JP5726603B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and an assembled battery using the same.

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. Nonaqueous electrolyte secondary batteries used in these fields need to be repeatedly charged and discharged for a long time. In particular, a non-aqueous electrolyte using a compound in which desorption and insertion of lithium ions as an active material proceeds at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less as an active material in the negative electrode. Since secondary batteries are difficult to deposit lithium metal, safety and cycle characteristics can be expected to improve. Non-aqueous electrolyte secondary batteries using lithium titanate as an active material for the negative electrode represented by Patent Document 1 have been developed. Has been. However, a non-aqueous electrolyte secondary battery using lithium titanate as an active material for the negative electrode has a problem that gas is generated every time the charge / discharge cycle is repeated, and as a result, the battery performance deteriorates every time the cycle is repeated. is there.

JP2007-294164A

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery having excellent cycle stability.

  As a result of intensive studies by the present inventors in order to solve the above problem, when a carbon material containing boron is contained in the negative electrode and / or the positive electrode, gas generation is suppressed even if the charge / discharge cycle is repeated. As a result, the present invention has been completed.

That is, the present invention is a non-aqueous electrolyte secondary battery including a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. The negative electrode has a lithium ion desorption and insertion of 0.3 V (vs. Li + as an active material). / Li) to 2.0 V (vs. Li + / Li) or less, lithium titanate is included as a compound, and the negative electrode includes an active material and a conductive additive, and 100 parts by weight of the active material. 1 to 30 parts by weight of a conductive auxiliary agent, and the negative electrode conductive auxiliary agent is a carbon material containing 0.1 wt% or more and 10 wt% or less of boron, including vapor grown carbon fiber, carbon nanotubes, Ri 1 or more carbon materials der selected from the group consisting of acetylene black and ketjen black, said positive electrode comprises an active material, and a conductive additive and active material 100 fold 1 part by weight or more and 30 parts by weight or less of a conductive additive, and the positive electrode conductive additive is a carbon material containing 0.1 wt% or more and 10 wt% or less of boron, and vapor phase growth The present invention relates to a non-aqueous electrolyte secondary battery that is one or more carbon materials selected from the group consisting of carbon fibers, carbon nanotubes, acetylene black, and ketjen black .

  In the nonaqueous electrolyte secondary battery of the present invention, it is preferable that lithium titanate has a spinel structure.

  In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode preferably contains a lithium manganese compound as an active material.

In the non-aqueous electrolyte secondary battery of the present invention, the lithium manganese compound is Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is 2 to 13 groups) And an element belonging to the third and fourth periods).

The non-aqueous electrolyte secondary battery of the present invention is Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group 2 to 13, It is preferable that M contained in the element belonging to 4 periods is at least one selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe, and Cr.

  The assembled battery of the present invention is formed by connecting a plurality of the nonaqueous electrolyte secondary batteries of the present invention.

  The nonaqueous electrolyte secondary battery of the present invention is excellent in cycle stability.

The present invention uses a negative electrode containing a 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 as a negative electrode active material. In the nonaqueous electrolyte secondary battery, a carbon material containing 0.1 wt% or more and 10 wt% or less of boron is included in the positive electrode and / or the negative electrode. Thus, when a 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 used, the positive electrode and / or It is assumed that the state where the reactivity between the conductive additive contained in the negative electrode and the electrolytic solution becomes high is suppressed, and the promotion of the electrolytic solution decomposition is prevented.

<1. Negative electrode active material>
The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention has an insertion / extraction reaction of lithium ions as an active material (hereinafter referred to as negative electrode active material) of 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. .Li ⁺ / Li) including compounds that proceed below. When the voltage is 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, a lithium battery is not deposited 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 negative electrode active material is 2.0 V (vs. Li). Li ⁺ / Li) or less, and end at 0.3 V (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 of the lithium ion insertion / desorption reaction (vs. Li ⁺ / Li) was determined 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, It can be obtained 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 more and 2.0 V (vs. Li ⁺ / Li) or less is lithium titanate, titanium dioxide, pentoxide Niobium, molybdenum dioxide, and the like are preferable, and lithium titanate and titanium dioxide are more preferable, and lithium titanate is more preferable from the viewpoint of high stability of the negative electrode active material. One type of these negative electrode active materials may be used, or two or more types may be used.

