Method for manufacturing nickel-hydrogen storage battery

Abstract

The present application provides a kind of reducing the initial internal resistance of nickel-hydrogen storage battery, the manufacturing method of nickel-hydrogen storage battery of improving initial output performance.The manufacturing method of nickel-hydrogen storage battery is provided with the manufacturing method of nickel-hydrogen storage battery comprising nickel hydroxide as active material positive electrode, comprising hydrogen storage alloy as active material negative electrode and alkaline electrolyte, wherein, in the range of SOC as the charge state of the battery module of nickel-hydrogen storage battery, including: high SOC state comprising SOC 100%;And low SOC state lower than high SOC state, the method has high SOC charge and discharge step, while maintaining the upper limit value and lower limit value of the SOC of battery module in high SOC state, repeatedly charge and discharge for multiple times.The manufacturing method of nickel-hydrogen storage battery according to the present application can reduce the initial internal resistance of nickel-hydrogen storage battery, and can more highly ensure the initial output performance.

Description

Technical Field

[0001] This invention relates to a method for manufacturing nickel-metal hydride batteries, and more particularly, to a method for manufacturing nickel-metal hydride batteries that more preferably activates the negative electrode. Background Technology

[0002] In recent years, nickel-metal hydride (NiMH) batteries have been used as power sources for portable devices, mobile devices, and electric and hybrid vehicles. NiMH batteries offer advantages such as high energy density and excellent reliability, but their initial output may decrease immediately after assembly. Therefore, a technique for activating the hydrogen storage alloy used as the negative electrode material has been proposed (see, for example, Patent Document 1).

[0003] In the technology described in Patent Document 1, the positive electrode active material, including nickel hydroxide, in the positive electrode of a nickel-metal hydride battery is activated. The battery with the activated positive electrode is subjected to one or more charge-discharge cycles, thereby activating a hydrogen storage alloy, which serves as the active material of the negative electrode. Furthermore, during the activation of this hydrogen storage alloy, the battery is brought to an overcharge state in at least one of the one or more charge-discharge cycles.

[0004] In the technology described in Patent Document 1, during the negative electrode activation step, the battery is charged until it reaches an overcharged state, causing what is called cracking (fissures) on the surface of the hydrogen storage alloy in the negative electrode. This micronizes the hydrogen storage alloy in the negative electrode, increasing its surface area. By increasing the surface area of ​​the hydrogen storage alloy as described above, the initial DC-IR (internal resistance) of the nickel-metal hydride battery can be reduced. After the battery reaches an overcharged state, it is discharged to a low charge state, such as below 20%. Existing technical documents Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-153261 Summary of the Invention The problem that the invention aims to solve

[0006] Furthermore, in the manufacturing process of nickel-metal hydride (NiMH) batteries, the cycle time for manufacturing one NiMH battery is already determined. Extending the time of the negative electrode activation step can increase the number of charge-discharge cycles in this step while maintaining the existing charge-discharge conditions, thus maximizing the activation of the NiMH battery. However, due to limitations in production time, such as cycle time, the increase in the number of charge-discharge cycles is also limited. Methods for solving problems

[0007] One aspect of the present invention is a method for manufacturing a nickel-metal hydride battery comprising a positive electrode containing nickel hydroxide as an active material, a negative electrode containing a hydrogen storage alloy as an active material, and an alkaline electrolyte. The method includes a high SOC range for the state of charge (SOC) of the nickel-metal hydride battery, comprising a high SOC of 100% and a low SOC range lower than the high SOC range. The method includes a high SOC charge-discharge step, in which the upper and lower limits of the SOC of the nickel-metal hydride battery are maintained at the high SOC range while repeatedly performing multiple charge-discharge cycles.

[0008] By repeatedly performing high-SOC charge-discharge cycles at 100% SOC, hydrogen diffuses into the alloy, causing it to become brittle. While brittleness alone promotes micronization, repeated charge-discharge cycles with hydrogen encapsulated within the alloy cause both brittleness and expansion / contraction, promoting the activation of the micronized negative electrode. Furthermore, in the high-SOC charge-discharge cycle, since repeated high-SOC cycles occur without reaching a low SOC, the time required to discharge to a low SOC can be reduced. This increases alloy expansion / contraction or shortens the activation time for the negative electrode, enabling efficient activation of the micronized negative electrode. Because the negative electrode can be activated through alloy micronization in this way, the initial internal resistance (DC-IR) of the nickel-metal hydride battery can be reduced.

