JP2012190731A - Nonaqueous electrolyte secondary battery, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high capacity, a high level of safety, excellent high-temperature storage characteristics, and excellent cycle characteristics while using a lithium-containing complex oxide rich in Ni.SOLUTION: In a nonaqueous electrolyte secondary battery, at least a portion of a positive electrode active material contains a layered lithium/nickel/cobalt/manganese complex oxide (A) of specific composition, the titration amount of hydrochloric acid required for neutralization of an alkali in a positive electrode mixture layer is less than or equal to 14 ml, at least a portion of a binder contains 0.1-0.5 pt.mass of a polymer capable of dissolving in a solvent other than polyvinylidene fluoride with respect to 100 pts.mass of the positive electrode active material, and a nonaqueous electrolyte contains cyclohexylbenzene having a percentage of 0.2 to 1.5 mass% with respect to the total mass of the solvent in the nonaqueous electrolyte.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having high safety and high-temperature storage characteristics while having a positive electrode active material with a large amount of Ni (nickel), and a method for producing the same.

  2. Description of the Related Art In recent years, 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 are more compact and lighter due to the high power consumed by the backlight and drawing control of the liquid crystal display panel and the secondary battery capacity is still insufficient. Is in a difficult situation. Therefore, there is an urgent need to increase the power capacity, particularly the discharge capacity when the voltage of the unit cell is 3.3 V or higher.

  A positive electrode used in a non-aqueous electrolyte secondary battery such as a lithium ion battery includes, for example, an organic solvent such as N-methyl-2-pyrrolidone (NMP) added to a positive electrode active material, a conductive additive, and a binder. To prepare a slurry for forming a positive electrode mixture layer, such as a paste, and applying the slurry for forming a positive electrode mixture layer on the surface of a conductive substrate serving as a current collector, and drying and removing the solvent. It is manufactured through a step of forming a positive electrode mixture layer having a thickness and density adjusted by pressing or the like.

  As a method for achieving a higher capacity of the non-aqueous electrolyte secondary battery having such a positive electrode, for example, the density of the positive electrode (the density of the positive electrode mixture layer) is increased and the filling amount of the positive electrode active material in the positive electrode is increased. There are a method of increasing and a method of increasing the charging voltage. However, in the former method, the permeability of the electrolyte solution into the positive electrode mixture layer is lowered, and problems such as battery manufacturing problems and characteristic deteriorations occur. Furthermore, the latter method has problems such as a decrease in battery safety associated with high voltage charging.

  In addition, lithium-cobalt composite oxide containing lithium (Li) and cobalt (Co) is widely used as the positive electrode active material of the non-aqueous electrolyte secondary battery, but the capacity per unit mass is more than this. The use of lithium / nickel / cobalt composite oxides with large Ni added as the positive electrode active material has been studied to increase the capacity of the battery.

  However, lithium-containing composite oxides with a large amount of Ni, such as lithium / nickel / cobalt composite oxides, are liable to be mixed with alkalis such as lithium hydroxide and lithium carbonate as impurities during synthesis. Sometimes it decomposes and generates carbon dioxide and hydrogen gas, which causes battery swelling. In addition, lithium-containing composite oxides with a large amount of Ni, such as lithium-nickel-cobalt composite oxides, have a large amount of Li ion extraction during charging, which can increase the capacity of the battery, but structurally It is unstable, for example, when the battery is short-circuited and generates heat, it decomposes and releases oxygen, which is likely to cause a safety problem.

  Techniques for avoiding such problems are also being studied. For example, Patent Document 1 uses a positive electrode configured by reducing the alkali amount of the entire positive electrode active material while using a lithium-containing composite oxide having a large amount of Ni as a part of the positive electrode active material, and this positive electrode. Nonaqueous electrolyte secondary batteries have been proposed.

  According to the technique described in Patent Document 1, a non-aqueous electrolyte secondary battery having excellent high-temperature storage characteristics and improved safety by avoiding the problem of battery swelling caused by alkali in the positive electrode active material is obtained. Can do.

JP 2009-151959 A

  By the way, when future applications of non-aqueous electrolyte secondary batteries are deployed, it is expected that higher safety will be required than before, and in preparation for that, higher safety and higher safety are also required. The development of technology that can ensure safety is also required.

  The present invention has been made in view of the above circumstances, and its purpose is to use a non-aqueous electrolyte secondary solution having high safety and high-temperature storage characteristics while using a lithium-containing composite oxide with a large amount of Ni. It is in providing a battery and its manufacturing method.

The non-aqueous electrolyte secondary battery of the present invention that has achieved the above-mentioned object is a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of a current collector, A non-aqueous electrolyte secondary battery including a negative electrode, a separator, and a non-aqueous electrolyte, wherein at least a part of the positive electrode active material has a general formula LiNi _x Co _(1-xyz) Mn _y M ¹ _z O ₂ (0.5 ≦ x ≦ 0.9, 0.005 ≦ y ≦ 0.3, 0.003 ≦ z ≦ 0.05, and the element M ¹ is Li, Ni, Co, and Mn. And includes at least one element selected from the group consisting of Mg, Al, Ti, Sr, Zr, Nb, Ag, and Ba). Before containing complex oxide (A) and determined by the following neutralization titration method The titration amount of hydrochloric acid necessary for neutralization of alkali in the positive electrode mixture layer is 14 ml or less, and at least a part of the binder contains a polymer soluble in a solvent other than polyvinylidene fluoride, The content of the polymer that can be dissolved in the solvent is 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the positive electrode active material, and cyclohexylbenzene is added to the nonaqueous electrolytic solution in the total amount of the solvent in the nonaqueous electrolytic solution. A medium containing 0.2 to 1.5% by mass is used.

  Neutralization titration method: A positive electrode mixture layer collected from a positive electrode and weighed to about 20.0 g, and 100 ml of water having a pH of 7 and an electric conductivity of 2 μS / cm or less purified by an ion exchange method are added. After filling the container with nitrogen gas, the container is sealed, and the positive electrode mixture layer is immersed in water in the container while stirring with a magnetic stirrer for 60 minutes. Thereafter, 25.0 ml of the supernatant obtained by filtering the mixture of water and the positive electrode mixture layer in the container is weighed, and a few drops of a 0.1% by weight methyl orange solution are added to the sample solution. The sample solution was intermittently titrated with 0.02 mol / l hydrochloric acid while stirring with a magnetic stirrer, and the amount of hydrochloric acid added to the sample solution until the color of the sample solution changed from yellow to orange was measured. The titration amount of hydrochloric acid required for neutralization of alkali in the positive electrode mixture layer is used.

