JP2016207314A - Nonaqueous electrolyte secondary battery and battery pack thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery using a titanium-containing oxide as a negative electrode active material, which is little in the generation of gas during cycle operations and exhibits excellent cycle stability.SOLUTION: A nonaqueous electrolyte secondary battery of the present invention includes a negative electrode, a positive electrode, and a nonaqueous electrolyte interposed between the negative electrode and the positive electrode. The negative electrode includes a titanium-containing oxide as a negative electrode active material. The nonaqueous electrolyte contains a salt having a silsesquioxane structure. The content of the salt having a silsesquioxane structure is 0.01 wt.% or more with respect to 100 wt.% of the nonaqueous electrolyte.SELECTED DRAWING: None

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and its assembled battery.

In recent years, research and development of non-aqueous electrolyte secondary batteries used for portable devices, hybrid cars, electric cars, and household power storage have been actively conducted. Nonaqueous electrolyte secondary batteries used in these fields include lithium-containing cobalt composite oxides and lithium-containing nickel composite oxides as positive electrode active materials, carbon-based materials as negative electrode active materials, LiBF ₄ , LiPF _{6 and the} like as electrolyte solutions. Non-aqueous electrolytes in which lithium salts are dissolved in organic solvents are used, and research is ongoing to simultaneously satisfy multiple characteristics such as high capacity and high output. Furthermore, in recent years, heat generation and ignition phenomena of batteries have been reported, and development of batteries having higher safety than before has been demanded.

  A non-aqueous electrolyte secondary battery using a titanium-containing oxide such as lithium titanate or titanium dioxide as a negative electrode active material applied to a negative electrode current collector foil has been developed to satisfy such characteristics. (For example, patent document 1). However, in non-aqueous electrolyte secondary batteries using a titanium-containing oxide as the active material for the negative electrode, gas is generated due to the decomposition of the electrolyte due to the abnormally active sites on the active material surface during the charge / discharge cycle. Therefore, there is a problem that the battery swells and the battery characteristics deteriorate.

  In Patent Document 2, in a lithium ion secondary battery in which a nonaqueous electrolyte is supplied in a battery case, silsesquioxane is included in the nonaqueous electrolyte, and silsesquioxane and There is a description relating to suppressing a decrease in battery capacity when charging / discharging is repeated by the presence of the reaction product. However, since silsesquioxane itself generally has low solubility in organic solvents, it is considered that silsesquioxane that is not dissolved in the electrolyte solution causes deterioration in characteristics when the addition amount is large, and improvement is necessary. .

Japanese Patent No. 3502118 Japanese Patent No. 2014-093158

  The problem to be solved by the present invention is that in a non-aqueous electrolyte secondary battery using a titanium-containing oxide as a negative electrode active material, there is little gas generation during cycle operation and the non-aqueous electrolyte secondary battery exhibiting excellent cycle stability. The next battery is to provide.

  As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, the use of a titanium-containing oxide for the negative electrode and the addition of a salt having a silsesquioxane structure to the non-aqueous electrolyte results in ionicity on the electrode surface. A protective layer is formed, enabling efficient exchange of lithium ions, while suppressing gas generation due to decomposition of the solvent due to abnormally active sites on the active material surface, allowing both output characteristics and cycle characteristics to be compatible As a result, the present invention has been completed.

  In the present invention, since the silsesquioxane added to the non-aqueous electrolyte is a salt containing an anion and / or a salt having an ionic functional group, the above-mentioned protective film has high solubility in an electrolytic solution. Formation is performed effectively, and the effect of suppressing gas generation and preventing deterioration of battery characteristics is exhibited.

  That is, the present invention is a secondary battery comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte interposed between the negative electrode and the positive electrode, wherein the negative electrode includes a titanium-containing oxide as a negative electrode active material, The non-aqueous electrolyte contains a salt having a silsesquioxane structure, and the salt having the silsesquioxane structure is 0.01% by weight or more with respect to 100% by weight of the non-aqueous electrolyte. The present invention relates to a non-aqueous electrolyte secondary battery.

  Moreover, it is preferable that the said silsesquioxane structure can be represented by the following formula | equation (1).

  In the above formula, R may be the same or different, and each is a hydrogen atom or an organic group having 1 to 12 carbon atoms in which a hydrogen atom or a carbon atom may be substituted with another element. , N is an integer of 1-10.

