Deactivation method and deactivation apparatus

Abstract

This invention provides a novel deactivation method and apparatus for deactivating nickel-metal hydride batteries. [Solution] The inactivation method of the present disclosure includes a processing step of adding a processing solution containing anions with S to a nickel-metal hydride battery to inactivate the Ni contained in the nickel-metal hydride battery.

Description

Technical Field

[0001] The present disclosure relates to a deactivation method and a deactivation device.

Background Art

[0002] Conventionally, as a power storage device, in a sealed metal-hydrogen alkaline storage battery having a negative electrode mainly composed of a hydrogen storage alloy and a positive electrode, an oxidant supply means for supplying H2O2, K2S2O8, O2 gas, etc. as an oxidant for oxidizing hydrogen accumulated in the negative electrode has been proposed (see Patent Document 1). In this power storage device, it is said that a sealed metal-hydrogen alkaline storage battery with improved cycle characteristics can be provided by improving the utilization rate of the negative electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, nickel-hydrogen batteries use a hydrogen storage alloy for the negative electrode and have high reactivity with oxygen in the air. Although they are sealed in the cell during normal use, when recycling the battery, the battery is crushed, so the hydrogen storage alloy may react with oxygen in the atmosphere and generate heat. For example, after repeating charge-discharge cycles, there are many active Ni clusters in MH, and the heat generation during exposure to the atmosphere was large.

[0005] The present disclosure has been made to solve such problems, and the main object is to provide a novel deactivation method and a deactivation device for deactivating nickel-hydrogen batteries.

Means for Solving the Problems

[0006] Through diligent research to achieve the above-mentioned objectives, the present inventors discovered that using sulfur-based anions can more efficiently deactivate the Ni metal contained in nickel-metal hydride batteries, thus completing the invention disclosed herein.

[0007] In other words, the deactivation method disclosed herein is A process to inactivate Ni contained in a nickel-metal hydride battery using a processing solution in which anions containing S are dissolved. It includes.

[0008] Furthermore, the deactivation device disclosed herein is A deactivation device for inactivating nickel-metal hydride batteries, A processing unit that performs an inactivation treatment to deactivate the Ni contained in nickel-metal hydride batteries using a processing solution in which anions containing S are dissolved. It is something that is provided. [Effects of the Invention]

[0009] This deactivation method and apparatus can provide a novel deactivation method and apparatus for deactivating nickel-metal hydride batteries. The reason for this effect is presumed to be, for example, that sulfur-based anions contained in the processing solution react with the Ni metal, thereby stabilizing the Ni. [Brief explanation of the drawing]

[0010] [Figure 1] A flowchart illustrating an example of a battery recycling processing routine. [Figure 2] A cross-sectional diagram illustrating the general structure of the Ni-MH secondary battery 20. [Figure 3] Measurement results of the micro-Raman system in Experimental Example 3. [Modes for carrying out the invention]

[0011] (Inactivation method) The deactivation method disclosed herein is a process for deactivating nickel-metal hydride batteries that is performed in the process of recycling nickel-metal hydride batteries. Figure 1 is a flowchart of an example of a nickel-metal hydride battery recycling process routine. This recycling process is an example of recycling a vehicle battery such as that of a HEV. In this routine, the battery pack is recovered from the HEV (S10), the battery pack is disassembled (S20), the hydrogen storage alloy MH is deactivated by injecting an inactivating solution (S30), the Ni metal is oxidized with a processing solution (S40), crushed (S50), dissolved to recover the elements (S60), an active material is synthesized using the recovered elements (S70), and re-cell formation is attempted (S80). This deactivation process may be performed in S40 of this routine.

