Positive electrode precursor, positive electrode, and alkaline storage battery

Abstract

A positive electrode precursor 23 according to the present invention can be used for a positive electrode 20 of an alkaline storage battery 10 and is characterized by: containing a layered double hydroxide (LDH) that contains, as constituent elements, Ni and at least one metal element selected from Co, Fe, Al, and Mn; and the charge / discharge capacity thereof being developed by using an electrochemical oxidation treatment.　The positive electrode precursor 23 according to the present invention is capable of providing a positive electrode that suppresses decreases in the discharge capacity due to charging / discharging having been repeatedly performed, and that can improve the life cycle of the alkaline storage battery.

Description

Positive electrode precursor, positive electrode, and alkaline storage battery Cross-reference

[0001] This application claims priority under Japanese Patent Application No. 2024-174579, filed in Japan on 3 October 2024, and all contents of said application are incorporated herein by reference.

[0002] This invention relates to a positive electrode precursor, a positive electrode, and an alkaline storage battery.

[0003] In recent years, nickel-zinc batteries have been used in a variety of applications, including electric vehicles, power tools, and energy storage. Nickel-zinc batteries are a new type of rechargeable battery that uses nickel as the active material for the positive electrode and zinc as the active material for the negative electrode. They have a higher energy density and improved lifecycle than conventional lead-acid batteries, and are attracting attention as an efficient energy source.

[0004] Patent Document 1 describes a nickel-zinc storage battery comprising a positive electrode, a negative electrode, an alkaline electrolyte, and a separator. In the nickel-zinc storage battery described in Patent Document 1, nickel oxyhydroxide is used as the active material for the positive electrode, zinc is used as the active material for the negative electrode, and an aqueous solution containing alkali metal hydroxide is used as the alkaline electrolyte. The nickel-zinc storage battery described in Patent Document 1 is said to improve the reliability of the nickel-zinc storage battery by using a separator made of an inorganic solid electrolyte that conducts hydroxide ions, thereby ensuring the isolation of the alkaline electrolyte between the positive and negative electrodes and the conductivity of hydroxide ions, and further physically preventing the separation of the separator by zinc dendrites generated during charging.

[0005] International Publication No. 2013 / 118561

[0006] Incidentally, in order to use electrode materials such as nickel oxyhydroxide and zinc as electrodes in rechargeable batteries, it is important that a reversible oxidation-reduction reaction takes place on the surface of the electrode's active material. However, it is not easy to induce a reversible oxidation-reduction reaction on the surface of the active material. In nickel-zinc rechargeable batteries, it is known that the activity of nickel oxyhydroxide is lost due to the interaction between zinc and nickel in the alkaline electrolyte. When the activity of nickel oxyhydroxide is lost, there is a problem in that the discharge capacity decreases compared to the initial state after repeated charging and discharging.

[0007] The present invention aims to solve the aforementioned problems and to provide a positive electrode precursor used in the positive electrode of an alkaline storage battery, which suppresses the decrease in discharge capacity when repeated charging and discharging occurs and improves the life cycle of the positive electrode precursor.

[0008] Another aspect of the present invention aims to provide a positive electrode that can suppress the decrease in discharge capacity when repeated charging and discharging occurs, thereby improving the lifecycle.

[0009] Furthermore, another aspect of the present invention aims to provide an alkaline storage battery having a positive electrode in which the decrease in discharge capacity when repeated charging and discharging is suppressed and the life cycle is improved.

[0010] [1] The positive electrode precursor of this application example is a positive electrode precursor used in the positive electrode of an alkaline storage battery, and is characterized by containing a layered double hydroxide containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements, and exhibiting charge / discharge capacity by electrochemical oxidation treatment.

[0011] [2] In the cathode precursor of this application example, it is preferable that the layered double hydroxide contains both divalent Ni and trivalent Ni as Ni.

[0012] [3] In the cathode precursor of this application example, it is preferable that the layered double hydroxide changes from divalent Ni to trivalent Ni by the oxidation treatment.

[0013] [4] In the positive electrode precursor of this application example, it is preferable that the oxidation treatment be performed with a volume of 0.001 times or more and 1000 times or less of the volume of the positive electrode precursor.

[0014] [5] In the positive electrode precursor of this application example, it is preferable that the molar ratio of Ni to the metal element in the layered double hydroxide is 1:1 to 4:1.

[0015] [6] In the positive electrode precursor of this application example, the molar ratio of Ni to the metal element in the layered double hydroxide is preferably 1:1 to 3:1.

[0016] [7] In the positive electrode precursor of this application example, it is preferable that the conductivity increases as a result of the oxidation treatment.

[0017] [8] The positive electrode in this application example is a positive electrode used in an alkaline storage battery, and is characterized in that the positive electrode includes the positive electrode precursor described above.

[0018] [9] In the positive electrode of this application example, it is preferable that the amount of anions incorporated between the layers of the layered double hydroxide changes in accordance with the change in the valence of Ni during charging and discharging.

[0019]

[10] The alkaline storage battery of this application example is characterized by including the positive electrode and the alkaline electrolyte described above.

