AU2017235920B2 - Lead-acid battery and current collector - Google Patents

Abstract

OF THE DISCLOSURE A lead-acid battery includes a positive electrode current collector. The positive electrode current collector includes: an outer frame portion having transverse frame members and longitudinal frame members; and an inner cross member formed in the inside of the outer frame portion. Assuming a cross-sectional area of the longitudinal frame member as S (mm2) and a thickness of the longitudinal frame member as t (mm), S > t2 /2 is satisfied. The inner cross member includes a bold inner cross member having a cross-sectional area which exceeds t2/4. With respect to a grid formed of the longitudinal frame member and the bold inner cross member or a grid formed of the longitudinal frame member, the transverse frame member and the bold inner cross member, assuming a volume of the grid as V (cm3), a length of a portion of the longitudinal frame member which forms the grid as L (mm) and a width of the longitudinal frame member as d (mm), a following formula (1) is satisfied. (S x d) / (V x L2) > 0.002 ..... formula (1) 1/12 FIG. 1 25 10 1- I i 21 i i 22 24 In lil

Description

1/12

FIG. 1 10

1-

I i 21 i i 22 24

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LEAD-ACID BATTERY AND CURRENT COLLECTOR FIELD

This disclosure relates to a lead-acid battery and a current collector.

BACKGROUND

In recent years, aiming at the reduction of CO 2 emission, the number

of power generation facilities which generate electric power using natural

energy such as solar energy and wind energy has been steadily increased.

In these power generation facilities, electric power generation timing cannot

be controlled. Accordingly, a battery facility is used in combination with

such a power generation facility on an electric power generation side and/or a

consumer side thus realizing leveling of electric power. A lead-acid battery

is often used as such a battery.

For example, JP 10-188999 A discloses a lead-acid battery and, more

particularly, a positive electrode grid of the lead-acid battery where a

cross-sectional area of the longitudinal frame member of the positive

electrode grid frame is set two or more times as large as a cross-sectional

area of a transverse frame member, and a compression ratio of a separator is

set to 1.1 or more.

SUMMARY

When a lead-acid battery is used for the above-mentioned leveling of

electric power generated using natural energy, charging and discharging are

repeated (i.e., such a usage corresponds to a cycle application). The inventor of this disclosure has found that, in a conventional lead-acid battery for cycle use, a life may be largely shortened due to breaking of a current collector. An object of this disclosure is to provide a lead-acid battery capable of sustaining a life even when the lead-acid battery is used particularly in the above-mentioned application, and to provide a current collector used in the lead-acid battery.

In the studies for overcoming the above-mentioned drawback, the

inventor of this disclosure has found that a conventional lead-acid battery for

cycle use exhibits a short life particularly when the lead-acid battery is used

within a range where a depth of discharge is large. For example, in a cycle

life test where DoD (Depth of Discharge) is 70% at 25°C, a valve-regulated

lead-acid battery (VRLA) for cycle use exhibited a very short life. As a

cause of such a drawback, the inventor of this disclosure found that the

expansion of a positive active material generated along with

charge/discharge cycle is remarkably increased and hence, a stress is applied

to a longitudinal frame member of the positive electrode grid whereby the

longitudinal frame member is broken along grain boundaries.

A lead-acid battery according to an aspect of this disclosure includes

a positive electrode current collector made of lead or a lead alloy. The

positive electrode current collector includes: an outer frame portion having

first and second transverse frame members and first and second longitudinal

frame members; a plurality of inner cross members formed in an intersecting

manner in the inside of the outer frame portion; and a current collecting lug

portion integrally formed on an outer side of the outer frame portion at a

position of the first transverse frame member close to the first longitudinal frame member. Assuming a cross-sectional area of the longitudinal frame member on a cross section perpendicular to an extending direction of the longitudinal frame member as S (mm2) and a thickness of the longitudinal frame member as t (mm), S > t 2 /2 is satisfied. The plurality of inner cross members include a bold inner cross member having a cross-sectional area which exceeds t 2 /4 on a cross section perpendicular to an extending direction of the bold inner cross member. With respect to at least one of a grid formed of the longitudinal frame member and the bold inner cross member without being traversed by said other bold inner cross members or a grid formed of the longitudinal frame member, the transverse frame member and the bold inner cross member without being traversed by said other bold inner cross members, assuming a volume of the grid as V (cm3), a length of a portion of the longitudinal frame member which forms the grid as L (mm) and a width of the longitudinal frame member as d (mm), a following formula (1) is satisfied.

(S x d) / (V x L2) > 0.002 ..... formula (1)

A current collector according to another aspect of this disclosure

includes: an outer frame portion having first and second transverse frame

members and first and second longitudinal frame members; a plurality of

inner cross members formed in an intersecting manner in the inside of the

outer frame portion; and a current collecting lug portion integrally formed on

an outer side of the outer frame portion at a position of the first transverse

frame member close to the first longitudinal frame member. Assuming a

cross-sectional area of the longitudinal frame member on a cross section

perpendicular to an extending direction of the longitudinal frame member as

S (mm2) and a thickness of the longitudinal frame member as t (mm), S > t 2 /2

is satisfied. The plurality of inner cross members include a bold inner cross

member having a cross-sectional area which exceeds t 2 /4 on a cross section

perpendicular to an extending direction of the bold inner cross member.

With respect to at least one of a grid formed of the longitudinal frame

member and the bold inner cross member without being traversed by said

other bold inner cross members or a grid formed of the longitudinal frame

member, the transverse frame member and the bold inner cross member

without being traversed by said other bold inner cross members, assuming a

volume of the grid as V (cm3), a length of a portion of the longitudinal frame

member which forms the grid as L (mm) and a width of the longitudinal

frame member as d (mm), a following formula (1) is satisfied.

(S x d) / (V x L2) > 0.002 ..... formula (1)

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view exemplifying a positive electrode current

collector of a lead-acid battery according to one embodiment of this

disclosure.

FIG. 2 is a view for further describing the positive electrode current

collector in FIG. 1.

FIG. 3 is a graph showing a relationship, in a test battery according

to one embodiment of this disclosure, between a parameter in this disclosure

and the number of life cycles of a lead-acid battery and the number of

portions where breaking occurs in a frame member.

