JP2010020932A - Negative electrode composition for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage battery, i.e. a secondary battery, which can enhance a use rate of an active material and can obtain a high energy density, by using a raw material with substantially the same level of cost as that in a conventional storage battery, in particular, for a negative electrode plate of the secondary battery. <P>SOLUTION: The storage battery capable of enhancing the use rate of the active material and capable of obtaining the high energy density is provided by using, as a negative electrode, a kneaded mixture containing an active material raw material comprising mainly a metal oxide, and carbon containing about 50% of particle having about 20 nano-meter or less of particle diameter, at an amount to bring 1.7 ml or more of total oil absorption amount per one mole of the active material raw material. The kneaded mixture is prepared by kneading a primary kneaded mixture generated by kneading the carbon with water and an aqueous polyvinyl alcohol solution, and the active material raw material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode composition for a secondary battery that has a high energy density and can be produced at low cost.

  Conventionally, various secondary batteries are known. For example, there are lead storage batteries as inexpensive ones and lithium ion batteries as high energy density ones. Needless to say, a secondary battery that is both inexpensive and has a high energy density is ideal. In particular, there is a great demand for an inexpensive and high energy density storage battery in applications such as a hybrid vehicle or an electric vehicle that performs start-up drive by the storage battery. The price of a storage battery is most dependent on its material cost. For example, in a hybrid vehicle, an expensive nickel metal hydride storage battery is used, but nickel used for the positive electrode of the nickel metal hydride storage battery and noble metal used for the negative electrode are very expensive materials. In addition, lithium-ion batteries are also forced to use expensive materials.

  On the other hand, a conventional lead-acid battery generally has a manufacturing method in which dilute sulfuric acid is added to an active material raw material called lead powder obtained by oxidizing lead to form a paste, and this paste is filled in a grid-shaped current collector. . Then, by forming this, the positive electrode contains an active material called lead dioxide and the negative electrode contains spongy lead. These active materials change to lead sulfate (discharge active material) when the battery is discharged. Since the volume increases with the change to the discharge active material, the pores of the porous structure in the active material become small, and the diffusion of the electrolytic solution into the active material becomes difficult.

  Moreover, electrical resistance increases by changing to lead sulfate which is an electrical insulator. Generally, when lead sulfate exceeds 70%, the electrical resistance increases rapidly. Therefore, it has been theoretically impossible to discharge the active material by 70% or more, that is, to make the utilization factor of the active material 70% or more. Actually, since it is also influenced by the magnitude of the discharge current, the utilization rate of low rate discharge is generally about 40%, and the utilization rate of high rate discharge is about 20%.

  In order to increase the utilization rate of the active material, it is a necessary condition to increase the bulk density of the composition, that is, the porosity, but it is conventionally known that the charge / discharge cycle life is drastically reduced as a contradiction, Increasing the porosity and improving the utilization rate of the active material is a difficult technique and remains unsolved.

  Lead-acid batteries are preferred in that they are inexpensive, but because the active material utilization rate is low, the amount of lead used has to be increased, resulting in a further increase in the weight of lead that is even dense. The energy density is reduced. The current energy density of lead-acid batteries is insufficient for hybrid vehicles and electric vehicles and cannot be used.

In Patent Document 1, for the purpose of extending the life of a lead storage battery, lead powder, 13% by weight diluted sulfuric acid with respect to the lead powder, and 12% by weight water with respect to the lead powder, lead as a negative electrode additive. 0.1-0.3 wt% DBP oil absorption of 100-300 ml / 100 g of amorphous carbon and / or lead powder of 0.4-0.6 wt% sodium lignin sulfonate A negative electrode paste prepared by adding and kneading is disclosed.
JP 2002-63905 A

  There is a demand for a secondary battery that is both inexpensive and has a high energy density, but these have been considered to have a contradictory relationship and have not yet been realized. Patent Document 1 aims at extending the life of lead-acid batteries. Therefore, in the technique of Patent Document 1, there is no improvement in the utilization factor of the active material, and the utilization factor of the active material exceeding 70% at which a high energy density can be obtained is not realized.

  As described above, the main cause of the low energy density of the lead storage battery is that the utilization factor cannot be increased to 70% or more because the electrical resistance of the active material increases during discharge. In addition, the utilization factor is further reduced in the usage mode in which discharging is performed with a large current. Moreover, it is said that the utilization factor and lifetime of an active material have a contradictory relationship. That is, when the utilization rate is increased, there is a fatal problem that the charge / discharge cycle life is reduced.

  On the other hand, the high cost of a lithium ion battery is due to its essential materials, so it is difficult to reduce the cost.

  Accordingly, an object of the present invention is to provide a storage battery, that is, a secondary battery that can obtain a high energy density by using a raw material having a cost comparable to that of a lead storage battery. More specifically, it aims at providing the negative electrode composition for secondary batteries which improved the utilization factor of the active material with the low-cost raw material about the negative electrode plate of a secondary battery.

In order to achieve the above object, the present invention provides the following configurations.
The negative electrode composition for a secondary battery according to claim 1 comprises an active material raw material mainly composed of a metal oxide and carbon containing about 50% of particles having a particle diameter of about 20 nanometers or less in 1 mol of the active material raw material. On the other hand, it is a kneaded product containing an amount that gives a total oil absorption of 1.7 ml or more.

A negative electrode composition for a secondary battery according to claim 2 comprises an active material raw material mainly composed of a metal oxide and carbon containing about 50% of particles having a particle diameter of about 20 nanometers or less with respect to the active material raw material. It is a kneaded product containing 3.5 × 10 ⁻¹ mass percent or more.

