Method for manufacturing alkaline secondary battery

Abstract

The control device of the manufacturing device of the nickel-hydrogen storage battery controls the charging current so that the single cell voltage of the t1-t2 range is maintained at 0.2 [V] by the first stage of charging (S2). Also, the charging current is controlled so that the single cell voltage of the t2-t3 range is maintained at 1.0 [V] by the second stage of charging (S4) when the current value is lower than the threshold value Aend1 (S3: Yes). When the current value is lower than the threshold value Aend2 (S5: Yes), the Co charging process is ended. By the effective Co charging process, the conductive Co network formed by CoOOH of the positive electrode can be improved, and the output characteristics can be improved.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an alkaline secondary battery, and more particularly, to a method for manufacturing an alkaline secondary battery in which the activity of a cobalt cathode is more preferably performed. Background Technology

[0002] In alkaline secondary batteries, a paste comprising nickel hydroxide powder and cobalt compound powders such as metallic cobalt (Co) and cobalt monoxide (CoO) is prepared. Furthermore, a paste-type nickel cathode is fabricated non-sintered by filling this paste into a nickel mesh serving as a current collector. In such alkaline secondary batteries, the cobalt compounds exhibit poor activity immediately after assembly, resulting in a high initial DC internal resistance (DC-IR). Therefore, the battery is activated by charging and discharging it under specified conditions using a cobalt charging process.

[0003] For example, a nickel-cadmium secondary battery, as an example of the alkaline secondary battery described in Patent Document 1, is manufactured by the following method. First, a paste containing nickel hydroxide powder and cobalt compound powder such as cobalt monoxide (CoO) is prepared. This paste is then filled into a nickel mesh serving as a current collector, thereby creating a paste-type nickel positive electrode. Next, a separator is sandwiched between the positive and negative electrodes to create an electrode assembly. This electrode assembly, along with an alkaline electrolyte, is placed in a container and the container is sealed. An initial charge and discharge cycle is then performed to activate the secondary battery.

[0004] like Figure 14 As shown, the initial charging process is performed under constant current. First, in the positive electrode, cobalt monoxide (CoO), which has a low oxidation potential, is oxidized to cobalt hydroxide (CoOOH). With this oxidation reaction, the voltage of the secondary battery increases. This, in turn, causes nickel hydroxide (Ni(OH)2), which has a high oxidation potential, to oxidize. Because cobalt hydroxide has high conductivity, it improves the conductivity between nickel hydroxide and the current collector, thus increasing the utilization rate of the positive electrode.

[0005] This invention allows for more efficient activation of secondary batteries.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 7-211353 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, when using a constant current for initial charging, the complete oxidation of cobalt monoxide requires a long time of more than 10 hours, which leads to poor mass production.

[0011] The problem to be solved by the method for manufacturing an alkaline secondary battery of the present invention is to improve the output characteristics of the alkaline secondary battery through effective positive electrode activation.

[0012] Methods for solving problems

[0013] To address the aforementioned issues, the alkaline secondary battery manufacturing method of the present invention relates to a method for manufacturing an alkaline secondary battery comprising a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, wherein the initial charging step includes the following stages: A first stage, at the positive electrode potential, to convert the metallic cobalt or cobalt compound into HCoO2. - The potential is adjusted so that the charging rate gradually changes from a high rate to a low rate to charge the aforementioned alkaline secondary battery; and in the second stage, at the positive electrode potential, the charging rate is gradually reduced from HCoO2. - The potential changes to CoOOH, causing the charging rate to gradually change from a high rate (higher than in the first stage) to a low rate for charging the alkaline secondary battery.

[0014] In the first and second stages of the aforementioned industry process, the charging current can be reduced as the resistance of the positive electrode increases, so that the positive electrode potential remains constant at the set potential. In this case, experimental results showing the relationship between the single-cell voltage with a constant positive electrode potential and the applied charging current can be pre-recorded in the first and second stages, and the applied charging current can be controlled based on the data from the experimental results while measuring the single-cell voltage to keep the positive electrode potential constant.

[0015] Additionally, in both the first and second stages described above, the charging current can be reduced as the resistance of the positive electrode increases, thereby keeping the individual cell voltage constant at the set potential. In this case, in the first stage described above, charging can begin at a predetermined rate within the range of 0.1 to 0.4V for the individual cell voltage, and in the second stage described above, charging can begin at a higher charging rate than the initial charging rate in the first stage, within the range of 0.8 to 1.2V for the individual cell voltage.

[0016] The first stage can be carried out until the charging current value reaches below a preset threshold, and the second stage can also be carried out until the charging current value reaches below a preset threshold.

[0017] The first stage mentioned above can be achieved by gradually increasing the charging current value at the beginning of charging.

[0018] The above-mentioned alkaline secondary battery can be preferably used when it is a nickel-metal hydride battery.