FIG. 4 is a graph showing a relationship, in the test battery according to one embodiment of this disclosure, between the parameter in this disclosure and a maximum elongation rate of the positive electrode plate in a transverse direction.

FIG. 5 is a graph showing a relationship, in another test battery

according to one embodiment of this disclosure, between the parameter in

this disclosure and the number of life cycles of a lead-acid battery and the

number of portions where breaking occurs in a frame member.

FIG. 6 is a graph showing a relationship, in another test battery

according to one embodiment of this disclosure, between the parameter in

this disclosure and a maximum elongation rate of the positive electrode plate

in a transverse direction.

FIG. 7 is a view of the positive electrode current collector of the

lead-acid battery for describing a portion where breaking occurs in a

longitudinal frame member.

FIG. 8 is a graph showing rates of portions where breaking occurs in

the longitudinal frame member of the positive electrode current collector of

the lead-acid battery.

FIG. 9 is a view showing one example of a positive electrode current

collector of a lead-acid battery according to this disclosure.

FIG. 10 is a view showing another example of the positive electrode

current collector of the lead-acid battery according to this disclosure.

FIG. 11 is a view showing still another example of the positive

electrode current collector of the lead-acid battery according to this

disclosure.

FIG. 12 is a view showing still another example of the positive electrode current collector of the lead-acid battery according to this disclosure.

FIG. 13 is a view showing still another example of the positive

electrode current collector of the lead-acid battery according to this

disclosure.

FIG. 14 is a view showing a positive electrode current collector of a

lead-acid battery according to a modification of the embodiment of this

disclosure.

DESCRIPTION OF EMBODIMENTS

According to an aspect of this disclosure, there is provided a lead-acid

battery including a positive electrode current collector made of lead or a lead

alloy. The positive electrode current collector includes: an outer frame

portion having first and second transverse frame members and first and

second longitudinal frame members; a plurality of inner cross members

formed in an intersecting manner in the inside of the outer frame portion;

and a current collecting lug portion integrally formed on an outer side of the

outer frame portion at a position of the first transverse frame member close

to the first longitudinal frame member. Assuming a cross-sectional area of

the longitudinal frame member on a cross section perpendicular to an

extending direction of the longitudinal frame member as S (mm2) and a

thickness of the longitudinal frame member as t (mm), S > t 2 /2 is satisfied.

The plurality of inner cross members include a bold inner cross member

having a cross-sectional area which exceeds t 2 /4 on a cross section

perpendicular to an extending direction of the bold inner cross member.

With respect to at least one of a grid formed of the longitudinal frame

member and the bold inner cross member without being traversed by said

other bold inner cross members or a grid formed of the longitudinal frame

member, the transverse frame member and the bold inner cross member

without being traversed by said other bold inner cross members, assuming a

volume of the grid as V (cm3), a length of a portion of the longitudinal frame

member which forms the grid as L (mm) and a width of the longitudinal

frame member as d (mm), a following formula (1) is satisfied.

(S x d) / (V xL2) > 0.002 ..... formula (1)

According to the lead-acid battery and the current collector of this

disclosure, breaking of the current collector can be suppressed and

shortening of a life of the lead-acid battery can be suppressed.

The grid which is formed of the first transverse frame member, the

second longitudinal frame member and the bold inner cross members may be

configured to satisfy the formula (1).

The grid which is formed of the first transverse frame member, the

first longitudinal frame member and the bold inner cross members may be

configured to satisfy the formula (1).

The grid including the second longitudinal frame member may be

configured to satisfy the formula (1).

The inner cross members may include at least one of longitudinal

cross members arranged parallel to the longitudinal frame member and

transverse cross members arranged parallel to the transverse frame

member.

The plurality of inner cross members may further include a fine inner cross member having a cross-sectional area of t 2 /4 or less, and the fine inner cross member may be disposed in the inside of the grid.

A following formula (2) may be satisfied.

(S x d) / (V x L2) > 0.0032 ..... formula (2)

Hereinafter, a valve-regulated lead-acid battery (VRLA) according to

one embodiment of this disclosure is described with reference to the

drawings.

The valve-regulated lead-acid battery of this embodiment includes:

paste type positive electrode plates and paste type negative electrode plates;

separators each of which is disposed between the positive electrode plate and

the negative electrode plate and retains an electrolyte solution; and a

container for housing the positive electrode plates, the negative electrode

plates and the separators.

A positive electrode plate and a negative electrode plate are

respectively formed such that an active material paste is filled in a

grid-shaped positive electrode current collector made of lead or a lead alloy (a

Pb-Ca-based alloy, a Pb-Ca-Sn-based alloy or the like), an active paste is

filled in a grid-shaped negative electrode current collector made of lead or a

lead alloy (a Pb-Ca-based alloy, a Pb-Ca-Sn-based alloy or the like) and,

thereafter, the pastes are aged and dried. In this specification, an active

material means a material obtained by removing a current collector from an

electrode plate, and an additive and the like are included in the active

material. The active material is also referred to as an electrode material.

As a separator, an AGM separator which is made of fine glass fibers, silica

powder and the like is used, for example. A dilute sulfuric acid which is an electrolyte solution is impregnated into the separator. The container is formed of: a rectangular-parallelepiped container body with one surface thereof opened; and a lid which closes the opening of the container body, for example. The container is formed by injection molding mainly using thermoplastic plastic as a material, for example. The positive electrode plate, the negative electrode plate, the separator and the container can have suitable configurations according to purposes or applications.

(Structure of positive electrode current collector)

Next, a positive electrode plate which a valve-regulated lead-acid

battery of this embodiment includes is further described.

FIG. 1 is a view schematically showing a positive electrode current

collector 10 forming a positive electrode plate in this embodiment. The

positive electrode current collector 10 includes: an outer frame portion 15

formed into a rectangular shape; and a plurality of inner cross members 24

formed in the inside of the outer frame portion 15 in an intersecting manner

thus forming a grid in cooperation with the outer frame portion 15.