A negative electrode composition for a secondary battery according to claim 3 is obtained by drying a kneaded material containing an active material raw material mainly composed of a metal oxide and carbon containing approximately 50% of particles having a particle diameter of approximately 20 nanometers or less. The carbon is contained in such an amount that the bulk density in the unformed state is 2.2 × 10 ⁻¹ milliliter / gram or more.

  A negative electrode composition for a secondary battery according to a fourth aspect is characterized in that in any one of the first to third aspects, the carbon is acetylene black.

  The negative electrode composition for a secondary battery according to claim 5 is any one of claims 1 to 4, wherein the kneaded product is a primary kneaded product produced by kneading the carbon with water and a polyvinyl alcohol aqueous solution, It is a kneaded material produced by kneading the active material raw material.

  The negative electrode composition for a secondary battery according to a sixth aspect is the negative electrode composition for a secondary battery according to the fifth aspect, wherein the polyvinyl alcohol aqueous solution has a dissolution amount in water of approximately 1 mass percent or less under conditions of a dissolution temperature of 40 ° C and a dissolution time of 30 minutes. It is characterized in that a certain polyvinyl alcohol is dispersed in water and heated to about 60 ° C. or higher to be dissolved almost completely.

A negative electrode composition for a secondary battery according to a seventh aspect is the negative electrode composition for a secondary battery according to the fifth aspect, wherein the polyvinyl alcohol aqueous solution is obtained by dispersing polyvinyl alcohol having a saponification degree of 98 mol% or more and a polymerization degree of 1.7 × 10 ³ or more in water. It is characterized by being substantially completely dissolved by heating to about 60 ° C. or higher.

  In the present invention, in order to improve the utilization rate by the negative electrode composition for secondary batteries, a configuration in which the electrolytic solution (dilute sulfuric acid) and the active material can be sufficiently brought into contact with each other and an increase in electrical resistance is not realized. Specifically, a conductive network is formed in the negative electrode plate, and the network has innumerable holes for supporting the electrolytic solution, thereby increasing the bulk density of the negative electrode plate. In other words, by increasing the porosity, the amount of the electrolyte present in the negative electrode plate is increased, and the penetration of the electrolyte from the outside of the negative electrode plate is facilitated. It constituted so that it could fully supply. Specifically, it is preferable that carbon containing approximately 50% of particles having a particle diameter of approximately 20 nanometers or less is contained in the active material raw material. The carbon content is such that the total oil absorption is 1.7 ml or more per mole of the active material raw material.

In the negative electrode plate, a conductive network can be formed by containing carbon which is a particle chain structure material. The particle chain structure material refers to a material in which a plurality of particulate materials are fused to each other and extend in a chain shape as a whole. Such carbon is preferably carbon in which individual particles in the chain-like particles contain approximately 50% of particles having a particle diameter of approximately 20 nanometers or less. The carbon content is 3.5 × 10 ⁻¹ mass percent or more with respect to the active material raw material.

Lead powder, which is an active material raw material, is uniformly dispersed in a conductive network formed of carbon having a fine particle diameter as described above, and is arranged together with the conductive network. Carbon, which is a particle chain structure substance, is entangled vertically and horizontally to form a network, and at the same time, the smaller the particle diameter, the more the conductive network develops, and an infinite number of pores are formed to form a porous structure. These holes can hold a sufficient amount of electrolyte. In addition, good conductivity can be maintained with carbon. In order to maintain the discharge, the dilute sulfuric acid retained in these holes is continuously supplied to the dispersed active material raw material. As a result, the conductive network can prevent a rapid increase in electrical resistance immediately before the end of discharge.
Further, lead powder as an active material raw material is uniformly dispersed in a conductive network formed of carbon having such a fine particle diameter, and when used as a negative electrode of a lead storage battery, the capacity of the battery increases.

Further, a kneaded product containing carbon containing approximately 50% of particles having a particle diameter of approximately 20 nanometers or less is dried, and an amount of carbon that has a bulk density of 2.2 × 10 ⁻¹ milliliter / gram or more in an unformed state. By containing it, a sufficient amount of electrolyte can be retained.

  Furthermore, the primary kneaded material produced by kneading carbon with water and an aqueous polyvinyl alcohol solution and the kneaded material produced by kneading the active material raw material have a more uniformly dispersed carbon, The formation is promoted, and the active material utilization rate of the negative electrode using this kneaded product is greatly improved.

In addition, polyvinyl alcohol exhibits an effect as a dispersant for the kneaded material while ensuring the conductivity of carbon, and can also improve the adhesion of the negative electrode paste to the electrode plate.
Polyvinyl alcohol aqueous solution is a solution in which polyvinyl alcohol having a dissolution amount in water of 1 mass percent or less under conditions of a dissolution temperature of 40 ° C. and a dissolution time of 30 minutes is dispersed in water, and heated to about 60 ° C. or more to be almost completely dissolved. What was made to be suitable is suitable.

The polyvinyl alcohol aqueous solution is preferably one in which polyvinyl alcohol having a saponification degree of 98 mol% or more and a polymerization degree of 1.7 × 10 ³ or more is dispersed in water and heated to about 60 ° C. or more to be dissolved almost completely. It is.

  By being able to reduce lead powder, the cost of the storage battery can be further reduced, and the energy density can be greatly improved. As a result, the weight can be reduced as compared with the conventional storage battery with the same battery capacity. As a result, the battery becomes extremely suitable for a hybrid vehicle storage battery and an electric vehicle. Although significant improvements in active material utilization have been impossible over the past hundred years, the present invention has made it possible for the first time. It can be said that its industrial value is extremely high.

  Moreover, by using the negative electrode composition of the present invention, it was possible to produce a lead-acid battery with a significantly improved charge / discharge cycle life that had been impossible in the past.

