Conductive material dispersion, positive electrode slurry for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

A conductive material liquid dispersion disclosed in the present invention comprises: a conductive material containing carbon nanotubes; a dispersing agent; and an aprotic polar solvent. The dispersing agent comprises a polyvinylpyrrolidone and a cellulose derivative.

Description

[Technical Field]

[0001] This disclosure relates to a conductive material dispersion, a positive electrode slurry for a non-aqueous electrolyte secondary battery, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries are widely used in consumer and automotive applications due to their high output and high energy density. In recent years, there has been a growing demand for even greater durability and energy density in non-aqueous electrolyte secondary batteries.

[0003] One known method for improving the performance of non-aqueous electrolyte secondary batteries is to enhance the conductivity of the positive electrode mixture layer. For example, adding conductive materials such as carbon nanotubes to the positive electrode mixture has been a conventional practice. When using conductive materials that tend to aggregate, such as carbon nanotubes, it is important to uniformly disperse the conductive material within the positive electrode mixture layer.

[0004] Patent Document 1 (Japanese Patent Publication No. 2020-19705) describes a dispersion liquid used in the manufacture of electrodes, comprising "bundle-type carbon nanotubes, a dispersion medium, and a partially hydrogenated nitrile rubber having a residual double bond (RDB) value of 0.5 to 40% by weight calculated by the following mathematical formula 1, wherein the dispersed particle size of the carbon nanotubes is the particle size distribution D 50 A carbon nanotube dispersion characterized by having a particle size of 3 to 10 μm. [Mathematical formula 1] RDB (weight %) = BD weight / (BD weight + HBD weight) × 100. In the above mathematical formula 1, BD means structural units derived from conjugated dienes, and HBD means structural units derived from hydrogenated conjugated dienes. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-19705 [Overview of the project] [Problems that the invention aims to solve]

[0006] Currently, there is a need to further improve the properties of cathodes using conductive materials such as carbon nanotubes. In this context, one of the objectives of this disclosure is to provide a dispersion in which carbon nanotubes are well dispersed. [Means for solving the problem]

[0007] One aspect of this disclosure relates to a conductive material dispersion. The conductive material dispersion comprises a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent, wherein the dispersant includes polyvinylpyrrolidones and cellulose derivatives.

[0008] Another aspect of this disclosure relates to a cathode slurry for a non-aqueous electrolyte secondary battery, comprising a conductive material dispersion relating to this disclosure and a lithium-containing transition metal oxide.

[0009] Another aspect of this disclosure relates to a cathode for a non-aqueous electrolyte secondary battery, prepared using the cathode slurry relating to this disclosure.

[0010] Another aspect of this disclosure relates to a non-aqueous electrolyte secondary battery, including a positive electrode for a non-aqueous electrolyte secondary battery relating to this disclosure. [Effects of the Invention]

[0011] According to this disclosure, a dispersion in which carbon nanotubes are dispersed with good dispersibility can be obtained. Furthermore, according to this disclosure, a positive electrode slurry, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery can be obtained using this dispersion. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings. [Modes for carrying out the invention]

[0012] The embodiments relating to this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B".

[0013] (Conductive material dispersion) The conductive material dispersion of this embodiment comprises a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent. The conductive material dispersion of this embodiment may be referred to as "dispersion (D)" below. The dispersant includes polyvinylpyrrolidones and cellulose derivatives.

[0014] Because carbon nanotubes tend to aggregate, it is important to disperse them well. If the carbon nanotubes in the dispersion aggregate, they will remain aggregated in the positive electrode mixture layer of the electrode plate manufactured using that dispersion. Therefore, it is important to disperse the carbon nanotubes well in the dispersion.

