JP2002298926A - Aging method for lithium secondary battery, and manufacturing method for lithium secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aging method for manufacturing a lithium secondary battery having a small quantity of self-discharging and restrained from the increase of internal resistance, and to provide a manufacturing method for such a lithium secondary battery. SOLUTION: Aging performed to make a nonaqueous electrolyte permeate an electrode body until the time immediately before conditioning for preparing the battery into an actually usable state by charging and discharging after forming the battery is performed while performing cathodic polarization by short-circuiting a negative electrode and a third pole. The manufacturing method for the lithium secondary battery comprises a batter forming process; an aging process for aging the battery after formed while performing cathodic polarization by short-circuiting the negative electrode and the third pole; and a conditioning process for preparing the battery into the actually usable state by charging and discharging the battery immediately after aging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for storing and storing lithium.
The present invention relates to an aging treatment method for performing infiltration of a non-aqueous electrolyte into an electrode body of a lithium secondary battery utilizing a desorption phenomenon after the formation of the battery.

[0002]

2. Description of the Related Art As mobile phones and personal computers become smaller,
In the field of communication devices and information-related devices, lithium secondary batteries have been commercialized and widely used because of their high energy densities as power sources for these devices. Also, in the field of automobiles, the development of electric vehicles is urgent due to resource and environmental issues, and lithium secondary batteries are being studied as power sources for electric vehicles.

Generally, a lithium secondary battery is formed by inserting an electrode body having a positive electrode and a negative electrode into a battery case, injecting a non-aqueous electrolyte, and sealing the battery case. Then, after the battery is formed, a so-called aging process for preserving the battery at a predetermined temperature is performed, and then a conditioning process for adjusting the battery to a practically usable state by performing charging and discharging is performed.

Here, the aging treatment is a treatment performed to sufficiently infiltrate the non-aqueous electrolyte into the electrode body. The aging treatment is started immediately after the battery is formed, and when the next conditioning treatment is started, specifically, It ends when the first charge is started. The time required for the aging process varies depending on the shape of each battery, the size of the electrodes, the pressure between the electrodes, the permeability of the electrolyte to the separator, and the temperature and pressure at the time of injection of the electrolyte. It is. And the time for performing the aging process is easy for the manufactured battery to self-discharge,
It is known that it greatly affects battery characteristics such as the magnitude of internal resistance.

[0005] For example, if the aging treatment time is too short, the non-aqueous electrolyte does not sufficiently infiltrate the electrode body, so that the active material is damaged due to the lack of the electrolyte and the internal resistance of the battery is increased. . In addition, since the charge / discharge is locally insufficient, the self-discharge amount of the battery may be increased. That is, in order to infiltrate the non-aqueous electrolyte into the electrode body, it is necessary to ensure sufficient time for the aging treatment, but if the time for the aging treatment is too long,
The self-discharge amount of the manufactured battery becomes large.

On the other hand, when actually manufacturing a battery, a battery similar to the battery to be manufactured is preliminarily manufactured, and the battery to be manufactured is analyzed based on the result of analyzing the characteristics of the preliminarily manufactured battery. At present, the aging processing time is determined uniformly. However, this preliminary study may not be sufficient, or there may be variations in storage conditions, such as the presence of a temperature distribution inside a thermostat for storing batteries. Therefore, even when the aging treatment is performed based on the above preliminary study, the infiltration state of the non-aqueous electrolyte differs depending on the battery, and as a result, the self-discharge of the manufactured battery and the magnitude of the internal resistance are large. However, there has been a problem that a large variation occurs in the battery characteristics such as the battery characteristics.

As an attempt to uniformly shorten the aging treatment time of a battery in order to prevent excessive aging, Japanese Patent Application Laid-Open No. Hei 6-290811 discloses a method of starting charge / discharge as a conditioning treatment immediately after battery formation. Have been. However, this method needs to integrate a device for injecting a non-aqueous electrolyte into the battery and a device for charging and discharging in a dry room for forming the battery. Absent. Further, since the aging treatment time is too short, there is a problem that the internal resistance of the battery is increased as described above.

[0008]

The present inventor has conducted a number of experiments on the aging treatment and investigated the relationship between the aging treatment time and the battery characteristics. As a result, if the aging time is too long, Cu ions elute from the copper current collector or the copper negative electrode terminal of the negative electrode, and the eluted Cu ions precipitate during charge / discharge as the next conditioning process. It has been found that the self-discharge amount of the battery is increased by causing a micro short circuit (micro short-circuit) of the battery or by becoming a shuttle substance for an oxidation-reduction reaction. And, it was found that the Cu ion elution reaction was related to the negative electrode potential.

