AU2015258219B2 - Lead-acid battery - Google Patents

Abstract

OF THE DISCLOSURE In a negative electrode material of a negative electrode plate of a lead-acid battery, a concentration of Ba sulfate contained in the electrode material after full charge is 1.0 mass% or more, and the Na concentration in the electrolyte solution is 0.04 mol/L or less. The lead-acid battery is excellent in terms of charge acceptance performance in the case where the battery is charged after some time following discharge. 1/6 FIG. 1 12 A A A A A A < x' x V x Nx. \ 13 6 13 w

Description

1/6

FIG. 1

12

A A A A A A

< x' x V x

Nx. \

13 6 13 w

LEAD-ACID BATTERY FIELD

The present invention relates to a lead-acid battery.

BACKGROUND

JP-A-2012-142185 discusses improving the life performance of a

lead-acid battery in an idling-stop mode at both normal and high

temperatures. For this purpose, it proposes that: a Pb-Sn-Sb alloy layer is

provided on the surface of a negative electrode grid; Li and Al are contained

in electrolyte solution; and Na concentration of the electrolyte solution is set

to be 0.04 mol/L or less.

In addition, for the electrode material of the negative electrode, 0.6

mass% of Ba sulfate is contained relative to 98.8 mass% of a lead powder.

However, changing the Ba sulfate concentration from 0.6 mass% has not

been considered.

In JP-A-2001-23682, the volume of an element of a sealed type

lead-acid battery is defined by the height of electrode plates x the width of

the electrode plates x the thickness of the element. It is disclosed that when

the mass of a negative active material per unit volume of the element is 0.84

g/cm3 or more and 1.20 g/cm 3 or less, the high-rate discharge performance improves. However, the influences of the Ba sulfate concentration and the

Na concentration have not been examined.

JP-A-2003-178806 discusses the influences of the mass of the positive

active material and the mass of the negative active material in a valve-regulated lead-acid battery, and shows an example in which the density of the positive active material is 4.20 g/cm 3 , andthemass ratio between the positive active material and the negative active material is 1.2.

SUMMARY

In a mode like an idling-stop mode, a lead-acid battery is not

sufficiently charged, and thus the crystallization of lead sulfate is likely to

proceed in the negative active material. In addition, the battery is not

charged to generate a large amount of gas, and thus the electrolyte solution

is likely to be stratified. When the electrolyte solution is stratified, some

electrode plates are used locally, causing a further decrease in the life

performance.

In order to solve these problems, it is necessary to improve the charge

acceptance performance and suppress the crystallization of lead sulfate. Ba

sulfate improves the charge acceptance performance in the case where the

battery is charged without being remained untouched after the discharge.

However, it has been revealed that in the case where the battery is charged

after some time has passed since the discharge, the charge acceptance

performance is reduced by Ba sulfate. In order to suppress the

crystallization of lead sulfate, the charge acceptance performance

immediately after discharge and that after being remained untouched are

both important. In addition, internal resistance is an important index,

which indicates the degradation state of the lead-acid battery, and is also

used to determine whether idling-stop is possible in idling-stop vehicles.

When there is a small increase in the internal resistance in accordance with the progress of charge-discharge cycles, this indicates that the degradation of electrode plates is slow, the degradation of electrode plates is uniformly progressing, etc.

The present invention is aimed at providing a lead-acid battery

whose charge acceptance performance does not decrease much even in the

case where the battery is charged after some time has passed since the

discharge.

An aspect of the present invention provides a lead-acid battery

including a positive electrode plate, a negative electrode plate, and an

electrolyte solution placed in a cell chamber of a container. In a negative

electrode material of the negative electrode plate, the concentration of Ba

sulfate contained in the electrode material after full charge is 1.0 mass% or

more, and the Na concentration in the electrolyte solution is 0.04 mol/L or

less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a negative electrode plate.

FIG. 2 is a plan view of part of a lead-acid battery with a lid removed.

FIG. 3 is a characteristic diagram showing the charge acceptance

performance with being remained untouched (standing) under conditions

where NP/V is fixed to 1.40 g/cm 3, the Na concentration is varied within a

range of 0.015 mol/L to 0.1 mol/L, and the Ba sulfate concentration is varied

within a range of 0.5 mass% to 4 mass% (expressed as a value relative to the

charge acceptance performance in the case where the Ba sulfate

concentration is 0.5 mass% at each Na concentration (= 100)).

FIG. 4 is a characteristic diagram showing the rate of increase in the

internal resistance at the 2000t1h cycle under conditions where NP/V is fixed

to 1.40 g/cm 3 , the Na concentration is varied within a range of 0.015 mol/L to

0.1 mol/L, and the Ba sulfate concentration is varied within a range of 0.5

mass% to 4 mass%.

FIG. 5 is a characteristic diagram showing the rate of increase in the

internal resistance at the 2000th cycle under conditions where NP/V is varied

within a range of 1.25 g/cm 3 to 1.70 g/cm 3 . FIG. 6 is a characteristic diagram showing the number of life cycles

under conditions where the density of the positive electrode material is 3 3 varied within a range of 3.7 g/cm to 4.2 g/cm .

FIG. 7 is a characteristic diagram showing the number of life cycles

under conditions where graphite is contained in the negative electrode

material.

FIG. 8 is a characteristic diagram showing the number of life cycles

under conditions where Al is contained in the electrolyte solution.