[0015] Numerous dispersants exist that can be added to dispersions to improve the dispersibility of carbon nanotubes. Furthermore, there are countless possible mixing ratios for these dispersants. Therefore, there are countless combinations of dispersant types and their mixing ratios, and the effects of these combinations have not been sufficiently studied. Moreover, it is difficult for those skilled in the art to predict what effects will be obtained when different types and mixing ratios of dispersants are combined. If the effects of these combinations could be predicted, the optimal combination could be determined without experimentation. However, in reality, predicting the effects of these combinations is difficult. As a result of our research, the inventors of this invention have discovered a new combination that yields a specific effect. Specifically, they found that by mixing carbon nanotubes and additives (dispersants) in a predetermined ratio, the dispersibility of carbon nanotubes is specifically enhanced, as shown in the examples. This invention is based on this new finding.

[0016] (Dispersant) Examples of cellulose derivatives used as dispersants include alkylcelluloses such as methylcellulose, hydroxyalkylcelluloses, and their alkali metal salts. Examples of alkali metals that form alkali metal salts include potassium and sodium. Among these, methylcellulose, ethylcellulose, and hydroxypropylmethylcellulose are preferred. The weight-average molecular weight of the cellulose derivative may be in the range of 1,000 to 1,000,000 (for example, 10,000 to 1,000,000). In terms of enhancing the effects of the composition of this disclosure, the weight-average molecular weight of the cellulose derivative may be in the range of 10,000 to 200,000.

[0017] The polyvinylpyrrolidones are at least one selected from the group consisting of polyvinylpyrrolidone and polyvinylpyrrolidone derivatives. Examples of the polyvinylpyrrolidone derivatives include polymers in which the hydrogen atoms of polyvinylpyrrolidone are substituted with other substituents, such as alkylated polyvinylpyrrolidone and the like. As the polyvinylpyrrolidones, only polyvinylpyrrolidone may be used, or a copolymer of vinylpyrrolidone and other single molecules may be used. Examples of the other single molecules include styrene-based and vinyl acetate-based single molecules.

[0018] The weight average molecular weight of the polyvinylpyrrolidones may be in the range of 1,000 to 2,000,000. In terms of enhancing the effects of the configuration of the present disclosure, the weight average molecular weight of the polyvinylpyrrolidones may be in the range of 5,000 to 1,000,000.

[0019] In the dispersion (D), the amount of the cellulose derivative with respect to 100 parts by mass of the polyvinylpyrrolidones is preferably in the range of 30 to 400 parts by mass (for example, in the range of 100 to 400 parts by mass or in the range of 300 to 400 parts by mass). By setting the amount in the range of 30 to 400 parts by mass, as shown in the examples, particularly high effects can be obtained.

[0020] In the dispersion of carbon nanotubes, the polyvinylpyrrolidones have a certain effect on improving the dispersibility due to the good wettability to the carbon nanotubes, but there are problems with the long-term dispersion stability due to the small steric hindrance. On the other hand, by using a combination of the polyvinylpyrrolidones and the cellulose derivative, the following specific effects can be obtained. For the cellulose derivative that has a high steric hindrance and exhibits long-term dispersion stability but has a low affinity for aprotic polar solvents, the polyvinylpyrrolidones function not only as a dispersant but also as a dispersion aid, enabling both good dispersibility and long-term dispersion stability.

[0021] The dispersant may further contain nitrile rubber. Examples of nitrile rubber include copolymers of monomers containing acrylonitrile and diene (e.g., butadiene). Examples of nitrile rubber include acrylonitrile-based rubbers such as acrylonitrile-butadiene rubber (NBR) and hydrogenated acrylonitrile-butadiene rubber (H-NBR). When the dispersant contains polyvinylpyrrolidones, cellulose derivatives, and nitrile rubber, particularly high effects can be obtained as shown in the examples.

[0022] In the dispersion (D), the amount of nitrile rubber relative to 100 parts by mass of polyvinylpyrrolidones may be in the range of 30 to 500 parts by mass (e.g., in the range of 100 to 300 parts by mass). By setting the amount in the range of 100 to 300 parts by mass, particularly high effects can be obtained as shown in the examples.

