JP2017152337A - Negative electrode for nonaqueous lithium ion secondary battery, manufacturing method thereof, and nonaqueous lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode arranged by use of graphite as a negative electrode active material, which can be manufactured with aqueous materials, and which can improve lithium ion input and output characteristics and the endurance against Li precipitation.SOLUTION: A negative electrode for a nonaqueous lithium ion secondary battery according to the present invention comprises: graphite; a hydrophilic carbon black; and an aqueous binder. Supposing that the average particle diameter of the graphite is r, the specific weight is d, the average particle diameter of the hydrophilic carbon black is r, the specific weight is d, and the percentage of the hydrophilic carbon black added to the graphite is x mass%, a coverage (=x(r/4r)(d/d)), which is a percentage of the hydrophilic carbon black coating the graphite, is 6.1-46.4%.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode for a non-aqueous lithium ion secondary battery, a method for producing the same, and a non-aqueous lithium ion secondary battery.

Non-aqueous lithium ion secondary batteries have already been put to practical use in fields related to information communication equipment such as personal computers and mobile phones because they can not only achieve high voltage and high energy density, but also can be reduced in size and weight. In recent years, it is also used as a power source mounted on electric vehicles and hybrid vehicles due to resource issues and environmental issues. Such a non-aqueous lithium ion secondary battery is composed of a lithium transition metal composite oxide as a positive electrode active material, a carbon material as a negative electrode active material, and a Li salt dissolved in an organic solvent as an electrolytic solution. Generally, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and their derivatives having a layered structure or a spinel structure are used as the positive electrode active material, and graphite, amorphous carbon, alloy, etc. are used as the negative electrode active material Has been. In many cases, LiPF ₆ is used as the electrolyte solvent, which is a mixture of combustible chain carbonate and cyclic carbonate, and lithium salt because of its high conductivity.

  However, since the non-aqueous lithium ion secondary battery exhibits a high negative electrode reaction resistance particularly at low temperatures, there is a big problem that low temperature input / output is low. Moreover, since it shows a very low charge / discharge potential close to the potential of Li, there is a concern of Li precipitation due to an increase in polarization at the time of input at a low temperature. For this reason, it has been proposed to improve the input / output of a lithium ion secondary battery by coating the surface of graphite particles with pitch, an organic compound or a polymer compound and firing or graphitizing (Patent Documents 1 to 4).

  On the other hand, it has been reported that charge / discharge characteristics are improved by supporting graphitized nanocarbon particles or amorphous carbon particles such as carbon black on the surface of the graphite particles. For example, a method of attaching carbonaceous or graphite particles to hydrophilic graphite particles (Patent Document 5), a method of adding carbon black to graphite (Patent Document 6), a graphite raw material and carbon black are mixed and heat-treated. Thus, a method of fixing carbon black on the graphite surface (Patent Document 7) has been proposed.

JP-A-5-307959 Japanese Patent No. 5061437 Japanese Patent No. 5153055 Japanese Patent No. 5772939 JP 2005-243447 A JP 2004-171901 A JP 2003-346804 A

  However, in Patent Documents 1 to 4, when the dispersion medium of the binder used to produce the negative electrode is an aqueous solvent, the conductivity between the particles is not sufficient, and thus the charge / discharge characteristics may not be sufficiently exhibited. In addition, the use of aqueous solvents and binders is desired for safety and environmental considerations when coating negative electrodes, and excellent charge / discharge characteristics are exhibited even when aqueous solvents and binders are used. There is a need for surface modification of graphite particles.

  Moreover, in patent documents 5-7, although the electrical conductivity between particle | grains is improved, it is not fundamental improvement with respect to the increase in the negative electrode reaction resistance especially in low temperature. Also, by supporting carbon black on the surface of the graphite particles, the surface of the graphite particles becomes hydrophobic, so that aggregation is likely to occur during negative electrode coating using an aqueous solvent / binder, and a uniform coating film is obtained. It becomes difficult.

  The present invention has been made to solve such problems, and in a negative electrode using graphite as a negative electrode active material, it can be manufactured in an aqueous system, and improves the input / output characteristics of lithium ions and Li precipitation resistance. Main purpose.