[0009] In the above-mentioned method for manufacturing nickel-metal hydride batteries, the positive electrode, negative electrode, and alkaline electrolyte can be housed in a casing equipped with an vent valve. The manufacturing method of the nickel-metal hydride battery described above may further include an intermediate deep discharge step, in which the nickel-metal hydride battery is discharged before the high SOC charge-discharge step is performed, until a predetermined SOC of less than 10% is reached.

[0010] During the activation step, prolonged high-charge states can cause the internal pressure of the NiMH battery to rise due to gases generated in side reactions. In contrast, by performing an intermediate deep discharge step—discharging to a low-charge state before the high-SOC charge / discharge step—excessive increases in the internal pressure of the NiMH battery during or after the high-SOC charge / discharge step can be prevented.

[0011] In the above-mentioned method for manufacturing nickel-metal hydride batteries, the high state of charge (SOC) can be in the range of SOC being 80% or higher and 150% or lower. According to the above manufacturing method, the hydrogen content of the alloy in the high SOC state can be increased, so it is possible to repeatedly charge and discharge the alloy in a state in which hydrogen is trapped in it.

[0012] The manufacturing method of the nickel-metal hydride battery described above may include a refresh charge-discharge step, which, after the high SOC charge-discharge step described above, involves charging until the SOC reaches 100% or more but is below the upper limit value, and discharging until the SOC reaches 10% or less.

[0013] During the activation step, prolonged high-charge states can lead to a memory effect, where voltage drops even when residual capacity remains during discharge. Therefore, this memory effect can be eliminated by performing a refresh charge-discharge step after the activation step.

[0014] In the above-mentioned method for manufacturing nickel-metal hydride batteries, at least one of the charging rate and discharging rate in the high SOC charging and discharging step can be above 2.3C and below 4.6C. This shortens the cycle time, thus increasing the number of charge-discharge cycles under the time constraints of nickel-metal hydride battery manufacturing. Consequently, it promotes the activation of the micronized negative electrode.

[0015] In the above-mentioned high SOC charging and discharging steps, the SOC of the nickel-metal hydride battery can be maintained at the high SOC state for more than 1 hour. According to the above method, by maintaining the charging state at a high charge state for more than 1 hour, the hydrogen storage alloy can be embrittled to the point that the internal resistance can be reduced. The effects of the invention

[0016] According to the manufacturing method of the nickel-metal hydride battery of the present invention, the initial internal resistance of the nickel-metal hydride battery can be reduced, and the initial output performance can be better guaranteed. Attached Figure Description

[0017] Figure 1 This is a perspective view of a nickel-metal hydride battery manufactured using a nickel-metal hydride battery manufacturing method, including a partial cross-sectional structure. Figure 2 This is a flowchart illustrating the steps of the manufacturing method in this embodiment. Figure 3 This is a graph showing the change in the SOC of the negative electrode during the activation step of this embodiment. Figure 4 This is a graph showing the change in internal pressure of the battery module during the activation step of this embodiment, presented as a time series. Figure 5 This is a graph showing the change in the SOC of the negative electrode during the previous activation steps. Figure 6 This is a graph showing the variation of the internal resistance of the module in this embodiment relative to the internal resistance of a conventional battery module. Figure 7This is a graph showing the change in the state of charge (SOC) of the negative electrode during the existing activation steps. Figure 8 This is a time-series graph showing the changes in the internal pressure of the battery module during the existing activation process. Detailed Implementation

[0018] Reference Figures 1 to 8 One embodiment of the method for manufacturing the nickel-metal hydride battery of the present invention will be described. <Composition of Nickel-Metal Hydrate Batteries> Figure 1 An example of a nickel-metal hydride battery is shown. The nickel-metal hydride battery of this embodiment is a battery module 11 formed by connecting multiple individual cells 30 in series.

