Nickel electrode for alkaline secondary battery and alkaline secondary battery comprising the same

Abstract

A battery (2) is provided with a container (10) and an electrode group (6) that is housed together with an alkaline electrolyte (4) in the container (10), the electrode group (6) including a nickel electrode (14) as a positive electrode and a negative electrode (12) combined via a separator (8), the nickel electrode (14) being provided with a positive electrode core material and a positive electrode mixture filled in the positive electrode core material, the positive electrode mixture including nickel hydroxide as a positive electrode active material, the nickel hydroxide containing a sulfate, the weight ratio of the S component contained in the sulfate with respect to the Ni component in the nickel hydroxide being 0.28% or more and 1.50% or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a nickel electrode for an alkaline secondary battery, and an alkaline secondary battery comprising the same. BACKGROUND

[0002] As a positive electrode used in an alkaline secondary battery, a nickel electrode is generally used. As the nickel electrode, a non-sintered nickel electrode is widely used. The non-sintered nickel electrode is manufactured, for example, by filling a positive electrode active material slurry containing nickel hydroxide particles as a positive electrode active material in a foamed nickel (positive electrode core material) of a three-dimensional network structure, drying, and then performing press molding. The non-sintered nickel electrode can increase the filling amount of nickel hydroxide, and thus has a large capacity per unit volume, which contributes to the increase in capacity of the alkaline secondary battery.

[0003] The alkaline secondary battery in which the non-sintered nickel electrode is used to achieve the increase in capacity has been used for various electronic devices, electrical devices, hybrid electric vehicles, and the like.

[0004] However, when the alkaline secondary battery is repeatedly charged and discharged, the actual usable charge capacity decreases due to so-called memory effect. In particular, when shallow depth discharging is repeatedly performed, the discharge voltage decreases at the boundary of the depth of discharge, and the discharge capacity decreases.

[0005] As a method for eliminating such memory effect, it is known that full discharge is performed after full charge, and so-called refresh charge / discharge is performed (for example, refer to Patent Document 1 and the like).

[0006] PRIOR ART DOCUMENTS

[0007] PATENT DOCUMENTS

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-095167 SUMMARY OF THE INVENTION

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] However, the above-described refresh charge / discharge does not prevent the occurrence of memory effect, and thus cannot be said to be a complete solution.

[0011] Further, in the use for hybrid electric vehicles and the like, in order to suppress overcharging and overdischarging, upper and lower limits are set for the state of charge (SOC). Therefore, it is difficult to perform refresh charge / discharge from the beginning, and it is difficult to eliminate, prevent, or suppress memory effect.

[0012] Therefore, it is desirable to develop an alkaline secondary battery in which memory effect is less likely to occur.

[0013] The present application has been achieved based on the above-described circumstances, and has an object to provide a nickel electrode for alkaline secondary batteries capable of reducing the influence of memory effect, and an alkaline secondary battery including the nickel electrode.

[0014] Technical solution adopted to solve technical problem

[0015] According to the present application, it is possible to provide a nickel electrode for alkaline secondary batteries, which has a positive electrode core material and a positive electrode mixture filled in the positive electrode core material, the positive electrode mixture including nickel hydroxide as a positive electrode active material, the nickel hydroxide containing a sulfate, a weight ratio of an S component contained in the sulfate with respect to a Ni component in the nickel hydroxide being 0.28% or more and 1.50% or less.

[0016] The nickel hydroxide preferably includes Al as a solid solution element.

[0017] Further, the present application provides an alkaline secondary battery including a container, and an electrode group that is housed together with an alkaline electrolyte in the container, the electrode group including a positive electrode and a negative electrode that are combined via a separator, the positive electrode being any of the nickel electrodes for alkaline secondary batteries described above.

[0018] The negative electrode preferably includes a hydrogen storage alloy.

[0019] Effects of the Invention

[0020] The nickel electrode for alkaline secondary batteries of the present application has a positive electrode core material and a positive electrode mixture filled in the positive electrode core material, the positive electrode mixture including nickel hydroxide as a positive electrode active material, the nickel hydroxide containing a sulfate, a weight ratio of an S component contained in the sulfate with respect to a Ni component in the nickel hydroxide being 0.28% or more and 1.50% or less. By making the weight ratio of the S component contained in the sulfate with respect to the Ni component in the nickel hydroxide 0.28% or more and 1.50% or less, it is possible to reduce the influence of memory effect of the alkaline secondary battery. Therefore, according to the present application, it is possible to provide a nickel electrode for alkaline secondary batteries capable of reducing the influence of memory effect, and an alkaline secondary battery including the nickel electrode.

