KR20090125254A - Method for producing electrode slurry for lithium ion secondary battery - Google Patents

Abstract

Disclosed is a method for producing an electrode slurry which is used for producing a lithium ion secondary battery having high capacity and excellent charge/discharge cycle characteristics. Specifically disclosed is a method for producing an electrode slurry for lithium ion secondary batteries, which contains an electrode active material, a carboxymethyl cellulose, a binder and water. In this method, an electrode slurry is produced by the following steps (1)-(3) using two kinds of carboxymethyl celluloses having different aqueous solution viscosities. (Step 1) A step for preparing an aqueous solution (A') by dissolving a carboxymethyl cellulose having a lower viscosity in water (Step 2) A step for preparing a mixture (A") by mixing the aqueous solution (A') with the electrode active material (Step 3) A step for mixing a carboxymethyl cellulose having a higher viscosity and a binder.

Description

The manufacturing method of the slurry for lithium ion secondary battery electrodes {METHOD FOR PRODUCING ELECTRODE SLURRY FOR LITHIUM ION SECONDARY BATTERY}

The present invention relates to a method for producing a slurry for lithium ion secondary battery electrodes. Moreover, this invention relates to the electrode slurry manufactured by the manufacturing method of this electrode slurry, Furthermore, it is related with the electrode using this electrode slurry, and the lithium ion secondary battery using this electrode.

In recent years, the spread of portable terminals such as notebook computers, cellular phones, PDAs, and the like is remarkable. Lithium ion secondary batteries (hereinafter may be simply referred to as "batteries") are frequently used in secondary batteries used for power sources of these portable terminals. The portable terminal demands more comfortable portability, and the miniaturization, thinning, weight reduction, and high performance are rapidly progressing. As a result, portable terminals have been used in various places. Along with the increase in the use range, the battery, which is a power source, is also required to be smaller, thinner, lighter, and higher in performance as in the case of a portable terminal.

In order to improve the performance of a battery, improvement of an electrode, electrolyte solution, and the other battery member is examined. Typically, the electrode is manufactured as follows. That is, a binder and a liquid medium are mixed, and optional additives are added as needed to obtain a binder composition, an electrode active material is added thereto to form a slurry for electrodes, and the resulting electrode slurry is applied to a current collector and dried. By forming an electrode active material layer.

Patent Literature 1 discloses a composition for battery electrodes obtained by mixing and dispersing an electrode active material in a binder (composition) containing a carboxymethyl cellulose having a degree of etherification of 0.5 to 1 and an average degree of polymerization of 300 to 1,800 and a polymer latex (electrode) Slurry) has been proposed. It is described that this composition for battery electrodes provides the electrode excellent in discharge characteristics, high capacity | capacitance, charge / discharge cycle characteristics, and stability. However, it is not clear how much the battery capacity is. In recent years, it is desired to prolong the use time of a mobile terminal, to prolong the life of battery characteristics, to shorten the charging time, and the like. It became. In the composition for battery electrodes mentioned above, it was inadequate for achieving the high capacity | capacitance of a battery requested | required and the charge-discharge cycle characteristic.

Patent Document 1: Japanese Patent Application Laid-Open No. 11-67213

Disclosure of Invention

Problems to be Solved by the Invention

Disclosure of Invention An object of the present invention is to provide a method for producing an electrode slurry for producing a lithium ion secondary battery having a high capacity and excellent charge / discharge cycle characteristics in view of the present state of the art.

Means to solve the problem

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the said objective, in the method of manufacturing the slurry for lithium ion secondary battery electrodes containing an electrode active material, a carboxymethylcellulose, a binder, and water, the aqueous solution viscosity of a different range is used. When the slurry for electrodes is manufactured by using two types of carboxymethylcellulose which has, and mixing the said electrode active material and the aqueous solution of the low viscosity among the two types of carboxymethylcellulose first, the smoothness of an electrode surface, It was found that the binding property was excellent. In addition, it was found that the use of the slurry for the electrode can produce an electrode containing a large amount of electrode active material, and it is possible to achieve higher capacity of the battery and better improvement of charge / discharge cycle characteristics. The invention has been completed.

Thus, according to the first of the present invention, in the method for producing a slurry for lithium ion secondary battery electrodes containing an electrode active material, carboxymethyl cellulose, a binder and water, the carboxymethyl cellulose is the following carboxymethyl cellulose (A ) And (B), and further comprising the following steps (1) to (3), there is provided a method for producing an electrode slurry.

Carboxymethyl cellulose (A) having an aqueous solution viscosity of 1% by mass to 100 to 2,000 mPa · s

A carboxymethyl cellulose (B) having an aqueous solution viscosity of 1% by mass is 2,000 mPa · s or more higher than the carboxymethyl cellulose (A).

(Step 1) A step of dissolving the carboxymethyl cellulose (A) in water to prepare an aqueous solution (A ').

(Step 2) A step of mixing the aqueous solution (A ') and the electrode active material to prepare a mixture (A' ').

(Step 3) mixing the carboxymethyl cellulose (B) and a binder in the mixture (A '')

Moreover, it is preferable to have following process (1 ') before (process 3).

(Step 1 ') A step of dissolving the carboxymethyl cellulose (B) in water to prepare an aqueous solution (B').

