JP3540557B2 - Nickel electrode for alkaline storage battery and method for producing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nickel electrode for an alkaline storage battery such as a nickel-hydrogen storage battery, a nickel-cadmium storage battery, and a nickel-zinc storage battery using nickel hydroxide as a positive electrode active material and a method for producing the same, and in particular, to increasing the capacity of the nickel electrode. It is about.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the rapid spread of portable electronic and communication devices, there has been a demand for higher performance storage batteries than ever. Against this background, various methods for improving the utilization rate of the nickel hydroxide active material have been proposed for alkaline storage batteries using nickel hydroxide as a positive electrode active material in order to further enhance the performance of the storage battery. .
[0003]
As a method of improving the utilization rate of the nickel hydroxide active material, there is a method of adding a cobalt compound to the positive electrode. Although the cobalt compound has a low conductivity in a divalent state, it changes into a higher-order cobalt compound having a good conductivity when charged, and since the higher-order cobalt compound is difficult to discharge, even if the discharge is performed, It is possible to remain in the positive electrode and maintain high conductivity in the positive electrode. For this reason, it is possible to improve the utilization rate of the active material.
[0004]
As a method of adding the cobalt compound, for example, there are methods proposed in JP-A-57-205968 and JP-A-7-272723. In the method proposed in JP-A-57-205968, nickel and cobalt are simultaneously precipitated as hydroxides from a nitrate solution. On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 7-272723, a nickel-cobalt eutectic mixture is used as an active material, and the nickel hydroxide corresponds to the (1,0,1) plane in X-ray diffraction of nickel hydroxide. By defining the half width of the peak to be 0.6 or more, the activity of nickel hydroxide is increased to improve charge acceptability.
[0005]
[Problems to be solved by the invention]
However, in the method proposed in JP-A-57-205968, a large amount of cobalt is required to obtain the effect of improving the utilization rate of the active material, and the charging of the nickel hydroxide active material contributing to the charge / discharge reaction is required. Since the amount is reduced, the capacity of the electrode plate is reduced, and the operating voltage is also reduced. On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 7-272723, a large amount of cobalt is similarly required to obtain the effect of improving the active material utilization, and the nickel hydroxide active material contributing to the charge / discharge reaction is also required. Since the filling amount is reduced, there is a problem that the electrode plate capacity is reduced and the operating voltage is also reduced.
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a nickel electrode for an alkaline storage battery in which the operating voltage is reduced without lowering the operating voltage.
[0006]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve the above-mentioned problem, the nickel electrode for an alkaline storage battery of the present invention has a half-value width of a peak corresponding to a (1,0,1) plane in X-ray diffraction on a surface of a nickel electrode holding an active material. (Half width) is characterized by comprising a layer mainly composed of β-cobalt hydroxide having low crystallinity of 0.3 or more.
[0007]
Since cobalt hydroxide has low activity, even if a single layer of cobalt hydroxide is simply provided on the surface of the active material, conversion to cobalt oxyhydroxide cannot be effectively performed by electrochemical oxidation by subsequent charging, and water Cobalt oxyhydroxide cannot be uniformly covered on the nickel oxide active material, and the active material utilization does not improve. However, if a layer mainly composed of β-cobalt hydroxide having a low crystallinity is provided on the surface of the nickel electrode holding the positive electrode active material as in the present invention, the β-hydroxyl having a low crystallinity may be provided. Since cobalt has high activity, subsequent electrochemical oxidation is easily caused.
[0008]
For this reason, the surface of the nickel hydroxide active material is covered with active cobalt hydroxide, and is irreversibly converted to cobalt oxyhydroxide by an electrochemical oxidation reaction by subsequent charging, so that a conductive matrix can be effectively formed. Become. As a result, deep discharge becomes possible, and the active material utilization rate of the nickel electrode is improved.
[0009]
The layer mainly composed of low-crystallinity β-cobalt hydroxide, in which the half-width of the peak corresponding to the (1,0,1) plane in the X-ray diffraction is 0.3 or more, is formed by β-hydroxylation. It is preferable that the layer contains 70% by weight or more of cobalt. In this way, by defining β-cobalt hydroxide having low crystallinity and defining the amount of formation, it is possible to form an optimal conductive network in the electrode, and the active material utilization rate is further improved. I do.
