JP2018174038A - Binder for lithium ion secondary battery negative electrode, negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

A negative electrode binder for a lithium ion secondary battery having excellent cycle characteristics, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the binder.
A polymer having a plurality of cyclic molecules and a linear polymer, wherein the linear polymer penetrates the plurality of cyclic molecules and is attached to both ends of the linear polymer. The binder for lithium ion secondary battery negative electrodes which has the terminal group which becomes a steric hindrance with respect to the said cyclic molecule.
[Selection] Figure 2

Description

  The present invention relates to a negative electrode binder for lithium ion secondary batteries, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery using the same.

  Lithium ion secondary batteries are used as a power source for a wide variety of products such as portable electronic devices, power tools, drones, XEVs, stationary power sources, and the like. And with the miniaturization and high functionality of products, further increase in energy density is expected for lithium ion secondary batteries serving as these power sources.

At present, carbon materials such as graphite are often used as negative electrode active materials for lithium ion secondary batteries. However, in order to increase the energy density, in recent years, such as Si, SiO _x , Sn, etc., which have a larger discharge capacity than graphite. Many alloy negative electrode active materials have been studied.

  However, when a material such as Si is used as the negative electrode active material, the expansion and contraction of the negative electrode active material accompanying charge / discharge is large. Therefore, the conductive path between the negative electrode active material particles in the negative electrode mixture layer is repeatedly generated by repeated charge / discharge. It is said that cutting, peeling between the negative electrode mixture layer and the current collector, and the like occur, resulting in deterioration of cycle characteristics. Therefore, when an active material having a large expansion and contraction, such as Si, is used as the negative electrode active material, a contrivance is made to maintain the electrode structure by using a high-strength binder such as polyimide.

Patent Document 1 discloses a negative electrode for a lithium secondary battery in which an active material layer containing active material particles containing silicon and / or a silicon alloy and a binder is disposed on the surface of a current collector made of a conductive metal foil. The binder has mechanical properties of a tensile strength of 50 N / mm ² or more, a breaking elongation of 10% or more, a strain energy density of 2.5 × 10 ⁻³ J / mm ³ or more, and an elastic modulus of 10,000 N / mm ² or less. A negative electrode for a lithium secondary battery is disclosed. Polyimide is disclosed as an example of the binder. Patent Document 2 discloses a cyclic molecule, a linear molecule that includes the cyclic molecule in a skewered manner, and blocking groups that are arranged at both ends of the linear molecule so that the cyclic molecule is not detached from the skewered molecule. Disclosed is a liquid crystalline polyrotaxane essentially consisting of a polyrotaxane having a liquid crystal polyrotaxane, wherein the cyclic molecule has a mesogenic group and has liquid crystallinity. Patent Document 3 discloses a plurality of polyrotaxanes in which capping groups are arranged at both ends of a pseudopolyrotaxane in which openings of a cyclic molecule are included in a skewered manner by linear molecules so that the cyclic molecules are not detached. A crosslinked polyrotaxane obtained by crosslinking is disclosed.

International Publication No. 2004/004031 JP 2007-262402 A International Publication No. 2001/088356

  However, the technique described in Patent Document 1 is insufficient for improving the cycle characteristics, and further improvement is desired.

  Accordingly, the present invention has been made to solve the above problems, and has a negative electrode binder for a lithium ion secondary battery excellent in cycle characteristics, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the same. The purpose is to provide.

  In order to solve the above problems, the present invention provides a polymer having a plurality of cyclic molecules and a linear polymer, wherein the linear polymer penetrates the plurality of cyclic molecules, Provided is a lithium ion secondary battery negative electrode binder having terminal groups that are sterically hindered with respect to the plurality of cyclic molecules at both ends of a linear polymer.

  According to this configuration, the lithium ion secondary battery using this negative electrode has excellent cycle characteristics. Although this effect is not necessarily clear, it is considered as follows. The polymer of the present invention has a structure in which a linear polymer penetrates a cyclic molecule. Furthermore, it has an end group which becomes a steric hindrance so that the cyclic molecule does not escape from the linear molecule at both ends of the linear polymer. When an external force is applied to the polymer, the cyclic molecule moves on the linear polymer chain and prevents excessive elongation of the linear polymer. Negative electrode active materials such as graphite and silicon expand when they occlude lithium ions. When expanded, the polymer bound to the negative electrode active material extends together with the negative electrode active material. Since the polymer of the present invention does not cause excessive elongation due to the mechanism as described above, the active material and the current collector to which the polymer is bound, between the active materials, and the active material and the conductive auxiliary agent, respectively. Suppresses the decrease in the binding force. As a result, the cycle characteristics of the lithium ion secondary battery using the negative electrode containing the polymer are improved. On the other hand, linear polymers such as polyacrylic acid have a large elongation, and the binding force decreases due to peeling of the binding points where the polymer is bound to other substances or by breaking the polymer chain itself. Resulting in. When the binding force is reduced, the negative electrode active material is peeled off from the current collector and the resistance is increased, and the negative electrode active material cannot be sufficiently charged and discharged.