  As a result of diligent research to achieve the above-mentioned object, the present inventors have found that the object can be achieved by adding an appropriate amount of hydrophilic carbon black to graphite as a negative electrode active material, and the present invention has been completed. It was.

That is, the negative electrode for a non-aqueous lithium ion secondary battery according to the present invention includes graphite as a negative electrode active material, hydrophilic carbon black, and an aqueous binder. (1) The average particle diameter of the graphite is r ₁ , and the specific gravity. Is d ₁ , the average particle diameter of the hydrophilic carbon black is r ₂ , the specific gravity is d ₂ , and the addition ratio of the hydrophilic carbon black to the graphite is x mass%, the hydrophilic carbon black contains the graphite. Whether the covering ratio (= x (r ₁ / 4r ₂ ) (d ₁ / d ₂ )), which is the covering ratio, is 6.1% to 46.4%, or (2) the hydrophilic carbon black Is added to the graphite in an amount of 0.2% by mass or more and 1.5% by mass or less. Note that the units of r ₁ and r _{2 and} the units of d ₁ and d ₂ are the same (the same applies hereinafter).

  The non-aqueous lithium ion secondary battery of the present invention includes the above-described negative electrode for a non-aqueous lithium ion secondary battery, a positive electrode, and a non-aqueous electrolyte.

  The method for producing a negative electrode for a non-aqueous lithium ion secondary battery according to the present invention includes: (1) a covering ratio of 6.1% to 46.4% in a negative electrode paint containing graphite and an aqueous binder, or (2) Obtained after adding and mixing an aqueous dispersion of the hydrophilic carbon black such that the ratio of the hydrophilic carbon black to the graphite is 0.2% by mass or more and 1.5% by mass or less. The mixed liquid is applied onto a negative electrode current collector and dried, and then subjected to a rolling treatment to form a negative electrode.

  In the negative electrode for a non-aqueous lithium ion secondary battery of the present invention, an appropriate amount of hydrophilic carbon black is supported on the surface of graphite particles as a negative electrode active material. Thereby, it becomes possible to manufacture by an aqueous system. In addition, input / output characteristics of lithium ions and Li precipitation resistance are improved. The reason is presumed as follows. Lithium ions are stabilized in a non-aqueous electrolyte in a structure in which a solvent is coordinated, that is, in a solvated state. When this solvated lithium ion is inserted into the graphite as the negative electrode active material, it is desolvated by the action of the SEI coating and the lithium ion is inserted into the graphite. In the process of inserting lithium ions, it has been reported that the activity barrier in the process of desolvation of lithium ions is particularly large and rate limiting (J. Electochem. Soc., 152, A2151 (2005)). The effect of improving the lithium ion input / output characteristics and Li precipitation resistance described above is to support an appropriate amount of hydrophilic carbon black on the graphite surface, thereby reducing the active barrier of the lithium ion desolvation process and reducing the negative electrode reaction. It is presumed that it was obtained because the resistance was reduced.

The schematic diagram which shows an example of the non-aqueous lithium ion secondary battery 20 of this invention. The graph which shows the relationship between the addition ratio (mass%) with respect to graphite of hydrophilic carbon black, the coverage of hydrophilic carbon black, and Li precipitation limit electric current value. The SEM photograph of the negative electrode sheet | seat without hydrophilic carbon black addition. The SEM photograph of the negative electrode sheet which added 1 mass% of hydrophilic carbon black. The SEM photograph of the negative electrode sheet which added 5 mass% of hydrophilic carbon black.

The non-aqueous lithium ion secondary battery of the present invention includes a negative electrode for a non-aqueous lithium ion secondary battery, a positive electrode, and a non-aqueous electrolyte. Among these, the negative electrode for non-aqueous lithium ion secondary batteries includes graphite as a negative electrode active material, hydrophilic carbon black, and an aqueous binder. (1) The average particle diameter of graphite is r ₁ and the specific gravity is d _1. , When the average particle diameter of hydrophilic carbon black is r ₂ , the specific gravity is d ₂ , and the addition ratio of hydrophilic carbon black to graphite is x mass%, The coverage of the formula is 6.1% or more and 46.4% or less, or (2) the addition ratio of hydrophilic carbon black to graphite is 0.2% by mass or more and 1.5% by mass or less.
Coverage (%) = x (πr ₂ ² / 4πr ₁ ² ) (r ₁ ³ / r ₂ ³ ) (d ₁ / d ₂ )
= X (r ₁ / 4r ₂ ) (d ₁ / d ₂ )

(Negative electrode)
The negative electrode for non-aqueous lithium ion secondary batteries includes graphite as a negative electrode active material, hydrophilic carbon black, and an aqueous binder.