[0010]
The manufacturing method of an alkaline storage battery of nickel electrodes of the present invention positive electrode active material holding step for holding the positive electrode active material mainly composed of nickel hydroxide electrode comprising an active material retainer, this active material holding step The electrode holding the active material is immersed in an aqueous solution containing a cobalt compound to immerse the electrode in the aqueous solution containing the cobalt compound, and the cobalt compound held on the surface of the electrode is alkali-treated by the impregnation step. An alkaline treatment step of substituting a cobalt compound with β-cobalt hydroxide having a half width of a peak corresponding to a (1,0,1) plane in X-ray diffraction of 0.3 or more. And
[0011]
As described above, when the cobalt compound is held on the surface of the electrode and then replaced with cobalt hydroxide by an alkali treatment, β-cobalt hydroxide having low crystallinity is formed on the surface of the electrode. Since β-cobalt hydroxide having low crystallinity has high activity, electrochemical oxidation due to subsequent charging easily occurs easily. For this reason, the surface of the nickel hydroxide active material is covered with active cobalt hydroxide, and is irreversibly converted to cobalt oxyhydroxide by an electrochemical oxidation reaction by subsequent charging, so that a conductive matrix can be effectively formed. Become. As a result, deep discharge becomes possible, and the active material utilization rate of the nickel electrode is improved.
[0012]
Then, cobalt nitrate cobalt compound is a strong acid salts of cobalt, and cobalt oxalate, cobalt phosphate, cobalt acetate, it is not preferable to choose from a weak acid salt or an organic acid cobalt cobalt consisting of formic acid cobalt.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
1. Preparation of Sintered Substrate A thickener such as carboxymethylcellulose and water are kneaded with nickel powder to prepare a slurry, and the slurry is applied to a conductive core made of a porous nickel body. Thereafter, the conductive core coated with the slurry is sintered under a reducing atmosphere to produce a sintered substrate.
[0014]
2. Production of Nickel Electrode (1) Reference Electrode The sintered substrate produced as described above was immersed in an aqueous solution mainly composed of nickel nitrate, and the pores of the sintered substrate were impregnated with an aqueous solution mainly composed of nickel nitrate. Thereafter, the substrate is dried to deposit nickel nitrate in the pores of the sintered substrate. The sintered substrate on which nickel nitrate has been deposited is immersed in an aqueous sodium hydroxide solution to replace the nickel nitrate deposited in the pores with nickel hydroxide. Thereafter, the process returns to the operation of immersing the sintered substrate again in an aqueous solution mainly composed of nickel nitrate, and the same operation as described above is repeated a predetermined number of times to fill the pores of the sintered substrate with nickel hydroxide. The electrode thus filled with nickel hydroxide in the pores of the sintered substrate is used as a reference electrode.
[0015]
(2) Example 1
The reference electrode prepared as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate at 25 ° C. to hold cobalt nitrate on the surface of the reference electrode filled with nickel hydroxide. Next, the reference electrode having cobalt nitrate retained on the surface is dried at 80 ° C., and then subjected to an alkali treatment of immersion in an 8N aqueous solution of sodium hydroxide at 25 ° C. to replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce the nickel electrode of Example 1. At this time, the half width (half width) of the peak corresponding to the X-ray diffraction peak (1,0,1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.30. . At this time, the weight of the cobalt hydroxide formed on the surface of the reference electrode was 2.1% by weight based on the total active material composed of nickel hydroxide and cobalt hydroxide.
[0016]
(3) Example 2
The reference electrode prepared as described above is immersed in a 1.35 mol / l aqueous solution of cobalt acetate at 25 ° C. to deposit cobalt acetate on the surface of the reference electrode filled with nickel hydroxide. Next, the reference electrode having cobalt acetate on the surface is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N-sodium hydroxide at 80 ° C. to replace cobalt acetate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 2. At this time, the half-value width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.31.
[0017]
(4) Example 3
The reference electrode produced as described above is immersed in a 1.8 mol / l aqueous solution of cobalt acetate at 80 ° C. to deposit cobalt acetate on the surface of the reference electrode filled with nickel hydroxide. Next, the reference electrode having cobalt acetate retained on the surface is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N-sodium hydroxide at 25 ° C. to replace cobalt acetate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 3. At this time, the half-value width of the peak corresponding to the X-ray diffraction peak (1,0,1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.46.
