Electrode material, electrode slurry, manufacturing method for electrode material, electrode, and manufacturing method for electrode

Abstract

To provide an electrode material for a secondary battery in which the decrease in electrode capacity is suppressed and the cycle characteristic is excellent, an electrode slurry, a manufacturing method for the electrode material, an electrode, and a manufacturing method for the electrode.SOLUTION: An electrode material 1 for a secondary battery includes an electrode active material 10, and the entire surface of the electrode active material 10 is covered with a nonaqueous binder 20 in a shell shape.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electrode material for a secondary battery, an electrode slurry, a method for producing an electrode material, an electrode, and a method for producing an electrode. [Background technology]

[0002] Electrodes constituting secondary batteries such as lithium ion secondary batteries are generally produced by applying a slurry, in which an electrode active material, a binder, and a conductive assistant are dispersed, to a current collector and drying the slurry.

[0003] Conventionally, polyvinylidene fluoride (PVDF), which has excellent properties such as mechanical strength, adhesiveness, and oxidation resistance, has been widely used as a binder for electrodes.

[0004] However, since PVDF is insoluble in water, it is necessary to prepare a slurry by dissolving PVDF in an organic solvent such as N-methyl-pyrrolidone (NMP), and there is a problem that the use of an organic solvent increases the environmental load. Therefore, in recent years, there has been a demand for the development of an aqueous binder that can be dispersed in an aqueous solvent with a low environmental load.

[0005] Carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) have been developed as aqueous binders for use in negative electrodes. However, when these aqueous binders are used directly in positive electrodes, there is a problem that they are subject to oxidation degradation in the positive electrode environment.

[0006] Patent Document 1 discloses a binder composed of an acrylic polymer as an aqueous binder used for a positive electrode. This aqueous binder does not dissolve in water, and is dispersed as suspended particles in an aqueous solvent to prepare a positive electrode slurry. When this positive electrode slurry is applied to a current collector and dried to prepare a positive electrode, the aqueous binder is unevenly distributed in the recesses between the positive electrode active materials while maintaining its particle shape. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-91789 A Summary of the Invention [Problem to be solved by the invention]

[0008] The aqueous binder disclosed in Patent Document 1 is effective in terms of oxidation resistance, but since the aqueous binder contains lithium, when the aqueous binder is dispersed in an aqueous solvent together with the aqueous active material and the conductive additive to prepare a positive electrode slurry, the transition metal such as lithium in the positive electrode active material dissolves in the aqueous solvent, resulting in a decrease in the positive electrode capacity. This problem may also occur in the case of a negative electrode using a material containing lithium as the negative electrode active material.

[0009] In addition, since the aqueous binder is only unevenly distributed in the recesses between the positive electrode active materials, it is difficult to uniformly disperse the aqueous binder in the positive electrode. Therefore, the binding between the positive electrode active materials and between the positive electrode active materials and the current collector is weakened, resulting in a problem that the cycle characteristics of the secondary battery are deteriorated. Note that such a problem may also occur when the aqueous binder is used in the negative electrode.

[0010] The present invention has been made in view of the above points, and has an object to provide an electrode material, an electrode slurry, a method for manufacturing an electrode material, an electrode, and a method for manufacturing an electrode for a secondary battery that suppresses a decrease in electrode capacity and has excellent cycle characteristics. [Means for solving the problem]

[0011] The electrode material according to the present invention is an electrode material for a secondary battery, and contains an active material, the entire surface of which is coated with a non-aqueous binder in the form of a shell.

[0012] In a preferred embodiment, a part of the surface of the electrode active material is covered with a metal oxide, and the non-aqueous binder covers the entire surface of the electrode active material in the form of a shell so as to cover the metal oxide.

[0013] The electrode slurry according to the present invention is an electrode slurry containing an electrode mixture, the electrode mixture containing an active material whose entire surface is coated with a shell-like coating of a non-aqueous binder, and a conductive assistant, and the electrode mixture is dispersed in an aqueous solvent.

[0014] The method for producing an electrode material according to the present invention is a method for producing an electrode material for a secondary battery, and includes the steps of dissolving a powder of a non-aqueous binder in a non-aqueous solvent and dispersing a powder of an electrode active material in the non-aqueous solvent, and evaporating the non-aqueous solvent to coat the entire surface of the electrode active material with the non-aqueous binder in a shell-like shape.

[0015] The electrode according to the present invention is an electrode for a secondary battery comprising an electrode mixture formed on a current collector, the electrode mixture comprising an electrode material in which the entire surface of an electrode active material is coated with a shell-like coating of a non-aqueous binder, and a conductive assistant, the electrode active material contained in the electrode material is dispersed in a state in which the entire surface is coated with a shell-like coating of the non-aqueous binder, and when the sum of the volumes of the non-aqueous binders coating the entire surface of the electrode active material is V1 and the sum of the volumes of the non-aqueous binders present in the region surrounded by the electrode active material coated with the non-aqueous binder is V2, V1>V2.

[0016] The electrode according to the present invention is an electrode for a secondary battery comprising an electrode mixture formed on a current collector, the electrode mixture comprising an electrode material in which the entire surface of an electrode active material is coated with a shell-like coating of a non-aqueous binder, and a conductive assistant, the electrode active material contained in the electrode material is dispersed in a state in which the entire surface is coated with a shell-like coating of the non-aqueous binder, and when the sum of the volumes of the areas surrounded by the electrode active material coated with the non-aqueous binder is V3 and the sum of the volumes of the non-aqueous binder present in the areas surrounded by the electrode active material coated with the non-aqueous binder is V2, V3>V2.