  The plurality of cyclic molecules is preferably a lithium ion secondary battery negative electrode binder that is at least one selected from cyclodextrin, crown ether, thiocrown ether, calixarene, and thiocalixarene.

  According to such a configuration, the lithium ion secondary battery using the binder for the negative electrode of the lithium ion secondary battery can obtain more excellent cycle characteristics.

  The terminal group is preferably a binder for a negative electrode of a lithium ion secondary battery, which is adamantaneamine or dinitrobenzene.

  According to this configuration, the lithium ion secondary battery using this negative electrode active material can obtain more excellent cycle characteristics.

  The linear polymer is preferably a lithium secondary battery negative electrode binder which is at least one selected from polyethylene glycol, polyethylene, polypropylene, polypropylene oxide, polyvinyl alcohol, and polyvinylidene fluoride. Although this effect is not necessarily clear, it is considered that the linear polymer does not dissolve in the electrolyte solvent used in the lithium ion secondary battery or swells moderately.

  According to this configuration, the lithium ion secondary battery using this negative electrode active material can obtain more excellent cycle characteristics.

  A binder for a lithium ion secondary battery negative electrode in which the linear polymer is cross-linked through the cyclic molecules is preferable.

  According to such a configuration, the lithium ion secondary battery using the binder for the negative electrode of the lithium ion secondary battery can obtain more excellent cycle characteristics. Although this effect is not necessarily clear, it is considered that when the linear polymer is cross-linked through the cyclic molecules, the linear polymer easily follows when the active material expands and contracts. .

  A negative electrode for a lithium ion secondary battery in which an active material layer having the binder for a lithium ion secondary battery and an active material is formed on a current collector is preferable.

A negative electrode for a lithium ion secondary battery in which the active material contains at least one selected from graphite, silicon, and SiO _x (0 <X <2) is preferable.

  The lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries, electrolyte, and a positive electrode is preferable.

  According to such a configuration, when the negative electrode for a lithium ion secondary battery is used, the binder contained in the negative electrode mixture follows the expansion and contraction of the active material. Therefore, the lithium ion secondary battery of the present invention has an excellent cycle. Has characteristics.

  According to this invention, the lithium ion secondary battery using the binder for lithium ion secondary batteries of this invention has the outstanding cycling characteristics.

FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to this embodiment. 1 is a chemical formula showing the structure of a binder according to Example 1.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

Hereinafter, the case where an electrode is an electrode used for a lithium ion secondary battery will be specifically described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery 100 according to this embodiment.

  The lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30.

  The laminated body 30 is configured such that a pair of the positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 18 interposed therebetween. The positive electrode 10 is obtained by providing a positive electrode mixture layer 14 on a plate-like (foil-like) positive electrode current collector 12. The negative electrode 20 is obtained by providing a negative electrode mixture layer 24 on a plate-like (foil-like) negative electrode current collector 22. The positive electrode mixture layer 14 and the negative electrode mixture layer 24 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

  Hereinafter, the positive electrode 10 and the negative electrode 20 are collectively referred to as an electrode, the positive electrode current collector 12 and the negative electrode current collector 22 are collectively referred to as a current collector, and the positive electrode mixture layer 14 and the negative electrode mixture layer 24 are collectively referred to. It is called a mixture layer.

  First, the positive electrode 10 and the negative electrode 20 will be specifically described.

(Positive electrode)
The positive electrode 10 is obtained by providing a positive electrode mixture layer 14 on a plate-like (foil-like) positive electrode current collector 12.

(Positive electrode current collector)
The positive electrode current collector 12 may be any material that is not easily corroded by charging and is electronically conductive. For example, a metal foil such as aluminum, stainless steel, or nickel can be used.

(Positive electrode mixture layer)
The positive electrode mixture layer 14 includes a positive electrode active material, a binder, and a conductive additive.

