JP2015090857A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which enables the improvement in the thermal stability when a battery is stored in a high-temperature condition and battery characteristics.SOLUTION: A lithium ion secondary battery comprises: a positive electrode active material including a lithium nickel complex oxide; and a nonaqueous electrolyte which contains at least one disulfonate selected from a group consisting of a cyclic disulfonate ester and a chain disulfonate ester, and at least one carbonate selected from a group consisting of a vinylene carbonate and a vinyl ethylene carbonate and having an unsaturated bond. The nonaqueous electrolyte includes 0.05 mass % or more and 0.5 mass% or less of the disulfonate to the total mass of the nonaqueous electrolyte, and 0.2 mass% or more and 1.5 mass% or less of the carbonate having an unsaturated bond to the total mass of the nonaqueous electrolyte.

Description

  The present invention relates to a lithium ion secondary battery.

  2. Description of the Related Art In recent years, a technique using a lithium nickel composite oxide as a positive electrode active material that realizes a high potential and a high capacity in a lithium ion secondary battery has been proposed.

  Here, in a lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material, a large amount of gas is generated or battery characteristics deteriorate when stored at a high temperature in a fully charged state. That was a problem.

  Therefore, Patent Document 1 discloses a technique for improving thermal stability at high temperature by adding, for example, a cyclic carbonate having an unsaturated bond to an electrolytic solution.

JP 2004-139743 A

  However, the technique disclosed in Patent Document 1 has a problem that the internal resistance of the lithium ion secondary battery is increased, and battery characteristics such as output are decreased.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is a new and improved that can improve the thermal stability and battery characteristics during high-temperature storage. The object is to provide a lithium ion secondary battery.

ただし、前記化学式（１）および（２）において、Ｒ_１およびＲ_２は、互いに独立して、置換または非置換の炭素数１〜５のアルキレン（ａｌｋｙｌｅｎｅ）基、および置換または非置換の炭素数１〜５のフルオロアルキレン（ｆｌｕｏｒｏａｌｋｙｌｅｎｅ）基からなる群より選択された１つであり、Ｒ_３およびＲ_４は、互いに独立して、置換または非置換の炭素数１〜４のアルキル（ａｌｋｙｌ）基、および置換または非置換の炭素数１〜４のフルオロアルキル（ｆｌｕｏｒｏａｌｋｙｌ）基からなる群より選択された１つであり、ｘおよびｙは、互いに独立して、０〜５から選択された整数である。 In order to solve the above-described problem, according to an aspect of the present invention, a positive electrode active material including a lithium nickel composite oxide, a cyclic disulfonate represented by the following chemical formula (1), and a chemical formula ( 2) selected from the group consisting of at least one disulfonic acid ester selected from the group consisting of linear disulfonic acid esters represented by 2), vinylene carbonate and vinyl ethylene carbonate A non-aqueous electrolyte containing at least one or more types of carbonate having an unsaturated bond, wherein the non-aqueous electrolyte contains the disulfonic acid ester in an amount of 0. 0 to the total mass of the non-aqueous electrolyte. Contains from 05% by weight to 0.5% by weight Said containing 0.2 wt% to 1.5 wt% or less carbonate having an unsaturated bond relative to the total mass of the nonaqueous electrolytic solution, there is provided a lithium ion secondary battery.

In the chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms and a substituted or unsubstituted carbon number. One selected from the group consisting of 1 to 5 fluoroalkylene groups, wherein R ₃ and R ₄ are each independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms. , And one selected from the group consisting of substituted or unsubstituted fluoroalkyl groups having 1 to 4 carbon atoms, and x and y are each independently an integer selected from 0 to 5 is there.

  According to this aspect, since the lithium ion secondary battery according to an embodiment of the present invention suppresses gas generation and resistance increase during high temperature storage, thermal stability and battery characteristics are improved.

In the chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 or 2 carbon atoms, and R ₃ and R ₄ are independently , A substituted or unsubstituted methyl group, and a substituted or unsubstituted fluoromethyl group, and x and y are each independently an integer selected from 1 to 3 May be.

  According to this aspect, since the lithium ion secondary battery according to one embodiment of the present invention further suppresses gas generation and resistance increase during high temperature storage, thermal stability and battery characteristics are improved.

ただし、前記化学式（３）において、Ｒｆ_１およびＲｆ_２は、互いに独立して、フッ素および炭素数１〜４のフルオロアルキル（ｆｌｕｏｒｏａｌｋｙｌ）基からなる群より選択された１つを表す。 The non-aqueous electrolyte may further include an imide lithium salt represented by the following chemical formula (3).