[0017] The method for manufacturing an electrode for a secondary battery according to the present invention includes the steps of forming an electrode material in which the entire surface of an electrode active material is covered in a shell shape with a non-aqueous binder, dispersing an electrode mixture containing the electrode material and a conductive assistant in an aqueous solvent to form an electrode slurry, and applying the electrode slurry onto a current collector and then drying the applied film. Effect of the Invention

[0018] According to the present invention, it is possible to provide an electrode material, an electrode slurry, a method for producing an electrode material, an electrode, and a method for producing an electrode for a secondary battery which suppresses a decrease in electrode capacity and has excellent cycle characteristics. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a schematic structure of a positive electrode material according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a schematic structure of a positive electrode plate produced using a positive electrode slurry containing a positive electrode material in the present embodiment. [Diagram 3] FIG. 2 is a diagram showing a schematic structure of a positive electrode plate produced using a positive electrode slurry containing a positive electrode material in the present embodiment. [Figure 4] FIG. 10 is a diagram showing a schematic structure of a positive electrode plate produced using a positive electrode slurry containing a positive electrode material in another embodiment of the present invention. [Diagram 5] FIG. 2 is a diagram showing a schematic diagram of a modified example 1 of a positive electrode material. [Figure 6] FIG. 2 is a diagram showing a schematic diagram of a modified example 2 of the positive electrode material. [Figure 7] FIG. 1 is a diagram showing a schematic diagram of a modified example 3 of a positive electrode material. [Figure 8A] 1 is a photograph taken by SEM of a cross section of the positive electrode plate produced in Example 1. [Figure 8B] This is a SEM photograph of the cross section of a positive electrode plate after the fluorine components in the positive electrode plate were dyed. [Figure 9A] 1 is a photograph taken by SEM of a cross section of a positive electrode plate produced in Comparative Example 1. [Figure 9B]This is a SEM photograph of the cross section of a positive electrode plate after the fluorine components in the positive electrode plate were dyed. [Figure 10A] 1 is a photograph taken by SEM of a cross section of a positive electrode plate produced in Example 2. [Figure 10B] This is a SEM photograph of the cross section of a positive electrode plate after the fluorine components in the positive electrode plate were dyed. [Figure 11A] 1 is a photograph taken by SEM of a cross section of a positive electrode plate produced in Comparative Example 2. [Figure 11B] This is a SEM photograph of the cross section of a positive electrode plate after the fluorine components in the positive electrode plate were dyed. [Figure 12A] 1 is a photograph taken by SEM of a cross section of a resin-embedded positive electrode plate produced in Example 1. [Figure 12B] 1 is a photograph showing, in a line diagram, the portion in contact with the positive electrode active material in a region in which the fluorine component in the positive electrode plate is dyed. [Figure 13A] 1 is a photograph taken by SEM of a cross section of a resin-embedded positive electrode plate produced in Comparative Example 1. [Figure 13B] 1 is a photograph showing, in a line diagram, the portion in contact with the positive electrode active material in a region in which the fluorine component in the positive electrode plate is dyed. [Figure 14] 1 is a graph showing the measurement results of cycle characteristics of a lithium ion battery produced using the positive electrode material produced in Example 1. [Figure 15] 1 is a graph showing the measurement results of cycle characteristics of a lithium ion battery produced using the positive electrode material produced in Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiment, a positive electrode will be described as an example of an electrode of a secondary battery, but the present invention is not limited thereto, and can also be applied to a negative electrode. That is, in this specification, when the term "electrode" is used, it includes a positive electrode and a negative electrode. For example, "electrode material" includes a positive electrode material and a negative electrode material, "electrode active material" includes a positive electrode active material and a negative electrode active material, "electrode mixture" includes a positive electrode mixture and a negative electrode mixture, and "electrode slurry" includes a positive electrode slurry and a negative electrode slurry.

[0021] The cathode material in this embodiment is a cathode material for a secondary battery, and as shown in the schematic diagram of Fig. 1, the cathode material 1 includes a cathode active material 10, and the entire surface of the cathode active material 10 is covered in a shell shape with a non-aqueous binder 20. Here, the non-aqueous binder 20 is made of a fluorine-based resin that is insoluble in an aqueous solvent such as water, but is soluble in a non-aqueous solvent such as an organic solvent, and typically includes polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine-based rubber, etc.

[0022] The secondary battery to which the positive electrode material of the present embodiment is applied includes a lithium ion secondary battery, a lithium sulfur secondary battery, etc. In addition, the positive electrode active material is, for example, LiCoO2, LiNiO2, LiNi 0.8 Co 0.2 Lithium-containing composite oxides such as LiO2, LiMn2O4, LiFePO4, and LiNiCoMnO2 are included. The positive electrode active material is preferably made of two or more types of positive electrode active materials having different particle sizes. The positive electrode active material having a small particle size can be formed, for example, by using a flux method.

[0023] The positive electrode material 1 in this embodiment can be produced by a process of dissolving a powder of the non-aqueous binder 20 in a non-aqueous solvent, dispersing a powder of the positive electrode active material 10 in the non-aqueous solvent, and heating and evaporating the non-aqueous solvent to coat the entire surface of the positive electrode active material 10 in a shell shape with the non-aqueous binder 20. The non-aqueous solvent may be dried in a vacuum at room temperature without heating.

[0024] Here, the non-aqueous solvent is made of a material capable of dissolving the powder of the non-aqueous binder 20, and contains an organic solvent such as N-methyl-2-pyrrolidone (NMP).

[0025] The amount of non-aqueous binder 20 used in the process of producing the positive electrode material 1 may be appropriately determined according to the amount of positive electrode active material 10 within a range that can coat the entire surface of positive electrode active material 10 in a shell-like shape.

[0026] The positive electrode slurry in this embodiment includes a positive electrode mixture containing the positive electrode material 1 and a conductive assistant, and the positive electrode mixture is dispersed in an aqueous solvent. Note that the non-aqueous binder 20 that covers the surface of the positive electrode active material 10 is not dissolved in the aqueous solvent.

[0027] Here, the aqueous solvent is made of a material in which the powder of the non-aqueous binder 20 does not dissolve, and includes water or a dispersant such as polyvinylpyrrolidone (PVP). The conductive assistant is not particularly limited, but preferably includes cellulose nanofiber. Since the aqueous solvent has low viscosity, a positive electrode slurry with an appropriate viscosity can be obtained by using cellulose nanofiber, which has high viscosity, as a conductive assistant.

