Valve regulated lead-acid battery

Abstract

A valve regulated lead-acid battery includes a positive electrode current collector which is a punched current collector obtained by punching a rolled sheet of lead alloy and in which the average interlayer distance in a layered current collector structure at a cross-section parallel to the rolling direction and along the thickness direction of the current collector is not less than 25 m and not more than 180 m.

Claims

1. A valve regulated lead-acid battery comprising: a positive electrode current collector and a positive active material; a negative electrode current collector and a negative active material; and a liquid holding body, wherein the positive electrode current collector is a punched current collector obtained by punching a rolled sheet of lead alloy, the average interlayer distance of a layered current collector structure at a cross-section of the current collector in a thickness direction is not less than 25 m and not more than 180 m, the positive electrode current collector is composed of a PbCaSn alloy, and where x is a Ca content and y is a Sn content in terms of mass %, the requirements of 0.03x0.09 and 9.16x+0.525y2.0 are satisfied.

2. A valve regulated lead-acid battery comprising: a positive electrode current collector and a positive active material; a negative electrode current collector and a negative active material; and a liquid holding body, wherein the positive electrode current collector is a punched current collector obtained by punching a rolled sheet of lead alloy, the average interlayer distance in a layered current collector structure at a cross-section parallel to the rolling direction and along the thickness direction of the current collector is not less than 25 m and not more than 180 m, the positive electrode current collector is composed of a PbCaSn alloy, and where x is a Ca content and y is a Sn content in terms of mass %, the requirements of 0.03x0.09 and 9.16x+0.525y2.0 are satisfied.

3. The valve regulated lead-acid battery according to claim 1, wherein the positive electrode current collector includes a frame on four sides.

4. The valve regulated lead-acid battery according to claim 1, wherein the average interlayer distance in the layered current collector structure is not less than 50 m and not more than 180 m.

5. The valve regulated lead-acid battery according to claim 1, wherein the average interlayer distance in the layered current collector structure is not less than 25 m and not more than 150 m.

6. The valve regulated lead-acid battery according to claim 1, wherein the average interlayer distance in the layered current collector structure is not less than 50 m and not more than 150 m.

7. A method for producing a valve regulated lead-acid battery comprising providing a positive electrode current collector and a positive active material, a negative electrode current collector and a negative active material, and a liquid holding body in a container, wherein the positive electrode current collector is a punched current collector obtained by punching a rolled sheet of lead alloy and in which the average interlayer distance in a layered current collector structure at a cross-section parallel to the rolling direction and along the thickness direction of the current collector is not less than 25 m and not more than 180 m, the positive electrode current collector is composed of a PbCaSn alloy, and where x is a Ca content and y is a Sn content in terms of mass %, the requirements of 0.03x0.09 and 9.16x+0.525y2.0are satisfied.

8. A method for producing a valve regulated lead-acid battery comprising providing a positive electrode current collector and a positive active material, a negative electrode current collector and a negative active material, and a liquid holding body in a container, wherein the positive electrode current collector is a punched current collector obtained by punching a rolled sheet of lead alloy prepared in such a manner that the rolling reduction ratio is 60 to 90% and in which the average interlayer distance in a layered current collector structure at a cross-section parallel to the rolling direction and along the thickness direction of the current collector is not less than 25 m and not more than 180 m, the positive electrode current collector is composed of a PbCaSn alloy, and where x is a Ca content and y is a Sn content in terms of mass %, the requirements of 0.03x0.09and 9.16x+0.525y2.0 are satisfied.

9. The valve regulated lead-acid battery according to claim 2, wherein the positive electrode current collector includes a crosspiece having a rectangular cross-section, and has a frame on four sides.

10. The valve regulated lead-acid battery according to claim 2, wherein the average interlayer distance in the layered current collector structure is not less than 50 m and not more than 180 m.

11. The valve regulated lead-acid battery according to claim 2, wherein the average interlayer distance in the layered current collector structure is not less than 25 m and not more than 150 m.

12. The valve regulated lead-acid battery according to claim 2, wherein the average interlayer distance in the layered current collector structure is not less than 50 m and not more than 150 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: a view schematically showing a punched grid (a) and an expanded grid (b).

(2) FIG. 2: a view showing the compositions of positive electrode grids in examples.

(3) FIGS. 3(a) and 3(b) each show a photograph of a sample after a corrosion test, where both the samples in FIG. 3(a) and FIG. 3(b) have a composition 1, and the average interlayer distance in the grid structure is 125 m in FIGS. 3(a) and 199 m in FIG. 3(b).

