JP7064399B2 - A method for manufacturing an additive for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode for a non-aqueous electrolyte secondary battery, and a positive electrode for a non-aqueous electrolyte secondary battery. - Google Patents

Description

The present invention relates to an additive for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode for a non-aqueous electrolyte secondary battery, and a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery.

In recent years, non-aqueous electrolyte secondary batteries (non-aqueous secondary batteries) represented by lithium-ion secondary batteries, which have high energy density and high capacity, as drive power sources for mobile terminal devices such as mobile phones and laptop computers. Is widely used. The mobile terminal devices are becoming higher in performance, smaller in size, and lighter in weight, and non-aqueous electrolyte secondary batteries are being used in hybrid electric vehicles (HEVs), electric tools, and the like. , It is being studied to increase the capacity and output of non-aqueous electrolyte secondary batteries. Further, as the capacity and output of the non-aqueous electrolyte secondary battery are increased, it is also required to suppress the deterioration of the battery characteristics due to the expansion and contraction of the electrode due to repeated charging and discharging.

The electrode is usually produced by combining an active material, a conductive auxiliary agent, a binder, an organic solvent, and the like, dispersing the electrode, forming a slurry, applying the mixture on a current collector, and drying and solidifying the electrode. As the binder, an organic fluorine compound such as PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) is usually used. Further, Patent Documents 1 and 2 describe the use of an organic fluorine compound such as a vinylidene fluoride-based copolymer. However, these fluorine compounds are inferior in decomposability in the natural environment and have a large environmental load. Therefore, it has been studied to use a polysaccharide such as a cellulose derivative having a small environmental load as a binder instead of the organic fluorine compound.

Patent Document 3 describes "a current current collector and a positive electrode active material composition formed on the current current collector and containing a positive electrode active material, a thickener containing a nonionic cellulose-based compound, a conductive agent, and a binder. A positive electrode for a lithium secondary battery, characterized by comprising a physical layer. "

Japanese Patent No. 5979206 Japanese Patent No. 6095654 Japanese Unexamined Patent Publication No. 2004-349263

Journal of Polymer science, part A: Polymer Chemistry 2013, 51, 3590-3597

A non-aqueous electrolyte secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator, and the like. However, the conventional electrode containing a cellulose derivative does not have sufficient electrolyte resistance and swells due to the electrolyte, resulting in deterioration of battery characteristics. connected.

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

The first aspect of the present invention relates to a non-aqueous electrolyte secondary battery positive electrode additive containing dihydroxypropyl cellulose and having a dihydroxypropyl substitution degree (DS) of 0.1 or more.

In the non-aqueous electrolyte secondary battery positive electrode additive, the average number (MS) of dihydroxypropyl groups bonded per glucose unit of the dihydroxypropyl cellulose may be 0.5 or more and 10 or less.

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

The third aspect of the present invention is a step of preparing 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 agent, and an organic solvent, and a foil-shaped current collector of the slurry. The present invention relates to a method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery, which comprises a step of applying on the surface.

According to the present invention, 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. Can be provided.

[Additive for positive electrode of non-aqueous electrolyte secondary battery]
The additive for the positive electrode of a non-aqueous electrolyte secondary battery of the present disclosure contains dihydroxypropyl cellulose, and the dihydroxypropyl substitution degree (DS) of the dihydroxypropyl cellulose is 0.1 or more.

The additive for the positive electrode of a non-aqueous electrolyte secondary battery of the present disclosure has a small environmental load, is excellent in solubility in an organic solvent used for producing an electrode of a non-aqueous electrolyte secondary battery, and has excellent electrolyte resistance. Therefore, according to the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure, it is possible to obtain a positive electrode for the non-aqueous electrolyte secondary battery having a small environmental load and excellent electrolyte resistance.

A non-aqueous electrolyte secondary battery is a general term for a secondary battery using an electrolyte other than an aqueous solution, and examples of the electrolyte other than the aqueous solution include an organic electrolyte, a polymer gel electrolyte, a solid electrolyte, a polymer electrolyte, and a molten salt electrolyte. Can be mentioned. Examples of the non-aqueous 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.

