JP2016046037A - Manufacturing method of negative electrode for lithium ion battery and lithium ion battery obtained by the manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a lithium ion battery that can respond to a long life and a high-speed load variation and satisfies long life/high input-output characteristics.SOLUTION: A manufacturing method of a negative electrode for a lithium ion battery includes the steps of: coating a negative electrode mixture paste on a current collector, the negative electrode mixture paste containing amorphous carbon, as a negative electrode active material, and a binder resin having a glass transition temperature of 30°C or above; and compressing the negative electrode mixture paste having been coated. During the compression step, the negative electrode mixture paste is heated at a temperature of the glass transition temperature of the binder resin or above and 150°C or below.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a negative electrode for a lithium ion battery and a lithium ion battery obtained by the method.

  Lithium ion batteries are secondary batteries with high energy density, and are used as power sources for portable devices such as notebook computers and mobile phones, taking advantage of their characteristics. There are various types of lithium ion batteries. Cylindrical lithium ion batteries employ a wound structure of a positive electrode, a negative electrode, and a separator. For example, a positive electrode material and a negative electrode material are respectively applied to two strip-shaped metal foils, a separator is sandwiched therebetween, and these laminated bodies are wound in a spiral shape to form a wound group. The wound group is accommodated in a cylindrical battery can serving as a battery container, and after injecting an electrolytic solution, the cylindrical lithium ion battery is formed.

  As the cylindrical lithium ion battery, a 18650 type lithium ion battery is widely used as a consumer lithium ion battery. The outer diameter of the 18650 type lithium ion battery is 18 mm in diameter and is small with a height of about 65 mm. As the positive electrode active material of the 18650 type lithium ion battery, lithium cobaltate, which is characterized by high capacity and long life, is mainly used, and the battery capacity is generally 1.0 Ah to 2.0 Ah (3.7 Wh to 7. 4 Wh).

  In recent years, lithium-ion batteries are expected to be used not only for consumer applications such as portable devices but also for large-scale power storage systems for natural energy such as solar power and wind power generation. In a large-scale power storage system, the amount of power per system is required on the order of several MWh.

  For example, Patent Document 1 below discloses a cylindrical lithium ion battery having an electrode winding group in which a positive electrode, a negative electrode, and a separator are wound around a cylindrical battery container. This battery has a discharge capacity of 30 Ah or more, a positive electrode active material mixture containing lithium-manganese composite oxide is used for the positive electrode, and a negative electrode active material mixture containing amorphous carbon is used for the negative electrode. ing.

International Publication No. 2013/128677

In a large-scale power storage system, it is necessary to be able to cope with a long-life and high-speed load fluctuation, and a lithium ion battery satisfying a long life and high input / output characteristics is desired.
However, the battery described in Patent Document 1 cannot be said to be sufficient in high input / output characteristics.

  This invention is made | formed in view of the said subject, and is providing the lithium ion battery excellent in an input-output characteristic.

Specific means for solving the above problems are as follows.
<1> Lithium ions including a step of coating a current collector with a negative electrode mixture paste containing amorphous carbon as a negative electrode active material and a binder resin having a glass transition temperature of 30 ° C. or higher, and a step of compressing It is a manufacturing method of the negative electrode for batteries, Comprising: In the said compression process, the manufacturing method of the negative electrode for lithium ion batteries heated at the glass transition temperature of the said binder resin above 150 degreeC.
<2> The method for producing a negative electrode for a lithium ion battery according to <1>, wherein the binder resin is acrylic polymer particles.
<3> The method for producing a negative electrode for a lithium ion battery according to <1> or <2>, wherein the composite material density of the negative electrode is 1 g / cm ³ or more and 1.5 g / cm ³ or less.
<4> A lithium ion battery comprising a negative electrode obtained by the method for producing a negative electrode for a lithium ion battery according to any one of <1> to <3>.

  According to the present invention, it is possible to provide a lithium ion battery having excellent input / output characteristics.

It is sectional drawing of the lithium ion battery of this Embodiment.

  In the following embodiments, when ranges are shown as A to B, A or more and B or less are shown unless otherwise specified.

(Embodiment)
First, an outline of the lithium ion battery will be briefly described. The lithium ion battery has a positive electrode, a negative electrode, a separator, and an electrolytic solution in a battery container. A separator is disposed between the positive electrode and the negative electrode.
When charging the lithium ion battery, a charger is connected between the positive electrode and the negative electrode. At the time of charging, lithium ions inserted into the positive electrode active material are desorbed and released into the electrolytic solution. The lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the negative electrode. The lithium ions that have reached the negative electrode are inserted into the negative electrode active material constituting the negative electrode.
When discharging, an external load is connected between the positive electrode and the negative electrode. At the time of discharging, the lithium ions inserted into the negative electrode active material are desorbed and released into the electrolytic solution. At this time, electrons are emitted from the negative electrode. Then, the lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the positive electrode. The lithium ions reaching the positive electrode are inserted into the positive electrode active material constituting the positive electrode. At this time, when lithium ions are inserted into the positive electrode active material, electrons flow into the positive electrode. In this way, discharge is performed by the movement of electrons from the negative electrode to the positive electrode.
In this manner, charging / discharging can be performed by inserting and desorbing lithium ions between the positive electrode active material and the negative electrode active material. A configuration example of an actual lithium ion battery will be described later (see, for example, FIG. 1).

  Next, a positive electrode, a negative electrode, an electrolytic solution, a separator, and other components that are components of the lithium ion battery according to the present embodiment will be sequentially described.

1. Positive electrode In this embodiment mode, the positive electrode shown below is applicable to a high-capacity, high-input / output lithium ion battery. The positive electrode (positive electrode plate) of the present embodiment is composed of a current collector and a positive electrode mixture (positive electrode mixture) formed thereon. The positive electrode mixture is a layer including at least a positive electrode active material provided on the current collector. As the positive electrode active material, those commonly used in this field can be used, and examples include lithium-containing composite metal oxides, olivine-type lithium salts, chalcogen compounds, and manganese dioxide. The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, and Mn, Al, Co, and Ni. Mg, etc. are preferred. One kind or two or more kinds of different elements may be used. Among these, lithium-containing composite metal oxides are preferable. Examples of the lithium-containing composite metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _{1 -y} O ₂ , Li _x Co _y M _{1 -y} O _z , and Li _{x. Ni 1-y M y O z} , Li x Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F ( in the respective formulas, M is Na, Mg, Sc, Y , Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B. x = 0 to 1.2, y = 0 to 0. 0.9 and z = 2.0 to 2.3.). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging. Further, as the olivine type lithium salts such as LiFePO _4. Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

  In this embodiment, from the viewpoint of high capacity and safety, layered type lithium / nickel / manganese / cobalt composite oxide (NMC) and spinel type lithium / manganese oxide (spinel type lithium / manganese composite) are used as the positive electrode active material. More preferably, a mixed active material with an oxide, sp-Mn) is included. The positive electrode mixture is formed (applied) on both surfaces of the current collector, for example.

