JP2020007474A - Aromatic aliphatic mixed cellulose ester, additive for nonaqua electrolyte secondary battery positive electrode, positive electrode for nonaqua electrolyte secondary battery, and manufacturing method of positive electrode for nonaqua electrolyte secondary battery - Google Patents

Abstract

To provide an electrode of a nonaqua electrolyte secondary battery small in environmental load and having excellent electrolyte resistance.SOLUTION: There is provided aromatic aliphatic mixed cellulose ester having aromatic acyl group substitution degree (DS) of 0.1 to 2.9, and aliphatic acyl group substitution degree (DS) of 0.1 to 2.9.SELECTED DRAWING: None

Description

  The present invention relates to an aromatic / aliphatic mixed cellulose ester, an additive for a non-aqueous electrolyte secondary battery positive electrode, a positive electrode for a non-aqueous electrolyte secondary battery, and a method for producing a positive electrode for a non-aqueous electrolyte secondary battery.

  2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries (non-aqueous secondary batteries) represented by lithium ion secondary batteries having a high energy density and a high capacity have been used as driving power supplies for mobile terminal devices such as mobile phones and notebook personal computers. Is widely used. The mobile terminal devices are being improved in performance, downsizing and weight reduction, and non-aqueous electrolyte secondary batteries are being used in hybrid vehicles (HEV), electric power tools and the like. It has been studied to increase the capacity and output of non-aqueous electrolyte secondary batteries. In addition, with the increase in capacity and output of nonaqueous electrolyte secondary batteries, it is also required to suppress deterioration in battery characteristics due to expansion and contraction of electrodes due to repeated charge and discharge.

  The production of an electrode is usually performed by combining an active material, a conductive assistant, a binder, an organic solvent, and the like, dispersing the slurry, applying the slurry, applying the slurry on a current collector, and drying and solidifying the slurry. As the binder, an organic fluorine compound such as PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) is usually used. Patent Documents 1 and 2 describe the use of an organic fluorine compound such as a vinylidene fluoride copolymer. However, these fluorine compounds are poor in decomposability under a natural environment and have a large environmental load. For this reason, use of a polysaccharide such as a cellulose derivative having a small environmental load as a binder instead of the organic fluorine compound has been studied.

  Patent Literature 3 discloses “a current collector and a positive electrode active material formed on the current collector and containing a positive electrode active material, a thickener containing a nonionic cellulose compound, a conductive agent, and a binder. A positive electrode for a lithium secondary battery, comprising:

Japanese Patent No. 5797206 Japanese Patent No. 6095654 JP 2004-349263 A

  A non-aqueous electrolyte secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator, and the like.However, conventional electrodes containing a cellulose derivative do not have sufficient electrolyte resistance, swell with the electrolyte, and deteriorate battery characteristics. connected.

  The present invention provides an additive for a positive electrode of a non-aqueous electrolyte secondary battery having a small environmental load, excellent solubility in an organic solvent used for producing an electrode of a non-aqueous electrolyte secondary battery, and excellent electrolyte resistance. The purpose is to do.

A first aspect of the present invention is that an aromatic acyl group substitution degree (DS _Bz ) is 0.1 or more and 2.9 or less, and an aliphatic acyl group substitution degree (DS _St ) is 0.1 or more and 2.9 or less. The present invention relates to a mixed aromatic-aliphatic cellulose ester.

A second aspect of the present invention includes an aromatic-aliphatic mixed cellulose ester, wherein the aromatic-aliphatic mixed cellulose ester has an aromatic acyl group substitution degree (DS _Bz ) of 0.1 to 2.9, and a saturated fatty acid. The present invention relates to an additive for a positive electrode of a non-aqueous electrolyte secondary battery, having a degree of substitution of group acyl group (DS _St ) of 0.1 or more and 2.9 or less.

  The third aspect of the present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, comprising the additive for a positive electrode for a non-aqueous electrolyte secondary battery.

  A fourth step of the present invention is to prepare a slurry by dispersing the additive for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode active material, a conductive auxiliary, and an organic solvent, and to form the slurry into a foil-like current collector. And a method of producing a positive electrode for a non-aqueous electrolyte secondary battery.

  According to the present invention, an environmental load is small, the solubility in an organic solvent used for producing an electrode of a non-aqueous electrolyte secondary battery is excellent, and the additive for a positive electrode of a non-aqueous electrolyte secondary battery having excellent electrolyte resistance is provided. Can be provided.

[Aromatic and aliphatic mixed cellulose ester]
The aromatic-aliphatic mixed cellulose ester of the present disclosure refers to an aromatic-aliphatic mixed cellulose ester in which the hydrogen of the hydroxyl group of cellulose is substituted with an aromatic acyl group and a saturated aliphatic acyl group. The degree of acyl group substitution (DS _Bz ) is 0.1 or more and 2.9 or less, and the degree of substitution of saturated aliphatic acyl group (DS _St ) is 0.1 or more and 2.9 or less.