The outer frame portion 15 is formed of a first transverse frame

member 11, a second transverse frame member 12, a first longitudinal frame

member 13 and a second longitudinal frame member 14. A current

collecting lug portion 25 is formed on an end of the first transverse frame

member 11 on a side of the first longitudinal frame member 13 such that the

current collecting lug portion 25 is integrally formed on an outer side of the

outer frame portion 15. Leg portions 26 are formed on an outer side of the

second transverse frame member 12. In this specification, a side on which

the current collecting lug portion 25 is disposed in FIG. 1 may be referred to as "upper side", and a side on which the leg portions 26 are disposed in FIG.

1 may be referred to as "lower side". The description of "upper side", and

"lower side" and the description of "longitudinal" and "lateral" in the

transverse frame member 11, the longitudinal frame member 13 or the like

are used for the sake of convenience of expression. Accordingly, none of

these descriptions limits the direction or the like of the positive electrode

current collector 10 when the positive electrode current collector 10 is used.

The inner cross members 24 include: longitudinal inner cross

members 21 arranged parallel to the longitudinal frame members 13 and 14;

and transverse inner cross members 22 and 23 arranged parallel to the

transverse frame members 11 and 12. Lateral inner cross members are

classified depending on a thickness into the transverse bold cross members

22 and the transverse fine cross members 23 having a smaller thickness

than the transverse bold cross member 22. To be more specific, the

transverse inner cross members includes, assuming a thickness (a size in a

direction perpendicular to a paper on which FIG. 1 is drawn) of the

longitudinal frame member 13 and 14 as "t", the transverse inner cross

members 22 each having a cross-sectional area which exceeds t 2/4, and the

transverse fine cross members 23 each having a cross-sectional area of t 2 /4 or

less. In the example shown in FIG. 1, both the longitudinal inner cross

members 21 and the transverse bold cross member 22 are respectively

arranged equidistantly inside the outer frame portion 15. The transverse

fine cross members 23 are substantially equidistantly arranged between two

transverse bold cross members 22, and between the transverse bold cross

member 22 and the first transverse frame member 11 or the second transverse frame member 12. A distance between the first transverse frame member 11 and the transverse fine cross member 23 disposed closest to the first transverse frame member 11 and a distance between the second transverse frame member 12 and the transverse fine cross member 23 disposed closest to the second transverse frame member 12 are set smaller than a distance between two transverse fine cross members 23 or a distance between the transverse fine cross member 23 and the transverse bold cross member 22.

In this embodiment, the positive electrode current collector 10 is

manufactured by a casting method. That is, using a casting mold which

corresponds to the above-described thicknesses and arrangement of the

respective frame members and the respective cross members, the positive

electrode current collector 10 may be formed using lead or a lead alloy as a

material.

FIG. 2 is a view for describing the configuration of the positive

electrode current collector 10 in more detail. A part I in FIG. 2 corresponds

to a view showing an area around a right upper portion in FIG. 1 in an

enlarged manner. In FIG. 2, only the smaller number of transverse fine

cross members 23 than the number of transverse fine cross members 23 in

FIG.1 is shown. FIG. 2 also shows a part II and a part III together with the

part I. The part II is a view of the positive electrode current collector 10

within a range shown in the part I as viewed from a right side in the drawing.

Shapes of the first transverse frame member 11, the transverse bold cross

members 22 and the transverse fine cross members 23 are indicated by a

solid line in a see-through manner in addition to the longitudinal frame member 14. The part III is a view showing cross sections of the longitudinal frame member 14 and the longitudinal inner cross member 21 as viewed from below. The transverse frame member 11 has a hexagonal cross section, and other members have a rhombic cross section. The cross-sectional shapes of the transverse frame member 11 and other frame members and inner cross members are not limited to such shapes.

In the positive electrode current collector 10 in this disclosure, by

establishing a predetermined relationship between a volume of a grid formed

of members including the longitudinal frame member 13 or 14 and a length

and a cross-sectional area of the longitudinal frame member 13 or 14 at a

portion which forms the grid, even when the positive electrode current

collector 10 is used within a range where a depth of discharge is large, it is

possible to prevent shortening of a life of the positive electrode current

collector 10.

To be more specific, consider a case where the grid is formed of the

second longitudinal frame member 14, the longitudinal inner cross member

21 disposed closest to the second longitudinal frame member 14, the first

transverse frame member 11 and the transverse bold cross member 22

disposed closest to the first transverse frame member 11 (the right upper

grid among grids where the transverse fine members 23 are ignored in FIG.

1 and FIG. 2). Assume a volume of the grid as V (cm3), a width and a

cross-sectional area of the second longitudinal frame member 14 as d (mm)

and S (mm2), and a length of the second longitudinal frame member 14 at a

portion which forms the grid (a distance between the first transverse frame

member 11 and the transverse inner cross member 22 in this embodiment) as L (mm). By forming the positive electrode current collector 10 such that the following formula (1) is satisfied, even when the positive electrode current collector 10 is used within a range where a depth of discharge is large, it is possible to prevent shortening of a life of the positive electrode current collector 10 and, eventually, shortening of a life of the lead-acid battery.

(S x d) / (V x L2) 0.002 ..... formula (1)

The description has been made with respect to the grid sandwiched

between the first transverse frame member 11 and the transverse bold cross

member 22 (the right upper grid of the positive electrode current collector 10

in FIG. 1 and FIG. 2). The same goes for the grid between two transverse

bold cross members 22 or the grid between the transverse bold cross member

22 and the second transverse frame member 12. The same also goes for the

grid formed on a side of the first longitudinal frame member 13. For

example, in FIG. 2, consider a case where the grid is formed of the transverse

bold cross member 22 disposed closest to the first transverse frame member

11, the transverse bold cross member 22 disposed second closest to the first

transverse frame member 11 (assume a distance between these transverse

bold cross members 22 as "L.'), the second longitudinal frame member 14 and

the longitudinal inner cross member 21 disposed closest to the second

longitudinal frame member 14. In this case, it is sufficient that the grid be

formed to satisfy the following formula.

