Electrode slurry, nonaqueous secondary battery electrode, and nonaqueous secondary battery

Abstract

This electrode slurry includes a binder polymer, a cellulose derivative, an electrode active material, and an aqueous medium. Given that the peel strength of an electrode active material layer having a thickness of 130 μm is P(T) [mN / mm], a ratio [P(180) / P(90)] of P(180) to P(90) is 0.50 or more, wherein the electrode active material layer is obtained by applying the electrode slurry to a copper foil and drying the resultant for 4 minutes at T°C.

Description

Electrode slurry, non-aqueous secondary battery electrode, and non-aqueous secondary battery

[0001] The present disclosure relates to an electrode slurry, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery.

[0002] A non-aqueous secondary battery includes, for example, a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte solution. A non-aqueous secondary battery is a secondary battery in which ions move between the positive electrode and the negative electrode to charge and discharge the battery.

[0003] A typical example of a non-aqueous secondary battery is a lithium-ion secondary battery. Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, electronic devices, communication devices, and the like due to their compact size and lightweight design. Recently, they have also been used in electric vehicles and hybrid vehicles due to their environmentally friendly application. In this context, there has been a strong demand for non-aqueous secondary batteries with higher output, higher capacity, and longer life.

[0004] A commonly used electrode for a non-aqueous secondary battery is one in which an electrode active material layer is formed on a metal current collector. The current collector is typically made of a metal foil such as aluminum or copper. The electrode active material layer contains an electrode active material, a binder, and, if necessary, a conductive additive. The electrode active material is a substance capable of inserting and extracting ions that serve as charge carriers. The binder serves to bind active materials together and to bind the active material to the current collector.

[0005] In the process of producing an electrode for a non-aqueous secondary battery, for example, a slurry (electrode slurry) in which an electrode binder and an electrode active material are dissolved or dispersed in water is applied to the surface of a current collector and dried to form an electrode active material layer on the current collector.

[0006] For example, Patent Document 1 describes a slurry for lithium ion secondary battery electrodes obtained using a binder for lithium ion secondary battery electrodes, an electrode active material, and carboxymethyl cellulose. It also describes that the binder for lithium ion secondary battery electrodes is obtained by emulsion polymerization of an ethylenically unsaturated monomer containing styrene, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent. Patent Document 2 describes a secondary battery electrode having an electrode layer containing at least one polymer selected from the group consisting of a styrene-butadiene copolymer and a copolymer obtained from a (meth)acrylic acid ester and a vinyl monomer having an acid component, and a specific nonionic surfactant.

[0007] JP 2011-243464 A JP 2014-239070 A

[0008] In a non-aqueous secondary battery, it is desirable to keep the electrical resistance (electrode resistance) within the electrode active material layer and between the electrode active material layer and the current collector low. Therefore, an object of the present disclosure is to provide an electrode slurry, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery that can keep the electrode resistance low.

[0009] The present disclosure includes the following aspects. <1> An electrode slurry comprising a binder polymer, a cellulose derivative, an electrode active material, and an aqueous medium, wherein the electrode slurry has a peel strength of 130 μm when the electrode active material layer is applied to a copper foil and then dried at T°C for 4 minutes, and the peel strength is P(T) [mN / mm]. <2> The electrode slurry according to <1>, wherein the ratio of P(180) to P(90) [P(180) / P(90)] is 0.50 or more. <3> The electrode slurry according to <1> or <2>, wherein the ratio of P(150) to P(90) [P(150) / P(90)] is 0.60 or more. <4> The binder polymer is an ammonium salt of a sulfo group (-SO ３ NH ４<5> The electrode slurry according to any one of <1> to <3>, further comprising a surfactant, wherein the content of the surfactant having no ethylenically unsaturated bond is 2.0 × 10 －４ % by mass or less. <6> The electrode slurry according to any one of <1> to <4>, which is for a non-aqueous secondary battery electrode. <7> The electrode slurry according to any one of <1> to <6>, which is for a lithium ion secondary battery negative electrode. <8> A non-aqueous secondary battery electrode comprising an electrode active material layer formed from the electrode slurry according to any one of <1> to <7>. <9> A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to <8>.

[0010] According to the present disclosure, it is possible to provide an electrode slurry, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery that can keep electrode resistance low.

[0011] Hereinafter, nonaqueous secondary battery electrodes and nonaqueous secondary batteries will be described as embodiments of the present disclosure. Note that the present disclosure is not limited to the embodiments described below. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In this disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In this disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, the content or amount of each component refers to the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.