[0019] The effects of the invention

[0020] The method for manufacturing the alkaline secondary battery of the present invention can improve the output characteristics of the alkaline secondary battery through optimized positive electrode activation. Attached Figure Description

[0021] Figure 1 This is a perspective view showing the structure of the nickel-metal hydride battery according to this embodiment.

[0022] Figure 2 This is a cross-sectional view of the laminate in the nickel-metal hydride battery of this embodiment.

[0023] Figure 3 This is a schematic diagram showing the manufacturing apparatus for the nickel-metal hydride battery according to this embodiment.

[0024] Figure 4 This is a flowchart illustrating the cobalt charging process of this embodiment.

[0025] Figure 5 This is a graph showing the relationship between time and cell voltage in the cobalt charging process of this embodiment.

[0026] Figure 6 This is a graph showing the relationship between charging time and current value in the cobalt charging process of this embodiment.

[0027] Figure 7 This is a graph showing the relationship between the positive electrode potential and the response current in the cobalt charging process of this embodiment.

[0028] Figure 8 This is a graph showing the relationship between capacity and voltage of a nickel-metal hydride battery in this embodiment compared to the prior art.

[0029] Figure 9 This is a graph showing the improvement of DC-IR in a cobalt charging process at 60% SOC compared to the prior art.

[0030] Figure 10 This is a graph showing the improvement of DC-IR in a cobalt charging process at SOC 20% compared with the prior art.

[0031] Figure 11 This is a graph showing the improvement in Co network quantity in the cobalt charging process compared to the prior art in this embodiment.

[0032] Figure 12 This is a diagram illustrating the method for controlling the time and potential of the positive electrode potential in the cobalt charging process of the first embodiment.

[0033] Figure 13 This is a diagram illustrating the method for controlling the time and potential of the positive electrode potential in the cobalt charging process of the second embodiment.

[0034] Figure 14 This is a graph showing the relationship between time and cell voltage in the prior art cobalt charging process. Detailed Implementation

[0035] The following is for reference Figures 1-11 The method for manufacturing an alkaline secondary battery according to the present invention will be described by way of manufacturing a nickel-metal hydride battery comprising a positive electrode with nickel hydroxide (Ni(OH)2) as the positive electrode active material, a negative electrode with a hydrogen storage alloy as the negative electrode active material, and an alkaline electrolyte.

[0036] <Summary of this implementation method>

[0037] The manufacturing method of the nickel-metal hydride battery 11 according to this embodiment includes an initial charging step for initially charging the nickel-metal hydride battery 11. The initial charging step includes a first stage and a second stage. In the first stage, at a positive electrode potential, the battery is converted from metallic cobalt or a cobalt compound to HCoO2. - The potential is adjusted so that the charging rate gradually changes from a high rate to a low rate to charge the nickel-metal hydride battery 11. In the second stage, at the positive electrode potential, the charge is generated from HCoO2. - The potential changes to CoOOH, causing the charging rate to gradually decrease from a high rate (higher than in the first stage) to a low rate when charging the nickel-metal hydride battery 11. That is, in the first stage, the positive electrode potential changes from metallic cobalt or cobalt compounds to HCoO2 at the positive electrode. - The first stage involves gradually decreasing the charging rate from the initial stage at a specific potential. In the second stage, the positive electrode potential is adjusted to reduce the charge rate from HCoO2. - The change to the second potential of CoOOH causes the charging rate to gradually decrease from the second initial charging rate, which is higher than the first initial charging rate.

[0038] <Principle of this implementation method>

[0039] The cobalt charging process in this embodiment is divided into two stages. The cobalt charging process is equivalent to the initial charging process. That is, the added metallic cobalt or cobalt compound is transformed into divalent Co(II), and then further transformed into trivalent Co(III). This is the process of converting metallic cobalt or cobalt compound into HCoO2. - Changes, and the effects of HCoO2 - The change towards CoOOH. Ultimately, the discharge performance of the positive electrode is determined by a sufficient amount of CoOOH.

[0040] Furthermore, if metallic cobalt or cobalt compounds are transformed into HCoO2 - The potential of HCoO2 - By comparing the potential at which it changes to CoOOH, the change from metallic cobalt or cobalt compounds to HCoO2 is observed.- The potential is even lower. The inventors have realized that if the potential of the positive electrode is made lower, as in the prior art, focusing only on the potential from HCoO2... - If the positive electrode potential of the reaction that transforms into CoOOH is not high enough, then metallic cobalt or cobalt compounds cannot be fully transformed into HCoO2. - Therefore, there is still room for improvement in the activation of the positive electrode.

[0041] If the initial charge is performed with a constant current as described above, the internal resistance of the secondary battery varies due to manufacturing conditions, thus the voltage applied to the secondary battery will vary depending on the battery. As a result, depending on the magnitude of the internal resistance of the secondary battery, the voltage applied to the secondary battery will be higher than the oxidation potential of metallic cobalt or cobalt compounds, thus causing problems such as the metallic cobalt or cobalt compounds not being converted into CoOOH and reduced utilization of the positive electrode.