However, in the chemical formula (3), Rf ₁ and Rf ₂ each independently represents one selected from the group consisting of fluorine and a fluoroalkyl group having 1 to 4 carbon atoms.

  According to this aspect, since the lithium ion secondary battery according to one embodiment of the present invention further suppresses gas generation and resistance increase during high temperature storage, thermal stability and battery characteristics are improved.

In the chemical formula (3), Rf ₁ and Rf ₂ may be fluorine (F).

  According to this aspect, since the lithium ion secondary battery according to one embodiment of the present invention further suppresses gas generation and resistance increase during high temperature storage, thermal stability and battery characteristics are improved.

The lithium nickel composite oxide may have a composition represented by the following general formula (1).
Li _a (Ni _b M _b-1 ) O ₂ (1)
In the general formula (1),
M is one or more kinds of metals other than Ni,
a is 1.0 ≦ a ≦ 1.2,
b is 0.5 ≦ b ≦ 1.0.

  According to this aspect, the lithium ion secondary battery according to an embodiment of the present invention can be more suitably used because gas generation and deterioration of battery characteristics during high-temperature storage are effectively suppressed.

  As described above, according to the present invention, it is possible to improve the thermal stability and battery characteristics during high temperature storage.

It is explanatory drawing explaining the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Overview of Lithium Ion Secondary Battery According to One Embodiment of the Present Invention>
First, an outline of a lithium ion secondary battery according to an embodiment of the present invention will be described.

  The lithium ion secondary battery which concerns on one Embodiment of this invention contains lithium nickel complex oxide as a positive electrode active material. A lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material can realize a high potential and a high discharge capacity, but a large amount of gas is generated when stored at a high temperature in a fully charged state. Battery characteristics will deteriorate.

  In particular, a lithium ion secondary battery using a lithium nickel composite oxide represented by the following general formula (1) having a high nickel (Ni) ratio as a positive electrode active material has a high energy density. A solution to the above problem has been desired.

Li _a (Ni _b M _b-1 ) O ₂ (1)
However, in the said General formula (1), M is one or more types of metals other than Ni, a is 1.0 <= a <= 1.2, b is 0.5 <= b <= 1. 0.

  Therefore, the present inventor has come up with the present invention by examining the above-mentioned problems in detail. A lithium ion secondary battery according to an embodiment of the present invention contains a disulfonic acid ester and a carbonate having an unsaturated bond in the nonaqueous electrolytic solution at the same time within the concentration range specified in the present invention. Thus, gas generation, capacity reduction, and resistance increase during high-temperature storage can be suppressed. Therefore, according to the lithium ion secondary battery which concerns on one Embodiment of this invention, it is possible to improve the thermal stability and battery characteristic at the time of high temperature storage.

  Here, the disulfonic acid ester in the above is at least selected from the group consisting of a cyclic disulfonic acid ester represented by the following chemical formula (1) and a chain disulfonic acid ester represented by the following chemical formula (2), for example. One or more disulfonic acid esters.

In the above chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms, and a substituted or unsubstituted carbon atom having 1 to 5 carbon atoms. R ₃ and R ₄ are each independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted carbon number. It is one selected from the group consisting of 1 to 4 fluoroalkyl groups, and x and y are each independently an integer selected from 0 to 5.

  Moreover, the carbonate which has an unsaturated bond in the above is at least 1 or more types of carbonate selected from the group which consists of vinylene carbonate and vinyl ethylene carbonate, for example.

  Furthermore, the disulfonic acid ester and the carbonate having an unsaturated bond may be used as a mixture of plural kinds.

<2. Configuration of lithium ion secondary battery>
Below, with reference to FIG. 1, the specific structure of the lithium ion secondary battery 10 which concerns on one Embodiment of this invention mentioned above is demonstrated. FIG. 1 is an explanatory view illustrating the configuration of a lithium ion secondary battery according to an embodiment of the present invention.

  As shown in FIG. 1, a lithium ion secondary battery 10 is a lithium ion secondary battery using a lithium nickel composite oxide as a positive electrode active material, and includes a positive electrode 20, a negative electrode 30, a separator layer 40, . The form of the lithium ion secondary battery 10 is not particularly limited. For example, the lithium ion secondary battery 10 may be any one of a cylindrical shape, a square shape, a laminate shape, a button shape, and the like.

  The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 may be any conductor as long as it is made of, for example, aluminum, stainless steel, nickel-plated steel, or the like.