First, an outline of an embodiment of the present invention will be described. Details will be described in the following embodiments.
The negative electrode composition for secondary batteries according to the present invention (abbreviated as “negative electrode composition” or “composition”) is substantially intended for lead-acid batteries. The negative electrode composition is a paste-like kneaded product in which an active material raw material is a main component and other necessary components are added. This kneaded product is filled, aged and dried (unformed state) in a negative electrode plate which is a grid-shaped current collector, and then this negative electrode plate is incorporated into a storage battery and a conversion process is performed to complete a lead storage battery.

  The kneaded material which is a negative electrode composition contains the active material raw material containing the metal and the oxide of the metal, and carbon. The active material raw material is lead powder. And carbon is made into the quantity from which a total oil absorption becomes 1.7 ml or more with respect to 1 mol of active material raw materials. The “total oil absorption amount” is the total oil absorption amount of carbon in the carbon content per mole of the active material raw material in the relationship between the relative content of carbon and the active material raw material contained in the composition (described later) This is a value different from the DBP oil absorption, which is an indicator of carbon characteristics). The kneading medium is water.

As a measure of the porosity of the negative electrode composition of the present invention, the bulk density is 2.2 × 10 ⁻¹ ml / g or more in an unformed state after being filled in a grid-like current collector and dried. .

  Furthermore, it is preferable to contain polyvinyl alcohol (PVA) in the above composition. Polyvinyl alcohol is added for the purpose of improving the dispersibility of carbon or the like, but also contributes to increasing the adhesion strength when the kneaded product is filled in a grid-like current collector.

  The negative electrode composition according to the present invention is produced by the following production process (specifically, a kneaded material production process). In the first kneading step, carbon is kneaded together with an aqueous polyvinyl alcohol solution and water to produce a first kneaded product. Next, in the second kneading step, an active material raw material and other additives are added to the first kneaded material and further kneaded to produce a second kneaded material. The obtained 2nd kneaded material is said negative electrode composition. The conventional negative electrode composition has not been kneaded in such two steps. In the present invention, a negative electrode composition having a suitable bulk density, oil absorption amount, and utilization rate can be obtained through two kneading steps.

  The utilization rate of the negative electrode active material according to the present invention is 70% or more for 0.06A discharge about 40 hour rate discharge (low rate discharge) and 6A discharge about 10 minute rate discharge (high rate) when a grid-like current collector is used. The discharge was 40% or more. At any discharge rate in the low rate discharge and the high rate discharge, the utilization rate was remarkably improved as compared with the conventional lead acid battery. As the current collector, a conventional lattice can be used, or the kneaded material can be applied to a sheet-like material such as a lead sheet. When filling the grid-like current collector, a certain degree of viscosity is required, so that the amount of water as the kneading medium is set to be small relative to the other components to obtain a paste-like kneaded product. On the other hand, when applying to a sheet | seat, the quantity of water is increased and viscosity is made low and it is set as a slurry-like kneaded material. Whether the kneaded product before application to the electrode plate is a paste or a slurry, the effects of the present invention can be obtained similarly.

  The electrode plate in which the grid current collector is filled with the paste can basically be used for all uses of the conventional lead-acid battery, and can be lighter in the same battery capacity. A lead-acid battery using a sheet electrode can form a cylindrical battery. In that case, by winding the electrode plate in a spiral, a battery having excellent high-rate discharge and strong vibration resistance is obtained. This is particularly suitable for hybrid vehicles and electric vehicles. Currently, nickel-metal hydride batteries and lithium ion batteries are being used or studied in hybrid vehicles, but both have the problem of high costs. The lead-acid battery according to the present invention is suitable for practical use because it is much cheaper than those.

  As described above, the lead-acid battery using the negative electrode composition according to the present invention is capable of discharging with a large current, has a long life, has a high active material utilization rate, and is low in cost. Compared to lithium ion batteries and nickel / hydrogen batteries, charge / discharge management is simpler. Its optimal use is the hybrid use of engine and storage battery in automotive applications. In this application, regenerative electric power during braking of an automobile is charged into a storage battery, and electric power is taken out from the storage battery at the time of starting, thereby reducing gasoline consumption. Since automobile companies are environmentally favorable due to energy saving and exhaust gas reduction, they are focusing on hybrid cars now and in the future, and it can be said that the industrial applicability of the present invention is extremely high.

  Moreover, a general storage battery is often used for float charging. This is a system that supplies power from a storage battery to a load in the event of a power failure, and is generally discharged at a rate of about 10 minutes. When such a storage battery is used with a conventional lead storage battery, a short-time discharge, that is, a large current discharge is generated, so that the active material utilization rate which is not originally high further decreases. Therefore, a lead storage battery having a large rated capacity must be prepared, which is large and heavy. The lead storage battery using the negative electrode composition of the present invention has an active material utilization rate as high as about twice or more that of a conventional lead storage battery, can be discharged by a large current, and can be lightweight.

The negative electrode composition for a secondary battery according to the present invention is substantially intended for a lead storage battery. The negative electrode composition is a paste-like kneaded product with lead powder as an active material raw material as the main component and other necessary components added, and this is filled in an electrode plate and aged and dried. Including.
The paste-like kneaded product is filled into a grid-shaped current collector, aged and dried (unformed state), and then the negative electrode plate is incorporated into a storage battery case, and a chemical conversion process is performed, whereby the active material raw material becomes an active material, Completed as a lead-acid battery. Therefore, the “active material raw material” in the claims and the specification of the present application refers to the raw material. The “active material raw material” refers to a raw material that is formed into an active material that is a target product.
Further, as described above, the paste is a negative electrode composition, but the paste as the negative electrode composition is filled in a grid current collector (lattice electrode plate) and dried, and further, the formed one is also collectively referred to as a negative electrode composition. It may be referred to as a product or a composition, or a negative electrode plate or an electrode plate. That is, the negative electrode plate and the electrode plate may mean the lattice itself or the one filled with the negative electrode composition.