[0020]

[11] In the alkaline storage battery of this application example, it is preferable that a negative electrode is further included, and the negative electrode contains zinc as a negative electrode active material.

[0021] The positive electrode precursor in this application example includes a layered double hydroxide containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements. A layered double hydroxide (LDH) is a double hydroxide in which trivalent metal ions are solid-dissolved in divalent metal ions. An LDH has a layered structure in which the hydroxide base layer (host layer) has a positive charge and anions (interlayer anions) are sandwiched between the hydroxide base layers. In an LDH, anions can be inserted into the interlayer during charging, and the inserted anions can be removed during discharge (reduction).

[0022] The positive electrode precursor according to this application is a positive electrode precursor containing LDH, which contains Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements, and is a positive electrode precursor that exhibits charge / discharge capacity by electrochemical oxidation treatment. The positive electrode precursor according to this application has high reversibility in a charge / discharge cycle in which charging, which inserts anions between layers, and discharging, which removes anions from between layers, are repeated. In other words, the positive electrode precursor according to this application can provide a positive electrode precursor with improved lifecycle, as the decrease in discharge capacity is suppressed when charge / discharge is repeated.

[0023] Furthermore, the positive electrode in this application example suppresses the decrease in discharge capacity when charging and discharging is repeated, providing a positive electrode with an improved lifecycle.

[0024] Furthermore, the alkaline battery in this application example provides an alkaline battery with a positive electrode that suppresses the decrease in discharge capacity when repeatedly charged and discharged, thereby improving the lifecycle.

[0025] FIG. 1 is a conceptual diagram showing an alkaline storage battery 10 using a positive electrode precursor 23 according to an embodiment. FIG. 2 is a diagram showing XRD profiles of the positive electrode precursor according to Example 1, the positive electrode precursor according to Example 2, and the positive electrode precursor according to Comparative Example 1. FIG. 3 is a diagram showing an XPS profile of the positive electrode precursor according to Example 1. FIG. 4 is a diagram showing measurement results of conductivity before and after oxidation treatment of the positive electrode precursor according to Example 1. FIG. 5 is a cross-sectional view showing the configuration of a measurement cell 110 used to measure the battery performance of an alkaline storage battery. FIG. 6 is a diagram showing charge / discharge cycles in a charge / discharge test. FIG. 7 is a diagram showing a charge / discharge curve of an alkaline storage battery using the positive electrode precursor according to Example 1. FIG. 8 is a diagram showing cycle characteristics of an alkaline storage battery using the positive electrode precursor according to Example 2.

[0026] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described. The embodiments described below show preferred forms for carrying out the invention and do not limit the invention according to the claims. Also, not all of the elements and combinations thereof described in the embodiments are essential to the present invention.

[0027] 1. Alkaline storage battery FIG. 1 is a conceptual diagram showing an alkaline storage battery 10 using a positive electrode precursor 23 according to an embodiment. As shown in FIG. 1, the alkaline storage battery 10 includes a positive electrode 20, a negative electrode 30, and an alkaline electrolyte 40.

[0028] 2. Positive electrode The positive electrode 20 is a positive electrode used in the alkaline storage battery 10 and includes a positive electrode precursor 23. The positive electrode precursor 23 will be described in detail later.

[0029] The negative electrode 30 contains zinc and / or zinc oxide as a negative electrode active material. Zinc may be included in any form as long as it has suitable electrochemical activity for the negative electrode 30. Examples of forms in which zinc can be included in the negative electrode 30 include metallic zinc, zinc compounds, and zinc alloys. The negative electrode 30 may be configured as a gel, or it may be mixed with an alkaline electrolyte 40 to form a negative electrode composite material. The shape of the negative electrode 30 is not particularly limited, but it is preferably in powder form. This increases the surface area and allows it to handle high-current discharge.

[0030] The alkaline electrolyte 40 is separated into a positive electrode electrolyte 42 into which the positive electrode 20 is immersed, and a negative electrode electrolyte 44 into which the negative electrode 30 is immersed. Preferably, zinc compounds such as zinc oxide and zinc hydroxide are added to the negative electrode electrolyte 44 to suppress the self-dissolution of zinc and / or zinc oxide. The alkaline electrolyte 40 may be present in the form of a positive electrode composite material by mixing the positive electrode 20 and the alkaline electrolyte 40, and / or in the form of a negative electrode composite material by mixing the negative electrode 30 and the alkaline electrolyte 40. Alternatively, the alkaline electrolyte 40 may be gelled to prevent leakage of the alkaline electrolyte 40.

[0031] When the alkaline electrolyte 40 is separated into a positive electrode electrolyte 42 and a negative electrode electrolyte 44, it is preferable that the positive electrode 20 and positive electrode electrolyte 42 and the negative electrode 30 and negative electrode electrolyte 44 are separated by a separator 50 so that hydroxide ions contained in the alkaline electrolyte 40 can conduct. Furthermore, even if the alkaline electrolyte 40 is not completely separated into a positive electrode electrolyte 42 and a negative electrode electrolyte 44, it is preferable that the positive electrode 20 and the negative electrode 30 are separated by a separator 50 so that hydroxide ions can conduct.

