Inactivation method and inactivation device

Abstract

An inactivation method according to the present disclosure comprises an inactivation step for inactivating a nickel hydrogen battery by reacting, with a positive electrode and / or a negative electrode of the nickel hydrogen battery, an inactivation liquid having dissolved therein an anion including N and O and / or a cation including N and H.

Description

Inactivation method and inactivation device

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

[0002] A conventional electricity storage device proposed is a sealed metal-hydrogen alkaline storage battery having a negative electrode primarily made of a hydrogen storage alloy and a positive electrode, and equipped with an oxidizing agent supply means for supplying an oxidizing agent to oxidize hydrogen stored in the negative electrode (see Patent Document 1). It is claimed that this electricity storage device can provide a sealed metal-hydrogen alkaline storage battery with improved cycle characteristics by improving the utilization rate of the negative electrode. Another proposed method for stabilizing a dissolved and pulverized hydrogen storage alloy involves exposing the pulverized hydrogen storage alloy powder to a carbon dioxide atmosphere and then removing it from the atmosphere (see Patent Document 2). It is claimed that this stabilization method can stabilize the hydrogen storage alloy without forming an oxide film on the surface.

[0003] JP-A-5-251108 JP-A-10-195503

[0004] When recycling commonly used nickel-metal hydride batteries, it has been necessary to inactivate the batteries in order to ensure safer recycling. In the stabilization method of Patent Document 2, a process for stabilizing the hydrogen storage alloy has been considered, but the process for treating the batteries as batteries has not yet been fully considered.

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

[0006] As a result of extensive research to achieve the above-mentioned object, the present inventors have discovered that by using a nitrogen-containing anion and a nitrogen-containing cation, a nickel-metal hydride battery can be more efficiently inactivated through its oxidation-reduction cycle, and have thus completed the invention of the present disclosure.

[0007] That is, the deactivation method of the present disclosure includes a deactivation step of causing a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved to react with the positive electrode and / or negative electrode of the nickel-metal hydride battery, thereby deactivating the nickel-metal hydride battery.

[0008] The deactivation device of the present disclosure is a deactivation device for deactivating a nickel-metal hydride battery, and includes a processing unit that performs a deactivation process to deactivate the nickel-metal hydride battery by causing a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved to react with the positive electrode and / or negative electrode of the nickel-metal hydride battery.

[0009] This deactivation method and deactivation device can provide a novel deactivation method and deactivation device for deactivating nickel-metal hydride batteries. The reason for this effect is presumably due to, for example, an oxidation-reduction reaction of nitrogen-containing cations and nitrogen-containing anions contained in the deactivation solution, which causes the deactivation reaction to proceed at the positive and negative electrodes.

[0010] A flowchart showing an example of a battery recycling processing routine. A cross-sectional view showing the schematic configuration of a Ni-MH secondary battery 20. A five-cycle discharge curve of a small-sized Ni-MH battery. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using KNO2 and the results of ammonia detection. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using NaNO2. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using KNO3 and the results of ammonia and nitrite detection. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using (NH4)2SO4 and the results of nitrite detection. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using K3Fe(CN)6. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using 1,5-dihydroanthraquinone. A diagram showing the deactivation behavior of a small-sized Ni-MH battery using 1,2-naphthoquinone-4-sodium sulfonate. A diagram showing the relationship between nitrite ion concentration and deactivation time for Experimental Examples 10 to 13. A relationship diagram between the injection amount of sodium nitrite aqueous solution and the inactivation time in Examples 11, 13, and 14. A relationship diagram between the concentration of sodium nitrite aqueous solution and ammonium nitrate and the inactivation time in Experimental Examples 11, and 16 to 19. A relationship diagram between the inactivation index of the inactivating agent and the inactivation time in Experimental Examples 10 to 19.

[0011] (Deactivation Method) The deactivation method disclosed herein is a process for deactivating nickel-metal hydride batteries that is performed during the process of recycling nickel-metal hydride batteries. FIG. 1 is a flowchart showing an example of a nickel-metal hydride battery recycling process routine. This recycling process is, for example, an example of a process for recycling automotive batteries, such as those used in HEVs. In this routine, a battery pack is recovered from an HEV (S10), disassembled (S20), deactivated by injecting a deactivating solution (S30), oxidized (S40), crushed (S50), dissolved to recover elements (S60), and active materials are synthesized using the recovered elements (S70) for reassembly into cells (S80). This deactivation process may be performed in S30 of this routine.