  The aromatic acyl group refers to an acyl group having an unsubstituted aromatic ring and an aromatic ring substituted with a hydroxyl group, a halogen atom, and an alkyl group having 1 to 4 carbon atoms. Examples of the aromatic acyl group include a benzoyl group, a 2-methylbenzoyl group, a 2-methoxybenzoyl group, a 4-methylbenzoyl group, and a 4-methoxybenzoyl group. Among these, a benzoyl group is desirable.

  The saturated aliphatic acyl group refers to a saturated aliphatic acyl group having 14 to 20 carbon atoms, and may be linear or branched. Examples of the saturated aliphatic acyl group include a myristoyl group, a pentadecanoyl group, a palmitoyl group, a heptadecanoyl group, a stearoyl group, an isostearoyl group, a nonadecanoyl group, and an icosanoyl group. Among these, a stearoyl group is preferable.

  The aromatic / aliphatic mixed cellulose esters of the present disclosure include cellulose benzoate stearate.

  The mixed aromatic / aliphatic cellulose ester of the present disclosure has a small environmental load, has excellent solubility in an organic solvent used for producing an electrode of a nonaqueous electrolyte secondary battery, and has excellent electrolyte resistance. Therefore, by adding the aromatic-aliphatic mixed cellulose ester of the present disclosure, it is possible to obtain a positive electrode for a non-aqueous electrolyte secondary battery having a small environmental load and excellent electrolyte resistance.

Although the aromatic acyl group substitution degree (DS _Bz ) of the aromatic / aliphatic mixed cellulose ester of the present disclosure is 0.1 or more and 2.9 or less, it is preferably 1.8 or more and 2.8 or less, and is 2.2 or more. 2.7 or less is more preferable. The degree of substitution of the saturated aliphatic acyl group (DS _St ) is 0.1 to 2.9, preferably 0.15 to 1.0, more preferably 0.2 to 0.7. When the degree of substitution of the aromatic acyl group (DS _Bz ) and the degree of substitution of the saturated aliphatic acyl group (DS _St ) are within the above ranges, the organic solvent used for preparing the electrode of the non-aqueous electrolyte secondary battery, particularly N- Excellent solubility in methyl-2-pyrrolidone (NMP). Further, it has excellent swelling resistance and dissolution resistance to an electrolyte that can be used for a nonaqueous electrolyte secondary battery, particularly to ethylene carbonate and propylene carbonate.

Here, the aromatic acyl group substitution degree (DS _Bz ) refers to an aromatic acyl group that substitutes a hydrogen atom of a hydroxyl group (hydroxyl group at the 2-, 3-, and 6-position) per repeating unit (glucopyranose unit) of cellulose. Shows the number of groups (average value). The degree of substitution of a saturated aliphatic acyl group (DS _St ) refers to a saturated aliphatic group that substitutes a hydrogen atom of a hydroxyl group (hydroxyl group at the 2-, 3-, and 6-position) per repeating unit (glucopyranose unit) of cellulose. Shows the number (average value) of acyl groups.

The degree of substitution of the aromatic acyl group (DS _Bz ) and the degree of substitution of the saturated aliphatic acyl group (DS _St ) can be measured by the following methods. It can be measured by a method according to ASTM: D-817-91, ¹³ C-NMR, or ¹ H-NMR.

Hereinafter, examples of the conditions when the degree of substitution of the aromatic acyl group (DS _Bz ) and the degree of substitution of the saturated aliphatic acyl group (DS _St ) of cellulose benzoate stearate are quantified by ¹ H-NMR will be described.

Apparatus: JEOL JNM ECA-500
Temperature: 30 ° C
Solvent: CDCl ₃
Sample concentration: 0.8 wt%
Calculation:
Degree of substitution of aromatic acyl group (DS _Bz ) = 7α / 5β
Saturated aliphatic acyl group substitution degree (DS _St ) = 7γ / 35β
α: integrated value of 8.1 to 6.7 ppm β: integrated value of 5.5 to 2.7 ppm γ: integrated value of 2.0 to 0.4 ppm

Further, for the aromatic / aliphatic mixed cellulose ester of the present disclosure, the number of hydroxyl groups in which the hydrogen of the hydroxyl group of cellulose is not substituted is determined by the number of hydroxyl groups (2-, 3-, and 6-positions) per repeating unit (glucopyranose unit) of cellulose. The number (average value) of the number of hydroxyl groups is represented by _DSOH . _{DS OH} aromatic aliphatic mixed cellulose ester of the present disclosure is preferably 0 or 2.8 or less, more preferably 0 to 1.5, more preferably 0 to 1.0. If the degree of substitution of the hydroxyl group is too high, it dissolves or swells in an electrolyte that can be used for a nonaqueous electrolyte secondary battery, particularly, ethylene carbonate, propylene carbonate, or the like, and has an undesirable effect.