[0028] The positive electrode plate in this embodiment can be produced by applying the positive electrode slurry to a current collector and then drying the coating film. The coating film may be dried by thermocompression bonding the positive electrode slurry and the current collector with a roll press or the like.

[0029] In the positive electrode material 1 in this embodiment, the entire surface of the positive electrode active material 10 is covered in a shell shape with the non-aqueous binder 20, so that even if a positive electrode mixture containing the positive electrode material 1 and a conductive additive is dispersed in an aqueous solvent to prepare a positive electrode slurry, lithium of the positive electrode active material 10 does not dissolve into the aqueous solvent. As a result, it is possible to suppress a decrease in the positive electrode capacity caused by lithium dissolving into the aqueous solvent.

[0030] In addition, when a positive electrode plate is produced using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the non-aqueous binder 20 does not dissolve in an aqueous solvent, so that the positive electrode active material 10 is uniformly dispersed in a state in which the entire surface is covered with the non-aqueous binder 20 in a shell shape, as shown in the schematic diagram of Fig. 2. Therefore, the non-aqueous binder 20 is also uniformly dispersed, and the positive electrode active material 10 can be uniformly bound to each other and to the current collector by the non-aqueous binder 20 throughout the positive electrode, thereby realizing a secondary battery with excellent cycle characteristics.

[0031] In particular, when the positive electrode active material 10 contains two or more types of positive electrode active material 10 having different particle sizes, the positive electrode active material 10 is dispersed more uniformly, and the binding between the positive electrode active material 10 and between the positive electrode active material 10 and the current collector via the non-aqueous binder 20 is enhanced, resulting in further improvement of the cycle characteristics.

[0032] In addition, the positive electrode material 1 in this embodiment has a structure in which the entire surface of the positive electrode active material 10 is covered with the non-aqueous binder 20 in a shell shape, but it also includes a structure in which only a part of the surface is covered with the non-aqueous binder 20.

[0033] When a positive electrode mixture containing a conventional non-aqueous binder 20 such as PVDF is dispersed in an organic solvent to prepare a positive electrode slurry, the conductive assistant such as carbon black contained in the positive electrode mixture does not dissolve in the organic solvent, and furthermore, the small holes on the nanometer level absorb the organic solvent, so that a large amount of organic solvent is used.

[0034] On the other hand, an organic solvent (non-aqueous solvent) is also used to prepare the positive electrode material 1 in this embodiment, but since the organic solvent only contains the positive electrode active material 10 and the non-aqueous binder 20 that dissolves in the organic solvent, the amount of non-aqueous solvent used can be significantly reduced compared to the case where a positive electrode mixture containing a conventional non-aqueous binder 20 such as PVDF is dispersed in an organic solvent to prepare a positive electrode slurry. As a result, since the positive electrode in this embodiment is manufactured using a positive electrode slurry in which a positive electrode mixture containing the positive electrode material 1 and a conductive assistant is dispersed in an aqueous solvent, the amount of non-aqueous solvent used when manufacturing a secondary battery can be significantly reduced.

[0035] In addition, the positive electrode material 1 in this embodiment can obtain the effects of suppressing the decrease in the positive electrode capacity and improving the cycle characteristics by covering the entire surface of the positive electrode active material 10 with the nonaqueous binder 20 in a shell-like shape. Therefore, in order to obtain such an effect, the amount of the nonaqueous binder 20 used in the process of producing the positive electrode material 1 may be within a range in which the entire surface of the positive electrode active material 10 can be covered in a shell-like shape according to the amount of the positive electrode active material 10. Usually, a minimum amount of the nonaqueous binder 20, including an excess amount, may be used in consideration of the variation in size of the positive electrode active material 10 and the variation in the manufacturing process of the positive electrode material 1.

[0036] As described above, when a positive electrode plate is produced using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the positive electrode active material 10 is uniformly dispersed in a state in which the entire surface is covered with the nonaqueous binder 20 in a shell shape, as shown in the schematic diagram of Fig. 3. At this time, since only a minimum amount of the nonaqueous binder 20 is used, in the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20, only an excess amount of the nonaqueous binder 40 exists, and most of the region 50 is in a void state.

[0037] Therefore, when the total volume of the nonaqueous binder 20 covering the entire surface of the positive electrode active material 10 is V1 and the total volume of the nonaqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20 is V2, there is a relationship of V1>V2. In addition, when the total volume of the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20 is V3, there is a relationship of V3>V2.

[0038] In addition, when the positive electrode mixture formed on the current collector is viewed in a cross section perpendicular to the film thickness direction, the above relationship is A1>A2, where A1 is the total area of ​​the nonaqueous binder 20 covering the entire surface of the positive electrode active material 10, and A2 is the total area of ​​the nonaqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20. In addition, when A3 is the total area of ​​the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20, A3>A2.

[0039] Incidentally, in the positive electrode material 1 of the present embodiment, the entire surface of the positive electrode active material 10 is covered in a shell shape with the nonaqueous binder 20. Therefore, even if a positive electrode mixture containing the positive electrode material 1 and a conductive additive is dispersed in an aqueous solvent to prepare a positive electrode slurry, lithium of the positive electrode active material 10 does not dissolve into the aqueous solvent, and therefore a decrease in the positive electrode capacity can be suppressed.

[0040] Furthermore, when a positive electrode plate is produced using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the non-aqueous binder 20 does not dissolve in an aqueous solvent, so the positive electrode active material 10 is uniformly dispersed in a state in which the entire surface is covered with a shell-like coating of the non-aqueous binder 20. Therefore, the non-aqueous binder 20 is also uniformly dispersed, and the positive electrode active material 10 can be uniformly bound to each other and to the current collector by the non-aqueous binder 20 throughout the positive electrode, thereby realizing a secondary battery with excellent cycle characteristics.

[0041] Such an effect is obtained by coating the surface of the positive electrode active material 10 with the non-aqueous binder 20 in a shell-like manner, and therefore the entire surface of the positive electrode active material 10 does not necessarily have to be completely coated with the non-aqueous binder 20 in a shell-like manner. Even when only a portion of the surface of the positive electrode active material 10 is coated with the non-aqueous binder 20 in a shell-like manner, such an effect can be obtained.