[0012] The weight-average molecular weight of the cellulose derivative is a pullulan-equivalent value measured by GPC. Specific measurement conditions are as follows: GPC device: GPC-101 (manufactured by Resonac Co., Ltd.) Solvent: 0.1 M NaNO ３ Aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm I.D. x 300 mm) x 2 Reference column: Shodex Column Ohpak SB-800 RL (8.0 mm I.D. x 300 mm) x 2 Column temperature: 40°C Sample concentration: 0.1% by mass Detector: RI-71S (Shimadzu Corporation) Flow rate: 1 ml / min Molecular weight standard: Pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (Resonac Corporation))

[0013] <1. Electrode Slurry> The electrode slurry of the present disclosure is an electrode slurry containing a binder polymer, a cellulose derivative, an electrode active material, and an aqueous medium, wherein the electrode slurry is applied to a copper foil and then dried at T°C for 4 minutes to obtain an electrode active material layer having a thickness of 130 μm, and the peel strength of the electrode active material layer is P(T) [mN / mm]. The ratio of P(180) to P(90) [P(180) / P(90)] is 0.50 or more.

[0014] Electrodes obtained using the electrode slurry having the above configuration have low electrode resistance. The reason for this is unclear, but is presumed to be as follows. One cause of the increase in electrode resistance is thought to be the accumulation and segregation of low-conductivity components within the electrode. It has been found that electrode slurries prone to component segregation within the electrode are more susceptible to component segregation when dried at high temperatures to obtain an electrode active material layer, resulting in a decrease in peel strength. Furthermore, even when such electrode slurries are dried at low temperatures to obtain an electrode active material layer, component segregation within the electrode is thought to progress, resulting in high electrode resistance. Conversely, electrode slurries with little decrease in peel strength of the electrode active material layer obtained by drying at high temperatures are thought to suppress component segregation even in electrode active material layers obtained by drying at low temperatures, thereby suppressing an increase in electrode resistance. Under the above circumstances, it has been found that when the high-temperature drying condition is 180°C and the low-temperature drying condition is 90°C, electrode resistance can be kept low when the peel strength ratio [P(180) / P(90)] is 0.50 or higher.

[0015] The peel strength P(T) [mN / mm] of the electrode active material layer is measured by the method described in the Examples and is the average value of three measurements.

[0016] The ratio of P(180) to P(90) [P(180) / P(90)] is 0.50 or more, preferably 0.60 or more, and more preferably 0.70 or more. When the ratio [P(180) / P(90)] is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. It is presumed that an electrode slurry that suppresses a decrease in peel strength when an electrode active material layer is formed by drying at a high temperature such as 180°C suppresses the segregation of components in the electrode, thereby suppressing an increase in electrode resistance. The ratio [P(180) / P(90)] is preferably closer to 1.

[0017] The ratio [P(150) / P(90)] is preferably 0.60 or more, more preferably 0.70 or more, and even more preferably 0.75 or more. When the ratio [P(150) / P(90)] is in the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. It is preferable that the decrease in peel strength is suppressed even when the electrode active material layer is formed by drying at a medium temperature such as 150°C. The ratio [P(150) / P(90)] is preferably closer to 1.

[0018] The ratio [P(120) / P(90)] is preferably 0.65 or more, more preferably 0.75 or more, and even more preferably 0.80 or more. When the ratio [P(120) / P(90)] is in the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. Even when the electrode active material layer is formed by drying at a medium temperature such as 120°C, it is preferable that the decrease in peel strength is suppressed. The ratio [P(120) / P(90)] is preferably closer to 1.

[0019] P(180) is preferably 1.0 mN / mm or more, more preferably 1.5 mN / mm or more, and even more preferably 1.8 mN / mm or more. When the P(150) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because segregation of components in the electrode is suppressed and a sufficient conductive path is formed. The higher the P(180), the better. There is no particular upper limit, but it may be 20 mN / mm or less.

[0020] P(150) is preferably 1.0 mN / mm or more, more preferably 1.5 mN / mm or more, and even more preferably 2.0 mN / mm or more. When the P(150) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because segregation of components in the electrode is suppressed and a sufficient conductive path is formed. The higher the P(150), the better. There is no particular upper limit, but it may be 20 mN / mm or less.

[0021] P(120) is preferably 1.0 mN / mm or more, more preferably 1.6 mN / mm or more, and even more preferably 2.2 mN / mm or more. When the P(120) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because segregation of components in the electrode is suppressed and a sufficient conductive path is formed. The higher the P(120), the better. There is no particular upper limit, but it may be 20 mN / mm or less.

[0022] P(90) is preferably 2.0 mN / mm or more, more preferably 2.5 mN / mm or more, and even more preferably 3.0 mN / mm or more. When the P(90) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because segregation of components in the electrode is suppressed and a sufficient conductive path is formed. A higher P(90) is preferable, and although there is no particular upper limit, it may be 20 mN / mm or less.

