Dispersion liquid set for secondary battery electrode, carbon nanotube dispersion liquid, fiber dispersion liquid, dispersion liquid for secondary battery electrode, slurry composition for secondary battery electrode, secondary battery electrode, secondary battery, and method for producing dispersion liquid for secondary battery electrode

Abstract

The purpose of the present invention is to provide a dispersion liquid set which is for a secondary battery electrode and which makes it possible to form a secondary battery electrode that can enable a secondary battery to exhibit excellent cycle characteristics. This dispersion liquid set for a secondary battery electrode comprises: a carbon nanotube dispersion liquid which contains carbon nanotubes 1, a dispersant 1, and a solvent 1; and a fiber dispersion liquid which contains fibers and a solvent 2. The average length of the carbon nanotubes 1 is not more than 1 μm. The average length of the fibers is not less than 1.5 times the average length of the carbon nanotubes 1.

Description

Dispersion set for secondary battery electrodes, carbon nanotube dispersion, fiber dispersion, dispersion for secondary battery electrodes, slurry composition for secondary battery electrodes, electrodes for secondary batteries and secondary batteries, and method for manufacturing dispersion for secondary battery electrodes.

[0001] The present invention relates to a dispersion set for secondary battery electrodes, a carbon nanotube dispersion, a fiber dispersion, a dispersion for secondary battery electrodes, a slurry composition for secondary battery electrodes, a secondary battery electrode, and a secondary battery, as well as a method for producing a dispersion for secondary battery electrodes.

[0002] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are used in a variety of electronic devices, such as logic circuits and other electronic circuits; DRAM, SRAM, NRAM and other memory devices; semiconductor devices; interconnects; complementary MOS and bipolar transistors and other electronic components; chemical sensors such as detectors for trace gases; and biosensors such as measuring instruments for DNA and proteins, due to their excellent mechanical strength, optical properties, electrical properties, thermal properties, and molecular adsorption capacity.

[0003] Furthermore, in recent years, CNTs have also been used as conductive materials in slurry compositions for secondary battery electrodes, which are used to form the electrode composite layer of secondary batteries, such as non-aqueous electrolyte secondary batteries using organic solvent electrolytes (hereinafter sometimes abbreviated as "non-aqueous secondary batteries") and all-solid-state secondary batteries using solid electrolytes instead of organic solvent electrolytes. Secondary battery electrodes undergo significant expansion and contraction due to charging and discharging, which reduces the conductivity of the electrodes and degrades the cycle characteristics of the secondary battery. However, by using CNTs as a conductive material in the slurry for secondary battery electrodes, the decrease in conductivity is suppressed, and a secondary battery with excellent cycle characteristics can be obtained.

[0004] In order to fully utilize the properties of CNTs, it is necessary to disperse them in a solvent, and CNT-containing dispersions (CNT dispersions) have been proposed. For example, Patent Document 1 discloses a CNT dispersion containing CNTs, a dispersant, and a solvent, wherein the particle size distribution curve has particle size distribution peaks in the range of particle diameters from 0.1 μm to 3 μm and in the range of particle diameters from 10 μm to 100 μm, and the cumulative particle diameter D50 is 4 μm or more. According to Patent Document 1, the CNT dispersion has high conductivity and good stability over time, and by using the CNT dispersion, it is possible to provide a secondary battery with excellent rate characteristics and cycle characteristics.

[0005] Japanese Patent Publication No. 2024-000897

[0006] However, in recent years, there has been a demand for further performance improvements in secondary batteries, and the conventional CNT dispersion described above had room for improvement in terms of enabling secondary batteries to exhibit sufficiently excellent cycle characteristics.

[0007] Therefore, the present invention aims to provide a dispersion liquid set for secondary battery electrodes, a dispersion liquid for secondary battery electrodes, and a slurry composition for secondary battery electrodes, which are capable of forming electrodes for secondary batteries that exhibit excellent cycle characteristics in secondary batteries, as well as a carbon nanotube dispersion liquid and a fiber dispersion liquid used in the dispersion liquid for secondary battery electrodes. Furthermore, the present invention aims to provide electrodes for secondary batteries that exhibit excellent cycle characteristics in secondary batteries. Moreover, the present invention aims to provide a secondary battery with excellent cycle characteristics. Furthermore, the present invention aims to provide a method for producing a dispersion liquid for secondary battery electrodes that is capable of forming electrodes for secondary batteries that exhibit excellent cycle characteristics in secondary batteries.

[0008] The inventors diligently conducted research with the aim of solving the above problems. As a result, the inventors discovered that a secondary battery with excellent cycle characteristics can be formed by using a dispersion set comprising a CNT dispersion containing CNTs with an average length of 1 μm or less and a fibrous dispersion containing fibrous material with an average length of 1.5 times or more than that of the CNTs, and thus completed the present invention.

[0009] In other words, the present invention aims to advantageously solve the above problems, and according to the present invention, the following secondary battery electrode dispersion sets [1] to [7], secondary battery electrode dispersions [8] and

[17] , secondary battery electrode slurry compositions [9] to

[11] , secondary battery electrode

[12] , secondary battery

[13] , carbon nanotube dispersion

[14] , fiber dispersion

[15] , and a method for producing the secondary battery electrode dispersion

[16] are provided.

[0010] [1] A dispersion set for secondary battery electrodes comprising a carbon nanotube dispersion containing carbon nanotubes 1, a dispersant 1, and a solvent 1, and a fibrous material dispersion containing fibrous material and a solvent 2, wherein the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous material is 1.5 times or more the average length of the carbon nanotubes 1. Thus, a dispersion set for secondary battery electrodes (hereinafter sometimes simply referred to as "dispersion set") comprising a CNT dispersion containing CNTs 1 with an average length of 1.5 times or less than the above value, and a fibrous material dispersion containing fibrous material with an average length of 1.5 times or more the average length of the CNTs 1 in the CNT dispersion, can enable secondary batteries to exhibit excellent cycle characteristics. In this invention, the "average length" of the CNTs 1 and fibrous material can be measured using the method described in the examples of this specification.

[0011] [2] The secondary battery electrode dispersion set according to [1] above, wherein the average aspect ratio of the carbon nanotubes 1 is 60 or less. If the average aspect ratio of CNTs 1 in the CNT dispersion is less than or equal to the above value, the cycle characteristics of the secondary battery can be further improved. In this invention, the "average aspect ratio" of CNTs 1 can be measured using the method described in the examples of this specification.

[0012] [3] The secondary battery electrode dispersion set according to [1] or [2] above, wherein the average aspect ratio of the fibers is 100 or more. If the average aspect ratio of the fibers in the fiber dispersion is equal to or greater than the above value, the cycle characteristics of the secondary battery can be further improved. In this invention, the "average aspect ratio" of the fibers can be measured using the method described in the examples of this specification.

[0013] [4] A secondary battery electrode dispersion set according to any one of [1] to [3] above, wherein the content of carbon nanotubes 1 in the carbon nanotube dispersion is 0.01% by mass or more and 1% by mass or less. If the content of CNT 1 in the CNT dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0014] [5] A secondary battery electrode dispersion set according to any one of [1] to [4] above, wherein the content of the fibers in the fiber dispersion is 0.01% by mass or more and 1% by mass or less. If the content of the fibers in the fiber dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0015] [6] A dispersion liquid set for secondary battery electrodes according to any one of [1] to [5] above, wherein the fiber material is carbon nanotube 2. If CNT is used as the fiber material in the fiber dispersion liquid, the cycle characteristics of the secondary battery can be further improved.

[0016] [7] A secondary battery electrode dispersion set according to any one of [1] to [6] above, wherein the carbon nanotube 1 in the carbon nanotube dispersion contains single-walled carbon nanotubes. If the CNT dispersion contains single-walled carbon nanotubes, the cycle characteristics of the secondary battery can be further improved.

[0017] [8] A dispersion liquid for a secondary battery electrode, comprising a carbon nanotube dispersion liquid containing carbon nanotubes 1, a dispersant 1, and a solvent 1, and a fibrous body dispersion liquid containing a fibrous body and a solvent 2, wherein the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous body is 1.5 times or more the average length of the carbon nanotubes 1. According to the above-described dispersion liquid for a secondary battery electrode, excellent cycle characteristics can be exhibited in the secondary battery.

[0018] [9] A slurry composition for a secondary battery electrode, comprising the dispersion liquid for a secondary battery electrode according to [8] above, an electrode active material, and a binder. According to the slurry composition for a secondary battery electrode (hereinafter sometimes simply referred to as "slurry composition") comprising the above-described dispersion liquid for a secondary battery electrode, an electrode active material, and a binder, excellent cycle characteristics can be exhibited in the secondary battery.