  The manufacturing method of the present invention is a method for manufacturing the non-aqueous electrolyte secondary battery of the present invention, for forming a positive electrode mixture layer containing a positive electrode active material, a conductive additive, a binder and a solvent. A step of preparing a positive electrode having a positive electrode mixture layer on one or both sides of the current collector using the positive electrode mixture layer forming slurry, and the content of cyclohexylbenzene is 0 in the total amount of the solvent The step of preparing a non-aqueous electrolyte of 1 to 1.5% by mass and the step of assembling a battery using the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte, and the positive electrode mixture In preparing the layer forming slurry, a solution in which a polymer that can be dissolved in a solvent other than polyvinylidene fluoride as a binder is dissolved in the solvent is used.

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous-electrolyte secondary battery provided with high safety | security and a high temperature storage characteristic can be provided, using lithium containing complex oxide with much Ni amount.

It is a figure which shows typically an example of the nonaqueous electrolyte secondary battery of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. It is a perspective view of the nonaqueous electrolyte secondary battery shown in FIG.

  For the non-aqueous electrolyte solution according to the non-aqueous electrolyte secondary battery of the present invention, for example, a solution in which a lithium salt is dissolved in a non-aqueous solvent is used. The non-aqueous electrolyte contains cyclohexylbenzene. Thereby, the high temperature storage characteristic and safety | security of a battery can be improved.

  When the battery is stored in a charged state at a high temperature, the cyclohexylbenzene in the non-aqueous electrolyte decomposes on the positive electrode side, and the decomposition product forms a film on the positive electrode surface. It is considered that gas generation due to decomposition of alkali can be suppressed and swelling of the battery can be suppressed.

  Also, when the battery is exposed to a very high temperature, overcharged, or a metal foreign object such as a nail is stabbed or short-circuited, the cyclohexylbenzene decomposes due to the internal temperature rise, The decomposition product forms a film on the surface of the positive electrode to increase the internal resistance and suppress the reaction with the non-aqueous electrolyte, thereby suppressing the thermal runaway, ignition, and explosion of the battery, improving safety. I think that.

  The content of cyclohexylbenzene in the nonaqueous electrolytic solution used in the battery is 0.2% by mass or more, preferably 0.3% in the total amount of the solvent of the nonaqueous electrolytic solution, from the viewpoint of ensuring the above-mentioned effects satisfactorily. % Or more. However, cyclohexylbenzene in the non-aqueous electrolyte gradually decomposes even during normal use of the battery, causing an increase in the resistance of the positive electrode and clogging of the separator, thereby causing charge / discharge cycle characteristics and load characteristics of the battery. It may cause deterioration of battery characteristics. Therefore, in the battery of the present invention, the content of cyclohexylbenzene in the nonaqueous electrolyte to be used is 1.5% by mass or less, preferably 1.0% by mass or less, based on the total amount of the solvent of the nonaqueous electrolyte, and further described below. As such, by using a specific amount of a polymer (polymer other than polyvinylidene fluoride) that can be dissolved in a solvent as a part of the binder related to the positive electrode mixture layer, the deterioration of battery characteristics due to cyclohexylbenzene is suppressed. is doing.

  Examples of the solvent for the non-aqueous electrolyte include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran An aprotic organic solvent such as ethylene derivatives, diethyl ether, and 1,3-propane sultone can be used singly or as a mixed solvent in which two or more are mixed.

The inorganic ion salt according to the non-aqueous electrolyte 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} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] At least one selected from the group consisting of: The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  The positive electrode according to the non-aqueous electrolyte secondary battery of the present invention has a structure having a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of a current collector. .

In the positive electrode according to the battery of the present invention, a layered lithium / nickel / cobalt / manganese composite oxide (A) represented by the following general formula (1) [hereinafter simply referred to as compound (A)] Contains].
_{LiNi x Co (1-x-} y-z) Mn y M 1 z O 2 (1)
[In the general formula (1), 0.5 ≦ x ≦ 0.9, 0.005 ≦ y ≦ 0.3, 0.003 ≦ z ≦ 0.05, and the element M ¹ is Li, Ni, Co And at least one element selected from the group consisting of Mg, Al, Ti, Sr, Zr, Nb, Ag, and Ba. ]

  In the compound (A), Ni is a component that contributes to the capacity improvement, and the amount x of Ni in the general formula (1) is 0.5 or more, preferably 0. 75 or more. However, if the amount of Ni in the compound (A) is too large, the amount of other elements decreases and the effects of these cannot be ensured satisfactorily. Therefore, the amount x of Ni in the general formula (1) is , 0.9 or less, preferably 0.88 or less.

  In addition, since Mn is present in the crystal lattice in the compound (A), the layered structure can be stabilized together with Ni, and the thermal stability of the compound (A) can be improved. Can be obtained. The amount y of Mn in the general formula (1) is 0.005 or more, preferably 0.01 or more, from the viewpoint of ensuring the effect of improving the safety of the battery. If the amount of Mn in the compound (A) is too large, the amount of other elements decreases, and the effects of these cannot be secured satisfactorily. Therefore, the amount y of Mn in the general formula (1) is 0. .3 or less, preferably 0.2 or less.

Further, compound (A), as the element ^{M 1,} Li, Ni, a metal element other than Co and Mn, are selected Mg, Al, Ti, Sr, Zr, Nb, from the group consisting of Ag and Ba It contains at least one element, and by containing these elements, the stability can be improved and a positive electrode capable of constituting a highly safe battery can be obtained. Such effect element ^{M 1} from the viewpoint of satisfactorily ensuring the amount z of the element ^{M 1} in the general formula (1) is 0.003 or higher, preferably 0.01 or more. However, if the amount of the element M ^{1 in} the compound (A) is too large, the amount of other elements decreases, and the effects of these cannot be secured satisfactorily. Therefore, the element M ¹ in the general formula (1) The amount z of is 0.05 or less, preferably 0.04 or less.

  Further, the compound (A) contains Co, but if Co is present in the crystal lattice, an irreversible reaction occurs from the phase transition of the compound (A) due to the detachment and insertion of Li during charge / discharge of the battery. Can be relaxed and the reversibility of the crystal structure of the compound (A) can be increased, so that a positive electrode capable of constituting a battery having a long charge / discharge cycle life can be obtained. In the general formula (1), the amount of Co is represented by “1-xyz”, and specifically, 0.07 to 0.3 is preferable.

