JP6690358B2 - Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery using the same, and lithium ion secondary battery using the same - Google Patents

Description

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

Lithium-ion secondary batteries, compared to nickel-cadmium batteries, nickel-hydrogen batteries, etc.
Because of its light weight and high capacity, it is widely applied as a power source for portable electronic devices. In recent years, it has been installed in hybrid vehicles and electric vehicles. With the recent miniaturization and higher functionality of portable electronic devices, it is expected that the lithium-ion secondary batteries used as the power sources for these devices will have even higher capacities. Currently, as negative electrode active materials for lithium ion secondary batteries, in addition to carbon materials such as graphite, many alloy-based negative electrode active materials such as silicon and silicon oxide having a larger discharge capacity than graphite are being studied.

However, when a material such as silicon is used as the negative electrode active material, since the negative electrode active material expands and contracts greatly with charging and discharging, the conductive path between the negative electrode active material particles in the negative electrode mixture layer due to repeated charging and discharging. It is said that the cycle characteristics are deteriorated due to disconnection of the negative electrode, peeling between the negative electrode mixture layer and the current collector, and the like. Therefore, when a silicon-based negative electrode active material is used as the negative electrode active material, an attempt is made to maintain the electrode structure by using a high-strength binder such as polyimide.

  Patent Document 1 discloses a means for improving the cycle characteristics of a lithium ion secondary battery when a silicon-based negative electrode active material is included as the negative electrode active material. The negative electrode for a lithium-ion secondary battery of Patent Document 1 is characterized in that a binder improving agent is used when a negative electrode active material slurry containing a negative electrode active material and a binder material is prepared. Here, as the binder material, at least one selected from the group consisting of polyimide, polyamide, and polyamideimide, and prepolymers thereof is described, and as the binding agent, a polyvalent carboxylic acid and its derivative, And at least one selected from the group consisting of polyvalent amines.

WO2012 / 017738

However, the technique described in Patent Document 1 is not sufficient for improving cycle characteristics, and further improvement is desired.

Therefore, the present invention has been made to solve the above problems, and an object thereof is to provide a negative electrode active material for a lithium-ion secondary battery having excellent cycle characteristics, a negative electrode using the same, and a lithium-ion secondary battery. And

In order to solve the above problems, the present invention provides a negative electrode active material for a lithium ion secondary battery, which has a coating film containing a polymer of a catechol derivative formed on the surface thereof.

  According to this structure, the lithium ion secondary battery using this negative electrode active material has excellent cycle characteristics. Although this action effect is not always clear, the polymer of the catechol derivative improves the binding property between the negative electrode active material and the binder, and thus prevents the conductive path between the negative electrode active material particles from being cut even by repeated charging and discharging. It is presumed that this is due to what they are doing. This is effective for any type of negative electrode active material having various surface properties ranging from hydrophilic to hydrophobic due to the excellent binding property of the catechol derivative polymer having both hydrophilicity and hydrophobicity. Is considered to be obtained.

  The thickness of the coating film according to the present invention is preferably 1 nm to 200 nm.

  According to this structure, the lithium-ion secondary battery using this negative electrode active material can obtain more excellent cycle characteristics and also have improved rate characteristics.

  Further, the catechol derivative according to the present invention includes dopamine, gallic acid, pyrogallol, 3-methylcatechol, 4-methylcatechol, catechol-4-acetic acid, noradrenaline, adrenaline, 3- (3,4-dihydroxyphenyl) -L. -Alanine, 5,6-dihydroxyindole, catechin, isoflavone ellagic acid, 4-tert-butylpyrocatechol, 5-sec-butylpyrogallol, 4-phenylpyrogallol, 4-methyl-1,2,3-benzenetriol, 4 It is preferably at least one selected from the group of 5,6-trichloropyrogallol, 4,5,6-trimethylpyrogallol, 4,5-dimethylpyrogallol and 4,6-dimethylpyrogallol.

  According to this structure, the lithium-ion secondary battery using this negative electrode active material can obtain more excellent cycle characteristics and also have improved rate characteristics.

  The negative electrode active material according to the present invention preferably contains any one of a metal containing Si as a main component, a metal containing Sn as a main component, and SiO.

  According to this structure, the lithium-ion secondary battery using this negative electrode active material can obtain more excellent cycle characteristics and also have improved rate characteristics.

  The negative electrode for a lithium ion secondary battery according to the present invention has a composition in which a mixture layer containing the negative electrode active material for a lithium ion secondary battery and a binder is formed on a negative electrode current collector.

  The binder according to the present invention is preferably a polymer having a hydroxyl group, a carboxyl group, an amino group, an amide group or an imide group.

  According to this structure, a chemical bond is formed between the hydroxyl group in the polymer of the catechol derivative and the hydroxyl group, carboxyl group, amino group, amide group or imide group present in the binder in the negative electrode. As a result, the negative electrode active material particles and the binder are firmly bonded. Similarly, hydroxyl groups are present on the surface of the copper foil which is the current collector or the surface of carbon black which is the conductive additive. As a result of forming a chemical bond, the hydroxyl group and the hydroxyl group in the polymer of the catechol derivative are strongly bonded. Due to these effects, cycle characteristics are improved.

  The binder according to the present invention is polyacrylic acid, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl hydroxide copolymer, acrylic acid ester-aminoethyl acrylate copolymer, polyamic acid. It is preferably one selected from the group consisting of or a mixture thereof.

  According to this structure, the hydroxyl group in the polymer of the catechol derivative and the hydroxyl group in the binder are easy to form a chemical bond and the cycle characteristics are improved, which is preferable.

  The binder according to the present invention is preferably polyamide, polyimide, polyamide-imide, or a mixture thereof.

  According to such a configuration, the hydroxyl group in the polymer of the catechol derivative and the oxygen atom in the binder easily form a chemical bond, and the cycle characteristics are improved, which is preferable.

  It is preferable that the polymer of the catechol derivative according to the present invention and the binder are covalently bonded.