  Hereinafter, each example of the present invention when applied to a negative electrode plate using a grid-like current collector will be described.

In Example 1, paste Nos. 1 to 11 were prepared from the negative electrode composition shown in Table 1, and various tests described later were performed using the negative electrode plate filled with the paste.

<Preparation of sample>
Table 1 is a list showing the component composition of the negative electrode composition subjected to the test.
In the composition in Table 1, acetylene black-1 and acetylene black-2, which are carbon, are selectively blended and are not used at the same time.
Acetylene black-1 or acetylene black-2 is blended with lead powder, PVA-124 aqueous solution (concentration 6%), lignin, BaSO ₄ (barium sulfate) and water in Table 1.
Therefore, there are two types of test results, one using acetylene black-1 and the other using acetylene black-2. These are the paste Nos. Of the present invention. 3-11.
Paste No. 1 is based on the prior art and is used as a comparative example.
Paste No. 2 does not use carbon (acetylene black-1 or acetylene black-2). Therefore, the PVA-124 aqueous solution (concentration 6%) is not used. Moreover, it is a comparative example which does not mix | blend sulfuric acid in a prior art.
Here, the concentration 6% of the PVA-124 aqueous solution (concentration 6%) means that 6 g of PVA-124 powder is dissolved in 94 g of water. A method for producing the PVA aqueous solution will be described in Example 4. PVA is an abbreviation for polyvinyl alcohol, and the number indicates a product number.

  The paste means a kneaded product in a paste state before kneading after kneading the composition composed of the components shown in Table 1. However, when measuring the bulk density of the negative electrode composition, the electrode plate is filled and aged and dried. When measuring the active material utilization, chemical conversion is further performed.

  In Table 1, the amount of lead powder is made constant and the amount of carbon is changed. As the amount of carbon changes, the amount of aqueous PVA-124 solution and the amount of water are changed.

Lead powder is a main component of the active material, and the oxidation degree of lead is about 75 to 80%.
As for carbon, acetylene black-1 with a DBP oil absorption of 220 ml / 100 g and acetylene black-2 with a DBP oil absorption of 160 ml / 100 g (both manufactured by Denki Kagaku Kogyo) were used. Polyvinyl alcohol (manufactured by Kuraray Co., Ltd.) was PVA-124 having a saponification degree of 98 mol% to 99 mol% and a polymerization degree of 2400.

FIG. 8 shows the cumulative particle size distribution of carbon particles of acetylene black-1 and acetylene black-2. AB-1 is a cumulative curve of acetylene black-1 and AB-2 is a cumulative curve of acetylene black-2.
In this curve, the accumulation of the frequency of the particle diameter is started from the particle having the smallest particle diameter, and the accumulation of the frequency of the particle diameter of the maximum particle diameter is completed, and the accumulation is 100%.
Acetylene black-1 has approximately 50% of particles having a particle diameter of approximately 20 nanometers or less.
Acetylene black-2 has approximately 50% of particles having a particle diameter of approximately 28 nanometers or less.
3 and 4 to be described later, acetylene black-1 in which many particles having a small particle size are distributed has a higher active material utilization rate.

  In Example 1, a paste comprising the composition of Table 1 was prepared, and (1) lead powder filling amount (g), (2) bulk density (ml / g), and (3) active material utilization rate (%). Measure and clarify these relationships.

<Method for producing negative electrode plate>
Paste Nos. 3 to 11 in Table 1 were mixed with carbon, a PVA-124 aqueous solution and water and kneaded for 30 minutes, then mixed with lead powder and further added with lignin and barium sulfate (BaSO ₄ ). Further, kneading was performed for 30 minutes.

  Paste No. 1 produced as a comparative example is a mixture of lead powder, lignin, barium sulfate, water and sulfuric acid mixed in the amounts shown in Table 1 and simply kneaded. Paste No. 2 is composed of lead powder, lignin, Barium sulfate and water are mixed in the amounts shown in Table 1 and simply kneaded.

  The paste thus produced was filled into a 2 mm thick grid-like current collector, then aged at 98% humidity and a temperature of 45 ° C. for 24 hours, and then dried at 60 ° C. for 24 hours to obtain a thickness of 2 A 2 mm negative electrode plate was formed.

  Next, a fine glass fiber separator was brought into contact with both sides of the single negative electrode plate, and further, one positive electrode plate was brought into contact with the outside thereof. With such a configuration, the theoretical capacity of the active material has a large excess of the positive electrode, and thus the utilization rate of the target negative electrode active material can be evaluated. These electrode plate groups were inserted into the battery case, and an ABS resin spacer was loaded in the gap between the battery case and the electrode plate group. Dilute sulfuric acid having a specific gravity of 1.223 was injected into the battery case, and 300% of the theoretical capacity of the positive electrode was passed to conduct chemical conversion. The specific gravity of the electrolytic solution after chemical conversion was set to 1.320.

  Then, the capacity | capacitance test was done about the electrode group inserted in said battery case. Two types of capacity tests, 0.06 A (ampere) and 6 A, were used. 0.06A is a low rate discharge with a rate of about 40 hours, and 6A is a high rate discharge with a rate of about 10 minutes. The respective discharge end voltages were 1.7 V (volt) and 1.2 V per cell. The temperature is 25 ° C.