[0019]

[10] The slurry composition for a secondary battery electrode according to [9] above, wherein the electrode active material contains a silicon-based negative electrode active material. If the electrode active material contains a silicon-based negative electrode active material, the capacity of the resulting secondary battery can be improved. In addition, the silicon-based negative electrode active material has particularly large expansion and contraction during charge and discharge. By using the slurry composition of the present invention, the disconnection of the conductive path in the electrode composite layer due to the large expansion and contraction during charge and discharge can be effectively suppressed, and as a result, the cycle characteristics of the secondary battery can be further enhanced.

[0020]

[11] The slurry composition for a secondary battery electrode according to [9] or

[10] above, wherein the ratio of the content of the carbon nanotubes 1 to the content of the fibrous body (content of the carbon nanotubes 1 / content of the fibrous body) is 1 / 99 or more and 99 / 1 or less in terms of mass ratio. If the mass ratio of the content of CNT1 to the content of the fibrous body in the slurry composition is within the above range, the cycle characteristics of the secondary battery can be further enhanced.

[0021]

[12] An electrode for a secondary battery, comprising an electrode composite layer formed using the slurry composition for a secondary battery electrode according to any one of [9] to

[11] above. An electrode comprising an electrode composite layer obtained by using any of the above-described slurry compositions can exhibit excellent cycle characteristics in the secondary battery.

[0022]

[13] A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein the negative electrode is the electrode for a secondary battery described in

[12] above. By using the above-described electrode for a secondary battery as the negative electrode, a secondary battery having excellent cycle characteristics can be manufactured.

[0023]

[14] A carbon nanotube dispersion used in a dispersion for a secondary battery electrode containing a carbon nanotube dispersion and a fibrous body dispersion. The carbon nanotube dispersion contains carbon nanotubes 1, a dispersant 1, and a solvent 1. The fibrous body dispersion contains a fibrous body and a solvent 2. The average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous body is 1.5 times or more the average length of the carbon nanotubes 1.

[0024]

[15] A fibrous body dispersion used in a dispersion for a secondary battery electrode containing a carbon nanotube dispersion and a fibrous body dispersion. The carbon nanotube dispersion contains carbon nanotubes 1, a dispersant 1, and a solvent 1. The fibrous body dispersion contains a fibrous body and a solvent 2. The average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous body is 1.5 times or more the average length of the carbon nanotubes 1.

[0025]

[16] A method for manufacturing a dispersion for a secondary battery electrode, comprising: a step of obtaining a carbon nanotube dispersion containing carbon nanotubes 1, a dispersant 1, and a solvent 1, wherein the average length of the carbon nanotubes 1 is 1 μm or less; a step of obtaining a fibrous body dispersion containing a fibrous body and a solvent 2, wherein the average length of the fibrous body is 1.5 times or more the average length of the carbon nanotubes 1; and a step of mixing the carbon nanotube dispersion and the fibrous body dispersion to obtain a dispersion for a secondary battery electrode. According to such a method for manufacturing a dispersion for a secondary battery electrode, a dispersion for a secondary battery electrode that can exhibit excellent cycle characteristics in a secondary battery can be efficiently manufactured.

[0026]

[17] A dispersion for secondary battery electrodes comprising carbon nanotubes, fibers, a dispersant, and a solvent, wherein the average length of the carbon nanotubes is 1 μm or less, and the average length of the fibers is 1.5 times or more the average length of the carbon nanotubes. Such a dispersion for secondary battery electrodes allows the secondary battery to exhibit excellent cycle characteristics.

[0027] According to the present invention, it is possible to provide a dispersion liquid set for secondary battery electrodes capable of forming secondary battery electrodes that exhibit excellent cycle characteristics in secondary batteries, a dispersion liquid for secondary battery electrodes, a slurry composition for secondary battery electrodes, and a carbon nanotube dispersion liquid and a fiber dispersion liquid used in the dispersion liquid for secondary battery electrodes. Furthermore, according to the present invention, it is possible to provide a secondary battery electrode capable of exhibiting excellent cycle characteristics in secondary batteries. Moreover, according to the present invention, it is possible to provide a secondary battery with excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a method for producing a dispersion liquid for secondary battery electrodes capable of forming secondary battery electrodes that exhibit excellent cycle characteristics in secondary batteries.

[0028] Embodiments of the present invention will be described in detail below. Here, the secondary battery electrode dispersion set of the present invention can be used to prepare a secondary battery electrode dispersion, for example, the secondary battery electrode dispersion of the present invention. Furthermore, the secondary battery electrode dispersion of the present invention can be used to prepare a secondary battery electrode slurry composition of the present invention, which can be manufactured, for example, by the method for manufacturing the secondary battery electrode dispersion of the present invention. The carbon nanotube dispersion and fibrous dispersion of the present invention are used in the secondary battery electrode dispersion, for example, the secondary battery electrode dispersion of the present invention. Furthermore, the secondary battery electrode slurry composition of the present invention can be used to form electrodes (secondary battery electrodes) of secondary batteries such as non-aqueous secondary batteries and all-solid-state secondary batteries, and the secondary battery electrode of the present invention is characterized by comprising an electrode composite layer formed from the secondary battery electrode slurry composition of the present invention. Furthermore, the secondary battery of the present invention is characterized by comprising a secondary battery electrode made using the secondary battery electrode slurry composition of the present invention as the negative electrode. Note that each component disclosed herein, as well as preferred embodiments, numerical ranges, and thresholds defining such numerical ranges shown with respect to each component, can be independently combined with each other in any manner.

[0029] (Dispersion Set for Secondary Battery Electrodes) The dispersion set of the present invention comprises a CNT dispersion and a fiber dispersion. In the dispersion set of the present invention, the CNT dispersion and the fiber dispersion exist separately, and are mixed when the dispersion set of the present invention is used. Here, the dispersion set of the present invention is characterized in that the average length of CNT1 in the CNT dispersion is 1 μm or less, and the average length of the fibers in the fiber dispersion is 1.5 times or more the average length of CNT1 in the CNT dispersion. The dispersion set of the present invention may also contain dispersions other than the CNT dispersion and fiber dispersion described above (other dispersions). In one embodiment, the dispersion set of the present invention comprises a first container containing the CNT dispersion and a second container containing the fiber dispersion, and optionally further comprises containers other than the first and second containers (other containers). Here, the other containers contain the other dispersions described above.

[0030] Furthermore, since the dispersion liquid set of the present invention includes a CNT dispersion liquid containing CNT1 with an average length of 1 μm or less, and a fibrous material dispersion liquid containing fibrous material with an average length of 1.5 times or more that of the CNT1, electrodes capable of exhibiting excellent cycle characteristics in secondary batteries can be manufactured using this dispersion liquid set. The reason why the above effects are obtained by using this dispersion liquid set of the present invention is not clear, but it is presumed to be as follows.

[0031] In secondary batteries such as lithium-ion secondary batteries, the SEI (Solid Electrolyte Interphase) film formed at the electrode-electrolyte interface is thought to play a role in inserting and deinserting lithium ions into and out of the electrode, while also contributing to improved performance such as suppressing the decomposition of the electrolyte. On the other hand, if the SEI film becomes too thick due to repeated peeling and reforming, the electrical resistance increases, and the SEI film may adversely affect the battery's lifespan and efficiency. Furthermore, it is known that in the electrode composite layer, gaps can form between electrode active materials due to the expansion and contraction of the electrode active materials accompanying the charging and discharging of the secondary battery, causing the conductive paths to be severed. In contrast, the dispersion set of the present invention contains CNT1 with an average length of 1 μm or less in the CNT dispersion, and contains fibers with an average length of 1.5 times or more than the CNT1 in the fiber dispersion. First, since the average length of CNT1 in the CNT dispersion is 1 μm or less, it can be said that the CNT dispersion contains a sufficient number of short CNTs. Such CNTs can contribute to promoting adhesion between the electrode active material and the SEI coating within the electrode composite layer. Therefore, peeling and detachment of the SEI coating from the electrode active material can be suppressed, as well as the formation of new SEI coatings and the thickening of existing SEI coatings. On the other hand, the fibers in the fiber dispersion are relatively long, with an average length of 1.5 times or more that of the CNTs. Therefore, even after the electrode active material repeatedly expands and contracts due to charging and discharging of the secondary battery, conductive paths can be maintained by connecting the electrode active material. The adhesion-promoting effect of the short CNTs and the bridging effect between the electrode active material by the long fibers combine to suppress the deterioration of the secondary battery's cycle characteristics associated with charging and discharging when an electrode composite layer is formed using a slurry composition containing the dispersion set of the present invention. For the reasons stated above, it is believed that using the dispersion set of the present invention can enable secondary batteries to exhibit excellent cycle characteristics.

[0032] <Carbon Nanotube Dispersion> The CNT dispersion contains CNTs 1, a dispersant 1, and a solvent 1, and optionally further contains other components. Here, the CNT dispersion is characterized in that the average length of the CNTs 1 is 1 μm or less.