  The polymer of the catechol derivative according to the present invention and the binder are preferably hydrogen-bonded.

  A lithium-ion secondary battery having excellent cycle characteristics can be obtained by using the above-described negative electrode for a lithium-ion secondary battery according to the present invention and configuring a lithium-ion secondary battery including an electrolyte and a positive electrode.

  According to the present invention, the lithium ion secondary battery using the negative electrode active material of the present invention has excellent cycle characteristics.

FIG. 1 is a schematic cross-sectional view showing a lithium-ion secondary battery according to this embodiment. FIG. 2 is a flowchart showing a method for manufacturing the negative electrode active material for a lithium ion secondary battery according to this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are not limited to the illustrated ratios.

Hereinafter, a case where the electrode is an electrode used in 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 laminated body 30, a case 50 that houses the laminated body 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminated body 30.

  The laminated body 30 includes a pair of positive electrodes 10 and negative electrodes 20 which are arranged to face each other with the separator 18 interposed therebetween. The positive electrode 10 has a positive electrode mixture layer 14 provided on a plate-shaped (foil-shaped) positive electrode current collector 12. The negative electrode 20 has a negative electrode mixture layer 24 provided on a plate-shaped (foil-shaped) 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, respectively. Leads 60 and 62 are connected to the ends of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the ends 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. And called the mixture layer.

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

(Positive electrode)
The positive electrode 10 has a positive electrode mixture layer 14 provided on a plate-shaped (foil-shaped) positive electrode current collector 12.

(Positive electrode current collector)
The positive electrode current collector 12 may be made of a material that is not easily corroded by charging and is electrically conductive, and 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 contains a positive electrode active material, a binder, and a conductive additive.

(Cathode active material)
The positive electrode active material is a lithium ion storage / release, insertion / desorption (intercalation / deintercalation), or a counter anion of the lithium ion (eg, PF ₆ ⁻ , BF ₄ ⁻ or ClO ₄ ⁻ ). There is no particular limitation as long as it is possible to reversibly perform the dope and the undoping, and a positive electrode active material used in known lithium ion secondary batteries can be used. Examples thereof include lithium-containing metal oxides, lithium-containing metal phosphorus oxides, and lithium-free fluorides. Examples of the lithium-containing metal oxide include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and the general formula: LiNi _x Co _y Mn _z O ₂ ( x + y + z = 1) mixed 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) ), Lithium titanate (Li ₄ Ti ₅ O ₁₂ ), FeF _{3 and the} like.

(binder)
A binder is added to the positive electrode mixture layer in order to bond the positive electrode active material and the positive electrode active material, the positive electrode active material and the conductive auxiliary agent, and the positive electrode active material and the current collector. The properties required of the binder are that it does not dissolve in the electrolyte solution, that it has oxidation resistance, and that it has good adhesiveness. As the binder used for the positive electrode mixture layer, polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl Vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), polyamide (PA), Polyimide (PI), Polyamideimide (PAI), Polybenzimidazole (PBI), Polypropylene (PP) grafted with maleic anhydride, Polyethylene grafted with maleic anhydride (PE), or the like and mixtures thereof. Among them, PVDF is particularly preferable.

  The content of the binder in the positive electrode mixture layer 14 is not particularly limited, but it is preferably 1% by mass to 15% by mass, and preferably 3% by mass, based on the total mass of the positive electrode active material, the conductive additive and the binder. It is more preferably from 10 to 10% by mass. By setting the content of the binder in the above range, it is possible to suppress the tendency of the obtained mixture layer that the amount of the binder is too small to form a strong positive electrode mixture layer. Further, it is possible to suppress the tendency that the amount of the binder that does not contribute to the discharge capacity increases and it becomes difficult to obtain a sufficient volume energy density.

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

  The content of the conductive auxiliary agent in the positive electrode mixture layer 14 is not particularly limited, but when the conductive auxiliary agent is added, it is usually 0.5 based on the total mass of the positive electrode active material, the conductive auxiliary agent and the binder. The content is preferably 20% by mass to 20% by mass, and more preferably 1% by mass to 12% by mass.

(Negative electrode)
The negative electrode 20 has a negative electrode mixture layer 24 provided on a plate-shaped (foil-shaped) 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 can be used.

(Negative electrode mixture layer)
The negative electrode mixture layer 24 contains 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 proceed with occlusion and release of lithium ions, desorption and insertion of lithium ions, and the negative electrode active material used in known lithium ion secondary batteries is used. can do. For example, natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fibers (MCF), cokes, glassy carbon, carbon materials such as organic compound fired bodies, lithium such as silicon, silicon alloys, SiO, aluminum and tin. Examples thereof include metals that can be combined, alloys thereof, composite materials of these metals and carbon materials, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), oxides such as SnO ₂ , and the like. In particular, silicon, a silicon alloy, SiO, a silicon composite material (these silicon-containing active materials will be referred to as silicon hereinafter), which has a large volume expansion coefficient during charging and causes a problem of separation from a binder, a current collector or a conductive additive. The present invention is particularly effective in the case of using a negative electrode active material), tin, tin alloy, or the like as the negative electrode active material.

  The silicon-based negative electrode active material according to this embodiment may be made of silicon, a silicon alloy, SiO, a silicon composite material, or a mixture thereof. Here, silicon has the same meaning as any of Si, silicon, silicon, silicon, and silicon.

The shape of the silicon-based negative electrode active material is not particularly limited. When the silicon-based negative electrode active material is particles, the average particle size is such that an electrochemical reaction easily occurs (Li ⁺ easily inserts into and desorbs from Si), and a thin film (thickness several μm to several tens μm). Considering the ease of forming the electrode, the thickness is preferably several nm to 20 to 30 μm. The average particle diameter is the volume average particle diameter in the particle size distribution measurement by the laser light diffraction method. The silicon-based negative electrode active material may be nanowires or thin pieces. In the case of nanowires, the average diameter thereof is preferably several nm to 20 to 30 μm, and the average length thereof is preferably several μm to 20 to 30 μm. In the case of a thin piece, the thickness is preferably several nm to 20 to 30 μm and the diameter is preferably several μm to 20 to 30 μm. The average diameter or average length in the present invention is obtained by SEM (scanning electron microscope) observation.