[0012] In the deactivation step, a deactivating solution containing dissolved anions containing N and O and / or cations containing N and H is reacted with the positive electrode and / or negative electrode of the nickel-metal hydride battery to deactivate the nickel-metal hydride battery. The deactivating solution may be a solution capable of a shuttle reaction in which the substance produced after desorbing H from Ni-MH inserts H into the positive electrode and then desorbs H again from the negative electrode. Here, for convenience, a compound containing either anions containing N and O and / or cations containing N and H is referred to as a "nitrogen-containing salt." This deactivating solution is preferably an aqueous solution using water as the solvent. Furthermore, this deactivating solution is preferably alkaline, and may be made alkaline by dissolving an alkali metal hydroxide. Examples of alkali metals include Li, Na, and K, with K and Na being preferred. The deactivating solution preferably contains, as nitrogen-containing salts, nitrate anions, nitrite anions, and one or more of primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations. 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. The deactivating solution may contain alkali cations as counter cations for the nitrate and nitrite anions. The deactivating solution may also contain sulfate anions and / or halogens as counter anions for the ammonium cation. Examples of nitrogen-containing salts contained in the deactivating solution include sodium nitrate, potassium nitrate, lithium nitrate, sodium nitrite, potassium nitrite, and lithium nitrite. Of these, sodium nitrite and potassium nitrite are more preferred from the standpoint of solubility, etc. Examples of nitrogen-containing salts contained in the deactivating solution include ammonium sulfate.

[0013] The concentration of the nitrogen-containing salt contained in the deactivation 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 determined appropriately depending on the solubility in the alkaline electrolyte in the cell, but may be 6 M or lower, or even higher depending on the composition of the alkaline electrolyte. Furthermore, if the deactivation solution is not dissolved in the alkaline electrolyte at the injection stage, the concentration may be higher, such as 6 M or higher, 10 M or higher, or 30 M or lower. Furthermore, the pH of the deactivation solution is preferably 3 or higher, and may be 8 or 9 or higher. In this deactivation step, the deactivation treatment may be performed at room temperature, for example, in the range of 20°C to 25°C. The treatment temperature may be in the range of -20°C to 100°C. In this step, the amount of deactivation solution added may be selected appropriately depending on the concentration of the nitrogen-containing salt, the treatment temperature, and the size of the nickel-metal hydride battery. The treatment time for the deactivation treatment may be appropriately selected depending on the size of the nickel-metal hydride battery, the amount and concentration of the deactivation solution added, and the type of salt. This treatment time may be, for example, in the range of 1 hour to 24 hours. In the deactivation treatment, after the deactivation solution is injected into the nickel-metal hydride battery, the battery may be left to stand, or may be held while being vibrated. This treatment does not require any special processing, and may simply be left to stand.

[0014] The deactivation step may use a deactivation solution whose deactivation index, calculated by dividing the capacity (mAh) of the nickel-metal hydride battery to be deactivated by the number of proton reactions at the positive and negative electrodes multiplied by the amount (mol) of the deactivation substance containing an anion containing N and O and / or a cation containing N and H, falls within a predetermined range. In this step, it is preferable to use a deactivation solution in which the solvent and deactivation substance are selected and their concentrations and amounts are adjusted so that the deactivation index falls within the predetermined range. Here, the reaction number is the amount of hydrogen reacting with one molecule of the deactivation substance. The reaction number can be determined by which of the following formulas (1) to (3) occurs. For example, the reaction number is "6" for NaNO2 or KNO2, and "14" for NH4NO3. This deactivation index is preferably smaller, for example, within the range of 4 Ah / mol to 75 Ah / mol, more preferably 50 Ah / mol or less, and even more preferably 40 Ah / mol or less.

[0015] In the deactivation step, a deactivating solution may be injected into the electrolyte while the electrodes of the nickel-metal hydride battery are constrained. In this deactivation step, a deactivating solution containing ammonium nitrate as a deactivating substance in a range of 2 mol / L to 8 mol / L is preferably used. Ammonium nitrate is preferred because it has a relatively high solubility in water as a solvent, making it easy to increase the concentration, is relatively inexpensive, and is easier to handle. The concentration of the deactivating substance in the deactivating solution has an appropriate range, taking into account the functionality after injection into the cell, and is more preferably 2 mol / L or more and more preferably 8 mol / L or less.

