DESCRIPTION
EXPANDED GRID, MANUFACTURING METHOD FOR SAME, LEAD-ACID
BATTERY ELECTRODE PLATE USING SAME, AND LEAD-ACID BATTERY
5
TECHNICAL FIELD
[0001] The present disclosure relates to an expanded grid, a method for manufacturing the
expanded grid, a lead-acid battery electrode plate using the expanded grid, and a lead-acid
battery.
10
BACKGROUND ART
[0002] Lead-acid batteries have characteristics such as low cost, stabilized output, and
suitability for great current discharging, and have been broadly used in fields of, e.g., start-up
of vehicles, main power supplies for electric vehicles or electric tools, and backup power
15 supplies.
[0003] The lead-acid batteries mainly include liquid type lead-acid batteries which arc
open type (vented) lead-acid batteries, and valve regulated lead-acid batteries which arc
hermetic lead-acid batteries. Of those batteries, the valve regulated lead-acid batteries are
maintenance-free, and therefore have been more broadly used. The valve regulated lead-
20 acid battery includes components such as positive electrode plates, negative electrode plates,
separators, an electrolyte, and a casing with a safety valve. For the positive electrode plates,
pasted electrode plates are used, which are each formed in such a manner that an alloy grid
manufactured by a special process is filled with an active material. Grids used for the leadacid
batteries can be classified into two main types of cast grids and expanded grids. As
25 compared to the cast grids, the expanded grids have advantages such as saving of material
2
cost, less variation in weight of manufactured grids, and significant improvement in
production efficiency. Thus, the expanded grids have been increasingly used nowadays,
instead of using the conventional cast grids.
[0004] Typically, expansion is employed to manufacture the expanded grids. For
5 example, Patent Document 1 discloses a punching shear type expander. The expander
mainly includes upper and lower blades, and each blade has a teeth-shaped structure. A lead
sheet fed into the expander is punched in the vertical direction with the upper and lower
blades facing each other. Then, the punched lead sheet is expanded in the horizontal
direction to form a net-shaped structure.
10 [0005] The following disadvantages are likely to occur in the expanded grids manufactured
using the expansion. That is, when the lead sheet is expanded in the horizontal direction,
grid bars forming meshes are pulled into a linear shape, and therefore stress on the grid bars
increases. Moreover, each intersection (i.e., each joint) between adjacent ones of the grid
bars is pulled too much, and therefore the grid bar(s) is easily ruptured. In particular, rupture
15 of the grid bard(s) is likely to occur during a very short period of time of crystal growth on the
electrode plate. For such reasons, the grid cannot be effectively used because of influence
on distribution of current collecting properties of the grid and detachment of the active
material applied around the ruptured part(s) of the grid bar(s). This results in a decrease in
discharge capacity. Moreover, since the grid bar(s) is ruptured, corrosion of the grid is more
20 likely to occur, resulting in short battery life. In order to overcome the foregoing
disadvantages, Patent Document 2 proposes that thermal processing is applied to an expanded
grid formed using expansion to relieve stress applied to the expanded grid during expansion
deformation thereof, thereby manufacturing a high-capacity long-life lead-acid battery.
[0006] If process conditions for expansion step are changed, or, e.g., the moving speed of a
25 lead sheet and the punching speed of a die do not match with each other, distortion may occur
in some of grid bars forming meshes. In this case, an expanded grid after the expansion step
is not flat, and such non-flatness influences stability in subsequent electrode plate production.
Typically, since distortion occurs randomly, it is impossible to control the number of distorted
grid bars and the degree of distortion. Thus, deliberate study has not been currently
5 conducted on distortion caused when expanded grids are manufactured using expansion.
Moreover, since distortion indicates low productivity in the field of expanded grids, there is a
need to avoid distortion as much as possible.
CITATION LIST
10 PATENT DOCUM ENT
[0007] PATENT DOCUMENT 1: Chinese Patent Application No. CN1126378A
PATENT DOCUMENT 2: Japanese Unexamined Patent Publication No. 2003-
157853
15 SUMMARY OF THE INVENTION
TECHNICAL PROBLEM
[0008] The inventors of the present disclosure have further conducted study on causes for
stress on an expanded grid and distortion of the expanded grid in the course of a conventional
expansion step. The results show that process conditions for expansion step are intentionally
20 adjusted to control distortion of the expanded grid, thereby relieving stress on grid bars.
Moreover, the inventors of the present disclosure have found that the expanded grid having a
predetermined distortion rate and a predetermined distortion degree is used for a lead-acid
battery to realize unexpected advantages, resulting in excellent discharge capacity and
excellent battery cycle life. This leads to completion of the present disclosure.
25
4
SOLUTION TO THE PROBLEM
[0009] Specifically, an expanded grid of the present disclosure is formed by expansion, and
includes grid bars forming a plurality of diamond-shaped meshes. At least one of the grid
bars is a distorted grid bar, and defines a protruding curved part. A distortion degree W
5 indicating a degree of curvature of the distorted grid bar is determined according to a first
expression:
W = (D2-D1)/D1 (1)
where, in a projection view of the expanded grid, Dl represents a distance between nondistorted
two of the grid bars being parallel to each other and opposing each other in one of
10 the diamond-shaped meshes, the distance being a length of a side of the one of the diamondshaped
meshes and being measured parallel to the remaining two of the grid bars in the one of
the diamond-shaped meshes, D2 represents a distance between a top of the curvature of the
distorted grid bar in another one of the diamond-shaped meshes and another one of the grid
bars being parallel to the distorted grid bar and opposing the distorted grid bar in the another
15 one of the diamond-shaped meshes, the distance being measured parallel to the remaining two
of the grid bars in the another one of the diamond-shaped meshes, and D2 > Dl is satisfied.
The distortion degree W falls within a range of 0.09 to 0.19. The "distorted" means
curvature of a grid bar (strand) which is originally in a linear shape, and such curvature
deforms a diamond-shaped mesh of a grid.
20 [0010] The distortion degree W preferably falls within a range of 0.11 to 0.17.
[0011] A distortion rate which is a percentage of the number of the distorted grid bar of the
expanded grid in the total number of the grid bars of the expanded grid preferably falls within
a range of 5 to 20%.