The BET method (Brunauer, Emmett, Teller method) of the silicon-based negative electrode active material preferably has a specific surface area of 0.5 to 100 m ² / g, more preferably 1 to ²⁰ m ² / g. If it is less than 0.5 m ² / g, an electrochemical reaction (easiness of Li ⁺ insertion into and desorption from Si) hardly occurs, and if it exceeds 100 m ² / g, the silicon-based negative electrode active material becomes an electrode. If the binder is not added in a larger amount than usual, it becomes difficult to form an electrode and it becomes difficult to reduce the capacity and energy per unit volume of the electrode.

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

  Among the silicon-based negative electrode active materials, silicon is an element having an atomic number of 14 and forms an alloy with lithium.

  Silicon forms alloys with various elements. The silicon alloy according to this embodiment may be any silicon alloy. Elements forming alloys with silicon include 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 silicon alloy may be an intermetallic compound or silicide that forms a compound with silicon in a specific ratio. The 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 is fine nano-sized Si clusters dispersed in a SiO ₂ matrix.

  Examples of the silicon composite material include those obtained by coating the surface of silicon, a silicon alloy or SiO particles with a conductive material such as a carbon material, Al, Ti, Fe, Ni, Cu, Zn, Ag and Sn. For example, a silicon particle whose surface is coated with a carbon material with a thickness of several nm, a graphite powder with a particle diameter of several μm, or a carbon nanotube may be used.

  Although the coating amount of the carbon material is not particularly limited, it is preferably 0.01 to 30% by mass, and 0.1 to 20% by mass with respect to the whole particles obtained by coating the surface of silicon, silicon alloy or SiO particles with the carbon material. Mass% is more preferable. When the coating amount of the carbon material is 0.01% by mass or more, sufficient conductivity can be maintained. As a result, the cycle characteristics of the negative electrode active material for a lithium ion secondary battery can be improved. Further, when the coating amount of the carbon material exceeds 30% by mass, the proportion of the carbon material in the whole active material increases and the discharge capacity decreases.

  The method of coating the surface of silicon, silicon alloy or SiO 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 of coating a polymer on the surface and then pyrolyzing and carbonizing the polymer can be mentioned.

(Coating)
The surface of the particles of the negative electrode active material of this embodiment is coated with a polymer of a catechol derivative.

  Examples of the catechol derivative include dopamine, 3-methylcatechol, 4-methylcatechol, catechol-4-acetic acid, noradrenaline, adrenaline, 3- (3,4-dihydroxyphenyl) -L-alanine, 5,6-dihydroxyindole and catechin. , Isoflavone, gallic acid, ellagic acid, 4-tert-butylpyrocatechol, pyrogallol, 5-sec-butylpyrogallol, 4-phenylpyrogallol, 4-methyl-1,2,3-benzenetriol 4,5,6- Trichloropyrogallol, 4,5,6-trimethylpyrogallol, 4,5-dimethylpyrogallol, 4,6-dimethylpyrogallol and the like can be mentioned.

  Among the above-mentioned catechol derivatives, dopamine is preferable because it has a very good coverage on the surface of the negative electrode active material. The structural formula of dopamine is shown in the following chemical formula (1).

  The catechol derivative is not limited to those exemplified above.

  The coating of the catechol derivative polymer on the negative electrode active material is not limited to this, but includes a wet method, a chemical vapor deposition method, a sputtering method, and the like.

  The wet method will be described below. A flow chart of the wet method is shown in FIG. An aqueous solution in which a catechol derivative is dissolved in water is prepared. The concentration of the catechol derivative in the aqueous solution is 0.001M to 0.5M. If it is less than 0.001M, the amount of the polymer coated on the negative electrode active material is small, and the effect is small. When it exceeds 0.5 M, the amount of the polymer coated on the negative electrode active material is too large, and the discharge capacity per weight or volume of the negative electrode active material decreases, which is not preferable. Further, a polymer which is not coated with the negative electrode active material and precipitates in the aqueous solution is also generated. Therefore, a step of separating the negative electrode active material and the polymer is further required, which is not preferable.

In addition, a buffer solution (buffer agent) may be added to keep the pH of the aqueous solution in an appropriate range. Examples of the buffer solution (buffer agent) are trishydroxymethylaminomethane buffer solution (pH = 8.0), acetate buffer solution (pH = 4.8), glycine buffer solution (pH = 2.4), phosphoric acid. Buffer solution (pH = 2.2), phthalate buffer solution (pH = 4.0), citric acid (pH = 3.1), barbituric acid buffer solution (pH = 4.0), succinate buffer solution ( pH = 4.2), carbonate buffer solution (pH = 6.4), phosphate buffer solution (pH = 7.2), borate buffer solution (pH = 9.2), glycine buffer solution (pH = 9.2). 6) etc.

  The temperature of the aqueous solution is preferably 20 ° C to 60 ° C. When the temperature is lower than 20 ° C, the polymerization is less likely to occur, and when the temperature is higher than 60 ° C, the polymerization rate becomes too fast and the ratio of the polymer which is not coated with the active material and precipitates in the aqueous solution increases.

  In the aqueous solution, the catechol derivative is polymerized on the surface of the negative electrode active material to cover the surface. Oxygen is involved in the polymerization. The oxygen concentration in the aqueous solution is preferably several ppm to the saturated dissolved oxygen concentration. For example, the water temperature and the saturated dissolved oxygen concentration are listed below for reference. The value before the parentheses is the saturated dissolved oxygen concentration, and the water temperature inside the parentheses. 8.84 ppm (20 ° C.), 8.11 ppm (25 ° C.), 7.53 ppm (30 ° C.), 6.59 ppm (40 ° C.), 5.5 ppm (50 ° C.), 5.0 ppm (60 ° C.). Also, oxygen gas may be bubbled into the aqueous solution.

