JP2014063702A - Method for manufacturing negative electrode active material, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active material for a nonaqueous electrolyte secondary battery, exhibiting excellent cycle stability without gas generation.SOLUTION: A negative electrode active material mainly consisting of lithium titanate is immersed or placed in an aqueous solution or atmosphere, where a fluorine-containing compound is included, at a predetermined temperature for a predetermined time, and thereby a negative electrode active material in which the halogen element is present at a part of a surface of the negative electrode active material is manufactured. Accordingly, a negative electrode active material having a surface on which fluorine is added can be obtained by means of a simple process.

Description

  The present invention relates to a method for producing a negative electrode active material and a non-aqueous electrolyte secondary battery using the negative electrode active material produced by the method.

  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 required to have high safety. In order to satisfy the demand, batteries using a titanium-based material as an electrode active material have been developed. However, a battery using a titanium-based material as an electrode active material has a problem in that gas is generated due to a reaction between the surface of the electrolytic solution and the negative electrode active material, and cycle stability is lowered.

In order to solve the problem, for example, Patent Documents 2 to 3 disclose techniques for subjecting a titanium-based material to fluorination treatment.
In Patent Document 1, a fluorine compound (lithium fluoride) is mixed with titanium dioxide and lithium carbonate and fired to obtain a negative electrode active material made of fluorinated lithium-containing titanium oxide, which is applied to the electrode to form a negative electrode. A secondary battery is manufactured.

Patent Document 2 manufactures a secondary battery including a non-aqueous electrolyte to which hydrofluoric acid or water is added. After charging / discharging the fabricated secondary battery, the negative electrode was taken out and measured by X-ray spectroscopy, and it was confirmed that a fluoride layer was present on the surface of the negative electrode.
Patent Document 3 discloses that a negative electrode obtained by applying a negative electrode active material to an electrode and drying it, Mn (PF ₆ ) ₂ , lithium hexafluorophosphate (LiPF ₆ ), ethylene carbonate (EC), and diethyl carbonate (DEC). The surface of the negative electrode is treated by immersing it in a non-aqueous treatment solution dissolved in a mixed solvent of It has been confirmed that manganese fluoride (Examples 3, 9, 15) or cobalt fluoride (Examples 6, 12, 18) is formed on the surface of the negative electrode.

JP 2005-302601 A JP 2010-231960 A JP 2008-059980 A

  However, in the technique described in Patent Document 1, fluoride is mixed with the precursor of the negative electrode active material in a stage before firing, and after firing, the fluoride is not only inside the surface of the negative electrode active material, but also inside. It is assumed that there are many. Since it is thought that only the fluoride present on the surface of the negative electrode active material is related to the migration and desorption and insertion of lithium ions, it is not necessary to mix the fluoride up to the inside of the negative electrode active material. On the contrary, the physical properties of the negative electrode active material may be reduced.

In the technique described in Patent Document 2, a secondary battery must be manufactured using a non-aqueous electrolyte containing additives such as hydrofluoric acid and water, and the non-aqueous electrolyte in the secondary battery as a finished product Corrosion problems to electrodes and containers are expected.
In the technique described in Patent Document 3, one extra step of electrochemically forming a fluoride layer on the surface of the negative electrode must be provided after the negative electrode is produced using the negative electrode active material. The manufacturing process of a secondary battery increases.

  An object of the present invention is to provide a method for producing a negative electrode active material that does not generate gas during cycle operation and exhibits excellent cycle stability, and a nonaqueous electrolyte secondary battery using the negative electrode active material produced by the method It is to be.

As a result of repeated studies by the present inventors, it has been found that by using a solution or atmosphere containing a halogenated material, the surface of the negative electrode active material can be easily halogenated without lowering the stability of the active material. It came to be completed.
The method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a lithium ion insertion / extraction reaction of 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li). The negative electrode active material that proceeds below is immersed or placed in a solution or atmosphere containing a compound containing a halogen element at a predetermined temperature for a predetermined time, so that the part of the surface of the negative electrode active material is This is a method for producing a negative electrode active material in which a halogen element is present.

The solution containing the halogen-containing compound may be a solution obtained by dissolving the halogen-containing compound in an aqueous solvent.
The halogen element is typically fluorine.
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. Also good.