[0023] The ratio of P(180) to P(150) [P(180) / P(150)] is preferably 0.75 or more, more preferably 0.85 or more, and even more preferably 0.90 or more. When the ratio [P(180) / P(150)] is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. It is presumed that an electrode slurry that suppresses a decrease in peel strength when an electrode active material layer is formed by drying at a high temperature range, such as 150°C to 180°C, suppresses the segregation of components in the electrode, thereby suppressing an increase in electrode resistance. The ratio [P(180) / P(150)] is preferably closer to 1.

[0024] The electrode slurry is preferably used for producing an electrode for a non-aqueous secondary battery, more preferably for producing an electrode for a lithium ion secondary battery, and even more preferably for producing a negative electrode for a lithium ion secondary battery.

[0025] [1-1. Binder Polymer] Preferred examples of the binder polymer include, but are not limited to, copolymers of aromatic ethylenically unsaturated compounds, nonionic (meth)acrylic acid esters, and anionic unsaturated compounds. The binder polymer may have a crosslinked structure. Particles formed by the binder polymer may contain a surfactant or the like.

[0026] The aromatic ethylenically unsaturated compound is a nonionic aromatic compound having an ethylenically unsaturated bond. Hereinafter, unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability. Examples of the aromatic ethylenically unsaturated compound include styrene, t-butylstyrene, p-methylstyrene, and benzyl (meth)acrylate.

[0027] The nonionic (meth)acrylic acid ester is preferably a nonionic aliphatic compound having one (meth)acryloyl group. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. The (meth)acrylic acid alkyl ester may have a hydroxy group. Examples of nonionic (meth)acrylic acid esters having a hydroxy group include, but are not limited to, hydroxymethyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate.

[0028] Anionic unsaturated compounds are compounds having anionic functional groups. Examples of the anionic functional groups include carboxyl groups, sulfo groups, and phosphate groups. The anionic functional groups may form salts. Examples of anionic unsaturated compounds include, but are not limited to, acrylic acid, itaconic acid, and sodium p-styrenesulfonate.

[0029] From the viewpoint of polymerization stability of the binder, the binder polymer is an ammonium salt of a sulfo group (—SO ３ NH ４ ) is preferably present.

[0030] When the binder polymer has a crosslinked structure, it may be a polymer polymerized using a monomer having a crosslinkable functional group, such as, but not limited to, divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate.

[0031] The binder polymer may be a polymer polymerized using a polymerizable surfactant, which is a compound that has an ethylenically unsaturated bond and functions as a surfactant.

[0032] The glass transition temperature Tg of the binder polymer is preferably −30° C. or higher, more preferably −20° C. or higher, and even more preferably −10° C. or higher. This is because, when the glass transition temperature Tg of the binder polymer is within the above range, the cycle characteristics of a nonaqueous secondary battery including a nonaqueous secondary battery electrode of the present disclosure are improved. The glass transition temperature Tg of the binder polymer is preferably 100° C. or lower, more preferably 50° C. or lower, and even more preferably 30° C. or lower. This is because, when the glass transition temperature Tg of the binder polymer is within the above range, the adhesion of an electrode active material layer containing the binder polymer to a current collector foil is improved.

[0033] [1-2. Cellulose Derivatives] Cellulose derivatives have a structure in which at least a portion of the hydrogen atoms of hydroxyl groups contained in cellulose are substituted. The cellulose derivative is thought to significantly contribute to the formation of conductive paths between electrode active materials and between the electrode active material and the current collector in the electrode active material layer. Furthermore, adding the cellulose derivative to an electrode slurry containing the electrode active material in the electrode manufacturing process tends to facilitate dispersion of the electrode active material, thereby reducing the manufacturing cost of the electrode.

[0034] Examples of cellulose derivatives include carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, and salts of CMC. One type of cellulose derivative may be used alone, or two or more types may be used in combination. The cellulose derivative preferably contains at least one selected from the group consisting of CMC and salts of CMC, and more preferably contains a salt of CMC. Examples of salts of CMC include alkali metal salts of CMC and ammonium salts of CMC, and alkali metal salts of CMC are preferred. The alkali metal in the alkali metal salt is preferably Na, K, or Li, and more preferably Na.

[0035] The weight-average molecular weight of the cellulose derivative is preferably 800,000 or more, more preferably 1,200,000 or more, and even more preferably 1,600,000 or more. Setting the weight-average molecular weight of the cellulose derivative within the above range further improves the binding strength between electrode active materials and between the electrode active material and the current collector. Furthermore, setting the weight-average molecular weight of the cellulose derivative within the above range is thought to contribute to the formation of conductive paths between the electrode active materials and between the electrode active material and the current collector, thereby further reducing electrode resistance.

