JP2012150972A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery which suppresses deterioration during high temperature storage while facilitating electrode winding in manufacture.SOLUTION: The lithium ion battery includes: a positive electrode capable of absorbing/desorbing lithium ions; a negative electrode 3 capable of absorbing/desorbing lithium ions; a separator arranged between the positive electrode and the negative electrode 3; and an electrolyte. A binder of a negative electrode mixture layer 2 contains polyvinylidene fluoride, and the crystallinity of the polyvinylidene fluoride in the negative electrode mixture layer 2 is higher on a collector 1 side than on a separator side. A value of Rcomputed by (formula 1) based on an absorbance (A) at 736 cmand an absorbance (A) at 840 cmobtained by an IR measurement is larger than 1.5 on the collector 1 side, and is equal to or less than 1.5 on the separator side. R=A/A...(formula 1)

Description

  The present invention relates to a lithium ion battery.

  One of the factors that cause deterioration of a lithium ion battery during high temperature storage is a phenomenon in which the negative electrode mixture layer is peeled off from the negative electrode current collector. One factor that causes the negative electrode mixture to peel off from the negative electrode current collector during high-temperature storage is that solvent molecules enter between the binder (binder) molecules in the electrolyte, causing the binder to swell, and between the current collector and the mixture. This is due to the change in binding.

  One measure for suppressing the swelling of the binder is to improve the crystallinity of the binder. Japanese Patent Application Laid-Open No. 2002-313318 (Patent Document 1) describes a specification using a crystalline polymer for a mixture layer. The positive electrode mixture layer has a two-layer structure, in which the outer active material layer contains active material particles, conductive auxiliary agent particles, binder particles and crystalline polymer particles, and the inner active material layer contains crystalline polymer particles. There is no disclosure. This configuration can suppress heat generation during overcharge, achieve high thermal stability, and excellent high rate discharge characteristics. By using crystalline polymer particles in the active material layer, it becomes difficult for the solvent to enter between the polymer molecules, swelling of the polymer particles can be suppressed, and peeling due to a change in binding can be suppressed.

JP 2002-313318 A

  However, if the crystallinity of the mixture is high, the mixture becomes hard, and it is difficult to wind it during winding, and the electrode is easily broken. For this reason, it is a big subject to improve the adhesion between the current collector and the mixture by crystallization of the electrode and the ease of winding the electrode.

  Accordingly, an object of the present invention is to provide a lithium ion battery that achieves both suppression of deterioration during high-temperature storage and ease of electrode winding during production.

In general, a lithium ion battery includes a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Have. A feature of the present invention is that polyvinylidene fluoride is used as a binder for the negative electrode mixture layer, and the crystallinity of the binder in the negative electrode is higher on the current collector side than on the separator side. Specifically, from the absorbance (A ₇₃₆ ) of ₇₃₆ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained by infrared spectroscopy (IR) measurement in the vicinity of the current collector-side interface in the negative electrode ( The value of R ₁ calculated by Equation 1) is greater than 1.5 on the current collector side and 1.5 or less on the separator side.
R ₁ = A ₇₆₃ / A ₈₄₀ (Formula 1)

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion battery which implement | achieves a long life also at the time of high temperature storage can be provided.

The figure which shows the negative electrode of the lithium ion battery which concerns on embodiment. FIG. 3 is a cross-sectional view showing one side of a wound battery according to Example 1;

  From the viewpoints of environmental protection and energy saving, hybrid vehicles using an engine and a motor as a power source have been developed and commercialized. In the future, fuel cell hybrid vehicles that use fuel cells instead of engines are also actively developed. A secondary battery capable of repeatedly charging and discharging electricity as an energy source of this hybrid vehicle is an essential technology.

  Among them, the lithium ion battery is a battery having a high operating voltage and a high energy density that easily obtains a high output, and is becoming increasingly important as a power source for a hybrid vehicle in the future. High power, high energy density, and long life are important issues in the use of hybrid vehicles for electric vehicles. Therefore, by changing the crystallinity of the binder in the electrode mixture layer of the negative electrode in the layer direction, it is possible to achieve both long life during high temperature storage with high adhesion and ease of winding the electrode during production. did.