[0012] The distortion rate more preferably falls within a range of 6 to 17%.
25 [0013] The distortion rate much more preferably falls within a range of 7 to 15%.
5
[0014] A lead-acid battery electrode plate of the present disclosure includes the foregoing
expanded grid; and an active material with which the expanded grid is filled.
[0015] A lead-acid battery of the present disclosure includes the foregoing electrode plate.
[0016] The foregoing electrode plate is preferably a positive electrode plate.
5 [0017] A method for manufacturing the expanded grid of the present disclosure includes
the steps of: (1) an expansion step of, after a series of strokes each performed every time a
lead sheet moves in a length direction thereof by a predetermined distance, forming a netshaped
sheet in which the plurality of diamond-shaped meshes are formed, each stroke
including the step of moving an upper die of a punching die for punching the lead sheet
10 relative to a lower die of the punching die to form a plurality of diagonally-extending slits in
the length direction of the lead sheet while expanding the slits in a direction perpendicular to
a lead sheet surface and the step of returning the upper die of the punching die to an original
position; (2) a shaping step of shaping the net-shaped sheet in a horizontal direction wilh a
guide roller to form a flat net-shaped body; and (3) a cutting step of cutting the net-shaped
15 body to predetermined shape and dimensions to form the expanded grid. A cutting depth of
the upper die and/or the number of strokes of the upper die at the expansion step are
controlled to cause the expanded grid to have a predetermined distortion degree and/or a
predetermined distortion rate.
[0018] The cutting depth preferably falls within a range of 2.965 to 3.045 mm.
20 [0019] The cutting depth more preferably falls within a range of 2.98 to 3.03 mm.
[0020] The number of strokes preferably falls within a range of 600 to 1800 rpm.
[0021] The number of strokes more preferably falls within a range of 750 to 1500 rpm.
[0022] The number of strokes much more preferably falls within a range of 800 to 1300
rpm.
25
ADVANTAGES OF THE INVENTION
[0023] According to the expanded grid manufacturing method of the present disclosure, an
expanded grid whose distortion rate and distortion degree fall within predetermined ranges
can be manufactured with high yield rate. Such an expanded grid can be used for a lead-acid
5 battery to realize excellent discharge capacity and excellent cycle life.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] [FIG. 1] FIG. 1(a) is a schematic front view illustrating a conventional expanded
grid. FIG. 1(b) is a schematic enlarged partial view illustrating the conventional expanded
10 grid.
[FIG. 2] FIG. 2(a) is a schematic front view illustrating an expanded grid of the
present disclosure. FIG. 2(b) is a schematic enlarged partial view illustrating the expanded
grid of the present disclosure.
[FIG. 3] FIG. 3 is a projection view illustrating the state in which some of grid
15 bars of the expanded grid of the present disclosure are distorted.
[FIG. 4] FIGS. 4(a) and 4(b) are schematic views illustrating states upon
punching of a lead sheet with a punching die of the present disclosure. FIG. 4(a) illustrates
the state before punching. FIG. 4(b) illustrates the state after punching.
[FIG. 5] FIG. 5 is a schematic view illustrating a cutting depth upon punching of
20 the lead sheet with the punching die of the present disclosure.
[FIG. 6] FIG. 6 is a graph illustrating a relationship between the cutting depth of
a punching die and the distortion degree of a grid bar.
[FIG. 7] FIG. 7 is a graph illustrating a relationship between the number of
strokes of a punching die and a distortion rate.
25 [FIG. 8] FIG. 8 is a schematic perspective cutaway view illustrating a lead-acid
7
battery of the present disclosure.
DESCRIPTION OF EMBODIMENTS
[0025] For improvement of battery performance and battery life, focused attention has been
5 conventionally placed on study of the method for forming an active material (lead paste),
alloy constituents of a grid, etc. However, the inventors of the present disclosure have
considered that easily-rupturable grid bars forming an expanded grid significantly influence
battery performance and battery life. Thus, the inventors of the present disclosure have
focused on modification of the shape of the expanded grid, and have expected that
10 modification of an expanded grid structure improves battery performance such as discharge
capacity and battery life.
[0026] The present disclosure will be described below with reference to a specific
embodiment, but is not limited to such a specific embodiment described below.
[0027] (Expanded Grid of the Present Disclosure)
15 Referring to FIGS. 1(a) and 1(b), a plurality of meshes are formed in a conventional
expanded grid. Each mesh other than irregular-shaped meshes at an end part of the
expanded grid is formed of four grid bards, and the projection shape of the mesh on the plane
is substantially diamond shape. Each grid bar forming the meshes is typically in a linear
shape.
20 [0028] It has been conventionally considered that a mesh part of an flawless expanded grid
should be flat without distortion and that a yield rate is lowered due to distortion of grid bars
forming meshes. Since distortion occurs randomly, it is impossible to control distortion in
production of expanded grids.
[0029] However, an attempt has been made by the inventors of the present disclosure to
25 overcome such conventional technical bias. The inventors of the present disclosure have
8
intentionally adjusted the step of expanding an expanded grid to cause distortion in some of
grid bars of a manufactured expanded grid. That is, some of the grid bars are curved to
change from an original linear shape to a non-linear shape.
[0030] FIGS. 2(a) and 2(b) are schematic views of an expanded grid 1 of the present
5 disclosure. Referring to FIG. 2(a), a plurality of meshes i are formed in the expanded grid 1.
Each mesh i is surrounded by four grid bars g, and is formed in a substantially diamond
projection shape. According to the present disclosure, distortion of a grid bar g' forming a
mesh i' occurs, and the grid bar g' is formed in a non-linear shape so as to define a protruding
curved part la.
10 [0031] The inventors of the present disclosure have found that the degree of curvature of a
distorted grid bar of an expanded grid influences performance of a battery. When the degree
of curvature of a grid bar of an expanded grid falls within a suitable range, the cycle life and
discharge capacity of a battery can be significantly improved.