After preparing the catechol derivative aqueous solution, the negative electrode active material to be coated next is added. When the negative electrode active material and the aqueous solution are in contact with each other, the surface of the negative electrode active material is covered with the catechol derivative polymer.
As an example of a catechol derivative polymer, the structural formula of polydopamine is shown in the following chemical formula (2).

式（２）において、ｐ、ｏ、ｎ及びｍは、任意の整数である。

In Formula (2), p, o, n, and m are arbitrary integers.

  When the negative electrode active material is added, the aqueous solution is preferably stirred so that the active material does not settle. Further, in order to prevent the negative electrode active material from settling or to take in oxygen in the atmosphere into the aqueous solution, it is preferable to continue stirring after the addition.

  The timing of introducing the negative electrode active material into the catechol derivative aqueous solution may be as early as possible after preparing the catechol derivative aqueous solution. This is because when the catechol derivative powder is added to water, polymerization of the catechol derivative starts in a short time. For example, when the catechol derivative is dopamine, the polymerization starts within 1 minute. After the catechol derivative aqueous solution was prepared, the polymer of the catechol derivative was deposited in the aqueous solution after a lapse of time without adding the negative electrode active material, and when the negative electrode active material was subsequently added, the catechol to the negative electrode active material was added. The coverage of the derivative polymer is reduced.

Further, it is desirable to add the negative electrode active material to the aqueous solution after preparing the aqueous solution of the catechol derivative. On the contrary, it is not preferable to dissolve the catechol derivative in water after putting the negative electrode active material in water. The reason is that when the negative electrode active material is water-repellent, even if the negative electrode active material is first introduced into water, the negative electrode active material cannot be dispersed in water due to the water repellency. Since the negative electrode active material floats on the surface of water that cannot be dispersed, it becomes difficult to dissolve the catechol derivative in water.

The amount of the catechol derivative polymer coating the surface of the negative electrode active material is determined by appropriately adjusting the following parameters (1) to (6).
(1) Concentration of catechol derivative in aqueous solution (2) Concentration of buffer in aqueous solution (3) Time for dispersing (stirring) negative electrode active material in aqueous solution (4) Ratio of aqueous solution to negative electrode active material (5) Aqueous solution Dissolved oxygen concentration (6) Temperature of aqueous solution

  After the negative electrode active material is dispersed (stirred) in the aqueous solution for a predetermined time, the dispersion is filtered, and the negative electrode active material and the aqueous solution are separated by a filter.

  After the above separation, the negative electrode active material is washed with water (pure water). As a cleaning method, the negative electrode active material remaining on the filter may be vacuumed with water. Alternatively, the negative electrode active material remaining on the filter may be dispersed again in fresh water (pure water) and filtered.

  After filtration, the negative electrode active material is dried to evaporate water. The drying temperature is preferably 60 ° C to 100 ° C in consideration of workability.

(binder)
A binder is added to the negative electrode mixture layer in order to bond the negative electrode active material and the negative electrode active material, the negative electrode active material and the conductive additive, and the negative electrode active material and the current collector. The properties required of the binder are that it does not dissolve in the electrolyte, that it has resistance to reduction, and that it has good adhesion. As the binder used for the negative electrode mixture layer, polyvinylidene fluoride (PVDF) or its copolymer, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl Vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), polyamide (PA), polyimide (PI), polyamide imide (PAI), polybenzimidazole (PBI), styrene butadiene rubber (SBR), carboxymethyl cellulose, polyacrylic acid, maleic anhydride Rafting polypropylene (PP), or the like and mixtures thereof. Of these, polyamideimide is preferable. In addition, polyimide is added as a polyamic acid as a precursor, and heat-treated after forming the electrode to become polyimide.

  The content of the binder in the negative electrode mixture layer 24 is not particularly limited, but it is preferably 1% by mass to 15% by mass, and preferably 3% by mass, based on the total mass of the negative electrode active material, the conductive additive and the binder. It is more preferably from 10 to 10% by mass. By setting the content of the binder within the above range, it is possible to suppress the tendency of the obtained negative electrode mixture layer that the amount of the binder is too small to form a strong negative electrode mixture layer. Further, it is possible to suppress the tendency that the amount of the binder that does not contribute to the discharge capacity increases and it becomes difficult to obtain a sufficient volume energy density. The content of the conductive additive in the negative electrode mixture layer 24 is not particularly limited, but when the conductive additive is added, it is generally preferably 0.5% by mass to 20% by mass with respect to the active material. It is more preferable that the content is from 12 to 12% by mass.

(Conduction Aid) The conduction aid such as the carbon material used in the positive electrode described in paragraph 0036 can be used in the negative electrode.

Next, a method for manufacturing the electrodes 10 and 20 according to the present embodiment will be described. The method of manufacturing the electrodes 10 and 20 according to the present embodiment includes a step of applying a coating material containing an active material, a binder, and a conductive auxiliary agent onto a current collector (hereinafter, may be referred to as “application step”), and a collection step. A step of removing the solvent in the coating material applied on the electric body (hereinafter, sometimes referred to as “solvent removing step”).

(Coating process)
The coating process of coating the current collectors 12 and 22 will be described. The coating material includes an active material, a binder, a conductive additive and a solvent. The method of mixing the components that make up the coating material, such as the active material, the binder, the conductive additive and the solvent, is not particularly limited, and the order of mixing is also 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 the obtained mixture and mixed to prepare a coating material. The active material, the binder, the conductive additive and the solvent described above are applied to the current collectors 12 and 22. The coating method is not particularly limited, and a method that is usually used when producing an electrode can be used. For example, a slit die coating method and a doctor blade method may be mentioned.