  The lithium ion battery of this invention should just be equipped with the above negative electrodes, and there is no restriction | limiting in particular about another component and structure. As other configurations, various components and structures applied in conventionally known lithium ion batteries can be employed.

  In general, a lithium ion battery includes a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Have. The positive electrode has a positive electrode mixture and a positive electrode current collector. The positive electrode mixture layer refers to a mixture layer formed by applying a positive electrode mixture containing a positive electrode active material, a conductive agent, and a binder to a positive electrode current collector. The negative electrode has a negative electrode mixture and a negative electrode current collector. The negative electrode mixture layer refers to a mixture layer formed by applying a negative electrode mixture containing a negative electrode active material, a conductive agent, and a binder to a negative electrode current collector.

  In FIG. 1, the example of sectional drawing of an electrode is shown. As shown in FIG. 1, the negative electrode 3 has a structure in which a negative electrode mixture layer 2 is provided on both surfaces of a copper foil (negative electrode current collector 1). The negative electrode mixture layer is a mixture of a negative electrode active material and a binder, and is applied to a current collector. The binder crystallinity in the negative electrode mixture layer was different between the copper foil side and the separator side, and the polyvinylidene fluoride on the copper foil side had a high crystallinity.

  The binding property between the current collector and the active material is weaker than the binding property between the active materials, and the negative electrode mixture layer is peeled off at the interface of the negative electrode current collector when the battery is stored at a high temperature. It is necessary to maintain the current state of adhesion between the active material and the active material and to improve the adhesion between the current collector and the mixture. Therefore, the crystallinity of the binder near the current collector was increased. On the other hand, if the entire mixture layer, especially the binder on the separator side in the mixture layer is excessively crystallized, it becomes difficult to maintain the flexibility of the electrode. Since it becomes difficult to wind at the time of winding or cracks of the mixture layer, it is preferable to lower the crystallinity in the vicinity of the current collector, particularly to maintain the current crystallinity. The binder is preferably polyvinylidene fluoride because it is a polymer that partially crystallizes.

The crystallinity is related to the value of R ₁ as calculated by absorbance 760 cm ^-1 obtained by IR measurement (A ₇₆₀₎ and absorbance at 840 cm ^-1 from (A ₈₄₀₎ (Equation 1), high crystallinity As a result, the value of R ₁ also increases.
R ₁ = A ₇₆₃ / A ₈₄₀ (Formula 1)

A ₇₆₃ is the absorbance attributed to the α-type crystal structure, and A ₈₄₀ is the absorbance attributed to the β-type crystal structure. The value of R ₁ indicates the ratio of α-type crystal structure and β-type crystal structure in the crystalline region of polyvinylidene fluoride.

The α-type crystal structure of polyvinylidene fluoride is a hydrogen atom (or fluorine atom) bonded to one adjacent carbon atom with respect to a fluorine atom (or hydrogen atom) bonded to one main chain carbon in the polymer molecule. ) Is located at the trans position, and the hydrogen atom (or fluorine atom) bonded to the carbon atom adjacent to the other side (reverse side) is located at the Gauche position (60 degree position). The molecular chain is a TG ⁺ TG ⁻ type, and the dipole efficiency of the C—F ₂ and C—H ₂ bonds is perpendicular to and parallel to the molecular chain. Each has a component. Doing IR analysis polyvinylidene fluoride having an α-type crystal structure, 1212Cm ^-1, has a 1183 cm ^-1 and 763cm ^-1 near the characteristic peaks (characteristic absorptions), in a powder X-ray diffraction 2 [Theta] = 17 It has characteristic peaks around .7 degrees, 18.3 degrees, and 19.9 degrees.
The β crystal structure of polyvinylidene fluoride is that the fluorine atom and the hydrogen atom bonded to the carbon atom adjacent to one principal carbon in the polymer molecule are each in the trans configuration (TT structure), that is, to the adjacent carbon atom. A fluorine atom and a hydrogen atom to be bonded are present at a position of 180 degrees when viewed from the direction of the carbon-carbon bond. The carbon-carbon bond in which the TT-type structure part constitutes the TT-type main chain has a planar zigzag structure, and the dipole efficiency of the C—F ₂ and C—H ₂ bonds has a component perpendicular to the molecular chain. Have. Doing IR for β crystal structure, 1274Cm ^-1, it has a 1163Cm ^-1 and 840 cm ^-1 near the characteristic peaks (characteristic absorptions), in a powder X-ray diffraction analysis is a characteristic in the vicinity of degrees 2 [Theta] = 21 Has a peak.