  The aromatic-aliphatic mixed cellulose ester of the present disclosure can be prepared by reacting cellulose with a halide of an aromatic carboxylic acid and a halide of a saturated aliphatic carboxylic acid in the presence of a base catalyst.

[Non-aqueous electrolyte secondary battery positive electrode additive]
The additive for a positive electrode of a nonaqueous electrolyte secondary battery according to the present disclosure contains an aromatic-aliphatic mixed cellulose ester, and the aromatic-aliphatic mixed cellulose ester has an aromatic acyl group substitution degree (DS _Bz ) of 0.1 or more. 2.9 or less, and the degree of substitution of the saturated aliphatic acyl group (DS _St ) is 0.1 or more and 2.9 or less.

  The additive for a positive electrode of a non-aqueous electrolyte secondary battery according to the present disclosure has a small environmental load, has excellent solubility in an organic solvent used for manufacturing an electrode of the non-aqueous electrolyte secondary battery, and has excellent electrolyte resistance. Therefore, according to the additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure, a positive electrode for a nonaqueous electrolyte secondary battery having a small environmental load and excellent electrolyte resistance can be obtained.

  Non-aqueous electrolyte secondary battery is a general term for secondary batteries using electrolytes other than aqueous solutions. Examples of electrolytes other than aqueous solutions include organic electrolytes, polymer gel electrolytes, solid electrolytes, polymer electrolytes, and molten salt electrolytes. Is mentioned. Examples of the nonaqueous electrolyte secondary battery include a lithium ion battery and a lithium ion capacitor.

  The non-aqueous electrolyte secondary battery can include at least a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode.

  The production of an electrode (especially a positive electrode) of a nonaqueous electrolyte secondary battery is performed, for example, by dispersing an active material, a conductive auxiliary agent, a binder, an organic solvent, and the like to form a slurry, applying the slurry on a current collector, and drying and solidifying The organic solvent is, for example, an aromatic solvent such as N-methyl-2-pyrrolidone (NMP), toluene or xylene; an amide such as dimethylformamide or dimethylacetamide. Known solvents include ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as acetate; and hydrocarbon solvents such as hexane and cyclohexane. These organic solvents may be used alone or in combination of two or more.

When the degree of substitution of the aromatic acyl group (DS _Bz ) of the aromatic-aliphatic mixed cellulose ester is from 0.1 to 2.9, it is preferably from 1.8 to 2.8, and more preferably from 2.2 to 2.7. The following is more preferred. The degree of substitution of the saturated aliphatic acyl group (DS _St ) is 0.1 to 2.9, preferably 0.15 to 1.0, more preferably 0.2 to 0.7. When the degree of substitution of the aromatic acyl group (DS _Bz ) and the degree of substitution of the saturated aliphatic acyl group (DS _St ) are within the above ranges, the organic solvent used for preparing the electrode of the non-aqueous electrolyte secondary battery, particularly N- Excellent solubility in methyl-2-pyrrolidone (NMP). Further, it has excellent swelling resistance and dissolution resistance to an electrolyte that can be used for a nonaqueous electrolyte secondary battery, particularly to ethylene carbonate and propylene carbonate.

  Further, by adding the additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure to an electrode, an electrode having high flexibility and excellent adhesion between an electrode coating film and a current collector can be obtained.

  The additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure can improve the binding between active materials, and the adhesion between a coating film and a current collector, and is therefore preferably added as a binder constituting an electrode. . The binder binds the active materials or binds the coating film and the current collector to maintain a conductive network structure.

  The additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure may be used in combination with a conventionally known organic fluorine compound such as PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene) as a binder.

  The additive for a positive electrode of a non-aqueous electrolyte secondary battery according to the present disclosure has excellent solubility in an organic solvent used for manufacturing an electrode of a non-aqueous electrolyte secondary battery, and therefore, the addition thereof facilitates the manufacture of the electrode.

[Positive electrode for non-aqueous electrolyte secondary battery]
The positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure contains the additive for a positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode for a nonaqueous electrolyte secondary battery according to the present disclosure has a small environmental load and has excellent electrolyte resistance. Further, it has high flexibility and excellent adhesion between the electrode coating film and the current collector.

