JP2020184473A - Method for producing negative electrode active material composite for nonaqueous secondary battery - Google Patents

Abstract

To provide a method for producing a negative electrode active material for nonaqueous secondary batteries, the negative electrode active material being excellent in charge/discharge characteristics and being applicable to nonaqueous secondary batteries such as, for example, lithium ion secondary batteries and sodium ion secondary batteries.SOLUTION: A method for producing a negative electrode active material for nonaqueous secondary batteries includes the steps of: (1) mixing an aqueous solution containing a compound having a conjugated polyvalent carboxylic acid salt (COOM) structure showing water solubility, favorably a metal constituting a carboxylic acid salt of the compound being an alkaline metal element, with a carbon material to obtain a mixture; and (2) distilling off water in the mixture.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a negative electrode active material composite for a non-aqueous secondary battery.

Conventionally, carbon materials such as graphite and hard carbon are known as negative electrode active materials for non-aqueous secondary batteries such as lithium ion secondary batteries. Further, as a new negative electrode active material for a non-aqueous secondary battery, dilithium terephthalate, which is an organic compound, is being studied. (Non-Patent Document 1). As a negative electrode active material for a non-aqueous secondary battery using such an organic compound, Patent Document 1 describes an organic skeleton layer containing an aromatic compound having an aromatic ring structure and a carboxylic acid anion portion, and the carboxylic acid. For electrodes using a negative electrode active material for non-aqueous secondary batteries, which has an alkali metal element layer in which an alkali metal element coordinates with oxygen contained in the anion portion to form a skeleton, the electrode is made higher by heat treatment. It is described that the charge / discharge capacity was expressed. Further, Patent Document 2 describes an organic active material which is a compound having an aromatic ring structure and two or more COOX groups (X is Li or Na) bonded to the end of the aromatic ring structure, and carbon. It is described that when a compound obtained by combining a material with a planetary ball mill as a negative electrode active material for a sodium ion secondary battery, a higher charge / discharge capacity was exhibited as compared with that before the treatment.

Japanese Unexamined Patent Publication No. 2014-162211 Japanese Unexamined Patent Publication No. 2015-037016

Nature Materials, 2009, Volume 8, p. 120-125

However, in the method disclosed in Patent Document 1, when the electrode is fired, the electrode contracts due to heating, the shape of the electrode becomes irregular, safety cannot be guaranteed, the electrode thickness changes, and charging / discharging occurs due to an increase in resistance. There is a problem that the capacity cannot be obtained. Further, the method disclosed in Patent Document 2 has a problem that sufficient charge / discharge characteristics cannot be obtained because the formation of a conductive path between the negative electrode active material and the carbon material is insufficient. Therefore, an object of the present invention is to provide a method for producing a negative electrode active material for a non-aqueous secondary battery, which has a sufficient charge / discharge capacity and can be applied to a non-aqueous secondary battery such as a lithium ion secondary battery. ..

According to the present invention, the above object is
[1] (1) A step of mixing an aqueous solution containing a compound having a conjugated polyvalent carboxylate structure showing water solubility with a carbon material to obtain a mixture, and (2) a step of distilling off water in the mixture. Method of manufacturing negative electrode active material for non-aqueous secondary batteries, including
[2] The production method according to the above [1], wherein the metal constituting the carboxylate of the compound is an alkali metal element.
[3] The production method according to [1] or [2] above, wherein the compound has 4 to 14 carbon atoms.
[4] The production method according to any one of the above [1] to [3], wherein the structure of the compound is at least one selected from the compounds represented by the following formulas (I) to (III).
Is achieved by providing.

（I）

(I)

(In the formula, m represents an integer of 1 to 2, M represents a metal element, and R ¹ and R ² each independently have at least one selected from the group consisting of a hydroxyl group, a halogen, and a carboxyl group as substituents. Represents either an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group which may have one)

（II）

(II)

(In the formula, n represents an integer of 1 to 2, M represents a metal element, and R ³ , R ⁴ , R ⁵ and R ⁶ are independently substituted groups consisting of a hydroxyl group, a halogen and a carboxyl group. Represents either an alkyl group having 1-2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group, which may have at least one selected)

（III）

(III)

(In the formula, M represents a metal element, and R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ and R ¹² are at least one independently selected from the group consisting of hydroxyl groups, halogens and carboxyl groups as substituents. Represents either an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group which may have one)

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for producing a negative electrode active material for a non-aqueous secondary battery, which exhibits a sufficient charge / discharge capacity and can be applied to a non-aqueous secondary battery such as a lithium ion or sodium ion secondary battery.

