Separator for lead storage battery

Abstract

The present invention provides a separator for a sealed lead storage battery which has improved battery capacity and battery life, good battery assembly performance, and at the same time maintains the basic physical properties, liquid absorbency, required for separator characteristics for a sealed lead storage battery. The aspect ratio (average fiber length / average fiber diameter) of the glass fibers in the separator is 130 to 205, the tensile strength of the separator is 0.20 N / mm 2 The above, the elongation at break of the separator is 2.0% or more and less than 9.0%.

Description

Technical Field

[0001] This invention relates to separators for sealed lead-acid batteries. More specifically, its object is to optimize the selection of separator materials, taking into account improvements in battery capacity and lifespan, which are important battery characteristics, as well as good battery assemblability. This optimization involves specifying the range of aspect ratio (average glass fiber length / average glass fiber diameter), basic physical properties (tensile strength, elongation), and liquid absorption rate of the glass fiber separator material. Background Technology

[0002] In the past, extensive research has been conducted on separator materials in sealed lead-acid batteries to improve battery capacity and battery life, which are important aspects of battery characteristics.

[0003] As the separator, a component that significantly impacts battery capacity, improving the seal between the separator and the battery electrodes becomes crucial. Specifically, it's important to rapidly supply the electrolyte held in the separator to the electrode side; the ease of electrolyte movement at the interface between the electrode and the separator is key to improving battery life.

[0004] At this point, given that the separator between the electrodes of the battery is required to absorb a large amount of electrolyte, the question arises as to how to make the separator itself swell.

[0005] In addition, the basic physical properties of the separator itself (tensile strength, elongation) also have a significant impact on the battery life due to the repeated charging and discharging reactions of the battery.

[0006] As a separator material, the main research focuses on three types of separators: (1) separators formed solely of glass fibers, (2) separators formed of glass fibers and organic fibers, and (3) separators formed by further adding inorganic powders to glass fibers and organic fibers.

[0007] In the past, as a separator material, which has the highest liquid absorption rate, it was proposed to improve gas permeability, which is the opposite property, by forming it only from glass fibers, with glass fibers having an average fiber diameter of less than 2 μm and an average fiber length of less than 2 mm as the main body, while maintaining the liquid absorption rate of the separator (see Patent Document 1).

[0008] In addition, a separator made solely of glass fiber was also proposed, with the sheet having a tensile elongation of approximately 9–15% and a density of 0.11–0.14 g / cm³. 3 This range leads to an increase in liquid absorption rate and a higher discharge rate (see Patent Document 2).

[0009] Numerous patents have been filed regarding separators composed of glass fibers and organic fibers. It is known that by adding organic fibers compared to separators composed solely of glass fibers, the organic fibers are bonded to the glass fibers through thermal fusion, thereby increasing the sheet strength. However, organic fibers themselves have poor hydrophilicity, which leads to a decrease in the liquid absorption rate of the separator.

[0010] To compensate for this, the following countermeasures were taken: by using organic fibers with large fiber diameters (generally fibers with an average fiber diameter of 10 μm or more), the pore size of the separator is locally increased, thereby making it easier to ensure liquid absorption rate. On the other hand, regarding battery life, there is another disadvantage: an increased risk of dendrite short circuits.

[0011] In order to extend the battery life, a solution was proposed to combine hydrophilic inorganic powder (silica powder) to reduce the pore size of the separator in the closed lead-acid battery using organic fibers and to prevent dendrite short circuits (see Patent Document 3). However, it still has the following disadvantages: the density of the sheet increases, resulting in a decrease in the liquid absorption rate and thus a decrease in the battery capacity. Therefore, it can only be used in long-life batteries with small capacity.

[0012] Furthermore, while using highly hydrophilic cellulose fibers such as pulp may potentially suppress the decrease in water content, the lack of tolerance to sulfuric acid (the electrolyte) after the separator is assembled into the battery leads to the dissolution of these fibers, negatively impacting the battery reaction. Additionally, the incorporation of highly hydrophilic silica powder can clog the pores of the separator, resulting in reduced liquid absorption. Therefore, existing separator designs still have problems.