(Positive electrode active material)
The positive electrode active material is occlusion / release of lithium ions, insertion / desorption (intercalation / deintercalation), or a counter anion of the lithium ions (for example, PF ₆ ⁻ , BF ₄ ⁻ or ClO ₄ ⁻ ). There is no particular limitation as long as the doping and dedoping can proceed reversibly, and a positive electrode active material used in a known lithium ion secondary battery can be used. For example, lithium-containing metal oxide, lithium-containing metal phosphorus oxide, and the like can be given. Examples of the lithium-containing metal oxide include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z O ₂ ( x + y + z = 1), composite metal oxide, lithium vanadium compound (LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ ), olivine-type LiMPO ₄ (where M represents Co, Ni, Mn or Fe) ) And lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

Further, if the negative electrode is doped with lithium ions in advance, a positive electrode active material not containing lithium can also be used. Non-lithium-containing metal oxides (such as MnO ₂ and V ₂ O ₅ ), lithium-free metal sulfides (such as MoS ₂ ), and lithium-free fluorides (such as FeF ₃ and VF ₃ ) are also included.

(binder)
In order to adhere the positive electrode active material and the positive electrode active material, the positive electrode active material and the conductive additive, and the positive electrode active material and the current collector, a binder is added to the positive electrode mixture layer. Properties required for the binder include not being dissolved in the electrolytic solution, oxidation resistance, and good adhesion. As a binder used for the positive electrode mixture layer, polyvinylidene fluoride (PVDF) or a copolymer thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI) ), Polyethersulfone (PES), polyacrylic acid (PA) and its copolymer, cross-linked metal ion of polyacrylic acid (PA) and its copolymer, polypropylene grafted with maleic anhydride (PP), Examples thereof include polyethylene (PE) grafted with maleic anhydride or a mixture thereof. Among these, PVDF is particularly preferable.

  The binder content in the positive electrode mixture layer 14 is not particularly limited, but is preferably 1% by mass to 15% by mass based on the total mass of the positive electrode active material, the conductive additive, and the binder, More preferably, the content is from 5% by mass to 5% by mass. When the amount of the binder is too small, there is a tendency that a positive electrode having sufficient adhesive strength cannot be formed. On the other hand, when the amount of the binder is too large, a general binder is electrochemically inactive and thus does not contribute to the discharge capacity, and it tends to be difficult to obtain a sufficient volume or mass energy density.

(Conductive aid)
The conductive auxiliary agent is not particularly limited as long as it improves the electronic conductivity of the positive electrode mixture layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon materials such as carbon black, carbon nanotubes, and graphene, metal fine powders such as copper, nickel, stainless steel, and iron, conductive oxides such as ITO, and mixtures thereof.

  The content ratio of the conductive additive in the positive electrode mixture layer 14 is not particularly limited, but when adding the conductive additive, it is usually 0.5 based on the total mass of the positive electrode active material, the conductive additive and the binder. It is preferable that it is mass%-20 mass%, and it is more preferable to set it as 1 mass%-5 mass%.

(Negative electrode)
The negative electrode 20 is obtained by providing a negative electrode mixture layer 24 on a plate-like (foil-like) negative electrode current collector 22.

(Negative electrode current collector)
The negative electrode current collector 22 may be any conductive plate material, and for example, a metal foil such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin foil can be used.

(Negative electrode mixture layer)
The negative electrode mixture layer 24 includes a negative electrode active material, a binder, and a conductive auxiliary agent in an amount as necessary.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly advance the insertion and extraction of lithium ions and the insertion and desorption of lithium ions. The negative electrode active material used in known lithium ion secondary batteries is used. can do. For example, it combines with natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), coke, glassy carbon, carbon materials such as organic compound fired bodies, lithium such as Si, SiO _x , Sn, and aluminum. Metals, alloys thereof, composite materials of these metals and carbon materials, oxides such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), SnO ₂ , and the like. Here, Si and SiO _x are described as Si-based negative electrode active materials.

The shape of the Si-based negative electrode active material is not particularly limited. In the case where the Si-based negative electrode active material is a particle, the average particle size is such that the electrochemical reaction is likely to occur (Li ⁺ is easy to be inserted into and desorbed from Si) and a thin film (thickness of several μm to several tens of μm) In consideration of easiness to make an electrode, the thickness is preferably several nm to 20 to 30 μm. In addition, an average particle diameter is a volume average particle diameter in the particle size distribution measurement by a laser beam diffraction method. The Si-based negative electrode active material may be nanowires or flakes. In the case of nanowires, the average diameter is preferably several nm to 20 to 30 μm, and the average length is preferably several μm to 20 to 30 μm. In the case of a thin piece, the thickness is preferably from several nm to 20 to 30 μm, and the diameter is preferably from several μm to 20 to 30 μm. In addition, the average diameter or average length in this invention is calculated | required from SEM (scanning electron microscope) observation.

Si-based BET method of the negative electrode active material (Brunauer, Emmett, Teller method) specific surface area by, 0.5~100m ² / g is desirable, 1-20 m ² / g is more preferable. When it is smaller than 0.5 m ² / g, an electrochemical reaction (ease of Li ⁺ being easily inserted into and desorbed from Si) hardly occurs, and when it exceeds 100 m ² / g, a Si-based negative electrode active material is converted into an electrode. If the binder is not added more than usual, it becomes difficult to form an electrode, and the capacity and energy per unit volume of the electrode decrease.