[0012] In the S30 deactivation process, an inactivating solution that deactivates the Ni-MH of the nickel-metal hydride battery is reacted with the positive and / or negative electrodes of the nickel-metal hydride battery to deactivate it. The inactivating solution may be a solution in which an inactivating compound that deactivates Ni-MH is dissolved. The inactivating solution may be a solution that allows for a shuttle reaction in which the substance produced after deactivating H from Ni-MH inserts H into the positive electrode, and then H is deactivated again from the negative electrode. This inactivating solution is preferably an aqueous solution with water as the solvent. Furthermore, this inactivating solution is preferably alkaline, and may be made alkaline by dissolving an alkali metal hydroxide. Examples of alkali metals include Li, Na, and K, of which K and Na are preferred. This inactivating solution is preferably pH 8 or higher, and may be pH 9 or higher or 10 or higher. Furthermore, this inactivating solution can have a pH of 14 or lower, more preferably 12 or lower. The concentration of the inactivating compound in the inactivating solution is preferably higher, preferably 0.1 mol / L (M) or higher, more preferably 0.2 M or higher, and may be 0.5 M or higher or 1 M or higher. This concentration is appropriately determined according to the solubility in the alkaline electrolyte in the cell, but may be 6 M or lower, and may be higher depending on the composition of the alkaline electrolyte. Furthermore, if this inactivating solution is not dissolved in the alkaline electrolyte at the injection stage, the concentration may be higher, may be 6 M or higher or 10 M or higher, and may be 30 M or lower. In this deactivation step, the deactivation treatment may be carried out at room temperature, for example, in the range of 20°C to 25°C. Note that this deactivation treatment temperature may be in the range of -20°C to 100°C. In this step, the amount of inactivating solution added should be appropriately selected according to the concentration of the nitrogen-containing salt, the treatment temperature, and the scale of the nickel-metal hydride battery. Furthermore, the treatment time for the deactivation treatment should be appropriately selected according to the scale of the nickel-metal hydride battery, the amount and concentration of the inactivating solution added, and the type of salt. This processing time may be, for example, in the range of 0.5 hours to 24 hours. In the deactivation treatment, after injecting the deactivating solution into the nickel-metal hydride battery, it may be, for example, left to stand or held while being vibrated. No special treatment is required for this process; it is sufficient to leave it to stand.Alternatively, in the deactivation treatment, electrodes and electrode active materials are removed from the nickel-metal hydride battery and immersed in an deactivation solution. After this, they may be held still or held while being vibrated. It is more preferable to handle the components of the nickel-metal hydride battery in an inert atmosphere such as nitrogen, He, or Ar. In this deactivation treatment, Ni metal may be formed on the electrodes. The Ni metal may include, for example, Ni clusters composed of nanoscale fine particles.

[0013] The inactivating solution may be, for example, a solution in which an anion containing N and O, and / or a cation containing N and H are dissolved. Here, a compound containing either an anion containing N and O, and / or a cation containing N and H, is conveniently referred to as a "nitrogen-containing salt." The inactivating solution preferably contains, as a nitrogen-containing salt, a nitrate anion, and one or more of the following: primary ammonium cation, secondary ammonium cation, tertiary ammonium cation, and quaternary ammonium cation. In each ammonium cation, hydrogen may be substituted with an alkyl group or an aryl group. Examples of alkyl groups include methyl, ethyl, and propyl groups. Examples of aryl groups include phenyl, tolyl, and xyl groups. This inactivating solution may contain an alkali cation as a counter-cation for nitrate and nitrite anions. Furthermore, this inactivating solution may contain a sulfate anion and / or a halogen as counter-anions for ammonium cations. Examples of nitrogen-containing salts in this inactivating solution include sodium nitrate, potassium nitrate, lithium nitrate, sodium nitrite, potassium nitrite, and lithium nitrite, of which sodium nitrite and potassium nitrite are more preferred from the viewpoint of solubility. Furthermore, examples of nitrogen-containing salts in this inactivating solution include ammonium sulfate.