This invention prescribes | regulates the negative electrode active material manufactured with the manufacturing method mentioned above.
Further, the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention is one in which fluorine is present on a part of the surface of a negative electrode active material comprising a titanium-containing composite oxide, and the titanium-containing composite oxide As a result of surface analysis by X-ray photoelectron analysis (ESCA), the ratio F / Ti of the peak intensity between Ti and F is 0.01 or more and 1 or less.

  Moreover, the negative electrode for nonaqueous electrolyte secondary batteries uses the negative electrode active material. A nonaqueous electrolyte secondary battery can be manufactured using this negative electrode. Moreover, a secondary battery module can be completed by connecting a plurality of the nonaqueous electrolyte secondary batteries.

  The negative electrode active material of the present invention can be easily produced, and a nonaqueous electrolyte secondary battery using the negative electrode active material is excellent in cycle stability.

Embodiments of the present invention will be described below.
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 active material>
The negative electrode active material used in the non-aqueous secondary battery of the present invention is only required to undergo lithium ion insertion / extraction reaction at a potential lower than that of the positive electrode, and the potential is 0.3 V (vs. Li ⁺ / Li ) Or more and 2.0 V (vs. Li ⁺ / Li) or less. Within the range of the potential, there is no deposition of lithium metal on the negative electrode, and a practical battery voltage can be expressed.

When the insertion / desorption reaction of lithium ions proceeds at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, the insertion of lithium ions into the negative electrode active material is 2.0 V. (vs.Li ⁺ / Li) begins below, it is to end with 0.3V (vs.Li ⁺ / Li) or more. On the other hand, if the lithium ion desorption reaction proceeds at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, the lithium ion desorption from the negative electrode active material is 0. It starts at 3 V (vs. Li ⁺ / Li) or higher and ends at 2.0 V (vs. Li ⁺ / Li) or lower.

The voltage value (vs. Li ⁺ / Li) of the lithium ion insertion / desorption reaction is measured, for example, by measuring the charge / discharge characteristics of the working electrode using the negative electrode active material and the half cell using lithium metal as the counter electrode, and starting the plateau And by reading the voltage value at the end. If plateau had two or more places, as long plateau lowest voltage value is 0.3V (vs.Li ⁺ / Li) or more, plateau highest voltage value is 2.0V (vs.Li ⁺ / Li) It may be the following. The working electrode, electrolytic solution, and separator used for the half battery can be the same as those described later.

The negative electrode active material in which the 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 lithium titanate, titanium dioxide, H _2. Titanium-containing composite oxides typified by Ti ₁₂ O ₂₅ and metal oxides such as niobium pentoxide and molybdenum dioxide are preferable, and lithium titanate, titanium dioxide, H ₂ Ti are preferred because the negative electrode active material has high stability. ₁₂ O ₂₅ is more preferable. 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.
The lithium titanate used in the present invention preferably has a spinel structure and a ramsdellite type, and particularly preferably has a spinel structure because the expansion and contraction of the active material in the reaction of insertion / extraction of lithium ions is small. The molecular formula is represented by Li ₄ Ti ₅ O ₁₂ .
The titanium dioxide used in the present invention is preferably anatase type or bronze type.
One type of these negative electrode active materials may be used, or two or more types may be used.

According to the present invention, 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 performed on the surface. There is a halogen element in the part. Examples of the halogen element include chlorine, fluorine, and bromine, and fluorine is particularly preferable because it has a great effect of suppressing reactivity with the electrolytic solution.
The negative electrode active material in which the insertion / extraction reaction of the lithium ion of the present invention proceeds at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less exists on a part of the surface. The halogen element can be measured by, for example, X-ray photoelectron spectroscopy (hereinafter referred to as ESCA (Electron Spectroscopy for Chemical Analysis)). Although the kind of ESCA used for this invention is not specifically limited, It is preferable to carry out on the following conditions.

The X-ray source of ECSA is exemplified by AlKα, MgKα, or AgKα, but is preferably AlKα that is generally used.
The X-ray intensity is preferably 1 kV or more and 20 kV or less. If it is less than 1 kV, the element to be measured may not be detected, and if it is greater than 20 kV, the sample may be destroyed. The measurement range is preferably a circle having a diameter of 100 μm or more. If it is less than 100 μm, the element to be measured may not be detected.

