calculated by Mn / M using the number average molecular weight (Mn) calculated above, and the degree of polymerization (Gw) of the weight average molecular weight was calculated by Mw / M using the weight average molecular weight (Mw) calculated above (see FIG. 11).

[0044] In GPC analysis, when the staple fiber polymer is acrylic fiber, polyester fiber, polyethylene terephthalate fiber (PET fiber), or polyarylate fiber, the reference material used to determine Mn and Mw is polymethyl methacrylate (PMMA). When the staple fiber polymer is polypropylene fiber (PP fiber) or polyethylene fiber (PE fiber), the reference material used to determine Mn and Mw is polystyrene (PS).

[0045] The Mn and Mw of acrylic fibers, polyester fibers, PET fibers, polyarylate fibers, PP fibers and PE fibers were measured using the following apparatus under the following conditions.

[0046] (GPC measurement of acrylic fiber, polyester fiber, PET fiber, and polyarylate fiber) GPC apparatus: HLC-8420GPC (manufactured by Tosoh Corporation) Column: Shodex HFIP-LG (manufactured by Shodex Corporation), HFIP-806M (manufactured by Tosoh Corporation) (two columns) Eluent: HFIP, 10 mM CF3Coona Temperature: 40°C Concentration: 0.1% by mass Flow rate: 0.8 mL / min Injection amount: 100 μL Pretreatment: filtration (0.2 μm pore size filter) Solubility: complete dissolution Detector: differential refractometer

[0047] (GPC Measurement of PP Fiber and PE Fiber) GPC Apparatus: HLC-8321GPC / HT (manufactured by Tosoh Corporation) Column: TSKgel guardcolumn HHR(S), TSKgel GMHHR-H(S)HT (two columns, manufactured by Tosoh Corporation) Eluent: ortho-dichlorobenzene (o-DCB) Temperature: 145°C Concentration: 0.1% by mass Flow rate: 1.0 mL / min Injection volume: 300 μL Solubility: Complete dissolution Detector: Differential refractometer

[0048] The life performance of Example 1 was evaluated using the following test method. (High-Temperature Overcharge Life Performance (Light-Load Life Test)) High-temperature overcharge life performance was evaluated based on the life of the lead-acid battery during a high-temperature overcharge durability test according to the following procedure. (a) The battery was placed in an air chamber at 75°C ± 3°C throughout the entire test period. (b) The battery was connected to a life test device, and the following discharge and charge cycles were continuously repeated. This discharge and charge cycle constituted one life (one cycle). Discharge: 60 seconds ± 1 second at a discharge current of 25.0 A ± 0.1 A; Charge: 600 seconds ± 1 second at a charge voltage of 14.80 V ± 0.03 V (limited current of 25.0 A ± 0.1 A); (c) During the test, the battery was left for 56 hours every 480 cycles, and then continuously discharged for 30 seconds at the rated cold cranking current Icc, recording the voltage at the 30th second. The charge in (b) was then performed. These discharges and charges are also counted in the life cycle (number of cycles). (d) The test is terminated when it is confirmed that the voltage measured at 30 seconds in the (c) tests is 7.2 V or less and does not rise again. The total number of cycles at this point is used as an index of life performance. Hereinafter, high-temperature overcharge life performance may be simply referred to as life performance. The life performance shown in Figures 5, 7 to 10, and 12 refers to high-temperature overcharge life performance. The rated cold cranking current Icc is a current value corresponding to the performance rank defined in JIS D 5301:2019.

[0049] (20-Hour Rate Capacity Performance (20-Hour Rate Test)) The 20-hour rate capacity performance is evaluated based on the capacity of the lead-acid battery during the 20-hour rate test described below. a) The sample is charged at a current 3.42 times the 20-hour rate current I20 until the terminal voltage during charging or the temperature-converted electrolyte density measured every 15 minutes shows a constant value three times in a row. The electrolyte level is filled to its highest level. The temperature conversion of the electrolyte density is performed using the following formula. Hereinafter, the 20-hour rate capacity performance may be simply referred to as capacity performance. The capacity performance shown in FIG. 6 refers to the 20-hour rate capacity performance.