It is preferable that the density | concentration of the said aqueous solution (A ') is 0.5-4.0 mass%.

It is preferable that the usage-amount of the said carboxymethylcellulose (A) is 0.1-1.0 mass part with respect to 100 mass parts of said electrode active materials.

It is preferable that the etherification degree of the said carboxymethylcellulose (A) and (B) is 0.5-1.6.

It is preferable that the average degree of polymerization of the said carboxymethylcellulose (A) and (B) is 300-2,000.

According to the 2nd of this invention, the slurry for electrodes manufactured by the manufacturing method of the said slurry for electrodes is provided.

According to the 3rd of this invention, the electrode provided by apply | coating the said slurry for electrodes to an electrical power collector, and then removing water and forming an electrode active material layer is provided.

According to the 4th of this invention, the lithium ion secondary battery which uses the said electrode is provided.

Effects of the Invention

According to the manufacturing method of the slurry for lithium ion secondary battery electrodes of this invention, the lithium ion secondary battery which has high capacity and excellent charge / discharge cycle characteristics is provided. The battery provided in the present invention can be suitably used as a small secondary battery for electronics and a secondary battery for power, such as for automobiles.

Best Mode for Carrying Out the Invention

(Slurry for electrode)

The slurry for electrodes of this invention is a slurry for lithium ion secondary battery electrodes containing an electrode active material, a carboxymethylcellulose, a binder, and water, and can be used for any of a positive electrode and a negative electrode.

(Electrode active material)

The electrode active material used in the present invention may be any one capable of reversibly inserting and discharging lithium ions by applying a potential in the electrolyte, and may be used either as an inorganic compound or an organic compound.

Examples of the electrode active material for the positive electrode include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFeVO ₄ , Li _x Ni _y Co _z Mn _w O ₂ (where x + y + z + w = 2) and the like. Lithium-containing composite metal oxides; Lithium-containing composite metal oxooxide salts such as LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ ; Transition metal sulfides such as TiS ₂ , TiS ₃ , and amorphous MoS ₃ ; Transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , Mo 0 ₃ , V ₂ 0 ₅ , V ₆ 0 _13, and the like; And the compound etc. which substituted a part of transition metal in these compounds with another metal are illustrated. Moreover, conductive polymers, such as polyacetylene and poly-p-phenylene, can also be used. Moreover, what coat | covered a carbon material and an inorganic compound to one part or whole surface of these surfaces is also used.

Moreover, as an electrode active material for negative electrodes, carbon materials, such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch type carbon fiber, conductive polymers, such as polyacene, etc. are mentioned, for example. . Moreover, metals, such as Si, Sn, Sb, Al, Zn, and W which can be alloyed with lithium, are also mentioned. The electrode active material can also use the thing which made the electrically conductive material adhere to the surface by a mechanical modification method.

Among these, lithium-containing composite metal oxides and lithium-containing lithium ions as positive electrode active materials because they are easy to obtain a high capacity, are stable at high temperatures, and have a small volume change associated with intercalating and releasing lithium ions, thereby making it easy to reduce the electrode thickness change rate. As a composite metal oxo oxide and a negative electrode active material, a carbon material is preferable, and the carbon material which has graphite structures, such as artificial graphite, natural graphite, and the natural graphite which modified the surface by carbonaceous material, is more preferable.

Since the particle shape of an electrode active material can make the porosity in an electrode active material layer small, it is preferable to set it as spherical shape. In addition, about the particle diameter, a mixture of small particles having a volume average particle diameter of 0.8 to 2 µm and relatively large particles having a volume average particle diameter of 3 to 8 µm, and particles having a particle diameter distribution broadly from 0.5 to 20 µm, desirable. When particle | grains whose particle diameter is 50 micrometers or more are contained, it is preferable to remove this and use by sieving. Since the density of the electrode active material layer can be increased and a high capacity electrode can be made, the tap density of the electrode active material is preferably 2 g / cm 3 or more in the positive electrode and 0.8 g / cm 3 or more in the negative electrode. The tap density can be measured according to JIS Z 2512: 2006.

The quantity of the electrode active material in the slurry for electrodes of this invention is 40-80 mass% of the slurry for electrodes normally. If the amount of the electrode active material is within this range, a slurry for electrodes suitable for coating on the current collector can be prepared, and there is no dropout of the electrode active material from the current collector, so that an electrode having a sufficient function can be produced.

(water)

Examples of the water used in the present invention include water (ion exchange water) treated with an ion exchange resin and water (ultra pure water) treated with a reverse osmosis membrane water purification system.

As for the electrical conductivity of water, it is preferable to use water of 0.5 mS / m or less. When exceeding this, the effect of deteriorating the dispersibility of the active material in a slurry by the adsorption amount change of the carboxymethylcellulose to an active material, etc., will produce the effect of reducing the uniformity of an electrode.

(Carboxymethyl cellulose)

Carboxymethyl cellulose is an anionic water-soluble polymer obtained by reacting cellulose with a base such as sodium hydroxide, followed by reacting monochloroacetic acid or the like, and partially replacing (etherifying) the hydroxyl group of cellulose with a carboxymethyl group. The number of etherified hydroxyl groups per structural unit (anhydrous glucose) is called the degree of etherification. Carboxymethyl cellulose with an etherification degree of 1 has the structures of the following general formulas (1) and (2).