(Solvent removal step)
Then, the solvent in the coating material applied on the current collectors 12 and 22 is removed. The removing method is not particularly limited, and the current collectors 12 and 22 to which the coating material is applied may be dried, for example, in an atmosphere of 60 ° C to 150 ° C. Then, the electrodes on which the mixture layers 14 and 24 are thus formed may be thereafter subjected to a press treatment, for example, by a roll press device or the like, if necessary. The linear pressure of the roll press can be, for example, 100 to 1000 kgf / cm.

Through the above steps, the electrode according to this embodiment can be manufactured.

Here, other components 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, and for example, in the present embodiment, an electrolyte solution containing a lithium salt (aqueous electrolyte solution, electrolyte solution using an organic solvent) can be used. However, since the electrolyte aqueous solution has a low decomposition voltage electrochemically, the withstand voltage during charge and discharge is limited to a low level, and therefore an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent is preferable. As the electrolyte solution, a solution obtained by dissolving a lithium salt 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. _{(SO 2 C 2 F 5)} 2, LiN (SO 2 CF 3) (SO 2 C 4 F 9), LiN (COC 2 F 5) 2, a salt such as 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, dimethyl 2,5-dioxahexanedioate, 2, 5, and 5. -Dioxahexane diacid diethyl, furan, 2,5-dimethylfuran, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, dimethoxymethane, dimethoxyethane, 1,2-difuran. 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-ethoxydodecofluorohexane, methylnonafluorobutyl ether, ethylnonafluorobutyl ether and the like are preferable. These may be used alone or as a mixture of two or more kinds at any ratio.

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, and includes, for example, a single-layer microporous film or a laminated microporous film of a film made of polyethylene, polypropylene, or polyolefin, or a dry or wet method of a mixed film of the above polymers. The 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.

(Exterior body)
The outer package 50 seals the laminate 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 intrusion of moisture or the like into the electrochemical device 100 from the outside. For example, as the exterior body 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. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the polymer film 54. For example, a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide is preferable as the material of the outer polymer film 54, and polyethylene (PE), polypropylene (PP) or the like is preferable as the material of the inner polymer film 54. 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, respectively, by a known method, 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. It is only necessary to insert 18 into the exterior body 50 together with the electrolytic solution and heat-seal the inlet of the exterior body 50.

The preferred embodiment of the method for producing the electrode, the electrode obtained thereby, and the lithium ion secondary battery including the electrode has been described in detail above, but the present invention is not limited to the above embodiment. .

For example, the electrodes can be used in electrochemical devices other than lithium ion secondary batteries. Examples include electric double layer capacitors. These electrochemical devices can be used for applications such as mobile phones (including smartphones), notebook personal computers, digital cameras, electric drills, vehicles, and stationary power sources.

(Example)
Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. Experimental conditions such as the type of catechol derivative in each example and comparative example, battery characteristics, and battery thickness are summarized in Tables 1 to 6.

(Example 1)
A battery was manufactured by the following method and evaluated.

<Preparation of negative electrode active material>
To 1000 cm ³ of distilled water, 1.211 g of trishydroxymethane hydrochloride (manufactured by Junsei Chemical Co., Ltd., hereinafter referred to as tris) and 1.896 g of dopamine (manufactured by Tokyo Kasei Kogyo Co., Ltd.) were placed in this order and dissolved. The concentration of tris and dopamine is about 0.01 M (because it was not messed up to 1000 cm ³ , the concentration is about 0.01 M). Here, M = molL ⁻¹ . The pH of this aqueous solution was 8.0. Dopamine polymerizes to form a film on the surface of the negative electrode active material. tris is a pH buffer.
As the negative electrode active material, 40 g of graphite having an average particle size (D ₅₀ ) of 10 μm was prepared. This graphite has a hydrophobic surface and is difficult to disperse in water. 40 g of graphite was added to the above aqueous solution while stirring with a stirrer. The time from the addition of graphite to the end of stirring is called the reaction time. In this example, the reaction time was 220 minutes. The graphite was uniformly dispersed as soon as it was added to the aqueous solution. This aqueous solution was filtered with a filter to take out graphite. Further, this graphite was dispersed in 250 ml of fresh distilled water and filtered. This washing operation was repeated 3 times. The treated graphite was then dried at 60 ° C for 12 hours. By thermogravimetry, the content of polydopamine in the treated graphite was 0.3% by mass. The thickness of polydopamine on graphite was measured by TOF-SIMS (time-of-flight secondary ion mass spectrometry), and it was about 10 nm.

<Production of negative electrode>
The above-mentioned graphite coated with polydopamine, carbon black (DAB50 manufactured by Denki Kagaku Kogyo Co., Ltd.) and a 15 mass% aqueous solution of polyacrylic acid as a binder were weighed in 10 g, 0.231 g and 7.584 g resin containers, respectively. A coating material was prepared by mixing with a stirrer (product name: Hybrid Mixer, manufactured by Keyence Co., Ltd.) that revolves around its axis. This coating material was applied to a copper foil (thickness 10 μm) as a current collector by the doctor blade method, dried at 90 ° C., and rolled at a linear pressure of 600 kgf / cm. This negative electrode was heat-treated at 150 ° C. for 20 hours in a vacuum atmosphere.
In addition, in order to weld the external lead terminals (leads), the current collector was provided with a portion to which no paint was applied. When the negative electrode was analyzed by infrared spectroscopy, an ester bond was confirmed. This ester bond is formed by dehydration condensation of the hydroxyl group of polydopamine and the hydroxyl group of the carboxyl group of polyacrylic acid. That is, polydopamine and polyacrylic acid are covalently bonded.

