JP2011192580A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery excellent in high temperature storage characteristic. <P>SOLUTION: In the nonaqueous secondary battery, on one surface or both surfaces of a current collector, a positive electrode is provided which has a positive electrode mixture layer containing a layered lithium-nickel-cobalt complex oxide (A) represented by general formula: LiNiCo<SB>(1-x-y)</SB>M<SP>1</SP><SB>y</SB>O<SB>2</SB>(where 0.65≤x≤0.90, 0.02≤y≤0.06, and M<SP>1</SP>is at least one of a metal element selected from a group composed of Al, Mg, Ti, Mn and Zr) and a layered lithium-cobalt complex oxide (B) represented by general formula: LiCo<SB>(1-z)</SB>M<SP>2</SP><SB>z</SB>O<SB>2</SB>(where 0.005≤z≤0.03, and M<SP>2</SP>is at least one of the metal element selected from the group composed of Al, Mg, Ti, Mn and Zr), and a nonaqueous electrolyte containing fluoroalkyl-modified silicone in an amount of 0.1-2 mass% is used. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous secondary battery having excellent high-temperature storage characteristics.

  In recent years, non-aqueous secondary batteries have become one of the essential components that are indispensable as power sources for personal computers and mobile phones, and as power sources for electric vehicles and output storage. In particular, there is a demand for further miniaturization and weight reduction in small mobile electronic devices such as mobile phones, portable game machines, and PDAs. However, these devices have high power consumption for the backlight and drawing control of the liquid crystal display panel, and the capacity of the non-aqueous secondary battery is still insufficient. It is difficult to reduce the weight. For these reasons, a further increase in capacity is required for non-aqueous secondary batteries.

  Currently, a lithium-cobalt composite oxide containing lithium (Li) and cobalt (Co) is widely used as a positive electrode active material of a non-aqueous secondary battery, but the capacity per unit mass is larger than this. It has been studied to increase the capacity by using lithium-nickel-cobalt composite oxide to which nickel (Ni) is added as the positive electrode active material.

  However, a battery configured using a positive electrode active material having a large amount of nickel, such as lithium / nickel / cobalt composite oxide, has a problem that, for example, it tends to swell when stored in a charged state at a high temperature. A positive electrode active material with a large amount of nickel, such as a lithium / nickel / cobalt composite oxide, contains a relatively large amount of an alkaline component as an impurity, and this alkaline component is one of the causes of battery swelling.

  On the other hand, a technique for solving the above-mentioned problem that occurs with an increase in capacity of a non-aqueous secondary battery has also been developed. For example, in Patent Document 1, a layered lithium / nickel / cobalt composite oxide having a specific composition and a layered lithium / cobalt composite oxide having a specific composition are used as a positive electrode active material, and a mixture of these composite oxides is used. A non-aqueous secondary battery has been proposed that can suppress the swelling of the battery during high-temperature storage while increasing the capacity by reducing the amount of alkali.

JP 2009-151959 A

  An object of this invention is to provide the non-aqueous secondary battery excellent in the high temperature storage characteristic by the method different from patent document 1. FIG.

The non-aqueous secondary battery of the present invention that has achieved the above object is a non-aqueous secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte (hereinafter abbreviated as “electrolyte”), the positive electrode Is the following general formula (1) on one or both sides of the current collector:
LiNiCo _(1-xy) M ¹ _y O ₂ (1)
[However, in the general formula (1), 0.65 ≦ x ≦ 0.90, 0.02 ≦ y ≦ 0.06, and M ¹ is selected from the group consisting of Al, Mg, Ti, Mn, and Zr. Is at least one metal element selected]
A layered lithium / nickel / cobalt composite oxide (A) represented by the following general formula (2)
LiCo _(1-z) M ² _z O ₂ (2)
[However, 0.005 ≦ z ≦ 0.03, and M ² is at least one metal element selected from the group consisting of Al, Mg, Ti, Mn, and Zr]
And a positive electrode mixture layer containing a layered lithium-cobalt composite oxide (B) represented by the formula (1), wherein the electrolyte contains 0.1 to 2% by mass of fluoroalkyl-modified silicone. It is characterized by that.

  Lithium transition metal composite oxides such as layered lithium / nickel / cobalt composite oxide (A) and layered lithium / cobalt composite oxide (B) include lithium carbonate, cobalt oxide, and hydroxide used as raw materials. Unreacted substances such as nickel and nickel oxide are mixed as impurities. Further, during the formation reaction of the lithium transition metal composite oxide or after the completion of the reaction, lithium reacts with moisture in the air to become lithium hydroxide. In particular, in the layered lithium / nickel / cobalt composite oxide (A) having a relatively large amount of nickel, the content of such an alkali component increases.

  When the amount of alkaline components present in the layered lithium / nickel / cobalt composite oxide (A) or the layered lithium / cobalt composite oxide (B) is large, for example, when the battery is charged and stored in a high temperature environment In addition, a decomposition reaction of the alkali component occurs, and carbon dioxide gas and hydrogen gas are generated, which causes the battery to swell.