  Examples of graphite include artificial graphite, pyrolytic graphite and the like, in addition to natural graphite such as flaky graphite and flaky graphite.

  Hydrophilic carbon black is a carbon black that can maintain a dispersed state in an aqueous solvent (a solvent mainly composed of water, particularly water) without adding a surfactant or the like. It has been. Hydrophilic carbon black is characterized by having a functional group such as a carboxyl group or a hydroxyl group on the particle surface, thereby preventing aggregation of particles in an aqueous solvent and exhibiting high dispersibility. In the case of hydrophilic carbon black, generally, these functional groups are present on the surface of carbon black in an amount of 50 μmol / g or more, so that high dispersibility can be exhibited. The ratio (coverage) of the hydrophilic carbon black covering graphite is preferably 6.1% or more and 46.4% or less, and more preferably 14.7% or more and 36.7% or less. If the coverage is less than 6.1%, the input / output characteristics of lithium ions and the resistance to Li precipitation are not sufficiently improved, which is not preferable. If the coverage exceeds 46.4%, the Li deposition resistance and the initial charge / discharge efficiency decrease, which is not preferable. The reason why the Li precipitation resistance is lowered is considered to be that the graphite particle surface is coated with a plurality of layers of hydrophilic carbon black and the conduction process of lithium ions is hindered. Moreover, the addition ratio of hydrophilic carbon black to graphite is preferably 0.2% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 1.2% by mass or less. When the addition ratio is less than 0.2% by mass, the input / output characteristics of lithium ions and the resistance to Li precipitation are not sufficiently improved, which is not preferable. On the other hand, when the addition ratio exceeds 1.5% by mass, the Li precipitation resistance and the initial charge / discharge efficiency decrease, which is not preferable. The reason why the Li precipitation resistance is lowered is considered to be that the graphite particle surface is coated with a plurality of layers of hydrophilic carbon black and the conduction process of lithium ions is hindered.

  An aqueous binder refers to a binder using water as a solvent or dispersion medium. Examples of the water-based binder include thermoplastic resins, polymers having rubber elasticity, polysaccharides, and the like, and a mixture thereof may be used. Specifically, for example, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, styrene butadiene rubber, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, Examples include polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and cellulose resin (carboxymethyl cellulose, hydroxypropyl cellulose, etc.). . Among these, a mixed binder of styrene-butadiene rubber and carboxymethyl cellulose is preferable because of its high binding force.

  The negative electrode is a negative electrode paint containing graphite and a water-based binder, and (1) the coverage is 6.1% or more and 46.4% or less, or (2) the ratio of addition of hydrophilic carbon black to graphite is After adding and mixing an aqueous dispersion of hydrophilic carbon black so that the content is 0.2% by mass or more and 1.5% by mass or less, the obtained mixed solution is applied onto the negative electrode current collector and dried. Then, it may be produced by rolling. Examples of the aqueous dispersion of hydrophilic carbon black include Aqua-Black 162 and Aqua-Black 001 manufactured by Tokai Carbon Co., Ltd. The negative electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil or mesh formed of a metal such as copper, stainless steel, or nickel-plated steel can be used. The thickness of the negative electrode current collector is, for example, 1 to 500 μm. According to this manufacturing method, when a mixed liquid obtained by adding an aqueous dispersion of hydrophilic carbon black to a negative electrode coating is applied to the negative electrode current collector, no aggregation occurs in the mixed liquid and a uniform coating film is obtained. It becomes possible.