  The positive electrode active material layer 22 includes at least a positive electrode active material and a conductive agent, and may further include a binder. In addition, content in particular of a positive electrode active material, a electrically conductive agent, and a binder is not restrict | limited, Any may be sufficient if it is content applied in the conventional lithium ion secondary battery.

  The positive electrode active material is, for example, a lithium nickel composite oxide. For example, the positive electrode active material is a lithium nickel composite oxide having a high Ni ratio, and specifically, may be a lithium nickel composite oxide represented by the following general formula (1).

Li _a (Ni _b M _b-1 ) O ₂ (1)

  In the general formula (1), M is one or more metals other than Ni, a is 1.0 ≦ a ≦ 1.2, and b is 0.5 ≦ b ≦ 1.0. There may be.

  The lithium ion secondary battery according to one embodiment of the present invention can suppress gas generation, capacity reduction, and resistance increase during high temperature storage. Therefore, it is possible to use, as the positive electrode active material, a lithium nickel composite oxide having the above composition, which has high energy density and has been desired to improve thermal stability and electrical characteristics during high temperature storage.

  Examples of the conductive agent include carbon black such as ketjen black and acetylene black, natural graphite, and artificial graphite. In addition, a conductive agent will not be restrict | limited especially if it is for improving the electroconductivity of a positive electrode.

  Examples of the binder include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butylene rubber, acrylonitrile butadiene rubber, and acrylonitrile butadiene rubber. ), Fluoroelastomer, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, and the like. The binder is not particularly limited as long as it can bind the positive electrode active material and the conductive agent onto the current collector 21.

  The positive electrode active material layer 22 includes, for example, a slurry in which a positive electrode active material, a conductive agent, and a binder are dispersed in a suitable organic solvent (for example, N-methyl-2-pyrrolidone). slurry) is applied onto the current collector 21, dried and rolled.

  The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 may be any material as long as it is a conductor. For example, the current collector 31 is made of aluminum, stainless steel, nickel-plated steel, or the like.

Here, the negative electrode active material layer 32 includes at least a negative electrode active material, and may further include a binder. Examples of the negative electrode active material include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si), tin (Sn), or oxides thereof. A mixture of fine particles of graphite and a graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, and titanium oxide (TiO _x ) compounds such as Li ₄ Ti ₅ O ₁₂ can be used. . Note that the oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, as the negative electrode active material, for example, metallic lithium can be used.

  Further, as the binder, the same binder as that constituting the positive electrode active material layer 22 can be used. Note that the mass ratio between the negative electrode active material and the binder is not particularly limited, and the mass ratio employed in the conventional lithium ion secondary battery is also applicable in the present invention.

  The separator layer 40 includes a separator 41 and an electrolytic solution 43.

The separator 41 is not particularly limited as long as it is used as a separator of a lithium ion secondary battery, and any separator can be used. As the separator 41, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. The separator may be coated with an inorganic material such as Al ₂ O ₃ or SiO ₂ , and may contain the above-described inorganic material as a filler. Examples of the material constituting the separator include, for example, polyolefin resins represented by polyethylene, polypropylene, and the like, polyethylene terephthalate, and polybutylene terephthalate. Polyester resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinylether (perfluorovinylether) ) Copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-fluoroethylene copolymers, vinylidene fluoride- Hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, fluoride Vinylidene-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene- It can be used tetrafluoroethylene copolymer. The porosity of the separator is not particularly limited, and the porosity of the separator of the conventional lithium ion secondary battery can be arbitrarily applied.

  The electrolytic solution 43 includes a lithium salt, a solvent, a disulfonic acid ester as a first additive, and a carbonate having an unsaturated bond as a second additive.

The lithium salt is an electrolyte of the electrolytic solution 43. Lithium _{salt, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, LiSbF 6, LiSO 3 CF 3, LiC (SO 2 CF 2 CF 3) 3, LiC (SO 2 CF 3) 3, LiI, LiCl, LiF, _{LiPF 5 (SO 2 CF 3)} , LiPF 4 (SO 2 CF 3) may be a ₂ or the like. These lithium salts can be used alone or in admixture of two or more. The concentration of the lithium salt is not particularly limited, but is contained in the electrolytic solution 43 at a concentration of about 0.5 to 2.0 mol / L, for example.