  Therefore, in the non-aqueous secondary battery of the present invention, in addition to using the layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / cobalt composite oxide (B) having the above composition as the positive electrode active material. By using an electrolytic solution containing a specific amount of fluoroalkyl-modified silicone, the generation of gas due to decomposition of the alkali component contained in the positive electrode active material is suppressed, and the occurrence of swelling during high-temperature storage is suppressed, It enhances its high-temperature storage characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous secondary battery excellent in the high temperature storage characteristic can be provided.

It is a figure which shows typically an example of the non-aqueous secondary battery which concerns on this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the non-aqueous secondary battery shown in FIG. It is a graph showing the particle size distribution of the layered lithium-nickel-cobalt composite oxide (A) used in the examples. It is a graph showing the particle size distribution of the layered lithium-cobalt composite oxide (B) used in the examples.

  The positive electrode according to the non-aqueous secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material, a conductive auxiliary agent, a binder and the like on one side or both sides of a current collector. The agent layer includes a layered lithium / nickel / cobalt composite oxide (A) represented by the general formula (1) and a layered lithium / cobalt composite oxide represented by the general formula (2) as a positive electrode active material. (B).

  In the layered lithium / nickel / cobalt composite oxide (A), Ni is a component that contributes to an increase in capacity. Therefore, if the Ni ratio x in the layered lithium / nickel / cobalt composite oxide (A) is too small, it is difficult to increase the capacity of the battery. Therefore, x is 0.65 or more, preferably 0.7 or more. And However, if the Ni ratio x in the layered lithium / nickel / cobalt composite oxide (A) is too large, the charge / discharge efficiency and charge / discharge cycle characteristics of the battery may be lowered. To do.

Layered lithium-nickel-cobalt composite oxide (A), the element M ¹ is, for example, a component that contributes to improved safety during assumed nail penetration test a case where a metal strip is stuck to the battery. Layered lithium-nickel-cobalt composite oxide (A) is, as the element ^{M 1,} Al, Mg, Ti, Mn, may contain only one kind of the elements Zr, 2 kinds of these The above elements may be contained.

The ratio y of the element M ¹ in the layered lithium-nickel-cobalt composite oxide (A), from the viewpoint of ensuring the effect of the by the inclusion of elements M ^1, 0.02 or more, preferably 0.03 or more and To do. Incidentally, layered lithium-nickel-cobalt composite oxide in (A), Co is a component contributing to the capacity increases with Ni, the ratio y of the element M ¹ in the layered lithium-nickel-cobalt composite oxide (A) If it is too large, the ratio of Ni or Co becomes small and the capacity may be reduced. Therefore, y is set to 0.06 or less, preferably 0.05 or less.

In the layered lithium-cobalt composite oxide (B), the element M ² is a component that contributes to improvement of the high-temperature storage characteristics of the battery and charge / discharge cycle characteristics (particularly charge / discharge cycle characteristics at a high voltage). Layered lithium-cobalt composite oxide (B), as the element ^{M 2,} Al, Mg, Ti, Mn, may contain only one kind of the elements Zr, of two or more of these An element may be contained.

The ratio z of the element ^{M 2} in the layered lithium-cobalt complex oxide (B), from the viewpoint of ensuring the effect of the by the inclusion of elements ^{M 2,} 0.005 or higher, preferably 0.01 or more. In the layered lithium / cobalt composite oxide (B), Co is a component that contributes to an increase in capacity. However, if the ratio z of the element M ² in the layered lithium / cobalt composite oxide (B) is too large, Z may be 0.03 or less, preferably 0.02 or less, since the ratio may decrease and the capacity may decrease.

When used for forming the positive electrode, the layered lithium / nickel / cobalt composite oxide (A) in which the particle size distribution is d10 = 5 to 10 μm, d50 = 10 to 15 μm and d90 = 15 to 20 μm, and the particle size distribution is It is preferable to use a layered lithium-cobalt composite oxide (B) in which d10 = 1 to 10 μm, d50 = 10 to 20 μm, and d90 = 15 to 25 μm. By using composite oxides (A) and (B) having different particle size distributions in this way, it becomes easy to increase the density of the positive electrode mixture layer to, for example, 3.5 g / cm ³ or more. It is possible to further increase the capacity by increasing the filling amount of the active material.

  In addition, the particle size distribution of the layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / cobalt composite oxide (B) referred to in this specification is determined by substituting these composite oxides (A) or (B) in water. Dispersed and measured using Microtrac (manufactured by Hosokawa Micron) under conditions of particle permeability: transmission, particle refractive index: 2.42, solvent refractive index: 1.33, d10, d50 and d90 are Are the particle diameters at 10%, 50% and 90% of the volume-based cumulative fractions, respectively.

  The ratio of layered lithium / nickel / cobalt composite oxide (A) to layered lithium / cobalt composite oxide (B) is as follows: layered lithium / nickel / cobalt composite oxide (A) and layered lithium / cobalt composite oxide (B) When the total amount of the product (B) is 100% by mass, the content of the layered lithium / nickel / cobalt composite oxide (A) is preferably 10% by mass or more, and more preferably 15% by mass or more. Is more preferable, and is preferably 30% by mass or less. In other words, when the total amount of the layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / cobalt composite oxide (B) is 100% by mass, the layered lithium / cobalt composite oxide (B) is contained. The rate is preferably 70% by mass or more, preferably 90% by mass or less, and more preferably 85% by mass or less. By using the layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / cobalt composite oxide (B) at such a ratio, the battery has a higher capacity while ensuring better battery characteristics. can do.