[0032] The separator 50 can be appropriately selected from materials known in the field of zinc storage batteries, having conductivity for hydroxide ions and capable of suppressing short circuits between the positive and negative electrodes caused by zinc dendrites. By using the separator 50, it is possible to ensure conductivity for hydroxide ions while suppressing short circuits between the positive and negative electrodes caused by the growth of zinc dendrites, thereby extending the lifespan of the alkaline storage battery 10.

[0033] 3. Positive electrode precursor The positive electrode precursor 23 functions as a positive electrode active material of the positive electrode 20 constituting the alkaline storage battery 10. The positive electrode precursor 23 contains LDH containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements. Further, the positive electrode precursor 23 exhibits charge and discharge capacity by electrochemical oxidation treatment.

[0034] LDH is a compound in which divalent and trivalent ions mainly form a layered hydroxide, and anions such as carbonate ions are inserted between the layers to balance the charge. General LDH has a general formula of A ８－ｘ B ｘ (OH) １６ CO ２ ·nH ２ 0 (A = Mg ２＋ , Fe ２＋ , Zn ２＋ , Ca ２＋ Li ２＋ , Ni ２＋ , Ca ２＋ , Cu ２＋ 、B = Al ３＋ , Fe ３＋ , Mn ３＋ , V ３＋ , Co ３＋ , Ni ３＋ , Ni ３＋ , 2 ≤ x ≤ 5). Further, the divalent ions (A) and trivalent ions (B) can be selected from a wide range of candidates.

[0035] On the other hand, in the positive electrode precursor 23 according to the embodiment, the layered double hydroxide contains divalent ions and trivalent ions, that is, as constituent elements, Ni and at least one metal element selected from Co, Fe, Al, and Mn.

[0036] The positive electrode precursor 23 exhibits charge and discharge capacity by performing charge and discharge on the alkaline storage battery 10 including the positive electrode precursor 23 as the positive electrode 20, that is, by electrochemical oxidation treatment.

[0037] In the alkaline storage battery according to the prior art, β - Bi(OH) ２However, it is known that oxidation changes it to γ-NiOOH, which is expected to improve the charge-discharge capacity. However, α-Ni(OH) generated by reduction during discharge ２ Because it is unstable, β-Ni(OH) ２ It changes to α-Ni(OH) ２ β-Ni(OH) ２ When the transition occurs, volume contraction occurs, leading to the problem of electrode degradation.

[0038] On the other hand, the positive electrode precursor 23 contains LDH. LDH contains Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements. As described above, anions are inserted between the layers of LDH during charging (oxidation), and the anions inserted between the layers are desorbed during discharging (reduction). The interlayer distance of the hydroxide base layer changes with the insertion or desorption of anions. However, the change in the interlayer distance of the hydroxide base layer due to charging and discharging is reversible, and no electrode degradation occurs.

[0039] In the positive electrode precursor 23, LDH itself participates in the charge-discharge reaction of the positive electrode 20. The LDH contained in the positive electrode precursor 23 contains Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements. Therefore, the positive electrode 20 containing the positive electrode precursor 23 can suppress degradation of the positive electrode 20 even after repeated charge-discharge.

[0040] The positive electrode precursor 23 is a positive electrode precursor 23 that exhibits charge / discharge capacity through electrochemical oxidation treatment. In this specification, "electrochemical oxidation treatment" refers to the process of creating an alkaline storage battery 10 containing the positive electrode precursor 23 as the positive electrode 20, and then oxidizing the electrode by charging the alkaline storage battery 10. Hereafter, "electrochemical oxidation treatment" may be simply referred to as "oxidation treatment."

[0041] The oxidation treatment may be carried out by a cumulative oxidation treatment in which the alkaline storage battery 10 containing the positive electrode precursor 23 is repeatedly charged and discharged, or by a continuous oxidation treatment in which charging is continued until a predetermined charge capacity is reached. By performing an oxidation treatment on the LDH, the charge and discharge capacity can be made to develop in the positive electrode precursor 23.

[0042] The layered double hydroxide contains both divalent and trivalent Ni as Ni. Because the layered double hydroxide contains both divalent and trivalent Ni, the divalent Ni can be converted to trivalent Ni by electrochemical oxidation. This increases the amount of intercalation anions that can be incorporated between the layers of the layered double hydroxide, thereby enabling the positive electrode precursor 23 to exhibit charge-discharge capacity. Furthermore, the trivalent Ni in the hydroxide base layer of the layered double hydroxide can be converted to divalent Ni by electrochemical reduction. This allows the intercalation anions inserted between the layers of the layered double hydroxide to be removed.

[0043] The electrochemical oxidation treatment is preferably performed with a volume of 0.001 to 1000 times the volume of the positive electrode precursor 23, more preferably with a volume of 0.01 to 500 times, and even more preferably with a volume of 0.1 to 100 times. By performing the electrochemical oxidation treatment with a volume of 0.001 times or more the volume of the positive electrode precursor 23, it is possible to promote the change in the valence state of the metal elements. On the other hand, by performing the electrochemical oxidation treatment with a volume of 1000 times or less the volume of the positive electrode precursor 23, it is possible to suppress the decrease of the alkaline electrolyte 40 due to electrolysis.

