JP6111806B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a nonaqueous electrolyte secondary battery including a specific charge / discharge treatment step .

In recent years, non-aqueous electrolyte secondary batteries have been actively researched and developed for portable devices, hybrid vehicles, electric vehicles, and household power storage applications. Non-aqueous electrolyte secondary batteries used in these fields are used after repeated long-term charge / discharge cycles.
However, in the conventional non-aqueous electrolyte secondary battery, the higher the temperature in the room where the battery is exposed, the more gas is generated during storage or charge / discharge cycles. As a result, the battery swells due to internal pressure, and the battery characteristics deteriorate. There was a problem of doing.

In order to solve this problem, Patent Document 1 uses lithium titanate as a negative electrode active material, and supports carbon derived from alcohol on the surface when the negative electrode active material is manufactured. Then, in the initial charge / discharge process of the nonaqueous electrolyte secondary battery, a method (Example 1) in which the potential of the negative electrode is set to 1.0 V (vs. Li ⁺ / Li) or less has been studied. This method can be performed by charging a nonaqueous electrolyte secondary battery in which the capacity of the negative electrode is smaller than the capacity of the positive electrode. It is clear from the description of paragraphs 0022 and 0023 of Patent Document 1 that the capacity of the negative electrode is smaller than the capacity of the positive electrode.

According to Patent Document 1, carbon is supported on lithium titanate, which is a negative electrode active material, and further, a process of reducing the potential of the negative electrode to 1.0 V (vs. Li ⁺ / Li) or less with respect to lithium is performed. It is described that the liquid or additive is decomposed to form a protective film on the negative electrode, and as a result, the reactivity between the negative electrode and the electrolytic solution is reduced, and gas generation is suppressed (paragraph 0031).

  Patent Document 2 describes a lithium ion secondary battery including a negative electrode active material in which metal particles constituting a negative electrode current collector are formed on the surface of a negative electrode active material. In this method of manufacturing a lithium ion secondary battery, at the time of initial charge / discharge after battery manufacture, the lithium ion secondary battery is discharged until the voltage between the positive electrode plate and the negative electrode plate becomes 0 V (paragraph 0021). As a result, the metal constituting the negative electrode current collector is eluted from the negative electrode current collector into the electrolytic solution, and then the metal is removed from the electrolytic solution (metal ion-containing solution) when the lithium ion secondary battery is charged. To be deposited on the surface.

JP 2007-323958 A JP 2012-089348 A

  However, according to the manufacturing method of Patent Document 1, the potential of the negative electrode is set to 1.0 V (vs. Li + / Li) by charging a non-aqueous electrolyte secondary battery in which the capacity of the negative electrode is smaller than that of the positive electrode. Although it is described below, when this method is performed, it is difficult to control the negative electrode potential, and when the potential of the negative electrode is lowered to around 0.0 V (vs. Li + / Li), lithium dendrite is generated and short-circuiting occurs inside the battery. It is dangerous because it occurs.

  Patent Document 2 employs a process of discharging a lithium ion secondary battery until the voltage between the positive electrode plate and the negative electrode plate becomes 0 V at the time of initial charge / discharge. The purpose of discharging the lithium ion secondary battery until the voltage between the positive electrode plate and the negative electrode plate becomes 0 V during the initial charge / discharge after the manufacture of the battery is to protect from the decomposition solution of the electrolyte or additive The “metal” constituting the negative electrode current collector, not the coating, is eluted from the negative electrode current collector into the electrolytic solution. Patent Document 2 does not include a description paying attention to the relationship between the capacities of the positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery which does not generate gas during cycle operation and exhibits excellent cycle stability in a non-aqueous electrolyte secondary battery.

  In view of the above circumstances, as a result of intensive investigations by the present inventors, a non-design designed so that A <B is satisfied when the capacity per unit area of the positive electrode is A and the capacity per unit area of the negative electrode is B. In the charge / discharge treatment step of the water electrolyte secondary battery, by including a step of holding the positive electrode potential with respect to the negative electrode until it reaches 0.0 V and holding for a certain period of time, the gas generated during storage or during the charge / discharge cycle is reduced. The inventors have found that it can be suppressed, and have completed the present invention.

  That is, the present invention is a method of manufacturing a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte interposed between the positive electrode and the negative electrode, wherein the capacity per unit area of the positive electrode is defined as A. When the capacity per unit area of the negative electrode is B, the positive electrode satisfying A <B and the negative electrode are prepared, and the nonaqueous electrolyte is interposed between the positive electrode and the negative electrode, This is a method for carrying out a charge / discharge treatment step in which the electric potential of the positive electrode with respect to the negative electrode is discharged until it reaches 0.0 V and then held for a certain period of time.

  According to the present invention, by reducing the potential of the positive electrode to the same potential as that of the negative electrode, the electrolyte solution or additive can be decomposed not only by the negative electrode but also by the positive electrode. As a result, a protective film derived from the electrolytic solution or the decomposition product of the additive can be formed on the negative electrode and the positive electrode. In particular, in the present invention, the electrode of the non-aqueous electrolyte secondary battery is designed so that the capacity A per unit area of the positive electrode is smaller than the capacity B per unit area of the negative electrode. It is also advantageous for forming a protective coating. The reason is as follows.

When the nonaqueous electrolyte secondary battery satisfying A <B is discharged until the potential of the positive electrode with respect to the negative electrode reaches 0.0 V, the potential of the positive electrode is maintained while maintaining the potential of the negative electrode at the decomposition potential of the electrolyte or additive. The potential can be lowered to the decomposition potential of the electrolyte or additive. From this, not only the negative electrode but also the positive electrode can be formed with a protective film derived from the decomposition solution of the electrolyte or additive. On the other hand, when a non-aqueous electrolyte secondary battery satisfying A> B is discharged until the potential of the positive electrode with respect to the negative electrode reaches 0.0 V, the potential of the negative electrode rises without decreasing the potential of the positive electrode. Therefore, the potential of the positive electrode is in a higher potential state than the decomposition potential of the electrolytic solution or additive. Therefore, a protective film is not formed on the positive electrode.
In addition, the nonaqueous electrolyte secondary battery manufactured by the method for manufacturing a nonaqueous electrolyte secondary battery of the present invention has a protective film derived from a decomposition product of the electrolyte or additive on the negative electrode and the positive electrode. There is little gas generation at the time of use and expresses excellent cycle stability.