[0036] The weight-average molecular weight of the cellulose derivative is preferably 10 million or less, more preferably 5 million or less, and even more preferably 3 million or less. When the weight-average molecular weight of the cellulose derivative is within the above range, an increase in the viscosity of the liquid tends to be suppressed during the electrode production process when producing a liquid containing the cellulose derivative, such as a slurry containing the cellulose derivative and an electrode active material. This enables sufficient stirring, improving quality and reducing the production costs required for stirring. Furthermore, improved application of the cellulose derivative-containing liquid to the electrode reduces production costs, and electrode quality is improved by making it easier to control the film thickness. The weight-average molecular weight of the cellulose derivative may be 800,000 to 10 million, 1.2 million to 5 million, or 1.6 million to 3 million.

[0037] [1-3. Electrode active material] The electrode active material is a material capable of intercalating / deintercalating ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0038] When the electrode is a negative electrode, the electrode active material, i.e., the negative electrode active material, preferably contains at least one selected from the group consisting of a carbon material, a silicon-containing material, and a titanium-containing material. Examples of carbon materials used as the electrode active material include cokes such as petroleum coke, pitch coke, and coal coke; carbonized organic polymers; and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials include silicon itself and silicon compounds such as silicon oxide. Examples of titanium-containing materials include lithium titanate. These materials may be used alone, in combination of two or more types, or in a composite of two or more types.

[0039] The negative electrode active material preferably contains at least one selected from the group consisting of a carbon material and a silicon-containing material, more preferably contains a carbon material, particularly preferably contains graphite, and most preferably contains artificial graphite, because the effects of the present disclosure are particularly enhanced when the negative electrode active material contains these materials.

[0040] When the electrode is a positive electrode, the electrode active material, i.e., the positive electrode active material, is a material having a nobler standard electrode potential than the negative electrode active material. Examples of the positive electrode active material include lithium composite oxides containing nickel, such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides; lithium cobalt oxide (LiCoO ２ ) ; Spinel-type lithium manganese oxide (LiMn ２ O ４ ); olivine-type lithium iron phosphate; TiS ２ Chalcogen compounds such as MnO ２ , MoO ３ , V ２O ５ As the positive electrode active material, one of these substances may be used alone, or two or more of them may be used in combination.

[0041] From the viewpoint of particularly maximizing the effects of the present disclosure, the electrode active material preferably contains 50 mass % or more of graphite, more preferably 70 mass % or more, and even more preferably 90 mass % or more.

[0042] [1-4. Aqueous Medium] The aqueous medium is preferably at least one selected from the group consisting of water and hydrophilic solvents. The hydrophilic solvent may be used alone or in combination of two or more. Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium is preferably water. A mixture of water and a hydrophilic solvent may also be used as the aqueous medium.

[0043] [1-5. Content of each component in electrode slurry] In the electrode slurry, the content of the binder polymer relative to 100 parts by mass of the electrode active material is preferably 0.50 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, in order to sufficiently bind the electrode active materials together and between the electrode active material and the current collector.

[0044] In the electrode slurry, the content of the binder polymer relative to 100 parts by mass of the electrode active material is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, in order to increase the content of the electrode active material in the electrode active material layer produced using the electrode slurry and improve the capacity of the electrode.

[0045] In the electrode slurry, the content of the cellulose derivative relative to 100 parts by mass of the electrode active material is preferably 0.50 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, in order to facilitate dispersion of the electrode active material in the electrode slurry.

[0046] In the electrode slurry, the content of the cellulose derivative per 100 parts by mass of the electrode active material is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. This is to prevent an unnecessary increase in the viscosity of the electrode slurry. Also, this is to increase the content of the electrode active material in the electrode active material layer produced using the electrode slurry, thereby improving the capacity of the electrode.

[0047] In the electrode slurry, the content of the aqueous medium relative to 100 parts by mass of the electrode active material is preferably 50 parts by mass or more, more preferably 75 parts by mass or more, and even more preferably 100 parts by mass or more, in order to facilitate dispersion of the electrode active material in the electrode slurry and to improve the coatability of the electrode slurry.

[0048] In the electrode slurry, the content of the aqueous medium relative to 100 parts by mass of the electrode active material is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less, in order to increase the viscosity of the electrode slurry to a level that improves coatability and to shorten the drying time after coating of the electrode slurry.

[0049] In the electrode slurry, it is preferred that the content of the binder polymer relative to 100 parts by mass of the electrode active material is 0.50 parts by mass or more and 6.0 parts by mass or less, the content of the cellulose derivative relative to 100 parts by mass of the electrode active material is 0.50 parts by mass or more and 6.0 parts by mass or less, and the content of the aqueous medium relative to 100 parts by mass of the electrode active material is 50 parts by mass or more and 300 parts by mass or less.