[0044] The LDH contained in the positive electrode precursor 23 preferably has a molar ratio of Ni to metal element of 1:1 to 4:1, and more preferably 1:1 to 3:1. By having a molar ratio of Ni to metal element in the LDH within the above numerical range, a high output capacity can be achieved when the positive electrode precursor 23 is used as the positive electrode 20 of the alkaline storage battery 10.

[0045] The LDH contained in the positive electrode precursor 23 preferably contains a combination of Ni and Co as constituent elements. This can improve the expression capacity of the positive electrode precursor 23.

[0046] 4. Method for Manufacturing the Cathode Precursor Next, the method for manufacturing the cathode precursor will be described. A precipitating agent is added to a synthetic sample consisting of a nitrate or chloride of a divalent metal and a trivalent metal, and together with distilled water, it is placed in a heat-resistant reaction vessel, such as a PTFE (polytetrafluoroethylene) vessel. Examples of precipitating agents include urea and hexamethylenetetramine. The synthetic sample is dissolved in the distilled water by applying ultrasound to the mixture of the synthetic sample, precipitating agent, and distilled water.

[0047] The positive electrode precursor 23 according to this embodiment can be produced, for example, by a hydrothermal synthesis method. Specifically, a reaction vessel containing the synthesis sample and precipitant is fixed in a sealed metal container and heated in an oven. The oven temperature at this time is, for example, 100°C to 250°C, and the heating time is, for example, 6 hours to 72 hours. After the reaction, the metal container in which the reaction vessel is fixed is removed from the oven, and the reaction vessel is left inside the metal container to cool at room temperature.

[0048] After cooling, the contents of the reaction vessel are removed to another container and distilled water is added. Unreacted synthetic samples and impurities are dissolved by applying ultrasound or other means, and the supernatant is removed. This process is repeated several times to increase the purity of the product. The product, after the unreacted synthetic samples have been removed, is dried until the water evaporates to obtain the cathode precursor 23.

[0049] In the above-described method for producing the positive electrode precursor, the case in which the positive electrode precursor 23 is produced by hydrothermal synthesis was described, but the method for producing the positive electrode precursor is not limited to hydrothermal synthesis. The positive electrode precursor 23 may also be produced by other known methods such as coprecipitation.

[0050] 5. Examples (Example 1) Synthesis of Cathode Precursor As synthesis samples, 0.727 g of nickel nitrate hexahydrate (divalent metal), 0.728 g of cobalt nitrate hexahydrate (trivalent metal), and 1.75 g of urea as a precipitating agent were weighed out and placed in a PTFE reaction vessel along with 25 g of distilled water. Then, ultrasonic waves were applied to the contents of the reaction vessel using an ultrasonic cleaner to dissolve the synthesis samples in the distilled water.

[0051] The reaction vessel was fixed to a metal container and left in an oven pre-set to 220°C for 24 hours to synthesize LDH. After 24 hours, the metal container was removed from the oven, and the reaction vessel, still fixed to the metal container, was left to cool for 2 hours.

[0052] Subsequently, the reaction vessel was removed from the metal container, its contents were transferred to a PP (polypropylene) container, 100 mL of distilled water was added, and then ultrasonic waves were applied for 15 minutes using an ultrasonic cleaner. After ultrasonic treatment, the mixture was left to stand for 2 hours, and the supernatant was removed by decantation. The process of adding 100 mL of distilled water, applying ultrasonic waves, letting it stand, and decanting was repeated twice.

[0053] Finally, the purified product was dried on a hot plate at 70°C until the water evaporated to obtain the cathode precursor 23 according to Example 1.

[0054] - Preparation of the positive electrode Using the positive electrode precursor according to Example 1 prepared as described above, a positive electrode 120 (see Figure 5) was prepared. 0.2 g of the positive electrode precursor, 0.037 g of PTFE (polytetrafluoroethylene, 60 wt% aq, binder), and 0.2 g of water were mixed in a mortar. When the mixture formed a mass, it was placed in a plastic bag and rolled out to a thickness of 0.05 mm to create a paste.

[0055] Furthermore, the paste was cut into 20 mm x 20 mm pieces. The cut pieces of paste were pressed onto a current collector 122 made of foamed nickel measuring 20 mm x 20 mm under a pressure of 30 MPa, and air-dried for one day to form the positive electrode 120 according to Example 1. The positive electrode 120 thus prepared was stored in a plastic bag until use.

[0056] - Preparation of a test measurement cell A measurement cell 110 was prepared using the positive electrode 120 according to Example 1, which was prepared as described above. Figure 5 is a cross-sectional view illustrating the configuration of the measurement cell 110 used to measure the battery performance of an alkaline storage battery. Note that the hatching indicating a cross-section is omitted in Figure 5.

[0057] The measuring cell 110 has a positive electrode 120, a negative electrode 130, and a separator 150. The positive electrode 120 is the positive electrode 120 according to Example 1, which was prepared as described above. For the negative electrode 130, zinc oxide and PTFE emulsion (Polyflon manufactured by Daikin Corporation) were mixed in a ratio of 9:1, formed into a paste, and attached to a zinc plate to be used as the negative electrode 130. A Cu mesh was attached to the negative electrode 130 as a current collector 132.