  In addition, while ensuring safety, layered lithium-nickel-manganese-cobalt composite oxide (NMC) and spinel-type lithium-manganese oxide ( NMC / sp-Mn, which is a mass ratio (mixing ratio) to (sp-Mn), is preferably 10/90 or more and 65/35 or less. The mass ratio may be simply referred to as “mass ratio of active material”. When the mass ratio (NMC / sp-Mn) of the active material is 10/90 or more, a high battery energy density can be obtained. On the other hand, when the mass ratio (NMC / sp-Mn) of the active material is 65/35 or less, the safety is high and it is not necessary to strengthen other safety measures. From the above viewpoint, NMC / sp-Mn is preferably 20/80 or more and 60/40 or less, and more preferably 30/70 or more and 55/45 or less.

From the viewpoint of input / output characteristics and battery life, the average particle size (D _NMC ) of the layered lithium / nickel / manganese / cobalt composite oxide ( _NMC ) and the spinel type lithium / manganese oxide (sp-Mn) The ratio D _sp-Mn / D _NMC of the average particle diameter (D _sp-Mn ) is preferably 1 to 3.
When the average particle size ratio (D _sp-Mn / D _NMC ) of the active material is 1 or more, a long battery life can be obtained. On the other hand, when the average particle size ratio (D _sp-Mn / D _NMC ) of the active material is 3 or less, the input / output characteristics are excellent.

When the positive electrode mixture density is 2.4 g / cm ³ or more, the resistance of the positive electrode is low, and the input / output characteristics are excellent. On the other hand, if the positive electrode mixture density is 2.7 g / cm ³ or less, the safety is high and it is not necessary to strengthen other safety measures. From this point of view, positive electrode density, more preferably at most 2.45 g / cm ³ or more 2.6 g / cm ^3.

When the coating amount of the positive electrode mixture is 175 g / m ² or more, the amount of the active material contributing to charging / discharging is sufficient, and a high battery energy density is obtained. On the other hand, when the coating amount of the positive electrode mixture is 250 g / m ² or less, the resistance of the positive electrode mixture is lowered and the input / output characteristics are excellent. From the above viewpoint, the single-side coating amount of the positive electrode mixture to the positive electrode current collector is more preferably 180 g / m ² or more and 230 g / m ² or less, and 185 g / m ² or more and 220 g / m ² or less. More preferably it is.

  Considering the amount of single-sided application of the positive electrode mixture to the positive electrode current collector and the density of the positive electrode mixture, the thickness of the single-sided coating film on the positive electrode current collector of the positive electrode mixture ([positive electrode thickness−positive electrode current collector] The thickness] / 2) is preferably 60 to 100 μm, more preferably 65 to 95 μm, and still more preferably 70 to 90 μm.

  Thus, in the positive electrode mixture, by setting the positive electrode mixture density, the positive electrode mixture application amount, and the mass ratio (NMC / sp-Mn) of the active material to the above ranges, the discharge capacity is 30 Ah or more and less than 110 Ah. Even in the lithium ion battery, a battery with high input / output and high energy density can be realized while ensuring safety.

Further, as the layered lithium / nickel / manganese / cobalt composite oxide (NMC), it is preferable to use one represented by the following composition formula (Formula 1).
Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (Formula 1)
In the above composition formula (Formula 1), (1 + δ) is a composition ratio of Li (lithium), x is a composition ratio of Mn (manganese), y is a composition ratio of Ni (nickel), (1-xyz) Indicates the composition ratio of Co (cobalt). z represents the composition ratio of the element M. The composition ratio of O (oxygen) is 2.
The elements M are Ti (titanium), Zr (zirconium), Nb (niobium), Mo (molybdenum), W (tungsten), Al (aluminum), Si (silicon), Ga (gallium), Ge (germanium), and Sn. It is at least one element selected from the group consisting of (tin).
-0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z ≦ 1.0, 0 ≦ z ≦ 0.1.

Moreover, it is preferable to use what is represented by the following compositional formula (Formula 2) as spinel type lithium manganese oxide (sp-Mn).
Li _{(1 + η)} Mn _(2-λ) M ′ _λ O ₄ (Chemical formula 2)
In the above composition formula (Formula 2), (1 + η) represents the composition ratio of Li, (2-λ) represents the composition ratio of Mn, and λ represents the composition ratio of the element M ′. The composition ratio of O (oxygen) is 4.
The element M ′ is at least one element selected from the group consisting of Mg (magnesium), Ca (calcium), Sr (strontium), Al, Ga, Zn (zinc), and Cu (copper).
0 ≦ η ≦ 0.2 and 0 ≦ λ ≦ 0.1.

  Thus, a mixture of layered lithium / nickel / manganese / cobalt composite oxide (NMC) and spinel type lithium / manganese oxide (sp-Mn) is used as the positive electrode active material (positive electrode active material). Thus, even when the capacity is increased, the stability of the positive electrode during charging can be improved and heat generation can be suppressed. As a result, a battery with excellent safety can be provided. In addition, charge / discharge cycle characteristics and storage characteristics can be improved.

  Mg or Al is preferably used as the element M ′ in the composition formula (Formula 2). By using Mg or Al, the battery life can be extended. In addition, the safety of the battery can be improved.

When spinel type lithium manganese oxide (sp-Mn) is used as the positive electrode active material, since Mn in the compound is stable in the charged state, heat generation due to the charging reaction can be suppressed. Thereby, the safety | security of a battery can be improved. That is, heat generation at the positive electrode can be suppressed, and the safety of the battery can be improved.
Furthermore, since the elution of Mn can be reduced by adding the element M ′, storage characteristics and charge / discharge cycle characteristics can be improved.

Thus, spinel type lithium manganese oxide (sp-Mn) has useful characteristics, but spinel type lithium manganese oxide (sp-Mn) itself has a small theoretical capacity and a low density. Therefore, when only a spinel type lithium manganese oxide (sp-Mn) is used as a positive electrode active material to constitute a battery, it is difficult to increase the battery capacity (discharge capacity). On the other hand, the layered lithium-nickel-manganese-cobalt composite oxide (NMC) has a large theoretical capacity, and has a theoretical capacity equivalent to that of LiCoO ₂ which is widely used as a positive electrode active material for lithium ion batteries.

  Hereinafter, the positive electrode mixture and the current collector will be described in detail. The positive electrode mixture contains a positive electrode active material, a binder, and the like, and is formed on the current collector. Although there is no restriction | limiting in the formation method, For example, it forms as follows. The positive electrode active material, the binder, and other materials such as a conductive material and a thickener used as needed are mixed in a dry form to form a sheet, which is pressure-bonded to the current collector (dry method). In addition, a positive electrode active material, a binder, and other materials such as a conductive material and a thickener used as necessary are dissolved or dispersed in a dispersion solvent to form a slurry, which is applied to a current collector and dried. (Wet method).