If R ₁ measured with the mixture in the vicinity of the current collector is greater than 1.5, the crystallinity of the binder becomes high and peeling is suppressed.
It is more preferable that the value of R ₁ is 1.7 or more. The crystallinity is further improved, and peeling does not occur even when the electrode is stored in an environment of 70 ° C.

On the other hand, the crystallinity of the mixture to be measured near the surface of the separator side is calculated by absorbance 760 cm ^-1 obtained by IR measurement (A ₇₆₀₎ and absorbance at 840 cm ^-1 from (A ₈₄₀₎ (Equation 1) The value of R ₁ is 1.5 or less. Within this range, it is possible to maintain sufficient flexibility when the electrode is wound. As a result, it is possible to achieve both long-term high adhesion during high-temperature storage and ease of winding during winding. In addition, the battery life can be extended by improving the adhesion between the negative electrode current collector and the negative electrode mixture layer during high-temperature storage.

  Polyvinylidene fluoride is a polymer that is partially crystallized, and the ratio of crystals increases by heat treatment. It is possible to increase the crystallinity by maintaining a high temperature in the vicinity of the current collector of the negative electrode mixture layer, while lowering the temperature on the separator side (surface side) to bring the crystallinity to the current state. be able to.

  For example, the copper foil is heated from at least one surface of the negative electrode current collector, and the negative electrode mixture-containing composition for forming the negative electrode mixture layer is applied to the surface opposite to the surface heated from the copper foil. When applying, it is desirable that air is blown on the applied surface so that the electrode surface temperature is 120 ° C. or lower. Then, it dries at 60-150 degreeC, adjusts thickness and density by pressing after that, and forms a negative mix layer.

  Further, the configuration of other lithium ion batteries will be described. The electrode mixture is applied onto a current collector on a slurry to which a solvent is added. Solvents for forming the slurry include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, and tetramethylurea. , Triethyl phosphate, trimethyl phosphate, and the like can be used. In particular, nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide are preferable because of high solubility of the binder resin. These solvents may be used alone or in combination.

The positive electrode is LiMn _x M1 _y M2 _z O ₂ (wherein, M1 is selected from Co, Ni, M2 is selected from Co, Ni, Al, B, Fe, Mg, Cr as a positive electrode active material) At least one, x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.4, 0.05 ≦ z ≦ 0.4) containing a lithium composite oxide preferable.

  The positive electrode 6 is formed by applying a positive electrode mixture layer 5 containing a positive electrode active material and a binder onto a current collector 4 such as an aluminum foil. Moreover, you may add a electrically conductive agent to the positive mix layer for reduction of electronic resistance.

The positive electrode active material has a composition formula Li _α Mn _x M 1 _y M 2 _z O ₂ (wherein M 1 is at least one selected from Co and Ni, and M 2 is Co, Ni, Al, B, Fe, Mg, Cr) X + y + z = 1, 0 <α <1.2, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.4, 0.05 ≦ z ≦ 0.4. ) Is preferable. Among these, it is more preferable that M1 is Ni or Co and M2 is Co or Ni. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is more preferable. In the composition, if Ni is increased, the capacity can be increased, if Co is increased, the output at a low temperature can be improved, and if Mn is increased, the material cost can be suppressed. In addition, the additive element is effective in stabilizing the cycle characteristics. In addition, the general formula LiM _x PO ₄ (M: Fe or Mn, 0.01 ≦ X ≦ 0.4) and LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ An orthorhombic phosphate compound having symmetry of the space group Pmnb where X ≦ 0.4) may be used. In particular, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ has high low-temperature characteristics and high cycle stability, and is suitable as a lithium battery material for hybrid vehicles (HEV). The binder may be any material as long as the material constituting the positive electrode and the current collector for the positive electrode are in close contact. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene-butadiene, or the like. Examples include rubber. The conductive agent is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.

  As the negative electrode current collector, a metal foil such as stainless steel, copper, nickel, titanium, or a metal mesh can be used. In particular, copper is preferable, and zirconia and zinc-containing copper having high heat resistance are also preferable.