  That is, when the content of the layered lithium / nickel / cobalt composite oxide (A) is small, the filling property of the active material in the positive electrode mixture layer is improved, and a higher density positive electrode mixture layer can be formed. If the content of the layered lithium / nickel / cobalt composite oxide (A) is too small, the capacity per unit mass of the positive electrode active material tends to decrease, and as a result, the battery capacity may decrease. It is not preferable. In addition, when the content of the layered lithium / nickel / cobalt composite oxide (A) is large, the capacity per unit mass of the positive electrode active material increases. However, when the content is too large, the battery voltage at the end of discharge rapidly decreases. In addition, it is difficult to improve the filling property of the active material in the positive electrode mixture layer, and the battery capacity tends to decrease.

  Examples of conductive aids used for the positive electrode include graphites such as natural graphite (eg, flaky graphite) and artificial graphite; carbons such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Carbon materials such as bon blacks; carbon fibers are preferable. In addition, for the positive electrode, conductive assistants other than carbon materials, for example, conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; Conductive metal oxides such as titanium; organic conductive materials such as polyphenylene derivatives; and the like can also be used.

Incidentally, the carbon material used as a conductive additive, for example, the specific surface area is preferably from less than ^{50 m} 2 / g or more 1500 m ² / g. If the carbon material has such a specific surface area, it is possible to reduce the content in the positive electrode mixture layer while suppressing deterioration of the battery characteristics, and thus it becomes possible to form a higher density positive electrode mixture layer. Further increase in battery capacity can be achieved. The specific surface area of the carbon material is more preferably 800 m ² / g or less.

  Among the various conductive aids exemplified above, acetylene black, ketjen black, and other carbon blacks are particularly preferable in terms of easy availability of those having the specific surface area.

  When using together the carbon material which has the said specific surface area, and another conductive support agent (carbon material which has a specific surface area other than the above, or conductive support agents other than a carbon material), in the conductive support agent whole quantity, The carbon material having a specific surface area of, for example, is preferably 30% by mass or more, and more preferably 50% by mass or more. Of course, only the carbon material having the specific surface area (that is, 100% by mass) may be used.

  Rubber is preferably used as the binder for the positive electrode. By using rubber as the binder, it becomes easy to reduce the specific surface area of the positive electrode mixture layer as described above.

  In addition, as will be described in detail later, in manufacturing the positive electrode, a layered lithium / nickel / cobalt composite oxide (A), a layered lithium / cobalt composite oxide (B), a conductive additive, a binder, and the like are contained. A production method using a positive electrode mixture-containing composition obtained by dispersing a positive electrode mixture in an organic solvent such as N-methyl-2-pyrrolidone (NMP) (the binder may be dissolved) is usually employed. . Therefore, the binder (binder) used for the positive electrode according to the battery of the present invention is preferably a polymer (rubber) that can be dissolved or dispersed in an organic solvent such as NMP.

  Specific examples of rubbers that can be dissolved or dispersed in organic solvents such as NMP, which are suitable as binders, include poly 1,3-butadiene, polyisoprene, isoprene-isobutylene copolymers, natural rubber, styrene-1,3-butadiene. Copolymer (SBR), styrene-isoprene copolymer, 1,3-butadiene-isoprene-acrylonitrile copolymer, styrene-1,3-butadiene-isoprene copolymer, 1,3-butadiene-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene Methyl methacrylate copolymer, styrene-acrylonitrile-1,3-butadiene-itaconic acid copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer, styrene-1,3- Tadiene-itaconic acid-methyl methacrylate-acrylonitrile copolymer, acrylonitrile-1,3-butadiene-methacrylic acid-methyl methacrylate copolymer, 1,3-butadiene-styrene-methyl methacrylate copolymer, styrene-1,3-butadiene-itacon Diene rubber such as acid-methyl methacrylate-acrylonitrile copolymer, styrene-acrylonitrile-1,3-butadiene-methyl methacrylate-fumaric acid copolymer; Olefin rubber such as ethylene-propylene copolymer, ethylene-propylene-diene copolymer; styrene Ethylene-butadiene copolymer, styrene-butadiene-propylene copolymer, styrene-n-butyl acrylate-itaconic acid-methyl methacrylate-acrylonite And the like; Rukoporima, styrene - acrylate n- butyl - itaconic acid - - Methyl methacrylate styrene rubbers such as acrylonitrile copolymer. These rubbers may be used alone or in combination of two or more.