An embodiment of the present invention will be described as follows. The present invention is not limited to the following description. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
<1. Negative electrode>
The negative electrode active material contained in the negative electrode of the non-aqueous electrolyte secondary battery of the present invention may be natural graphite, artificial graphite, mesocarbon microbeads as long as the lithium ion insertion / extraction reaction proceeds at a lower potential than the positive electrode. And carbon materials such as graphite, Si, Sn, oxides thereof and compounds with nitrogen, lithium titanate, titanium dioxide, niobium pentoxide, molybdenum dioxide and the like.

When the potential of the positive electrode with respect to the negative electrode reaches 0.0 V, the possibility of deposition of lithium metal on the negative electrode is extremely low. Therefore, the negative electrode active material used in the nonaqueous electrolyte secondary battery of the present invention is lithium ion It is preferable that the insertion / elimination reaction proceeds at 0.1 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less.
In particular, a negative electrode active material in which insertion / extraction reaction of lithium ions proceeds at 0.3 V (vs. Li ⁺ / Li) or higher and 2.0 V (vs. Li ⁺ / Li) or lower is preferable.

The negative electrode active material in which the insertion / extraction reaction of lithium ions proceeds at 0.1 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less is Si, Sn, its oxide, and nitrogen And the like.
The negative electrode active material in which the insertion / extraction reaction of lithium ions proceeds at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less is lithium titanate, titanium dioxide, pentoxide Niobium, molybdenum dioxide, and the like are preferable, and lithium titanate, titanium dioxide, and H ₂ Ti ₁₂ O ₂₅ are more preferable from the viewpoint of high stability of the negative electrode active material. These negative electrode active materials may contain a trace amount of elements other than lithium and titanium, such as Nb, for example, in order to improve conductivity or stability.

Interpolation Nyuhan response of lithium ions 0.1V (vs.Li + / Li) or 2.0V to proceed in (vs.Li + / Li) or less, a lithium ion insertion into the negative electrode active material is 2.0V (vs. Li + / Li) or less, and end at 0.1 V (vs. Li + / Li) or more. On the other hand, when the desorption reaction of lithium ions proceeds at 0.1 V (vs. Li + / Li) or more and 2.0 V (vs. Li + / Li) or less, the desorption of lithium ions from the negative electrode active material is 0.1 V. It starts at (vs. Li + / Li) or higher and ends at 2.0 V (vs. Li + / Li) or lower.

One type of these negative electrode active materials may be used, or two or more types may be used.
The potential (vs. Li ⁺ / Li) of the lithium ion insertion / desorption reaction is measured, for example, by measuring the charge / discharge characteristics of a working electrode using a negative electrode active material and a half cell using lithium metal as a counter electrode, And it can obtain | require by reading the voltage value at the time of completion | finish. When there are two or more plateaus, the lowest potential plateau may be 0.1 V (vs. Li ⁺ / Li) or higher, and the highest potential plateau is 2.0 V (vs. Li ⁺ / Li). The following is sufficient. The working electrode, electrolytic solution, and separator used for the half battery can be the same as those described later.

  The negative electrode may further contain a conductive additive. Although it does not specifically limit as a conductive support material, A metal material and a carbon material are preferable. Examples of the metal material include copper and nickel, and examples of the carbon material include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These conductive aids may be used alone or in combination of two or more.

In the present invention, the amount of the conductive additive contained in the negative electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. is there. If it is the said range, the electroconductivity of a negative electrode will be ensured. Moreover, adhesiveness with the below-mentioned binder is maintained, and adhesiveness with a collector can fully be obtained.
In the present invention, a binder may be used for the negative electrode in order to bind the active material to the current collector. The binder is not particularly limited, and for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, acrylic resin, and derivatives thereof is used. be able to. The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of easy production of the negative electrode. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. You may add a dispersing agent and a thickener to these.

In the present invention, the amount of the binder contained in the negative electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. If it is the said range, the adhesiveness of a negative electrode active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.
As a preferred embodiment of the negative electrode in the present invention, it is prepared by forming a mixture of a negative electrode active material, a conductive additive and a binder on a current collector. From the ease of the preparation method, the mixture and the solvent are used. A method of preparing a negative electrode by removing the solvent after preparing the slurry and coating the obtained slurry on a current collector is preferable.

The current collector that can be used for the negative electrode is preferably copper, SUS, nickel, titanium, aluminum, or an alloy thereof.
As the current collector, a metal material (copper, SUS, nickel, titanium, and alloys thereof) coated with a metal that does not react with the potential of the negative electrode can be used.
A method for producing the slurry is not particularly limited, but it is preferable to use a ball mill, a planetary mixer, a jet mill, or a thin-film swirl mixer because the negative electrode active material, the conductive additive, the binder, and the solvent can be mixed uniformly. Although the production of the slurry is not particularly limited, it may be produced by mixing the negative electrode active material, the conductive additive, and the binder and then adding a solvent, or the negative electrode active material, the conductive additive, the binder, and the solvent together. You may mix and produce.

The solid content concentration of the slurry is preferably 30 wt% or more and 80 wt% or less. If it is less than 30 wt%, the viscosity of the slurry tends to be too low, whereas if it is higher than 80 wt%, the viscosity of the slurry tends to be too high, and it may be difficult to form an electrode described later.
The solvent used for the slurry is preferably a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Moreover, you may add a dispersing agent and a thickener to these.

  The formation of the negative electrode on the current collector is not particularly limited. For example, a method of removing the solvent after applying the slurry with a doctor blade, a die coater, a comma coater or the like, or a method of removing the solvent after applying with a spray. preferable. The method for removing the solvent is preferable because it is easy to dry using an oven or a vacuum oven. Examples of the atmosphere include room temperature or high temperature air, an inert gas, and a vacuum state. The negative electrode may be formed before or after the above-described positive electrode is formed. Moreover, you may compress a negative electrode using a roll press machine etc. after negative electrode preparation. The electrode may be compressed before or after the positive electrode is formed.