(S x d) / (Vx L' 2) 0.002

In the part I in FIG. 2 which is a plan view, for example, a volume V

of the grid can be defined as a product of an area surrounded by the respective members forming the grid and a thickness "t" of the longitudinal frame member 14. In this embodiment, an area of the grid may be defined as an area surrounded by center lines of the respective members forming the grid. When the frame member having a hexagonal cross section is used as in the case of the transverse frame member 11 shown in a part II in FIG. 2, a volume inside apexes positioned on both ends of the frame member in a thickness direction of the positive electrode current collector 10 and disposed closer to the inside of the grid in a cross section of the frame member can be calculated as the volume of the grid. When the similar definition is applied to the member having a rhombic cross section (the longitudinal frame member 14, the longitudinal inner cross member 21, the transverse bold cross member 22), the member has only one pair of apexes positioned on both ends of each member in a thickness direction of the positive electrode current collector 10 so that apexes means a center line of the member.

With respect to the longitudinal frame members 13, 14 and the

longitudinal inner cross members 21, a cross-sectional area means a

cross-sectional area taken along a plane perpendicular to an extending

direction of the member. A width of the longitudinal frame member 13, 14

means a size in an extending direction of the transverse frame members 11

and 12.

In a portion included in one grid, when the widths and the

cross-sectional areas of the respective members are not uniform, a

cross-sectional area and a width of the corresponding portion at a center

portion in the length direction of the longitudinal frame member are used in

the above-mentioned formula. This is because the largest stress is applied to the center portion of the member so that strength at such a portion is important.

Next, the reason that breaking can be suppressed when the formula

(1) is satisfied is considered as follows.

First, inventor of this disclosure has found that when the

valve-regulated lead-acid battery is used within a range where a depth of

discharge is large, the expansion of a positive active material caused by a

charge/discharge cycle is remarkably increased so that a stress is applied to

the members of the positive electrode current collector 10 whereby the

member is broken due to intergranular fracture. According to this finding,

in the positive electrode current collector 10, corresponding to the increase of

the volume of the grid formed of the members, a change in size of the grid

due to the expansion of the positive active material is increased relatively.

Accordingly, a stress applied to the members is increased thus easily causing

breaking in the members.

In this embodiment, in the case of the inner cross members 24, a

positive active material is filled and exists on both sides of the individual

frame member. Accordingly, a stress generated due to the expansion of the

positive active material is applied to the inner cross member 24 from both

sides so that the stress is canceled or reduced. On the other hand, in the

case of the frame members forming the outer frame portion 15, a positive

active material exists only on an inner side of the positive electrode current

collector 10 and hence, unlike the inner cross members 24, a stress is not

canceled so that breaking is liable to occur on the frame member which forms

the outer frame portion 15.

A force which resists a stress applied to the frame member (resistant

force) changes depending on a width, a cross-sectional area or a length of the

longitudinal frame member 13 or 14 which forms the grid. When a width

and a cross-sectional area of the longitudinal frame member 13 or 14 which

forms the grid are decreased or when a length of the longitudinal frame

member 13 or 14 is increased, a resistant force is lowered so that breaking is

liable to occur. In view of the above, breaking can be suppressed by

designing volumes of the grids and widths, cross-sectional areas and lengths

of the longitudinal frame members 13 and 14 forming the grids such that a

stress applied to the longitudinal frame members 13 and 14 is reduced or a

resistant force of the longitudinal frame members 13 and 14 is increased.

Further, to facilitate the flow of an electric current from the current

collecting lug portion 25 to a leg portion 26 side, all longitudinal inner cross

members 21 are respectively formed of a bold member, and a distance

between each two longitudinal inner cross members 21 is set narrower than

a distance between each two transverse bold cross members 22 so that the

grids surrounded by the bold members have a longitudinally elongated

rectangular shape. The bold member indicates a frame member having a

cross-sectional area exceeding t 2/4. To be more specific, the bold members

are the transverse bold cross members 22, the transverse frame members 11

and 12, and the longitudinal frame members 13 and 14. The transverse

frame members 11 and 12 and the longitudinal frame members 13 and 14

have further larger cross-sectional areas, that is, cross-sectional areas

exceeding t 2/2.

As has been described above, the longitudinal frame member 13 or 14 is more likely to be broken by being affected by a stress than the transverse frame member 11 or 12 and hence, setting of sizes of the longitudinal frame members 13 and 14 is important. Inventor of this disclosure has found that when the inner cross members 24 include the transverse bold cross members

22 and the transverse fine cross members 23 which differ from each other in

cross-sectional area, the transverse fine cross members 23 having a

cross-sectional area of t 2 /4 or less do not affect ease of breaking (strength) of

the positive electrode current collector 10 (this finding described later).

Accordingly, in the formula (1) and the like, the grid is considered to include

the transverse bold cross member 22 in a mode irrelevant to the transverse

fine cross members 23. Further, the grid is considered where the grid is not

traversed by other bold members. For example, although it may be possible

to consider that "grid" is formed of: the second longitudinal frame member

14; the second longitudinal inner cross member 21 counted from a right side

in FIG. 1 among the longitudinal inner cross members 21; the first

transverse frame member 11; and the uppermost transverse bold cross

member 22 among the transverse bold cross members 22, the grid is

traversed by the first longitudinal inner cross member 21 counted from the

right side among the longitudinal inner cross members 21. Accordingly,

such a grid is not considered as the grid according to this disclosure.

Next, the valve-regulated lead-acid battery is manufactured using

the current collector 10 having the above-mentioned configuration.

First, a positive electrode material in a paste form was prepared by

mixing lead powder and synthetic resin fibers together with water and a

sulfuric acid. The positive electrode material in a paste form was filled into the positive electrode current collector 10 which is a cast grid made of a

Pb-Ca-Sn-based alloy and, then, the positive electrode material in a paste

form was aged and dried thus forming an unformed positive electrode plate.

A negative electrode material in a paste form was prepared by mixing

lead powder, synthetic resin fibers, a shrink-proofing agent, carbon black and

BsSO4 together with water and a sulfuric acid. The negative electrode

material in a paste form was filled into a cast grid made of a Pb-Ca-Sn-based

alloy and, then, the negative electrode material in a paste form was aged and

dried thus forming an unformed negative electrode plate.