  The solvent is a non-aqueous solvent that dissolves each of the lithium salt and the additive. Examples of the solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate; γ-butyrolactone, Cyclic esters such as valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; methyl formate te), methyl acetate, methyl butyrate and other chain esters; tetrahydrofuran (tetrahydrofuran) or a derivative thereof; 1,3-dioxane, 1,4-dioxane ( Ethers such as 1,4-dioxane), 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme; Nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; Sulfide (ethylene sulfide), sulfolane (Sulfolane), alone sultone (sultone) or derivatives thereof, or their although two or more can be used as a mixture, but is not limited thereto. In addition, when mixing and using 2 or more types of solvents, the mixing ratio used by the conventional lithium ion secondary battery is applicable for the mixing ratio of each solvent.

  Specifically, the disulfonic acid ester as the first additive is a cyclic disulfonic acid ester having a structure represented by the following chemical formula (1) or a chain disulfone having a structure represented by the chemical formula (2). It is an acid ester.

In the above chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms and a substituted or unsubstituted fluoro group having 1 to 5 carbon atoms. One selected from the group consisting of alkylene groups, and R ₃ and R ₄ , independently of each other, are substituted or unsubstituted alkyl groups having 1 to 4 carbon atoms, and substituted or unsubstituted carbon atoms having 1 to 4 is one selected from the group consisting of 4 fluoroalkyl groups, and x and y are each independently an integer selected from 0 to 5.

Further, the first additive is specifically, in the above chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 or 2 carbon atoms. And R ₃ and R ₄ are each independently one selected from a substituted or unsubstituted methyl group and a substituted or unsubstituted fluoromethyl group, and x and y are independently of each other The disulfonic acid ester which is an integer selected from 1 to 3 may be used.

  Further, more specifically, the first additive may be at least one disulfonic acid ester selected from the following compounds (11), (12) and (21) to (24). .

  The carbonate having an unsaturated bond as the second additive is specifically a cyclic carbonate having an unsaturated bond. More specifically, the second additive may be vinylene carbonate or vinyl ethylene carbonate.

  A lithium ion secondary battery according to an embodiment of the present invention includes both the first additive and the second additive in the electrolytic solution 43, as demonstrated in the examples described later. Gas generation, capacity reduction, and resistance increase during high temperature storage can be suppressed. Specifically, when the electrolytic solution 43 includes the first additive and does not include the second additive, the amount of gas generated during high-temperature storage is significantly increased. In addition, when the electrolytic solution 43 includes the second additive and does not include the first additive, the resistance increase rate during high-temperature storage increases.

  Moreover, the addition density | concentration of the disulfonic acid ester which is a 1st additive is 0.05 to 0.5 mass% with respect to the total mass of electrolyte solution. As demonstrated in the examples described later, when the first additive has a concentration within these ranges, in the lithium ion secondary battery, gas generation, capacity reduction, and resistance increase during high-temperature storage are observed. It is suppressed. Specifically, when the concentration of the disulfonic acid ester is less than 0.05% by mass, the amount of gas generated during high-temperature storage increases and the resistance increase rate increases. On the other hand, when the concentration of the disulfonic acid ester exceeds 0.5% by mass, the amount of gas generated during high-temperature storage is significantly increased.

  Furthermore, the addition density | concentration of the carbonate which has an unsaturated bond which is a 2nd additive is 0.2 to 1.5 mass% with respect to the total mass of electrolyte solution. As demonstrated in the examples described later, when the second additive has a concentration within these ranges, in the lithium ion secondary battery, gas generation, capacity reduction, and resistance increase during high-temperature storage are observed. It is suppressed. Specifically, when the concentration of the carbonate having an unsaturated bond is less than 0.2% by mass, the amount of gas generated during high-temperature storage is significantly increased. On the other hand, when the concentration of the carbonate having an unsaturated bond exceeds 1.5% by mass, the amount of gas generated during high-temperature storage increases and the resistance increase rate increases.

  Furthermore, the electrolytic solution 43 may contain an imide lithium salt that is a third additive.

  Specifically, the imide lithium salt as the third additive may be an imide lithium salt having a structure represented by the following chemical formula (3).

In the chemical formula (3), Rf ₁ and Rf ₂ each independently represent one selected from the group consisting of fluorine and a fluoroalkyl group having 1 to 4 carbon atoms.

  The third additive may specifically be the following compound (31) which is an imide lithium salt.

  The lithium ion secondary battery according to an embodiment of the present invention includes the above third additive in the electrolytic solution 43, so that gas generation and capacity during high-temperature storage are demonstrated, as will be demonstrated in Examples described later. Reduction and increase in resistance are further suppressed. Here, the additive concentration of the third additive is not particularly limited as long as it is an additive concentration acceptable as an additive for the electrolyte in a general lithium ion secondary battery. It is 0.5 mass% or more and 2.0 mass% or less with respect to mass. When the third additive is added to the electrolytic solution 43 at a concentration in such a range, the lithium ion secondary battery according to one embodiment of the present invention has gas generation, capacity reduction, and resistance increase during high-temperature storage. Remarkably suppressed.