[0032] In the present specification, a "distortion degree" means the degree of curvature of a
15 grid bar of an expanded grid. For the sake of simplicity of calculation, the expanded grid of
the present disclosure is orthogonally projected on the plane parallel to the expanded grid of
the present disclosure to form a projection view (see FIG. 3) showing the state in which some
of the grid bars of the expanded grid of the present disclosure are distorted. Referring to the
projection view, a distortion degree W is determined according to the following first
20 expression:
W = (D2-D1)/D1 (1)
where "Dl" represents a distance between non-distorted two of the grid bars being parallel to
each other and opposing each other in one of the diamond-shaped meshes, the distance being
measured parallel to the remaining two of the grid bars in the one of the diamond-shaped
25 meshes, and "D2" represents a distance between the top of curvature of a distorted one of the
9
grid bars in another one of the diamond-shaped meshes and another one of the grid bars being
parallel to the distorted grid bar and opposing the distorted grid bar in the another one of the
diamond-shaped meshes, the distance being measured parallel to the remaining two of the
grid bars in the another one of the diamond-shaped meshes.
5 [0033] As will be seen from the projection view, some meshes i of the expanded grid are in
a normal diamond shape. On the other hand, other meshes i' are deformed such that one of
the grid bars forming each mesh i' is distorted to define the upwardly-protruding curved part
la. Referring to FIG. 3, the distance Dl is a distance between a non-distorted grid bar gl
and a grid bar g2 being parallel to the grid bar gl and opposing the grid bar gl. In the case
10 where the mesh i is in a diamond shape, the distance Dl is equal to the length of a side of the
diamond shape, i.e., the length of each non-distorted grid bar. On the other hand, the
distance D2 is a distance between the top of a curved part la of a distorted grid bar gl' and a
grid bar g2 being parallel to the grid bar gl' and opposing the grid bar gl', and the grid bar
gl' forms a curved part outwardly protruding from a straight line (see a dashed line in the
15 figure) on which the grid bar gl is positioned. Thus, the distance D2 is slightly longer than
the length of the side of the diamond shape, and a ratio of D2/D1 is greater than one.
[0034] The inventors of the present disclosure have conducted many tests to prove that
positive influence is provided on battery properties such as discharge capacity and cycle life
when the distortion degree W of a grid bar falls within a range of 0.09 to 0.19. A higher
20 distortion degree W indicates a higher degree of curvature of a grid bar. A distortion degree
W of 0.19 or more indicates that a grid bar is significantly deformed. In this case, rupture of
the grid bar(s) is likely to occur, and negative influence is provided on battery life properties.
On the other hand, if the distortion degree W is less than 0.09, it is less likely to show the
above-described positive influence brought by curvature of grid bars. Note that the
25 distortion degree W preferably falls within a range of 0.11 to 0.17.
10
[0035] Reasons for bringing about the positive influence of the distortion degree on the
battery performance are assumed as follows. That is, since the surface area of a curved grid
bar is larger than that of a linear grid bar, a contact area between an active material and an
expanded grid per unit volume is larger in the case of the curved grid bar than in the case of
5 the liner grid bar. Thus, a larger reaction area can be ensured, and therefore current
collecting properties of the grid can be improved. As a result, current distribution of the grid
can be improved, and the rate of active material utilization increases. Distortion of grid bars
allows an increase in rate of active material utilization without increasing a battery volume,
thereby increasing the discharge capacity of a battery.
10 [0036] Liner grid bars are susceptible to action of stress during an expansion step, and lack
deformability thereof. For such reasons, rupture of the linear grid bar(s) is much more likely
to occur while a grid is being extended in an electrode plate height direction in the use of a
battery. The ruptured linear grid bar(s) provides great negative influence on current
collecting properties and life of the grid. On the other hand, curved grid bars have, because
15 of the shape of the curved grid bars themselves, a function to relieve a certain degree of stress
applied at an expansion step. Moreover, while a grid is being extended in an electrode plate
height direction, the curved grid bar has higher deformability than that of the liner grid bar.
Thus, distortion of grid bars can relieve stress on the grid bars. As a result, the life of a grid
can be extended, and therefore life properties of a battery can be improved.
20 [0037] As described above, only one (i.e., the grid bar g') of the four grid bars forming the
mesh i' is distorted, but the present disclosure is not limited to such a configuration. Two or
more distorted grid bars g' may be formed. However, the number of distorted grid bars of
each mesh is preferably equal to or less than two, considering uniformity of distribution of
distorted grid bars in an expanded grid.
25 [0038] The tests conducted by the inventors of the present disclosure further show that the
11
cycle life and discharge capacity of a battery can be more significantly improved when the
ratio of the number of distorted grid bars of an expanded grid falls within a suitable range.
[0039] In the present specification, the "distortion rate" means the ratio of occurrence of
distortion of an expanded grid. That is, the "distortion rate" is defined as the percentage of
5 the number of distorted grid bars of an expanded grid in the total number of grid bars of the
expanded grid.
[0040] In the present disclosure, as long as a grid bar(s) of an expanded grid has a
predetermined distortion degree, a certain degree of improvement of battery performance can
be realized as compared to a conventional expanded grid. Thus, the range of the distortion
10 rate is not limited. However, if the distortion rate is too low, e.g., lower than 5%, the
advantages of the present disclosure may not be realized due to too few distorted grid bars.
On the other hand, if the distortion rate is too high, e.g., higher than 20%, excessive use of an
active material as described later may occur. Thus, it is necessary that the distortion rate of
grid bars of an expanded grid falls within a range of 5 to 20%. Note that the distortion rate
15 is preferably within a range of 6 to 17%, and more preferably a range of 7 to 15%.
[0041] Reasons for bringing about the positive influence of the distortion rate on the
battery performance are assumed as follows. That is, if the distortion rate is equal to or
higher than 6%, a contact area between an active material and an expanded grid moderately
increases due to distorted grid bars, and therefore the rate of active material utilization can be
20 increased. However, if the rate of active material utilization is too high, such a state may
adversely influence battery life. The tests prove that, when the distortion rate of grid bars
exceeds 20%, the rate of active material utilization sometimes reaches 40% or more.