The present invention has been made on the basis of the above-mentioned findings, and has a sufficient self-discharge amount by suppressing the elution of Cu ions from the negative electrode which affects battery characteristics while securing a sufficient aging treatment time. It is an object of the present invention to provide an aging treatment method capable of manufacturing a lithium secondary battery having a small internal resistance and suppressing an increase in internal resistance.

It is another object of the present invention to provide a method of manufacturing a lithium secondary battery having a small self-discharge amount and a suppressed increase in internal resistance by including the aging treatment method.

[0011]

(1) An aging treatment method for a lithium secondary battery according to the present invention is directed to a negative electrode mixture containing a positive electrode and a negative electrode active material using a material capable of occluding and releasing lithium as a positive electrode active material. Secondary battery formed by housing a battery case with an electrode body having a negative electrode formed in a layer shape on the surface of a copper current collector, and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent On the other hand, after forming the battery, the aging treatment method performed to infiltrate the non-aqueous electrolyte into the electrode body until immediately before the conditioning process of adjusting the battery to a practically usable state by performing charging and discharging. Aging is performed while performing a negative polarization operation by short-circuiting the negative electrode and the third electrode.

That is, the aging treatment method for a lithium secondary battery of the present invention focuses on the negative electrode potential when Cu ions are eluted from the copper current collector constituting the negative electrode during aging, and makes the negative electrode more negative than the potential. Aging is performed while negatively polarizing to an appropriate potential. Hereinafter, the relationship between the reaction in the battery and the negative electrode potential in the aging treatment will be described, and the significance of negative polarization will be described.

In general, unavoidable moisture is adsorbed on the electrode, and this moisture reacts with the electrolyte in the non-aqueous electrolyte,
Generates acid components such as HF and H ₃ PO ₄ . For example, the reaction formulas when LiPF ₆ is used as the electrolyte are shown in (Formula 1) and (Formula 2).

LiPF ₆ + H ₂ O → LiF + 2HF + POF ₃ (formula 1) POF ₃ + 3H ₂ O → H ₃ PO ₄ + 3HF (formula 2) On the other hand, the surface of the copper current collector constituting the negative electrode is: It is covered with Cu ₂ O generated in the atmosphere. Therefore, at the interface between the negative electrode and the electrolytic solution, the metal / oxide equilibrium potential corresponding to the H ⁺ ion concentration of the acid component is obtained. The reaction equation of the equilibrium reaction of Cu / Cu ₂ O is shown in (Equation 3). The potential E ₀ at that time is also shown.

2Cu + H ₂ O → Cu ₂ O + 2H ⁺ + 2e (Equation 3) E ₀ = 0.471−0.059pH (H / H ⁺ standard) Also, when the pH is greatly reduced, Cu of the copper current collector is reduced. Is C
It elutes as u ²⁺ ions (anode reaction) and ^reaches the equilibrium potential of Cu / Cu ²⁺ regardless of the H ⁺ ion concentration. This reaction formula is shown in (Formula 4). The potential E ₀ at that time is also shown.

Cu → Cu ²⁺ + 2e (Equation 4) E ₀ = 0.337-0.0295 Log [Cu ²⁺ ]
(H / H ⁺ standard) On the other hand, as the cathode reaction, a reaction of generating H ₂ from H ^{+ of the} acid component and a reaction between dissolved oxygen in the non-aqueous electrolyte and water attached to the electrode are considered. Each reaction formula is shown in (Formula 5) and (Formula 6). The potential E ₀ at that time is also shown.

2H ⁺ + 2e → H ₂ (Equation 5) E ₀ = 0.059 Log [H ⁺ ] −0.0296p
_{[H 2] (H / H} + reference, p [H _2] is the hydrogen partial _{pressure) O 2 + 2H 2 O +} 4e → 4OH - ··· ( Equation _{6) E 0 = 0.401-0.0147Log [OH} -] +0.
0591 p [O ₂ ] (H / H ⁺ standard, p [O ₂ ] is oxygen partial pressure) In the electrode reaction in the electrolyte infiltration state of the negative electrode, the various reactions described above were balanced as the sum of the anodic reaction and the cathodic reaction. The negative electrode potential is a natural immersion potential as a so-called hybrid anode / cathode potential.

When the aging process is started, for example,
By the reaction shown in (Equation 1) and (Equation 2), the acid component (HF,
H ₃ PO ₄ ) is generated, and the equilibrium reaction shown in (Equation 3) proceeds to the left by the action of the H ⁺ ion, and Cu ₂ O is reduced and removed. When aging is further continued, Cu ₂ O on the current collector surface of the negative electrode disappears, and the above-described reduction reaction of Cu ₂ O ends. On the other hand, since the pH near the negative electrode decreases due to the presence of the acid component, the reaction shown in (Equation 4) proceeds, and Cu ions are eluted from the copper current collector.