  As described above, a lithium-containing composite oxide with a large amount of Ni, such as compound (A), usually contains a large amount of alkali as an impurity during synthesis. However, in the positive electrode according to the battery of the present invention, The amount of alkali in the positive electrode mixture layer is limited so that the titration amount of hydrochloric acid required for neutralization of alkali in the positive electrode mixture layer obtained by the neutralization titration method is 14 ml or less, and cyclohexylbenzene is added. Together with the use of the non-aqueous electrolyte contained in a specific amount, the battery in a charged state is prevented from being swollen at high temperature, and the high-temperature storage characteristics of the battery are enhanced. The titration amount of hydrochloric acid required for neutralization of alkali in the positive electrode mixture layer determined by the neutralization titration method is more preferably 12 ml or less.

  Since the alkali in the positive electrode mixture layer is derived from the positive electrode active material, the alkali amount in the positive electrode mixture layer is adjusted to the above value by reducing the alkali amount in the positive electrode active material used for the positive electrode. can do.

  The amount of alkali in the positive electrode active material is such that, for example, the positive electrode active material is washed with water to remove alkali such as lithium hydroxide or lithium carbonate, or the positive electrode active material [for example, compound (A)] having a large amount of alkali and the amount of alkali is small. It can be reduced by mixing with a positive electrode active material.

  For example, in the compound (A), when the amount of Ni is particularly large, the amount of alkali is also large. Therefore, it is preferable to remove the alkali by rinsing with water. While the amount cannot be sufficiently reduced, the compound (A) may be deactivated when the number of washings is increased. Therefore, in the case of the compound (A) having a particularly large amount of Ni [for example, the amount x of Ni in the general formula (1) is about 0.8 to 0.9], washing with water is repeated about once or twice. Thus, it is preferable to reduce the alkali amount in the total amount of the positive electrode active material by mixing with another positive electrode active material (lithium-containing composite oxide) having a small alkali amount after reducing the alkali amount to some extent.

  On the other hand, among compounds (A), those with a small amount of Ni [for example, the amount x of Ni in the general formula (1) is about 0.5 to 0.7] have a relatively small amount of alkali. The amount of alkali can be adjusted to the above value by washing once with water, and deactivation can be suppressed. Therefore, only the compound (A) may be used as the positive electrode active material, and the amount of alkali can be adjusted without washing with water. It may be used by mixing with a small amount of another positive electrode active material (lithium-containing composite oxide) and reducing the amount of alkali in the total amount of the positive electrode active material.

When another positive electrode active material is used together with the compound (A), such a positive electrode active material includes a lithium-containing composite oxide that has been used as a positive electrode active material of a conventionally known non-aqueous electrolyte secondary battery. Of these products, those having a small amount of alkali can be used without particular limitation, but the layered lithium-cobalt composite oxide (B) represented by the following general formula (5) [hereinafter referred to as “compound (B)” ] Is preferably used.
LiNi _a Co _(1- abc ₎ Mn _b M ² _c O ₂ (2)
[In the general formula (2), 0 ≦ a ≦ 0.03, 0 ≦ b ≦ 0.02, 0.002 ≦ c ≦ 0.02, and the element M ² is other than Li, Ni, Co, and Mn. It is a metal element and contains at least one element selected from the group consisting of Mg, Al, Ti, Sr, Zr, Nb, Ag, and Ba. ]

  In the compound (B), Ni and Co are components that contribute to capacity improvement. However, as described above, if the amount of Ni is excessively increased, for example, the amount of alkali as an impurity may be excessively increased. The amount a of Ni in the general formula (2) is preferably 0.03 or less, and more preferably 0.02 or less. Further, the compound (B) may not contain Ni [that is, the amount a of Ni in the general formula (2) may be 0].

  Further, in the compound (B), when Mn is present in the crystal lattice, the layered structure can be stabilized together with Ni, and the thermal stability of the compound (B) can be improved. Can be obtained. The amount b of Mn in the general formula (2) is preferably 0.02 or less, and more preferably 0.015 or less. Moreover, although the amount b of Mn in the said General formula (2) may be 0, it is preferable that it is 0.005 or more from a viewpoint of ensuring the said effect.

Furthermore, compound (B), as the element ^{M 2,} Li, Ni, a metal element other than Co and Mn, are selected Mg, Al, Ti, Sr, Zr, Nb, from the group consisting of Ag and Ba Since at least one kind of element is contained, and the inclusion of these elements can increase the stability thereof, it is possible to further improve the safety of the battery constituted using the compound (B). It becomes. This effect from the viewpoint of satisfactorily ensuring by elements ^{M 2,} the amount c of the element ^{M 2} in the formula (2) is 0.002 or more, preferably 0.004 or more. However, if the amount of the element M ^{2 in} the compound (B) is too large, the amount of other elements decreases, and the effects of these cannot be ensured satisfactorily. Therefore, the element M ² in the general formula (2) Is preferably 0.02 or less, more preferably 0.015 or less.

  In addition, as described above, in the compound (B), Co is a component that contributes to an increase in capacity. In the general formula (2), the amount of Co is represented by “1-abc”. Specifically, it is preferably 0.980 to 0.998.

  For example, when the compound (A) and the compound (B) are used in combination, their ratio may be set within a range in which the alkali amount in the positive electrode mixture layer can be adjusted to the above value. From the viewpoint of favorably securing the effect of use (particularly the effect of increasing the capacity), when the positive electrode active material is 100% by mass, the amount of the compound (A) is preferably 10% by mass or more, More preferably, the content is 20% by mass or more.

  Further, as described above, only the compound (A) may be used as the positive electrode active material, but when the compound (A) and the compound (B) are used in combination, the positive electrode active material is 100% by mass. The amount of the compound (A) is preferably 30% by mass or less, and more preferably 25% by mass or less.

  In the positive electrode according to the battery of the present invention, a solvent other than polyvinylidene fluoride (PVDF) is used in at least a part of the binder of the positive electrode mixture layer (a solvent used in the slurry for forming the positive electrode mixture layer). (Hereinafter, simply referred to as “polymer soluble in a solvent”).

  The polymer soluble in the solvent forms a film on the surface of the positive electrode active material particles in the positive electrode mixture layer. This film suppresses the decomposition reaction of cyclohexylbenzene in the non-aqueous electrolyte under the normal use conditions of the battery (charge / discharge conditions under which the battery is normally used). On the other hand, the film made of a polymer that can be dissolved in the solvent formed on the surface of the positive electrode active material particles is used under high temperature storage conditions of the battery or under conditions that require safety (conditions in which the battery becomes abnormally hot). In the lower part, the film formation on the positive electrode surface by cyclohexylbenzene is not inhibited.