  In addition to the first to third additives described above, the electrolyte solution 43 may be added with various other additives such as a negative electrode SEI (Solid Electrolyte Interface) forming agent and a surfactant. Examples of such additives include succinic anhydride, lithium bisoxalate (lithium bis (oxalate)), lithium tetrafluoroborate, dinitrile compound, propane sultone ( Propane sultone, butane sultone, propene sultone, 3-sulfolene, fluorinated allyl ether, fluorinated acrylate, etc. can be used. . In addition, as the concentration of the additive, the concentration of the additive in a general lithium ion secondary battery can be used.

<3. Manufacturing method of lithium ion secondary battery>
Then, the manufacturing method of the lithium ion secondary battery 10 is demonstrated.

  The positive electrode 20 is manufactured as follows. First, a mixture of a positive electrode active material, a conductive agent, and a binder in a desired ratio is dispersed in an organic solvent (for example, N-methyl-2-pyrrolidone) to form a slurry. Next, the positive electrode active material layer 22 is formed by forming (for example, coating) the slurry on the current collector 21 and drying the slurry. The coating method is not particularly limited, and for example, a knife coater method, a gravure coater method, or the like may be used. The following coating steps are also performed by the same method. Furthermore, the positive electrode active material layer 22 is compressed to a desired thickness by a compressor. Thereby, the positive electrode 20 is manufactured. Here, the thickness of the positive electrode active material layer 22 is not particularly limited as long as the positive electrode active material layer of the lithium ion secondary battery has a thickness.

  The negative electrode 30 is also manufactured in the same manner as the positive electrode 20. First, a slurry is formed by dispersing a mixture of a negative electrode active material and a binder in a desired ratio in an organic solvent (for example, N-methyl-2-pyrrolidone). Next, the slurry is formed (for example, coated) on the current collector 31 and dried to form the negative electrode active material layer 32. Further, the negative electrode active material layer 32 is compressed to a desired thickness by a compressor. Thereby, the negative electrode 30 is manufactured. Here, the thickness of the negative electrode active material layer 32 is not particularly limited as long as the negative electrode active material layer of the lithium ion secondary battery has a thickness. Further, when metal lithium is used for the negative electrode active material layer 32, a metal lithium foil may be stacked on the current collector 31.

  Subsequently, an electrode structure is manufactured by sandwiching the separator 41 between the positive electrode 20 and the negative electrode 30. Further, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a square shape, a laminate shape, a button shape, etc.) and inserted into a container having the shape. Furthermore, each pore in the separator 41 is impregnated with the electrolytic solution by injecting the electrolytic solution 43 added with the above-described disulfonic acid ester and the above-described unsaturated bond carbonate as additives into the container. . Thereby, the lithium ion secondary battery 10 is manufactured.

  Below, the Example which concerns on one Embodiment of this invention is described.

Example 1
A lithium ion secondary battery according to Example 1 was manufactured by the following method. First, 98 parts by mass of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , 1 part by mass of polyvinylidene fluoride, and 1 part by mass of carbon black were dispersed in N-methyl-2-pyrrolidone to form a slurry. . Then, the positive electrode was manufactured by coating the slurry on an aluminum foil as a current collector and drying it to form a positive electrode active material layer.

  Next, 98 parts by mass of artificial graphite, 1 part by mass of styrene butadiene rubber, and 1 part by mass of carboxymethyl cellulose were dispersed in N-methyl-2-pyrrolidone to form a slurry. Then, the negative electrode was manufactured by coating the slurry on an aluminum foil as a current collector and drying it to form a negative electrode active material layer.

In addition, a porous polyethylene film (thickness 12 μm) was prepared as a separator, and the separator was sandwiched between a positive electrode and a negative electrode, whereby an electrode structure was manufactured and stored in a battery container. On the other hand, lithium hexafluorophosphate (LiPF ₆ ) was added at 1.0 mol / liter to a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:40:30. An electrolyte was prepared by dissolving at a concentration of L. Furthermore, the compound (11) and vinylene carbonate were added to the electrolyte solution as additives. The additive concentration is 0.5% by mass for compound (11) and 1% by mass for vinylene carbonate with respect to the total mass of the electrolytic solution (that is, a combination of the solvent, LiPF ₆ , and various additives).

  Next, the electrolyte solution having the above composition was injected into the battery container so that the pores in the separator were impregnated with the electrolyte solution. Thus, a lithium ion secondary battery according to Example 1 was manufactured.