[Method of manufacturing positive electrode for non-aqueous electrolyte secondary battery]
The method of manufacturing a positive electrode for a non-aqueous electrolyte secondary battery of the present disclosure includes a step of preparing a slurry by dispersing the positive electrode additive for a non-aqueous electrolyte secondary battery, a positive electrode active material, a conductive auxiliary, and an organic solvent, Applying the slurry onto a foil-like current collector.

(Step of preparing slurry)
In the step of preparing the slurry, the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive auxiliary, and the organic solvent are dispersed.

  The method of dispersing the additive for the positive electrode of the nonaqueous electrolyte secondary battery, the positive electrode active material, the conductive additive, and the organic solvent is not particularly limited, and a known method can be employed. The order of adding the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive additive, and the organic solvent is not particularly limited. For example, a slurry is prepared by adding an additive for the positive electrode of the non-aqueous electrolyte secondary battery (for example, the mixed cellulose ester of the aromatic / aliphatic), a positive electrode active material, and a conductive additive to an organic solvent and dispersing the same. And a method of adding and dispersing a positive electrode active material to an organic solvent, adding and dispersing a conductive auxiliary to the organic solvent, and further adding the additive for the positive electrode of the nonaqueous electrolyte secondary battery (for example, the aromatic aliphatic A method of preparing a slurry by adding and dispersing a mixed cellulose ester).

  Dispersion may be performed using a pulverizer or a classifier. Examples thereof include a mortar, a ball mill, a bead mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air jet mill, and a sieve.

  Here, the slurry refers to a suspension obtained by suspending the nonaqueous electrolyte secondary battery positive electrode additive, the positive electrode active material, and a conductive auxiliary in an organic solvent, and the slurry includes the nonaqueous electrolyte. In addition to the secondary battery positive electrode additive, the positive electrode active material, and the conductive additive, an arbitrary component may be included.

(Additive for non-aqueous electrolyte secondary battery positive electrode)
As described above, the additive for the positive electrode of the nonaqueous electrolyte secondary battery contains an aromatic-aliphatic mixed cellulose ester.

  The content of the additive for a positive electrode of a nonaqueous electrolyte secondary battery in the slurry is preferably from 0.1% by mass to 10% by mass, and more preferably from 0.1% by mass to 10% by mass, based on the whole solid content of the slurry excluding the organic solvent. The content is more preferably not less than 8% by mass and more preferably not less than 0.1% by mass and not more than 5% by mass.

  As described above, the non-aqueous electrolyte secondary battery positive electrode additive can improve the binding between active materials and the adhesion between the coating film and the current collector. It is suitable as. At this time, a conventionally known organic fluorine compound such as PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) may be used in combination with the additive for a positive electrode of a nonaqueous electrolyte secondary battery according to the present disclosure. .

  Further, the additive for a positive electrode of a non-aqueous electrolyte secondary battery of the present disclosure can enhance the dispersibility of a material constituting an electrode, and is therefore suitable as a dispersant for a positive electrode of a non-aqueous electrolyte secondary battery.

  For example, in the step of preparing the slurry, a positive electrode active material is added and dispersed in an organic solvent, a conductive additive is added and dispersed, and the nonaqueous electrolyte secondary battery positive electrode additive (for example, When the method of preparing a slurry by adding and dispersing the above-mentioned aromatic / aliphatic mixed cellulose ester) is used, in place of the conductive auxiliary, a conductive auxiliary, the non-aqueous electrolyte secondary battery positive electrode additive (For example, the aromatic-aliphatic mixed cellulose ester) and a small amount of an organic solvent dispersed therein can be used. Since the conductive additive has a smaller particle size and poor dispersibility as compared with the active material, the additive for the positive electrode of the non-aqueous electrolyte secondary battery (for example, the aromatic-aliphatic mixed cellulose ester) and a small amount of an organic solvent are used in advance. By dispersing the slurry, the whole obtained slurry can be more uniformly dispersed.

(Positive electrode active material)
The positive electrode active material refers to a material that is directly involved in charging and discharging in a secondary battery and is used for a positive electrode.

As the positive electrode active material, for example, conventionally known materials used in lithium ion secondary batteries, for example, lithium-transition metal composite oxides and lithium-transition metal phosphate compounds capable of inserting and extracting lithium ions Is mentioned. Examples of the lithium-transition metal composite oxide include LiMnO ₂ , LiCoO ₂ , and LiNiO ₂ , and examples of the lithium-transition metal phosphate compound include LiFePO ₄ .

  The content of the positive electrode active material in the slurry is preferably from 70% by mass to 99% by mass, more preferably from 80% by mass to 99% by mass, based on the entire solid content of the slurry excluding the organic solvent.

(Conductive agent)
The conductive assistant refers to a substance that assists conductivity between active materials.