[0019] The battery module 11 has an integrated battery compartment 10 that is a rectangular battery case. The integrated battery compartment is composed of a housing 13 that can accommodate multiple individual batteries 30 and a cover 14 that seals the opening 16 of the housing 13.

[0020] The housing 13 and cover 14 constituting the integrated battery cell 10 are constructed of polypropylene (PP) and polyphenylene ether (PPE), which are resin materials resistant to alkaline electrolytes (hereinafter referred to as electrolytes). Furthermore, partitions 18 separating multiple individual cells 30 are formed inside the integrated battery cell 10, and the portions separated by these partitions 18 constitute the cell 15 for each individual cell 30. For example, six cell 15 constitute individual cells 30 in the integrated battery cell 10.

[0021] The electrode assembly 20, together with the electrolyte, is housed in an electrode cell 15, which is partitioned in this way. The electrolyte is, for example, an aqueous solution of potassium hydroxide, in which potassium hydroxide is the main solute component. The electrode assembly 20 consists of multiple positive electrode plates 21, multiple negative electrode plates 22, and separators 23. The positive electrode plates 21 and negative electrode plates 22 are rectangular, and they are alternately arranged with separators 23 in between. The direction in which the positive electrode plates 21, negative electrode plates 22, and separators 23 are laminated is the lamination direction. The positive current collector 24 is bonded to the side end of the positive electrode plate 21, and the negative current collector 25 is bonded to the side end of the negative electrode plate 22.

[0022] Multiple electrode assembly 20 are electrically connected in series via a through hole 32 located on the upper part of the partition 18. The total output of the electrode assembly 20 connected in series like this, i.e., multiple single cells 30, is taken out from the positive terminal 29A and the negative terminal (not shown).

[0023] On the other hand, the cover 14 is provided with an exhaust valve 141 and a sensor mounting hole 142 for mounting a sensor for detecting the temperature of the electrode assembly 20. When the internal pressure of the integrated electrode tank 10 reaches a predetermined pressure, the exhaust valve 141 opens to discharge the gas generated inside the integrated electrode tank 10. It should be noted that the exhaust valve 141 is not particularly limited, for example, it is an exhaust valve that cannot be closed once opened.

[0024] <Composition of the electrode assembly> The positive electrode plate 21 comprises a substrate and a positive electrode composite material. The substrate has multiple pores and its main component is metal, such as a foamed nickel substrate. The positive electrode composite material includes a positive electrode active material and additives. The positive electrode active material is a nickel oxide such as nickel hydroxide or nickel oxohydroxide. The additives include conductive materials and binders. The conductive material is a metal compound, in this case a cobalt compound such as cobalt oxohydroxide (CoOOH), and its surface is coated with nickel oxide. The highly conductive cobalt oxohydroxide forms a conductive network within the positive electrode, improving the utilization rate of the positive electrode ("discharge capacity / theoretical capacity" percentage). The positive electrode composite material is held within the substrate.

[0025] The negative electrode plate 22 comprises a substrate and a negative electrode composite material. The substrate has multiple pores and its main component is metal, such as perforated metal that has undergone punching processing. The negative electrode composite material includes a hydrogen storage alloy, a binding agent such as carbon black, and a styrene-butadiene copolymer binder, which are retained within the substrate.

[0026] Hydrogen storage alloys are alloys that reversibly encapsulate and release hydrogen. When "A" is the element that forms hydrides and "B" is the element that does not form hydrides, hydrogen storage alloys can be of type AB, type AB5, or combinations thereof. Type AB hydrogen storage alloys can use TiCo, ZrCo, etc. Type AB5 hydrogen storage alloys can use MmNi5, etc. It should be noted that "Mm" refers to a mixed rare earth metal as an alloy containing multiple rare earth elements. In particular, as MmNi5, it is appropriate to use MmNi obtained by replacing a portion of nickel (Ni) with Co, Mn, Al, etc. 5-x (Co,Mn,Al) x Series alloy, MmNi 5-x (Co,Mn,Al,Fe) x Rare earth metal alloys. The mixed rare earth metals include at least one of lanthanum (La), cerium (Ce), neodymium (Nd), and samarium (Sm).