Next, eight positive electrode plates and nine negative electrode

plates were stacked with each other with separators formed of an extremely

fine glass mat interposed between the positive electrode plate and the

negative electrode plate thus forming a group of electrode plates. A

pressure was applied to the group of the electrode plates until a length of the

group of the electrode plates became equal to an inner size of a container and,

then, the group of the electrode plates was housed in the container. By

adding pure lead as lead to be added, positive electrode straps and negative

electrode straps for connecting the electrode plates with each other were

formed respectively. In this embodiment, a Pb-Sn-based alloy may be also

used for forming the straps in place of pure lead.

A lid was adhered to the container and, thereafter, a sulfuric acid was

filled into the container as an electrolyte solution through a solution filling

portion of the lid so as to perform formation in the container. Due to such

treatment, a valve-regulated lead-acid battery having a nominal capacity of

500Ah (10hR (hour rate)) and a nominal voltage of 2 V was prepared.

Next, Table 1 shows a result of a cycle test on test batteries A

prepared as described above. The cycle test was carried out under the

following conditions.

Discharge with DoD of 70%: 25°C, 0.2CA x 3.5h

Normal charge: 25°C, constant voltage of 2.42 V (Imax = 0.2CA),

amount of charge /discharge capacity = 1.02

Uniform charge: 25 0 C, every six cycles, normal charge + constant

voltage of 2.42 V (Imax = 0.2CA) x 8h

Life judging condition: point of time that end-of-discharge voltage in

discharge with DoD of 70% becomes lower than 1.7 V.

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In all positive electrode current collectors of the test batteries A, it

was assumed that a distance between each two transverse bold cross

members 22 and a distance between the transverse frame member 11 or 12

and the transverse bold cross member 22 were equal, that is, "L". With

respect to the lead-acid batteries A-1 to A-15 which respectively include

different positive electrode current collectors where although a thickness "t"

of the longitudinal frame member is set to 6.0 mm in all current collectors, a

width "d", a cross-sectional area S and a length L of a portion of the

longitudinal frame member forming a grid are changed among the current

collectors, a relationship between a value of (S x d) / (V x L2) on the left side

of the formula (1), the number of life cycles, the number of portions where

breaking occurs in the longitudinal frame member, and a maximum

elongation rate of the positive electrode plate in the transverse direction is

shown in Table 1.

As shown in Table 1, with respect to the lead-acid batteries A-1 to A-4

where a value of (S x d) / (V x L2) was set to less than 0.002, breaking

occurred in the longitudinal frame member at least at one portion. The

smaller a value of (S x d) / (V x L2), the larger the number of portions where

breaking occurs became. On the other hand, with respect to the lead-acid

batteries A-5 to A-15 where a value of (S x d) / (V x L2) was set equal to or

more than 0.002, no breaking occurred in the longitudinal frame member.

Such results and other results are shown in graphs in FIG. 3 and FIG. 4. As

shown in FIG. 3, when a value of (S x d) / (V x L2) exceeded 0.002, the

number of portions where breaking occurs in the frame member was

remarkably reduced and the number of life cycles was remarkably increased.

Further, as shown in FIG. 4, a maximum elongation rate of the positive

electrode plate in the transverse direction became remarkably smaller when

a value of (S x d) / (V x L2) was around 0.002.

Table 2 shows results of a cycle test with respect to other test

batteries B. The test batteries B are also VRLAs which respectively use a

positive electrode current collector 10 having rectangular grids as shown in

FIG. 1 and FIG. 2. Each test battery B had a nominal capacity of

200Ah/l0hR (formed of eight positive electrode plates and nine negative

electrode plates).

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In all positive electrode current collectors of the test batteries B, it

was assumed that a distance between each two transverse bold cross

members 22 and a distance between the transverse frame member 11 or 12

and the transverse bold cross member 22 were equal, that is, "L". With

respect to the lead-acid batteries B-1 to B-15 which respectively include

different positive electrode current collectors where although a thickness "t"

of the longitudinal frame member is set to 3.8 mm in all current collectors, a

width "d", a cross-sectional area S and a length L of a portion of the

longitudinal frame member forming a grid are changed among the current

collectors, a relationship between a value of (S x d) / (V x L2) on the left side

of the formula (1), the number of life cycles, the number of portions where

breaking occurs in the longitudinal frame member, and a maximum

elongation rate of the positive electrode plate in the transverse direction is

shown in Table 2.

As shown in Table 2, also in this case, when a value of (S x d) / (V x

L2) is 0.002 or more, no breaking occurred in the longitudinal frame member.

Further, as also shown in graphs in FIG. 5 and FIG. 6, using a point where a

value of (S x d) / (V x L2) is 0.002 as a boundary, the number of portions

where breaking occurs in the longitudinal frame member was remarkably

reduced, and the number of life cycles was remarkably increased. A

maximum elongation rate of the positive electrode plate in the transverse

direction was also remarkably lowered.

As described above, the formula (1) was satisfied so that breaking in

the positive electrode current collector 10 was remarkably suppressed

whereby a life of the lead-acid battery could be increased.

As shown in Table 1, Table 2, FIG. 4 and FIG. 6, when the following

formula (2) is satisfied, elongation of the positive electrode plate in the

transverse direction can be suppressed.

(S x d) / (V x L2) 0.0032 ..... formula (2)

In the same manner, when the following formula (3) is satisfied,

elongation of the positive electrode plate in the transverse direction can be

suppressed with more certainty.

(S x d) / (V x L2) 0.0046 ..... formula (3)

(Fine inner cross member)

Next, it is described hereinafter that, among the inner cross members

24, the transverse fine cross members 23 do not affect ease of breaking of the

positive electrode current collector 10.

