JP2011249046A - Method of manufacturing lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a lithium ion secondary battery capable of making uniform a lithium ion concentration within an anode.SOLUTION: A power generating element is formed using an anode including metallic lithium on an anode activating material layer surface or internally. A battery cell comprising the power generating element is charged to a first predetermined voltage and then discharged to a second predetermined voltage. During discharging, the second predetermined voltage is maintained for a predetermined time.

Description

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

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a lithium ion secondary battery used for a mobile phone, a notebook computer, or the like. Therefore, lithium ion secondary batteries having a relatively high theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon that is advantageous in terms of charge / discharge cycle life and cost, particularly graphite-based materials, has been used for the negative electrode of a lithium ion secondary battery. Recently, materials capable of being alloyed with lithium have been studied as high-capacity negative electrode active materials. For example, Si material occludes and releases 4.4 mol of lithium ions per mol during charge / discharge, and Li ₂₂ Si ₅ has a theoretical capacity of about 4200 mAh / g. Thus, since the material which can be alloyed with lithium can increase the energy density of an electrode, it is anticipated as a negative electrode material in a vehicle use.

  However, many of the lithium ion secondary batteries using such a carbon material having a large capacity or a material alloyed with lithium as a negative electrode active material have a large irreversible capacity during initial charge / discharge. For this reason, there exists a problem that the capacity utilization factor of the filled positive electrode falls and the energy density of a battery falls. Here, the irreversible capacity refers to the amount of lithium remaining in the negative electrode even after the discharge in the lithium ion secondary battery, in which all of the lithium occluded in the negative electrode during the initial charge cannot be released by the discharge. means. This irreversible capacity problem has become a major development issue in the practical application to vehicle applications that require high capacity.

  Therefore, as a method for compensating for the loss of battery capacity due to this irreversible capacity, there is doping of lithium ions into the negative electrode. In this method, when assembling the cell, the lithium metal foil is overlaid on the negative electrode surface, the positive electrode and the separator are stacked, and the electrolytic solution is injected to intercalate lithium into the negative electrode active material. Is what is starting. Furthermore, in order to make the intercalation reaction proceed uniformly, high-temperature aging and charging at the upper and lower limit voltages of the battery before aging are performed (see Patent Document 1).

JP-A-9-283179

  However, in the conventional method described above, diffusion of lithium ions is still insufficient, and in particular, the concentration of lithium ions in the in-plane direction is not uniform. Specifically, the lithium ion concentration in the negative electrode active material in the portion where the lithium metal foil is overlaid is high, and the lithium ion concentration in the portion where the lithium is not overlaid is low.

  Therefore, an object of the present invention is to provide a method for producing a lithium ion secondary battery that can make the lithium ion concentration in the negative electrode uniform.

  In order to achieve the above object, a method for producing a lithium ion secondary battery of the present invention forms a negative electrode containing lithium on the surface or inside of a negative electrode active material layer, and uses this negative electrode to form a power generation element. And after charging the battery cell which consists of this electric power generation element to the 1st predetermined voltage, it discharges to the 2nd predetermined voltage. In this discharge, the second predetermined voltage is maintained for a predetermined time.

  According to the present invention, the voltage during and after the discharge can be held to some extent, so that the driving force for moving the lithium ions is kept long, and the incarnation is promoted to promote the lithium ions in the negative electrode. The concentration can be made uniform.

It is sectional drawing which shows the lithium ion secondary battery which concerns on one Embodiment of this invention. It is sectional drawing for demonstrating the structure of a negative electrode. It is a top view (Drawing 3 (a)) and a sectional view (Drawing 3 (b)) for explaining a modification of a structure of a negative electrode. It is a graph which shows the relationship between the capacity | capacitance of a general negative electrode, and negative electrode potential. It is the figure which showed typically the lithium ion diffusion driving force by charging / discharging process. It is a schematic sectional drawing for demonstrating manufacture of the cell for a test. It is explanatory drawing for demonstrating the retention time in the conditions of an electrochemical process (charging / discharging process). It is a graph which shows the result of deviation (%) with the average value of lithium dope capacity.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Moreover, the size and ratio of each member in the drawings are exaggerated for convenience of explanation, and are different from the actual size and ratio.

  Lithium ion secondary batteries have various forms and structures, such as stacked (flat) batteries and wound (cylindrical) batteries, for example, when distinguished by form and structure. Although these forms can be applied to the following embodiments, a case where a stacked (flat) battery structure is employed will be described here. Of course, the present invention itself can be implemented even with a structure other than a stacked (flat) battery structure such as a wound (cylindrical) battery. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  FIG. 1 is a cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention.

  In FIG. 1, a laminated type (internal parallel connection type) lithium ion secondary battery that is not a bipolar type is taken as an example, but the present invention should not be limited to this. For example, a bipolar battery (internal series connection type) stacked battery may be used. A bipolar stacked battery uses a bipolar current collector in which a positive electrode is formed on one surface of a current collector and a negative electrode on the other surface, and an electrolyte layer is sandwiched between the positive electrode and the negative electrode. It is a battery that is stacked in the form of

  As shown in FIG. 1, the lithium ion secondary battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior. Have. Specifically, the power generation element 21 is housed and sealed by using a polymer-metal composite laminate sheet as the battery exterior and joining all of its peripheral parts by thermal fusion.

  The power generation element 21 includes a positive electrode in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11, an electrolyte layer 17, and a negative electrode in which the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. It has a stacked configuration. Specifically, the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19.

  Therefore, it can be said that the lithium ion battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode active material layer 12 is disposed only on one side of the outermost positive electrode current collector located in both outermost layers of the power generation element 21. 1, the arrangement of the positive electrode and the negative electrode is reversed so that the outermost negative electrode current collector is positioned in both outermost layers of the power generation element 21, and the negative electrode is formed only on one side of the outermost negative electrode current collector. An active material layer may be arranged.