  The Si-based negative electrode active material may be crystalline or amorphous. The amorphous Si-based negative electrode active material is produced by a melt span method, a gas atomization method, or the like.

  Si in the Si-based negative electrode active material is an element having an atomic number of 14 and forms an alloy with lithium.

  Si forms alloys with various elements. The Si alloy according to the present embodiment may be any Si alloy. Elements that make an alloy with Si are Ba, Mg, Al, Ca, Ti, Sn, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Y, Zr, Nb, Mo, Ba, W, Au etc. are mentioned.

The Si alloy may be an intermetallic compound that forms a compound at a specific ratio with Si, that is, a silicide. Silicide is Mg ₂ Si, Ca ₂ Si, CaSi ₂ Al ₂ , TiSi ₂ , Ti ₅ Si ₃ , VSi ₂ , FeSi ₂ , CoSi ₂ , Nb ₃ Ni ₂ Si, MoSi ₂ , Mo ₃ Si, Mo ₅ Si _3. , Mo ₅ SiB ₂ , and the like.

SiO _x is a fine nano-sized Si cluster dispersed in a SiO ₂ matrix.

Examples of the Si composite material include those in which the surface of Si, Si alloy or SiO _x particles is coated with a conductive material such as a carbon material, Al, Ti, Fe, Ni, Cu, Zn, Ag, or Sn. For example, the surface of the Si particles may be coated with a carbon material with a thickness of several nm, the powder coated with graphite powder having a particle size of several μm, or the carbon nanotubes may be coated.

The coating amount of the carbon material is not particularly limited, but is preferably 0.01 to 30% by mass with respect to the entire particle in which the surface of the Si, Si alloy or SiO _x particle is coated with the carbon material, 20 mass% is more preferable. Sufficient conductivity can be maintained by setting the coating amount of the carbon material to 0.01% by mass or more. As a result, the cycle characteristics when the negative electrode active material for a lithium ion secondary battery is obtained can be improved. On the other hand, when the coating amount of the carbon material exceeds 30% by mass, the ratio of the carbon material to the entire active material increases and the discharge capacity decreases.

The method for coating the surface of Si, Si alloy or SiO _x particles with a conductive material is not particularly limited. For example, a mechanical alloying method, a chemical vapor deposition method, a wet method, or a method in which a polymer is coated on the surface and then pyrolytic carbonization is exemplified.

(binder)
A polymer having a plurality of cyclic molecules and a linear polymer, wherein the linear polymer penetrates the plurality of cyclic molecules, and the cyclic molecules are attached to both ends of the linear polymer. It is preferable that it is a binder for lithium ion secondary battery negative electrodes which has the terminal group used as a steric hindrance. In general, a molecule in which a linear molecule passes through a ring of a cyclic molecule and both ends of the linear molecule are fixed with large end groups is called a polyrotaxane. Such a polymer is sold by Advanced Soft Materials Co., Ltd. under the trade name “Celum Superpolymer”. In this polymer, a cyclic molecule (cyclodextrin) penetrates a linear polymer (polyethylene glycol), and both ends of the linear polymer have terminal groups that are sterically hindered with respect to the cyclic molecule. Is a molecule. Linear polymers include, for example, polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide, polyethylene, polypropylene, other polyolefin resins such as copolymer resins with olefin monomers, polyvinyl alcohol, polyvinylidene fluoride, polyvinyl pyrrolidone. , Poly (meth) acrylic acid, casein, polyester resin, polystyrene resins such as polystyrene and acrylonitrile-styrene copolymer resin, polymethyl methacrylate, (meth) acrylic acid ester copolymer, acrylonitrile-methyl acrylate copolymer resin, etc. Acrylic resin, polyvinyl butyral resin, polyisobutylene, polytetrahydrofuran, polyaniline, acrylonitrile-butadiene-styrene copolymer ABS resin), polyamides such as nylon, polyimides, selected from the group consisting of. The terminal group is selected from the group consisting of dinitrophenyl groups, cyclodextrins, adamantane groups, trityl groups, fluoresceins, silsesquioxanes, pyrenes, and benzenes. Cyclic dextrin of a cyclic molecule modified with a compound selected from the group consisting of an isocyanate group, a thioisocyanate group, an oxirane group, an oxetane group, a carbodiimide group, a silanol group, an oxazoline group, and an aziridine group crosslinks the cyclic molecules. be able to.