In the present invention, the thickness of the negative electrode is preferably 10 μm or more and 200 μm or less. If it is 10 μm or less, it may be difficult to obtain a desired capacity, and if it is thicker than 200 μm, it may be difficult to obtain a desired output density.
In the present invention, the density of the negative electrode is preferably 1.0 g / cm ³ or more and 3.0 g / cm ³ or less. If it is less than 1.0 g / cm ³ , the contact with the negative electrode active material and the conductive additive becomes insufficient, and the electronic conductivity may decrease. When it is larger than 3.0 g / cm ³ , an electrolyte solution described later is less likely to penetrate into the negative electrode, and lithium conductivity may be lowered. The negative electrode may be compressed to a desired thickness and density. Although compression is not specifically limited, For example, it can carry out using a roll press, a hydraulic press, etc. The electrode may be compressed before or after the above-described positive electrode is formed.

In the present invention, the unit area of the negative electrode, for example, the electric capacity per 1 cm ² is preferably 0.5 mAh or more and 6.0 mAh or less. If it is less than 0.5 mAh, the size of the battery having a desired capacity may be increased. On the other hand, if it is more than 6.0 mAh, it may be difficult to obtain a desired output density. Calculation of the electric capacity per 1 cm < ² > of a negative electrode can be calculated by measuring a charging / discharging characteristic after producing a half cell which made lithium metal a counter electrode after negative electrode preparation. Control of the electric capacity per 1 cm ^{2 of} negative electrode of the negative electrode is not particularly limited, but is controlled by a method of controlling by the weight of the negative electrode formed per unit area of the current collector, for example, by the coating thickness at the time of the above-described negative electrode coating be able to.

<2. Positive electrode>
The positive electrode active material used for the positive electrode of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and may be a lithium transition metal compound, such as a lithium cobalt compound, a lithium nickel compound, a lithium manganese compound, and a lithium iron compound. Illustrated. Moreover, a transition metal is not limited to one type, Two or more types may be sufficient. For example, a lithium cobalt nickel manganese compound, a lithium nickel manganese compound, etc. are illustrated. Moreover, since the effect which improves the stability of a lithium transition metal compound is high, elements, such as aluminum, magnesium, titanium, may be contained in trace amounts, for example.

As the lithium manganese compound, since the positive electrode active material has high stability, Li _{1 + x} MyMn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group 2 to 13 And a lithium manganese compound represented by at least one selected from the group consisting of elements belonging to the third to fourth periods. When x <0, the capacity of the positive electrode active material tends to decrease. Further, when x> 0.2, there is a tendency that many impurities such as lithium carbonate are included. When y = 0, the stability of the positive electrode active material tends to be low. Further, when y> 0.6, a large amount of impurities such as M oxide tends to be contained.

The surface of the positive electrode active material may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.
You may make the positive electrode used for the nonaqueous electrolyte secondary battery of this invention contain a conductive support material. Although the said conductive support material is not specifically limited, The thing similar to the said negative electrode can be used.
The positive electrode may contain a binder. The binder is not particularly limited, and the same binder as the negative electrode can be used.

The amount of the binder contained in the positive electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. If it is the said range, the adhesiveness of a positive electrode active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.
Examples of the method for producing the positive electrode include a method in which a mixture of a positive electrode active material, a conductive additive, and a binder is applied on a current collector. From the ease of the production method, the mixture and the solvent are used. A method of preparing a positive electrode by preparing a slurry by coating the obtained slurry on a current collector and then removing the solvent is preferable.

The current collector used for the positive electrode is preferably aluminum or an alloy thereof. The aluminum is not particularly limited because it is stable in a positive electrode reaction atmosphere, but is preferably high-purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99 and the like.
Note that the current collector may be a metal whose surface is covered with aluminum other than aluminum (copper, SUS, nickel, titanium, and alloys thereof).
Although the production of the slurry is not particularly limited, it is preferable to use a ball mill, a planetary mixer, a jet mill, or a thin film swirl mixer because the positive electrode active material, the conductive additive, the binder, and the solvent can be mixed uniformly. Although the preparation of the slurry is not particularly limited, it may be prepared by mixing the positive electrode active material, the conductive additive, and the binder and then adding a solvent, or the positive electrode active material, the conductive additive, the binder, and the solvent together. You may mix and produce.

The solid content concentration of the slurry is preferably 30 wt% or more and 80 wt% or less. If it is less than 30 wt%, the viscosity of the slurry tends to be too low. On the other hand, if it is higher than 80 wt%, the viscosity of the slurry tends to be too high, so that it may be difficult to form an electrode described later.
The solvent used for the slurry is preferably a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Moreover, you may add a dispersing agent and a thickener to these.

  The formation of the positive electrode on the current collector is not particularly limited. For example, a method of removing the solvent after applying the slurry by a doctor blade, a die coater, a comma coater or the like, or a method of removing the solvent after applying by spraying. preferable. The method for removing the solvent is preferable because it is easy to dry using an oven or a vacuum oven. Examples of the atmosphere for removing the solvent include air, an inert gas, and a vacuum state. The temperature at which the solvent is removed is not particularly limited, but is preferably 60 ° C. or higher and 250 ° C. or lower. When the temperature is lower than 60 ° C., it may take time to remove the solvent. When the temperature is higher than 250 ° C., the binder may be deteriorated. The positive electrode may be formed before or after forming the negative electrode described later.

The thickness of the positive electrode is preferably 10 μm or more and 200 μm or less. If it is less than 10 μm, it may be difficult to obtain a desired capacity, while if it is thicker than 200 μm, it may be difficult to obtain a desired output density.
The density of the positive electrode of the present invention is preferably 1.0 g / cm ³ or more and 4.0 g / cm ³ or less. If it is less than 1.0 g / cm ³ , the contact with the positive electrode active material and the conductive additive becomes insufficient, and the electronic conductivity may decrease. On the other hand, if it is larger than 4.0 g / cm ³ , the electrolytic solution is less likely to penetrate into the positive electrode, and the lithium conductivity may decrease.

The positive electrode of the present invention may be compressed to a desired thickness and density. Although compression is not specifically limited, For example, it can carry out using a roll press, a hydraulic press, etc. The electrode may be compressed before or after the later-described negative electrode is formed.
The positive electrode of the present invention preferably has a unit area, for example, an electric capacity per 1 cm ^{2 of the} positive electrode of 0.5 mAh or more and 5.0 mAh or less. When it is less than 0.5 mAh, the size of a battery having a desired capacity tends to increase, and when it exceeds 5.0 mAh, it tends to be difficult to obtain a desired output density. The electric capacity per 1 cm ² of the positive electrode may be calculated by measuring charge / discharge characteristics after preparing a positive electrode and then preparing a half battery using lithium metal as a counter electrode.