<Test results>
(1) About lead powder filling amount Table 2 shows the measurement results of the lead powder filling amount (four samples of the same prepared paste). FIG. 1 is a graph of Table 2. Paste no. The lead powder filling amount of 1 is shown in the rightmost column of Table 2.
The lead powder filling amount refers to the mass (g) of the lead powder filled in the negative electrode plate in a state of being aged and dried after filling the paste prepared as described above into the lattice which is the negative electrode plate.
The paste filled in the grid which is the negative electrode plate naturally contains the components shown in Table 1. However, moisture having a relatively large mass ratio is not contained because it is dried, and most of the mass is lead powder.
The purpose of measuring the amount of lead powder filling is reduced by adding bulky carbon to the negative electrode composition, whereas the composition filled in the electrode plate is mostly lead powder in the prior art. This is to check the amount of lead powder filled.
That is, although the mass (g) of carbon itself is small, it is bulky, so the volume of the negative electrode composition increases and the amount of lead powder filled in the lattice decreases.

In FIG. 1, the plot of the mark ● with the carbon amount of 0 g is the comparative example data of Paste No. 1, which is the prior art, and the plot of the ◆ mark with the carbon amount of 0 g is the comparative example data of Paste No. 2.
Paste Nos. 3 to 11 of the present invention have a carbon amount of not 0 g but are plots of ◆ and black square marks.
The ♦ mark plot is acetylene black-1 (AB-1), and the black square mark plot is acetylene black-2 (AB-2).

Paste No. 1 according to the present invention. The lead powder filling amount of 3 to 11 is the paste No. of Comparative Example. The amount of lead powder filling is smaller than 1 and 2, and the amount of lead powder filling decreases as the amount of carbon increases.
(1) The largest amount of carbon (8.6 g) Paste No. 7 of the present invention is about 45% of the lead powder filling amount of the paste of the prior art.
(2) Paste No. 3 of the present invention with the least amount of carbon (0.7 g) is about 95% of the lead powder filling amount of the paste of the prior art.
(3) Next, the amount of carbon is the smallest (1.4 g). No. 4, about 87% of the lead powder filling amount of the prior art paste

  The reason why the lead powder filling amount is reduced in the paste of the present invention is that the volume of the paste is greatly increased even when the carbon is bulky and the amount of carbon is smaller than that of the lead powder.

(2) About bulk density Table 3 shows the measurement results of the bulk density. FIG. 2 is a graph of Table 3. The bulk density of the prior art is shown in the rightmost column of Table 3.
The bulk density is the reciprocal of the mass density, the unit is represented by “ml / g”, and is used when comparing the volume (ml) with the same mass (g).
The purpose of measuring the bulk density is that, in the prior art, most of the composition filled in the electrode plate is lead powder, whereas in the present invention, the porosity is increased by adding bulky carbon to the negative electrode composition. This is to see how it increases.
That is, the greater the porosity, the more sulfuric acid is stored in the vicinity of the active material (lead) and the better the discharge characteristics.

In FIG. 2, the plot of ● with a carbon amount of 0 g is the comparative example data of Paste No. 1, which is a conventional technology, and the plot of ◆ with the carbon amount of 0 g is the comparative example data of Paste No. 2.
Paste Nos. 3 to 11 of the present invention have a carbon amount of not 0 g but are plots of ◆ and black square marks.
The ♦ mark plot is acetylene black-1 (AB-1), and the black square mark plot is acetylene black-2 (AB-2).

The paste Nos. 3 to 11 of the present invention have a higher bulk density than the paste of the comparative example, and the bulk density increases as the amount of carbon increases.
(1) Paste No. 7 of the present invention having the largest amount of carbon (8.6 g) is about 160% of the bulk density of the paste of the prior art.
(2) Paste No. 3 of the present invention with the least amount of carbon (0.7 g) is about 110% of the bulk density of the prior art paste.
(3) Next, the amount of carbon is the smallest (1.4 g). The paste No. 4 of the present invention is about 130% of the bulk density of the paste of the prior art.
A method for measuring the bulk density will be described later.

(3) About active material utilization rate Table 4 and Table 5 show the measurement and calculation results of the active material utilization rate. FIG. 3 is a graph of Table 4, and FIG. 4 is a graph of Table 5. Prior art paste no. The active material utilization rate of 1 is shown in the rightmost column of Tables 4 and 5.
Table 4 shows the low rate discharge 0.06A, and Table 5 shows the high rate discharge 6A.
The active material utilization rate is an important index that shows how much capacity the storage battery can be secured with less active material. Especially in lead storage batteries, the active material material is lead, so it is important to reduce the weight of lead storage batteries. It is the most important issue.

3 and 4, the carbon amount is 0 g and the ● mark plot is the comparative example data of Paste No. 1, which is the prior art, and the carbon amount is 0 g and the ◆ mark plot is the comparative example data of Paste No. 2. is there.
Paste Nos. 3 to 11 of the present invention have a carbon amount of not 0 g but are plots of ◆ and black square marks.
The asterisk plot is acetylene black-1 (♦: AB-1), and the black square plot is acetylene black-2 (AB-2).

The paste Nos. 3 to 11 of the present invention have higher active material utilization than the comparative paste, and the active material utilization is further increased as the amount of carbon increases. Hereinafter, the utilization rate will be compared.
(A) At 0.06A, which is a low rate discharge (1) The amount of carbon is the largest (8.6 g), and paste No. 7 of the present invention is about 154% of the active material utilization rate of the prior art paste.
(2) Paste No. 3 of the present invention with the least amount of carbon (0.7 g) is approximately 110% of the active material utilization rate of the prior art paste.
(3) Next, the amount of carbon is the smallest (1.4 g). The paste No. 4 of the present invention is about 124% of the active material utilization rate of the paste of the prior art.
(B) In 6A, which is a high rate discharge (1) The amount of carbon is the largest (8.6 g), and paste No. 7 of the present invention is about 250% of the active material utilization rate of the conventional paste
(2) Paste No. 3 of the present invention with the least amount of carbon (0.7 g) is about 120% of the active material utilization of the paste of the prior art.
(3) Next, the amount of carbon is the smallest (1.4 g). The paste No. 4 of the present invention is about 150% of the active material utilization rate of the paste of the prior art.

