JP7107649B2 - Battery manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a battery such as a lithium ion secondary battery.

In manufacturing a battery such as a lithium ion secondary battery, it is conceivable that metal foreign matters such as iron and copper are mixed into the electrode body. Such metallic foreign matter gradually dissolves in the electrolytic solution after the electrolytic solution is injected into the assembled battery, so that metal ions derived from the metallic foreign matter are present at a high concentration in the vicinity of the metallic foreign matter. During main charging, if the potential of the negative electrode drops and the high-concentration metal ions precipitate on the negative plate in a dendrite-like form, they may break through the separator and reach from the negative plate to the positive plate, causing a short circuit. .

In order to prevent such a short circuit from occurring, for example, in Patent Document 1, the battery is charged (preliminarily charged) until the positive electrode potential exceeds the dissolution potential of the metallic foreign matter, and then the battery is charged at this positive electrode potential. It is described that the battery is left for a period of time and then subjected to an initial conditioning charge (main charge) (see claim 1 of Patent Document 1, etc.). By standing, the metal foreign matter is dissolved in the electrolytic solution, and the metal ions derived from the metal foreign matter are diffused over a wide range from the place where the metal foreign matter was present. It is thought that this is because it is possible to prevent intensive dendrite-like precipitation at , thereby preventing a short circuit.

WO2013/035187

However, in the method of Patent Document 1 described above, the metal ions derived from the metallic foreign matter are diffused only by leaving the battery after precharging, so the metal derived from the metallic foreign matter concentrates on the negative electrode plate to form dendrites. In order to prevent short-circuiting due to deposition, it was necessary to leave the battery for a long time.

The present invention has been made in view of such a situation, and provides a method for manufacturing a battery that can prevent short circuits caused by metallic foreign matter by promoting the diffusion of metal ions derived from metallic foreign matter dissolved in an electrolytic solution. intended to

One aspect of the present invention for solving the above problems is a method for manufacturing a battery, wherein the battery includes a lithium ion diode containing a lithium transition metal composite oxide as a positive electrode active material and a carbon material as a negative electrode active material. An injection step of injecting an electrolytic solution into a battery that is a secondary battery and has not been injected, a main charging step of conditioning charging the battery after the above injection step, and a main charging step after the above injection step Before the process, the battery temperature Te of the battery is set to 30 ° C. or higher, and the battery voltage Ve of the battery is fluctuated up and down to promote diffusion of metal ions derived from metallic foreign substances dissolved in the electrolyte. After the voltage change step, the liquid injection step, and before the voltage change step, the battery voltage is lower than the battery voltage V1 reached in the main charging step, and the positive electrode potential is higher than the iron dissolution potential. a pre-charging step of pre-charging to a battery voltage V2 which is high and the negative electrode potential is higher than the deposition potential of the iron ions dissolved in the electrolytic solution.

In the battery manufacturing method described above, the battery voltage Ve is fluctuated up and down in the voltage fluctuation step after the injection step and before the main charging step. In this voltage fluctuation step, when the battery voltage Ve increases, the positive electrode plate and the negative electrode plate attract each other and the distance between them narrows. get wider. In this manner, the interval between the positive plate and the negative plate vibrates. This promotes movement of the electrolytic solution between the positive electrode plate and the negative electrode plate, and promotes diffusion of metal ions derived from metallic foreign matter contained in the electrolytic solution. Thus, even if metallic foreign matter is mixed into the electrode body during the manufacturing process, the diffusion of metal ions derived from the metallic foreign matter can be promoted to prevent a short circuit caused by the metallic foreign matter.
Furthermore, in a lithium ion secondary battery containing a lithium transition metal composite oxide as a positive electrode active material and a carbon material as a negative electrode active material, a preliminary charging step of precharging to the battery voltage V2 described above is performed before the voltage changing step. As a result, the potential of the positive electrode increases, and foreign metal particles (especially foreign particles of iron) tend to dissolve in the electrolytic solution on the positive electrode plate. On the other hand, the negative electrode potential does not become too low, and metals derived from foreign metals (especially iron foreign substances) are less likely to deposit on the negative electrode plate. In addition, in the voltage variation step described above, the diffusion of the metal ions derived from the metallic foreign matter can be promoted, so that the short circuit caused by the metallic foreign matter can be prevented more reliably.

The frequency fe of the vertical fluctuation of the battery voltage Ve in the "voltage fluctuation step" is preferably 0.1 to 100 Hz (the vertical fluctuation of the battery voltage Ve is repeated 0.1 to 100 times per second). Furthermore, it is particularly preferable to set the frequency fe to 0.1 to 10 Hz (the battery voltage Ve repeats vertical fluctuations 0.1 to 10 times per second). When the frequency is set to such a low frequency, the gap between the positive electrode plate and the negative electrode plate changes slowly, so that the electrolyte solution moves easily according to the change in the gap, and the diffusion of metal ions derived from metallic foreign matter is further promoted. be.