The method for producing a negative electrode active material for a non-aqueous secondary battery of the present invention has a conjugated polyvalent carboxylic acid salt structure exhibiting water solubility (the carboxylic acid salt portion is usually a carboxylic acid metal salt and can be referred to as COOM. Is characterized by including a step of mixing an aqueous solution containing a compound having a metal element) with a carbon material to obtain a mixture, and (2) a step of distilling off water in the mixture.

The aqueous solution used in the step (1) can be prepared, for example, as follows. An aqueous solution containing a compound having a metal (M) constituting the conjugated polyvalent carboxylic acid salt is mixed with a dispersion of the conjugated polyvalent carboxylic acid. At the time of the mixing, it may be heated to about 30 ° C. to 90 ° C. By the mixing, a compound having a conjugated polyvalent carboxylic acid salt structure is formed, and water in the mixed solution is distilled off with an evaporator or the like to obtain a compound having a conjugated polyvalent carboxylic acid salt structure. The aqueous solution can be obtained by dissolving this compound in water. When the dispersion medium in the dispersion is water, the mixed solution may be used as it is as an aqueous solution.

The carbon number of the compound having a conjugated polyvalent carboxylic acid salt structure exhibiting water solubility is not particularly limited as long as it exhibits water solubility, and is preferably 4 to 30, more preferably 4 to 20, and availability. From the viewpoint of excellent stability of the compound as a raw material and structural stability in the battery, 4 to 14 are more preferable. Here, showing water solubility means that 1 g or more is dissolved in 100 g of water at 20 ° C. The carboxylate moiety in the compound having a conjugated polyvalent carboxylate structure showing water solubility can also be expressed as COOM. M represents a metal element, preferably an alkali metal element, and examples thereof include Li, Na, and K. From the viewpoint of battery drive voltage, Li and Na are particularly preferable. Among the compounds, the number of COOM groups of the compound having a conjugated polyvalent carboxylate structure showing water solubility is 2 or more, and from the viewpoint of stability constituting the crystal structure of the compound, it may be 2-4. It is preferably 2, and more preferably 2. When the number of COOM groups is 2, the bonding position is preferably the position where the distance between the bonding points of the aromatic ring structure is maximized. The compound having a conjugated polyvalent carboxylic acid salt structure may have a functional group such as a hydroxyl group, a halogen such as fluorine or chlorine, or a non-conjugated carboxylic acid. When the compound having a conjugated carboxylate structure has an aromatic ring, the number of aromatic rings is preferably 1 to 2 and more preferably 1 from the viewpoint of water solubility. The ring structure of the aromatic ring may be an aromatic hydrocarbon in which the element constituting the ring structure is only carbon, or an aromatic heterocycle having a hetero atom, and may be an aromatic heterocycle in the above aromatic ring structure. Examples of the aromatic ring include structures such as a five-membered ring, a six-membered ring, a seven-membered ring, and an eight-membered ring. Above all, a five-membered ring or a six-membered ring is preferable from the viewpoint of making the charge / discharge characteristics more excellent. Specific examples of the compound having a conjugated polyvalent carboxylic acid salt structure exhibiting water solubility include the structures of the following formulas (I) to (III).

（I）

(I)

(In the formula, m represents an integer of 1 to 2, and R ¹ and R ² may each independently have at least one selected from the group consisting of a hydroxyl group, a halogen and a carboxyl group as a substituent. Represents either 1 to 2 alkyl groups, hydrogen, carboxyl groups or chloride carboxyl groups)

（II）

(II)

(In the formula, n represents an integer of 1 to 2, and R ³ , R ⁴ , R ⁵ and R ⁶ each independently have at least one selected from the group consisting of hydroxyl groups, halogens and carboxyl groups as substituents. It represents either an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group).

（III）

(III)

(In the formula, R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ and R ¹² may each independently have at least one selected from the group consisting of hydroxyl groups, halogens and carboxyl groups as substituents. (Represents any of an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, and a chloride carboxyl group) The chlorided carboxyl group is usually a metal carboxylate base and can be represented by COOM.
Specific compounds include dilithium maleate, dilithium fumarate, dilithium terephthalate, dilithium 2,6-naphthalenedicarboxylic acid, disodium maleate, disodium fumarate, disodium terephthalate, and di-naphthalenedicarboxylic acid Examples include sodium. Of these, dilithium fumarate and dilithium terephthalate are preferable because they can improve the theoretical capacity per weight of the obtained negative electrode active material for a non-aqueous secondary battery.