[0058] The separator 150 has a positive electrode side separator 152 made of a 100 μm thick nonwoven fabric placed around the positive electrode 120, and a negative electrode side separator 154 made of a 25 μm thick cellophane placed around the negative electrode 130. The separator 150 is placed around both the positive electrode 120 and the negative electrode 130. Therefore, the region between the positive electrode 120 and the negative electrode 130 has a two-layer structure with the positive electrode side separator 152 and the negative electrode side separator 154 placed therein.

[0059] - Oxidation Treatment Using the measurement cell 110 according to Example 1 prepared as described above, an electrochemical oxidation treatment (cumulative oxidation treatment) was performed on the positive electrode precursor (symbols omitted). The conditions for the oxidation treatment are shown below. Oxidation Treatment Conditions (Cumulative Oxidation Treatment) During charging: Control current: 200 mA / g Stop condition: 1.8 V During discharging: Control current: 200 mA / g Stop condition: 0.8 V

[0060] (Example 2) The cathode precursor and cathode 120 according to Example 2 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 1, except that hexamethylenetetramine was used as a precipitating agent. The measurement cell 110 according to Example 2 was subjected to oxidation treatment in the same manner as the measurement cell 110 according to Example 1, except that the cathode 120 according to Example 2 was used.

[0061] (Example 3) The measurement cell 110 according to Example 3 was manufactured in the same manner as the measurement cell 110 in Example 2, except that the positive electrode 120 according to Example 2 was subjected to electrochemical oxidation treatment by continuous oxidation treatment. The conditions for the oxidation treatment by continuous oxidation treatment are shown below. Oxidation treatment conditions (continuous oxidation treatment) During charging: Control current: 200 mA / g Stop condition: When 1000 mAh / g is reached

[0062] (Example 4) The cathode precursor and cathode 120 according to Example 4 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 2, except that the addition ratio of nickel nitrate hexahydrate and cobalt nitrate hexahydrate, which are LDH synthesis samples, was changed to 1:1. The measurement cell 110 according to Example 4 was manufactured in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 4 was used.

[0063] (Example 5) The cathode precursor and cathode 120 according to Example 5 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 2, except that the addition ratio of nickel nitrate hexahydrate and cobalt nitrate hexahydrate, which are LDH synthesis samples, was changed to 3:1. The measurement cell 110 according to Example 5 was manufactured in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 5 was used.

[0064] (Example 6) The cathode precursor and cathode 120 according to Example 6 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 2, except that the addition ratio of nickel nitrate hexahydrate and cobalt nitrate hexahydrate, which are LDH synthesis samples, was changed to 4:1. The measurement cell 110 according to Example 6 was manufactured in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 6 was used.

[0065] (Example 7) The cathode precursor and cathode 120 according to Example 7 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 1, except that the addition ratio of nickel nitrate hexahydrate and cobalt nitrate hexahydrate, which are LDH synthesis samples, was changed to 5:1. The measurement cell 110 according to Example 7 was manufactured in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 7 was used.

[0066] (Example 8) The cathode precursor and cathode 120 according to Example 8 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 2, except that the cobalt nitrate hexahydrate, which is the LDH synthesis sample, was changed to aluminum nitrate nonahydrate. The measurement cell 110 according to Example 8 was subjected to oxidation treatment in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 8 was used.

[0067] (Example 9) The cathode precursor and cathode 120 according to Example 9 were manufactured in the same manner as the cathode precursor and cathode 120 according to Example 2, except that the cobalt nitrate hexahydrate, which is the LDH synthesis sample, was changed to manganese nitrate hexahydrate. The measurement cell 110 according to Example 9 was subjected to oxidation treatment in the same manner as the measurement cell 110 according to Example 3, except that the cathode 120 according to Example 9 was used.

[0068] (Comparative Example) As a cathode precursor, nickel hydroxide (Ni(OH) ２ Using the same method as the measurement cell 110 in Example 1, the comparative example measurement cell 110 was manufactured.

[0069] [Evaluation 1] The cathode precursors according to Examples 1 to 7 and the comparative example, manufactured as described above, were evaluated for their expression capacity after oxidation treatment and their capacity retention rate after 150 cycles. The evaluation results are shown in Table 1.

[0070]

[0071] The cathode precursors in Examples 1 to 9 showed a very high level of capacity retention, with a capacity retention rate of 97% or more after 150 cycles. On the other hand, the cathode precursor in Comparative Example 1 showed Ni(OH) ２ Although it is composed of the above, the capacity retention rate after 150 cycles is 77%. The cathode precursors according to Examples 1 to 7 contain a layered double hydroxide containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements, and are characterized by exhibiting charge / discharge capacity through electrochemical oxidation treatment. It has been confirmed that having such characteristics suppresses the decrease in discharge capacity when charge / discharge is repeated, and improves the life cycle.