[0033] <<CNT1>> A CNT dispersion typically contains multiple CNTs 1, and at least a portion of these multiple CNTs 1 form a CNT bundle. Here, a CNT bundle is formed when multiple CNTs are bundled together along the long axis of the CNT. CNT1 preferably contains single-layer to five-layer CNTs, and more preferably single-layer CNTs. Furthermore, CNT1 more preferably mainly contains single-layer to five-layer CNTs, and even more preferably mainly contains single-layer CNTs. In this invention, "mainly containing" a certain CNT means that more than half of the total number of multiple CNTs is that particular CNT.

[0034] [Properties of CNT1] -Average Length- The average length of CNT1 in the CNT dispersion must be 1 μm or less. If the average length of CNT1 exceeds 1 μm, the cycle characteristics of the secondary battery will deteriorate. Preferably, the average length of CNT1 in the CNT dispersion is 0.9 μm or less, more preferably 0.8 μm or less, and even more preferably 0.7 μm or less. If the average length of CNT1 is 0.9 μm or less, the cycle characteristics of the secondary battery can be further improved. Furthermore, the lower limit of the average length of CNT1 in the CNT dispersion is not particularly limited and can be, for example, 0.05 μm or more, or 0.1 μm or more. The average length of CNT1 in the CNT dispersion can be adjusted, for example, by changing the length of the raw material CNT (CNT used as a raw material when preparing the CNT dispersion), the type and amount of dispersant 1, and the conditions of the dispersion treatment.

[0035] ―Average Aspect Ratio― The average aspect ratio of CNT1 in the CNT dispersion is preferably 60 or less, and more preferably 55 or less. If the average aspect ratio of CNT1 is 60 or less, the cycle characteristics of the secondary battery can be further improved. The lower limit of the average aspect ratio of CNT1 in the CNT dispersion is not particularly limited and can be, for example, 5 or more, or 10 or more. The average aspect ratio of CNT1 in the CNT dispersion can be adjusted, for example, by changing the aspect ratio of the raw material CNTs, the type and amount of dispersant 1, and the conditions of the dispersion process.

[0036] [Content Ratio] The content ratio of CNT1 in the CNT dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, preferably 1% by mass or less, more preferably 0.75% by mass or less, and even more preferably 0.5% by mass or less, based on the total amount of the CNT dispersion as 100% by mass. If the content ratio of CNT1 in the CNT dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0037] <<Dispersant 1>> Examples of dispersant 1 included in the CNT dispersion include water-soluble polymers such as cellulose polymers, polycarboxylic acids, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl methyl ether, poly-N-vinylacetamide, polyacrylamide, and polyimide. In the present invention, a polymer is said to be "water-soluble" if, when 0.5 g of the polymer (in terms of solid content) is dissolved in 100 g of water at a temperature of 25°C, the amount of insoluble content is less than 10.0% by mass.

[0038] Examples of cellulosic polymers include carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and their salts and derivatives. Examples of polycarboxylic acids include polyacrylic acid, polymethacrylic acid, alginic acid, and their salts and derivatives. Examples of the salts include alkali metal salts such as sodium salts and ammonium salts. Examples of the derivatives include esters such as alkyl esters and ethers.

[0039] The dispersant 1 described above may be used alone or in combination of two or more types in any ratio. Among these, from the viewpoint of further improving the cycle characteristics of the secondary battery, a cellulosic polymer is preferred as the dispersant 1, and carboxymethylcellulose and its salts are more preferred.

[0040] The weight-average molecular weight of the dispersant 1 is preferably 100,000 or more, more preferably 200,000 or more, preferably 1,000,000 or less, and more preferably 500,000 or less. If the weight-average molecular weight of the dispersant 1 is within the above range, the cycle characteristics of the secondary battery can be further improved. The weight-average molecular weight of the dispersant can be measured, for example, using gel permeation chromatography (GPC).

[0041] [Content Ratio] The content ratio of dispersant 1 in the CNT dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, preferably 1% by mass or less, more preferably 0.75% by mass or less, and even more preferably 0.5% by mass or less, based on the total amount of the CNT dispersion as 100% by mass. If the content ratio of dispersant 1 in the CNT dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0042] The content of dispersant 1 in the CNT dispersion is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, preferably 200 parts by mass or less, and more preferably 150 parts by mass or less, per 100 parts by mass of CNT 1. If the ratio of dispersant 1 to CNT 1 in the CNT dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0043] <<Solvent 1>> The CNT dispersion may contain only water as solvent 1, or only an organic solvent (e.g., esters, ketones, alcohols), or solvent 1 may be a mixture of water and an organic solvent. From the viewpoint of further improving the cycle characteristics of the secondary battery, it is preferable that the CNT dispersion contains water as solvent 1. The CNT dispersion may contain one type of organic solvent, or two or more types of organic solvents.

[0044] Here, the CNT dispersion preferably contains 70% by mass or more, more preferably 90% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass, based on 100% by mass of the total amount of solvent 1 (i.e., the CNT dispersion contains only water as solvent 1). If the proportion of water in solvent 1 in the CNT dispersion is above the above lower limit, the cycle characteristics of the secondary battery can be further improved.

[0045] <<Other Components>> Other components that the CNT dispersion may optionally contain include conductive materials other than CNTs, polymer components other than the dispersant 1 described above, antioxidants, resins, etc. The CNT dispersion may contain only one type of other component, or it may contain two or more types. The proportion of other components contained in the CNT dispersion is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass (i.e., the CNT dispersion does not contain any other components), based on the total amount of the CNT dispersion as 100% by mass.

[0046] <<Preparation of CNT Dispersion>> A CNT dispersion can be prepared by subjecting a mixed solution containing, for example, CNT 1, dispersant 1, and solvent 1, and optionally other components, to a dispersion treatment. Known dispersion methods such as ultrasonic dispersion, jet mill dispersion, high-shear stirring dispersion, and bead mill dispersion can be used.

[0047] <Fiber Dispersion> The fiber dispersion contains fibers and solvent 2, and optionally further contains dispersant 2 and other components. Here, the fiber dispersion is characterized in that the average length of the fibers described above is 1.5 times or more the average length of CNT1 in the CNT dispersion.

[0048] <<Fibers>> A fibrous dispersion typically contains multiple fibers, at least a portion of which form a fibrous bundle. Here, a fibrous bundle is formed when multiple fibers are bundled together (in a bundle-like manner) along the long axis of the fibers.

[0049] Examples of fibrous materials included in the fibrous dispersion include fibrous polymers such as CNTs and cellulose nanofibers. In particular, from the viewpoint of further improving the cycle characteristics of secondary batteries, it is preferable to use CNTs and cellulose nanofibers as the fibrous material, and it is more preferable to use CNTs. The above-mentioned fibrous materials may be used individually or in combination of two or more in any ratio. Furthermore, the CNTs used as fibrous materials (hereinafter referred to as "CNT2") preferably contain single-layer to five-layer CNTs, and more preferably contain single-layer CNTs. Moreover, it is more preferable that the CNT2 used as fibrous materials mainly contain single-layer to five-layer CNTs, and even more preferable that mainly contain single-layer CNTs.

[0050] [Properties of the Fibers] -Average Length- The average length of the fibers in the fiber dispersion is preferably 0.8 μm or more, more preferably 1 μm or more, even more preferably 1.2 μm or more, and particularly preferably 1.4 μm or more. If the average length of the fibers is 0.8 μm or more, the cycle characteristics of the secondary battery can be further improved. Furthermore, the upper limit of the average length of the fibers in the fiber dispersion is not particularly limited and can be, for example, 50 μm or less, or 30 μm or less. The average length of the fibers in the fiber dispersion can be adjusted, for example, by changing the length of the raw material fibers (fibers used as raw materials when preparing the fiber dispersion), the type and amount of dispersant 2, and the conditions of the dispersion treatment.

[0051] ―Average Aspect Ratio― The average aspect ratio of the fibers in the fiber dispersion is preferably 100 or more, more preferably 125 or more, and even more preferably 150 or more. If the average aspect ratio of the fibers is 100 or more, the cycle characteristics of the secondary battery can be further improved. The upper limit of the average aspect ratio of the fibers is not particularly limited and can be, for example, 2000 or less, or 1000 or less. The average aspect ratio of the fibers in the fiber dispersion can be adjusted, for example, by changing the aspect ratio of the raw material fibers, the type and amount of dispersant 2, and the conditions of the dispersion treatment.

[0052] Furthermore, the average length of the fibers in the fiber dispersion must be at least 1.5 times the average length of CNT1 in the CNT dispersion. If the average length of the fibers in the fiber dispersion is less than 1.5 times the average length of CNT1 in the CNT dispersion, the cycle characteristics of the secondary battery will deteriorate. Preferably, the average length of the fibers in the fiber dispersion is at least 1.7 times the average length of CNT1 in the CNT dispersion, and more preferably 1.9 times or more. If the average length of the fibers in the fiber dispersion is at least 1.7 times the average length of CNT1 in the CNT dispersion, the cycle characteristics of the secondary battery can be further improved. There is no particular upper limit; for example, the average length of the fibers in the fiber dispersion can be 150 times or less, or 100 times or less, the average length of CNT1 in the CNT dispersion.