[0021] Brief Description of the Drawings

[0022] Figure 1 is a cross-sectional view schematically showing a nickel-hydrogen secondary battery of an embodiment of the present application.

[0023] Figure 2 is a graph showing discharge curves before and after a partial charge-discharge test of Example 1.

[0024] Figure 3 is a graph showing discharge curves before and after a partial charge-discharge test of Comparative Example 1.

[0025] Figure 4 The accompanying photograph is a secondary electron image based on SEM of the positive electrode active material powder of Example 2.

[0026] Figure 5 This is a graph showing the relationship between the ratio of S to Ni (S / Ni) and the voltage drop (ΔV) during residual discharge. Detailed Implementation

[0027] Hereinafter, the alkaline secondary battery to which the present invention is applicable will be described with reference to the accompanying drawings. There is no particular limitation on the alkaline secondary battery to which the present invention is applicable; for example, the present invention can be applied to... Figure 1 The following explanation uses the single-plate nickel-metal hydride secondary battery (hereinafter referred to as battery) 2 as an example.

[0028] like Figure 1 As shown, the battery 2 includes a sealable acrylic resin container 10. An alkaline electrolyte 4 and an electrode assembly 6 are disposed within the container 10. The alkaline electrolyte 4 can be a commonly used alkaline electrolyte in nickel-metal hydride secondary batteries. For example, an alkaline electrolyte containing KOH, NaOH, and LiOH as solutes is preferred.

[0029] Electrode assembly 6 is formed by sandwiching a positive electrode (nickel electrode) 14 between two negative electrodes 12 insulated by a diaphragm 8. A positive electrode lead 16 is mounted on the positive electrode 14, extending to the outside of the container 10 through a positive electrode lead through-hole 20 provided on the upper wall 18 of the container 10. Similarly, a negative electrode lead 22 is mounted on the negative electrode 12, extending to the outside of the container 10 through a negative electrode lead through-hole 24 provided on the upper wall 18 of the container 10. The positive electrode lead through-hole 20 and the negative electrode lead through-hole 24 maintain liquid tightness.

[0030] A threaded hole 28 is provided on one side wall 26 of the container 10, and a pressure screw 30 is provided that mates with the threaded hole 28. An acrylic resin pressure plate 32 is provided at the end of the pressure screw 30. This pressure plate 32 clamps the electrode assembly 6 between itself and the other side wall 32 of the container 10. Here, when the pressure screw 30 is rotated and pushed into the container 10, pressure is applied to the electrode assembly 6 through the pressure plate 32. Furthermore, the threaded hole 28 is kept liquid-tight.

[0031] Next, the negative electrode 12 will be explained in detail.

[0032] The negative electrode 12 has a strip-shaped conductive negative electrode core, in which a negative electrode agent is retained.

[0033] As the negative core, for example, punched metal made of a sheet metal material in which through-holes are distributed, or a sintered substrate obtained by die forming and sintering of metal powder can be used. The negative electrode mixture is not only filled in the through-holes of the negative core, but also formed in layers and held on both surfaces of the negative core.

[0034] The negative electrode mixture contains hydrogen storage alloy particles capable of storing and releasing hydrogen as a negative electrode active material, a conductive material, and a binder. The binder functions to bond the hydrogen storage alloy particles, the negative electrode additive, and the conductive material to each other, and also functions to bond the negative electrode mixture to the negative core. Here, as the binder, a hydrophilic or hydrophobic polymer or the like can be used, and as the conductive material, carbon black or graphite can be used. In addition, a negative electrode additive can be added as needed.

[0035] As the hydrogen storage alloy in the hydrogen storage alloy particles, there is no particular limitation, and a hydrogen storage alloy used in a typical nickel-hydrogen secondary battery is preferable. More preferably, a rare earth-Mg-Ni-based hydrogen storage alloy is used. The composition of the rare earth-Mg-Ni-based hydrogen storage alloy can be freely selected, but a rare earth-Mg-Ni-based hydrogen storage alloy represented by general formula (I), for example, is preferably used.