Control of the electric capacity per 1 cm ^{2 of the} positive electrode of the positive electrode is not particularly limited, but is controlled by the method of controlling by the weight of the positive electrode formed per unit area of the current collector, for example, by the coating thickness at the time of the slurry coating described above can do.
<3. Separator>
The separator used for the non-aqueous electrolyte secondary battery of the present invention may be any material that is installed between the positive electrode and the negative electrode and has no electronic conductivity and lithium ion conductivity. For example, nylon, cellulose, Examples include polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, and woven fabrics, nonwoven fabrics, and microporous membranes of two or more of them. The separator may include various plasticizers, antioxidants, flame retardants, and may be coated with a metal oxide or the like.

The thickness of the separator is preferably 10 μm or more and 100 μm or less. When the thickness is less than 10 μm, the positive electrode and the negative electrode may come into contact with each other. When the thickness is greater than 100 μm, the battery resistance may increase. From the viewpoint of economy and handling, it is more preferably 15 μm or more and 50 μm or less.
<4. Non-aqueous electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but the polymer is impregnated with an electrolytic solution obtained by dissolving a solute in a non-aqueous solvent, or an electrolytic solution obtained by dissolving a solute in a non-aqueous solvent. A gel electrolyte or the like can be used.

  The non-aqueous solvent preferably includes a cyclic aprotic solvent and / or a chain aprotic solvent. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones and cyclic ethers. Examples of the chain aprotic solvent include chain carbonates, chain carboxylic acid esters and chain ethers. In addition to the above, a solvent generally used as a solvent for nonaqueous electrolytes such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, propion For example, methyl acid can be used. These solvents may be used alone or as a mixture of two or more. However, in view of the ease of dissolving the solute described below and the high conductivity of lithium ions, a mixture of two or more of these solvents. Is preferably used. A gel electrolyte in which an electrolyte is impregnated in a polymer can also be used.

The solute is not particularly limited. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO ₂ CF ₃ ) _2, etc. are dissolved in the solvent. It is preferable because it is easy to do. The concentration of the solute contained in the electrolytic solution is preferably 0.5 mol / L or more and 2.0 mol / L or less. If it is less than 0.5 mol / L, the desired lithium ion conductivity may not be exhibited. On the other hand, if it is higher than 2.0 mol / L, the solute may not be dissolved any more. The non-aqueous electrolyte may contain a trace amount of additives such as a flame retardant and a stabilizer.

<5. Non-aqueous electrolyte secondary battery>
The positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery of the present invention may have a form in which the same electrode is formed on both surfaces of the current collector, or may be a bipolar electrode.
The nonaqueous electrolyte secondary battery of the present invention may be one obtained by winding or laminating a separator disposed between the positive electrode side and the negative electrode side. The positive electrode, the negative electrode, and the separator contain a nonaqueous electrolyte that is responsible for lithium ion conduction.

The relationship between the electric capacity of the positive electrode and the electric capacity of the negative electrode in the nonaqueous electrolyte secondary battery of the present invention preferably satisfies the following inequality (1).
A <B (1)
However, in said inequality (1), A shows the electrical capacity per 1 cm < ² > of positive electrodes, and B shows the electrical capacity per 1 cm < ² > of negative electrodes.

If the inequality (1) is satisfied, when the potential of the positive electrode with respect to the negative electrode reaches 0.0 V by discharging the nonaqueous electrolyte secondary battery, the potential of the positive electrode is lowered to the decomposition potential of the electrolyte or additive. be able to.
The relationship between the positive electrode capacity and the negative electrode capacity in the nonaqueous electrolyte secondary battery of the present invention more preferably satisfies the following inequality (2).

1 <B / A ≦ 1.2 (2)
However, in said inequality (2), A shows the electrical capacity per 1 cm < ² > of positive electrodes, and B shows the electrical capacity per 1 cm < ² > of negative electrodes.
When B / A is 1 or less, when the potential of the positive electrode with respect to the negative electrode reaches 0.0 V due to the discharge of the nonaqueous electrolyte secondary battery, the potential of the positive electrode reaches the decomposition potential of the electrolyte or additive. On the other hand, if B / A is greater than 1.2, there may be a side reaction due to the large amount of negative electrode active material not involved in the battery reaction. Moreover, it is because the cost of a battery increases because an excess negative electrode is used.

The area ratio between the positive electrode and the negative electrode in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but preferably satisfies the following inequality (3).
1 ≦ D / C ≦ 1.2 (3)
However, C shows the area of a positive electrode, D shows the area of a negative electrode.
If D / C is less than 1, when the potential of the positive electrode with respect to the negative electrode reaches 0.0 V, there is a portion where the potential of the positive electrode cannot be lowered to the decomposition potential of the electrolyte or additive. There is a possibility that a protective film is not formed at the part, and a gas is generated.
On the other hand, if D / C is greater than 1.2, the negative electrode active material not involved in the battery reaction may cause a side reaction because the portion of the negative electrode that is not in contact with the positive electrode is large. Although control of the area of a positive electrode and a negative electrode is not specifically limited, For example, in the case of slurry coating, it can carry out by controlling the coating width.

The area ratio between the separator and the negative electrode used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but preferably satisfies the following inequality (4).
1 ≦ E / D ≦ 1.5 (4)
However, D shows the area of a negative electrode and E shows the area of a separator.
When E / D is less than 1, the positive electrode and the negative electrode are in contact with each other. When E / D is greater than 1.5, the volume required for the exterior increases, and the output density of the battery may decrease.

The amount of the nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but is preferably 0.1 mL or more per 1 Ah of battery capacity. If it is less than 0.1 mL, the conduction of lithium ions accompanying the electrode reaction may not catch up, and the desired battery performance may not be exhibited.
The nonaqueous electrolyte may be added to the positive electrode, the negative electrode, and the separator in advance, or may be added after winding or laminating a separator disposed between the positive electrode side and the negative electrode side.

