JP5224581B2 - Nickel metal hydride storage battery - Google Patents

Description

  The present invention relates to a nickel metal hydride storage battery using a hydrogen storage alloy as a negative electrode material.

  Nickel metal hydride storage batteries using a hydrogen storage alloy as a negative electrode material are (a) high capacity, (b) strong against overcharge and overdischarge, (c) capable of high-efficiency charge / discharge, (d ) It has features such as cleanliness and is used in various applications.

As a negative electrode material for such a nickel metal hydride storage battery, an AB ₅ rare earth-Ni alloy having a CaCu ₅ type crystal structure that exhibits excellent cycle characteristics has been put into practical use. However, when the AB ₅ rare earth-Ni alloy is used as an electrode material, the discharge capacity is about 300 mAh / g, and it is difficult to further improve the discharge capacity using the alloy. It has become.

On the other hand, attention has been focused on rare -Mg-Ni-based alloy as a new hydrogen absorbing alloy, the use of such a rare earth--Mg-Ni based alloy as an electrode material, the discharge capacity obtained above the AB ₅ type alloy (Patent Document 1 etc.).
JP-A-11-323469

  According to the researches of the present inventors, among such rare earth-Mg—Ni-based alloys, in particular, a structure in which the crystal phase constituting the alloy is laminated in the C-axis direction of the crystal structure (hereinafter simply referred to as “rear structure”). It has been found that a hydrogen storage alloy having a “C-axis laminated structure” can exhibit a higher discharge capacity than a rare earth-Mg—Ni-based hydrogen storage alloy having no C-axis laminated structure.

  However, as a result of further research on a special rare earth-Mg-Ni alloy having such a C-axis laminated structure, the pressure at which the alloy releases hydrogen (hereinafter also referred to as hydrogen equilibrium pressure) A problem has been found that, depending on the amount of hydrogen occluded in the alloy (hereinafter also referred to as occluded hydrogen amount), the hydrogen equilibrium pressure varies greatly as the occluded hydrogen amount changes. In other words, since the range of the hydrogen equilibrium pressure that can be used in the nickel-metal hydride storage battery is limited, the amount of stored hydrogen that can be used for the electrode reaction is reduced in the nickel-metal hydride battery that has a hydrogen storage alloy with a large fluctuation in the hydrogen equilibrium pressure. It becomes a battery with a small discharge capacity.

  Therefore, the present invention suppresses, as much as possible, the fluctuation of the hydrogen equilibrium pressure depending on the amount of stored hydrogen in a nickel-metal hydride storage battery using a rare earth-Mg—Ni alloy having a C-axis stacking structure. One object is to provide a nickel metal hydride storage battery having a large chemical capacity.

  As a result of intensive studies by the present inventors to solve the above problems, 3B group elements (excluding Al) and 4B group are compared with rare earth-Mg-Ni based hydrogen storage alloys having a C-axis stacked structure. By adding either the element or the group 5B element, it was found that the fluctuation of the hydrogen equilibrium pressure depending on the amount of stored hydrogen can be greatly reduced and the hydrogen storage capacity can be increased, and the present invention has been conceived. It was.

  That is, the present invention is a nickel metal hydride storage battery including a negative electrode containing a La—Mg—Ni-based hydrogen storage alloy, wherein the hydrogen storage alloy has a plurality of crystal phases stacked in the C-axis direction of the crystal structure. The hydrogen storage alloy has a laminated structure, and contains one or more elements selected from the group consisting of group 3B elements (excluding Al), group 4B elements, and group 5B elements. A nickel-metal hydride storage battery is provided.

Further, the present invention is pre-SL group 3B element is indium, the Group 4B element is tin, the nickel-metal hydride storage battery, wherein the group 5B element is either one or both of antimony and bismuth Is to provide.