The ratio of the halogen element present on a part of the surface of the negative electrode active material can be defined by the ratio of the 2p peak intensity of titanium and the 1s peak intensity of the halogen element by ESCA. The peak intensity can be calculated from the area of the detected peak. For example, the 2p peak intensity of titanium can be calculated by the sum of the 2p _1/2 peak area of titanium and the 2p _3/2 peak area. On the other hand, in the case of the peak intensity of a halogen element, for example, the peak intensity of fluorine, it can be calculated from the peak area of 1 s of fluorine.
The ratio of the 2p peak intensity of titanium to the 1s peak intensity of the halogen element (1s peak intensity of the halogen element) / (2p peak intensity of titanium) is preferably 0.01 or more and 1 or less. 0.01 or more and 0.5 or less is more preferable, and 0.01 or more and 0.3 or less is particularly preferable. If it is less than 0.01, the effect of suppressing gas generation is small, and if it is more than 1, the structure of the negative electrode active material may collapse.

A halogen element is present on a part of the surface of 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. Examples of the method include a method of treating with a solution containing a compound containing a halogen element and a method of treating with a gas containing a halogen element.
In the method of treating with a solution containing a halogen element-containing compound, the negative electrode active material is immersed or diffused in a solution containing a halogen element-containing compound (usually in a powder form) at a predetermined temperature for a predetermined time. Can be done.

Examples of the solution containing a compound containing a halogen element include those obtained by dissolving a compound containing a halogen element in an aqueous solvent or a non-aqueous solvent, but an aqueous solution that is easy to handle is preferable.
In the case of an aqueous solution, a halogen element ion may be present in the solvent, and examples of the compound containing a halogen element include a compound in which hydrogen halide is dissolved in water or a compound in which a halide salt is dissolved in an acid aqueous solution. For example, when the halogen element is fluorine, an aqueous solution containing hydrogen fluoride, or a solution in which sodium fluoride is dissolved in an aqueous hydrochloric acid solution is exemplified.

  The concentration of halogen element ions contained in the solution is preferably 0.001 mol / L or more and 5.0 mol / L or less, and more preferably 0.01 mol / L or more and 3.0 mol / L or less. Furthermore, since dissolution of the negative electrode active material is extremely small and a halogen element can be present on the surface of the negative electrode active material, 0.01 mol / L or more and 1.0 mol / L or less are particularly preferable.

The temperature at the time of treatment with a solution containing a compound containing a halogen element is preferably higher than the freezing point of the solvent and lower than the boiling point. Since the reactivity is not lowered and the influence of the utility cost is small, it is preferably room temperature or 5 ° C. or more and less than 40 ° C. If the temperature is lower than 5 ° C, the reaction proceeds slowly. On the other hand, if the temperature is higher than 40 ° C, the negative electrode active material may be dissolved.
The time for treatment with a solution containing a compound containing a halogen element is preferably 1 minute to 100 hours or less. It is preferably 1 minute to 100 hours because the reactivity is not lowered and the influence of utility costs is small. On the other hand, when the time is shorter than 1 minute, the halogen element may not adhere to the surface of the negative electrode active material.

  In the case of treating with a compound containing a gaseous halogen element, the negative electrode active material is placed in a gas flow type furnace, and the compound containing the gaseous halogen element is circulated in the furnace while at a desired temperature, For example, the method of heating at the temperature of 500-950 degreeC for 1 minute-200 hours is illustrated. Examples of the compound containing a gaseous halogen element include fluorine, methyl fluoride, bromine, methyl bromide, chlorine, and methyl chloride.

The particle diameter of the negative electrode active material of the present invention is preferably 0.1 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less from the viewpoint of handling. The particle diameter is a value obtained by measuring the size of each particle from SEM and TEM images and calculating the average particle diameter.
The specific surface area of the negative electrode active material of the present invention is preferably 0.1 m ² / g or more and 50 m ² / g or less because a desired output density is easily obtained. The specific surface area may be calculated by measurement using a mercury porosimeter or BET method.