[0014] The oxidation treatment step of S40 includes a treatment step (S41) to deactivate the Ni metal, and may further include a sulfur compound stabilization step (S42). In the treatment step, a treatment is performed to deactivate the Ni metal contained in the nickel-metal hydride battery using a treatment solution in which anions containing S are dissolved. In this step, the treatment solution may be added to the nickel-metal hydride battery, or the electrodes may be removed from the nickel-metal hydride battery in an inert atmosphere and immersed in the treatment solution, or the electrodes may be brought into contact with the treatment solution. The treatment solution contains anions containing S, such as S 2- and SH -The treatment solution may contain one or more of the following: Furthermore, the treatment solution may contain one or more of alkali metal ions and ammonium ions as cations. Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions, with sodium ions being more preferred. Examples of sulfur compounds included in the treatment solution include NaHS, KHS, (NH4)2S, Na2S, and K2S, with NaHS being preferred. The treatment solution is preferably an aqueous solution, and the concentration of the sulfur compound is preferably 10% by mass or more, more preferably 15% by mass or more, and more preferably 20% by mass or more. Furthermore, the concentration of the sulfur compound is preferably below the saturation level, and may be 50% by mass or less, or 45% by mass or less. Furthermore, the treatment solution is preferably alkaline. The pH of the treatment solution is preferably 8 or higher, and may be 9 or higher, or 10 or higher. Furthermore, the pH of the treatment solution can be 14 or lower, more preferably 12 or lower. This processing step may be carried out at room temperature, for example, in the range of 20°C to 25°C. Alternatively, the processing temperature may be in the range of -20°C to 100°C. In this processing step, the amount of processing solution added should be appropriately selected according to the concentration of the sulfur compound, the processing temperature, and the scale of the nickel-metal hydride battery (e.g., Ni content). When adding an excess amount of processing solution in this step, it is preferable to avoid an excessive amount of excess sulfur compound. Furthermore, the processing time should be appropriately selected according to the scale of the nickel-metal hydride battery, the amount and concentration of the processing solution added, and the type of salt. For example, the processing time may be in the range of 1 hour to 24 hours. After applying the processing solution to the nickel-metal hydride battery in the processing step, it may be held undisturbed, or held while being vibrated. In this process, no special treatment is required; it is sufficient to simply let it stand.

[0015] In the stabilization step of the sulfur compound in S42, a stabilizing solution containing one or more of an oxidizing agent and transition metal ions is used to stabilize the remaining S anions into any one of thiosulfate ions, sulfate ions, and transition metal sulfide compounds. Examples of the oxidizing agent include peroxides, chlorates, permanganates, nitrates, etc. Examples of the transition metal ions include ions such as Mn, Fe, Co, Ni, Cu, Zn, etc. In this stabilization treatment of the sulfur compound, it may be carried out at room temperature, for example, in the range of 20°C or higher and 25°C or lower. Note that this temperature may also be in the range of -20°C to 100°C. The addition amount and concentration of the stabilizing solution, etc., may be appropriately set to an amount capable of neutralizing it according to the addition amount and concentration of the treatment solution.

[0016] [Nickel-hydrogen battery] The nickel-hydrogen battery to be inactivated will be described. A nickel-hydrogen battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an ion conduction medium interposed between the positive electrode and the negative electrode for conducting carrier ions. As the positive electrode active material, for example, nickel oxide compounds such as nickel oxyhydroxide are used. Also, as the negative electrode active material, a hydrogen storage alloy or hydrogen compound containing hydrogen is used. As the ion conduction medium, as an electrolyte solution, an alkaline solution such as an aqueous potassium hydroxide solution is used. The shape of this nickel-hydrogen battery is not particularly limited, and examples include coin type, button type, sheet type, laminated type, cylindrical type, flat type, square type, etc. Also, it may be a large-sized one used in electric vehicles, etc. An example of the nickel-hydrogen battery is shown in FIG. 2. FIG. 2 is a cross-sectional view showing the schematic configuration of a coin-type nickel-hydrogen battery 20. As shown in FIG. 2, the nickel-hydrogen battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material provided at the lower part of this battery case 21, a negative electrode 23 having a negative electrode active material provided at a position facing the positive electrode 22 through a separator 24, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 for sealing the battery case 21 through the gasket 25.

