JP2007035339A - Control valve type lead-acid storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control valve type lead-acid storage battery used for auxiliary equipment of a hybrid car, of which lead ion is reduced at an anode at charging, prevented from short circuit between a cathode and the anode caused by dendritic electrodeposition substance of lead. <P>SOLUTION: The control valve type lead-acid battery uses a lattice made of lead or lead alloy not including antimony for a cathode plate and an anode plate. Ratio (B/A) of mass (B) of sulfuric acid contained in electrolyte liquid to a mass (A) of cathode activator is not less than 0.40 and not more than 0.52, and 10g/l to 30g/l of tetra-sodium borate is contained in the electrolyte liquid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a valve-regulated lead-acid battery.

In recent years, efforts have been made to reduce CO ₂ by improving automobile fuel efficiency from the viewpoint of the global environment. A so-called hybrid vehicle that combines an engine and an electric motor has been put into practical use and is in the stage of widespread use.

  On the other hand, a conventional automobile is equipped with a lead storage battery mainly for engine start. This lead-acid battery supplies electric power to ECUs and various auxiliary machines that perform various controls of the vehicle, but since the engine is charged by an alternator after starting the engine, the SOC (charged state) of the lead-acid battery is 80 to 100%. It is kept relatively high.

  On the other hand, in a hybrid vehicle, an electric motor is driven by a main battery such as a Ni-MH battery, and a lead storage battery used as a sub battery is used as a power source for auxiliary equipment such as an ECU. Such lead-acid batteries for auxiliary machines are usually installed in the space in the passenger compartment, under the passenger compartment, or in the trunk or under the trunk instead of being installed in the conventional engine room due to the space in the vehicle. It is. Therefore, instead of an open-liquid type lead acid battery in which oxygen and hydrogen gas are easily discharged during charging, a negative electrode absorption control valve type lead acid battery that suppresses hydrogen gas generation at the negative electrode by absorbing oxygen gas at the negative electrode. Use.

  The hybrid vehicle is equipped with various ECUs such as an ECU for controlling the main battery in addition to an ECU for controlling the engine, and accordingly, dark current flowing through the ECU is at a higher level than that of a normal vehicle. .

  Since the dark current continues to flow even when the vehicle is completely stopped, the lead storage battery is overdischarged when the vehicle is used less frequently. In particular, in the control valve type lead acid battery, the amount of sulfuric acid in the electrolytic solution is limited to be smaller than that of the open liquid type lead acid battery, so that the discharge capacity is small and the battery is more easily overdischarged. Moreover, since the sulfuric acid concentration of the electrolytic solution in the overdischarged state is lower than that in the case of the liquid lead acid battery, a short circuit between the positive electrode and the negative electrode is likely to occur.

  Such a short circuit is caused by an increase in the solubility of lead sulfate, which is a discharge product, in the electrolytic solution as the sulfuric acid concentration in the electrolytic solution decreases. When lead sulfate is dissolved, lead sulfate is present as lead ions. However, when the lead storage battery is charged, lead ions are reduced on the negative electrode and deposited as dendritic deposits. When this dendritic electrodeposit penetrates the separator, the positive electrode and the negative electrode are short-circuited.

In order to suppress a short circuit that occurs when a lead storage battery is overdischarged, it is known to add sodium sulfate to the electrolyte (see, for example, Patent Document 1). Sodium sulfate acts as a buffering agent that increases the degree of ionization of sulfate ions when sulfate ions are deficient in the dilute sulfuric acid electrolyte. And since the fall of the sulfate ion concentration at the time of overdischarge is suppressed and the solubility of lead ion falls, the growth of a dendritic electrodeposit and a short circuit by this are suppressed.
JP-A-4-171672

  As described in Patent Document 1, by adding sodium sulfate to the electrolytic solution, there is an effect of suppressing dendritic electrodeposits and internal short circuit caused by overdischarge of the lead storage battery. Tended to have a larger dark current than ordinary vehicles, and the effect of preventing an internal short circuit was insufficient only by adding sodium sulfate.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention uses a lead or lead alloy lattice containing no antimony for the positive electrode plate and the negative electrode plate, The ratio of sulfuric acid mass (B) (B / A) is 0.40 or more and 0.52 or less, and 10 g / l to 30 g / l of sodium tetraborate is contained in the electrolytic solution. It shows a lead storage battery.