[0050] [1-5. Other Components] The electrode slurry contains a binder polymer, a cellulose derivative, an electrode active material, and an aqueous medium, and may contain other components such as a conductive aid, a surfactant having no ethylenically unsaturated bond, other additives, etc. The content of the surfactant having no ethylenically unsaturated bond (non-polymerizable surfactant) in the electrode slurry is 2.0 × 10 －４ It is preferably 1.0 × 10 mass% or less. －４It is more preferably % by mass or less, and may be 0% by mass (i.e., not contained), or may be more than 0% by mass.

[0051] [1-6. Relationship between the Structure of the Electrode Active Material Layer and P(T), etc.] The ratio [P(180) / P(90)] of 0.50 or more may be achieved by any method, and can be achieved by combining the structures and components of the electrode active material layer described above. Examples include using a cellulose derivative having a weight-average molecular weight within the above range, using a binder polymer having a glass transition temperature Tg within the above range, or a combination thereof.

[0052] <2. Manufacturing Method of Non-Aqueous Secondary Battery Electrode> An electrode can be manufactured, for example, by applying an electrode slurry containing an electrode active material and a dispersion medium to a current collector, drying the slurry to form an electrode active material layer, and then cutting the layer to an appropriate size. The method for applying the electrode slurry to the current collector is not particularly limited, and examples include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dipping method, and squeeze method. Among these, considering the physical properties of the electrode slurry, such as viscosity, and drying properties, the doctor blade method, knife method, or extrusion method is preferred. Using these application methods tends to produce an electrode active material layer with a smooth surface and small thickness variation.

[0053] The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When applying the electrode slurry to both sides of the current collector, the electrode slurry may be applied to each side sequentially, or may be applied to both sides at once. The electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, etc. The amount of electrode slurry to be applied depends on the properties of the electrode slurry, but is generally 15 mg / cm. ２ It is preferable that the amount of the electrode paste applied to each surface be less than 1000 ppm (when applied to both surfaces, the amount applied per surface). This is because the occurrence of cracks on the electrode surface can be suppressed during the drying process of the electrode slurry.

[0054] An electrode active material layer is formed on the current collector by drying the electrode slurry applied to the current collector. The method for drying the electrode slurry is not particularly limited, and examples include hot air, reduced pressure or vacuum environment, (far) infrared rays, and low-temperature air, which can be used alone or in combination of two or more. The drying temperature and drying time of the electrode slurry can be appropriately adjusted depending on the nonvolatile content concentration in the electrode slurry, the amount applied to the current collector, and the like. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 200°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0055] The electrode sheet in which the electrode active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0056] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed. Pressing allows the electrode active material to be more firmly bonded to the current collector, and further reduces the thickness of the electrode, thereby enabling the non-aqueous battery to be miniaturized. As the pressing method, a general method can be used, and it is preferable to use a mold pressing method or a roll pressing method. In the case of the mold pressing method, the pressing pressure is not particularly limited, but is preferably 0.1 t / cm. ２ ~5t / cm ２ In the case of the roll press method, the linear pressure is not particularly limited, but is preferably 0.1 t / cm to 5 t / cm. When the press pressure or linear pressure is within the above range, the above effects of pressing can be obtained, while a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material tends to be suppressed.

[0057] 3. Nonaqueous Secondary Battery Electrode The nonaqueous secondary battery electrode of the present disclosure includes an electrode active material layer formed from the electrode slurry of the present disclosure. The electrode active material layer may be provided on a current collector. Examples of the shape of the electrode include, but are not limited to, a laminate and a wound body. The area on which the electrode active material layer is formed on the current collector is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector or on a portion of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both surfaces of the current collector or on only one surface.

[0058] [3-1. Current Collector] The current collector is preferably made of a metal, and preferably contains a metal such as iron, copper, aluminum, nickel, or stainless steel as its main component. When the nonaqueous secondary battery electrode is a negative electrode of a lithium-ion secondary battery, the current collector preferably contains copper as its main component. The phrase "containing metal A as its main component" includes cases where unavoidable impurities are contained in addition to metal A, cases where two or more metals including metal A are used in combination and metal A has the largest mass ratio, and cases where metal A is an alloy of two or more metals including metal A and metal A has the largest mass ratio. The thickness of the current collector is preferably 0.001 mm to 0.5 mm. The current collector may be a metal sheet.

[0059] [3-2. Electrode active material layer] The thickness of the electrode active material layer is preferably 100 μm or more, more preferably 110 μm or more, and even more preferably 120 μm or more. When the thickness of the electrode active material layer is within the above range, the charge / discharge capacity of the non-aqueous secondary battery tends to be improved. The thickness of the electrode active material layer is preferably 200 μm or less, more preferably 170 μm or less, and even more preferably 150 μm or less. When the thickness of the electrode active material layer is within the above range, the electrode resistance of the non-aqueous secondary battery tends to be reduced.