  The non-aqueous electrolyte secondary battery of the present invention may be wound or laminated with a laminate film after the laminate is wound, or may be rectangular, elliptical, cylindrical, coin-shaped, button-shaped, or sheet-shaped. It may be packaged with a metal can. The exterior may be provided with a mechanism for releasing the generated gas. The number of stacked layers can be stacked until a desired voltage value and battery capacity are exhibited.

The nonaqueous electrolyte secondary battery of the present invention can be made into a battery module by connecting a plurality of the nonaqueous electrolyte secondary batteries. The battery module of the present invention can be produced by appropriately connecting in series or in parallel according to a desired size, capacity, and voltage. Moreover, it is preferable that a control circuit is attached to the battery module in order to confirm the state of charge of each battery and improve safety.
<6. Manufacturing method of non-aqueous electrolyte secondary battery>
In the method for producing a non-aqueous electrolyte secondary battery of the present invention, as an initial charge / discharge treatment step of the non-aqueous electrolyte secondary battery, a step of holding for a certain time after discharging the potential difference of the positive electrode with respect to the negative electrode to reach 0.0 V Is included.

The potential difference between the positive electrode and the negative electrode means the battery voltage. That is, discharging until the potential difference between the positive electrode and the negative electrode reaches 0.0V means discharging to a battery voltage of 0.0V.
In the present invention, if the inequality (1) described above regarding the relationship between the electric capacity of the positive electrode and the electric capacity of the negative electrode in the nonaqueous electrolyte secondary battery is satisfied, the potential difference between the negative electrode and the positive electrode is 0.0 V. By discharging, the potential of the positive electrode can be lowered to the potential of the negative electrode.

  By reducing the potential of the positive electrode to the negative electrode, the electrolyte solution or additive can be decomposed at the positive electrode. As a result, not only the negative electrode but also the positive electrode can be formed with a protective film derived from the electrolyte or additive decomposition product. In this regard, Patent Document 1 focuses only on forming a protective coating on the “negative electrode”, but according to the present invention, a protective coating derived from the decomposition product of the electrolyte or additive is also formed on the positive electrode. You can be sure.

  That is, many common electrolyte solutions and additives decompose near the negative electrode potential to form a protective film. When discharging until the potential of the positive electrode with respect to the negative electrode reaches 0.0 V, the potential of the positive electrode is decreased to the decomposition potential of the electrolyte or additive while maintaining the potential of the negative electrode at the decomposition potential of the electrolyte or additive. can do. From this, not only the negative electrode but also the positive electrode can be formed with a protective film derived from the decomposition solution of the electrolyte or additive.

  As a method of discharging until the potential difference of the positive electrode with respect to the negative electrode reaches 0.0 V, the non-aqueous electrolyte secondary battery having no electrical history may be charged at least once and then discharged to 0.0 V. A method of stopping the discharge when the current reaches 0.0 V by constant current discharge (so-called CC discharge) may be used, or after discharging to 0.0 V by constant current discharge, the current value is at a low potential of 0.0 V. A constant voltage discharge (so-called CCCV discharge) may be performed until a constant value is reached.

The current value in the case of constant current discharge is preferably 0.05 to 5 times the battery capacity. If it is less than 0.05 times, it takes a long time to discharge, so the manufacturing process becomes longer and the cost increases. On the other hand, when the value is larger than 5 times, the current value is large, so that the battery generates heat, and as a result, the battery performance may be deteriorated.
From the viewpoint of the cost and the heat generation of the battery, the current value in the case of constant current discharge is preferably 0.1 to 3 times the capacity of the battery.

The current value for stopping the constant voltage discharge is preferably not less than 0.01 times and not more than 0.5 times the current value of the constant current discharge. If it is less than 0.01 times, it takes a long time to discharge, so the manufacturing process becomes longer and the cost increases. On the other hand, when it is larger than 0.5 times, the influence when the discharge is stopped by the constant current discharge is not changed.
After discharging until the potential difference of the positive electrode with respect to the negative electrode reaches 0.0 V, the time for holding for a certain time is preferably 5 hours or more and 500 hours or less. If it is less than 5 hours, the effect of suppressing the gas generation during the cycle operation is small, and if it is longer than 500 hours, the manufacturing process becomes long and the cost increases. More preferably, it is 8 hours or more and 400 hours or less, particularly preferably 10 hours or more and 350 hours or less, in view of gas generation suppression and cost.

  After discharging until the potential difference of the positive electrode with respect to the negative electrode reaches 0.0 V, the temperature when holding for a certain time is preferably 10 ° C. or higher and 100 ° C. or lower. If it is less than 10 degreeC, there exists a possibility that reaction with electrolyte solution, a positive electrode, and a negative electrode may not advance, and when higher than 100 degreeC, there exists a possibility that electrolyte solution may deteriorate by itself. More preferably, they are 20 degreeC or more and 80 degrees C or less, Most preferably, they are 20 degreeC or more and 60 degrees C or less.

The state of holding for a certain period of time after discharging until the potential difference between the positive electrode and the negative electrode reaches 0.0 V is not particularly limited, but is preferably an open circuit state.
In the method for producing a non-aqueous electrolyte secondary battery of the present invention, as the charge / discharge treatment step of the non-aqueous electrolyte secondary battery, “a step of holding the potential difference of the positive electrode with respect to the negative electrode until reaching 0.0 V and holding for a certain period of time” And “holding for a certain period of time after charging until the potential of the positive electrode with respect to the negative electrode reaches a value selected from a range of 2.5 V or more and 3.5 V or less” may be included. In this case, after the “step of holding for a predetermined time after discharging until the potential difference of the positive electrode with respect to the negative electrode reaches 0.0 V”, the “positive electrode potential with respect to the negative electrode is within the range of 2.5 V to 3.5 V. A process of charging for a certain period of time after charging until the selected value is reached may be performed, or vice versa, or a charge / discharge cycle may be interposed therebetween.

  As a method of charging until the potential of the positive electrode with respect to the negative electrode reaches a value selected from the range of 2.5 V or more and 3.5 V or less, the constant current charging is performed within the range of 2.5 V or more and 3.5 V or less. A method of stopping charging when reaching a value selected from the above (so-called CC charging) may be used, or a value selected from a range of 2.5 V or more and 3.5 V or less by constant current charging. Then, the battery may be charged at a constant voltage with a value selected from a range of 2.5 V or more and 3.5 V or less at a constant voltage until constant current charging (so-called CCCV charging) is performed.