However, if the rate of active material utilization exceeds 40%, active material reaction may
proceed too much, resulting in shortening of battery life. For such reasons, it is necessary
25 that the upper limit of the distortion rate is equal to or lower than 20%, and preferably equal
12
to or lower than 17%. When the distortion rate falls within a range of 6 to 17%, an
advantage that battery charging efficiency and reaction speed between sulfuric acid and an
active material are best balanced can be realized.
[0042] The inventors of the present disclosure have further conducted study on influence of
5 a distorted part on battery performance. Specifically, evaluation is made for upper, middle,
and lower parts of an expanded grid. The results show that, regardless of which of the
upper, middle, and lower parts of the expanded grid includes a distorted grid bar(s), the same
advantages can be basically realized as long as the distortion degree falls within a suitable
range and the distortion rate across the entirety of the expanded grid is equal to or lower than
10 20%.
[0043] (Method for Manufacturing Expanded Grid according to Present Disclosure)
In a manufacturing method of the present disclosure, a lead sheet which is a raw
material of an expanded grid is fed to a punching die used for typical expansion, and
conditions for expansion step are specifically adjusted. As a result, the expanded grid of the
15 present disclosure, i.e., an expanded grid including some distorted grid bars, can be
manufactured.
[0044] The method for manufacturing the expanded grid according to the present
disclosure includes the following steps:
(1) an expansion step of, after a series of strokes each performed every time a lead
20 sheet moves in a length direction thereof by a predetermined distance, forming a net-shaped
sheet in which a plurality of diamond-shaped meshes are formed, each stroke including the
step of moving an upper die of a punching die for punching the lead sheet relative to a lower
die of the punching die to form a plurality of diagonally-extending slits in the length direction
of the lead sheet while expanding the slits in a direction perpendicular to a lead sheet surface
25 and the step of returning the upper die of the punching die to an original position;
13
(2) a shaping step of shaping the net-shaped sheet in the horizontal direction with guide
rollers to form a flat net-shaped body; and
(3) a cutting step of cutting the net-shaped body to predetermined shape and
dimensions to form expanded grids.
5 [0045] Lead alloy foil used typically in the art, such as Pb alloy foil containing at least one
of Ca or Sn, can be used as the material of the lead sheet. However, the lead sheet is
preferably made of a Pb-Ca-Sn ternary alloy, considering corrosion resistance and mechanical
strength. The use of the lead sheet having such an alloy composition can easily improve
cycle life properties of a lead-acid battery.
10 [0046] Examples of the punching die used at the expansion step include a punching die
including a movable die (upper die) 2 with a plurality of bits and a fixed die (lower die) 3
with a plurality of ridges as illustrated in FIG. 4. The bits of the movable die 2 are
distributed so as to form a V-shape which is, as viewed in the plane, symmetric with respect
to a middle line of a lead sheet 4 in a width direction thereof, and the ridges of the fixed die 3
15 are distributed so as to form a V-shape which is, as viewed in the plane, symmetric with
respect to the middle line of the lead sheet 4 in the width direction thereof. The lead sheet 4
is punched after the lead sheet 4 is fed between the movable die 2 and the fixed die 3 in a
length direction of the lead sheet 4. In this case, arrangement of the bits of the movable die
2 and the ridges of the fixed die 3 is adjusted such that a middle part of the lead sheet 4 in the
20 width direction thereof is not punched. When each bit of the movable die 2 punches the lead
sheet 4 in a direction indicated by an arrow in FIG. 4(a) and passes an upper end of a
corresponding one of the ridges of the fixed die 3, the lead sheet 4 is cut in the length
direction thereof such that plural lines of diagonally-extending slits are formed in a V-shapc,
and each bit of the movable die 2 presses the lead sheet 4 downward to expand a
25 corresponding one of the slits in a direction perpendicular to a surface of the lead sheet 4.
14
Then, the movable die 2 returns to an original position. Such a punching step is referred to
as a "stroke." A series of strokes are each performed every time the lead sheet 4 moves
toward the front in the length direction thereof by a predetermined distance. As a result,
plural lines of diagonally-extending slits are formed in the lead sheet 4. A connection part
5 between adjacent ones of the slits in each slit line corresponds to a middle part of the slit in
adjacent one of the slit lines. Thus, when the slits are expanded, a plurality of diamondshaped
meshes are formed. The foregoing step is repeated to form a net-shaped sheet in
which a plurality of diamond-shaped meshes are formed.
[0047] Then, the net-shaped sheet formed as just described is flattened (i.e., shaped) in the
10 horizontal direction with a pair of guide rollers, and is expanded in the horizontal direction.
As a result, a flat net-shaped body is formed. Subsequently, the net-shaped body is, as
necessary, cut to predetermined shape and dimensions, and an ear part is formed in the middle
part of the lead sheet 4. As a result, an expanded grid is manufactured.
[0048] The manufacturing method of the present disclosure has the following features.
15 That is, since the cutting depth of the movable die at the expansion step is controlled by an
external unit, such control allows the manufactured expanded grid to have a predetermined
distortion degree. Further, since the punching speed of the movable die is controlled by an
external unit, such control allows the manufactured expanded grid to have a predetermined
distortion rate.
20 [0049] The inventors of the present disclosure have found that the conditions for expansion
step and occurrence of distortion closely relate to each other and that two conditions of the
cutting depth of a die and the punching speed of the die can be optimized to control the
distortion degree and distortion rate of a manufactured expanded grid.
[0050] Referring to FIG. 5, the "cutting depth" of the movable die means a maximum
25 distance t by which the bit of the movable die 2 moves downward relative to an upper end
15
surface of the fixed die 3 during a single stroke, and the unit for cutting depth is "mm."
[0051] At the expansion step, a greater cutting depth of the movable die results in a greater
curvature of the grid bar and a higher distortion degree. Referring to FIG. 6, the cutting
depth t and the distortion degree W of the expanded grid are directly proportional to each
5 other. When the cutting depth t is small, the distortion degree W is close to zero. The
degree of curvature of the grid bar gradually increases with increasing the cutting depth t.