Moreover, it is particularly preferable that the time for performing the "voltage change step" is 0.5 minutes or longer, and more preferably 1 minute or longer. By lengthening the time for performing the voltage fluctuation step in this way, the number of times the interval between the positive electrode plate and the negative electrode plate changes increases, so the movement of the electrolyte solution is further promoted, and the diffusion of metal ions derived from the metal foreign matter is further facilitated. because it promotes On the other hand, it is preferable to shorten the time required for the voltage change process by setting the time of the voltage change process to 10 minutes or less, more preferably 3 minutes or less.

Also, the "voltage change process" is performed with the battery temperature Te set to 30 ° C. or higher . This is because, when the battery temperature Te is increased, the viscosity of the electrolyte decreases, which promotes the movement of the electrolyte between the positive electrode plate and the negative electrode plate, thereby facilitating the diffusion of metal ions derived from metallic foreign matter. On the other hand, it is particularly preferable to perform the voltage fluctuation step at a battery temperature Te of 60° C. or lower, more preferably 50° C. or lower. This is because if the battery temperature Te is too high, the characteristics of the battery may change, such as deterioration of the battery.

"Conditioning charge" in the "main charge step" is charge performed to stabilize battery performance. Specifically, it is preferable to charge the battery to a battery voltage corresponding to SOC 70% or more, and further to a battery voltage corresponding to SOC 90% or more. By charging the battery to a high state of charge in this manner, even if metallic foreign matter remains in the main charging process, the metallic foreign matter can be dissolved on the positive electrode plate. In addition, for example, in a lithium ion secondary battery, a good SEI (Solid Electrolyte Interphase) film is formed on the negative electrode plate, and the battery performance can be improved, such as good cycle characteristics of the battery.

Further, the above battery manufacturing method further comprises a pre-variation leaving step of leaving the battery for 0.5 hours or longer after the preliminary charging step and before the voltage changing step. is preferred.

After the pre-charging step and before the voltage fluctuation step, the above-described standing step before fluctuation is performed and the battery is left for 0.5 hours or longer. Therefore, it is possible to more reliably dissolve the metallic foreign matter in the electrolytic solution. In addition, in the voltage variation step described above, the diffusion of the metal ions derived from the metallic foreign matter can be promoted, so that the short circuit caused by the metallic foreign matter can be prevented more reliably. It is more preferable that the battery is left to stand in this pre-variation leaving step for one hour or longer.

Further, the method for manufacturing a battery according to any one of the above, further comprising a post-variation leaving step of leaving the battery for 0.5 hours or longer after the voltage changing step and before the main charging step. A manufacturing method is preferred.

After the voltage fluctuation step and before the main charging step, the post-variation leaving step is performed and the battery is left for 0.5 hours or longer. The resulting short circuit can be prevented more reliably. It is more preferable that the battery is left to stand in this post-variation standing step for one hour or longer.

1 is a perspective view of a battery according to an embodiment and reference form; FIG. 1 is a cross-sectional view of a battery according to an embodiment and a reference form; FIG. 2 is a flow chart showing a manufacturing process of batteries according to an embodiment , Examples 1 and 2, and Reference Examples 4 and 5. FIG. 5 is a graph showing the relationship between the waveform of the applied voltage applied to the battery and the vertical fluctuation of the battery voltage Ve in the voltage fluctuation process according to the embodiment. 3 is a flow chart showing a manufacturing process of a battery according to Reference Embodiment and Reference Examples 1 to 3. FIG. 1 is a plan view of batteries according to Examples 1 and 2 , Reference Examples 1 to 5 , and Comparative Examples 1 and 2. FIG. FIG. 2 is a plan view of electrode bodies and the like according to Examples 1 and 2 , Reference Examples 1 to 5 , and Comparative Examples 1 and 2; 5 is a flow chart showing a manufacturing process of a battery according to Comparative Example 1. FIG. 6 is a flow chart showing a manufacturing process of a battery according to Comparative Example 2. FIG.

(embodiment)
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a perspective view and a cross-sectional view of a battery 1 according to this embodiment. In the following description, the battery vertical direction BH, the battery horizontal direction CH, and the battery thickness direction DH of the battery 1 are defined as the directions shown in FIGS. 1 and 2 . This battery 1 is a prismatic sealed lithium ion secondary battery mounted in a vehicle such as a hybrid car, a plug-in hybrid car, an electric car, or the like. The battery 1 includes a battery case 10, an electrode body 20 housed therein, a positive electrode terminal member 50 and a negative electrode terminal member 60 supported by the battery case 10, and the like. Further, the battery case 10 contains an electrolytic solution 17 , part of which is impregnated in the electrode assembly 20 .