  The salt having the silsesquioxane structure preferably has a cage silsesquioxane structure.

  The salt having the silsesquioxane structure preferably includes a halogen anion in the molecule.

  Moreover, it is preferable that at least one of the R has a polymerizable functional group and / or an ionic functional group.

  The titanium-containing oxide is preferably lithium titanate and / or titanium dioxide.

Further, in the positive electrode, the positive electrode active material is Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is 2 to 13 and It is preferable to include a spinel type lithium manganate represented by at least one selected from the group consisting of elements belonging to four periods.

  The present invention also relates to an assembled battery formed by connecting a plurality of the nonaqueous electrolyte secondary batteries.

  According to the present invention, a non-aqueous electrolyte secondary battery that does not generate gas during a charge / discharge cycle and has excellent cycle stability can be obtained.

  An embodiment of the present invention will be described as follows, but the present invention is not limited to this.

  The nonaqueous electrolyte secondary battery of the present invention can be a lithium ion battery comprising a negative electrode, a positive electrode, a separator, a nonaqueous electrolyte, and an exterior material. Each of the positive electrode and the negative electrode is formed with an active material layer containing an active material capable of inserting and removing lithium ions, and charging and discharging of the lithium ion secondary battery of the present invention by this insertion and removal. Is done.

<1. Negative electrode>
In the negative electrode used in the nonaqueous electrolyte secondary battery of the present invention, a negative electrode active material layer containing at least a negative electrode active material is formed on both surfaces of a metal current collector. Titanium-containing oxide is included as a negative electrode active material. As the titanium-containing oxide, lithium titanate and / or titanium dioxide are preferable. Among these, lithium titanate is more preferable because of high stability of the material itself, and spinel-structured lithium titanate is particularly preferable from the viewpoint of small expansion and contraction of the active material in the reaction of insertion / extraction of lithium ions. Lithium titanate may contain a small amount of elements other than lithium such as Nb and titanium, for example.

  Examples of titanium dioxide include B-type titanium dioxide, anatase-type titanium dioxide, and ramsdellite-type titanium dioxide. B-type titanium dioxide is preferred because of its low irreversible capacity and excellent cycle stability. .

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

  One type of titanium-containing oxide may be used, or two or more types may be used in combination.

  The titanium-containing oxide according to the present invention may have an average particle size of 1 μm or more and 20 μm or less from the viewpoint of suppressing side reactions, but preferably 2 μm or more and 15 μm or less from the viewpoint of cycle characteristics. Preferably, they are 3 micrometers or more and 10 micrometers or less.

The titanium-containing oxide according to the present invention may have a specific surface area of 1 m ² / g or more and 25 m ² / g or less, and since it exhibits good cycle characteristics, 1.5 m ² / g or more. 20 m ² / g or less is preferable, and from the balance with suppression of side reactions, 2 m ² / g or more and 15 m ² / g or less are more preferable.

  The negative electrode of the present invention may contain a conductive additive, and the conductive additive is not particularly limited, but a metal material and a carbon material are preferable. Examples of the metal material include copper and nickel, and examples of the carbon material include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These conductive aids may be used alone or in combination of two or more. In the present invention, the amount of the conductive additive contained in the negative electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. If it is the said range, the electroconductivity of a negative electrode will be ensured. Moreover, the adhesiveness with the below-mentioned binder is maintained and sufficient adhesiveness with a collector can be obtained.

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

  The negative electrode of the present invention is produced by forming a mixture of a negative electrode active material, a conductive additive, and a binder on a current collector. From the ease of the production method, a slurry is produced with the above mixture and solvent, A method is preferred in which the obtained slurry is applied on a current collector and then the solvent is removed.

  The current collector that can be used in the negative electrode of the present invention is preferably copper, SUS, nickel, titanium, aluminum, or an alloy thereof. The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. As the current collector, a metal material (copper, SUS, nickel, titanium, and alloys thereof) coated with a metal that does not react with the potential of the negative electrode can be used.

  In the present invention, the thickness of the negative electrode is not particularly limited, but is preferably 10 μm or more and 200 μm or less.