[0027] The spacer 23 may be a nonwoven fabric, a resin membrane with multiple micropores, a sheet capable of holding other liquids, or a combination thereof. For example, the spacer 23 may be a nonwoven fabric made of an olefin-based resin such as polypropylene, or a spacer made by performing a hydrophilic treatment such as sulfonation on the nonwoven fabric. The spacer 23 may be a single layer or composed of multiple layers.

[0028] The electrolyte is held in spacer 23. The electrolyte is an alkaline aqueous solution with potassium hydroxide (KOH) as the main solute. <Battery Module 11> The state of charge of battery module 11 is represented by SOC (State of Charge). SOC is the ratio of the actual amount of charge to the rated capacity of battery module 11. In addition to being calculated based on the charge and discharge history of battery module 11, SOC can also be calculated using known methods such as the inter-terminal voltage (OCV, etc.) between open terminals or the estimation of resistance and electromotive force.

[0029] The charging reaction at the positive electrode of a nickel-metal hydride battery is represented by equation (1). Furthermore, at the end of the charging process when the state of charge (SOC) is close to 100%, the reaction represented by equation (2) occurs at the positive electrode. The charging reaction at the negative electrode is represented by equation (3). Additionally, at the negative electrode, as represented by equation (4), water in the electrolyte undergoes electrolysis. During discharge, the reaction proceeds in the reverse direction.

[0030] ·positive electrode Ni(OH)₂+OH - →NiOOH+H2O+e - …(1) OH - →1 / 4O2 + 1 / 2H2O + e - …(2) ·negative electrode M + H₂O + e - →MH+OH - …(3) H2O+e - →1 / 2H₂ + OH⁻ - …(4) If reactions (2) and (4) are combined, then as shown in reaction (5), a reaction is formed to generate oxygen (oxygen molecules: O2) and hydrogen (hydrogen molecules: H2) through the electrolysis of water. In this case, the gas ratio as the ratio of oxygen to hydrogen (H2 / O2 ratio) is "2".

[0031] 2H₂O→2H₂+O₂…(5) <Manufacturing Method of Battery Module 11> Reference Figure 2 The manufacturing method of battery module 11 is described.

[0032] Figure 2 The manufacturing method of the battery module 11 shown illustrates the steps after manufacturing the electrode assembly 20. The manufacturing method includes a module assembly step (S10), a cobalt charging step (S11), an activation step (S12), an aging step (S13), an inspection step (S14), and a battery pack assembly step (S15).

[0033] In the module assembly step (S10), the electrode assembly 20 is stored in the battery cell 15, the bonding parts of the electrode assembly 20, current collectors 24, 25, etc. are bonded, electrolyte is injected, and the opening of the housing 13 is sealed using the cover 14, thereby assembling the battery module 11.

[0034] Next, the cobalt charging step (S11) will be explained. In this step, cobalt and cobalt hydroxide in the positive electrode form cobalt oxohydroxide, constructing a conductive network with cobalt oxohydroxide as the main component. Additionally, in this step, a discharge reserve is formed in the negative electrode to prevent polarity reversal in case of over-discharge. It should be noted that, since a low charging rate is required to construct the conductive network, and the active material in the uncharged negative electrode is not activated and therefore difficult to charge at a high rate, charging is performed at a low rate. The conditions for the cobalt charging step are not particularly limited; for example, charging is performed at a charging rate of 0.05C or higher and 0.2C or lower until a predetermined SOC of 10% or higher and 30% or lower is reached. When the predetermined SOC is reached, discharge is performed at a discharge rate until the predetermined SOC is reached again.

[0035] Next, the activation step (S12) will be explained. It should be noted that in the charging and discharging steps below, the charging and discharging can be performed at a fixed rate, or the rate can be changed midway through the charging and discharging process. It should be noted that the charging rate, discharging rate, and time conditions in the activation step are set such that the internal pressure of the battery module 11 in the first activation step will not reach the opening pressure of the exhaust valve 141.

[0036] The activation process includes an overcharge step, a regular charge and discharge step, an intermediate deep discharge step, a high SOC charge and discharge step, and a refresh charge and discharge step. The overcharge step is used to create new fractures (cracks) on the surface of the hydrogen storage alloy, serving as the starting point for micronization. In this step, charging continues until the State of Charge (SOC) reaches the upper limit, which is between 100% and 150%. Afterward, discharging occurs immediately upon reaching the upper limit of the SOC.

