JP2014099291A - Anode active material, method of producing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which exhibits excellent cycle stability without generating a gas during initial charging.SOLUTION: An anode active material containing a titanium composite oxide or a titanium oxide in which an insertion/desorption reaction of lithium ions proceeds at 0.3 to 2.0 V (vs. Li/Li) inclusive is treated with a silylating agent containing a silyl group, thereby producing an anode active material on at least part of the surface of which a hydroxyl group existing is protected by a silyl group represented by formula (1).

Description

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

  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, and in order to satisfy these requirements, desorption of lithium ions such as lithium titanate and titanium dioxide is used as the negative electrode active material. In addition, a battery using a titanium-based material whose insertion proceeds at 0.3 V (vs. Li + / Li) or higher and 2.0 V (vs. Li + / Li) or lower has been developed. However, a battery using a titanium-based material as the negative electrode active material has a hydroxyl group or the like on the surface of the negative electrode active material, so that a reaction with the electrolyte occurs due to charge / discharge, resulting in a decrease in cycle stability. There was a problem of doing.

In order to solve the decrease in cycle stability, a means for coating the surface of the titanium-based material with a silyl group can be considered. For example, Patent Document 1 discloses that a compound having a trialkylsilyl group is added to a dispersion material used when a negative electrode active material is kneaded to prepare a slurry, or a compound having a trialkylsilyl group is added to a nonaqueous electrolyte. Discloses a technique for forming a coating containing a trialkylsilyl group on the surface of a negative electrode active material during charging and discharging of a non-aqueous electrolyte secondary battery using the negative electrode active material by adhering to the negative electrode active material . In Patent Document 1, the coating film containing a trialkylsilyl group is stable, suppresses a side reaction between a titanium oxide compound having a TiO ₂ (B) structure and a nonaqueous electrolyte, and subsequently decomposes the nonaqueous electrolyte. It can be suppressed (paragraph [0024]).

  Patent Documents 2 and 3 disclose nonaqueous electrolytes to which a compound having a trialkylsilyl group is added.

JP 2012-0669352 A Special table 2009-110490 JP 2001-057237 A

Prior art documents listed above include adding a compound having a silyl group to a dispersing material or non-aqueous electrolyte used when preparing a negative electrode slurry, or attaching a compound having a trialkylsilyl group to a negative electrode active material. Thus, a non-aqueous electrolyte secondary battery that modifies the surface of the negative electrode during charging and discharging is disclosed.
However, in a non-aqueous electrolyte secondary battery having such a structure, even if a compound having a silyl group is added to the dispersion material or the non-aqueous electrolyte, or a compound having a silyl group is attached to the negative electrode active material, the battery is charged. It is thought that the coating containing a silyl group formed on the negative electrode active material during discharge is only physically attached to the surface. Further, it is expected that the compound and the negative electrode active material do not sufficiently react at the time of coating formation, and it is difficult to obtain the effect of extending the life, that is, improving the cycle characteristics.

In addition, it is expected that a compound having an unreacted silyl group reacts with the positive electrode active material and the electrolytic solution to cause deterioration of battery performance.
In other words, it is considered that forming a coating containing a sufficient amount of silyl groups on the negative electrode active material is effective in suppressing gas generation and deterioration in cycle characteristics. When a similar film is formed, a good effect cannot be expected, which may lead to problems such as increased resistance. Therefore, rather than using an additive that can react with both positive, negative, and electrode active materials during charge / discharge of the non-aqueous electrolyte secondary battery, treat the negative electrode active material before making the non-aqueous electrolyte secondary battery. More preferably, the surface of the negative electrode active material is protected with a silyl group.

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

  In view of the above circumstances, as a result of repeated studies by the present inventors, by using a solution containing a silylating agent containing a silyl group, lithium ions can be eliminated and inserted without reducing the stability of the active material. The present inventors have found a technique for protecting a hydroxyl group present on the surface of a compound that proceeds at a voltage of 0.3 V (vs Li + / Li) or higher and 2.0 V (vs Li + / Li) or lower with a silyl group, and completed the present invention.

