Lead acid storage battery and method for producing the same

The invention provides a lead acid storage battery with a high utilization at a high rate discharge by incorporating a lead ion solubility adjusting agent into the electrolyte. The agent is selected from polysaccharides, chelating agents, their derivatives, and hydrazinium sulfate.

BACKGROUND OF THE INVENTION 
The present invention relates to an improvement of a lead acid storage 
battery. 
The lead acid storage battery is generally a storage battery using lead 
dioxide in the positive electrode and lead in the negative electrode as 
active materials, and dilute sulfuric acid as an electrolyte. And it is 
the secondary battery most widely used for portable equipment, motor 
vehicles, industrial applications, and recently for electric vehicles. As 
a method for producing this lead acid storage battery, there have been 
historically known paste process, clad process, and Tudor process. 
Recently, a method of kneading and filling a special resin and lead powder 
in a lead or lead alloy current collector has been known. 
In the battery configuration, too, a wide variety of forms are now put to 
practical uses from the conventional configuration using an abundant 
amount of electrolyte to a sealed-type battery which is so limited that 
the electrolyte is absorbed in a glass mat and oxygen evolving from the 
positive electrode during overcharging is ionized on the negative 
electrode. 
In any application, size and weight reduction is a common subject, and the 
utilization improvement of the active material is an endless proposition. 
However, the fact is that, in the unitization of the active material, the 
lead acid storage battery is limited to a low level as compared with other 
battery systems. Recently in particular, the low utilization at a high 
rate discharge has been a block to further widening applications. 
It is known that the utilization even at a low rate discharge of not higher 
than 0.1 C by the theoretical filling capacity standard is generally at 
most 50-55% at the positive electrode and 60% or so at the negative 
electrode on the theoretical filling capacity and drops below a level of 
20% at a high rate discharge exceeding 5 C. Generally, the theoretical 
filling amount of the negative electrode is large as compared with the 
positive electrode, and the utilization of the positive electrode 
determines the battery capacity in many cases. 
In a long history, much research has been done to solve the problem of low 
utilization. But no means to essentially improve the utilization has been 
born. It is considered that the factor to determine the utilization at a 
high rate discharge is the diffusion or supply of sulfuric acid. To 
facilitate this supply of sulfuric acid, a method of adding a surfactant 
or the like to the electrolyte has been tried without practical results, 
and thus no good way to improve the utilization has been found out except 
for forming a configuration suited for the diffusion of sulfuric acid. In 
other words, it has been thought that once a structure is decided upon, 
there is no means to raise the utilization of the active material. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the present invention to find out a way to break through 
the barrier limiting the diffusion of sulfuric acid within a formed 
suitable structure and to provide a lead acid storage battery with a high 
utilization at a high rate discharge. 
The present invention is based on a discovery that the addition of a 
certain special compound in a very small amount is effective in remarkably 
raising the utilization of the active material, especially at a high rate 
discharge. 
The present invention provides a lead acid storage battery comprising a 
power generating element and at least one compound selected from the group 
consisting of a polysaccharide and its derivatives, a chelating agent and 
its derivatives, and hydrazinium sulfate which is added to the power 
generating element as a solubility adjusting agent for lead ions. The 
power generating element comprises a positive electrode, a negative 
electrode, a separator interposed between the positive electrode and 
negative electrode, and an electrolyte. 
The reason the addition of this lead ion solubility adjusting agent 
improves the utilization is not clarified yet. But if the solubility 
adjusting agent for lead ions selected from the group consisting of a 
polysaccharide, a chelating agent and their derivatives is added in a 
small amount, a phenomenon will arise that the activity of Pb.sup.2+ in a 
strong acid aqueous solution of sulfuric acid will change greatly. 
The reaction in the lead acid storage battery both at the positive 
electrode and the negative electrode is generally called dissolution and 
deposition reaction, in which PbO.sub.2 at the positive electrode and Pb 
at the negative electrode each produce Pb.sup.2+ ions electrochemically 
first, which then chemically react with the sulfuric acid radical to 
produce lead sulfate. At both electrodes, therefore, the discharge 
potential is influenced by Pb.sup.2 ion. If Pb.sup.2+ increases in the 
system of formation reaction product, then the positive electrode 
potential drops while the negative electrode potential rises, resulting in 
a decrease in terminal voltage. But it is thought that the negative 
electrode, where the sulfuric acid radical is easy to move, is not so much 
influenced by the Pb.sup.2+ accumulated as a result of formation of lead 
sulfate as the positive electrode. 
