JP2013098034A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery offering excellent cycle stability.SOLUTION: The nonaqueous electrolyte secondary battery includes a negative electrode composed of lithium titanate; a nonaqueous electrolyte that contains a phosphate with a substituent, which is typically an alkyl group such as a 2H-hexafluoroisopropyl group or a 2,2,2-trifluoroethyl group; and a positive electrode that contains Li1+xMyMn2-x-yO4, where 0≤x≤0.2, 0<y≤0.6, and M represents an element that belongs to one of groups 2-13, and period 3 or 4.

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. However, the conventional non-aqueous electrolyte secondary battery has a problem that when the charge / discharge cycle is repeated, the negative electrode made of the carbon-based material deteriorates due to the volume change accompanying the insertion / extraction of lithium, and the capacity of the battery decreases. In order to solve this problem, a non-aqueous electrolyte using a lithium titanate having a spinel structure, which is a robust material with almost no volume change due to insertion / extraction of lithium as a negative electrode material, as in Non-Patent Document 1. Secondary batteries have been proposed. However, when lithium titanate is repeatedly charged and discharged, gas may be generated due to reaction with the electrolytic solution and cycle stability may be deteriorated.

Chemistry Letters, 35, 848 (2006)

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

  In view of the above circumstances, as a result of repeated studies by the present inventors, it has been found that a nonaqueous electrolyte secondary battery excellent in cycle stability can be obtained by including a phosphate ester compound in a nonaqueous electrolyte. The invention has been completed.

  That is, the present invention is a nonaqueous electrolyte secondary battery comprising a negative electrode made of lithium titanate, a positive electrode, a separator, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is represented by the following general formula (1);

Wherein each R ¹ , R ² and R ³ is a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C4-C20 heteroaryl group. Represents a C7 to C20 aralkyl group and a C4 to C20 heteroaralkyl group, which may be the same as or different from each other.Alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aralkyl group and hetero The aralkyl group may have a substituent.) The present invention relates to a nonaqueous electrolyte secondary battery containing a phosphate ester compound represented by:

  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, at least one of R ¹ , R ² and R ³ in the general formula (1) is a C1-C20 alkyl group (which may have a substituent). It is preferable that

In the nonaqueous electrolyte secondary battery of the present invention, R ¹ , R ² and R ³ in the general formula (1) are all 2H-hexafluoroisopropyl groups or 2,2,2-trifluoroethyl groups. It is more preferable.

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 2). It is preferably a compound represented by a group 13 and an element belonging to the third to fourth periods.

In the non-aqueous electrolyte secondary battery of the present invention, Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group of 2 to 13 and the third group. It is preferable that M contained in ˜4 period elements 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.

  An embodiment of the present invention will be described as follows. The present invention is not limited to the following description.

  The nonaqueous electrolyte secondary battery of the present invention has a negative electrode containing lithium titanate as a negative electrode active material.

Examples of the lithium titanate, those represented with _Li 4 _Ti 5 _{O 12} as the molecular formula is preferred. In the case of a spinel structure, the expansion and contraction of the active material in the reaction of insertion / extraction of lithium ions is small, which is particularly preferable. 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 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.

  In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode is not particularly limited, but preferably includes a lithium manganese compound as the positive electrode active material.

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 a 3-4 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.

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. It is preferable that at least one of them 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.

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. At least one kind) preferably has a half width of (400) plane of powder X-ray diffraction by CuKα of 0.5 ° or less. 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.

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. At least one kind) 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.

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 particle size of at least one kind is preferably from 0.5 μm to 50 μm, and more preferably from 1 μm to 30 μm 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.

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 specific surface area of at least one selected from the range of 0.1 m ² / g or more and 50 m ² / g or less is preferable because a desired output density is easily obtained. The specific surface area can be calculated by measurement by the BET method.

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 bulk density of at least one selected from the above 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.

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. Can be obtained by heat-treating a lithium compound, a manganese compound, and a compound of M at 500 ° C. or higher and 1500 ° C. or lower. 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. The heat treatment may be performed by mixing a lithium compound, a manganese compound, and a compound of M, or may be heat-treated with a lithium compound after heat-treating the manganese compound and the M compound. 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.