  That is, in the negative electrode active material used in the nonaqueous electrolyte secondary battery of the present invention, lithium ion desorption and insertion proceeds at 0.3 V (vs Li + / Li) or more and 2.0 V (vs Li + / Li) or less. The hydroxyl group present on at least a part of the surface of the compound is represented by the following formula (1):

It is protected with a silyl group represented by Here, “protection” means that the desorption and insertion of lithium ions proceeds at 0.3 V (vs Li + / Li) or more and 2.0 V (vs Li + / Li) or less on the surface of Ti—O—H of the compound. It means that a hydrogen atom is substituted with a silyl group (SiR ¹ R ² R ³ ). That is, this silyl group is physically attached to the surface of a compound in which the desorption and insertion of lithium ions proceeds at 0.3 V (vs Li + / Li) or more and 2.0 V (vs Li + / Li) or less. Instead, they are bonded to the surface Ti—O oxygen atoms by chemical bonds. When a coating containing a silyl group is physically attached to the surface, this coating may peel off from the surface. On the other hand, when the silyl group is bonded to the surface Ti—O oxygen atom by a chemical bond, it is preferable because physical separation of the silyl group from the surface does not occur. Here, R ¹ , R ² and R ³ of the silyl group are C1-C20 alkyl groups, C2-C20 alkenyl groups, C2-C20 alkynyl groups, C6-C20 aryl groups, C4-C20 heteroaryl groups, It represents a C7 to C20 aralkyl group or a C5 to C20 heteroaralkyl group, and R ¹ , R ² and R ³ may be the same or different from each other. The alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aralkyl group, and heteroaralkyl group may have a substituent. That is, R ¹ , R ² and R ³ are not hydrolyzable functional groups.

In the present invention, “may have a substituent” means that it may be substituted with another atom or substituent. The “substituent” is not particularly limited as long as it does not adversely affect the reaction, and specific examples thereof include an alkyl group, a nitro group, a nitroxy group, an amino group, a cyano group, and an azide group.
Although it does not specifically limit as a C1-C20 alkyl group, For example, a methyl group, an ethyl group, n-propyl group, isopropyl group, cyclopropyl group, n-butyl group, sec-butyl group, tert-butyl Group, cyclobutyl group, n-pentyl group, cyclopentyl group, n-hexyl group, n-heptyl group, cyclohexyl group, n-octyl group, n-decyl group, and the like.

Examples of the C2-C20 alkenyl group include a vinyl group, a propenyl group, an isopropenyl group, a cyclopropenyl group, a butenyl group, a cyclobutenyl group, a cyclopentenyl group, a hexenyl group, and a cyclohexenyl group.
Examples of the C2-C20 alkynyl group include ethynyl group, propynyl group, phenylethynyl group, cyclopropylethynyl group, butynyl group, pentynyl group, cyclobutylethynyl group, hexynyl group and the like.

Examples of the C6-C20 aryl group include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a terphenyl group, and a 3,4,5-trifluorophenyl group.
Examples of the heteroaryl group include pyrrolinyl group, pyridyl group, quinolyl group, imidazolyl group, furyl group, indolyl group, thienyl group, oxazolyl group, thiazolyl group, 2-phenylthiazolyl, 2-anisylthiazolyl group, etc. Is mentioned.

Examples of the aralkyl group include benzyl group, chlorobenzyl group, bromobenzyl group, salicyl group, α-hydroxybenzyl group, phenethyl group, α-hydroxyphenethyl group, naphthylmethyl group, anthracenylmethyl group, 3,5- A difluorobenzyl group, a trityl group, etc. are mentioned.
Examples of the heteroaralkyl group include a pyridylmethyl group, a difluoropyridylmethyl group, a quinolylmethyl group, an indolylmethyl group, a furfuryl group, and a thienylmethyl group. Alternatively, R ¹ and R ² may be combined to form a ring, and examples thereof include a cyclohexyl group and a phenyl group.