Accordingly, the distortion degree W also increases. When the distortion degree W exceeds
a certain level, the distortion degree W sharply increases. In order to set the distortion
degree W within a preferable range (0.09 to 0.19), it is, as will be seen from FIG. 6, necessary
10 that the cutting depth t is set within a range of 2.965 to 3.045 mm. If the cutting depth t is
less than 2.965 mm, the distortion degree W is less than 0.09. In such a case, the grid bars
are in a substantially linear shape, and therefore the advantages of the curved grid bars of the
present disclosure cannot be realized. Conversely, if the cutting depth t exceeds 3.045 mm,
the distortion degree W exceeds 0.19. In such a case, great stress is generated during
15 processing of the expanded grid, and therefore the grid bars become easily-rupturable due to a
decrease in cross-sectional area of each grid bar. As a result, negative influence may be
provided on battery performance. In order to manufacture an expanded grid having a
predetermined distortion degree, the cutting depth of the die should fall within a range of
2.965 to 3.045 mm, preferably a range of 2.97 to 3.04 mm, and more preferably a range of
20 2.98 to 3.03 mm.
[0052] The punching speed of the movable die is represented by the number of strokes.
The number of strokes is the number of punching steps completed per unit time (i.e., one
minute), and the unit for the number of strokes is "rpm." For example, if the number of
strokes is 100 rpm, it means that the lead sheet is punched 100 times per minute with the bits
25 of the movable die. A higher number of strokes results in a higher punching speed of the
16
die, and the efficiency of manufacturing expanded grids is improved accordingly.
[0053] An attempt has been previously made to increase the number of strokes to enhance
productivity of expanded grids. However, the results show, e.g., the following disadvantage:
distortion, i.e., curvature of grid bars forming meshes, occurs in a manufactured expanded
5 grid due to too many strokes, and provides negative influence on productivity. For such
reasons, at a conventional expansion step, the number of strokes has been typically limited to
equal to or less than 500 rpm in order to avoid the foregoing disadvantage and manufacture
flat expanded grids each having no distortion.
[0054] As will be seen from FIG. 7, the inventors of the present disclosure have, as a result
10 of study, found that there is a certain proportional relationship between the number of strokes
of the die at the expansion step and the distortion rate of the expanded grid. A higher
number of strokes results in a higher probability of occurrence of distortion, and the distortion
rate increases accordingly. If the number of strokes falls below 500 rpm, the distortion rate
is equal to or lower than 3%. If the number of strokes exceeds 600 rpm, the distortion rate is
15 close to 5%. If the number of strokes exceeds 1800 rpm, the distortion rate exceeds 20%.
Thus, in order to manufacture an expanded grid having a predetermined distortion rate, the
number of strokes of the die should fall within a range of 600 to 1800 rpm, preferably a range
of 750 to 1500 rpm, and more preferably a range of 800 to 1300 rpm. In the present
disclosure, the number of strokes higher than that of the conventional method can be
20 employed, and therefore expanded grids can be manufactured with high production efficiency.
[0055] Causes for influence of the number of strokes on the distortion rate are assumed as
follows. That is, if the number of strokes exceeds 600 rpm, the speed of forward movement
of the lead sheet tends not to match, to some extent, with the speed of forming slits by
downward punching of the lead sheet with the bits of the movable die, and therefore the grid
25 bars receive non-uniform force. As a result, distortion occurs in some of the grid bars. If
17
the number of strokes falls below 500 rpm, a sufficient number of distorted grid bars cannot
be formed in the expanded grid, and therefore the advantages of the present disclosure cannot
be realized. However, if the number of strokes is too high, an excessive number of distorted
grid bars are formed, and therefore the entirety of the expanded grid becomes rough. Such
5 roughness may influence productivity.
[0056] At the expansion step of the present disclosure, the cutting depth of the upper die is
preferably set within a range of 2.97 to 3.04 mm to set the distortion degree of the grid bar of
the manufactured expanded grid within a range of 0.09 to 0.19. Moreover, the number of
strokes of the upper die is preferably set within a range of 600 to 1800 rpm to set the
10 distortion rate of the manufactured expanded grid within a range of 5 to 20%.
[0057] The cutting depth of the upper die is more preferably set within a range of 2.98 to
3.03 mm to set the distortion degree of the grid bar of the manufactured expanded grid within
a range of 0.11 to 0.17. Moreover, the number of strokes of the upper die is more preferably
set within a range of 750 to 1500 rpm to set the distortion rate of the manufactured expanded
15 grid within a range of 6 to 17%. Further, the number of strokes of the upper die is much
more preferably set within a range of 800 to 1300 rpm to set the distortion rate of the
manufactured expanded grid within a range of 7 to 15%.
[0058] According to the expanded grid manufacturing method of the present disclosure, the
number of strokes of the bits of the movable die and the cutting depth of the bits of the
20 movable die at the expansion step are controlled, and therefore an expanded grid having a
predetermined distortion rate and a predetermined distortion degree can be easily
manufactured. Accordingly, a lead-acid battery can be manufactured, which is suitable for
the purposes of increasing discharge capacity and increasing cycle life and which has
excellent discharge capacity and excellent cycle properties.
25 [0059] In the present embodiment, two conditions of the cutting depth of the die and the
18
punching speed of the die are adjusted to control the distortion degree and distortion rate of
the manufactured expanded grid. However, the present disclosure is not limited to such a
configuration. As long as an expanded grid having a predetermined distortion degree and a
predetermined distortion rate can be manufactured, other process condition(s) at the
5 expansion step or a subsequent step may be adjusted in the present disclosure. Various
methods such as adjustment of the moving speed of the lead sheet, the height of the movable
die, or the pressing force of the guide rollers and addition of a guide roller(s) in the horizontal
direction can be used to set the distortion degree and the distortion rate within a
predetermined range. Any one of these methods may be used independently, or one or more
10 of these methods may be combined with the adjustment method of the present embodiment.
[0060] The expanded grid of the present disclosure can be used for any types of batteries
using expanded grids. A lead-acid battery will be described below as an example.
[0061] (Lead-Acid Battery)
The expanded grid of the present disclosure can be used in manufacturing of a lead-
15 acid battery of the present disclosure. The method for manufacturing the lead-acid battery of
the present disclosure is the same as a typical manufacturing method, except that the
expanded grid of the present disclosure is used.