[0036] Ln 1-a Mg a Ni b-c-d Al c M d ... (I)

[0037] In general formula (I), Ln represents at least one element selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr, and Ti, M represents at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B, and subscripts a, b, c, and d each represent a number satisfying the relationships of 0.01 ≤ a ≤ 0.30, 2.8 ≤ b ≤ 3.9, 0.05 ≤ c ≤ 0.30, and 0 ≤ d ≤ 0.50.

[0038] Next, the above hydrogen storage alloy particles can be obtained, for example, as follows.

[0039] First, the metal raw materials are weighed and mixed to achieve a prescribed composition, and the mixture is melted with, for example, an induction melting furnace and then cooled to produce an ingot. The obtained ingot is subjected to heat treatment by being held at 900 to 1200°C for 5 to 24 hours in an inert gas atmosphere. Subsequently, the ingot cooled to room temperature is pulverized and sieved to obtain hydrogen storage alloy particles of a desired particle diameter.

[0040] Further, the negative electrode 12 can be produced, for example, as follows.

[0041] First, a hydrogen storage alloy particle aggregate, i.e., hydrogen storage alloy powder, an electrically conductive material, a binder, and water are mixed to produce a negative electrode mixture paste. The resulting negative electrode mixture paste is applied to a negative electrode core material, which is then dried. After drying, the negative electrode core material to which hydrogen storage alloy particles and the like are attached is subjected to roll pressing and cutting. In this way, the negative electrode 12 is produced. In addition, a negative electrode lead 22 is connected to a prescribed position of the negative electrode 12.

[0042] The resulting negative electrode 12 is wrapped with a separator 8. Here, as the material of the separator 8, a material obtained by imparting a hydrophilic functional group to a nonwoven fabric made of a polyamide fiber, or a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene, for example, can be used. Specifically, a nonwoven fabric in which a polyolefin fiber imparted with a sulfonic acid group by sulfonation treatment is used as the main component is preferably used. Here, the sulfonic acid group is imparted by treating the nonwoven fabric with an acid containing a sulfonic acid group such as sulfuric acid or oleum. A battery using the separator 8 containing a fiber having a sulfonic acid group exhibits excellent self-discharge performance.

[0043] Next, the positive electrode 14 will be described in detail.

[0044] The positive electrode 14 includes an electrically conductive positive electrode core material having a porous structure, and a positive electrode mixture held in the pores of the positive electrode core material.

[0045] As such a positive electrode core material, a metal body in the form of a mesh, a sponge, or a fiber to which nickel plating has been performed, or foamed nickel, for example, can be used.

[0046] The positive electrode mixture contains a positive electrode active material, an electrically conductive material, a positive electrode additive, and a binder. The binder functions to bond the positive electrode active material, the electrically conductive material, and the positive electrode additive, and also functions to bond the positive electrode mixture to the positive electrode core material. Here, as the binder, carboxymethyl cellulose, methyl cellulose, a PTFE (polytetrafluoroethylene) dispersion, an HPC (hydroxypropyl cellulose) dispersion, or the like, for example, can be used.

[0047] As the electrically conductive material, one or two or more selected from a cobalt compound such as cobalt oxide (CoO) and cobalt hydroxide (Co(OH)2), and cobalt (Co), for example, can be used. The electrically conductive material is added to the positive electrode mixture as needed, and can be included in the positive electrode mixture in a coated form in which the surface of the positive electrode active material is covered, in addition to a powder form.

[0048] The positive electrode additive is added as needed to improve the characteristics of the positive electrode, and yttrium oxide, zinc oxide, or the like, for example, can be used.

[0049] As the positive electrode active material, nickel hydroxide is used. In addition, sulfate is contained in this nickel hydroxide, and specifically, SO4 is contained. The weight ratio of this sulfate to the Ni component in the nickel hydroxide is preferably set to 14.3% or more and 30% or less.