[0037] The conventional charge-discharge step involves expanding and contracting the hydrogen storage alloy within a SOC range of 10% to 100%, promoting micronization starting with the cracking that occurs during the overcharge step. In this step, charging continues until the SOC reaches the upper limit of the aforementioned range (10% to 100%). Once the upper limit is reached, discharging immediately continues until the SOC reaches the lower limit of the same range. Then, charging continues immediately after the lower limit is reached. This charge-discharge cycle is repeated until a predetermined number of cycles is reached. Preferably, the upper limit of the SOC in the conventional charge-discharge step is lower than the upper limit of the SOC in the overcharge step.

[0038] Next refer to Figure 3 and Figure 4 The intermediate deep discharge step is explained. The intermediate deep discharge step is a step to reduce the internal pressure of battery module 11. The intermediate deep discharge step is... Figure 3 The process is carried out during the time period T1 to T2. During the discharge of battery module 11, as represented by the reverse reaction formula of the above equation (5), a side reaction in which hydrogen and oxygen are consumed occurs. In this step, the discharge continues until the SOC reaches a lower limit of 10% or less. The lower limit of SOC in the intermediate deep discharge step can be lower than the lower limit of SOC in the conventional charge and discharge step. However, the lower the SOC in the side reaction, the lower the internal pressure of battery module 11 tends to be, so the SOC can be less than 5% or less, or the SOC can be less than 2%. In addition, the discharge rate can be, for example, 2.3C or more and 4.6 or less. Furthermore, the state in which the SOC reaches the lower limit can be maintained for a predetermined time, for example, 30 minutes to 1 hour.

[0039] like Figure 4 As shown, the internal pressure of the battery module 11 decreases around the time T1 to T2 during the intermediate deep discharge step. By reducing the internal pressure in advance in this way, even if the internal pressure rises due to the subsequent high SOC charge and discharge step, it is possible to prevent the internal pressure from reaching the opening pressure of the exhaust valve 141.

[0040] Next refer to Figure 3 The high SOC charge / discharge steps are explained. The high SOC charge / discharge steps are described below. Figure 3The high SOC charge / discharge step is performed during time T2 to T3. This high SOC charge / discharge step is used to embrittle the metal by trapping hydrogen atoms or molecules within the hydrogen storage alloy. The mechanism by which the metal embrittles through contact between hydrogen and the alloy is not yet clear, but the alloy becomes embrittled by continuously maintaining a high SOC. The inventors have discovered that by dividing the SOC variation range into a high SOC state including 100% and a low SOC state (lower than the high SOC state), a multiplier effect promoting the micronization of the negative electrode encapsulation alloy can be obtained by repeatedly performing charge and discharge while maintaining the high SOC state. The SOC variation range is not particularly limited, for example, it is 0% or more and 150% or less. It should be noted that the SOC variation range may differ from the usable range when the battery module 11 is used after shipment. In addition, the low SOC state includes at least 50% SOC. The range of SOC from minimum to maximum value (ΔSOC) in the low SOC state can be above 60% and below 130%, above 90% and below 120%, or above 100% and below 110%. The range of SOC from minimum to maximum value (ΔSOC) in the high SOC state can be above 20% and below 80%, above 30% and below 60%, or above 40% and below 50%. A high SOC state can be a state where the SOC of battery module 11 is above 80% and below 150%, or above 90% and below 150%. In the low SOC state, the SOC of battery module 11 can be above 0% and below 80%, or above 0% and below 90%. Regarding the range of SOC and SOC in the low and high SOC states, a range of arbitrary combinations of the above upper and lower limits is also assumed.

[0041] The high SOC charge / discharge cycle is preferably performed for more than 1 hour. Furthermore, during the high SOC charge / discharge cycle, the charge / discharge is repeatedly performed at a high rate of 2.3C or higher and 4.6C or lower. By repeatedly performing charge / discharge at such a high rate, the number of charge / discharge cycles can be increased.