In the case of constant current charging, the current value is preferably 0.05 to 5 times the battery capacity. If it is less than 0.05 times, it takes time to charge, so the manufacturing process becomes longer and the cost increases. On the other hand, when the value is larger than 5 times, the current value is large, so that the battery generates heat, and as a result, the battery performance may be deteriorated.
From the viewpoint of the cost and heat generation, the current value in the case of constant current charging is preferably 0.1 to 3 times the battery capacity. In the above range, the time required for charging and the heat generation of the battery are small.

The current value for stopping charging is preferably 0.01 times or more and 0.5 times or less with respect to the current value of constant current charging. If it is less than 0.01 times, it takes time to charge, so the manufacturing process becomes longer and the cost increases. On the other hand, when it is larger than 0.5 times, the effect is not different from when charging is stopped by constant current charging.
After charging until the potential of the positive electrode with respect to the negative electrode reaches a value selected from the range of 2.5 V or more and 3.5 V or less, the holding time for a certain period of time may be 5 hours or more and 500 hours or less. preferable. If it is less than 5 hours, the effect of suppressing the gas generation during the cycle operation is small, and if it is longer than 500 hours, the manufacturing process becomes long and the cost increases. More preferably, it is 8 hours or more and 400 hours or less, particularly preferably 10 hours or more and 350 hours or less, in view of gas generation suppression and cost.

  After charging until the potential difference of the positive electrode with respect to the negative electrode reaches a value selected from the range of 2.5 V or more and 3.5 V or less of the positive electrode potential with respect to the negative electrode, the temperature when holding for a certain time is 10 ° C. or more It is preferable that it is 100 degrees C or less. If it is less than 10 degreeC, there exists a possibility that the effect of a charging / discharging process may not be acquired, and when higher than 100 degreeC, there exists a possibility that electrolyte solution may deteriorate by itself. More preferably, they are 20 degreeC or more and 80 degrees C or less, Most preferably, they are 20 degreeC or more and 60 degrees C or less.

The state of holding for a certain period of time after charging until the potential of the positive electrode with respect to the negative electrode reaches a value selected from the range of 2.5 V or more and 3.5 V or less is not particularly limited. Preferably there is.
The production method of the present invention preferably includes a step of removing gas generated after the charge / discharge treatment step. If the gas generated by the charge / discharge treatment process is not removed, battery performance may be reduced.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.
(1. Production of negative electrode)
Li ₄ Ti ₅ O ₁₂ as a negative electrode active material is described in the literature (“Zero-Strain Insertion Material of Li [Li1 / 3Ti5 / 3] O4 for Rechargeable Lithium Cells” J. Electrochem. Soc., Volume 142, Issue 5, pp. 1431-1435 (1995)).

That is, first, titanium dioxide and lithium hydroxide were mixed so that the molar ratio of titanium and lithium was 5: 4, and then this mixture was heated at 800 ° C. for 12 hours in a nitrogen atmosphere. A negative electrode active material used in the examples was prepared.
100 parts by weight of the negative electrode active material, 6.8 parts by weight of a conductive additive (acetylene black), and 6.8 parts by weight of a binder (solid content 12 wt%, NMP solution) are mixed to prepare a slurry. did. This slurry was applied to an aluminum foil (20 μm), and then vacuum dried at 170 ° C. to prepare a negative electrode (50 cm ² ).

The capacity of the negative electrode was measured by the following charge / discharge test.
An electrode was applied to one side of the aluminum foil under the same conditions as described above, and a working electrode was punched out to 16 mmΦ. Li metal was punched out to 16 mmΦ as a counter electrode. Using these electrodes, the working electrode (single-sided coating) / separator / counter electrode (Li metal) were stacked in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 30/70 vol%, LiPF ₆ 1 mol / L) was added in an amount of 0.15 mL to prepare a half cell. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). The half-cell was subjected to constant current discharge (end voltage: 1.0 V) and constant current charge (end voltage: 2.0 V) at 25 ° C. and 1.0 mA five times, and the first result was taken as the negative electrode capacity. As a result, the capacity of the negative electrode was 2.6 mAh / cm ² .

(2. Production of positive electrode)
The positive electrode active material Li _1.1 Al _0.1 Mn _1.8 O ₄ is described in the literature ("Lithium Aluminum Manganese Oxide Having Spinel-Framework Structure for Long-Life Lithium-Ion Batteries" Electrochemical and Solid-State Letters Volume 9, Issue 12 , Pages A557 (2006)).

  That is, an aqueous dispersion of manganese dioxide, lithium carbonate, aluminum hydroxide, and boric acid was prepared, and a mixed powder was prepared by a spray drying method. At this time, each amount of manganese dioxide, lithium carbonate, and aluminum hydroxide was prepared such that the molar ratio of lithium, aluminum, and manganese was 1.1: 0.1: 1.8. Next, the mixed powder was heated at 900 ° C. for 12 hours in an air atmosphere, and then again heated at 650 ° C. for 24 hours. Finally, the powder was washed with water at 95 ° C. and dried to prepare a positive electrode active material.

100 parts by weight of this positive electrode active material, 6.8 parts by weight of a conductive additive (acetylene black), and 6.8 parts by weight of a binder (solid content concentration 12 wt%, NMP solution) were mixed to prepare a slurry. The slurry was applied to an aluminum foil (thickness 20 μm), and then vacuum dried at 170 ° C. to produce a positive electrode (50 cm ² ).
The capacity of the positive electrode was measured by the following charge / discharge test.

In the same manner as described above, an electrode coated on one surface of an aluminum foil was punched into a working electrode of 16 mmΦ, and a Li metal was punched out of 16 mmΦ as a counter electrode. Using these electrodes, the working electrode (single-sided coating) / separator / counter electrode (Li metal) were stacked in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 30/70 vol%, LiPF ₆ 1 mol / L) was added in an amount of 0.15 mL to prepare a half cell. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). The half-cell was subjected to constant current charging (end voltage: 4.5 V) and constant current discharge (end voltage: 3.5 V) at 25 ° C. and 0.4 mA five times, and the first result was taken as the positive electrode capacity. As a result, the capacity of the positive electrode was 2.5 mAh / cm ² . Thus, although the area of the positive electrode is the same as the area of the negative electrode, the capacity per unit area of the positive electrode is smaller than the capacity per unit area of the negative electrode (see inequality (1)).