[0050] Here, the sulfate is generated in the manufacturing process of the nickel hydroxide described below, but since it is not a substance directly involved in the battery reaction, it has been conventionally removed as much as possible. However, the present inventors have earnestly studied to reduce the memory effect of the alkaline secondary battery, and as a result, it has been found that when the sulfate that has been conventionally desired to be reduced as much as possible is contained in a larger amount than conventionally, it has a good effect on reducing the memory effect. Specifically, when the S component contained in the sulfate is contained in an amount of 0.28% or more in terms of the weight ratio with respect to the Ni component in the nickel hydroxide, a reduction in the memory effect can be observed. That is, the greater the value of the weight ratio of the S component to the Ni component in the nickel hydroxide than 0.28%, the more the effect of reducing the memory effect can be obtained. However, when the weight ratio of the S component contained in the sulfate to the Ni component in the nickel hydroxide is greater than 1.50%, the capacity of the positive electrode is significantly reduced, and therefore the upper limit of the S component contained in the sulfate is set to 1.50% or less.

[0051] As the manufacturing method of the positive electrode active material, for example, it can be operated by the following steps.

[0052] First, weighed nickel sulfate is put into water to prepare an aqueous solution containing nickel sulfate. Next, while stirring the obtained aqueous solution, an aqueous sodium hydroxide solution is slowly added to react, thereby precipitating nickel hydroxide particles. Here, it is preferable that Al is solid-solved in the nickel hydroxide. In the case of solid-solution of Al, weighed nickel sulfate and aluminum sulfate to obtain a prescribed composition are put into water to prepare a mixed aqueous solution containing these nickel sulfate and aluminum sulfate.

[0053] Next, while stirring the obtained mixed aqueous solution, an aqueous sodium hydroxide solution is slowly added to react, thereby precipitating particles mainly composed of nickel hydroxide and solid-solved with Al. Thereby, particles of Ni(OH)2are obtained. The particles of Ni(OH)2solid-solved with Al have an α-type crystal structure, and form a large space in the crystal structure, and therefore can contain a large amount of sulfate.

[0054] In addition, it is preferable that Yb, Co, or the like is also solid-solved in the Ni(OH)2. In order to solid-solve these elements, ytterbium sulfate, cobalt sulfate is also added to prepare the above mixed aqueous solution.

[0055] The positive electrode 14 can be manufactured, for example, as follows.

[0056] First, a conductive material, a positive electrode additive, water, and a binder are added to the collection of the positive electrode active material particles, i.e., the positive electrode active material powder obtained above, and mixed to produce a positive electrode mixture slurry. The obtained positive electrode mixture slurry is filled into, for example, foamed nickel, and a drying process is performed. After drying, the foamed nickel filled with the nickel hydroxide particles or the like is rolled and then cut. Thus, the positive electrode 14 carrying the positive electrode mixture is obtained. Further, the positive electrode lead 16 is connected at a prescribed position of the positive electrode 14.

[0057] A predetermined number of the positive electrodes 14 obtained above are prepared, and a prescribed number of the negative electrodes 12 combined with the separators 8 obtained above are prepared. Further, by forming a laminate in a state where one piece of the positive electrode 14 is interposed between two pieces of the negative electrode 12, the electrode group 6 is obtained. This electrode group 6 is disposed between the other side wall 34 and the pressure plate 32 in the container 10. Further, by turning the pressure screw 30, the electrode group 6 is held in the container 10 in a state of being pressed. Next, a prescribed amount of the alkaline electrolyte 4 is injected into the container 10. Then, the container 10 containing the electrode group 6 and the alkaline electrolyte 4 is sealed with a rubber seal not shown. At this time, the positive electrode lead 16 is disposed so as to extend to the outside of the container 10 through the positive electrode lead through-hole 20, and the negative electrode lead 22 is also disposed so as to extend to the outside of the container 10 through the negative electrode lead through-hole 24. Thus, the battery 2 of the present application is obtained. The obtained battery 2 is subjected to an initial activation process to be in a usable state.

[0058] Example

[0059] 1. Manufacture of battery

[0060] (Example 1)

[0061] (1) Manufacture of positive electrode

[0062] Nickel sulfate, aluminum sulfate, and ytterbium sulfate as starting materials were weighed in such a manner as to achieve a prescribed composition. The weighed nickel sulfate, aluminum sulfate, and ytterbium sulfate were added to a 1 mol / L aqueous solution of sulfuric acid to prepare a mixed aqueous solution. While the obtained mixed aqueous solution was stirred, a 10 mol / L aqueous solution of sodium hydroxide was slowly added to the mixed aqueous solution to allow a reaction to proceed, in which the pH was stabilized at 13 to 14, to produce nickel hydroxide particles in which Al and Yb were solid-solved as a main component of nickel hydroxide. Thus, a collection of nickel hydroxide particles in which Al and Yb were solid-solved, i.e., a nickel hydroxide powder (positive electrode active material powder), was obtained.