[0060] The thickness of the electrode active material layer is measured with a micrometer and is defined as the arithmetic mean value of measurements obtained at three arbitrarily selected points. When the electrode active material layer is provided on both sides of the current collector, the thickness of the electrode active material layer is the thickness per side.

[0061] The electrode active material layer preferably contains 80% by mass or more of the electrode active material, more preferably 90% by mass or more, and even more preferably 93% by mass or more. When the content of the electrode active material in the electrode active material layer is within the above range, the charge / discharge capacity of the nonaqueous secondary battery tends to be improved.

[0062] The content of the electrode active material in the electrode active material layer is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. When the content of the electrode active material in the electrode active material layer is within the above range, bonding between the electrode active materials and between the electrode active material and the current collector is facilitated, and the content of components for forming a conductive path, such as the binder polymer and cellulose derivative described below, is easily ensured. The content of the electrode active material in the electrode active material layer is preferably 80% by mass to 99% by mass, more preferably 90% by mass to 98% by mass, and even more preferably 93% by mass to 97% by mass. Details of examples of materials used as the electrode active material will be described later.

[0063] The content of the binder polymer in the electrode active material layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. When the content of the binder polymer in the electrode active material layer is within the above range, the binding strength between the electrode active materials and between the electrode active material and the current collector tends to be improved. The content of the binder polymer in the electrode active material layer is preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 3.0% by mass or less. When the content of the binder polymer in the electrode active material layer is within the above range, the content of the electrode active material in the electrode active material is easily increased.

[0064] The content of the cellulose derivative in the electrode active material layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. When the content of the cellulose derivative in the electrode active material layer is within the above range, the binding strength between the electrode active materials and between the electrode active material and the current collector tends to be improved. The content of the cellulose derivative in the electrode active material layer is preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 3.0% by mass or less. When the content of the cellulose derivative in the electrode active material layer is within the above range, the content of the electrode active material in the electrode active material is increased.

[0065] The total content of the electrode active material, binder polymer, and cellulose derivative in the electrode active material layer is preferably 81% by mass or more, more preferably 91% by mass or more, and even more preferably 95% by mass or more. When the total content is within the above range, the content of the electrode active material can be increased, and the electrode resistance tends to be reduced.

[0066] 4. Non-aqueous Secondary Battery The non-aqueous secondary battery of the present disclosure includes the non-aqueous secondary battery electrode of the present disclosure. A lithium-ion secondary battery will be described as a preferred example of the non-aqueous secondary battery of the present disclosure, but the battery configuration is not limited to that described here. The non-aqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, an electrolyte, and, if necessary, components such as a separator, housed in an exterior body, and the above-described electrodes are used for one or both of the positive electrode and the negative electrode. 4-1. Electrolyte Solution The electrolyte solution is preferably a non-aqueous liquid having ion conductivity. Examples of the electrolyte solution include a solution in which the electrolyte is dissolved in an organic solvent and an ionic liquid, and a solution in which the electrolyte is dissolved in an organic solvent is preferred. This is because using a solution in which the electrolyte is dissolved in an organic solvent as the electrolyte solution reduces production costs and produces a non-aqueous battery with low internal resistance.

[0067] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material, etc. The electrolyte can be LiClO ４ , LiBF ６ , LiPF６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２ Examples of the electrolyte include lithium carboxylate, lithium cations of N, and aliphatic carboxylates. Other alkali metal salts can also be used as the electrolyte.

[0068] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The organic solvent may be used alone or in combination of two or more. Among these, carbonate ester compounds are preferred as the organic solvent, and linear carbonate ester compounds are more preferred. The linear carbonate ester compounds may be used alone or in combination of two or more. Examples of linear carbonate ester compounds include diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC).

[0069] [4-2. Exterior Body] The exterior body may be a laminate of aluminum foil and a resin film, but is not limited to this. The shape of the battery is not particularly limited, and examples include coin type, button type, sheet type, cylindrical type, square type, and flat type.

[0070] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the examples described below. In the following examples, a negative electrode of a lithium ion battery is prepared as an example of an electrode. Note that the water used in the following examples and comparative examples is ion-exchanged water unless otherwise specified.

[0071] <1. Synthesis of Binder Polymer> [1-1. Synthesis Example 1] A monomer emulsion was prepared by mixing and emulsifying the types and amounts of monomers shown in Synthesis Example 1 in Table 1 with 200 parts by mass of water. Aqualon KH10 is a polymerizable surfactant, and is polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Next, a radical polymerization initiator of the type and amount shown in Synthesis Example 1 in Table 1 was each dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution.