[0042] In the invention described in Patent Document 1, the initial charging process is performed through two or more stages of constant voltage charging, and the voltage of these two or more stages is set to gradually increase within a range below 1.3V. The reason for setting the constant voltage charging voltage below 1.3V is that if the set voltage is higher than 1.3V, the oxidation reaction of nickel hydroxide powder will occur simultaneously, resulting in unoxidized cobalt compounds and residual residue, thus reducing the utilization rate of the positive electrode. However, in the invention described in Patent Document 1, the minimum set voltage is at least 1.1V. At this voltage, CoO dissolves in the alkaline electrolyte, preventing the sufficient formation of HCoO2. - The problem.

[0043] Through experiments addressing this problem, the inventors have obtained the following insights: In order to fully generate CoOOH, the prerequisite CoO must be dissolved in an alkaline electrolyte to fully generate HCoO2. - This is very important. As a result, the inventor conceived of the structure of this invention.

[0044] In the cobalt charging process of this embodiment, in order to maintain the conversion of metallic cobalt or cobalt compounds into HCoO2 - By applying at least two stages of low-rate reduction to the initial charging current rate, the conductive network of CoOOH in the positive electrode is strengthened. This results in good high-rate discharge performance, thus improving output characteristics. In particular, the DC-IR in the low SOC region is significantly improved.

[0045] <Composition of NiMH Battery 11>

[0046] Figure 1 This is a perspective view showing the structure of the nickel-metal hydride battery 11 according to this embodiment. Figure 2This is a cross-sectional view of the laminated body of the battery cell 12 provided in the nickel-metal hydride battery 11 of this embodiment. First, the manufacturing method of the nickel-metal hydride battery 11 of this embodiment will be described.

[0047] <Battery Module>

[0048] like Figure 1 As shown, the nickel-metal hydride battery 11 is configured as a battery module comprising multiple battery cells 12. For example, the nickel-metal hydride battery 11 is a square plate-shaped sealed battery. The nickel-metal hydride battery 11 includes an integrated battery case 13 capable of housing multiple (here, 6) battery cells 12, and a cover 14 sealing the opening of the integrated battery case 13. The integrated battery case 13 and the cover 14 are formed, for example, from a resin material. Multiple (here, 6) battery cells 12 electrically connected in series are housed in the integrated battery case 13. The power of these battery cells 12 is drawn from the positive terminal 13a and the negative terminal 13b provided in the integrated battery case 13.

[0049] <12 battery cells>

[0050] like Figure 2 As shown, the battery cell 12 includes a laminate composed of an electrode assembly 20 and current collectors 21 and 22, and an electrolyte contained together with the laminate within an integrated battery case 13. The electrode assembly 20 includes a plate-shaped positive electrode 15 and a negative electrode 16 laminated together with a separator 17. The end 15a of the positive electrode 15 is engaged with the mating surface of the positive current collector 21. The end 16a of the negative electrode 16 is engaged with the mating surface of the negative current collector 22.

[0051] <Negative Plate 16>

[0052] Next, the negative electrode plate 16 will be described. The negative electrode plate 16 includes a core material and a hydrogen storage alloy loaded on the core material. The type of hydrogen storage alloy is not particularly limited, for example, it is an alloy of mixed rare earth metals and nickel, which is a mixture of rare earth elements, or an alloy in which a portion of the alloy is replaced with metals such as aluminum, cobalt, and manganese. The negative electrode plate 16 is manufactured by adding a thickening material such as carbon black and a binder such as styrene-butadiene copolymer to the hydrogen storage alloy, processing it into a paste, filling it into a core material such as a perforated metal, and then drying, rolling, and cutting it.

[0053] Electrolyte

[0054] Next, the electrolyte will be described. The electrolyte is held in the separator 17, and ion conduction occurs between the positive electrode 15 and the negative electrode 16.

[0055] The electrolyte is an alkaline aqueous solution with potassium hydroxide (KOH) as the main solute.

[0056] <Positive Plate 15>

[0057] Next, the positive electrode plate 15 will be described. The positive electrode plate 15 has a substrate composed of a three-dimensional porous body made of nickel, and a positive electrode composite material supported on the substrate. The substrate functions as a carrier for loading filler materials and as a current collector. The paste used as the positive electrode composite material contains positive electrode active material particles with nickel hydroxide as the main component, cobalt (Co) metal which functions as a conductive material, a thickening material, and a binder. In this embodiment, metallic cobalt (Co) is shown, but it may also contain cobalt oxide, represented by cobalt monoxide (CoO), cobalt compounds, etc.

[0058] The positive electrode active material particles used in the product have a coating layer on the surface of the nickel hydroxide particles. This coating layer is mainly composed of cobalt hydroxide oxide (CoOOH). In the process of manufacturing the positive electrode plate 15, the positive electrode plate 15 is manufactured using CoOOH with a β-type crystal structure. When the nickel-metal hydride battery using this positive electrode plate 15 is initially charged after assembly (initial charge), the resistance of the β-type CoOOH decreases due to a change in crystallinity.