The positive electrode active material is used in powder form (particulate form) and mixed. The shape of the particles may be a lump, polyhedron, sphere, ellipsoid, plate, needle, column, or the like.
Among them, it is preferable that the primary particles are aggregated to form secondary particles, and the shape of the secondary particles is spherical or elliptical.

  The median diameter d50 of the positive electrode active material particles (in the case where the primary particles aggregate to form secondary particles), the median diameter d50 of the secondary particles can be adjusted within the following range. The lower limit of the range is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is 30 μm or less, preferably 25 μm or less, more preferably 15 μm or less.

  Above the lower limit, the tap density (fillability) is high, and a desired tap density can be easily obtained. When the upper limit is below the upper limit, the diffusion time of lithium ions in the particles is short, and the battery performance is excellent. Moreover, when it is below the above upper limit, the mixing property with other materials such as a binder and a conductive material is good when the electrode is formed. Therefore, when this mixture is slurried and applied, it cannot be applied uniformly and the occurrence of problems such as streaking can be suppressed. The median diameter d50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method.

  The range of the average particle size of the primary particles in the case where the primary particles are aggregated to form secondary particles is as follows. The lower limit of the range is 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, still more preferably 0.1 μm or more, and the upper limit is 3 μm or less, preferably 2 μm or less, more preferably 1 μm. Hereinafter, it is more preferably 0.6 μm or less. When the amount is not more than the above upper limit, spherical secondary particles are easily formed, and battery performance such as output characteristics is improved by improving tap density (fillability) and specific surface area. Moreover, since the crystallinity is high above the above lower limit, charge / discharge reversibility is excellent.

When layered lithium / nickel / manganese / cobalt composite oxide (NMC) or spinel type lithium / manganese oxide (sp-Mn) is used as the positive electrode active material, the range of the BET specific surface area of the particles is as follows. It is. The lower limit of the range is 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, and the upper limit is 4.0 m ² / g or less, preferably 2 .5m ² / g, more preferably at most 1.5 m ² / g. Above the lower limit, battery performance is good. When the amount is not more than the above upper limit, the tap density is easily increased, and the mixing property with other materials such as a binder and a conductive material is good. Therefore, the applicability when slurrying and applying this mixture is good. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.

  Examples of the conductive material for the positive electrode include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. Can be mentioned. Of these, one type may be used alone, or two or more types may be used in combination.

  About the content (addition amount, ratio, amount) of the conductive material, the range of the content of the conductive material with respect to the mass of the positive electrode mixture is as follows. The lower limit of the range is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and the upper limit is 50% by mass or less, preferably 30% by mass or less, more preferably 15%. It is below mass%. Above the lower limit, the conductivity is sufficient. Moreover, battery capacity is favorable in it being below the said upper limit.

  The binder for the positive electrode active material is not particularly limited, and when the positive electrode mixture is formed by a coating method, a material having good solubility and dispersibility in the dispersion solvent is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate , Ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer and other soft resinous polymers; polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer Examples thereof include fluorine polymers such as polymers and polytetrafluoroethylene / vinylidene fluoride copolymers; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), and the like. Of these, one type may be used alone, or two or more types may be used in combination. From the viewpoint of the stability of the positive electrode, it is preferable to use a fluorine-based polymer such as polyvinylidene fluoride (PVdF) or a polytetrafluoroethylene / vinylidene fluoride copolymer.

  Regarding the content (addition amount, ratio, amount) of the binder, the range of the content of the binder with respect to the mass of the positive electrode mixture is as follows. The lower limit of the range is 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass. Hereinafter, it is more preferably 10% by mass or less. When the binder content is 0.1% by mass or more, the positive electrode active material can be sufficiently bound, the positive electrode has high mechanical strength, and battery performance such as cycle characteristics is good. Moreover, battery capacity and electroconductivity are favorable in it being 80 mass% or less.

In order to improve the packing density of the positive electrode active material, the layer formed on the current collector using the wet method or the dry method is preferably consolidated by a hand press, a roller press, or the like.
The material of the current collector for the positive electrode is not particularly limited, and specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.

  There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Specific examples of the metal material include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a foam metal, and the carbonaceous material includes a carbon plate, a carbon thin film, A carbon cylinder etc. are mentioned. Among these, it is preferable to use a metal thin film. In addition, you may form a thin film suitably in mesh shape. The thickness of the thin film is arbitrary, but the range is as follows. The lower limit of the range is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. Above the lower limit, the strength required for the current collector can be obtained. Moreover, if it is below the above upper limit, the flexibility is high and the workability is good.

2. Negative electrode In this embodiment, the negative electrode shown below is applicable to a high-output and high-capacity lithium ion battery. The negative electrode (negative electrode plate) of the present embodiment is composed of a current collector and a negative electrode mixture (negative electrode mixture) formed on both sides (or one side) thereof. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions. Amorphous carbon is used as the negative electrode active material. From the viewpoint of input / output characteristics and life characteristics, graphitizable carbon is preferable among the amorphous carbons. The graphitizable carbon is a carbon material that easily becomes graphite by heating at 2000 to 3000 ° C. On the other hand, there are also non-graphitizable carbons that are difficult to become graphite. The amorphous carbon can be produced, for example, by heat-treating petroleum pitch, polyacene, polyparaphenylene, polyfurfuryl alcohol, polysiloxane, etc., and by changing the firing temperature, graphitizable carbon can be produced. Or non-graphitizable carbon. For example, a firing temperature of about 500 ° C. to 800 ° C. is suitable for producing non-graphitizable carbon, and a firing temperature of about 800 ° C. to 1000 ° C. is suitable for producing graphitizable carbon. The graphitizable carbon preferably has a carbon network interlayer (d002) in the X-ray wide angle diffraction method of 0.34 nm to 0.36 nm, more preferably 0.341 nm to 0.355 nm. More preferably, it is 0.342 nm or more and 0.35 nm or less.

  The average particle diameter (50% D) of the amorphous carbon is preferably 2 to 50 μm. When the average particle diameter is 5 μm or more, the specific surface area can be in an appropriate range, the initial charge / discharge efficiency of the lithium ion battery is excellent, and the contact between the particles is good and the input / output characteristics tend to be excellent. On the other hand, when the average particle size is 30 μm or less, unevenness is hardly generated on the electrode surface, and the short circuit of the battery can be suppressed, and the diffusion distance of Li from the particle surface to the inside becomes relatively short, so the input / output characteristics of the lithium ion battery Tend to improve. In this respect, the average particle size is more preferably 5 to 30 μm, and still more preferably 10 to 20 μm. For example, the particle size distribution can be measured by dispersing a sample in purified water containing a surfactant and measuring with a laser diffraction particle size distribution measuring device (for example, product name: SALD-3000J, manufactured by Shimadzu Corporation). The average particle size is calculated as 50% D.