The lithium titanate preferably has a spinel structure, and a molecular formula represented by Li ₄ Ti ₅ O ₁₂ is preferable. In the case of the spinel structure, the expansion and contraction of the active material in the reaction of lithium ion insertion / extraction is small. Lithium titanate may contain a small amount of elements other than lithium such as Nb and titanium, for example.

  Lithium titanate preferably has a half width of (400) plane of powder X-ray diffraction by CuKα of 0.5 ° or less. If it is larger than 0.5 °, the crystallinity of lithium titanate is low, and the stability of the electrode may be lowered.

  The lithium titanate preferably has a lithium content of 90% or more in the 8a site according to the Rietveld analysis by X-ray diffraction. If it is less than 90%, since there are many defects in the crystal of lithium titanate, the stability of the electrode may be lowered.

  Lithium titanate can be obtained by heat-treating a lithium compound and a titanium compound at 500 ° C. or higher and 1500 ° C. or lower. When the temperature is lower than 500 ° C. or higher than 1500 ° C., lithium titanate having a desired structure tends to be difficult to obtain. In order to improve the crystallinity of lithium titanate, after the heat treatment, the heat treatment may be performed again at a temperature of 500 ° C. or higher and 1500 ° C. or lower. The temperature of the reheating treatment may be the same as or different from the initial temperature. The heat treatment may be performed in the presence of air or in the presence of an inert gas such as nitrogen or argon. Although it does not specifically limit in heat processing, For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln etc. can be used.

  As the lithium compound, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, lithium halide and the like can be used. These lithium compounds may be used alone or in combination of two or more.

  Although it does not specifically limit as a titanium compound, For example, titanium oxides, such as titanium dioxide and a titanium monoxide, can be used.

  The compounding ratio of the lithium compound and the titanium compound may be slightly widened depending on the properties of the raw materials and the heating conditions, and the atomic ratio of lithium and titanium, and Ti / Li = 1.25.

  The surface of the lithium titanate may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.

  The particle diameter of lithium titanate is preferably 0.5 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 lithium titanate 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 bulk density of lithium titanate is preferably 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. Cathode active material>
The active material (hereinafter, positive electrode active material) contained in the positive electrode used in the nonaqueous electrolyte secondary battery of the present invention is preferably a lithium manganese compound because of excellent cycle characteristics.

The lithium manganese compound, for _{example, Li 2 MnO 3, Li a} M b Mn 1-b N c O 4 (0 <a ≦ 2,0 ≦ b ≦ 0.5,1 ≦ c ≦ 2, M is 2 elements belonging to group 13 in and third and fourth period, N is the element belonging to 14 to 16 group is and the third _{period), Li 1 + x M y} Mn 2-x-y O 4 (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, and M is at least one selected from the group consisting of elements belonging to Group 2 to 13 and belonging to the third to fourth periods. Here, M is at least one selected from elements belonging to Groups 2 to 13 and belonging to the 3rd to 4th periods, but Al, Mg, Zn, Ni, Co, Fe and Cr are preferred, Al, Mg, Zn, Ni and Cr are more preferred, and Al, Mg, Zn and Ni are even more preferred. Further, N here is preferably Si, P, or S because the effect of improving the stability is large.

Especially, since the stability of the positive electrode active material is high, Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group 2 to 13 and A lithium manganese compound represented by at least one selected from the group consisting of elements belonging to the third to fourth periods 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 lithium manganese compound preferably has a spinel structure. The spinel structure is preferable because the expansion and contraction of the active material in the lithium ion insertion / extraction reaction is small.

  The lithium manganese compound preferably has a half width of 0.5 ° or less on the (400) plane of powder X-ray diffraction by CuKα. When it is larger than 0.5 °, the crystallinity of the positive electrode active material is low, and thus the stability of the electrode may be lowered.

  The lithium manganese compound preferably has a lithium content of 90% or more in the 8a site according to the Rietveld analysis by X-ray diffraction. If it is less than 90%, there are many defects in the crystal of the positive electrode active material, and the stability of the electrode may be lowered.

  The particle size of the lithium manganese compound is preferably 0.5 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 here is a value obtained by measuring the size of each particle from the SEM and TEM images and calculating the average particle diameter.

The specific surface area of the lithium manganese compound 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 can be calculated by measurement by the BET method.