  Examples of the conductive assistant include conductive carbon such as carbon black, carbon nanotube, acetylene black, Ketjen black, graphite, and vapor grown carbon fiber. These conductive aids may be used alone or in combination of two or more.

  The content of the conductive additive in the slurry is preferably from 1% by mass to 25% by mass, and more preferably from 1% by mass to 20% by mass, based on the entire solid content of the slurry excluding the organic solvent.

(Organic solvent)
Examples of the organic solvent include aromatic solvents such as N-methyl-2-pyrrolidone (NMP), toluene, and xylene; amide solvents such as dimethylformamide and dimethylacetamide; ketone solvents such as methyl ethyl ketone and cyclohexanone. Ester solvents such as acetate; and hydrocarbon solvents such as hexane and cyclohexane. These solvents may be used alone or in combination of two or more.

  Further, as described above, the additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure is particularly excellent in solubility in N-methyl-2-pyrrolidone (NMP). Therefore, N-methyl-2-pyrrolidone (NMP) is suitable as the organic solvent used for preparing the slurry.

  The content of the organic solvent in the slurry is preferably from 50 parts by mass to 300 parts by mass, and more preferably from 75 parts by mass to 150 parts by mass, with the solid content of the slurry excluding the organic solvent being 100 parts by mass.

(Optional component)
In the slurry, in addition to the additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure, a positive electrode active material, a conductive auxiliary and an organic solvent, if necessary, a dispersant, a leveling agent, an antioxidant, and a thickener And any other conventionally known optional components.

  As the dispersant, a polymer compound having a hydrophobic chain and a hydrophilic group; an anionic compound having a sulfate, a sulfonate, a phosphate, or the like; a cationic compound such as an amine can be used. Specifically, for example, cellulose, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, and the like can be used.

(Step of applying the slurry on a foil-shaped current collector)
In the step of applying the slurry on the foil-shaped current collector, a conventionally known method can be adopted as a method of applying the slurry to the foil-shaped current collector. Examples of the method for applying the slurry to the current collector include a bar coating method, a spray coating method, a roll coating method, a doctor blade method, a flow coating method, a dip coating method, a screen printing method, and an ink jet method.

The thickness and area of the coating film formed by applying the slurry are not particularly limited, and the coating amount, the coating area, and the like may be appropriately adjusted according to the application, and the coating may be performed. Further, it may be applied to one surface of the foil-shaped current collector, or may be applied to both surfaces. The amount of application may be, for example, a basis weight of one side of 100 g / m ² or more and 500 g / m ² or less.

  As a material for forming the current collector, a conventionally known material can be used. For example, it is preferable to use aluminum which is known as a positive electrode current collector of a lithium ion secondary battery. When aluminum known as a positive electrode current collector is used, copper can be used as a negative electrode current collector. The thickness of the positive electrode current collector may be 1 μm or more and 100 μm or less.

(Optional process)
After the step of applying the slurry on the foil-shaped current collector, the applied slurry may be dried. By drying the slurry, mainly the organic solvent and the like are removed, and the coating film is fixed on the foil-shaped current collector.

  Drying conditions (eg, drying temperature and required time) may be appropriately determined according to the solid content of the slurry, the material contained in the slurry, the thickness of the target coating film, and the like. The temperature is preferably lower than the flash temperature of the organic solvent contained in the slurry and lower than the temperature at which oxidation or discoloration of the current collector occurs. For example, when N-methyl-2-pyrrolidone is used as the organic solvent and aluminum is used as the current collector, the drying temperature is preferably from 60 ° C to 130 ° C, more preferably from 70 ° C to 110 ° C.

  As a drying method, for example, a suitable drying device such as a hot air device, a low-humidity air device, a vacuum device, various infrared devices, an electromagnetic induction device, a microwave device, or a drying promoting means such as a blower can be used alone or in combination. .

  In addition, drying may be performed in a plurality of times. For example, drying may be performed once when arranged on one side of the current collector, and twice when arranged on both sides.

  As the thickness of the dried coating film formed on the current collector, a conventionally known thickness can be adopted. For example, it may be 5 μm or more and 200 μm or less.

[Non-aqueous electrolyte secondary battery]
When a non-aqueous electrolyte secondary battery is manufactured using the positive electrode for a non-aqueous electrolyte secondary battery manufactured by the above-described method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery, it may be manufactured by a conventionally known method.

  At least, the non-aqueous electrolyte secondary battery can include a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode. When a lithium ion secondary battery is manufactured as a non-aqueous electrolyte secondary battery, examples of the electrolyte (especially, electrolyte solution) include ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. Organic solvents such as carbonates can be used.