Here, the case where aging is performed while using Al as the third pole and short-circuiting the negative electrode with the third pole will be described. In addition, the third electrode means an electrode present in the battery other than the positive electrode and the negative electrode. FIG. 1 shows the relationship between the above-described equilibrium potentials of the anodic and cathodic reactions and the anodic reactions of various metals. From FIG.
Since Al is a metal that is lower than copper, when the negative electrode is made conductive with Al, the negative electrode potential drops to a potential lower than the spontaneous immersion potential, and is so-called negatively polarized. As a result, the negative electrode potential becomes
Since the potential is lower than the potential at which the Cu ion elution reaction shown in (Equation 4) proceeds, the elution of Cu ions is suppressed. That is, the negative polarization operation means an operation of lowering the negative electrode potential to a lower potential that does not cause elution of Cu ions.

As described above, according to the aging treatment method of the present invention, the aging is performed while performing the negative polarization operation by short-circuiting the negative electrode and the third electrode. Elution of Cu ions is suppressed. That is, a sufficient aging time can be secured for each battery without strictly determining the aging processing time for each battery. Further, according to the aging treatment method of the present invention, even when moisture that has entered the battery during the formation of the battery reacts with the electrolyte in the electrolytic solution to generate an acid, the corrosion reaction of the negative electrode due to the acid is suppressed. Therefore, the allowable moisture concentration in the battery forming step can be increased.

(2) The method for producing a lithium secondary battery of the present invention including the above-mentioned aging treatment method comprises the steps of:
An electrode body including a negative electrode in which a negative electrode mixture containing a positive electrode and a negative electrode active material, which have a removable substance as a positive electrode active material, is formed in a layer on the surface of a copper current collector, and a lithium salt in an organic solvent. A method for manufacturing a lithium secondary battery formed by housing a dissolved nonaqueous electrolyte in a battery case, wherein the battery is formed by housing the electrode body in the battery case together with the nonaqueous electrolyte. An aging treatment step of aging the battery formed by infiltrating the non-aqueous electrolyte into the electrode body while performing a negative polarization operation by short-circuiting the negative electrode and the third electrode; And a conditioning process for adjusting the battery to a practically usable state by charging and discharging the battery immediately after the process.

That is, the method for manufacturing a lithium secondary battery of the present invention includes the above-mentioned aging method between the battery forming step and the conditioning step. In the method for manufacturing a lithium secondary battery of the present invention, the cause of micro short-circuit of the battery and the elution of Cu ions serving as a shuttle substance of the oxidation-reduction reaction are suppressed in the aging treatment. This is a method for easily manufacturing a lithium secondary battery in which an increase in resistance is suppressed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the aging treatment method for a lithium secondary battery according to the present invention will be described in detail. First, the configuration and structure of a lithium secondary battery to which the aging method of the present invention is applied will be described.
An embodiment of a method for manufacturing a lithium secondary battery including the aging treatment method of the present invention will be described.

<Structure of Lithium Secondary Battery> In general, a lithium secondary battery includes a positive electrode and a negative electrode that occlude and release lithium, a separator sandwiched between the positive electrode and the negative electrode, and a positive electrode and a negative electrode. A non-aqueous electrolyte for transferring lithium between the lithium secondary batteries, to which the aging treatment method of the present invention can be applied, also complies with this configuration.
Hereinafter, each component will be described.

The positive electrode is prepared by mixing a conductive material and a binder with the positive electrode active material, adding an appropriate solvent as needed, and forming a paste-like positive electrode mixture into a current collector made of a metal foil such as aluminum. It can be formed by applying to the body surface, drying, and then increasing the active material density by pressing.

As the positive electrode active material, a material capable of inserting and extracting lithium is used. For example, from the viewpoint that a 4V class secondary battery can be formed, the basic composition is LiCoO ₂ , Li
A lithium transition metal composite oxide having a layered rock salt structure such as NiO ₂ and LiMnO ₂ and a lithium transition metal composite oxide having a spinel structure having a basic composition such as LiMn ₂ O ₄ can be used. Above all, a lithium transition metal composite oxide having a layered rock salt structure having a basic composition of LiNiO ₂ is lower in price than a lithium transition metal composite oxide having Co as a central metal, and has a higher secondary discharge capacity per unit weight. This is preferable because a battery can be configured.