  Furthermore, the invention according to claim 2 of the present invention is the control valve type lead-acid battery according to claim 1, which has a free electrolyte for immersing the lower part of the positive electrode plate and the negative electrode plate.

  The lead-acid battery of the present invention generates a dendritic deposit during overdischarge and the inside of the battery even when it is used for a vehicle having a dark current larger than that of a general vehicle such as a hybrid vehicle. Short circuit can be suppressed.

  The configuration of the control valve type lead storage battery of the present invention will be described.

  The control valve type lead storage battery of the present invention uses lead or a lead alloy containing no antimony as a lattice alloy of the positive electrode and the negative electrode. In order to ensure the mechanical strength and corrosion resistance required for the lattice, Sn having a concentration of about 0.2% to 2.0% by mass and Ca having a concentration of about 0.03% to 0.1% by mass are used. It is possible to add.

  The positive and negative grids are filled with an active material paste obtained by kneading known lead powder for lead-acid batteries such as ball mill type lead powder and Burton type lead powder with water and dilute sulfuric acid. . In addition, a red lead can be added in lead powder for the purpose of the chemical conversion efficiency and utilization rate improvement of a positive electrode active material. Further, a conductive agent such as a shrink preventing agent (barium sulfate, lignin) for suppressing shrinkage of the negative electrode active material or carbon for improving conductivity can be added. Furthermore, in order to ensure the mechanical strength of the active material, a synthetic fiber (polyester fiber or the like) having a length of about 1 to several tens mm can be added.

  After filling the positive electrode / negative electrode active material with an active material paste, it is aged and dried to obtain an unformed positive electrode plate and negative electrode plate. A control valve type lead storage battery is assembled by combining these positive / negative electrode plates and a mat separator made of acid-resistant glass fiber or polypropylene resin fiber.

In the control valve type lead-acid battery of the present invention, the ratio of the mass of sulfuric acid (B) and the mass of positive electrode active material (PbO ₂ ) (A) contained in the electrolyte is (B / A) of 0.40 or more, and It is made into the range of 52 or less, and 10.0 g / l-30 g / l of sodium tetraborate is included in electrolyte solution.

  Sodium tetraborate increases the ionization degree of sulfuric acid and increases the sulfuric acid ion concentration in the electrolytic solution in a state in which the amount of sulfuric acid in the electrolytic solution is reduced, thereby bringing the discharge product (lead sulfate) into the electrolytic solution. As a result, it is considered that the precipitation of the dendritic electrodeposit on the negative electrode and the internal short circuit of the battery due to this are suppressed.

  Such an internal short-circuit suppressing effect by sodium tetraborate is particularly effective when the ratio (B / A) of the sulfuric acid mass (B) to the positive electrode active material amount (A) is 0.40 or more and 0.52 or less. Can be obtained, most notably. In the region where this ratio is less than 0.40, the effect of sodium tetraborate is not significantly different from the conventionally known effect of adding sodium sulfate.

  Moreover, in the region where the ratio (B / A) exceeds 0.52, the effect of suppressing internal short circuit is hardly improved, and the gas absorption efficiency at the negative electrode is lowered, and the liquid reduction due to gas generation becomes large, which is not preferable.