Among them, the battery case 10 has a rectangular parallelepiped box shape and is made of metal (aluminum in this embodiment). The battery case 10 is composed of a case main body member 11 in the shape of a bottomed square cylinder with an opening only on the upper side, and a case cover member 13 in the shape of a rectangular plate welded so as to close the opening of the case main body member 11 . be. A positive electrode terminal member 50 made of aluminum is fixed to the case lid member 13 while being insulated from the case lid member 13 . The positive electrode terminal member 50 is connected to the positive electrode plate 21 of the electrode body 20 in the battery case 10 to be conductive, and extends through the case lid member 13 to the outside of the battery. A negative electrode terminal member 60 made of copper is fixed to the case lid member 13 while being insulated from the case lid member 13 . The negative electrode terminal member 60 is connected to the negative electrode plate 31 of the electrode body 20 in the battery case 10 for electrical continuity, and extends through the case lid member 13 to the outside of the battery.

The electrode body 20 has a flat shape and is accommodated in the battery case 10 in a laid down state. Between the electrode body 20 and the battery case 10, a bag-shaped insulating film enclosure 19 made of an insulating film is arranged. The electrode body 20 is formed by stacking a strip-shaped positive electrode plate 21 and a strip-shaped negative electrode plate 31 with a pair of strip-shaped porous resin membrane separators 41 interposed therebetween, and wound around an axis to form a flat shape. It is compressed.

The positive electrode plate 21 is formed by providing strip-shaped positive electrode active material layers at predetermined positions on both main surfaces of a positive electrode collector foil made of strip-shaped aluminum foil. This positive electrode active material layer is composed of a positive electrode active material, a conductive material, and a binder. In this embodiment, a lithium-transition metal composite oxide, specifically a lithium-nickel-cobalt-manganese-based composite oxide, is used as the positive electrode active material. Further, the negative electrode plate 31 is formed by providing strip-shaped negative electrode active material layers at predetermined positions on both main surfaces of a negative electrode collector foil made of strip-shaped copper foil. This negative electrode active material layer is composed of a negative electrode active material, a binder, and a thickener. In this embodiment, a carbon material, specifically graphite, is used as the negative electrode active material.

Next, a method for manufacturing the battery 1 will be described (see FIG. 3). First, in the "assembling step S1", the unfilled battery 1x is assembled. Specifically, the positive electrode plate 21 and the negative electrode plate 31 are stacked and wound with a pair of separators 41 interposed therebetween, and compressed into a flat shape to form the electrode body 20 . Next, the case lid member 13 is prepared, and the positive electrode terminal member 50 and the negative electrode terminal member 60 are fixed thereto (see FIGS. 1 and 2). After that, the positive electrode terminal member 50 and the negative electrode terminal member 60 are welded to the positive electrode plate 21 and the negative electrode plate 31 of the electrode assembly 20, respectively. Next, the electrode body 20 is covered with the insulating film surrounding body 19 and inserted into the case body member 11 , and the opening of the case body member 11 is closed with the case lid member 13 . Then, the battery case 10 is formed by welding the case body member 11 and the case lid member 13 together. Thus, an unfilled battery 1x is formed. In this assembly step S1, foreign metal such as iron or copper may enter the electrode body 20 of the battery 1x, specifically between the positive electrode plate 21 and the separator 41. FIG.

Next, in the "filling step S2", the electrolytic solution 17 is injected into the unfilled battery 1x. Specifically, the electrolytic solution 17 is injected into the battery case 10 through the injection hole 13 h , and then the injection hole 13 h is sealed with the sealing member 15 . After that, the battery 1 is left to stand for 0.5 hours to further impregnate the electrode body 20 with the injected electrolytic solution 17 . This liquid injection step S2 is performed at a temperature of 20.degree. It should be noted that the metal foreign matter mixed in the assembly step S1 gradually dissolves in the electrolytic solution 17 after the electrolytic solution 17 is injected.

Next, in a "preliminary charging step S3", the battery 1 is preliminarily charged to a battery voltage V2 (V2=1.5 V in this embodiment). This battery voltage V2 is lower than the battery voltage V1 (V1=4.1 V in this embodiment) reached in the main charging step S7 described later, and the positive electrode potential is the melting potential at which iron dissolves (3.2 V vs. Li/Li+), and the negative electrode potential is higher than the deposition potential (2.3 V vs. Li/Li+) at which iron ions dissolved in the electrolytic solution 17 are deposited. Specifically, a charging/discharging device is connected to the battery 1, and at a temperature of 20° C., constant current constant voltage (CCCV) charging is performed to increase the battery voltage Ve from about 0 V to the battery voltage V2 at a constant current of 0.5 C. = 1.5 V, this battery voltage V2 = 1.5 V was maintained for 2 minutes. When the preliminary charging step S<b>3 is performed as described above, the potential of the positive electrode increases and exceeds the dissolution potential of iron. On the other hand, since the negative electrode potential does not become too low (because it remains higher than the deposition potential of iron ions), it is difficult for the metal derived from metallic foreign matter to deposit on the negative electrode plate 31 .