  Further, as the negative electrode active material, carbonaceous materials other than the amorphous carbon, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, Sn and Si, etc. A material capable of forming an alloy with lithium may be used in combination. These may be used alone or in combination of two or more.

  The metal composite oxide is not particularly limited as long as it can occlude and release lithium. However, a material containing both Ti (titanium), Li (lithium), and Ti and Li has a high current density. This is preferable from the viewpoint of discharge characteristics.

  Examples of the carbonaceous material other than the amorphous carbon include natural graphite, a composite carbonaceous material in which a film formed by a dry CVD (Chemical Vapor Deposition) method or a wet spray method is formed on natural graphite, epoxy, phenol, etc. And artificial graphite obtained by firing using a resin material or a pitch-based material obtained from petroleum or coal as a raw material.

  In addition, lithium metal that can occlude and release lithium by forming a compound with lithium, and Group 4 elements such as silicon, germanium, and tin that can occlude and release lithium by forming a compound with lithium and inserting it in the crystal gap These oxides or nitrides may be used in combination with the amorphous carbon.

  In addition, as a preferred form, there is a form in which a carbonaceous material that is not symmetric when the volume-based particle size distribution is centered on the median diameter is used as the second carbonaceous material (conductive material). Further, as the second carbonaceous material (conductive material), a form using a carbonaceous material having a different Raman R value from the carbonaceous material used as the negative electrode active material, or as the second carbonaceous material (conductive material), as the negative electrode active material There is a form using a carbonaceous material having a different X-ray parameter from the first carbonaceous material used.

  There is no restriction | limiting in particular as a material of the electrical power collector for negative electrodes, As a specific example, metal materials, such as copper, nickel, stainless steel, nickel plating steel, are mentioned. Among these, copper is preferable from the viewpoint of ease of processing and cost.

  There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Specific examples include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among these, a metal thin film is preferable, and a copper foil is more preferable. The copper foil includes a rolled copper foil formed by a rolling method and an electrolytic copper foil formed by an electrolytic method, both of which are suitable for use as a current collector.

  The thickness of the current collector is not limited, but when the thickness is less than 25 μm, its strength can be increased by using a strong copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) rather than pure copper. Can be improved.

Although there is no restriction | limiting in particular in the structure of the negative electrode compound material formed using the negative electrode active material, The range of the negative electrode compound material density is as follows. The lower limit of the negative electrode composite density is preferably 1.0 g / cm ³ or more, and more preferably 1.1 g / cm ³ or more. The upper limit of the negative electrode composite density is preferably 1.5 g / cm ³ or less, more preferably 1.4 g / cm ³ or less, and still more preferably 1.3 g / cm ³ or less.

  If it is less than the above upper limit, the particles of the negative electrode active material are less likely to be destroyed, and the initial irreversible capacity is increased and the permeability of the non-aqueous electrolyte solution near the interface between the current collector and the negative electrode active material is reduced. Degradation of current density charge / discharge characteristics can be suppressed. Moreover, since the electroconductivity between negative electrode active materials is high as it is more than the said minimum, battery resistance is restrained low and the capacity | capacitance per unit volume is fully obtained.

As the binder resin of the negative electrode active material (hereinafter sometimes referred to as a binder), a binder resin having a glass transition temperature of 30 ° C. or higher is used. Examples of the binder resin having a glass transition temperature of 30 ° C. or higher include acrylic polymers.
Among the acrylic polymers, water-dispersible acrylic polymer particles are particularly preferable.

  The addition amount of the acrylic polymer is preferably in the range of 0.5% to 5.0% with respect to the total mass of the composite material from the viewpoint of electrode formability and energy density, and is preferably 0.5% to 2.0%. It is more preferable that it is in the range.

  Further, when water-dispersible acrylic polymer particles are used, it is preferable to use a thickener that is soluble in water. The thickener is used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used alone or in combination of two or more.

The range of the content of the thickener relative to the mass of the negative electrode mixture when the thickener is used is as follows. The lower limit of the range is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably. Is 2% by mass or less.
Above the above lower limit, the applicability of the slurry is good. Moreover, the ratio of the negative electrode active material to a negative electrode compound is high as it is below the said upper limit, and the resistance between high battery capacity and low negative electrode active materials is obtained.

  The positive electrode coating amount is preferably such that the discharge capacity per unit area of the negative electrode is 1.0 to 1.5 when the discharge capacity per unit area of the positive electrode is 1, 1.1 to 1.3 It is more preferable from the viewpoint of life and energy density to be in the range of.

  About the temperature range of a hot press, it is Tg or more and 150 degrees C or less on an installation, and it is preferable from a viewpoint on input-output characteristics and an installation that it is Tg or more and 130 degrees C or less.

  The water-dispersible acrylic polymer particles (hereinafter referred to as acrylic polymer particles) include, for example, a structural unit derived from monomer (meth) acrylonitrile and a compound having two or more ethylenically unsaturated bonds (hereinafter referred to as “ And a structural unit derived from a “crosslinking agent”.

  One type of monomer constituting each structural unit may be selected and used for polymerization in each structural unit, or a plurality of types may be selected and used for polymerization. Further, one type of monomer may be selected as a monomer constituting a specific structural unit, and a plurality of types of monomers may be selected as monomers constituting other structural units.

  Moreover, the said acrylic polymer should just contain each structural unit mentioned above, and there is no restriction | limiting in particular about the coupling | bonding order of each structural unit. The specific copolymer may be either a block copolymer or a random copolymer, and is preferably a random copolymer.

  The content of structural units derived from (meth) acrylonitrile in the acrylic polymer is the total structure derived from monomers of the acrylic polymer from the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode. On the basis of the number of units (100 mol%), it is preferably 20 mol% to 70 mol%, and more preferably 30 mol% to 60 mol% from the viewpoint of excellent adhesion and storage stability of the electrode mixture slurry, More preferably, it is 35 mol% to 45 mol%.

  The compound having two or more ethylenically unsaturated bonds (crosslinking agent) includes two or more functional groups containing an ethylenically unsaturated bond and an organic group that is a divalent or higher linking group that links the functional groups to each other. If it is a compound which has this, there will be no restriction | limiting in particular. The compound having two or more ethylenically unsaturated bonds is preferably, for example, a compound represented by the following general formula (I).