[0062] The lead-acid battery manufacturing method of the present disclosure includes, e.g.,
the step of filling a flat net-shaped body formed at the above-described shaping step with lead
20 paste. The lead paste used as the active material is formed in such a manner that water and
sulfuric acid are mixed with lead powder containing lead oxide of 60 to 90% by mass and
lead metal of 10 to 40% by mass. The lead paste may be applied to the net-shaped body
from one side thereof, or may be applied to the net-shaped body from both sides thereof.
Then, at the cutting step, the net-shaped body filled with the lead paste is cut to predetermined
25 dimensions, and an ear part is formed. As a result, an expanded grid filled with the active
19
material is formed. Then, an electrode plate of the present disclosure is formed after
maturation and drying.
[0063] Since influence of a positive electrode plate on performance of a lead-acid battery is
relatively greater than that of a negative electrode plate, the advantages of the expanded grid
5 of the present disclosure are more noticeable in a positive electrode plate than in a negative
electrode plate. For such reasons, the electrode plate of the present disclosure is preferably
used as a positive electrode plate of a lead-acid battery.
[0064] Referring to FIG. 8, a lead-acid battery 11 of the present disclosure includes a
container 8 and a plurality of cells divided by partitions in the container 8. A single
10 electrode plate group is housed in each cell. The electrode plate group is configured such
that positive electrode plates 5, negative electrode plates 6, and separators 7 each interposed
between the positive electrode plate 5 and the negative electrode plate 6 are alternately
stacked on each other. A positive electrode strap of each cell extends over the partition to be
directly welded to a negative electrode strap of adjacent one of the cells or to be welded to the
15 negative strap of adjacent one of the cells through a pole, and therefore the cells are connected
together in series. A battery inner cover 9 formed with a safety valve is attached to an
opening of the container 8. Positive and negative electrode poles provided respectively at
both side ends of the container 8 are connected respectively to positive and negative terminals
provided on the battery inner cover 9, and the container 8 and the battery inner cover 9 arc
20 bonded together with an adhesive. Then, an electrolyte (not shown in the figure) is
introduced into the container 8. After introduction of the electrolyte, a battery outer cover
10 is hermetically fixed to the container 8 and the battery inner cover 9. As a result, the
lead-acid battery 11 of the present disclosure is manufactured.
[0065] A sulfuric acid solution used typically in the field of lead-acid batteries can be used
25 as the electrolyte without any limitation. For example, a diluted sulfuric acid of 1.1 to 1.4
20
g/ml in concentration may be used. For a valve regulated lead-acid battery, e.g.. an
electrolyte adsorbed, using adsorption action thereof, onto a separator mainly made of glass
fibers may be used, or gel of a colloid electrolyte may be used.
[0066] In the lead-acid battery of the present disclosure, the grid bars of the expanded grid
5 are distorted, and therefore the contact area between the expanded grid and the active material
is large. Thus, the rate of active material utilization increases, resulting in improvement of
the discharge capacity of the battery. In the use of a lead-acid battery, lead contained in a
positive electrode grid may be gradually oxidized into lead oxide, and the volume of the grid
may increases. This brings about enlargement of the entirety of the grid in an electrode plate
10 height direction. According to the present disclosure, since the curved grid bars are used,
stress acting on the expanded grid during crystal growth can be relieved, and the possibility of
rupturing the grid bar(s) can be reduced. Consequently, battery cycle life can be improved.
[0067] The expanded grid of the present disclosure including the distorted grid bars is used
for the positive electrode plate of the lead-acid battery of the present disclosure, and the
15 distortion degree and distortion rate of the expanded grid each fall with a suitable range.
Thus, excellent discharge capacity and excellent cycle life can be realized.
[0068] Examples
Examples and comparative examples of the present disclosure will be described
below in detail, but the present disclosure is not limited to such examples.
20 [0069] First Example
(Formation of Positive Electrode Plate)
While a lead sheet made of a Pb-Ca-Sn ternary alloy was fed to a punching die,
movement of a movable die relative to a fixed die was controlled by an external unit to
repeatedly punch the lead sheet in the vertical direction. Then, the formed net-shaped sheet
25 is shaped in the horizontal direction with a pair of guide rollers used as a shaping die, and a
21
flat net-shaped body is formed.
[0070] Subsequently, lead powder which is a raw material, water, and sulfuric acid were
mixed together in a weight ratio of 100:15:10, thereby forming positive electrode lead paste.
The net-shaped body was filled with the positive electrode lead paste. Then, the net-shaped
5 body filled with the lead paste was cut to predetermined shape and dimensions, thereby
forming an expanded grid filled with the lead paste. The expanded grid was matured and
dried, thereby forming a positive electrode plate (having a vertical length of 139 mm, a
horizontal length of 64 mm, and a thickness of 2.9 mm) of the present disclosure.
[0071] Meanwhile, the external unit adjusted the cutting depth of the movable die and the
10 number of strokes of the movable die to control the distortion degree and distortion rate of the
expanded grid to desired values.
[0072] (Formation of Negative Electrode Plate)
A non-distorted flat net-shaped body formed by typical expansion was used. Lead
powder which is a raw material, water, and sulfuric acid were mixed together in a weight ratio
15 of 100:5:10, thereby forming negative electrode lead paste. Then, the net-shaped body was
filled with the negative electrode lead paste, and then was cut to predetermined shape and
dimensions. After maturation and drying, a negative electrode plate (having a vertical length
of 142 mm, a horizontal length of 65 mm, and a thickness of 1.70 mm) was formed.
[0073] (Formation of Lead-Acid Battery)
20 A plurality of positive electrode plates formed as described above and a plurality of
negative electrode plates formed as described above were alternately stacked on each other in
the state in which a separator mainly made of glass fibers is interposed between the positive
electrode plate and the negative electrode plate. Ear parts of the electrode plates having the
same polarity were welded together to form a strap. Then, each electrode plate group was
25 housed in a corresponding one of six cells of a container divided by partitions. In the present
22
example, the straps were, without using poles, welded together to connect the electrode plate
groups in series.