[0023] When preparing a positive electrode slurry for a non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) by combining the dispersion (D) and a lithium-containing composite oxide, it is preferable to use chemically stable cellulose derivatives and nitrile rubber in addition to polyvinylpyrrolidones. The presence of these suppresses side reactions of the lithium component of the positive electrode active material and improves the long-term dispersion stability of the positive electrode slurry. In particular, in recent years, positive electrode active materials with a high Ni ratio, which are often used in non-aqueous electrolyte secondary batteries characterized by high energy density, are prone to side reactions. Therefore, the effect of the above combination of materials is particularly significant.

[0024] The dispersion (D) may further contain polyvinylidene fluoride. Note that polyvinylidene fluoride is not included in the examples of the dispersant. The amount of polyvinylidene fluoride relative to 100 parts by mass of polyvinylpyrrolidones may be in the range of 50 to 5000 parts by mass (e.g., in the range of 200 to 2000 parts by mass).

[0025] There are no particular limitations on the weight-average molecular weight of the acrylonitrile rubber and polyvinylidene fluoride; they should be within the range suitable for use as additives in the dispersion (D). For example, the weight-average molecular weight of the nitrile rubber may be in the range of 5,000 to 2,000,000. The weight-average molecular weight of the polyvinylidene fluoride may be in the range of 100,000 to 3,000,000.

[0026] The dispersion (D) may contain other dispersants besides those described above. Known dispersants may be used as such other dispersants. However, the proportion of other dispersants to the total dispersants should be small, for example, 10% by mass or less.

[0027] (Conductive material) Examples of conductive materials include those containing carbon. Examples of conductive materials containing carbon include conductive carbon particles such as carbon black, graphene, carbon fibers, and fibrous conductive carbon materials such as carbon nanotubes. The conductive material contained in dispersion (D) contains carbon nanotubes as an essential component. Fibrous conductive carbon materials may be referred to as "carbon fibers" below. Since carbon nanotubes are preferred carbon fibers, carbon fibers can be read as carbon nanotubes in the following description. The proportion of carbon nanotubes in all conductive materials is, for example, 50% by mass or more, and is preferably in the range of 66 to 100% by mass (for example, in the range of 80 to 100% by mass or 90 to 100%).

[0028] The carbon nanotube content in the dispersion (D) is preferably in the range of 0.1% by mass to 10% by mass.

[0029] When carbon nanotubes are used as a conductive material, particularly high effectiveness can be obtained by using a dispersant containing polyvinylpyrrolidones and cellulose derivatives, as shown in the examples.

[0030] Carbon nanotubes are tiny carbon fibers with a fiber diameter in the nanoscale. When carbon nanotubes are used as a conductive material, even a small amount can reduce the resistance of the positive electrode mixture layer.

[0031] The average fiber length of carbon nanotubes may be 1 μm or more. In this case, the aspect ratio (ratio of fiber length to outer diameter) of the carbon nanotubes, which are carbon fibers, becomes extremely large. Carbon fibers with a large aspect ratio make linear contact with the active material and current collector, rather than point contact. The highly conductive carbon fibers are interposed between the particles of the positive electrode active material, forming linear contact points with the particles, thereby improving the DC resistance (DCR) of the battery.

[0032] In addition, carbon fibers exhibit excellent conductivity with only a small amount of addition. Because they occupy only a small volume within the positive electrode mixture layer, the proportion of positive electrode active material in the positive electrode mixture layer can be increased, thereby increasing the capacity. Furthermore, as mentioned above, the drawbacks (increased resistance) that occur when the mixture layer is made thicker or more compressed can be suppressed by using carbon fibers. Therefore, by using carbon fibers, it is possible to make the mixture layer thicker or more compressed. On the other hand, when further increasing such capacity, it is particularly important to improve the dispersibility of carbon nanotubes in the carbon nanotube dispersion.

[0033] Here, the average fiber length of carbon fibers is determined by image analysis using a scanning electron microscope (SEM). The average fiber length of carbon fibers can be determined, for example, by arbitrarily selecting multiple carbon fibers (e.g., 100), measuring their lengths, and taking the arithmetic mean. Furthermore, fiber length refers to the length of a carbon fiber when it is stretched in a straight line.