[0018]
(5) Comparative example A
The reference electrode prepared as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate at 25 ° C. to hold cobalt nitrate on the surface of the reference electrode filled with nickel hydroxide. Next, the reference electrode having cobalt nitrate retained on the surface is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 80 ° C. to replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, drying is performed at 100 ° C. to produce a nickel electrode of Comparative Example A. At this time, the half-value width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.27.
[0019]
3. Measurement of Energy Density The reference electrodes prepared as described above, the nickel electrodes of Examples 1 to 3 and Comparative Example A were charged in a potassium hydroxide aqueous solution having a specific gravity of 1.2 at a charging current of 0.1 C using a nickel plate as a counter electrode. After charging for an hour, the electrode was discharged at a discharge current of 0.25 C until the electrode potential became -1.5 V with respect to the nickel counter electrode. From this discharge time, per 1 g of the total active material comprising nickel hydroxide and cobalt hydroxide was used. Of the peak corresponding to the X-ray diffraction peak (1,0,1) plane of β-cobalt hydroxide formed on the surface of the reference electrode. ) And the unit active material capacity (active material energy density) yielded the results shown in FIG.
[0020]
As is clear from FIG. 1, if the half width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide formed on the surface of the reference electrode is 0.3 or more, It can be seen that the active material energy density is effectively improved. That is, the nickel electrode formed on the surface of the reference electrode with cobalt hydroxide having a half width of 0.3 or more of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide is an active material. The utilization rate will be improved.
[0021]
4. Examination of the amount of cobalt hydroxide Next, the amount of cobalt hydroxide formed on the surface of the reference electrode will be examined.
(1) Example 4
The reference electrode prepared as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate containing 30% by weight of nickel nitrate at 25 ° C., and the surface of the reference electrode filled with nickel hydroxide is coated with nickel nitrate-cobalt nitrate. Retain the eutectic. A reference electrode having a surface on which a nickel nitrate-cobalt nitrate eutectic mixture is held is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace nickel nitrate with cobalt hydroxide. And replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 4. At this time, among the generated cobalt hydroxides, the half width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide was 0.36.
[0022]
(2) Embodiment 5
The reference electrode prepared as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate containing 20% by weight of nickel nitrate at 25 ° C., and nickel nitrate-cobalt nitrate is placed on the surface of the reference electrode filled with nickel hydroxide. Retain the eutectic. A reference electrode having a surface on which a nickel nitrate-cobalt nitrate eutectic mixture is held is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace nickel nitrate with nickel hydroxide. And replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 5. At this time, the half width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.35.
[0023]
(3) Comparative example B
The reference electrode prepared as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate containing 50% by weight of nickel nitrate at 25 ° C., and the surface of the reference electrode filled with nickel hydroxide is coated with nickel nitrate-cobalt nitrate. Retain the eutectic. A reference electrode having a surface on which a nickel nitrate-cobalt nitrate eutectic mixture is held is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace nickel nitrate with nickel hydroxide. And replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Comparative Example B. At this time, the half width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.35.
[0024]
(4) Comparative example C
The reference electrode fabricated as described above is immersed in a 2 mol / l aqueous solution of cobalt nitrate containing 35% by weight of nickel nitrate at 25 ° C., and nickel nitrate-cobalt nitrate is placed on the surface of the reference electrode filled with nickel hydroxide. Retain the eutectic. A reference electrode having a surface on which a nickel nitrate-cobalt nitrate eutectic mixture is held is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace nickel nitrate with nickel hydroxide. And replace cobalt nitrate with cobalt hydroxide. Thereafter, after washing with water, drying is performed at 100 ° C. to produce a nickel electrode of Comparative Example C. At this time, among the generated cobalt hydroxides, the half width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide was 0.36.
[0025]
After the nickel electrodes of Examples 4 and 5 and Comparative Examples B and C prepared as described above were charged in a potassium hydroxide aqueous solution having a specific gravity of 1.2 with a nickel plate as a counter electrode at a charging current of 0.1 C for 16 hours, The electrode was discharged at a discharge current of 0.25 C until the electrode potential became -1.5 V with respect to the nickel counter electrode. From this discharge time, the discharge capacity per unit of 1 g of the entire active material comprising nickel hydroxide and cobalt hydroxide (unit: Active material capacity), the weight% of nickel nitrate contained in the aqueous cobalt nitrate solution, that is, the ratio (weight%) of cobalt hydroxide to nickel hydroxide formed on the substrate surface and the unit active material capacity (active material energy) (Density), the result was as shown in FIG.