[Formula 1]

[Formula 2]

(Wherein X represents a group selected from Na, NH ₄ , Ca, K, Li, Al, Mg and H)

The carboxymethyl cellulose whose etherification degree exceeds 1 contains the structure in which the remaining hydroxyl group was further etherified in the said General formula (2).

The degree of etherification is usually 0.4 to 1.7, preferably 0.5 to 1.6, and more preferably 0.55 to 1.5. When etherification degree is this range, the workability of the slurry for electrodes obtained is favorable, and binding property is also favorable.

Moreover, the number which carboxymethylcellulose has per unit molecule of the unit represented by the said General formula (1) or the said General formula (2) is called average polymerization degree. 300-2,000 are preferable, as for an average polymerization degree, 400-1,800 are more preferable, and 500-1,600 are especially preferable. Dispersibility of an electrode active material is favorable in average polymerization degree being this range, and binding property is also favorable.

X in the general formula (2) is preferably in the Na, NH _4, Li, K, and H. Moreover, you may have two or more types of structures in which X differs. When X is these, the dispersibility of an electrode active material is favorable and the workability of the slurry for electrodes becomes also favorable.

(Aqueous solution viscosity)

The viscosity (hereinafter, simply referred to as "aqueous solution viscosity") of 1 mass% aqueous solution of carboxymethylcellulose in this invention is a single cylindrical rotational viscometer (25 degreeC, rotation speed = 60 rpm, spindle shape according to JISZ 8803: 1991). : No. 4) says the value of 1 minute after a measurement start.

The aqueous solution viscosity is usually adjusted to the average degree of polymerization. The higher the average degree of polymerization, the higher the aqueous solution viscosity.

(Carboxymethyl cellulose (A))

The carboxymethyl cellulose (A) has an aqueous solution viscosity of 100 to 2,000 mPa · s, and is prepared in the aqueous solution (A ′) in step 1 in the production method of the present invention, and mixed with the electrode active material before the carboxymethyl cellulose (B). Will be. 0.5-4.0 mass% is preferable, and, as for the density | concentration of aqueous solution (A '), 0.5-3.0 mass% is more preferable. When aqueous solution viscosity and aqueous solution concentration are this range, mixing with an electrode active material becomes easy, and stability of the slurry for electrodes obtained also becomes favorable.

0.1-1.0 mass part is preferable with respect to 100 mass parts of electrode active materials, and, as for the usage-amount of carboxymethylcellulose (A), 0.2-0.8 mass part is more preferable. If the usage-amount is this range, stability of the slurry for electrodes obtained will become favorable, and the homogeneity of an electrode will also become favorable.

(Carboxymethyl cellulose (B))

The carboxymethyl cellulose (B) has an aqueous solution viscosity of 2,000 mPa · s or more higher than the carboxymethyl cellulose (A), and is mixed with the electrode active material after the carboxymethyl cellulose (A) in the production method of the present invention.

As for the aqueous solution viscosity of carboxymethylcellulose (B), it is more preferable that it is 3,000 mPa * s or more higher than the said carboxymethylcellulose (A), and it is especially preferable that it is 4,000 mPa * s or more high. The upper limit of the aqueous solution viscosity of carboxymethylcellulose (B) is 12,00 mPa * s. When aqueous solution viscosity is this range, binding property of an electrode active material layer and an electrical power collector will become favorable.

It is preferable to prepare and use carboxymethylcellulose (B) as aqueous solution normally similarly to carboxymethylcellulose (A).

0.5-2.0 mass% is preferable, and, as for the density | concentration of the aqueous solution of carboxymethylcellulose (B), 0.5-1.5 mass% is more preferable. If concentration is in this range, adjustment and handling of aqueous solution are easy.

Moreover, 0.2-1.5 mass parts is preferable as solid content with respect to 100 mass parts of electrode active materials, and, as for the usage-amount of carboxymethylcellulose (B), 0.2-1.0 mass part is more preferable. When the usage-amount is this range, the workability of an electrode slurry becomes favorable and the intensity | strength of the electrode obtained also becomes favorable.

(Binder)

The binder used in the present invention is usually a polymer latex, and examples thereof include SB latex, acrylic latex, NBR latex, fluorine latex, and silicone latex. SB-based latex, acrylic latex, and NBR-based latex are preferable, and SB-based latex and acrylic latex are more preferable because of excellent binding property with the electrode active material and strength and flexibility of the obtained electrode.

SB-based latex is an aqueous dispersion of a polymer containing an aromatic vinyl monomer and a conjugated diene monomer or a polymer further copolymerizable with these, and the polymer contains a polar monomer such as acrylonitrile, acrylic acid, methacrylic acid, etc. It is desirable to.

The acrylic latex contains a polymer containing a monomer selected from the group consisting of acrylic acid derivatives such as acrylic acid, methacrylic acid and acrylic acid esters and methacrylic acid derivatives such as methacrylic acid esters, or further monomers copolymerizable with these. It is an aqueous dispersion of the polymer to be mentioned, and it is preferable to contain polar monomers, such as acrylic acid, methacrylic acid, or acrylonitrile, as a polymer.

NBR latex is an aqueous dispersion of a polymer containing an acrylonitrile monomer and a conjugated diene monomer, or a polymer further copolymerizable with these, and preferably a polymer containing ethylenically unsaturated carboxylic acid.