(3. Manufacture of non-aqueous electrolyte secondary batteries)
A non-aqueous electrolyte secondary battery was produced as follows.
As the electrode, an electrode obtained by coating only one side of a positive electrode or a negative electrode on one side of an aluminum foil was used. Cellulose unwoven cloth (25 μm, 55 cm ² ) was used as the separator. First, the prepared positive electrode (single-sided coating), negative electrode (single-sided coating), and separator were laminated in the order of positive electrode (single-sided coating) / separator / negative electrode (single-sided coating). Next, aluminum tabs were vibration welded to the positive and negative electrodes at both ends, and then placed in a bag-like aluminum laminate sheet. A nonaqueous electrolyte secondary battery A was prepared by putting 2 mL of a nonaqueous electrolyte (ethylene carbonate / propylene carbonate / methylethyl carbonate = 15/15/70 vol%, LiPF ₆ 1 mol / L) and then sealing it under reduced pressure. did.

(4. Implementation of initial charge / discharge treatment process according to the present invention)
<Example 1>
The non-aqueous electrolyte secondary battery A was connected to a charging / discharging device (HJ1005SD8, manufactured by Hokuto Denko) and charged at a constant current and a constant voltage up to 2.7 V at 25 mA. That is, since the voltage was low at the beginning of charging, constant current charging was performed at 25 mA, and when the amount of charging gradually increased and the cell voltage reached 2.7 V, constant voltage charging was started from here. Constant voltage charge was stopped at the point when the charging current value dropped to 2.5 mA.

Next, a constant current was discharged to 0.0 V at 25 mA. This charging / discharging was performed in an environment of 25 ° C.
The nonaqueous electrolyte secondary battery A discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 5 hours, and then a hole was formed in the aluminum laminate sheet to remove the generated gas. After removal, the holes in the aluminum laminate sheet were closed. Thus, the charge / discharge treatment of the nonaqueous electrolyte secondary battery of Example 1 was performed.

<Example 2>
The non-aqueous electrolyte secondary battery A was charged and discharged in the same manner as in Example 1 except that the non-aqueous electrolyte secondary battery A discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 24 hours. .
<Example 3>
The non-aqueous electrolyte secondary battery A was charged and discharged in the same manner as in Example 1 except that the non-aqueous electrolyte secondary battery A discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 168 hours. .

<Example 4>
In Example 3, the following step A was performed between the step “the nonaqueous electrolyte secondary battery A discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 168 hours” and the step “removed the generated gas”. The charge / discharge treatment of the nonaqueous electrolyte secondary battery was performed.
(Additional step A): Under a 25 ° C. environment, constant current charging was performed up to 2.7 V at 25 mA. Next, the charged nonaqueous electrolyte secondary battery A was stored in an open circuit state at 60 ° C. for 168 hours. Finally, after being left in an environment of 25 ° C. for 2 hours, a constant current was discharged to 2.0 V at 25 mA.

<Example 5>
In Example 3, the following process B was performed between the process of “stored the nonaqueous electrolyte secondary battery A discharged to 0.0 V in an open circuit state at 60 ° C. for 168 hours” and the process of “removed the generated gas”. The charge / discharge treatment of the nonaqueous electrolyte secondary battery was performed.
(Additional process B): Under a 25 ° C. environment, constant current charging was performed up to 3.0 V at 25 mA. Next, the charged nonaqueous electrolyte secondary battery A was stored in an open circuit state at 60 ° C. for 168 hours. Finally, after being left in an environment of 25 ° C. for 2 hours, a constant current was discharged to 2.0 V at 25 mA.

<Example 6>
In Example 6, a positive electrode different from the positive electrode of the nonaqueous electrolyte secondary battery A used in Examples 1 to 5 was used.
LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material, “Solid-state redox potentials for Li [Me1 / 2Mn3 / 2] O4 (Me: 3d-transition metal) having spinel-framework structures: a series of 5 It was produced by the method described in Journal of Power Sources, Vol. 81-82, pp. 90-94 (1999).

That is, lithium hydroxide, manganese oxide hydroxide, and nickel hydroxide were mixed so that the molar ratio of lithium, manganese, and nickel was 1: 1.5: 0.5. Next, the mixture was heated at 550 ° C. in an air atmosphere, and then heated again at 750 ° C. to prepare a positive electrode active material.
The steps of adding the conductive additive, applying the slurry to the aluminum foil, producing the negative electrode, and producing the non-aqueous electrolyte secondary battery are as described above. This is referred to as a non-aqueous electrolyte secondary battery B.

This non-aqueous electrolyte secondary battery B was connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko) and charged at a constant current and a constant voltage up to 3.4 V at 25 mA. Constant voltage charge was stopped at the point when the current value dropped to 2.5 mA.
Next, a constant current was discharged to 0.0 V at 25 mA. This charging / discharging was performed in an environment of 25 ° C. The nonaqueous electrolyte secondary battery B discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 5 hours, and then a hole was formed in the aluminum laminate sheet to remove the generated gas. After removal, the hole was plugged into the aluminum laminate sheet.

<Example 7>
The nonaqueous electrolyte secondary battery B was charged and discharged in the same manner as in Example 6 except that the nonaqueous electrolyte secondary battery B discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 24 hours.
<Example 8>
The nonaqueous electrolyte secondary battery B was charged and discharged in the same manner as in Example 6 except that the nonaqueous electrolyte secondary battery B discharged to 0.0 V was stored in an open circuit state at 60 ° C. for 168 hours.

<Example 9>
In Example 8, the following process C was performed between the process of “retaining nonaqueous electrolyte secondary battery B discharged to 0.0 V in an open circuit state at 60 ° C. for 168 hours” and the process of “removing the generated gas”. In addition, charge / discharge treatment of the nonaqueous electrolyte secondary battery was performed.
(Additional process C): Constant current charge to 3.4V was performed at 25 mA in a 25 degreeC environment. Next, the charged non-aqueous electrolyte secondary battery B was stored in an open circuit state at 60 ° C. for 168 hours. Finally, after being left in an environment of 25 ° C. for 2 hours, a constant current was discharged at 25 mA to 2.5 V.