The inventors found that the aforementioned polysaccharide, chelating agent 
and their derivatives are effective in changing the activity of Pb.sup.2+ 
in dilute sulfuric acid as a strong acid used in the lead acid storage 
battery. 
Furthermore, the inventors discovered that hydrazinium sulfate acts as a 
lead ion solubility adjusting agent in the same way as in the 
aforementioned compounds and that coexistence with the aforementioned 
polysaccharide, chelating agent or their derivatives in particular will 
yield synergistic effects of accelerating the increase rate of utilization 
and further enhancing the effect of polysaccharide, chelating agent, etc. 
Hydrazinium sulfate is a substance which is generally used as an additive 
for removing oxides in alkaline solutions but its properties are not known 
well. Especially in the acid systems of dilute sulfuric acid, no 
information is available. Therefore, the mechanism of the additive effect 
of hydrazinium sulfate that the utilization of the positive electrode 
increases with the progress of charge and discharge cycles is not 
clarified yet. However, it is assumed that some change takes place in the 
dissolved state of lead ions, which works to form lead dioxide which 
facilitates charging and discharging or to form a structure thereof at the 
time of charging. 
The effect of hydrazinium sulfate on lead oxides in the dissolved state is 
clear from the following examples. If, for example, the powder of positive 
electrode active material is suspended in the usual dilute sulfuric acid, 
a dark brown turbidity may result. In the dilute sulfuric acid mixed with 
hydrazinium sulfate, however, the brown turbidity fast diminishes and 
changes are observed in the solubility and decomposability of fine 
particles of the active material. In the hydrazinium sulfate containing 
dilute sulfuric acid, much oxygen gas will evolve as compared with the 
unmixed dilute sulfuric acid; it is possible to convert a part of lead 
dioxide to lead sulfate or bivalent lead ions through decomposition. With 
the addition of hydrazinium sulfate alone, however, no change is observed 
basically in the potential of the positive electrode. This is different 
from the case where the polysaccharide, chelating agent, or derivative 
thereof is added. 
As to the solubility of lead dioxide, the positive electrode active 
material remains mostly solid in the dilute sulfuric acid system, and in 
this way, it is thought that lead dioxide and lead sulfate may act 
differently, compared to their action in an alkaline solution. 
Anyway, the effect of adding hydrazinium sulfate is distinguished in that, 
although slow, it can be produced after discharging and charging are 
repeated. 
If, however, the polysaccharide or chelating agent coexists with 
hydrazinium sulfate, that effect will be not only to accelerate the 
increase rate of utilization of the active material but also to further 
raise the utilization level eventually reached with the addition of the 
polysaccharide or chelating agent. This is attributable to the synergistic 
effect of regenerating the structure of active lead oxide and the activity 
adjusting effect. 
While the novel features of the invention are set forth particularly in the 
appended claims, the invention, both as to organization and content, will 
be better understood and appreciated, along with other objects and 
features thereof, from the following detailed description taken in 
conjunction with the drawings.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, the power generating element is 
added with a polysaccharide, chelating agent, their derivative or 
hydrazinium sulphate as a solubility adjusting agent for lead ions. 
The total amount of the lead ion solubility adjusting agent selected from 
the polysaccharide, chelating agent and their derivatives is preferably 
not larger than 100 ppm by weight, based on the weight of the electrolyte. 
The amount of the hydrazinium sulphate is preferably not less than 100 
mg/l, based on the volume of the electrolyte. 
As to the solubility adjusting agent for lead ions, the compounds that can 
be used are, in addition to the aforementioned compounds, those in which 
an open circuit potential of the positive electrode in a charged state in 
the dilute sulfuric acid containing the compound in a specific 
concentration range is higher than that in the dilute sulfuric acid 
without the compound. 
Also suitable are the compounds in which the solubility of lead ions in the 
dilute sulfuric acid containing the compound in a specific range of 
concentration is higher than that in the dilute sulfuric acid without the 
compound and an open circuit potential of the positive electrode in a 
charged state in the dilute sulfuric acid containing the compound in the 
specific concentration range is higher than that in the dilute sulfuric 
acid without the compound. 
In the way of comparing the open circuit potential of the positive 
electrode with the potential in the dilute sulfuric acid with no additive 
in the charged state, or in the way of comparing the potential of 
electrolytic oxide of lead or lead alloy with the potential in the dilute 
sulfuric acid with no additive, the type and addition amount of the 
solubility adjusting agent for lead ions can be determined. 