一般式（Ｉ）中、Ｒ^１はそれぞれ独立に、水素原子又はメチル基を示す。Ｒ^２は、ｎ価の有機基を示す。ｎは２〜６の数を示し、３〜４であることが好ましい。ｎは一般式（Ｉ）で表される化合物が単一の分子種である場合、整数である。
Ｒ^２で示されるｎ価の有機基としては、炭素数２〜２０の脂肪族炭化水素からｎ個の水素原子を取り除いて構成される炭素数が２〜２０であるｎ価の脂肪族炭化水素基；炭素数２〜４のアルキレングリコールが２以上エーテル結合してなるポリアルキレングリコールの両末端からヒドロキシ基を取り除いて構成されるポリアルキレンオキシアルキレン基；グリセリン、ジグリセリン、ネオペンチルグリコール、ペンタエリスリトール、ジペンタエリスリトール、トリメチロールプロパン等の炭素数３〜２０の多価アルコール又はそのヒドロキシアルキル化物からｎ個のヒドロキシ基を取り除いて構成されるｎ価の有機基；イソシアヌル酸又はそのヒドロキシアルキル化物からｎ個のヒドロキシ基を取り除いて構成されるｎ価の有機基；などを挙げることができる。
これらの２以上のエチレン性不飽和結合を有する化合物は１種単独で又は２種類以上組み合わせて用いることができる。

In general formula (I), R < ¹ > shows a hydrogen atom or a methyl group each independently. R ² represents an n-valent organic group. n shows the number of 2-6, and it is preferable that it is 3-4. n is an integer when the compound represented by formula (I) is a single molecular species.
The n-valent organic group represented by R ² is an n-valent aliphatic hydrocarbon having 2 to 20 carbon atoms formed by removing n hydrogen atoms from an aliphatic hydrocarbon having 2 to 20 carbon atoms. Group: a polyalkyleneoxyalkylene group formed by removing hydroxyl groups from both ends of a polyalkylene glycol formed by ether-linking two or more alkylene glycols having 2 to 4 carbon atoms; glycerin, diglycerin, neopentyl glycol, pentaerythritol N-valent organic group formed by removing n hydroxy groups from a polyhydric alcohol having 3 to 20 carbon atoms such as dipentaerythritol, trimethylolpropane or the like, or a hydroxyalkylated product thereof; from isocyanuric acid or a hydroxyalkylated product thereof n-valent organic group constituted by removing n hydroxy groups; Can be mentioned.
These compounds having two or more ethylenically unsaturated bonds can be used singly or in combination of two or more.

The content of the structural unit derived from the compound having two or more ethylenically unsaturated bonds in the acrylic polymer increases the storage elastic modulus in the rubber-like region of the specific copolymer, and the active material in charge / discharge of the energy device. From the viewpoint of making it easy to follow expansion and contraction, it is preferably 0.01 parts by mass to 5.0 parts by mass with respect to 100 parts by mass of the monomer-derived total mass in the acrylic polymer, and 0.05 parts by mass. It is more preferably from 3.0 parts by weight to 3.0 parts by weight, and even more preferably from 0.02 parts by weight to 0.2 parts by weight.
Moreover, when the content rate of the structural unit derived from the compound which has an ethylenically unsaturated bond of 2 or more in an acrylic polymer is prescribed | regulated by mol%, the total structural unit number (100 mol%) derived from the monomer in an acrylic polymer is used. On the other hand, it is preferably 0.001 mol% to 1.0 mol%, more preferably 0.005 mol% to 0.5 mol%, and still more preferably 0.02 mol% to 0.2 mol%.

  Furthermore, the molar ratio of the content of the structural unit derived from the compound having two or more ethylenically unsaturated bonds to the content of the structural unit derived from (meth) acrylonitrile in the acrylic polymer is not particularly limited. From the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode, the molar ratio is preferably 0.008 mol% to 0.8 mol%, and 0.03 mol% to 0.3 mol%. More preferably.

  The acrylic polymer contains structural units derived from other monomers other than structural units derived from (meth) acrylonitrile and structural units derived from compounds having two or more ethylenically unsaturated bonds, as necessary. May be. Examples of the other monomer include a monomer represented by the following general formula (II) and an acidic functional group-containing monomer.

In the general formula (II), R ²¹ represents a hydrogen atom or a methyl group. R ²² represents a 2-cyanoethyl group, an alkyl group having 3 to 20 carbon atoms, or a hydroxyalkyl group having 5 to 20 carbon atoms.
The alkyl group having 3 to 20 carbon atoms in R ²² may be a branched alkyl group or a linear alkyl group, and is preferably a linear alkyl group. The number of carbon atoms of the alkyl group represented by R ²² is preferably 3 to 12, and more preferably 3 to 8.

  The total content of the structural unit derived from the monomer represented by the general formula (II) is a single amount in the specific copolymer from the viewpoint of excellent adhesion between the current collector and the mixture layer in the energy device electrode. It is preferably 30 mol% to 80 mol%, based on the total structural unit amount derived from the body (100 mol%), and from the viewpoint of excellent adhesion and storage stability of the electrode mixture slurry, it is 40 mol% to 70 mol%. It is more preferable, and it is still more preferable that it is 55 mol%-65 mol%.

  The acrylic polymer is preferably used as water-dispersed acrylic polymer particles.

The acrylic polymer particles preferably have a particle size of 500 nm or less, and more preferably 400 nm or less from the viewpoint of adhesion and battery characteristics. Although there is no restriction | limiting in particular in a lower limit, it is preferable that it is 100 nm or more from a practical viewpoint, and it is more preferable that it is 200 nm or more.
Here, the particle diameter is an average particle diameter, and can be measured using a commercially available measuring device by a dynamic light scattering method.

The lower limit of the glass transition temperature (Tg) of the binder resin is 30 ° C. or higher, which is higher than the storage temperature of the electrode mixture slurry. From the viewpoint of storage stability, the lower limit of the glass transition temperature (Tg) of the binder resin is preferably 35 ° C. or higher, and more preferably 40 ° C. or higher. Moreover, although there is no restriction | limiting in the upper limit of glass transition temperature (Tg), it is preferable that it is 120 degreeC from a viewpoint of adhesiveness, it is more preferable that it is 80 degreeC, and it is still more preferable that it is 50 degreeC. If the glass transition temperature is 30 ° C. or higher, the electrode mixture slurry tends to be more excellent in storage stability. Moreover, if the glass transition temperature is 120 ° C. or lower, the adhesiveness of the energy device electrode tends to be better.
The glass transition temperature of the binder resin can be measured under normal measurement conditions by dynamic viscoelasticity measurement (DMA).

  The storage modulus of the binder resin is not particularly limited and can be appropriately selected depending on the purpose and the like. The storage elastic modulus of the binder resin is preferably 1 to 60 MPa, more preferably 2 to 50 MPa, and further preferably 3 to 20 MPa at 60 ° C. from the viewpoint of cycle characteristics at a high temperature of the energy device. preferable. The storage modulus of the binder resin can be measured by forming the binder resin into a film and measuring the dynamic viscoelasticity (DMA).

3. Electrolytic Solution The electrolytic solution of the present embodiment is composed of a lithium salt (electrolyte) and a non-aqueous solvent that dissolves the lithium salt. You may add an additive as needed.