[0059] During the initial charging (sometimes simply referred to as charging) of a nickel-metal hydride battery, the Co contained in the positive electrode alloy undergoes electrochemical oxidation, producing CoO and HCoO2. - CoOOH is deposited in the form of cobalt. At this time, the CoOOH generated by the oxidation of cobalt is deposited between the positive electrode active material particles, or between the positive electrode active material and the substrate, filling the gaps between the positive electrode active material particles and between the positive electrode active material and the substrate. Therefore, the CoOOH forming the coating layer before initial charging, and the coating layer containing cobalt-derived CoOOH, constitute a high-density layer that reduces the gaps between the positive electrode active material particles. This elemental CoOOH also forms a conductive network within the positive electrode connecting the nickel hydroxide particles and between the nickel hydroxide particles and the substrate.

[0060] By forming this CoOOH-based conductive network, the utilization rate of the positive electrode active material can be improved. The utilization rate of the positive electrode active material is calculated as the ratio of the discharge capacity to the theoretical capacity obtained by multiplying the weight of the positive electrode active material by the theoretical capacity of the active material. It should be noted that CoOOH is stable within the operating voltage range of nickel-metal hydride batteries; therefore, as long as the nickel-metal hydride battery operates within this voltage range, CoOOH will not be reduced to cobalt or other compounds.

[0061] <Ni-MH Battery Manufacturing Equipment 30>

[0062] Figure 3 This is a schematic diagram showing a partial configuration of an example of a nickel-metal hydride battery manufacturing apparatus 30. In the nickel-metal hydride battery manufacturing apparatus 30, as part of its function, such as... Figure 3As shown, the apparatus includes a charging / discharging device 32 capable of charging and discharging a nickel-metal hydride (NiMH) battery 11, and a control device 31 for controlling the charging / discharging device 32. The control device 31 includes a computer and controls the charging / discharging device 32 via control signals. The charging / discharging device 32 controls the charging or discharging of the NiMH battery 11 based on signals from the control device 31. The control device 31 executes control to charge and discharge the NiMH battery 11 at a predetermined voltage or current based on a stored program. The control is based on measurements from a voltmeter 34 that measures the voltage of each individual cell of the NiMH battery 11, and an ammeter 33 that measures the current flowing through the NiMH battery 11. The voltmeter 34 can measure the voltage of each individual cell 12. The manufacturing apparatus 30 for these NiMH batteries 11 is used for processes such as cobalt charging.

[0063] <Manufacturing Method of Nickel-Metal Hydrate Battery 11>

[0064] Next, the manufacturing method of the nickel-metal hydride battery 11 will be described. The manufacturing method of the nickel-metal hydride battery 11 includes a positive electrode manufacturing process, a negative electrode manufacturing process, an assembly process, a cobalt charging process, and a post-process.

[0065] <Positive electrode manufacturing process>

[0066] In the positive electrode fabrication process, a specified amount of cobalt and thickening materials are added to the coated positive electrode active material particles and mixed to form a paste. This paste is then filled into a substrate composed of a foamed nickel three-dimensional porous body. After drying the filled substrate, it is press-molded and cut to a specified size, thereby fabricating the positive electrode plate 15.

[0067] <Negative electrode manufacturing process>

[0068] In the negative electrode fabrication process, hydrogen storage alloy powder is immersed in an alkaline aqueous solution, stirred, washed, and dried. A binder is then added to the dried hydrogen storage alloy powder, and the mixture is kneaded to create an active material paste. This active material paste is then coated onto a core material such as a perforated metal core. The coated core material is then dried, rolled, and cut to produce the negative electrode plate 16.

[0069] Assembly Process

[0070] In the assembly process, the positive electrode plate 15 and the negative electrode plate 16 are laminated with a separator 17 made of non-woven fabric or the like, which is made of alkali-resistant resin. Furthermore, the end 15a of the positive electrode plate 15 is joined to the current collector plate 21 by welding or the like, and the end 16a of the negative electrode plate 16 is joined to the current collector plate 22 by welding or the like, to create a laminate. The laminate is then placed together with an electrolyte containing potassium hydroxide as the main solute in an integrated battery case 13 and sealed.

[0071] <Cobalt charging process>

[0072] The cobalt charging process is a process in which the Co contained in the positive electrode material is electrochemically oxidized and deposited in the form of CoOOH by charging the nickel-metal hydride battery 11 with a specified voltage.

[0073] Figure 4 This is a flowchart illustrating the cobalt charging process of this embodiment. Figure 5 This is a graph showing the relationship between time (seconds) and cell voltage (V) in the cobalt charging process of this embodiment. Figure 6 This is a graph showing the relationship between charging time [seconds] and current value [A] in the cobalt charging process of this embodiment. The following is a description of the process. Figure 4 The flowchart illustrates the cobalt charging process.