As a binder for positive electrodes, since it is excellent in the oxidation resistance in filling, the acryl-type latex which is a dispersion of the saturated polymer which does not have an unsaturated bond in a polymer main chain is preferable.

Moreover, as a binder for negative electrodes, since it is excellent in reduction resistance and a strong binding force can be obtained, SB type latex and NBR type latex are preferable.

These polymer latexes can be produced, for example, by emulsion polymerization of the monomers. 50-500 nm is preferable and, as for the average particle diameter of the polymer particle in this polymer latex, 70-400 nm is more preferable. If average particle diameter is this range, the intensity | strength and flexibility of the electrode obtained will become favorable.

Solid content concentration of this polymer latex is 15-70 mass% normally, 20-65 mass% is preferable, and 30-60 mass% is more preferable. When solid content concentration is this range, workability in electrode slurry manufacture is favorable.

The usage-amount of this polymer latex is 0.1-10 mass parts as solid content normally with respect to 100 mass parts of electrode active materials, and 0.5-8 mass parts is preferable. If the amount of use is within this range, the strength and flexibility of the resulting electrode become good.

(Method for Producing Slurry for Electrode)

The slurry for electrodes is prepared by following process 1, process 2, and process 3.

(Step 1) A step of dissolving the carboxymethyl cellulose (A) in water to prepare an aqueous solution (A ').

(Step 2) A step of mixing the aqueous solution (A ') and the electrode active material to prepare a mixture (A' ').

(Step 3) mixing the carboxymethyl cellulose (B) and a binder in the mixture (A '')

In process 2, the carboxymethylcellulose (A) whose aqueous solution viscosity is 100-2,000 mPa * s is used. Carboxymethyl cellulose in this viscosity range is excellent in the dispersibility of the active material, but the binding strength to the active material and the current collector is low. Therefore, when a battery using an electrode manufactured using only carboxymethyl cellulose in this viscosity range is repeatedly charged and discharged, the battery internal resistance may increase due to peeling of the electrode active material layer and the current collector, and the capacity retention may be lowered.

In step 3, carboxymethyl cellulose (B) having an aqueous solution viscosity of 2,000 mPa · s or more higher than carboxymethyl cellulose (A) is used. Although carboxymethyl cellulose (B) is inferior to the dispersibility of an active material than carboxymethyl cellulose (A), an electrode with strong binding property is obtained. Therefore, a battery using an electrode produced using only carboxymethyl cellulose (B) may have a capacity retention rate deteriorated due to nonuniformity of the active material in the electrode.

This invention provides the process of manufacturing the electrode excellent in the dispersibility and binding property of an active material using the carboxymethylcellulose which has said two types of different aqueous solution viscosity and a characteristic. Each process is demonstrated below.

(Step 1)

Step 1 is a step of dissolving the carboxymethyl cellulose (A) in water to prepare an aqueous solution (A '). As a preparation method of aqueous solution (A '), the method of using mixing apparatuses, such as a blade type stirrer, etc. are mentioned.

(Process 2)

Step 2 is a step of mixing the aqueous solution (A ′) and the electrode active material obtained in Step 1 to prepare a mixture (A ″). Although it does not specifically limit as a method of mixing aqueous solution (A) and an electrode active material, Usually, a mixer, such as a ball mill, a sand mill, a pigment disperser, a brain trajectory, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer. Mix using. Although mixing time is not specifically limited, It is preferable to mix until the particle diameter of the aggregate measured by the gauge (particle gauge) based on JISK5600-2-5: 1999 becomes 100 micrometers or less.

When the particle diameter of the aggregate is larger than 100 µm, when the resulting battery is charged and discharged, deformation occurs due to expansion and contraction of the active material, the electrode active material layer is peeled from the current collector of the electrode, or the battery internal resistance is increased, thereby increasing the capacity retention rate. The problem that this is reduced or becomes easy to arise.

(Process 3)

Step 3 is a step of mixing the carboxymethyl cellulose (B) and a binder in the mixture (A '') obtained in step 2.

The carboxymethyl cellulose (B) and the binder are preferably prepared as an aqueous solution before addition and mixing.

When the aqueous solution of carboxymethyl cellulose (B) or the aqueous solution of the binder is added and mixed in step 2, the time required for step 2 becomes long, and the resulting electrode slurry becomes unstable.

If the aqueous solution of carboxymethyl cellulose (B) or the aqueous solution of the binder is mixed with the electrode active material before Step 2, the resulting electrode slurry, which is required for a long time for mixing, becomes unstable, and the electrode active material layer and the collection The overall binding property is also lowered.

A carboxymethyl cellulose (B) and a binder may be added and mixed simultaneously, and may be added and mixed separately, respectively. When adding and mixing separately, you may order either first. The method of mixing a binder after mixing carboxymethyl cellulose (B) is preferable. The mixing method may be the same as that of step 2.

(Challenge)

The slurry for electrodes of this invention may contain a electrically conductive material. As the conductive material, conductive carbon such as acetylene black, Ketjen black, carbon black, graphite, vapor grown carbon fiber, and carbon nanotube can be used. By using a electrically conductive material, the electrical contact of electrode active materials can be improved, and the discharge rate characteristic of a battery can be improved. The usage-amount of a electrically conductive material is 0-20 mass parts normally with respect to 100 mass parts of electrode active materials, Preferably it is 1-10 mass parts.