The term “basic composition” means a typical composition of each of the above-mentioned complex oxides. In addition to those represented by the above-mentioned composition formulas, for example, a lithium site or a transition metal site may be replaced by one or more other compounds. It also includes compositions such as those partially substituted with more than one kind of element. Further, the stoichiometric composition is not necessarily limited to the stoichiometric composition. For example, a non-stoichiometric composition in which a cation element such as Li or Ni which is inevitably produced in the manufacturing process is deficient, or an oxygen element is deficient Including things. Further, one of the lithium transition metal composite oxides may be used, or two or more of them may be used in combination.

The conductive material used for the positive electrode is for ensuring the electron conductivity of the positive electrode active material layer, and is made of carbon material powder such as carbon black, acetylene black and graphite.
A species or a mixture of two or more species can be used. The binder plays a role of binding the active material particles, and is made of polytetrafluoroethylene, polyvinylidene fluoride, a fluorine-containing resin such as fluororubber, polypropylene,
A thermoplastic resin such as polyethylene can be used.
An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent in which the active material, the conductive material, and the binder are dispersed.

The negative electrode is formed by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium, adding an appropriate solvent and forming a paste-like negative electrode mixture on the surface of the current collector in a layered manner. can do. Here, the current collector is made of copper, which is a relatively noble metal.For example, a negative electrode mixture may be applied to the surface of a copper foil current collector, dried, and pressed to form a negative electrode. . The term “made of copper” is a concept including a copper alloy to which other elements are slightly added in addition to pure copper, and it is sufficient that copper is included as a main constituent element. As the negative electrode active material, for example, natural graphite, spherical or fibrous artificial graphite, easily graphitizable carbon such as coke, hardly graphitizable carbon such as a phenol resin fired body, or the like can be used. As in the case of the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride or the like is used as the negative electrode binder, and N-methyl-2 is used as the solvent.
-Organic solvents such as pyrrolidone can be used.

The separator sandwiched between the positive electrode and the negative electrode separates the positive electrode from the negative electrode, holds the electrolytic solution and allows ions to pass through, and uses a thin microporous film such as polyethylene or polypropylene. Can be.

The non-aqueous electrolyte is a solution in which an electrolyte is dissolved in an organic solvent. Examples of the organic solvent include aprotic organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and the like.
One kind of γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride and the like, or a mixture of two or more kinds thereof can be used. As the electrolyte to be dissolved, LiI, LiCl which generates lithium ions when dissolved are used.
O ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like can be used.

<Structure of Lithium Secondary Battery> FIG. 2 shows a cross section of a cylindrical lithium secondary battery as an example of a lithium secondary battery having the above-mentioned components and to which the aging treatment method of the present invention can be applied. The present lithium secondary battery 1 includes an electrode body 10, a battery case 20 for sealing the electrode body 10 together with a non-aqueous electrolyte, and a positive electrode terminal 30 and a negative electrode terminal 40 attached to the battery case 20 and electrically connected to the electrode body 10. It is configured.

The electrode body 10 includes a sheet-shaped positive electrode 11 and a sheet-shaped negative electrode 12 with a separator 13 interposed therebetween, and a wound core 14.
In the form of a roll wound around. Incidentally, the positive electrode 11 is formed by forming a positive electrode mixture layer containing a lithium transition metal composite oxide as an active material on both surfaces of an aluminum foil current collector, and the negative electrode 12 is formed on both surfaces of a copper foil current collector as an active material. A negative electrode mixture layer containing a carbon material is formed, and the separator 13 is made of a porous polyethylene sheet. The winding core 14 is formed of an aluminum alloy winding core 14a located on the positive electrode terminal side, and a resin winding wound coaxially and screwed to the aluminum winding core 14a and located on the negative electrode terminal side. And a core 14b. Battery case 20
Is a cylindrical outer can 21 made of aluminum and an outer can 2
1 is formed of a disc-shaped positive electrode side cover plate 22 and a negative electrode side cover plate 23 made of aluminum, which are respectively joined to both open ends. Each of the positive-side cover plate 22 and the negative-side cover plate 23 is provided with a safety valve 24 that opens when the internal pressure of the battery case 20 exceeds a predetermined pressure (the positive electrode side is not shown). The side cover plate 23 is further provided with an electrolyte injection port 25, and an injection hole plug 26 for sealing the electrolyte injection port 25 is screwed and attached thereto.