  The positive electrode current collector 11 and the negative electrode current collector 12 are respectively attached with a positive electrode tab 25 and a negative electrode tab 27 that are electrically connected to each electrode (positive electrode and negative electrode). Each of these tabs (25, 27) is led out of the laminate sheet 29 so as to be sandwiched between end portions of the laminate sheet 29. The positive electrode tab 25 and the negative electrode tab 27 are ultrasonic welded or resistance welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. May be attached.

Each member will be described in detail below [Negative electrode]
The negative electrode has a structure in which a lithium layer is provided on the surface of the negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material and an electrolyte.

  2 is a cross-sectional view for explaining the structure of the negative electrode, and FIG. 3 is a plan view (FIG. 3 (a)) and a cross-sectional view (FIG. 3 (b)) for further explaining a modification thereof.

  The negative electrode has a structure in which a current collector 1, a negative electrode active material layer 2, and a lithium layer 3 are sequentially stacked. 2 and 3 show the structure in which the negative electrode active material layer 2 and the lithium layer 3 are laminated only on one side of the current collector 1, but when the battery shown in FIG. 1, a negative electrode active material layer 2 and a lithium layer 3 are laminated on both surfaces. In FIG. 1, the lithium layer is not shown.

  FIG. 2 shows an example in which the lithium layer 3 is disposed on the entire surface of the negative electrode active material layer 2. FIG. 3 shows an example in which the lithium layer 3 is partially disposed on the surface of the negative electrode active material layer 2. That is, in this negative electrode, the lithium layer 3 only needs to be present on the surface of the negative electrode active material layer, and may be in a form attached to at least a part of the surface of the negative electrode active material layer. Further, another layer may be interposed between the negative electrode active material layer 2 and the lithium layer 3. However, in order to avoid a decrease in the reaction area of the electrode reaction and an increase in liquid resistance, it is preferable that the lithium layer and the negative electrode active material layer are in contact with each other without any other substance or layer. The adhesion of the lithium layer to the negative electrode active material layer may be due to physical interaction or chemical interaction.

  As shown in FIG. 2, when the lithium layer 3 is disposed on the entire surface of the negative electrode active material layer 2, lithium ions diffuse relatively uniformly with respect to the negative electrode active material layer 2 (meaning that compared with FIG. 3). To do. However, there is still a part that does not diffuse sufficiently. For example, the diffusion in the in-plane direction of the negative electrode active material layer 2 proceeds non-uniformly, or the diffusion in the depth direction far from the lithium layer 3 is not sufficiently performed. Further, since the lithium layer 3 does not exist on the side surface of the negative electrode active material layer 2, lithium ions do not sufficiently flow at the end of the negative electrode active material layer 2.

  On the other hand, in the example shown in FIG. 3, since the lithium layers 3 are scattered, the diffusion of the negative electrode active material layer 2 in the in-plane direction is inevitably insufficient. In addition, the shape of the interspersed lithium layers 3 shown in FIG. 3 is not limited to a quadrangle, and may be a circle (particle shape) or other shapes, and is not particularly limited. Further, the lithium layer 3 may be disposed not only on the surface of the negative electrode active material layer (whether provided on the entire surface as shown in FIG. 2 or scattered as shown in FIG. 3).

(Negative electrode active material layer)
The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and examples thereof include carbon materials and materials that alloy with lithium. In some cases, two or more of these negative electrode active materials may be used in combination. Among them, it is preferable to contain an element that can be alloyed with lithium. Examples of the form containing an element that can be alloyed with lithium include simple elements that can be alloyed with lithium, oxides and carbides containing these elements, and the like.

  By using a material that is alloyed with lithium, a high-capacity battery having a higher energy density than that of a carbon-based material can be obtained. In addition, the material that is alloyed with Li causes a rapid exothermic reaction when Li is pre-doped, and the calorific value is increased as compared with other negative electrode active materials such as a carbon material. When there is a possibility that the binder in the negative electrode active material layer is thermally melted due to such a rapid exothermic reaction, a process of aging before the first charge after the battery is manufactured, instead of pre-occlusion at the time of the first charge as described later It can be said that it is a desirable form to pre-occlude by providing. In the aging treatment, since no voltage is applied between the electrodes, the release (diffusion) speed of Li ions from the lithium layer 3 is slow, and it can be said that rapid reaction between Li and the negative electrode active material can be suppressed. . If necessary, it can be said that the battery sealed with the exterior material may be water-cooled during the aging process.

  In this embodiment, as will be described later, in addition to this aging process (or by omitting the aging process), one or several times of charge / discharge is performed in order to make the lithium ion concentration uniform. Therefore, when it is provided as a secondary battery, it is in a state after charge / discharge for making the lithium ion concentration uniform.

Elements that can be alloyed with lithium are not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl and the like can be mentioned. Among these, from the viewpoint that a battery excellent in capacity and energy density can be configured, the negative electrode active material contains at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. It is preferable to include Si, Sn elements are more preferable, and Si is particularly preferable. As the oxide, silicon monoxide (SiO), tin dioxide (SnO ₂ ), tin monoxide (SnO), or the like can be used. These may be used individually by 1 type and may use 2 or more types together.

In addition, carbon materials such as graphite, soft carbon, and hard carbon, metal materials, lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ), and other conventional materials A known negative electrode active material can be used. In some cases, two or more of these negative electrode active materials may be used in combination.

  However, in order to improve the capacity, it is preferable to include a large amount of a negative electrode active material containing an element that can be alloyed with lithium in the active material. In a more preferred form, specifically, in the negative electrode active material, the active material containing an element capable of alloying with lithium is 60% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably. 100% by mass is contained.

  The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 50 μm, and further preferably 1 to 20 μm. However, forms outside these ranges can also be employed. In addition, the value measured by the laser diffraction type particle size distribution measurement (laser diffraction scattering method) shall be employ | adopted for the average particle diameter of an active material here.

(Negative electrolyte)
Examples of the electrolyte component of the negative electrode include an electrolytic solution or a gel electrolyte. The “electrolyte component” means a substance that ionizes into a cation and an anion when dissolved in a solvent. Among these, the electrolyte component used for the negative electrode is preferably a gel electrolyte.