[0050] D20 = DT + 0.0007 (T - 20), where D20 is the density of the electrolyte at 20°C (g / cm ３) DT: Density of the electrolyte at T ° C (g / cm ３ ) T: Temperature of the electrolyte when measuring the density (°C) b) Place the sample in a water bath at 25±2°C throughout the entire test period. The water level should be 15 to 25 mm below the top surface of the sample. If multiple samples are placed in the same water bath, the distance between them and to the water bath wall should be at least 25 mm. c) 1 to 5 hours after the charging step a) above is completed, confirm that the electrolyte temperature is 25±2°C. Then, discharge the sample at a 20-hour rate current of I20 until the terminal voltage drops to 10.50±0.05 V, and record the discharge duration, t hours. d) Calculate the battery's effective 20-hour rate capacity, C20,e (Ah), using the following formula: C20,e = I20 x t, where I20 is the 20-hour rate current (A) and t is the discharge duration (hours).

[0051] (Fully Charged State) In this specification, the fully charged state of a flooded lead-acid battery is defined by JIS D5301:2019. More specifically, the fully charged state is defined as a state in which a lead-acid battery is charged at a current 2I20 (unit: A), which is twice the 20-hour rate current I20, until the terminal voltage (unit: V) during charging or the electrolyte density converted to 20°C temperature, measured every 15 minutes in a water tank at 25°C ± 2°C, shows a constant value to three significant digits three times consecutively. Note that the 20-hour rate current I20 is a current (A) that is 1 / 20 of the Ah value listed in the rated capacity. The value listed as the rated capacity is in Ah (ampere-hour). The unit of the current set based on the value listed as the rated capacity is A (ampere). Furthermore, for valve-regulated lead-acid batteries, the fully charged state refers to a state in which constant-current, constant-voltage charging is performed in an air tank at 25°C ± 2°C at a current 5I20 (unit: A) that is five times the 20-hour rate current I20, at 2.67 V / cell (16.00 V for a lead-acid battery with a rated voltage of 12 V), and charging is terminated when the total charging time reaches 24 hours. A fully charged lead-acid battery is a lead-acid battery that has already been formed and charged to a fully charged state. The timing for charging a lead-acid battery to a fully charged state may be immediately after formation, as long as it is after formation, or after a certain period of time (e.g., 720 hours or less) has elapsed since formation. For example, a lead-acid battery that has been formed and is currently in use (preferably in the early stages of use) may be charged.

[0052] (Information on Short Fibers of Samples) Acrylic fibers, polyester fibers, PET fibers, polyarylate fibers, PP fibers, and PE fibers were used as short fibers for the positive electrode material in each sample. For the PET fibers and polyarylate fibers, fibers with a fiber diameter of 1.0 dtex and fibers with a fiber diameter of 3.0 dtex were used. For the PET fibers and polyarylate fibers, fibers with a fiber length of 5 mm and fibers with a fiber length of 3 mm were used, respectively.

[0053] (Description of Each Sample) Hereinafter, each sample of Example 1 will be described with reference to Figures 11 and 12. In all tests in Example 1 of the present disclosure, sample S12 (shown surrounded by a thick line in Figure 12) was used as a control for each sample of the lead-acid battery.

[0054] (GPC Measurement Results) From the GPC measurement results, the Mn and Mw of each sample were determined (see FIG. 11 ). For the samples in FIG. 11 , performance evaluation tests (lifetime test and 20-hour rate test) were conducted under the above conditions, and performance evaluation was performed on two items: lifetime performance and capacity performance. The results are shown in FIG. 12 . The "Capacity Performance" item in FIG. 12 is the result of the 20-hour rate capacity test according to JIS D5301:2019. The "Lifetime Performance" item is the result of the light-load life test according to JIS D5301:2019. Furthermore, PE fiber, PP fiber, acrylic fiber, polyester fiber, polyarylate fiber, and PET fiber were used as short fibers, and each is shown in the material section of FIGS. 11 and 12 .