(4) FIG. 4 is a view showing a method for determining an average interlayer distance.

(5) FIG. 5 is a view showing a relationship between a rolling reduction rate and an average interlayer distance.

(6) FIG. 6 shows a relationship between a rolling direction and a current collector.

MODE FOR CARRYING OUT THE INVENTION

(7) Optimum examples of the invention of the present application will be shown below. In implementation of the invention of the present application, examples may be appropriately changed in accordance with common knowledge of a person skilled in the art and disclosures of prior arts.

(8) Hereinafter, the current collector will be simply referred to as a grid in examples.

EXAMPLES

(9) Examples will be described with reference to FIGS. 1 to 3 and Tables 1 to 3. A punched grid 2 is shown in FIG. 1(a), and an expanded grid 10 is shown in FIG. 1(b) for comparison.

(10) Reference numeral 4 denotes an ear, reference numerals 5 and 6 each denote a frame, and reference numeral 7 denotes a leg. The expanded grid 10 has no frame 6. The punched grid 2 has the frame 6, so that extension of the grid due to corrosion is suppressed, and the whole positive electrode plate is easily charged and discharged uniformly.

(11) As positive electrode grid materials, PbCaSn alloy sheets with compositions 1 to 11, respectively, were provided as shown in Table 1 and FIG. 2. The range of optimum examples corresponds to the inside of the slanted line in FIG. 2, and where x is a Ca content in terms of mass %, the requirement of 0.03x0.09 is satisfied. Where y is a Sn content in terms of mass %, the requirement of y2.0 is satisfied, and the slanted boundary line extending from the lower left part to the upper right part in FIG. 2 meets the relationship of 9.16x+0.525=y. Rolled sheets with average interlayer distances of 14 m, 26 m, 62 m, 125 m, 178 m and 199 m, respectively, were produced with the rolling reduction ratio changed in a cold process. Next, the rolled sheet was punched to prepare a positive electrode grid having a thickness of 3 mm. Besides, an expanded grid was produced from the rolled sheet with an average interlayer distance of 62 m, and another positive electrode grid was produced by casting. For producing rolled sheets having the same average interlayer distance, the rolling reduction ratio was adjusted according to the grid composition, and the rolling reduction ratio was changed to achieve a required average interlayer distance. For typical positive electrode grids, the average interlayer distance in the rolled structure is shown in Table 2.

(12) The rolling reduction ratio means how the thickness of a slab that is a mass of lead alloy is changed after it is formed into a sheet as compared to the thickness before rolling when the slab passes through a rolling apparatus such as a roll to be formed into the sheet. The rolling reduction ratio is given by the formula: (slab thicknesssheet thickness)/slab thickness100 (%).

(13) TABLE-US-00001 TABLE 1 Ca Sn Composition (mass %) (mass %) Composition 1 0.03 0.8 Composition 2 0.03 1.5 Composition 3 0.03 2 Composition 4 0.06 1.2 Composition 5 0.06 1.7 Composition 6 0.09 1.5 Composition 7 0.09 2 Composition 8 0.03 0.6 Composition 9 0.06 2.2 Composition 10 0.09 1.2 Composition 11 0.1 1.7

(14) TABLE-US-00002 TABLE 2 Average interlayer distance in rolled structure Samples (m) Example 15 26 Example 1 62 Example 8 125 Example 16 178

(15) As an unformed positive active material, 99.9 mass % of a lead powder formed by a ball mill method, and 0.1 mass % of synthetic resin fibers were formed into a paste with sulfuric acid having a specific gravity of 1.16 at 25 C., the paste was filled into positive electrode grids, and dried and cured, and the positive electrode grids were connected together with a strap to prepare an element including four positive electrode plates. The composition, density and so on of the positive active material are arbitrary.

(16) Negative electrode grids containing 0.1 mass % of Ca, 0.7 mass % of Sn and 0.02 mass % or less of Al, with the remainder including Pb and inevitable impurities, were produced by casting. The composition of the negative electrode grid, the type of grid such as a cast or punched grid, and parameters such as an average interlayer distance are arbitrary. As a negative active material, 98.3 mass % of a lead powder formed by a ball mill method, 0.1 mass % of synthetic resin fibers, 0.1 mass % of carbon black, 1.4 mass % of BaSO.sub.4, and 0.1 mass % of lignin were formed into a paste with sulfuric acid having a specific gravity of 1.14 at 25 C., and the paste was filled into the negative electrode grids. The paste was dried and cured, and the negative electrode grids were connected together with a strap to prepare an element including five negative electrode plates.