FIG. 9 is a characteristic diagram showing the number of life cycles

under conditions where Li is contained in the electrolyte solution.

DESCRIPTION OF EMBODIMENTS

According to an aspect of the present invention, there is provided a

lead-acid battery including a positive electrode plate, a negative electrode

plate, and an electrolyte solution placed in a cell chamber of a container, in a

negative electrode material of the negative electrode plate, the concentration

of Ba sulfate contained in the electrode material after full charge is 1.0 mass% or more, and the Na concentration in the electrolyte solution is 0.04 mol/L or less.

An increase in the Ba sulfate concentration in the negative electrode

material results in the improvement of the charge acceptance performance in

the case where the battery is charged without standing following discharge.

However, the present inventors have found that when only the Ba sulfate

concentration is increased, in the case where the battery is charged after

standing following discharge, the charge acceptance performance rather

decreases. Further, to deal with this, the present inventors have found that

when the Na concentration in the electrolyte solution is 0.04 mol/L or less, a

decrease in the charge acceptance performance after standing due to the

addition of Ba sulfate can be suppressed (FIG. 3). That is, when the Na

concentration in the electrolyte solution is limited to 0.04 mol/L or less, and

the Ba sulfate concentration in the negative electrode material is 1.0 mass%

or more, a lead-acid battery, in which a decrease in the charge acceptance

performance in the case where the battery is charged after standing

following discharge is suppressed, is obtained. In conventional lead-acid

batteries, in order to suppress a penetration short circuit, the Na

concentration in the electrolyte solution is generally made about 0.1 mol/L to

0.2 mol/L. Therefore, it is not easy to conceive of a Na concentration of 0.04

mol/L or less.

Further, when the Na concentration in the electrolyte solution is

limited to 0.04 mol/L or less, and the Ba sulfate concentration in the negative

electrode material is 1.2 mass% or more, an increase in the internal

resistance of a lead-acid battery in accordance with the progress of charge-discharge cycles when used under PSOC (Partial State of Charge) conditions can be suppressed (FIG. 4). Meanwhile, even when the Na concentration in the electrolyte solution is limited to 0.04 mol/L or less, if the

Ba sulfate concentration in the negative electrode material is 1.0 mass% or

less, the suppressing effect on an increase in the internal resistance in

accordance with the progress of charge-discharge cycles is small. Thus, the

tendency is significantly different between Ba sulfate concentrations of 1.0

mass% or less and 1.2 mass% or more (FIG. 4). In addition, in the case

where the Na concentration in the electrolyte solution is more than 0.04

mol/L, even when the Ba sulfate concentration in the negative electrode

material is 1.2 mass% or more, the rate of increase in the internal resistance

in accordance with the progress of charge-discharge cycles does not

significantly change (FIG. 4). It has been heretofore unknown that an

increase in the internal resistance in accordance with the progress of

charge-discharge cycles is suppressed in the case where the Ba sulfate

concentration in the negative electrode material is 1.2 mass% or more and

the Na concentration in the electrolyte solution is 0.04 mol/L or less. Thus,

this is an unexpected result.

Incidentally, in place of Ba sulfate, it is also possible to use elemental

Ba or a Ba compound such as Ba carbonate. This is because even when

elemental Ba or a Ba compound is added to the negative electrode material,

it turns into Ba sulfate after addition. Elemental Ba or a Ba compound is

added such that the concentration in terms of Ba sulfate will be 1.0 mass% or

more, preferably 1.2 mass% or more, relative to the mass of the negative

electrode material after full charge. As a concentration in terms of Ba, addition is made such that the concentration will be 0.6 mass% or more, preferably 0.7 mass% or more, relative to the mass of the negative electrode material after full charge.

When the Ba sulfate concentration in the negative electrode material

is more than 4.0 mass%, the paste of the negative electrode material becomes

so hard that it is difficult to apply the paste to a negative electrode current

collector. Therefore, it is preferable that the Ba sulfate concentration in the

negative electrode material after full charge is 4.0 mass% or less, more

preferably 3.5 mass% or less. As a concentration in terms of Ba, it is

preferable that the concentration is 2.4 mass% or less, more preferably 2.1

mass% or less, relative to the mass of the negative electrode material after

full charge.

The Na concentration of the electrolyte solution is the lower the

better. In the aspect of the present invention, the Na concentration is 0.04

mol/L or less, preferably 0.035 mol/L or less. Na is mixed in from lignin or

the like added to the negative electrode material. Therefore, it is difficult to

make the Na concentration 0, and the concentration is practically 0.001

mol/L or more. When the Na concentration is limited, it becomes necessary

to reduce the amount of lignin or the like added to the negative electrode

material, resulting in a decrease in the life performance of the lead-acid

battery. Therefore, it is more preferable that the Na concentration is 0.005

mol/L or more. In addition, Li, Al, and the like in the electrolyte solution do

not inhibit the effect of Ba sulfate (improvement of charge acceptance

performance), and thus their contents are arbitrary.

When the total mass of negative electrode plates in a cell chamber is expressed as NP (g), and the volume defined by the height h (cm) of the negative electrode plates x the width w (cm) of the negative electrode plates x the inside dimension d (cm) of the cell chamber in a direction perpendicular to the negative electrode plates is expressed as V (V = hwd), it is preferable that NP/V is 1.3 g/cm 3 or more and 1.6 g/cm 3 or less. It is more preferable that NP/V is 1.4 g/cm 3 or more and 1.5 g/cm 3 or less. Incidentally, the height and width of a negative electrode plate are determined ignoring the parts projecting from the negative electrode plate, such as lugs and feet.