[0072] Furthermore, it can be confirmed that charge / discharge capacity is exhibited in all positive electrode precursors of Examples 1 to 9 by oxidation treatment. The magnitude of the exhibited capacity depends on the molar ratio of Ni to the metal element (at least one metal element selected from Co, Fe, Al, and Mn) contained in the LDH. The molar ratio of Ni to the metal element is preferably 1:1 to 4:1 (see Examples 1 to 6), and more preferably 1:1 to 3:1 (see Examples 1 to 5).

[0073] [Evaluation 2] XRD Analysis XRD analysis was performed on the cathode precursors of Example 1, Example 2, and the comparative example. Specifically, the XRD profiles of each cathode precursor were measured using an X-ray diffractometer (Rigaku MiniFlex 600).

[0074] Figure 2 shows the XRD profiles of the cathode precursors according to Example 1, Example 2, and Comparative Example 1. As can be seen from Figure 2, the cathode precursors according to Example 1 and Example 2 show peaks attributable to the (003) and (006) planes of Ni-Co-LDH, confirming that the cathode precursors have an LDH structure. On the other hand, the cathode precursor according to the Comparative Example shows Ni(OH) ２ Therefore, no peak is observed at the corresponding location.

[0075] [Evaluation 3] The cathode precursor according to Example 1 was analyzed by X-ray photoelectron spectroscopy (XPS). Specifically, the evaluation was performed using an X-ray photoelectron analyzer (Thermo Fisher Scientific, K-Alpha+).

[0076] Figure 3 shows the XPS profile of the cathode precursor according to Example 1. Figure 3(a) compares the XPS profile of the cathode precursor according to Example 1 during fabrication with the XPS profile after electrochemical oxidation treatment. In Figure 3(a), the horizontal axis represents the binding energy of the emitted photoelectrons, and the vertical axis represents the intensity of the photoelectrons with that binding energy.

[0077] The XPS profile of the cathode precursor during fabrication is shown in Figure 3(a), with divalent Ni (Ni) around 854 eV. ２＋ There is a peak originating from ) and also a peak around 869 eV of trivalent Ni (Ni ３＋ A peak originating from ) is observed. In other words, the cathode precursor during fabrication contains both divalent and trivalent Ni.

[0078] When the cathode precursor is subjected to oxidation treatment, the peak intensity around 861 eV, which originates from trivalent Ni, decreases, while the peak intensity around 863 eV, which also originates from trivalent Ni, increases. This is thought to be because the oxidation treatment causes the same trivalent Ni to shift to a higher energy state.

[0079] Figure 3(b) compares the XPS profile during charging and the XPS profile during discharging of the cathode precursor after oxidation treatment. In Figure 3(b), the horizontal axis represents the binding energy of the emitted photoelectrons, and the vertical axis represents the intensity of the photoelectrons with that binding energy.

[0080] In the discharged state, as shown in Figure 3(b), the peak intensity of the trivalent Ni peak around 861 eV is greater than that of the other peaks originating from trivalent Ni. On the other hand, in the charged state, the peak intensity of the trivalent Ni peak around 863 eV is greater than that of the other peaks originating from trivalent Ni. This is thought to be because, similar to the case when the positive electrode precursor is oxidized, charging causes the same trivalent Ni to shift to a higher energy level.

[0081] Furthermore, comparing the peak intensity of trivalent Ni in the discharged state with that of the charged state, the peak intensity of trivalent Ni is greater in the charged state. This confirms that trivalent Ni increases with charging and decreases with discharging.

[0082] [Evaluation 4] Conductivity Measurement The conductivity of the positive electrode precursor according to Example 1 was measured and compared before and after oxidation treatment. Specifically, for the powder samples of the positive electrode precursor before and after oxidation treatment, the cross-sectional area was 0.5 cm². ２ The sample was placed in a measuring container and compressed from above and below with a pressure of 20 MPa to prepare an evaluation sample. The resistance (Ω) of the evaluation sample was measured, and the resistivity (Ω·cm) and conductivity (mS·cm) were determined from the obtained resistance value. The results are shown in Figure 4 and Table 2.

[0083]

[0084] As shown in Table 2, the positive electrode precursor according to Example 1 had an conductivity of 0.0174 mS / cm before oxidation treatment, while after oxidation treatment, the conductivity increased to 0.0267 mS / cm. In other words, it can be seen that the conductivity of the positive electrode precursor according to the embodiment increases after oxidation treatment. When the positive electrode precursor according to the embodiment is used as the positive electrode 120 of the alkaline storage battery 10, the resistance value of the electrode can be reduced, which contributes to improving the charge and discharge characteristics.

[0085] [Evaluation 5] Oxidation Treatment and Capacity Performance (1) The relationship between oxidation treatment and capacity performance was evaluated using the positive electrode precursor and measurement cell 110 according to Example 1. Figure 6 is a diagram illustrating the charge-discharge cycle used in the oxidation treatment. Figure 7 is a diagram illustrating the charge-discharge curve of an alkaline storage battery using the measurement cell 110 according to Example 1.