[0042] For example, when the same amount of non-aqueous binder 20 is used to prepare a positive electrode plate using a positive electrode slurry in this embodiment in which a positive electrode mixture including a positive electrode material 1 in which a portion of the surface of the positive electrode active material 10 is covered in a shell shape with the non-aqueous binder 20 is dispersed in an aqueous solvent, a comparison is made with a case in which a positive electrode plate is prepared using a positive electrode slurry in which a positive electrode mixture including the non-aqueous binder 20 is dispersed in an organic solvent according to a conventional method. As a result, it has been confirmed that the secondary battery prepared according to this embodiment has superior characteristics in terms of positive electrode capacity and cycle characteristics compared to the secondary battery prepared according to the conventional method.

[0043] The positive electrode material 1 in which a portion of the surface of the positive electrode active material 10 is coated in a shell-like shape with the non-aqueous binder 20 may be produced by setting the amount of the non-aqueous binder 20 used in the production process of the positive electrode material 1 to a range that allows a portion of the surface of the positive electrode active material 10 to be coated in a shell-like shape.

[0044] In addition, when a part of the surface of the positive electrode active material 10 is coated with the non-aqueous binder 20 in a shell shape, in order to achieve the effects of the present invention, it is preferable that 50% or more of the surface of the positive electrode active material 10 is coated with the non-aqueous binder 20, and it is more preferable that 70% or more of the surface of the positive electrode active material 10 is coated with the non-aqueous binder 20.

[0045] When a positive electrode plate is produced using a positive electrode slurry containing such a positive electrode material 1, the positive electrode active material 10 is uniformly dispersed in a state in which a part of the surface is covered with a shell-like coating of the nonaqueous binder 20, as shown in the schematic diagram of Fig. 4. In this case, since a smaller amount of the nonaqueous binder 20 is used compared to the case in which the nonaqueous binder 20 is covered in a shell-like coating on the entire surface of the positive electrode active material 10, the nonaqueous binder 40 is hardly present in the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20, and the region is in a void state.

[0046] Therefore, similarly to the case where the nonaqueous binder 20 is coated in a shell shape over the entire surface of the positive electrode active material 10, when the total volume of the nonaqueous binder 20 coating a part of the surface of the positive electrode active material 10 is V1 and the total volume of the nonaqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 coated with the nonaqueous binder 20 is V2, there is a relationship of V1>V2. Also, when the total volume of the region 50 surrounded by the positive electrode active material 10 coated with the nonaqueous binder 20 is V3, there is a relationship of V3>V2.

[0047] In addition, when the positive electrode mixture formed on the current collector is viewed in a cross section perpendicular to the film thickness direction, the above relationship is A1>A2, where A1 is the total area of ​​the nonaqueous binder 20 covering a part of the surface of the positive electrode active material 10, and A2 is the total area of ​​the nonaqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20. In addition, when A3 is the total area of ​​the region 50 surrounded by the positive electrode active material 10 covered with the nonaqueous binder 20, A3>A2.

[0048] <Example of modification> In the above embodiment, the cathode material 1 has a structure in which the entire surface or a part of the surface of the cathode active material 10 is covered in a shell shape with the nonaqueous binder 20, but if the thickness of the covering nonaqueous binder 20 is too thick, the electrical resistance at the surface of the cathode active material 10 increases, which may lead to a decrease in battery capacity. In this modified example, a structure of the cathode material 1 that can suppress the decrease in battery capacity caused by an increase in the thickness of the nonaqueous binder 20 is shown.

[0049] 5 is a schematic diagram showing a modified example 1 of the positive electrode material 1, in which a part of the surface of the positive electrode active material 10 is covered with a metal oxide 30, and the non-aqueous binder 20 forms a shell-like coating on the entire surface of the positive electrode active material 10 so as to cover the metal oxide 30. This structure can suppress an increase in electrical resistance on the surface of the positive electrode active material 10, and therefore can suppress a decrease in battery capacity while maintaining the effect of improving binding property by the non-aqueous binder 20 (improving cycle characteristics).

[0050] The cathode material 1 in this modified example 1 can be produced by carrying out a step of adhering a metal oxide 30 to a part of the surface of the cathode active material 10 before a step of coating the entire surface of the cathode active material 10 in a shell shape with a non-aqueous binder 20. In this way, the entire surface of the cathode active material 10 can be coated in a shell shape with the non-aqueous binder 20 so as to cover the metal oxide 30.

[0051] The metal oxide 30 that coats the surface of the positive electrode active material 10 is not particularly limited as long as it is a material with low electrical resistance, and for example, titanium oxide, niobium oxide, titanium-containing oxide, etc. Coating the surface of the positive electrode active material 10 with the metal oxide 30 can be performed, for example, by mixing the positive electrode active material 10 and the metal oxide 30 and sintering or firing them.

[0052] FIG. 6 is a diagram showing a schematic diagram of a modified example 2 of the positive electrode material 1, in which the entire surface of the positive electrode active material 10 is covered with either a non-aqueous binder 20 or a metal oxide 30 in a shell-like structure.

[0053] FIG. 7 is a schematic diagram showing a modified example 3 of the positive electrode material 1. In the modified example 3, the entire surface of the positive electrode active material 10 is covered with a shell-like layer of metal oxide 30, and a portion of the surface of the metal oxide 30 is covered with a non-aqueous binder 20.

[0054] In the positive electrode material 1 having the structure shown in FIGS. 6 and 7, the entire surface of the positive electrode active material 10 is not coated with the nonaqueous binder 20, but a part of or the entire surface of the positive electrode active material 10 is coated with the metal oxide 30. Therefore, it is possible to suppress a decrease in battery capacity while maintaining the effect of improving the binding property by the nonaqueous binder 20.

[0055] The cathode material 1 having the structure shown in FIGS. 6 and 7 can be manufactured by the steps of adhering a metal oxide 30 to a part of the surface or the entire surface of a cathode active material 10, dissolving a powder of a non-aqueous binder 20 in a non-aqueous solvent, dispersing the powder of the cathode active material 10 having the metal oxide 30 adhered to its surface in the non-aqueous solvent, and evaporating the non-aqueous solvent.