In the conventional control valve type lead acid battery, the ratio of the sulfuric acid mass (B) and the positive electrode active material (PbO ₂ ) amount (A) is 0.3 to 0.35. This ratio is relatively high at 0.40 to 0.52. Therefore, in a configuration in which all the electrolyte is impregnated and fixed to the positive electrode plate, the negative electrode plate, and the separator, the sulfuric acid concentration of the electrolyte solution must be increased. In general, when the sulfuric acid concentration in the electrolytic solution exceeds 44.2%, sulfation, softening of the positive electrode active material, and reduction in charge acceptability become significant. To avoid this, the electrolytic solution released from the electrode plate and the separator must be present. It is preferable to set the sulfuric acid concentration of the electrolytic solution to a lower value. However, it is preferably 35% or more from the viewpoint of battery capacity.

  In the case of a battery having a free electrolyte solution, for example, when a charging operation is performed with the battery inverted, the internal electrolyte solution may leak to the outside when the control valve is opened. A storage battery is usually fixed to a vehicle and used, and the battery is never used in an inverted state in normal use. Therefore, even if it has a free electrolyte, there is no practical problem.

  The control valve type lead storage battery of the present invention having the above configuration can suppress an internal short circuit during overdischarge even when it is used as a lead storage battery for auxiliary equipment of a hybrid vehicle having a relatively large dark current. .

Example 1
Hereinafter, the effects of the present invention will be described with reference to examples.

In this example, the ratio (B / A) of the amount (A) of the positive electrode active material (PbO ₂ ) to the mass of sulfuric acid (B) in the electrolytic solution and the amount of sodium tetraborate added in the electrolytic solution are varied. 2V44Ah control valve type lead acid battery was made.

  For comparison, a battery in which sodium sulfate was changed in place of sodium tetraborate was prepared.

A grid obtained by expanding a rolled sheet of Pb-1.6 mass% Sn-0.06 mass% Ca as a positive electrode plate together with ball mill type lead powder (Pb0: 75 mass parts, Pb: 25 mass parts), Lead paste (Pb ₃ O ₄ : 95 parts by mass, PbO: 5 parts by mass) was added, and a paste filled with paste obtained by kneading these with water and dilute sulfuric acid was used.

  After adding lignin, barium sulfate, and acetylene black to the above-mentioned ball mill type lead powder to a grid obtained by expanding a rolled sheet of Pb-0.20 mass% Sn-0.07 mass% Ca as a negative electrode plate, A paste filled with paste obtained by kneading water and dilute sulfuric acid was used.

  The positive electrode plate was sandwiched between U-folded glass fiber mat separators and combined with the negative electrode plate to prepare an electrode plate group. The configuration of the electrode plate group is six positive plates and seven negative plates. And after accommodating the electrode plate group in the battery case, the lid was joined, the electrolytic solution was injected from the injection port provided in the lid, and after chemical conversion charging, the valve body was attached to the injection port. Tables 1 and 2 show the configurations of these batteries.

  In addition, the sulfuric acid concentration before the additive addition of the electrolyte solution of the battery of Table 1 and Table 2 was 44.2 mass%. In this case, a free electrolytic solution was generated in which the ratio (B / A) was 0.40 or more and the electrode plate or separator could not be impregnated and held. Here, the electrolytic solution having a sulfuric acid concentration of 44.2% by mass and an additive (sodium tetraborate or sodium sulfate) of 5 to 50 g / l is composed of 44.2 parts by mass of sulfuric acid and 63.8 parts by mass of water. It means an electrolytic solution obtained by adding 5 to 50 g of sodium tetraborate or sodium sulfate to 1 liter of the mixed electrolyte solution stock (sulfuric acid concentration: 44.2% by mass).

  Each battery shown in Table 1 and Table 2 was subjected to an overdischarge cycle test and a 5-hour rate capacity test (25 ° C., 8.8 A discharge, 1.75 V termination). The overdischarge test conditions are as follows.

Test temperature: 25 ° C
Test procedure:
(1) Discharge (2.2 A constant current discharge, end voltage 1.75 V)
(2) Overdischarge (170Ω, 1 week)
(3) Recovery charge (2.33V constant voltage, maximum current 50A, 2 hours)
(4) Decomposition investigation (decomposes n = 3 every week), number of weeks in which short circuit due to dendritic electrodeposits was confirmed
Is overdischarged short circuit life, and the test is completed.