[0086] An alkaline storage battery equipped with a positive electrode precursor and a measurement cell 110 according to Example 1 was subjected to an oxidation treatment by performing a charge-discharge cycle as shown in Figure 6. The conditions for the charge-discharge cycle are described below. Oxidation treatment conditions (cumulative oxidation treatment) During charging: Control current: 200 mA / g Stop condition: 1.8 V During discharging: Control current: 200 mA / g Stop condition: 0.8 V

[0087] Figure 7 shows the charge and discharge curves before and after oxidation treatment (50th cycle). The dashed line shows the charge curve, and the solid line shows the discharge curve. From Figure 7, it can be confirmed that the alkaline storage battery equipped with the positive electrode precursor according to Embodiment 1 has improved charge and discharge capacity at a terminal voltage of 1.5V from 150mAh / g (before oxidation treatment) to 240mAh / g (after oxidation treatment). In other words, it can be seen that the positive electrode precursor according to the embodiment exhibits increased charge capacity by undergoing oxidation treatment.

[0088] [Evaluation 6] Oxidation treatment and capacity performance (2) The relationship between oxidation treatment and capacity performance was evaluated using the measurement cell 110 according to Example 2 and the measurement cell 110 according to Example 3. Specifically, an alkaline storage battery equipped with the measurement cell 110 according to Example 2 and an alkaline storage battery equipped with the measurement cell 110 according to Example 3 were subjected to the oxidation treatment by performing the charge-discharge cycle shown in Figure 6.

[0089] Figure 8 is a diagram illustrating the cycle characteristics of an alkaline storage battery equipped with a measurement cell 110 according to Example 2 and an alkaline storage battery equipped with a measurement cell 110 according to Example 3.

[0090] Figure 8(a) shows the relationship between the number of cycles and the charge / discharge capacity when cumulative oxidation treatment is performed. Specifically, it shows the relationship between the number of cycles (horizontal axis) and the charge capacity and discharge capacity (vertical axis) when cumulative oxidation treatment is performed on an alkaline storage battery equipped with the measurement cell 110 according to Example 2.

[0091] The charging capacity remains stable at approximately 200 mAh / g regardless of the number of cycles. On the other hand, the discharge capacity is small when the number of cycles is low and increases as the number of cycles increases. The irreversible capacity, which is the difference between the charging capacity and the discharge capacity, cumulatively reaches approximately 1000 mAh / g.

[0092] Figure 8(b) shows the effect of the oxidation treatment method on discharge capacity. Specifically, it shows the relationship between the number of cycles and discharge capacity for cases where the oxidation treatment is performed by cumulative oxidation treatment and by continuous oxidation treatment. The cumulative oxidation treatment was evaluated using an alkaline storage battery equipped with the measurement cell 110 according to Example 2, and the continuous oxidation treatment was evaluated using an alkaline storage battery equipped with the measurement cell 110 according to Example 3.

[0093] In cumulative oxidation treatment, the discharge capacity increases with the number of cycles, reaching 200 mAh / g around the 30th cycle and then converging. On the other hand, in continuous oxidation treatment, the heat dissipation capacity reaches 180 mAh / g from the first cycle, reaching 200 mAh / g around the 10th cycle and then converging. Figure 8(b) shows that by performing continuous oxidation treatment, the discharge capacity can be increased with a smaller number of cycles.

[0094] The following describes the effects of the positive electrode precursor 23, positive electrode 20, and alkaline battery 10 according to this embodiment.

[0095] (1) The positive electrode precursor 23 according to the embodiment contains LDH containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements, and exhibits charge / discharge capacity by electrochemical oxidation treatment. LDH is a double hydroxide in which trivalent metal ions are solid-solved in divalent metal ions, and has a laminated structure in which the hydroxide base layer (host layer) has a positive charge and anions (interlayer anions) are sandwiched between the hydroxide base layers. With LDH, anions are inserted between the layers during charging, and the inserted anions can be removed during discharge (reduction). Here, the positive electrode precursor 13 contains LDH as constituent elements, which includes Ni and at least one metal element selected from Co, Fe, Al, and Mn, and the positive electrode precursor 13 exhibits charge / discharge capacity by electrochemical oxidation treatment, and has high reversibility in a charge / discharge cycle in which anions are inserted between the layers for charging and anions are released from between the layers for discharge. In other words, according to the positive electrode precursor 13 of the embodiment, it is possible to provide a positive electrode precursor 23 for an alkaline storage battery 10 in which the decrease in discharge capacity is suppressed when charge / discharge is repeated and the life cycle is improved.

[0096] (2) In the positive electrode precursor 23 according to the embodiment, it is preferable that the layered double hydroxide contains both divalent Ni and trivalent Ni as Ni. This allows the divalent Ni to be changed to trivalent Ni by electrochemical oxidation treatment. Consequently, the amount of interlayer anions that can be incorporated between the layers of the layered double hydroxide can be increased, and the positive electrode precursor 23 can exhibit charge-discharge capacity.

[0097] (3) In the positive electrode precursor 23 according to the embodiment, it is preferable that the layered double hydroxide is changed from divalent Ni to trivalent Ni by oxidation treatment. This makes it possible to increase the amount of interlayer anions that can be incorporated between the layers of the layered double hydroxide, and to give the positive electrode precursor 23 charge and discharge capacity.