  Therefore, in addition to using the compound (A) having the specific composition as the positive electrode active material and further using a nonaqueous electrolytic solution containing a specific amount of cyclohexylbenzene, the binder for the positive electrode mixture layer is used as a PVDF. By using a polymer that is soluble in a solvent other than the above, it is possible to improve the high-temperature storage characteristics and safety of the battery while suppressing deterioration of the battery characteristics under normal use conditions.

  In the present invention, as a binder, a polymer that can be dissolved in a solvent other than PVDF as an essential component is that PVDF has a large binding force, while drying to form a positive electrode mixture layer (details) Is likely to shrink and harden, and the action of coating the surface of the positive electrode active material particles is small. Therefore, if only PVDF is used as a binder to coat the surface of the positive electrode active material particles well, a large amount This is because it is necessary to use the PVDF, and the battery capacity is reduced.

  The positive electrode according to the battery of the present invention is a positive electrode mixture layer formed by dissolving or dispersing a positive electrode active material containing the compound (A), a conductive additive and a binder containing a polymer soluble in the solvent in the solvent. In general, it is produced through a process of using a slurry for coating and applying it to the surface of the current collector. In this case, the solvent used for the positive electrode mixture layer forming slurry is preferably an organic solvent such as N-methyl-2-pyrrolidone (NMP). Accordingly, the polymer that can be dissolved in the solvent includes those that can be dissolved in the solvent as described above, specifically, at least one monomer selected from the group consisting of acrylonitrile, acrylic acid ester, and methacrylic acid ester. Copolymer formed by two or more monomers; Hydrogenated nitrile rubber; Vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE); Vinylidene fluoride-tetrafluoroethylene copolymer (VDF-TFE) Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); As the polymer that can be dissolved in the solvent, for example, only one of the above-described examples may be used, or two or more may be used in combination.

  The copolymer formed by two or more monomers including at least one monomer selected from the group consisting of acrylonitrile, acrylic acid ester and methacrylic acid ester includes acrylonitrile, acrylic acid ester and methacrylic acid ester. A copolymer formed by two or three of these monomers, one or more of acrylonitrile, acrylic acid ester and methacrylic acid ester, and other monomers [for example, 2 chloroethyl vinyl ether, methyl vinyl ketone, Vinylidene fluoride (VDF), chlorotrifluoroethylene (CTFE), trifluoroethylene (TFE), and the like]. Among these, a copolymer of acrylonitrile, acrylic acid ester, and methacrylic acid ester is more preferable, and the composition ratio (mass ratio) of acrylonitrile, acrylic acid ester, and methacrylic acid ester is 1: 2: 1 or 1: 2. : 2 is particularly preferred.

  From the viewpoint of favorably securing the above-described effect of the polymer that can be dissolved in the solvent, the amount of the polymer that can be dissolved in the solvent is 0.1 parts by mass or more, preferably 0.2 parts by mass with respect to 100 parts by mass of the positive electrode active material. Not less than part by mass. However, if the amount of the polymer that can be dissolved in the solvent is too large, for example, the polymer film formed on the surface of the positive electrode active material particles becomes too thick, which may cause a decrease in battery characteristics. Therefore, the amount of the polymer that can be dissolved in the solvent is 0.5 parts by mass or less, preferably 0.35 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

  In addition to the polymer that can be dissolved in the solvent exemplified above, other binders may be used as the binder. In the battery of the present invention, from the viewpoint of maintaining high battery characteristics, the amount of the polymer that can be dissolved in the solvent is limited as described above. In this case, however, the binding of each component in the positive electrode mixture layer is not possible. Since it may be sufficient, it is preferable to use a polymer that can be dissolved in a solvent and another binder in the binder of the positive electrode mixture layer. It is more preferable to use together.

  In the case of using a polymer that can be dissolved in a solvent and another binder in combination, the amount of the binder in the positive electrode mixture layer ( The total amount of the polymer soluble in the solvent and the other binder is preferably set to the amount described later.

  Examples of the conductive additive contained in the positive electrode according to the battery of the present invention include graphites such as natural graphite (such as flake graphite) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. It is preferable to use carbon materials such as carbon blacks; conductive fibers such as metal fibers; carbon fluorides; metal powders such as aluminum; zinc oxide; potassium titanate, etc. Conductive whiskers, conductive metal oxides such as titanium oxide, organic conductive materials such as polyphenylene derivatives, and the like can also be used.

  In the positive electrode mixture layer according to the battery, the amount of the positive electrode active material is preferably 96.5 to 98.1% by mass, and the amount of the binder is preferably 1.0 to 1.5% by mass. The amount of the conductive auxiliary is preferably 0.9 to 2.0% by mass.

  The positive electrode current collector is not particularly limited as long as it is an electron conductor that is substantially chemically stable in the battery that is 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 an 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 positive electrode electrical power collector is not specifically limited, For example, it is preferable that it is 5-50 micrometers.

  In producing the positive electrode, for example, a positive electrode mixture layer forming slurry in which a positive electrode active material, a binder and a conductive additive are dissolved or dispersed in a solvent is prepared, and this is applied to one or both sides of the positive electrode current collector. For example, a method of removing the solvent in the slurry by drying and applying a press treatment such as calendering as necessary to form a positive electrode mixture layer is employed. However, the positive electrode according to the battery of the present invention may be manufactured by other methods.

  In preparing the slurry for forming the positive electrode mixture layer, it is preferable to use a solution in which a rubber that can be dissolved in a solvent is dissolved in the solvent (the solvent of the slurry). That is, it is preferable to prepare a slurry for forming a positive electrode mixture layer by mixing a polymer solution that can be dissolved in a solvent with a positive electrode active material, a conductive auxiliary agent, or the like. In this case, a rubber film that can be dissolved in a solvent can be formed better on the surface of the positive electrode active material particles, so that it is possible to manufacture a battery that can better suppress the deterioration of battery characteristics due to cyclohexylbenzene. It becomes.

  In the slurry for forming the positive electrode mixture layer, the concentration of the solid content (components other than the solvent; the same shall apply hereinafter) including the positive electrode active material, the binder, and the conductive additive is, for example, 72 to 86% by mass. preferable.

  There is no restriction | limiting in particular about the method of apply | coating the slurry for positive mix layer formation to the surface of a positive electrode electrical power collector, The various application | coating method conventionally known is employable. Moreover, as conditions at the time of a press process, it is preferable that a linear pressure shall be 700-2000 kgf / cm, for example.