[0013] Existing technical documents

[0014] Patent documents

[0015] Patent Document 1: Japanese Patent Application Publication No. 2-66850

[0016] Patent Document 2: Japanese Patent Application Publication No. 7-201310

[0017] Patent Document 3: Japanese Patent Application Publication No. 2003-100276 Summary of the Invention

[0018] The problem that the invention aims to solve

[0019] In Patent Document 1, the embodiments show a tendency for a decrease in the tensile strength, a fundamental physical property of the separator related to battery life. Furthermore, while improvements in liquid absorption rate and absorbency, comparable to the separator's liquid retention, are emphasized, along with improvements in absorption speed and gas permeability, the liquid absorption rate itself is not improved. Additionally, no specific range is specified for the average fiber diameter and average fiber length of the glass fibers; however, as described herein, a preferred fiber length range of 0.2 mm to 2.0 mm is described. Therefore, regarding the aspect ratio of the glass fibers, cases with excessively large aspect ratios, ranging from 200 to 1000, are also included. If the aspect ratio is too large, the elongation at break of the separator becomes very large. During the assembly process of assembling the separator into the lead-acid battery, the separator elongates when pulled out. Therefore, due to the dimensional changes in the width and thickness of the separator, it becomes narrower compared to the dimensions of the battery electrodes, resulting in a short circuit in the battery during the assembly process.

[0020] Furthermore, Patent Document 2 describes the following: if the elongation at break of the separator is 9% to 15%, and the density of the separator is 0.11 to 0.14 g / cm³. 3 For a separator used in a closed lead-acid battery with a relatively low density, the liquid retention capacity of the separator is increased, and its characteristic is that the fiber length is 3 to 10 mm, which is very long.

[0021] In this case, similarly to the above, due to the elongation of the separator, the deformation during processing increases, causing inconsistencies in size with the battery electrodes, leading to frequent manufacturing defects. Furthermore, the density of the separator is 0.11–0.14 g / cm³. 3 Because of its low density, the liquid retention capacity of the separator increases. However, conversely, due to the increased liquid retention capacity, the weight of the separator itself also increases due to the weight of the absorbed liquid. Therefore, the strength of the separator cannot withstand its own weight, and it will collapse (be unable to maintain its shape).

[0022] Furthermore, in Patent Document 3, a scheme is proposed that incorporates hydrophilic inorganic powder (silica powder) into the separator without compromising its hydrophilicity, taking into account the content of organic fibers. In this case, the density of the separator becomes higher, resulting in a smaller electrolyte volume, a lower liquid absorption rate of the separator, and a lower battery capacity.

[0023] As mentioned above, for conventional separators used in sealed lead-acid batteries, studies have been conducted on the basic physical properties of the separator, which are directly related to the long life of the battery, and the liquid absorption rate of the separator, which is directly related to the improvement of battery capacity. However, this was only for the purpose of improving the characteristics of lead-acid batteries, and no research has been conducted on solving problems in the battery assembly process.

[0024] Regarding the glass fiber used in the separator material, the properties of the separator can be significantly affected by considering the relationship between a defined range of average fiber diameter and average fiber length (range of aspect ratio) and the elongation of the separator. In existing patents that do not adequately consider this relationship, improvements are still needed in establishing the selection criteria for the optimal material for separators used in sealed lead-acid batteries.

[0025] This invention was made with the consideration of the following situation, and aims to provide a separator that can simultaneously optimize the basic physical properties and liquid absorption properties of the separator for sealed lead-acid batteries by finding the optimal conditions for the aspect ratio (average fiber length / average fiber diameter), tensile strength, and elongation of the glass fibers in the separator while taking into account the improvement of battery capacity and battery life and good battery assembly performance.

[0026] Methods for solving problems

[0027] To address the aforementioned issues, in-depth research was conducted, resulting in the discovery of optimal conditions for the aspect ratio (average fiber length / average fiber diameter) of the glass fibers within the separator, as well as the tensile strength and elongation of the separator. Furthermore, this method provides the separator with optimal basic physical properties, liquid absorption, and dimensional stability when assembled into a sealed lead-acid battery, making it the best separator for sealed lead-acid batteries.

[0028] That is, in the sealed lead-acid battery separator of the present invention, after the separator is assembled into the battery, in order to minimize the components that dissolve into the electrolyte and prevent adverse effects on the battery reaction, it is preferable to use only glass fiber as the separator material.