  Examples of the electrolyte include, but are not limited to, ion conductive polymers (solid polymer electrolytes) including polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. .

The electrolyte component includes a supporting salt (lithium salt). For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiTaF ₆ , LiAlCl ₄ , Li ₂ B ₁₀ Cl ₁₀ ; LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li Organic acid anion salts such as (C ₂ F ₅ SO ₂ ) ₂ N can be mentioned. These supporting salts may be used alone or in combination of two or more.

(Lithium layer)
The lithium layer functions as a lithium (ion) pre-occlusion layer for compensating for the irreversible capacity of the electrode generated in the first charge / discharge. The form of the lithium layer is not particularly limited as long as it is a layer containing lithium, but is preferably a metal foil containing 90% by mass or more of metallic lithium. More preferably, it contains 95% by mass or more of metallic lithium, and more preferably 99% by mass.

  As such a metal foil containing lithium, in addition to the foil of metal lithium alone, for example, Li-Al, Li-Al-Mn, Li-Al-Mg, Li-Al-Sn, Li-Al-In, Li-Al-Cd or the like may be used.

  Although there is no restriction | limiting in particular in the thickness of a lithium layer, From the viewpoint of high energy density, the thinner one is preferable as long as it can occlude lithium for compensating the irreversible capacity of an electrode. If an example is given, the thickness of a lithium layer is 1-100 micrometers, More preferably, it is 10-50 micrometers.

  As described above, the lithium layer may be disposed so as to cover the entire surface of the negative electrode active material layer, or may be disposed on only a part of the surface. Preferably, the lithium layer covers 20 to 100% of the surface area of the negative electrode active material layer. The lithium layer preferably has a uniform thickness. In the case where the lithium layer is disposed only on a part of the surface, it can be disposed in any form such as a stripe shape, a frame shape, or an island shape. Preferably, the lithium layers are arranged at regular intervals.

(Other)
In addition, a binder may be added to the negative electrode for the purpose of maintaining the electrode structure by binding the active materials to each other or the active material, the active material, and the current collector.

  Further, lithium powder may be introduced into the negative electrode active material instead of the lithium layer 3. The introduction of lithium powder also has an effect of compensating for the irreversible capacity of the active material layer. However, even when lithium powder is introduced, the lithium powder may not be evenly distributed in the negative electrode active material. Even when the lithium powder is not evenly distributed, the lithium ion concentration can be made uniform in this embodiment.

  The lithium powder to be introduced may be, for example, a single lithium metal particle or a form in which the surface of the lithium metal particle is covered with a film. When a film is applied, the metal may be completely covered or a part thereof may be exposed. The film portion is preferably formed by coating the surface with fine particles of an inorganic compound such as organic rubber, organic resin, or metal carbonate.

  Although there is no restriction | limiting in particular about the average particle diameter of such a lithium powder, Preferably it is 1-200 micrometers, More preferably, it is 3-50 micrometers. An average particle size of 1 μm or more is preferable because it is easy to handle. On the other hand, an average particle size of 200 μm or less is preferable in that the in-plane dispersion state of the electrode becomes good. As the average particle size of the lithium powder, a value measured by laser diffraction particle size distribution measurement (laser diffraction scattering method) is adopted. In addition, the average particle diameter of lithium powder shall use the average particle of only lithium powder of a core part in the case of lithium powder which has a film | membrane. Further, the shape of the lithium powder is not particularly limited, and may have any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape.

  When the lithium powder is used, the content in the negative electrode active material layer is used to compensate for the irreversible capacity of the electrode (negative electrode) generated in the first charge / discharge. It is desirable that the amount be less than or equal to the amount that compensates for the irreversible capacity. The optimum content of the lithium powder varies depending on the amount and material of the negative electrode active material, and the irreversible capacity decreases according to the content, but if it is too much, the amount of unreacted lithium not involved in the reaction increases, and the volume of the battery Efficiency may decrease. Therefore, it is preferable to determine the optimal lithium powder content after separately obtaining the initial efficiency of the negative electrode active material layer, and if it is appropriately determined according to the thickness (use amount) of the negative electrode active material layer in battery design Good. When an example is given, it is preferable that it is 1-30 mass% with respect to the whole lithium powder and electrolyte component, and it is more preferable that it is 5-15 mass%. If it is such a range, the irreversible capacity | capacitance of a negative electrode can fully be compensated.

  When such a lithium powder is used, it is not necessary to provide a lithium layer for lithium supplementation, so that the entire structure of the negative electrode can be made easier than when the lithium layer 3 is provided.

  In the present embodiment, as described above, the lithium disposed on the surface or inside of the negative electrode active material layer has any shape, such as lithium foil (including plate shape) such as the lithium layer 3, particles, or powder. It may be something like this.

[Positive electrode]
The positive electrode includes a positive electrode active material and an electrolyte.

(Positive electrode active material layer)
The positive electrode active material to be the positive electrode active material layer is not particularly limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used in a nonaqueous electrolyte secondary battery can be used. Specifically, a lithium-transition metal composite oxide is preferable. For example, a Li—Mn composite oxide such as LiMn ₂ O _4, a Li—Ni composite oxide such as LiNiO ₂ , LiNi _0.5 Mn _0. A Li—Ni—Mn based composite oxide such as ₅ O ₂ can be given. The positive electrode active material is not limited to these, and may be a compound such as a fluorine compound that does not contain lithium. In some cases, two or more positive electrode active materials may be used in combination.

(Cathode electrolyte)
The electrolyte used for the positive electrode includes at least an electrolyte component, and preferably includes only the electrolyte component. As the electrolyte component of the positive electrode, any of an electrolytic solution, a gel electrolyte, and an all solid electrolyte can be used, but an electrolytic solution or a gel electrolyte is preferably used. Examples of the all solid polymer electrolyte include all solid polymer electrolytes such as PEO and PPO, and inorganic solid electrolytes having ion conductivity such as ceramic. The all solid polymer electrolyte contains a lithium salt to ensure ionic conductivity.