[0034] The average fiber diameter (outer diameter) of carbon fibers is, for example, 20 nm or less, but may also be 15 nm or less. Here, the average fiber diameter of carbon fibers is determined by image analysis using a transmission electron microscope (TEM). The average fiber diameter of carbon fibers can be determined, for example, by arbitrarily selecting several carbon fibers (e.g., 100 fibers), measuring their fiber diameters, and taking the arithmetic mean of these measurements. Furthermore, fiber diameter refers to the length in the direction perpendicular to the fiber length direction.

[0035] Carbon nanotubes may be single-walled, double-walled, or multi-walled, and may consist of at least two of these. Carbon nanotubes with an average fiber diameter of 20 nm or less are preferred because a large effect can be obtained with a small amount. The average fiber length of the carbon nanotubes is preferably 1 μm or more from the viewpoint of ensuring electron conduction inside the positive electrode. On the other hand, there is no upper limit to the fiber length if they are properly arranged inside the positive electrode, but considering that the particle diameter of the positive electrode active material is generally between 1 μm and 20 μm, a length of a similar length is considered appropriate. That is, the average fiber length of the carbon nanotubes may be, for example, between 1 μm and 20 μm.

[0036] In dispersion (D), the amount of dispersant per 100 parts by mass of carbon nanotubes may be in the range of 30 to 300 parts by mass (for example, in the range of 30 to 50 parts by mass).

[0037] (Aprotic polar solvent) The dispersion (D) contains an aprotic polar solvent (aprotic polar dispersion medium) as the dispersion medium. Examples of aprotic polar solvents include N-methyl-2-pyrrolidone (hereinafter sometimes referred to as "NMP"). The dispersion medium may consist of only one type of liquid or a mixture of multiple types of liquids. If the dispersion medium contains NMP, the proportion of NMP in the dispersion medium may be in the range of 50 to 100% by mass (for example, in the range of 80 to 100% by mass). The dispersion medium may consist of NMP alone.

[0038] The proportion of aprotic polar solvent (dispersion medium) in the dispersion (D) should be selected considering the dispersibility of carbon nanotubes and the stability of the dispersion (D). The proportion of aprotic polar solvent in the dispersion (D) may be in the range of 10 to 99 parts by mass.

[0039] The dispersion (D) of this embodiment satisfies the following condition (1). Preferably, the dispersion (D) satisfies at least one of (2) to (6). (2) to (6) can be combined in any way. (1) Dispersion (D) contains a dispersant, the dispersant contains polyvinylpyrrolidones and cellulose derivatives. (2) The mass ratio of the components contained in dispersion (D) may be in the range of polyvinylpyrrolidones:cellulose derivatives:acrylonitrile rubber:polyvinylidene fluoride = 100:30 to 400:0 to 300:0 to 5000. The ratio of other components to polyvinylpyrrolidones may be changed to the range described above. (3) Examples of cellulose derivatives include methylcellulose, ethylcellulose, and hydroxypropylmethylcellulose. (4) The dispersant includes acrylonitrile rubber. The acrylonitrile rubber may be, for example, NBR or H-NBR. (5) The dispersion (D) contains polyvinylidene fluoride. (6) Polyvinylpyrrolidones are polyvinylpyrrolidones.

[0040] The dispersion (D) of this embodiment can be used to form the composite layer (active material layer) of the electrodes of a battery. For example, the dispersion (D) can be used to form the composite layer of the electrodes (positive electrode, negative electrode) of a non-aqueous electrolyte secondary battery, and is particularly preferably used for the positive electrode composite layer. At least a portion of the dispersant contained in the dispersion (D) may function as a binder in the composite layer.