Next, the battery 1 is left in the "pre-change leaving step S4". In this embodiment, the battery 1 is left for 3 hours. This standing step S4 before change is performed at a temperature of 20.degree. However, the battery 1 was transferred to a constant temperature bath at 30° C. after 2 hours from the start of standing (1 hour before the end of standing). Therefore, the battery temperature Te of the battery 1 is 30° C. at the end of the standing-before-change step S4, and the voltage change step S5, which will be described later, can be performed at the battery temperature Te=30° C. FIG. By performing such standing-before-variation step S<b>4 , metallic foreign matter existing on the positive electrode plate 21 dissolves in the electrolytic solution 17 even during this standing. Therefore, it is possible to more reliably dissolve the metallic foreign matter in the electrolytic solution 17 .

Next, in the "voltage fluctuation step S5", the battery voltage Ve of the battery 1 is fluctuated up and down. In this embodiment, the voltage change step S5 is performed with the battery temperature Te set to 30° C. as described above. First, an impedance measuring device (manufactured by Solartron: 1255WB) is connected to the battery 1 . At that time, a current limiting resistor of 10Ω is connected in series between the negative terminal member 60 of the battery 1 and the positive terminal of the impedance measuring instrument.

Then, the upper limit applied voltage of the impedance measuring instrument was set to 3.2 V, the lower limit applied voltage to −3.2 V, and the frequency fe to fe=2.0 Hz. is applied to vary the battery voltage Ve up and down. This application of the pulse voltage (the fluctuation of the battery voltage Ve up and down) is performed for 2 minutes. As shown in FIG. 4, when a high pulse voltage is applied to the battery 1 from the impedance measuring device, the battery voltage Ve gradually increases. Conversely, when a low pulse voltage is applied, the battery voltage Ve gradually increases. As a result, the battery voltage Ve fluctuates up and down like a triangular wave. However, before and after this voltage change step S5, the battery voltage Ve does not change (battery voltage Ve=battery voltage V2=1.5V).

In this voltage change step S5, when the battery voltage Ve increases, the positive electrode plate 21 and the negative electrode plate 31 attract each other and the distance between them narrows. The interval between the negative electrode plates 31 is widened. In this way, the interval between the positive electrode plate 21 and the negative electrode plate 31 vibrates. This promotes the movement of the electrolytic solution 17 between the positive electrode plate 21 and the negative electrode plate 31 , thereby promoting the diffusion of metal ions derived from metallic foreign matter contained in the electrolytic solution 17 .

Next, the battery 1 is left in the "post-variation leaving step S6". In this embodiment, the battery 1 is transferred to a constant temperature bath at 20° C. and left for 2 hours. By performing such a post-change standing step S6, the metal ions derived from the metallic foreign matter are diffused even during this standing.

Next, in the "main charging step S7", the battery 1 is subjected to main charging (conditioning charging). Specifically, a charging/discharging device is connected to the battery 1, and at a temperature of 20° C., the battery voltage Ve changes to the battery voltage V1=4.1 V at a constant current of 1 C by constant current constant voltage (CCCV) charging. After the battery was charged to V1, this battery voltage V1=4.1 V was maintained for 2 minutes. When this main charging step S7 is performed, the potential of the negative electrode decreases and becomes lower than the deposition potential of iron ions, so metals derived from metallic foreign matter such as iron are likely to be deposited on the negative electrode plate 31 . However, in this embodiment, at the start of the main charging step S7, the metal ions derived from the metal foreign matter have already diffused over a wide range from the place where the metal foreign matter was present, and there is no place where the concentration of metal ions is high. Therefore, the metal derived from the metallic foreign matter does not precipitate intensively on the negative electrode plate 31 in the form of dendrites, and the short circuit due to the metallic foreign matter does not occur.

Next, in the "aging step S8", the battery 1 is left to age. Specifically, the battery 1 after the main charge is aged by being left at a temperature of 60° C. for 20 hours with the terminals open.