The La—Mg—Ni-based hydrogen storage alloy includes rare earth elements, Mg, and Ni, and the number of Ni atoms is larger than three times the total of the number of rare earth elements and the number of Mg atoms. In the present invention, one or more elements selected from the group consisting of group 3B elements (excluding Al), group 4B elements and group 5B elements are added. Therefore, a part of Ni is substituted with these additive elements.
In particular, it is a La—Mg—Ni-based hydrogen storage alloy having a stacked structure in which a plurality of crystal phases are stacked in the C-axis direction of the crystal structure, and includes a group 3B element (excluding Al), a group 4B element, and a group 5B The composition containing one or more elements selected from the group consisting of elements has a composition of the following general formula R1 _v R2 _x R3 _y R4 _z
(Where R1 is one or more elements selected from the group consisting of Y and rare earth elements, and R2 is one or more elements selected from the group consisting of Mg, Ca, Sr, and Ba) Element, R3 is one or more elements selected from the group consisting of Ni, Co, Cu, Mn, Al, Cr, Fe, Zn, V, Nb, Ta, Ti, Zr and Hf, and R4 is Al One or more elements selected from the group consisting of Group 3B elements, Group 4B elements and Group 5B elements, and v, x, y and z are 15 ≦ v ≦ 19 and 2 ≦ x ≦ 6, respectively. 76 ≦ y ≦ 80, 0.5 ≦ z ≦ 2.5, and v + x + y + z = 100.)
The alloy represented by can be used suitably.

  In the present invention, the atomic percent refers to the percentage of the number of specific atoms with respect to the total number of atoms present. Thus, for example, an alloy containing 1 atomic percent of calcium means a ratio that includes 1 calcium atom out of 100 atoms in the alloy.

According to the present invention, in a La—Mg—Ni-based hydrogen storage alloy having a stacked structure in which a plurality of crystal phases are stacked in the C-axis direction of the crystal structure, a 3B group element (excluding Al), a 4B group element, and a 5B By including one or more elements selected from the group consisting of group elements, the difference in hydrogen occupancy energy between different crystal phases stacked in the C-axis direction is reduced, and the amount of occluded hydrogen is reduced. It is presumed that the crystal structure has a suppressed fluctuation of the hydrogen equilibrium pressure due to the change.
If the fluctuation of the hydrogen equilibrium pressure due to the change in the amount of stored hydrogen is suppressed, the hydrogen stored in the alloy can be used effectively. As a result, the electrochemical capacity of the battery using the alloy is reduced. Can be increased.

  As described above, according to the nickel metal hydride storage battery of the present invention, the excellent characteristics of the La—Mg—Ni based hydrogen storage alloy are exhibited, and at the same time, due to the disadvantages of the La—Mg—Ni based hydrogen storage alloy. The fluctuation of the existing hydrogen equilibrium pressure is reduced, and a highly efficient battery capable of efficiently using the stored hydrogen is provided.

  The nickel-metal hydride storage battery according to the present invention is a nickel-metal hydride storage battery including a negative electrode containing La—Mg—Ni-based hydrogen storage alloy particles, in which a plurality of crystal phases are stacked in the C-axis direction of the crystal structure. And the hydrogen storage alloy is one or more elements selected from the group consisting of group 3B elements (excluding Al), group 4B elements and group 5B elements (hereinafter also referred to as additive elements). ).

In the present invention, the crystal phase stacked in the C-axis direction includes a crystal phase having a hexagonal Pr ₅ Co ₁₉ type crystal structure (hereinafter also simply referred to as Pr ₅ Co ₁₉ phase), a rhombohedral Ce ₅ Co ₁₉ type. A crystal phase having a crystal structure (hereinafter also simply referred to as Ce ₅ Co ₁₉ phase), a crystal phase having a hexagonal Ce ₂ Ni ₇ type crystal structure (hereinafter also simply referred to as Ce ₂ Ni ₇ phase), and Gd ₂ Co Examples thereof include a crystal phase having a _7- type crystal structure.

Here, the Pr ₅ Co ₁₉ type crystal structure is a crystal structure in which three AB ₅ units are inserted between A ₂ B ₄ units, and the Ce ₅ Co ₁₉ type crystal structure is an A ₂ B ₄ unit. In the meantime, it is a crystal structure in which 3 units of AB ₅ units are inserted, and the Ce ₂ Ni ₇ type crystal structure is a crystal structure in which 2 units of AB ₅ units are inserted between A ₂ B ₄ units, The Gd ₂ Co _{7 type} crystal structure is a crystal structure in which two AB ₅ units are inserted between A ₂ B ₄ units.
The A ₂ B ₄ unit is a crystal lattice having a hexagonal MgZn ₂ type crystal structure (C14 structure) or a hexagonal MgCu ₂ type crystal structure (C15 structure), and the AB ₅ unit is a hexagonal CaCu ₅ unit. It is a crystal lattice with a type crystal structure.
In general, A represents any element selected from the group consisting of rare earth elements and Mg, and B represents any element selected from the group consisting of transition metal elements and Al.

