SEPARATOR FOR LEAD ACID BATTERIES

Abstract

[Problem] To provide an optimum separator that simultaneously has basic physical properties essential for the characteristics of a separator for valve-regulated lead acid batteries and liquid absorbability while taking into account the improvement of the battery capacity and battery life and the good battery assembly performance.

[Solution] The aspect ratio (average fiber length/average fiber diameter) of a glass fiber in a separator is 130 to 205, the tensile strength of the separator is 0.20 N/mm.sup.2 or more, and the elongation percentage at break of the separator is 2.0% or more and less than 9.0%.

Claims

1: A separator for valve-regulated lead acid batteries, comprising a glass fiber, wherein the glass fiber in the separator has an average fiber diameter of 2 m or less, the glass fiber in the separator has an aspect ratio (average fiber length/average fiber diameter) within a range of 130 to 205, the separator has a tensile strength of 0.20 N/mm.sup.2 or more, and the separator has an elongation percentage at break within a range of 2.0% or more and less than 9.0%.

2: The separator for valve-regulated lead acid batteries according to claim 1, wherein only the glass fiber is used as a constituent material of the separator.

3: The separator for valve-regulated lead acid batteries according to claim 1, wherein the separator has a liquid absorption ratio of 85% or more.

4: A valve-regulated lead acid battery using a separator for valve-regulated lead acid batteries, wherein the separator for valve-regulated lead acid batteries is formed of a glass fiber, the glass fiber in the separator has an average fiber diameter of 2 m or less, the glass fiber in the separator has an aspect ratio (average fiber length/average fiber diameter) within a range of 130 to 205, the separator has a tensile strength of 0.20 N/mm.sup.2 or more, and the separator has an elongation percentage at break within a range of 2.0% or more and less than 9.0%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is a schematic diagram showing a state of a defect at the time of assembling a battery or at the time of a battery reaction when the elongation of a separator is remarkably large.

DESCRIPTION OF EMBODIMENTS

[0035] The range of the aspect ratio (average fiber length/average fiber diameter) in the separator of the glass fiber to be used for the separator for valve-regulated lead acid batteries of the invention is preferably 130 to 205.

[0036] In the separator for valve-regulated lead acid batteries, when the aspect ratio of the glass fiber in the separator is less than 130, the liquid absorption ratio is lower than 85%, and the life and capacity characteristics of the battery significantly deteriorate.

[0037] On the other hand, when the aspect ratio exceeds 205, the elongation percentage at break of the separator becomes very large, and in the assembly step when the separator is incorporated into the lead acid battery, the separator elongates when the separator is pulled out, so that the width and thickness dimensions of the separator change. Further, also during the battery reaction, the separator repeatedly expands and contracts, so that the width and thickness dimensions of the separator change and become narrower than the dimensions of the battery electrode. Therefore, a defect in the assembly step and a defect that causes a battery short-circuiting in the battery reaction occur.

[0038] The tensile strength of the separator for valve-regulated lead acid batteries of the invention is preferably 0.20 N/mm.sup.2 or more.

[0039] When the tensile strength of the separator for valve-regulated lead acid batteries is lower than 0.20 N/mm.sup.2, the battery assembly performance and the basic physical properties in the charging/discharging reaction deteriorate, and the battery life decreases.

[0040] The range of the elongation percentage of the separator for valve-regulated lead acid batteries of the invention is preferably within the range of 2.0% or more and less than 9.0%, and more preferably within the range of 2.5% or more and 7.5% or less.

[0041] An AGM separator is shipped mainly in a roll form at the time of shipment. At this time, if the elongation percentage is less than 2.0%, a crack occurs on the surface of the separator, and the product becomes defective and cannot be shipped.

[0042] On the other hand, in the charging/discharging reaction when the battery is used, the electrolyte is repeatedly absorbed and released, so that the separator expands and contracts. The separator with an elongation percentage of 9.0%. or more as measured under a room temperature condition elongates downward with the battery reaction, and the width of the separator is narrowed, and therefore, a deviation from the width of the electrode plate occurs.

EXAMPLES

[0043] The invention will be described more specifically below with reference to Examples and Comparative Examples, but the invention is not limited to the following Examples without departing from the gist thereof.