  In addition to the rubber, other binders can be used for the binder of the positive electrode mixture layer. The binder other than rubber used for the binder of the positive electrode mixture layer is also preferably a polymer that can be dissolved or dispersed in an organic solvent such as NMP. Examples of such polymers include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene ionomer, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, chlorinated polyethylene, chlorosulfonated polyethylene, and other olefin polymers; polymethyl methacrylate, polymethyl acrylate , Polyethyl acrylate, polybutyl acrylate, acrylate-acrylonitrile copolymer, 2-ethylhexyl acrylate-methyl acrylate-acrylic acid-methoxypolyethylene glycol monomethacrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide, poly-N-isopropylacrylamide (Meth) acrylic polymers such as poly-N, N-dimethylacrylamide; Polyamide and polyimide polymers such as lyamide 6, polyamide 66, polyamide 11, polyamide 12, aromatic polyamide, polyimide; ester polymers such as polyethylene terephthalate and polybutylene terephthalate; polyvinylidene fluoride (PVDF), polytetrafluoroethylene , Polyhexafluoropropylene, vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (VDF-HFP-TFE) copolymer, vinylidene fluoride-pentafluoropropylene (VDF-) PFP) copolymer, vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene (VDF-PF) -TFE) copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene (VDF-PFMVE-TFE) copolymer, vinylidene fluoride-chlorotrifluoroethylene (VDF-CTFE) copolymer and other fluorine-based polymers; .

  Furthermore, polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene, poly (2-methoxyethoxyethylene), poly (3-morphinylethylene), polyvinyl sulfonic acid and the like can also be used as the binder. Also, block polymers such as polystyrene-polybutadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-isoprene block copolymer, styrene-ethylene-propylene-styrene block copolymer, etc. It can be used as a binder.

  The current collector for the positive electrode is not particularly limited as long as it is an electron conductor that is substantially chemically stable in the battery being constructed. For example, as a material constituting the current collector, in addition to aluminum or its alloy, stainless steel, nickel or its alloy, titanium or its alloy, carbon, conductive resin, carbon or titanium on the surface of aluminum or stainless steel What processed this is used. Of these, aluminum and aluminum alloys are particularly preferable. These materials can also be used after oxidizing the surface. Moreover, it is preferable to give unevenness | corrugation to the collector surface by surface treatment. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although the thickness of a collector is not specifically limited, For example, it is preferable that it is 5-50 micrometers.

  The positive electrode according to the battery of the present invention includes, for example, a positive electrode mixture containing a layered lithium / nickel / cobalt composite oxide (A), a layered lithium / cobalt composite oxide (B), a conductive additive and a binder. The positive electrode mixture-containing composition was prepared by dispersing in an organic solvent such as NMP (the binder may be dissolved), and this was applied to a current collector and dried to remove the solvent, It can be manufactured through a step of adjusting the thickness and density of the positive electrode mixture layer by applying a press treatment such as calendering.

  As a method for preparing a positive electrode mixture-containing composition (paste, slurry, etc.), for example, (1) a conductive assistant, a binder, and a solvent are kneaded in advance with a strong shearing dispersion device, and a positive electrode active material is added to this dispersion. (2) A mixture of a positive electrode active material, a binder, and a solvent is dispersed to form a dispersion such as a paste. A method of preparing a dispersion by kneading an agent, a binder and a solvent with a strong shearing dispersion device to add another dispersion to the former dispersion, and (3) positive electrode active And a method in which a mixture of a substance, a conductive additive, a binder, and a solvent is kneaded with a high shear disperser.

  The layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / cobalt composite oxide (B), which are positive electrode active materials, are prepared in advance as a mixture, and this mixture is prepared as a positive electrode mixture-containing composition. The layered lithium / nickel / cobalt composite oxide (A) and the layered lithium / nickel / cobalt composite oxide (B) may be directly used for the preparation of the positive electrode mixture-containing composition without mixing. I do not care.

Examples of the high shear dispersion device used for preparing the positive electrode mixture-containing composition include, for example, a triaxial planetary mixer having two blades for kneading and one high-speed stirrer; A four-axis planetary mixer equipped with two blades and two high-speed stirrers (such as “Planetary Dispa (trade name)” manufactured by Asada Tekko Co., Ltd.); a three-axis planetar with three blades Lee mixer [Intrie Corporation's “Trimix (trade name)” etc.]; Media mill represented by mill; Kneader; Continuous twin-screw kneader; Colloid mill; Roll mill; A homogenizer type disperser that generates a jet flow and disperses by shearing between liquid and liquid; high speed rotating homogenizer capable of high speed operation of 3000 to 20000 min ⁻¹ with improved mechanical accuracy Examples include Clairemix (trade name, manufactured by M Technique Co., Ltd.) and universal mixer (trade name, manufactured by POWREC Co., Ltd.).

  When the positive electrode mixture-containing composition is applied to a current collector and dried and then subjected to press treatment, for example, the linear pressure is preferably set to 700 to 2000 kgf / cm, whereby the positive electrode mixture layer It becomes easy to adjust the thickness and density of the film to suitable values described later.

The density of the positive electrode mixture layer of the positive electrode according to the present invention is preferably 3.5 g / cm ³ or more, and more preferably 3.7 g / cm ³ or more. The capacity of the positive electrode mixture layer can be further increased by increasing the filling amount of the positive electrode active material by increasing the density of the positive electrode mixture layer in this way. However, if the density of the positive electrode mixture layer is too high, the permeability of the electrolytic solution into the positive electrode mixture layer is lowered, and battery characteristics may be impaired. preferably 3 g / cm ³ or less, more preferably 4.2 g / cm ³ or less.