  The negative electrode active material is preferably composed of at least one of a carbonaceous material, an oxide containing a group IV element, and a nitride containing a group IV element.

Negative electrode active materials include natural graphite, composite carbonaceous materials with a film formed by dry CVD (Chemical Vapor Dposition) method and wet spray method on natural graphite, resin raw materials such as epoxy and phenol, petroleum and coal Carbonaceous materials such as artificial graphite and amorphous carbon materials produced by firing from pitch-based materials obtained from the above, or lithium metal that can occlude and release lithium by forming a compound with lithium, lithium and a compound An oxide or nitride of a Group 4 element such as silicon, germanium, or tin that can be formed and inserted into a crystal gap to occlude and release lithium can be used. In particular, the carbonaceous material is a material having high conductivity, and excellent in terms of low temperature characteristics and cycle stability. Among the carbonaceous materials, a material having a wide carbon network surface layer (d ₀₀₂ ) is excellent in rapid charge / discharge and low temperature characteristics, and is suitable. However, since a material with a wide d ₀₀₂ may have a reduced capacity and a low charge / discharge efficiency at the initial stage of charging, d ₀₀₂ is preferably 0.39 nm or less. May be called. Furthermore, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like may be mixed to constitute the electrode. Alternatively, a material having the characteristics shown in (1) to (3) below may be used as the graphite material.
(1) peak in the range of 1300～1400Cm ^-1 measured by Raman spectrum intensity (I _D) and the peak intensity in the range of 1580～1620Cm ^-1 as measured by Raman spectroscopy spectra (I _G) and the The R value (I _D / I _G ), which is an intensity ratio, is 0.2 or more and 0.4 or less. (2) The half-value width Δ value of a peak in the range of 1300 to 1400 cm ⁻¹ measured by a Raman spectroscopic spectrum is 40 cm ^-1 or more 100 cm ^-1 or less (3) the intensity ratio X values of the peak intensity of the (110) plane in X-ray diffraction (I ₍₁₁₀₎₎ and (004) plane peak intensity (I ₍₀₀₄₎₎ (I ₍₁₁₀₎ / I ₍₀₀₄₎ ) is 0.1 or more and 0.45 or less.

  Note that a conductive agent may be further added to the negative electrode mixture layer in order to reduce electronic resistance. The conductive agent is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.

  As the solvent used in the electrolytic solution, those containing ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) are preferable from the viewpoint of low temperature characteristics and film formation on the negative electrode.

The lithium salt used in the electrolytic solution is not particularly limited, but for inorganic lithium salts, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiI, LiCl, LiBr, etc., and for organic lithium salts, LiB [OCOCF ₃ ] ₄ , LiB [OCOCF ₂ CF ₃ ] ₄ , LiPF ₄ (CF ₃ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ or the like can be used. In particular, LiPF ₆ frequently used in consumer batteries is a suitable material because of the stability of quality. LiB [OCOCF ₃ ] ₄ is an effective material because it has good dissociation and solubility and shows high conductivity at a low concentration.

  Examples of the separator used in the lithium ion battery include a microporous film made of polyolefin such as polyethylene and polypropylene, and a nonwoven fabric. From the viewpoint of increasing the capacity of the battery, the thickness of the separator is preferably 20 μm or less, and more preferably 18 μm or less. By using a separator having such a thickness, the capacity per volume of the battery can be increased. However, if the separator is made too thin, the handleability is impaired, or the separation between the positive and negative electrodes is insufficient and short-circuiting is likely to occur, so the lower limit of the thickness is preferably 10 μm.

  The lithium ion battery of the present invention has high output and long life, and can be widely used as a power source for hybrid vehicles, a power source for electric control systems of vehicles, and a backup power source, such as railways, power tools, forklifts, etc. It is also suitable as a power source for industrial equipment.

As described above, polyvinylidene fluoride is used as the binder for the negative electrode mixture layer, and the crystallinity of the binder is higher on the current collector side than on the separator side. The value of R ₁ calculated by (Equation 1) from the absorbance (A ₇₃₆ ) of ₇₃₆ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained from the IR measurement of the agent layer is greater than 1.5, and the separator side It is preferable to constitute a lithium ion battery using a negative electrode having an R ₁ value of 1.5 or less obtained from IR measurement of the mixture layer.