(17) A liquid holding body such as a retainer mat was disposed between the positive electrode plate and the negative electrode plate, they were stored in a container while a pressure was applied, sulfuric acid was added as an electrolyte solution, and container formation was performed to prepare a valve regulated lead-acid battery having a capacity of 60 A.Math.h. Silica gel etc. may be used as the liquid holding body, and the configuration of the valve regulated lead-acid battery is arbitrary except for the positive electrode grid. For example, the negative electrode grid may be a cast, expanded or a punched negative electrode grid. The compositions of the positive active material and the negative active material are arbitrary.

(18) A float life test accelerated at a high temperature was conducted in the assumption of a stationary VRLA battery. A charge voltage of 2.23 V was applied at 60 C. at all times, and a discharge capacity was determined every month from an amount of electricity until the terminal voltage decreased to 1.75 V at a discharge current of 0.2 CA at 25 C. The VRLA battery was considered to reach the end of float life at the time when the discharge capacity decreased to 80% or less of the initial value. A vibration with an acceleration of 1.2 G was applied in each of XYZ directions to the VRLA battery which reached the end of float life, and the vibration frequency was swept from 1 Hz to 30 Hz in 45 seconds. After the vibration was applied, the discharge capacity was measured again under the above-mentioned conditions. Values obtained by converting the high-temperature-accelerated float life to a life at normal temperature (25 C.), and capacity holding ratios after the vibration test with the initial capacity set to 100% are shown in Table 3.

(19) TABLE-US-00003 TABLE 3 Capacity holding Average interlayer High-temperature- ratio after vibration Grid distance in accelerated float test at the last production Alloy rolled structure life years stage of life Samples method composition (m) (25 C. equivalent) (initial capacity: 100) Comparative Casting Composition 2 15.2 45.3 Example 1 Comparative Casting Composition 5 16.0 44.0 Example 2 Comparative Casting Composition 6 14.7 46.1 Example 3 Comparative Expanding Composition 2 62 8.4 78.7 Example 4 Comparative Expanding Composition 5 62 9.2 78.4 Example 5 Comparative Expanding Composition 6 62 7.9 79.0 Example 6 Example 1 Punching Composition 1 62 14.0 77.4 Example 2 Punching Composition 2 62 14.8 76.0 Example 3 Punching Composition 3 62 13.9 77.2 Example 4 Punching Composition 4 62 14.5 76.1 Example 5 Punching Composition 5 62 15.1 76.0 Example 6 Punching Composition 6 62 14.2 77.2 Example 7 Punching Composition 7 62 13.9 77.7 Example 25 Punching Composition 8 62 11.2 78.9 Example 26 Punching Composition 9 62 12.6 77.8 Example 27 Punching Composition 10 62 10.8 79.5 Example 28 Punching Composition 11 62 12.4 78.2 Example 8 Punching Composition 1 125 13.8 76.2 Example 9 Punching Composition 2 125 14.5 75.7 Example 10 Punching Composition 3 125 14.1 76.5 Example 11 Punching Composition 4 125 14.3 75.6 Example 12 Punching Composition 5 125 14.8 75.3 Example 13 Punching Composition 6 125 13.8 75.8 Example 14 Punching Composition 7 125 13.6 76.7 Example 29 Punching Composition 8 125 10.8 78.4 Example 30 Punching Composition 9 125 12.2 77.1 Example 31 Punching Composition 10 125 10.1 78.4 Example 32 Punching Composition 11 125 11.9 77.6 Comparative Punching Composition 1 14 11.6 79.2 Example 7 Example 15 Punching Composition 1 26 13.2 78.0 Example 1 Punching Composition 1 62 14.0 77.4 Example 8 Punching Composition 1 125 13.8 76.2 Example 16 Punching Composition 1 178 13.9 75.3 Comparative Punching Composition 1 199 14.2 64.6 Example 8 Comparative Punching Composition 1 14 12.5 78.2 Example 9 Example 17 Punching Composition 2 26 13.9 77.4 Example 2 Punching Composition 2 62 14.8 76.0 Example 9 Punching Composition 2 125 14.5 75.7 Example 18 Punching Composition 2 178 14.6 75.1 Comparative Punching Composition 2 199 14.6 61.9 Example 10 Comparative Punching Composition 4 14 12.2 78.3 Example 11 Example 19 Punching Composition 4 26 13.7 77.9 Example 4 Punching Composition 4 62 14.5 76.1 Example 11 Punching Composition 4 125 14.3 75.6 Example 20 Punching Composition 4 178 14.5 75.1 Comparative Punching Composition 4 199 14.7 61.7 Example 12 Comparative Punching Composition 6 14 10.8 79.6 Example 13 Example 21 Punching Composition 6 26 13.2 78.1 Example 6 Punching Composition 6 62 14.2 77.2 Example 13 Punching Composition 6 125 13.8 75.8 Example 22 Punching Composition 6 178 14.1 75.3 Comparative Punching Composition 6 199 14.3 64.1 Example 14 Comparative Punching Composition 7 14 11.9 79.2 Example 15 Example 23 Punching Composition 7 26 13.4 78.5 Example 7 Punching Composition 7 62 13.9 77.7 Example 14 Punching Composition 7 125 13.6 76.7 Example 24 Punching Composition 7 178 13.7 75.4 Comparative Punching Composition 7 199 14.0 67.3 Example 16 Preferably, the life is 13 years or more, and the capacity holding ratio is 75% or more.