(Thickener)

The slurry for electrodes of this invention may contain thickeners other than the said carboxymethylcellulose. As a thickener, the copolymer of ethylene and vinyl alcohol, the alkali metal salt of polyacrylic acid, polyethylene oxide, etc. are mentioned, for example.

(electrode)

The electrode of this invention is an electrode which has an electrode active material layer and an electrical power collector which apply | coat and dry (remove water) the slurry for electrodes of this invention. Although the manufacturing method of the electrode of this invention is not specifically limited, For example, it is a method of apply | coating and heat-drying the said electrode slurry on at least one side, preferably both surfaces of an electrical power collector, and forming an electrode active material layer. The method of apply | coating the slurry for electrodes to an electrical power collector is not specifically limited. For example, methods, such as a doctor blade method, a dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, and the brush coating method, are mentioned. As a drying method, the drying method by drying, vacuum drying, irradiation with (far) infrared rays, an electron beam, etc. is mentioned, for example by warm air, hot air, and low humidity wind. Drying time is 5-30 minutes normally, and drying temperature is 40-180 degreeC normally.

Subsequently, it is preferable to make the porosity of an electrode active material layer low by a pressurization process using a metal mold | die press, a roll press, etc. The range with a porosity is 5%-15%, More preferably, it is 7%-13%. If the porosity is too high, the charging efficiency and the discharge efficiency deteriorate. If the porosity is too low, it is difficult to obtain a high volume capacity, or the electrode active material layer is easily peeled off from the current collector, which causes a problem that defects are likely to occur. The space | gap of an active material layer means the cavity which arises between active materials, and a porosity can be computed from the difference of the theoretical density and the measured density calculated | required from the density and the compounding quantity of the material which comprise an active material.

Moreover, when using curable polymer as a binder, it is preferable to harden | cure.

The thickness of the electrode active material layer of the electrode of this invention is 5 micrometers or more and 300 micrometers or less normally, Preferably they are 30 micrometers or more and 250 micrometers or less.

(Current collector)

The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. In order to have heat resistance, a metal material is preferable. For example, iron, copper, aluminum, nickel, stainless steel , Titanium, tantalum, gold, platinum and the like. Especially, aluminum is especially preferable for the positive electrode of a nonaqueous electrolyte secondary battery, and copper is especially preferable for the negative electrode. Although the shape of an electrical power collector is not specifically limited, It is preferable that it is a sheet form with a thickness of about 0.001-0.5 mm. In order that a collector may raise adhesive strength with an electrode active material layer, it is preferable to use it, roughening previously. As a roughening method, a mechanical polishing method, an electrolytic polishing method, a chemical polishing method, etc. are mentioned. In the mechanical polishing method, a polishing cloth on which abrasive particles are fixed, a wire brush having an abrasive stone, an emery buff, a steel wire, or the like is used. Moreover, in order to improve the adhesive strength and electroconductivity of an electrode active material layer, you may form an intermediate | middle layer in the electrical power collector surface.

(Lithium ion secondary battery)

The lithium ion secondary battery of this invention is a lithium ion secondary battery provided with the electrode of this invention as at least one electrode of a positive electrode and a negative electrode. In order to show the effect of this invention more favorably, it is preferable to use for the thick one of the positive electrode or the negative electrode, and it is more preferable to use for both the positive electrode and the negative electrode.

(Electrolyte amount)

Although the electrolyte solution used for this invention is not specifically limited, For example, what melt | dissolved lithium salt in the non-aqueous solvent as a supporting electrolyte can be used. As the lithium salt, for example, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ And lithium salts such as NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. LiPF ₆ , LiClO ₄ , CF ₃ SO ₃ Li especially soluble in solvents and showing high dissociation degree

Is preferably used. These can be used individually or in mixture of 2 or more types. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less with respect to the electrolyte. Even if the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered and the charging and discharging characteristics of the battery are lowered.

The solvent used for the electrolytic solution is not particularly limited as long as it dissolves the supporting electrolyte. Typically, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate ( BC) and alkyl carbonates, such as methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur-containing compounds such as sulfolane and dimethyl sulfoxide are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used individually or in mixture of 2 or more types.

As the electrolytic solution other than the above, there may be mentioned inorganic solid electrolyte of polyethylene oxide, polymer electrolyte, a gel-like polymer electrolyte impregnated with the electrolyte, such as polyacrylonitrile, or, such as LiI, Li ₃ N.

(Method of manufacturing battery)

The manufacturing method of the lithium ion secondary battery of this invention is not specifically limited. For example, the negative electrode and the positive electrode are overlapped with each other via a separator, and the negative electrode and the positive electrode are overlapped according to the shape of the battery, or folded into the battery container, and the electrolyte is injected into the battery container to seal the inlet. If necessary, an expanded metal, an overcurrent preventing element such as a fuse, a PTC element, a lead plate, or the like may be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat type.

Examples of the separator include microporous membranes or nonwoven fabrics made of polyolefin such as polyethylene and polypropylene; A well-known thing, such as porous resin containing an inorganic ceramic powder, can be used.