[0053] [Content Ratio] The content ratio of fibers in the fiber dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, preferably 1% by mass or less, more preferably 0.8% by mass or less, even more preferably 0.6% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.4% by mass or less, based on the total amount of the fiber dispersion as 100% by mass. If the content ratio of fibers in the fiber dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0054] <<Dispersant 2>> The fibrous dispersion may or may not contain dispersant 2. When the fibrous dispersion contains CNT2 as fibrous material, it is preferable that the fibrous dispersion contains dispersant 2 from the viewpoint of further improving the cycle characteristics of the secondary battery.

[0055] Examples of dispersant 2 include those similar to dispersant 1 described above in the "CNT dispersion" section. In particular, from the viewpoint of further improving the cycle characteristics of secondary batteries, it is preferable to use a cellulosic polymer as dispersant 2, and more preferably to use carboxymethylcellulose and its salts. Furthermore, the preferred range of weight-average molecular weight of dispersant 2 can be the same as the preferred range of weight-average molecular weight of dispersant 1. Dispersant 1 and dispersant 2 may be the same or different, but it is preferable that dispersant 1 and dispersant 2 are the same.

[0056] [Content Ratio] When the fiber dispersion contains dispersant 2, the content ratio of dispersant 2 in the fiber dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, preferably 1% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.6% by mass or less, based on the total amount of the fiber dispersion as 100% by mass. If the content ratio of dispersant 2 in the fiber dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0057] When the fiber dispersion contains dispersant 2, the amount of dispersant 2 in the fiber dispersion is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, preferably 200 parts by mass or less, and more preferably 150 parts by mass or less, per 100 parts by mass of fiber. If the ratio of dispersant 2 to fiber in the fiber dispersion is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0058] <<Solvent 2>> Solvent 2 can be the same as solvent 1 described above in the "CNT dispersion" section. The preferred type and proportion of solvent 2 can be the same as those described in the "Solvent 1" section. Solvent 1 and solvent 2 may be the same or different, but it is preferable that solvent 1 and solvent 2 are the same.

[0059] <<Other Components>> Other components that the fiber dispersion may optionally contain include conductive materials other than the fibers mentioned above, polymer components other than the dispersant 2 mentioned above, antioxidants, resins, etc. The fiber dispersion may contain only one type of other component, or two or more types. The proportion of other components contained in the fiber dispersion is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass (i.e., the fiber dispersion does not contain any other components), based on the total amount of the fiber dispersion as 100% by mass.

[0060] <<Preparation of Fiber Dispersion>> A fiber dispersion can be prepared, for example, by subjecting a mixed solution containing fiber and solvent 2, and optionally further containing dispersant 2 and other components, to a dispersion treatment. As the dispersion treatment, the known dispersion treatment method described above in the "CNT Dispersion" section can be used.

[0061] <Other Dispersions> The dispersion set of the present invention is not particularly limited as long as it does not significantly impair the desired effect, and may include dispersions other than the CNT dispersion and fiber dispersion described above (other dispersions). Other dispersions are not particularly limited and include, for example, known dispersions used in the preparation of slurry compositions for secondary battery electrodes.

[0062] (Dispersion for secondary battery electrodes) The dispersion for secondary battery electrodes of the present invention has two embodiments (embodiments 1 and 2). In embodiment 1, the dispersion for secondary battery electrodes of the present invention includes a CNT dispersion containing CNT 1, a dispersant 1, and a solvent 1, and a fibrous dispersion containing fibrous material and a solvent 2. In embodiment 2, the dispersion for secondary battery electrodes of the present invention includes CNT, fibrous material, a dispersant, and a solvent. Hereinafter, the dispersion for secondary battery electrodes of embodiment 1 will be referred to as "dispersion for secondary battery electrodes 1," and the dispersion for secondary battery electrodes of embodiment 2 will be referred to as "dispersion for secondary battery electrodes 2." Hereinafter, the dispersion for secondary battery electrodes 1 of the present invention is characterized in that the average length of the CNT 1 is 1 μm or less, and the average length of the fibrous material is 1.5 times or more the average length of the CNT 1, and the dispersion for secondary battery electrodes 2 of the present invention is characterized in that the average length of the CNT is 1 μm or less, and the average length of the fibrous material is 1.5 times or more the average length of the CNT. Furthermore, for the same reasons explained in the section on "Dispersion Set for Secondary Battery Electrodes," the dispersions 1 and 2 for secondary battery electrodes of the present invention enable secondary batteries to exhibit excellent cycle characteristics. Note that the dispersions for secondary battery electrodes of the present invention do not contain the binder and electrode active material described later.

[0063] <Dispersion 1 for secondary battery electrodes> As described above, the dispersion 1 for secondary battery electrodes of the present invention comprises a CNT dispersion containing CNT 1, a dispersant 1, and a solvent 1, and a fibrous dispersion containing a fiber and a solvent 2. In a preferred embodiment, the dispersion 1 for secondary battery electrodes of the present invention can be obtained by mixing the dispersion set of the present invention described above. That is, the dispersion 1 for secondary battery electrodes of the present invention is preferably a mixture of the CNT dispersion, the fibrous dispersion, and any other dispersion, and contains at least the CNT 1, the fiber and the dispersant 1, and a solvent, and optionally further contains a dispersant 2. The dispersion 1 for secondary battery electrodes of the present invention may optionally further contain components other than those described above (other components). Furthermore, the solvent contained in the dispersion 1 for secondary battery electrodes may all be derived from the dispersion set, or it may be newly added to the dispersion for secondary battery electrodes separately from the solvent derived from the dispersion set. When adding a solvent to the secondary battery electrode dispersion 1 in addition to the solvent derived from the dispersion set, it is preferable that the added solvent be of the same type as the solvent derived from the dispersion set.

[0064] The total content of CNTs 1 and fibers in the secondary battery electrode dispersion 1 is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, based on the total amount of the secondary battery electrode dispersion 1 as 100% by mass. If the total content of CNTs 1 and fibers in the secondary battery electrode dispersion 1 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0065] The total content ratio of dispersant 1 and dispersant 2 in the secondary battery electrode dispersion 1 is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, based on the total amount of the secondary battery electrode dispersion 1 as 100% by mass. If the total content ratio of dispersant 1 and dispersant 2 in the secondary battery electrode dispersion 1 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0066] Furthermore, the ratio of the CNT1 content to the fiber content in the secondary battery electrode dispersion 1 (CNT1 content / fiber content) is preferably 1 / 99 or more, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, preferably 99 / 1 or less, more preferably 90 / 10 or less, and even more preferably 80 / 20 or less by mass ratio. If the ratio of the CNT1 content to the fiber content in the secondary battery electrode dispersion 1 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0067] <Dispersion liquid 2 for secondary battery electrodes> As described above, the dispersion liquid 2 for secondary battery electrodes of the present invention contains CNTs, fibers, a dispersant, and a solvent, and optionally contains other components.

[0068] The CNTs, fibers, dispersant, and solvent contained in the dispersion liquid 2 for secondary battery electrodes of the present invention can be the same as those described above in the section on "Dispersion liquid set for secondary battery electrodes," respectively.

[0069] The total content of CNTs and fibers in the secondary battery electrode dispersion 2 is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, based on the total amount of the secondary battery electrode dispersion 2 as 100% by mass. If the total content of CNTs and fibers in the secondary battery electrode dispersion 2 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0070] Furthermore, the content of the dispersant in the secondary battery electrode dispersion 2 is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, preferably 2% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1% by mass or less, based on the total amount of the secondary battery electrode dispersion 2 as 100% by mass. If the content of the dispersant in the secondary battery electrode dispersion 2 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0071] Furthermore, the ratio of the CNT content to the fiber content in the secondary battery electrode dispersion 2 (CNT content / fiber content) is preferably 1 / 99 or more, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, preferably 99 / 1 or less, more preferably 90 / 10 or less, and even more preferably 80 / 20 or less, in terms of mass ratio. If the ratio of the CNT content to the fiber content in the secondary battery electrode dispersion 2 is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0072] <Preparation of the dispersion for secondary battery electrodes> The dispersion for secondary battery electrodes of the present invention can be manufactured, for example, using the method for manufacturing the dispersion for secondary battery electrodes of the present invention, as described later.