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

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode is the positive electrode and the non-aqueous electrolyte is the non-aqueous electrolyte. In addition, there is no restriction | limiting in particular about another structure and structure, The structure and structure employ | adopted by the nonaqueous electrolyte secondary battery known conventionally can be applied.

  For the negative electrode, for example, a negative electrode active material, a binder, and, if necessary, a negative electrode mixture layer containing a conductive auxiliary agent or the like may be used on one side or both sides of the current collector. it can.

  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 negative electrode mixture layer 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, the amount of conductive additive in the negative electrode mixture layer is desirably 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, various binders exemplified above as the binder for the positive electrode, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), ethylene-acrylic acid copolymer or the copolymer. Na ⁺ ion cross-linked product, ethylene-methacrylic acid copolymer or Na ⁺ ion cross-linked product of the copolymer, ethylene-methyl acrylate copolymer or Na ⁺ ion cross-linked product of the copolymer, ethylene-methyl methacrylate A copolymer or a Na ⁺ ion crosslinked product of the copolymer can be used, and 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 negative electrode mixture layer is preferably 1 to 5% by mass, for example.

  The negative electrode is prepared by, for example, preparing a negative electrode mixture layer forming slurry by dissolving or dispersing a negative electrode active material, a binder, and a conductive auxiliary agent in a solvent, if necessary, on one side of the current collector or It can be produced by a method of applying to both surfaces, drying to remove the solvent in the slurry, and further applying a press treatment such as calendering as necessary to form a negative electrode mixture layer. However, the negative electrode according to the battery of the present invention may be manufactured by other methods.

  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 used for the negative electrode is not particularly limited as long as it is a substantially chemically stable electronic conductor in the nonaqueous electrolyte 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 an 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.

  In the battery of the present invention, the positive electrode and the negative electrode are laminated with the separator interposed therebetween, and the laminated electrode body is wound in a spiral shape, and the cross section is formed into a flat shape as necessary. Thus, a wound electrode body can be used.

  For the separator, for example, 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%.

  As the battery outer casing, a steel or aluminum (aluminum alloy) cylindrical casing (such as a cylinder or a rectangular cylinder), a laminate outer casing made of a metal-deposited laminated film, or the like can be used. For example, when assembling the battery, the electrode body is accommodated in such an exterior body, the terminals of the exterior body and the electrodes of the electrode body are electrically connected according to a conventional method, and the nonaqueous After injecting the electrolytic solution into the outer package, the outer package may be sealed according to a conventional method, whereby the nonaqueous electrolyte secondary battery of the present invention can be manufactured.

  In the battery of the present invention, by adopting the configuration described so far, the thickness in the fully charged state is A (mm), and the thickness after being stored in the fully charged state in an environment of 85 ° C. for 24 hours is B (mm). ), The difference B-A between B and A can be 1 mm or less, and thus the amount of swelling during high-temperature storage is small, and good high-temperature storage characteristics can be ensured.

  The “full charge state” of the battery in this specification is a state in which the battery is charged at a constant voltage of 1.0 C up to 4.2 V and then charged at a constant voltage until the charging time reaches 2.5 hours. .

  The nonaqueous electrolyte secondary battery of the present invention can be used in the same applications as conventionally known nonaqueous electrolyte 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 slurry for forming positive electrode mixture layer>
Hydrogenated nitrile rubber, which is a polymer that can be dissolved in a solvent, was dissolved in NMP to prepare a polymer solution having a hydrogenated nitrile rubber concentration of 3 mass%. Also, PVDF was dissolved in NMP to prepare a PVDF solution having a PVDF concentration of 12% by mass.

A biaxial kneading extruder (“KRC Kneader” manufactured by Kurimoto Iron Works) was used for the preparation of the slurry for forming the positive electrode mixture layer. From the discharge port side of the twin-screw kneading extruder, the hopper charged with the PVDF solution, the hopper charged with the polymer solution, and the metering feeder are arranged in this order. The agent, the polymer solution, and the PVDF solution can be added in this order. Compound (A) which is a positive electrode active material: LiNi _0.5 Co _0.17 Mn _0.3 Mg _0.03 O ₂ and compound (B): LiCo _0.997 Al _0.003 O ₂ are combined with compound (A ) / Compound (B) = mixture mixed at a mass ratio of 30/70: 97.4 parts by mass and acetylene black as a conductive auxiliary agent: 1.5 parts by mass in a quantitative feeder as a powder feeder The polymer solution: 6.7 parts by mass (the ratio of the polymer that can be dissolved in the solvent in the amount of 100% by mass of all components excluding the solvent in the prepared slurry is 0.2% by mass); The PVDF solution: 7.5 parts by mass (the ratio of PVDF in 100% by mass of all components excluding the solvent in the prepared slurry was 0.9% by mass) was put into each hopper with a metering pump. The solid content concentration (concentration of components excluding the solvent) of the slurry when the powder and the polymer solution were kneaded was 93.8% by mass. Moreover, content of the polymer which can be melt | dissolved in the said solvent with respect to 100 mass parts of positive electrode active materials was 0.2 mass part.

  The material adjusted to such a predetermined amount ratio is charged into a twin-screw kneading extruder while being controlled so as to have a predetermined amount per unit time, and kneaded at a rotational speed of 100 rpm and a temperature of 32 ° C., A paste-like kneaded product was obtained. Then, the obtained kneaded product is put into a planetary mixer (“TK Hibis Disper Mix” manufactured by Tokushu Kika Kogyo Co., Ltd.), mixed with NMP, and a slurry for forming a positive electrode mixture layer having a viscosity suitable for coating. (The solid content concentration excluding the solvent was 83% by mass).

<Preparation of positive electrode>
The slurry for forming a positive electrode mixture layer is passed through a thickness of 70 mesh to remove coarse particles, and then uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 12 μm and dried. Furthermore, the press process was performed and the positive electrode which has a positive mix layer whose thickness (thickness per single side | surface of a collector) is 56 micrometers on both surfaces of the collector was produced. About the positive electrode mixture layer of the obtained positive electrode, the titration amount of hydrochloric acid calculated | required by the said neutralization titration method was 10.6 ml.

<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 for forming a negative electrode mixture layer. This negative electrode mixture layer forming slurry 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 obtain both sides of the current collector. In addition, a negative electrode having a negative electrode mixture layer having a thickness (thickness per one side of the current collector) of 62 μm was prepared.