[0042] In addition, such as Figure 3 As shown, in the high SOC charge-discharge cycle, the charge-discharge process can be repeated in such a way that the upper limit of SOC increases with the number of charge-discharge cycles. With an increasing upper limit, the amount of hydrogen trapped in the alloy increases slowly, thus making it prone to embrittlement. Alternatively, the upper limit of SOC can be fixed.

[0043] like Figure 4As shown, during the high SOC charge / discharge steps (times T2 to T3), the internal pressure of the battery module 11 increases with charging and decreases with discharging. Even if the internal pressure increases overall during the high SOC charge / discharge steps, it will fall below a predetermined range below the opening pressure of the exhaust valve 141 by performing intermediate deep discharge beforehand.

[0044] Next, the refresh charge / discharge steps will be explained. Typically, batteries, including nickel-metal hydride batteries, may develop a memory effect, which narrows the charge / discharge range, depending on usage conditions. This effect becomes particularly significant when repeatedly charging and discharging within a narrow SOC range, such as in high SOC charge / discharge steps. Therefore, after performing a high SOC charge / discharge step, the battery module 11 is fully charged and then deeply discharged to eliminate the memory effect. The refresh charge / discharge steps are performed in… Figure 3 The process is performed during the period T3 to T4 shown. There are no particular limitations on the charging and discharging rates for the refresh charge / discharge steps; for example, it can be performed at the same rate as the high SOC charge / discharge steps.

[0045] like Figure 4 As shown, during the refresh charge / discharge steps (T3~T4), the internal pressure of the battery module 11 tends to rise. Therefore, the charging rate and other parameters are adjusted so that the exhaust valve 141 does not reach the opening pressure.

[0046] When performing the activation step as described above, an aging step (S13) is then performed. In the aging step, for example, after the battery module 11 is fully charged, it is stored for a predetermined period at a predetermined temperature with both connection terminals open. The predetermined temperature is, for example, 50°C.

[0047] The inspection step (S14) is a step of inspecting the battery module 11, and assembling a battery pack using a predetermined number of battery modules 11 that have been determined to be good through inspection (S15). Next refer to Figure 5 The following explanation addresses the case where a high SOC charge / discharge step was not performed during the activation process. After the standard charge / discharge steps, charge / discharge steps (times T10-T11) and refresh charge / discharge steps (T11-T12) are performed within the SOC variation range. In this example of the charge / discharge steps, discharge continues until a low SOC is reached, unlike the high SOC charge / discharge steps. In this example of the charge / discharge steps, an overcharged state exceeding 100% SOC is maintained for approximately 30 minutes, followed by discharge until the SOC reaches approximately 10%-20%, and this charge / discharge cycle is repeated twice.

[0048] Figure 6 Is for such Figure 5The graph shows a comparison of the internal resistance (DC-IR) of the battery module that underwent an activation step with a change in SOC, and the internal resistance of battery module 11 that underwent a high SOC charge / discharge step. The internal resistances of the three battery modules that underwent the activation step including a high SOC charge / discharge step are all lower than the internal resistances of the three battery modules that did not undergo the activation step. Furthermore, when the average internal resistance 50 of the three battery modules that did not undergo the activation step is set to "100%", the internal resistances of the three battery modules that underwent the activation step including a high SOC charge / discharge step are 98% or higher and 99.3% or lower, and their average value 51 is 98.8%. It should be noted that the high SOC charge / discharge step and the charge / discharge step performed instead of the high SOC charge / discharge step (times T10 to T11) have the same duration, and the refresh charge / discharge step time is also fixed.

[0049] Reference Figure 7 The activation step, which omits the intermediate deep discharge step, will be explained. Figure 7 The changes in SOC and internal pressure during the high SOC charge / discharge steps (T20-T21) and refresh charge / discharge steps (T21-T22) are shown. The overall time required for the activation step is also shown. Figure 3 and Figure 4 The activation steps in the example shown require the same total time (T1 to T4). In the high SOC charge / discharge steps (T20 to T21), when the upper limit of the high SOC state is reached, discharge continues until the lower limit of the high SOC state is reached, and then this charge / discharge process is repeated. At the end of the high SOC charge / discharge steps, a refresh step is performed.