[0098] (4) In the positive electrode precursor 23 according to the embodiment, it is preferable to perform the oxidation treatment with a volume of 0.001 times or more and 1000 times or less of the volume of the positive electrode precursor 23. By performing the electrochemical oxidation treatment with a volume of 0.001 times or more of the volume of the positive electrode precursor 23, it is possible to promote the change in the valence of the metal elements. On the other hand, by performing the electrochemical oxidation treatment with a volume of 1000 times or less of the volume of the positive electrode precursor 23, it is possible to suppress the decrease of the alkaline electrolyte 40 due to electrolysis.

[0099] (5) In the positive electrode precursor 23 according to the embodiment, LDH contains a combination of Ni and Co as constituent elements, and the molar ratio of Ni to the metal element is preferably 1:1 to 4:1. By having the positive electrode precursor 23 with such a configuration, the decrease in the discharge capacity of the positive electrode precursor 23 can be further suppressed when charging and discharging is repeated.

[0100] (6) In the positive electrode precursor 23 according to the embodiment, LDH contains a combination of Ni and Co as constituent elements, and the molar ratio of Ni to the metal element is preferably 1:1 to 3:1. By having the positive electrode precursor 23 in this configuration, the decrease in the discharge capacity of the positive electrode precursor 23 can be further suppressed when charging and discharging is repeated.

[0101] (7) In the embodiment, it is preferable that the conductivity of the positive electrode precursor 23 increases by oxidation treatment. This makes it possible to provide a positive electrode precursor 23 that has good charge-discharge efficiency and can handle high-current discharge when the positive electrode 20 containing the positive electrode precursor 23 is used as the positive electrode 20 of an alkaline storage battery 10.

[0102] (8) The positive electrode 20 used in the alkaline storage battery 10 according to the embodiment includes the positive electrode precursor 23 described above. According to the positive electrode 20 according to the embodiment, for the same reasons as described above, the decrease in discharge capacity when charging and discharging is repeated is suppressed, and a positive electrode 20 for alkaline storage battery 10 with an improved life cycle can be provided.

[0103] (9) In the alkaline storage battery 10 according to this embodiment, it is preferable that the amount of anions incorporated between the layers of the layered double hydroxide changes in accordance with the change in the valence of Ni during charging and discharging. This suppresses deterioration of the positive electrode 20 even when repeated charging and discharging is performed, and provides a positive electrode 20 for alkaline storage battery 10 with an improved life cycle.

[0104] (10) The alkaline storage battery 10 according to the embodiment includes the positive electrode 20 described above and an alkaline electrolyte 40. According to the alkaline storage battery 10 according to the embodiment, for the same reasons as described above, the decrease in discharge capacity when charging and discharging is repeated is suppressed, and an alkaline storage battery 10 with an improved life cycle can be provided.

[0105] (11) The alkaline storage battery 10 according to the embodiment further includes a negative electrode 30, the negative electrode 30 containing zinc as a negative electrode active material. This makes it possible to provide an alkaline storage battery 10 with an improved life cycle.

[0106] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0107] 10... Alkaline battery, 20... Positive electrode, 23... Positive electrode precursor, 30... Negative electrode, 40... Alkaline electrolyte, 42... Positive electrode electrolyte, 44... Negative electrode electrolyte, 50... Separator

Claims

1. A positive electrode precursor used in the positive electrode of an alkaline storage battery, comprising a layered double hydroxide containing Ni and at least one metal element selected from Co, Fe, Al, and Mn as constituent elements, and characterized in that it exhibits charge / discharge capacity by electrochemical oxidation treatment.

2. A cathode precursor according to claim 1, characterized in that the layered double hydroxide contains divalent Ni and trivalent Ni as Ni.

3. A cathode precursor according to claim 2, characterized in that the layered double hydroxide changes from divalent Ni to trivalent Ni by the oxidation treatment.

4. A positive electrode precursor according to any one of claims 1 to 3, characterized in that the oxidation treatment is performed with a volume of 0.001 times or more and 1000 times or less of the volume of the positive electrode precursor.

5. A positive electrode precursor according to any one of claims 1 to 4, characterized in that the molar ratio of Ni to the metal element in the layered double hydroxide is 1:1 to 4:

1.

6. A positive electrode precursor according to any one of claims 1 to 4, characterized in that the molar ratio of Ni to the metal element in the layered double hydroxide is 1:1 to 3:

1.

7. A positive electrode precursor according to any one of claims 1 to 6, characterized in that its conductivity increases upon oxidation treatment.

8. A positive electrode used in an alkaline storage battery, characterized in that the positive electrode includes a positive electrode precursor described in any one of claims 1 to 7.

9. A positive electrode according to claim 8, characterized in that the amount of anions incorporated between the layers of the layered double hydroxide changes in accordance with the change in the valence of Ni during charging and discharging.

10. An alkaline storage battery comprising a positive electrode according to claim 8 or 9 and an alkaline electrolyte.

11. An alkaline storage battery according to claim 10, further comprising a negative electrode, wherein the negative electrode contains zinc as a negative electrode active material.

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