[Production of Separator Sheet]

[0044] Separator sheets (all hand-made products) of Examples 1 to 6 and Comparative Examples 1 to 5 were produced by the following procedure.

[0045] 15 g of each of various glass fibers (C glass) was put in a container of a mixer (National Cooking Mixer MX-915C manufactured by National Panasonic), and water was added to 1000 mL. At this time, the pH in the container was adjusted to 3.0. The value of a slidac connected to the mixer was set to 70 to 150 V, and the mixture was subjected to disaggregation for 30 seconds to 20 minutes. After disaggregation, all the water containing the glass fiber in the mixer container was put into a TAPPI apparatus (hand-made sheet making apparatus) containing water at pH 3.0, followed by mixing with a stirring rod, and then, dehydration, thereby producing a wet paper sheet. Thereafter, the sheet was dried in a dryer (drying conditions: 120 C., 1 hour), thereby producing a separator sheet (thickness: 1 mm).

[0046] For the glass fibers in the produced separator sheets (after forming separator sheets), the average fiber diameter and the average fiber length were measured by the following methods.

[0047] The results are shown in Table 1.

[Average Fiber Diameter (m)]

[0048] On the separator sheet (300 mm200 mm), samples of about 5 mm5 mm square were collected from 9 locations (upper row: 3 locations, middle row: 3 locations, lower row: 3 locations). These samples were photographed with a scanning electron microscope (SEM) (2000) and printed out, and then, a line was drawn diagonally in the electron micrographs, and the fiber diameter of a fiber overlapping this line was measured with a scale (30 to 40 fibers/sheet9 locations=about 350 fibers/sample).

[Average Fiber Length (m)]

[0049] The measurement was performed using a Diamscope measurement apparatus manufactured by Cottonscope Pty Ltd. (analysis software Ver. 2.84).

[0050] For the produced separator sheets, the tensile strength, elongation percentage, and liquid absorption ratio were measured by the following methods.

[0051] The results are shown in Table 1.

[Tensile Strength (N/mm.SUP.2.)]

[0052] The separator sheet was cut to a size of 250 mm10 mm, and the tensile strength (breaking strength, N/mm.sup.2) was measured under the conditions of a crosshead speed of 25 mm/min and a chuck distance of 100 mm using an autograph (manufactured by Shimadzu Corporation).

[Elongation Percentage (%)]

[0053] The elongation percentage (%) at break in the tensile strength measurement was measured.

[Liquid Absorption Ratio ( )]

[0054] The separator sheet was cut to a size of 250 mm10 mm, and enough water (24 C.) was placed in a petri dish, and the cut sheet was soaked therein for 60 minutes, and thereafter, the sheet was pulled out of the water and held for 5 minutes, and then, a difference (B-A) between the sample weight A before soaking in water and the sample weight B after soaking in water was determined, and [(B-A)/A]100 was defined as the liquid absorption ratio ( ).

TABLE-US-00001 TABLE 1 Compar- Compar- Compar- Compar- Compar- ative ative ative ative ative Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple ple ple ple ple ple ple ple ple ple ple Material Item Unit 1 2 3 4 5 6 1 2 3 4 5 Formu- Average fiber m 0.8 0.6 0.8 0.8 3.8 0.6 3.8 0.5 2.0 0.8 0.8 0.8 0.5 0.8 3.8 lation diameter Glass Blending ratio % 100 50 50 70 30 50 50 100 100 100 100 100 100 70 30 fiber Separ- Blending Single Com- Com- Com- Single Single Single Single Single Single Com- ator configuration posite posite posite posite of glass fiber Average fiber m 0.8 0.7 1.1 0.9 0.5 2.0 0.8 0.8 0.8 0.5 1.1 diameter of glass fiber Average fiber m 145 126 141 155 111 265 97 100 106 138 121 length of glass fiber Aspect ratio 174 190 130 176 205 133 117 121 127 255 112 (average fiber length/average fiber diameter) of glass fiber Tensile N/mm.sup.2 0.62 1.07 0.81 0.62 0.41 0.51 0.24 0.12 0.26 0.46 0.51 strength Elongation % 8.3 2.7 2.3 3.8 8.5 5.9 0.4 0.8 2.7 11.2 1.8 percentage Liquid % 93.1 86.5 87.3 88.4 88.3 91.2 82.6 83.4 83.8 90.8 84.7 absorption ratio

Examples 1 to 6

[0055] The separator sheets of Examples 1 to 6 are separator sheets, in which the aspect ratio of the glass fiber is 130 to 205, the tensile strength is 0.41 to 1.07 N/mm.sup.2, and the elongation percentage is 2.3 to 8.5%, and which are composed of a single glass fiber or a composite fiber (one obtained by mixing two or more types of glass fibers having different average fiber diameters).