<About utilization rate>
As described above, lead powder as a raw material is mainly lead oxide, but also includes lead that is not oxidized and in a metallic state. Lead oxide reacts with sulfuric acid in the electrolytic solution, and changes to lead as an active material by chemical conversion. Lead thus produced is regarded as an active material. Whether or not the metal lead originally contained is regarded as an active material is debated. Here, the utilization rate of the active material in the discharge was calculated on the assumption that the metal lead originally contained in the raw material became an active material.
<Utilization rate calculation method>
If the weight of the lead powder filled in the grid current collector is E,
F = E × 207/223 × (1 / 3.866)
Here, F is a capacity when it is assumed that the lead powder is all changed to lead by chemical conversion, that is, a theoretical capacity, 207 is a molecular weight of lead, 223 is a molecular weight of lead oxide (PbO), and 3.866 is Assuming that all of the lead has been discharged and changed to lead sulfate, this is the amount of lead necessary to discharge 1 ampere hour (Ah). The active material utilization rate (%) is
Utilization rate of active material (%) = negative electrode discharge capacity (actual value) / F × 100
Can be calculated as
In the present invention, it was calculated that all lead would be converted to lead after chemical conversion, but in fact, it is unclear whether or not the metallic lead existing from the beginning in the lead powder is used as the active material. This means that the rate was calculated slightly.
That is, when the contribution to the utilization ratio of metallic lead is low, the utilization ratio of the active material of the present invention is higher than that shown in this example.

Referring to Table 5 and FIG. 4 showing the high rate discharge characteristics using the paste of the present invention, in the active material utilization rate of paste No. 3 using 0.7 g of acetylene black-1 (◆: AB-1), Prior art paste no. The active material utilization rate of 1 is about 120%. That is, it is about 20% higher than the prior art.
In the category of using the conventional technology, an improvement of the active material utilization rate of 20% is usually not possible. This can be achieved by an invention that transcends the prior art.

Here, in the negative electrode composition containing acetylene black-1, the total oil absorption amount is calculated with respect to 1 mol of lead powder as an active material raw material.
Since 200 g of the lead powder used is composed of 150 g of lead oxide and 50 g of metal lead, 150/223 = 0.673 (mol) of lead oxide and 50/207 = 0. 242 (mol). That is, the total molar amount of the lead powder is 0.673 + 0.242 = 0.915 (mol).
The amount of oil absorption of acetylene black-1: 0.7 g is 220 ml / 100 g × 0.7 g = 1.54 ml.
Since the total oil absorption amount of carbon with respect to 0.915 mol of lead powder is 1.54 ml, the oil absorption amount converted per mol is 1.54 (ml) /0.915 (mol) = 1.683 (ml). / Mol). The above description can be expressed by the following formula. (When calculation is performed at once without rounding off)
220 (ml / 100 g) × 0.7 (g) / (150 (g) / 223 + 50 (g) / 207) = 1.485 (ml / mol)
When the lead oxide component is 80% and the lead component is 20%, it is expressed by the following formula.
220 (ml / 100 g) × 0.7 (g) / (160 (g) / 223 + 40 (g) / 207) = 1.661 (ml / mol)
The average value of both is (1.685 + 1.691) /2=1.688.
Therefore, the present invention exceeds the prior art by 20% or more by containing acetylene black-1 in an amount such that the total oil absorption is 1.7 ml or more per 1 mol of lead powder.

  Moreover, according to Table 3, the bulk density when acetylene black-1 is 0.7 g is 0.220 ml / g, and acetylene black-1: 0.7 g with respect to 200 g of lead powder is 0.7 (g ) / 200 (g) × 100 (%) = 0.35 (%), and becomes 0.35 mass%.

The test results of (1), (2) and (3) will be considered.
By adding carbon to the negative electrode composition, the lead powder filling amount decreases and the bulk density increases. By increasing the bulk density, sulfuric acid is abundant around the active material and the active material utilization rate is improved. That is, there is an improvement in the active material utilization rate while reducing lead powder. Battery performance can be improved while reducing lead, which is a major component of lead-acid batteries, and reducing costs.

  When the bulk density is small, it is necessary to supply more electrolyte solution (dilute sulfuric acid) necessary for the active material to discharge from the outside of the electrode plate. Since it can supply from the vicinity, it becomes easier to discharge. Therefore, the results shown in FIGS. 4 and 5 are obtained. The utilization factor is an absolutely necessary item for improving the energy density of the battery. Moreover, since the active material of a battery can be decreased if a utilization factor is high, the significance of cost reduction is also great.

<Life test results>
The cycle life test by repeating the charge / discharge cycle was performed under the following conditions.
(A) Discharge: 7A
(B) End-of-discharge voltage: 1.5 V / cell (c) Charge: 2.45 V, 5 hours (d) Battery electrode plate configuration: 3 positive electrodes, 4 negative electrodes Charge amount is approximately 105% of discharge amount Met. The temperature is 25 ° C.
The cycle life test results are shown in Table 6.

  Paste Nos. 3 to 11 of the present invention have confirmed 600 charge / discharge cycles and have not yet reached the end of their lives.

  Prior art paste no. 1 was exhausted at 400 cycles. This is considered to be because carbon was contained in the negative electrode composition.

In Example 2, the change in the life of the battery (negative electrode plate) was tested according to the type of polyvinyl alcohol.
Table 7 lists the types of polyvinyl alcohol and the components of the composition.