[0074] <Phase 1 Pre-charge (S1)>

[0075] At the start of the cobalt charging process (start), control device 31 (refer to...) Figure 3 The first stage of pre-charging (S1) is performed. Pre-charging S1 is equivalent to pre-application. Figure 6 During the pre-charging process from t0 to t1, a charging current [A] is applied in a manner that slowly increases the current value from zero, thereby raising the individual cell voltage [V]. For example... Figure 5 As shown, when the individual cell voltage [V] reaches the target voltage (e.g., 0.2 [V]), the control device 31 switches to the first stage of charging.

[0076] <Phase 1 Charging (S2)>

[0077] Control device 31 controls the charging current to maintain the voltage in the t1-t2 range when the cell voltage reaches the target voltage (e.g., 0.2V) after the pre-charging in the first stage. In the initial stage of the reaction in the t1-t2 range, there is more unreacted Co and the reaction resistance is relatively low. Therefore, in the initial stage of the reaction in the t1-t2 range, the charging current used to maintain the voltage is relatively large, and charging is performed at a relatively high charging rate. Subsequently, if charging is performed with the same current for a certain period of time, as charging progresses, the amount of unreacted Co decreases and the reaction resistance increases. Therefore, the charging current used to maintain the same voltage is relatively small, and charging can be performed at a lower charging rate.

[0078] In the first stage S2 of this embodiment, the individual cell voltage is maintained around 0.2 [V]. Therefore, for example, a threshold Vmax1, which is higher than 0.2 [V], is set as the upper limit. When the individual cell voltage exceeds the threshold Vmax1, the control device 31 reduces the applied charging current [A] by a certain amount. This reduction amount is set to a predetermined value. In addition, this reduction amount is set to a threshold Vmin1 (e.g., 0.1 [V]) that is not lower than the lower limit of the individual cell voltage. Therefore, the control device 31... Figure 6 The charging current [A] is reduced in a stepwise manner, so that... Figure 5 In the t1 to t2 interval shown, the single-cell voltage [V] remains approximately constant at 0.2 [V] within a certain range of 0.1 to 0.3 [V]. That is, in the first stage S2, the control device 31 acquires the measured single-cell voltage of the nickel-metal hydride battery 11, and determines the single-cell voltage based on the change from metallic cobalt or cobalt compounds to HCoO2 in the positive electrode. - The charging rate is gradually reduced from the first initial charging rate by setting a first voltage value (e.g., 0.2 [V]). In one example, the control device 31 can gradually reduce the charging rate from the first initial charging rate so that the cell voltage is within a first voltage range including the first voltage value. In one example, the control device 31 can reduce the charging rate when the cell voltage is greater than a first upper limit threshold Vmax1 so that the cell voltage is within the first voltage range. In one example, before the first stage S2, the control device 31 can perform a pre-charge S1 that gradually increases the charging rate until the cell voltage [V] reaches the first voltage value. In one example, the first initial charging rate can be set to the charging rate set in the pre-charge S1 when the cell voltage reaches the first voltage value. In one example, the first voltage value of the cell voltage of the nickel-metal hydride battery 11 is 0.2 [V], but there is no particular limitation as long as the value is in the range of 0.1 to 0.4 [V]. When the single-cell voltage of the nickel-metal hydride battery 11 is 0.1 to 0.4 V, the metallic cobalt or cobalt compound in the positive electrode will also change into HCoO2. - .

[0079] Using the control device 31, if the charging current is greater than the predetermined termination current Aend1 (S3: No), the first stage of charging continues (S2). When the charging current reaches or falls below the predetermined termination current Aend1 (S3: Yes), the first stage of charging ends and the process moves to the second stage of charging (S4).

[0080] <Phase 2 Charging (S4)>

[0081] During the second stage of charging, the control device maintains... Figure 5The charging current is controlled by the voltage within the t2-t3 range shown. In the initial stage of the reaction within the t2-t3 range, unreacted HCoO2... - The reaction resistance is relatively small. Therefore, in the initial stage of the reaction within the t2-t3 range, a relatively large charging current is used to maintain the voltage, and charging is carried out at a high charging rate. Subsequently, if charging is carried out with the same current for a certain period of time, the unreacted HCoO2 will... - The resistance decreases, and the reaction resistance increases. Therefore, the charging current used to maintain the same voltage is relatively small, allowing charging to be performed at a lower charging rate.