The bulk density of the lithium manganese compound is preferably 0.2 g / cm ³ or more and 2.0 g / cm ³ or less. When the amount is less than 0.2 g / cm ³ , a large amount of solvent is required when preparing a slurry described later, which is economically disadvantageous. When the amount is greater than 2.0 g / cm ³ , mixing with a conductive additive and a binder described later is not possible. It tends to be difficult.

  Depending on the lithium compound, the manganese compound, and the target compound, the lithium manganese compound can be obtained by further heat-treating the M compound and the N compound at 500 ° C. or more and 1500 ° C. or less. When the temperature is lower than 500 ° C. or higher than 1500 ° C., a positive electrode active material having a desired structure may not be obtained. Depending on the lithium compound, the manganese compound, and the target compound, the heat treatment may be performed by mixing the M compound and / or the N compound, or heating the manganese compound and the M compound and / or the N compound. You may heat-process with a lithium compound after processing. In order to improve the crystallinity of the positive electrode active material, after the heat treatment, the heat treatment may be performed again at 500 ° C. or more and 1500 ° C. or less. The temperature of the reheating treatment may be the same as or different from the initial temperature. The heat treatment may be performed in the presence of air or in the presence of an inert gas such as nitrogen or argon. Although it does not specifically limit in heat processing, For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln etc. can be used.

  As the lithium compound, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, lithium halide and the like can be used. These lithium compounds may be used alone or in combination of two or more.

  As the manganese compound, for example, manganese oxide such as manganese dioxide, manganese carbonate, manganese nitrate, manganese hydroxide and the like can be used. These manganese compounds may be used alone or in combination of two or more.

As the compound of M, for example, carbonate, oxide, nitrate, hydroxide, sulfate and the like can be used. The amount of M contained in Li _{1 + x} M _y Mn _2−xy O ₄ can be controlled by the amount of the M compound during the heat treatment. One type of M compound may be used, or two or more types may be used.

As the N compound, for example, phosphorus oxides, sulfates, silicic oxides and the like can be used. For ease of synthesis, compounds of manganese and N, such as manganese phosphates, manganese sulfates, manganese Silica oxide is preferably used. The amount of N contained in Li _a M _b Mn _1-b N _c O ₄ can be controlled by the amount of N compound during the heat treatment. One type of N compound may be used, or two or more types may be used.

Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is selected from the group consisting of elements belonging to Groups 2 to 13 and belonging to the 3rd to 4th periods. The compounding ratio of the lithium compound, the manganese compound and the M compound is 1 + x (lithium), 2-xy (manganese), and the atomic ratio of lithium, manganese and M, respectively. y (M), provided that 0 ≦ x ≦ 0.2 and 0 <y ≦ 0.6. For example, when a positive electrode active material having an atomic ratio of 1.5 of Mn / Li is produced, a slight width may be provided around the blending ratio of 1.5 depending on the properties of the raw materials and heating conditions.

  The surface of the positive electrode active material used in the nonaqueous electrolyte secondary battery 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.

<3. Conductive aid>
The positive electrode and / or negative electrode of the nonaqueous electrolyte secondary battery of the present invention contains a carbon material containing 0.1 wt% or more and 10 wt% or less of boron (hereinafter sometimes referred to as “the carbon material of the present invention”). It is contained as a conductive aid. The carbon material containing boron is a carbon material in which a part of carbon atoms is substituted with boron atoms. By containing 0.1 wt% or more and 10 wt% or less of boron in the carbon material, the reactivity between the carbon material and the electrolytic solution is lowered, and as a result, the cycle characteristics of the nonaqueous electrolyte secondary battery are improved.

  The method of measuring the amount of boron contained in the carbon material is preferably a method of quantifying by ICP emission analysis (Inductivity Coupled Plasma Emission Spectroscopy). The method for qualifying boron contained in the carbon material can be calculated from ICP emission spectroscopic analysis or X-ray photoelectron spectroscopic analysis.

  The amount of boron contained in the carbon material is 0.1 wt% or more and 10 wt% or less. When the amount of boron contained in the carbon material is 0.1 wt% or more and 10 wt% or less, the reactivity with the electrolytic solution is suppressed while maintaining good conductivity, and the decomposition of the electrolytic solution is reduced. When the amount is less than 0.1 wt%, the reactivity between the carbon material and the electrolytic solution does not decrease, and the decomposition of the electrolytic solution is not suppressed. On the other hand, if the carbon material contains more than 10 wt%, the higher-order structure of the material is damaged, and the electron conduction path is interrupted. As a result, the electron conduction in the electrode is lowered, and the battery performance is lowered. Since the effect of reducing the reactivity between the carbon material and the electrolytic solution is high, the amount of boron contained in the carbon material is preferably 0.2 wt% or more and 8 wt% or less, more preferably 0.5 wt% or more and 5 wt%. % Or less.