<Production of electrode body>
The positive electrode and the negative electrode are overlapped via a separator (a polyethylene porous film having a thickness of 14 μm and an air permeability of 300 seconds / 100 cm ³ ), wound in a spiral shape, and then the cross section becomes flat. In this way, a flat wound electrode body was produced.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1.2 mol / l in a mixed solvent of methyl ethyl carbonate, diethyl carbonate and ethylene carbonate (volume ratio 2: 1: 3), and 2% by mass of vinylene carbonate (VC) and vinyl. A nonaqueous electrolytic solution was prepared by adding 0.5% by mass of ethylene carbonate (V-EC) and 0.2% by mass of cyclohexylbenzene (CB).

<Battery assembly>
A square nonaqueous electrolyte secondary battery was assembled using the electrode body and the nonaqueous electrolyte. 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. Thereafter, the electrode body was accommodated inside the outer can, and the lid was welded and fixed to the opening of the outer can. Finally, a nonaqueous electrolytic solution is injected into the outer can through a liquid injection hole provided in the lid to obtain a thickness of 4.6 mm, a width of 36 mm, and a height of 51 mm. The structure shown in FIG. A rectangular nonaqueous electrolyte secondary battery having an external appearance was produced.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 is spirally wound through the separator 3 as described above, and then pressurized so as to be flattened, and is accommodated in a rectangular tube-shaped outer can 4 together with the electrolyte as a flat wound electrode body 6. ing. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The outer can 4 is made of an aluminum alloy and constitutes an outer casing of the battery. The outer can 4 also serves as a positive electrode terminal. And the insulator 5 which consists of a polyethylene sheet is arrange | positioned at the bottom part of the armored can 4, From the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3, it connects to each one end of the positive electrode 1 and the negative electrode 2 The positive electrode lead body 7 and the negative electrode lead body 8 thus drawn are drawn out. Further, a stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the outer can 4 through a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the armored can 4, and the opening part of the armored can 4 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the outer can 4 and the lid plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13. The terminal 11 functions as a negative electrode terminal by conducting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, but depending on the material of the outer can 4, the sign may be reversed. There is also.

  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 side portion of the flat wound electrode body is not cross-sectional.

Example 2
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 0.5% by mass, and a square shape was obtained in the same manner as in Example 1 except that this non-aqueous electrolyte was used. A non-aqueous electrolyte secondary battery was produced.

Example 3
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 1.5% by mass, and a rectangular shape was prepared in the same manner as in Example 1 except that this nonaqueous electrolytic solution was used. A non-aqueous electrolyte secondary battery was produced.

Example 4
A polymer solution was prepared so that the concentration of the hydrogenated nitrile rubber was 7% by mass, and the positive electrode active material was compound (A): LiNi _0.876 Co _0.1 Mn _0.012 Mg _0.01 Ba _0.002. O ₂ and compound (B): LiCo _0.997 Al _0.003 O ₂ were mixed at a mass ratio of compound (A) / compound (B) = 30/70, and the polymer solution: 6.7 parts by mass (The ratio of the polymer that can be dissolved in the solvent in 100% by mass of the total components excluding the solvent in the prepared slurry is 0.4% by mass) and the PVDF solution: 5.8 parts by mass (in the prepared slurry) The ratio of PVDF in 100% by mass of all components excluding the solvent is 0.7% by mass) in a separate hopper with a metering pump, and the slurry when the powder and the polymer solution are kneaded. A slurry for forming a positive electrode mixture layer was prepared in the same manner as in Example 1 except that the solid content concentration of Li (concentration of components excluding the solvent) was 94.0% by mass. In the slurry for forming a positive electrode mixture layer, the content of the polymer soluble in the solvent with respect to 100 parts by mass of the positive electrode active material was 0.4 parts by mass. And the positive electrode was produced like Example 1 except having used this slurry for positive mix layer formation.

  About the positive electrode mixture layer of the obtained positive electrode, the titration amount of hydrochloric acid calculated | required by the said neutralization titration method was 13.5 ml.

  Further, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 1.5% by mass.

  And the square non-aqueous electrolyte secondary battery was produced like Example 1 except having used the said positive electrode and the said non-aqueous electrolyte.

Example 5
A slurry for forming a positive electrode mixture layer was prepared in the same manner as in Example 4 except that the polymer soluble in the solvent was changed to a VDF-TFE copolymer (composition ratio of each monomer was 9: 1 by mass ratio). A positive electrode was prepared in the same manner as in Example 1 except that this positive electrode mixture layer forming slurry was used. About the positive electrode mixture layer of the obtained positive electrode, the titration amount of hydrochloric acid calculated | required by the said neutralization titration method was 11.0 ml.

  And the square non-aqueous-electrolyte secondary battery was produced like Example 4 except having used the said positive electrode.

Comparative Example 1
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that CB was not added, and a rectangular non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this non-aqueous electrolyte was used. Produced.

Comparative Example 2
The PVDF solution: 7.5 parts by mass (the ratio of PVDF in 100% by mass of all components excluding the solvent in the prepared slurry is 0.9% by mass), and the PVDF solution: 1.7 parts by mass ( The ratio of PVDF in 100% by mass of all components in the slurry to be prepared is 0.2% by mass) in a separate hopper with a metering pump, and the powder and the PVDF solution are first added. The slurry for forming the positive electrode mixture layer was prepared in the same manner as in Example 1 except that the solid content concentration (concentration of components excluding the solvent) of the slurry when charged and kneaded was 93.8% by mass. A positive electrode was prepared in the same manner as in Example 1 except that this slurry was prepared. About the positive electrode mixture layer of the obtained positive electrode, the titration amount of hydrochloric acid calculated | required by the said neutralization titration method was 12.2 ml.

  In addition, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 0.2% by mass.

  And the square non-aqueous electrolyte secondary battery was produced like Example 1 except having used the said positive electrode and the said non-aqueous electrolyte.

Comparative Example 3
Polymer solution prepared in the same manner as in Example 1 except that the concentration of the hydrogenated nitrile rubber was changed to 9% by mass: 7.8 parts by mass (the amount in 100% by mass of all components excluding the solvent in the prepared slurry) The ratio of the soluble polymer is 0.7% by mass) and the PVDF solution: 3.3 parts by mass (the amount of PVDF in 100% by mass of all components excluding the solvent in the prepared slurry is 0.4% by mass) %) In a separate hopper with a metering pump, and the solid content concentration of the slurry (concentration of components excluding the solvent) when the powder and the polymer solution are kneaded is 93.3 mass%. A positive electrode mixture layer forming slurry was prepared in the same manner as in Example 1 except for the above. In the slurry for forming a positive electrode mixture layer, the content of the polymer that can be dissolved in the solvent with respect to 100 parts by mass of the positive electrode active material was 0.7 parts by mass.