To prepare an electrode (particularly a positive electrode) for a non-aqueous electrolyte secondary battery, for example, an active material, a conductive auxiliary agent, a binder, an organic solvent, etc. are dispersed and made into a slurry, and the slurry is applied onto a current collector and dried and solidified. Then, when it is carried out by forming a coating film, as the organic solvent, for example, an aromatic solvent such as N-methyl-2-pyrrolidone (NMP), toluene or xylene; an amide such as dimethylformamide or dimethylacetamide. System solvents; Ketone solvents such as methyl ethyl ketone and cyclohexanone; Estel solvents such as acetates; Hydrocarbon solvents such as hexane and cyclohexane are known. Further, these organic solvents may be used alone or in combination of two or more.

In dihydroxypropyl cellulose, hydrogen in the hydroxyl group of cellulose is substituted with a dihydroxypropyl group; hydrogen in one or two hydroxyl groups of the dihydroxypropyl group in which hydrogen in the hydroxyl group of cellulose is substituted is further substituted with a dihydroxypropyl group. , And those in which a large number of dihydroxypropyl groups are bonded to each other, such as those in which a dihydroxypropyl group is further bonded to a dihydroxypropyl group in which hydrogen of one or two hydroxyl groups of the dihydroxypropyl group is substituted, are also included.

The dihydroxypropyl substitution degree (DS) of the dihydroxypropyl cellulose is 0.1 or more, preferably 0.2 or more and 2.0 or less, and more preferably 0.3 or more and 1.0 or less. When the dihydroxypropyl substitution degree (DS) is in the above range, the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure is an organic solvent used for producing the electrode of the non-aqueous electrolyte secondary battery, particularly N-methyl. -Excellent solubility in 2-pyrrolidone (NMP). In addition, it is excellent in swelling resistance and solubility resistance to electrolytes that can be used in non-aqueous electrolyte secondary batteries, particularly ethylene carbonate and propylene carbonate.

Here, the degree of substitution (DS) is the number of hydroxyl groups (2-position, 3-position, and 6-position hydroxyl groups) per repeating unit (glucopyranose unit) of cellulose in which hydrogen is substituted. (Average value) is shown.

The degree of dihydroxypropyl substitution (DS) can be measured by the following method. ASTM: Measurement can be performed by a method according to D-817-91, ¹³ C-NMR, and ¹ H-NMR. Specifically, the method disclosed in Non-Patent Document 1 can be used. That is, the degree of substitution (DS) can be quantified by measuring ¹³ C-NMR in DMSO. Based on the fact that the peak of the carbon atom of glucose is detected in different chemical shifts depending on whether the oxygen atom bonded to C2, C3, C4 of glucose is not substituted (C-OH) or is substituted with a carbon atom. ing.

In dihydroxypropyl cellulose, the average number (MS) of dihydroxypropyl groups bonded per glucose unit is preferably 0.5 or more and 10 or less, more preferably 0.7 or more and 5.0 or less, and 0.9 or more and 2.5. The following is more preferable. Due to the above range of MS, the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure is an organic solvent used for producing the electrode of the non-aqueous electrolyte secondary battery, particularly N-methyl-2-pyrrolidone (NMP). ) Has excellent solubility.

The average number of dihydroxypropyl groups bound per glucose unit (MS) can be measured by the following method. It can be quantified by measuring ¹ H-NMR after completely propionyl esterifying dihydroxypropyl cellulose as in the procedure described in Non-Patent Document 1. Dihydroxypropyl cellulose has two types of OH groups, an OH group directly bonded to the cellulose skeleton and an OH group bonded to the dihydroxypropyl group, and these two types of OH groups per glucose ring. The number of is 3+ (MS).

Dihydroxypropyl cellulose can be prepared by reacting cellulose with glycidol or epichlorohydrin under a base catalyst.

Further, by adding the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure to the electrode, it is possible to obtain an electrode having high flexibility and excellent adhesion between the electrode coating film and the current collector.