[0041] (Positive electrode slurry) When forming a positive electrode mixture layer for a non-aqueous electrolyte secondary battery using dispersion (D), first, a positive electrode slurry (positive electrode slurry for a non-aqueous electrolyte secondary battery) is prepared using dispersion (D). The positive electrode slurry can be prepared by mixing positive electrode active material (positive electrode active material for a non-aqueous electrolyte secondary battery), dispersion (D), and other substances as needed (other components such as thickeners or other dispersion media). In other words, it is possible that the positive electrode slurry contains dispersion (D). From another viewpoint, the positive electrode slurry may be a slurry containing the components of dispersion (D) and the positive electrode active material. That is, one example of a positive electrode slurry contains positive electrode active material, a conductive material including carbon nanotubes, a dispersant, and an aprotic polar solvent, and the dispersant includes polyvinylpyrrolidones and cellulose derivatives. There are no particular limitations on the positive electrode active material. The active material may be any active material usable for the target battery, and known active materials may be used. For example, examples of positive electrode active materials include composite oxides containing lithium and transition metals. An example of a positive electrode slurry relating to this disclosure includes a conductive material dispersion (dispersion (D)) relating to this disclosure and a lithium-containing transition metal oxide.

[0042] (Positive electrode for non-aqueous electrolyte secondary batteries) An example of a positive electrode for a non-aqueous electrolyte secondary battery according to this disclosure is a positive electrode made using the positive electrode slurry described above. There are no limitations on the method of making a positive electrode using the positive electrode slurry, and known methods may be used. For example, a positive electrode containing a positive electrode mixture layer can be obtained by applying the positive electrode slurry to the surface of a positive electrode current collector to form a coating film, and then drying the coating film. The dried coating film may be rolled as needed. The positive electrode mixture layer may contain components contained in the positive electrode slurry, but at least a portion of the solvent may be removed. One example of a positive electrode mixture layer includes a positive electrode active material, a conductive material including carbon nanotubes, and a dispersant, the dispersant of which includes polyvinylpyrrolidones and cellulose derivatives. The positive electrode mixture layer may be formed on one surface of the positive electrode current collector or on both surfaces. The positive electrode mixture layer may contain optional components such as a thickener. Known materials may be used for these optional components. The ratio of components contained in the positive electrode slurry is reflected in the ratio of components in the positive electrode mixture layer. Therefore, by changing the ratio of components contained in the positive electrode slurry, the ratio of components in the positive electrode mixture layer can be changed.

[0043] There are no particular limitations on the positive electrode current collector, and known current collectors that can be used in the positive electrode of a non-aqueous electrolyte secondary battery may be used. Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0044] Examples of positive electrode active materials include composite oxides containing lithium and transition metals. Such composite oxides may be referred to as "lithium-containing composite oxides" in this specification. Lithium-containing composite oxides may have a layered structure (e.g., a rock salt crystal structure). The positive electrode active material has the compositional formula Li y Ni x M 1-xO₂ (where 0.8 ≤ x ≤ 1, 0 < y ≤ 1.2, and M contains at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, Sr, Ca, and B.) may be a lithium-containing composite oxide. M may be at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, Sr, Ca, and B. Among them, M preferably contains at least one selected from the group consisting of Co, Mn, Al, and Fe. In the above example, M is typically a metal element. From the viewpoint of the stability of the crystal structure, M may contain Al. The value of y indicating the composition ratio of lithium increases or decreases by charge and discharge. Specific examples of such composite oxides include lithium-nickel-cobalt-aluminum composite oxide (LiNi 0.9 Co 0.05 Al 0.05 O₂, etc.).

[0045] (Non-aqueous electrolyte secondary battery) The non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure. More specifically, the non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure, a negative electrode, and a non-aqueous electrolyte, and optionally includes other components (separator, case, etc.). There is no particular limitation on the components other than the positive electrode, and any component that can be used in a non-aqueous electrolyte may be used, and known components may be used. For example, as the negative electrode, a negative electrode including a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector may be used. The negative electrode mixture layer may contain a negative electrode active material as an essential component, and may contain a binder, a thickener, a conductive material, etc. as optional components. As the negative electrode active material, metallic lithium, a lithium alloy, etc. may be used, but a material capable of electrochemically intercalating and releasing lithium ions is preferably used. Examples of such materials include carbonaceous materials, Si-containing materials, etc. The negative electrode active material may contain a Si-containing material or may be a Si-containing material. The negative electrode may contain one type of negative electrode active material or may contain a combination of two or more types.