  The crystal phase having each crystal structure can be identified by, for example, performing X-ray diffraction measurement on the pulverized alloy powder and analyzing the obtained X-ray diffraction pattern by the Rietveld method. .

Examples of the group 3B element other than aluminum (Al), Ru with Lee indium (an In).
When indium (In) is used, fluctuations in the hydrogen equilibrium pressure due to the amount of occluded hydrogen are more effectively suppressed than when other 3B group elements are used.
In addition, although elements other than aluminum are mentioned as a 3B group element used by this invention, it is not the intention which excludes aluminum. Although aluminum has been conventionally used as a constituent element of a hydrogen storage alloy, a hydrogen storage alloy containing aluminum can be used in the present invention as well.

Further, examples of the Group 4B elements, Ru using the scan's (Sn).
When tin (Sn) is used, fluctuations in the hydrogen equilibrium pressure due to the amount of occluded hydrogen are more effectively suppressed as compared with the case where other group 4B elements are used.

Further, examples of the Group 5B elements, A Nchimon (Sb), Ru using bismuth (Bi).
When antimony (Sb) and bismuth (Bi) are used, fluctuations in the hydrogen equilibrium pressure due to the amount of occluded hydrogen are more effectively suppressed than when other 5B group elements are used. Become.

The addition amount of these additive elements is preferably 0.5 atomic percent or more and 2.5 atomic percent or less, as described above as z meaning the content ratio of R4 in the general formula, and 0.7 atomic percent. % To 2.1 atomic% or more is more preferable.
By making the addition amount 0.5 atomic% or more, the effect of suppressing the fluctuation of the hydrogen equilibrium pressure by the additive element can be more easily exerted, and by making the addition amount 2.5 atomic% or less, the CaCu ₅ type crystal The generation amount of the structural phase can be reduced and the discharge capacity can be increased.

  Further, from the viewpoint of facilitating solid solution of the additive element in the alloy, the amount of Mg added is preferably 6.0 atomic percent or less, and 2.5 atomic percent or more and 4.2 atomic percent or less. Is more preferable.

Furthermore, the La—Mg—Ni-based hydrogen storage alloy used in the present invention preferably has an electron concentration of 0.67 to 0.82, more preferably 0.72 to 0.80, and still more preferably 0.8. Elements may be blended so as to have an electron concentration of 72 or more and 0.76 or less.
If the electron concentration is in the above range, the segregation of Mg and the above additive elements is suppressed, the lattice constituting the laminated structure is stably generated, and the discharge capacity is increased.

  The electron concentration means an average value of the number of valence electrons of atoms contained in the crystal lattice, and the number of valence electrons of each atom is obtained using the following values. That is, Y and rare earth elements = 3, Mg, Ca, Sr and Ba = 2, Ni, Co, Mn, Fe = 0, Cu = 1, Zn = 2, Cr = 6, V, Nb, Ta = 5, Ti , Zr, Hf = 4, Group 3B element = 3, Group 4B element = 4, Group 5B element = 5.

  The La—Mg—Ni-based hydrogen storage alloy used in the present invention contains a rare earth element, Mg, Ni and the additive element, and the total number of Ni atoms and additive elements is the number of rare earth elements and Mg atoms. It means an alloy that is greater than 3 times the total number and less than 5 times.

The composition of the alloy has the following general formula R1 _v R2 _x R3 _y R4 _z
An alloy represented by
Here, in the above general formula, R1 is one or more elements selected from the group consisting of Y and rare earth elements, preferably a group consisting of La, Ce, Pr, Nd, Sm and Y One or more elements selected from the above.
R2 is one or more elements selected from the group consisting of Mg, Ca, Sr, and Ba, preferably at least one element of Mg or Ca.
R3 is one or more elements selected from the group consisting of Ni, Co, Cu, Mn, Al, Cr, Fe, Zn, V, Nb, Ta, Ti, Zr and Hf, preferably Ni , One or more elements selected from the group consisting of Co and Al.
R4 is, 3B group elements except Al, be one or more elements selected from the group consisting of Group 4B elements and Group 5B elements are selected from the group consisting of an In, Sn, Sb and Bi One or more elements.