(A) Gel electrolyte (polymer gel electrolyte)
The gel electrolyte (polymer gel electrolyte) refers to an electrolyte solution held in a matrix polymer (host polymer). The use of a gel electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost, the electrolyte is prevented from flowing out to the current collector, and the ion conductivity between the layers can be easily blocked.

  The gel electrolyte (polymer gel electrolyte) is produced by adding an electrolyte solution usually used in a lithium ion battery to an all solid polymer electrolyte such as PEO or PPO. Moreover, what hold | maintained electrolyte solution in polymer | matrix frame | skeleton which does not have lithium ion conductivity, such as PVDF, PAN, and PMMA, is also contained in gel electrolyte (polymer gel electrolyte). The ratio of the polymer constituting the gel electrolyte and the electrolytic solution is not particularly limited. If 100% of the polymer is an all solid polymer electrolyte and 100% of the electrolyte is a liquid electrolyte, all of the intermediates are included in the concept of gel electrolyte (polymer gel electrolyte).

  Examples of the matrix polymer used as the gel electrolyte include a polymer having polyethylene oxide in the main chain or side chain (PEO), a polymer having polypropylene oxide in the main chain or side chain (PPO), polyethylene glycol (PEG), polyacrylonitrile ( PAN), polymethacrylic acid ester, polyvinylidene fluoride (PVDF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), poly (methyl acrylate) (PMA), poly (methyl) Methacrylate) (PMMA). In addition, mixtures of the above-described polymers, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used. Among these, it is desirable to use PEO, PPO and their copolymers, PVDF, PVDF-HFP.

Moreover, as an electrolytic solution (plasticizer) used for the gel electrolyte, an electrolytic solution usually used for a lithium ion battery can be used. And such electrolyte, an electrolyte salt are those dissolved in a solvent, as the electrolyte _{salt, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiSbF 6, LiAlCl 4, Li 2 B 10 Cl 10, _{LiI, LiBr, LiCl, LiAlCl,} LiHF 2, inorganic acid anion salts such as _{LiSCN, LiCF 3 SO 3, Li} (CF 3 SO 2) 2 N, LiBOB ( lithium bis oxide borate), LiBETI (lithium bis (perfluoro And an organic acid anion salt such as Li (C ₂ F ₅ SO ₂ ) ₂ N). These electrolyte salts may be used alone or in the form of a mixture of two or more. As the solvent, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane , Sulfolane, acetonitrile and the like. Of these, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred. These solvents may be used alone or in the form of a mixture of two or more. The concentration of the lithium salt in the electrolytic solution is not particularly limited, but usually about 0.5 to 2.5 mol / liter is preferable.

  In addition, what is necessary is just to use the ratio of the electrolyte solution in a gel electrolyte in the range currently used for the normal lithium ion battery.

(B) Liquid electrolyte (electrolyte)
Examples of the electrolytic solution include those obtained by dissolving an electrolyte salt in a solvent. Here, the electrolyte salt is not particularly limited. _{Specifically, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiSbF 6, LiAlCl 4, Li 2 B 10 Cl 10, LiI, LiBr, LiCl, LiAlCl, LiHF 2, inorganic acid anions such as LiSCN Ionic salt, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiBOB (lithium bisoxide borate), LiBETI (lithium bis (perfluoroethylenesulfonylimide); Li (C ₂ F ₅ SO ₂ ) ₂ N Organic acid anion salts, etc.). These electrolyte salts may be used alone or in the form of a mixture of two or more. Also, the solvent is not particularly limited. Specifically, examples of the solvent include EC, PC, GBL, DMC, and DEC. These solvents may be used alone or in the form of a mixture of two or more.

(Common to negative electrode / positive electrode)
In addition to the components described above, the negative electrode and the positive electrode active material layer may further include a conductive agent, a binder, and the like for increasing electrical conductivity as necessary.

  The compounding ratio of the components contained in the negative electrode and the positive electrode active material layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a nonaqueous electrolyte secondary battery can be referred suitably. For example, the thickness of the active material layer is about 2 to 100 μm.

(Conductive agent)
The conductive agent refers to an additive blended to improve conductivity. The conductive agent that can be used in the present embodiment is not particularly limited, and conventionally known forms can be appropriately referred to. Examples thereof include carbon materials such as acetylene black, carbon materials such as graphite and carbon fiber. When the conductive agent is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

(binder)
Examples of the binder include, but are not limited to, thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), and acrylic resins, epoxy resins, Examples thereof include thermosetting resins such as polyurethane resins and urea resins, and rubber-based materials such as styrene-butadiene rubber (SBR).

[Current collector]
The current collector is made of a conductive material on both the positive electrode side and the negative electrode side. The positive electrode side and the negative electrode side may be made of the same material or different materials. For example, a metal or a conductive polymer can be employed. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum and copper are preferable from the viewpoints of electron conductivity and battery operating potential.

  The size and thickness of the current collector are not particularly limited as long as the current collector has a size suitable for the battery capacity and can function as a current collector.

[Electrolyte layer]
The electrolyte layer functions as a spatial partition (spacer) between the positive electrode and the negative electrode. In addition to this, it also has a function of holding an electrolyte component that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging.

  There is no restriction | limiting in particular in the electrolyte component which comprises an electrolyte layer, A liquid electrolyte (electrolytic solution), a gel electrolyte, an all-solid electrolyte, etc. may be used suitably.

  About each electrolyte component, it is the same as that of what was demonstrated in the column of the said active material layer, and omits description here.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene, hydrocarbon such as polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), glass fiber, or the like.

  The polymer solid electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of a polymer solid electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

[Positive electrode tab and negative electrode tab]
The positive electrode tab and the negative electrode tab are electrically connected to each current collector for the purpose of taking out current outside the battery. The material may be the same as or different from the current collector. Furthermore, it is good also as a positive electrode tab and a negative electrode tab by extending each electrical power collector.