[0055] The short fibers contained in the positive electrode material used in S1 of FIG. 11 and S10 of FIG. 12 are the same sample. S2 and S3 of FIG. 11 have in common the use of PP fiber, but the Mn, Gn, Mw, and Gw are different. S2 of FIG. 11 and the short fibers contained in the positive electrode material used in S100, S101, and S11 of FIG. 12 are the same sample. S3 of FIG. 11 and the short fibers contained in the positive electrode material used in S12 of FIG. 12 are the same sample. S4, S5, and S6 of FIG. 11 have in common the use of acrylic fiber, but the Mn, Gn, Mw, and Gw are different. S4 of FIG. 11 and the short fibers contained in the positive electrode material used in S13 and S14 of FIG. 12 are the same sample. S13 and S14 of FIG. 12 have different short fiber contents. S7, S8, and S9 in Figure 11 have in common the use of PET fiber, but differ in Mn, Gn, Mw, and Gw. S7 in Figure 11 is the same sample as the short fibers contained in the positive electrode material used in S17, S18, S19, S20, S21, S22, and S23 in Figure 12. S17 to S23 differ from each other in short fiber content, fiber diameter, and fiber length. S8 in Figure 11 is the same sample as the short fibers contained in the positive electrode material used in S24 in Figure 12. S9 in Figure 11 is the same sample as the short fibers contained in the positive electrode material used in S25 in Figure 12.

[0056] The "content" item in Fig. 12 refers to the content of short fibers. The capacity performance and life performance items in Fig. 12 are shown as relative values, with sample S12 set to 100. In the graphs of Figs. 5 to 10, the reference value "100" is indicated by a bold line. Hereinafter, life performance (%) may also be referred to as the number of life cycles (%).

[0057] (Results of Performance Evaluation Test) Under the above conditions, performance evaluation was carried out on two items, life performance and capacity performance, in performance evaluation tests (life test and 20-hour rate test). The evaluation results are shown in Figs. 5 to 10 and 12.

[0058] FIG. 5 is a graph showing the correlation between Gn (degree of polymerization of number-average molecular weight) and life performance (%) using samples (S11, S12, S14, S15, S16, S19, S21, S24, S25, and S163 shown in FIG. 12 ). In the evaluation of life performance, samples with Gn of 1040 or less had life cycle counts (%) of 100 or more, demonstrating improved life performance (see FIG. 12 ). Furthermore, according to S10, S100, and S101 in FIG. 12 , when Gn was greater than 1040, the life cycle count (%) was less than 100, confirming that the life performance criteria were not met. When Gn was greater than 1040, the degree of polymerization was high and the number of repeating monomer units was increased, resulting in more sites bonded by the polymerization reaction, which is thought to increase the impact of acid decomposition.

[0059] FIG. 6 is a graph showing the correlation between the content (%) and capacity performance (%) using samples (S17, S18, S19, S23, S222, and S224 shown in FIG. 12). For samples with a content of less than 0.5% by mass, the capacity performance was comparable to the reference value of "100." In the evaluation of capacity performance, samples with a content of less than 0.5% by mass did not show a significant improvement in 20-hour capacity performance (see FIG. 12).

[0060] FIG. 7 is a graph showing the correlation between the content (%) and the life performance (%) using samples (S17, S18, S19, S23, S222, and S224 shown in FIG. 12 ). For samples with a content greater than 0.01% by mass, the life performance was greater than or equal to 100. For samples with a content greater than 0.01% by mass, the life performance improved (see FIG. 12 ). From the results shown in FIGS. 6 and 7 , for samples with a short fiber content greater than 0.01% by mass and less than 0.5% by mass, the capacity performance was evaluated as 100 and the life performance was evaluated as 100 or greater. Therefore, it was confirmed that the life performance and capacity performance improved when the short fiber content of the present disclosure was greater than 0.01% by mass and less than 0.5% by mass.

[0061] FIG. 8 is a graph showing the correlation between fiber diameter (dtex) and lifespan performance (%) using samples (S19 and S21 shown in FIG. 12). In the evaluation of lifespan performance, both samples achieved a result of "100" or higher. Specifically, all samples achieved a value of "175" or higher. Therefore, lifespan performance was significantly improved for fiber diameters of 3.0 dtex and 1.0 dtex (see FIG. 12). Furthermore, lifespan performance was improved by approximately 17% for short fibers with a smaller fiber diameter of 1.0 dtex compared to those with a fiber diameter of 3.0 dtex (see FIG. 12).

[0062] FIG. 9 is a graph showing the correlation between fiber length (mm) and lifespan performance (%) using samples (S19 and S20 shown in FIG. 12). In the evaluation of lifespan performance, both samples achieved a score of "100" or higher. Specifically, all samples achieved a score of "170" or higher. Therefore, lifespan performance was significantly improved for fiber lengths of 5 mm and 3 mm (see FIG. 12). Furthermore, the shorter fiber length of 3 mm improved lifespan performance by about 5% compared to the shorter fiber length of 5 mm (see FIG. 12).