In the present invention, the density of the negative electrode is preferably 1.0 g / cm ³ or more and 3.0 g / cm ³ or less, has sufficient contact with the negative electrode active material and the conductive additive, and will be described later as a non-aqueous electrolyte. Is more preferable to be 1.3 g / cm ³ or more and 2.7 g / cm ³ or less, and the contact with the negative electrode active material and the conductive additive and the penetration into the negative electrode of the nonaqueous electrolyte. The balance of easiness is most preferably 1.5 g / cm ³ or more and 2.5 g / cm ³ or less.

  The density of the negative electrode can be controlled by compressing the electrode to a desired thickness. Although the said 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 positive electrode described later is formed.

  The density of the negative electrode can be calculated from the thickness and weight of the negative electrode active material layer.

<2. Positive electrode>
In the positive electrode used in the nonaqueous electrolyte secondary battery of the present invention, a positive electrode active material layer containing at least a positive electrode active material is formed on both surfaces of a metal current collector. It does not specifically limit as a positive electrode active material, A metal oxide, lithium transition metal complex oxide, etc. can be used. Among these, Li _{1 + x} M _y M _n2−xy O 4 (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group of 2 to 13 and shows good cycle characteristics. Spinel-type lithium manganate represented by at least one selected from the group consisting of elements belonging to the third to fourth periods is preferable. Li _{1 + x} M _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, M is a group consisting of elements belonging to Groups 2 to 13 and belonging to the 3rd to 4th periods. The spinel-type lithium manganate represented by (at least one selected) has a large effect of improving the stability of the positive electrode active material itself, and therefore the element belonging to Group 2-13 and belonging to the 3rd to 4th period is Al. Mg, Zn, Ni, Co, Fe, Ti, Cu, Zr, and Cr are preferable, Al, Mg, Zn, Ni, Ti, and Cr are more preferable, and the effect of improving the stability of the positive electrode active material itself is particularly large. Therefore, Al, Mg, Zn, Ti and Ni are particularly preferable.

Among these, in combination with the non-aqueous electrolyte will be described later, the gas generation decreases, and since the effect of the higher voltage of the charge voltage is _{high, Li 1 + x Al y Mn} 2-x-y O 4 (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Mg _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Zn _y Mn _{2− x-y O 4 (0 ≦} x ≦ 0.1,0 <y ≦ 0.1), Li 1 + x Cr y Mn 2-x-y O 4 (0 ≦ x ≦ 0.1,0 <y ≦ 0. 1) Li _{1 + x} Ni _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.05, 0.45 ≦ y ≦ 0.5), Li _{1 + x} Ni _yz Al _z Mn _2−xy O ₄ (0 ≦ x ≦ 0.05,0.45 ≦ y ≦ 0.5,0.005 ≦ z ≦ 0.03), and _{Li 1 + x Ni y-z} Ti z Mn 2-x Preferably one selected from _{y O 4 (0 ≦ x ≦} 0.05,0.45 ≦ y ≦ 0.5,0.005 ≦ z ≦ 0.03), greater effect can be _{obtained, Li 1} + x Al _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.1, 0 <y ≦ 0.1), Li _{1 + x} Mg _y Mn _2−xy O ₄ (0 ≦ x ≦ 0.1, 0 < _{y ≦ 0.1), Li 1 +} x Ni y Mn 2-x-y O 4 (0 ≦ x ≦ 0.05,0.45 ≦ y ≦ 0.5), and _{Li 1 + x Ni y-z} Ti z Mn 2 _{-x-y O 4 (0 ≦} x ≦ 0.05,0.45 ≦ y ≦ 0.5,0.005 ≦ z ≦ 0.03) is particularly preferred.

  What is necessary is just to select suitably from these considering the combination with a negative electrode active material. A plurality of positive electrode active materials may be used in combination.

  The surface of the positive electrode active material used in the present invention may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.

  The positive electrode of the present invention may contain a conductive additive. Although it does not specifically limit as a conductive support material, A carbon material is preferable. Examples thereof include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These carbon materials may be used alone or in combination of two or more. The amount of the conductive additive contained in the positive electrode of the present invention is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. If it is the said range, the electroconductivity of a positive electrode is ensured. Moreover, the adhesiveness with the below-mentioned binder is maintained and sufficient adhesiveness with a collector can be obtained.