In order to obtain better cycle stability in the battery having an electrode configuration in the present invention, R ¹ , R ² and R ^{3 of the} silyl group represented by the general formula (1) are C1-C8 alkyl groups, It is preferably a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C6-C10 aryl group, a C4-C10 heteroaryl group, a C7-C12 aralkyl group, or a C5-C10 heteroaralkyl group, Particularly preferred are a methyl group, an ethyl group, a tert-butyl group, a phenyl group, and a vinyl group. The alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aralkyl group, and heteroaralkyl group may have a substituent.

The compound in which the desorption and insertion of lithium ions proceeds at 0.3 V (vs Li + / Li) or more and 2.0 V (vs Li + / Li) or less is, for example, a titanium composite oxide or a titanium oxide.
In the method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery according to the present invention, the surface of the negative electrode active material is treated with a silylating agent containing a silyl group, whereby at least a part of the surface of the negative electrode active material is obtained. This is a method for producing a negative electrode active material in which an existing hydroxyl group is protected by a silyl group represented by the formula (1).

The method for treating the negative electrode active material with the silylating agent may be a heat treatment.
The negative electrode for a non-aqueous electrolyte secondary battery of the present invention is a negative electrode produced by including the negative electrode active material. The nonaqueous electrolyte secondary battery of the present invention uses the negative electrode.

  The nonaqueous electrolyte secondary battery using the negative electrode containing the negative electrode active material of the present invention has little gas generation and is excellent in cycle stability.

It is the graph which plotted the relationship between the capacity | capacitance maintenance factor of each Example, and the ratio of the peak intensity of Ti and Si measured in each synthesis example applicable to each Example.

Embodiments of the present invention will be described below. The scope of the present invention is defined by the scope of the claims, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.
<1. Negative electrode active material>
The compound used for preparing the negative electrode active material of the present invention is sufficient if the insertion / extraction reaction of lithium ions proceeds 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. Hereinafter, this compound is sometimes referred to as “the compound”. 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 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 compound is 2.0 V (vs. Li). ⁺ / Li) or less, and ends at 0.3 V (vs. Li ⁺ / Li) or more. On the other hand, when 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 compound 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 compound 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 compound is preferably a titanium-containing composite oxide typified by lithium titanate, titanium dioxide, H ₂ Ti ₁₂ O ₂₅ , or a metal oxide such as niobium pentoxide and molybdenum dioxide, since the stability of the compound is high. More preferred are lithium titanate, titanium dioxide, and H ₂ Ti ₁₂ O ₂₅ . These compounds 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 compound in the reaction of insertion / extraction of lithium ions is small. As Li ₄ Ti ₅ O ₁₂ .
The titanium dioxide used in the present invention is preferably anatase type or B type (bronze type) titanium dioxide. These titanium dioxides may be used alone or in combination of two or more.

  The negative electrode active material of the present invention is present on at least a part of the surface of a compound 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. The hydroxyl group is represented by the following formula (1):

It is protected with a silyl group represented by Here, the meanings of R ¹ , R ² and R ³ of the silyl group are as already described in the section [Means for Solving the Problems].
The presence of this silyl group can be measured, for example, with an X-ray photoelectron spectroscopy (ESCA).
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 ESCA is exemplified by AlKα, MgKα, AgKα, etc., but AlKα is preferable because it is widely used.

The intensity of the X-ray 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 the thickness is less than 100 μm, the element to be measured may not be detected.

The ratio of the titanium element and the silyl group on the surface of the negative electrode active material can be defined by the ratio of the 2p peak intensity of titanium measured by ESCA and the 2p peak intensity of silicon (Si) element. 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. The 2p peak intensity of silicon can be calculated similarly.

