JP2007035356A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of keeping high power even when charge and discharge are repeatedly executed in a high-temperature environment. <P>SOLUTION: In this lithium ion secondary battery, a positive electrode active material contains, as a main constituent, a compound represented by a basic composition formula Li<SB>t</SB>Mg<SB>x</SB>Ni<SB>y</SB>Me<SB>z</SB>O<SB>2</SB>, where Me is one or more kinds selected from Al, Co and Mn; 0.8≤t≤1.3; 0.01≤x≤0.2; 0.6≤y≤0.98; 0.01≤z≤0.2; and x+y+z=1. A negative electrode active material thereof contains, as a main constituent, hardly graphitizable carbon or easily graphitizable carbon. A nonaqueous electrolyte thereof contains, in an organic solvent, at least an anion compound represented by formula (1). In formula (1), M is a transition metal or a group III, IV or V element in the periodic table; and (b), (m), (n) and (q) are 1 to 3, 1 to 4, 0 to 8, and 0 or 1, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery using insertion / extraction of lithium ions.

Conventionally, a lithium ion secondary battery using a lithium composite oxide as a positive electrode active material, a carbon material as a negative electrode active material, and a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent has a high energy density. For example, it has been studied as a battery for hybrid vehicles.
In particular, a lithium ion secondary battery using layered nickel having a basic composition of LiNiMeO ₂ as a positive electrode active material can exhibit excellent discharge performance and charge performance (see Patent Document 1). Furthermore, a lithium ion secondary battery using layered nickel as the positive electrode active material has high regenerative energy recovery efficiency during braking. Therefore, a lithium secondary battery containing layered nickel as a positive electrode active material is considered promising as a battery for a hybrid vehicle.

However, in a lithium ion secondary battery using layered nickel having a basic composition of LiNiMeO ₂ as a positive electrode active material, for example, when charging and discharging are repeated in a high temperature environment of about 60 ° C., the internal resistance of the battery is remarkable. There was a problem of causing a rise.
In addition, as a characteristic of the on-vehicle battery, even if charging / discharging is repeated from a low temperature environment of about −30 ° C. to a high temperature environment of about 60 ° C., in addition to small capacity deterioration, the increase in internal resistance of the battery is small Required. Therefore, a lithium ion secondary battery excellent in charge / discharge cycle characteristics at a high temperature is particularly required for a vehicle-mounted battery.

JP 2000-323122 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a lithium ion secondary battery capable of maintaining a high output even when charging and discharging are repeated in a high temperature environment.

｛但し、Ｍは、遷移金属、周期律表のIII族、IV族、又はV族元素、ｂは１〜３、ｍは１〜４、ｎは０〜８、ｑは０又は１をそれぞれ表し、Ｒ¹は、Ｃ₁〜Ｃ₁₀のアルキレン、Ｃ₁〜Ｃ₁₀のハロゲン化アルキレン、Ｃ₆〜Ｃ₂₀のアリーレン、又はＣ₆〜Ｃ₂₀のハロゲン化アリーレン（これらのアルキレン及びアリーレンはその構造中に置換基、ヘテロ原子を持ってもよく、またｍ個存在するＲ¹はそれぞれが結合してもよい。）、Ｒ²は、ハロゲン、Ｃ₁〜Ｃ₁₀のアルキル、Ｃ₁〜Ｃ₁₀のハロゲン化アルキル、Ｃ₆〜Ｃ₂₀のアリール、Ｃ₆〜Ｃ₂₀のハロゲン化アリール、又はＸ³Ｒ³（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持ってもよく、またｎ個存在するＲ²はそれぞれが結合して環を形成してもよい。）、Ｘ¹、Ｘ²、Ｘ³は、Ｏ、Ｓ、又はＮＲ⁴、Ｒ³、Ｒ⁴は、それぞれが独立で、水素、Ｃ₁〜Ｃ₁₀のアルキル、Ｃ₁〜Ｃ₁₀のハロゲン化アルキル、Ｃ₆〜Ｃ₂₀のアリール、Ｃ₆〜Ｃ₂₀のハロゲン化アリールをそれぞれ示す（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持ってもよく、また複数個存在するＲ³、Ｒ⁴はそれぞれが結合して環を形成してもよい。）。｝ The present invention relates to a lithium ion secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent.
The positive electrode active material has a basic composition formula Li _t Mg _x Ni _y Me _z O ₂ (Me is one or more selected from Al, Co, and Mn, 0.8 ≦ t ≦ 1.3, 0.01 ≦ x ≦ 0.2, 0.6 ≦ y ≦ 0.98, 0.01 ≦ z ≦ 0.2, x + y + z = 1) as a main component,
The negative electrode active material is composed mainly of graphite, non-graphitizable carbon, or graphitizable carbon,
The non-aqueous electrolyte solution is a lithium ion secondary battery characterized in that it contains at least an anionic compound represented by the following general formula (1).