  The results of the above overdischarge test are shown in FIG. In the legend of FIG. 1, Na sulfate and Na borate indicate sodium sulfate and sodium borate respectively added to the electrolytic solution.

  From the results shown in FIG. 1, the ratio (B / A) of the mass of sulfuric acid (B) to the amount of positive electrode active material (A) is in the range of 0.4 to 0.52, and the amount of sodium tetraborate added is 10 g / It can be seen that it has an excellent overdischarge short-circuit life in the range of 1 or more.

  In the battery to which sodium sulfate was added, the overdischarge short-circuit life increased linearly as the ratio (B / A) increased, but when sodium tetraborate was added, the ratio (B / A) was 0.40 or more. The overdischarge short-circuit life increases abruptly. The ratio (B / A) is maximum at 0.52.

  Next, Table 3 shows the results of a 5-hour rate discharge capacity test when sodium tetraborate is used as an electrolytic solution additive, and Table 4 shows the results when sodium sulfate is used.

  From the results shown in Tables 3 and 4, by adding sodium sulfate or sodium tetraborate into the electrolytic solution, the 5-hour rate capacity gradually decreases. In particular, the addition of 50 g / l of sodium tetraborate is not preferable because the capacity is significantly reduced. Therefore, in this invention, the upper limit of sodium tetraborate shall be 30 g / l or less.

(Example 2)
Next, the batteries 17 to 31 of Examples and the sulfuric acid concentrations in the electrolytes of these batteries were set to 49.0% by mass, and batteries 67 to 81 were prepared in a state where there was no electrolyte released from the electrode plate group. These batteries were subjected to a heavy load life test shown in JIS D5301. The heavy load life test conditions are as follows.

(Heavy load life test conditions)
(1) Discharge (20A constant current, 1 hour)
(2) Charging (5A constant current, 5 hours)
(3) Capacity check (20A constant current discharge, discharge end voltage every 25 cycles of the above discharge-charge
10.2V)
(4) Test temperature (40 ° C liquid phase)
The test ends when the discharge capacity (20A × discharge time product) in the capacity check is reduced to 22Ah, which is 50% of the initial value, and the relationship line between the number of discharge-charge cycles and the discharge capacity in (3) From this, the number of life cycles was determined. These results are shown in Table 5 together with the configuration of the battery.

  From the results shown in Table 5, according to the present invention, the life cycle characteristics can be remarkably improved by reducing the sulfuric acid concentration in the electrolytic solution. This is presumed to be due to the suppression of the softening of the positive electrode active material due to the increase in sulfuric acid concentration and the sulfation of the negative electrode active material. In addition, it is considered that the free electrolyte solution facilitates the replenishment of sulfate ions in the electrolyte solution to the active material, and the life is extended by increasing the battery capacity.

  As described above, according to the present invention, a lead storage battery having excellent heavy load life characteristics can be obtained by suppressing the internal short circuit of the battery due to the dendritic electrodeposit during overdischarge and further having a free electrolyte. Obtainable.

  Since the lead storage battery of the present invention remarkably suppresses an internal short circuit even at the time of overdischarge, it is suitable for an application that is easily overdischarged by dark current, such as a lead storage battery for a hybrid vehicle auxiliary machine.

The figure which shows the overdischarge short circuit life test result in an Example

Claims (2)

Using lead or lead alloy grids that do not contain antimony on the positive and negative plates,
The ratio (B / A) of the sulfuric acid mass (B) in the electrolytic solution to the positive electrode active material amount (A) is 0.40 or more and 0.52 or less,
And the control valve type lead acid battery characterized by including 10 g / l-30 g / l of sodium tetraborate in electrolyte solution. The control valve type lead acid battery of Claim 1 which has the free electrolyte which immerses the lower part of a positive electrode plate and a negative electrode plate.

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