  The positive electrode of the present invention may contain a binder. The binder is not particularly limited, and for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, 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 positive electrode. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. You may add a dispersing agent and a thickener to these. The amount of the binder contained in the positive electrode of the present invention is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. If it is the said range, the adhesiveness of a positive electrode active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.

  The positive electrode of the present invention is produced by forming a mixture of a positive electrode active material, a conductive additive, and a binder on a current collector. From the ease of the production method, a slurry is produced with the above mixture and solvent, A method is preferred in which the obtained slurry is applied on a current collector and then the solvent is removed. Conventionally known conditions and methods may be used to prepare the slurry. Moreover, what is necessary is just to use a conventionally well-known condition and method also about coating and solvent removal.

  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 thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. 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.

  The thickness of the positive electrode of the present invention is not particularly limited, but is preferably 10 μm or more and 200 μm or less.

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, has sufficient contact with the positive electrode active material and the conductive additive, and has a nonaqueous electrolyte described later. Since it is easy to penetrate into the positive electrode, 1.5 g / cm ³ or more and 3.5 g / cm ³ or less are more preferable, contact with the positive electrode active material and conductive additive, and penetration of the nonaqueous electrolyte into the positive electrode. It is particularly preferably 2.0 g / cm ³ or more and 3.0 g / cm ³ or less, where the balance of ease is most achieved.

  The density of the positive electrode can be controlled by compressing the electrode to a desired thickness. Although the said 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 negative electrode is formed.

  The density of the positive electrode can be calculated from the thickness and weight of the positive electrode active material layer.

<3. Separator>
The separator used for the non-aqueous electrolyte secondary battery of the present invention may be any structure as long as it is installed between the positive electrode and the negative electrode described above and has an insulating property and can contain the non-aqueous electrolyte described later. Polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, polyethylene terephthalate, and composites of two or more of them, woven fabrics, nonwoven fabrics, microporous membranes, and the like.

  The separator may contain various plasticizers, antioxidants, flame retardants, and may be coated with a metal oxide or the like.

  The thickness of the separator is not particularly limited, but is preferably 10 μm or more and 100 μm or less, and more preferably 15 μm or more and 50 μm or less.

  The separator has a porosity of preferably 30% or more and 90% or less, more preferably 35% or more and 85% or less from the viewpoint of ensuring the diffusibility of lithium ions and preventing short circuit. Since balance is particularly excellent, 40% or more and 80% or less are particularly preferable.

<4. Non-aqueous electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is interposed between the negative electrode and the positive electrode, and has a function of mediating ion transmission therebetween.

  The non-aqueous electrolyte contains a salt having a silsesquioxane structure in an amount of 0.01% by weight or more with respect to 100% by weight of the non-aqueous electrolyte. As a result, an ionic protective layer is formed on the electrode surface, enabling efficient transfer of lithium ions, while suppressing gas generation due to decomposition of the solvent due to abnormally active sites on the surface of the active material. It is possible to achieve both characteristics and cycle characteristics.

  The nonaqueous solvent used for the nonaqueous electrolyte 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 in combination of two or more.

Lithium salts used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), Li [N (SO ₂ CF ₃ ) ₂ ], Li [N N (SO ₂ C ₂ F ₅ ) ₂ ], Li [N (SO ₂ F) ₂ ], Li [N (CN) ₂ ], and the like can be given. LiClO ₄ , LiBF ₄ , LiPF ₆ , Li [N (SO ₂ F) ₂ ], and Li [N (CN) ₂ ] are preferable because of high solubility and good cycle characteristics.

  The concentration of the lithium salt is preferably 0.5 mol / L or more and 2.0 mol / L or less.

  The silsesquioxane structure is represented by the following formula (1).

  In the above formula, R may be the same or different, and each is a hydrogen atom or an organic group having 1 to 12 carbon atoms in which a hydrogen atom or a carbon atom may be substituted with another element. , N is an integer of 1-10.