{However, M is a transition metal, a group III, IV or V element of the periodic table, b is 1 to 3, m is 1 to 4, n is 0 to 8, q is 0 or 1 respectively. , R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene (the alkylene and arylene have the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ Alkyl halides, C ₆ -C ₂₀ aryls, C ₆ -C ₂₀ aryl halides, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structures, the n number R ² each may combine with each other to form a ring present.), X ^{1, 2,} X ³ is O, S, or NR ^4, R ^3, R ⁴ are, each independently, hydrogen, alkyl of C ₁ -C _10, alkyl halide C ₁ ~C _10, C ₆ ~C ₂₀ aryls and C ₆ -C ₂₀ aryl halides are shown respectively. (These alkyls and aryls may have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ are respectively May combine to form a ring. }

The lithium ion secondary battery of this invention has the non-aqueous electrolyte containing the anion compound represented by the said General formula (1).
Therefore, when the lithium ion secondary battery is charged once or more, all or a part of the anion compound is decomposed, and the surface of the positive electrode or / and the negative electrode, the surface of the positive electrode active material or / and the negative electrode active material or not. In addition, a coating such as a low-resistance and stable coating can be formed. Therefore, the lithium ion secondary battery can smoothly store and release lithium ions.
Moreover, the said covering can suppress that a high resistance film is formed on the surface of the said positive electrode active material and / or the said negative electrode active material, for example in a high temperature environment of about 60 degreeC. Therefore, an increase in the internal resistance of the lithium ion secondary battery can be suppressed and a high output can be exhibited.

The high-resistance film is particularly likely to occur when the lithium ion secondary battery is repeatedly used in a high temperature environment of, for example, 60 ° C., and can inhibit the electrode reaction and reduce the output voltage.
In the lithium ion secondary battery of the present invention, the covering can prevent the formation of the high-resistance film. Therefore, an excellent output voltage can be exhibited even when it is repeatedly used in a high temperature environment of 60 ° C., for example.

Further, in the present invention, the as a positive electrode active material contains a compound represented by the basic formula _{Li t Mg x Ni y Me z} O 2, graphite as the negative electrode active material, non-graphitizable carbon, or graphitizable Contains carbonized carbon. Therefore, the lithium ion secondary battery has a low internal resistance and can exhibit a high output, and can maintain the high output even when charging and discharging are repeated. That is, as the positive electrode active material and the negative electrode active material, by combining a specific material as described above and using a non-aqueous electrolyte containing the anion compound, the effect of suppressing the increase in internal resistance is remarkably exhibited. can do.

  As described above, according to the present invention, it is possible to provide a lithium ion secondary battery capable of maintaining a high output even when charging and discharging are repeatedly performed in a high temperature environment.

The lithium ion secondary battery of the present invention has a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent.
The lithium ion secondary battery mainly comprises the positive electrode and the negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and the non-aqueous electrolyte that moves lithium between the positive electrode and the negative electrode. Can be configured as an element.

  The positive electrode is, for example, a mixture of a positive electrode active material and a conductive material and a binder, and an appropriate solvent added to form a paste-like positive electrode mixture, which is a current collector made of a metal foil such as aluminum or stainless steel. It can be formed by applying and drying on the surface and compressing to increase the electrode density as necessary.

In the present invention, the positive electrode active material has a basic composition formula Li _t Mg _x Ni _y Me _z O ₂ (Me is one or more selected from Al, Co, and Mn, 0.8 ≦ t ≦ 1.3, 0. 01 ≦ x ≦ 0.2, 0.6 ≦ y ≦ 0.98, 0.01 ≦ z ≦ 0.2, x + y + z = 1) as a main component.
In the compound represented by the above basic composition formula, when t, x, y, and z are out of the above ranges, there is a risk that the output and capacity may be suddenly reduced or the internal resistance is increased during charging and discharging. There is a fear.
Further, the compound represented by the above basic composition formula Li _t Mg _x Ni _{y Mez} O ₂ includes not only a stoichiometric composition but also a non-stoichiometric composition in which some elements are deficient. .

  Further, the conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or more carbon powder materials such as carbon black, acetylene black, natural graphite, artificial graphite, and cokes are used. Can be used.

The binder serves to bind the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. Etc. can be used. In addition, an aqueous dispersion of a cellulose-based or styrene-butadiene rubber that is an aqueous binder can also be used.
As a solvent for dispersing these active material, conductive material, and binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

Next, the negative electrode is prepared by mixing a negative electrode active material with a binder, adding a suitable solvent as a dispersing agent to form a slurry, applying the slurry to the surface of a metal foil current collector such as copper, and drying. Then, it can be formed by pressing. Similarly to the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride can be used as a binder to be mixed with the negative electrode active material, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent.
In the present invention, the negative electrode active material contains graphite, non-graphitizable carbon (hard carbon), or graphitizable carbon (soft carbon) as a main component.

  As a separator to be narrowly attached to the positive electrode and the negative electrode, the positive electrode and the negative electrode are separated to hold a non-aqueous electrolyte. For example, a thin microporous film such as polyethylene or polypropylene can be used.

Next, the nonaqueous electrolytic solution contains the anionic compound represented by the general formula (1).
In the said General formula (1), the valence b of an anion is 1-3. When b is larger than 3, the crystal lattice energy of the salt of the anionic compound is increased, so that it is difficult to form the anionic compound by dissolving the salt of the anionic compound in the nonaqueous electrolytic solution. Therefore, b = 1 is most preferable.
For the same reason, the valence of the cation constituting the salt of the anionic compound is preferably 1 to 3, and most preferably the valence of the cation is 1. Examples of such cations include lithium ions, sodium ions, rubidium ions, cesium ions, potassium ions, tetraalkylammonium ions, and protons.

  The anion compound represented by the general formula (1) has an ionic metal complex structure, and M at the center is a transition metal, a group III, IV, or V element of the periodic table. Chosen from.

In the non-aqueous electrolyte, the electrolyte compound composed of the anion compound and the cation represented by the general formula (1) is ionized, and M in the general formula (1) is Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and the cation is at least Li ⁺ or Na ⁺ One is preferable (claim 2).
In this case, the nonaqueous electrolytic solution containing the anionic compound can be easily prepared by dissolving the electrolytic compound in the nonaqueous electrolytic solution. In this case, the anion compound or the electrolyte compound can be easily synthesized.

  More preferably, M in the general formula (1) is Al, B, or P. In this case, in addition to facilitating the synthesis of the anion compound or the electrolyte compound, the toxicity can be lowered, and the production cost can be reduced.

In addition to the electrolyte compound composed of the anion compound and the cation represented by the general formula (1), another electrolyte is added to the non-aqueous electrolyte as the electrolyte. Is preferably 2 to 80% by weight based on the total electrolytic mass (claim 3).
When the amount of the electrolyte compound added is less than 2% by weight, the internal resistance of the lithium ion secondary battery may increase due to repeated charge and discharge. The reason for this is considered that the anion compound does not sufficiently form a coating such as a coating on the surface of the positive electrode or / and the negative electrode, or on the surface of the positive electrode active material or / and the negative electrode active material. . Moreover, when the addition amount of the said electrolyte compound exceeds 80 weight%, there exists a possibility that the initial stage discharge capacity of a lithium ion secondary battery may fall. The reason for this is considered to be that the thickness of the covering becomes unnecessarily thick.

The non-aqueous electrolyte solution, as other electrolytes other than the above electrolyte _{compounds, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, or it is preferable that at least one member selected from LiSbF ₆ is added (Claim 4).
In this case, since LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , or LiSbF ₆ has a relatively high ionic conductivity and is electrochemically stable, a lithium ion secondary battery having a high charge / discharge capacity is obtained. Obtainable.

Next, the ligand part of the anionic compound (ionic metal complex) will be described.
Hereinafter, in the present specification, an organic or inorganic part bonded to M in the general formula (1) is referred to as a ligand.

R ¹ in general formula (1) is selected from C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene. It consists of things. These alkylene and arylene may have a substituent or a hetero atom in the structure. Specifically, instead of hydrogen on alkylene and arylene, halogen, chain or cyclic alkyl group, aryl group, alkenyl group, alkoxy group, aryloxy group, sulfonyl group, amino group, cyano group, carbonyl group, acyl Examples thereof include a group, an amide group, a hydroxyl group, and a structure in which nitrogen, sulfur, or oxygen is introduced instead of carbon on alkylene and arylene.
Furthermore, when a plurality of R ¹ are present (when q = 1 and m = 2 to 4), each may be bonded, and examples thereof include a ligand such as ethylenediaminetetraacetic acid.

R ² is selected from halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkyl halide, C ₆ -C ₂₀ aryl, C ₆ -C ₂₀ aryl halide, or X ³ R ³ It consists of things. Similarly to R ¹ , alkyl or aryl may have a substituent or a heteroatom in the structure, and when there are a plurality of R ² (when n = 2 to 8), each R ² is They may combine to form a ring.
Preferably, R ² is an electron-withdrawing group, particularly fluorine. In this case, the solubility and dissociation degree of the salt of the anionic compound can be improved, and the effect of improving the ionic conductivity can be obtained. Furthermore, in this case, the oxidation resistance is improved, thereby preventing the occurrence of side reactions.

X ¹ , X ² , and X ³ are each independently O, S, or NR ⁴ , and the ligand is bonded to M through these heteroatoms. Here, it is not impossible to combine other than O, S, and N, but the synthesis becomes very complicated. As a feature of the compound represented by the general formula (1), there is a bond between X ¹ and M by X ² in the same ligand, and these ligands form a chelate structure with M. . The constant q in this ligand is 0 or 1. When q = 0, the chelate ring becomes a five-membered ring, and the complex structure of the anionic compound is stabilized. Therefore, in this case, it is possible to prevent side reactions other than the formation of the coating.

R ³ and R ⁴ are each independently hydrogen, C _{1 to} C ₁₀ alkyl, C _{1 to} C ₁₀ alkyl halide, C _{6 to} C ₂₀ aryl, or C _{6 to} C ₂₀ aryl halide. These alkyls and aryls may have a substituent or a heteroatom in the structure, and when a plurality of R ³ and R ⁴ are present, each may be bonded to form a ring. .

The constants m and n related to the number of ligands described above are determined by the type of M at the center, and m is 1 to 4 and n is 0 to 8.
It in ^{R 1, R 2, R 3} , R 4 described above, C ₁ -C ₁₀ indicates 1 to 10 carbon atoms, C ₆ -C ₂₀ is 6 to 20 carbon atoms Indicates.

As the anion compound represented by the general formula (1), it is preferable to use one or more types represented by the following formulas (2) to (5) (Claim 5).
In this case, the solubility and dissociation degree of the salt of the anionic compound can be improved, and the ionic conductivity of the non-aqueous electrolyte can be improved. Furthermore, in this case, oxidation resistance can be improved.

As the anionic compound, it is preferable to use a compound represented by the above formula (4).
In this case, it is possible to further suppress a decrease in output when the charge / discharge cycle is repeated.

As a method for synthesizing the anion compound, for example, in the case of a compound represented by the following formula (2), after reacting LiBF ₄ and 2-fold moles of lithium alkoxide in a non-aqueous solvent, oxalic acid is added. Then, there is a method of substituting alkoxide bonded to boron with oxalic acid. In this case, a lithium salt of a compound represented by the following formula (2) can be obtained.

  As the organic solvent for dissolving the anionic compound and the electrolyte, an aprotic organic solvent can be used. As such an organic solvent, for example, a mixed solvent composed of one or more selected from cyclic carbonate, chain carbonate, cyclic ester, cyclic ether, chain ether, and the like can be used.

  Here, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Examples of the cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. As the organic solvent, any one of these can be used alone, or two or more kinds can be mixed and used.

  In addition, the anion compound contained in the non-aqueous electrolytic solution is obtained by charging the lithium ion secondary battery one or more times, whereby all or part of the anion compound is decomposed, and the positive electrode or / and the A coating such as a film can be formed by coating the surface of the negative electrode or the surface of the positive electrode active material or / and the negative electrode active material. The coating can be detected by, for example, X-ray photoelectron spectroscopy (XPS) or IR analysis.

  Examples of the shape of the lithium ion secondary battery include a paper type, a coin type, a cylindrical type, and a square type. As said battery case which accommodates a positive electrode, a negative electrode, and a non-aqueous electrolyte, the thing corresponding to these shapes can be used.

Example 1
Next, an embodiment of the lithium ion secondary battery of the present invention will be described with reference to FIG.
As shown in FIG. 1, the lithium ion secondary battery 1 of this example contains a positive electrode 2 containing a compound represented by LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ as a positive electrode active material, and graphite as a negative electrode active material. And a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent. The nonaqueous electrolytic solution contains an anionic compound represented by the following formula (4).

Hereinafter, the lithium ion secondary battery 1 of this example will be described in detail with reference to FIG.
As shown in FIG. 1, the lithium ion secondary battery 1 of this example includes a positive electrode 2, a negative electrode 3, a separator 4, a gasket 59, a battery case 6, and the like. The battery case 6 is a 18650-type cylindrical battery case, and includes a cap 63 and an outer can 65. In the battery case 6, a sheet-like positive electrode 2 and a negative electrode 3 are arranged in a wound state together with a separator 4 sandwiched between the positive electrode 2 and the negative electrode 3.
A gasket 59 is disposed inside the cap 63 of the battery case 6, and a non-aqueous electrolyte is injected into the battery case 6.

The positive electrode 2 contains a compound represented by LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ as a positive electrode active material, and the negative electrode 3 contains graphite as a negative electrode active material.
The positive electrode 2 and the negative electrode 3 are respectively provided with a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 by welding. The positive electrode current collector lead 23 is connected to the positive electrode current collector tab 235 disposed on the cap 63 side by welding. Further, the negative electrode current collecting lead 33 is connected by welding to a negative electrode current collecting tab 335 disposed on the bottom of the outer can 65.

In addition, the non-aqueous electrolyte is prepared by mixing a lithium salt of an anionic compound represented by the above formula (4) (LiPF ₂ (C ₂ O ₄ ) in an organic solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 30:70. ₂ ) (hereinafter referred to as LPFO as appropriate) and LiPF ₆ are added as electrolytes and injected into the battery case 6.

Next, the manufacturing method of the lithium ion secondary battery 1 of this example is demonstrated using FIG.
First, the nonaqueous electrolyte solution was prepared as follows.
That is, first, an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7, and LiPF ₆ and LPFO are in a weight ratio of LiPF ₆ : LPFO = 92: 8. The mixed mixed supporting salt was added so as to have a concentration of 1M to prepare a nonaqueous electrolytic solution.

Next, the positive electrode 2 and the negative electrode 3 were prepared as follows.
In producing the positive electrode 2, first, a compound represented by LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ is prepared as a positive electrode active material, the positive electrode activator, carbon black as a conductive material, and a binder. As a dispersion material, polyvinylidene fluoride was mixed, an appropriate amount of N-methyl-2-pyrrolidone was added as a dispersion material, and dispersed to obtain a slurry-like positive electrode mixture. The mixing ratio of the positive electrode active material, the conductive material, and the binder was, by weight ratio, positive electrode active material: conductive material: binder = 85: 10: 5.

Next, the positive electrode mixture obtained as described above was applied to both sides of an aluminum foil current collector having a thickness of 20 μm and dried. Then, it densified with the roll press, cut out in the shape of 52 mm width x 450 mm length, and produced the sheet-like positive electrode 2. In addition, the adhesion amount of the positive electrode active material was about 7 mg / cm ² per side.

  On the other hand, in producing the negative electrode 3, first, artificial graphite was prepared as a negative electrode active material. The negative electrode active material and polyvinylidene fluoride as a binder were mixed, an appropriate amount of N-methyl-2-pyrrolidone was added as a dispersing agent, and dispersed to obtain a slurry-like negative electrode mixture. The mixing ratio of the negative electrode active material and the binder was a weight ratio of negative electrode active material: binder = 95: 5.

Next, the negative electrode mixture obtained as described above was applied to the surface of a copper foil current collector having a thickness of 10 μm and dried. Then, it densified with the roll press, cut out into the shape of 54 mm width x 500 mm length, and produced the sheet-like negative electrode 3. In addition, the adhesion amount of the negative electrode active material was about 4 mg / cm ² per side.

  Next, as shown in FIG. 1, a positive electrode current collecting lead 23 and a negative electrode current collecting lead 33 were welded to the sheet-like positive electrode 2 and negative electrode 3 obtained as described above, respectively. The positive electrode 2 and the negative electrode 3 were wound in a state where a polyethylene separator 4 having a width of 56 mm and a thickness of 25 μm was sandwiched between them, and a roll-shaped electrode body was produced.

  Subsequently, the roll-shaped electrode body was inserted into an 18650-type cylindrical battery case 6 including an outer can 65 and a cap 63. At this time, the positive electrode current collecting lead 23 is welded to the positive electrode current collecting tab 235 disposed on the cap 63 side of the battery case 6 and the negative electrode current collecting lead 335 is disposed on the negative electrode current collecting tab 335 disposed on the bottom of the outer can 65. 33 was connected by welding.

  Next, the battery case 6 was impregnated with the non-aqueous electrolyte prepared as described above. A gasket 59 is disposed inside the cap 63, and the cap 63 is disposed in the opening of the outer can 65. Subsequently, the battery case 6 was sealed by caulking the cap 63, and the lithium ion secondary battery 1 was produced. This was designated as battery E1.

Further, in this example, the battery E1 is different from the 14 kinds of lithium in which the mixing ratio of the electrolyte (LiPF ₆ and LPFO) in the non-aqueous electrolyte, the type of the positive electrode active material, and the type of the negative electrode active material are different. Ion secondary batteries (battery E2 to battery E9 and battery C1 to battery C6) were further produced.

Specifically, the battery E2 was prepared by mixing LiPF ₆ and LPFO in a weight ratio of LiPF ₆ : LPFO = 92: 8 in an organic solvent in which EC and DEC were mixed at a volume ratio of 3: 7. It was produced in the same manner as the battery E1 except that a nonaqueous electrolytic solution (concentration 1M) obtained by dissolving the mixed supporting salt was used.

The battery E3 is a mixed supporting salt in which LiPF ₆ and LPFO are mixed at a weight ratio of LiPF ₆ : LPFO = 84: 16 in an organic solvent in which EC and DEC are mixed at a volume ratio of 3: 7. A battery was prepared in the same manner as the battery E1 except that a non-aqueous electrolyte solution (concentration: 1M) was used.

In addition, the battery E4 is a mixed supporting salt in which LiPF ₆ and LPFO are mixed at a weight ratio of LiPF ₆ : LPFO = 98: 2 in an organic solvent in which EC and DEC are mixed at a volume ratio of 3: 7. A battery was prepared in the same manner as the battery E1 except that a non-aqueous electrolyte solution (concentration: 1M) was used.

  Battery E5 was prepared in the same manner as Battery E1, except that graphitizable carbon was used as the negative electrode active material.

  Battery E6 was prepared in the same manner as Battery E1, except that non-graphitizable carbon was used as the negative electrode active material.

Battery E7 was produced in the same manner as battery E1, except that LiMg _0.03 Co _0.15 Al _0.05 Ni _0.75 O ₂ was used as the positive electrode active material.

Battery E8 was produced in the same manner as Battery E1, except that LiMg _0.05 Co _0.15 Al _0.03 Ni _0.75 O ₂ was used as the positive electrode active material.

The battery 9 was produced in the same manner as the battery E1 except that LiMg _0.05 Co _0.15 Ni _0.8 O ₂ was used as the positive electrode active material.

The battery C1 uses a nonaqueous electrolytic solution (concentration 1M) obtained by dissolving only LiPF ₆ in an organic solvent in which EC and DEC are mixed at a volume ratio of 3: 7, and LiCo _0.15 Al is used as the positive electrode active material. _A battery was manufactured in the same manner as the battery E1 except that _0.05 Ni _0.8 O ₂ was used.

The battery C2 uses a non-aqueous electrolyte (concentration 1M) obtained by dissolving only LiPF ₆ in an organic solvent in which EC and DEC are mixed at a volume ratio of 3: 7, and LiCo _0.15 Al _0.05 is used as the positive electrode active material. A battery was manufactured in the same manner as the battery E1 except that Ni _0.8 O ₂ was used and graphitizable carbon was used as the negative electrode active material.

The battery C3 uses a non-aqueous electrolyte (concentration 1M) obtained by dissolving only LiPF ₆ in an organic solvent in which EC and DEC are mixed at a volume ratio of 3: 7, and LiCo _0.15 Al _0.05 is used as the positive electrode active material. A battery was produced in the same manner as the battery E1 except that Ni _0.8 O ₂ was used and non-graphitizable carbon was used as the negative electrode active material.

Battery C4 was produced in the same manner as Battery E1, except that LiCo _0.15 Al _0.05 Ni _0.8 O ₂ was used as the positive electrode active material.

Battery C5 was prepared in the same manner as Battery E1, except that LiCo _0.15 Al _0.05 Ni _0.8 O ₂ was used as the positive electrode active material and graphitizable carbon was used as the negative electrode active material.

Battery C6 was produced in the same manner as Battery E1, except that LiCo _0.15 Al _0.05 Ni _0.8 O ₂ was used as the positive electrode active material and non-graphitizable carbon was used as the negative electrode active material.

(Experimental example)
Next, in this example, for each of the batteries (battery E1 to battery E9 and battery C1 to battery C6) produced in Example 1, the following charge / discharge cycle test was performed in a high temperature environment of 60 ° C., and the internal resistance The rate of increase was measured.
"Charge / discharge cycle test"
Under a temperature condition of 60 ° C., which is regarded as the upper limit of the actual use temperature range of the battery, each battery is charged to a charge upper limit voltage of 4.1 V at a constant current of a current density of ² mA / cm ² and then a current density of 2 mA / Charging / discharging for discharging to a discharge lower limit voltage of 2.5 V with a constant current of cm ² was defined as one cycle, and this cycle was performed for a total of 500 cycles. And the discharge capacity was measured about each lithium secondary battery for every cycle.
The discharge capacity is determined by measuring the discharge current value (mA) for each cycle, and multiplying this discharge current value by the time (hr) required for discharge, to obtain the weight of the positive electrode active material in the battery. It can be calculated by dividing by (g).

“Evaluation of rate of increase in internal resistance”
Each battery was adjusted to 50% of the battery capacity (SOC = 50%), a current of 0.5A, 1A, 2A, 3A, and 5A was applied to measure the battery voltage after 10 seconds. The applied current and voltage were linearly approximated, and the internal resistance was determined from the slope.
The internal resistance increase rate can be calculated by the following equation (a) where the internal resistance after charging / discharging is resistance B and the internal resistance before charging / discharging is resistance A (initial internal resistance). The results are shown in Table 1.
Internal resistance increase rate (%) = (resistance B + resistance A) × 100 / resistance A (a)

As is known from Table 1, in any case of using any positive electrode active material and negative electrode active material, the effect of reducing the rate of increase in internal resistance is recognized by the addition of LPFO. However, the lithium secondary battery (battery C1 to battery C6) using LiCo _0.15 Al _0.05 Ni _0.8 O ₂ as the positive electrode active material is also internal even when LPFO is added (battery C4, battery C5, and battery C6). The resistance increase rate is large. Therefore, the improvement effect by LPFO is small.

On the other hand, batteries E1 to E6 containing LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ as the positive electrode active material, battery E7 containing LiMg _0.03 Co _0.15 Al _0.05 Ni _0.75 O ₂ as the positive electrode active material, and positive electrode active material In the battery E8 containing LiMg _0.05 Co _0.15 Al _0.03 Ni _0.75 O ₂ and the battery E9 containing LiMg _0.05 Co _0.15 Ni _0.8 O ₂ as the positive electrode active material, the rate of increase in internal resistance is increased by adding LPFO. It turns out that it improves significantly. It can also be seen that the rate of increase in internal resistance can be further reduced by using graphite, non-graphitizable carbon, or graphitizable carbon as the negative electrode active material.

Thus, LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ , LiMg _0.03 Co _0.15 Al _0.05 Ni _0.75 O ₂ , LiMg _0.05 Co _0.15 Ni _0.8 O ₂ , or LiMg _0.05 Co _0.15 Al _0.03 Ni _0.75 O ₂ are used as the positive electrode active material. Lithium ion secondary batteries (battery E1 to battery E9) that contain graphite, non-graphitizable carbon, or graphitizable carbon as a negative electrode active material, and LPFO added to the electrolyte solution are charged and discharged. It can be seen that the increase in internal resistance can be suppressed even when repeated, and a high output can be exhibited.

In this example, as the positive electrode active material, LiMg _0.05 Co _0.15 Al _0.05 Ni _0.75 O ₂ , LiMg _0.03 Co _0.15 Al _0.05 Ni _0.75 O ₂ , LiMg _0.05 Co _0.15 Ni _0.8 O ₂ , and LiMg _0.05 Co _0.15 Al _0.03 Ni _0.75 O ₂ was used, but Li _t Mg _x Ni _{y Mez} O ₂ having the same structure as these compounds (Me is one or more selected from Al, Co, and Mn, 0.8 ≦ t ≦ 1 .3, 0.01 ≦ x ≦ 0.2, 0.6 ≦ y ≦ 0.98, 0.01 ≦ z ≦ 0.2, x + y + z = 1), the same effect can be obtained.