[0073] (Slurry Composition for Secondary Battery Electrodes) The slurry composition of the present invention is a composition used for forming an electrode composite layer, and comprises an electrode active material, a binder, and the above-described dispersion liquid for secondary battery electrodes of the present invention. That is, the slurry composition of the present invention usually contains an electrode active material, a binder, the above-described CNT1, fiber and dispersant 1, and a solvent, and optionally contains dispersant 2. The slurry composition of the present invention may optionally further contain components other than those listed above. Furthermore, the solvent contained in the slurry composition may be entirely derived from the dispersion liquid for secondary batteries, or it may be newly added to the slurry composition separately from the solvent derived from the dispersion liquid for secondary batteries. When a new solvent is added to the slurry composition separately from the solvent derived from the dispersion liquid for secondary batteries, it is preferable that the added solvent is of the same type as the solvent derived from the dispersion liquid for secondary batteries. Since the slurry composition of the present invention contains the above-described dispersion liquid for secondary batteries, it can enable secondary batteries to exhibit excellent cycle characteristics. In the following description, we will explain the case where the slurry composition for secondary battery electrodes is a slurry composition for lithium-ion secondary battery electrodes as an example, but the present invention is not limited to the example below.

[0074] <Electrode Active Material> Electrode active material is a substance that transfers electrons at the electrodes of a secondary battery. For example, in the case of a lithium-ion secondary battery, the electrode active material is usually a substance that can intercalate and release lithium.

[0075] Furthermore, the positive electrode active material for lithium-ion secondary batteries is not particularly limited to lithium-containing cobalt oxide (LiCoO2). ２ ), lithium manganese (LiMn ２ O ４ ), lithium-containing nickel oxide (LiNiO ２ ), Co-Ni-Mn lithium-containing composite oxide (Li(CoMnNi)O ２ ), Ni-Mn-Al lithium-containing composite oxide, Ni-Co-Al lithium-containing composite oxide, olivine-type lithium iron phosphate (LiFePO) ４ ), olivine-type lithium manganese phosphate (LiMnPO ４), Li ２ MnO ３ -LiNiO ２ -type solid solution, Li １＋ｘ Mn ２－ｘ O ４ (0 < X < 2), a lithium-excess spinel compound represented by Li[Ni ０．１７ Li ０．２ Co ０．０７ Mn ０．５６ O ２ , LiNi ０．５ Mn １．５ O ４ and other known cathode active materials such as these. Note that the amount and particle diameter of the cathode active material are not particularly limited and can be the same as those of the conventionally used cathode active materials.

[0076] Also, examples of the anode active material for a lithium-ion secondary battery include carbon-based anode active materials, metal-based anode active materials, and anode active materials combining these.

[0077] Here, the carbon-based anode active material refers to an active material having carbon as the main skeleton into which lithium can be inserted (also referred to as "doped"). Examples of the carbon-based anode active material include carbonaceous materials. And examples of the carbonaceous materials include graphitizable carbon and non-graphitizable carbon having a structure close to an amorphous structure typified by glassy carbon. Here, examples of the graphitizable carbon include carbon materials made from tar pitch obtained from petroleum or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Also, examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin fired bodies (PFA), hard carbon, etc.

[0078] Furthermore, a metallic anode active material is an anode active material containing a metal, and typically contains an element in its structure that allows for lithium insertion, and has a theoretical electrical capacity of 500 mAh / g or more per unit mass when lithium is inserted. Examples of metallic anode active materials include lithium metal, elemental metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, and phosphides. Among these, silicon-containing active materials (silicon-based anode active materials) are preferred as metallic anode active materials. This is because using silicon-based anode active materials allows for higher capacity lithium-ion secondary batteries.

[0079] In this context, silicon-based negative electrode active materials exhibit particularly large expansion and contraction during charging and discharging. By using the slurry composition of the present invention, the disruption of conductive paths in the negative electrode composite layer caused by large expansion and contraction during charging and discharging can be effectively suppressed, and as a result, the deterioration of the cycle characteristics of the secondary battery can be effectively suppressed.

[0080] Examples of silicon-based negative electrode active materials include silicon (Si), silicon-containing alloys, SiO₂, and SiO₂. ｘ Examples include composites of Si-containing material and conductive carbon, which are obtained by coating or compounding Si-containing material with conductive carbon. These silicon-based negative electrode active materials may be used individually or in combination of two or more types. The amount and particle size of the negative electrode active material are not particularly limited and can be the same as those of conventionally used negative electrode active materials.

[0081] When the negative electrode active material includes a silicon-based negative electrode active material, the proportion of the silicon-based negative electrode active material per 100 parts by mass of the negative electrode active material is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, preferably 50 parts by mass or less, and more preferably 40 parts by mass or less.

[0082] <Binding agent> The binding agent is used to hold components such as electrode active material contained in the electrode mixture layer in the electrode mixture layer, which is formed on the current collector using a slurry composition containing a dispersion liquid for secondary battery electrodes, so that they do not detach from the electrode mixture layer.

[0083] As a binder, any polymer capable of exhibiting binding ability inside a secondary battery can be used, and no particular limit is imposed. Examples of binders that can be used include fluorine-based polymers such as polyvinylidene fluoride (PVdF) (polymers mainly containing fluorine-containing monomer units); aliphatic conjugated diene / aromatic vinyl copolymers such as styrene-butadiene copolymer (SBR) (polymers mainly containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units) and their hydrides; aliphatic conjugated diene / acrylonitrile copolymers such as butadiene-acrylonitrile copolymer (NBR) and their hydrides; polymers containing (meth)acrylic acid ester monomer units (acrylic polymers); and polyvinyl alcohol-based polymers such as polyvinyl alcohol (PVA). In this invention, "monomer unit" of a polymer means "a repeating unit derived from the monomer contained in the polymer obtained using that monomer." Furthermore, in the present invention, "mainly containing" one or more types of monomer units means that "when the total amount of monomer units contained in the polymer is taken as 100% by mass, the content ratio of the one type of monomer unit, or the sum of the content ratios of the multiple types of monomer units, exceeds 50% by mass."

[0084] Among the above, from the viewpoint of further improving the cycle characteristics of secondary batteries, it is preferable to use an aliphatic conjugated diene / aromatic vinyl copolymer as the binder. The binder may be used alone, or two or more may be used in any ratio.

[0085] <<Aromatic Vinyl Monomer Units>> Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. These may be used individually or in combination of two or more. Among these, styrene is preferred.

[0086] <<Aliphatic Conjugated Diene Monomer Units>> Examples of aliphatic conjugated diene monomers that can form aliphatic conjugated diene monomer units include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used individually or in combination of two or more. In this invention, "aliphatic conjugated diene monomer units" also include structural units (hydride units) obtained by further hydrogenating monomer units contained in polymers obtained using aliphatic conjugated diene monomers. Among the aliphatic conjugated diene monomers mentioned above, 1,3-butadiene is preferred. In other words, 1,3-butadiene units and 1,3-butadiene hydride units are preferred as aliphatic conjugated diene monomer units.

[0087] <<Other Repeating Units>> The aliphatic conjugated diene / aromatic vinyl copolymer described above may contain other repeating units in the aromatic vinyl monomer units and aliphatic conjugated diene monomer units, and are not particularly limited. Examples include monomer units derived from known monomers (other monomers) copolymerizable with the aromatic vinyl monomers and aliphatic conjugated diene monomers described above. These other monomers may be used individually or in combination of two or more.

[0088] Furthermore, the amount of binder in the slurry composition may be 0.5 parts by mass or more and 15 parts by mass or less in terms of solid content per 100 parts by mass of electrode active material.

[0089] <<Method for preparing the binder>> The method for preparing the binder consisting of the polymer described above is not particularly limited. The polymer used as a binder can be produced, for example, by polymerizing a monomer composition containing the monomers described above in a solvent and optionally performing hydrogenation. The content ratio of each monomer in the monomer composition can be determined according to the content ratio of the desired monomer unit (structural unit) in the polymer used as a binder.

[0090] Furthermore, there are no particular restrictions on the polymerization method; any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. In addition, any polymerization reaction such as ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, or addition polymerization can be used. During polymerization, known additives such as emulsifiers, dispersants, polymerization initiators, and polymerization accelerators can be used as needed. The amounts of these additives used can also be those commonly used.

[0091] <Dispersion for secondary battery electrodes> As the dispersion for secondary battery electrodes, for example, the dispersion 1 or 2 for secondary battery electrodes of the present invention described above can be used.

[0092] The total content of CNT1 and fibrous material in the slurry composition is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less, based on solid content, per 100 parts by mass of electrode active material. If the total content of CNT1 and fibrous material per 100 parts by mass of electrode active material in the slurry composition is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0093] The ratio of CNT1 content to fiber content in the slurry composition (CNT1 content / fiber content) is preferably 1 / 99 or more, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, preferably 99 / 1 or less, more preferably 90 / 10 or less, and even more preferably 80 / 20 or less, in terms of mass ratio. If the ratio of CNT1 content to fiber content in the slurry composition is within the above range, the cycle characteristics of the secondary battery can be further improved.