When the Ba sulfate concentration in the negative electrode material

and the Na concentration of the electrolyte solution are determined as

described above (according to the aspect of the present invention), and NP/V

is 1.3 g/cm 3 or more and 1.6 g/cm 3 or less, an increase in the internal

resistance in accordance with the progress of charge-discharge cycles can be

suppressed (FIG. 5). When NP/V is 1.4 g/cm 3 or more and 1.5 g/cm 3 or less,

an increase in the internal resistance in accordance with the progress of

charge-discharge cycles can be even more suppressed (FIG. 5). It has been

heretofore unknown that NP/V is associated with an increase in the internal

resistance in accordance with the progress of charge-discharge cycles.

Therefore, it can be said that it is an unexpected result that an increase in

the internal resistance with the progress of charge-discharge cycles can be

suppressed by making NP/V 1.3 g/cm 3 or more and 1.6 g/cm 3 or less,

preferably 1.4 g/cm 3 or more and 1.5 g/cm 3 or less.

It is preferable that the density of the positive electrode material is

3.8 g/cm 3 or more, more preferably 3.9 g/cm 3 or more. In the case where the

Ba sulfate concentration in the negative electrode material is 1.0 mass% or more, and the Na concentration in the electrolyte solution is 0.04 mol/L or less, when the density of the positive electrode material is 3.8 g/cm 3 or more, the life performance of the lead-acid battery significantly improves (FIG. 6).

Meanwhile, not in the case where the Ba sulfate concentration in the

negative electrode material is 1.0 mass% or more and the Na concentration

in the electrolyte solution is 0.04 mol/L or less, when the density of the

positive electrode material is 3.8 g/cm 3 or more, the life performance of the

lead-acid battery rather decreases (FIG. 6). It is an unexpected result that

only in the case where the Ba sulfate concentration in the negative electrode

material is 1.0 mass% or more and the Na concentration in the electrolyte

solution is 0.04 mol/L or less, the life performance is improved by making the

density of the positive electrode material 3.8 g/cm 3 or more.

When the density of the positive electrode material is more than 5.0

g/cm3 , the influence of a decrease in the capacity of the lead-acid battery becomes non-negligible. Therefore, it is preferable that the density of the

positive electrode material is 5.0 g/cm 3 or less, more preferably 4.3 g/cm 3 or

less, and particularly preferably 4.2 g/cm 3 or less.

It is preferable that the negative electrode material contains graphite.

Graphite in the negative electrode material significantly improves the life

performance of the lead-acid battery in the case where the Ba sulfate

concentration in the negative electrode material is 1.0 mass% or more and

the Na concentration in the electrolyte solution is 0.04 mol/L or less. Even

not in the case where the Ba sulfate concentration in the negative electrode

material is 1.0 mass% or more and the Na concentration in the electrolyte

solution is 0.04 mol/L or less, the life performance is improved by the presence of graphite in the negative electrode material (FIG. 7). However, the improving effect on the life performance caused by the presence of graphite in the negative electrode material is remarkable in the case where the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more and the Na concentration in the electrolyte solution is 0.04 mol/L or less (FIG. 7). It is an unexpected result that in the case where the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more and the Na concentration in the electrolyte solution is 0.04 mol/L or less, the improving effect on the life performance caused by the presence of graphite in the negative electrode material is remarkable.

When the content of graphite in the negative electrode material is 0.5

mass% or more, the improving effect on the life performance is significant,

and thus this is preferable. When the content of graphite in the negative

electrode material is 0.7 mass% or more, the improving effect on the life

performance is more significant, and thus this is more preferable. In

addition, it is preferable that the graphite is flake graphite.

When the content of graphite in the negative electrode material is

more than 2.5 mass%, the paste of the negative electrode material becomes

so hard that it is difficult to apply the paste to the negative electrode current

collector. Therefore, it is preferable that the content of graphite in the

negative electrode material is 2.5 mass% or less, more preferably 2.0 mass%

or less.

It is preferable that the electrolyte solution contains Al. Al in the

electrolyte solution significantly improves the life performance of the

lead-acid battery in the case where the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more and the Na concentration in the electrolyte solution is 0.04 mol/L or less. Even not in the case where the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more and the Na concentration in the electrolyte solution is 0.04 mol/L or less, the life performance is improved by the presence of Al in the electrolyte solution (FIG. 8). However, the improving effect on the life performance caused by the presence of Al in the electrolyte solution is remarkable in the case where the Ba sulfate concentration in the negative electrode material is

1.0 mass% or more and the Na concentration in the electrolyte solution is

0.04 mol/L or less (FIG. 8). It is an unexpected result that in the case where

the Ba sulfate concentration in the negative electrode material is 1.0 mass%

or more and the Na concentration in the electrolyte solution is 0.04 mol/L or

less, the improving effect on the life performance caused by the presence of

Al in the electrolyte solution is remarkable.

When the Al concentration in the electrolyte solution is 0.02 mol/L or

more, the improving effect on the life performance is significant, and thus

this is preferable. When the Al concentration in the electrolyte solution is

0.05 mol/L or more, the improving effect on the life performance is more

significant, and thus this is more preferable. In addition, when the Al

concentration in the electrolyte solution is 0.2 mol/L or less, the improving

effect on the life performance is significant, and thus this is preferable.