[0063] FIG. 10 is a graph showing the correlation between monomer molecular weight and lifespan performance (%) using samples (S10, S12, S14, S19, and S161 shown in FIG. 12). The results for samples with a monomer molecular weight of 42 or more were "100" or higher. More specifically, the results for samples with a monomer molecular weight of 53 or more were "125" or higher, indicating improved lifespan performance (see FIG. 12). Therefore, when the monomer molecular weight of the short fiber is 42 or higher, the lifespan performance is improved.

[0064] Example 2 In Example 2, several lead-acid batteries were fabricated using the pore volume of the positive electrode material as a parameter, and their life performance was tested. Specifically, the ratio V1 / V0 of the pore volume V1 of the positive electrode material having a pore diameter of 1 μm or more and 10 μm or less to the total pore volume V0 of the positive electrode material was 0.01 or more and 0.80 or less. Note that the ratio V1 / V0 for each sample in Example 1 was 0.1. The pore volume of the positive electrode material was adjusted by adjusting the amount of lead powder, water, and sulfuric acid in the positive electrode paste.

[0065] The life performance of Example 2 was evaluated using the following test method. The test method differed from that of Example 1 in two respects: temperature and discharge time. (Overcharge Life Performance (Light-Load Life Test)) Overcharge life performance was evaluated based on the life of the lead-acid battery during an overcharge durability test according to the following procedure. (a) The battery was placed in an air chamber at 40°C ± 3°C throughout the entire test period. (b) The battery was connected to a life test device, and the following discharge and charge cycles were continuously repeated. This discharge and charge cycle constituted one life (one cycle). Discharge: 240 seconds ± 1 second at a discharge current of 25.0 A ± 0.1 A; Charge: 600 seconds ± 1 second at a charge voltage of 14.80 V ± 0.03 V (limited current of 25.0 A ± 0.1 A); (c) During the test, the battery was left for 56 hours every 480 cycles, and then continuously discharged for 30 seconds at the rated cold cranking current Icc, recording the voltage at the 30th second. Then, the charging (b) is carried out. These discharges and charges are also added to the life cycle (number of cycles). The test is terminated when it is confirmed that the voltage measured at 30 seconds in the test (d) and (c) is 7.2 V or less and does not rise again, and the total number of cycles at this time is used as an index of life performance. The rated cold cranking current Icc is a current value according to the performance rank defined in JIS D 5301:2019.

[0066] In general, the smaller the pore volume of the positive electrode material, the smaller the initial capacity performance but the improved lifespan performance. On the other hand, the larger the pore volume of the positive electrode material, the greater the initial capacity performance but the reduced lifespan performance. In Example 1, it was confirmed that the lifespan performance was improved by combining a positive electrode material with short fibers having a low degree of polymerization. Therefore, it was thought that a high-capacity, long-life lead-acid battery could be designed by combining a positive electrode material with a large pore volume and short fibers having a low degree of polymerization. The mechanism is that by using short fibers with a low degree of polymerization, the degree of adhesion between the positive electrode active materials can be maintained even when the pore volume of the positive electrode material is large.

[0067] (Measurement of pore distribution and total pore volume of positive electrode material) Hereinafter, a method for measuring the pore distribution and total pore volume of a positive electrode material, and a method for analyzing the positive electrode material or its constituent components will be described. Unpulverized sample A is used for the measurement or analysis.

[0068] Before measurement, 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 to remove sulfuric acid from the positive electrode plate. The washing is continued until a pH test paper is pressed against the washed positive electrode surface and no change in color is confirmed. The washed positive electrode plate is dried at 60±5°C until it is completely dry. Next, the positive electrode material is separated from the positive electrode plate to obtain unpulverized sample A.

[0069] For unpulverized sample A, the pore distribution and total pore volume V0 of sample A are measured using a mercury porosimeter. The volume V1 of pores P1 with a pore diameter of 1 μm to 10 μm is calculated from the pore distribution, and the ratio V1 / V0 is obtained by dividing the volume V1 by the total pore volume V0. The measurement pressure range is 0.5 psia to 33,000 psia (≒ 3.447 kPa to 227,528 kPa). The pore distribution is determined for pore diameters in the range of 17 nm to 340 μm. An automatic porosimeter (Autopore IV9505) manufactured by Shimadzu Corporation is used as the mercury porosimeter.