[0056] The amount of metal oxide 30 used in the process of producing the positive electrode material 1 may be appropriately determined according to the amount of positive electrode active material 10 within a range capable of covering a part or the entire surface of the positive electrode active material 10 . EXAMPLES

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0058] [Example 1] <Preparation of cathode material> 0.05g of non-aqueous binder (PVDF) powder was dissolved in 0.45g of non-aqueous solvent (NMP solvent), and 0.95g of positive electrode active material (lithium iron phosphate (LiFePO4)) powder was dispersed in the non-aqueous solvent. The non-aqueous solvent was then heated at 100°C for 2 minutes to evaporate. This produced a positive electrode material 1 in which the entire surface of the positive electrode active material 10 was covered with the non-aqueous binder in a shell shape.

[0059] <Preparation of positive electrode plate> The positive electrode material 1 prepared by the above method, a conductive assistant (containing cellulose nanofibers), and a dispersant were mixed in a mass ratio of 95:4:1 in an aqueous solvent (pure water) to prepare a positive electrode slurry.

[0060] This positive electrode slurry was applied to a positive electrode current collector (aluminum foil), heated at 100° C. for 6 minutes to dry, and then pressed together with the aluminum foil to produce a positive electrode plate.

[0061] [Example 2] A positive electrode plate was produced in the same manner as in Example 1, except that a ternary material (LiNiCoMnO2) was used as the positive electrode active material.

[0062] [Comparative Example 1] Using a conventional method, a positive electrode active material (lithium iron phosphate), a conductive additive (acetylene black), and a binder (PVDF) were mixed in a mass ratio of 90:5:5 in an organic solvent (NMP) to form a positive electrode slurry, and a positive electrode plate was produced in the same manner as in Example 1.

[0063] [Comparative Example 2] A positive electrode plate was produced in the same manner as in Comparative Example 1, except that a ternary material (LiNiCoMnO2) was used as the positive electrode active material.

[0064] <Evaluation of the dispersion state of non-aqueous binder in positive electrode plate> FIG. 8A is a photograph of the cross section of the positive plate prepared in Example 1 taken with a SEM (scanning electron microscope), and FIG. 8B is a photograph of the fluorine component (PVDF) in the positive plate taken with an EDS (energy dispersive X-ray spectroscopy) of the cross section of the positive plate at the same position, in which the area where the fluorine component was detected by the EDS has been dyed and highlighted.

[0065] The SEM cross-sectional photographs were taken by preparing a cross-section of the prepared positive electrode plate sample using a focused ion beam (FIB), and then photographing the conductively treated cross-section under conditions of an acceleration voltage of 15 kV and a magnification of 2000 times.

[0066] 8B, it was confirmed that many areas on the surface of the positive electrode active material 10 were covered in a shell shape with the non-aqueous binder (PVDF) 20. It was also confirmed that the amount of the binder (PVDF) 20 present in the gaps formed between the positive electrode active materials 10 was small.

[0067] That is, when the sum of the volumes of the binder (PVDF) 20 covering the surface of the positive electrode active material 10 is V1 and the sum of the volumes of the binder (PVDF) 20 present in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is V2, it was confirmed that there is a relationship of V1>V2. In addition, when the sum of the volumes of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is V3, it was confirmed that there is a relationship of V3>V2.

[0068] In addition, in the cross section of the positive electrode mixture, when the sum of the areas of the binder (PVDF) 20 covering the surface of the positive electrode active material 10 is A1 and the sum of the areas of the binder (PVDF) 20 present in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is A2, it was confirmed that there is a relationship of A1>A2. In addition, when the sum of the areas of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is A3, it was confirmed that there is a relationship of A3>A2.

[0069] 9A is a SEM photograph of the cross section of the positive plate produced in Comparative Example 1, and FIG. 9B is a photograph of the fluorine component (PVDF) in the positive plate taken by EDS (energy dispersive X-ray spectroscopy) at the same position of the cross section of the positive plate, in which the area where the fluorine component was detected by EDS was dyed and highlighted. The SEM cross section photograph was taken under the same conditions as in Example 1.

[0070] As shown in FIG. 9B, in the positive electrode plate produced in Comparative Example 1, it was confirmed that the binder (PVDF) 20 was dispersed among the positive electrode active materials 10, but the area on the surface of the positive electrode active materials 10 that was covered with the binder (PVDF) in a shell-like shape was hardly confirmed. That is, in the positive electrode plate produced in Comparative Example 1, it was confirmed that the binder (PVDF) was present in a state of being pressed into the gaps formed between the positive electrode active materials 10. That is, it was confirmed that the binder (PVDF) was not present around the positive electrode active material 10 in a state of covering the positive electrode active material 10 with a thin film in a shell-like shape as in Example 1, but was present so as to fill the gaps formed between the positive electrode active materials 10.

[0071] FIG. 10A is a photograph of the cross section of the positive electrode plate prepared in Example 2 taken by SEM, and the particle size of the positive electrode active material (LiNiCoMnO2) used in Example 2 is smaller than that of the positive electrode active material (LiFePO4) used in Example 1. FIG. 10B is a photograph of the fluorine component (PVDF) in the positive electrode plate taken by EDS (energy dispersive X-ray spectroscopy) at the same position of the cross section of the positive electrode plate, and the area where the fluorine component was detected by this EDS is dyed and highlighted. The SEM cross section photograph was taken under the same conditions as in Example 1.

[0072] 10B, in the positive electrode plate produced in Example 2, it was confirmed that many areas on the surface of the positive electrode active material 10 were covered in a shell shape with the non-aqueous binder (PVDF) 20, similarly to Example 1. It was also confirmed that the amount of the binder (PVDF) 20 present in the gaps formed between the positive electrode active materials 10 was small.

[0073] That is, when the sum of the volumes of the binder (PVDF) 20 covering the surface of the positive electrode active material 10 is V1 and the sum of the volumes of the binder (PVDF) present in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is V2, it was confirmed that there is a relationship of V1>V2. In addition, when the sum of the volumes of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) is V3, it was confirmed that there is a relationship of V3>V2.