Since the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure can improve the bondability between active materials and the adhesion between the coating film and the current collector, it is also preferable to add it as a binder constituting the electrode. .. The binder is a binder that binds active materials to each other or a coating film to a current collector to maintain a conductive network structure.

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

Since the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure has excellent solubility in the organic solvent used for producing the electrode of the non-aqueous electrolyte secondary battery, the addition facilitates the production of the electrode.

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

[Manufacturing method of positive electrode for non-aqueous electrolyte secondary battery]
The method for producing a positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure includes a step of dispersing the additive for the positive electrode of the non-aqueous electrolyte secondary battery, a positive electrode active material, a conductive auxiliary agent, and an organic solvent to prepare a slurry. It has a step of applying the slurry onto a foil-shaped current collector.

(Step to prepare 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 agent, and the organic solvent are dispersed.

The method for dispersing the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive auxiliary agent, and the organic solvent is not particularly limited, and a known method can be adopted. The order of addition of the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive auxiliary agent, and the organic solvent is not particularly limited. For example, a method of adding an additive for a positive electrode of a non-aqueous electrolyte secondary battery (for example, the dihydroxypropyl cellulose), a positive electrode active material, and a conductive auxiliary agent to an organic solvent and dispersing them to prepare a slurry; A positive electrode active material is added and dispersed, a conductive auxiliary agent is added and dispersed, and an additive for the positive electrode of the non-aqueous electrolyte secondary battery (for example, the dihydroxypropyl cellulose) is further added to the organic solvent. Examples thereof include a method of preparing a slurry by dispersing.

Dispersion may be performed using a crusher or a classifier. For example, 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 airflow type jet mill, a sieve and the like can be mentioned.

Here, the slurry means a suspension in which the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, and the conductive auxiliary agent are suspended in an organic solvent, and the slurry includes the non-aqueous electrolyte. In addition to the additive for the positive electrode of the secondary battery, the positive electrode active material and the conductive auxiliary agent, any component may be contained.

(Additive for positive electrode of non-aqueous electrolyte secondary battery)
As described above, the additive for the positive electrode of the non-aqueous electrolyte secondary battery contains dihydroxypropyl cellulose.

The content of the additive for the positive electrode of the non-aqueous electrolyte secondary battery in the slurry is preferably 0.1% by mass or more and 10% by mass or less, preferably 0.1% by mass, based on the total solid content of the slurry excluding the organic solvent. 8% by mass or more is more preferable, and 0.1% by mass or more and 5% by mass or less is further preferable.

The additive for the positive electrode of a non-aqueous electrolyte secondary battery is suitable as a binder for the positive electrode of a non-aqueous electrolyte secondary battery because it can improve the bondability between active materials and the adhesion between the coating film and the current collector. .. At this time, an organic fluorine compound such as PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) conventionally known as a binder may be used in combination with the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure. ..

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

For example, in the step of preparing the slurry, the positive electrode active material is added and dispersed with respect to the organic solvent, the conductive auxiliary agent is added and dispersed, and further, the additive for the positive electrode of the non-aqueous electrolyte secondary battery (for example). , The dihydroxypropyl cellulose) is added and dispersed to prepare a slurry, and instead of the conductive auxiliary agent, a conductive auxiliary agent and the additive for the positive electrode of the non-aqueous electrolyte secondary battery (for example, the above-mentioned Dihydroxypropyl cellulose) and a small amount of organic solvent dispersed therein can be used. Since the conductive auxiliary agent has a smaller particle size and poor dispersibility than the active material, it is previously dispersed with the non-aqueous electrolyte secondary battery positive electrode additive (for example, the dihydroxypropyl cellulose) and a small amount of organic solvent. By setting, the entire obtained slurry can be dispersed more uniformly.

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

Examples of the positive electrode active material include conventionally known materials used in lithium ion secondary batteries, such as a lithium-transition metal composite oxide and a lithium-transition metal phosphoric acid compound capable of storing and releasing lithium ions. Can be mentioned. Examples of the lithium-transition metal composite oxide include LiMnO ₂ , LiCoO ₂ , and LiNiO ₂ , and examples of the lithium-transition metal phosphoric acid compound include LiFePO ₄ .