[0063] A part of the obtained nickel hydroxide was taken as a sample for composition analysis and a sample for crystal structure analysis, and the remainder was used for the manufacture of a positive electrode.

[0064] Here, the sample for the composition analysis was subjected to the composition analysis using a high-frequency inductively coupled plasma (ICP) emission spectroscopic analysis device, and the results confirmed that Ni was 41.9%, Al was 3.81%, Yb was 7.38%, and sulfate (SO4) was 10.20%. From the results, it was confirmed that the ratio of the sulfate (SO4) to Ni in the nickel hydroxide particles was 10.20 / 41.9 = 24.3%. In addition, the sulfate (SO4) was formed from the starting raw materials and the aqueous sulfuric acid solution in the above manufacturing process.

[0065] Next, the sample for the crystal structure analysis was subjected to X-ray diffraction (XRD) analysis. A powder XRD device (MiniFlex600 manufactured by Rigaku Corporation) was used in the analysis. The analysis conditions here were that the X-ray source was CuKa, the tube voltage was 40 kV, the tube current was 15 mA, the scanning rate was 5 degrees / minute, and the step width was 0.02 degrees. From the spectrum of the analysis results, it was confirmed that the nickel hydroxide was Ni(OH)2having an α-type crystal structure.

[0066] Next, 7 parts by weight of a cobalt hydroxide powder, 0.104 parts by weight of a HPC (hydroxypropyl cellulose) powder, 0.28 parts by weight of a PTFE (polytetrafluoroethylene) powder, and 78 parts by weight of water were added to 100 parts by weight of the positive electrode active material powder obtained above, and they were kneaded to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was filled into a sheet-shaped foamed nickel serving as a positive electrode core material. Then, the slurry of the positive electrode mixture filled in the foamed nickel was dried, and then the foamed nickel filled with the positive electrode mixture was roll-pressed to increase the amount of the positive electrode active material per unit volume, and was cut into a square of 30 mm in length and 30 mm in width to obtain a positive electrode (nickel electrode) 14. In addition, the thickness of the positive electrode 14 was 0.80 mm. Furthermore, a positive electrode lead 16 was welded to a part of the positive electrode 14. The capacity of the positive electrode 14 was 300 mAh.

[0067] (2) Manufacture of a negative electrode

[0068] First, La, Sm, Zr, Mg, Ni, and Al were weighed, and a mixture of them in a prescribed ratio was prepared. The obtained mixture was melted in an argon atmosphere using a high-frequency induction melting furnace, and after the melt was poured into a mold, it was cooled to room temperature to serve as an ingot of a hydrogen storage alloy.

[0069] Next, the ingot was subjected to heat treatment at 1000°C for 10 hours in an argon atmosphere. Then, the ingot of the hydrogen storage alloy cooled to room temperature after the heat treatment was mechanically pulverized in an argon atmosphere to obtain a powder composed of hydrogen storage alloy particles. The obtained powder was subjected to sieving to obtain a hydrogen storage alloy powder of a prescribed particle size. The particle size of the particles of the obtained hydrogen storage alloy powder was measured using a laser diffraction scattering particle size distribution measuring device, and as a result, the volume average particle size (MV) of the hydrogen storage alloy particles was 65 μm.

[0070] A sample taken from the hydrogen storage alloy powder was set on a luminescence spectrum analyzing device, and composition analysis was performed by ICP luminescence spectrum analysis. As a result, the composition of the hydrogen storage alloy was (La 0.30 Sm 0.69 Zr 0.01 ) 0.89 Mg 0.11 Ni 3.33 Al 0.17 .

[0071] With respect to 100 parts by weight of the obtained hydrogen storage alloy powder, 0.2 parts by weight of sodium polyacrylate, 0.04 parts by weight of carboxymethyl cellulose, 1.5 parts by weight of a dispersion of a solid content of 50% of styrene-butadiene rubber (SBR), 0.3 parts by weight of carbon black, and 22.4 parts by weight of water were added and kneaded to produce a paste of a negative electrode mixture.