  The lithium salt is not particularly limited as long as it is a lithium salt that can be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion battery. For example, the following inorganic lithium salt, fluorine-containing organic lithium salt, or oxalate borate salt Is mentioned.

Examples of the inorganic lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiSbF inorganic fluoride salts and the like _6, LiClO _4, Libro 4, LiIO and perhalogenate such as _4, an inorganic chloride salts such as LiAlCl _4, etc. Is mentioned.

Examples of the fluorine-containing organic lithium salt include perfluoroalkane sulfonates such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C Perfluoroalkanesulfonylimide salt such as ₄ F ₉ SO ₉ ); perfluoroalkanesulfonylmethide salt such as LiC (CF ₃ SO ₂ ) ₃ ; Li [PF ₅ (CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂ CF ₃ ) ₂ ], Li [PF ₃ (CF ₂ CF ₂ CF ₃ ) ₃ ], Li [PF ₅ (CF ₂ CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF _{2 CF 2 CF 2 CF 3) 2} ], Li [PF 3 (CF 2 CF 2 CF 2 CF 3) 3] fluoroalkyl hexafluorophosphate salts such like.

  Examples of the oxalatoborate salt include lithium bis (oxalato) borate and lithium difluorooxalatoborate.

These lithium salts may be used alone or in combination of two or more. Among them, lithium hexafluorophosphate (LiPF ₆ ) is preferable when comprehensively judging the solubility in a solvent, charge / discharge characteristics in the case of a secondary battery, output characteristics, cycle characteristics, and the like.

A preferable example in the case of using two or more lithium salts is a combination of LiPF ₆ and LiBF ₄ . In this case, the proportion of LiBF _{4 in} the total of both is preferably 0.01% by mass or more and 20% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less. . Another preferred example is the combined use of an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt. In this case, the proportion of the inorganic fluoride salt in the total of both is 70% by mass or more and 99% by mass. % Or less, more preferably 80% by mass or more and 98% by mass or less. According to the above two preferred examples, characteristic deterioration due to high temperature storage can be suppressed.

  Although there is no restriction | limiting in particular in the density | concentration of the electrolyte in nonaqueous electrolyte solution, The density | concentration range of an electrolyte is as follows. The lower limit of the concentration is 0.5 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Further, the upper limit of the concentration is 2 mol / L or less, preferably 1.8 mol / L or less, more preferably 1.7 mol / L or less. When the concentration is 0.5 mol / L, the electric conductivity of the electrolyte is sufficient. Moreover, since a viscosity does not rise that a density | concentration is 2 mol / L or less, electrical conductivity does not fall. Thus, since the electrical conductivity does not decrease, high lithium ion battery performance can be obtained.

  The non-aqueous solvent is not particularly limited as long as it is a non-aqueous solvent that can be used as an electrolyte solvent for a lithium ion battery. For example, the following cyclic carbonate, chain carbonate, chain ester, cyclic ether, and chain Examples include ether.

  As the cyclic carbonate, those having 2 to 6 carbon atoms of the alkylene group constituting the cyclic carbonate are preferable, and those having 2 to 4 are more preferable. Specific examples include ethylene carbonate, propylene carbonate, butylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate are preferable.

  As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the two alkyl groups is preferably 1 to 5, and more preferably 1 to 4. Specifically, symmetrical chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Is mentioned. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.

  Examples of chain esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate. Among them, it is preferable to use methyl acetate from the viewpoint of improving the low temperature characteristics.

  Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. Of these, tetrahydrofuran is preferably used from the viewpoint of improving input / output characteristics.

  Examples of chain ethers include dimethoxyethane and dimethoxymethane.

  These may be used alone or in combination of two or more, but it is preferable to use a mixed solvent in which two or more compounds are used in combination. For example, it is preferable to use a high dielectric constant solvent of cyclic carbonates in combination with a low viscosity solvent such as chain carbonates or chain esters. One of the preferable combinations is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the non-aqueous solvent is 80% by volume or more, preferably 85% by volume or more, more preferably 90% by volume or more, and the cyclic carbonates and the chain carbonates. It is preferable that the cyclic carbonates have a capacity in the following range with respect to the total of the above. The lower limit of the capacity of the cyclic carbonates is 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and the upper limit is 50% by volume or less, preferably 35% by volume or less, more preferably 30%. The capacity is less than%. By using such a combination of non-aqueous solvents, battery cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity and high-load discharge capacity after high-temperature storage) are improved.

  Specific examples of preferred combinations of cyclic carbonates and chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate And ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

  The additive is not particularly limited as long as it is an additive for a non-aqueous electrolyte solution of a lithium ion battery. For example, nitrogen, sulfur or a heterocyclic compound containing nitrogen and sulfur, a cyclic carboxylic acid ester, and fluorine-containing material A cyclic carbonate and vinylene carbonate are mentioned.

Although there is no limitation in particular in the ratio of the additive in a non-aqueous electrolyte solution, the range is as follows. In addition, when using a some additive, the ratio of each additive is meant. The lower limit of the ratio of the additive to the non-aqueous electrolyte is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and the upper limit is preferably 5%. It is not more than mass%, more preferably not more than 3 mass%, still more preferably not more than 2 mass%.
By using the other additives, it is possible to suppress a rapid electrode reaction at the time of abnormality due to overcharge, improve capacity maintenance characteristics and cycle characteristics after high temperature storage, and improve input / output characteristics.

4). Separator The separator is not particularly limited as long as it has ion permeability while electronically insulating the positive electrode and the negative electrode, and has resistance to oxidation on the positive electrode side and reducibility on the negative electrode side. As a material (material) of the separator satisfying such characteristics, a resin, an inorganic material, glass fiber, or the like is used.

  As the resin, an olefin polymer, a fluorine polymer, a cellulose polymer, polyimide, nylon, or the like is used. Specifically, it is preferable to select from materials that are stable with respect to non-aqueous electrolytes and have excellent liquid retention properties. For example, porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene may be used. preferable.

  As the inorganic material, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used. For example, what made the said inorganic substance of fiber shape or particle shape adhere to thin film-shaped base materials, such as a nonwoven fabric, a woven fabric, and a microporous film, can be used as a separator. As a thin film-shaped substrate, a substrate having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition, for example, a separator in which a composite porous layer is formed using the above-described inorganic material in a fiber shape or a particle shape by using a binder such as a resin can be used as a separator. Furthermore, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to form a separator. For example, a composite porous layer in which alumina particles having a 90% particle size of less than 1 μm are bound using a fluororesin as a binder may be formed on the surface of the positive electrode.

5). Other constituent members As other constituent members of the lithium ion battery, a cleavage valve may be provided. By opening the cleavage valve, it is possible to suppress an increase in pressure inside the battery and to improve safety.