<Example 10>
In Example 8, the following process D was performed between the process of “storing the nonaqueous electrolyte secondary battery B discharged to 0.0 V in an open circuit state at 60 ° C. for 168 hours” and the process of “removing the generated gas”. In addition, charge / discharge treatment of the nonaqueous electrolyte secondary battery was performed.
(Additional process D): It charged with constant current to 3.5V at 25 mA in a 25 degreeC environment. Next, the charged non-aqueous electrolyte secondary battery B was stored in an open circuit state at 60 ° C. for 168 hours. Finally, after being left in an environment of 25 ° C. for 2 hours, a constant current was discharged at 25 mA to 2.5 V.

<Comparative Example 1>
No charge / discharge treatment was performed on the nonaqueous electrolyte secondary battery A.
That is, the charge / discharge treatment process of Example 1 (the nonaqueous electrolyte secondary battery A was connected to the charge / discharge device, and constant current / constant voltage charge was performed at 25 mA up to 2.7 V. The constant voltage charge has a current value of 2.5 mA. Then, it was discharged at a constant current of 25 mA to 0.0 V. This charge / discharge was performed in an environment of 25 ° C. The non-aqueous electrolyte secondary battery discharged to 0.0 V was opened. In this state, after storing at 60 ° C. for 5 hours, the non-aqueous electrolyte secondary battery A was directly subjected to measurement without performing the process of removing generated gas.

<Comparative example 2>
No charge / discharge treatment was performed on the nonaqueous electrolyte secondary battery B.
That is, the charging / discharging treatment process of Example 6 (the nonaqueous electrolyte secondary battery B was connected to the charging / discharging device, and constant current / constant voltage charging was performed up to 3.4 V at 25 mA. Then, it was discharged at a constant current of 25 mA to 0.0 V. This charge / discharge was performed in an environment of 25 ° C. The non-aqueous electrolyte secondary battery discharged to 0.0 V was opened. In this state, after storing at 60 ° C. for 5 hours, the non-aqueous electrolyte secondary battery B was subjected to measurement as it was without performing the process of removing the generated gas.

(5. Measurement of cycle characteristics)
The nonaqueous electrolyte secondary batteries of Examples 1 to 10 and Comparative Examples 1 and 2 were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko Co., Ltd.), and cycle characteristics were evaluated.
As the cycle characteristics, 60 ° C., 25 mA constant current charging, and 25 mA constant current discharging were repeated 500 times. The charge end voltage and discharge end voltage in Examples 1 to 5 and Comparative Example 1 at this time were set to 2.7 V and 2.0 V, respectively. Moreover, the charge end voltage and discharge end voltage of Examples 6 to 10 and Comparative Example 2 were 3.4 V and 2.5 V, respectively.

  Table 1 shows the value of the discharge capacity at the 500th time (capacity maintenance ratio%) and the presence or absence of gas generation when the first discharge capacity is 100. The presence or absence of gas generation was confirmed by cell swelling after cooling at 25 ° C. for 2 hours.

As is clear from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 10 of the present invention do not generate gas and are more cycle stable than the nonaqueous electrolyte secondary batteries of Comparative Examples 1 and 2. It can be seen that is improved.
(6. Evaluation of gas generation during high-temperature storage)
The nonaqueous electrolyte secondary batteries of Examples 1 to 10 and Comparative Examples 1 and 2 were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko Corporation), and the amount of gas generated during high-temperature storage was evaluated.

  The nonaqueous electrolyte secondary batteries of Examples 1 to 10 and Comparative Examples 1 and 2 were charged at a constant current of 60 ° C. and 25 mA. The end-of-charge voltage in Examples 1 to 5 and Comparative Example 1 at this time was set to 2.7V. Moreover, the charge end voltage of Examples 6-10 and Comparative Example 2 was 3.4V. These nonaqueous electrolyte secondary batteries were left in an environment of 60 ° C. for 2 weeks. The presence or absence of gas generation was confirmed by cell swelling after cooling at 25 ° C. for 2 hours. The results are shown in Table 2.

  As is clear from Table 2, it was confirmed that the nonaqueous electrolyte secondary batteries of Examples 1 to 10 of the present invention did not generate gas.

Claims (7)

A method for producing a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode,
When the capacity per unit area of the positive electrode is A and the capacity per unit area of the negative electrode is B, the positive electrode and the negative electrode satisfying A <B are prepared,
A charge / discharge treatment step of holding for a certain period of time after discharging the potential of the positive electrode with respect to the negative electrode to reach 0.0 V with the nonaqueous electrolyte interposed between the positive electrode and the negative electrode ;
Forming a protective film derived from a decomposition product of an electrolytic solution or an additive constituting the nonaqueous electrolyte on the positive electrode and the negative electrode;
The manufacturing method of the nonaqueous electrolyte secondary battery which implements.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the time for which the potential of the positive electrode with respect to the negative electrode is discharged until discharging reaches 0.0 V for a predetermined time is 5 hours or more and 500 hours or less.   The charge / discharge treatment step further includes a step of holding the positive electrode with respect to the negative electrode until the potential of the positive electrode reaches a value selected from a range of 2.5 V or more and 3.5 V or less, and then holding for a certain time. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 1 or Claim 2.   The time for which the potential of the positive electrode with respect to the negative electrode is held for a predetermined time after charging until reaching a value selected from a range of 2.5 V or more and 3.5 V or less is 5 hours or more and 500 hours or less. Item 4. A method for producing a nonaqueous electrolyte secondary battery according to Item 3.   The method for producing a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the charge / discharge treatment step further includes a step of removing the generated gas.   In the negative electrode active material included in the negative electrode included in the non-aqueous electrolyte secondary battery, lithium desorption and insertion proceed at 0.3 V (vs. Li + / Li) or more and 2.0 V (vs. Li + / Li). The manufacturing method of the nonaqueous electrolyte secondary battery of any one of Claims 1-5 which is a negative electrode active material.   The negative electrode active material in which desorption and insertion of lithium ions proceeds at 0.3 V (vs. Li + / Li) or higher and 2.0 V (vs. Li + / Li) or lower is a titanium-containing composite oxide. The manufacturing method of the nonaqueous electrolyte secondary battery of any one of Claims 1-6.