V, x, y and z are numbers satisfying v + x + y + z = 100,
v satisfies 15.0 ≦ v ≦ 19.0, preferably 16.7 ≦ v ≦ 18.6, and x satisfies 2.0 ≦ x ≦ 6.0, preferably 2 0.5 ≦ x ≦ 4.2, y satisfies 76.0 ≦ y ≦ 80.0, preferably 76.0 ≦ y ≦ 79.3, and z is 0 0.5 ≦ z ≦ 2.5, preferably 0.7 ≦ z ≦ 2.1.

  In particular, in the present invention, an alloy satisfying 3.3 ≦ (y + z) / (v + x) ≦ 3.9 in the composition can be used more suitably. By using an alloy having such a composition, hydrogen can be reversibly occluded and released near normal temperature and pressure, and there is an effect that a high hydrogen storage capacity is exhibited. Furthermore, it is more preferable to satisfy 3.58 ≦ (y + z) / (v + x) ≦ 3.82, and by using an alloy having such a composition, the above effect becomes more remarkable.

Next, the manufacturing method of the nickel hydride storage battery which concerns on this invention is demonstrated.
First, a method for producing a hydrogen storage alloy as one embodiment includes a melting step of melting an alloy raw material blended to have a predetermined composition ratio as described above, and cooling the molten alloy raw material at 1000 K / second or more. A cooling step of rapidly solidifying at a rate, and an annealing step of annealing the cooled alloy in a pressurized inert gas atmosphere in a temperature range of 860 ° C. or higher and 1000 ° C. or lower.

More specifically, first, a predetermined amount of raw material ingot (alloy raw material) is weighed based on the chemical composition of the target hydrogen storage alloy.
In the melting step, the alloy raw material is put in a crucible and heated to, for example, 1200 ° C. or higher and 1600 ° C. or lower in an inert gas atmosphere or in a vacuum to melt the alloy raw material.

  In the cooling step, the molten alloy material is cooled and solidified. The cooling rate is preferably 1000 K / second or more (also called rapid cooling). By rapidly cooling at 1000 K / second or more, there is an effect that the alloy composition is refined and homogenized. The cooling rate can be set in a range of 1000000 K / second or less.

  As the cooling method, specifically, a melt spinning method having a cooling rate of 100,000 K / second or more, a gas atomizing method having a cooling rate of about 10,000 K / second, or the like can be preferably used.

  In the annealing step, heating is performed at 860 ° C. or higher and 1000 ° C. or lower using, for example, an electric furnace in a pressurized state under an inert gas atmosphere. The pressurizing condition is preferably 0.2 MPa (gauge pressure) or more and 1.0 MPa (gauge pressure) or less. Moreover, it is preferable that the processing time in this annealing process shall be 3 hours or more and 50 hours or less.

  The hydrogen storage alloy thus obtained tends to have a stacked structure in which a plurality of crystal phases are stacked in the C-axis direction of the crystal structure. In particular, by using the alloy raw material as described above, the hydrogen storage alloy The occlusion alloy contains one or more elements selected from the group consisting of group 3B elements (excluding Al), group 4B elements and group 5B elements.

The hydrogen storage alloy electrode according to the present invention comprises, for example, a hydrogen storage alloy produced as described above as a hydrogen storage medium. When the hydrogen storage alloy is used for an electrode as a hydrogen storage medium, the hydrogen storage alloy is preferably used after being pulverized.
The hydrogen storage alloy may be pulverized at the time of electrode fabrication either before or after annealing, but since the surface area is increased by pulverization, it is desirable to pulverize after annealing from the viewpoint of preventing surface oxidation of the alloy. The pulverization is preferably performed in an inert atmosphere to prevent oxidation of the alloy surface.
For the pulverization, for example, mechanical pulverization or hydrogenation pulverization is used.