(Positive electrode)
For the positive electrode, for example, a positive electrode active material, a conductive material, and a binder are mixed, and an appropriate solvent is added to form a paste-like positive electrode mixture, which is applied to the surface of the positive electrode current collector and dried. The electrode may be compressed to increase the electrode density.

As the positive electrode active material, an oxide containing lithium and a transition metal element can be used. Specifically, lithium manganese composite oxides such as LiMnO ₂ and LiMn ₂ O ₄ , lithium cobalt composite oxides such as LiCoO ₂ , LiNiO ₂ and LiNi _x M _1-x O ₂ (x is 0 <x <1, M is a metal element other than Li and Ni, and is preferably one or more selected from the group consisting of Co, Mn, Fe, Mg, and Al), LiV ₂ O _{3 and the} like A lithium vanadium composite oxide or the like can be used.

  The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black (AB), A mixture of one or more of carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability.

  The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used.

  Examples of the solvent for dispersing the positive electrode active material, the conductive material, and the binder include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N-dimethyl. Organic solvents such as aminopropylamine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more.

  Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape.

  The positive electrode current collector includes aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum and copper for the purpose of improving adhesion, conductivity and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the positive electrode current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber group formed body. The thickness of the positive electrode current collector is, for example, 1 to 500 μm.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, a supporting salt (lithium salt) is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate (DEC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl Chain carbonates such as n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate and t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, Chain esters such as methyl formate, methyl acetate, ethyl acetate, methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, diethoxyethane, acetonitrile, benzonitrile, etc. Nitriles, tetrahydrofurans such as tetrahydrofuran and methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, Examples include LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. The supporting salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. If the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and if it is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

(Secondary battery)
The non-aqueous lithium ion secondary battery of the present invention may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the non-aqueous electrolyte. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin fine olefin resin such as polyethylene or polypropylene is used. A porous membrane is mentioned. These may be used alone or in combination. The shape of the nonaqueous lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a rectangular type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. FIG. 1 is a schematic view showing an example of a non-aqueous lithium ion secondary battery 20 of the present invention. The non-aqueous lithium ion secondary battery 20 includes a cup-shaped metal battery case 21, a positive electrode 22 having a positive electrode active material, and a negative electrode active material having a negative electrode active material. A negative electrode 23 provided at a position facing the separator 24 via a separator 24, a gasket 25 formed of an insulating material, and a battery case 21 disposed in the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. And a metal sealing plate 26. In this non-aqueous lithium ion secondary battery 20, a non-aqueous electrolyte solution 27 is filled between a positive electrode 22 and a negative electrode 23. Further, as described above, the negative electrode 23 includes graphite as a negative electrode active material, hydrophilic carbon black, and an aqueous binder, and (1) the coverage is 6.1% or more and 46.4% or less. (2) The addition ratio of hydrophilic carbon black to graphite is 0.2% by mass or more and 1.5% by mass or less.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[Experimental Example 1]
(Battery production)
Spherical natural graphite particles (average particle size 10 μm) were prepared as the negative electrode active material, and a mixture of styrene-butadiene rubber and carboxymethyl cellulose was prepared as the aqueous binder. Spherical natural graphite particles, styrene-butadiene rubber, and carboxymethyl cellulose were weighed so as to have a mass ratio of 98: 1: 1, and these materials were dispersed in water. To this, a hydrophilic carbon black dispersion (manufactured by Tokai Carbon Co., Ltd., Aqua-Black 162, average particle size 100 nm, the same applies hereinafter) was added and kneaded to prepare a composition for forming a negative electrode mixture layer. When the average particle diameter of graphite is r ₁ , the specific gravity is d ₁ , the average particle diameter of hydrophilic carbon black is r ₂ , the specific gravity is d ₂ , and the addition ratio of hydrophilic carbon black to graphite is x mass%. The ratio of hydrophilic carbon black to graphite so that the covering ratio (= x (r ₁ / 4r ₂ ) (d ₁ / d ₂ )), which is the ratio in which carbon black covers graphite, is 30.6%. The addition ratio was set to 1% by mass, and the total mass of graphite and hydrophilic carbon black was adjusted to be 98% by mass of the above-mentioned 98: 1: 1. This was applied to a negative electrode current collector (copper foil) having a thickness of 10 μm so that the basis weight of the composite material was 5 mg / cm ² . Then, it is dried in a vacuum at 120 ° C. for 6 hours, and is subjected to a rolling process using a roll press, thereby forming a negative electrode mixture layer having a mixture density of 1.1 g / cm ^{3 on} the negative electrode current collector. A negative electrode sheet was prepared. The specific gravity d ₁ was 2.2 g / cm ³ and the specific gravity d ₂ was 1.8 g / cm ³ .