In a preferred method for producing the lead acid storage battery of the 
present invention, at least the positive electrode is wetted with a dilute 
sulfuric acid solution with a high concentration of at least one lead ion 
solubility adjusting agent selected from the group consisting of a 
polysaccharide, a chelating agent, their derivatives, and hydrazinium 
sulfate, and after charging and discharging are repeated, a storage 
battery is configured using a dilute sulfuric acid solution with a low 
concentration of the above-mentioned lead ion solubility adjusting agent. 
The examples of polysaccharides and its derivatives are given in the 
following. Mannit, or mannitol (C.sub.6 H.sub.14 O.sub.6), is a kind of 
hexitol and is classified into L-type and D-type. Mannose (C.sub.6 
H.sub.12 O.sub.6) is a kind of aldohexose polysaccharide and can be 
reduced to mannitol. Mannonic acid (C.sub.6 H.sub.12 O.sub.7) is an 
oxidized derivative of mannose. Manool (C.sub.20 H.sub.34 O) and 
manninotriose (C.sub.18 H.sub.32 O.sub.16) are a kind of trisaccharide. 
Mandelic acid (C.sub.8 H.sub.8 O.sub.3) is one of .alpha.-hydroxy acids. 
Not only those mannan types but also disaccharides such as maltose and 
trisaccharides show a similar behavior although different in degree. Those 
have macromolecular structures and, in addition, possess functional groups 
with a high polarity like CH.sub.2 OH group and COOH group. And since 
hydrogen at the end is substituted by an alkali ion, they are generally 
stabilized in many cases. 
Though generally not called chelating agent, those polysaccharides and 
their derivatives, if added to dilute sulfuric acid in a proper amount, 
not larger than 1,000 ppm, greatly change the solubility of lead ions as 
can be measured by ICP spectrometry. This is because the molecules of the 
dissolved polysaccharides or their derivatives coordinate to Pb.sup.2+ and 
raise the apparent lead solubility in dilute sulfuric acid more than in 
dilute sulfuric acid with no additive; polysaccharides and their 
derivatives exhibit a function as a kind of lead ion solubility adjusting 
agent in dilute sulfuric acid. 
According to the traditional understanding, the potential of the active 
material lead dioxide decreases with the increase in the amount of 
dissolved Pb.sup.2+. In the dilute sulfuric acid containing the 
above-mentioned lead solubility adjusting agent, however, the potential of 
the positive electrode rises, showing a phenomenon reverse to the 
aforementioned phenomenon in a relationship between the potential and the 
solubility. This indicates that the coordination of the additive molecules 
probably decreases the real activity of lead ions inside the porous active 
material in a region where the apparent lead ion solubility rises. It is 
surmised that in the pores of the positive electrode where the diffusion 
of sulfuric acid is hindered, the activity of lead ions in the electrolyte 
containing a compound exhibiting the lead ion solubility adjusting 
function of the present invention practically decreases as compared with 
the electrolyte with no additive, resulting in a rise in potential and an 
improvement in utilization. 
The inventors discovered that a behavior similar to that is observed with 
compounds called chelating agent. Among them, it was found that the 
compounds which show high chelate stabilization for lead ions, that is, an 
alkali-stabilized compound hydrate of ethylenediaminetetraacetic acid 
(hereinafter referred to as "EDTA") C.sub.10 H.sub.13 N.sub.2 O.sub.8 
K.sub.3.2H.sub.2 O, ethylenedioxy bis(ethylamine)-N, N, N', N' tetraacetic 
acid (hereinafter referred to as "GEDTA") [CH.sub.2 OCH.sub.2 CH.sub.2 
N(CH.sub.2 COOH).sub.2 ].sub.2, diethylenetriamine pentaacetic acid 
(hereinafter referred to as "DTPA") [HOOCCH.sub.2).sub.2 NCH.sub.2 
CH.sub.2 ].sub.2 NCH.sub.2 COOH, trans-1, 2-cyclohexanediamine-N,N,N',N' 
tetraacetic acid hydrate (hereinafter referred to as "CyDTA") C.sub.6 
H.sub.10 N.sub.2 (CH.sub.2 COOH).sub.4.H.sub.2 O, triethylene tetramine-N, 
N, N', N, N'", N'" hexaacetic acid (hereinafter referred to as "TTHA") 
[CH.sub.2 N(CH.sub.2 COOH)CH.sub.2 CH.sub.2 N(CH.sub.2 COOH).sub.2 
].sub.2, nitrilotriacetic acid (hereinafter referred to as "NTA") 
(HOCOCH.sub.2).sub.3 N are effective in improving the solubility of lead 
ions and the potential behavior and utilization in a very small amount in 
the same way as in the aforementioned polysaccharides. 