When the Al concentration in the electrolyte solution is 0.15 mol/L or less,

the improving effect on the life performance is more significant, and thus

this is more preferable.

It is preferable that the electrolyte solution contains Li. Li in the electrolyte solution improves the life performance of the lead-acid battery in the case where the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more and the Na concentration in the electrolyte solution is 0.04 mol/L or less (FIG. 9). Meanwhile, not in the case where the

Ba sulfate concentration in the negative electrode material is 1.0 mass% or

more and the Na concentration in the electrolyte solution is 0.04 mol/L or

less, the life performance of the lead-acid battery rather decreases when Li is

contained in the electrolyte solution (FIG. 9). It is an unexpected result

that only in the case where the Ba sulfate concentration in the negative

electrode material is 1.0 mass% or more and the Na concentration in the

electrolyte solution is 0.04 mol/L or less, the life performance is improved by

the presence of Li in the electrolyte solution.

When the Li concentration in the electrolyte solution is 0.02 mol/L or

more, the improving effect on the life performance is significant, and thus

this is preferable. When the Li concentration in the electrolyte solution is

0.05 mol/L or more, the improving effect on the life performance is still more

significant, and thus this is more preferable. When the Li concentration in

the electrolyte solution is 0.1 mol/L or more, the improving effect on the life

performance is still more significant, and thus this is still more preferable.

When the Li concentration in the electrolyte solution is more than 0.2

mol/L, the charge acceptance performance decreases. Therefore, it is

preferable that the Li concentration in the electrolyte solution is 0.2 mol/L or

less, more preferably 0.15 mol/L or less.

The lead-acid battery according to the aspect of the present invention

is excellent in terms of charge acceptance performance both immediately after discharge and after standing, and thus is suitable for use as a lead-acid battery for idling-stop and the like, which is not sufficiently charged.

Hereinafter, examples will be shown. To implement the invention,

the examples may be suitably modified according to the common knowledge

of those skilled in the art and the disclosure of related art. Incidentally, in

the examples, a negative electrode material may be referred to as a negative

active material, while a positive electrode material may be referred to as a

positive active material. In addition, a negative electrode plate is made of a

negative electrode current collector (negative electrode grid) and a negative

electrode material (negative active material), while a positive electrode plate

is made of a positive current collector (positive electrode grid) and a positive

electrode material (positive active material). Solid constituents other than

the current collectors (grids) belong to electrode materials (active materials).

The concentrations of Ba sulfate and graphite in the negative

electrode material and Na, Al, Li, and like additives in the electrolyte

solution, the density of the positive electrode material, and the like are

values in a fully charged state. Incidentally, a fully charged state is a state

in which the battery has been charged at 5-hour rate current until the

terminal voltage during discharge measured every 15 minutes shows a

constant value 3 times in a row.

EXAMPLES

A negative active material was prepared by mixing a lead powder,

which was obtained by a ball-mill method, with a predetermined amount of

Ba sulfate (average primary particle size: 0.79 m, average secondary

particle size: 2.5 [tm), carbon, lignin, and plastic fibers as a reinforcing

material to make the total 100 mass% with the lead powder. The Ba sulfate

concentration was varied within a range of 0.5 mass% to 4.0 mass% relative

to the amount of negative active material after full charge. The lignin

content was 0.2 mass%, but the concentration is arbitrary. In addition, the

production method for the lead powder, the oxygen content, and the like are

arbitrary, and other additives, water-soluble synthetic polyelectrolytes, and

the like may also be contained. Incidentally, in place of Ba sulfate, it is also

possible to use elemental Ba or a Ba compound such as Ba carbonate.

The mixture was pasted with water and sulfuric acid, and the paste

was applied to and filled in an expanded negative electrode grid made of a

Pb-Ca-Sn-based alloy, then aged, and dried. Incidentally, the amount of

water at the time of pasting and applying conditions were varied to adjust

the density and thickness of the negative active material, thereby adjusting

the mass of the negative electrode plate. In addition, the negative electrode

grid may be a cast grid, a punched grid, or the like.

The mass of the negative electrode plate was adjusted by adjusting

the mass of the negative active material, but may also be adjusted by

adjusting the mass of the negative electrode grid by adjusting the width, the

number, or the like of crosspieces of the negative electrode grid. An increase

in the mass of the negative active material and an increase in the mass of the

negative electrode grid have the same effects.

A positive active material was prepared by mixing a lead powder,

which was obtained by a ball-mill method, with plastic fibers as a reinforcing material, and the mixture was pasted with water and sulfuric acid. The paste was applied to an expanded positive electrode grid made of a

Pb-Ca-Sn-based alloy, then aged, and dried. Incidentally, the amount of

water at the time of pasting was varied to adjust the density of the positive

active material. In addition, the positive electrode grid may be a cast grid, a

punched grid, or the like.

Unformed (not yet subjected to formation) negative electrode plates

were each covered with a polyethylene separator. Six unformed negative

electrode plates and five unformed positive electrode plates were alternately

layered, and the negative electrode plates and the positive electrode plates

were each connected with a strap to make an element. In addition, the

thickness of the separator was adjusted according to changes in the

thickness of the negative electrode plates caused by the adjustment of the

mass of the negative electrode plates. Incidentally, it is also possible to

cover positive electrode plates with a separator. The element was placed in

a cell chamber of the container, and sulfuric acid having a specific gravity of

1.230 was added at 20°C to perform container formation, thereby giving a

flooded type lead-acid battery of B20 size. It may also be a valve-regulated

lead-acid battery. After formation, a predetermined amount of sodium

sulfate was added to the electrolyte solution, and the Na concentration of the

electrolyte solution was adjusted within a range of 0.015 mol/L to 0.10 mol/L.