[0082] In the second stage S4 of this embodiment, the individual cell voltage is maintained at 1.0 [V], for example, a threshold Vmax2 is set as the upper limit, which is 1.2 [V] higher than 1.0 [V]. When the individual cell voltage exceeds the threshold Vmax2, the control device 31 reduces the applied current [A] by a certain amount. This reduction amount is set to a predetermined value. In addition, this reduction amount is set to a threshold Vmin2 (e.g., 0.8 [V]) that is not lower than the lower limit of the individual cell voltage. Therefore, the control device 31... Figure 6 The charging current [A] is reduced in a stepwise manner, so that... Figure 5 In the t2-t3 interval shown, the single-cell voltage [V] remains approximately constant at 1.0 [V] within a certain range of 0.8-1.2 [V]. That is, in the second stage S4, the control device 31 acquires the measured single-cell voltage of the nickel-metal hydride battery 11, and determines the single-cell voltage based on the concentration of HCoO2 in the positive electrode. - The charging rate is gradually reduced from a second initial charging rate higher than the first initial charging rate by changing to a second voltage value of CoOOH (e.g., 1.0 [V]). In one example, the control device 31 can gradually reduce the charging rate from the second initial charging rate so that the cell voltage is within a second voltage range including the second voltage value. In one example, the control device 31 can reduce the charging rate when the cell voltage is greater than a second upper limit threshold Vmax2 so that the cell voltage is within the second voltage range. In one example, the second voltage value of the cell voltage of the nickel-metal hydride battery 11 is 1.0 [V], but there is no particular limitation as long as the value is within the range of 0.8 to 1.2 [V]. When the cell voltage is 0.8 to 1.2 [V], the HCoO2 in the positive electrode... - It will also change into CoOOH.

[0083] Using the control device 31, if the charging current is greater than the specified termination current Aend2 (S5: No), the second stage of charging continues (S4). When the charging current reaches or falls below the specified termination current Aend2 (S5: Yes), the second stage of charging ends (end).

[0084] (Function of the first embodiment)

[0085] <Positive electrode potential [V] and response current [A]>

[0086] Figure 7 This is a graph showing the relationship between the positive electrode potential [V] and the response current [A] in the cobalt charging process of this embodiment. The positive electrode potential [V] is the potential relative to the mercury oxide reference electrode (Hg / HgO).

[0087] like Figure 7 As shown, when the monomer voltage is maintained at approximately 0.2 [V], the positive electrode potential [V] is approximately -0.65 [V]. At this positive electrode potential [V], Co is converted to HCoO2. - Cobalt dissolves in the electrolyte. On the other hand, at this positive electrode potential [V], HCoO2... - Co is converted to CoOOH and Ni(OH)2 is converted to NiOOH, so no current is consumed, and Co can be converted to HCoO2 without waste. - .

[0088] Furthermore, when the monomer voltage is maintained at approximately 1.0 [V], the positive electrode potential [V] is approximately 0.15 [V]. At this positive electrode potential [V], HCoO2 - It transforms into CoOOH, thus generating CoOOH at the positive electrode without any waste. This is because Co has already been transformed into HCoO2 without any waste. - Therefore, at this positive electrode potential [V], the formation of CoOOH will not be hindered. In addition, since the positive electrode potential [V] is too low for Ni(OH)2 to become NiOOH, the formation of CoOOH will not be hindered and CoOOH can be generated effectively.

[0089] Therefore, after the cobalt charging process, a high-rate charging is performed. When the positive electrode potential [V] is approximately 0.2–0.5 [V], Ni(OH)₂ transforms into NiOOH, thus activating the positive electrode. At this point, Co has also been efficiently converted to HCoO₂ without any waste. - It transforms into CoOOH, so there is no problem in keeping the positive electrode potential [V] approximately 0.2 to 0.5 [V].

[0090] Increased battery capacity

[0091] Figure 8 A graph illustrating the relationship between capacity and voltage of the nickel-metal hydride battery of this embodiment. Figure 8 In the existing cobalt charging process, indicated by dashed lines, the first stage of charging is not performed, resulting in a low amount of CoOOH generated. In the cobalt charging process of this embodiment, CoOOH can be efficiently generated from Co without waste, thus increasing the battery capacity compared to the past.

[0092] As a result, the production amount of CoOOH in the positive electrode can be increased, and the conductive network can be made firm.

[0093] <Improvement of DC-IR>

[0094] Figure 9 This is a graph showing the improvement of DC-IR at SOC 60% in the cobalt charging process when comparing this embodiment with the prior art. As Figure 9 shown, in this embodiment, since the production amount of CoOOH in the positive electrode can be increased and the conductive network can be made firm, it can be seen that the DC-IR is improved by about 1% compared with the case of implementing the existing cobalt charging process.

[0095] Figure 10 This is a graph showing the improvement of DC-IR at SOC 20% in the cobalt charging process when comparing this embodiment with the prior art. As Figure 10 shown, in this embodiment, since the production amount of CoOOH in the positive electrode can be increased and the conductive network can be made firm, it can be seen that the DC-IR is improved by about 3% compared with the case of implementing the existing cobalt charging process.

[0096] Thus, compared with the nickel-metal hydride battery that has implemented the existing cobalt charging process, the conductive network of the nickel-metal hydride battery 11 that has implemented the cobalt charging process of this embodiment is firm and the DC-IR is reduced. Especially at SOC 20%, a remarkable effect has been confirmed.