[0046] (Non-aqueous electrolyte) A non-aqueous electrolyte (non-aqueous electrolyte solution) contains a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that undergoes ion dissociation in the electrolyte solution. The solute may include, for example, a lithium salt. Components of the electrolyte solution other than the solvent and solute are additives. Various additives may be included in the electrolyte solution. A non-aqueous electrolyte used in non-aqueous electrolyte secondary batteries may also be used as the non-aqueous electrolyte.

[0047] (Separator) A separator is interposed between the positive and negative electrodes. The separator has high ion permeability and possesses appropriate mechanical strength and insulating properties. Microporous thin films, woven fabrics, nonwoven fabrics, etc., can be used as separators. Polyolefins such as polypropylene and polyethylene are preferred as the material of the separator.

[0048] One example of the structure of a non-aqueous electrolyte secondary battery is a structure in which an electrode group, in which a positive electrode and a negative electrode are wound around each other with a separator, is housed together with the non-aqueous electrolyte in an outer casing. However, it is not limited to this, and other forms of electrode groups may be used. For example, a stacked electrode group in which the positive electrode and negative electrode are stacked with a separator in between may also be used. The form of the non-aqueous electrolyte secondary battery is also not limited, and may be cylindrical, prismatic, coin-type, button-type, laminate-type, etc. [Examples]

[0049] The present disclosure will be described below in detail based on examples, but the present disclosure is not limited to the following examples.

[0050] In this example, several conductive material dispersions were prepared by changing the type and amount of dispersant. These conductive material dispersions were then evaluated.

[0051] (Preparation of conductive material dispersion) First, carbon nanotubes (conductive material) and a dispersant were mixed at a predetermined mass ratio and dispersed in N-methyl-2-pyrrolidone (NMP) to prepare dispersion liquids A1 to A5 and C1 to C2. The average fiber length and average fiber diameter of the carbon nanotubes were 1 μm and 10 nm, respectively. The ratio of the carbon nanotubes to the dispersant was the mass ratio shown in Table 1. Also, the ratio of the components constituting the dispersant was the ratio shown in Table 1. The proportion of the carbon nanotubes in the dispersion liquid was set to about 5% by mass.

[0052] After applying the obtained dispersion liquid onto an insulating plate and drying it, a coating film was formed. Then, the sheet resistance of the coating film was measured by the four-terminal method.

[0053] Next, a positive electrode slurry was prepared using the above dispersion liquid. Specifically, a plurality of positive electrode slurries SA1 to SA5 and SC1 to SC2 were prepared by mixing each of the above plurality of dispersion liquids with a positive electrode active material. As the positive electrode active material, particles of a composite oxide (LiNi 0.9 Co 0.05 Al 0.05 O2) were used. Then, the sedimentation property of the prepared positive electrode slurry was evaluated.

[0054] The sedimentation property of the positive electrode slurry was evaluated using the centrifugal sedimentation method. The positive electrode slurry prepared above was centrifuged at a rotational speed of 1000 rpm for 1 hour. Using the sample after centrifugation, the supernatant and the sediment part were each dried to evaluate the solid content fraction, and the difference was used as the numerical value of the sedimentation property.

[0055] Table 1 shows some of the preparation conditions of the dispersion liquid and the evaluation results of the dispersion liquid and the positive electrode slurry. Note that dispersion liquids C1 and C2 are dispersion liquids of comparative examples.

[0056]

Table 1

[0057] The sheet resistance values ​​in Table 1 are relative values, with the sheet resistance of the coating film formed using dispersion C1 set to 100%. A smaller sheet resistance value indicates better dispersion of carbon nanotubes. The settling properties of the cathode slurry in Table 1 are relative values, with the measured value for slurry SA1 set to 100%. A smaller value indicates lower settling (i.e., higher dispersibility and dispersion stability).

[0058] As shown in Table 1, using polyvinylpyrrolidones and cellulose derivatives as dispersants reduced the sheet resistance of the coating film and improved the dispersibility of the positive electrode slurry. Particularly good results were obtained when polyvinylpyrrolidones, cellulose derivatives, and acrylonitrile-based rubber were used as dispersants.