  Moreover, you may provide the structure part which discharge | releases inert gas (for example, carbon dioxide) with a temperature rise. By providing such a component, when the temperature inside the battery rises, the cleavage valve can be opened quickly due to the generation of inert gas, and safety can be improved. Examples of the material used for the above components include lithium carbonate and polyalkylene carbonate resin. Examples of the polyalkylene carbonate resin include polyethylene carbonate, polypropylene carbonate, poly (1,2-dimethylethylene carbonate), polybutene carbonate, polyisobutene carbonate, polypentene carbonate, polyhexene carbonate, polycyclopentene carbonate, polycyclohexene carbonate, and polycyclohexane. Examples include heptene carbonate, polycyclooctene carbonate, and polylimonene carbonate. As a material used for the said structural part, lithium carbonate, polyethylene carbonate, and polypropylene carbonate are preferable.

(Method for producing negative electrode for lithium ion battery)
Although the negative electrode for lithium ion batteries of this embodiment can be manufactured using a known electrode manufacturing method without particular limitation, for example, a negative electrode mixture containing the binder resin composition, a solvent, a negative electrode active material, and the like. The paste can be applied to at least one surface of the current collector, and then the solvent can be removed by drying, followed by compression to form a negative electrode mixture layer on the current collector surface.

Here, application | coating can be performed using a comma coater, for example. Application is preferably such that the capacity ratio of the positive electrode to the negative electrode (negative electrode capacity / positive electrode capacity) is 1 or more and less than 1.2. The removal of the solvent is performed, for example, by drying at 50 to 150 ° C., preferably 80 to 120 ° C. for 1 to 20 minutes, preferably 3 to 10 minutes. The compression (hereinafter sometimes referred to as pressing) is performed at a temperature equal to or higher than the glass transition temperature of the binder resin using, for example, a roll press machine or a hot press machine, and the bulk density of the negative electrode mixture layer is 1 to 1.5 g. It is hot-pressed so as to be / cm ³ . In the present embodiment, the compression is preferably performed at a temperature that is 20 ° C to 100 ° C higher than the glass transition temperature of the binder resin, and more preferably at a temperature that is 30 ° C to 80 ° C higher. Furthermore, in order to remove the residual solvent and adsorbed water in the electrode, for example, vacuum drying may be performed at 100 to 150 ° C. for 1 to 20 hours.

(Lithium ion battery)
First, an embodiment in which the present invention is applied to a laminated battery will be described.

  A laminate-type lithium ion battery can be produced, for example, as follows. First, the positive electrode and the negative electrode are cut into squares, and tabs are welded to the respective electrodes to produce positive and negative electrode terminals. A laminated body in which the positive electrode, the insulating layer, and the negative electrode are laminated in this order is prepared, and in that state, accommodated in an aluminum laminate pack, and the positive and negative electrode terminals are taken out of the aluminum laminate pack and sealed. Next, the nonaqueous electrolyte is poured into the aluminum laminate pack, and the opening of the aluminum laminate pack is sealed. Thereby, a lithium ion battery is obtained.

  Next, an embodiment in which the present invention is applied to an 18650 type cylindrical lithium ion battery will be described with reference to the drawings.

  As shown in FIG. 1, the lithium ion battery 1 of the present embodiment has a bottomed cylindrical battery container 6 made of nickel-plated steel. The battery case 6 accommodates an electrode group 5 in which a strip-like positive electrode plate 2 and a negative electrode plate 3 are wound in a spiral shape with a separator 4 interposed therebetween. In the electrode group 5, the positive electrode plate 2 and the negative electrode plate 3 are wound in a spiral shape in cross section via a separator 4 made of a polyethylene porous sheet. For example, the separator 4 has a width of 58 mm and a thickness of 30 μm. A ribbon-like positive electrode tab terminal made of aluminum and having one end fixed to the positive electrode plate 2 is led out on the upper end surface of the electrode group 5. The other end of the positive electrode tab terminal is joined by ultrasonic welding to the lower surface of a disk-shaped battery lid that is disposed on the upper side of the electrode group 5 and serves as a positive electrode external terminal. On the other hand, a ribbon-like negative electrode tab terminal made of copper with one end fixed to the negative electrode plate 3 is led out on the lower end surface of the electrode group 5. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery container 6 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are led out to the opposite sides of the both end faces of the electrode group 5, respectively. In addition, the insulation coating which abbreviate | omitted illustration is given to the outer peripheral surface whole periphery of the electrode group 5. FIG. The battery lid is caulked and fixed to the upper part of the battery container 6 via an insulating resin gasket. For this reason, the inside of the lithium ion battery 1 is sealed. In addition, a non-aqueous electrolyte (not shown) is injected into the battery container 6.

  Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.

Synthesis example <acrylic polymer>
In a 0.5 liter three-necked flask equipped with a stirrer, thermometer, condenser, and liquid feed pump, 335 g of water and 2% of carboxymethyl cellulose (trade name: CMC # 2200, manufactured by Daicel Finechem Co., Ltd.) as an emulsifier 21.46 g of an aqueous solution was added, and after the pressure was reduced to 2.6 kPa (20 mmHg) with an aspirator, the operation of returning to normal pressure with nitrogen was repeated three times to remove dissolved oxygen. The flask was maintained in a nitrogen atmosphere, heated to 60 ° C. with an oil bath while stirring, and 0.26 g of potassium persulfate was dissolved in 8 g of water and added to the three-necked flask.

After adding potassium persulfate, 16.98 g of acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) (a proportion of 40 mol% in the total monomer amount (100 mol%)), a single amount represented by the general formula (II) 68.26 g of butyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) (R ²¹ is a methyl group and R ²² is a butyl group having 4 carbon atoms) (a proportion of 60 mol% in the total monomer amount (100 mol%)) ), An ethoxylated pentaerythritol tetraacrylate (made by Shin-Nakamura Chemical Co., Ltd.), a compound represented by the general formula (I) (R ¹ is a hydrogen atom, n is 4, and R ² is an ethoxylated pentaerythritol group) Name: ATM-4E) A monomer composition which is a mixture of 0.34 g (a ratio of 0.04 mol% with respect to the total monomer amount (100 mol%)) is dropped over 2 hours with a liquid feed pump. Emulsion polymerization was performed. The reaction conversion rate of the monomer after completion of dropping of the monomer composition was 51%. After stirring for 1 hour, the temperature was raised to 80 ° C., and stirring was further continued for 2 hours to obtain an aqueous dispersion of acrylic polymer particles. About 1 ml of the obtained aqueous dispersion was weighed in an aluminum pan, dried on a hot plate heated to 160 ° C. for 15 minutes, and the non-volatile content was calculated from the residual mass to find 15.3% (copolymer yield 98 %)Met. The glass transition temperature was 47 ° C., and the storage elastic modulus at 60 ° C. was 8.7 MPa. The glass transition temperature and the storage elastic modulus at 60 ° C. were measured by the dynamic viscoelasticity measurement shown below.