The positive electrode terminal 30 is made of aluminum and includes a current collector 30a and a bolt-shaped external terminal 30b.
The current collecting portion 30a is screwed and connected to the aluminum winding core portion 14a of the winding core 14, and the external terminal portion 30b is connected to the positive electrode side cover plate 22 of the battery case 20 with its tip protruding outside the battery.
Gasket 31 into positive electrode terminal mounting hole 22a provided in
, And is attached by a washer 32 and a nut 33, and is insulated from the battery case 20. Current collector 30
A band-shaped positive electrode lead 11 a made of aluminum extending from the positive electrode 11 is joined to the periphery of the terminal a, and electrical conduction between the positive electrode terminal 30 and the positive electrode 11 of the electrode body 10 is secured.

The negative electrode terminal 40 is made of copper and has a current collector 40a.
And a bolt-shaped external terminal portion 40b.
Numeral 0a is screwed and connected to the resin winding core portion 14b of the winding core 14, and the external terminal portion 40b is provided on the negative electrode side cover plate 23 of the battery case 20 with its tip protruding outside the battery. It is attached to the negative electrode terminal mounting hole 23 a via a gasket 41 by a washer 42 and a nut 43, and is insulated from the battery case 20. A strip-shaped copper negative electrode lead 12a extending from the negative electrode 12 is joined to the periphery of the current collecting portion 40a, and electrical conduction between the negative electrode terminal 40 and the negative electrode 12 of the electrode body 10 is ensured.

<Method of Manufacturing Lithium Secondary Battery> As an example of a lithium secondary battery to which the aging treatment method of the present invention can be applied, a method of manufacturing a lithium secondary battery having the above structure includes a battery forming step, an aging treatment step, The description will be made in the order of the conditioning processing steps.

(1) Battery Forming Step This step is a step of forming a battery as shown in FIG. 2 above by housing the electrode body together with the non-aqueous electrolyte in a battery case. First, the positive electrode and the negative electrode formed as described above are laminated via a separator to form an electrode body, and a current collecting lead or the like is provided between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside. And connect it to the battery case. The positive terminal and the negative terminal are insulated from the battery case. Then, a non-aqueous electrolyte is injected from the electrolyte injection port, and the battery case is sealed to form a battery.

(2) Aging Treatment Step This step is a step of aging the battery by infiltrating the electrode body with a non-aqueous electrolyte while performing a negative polarization operation by short-circuiting the negative electrode and the third electrode. . The aging process is
The process starts immediately after the non-aqueous electrolyte is injected into the battery case in the battery forming process, and ends when the first charging is started in the conditioning process performed after this process.

Aging is performed by storing the battery after forming the battery at a predetermined temperature while performing a negative polarization operation by short-circuiting the negative electrode and the third electrode. As described above, the negative polarization operation is an operation for lowering the negative electrode potential to a base potential that does not cause elution of Cu ions, and has the same effect as starting charging immediately after forming the battery. The negative polarization operation may be performed, for example, by forming a battery having a structure in which the third electrode can be inserted into the battery case, and conducting the third electrode and the negative electrode. Here, the third electrode desirably contains a metal lower than copper constituting the negative electrode. Examples of the metal lower than copper include Li, Al, Mg, Zn, and the like.
Fe, Ni and the like can be mentioned. In particular, it is preferable to use Li or Al since the negative electrode can be negatively polarized to a lower potential.

When the battery case contains a metal that is more noble than copper, the negative polarization operation can be performed with the battery case serving as the third pole. In this case, the negative electrode may be electrically connected to the battery case. The positive and negative terminals need to be insulated from the battery case. Therefore, if the battery case is configured as the third pole, the battery can be further reduced in size, and no special parts or the like for negative polarization operation are required, and the aging process and the subsequent conditioning process can be performed. It can be done simply by switching connection terminals. In particular, Al is lightweight, inexpensive, and excellent in moldability, so that it is practical as a material for a battery case. Therefore, when the negative polarization operation is performed using the battery case made of Al as the third pole, effective negative polarization can be easily performed at lower cost.

When terminating aging, it is desirable to perform a negative polarization operation, that is, to cancel a short circuit between the negative electrode and the third electrode. Aging is terminated while the negative electrode and the third electrode are short-circuited, and charging in the next conditioning process is started. For example, when the battery case made of Al and the negative electrode are short-circuited, This is because movable Li ions may cause an alloying reaction with Al and damage the battery case.

The temperature at which the battery is stored is not particularly limited, and the storage temperature may be appropriately determined, for example, about room temperature. The storage method is not particularly limited. For example, the battery can be stored in a thermostat.