  The carbon material of the present invention may contain nitrogen in addition to boron.

  The carbon material is not particularly limited as long as an electron conduction path in the electrode can be formed. For example, natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, channel black, Examples thereof include those obtained by graphitizing a polymer such as thermal black, furnace black, glassy carbon, or polyimide and then pulverizing it. Among these, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black are more preferable because they easily contain boron. Also, vapor grown carbon fiber, carbon nanotube, acetylene black, and ketjen black are particularly preferable because they easily form an electron conduction path in the electrode. These carbon materials may be used alone or in combination of two or more.

  The carbon material of the present invention preferably has a primary particle size of 10 nm or more and 10,000 nm or less. When the thickness is less than 10 nm, it is difficult to handle, and thus the electrode production tends to be difficult. On the other hand, when it is larger than 10,000 nm, the conductive additive may not be uniformly dispersed in the electrode. In the carbon material of the present invention, primary particles may be aggregated. In that case, the particle diameter is preferably 10,000 nm or less. The particle diameter can be directly measured by observation with a transmission electron microscope (TEM). Moreover, when the particle diameter becomes large through the step of containing boron, it may be pulverized with a ball mill or the like to obtain a desired particle diameter.

The carbon material of the present invention preferably has a specific surface area of 1 m ² / g or more and 2000 m ² / g or less. If it is less than 1 m ² / g, the number of contact points between the active material and the conductive additive may be reduced and the battery resistance may increase. On the other hand, when it is larger than 2000 m ² / g, it is difficult to handle, and thus it tends to be difficult to produce an electrode. The specific surface area here can be calculated by measurement by the BET method.

  The carbon material of the present invention can be produced by producing a mixture of a carbon material and a boron compound and then heat-treating the mixture. As the boron compound, for example, boron carbide, boron nitride, boron oxide, boric acid, or the like that can be easily contained in the carbon material after heat treatment can be used. These boron compounds may be used alone or in combination of two or more.

  A method for producing a mixture of the carbon material and the boron compound is not particularly limited, but a propeller type stirrer or the like that can be uniformly mixed is preferable. The heat treatment of the mixture of the carbon material and the boron compound is preferably held for 10 minutes or more in a non-oxidizing atmosphere and 2500 ° C. or higher. When the heating temperature is less than 2500 ° C. and the holding time is less than 10 minutes, the carbon material may not contain boron. The furnace used for the heat treatment is not particularly limited, but a non-oxidizing atmosphere such as a high-frequency induction heating furnace or a graphitization furnace and a furnace that can be set to 2500 ° C. or higher are preferable.

  The non-oxidizing atmosphere can be obtained by replacing with an inert gas such as helium gas, nitrogen gas or argon gas. The inert gas used here may be used alone or in combination of two or more.

  After the boron is contained in the carbon material, it may be washed with an acid aqueous solution, an alkali aqueous solution, or water in order to remove impurities. A sulfuric acid aqueous solution, a hydrochloric acid aqueous solution, a nitric acid aqueous solution can be used as the acid aqueous solution, and a sodium hydroxide aqueous solution can be used as the alkaline aqueous solution.

  In the present invention, the amount of the conductive additive contained in either the negative electrode or the positive electrode or in both the negative electrode and the positive electrode is preferably 1 part by weight or more with respect to 100 parts by weight of the negative electrode active material (or the positive electrode active material). 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less. If it is the said range, the electroconductivity of an 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, when the conductive additive contained in one of the negative electrode and the positive electrode is a carbon material containing boron, the conductive additive contained in the other can be a carbon material containing no boron. The carbon material not containing boron is not particularly limited as long as an electron conduction path in the electrode can be formed. For example, natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black , Channel black, thermal black, furnace black, glassy carbon, or a polymer such as polyimide that has been graphitized and then pulverized. In addition to the carbon material, conductive metal powder such as copper, nickel, aluminum, and iron can also be used.

<4. Binder>
You may use a binder for the negative electrode and positive electrode which are used for the nonaqueous electrolyte secondary battery of this invention. 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, and derivatives thereof can be used. . The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of easy production of the negative electrode and 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.