[Positive lead and negative lead]
You may electrically connect between the collector 11 and tabs (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known nonaqueous electrolyte secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect the product (for example, automobile parts, especially electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Exterior]
As the exterior, a laminate sheet 29 as shown in FIG. 1 can be used. For example, the laminate sheet may be configured as a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order. In addition, as the exterior, a conventionally known metal can case may be used.

  In the lithium ion secondary battery 10 having such a structure, when the electrolyte of the negative electrode includes the lithium layer 3 (or lithium powder), irreversible capacity lithium can be compensated. In addition, the battery can be produced without including unnecessary components such as a binder present on the negative electrode surface that may cause an increase in battery resistance.

[Battery manufacturing method]
The method for producing the lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced by applying a conventionally known method. One example will be described below.

  First, a negative electrode and a positive electrode are prepared.

  The negative electrode comprises a step of forming a negative electrode active material layer on both surfaces of the negative electrode current collector, and subsequently attaching a lithium layer, which is a metal lithium foil, on the negative electrode active material layer. Alternatively, a lithium layer may be attached to both surfaces of the negative electrode current collector, and a negative electrode active material layer may be formed thereon, and a lithium layer may be disposed in the negative electrode active material layer.

  The negative electrode active material layer prepares a negative electrode active material slurry by dispersing a mixture of an electrode slurry containing an electrode material such as a negative electrode active material, a conductive agent and a binder or a precursor thereof in a slurry viscosity adjusting solvent. The slurry viscosity adjusting solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP). The slurry is converted into ink from the solvent and the solid content using a homogenizer or a kneader.

  Next, the slurry is applied to one surface of the current collector. The application means for applying the slurry to the current collector is not particularly limited. For example, commonly used means such as a self-propelled coater, a doctor blade method, and a spray method can be employed.

  Subsequently, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the slurry and the volatilization rate of the slurry viscosity adjusting solvent. The density, porosity, and thickness of the electrode are adjusted by pressing the obtained dried product. When a binder precursor is used, the precursor is polymerized by heat treatment, preferably under reduced pressure, to obtain a negative electrode active material layer.

  Thereafter, a negative electrode active material layer is similarly formed on the other surface of the current collector.

  The method for attaching the lithium layer is not particularly limited, and a conventionally known method can be used.

  For example, a metal lithium foil may be attached to the surface of the negative electrode active material layer, or may be prepared by a vapor phase method such as vapor deposition.

Also, a method of attaching metallic lithium powder can be used. At this time, an insulating material such as SiO ₂ or Al ₂ O ₃ , an organic binder, or the like may be added and adhered to the metal lithium powder. Alternatively, lithium composite particles containing powdery lithium, an insulating material, a conductive material, an organic binder, and the like may be manufactured and applied to the surface of the negative electrode active material layer. Among them, the method of attaching the metal lithium foil is preferable because a uniform film having an appropriate thickness is obtained and the cost is low.

  The method for attaching the metal foil to the surface of the negative electrode active material layer is not particularly limited. For example, it is possible to use a technique of pressure bonding by an ordinary press method such as a flat plate press or a roll press under an inert gas or in dry air.

  Similarly to the negative electrode, the positive electrode is manufactured by preparing a slurry to be a positive electrode active material layer, applying the slurry to the surface of the current collector, and drying (the positive electrode has no step of attaching a lithium layer).

[battery]
A unit cell may be manufactured by laminating the prepared positive electrode and negative electrode so that the positive electrode and the negative electrode face each other with a separator interposed therebetween. Then, the stacking of separators and electrodes is repeated until the number of single cells reaches a desired number. According to such a manufacturing method, a separator can be formed by a simpler method, and a power generation element having high adhesion between the separator and the active material layer can be produced.

  Then, the lead of each positive electrode and negative electrode is bundled and welded, and the laminate is placed in a laminated aluminum film bag with a structure in which the lead of the positive and negative electrodes is taken out, and an electrolyte is injected by a liquid injector. The end is sealed under reduced pressure to obtain a battery.

  In the above description, a laminated battery in which the electrolyte is a liquid electrolyte has been described as an example. However, a laminated battery in which a gel electrolyte or an intrinsic polymer electrolyte is used, and a bipolar battery using the electrolyte described here are manufactured. Can be implemented with reference to a known technique, and is omitted here.

  The battery obtained as described above is the one before pre-doping. Here, this pre-dope is called a battery structure. In this embodiment, in order to dope lithium to the manufactured battery structure, charge / discharge for equalizing the lithium ion concentration is performed together with an aging treatment.

  The aging treatment is performed at a temperature of preferably 20 to 80 ° C., more preferably 40 to 60 ° C. from the viewpoint of completing lithium doping in a short time. Further, the aging time may be appropriately determined so that the voltage of the battery after aging becomes a desired level, but is usually about 24 to 180 hours.

  In addition, you may abbreviate | omit this aging process by repeating charging / discharging for making the lithium ion density | concentration mentioned later uniform.

  After aging (or without aging), charge / discharge is performed to make the lithium ion concentration uniform.

  In the charging / discharging process, a charging process is first performed. In the charging process, the battery voltage after charging is charged with a voltage (first predetermined voltage) that is less than 100% of SOC in the cell design. It is desirable that the temperature during charging be within the usable temperature range and as high as possible.

  The reason for setting the voltage to less than 100% SOC in this charging process is to suppress the generation of dendrites. In principle, the driving force for diffusing lithium ions is improved by charging at a voltage of SOC 100%. However, when the SOC is charged to 100%, a Li metal dendride is generated on the negative electrode surface. Further, when the SOC is charged to 100%, there is a possibility that a portion exceeding the full charge is partially formed in the negative electrode due to the non-uniformity of the lithium ion concentration, thereby causing dendride. And once the dendride that has been generated does not disappear, repeated charging and discharging thereafter may cause a vicious circle in which the generated dendride hinders the movement of lithium ions and the lithium ion concentration becomes more uneven. There is. For this reason, in this embodiment, generation of dendrites is suppressed by setting the voltage to less than 100% SOC.