[0016] During the passivation treatment, it is presumed that the reactions represented by the following formulas (1) to (3) proceed at the positive and negative electrodes. For example, in a passivation solution containing ammonia cations, the reaction represented by formula (1) proceeds at the positive electrode, deactivating Ni and generating nitrite anions. In addition, in a passivation solution containing nitrate anions, the reaction represented by formula (2) proceeds at the negative electrode, deactivating the hydrogen storage alloy and generating nitrite anions. Furthermore, in the presence of nitrite anions at the negative electrode, the reaction represented by formula (3) proceeds, deactivating the hydrogen storage alloy and generating ammonium salts. Therefore, it is presumed that the presence of any of the nitrogen-containing salts in the passivation solution causes the reactions represented by formulas (1) to (3) to proceed cyclically at the positive and negative electrodes, resulting in efficient battery passivation.

[0017]

[0018] [Nickel-metal hydride battery] The nickel-metal hydride battery to be deactivated will now be described. A nickel-metal hydride battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an ion-conducting medium interposed between the positive and negative electrodes to conduct carrier ions. The positive electrode active material may be a nickel oxide compound such as nickel oxyhydroxide. The negative electrode active material may be a hydrogen-storing alloy or a hydrogen compound containing hydrogen. The ion-conducting medium may be an alkaline solution such as a concentrated potassium hydroxide aqueous solution as an electrolyte. The shape of this nickel-metal hydride battery is not particularly limited, and examples include coin, button, sheet, laminated, cylindrical, flat, and rectangular types. Large nickel-metal hydride batteries for use in electric vehicles and the like may also be used. An example of a nickel-metal hydride battery is shown in FIG. 2. FIG. 2 is a cross-sectional view showing the schematic configuration of a coin-type nickel-metal hydride battery 20. As shown in FIG. 2 , the nickel-metal hydride battery 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and provided at the bottom of the battery case 21, a negative electrode 23 having a negative electrode active material and provided in a position facing the positive electrode 22 with a separator 24 interposed therebetween, a gasket 25 made of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 and sealing the battery case 21 via the gasket 25.

[0019] [Deactivation Apparatus] The deactivation apparatus is configured as an apparatus for carrying out the above-described deactivation method. This apparatus includes, for example, a processing unit that performs deactivation treatment to deactivate a nickel-metal hydride battery by reacting a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved with the positive electrode and / or negative electrode of the nickel-metal hydride battery. The processing unit may include an injection unit that injects the deactivating solution into the nickel-metal hydride battery, and a setting unit that sets the nickel-metal hydride battery.

[0020] The deactivation method and deactivation device described above can provide a novel deactivation method and deactivation device for deactivating nickel-metal hydride batteries. The reason for this effect is presumably due to, for example, an oxidation-reduction reaction of nitrogen-containing cations and nitrogen-containing anions contained in the deactivation solution, which causes the deactivation reaction to proceed at the positive and negative electrodes.

[0021] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

[0022] The present disclosure may be implemented as any one of the following [1] to [6]. [1] A deactivation method including a deactivation step of reacting a deactivating solution containing dissolved anions containing N and O and / or cations containing N and H with a positive electrode and / or a negative electrode of a nickel-metal hydride battery to deactivate the nickel-metal hydride battery. [2] The deactivation method according to [1], wherein the deactivating solution is a solution capable of a shuttle reaction in which a substance produced upon desorption of H from Ni-MH inserts H into the positive electrode and then desorbs H from the negative electrode again. [3] The deactivation method according to [1] or [2], wherein the deactivating solution contains nitrate anions, nitrite anions, and one or more of primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations. [4] The deactivation method according to [3], wherein the deactivating solution is an alkali cation for the nitrate anions and nitrite anions, and contains a sulfate anion and / or a halogen for the ammonium cation. [5] The deactivation method according to any one of [1] to [4], wherein the deactivation solution is alkaline. [6] The deactivation step uses the deactivation solution, wherein the solvent and the deactivation substance are selected and the concentration and amount thereof are adjusted so that the deactivation index, obtained by dividing the capacity (mAh) of the nickel-metal hydride battery to be deactivated by the number of proton reactions at the positive and negative electrodes multiplied by the amount (mol) of the deactivation substance containing an anion containing N and O and / or a cation containing N and H, is in the range of 4 Ah / mol to 75 Ah / mol. [7] The deactivation method according to any one of [1] to [6], wherein the deactivation solution contains ammonium nitrate as a deactivation substance in the range of 2 mol / L to 8 mol / L. [8] A deactivation device for deactivating a nickel-metal hydride battery, the deactivation device comprising: a processing unit that performs a deactivation process for deactivating the nickel-metal hydride battery by reacting a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved with the positive electrode and / or negative electrode of the nickel-metal hydride battery.