Although an Example is given to the following and this invention is demonstrated, this invention is not limited to these. In addition, the part and% in a present Example are a mass reference | standard unless there is particular notice.

The test in an Example and a comparative example was implemented with the following method.

(Assessment Methods)

Aqueous solution viscosity

1 mass part of carboxymethylcellulose was melt | dissolved in 99 mass parts of ion-exchange water, and the measurement sample was prepared. This was measured with a single cylindrical rotational viscometer (25 degreeC, rotation speed = 60 rpm, spindle shape: 4) according to JIS Z 8803: 1991, the value of 1 minute after the measurement start was calculated | required, and it was set as the aqueous solution viscosity.

<Etherification degree>

Ether degree (substitution degree) is calculated | required by the following method and formula.

First, 0.5-0.7 g of samples are measured precisely and incinerated in a magnetic crucible. After cooling, the obtained ash was transferred to a 500 ml beaker, about 250 ml of water, and 35 ml of N / 10 sulfuric acid were further added by pipette to boil for 30 minutes. This is cooled, a phenolphthalein indicator is added, and the excess acid is reverse titrated with N / 10 potassium hydroxide to calculate the degree of substitution from the following equation.

A = (a × f-b × f ¹ ) / sample (g)-alkalinity (or + acidity)

Degree of substitution = 162 × A / (10000-80A)

A: ml of N / 10 sulfuric acid consumed in bound alkali metal ions in 1 g of sample

a: use of N / 10 sulfuric acid

f: potency coefficient of N / 10 sulfuric acid

b: titration ml of N / 10 potassium hydroxide

f ¹ : Potency coefficient of N / 10 potassium hydroxide

In addition, alkalinity (or acidity) is calculated | required by the following method and formula.

About 1 g of a sample is dissolved in 200 ml of water, 5 ml of N / 10 sulfuric acid is added thereto, and after boiling for 10 minutes, the mixture is cooled, a phenolphthalein indicator is added, and titrated with N / 10 potassium hydroxide. The appropriate amount at this time is made Sml. At the same time, a blank test is carried out, and the appropriate amount at that time is Bml, and the alkalinity (or acidity) is obtained from the following equation. If the (B-S) x f value is a positive value, alkalinity is obtained, and if it is negative, an acidity is obtained.

Alkalinity (acidity) = (B-S) x f / sample (g)

f: potency coefficient of N / 10 potassium hydroxide

<Average degree of polymerization>

The average degree of polymerization of carboxymethyl cellulose is a value measured using the viscosity method. Viscosity method is based on Staudinger's law of viscosity:

{η} = Km × P ×

는 정수이다. 0.1N 의 NaCl 을 용매로서 우베로데 점도계를 이용하고 극한 점도를 구하여 평균 중합도를 산출하였다. Obtained by In the formula, P is the average degree of polymerization, {η} is the viscosity, Km and

Is an integer. 0.1N NaCl was used as a solvent and the intrinsic viscosity was calculated | required using the Uberode viscometer, and average polymerization degree was computed.

<Particle size of electrode slurry>

The electrode slurry was calculated | required as follows with the gauge (particle gauge) based on JISK5600-2-5: 1999. The third largest particle size of the point of occurrence of the line observed on the gauge is measured. The measurement was carried out six times to determine the measured maximum value. The smaller the particle size, the better the dispersibility.

Surface Roughness of Electrode Ra

The surface roughness Ra of the electrode was evaluated by the following method. The electrode was cut out to the rectangle of 10 mm x 50 mm, and five sample pieces were produced. The measurement was performed with a stylus type surface roughness measuring instrument (radius of the tip of the stylus = 0.5 µm) according to JIS B 0651: 2001 (ISO 3274: 1996). Arithmetic mean roughness Ra was measured from the obtained contour curve according to JIS B0601: 2001 (ISO 4287: 1997). The measurement was performed with five sample pieces and the average value was computed. The smaller the surface roughness Ra, the smoother the surface of the electrode and the smaller the variation in capacitance.

Peel Strength of Electrodes

The electrode was cut into a rectangle of 2.5 cm in width x 10 cm in length to form a test piece, and the electrode active material layer surface was fixed up. After attaching a plate tape to the electrode active material layer surface of a test piece, the stress at the time of peeling a cellophane tape in 180 degree direction at the speed of 50 mm / min was measured from one end of a test piece. The measurement was performed 10 times, the average value was calculated | required and this was made into the peeling strength. It shows that the larger the peeling strength is, the larger the binding force of the active material layer to the current collector is.

<Battery characteristics>

(Negative electrode test)

The evaluation at the time of making the electrode of this invention the negative electrode was performed as follows.

The negative electrode is cut out into a disk shape having a diameter of 15 mm, and a separator made of a disk-shaped porous film made of a polypropylene having a diameter of 18 mm and a thickness of 25 µm on the active material layer surface side of the negative electrode, a metal lithium used as a positive electrode, and an expanded metal. It was laminated in order and this was accommodated in the stainless steel coin-type exterior container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with the polypropylene packing. The electrolyte is injected into the container so that no air remains, and the outer container is fixed by capping a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed to obtain a lithium of 20 mm in diameter and about 2 mm in thickness. An ion coin battery was prepared.