  Although the content rate of the binder in the negative electrode mixture layer 24 is not particularly limited, it is preferably 1% by mass to 15% by mass based on the total mass of the negative electrode active material, the conductive additive, and the binder, and is preferably 3% by mass. More preferably, it is 10 mass%. When the amount of the binder is too small, there is a tendency that a negative electrode having sufficient adhesive strength cannot be formed. Conversely, if the amount of the binder is too large, the binder is generally electrochemically inactive, so that it does not contribute to the discharge capacity, and it tends to be difficult to obtain a sufficient volume or mass energy density. Although the content rate of the conductive support agent in the negative electrode mixture layer 24 is not particularly limited, it is usually preferably 0.5% by mass to 20% by mass with respect to the active material when the conductive auxiliary agent is added. It is more preferable to set it as mass%-12 mass%.

(Conductive aid)
Conductive aids such as carbon materials used in the positive electrode described in paragraph 0039 can also be used in the negative electrode.

  Next, the manufacturing method of the electrodes 10 and 20 concerning this embodiment is demonstrated. The manufacturing method of the electrodes 10 and 20 according to this embodiment includes a step of applying a paint containing an active material, a binder, and a conductive additive on a current collector (hereinafter, also referred to as “application step”), and a collector. And a step of removing the solvent in the paint applied on the electric body (hereinafter, also referred to as “solvent removal step”).

(Coating process)
An application process for applying the paint to the current collectors 12 and 22 will be described. The paint includes an active material, a binder, a conductive aid, and a solvent. The mixing method of the components constituting the coating material such as the active material, the binder, the conductive auxiliary agent and the solvent is not particularly limited, and the mixing order is not particularly limited. For example, first, an active material and a conductive additive are dry-mixed, and a solution containing a binder is added to and mixed with the obtained mixture to prepare a paint. The active material, binder, conductive additive and solvent described above are applied to the current collectors 12 and 22. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

(Solvent removal step)
Subsequently, the solvent in the paint applied on the current collectors 12 and 22 is removed. The removal method is not particularly limited, and the current collectors 12 and 22 coated with the paint may be dried at, for example, 60 ° C. to 150 ° C. And the electrode in which the mixture layers 14 and 24 were formed in this way can be pressed with a roll press apparatus etc. as needed after that, for example, and it can be made a desired electrode density. The linear pressure of the roll press can be set to 100 to 2000 kgf / cm, for example.

  The electrode concerning this embodiment can be produced through the above process.

  Here, another component of the lithium ion secondary battery 100 using the electrode manufactured as described above will be described.

(Electrolytes)
The electrolyte is contained in the positive electrode mixture layer 14, the negative electrode mixture layer 24, and the separator 18. The electrolyte is not particularly limited. For example, in the present embodiment, an electrolyte solution containing lithium salt (an electrolyte solution using an organic solvent) can be used. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₂ F ₅ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN A salt such as (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiN (COC ₂ F ₅ ) ₂ , LiBC ₄ O ₈ can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diallyl carbonate, 2,5-dioxahexane diacid dimethyl, 2, 5 -Dioxahexane diacid diethyl, furan, 2,5-dimethylfuran, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, dimethoxymethane, dimethoxyethane, 1,2-di Ethoxyethane, diglyme, triglyme, tetraglyme, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, methyl difluoroacetate, ethyl trifluoroacetate Methyl propionate, ethyl propionate, propyl propionate, methyl formate, ethyl formate, ethyl butyrate, isopropyl butyrate, methyl isobutyrate, methyl cyanoacetate, vinyl acetate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε -Caprolactone, γ-hexanolactone, γ-undecalactone, trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, trioctyl phosphate, triphenyl phosphate, methoxy-nonafluorobutane, ethoxy-nonafluorobutane 1-methoxyheptafluoropropane, 2-trifluoromethyl-3-ethododecoforohexane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether and the like are preferable. These may be used alone or in combination of two or more at any ratio.