The paste is a paste no. 1. Paste No. 1 containing different types of PVA and carbon. 12-15. The carbon used was acetylene black-2.
In the components of Table 7, PVA (g) is the mass of the powdered PVA itself. In the preparation of the composition, PVA is dissolved in water to obtain an aqueous solution having a concentration of about 6%. A method for producing an aqueous PVA solution is described in Example 4.
In addition, the manufacturing method as a battery from manufacture of a paste from the composition of Table 7 in this Example 2 to filling of a lattice, ripening / drying to chemical conversion is the same as that of Example 1, and redundant description is omitted. Omitted.

<Test results>
Table 8 shows the cycle life of the battery using the negative electrode plate made of the paste corresponding to Table 7.

PVA-117 and PVA-124 both have a saponification degree of 98 mol% to 99 mol%, and the polymerization degrees are 1700 and 2400, respectively. The higher the degree of saponification and the higher the degree of polymerization, the less water-soluble.
Regarding the cycle life, the higher the degree of saponification, the better. Each paste No. using PVA-117 and PVA-124 having a saponification degree of 98 mol% to 99 mol% was used. Nos. 12 and 13 had a cycle life of 600 cycles or more and the lifetime was not exhausted. However, paste Nos. 12 and 13 using PVA-217 and PVA-224 having a low saponification degree of 87 mol% to 89 mol%, respectively. Nos. 14 and 15 had a cycle life of 300 cycles, and the lifetime was exhausted. Cycle life is worse than that using prior art pastes.

The PVA in which carbon is dispersed is preferably a poorly water-soluble PVA.
PVA having a high degree of saponification is hardly water-soluble because it contains almost no acetic acid group in the molecule. Conversely, PVA containing acetic acid groups and having a low saponification degree is easily soluble in water, and acetic acid groups contained in the PVA have an adverse effect on the battery. In particular, when the battery is charged and discharged, the temperature of the battery electrode plate rises, so that a large amount of acetic acid groups contained in the PVA dissolves in the electrolyte solution, thereby shortening the battery life.

Even in the results of the cycle life test shown in Table 8, those using poorly water-soluble PVA-117 and PVA-124 have better cycle life than those using PVA-217 and PVA-214 having high water solubility. And those using PVA-217 and PVA-214 with high water solubility have a short cycle life.
Note that the cycle life test method is the same as that of the first embodiment, and a duplicate description is omitted.

In Example 3, the following tests were carried out using four combinations of PVA-124 and PVA-117 with acetylene black-1 and acetylene black-2.
The paste is composed of 200 g of lead powder mainly composed of lead oxide, acetylene black, PVA, water, lignin, barium sulfate, and the like. Here, the test was simplified to obtain the temperature of water for dissolving PVA, which is a hardly soluble property, in 30 minutes in the relationship between acetylene black, PVA and water.
In the actual paste kneading, the amount of carbon changes, so that PVA is used at the PVA aqueous solution concentration (%) in Table 9 and Table 10 with respect to water. An experiment was conducted to determine the temperature of water required to produce a concentrated aqueous solution.
Those using PVA-124 are shown in Table 9, and those using PVA-117 are shown in Table 10.

Polyvinyl alcohol subjected to the test (all manufactured by Kuraray Co., Ltd.) is commercially available as a powder. As shown in Table 8, the saponification degree and the polymerization degree are different from each other.
PVA-117 and PVA-124 have a saponification degree as high as 98 mol% to 99 mol% as compared with the other two types, and the polymerization degrees are 1700 and 2400, respectively.
PVA-217 and PVA-224 have a saponification degree as low as 87 mol% to 89 mol% and polymerization degrees of 1700 and 2400, respectively. The higher the degree of saponification, the less water-soluble.

FIG. 5 is a graph of Table 9, and FIG. 6 is a graph of Table 10.
This will be described with reference to FIGS.
The horizontal axis represents the amount of carbon (acetylene black-1 or acetylene black-2), and the necessary amount of polyvinyl alcohol is obtained from the amount of carbon necessary for the negative electrode composition. Moreover, the amount of water required is calculated | required according to the amount of carbon. Therefore, the amount of PVA and water with the amount of carbon as a variable is required. This determines the PVA concentration.
In the production of the negative electrode composition, as the amount of carbon increases, the proportion of water necessary for kneading decreases relatively.
Since the amount of PVA is mixed at a constant ratio with respect to the amount of carbon, as the amount of carbon increases, the amount of PVA relative to the amount of water increases and the concentration of the PVA aqueous solution increases. As the concentration of PVA increases, the minimum melting temperature required accordingly increases. This means that the amount of carbon is taken on the horizontal axis.

  From the results shown in FIGS. 5 and 6, it can be seen that as the amount of carbon on the horizontal axis increases, the temperature of water required for dissolving PVA must be increased. Therefore, in order to dissolve PVA in water in a relatively short time to form a PVA aqueous solution, the temperature of the water to be dissolved must be increased.

In Example 4, paste No. 1 in Table 11 was used. The PVA dissolution results when the PVA aqueous solution was produced by changing the dissolution temperature of PVA as shown in 16 to 18 and the active material utilization when this PVA aqueous solution was used were tested.
Table 11 shows the components of the paste composition, the PVA dissolution method, and the dissolution results based on this.
In the components of Table 11, PVA is the mass of the powder PVA itself, and in the preparation of the composition, PVA is dissolved in water to give an aqueous solution with a concentration of about 6%. A PVA aqueous solution is produced by mixing 6% by mass. Therefore, a part of 80.8 g of the water in Table 11 is also distributed to the PVA aqueous solution, and the rest is used for the water for kneading the carbon and the PVA aqueous solution.
In addition, the manufacturing method as a battery from manufacture of a paste from the composition of Table 11 in this Example 4 to filling of a lattice, aging / drying to chemical conversion is the same as that of Example 1, and overlapping explanation Omitted. The capacity test for measuring the active material utilization rate is also the same as in Example 1.
Table 12 shows the active material utilization when the negative electrode plate manufactured according to Table 11 is used as a battery.