  In the present invention, the amount of the binder contained in the negative electrode and the positive electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material (or positive electrode active material). Less than parts by weight. If it is the said range, the adhesiveness of a negative electrode active material (or positive electrode active material) and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.

<5. Negative electrode>
A preferable embodiment of the negative electrode used in the nonaqueous electrolyte secondary battery of the present invention includes a negative electrode produced by forming a mixture of a negative electrode active material, a conductive additive, and a binder on a current collector. . In view of the ease of the production method, a method of producing a negative electrode by producing a slurry with the above mixture and solvent, coating the obtained slurry on a current collector, and then removing the solvent is preferable.

The current collector that can be used for the negative electrode of the present invention is a metal that is stable at 0.3 V (vs. Li ⁺ / Li) or more and 2.0 V (vs. Li ⁺ / Li) or less, such as copper, SUS, nickel. Titanium, aluminum and alloys thereof are preferred, and aluminum is particularly preferred because of its high stability. Aluminum is not particularly limited since it is stable in the positive electrode and negative electrode reaction atmospheres, but is preferably high-purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99 and the like.

  The surface roughness Ra of the current collector is preferably 0.05 μm or more and 0.5 μm or less. If the thickness is less than 0.05 μm, the adhesion to the negative electrode may be lowered, and if it is larger than 0.5 μm, it may be difficult to form the negative electrode uniformly. The surface roughness Ra can be measured using a light wave interference type surface roughness measuring instrument or the like.

  The electrical resistance of the current collector is preferably 5 μΩ · cm or less. If it is higher than 5 μΩ · cm, the battery performance may be reduced. Electrical resistance can be measured by the four probe method.

  The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, handling is difficult from the viewpoint of production, and if it is thicker than 100 μm, it is disadvantageous from an economic viewpoint.

  As the current collector, a metal material other than aluminum (copper, SUS, nickel, titanium, and alloys thereof) coated with aluminum can also be used.

  The production of 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 preparation of the slurry is not particularly limited, it may be prepared by mixing the negative electrode active material, the conductive additive, and the binder and then adding a solvent, or the negative electrode active material, the conductive additive, the binder, and the solvent together. You may mix and produce.

  The solid content concentration of the slurry is preferably 30 wt% or more and 80 wt% or less. If it is less than 30 wt%, the viscosity of the slurry tends to be too low, whereas if it is higher than 80 wt%, the viscosity of the slurry tends to be too high, and it may be difficult to form an electrode described later.

  The solvent used for the slurry is preferably a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Moreover, you may add a dispersing agent and a thickener to these.

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

  In the present invention, the thickness of the negative electrode is preferably 10 μm or more and 200 μm or less. If it is 10 μm or less, it may be difficult to obtain a desired capacity, and if it is thicker than 200 μm, it may be difficult to obtain a desired output density.

In the present invention, the density of the negative electrode is preferably 1.0 g / cm ³ or more and 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 3.6 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 3.6 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.

<6. Positive electrode>
Examples of the method for producing the positive electrode of the present invention include a method for producing a positive electrode by applying a mixture of a positive electrode active material, a conductive additive and a binder onto a current collector. In view of the ease of the production method, a method of producing a positive electrode by producing a slurry with the mixture and a solvent, coating the obtained slurry on 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.

  The surface roughness Ra of the current collector is preferably 0.05 μm or more and 0.5 μm or less. If the thickness is less than 0.05 μm, the adhesion between the positive electrode and the negative electrode may be lowered. If the thickness is more than 0.5 μm, it may be difficult to form the positive electrode and the negative electrode uniformly. The surface roughness Ra can be measured using a light wave interference type surface roughness measuring instrument or the like.

  The electrical resistance of the current collector is preferably 5 μΩ · cm or less. If it is higher than 5 μΩ · cm, the battery performance may be reduced. Electrical resistance can be measured by the four probe method.

  The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, handling is difficult from the viewpoint of production, and if it is thicker than 100 μm, it is disadvantageous from an economic viewpoint.

