JP4661145B2 - Manufacturing method of lithium ion secondary battery - Google Patents

Description

The present invention relates to a battery manufacturing method, and more particularly, to a charging condition after assembling a lithium ion secondary battery.

  In recent years, the performance of portable electronic devices such as mobile phones and personal digital assistants largely depends on the performance of not only the semiconductor elements and electronic circuits that are mounted, but also the chargeable / dischargeable secondary batteries. In addition to increasing battery capacity, it is desirable to achieve light weight and compactness at the same time. As a secondary battery that meets these demands, a nickel-hydrogen storage battery with an energy density approximately twice that of a nickel-cadmium storage battery was developed, and then a lithium-ion secondary battery that exceeded this level was developed for use in equipment. It is properly used according to the situation.

These batteries are manufactured by mainly storing a plate group in which a positive electrode plate and a negative electrode plate are wound through a separator, in a battery can, injecting an electrolyte, and caulking or laser sealing. .

For example, a lithium ion secondary battery has a process of repeating a charge / discharge cycle several times for the purpose of stabilizing the battery performance after the battery is assembled. As the initial charging condition of the battery, for example, a method of charging at a low rate such that the charging current is 0.2 ItA or less until the potential of the negative electrode becomes 0.3 V and then charging to 100% of the battery capacity is proposed. (For example, refer to Patent Document 1).
JP 2002-208440 A

  However, since the conventional lithium ion secondary battery is charged 100% with respect to the battery capacity, when metal foreign matter such as iron is mixed in the positive electrode, the metal foreign matter in the positive electrode is eluted by the potential of the positive electrode. Then, it is deposited on the negative electrode through the separator. When a metal conduction path is formed in the separator, there is a drawback that a phenomenon of causing a short circuit between the positive and negative electrodes occurs, resulting in a voltage failure of the battery.

LiCoO ₂ , which is a positive electrode active material commonly used in lithium ion secondary batteries, has a potential that rises during the initial charge, and shows a potential of 4.0 V or higher with respect to the lithium electrode during normal charge. If a metal foreign matter such as iron is present, it becomes a metal ion and dissolves in the electrolytic solution. In addition, the potential of graphite, which is a general negative electrode active material, drops in potential at the first charge, shows a potential of 0.5 V or less with respect to the lithium electrode during normal charge, and the metal ions eluted at the positive electrode pass through the separator on the negative electrode. It precipitates in. At that time, the positive electrode and the negative electrode are electrically connected to each other by the metal foreign matter, and a voltage failure of the battery occurs.

Therefore, the present invention solves such a conventional problem and provides a method for producing a lithium ion secondary battery with few battery voltage defects.

In order to solve the above-described conventional problems, the method of manufacturing a lithium ion secondary battery according to the present invention is performed until the battery reaches 5% to 50% in the upright state when the lithium ion secondary battery is charged for the first time. After charging with a constant current , the battery is kept upright for a storage time of 1 hour to 7 days.

By using the method for manufacturing a lithium ion secondary battery of the present invention, when metal foreign matter such as iron is mixed in the positive electrode plate, the metal ions eluted from the positive electrode in the first charge are uniformly diffused in the non-aqueous electrolyte. Is done. For this reason, when charged after the first charge, local metal deposition on the negative electrode can be prevented, and a minute short circuit between the positive and negative electrodes via the separator can be suppressed.

  According to the present invention, even if a metal foreign matter such as iron is mixed in the positive electrode plate, a minute short circuit between the positive and negative electrodes through the separator can be prevented, and the yield in voltage failure can be improved.

The method for producing a lithium ion secondary battery according to the present invention is characterized in that at the first charging, the battery capacity is charged 5% to 50% and a storage time of 1 hour to 7 days is provided. It is a manufacturing method.

By setting such a condition, the potential of the positive electrode is equal to or higher than the potential at which metal elution is promoted (3.
5V), and the metal ions eluted from the positive electrode are uniformly diffused in the electrolyte. Therefore, it is in a diffused state when it is deposited on the negative electrode. Similarly, when the battery is charged after the first time, local deposition of metal on the negative electrode can be prevented, and a minute short circuit between the positive electrode and the negative electrode via the separator can be suppressed.