  SEM observation was performed in order to confirm the hydrophilic carbon black dispersion degree of the graphite particle surface in the produced negative electrode sheet. SEM observation was performed using Hitachi High-Technologies S-3600N at an acceleration voltage of 10 kV and an observation magnification of 10,000 times.

LiNi _0.8 Co _0.15 Al _0.05 O ₂ that is a positive electrode active material, acetylene black (AB) that is a conductive material, and PVDF that is a binder are weighed so as to have a mass ratio of 85: 10: 5. The material was dispersed in NMP to prepare a paste-like composition for forming a positive electrode mixture layer. This was applied to a positive electrode current collector (aluminum foil) having a thickness of 15 μm so that the basis weight of the composite material was 7 mg / cm ² . Then, it is dried in a vacuum at 120 ° C. for 6 hours, and subjected to a rolling process using a roll press machine, whereby a positive electrode mixture layer having a mixture density of 2.1 g / cm ³ is formed on the positive electrode current collector. A positive electrode sheet was prepared.

A part of the mixture of the positive electrode sheet was peeled off and an aluminum positive electrode terminal was attached by ultrasonic welding. Similarly, a part of the mixture of the negative electrode sheet was peeled off, and a nickel negative electrode terminal was attached by ultrasonic welding. An aluminum laminate cell was manufactured by using a single-layer separator made of polyethylene for the positive electrode sheet and the negative electrode sheet to which each terminal was attached. As the non-aqueous electrolyte, a solution in which 1M LiPF ₆ was dissolved in a non-aqueous solvent having a volume ratio of EC, DMC, and EMC of 3: 4: 3 was used. The following evaluation was performed using the 10 mAh-class aluminum laminate cell thus produced.

(Battery evaluation)
The aluminum laminate cell was charged and discharged in an environment of 20 ° C. The charging / discharging conditions reached 4.1V by constant current charging of 2 mA, and then discharged to 3.0 V by constant current of 2 mA. The initial charge / discharge efficiency was calculated from the charge capacity and discharge capacity. The battery after the first charge / discharge was adjusted to SOC 50% (battery voltage 3.7V), and then the battery was kept in an environment of −10 ° C., and AC impedance measurement was performed (amplitude voltage 5 mV, frequency range). 100 kHz to 0.002 Hz). The resistance of the high frequency side arc was calculated by fitting the obtained impedance spectrum to an equivalent circuit, and this was used as the negative electrode reaction resistance (J. Power Sources., 174, 1131 (2007)).

  Li precipitation durability evaluation was performed as follows. First, in order to evaluate the battery capacity before the durability test, the battery was subjected to constant current charging (2 mA) to 4.1 V in a 20 ° C. environment, and then constant voltage charging was performed at 4.1 V for 1 hour. Then, after carrying out a constant current discharge (2mA) to 3V, the constant voltage discharge was implemented at 3V for 1 hour. The discharge capacity calculated in this way was defined as the capacity before durability. The Li precipitation durability test was performed as follows. After maintaining the battery adjusted to SOC 50% (battery voltage 3.7V) in an environment of −10 ° C., charge at 100 mA for 20 seconds, pause for 5 minutes, and then discharge at 100 mA for 20 seconds. A pause was established. After repeating this cycle 50 times, the capacity was evaluated in the same procedure as before the endurance, and the capacity retention ratio before and after the endurance was calculated. Perform the same durability test at 120 mA, 140 mA, 160 mA, 180 mA, and 200 mA, extrapolate the current value with a capacity retention rate of 95%, calculate the current value per mass of the negative electrode mixture, and determine the Li precipitation limit It was defined as the current value.