[0029] The separator for the sealed lead-acid battery of the present invention is preferably made of glass fiber with an average fiber diameter of 2.0 μm or less, an aspect ratio (average fiber length / average fiber diameter) within the separator body in the range of 130 to 205, and a tensile strength of 0.20 N / mm. 2 The separator is preferably a separator with an elongation at break of 2.0% or more and less than 9.0%, and preferably an elongation at break of 2.5% or more and less than 7.5%.

[0030] In the separator of a sealed lead-acid battery, an aspect ratio of less than 130 means that the average fiber length of the separator is relatively shorter. In sealed lead-acid batteries where the liquid absorption rate is less than 85% and the electrolyte volume becomes the rate-limiting reaction, the battery's lifespan and capacity characteristics are significantly reduced.

[0031] On the other hand, an aspect ratio exceeding 205 means that the average fiber length of the separator becomes relatively longer, the separator becomes less dense, and the elongation at break also increases. Therefore, due to the increased liquid absorption, the weight of the separator itself also increases, so the separator's strength cannot withstand its own weight, causing it to collapse or fail to maintain its shape.

[0032] Additionally, if the tensile strength of the separator in a sealed lead-acid battery is less than 0.20 N / mm... 2 If this happens, the battery's assembly performance, basic physical properties during charge and discharge reactions will decrease, and the battery life will be reduced.

[0033] Furthermore, regarding the elongation of separators used in sealed lead-acid batteries, AGM separators are primarily shipped in rolls and pulled out of the rolls for use during battery assembly. During the assembly of the separator and battery electrodes, the separator is typically used to wrap the battery electrodes in a U-shape. If the elongation at break of the separator is less than 2.0%, cracks will form on the separator surface when it is bent into a U-shape during processing, resulting in defective products that cannot be shipped.

[0034] On the other hand, during the charging and discharging reactions of the battery, the separator expands and contracts due to the repeated absorption and release of electrolyte. When the elongation of the sheet measured at room temperature is 9.0% or more, the separator is stretched by the force applied during stretching, causing changes in its dimensions in both the width and thickness directions. These changes in the electrode spacing and dimensions, designed to prevent side short circuits in the battery electrodes, became a cause of early battery short circuits.

[0035] Thus, in the separator for a sealed lead-acid battery of the present invention, by optimizing the range of the aspect ratio and the range of the tensile strength and elongation of the separator made of glass fiber used as material, a separator that is optimal for extending battery life and improving capacity can be provided.

[0036] It should be noted that the aspect ratio of the glass fibers in the separator (fiber length adjustment) can be easily adjusted by adjusting the dissociation conditions based on the papermaking process.

[0037] Invention Effects

[0038] The separator for sealed lead-acid batteries of the present invention optimizes the basic physical properties and liquid absorption of the separator by optimizing the aspect ratio (average fiber length / average fiber diameter), tensile strength, and elongation of the glass fiber separator used in the separator. Attached Figure Description

[0039] Figure 1 This is a schematic diagram illustrating adverse conditions during battery assembly or battery reaction when the elongation of the separator increases significantly. Detailed Implementation

[0040] The aspect ratio (average fiber length / average fiber diameter) of the glass fiber separator used in the sealed lead-acid battery separator of the present invention is preferably in the range of 130 to 205.

[0041] In the separator of a sealed lead-acid battery, if the aspect ratio of the glass fiber inside the separator is less than 130, the liquid absorption rate is less than 85%, and the battery life and capacity characteristics are significantly reduced.

[0042] On the other hand, when the aspect ratio exceeds 205, the elongation at break of the separator becomes very large. During the assembly process of assembling the separator into the lead-acid battery, the separator elongates when pulled out, thus changing its width and thickness. Furthermore, the separator repeatedly expands and contracts during the battery reaction, causing further changes in its width and thickness relative to the battery electrodes. Therefore, defects can occur during the assembly process, as well as short circuits during the battery reaction.

[0043] The tensile strength of the separator for the sealed lead-acid battery of the present invention is preferably 0.20 N / mm. 2 above.

[0044] When the tensile strength of the separator in a sealed lead-acid battery is less than 0.20 N / mm 2 When the battery is in use, its assembly performance and basic physical properties during charging and discharging decrease, resulting in a shorter battery life.

[0045] The elongation of the separator for the sealed lead-acid battery of the present invention is preferably in the range of 2.0% or more and less than 9.0%, more preferably in the range of 2.5% or more and less than 7.5%.