Next, in a "short-circuit detection step S9", the battery 1 is discharged (self-discharged) by being left with the terminals open, and the amount of voltage drop ΔVe of the battery voltage Ve during the standing is measured. Detects the presence or absence of an internal short circuit. Specifically, the battery voltage Va measured after two days from the end of the aging step S8 (the start of the short-circuit detection step S9) after the battery 1 is left open at a temperature of 20° C., The amount of voltage drop ΔVe=Va−Vb is calculated from the battery voltage Vb measured seven days after the end of the aging step S8 (the start of the short-circuit detection step S9). Then, the obtained voltage drop amount ΔVe of the battery 1 is compared with a predetermined reference drop amount ΔVr. The battery 1 is determined to be defective with a short circuit and removed. On the other hand, when the amount of voltage drop ΔVe of the battery 1 is smaller than the reference amount of drop ΔVr (ΔVe≦ΔVr), the battery 1 is judged to be non-defective with no internal short circuit.
After the short-circuit detection step S9, various other tests are performed on the battery 1 determined to be non-defective. Thus, the battery 1 is completed.

(Reference form)
Next, a reference form will be described. In the embodiment, after the liquid injection step S2, the preliminary charging step S3 and the standing-before-change step S4 are performed, and then the voltage variation step S5 is performed (see FIG. 3). On the other hand, in the present embodiment, the pre-charging step S3 and the standing-before-fluctuation step S4 are not performed, and the voltage-fluctuation step S5 is performed following the injection step S2 (see FIG. 5). In this reference embodiment, the battery temperature Te was set to 30.degree. Also, the standing time in the post-change standing step S6 was set to 2 hours in the embodiment, but was set to 6 hours in the present embodiment.

As described above, after the electrolytic solution 17 is injected into the battery 1x, metallic foreign substances are gradually dissolved in the electrolytic solution 17. FIG. Therefore, at the start of the voltage change step S<b>5 of the present embodiment, all or part of the metallic foreign matter is dissolved and metallic ions are generated in the electrolytic solution 17 . Therefore, when the movement of the electrolytic solution 17 between the positive electrode plate 21 and the negative electrode plate 31 is promoted by the vertical fluctuation of the battery voltage Ve, the diffusion of the metal ions derived from the metallic foreign matter contained in the electrolytic solution 17 is promoted. , it is possible to prevent a short circuit caused by metallic foreign matter.

(Examples, reference examples and comparative examples)
Next, the results of tests conducted to verify the effects of the present invention will be described. As Examples 1 and 2 , Reference Examples 1 to 5 , and Comparative Examples 1 and 2, laminated lithium ion secondary batteries (hereinafter also simply referred to as “batteries”) 100 shown in FIGS. 6 and 7 were manufactured.
In these batteries 100, an electrode assembly 120, an electrolytic solution 117, and the like are housed inside an exterior body 110 made of a laminated film in the form of a bag. Among them, the electrode body 120 is formed by stacking one rectangular positive electrode plate 121 and one rectangular negative electrode plate 131 with one rectangular separator 141 interposed therebetween.

The positive electrode plate 121 has a positive electrode active material layer with a size of 23 mm×23 mm at a predetermined position on one main surface (the main surface facing the negative electrode plate 131) of a positive current collecting foil made of rectangular aluminum foil. It is provided in a rectangular shape. A positive electrode tab 150 made of a strip-shaped aluminum plate is joined to the positive electrode plate 121 and extends from the inside of the exterior body 110 to the outside. On the other hand, in the negative electrode plate 131, a negative electrode active material layer having a size of 25 mm×25 mm is placed at a predetermined position on one main surface (the main surface facing the positive electrode plate 121) of a negative electrode collector foil made of rectangular copper foil. It is provided in a rectangular shape. A negative electrode tab 160 made of a strip-shaped copper plate is joined to the negative electrode plate 131 and extends from the inside of the exterior body 110 to the outside.

In these batteries 100, when assembling the unfilled battery 100x, a metallic foreign matter having a diameter of 200 μm and a thickness of 10 μm was placed between the central portion of the positive electrode active material layer of the positive electrode plate 121 and the separator 141. Disc-shaped iron lumps were placed in each of them.

In Examples 1 and 2 and Reference Examples 4 and 5 , similarly to the embodiment (see FIG. 3), after performing the liquid injection step S2 on the unfilled battery 100x, the pre-charging step S3 and the standing-before-fluctuation step S4 were performed. , the voltage change step S5 and the post-change leaving step S6 were performed. After that, without performing the respective steps S7 to S9 after the main charging step S7, the battery 100 was disassembled, and the portion of the positive electrode plate 121 that was in contact with the foreign metal and the portion of the separator 141 that was in contact with the foreign metal were removed. The dissolution state (undissolved state) of the metal foreign matter was investigated by observing each of the dissolving portions with a scanning electron microscope.