[0072] Next, the negative electrode mixture paste was applied to both faces of an iron-made perforated plate serving as a negative electrode core so as to be uniform and have a constant thickness. The thickness of the perforated plate was 60 μm, and the surface thereof was subjected to nickel plating. In addition, the through holes of the perforated plate were also filled with the negative electrode mixture paste. Thus, an intermediate product of a negative electrode was produced.

[0073] After the paste was dried, the intermediate product of the negative electrode, which retained the hydrogen storage alloy powder and the like, was further roll-pressed to increase the amount of the alloy per unit volume, and then cut into 35 mm in the vertical direction and 35 mm in the horizontal direction to produce a negative electrode 12. Here, the thickness of the negative electrode was 0.25 mm. In addition, the capacity of the negative electrode was 540 mAh.

[0074] (3) Assembly of nickel-hydrogen secondary battery

[0075] One piece of the positive electrode 14 and two pieces of the negative electrode 12 obtained as described above were prepared. The negative electrode 12 was wrapped with a separator 8. The negative electrode 12 wrapped with the separator 8 was arranged on both sides of the positive electrode 14 to be combined to form an electrode group 6. Here, the separator 28 was formed of a non-woven fabric of polypropylene fibers subjected to sulfonation treatment, and the thickness thereof was 0.16 mm (weight per unit area: 55 g / m 2). The electrode group 6 is disposed between the pressing plate 32 and the other side wall 34 in the container 10. Then, the pressing screw 30 is turned to press the electrode group 6 with a torque of 20 kgf-cm.

[0076] On the other hand, an alkaline electrolyte (9.4 N) composed of an aqueous solution containing KOH, NaOH and LiOH was prepared.

[0077] Next, a prescribed amount of the prepared alkaline electrolyte was injected into the container 10. Then, the container 10 was sealed with a rubber seal not shown, and the nickel-hydrogen secondary battery 2 was assembled.

[0078] (4) Initial activation treatment

[0079] For the battery 2, it was left to stand in an environment at a temperature of 60°C for 12 hours. Then, the positive electrode capacity (300 mAh) was set to 1 It, and after charging at 0.02 It for 5 hours, followed by charging at 0.10 It for 15 hours, and then discharging at 0.2 It until the battery voltage reached 1.0 V, the charging and discharging operation was performed once. By this initial activation treatment, the battery 2 was brought to a usable state.

[0080] (Example 2)

[0081] A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that ytterium sulfate was removed from the starting material at the time of manufacturing the positive electrode active material, and the solid-solution element was changed to only Al. In addition, the positive electrode active material in Example 2 was subjected to composition analysis measurement by ICP, and the results were Ni 43.7%, Al 5.02%, and sulfate 9.00%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Example 2 was 9.00 / 43.7 = 20.6%.

[0082] (Example 3)

[0083] A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that ytterium sulfate was removed from the starting material at the time of manufacturing the positive electrode active material, and instead, cobalt sulfate was added, and the solid-solution element was changed to Al and Co. In addition, the positive electrode active material in Example 3 was subjected to composition analysis measurement by ICP, and the results were Ni 42.3%, Al 3.60%, Co 2.57%, and sulfate 6.84%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Example 3 was 6.84 / 42.3 = 16.2%.

[0084] (Example 4)

[0085] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that ytterium sulfate was removed from the starting materials for producing the positive electrode active material, manganese sulfate was added instead, and the solid solution element was changed to Al and Mn. In addition, the positive electrode active material in Example 4 was subjected to composition analysis measurement by ICP, and the results were Ni 44.3%, Al 3.83%, Mn 2.54%, and sulfate 6.72%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Example 4 was 6.72 / 44.3 = 15.2%.

[0086] (Example 5)

[0087] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that ytterium sulfate was removed from the starting materials for producing the positive electrode active material, the solid solution element was changed to only Al, and the amount of Al was reduced to 3.92%, which was less than in Example 1. In addition, the positive electrode active material in Example 5 was subjected to composition analysis measurement by ICP, and the results were Ni 48.7%, Al 3.92%, and sulfate 6.98%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Example 5 was 6.98 / 48.7 = 14.3%.

[0088] (Example 6)

[0089] A nickel-hydrogen secondary battery was produced in the same manner as in Example 3, except that the amount of cobalt sulfate added to the starting materials was adjusted, and the amount of the sulfate was increased to 8.26%, which was more than in Example 3. In addition, the positive electrode active material in Example 6 was subjected to composition analysis measurement by ICP, and the results were Ni 42.6%, Al 3.57%, Co 5.35%, and sulfate 8.26%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Example 6 was 8.26 / 42.6 = 19.4%.