As the electrolyte, LiPF ₆ was dissolved in a mixed solvent formed by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in EC: DEC = 1: 2 (volume ratio at 20 ° C.) at a concentration of 1 mol / liter. Solution was used.

The obtained coin battery was charged and discharged at a constant current method of 1.2 C at 25 ° C. at 1.2 V, and charged and discharged to discharge to 0 V each five times, and the battery capacity was measured each time. The ratio of the discharge capacity to the one charge capacity was expressed as a percentage to obtain initial efficiency. The average value of the repeatedly measured discharge capacity was made into discharge capacity (mAh / g: per active material).

In addition, the cycle test was performed similarly and the value which computed the ratio of the discharge capacity of the 50th cycle with respect to the discharge capacity of 5 cycles as a percentage was made into capacity retention ratio. The larger this value, the smaller the discharge capacity decreases, which is a good result.

(Positive electrode test)

The evaluation at the time of making the electrode of this invention a positive electrode was performed as follows.

A coin battery was manufactured in the same manner as the negative electrode test using the negative electrode as the metallic lithium.

The initial efficiency, discharge capacity and capacity retention rate were determined in the same manner as in the negative electrode test except that the battery was charged at 4.2 V and discharged to 3 V.

(Manufacture example 1)

In a 5 MPa pressure-resistant autoclave equipped with a stirrer, 39 parts by mass of styrene, 50 parts by mass of 1,3-butadiene, 10 parts by mass of acrylonitrile, 1 part by mass of divinylbenzene as a crosslinking agent, 2 parts by mass of sodium dodecylbenzenesulfonate, 150 parts by mass of ion-exchanged water and 1 part by mass of potassium persulfate were added as a polymerization initiator, and the mixture was sufficiently stirred, and then heated to 60 ° C to initiate polymerization. When the monomer consumption reached 99.0%, the mixture was cooled to stop the reaction to obtain an SB-based latex (binder (L)) having a solid content concentration of 41%.

(Manufacture example 2)

In a 5 MPa internal pressure autoclave equipped with a stirrer, 80 parts by mass of 2-ethylhexyl acrylate, 5 parts by mass of acrylic acid, 14 parts by mass of acrylonitrile, 1 part by mass of ethylene glycol dimethacrylate as a crosslinking agent, sodium dodecylbenzenesulfonate 3 3 parts by mass of potassium persulfate was added as a mass part, 150 parts by mass of ion-exchanged water and a polymerization initiator, and the mixture was sufficiently stirred, and then heated to 60 ° C to initiate polymerization. When the monomer consumption reached 98.0%, the reaction was cooled to stop the reaction to obtain an acrylic latex (binder (M)) having a solid content concentration of 41%.

(Example 1)

<Production of Slurry for Negative Electrode>

As carboxymethyl cellulose (A), 1 mass% aqueous solution (Al ') was prepared using the carboxymethyl cellulose ("Cellogen WSC" by Daiichi Kogyo Pharmaceutical Co., Ltd.) whose solution viscosity is 200 mPa * s. Moreover, 1 mass% aqueous solution (B1 ') was prepared using carboxymethyl cellulose ("Cellogen BSH-12" by Dai-ichi Kogyo Pharmaceutical Co., Ltd.) whose solution viscosity is 8,000 mPa * s as carboxymethyl cellulose (B).

In a planetary mixer equipped with a disper, 100 parts by mass of artificial graphite having an average particle diameter of 24.5 µm was added as an active material, and 80 parts by mass of the aqueous solution (A1 ') was added thereto, and adjusted to a solid content concentration of 53.5 mass% with ion-exchanged water. Then, it mixed at 25 degreeC for 60 minutes. Next, 20 mass parts of aqueous solution (B1 ') was added to this, after adjusting to 44 mass% of solid content concentration with ion-exchange water, it mixed at 25 degreeC for 15 minutes. Next, 2.9 mass parts of binders (L) obtained in the manufacture example 1 were put, and also it mixed for 10 minutes. This was degassed under reduced pressure to obtain a glossy electrode slurry having good fluidity. Table 1 shows the evaluation results of the particle size of the slurry for electrodes.

<Production of a negative electrode electrode coin battery>

The slurry for electrodes was apply | coated so that the film thickness after drying might be about 100 micrometers on copper foil of thickness 18micrometer with a doctor blade, and after 20 minutes drying at 50 degreeC, it heat-processed at 110 degreeC for 20 minutes, and obtained the electrode disk. After rolling this electrode disk with a roll press, it dried for 12 hours at 60 degreeC and 0.1 kPa, and obtained the 90-micrometer-thick electrode for negative electrodes. Table 1 shows the evaluation results of the surface roughness (Ra) of the electrode and the peeling strength of the electrode. Table 1 shows the battery characteristics of the coin battery using the obtained negative electrode.

(Example 2)

Evaluation similar to Example 1 was performed except having changed the aqueous solution of carboxymethylcellulose (A) and carboxymethylcellulose (B) as shown in Table 1. The results are shown in Table 1.

(Example 3)

<Production of Positive Slurry>

As carboxymethyl cellulose (A), 2 mass% aqueous solution (A3 ') was prepared using the carboxymethyl cellulose ("Cellogen 3H" by Dai-ichi Kogyo Pharmaceutical Co., Ltd.) whose solution viscosity is 1200 mPa * s. Moreover, 1 mass% aqueous solution (B3 ') was prepared using carboxymethyl cellulose ("Cellogen BSH-12" by Daiichi Kogyo Pharmaceutical Co., Ltd.) whose solution viscosity is 8,000 mPa * s as carboxymethyl cellulose (B).