[0094] <Other Components> Other components that can be incorporated into the slurry composition are not particularly limited and include thickeners, as well as other components similar to those that can be incorporated into the CNT dispersion and fiber dispersion described above. Examples of thickeners include carboxymethylcellulose and its salts. Note that the other components may be used individually or in combination of two or more in any ratio.

[0095] Herein, the slurry composition of the present invention is not particularly limited, but when the length distribution (based on the number of particles) of the fibrous material in the slurry composition is taken, it may have two peaks: a peak corresponding to CNT1 derived from the CNT dispersion and a peak corresponding to the fibers derived from the fibrous material dispersion.

[0096] <Preparation of Slurry Composition for Secondary Battery Electrodes> The slurry composition described above can be prepared by mixing the above components using known mixing methods. Such mixing can be performed using, for example, a ball mill, sand mill, bead mill, pigment disperser, lye crusher, ultrasonic disperser, homogenizer, planetary mixer, or film mixer. The mixing order of the components is not particularly limited, and the CNT dispersion and the fiber dispersion may be mixed together before being mixed with other components (electrode active material, binder, and any other components), or they may be mixed separately with other components.

[0097] (Electrodes for secondary batteries) The electrode of the present invention comprises an electrode composite layer formed using the slurry composition of the present invention described above, and usually comprises a current collector and an electrode composite layer formed on the current collector. The electrode composite layer is usually a layer obtained by drying the slurry composition of the present invention, and contains at least an electrode active material, a binder, CNTs, fibers, and dispersant 1, and optionally contains dispersant 2 and other components. The components contained in the electrode composite layer are those contained in the slurry composition described above, and the preferred ratio of each component is the same as the preferred ratio of each component in the slurry composition. Furthermore, when a particulate polymer is used as a binder, the particulate polymer may be in particle form in the electrode composite layer (i.e., it may be contained in the electrode composite layer as a particulate polymer), or it may be in any other shape.

[0098] Furthermore, since the electrodes of the present invention are manufactured using the slurry composition of the present invention, they can exhibit excellent cycle characteristics in secondary batteries. Here, the current collector is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. These materials may be used individually or in combination of two or more materials in any ratio.

[0099] <Method for Forming Electrodes> Here, the electrode composite layer of the electrode of the present invention can be formed by, for example, the following methods: 1) applying the slurry composition of the present invention to the surface of a current collector and then drying it; 2) immersing a current collector in the slurry composition of the present invention and then drying it; and 3) applying the slurry composition of the present invention onto a release substrate, drying it to produce an electrode composite layer, and transferring the obtained electrode composite layer to the surface of a current collector. Among these, method 1) is particularly preferred because it allows for easy control of the thickness of the electrode composite layer. Method 1) more specifically includes the steps of applying the slurry composition onto a current collector (application step) and drying the slurry composition applied onto the current collector to form an electrode composite layer on the current collector (drying step).

[0100] <<Coating Process>> The method for coating the slurry composition onto the current collector is not particularly limited and known methods can be used. Specifically, coating methods such as the doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method can be used. In this case, the slurry composition may be coated on one side of the current collector or on both sides. The thickness of the slurry film on the current collector before drying after coating can be appropriately set according to the thickness of the electrode composite layer obtained after drying.

[0101] <<Drying Process>> The method for drying the slurry composition on the current collector is not particularly limited and known methods can be used, for example, drying methods using hot air, hot air, or low-humidity air, vacuum drying, or drying methods using irradiation such as infrared rays and electron beams can be used. By drying the slurry composition on the current collector in this way, an electrode composite layer is formed on the current collector, and an electrode comprising a current collector and an electrode composite layer located on the current collector can be obtained.

[0102] Furthermore, after the drying process, the electrode composite layer may be subjected to pressure treatment using a die press or roll press. Pressure treatment improves the adhesion between the electrode composite layer and the current collector, and can further increase the density of the resulting electrode composite layer. In addition, if the electrode composite layer contains a curable polymer, it is preferable to cure the polymer after the formation of the electrode composite layer.

[0103] (Secondary Battery) The secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and uses the electrode of the present invention described above as the negative electrode. Furthermore, since the secondary battery of the present invention is manufactured using the electrode of the present invention described above as the negative electrode, it has excellent cycle characteristics. In the following description, the case in which the secondary battery is a lithium-ion secondary battery will be described as an example, but the present invention is not limited to the example below.

[0104] <Positive Electrode> The positive electrode of the secondary battery of the present invention is not particularly limited, and any known positive electrode used in secondary batteries can be used. Specifically, as the positive electrode, a positive electrode can be used which a positive electrode composite layer is formed on a current collector using a known manufacturing method.

[0105] The positive electrode active material incorporated into the positive electrode composite layer is not particularly limited, and any known positive electrode active material used in secondary batteries can be used. Examples of positive electrode active materials incorporated into the positive electrode composite layer include those described above in the section on "Slurry Composition for Secondary Battery Electrodes." One type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0106] Aluminum foil is particularly preferred as the current collector for the positive electrode. The material used for the positive electrode current collector may be a single type, or two or more types may be combined in any ratio.

[0107] <Electrolyte> Typically, an organic electrolyte is used as the electrolyte, which is obtained by dissolving a supporting electrolyte in an organic solvent. For example, lithium salts are used as the supporting electrolytes in lithium-ion secondary batteries. Examples of lithium salts include LiPF4. ６ LiAsF ６ LiBF ４ LiSbF ６ LiAlCl ４ LiClO ４ CF ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Examples include NLi. Among them, LiPF is highly soluble in solvents and exhibits a high degree of dissociation. ６ LiClO ４ CF ３ SO ３Li is preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in any ratio. Generally, the lithium ion conductivity tends to increase as the degree of dissociation of the supporting electrolyte increases; therefore, the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0108] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. A mixture of these solvents may also be used. Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. In addition, known additives can be added to the electrolyte.

[0109] <Separator> The separator is not particularly limited, and for example, those described in Japanese Patent Application Publication No. 2012-204303 can be used. Among these, a microporous membrane made of polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows for a thinner overall film thickness of the separator, thereby increasing the ratio of electrode active material in the secondary battery and thus increasing the capacity per unit volume.

[0110] Furthermore, the secondary battery of the present invention can be manufactured, for example, by overlapping a positive electrode and a negative electrode with a separator in between, winding or folding them as needed according to the battery shape, placing them in a battery container, injecting an electrolyte into the battery container, and sealing it. In this secondary battery of the present invention, the electrode of the present invention described above is used as the negative electrode. In addition, the secondary battery of the present invention may be provided with an overcurrent prevention element such as a fuse or PTC element, expanded metal, or lead plate as needed to prevent pressure rise inside the secondary battery, overcharging and overdischarging, etc. The shape of the secondary battery may be any of the following: coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc.

[0111] (Method for producing a dispersion for secondary battery electrodes) The method for producing a dispersion for secondary battery electrodes of the present invention comprises the steps of: obtaining a CNT dispersion containing CNT 1, a dispersant 1, and a solvent 1 (CNT dispersion preparation step); obtaining a fibrous dispersion containing fibrous material and a solvent 2 (fibrous dispersion preparation step); and mixing the CNT dispersion and the fibrous dispersion to obtain a dispersion for secondary battery electrodes (mixing step). The method for producing a dispersion for secondary battery electrodes of the present invention may include steps other than the CNT dispersion preparation step, the fibrous dispersion preparation step, and the mixing step. Furthermore, the method for producing a dispersion for secondary battery electrodes of the present invention is characterized in that the average length of CNT 1 in the CNT dispersion is 1 μm or less, and the average length of fibrous material in the fibrous dispersion is 1.5 times or more the average length of CNT 1 in the CNT dispersion.

[0112] <CNT Dispersion Preparation Process> The method for preparing the CNT dispersion in the CNT dispersion preparation process is not particularly limited. For example, a CNT dispersion can be prepared by subjecting a mixed solution containing CNT 1, dispersant 1, and solvent 1, and optionally containing other components, to a dispersion treatment. Known dispersion treatment methods such as ultrasonic dispersion, jet mill dispersion, high-shear stirring dispersion, and bead mill dispersion can be used. The preferred examples, content ratios, and properties of each component in the CNT dispersion are as described above in the section on "Dispersion Set for Secondary Battery Electrodes".

[0113] <Preparation Process for Fiber Dispersion> The method for preparing the fiber dispersion in the preparation process is not particularly limited. For example, the fiber dispersion can be prepared by subjecting a mixed solution containing fibers and solvent 2, and optionally further containing dispersant 2 and other components, to a dispersion treatment. The same dispersion treatment method as in the preparation process for CNT dispersion can be used for the dispersion treatment. Furthermore, preferred examples of each component in the fiber dispersion, their content ratios, properties, etc., are as described above in the section on "Dispersion Set for Secondary Battery Electrodes". When using CNT 2 as the fibers, it is preferable to include dispersant 2 in the mixed solution.