  As the current collector, a metal whose surface is coated with aluminum other than aluminum (copper, SUS, nickel, titanium, and alloys thereof) can also 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 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 may be combined 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 electrodes 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 positive electrode on the current collector is not particularly limited. For example, a method of removing the solvent after applying the slurry with a doctor blade, a die coater, a comma coater, or the like, or a method of removing the solvent after applying with a spray. preferable. The method for removing the solvent is preferable because it is easy to dry using an oven or a vacuum oven. Examples of the atmosphere for removing the solvent include air, an inert gas, and a vacuum state. The temperature for removing the solvent is not particularly limited, but is preferably 60 ° C. or higher and 250 ° C. or lower. When the temperature is lower than 60 ° C., it may take time to remove the solvent. When the temperature is higher than 250 ° C., the binder may be deteriorated. The positive electrode may be formed before or after forming the negative electrode described later.

  The thickness of the positive electrode 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 3.0 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 3.0 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.

<7. 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, microporous membranes, etc., which are a combination of two or more thereof. 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.

<8. 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. In addition, a solid polymer electrolyte such as gel electrolyte, polyethylene oxide, and polypropylene oxide, or an inorganic solid electrolyte such as sulfide glass and oxynitride can be used.

  The non-aqueous solvent preferably contains a cyclic aprotic solvent and / or a chain aprotic solvent because the solute described later is easily dissolved. 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, dimethyl 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.

Although 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.

<9. Non-aqueous electrolyte secondary battery>
The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery of the present invention may have a form in which the same electrode is formed on both surfaces of the current collector, and the positive electrode is formed on one surface of the current collector and the negative electrode is formed on one surface. 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 in the layer where each positive electrode side and the negative electrode side face each other, 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 Example 1)
A carbon material containing 0.10 wt% boron as a conductive additive was produced as follows.

First, 20 g of carbon material (acetylene black) and 0.1 g of boron carbide were mixed with a propeller type stirrer. Next, this mixture was heated in a high-frequency induction heating furnace at 2700 ° C. for 1 hour. At this time, the inside of the furnace was filled with argon gas. Finally, the carbon material containing boron was produced by standing to cool. When the carbon material was quantified by ICP emission spectroscopic analysis, it contained 0.10 wt% of boron. As a result of measuring the specific surface area of the carbon material containing 0.10 wt% of boron by the BET method, it was 70 m ² / g. Moreover, it was 40 nm as a result of measuring a primary particle diameter by TEM.

(Synthesis Example 2)
A carbon material containing 0.52 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 0.5 g of boron carbide were used in Synthesis Example 1.

(Synthesis Example 3)
A carbon material containing 1.1 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 1.0 g of boron carbide were used in Synthesis Example 1.

(Synthesis Example 4)
A carbon material containing 5.1 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 5.0 g of boron carbide were used in Synthesis Example 1.

(Synthesis Example 5)
A carbon material containing 10.0 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 10.0 g of boron carbide were used in Synthesis Example 1.

(Comparative Synthesis Example 1)
A carbon material containing 0.05 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 0.05 g of boron carbide were used in Synthesis Example 1.

(Comparative Synthesis Example 2)
A carbon material containing 20.0 wt% boron was prepared in the same manner as in Synthesis Example 1 except that 20 g of carbon material (acetylene black) and 20.0 g of boron carbide were used in Synthesis Example 1.

(Manufacture of negative electrode)
The negative electrode active material Li ₄ Ti ₅ O ₁₂ was prepared by the method described in the literature (Journal of Electrochemical Society, 142, 1431 (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 obtain a negative electrode active material. Produced.

100 parts by weight of this negative electrode active material, 6.8 parts by weight of conductive additive (carbon material containing 0.10 wt% of boron prepared in Synthesis Example 1), and binder (PVdF, solid content concentration 12 wt%, NMP) The solution was mixed with 6.8 parts by weight of a solid content to prepare a slurry. After coating this slurry on an aluminum foil (20 μm), a negative electrode (single-side coating) (50 cm ² ) was produced by vacuum drying at 150 ° C.

  The capacity of the negative electrode was measured by the following charge / discharge test.

The above-mentioned electrode was punched out to 16 mmΦ to produce a working electrode. Li metal was punched out to 16 mmΦ as a counter electrode. Using these electrodes, a working electrode (single-sided coating) / separator (polyolefin-based porous membrane, thickness 25 μm) / 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 in an amount of 0.15 mL to prepare a half-cell. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). 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 taken 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 was produced by the method described in the literature (Electrochemical and Solid-State Letters, 9 (12), 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.

A slurry was prepared by mixing 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 (PVdF, solid concentration 12 wt%, NMP solution). . After coating this slurry on an aluminum foil (20 μm), a positive electrode (single-side coating) (50 cm ² ) was produced by vacuum drying at 150 ° C.