  The acrylic polymer aqueous dispersion obtained in the synthesis example was cast on a polypropylene film, air-dried, and further dried in a blow-type dryer at 120 ° C. for 5 hours to evaluate the binder resin film (film thickness 30 μm). Got. Dynamic viscoelasticity measurement (DMA) was performed using the evaluation binder resin film. The DMA measurement conditions are shown below.

(DMA measurement conditions)
Measuring instrument: RSA-III [manufactured by TA instruments]
Test mode: Tensile Measurement temperature: -50 ° C to 250 ° C
Temperature increase rate: 10 ° C / min
Test frequency: 1Hz
Distance between chucks: 25 mm (initial)

Example 1
[Production of positive electrode plate]
The positive electrode plate was produced as follows. The positive electrode active material layered type lithium / nickel / manganese / cobalt composite oxide (NMC) and spinel type lithium / manganese oxide (sp-Mn) are mass ratio of predetermined active material (NMC / sp-Mn). Mixed. To this mixture of positive electrode active materials, scaly graphite (average particle size: 20 μm) and acetylene black as conductive materials and polyvinylidene fluoride as binder are sequentially added and mixed to obtain a mixture of positive electrode materials. It was. The mass ratio was active material: conductive material: binder = 90: 5: 5. Further, N-methyl-2-pyrrolidone (NMP), which is a dispersion solvent, was added to the above mixture and kneaded to form a slurry. This slurry was applied substantially evenly and uniformly to both surfaces of a 20 μm thick aluminum foil as a positive electrode current collector. Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the positive electrode mixture was 2.55 g / cm ³ and the coating amount of the positive electrode mixture was 190 g / m ² .

[Production of negative electrode plate]
Daiichi Kogyo Seiyaku Co., Ltd. carboxymethylcellulose, trade name: # 2200 (hereinafter referred to as CMC) 1.5g, weighed with 98.5g of pure water, stirred well until completely dissolved, 1.5% CMC aqueous solution Produced. Next, 60 g of amorphous carbon (graphitizable carbon), 41.2 g of the CMC aqueous solution and 13.0 g of pure water were mixed with a mixer (trade name: TK Hibismix f model.03 (“Hibismix” Registered trademark), manufactured by Primix Co., Ltd.), and mixed for 1.5 hours at a rotation speed of a stirring blade of 6 min ⁻¹ . Thereafter, 27.7 g of pure water was added, and the mixture was again mixed for 1 hour at a stirring blade speed of 10 min ⁻¹ . Next, 7 g of the acrylic polymer obtained in the above synthesis example was added and mixed for 0.5 hour at a stirring blade speed of 20 min ⁻¹ to prepare a negative electrode slurry.

The above negative electrode mixture paste was applied on a rolled copper foil (thickness: 10 μm) manufactured by Nippon Steel & Sumitomo Metal Corporation with a gap adjusted to 80 g / m ² and then dried with a hot air dryer at 80 ° C. did. This negative electrode was pressed to a composite layer density of 1.2 g / cm ³ with a hot press at 80 ° C. to produce a negative electrode.

[Production of battery]
(Production of laminated battery)
A positive electrode cut into a 13.5 cm ² square (30 mm × 45 mm) is a polyethylene porous sheet separator (trade name: Hypore (“Hypore” is a registered trademark)), manufactured by Asahi Kasei E-Materials Co., Ltd., thickness Was laminated with a negative electrode cut into 14.3 cm ² squares (31 mm × 46 mm). This laminate is put into an aluminum laminate container (trade name: aluminum laminate film, manufactured by Dai Nippon Printing Co., Ltd.), and a non-aqueous electrolyte (ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate = 2/2 / containing 1M LiPF ₆ ). 1 mL of 3 mixed solutions (volume ratio) with 0.8% by mass of vinylene carbonate added to the total amount of the mixed solution, trade name: Sollite (“Solite” is a registered trademark), manufactured by Mitsubishi Chemical Corporation) Then, an aluminum laminate container was thermally welded to produce a battery for electrode evaluation.

  The first charge is a constant current-constant voltage charge (hereinafter referred to as CCCCV) with a current value of 0.5 C, a charge termination condition of 4.2 V, and a termination condition of 5 hours or a lower limit current value of 0.01 C. Then, after 15 minutes of rest, constant current discharge (hereinafter referred to as CC) was performed until the battery voltage reached 2.7 V, and charging and discharging were performed for 3 cycles, with 15 minutes of rest as one cycle. After the initial charge, the output characteristics from 0.5 to 5C were measured. After measurement of the discharge characteristics, constant current charging (constant current charge: hereinafter referred to as CC charging) with the charging condition up to an upper limit voltage of 4.2 V was performed, and input characteristics up to 0.5 to 5 C were measured. The rest time after charging and discharging in the charge / discharge test was 15 minutes. As the charge / discharge tester, a trade name: IEM1214 (5V, 1A, manufactured by IEM Co., Ltd.) was used. “C” used as a unit of current value means “current value (A) / battery discharge capacity (Ah)”.

Output characteristics and input characteristics were calculated from the following equations.
Output characteristics (%) = [discharge capacity at 5 C / discharge capacity at 0.5 C] × 100
Input characteristics (%) = [Charge capacity at 5C / Charge capacity at 0.5C] × 100

(Example 2)
The test was performed in the same manner as in Example 1 except that the coated and dried negative electrode was pressed to a composite density of 1.2 g / cm ³ with a 120 ° C. hot press.

(Comparative Example 1)
The coated / dried negative electrode was tested in the same manner as in Example 1 except that it was pressed to a composite density of 1.2 g / cm ³ with a press at 25 ° C., which was lower than the glass transition temperature of the binder resin. .

  As shown in Table 1, Examples 1 and 2 in which the coated and dried negative electrode was compressed by heating at a glass transition temperature of the binder resin to 150 ° C. or less were comparative examples compressed at a temperature lower than the glass transition temperature of the binder resin. It was confirmed that the output characteristics and the input characteristics were superior to 1.

  DESCRIPTION OF SYMBOLS 1 ... Lithium ion battery, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Electrode group, 6 ... Battery container.

Claims (4)

  A negative electrode for a lithium ion battery comprising a step of coating a negative electrode mixture paste containing amorphous carbon as a negative electrode active material and a binder resin having a glass transition temperature of 30 ° C. or more on a current collector, and a step of compressing A method for producing a negative electrode for a lithium ion battery, wherein in the compression step, heating is performed at a glass transition temperature of the binder resin to 150 ° C. or less.   The method for producing a negative electrode for a lithium ion battery according to claim 1, wherein the binder resin is acrylic polymer particles. ^{3. The} method for producing a negative electrode for a lithium ion battery according to claim 1, wherein a composite material density of the negative electrode is 1 g / cm ³ or more and 1.5 g / cm ³ or less.   A lithium ion battery provided with the negative electrode obtained by the manufacturing method of the negative electrode for lithium ion batteries in any one of Claims 1-3.

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