[0074] In addition, in the cross section of the positive electrode mixture, when the sum of the areas of the binder (PVDF) 20 covering the surface of the positive electrode active material 10 is A1 and the sum of the areas of the binder (PVDF) 20 present in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is A2, it was confirmed that there is a relationship of A1>A2. In addition, when the sum of the areas of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20 is A3, it was confirmed that there is a relationship of A3>A2.

[0075] 11A is a SEM photograph of the cross section of the positive plate produced in Comparative Example 2, and FIG. 11B is a photograph of the fluorine component (PVDF) in the positive plate taken by EDS (energy dispersive X-ray spectroscopy) at the same position of the cross section of the positive plate, in which the area where the fluorine component was detected by EDS was dyed and highlighted. The SEM cross-sectional photograph was taken under the same conditions as in Example 1.

[0076] As shown in FIG. 11B, in the positive electrode plate produced in Comparative Example 2, it was confirmed that the binder (PVDF) 20 was dispersed between the positive electrode active materials 10, as in Comparative Example 1, but the area covered with the binder (PVDF) in a shell shape on the surface of the positive electrode active materials 10 was hardly confirmed. That is, it was confirmed that in the positive electrode plate produced in Comparative Example 1, the binder (PVDF) exists in a state of being pressed into the gap formed between the positive electrode active materials 10. That is, it was confirmed that the binder (PVDF) does not exist around the positive electrode active material 10 in a state of covering the positive electrode active material 10 with a thin film in a shell shape as in Example 1, but the binder (PVDF) exists so as to fill the gap formed between the positive electrode active materials 10.

[0077] <Measurement of coverage> Based on the SEM photograph of FIG. 8B (Example 1) and the SEM photograph of FIG. 9B (Comparative Example 1), the coverage C (%) defined by the following formula (1) was measured in a cross section of the positive electrode mixture formed on the positive electrode current collector.

[0078] C = (C2 ÷ C1) × 100 (1) In formula (1), C1 represents the perimeter of the positive electrode active material 10, and C2 represents the total length of the contact portion of the binder (PVDF) that is in contact with the perimeter of the positive electrode active material 10.

[0079] As a result, the coverage rate of the positive electrode plate produced in Example 1 was 60%, whereas the coverage rate of the positive electrode plate produced in Comparative Example 1 was 23%.

[0080] However, when observing the cross section of a positive electrode plate by SEM, the binder (PVDF) present at the back of the cross section may be imaged as being present on the same plane as the cross section. Therefore, in order to avoid such an influence, the positive electrode plates prepared in Example 1 and Comparative Example 1 were embedded in resin, and then the resin-embedded positive electrode plates were cross-sectioned using the BIB (Broad Ion Beam) method, and the cross section treated for electrical conductivity was photographed under conditions of an acceleration voltage of 15 kV and a magnification of 3000 times to obtain a SEM cross-sectional photograph.

[0081] FIG. 12A is a SEM photograph of a cross section of a resin-embedded positive electrode plate prepared in Example 1, and FIG. 12B is a photograph of the fluorine component (PVDF) in the positive electrode plate, obtained by photographing the cross section of the positive electrode plate at the same position using EDS (energy dispersive X-ray spectroscopy), staining the area where the fluorine component was detected by EDS, and illustrating in a line diagram the portion 20 in the stained area that is in contact with the positive electrode active material 10.

[0082] Similarly, FIG. 13A is a SEM photograph of a cross section of a resin-embedded positive electrode plate prepared in Comparative Example 1, and FIG. 13B is a photograph in which the fluorine component (PVDF) in the positive electrode plate is photographed by EDS (energy dispersive X-ray spectroscopy) at the same position of the cross section of the positive electrode plate, the area where the fluorine component was detected by EDS is stained, and the portion 20 in the stained area that is in contact with the positive electrode active material 10 is shown in a line diagram.

[0083] Based on the SEM photographs of Fig. 12B (Example 1) and Fig. 13B (Comparative Example 1), the coverage C (%) defined by the above formula (1) was measured in the cross section of the positive electrode mixture formed on the positive electrode current collector. As a result, the coverage was 37% for the positive electrode plate produced in Example 1, whereas the coverage was 10% for the positive electrode plate produced in Comparative Example 1.

[0084] The reason why the coverage rate C of the resin-embedded positive electrode plate is smaller than the coverage rate C of the non-resin-embedded positive electrode plate is believed to be that when the positive electrode plate is embedded in resin, and then the resin is hardened by heating, a part of the binder (PVDF), which is particularly thinly coated, peels off from the surface of the positive electrode active material 10 due to the influence of the difference in the expansion coefficients of the positive electrode active material and the resin, etc.

[0085] From the above results, in the cross section of the positive electrode mixture formed on the positive electrode current collector, the coverage C of the resin-embedded positive electrode plate is preferably 30% or more.

[0086] <Evaluation of cycle characteristics of lithium-ion secondary batteries> The positive electrode plate produced in Example 1 and a negative electrode plate (lithium metal foil) were wound with a separator interposed therebetween to produce an electrode body, and this electrode body was housed in a battery case together with a non-aqueous electrolyte to produce a lithium ion secondary battery.

[0087] The fabricated lithium-ion secondary battery was repeatedly charged and discharged at a charge / discharge rate of 1C to measure the change in discharge capacity [mAh / g] and to determine the cycle characteristics.

[0088] FIG. 14 is a graph showing the measurement results of cycle characteristics. The graph indicated by arrow A shows the cycle characteristics of the lithium-ion secondary battery produced using the positive electrode material of Example 1, and the graph indicated by arrow B shows the cycle characteristics of the lithium-ion secondary battery produced using the positive electrode material of Comparative Example 1.