As the compound having a metal (M) constituting the conjugated polyvalent carboxylate, an alkali metal compound is preferable. Examples of the alkali metal compound include alkali metal hydroxides and alkali metal oxides. Of these, hydroxides are preferable from the viewpoint of reactivity with water and safety. Examples of the alkali metal include Li, Na, K and the like, and among them, Li and Na are preferable in that the theoretical capacity per weight of the negative electrode active material obtained can be improved.

Examples of the compound having a conjugated polyvalent carboxylic acid that is chloride and water-soluble include maleic acid, fumaric acid, citraconic acid, mesaconic acid, muconic acid, acontic acid, terephthalic acid, 2-methyl-terephthalic acid, 1, Examples thereof include 2,4-benzenetricarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, 4,4'-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid. Of these, maleic acid, fumaric acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoints of operability, availability, and battery capacity per weight.

The concentration of the compound in the aqueous solution containing the compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility varies depending on the compound, but is preferably 1% by mass or more, more preferably 5% by mass or more. Further, from the viewpoint of making the solubility of the compound in an aqueous solution appropriate and the viscosity when mixed with a carbon material, 20% by mass or less is preferable, and 10% by mass or less is more preferable. When a compound having a conjugated polyvalent carboxylic acid salt structure that shows water solubility when the concentration is too low is precipitated on a carbon material, it is sequentially precipitated in the previously precipitated portion to form a large crystal, and dispersibility cannot be guaranteed. , It takes time to distill off water in the step (2), and the efficiency of compounding may be deteriorated.

In the present invention, the preferable mixing ratio of the compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility and the carbon material as a carrier differs depending on the compound due to the difference in crystallinity, but generally, it is based on the carbon material. From the viewpoint of compounding a compound having a conjugated polyvalent carboxylic acid salt structure exhibiting water solubility, a compound having a conjugated polyvalent carboxylic acid salt structure exhibiting water solubility in a carbon material is usually 100: 1-1. The range is 1, more preferably 50: 1 to 1.2: 1, and even more preferably 10: 1 to 1.5: 1. When the carbon material ratio increases, the substantial concentration of the battery active material decreases, the battery capacity decreases, and when the carbon ratio decreases, a compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility without conductivity becomes crystals. It is not preferable because the rate of precipitation increases and the battery capacity decreases as a result.

In step (1), an aqueous solution containing a compound having a conjugated polyvalent carboxylate structure exhibiting water solubility and a carbon material are mixed. As a method of mixing, a carbon material may be added to an aqueous solution containing a compound having a conjugated polyvalent carboxylate structure showing water solubility and mixed, or an aqueous solution may be added to the carbon material and mixed. .. The method of addition is not particularly limited, and one of them may be added sequentially and mixed, or one of them may be added and mixed all at once. The mixing method is not particularly limited, and it can be mixed by a method that does not apply shear force by mixing such as general stirring and planetary stirring, or a thin film swirling method such as a kneader or a kneader or a fill mix. A method of dispersing and mixing with a shearing force such as the above may be used. The solid content concentration in the mixed solution is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or more, and particularly preferably 20% by mass or more. preferable. Further, it is preferably 80% by mass or less, more preferably 60% by mass or less, further preferably 50% by mass or less, and particularly preferably 30% by mass or less. If the solid content concentration is too high, compounds having a conjugated polyvalent carboxylic acid salt structure that shows water solubility in the carbon material at the time of compounding are unevenly distributed, which may result in a heterogeneous complex. Not only is it uneconomical because it requires a large amount of energy, but when it is dispersed using shearing force, it is difficult for shearing force to be applied, resulting in a non-uniform composite, and the charge / discharge capacity may decrease. By setting the above range, it is possible to combine more uniformly.

The carbon material is not particularly limited as long as it is an electron conductive material, for example, graphite such as natural graphite (scaly graphite, scaly graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle. One type of coke or carbon fiber may be used, or a plurality of types may be mixed and used. Of these, carbon black or acetylene black is preferable from the viewpoint of electron conductivity and coatability when the collector electrode is coated to form an electrode.