  The additive for a positive electrode of a nonaqueous electrolyte secondary battery according to the present disclosure is unlikely to swell with an organic solvent of these carbonates, particularly, ethylene carbonate and propylene carbonate. Therefore, the electrode containing the additive for a positive electrode of a nonaqueous electrolyte secondary battery according to the present disclosure is excellent in electrolyte resistance, particularly swelling resistance and dissolution resistance, even when these carbonates are used as an electrolyte. Therefore, the non-aqueous electrolyte secondary battery constituted by the electrode containing the additive for a positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure has battery characteristics even when the electrode is repeatedly expanded and contracted by repeated charge and discharge. Is expected to suppress the decrease in

  EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the technical scope of the present invention is not limited by these Examples.

(Example A-1)
30 g of cellulose, 156 g of benzoyl chloride, and 300 g of pyridine were placed in a round-bottom flask equipped with a stirrer and a condenser, and stirred at room temperature. Thereafter, the temperature was raised to 100 ° C., and the stirring time was adjusted so that the degree of substitution (DS _Bz ) became 2.55.

  1500 g of methanol was added to the obtained reaction solution to obtain a wet cake of crude cellulose benzoate as a base white solid.

  Methanol was added to the obtained wet cake, and the resultant was washed by stirring and then drained. After repeating the washing operation with methanol three more times, the solvent was replaced with water. It was dried with a hot air drier to obtain 65 g of cellulose benzoate.

The obtained cellulose benzoate (DS _Bz = 2.55), 100 g of stearyl chloride, 600 g of pyridine, and 2 g of 4-dimethylaminopyridine were placed in a round bottom flask equipped with a stirrer and a condenser, and stirred at 80 ° C. for 5 hours.

  2000 g of ethanol was added to the obtained reaction solution to obtain a wet cake of crude cellulose benzoate stearate as a white base solid.

  Ethanol was added to the obtained wet cake, which was washed by stirring and drained. After repeating the washing operation with ethanol three more times, the solvent was replaced with water. It was dried with a hot air drier to obtain 75 g of cellulose benzoate stearate.

For the obtained cellulose benzoate stearate, the degree of benzoyl substitution (DS _Bz ) and the degree of stearoyl substitution (DS _St ) were measured by the following method, and the electrolyte resistance and the dissolution in an organic solvent used for producing an electrode were measured. Sex was evaluated respectively. The results are shown in Table 1.

(Degree of benzoyl substitution (DS _Bz ) and degree of stearoyl substitution (DS _St ))
The degree of substitution of the aromatic acyl group (DS _Bz ) and the degree of substitution of the saturated aliphatic acyl group (DS _St ) were quantified by ¹ H-NMR under the following conditions.
Apparatus: JEOL JNM ECA-500
Temperature: 30 ° C
Solvent: CDCl ₃
Sample concentration: 0.8 wt%
Calculation:
Degree of substitution of aromatic acyl group (DS _Bz ) = 7α / 5β
Saturated aliphatic acyl group substitution degree (DS _St ) = 7γ / 35β
α: integrated value of 8.1 to 6.7 ppm β: integrated value of 5.5 to 2.7 ppm γ: integrated value of 2.0 to 0.4 ppm

(Electrolyte resistance)
About 0.1 g of a sample was placed in a 9-ml sample tube so that the sample concentration was about 5% by mass, and then about 2 g of an organic solvent was placed as an electrolyte. The mixture was stirred at 45 ° C. overnight, and the inside of the sample tube was visually observed. When ethylene carbonate was used as the organic solvent and when propylene carbonate was used as the organic solvent, the electrolyte resistance was evaluated for each case.

The electrolyte resistance was evaluated according to the following criteria.
A: The sample does not dissolve in the organic solvent, does not swell, and remains powdery.
B: The sample does not dissolve in the organic solvent, but swells and no powder remains.
C: The sample is almost dissolved in the organic solvent. There is no swelling part and it is a little dirty or a transparent solution.

(Solubility in organic solvents)
About 0.1 g of the sample was placed in a 9-ml sample tube so that the sample concentration was about 5% by mass, and then about 2 g of N-methyl-2-pyrrolidone (NMP). The mixture was stirred at 45 ° C. overnight, and the inside of the sample tube was visually observed.

The solubility in organic solvents was evaluated according to the following criteria.
A: The sample does not dissolve in the organic solvent, does not swell, and remains powdery.
B: The sample does not dissolve in the organic solvent, but swells and no powder remains.
C: The sample is almost dissolved in the organic solvent. There is no swelling part and it is a little dirty or a transparent solution.

(Comparative Example A-1)
Cellulose triacetate (acetyl substitution degree: 2.9, LT-35: manufactured by Daicel Co., Ltd.) was evaluated for electrolyte resistance and solubility in an organic solvent used for producing an electrode by the methods described above. The results are shown in Table 1.