[Experiment 2]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1, except that the negative electrode sheet was prepared with the addition ratio of hydrophilic carbon black to graphite so that the coverage was 15.3%. It was.

[Experiment 3]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1 except that the negative electrode sheet was prepared without adding hydrophilic carbon black.

[Experimental Example 4]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1 except that the negative electrode sheet was prepared with the addition ratio of hydrophilic carbon black to graphite being 0.1% by mass so that the coverage was 3.1%. It was.

[Experimental Example 5]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1, except that the negative electrode sheet was prepared by setting the addition ratio of hydrophilic carbon black to graphite so that the coverage was 61.1%.

[Experimental Example 6]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1, except that the negative electrode sheet was prepared by setting the addition ratio of hydrophilic carbon black to graphite so that the coverage was 91.7%.

[Experimental Example 7]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1 except that the negative electrode sheet was prepared by setting the addition ratio of hydrophilic carbon black to graphite so that the coverage was 152.8%.

[Experimental Example 8]
Except for producing a negative electrode sheet by adding 0.5% by mass of carbon black (Tokai Carbon Co., Ltd., Talker Black # 5500, average particle size 25 nm, the same applies hereinafter) not subjected to hydrophilic treatment to graphite. In the same manner as in Experimental Example 1, battery preparation and battery evaluation were performed.

[Experimental Example 9]
Battery preparation and battery evaluation were performed in the same manner as in Experimental Example 1, except that a negative electrode sheet was prepared by adding 0.25 mass% of carbon black not subjected to hydrophilic treatment to graphite.

[Experimental result]
Table 1 shows the additive species, the addition ratio, the coverage, the initial charge / discharge efficiency, the negative electrode reaction resistance, and the Li precipitation limit current value of Experimental Examples 1 to 9.

  As can be seen from Table 1, when hydrophilic carbon black is supported on the graphite surface, it is clear that the negative electrode reaction resistance decreases as the coverage increases or as the addition ratio of hydrophilic carbon black increases. It became. On the other hand, the Li precipitation limit current value is almost the maximum when the coverage is 15.3% or 30.6%, or the addition ratio of hydrophilic carbon black is 0.5% by mass or 1% by mass, and the coverage is It is found that the Li deposition limit current value decreases when 3.1% or less or the addition ratio is 0.1 mass% or less, or when the coverage is 61.1% or more or the addition ratio is 2 mass% or more. It was. When the coverage is 3.1% or less or the addition ratio is 0.1% by mass or less, it is considered that the amount of addition is too small and the effect of reducing the negative electrode reaction resistance is small, so that the Li deposition limit current value is not improved. In addition, when the coverage is 61.1% or more or the addition ratio is 2% by mass or more, the negative electrode reaction resistance is reduced, but the hydrophilic carbon black present on the graphite surface is inserted into and removed from lithium ions during actual battery input. It is presumed that the Li deposition limit current value has decreased due to a barrier against separation.

  The relationship between the ratio of hydrophilic carbon black to graphite, the coverage of hydrophilic carbon black, and the Li precipitation limit current value is shown in the graph of FIG. In FIG. 2, CB is an abbreviation for carbon black. In this graph, the line where the Li precipitation limit current value is 5% higher than the value of Experimental Example 3 in which hydrophilic carbon black was not added is taken as the border line, and the coverage at which the Li precipitation limit current value exceeds this border line. When the addition ratio of hydrophilic carbon black was determined, the former was 6.1% to 46.4% and the latter was 0.2% to 1.5% by mass. On the other hand, when the covering ratio and the addition ratio of hydrophilic carbon black, which are equal to or higher than those of Experimental Example 2, were determined, the former was 14.7% to 36.7% and the latter was 0.5 mass. % To 1.2% by mass.