  In the above formula (1), R represents a hydrogen atom; an alkyl group such as a methyl group or an ethyl group; an alkenyl group such as a vinyl group or an allyl group; an alkynyl group such as an ethynyl group or a propynyl group; a cyclohexyl group or a norbornanyl group; An aryl group such as a phenyl group which may have an alkyl group; a trialkylsilyl group such as a trimethylsilyl group; a trialkylsiloxy group such as a trimethylsiloxy group; bonded to a carbon atom of these functional groups Examples include a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, a trifluoromethylphenyl group, etc., in which part or all of the hydrogen atoms are substituted with a halogen atom, a cyano group, or the like. From the viewpoint of gas suppression, at least one of R is preferably a polymerizable functional group. As for carbon number of these functional groups, 2-8 are preferable from a soluble viewpoint. Examples of the polymerizable functional group in R include a vinyl group, an allyl group, a styryl group, and an acryloyl group. A vinyl group and an allyl group are preferable from the viewpoint of cycle characteristics, and a vinyl group is particularly preferable from the viewpoint of gas suppression.

  Further, n in the above formula is preferably 2 to 8 from the viewpoint of cycle characteristics, and 4 or 5 is particularly preferable from the viewpoint of gas suppression.

  The silsesquioxane structure is not particularly limited, and may be a cage type, a ladder type, or a random type, or a mixture of two or more types. Among these, a cage type or a ladder type is preferable from the viewpoint of cycle characteristics, and a cage type is particularly preferable from the viewpoint of gas suppression.

  The cage silsesquioxane (T8) with n = 4 is represented by the following formula (2).

  Moreover, as cage-type silsesquioxane (T10) of n = 5, it represents with the following formula | equation (3).

  The salt having a silsesquioxane structure preferably includes an anion in the molecule. The anion to be included is not particularly limited, but a halide ion is preferable from the viewpoint of the stability of the inclusion state, and a fluoride ion is particularly preferable because of a good balance of performance. When the salt having the silsesquioxane structure includes an anion in the molecule, it has a counter cation, but is not particularly limited, and is not limited to alkali metal ions, alkaline earth metal ions, tetraalkylammonium ions, tetraalkyls. Examples thereof include phosphonium ions and imidazolium ions. From the viewpoint of output characteristics and solubility, lithium ion, sodium ion, magnesium ion, tetraalkylammonium ion and imidazolium ion are preferable. Tetraalkylammonium ions, tetraalkylphosphonium ions, and imidazolium ions may be contained in R.

  When the salt having the silsesquioxane structure does not include an anion in the molecule, at least one of the R has an ionic functional group.

  Examples of the ionic functional group in R include a cationic tetraalkylammonium group, an imidazolium group, a tetraalkylphosphonium group; an anionic phosphate group, a carboxylate group, and a nitrate group. From the viewpoint of cycle characteristics, a cationic functional group is preferable, and from the viewpoint of gas suppression, a tetraalkylammonium group and an imidazolium group are particularly preferable. When R has an ionic functional group, the counter ion is not particularly limited, but as a cation, an alkali metal ion, an alkaline earth metal ion, a tetraalkylammonium ion, a tetraalkylphosphonium ion, an imidazolium ion Examples of the anion include amide anion, perchlorate ion, tetrafluoroborate ion, hexafluorophosphate ion, and trifluoromethylsulfonate ion.

  The amount of the salt having a silsesquioxane structure may be 0.01% or more with respect to 100% by weight of the non-aqueous electrolyte, but is preferably 0.05% or more and 10% or less from the viewpoint of cycle characteristics, and the most balanced Is preferably 0.1% or more and 5% or less.

  The nonaqueous electrolyte may be included in the positive electrode, the negative electrode, and the separator in advance, or may be added after laminating a separator disposed between the positive electrode and the negative electrode. Further, a gel electrolyte in which a polymer is impregnated with an electrolytic solution in which a solute is dissolved in a nonaqueous solvent can be used.

<5. Exterior material>
As a material of the exterior material according to the present invention, a laminate film that can be sealed by heat sealing, prevents moisture from entering from outside, and conversely prevents leakage of nonaqueous electrolyte from inside. Use. A specific example is a composite film in which a metal foil is provided with a thermoplastic resin layer for heat sealing. The metal foil is not particularly limited as long as it prevents the intrusion of moisture from the outside and improves the strength of the entire sheet, but an aluminum foil can be suitably used from the viewpoint of moisture barrier properties, weight, and cost. If the strength of the entire sheet can be secured, a metal layer may be provided by vapor deposition or sputtering instead of the metal foil.

  The composition of the thermoplastic resin layer is not particularly limited, but polyethylene and polypropylene can be suitably used from the viewpoint of the heat-sealable temperature range and the non-aqueous electrolyte barrier property.