FIG. 1 illustrates a negative electrode plate 2, where numerals 4 and

6 denote upper and lower frames, numeral 8 denotes a crosspiece, and

numeral 10 denotes a negative active material. Numeral 12 denotes a lug

and numeral 13 denotes a foot. The height of the grid excluding the lug 12 and the feet 13 is defined as the height h of the negative electrode plate 2, and the width of the negative electrode plate 2 is expressed as w. If there is a projection in the width direction, the width w is determined excluding the projection.

FIG. 2 illustrates a lead-acid battery 20, where numeral 22 denotes a

container, numeral 23 denotes a partition, and six cell chambers 24 are

arranged in series. Numeral 26 denotes a strap on the negative electrode

side, numeral 27 denotes a strap on the positive electrode side, numerals 28

and 29 denote cell-connecting conductors, and numeral 30 denotes a pole.

Numeral 2 denotes the negative electrode plate as mentioned above, numeral

32 denotes a positive electrode plate, and numeral 34 denotes a separator

that may also cover the positive electrode plate 32. The inside dimension of

the cell chamber 24 in the direction perpendicular to the plates 2 and 32 is

expressed as d. Using the inside dimension d, the height h of the negative

electrode plates 2, and the width w of the negative electrode plates, the

effective volume V of the cell chamber 24 is defined as V = hwd.

The concentration of Ba contained in the formed negative active

material is quantified as follows. A lead-acid battery ina fully charged

state is disassembled, the negative electrode plates are washed with water

and dried to remove the sulfate content, and the negative active material is

collected. The negative active material is ground, a 300 g/L hydrogen

peroxide solution is added in an amount of 20 mL per 100 g of the negative

active material. Further, (1+3) nitric acid, which is prepared by diluting 60

mass% concentrated nitric acid with three times its volume of ion exchange

water, is added and then is heated for 5 hours with stirring, thereby dissolving lead as lead nitrate. Furthermore, Ba sulfate is dissolved, and the Ba concentration in the solution is quantified by atomic absorption measurement and converted into the Ba concentration in the negative active material. The Ba sulfate concentration in the negative active material can be determined from the Ba concentration in the negative active material.

For the concentrations of Na, Al, and Li in the electrolyte solution,

the electrolyte solution is extracted from the lead-acid battery in a fully

charged state, and each concentration is quantified by ICP analysis.

The content of graphite in the negative active material is quantified

asfollows. A lead-acid battery in a fully charged state is disassembled, the

negative electrode plates are washed with water and dried to remove the

sulfate content, and the negative active material is collected. The negative

active material is ground, a hydrogen peroxide solution having a

concentration of 300 g/L is added in an amount of 20 mL per 100 g of the

negative active material. Further, (1+3) nitric acid, which is prepared by

diluting 60 mass% concentrated nitric acid with three times its volume of ion

exchange water, is added and then is heated for 5 hours with stirring,

thereby dissolving lead as lead nitrate. Next, solid matters such as

graphite, carbon, and the reinforcing material are separated by filtration.

The solid matters obtained by filtration are dispersed in water. The

dispersion liquid is sieved twice using a sieve having a size of 1.4 mm to

remove the reinforcing material. Next, centrifugal separation is performed

at 3000 rpm for 5 minutes, and carbon and graphite are extracted from the

supernatant and the upper precipitate.

Next, the extracted carbon and graphite are separated. 15 mL of

VANILLEX N manufactured by Nippon Paper Industries Co., Ltd., is added

per 100 mL of the supernatant and upper precipitate extracted, followed by a

stirring operation.

After the above operation, a centrifugation operation is performed at

3000 rpm for 5 minutes, and the supernatant and precipitate are all passed

through a sieve having a size of 20 tm. Graphite does not to pass through

the sieve and thus remains on the sieve. A large amount of hot water is

poured over graphite remaining on the sieve to remove VANILLEX N,

followed by washing with water and drying. The graphite washed with

water and dried was weighed, and the weight is converted into the content of

graphite in the negative active material.

The quantification method for the density of the positive electrode

material is as follows. The formed positive electrode material in a fully

charged state is washed with water and dried, and the positive electrode

material is separated from the positive electrode grid. The separated

positive electrode material is, in an unground state, measured for the density

by the following procedures.

a) The apparent density (g/cm3) of the positive electrode material

including closed pores is measured by a pycnometer method.

b) The open pore volume per unit mass (cm3/g) of the positive

electrode material is measured by a mercury intrusion method. In the

mercury intrusion method, pressure is applied to the maximum pressure of

4.45 psia (30.7KPa), the contact angle is set to be 130 , and the mercury

surface tension is set to be 484 dynes/cm.

c) The density of the positive electrode material is determined as follows: 1 + [(1+ apparent density of positive electrode material) + (open pore volume per unit mass of positive electrode material)]. As mentioned above, the density of the positive electrode material is the density of the closed pores, open pores, and the positive electrode material in the formed positive electrode material after full charge.