[0026]
As is clear from FIG. 2, it can be seen that the active material energy density is effectively improved when the cobalt hydroxide formed on the surface of the reference electrode is 70% by weight or more. That is, a nickel electrode having 70% by weight or more formed on the surface of the reference electrode as cobalt hydroxide has an improved utilization ratio of the active material.
[0027]
5. Examination of addition position of cobalt hydroxide Next, the addition position of cobalt hydroxide to be added to the nickel electrode will be examined.
(1) Embodiment 6
The reference electrode prepared as described above is immersed in a 1.0 mol / l aqueous solution of cobalt nitrate at 25 ° C. to hold cobalt nitrate on the surface of the reference electrode filled with nickel hydroxide. After the reference electrode having cobalt nitrate retained on the surface is dried at 80 ° C., it is subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 6. At this time, the half-value width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.31. At this time, the weight of cobalt hydroxide formed on the surface of the reference electrode was 0.9% by weight based on the total active material composed of nickel hydroxide and cobalt hydroxide.
[0028]
(2) Example 7
The reference electrode prepared as described above is immersed in a 2.8 mol / l aqueous solution of cobalt nitrate at 25 ° C. to deposit cobalt nitrate on the surface of the reference electrode filled with nickel hydroxide. The reference electrode having cobalt nitrate deposited on its surface is dried at 80 ° C., and then subjected to an alkali treatment of immersion in 8N sodium hydroxide at 25 ° C. to replace cobalt nitrate with cobalt hydroxide. Then, after washing with water, it is dried at 100 ° C. to produce a nickel electrode of Example 7. At this time, the half-value width of the peak corresponding to the X-ray diffraction peak (1, 0, 1) plane of β-cobalt hydroxide among the generated cobalt hydroxide was 0.32. At this time, the weight of the cobalt hydroxide formed on the surface of the reference electrode was 3.1% by weight based on the entire nickel hydroxide active material.
[0029]
(3) Comparative example D
The sintered substrate prepared as described above was immersed in an aqueous solution obtained by adding 1% by weight, 3% by weight, and 5% by weight of cobalt nitrate to nickel nitrate, and cobalt nitrate was added into the pores of the sintered substrate. After being impregnated with an aqueous solution of nickel nitrate, it is dried to deposit a eutectic mixture of nickel nitrate and cobalt nitrate in the pores of the sintered substrate. Then, after drying the sintered substrate on which the nickel nitrate-cobalt nitrate eutectic mixture is deposited, the substrate is immersed in an aqueous solution of sodium hydroxide to replace nickel nitrate with nickel hydroxide and to convert cobalt nitrate into cobalt hydroxide. Let it be replaced.
[0030]
Thereafter, the process returns to the operation of immersing the sintered substrate again in an aqueous solution in which 1% by weight, 3% by weight, and 5% by weight of cobalt nitrate are added to nickel nitrate, and the same operation as described above is repeated a predetermined number of times. Nickel hydroxide and cobalt hydroxide are filled in the pores of the bonding substrate. In this way, three types of nickel electrodes having different addition amounts of cobalt are produced, and are used as a nickel electrode of Comparative Example D. In the nickel electrode of Comparative Example D thus produced, cobalt is present in the form of a solid solution in the nickel hydroxide active material.
[0031]
The nickel electrodes of Examples 6 and 7 and Comparative Example D prepared as described above were charged in a potassium hydroxide aqueous solution having a specific gravity of 1.2 with a nickel plate as a counter electrode at a charging current of 0.1 C for 16 hours. Discharge was performed at a discharge current of 25 C until the electrode potential became -1.5 V with respect to the nickel counter electrode. From this discharge time, the discharge capacity per 1 g of the total active material comprising nickel hydroxide and cobalt hydroxide (unit active material) Capacity), and the relationship between the amount of cobalt added to the total active material and the active material energy density ratio when the active material energy density using the reference electrode is 100 is obtained. The result shown in FIG. 3 is obtained. .
[0032]
As is clear from FIG. 3, the half-width of the peak corresponding to the (1,0,1) plane in the X-ray diffraction peak has β-cobalt hydroxide of 0.3 or more on the surface of the nickel hydroxide active material. It can be seen that the nickel electrode has a higher effect of improving the energy density than the nickel electrode of Comparative Example D in which cobalt is present as a solid solution in the nickel hydroxide active material.