  In order to improve the adhesion between the metal foil and the thermoplastic resin, an adhesive layer may be provided between them, or the surface opposite to the one provided with the thermoplastic resin layer to prevent oxidation of the metal foil. In addition, a protective layer may be provided.

<6. 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.

  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 area of the electrode active material layer in the nonaqueous electrolyte secondary battery of the present invention can be appropriately selected depending on the design of the battery, but it is preferable to satisfy the following formula (4) from the viewpoint of cycle stability and safety.

  However, A shows the area of a positive electrode active material layer, B shows the area of a negative electrode active material layer.

  Moreover, the area ratio between the negative electrode active material layer and the separator is not particularly limited, but it is preferable that the following formula (5) is satisfied.

  However, B shows the area of a negative electrode active material layer, C shows the area of a separator.

   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 (6).

However, in said formula (6), E shows the electrical capacity per 1 cm < ² > of positive electrodes, D shows the electrical capacity per 1 cm < ² > of negative electrodes.

  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.

<7. Battery pack>
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.

(Example of positive electrode production)
As the positive electrode active material used for the positive electrode, spinel type lithium manganate (Li _1.1 Al _0.1 Mn _1.8 O ₄ ) was used.

Spinel type lithium manganate (Li _1.1 Al _0.1 Mn _1.8 O ₄ ), conductive additive (acetylene black), and binder (PVdF) are each 100 parts by weight and 5 parts by weight in solid content concentration. , And 5 parts by weight to prepare a slurry. The binder used was an N-methyl-2-pyrrolidone (NMP) solution adjusted to a solid content concentration of 5 wt%, and the viscosity was adjusted by further adding NMP so as to facilitate the coating described later.

This slurry was coated on an aluminum foil (20 μm) on one side and dried in an oven at 120 ° C., then the back side was coated and dried in the same manner, and further vacuum dried at 170 ° C. to obtain a positive electrode (single side 50 cm ² ). Was made.

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

In the same manner as described above, an electrode coated on one surface of an aluminum foil was punched into a working electrode of 16 mmΦ, and a Li metal was punched out of 16 mmΦ as a counter electrode. Using these electrodes, a working electrode (single-sided coating) / separator / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol). %, LiPF ₆ 1 mol / L) was added to prepare a half cell. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). 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 the capacity of the positive electrode of the discharge capacity. It was. As a result, the capacity of the positive electrode was 1.0 mAh / cm ² .

(Example of negative electrode production)
As the negative electrode active material, spinel type lithium titanate (Li _4/3 Ti _5/3 O ₄ ) having an average particle diameter of 5 μm and a specific surface area of 4 m ² / g was used. The negative electrode active material, the conductive additive (acetylene black), and the binder (PVdF) were mixed at a solid concentration of 100 parts by weight, 5 parts by weight, and 5 parts by weight, respectively, to prepare a slurry. The binder used was an NMP solution prepared with a solid content concentration of 5 wt%, and the viscosity was adjusted by further adding NMP so that it can be easily applied as described below. The slurry was applied to an aluminum foil (20 μm), dried in an oven at 120 ° C., and then vacuum dried at 170 ° C. to prepare a negative electrode (55 cm ² ).

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

An electrode was applied to one side of the aluminum foil under the same conditions as described above, and a working electrode was punched out to 16 mmΦ. Li metal was punched out to 16 mmΦ as a counter electrode. Using these electrodes, a working electrode (single-sided coating) / separator / Li metal was laminated in this order in a test cell (HS cell, manufactured by Hosen Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol). %, 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 result of the fifth discharge capacity was determined as the negative electrode capacity. It was. As a result, the capacity of the negative electrode was 1.2 mAh / cm ² .