[0050] like Figure 8 As shown, when a high SOC charge / discharge step is performed continuously for an extended period without intermediate deep discharge, the internal pressure of the battery module 11 reaches the opening pressure of the vent valve 141. Consequently, the vent valve 141 opens, releasing the gas inside the battery module 11 to the outside. The opening pressure of the vent valve 141 is set to be near the maximum value of the pressure tolerance range that will not adversely affect battery characteristics even if valve opening occurs within the battery module 11. Therefore, if the vent valve 141 is designed to remain closed after opening, when the vent valve 141 is open, not only will the battery module 11 become unusable, but the continuous generation of gas will cause the internal pressure to reach the opening pressure, potentially leading to electrolyte depletion and other adverse effects on battery characteristics. Therefore, in the case of a high SOC charge / discharge step, as shown in the above embodiment, an intermediate deep discharge step can be performed beforehand prior to the high SOC charge / discharge step.

[0051] The effects of the above-described embodiments will be explained. (1) By repeatedly performing high-SOC charge-discharge cycles with a high SOC state of 100%, hydrogen diffuses into the alloy, causing the alloy to become brittle. Even if micronization progresses simply by maintaining a high SOC and causing the alloy to become brittle, repeated charge-discharge cycles with hydrogen trapped in the alloy allow for both brittleness and expansion / contraction, promoting the activation of the micronized negative electrode. Furthermore, in the high-SOC charge-discharge cycle, since the charge-discharge cycle is repeated at a high SOC without reaching a low SOC state, the time required to discharge to a low SOC can be reduced. Therefore, the expansion and contraction of the alloy can be increased, or the activation time for the negative electrode can be shortened, thereby enabling efficient activation of the micronized negative electrode. Since the negative electrode can be activated through alloy micronization in this way, the initial internal resistance of the nickel-metal hydride battery can be reduced.

[0052] (2) In the above embodiment, an intermediate deep discharge step is performed before the high SOC charge / discharge step to a low charge state. This prevents the internal pressure of the battery module 11 from reaching the opening pressure of the exhaust valve 141 during or after the high SOC charge / discharge step.

[0053] (3) The high SOC state is defined as SOC above 80% and below 150%. Therefore, the hydrogen encapsulation of the alloy in the high SOC state can be increased, thereby enabling repeated charging and discharging in the state of hydrogen encapsulation in the alloy.

[0054] (4) In the above embodiment, a refresh charge-discharge step is performed after the high SOC charge-discharge step. This eliminates or eliminates the memory effect generated or enhanced by performing the high SOC charge step.

[0055] (5) In the above embodiment, the charge rate and discharge rate of the high SOC charge / discharge step are 2.3C or higher and 4.6C or lower. This shortens the time per cycle, thus increasing the number of charge / discharge cycles under the constraint of cycle time in manufacturing nickel-metal hydride batteries. This promotes the activation of the micronized negative electrode.

[0056] (6) In the above embodiment, during the high SOC charge / discharge step, the SOC of the nickel-metal hydride battery is maintained at the high SOC state for more than 1 hour. Therefore, by maintaining the charging state at a high charge state for more than 1 hour, the hydrogen storage alloy can be sufficiently embrittled to the point that the internal resistance of the battery module 11 can be reduced.

[0057] <Variation Example> The above implementation method can be modified as follows. This implementation method and the following modifications can be combined with each other to implement the same method within the scope of technical inconsistency.

[0058] • In the above embodiments, the conventional charge / discharge step and the intermediate deep discharge step are separate steps. Alternatively, or in addition to this operation, deep discharge can be performed during the conventional charge / discharge step until a low SOC of 10% is reached. In this case, the conventional charge / discharge step also serves as the intermediate deep discharge step, so the intermediate deep discharge step can be omitted.

[0059] • In the above embodiments, the time required for the high SOC charging and discharging step is more than 1 hour, but it can also be less than 1 hour depending on the cycle time. In the above embodiments, the charging rate and discharging rate of the high SOC charging and discharging steps are 2.3C or higher and 4.6C or lower, but at least one of the charging rate and discharging rate is within this range. Alternatively, the charging rate and discharging rate of the high SOC charging and discharging steps can be less than 2.3C or greater than 4.6C depending on the cycle time.