The content of the positive electrode active material in the slurry is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 99% by mass or less, based on the total solid content of the slurry excluding the organic solvent.

(Conductive aid)
The conductive auxiliary agent is a substance that assists the conduction between active materials.

Examples of the conductive auxiliary agent include conductive carbons such as carbon black, carbon nanotubes, acetylene black, ketjen black, graphite, and vapor-grown carbon fibers. These conductive aids may be used alone or in combination of two or more.

The content of the conductive auxiliary agent in the slurry is preferably 1% by mass or more and 25% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, based on the total 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; and ketone solvents such as methylethylketone and cyclohexanone. Examples thereof include ester solvents such as acetic acid esters; 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 the positive electrode of the non-aqueous 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 50 parts by mass or more and 300 parts by mass or less, and more preferably 75 parts by mass or more and 150 parts by mass or less, with the solid content of the slurry being 100 parts by mass excluding the organic solvent.

(Optional ingredient)
In addition to the additives for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive auxiliary agent and the organic solvent of the present disclosure, the slurry includes a dispersant, a leveling agent, an antioxidant, and a thickener, if necessary. It may contain a conventionally known arbitrary component such as.

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; and a cationic compound such as an amine can be used. Specifically, for example, cellulose, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone and the like can be used. Further, the dihydroxypropyl cellulose contained in the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure can enhance the dispersibility of the material constituting the electrode, and thus can be used as a dispersant for the positive electrode of the non-aqueous electrolyte secondary battery. Is also suitable.

(Step of applying the slurry onto a foil-shaped current collector)
In the step of applying the slurry to 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 of 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 inkjet method.

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

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

(Arbitrary 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 organic solvents and the like are removed, and the coating film is fixed on the foil-shaped current collector.

The drying conditions (for example, the drying temperature and the 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. It is preferable that the temperature is lower than the ignition temperature of the organic solvent contained in the slurry and lower than the temperature at which the current collector is oxidized or discolored. 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 60 ° C. or higher and 130 ° C. or lower, and more preferably 70 ° C. or higher and 110 ° C. or lower.

As the drying method, for example, an appropriate 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. ..

Further, the drying may be carried out in a plurality of times, for example, once when it is arranged on one surface of the current collector, and twice when it is arranged on both sides.

As the thickness of the coating film after drying formed on the current collector, a conventionally known thickness can be adopted. For example, it may be 10 μm or more and 80 μm.

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

At the very 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, the electrolyte (particularly the electrolytic solution) may be, for example, ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate or the like. Organic solvents such as carbonates can be used.

The additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure is less likely to swell due to the organic solvents of these carbonates, particularly ethylene carbonate and propylene carbonate. Therefore, the electrode containing the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure is excellent in electrolyte resistance, particularly swelling resistance and solubility resistance, even if the organic solvent of these carbonates is used as an electrolyte. Therefore, the non-aqueous electrolyte secondary battery composed of the electrode containing the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure has battery characteristics even if the electrode is repeatedly expanded and contracted due to repeated charging and discharging. It is expected to suppress the decrease in the battery.

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

(Example A-1)
A mixture of 800 g of water, 60 g of NaOH, and 40 g of urea is placed in a round bottom flask equipped with a stirrer and a cooling tube, 20 g of cellulose (“microcrystalline cellulose”) is added to the mixture, and the mixture is -20 ° C. for 12 hours. Stirred. Subsequently, 140 g of glycidol was added dropwise to the mixed solution, and stirring was continued at room temperature for 24 hours. Further, 93 g of acetic acid was added to neutralize NaOH, and then 1600 g of methanol was added to precipitate the produced dihydroxypropyl cellulose. The obtained precipitate was collected by filtration and washed repeatedly with 1000 mL of methanol to obtain 30.1 g of dihydroxypropyl cellulose.

For the obtained dihydroxypropyl cellulose, the dihydroxypropyl cellulose substitution degree (DS), the average number of dihydroxypropyl groups bonded per glucose unit (MS) were measured by the following methods, and the electrolyte resistance and the electrode were measured. The solubility in the organic solvent used for the production was evaluated. The results are shown in Table 1.