[0089] 14, the cycle characteristics of the lithium ion secondary battery produced using the positive electrode material of Example 1 show that the number of cycles until the discharge capacity decreases to 1 / 3 of the initial capacity is improved by about twice as much as the cycle characteristics of the lithium ion secondary battery produced using the positive electrode material of Comparative Example 1. This is because the positive electrode active material 10 is uniformly dispersed in a state in which the entire surface is covered with the non-aqueous binder 20 in a shell shape, and the non-aqueous binder 20 is also uniformly dispersed, and the positive electrode active material 10 is uniformly bound to each other and to the current collector by the non-aqueous binder 20 throughout the positive electrode.

[0090] 14, the initial capacity of the lithium ion secondary battery produced using the positive electrode material of Example 1 is slightly lower than the initial capacity of the lithium ion secondary battery produced using the positive electrode material of Comparative Example 1. This is believed to be because the entire surface of the positive electrode active material 10 is covered with the nonaqueous binder 20 in a shell shape, increasing the electrical resistance on the surface of the positive electrode active material 10.

[0091] [Example 3] <Preparation of cathode material> A powder of the positive electrode active material (lithium iron phosphate) and a powder of metal oxides (titanium oxide and niobium oxide) were mixed in a mass ratio of 99.8:0.2, and the mixture was sintered at a temperature of 800° C. for 180 minutes to adhere the metal oxide 30 to the surface of the positive electrode active material 10.

[0092] Thereafter, in the same manner as in Example 1, the entire surface of the positive electrode active material 10 was coated with a non-aqueous binder (PVDF) in a shell shape so as to cover the metal oxide, thereby producing a positive electrode material 1 having the structure shown in FIG.

[0093] <Evaluation of cycle characteristics of lithium ion secondary batteries> A lithium ion secondary battery was produced using the positive electrode material 1 produced in Example 3 in the same manner as in Example 1, and the cycle characteristics were measured.

[0094] FIG. 15 is a graph showing the measurement results of cycle characteristics, in which the graph indicated by arrow A shows the cycle characteristics of the lithium ion secondary battery produced using the positive electrode material of Example 1, the graph indicated by arrow B shows the cycle characteristics of the lithium ion secondary battery produced using the positive electrode material of Comparative Example 1, and the graph indicated by arrow C shows the cycle characteristics of the lithium ion secondary battery produced using the positive electrode material of Example 3.

[0095] As shown in Fig. 15, the initial capacity of the lithium ion secondary battery produced using the positive electrode material of Example 3 is improved compared to the initial capacity of the lithium ion secondary battery produced using the positive electrode material of Example 1. This is believed to be because the metal oxide 30 with low electrical resistance is attached to the surface of the positive electrode active material 10, thereby suppressing an increase in electrical resistance on the surface of the positive electrode active material 10. The improvement in cycle characteristics due to the non-aqueous binder 20 being coated in a shell shape on the entire surface of the positive electrode active material 10 is maintained.

[0096] Although the present invention has been described above with reference to the preferred embodiments, such description is not limiting and, of course, various modifications are possible.

[0097] For example, in the above embodiment, the method of manufacturing the positive electrode material 1 is described in which the powder of the non-aqueous binder 20 is dissolved in a non-aqueous solvent, the powder of the positive electrode active material 10 is dispersed in the non-aqueous solvent, and then the non-aqueous solvent is evaporated to coat the entire surface of the positive electrode active material 10 in a shell shape with the non-aqueous binder 20. However, the present invention is not limited to this method. For example, if the average particle size of the non-aqueous binder 20 is about half or less of the average particle size of the positive electrode active material 10, the positive electrode active material 10 may be manufactured by mixing and heating the powder of the positive electrode active material 10 and the powder of the finely divided non-aqueous binder 20 without using an aqueous solvent such as water or a non-aqueous solvent such as an organic solvent. In this case, the average particle size of the positive electrode active material 10 is preferably in the range of 1 μm to 10 μm.

[0098] In the above embodiment, the positive electrode is used as an example of the electrode of the secondary battery. However, the negative electrode may be made of lithium titanate (Li4Ti5O 12Even when a negative electrode active material containing lithium such as graphite or silicon is used, the lithium of the negative electrode active material does not dissolve in the aqueous solvent, so that a decrease in the negative electrode capacity can be suppressed. Even when a negative electrode active material such as graphite or silicon is used in the negative electrode, the negative electrode active materials are bound to each other and to the current collector by the uniformly dispersed non-aqueous binder, so that a secondary battery with excellent cycle characteristics can be realized. [Explanation of symbols]

[0099] 1. Cathode material (electrode material) 10 Cathode active material (electrode active material) 20, 40 Non-aqueous binder 30 Metal Oxides 50 Region surrounded by positive electrode active material coated with non-aqueous binder

Claims

1. An electrode material for a secondary battery, An electrode active material is included, The electrode material, wherein the entire surface of the electrode active material is covered with a non-aqueous binder in the form of a shell.

2. A portion of the surface of the electrode active material is coated with a metal oxide, The electrode material according to claim 1 , wherein the non-aqueous binder coats the entire surface of the electrode active material in a shell-like form so as to cover the metal oxide.

3. An electrode material for a secondary battery, An electrode active material is included, The electrode material, wherein the entire surface of the electrode active material is covered in a shell shape with either a non-aqueous binder or a metal oxide.

4. An electrode material for a secondary battery, An electrode active material is included, The entire surface of the electrode active material is covered with a metal oxide in a shell shape, A part of the surface of the metal oxide is coated with a non-aqueous binder.

5. The electrode material according to any one of claims 1 to 4, wherein the non-aqueous binder contains a fluorine-based resin.

6. The electrode material according to any one of claims 1 to 4, wherein the electrode active material is a positive electrode active material.

7. The electrode material according to any one of claims 1 to 4, wherein the electrode active material is made of a lithium-containing composite oxide.

8. An electrode slurry containing an electrode mixture, The electrode mixture contains the electrode material according to any one of claims 1 to 4 and a conductive assistant, The electrode mixture is dispersed in an aqueous solvent.

9. The electrode slurry according to claim 8 , wherein the non-aqueous binder coating the surface of the electrode active material is not dissolved in the aqueous solvent.