(3) Conditioning Treatment Step This step is a step of charging and discharging the battery immediately after the previous aging treatment to adjust the battery to a practically usable state. Charging and discharging may be performed by a method usually performed as conditioning processing.At a predetermined temperature, charging is performed at a current density as small as possible to a predetermined voltage, and similarly, discharging is performed at a current density as small as possible to a predetermined voltage. Just do it. For example, in the case of a 4V-class battery, the battery is charged at a constant current of 0.2 to ² mA / cm ² to a battery voltage of about 4 V, and then charged at a constant current of 1 to ² mA / cm ^2. The discharge may be performed up to about 3V. The number of times of charging / discharging is not particularly limited, and may be one or more times.

<Allowance of Other Embodiments> The embodiments of the aging treatment method for the lithium secondary battery and the method for manufacturing the lithium secondary battery including the same according to the present invention have been described above. The aging treatment method for a lithium secondary battery and the method for manufacturing a lithium secondary battery including the same according to the present invention include various modifications and improvements based on the knowledge of those skilled in the art, including the above embodiment. It can be implemented in various forms described above.

[0045]

EXAMPLES Based on the above embodiment, after actually forming a lithium secondary battery, an aging treatment and a conditioning treatment were performed to produce various batteries. Then, the discharge capacity and the internal resistance of those batteries were measured, and the battery characteristics were evaluated. Hereinafter, these contents will be described.

<Experiment 1> (1) Production of Lithium Secondary Battery (a) Formation of Battery In Experiment 1, a plurality of lithium secondary batteries having the above-described structure shown in FIG. 2 were produced. The positive electrode 11 was formed using LiNiO ₂ as a positive electrode active material. First, the active material L
85 parts by weight of iNiO ₂ , 10 parts by weight of carbon black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder, N-methyl-2-pyrrolidone as a solvent was added, and the mixture was kneaded to obtain a paste. A positive electrode mixture was prepared. Next, this positive electrode mixture was applied to both surfaces of an aluminum foil current collector having a thickness of 15 μm, dried, and roll-pressed to obtain a sheet-shaped positive electrode 11. The size of the positive electrode 11 was 124 mm × 3050 mm, and the coating thickness of the positive electrode mixture after dry pressing was 70 μm per side.

The negative electrode 12 was formed using graphitized mesocarbon microbeads (MCMB) as the negative electrode active material. First, 90 parts by weight of MCMB as an active material, 10 parts by weight of polyvinylidene fluoride as a binder are mixed, N-methyl-2-pyrrolidone is added as a solvent, and the mixture is kneaded to prepare a paste-like negative electrode mixture. did. Next, this negative electrode mixture was applied to both sides of a copper foil current collector having a thickness of 10 μm, dried, and roll-pressed to obtain a sheet-shaped negative electrode 12.
The size of the negative electrode 12 was 128 mm × 3200 mm, and the coating thickness of the negative electrode mixture after dry pressing was 75 μm per side.

The positive electrode 11 and the negative electrode 12 were sandwiched between them and a polyethylene separator 13 having a thickness of 25 μm and a width of 132 mm was sandwiched therebetween to form a roll-shaped electrode body 10. The electrode body 10 is inserted into the cylindrical battery case 20 made of aluminum, and the non-aqueous electrolyte is supplied through the electrolyte injection port 25 by 50.
Then, the battery case 20 was sealed to form a battery. The non-aqueous electrolyte is prepared by mixing Li in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7.
The PF ₆ was used at a concentration of 1M. The outer case 21 of the battery case 20 has a thickness of 0.3 mm and an outer diameter of 3 mm.
The positive-side cover plate 22 and the negative-side cover plate 23 have a thickness of 0.3 mm and an outer diameter substantially equal to the inner diameter of the outer can 21.

(B) Aging treatment The formed secondary batteries were aged in 10 groups each, divided into three groups (# 1 to # 3). For aging, put the batteries of each group in a 20 ° C
Performed by storing for hours. In the battery of the # 1 group, the negative electrode terminal 40 and the battery case 20 are short-circuited with a clip.
0 was short-circuited with metallic lithium as the third pole, and aging was performed while performing a negative polarization operation. on the other hand,#
The batteries of the three groups were aged without performing the negative polarization operation.

(C) Conditioning Processing After the above-mentioned predetermined aging time, conditioning processing was performed on the batteries of each group of # 1 to # 3.
The batteries of the # 1 and # 2 groups were subjected to conditioning processing by releasing the short circuit between the negative electrode terminal and the battery case or metallic lithium, respectively.

The charging and discharging were performed at a temperature of 25 ° C. First, the battery voltage was 4.2 at a constant current of 0.25 mA / cm ^2.
V and a constant voltage charge at the battery voltage (total charge time 6 hours), and then a current density of 1 mA
A cycle of discharging at a constant current of / cm ^{2 to} a battery voltage of 3.0 V was defined as one cycle, and a total of four cycles were performed. The discharge capacity of the fourth cycle was used as the initial discharge capacity of each lithium secondary battery.