(Example A-2)
24.8 g of dihydroxypropyl cellulose was obtained in the same manner as in Example A-1 except that the amount of glycidol charged was changed to 90 g.

For the obtained dihydroxypropyl cellulose, the dihydroxypropyl cellulose substitution degree (DS), the average number of dihydroxypropyl groups bonded per glucose unit (MS) were measured by the following methods, and the electrolyte resistance and the electrode were measured. The solubility in the organic solvent used for the production was evaluated. The results are shown in Table 1.

(Degree of Substitution of Dihydroxypropyl Cellulose (DS))
Quantified by measuring ¹³ C-NMR in DMSO.

(Average number of dihydroxypropyl groups bound per glucose unit (MS))
After complete propionyl esterification of dihydroxypropyl cellulose, it was quantified by measuring ¹ H-NMR.

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

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

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

Solubility in organic solvents was evaluated according to the following criteria.
A: The sample does not dissolve in organic solvents, does not swell, and remains powdery.
B: The sample does not dissolve in the organic solvent, but it is swollen and no powder remains.
C: The sample is almost dissolved in an organic solvent. There is no swelling part, and it is a slightly turbid or 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 above method. 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 above method. The results are shown in Table 1.

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

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

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

As shown in Table 1, the additive for the positive electrode of the non-aqueous electrolyte secondary battery of the present disclosure has excellent solubility in the organic solvent used for producing the electrode of the non-aqueous electrolyte secondary battery, and also has excellent solubility in the electrolyte. Has excellent electrolyte resistance without dissolving or swelling.

(Example B-1)
Lithium cobaltate (LiCoO ₂ ) (manufactured by Nippon Kagaku Kogyo, Celseed C5H) 100 parts by mass, carbon black (manufactured by Denka Kagaku Kogyo, Denka Black) 2 parts by mass, dihydroxypropyl cellulose obtained by Example A-1 by 2 parts by mass. Was dispersed in N-methyl-2-pyrrolidone to prepare a slurry (in other words, a slurry-like positive electrode mixture). The amount of N-methyl-2-pyrrolidone added is appropriately adjusted according to the intrinsic viscosity (extreme viscosity) of dihydroxypropyl cellulose, and the viscosity of the mixture is 25 ° C. using an E-type viscometer and the shear rate is 2s ^-1 . When the measurement was carried out in, the temperature was adjusted to 5000 to 30000 mPa · s. The amount of N-methyl-2-pyrrolidone added was 120 parts by mass with respect to 100 parts by mass of the total content of lithium cobalt oxide (LiCoO ₂ ), carbon black, and dihydroxypropyl cellulose obtained by Example A-1. rice field.

The slurry (in other words, a positive electrode mixture) is applied on an Al (aluminum) foil having a thickness of 15 μm with a bar coater (bar coat method), dried with hot air at 110 ° C. for 30 minutes, and the amount of one-sided grain is 200 g / m ² . A single-sided coated electrode (positive electrode) was prepared. With respect to the obtained electrode, the adhesion 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 film 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 electrodes was visually evaluated according to the following criteria. The less cracked or peeled off, the more flexible the electrode is, and the better the adhesion between the electrode coating film and the current collector.
A: No cracks were found B: Cracks were found on the surface C: Cracks occurred and peeling occurred.

(Example B-2)
Lithium cobaltate (LiCoO ₂ ) (manufactured by Nippon Kagaku Kogyo, Celseed C5H) 100 parts by mass, carbon black (manufactured by Denka Kagaku Kogyo, Denka Black) 2 parts by mass, polyvinylidene fluoride-hexafluoropropylene copolymer (Alchema Co., Ltd.) Manufactured by) 2 parts by mass and 2 parts by mass of the dihydroxypropyl cellulose 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). .. The amount of N-methyl-2-pyrrolidone added was appropriately adjusted according to the intrinsic viscosity (extreme viscosity) of the vinylidene fluoride-based copolymer and dihydroxypropyl cellulose, and the viscosity of the mixture was adjusted using an E-type viscometer. When the measurement was performed at 25 ° C. and a shear rate of 2s ^-1 , the viscosity was adjusted to 5000 to 30,000 mPa · s. The amount of N-methyl-2-pyrrolidone added is the total content of lithium cobalt oxide (LiCoO ₂ ), carbon black, polyvinylidene fluoride-hexafluoropropylene copolymer, and dihydroxypropyl cellulose obtained by Example A-1. Was 135 parts by mass with respect to 100 parts by mass.