(Examples 2-18, Comparative Examples 1-12)
Lithium ion secondary batteries according to Examples 2 to 18 and Comparative Examples 1 to 12 were manufactured in the same manner as in Example 1. Here, Examples 2-18 and Comparative Examples 1-12 differ from Example 1 in the compounds added as additives and their concentrations. The compounds added as additives and their concentrations are shown in Tables 1 and 2. Here, in Tables 1 and 2, “VC” represents vinylene carbonate, and “VEC” represents vinyl ethylene carbonate. “-” Indicates that the corresponding additive was not added.

(Examples 19 to 23, Comparative Examples 13 to 17)
Lithium ion secondary batteries according to Examples 19 to 23 and Comparative Examples 13 to 17 were manufactured in the same manner as in Example 1. Here, Example 19 uses LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as the positive electrode active material instead of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in Example 1. Only the difference was. In addition, Examples 20 to 23 and Comparative Examples 13 to 17 differ from Example 19 in the compounds added as additives and the concentrations thereof. The compounds added as additives and their concentrations are shown in Table 3. Here, the notation in Table 3 is the same as in Tables 1 and 2.

(Examples 24-26, Comparative Examples 18-20)
Lithium ion secondary batteries according to Examples 24 to 26 and Comparative Examples 18 to 20 were manufactured in the same manner as in Example 1. Here, Example 24 uses LiNi _0.8 Co _0.1 Mn _0.1 O ₂ as the positive electrode active material instead of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ in Example 1. Only the difference was. In addition, Examples 25 and 26 and Comparative Examples 18 to 20 are different from Example 21 in the compounds added as additives and the concentrations thereof. The compounds added as additives and their concentrations are shown in Table 4. Here, the notation in Table 4 is the same as in Tables 1 and 2.

(High temperature storage test)
Then, the high temperature storage test was done with respect to the lithium ion secondary battery which concerns on Examples 1-26 manufactured above and Comparative Examples 1-20. Specifically, CC-CV charging (constant current constant voltage charging) is performed on the lithium ion secondary battery until the battery voltage reaches 4.2 V, and the battery is left in a temperature environment of 60 ° C. for 60 days after full charging. did. In addition, the DC resistance, capacity, and volume of the lithium ion secondary battery are measured before and after being left, and the DC resistance increase rate due to high-temperature storage, recovery capacity (that is, capacity retention rate before and after being left), gas generation amount (that is, The amount of increase in volume before and after standing was calculated.

  Here, the DC resistance increase rate is a value obtained by dividing the increase in DC resistance before and after being left by the DC resistance before being left. The recovery capacity is a value obtained by dividing the capacity of the lithium ion secondary battery after being left by the capacity of the lithium ion secondary battery before being left. Further, the gas generation amount is a value obtained by dividing the volume increase of the lithium ion secondary battery before and after being left by the capacity and correcting it per unit capacity.

  Specifically, the direct current resistance was calculated from the IR drop after discharging at 1C, 2C, 3C, and 6C in the state of 50% charge and measuring the IR drop. In addition, the capacity of the lithium ion secondary battery is such that CC-CV charging (constant current constant voltage charging) is performed at 0.5 C until the battery voltage becomes 4.2 V, and the battery voltage becomes 2.8 V. The capacity measured when CC discharge (constant current discharge) was performed at 0.2 C was used. Furthermore, the volume of the lithium ion secondary battery was measured by the Archimedes method.

The result of said high temperature storage test is shown to Tables 1-4. Tables 1 and 2 show the results of the lithium ion secondary battery in which the positive electrode active material is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and Table 3 shows that the positive electrode active material is LiNi _0.5. Table 4 shows the results of the lithium ion secondary battery that is Co _0.2 Mn _0.3 O ₂ , and Table 4 shows the lithium ion secondary battery in which the positive electrode active material is LiNi _0.8 Co _0.1 Mn _0.1 O _2. It is a result of a battery.

  First, in Table 1, the evaluation result of Examples 1-9 and Comparative Examples 1-8 which measured the effect by the 1st-3rd additive is shown.

  Referring to Table 1, in Examples 1 to 9, compared to Comparative Examples 1 to 8, the DC resistance increase rate and the amount of gas generation decreased, and the recovery capacity increased. Therefore, it can be seen that Examples 1 to 9 to which the first additive and the second additive are added have improved thermal stability and battery characteristics during high-temperature storage. Further, Examples 2, 3, 5 and 7 to which the compound (31) as the third additive was added were compared to Examples 1, 4, 8 and 9 to which the compound (31) was not added. Further, the DC resistance increase rate and gas generation amount are decreasing, and the recovery capacity is increasing. Therefore, it can be seen that Examples 2, 3, 5 and 7 to which the compound (31) as the third additive was added further improved in thermal stability and battery characteristics during high-temperature storage.