[0072]

[0073] A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was charged with 150 parts by mass of water and heated to 75°C. The monomer emulsion and the polymerization initiator aqueous solution were continuously fed into the separable flask over a period of 3 hours while stirring at 75°C, respectively, to carry out emulsion polymerization, yielding an emulsion. The resulting emulsion was cooled to room temperature (25°C). To the cooled emulsion, 17 parts by mass of 25% ammonia water (basic substance in Table 1: 4.25 parts by mass of ammonia, 12.75 parts by mass of water) and 130 parts by mass of water were added. Rongalit SFS, used as the radical polymerization initiator, was manufactured by Sumitomo Seika Chemicals Co., Ltd. This process yielded an emulsion containing binder polymer (A1). The solubility of binder polymer (A1) in water was 0.50 g / 100 gH. ２ It was below O.

[0074] [1-2. Synthesis Example 2] The types and amounts of monomers shown in Synthesis Example 2 in Table 1 were mixed with 200 parts by mass of water and emulsified to prepare a monomer emulsion. Next, the types and amounts of radical polymerization initiators shown in Synthesis Example 2 in Table 1 were dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution. 200 parts by mass of water was placed in a 5 MPa pressure vessel equipped with a stirrer, and the temperature was raised to 60°C at an internal pressure of 1.0 MPa. The monomer emulsion and the aqueous polymerization initiator solution were each added simultaneously to this pressure vessel, and the mixture was stirred at 60°C for 8 hours to perform emulsion polymerization, thereby obtaining an emulsion. The resulting emulsion was cooled to room temperature (25°C). To the cooled emulsion, 5.3 parts by mass of 25% ammonia water (basic substance in Table 1: 1.325 parts by mass of ammonia, 3.975 parts by mass of water) and 130 parts by mass of water were added. This step yielded an emulsion containing the binder polymer (A2). The solubility of the binder polymer (A2) in water was 0.50 g / 100 gH. ２ It was below O.

[0075] [1-3. Measurement of nonvolatile content concentration] 1 g of each of the emulsions obtained in Synthesis Examples 1 and 2 was weighed into a 5 cm diameter aluminum dish and dried at 105°C for 1 hour while circulating air in a dryer at 1 atmosphere (1013 hPa), and the mass of the remaining components was measured to determine the nonvolatile content concentration (mass%). The measured values ​​of the nonvolatile content concentrations of the emulsions obtained in Synthesis Examples 1 and 2 are shown in Table 1.

[0076] [1-4. Measurement of Glass Transition Point] The emulsions obtained in Synthesis Examples 1 and 2 were each dried at 105°C for 1 hour under circulating air in a dryer at 1 atmosphere (1013 hPa), and the remaining components were removed and placed in a sample pan for DSC measurement. The DSC measurement was performed using an EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation at a heating rate of 10°C / min under a nitrogen gas atmosphere. For each Synthesis Example, the peak top temperature of the DSC chart obtained as the temperature derivative of DSC was taken as the glass transition point (°C) of the binder polymer (A1) or binder polymer (A2). The measured values ​​of the glass transition points of the binder polymer (A1) and binder polymer (A2) are shown in Table 1.

[0077] <2. Negative Electrode Slurry> [2-1. Preparation of Negative Electrode Slurry] In the Examples and Comparative Examples, the binder polymer, cellulose derivative, and electrode active material (negative electrode active material) types shown in Table 2 were used and mixed with water as a liquid medium in the amounts shown in Table 2 to prepare negative electrode slurries. The amount of water added in this step was adjusted so that the total amount, including the water contained in the emulsion, was the amount shown in Table 2. The binder polymers used were the binder polymer (A1) synthesized in Synthesis Example 1 and the binder polymer (A2) synthesized in Synthesis Example 2. In both the Examples and Comparative Examples, sodium carboxymethylcellulose (CMC-Na) with a degree of etherification of 0.70 and a weight-average molecular weight of 2,000,000 was used as the cellulose derivative. The solubility of CMC-Na in water was 10 g / 100 gH. ２ The electrode active material used in all Examples and Comparative Examples was artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.).

[0078] [2-2. Nonvolatile content of negative electrode slurry] For each of the negative electrode slurries obtained in the examples and comparative examples, 1 g of the mixture was weighed out onto a 5 cm diameter aluminum dish, and the mixture was dried at 1 atmosphere (1013 hPa) in a dryer at 130°C for 1 hour while circulating air. The mass of the remaining components was measured, and the nonvolatile content (mass%) was determined. The nonvolatile content concentrations of the electrode slurries prepared in the examples and comparative examples are shown in Table 2.

[0079] <3. Negative Electrode> [3-1. Fabrication of Negative Electrode] The negative electrode slurry was applied to one side of a 10 μm thick copper foil (negative electrode current collector) by a direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after drying, described below, would be 130 μm per side. The negative electrode current collector to which the negative electrode slurry had been applied was dried by conveying it through a 1.6 m long drying furnace set at the temperature shown in Table 2 at the speed shown in Table 2, thereby obtaining a negative electrode sheet in which a negative electrode active material layer was formed on the current collector.

