JP2002298925A - 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 that can easily determine the optimum aging time of individual batteries without damaging electrodes, and to provide a manufacturing method for a lithium secondary battery having a small quantity of self-discharging and restrained from the increase of internal resistance. SOLUTION: Aging processing performed to make a nonaqueous electrolyte permeate an electrode body until the time immediately before conditioning for preparing the battery into an actually usable sate by charging and discharging after forming the battery, is performed while monitoring the aging effect of negative electrode potential V. The manufacturing method for the lithium secondary battery comprises a battery forming process; an aging process for performing the aging of the battery after formed while monitoring the aging effect of the negative electrode potential V; 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.

[0007]

In view of the above problems, as an attempt to find the optimum aging time for each battery, the AC resistance between the positive and negative electrodes was measured during aging, and the value of the electrolyte solution was determined from the measured value. A method of determining the end of aging of each battery by judging the infiltration state was studied. However, this method requires complicated equipment, and
It is not practical because it is difficult to apply an alternating current to all batteries for a long time or in a timely manner within a voltage amplitude range that does not damage the electrodes.

The present inventor conducted a number of experiments on the aging process and investigated the relationship between the aging process time and the battery characteristics. As a result, if the aging treatment time is too long, Cu ions elute from the copper current collector of the negative electrode, the copper negative electrode terminal, and the like, 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. Then, it was found that the potential of the negative electrode changed during aging, and the change in the negative electrode potential was related to the elution reaction of Cu ions.

The present invention has been made on the basis of the above findings. By focusing on the change over time of the negative electrode potential, the optimum aging treatment time for each battery can be easily determined without damaging the electrodes. An object of the present invention is to provide an aging treatment method that can perform the aging treatment.

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 monitoring a change over time in the negative electrode potential V.

That is, the aging treatment method for a lithium secondary battery of the present invention focuses on the aging of the negative electrode potential during aging and performs aging while monitoring the aging of the negative electrode potential.

As described above, the negative electrode potential changes during aging. As will be described later in detail, after the start of aging, the negative electrode potential continues to increase, reaches a maximum at a certain point, slightly decreases, and thereafter stabilizes to a substantially constant value. That is, the change over time of the negative electrode potential can be roughly divided into a rising region and a stable region. The elution of Cu ions from the negative electrode or the like is considered to occur after the negative electrode potential has finished rising, that is, in a region where the negative electrode potential starts to fall and stabilizes thereafter. In a preliminary study, the battery in which the negative electrode potential reached the stable region was disassembled, and the state of infiltration of the electrolyte into the electrode body was examined. As a result, the entire electrode was wet with the electrolyte. That is, it is considered that the electrode was well adapted to the electrolyte and exhibited a stable potential. Therefore, it is considered that the electrolyte has already sufficiently infiltrated the electrode body at the time when the negative electrode potential becomes maximum. Therefore, in order to suppress the elution of Cu ions and sufficiently infiltrate the electrolyte into the electrode body, aging may be terminated immediately before the increased negative electrode potential decreases.

As described above, by performing aging while monitoring the time-dependent change in the negative electrode potential, the aging method of the present invention makes it possible to easily determine the timing of the end of aging of each battery, and to optimize the aging process for each battery. This is a way to secure time.

The behavior of the negative electrode potential with time varies depending on the aging temperature. For example, when aging is performed at a high temperature, the negative electrode potential rises quickly, and conversely, at a temperature around room temperature, the negative electrode potential rises slowly. Therefore, for example, if you want to end aging early, such as performing aging at high temperature,
The aging treatment method of the present invention is a method capable of freely controlling the aging treatment time.

(2) In the method for manufacturing a lithium secondary battery of the present invention including the above-mentioned aging treatment method, the method for storing lithium
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. A forming step, an aging step of aging the battery formed by infiltrating the non-aqueous electrolyte into the electrode body while monitoring a change over time of the negative electrode potential V, and charging and discharging the battery immediately after the aging process And a conditioning process for adjusting the battery to a practically usable state.

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. The method for producing a lithium secondary battery according to the present invention can optimize the aging time for each battery, and thus has a small self-discharge amount and a suppressed increase in internal resistance. Can be easily manufactured.

(3) The relationship between the reaction in the battery during the aging process and the negative electrode potential will be described below.