The obtained lead-acid battery was discharged from the fully charged

state at 5-hour rate current for 30 minutes, and then charged at a constant

voltage of 14.5 V for 10 seconds, and the quantity of electricity at that time

was measured as the charge acceptance performance without standing

(without being remained untouched). In addition, the battery was

discharged from the fully charged state at 5-hour rate current for 30 minutes,

allowed to stand (be remained untouched) for 12 hours, and then charged at

a constant voltage of 14.5 V for 10 seconds, and the quantity of electricity at

that time was measured as the charge acceptance performance with

standing.

As a life test, a 1000-cycle test was performed in one week in

accordance with the standard of Battery Association of Japan (SBA SO101

9.4.5) modified as follows:

a cycle including discharge at 1-hour rate current for 59 seconds,

discharge at 300 A for 1 second, and charge at 14 V for 60 seconds was

performed;

a pause of 2 hours was given every 30 cycles; and

the internal resistance was measured every 1000 cycles.

Incidentally, the internal resistance was measured by an alternating current

four-probe method. Then, when the discharge voltage became less than 7.2

V, it was defined as the life. The results are shown in Table 1 and FIGS. 3 to

5. The charge acceptance performance (with standing and without

standing) and the number of life cycles are expressed as values relative to

the sample A19 in Table 1 as 100 (comparative example in which NP/V is

1.40 g/cm3 , the Na concentration is 0.10 mol/L, and Ba sulfate is 0.5 mass%).

In addition, the internal resistance is expressed as a value relative to the

internal resistance of each lead-acid battery before the life test as 1.

[Table 1] Charge acceptance performance Rate of Life Na Ba Sulfate NP/V concentration concentration Without With increase in cycle, Remarks (g/cm3) (mol/L) (mass%) standing, standing, internal relative relative to relative to resistance toA19 I_ A19 A19

0.015 0.5 115 123 1.10 116 Comparative Al 1.40 example A2 1.40 0.015 1.0 118 121 1.09 119 Example A3 1.40 0.015 1.2 118 119 1.07 128 Example A4 1.40 0.015 2.0 122 117 1.06 134 Example A5 1.40 0.015 3.0 124 116 1.07 135 Example A6 1.40 0.015 4.0 125 115 1.06 135 Example 0.035 0.5 112 117 1.14 113 Comparative A7 1.40 example A8 1.40 0.035 1.0 115 113 1.13 116 Example A9 1.40 0.035 1.2 116 112 1.10 123 Example AlO 1.40 0.035 2.0 119 111 1.10 128 Example All 1.40 0.035 3.0 121 108 1.09 129 Example A12 1.40 0.035 4.0 121 107 1.09 128 Example 1.40 0.05 0.5 106 110 1.20 108 Comparative A13 example

1.40 0.05 1.0 111 103 1.19 111 Comparative A14 example

0.05 1.2 112 101 1.19 117 Comparative A15 1.40 example

0.05 2.0 117 96 1.19 119 Comparative A16 1.40 example

0.05 3.0 120 89 1.18 119 Comparative A17 1.40 Example 1.40 0.05 4.0 121 88 1.18 119 Comparative A18 example

1.40 0.10 0.5 100 100 1.21 100 Comparative A19 example

A20 1.40 0.10 1.0 105 94 1.20 103 Comparative Example

1.40 0.10 1.2 106 92 1.20 106 Comparative A21 example

A22 1.40 0.10 2.0 110 87 1.20 108 Comparative example

1.40 0.10 3.0 113 81 1.19 110 Comparative A23 Example 0.10 4.0 114 80 1.19 112 Comparative A24 1.40 Example B2 1.25 0.015 2.0 120 115 1.12 116 Example B2 1.30 0.015 2.0 121 118 1.08 126 Example B3 1.60 0.015 2.0 123 118 1.06 141 Example B4 1.60 0.015 2.0 122 116 1.10 133 Example B5 1.70 0.015 2.0 122 115 1.16 113 Example

Table 1 shows that with an increase in the concentration of Ba sulfate contained in the negative active material, the charge acceptance performance with standing improves, but the charge acceptance performance with standing decreases. FIG. 3 is a graph showing the charge acceptance performance of the lead-acid batteries Al to A24 with standing in Table 1.

The charge acceptance performance is expressed as a value relative to the

charge acceptance performance with standing of each lead-acid battery

having a Ba sulfate concentration of 0.5 mass% at each Na concentration(

100). In the case where the Na concentration of the electrolyte solution is

0.05 mol/L or 0.10 mol/L, when the Ba sulfate concentration in the negative

active material is 1.0 mass% or more, the charge acceptance performance

with standing significantly decreases (FIG. 3). Meanwhile, in the case

where the Na concentration of the electrolyte solution is 0.015 mol/L or 0.035

mol/L, even when the Ba sulfate concentration in the negative active

material is 1.0 mass% or more, the charge acceptance performance with

standing does not decrease as much as in the case where the Na

concentration of the electrolyte solution is 0.05 mol/L or 0.10 mol/L (FIG. 3).

Therefore, it can be said that the suppressing effect on a decrease in the

charge acceptance performance with standing is high in the case where the

Na concentration of the electrolyte solution is 0.04 mol/L or less and the Ba

sulfate concentration in the negative active material is 1.0 mass% or more.