[0080] [3-2. Various Measurements of Negative Electrode] [3-2-1. Measurement of Peel Strength of Negative Electrode Active Material Layer] Each negative electrode sheet prepared in the Examples and Comparative Examples was cut to a size of 25 mm x 100 mm to prepare a test specimen. The negative electrode active material layer on the test specimen was attached to a 50 mm wide, 200 mm long SUS plate using double-sided tape (NITTOTAPE (registered trademark) No. 5, manufactured by Nitto Denko Corporation) so that the center of the test specimen coincided with the center of the SUS plate. The double-sided tape was attached so as to cover the entire area of ​​the test specimen.

[0081] After leaving the test piece and the SUS plate in a bonded state for 10 minutes, the negative electrode active material layer was peeled off 20 mm in the longitudinal direction from one end of the test piece, and the copper foil side of the test piece was folded back 180°. This portion (the copper foil side of the test piece from which the negative electrode active material layer was peeled off) was gripped with the upper chuck of the tester. Furthermore, one end of the SUS plate from which the negative electrode active material layer was peeled off was gripped with the lower chuck. In this state, the copper foil was peeled off from the test piece at a rate of 100±10 mm / min, and a graph of peel length (mm) vs. peel force (mN) was obtained. In the graph obtained, the average peel force (mN) at peel lengths of 10 mm to 45 mm was calculated, and the value obtained by dividing the average peel force by the width of the test piece (25 mm) was taken as the peel strength (mN / mm) of the negative electrode active material layer. In both the Examples and Comparative Examples, no peeling occurred between the double-sided tape and the SUS plate, and no peeling occurred at the interface between the double-sided tape and the negative electrode active material layer during the test.

[0082] [3-2-2. Rate of change in peel strength of negative electrode active material layer] The ratio [P(T) / P(90)] of the peel strength of the negative electrode active material layer obtained by drying at each temperature to the peel strength of the negative electrode active material layer obtained by drying at 90°C was calculated.

[0083] [3-2-3. Resistance Measurement] The obtained negative electrode sheet was cut into a size of 52 mm x 42 mm, and a conductive tab was attached to prepare a negative electrode. The resistance (mΩ cm) of the negative electrode active material layer was measured using an electrode resistance measurement system XF057 manufactured by Hioki E.E. ２ ) and the interface resistance (mΩ cm ２ ) was measured.

[0084]

[0085] 4. Evaluation Results The electrode having the electrode active material layer obtained from the electrode slurry of Example 1 has a ratio of P(180) to P(90) [P(180) / P(90)] of 0.50 or more, and exhibits low resistance of the negative electrode active material layer and low interfacial resistance between the negative electrode active material layer and the current collector regardless of the drying temperature. On the other hand, the electrode having the electrode active material layer obtained from the electrode slurry of Comparative Example 1, in which the ratio [P(180) / P(90)] is less than 0.50, exhibits high resistance of the negative electrode active material layer and high interfacial resistance between the negative electrode active material layer and the current collector regardless of the drying temperature. From the above, it can be seen that by checking the peel strength ratio [P(180) / P(90)] and setting this value to 0.50 or more, it is possible to suppress increases in the resistance of the negative electrode active material layer and the interfacial resistance between the negative electrode active material layer and the current collector regardless of the drying temperature of the electrode slurry.

[0086] The disclosure of Japanese Patent Application No. 2024-089278 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated by reference into this specification to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An electrode slurry comprising a binder polymer, a cellulose derivative, an electrode active material, and an aqueous medium, wherein the electrode slurry is applied to a copper foil and then dried at T°C for 4 minutes to obtain an electrode active material layer having a thickness of 130 μm, and the peel strength of the electrode active material layer is P(T) [mN / mm]. The ratio of P(180) to P(90) [P(180) / P(90)] is 0.50 or more.

2. The electrode slurry according to claim 1, wherein the ratio of P(150) to P(90) [P(150) / P(90)] is 0.60 or more.

3. The electrode slurry according to claim 1, wherein the ratio of P(120) to P(90) [P(120) / P(90)] is 0.65 or more.

4. The binder polymer is an ammonium salt of a sulfo group (—SO ３ NH ４ 10. The electrode slurry of claim 1, wherein 5. A surfactant is further contained, and the content of the surfactant having no ethylenically unsaturated bond is 2.0 x 10 －４ 2. The electrode slurry according to claim 1, wherein the content of the cations in ...

6. The electrode slurry according to claim 1, which is for use in a non-aqueous secondary battery electrode.

7. The electrode slurry according to claim 1, which is for use in a negative electrode of a lithium ion secondary battery.

8. A non-aqueous secondary battery electrode comprising an electrode active material layer formed from the electrode slurry according to any one of claims 1 to 7.

9. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to claim 8.

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