The X-ray diffraction described above was performed using CuKα radiation, and the measurement conditions were a tube voltage of 30 kV, a tube current of 12.5 mA, and a scanning speed of 2 deg / min.
[0033]
As described above, in the present invention, β-cobalt hydroxide having an X-ray diffraction peak (1, 0, 1) plane having a half width of 0.3 or more is applied to the surface of a substrate filled with a nickel hydroxide active material. As it is formed, the highly active cobalt hydroxide adheres uniformly to the electrode surface, effectively conducting the oxidation reaction from cobalt hydroxide to cobalt oxyhydroxide during charging. A matrix can be formed, and the active material utilization rate is improved. Further, if the amount of cobalt hydroxide in the layer mainly composed of cobalt hydroxide formed on the electrode surface is 70% by weight or more, the conductivity of the nickel electrode can be sufficiently increased. , A nickel electrode having a large value can be obtained.
[0034]
In order to obtain β-cobalt hydroxide having a half-width of the X-ray diffraction peak (1, 0, 1) plane of 0.3 or more in each of the above-described examples, a substrate filled with a nickel hydroxide active material was used. In the case of immersion in cobalt nitrate, it was realized by setting the temperature of the alkali treatment solution composed of sodium hydroxide to 25 ° C., or by using cobalt acetate as a starting material for cobalt hydroxide, By adjusting the concentration of the alkali treatment solution, β-cobalt hydroxide having a half width of the X-ray diffraction peak (1, 0, 1) plane of 0.3 or more can be obtained. As a starting material for cobalt hydroxide, in addition to cobalt nitrate and cobalt acetate, an organic acid cobalt such as cobalt formate, cobalt oxalate, and cobalt phosphate or a cobalt weak acid salt is used, and the cobalt liquid immersion temperature is adjusted. , Β-cobalt hydroxide having a half width of the X-ray diffraction peak (1, 0, 1) plane of 0.3 or more can be obtained.
[0035]
In each of the embodiments described above, the example of the sintered nickel electrode is described. However, the nickel electrode of the present invention can be applied to a non-sintered nickel electrode such as a paste type.
[Brief description of the drawings]
FIG. 1 is a view showing the relationship between the half-value width of the X-ray diffraction peak (1, 0, 1) plane of cobalt hydroxide and the energy density of a positive electrode active material.
FIG. 2 is a diagram showing a relationship between a ratio of cobalt hydroxide in a layer mainly composed of cobalt hydroxide of a surface layer of a nickel electrode and an energy density of a positive electrode active material.
FIG. 3 is a diagram showing the relationship between the amount of cobalt added and the energy density ratio of a positive electrode active material.

Claims (4)

A nickel electrode for an alkaline storage battery including a positive electrode active material containing nickel hydroxide as a main component,
A layer mainly composed of β-cobalt hydroxide having a half width of a peak corresponding to the (1,0,1) plane in X-ray diffraction of 0.3 or more is formed on the surface of the nickel electrode holding the positive electrode active material. A nickel electrode for an alkaline storage battery, comprising: a nickel electrode; The nickel electrode for an alkaline storage battery according to claim 1, wherein the layer mainly composed of β-cobalt hydroxide is a layer containing 70% by weight or more of β-cobalt hydroxide. A method for producing a nickel electrode for an alkaline storage battery including a positive electrode active material containing nickel hydroxide as a main component,
And active material holding step for holding the positive electrode active material mainly composed of nickel hydroxide electrode comprising an active material retainer,
And impregnating step of holding a cobalt compound on the surface of the active material holding step by the positive electrode active material of the electrode obtained by holding the by immersing in an aqueous solution containing a cobalt compound the electrodes,
The cobalt compound held on the surface of the electrode by the impregnation step is subjected to alkali treatment, and β-hydroxylation in which the half width of a peak corresponding to the (1,0,1) plane in X-ray diffraction is 0.3 or more. A method for producing a nickel electrode for an alkaline storage battery, comprising: an alkali treatment step of substituting with cobalt. 4. The method according to claim 3, wherein the cobalt compound is selected from a strong acid salt such as cobalt nitrate, or any one of a cobalt weak acid salt composed of cobalt oxalate, cobalt phosphate, cobalt acetate and cobalt formate, and cobalt organic acid. A method for producing a nickel electrode for an alkaline storage battery according to the above.

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