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) 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. The reduction reaction of Cu ₂ O appears as a change in potential of the negative electrode, and the potential of the negative electrode increases as the reaction proceeds. FIG. 1 shows a change with time of the negative electrode potential in the aging treatment. In FIG. 1, the solid line shows the result of aging at a temperature of 25 ° C., and the broken line shows the result of aging at a temperature of 60 ° C. The reduction reaction of Cu ₂ O appears as a potential increase region (a) in the time-dependent change of the negative electrode potential shown in FIG. Since this reaction is completed in a relatively short time at a high temperature, when aging is performed at a high temperature, the potential of the negative electrode sharply increases as shown by a broken line.
Conversely, at a temperature of about room temperature, the moisture adsorbed inside the electrode gradually reacts, so that the potential of the negative electrode slowly rises as shown by the solid line. The reduction reaction of Cu ₂ O is caused by the so-called infiltration of the electrolyte into the electrode body, such as the size of the electrodes, the state of pressure between the electrodes, the permeability of the electrolyte to the separator, and the ease with which bubbles are removed from the electrodes. Therefore, the change in the potential of the negative electrode is an effective parameter for judging the degree of infiltration of the electrolytic solution.

When the Cu ₂ O on the surface of the current collector of the negative electrode disappears, the above-mentioned 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. Then, as the Cu ion elution reaction proceeds, the polarization resistance of the anodic reaction decreases, and the negative electrode potential decreases. That is, in the change with time of the negative electrode potential shown in FIG. 1, the elution reaction of Cu ions appears as a stable region (b) including a decrease in potential. Therefore, if aging is terminated immediately before the negative electrode potential decreases, elution of Cu ions can be suppressed.

As described above, by monitoring the negative electrode potential, excessive aging can be suppressed.
An aging treatment for sufficiently infiltrating the electrolyte into the electrode body while suppressing the elution of Cu ions can be performed.

[0027]

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 has a positive electrode and a negative electrode that occlude and desorb 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 them, and a lithium secondary battery 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 a 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 basic composition means a typical composition of each of the above composite oxides. In addition to the one represented by the above composition formula, for example, a lithium site or a transition metal site may be replaced with one or more other types. 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 a 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 inserting and extracting 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, copper, which is a relatively noble metal, is used for the current collector, and “made of copper” means pure copper,
This concept includes a copper alloy to which other elements are slightly added. 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. 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 can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent.

The separator sandwiched between the positive electrode and the negative electrode separates the positive electrode from the negative electrode and holds the electrolyte while allowing ions to pass therethrough. Use a thin microporous membrane such as polyethylene or polypropylene. Can be.

The non-aqueous electrolyte is obtained by dissolving an electrolyte 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 container 20 and conducting 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 sandwiched between a separator 13 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
A cylindrical outer can 21 made of stainless steel;
And a stainless disk-shaped positive-side cover plate 22 and a negative-side cover plate 23, which are joined to the two open ends, respectively. 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 container 20. Current collector 30a
A strip-shaped aluminum positive electrode lead 11a extending from the positive electrode 11 is joined to the periphery thereof, 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 23a by a washer 42 and a nut 43 via a gasket 41, and is insulated from the battery container 20. Negative electrode 1 is provided in current collector 40a.
A strip-shaped copper negative electrode lead 12 a extending from the second electrode 2 is joined to the periphery thereof, and electrical conduction between the negative electrode terminal 40 and the negative electrode 12 of the electrode body 10 is secured.

<Method of Manufacturing Lithium Secondary Battery> As an example of a lithium secondary battery to which the aging method of the present invention can be applied, a method of manufacturing a lithium secondary battery having the above structure includes a battery forming process, an aging process, 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. 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 monitoring the change with time of the negative electrode potential V. Aging treatment is started immediately after the non-aqueous electrolyte is injected into the battery case in the battery forming step,
The process 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 monitoring the change over time of the negative electrode potential V. The method for monitoring the negative electrode potential is not particularly limited. For example, a battery having a structure in which a third electrode (reference electrode) other than the positive and negative electrodes can be inserted into the battery case may be formed, and the negative electrode potential may be measured with reference to the reference electrode. The negative electrode potential may be measured using, for example, an electrometer having a large input resistance (≧ 10 ¹⁰ Ω voltmeter).