  The reason why charging of 5% to 50% of the battery capacity is most effective at the time of the first charge is that in an actual battery, potential unevenness occurs on the spiral electrode plate, and the insulating film on the electrode plate This is because the charging depth becomes an appropriate condition on the battery configuration of the actual battery.

  The storage time after the first charge is preferably set to at least one hour because it takes time to elute and diffuse the metallic foreign matter on the positive electrode. Regarding the upper limit of the storage time, the upper limit was set within 7 days from the standpoint of actual productivity in consideration of the time required for metal elution and diffusion at the positive electrode to be completed.

  In a preferred embodiment of the present invention, the battery is charged in an upright state at the first charge.

  In a further preferred embodiment of the present invention, the battery is stored in an upright state after the first charge.

  The reason why the effect can be obtained by charging and storing the battery in an upright state is that, in the electrode plate group in which the positive electrode plate and the negative electrode plate are wound in a spiral shape via a separator, metal deposition / diffusion is caused by gravity. It is presumed that the action acts in a direction not penetrating the separator.

  Moreover, since elution and diffusion of metallic foreign matter also affect the battery temperature, it is better that the environmental temperature is high, and the environmental temperature is preferably 20 ° C to 80 ° C, more preferably 20 ° C to 60 ° C, and most preferably. Is 25 ° C to 35 ° C.

  In a further preferred embodiment of the present invention, it is preferable to charge at a low rate of 0.2 C or less until the potential of the negative electrode becomes 0.3V. Thereafter, until the battery capacity reaches 5% to 50%, the charging current may be charged at a low rate of 0.2 ItA or less, or may be charged at a current exceeding 0.2 ItA.

  In this way, by charging at a low rate, the metal ions of the metal foreign matter eluted from the positive electrode diffuse due to the potential gradient, and can prevent local precipitation on the negative electrode, further reducing battery voltage failure. Will be able to.

  Therefore, this secondary battery manufacturing method can reduce voltage failure due to a minute short circuit of the battery.

  A cylindrical lithium ion secondary battery will be described below as an example of the secondary battery.

  FIG. 1 is a schematic vertical sectional view of a cylindrical lithium ion secondary battery which is an embodiment of the present invention.

A positive electrode plate 1 in which a positive electrode mixture (not shown) is coated on a strip-shaped aluminum foil current collector (not shown), and a negative electrode mixture (not shown) on a strip-shaped copper foil current collector (not shown). The electrode plate group wound in a spiral shape with a separator 5 made of a microporous polyethylene film having a thickness of 25 μm disposed between the positive electrode plate 1 and the positive electrode plate 1 together with the non-aqueous electrolyte Is housed in a bottomed cylindrical battery can 8 that is open. The battery can 8 is hermetically sealed by caulking the upper end opening of the battery can 8 to the outer periphery of the battery lid 10 via an insulating packing 9 made of polypropylene. An aluminum positive electrode lead 2 welded to an aluminum foil current collector (not shown) is connected to the battery lid 10 by welding. A nickel negative electrode lead 4 welded to a copper foil current collector (not shown) is connected to a battery can 8 by welding. An upper insulating ring 6 is disposed above the electrode plate group to insulate it from the battery lid 10. A lower insulating ring 7 is disposed below the electrode plate group to insulate it from the battery can 8.

Example 1
A positive electrode plate 1 using lithium cobaltate (hereinafter abbreviated as LiCoO ₂ ) as a positive electrode active material and a negative electrode plate 3 using scaly graphite coke capable of occluding and releasing lithium as a negative electrode active material are microporous. A bottomed cylindrical battery can 8 having an open upper end is formed by spirally winding an electrode plate group insulated on both sides of a porous polyethylene resin via a three-layer separator 5 made of a microporous polypropylene resin. After storing and injecting a predetermined amount of nonaqueous electrolyte, the battery can 8 and the sealing plate 10 were caulked and sealed.

As a non-aqueous electrolyte, ethylene carbonate (hereinafter abbreviated as EC) and diethyl carbonate (hereinafter abbreviated as DEC) are mixed at a volume ratio of 50:50 in a non-aqueous solvent, and lithium hexafluorophosphate (hereinafter, referred to as solute) is mixed. And abbreviated as LiPF ₆ ) to a concentration of 1.0 mol / L.

  A cylindrical lithium ion secondary battery having a diameter of 18.0 mm and a total height of 65.0 mm and a battery capacity of 2000 mAh was produced.