  The ratio between the 2p peak intensity of the titanium element and the 2p peak intensity of the silicon element is (2p peak intensity of the silicon element) / (2p peak intensity of the titanium element) of 0.01 or more and 1 or less. Is more preferably 0.01 or more and 0.75 or less, and particularly preferably 0.01 or more and 0.5 or less. If it is less than 0.01, the effect of suppressing gas generation and cycle stability reduction is small, and if it is greater than 1, the structure of the negative electrode active material may be collapsed.

  The method for protecting the hydroxyl group present on a part of the surface of the compound with the silyl group is carried out by treating the compound with a silylating agent. In this case, a method using a solvent and a method using no solvent are exemplified. In the method using a solvent, an aprotic solvent may be used. The aprotic solvent used here is preferably dehydrated in order to suppress the reaction between the silylating agent and water in the solvent.

In a method that does not use a solvent, the compound may be treated with a liquid, gaseous, or solid silylating agent.
The aprotic solvent mentioned here is not particularly limited, but linear and cyclic alkanes, benzene and benzene derivatives, diethyl ether, chloroform, ethyl acetate, encamethylene, 1,2-dimethoxyethane, tetrahydrofuran, dioxane, acetone. , Hexamethyldisiloxane, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone (NMP), and organic carbonate. High solubility of silylating agent benzene, toluene, xylene, chlorobenzene, diethyl ether, acetone, acetonitrile, N, N-dimethylformamide, dioxane, dimethyl sulfoxide, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, 1,2- Dimethoxyethane, hexane, heptane and octane are preferred.

A benzene derivative refers to a compound in which one or more hydrogen atoms of benzene are substituted with a functional group. The functional group herein is not particularly limited, and examples thereof include an alkyl group, a halogen group, a nitro group, a cyano group, a vinyl group, an allyl group, an aryl group, an aralkyl group, and an alkoxy group.
The silylating agent used here preferably contains a silyl group represented by the general formula (1) and is hydrolyzable. The compound containing such a silyl group is represented by the following formulas (2) and (3):

It can be expressed as Here, the meanings of R ¹ , R ² and R ³ are as described in the section [Means for Solving the Problems]. X in the general formula (2) is not particularly limited as long as it provides hydrolyzability to a compound containing a silyl group, and includes a halogen group, an alkoxy group, a fluoroalkoxyl group, an amino group, a cyano group, and the like. . That is, the silylating agent of the general formula (2) has only one hydrolyzable functional group. Similarly, the silylating agent of the general formula (3) has only one hydrolysis functional group attached to the silyl group. Having only one hydrolyzable functional group eliminates the possibility of further side reactions between moisture and silyl groups after protecting the surface of the negative electrode active material, and prevents further gas generation and deterioration of cycle stability. Is preferable. Specific examples of silylating agents include 1,1,1,3,3,3-hexamethyldisilazane, bistriethylsilylamine, chlorotrimethylsilane, bromotrimethylsilane, iodotrimethylsilane, chlorotriethylsilane, chloromethyldiphenylsilane Chlorodimethylphenylsilane, methoxytrimethylsilane, trimethylsilane, chlorotert-butyldimethylsilane, bromotert-butyldimethylsilane, chlorotriphenylsilane, chlorotrivinylsilane, and the like. Since the hydroxyl group present on a part of the surface of the compound is efficiently protected and the influence on cost is small, chlorotrimethylsilane, methoxytrimethylsilane, 1,1,1,3,3,3-hexa Methyl disilazane, chlorotrivinylsilane and bistriethylsilylamine are preferred.

The atmosphere for treating the compound with a silylating agent is preferably an inert gas atmosphere. The temperature at which the compound is treated with a silylating agent is preferably less than the decomposition temperature of the silylating agent.
Moreover, when using a solvent, it is preferable that the temperature at the time of processing the said compound with a silylating agent is higher than the freezing point of a solvent, and is below a boiling point. It is preferably 5 ° C. or more and less than 250 ° C. because the reactivity is not lowered and the influence of the utility cost is small. If the temperature is lower than 5 ° C, the reaction proceeds slowly. On the other hand, if the temperature is higher than 250 ° C, the silylating agent may be evaporated and decomposed.