[0074] Subsequently, a sulfuric acid solution of 170 mm was, as an electrolyte, introduced
into each cell in a sulfuric acid concentration of 1.242 g/ml. Then, the container was sealed
5 with inner and outer covers being attached to an opening of the container. After chemical
processing, a lead-acid battery having a capacity of 20 Ah was formed.
[0075] For the following measurement of the distortion degree and the distortion rate, the
lead paste was, after disassembly of the battery, removed from the positive electrode plate,
and the expanded grid was removed from the positive electrode plate. In the present
10 example, the measured distortion degree was 0.09, and the measure distortion rate was 11%.
[0076] (1) Measurement of Distortion degree
First, an orthographic projection view of the expanded grid removed from the
disassembled battery was formed on the plane parallel to the expanded grid. Subsequently,
the followings were measured using measurement equipment: the length of a side of a
15 diamond-shaped mesh; and a distance between the top of curvature of a distorted one of grid
bars in another diamond-shaped mesh and another one of the grid bars opposing the distorted
grid bar in the another diamond-shaped mesh, the distance being measured parallel to the
remaining two of the grid bars in the another diamond-shaped mesh. The distance between
the top of the curved grid bar and the opposing grid bar was divided by the length of the side
20 of the diamond-shaped mesh, thereby obtaining the ratio therebetween. A value obtained by
subtracting one from such a ratio was recorded as the distortion degree. The foregoing
measurement was conducted for expanded grids of ten batteries, and an average of ten
distortion degrees obtained by the measurement was obtained as the distortion degree of the
expanded grid.
25 [0077] (2) Measurement of Distortion rate
23
For the expanded grid removed from the disassembled battery, statistics on the total
number of grid bars and the number of distorted grid bars were taken. The number of
distorted grid bars was divided by the total number of grid bars. The obtained percentage
was recorded as the distortion rate. The foregoing measurement was conducted for
5 expanded grids of ten batteries, and an average of ten distortion rates obtained by the
measurement was obtained as the distortion rate of the expanded grid.
[0078] Second Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
10 distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.11. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0079] Third Example
15 In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.14. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
20 similar to that of the first example.
[0080] Fourth Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
25 is 0.17. Other process for forming the positive electrode plate was similar to that of the first
24
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0081] Fifth Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
5 number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.19. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
10 [0082] First Comparative Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.08. Other process for forming the positive electrode plate was similar to that of the first
15 example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0083] Second Comparative Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
20 distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.21. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0084] Sixth Example
25 In formation of a positive electrode plate, the cutting depth of a movable die and the
25
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 6% and that the distortion degree of the expanded grid is
0.14. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
5 similar to that of the first example.
[0085] Seventh Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 7% and that the distortion degree of the expanded grid is
10 0.14. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0086] Eighth Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
15 number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11% and that the distortion degree of the expanded grid
is 0.14. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
20 [0087] Ninth Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 15% and that the distortion degree of the expanded grid
is 0.14. Other process for forming the positive electrode plate was similar to that of the first
25 example, and a negative electrode plate and a lead-acid battery were formed in a manner
26
similar to that of the first example.
[0088] Tenth Example
In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
5 distortion rate of an expanded grid is 17% and that the distortion degree of the expanded grid
is 0.14. Other process for forming the positive electrode plate was similar to that of the first
example, and a negative electrode plate and a lead-acid battery were formed in a manner
similar to that of the first example.
[0089] Eleventh Example
10 In formation of a positive electrode plate, the cutting depth of a movable die and the
number of strokes of the movable die were adjusted by an external unit such that the
distortion rate of an expanded grid is 11%> and that the distortion degree of the expanded grid
is 0.14. Similarly, in formation of a negative electrode plate, the cutting depth of the
movable die and the number of strokes of the movable die were adjusted by the external unit
15 such that the distortion rate of an expanded grid is 11%> and that the distortion degree of the
expanded grid is 0.14. Other process for forming the positive and negative electrode plates
was similar to that of the first example, and a lead-acid battery was formed in a manner
similar to that of the first example.
[0090] For the lead-acid batteries of the first to eleventh examples and the first and second
20 comparative examples, an evaluation test of battery performance was conducted under the
following conditions.
[0091] (A) Evaluation on Discharge Capacity
Constant current discharging of the fully-charged battery was performed with a
discharge current of 0.05 C under an environmental temperature of 25±2°C. The
25 discharging was terminated when a discharge cutoff voltage reached 1.75 V/cell. A first
27
table shows a discharge time (in units of minutes) of each battery. The discharge capacity of
the battery was evaluated based on the discharge time.
[0092] (B) Evaluation on Cycle Life
(1) Measurement of Initial Capacity Co
5 First, constant current discharging of the fully-charged battery was performed with
a discharge current of 0.25 C under an environmental temperature of 25+2°C. The
discharging was terminated when a discharge cutoff voltage reached 1.75 V/cell. Using a
discharge time h0 of the battery, an initial capacity Co was obtained according to the following
expression.
10 [0093] Initial Capacity Co = Discharge Current (I) x Discharge Time (ho)
[0094] (2) Recovery Charging
After the foregoing measurement, constant voltage charging of the battery was
performed with a charge voltage of 2.275 V/cell under an environmental temperature of
25±2°C. The battery was charged to a fully-charged state with a maximum charge current of
15 0.4 C for 6 to 16 hours.
[0095] (3) High-Temperature Trickle Charging
The battery was placed in a constant-temperature bath under a temperature of
60±2°C. Constant voltage charging of the battery was continuously performed with a charge
voltage of 2.275 V/cell for three weeks.
20 [0096] (4) Measurement of Discharge Capacity C
After removal of the battery from the constant-temperature bath, the battery was left
standing at an environmental temperature of 25+2°C for 12 to 25 hours. Then, discharging
of the battery was performed under the same conditions as those described in (I). The
discharge time h of the battery in such a state was measured, and a discharge capacity C was
25 obtained according to the following expression. The foregoing steps form a single
28
charge/discharge cycle.
[0097] Discharge Capacity C = Discharge Current (I) x Discharge Time (h)
[0098] (5) After repetition of the steps of (2)-(4), the test was terminated when the
discharge capacity C obtained by the measurement reached below 50% of the initial capacity
5 C0. The first table shows the number of charge/discharge cycles. The cycle life of the
battery was evaluated based on the number of charge/discharge cycles.