  Further, a positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture layer forming slurry was used. With respect to the positive electrode mixture layer of the positive electrode obtained, the titration amount of hydrochloric acid obtained by the neutralization titration method was 9.0 ml.

  And the square non-aqueous-electrolyte secondary battery was produced like Example 1 except having used the said positive electrode.

Comparative Example 4
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 2.0% by mass, and a square shape was obtained in the same manner as in Example 4 except that this nonaqueous electrolytic solution was used. A non-aqueous electrolyte secondary battery was produced.

Comparative Example 5
A polymer solution is prepared so that the concentration of hydrogenated nitrile rubber is 7% by mass, and the positive electrode active material is compound (A): LiNi _0.95 Co _0.038 Mg _0.01 Ba _0.002 O ₂ and a compound. (B): LiCo _0.997 Al _0.003 O ₂ was mixed at a mass ratio of compound (A) / compound (B) = 30/70, and the polymer solution: 6.7 parts by mass (prepared The ratio of the polymer that can be dissolved in the solvent in 100% by mass of all components in the slurry excluding the solvent is 0.4% by mass) and the PVDF solution: 5.8 parts by mass (excluding the solvent in the prepared slurry) When the ratio of PVDF in 100% by mass of all components is 0.7% by mass), each is put into a separate hopper with a metering pump, and the powder and the polymer solution soluble in the solvent are kneaded. The solid content of slurry (concentration of the components except the solvent), except that was made to be 94.0 wt%, were prepared in to the positive electrode mixture layer-forming composition as in Example 1. In the slurry for forming a positive electrode mixture layer, the content of the polymer soluble in the solvent with respect to 100 parts by mass of the positive electrode active material was 0.4 parts by mass. And the positive electrode was produced like Example 1 except having used this slurry for positive mix layer formation.

  With respect to the positive electrode mixture layer of the obtained positive electrode, the titration amount of hydrochloric acid obtained by the neutralization titration method was 15.1 ml.

  Further, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of CB added was changed to 1.5% by mass.

  And the square non-aqueous electrolyte secondary battery was produced like Example 1 except having used the said positive electrode and the said non-aqueous electrolyte.

  Table 1 shows the configuration of the positive electrode active material used in the batteries of Examples and Comparative Examples, Table 2 shows the configuration of the binder related to the positive electrode mixture layer, and hydrochloric acid used for neutralization of the alkali related to the positive electrode mixture layer Table 3 shows the titration amount and the amount of CB in the non-aqueous electrolyte.

  The following characteristic evaluation was performed about the nonaqueous electrolyte secondary battery of Examples 1-5 and Comparative Examples 1-5. These evaluation results are shown in Table 4.

<Discharge capacity>
For each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 5, after charging at a constant current of 1.0 C up to 4.2 V, the battery was then charged at a constant voltage until the charging time reached 2.5 hours. A constant current discharge was performed until the battery voltage was 3.0 V at 0.0 C, and the discharge capacity at that time was determined (note that the lithium-based battery voltage at the time of the constant current charge is 4.3 V). In Table 4, the discharge capacity obtained for each battery is shown as a relative value when the discharge capacity of Example 1 is taken as 100.

<Battery swelling measurement after high temperature storage>
About each battery of Examples 1-5 and Comparative Examples 1-5, after performing constant current-constant voltage charge to 4.2V on the same conditions as the said discharge capacity measurement, it stores for 24 hours in an environment of 85 degreeC, The thickness (B) of the battery after taking out was measured, and the change (swelling; B-A) from the thickness (A) of the battery before storage was determined.

<Nail penetration test>
About each battery of Examples 1-5 and Comparative Examples 1-5, after charging with a constant current of 1.0C to 4.25V, after that, constant voltage charge was performed until charge time became 2.5 hours. Each battery after charging was pierced with a 2.5 mmφ nail at a speed of 0.1 mm / second in an environment of 25 ° C., and when the battery voltage reached 4.1 V, the nail was stopped and the battery temperature was measured. Then, the time from when the battery voltage reached 4.1 V until the battery temperature reached 150 ° C. was examined.

<Charge / discharge cycle characteristics evaluation>
For each of the batteries of Examples 1 to 5 and Comparative Examples 1 to 5, after charging at a constant current of 1.0 C up to 4.2 V, the battery was then charged at a constant voltage until the charging time reached 2.5 hours. A series of operations in which the battery voltage was discharged at a constant current to 3.0 V at 0.0 C was taken as one cycle, and this was repeated (the lithium-based battery voltage at the time of constant current charging was 4.3 V) .) In Table 4, it shows by the maintenance factor (%) with respect to the discharge capacity of the 1st cycle of the discharge capacity of the 500th cycle obtained about each battery.

  As is clear from the results shown in Table 4, the batteries of Examples 1 to 5 using the positive electrode having a proper configuration and the nonaqueous electrolytic solution containing an appropriate amount of CB show battery swelling after high-temperature storage. In addition, the time until the temperature during the nail penetration test reaches 150 ° C. is long, high safety is ensured, the discharge capacity is large, and the charge / discharge cycle characteristics are also good.

  On the other hand, the battery of Comparative Example 1 using the non-aqueous electrolyte containing no CB has a large battery swelling during high temperature storage, and the time until the battery temperature reaches 150 ° C. is short even during the nail penetration test. In the battery of the example, this is the reason why the battery swelling suppression effect during high temperature storage and the safety during the nail penetration test were excellent, but CB in the non-aqueous electrolyte decomposed on the positive electrode side during high temperature storage. Thus, it is considered that the decomposition product formed a film on the surface of the positive electrode, thereby suppressing gas generation due to decomposition of alkali in the positive electrode mixture layer and suppressing swelling of the battery. Even during the nail penetration test, as with high temperature storage, CB decomposes on the positive electrode side due to the temperature rise inside the battery, and the decomposition product forms a film on the positive electrode surface, thereby increasing the internal resistance. It is thought that the reaction with the electrolytic solution could be suppressed.