Next, step (2) will be described. In this step, the water in the mixture is distilled off. The method for distilling water is not particularly limited, and examples thereof include a method of heating the mixture to evaporate the water, a method of placing the mixture under reduced pressure to evaporate the water, and the like. Further, as a method of heating the mixture and evaporating water, a method of exposing to hot air for heating or a method of directly heating with a heater or the like may be used. As the temperature at which water is distilled off, the water of crystallization of the compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility is further used by heat transfer by an air flow, heat transfer by a heater, and further under normal pressure and reduced pressure. Generally, it is in the range of 40 ° C. to 300 ° C., more preferably in the range of 60 ° C. to 250 ° C. If the temperature is too low, it takes time to distill water and the economy is impaired, which is not preferable. If the temperature is too high, the target product is lost due to thermal decomposition of a compound having a conjugated polyvalent carboxylate structure showing water solubility. There is a risk of doing it. In the present invention, the composite can be strengthened by further heat-treating the composite from which water has been distilled off to further drive the drying. The temperature of the heat treatment is preferably 250 ° C to 450 ° C. The heat treatment time is preferably 2 hours to 4 hours.

In the present invention, an aqueous solution of a compound having a conjugated polyvalent carboxylate structure showing water solubility is added to and mixed with a carbon material (step (1)), and then a step of distilling off water (2) is performed a plurality of times to form a composite. It doesn't matter.

Further, in the present invention, the step of electrodeification described later is included in the step (2), a thickener such as carboxymethyl cellulose and a binder such as styrene-butadiene rubber are added, and the electrode is directly placed on a collecting electrode such as a copper foil. It is also possible to apply and dry the material at once to create a composite and electrodes that are active materials. At that time, the amounts of the thickener and the binder are not particularly limited, but the thickener is usually 0.1 to 5 parts by mass, more preferably 0.3, based on 100 parts by mass of the composite. ~ 3 parts by mass, the binder is 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass.

The composite obtained by the production method of the present invention has a state in which a compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility in a carbon material is attached to the surface. The specific state between the functional group such as a carboxyl group on the surface of the carbon material and the compound having a conjugated polyvalent carboxylate structure showing water solubility is not clear, but the state in which the carbon material is adsorbed on the particles of the compound. Alternatively, it is presumed that the compound is partially chemically bonded to the carbon material.

The negative electrode active material obtained in the present invention is used as an electrode (negative electrode) of a non-aqueous electrolyte secondary battery. For the electrode, for example, the negative electrode active material and the binder are mixed, an appropriate solvent is added to form a paste-like electrode mixture, which is applied and dried on the surface of the current collector, and if necessary. It can be obtained by compressing and forming. The binder is not particularly limited as long as it does not react with the electrolytic solution, such as PVDF (polyvinylidene fluoride) and polytetrafluoroethylene. Among them, PVDF is preferable because PVDF adhering to the surface of the active material does not hinder the movement of lithium ions and good input / output characteristics can be obtained. If the amount of the binder added is too large, the resistance of the obtained electrode becomes large, so that the internal resistance of the battery becomes large and the battery characteristics may be deteriorated. Further, if the amount of the binder added is too small, the bonding between the particles of the negative electrode material and the current collector may be insufficient. The amount of the binder added varies depending on the type of binder used, but for example, a PVDF-based binder is preferably 1 to 30 parts, more preferably 5 to 20 parts with respect to 100 parts of the complex. The current collector is not particularly limited as long as it is made of a conductive material, and for example, a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum can be used. One of these may be used alone, or two or more of them may be used in combination at any ratio.

For the counter electrode (positive electrode) of the electrode, for example, a paste-like electrode mixture prepared by mixing an electrode active material, a binder, and a conductive material and adding an appropriate solvent is applied and dried on the surface of the current collector. It can be obtained by compressing and forming as needed. The electrode active material includes a metal Li, a layered oxide system (represented as LiMO _2, and M is a metal: for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , or LiNixCoyMozO ₂ (where x, y, z are x, y, z). (Representing composition ratio)), olivine type (represented by LiMPO ₄ , M is a metal: for example LiFePO ₄ ), spinel type (represented by LiM ₂ O ₄ , M is a metal: for example LiMn ₂ O ₄ ) Metallic chalcogen compounds are preferable, and these chalcogen compounds may be mixed and used as necessary. A positive electrode is formed by molding these positive electrode materials together with an appropriate binder and a carbon material for imparting conductivity to the electrodes and forming a layer on the conductive current collector.