In a planetary mixer equipped with a disper, 100 parts by mass of LiCoO ₂ having an average particle diameter of 10 μm and 2.5 parts by mass of acetylene black were added as active materials, and 30 parts by mass of the aqueous solution (A3 ′) was added thereto, followed by mixing at 25 ° C. for 60 minutes. It was. Next, 20 mass parts of aqueous solution (B3 ') was added to this, and also it mixed at 25 degreeC for 15 minutes. Next, 3.1 mass parts of binders (M) obtained in the manufacture example 2 were put, and also it mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry for electrodes having good gloss fluidity. Table 1 shows the evaluation results of the particle size of the slurry for electrodes.

<Production of an electrode / coin battery for a positive electrode>

The slurry for electrodes was apply | coated so that the film thickness after drying might be about 110 micrometers on aluminum foil of thickness 20micrometer with a doctor blade, and it dried at 110 degreeC for 20 minutes after drying at 50 degreeC for 20 minutes. Next, it pressed by the roll press so that the density of an electrode active material layer might be 3.6x10 <^3> kg / m <^3> . Subsequently, it dried for 12 hours at 60 degreeC and 0.1 kPa, and obtained the electrode for positive electrodes of 90 micrometers in thickness. Table 1 shows the evaluation results of the surface roughness (Ra) of the electrode and the peeling strength of the electrode. Table 1 shows battery characteristics of the coin battery using the obtained positive electrode.

(Comparative Example 1)

Evaluation similar to Example 1 was performed except having changed the aqueous solution of carboxymethylcellulose (A) and carboxymethylcellulose (B) as shown in Table 1. The results are shown in Table 1.

(Comparative Example 2)

Evaluation similar to Example 1 was performed except changing the aqueous solution of carboxymethylcellulose (A) as shown in Table 1, and not using carboxymethylcellulose (B). The results are shown in Table 1.

(Comparative Example 3)

The aqueous solution of carboxymethyl cellulose (B) was changed as shown in Table 1, and the same evaluation as in Example 1 was performed except that carboxymethyl cellulose (A) was not used. The results are shown in Table 1.

According to the result shown in Table 1, the electrode slurry of this invention had favorable dispersibility, the surface roughness and peeling strength of the electrode obtained using this were also favorable, and the battery using this electrode was excellent in the battery characteristic. On the other hand, Comparative Example 1 using two kinds of carboxymethyl celluloses having no predetermined viscosity difference and Comparative Example 2 using only carboxymethyl cellulose having a low solution viscosity showed poor peel strength and battery characteristics of the electrode. Comparative Example 3 using only carboxymethyl cellulose having a high solution viscosity showed a high peel strength of the electrode, but the surface roughness and the battery characteristics of the electrode were inferior.

Claims (9)

In the method for producing a slurry for lithium ion secondary battery electrodes containing an electrode active material, carboxymethyl cellulose, a binder and water, the carboxymethyl cellulose has the following carboxymethyl cellulose (A) and (B), and It has the following process (1)-(3), The manufacturing method of the slurry for electrodes characterized by the above-mentioned. Carboxymethyl cellulose (A) having an aqueous solution viscosity of 1% by mass to 100 to 2,000 mPa · s A carboxymethyl cellulose (B) having an aqueous solution viscosity of 1% by mass is 2,000 mPa · s or more higher than the carboxymethyl cellulose (A). (Step 1) A step of dissolving the carboxymethyl cellulose (A) in water to prepare an aqueous solution (A '). (Step 2) A step of mixing the aqueous solution (A ') and the electrode active material to prepare a mixture (A' '). (Step 3) mixing the carboxymethyl cellulose (B) and a binder in the mixture (A '') The method of claim 1, Furthermore, before (step 3), it has the following process (1 '), The manufacturing method of the slurry for electrodes characterized by the above-mentioned. (Step 1 ') A step of dissolving the carboxymethyl cellulose (B) in water to prepare an aqueous solution (B'). The method according to claim 1 or 2, The concentration of the said aqueous solution (A ') is 0.5-4.0 mass%, The manufacturing method of the electrode slurry. The method according to any one of claims 1 to 3, The usage-amount of the said carboxymethylcellulose (A) is 0.1-1.0 mass part with respect to 100 mass parts of said electrode active materials, The manufacturing method of the slurry for electrodes characterized by the above-mentioned. The method according to any one of claims 1 to 4, The manufacturing method of the slurry for electrodes whose etherification degree of the said carboxymethylcellulose (A) and (B) is 0.5-1.6. The method according to any one of claims 1 to 5, The manufacturing method of the slurry for electrodes whose average degree of polymerization of the said carboxymethylcellulose (A) and (B) is 300-2,000. The slurry for electrodes manufactured by the manufacturing method of the slurry for electrodes in any one of Claims 1-6. The electrode formed by apply | coating the slurry for electrodes of Claim 7 to an electrical power collector, and then removing water and forming an electrode active material layer. The lithium ion secondary battery which uses the electrode of Claim 8.