<Production of positive electrode>
As a positive electrode active material, LiNi _0.8 Co ₀ . ₁₅ Al _0.05 O ₂ 85 g, carbon black (manufactured by Denki Kagaku Kogyo KK, DAB50) 5 g, graphite (manufactured by Timcal KK, trade name: KS-6), and polyvinylidene fluoride as a binder. 50 g of (PVDF) solution (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 paint. This coating material was applied to an aluminum foil (thickness 20 μm) as a current collector by the doctor blade method, dried at 90 ° C. and rolled. In addition, in order to weld the external lead terminals (leads), the current collector was provided with a portion to which no paint was applied.

<Production of battery>
The positive electrode, the negative electrode and the separator (microporous film made of polyolefin) produced as described above were cut into predetermined dimensions. Then, the positive electrode, the negative electrode, and the separator were laminated in this order. When laminating, a small amount of hot melt adhesive (ethylene-methacrylic acid copolymer) was applied and fixed so that the positive electrode, the negative electrode, and the separator were not displaced. 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 property between the external terminal and the outer package, polypropylene (PP) grafted with maleic anhydride was wrapped around and thermally bonded to the external lead terminal. The battery outer casing that encloses the battery element in which the positive electrode, the negative electrode, and the separator are laminated is made of an aluminum laminate material, and its configuration is PET (thickness 12 μm) / Al (thickness 40 μm) / PP (thickness 50 μm). Was prepared (PET is an abbreviation for polyethylene terephthalate). At this time, the bag was made so that the PP was on the inside. Electrolysis in which a battery element was placed in this outer package and LiPF ₆ was dissolved to 1M in an electrolyte solution (a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 30: 70 vol%)). Liquid) was added in an appropriate amount, and the outer casing was vacuum-sealed to produce a lithium ion secondary battery.

(Battery test method)
The charge / discharge test was conducted in a constant temperature bath at 25 ° C. The charge / discharge current notation is hereinafter referred to as C (see) rate notation. nC (mA) is a current that can charge / discharge the nominal capacity (mAh) at 1 / n (h). For example, in the case of a battery having a nominal capacity of 70 mAh, the current of 0.05 C is 3.5 mA (calculation formula 70 × 0.05 = 3.5). Similarly, the 0.2C current is 14 mA and the 2C current is 140 mA. In the first cycle, the battery was charged at 0.05 C for 3 hours and then charged at 0.2 C to a constant current constant voltage (referred to as CCCV) up to 4.2V. The discharge was 0.2 C to 3.0 V. For the charging after the second cycle, CCCV charging was performed at 0.5 C to 4.2 V. From the 2nd cycle to the 9th cycle, the discharge current was discharged at 0.2C, 0.5C, 1C and 2C for 2 cycles each, and the discharge rate characteristics of the battery were examined. The discharge capacity at each discharge rate was standardized with the average value of the 0.2 C discharge capacity set to 100. Table 2 shows the 2C discharge capacity.

  In addition, a cycle characteristic test (cycle life test) was performed on another battery. The charge and discharge conditions were 0.5 C, CCCV charge up to 4.2 V, and 1 C discharge up to 3.0 V. This charging / discharging was repeated up to 500 icules. Table 2 shows the relationship between the number of cycles and the discharge capacity. In Table 2, the discharge capacity in the first cycle is 100 and the discharge capacity in the 500th cycle is standardized (referred to as relative discharge capacity).

(Battery thickness change rate)
Further, the battery thickness before the start of charging / discharging and the battery thickness after the end of the rate characteristic, that is, after the ninth cycle were measured, and the battery thickness change rate defined by the following formula (3) was obtained.
Battery thickness change rate (%) = Battery thickness after 9th cycle discharge / Battery thickness before charge / discharge is started × 100 (3)
The results are shown in Table 2.

(Example 2)
The same procedure as in Example 1 was carried out except that the negative electrode active material was changed to silicon having D ₅₀ of 10 μm and the reaction time was changed to 5 minutes.

(Example 3)
The same procedure as in Example 2 was repeated except that the reaction time was 15 minutes.

(Example 4)
The procedure of Example 2 was repeated except that the reaction time was 1 hour and 40 minutes.

(Example 5)
The procedure of Example 2 was repeated except that the reaction time was 3 hours and 30 minutes.

(Example 6)
The same procedure as in Example 2 was repeated except that the reaction time was 7 hours and 10 minutes.

(Example 7)
The procedure of Example 2 was repeated except that the reaction time was 18 hours and 40 minutes.

(Example 8)
The procedure of Example 2 was repeated except that the reaction time was 36 hours and 30 minutes.

(Example 9)
The same procedure as in Example 2 was repeated except that the reaction time was 56 hours.

(Example 10)
The procedure of Example 2 was repeated except that the reaction time was changed to 75 hours.

(Example 11)
The same procedure as in Example 2 was repeated except that the reaction time was 79 hours.

(Example 12)
The same procedure as in Example 5 was performed except that gallic acid was used as the catechol derivative.

(Example 13)
The same procedure as in Example 5 was performed except that pyrogallol was used as the catechol derivative.

(Example 14)
The same procedure as in Example 5 was performed except that 3-methylcatechol was used as the catechol derivative.

(Example 15)
The same procedure as in Example 5 was carried out except that 4-methylcatechol was used as the catechol derivative.

(Example 16)
The same procedure as in Example 5 was performed except that catechol-4-acetic acid was used as the catechol derivative.

(Example 17)
The same procedure as in Example 5 was repeated except that norepinephrine was used as the catechol derivative.

(Example 18)
The same procedure as in Example 5 was performed except that the catechol derivative was changed to adrenaline.

(Example 19)
The procedure of Example 5 was repeated, except that the catechol derivative was 3- (3,4-dihydroxyphenyl) -L-alanine.

(Example 20)
The procedure of Example 5 was repeated except that the catechol derivative was 5,6-dihydroxyindole.

(Example 21)
The same procedure as in Example 5 was performed except that catechin was used as the catechol derivative.

(Example 22)
The same procedure as in Example 5 was carried out except that isoflavone was used as the catechol derivative.

(Example 23)
The same procedure as in Example 5 was carried out except that ellagic acid was used as the catechol derivative.