The negative electrode active material of the present invention preferably has a bulk density of 0.2 g / cm ³ or more and 1.5 g / cm ³ or less. 0.2 g / cm in the case of less than ³ tend to be economically disadvantageous because it requires a large amount of solvent in the step of preparing the slurry described below, 1.5 g / cm ³ greater than the later of conductive agent, and a binder Tend to be difficult to mix.
<2. Negative electrode>
The negative electrode of the present invention contains at least the negative electrode active material.

  The negative electrode of the present invention may further contain a conductive additive, and the conductive additive is not particularly limited, but 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, and the binder is not particularly limited. For example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) ), At least one selected from the group consisting of styrene-butadiene rubber, polyimide, acrylic resin, and derivatives thereof. 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 in the negative electrode of the present invention 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 method of forming the negative electrode on the current collector is not particularly limited. For example, after applying the slurry by a doctor blade, die coater, comma coater, etc., the method of removing the solvent, or the method of removing the solvent after applying by spraying Is preferred. 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 weight density of the negative electrode 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 negative electrode active material and the conductive additive becomes insufficient, and the electronic conductivity may decrease. When it is larger than 4.0 g / cm ³ , an electrolyte solution described later hardly penetrates 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 electric capacity per 1 cm ² of the negative electrode 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. The electric capacity per 1 cm ^{2 of} negative electrode of the negative electrode is not particularly limited, but can be controlled by the 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 negative electrode coating described above. it can.

<3. Positive electrode>
The positive electrode active material contained in the positive electrode used in 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. Is exemplified. Further, the transition metal is not limited to one type, and may be two or more types, and examples thereof include a lithium cobalt nickel manganese compound and a lithium nickel manganese compound. 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 stability of the positive electrode active material is particularly high, Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is A lithium manganese compound represented by at least one selected from the group consisting of elements belonging to Groups 2 to 13 and belonging to the third to fourth periods is particularly preferable. 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 of the present invention may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.
The positive electrode of the present invention may contain a conductive additive. Although it does not specifically limit as a conductive support material, A carbon material is preferable. Examples thereof include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These carbon materials may be used alone or in combination of two or more.

The amount of the conductive additive contained in the positive electrode of the present invention 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 electroconductivity of a positive electrode will be ensured. Moreover, adhesiveness with the below-mentioned binder is maintained, and adhesiveness with a collector can fully be obtained.
The positive electrode of the present invention may contain a binder. 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 positive 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.

The amount of the binder contained in the positive electrode of the present invention 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 of the present invention include a method of producing a positive electrode active material, a conductive additive, and a binder by coating a current collector on the current collector. In addition, a method of preparing a positive electrode by preparing a slurry with a solvent and applying the obtained slurry onto a current collector and then removing the solvent is preferable.

The current collector used for the positive electrode of the present invention is preferably aluminum and its alloys. 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).
The method for preparing 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 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 method of forming the positive electrode on the current collector is not particularly limited. For example, the method of removing the solvent after applying the slurry with a doctor blade, die coater, comma coater or the like, or the method of removing the solvent after applying with a spray Is preferred. 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. If the temperature is lower than 60 ° C, it may take time to remove the solvent. If the temperature is higher than 250 ° C, the binder may deteriorate. The positive electrode may be formed before or after forming the negative electrode described later.

The thickness of the positive electrode of the present invention 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 weight 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.
In the positive electrode of the present invention, the electric capacity per 1 cm ² of the positive electrode is preferably 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.

The electric capacity per 1 cm ^{2 of the} positive electrode of the positive electrode is not particularly limited, but is controlled by the weight of the positive electrode formed per current collector unit area, for example, by the coating thickness at the time of the slurry application described above. Can do.
<4. 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 be in contact with each other. When the thickness is greater than 100 μm, the resistance of the battery may be increased. From the viewpoint of economy and handling, it is more preferably 15 μm or more and 50 μm or less.
<5. Non-aqueous electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but a polymer is impregnated with an electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or an electrolytic solution in which a solute is dissolved 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.

<6. Non-aqueous electrolyte secondary battery>
The positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery of the present invention may be in the form in which the same electrode is formed on both sides of the current collector, and the positive electrode is formed on one side of the current collector and the negative electrode is formed on one side. Alternatively, it may be a bipolar electrode. For example, in the case of a bipolar electrode, a separator is disposed between the positive electrode side and the negative electrode side of the adjacent bipolar electrode, and the positive electrode and An insulating material is disposed around the negative 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 ratio of 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 formula (1).