The density of the positive electrode mixture layer here is measured by the following method. First, it cuts a positive electrode to a size of 1 cm × 1 cm, a thickness micrometer _{(l 1),} measuring the mass _{(m 1)} a precision balance. Next, we scraped off the positive electrode mixture layer, and extract only the collector, measuring the thickness of the current collector (l _c) mass (m _c) in the same manner as the positive electrode. From the obtained thickness and mass, the positive electrode mixture layer density (d _ca ) is determined by the following formula ( _note that the unit of thickness is cm and the unit of mass is g).
d _ca = (m ₁ −m _c ) / (l ₁ −l _c )

  In addition, the thickness of the positive electrode mixture layer (when the positive electrode mixture layer is formed on both sides of the current collector, the thickness per one surface thereof) is preferably 30 to 80 μm.

  The amount of the positive electrode active material in the total amount of the positive electrode mixture layer is preferably 96 to 99% by mass. The amount of the conductive auxiliary in the positive electrode mixture layer is preferably 1.0 part by mass or more, more preferably 1.2 parts by mass or more, with respect to 100 parts by mass of the positive electrode active material. The amount is preferably 0.0 part by mass or less, and more preferably 1.5 parts by mass or less. Furthermore, the amount of the binder in the positive electrode mixture layer is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more with respect to 100 parts by mass of the positive electrode active material. The amount is preferably 0.0 part by mass or less, and more preferably 1.5 parts by mass or less.

  Further, the amount of rubber as a binder in the positive electrode mixture layer is preferably 0.1 parts by mass or more and more preferably 0.2 parts by mass or more with respect to 100 parts by mass of the positive electrode active material. Preferably, it is 0.6 parts by mass or less, and more preferably 0.4 parts by mass or less.

  For the electrolyte solution according to the nonaqueous secondary battery of the present invention, a solution in which a lithium salt is dissolved in a nonaqueous solvent is used.

In the battery of the present invention, an electrolytic solution containing a fluoroalkyl-modified silicone is used. In addition to the action of the element M ² contained in the layered lithium-cobalt composite oxide (B), the inside of the battery when the battery in a charged state is stored in a high temperature environment by the action of the fluoroalkyl-modified silicone in the electrolyte. The generation of gas can be suppressed and the occurrence of blistering can be suppressed.

  Specific examples of the fluoroalkyl-modified silicone that can be added to the electrolytic solution include those represented by the following structural formula (3).

The fluoroalkyl-modified silicone represented by the structural formula (3) preferably has a viscosity of 300 to 10000 mm ² / s. As such a fluoroalkyl-modified silicone, for example, a commercially available product such as “FS1265 series (trade name)” manufactured by Toray Dow Corning Co., Ltd. can be used.

  The content of the fluoroalkyl-modified silicone in the electrolytic solution used for the battery of the present invention is 0.1% by mass or more and 0.5% by mass or more from the viewpoint of ensuring the effect of the use well. preferable. However, if the amount of the fluoroalkyl-modified silicone in the electrolytic solution is too large, the charge / discharge cycle characteristics of the battery may be deteriorated. Therefore, the content of the fluoroalkyl-modified silicone in the electrolytic solution used in the battery of the present invention is 2% by mass or less.

  Examples of the non-aqueous solvent for constituting the electrolytic solution include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC). ), Γ-butyrolactone (γ-BL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide ( DMF), dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, Rahidorofuran derivatives, diethyl ether, an aprotic organic solvent such as 1,3-propane sultone as a singly mixed solvent or a mixture of two or more.

As the lithium salt for constituting the electrolytic solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3 ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] There may be mentioned at least one selected from salts. The concentration of these lithium salts in the electrolytic solution is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  In addition, it is preferable to add an ester having a C═C double bond outside the ring or an ester having a C═C double bond inside the ring to the electrolytic solution.

  The ester having a C═C double bond outside the ring and the ester having a C═C double bond in the ring (hereinafter, both may be collectively referred to as “ester having a C═C double bond”) ) Has a function of forming a surface protective film on the surface of the positive electrode active material during battery charging (particularly during initial charging), and the direct contact between the positive electrode and the electrolytic solution is suppressed by the surface protective film. In addition, the ester having a C═C double bond has an action of gradually reducing the circuit voltage of the battery when the charged battery is stored at a high temperature, for example. Therefore, when the battery of the present invention has an electrolytic solution containing an ester having a C═C double bond, even when stored in a charged state, for example, at a high temperature of about 150 ° C., the positive electrode and the electrolysis by the surface protective film Since the reaction between the positive electrode and the electrolyte is suppressed due to the effect of suppressing direct contact with the liquid and the decrease in battery voltage, the temperature rise of the battery due to such reaction can be suppressed, and the safety is further improved. It will be a thing.

  Examples of the ester having a C═C double bond outside the ring include vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinyl. Examples include ethylene carbonate, 5-methyl-4-vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, and the like.

  Examples of the ester having a C═C double bond in the ring include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, methyl ethyl vinylene carbonate, and the like. Can be mentioned.

  The ester having a C═C double bond outside the ring and the ester having a C═C double bond inside the ring are preferably used in combination.