  The battery of Comparative Example 4 using the non-aqueous electrolyte in which the amount of CB added was 2.0% by mass had a long time until the temperature during the nail penetration test reached 150 ° C., and the safety was good. However, the discharge capacity, the effect of suppressing battery swelling during high temperature storage, and the charge / discharge cycle characteristics are inferior. This is because the amount of CB in the battery was too large, and during high-temperature storage, the generation of gas due to the decomposition of CB itself increased more than the suppression of gas generation at the positive electrode, which caused the swelling during high-temperature storage to deteriorate. It is done. In addition, regarding the discharge capacity and charge / discharge cycle characteristics, since the amount of CB in the battery was too large, the resistance of the positive electrode increased, and the CB decomposition products generated in the charge / discharge cycle caused clogging of the separator. It is considered that the discharge capacity and charge / discharge cycle characteristics were deteriorated by these.

  Further, the battery of Comparative Example 2 using only PVDF as the binder of the positive electrode mixture layer is inferior in the effect of suppressing the battery swelling during high-temperature storage and the safety of the nail penetration test. Therefore, by using a polymer that can be dissolved in a solvent other than PVDF for the binder of the positive electrode mixture layer, the reactivity of the positive electrode is suppressed as in the case of using a non-aqueous electrolyte containing an appropriate amount of CB. It is thought that there is an effect to do. On the other hand, the battery of Comparative Example 3 in which the amount of the polymer that can be dissolved in the solvent with respect to the amount of the positive electrode active material is too large is inferior in discharge capacity.

Further, instead of the layered lithium / nickel / cobalt / manganese composite oxide (A), the LiN _0.95 Co _0.038 Mg _0.01 Ba _0.002 O ₂ containing no Mn was used. Although the battery has an increased discharge capacity due to an increase in the Ni ratio, the battery swells during high-temperature storage and the safety of the nail penetration test is also deteriorated. Among these, the decrease in the effect of suppressing battery swelling during high-temperature storage is thought to be due to an increase in gas generation during high-temperature storage due to the large amount of residual alkali in the positive electrode mixture layer. Moreover, it is thought that the safety | security fall in the battery of the comparative example 5 was because the heat_generation | fever at the time of a short circuit became quick because the lithium containing complex oxide with much Ni amount was structurally unstable in the charging state.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (6)

A nonaqueous electrolyte solution comprising a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one or both sides of a current collector, a negative electrode, a separator, and a nonaqueous electrolyte solution A secondary battery,
At least a part of the positive electrode active material has a general formula of LiNi _x Co _(1-xyz) Mny _y M ¹ _z O ₂ (0.5 ≦ x ≦ 0.9, 0.005 ≦ y ≦ 0. 3, 0.003 ≦ z ≦ 0.05, and the element M ¹ is a metal element other than Li, Ni, Co, and Mn, and is made of Mg, Al, Ti, Sr, Zr, Nb, Ag, and Ba. A layered lithium-nickel-cobalt-manganese composite oxide (A) represented by (including at least one element selected from the group),
The titration amount of hydrochloric acid required for neutralization of alkali in the positive electrode mixture layer obtained by the following neutralization titration method is 14 ml or less,
At least a part of the binder contains a polymer that can be dissolved in a solvent other than polyvinylidene fluoride, and the content of the polymer that can be dissolved in the solvent is 0.000 parts by mass with respect to 100 parts by mass of the positive electrode active material. 1 to 0.5 parts by mass,
A non-aqueous electrolyte secondary battery in which cyclohexylbenzene is contained in an amount of 0.2 to 1.5 mass% in the total amount of the solvent of the non-aqueous electrolyte is used as the non-aqueous electrolyte.
The neutralization titration method:
Nitrogen gas in a container containing a positive electrode mixture layer collected from the positive electrode and weighed to about 20.0 g, and 100 ml of water having a pH of 7 and an electric conductivity of 2 μS / cm or less purified by an ion exchange method. Then, the container is sealed, and the positive electrode mixture layer is immersed in water in the container while stirring with a magnetic stirrer for 60 minutes. Thereafter, 25.0 ml of the supernatant obtained by filtering the mixture of water and the positive electrode mixture layer in the container is weighed, and a few drops of a 0.1% by weight methyl orange solution are added to the sample solution. The sample solution was intermittently titrated with 0.02 mol / l hydrochloric acid while stirring with a magnetic stirrer, and the amount of hydrochloric acid added to the sample solution until the color of the sample solution changed from yellow to orange was measured. The titration amount of hydrochloric acid required for neutralization of alkali in the positive electrode mixture layer is used. As the positive electrode active material, the general formula LiNi _a Co _(1- abc ₎ Mn _b M ² _c O ₂ (0 ≦ a ≦ 0.03, 0 ≦ b ≦ 0.02, 0.002 ≦ c ≦ 0) is .02, the element ^{M 2} is Li, Ni, a metal element other than Co and Mn, Mg, Al, Ti, Sr, Zr, Nb, at least one selected from the group consisting of Ag and Ba 2. The non-aqueous electrolyte 2 according to claim 1, wherein the layered lithium / cobalt composite oxide (B) represented by (including the element) is contained together with the layered lithium / nickel / cobalt / manganese composite oxide (A). Next battery.   A copolymer formed by two or more monomers including at least one monomer selected from the group consisting of acrylonitrile, acrylic acid esters and methacrylic acid esters, wherein the polymer soluble in a solvent other than polyvinylidene fluoride, hydrogen A nitrile rubber, a vinylidene fluoride-chlorotrifluoroethylene copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, or a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer. The nonaqueous electrolyte secondary battery as described.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, comprising polyvinylidene fluoride as a binder together with a polymer that can be dissolved in a solvent other than polyvinylidene fluoride.   The difference between B and A when the thickness of the battery in a fully charged state is A (mm) and the thickness of the battery after being stored in an environment of 85 ° C. for 24 hours in a fully charged state is B (mm) B -A is 1 mm or less, The nonaqueous electrolyte secondary battery in any one of Claims 1-4. A method for producing the non-aqueous electrolyte secondary battery according to claim 1,
A positive electrode mixture layer forming slurry containing a positive electrode active material, a conductive additive, a binder and a solvent is prepared, and the positive electrode mixture is formed on one or both surfaces of the current collector using the positive electrode mixture layer forming slurry. Producing a positive electrode having a layer;
A step of preparing a nonaqueous electrolytic solution having a cyclohexylbenzene content of 0.2 to 1.5 mass% in the total amount of the solvent;
And assembling a battery using the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte,
In preparing the slurry for forming the positive electrode mixture layer, a non-aqueous electrolyte solution is used in which a polymer that can be dissolved in a solvent other than polyvinylidene fluoride as a binder is dissolved in the solvent. A method for manufacturing a secondary battery.

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