  On the other hand, Comparative Examples 1 to 6 contain the first additive, but do not contain the second additive, so the recovery capacity is lower than in Examples 1 to 9, and the amount of gas generated is greatly increased. Has increased. Moreover, although the comparative examples 7 and 8 contain the 2nd additive, since the 1st additive is not included, the direct current | flow resistance increase rate and the gas generation amount are increasing with respect to Examples 1-9. . Therefore, it can be seen that Comparative Examples 1 to 8 have deteriorated thermal stability and battery characteristics during high temperature storage.

  Next, in Table 2, the evaluation results of Examples 10 to 18 and Comparative Examples 9 to 12 in which the concentration was changed for each of the first to third additives were shown.

  Referring to Table 2, in Examples 10 to 18, the concentration of the compound (11) as the first additive and the concentration of VC as the second additive are within the scope of the present invention, and the DC resistance increase It can be seen that the rate and gas generation rate are decreasing and the recovery capacity is increasing. Therefore, it can be seen that Examples 10 to 18 have improved thermal stability and battery characteristics during high temperature storage.

  In addition, in Examples 16 to 18, the compound (31) as the third additive is added in an amount of 0.5 to 2.0% by mass, and the Example 11 in which the third additive is not added. Further, it can be seen that the DC resistance increase rate and the amount of gas generation are further decreased and the recovery capacity is increased. Therefore, it can be seen that Examples 16 to 18 are further improved in thermal stability and battery characteristics during high-temperature storage.

  On the other hand, in Comparative Examples 9 and 10, the concentration of the compound (11) as the first additive is out of the scope of the present invention, and the amount of gas generated is increased. Therefore, it can be seen that Comparative Examples 9 and 10 have reduced thermal stability during high temperature storage. Further, in Comparative Examples 11 and 12, the concentration of VC as the second additive is out of the scope of the present invention, the DC resistance increase rate and the gas generation amount are increased, and the recovery capacity is decreased. Therefore, it can be seen that Comparative Examples 11 and 12 have deteriorated thermal stability and battery characteristics during high temperature storage.

Further, in Table 3 _shows the evaluation results of Examples 19 to 23 and Comparative Examples 13 to 17 using LiNi _0.5 Co _{0.2 Mn} 0.3 _{O 2} as the positive electrode active material.

  Referring to Table 3, in Examples 19 to 23, compared with Comparative Examples 13 to 17, the DC resistance increase rate and the amount of gas generation decreased, and the recovery capacity increased. Therefore, it can be seen that Examples 19 to 23 to which the first additive and the second additive are added have improved thermal stability and battery characteristics during high-temperature storage. Further, Examples 20 and 21 to which the compound (31) as the third additive was added were more effective in increasing the DC resistance than Examples 19, 22, and 23 to which the compound (31) was not added. Gas generation is decreasing. Therefore, it can be seen that Examples 20 and 21 to which the compound (31) as the third additive was added have further improved thermal stability and battery characteristics during high-temperature storage.

  On the other hand, Comparative Examples 14 and 15 contain the first additive, but do not contain the second additive, so that the recovery capacity is reduced compared to Examples 19 to 23, and the amount of gas generated is increased. doing. Moreover, although the comparative examples 16 and 17 contain the 2nd additive, since the 1st additive is not included, the direct current | flow resistance increase rate and the gas generation amount are increasing with respect to Examples 19-23. . Therefore, it can be seen that Comparative Examples 14 to 17 have deteriorated thermal stability and battery characteristics during high temperature storage.

In addition, in Table 4 _shows the evaluation results of Examples 24-26 and Comparative Examples 18-20 with LiNi _0.8 Co _{0.1 Mn} 0.1 _{O 2} as the positive electrode active material.

  Referring to Table 4, in Examples 24 to 26, the DC resistance increase rate and gas generation amount decreased and the recovery capacity increased compared to Comparative Examples 18 to 20. Therefore, it can be seen that Examples 24 to 26 to which the first additive and the second additive are added have improved thermal stability and battery characteristics during high-temperature storage. Further, Example 25 to which the compound (31) as the third additive was added had a higher DC resistance increase rate and gas generation amount than Examples 24 and 26 to which the compound (31) was not added. is decreasing. Therefore, it can be seen that Example 24 to which the compound (31) as the third additive was added further improved in thermal stability and battery characteristics during high-temperature storage.