  As a result of SEM observation of the negative electrode sheet, only graphite particles were observed as shown in FIG. In the negative electrode sheet having a covering rate of 30.6% (hydrophilic carbon black 1% by mass) in Experimental Example 1, the graphite surface was dispersed almost uniformly as shown in FIG. A fine point) was covered. On the other hand, in the negative electrode sheet having a covering rate of 152.8% (hydrophilic carbon black 5 mass%) in Experimental Example 7, it was confirmed that hydrophilic carbon black was overlapped and covered as shown in FIG. It was. In Experimental Example 7, styrene-butadiene rubber and carboxymethyl cellulose, which are water-based binders, are present on the graphite surface, and it is assumed that the Li insertion path is blocked by the close contact between these and hydrophilic carbon black. Is done. The initial charge / discharge efficiency is also clearly lower in Experimental Examples 5 to 7 with a coverage of 61.1% or more (2% by mass or more of hydrophilic carbon black) compared to Experimental Example 3 without the addition of hydrophilic carbon black. It was. In Experimental Examples 8 and 9 in which the same investigation was performed using carbon black not subjected to hydrophilic treatment, the negative electrode reaction resistance reduction effect and the Li precipitation limit current value improvement effect were not confirmed. From this, it was shown that the carbon black supported on the graphite surface needs to be a carbon black having hydrophilicity.

  Among the above experimental examples 1 to 9, experimental examples 1 and 2 correspond to the examples of the present invention, and experimental examples 3 to 9 correspond to comparative examples. These experimental examples do not limit the present invention.

20 nonaqueous battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 nonaqueous electrolyte.

Claims (9)

Graphite, which is a negative electrode active material,
Hydrophilic carbon black,
An aqueous binder and
The average particle diameter of the graphite is r ₁ , the specific gravity is d ₁ , the average particle diameter of the hydrophilic carbon black is r ₂ , the specific gravity is d ₂ , and the addition ratio of the hydrophilic carbon black to the graphite is x mass%. When the ratio of the following formula, which is the ratio of the hydrophilic carbon black covering the graphite, is 6.1% or more and 46.4% or less,
Negative electrode for non-aqueous lithium ion secondary battery.
Coverage (%) = x (r ₁ / 4r ₂ ) (d ₁ / d ₂ ) The coverage is 14.7% or more and 36.7% or less.
The negative electrode for non-aqueous lithium ion secondary batteries according to claim 1. Graphite, which is a negative electrode active material,
Hydrophilic carbon black,
An aqueous binder and
The addition ratio of the hydrophilic carbon black to the graphite is 0.2% by mass or more and 1.5% by mass or less.
Negative electrode for non-aqueous lithium ion secondary battery. The addition ratio is 0.5 mass% or more and 1.2 mass% or less,
The negative electrode for non-aqueous lithium ion secondary batteries according to claim 3. A negative electrode for a non-aqueous lithium ion secondary battery according to any one of claims 1 to 4,
A positive electrode;
A non-aqueous electrolyte,
A non-aqueous lithium ion secondary battery. An aqueous dispersion of the hydrophilic carbon black was added to and mixed with a negative electrode paint containing graphite and an aqueous binder so that the coverage of the following formula was 6.1% or more and 46.4% or less. The resulting mixed liquid was applied onto a negative electrode current collector and dried, and then subjected to a rolling treatment to obtain a negative electrode.
A method for producing a negative electrode for a non-aqueous lithium ion secondary battery.
Coverage (%) = x (r ₁ / 4r ₂ ) (d ₁ / d ₂ )
Wherein r ₁ is the average particle diameter of the graphite, d ₁ is the specific gravity of the graphite, r ₂ is the average particle diameter of the hydrophilic carbon black, d ₂ is the specific gravity of the hydrophilic carbon black, and x is the hydrophilic (Addition ratio (mass%) of the functional carbon black to the graphite) The coverage is 14.7% or more and 36.7% or less.
The manufacturing method of the negative electrode for non-aqueous lithium ion secondary batteries of Claim 6. To the negative electrode paint containing graphite and an aqueous binder, the aqueous dispersion of the hydrophilic carbon black is added so that the addition ratio of the hydrophilic carbon black to the graphite is 0.2% by mass or more and 1.5% by mass or less. After mixing, the obtained mixed solution is applied on the negative electrode current collector and dried, and then subjected to a rolling treatment to obtain a negative electrode.
A method for producing a negative electrode for a non-aqueous lithium ion secondary battery. The addition ratio is 0.5% by mass or more and 1.2% by mass or less.
The manufacturing method of the negative electrode for non-aqueous lithium ion secondary batteries of Claim 8.