The voltage between terminals (voltage between positive and negative electrodes) is
As shown in (Equation 7), it is represented by the difference between the positive electrode potential and the negative electrode potential. Voltage between terminals = positive electrode potential−negative electrode potential (Equation 7) Here, since the positive electrode potential can be considered to be substantially constant during aging, a change in the potential of the negative electrode is directly reflected in a change in the voltage between terminals. Therefore, as a more practical method, instead of measuring the negative electrode potential during aging, an aspect in which aging is performed while measuring the inter-terminal voltage with a voltmeter or the like and monitoring the temporal change in the inter-terminal voltage is adopted. Can be.

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. In particular, when it is desired to end the aging early, it is desirable to store at a high temperature of, for example, about 60 ° C. as described above. The storage method is not particularly limited. For example, the battery can be stored in a thermostat.

As described above, the negative electrode potential continues to increase after the start of aging, reaches a maximum at a certain point, slightly decreases, and thereafter becomes a substantially constant value. Therefore, in order to sufficiently infiltrate the electrolyte into the electrode body while suppressing the elution of Cu ions from the negative electrode, aging may be terminated near the inflection point of the negative electrode potential. More specifically, the negative electrode potential V
Is desirably terminated when the time change rate of | dV / dt | ≦ 10 (mV / hr). If aging is continued, the negative electrode potential eventually takes a substantially constant value and stabilizes, so that | dV / dt | ≦
In some cases, 10 (mV / hr) is satisfied, but the end of aging is not intended. The desired end of the aging is near the inflection point of the negative electrode potential. To end the aging, charging in the next conditioning processing step may be started.

(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. The charge and discharge may be performed by a method usually performed as a conditioning process.The battery is charged to a predetermined voltage with a current density as small as possible at a predetermined temperature and similarly discharged to a predetermined voltage with a current density as small as possible. Should be performed. For example, if it is a 4V class battery,
The battery was 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 current density of 1 to ² mA / cm ^2.
Discharge may be performed to a battery voltage of about 3 V at a constant current of cm ² . 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.

[0049]

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 structure shown in FIG. 2 described above 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 a 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 SUS304, 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 0.5 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). The aging was performed by putting the batteries of each group in a thermostat at 20 ° C. and storing them for a predetermined time.

The batteries of the # 1 group all had an aging time of 10 hours. This is because, as a result of preliminarily performing aging while monitoring the temporal change of the inter-terminal voltage using the formed battery, the time required for the inter-terminal voltage to stabilize was 10 hours. It is adopted uniformly. The batteries of the # 2 group were aged while monitoring the voltage between terminals of each battery with a voltmeter, and | dV / dt | ≦ 5 (mV
/ Hr), the aging was terminated. The batteries of the # 3 group have a uniform aging time of 72
Time.

(C) Conditioning Processing After the aging time, the conditioning processing was performed on the batteries of each group of # 1 to # 3.
Charging and discharging were performed at a temperature of 25 ° C.
The battery was charged at a constant current of 5 mA / cm ^{2 up to} a battery voltage of 4.2 V, and the battery voltage was charged at a constant voltage (total charging time: 6 hours). Then, the battery voltage was charged at a constant current of 1 mA / cm ^{2 at} a current density of 1 mA / cm ^2. One cycle of discharging to 3.0 V was performed for a total of 4 cycles. 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-described # 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.

[0057]

[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, according to the method for manufacturing a lithium secondary battery of the present invention including the aging step of performing aging while monitoring the voltage between terminals, that is, the negative electrode potential,
It was confirmed that 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 in which a reference electrode can be inserted 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. Note that a metal Li piece was used for the reference electrode. The electrode body and the reference electrode have an outer diameter of 3
The battery was inserted into a glass cell having a length of 5 mm and a length of 12 mm, and 40 cc of a non-aqueous electrolyte was injected and sealed to form a battery. The non-aqueous electrolyte was prepared by mixing LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7.
A solution dissolved at a concentration of M was used.

(B) Aging treatment The formed secondary batteries are divided into two groups,
Put in a 5 ° C thermostat, and put the other in a 60 ° C thermostat,
Aging was started while monitoring the time-dependent changes in the negative electrode potential.