  Further, an additive may be further added to the electrolyte. Examples of the additive include those that produce a good SEI (Solid Electrolyte Interface) on the surface of the negative electrode active material, those that produce a good SEI on the negative electrode, and those that are effective in preventing overcharge. Specifically, acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, sebaconitrile, cyclohexylbenzene, fluorocyclohexylbenzene compound (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3- Cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (o-, m-, p-isomer), Diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-isomer), anisole, 2,4-difluoroanisole, terphenyl partially hydride (1,2-dicyclohexylbenzene, 2 Phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl), methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2- Isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, 2-propynylmethyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2- (Methanesulfonyloxy) propionic acid 2-propynyl, di (2-propynyl) oxalate, methyl 2-propini Luogizarate, ethyl 2-propynyl oxalate, di (2-propynyl) glutarate, 2-butyne-1,4-diyldimethanesulfonate, 2-butyne-1,4-diyldiformate, 2,4-hexadiyne -1,6-diyldimethanesulfonate, 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxide-1, Sultone such as 2-oxathiolan-4-yl acetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, ethylene sulfite, hexahydrobenzo [1,3,2] dioxathiolane-2 -Oxide (also called 1,2-cyclohexanediol cyclic sulfite), 5-vinyl-hex Cyclic sulfites such as hydro-1,3,2-benzodioxathiol-2-oxide, butane-2,3-diyldimethanesulfonate, butane-1,4-diyldimethanesulfonate, methylenemethanedisulfonate, etc. Sulfonic acid ester, divinyl sulfone, 1,2-bis (vinylsulfonyl) ethane, bis (2-vinylsulfonylethyl) ether, 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2,4 -Butane sultone, 1,3-propene sultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, methylene methane Disulfonate, ethylene sulfite, 4- (methylsulfonylmethyl) -1 3,2-dioxathiolane 2-oxide, butane-2,3-diyldimethanesulfonate, butane-1,4-diyldimethanesulfonate, dimethylmethane disulfonate, pentafluorophenylmethanesulfonate, divinylsulfone, bis (2-vinyl Sulfonylethyl) ether, trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris (2,2,2-trifluoroethyl) phosphate, bis (2,2,2-trifluoroethyl) methyl phosphate, phosphoric acid Bis (2,2,2-trifluoroethyl) ethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2 , 2,3,3-tetrafluoropropyl, bis (2,2-difluoroethyl) phosphate 2,2 , 2-trifluoroethyl, bis (2,2,3,3-tetrafluoropropyl) phosphate, 2,2,2-trifluoroethyl phosphate, (2,2,2-trifluoroethyl) phosphate (2,2 , 3,3-tetrafluoropropyl) methyl, tris phosphate (1,1,1,3,3,3-hexafluoropropan-2-yl), methyl methylene bisphosphonate, ethyl methylene bisphosphonate, methyl ethylene bisphosphonate , Ethyl ethylene bisphosphonate, methyl butylene bisphosphonate, ethyl butylene bisphosphonate, methyl 2- (dimethylphosphoryl) acetate, ethyl 2- (dimethylphosphoryl) acetate, methyl 2- (diethylphosphoryl) acetate, ethyl 2- (diethylphosphoryl) Acetate, 2-propynyl 2- (dimethylphosphori ) Acetate, 2-propynyl 2- (diethylphosphoryl) acetate, methyl 2- (dimethoxyphosphoryl) acetate, ethyl 2- (dimethoxyphosphoryl) acetate, methyl 2- (diethoxyphosphoryl) acetate, ethyl 2- (diethoxyphosphoryl) Acetate, 2-propynyl 2- (dimethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate, methyl pyrophosphate, ethyl pyrophosphate, acetic anhydride, propionic anhydride, or succinic anhydride, maleic anhydride, 2 -Allyl succinic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorosic Torihosufazen, there is an ethoxy heptafluoro cyclotetrasiloxane phosphazene.

  In the present embodiment, the electrolyte may be a gel electrolyte obtained by adding a gelling agent in addition to the liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

(Separator)
The separator 18 is an electrically insulating microporous film, for example, a single layer microporous film or a laminated microporous film made of polyethylene, polypropylene or polyolefin, or a dry method or a wet method using a mixture film of the polymer. Examples include a microporous membrane to be produced, or a nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, polyethylene, or polypropylene. Moreover, the microporous film which consists of glass fibers may be sufficient.

  A heat-resistant layer may be formed on one side or both sides of the separator. The heat-resistant layer is composed of inorganic particles such as alumina and a binder. As the binder, the binders described in paragraphs 0035 and 0073 can be used.

(Exterior body)
The exterior body 50 seals the laminated body 30 and the electrolyte solution therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the electrochemical device 100 from the outside. For example, as the outer package 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. As the metal foil 52, for example, an aluminum foil can be used, and as the polymer film 54, a film such as polypropylene can be used. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). preferable.

(Lead)
The leads 60 and 62 are made of a conductive material such as aluminum or nickel.

  Then, the leads 60 and 62 are welded to the positive electrode current collector 12 and the negative electrode current collector 22 by a known method, respectively, and a separator is provided between the positive electrode mixture layer 14 of the positive electrode 10 and the negative electrode mixture layer 24 of the negative electrode 20. 18 may be inserted into the outer package 50 together with the electrolytic solution in a state of sandwiching 18, and the entrance of the outer package 50 may be heat-sealed.

  The preferred embodiments of the negative electrode binder for lithium ion secondary batteries, the negative electrode for lithium ion secondary batteries using the same, and the lithium ion secondary battery using the same have been described above in detail. It is not limited to the embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. Table 1 shows the types of binder used in each example or comparative example.