(Comparative Example A-2)
Cellulose diacetate (acetyl substitution degree: 2.4, L-30: manufactured by Daicel Co., Ltd.) was evaluated for electrolyte resistance and solubility in an organic solvent used for producing an electrode by the methods described above. The results are shown in Table 1.

(Comparative Example A-3)
For methylcellulose (degree of methyl substitution: 1.8, manufactured by Wako Pure Chemical Industries, Ltd.), the electrolyte resistance and the solubility in an organic solvent used for producing an electrode were evaluated by the methods described above. The results are shown in Table 1.

(Comparative Example A-4)
PVDF (polyvinylidene fluoride: KYNAR (registered trademark) HSV900) was evaluated for electrolyte resistance and solubility in an organic solvent used for manufacturing an electrode by the above-described methods. The results are shown in Table 1.

(Comparative Example A-5)
PVDF (polyvinylidene fluoride: KYNAR (registered trademark) HSV1800) was evaluated for electrolyte resistance and solubility in an organic solvent used for producing an electrode by the above-described methods. The results are shown in Table 1.

  As shown in Table 1, the aromatic-aliphatic mixed cellulose ester and the additive for a positive electrode of a nonaqueous electrolyte secondary battery of the present disclosure have excellent solubility in an organic solvent used for manufacturing an electrode of a nonaqueous electrolyte secondary battery. It has excellent electrolyte resistance without dissolving or swelling in the electrolyte.

(Example B-1)
100 parts by mass of lithium cobaltate (LiCoO ₂ ) (manufactured by Nippon Chemical Industries, Cell Seed C5H), ₂ parts by mass of carbon black (manufactured by Denki Kagaku Kogyo, Denka Black), 2 parts by mass of cellulose benzoate stearate obtained by Example A-1 The resulting mixture was dispersed in N-methyl-2-pyrrolidone to prepare a slurry (in other words, a slurry-like positive electrode mixture). The addition amount of N-methyl-2-pyrrolidone is appropriately adjusted according to the inherent viscosity (intrinsic viscosity) of cellulose benzoate stearate, and the viscosity of the mixture is determined by using an E-type viscometer at 25 ° C. and a shear rate of 2 s ^−. When the measurement was performed at ¹ , the sample was adjusted to be 5000 to 30000 mPa · s. The addition amount of N-methyl-2-pyrrolidone was 120 parts by mass with respect to 100 parts by mass of the total content of lithium cobaltate (LiCoO ₂ ), carbon black, and cellulose benzoate stearate obtained in Example A-1. It became.

The slurry (in other words, the positive electrode mixture) is applied on a 15 μm-thick Al (aluminum) foil with a bar coater (bar coating method), and dried with hot air at 110 ° C. for 30 minutes, and the weight per side is 200 g / m ^2. The single-sided coated electrode (positive electrode) was produced. About the obtained electrode, the adhesiveness between the electrode coating film and the current collector was evaluated by the following method. The results are shown in Table 2.

(Adhesion: electrode bending test)
The adhesion between the electrode coating and the current collector was evaluated by the following method. The electrode was cut into a rectangle having a width of 25 mm and a length of 90 mm to obtain a test piece. The test piece was wound around a stainless steel rod having a diameter of 10 mm, and the presence or absence of cracks in the electrode was visually evaluated according to the following criteria. The less cracking or peeling, the higher the flexibility of the electrode, and the better the adhesion between the electrode coating and the current collector.
A: No cracks were observed B: Cracks were observed on the surface C: Cracks occurred and peeling occurred

(Example B-2)
100 parts by mass of lithium cobaltate (LiCoO ₂ ) (manufactured by Nippon Chemical Industry, Cell Seed C5H), ₂ parts by mass of carbon black (manufactured by Denki Kagaku Kogyo, Denka Black), polyvinylidene fluoride-hexafluoropropylene copolymer (Arkema Corporation) 2 parts by mass) and 2 parts by mass of the cellulose benzoate stearate obtained in Example A-1 were dispersed in N-methyl-2-pyrrolidone to prepare a slurry (in other words, a slurry-like positive electrode mixture). did. The addition amount of N-methyl-2-pyrrolidone is appropriately adjusted according to the inherent viscosity (intrinsic viscosity) of the vinylidene fluoride copolymer and cellulose benzoate stearate, and the viscosity of the mixture is measured using an E-type viscometer. , 25 ° C., and a shear rate of 2 s ⁻¹ , were adjusted to 5,000 to 30,000 mPa · s. The amount of N-methyl-2-pyrrolidone added was the total of lithium cobaltate (LiCoO ₂ ), carbon black, polyvinylidene fluoride-hexafluoropropylene copolymer, and cellulose benzoate stearate obtained in Example A-1. The content was 135 parts by mass with respect to 100 parts by mass.