FIG. 3 shows an example of the change over time in the negative electrode potential and the inter-terminal voltage of a battery aged in a constant temperature bath at 25 ° C. FIG. 4 shows an example of the change over time in the negative electrode potential and the inter-terminal voltage of a battery aged in a thermostat at 60 ° C. From FIGS. 3 and 4, it can be seen that the temporal change of the negative electrode potential and the temporal change of the inter-terminal voltage show a substantially symmetric behavior, and that the temporal change of the negative electrode potential is reflected in the temporal change of the inter-terminal voltage. You can check. Also, it can be confirmed that as the aging is performed at a higher temperature, the negative electrode potential rises faster.

The batteries in each of the constant temperature baths were further divided into two groups, and aging was performed while changing the aging time for each group. That is, in FIG. 3, when attention is paid to the negative electrode potential, a battery that has been aged near the inflection point of the negative electrode potential (A in the figure) is defined as a battery of the # 4 group,
The batteries which had been aged in the negative electrode potential stable region (B in the figure) were designated as # 5 group batteries. Similarly, in FIG. 4, the battery whose aging has been terminated near the inflection point of the negative electrode potential (C in the figure) is a battery of the # 6 group, and the aging has been terminated in the stable region of the negative electrode potential (D in the figure). The batteries thus obtained were taken as # 7 group batteries.

(C) Conditioning Process After the above-mentioned predetermined aging time, the conditioning process was performed on the batteries of each group of # 4 to # 7.
Charging and discharging were performed at a temperature of 25 ° C.
The battery was charged at a constant current of 5 mA / cm ^{2 up to} a battery voltage of 4.2 V, and the battery voltage was charged at a constant voltage (total charging time: 6 hours). Then, the battery voltage was charged at a constant current of a current density of 1 mA / cm ^2. One cycle of discharging to 3.0 V was performed for a total of 4 cycles. 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-described # 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.

[0068]

[Table 2]

As is clear from Table 2, in the batteries of the # 4 and # 6 groups whose aging was terminated near the inflection point of the negative electrode potential, the occurrence of defective batteries having a self-discharge rate of 50% or more was not observed. Was. On the other hand, in the batteries of the # 5 and # 7 groups whose aging was completed in the stable region of the negative electrode potential, four out of ten defective batteries were observed. Also, the values of the internal resistance of the batteries of the # 4 and # 6 groups are smaller than those of the batteries of the # 5 and # 7 groups, and the variation is small.

Therefore, aging was performed while monitoring the time-dependent change in the negative electrode potential, and it was confirmed that the battery that had undergone aging near the inflection point of the negative electrode potential had a small amount of self-discharge and a small internal resistance. did it.

[0071]

According to the aging method of the present invention,
The optimum aging time for each battery can be easily determined without damaging the electrodes. 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 a change with time of a negative electrode potential in an aging treatment.

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.

FIG. 3 shows changes over time in the negative electrode potential and the inter-terminal voltage of a battery aged at 25 ° C.

FIG. 4 shows a change over time in a negative electrode potential and a voltage between terminals of a battery aged at 60 ° C.

[Explanation of symbols]

 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 electrode terminal

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tohru Saeki 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. No. 41, Yokomichi, F-term in Toyota Central R & D Laboratories Co., Ltd. F-term (reference)

Claims (3)

[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 for infiltrating the non-aqueous electrolyte into the electrode body until immediately before the conditioning treatment for adjusting the negative electrode potential, wherein the lithium secondary battery performs aging while monitoring a change with time of the negative electrode potential V Aging treatment method. 2. The temporal change of the negative electrode potential V is | dV / d.
The aging treatment method for a lithium secondary battery according to claim 1, wherein the aging is terminated when t | ≦ 10 (mV / hr). 3. An electrode comprising a positive electrode using a material capable of inserting and extracting lithium as a positive electrode active material and a negative electrode comprising a negative electrode mixture containing a negative electrode active material 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 non-aqueous electrolytic solution while aging the battery body while monitoring a change over time of the negative electrode potential V; and aging. A conditioning process for charging and discharging the battery immediately after the process to adjust the battery to a practically usable state, and a method for manufacturing a lithium secondary battery comprising: