JP5124170B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery containing, as an electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent such as an organic solvent.

  Conventionally, lithium-ion secondary batteries using non-aqueous electrolytes have high voltage, high energy density, and can be reduced in size and weight. Therefore, information communication equipment mainly for information terminals such as personal computers and mobile phones. Practical use has progressed in this field, and it has become widely popular. In other fields, the development of electric vehicles has been urgently promoted due to environmental problems and resource issues, and the use of non-aqueous electrolyte lithium ion secondary batteries as batteries for hybrid vehicles has been studied.

A lithium ion secondary battery mainly includes a positive electrode, a negative electrode, and a non-aqueous electrolyte that moves lithium ions between the positive electrode and the negative electrode. In a lithium ion secondary battery, a nonaqueous electrolytic solution in which a Li salt such as LiPF ₆ is dissolved in an organic mixed solvent of a chain carbonate and a cyclic carbonate is generally used as the electrolytic solution.
In a lithium ion secondary battery, when charging / discharging is repeated, the positive electrode and the negative electrode deteriorate, the capacity may decrease, and the internal resistance of the battery may increase. So far, in order to improve the durability of lithium ion secondary batteries, various studies such as examination of the composition of the positive electrode active material, optimization of the battery configuration, surface treatment of the negative electrode active material, addition of additives to the electrolyte, etc. Attempts have been made.

Specifically, for example, a lithium ion secondary battery in which vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or the like is added to an electrolyte has been developed (see Patent Document 1).
In such a lithium ion secondary battery, VC and VEC are decomposed at a potential to which the negative electrode is exposed, and an electrochemically stable low-resistance film can be formed on the negative electrode surface. Therefore, deterioration of the negative electrode can be suppressed and durability can be improved.

However, the conventional lithium ion secondary battery has not yet been sufficiently durable. In the lithium ion secondary battery using VC or VEC as described above, the deterioration of the negative electrode can be suppressed to some extent. However, since the decomposition reaction of VC and VEC hardly occurs at the potential to which the positive electrode is exposed, Deterioration could hardly be suppressed.
In the lithium ion secondary battery, further improvement in durability has been desired particularly when long-term use of, for example, 10 years is assumed. That is, it has been desired to develop a lithium ion secondary battery in which a decrease in capacity and an increase in internal resistance are small when a large number of charge / discharge cycles of about 1000 cycles are repeated.

JP 2006-216378 A

  The present invention has been made in view of such conventional problems, and provides a lithium ion secondary battery that is excellent in durability, is less likely to have a reduced capacity even after repeated charging and discharging, and is difficult to increase in internal resistance. It is something to try.

The present invention relates to a positive electrode including a positive electrode active material composed of a compound capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material composed of a carbon-based material capable of occluding and releasing lithium ions, and a non-aqueous solvent. In a lithium ion secondary battery comprising at least a nonaqueous electrolytic solution obtained by dissolving an electrolyte,
The non-aqueous electrolyte includes, as the electrolyte , a main electrolyte composed of LiPF ₆ , a first sub-electrolyte represented by any of the following formulas (2) to (4) , and A ⁺ being Li ⁺ : A second subelectrolyte in which A ⁺ is K ⁺ and a third subelectrolyte in which A ⁺ is Na ⁺
The non-aqueous solvent contains 0.1% to 20% by weight of vinylene carbonate (VC) and / or vinylene ethylene carbonate (VEC) in a lithium ion secondary battery (claim 1) .

In the lithium ion secondary battery of the present invention, the non-aqueous electrolyte contains the main electrolyte, the first sub-electrolyte, the second sub-electrolyte, and the third sub-electrolyte as the electrolyte. As said non-aqueous solvent, 0.1 to 20 weight% of vinylene carbonate (VC) and / or vinylene ethylene carbonate (VEC) are contained. That is, the non-aqueous electrolyte contains the first sub-electrolyte in which A ⁺ is Li ⁺ among the sub-electrolytes, and the second sub-electrolyte in which A ⁺ is K ⁺ , and A ⁺ is Na ^+. It contains a third sub electrolyte is further a non-aqueous solvent, and the VC and / or VEC containing the specific amount.

Therefore, in the lithium ion secondary battery, the first sub-electrolyte , the second sub-electrolyte , the third sub-electrolyte, VC, and VEC are partially decomposed on the electrode, and are stable on the surfaces of the positive electrode and the negative electrode. A coating such as a simple coating can be formed. Therefore, in the above lithium ion secondary battery, even if charging and discharging are repeated many times, lithium ions are smoothly inserted and desorbed, the capacity is hardly lowered, and the internal resistance is hardly raised. The ion secondary battery can exhibit excellent durability.

Next, a preferred embodiment of the present invention will be described.
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 a non-aqueous 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.

  As the positive electrode, for example, a conductive material and a binder are mixed with the positive electrode active material, and an appropriate solvent is added to form a paste-like positive electrode mixture on the surface of the current collector made of metal foil, and then dried. If necessary, a sheet electrode or the like formed by compression to increase the electrode density can be used. Moreover, as the positive electrode, a pellet electrode obtained by press-molding the positive electrode mixture can be used.

  As the positive electrode active material, a compound capable of inserting and extracting lithium ions can be used. Specifically, for example, lithium transition metal composite oxides such as lithium manganese composite oxide, lithium cobalt composite oxide, and lithium nickel composite oxide can be used. Further, for example, lithium transition metal phosphate compounds such as lithium iron phosphate can be used.

  The conductive material is for ensuring electrical conductivity. For example, one or more carbon material powders such as carbon black, acetylene black, natural graphite, artificial graphite, and coke are mixed. 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.

  Moreover, as a material of a positive electrode electrical power collector, metals, such as aluminum and titanium, or its alloy can be used. Preferably, aluminum or an alloy thereof is used. In this case, the weight can be reduced and the energy density can be improved.

  Next, as the negative electrode, a negative electrode mixture obtained by mixing a negative electrode active material with a conductive agent and a binder as necessary and adding a suitable solvent as a dispersing agent to form a slurry is used as a current collector made of metal foil. The sheet electrode etc. which apply | coated and dried on the surface of this, and were compression-formed after that can be used. Moreover, as the negative electrode, a pellet electrode obtained by press-molding the negative electrode mixture can be used.

As the negative electrode active material, a carbon-based material capable of inserting and extracting lithium ions can be used.
As the carbon-based material used for the negative electrode active material, one or more selected from graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), amorphous carbon, and the like can be used. .

As in the case of the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride is used as the binder mixed with the negative electrode active material, and an organic solvent such as N-methyl-2-pyrrolidone is used as the solvent. Can do.
Further, as the material of the negative electrode current collector, metals such as copper, nickel, and stainless steel can be used. From the viewpoint of easy processing into a shape such as a thin film and low cost, copper is preferable.

  Moreover, as said separator, the porous sheet | seat which consists of polyolefin, such as polyethylene and a polypropylene, or a nonwoven fabric etc. can be used, for example.

｛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１〜８、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。）。｝ Then, the non-aqueous electrolyte as the electrolyte, and one or more primary electrolyte selected from _{LiPF 6, LiClO 4, LiBF 4} , LiAsF 6, and LiSbF _6, is represented by a general formula (1), A first subelectrolyte in which A ^{a +} is Li ⁺ , a second subelectrolyte in which A ^{a +} is K ⁺ , and a third subelectrolyte in which A ^{a +} is Na ⁺ can be contained.
Since the specific main electrolyte has a relatively excellent ion conductivity and is electrochemically stable, the charge / discharge capacity of the lithium ion secondary battery can be improved.

{However, M is a transition metal, group III, group IV, or group V element of the periodic table, b is 1-3, m is 1-4, n is 1-8, 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 present. May combine to form a ring. }

The contents of the first sub-electrolyte, the second sub-electrolyte, and the third sub-electrolyte in the non-aqueous electrolyte are preferably 0.01 mol / l to 0.3 mol / l. ).
If it is less than 0.001 mol / l, it may be difficult to sufficiently exhibit the effect of improving the durability. The reason for this is considered to be that an abdomen such as a film formed on the surface of the active material by the first to third subelectrolytes is not sufficiently formed. On the other hand, if it exceeds 10 mol%, the initial discharge capacity of the lithium ion secondary battery may be reduced. This is probably because the thickness of the coating formed on the surface of the active material becomes larger than necessary. The content of 0.001 mol / l to 10 mol / l described above is the total amount of the first sub-electrolyte, the second sub-electrolyte, and the third sub-electrolyte. More preferably, the content of the first sub-electrolyte, the second sub-electrolyte, and the third sub-electrolyte in the non-aqueous electrolyte is 0.02 mol / l to. The amount may be 0.1 mol / l, and more preferably 0.04 mol / l to 0.08 mol / l.

  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 first to third subelectrolytes is increased, so that it is difficult to dissolve the first to third subelectrolytes in the nonaqueous solvent. In order to avoid this, b = 1 is most preferable.

  The first to third sub-electrolytes represented by the general formula (1) have an ionic metal complex structure, and M at the center is a transition metal, group III of the periodic table, IV It is selected from group or V group elements.

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. It is preferable that it is either .
In this case, it becomes easy to dissolve the first to third sub-electrolytes in the non-aqueous solvent. In this case, the first to third subelectrolytes can be synthesized relatively easily.

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

Next, the ligand part of the 1st-3rd subelectrolyte represented by the said General formula (1) is demonstrated.
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, it is possible to obtain an effect that the solubility and dissociation degree of the first to third subelectrolytes are improved, and the ion conductivity is improved accordingly. 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 first to third subelectrolytes is stabilized. Therefore, in this case, the first to third subelectrolytes can be prevented from causing 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.

Specific examples of the substance represented by the general formula (1) include substances represented by the following formulas (2) to (4) (provided that A ⁺ is Li ⁺ , K ⁺ , or Na ^+). Is).

Preferably, the above-mentioned general formula (1), the better it is the formula (2) (claim 3).
In this case, the solubility and dissociation degree of the first to third subelectrolytes can be improved, and the ionic conductivity of the non-aqueous electrolyte can be improved. Furthermore, in this case, oxidation resistance can be improved. In addition, in the compound represented by the above formula (2), the complex structure is stabilized because the chelate ring in the structure is disposed. Therefore, in this case, the sub-electrolyte can exhibit an effect of further improving battery characteristics.

  As the non-aqueous solvent, an aprotic organic solvent can be used. Specifically, as the main component of the non-aqueous solvent, for example, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), γ- Lactones such as butyl lactone (GBL) and γ-valerolactone (GVL), nitriles such as acetonitrile, esters such as methyl acetate, methyl formate, methyl propionate, ethyl propionate, tetrahydrofuran, 2-methyltetrahydrofuran, 1 , 4-dioxane, 1,2-dimethoxyethane, ethers such as 1,2-diethoxyethane, amides such as dimethylformamide, and the like can be used. These can be used alone, or two or more kinds can be mixed and used.

In the present invention, the non-aqueous solvent contains 0.1% to 20% by weight of vinylene carbonate (VC) and / or vinylene ethylene carbonate (VEC).
If the contents of VC and VEC in the non-aqueous solvent are less than 0.1% by weight, the durability improving effect may not be sufficiently exhibited. On the other hand, if it exceeds 20% by weight, the internal resistance of the battery is increased, and the battery capacity may be reduced.
In addition, when it contains both VC and VEC, the total amount can be made into the range of 0.1 weight%-20 weight%.
More preferably, the content of VC and VEC is 1 to 10% by weight.

Example 1
Next, an embodiment of the lithium ion secondary battery of the present invention will be described with reference to FIG.
In this example, 13 types of lithium ion secondary batteries (battery E1 to battery E7 and battery C1 to battery C6) having different compositions of the electrolytic solution are produced, and the battery characteristics (durability) are evaluated.
First, the battery E1 is produced.
As shown in FIG. 1, the lithium ion secondary battery (battery E <b> 1) of this example is a cylindrical battery 1. The lithium ion secondary battery 1 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.

The positive electrode 2 contains a lithium nickel composite oxide having a layered structure as a positive electrode active material. In this example, LiNi _0.8 Co _0.15 Al _0.05 O ₂ containing Co and Al was used as the lithium nickel composite oxide.
The negative electrode 3 contains artificial 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.

A non-aqueous electrolyte is injected into the battery case 6.
As the non-aqueous electrolyte, the main electrolyte is a non-aqueous solvent obtained by further adding vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) to a mixed solvent composed of ethylene carbonate (EC) and diethyl carbonate (DEC). An electrolytic solution obtained by mixing (LiPF ₆ ) and the first to third sub-electrolytes is contained.

As said 1st-3rd subelectrolyte, the material represented by following formula (2) was used.

Hereinafter, the manufacturing method of the lithium ion secondary battery (sample E1) of this example will be described.
First, the nonaqueous electrolyte solution (sample e1) was produced as follows.
That is, first, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 to prepare a mixed solvent (EC / DEC). Next, vinylene carbonate (VC) 2 wt% and vinyl ethylene carbonate (VEC) 2 wt% were added to the mixed solvent 96 wt% to obtain a non-aqueous solvent. Next, LiPF ₆ as the main electrolyte, (LiPF ₂ (C ₂ O ₄ ) ₂ ) as the first sub-electrolyte, (KPF ₂ (C ₂ O ₄ ) ₂ ) as the _second sub-electrolyte, and (NaPF ₂ ) as the third sub-electrolyte (C ₂ O ₄ ) ₂ ) was prepared and dissolved in a non-aqueous electrolyte to prepare a non-aqueous electrolyte. At this time, each electrolyte is adjusted so that the concentration of the main electrolyte is 1M, the concentration of the first sub-electrolyte is 0.02M, the concentration of the third sub-electrolyte is 0.02M, and the concentration of the third sub-electrolyte is 0.02M. Dissolved. The nonaqueous electrolytic solution thus obtained is designated as sample e1. Table 1 shows the composition of sample e1.

Next, the positive electrode 2 and the negative electrode 3 were produced as follows.
In preparing the positive electrode 2, first, LiNi _0.8 Co _0.15 Al _0.05 O ₂ was prepared as a positive electrode active material. This positive electrode active material, carbon black as a conductive additive, and polyvinylidene fluoride as a binder are mixed, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersing agent is added and dispersed to form a slurry-like positive electrode composite. A material was prepared. The mixing ratio of the positive electrode active material, the conductive assistant and the binder was a weight ratio of positive electrode active material: conductive auxiliary agent: binder = 85: 10: 5.

Next, the positive electrode mixture obtained as described above was applied to both surfaces of an aluminum foil current collector having a thickness of 20 μm by a coater 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. The amount of positive electrode active material deposited was about 7.0 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. This negative electrode active material and polyvinylidene fluoride as a binder were mixed, and 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 both surfaces of a copper foil current collector having a thickness of 10 μm by a coater 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 5 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 connected to the positive electrode current collecting tab 235 arranged on the cap 63 side of the battery case 6 by welding, and the negative electrode current collecting lead is arranged on the negative electrode current collecting tab 335 arranged on the bottom of the outer can 65. 33 was connected by welding.

  Next, the battery case 6 was impregnated with the nonaqueous electrolyte solution (sample e1) 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.

In this example, 12 types of lithium ion secondary batteries (battery E2 to battery E7 and battery C1 to battery C6) having a different composition of the non-aqueous electrolyte from the battery E1 were further produced. Each battery (battery E2-battery E7 and battery C1-battery C6), except that 12 types of non-aqueous electrolytes (sample e2-sample e7 and sample c1-sample c6) having different compositions were used, It was produced in the same manner as the battery E1.
Samples e2 to e5 and samples c1 to c6 are non-aqueous electrolytes prepared by changing the contents of the first sub-electrolyte, the second sub-electrolyte, the third sub-electrolyte, VC, and VEC from those of the sample e1. . The composition is shown in Table 1.

Moreover, in the sample e6, the substance represented by the following formula (3) was used as the first to third subelectrolytes.

Moreover, in the sample e7, the substance represented by the following formula (4) was used as the first to third subelectrolytes.

Next, for the 13 types of lithium ion secondary batteries (battery E1 to battery E7 and battery C1 to battery C6) produced as described above, the following charge / discharge cycle test was performed, and the capacity retention rate before and after the test was determined. The resistance increase rate was examined.
"Charge / discharge cycle test"
Each battery (battery E1 to battery E7 and battery C1 to battery C6) is charged at a constant current density of ² mA / cm ² under a temperature condition of 60 ° C., which is regarded as the upper limit of the actual use temperature range of the battery. Charging / discharging for charging to a voltage of 4.1 V and then discharging to a discharge lower limit voltage of 3.0 V at a constant current of a current density of ² mA / cm ^{2 was} defined as one cycle, and this cycle was performed for a total of 1000 cycles.

"Capacity maintenance rate"
Before and after the charge / discharge cycle test, the discharge current value (mA) of each battery was measured, and the value obtained by multiplying this discharge current value by the time (hr) required for discharge was calculated as the weight of the positive electrode active material in the battery. The discharge capacity was calculated by dividing by (g). Then, when the discharge capacity before the charge / discharge cycle test was capacity A (initial capacity) and the discharge capacity after the charge / discharge cycle test was capacity B, the capacity retention rate was calculated by the following equation (a). The results are shown in Table 2. Table 2 shows the discharge capacity (initial capacity) before the charge / discharge cycle test together with the capacity maintenance rate.
Capacity maintenance rate (%) = capacity B / capacity A × 100 (a)

“Rise in resistance”
Each battery was adjusted to 50% (SOC = 50%) of the battery capacity under a temperature condition of 20 ° C., and a battery voltage after 10 seconds was measured by flowing a current of 0.5A, 1A, 2A, 3A, and 5A. The flowing current and voltage were linearly approximated, and the IV resistance (battery internal resistance) was determined from the slope.
The rate of increase in resistance can be calculated by the following equation (b), where IV resistance after the charge / discharge test is resistance B and IV resistance before the charge / discharge test is resistance A (initial IV resistance). The results are shown in Table 2. Table 2 shows the resistance value (initial resistance) before the charge / discharge cycle test together with the rate of increase in resistance.
Resistance increase rate (%) = (resistance B−resistance A) × 100 / resistance A (b)

As is known from Table 2, a non-aqueous electrolyte (sample e1 to sample e7) containing a first sub-electrolyte, a second sub-electrolyte and / or a third sub-electrolyte and containing VC and / or VEC is used. The lithium ion secondary batteries (battery E1 to battery E7) had a high capacity retention rate and a small resistance increase rate even in a long-term cycle test of 1000 cycles. That is, the batteries E1 to E7 showed excellent durability.
On the other hand, the non-aqueous electrolyte containing only one of the battery C1 and the battery C6 using the non-aqueous electrolyte (sample c1 and sample c6) not containing the sub-electrolyte, and the first to third sub-electrolytes ( Batteries C3 to C5 using samples c3 to c5), and batteries C2 using a nonaqueous electrolyte solution (sample c2) that does not contain VC and VEC, in particular, have a much higher resistance increase rate than the batteries E1 to E7. It had increased to. Therefore, it turns out that the durability with respect to the charge / discharge cycle is insufficient.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the lithium ion secondary battery concerning Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 6 Battery case

Claims (3)

A positive electrode containing a positive electrode active material made of a compound capable of occluding and releasing lithium ions, a negative electrode containing a negative electrode active material made of a carbon-based material capable of occluding and releasing lithium ions, and an electrolyte dissolved in a non-aqueous solvent In a lithium ion secondary battery comprising at least a nonaqueous electrolyte solution,
The non-aqueous electrolyte includes, as the electrolyte , a main electrolyte composed of LiPF ₆ , a first sub-electrolyte represented by any of the following formulas (2) to (4) , and A ⁺ being Li ⁺ : A second subelectrolyte in which A ⁺ is K ⁺ and a third subelectrolyte in which A ⁺ is Na ⁺
The said non-aqueous solvent contains 0.1 to 20 weight% of vinylene carbonate (VC) and / or vinylene ethylene carbonate (VEC), The lithium ion secondary battery characterized by the above-mentioned.

  2. The content of the first sub-electrolyte, the second sub-electrolyte, and the third sub-electrolyte in the non-aqueous electrolyte solution according to claim 1 is 0.01 mol / l to 0.3 mol / l. A featured lithium ion secondary battery. 3. The lithium ion secondary battery according to claim 1, wherein the first to third sub-electrolytes are represented by the following formula (2).

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