[0023] Below, specific examples of the deactivation method for nonaqueous secondary batteries according to the present disclosure will be described as experimental examples. Experimental Examples 1 to 4 and 10 to 19 correspond to working examples of the present disclosure, and Experimental Examples 5 to 9 correspond to reference examples.

[0024] (Experimental Example 1) (Creation of a Small Battery) A commercially available Ni-MH battery module for automotive use before electrolyte injection was disassembled to obtain a positive electrode, a negative electrode, and a separator. One side of the negative electrode was peeled off to create a single-sided coated product. The positive electrode and negative electrode were cut out to have a design capacity of 125 mAh. The positive electrode was placed in a separator bag and sandwiched between two single-sided coated negative electrodes, and Ni metal tabs were protruded from each of the positive and negative electrodes to form a small cell. The small cell was sandwiched between restraining devices and vacuum-impregnated with a model alkaline electrolyte (KOH: 6 M, NaOH: 1 M, LiOH: 1 M) to form a small cell.

[0025] (Activation of small batteries and charging before deactivation) The small cell was initially charged at a current value of 6.25 mA (1 / 20 C) for 24 hours, i.e., a capacity equivalent to 120% SOC. After a 10-minute pause, it was discharged at a current value of 12.5 mA (1 / 10 C) to a voltage lower limit of 1 V. From the second cycle onwards, it was charged at a current value of 12.5 mA (1 / 10 C) for 12 hours, i.e., a capacity equivalent to 120% SOC, and after a 10-minute pause, it was discharged at a current value of 12.5 mA (1 / 10 C) to a voltage lower limit of 1 V. This cycle was repeated up to five cycles to obtain an activated Ni-MH small cell. In addition, in order to evaluate the deactivation solution in the next test, the small cell was charged at a current value of 12.5 mA (1 / 10 C) for 12 hours, i.e., a capacity equivalent to 120% SOC. FIG. 3 shows the discharge curves of a small Ni-MH battery for five cycles (N=2).

[0026] (Preparation of Deactivating Solution) KNO2 was dissolved in a model alkaline electrolyte (KOH: 6 M, NaOH: 1 M, LiOH: 1 M) to a concentration of 1 M to obtain a deactivating solution.

[0027] (Inactivation test, confirmation of reaction products) After pouring the inactivation solution into a polytetrafluoroethylene beaker, the small cell was removed from the restraint and transferred to the beaker. The voltage between the positive and negative electrodes was then monitored in a thermostatic chamber at 20°C. Figure 4 shows the behavior of the inactivation of a small Ni-MH battery using KNO2 (N number = 2). As shown in Figure 4, it was found that injecting this inactivation solution into the electrolyte can reduce the battery voltage over time. In addition, the solution after inactivation was removed and ammonia was detected using the Nessler method. As a result, ammonium ions were detected from the KNO2 inactivation solution. This suggests that a reaction is progressing in which NO2 in the inactivation solution is reduced.

[0028] (Experimental Example 2) The same test as in Experimental Example 1 was conducted except that the salt dissolved in the model electrolyte was changed to NaNO2 and the solution was not analyzed, and the deactivation behavior of NaNO2 was evaluated. This was used as Experimental Example 2. Figure 5 shows the behavior of deactivation of a small Ni-MH battery with NaNO2. As shown in Figure 5, it was found that injecting this deactivation solution into the electrolyte can reduce the battery voltage over time.

[0029] (Experimental Example 3) Experimental Example 3 was conducted in the same manner as Experimental Example 1, except that the salt dissolved in the model electrolyte was changed to KNO3, the KNO3 concentration was set to 0.2 M, and the solution analysis was performed as described below. Figure 6 illustrates the behavior of a small Ni-MH battery deactivation with KNO3 (number of samples = 2). The solution in Experimental Example 3 was analyzed by extracting the deactivated solution and detecting nitrite ions using naphthylethylenediamine colorimetry and ammonium ions using the Nessler method. As shown in Figure 6, injecting this deactivation solution into the electrolyte reduced the battery voltage over time. Furthermore, analysis of the solution after deactivation detected ammonium ions and nitrite ions in the KNO3 deactivation solution. This suggests that a reduction reaction of NO3 in the deactivation solution was occurring.