  The addition amount of the ester having a C═C double bond in the ring in the electrolytic solution is 0.5% by mass or more in the total amount of the electrolytic solution from the viewpoint of more effectively exerting the action of the addition of these compounds. It is preferable that it is 0.9 mass% or more, and it is still more preferable that it is 1.8 mass% or more. However, if the amount of the ester having a C═C double bond in the ring is too large in the electrolyte, the voltage drop of the battery increases, so the amount of the ester having a C═C double bond in the ring Is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2.5% by mass or less in the total amount of the electrolytic solution. The addition amount of the ester having a C═C double bond outside the ring in the electrolytic solution is 0.2% by mass or more in the total amount of the electrolytic solution from the viewpoint of more effectively exerting the action of the addition of these compounds. It is preferable that it is 0.5 mass% or more, and it is still more preferable that it is 0.8 mass% or more. However, if the amount of the ester having a C═C double bond outside the ring is too large in the electrolyte, the voltage drop of the battery increases, so the amount of the ester having a C═C double bond outside the ring is increased. Is preferably 3% by mass or less, more preferably 2% by mass or less, and still more preferably 1.5% by mass or less in the total amount of the electrolytic solution.

  The non-aqueous secondary battery of the present invention is only required to have the positive electrode and the electrolytic solution, and there are no particular restrictions on the other configurations and structures, and it is employed in conventionally known non-aqueous secondary batteries. Each configuration and structure can be applied.

  Examples of the negative electrode include those formed by forming a negative electrode mixture layer containing a negative electrode active material on the current collector surface. The negative electrode mixture layer contains, in addition to the negative electrode active material, a binder and, if necessary, a conductive aid, and includes, for example, a negative electrode active material and a binder (further, a conductive aid). A negative electrode mixture-containing composition (slurry etc.) obtained by adding a suitable solvent to the mixture (negative electrode mixture) and kneading thoroughly is applied to the surface of the current collector and dried to obtain a desired thickness. Can be formed.

  Examples of the negative electrode active material include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by calcining pitch; furfuryl alcohol resin ( Carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of PFA), polyparaphenylene (PPP), and phenol resins. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include lithium alloys such as Li—Al, and alloys containing elements that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used. The amount of the negative electrode active material in the total amount of the negative electrode mixture is preferably 97 to 99% by mass, for example.

  The conductive aid is not particularly limited as long as it is an electron conductive material, and may not be used. Specific examples of conductive aids include acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon materials such as carbon fibers; and conductive fibers such as metal fibers. Carbon fluoride, metal powders such as copper and nickel, organic conductive materials such as polyphenylene derivatives, and the like. These may be used alone or in combination of two or more. . Among these, acetylene black, ketjen black and carbon fiber are particularly preferable. However, when a conductive additive is used for the negative electrode, it is desirable that the conductive additive amount in the total amount of the negative electrode mixture be 10% by mass or less in order to increase the capacity.

As a binder concerning a negative mix layer, any of a thermoplastic resin and a thermosetting resin may be sufficient. Specifically, for example, the same material as the binder according to the positive electrode of the present invention, an ethylene-acrylic acid copolymer, a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methacrylic acid copolymer, or the Copolymer Na ⁺ ion cross-linked product, ethylene-methyl acrylate copolymer or Na ⁺ ion cross-linked product of the copolymer, ethylene-methyl methacrylate copolymer or Na ⁺ ion cross-linked product of the copolymer, etc. These materials may be used alone or in combination of two or more.

Among these, PVDF, SBR, ethylene-acrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-acrylic acid A methyl copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl methacrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer is particularly preferable. The amount of the binder in the total amount of the negative electrode mixture is preferably 1 to 5% by mass, for example.

  The thickness of the negative electrode mixture layer (when the negative electrode mixture layer is formed on both sides of the current collector, the thickness per one surface thereof) is preferably 30 to 80 μm.

  The current collector for the negative electrode is not particularly limited as long as it is a substantially chemically stable electronic conductor in the non-aqueous secondary battery. Examples of the material constituting the current collector include stainless steel, nickel or an alloy thereof, copper or an alloy thereof, titanium or an alloy thereof, carbon, conductive resin, carbon, or the like on the surface of copper or stainless steel. A material obtained by treating titanium is used. Among these, copper and copper alloys are particularly preferable. These materials can also be used after oxidizing the surface. Moreover, it is preferable to give unevenness | corrugation to the collector surface by surface treatment. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although the thickness of a collector is not specifically limited, For example, it is preferable that it is 5-50 micrometers.

  The positive electrode and the positive electrode can be used in the form of a laminated electrode body obtained by laminating them via a separator or a wound electrode body obtained by winding the laminated electrode body.

  As the separator, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, what has a function which a hole is obstruct | occluded by fusion | melting of a structural material above a fixed temperature (for example, 100-140 degreeC), and raises resistance (namely, what has a shutdown function) is preferable. Specific examples of such a separator include a sheet (porous sheet), a nonwoven fabric or a woven fabric composed of a material such as polyethylene solvent, hydrophobic polymer such as polyethylene, polypropylene, or glass fiber having organic solvent resistance and hydrophobicity; And a porous material in which fine particles of the exemplified polyolefin polymer are fixed with an adhesive. The pore diameter of the separator is preferably such that the active material of the positive and negative electrodes, the conductive auxiliary agent, the binder and the like detached from the positive and negative electrodes do not pass through, and is preferably 0.01 to 1 μm, for example. The thickness of the separator is generally 8-30 μm, but is preferably 10-20 μm in the present invention. Further, the porosity of the separator is determined according to the constituent material and thickness, but is generally 30 to 80%.