The electrolytic solution of the non-aqueous electrolyte secondary battery is generally formed by dissolving an electrolyte in a non-aqueous solvent. Examples of the non-aqueous solvent include organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyl lactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane. Can be used alone or in combination of two or more. Further, as the electrolyte, LiClO ^{¬ 4} , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB (C ₆ H ₅ ) ₄ , LiN (SO ₃ CF ₃ ) _2, or the like is used. ..

The non-aqueous electrolyte secondary battery may include a separator between the positive electrode and the negative electrode. As the separator, a permeable or liquid-permeable separator made of a non-woven fabric or other porous material usually used for a secondary battery can be used. Alternatively, instead of the separator, or together with the separator, a solid electrolyte composed of a polymer gel impregnated with an electrolytic solution can be used.

The non-aqueous electrolyte secondary battery using the negative electrode active material obtained in the present invention exhibits a sufficient charge / discharge capacity, and is expected to be applied to various applications.

Hereinafter, the present invention will be specifically described with reference to Examples, but these do not limit the scope of the present invention. In addition, although each measurement method of a negative electrode active material is described below, each measurement result described in this specification including an Example is based on the value obtained by the following method.

(Charge / discharge test)
The coin cells obtained in each Example and Comparative Example were subjected to a charge / discharge test after measuring the DC resistance value before the first charge using a charge / discharge test device (manufactured by Toyo System Co., Ltd., “TOSCAT”). Lithium was doped at 0.26 mA with respect to the mass of the active material and doped to 5 mV with respect to the lithium potential. The initial capacity (mAh / g) at this time was defined as the charging capacity. Next, it was carried out at 0.26 mA with respect to the mass of the active material, dedoping was carried out until it became 3.0 V with respect to the lithium potential, and the discharged capacitance at this time constitutes an aromatic ring structure and a ring of the aromatic ring structure. The value converted per mass of the compound having two or more COOM groups bonded to the atom to be used was evaluated as the initial cell volume (mAh / g). Further, the capacity expressed in the flat potential region (0.95-1.05 V vs. Li ^/ Li ^{+ for} dilithium terephthalate) obtained by the initial discharge curve is defined as the initial flat region capacity, and the initial flat region capacity is further used. Dilithium terephthalate was divided by the theoretical volume of 301 mAh / g to obtain the compound utilization efficiency (%).

(Example 1)
Put terephthalic acid and ion-exchanged water in a three-necked flask, stir with a magnetic stirrer, disperse terephthalic acid in ion-exchanged water, and then add an aqueous solution of lithium hydroxide monohydrate in ion-exchanged water. It was added to the dispersion and stirred at 80 ° C. under reflux. With respect to 8.8 g of terephthalic acid, 4.2 g of lithium hydroxide monohydrate and 300 mL of ion-exchanged water were used. Then, it was transferred to a flask forming a content liquid, and ion-exchanged water was distilled off using a rotary evaporator. The precipitated powder was placed in a screw tube, the pressure was reduced to 19 Pa, and the mixture was dried at 60 ° C. to obtain dilithium terephthalate.
The obtained dilithium terephthalate was dissolved in ion-exchanged water to prepare a 15% by mass dilithium terephthalate aqueous solution. An operation of mixing a 15% by mass dilithium terephthalate aqueous solution with acetylene black (manufactured by Denka, product name "Denka Black Li-100") (solid content concentration in the mixture is 20% by mass) and drying at 80 ° C. for 5 minutes. Was repeated 6 times until the mass ratio of dilithium terephthalate to acetylene black was 2: 1 to obtain the negative electrode active material (1).
To prepare the negative electrode, 90 parts by weight of the negative electrode active material (A) and 10 parts by weight of PVDF (polyvinylidene fluoride) are mixed, NMP (N-methylpyrrolidone) is added, and the solid content concentration is 20 by using a ball mill. A slurry having a mass% was obtained. The obtained slurry was applied onto a copper foil having a thickness of 18 μm, dried, and then pressed to obtain an electrode having a thickness of 70 μm. The electrode obtained above was used as a negative electrode punched to a diameter of 14 mm, and a metallic lithium foil punched to a diameter of 15 mm was used as a positive electrode. As the electrolyte, a mixed solvent (volume ratio EC / EMC / DMC = 1/1/1) of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) was used as a solvent, and this solvent was used. LiClO ₄ was dissolved in 1 mol / L and used. A polypropylene film was used for the separator. A coin cell was prepared in a glove box under an argon atmosphere. This coin cell was subjected to a charge / discharge test according to the above method. The results are shown in Table 1.