[0030] (Experimental Example 4) The deactivation solution used in Experimental Example 1 was prepared and analyzed as follows. The deactivation solution was prepared by mixing a model electrolyte solution and a 0.5 M (NH4)2SO4 solution at a volume ratio of 2:1 to obtain a deactivation solution. The solution was analyzed by extracting the deactivated solution and detecting nitrite ions using naphthylethylenediamine colorimetry. Figure 7 shows the deactivation behavior of a small Ni-MH battery with (NH4)2SO4 (N number = 2). As shown in Figure 7, injecting this deactivation solution into the electrolyte solution was found to reduce the battery voltage in two stages over time. Furthermore, analysis of the solution after deactivation revealed that nitrite ions were detected in the (NH4)2SO4 deactivation solution. This suggests that a reaction in which the ammonium ions in the deactivation solution were oxidized was occurring.

[0031] (Experimental Examples 5 and 6) The deactivation solution used in Experimental Example 1 was modified as follows. The same test as in Experimental Example 1 was conducted, except that the K3Fe(CN)6 solution was adjusted to 10 mM in 6 M KOH. This resulted in Experimental Example 5, which evaluated the deactivation behavior of K3Fe(CN). Furthermore, the following deactivation solution was added to the evaluation cell in Experimental Example 5, and the deactivation behavior was evaluated. This resulted in Experimental Example 6, which evaluated the deactivation behavior of the evaluation cell in Experimental Example 5 by adding the following deactivation solution to 1 M KOH and adjusting the K3Fe(CN)6 solution to 100 mM. After adding the deactivation solution, the cell was left for 150 hours or more, and then disassembled in a glove box under an Ar atmosphere. The state of the solution and the cell were visually observed. Figure 8 illustrates the deactivation behavior of small Ni-MH batteries using K3Fe(CN)6 in Experimental Examples 5 and 6. As shown in Figure 8, a sufficient decrease in battery voltage was not achieved with 0.01 M K3Fe(CN)6. Furthermore, even with 0.1 M K3Fe(CN)6, it could not be said that a sufficient passivation effect was obtained. Furthermore, yellow crystals were precipitated on the negative electrode after passivation.

[0032] Experimental Example 7: The same test as in Experimental Example 1 was conducted except that the molecules dissolved in the model electrolyte solution in the preparation of the deactivation solution were changed to 1,5-dihydroanthraquinone, the concentration of 1,5-dihydroanthraquinone was set to 0.01 M, and the solution was not analyzed. This test evaluated the deactivation behavior of 1,5-dihydroanthraquinone, and was designated Experimental Example 7. Figure 9 shows the behavior of deactivation of a small Ni-MH battery with 1,5-dihydroanthraquinone (N number = 2). As shown in Figure 9, 1,5-dihydroanthraquinone was unable to achieve sufficient battery deactivation effects.

[0033] (Experimental Example 8) The same test as in Experimental Example 1 was conducted, except that the molecules dissolved in the model electrolyte solution when preparing the deactivation solution were changed to sodium 1,2-naphthoquinone-4-sulfonate, the concentration of sodium 1,2-naphthoquinone-4-sulfonate was set to 0.1 M, and the solution was not analyzed. This test evaluated the deactivation behavior of sodium 1,2-naphthoquinone-4-sulfonate, and this was designated Experimental Example 8. Figure 10 is a diagram showing the deactivation behavior of a small Ni-MH battery using sodium 1,2-naphthoquinone-4-sulfonate (number of subjects = 2). As shown in Figure 10, sodium 1,2-naphthoquinone-4-sulfonate was unable to achieve sufficient battery deactivation effects.

[0034] Experimental Example 9: The solubilities of nitric acid and nitrite salts in model alkaline electrolytes (6 M KOH, 1 M NaOH, and 1 M LiOH) were quantified using the following procedure. For the Li and Ca nitrite salts, 2 mmol of Li salt and 0.04 mmol of Ca salt were weighed, and 1000 μL of electrolyte was added dropwise and stirred. If any residue remained, an equal amount of electrolyte was added dropwise. If no residue remained, the volume was measured and the solubility was calculated. For the Na and K nitrite salts, 20 mmol of nitrite and nitrite salt were weighed, and 500 μL of electrolyte was added dropwise and stirred. If any residue remained, an equal amount of electrolyte was added dropwise. If no residue remained, the volume was measured and the solubility was calculated. Note that Ca(NO) did not completely dissolve in the above test, so the upper limit of solubility was evaluated. The quantified solubilities are summarized in Table 1. As for salt solubility (mol / L), sodium and potassium nitrites showed high solubility.