(2) Evaluation of Battery Characteristics Each of the batteries of the above-mentioned # 1 to # 3 groups was stored in a thermostat at a storage temperature of 25 ° C. for one month, and the discharge capacity after storage was measured. Then, the self-discharge rate was calculated using the formula [(1−discharge capacity / initial discharge capacity) × 100] (%). Table 1 shows the self-discharge rate of each group.

[0053]

[Table 1]

As is clear from Table 1, # 1 and # 2
The batteries in the group have a low self-discharge rate and a self-discharge rate of 5
The occurrence of defective batteries of 0% or more was not observed. On the other hand, the batteries of the # 3 group had a large self-discharge rate, and two out of ten defective batteries having a self-discharge rate of 50% or more were recognized. Therefore, it was confirmed that according to the method of manufacturing a lithium secondary battery of the present invention including the aging treatment step of performing aging while performing negative polarization operation, a secondary battery having a small amount of self-discharge can be manufactured.

<Experiment 2> (1) Production of Lithium Secondary Battery (a) Formation of Battery In Experiment 2, a plurality of secondary batteries having a structure capable of inserting the third electrode were produced. The positive electrode is LiNi _0.8 as a positive electrode active material.
It was formed using Co _0.15 Al _0.05 O ₂ . First, to 85 parts by weight of LiNi _0.8 Co _0.15 Al _0.05 O _{2 as} an active material,
10 parts by weight of carbon black as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder are mixed, and N-methyl-2-pyrrolidone is added as a solvent and kneaded to prepare a paste-like positive electrode mixture. did. Next, this positive electrode mixture was applied to both surfaces of a 15 μm-thick aluminum foil current collector, dried, and roll-pressed to obtain a sheet-shaped positive electrode. The size of the positive electrode was 77 mm × 3750 mm, and the coating thickness of the positive electrode mixture after dry pressing was 52 μm per side.

The negative electrode was formed using natural graphite as a negative electrode active material. First, 7.5 parts by weight of polyvinylidene fluoride as a binder is mixed with 92.5 parts by weight of natural graphite as an active material, N-methyl-2-pyrrolidone is added as a solvent, and the mixture is kneaded to form a paste. Was prepared. Next, this negative electrode mixture was applied to both sides of a copper foil current collector having a thickness of 10 μm, dried, and roll-pressed to obtain a sheet-shaped negative electrode. The size of the negative electrode was 81 mm × 4650 mm, and the coating thickness of the negative electrode mixture after dry pressing was 58 μm per side.

The above positive electrode and negative electrode were placed between them with a thickness of 25 mm.
A separator made of polyethylene having a width of 85 mm and a width of 85 mm was sandwiched between the separators to form a roll-shaped electrode body. In addition, each metal of Al, Mg, and Zn was appropriately selected for the third pole. The electrode body and the third pole were inserted into a glass cell having an outer diameter of 35 mm and a length of 120 mm, a non-aqueous electrolyte solution of 40 cc was injected, and the battery was sealed to form a battery. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 3: 7 was used.

(B) Aging treatment The formed secondary batteries were aged in 10 groups each, divided into four groups (# 4 to # 7). Aging was performed by storing the batteries of each group at room temperature for 3 days. Here, the batteries of the # 4 to # 6 groups were aged while performing the negative polarization operation by short-circuiting the negative electrode terminal 40 and the third electrode. As the third pole, #
The batteries of group 4 use metal Al, the batteries of group # 5 use metal Mg, and the batteries of group # 6 use metal Zn. On the other hand, the batteries of the # 7 group were aged without performing the negative polarization operation.

(C) Conditioning Processing After the above-mentioned predetermined aging processing was completed, conditioning processing was performed on the batteries of each group of # 4 to # 7. Charging and discharging are performed at a temperature of 25 ° C. First, charging is performed to a battery voltage of 4.2 V with a constant current of a current density of 0.25 mA / cm ² , and then constant voltage charging is performed at the battery voltage (total charging time of 6 hours). Time), then the current density is 1 mA / c
A cycle of discharging at a constant current of m ^{2 to} a battery voltage of 3.0 V was defined as one cycle, and a total of four cycles were performed. The discharge capacity of the fourth cycle was used as the initial discharge capacity of each lithium secondary battery.

(2) Evaluation of Battery Characteristics Each of the batteries of the above-mentioned # 4 to # 7 groups was stored in a thermostat at a storage temperature of 25 ° C. for one month as in Experiment 1.
The discharge capacity after storage was measured, and the self-discharge rate was calculated from the values of the discharge capacity after storage and the initial discharge capacity. Then, a battery having a self-discharge rate of 50% or more was determined as a defective battery, and its occurrence ratio was examined.