(Example 24)
The same procedure as in Example 5 was performed except that the catechol derivative was 4-tert-butylpyrocatechol.

(Example 25)
The same procedure as in Example 5 was carried out except that 5-sec-butylpyrogallol was used as the catechol derivative.

(Example 26)
The same procedure as in Example 5 was carried out except that 4-phenylpyrogallol was used as the catechol derivative.

(Example 27)
The same procedure as in Example 5 was repeated except that the catechol derivative was 4-methyl-1,2,3-benzenetriol.

(Example 28)
The same procedure as in Example 5 was repeated except that the catechol derivative was 4,5,6-trichloropyrogallol.

(Example 29)
The same procedure as in Example 5 was repeated except that the catechol derivative was 4,5,6-trimethylpyrogallol.

(Example 30)
The procedure of Example 5 was repeated except that the catechol derivative was 4,5-dimethylpyrogallol.

(Example 31)
The procedure of Example 5 was repeated except that the catechol derivative was 4,6-dimethylpyrogallol.

(Example 32)
The same procedure as in Example 5 was performed except that the negative electrode active material was changed to SiO 2. This SiO is a particle having an average particle diameter (D ₅₀ ) of 5 μm, and Si particles of nm size are dispersed in SiO ₂ . In addition, the surface of the SiO particles is covered with amorphous carbon.

(Example 33)
The same procedure as in Example 5 was carried out except that the water-soluble polyamide was used as the polyacrylic acid.

(Example 34)
The same operation as in Example 5 was performed, except that polyacrylic acid was changed to polyimide and the heat treatment condition of the negative electrode was changed to 350 ° C. under vacuum for 3 hours.

(Example 35)
The same operation as in Example 5 was performed except that the polyacrylic acid was changed to polyamideimide and the heat treatment conditions of the negative electrode were changed to 350 ° C. for 3 hours under vacuum.

(Example 36)
The same operation as in Example 5 was carried out except that the polyacrylic acid was changed to an ethylene-acrylic acid copolymer.

(Example 37)
The same operation as in Example 5 was performed except that the polyacrylic acid was changed to an ethylene-methacrylic acid copolymer.

(Example 38)
The same operation as in Example 5 was carried out except that the polyacrylic acid was changed to an ethylene-hydroxyvinyl acid copolymer.

(Example 39)
The same operation as in Example 5 was performed except that polyacrylic acid was changed to an acrylic acid ester-aminoethyl acrylate copolymer.

(Example 40)
The same operation as in Example 5 was performed except that the negative electrode was not heat-treated at 150 ° C. for 20 hours in a vacuum atmosphere. When the negative electrode was analyzed by infrared spectroscopy, hydrogen bonding was confirmed. This hydrogen bond is formed by a hydroxyl group of polydopamine and a hydroxyl group of a carboxyl group of polyacrylic acid.

(Comparative Example 1)
The same operation as in Example 1 was performed except that graphite not coated with the catechol derivative was used as the negative electrode active material.

(Comparative example 2)
The same operation as in Example 1 was performed except that silicon not coated with the catechol derivative was used as the negative electrode active material.

(Comparative example 3)
The same operation as in Example 1 was performed except that SiO that did not cover the catechol derivative was used as the negative electrode active material.

(Comparative example 4)
The same operation as in Comparative Example 2 was performed except that the polyacrylic acid was changed to a water-soluble polyamide.

(Comparative example 5)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to polyimide and the heat treatment condition of the negative electrode was changed to 350 ° C. under vacuum for 3 hours.

(Comparative example 6)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to polyamide-imide and the heat treatment condition of the negative electrode was changed to 350 ° C. under vacuum for 3 hours.

(Comparative Example 7)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to the ethylene-acrylic acid copolymer.

(Comparative Example 8)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to an ethylene-methacrylic acid copolymer.

(Comparative Example 9)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to the ethylene-vinyl hydroxide copolymer.

(Comparative Example 10)
The same operation as in Comparative Example 2 was performed except that the binder of the negative electrode was changed to an acrylic acid ester-aminoethyl acrylate copolymer.

(Comparative Example 11)
The same operation as in Comparative Example 2 was performed except that the negative electrode was not heat-treated at 150 ° C. for 20 hours in a vacuum atmosphere.

(Comparative Example 12)
A negative electrode was produced by the same method as in Patent Document 1.
<Production of negative electrode>
Silicon having D50 of 10 μm, carbon black (DAB50 manufactured by Denki Kagaku Kogyo Co., Ltd.), polyamic acid (Pyre-ML (registered trademark) 5019, number average molecular weight 100000) as a binder material for a binder, and a binder improving agent. Of diethyl pyromellitic acid (PMA-Et) of 10 g, 0.231 g, 1.138 g and 0.1 g, respectively, are weighed in a resin container and revolved around a rotation axis (agitator manufactured by KEYENCE CORPORATION, product name: hybrid mixer). And mixed to prepare a paint. This coating material was applied to a copper foil (thickness 10 μm) as a current collector by the doctor blade method, dried at 90 ° C., and rolled at a linear pressure of 600 kgf / cm. Then, a negative electrode was produced by heat-treating at 300 ° C. for 30 minutes under a vacuum condition (oxygen partial pressure: 26 Pa). The heat treatment converts the polyamic acid into polyimide (PI). In addition, in order to weld the external lead terminals (leads), the current collector was provided with a portion to which no paint was applied. Otherwise, the procedure was the same as in Example 1.

  Table 1 summarizes the catechol derivative, the negative electrode active material, the thickness of the polymer on the negative electrode active material, the content of the catechol polymer in the negative electrode active material, the type of binder, and the functional group of the binder.

  Table 2 shows heat treatment conditions, tris concentration, catechol derivative concentration, reaction time, relative discharge capacity after 500 cycles, 2C discharge capacity, and battery thickness change rate.