It has been heretofore unknown that the suppressing effect on a decrease in

the charge acceptance performance with standing is high in the case where

the Na concentration of the electrolyte solution is 0.04 mol/L or less and the

Ba sulfate concentration in the negative active material is 1.0 mass% or

more. Thus, this was an unexpected result.

Further, in the case where the Na concentration in the electrolyte

solution was 0.04 mol/L or less, when the Ba sulfate concentration in the

negative active material was 1.2 mass% or more, the rate of increase in the

internal resistance at the 2000th cycle was significantly suppressed (FIG. 4).

Meanwhile, even not in the case where the Na concentration in the

electrolyte solution was 0.04 mol/L or less, when the Ba sulfate concentration

in the negative active material was 1.0 mass%, the suppressing effect on the

rate of increase in the internal resistance at the 2000th cycle was small.

Thus, the tendency was significantly different between Ba sulfate

concentrations of 1.0 mass% or less and 1.2 mass% or more (FIG. 4). In

addition, in the case where the Na concentration in the electrolyte solution

was more than 0.04 mol/L, even when the Ba sulfate concentration in the

negative active material was 1.2 mass% or more, the rate of increase in the

internal resistance at the 2000th cycle did not change much (FIG. 4). It has

been heretofore unknown that an increase in the internal resistance in

accordance with the progress of charge-discharge cycles is suppressed in the

case where the Na concentration in the electrolyte solution is 0.04 mol/L or

less and the Ba sulfate concentration in the negative active material is 1.2

mass% or more. Thus, this was an unexpected result.

The samples B1 to B5 and the sample A4 in Table 1 show the

influence of the total mass NP of negative electrode plates per effective

volume V of the cell chamber (NP/V) on the rate of increase in the internal

resistance at the 2000th cycle. An increase in the internal resistance in

accordance with the progress of charge-discharge cycles was suppressed

when NP/V was 1.30 g/cm 3 or more and 1.60 g/cm 3 or less (FIG. 5). In particular, when NP/V was 1.40 g/cm 3 or more and 1.50 g/cm 3 or less, an increase in the internal resistance in accordance with the progress of charge-discharge cycles was significantly suppressed (FIG. 5). It has been heretofore unknown that the total mass NP of negative electrode plates per effective volume V of the cell chamber (NP/V) affects the rate of increase in the internal resistance in accordance with the progress of charge-discharge cycles. Therefore, it is an unexpected result that an increase in the internal resistance in accordance with the progress of charge-discharge cycles can be significantly suppressed when NP/V is 1.30 g/cm 3 or more and 1.60 g/cm 3 or less, preferably 1.40 g/cm 3 or more and 1.50 g/cm 3 or less.

FIG. 6 shows the influence of the density of the positive active

material on the life performance, and NP/V was set at 1.40 g/cm 3 . Taking

the number of life cycles of a battery, in which the Na concentration of the

electrolyte solution is 0.1 mol/L, the Ba sulfate concentration in the negative

active material is 0.5 mass%, and the density of the positive active material

is 3.70 g/cm 3 , as 100, the number of life cycles of each battery is shown. In

the case where the Na concentration in the electrolyte solution was 0.04

mol/L or less and the Ba sulfate concentration in the negative active material

was 1.0 mass% or more, when the density of the positive active material was

3.80 g/cm3 or more, the number of life cycles increased (FIG. 6). In

particular, when the density of the positive active material was 3.90 g/cm 3 or

more, the number of life cycles significantly increased. Meanwhile, in the

case where the Na concentration was 0.1 mol/L and the Ba sulfate

concentration was 0.5 mass%, when the density of the positive active

material was 3.80 g/cm 3 or more, the number of life cycles decreased (FIG. 6).

Therefore, it can be said that under conditions where the density of the

positive active material is 3.80 g/cm 3 or more, the tendency of the life test

results is completely different between the case where the Na concentration

in the electrolyte solution is 0.04 mol/L or less and the Ba sulfate

concentration in the negative active material is 1.0 mass% or more and other

cases.

The effect of the addition of graphite to the negative active material

and the effect of the addition of Al and Li to the electrolyte solution were

examined. As comparative examples, under conditions where the Na

concentration of the electrolyte solution was 0.1 mol/L and the Ba sulfate

concentration in the negative active material was 0.5 mass%, lead-acid

batteries having flake graphite contained in the negative active material and

lead-acid batteries having Al or Li contained in the electrolyte solution were

produced. In addition, as examples, under conditions where the Na

concentration in the electrolyte solution was 0.015 mol/L and the Ba sulfate

concentration in the negative active material was 2.0 mass%, lead-acid

batteries having flake graphite contained in the negative active material and

lead-acid batteries having Al or Li contained in the electrolyte solution were

produced. The production conditions were the same as in Example A4 and

Comparative Example A19, except for the concentrations of flake graphite,

Al, and Li. The test results of these batteries are shown in FIGS. 7 to 9.

Incidentally, in FIGS. 7 to 9, with respect to each of the case where the Na

concentration of the electrolyte solution was 0.1 mol/L and the Ba sulfate

concentration in the negative active material was 0.5 mass% and the case

where the Na concentration in the electrolyte solution was 0.015 mol/L and the Ba sulfate concentration in the negative active material was 2.0 mass%, the number of life cycles of each battery is shown taking the number of life cycles of a battery having no flake graphite contained in the negative active material and no Al or Li contained in the electrolyte solution as 100.