The differences between Examples 1 and 2 and Reference Examples 4 and 5 are as shown in Table 1. That is, in the voltage fluctuation step S5, in Example 1, the frequency fe for fluctuating the battery voltage Ve up and down was set to 1.0 Hz, and the battery temperature Te was set to 30.degree. Further, in Reference Example 4 , the frequency fe of the vertical fluctuation of the battery voltage Ve was set to 1.0 Hz, and the battery temperature Te was set to 25°C. In Example 2 , the frequency fe of fluctuations in the battery voltage Ve was set to 2.0 Hz, and the battery temperature Te was set to 30°C. In Reference Example 5 , the frequency fe of the vertical fluctuation of the battery voltage Ve was set to 2.0 Hz, and the battery temperature Te was set to 25°C.

Further, in Reference Examples 1 to 3, similarly to the reference embodiment (see FIG. 5), the pre-charging step S3 and the standing-before-fluctuation step S4 were not performed, and the injection step S2 followed by the voltage-fluctuation step S5 and the standing-after-fluctuation step S5 were performed. Step S6 was performed. Thereafter, in the same manner as in Examples 1 and 2 and Reference Examples 4 and 5, the steps S7 to S9 after the main charging step S7 were not performed, and the battery 100 was disassembled to investigate the dissolution state of the metallic foreign matter.
The differences between Reference Examples 1 to 3 are as shown in Table 1. That is, in the voltage fluctuation step S5, the frequency fe of the vertical fluctuation of the battery voltage Ve was set to 2.0 Hz in Reference Example 1, 5.0 Hz in Reference Example 2, and 100 Hz in Reference Example 3. The battery temperature Te in the voltage change step S5 was set to 25° C. in all of Reference Examples 1-3.

On the other hand, in Comparative Example 1, as shown in FIG. 8, after the injection step S2, the preliminary charging step S3 and the standing step S4A were performed (the voltage change step S5 was not performed). The standing step S4A was performed at a temperature of 20° C. for 24 hours. Thereafter, in the same manner as in Examples 1 and 2 and Reference Examples 1 to 5 , the steps S7 to S9 after the main charging step S7 were not performed, but the battery 100 was disassembled and the state of dissolution of the metallic foreign matter was investigated.
Furthermore, in Comparative Example 2, as shown in FIG. 9, the preliminary charging step S3 was not performed, and the standing step S4B was performed after the liquid injection step S2 (the voltage change step S5 was not performed). Note that the standing step S4B was performed at a temperature of 20° C. for 6 hours. Thereafter, in the same manner as in Examples 1 and 2, Reference Examples 1 to 5 , and Comparative Example 1, the steps S7 to S9 after the main charging step S7 were not performed, and the battery 100 was disassembled to check the dissolved state of the metallic foreign matter. investigated.

Then, the batteries 100 of Examples 1 and 2, Reference Examples 1 to 5 , and Comparative Examples 1 and 2 were evaluated based on the dissolved state of the metal foreign matter. As a result, in Comparative Examples 1 and 2, a large amount of metal foreign matter remained, and they were unsatisfactory (marked with x in Table 1).
On the other hand, in Examples 1 and 2 , the metal foreign matter was completely dissolved and not left at all, which was particularly good (marked with ⊚ in Table 1). Moreover, in Reference Examples 4 and 5, most of the metallic foreign matter was dissolved, which was particularly good (marked with ○ in Table 1). Moreover, in Reference Examples 1 and 2, most of the metal foreign matter was dissolved and only a part of the metal foreign matter remained, which was good (marked ● in Table 1). Also, in Reference Example 3, metal foreign matter remained more than in Reference Examples 1 and 2, but the amount was small and good (marked Δ in Table 1). The reason for such results is considered as follows.

That is, in Comparative Examples 1 and 2, since the voltage variation step S5 was not performed, the electrolyte solution 117 hardly moved between the positive electrode plate 121 and the negative electrode plate 131, and the metal (iron) foreign matter contained in the electrolyte solution 117 metal (iron) ions are difficult to diffuse. For this reason, metal ions derived from the metallic foreign matter continued to exist in the vicinity of the metallic foreign matter at a high concentration. As in Comparative Examples 1 and 2, when a large amount of metallic foreign matter remains before the main charging step S7, the metal precipitates intensively in a dendrite form on the negative electrode plate 131 during the main charging step S7. It has been found that short circuits are likely to occur

On the other hand, in Examples 1 and 2 and Reference Examples 1 to 5 , since the voltage change step S5 is performed, the movement of the electrolytic solution 117 between the positive electrode plate 121 and the negative electrode plate 131 is promoted, and the electrolytic solution 117 Diffusion of metal ions derived from metal foreign substances contained in is promoted. For this reason, it is considered that the concentration of metal ions derived from the metallic foreign matter did not increase in the vicinity of the metallic foreign matter, and the dissolution of the metallic foreign matter was promoted. As in Examples 1 and 2 and Reference Examples 1 to 5 , when the amount of metallic foreign matter remaining before the main charging step S7 is small, the smaller the amount of metallic foreign matter, the more the negative electrode plate 131 is removed during the main charging step S7. It has been found that the metal is less likely to deposit intensively in the form of dendrites, and that short circuits are less likely to occur.