The slurry (in other words, the positive electrode mixture) is applied on a 15 μm-thick Al (aluminum) foil with a bar coater (bar coating method), and dried with hot air at 110 ° C. for 30 minutes, and the weight per side is 200 g / m ^2. The single-sided coated electrode (positive electrode) was produced. About the obtained electrode, the adhesiveness of the electrode coating film and a collector was evaluated by the above-mentioned method. The results are shown in Table 2.

(Example B-3)
25 parts by mass of carbon black (CB) having an average primary particle size of 14 nm and a specific surface area of 290 m ² / g, 3.75 parts by mass of cellulose benzoate stearate obtained in Example A-1, N-methyl 2-pyrrolidone (NMP) 71.25 parts by mass were mixed to obtain a mixture having a volume of 87 ml. The mixture was dispersed in 87 cm ³ of zirconia beads having a diameter of 0.25 mm as medium particles using a sand mill at a disk rotation speed of 10 m / sec for 2 hours to obtain a CB slurry.

  At this time, the number N of the media particles of the zirconia beads was about 81500 / ml per CB slurry volume. The average particle size of the CB slurry measured by a laser diffraction scattering method was 202 nm.

Next, 40 parts by mass of the CB slurry, 85 parts by mass of lithium cobalt oxide (LiCoO ₂ ) (manufactured by Nippon Chemical Industry Co., Ltd., Cell Seed C5H) as a positive electrode active material, and 5 parts by mass of polyvinylidene fluoride (PVDF) were used as a solvent. using N- methyl 2-pyrrolidone (NMP), and mixed so that the solid content concentration became 45 mass%, the diameter is 87cm ³ using 0.25mm zirconia beads, disc circumferential speed of rotation in a sand mill 7 Mixing was performed at a speed of 0.5 m / sec for 15 minutes to prepare a slurry (in other words, a slurry-like positive electrode mixture).

The slurry (in other words, the positive electrode mixture) is applied on a 15 μm-thick Al (aluminum) foil with a bar coater (bar coating method), and dried with hot air at 110 ° C. for 30 minutes, and the weight per side is 200 g / m ^2. The single-sided coated electrode (positive electrode) was produced. About the obtained electrode, the adhesiveness of the electrode coating film and a collector was evaluated by the above-mentioned method. The results are shown in Table 2.

(Comparative Example B-1)
In the same manner as in Example B-2, 2 parts by mass of a polyvinylidene fluoride-hexafluoropropylene copolymer (manufactured by Arkema Corporation) and 2 parts by mass of the cellulose benzoate stearate obtained in Example A-1 were added. Instead of using it, a single-sided coated electrode (positive electrode) was produced using 4 parts by mass of a polyvinylidene fluoride-hexafluoropropylene copolymer (manufactured by Arkema Co., Ltd.). About the obtained electrode, the adhesiveness of the electrode coating film and a collector was evaluated by the above-mentioned method. The results are shown in Table 2.

(Comparative Example B-2)
In the same manner as in Example B-2, a single-side coated electrode (positive electrode) was produced using 2 parts by mass of cellulose benzoate (DS _Bz = 3.0) instead of using 2 parts by mass of cellulose benzoate stearate. About the obtained electrode, the adhesiveness of the electrode coating film and a collector was evaluated by the above-mentioned method. The results are shown in Table 2.

As shown in Table 2, the positive electrode for a nonaqueous electrolyte secondary battery according to the present disclosure has high flexibility and excellent adhesion between the electrode coating film and the current collector.

Claims (4)

An aromatic-aliphatic mixed cellulose having an aromatic acyl group substitution degree (DS _Bz ) of 0.1 or more and 2.9 or less, and a saturated aliphatic acyl group substitution degree (DS _St ) of 0.1 or more and 2.9 or less. ester. Containing aromatic-aliphatic mixed cellulose ester,
The aromatic-aliphatic mixed cellulose ester has an aromatic acyl group substitution degree (DS _Bz ) of 0.1 or more and 2.9 or less, and a saturated aliphatic acyl group substitution degree (DS _St ) of 0.1 or more and 2.9 or less. An additive for a positive electrode of a non-aqueous electrolyte secondary battery.   A positive electrode for a non-aqueous electrolyte secondary battery, comprising the additive for a positive electrode for a non-aqueous electrolyte secondary battery according to claim 2. A step of preparing a slurry by dispersing the nonaqueous electrolyte secondary battery positive electrode additive according to claim 2, a positive electrode active material, a conductive auxiliary, and an organic solvent,
Applying the slurry onto a foil-like current collector.