  In addition, as a minimum voltage value at the time of charge, Preferably it is 3.3V or more. The reason is as follows. In a battery in which a negative electrode partially bonded with Li and a positive electrode is combined, the open circuit voltage immediately after assembly and liquid injection is about 2.6V. Moreover, the width of the potential of the negative electrode to which Li is partially attached is about ± 0.7V. Therefore, 2.6 + 0.7V becomes 3.3V, and the driving force of Li can be exhibited more by applying a voltage higher than this.

  The reason why the battery is charged at a higher temperature within an allowable range is to increase the diffusibility of lithium ions. Usually, ions are diffused more easily at higher temperatures. This temperature may be a higher temperature within the possible range of the aging temperature described above, and is, for example, about 60 to 80 ° C.

  Lithium ions move to the negative electrode side to some extent by this charging step, but sufficient lithium ion concentration cannot be obtained by itself. Therefore, in this embodiment, a discharging process is further performed after this charging process. In this discharge step, the lithium ion diffusion driving force is maintained for a long time by discharging over a long time. Thereby, the lithium ion concentration is made uniform.

  In this discharging step, lithium ions in the negative electrode that have moved and diffused to the negative electrode side in the charging step are once transferred to the positive electrode side. If it does so, the lithium ion concentration in a negative electrode will become low entirely. The negative electrode having a low lithium ion concentration is a region in which the negative electrode potential easily changes. For this reason, since a slight non-uniform difference appears as a potential difference, a driving force for non-uniform relaxation (uniformization) of the lithium ion concentration occurs. The driving force further uniformizes the lithium ion concentration in the negative electrode (plane direction and depth direction).

Here, the region where the negative electrode potential is likely to change will be described. FIG. 4 is a graph showing the relationship between the capacity of a general negative electrode and the negative electrode potential. As shown in the figure, the general relationship between the negative electrode capacity and the negative electrode potential is non-uniform difference = capacity deviation Q _a = Q _b . On the other hand, the voltage is V _a > V _b . That is, the potential difference (Va> Vb) is different even at the same capacitance difference (Qa = Qb) during charging and discharging, and the driving force for Li diffusion is likely to work when Va. Therefore, since the driving force is more likely to work in the region where the cell voltage is low, the driving force for diffusing lithium ions is more likely to work on the discharge side.

  For this reason, in order to use more driving force during the discharge, it is effective to lengthen the discharge time.

  For this reason, in the case of charging and discharging with constant current and constant voltage, the charging stop current that is the timing for switching from charging to discharging, and the stopping current for terminating discharge are 1 / 250C or less, specifically 1 / 250C ~ 1 / 5000C.

  By setting such a termination current, charging is performed until the termination current value is reached, and switching to discharging is performed when the termination current value is reached. On the other hand, at the time of discharge, the discharge is performed until the end current value is reached, and the discharge ends when the end current value is reached. Therefore, the time until the end current is reached is the time for holding the discharge.

  The time for charging and discharging is defined by the end current for the following reason. The lithium ion concentration in the battery varies within the battery, and also varies from cell to cell when the battery is composed of a plurality of cells. Therefore, if the charge / discharge time is defined by the end current, even if there is a variation in the lithium ion concentration in the battery or from cell to cell, the time charge / discharge until the end current is reached can be executed.

  The end voltage (second predetermined voltage) at the time of discharge may be equal to or higher than the SOC 0% voltage in the cell design (of course, lower than the first predetermined voltage). This is because even if the SOC becomes 0%, the battery self-confidence does not stop discharging, and it is possible to maintain the discharge at SOC 0%. Therefore, the end voltage should be higher than the SOC 0% voltage in the cell design. .

  It is not necessary to end the charge / discharge operation over such a time, and it is assumed that a long time of discharge operation is performed as a result of the cycle integration by repeating a plurality of times of charge / discharge. It may be made to become. In the second and subsequent charging, charging is performed at a voltage less than 100% SOC. Also, the lower limit voltage value at this time is preferably 3.3 V or more.

  When charging / discharging is repeated, the current value of switching timing from charging to discharging and discharging to charging is also set to 1 / 250C or less, specifically 1 / 250C to 1 / 5000C.

  In addition to charging and discharging with constant current and constant voltage, when discharging with constant current, repeated charging and discharging should also take the time necessary to diffuse and equalize lithium ions. Can do. This is because, when discharging after charging, a force acts to keep the potential in the negative electrode constant in the battery. The concentration of lithium ions is made uniform by this action of keeping constant. At this time, constant voltage charging (discharging) is performed until the current value becomes extremely small, or constant current discharging is performed for a long time so that uniformization is sufficiently performed. In this case, the number of charge / discharge cycles may be 30 cycles or more, preferably 60 cycles or more, and more preferably 90 cycles or more.

  Furthermore, the effect | action by this charging / discharging process is demonstrated with reference to drawings. FIG. 5 is a diagram schematically showing the lithium ion diffusion driving force by the charge / discharge treatment.

  First, as shown in FIG. 5 (a), a battery structure before the electrolytic solution is put is assumed to have a structure in which the positive electrode and the negative electrode face each other, and metal lithium (Li) is placed on a part of the negative electrode. . In the figure, the numerical value on the side of each of the positive electrode and the negative electrode conceptually indicates the lithium concentration (maximum value is 100) (the same applies to FIGS. 5A to 5D). In the figure, the arrows conceptually indicate the driving force of lithium ions as the size of the arrows (the same applies to FIGS. 5A to 5D). In the state shown in FIG. 5A, since the electrolyte does not coexist, Li is only on the negative electrode.

  When an electrolytic solution is added to this, a battery structure (non-charged state) is completed. In this state, as shown in FIG. 5 (b), when the electrolytic solution enters, Li placed on the negative electrode is inserted into the negative electrode (which is Li-doped). However, at this time, the amount of Li in the negative electrode is not uniform.