1 ≦ B / A ≦ 1.2 (1)
In the above formula (1), A represents the electric capacity per 1 cm ² of the positive electrode, and B represents the electric capacity per 1 cm ² of the negative electrode.
When B / A is less than 1, the potential of the negative electrode may be a lithium deposition potential during overcharge, while when B / A is greater than 1.2, there are many negative electrode active materials not involved in the battery reaction. As a result, side reactions may occur.

Although the area ratio of the positive electrode to the negative electrode in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, it is preferable to satisfy the following formula (2).
1 ≦ D / C ≦ 1.2 (2)
(However, C represents the area of the positive electrode, and D represents the area of the negative electrode.)
When D / C is less than 1, for example, when B / A = 1 as described above, the capacity of the negative electrode is smaller than that of the positive electrode, so that the potential of the negative electrode may become a lithium deposition potential during overcharge. 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 formula (3).
1 ≦ F / E ≦ 1.5 (3)
(However, E represents the area of the negative electrode, and F represents the area of the separator.)
When F / E is less than 1, the positive electrode and the negative electrode are in contact with each other, and when F / E 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 formed into an assembled battery by connecting a plurality of the nonaqueous electrolyte secondary batteries. The assembled battery 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 assembled battery in order to confirm the state of charge of each battery and improve safety.

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.
(Synthesis of negative electrode active material)
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 are mixed so that the molar ratio of titanium and lithium is 5: 4, and then this mixture is heated at 800 ° C. for 12 hours in a nitrogen atmosphere to thereby obtain lithium titanate. Then, the following non-heat treatment was performed on this lithium titanate to obtain negative electrode active materials of Synthesis Examples 1 to 6.
(Synthesis Example 1)
As a fluorinating agent, 1 L of 1 M aqueous hydrochloric acid solution of 0.1 M sodium fluoride was prepared. The lithium titanate (50 g) was added to this solution and stirred at room temperature for 1 hour. Next, after removing the supernatant, it was washed 5 times with deionized water (1 L). Finally, lithium titanate having fluorine formed on the surface was prepared by vacuum drying at 105 ° C. for 12 hours. As a result of surface analysis of this lithium titanate by X-ray photoelectron analysis (ESCA), the ratio of the peak intensities of Ti and F was F / Ti = 0.112. “Quantum 2000” manufactured by ULVAC-PHI was used as the X-ray photoelectron analyzer. The X-ray source was AlKα, the X-ray intensity was 15 kV, and the measurement range was 100 μmφ.

(Synthesis Example 2)
A lithium titanate of Synthesis Example 2 was prepared in the same manner as Synthesis Example 1 except that the stirring time was 24 hours. As a result of surface analysis of this lithium titanate by ESCA, the ratio of the peak intensities of Ti and F was F / Ti = 0.082.
(Synthesis Example 3)
The lithium titanate of Synthesis Example 3 was prepared in the same manner as Synthesis Example 2 except that a 1M hydrochloric acid aqueous solution of 0.2M sodium fluoride was used. As a result of surface analysis of this lithium titanate by ESCA, the ratio of peak intensities of Ti and F was F / Ti = 0.21.
(Synthesis Example 4)
Lithium titanate of Synthesis Example 4 was prepared in the same manner as Synthesis Example 1 except that a 1 wt% hydrofluoric acid aqueous solution was used instead of 0.1 M sodium fluoride in 1M hydrochloric acid. As a result of surface analysis of this lithium titanate by ESCA, the ratio of peak intensities of Ti and F was F / Ti = 0.012.
(Synthesis Example 5)
Lithium titanate of Synthesis Example 5 was prepared in the same manner as Synthesis Example 2 except that a 1 wt% hydrofluoric acid aqueous solution was used instead of 0.1 M sodium fluoride in 1M hydrochloric acid. As a result of surface analysis of this lithium titanate by ESCA, the ratio of peak intensities of Ti and F was F / Ti = 0.10.
(Synthesis Example 6)
Lithium titanate of Synthesis Example 6 was prepared in the same manner as in Synthesis Example 3 except that a 5 wt% hydrofluoric acid aqueous solution was used instead of 0.1 M sodium fluoride in 1M hydrochloric acid. As a result of surface analysis of this lithium titanate by ESCA, the ratio of the peak intensities of Ti and F was F / Ti = 0.25.
<Example 1>
(Manufacture of negative electrode)
A slurry prepared by mixing 100 parts by weight of the negative electrode active material of Synthesis Example 1, 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). Was made. The slurry was applied to an aluminum foil (20 μm) and then vacuum dried at 170 ° C. to produce 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, a working electrode (single-sided coating) / separator / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol). %, LiPF6 1 mol / L) was added to prepare a half battery. 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 0.4 mA five times, and the fifth result was defined as the positive electrode capacity. As a result, the capacity of the negative electrode was 1.2 mAh / cm ² .
(Manufacture 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, the amounts of manganese dioxide, lithium carbonate and aluminum hydroxide were adjusted so 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 used in Example 1.