Comparing Examples 1 and 2 with Reference Examples 1 to 5 , in Reference Examples 4 and 5 , the metal foreign matter remained slightly, but in Examples 1 and 2 , the metal foreign matter was completely dissolved. This is because the battery temperature Te during the voltage change step S5 was higher in Examples 1 and 2 (Te=30° C.) than in Reference Examples 4 and 5 (Te=25° C.). When the battery temperature Te is increased, the viscosity of the electrolytic solution 117 is lowered, so that the movement of the electrolytic solution 117 between the positive electrode plate 121 and the negative electrode plate 131 is promoted, and diffusion of metal ions derived from metallic foreign matter is promoted.

In addition, the reason why the residual metallic foreign matter was less in Examples 1 and 2 and Reference Examples 4 and 5 than in Reference Examples 1 and 3 is that in Examples 1 and 2 and Reference Examples 4 and 5 , the preliminary charging step S3 and the variation This is because the pre-leaving step S4 was performed. When the preliminary charging step S<b>3 is performed, the potential of the positive electrode becomes higher than the dissolution potential of iron, and metal (iron) foreign matter on the positive electrode plate 121 is easily dissolved in the electrolytic solution 117 . Furthermore, in the standing-before-fluctuation step S<b>4 , metallic foreign matter existing on the positive electrode plate 21 dissolves in the electrolytic solution 117 . Furthermore, in the voltage variation step S5, diffusion of the metal ions derived from the metallic foreign matter is promoted, so that the dissolution of the metallic foreign matter is considered to have been promoted.

In addition, the reason why the remaining metal foreign matter was less in Reference Examples 1 and 2 than in Reference Example 3 is that in Reference Examples 1 and 2, the frequency fe of the vertical fluctuation of the battery voltage Ve in the voltage fluctuation step S5 was set to 10 Hz or less. is. Since the interval between the positive electrode plate 121 and the negative electrode plate 131 changes slowly by lowering the frequency fe in this way, the electrolytic solution 117 is easily moved according to the interval change, and the diffusion of metal ions derived from metallic foreign matter is prevented. thought to have been facilitated.

Next, for Reference Examples 1 to 3, the batteries 100 were manufactured without arranging the metal (iron) foreign matter in the electrode assembly 120, and the initial charge/discharge efficiency Ce (%) was determined. Specifically, as shown in FIG. 5, after performing the assembly step S1 to the post-variation leaving step S6, the battery 100 is charged from the battery voltage Ve=3.0V to 4.1V in the main charging step S7. A charged quantity of electricity Qa with which the battery 100 is charged during the period is obtained. Subsequently, the battery 100 is discharged from the battery voltage Ve=4.1V to 3.0V, and the discharged electric quantity Qb discharged from the battery 100 during this discharge is obtained. Then, the initial charge/discharge efficiency Ce was calculated by Ce=(Qb/Qa)×100(%). Table 1 shows the results.

The initial charge-discharge efficiency Ce is higher in Reference Example 2 (initial charge-discharge efficiency Ce = 83%) than in Reference Example 3 (initial charge-discharge efficiency Ce = 80%), and further Reference Example 2 (initial charge-discharge efficiency Ce = 83%) ), the initial charge-discharge efficiency Ce was higher in Reference Example 1 (initial charge-discharge efficiency Ce = 84%) than in Reference Example 2, and in Reference Example 2 compared to Reference Example 2. 1, the frequency fe of the vertical fluctuation of the battery voltage Ve in the voltage fluctuation step S5 is lowered. Since the interval between the positive electrode plate 121 and the negative electrode plate 131 changes slowly by lowering the frequency fe as described above, the electrolytic solution 117 can easily move in accordance with the change in the interval. Therefore, in this voltage change step S5, penetration of the electrolytic solution 117 into the electrode body 120 was promoted. As a result, the initial charge/discharge efficiency Ce is considered to have increased.

As described above, in the manufacturing method of the battery 1 of the embodiment and the reference form, after the injection step S2 and before the main charging step S7, the battery voltage Ve is fluctuated up and down in the voltage fluctuation step S5. there is In this voltage change step S5, when the battery voltage Ve increases, the positive electrode plate 21 and the negative electrode plate 31 attract each other and the distance between them narrows. The interval between the negative electrode plates 31 is widened. In this way, the interval between the positive electrode plate 21 and the negative electrode plate 31 vibrates. This promotes the movement of the electrolytic solution 17 between the positive electrode plate 21 and the negative electrode plate 31 , thereby promoting the diffusion of metal ions derived from metallic foreign matter contained in the electrolytic solution 17 . Thus, even if metal foreign matter such as iron or copper is mixed in the electrode body 20 of the battery 1 during the manufacturing process, diffusion of metal ions derived from the metal foreign matter can be promoted to prevent a short circuit caused by the metal foreign matter.