[0035]

[0036] (Results and Discussion) In solutions containing NO2 ions, NO3 ions, and NH4 ions, the battery voltage dropped below 1 V, confirming that the battery was discharging due to the effects of the solution. In analyses of the solutions in Experimental Examples 1 and 4 conducted to confirm the reactions in the above solutions, ammonia was detected in Experimental Example 1 and nitrous acid was detected in Experimental Example 4. In other words, it is inferred that a shuttle reaction involving these ions occurred between the positive and negative electrodes of the Ni-MH, causing the battery to discharge. Furthermore, since ammonia and nitrous acid were detected in the analysis of the solution in Experimental Example 3, it is inferred that nitrate ions were reduced to nitrite ions and then further reduced by the MH to produce ammonia, which then reduced the positive electrode. From these results, it is inferred that discharge due to the passivation solution is due to chemical reactions derived from the reaction formulas (1) to (3) described above. Experimental Examples 1 and 2 demonstrated that passivation of NO2 proceeds regardless of the cation species combined with it. On the other hand, it is believed that the cation species affects its solubility in the electrolyte. Therefore, the solubility of various nitrites and nitrates was quantified. The solubility of monovalent cations and nitrates and nitrites was higher than 0.1 M, indicating that they are preferable because they can be quickly discharged as a passivating solution. When comparing different anions, nitrites were found to have higher solubility than nitrates, with Na and K salts being the most soluble and most preferable. On the other hand, the solubility of nitrites and salts of divalent cations was significantly lower, indicating that they are not preferable.

[0037] In Experiments 5 and 6, methods for discharging batteries by using a shuttle reaction between the positive and negative electrodes, such as chemicals capable of utilizing transition metal valence changes or chemicals capable of utilizing stable radicals (collectively referred to as redox mediators (RMs)), were considered in addition to the shuttle reactions described above. Therefore, we investigated whether discharge was possible using potassium hexacyanoferrate (Experimental Examples 5 and 6), a common aqueous RM. First, in Experimental Example 5, potassium hexacyanoferrate was dissolved in the same high-concentration alkaline solution as the electrolyte to evaluate deactivation. However, the solubility of potassium hexacyanoferrate in alkaline solution was low, reaching only 0.01 M. Therefore, the concentration of reactive species was too low to allow discharge reactions to proceed, and the battery voltage barely dropped even after 250 hours. Reducing the alkaline concentration to increase the concentration of reactive species increased the solubility of potassium hexacyanoferrate. Therefore, a deactivating solution prepared by dissolving 0.1 M potassium hexacyanoferrate in 1 M KOH was dropped into the cell. However, even after 150 hours, only one of the two samples reached 1 V. Visual observation of the cell revealed the crystallization of yellow potassium hexacyanoferrate crystals, which were observed on the electrode surface and in the beaker. This suggests that even if an RM with low solubility in alkaline electrolyte is dissolved in a low-concentration alkaline solution and then added, salt crystallization occurs upon contact with the high-concentration alkaline solution present in the cell. The crystals obstruct the liquid flow path, dilute the RM concentration in the solution, and inhibit the shuttle reaction, resulting in a significantly longer reaction time. This phenomenon is presumed to be due to the low solubility of the salt in alkaline electrolyte.

[0038] Among molecules that function as RMs in alkaline solutions, Experimental Example 7 shows an RM that has low solubility in a model electrolyte but undergoes a reversible reaction, while Experimental Example 8 shows an RM that has high solubility in a model electrolyte but undergoes an irreversible reaction. Similar to Experimental Example 5, the discharge reaction of the low-solubility RM did not proceed, and no voltage drop was observed. On the other hand, in Experimental Example 8, which included an irreversible reaction, the voltage drop slowed midway, and the battery was not fully discharged down to 1 V. From the above results, it was inferred that in order to perform passivation, in addition to the shuttle reaction occurring between the positive and negative electrodes of the Ni-MH, it is desirable for the RM to have high solubility in the electrolyte and to have no reactions other than the shuttle reaction.