[0097] <Amount of Co network>

[0098] Figure 11 This is a graph showing the improvement of the amount of Co network in the cobalt charging process when comparing this embodiment with the prior art.

[0099] "dQ / dV" is the ratio of the change rate dQ / dt of the discharge capacity (discharge charge) to the change rate dV / dt of the positive electrode potential. "dQ / dV" represents the change in the discharge capacity per unit voltage and is used for the deterioration determination of each battery cell 12. The "amount of Co network" is a value obtained by exponentiating the dQ / dV value. As Figure 11 shown, when the amount of Co network based on the existing cobalt charging process is set to "100", the amount of Co network based on the cobalt charging process of this embodiment is "138", which is significantly increased. That is, it has been verified that the conductive network of the nickel-metal hydride battery 11 that has implemented the cobalt charging process of this embodiment has become firm.

[0100] (Effect of the First Embodiment)

[0101] (1) It can increase the amount of cobalt hydroxide (CoOOH) generated at the positive electrode.

[0102] (2) In addition to the second stage of charging in the prior art, the first stage of charging is performed in advance in this embodiment, thereby improving the charging efficiency of Co charging.

[0103] (3) With the improvement of charging efficiency, the amount of conductive Co network increases.

[0104] (4) DC-IR decreases by increasing the amount of Co network. For example, although improvements are also observed in intermediate SOCs of around 60%, the effect is particularly significant in low SOCs such as 20%.

[0105] (5) Because it can reduce DC-IR and increase battery capacity, it can improve output characteristics.

[0106] (6) Because it can improve the charging efficiency of Co charging, the Co charging process can be carried out in a short time.

[0107] (7) The end of the first stage of charging and the end of the second stage of charging can be easily determined using the individual cell voltage. Therefore, the configuration of the manufacturing apparatus for nickel-metal hydride batteries that perform the Co charging process can be simplified.

[0108] (8) The end of the first stage of charging and the end of the second stage of charging can be easily determined using the individual cell voltage. Therefore, the control device 31 can be easily controlled.

[0109] (Second Implementation)

[0110] In the first embodiment, the charging in both stages ends when the charging current falls below the predetermined termination currents Aend1 and Aend2. Alternatively, the charging intervals t1-t2 in the first stage and t2-t3 in the second stage can be timed in accordance with the tact time of the battery production line. Therefore, by pre-managing the current values ​​as described in the first embodiment using the same type of battery, the times t1-t2 and t2-t3 are stored in the control device 31.

[0111] (Effects of the second embodiment)

[0112] (9) Thus, by implementing time management, it is possible to correspond with the cycle time of the battery production line, thereby improving production efficiency.

[0113] (Third Implementation)

[0114] In the first embodiment, during the first and second stages of charging, the control device 31 controls the charging based on the individual cell voltage [V] in a manner that keeps the individual cell voltage [V] approximately constant. In the second embodiment, to further improve the accuracy of the cobalt charging process, the control is performed based on the positive electrode potential [V] in a manner that keeps the positive electrode potential [V] approximately constant.

[0115] Figure 12 This is a diagram illustrating the method for controlling the time and potential of the positive electrode potential in the cobalt charging process of the first embodiment. Figure 13 This is a diagram illustrating the method for controlling the time and potential of the positive electrode potential in the cobalt charging process of the second embodiment.

[0116] In the first embodiment, such as Figure 12 As shown, referring to the single-cell voltage [V] of voltmeter 34, the first stage of charging (S2) and the second stage of charging (S4) are performed based on this single-cell voltage. In the first embodiment, it is assumed that the positive electrode potential [V] and the single-cell voltage [V] have a strong correlation. In the first stage of charging, in order to make the positive electrode potential [V] "-0.65 [V]", the single-cell voltage [V] is maintained at around 0.2 [V]. In addition, in the second stage of charging, in order to make the positive electrode potential [V] "0.15 [V]", the single-cell voltage [V] is maintained at around 1.0 [V].

[0117] However, as Figure 12 As shown, even if the cell voltage [V] is kept constant, the positive electrode potential [V] will increase as the charging time progresses. This is because the cell voltage [V] is calculated from the difference between the positive electrode potential [V] and the negative electrode potential [V]. When the negative electrode potential [V] decreases as charging proceeds, even if the cell voltage [V] is kept constant, the positive electrode potential [V] will increase as the negative electrode potential [V] decreases.