It is generally known that acetic acid corrodes lead. If acetic acid raises 
the solubility of lead, then the addition of acetic acid must lower the 
potential of the positive electrode and increase the potential of the 
negative electrode. The chelating agent of the present invention shows a 
behavior opposite to acetic acid in the direction of change in potential 
and, therefore, is basically different from usual acetic acid in property. 
That is, it is conjectured that in the lead ions to be measured, there 
exist lead ions which actually work as an activity improver and lead ions 
which can not function as a chemically coordinated activity improver, and 
in usual measurements of dissolved lead by ICP spectrometry, the apparent 
solubility of the combination of the two is determined. Those additives, 
which shift the potential of the negative electrode in the lightly anodic 
direction, do not have much influence nor induce any particular adverse 
effect. 
As shown, polysaccharides, chelating agents, and their derivatives dissolve 
in the electrolyte and change the solubility of lead ions, creating a new 
effect. Therefore, those compounds, if applied on the electrode plate or 
separator, eventually dissolve in the electrolyte and show a similar 
effect. To have them work effectively inside the pores of the porous 
active material, however, they should be added in the form of powder or 
aqueous solution at the time of kneading the active material, or the 
unformed plate or the formed plate should be wetted with the electrolyte 
or aqueous solution containing those compounds; those methods are 
effective especially when the addition amount is very small. Those 
compounds can be combined freely if necessary. Also noted is that the 
conventional additives used in the electrode plate or electrolyte for 
other purposes such as, for example, lignin, lignosulfonic acid, sodium 
sulfate, potassium sulfate, potassium salt and sodium salt of tetraboric 
acid and a variety of surfactants have nothing to do with the mechanism of 
the present invention; and the present invention does not affect nor is 
affected by those conventional effects. 
Currently available hydrazinium sulfates are hydrazinium sulfate (1+) 
represented by the chemical formula (N.sub.2 H.sub.5).sub.2 SO.sub.4 and 
hydrazinium sulfate (2+) represented by the chemical formula N.sub.2 
H.sub.6 SO.sub.4. Hydrazinium sulfate (1+) is one with (H.sub.2 
N--NH.sub.3).sup.+ combined with SO.sub.4.sup.2- and N.sub.2 H.sub.5.sup.+ 
by hydrogen bonds. Hydrazinium sulfate (2+) is said to be composed of 
(H.sub.3 N--NH.sub.3).sup.2+ and SO.sub.4.sup.2-. Hydrazinium sulfate (1+) 
and hydrazinium sulfate (2+) are water soluble crystals with a solubility 
of 202 g/100 g and 3.4 g/100 g, respectively. Also, they can take the form 
of N.sub.2 H.sub.4.2H.sub.2 SO.sub.4. Those can be obtained by reacting 
hydrazine with sulfuric acid, and therefore even if this substance is 
added to sulfuric acid in the form of hydrazine, the effects obtained are 
similar to those produced with hydrazinium sulfate, and come within the 
scope of the present invention. But in making a preparation, it is 
preferable to handle it in the form of hyrazinium sulfate because it is 
stable when dissolved. At any rate, since hydrazinium sulfate is soluble, 
it will eventually dissolve in the electrolyte and exhibit the effect of 
improving the utilization in whichever stage or in whatever form it is 
added before the power generating element is put in operation--kneading 
into the active material, impregnating the unformed or formed plate in the 
form of solution, adding to the electrolyte for formation, adding to the 
finished electrolyte, impregnating the separator with the solution and 
drying, etc., for example. 
As to the preferred manufacturing process with the addition of hydrazinium 
sulfate to the power generating element of the lead acid storage battery, 
the simplest is to add hydrazinium sulfate to dilute sulfuric acid to be 
used in the electrolyte and to prepare an electrolyte for formation or a 
finished electrolyte. The form in which these kinds of hydrazinium sulfate 
are added may be either crystal state or solution state. 
As regards the amount of addition, several mg per liter of the electrolyte 
used as the power generating element can have some effect, but the 
addition at not lower than 100 mg/l is preferable to achieve substantial 
effects. 
Hydrazinium sulfate (1+) and hydrazinium sulfate (2+) produce similar 
results and can be used alone or in combination. Because hydrazinium 
sulfate (2+) is low in solubility (3.4 g/100 g), it can be prepared into a 
saturated solution of a fixed concentration by adding it excessively. 