  The hydrogen storage alloy electrode can be produced by mixing the hydrogen storage alloy powder obtained as described above with a binder such as a resin composition or a rubber composition and press-molding it into a predetermined shape. Then, by using the hydrogen storage alloy electrode as a negative electrode, a separately prepared nickel hydroxide electrode or the like as a positive electrode, and filling a potassium hydroxide aqueous solution or the like as an electrolyte, a nickel metal hydride storage battery according to the present invention can be manufactured. it can.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1
Preparation of La-Mg-Ni-based hydrogen storage alloy The raw material ingot was weighed into a crucible so that the chemical composition would be La _13.8 Pr _4.2 Mg _2.9 Ni _70.8 Al _3.1 In _1.0, and high-frequency melted in a reduced pressure argon gas atmosphere The material was melted by heating to 1500 ° C. using a furnace. After melting, it was quenched by applying a melt spinning method to solidify the alloy.
Next, after heat-treating the obtained alloy at 910 ° C. in an argon gas atmosphere pressurized to 0.2 MPa (gauge pressure, the same applies hereinafter), the obtained hydrogen storage alloy was pulverized and averaged A hydrogen storage alloy powder having a particle size (D50) of 20 μm was obtained.

Measurement of crystal structure and calculation of existence ratio The obtained hydrogen storage alloy powder was measured under the conditions of 40 kV, 100 mA (Cu tube) using an X-ray diffractometer (manufactured by Bruker AXS, product number M06XCE). Further, as a structural analysis, an analysis by a Rietveld method (analysis software: RIETRAN 2000) was performed to confirm whether or not it was a C-axis laminate.

Measurement of electrochemical capacity using nickel-metal hydride storage battery (open-type cell) 1) Preparation of electrode An open-type nickel-metal hydride storage battery was manufactured by using the hydrogen storage alloy powder as a negative electrode. Specifically, after adding 3 parts by weight of nickel powder (INCO, # 210) to 100 parts by weight of the hydrogen storage alloy powder obtained as described above, the thickener (methylcellulose) is dissolved. Then, 1.5 parts by weight of a binder (styrene butadiene rubber) is added to form a paste, which is applied to both sides of a nickel plated perforated steel plate (opening ratio 60%) having a thickness of 45 μm and dried. Then, it was pressed to a thickness of 0.36 mm to obtain a negative electrode. On the other hand, as the positive electrode, an excess capacity sintered nickel hydroxide electrode was used.

2) Production of open-type battery The electrodes produced as described above were sandwiched between positive electrodes via separators, and these electrodes were fixed with bolts so that a pressure of 1 kgf / cm ² was applied, and assembled into an open-type cell. As the electrolytic solution, a mixed solution composed of a 6.8 mol / L KOH solution and a 0.8 mol / L LiOH solution was used.

3-1) Measurement of hydrogen equilibrium pressure The hydrogen equilibrium pressure was determined by measuring a P (equilibrium hydrogen pressure) -C (hydrogen concentration) -T (temperature) curve for the produced open battery. Specifically, a technique called volumetric method or Siebelz method is used to change the hydrogen gas pressure applied to the sample at a constant temperature, measure the equilibrium pressure, and measure the amount of hydrogen reacted from the gas volume and pressure change. I went there. The measurement method is defined in JIS H7201 (1991) “Measurement Method of Pressure-Composition Isotherm (PCT Curve) of Hydrogen Storage Alloy”. In actual measurement, a pressure-composition isotherm (PCT curve) was measured at 80 ° C. using a PCT device (automatic Siebelz device) manufactured by Suzuki Shokan. The measurement results are shown in Table 1.

3-2) Evaluation by Hydrogen _{Equilibrium Pressure The} hydrogen equilibrium pressure (MPa) when the amount of occluded hydrogen is H / M (number of hydrogen atoms occluded per atom of alloy metal) = 0.1 is _defined as P _eq1 and H / _M The hydrogen equilibrium pressure when M = 0.8 is P _eq2, and the amount of change in the hydrogen equilibrium pressure when the amount of occlusion changes from H / M = 0.1 to H / M = 0.8, that is, hydrogen The slope of the equilibrium pressure was calculated as log (P _eq2 / P _eq1 ). The calculation results are shown in Table 1.

4) Measurement of electrochemical capacity The produced open-type battery is put in a 20 ° C. water tank, charged at 150% at 0.1 ItA, and the final voltage becomes 0.6 V (vs. Hg / HgO) at 0.2 ItA. Discharging was repeated 10 cycles. The maximum discharge capacity was defined as electrochemical capacity [mAh / g]. The measurement results are shown in Table 1.