[0056] The liquid absorption ratio showed 85% or more while sufficiently maintaining the basic physical properties (tensile strength: 0.20 N/mm.sup.2 or more, elongation percentage: 2.0% or more and less than 9.0%) required for the separator for valve-regulated lead acid batteries.

[0057] It was found that the separator sheets of Examples 1 to 6 all exhibit optimum basic physical properties (tensile strength and elongation percentage) and liquid absorbability.

Comparative Example 1

[0058] The separator sheet of Comparative Example 1 is a separator sheet, in which the aspect ratio of the glass fiber is 117, the tensile strength is 0.24 N/mm.sup.2, and the elongation percentage is 0.4%, and which is composed of a single glass fiber.

[0059] The tensile strength was 0.20 N/mm.sup.2 or more required for the separator for valve-regulated lead acid batteries, but the elongation percentage was less than 2.0%. Further, the aspect ratio of the glass fiber was also less than 130, and therefore, the liquid absorption ratio was also less than 85%.

Comparative Example 2

[0060] The separator sheet of Comparative Example 2 is a separator sheet, in which the aspect ratio of the glass fiber is 121, the tensile strength is 0.12 N/mm.sup.2, and the elongation percentage is 0.8%, and which is composed of a single glass fiber.

[0061] The tensile strength was less than 0.20 N/mm.sup.2 required for the separator for valve-regulated lead acid batteries, and also the elongation percentage was less than 2.0%. The aspect ratio of the glass fiber was less than 130, and also the liquid absorption ratio was less than 85%.

Comparative Example 3

[0062] The separator sheet of Comparative Example 3 is a separator sheet, in which the aspect ratio of the glass fiber is 127, the tensile strength is 0.26 N/mm.sup.2, and the elongation percentage is 2.7%, and which is composed of a single glass fiber.

[0063] The tensile strength was 0.20 N/mm.sup.2 or more required for the separator for valve-regulated lead acid batteries, and also the elongation percentage was within the range of 2.0% or more and less than 9.01, but the aspect ratio of the glass fiber was less than 130, and the liquid absorption ratio was less than 851.

Comparative Example 4

[0064] The separator sheet of Comparative Example 4 is a separator sheet, in which the aspect ratio of the glass fiber is 255, the tensile strength is 0.46 N/mm.sup.2, and the elongation percentage is 11.2%, and which is composed of a single glass fiber.

[0065] The tensile strength was 0.20 N/mm.sup.2 or more required for the separator for valve-regulated lead acid batteries, and the liquid absorption ratio was 85% or more, but the aspect ratio of the glass fiber exceeded 205, and therefore, the elongation percentage exceeded 9.0%.

Comparative Example 5

[0066] The separator sheet of Comparative Example 5 is a separator sheet, in which the aspect ratio of the glass fiber is 112, the tensile strength is 0.51 N/mm.sup.2, and the elongation percentage is 1.8%, and which is composed of a composite fiber (one obtained by mixing two or more types of glass fibers with different average fiber diameters).

[0067] The tensile strength was 0.20 N/mm.sup.2 or more required for the separator for valve-regulated lead acid batteries, but the elongation percentage was less than 2.0%, and also the aspect ratio of the glass fiber was less than 130. The liquid absorption ratio was also less than 851.

INDUSTRIAL APPLICABILITY

[0068] In the separator for valve-regulated lead acid batteries of the invention, by setting the aspect ratio (average fiber length/average fiber diameter) in the separator of the glass fiber to be used for the separator and the tensile strength and elongation percentage of the separator within specific ranges, an optimum separator that can simultaneously have basic physical properties and liquid absorbability required for the separator for valve-regulated lead acid batteries can be provided.

REFERENCE SIGNS LIST

[0069] 1: electrode [0070] 2: separator