[0017] [Inactivation device] The inactivation device is configured as a device that executes the processing steps of the above-described inactivation method. This device includes, for example, a processing unit that performs an inactivation process for inactivating Ni contained in a nickel-hydrogen battery using a processing solution in which an anion containing S is dissolved. The processing unit may include, for example, an injection unit that receives the processing solution into the nickel-hydrogen battery, and a stationary unit that stationary the nickel-hydrogen battery. In this inactivation device, the processing solution is injected into the nickel-hydrogen battery stationary in the stationary unit by the injection unit to inactivate the Ni metal. Alternatively, the processing unit may include a storage unit that stores the processing solution in such a manner that the nickel-hydrogen battery can be immersed. In this inactivation device, the electrodes of the nickel-hydrogen battery are immersed in the storage unit containing the processing solution to inactivate the Ni metal.

[0018] In the above-described inactivation method and inactivation device, a novel inactivation method and inactivation device for inactivating a nickel-hydrogen battery can be provided. The reason for obtaining such an effect is presumably, for example, that the sulfur-based anion contained in the processing solution reacts with the Ni metal and can stabilize the Ni.

[0019] Note that the present disclosure is not limited to the above-described embodiments at all, and it goes without saying that various embodiments can be implemented as long as they belong to the technical scope of the present disclosure.

[0020] For example, in the above-described embodiment, the inactivation solution has been described as containing a nitrogen-containing salt as an inactivation compound, but it is not particularly limited to a nitrogen-containing salt as long as it can realize the inactivation reaction of Ni-MH.

[0021] The present disclosure may be any of the following [1] to [7]. [1] A processing step of inactivating Ni contained in a nickel-hydrogen battery using a processing solution in which an anion containing S is dissolved, An inactivation method including the above. [2] The processing solution contains S 2- and SH - The inactivation method according to [1], which contains any one or more of the above. [3] The deactivation method according to [1] or [2], wherein the treatment solution comprises one or more alkali metal ions and ammonium ions as cations. [4] The treatment solution contains Na as a cation. + A method of deactivation described in any one of [1] to [3], including the above. [5] The inactivation method according to any one of [1] to [4], wherein the treatment solution is alkaline. A method of deactivation described in any one of [6] [1] to [5], A deactivation method comprising, after the processing step, a stabilization step in which the remaining S anion is stabilized to one of thiosulfate ions, sulfate ions, and sulfide transition metal compounds using a stabilizing solution containing one or more of an oxidizing agent and transition metal ions. [7] A deactivation device for deactivating nickel-metal hydride batteries, A processing unit that performs an inactivation treatment to deactivate the Ni contained in nickel-metal hydride batteries using a processing solution in which anions containing S are dissolved. A deactivation device equipped with the following features. [Examples]

[0022] The following describes experimental examples that specifically examine the method for deactivating nickel-metal hydride batteries according to this disclosure. Experimental Examples 1 to 5 correspond to embodiments of this disclosure, and Experimental Examples 6 to 8 correspond to reference examples.

[0023] (Experimental Example 1) (Making small batteries) A cell was fabricated using a positive electrode, negative electrode, and separator for an automotive Ni-MH battery. The positive and negative electrodes were cut to achieve a design capacity of 125 mAh. The positive electrode was placed in a separator bag and sandwiched between two negative electrodes. Ni metal tabs were extended from both the positive and negative electrodes to form a miniature cell. The miniature cell was then sandwiched between separators that extended beyond the restraint, and the restraint was used to vacuum impregnate it with alkaline electrolyte to form a miniature cell. The separator sandwiching the miniature cell served as the liquid junction, and a ceramic filter of an Hg / HgO reference electrode immersed in a 1M NaOH solution was pressed against the portion of the separator extending from the restraint to obtain a miniature cell capable of measuring the potential relative to the reference electrode.