(Examples 1-8, Comparative Examples 1-3)
A positive electrode and a negative electrode produced in the production example were used, and a cellulose-based unwoven cloth (25 μm, 60 cm ² ) was used as the separator. First, a positive electrode, a negative electrode, and a separator are laminated in the order of separator / negative electrode / separator / positive electrode / separator / negative electrode / separator, and then an aluminum tab is vibration welded to each uncoated portion of the positive electrode and negative electrode. It was sandwiched between two aluminum laminate films from above and below, and the three sides were heat-sealed twice at 180 ° C. for 7 seconds and fused. After putting 6 mL of nonaqueous electrolyte (ethylene carbonate / propylene carbonate / ethyl methyl carbonate = 15/15/70 vol%, LiPF ₆ 1 mol / L) containing salts having various silsesquioxane structures, The remaining side was heat-sealed twice at 180 ° C. for 7 seconds to obtain a nonaqueous electrolyte secondary battery. The counter ions of the salts having the silsesquioxane structure of Examples 1 to 6 are tetrabutylammonium ions, and the counter ions of the salts having the silsesquioxane structure of Examples 7 and 8 are hexafluorophosphate ions. .

(Evaluation of cycle characteristics of non-aqueous electrolyte secondary batteries)
The nonaqueous electrolyte secondary battery produced in the example or the comparative example was connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko Co., Ltd.), and the charge / discharge cycle operation was performed after the aging process.

  In the aging step, each non-aqueous electrolyte secondary battery was fully charged (2.7 V), then allowed to stand at 60 ° C. for 168 hours, and then gradually cooled to room temperature (25 ° C.).

  After the aging step, 60 ° C., 25 mA constant current charging, and 50 mA constant current discharging were repeated 500 times. The charge end voltage and discharge end voltage at this time were set to 2.7 V and 2.0 V, respectively. The stability of the cycle characteristics was evaluated based on the maintenance rate of the 500th discharge capacity when the first discharge capacity was 100. There was no gas generation, and the discharge capacity maintenance ratio at the 500th time was 80% or more as good and less than 80% as bad. The results are shown in Table 1. In the determination of gas generation, the volume of the battery before and after the charge / discharge cycle operation was measured by the Archimedes method, and when the amount of generated gas was less than 0.5 mL / Ah, no gas was generated. The case where it was 5 mL / Ah or more was regarded as having gas generation.

  In Examples 1 to 8, since a salt having a silsesquioxane structure is contained, a good film is formed in the vicinity of the negative electrode, gas generation is suppressed, and good cycle characteristics are obtained.

  On the other hand, in Comparative Example 1, since no salt having a silsesquioxane structure was added, a protective film was not formed, and the electrolyte was decomposed by the abnormally active sites of the negative electrode, and gas was generated. It is considered a thing. In Comparative Examples 2 and 3, it is presumed that gas generation could not be suppressed because silsesquioxane was not converted into a salt and the solubility in the nonaqueous electrolyte was low, so that good film formation was not possible.

From the above results, in the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte contains a titanium-containing oxide, and the non-aqueous electrolyte contains a salt having a silsesquioxane structure. It has been clarified that by containing the salt having 0.01% by weight or more with respect to 100% by weight of the nonaqueous electrolyte, gas generation is suppressed and excellent cycle characteristics are obtained.

Claims (8)

A secondary battery comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte interposed between the negative electrode and the positive electrode,
The negative electrode includes a titanium-containing oxide as a negative electrode active material,
The non-aqueous electrolyte contains a salt having a silsesquioxane structure,
The nonaqueous electrolyte secondary battery, wherein the salt having the silsesquioxane structure is 0.01 wt% or more with respect to 100 wt% of the nonaqueous electrolyte. The nonaqueous electrolyte secondary battery according to claim 1, wherein the silsesquioxane structure can be represented by the following formula (1).

(In the above formula (1), R may be the same or different, and in any case, a hydrogen atom or a hydrogen atom or a carbon atom having 1 to 12 carbon atoms in which another element may be substituted. An organic group, and n is an integer of 1 to 10)   The nonaqueous electrolyte secondary battery according to claim 1, wherein the salt having the silsesquioxane structure has a cage-type silsesquioxane structure.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the salt having a silsesquioxane structure includes a halogen anion in a molecule.   5. The nonaqueous electrolyte secondary battery according to claim 1, wherein at least one of R has a polymerizable functional group and / or an ionic functional group.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the titanium-containing oxide is lithium titanate and / or titanium dioxide. In the positive electrode, the positive electrode active material 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 and the third to fourth periods. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, comprising a spinel type lithium manganate represented by at least one selected from the group consisting of elements belonging to: An assembled battery formed by connecting a plurality of the nonaqueous electrolyte secondary batteries according to any one of claims 1 to 7.