Thus the cylindrical lithium ion secondary battery obtained non-aqueous electrolyte Note 23 ± 3 ° C. 12 hours after standing in an atmosphere after the liquid, the charging and discharging facility cylindrical battery of lithium ion secondary batteries to terminals Set 100,000 in an upright state with the lid side up and charge for the first time with a constant current of 0.1 ItA (200 mA) of battery capacity until the depth of charge reaches 5% of the battery capacity in an atmosphere of 30 ± 5 ° C The battery was left standing in an upright state in an atmosphere of 23 ± 3 ° C. for 1 hour. Next, for the purpose of ensuring the characteristics and reliability of the battery, a second charge / discharge was carried out, and a voltage test was performed after storage for 3 days in an environment of 45 ± 3 ° C.

(Example 2)
The battery was charged at a constant current of 0.5 ItA (1000 mA) until the first charge depth reached 20%, and was stored for 7 days until the second charge / discharge. A battery was fabricated and voltage inspection was performed.

(Example 3)
The battery was charged at a constant current of 0.2 ItA (400 mA) until the first charge depth reached 35%, and was stored for 3 days until the second charge / discharge. A battery was fabricated and voltage inspection was performed.

Example 4
The battery was charged at a constant current of 1.0 ItA (2000 mA) until the first charge depth reached 50%, and was stored for 1 hour until the second charge / discharge. A battery was fabricated and voltage inspection was performed.

( Reference Example 1 )
The battery was prepared in the same manner as in Example 4 except that the battery was set in the initial charge terminal in the state of being tilted in the horizontal direction, and after the initial charge was performed in that state, the battery was stored in the same state. A voltage test was performed.

( Reference Example 2 )
The battery was prepared in the same manner as in Example 2 except that the battery was set in the initial charge terminal in the horizontal direction and the battery was stored in the same state after the initial charge in that state. A voltage test was performed.

( Reference Example 3 )
Set the battery in the initial charge terminal in the state that the battery is tilted sideways, perform the initial charge in that state, and then store the battery in an upright state using the same method as in Reference Example 1. Fabricated and voltage tested.

( Reference Example 4 )
The battery is set in the same manner as in Reference Example 1 except that the battery is set in the first charging terminal in an upright state, and after the first charging in that state, the battery is stored in a state where the battery is tilted sideways. Fabricated and voltage tested.

(Comparative Example 1)
A battery was produced by the same method as in Example 1 except that charging was performed at a constant current until the initial charge depth reached 3%, and a voltage test was performed.

(Comparative Example 2)
A battery was produced by the same method as in Example 1 except that constant current was applied until the initial charge depth reached 5% and storage was performed for 30 minutes until the second charge / discharge.

(Comparative Example 3)
A battery was produced in the same manner as in Example 4 except that constant current was applied until the initial charge depth reached 50%, and the battery was stored for 30 minutes until the second charge / discharge, and a voltage test was performed.

(Comparative Example 4)
A battery was produced by the same method as in Example 2 except that charging was performed with a constant current until the initial charge depth reached 55%, and a voltage test was performed.

  The results of the voltage inspection thus obtained are shown in Table 1 as the voltage defect rate.

From the results of Table 1, Examples 1 to 4 and Reference Examples 1 to 4 had a lower voltage defect rate than Comparative Examples 1 to 4.

  It is considered that dissolution of metal foreign matters mainly composed of iron mixed into the positive electrode is promoted because the positive electrode potential is about 3.50 V or more based on the lithium electrode by the first charge. On the other hand, on the negative electrode, it is considered that the voltage gradually decreases to a potential (about 1.50 V) at which the metal is deposited as the initial charge proceeds. The ideal potential on the positive and negative electrodes is a potential at which metal foreign matters on the positive electrode are dissolved and metal ions are diffused in the nonaqueous electrolytic solution, and the dissolved metal ions are not deposited on the negative electrode. If the potential on the negative electrode is higher than the potential at which the deposition of metal ions proceeds, the mixed metal precipitates in a state where the metal ions are diffused without being concentrated locally on the negative electrode after being dissolved on the positive electrode. As a result, a conduction path between the positive electrode and the negative electrode is not formed via the separator, and the battery voltage does not fail. However, in reality, it is difficult to perform such an ideal positive / negative electrode potential operation. In particular, in the electrode plate configured by spirally winding between the two electrode plates via the separator, both the positive and negative electrode plates are respectively provided. Since potential unevenness occurs on the electrode plate, the initial charge depth, storage time, and storage conditions are closely related to voltage failure. Therefore, it was found that voltage defects can be reduced by controlling appropriate initial charge depth, storage time, and storage conditions.