[0090] (Comparative Example 1)

[0091] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that aluminum sulfate and ytterium sulfate were removed from the starting materials for producing the positive electrode active material, cobalt sulfate and zinc sulfate were added instead, and the solid solution element was changed to Co and Zn. In addition, the positive electrode active material in Comparative Example 1 was subjected to composition analysis measurement by ICP, and the results were Ni 53.0%, Co 0.64% (excluding surface Co), Zn 4.36%, and sulfate 0.19%. Therefore, the ratio of the sulfate to Ni in the positive electrode active material of Comparative Example 1 was 0.19 / 53.0 = 0.4%.

[0092] 2. Evaluation of the battery

[0093] (1) Capacity check

[0094] The operation of charging the batteries of Examples 1 to 6 and Comparative Example 1 after the activation treatment at 0.1 It for 16 hours and discharging the batteries at 0.2 It to 1.0 V of the battery voltage was repeated at 25°C until the positive electrode capacity reached the maximum.

[0095] (2) Partial charge and discharge test

[0096] After the positive electrode capacity reached the maximum capacity, the battery was charged at 0.1 It for 12 hours and then completely discharged at 0.1 It (until the battery voltage reached 1.0 V) (initial discharge). Subsequently, the charge and discharge cycle of SOC 50% to 110% was repeated, and the memory effect was intentionally reproduced. Details are as follows.

[0097] First, after charging at 0.11 It for 12 hours, discharging at 1.0 C for 0.5 hours (until the battery voltage became 1.0 V) and charging at 1.0 C for 0.6 hours were repeated 5 times as one cycle of charge and discharge operation. Then, the battery was completely discharged (residual discharge) at 0.1 It (until the battery voltage became 1.0 V).

[0098] For the batteries of Examples 1 to 6 and Comparative Example 1, the battery voltage at the initial discharge, the battery voltage at the residual discharge, and the difference between the battery voltage at the initial discharge and the battery voltage at the residual discharge (hereinafter referred to as the voltage drop ΔV at the residual discharge, or simply ΔV) were calculated, and the values are shown in Table 1. In addition, ΔV was calculated from the difference between the battery voltage at the initial discharge and the battery voltage at the residual discharge at SOC 40% (at a discharge depth of 60%).

[0099] In addition, for Examples 1 and Comparative Example 1, the discharge curve showing the relationship between the battery voltage at the initial discharge and the battery capacity, and the discharge curve showing the relationship between the battery voltage at the residual discharge and the battery capacity are shown in Figure 2 and Figure 3 .

[0100] 3. Analysis of Ni and S

[0101] The batteries of Examples 1 to 6 and Comparative Example 1 after the battery evaluation were disassembled, and the positive electrodes were taken out from the inside, respectively. The taken-out positive electrodes were washed with water and then left in a vacuum dryer for 12 hours to be in a completely dried state. The positive electrodes after the drying treatment were separated into positive electrode core materials and positive electrode active materials using an ultrasonic homogenizer, and then the positive electrode core materials were taken out by passing through a sieve having a pore size of 45 μm, and the positive electrode active material powder was collected. The collected positive electrode active material powder was observed on the surface using a scanning electron microscope (SEM), and at the same time, elemental analysis was performed by energy dispersive X-ray spectroscopy (EDS), that is, elemental analysis was performed by so-called SEM / EDS. The acceleration voltage at this time was 15 KeV.

[0102] According to the SEM image of the analysis result, mapping analysis of the entire area was performed by EDS. At this time, the magnification was set to 1000 times. If it is a magnification of this degree, it is a degree in which several tens of active material particles can be confirmed in the field of view. Here, as an example, the secondary electron image based on SEM of the positive electrode active material powder of Example 2 is shown in FIG. 8. Further, with respect to Examples 1 to 6 and Comparative Example 1, the analysis results for the elements that could be detected are shown in Table 2. In addition, with respect to oxygen and carbon, they were excluded from the analysis targets. Figure 4

[0103] According to the obtained analysis result, the ratio of the S component contained in the sulfate in the particles of the nickel hydroxide (positive electrode active material) to Ni (S / Ni [%]) was found. The obtained results are shown in Table 1 and Table 2.