[0070] (Description of Each Sample) Below, each sample of Example 2 will be described with reference to Figures 13, 14, and 15. Samples S26 to S29 in Figure 15 have in common the monomer molecular weight M of 42, the degree of polymerization Gn of 1036, and the content of 0.07%, but differ in that the ratios V1 / V0 are 0.01, 0.10, 0.70, and 0.80, respectively. Samples S30 to S33 have in common the monomer molecular weight M of 192, the degree of polymerization Gn of 0.07, and the ratios V1 / V0 are 0.01, 0.10, 0.70, and 0.80, respectively. Samples S34 to S36 have in common the monomer molecular weight M of 192, the degree of polymerization Gn of 29, and the ratio V1 / V0 of 0.70, but differ in that the content of 0.1%, 0.03%, and 0.5%, respectively.

[0071] The content percentage in Fig. 15 indicates the content percentage of short fibers. The life performance items in Fig. 15 are relative values ​​with the value of sample S29 set to 100. Hereinafter, life performance (%) may also be referred to as the number of life cycles (%).

[0072] (Performance Evaluation Test Results) Under the above conditions, a performance evaluation was conducted to evaluate the lifespan performance. The evaluation results are shown in Figures 13 and 14. Figure 13 is a graph showing the correlation between the ratio V1 / V0 and lifespan performance (%) using samples (S26, S27, S28, S29, S30, S31, S32, and S33 shown in Figure 15). In the lifespan performance evaluation, samples with a V1 / V0 ratio of 0.01 to 0.80 showed a lifespan cycle count (%) of 100 or more, indicating improved lifespan performance (see Figure 15). In particular, it was confirmed that the use of short fibers with a low degree of polymerization allowed the lifespan cycle count (%) to be maintained at 100 or more when the V1 / V0 ratio was in the high range (0.70 to 0.80).

[0073] FIG. 14 is a graph showing the correlation between the content (%) and the life performance (%) using samples (S32, S34, S35, and S36 shown in FIG. 15). For samples with a content of 0.03% by mass or more and 0.5% by mass or less, the number of cycles to life (%) was 100 or more, indicating improved life performance (see FIG. 14). In particular, by using short fibers with a low degree of polymerization, it was confirmed that the number of cycles to life (%) could be maintained at 100 or more even when the pore volume V1 / V0 was as large as 0.70 over a wide range of the content (0.03% by mass to 0.5% by mass).

[0074] 1: Lead-acid battery 2P: Positive electrode plate 3N: Negative electrode plate 4: Separator 5P: Positive electrode shelf 6N: Negative electrode shelf 7P: Positive electrode column 8: Through-connector 9N: Negative electrode column 11: Plate group 12: Battery case 13: Partition wall 14: Cell chamber 15: Lid 16N: Negative electrode terminal 17P: Positive electrode terminal 18: Vent plug 30P: Positive electrode current collector 33P: Positive electrode material 40: Short fiber 50: Positive electrode active material 52: Lead dioxide 64: Lead sulfate

Claims

1. A lead-acid battery comprising a positive electrode plate, the positive electrode plate comprising a positive electrode material, the positive electrode material including short fibers formed of a polymer, the short fibers having a monomer molecular weight: M of 42 or more and a degree of polymerization: Gn calculated from the number average molecular weight (Mn) using the following formula: 1040 or less, the content of short fibers in the positive electrode material being greater than 0.01 mass%. Formula: Gn = Mn / M (Gn: degree of polymerization, Mn: number average molecular weight, M: monomer molecular weight).

2. The lead-acid battery according to claim 1, wherein the content of short fibers in the positive electrode material is less than 0.5% by mass.

3. The lead-acid battery according to claim 1 or 2, wherein the monomer molecular weight: M is 180 or more, and the content of short fibers in the positive electrode material is 0.02 mass % or more and 0.3 mass % or less.

4. A lead-acid battery according to claim 1 or 2, wherein the fiber diameter of the short fibers is 0.5 dtex or more and 3.5 dtex or less.

5. A lead-acid battery according to claim 1 or 2, wherein the short fibers have a fiber length of 2 mm or more and 6 mm or less.

6. The lead-acid battery according to claim 1 or 2, wherein V1 / V0, which is the ratio of the pore volume V1 of the positive electrode material having a pore diameter of 1 μm or more and 10 μm or less to the total pore volume V0 of the positive electrode material, is 0.01 or more and 0.80 or less.

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