When hydrazinium sulfate is used together with a polysaccharide, chelating 
agent or their derivative, these additives can be added in the step of 
making the power generating element. They can also be added in a crystal 
or aqueous solution. In practice, the simplest way is to electroform in a 
dilute sulfuric acid electrolyte containing those additives or complete a 
lead acid storage battery using a dilute sulfuric acid electrolyte 
containing those additives. 
The present invention will now be described in more detail with reference 
to the following specific, non-limiting examples: 
FIG. 1 shows the configuration of a lead acid storage battery applying the 
present invention. Numeral 1 indicates a battery container, 2 a cover, 3 a 
safety valve or a release valve, 4 a positive electrode, 5 a negative 
electrode, 6 a positive electrode terminal, 7 a negative electrode 
terminal, 8 a separator, and 9 an electrolyte. 
If the electrolyte is wetted on a mat-like separator, the effect of the 
prevent invention remains unchanged. 
The positive and negative electrodes used were paste electrode plates for 
commercially available storage batteries. The size of the electrode plate 
was approximately 46 mm.times.55 mm. Storage batteries with a 5-hour rate 
capacity of 3.0 Ah were fabricated using two positive electrode plates 
having a theoretical filling capacity of about 3.0 Ah in terms of lead 
dioxide and three negative plates having a theoretical filling capacity of 
2.2 Ah. Using 36.5 wt % dilute sulfuric acid in the completely discharged 
state as a reference solution, the electrolyte was prepared by adding to 
it at least one compound selected from the group consisting of 
polysaccharides, chelating agents and their derivatives. Those storage 
batteries were examined for the utilizations at different discharge rates. 
Embodiment 1 
The above-mentioned reference dilute sulfuric acid solution was mixed with, 
as a compound selected from among polysaccharides and their derivatives, 
mannitol [A1], mannose [A2], mannonic acid [A3], manool [A4], 
manninotriose [A5], mandelic acid [A6] and, as chelating agents and their 
derivatives, EDTA [B1], DTA [B2], DTPA [B3], CyDTA [B4], TTHA [B5], NTA 
[B6]. Storage batteries were configured using electrolytes mixed with 50 
ppm of those compounds. With those storage batteries, the discharge 
rate/utilization relationship was examined. Those storage batteries were 
divided into [A series] and [B series]. Data codes are parenthesized in 
[], and no addition is indicated by [RO]. 
Embodiment 2 
Storage batteries were composed using the aforementioned reference dilute 
sulfuric acid solution mixed with 25 ppm of mannitol and 25 ppm of mannose 
[C1], 25 ppm of EDTA and 25 ppm of NTA [C2], and 25 ppm of mannitol and 25 
ppm of EDTA [C3] as the electrolyte, respectively. With those storage 
batteries, the discharge rate/utilization relation was examined. Those 
storage batteries are called [C series]. 
Embodiment 3 
Storage batteries were produced using the aforementioned reference dilute 
sulfuric acid solution mixed in a range of 1-1000 ppm of mannitol as the 
electrolyte. The utilization of those storage batteries at a discharge 
rate of 1 C was measured. Those storage batteries are called [D series]. 
Embodiment 4 
Storage batteries were produced using the aforementioned reference dilute 
sulfuric acid solution mixed in a range of 1-1000 ppm of EDTA as the 
electrolyte. The utilization of those storage batteries at the discharge 
rate of 1 C was measured. Those storage batteries are called [E series]. 
Embodiment 5 
Storage batteries [F] were produced using an electrode plate obtained by 
adding mannitol 1,000 ppm by weight of the active material to the kneading 
positive electrode active material at the time of its kneading, and the 
unmixed reference dilute sulfuric acid solution as the electrolyte. The 
discharge rate/utilization of those storage batteries was determined after 
10 cycles of charging and discharging. 
Embodiment 6 
Storage batteries were produced using, as an electrode plate, the 
conventional electroformed plate dipped in the reference solution 
containing mannitol in a saturated state [G1] and an electrode plate [G2] 
charged in the above-mentioned saturated solution and the unmixed 
reference dilute sulfuric acid solution as the electrolyte. 
The characteristics of the storage batteries of the examples are 
hereinafter described. 
Here, the theoretical filling amount of the positive electrode active 
material was set to 6 Ah/cell, but a capacity at a 5-hour rate discharge 
was 3 Ah, so 3 A discharge was taken as 1 C. And the utilization was 
expressed as 100% when the discharge capacity was 6 Ah. 