  Examples of the form of the battery of the present invention include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The non-aqueous secondary battery of the present invention can be applied to the same applications as conventionally known non-aqueous secondary batteries.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
Layered lithium / nickel / cobalt composite oxide (A): LiNi _0.85 Co _0.10 Al _0.05 O ₂ [particle size distribution: d10 = 7.4 μm, d50 = 10.1 μm, d90 = 15.5 μm] and layered lithium-cobalt composite oxide (B): LiCo _0.997 Al _0.001 Mg _0.001 Ti _0.001 O ₂ [particle size distribution is d10 = 5.4 μm, d50 = 16 0.0 μm, d90 = 23.3 μm] were used at a mass ratio of 10:90.

The positive electrode active material mixture and acetylene black [Denka Black (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.], powdered product, average primary particle size (electron microscopy): 40 nm, BET specific surface area : 65 m ² / g, DBP oil absorption: 180 cc / 100 g], and a binder, Nippon Zeon's rubber binder “BM720H (trade name)” and Kureha Chemical Co., Ltd. PVDF “KF polymer L # 1120 (product) Name) ”is mixed at a mass ratio of 100: 1.2: 0.2: 0.8, NMP as a solvent is added, and“ Clearmix CLM0.8 (trade name) manufactured by M Technique Co., Ltd. ” ) ”Was used for 30 minutes at a rotational speed of 10,000 min ⁻¹ to obtain a paste-like mixture. NMP which is a solvent was further added to this mixture, and the mixture was treated at a rotational speed of 10000 min ⁻¹ for 15 minutes to prepare a positive electrode mixture-containing composition.

The positive electrode mixture-containing composition is applied to both sides of an aluminum foil (thickness: 15 μm), which is a current collector, vacuum-dried at 120 ° C. for 12 hours, and further subjected to a press treatment, whereby both sides of the current collector are applied. In addition, a positive electrode having a positive electrode mixture layer having a thickness of 52 μm was prepared. The density of the positive electrode mixture layer after the press treatment determined by the above method was 3.82 g / cm ³ .

<Production of negative electrode>
Natural graphite: 97.5% by mass, SBR: 1.5% by mass, and carboxymethylcellulose (thickener): 1% by mass were mixed with water to prepare a slurry-like negative electrode mixture-containing composition. . This negative electrode mixture-containing composition was applied to both sides of a copper foil (thickness: 8 μm) as a current collector, vacuum-dried at 120 ° C. for 12 hours, and further subjected to a press treatment to form both sides of the current collector. A negative electrode having a negative electrode mixture layer with a thickness of 63 μm was prepared. The density of the negative electrode mixture layer after the press treatment obtained by the same method as the method for measuring the density of the positive electrode mixture layer was 1.65 g / cm ³ .

<Production of electrode body>
The positive electrode and the negative electrode were overlapped with a separator interposed therebetween, and these were wound to produce an electrode body. As the separator, a polyethylene porous film (air permeability: 300 seconds / 100 cm ³ ) having a thickness of 14 μm was used.

<Preparation of electrolyte>
In a mixed solvent of methyl ethyl carbonate, diethyl carbonate and ethylene carbonate (volume ratio 2: 1: 3), LiPF ₆ is dissolved at a concentration of 1.2 mol / l, and the fluoroalkyl represented by the structural formula (3) is obtained. An electrolyte solution was prepared by adding 0.1% by mass of modified silicone (viscosity: 1000 mm ² / s).

<Battery assembly>
A prismatic non-aqueous secondary battery was assembled using the electrode body and the electrolytic solution. First, a current collector plate was joined to each end face of the electrode body by welding. Next, the lead part of the current collecting plate was connected to an electrode terminal current collecting mechanism attached to the lid. Then, the electrode body was accommodated inside the positive electrode can, and the lid body was welded and fixed to the opening of the positive electrode can. Finally, an electrolytic solution is injected into the positive electrode can from a liquid injection hole provided in the lid, and the thickness is 4 mm, the width is 34 mm, and the height is 50 mm. The structure shown in FIG. A water secondary battery was produced.

  Here, the battery shown in FIGS. 1 and 2 will be described. The positive electrode 1 and the negative electrode 2 are formed into a rectangular positive electrode can 4 as the electrode body 6 having a winding structure wound in a spiral shape through the separator 3 as described above. It is housed with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, a metal foil, an electrolytic solution, and the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated.

  The positive electrode can 4 is made of an aluminum alloy and constitutes a battery exterior material. The positive electrode can 4 also serves as a positive electrode terminal. An insulator 5 made of a polyethylene sheet is arranged at the bottom of the positive electrode can 4, and the positive electrode 1 connected to one end of each of the positive electrode 1 and the negative electrode 2 from the electrode body 6 made of the positive electrode 1, the negative electrode 2 and the separator 3. A current collector plate 7 and a negative electrode current collector plate 8 are drawn out. A stainless steel terminal 11 is attached to an aluminum alloy cover plate 9 that seals the opening of the positive electrode can 4 via a polypropylene insulating packing 10, and an insulator 12 is connected to the terminal 11. A stainless steel lead plate (electrode terminal current collecting mechanism) 13 is attached.