A result of test batteries C and D is shown in Table 3. Table 3 shows

substantially the same contents as Table 1 and Table 2 with respect to the

test batteries C and D having a nominal capacity of 500Ah/lOhR (formed of

eight positive electrode plates and nine negative electrode plates) together

with the number of transverse fine cross members 23 in the positive

electrode current collector 10.

a)t 4-D CC o©

C) a( 3

C) o

a) C mC.)

ctc--- 1() C3) c t

(3) bj

4-D

C)

C4-4 C (3)C

4t C)

C)C)

cy:

-4

[c:

In the test batteries C, values of a thickness "t" and a width "d" of the

longitudinal frame member, a length L of the longitudinal frame member at

a portion forming a grid, a cross-sectional area S of the longitudinal frame

member and a volume V of a grid were set substantially equal to the

corresponding values in the test battery A-1 shown in Table 1. Inthetest

batteries C-1 to C-3, a value of (S x d) / (V x L2) was 0.0011 (smaller than

0.002) so that breaking occurred in the longitudinal frame member. Even

when the number of transverse fine cross members was increased to 16, 24

or 34, the number of portions where breaking occurred, the number of life

cycles and maximum elongation rate of the positive electrode plate in the

transverse direction were substantially equal. In the test batteries having

the larger number of transverse fine cross members, the number of portions

where breaking occurs was rather increased.

In the test batteries D, values of a thickness "t" and a width "d" of the

longitudinal frame member, a length L of a portion of the longitudinal frame

member forming a grid, a cross-sectional area S of the longitudinal frame

member and a volume V of a grid were set to substantially equal to the

corresponding values in the test battery A-12 shown in Table 1. Inthetest

batteries D-1 to D-3, a value of (S x d) / (V x L2) was 0.0077 (0.002 or more) so

that no breaking occurred in the longitudinal frame member. Even when

the number of transverse fine cross members 23 was changed to 12, 18 or 28,

substantially no influence was exerted on the number of portions where

breaking occurs, the number of life cycles and a maximum elongation rate of

the positive electrode plate in the transverse direction. Particularly, also in

the test battery D-1 having the smaller number of transverse fine cross members 23 than the test battery C-1 where breaking occurred, no breaking occurred.

The reason may be considered as follows. When a lead-acid battery

is used (or when a life test is performed), the positive electrode current

collector 10 is gradually corroded. The transverse fine cross members 23

are fine cross members provided to the positive electrode current collector 10

mainly for facilitating the filling of an active material paste to the positive

electrode current collector 10. Accordingly, the transverse fine cross

members 23 are corroded within a relatively short period after the lead-acid

battery is started to be used, so that the transverse fine cross members 23 do

not affect strength of the positive electrode current collector 10.

When a cross-sectional area of each transverse member is t 2 /4 or less

with respect to a thickness "t" of the longitudinal frame member, it is

apparent that the transverse member does not affect breaking of the positive

electrode current collector 10. Accordingly, the transverse bold cross

member 22 having a cross-sectional area of exceeding t 2 /4 is used as an

element for forming a grid considered in the formula (1).

As has been described heretofore, the transverse fine cross members

23 do not affect ease of breaking of the positive electrode current collector 10.

Accordingly, in designing the positive electrode current collector 10 for

suppressing breaking of the positive electrode current collector 10, it is

sufficient to consider only the transverse bold cross members 22. To acquire

favorable filling property of an active material paste, the transverse fine

cross members 23 are desirably arranged also in a grid considered in the

formula (1). The arrangement or the like of the transverse fine cross members 23 can be designed irrelevant to ease of breaking of the positive electrode current collector 10. Accordingly, the designing of the positive electrode current collector 10 can be simplified.

(Portions of positive electrode current collector where breaking occurs)

Next, portions of the positive electrode current collector 10 where

breaking easily occurs are described with reference to FIG. 7 and FIG. 8.

FIG. 7 shows an electrode plate 50 prepared using the positive electrode

current collector 10 shown in FIG. 1. In this embodiment, the electrode

plate 50 is divided into four parts in the longitudinal direction, and regions

on a side of the current collecting lug portion 25 (a side on the first

transverse frame member 11) are considered as regions A, B, C and D from

the top to the bottom. In the same manner, regions on a side opposite to the

current collecting lug portion 25 (a side of the second longitudinal frame

member 14) are considered as regions E, F, G and H from the top to the

bottom. The positive electrode current collector 10 shown in FIG. 1 includes

three transverse bold cross members 22 which are disposed equidistantly so

that the positions of the transverse bold cross members 22 agree with

boundaries between respective regions. However, it is not always the case

that the positions of the transverse bold cross members 22 are defined as the

boundaries between the respective regions. Accordingly, when the positive

electrode current collector 10 has a different grid shape, for example, when

the positive electrode current collector 10 has the numbers of the transverse

bold cross members 22 and the arrangement or the like different from the

respective regions (for example, FIG. 10 to FIG.12 and the like described

later), the boundaries between the respective regions do not agree with the positions of the transverse bold cross members 22.

To express the portions where breaking occurs in the first and second

longitudinal frame members 13 and 14 of the battery A-1 (having eight

positive electrode current collectors 10) shown in Table 1 along the regions A

to H shown in FIG. 7, the distribution of the portions where breaking occurs

is obtained as indicated by a graph in FIG. 8. As can be clearly understood

from FIG. 8, breaking occurred most frequently in the region E, that is, in a

grid which is disposed on an uppermost side (the side of the first transverse

frame member 11) and is remotest from the current collecting lug portion 25

(the side of the second longitudinal frame member 14). The closer to the

lower side (the side of the leg portions 26) the region is, the less the number

of breaking becomes. When the regions are disposed at the same height

(the region A and the region E, the region B and the region F or the like), the

region disposed remoter from the current collecting lug portion 25 has the

larger number of breaking.

In view of the above, by setting the portion where the number of

breaking is particularly large such that the portion satisfies the formula (1)

with certainty, even when other portions do not satisfy the formula (1), it is

possible to sufficiently suppress breaking in the longitudinal frame member.

Although a portion where breaking minimally occurs is not required to

satisfy the formula (1), a filling amount of the active material paste relative

to the positive electrode current collector 10 can be increased by making the

positive electrode current collector 10 satisfy the formula (1).

The positive electrode current collectors 10 prepared based on such a

consideration are illustrated in FIG. 9 to FIG. 13 which are schematic views.

In these drawings, the first and second transverse frame members 11 and 12,

the longitudinal inner cross members 21, and the transverse bold cross

members 22 are respectively simply indicated by a line, and the illustration

of the transverse fine cross members 23 is omitted.

In the case of the positive electrode current collector 10 shown in FIG.