[0114] <Mixing Process> In the mixing process, the CNT dispersion obtained in the CNT dispersion preparation process and the fiber dispersion obtained in the fiber dispersion preparation process are mixed to obtain a dispersion for secondary battery electrodes. The mixing method is not particularly limited, and known mixing methods can be used. Furthermore, the mixing ratio of the CNT dispersion and the fiber dispersion is not particularly limited, and for example, the mixture can be prepared so that the ratio of the CNT1 content to the fiber content in the resulting dispersion for secondary battery electrodes (CNT1 content / fiber content) is within the range described above in the "Dispersion for Secondary Battery Electrodes" section.

[0115] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing quantities refer to mass unless otherwise specified. In addition, in polymers produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer is usually equal to the ratio of that particular monomer to the total monomers used in the polymerization of the polymer (starting ratio), unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were performed using the following methods.

[0116] <Average Length and Aspect Ratio of CNT1> The CNT (CNT1) content in the CNT dispersions prepared in the examples and comparative examples was adjusted to 0.0013% by adding deionized water or removing the solvent to obtain a prepared sample. 5 μl of the obtained prepared sample was dropped onto a 10 mm square silicon substrate hydrophilized with oxygen plasma, and then the prepared sample was uniformly coated onto the silicon substrate by rotating the silicon substrate with a spinner. The spinner rotation speeds were set as follows: 1st: slop, 1 second; 2nd: 300 rpm, 40 seconds; 3rd: slop, 3 seconds; 4th: 4000 rpm, 60 seconds. After that, the silicon substrate was dried on a hot plate at 120°C for 5 minutes to obtain a sample for observation. Using a scanning electron microscope (SEM; Hitachi High-Technologies Corporation, product name "SU8220"), the diameter and length of all measurable CNTs captured at 100,000x magnification were measured at five randomly selected locations on the observation sample. The arithmetic mean of the lengths of all measured CNTs was taken as the average length, and the arithmetic mean of the diameters of all measured CNTs was taken as the average diameter. The average aspect ratio (average length / average diameter) was calculated by dividing the average length (μm) by the average diameter (μm). <Average length and average aspect ratio of fibrous material> The fibrous material content in the fibrous material dispersions prepared in the examples and comparative examples was adjusted to 0.0013% by adding ion-exchanged water or solvent removal to obtain prepared solution samples. Using the obtained prepared solution samples, the average length and average aspect ratio of the fibrous material were determined using the same method as the measurement method for "Average length and average aspect ratio of CNT1" described above. <Cycle Characteristics> The fabricated lithium-ion secondary battery was left standing for 24 hours in an environment of 25°C. Next, a charge-discharge operation was performed in which the cell voltage was charged to 4.2V using a constant current method of 0.1C and discharged to a cell voltage of 2.75V, and the initial capacity C0 was measured. Furthermore, the charge-discharge operation was repeated in which the cell voltage was charged to 4.2V using a constant current method of 0.5C in an environment of 25°C and discharged to a cell voltage of 2.75V using the same constant current method as the charging mode, and the capacity C1 after 100 cycles was measured. Then, the capacity retention rate (%) = (C1 / C0) × 100 was calculated and evaluated according to the following criteria. A higher value for this capacity retention rate indicates less decrease in discharge capacity and better cycle characteristics.A: Capacity retention rate of 90% or more. B: Capacity retention rate of 87% or more but less than 90%. C: Capacity retention rate of 84% or more but less than 87%. D: Capacity retention rate of less than 84%.

[0117] (Example 1) <Preparation of CNT dispersion> CNT-a (manufactured by Zeon Corporation, product name "ZEONANO® SG101"; CNT mainly containing single-walled CNTs) as CNT (CNT1) and sodium salt of carboxymethylcellulose (weight-average molecular weight: 300,000; hereinafter referred to as "CMC") as dispersant 1 were added to an appropriate amount of ion-exchanged water as solvent 1 to obtain a mixture. The obtained mixture was subjected to dispersion treatment at 120 MPa using "BERYU SYSTEM PRO" (manufactured by Biryu Co., Ltd.) to produce a CNT dispersion (content of CNT1: 0.4% by mass, content of dispersant 1: 0.4% by mass). The mixing ratio of CNT-a and CMC was CNT-a:CMC = 1:1 by mass. The average length and average aspect ratio of CNT1 were measured using this CNT dispersion. The results are shown in Table 1. <Preparation of Fiber Dispersion> CNT-b (manufactured by OCSiAl, product name "Tubal®"; CNT mainly containing single-walled CNTs) as the fiber (CNT2) and CMC (weight-average molecular weight: 300,000) as the dispersant 2 were added to an appropriate amount of ion-exchanged water as solvent 2 to obtain a mixture. The obtained mixture was subjected to dispersion treatment at 120 MPa using "BERYU SYSTEM PRO" (manufactured by Biryu Co., Ltd.) to produce a fiber dispersion (fiber content: 0.4 mass%, dispersant 2 content: 0.4 mass%). The mixing ratio of CNT-b and CMC was set to CNT-b:CMC = 1:1 by mass. The average length and average aspect ratio of the fibers were measured using this fiber dispersion. The results are shown in Table 1. <Preparation of aqueous dispersion containing binder> A aqueous dispersion containing binder was obtained by dispersing 60 parts of styrene-butadiene copolymer (manufactured by Nippon Zeon Co., Ltd., product name "BM451B"; hereinafter referred to as "SBR") as a binder in 40 parts of water. <Preparation of slurry composition for anode> Artificial graphite (volume average particle size: 24.5 μm, specific surface area: 3.5 m²) as a carbon-based anode active material in a planetary mixer with a disperser. ２87 parts of ( / g), 10 parts of SiO (a composite material coated with conductive carbon) as a silicon-based negative electrode active material, 0.015 parts of the above-mentioned CNT dispersion (equivalent to 1 min of CNT), 0.015 parts of the above-mentioned fibrous dispersion (equivalent to the fibrous content), and 2 parts of an aqueous solution of CMC (weight-average molecular weight: 300,000) as a thickener (equivalent to the solid content) were added. The solid content was adjusted to 58% with deionized water and mixed at room temperature for 60 minutes. Next, the solid content was adjusted to 50% with deionized water, and then 1.0 part of the above-mentioned aqueous dispersion containing the binder was added (equivalent to the solid content) to obtain a mixture. The obtained mixture was defoamed under reduced pressure to obtain a smooth negative electrode slurry composition. <Formation of the negative electrode> The negative electrode slurry composition obtained above was coated onto copper foil (thickness: 15 μm) as a current collector using a comma coater, with a dry film thickness of 68 μm and a coating amount of 3.6 mg / cm². ２ The mixture was applied in this manner. The copper foil coated with this negative electrode slurry composition was transported at a speed of 1.0 m / min in an oven at 100°C for 1 minute, and then in an oven at 120°C for 1 minute to dry the negative electrode slurry composition on the copper foil and obtain a negative electrode base. This negative electrode base was rolled in a roll press to obtain a negative electrode with a negative electrode composite layer thickness of 41 μm. The obtained negative electrode was cut to an electrode area of ​​30 mm × 40 mm and prepared by vacuum drying at 140°C for 10 hours. <Preparation of lithium-ion secondary battery> As the positive electrode, a commercially available positive electrode (NEI Corporation, NMC) was cut to an electrode area of ​​28 mm × 38 mm and vacuum dried at 120°C for 10 hours. A single-layer polypropylene separator (65 mm wide, 500 mm long, 25 μm thick; manufactured by dry process; porosity 55%) was prepared and cut to a size of 3.5 cm x 4.5 cm. An aluminum packaging material was prepared as the battery casing, and the positive electrode prepared above was placed so that the surface on the current collector side was in contact with the aluminum packaging material. Next, the above separator was placed on the surface of the positive electrode composite layer of the positive electrode. Furthermore, the above negative electrode was placed on the separator so that the surface on the negative electrode composite layer side faced the separator. After that, 1.0 M LiPF was used as the electrolyte. ６The solution (a mixed solvent of ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio), with fluoroethylene carbonate and vinylene carbonate each containing 2 volume% (solvent ratio) as additives) was filled into the container. Furthermore, to seal the opening of the aluminum packaging, the outer casing of the aluminum packaging was closed by heat sealing at 150°C, and a laminate cell type lithium-ion secondary battery was manufactured. The cycle characteristics of this lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0118] (Example 2) Except for using the CNT dispersion prepared as described below, a fiber dispersion, an aqueous dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then carried out in the same manner as in Example 1. The results are shown in Table 1. <Preparation of CNT dispersion> The CNT dispersion was prepared in the same manner as in Example 1, except that the dispersion treatment applied to the mixture was changed to a bead mill using zirconia beads with a diameter of 0.1 mm.