[0060] In the above embodiment, the refresh charge / discharge step is included in the activation step. Alternatively, if the memory effect is small, the refresh charge step may be omitted.

[0061] • In the above embodiments, a high SOC state is a range where the SOC is 80% or higher and 150% or lower. In the above embodiment, an intermediate deep discharge step is performed before the high SOC charge / discharge step. Alternatively, if the high SOC charge / discharge step can be performed before the internal pressure of the battery module 11 reaches the opening pressure of the exhaust valve 141, the intermediate deep discharge step can be omitted. Or, the intermediate deep discharge step can be performed midway through the high SOC charge / discharge step.

[0062] In the above embodiments, the activation step includes an overcharge step, a normal charge-discharge step, an intermediate deep discharge step, a high SOC charge-discharge step, and a refresh charge-discharge step, but the activation step only needs to include a high SOC charge-discharge step. In the activation step, at least one of the overcharge step, the normal charge-discharge step, the intermediate deep discharge step, and the refresh charge-discharge step can be combined with a high SOC charge-discharge step. Alternatively, additional activation steps besides these steps can be added.

[0063] In the above embodiment, the intermediate deep discharge step and the high SOC charge / discharge step are performed at fixed charge and discharge rates. Alternatively, the charge and discharge rates of at least one of these steps can be varied in stages.

[0064] In the above embodiment, each battery module 11 is activated before assembling the battery pack. Alternatively, the battery pack itself may be activated.

[0065] In the above embodiment, the nickel-metal hydride battery is specifically described as a battery module 11 formed by connecting multiple individual cells 30 in series. However, it is not limited to this method as long as the negative electrode contains a negative electrode active material. In a nickel-metal hydride battery, a single cell 30 can be used as a power generation element. In addition, the nickel-metal hydride battery is not limited to having a laminated plate assembly 20. It can also be a wound body formed by winding the positive and negative electrode plates with a separator in between. It can also be a structure in which positive electrode composite material and negative electrode composite material are filled into a button-shaped shell. There is no limitation on its structure.

[0066] The embodiments of the present invention have been described above through the above embodiments. However, the conditions of the charging and discharging steps, the upper and lower limits of the SOC, etc., can also be changed and set according to the situation in order to reduce the internal resistance (DC-IR) of the negative electrode to the target value. Explanation of symbols

[0067] 11… Battery modules as nickel-metal hydride batteries 21… The positive electrode plate as the positive electrode 22… The negative electrode plate as the negative electrode

Claims

1. A method for manufacturing a nickel-metal hydride (NiMH) battery, comprising a positive electrode containing nickel hydroxide as an active material, a negative electrode containing a hydrogen storage alloy as an active material, and an alkaline electrolyte, wherein... The range of SOC (State of Charge) for the nickel-metal hydride battery includes: a high SOC state containing 100% SOC; and a low SOC state lower than the high SOC state. The method includes a high SOC charge-discharge step, which maintains the upper and lower limits of the SOC of the nickel-metal hydride battery at the high SOC state while repeatedly performing multiple charge-discharge cycles, ensuring that the SOC does not reach a low SOC state. The high SOC state is defined as an SOC level between 80% and 150%. The charge-discharge cycle refers to charging the nickel-metal hydride battery until the State of Charge (SOC) reaches the upper limit value, and then discharging the nickel-metal hydride battery until the SOC reaches the lower limit value. In the high SOC charge / discharge step, the SOC of the nickel-metal hydride battery is maintained at the high SOC state for more than 1 hour.

2. The method for manufacturing a nickel-metal hydride battery as described in claim 1, wherein, The method further includes an intermediate deep discharge step, in which the nickel-metal hydride battery is discharged until a predetermined SOC of less than 10% is reached before the high SOC charge-discharge step.

3. The method for manufacturing a nickel-metal hydride battery as described in claim 1 or 2, wherein, It has a refresh charge / discharge step, which, after the high SOC charge / discharge step, performs charging until the SOC reaches 100% or more and is below the upper limit value, and discharges until the SOC reaches 10% or less.

4. The method for manufacturing a nickel-metal hydride battery as described in claim 1 or 2, wherein, The charging rate and discharging rate of the high SOC charging and discharging step are at least 2.3C or higher and 4.6C or lower.

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