FIG. 2 shows the discharge rate/utilization relations of [A series] in 
Embodiment 1, illustrating the effect of the addition of polysaccharides 
and their derivatives. The case of no addition [RO] shows a typical 
utilization characteristic made up of a flat section for low discharge 
rate and a slant section for high discharge rate. In the batteries of the 
present invention, little improvement was observed in utilization on the 
flat section but a remarkable effect was seen on the slant section for 
high discharge rate. Curves representing the characteristics are slightly 
different in shape depending on the compound added. 
FIG. 3 is also a diagram showing the discharge rate/utilization 
relationship of [B series] in Embodiment 1, which illustrates the effect 
of the addition of chelating agents and their derivatives. In this case, 
too, much improvement in utilization was observed as in the case of [A 
series]. Especially in the slant section, there was remarkable improvement 
in utilization in a region of relatively low discharge rate. It is thought 
that the shape and degree of those effects observed are probably closely 
related to the solubility of the respective compounds, the stability of 
coordination compound and others. 
FIG. 4 is a diagram showing the discharge rate/utilization relationship 
where two or more additives according to Embodiment 2 are used. Shown are 
the case where two kinds are selected from among the polysaccharides and 
their derivatives [C1], the case where two kinds are picked up from among 
the chelating agents and their derivatives [C2], and the case where one 
each is chosen from the former and the latter [C3]. In any case, the 
utilization on the slant section is improved as compared with the case of 
no addition [RO]. It is also shown that the mixing of polysaccharide 
compounds and chelating agent compounds can develop the respective 
characteristics comprehensively. 
FIG. 5 shows the effect and the amount of additives of the present 
invention citing the case of mannitol. Shown is the utilization at 1 C 
discharge in relation to the concentration of the additive. In the figure, 
the shown level represents the utilization for [RO] (the case of no 
addition), irrespective of the amount of the additive. With mannitol, a 
remarkable effect was observed in a region where the concentration of the 
additive was not higher than 100 ppm. When the concentration of additive 
exceeded 100 ppm, the utilization tended to drop instead. Such a 
borderline concentration between the effective region and the ineffective 
region (effective borderline region) is about 100 ppm with many additives 
of this kind, though slightly different by additives. 
Similarly, FIG. 6 shows a relationship between the addition amount of EDTA 
and the utilization at 1 C discharge. In this case, the same pattern was 
observed as in the mannitol that the effectiveness was observed in the low 
concentration region. 
As to the reason why such a phenomenon appears, FIG. 7 offers an important 
clue. This figure shows the relationship between the concentration of 
mannitol, the open circuit potential of the positive electrode in the 
electrolyte containing mannitol, and the saturated concentration of 
Pb.sup.2+ ions determined by adding excess lead sulfate to each 
electrolyte. As is evident from the figure, there is a good agreement 
between the change in utilization shown in FIG. 5 and the change in open 
circuit potential and the change in lead ion concentration in FIG. 7. But 
the behavior in potential and lead ion concentration is opposite to the 
generally known relationship as already mentioned. That is, the lead ion 
concentration measured here is an apparent concentration, and it is 
surmised that the actual activity dropped substantially because of 
coordination of the additive. Also noted is that those equilibrium 
relations do not appear to apply the case where the addition amount is 
large. 
Anyway, the above-mentioned effective region appears in the area where the 
addition amount is relatively very small. Moreover, the effective addition 
amount area can be predicted by measuring the open circuit potential as 
shown. It is possible to make a search for many other compounds which are 
not cited as examples here. 
Rather than a means of search, it is a means to indicate that a compound 
which increases the positive electrode potential as compared with the case 
of no addition lowers the activity of lead ions at the same time. 
[D'] in FIG. 7 is an open circuit potential measured in the absence of any 
active material by subjecting a lead plate to electrolytic oxidation. 
Shown is the potential of a relatively thin oxide layer unlike the porous 
lead dioxide represented by [D], which is lower than that of an electrode 
plate provided with many pores. Nevertheless, the potential changed in 
correspondence with relation to the concentration of the additive in the 
same way as in the case of an electrode plate, showing an effective 
concentration region and an ineffective region. In the ineffective region, 
too, a phenomenon was observed that the potential of oxidized lead on the 
surface was extremely low or fast dropped. In the effective concentration 
region, on the other hand, a relatively high and stable potential was 
observed. This shows that even without an electrode plate, electrolytic 
oxidation of a lead or lead alloy plate and subsequent examination of its 
stability enable a search on effective additive material and effective 
amount of addition. It is noted that [R'O] in FIG. 7 represents an open 
circuit potential measured in the absence of active material by subjecting 
a lead plate to electrolytic oxidation in the case where no lead ion 
solubility adjusting agent was added. 