The time for treating the compound with a silylating agent is preferably 1 minute to 200 hours or less. It is particularly 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 it is shorter than 1 minute, the hydroxyl group present on the surface of the compound may not be effectively protected with a silyl group.
In order to suppress the decomposition reaction between adsorbed water and a compound containing a silyl group, which may be present on the surface of the compound, the compound may be vacuum-heat dried before the treatment. It is preferable to use a compound immediately after vacuum heat drying.

The temperature at which vacuum heat drying is performed is preferably not higher than the decomposition temperature of the compound. The temperature is preferably 25 ° C. or more and less than 300 ° C. because the adsorbed water is effectively removed and the influence of the utility cost is small.
The method of treating the compound with a silylating agent using a solvent can be performed by diffusing the compound at a predetermined temperature and for a predetermined time in a solution containing the silylating agent.

Examples of the solution containing the silylating agent include a solution obtained by dissolving the silylating agent in the aprotic solvent.
When the silylating agent is liquid, the silylating agent may be added directly to the compound soaked in the solvent without dissolving it in the non-aqueous solvent.
The concentration of the silylating agent contained in the solution is preferably 0.001 mol / L or more and 10.0 mol / L or less, more preferably 0.01 mol / L or more and 5.0 mol / L or less, and has little influence on cost. Since the treatment time can be shortened and the hydroxyl group present on a part of the surface of the compound according to claim 1 can be effectively protected with a silyl group, 0.05 mol / L or more, 5.0 mol / L L or less is particularly preferable.

When the compound is treated with a liquid silylating agent without using a solvent, it can be carried out by adding the silylating agent to the compound and diffusing the compound at a predetermined temperature for a predetermined time.
When the compound is treated with a gaseous silylating agent without using a solvent, the compound is placed in a gas flow type furnace, and the gaseous silylating agent is allowed to flow through the furnace while being desired. The method of heating for 1 minute to 200 hours at the temperature of, for example, the temperature of 25-250 degreeC is illustrated.

In the case where the compound is treated with a solid silylating agent without using a solvent, a method is exemplified in which the silylating agent is mixed with the compound and then calcined at a desired temperature, for example, 25 to 250 ° C. The
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, the adhesiveness with the below-mentioned binder is maintained and sufficient adhesiveness with a collector can 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. 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. Specifically, polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE) are preferable. 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. N-methyl-2-pyrrolidone (NMP) is particularly preferable. 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. The aluminum is not particularly limited since it is stable in a negative electrode reaction atmosphere, but is preferably high-purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99 and the like.
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.

  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 negative electrode active material, the conductive additive, the binder, and the solvent can be uniformly mixed. 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.

  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 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 include room temperature or high temperature 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. 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 described later 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 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. Specifically, polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE) are preferable. 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. N-methyl-2-pyrrolidone (NMP) is particularly preferable. 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).

  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. 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 the above-described negative electrode is formed.

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 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.
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)
However, in said Formula (1), A shows the electrical capacity per 1 cm < ² > of positive electrodes, B shows the electrical capacity per 1 cm < ² > of negative electrodes.

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 overcharging. 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 lithium titanate>
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 in a nitrogen atmosphere at 800 ° C. for 12 hours to be used in the examples. A compound was made.
As described below, this negative electrode active material was subjected to a treatment for protecting a hydroxyl group present on at least a part of the surface with a silyl group (Synthesis Examples 1 to 10).