  The compounding ratio of the lithium compound, the manganese compound and the compound of M is such that the atomic ratio of lithium, manganese and M is 1 + x (lithium), 2-xy (manganese), and y (M), respectively, where 0 ≦ x ≦ It is selected in a range satisfying 0.2, 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.

  On the surface of the negative electrode active material and / or the positive electrode active material of the present invention (hereinafter sometimes simply referred to as “active material”), a carbon material, a metal oxide, Alternatively, it may be covered with a polymer or the like.

  The conductive aid that can be used in the negative electrode and / or positive electrode (hereinafter sometimes simply referred to as “electrode”) of the present invention is not particularly limited, but a carbon material is preferred. 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.

  In the present invention, the amount of the conductive additive contained in each 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 active material. 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.

  The binder that can be used in the electrode of the present invention is not particularly limited, but for example, at least selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof. One type can be used. The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of ease of production of the 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 each 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 active material. If it is the said range, the adhesiveness of an active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.

  The electrode of the present invention is produced by applying a mixture of an active material, a conductive additive and a binder onto a current collector. From the ease of the production method, a slurry is produced by using the above mixture and solvent. A method is preferred in which the electrode is prepared by removing the solvent after coating the resulting slurry on the current collector.

A current collector that can be used for the electrode of the present invention is a metal material 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 preferable, and aluminum is particularly preferable because of 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.

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

  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, it may be difficult to handle from the viewpoint of production, and if it is thicker than 100 μm, it may be disadvantageous from an economic viewpoint.

  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 active material, the conductive additive, the binder, and the solvent can be uniformly mixed. Although the preparation of the slurry is not particularly limited, the slurry may be prepared by mixing the active material, the conductive additive, and the binder and then adding the solvent, or the active material, the conductive additive, the binder, and the solvent may be mixed together. May be produced.

  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 electrode on the current collector is not particularly limited. For example, there is 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 room temperature or high temperature air, an inert gas, and a vacuum state. Although the temperature which removes a solvent is not specifically limited, It is preferable that they are 60 degreeC or more and 250 degrees C or less. 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. After producing the electrode, the electrode may be compressed using a roll press or the like.

  In the present invention, the thickness of the electrode is preferably 10 μm or more and 200 μm or less. If it is less than 10 μm, it may be difficult to obtain a desired capacity, 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 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 active material and the conductive additive becomes insufficient, and the electronic conductivity may be lowered. When it is larger than 4.0 g / cm ³ , an electrolyte solution described later hardly penetrates into the electrode, and lithium conductivity may be lowered. The 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.

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.

In this invention, it is preferable that the electrical capacitance per 1 cm < ² > of a positive electrode is 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, whereas when it exceeds 3.0 mAh, it tends to be difficult to obtain a desired output density.

The calculation of the electric capacity per 1 cm ² of each of the negative electrode and the positive electrode can be performed by measuring charge / discharge characteristics after preparing each electrode and then preparing a half battery using lithium metal as a counter electrode.

The electric capacity per 1 cm ^{2 of the} electrode is not particularly limited, but can be controlled by a method of controlling by the weight of the electrode formed per current collector unit area, for example, the coating thickness at the time of electrode coating described above.

  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, and when the thickness is more than 100 μm, the battery resistance may be increased. From the viewpoint of economy and handling, it is more preferably 15 μm or more and 50 μm or less.

  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 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, 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. For example, dimethyl carbonate and ethylene carbonate are exemplified as a preferred combination. 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.

  The nonaqueous electrolyte of the nonaqueous electrolyte secondary battery of the present invention contains a phosphate compound represented by the following general formula (1).

R ¹ , R ² and R ³ in the general formula (1) are each a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C4-C20 A heteroaryl group, a C7 to C20 aralkyl group, or a C4 to C20 heteroaralkyl group may be the same or different. The alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aralkyl group and heteroaralkyl group herein may have a substituent. In the present invention, “may have a substituent” means that the hydrogen atom 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 specifically, a hydroxyl group, an alkyl group, an alkoxyl group, an alkylthio group, a nitro group, a nitroxy group, an amino group, a cyano group, A carboxyl group, a halogen atom, an oxygen atom, a nitrogen atom, etc. are mentioned.