[0024] (Activation and pre-discharge of small batteries) The small cell was initially charged at a current of 6.25 mA (1 / 20 C) for 24 hours, reaching a capacity equivalent to 120% of its state of charge (SOC). After a 10-minute pause, it was discharged at a current of 125 mA (1 C) down to a voltage limit of 1 V. For subsequent cycles, it was charged at a current of 12.5 mA (1 / 10 C) for 1.2 hours, reaching a capacity equivalent to 120% of its SOC. After a 10-minute pause, it was discharged at a current of 125 mA (1 C) down to a voltage limit of 1 V. This cycle was repeated five times to obtain an active Ni-MH small cell. Before evaluating the processing solution, the cell was discharged to -0.6 V relative to the reference electrode at a current of 12.5 mA (1 / 10 C) to completely remove hydrogen from the MH before obtaining the sample.

[0025] (Injection of treatment solution) After releasing the cell constraints and removing the separator for the liquid junction, 125 μL of NaHS aqueous solution (15%) was injected between the negative electrode and the separator as a treatment solution. The cell was then restrained again and left for 24 hours.

[0026] (MH sampling for VSM measurement) After immersion in the treatment solution, the battery was placed in a glove box under an Ar atmosphere to obtain an inactivated MH negative electrode. The MH negative electrode was washed three times with deionized water, then air-dried under an Ar flow for more than 1 hour to obtain the MH negative electrode, and the MH was peeled off the electrode to obtain electrode powder. The electrode was peeled off in four separate locations from the negative electrode. The electrode powder was placed in a sample capsule for powder VSM measurement, and the sample volume was weighed. Then, paraffin was placed in the sample case, heated with a heat gun to melt the paraffin, and then cooled to solidify the sample inside the capsule to obtain a sample for VSM measurement.

[0027] (VSM measurement) To quantify the active Ni metal, VSM measurements were performed at room temperature. After pre-calibration with a standard Ni metal sample, a capsule containing the sample powder was attached to a sample holder, and a magnetic field of ±16 kOe was applied while vibrating at 100 Hz to measure the magnetization. The measured magnetization was divided by the electrode weight, which had been measured beforehand, to obtain the electrode's mass magnetization. The average of the mass magnetizations at two points on the electrode was taken as the sample's mass magnetization.

[0028] (Experimental Example 2) The same test was conducted as in Experimental Example 1, except that the treatment solution injected was a 45% NaHS aqueous solution, and the inactivation of treatment solutions at different concentrations was evaluated.

[0029] (Experimental Example 3) Ni metal pieces in an alkaline electrolyte solution (25 cm³). 3 and 15% NaHS solution 6cm 3 After immersing the Ni metal fragments in a solution of the two substances for five days, they were recovered, washed with water, and then the material formed on the surface was identified using a micro-Raman system with a 532 nm laser as the light source.

[0030] (Experimental Example 4) The same test was conducted as in Experimental Example 1, except that the treatment solution injected was a (NH4)2S aqueous solution (10%), and the anion species was S 2- The inactivation of the substance in the treatment solution was evaluated.

[0031] (Experimental Example 5) The same test was conducted as in Experimental Example 1, except that the treatment solution injected was a 10% KHS aqueous solution, and the inactivation with different cation species in the treatment solution was evaluated.

[0032] (Experimental Example 6) Samples were prepared using the same testing method as in Experimental Example 1, except that the treatment solution was not injected, and the effect of the treatment solution was confirmed.

[0033] (Experimental Example 7) The sample from Experimental Example 6 was exposed to the atmosphere overnight before sampling, and the amount of metallic Ni reduced by oxidation in the atmosphere was quantified to serve as an indicator of the effectiveness of the treatment solution.

[0034] (Experimental Example 8) The same test as in Example 1 was performed, except that the treatment solution in Experimental Example 1 was a 30% H2O2 solution and the electrodes were stripped in two places. The deactivation effect of Ni by a treatment solution using H2O2, a common oxidizing agent, was evaluated.