(20) For the cast grids (Comparative Examples 1 to 3), the float life was long, but the capacity holding ratio at the last stage of life was low, and this was due to collapse of the grid by grain boundary corrosion, and falling-off of the positive active material. For the expanded grids (Comparative Examples 4 to 6), the float life was extremely short, and particularly, the float life was markedly shorter as compared to the punched grids (Examples 2, 5 and 6) with the same grid composition and the same average interlayer distance. This indicates that since the corrosion current increased because a rolled sheet was used in the grid, and further, the current distribution became uneven because a grid frame was absent, the battery came into a poor charged state, so that the discharge capacity early decreased.

(21) On the other hand, when a punched grid was used, and the average interlayer distance was 26 m to 178 m, long float life performance was achieved, and a capacity holding ratio (ratio of capacities at the last stage of life and at the initial stage) of 75% or more was obtained even at the last stage of life. When the average interlayer distance was 14 m, the float life decreased to less than 13 years, and when the average interlayer distance was more than 180 m, the capacity holding ratio decreased to less than 75%.

(22) It was found that for the compositions 8 to 11 falling out of the optimum range (Examples 25 to 32), the float life was short. When the Ca concentration was less than 0.03 mass %, the strength of the grid was low from the initial stage, and when the Ca concentration was more than 0.09 mass %, corrosion easily progressed, and caused the grid to easily extend, so that a short circuit easily occurred. It was also found that when the Sn concentration fell out of the optimum range, corrosion easily progressed. The VRLA batteries of Examples 25 to 32 are included in the present invention in that the average interlayer distance is optimized to secure both float life performance and earthquake-proof characteristics at the last stage of life.

(23) For examining the relationship between the average interlayer distance in the positive electrode grid and corrosion, a rolled plate before punching was immersed in a sulfuric acid electrolyte solution having a specific gravity of 1.28, a corrosion test at a constant potential of 1.8 V as calculated in terms of a standard hydrogen electrode at 75 C. was conducted for 4 months, and the corrosion state was observed. A pure Pb electrode was used as a counter electrode, and an Ag/AgCl/KCl electrode was used as a reference electrode. The state of the sample after the corrosion test is shown for the rolled plate in Example 8 (FIG. 3(a)) and the rolled plate in Comparative Example 8 (FIG. 3(b)). In Comparative Example 8 where the average interlayer distance was 199 m, the rolled plate was broken by grain boundary corrosion.

(24) In examples, a punched grid is used, and the average interlayer distance is 25 m or more, so that exfoliation corrosion is suppressed, and the average interlayer distance is 180 m or less, so that grain boundary corrosion is suppressed. Accordingly, a VRLA battery excellent in float life and earthquake-proof characteristics at the last stage of life is obtained.

(25) In examples, a stationary VRLA battery has been described, but a charge method other than float charge may be used, and the VRLA battery may be used in applications other than stationary applications.

DESCRIPTION OF REFERENCE SIGNS

(26) 2 Punched grid 4 Ear part 5,6 Frame 7 Leg 8,12 Crosspiece 10 Expanded grid