Meanwhile, FIG. 8 shows cases where an effect of addition can be produced 
by adding manniotol at the time of kneading the active material as in 
Embodiment 5. It indicates that even if an electrolyte with no additive is 
used, the utilization can be eventually improved as the additive 
dissolves. [G1] in FIG. 9 shows that even if the electrode plate is wetted 
with the additives of the present invention at the level of electroformed 
plate in Embodiment 6, an effect can be obtained. Further, [G2] presents 
very important information that even if a high concentration region is 
passed through where no effect is produced and rather degradation is 
brought about instead, an effective region can be eventually brought back 
by applying the electrolyte in the region of low concentration or no 
addition. 
Hereinafter, the lead acid storage batteries to be used in Embodiments 7 to 
13 are described. For the positive and negative electrodes, paste 
electrode plates were used. The size of the electrode plate was about 
46.times.55 mm. Six cells were configured, each including two positive 
electrode plates having a theoretical filling capacity of about 3.0 Ah in 
terms of lead dioxide and three negative electrode plates having a 
theoretical filling capacity of 2.2 Ah, and the six cells were connected 
in series and a storage battery having a nominal voltage of 12 V and a 
5-hour rate capacity of 3.0 Ah was produced. The reference electrolyte 
used was 36.5 wt % dilute sulfuric acid in the completely charged state. 
It was mixed in the compositions given below with hydrazinium sulfate, 
polysaccharides, chelating agents or their derivatives in the specified 
quantities on the basis of the embodiments shown below. It is noted here 
that the capacity of the battery is restricted by the positive electrode 
capacity. 
Those storage batteries were charged and discharged by combining a 
constant-current discharge at a constant current (15 A) equivalent to 5 
C(A) with a constant-voltage-constant-current charging at a set current of 
15 A and a set voltage of 13.5 V, using a positive electrode filling 
capacity of 1 C (A) as reference. Subsequently, the changes in utilization 
were examined. 
The effect of hydrazinium sulfate is observed in a wide range, but the 
examples where characteristic effects were observed are hereinafter 
described. 
Embodiment 7 
One g/l of hydrazinium sulfate (+1) was added to dilute sulfuric acid to 
prepare an electrolyte. This storage battery is called [H1]. 
Embodiment 8 
One g/l of hydrazinium sulfate (+2) was added to dilute sulfuric acid to 
prepare an electrolyte. This storage battery is called [H2] 
Embodiment 9 
0.5 g/l of hydrazinium sulfate (+1) and 0.5 g/l of hydrazinium sulfate (+2) 
were added to dilute sulfuric acid to prepare an electrolyte. This storage 
battery is called [H3]. 
Embodiment 10 
One g/l of hydrazinium sulfate (+1) and 20 mg/l of mannitol were added to 
dilute sulfuric acid to prepare an electrolyte. This storage battery is 
called [I1]. 
Embodiment 11 
One g/l of hydrazinium sulfate (+2) and 20 mg/l of mannitol were added to 
dilute sulfuric acid to prepare an electrolyte. This storage battery is 
called [I2]. 
Embodiment 12 
One g/l of hydrazinium sulfate (+1) and 50 mg/l of EDTA were added to 
dilute sulfuric acid to prepare an electrolyte. This storage battery is 
called [J1]. 
Embodiment 13 
One g/l of hydrazinium sulfate (+2) and 50 mg/l of EDTA were added to 
dilute sulfuric acid to prepare an electrolyte. This storage battery is 
called [J2]. 
COMATIVE EXAMPLES 
As comparative examples, a storage battery [RO] using an electrolyte of 
36.5 wt % dilute sulfuric acid containing no additives, a storage battery 
[D1] using an electrolyte of 36.5 wt % dilute sulfuric acid containing no 
hydrazinium sulfate but 20 mg/l of mannitol, and a storage battery [E1] 
using an electrolyte of 36.5 wt % dilute sulfuric acid containing no 
hydrazinium sulfate but 20 mg/l of EDTA were fabricated. 
These storage batteries were discharged at a current of 15 A corresponding 
to 5 C based on a 5-hour rate capacity of the positive electrode. FIG. 10, 
FIG. 11 and FIG. 12 are diagrams showing the resultant relationship 
between the charge-discharge cycles and the utilization of the active 
material and illustrating the effects of the present invention. 