(Synthesis Example 1)
15 g of lithium titanate was added to the flask and vacuum dried at 100 ° C. for 3 hours.
The flask was filled with nitrogen, and toluene (20 mL) and 1,1,1,3,3,3-hexamethyldisilazane (2 mL) were added to the flask, respectively, and then stirred while refluxing for 1 hour in a nitrogen environment. . Next, the mixed solution was filtered, and the powder was washed with toluene and hexane three times each (25 mL × 3 each). Finally, a negative electrode active material in which a hydroxyl group present on a part of the surface of lithium titanate was protected with a silyl group was prepared by vacuum drying at 80 ° C. for 3 hours. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.04.

(Synthesis Example 2)
A negative electrode active material of Synthesis Example 2 was prepared in the same manner as Synthesis Example 1 except that the stirring time was 10 hours. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.06.
(Synthesis Example 3)
A negative electrode active material of Synthesis Example 3 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 negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.11.

(Synthesis Example 4)
A negative electrode active material of Synthesis Example 4 was prepared in the same manner as Synthesis Example 2 except that 4 mL of 1,1,1,3,3,3-hexamethyldisilazane was used. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.10.
(Synthesis Example 5)
A negative electrode active material of Synthesis Example 5 was prepared in the same manner as in Synthesis Example 2 except that the stirring time was 48 hours and 8 mL of 1,1,1,3,3,3-hexamethyldisilazane was used. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.23.

(Synthesis Example 6)
15 g of lithium titanate was added to the flask and vacuum dried at 100 ° C. for 3 hours.
After filling the flask with nitrogen, N, N-dimethylformamide (20 mL), chlorotrimethylsilane (1 mL), and imidazole (0.5 g) were added to the flask, respectively, and stirred at 45 ° C. for 10 hours. Next, the mixed solution was filtered, and the powder was washed with N, N-dimethylformamide and toluene three times each (25 mL × 3 each). Finally, a negative electrode active material in which a hydroxyl group present on a part of the surface of lithium titanate was protected with a silyl group was prepared by vacuum drying at 80 ° C. for 3 hours. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.03.

(Synthesis Example 7)
A negative electrode active material of Synthesis Example 7 was prepared in the same manner as Synthesis Example 6 except that the temperature was set to 60 ° C. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.04.
(Synthesis Example 8)
A negative electrode active material of Synthesis Example 8 was prepared in the same manner as Synthesis Example 7 except that the stirring time was set to 24 hours. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.05.

(Synthesis Example 9)
A negative electrode active material of Synthesis Example 9 was prepared in the same manner as Synthesis Example 7 except that the stirring time was set to 72 hours. As a result of surface analysis of this negative electrode active material by ESCA, the ratio of peak intensities of Ti and Si was Si / Ti = 0.08.
(Synthesis Example 10)
The lithium titanate of Synthesis Example 10 was prepared in the same manner as Synthesis Example 9 except that 5 mL of chlorotrimethylsilane was added. As a result of surface analysis of this lithium titanate by ESCA, the peak intensity ratio of Ti and Si was Si / Ti = 0.12.

<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. This slurry was applied to an aluminum foil (15 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, 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). This 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 negative 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 10>
The nonaqueous electrolyte secondary batteries of Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10 and Example 10 were used as the anode active material of Synthesis Example 1. Other than using the negative electrode active materials of Synthesis Example 2, Synthesis Example 3, Synthesis Example 4, Synthesis Example 5, Synthesis Example 6, Synthesis Example 7, Synthesis Example 8, Synthesis Example 9 and Synthesis Example 10 instead of the materials. Obtained a nonaqueous electrolyte secondary battery in the same manner as in Example 1.

<Comparative Example 1>
The nonaqueous electrolyte secondary battery of Comparative Example 1 was the same as Example 1 except that a negative electrode active material not treated with a compound containing a silyl group was used instead of the negative electrode active material of Synthesis Example 1. A nonaqueous electrolyte secondary battery was obtained.
<Measurement of cycle characteristics>
The nonaqueous electrolyte secondary batteries of Examples 1 to 10 and Comparative Example 1 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 the discharge end voltage of Examples 1 to 10 and the comparative example at this time were set to 2.7 V and 2.0 V, respectively. Table 1 shows the discharge capacity (capacity retention ratio) at the 500th time when the first discharge capacity is 100. In addition, Table 1 shows the amount of gas generated after measurement of cycle characteristics.