9, compared to the positive electrode current collector 10 shown in FIG. 1, an

additional transverse bold cross member 22a is disposed between the first

transverse frame member 11 and the transverse bold cross member 22 (the

transverse bold cross member extending from the first longitudinal frame

member 13 to the second longitudinal frame member 14) disposed adjacently

to the first transverse frame member 11 so as to connect only the second

longitudinal frame member 14 and the longitudinal inner cross member 21

disposed adjacently to the second longitudinal frame member 14. With such

a configuration, a region E in FIG. 7 where breaking is likely to occur most

easily is divided into two grids each having a half size of the region E so that

a value of a volume V of the grid is decreased. Accordingly, the formula (1)

can be satisfied.

Next, in the case of the positive electrode current collector 10 shown

in FIG. 10, compared to the positive electrode current collector 10 shown in

FIG. 1, an additional transverse bold cross member 22b (a transverse bold

cross member extending from the first longitudinal frame member 13 to the

second longitudinal frame member 14, and having substantially the same

structure as the transverse bold cross member 22) is disposed in the vicinity

of the first transverse frame member 11. With such a configuration, the

regions A and E in FIG. 7 are respectively divided into two grids each having a half size of the region A or E so that a value of a volume V of the grid is decreased. Accordingly, the formula (1) can be satisfied.

Next, in the case of the positive electrode current collector 10 shown

in FIG. 11, compared to the positive electrode current collector 10 shown in

FIG. 1, the number of transverse bold cross members 22 is increased and, at

the same time, a distance between the first transverse frame member 11 and

the transverse bold cross member 22 is gradually increased from the side of

the first transverse frame member 11 to the side of the second transverse

frame member 12 in order. With such a configuration, the grid disposed

closer to the side of the first transverse frame member 11 can satisfy the

formula (1) with more certainty.

In the case of the positive electrode current collector 10 shown in FIG.

12, in an upper half (on the side of the first transverse frame member 11), the

number of transverse bold cross members 22 is increased so as to decrease a

size of each grid compared to a lower half (on the side of the second

transverse frame member 12). With such a configuration, the grids

disposed on the upper side can satisfy the formula (1). An area where the

number of transverse bold cross members 22 is increased is not limited to

"upper half', and the transverse bold cross members 22 may be arranged so

as to form a few rows of small grids from the top of the positive electrode

current collector 10.

In the case of the positive electrode current collector 10 shown in FIG.

13, a distance between the longitudinal frame member 13 and the

longitudinal inner cross member 21 disposed closest to the longitudinal

frame member 13 and a distance between the longitudinal frame member 14 and the longitudinal inner cross member 21 disposed closest to the longitudinal frame member 14 are set smaller than a distance between each two longitudinal inner cross members 21. With such a configuration, a grid which uses the longitudinal frame member 13 or 14 as a part of the grid configuration satisfies the formula (1) so that breaking in the longitudinal frame members 13 and 14 is suppressed. At the same time, with respect to a grid which do not include the longitudinal frame member 13 or 14 as the grid configuration (for example, a grid formed of two transverse bold cross members 22 and two longitudinal inner cross members 21), an amount of an active material in a paste form filled into the grid can be increased.

Besides the above-mentioned configuration, particularly with respect

to the portions shown in FIG. 7 and FIG. 8 where breaking is liable to occur,

breaking can be suppressed by adjusting a size of grids such that the formula

(1) is satisfied. All of FIG. 9 to FIG. 13 show the schematic structure of the

positive electrode current collector 10 and are not intended to show an

absolute size relationship or the like of the positive electrode current

collector 10. Further, with respect to grids other than the grids described to

satisfy the formula (1) (grids each of which includes the longitudinal frame

member 13 or 14 as a constitutional element), there is no problem even in the

case where such grids also satisfy the formula (1). The configurations

shown in FIG. 9 to FIG. 13 can be used in various combinations.

(Modification)

The description has been made with respect to the positive electrode

current collectors 10 where the longitudinal inner cross members 21 are

disposed parallel to the longitudinal frame members 13 and 14, and the transverse inner cross members 22 and 23 are disposed parallel to the transverse frame members 11 and 12 heretofore. However, this disclosure is not limited to such configurations. FIG. 14 shows a positive electrode current collector 10a of a modification. The positive electrode current collector 10a is substantially equal to the positive electrode current collector

10 shown in FIG. 1 with respect to that an outer frame portion is formed of a

first transverse frame member 11, a second transverse frame member 12, a

first longitudinal frame member 13 and a second longitudinal frame member

14, and the positive electrode current collector 10a includes transverse bold

cross members 22 and transverse fine cross members 23, a current collecting

lug portion 25, and leg portions 26.

However, in the positive electrode current collector 10a shown in FIG.

14, longitudinal inner cross members 31 are not arranged parallel to the

longitudinal frame members 13 and 14, but are obliquely arranged such that

the more the longitudinal inner cross members 31 extend toward a lower side

from an upper side, the more the longitudinal inner cross members 31 are

away from the side of the current collecting lug portion 25.

Also in this case, by making grids each of which includes portions of

the longitudinal frame member 13 or 14 satisfy the formula (1), breaking of

the longitudinal frame member 13 or 14 can be suppressed.

"Grid" in this case is exemplified in FIG. 14. For example, in FIG.

14, a grid 41 is a portion formed of a part of the second longitudinal frame

member 14, the first transverse frame member 11, two longitudinal inner

cross members 31 disposed adjacently to each other, and the transverse bold

cross member 22. In FIG. 14, the grid 41 has an elongated pentagonal shape and pointed by a numeral reference "Va". A grid 42 or 43 is a portion formed of a part of the second longitudinal frame member 14 or a part of the first longitudinal frame member 13, two longitudinal inner cross members

31 disposed adjacently to each other, and the transverse bold cross member

22.

In the same manner as the positive electrode current collector 10

shown in FIG. 1, assume a width and a cross-sectional area of the first or

second longitudinal frame member 13 or 14 as d (mm) and S (mm2),a volume

of the grid 41 as Va (cm3), and a length of a portion of the second longitudinal

frame member 14 forming the grid 41 as La. In such a case, the formula (1)

is established.

(S x d) / (Va x La2) > 0.002

By designing the positive electrode current collector 10a such that

the formula (1) is satisfied, breaking in the longitudinal frame members can

be suppressed.