[0059] As described above, it is clear that the properties are improved by the synergistic effect of polyvinylpyrrolidone (polyvinylpyrrolidone derivatives) and hydroxypropyl methylcellulose (cellulose derivative). Furthermore, this effect is thought to be particularly enhanced by the combination of polyvinylpyrrolidone, cellulose derivatives, and H-NBR. [Industrial applicability]

[0060] This disclosure can be used in conductive material dispersions, cathode slurries, cathodes for non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

Claims

1. A conductive material dispersion comprising a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent, The dispersant comprises polyvinylpyrrolidones and cellulose derivatives, A conductive material dispersion in which the amount of the cellulose derivative per 100 parts by mass of the polyvinylpyrrolidones is in the range of 30 to 400 parts by mass.

2. The conductive material dispersion according to claim 1, wherein the amount of the cellulose derivative per 100 parts by mass of the polyvinylpyrrolidones is in the range of 100 to 400 parts by mass.

3. The conductive material dispersion according to claim 1, wherein the dispersant further comprises a nitrile rubber.

4. The conductive material dispersion according to claim 3, wherein the amount of nitrile rubber per 100 parts by mass of polyvinylpyrrolidone is in the range of 100 to 300 parts by mass.

5. The conductive material dispersion according to any one of claims 1 to 4, wherein the carbon nanotube content is in the range of 0.1% by mass to 10% by mass.

6. The conductive material dispersion according to any one of claims 1 to 4, wherein the amount of the dispersant per 100 parts by mass of the carbon nanotubes is in the range of 30 to 300 parts by mass.

7. The conductive material dispersion according to any one of claims 1 to 6, wherein the average fiber diameter of the carbon nanotubes is 20 nm or less.

8. A conductive material dispersion comprising a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent, The dispersant comprises polyvinylpyrrolidones and cellulose derivatives, The aforementioned dispersant further comprises a nitrile rubber, and is a conductive material dispersion.

9. A conductive material dispersion comprising a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent, The dispersant comprises polyvinylpyrrolidones and cellulose derivatives, A conductive material dispersion liquid in which the amount of the dispersant per 100 parts by mass of the carbon nanotubes is in the range of 30 to 300 parts by mass.

10. The solvent contained in the conductive material dispersion consists solely of the aprotic polar solvent, The conductive material dispersion according to any one of claims 1 to 9, wherein the cellulose derivative is at least one of alkylcellulose, hydroxyalkylcellulose, and alkali metal salts thereof.

11. A positive electrode slurry for a non-aqueous electrolyte secondary battery, comprising a conductive material dispersion according to any one of claims 1 to 10 and a lithium-containing transition metal oxide.

12. A positive electrode for a non-aqueous electrolyte secondary battery, manufactured using the positive electrode slurry described in claim 11.

13. A non-aqueous electrolyte secondary battery comprising a positive electrode for a non-aqueous electrolyte secondary battery as described in claim 12.

14. A positive electrode slurry for a non-aqueous electrolyte secondary battery comprising a conductive material dispersion and a lithium-containing transition metal oxide, The conductive material dispersion comprises a conductive material containing carbon nanotubes, a dispersant, and an aprotic polar solvent. The aforementioned dispersant comprises polyvinylpyrrolidones and cellulose derivatives, and a lithium-containing transition metal oxide, comprising a cathode slurry for a non-aqueous electrolyte secondary battery.

15. The solvent contained in the conductive material dispersion consists solely of the aprotic polar solvent, The cathode slurry according to claim 14, wherein the cellulose derivative is at least one of alkylcellulose, hydroxyalkylcellulose, and alkali metal salts thereof.

16. A positive electrode for a non-aqueous electrolyte secondary battery, prepared using the positive electrode slurry described in claim 14 or 15.

17. A non-aqueous electrolyte secondary battery comprising a positive electrode for a non-aqueous electrolyte secondary battery as described in claim 16.

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