In Examples 1 to 4 and Reference Examples 1 to 4 , the initial charge depth is 5% to 50%, and the storage time after the initial charge is 1 hour to 7 days. Since it can be presumed that the metal ions are diffused in the electrolyte without locally precipitating on the negative electrode, it can be presumed that the voltage drop defect is low. The reason for setting the storage time to 7 days was set to a maximum of 7 days because it is not efficient due to problems such as storage space for 7 days or more in actual manufacturing operation.

The reason why the voltage failure in Reference Examples 1 to 4 was slightly higher than that in Examples 1 to 4 was that the battery storage state during the first charge and after the first charge was either in the horizontal direction or either one was in the horizontal direction. That is, since the cylindrical battery is in a collapsed state, it can be presumed that the metal foreign matter mixed in the positive electrode and the metal deposited on the negative electrode are insufficiently diffused and locally deposited through the separator. From this, it was found that it is more preferable to store the battery in the upright state at the time of the first charge and after the first charge.

  The reason why the voltage defect rate of Comparative Example 1 was high can be presumed to be that when the initial charge depth was 3% in an actual battery, the dissolution of metal foreign matter on the positive electrode was insufficient when compared with the Example.

  It can be presumed that the reason why the voltage failure rate of Comparative Examples 2 and 3 was high was that the storage time after the first charge was as short as 30 minutes and the diffusion time of metal ions was insufficient.

  From the above results, in the method of manufacturing the secondary battery, 5 to 50% of the battery capacity is charged at the time of the first charge, and a storage time of 1 hour to 7 days is provided, and at the time of the first charge and / or the first charge. The battery voltage failure rate can be reduced by setting the battery storage state later in the upright state, and the battery voltage failure rate can be reduced by setting the battery storage state in the upright state at the time of initial charge and after the first charge. It was found that it can be further reduced.

In the present invention, the case where LiCoO ₂ is used as a positive electrode material that reacts reversibly with lithium has been described. However, the inclusion of lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ , LiMn ₂ O ₄ ), etc. Similar effects were obtained even when lithium composite oxide was used.

  In the present invention, the case where coke is used as the negative electrode material reversibly reacting with lithium has been described. However, the same effect was obtained even when a carbon material such as graphite or amorphous was used.

  In the present invention, the case where a cylindrical lithium ion secondary battery is used has been described. However, even if the battery shape is different, such as a rectangular shape, the electrode plate group may be configured by winding positive and negative plates spirally through a separator. The same effect was obtained.

In the present invention, the case where LiPF ₆ is used as the solute has been described, but the same effect can be obtained with other lithium salts such as lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and the like. Obtained.

  In the present invention, the case where the electrolyte concentration is 1.0 mol / L has been described, but the same effect was obtained even when the solute concentration was 0.5 to 2.0 mol / L.

  In the present invention, the case where a mixed solvent of EC and DEC is used as the electrolytic solution has been described. As other non-aqueous solvents, for example, cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, and chain structures such as dimethoxyethane Similar effects were obtained even when chain esters such as ether and methyl propionate were used, or when these multicomponent mixed solvents were used.

Schematic sectional view showing the configuration of a cylindrical battery in an embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Positive electrode lead 3 Negative electrode plate 4 Negative electrode lead 5 Separator 6 Upper insulating ring 7 Lower insulating ring 8 Battery can 9 Insulating packing 10 Battery lid

Claims (2)

In a method of manufacturing a lithium ion secondary battery that is configured by winding a separator between positive and negative plates, after charging the battery at a constant current until reaching 5% to 50% of the battery capacity in the upright state at the first charge. A method for producing a lithium ion secondary battery in which the battery is kept in an upright state and provided with a storage time of 1 hour to 7 days. The method for producing a lithium ion secondary battery according to claim 1, wherein the environmental temperature at the first charge is 25 ° C. to 35 ° C. 3.