First, it was shown in FIG. 10, that, compared with the storage battery 
[RO] containing no hydrazinium sulfate, the utilizations in the 
hydrazinium sulfate (+1) containing storage battery [H1], the hydrazinium 
sulfate (+2) containing storage battery [H2], and the hydrazinium sulfate 
(+1) and hydrazinium sulfate (+2) containing storage battery [H3] all 
increased as the cycle advanced and then reached a constant level. 
That the utilization rises with the repeated discharging and charging 
cycles indicates that hydrazinium sulfate works to create a condition for 
the positive electrode readily to discharge in the charging step after 
discharging. 
There are no significant differences in the highest utilization eventually 
achieved in any form of hydrazinium sulfate, that is, between hydrazinium 
sulfate (+1) and hydrazinium sulfate (+2), but with regard to the time 
needed before the desired effect is achieved, the stronger reductive 
hydrazinium sulfate (+2) containing [H2] and [H3] appears to be quick in 
producing the effect. 
FIG. 11 is a diagram illustrating the effects of adding hydrazinium sulfate 
together with a polysaccharide to the power generating element. When 
mannitol, a representative of the polysacchrides, was used and mixed with 
hydrazinium sulfate (+1) [I1] and hydrazinium sulfate (+2)[I2], both 
showed a high final utilization as compared with the comparative example 
[D1] in which mannitol alone was added, and reached the maximum level of 
utilization quickly. Also, in the utilization and utilization increase 
rate, hydrazinium sulfate (+2) was slightly superior. 
FIG. 12 shows the effects of adding hydrazinium sulfate along with a 
chelating agent to the power generating element. As a representative 
chelating agent, EDTA was used, and when it was mixed with hydrazinium 
sulfate (+1) [J1] and hydrazinium sulfate (+2) [J2], both showed a high 
final utilization as compared with the comparative example [E1] in which 
EDTA alone was added, and reached the maximum utilization level quickly as 
in the case of mannitol. Also, in the utilization and utilization increase 
rate, hydrazinium sulfate (+2) was somewhat higher. 
As illustrated, it is suggested that hydrazinium sulfate will have a 
favorable effect on the form of lead dioxide which is formed by charging, 
if present in dilute sulfuric acid concurrently with a polysaccharide or 
chelating agent which is capable of adjusting the solubility and activity 
of lead ions by coordinating to lead ions. 
This mechanism is still unclarified. Especially, that the addition of 
hydrazinium sulfate causes decomposition of lead dioxide in part seems 
incompatible with creating a form of the active material with a high 
utilization. It is thought that those points are deeply related to the 
tendency to form a porous active material with a high distribution of fine 
pores. And in the charging process, decomposition, dissolution and 
deposition repeat delicately, recreating a new state of the active 
material as has not been formed before. Especially, when a polysaccharide 
and a chelating agent are present at the same time, that tendency is 
strong. 
Mannitol and EDTA as mentioned here are a fraction of the embodiments, and 
these effects are similarly observed with polysacchrides and chelating 
agents which coordinate to lead ions to adjust the activity and the 
dissolved concentration of lead ions and show a tendency to raise the 
solubility and the decomposability of lead dioxide together with 
hydrazinium sulfate. By the way, the presence in the storage battery of 
nitrogen of hydrazinium sulfate can be detected by ICP spectrometry or 
combining ICP spectrometry with mass spectrum. 
As has been described, the present invention is directed to improvements in 
the potential and utilization of lead acid storage batteries, of which 
potential has been considered to be determined by the concentration of 
dilute sulfuric acid and the structure of the active material, by adding, 
to dilute sulfuric acid, compounds which can adjust the solubility of lead 
ions. 
As shown above, the present invention aims at improving the utilization at 
a high rate discharge especially of lead acid storage batteries through 
the effect of conventional or new additives which have been considered to 
induce a change in the reaction mechanism of lead acid storage battery, 
and the application scope covers all types of lead acid batteries. 
Although the present invention has been described in terms of the presently 
preferred embodiments, it is to be understood that such disclosure is not 
to be interpreted as limiting. Various alterations and modifications will 
no doubt become apparent to those skilled in the art to which the present 
invention pertains, after having read the above disclosure. Accordingly, 
it is intended that the appended claims be interpreted as covering all 
alterations and modifications as fall within the true spirit and scope of 
the invention.