  The capacity of the positive electrode was measured by the following charge / discharge test.

The aforementioned electrode was punched to 16 mmΦ, and Li metal was punched to 16 mmΦ as a counter electrode. Using these electrodes, a working electrode (single-sided coating) / separator (polyolefin-based porous membrane, thickness 25 μm) / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a nonaqueous electrolyte (Ethylene carbonate / dimethyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) was added in an amount of 0.15 mL to prepare a half-cell. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). This 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)
First, the produced positive electrode, negative electrode, and separator were laminated in the order of positive electrode / separator / negative electrode. Here, a cellulose unwoven cloth (25 μm, 55 cm ² ) was used as the separator.
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 (ethylene carbonate / dimethyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) was added, a nonaqueous electrolyte secondary battery was produced by sealing while reducing the pressure.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 0.52 wt% of boron produced in Synthesis Example 2 was used as the conductive additive for the negative electrode.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 1.1 wt% of boron produced in Synthesis Example 3 was used as the conductive additive for the negative electrode.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 5.1 wt% boron produced in Synthesis Example 4 was used as the conductive additive for the negative electrode.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 10.0 wt% of boron produced in Synthesis Example 5 was used as the conductive additive for the negative electrode.

  The non-aqueous electrolyte secondary was the same as in Example 1 except that the carbon material containing 0.10 wt% of boron prepared in Synthesis Example 1 was used as the negative electrode conductive additive and the positive electrode conductive additive. A battery was produced.

  The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the carbon material containing 0.52 wt% of boron prepared in Synthesis Example 2 was used as the negative electrode conductive additive and the positive electrode conductive additive. A secondary battery was produced.

  The nonaqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the carbon material containing 1.1 wt% of boron prepared in Synthesis Example 3 was used as the conductive additive for the negative electrode and acetylene black as the conductive additive for the positive electrode. A secondary battery was produced.

  A non-aqueous electrolyte 2 was prepared in the same manner as in Example 1, except that acetylene black was used as the conductive additive for the negative electrode and a carbon material containing 5.1 wt% boron prepared in Synthesis Example 4 was used as the conductive additive for the positive electrode. A secondary battery was produced.

  The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the carbon material containing 10.0 wt% of boron prepared in Synthesis Example 5 was used as the conductive additive for the negative electrode and acetylene black as the conductive additive for the positive electrode. A secondary battery was produced.

  The nonaqueous electrolyte secondary was the same as in Example 1 except that the carbon material containing 0.1 wt% of boron prepared in Synthesis Example 1 was used as the conductive auxiliary material for both the negative electrode and the positive electrode. A battery was produced.

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 0.52 wt% of boron produced in Synthesis Example 2 was used for both the negative electrode and the positive electrode. .

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 1.1 wt% of boron produced in Synthesis Example 3 was used for both the negative electrode and the positive electrode. .

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 5.1 wt% of boron produced in Synthesis Example 4 was used for both the negative electrode and the positive electrode. .

  A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 10.0 wt% of boron produced in Synthesis Example 5 was used for both the negative electrode and the positive electrode. .

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ was used as the positive electrode active material.

The LiNi _0.5 Mn _1.5 O ₄ used here was prepared by the method described in the literature (Journal of PowerSources, 81-82, 90 (1999)).

  That is, lithium hydroxide, manganese oxide hydroxide, and nickel hydroxide were first mixed so that the molar ratio of lithium, manganese, and nickel was 1: 1.5: 0.5. Next, the mixture was heated at 550 ° C. in an air atmosphere, and then heated again at 750 ° C. to prepare a positive electrode active material.

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 6 except that LiNi _0.5 Mn _1.5 O ₄ produced in Example 16 was used as the positive electrode active material.

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 11 except that LiNi _0.5 Mn _1.5 O ₄ produced in Example 16 was used as the positive electrode active material.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that acetylene black was used for both the negative electrode and the positive electrode.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the conductive additive for the negative electrode.

(Comparative Example 3)
The non-aqueous electrolyte was the same as in Example 1 except that the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the conductive additive for the negative electrode and acetylene black as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the negative electrode and the positive electrode conductive additive.

(Comparative Example 5)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 was used as the conductive additive for the negative electrode.