  And this cover plate 9 is inserted in the opening part of the said positive electrode can 4, and the opening part of the positive electrode can 4 is sealed by welding the junction part of both, and the inside of a battery is sealed.

  The lid plate 9 is provided with a liquid injection hole (14 in the figure). When the battery is assembled, the electrolyte is injected into the battery from the liquid injection hole, and then the liquid injection hole is sealed. Stopped. The cover plate 9 is provided with an explosion-proof safety valve 15.

  In the battery of this Example 1, the positive electrode can 4 and the cover plate 9 function as positive terminals by directly welding the positive electrode current collector plate 7 to the cover plate 9, and the negative electrode current collector plate 8 is welded to the lead plate 13. The negative electrode current collector plate 8 and the terminal 11 are connected to each other through the lead plate 13 so that the terminal 11 functions as a negative electrode terminal. Sometimes it becomes.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Examples 2 to 4 and Comparative Examples 1 to 3
A square non-aqueous secondary battery was produced in the same manner as in Example 1 except that the addition amount of the fluoroalkyl-modified silicone in the electrolytic solution was changed as shown in Table 1.

  For the nonaqueous secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3, the following swelling rate measurement and charge / discharge cycle characteristic evaluation were performed.

<High temperature storage characteristics evaluation>
About the batteries of Examples 1 to 4 and Comparative Examples 1 to 3, constant current charging was performed until the current value of 800 mA reached 4.2 V, and then constant voltage charging was performed at 4.2 V. The total charging time for constant current charging and constant voltage charging was 2 hours. Each battery after charging was placed in a thermostatic bath, stored at 90 ° C. for 4 hours, and then the thickness of the battery was measured. Then, the battery thickness after storage in a thermostatic chamber was divided by the battery thickness before storage to calculate the “swell rate”, and the high-temperature storage characteristics of each battery were evaluated.

<Charge / discharge cycle characteristics evaluation>
About the battery of Examples 1-4 and Comparative Examples 1-3, constant current charge was performed until it became 4.2V with the electric current value of 800 mA, and then constant current charge was performed at 4.2V. The total charging time for constant current charging and constant voltage charging was 2 hours. Subsequently, the battery after charging was discharged at a constant current of 800 mA at a current value of 800 mA. The above charge and discharge were set as 1 cycle, this was repeated 500 cycles, discharge capacity was calculated | required, the value was divided | segmented by the discharge capacity of the 1st cycle, and the capacity | capacitance maintenance factor was computed.

  These results are shown in Table 1. A graph showing the particle size distribution of the layered lithium / nickel / cobalt composite oxide (A) used in the batteries of Examples 1 to 4 and Comparative Examples 1 to 3 is shown in FIG. The graphs showing the particle size distribution of

  As is apparent from Table 1, layered lithium / nickel / cobalt composite oxide (A) and layered lithium / cobalt composite oxide (B) are used as the positive electrode active material, and contain an appropriate amount of fluoroalkyl-modified silicone. The non-aqueous secondary batteries of Examples 1 to 4 using the electrolyte solution do not contain the fluoroalkyl-modified silicone or the amount of the electrolyte is not appropriate, compared to the batteries of Comparative Examples 1 to 3 using the electrolyte solution. Therefore, the swelling rate is small and high high temperature storage characteristics can be secured.

  Moreover, the capacity | capacitance maintenance factor at the time of charging / discharging cycling characteristics evaluation of the battery of Examples 1-4 is equal to or exceeds the battery of Comparative Examples 1-3.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (3)

A non-aqueous secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode is on one side or both sides of the current collector,
General formula LiNiCo _(1-xy) M ¹ _y O ₂ (where 0.65 ≦ x ≦ 0.90, 0.02 ≦ y ≦ 0.06, and M ¹ represents Al, Mg, Ti, A layered lithium-nickel-cobalt composite oxide (A) represented by (at least one metal element selected from the group consisting of Mn and Zr);
General formula LiCo _(1-z) M ² _z O ₂ (where 0.005 ≦ z ≦ 0.03, and M ² is at least one selected from the group consisting of Al, Mg, Ti, Mn and Zr) Layered lithium-cobalt composite oxide (B) represented by
And a positive electrode mixture layer containing
A non-aqueous secondary battery using 0.1 to 2% by mass of fluoroalkyl-modified silicone as the electrolytic solution. The nonaqueous secondary battery according to claim 1, wherein the density of the positive electrode mixture layer is 3.5 g / cm ³ or more.   Layered lithium / nickel / cobalt composite oxide (A) having a particle size distribution of d10 = 5 to 10 μm, d50 = 10 to 15 μm and d90 = 15 to 20 μm, and a particle size distribution of d10 = 1 to 10 μm, d50 = 10 The non-aqueous secondary battery according to claim 2, wherein the layered lithium-cobalt composite oxide (B) having ˜20 μm and d90 = 15-25 μm is used.

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