[0035] (Results and Discussion) Since MH, rare earth hydroxides, Ni oxides, and sulfides in the corroded layer are nonmagnetic, the magnetization is considered to be proportional to the amount of Ni in the ferromagnetic material. That is, the mass magnetization reflects the amount of Ni metal, and using the fact that the mass magnetization of Ni is σ = 56 emu / g, the amount of active metallic Ni in MH can be calculated from the mass magnetization. A comparison of experimental examples 6 and 7 showed that exposure of MH to the atmosphere oxidizes the active Ni clusters and oxidizes the metallic Ni surface, resulting in a decrease in the amount of Ni. Depending on the amount of Ni metal, the amount of heat generated may increase, which could lead to damage to recycling equipment and safety issues for workers.

[0036] Table 1 summarizes the average mass magnetization (emu / g) and Ni metal content (mass%) for experimental examples 1, 2, 4, and 5. Table 2 summarizes the average mass magnetization (emu / g) and Ni metal content (mass%) for experimental examples 6-8. A comparison between experimental examples 1-5 and experimental examples 6 and 7 shows that the amount of active Ni metal decreases more significantly with the treatment solution than when the MH anode is exposed to air. This indicates that it is possible to oxidize active Ni in the solution to produce stable NiS. Since NiS is stable in air, it is considered that there is no generation of hydrogen sulfide or heat generation due to oxidation. A comparison of experimental examples 1 and 2 shows that Ni clusters can be oxidized without significant dependence on the concentration of the NaHS aqueous solution.

[0037] Figure 3 shows the measurement results of the micro-Raman system in Experimental Example 3. It was shown that metallic Ni was oxidized by the NaHS aqueous solution, producing low-crystallinity NiS or Ni3S2 sulfide, thus oxidizing Ni. Examples 4 and 5 showed that metallic Ni was also oxidized by (NH4)2S aqueous solution and KHS aqueous solution. Experimental Example 8 showed that H2O2, a common oxidizing agent, had no oxidizing effect on the Ni clusters on the surface of MH. When the H2O2 solution came into contact with the positive electrode during injection, it foamed vigorously, suggesting that the disproportionation reaction H2O2 → H2O + 1 / 2O2 was accelerated by the positive electrode acting as a catalyst. In other words, it was shown that solution treatment in a Ni-MH cell using hydrogen peroxide is not possible.

[0038] The sulfides used for oxidation decompose in the atmosphere, gradually generating hydrogen sulfide. To suppress the generation of hydrogen sulfide, it is possible to oxidize the sulfides using hydrogen peroxide or an aqueous sodium perchlorate solution, converting them into thiosulfate ions or sulfate ions. In this disclosure, it is assumed that an aqueous solution of sulfide or hydrogen sulfide is injected into a Ni-MH battery to oxidize the Ni clusters, and then an oxidizing agent is injected into the Ni-MH battery to suppress the generation of hydrogen sulfide.

[0039] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0040] [Table 1]

[0041] [Table 2] [Industrial applicability]

[0042] This invention is applicable to the field of the battery industry. [Explanation of Symbols]

[0043] 20 Non-aqueous secondary battery, 21 Battery case, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Ion conducting medium.

Claims

1. A process to inactivate Ni contained in a nickel-metal hydride battery using a processing solution in which anions containing S are dissolved, An inactivation method including the following.

2. The aforementioned processing liquid is S 2- and SH - The deactivation method according to claim 1, comprising one or more of the following.

3. The deactivation method according to claim 1 or 2, wherein the treatment solution contains one or more alkali metal ions and ammonium ions as cations.

4. The aforementioned treatment solution contains Na as a cation. + The deactivation method according to claim 1 or 2, including the method described in claim 1 or 2.

5. The deactivation method according to claim 1 or 2, wherein the treatment solution is alkaline.

6. A method for deactivating according to claim 1 or 2, A deactivation method comprising, after the processing step, a stabilization step in which the remaining S anion is stabilized to one of thiosulfate ions, sulfate ions, and sulfide transition metal compounds using a stabilizing solution containing one or more of an oxidizing agent and transition metal ions.

7. A deactivation device for inactivating nickel-metal hydride batteries, A processing unit that performs an inactivation treatment to deactivate Ni contained in a nickel-metal hydride battery using a processing solution in which anions containing S are dissolved. A deactivation device equipped with the following features.

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