[0039]

[0040] Next, a small test battery was fabricated, and the injection of a deactivator into this small battery was investigated. While the above-mentioned test results were obtained by using an aqueous solution of salt dissolved in the electrolyte as the deactivating solution to release the constrained state of the cell, the following test was performed by injecting a deactivating solution of salt dissolved in ion-exchange water into the electrolyte of a constrained cell. The small battery was the same as in Experimental Examples 1 to 8 described above.

[0041] (Activation of small batteries and charging before deactivation) The small cells were initially charged at a current value of 6.25 mA (1 / 20 C) for 24 hours, i.e., a capacity equivalent to 120% SOC. After a 10-minute pause, they were discharged at a current value of 125 mA (1 C) to a voltage lower limit of 1 V. From the second cycle onwards, they were charged at a current value of 125 mA (1 C) for 1.2 hours, i.e., a capacity equivalent to 120% SOC, and after a 10-minute pause, they were discharged at a current value of 125 mA (1 C) to a voltage lower limit of 1 V. This cycle was repeated up to five cycles to obtain an activated Ni-MH small cell. In addition, to evaluate the deactivation solution in the next test, the small cells were charged at a current value of 125 mA (1 C) for 12 hours, i.e., a capacity equivalent to 120% SOC.

[0042] (Preparation of Deactivation Solution) NaNO2 was dissolved in ion-exchanged water to a concentration of 5 M to obtain a deactivation solution.

[0043] (Inactivation Test) (Experimental Examples 10-19) The inlet of the cell was opened, and 62.4 μL of 5M NaNO2 aqueous solution was injected into the separator. The voltage between the positive and negative electrodes was then monitored in a thermostatic chamber at 20°C, and the discharge time to 1 V was measured. This was designated Experimental Example 1. A battery was inactivated using the same procedure as in Experimental Example 10, except that the concentration of the inactivating solution was adjusted to 7M. ​​This was designated Experimental Example 11. A battery was inactivated using the same procedure as in Experimental Example 10, except that the nitrite in the inactivating solution was changed to KNO2 at a concentration of 10M. This was designated Experimental Example 12. A battery was inactivated using the same procedure as in Experimental Example 12, except that the concentration of the inactivating solution was adjusted to 13M. This was designated Experimental Example 13. This was designated Experimental Example 14. This was designated Experimental Example 15. Experimental Example 14 was a result of measuring the discharge time when a battery was deactivated using the same procedure as Experimental Example 11, except that the amount of deactivating solution injected was 124.8 μL, and the deactivating solution was doubled (N=3). Experimental Example 15 was a result of measuring the discharge time when a battery was deactivated using the same procedure as Experimental Example 11, except that the amount of deactivating solution injected was 187.4 μL, and the deactivating solution was tripled (N=3). Experimental Example 16 was a result of measuring the discharge time to 1 V when a battery was deactivated using the same procedure as Experimental Example 15, except that the deactivating solution was dissolved in ion-exchanged water to a concentration of 4 M NH4NO3. Experimental Example 17 was a result of measuring the discharge time to 1 V when a battery was deactivated using the same procedure as Experimental Example 16, except that the concentration of the deactivating solution was 5 M. Experimental Example 18 was a result of measuring the discharge time to 1 V when a battery was deactivated using the same procedure as Experimental Example 16, except that the concentration of the deactivating solution was 6 M. In addition, Experimental Example 19 was obtained by measuring the discharge time to 1 V when the battery was deactivated in the same manner as in Experimental Example 18, except that the concentration of the deactivating solution was changed to 8M.

[0044] (Results and Discussion) Table 3 summarizes the type of deactivating substance, concentration (mol / L) of the deactivating solution, amount (μL) injected, test method, time (hr) until cell voltage reached 1V or less, and deactivation index (Ah / mol) for Experimental Examples 10 to 19. The deactivation index is a value obtained by dividing the capacity (mAh) of the nickel-metal hydride battery to be deactivated by the amount (mol) of the deactivating substance multiplied by the number of proton reactions at the positive and negative electrodes. Figure 11 shows the relationship between nitrite ion concentration and deactivation time for Experimental Examples 10 to 13. Figure 12 shows the relationship between the amount of sodium nitrite aqueous solution injected and deactivation time for Examples 11, 13, and 14. Figure 13 shows the relationship between the concentration of sodium nitrite aqueous solution and ammonium nitrate and deactivation time for Experimental Examples 11 and 16 to 19. Figure 14 shows the relationship between the deactivation index and deactivation time for the deactivating agent for Experimental Examples 10 to 19.