  The C1-C20 alkyl group is not particularly limited, but for example, methyl group, hydroxymethyl group, 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, trifluoromethyl group, pentafluoroethyl group, Examples include 2,2-trifluoroethyl group, 1H, 1H-heptafluorobutyl group, 2H-hexafluoroisopropyl group, trifluoromethyl group, pentafluoroethyl group, perfluoro-t-butyl group.

  Examples of the C2-C20 alkenyl group include a vinyl group, a propenyl group, a styryl 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 C4-C20 heteroaryl group include pyrrolinyl, pyridyl, quinolyl, imidazolyl, furyl, indolyl, thienyl, oxazolyl, thiazolyl, 2-phenylthiazolyl, 2-anisylthia Examples include a zolyl group.

  Examples of the C7 to C20 aralkyl group include benzyl group, chlorobenzyl group, bromobenzyl group, salicyl group, α-hydroxybenzyl group, phenethyl group, α-hydroxyphenethyl group, naphthylmethyl group, anthracenylmethyl group, A 3,5-difluorobenzyl group, a trityl group, etc. are mentioned.

Examples of the C4 to C20 heteroaralkyl group include a pyridylmethyl group, a difluoropyridylmethyl group, a quinolylmethyl group, an indolylmethyl group, a furfuryl group, and a thienylmethyl group. Alternatively, ^{two of} R ¹ , R ² and R ³ may be combined to form a ring, and examples thereof include a cyclohexyl group and a phenyl group.

In the battery having the electrode configuration according to the present invention, in order to obtain better cycle stability, at least one of R ¹ , R ² and R ³ is a C1-C20 alkyl group (even if it has a substituent). Preferably a C1-C20 fluoroalkyl group. Specifically, methyl group, ethyl group, cyanoethyl group, 2,2,2-trifluoroethyl group, 1H, 1H-heptafluorobutyl group, 2H-hexafluoroisopropyl group, trifluoromethyl group, pentafluoroethyl group And a perfluoro-t-butyl group. Of these, 2,2,2-trifluoroethyl group and 2H-hexafluoroisopropyl group are preferable.

  The concentration of the phosphate ester compound represented by the formula (1) is not particularly limited as long as it does not adversely affect the battery characteristics. When the phosphate ester compound can dissolve the solute, the phosphate ester compound itself may be used as a non-aqueous solvent. That is, what melt | dissolved the said solute in the phosphate ester compound itself can be used as a non-aqueous electrolyte. When the solute is dissolved in a mixture of the non-aqueous solvent and the phosphoric ester compound to obtain a non-aqueous electrolyte, the weight ratio of the non-aqueous solvent to the phosphoric ester compound is as follows: Phosphate ester compound is preferably in the range of 1: 0.005 to 1: 3, and in order to obtain more stable battery characteristics, non-aqueous solvent: phosphate ester compound = 1: 0.005 to 1: 2. It is particularly preferable that the range is

  The phosphate ester compound is preferably mixed with a non-aqueous solvent in advance as described above, and the solute is dissolved in the obtained mixed solution to form a non-aqueous electrolyte, thereby producing a non-aqueous electrolyte secondary battery. In particular, the method of the nonaqueous electrolyte is not limited. Moreover, the phosphoric acid ester compound to be used may be one type, and may mix 2 or more types.

  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 are opposed, 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 become the deposition potential of lithium during overcharge. On the other hand, when B / A is greater than 1.2, a negative electrode active material that does not participate in the battery reaction is present. Side reactions may occur due to the large amount.

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.

(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.

100 parts by weight of the prepared positive electrode active material, 6.8 parts by weight of conductive additive (acetylene black), and 6.8 parts by weight of PVdF (solid content concentration 12 wt%, NMP solution) as a binder were mixed to prepare a slurry. Produced. After applying this slurry to an aluminum foil (20 μm), a positive electrode (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.

As described above, a positive 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). 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 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 the prepared negative electrode active material, 6.8 parts by weight of conductive additive (acetylene black), and 6.8 parts by weight of PVdF (solid content concentration 12 wt%, NMP solution) as a binder were mixed. A slurry was prepared. This slurry was applied to an aluminum foil (20 μm), and then vacuum dried at 150 ° C. to prepare a negative electrode (50 cm ² ).