[0099] Parameters of the battery and the test results are shown in the first table.
[0100] [First Table]
FIRST
COMPARATIVE
EXAMPLE
FIRST
EXAMPLE
SECOND
EXAMPLE
THIRD
EXAMPLE
FOURTH
EXAMPLE
FIFTH
EXAMPLE
SECOND
COMPARATIVE
EXAMPLE
SIXTH
EXAMPLE
SEVENTH
EXAMPLE
EIGHTH
EXAMPLE
NINTH
EXAMPLE
TENTH
EXAMPLE
ELEVENTH
EXAMPLE
POSITIVE ELECTRODE PLATE
GRID TYPE
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
DISTORTION
RATE %
6
7
II
15
17
II
DISTORTION
DEGREE
W =
(D2-DD/D1
0.08
0.09
0.11
0.14
0.17
0.19
0.21
0.14
0.14
0.14
0.14
0.14
0.14
NEGATIVE ELECTRODE PLATE
GRID TYPE
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
EXPANDED
DISTORTION
RATE %
0
0
0
0
0
0
0
0
0
0
0
0
11
DISTORTION
DEGREE
W =
(D2-D1)/ Dl
-
-
• -
-
-
-
-
-
-
-
-
-
0.14
EVALUATION RESULTS
DISCHARGE
TIME
(MINUTES)
1150
1250
1300
1330
1300
1250
1150
1250
1300
1330
1300
1250
1330
THE NUMBER
OF CYCLES
(THE NUMBER
OF TIMES)
8
10
1 1
13
12
10
8
10
12
13
12
10
13
10 [0101] As will be seen from the first table, in all of the lead-acid batteries of the first to
eleventh examples of the present disclosure using the expanded grids having predetermined
distortion degrees (a degree of 0.09 to 0.19), the discharge time exceeded 20 hours, and the
number of charge/discharge cycles was equal to or higher than 10. This shows that the leadacid
battery of the present disclosure has excellent discharge capacity and excellent cycle life.
29
On the other hand, in the batteries of the first and second comparative examples with the
distortion degrees falling outside the foregoing range, the discharge time was less than 20
hours, and the number of charge/discharge cycles was only eight. Moreover, in the batteries
of the second to fourth and seventh to ninth examples having distortion degrees of 0.11 to
5 0.17 and distortion rates of 7% to 15%, the discharge time exceeded 21 hours, and the number
of charge/discharge cycles was equal to or higher than 11. Further, in the battery of the
eleventh example using the expanded grids of the present disclosure for the positive and
negative electrode plates, the same advantages as those of the eighth example which does not
use the expanded grid of the present disclosure as the negative electrode plate were realized.
10
30
CLAIMS
1. An expanded grid formed by expansion, comprising:
grid bars forming a plurality of diamond-shaped meshes,
wherein at least one of the grid bars is a distorted grid bar, and defines a protruding
curved part,
a distortion degree W indicating a degree of curvature of the distorted grid bar is
determined according to a first expression:
W = (D2-D1)/D1 (1)
where, in a projection view of the expanded grid,
Dl represents a distance between non-distorted two of the grid bars being
parallel to each other and opposing each other in one of the diamond-shaped meshes, the
distance being a length of a side of the one of the diamond-shaped meshes and being
measured parallel to the remaining two of the grid bars in the one of the diamond-shaped
meshes,
D2 represents a distance between a top of the curvature of the distorted
grid bar in another one of the diamond-shaped meshes and another one of the grid bars being
parallel to the distorted grid bar and opposing the distorted grid bar in the another one of the
diamond-shaped meshes, the distance being measured parallel to the remaining two of the
grid bars in the another one of the diamond-shaped meshes, and
D2 > Dl is satisfied, and
the distortion degree W falls within a range of 0.09 to 0.19.
2. The expanded grid of claim 1, wherein
the distortion degree W falls within a range of 0.11 to 0.17.
3. The expanded grid of claim 1 or 2, wherein
a distortion rate which is a percentage of the number of the distorted grid bar of the
expanded grid in the total number of the grid bars of the expanded grid falls within a range of
5 to 20%.
4. The expanded grid of claim 3, wherein
the distortion rate falls within a range of 6 to 17%.
5. The expanded grid of claim 4, wherein
the distortion rate falls within a range of 7 to 15%.
6. A lead-acid battery electrode plate comprising:
the expanded grid of any one of claims 1-5; and
an active material with which the expanded grid is filled.
7. A lead-acid battery comprising:
the electrode plate of claim 6.
8. The lead-acid battery of claim 7, wherein
the electrode plate is a positive electrode plate.
9. A method for manufacturing the expanded grid of any one of claims 1-5,
comprising the steps of:
(1) an expansion step of, after a series of strokes each performed every time a lead
sheet moves in a length direction thereof by a predetermined distance, forming a net-shaped
sheet in which the plurality of diamond-shaped meshes are formed, each stroke including
the step of moving an upper die of a punching die for punching the lead
sheet relative to a lower die of the punching die to form a plurality of diagonally-extending
slits in the length direction of the lead sheet while expanding the slits in a direction
perpendicular to a lead sheet surface and
the step of returning the upper die of the punching die to an original
position;
(2) a shaping step of shaping the net-shaped sheet in a horizontal direction with a
guide roller to form a flat net-shaped body; and
(3) a cutting step of cutting the net-shaped body to predetermined shape and
dimensions to form the expanded grid,
wherein a cutting depth of the upper die and/or the number of strokes of the upper
die at the expansion step are controlled to cause the expanded grid to have a predetermined
distortion degree and/or a predetermined distortion rate.
10. The method of claim 9, wherein
the cutting depth falls within a range of 2.965 to 3.045 mm.
11. The method of claim 10, wherein
the cutting depth falls within a range of 2.98 to 3.03 mm.
12. The method of any one of claims 9-11, wherein
the number of strokes falls within a range of 600 to 1800 rpm.
13. The method of claim 12, wherein
the number of strokes falls within a range of 750 to 1500 rpm.
14. The method of claim 12, wherein
the number of strokes falls within a range of 800 to 1300 rpm.