<Evaluation method of gas generation amount>
Gas that is generated during measurement of cycle characteristics is outside the fixed part of the aluminum laminate sheet by pressing the part including the electrode and separator of the non-aqueous electrolyte secondary battery from above the aluminum laminate sheet and fixing it with a jig. Accumulated in the pocket. The amount of gas generated during the measurement of the cycle characteristics was calculated from the area of the gas pocket and the height of the gas pocket swollen by the generated gas, and converted to a gas amount for each Ah. In addition, the inside of a cell cannot be made into a complete vacuum state at the time of sealing an aluminum laminate sheet, and the gas pocket before the measurement of cycling characteristics has a fixed volume. Therefore, when the gas amount was converted for each Ah, it was determined that no gas was generated if this value was 2 cc / Ah or less (Table 1).

As is clear from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 10 of the present invention have no gas generation and have improved cycle stability than the nonaqueous electrolyte secondary battery of the comparative example. Yes.
Moreover, what plotted the relationship between the capacity maintenance rate of each Example of Table 1 and the ratio of the peak intensity of Ti and Si measured in the synthesis example corresponding to each Example is shown in FIG. According to FIG. 1, it can be seen that the capacity retention rate of 84% or more is that the peak intensity ratio of the synthesis example is 0.03 or more. Therefore, it is preferable to prepare the negative electrode active material so that the peak intensity ratio is 0.03 or more.

Claims (8)

A negative electrode active material used for a non-aqueous electrolyte secondary battery,
A hydroxyl group present on at least a part of the surface of the compound in which desorption and insertion of lithium ions proceeds at 0.3 V (vs Li + / Li) or more and 2.0 V (vs Li + / Li) or less is represented by the following formula (1): :

A negative electrode active material which is protected by a silyl group represented by the formula:
(Wherein R ¹ , R ² and R ³ of the silyl group are C1-C20 alkyl groups, C2-C20 alkenyl groups, C2-C20 alkynyl groups, C6-C20 aryl groups, C4-C20 heteroaryl groups) Represents a C7 to C20 aralkyl group or a C5 to C20 heteroaralkyl group, and R ¹ , R ² and R ³ may be the same as or different from each other, the alkyl group, alkenyl group, alkynyl group, The aryl group, heteroaryl group, aralkyl group, and heteroaralkyl group may have a substituent.)
  The compound in which desorption and insertion of the lithium ion proceeds at 0.3 V (vs Li + / Li) or higher and 2.0 V (vs Li + / Li) or lower is a titanium composite oxide or a titanium oxide. The negative electrode active material according to 1. The R ¹ , R ² and R ^{3 of the} silyl group represented by the general formula (1) are selected from a methyl group, an ethyl group, a tert-butyl group, a phenyl group, and a vinyl group. Item 5. The negative electrode active material according to Item 2. A method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery, comprising:
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 is treated with a silylating agent containing a silyl group. By doing so, the hydroxyl group present on at least part of the surface of the negative electrode active material is represented by the following formula (1):

The manufacturing method of the negative electrode active material protected by the silyl group represented by these. 5. The silylating agent containing a silyl group according to claim 4, wherein 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. The method of treating the negative electrode active material is heat treatment, and the hydroxyl group present on at least a part of the surface of the negative electrode active material is represented by the following formula (1):

The manufacturing method of the negative electrode active material protected by the silyl group represented by these.   The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode active material of any one of Claims 1-3.   A non-aqueous electrolyte secondary battery comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the negative electrode according to claim 6 is used as the negative electrode.   A secondary battery module in which a plurality of the nonaqueous electrolyte secondary batteries according to claim 7 are connected.

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