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

A negative electrode was coated on 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). %, 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). 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 .

(Production of phosphate ester compounds)
The boric acid ester compound in the present invention was synthesized by a dehydration condensation reaction of phosphoryl chloride and an alcohol corresponding to the method described in the literature (Journal of The Electrochemical Society, 158 (3), A337 (2011)).

(Manufacture of non-aqueous electrolyte secondary batteries)
A non-aqueous electrolyte secondary battery was produced as follows.

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). A cellulose nonwoven fabric (25 μm, 55 cm ² ) was used for 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. Nonaqueous electrolyte is a mixture of ethylene carbonate / dimethyl carbonate = 3: 7 (vol ratio) mixed with nonaqueous solvent and tri (2H-hexafluoroisopropyl) phosphate so that the weight ratio is 1: 0.01. And LiPF ₆ was dissolved at a concentration of 1 mol / L. After 2 mL of the obtained nonaqueous electrolyte was added, the 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 tri (2,2,2-trifluoroethyl phosphate) was used as the phosphoric ester compound.

A mixed nonaqueous solvent of ethylene carbonate / dimethyl carbonate = 3: 7 (vol ratio) and tri (2H-hexafluoroisopropyl) phosphate were mixed with the nonaqueous electrolyte so that the weight ratio was 1: 0.2. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a material prepared by dissolving LiPF ₆ at a concentration of 1 mol / L was used.

As a positive electrode active material, LiNi _0.5 Mn _1.5 O ₄ was produced 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, this mixture was heated at 550 ° C. in an air atmosphere, and then heated again at 750 ° C. to prepare LiNi _0.5 Mn _1.5 O ₄ .

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the produced LiNi _0.5 Mn _1.5 O ₄ 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 tri (2H-hexafluoroisopropyl) phosphate was not added to the nonaqueous electrolyte.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 4 except that tri (2H-hexafluoroisopropyl) phosphate was not added to the nonaqueous electrolyte.

(Measurement of cycle characteristics)
The nonaqueous electrolyte secondary batteries produced in the examples and comparative examples were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko), and 55 ° 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 3 and Comparative Example 1 at this time are 3 V and 2 V, respectively, and the charge end voltage and discharge end voltage of Example 4 and Comparative Example 2 are 3.5 V, respectively. And 2.5V. Table 1 shows the 100th discharge capacity when the first discharge capacity is 100.

  As is apparent from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 of the present invention have improved cycle stability as compared with the nonaqueous electrolyte secondary batteries of Comparative Examples 1 and 2.

Claims (8)

A nonaqueous electrolyte secondary battery comprising a negative electrode made of lithium titanate, a positive electrode, a separator, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is represented by the following general formula (1);

Wherein each R ¹ , R ² and R ³ is a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C6-C20 aryl group, a C4-C20 heteroaryl group. Represents a C7 to C20 aralkyl group and a C4 to C20 heteroaralkyl group, which may be the same as or different from each other.Alkyl group, alkenyl group, alkynyl group, aryl group, heteroaryl group, aralkyl group and hetero The aralkyl group may have a substituent.) A nonaqueous electrolyte secondary battery containing a phosphate ester compound represented by:   The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium titanate has a spinel structure.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode contains a lithium manganese compound as an active material. Formula (1) ^R 1, at least one of ^{R 2} and ^{R 3} in an alkyl group C1 to C20 (which may have a substituent.), One of the claims 1 to 3 one The nonaqueous electrolyte secondary battery according to item. Both the general formula in (1) of ^R 1, ^{R 2} and ^{R 3} are 2H- hexafluoroisopropyl group or 2,2,2-trifluoroethyl group, to any one of claims 1-4 The nonaqueous electrolyte secondary battery as described. 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 3rd to 4th periods) The nonaqueous electrolyte secondary battery according to any one of claims 3 to 5, which is a compound represented. M contained in 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 to fourth periods) The nonaqueous electrolyte secondary battery according to claim 6, which 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 7.