Also with respect to the grids 42 and 43, by setting volumes Vb and

Vc and lengths Lb and Le of the corresponding portion of the longitudinal

frame member such that the formula (1) is satisfied, breaking in the

longitudinal frame member can be suppressed.

Also in the positive electrode current collector 10a, the longitudinal

inner cross members 31 are arranged parallel to each other. However, it is

not indispensable that the longitudinal inner cross members 31 are arranged

parallel to each other. For example, the longitudinal inner cross members

31 may be radially arranged. It is also not indispensable that the

transverse bold cross members 22 are arranged parallel to the first transverse frame member 11 and the second transverse frame member 12, or the transverse bold cross members 22 are arranged parallel to each other.

It is also not indispensable for both the longitudinal inner cross members

and the transverse inner cross members to have a linear shape, and both the

longitudinal inner cross members and the transverse inner cross members

may have a curved shape. In both cases, by forming a grid which includes

the first or second longitudinal frame member 13 or 14 such that the formula

(1) is satisfied, breaking in the longitudinal frame member of the grid can be

suppressed.

The positive electrode current collector formed by casting has been

described as an example heretofore. However, the positive electrode current

collector is not limited to such an electrode current collector, and may be an

electrode current collector formed by other method such as a punched grid.

The description has been made by taking a VRLA battery as an example.

However, this disclosure is not limited to a VRLA battery, and is also

applicable to a liquid-type battery or the like.

According to the lead-acid battery and the current collector of this

disclosure, it is possible to suppress shortening of a life. Accordingly, this

disclosure is particularly effectively applicable as a lead-acid battery which

can be used over a long period even when the battery is used within a range

where a depth of discharge is large.

Throughout this specification and the claims which follow, unless the

context requires otherwise, the word "comprise", and variations such as

"comprises" and "comprising", will be understood to imply the inclusion of a

stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should

not be taken as, an acknowledgement or any form of suggestion that the

prior art forms part of the common general knowledge in Australia.

Claims (7)

What is claimed is:

1. A lead-acid battery comprising:

a positive electrode current collector made of lead or a lead alloy,

wherein the positive electrode current collector includes:

an outer frame portion having first and second transverse

frame members and first and second longitudinal frame members;

a plurality of inner cross members formed in an intersecting

manner in the inside of the outer frame portion; and

a current collecting lug portion integrally formed on an outer

side of the outer frame portion at a position of the first transverse frame

member close to the first longitudinal frame member, wherein

assuming a cross-sectional area of each of the first and second

longitudinal frame members on a cross section perpendicular to an extending

direction of each of the first and second longitudinal frame members as S

(mm2) and a thickness of each of the first and second longitudinal frame

members as t (mm), S > t2 /2 is satisfied,

the plurality of inner cross members include a bold inner cross

member having a cross-sectional area which exceeds t 2 /4 on a cross section

perpendicular to an extending direction of the bold inner cross member,

with respect to at least one of

a grid formed of at least one of the first and second

longitudinal frame members and one of the bold inner cross members

without being traversed by said other bold inner cross members or

a grid formed of at least one of the first and second longitudinal frame members, at least one of the first and second transverse frame members and one of the bold inner cross members without being traversed by said other bold inner cross members, assuming a volume of the grid as V (cm3), a length of a portion of each of the first and second longitudinal frame members which forms the grid as L

(mm) and a width of each of the first and second longitudinal frame members

as d (mm), a following formula (1) is satisfied,

(S x d) / (V x L2) > 0.002 ..... formula (1)

the plurality of inner cross members further include a fine inner

cross member having a cross-sectional area of t 2 /4 or less, and

the fine inner cross member is disposed in the inside of the grid.

2. The lead-acid battery according to claim 1, wherein the grid which is

formed of the first transverse frame member, the second longitudinal frame

member and the bold inner cross members is configured to satisfy the

formula (1).

3. The lead-acid battery according to claim 2, wherein the grid which is

formed of the first transverse frame member, the first longitudinal frame

member and the bold inner cross members is configured to satisfy the

formula (1).

4. The lead-acid battery according to any one of claims 1 to 3, wherein

the grid including the second longitudinal frame member is configured to

satisfy the formula (1).

5. The lead-acid battery according to any one of claims 1 to 4, wherein

the inner cross members include at least one of longitudinal cross members

arranged parallel to the longitudinal frame member and transverse cross

members arranged parallel to the transverse frame member.

6. The lead-acid battery according to any one of claims 1 to 5, wherein a

following formula (2) is satisfied.

(S x d) / (V x L2) > 0.0032 ..... formula (2)

7. A current collector comprising:

an outer frame portion having first and second transverse frame

members and first and second longitudinal frame members;

a plurality of inner cross members formed in an intersecting manner

in the inside of the outer frame portion; and

a current collecting lug portion integrally formed on an outer side of

the outer frame portion at a position of the first transverse frame member

close to the first longitudinal frame member, wherein

assuming a cross-sectional area of each of the first and second

longitudinal frame members on a cross section perpendicular to an extending

direction of each of the first and second longitudinal frame members as S

(mm2) and a thickness of each of the first and second longitudinal frame

members as t (mm), S > t2 /2 is satisfied,

the plurality of inner cross members include a bold inner cross

member having a cross-sectional area which exceeds t 2 /4 on a cross section perpendicular to an extending direction of the bold inner cross member, and with respect to at least one of a grid formed of at least one of the first and second longitudinal frame members and one of the bold inner cross members without being traversed by said other bold inner cross members or a grid formed of at least one of the first and second longitudinal frame members, at least one of the first and second transverse frame members and one of the bold inner cross members without being traversed by said other bold inner cross members, assuming a volume of the grid as V (cm3), a length of a portion of each of the first and second longitudinal frame members which forms the grid as L

(mm) and a width of each of the first and second longitudinal frame members

as d (mm), a following formula (1) is satisfied,

(S x d) / (V x L2) > 0.002 ..... formula (1)

the plurality of inner cross members further include a fine inner

cross member having a cross-sectional area of t 2 /4 or less, and

the fine inner cross member is disposed in the inside of the grid.