(Comparative Example 6)
The non-aqueous electrolyte is the same as in Example 1 except that the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 is used as the conductive additive for the negative electrode and acetylene black as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 7)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 was used as the negative electrode and the positive electrode conductive additive.

(Comparative Example 8)
A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 16 except that acetylene black was used as a conductive additive for both the negative electrode and the positive electrode.

(Comparative Example 9)
The non-aqueous electrolyte was the same as in Example 16 except that the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the conductive additive for the negative electrode, and acetylene black was used as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 10)
The non-aqueous electrolyte was the same as in Example 16, except that acetylene black was used as the conductive additive for the negative electrode, and the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 11)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 16 except that the carbon material containing 0.05 wt% of boron produced in Comparative Synthesis Example 1 was used as the conductive auxiliary material for both the negative electrode and the positive electrode. did.

(Comparative Example 12)
A nonaqueous electrolyte in the same manner as in Example 16 except that the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 was used as the conductive additive for the negative electrode, and acetylene black was used as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 13)
The nonaqueous electrolyte was the same as in Example 16, except that acetylene black was used as the conductive additive for the negative electrode and the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 was used as the conductive additive for the positive electrode. A secondary battery was produced.

(Comparative Example 14)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 16 except that the carbon material containing 20.0 wt% of boron produced in Comparative Synthesis Example 2 was used as the conductive auxiliary material for both the negative electrode and the positive electrode. did.

(Measurement of cycle characteristics)
The batteries of Examples 1 to 18 and Comparative Examples 1 to 14 were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko Corporation), and 25 ° C., 50 mA constant current charge, and 50 mA constant current discharge were repeated 100 times. The charge end voltage and discharge end voltage of Examples 1 to 15 and Comparative Examples 1 to 7 are 3 V and 1 V, respectively, and the charge end voltage and discharge end voltage of Examples 16 to 18 and Comparative Examples 8 to 14 are 4 V, respectively. And 2V. The cycle stability index was the value of the 100th discharge capacity when the first discharge capacity was 100. The results of Examples 1 to 15 and Comparative Examples 1 to 7 are shown in Table 1, and the results of Examples 16 to 18 and Comparative Examples 8 to 14 are shown in Table 2.

  As apparent from Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 to 15 of the present invention have improved cycle stability as compared with the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 7. Further, as is clear from Table 2, the non-aqueous electrolyte secondary batteries of Examples 16 to 18 of the present invention have improved cycle stability than the non-aqueous electrolyte secondary batteries of Comparative Examples 8 to 14.

Claims (6)

A nonaqueous electrolyte secondary battery comprising a negative electrode, a positive electrode, a separator, and a nonaqueous electrolyte,
The negative electrode contains lithium titanate as a compound in which desorption and insertion of lithium ions proceeds as an active material at 0.3 V (vs. Li + / Li) or more and 2.0 V (vs. Li + / Li) or less,
The negative electrode includes an active material and a conductive auxiliary, and includes 1 to 30 parts by weight of a conductive auxiliary with respect to 100 parts by weight of the active material,
The conductive aid of the negative electrode is a carbon material containing 0.1 wt% or more and 10 wt% or less of boron, and is one type selected from the group consisting of vapor grown carbon fiber, carbon nanotube, acetylene black, and ketjen black Ri carbon material der of the above,
The positive electrode includes an active material and a conductive additive, and includes 1 to 30 parts by weight of a conductive auxiliary with respect to 100 parts by weight of the active material,
The conductive auxiliary of the positive electrode is a carbon material containing 0.1 wt% or more and 10 wt% or less of boron, and one kind selected from the group consisting of vapor grown carbon fiber, carbon nanotube, acetylene black, and ketjen black A non-aqueous electrolyte secondary battery, which is the above carbon material . The nonaqueous electrolyte secondary battery according to claim 1 , wherein the lithium titanate has a spinel structure. The positive electrode includes a lithium manganese compound as an active material, a nonaqueous electrolyte secondary battery according to any one of claims 1-2. The lithium manganese compound is Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is an element belonging to Group 2-13 and the third and fourth periods) The nonaqueous electrolyte secondary battery of Claim 3 which is a compound represented by these. M contained in the Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is an element belonging to Groups 2-13, 3rd, 4th period) The nonaqueous electrolyte secondary battery according to claim 4 , wherein is at least one selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe, and Cr. An assembled battery formed by connecting a plurality of the nonaqueous electrolyte secondary batteries according to any one of claims 1 to 5 .