Example 1
<Production of negative electrode>
Si (average particle size 5 μm), polyrotaxane (manufactured by Advanced Soft Materials, trade name: Celm superpolymer SH3400P, weight average molecular weight 700,000), and carbon black (DAB50, manufactured by Denki Kagaku Kogyo Co., Ltd.) as binders , 83 parts by weight, 15 parts by weight, and 2 parts by weight, respectively, are weighed in a resin container, and an appropriate amount of DMF (dimethylform screen) is added as a solvent, and the agitator (revolution made by Keyence Co., Ltd.) : Hybrid mixer) to prepare a negative electrode paint. The structural formula of SH3400P is shown in FIG. In SH3400P, the linear polymer is polyethylene glycol, the cyclic molecule is polycaprolactone-grafted α-cyclodextrin, and the end group is adamantaneamine. In addition, a part of —OH group of α-cyclodextrin is substituted with a hydroxypropyl group. This negative electrode paint was applied to a copper foil (width 99 mm, thickness 10 μm) as a current collector by a doctor blade method, followed by drying at 110 ° C. to prepare a negative electrode having a negative electrode mixture layer on one side. The copper current collector was provided with a portion to which no paint was applied in order to weld the external lead terminal (lead). Similarly, the negative electrode paint was applied to one side, and a negative electrode having a negative electrode mixture layer on both sides was produced. Next, this negative electrode was pressed with a roll press so as to have a predetermined density.

<Preparation of positive electrode>
LiNi _0.8 Co ₀ . 85 g of ₁₅ Al _0.05 O ₂ , 5 g of carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., DAB50), 5 g of graphite (manufactured by Timcal Co., Ltd., trade name: KS-6), and polyvinylidene fluoride as a binder 50 g of (PVDF) solution (manufactured by Kureha Chemical Industry Co., Ltd., trade name: KF7305, NMP solution containing 5% by mass of PVDF) was weighed in a resin container and mixed with a hybrid mixer to prepare a positive electrode paint. This positive electrode paint was applied to an aluminum foil (thickness 20 μm) as a current collector by a doctor blade method and then dried at 110 ° C. to produce a positive electrode having a positive electrode mixture layer on one side. The aluminum current collector was provided with a portion where no positive electrode paint was applied in order to weld the external lead terminal (lead). Similarly, a positive electrode paint was applied to one side to produce a positive electrode having a positive electrode mixture layer on both sides. Next, this positive electrode was pressed with a roll press so as to have a predetermined density.

<Production of battery>
A negative electrode prepared in paragraph (0117), a positive electrode prepared in paragraph (0118), and a separator (polyethylene microporous film) were prepared and cut into predetermined dimensions. Subsequently, the positive electrode, the negative electrode, and the separator were laminated in this order. The laminate was fixed with tape so that the positive electrode, the negative electrode, and the separator were not displaced. An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. In order to improve the sealing performance between the external terminal and the exterior body, a polypropylene film grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. The battery outer package enclosing the battery element in which the positive electrode, the negative electrode, and the separator are laminated is made of an aluminum laminate material, and the structure is polyethylene terephthalate (thickness 12 μm) / aluminum (thickness 40 μm) / polypropylene (thickness 50 μm). I prepared something. At this time, the bag was made so that the polypropylene was inside. The battery element was inserted into the outer package, and LiPF ₆ was added to 1 M (1%) of an electrolyte solution (a mixed solvent of fluoroethylene carbonate (abbreviated as FEC) and diethyl carbonate (abbreviated as DEC) (FEC: DEC = 30: 70 vol%)). Remarks M = moldm ⁻³ ) was added in an appropriate amount, and the outer package was vacuum-sealed to produce a lithium ion secondary battery.

(Example 2)
<Production of negative electrode>
The binder was used in the same manner as in Example 1 except that the polyrotaxane varieties were changed and heat-treated. As a binder, a product name: Celm superpolymer SH3400M (weight average molecular weight 400,000) manufactured by Advanced Soft Materials, Inc. was used. SH3400M has basically the same structure as the polyrotaxane (SH3400P) of Example 1, but contains a crosslinking agent. In SH3400M, the linear polymer is polyethylene glycol, the cyclic molecule is polycaprolactone-grafted α-cyclodextrin, and the end group is adamantaneamine. SH3400M further contains polycarbonate diol as a crosslinking agent. The prepared negative electrode was heat-treated at 170 ° C. for 2 hours under vacuum. Next, this negative electrode was pressed with a roll press so as to have a predetermined density.