  When this battery structure is charged, as shown in FIG. 5 (c), Li is transferred from the positive electrode to the negative electrode (charged) to cause some diffusion of lithium ions. However, at the same time, the negative electrode potential is lowered and the driving force for Li diffusion is reduced, so that although the diffusion is performed to some extent, the charging operation alone does not become uniform.

  Therefore, by further performing a discharge operation, as shown in FIG. 5D, when Li is returned (discharged) to the positive electrode, the negative electrode potential increases and the driving force for Li diffusion increases. Moreover, during this discharge operation, the driving force remains high as described above. Therefore, the lithium ion concentration can be made uniform by performing this discharge operation.

  Hereinafter, the present invention will be further described using examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

  Test cells of Examples 1 to 9 and Comparative Examples 1 to 4 were manufactured as follows. FIG. 6 is a schematic cross-sectional view for explaining the production of the test cell.

(1) Production of negative electrode Hard carbon (average particle diameter 10 μm) as a negative electrode active material, acetylene black as a conductive auxiliary agent and polyimide (PVDF) as a binder are mixed in a mass ratio of 80:10:10 to obtain a slurry. It was.

  This slurry (to be the negative electrode negative electrode active material 2) was applied to a copper foil (thickness 10 μm) to be the negative electrode current collector 1 and dried at 80 ° C. with hot air. A current extraction tab 27 made of nickel was joined to the current collector 1 by ultrasonic welding, and punched out so that the electrode size was 50 mm × 10 mm. The thickness of the active material layer was 130 μm. Lithium metal foil (30 μm) was laminated on the negative electrode / negative electrode active material 2 and pressure-bonded by roll rolling to a part of the obtained negative electrode.

(2) Production of positive electrode LiMn ₂ O ₄ as a positive electrode active material, acetylene black as a conductive auxiliary agent, and PVDF as a binder were mixed at a mass ratio of 80:10:10 to obtain a positive electrode slurry. Next, the obtained positive electrode slurry was applied to an Al (aluminum) foil serving as a positive electrode current collector, dried with hot air at 130 ° C., and then roll-rolled to form a sheet. The thickness of the positive electrode active material layer was 120 μm. An aluminum current extraction tab was joined to the Al current collector by ultrasonic welding, and punched out so that the electrode size was 49 mm × 9 mm. In FIG. 6, the positive electrode active material layer and the current collector are collectively referred to as the positive electrode 4.

(3) Production of Battery Structure A polyethylene microporous film (thickness = 25 μm) was prepared as the separator 5. The separator is larger than the size of the negative electrode active material 2. Further, as the _{electrolyte, 1M LiPF 6 / (EC:} DEC) (EC: DEC = 4: 6 by volume) was used.

  The negative electrode, separator, and positive electrode prepared / prepared above were stacked in this order. The laminate was placed in a bag made of an aluminum laminate sheet as an exterior of the power generation element, and the electrolytic solution prepared above was injected. Under vacuum conditions, the opening of the aluminum laminate sheet bag was sealed so that the current extraction tabs connected to both electrodes were led out. In FIG. 6, the aluminum laminate sheet is not shown.

  Thus, a test cell in which the lithium layer 3 was formed on a part (end) of the negative electrode active material 2 was completed.

(4) Aging process The test cell produced above was subjected to aging treatment at 55 ° C. for 72 hours. The cell voltage after aging was 2.6 V (excluding Example 5).

(5) Electrochemical treatment (charge / discharge treatment)
The test cell produced above was connected to a charger / discharger, and electrochemical treatment was performed under the conditions of Examples 1 to 9 and Comparative Examples 1 to 4 shown in Table 1. 1C was set to 25 mA. Moreover, 0.01C at the time of the discharge of Examples 1-5 and Example 6, and the charge and discharge by the constant current constant voltage (CCCV) of the comparative example 2, charging of Examples 7-9 and Example 6, and a comparison Charging and discharging with constant current (CC) in Examples 3 to 4 were performed at 0.1C. In Table 1, the time per charge (h) and the time per discharge are the voltages shown in Table 1 for charging and discharging by constant voltage and constant current (CCCV), and the currents shown in the same way. It is the time per one time to reach. Therefore, in the examples and comparative examples in which the number of cycles is a plurality of times, the time required for the number of cycles is finally taken.

  FIG. 7 is an explanatory diagram for explaining the holding time under the conditions of electrochemical treatment (charge / discharge treatment). Conditions other than the holding time are as shown in Table 1.

  In each diagram of FIG. 7, max 4.2V is the maximum voltage value that can be charged (voltage value when SOC = 100%), and min2.5V is the minimum voltage value (SOC = 0% when considered) Voltage value).

  As shown in FIG. 7A, Examples 1 to 5 are constant current and constant voltage (CCCV) for both charging and discharging. Each holding time is the same. As shown in FIG. 7B, in Example 6, charging is a constant current (CC), and discharging is a constant current constant voltage (CCCV). Holding time is longer during discharging than during charging. As shown in FIG.7 (c), although Examples 7-9 and Comparative Examples 3-4 make constant current (CC) both in charge and discharge, they are performed several times. However, the holding time required for one charge / discharge is short. As shown in FIG. 7D, in Comparative Example 2, both charging and discharging are constant current (CC). Both the holding times for charging and discharging are short. For reference, FIG. 7E is a graph showing a charge / discharge operation for capacity confirmation that has been performed conventionally (for example, prior art documents). This graph shows a case where constant current and constant voltage charge (CCCV) is performed up to the maximum voltage (max 4.1 V) after the aging treatment, and then constant current discharge (CC) is performed at the minimum voltage (max 2.8 V).