(Example 2)
The negative electrode active material (A) of Example 1 was heat-treated at 400 ° C. for 3 hours to obtain a negative electrode active material (B). The evaluation was carried out in the same manner as in Example 1 except that the negative electrode active material (A) was replaced with the negative electrode active material (B) to prepare an electrode. The results are shown in Table 1.

(Example 3)
A negative electrode active material (referred to as a negative electrode active material (C)) was prepared and evaluated in the same manner as in Example 1 except that 8.1 g of fumaric acid was used instead of terephthalic acid in Example 1. The theoretical capacity of dilithium phthalate was 387 mAh / g, and the utilization efficiency was calculated. The results are shown in Table 1.

(Example 4)
A negative electrode active material (referred to as a negative electrode active material (D)) was prepared and evaluated in the same manner as in Example 3 negative electrode active material except that maleic acid was used instead of fumaric acid in Example 3. The theoretical capacity of dilithium maleate was 387 mAh / g, and the utilization efficiency was calculated. The results are shown in Table 1.

(Example 5)
In Example 4, a negative electrode active material (referred to as a negative electrode active material (E)) was prepared and evaluated in the same manner as in Example 4, except that the aqueous solution was not sequentially added to the carbon material but was added all at once. The results are shown in Table 1.

(Comparative Example 1)
60 parts by weight of dilithium terephthalate obtained in Example 1, 30 parts by weight of acetylene black, and 10 parts by weight of PVDF (polyvinylidene fluoride) were mixed, NMP (N-methylpyrrolidone) was added, and a planetary ball mill was used. A slurry-like electrode mixture having a solid content concentration of 20% was obtained. The obtained electrode mixture was applied onto a copper foil having a thickness of 18 μm, dried, and then pressed to obtain an electrode having a thickness of 70 μm, and the evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
Dilithium terephthalate obtained in Example 1 and acetylene black as a carbon material were placed in an agate crushing container containing agate balls so as to have a weight ratio of 2: 1 and treated with a mixer mill at a frequency of 15 Hz for 30 minutes. The negative electrode active material (F) was obtained. The evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

From Table 1, as compared with Comparative Examples 1 and 2, in the coin cell produced by using the negative electrode active materials A to F of Examples 1 to 5 obtained by the method of the present invention, the initial flat region capacity and the initial cell capacity were higher. The utilization efficiency was shown.

Claims (4)

Non-compounding, including (1) a step of mixing an aqueous solution containing a compound having a conjugated polyvalent carboxylic acid salt structure showing water solubility with a carbon material to obtain a mixture, and (2) a step of distilling off water in the mixture. A method for producing a negative electrode active material for an aqueous secondary battery. The method for producing a negative electrode active material for a non-aqueous secondary battery according to claim 1, wherein the metal constituting the carboxylate of the compound is an alkali metal element. The production method according to claim 1 or 2, wherein the compound has 4 to 14 carbon atoms. The production method according to any one of claims 1 to 3, wherein the structure of the compound is at least one selected from the compounds represented by the following formulas (I) to (III).

(I)
(In the formula, m represents an integer of 1 to 2, M represents a metal element, and R ¹ and R ² each independently have at least one selected from the group consisting of a hydroxyl group, a halogen, and a carboxyl group as substituents. It represents either an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group.)

(II)
(In the formula, n represents an integer of 1 to 2, M represents a metal element, and R ³ , R ⁴ , R ⁵ and R ⁶ are independently substituted groups consisting of a hydroxyl group, a halogen and a carboxyl group. It represents either an alkyl group having 1 to 2 carbon atoms, a hydrogen, a carboxyl group, or a chloride carboxyl group which may have at least one selected.)

(III)
(In the formula, M represents a metal element, and R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ and R ¹² are at least one independently selected from the group consisting of hydroxyl groups, halogens and carboxyl groups as substituents. It represents either an alkyl group having 1 to 2 carbon atoms, hydrogen, a carboxyl group, or a chloride carboxyl group which may have one.)