FIG. 7 shows the influence of the graphite content of the negative

active material on the life performance. When the negative active material

contains graphite, even in the case where the Na concentration in the

electrolyte solution is high and the Ba sulfate concentration in the negative

active material is low, the life performance improves. However, in the case

where the Na concentration is 0.04 mol/L or less and the Ba sulfate

concentration is 1.0 mass% or more, the life performance is improved even

more significantly by the presence of graphite in the negative active material.

When the content of graphite in the negative electrode material is within a

range of 0.7 mass% or more, the improving effect on the life performance is

particularly significant. It has been heretofore unknown that the

improving effect on the life performance caused by the presence of graphite

in the negative electrode material is remarkable in the case where the Na

concentration in the electrolyte solution is 0.04 mol/L or less and the Ba

sulfate concentration in the negative electrode material is 1.0 mass% or more.

Thus, this is an unexpected result.

FIG. 8 shows the influence of the Al concentration of the electrolyte

solution on the life performance. When the electrolyte solution contains Al,

even in the case where the Na concentration in the electrolyte solution is

high and the Ba sulfate concentration in the negative active material is low,

the life performance improves. However, in the case where the Na concentration is 0.04 mol/L or less and the Ba sulfate concentration is 1.0 mass% or more, the life performance is improved even more significantly by the presence of Al in the electrolyte solution. The improving effect on the life performance is particularly significant when the concentration of Al in the electrolyte solution is within a range of 0.05 mol/L or more. It has been heretofore unknown that the improving effect on the life performance caused by the presence of Al in the electrolyte solution is remarkable in the case where the Na concentration in the electrolyte solution is 0.04 mol/L or less and the Ba sulfate concentration in the negative electrode material is 1.0 mass% or more. Thus, this is an unexpected result.

FIG. 9 shows the influence of the Li concentration of the electrolyte

solution on the life performance. When the electrolyte solution contains Li,

in the case where the Na concentration in the electrolyte solution is high and

the Ba sulfate concentration in the negative active material is low, the life

performance decreases. Meanwhile, in the case where the Na concentration

is 0.04 mol/L or less and the Ba sulfate concentration is 1.0 mass% or more,

the life performance improves when the electrolyte solution contains Li.

The improving effect on the life performance is particularly significant when

the concentration of Li in the electrolyte solution is within a range of 0.05

mol/L or more. Therefore, it can be said that under conditions where the

electrolyte solution contains Li, the tendency of the life test results is

completely different between the case where the Na concentration in the

electrolyte solution is 0.04 mol/L or less and the Ba sulfate concentration in

the negative active material is 1.0 mass% or more and other cases.

Although the lead-acid batteries in the Examples are flooded type batteries, they may also be valve-regulated batteries. In addition, the lead-acid batteries can be used not only for idling-stop vehicles but also for charge-control vehicles, and are suitable as batteries for use under PSOC

(Partial State of Charge) conditions. However, the application is arbitrary.

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 (13)

What is claimed is:

1. A lead-acid battery, comprising:

a positive electrode plate;

a negative electrode plate;

an electrolyte solution; and

a container having a cell chamber in which the positive electrode

plate, the negative electrode plate and the electrolyte solution are

accommodated, wherein

a concentration of Ba sulfate contained in a negative electrode

material of the negative electrode plate is 1.0 mass% or more, and

a Na concentration in the electrolyte solution is 0.001 mol/L or more

and 0.04 mol/L or less in a fully charged state,

characterized in that a density of a positive electrode material of the 3 positive electrode plate in a fully charged state is 3.8 g/cm or more.

2. A lead-acid battery, comprising:

a positive electrode plate;

a negative electrode plate;

an electrolyte solution; and

a container having a cell chamber in which the positive electrode

plate, the negative electrode plate and the electrolyte solution are

accommodated, wherein

a concentration of Ba contained in a negative electrode material of

the negative electrode plate is 0.6 mass% or more, and a Na concentration in the electrolyte solution is 0.001 mol/L or more and 0.04 mol/L or less in a fully charged state, characterized in that a density of a positive electrode material of the 3 positive electrode plate in a fully charged state is 3.8 g/cm or more.

3. The lead-acid battery according to claim 1, wherein the concentration of

Ba sulfate contained in the negative electrode material is 1.2 mass% or more.

4. The lead-acid battery according to claim 2, wherein the concentration of

Ba contained in the negative electrode material is 0.7 mass% or more.

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

density of a positive electrode material of the positive electrode plate is 4.3 g/

cm 3 or less.

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

negative electrode material contains graphite.

7. The lead-acid battery according to claim 6, wherein the negative electrode

material contains graphite in an amount of 0.5 mass% or more.

8. The lead-acid battery according to any one of claims 1 to 7, wherein the

electrolyte solution contains Al.

9. The lead-acid battery according to claim 8, wherein the electrolyte solution contains Al in an amount of 0.02 mol/L or more.

10. The lead-acid battery according to any one of claims 1 to 9, wherein the

electrolyte solution contains Li.

11. The lead-acid battery according to claim 10, wherein the electrolyte

solution contains Li in an amount of 0.02 mol/L or more.

12. The lead-acid battery according to claim 6, wherein the negative

electrode material contains flake graphite.

13. The lead-acid battery according to any one of claims 1 to 12,

wherein the lead-acid battery is a lead-acid battery for an idling-stop

vehicle and/or

wherein the lead-acid battery is a flooded type lead-acid battery.