R ₁ = A ₇₃₆ / A ₈₄₀ (Formula 1)
Hereinafter, the best mode for carrying out the present invention will be described with reference to specific examples.

〔Example〕
(Production of wound battery)

  FIG. 2 shows a cross-sectional side view of the wound battery 100 of this example. The wound type battery of this example was manufactured by the method described below.

LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is used as the positive electrode active material, carbon black (CB1) and graphite (GF2) are used as the electronic conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. The solid weight at the time of drying was set to NMP (N-- as a solvent so that the ratio of LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB1: GF2: PVDF = 86: 9: 2: 3 A positive electrode material paste was prepared using methylpyrrolidone). This positive electrode material paste was applied to an aluminum foil to be the positive electrode current collector 4, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode mixture layer 5 on the positive electrode current collector 4. .

  Next, pseudo-anisotropic carbon, which is amorphous carbon, is used as the negative electrode active material, carbon black (CB2) is used as the conductive material, and PVDF is used as the binder. A slurry of the negative electrode mixture layer was prepared using NMP as a solvent so as to have a ratio of carbon: CB2: PVDF = 90: 5: 5. This negative electrode material slurry was applied to a copper foil to be the negative electrode current collector 1. During coating, the temperature of the copper foil is increased from the lower side to 130 ° C so that there is a temperature difference between the copper foil side and the separator side of the negative electrode material slurry. Thus, the temperature of the negative electrode material slurry was adjusted. Then, it dried and pressed at 80 degreeC, it dried at 120 degreeC, and the negative mix layer 2 was formed in the negative electrode collector 1. FIG.

  As an electrolytic solution, a solvent was mixed at a volume composition ratio EC: VC: DMC: EMC = 19.8: 0.2: 40: 40, and 1M LiPF6 was dissolved as a lithium salt to prepare an electrolytic solution.

  The separator 7 was sandwiched between the produced electrodes to form a wound group and inserted into the negative battery can 13. Then, one end of a nickel negative electrode lead 9 was welded to the negative electrode current collector 1 and the other end was welded to the negative electrode battery can 13 in order to collect the negative electrode current. In addition, in order to collect the positive electrode, one end of the positive electrode lead 8 made of aluminum is welded to the positive electrode current collector 4, the other end is subjected to current interruption welding, and further, the positive electrode battery lid 12 is electrically connected to the positive electrode via the current interruption valve. Connected. Further, a wound battery was manufactured by pouring and caulking the electrolyte. In FIG. 2, 10 is a positive electrode insulating material, 11 is a negative electrode insulating material, and 14 is a gasket.

  A wound battery of Example 2 was produced in the same manner as in Example 1 except that graphite was used as the negative electrode active material of the negative electrode mixture layer.

  The same as in Example 1 except that the temperature of the copper foil was 150 ° C. from the lower side, and the temperature of the negative electrode material slurry was adjusted to 120 ° C. or less by blowing air on the slurry surface from the upper side. Thus, a wound battery of Example 3 was produced.

  The graphite is used as the negative electrode active material of the negative electrode mixture layer and is heated from the lower side so that the temperature of the copper foil is 150 ° C. A wound battery of Example 4 was produced in the same manner as in Example 1 except that the temperature of the material slurry was adjusted.

[Comparative Example 1]
The negative electrode material slurry was applied on the negative electrode current collector without adjustment to provide a temperature difference on the copper foil side / separator side, dried at 80 ° C., pressed, dried at 120 ° C. A wound battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the agent layer was formed on the negative electrode current collector.

[Comparative Example 2]
The negative electrode material slurry is applied on the negative electrode current collector without adjustment to provide a temperature difference on the copper foil side / separator side, dried at 80 ° C., pressed, dried at 150 ° C. A wound battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the agent layer was formed on the negative electrode current collector.

[Comparative Example 3]
The negative electrode material slurry was applied to a copper foil to be the negative electrode current collector 1 while heating the copper foil to 120 ° C. from the opposite side of the application surface. At that time, air was blown from above, and the temperature of the negative electrode material slurry was adjusted so that the temperature of the coating surface was 150 ° C. Then, it dried and pressed at 120 degreeC and the negative mix layer 2 was formed in the negative electrode collector 1. FIG. Otherwise, a wound battery of Comparative Example 3 was produced in the same manner as in Example 1.