[0119] (Example 3) Except for using cellulose nanofiber (manufactured by Sugino Machine Co., Ltd., product name "BMa-100"; hereinafter referred to as "CNF") instead of CNT-b when preparing the fibrous dispersion, and not using dispersant 2, and changing the amount of fibrous dispersion added (equivalent to fibrous material) to 0.03 parts when preparing the anode slurry composition, CNT dispersion, fibrous dispersion, aqueous dispersion containing binder, anode slurry composition, anode, and lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0120] (Example 4) Except for using CNF instead of CNT-b when preparing the fiber dispersion and not using dispersant 2, and changing the amount of fiber dispersion added (equivalent to fiber content) when preparing the anode slurry composition to 0.03 parts, the CNT dispersion, fiber dispersion, aqueous dispersion containing binder, anode slurry composition, anode, and lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 2. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0121] (Example 5) Except for changing the amount of CNT dispersion added (equivalent to 1 min of CNT) to 0.0075 parts and the amount of fiber dispersion added (equivalent to fiber portion) to 0.0225 parts when preparing the slurry composition for the negative electrode, a CNT dispersion, a water dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0122] (Example 6) Except for changing the amount of CNT dispersion added (equivalent to 1 min of CNT) to 0.0225 parts and the amount of fiber dispersion added (equivalent to fiber portion) to 0.0075 parts when preparing the slurry composition for the negative electrode, a CNT dispersion, a water dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0123] (Example 7) Except for changing the amount of CNT dispersion added (equivalent to 1 min of CNT) to 0.025 parts and the amount of fiber dispersion added (equivalent to fiber portion) to 0.025 parts when preparing the slurry composition for the negative electrode, a CNT dispersion, a water dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0124] (Comparative Example 1) Except for not adding the CNT dispersion during the preparation of the anode slurry composition and changing the amount of fiber dispersion added (equivalent to the fiber content) to 0.03 parts, the fiber dispersion, aqueous dispersion containing a binder, anode slurry composition, anode, and lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0125] (Comparative Example 2) The CNT dispersion, aqueous dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1, except that the fibrous dispersion was not added during the preparation of the slurry composition for the negative electrode, and the amount of CNT dispersion added (equivalent to 1 minute of CNT) was changed to 0.03 parts. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0126] (Comparative Example 3) Except that the CNT dispersion was not added during the preparation of the anode slurry composition and the amount of fiber dispersion added (equivalent to the fiber content) was changed to 0.06 parts, the fiber dispersion, aqueous dispersion containing a binder, anode slurry composition, anode, and lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 3. The evaluation was then performed in the same manner as in Example 1. The results are shown in Table 1.

[0127] (Comparative Example 4) A fibrous dispersion, an aqueous dispersion containing a binder, a slurry composition for the negative electrode, a negative electrode, and a lithium-ion secondary battery were prepared or manufactured in the same manner as in Example 1, except that a CNT dispersion prepared as described below was used. The evaluation was then carried out in the same manner as in Example 1. The results are shown in Table 1. <Preparation of CNT dispersion> A CNT dispersion was prepared in the same manner as in Example 1, except that CNT-c (manufactured by Meijo Nanocarbon Co., Ltd., product name "MEIJO eDIPS®"; CNT mainly containing single-walled CNTs) was used instead of CNT-a, the content of CNT1 in the CNT dispersion was changed to 0.2% by mass, and the content of dispersant 1 in the CNT dispersion was changed to 0.2% by mass.

[0128] In Table 1 below, "CNT" refers to carbon nanotubes, "CNF" refers to cellulose nanofibers, "CMC" refers to the sodium salt of carboxymethylcellulose, "SiO" refers to a composite of SiO coated with conductive carbon, and "SBR" refers to a styrene-butadiene copolymer. Furthermore, "average length of fiber / average length of CNT1" is shown rounded to two decimal places.

[0129]

[0130] Table 1 shows that in Examples 1 to 7, which used a dispersion set containing a CNT dispersion containing CNTs with an average length of 1 μm or less and a fiber dispersion containing fibers whose average length is 1.5 times or more the average length of the CNTs in the dispersion, secondary batteries with excellent cycle characteristics were produced. On the other hand, in Comparative Examples 1 and 3, which did not contain a CNT dispersion, Comparative Example 2, which did not contain a fiber dispersion, and Comparative Example 4, in which the average length of CNTs was greater than 1 μm and the average length of the fibers was less than 1.5 times the average length of the CNTs, secondary batteries with excellent cycle characteristics were not produced.

[0131] According to the present invention, it is possible to provide a dispersion liquid set for secondary battery electrodes capable of forming secondary battery electrodes that exhibit excellent cycle characteristics in secondary batteries, a dispersion liquid for secondary battery electrodes, a slurry composition for secondary battery electrodes, and a carbon nanotube dispersion liquid and a fiber dispersion liquid used in the dispersion liquid for secondary battery electrodes. Furthermore, according to the present invention, it is possible to provide a secondary battery electrode capable of exhibiting excellent cycle characteristics in secondary batteries. Moreover, according to the present invention, it is possible to provide a secondary battery with excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a method for producing a dispersion liquid for secondary battery electrodes capable of forming secondary battery electrodes that exhibit excellent cycle characteristics in secondary batteries.

Claims

1. A dispersion liquid set for secondary battery electrodes, comprising a carbon nanotube dispersion liquid containing carbon nanotubes 1, a dispersant 1, and a solvent 1, and a fibrous material dispersion liquid containing fibrous material and a solvent 2, wherein the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous material is 1.5 times or more the average length of the carbon nanotubes 1.

2. The dispersion liquid set for secondary battery electrodes according to claim 1, wherein the average aspect ratio of the carbon nanotube 1 is 60 or less.

3. The dispersion liquid set for secondary battery electrodes according to claim 1, wherein the average aspect ratio of the fiber body is 100 or more.

4. The secondary battery electrode dispersion set according to claim 1, wherein the content ratio of the carbon nanotube 1 in the carbon nanotube dispersion is 0.01% by mass or more and 1% by mass or less.

5. The secondary battery electrode dispersion set according to claim 1, wherein the content of the fibers in the fiber dispersion is 0.01% by mass or more and 1% by mass or less.

6. The dispersion liquid set for secondary battery electrodes according to claim 1, wherein the fibrous material is carbon nanotube 2.

7. The carbon nanotube 1 in the carbon nanotube dispersion contains single-walled carbon nanotubes, as described in claim 1.

8. A dispersion for secondary battery electrodes comprising a carbon nanotube dispersion containing carbon nanotubes 1, a dispersant 1, and a solvent 1, and a fibrous dispersion containing fibrous material and solvent 2, wherein the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibrous material is 1.5 times or more the average length of the carbon nanotubes 1.

9. A slurry composition for secondary battery electrodes comprising the dispersion for secondary battery electrodes described in claim 8, an electrode active material, and a binder.

10. The slurry composition for secondary battery electrodes according to claim 9, wherein the electrode active material includes a silicon-based negative electrode active material.

11. The slurry composition for secondary battery electrodes according to claim 9, wherein the ratio of the content of carbon nanotubes 1 to the content of fibrous material (content of carbon nanotubes 1 / content of fibrous material) is 1 / 99 or more and 99 / 1 or less by mass ratio.

12. An electrode for a secondary battery comprising an electrode composite layer formed using the slurry composition for secondary battery electrodes described in any one of claims 9 to 11.

13. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the electrode for a secondary battery described in claim 12.

14. A carbon nanotube dispersion used in a secondary battery electrode dispersion comprising a carbon nanotube dispersion and a fiber dispersion, wherein the carbon nanotube dispersion contains carbon nanotubes 1, a dispersant 1, and a solvent 1, the fiber dispersion contains fibers and a solvent 2, the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibers is 1.5 times or more the average length of the carbon nanotubes 1.

15. A fibrous dispersion used in a secondary battery electrode dispersion comprising a carbon nanotube dispersion and a fibrous dispersion, wherein the carbon nanotube dispersion contains carbon nanotubes 1, a dispersant 1, and a solvent 1, the fibrous dispersion contains fibers and a solvent 2, the average length of the carbon nanotubes 1 is 1 μm or less, and the average length of the fibers is 1.5 times or more the average length of the carbon nanotubes 1.

16. A method for producing a dispersion for secondary battery electrodes, comprising the steps of: obtaining a carbon nanotube dispersion containing carbon nanotubes 1, a dispersant 1, and a solvent 1, wherein the average length of the carbon nanotubes 1 is 1 μm or less; obtaining a fibrous dispersion containing fibers and a solvent 2, wherein the average length of the fibers is 1.5 times or more the average length of the carbon nanotubes 1; and mixing the carbon nanotube dispersion and the fibrous dispersion to obtain a dispersion for secondary battery electrodes.

17. A dispersion for secondary battery electrodes comprising carbon nanotubes, fibers, a dispersant, and a solvent, wherein the average length of the carbon nanotubes is 1 μm or less, and the average length of the fibers is 1.5 times or more the average length of the carbon nanotubes.

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