Further, the internal resistance after storage was measured. Hereinafter, a method of measuring the internal resistance will be described. The battery of each group is charged to 50% of its capacity (SOC 50
%), The battery was discharged at 0.1 C for 10 seconds, and the voltage at the 10th second was measured. Next, discharge at 0.3C for 10 seconds, 1C for 10 seconds, 3C for 10 seconds, and 10C for 10 seconds.
The voltage at 0 seconds was measured. Charging was performed in the same manner, and the voltage at the 10th second was measured. Then, the current dependence of the voltage was determined, and the gradient of the current-voltage straight line was defined as the internal resistance. 1C is a current required to discharge the battery in one hour. Table 2 shows the percentage of defective batteries generated in each group and the average value of the internal resistance.

[0062]

[Table 2]

As is apparent from Table 2, in the batteries of the # 4 to # 6 groups that were aged while performing the negative polarization operation, no defective batteries with a self-discharge rate of 50% or more were observed. On the other hand, in the batteries of the # 7 group which was aged without performing the negative polarization operation, five out of ten defective batteries were observed. Also, the variation in the internal resistance value of the batteries of the # 4 to # 6 groups is smaller than that of the batteries of the # 7 group.

Therefore, it was confirmed that the battery which was subjected to aging while performing the negative polarization operation by short-circuiting the negative electrode and the third electrode was a battery having a small amount of self-discharge and a small internal resistance.

[0065]

According to the aging method of the present invention,
Even if the aging time is lengthened, elution of Cu ions from the negative electrode is suppressed. That is, a sufficient aging time can be secured for each battery without strictly determining the aging processing time for each battery. Further, according to the method for producing a lithium secondary battery of the present invention including the aging treatment method, it is possible to produce a lithium secondary battery having a small amount of self-discharge and a suppressed increase in internal resistance. it can.

[Brief description of the drawings]

FIG. 1 shows the relationship between the equilibrium potentials of the anodic and cathodic reactions in a battery and the anodic reactions of various metals.

FIG. 2 shows a cross section of a cylindrical lithium secondary battery which is an example of a battery to which the aging treatment method of the present invention can be applied.

[Description of Signs] 1: Cylindrical lithium secondary battery (sealed battery) 10: Electrode body 11: Positive electrode 12: Negative electrode 13: Separator 20: Battery case 21: Outer can 22: Positive side cover plate 23: Negative side cover Plate 30: Positive terminal 40: Negative terminal

Continuing from the front page (72) Inventor Tohru Saeki 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. Address 1 Toyota Central Research Laboratory Co., Ltd. F-term (reference) 5H017 AA03 AS02 AS10 CC01 EE01 5H029 AJ04 AJ06 AK03 AK18 AL06 AL07 AM02 AM03 AM04 AM05 AM07 BJ14 CJ11 CJ16 CJ23 CJ28 DJ01 DJ07 EJ01

Claims (4)

[Claims] 1. An electrode comprising a negative electrode in which a positive electrode using a material capable of occluding and releasing lithium as a positive electrode active material and a negative electrode mixture containing a negative electrode active material are formed in a layer on the surface of a copper current collector. A battery and a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent are stored in a battery case. An aging treatment method performed to infiltrate the non-aqueous electrolyte into the electrode body until immediately before the conditioning treatment to adjust the negative polarity operation by short-circuiting the negative electrode and the third electrode. Aging treatment method for a lithium secondary battery in which aging is performed. 2. The aging treatment method for a lithium secondary battery according to claim 1, wherein the third electrode contains a metal lower than copper. 3. The aging treatment method for a lithium secondary battery according to claim 2, wherein the battery case serves as the third electrode. 4. An electrode comprising a negative electrode in which a positive electrode using a material capable of occluding and releasing lithium as a positive electrode active material and a negative electrode mixture containing a negative electrode active material are formed in a layer on the surface of a copper current collector. Body and a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent in a battery case. A method for manufacturing a lithium secondary battery, comprising: forming the electrode body together with the non-aqueous electrolyte in the battery case. A battery forming step of forming a battery by storing the battery in a battery and aging the battery formed by infiltrating the non-aqueous electrolyte into the electrode body while performing a negative polarization operation by short-circuiting the negative electrode and the third electrode. An aging treatment step of performing charging and discharging of the battery immediately after the aging treatment, and a conditioning treatment step of adjusting the battery to a practically usable state. Method of manufacturing a pond.