  As can be seen from Table 2, Examples 1 to 40 using the negative electrode active material for a lithium ion secondary battery whose surface was coated with a polymer of a catechol derivative were compared with Comparative Examples 1 to 11 which were not coated, The capacity retention rate after 500 cycles was improved. In addition, the 2C discharge capacity was large. Further, the battery thickness change rate was also small, and it was confirmed that the lithium ion secondary battery was excellent in cycle characteristics, rate characteristics and dimensional stability.

  Comparing Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, Example 32 with Comparative Example 3, and Examples 33 to 39 with Comparative Examples 4 to 10, the weight of the catechol derivative on the surface of the negative electrode active material was compared. It can be seen that by covering the coalescence, a lithium ion secondary battery having excellent battery characteristics (cycle characteristics and rate characteristics) and dimensional stability can be obtained.

Further, in Examples 2 to 11, the thickness of the polymer of the catechol derivative is changed. According to this, when the thickness of the polymer is 1 nm or less, the improvement of the adhesion between the negative electrode active material and the binder, the negative electrode active material and the current collector, or the negative electrode active material and the conductive additive becomes insufficient, and the cycle There is a risk that the degree of improvement in characteristics will be small. Further, if the thickness of the polymer exceeds 200 nm, it becomes a resistance to Li ⁺ diffusion, and the rate characteristics may be deteriorated.

  Further, comparing Example 5 and Examples 12 to 31 with Comparative Example 2, a lithium ion secondary battery having excellent battery characteristics (rate characteristics and cycle characteristics) and dimensional stability can be obtained even with various catechol derivatives. I understand. Among various catechol derivatives, those using dopamine, gallic acid and pyrogallol are excellent in cycle characteristics.

  Further, comparing Example 5 and Examples 33 to 39 with Comparative Example 2 and Comparative Examples 4 to 10, the kind of binder is changed, but polyamide, polyimide or polyamide-imide is particularly excellent in cycle characteristics. .

  In addition, comparing Example 5 with Example 40, it can be seen that when heat treatment is performed as in Example 5, a lithium ion secondary battery having excellent rate characteristics, cycle characteristics and dimensional stability can be obtained. The reason for this is considered as follows. When heat-treated, the hydroxyl group in the polymer of the catechol derivative and the hydroxyl group present in the binder in the negative electrode are dehydrated and condensed to form a covalent bond. As a result, the negative electrode active material particles and the binder are firmly bonded to each other as compared with the case where the heat treatment is not performed. Similarly, hydroxyl groups are present on the surface of the copper foil which is the current collector or the surface of carbon black which is the conductive additive. The hydroxyl group and the hydroxyl group in the polymer of the catechol derivative are also dehydrated and condensed by heat treatment to form a covalent bond. As a result, the bond is stronger than in the case where no heat treatment is performed. In this way, since the active material and the binder, the current collector, and the conductive auxiliary agent are firmly bonded, the active material peels from the binder, the current collector, and the conductive auxiliary agent even when the active material expands and contracts. Since it is difficult, cycle characteristics are improved.

  When the negative electrode was not heat-treated as in Example 40, dehydration condensation did not occur. Therefore, it remains a hydrogen bond. Although hydrogen bonds are weaker than covalent bonds, cycle characteristics are improved in the same manner as above. In addition, an increase in battery thickness is suppressed as compared with the comparative example in which the polymer film of the catechol derivative is not provided.

  In addition, comparing Example 34 with Comparative Example 12, when the surface of the negative electrode active material was coated with a polymer of a catechol derivative, the battery characteristics (cycle characteristics and rate characteristics) and dimensional stability were better than those of diethyl pyromellitic acid. It can be seen that a lithium ion secondary battery having excellent properties is obtained.

The present invention is not limited to the above embodiment. The above-described embodiment is merely an example, and the present invention has substantially the same configuration as the technical idea described in the scope of claims of the present invention It is included in the technical scope of.

Claims (10)

Contains any one of a metal containing Si as a main component, a metal containing Sn as a main component, and SiO,
A negative electrode active material for a lithium ion secondary battery, having a coating film containing a polymer of a catechol derivative formed on the surface.   The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the coating has a thickness of 1 nm to 200 nm.   The catechol derivative is dopamine, gallic acid, pyrogallol, 3-methylcatechol, 4-methylcatechol, catechol-4-acetic acid, noradrenaline, adrenaline, 3- (3,4-dihydroxyphenyl) -L-alanine, 5, 6 -Dihydroxyindole, catechin, isoflavone ellagic acid, 4-tert-butylpyrocatechol, 5-sec-butylpyrogallol, 4-phenylpyrogallol, 4-methyl-1,2,3-benzenetriol, 4,5,6-trichloro The negative electrode active material for a lithium ion secondary battery according to claim 1 or 2, which is at least one selected from the group consisting of pyrogallol, 4,5,6-trimethylpyrogallol, 4,5-dimethylpyrogallol and 4,6-dimethylpyrogallol. material. A negative electrode for a lithium ion secondary battery, wherein a mixture layer containing the negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3 and a binder is formed on a negative electrode current collector. . The negative electrode for a lithium ion secondary battery according to claim 4 , wherein the binder is a polymer having a hydroxyl group, a carboxyl group, an amino group, an amide group or an imide group. The binder is selected from the group consisting of polyacrylic acid, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl hydroxide copolymer, acrylic ester-aminoethyl acrylate copolymer, polyamic acid. The negative electrode for a lithium ion secondary battery according to claim 4 , which is one selected from the above or a mixture thereof. The negative electrode for a lithium ion secondary battery according to claim 4 , wherein the binder is polyamide, polyimide, polyamideimide, or a mixture thereof. The negative electrode for a lithium ion secondary battery according to claim 6 , wherein the polymer of the catechol derivative and the binder are covalently bonded. The negative electrode for a lithium ion secondary battery according to claim 7 , wherein the polymer of the catechol derivative and the binder are hydrogen-bonded. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to any one of claims 4 to 9 , an electrolyte, and a positive electrode.

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