The slurry (in other words, a positive electrode mixture) is applied on an Al (aluminum) foil having a thickness of 15 μm with a bar coater (bar coat method), dried with hot air at 110 ° C. for 30 minutes, and the amount of one-sided grain is 200 g / m ² . A single-sided coated electrode (positive electrode) was prepared. With respect to the obtained electrode, the adhesion between the electrode coating film and the current collector was evaluated by the above 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 dihydroxypropyl cellulose obtained by 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. 87 ^cm3 of zirconia beads having a diameter of 0.25 mm were used as medium particles for this mixture, and the mixture was dispersed using a sand mill at a disk rotation peripheral speed of 10 m / sec for 2 hours to obtain a CB slurry.

The number of medium particles N of the zirconia beads at this time was about 81500 particles / ml per CB slurry volume. Moreover, when the average particle diameter of this CB slurry was measured by the laser diffraction scattering method, it was 202 nm.

Next, 40 parts by mass of this CB slurry, 85 parts by mass of lithium cobalt oxide (LiCoO ₂ ) (Celseed C5H manufactured by Nippon Chemical Industries, Ltd.) as a positive electrode active material, and 5 parts by mass of polyvinylidene fluoride (PVDF) as a solvent. Mix with N-methyl 2-pyrrolidone (NMP) so that the solid content concentration is 45% by mass, use 87 cm ³ of zirconia beads with a diameter of 0.25 mm, and use a sand mill to rotate the disk at a peripheral speed of 7. Mixing was carried out at a rate of .5 m / sec for 15 minutes to prepare a slurry (in other words, a slurry-like positive electrode mixture).

The slurry (in other words, a positive electrode mixture) is applied on an Al (aluminum) foil having a thickness of 15 μm with a bar coater (bar coat method), dried with hot air at 110 ° C. for 30 minutes, and the amount of one-sided grain is 200 g / m ² . A single-sided coated electrode (positive electrode) was prepared. With respect to the obtained electrode, the adhesion between the electrode coating film and the current collector was evaluated by the above method. The results are shown in Table 2.

(Comparative Example B-1)
Instead of using 2 parts by mass of the polyvinylidene fluoride-hexafluoropropylene copolymer (manufactured by Arkema Co., Ltd.) and 2 parts by mass of the dihydroxypropyl cellulose obtained by Example A-1, both polyvinylidene fluoride and hexafluoropropylene. A single-sided coated electrode (positive electrode) was prepared by the same method as in Example B-2 using 4 parts by mass of a polymer (manufactured by Arkema Co., Ltd.). With respect to the obtained electrode, the adhesion between the electrode coating film and the current collector was evaluated by the above method. The results are shown in Table 2.

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

Claims (4)

Contains dihydroxypropyl cellulose,
An additive for a non-aqueous electrolyte secondary battery positive electrode having a dihydroxypropyl substitution degree (DS) of 0.1 or more for the dihydroxypropyl cellulose. The additive for a non-aqueous electrolyte secondary battery positive electrode according to claim 1, wherein the average number (MS) of dihydroxypropyl groups bonded per glucose unit of the dihydroxypropyl cellulose is 0.5 or more and 10 or less. A positive electrode for a non-aqueous electrolyte secondary battery containing the additive for the positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2. The step of preparing a slurry by dispersing the additive for the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode active material, the conductive auxiliary agent, and the organic solvent according to claim 1 or 2.
A method for manufacturing a positive electrode for a non-aqueous electrolyte secondary battery, which comprises a step of applying the slurry onto a foil-shaped current collector.