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. This slurry was applied to an aluminum foil (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, a working electrode (single-sided coating) / separator / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol). %, LiPF ₆ 1 mol / L) was added 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 fifth result was taken as the positive electrode capacity. As a result, the capacity of the positive electrode was 1.0 mAh / cm ² .
(Manufacture of non-aqueous electrolyte secondary batteries)
The nonaqueous electrolyte secondary battery of Example 1 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. After 2 mL of nonaqueous electrolyte (propylene carbonate / methylethyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) was added, the nonaqueous electrolyte secondary battery of Example 1 was fabricated by sealing while reducing the pressure.

<Examples 2 to 6>
Each of the nonaqueous electrolyte secondary batteries of Example 2, Example 3, Example 4, Example 5, and Example 6 was replaced with Synthesis Example 2, Synthesis Example 3, and Synthesis, respectively, instead of the negative electrode active material of Synthesis Example 1. The negative electrode active materials of Example 4, Synthesis Example 5 and Synthesis Example 6 are used. A nonaqueous electrolyte secondary battery was manufactured in the same manner as Example 1 except for the above.

<Comparative example>
The nonaqueous electrolyte secondary battery of the comparative example uses a negative electrode active material not treated with a compound containing a halogen element, instead of the negative electrode active material of Synthesis Example 1. Other than that was carried out similarly to Example 1, and obtained the nonaqueous electrolyte secondary battery.
(Measurement of cycle characteristics)
The nonaqueous electrolyte secondary batteries of Examples 1 to 6 and the comparative example were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko), and the 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 the discharge end voltage in Examples 1 to 6 and the comparative example at this time were set to 2.7 V and 2.0 V, respectively. Table 1 shows the 500th discharge capacity and the presence / absence of gas generation when the first discharge capacity is 100.

  As is clear from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 6 of the present invention did not generate gas and had a capacity retention rate of 90 compared to the nonaqueous electrolyte secondary battery of the comparative example. It can be seen that the cycle stability is improved as compared with the comparative example in which the capacity retention ratio is 75% or more.

Claims (10)

A method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery, comprising:
A solution containing a halogen element as a negative electrode active material in which 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 Alternatively, a method for producing a negative electrode active material in which the halogen element is present on a part of the surface of the negative electrode active material by immersing or setting in an atmosphere at a predetermined temperature for a predetermined time.   The method according to claim 1, wherein the solution containing the halogen-containing compound is obtained by dissolving the halogen-containing compound in an aqueous solvent.   The method according to claim 1, wherein the halogen element is fluorine. 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 method according to any one of claims 1 to 3.   The negative electrode active material manufactured by the method of any one of Claims 1-4.   6. The titanium-containing composite oxide is subjected to surface analysis by X-ray photoelectron analysis (ESCA), and as a result, the peak intensity ratio F / Ti between Ti and F is 0.01 or more and 1 or less. The negative electrode active material as described. A negative electrode active material for a non-aqueous electrolyte secondary battery in which fluorine is present on a part of the surface of a negative electrode active material comprising a titanium-containing composite oxide,
As a result of surface analysis of the titanium-containing composite oxide by X-ray photoelectron analysis (ESCA), the ratio F / Ti of the peak intensity of Ti and F is 0.01 or more and 1 or less. .   The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode active material of any one of Claims 5-7.   A non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery according to claim 8.   A secondary battery module in which a plurality of the nonaqueous electrolyte secondary batteries according to claim 9 are connected.