(Comparative Example 1)
<Production of negative electrode>
The same procedure as in Example 1 was performed except that the binder was changed to polyacrylic acid (weight average molecular weight of 798,000) and heat treatment was performed. The prepared negative electrode was heat-treated at 200 ° C. for 15 hours under vacuum. Next, this negative electrode was pressed with a roll press so as to have a predetermined density.

(Battery test method)
Evaluation of the lithium ion secondary battery produced in the paragraph (0119) was carried out by a charge / discharge cycle test. The charge / discharge test was performed in a constant temperature bath at 25 ° C. Hereinafter, the charge / discharge current is expressed in C (sea) rate. nC (mA) is a current that can charge and discharge the nominal capacity (mAh) at 1 / n (h). For example, in the case of a battery with a nominal capacity of 70 mAh, the current of 0.05 C is 3.5 mA (calculation formula 70 × 0.05 = 3.5).

  The charge / discharge cycle test conditions were as follows. In the first cycle, the battery was charged at 0.05 C for 3 hours, and then charged at C to 0.2 V at 0.2 C. Discharge was discharged to 3.0V at 0.2C. After the second cycle, the CCCV charge was performed up to 4.2V at 0.5C and discharged to 3.0V at 1C. The CCCV charging is a charging method in which charging is first performed to a predetermined voltage with a predetermined constant current, and charging is performed until the voltage is attenuated to a predetermined current after reaching the predetermined voltage. In the current charge / discharge cycle test, the predetermined current was set to 0.05C. This charge / discharge cycle test was repeated up to 500 cycles.

  Table 2 shows the capacity retention ratio obtained by standardizing the discharge capacity after 200 cycles, assuming that the discharge capacity of the first cycle is 100. The example shows a higher capacity retention rate than the comparative example. This is considered as follows. A polyrotaxane as a binder has a structure in which a linear polymer penetrates a cyclic molecule. When an external force is applied to the polymer, the cyclic molecule moves on the linear polymer chain and prevents excessive elongation of the linear polymer. On the other hand, Si, which is a negative electrode active material, expands when lithium ions are occluded. When expanded, the polymer bound to the negative electrode active material extends together with the negative electrode active material. Since the polymer of the present invention does not cause excessive elongation due to the mechanism as described above, the active material and the current collector to which the polymer is bound, between the active materials, and the active material and the conductive auxiliary agent, respectively. Suppresses the decrease in the binding force. As a result, the cycle characteristics of the lithium ion secondary battery using the negative electrode containing the polymer are improved. On the other hand, linear polymers such as polyacrylic acid, when stretched, have a lower binding force due to peeling of the binding points where the polymer is bound to other substances or by breaking the polymer chain itself. Resulting in. When the binding force is reduced, the negative electrode active material is peeled off from the current collector and the resistance is increased, and the negative electrode active material cannot be sufficiently charged and discharged.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

  The negative electrode for lithium ion secondary batteries excellent in cycle characteristics and a lithium ion secondary battery using the same according to the present invention are obtained. This is suitably used as a power source for portable electronic devices, and is also used as an electric vehicle, a household battery, and an industrial storage battery.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode current collector, 24 ... Negative electrode active material layer, 30 ... Laminated body, 50 ... Outer body, 62 ... Positive electrode lead, 60 ... Negative electrode lead, 100 ... Lithium ion secondary battery

Claims (8)

  A polymer having a plurality of cyclic molecules and a linear polymer, wherein the linear polymer penetrates the plurality of cyclic molecules, and the plurality of cyclic molecules at both ends of the linear polymer. A binder for a negative electrode of a lithium ion secondary battery, having a terminal group that becomes a steric hindrance to a molecule.   The binder for a lithium ion secondary battery negative electrode according to claim 1, wherein the plurality of cyclic molecules is at least one selected from cyclodextrin, crown ether, thiocrown ether, calixarene, and thiocalixarene.   The binder for a lithium ion secondary battery negative electrode according to any one of claims 1 and 2, wherein the terminal group is adamantaneamine or dinitrobenzene.   The lithium ion secondary battery negative electrode according to any one of claims 1 to 3, wherein the linear polymer is at least one selected from polyethylene glycol, polyoxymethylene, polypropylene oxide, polyvinyl alcohol, and polyvinylidene fluoride. Binder.   The binder for a lithium ion secondary battery negative electrode according to any one of claims 1 to 4, wherein the linear polymer is crosslinked through at least one of the plurality of cyclic molecules.   The negative electrode for lithium ion secondary batteries in which the active material layer which has the binder for lithium ion secondary battery negative electrodes and active material as described in any one of Claims 1-5 was formed on the electrical power collector. The negative electrode for a lithium ion secondary battery according to claim 6, wherein the active material contains at least one selected from graphite, silicon, and SiO _x (0 <X <2). The lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries of Claim 7, an electrolyte, and a positive electrode.

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