[0046] AGM separators are primarily shipped in rolls. If the elongation is less than 2.0%, cracks will appear on the surface of the separator, resulting in a defective product that cannot be shipped.

[0047] On the other hand, during the charging and discharging reactions of the battery, the electrolyte is repeatedly absorbed and released, resulting in the expansion and contraction of the separator. Separators with an elongation of 9.0% or more, measured at room temperature, extend downwards as the battery reacts, narrowing their width and thus causing a deviation from the width of the electrode plates.

[0048] Example

[0049] The following examples and comparative examples illustrate the present invention in more detail. However, the present invention is not limited to the following examples as long as it does not depart from its spirit.

[0050] [Fabrication of the separator sheet]

[0051] The separator sheets of Examples 1-6 and Comparative Examples 1-5 (all handmade) were prepared according to the following steps.

[0052] 15g of various glass fibers (C glass) were placed into the container of a mixer (National Cooking Mixer MX-915C manufactured by Nasshon), and water was added until the volume reached 1000ml. At this point, the pH of the container was adjusted to 3.0. The value of the sliding resistor voltage regulator linked to the mixer was set to 70-150V, and dissociation was performed for 30 seconds to 20 minutes. After dissociation, the water containing glass fibers in the mixer container was completely added to a papermaking apparatus (hand-made sheet production apparatus) containing water at pH 3.0. After mixing with a stirring rod, the mixture was dehydrated to produce wet papermaking sheets. Then, the sheets were dried using a dryer (drying conditions: 120℃, 1 hour) to produce separator sheets (thickness: 1mm).

[0053] For the glass fibers within the fabricated separator sheet (after becoming a separator sheet), the average fiber diameter and average fiber length are determined using the following methods.

[0054] The results are shown in Table 1.

[0055] [Average fiber diameter (μm)]

[0056] On a separator sheet (300mm × 200mm), samples of approximately 5mm × 5mm square were collected from 9 locations (3 at the top, 3 in the middle, and 3 at the bottom). These samples were photographed using a scanning electron microscope (SEM) at 2000x magnification. After printing them out, a line was drawn along the diagonal of the electron microscope image, and the fiber diameter of the fibers overlapping the line was measured using a scale bar (30–40 fibers / sheet × 9 locations = approximately 350 fibers / sample).

[0057] [Average fiber length (μm)]

[0058] Measurements were performed using a Diamscope measuring machine (analysis software Ver. 2.84) manufactured by Cottonscope.

[0059] For the fabricated separator sheet, the tensile strength, elongation, and liquid absorption rate were determined using the following methods.

[0060] The results are shown in Table 1.

[0061] Tensile strength (N / mm) 2)]

[0062] The separator sheet was cut to a size of 250mm × 10mm. Using an Autograph (manufactured by Shimadzu Corporation), the tensile strength (breaking strength, N / mm²) was measured under the conditions of a crosshead speed of 25mm / min and a chuck spacing of 100mm. 2 ).

[0063] [Elongation (%)]

[0064] Determine the elongation (%) at fracture during tensile strength testing.

[0065] [Liquid Absorption Rate (%)]

[0066] Cut the separator sheet to a size of 250mm × 10mm. Fill a petri dish with water (24℃) and immerse the cut sheet in the water for 60 minutes. Then, pull the sheet out of the water and hold it for 5 minutes. Measure the difference (BA) between the sample weight A before immersion in the water and the sample weight B after immersion in the water. Use "[(BA) / A] × 100" as the liquid absorption rate (%).

[0067] [Table 1]

[0068]

[0069] <Examples 1-6>

[0070] The separator sheets in Examples 1-6 are made of glass fiber with an aspect ratio of 130-205 and a tensile strength of 0.41-1.07 N / mm². 2 A separator sheet with an elongation of 2.3 to 8.5% and composed of a single glass fiber or composite fiber (a mixture of two or more types of glass fibers with different average fiber diameters).

[0071] While fully maintaining the basic physical properties required for the separator in a sealed lead-acid battery (tensile strength: 0.20 N / mm²), 2 While maintaining an elongation of 2.0% or more but less than 9.0%, the liquid absorption rate is shown to be 85% or more.