  On the other hand, although Comparative Examples 18 and 19 contain the first additive, but do not contain the second additive, the DC resistance increase rate and the amount of gas generation are increased compared to Examples 24-26. In addition, the recovery capacity has decreased. Moreover, although the comparative example 20 contains the 2nd additive, since the 1st additive is not included, the direct current | flow resistance increase rate and the gas generation amount are increasing with respect to Examples 24-26. Therefore, it can be seen that Comparative Examples 18 to 20 have deteriorated thermal stability and battery characteristics during high temperature storage.

  Referring to the evaluation results in Tables 3 and 4, the lithium ion secondary battery according to one embodiment of the present invention can be stored at a high temperature as in Tables 1 and 2 regardless of the lithium nickel composite oxide having any composition. It can be seen that the thermal stability at the time and the battery characteristics can be improved.

  As can be seen from the above evaluation results, according to one embodiment of the present invention, at least selected from the group consisting of a positive electrode active material containing a lithium nickel composite oxide, a cyclic disulfonate, and a chain disulfonate A non-aqueous electrolyte containing at least one disulfonic acid ester and at least one carbonate having an unsaturated bond selected from the group consisting of vinylene carbonate and vinylethylene carbonate, and containing the disulfonic acid ester. The carbonate having an unsaturated bond is contained in an amount of 0.05% by mass or more and 0.5% by mass or less with respect to the total mass of the nonaqueous electrolytic solution, and 0.2% by mass or more and 1% by mass with respect to the total mass of the nonaqueous electrolytic solution. It is possible to improve the thermal stability and battery characteristics during high-temperature storage by containing at 0.5 mass% or less.

  According to one embodiment of the present invention, the thermal stability and battery characteristics during high-temperature storage can be further improved by further including an imide lithium salt in the non-aqueous electrolyte.

  Furthermore, one embodiment of the present invention can be more suitably used for a lithium ion secondary battery using a lithium nickel composite oxide having a high Ni ratio as a positive electrode active material.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer 40 Separator layer 41 Separator 43 Electrolytic solution

Claims (5)

A positive electrode active material containing a lithium nickel composite oxide;
At least one disulfonic acid ester selected from the group consisting of a cyclic disulfonic acid ester represented by the following chemical formula (1) and a chain disulfonic acid ester represented by the following chemical formula (2), vinylene carbonate and vinyl A non-aqueous electrolyte containing at least one carbonate having an unsaturated bond selected from the group consisting of ethylene carbonate,
The non-aqueous electrolyte contains the disulfonic acid ester in an amount of 0.05% by mass to 0.5% by mass with respect to the total mass of the non-aqueous electrolyte, and the carbonate having the unsaturated bond is contained in the non-aqueous electrolyte. A lithium ion secondary battery that is contained in an amount of 0.2% by mass to 1.5% by mass with respect to the total mass of the electrolytic solution.

However, in the chemical formulas (1) and (2), R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 to 5 carbon atoms and a substituted or unsubstituted carbon group having 1 to 5 carbon atoms. R ₃ and R ₄ are each independently a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and a substituted or unsubstituted carbon number. It is one selected from the group consisting of 1 to 4 fluoroalkyl groups, and x and y are each independently an integer selected from 0 to 5. In the chemical formulas (1) and (2),
R ₁ and R ₂ are each independently a substituted or unsubstituted alkylene group having 1 or 2 carbon atoms; R ₃ and R ₄ are each independently a substituted or unsubstituted methyl group; The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is one selected from an unsubstituted fluoromethyl group, and x and y are each independently an integer selected from 1 to 3. The lithium ion secondary battery according to claim 1, wherein the non-aqueous electrolyte further includes an imide lithium salt represented by the following chemical formula (3).

However, in the chemical formula (3), Rf ₁ and Rf ₂ independently represent one selected from the group consisting of fluorine and a fluoroalkyl group having 1 to 4 carbon atoms. 4. The lithium ion secondary battery according to claim 3, wherein, in the chemical formula (3), Rf ₁ and Rf ₂ are fluorine. 5. The lithium ion secondary battery according to claim 1, wherein the lithium nickel composite oxide has a composition represented by the following general formula (1).
Li _a (Ni _b M _b-1 ) O ₂ (1)
In the general formula (1),
M is one or more kinds of metals other than Ni,
a is 1.0 ≦ a ≦ 1.2,
b is 0.5 ≦ b ≦ 1.0.

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