(6) Measurement of the amount of lithium doped into the negative electrode After performing the electrochemical treatment step (charging / discharging treatment), constant-current constant-voltage charging is performed up to 4.2 V, and then constant-current discharging is performed up to 2.5 V. Three cycles were performed. Thereafter, in order to confirm the uniformity of the amount of lithium in the negative electrode, a coin cell was prepared using an electrode that was disassembled and cut into five equal parts. Lithium metal (thickness 200 μm, φ16 mm size) was used as the counter electrode, and 1M LiPF ₆ / (EC: DEC) (EC: DEC = 4: 6 volume ratio) was used as the electrolyte. A 2032 size (outer diameter 20 mm, thickness 3.2 mm) was used for the coin cell. It was measured with a coin cell. The lithium dope capacity measured in the coin cell is defined as a deviation (%) from the average value using the following equation (1), and the results under each condition are shown in Table 2. In addition, the measurement position shown in Table 2 is a position where a is superimposed on the lithium layer 3, and b, c, d, and e are set as the distance from a is increased. The intervals a, b, c, d, and e are substantially equal (corresponding to a, b, c, d, and e shown in FIG. 6).

  {(Lithium doping capacity at each measurement position) − (Average value of lithium doping capacity from a to e)} ÷ Negative electrode charging capacity × 100 (1)

  Moreover, what put together the result of deviation (%) with the average value of the lithium dope capacity | capacitance by each Example and a comparative example in the graph was shown in FIG.

  As can be seen from Table 2 and FIG. 8, all of Examples 1 to 9 are less misaligned with the average value of the lithium doping capacity than Comparative Examples 1 to 4. That is, the uniformity of the lithium ion concentration is good. Especially, if the comparative example 1 only of aging and Examples 1-9 are contrasted, it turns out that the uniformity of each Example 1-9 is good. Further, comparing Examples 1 to 5 and Example 6 with Comparative Example 2, it can be seen that it is particularly effective to take a longer time during discharging than during charging. In particular, it can be seen that the charging / discharging end current is reduced to 1/250 C to 1/5000 C as in Examples 1 to 5 and Example 6 to provide a sufficient effect even if the number of times of charging and discharging is small. Moreover, even if it is charging / discharging by constant current from Example 7-9 (even if the time of discharge is constant current), it can aim at equalizing | homogenizing lithium ion concentration similarly by increasing the frequency of charging / discharging. I understand. In such a case, the number of times of charging / discharging is preferably 30 times or more from Examples 7 to 9, more preferably 60 times or more, and still more preferably 90 times or more. Thus, it can be seen that the discharge time per one time is short, but the holding time is sufficient by repeating the number of times.

  Further, FIG. 8 shows that lithium ions are scattered and well diffused in a portion far from the portion on which the lithium layer is placed. Therefore, as shown in FIG. 2, when the lithium layer is placed on the entire surface of the negative electrode active material layer, lithium ions can be distributed to the end portion. In addition, as shown in FIG. 3, even when the lithium layer is scattered, lithium ions can be dispersed throughout the entire surface direction of the negative electrode active material layer.

  As described above, the present embodiment has the following effects.

  By holding the discharge time for a predetermined time, the movement of lithium ions remaining in the negative electrode active material layer (that is, exceeding the positive electrode capacity and not moving to the positive electrode) is promoted by the potential difference in addition to diffusion due to the concentration gradient. For this reason, it can diffuse more in a negative electrode active material layer, and can make the amount of intercalation uniform. As a result, the capacity can be increased. In particular, by reducing the charge / discharge end current to 1/250 C to 1/5000 C, lithium ions can be sufficiently diffused even if the number of times of charge / discharge is small.

  In addition, when one discharge time is short, by repeating the charge / discharge process, the movement due to the potential difference is promoted in addition to the diffusion due to the lithium ion concentration gradient, similarly to the case where the one discharge time is lengthened. Can do. Therefore, also in this case, the amount of intercalation can be made uniform by further diffusing in the negative electrode active material layer. As a result, the capacity can be increased. In this case, the number of charge / discharge cycles is preferably 30 times or more, more preferably 60 times or more, and still more preferably 90 times or more. As a result, even if the discharge time per one time is short, the holding time is sufficient to allow the lithium ions to diffuse sufficiently as a whole.

  Further, by setting the first predetermined voltage, which is a voltage at the time of charging, to a voltage less than 100% of SOC, generation of dendrites can be suppressed.

  And the battery manufactured by this becomes a thing suitable as a battery mounted in a vehicle especially as a motor drive power supply. Here, the vehicle includes, for example, an automobile whose wheels are driven by a motor, and another vehicle (for example, a train). Examples of the automobile include a complete electric car that does not use gasoline, a hybrid automobile such as a series hybrid automobile and a parallel hybrid automobile, and a fuel cell automobile.

  The battery according to the embodiment described above is not limited to the structure of the stacked battery described above. For example, the amount of intercalation can be made uniform even in a bipolar battery. Moreover, it can also provide as an assembled battery which combined two or more battery itself. Of course, when it is set as an assembled battery, since it can mount in a vehicle, it cannot be overemphasized.

  Furthermore, the present invention is not limited to the above-described embodiments and examples, and it goes without saying that various modifications can be made by those skilled in the art.

1 negative electrode current collector,
2 negative electrode active material layer,
3 Lithium layer,
10 Lithium ion secondary battery,
11 positive electrode current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet.

Claims (5)

Forming a negative electrode containing lithium on the negative electrode active material layer surface or inside;
Forming a power generation element using the negative electrode;
Charging a battery cell comprising the power generation element to a first predetermined voltage;
After the step of charging up to the first predetermined voltage, discharging to a second predetermined voltage and maintaining the second predetermined voltage for a predetermined time;
A method for producing a lithium ion secondary battery, comprising:   The method of manufacturing a lithium ion secondary battery according to claim 1, wherein the charging step and the discharging step are repeated a plurality of times.   2. The method of manufacturing a lithium ion secondary battery according to claim 1, wherein the predetermined time is an accumulated time in the discharging process repeated a plurality of times.   The method for producing a lithium ion secondary battery according to any one of claims 1 to 3, wherein the predetermined time is a time until a discharge end current becomes 1 / 250C or less.   The method of manufacturing a lithium ion secondary battery according to any one of claims 1 to 3, wherein the first predetermined voltage is a voltage of less than 100% SOC.