[0045] As shown in Figure 11, the deactivation of nickel-metal hydride batteries was confirmed using aqueous solutions of NaNO2 or KNO2. Furthermore, as shown in Figure 12, it was found that by increasing the amount of deactivating solution injected, the deactivation time using NaNO2, which is cheaper and easier to use, can be further shortened. Furthermore, as shown in Figure 13, it was found that by using NH4NO3 as the deactivating substance, the time required for deactivation can be further shortened compared to NaNO2. This is presumed as follows. The deactivation reaction formulas for the nitrite, nitrate, and ammonium salt used in the deactivating solution proceed, for example, according to the above-mentioned formulas (1) to (3). Here, in Experimental Examples 10 to 15, the deactivating substance injected was NO2 - Only anions react with each other, and the reaction begins with formula (3). On the other hand, in Experimental Examples 16 to 19, the ammonium ion, which is a cation, reacts with formula (1), and the nitrate ion, which is an anion, reacts with formula (2), and the anion then reacts with formula (3), which is presumably why deactivation proceeds more efficiently. It is presumed that the reason the deactivation time did not shorten at NH4NO3 concentrations of 5M or higher is probably because the NH4NO3 concentration in the solution did not rise above 5M due to crystallization.

[0046] To compare the deactivation functions of different deactivators side-by-side using the above-mentioned reaction equations (1) to (3), we introduced the deactivation index (battery capacity) / (amount of deactivator) × (number of reactions). The number of reactions is the amount of hydrogen reacting with one molecule of deactivator. As shown in Figure 14, a relatively good linear relationship was obtained between the deactivation index and deactivation time. The battery capacity was introduced into the denominator because it is expected that the input amount range will vary depending on the battery type. In this disclosure, using the deactivation index as the axis, we inferred that the desirable range for deactivating ammonium ions, nitrate ions, and nitrite ions is 4 Ah / mol to 75 Ah / mol, more preferably 50 Ah / mol or less, and even more preferably 40 Ah / mol or less. The above results demonstrate that nickel-metal hydride batteries can be deactivated by using nitrogen-containing ions, such as nitrate-based anions and ammonium-based cations, as deactivation solutions.

[0047]

[0048] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present disclosure.

[0049] This application claims priority to Japanese Patent Application No. 2024-083112 filed on May 22, 2024 and Japanese Patent Application No. 2025-008996 filed on January 22, 2025, the entire contents of which are incorporated herein by reference.

[0050] The present invention is applicable to the field of the battery industry.

[0051] 20 nonaqueous secondary battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 ion conductive medium.

Claims

1. A deactivation method comprising: a deactivation step of reacting a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved with the positive electrode and / or negative electrode of a nickel-metal hydride battery to deactivate the nickel-metal hydride battery.

2. The deactivation method according to claim 1, wherein the deactivating solution is a solution capable of a shuttle reaction in which a substance produced after desorbing H from Ni-MH inserts H into the positive electrode and then desorbs H from the negative electrode again.

3. The inactivation method according to claim 1 or 2, wherein the inactivation solution contains one or more of nitrate anions, nitrite anions, and primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations.

4. The method of claim 3, wherein the inactivating solution contains alkali cations for nitrate and nitrite anions, and sulfate anions and / or halogens for ammonium cations.

5. The inactivation method according to claim 1 or 2, wherein the inactivation liquid is alkaline.

6. The deactivation method according to claim 1 or 2, wherein the deactivation step uses a deactivating solution in which a solvent and a deactivating substance are selected and their concentrations and amounts are adjusted so that a deactivation index, obtained by dividing the capacity (mAh) of the nickel-metal hydride battery to be deactivated by the number obtained by multiplying the amount (mol) of the deactivating substance containing an anion containing N and O and / or a cation containing N and H by the number of reactions of protons at the positive and negative electrodes, falls within the range of 4 Ah / mol to 75 Ah / mol.

7. The inactivation method according to claim 1 or 2, wherein the inactivation solution contains ammonium nitrate as an inactivating substance in the range of 2 mol / L or more and 8 mol / L or less.

8. A deactivation device for deactivating nickel-metal hydride batteries, comprising a processing unit that performs deactivation processing by reacting a deactivating solution in which anions containing N and O and / or cations containing N and H are dissolved with the positive electrode and / or negative electrode of the nickel-metal hydride battery to deactivate the nickel-metal hydride battery.

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