[0118] Therefore, in the third embodiment, as Figure 13 As shown, the control device 31 controls the circuit in a manner that maintains the positive electrode potential [V] constant. In this case, Figure 3The manufacturing apparatus 30 for the nickel-metal hydride battery 11 shown cannot detect the positive electrode potential [V]. Therefore, the storage unit of the control device 31 stores in advance experimental results on the relationship between the cell voltage [V] and the applied charging current [A] when the positive electrode potential is constant during the first and second charging stages. Additionally, the storage unit of the control device 31 stores in advance a "reference table (or graph)" the relationship between the cell voltage [V] and the positive electrode potential [V] during specified charging. Then, during the first and second charging stages, the control device 31 measures the cell voltage [V] with reference to the "reference table" using the target positive electrode potential [V] as a parameter, and controls the applied charging current [A] to remain constant based on the data from the experimental results.

[0119] (Effects of the third embodiment)

[0120] (10) Suitable for use in the first stage of charging, from metallic cobalt or cobalt compounds to HCoO2 - The changes and the changes in HCoO2 during the second stage of charging - The CoOOH is charged to the changing positive potential [V].

[0121] (11) By storing the relationship between the cell voltage [V] and the positive electrode potential [V] during specified charging as a "reference table (or graph)," it is possible to utilize... Figure 3 The simplified manufacturing apparatus shown is used to perform the appropriate cobalt charging process.

[0122] (Modified Example)

[0123] The present invention is not limited to the above-described embodiments, and may also be implemented as follows.

[0124] Regarding cobalt, metallic cobalt (Co) is illustrated in the embodiments, but cobalt oxide, represented by cobalt monoxide (CoO), cobalt compounds, or mixtures thereof may also be used.

[0125] In the implementation, regarding the control of the charging current [A] corresponding to the cell voltage [V], in Figure 6 The diagram shown illustrates a stepped, phased control. The magnitude of the current reduction can be adjusted appropriately. Furthermore, not limited to this example, other methods can also be implemented according to... Figure 6 The diagram shown illustrates continuous control in real time, presented as a continuous curve.

[0126] The numerical values ​​shown in the embodiments are illustrative, and can be appropriately modified according to the composition of the alkaline secondary battery to best implement the present invention.

[0127] In the battery module illustrated as an example, modifications can be made, or new materials or structures can be used, depending on the purpose. For instance, the battery casing may be made of metal instead of resin.

[0128] In this embodiment, a nickel-metal hydride battery 11 with a plate-like appearance and six battery cells 12 is used as an example for description, but the shape can also be cylindrical or other appearances, and it does not necessarily have to be a battery module with battery cells 12.

[0129] Alkaline secondary batteries are not limited to nickel-metal hydride batteries; they can also be used with nickel-cadmium batteries, nickel-zinc batteries, and so on.

[0130] The positive electrode, negative electrode, separator, electrolyte, etc. are not limited to the composition described in the embodiments.

[0131] Taking a flowchart as an example, processes can be added, removed, or replaced.

[0132] Furthermore, those skilled in the art can, of course, add to, remove from, or modify the structure to implement the invention, as long as they do not depart from the scope of the claims.

Claims

1. A method for manufacturing an alkaline secondary battery, comprising a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, wherein nickel hydroxide as an active material and metallic cobalt or a cobalt compound are present. The initial charging process includes the following stages: In the first stage, at a positive electrode potential, the metal cobalt or cobalt compound is transformed into HCoO2. - The potential is adjusted so that the charging rate gradually changes from a high rate to a low rate to charge the alkaline secondary battery; and In the second stage, at the positive electrode potential, from HCoO2 - The potential changes to CoOOH, causing the charging rate to gradually decrease from a high rate (higher than in the first stage) to a low rate when charging the alkaline secondary battery. In the first and second stages, the charging current is reduced as the resistance of the positive electrode increases, so that the individual cell voltage remains constant at the set voltage. In the first stage, charging begins at a specified rate within a single-cell voltage range of 0.1 to 0.4 V. In the second stage, charging begins at a higher charging rate than that at the start of charging in the first stage, within a single-cell voltage range of 0.8 to 1.2V.

2. The method for manufacturing an alkaline secondary battery as described in claim 1, characterized in that, In the first and second stages, the charging current is reduced as the resistance of the positive electrode increases, so that the positive electrode potential remains constant at the set potential.

3. The method for manufacturing an alkaline secondary battery as described in claim 2, characterized in that, In the first and second stages, experimental results were recorded in advance regarding the relationship between the cell voltage with a constant positive electrode potential and the applied charging current. While measuring the cell voltage, the applied charging current was controlled based on the data from the experimental results to keep the positive electrode potential constant.

4. The method for manufacturing an alkaline secondary battery as described in claim 1 or 2, characterized in that, The first stage continues until the charging current value reaches below a preset threshold.

5. The method for manufacturing an alkaline secondary battery as described in claim 1 or 2, characterized in that, The second stage continues until the charging current value reaches below a preset threshold.

6. The method for manufacturing an alkaline secondary battery as described in claim 1 or 2, characterized in that, The first stage involves pre-applying a gradually increasing charging current value at the start of charging.

7. The method for manufacturing an alkaline secondary battery as described in claim 1 or 2, characterized in that, The alkaline secondary battery is a nickel-metal hydride battery.

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