[0072] It can be seen that the separator sheets in Examples 1 to 6 all exhibited the best basic physical properties (tensile strength, elongation) and liquid absorption.

[0073] <Comparative Example 1>

[0074] The separator sheet in Comparative Example 1 is made of glass fiber with an aspect ratio of 117 and a tensile strength of 0.24 N / mm². 2 A separator sheet with an elongation of 0.4% and made of a single glass fiber.

[0075] The required tensile strength for the separator in a sealed lead-acid battery is 0.20 N / mm². 2 The above figures are true, but the elongation is less than 2.0%. Additionally, the aspect ratio of the glass fiber is less than 130, resulting in a liquid absorption rate of less than 85%.

[0076] <Comparative Example 2>

[0077] The separator sheet in Comparative Example 2 is made of glass fiber with an aspect ratio of 121 and a tensile strength of 0.12 N / mm². 2 A separator sheet with an elongation of 0.8% and made of a single glass fiber.

[0078] The tensile strength required for separators in sealed lead-acid batteries is less than 0.20 N / mm². 2 The elongation is also less than 2.0%. The aspect ratio of the glass fiber is less than 130, and the liquid absorption rate is less than 85%.

[0079] <Comparative Example 3>

[0080] The separator sheet in Comparative Example 3 is made of glass fiber with an aspect ratio of 127 and a tensile strength of 0.26 N / mm². 2 A separator sheet with an elongation of 2.7% and made of a single glass fiber.

[0081] The required tensile strength for the separator in a sealed lead-acid battery is 0.20 N / mm². 2 The above conditions also apply, with elongation ranging from 2.0% to less than 9.0%, an aspect ratio of less than 130, and a liquid absorption rate of less than 85%.

[0082] <Comparative Example 4>

[0083] The separator sheet in Comparative Example 4 is made of glass fiber with an aspect ratio of 255 and a tensile strength of 0.46 N / mm². 2 A separator sheet with an elongation of 11.2% and made of a single glass fiber.

[0084] The required tensile strength for the separator in a sealed lead-acid battery is 0.20 N / mm². 2 The liquid absorption rate is over 85%, but due to the aspect ratio of the glass fiber exceeding 205, the elongation exceeds 9.0%.

[0085] <Comparative Example 5>

[0086] The separator sheet in Comparative Example 5 is made of glass fiber with an aspect ratio of 112 and a tensile strength of 0.51 N / mm². 2 A separator sheet with an elongation of 1.8% and composed of composite fibers (a mixture of two or more types of glass fibers with different average fiber diameters).

[0087] The required tensile strength for the separator in a sealed lead-acid battery is 0.20 N / mm². 2 The above figures are true, but the elongation is less than 2.0%, and the aspect ratio of the glass fiber is less than 130. The liquid absorption rate is also less than 85%.

[0088] Industrial availability

[0089] The sealed lead-acid battery separator of the present invention provides an optimal separator that can simultaneously maintain the basic physical properties and liquid absorbency required for a sealed lead-acid battery separator by keeping the aspect ratio (average fiber length / average fiber diameter), tensile strength and elongation of the glass fiber separator within a specific range.

[0090] Explanation of reference numerals in the attached figures

[0091] 1 Electrode

[0092] 2. Separator

Claims

1. A sealed separator for lead-acid batteries, characterized in that: The glass fibers within the separator have an average fiber diameter of less than 2 μm, an aspect ratio (average fiber length / average fiber diameter) between 130 and 205, and a tensile strength of 0.20 N / mm². 2 The elongation at fracture of the aforementioned separator is in the range of 2.0% or more but less than 9.0%.

2. The separator for a sealed lead-acid battery according to claim 1, characterized in that, Only glass fiber is used as the constituent material of the separator.

3. The separator for a sealed lead-acid battery according to claim 1 or 2, characterized in that, The liquid absorption rate of the separator is over 85%.

4. A sealed lead-acid battery using a separator for sealed lead-acid batteries, characterized in that, The sealed lead-acid battery separator is made of glass fiber. The average fiber diameter of the glass fiber in the separator is less than 2 μm, the aspect ratio of the glass fiber (average fiber length / average fiber diameter) is in the range of 130 to 205, and the tensile strength of the separator is 0.20 N / mm². 2 The elongation at fracture of the aforementioned separator is in the range of 2.0% or more but less than 9.0%.

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