[0104] Further, the relationship between S / Ni and ΔV shown in Table 1 is shown in FIG. 9. Figure 5 .

[0105] [Table 1]

[0106]

[0107] [Table 2]

[0108]

[0109] 4. Investigation

[0110] According to the discharge curves of the initial discharge and the residual discharge after the partial charge and discharge of Example 1 and Comparative Example 1 shown in FIG. 10 and FIG. 11, respectively, it is known that the battery voltage decreases in the middle of the discharge at the time of the residual discharge compared to the initial discharge, and further, the discharge capacity also decreases. This is an influence caused by the memory effect. According to Table 1 and Table 2, it is known that the S / Ni ratio of the positive electrode active material of Example 1 is lower than that of Comparative Example 1. It is considered that the decrease in the discharge capacity at the time of the residual discharge is caused by the increase in the S / Ni ratio of the positive electrode active material. Figure 2 and Figure 3 , it is known that the battery voltage decreases in the middle of the discharge at the time of the residual discharge compared to the initial discharge, and further, the discharge capacity also decreases. This is an influence caused by the memory effect. According to Table 1 and Table 2, it is known that the S / Ni ratio of the positive electrode active material of Example 1 is lower than that of Comparative Example 1. It is considered that the decrease in the discharge capacity at the time of the residual discharge is caused by the increase in the S / Ni ratio of the positive electrode active material. Figure 5 ​As a result, the following facts can be known. In Comparative Example 1 in which the active material contains almost no sulfate and the ratio of the S component to Ni is extremely low, the value of the voltage drop ΔV at the time of residual discharge is 0.0132 V. In contrast, in Examples 1 to 6 in which the ratio of the S component to Ni is higher than in Comparative Example 1, the value of the voltage drop ΔV at the time of residual discharge is 0.0085 V or less, and the influence of the voltage drop is reduced. That is, it is known that the influence of the voltage drop in Examples 1 to 6 is reduced to about half that in Comparative Example 1. From this fact, it can be said that in the nickel hydroxide particles, by making the ratio of the S component contained in the sulfate to Ni 0.28% or more, the influence of the voltage drop accompanying the memory effect can be reduced. Until the ratio of S to Ni reaches 1.5%, the effect of reducing the influence of the voltage drop accompanying the memory effect can be obtained. In addition, in the nickel hydroxide particles, when the ratio of the S component contained in the sulfate to Ni is greater than 1.50%, the amount of the sulfate that contributes nothing to the battery reaction relatively increases, and becomes a cause of reduction in the capacity of the battery, and therefore it is considered that the ratio of the S component should be set to 1.50% or less.

[0111] Further, the present application is not limited to the above-described embodiments and examples, and various modifications can be made, for example, the alkaline secondary battery is not limited to the nickel-hydrogen secondary battery, and can be other alkaline secondary batteries. Further, the mechanical structure is not particularly limited, and in addition to the single plate type battery, a cylindrical battery, a square battery, and the like can also be used.

[0112] Explanation of symbols

[0113] 2 Nickel-hydrogen secondary battery

[0114] 6 Electrode group

[0115] 8 Separator

[0116] 10 Container

[0117] 12 Negative electrode

[0118] 14 Positive electrode (nickel electrode)

Claims

1. A nickel electrode for a alkaline secondary battery, comprising a positive electrode core material and a positive electrode mixture filled in the positive electrode core material, the positive electrode mixture contains nickel hydroxide as a positive electrode active material, the nickel hydroxide contains a sulfate, a weight ratio of the sulfate to a Ni component in the nickel hydroxide is 14.3% or more and 30% or less when the positive electrode mixture is manufactured, a weight ratio of a S component contained in the sulfate to the Ni component in the nickel hydroxide is 0.28% or more and 1.50% or less after the alkaline secondary battery is assembled and subjected to charge and discharge.

2. The nickel electrode for alkaline secondary batteries according to claim 1, characterized by the nickel hydroxide contains Al as a solid solution element.

3. An alkaline secondary battery comprising a container, and an electrode group that is housed together with an alkaline electrolyte in the container, the electrode group comprises a positive electrode and a negative electrode that are combined via a separator, the positive electrode is the nickel electrode for the alkaline secondary battery according to claim 1 or 2.

4. The alkaline secondary cell according to claim 3, wherein the negative electrode contains a hydrogen storage alloy.

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