The carbon in the components of Table 11 is acetylene black-1, and the polyvinyl alcohol is PVA-124.
Paste No. in Table 11 No. 16 was obtained by dispersing 6% of PVA with respect to the sum of the mass of water and the mass of PVA and dissolving it at a dissolution temperature of 90 ° C. for 5 hours. No. 17 was similarly dispersed and dissolved at a dissolution temperature of 50 ° C. for 5 hours to dissolve about 1/3. No. 18 was similarly dispersed and dissolved at a dissolution temperature of 25 ° C. for 5 hours, but hardly dissolved.

FIG. 7 is a graph of Table 12. Plot marks indicated by white graphics are low-rate discharge 0.06A, and plot marks indicated by solid black graphics are high-rate discharge 6A. There are 5 samples (indicated by 5 types of figures).
The horizontal axis is the PVA melting temperature (° C.), and there are 3 points. The vertical axis represents the active material utilization rate (%).
Those having a high melting temperature have a high active material utilization rate and small variations between samples, while those having a low melting temperature have a low active material utilization rate and large variations between samples. These variations are significant in high rate discharge.
These causes are that when the temperature of water is low, the solubility of PVA becomes low, and the amount of PVA for coating carbon decreases. Therefore, the carbon dispersion state is not uniform, and there is carbon that disperses satisfactorily to some extent and carbon that does not reach this, and the active material utilization rate varies.

  From the above results, the melting temperature of PVA is preferably a temperature of 60 ° C. or higher exceeding 50 ° C., more preferably about 90 ° C. or higher.

In Example 2, although the advantage (long life) of using poorly water-soluble PVA-117 and PVA-124 as a carbon dispersant was found, these PVA hardly dissolve in water at room temperature (the same dissolution concentration). It takes time to reach). Therefore, in order to prepare a PVA aqueous solution using poorly water-soluble PVA, PVA is dispersed in water and then heated (above 50 ° C. or even about 90 ° C.) to be completely dissolved, and then cooled (naturally It is effective to use a PVA aqueous solution (which is cooled to room temperature) for the preparation of the negative electrode composition. Once heated and completely dissolved, the PVA remains in a water-soluble state even when cooled, and even if this PVA aqueous solution is mixed with fresh water, the dissolution is not impaired.
In Example 1, an aqueous PVA solution with a concentration of 6% was produced by this method.

Finally, in order to show the characteristics of the negative electrode composition, the bulk density of the non-chemical electrode plate was measured. Table 13 shows a method for measuring the bulk density.
The bulk density of the unformed negative electrode composition is calculated by the following formula.
Bulk density of unformed negative electrode composition = volume of unformed negative electrode composition / weight of unformed negative electrode composition
= (D−B) / (C−A)

It is a graph which shows the measurement result of the lead powder filling amount of the negative electrode plate of the present invention. It is a graph which shows the measurement result of the bulk density of the negative electrode plate of this invention. It is a graph which shows the measurement result of the active material utilization factor of the negative electrode plate of this invention. It is a graph which shows the measurement result of the active material utilization factor of the negative electrode plate of this invention. It is a graph which shows the relationship between the amount of carbon and the melting temperature of PVA-124. It is a graph which shows the relationship between the amount of carbon and the melting temperature of PVA-117. It is a graph which shows the relationship between the PVA melt | dissolution method and a utilization factor. It is a graph which shows the cumulative particle size distribution of acetylene black.

Claims (7)

  An active material raw material mainly composed of a metal oxide and a carbon containing about 50% of particles having a particle diameter of about 20 nanometers or less are added in an amount such that the total oil absorption is 1.7 ml or more per mole of the active material raw material. A negative electrode composition for a secondary battery, which is a kneaded product. A kneaded material containing 3.5 × 10 ⁻¹ mass percent or more of an active material material mainly composed of a metal oxide and carbon containing approximately 50% of particles having a particle diameter of approximately 20 nanometers or less with respect to the active material material. A negative electrode composition for a secondary battery. A kneaded product containing an active material raw material mainly composed of a metal oxide and carbon containing approximately 50% of particles having a particle diameter of approximately 20 nanometers or less is dried to have a bulk density of 2.2 × 10 ^{−1 in an} unformed state. A negative electrode composition for a secondary battery comprising the carbon in an amount of at least milliliter / gram.   The said carbon is acetylene black, The negative electrode composition for secondary batteries in any one of Claims 1-3 characterized by the above-mentioned.   2. The kneaded material is a kneaded material generated by kneading the carbon material with water and a polyvinyl alcohol aqueous solution to produce a primary kneaded material and the active material raw material. The negative electrode composition for secondary batteries in any one of -4.   The polyvinyl alcohol aqueous solution is obtained by dispersing polyvinyl alcohol having a dissolution amount in water of 1 mass percent or less under conditions of a dissolution temperature of 40 ° C. and a dissolution time of 30 minutes in water, and heating it to about 60 ° C. or more to almost completely. The negative electrode composition for a secondary battery according to claim 5, wherein the negative electrode composition is dissolved. The polyvinyl alcohol aqueous solution is obtained by dispersing polyvinyl alcohol having a saponification degree of 98 mol% or more and a polymerization degree of 1.7 × 10 ³ or more in water and heating it to about 60 ° C. or more to dissolve it almost completely. The negative electrode composition for a secondary battery according to claim 5.