Further, when the positive electrode active material is a mixture of two or more, if one of them is Li _t Mg _x Ni _{y Mez} O ₂ (Me is one or more selected from Al, Co, and Mn), Similar effects can be obtained. At this time, as _{Li t Mg x Ni y Me z} O 2 than the positive electrode active material, a layered cobalt structures LiCoMeO ₂ (Me is Al, Mg, Fe, Co, 1 or more selected from Mn) or LiMn ₂ O ₄ When Mn spinel or the like having a basic skeleton is used, the effect of suppressing the rate of increase in internal resistance is considered to be small. Further, even when two or more types of negative electrode active materials for the negative electrode are used, it is considered that the same effect as in this example can be obtained if one of them is graphite, non-graphitizable carbon, or graphitizable carbon.
Further, in this example, LPFO was used as the salt of the anion compound, but a similar effect can be obtained by using the salt of the anion compound represented by the general formula (1).

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

Explanation of symbols

1 Lithium ion secondary battery 2 Positive electrode 3 Negative electrode 4 Separator

Claims (6)

In a lithium ion secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent,
The positive electrode active material has a basic composition formula Li _t Mg _x Ni _y Me _z O ₂ (Me is one or more selected from Al, Co, and Mn, 0.8 ≦ t ≦ 1.3, 0.01 ≦ x ≦ 0.2, 0.6 ≦ y ≦ 0.98, 0.01 ≦ z ≦ 0.2, x + y + z = 1) as a main component,
The negative electrode active material is composed mainly of graphite, non-graphitizable carbon, or graphitizable carbon,
The non-aqueous electrolyte contains at least an anionic compound represented by the following general formula (1).

{However, M is a transition metal, a group III, IV or V element of the periodic table, b is 1 to 3, m is 1 to 4, n is 0 to 8, q is 0 or 1 respectively. , R ¹ is C ₁ -C ₁₀ alkylene, C ₁ -C ₁₀ halogenated alkylene, C ₆ -C ₂₀ arylene, or C ₆ -C ₂₀ halogenated arylene (the alkylene and arylene have the structure) And R ¹ may be bonded to each other.), R ² is halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ Alkyl halides, C ₆ -C ₂₀ aryls, C ₆ -C ₂₀ aryl halides, or X ³ R ³ (these alkyls and aryls may have substituents, heteroatoms in their structures, the n number R ² each may combine with each other to form a ring present.), X ^{1, 2,} X ³ is O, S, or NR ^4, R ^3, R ⁴ are, each independently, hydrogen, alkyl of C ₁ -C _10, alkyl halide C ₁ ~C _10, C ₆ ~C ₂₀ aryls and C ₆ -C ₂₀ aryl halides are shown respectively. (These alkyls and aryls may have a substituent or a hetero atom in the structure, and a plurality of R ³ and R ⁴ are respectively May combine to form a ring. } In Claim 1, in the said non-aqueous electrolyte, the electrolyte compound which consists of the said anion compound and cation represented by the said General formula (1) is ionizing, and M in the said General formula (1) is Al , B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and the cation is Li ⁺ Or a lithium ion secondary battery characterized by being at least one of Na ⁺ .   3. The electrolyte according to claim 1 or 2, wherein the non-aqueous electrolyte is added with an electrolyte other than the electrolyte compound composed of the anion compound and the cation represented by the general formula (1) as the electrolyte. The amount of the electrolyte compound added is 2% by weight to 80% by weight in the total electrolytic mass. In claim 3, the non-aqueous electrolyte solution, as other electrolytes other than the above electrolyte _{compounds, LiPF 6, LiClO 4, LiBF} 4, LiAsF 6, or that one or more selected from LiSbF ₆ is added A featured lithium ion secondary battery. In any 1 item | term of Claims 1-4, 1 or more types represented by following formula (2)-(5) are used as said anion compound represented by said general formula (1), It is characterized by the above-mentioned. Lithium ion secondary battery.

  6. The lithium ion secondary battery according to claim 5, wherein a compound represented by the formula (4) is used as the anion compound.

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