Further, in the embodiment and the reference embodiment, the frequency fe of the vertical fluctuation of the battery voltage Ve in the voltage fluctuation step S5 is 0.1 to 100 Hz, further 0.1 to 10 Hz. Intervals change slowly. Therefore, the electrolytic solution 17 is easily moved according to the change in the distance, and the diffusion of the metal ions derived from the metallic foreign matter is further promoted.
Further, by increasing the time for performing the voltage change step S5 to 0.5 minutes or longer, or further to 1 minute or longer, the number of times the interval between the positive electrode plate 21 and the negative electrode plate 31 changes increases. is further promoted, and the diffusion of metal ions derived from metallic foreign matter is further promoted. On the other hand, the time required for the voltage change step S5 is set to 10 minutes or less, or even 3 minutes or less, so that the time required for the voltage change step S5 can be shortened.

Further, in the embodiment, the voltage change step S5 is performed with the battery temperature Te set to 30 ° C. or higher. When the battery temperature Te is increased, the viscosity of the electrolytic solution 17 is lowered, so the movement of the electrolytic solution 17 between the positive electrode plate 21 and the negative electrode plate 31 is promoted, and the diffusion of metal ions derived from metallic foreign matter is promoted. On the other hand, since the battery temperature Te is set at 60° C. or lower, further 50° C. or lower, it is possible to prevent deterioration of the battery due to excessively high battery temperature Te.

Furthermore, in the embodiment, since the pre-charging step S3 is performed before the voltage change step S5, the positive electrode potential is increased, and metal foreign matter on the positive electrode plate 21 is easily dissolved in the electrolytic solution 17. On the other hand, the negative electrode potential does not become too low, and metal derived from metallic foreign matter is less likely to deposit on the negative electrode plate 31 . It is difficult for metals derived from foreign metals (particularly iron foreign substances) to deposit on the negative electrode plate. In the voltage variation step S5, the diffusion of the metal ions derived from the metallic foreign matter can be promoted, so that the short circuit caused by the metallic foreign matter can be prevented more reliably.

In the embodiment, after the pre-charging step S3 and before the voltage fluctuation step S5, the pre-change standing step S4 is performed and the battery 1 is left to stand. is dissolved in the electrolytic solution 17, the metallic foreign matter can be dissolved in the electrolytic solution 17 more reliably. In the voltage variation step S5, the diffusion of the metal ions derived from the metallic foreign matter can be promoted, so that the short circuit caused by the metallic foreign matter can be prevented more reliably.

Further, in the embodiment and the reference form, after the voltage change step S5 and before the main charging step S7, the post-change standing step S6 is performed and the battery 1 is left to stand. diffuses. This makes it possible to more reliably prevent short circuits caused by metallic foreign matter.

Although the present invention has been described above with reference to the embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and can be appropriately modified and applied without departing from the gist of the present invention.
For example, in the embodiment and the reference embodiment, in the voltage fluctuation step S5, a bidirectional rectangular pulse voltage is applied to the battery 1 to fluctuate the battery voltage Ve up and down. Not limited. For example, a sinusoidal pulse voltage or a bidirectional triangular pulse voltage may be applied to the battery 1 to vary the battery voltage Ve up and down.

1,100 Battery 1x, 100x (Unfilled) Battery 17, 117 Electrolyte 20, 120 Electrode body 21, 121 Positive plate 31, 131 Negative plate 41, 141 Separator S1 Assembly step S2 Filling step S3 Preliminary charging step S4 Standing process before fluctuation S5 Voltage fluctuation process S6 Standing process after fluctuation S7 Main charging process S8 Aging process S9 Short-circuit detection process S4A, S4B Standing process

Claims (1)

A method for manufacturing a battery,
The battery is a lithium ion secondary battery containing a lithium transition metal composite oxide as a positive electrode active material and a carbon material as a negative electrode active material,
an injection step of injecting an electrolyte into an uninjected battery;
After the liquid injection step, a main charging step of conditioning charging the battery;
After the liquid injection step and before the main charging step, the battery temperature Te of the battery was set to 30° C. or higher, and the battery voltage Ve of the battery was fluctuated up and down to dissolve in the electrolytic solution. a voltage variation step for promoting diffusion of metal ions derived from metal foreign matter;
After the liquid injection step and before the voltage change step, the battery is set to a voltage lower than the battery voltage V1 reached in the main charging step, a positive electrode potential higher than the iron dissolution potential, and a negative electrode potential and a precharging step of precharging to a battery voltage V2 higher than the deposition potential of iron ions dissolved in the electrolytic solution.

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