(Examples 2-16 and Comparative Examples 1-20)
Hydrogen storage alloy particles having a raw material composition as shown in Table 1 below, specifically, a La—Mg—Ni-based hydrogen storage alloy having a C-axis stacked structure, and La—Mg—Ni not having a C-axis stacked structure A hydrogen storage alloy and an AB ₅ hydrogen storage alloy were prepared, and the hydrogen equilibrium pressure and electrochemical capacity of the nickel metal hydride storage battery were measured in the same manner as in Example 1. The obtained results are shown in Table 1.

  For each hydrogen storage alloy, the relationship between the amount of R4 element added and the electrochemical capacity was plotted on a graph. The graph is shown in FIG.

  As shown in Table 1 and FIG. 1, in a La—Mg—Ni-based hydrogen storage alloy having a C-axis stacked structure, a nickel-metal hydride storage battery using the alloy is prepared by adding the R4 element to produce the alloy. It can be seen that it has a tendency to increase the electrochemical capacity of This is considered to be due to the fact that in the La—Mg—Ni-based hydrogen storage alloy having a C-axis stacked structure, the hydrogen equilibrium pressure hardly changes with the amount of stored hydrogen.

More specifically, according to Table 1, when the value of log (P _eq2 / P _eq1 ) indicating the degree of change in the hydrogen equilibrium pressure with respect to the change in the amount of stored hydrogen is less than 1, the electric power of the nickel-metal hydride storage battery It can be seen that the chemical capacity is large.
This means that when the degree of change in the hydrogen equilibrium pressure accompanying the change in the amount of stored hydrogen is log (P _eq2 / P _eq1 ) <1, the increase in electrochemical capacity is significant. .
Further, according to Table 1, it is recognized that the electrochemical capacity of the nickel-metal hydride storage battery is large when the value of P _eq1 is 0.03 or more. This phenomenon is due to the fact that the pressure range that can be used electrochemically is expanded by setting P _eq1 to 0.03 MPa or more. As described above, in the present invention, in addition to suppressing the degree of change in the hydrogen equilibrium pressure accompanying the change in the amount of stored hydrogen, the electrochemical capacity is reduced by _setting the value of P _eq1 to 0.03 or more. It can be further increased.
As described above, when the degree of fluctuation of the hydrogen equilibrium pressure is log (P _eq2 / P _eq1 ) <1, and P _eq1 ≧ 0.03, the hydrogen is _maintained throughout the charge / discharge reaction period compared to the conventional case. Since the equilibrium pressure is maintained at a high level, the discharge performance is more efficient than the conventional one.

  Here, in Example 3 in which Sb was added to a La—Mg—Ni-based hydrogen storage alloy having a C-axis laminated structure, Example 4 in which Bi was also added, and Comparative Example 1 in which nothing was added, the storage hydrogen The change in hydrogen equilibrium pressure with respect to quantity was measured. The results are shown in FIG.

As shown in FIG. 2, in comparison with Comparative Example 1 in which nothing is added, in the example in which Sb or Bi as the R4 element is added, the slope of the hydrogen equilibrium pressure is small, and the fluctuation of the amount of occluded hydrogen is reduced. It can be seen that the hydrogen equilibrium pressure is difficult to change.
It is also recognized that the hydrogen equilibrium pressure of the example at H / M = 0.1 is larger than the hydrogen equilibrium pressure of the comparative example.

The graph which plotted the relationship between the addition amount of R4 element, and electrochemical capacity | capacitance. Example 3 in which Sb was added to a La—Mg—Ni-based hydrogen storage alloy having a C-axis laminated structure, Example 4 in which Bi was also added, and Comparative Example 1 in which nothing was added, The graph which showed the measurement result of equilibrium pressure.

Claims (1)

A nickel-metal hydride storage battery comprising a negative electrode containing a La-Mg-Ni-based hydrogen storage alloy,
The hydrogen storage alloy has a laminated structure in which a plurality of crystal phases are laminated in the C-axis direction of the crystal structure, and the hydrogen storage alloy is indium, tin, and one or both of antimony and bismuth. A nickel-metal hydride storage battery comprising one or more elements selected from the group consisting of:

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