  The batteries of Examples 1 to 4 and Comparative Examples 1 to 3 were subjected to the following tests.

(Bending test)
In order to evaluate the flexibility of the negative electrode, a negative electrode cut out to 30 mm × 10 mm was prepared, the negative electrode was bent 180 °, and then expanded to 0 °. When it was expanded to 0 °, it was marked as x when it was cracked or cracked, and marked as ◯ when it was not cracked. The results are shown in Table 1.

(Remaining rate evaluation)
In order to evaluate the residual ratio of the obtained negative electrode, 15 negative electrodes punched out to a diameter of 15 mmφ were prepared, and the electrolyte and the negative electrode were put in a polyethylene container and stored at 70 ° C. for 7 days. After storage, the remaining rate, which is the ratio of the current collector and the mixture adhering to each other, was investigated. The residual rate is defined as the ratio of the number of the mixture stored in the electrolyte and the number of the mixture not removed as shown in (Formula 2). The measurement results are shown in Table 1.
Residual rate (%) = area of negative electrode mixture after immersion in electrolyte / area of negative electrode mixture (Formula 2)

(Evaluation of crystallinity)
To evaluate the proportion of α-crystal structure of polyvinylidene fluoride obtained negative electrode and β crystal structure, using an infrared spectrophotometer, the absorbance of 763cm ^-1 (A _763), the absorbance of 840 cm ^-1 to (A ₈₄₀₎ It was measured. R ₁ as shown in (Formula 1) was calculated. The measurement results are shown in Table 1.

(Battery characteristics evaluation)
<Method for evaluating battery capacity during storage at 70 ° C.>
The battery was charged at a constant current of 0.6 A to 4.1 V, charged at a constant voltage of 4.1 V until the current value reached 20 mA, and after 30 minutes of operation stop, discharged to 2.6 V at 0.6 A. This operation was repeated three times. Next, the battery was charged at a constant current of 0.6 A up to 4.1 V, allowed to stand for 30 minutes, placed in a 70 ° C. constant temperature bath, and the voltage after standing for 30 days was measured. The measurement results are shown in Table 1.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode mixture layer 3 Negative electrode 4 Positive electrode collector 5 Positive electrode mixture layer 6 Positive electrode 7 Separator 8 Positive electrode lead 9 Negative electrode lead 10 Positive electrode insulating material 11 Negative electrode insulating material 12 Positive electrode battery lid 13 Negative electrode battery can 14 Gasket 100 Lithium ion battery

Claims (6)

In a lithium ion battery having a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte solution,
The negative electrode has a current collector and a negative electrode mixture layer provided on the current collector,
The negative electrode mixture layer has at least a negative electrode active material and a binder,
The lithium ion battery, wherein the binder has a higher crystallinity on the current collector side than on the separator side. The lithium ion battery according to claim 1,
The binder contains polyvinylidene fluoride, and is calculated by (Equation 1) from the absorbance (A ₇₆₃ ) of ₇₆₃ cm ^{−1 and} the absorbance (A ₈₄₀ ) of ₈₄₀ cm ⁻¹ obtained by infrared spectroscopy measurement of the polyvinylidene fluoride. The lithium ion battery is characterized in that the value of R ₁ is 1.5 or less on the surface on the separator side and greater than 1.5 at the interface between the current collector and the negative electrode mixture layer.
R ₁ = A ₇₆₃ / A ₈₄₀ (Formula 1) The lithium ion battery according to claim 1,
The lithium ion battery, wherein the current collector is a copper foil. The lithium ion battery according to claim 1,
The positive electrode is, in _{LiMn x M1 y M2 z O 2} ( wherein, at least one M1 is Co, chosen from Ni, at least one M2 is Co, Ni, Al, B, Fe, Mg, selected from Cr, x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.4, 0.05 ≦ z ≦ 0.4) Ion battery. The lithium ion battery according to claim 1,
A lithium ion battery, wherein the negative electrode is made of at least one of a carbonaceous material, an oxide containing a group IV element, and a nitride containing a group IV element. The lithium ion battery according to claim 1,
The lithium ion battery, wherein the electrolytic solution includes ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC).

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