10. The electrode slurry according to claim 8 , wherein the conductive assistant comprises cellulose nanofibers.

11. A method for producing an electrode material for a secondary battery, comprising: A step of dissolving a powder of a non-aqueous binder in a non-aqueous solvent and dispersing a powder of an electrode active material in the non-aqueous solvent; a step of evaporating the non-aqueous solvent to coat the entire surface of the electrode active material with the non-aqueous binder in a shell-like form; A method for producing an electrode material comprising the steps of:

12. The method further includes, before the two steps, a step of attaching a metal oxide to a portion of the surface of the electrode active material, The method for producing an electrode material according to claim 11 , wherein the entire surface of the electrode active material is coated with the non-aqueous binder in a shell shape so as to cover the metal oxide.

13. A method for producing an electrode material for a secondary battery, comprising: A step of attaching a metal oxide to a portion of a surface of an electrode active material; A step of dissolving a powder of a non-aqueous binder in a non-aqueous solvent, and dispersing a powder of the electrode active material having the metal oxide attached to the surface thereof in the non-aqueous solvent; evaporating the non-aqueous solvent; Including, In the step of evaporating the non-aqueous solvent, the entire surface of the electrode active material is covered in a shell shape with either the non-aqueous binder or the metal oxide.

14. A method for producing an electrode material for a secondary battery, comprising: depositing a metal oxide on the entire surface of the electrode active material; A step of dissolving a powder of a non-aqueous binder in a non-aqueous solvent, and dispersing the powder of the electrode active material having the metal oxide attached to the entire surface thereof in the non-aqueous solvent; evaporating the non-aqueous solvent; Including, In the step of evaporating the non-aqueous solvent, a portion of a surface of the metal oxide is covered with the non-aqueous binder.

15. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 1 to 4 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which the entire surface is covered with a shell-like non-aqueous binder, The total volume of the non-aqueous binder covering the entire surface of the electrode active material is V １ The total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is V ２ Then, V １ >V ２ That is, the electrode.

16. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 1 to 4 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which the entire surface is covered with a shell-like non-aqueous binder, In the cross section of the electrode mixture, the total area of ​​the nonaqueous binder covering the entire surface of the electrode active material is A １ The total area of ​​the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is A ２ Then, A １ >A ２ That is, the electrode.

17. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 1 to 4 and a conductive assistant, The electrode active material contained in the electrode material is uniformly dispersed in a state in which the entire surface is covered with a shell-like non-aqueous binder, The sum of the volumes of the regions surrounded by the electrode active material coated with the nonaqueous binder is V ３ The total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is V ２ Then, V ３ >V ２ That is, the electrode.

18. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 1 to 4 and a conductive assistant, The electrode active material contained in the electrode material is uniformly dispersed in a state in which the entire surface is covered with a shell-like non-aqueous binder, The sum of the areas of the regions surrounded by the electrode active material coated with the nonaqueous binder in the cross section of the electrode mixture is A ３ The total area of ​​the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is A ２ Then, A ３ >A ２ That is, the electrode.

19. A method for producing an electrode for a secondary battery, comprising the steps of: A step of forming an electrode material in which the entire surface of an electrode active material is covered with a non-aqueous binder in a shell shape by the method according to any one of claims 11 to 14; A step of dispersing an electrode mixture containing the electrode material and a conductive assistant in an aqueous solvent to form an electrode slurry; a step of applying the electrode slurry onto a current collector and then drying the applied film; A method for manufacturing an electrode, comprising:

20. An electrode material for a secondary battery, An electrode active material is included, An electrode material, wherein a portion of a surface of the electrode active material is covered with a non-aqueous binder in the form of a shell.

21. 21. The electrode material according to claim 20, wherein 50% or more of the surface of the electrode active material is covered with the non-aqueous binder.

22. The electrode material according to claim 20 , wherein the non-aqueous binder comprises a fluorine-based resin.

23. The electrode material according to claim 20 , wherein the electrode active material comprises a positive electrode active material.

24. The electrode material according to claim 20 , wherein the electrode active material comprises a lithium-containing composite oxide.

25. An electrode slurry containing an electrode mixture, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode mixture is dispersed in an aqueous solvent.

26. The electrode slurry according to claim 25 , wherein the non-aqueous binder coating the surface of the electrode active material is not dissolved in the aqueous solvent.

27. The electrode slurry according to claim 25 , wherein the conductive assistant comprises cellulose nanofibers.

28. A method for producing an electrode material for a secondary battery, comprising: A step of dissolving a powder of a non-aqueous binder in a non-aqueous solvent and dispersing a powder of an electrode active material in the non-aqueous solvent; a step of evaporating the non-aqueous solvent to coat a part of the surface of the electrode active material with the non-aqueous binder in a shell shape; A method for producing an electrode material comprising the steps of:

29. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which a part of the surface is covered with a shell-like non-aqueous binder, The total volume of the non-aqueous binder covering the entire surface of the electrode active material is V １ The total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is V ２ Then, V １ >V ２ That is, the electrode.

30. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which a part of the surface is covered with a shell-like non-aqueous binder, In the cross section of the electrode mixture, the total area of ​​the nonaqueous binder covering the entire surface of the electrode active material is A １ The total area of ​​the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is A ２ Then, A １ >A ２ That is, the electrode.

31. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which a part of the surface is covered with a shell-like non-aqueous binder, The sum of the volumes of the regions surrounded by the electrode active material coated with the nonaqueous binder is V ３ The total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is V ２ Then, V ３ >V ２ That is, the electrode.

32. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which a part of the surface is covered with a shell-like non-aqueous binder, The sum of the areas of the regions surrounded by the electrode active material coated with the nonaqueous binder in the cross section of the electrode mixture is A ３ The total area of ​​the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder is A ２ Then, A ３ >A ２ That is, the electrode.

33. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture contains the electrode material according to any one of claims 20 to 24 and a conductive assistant, The electrode active material contained in the electrode material is dispersed in a state in which a part of the surface is covered with a shell-like non-aqueous binder, An electrode, in which a coverage C defined by the following formula (1) is 30% or more in a cross section of the electrode mixture. C = (C ２ ÷C １ ) × 100 ... (1) (In formula (1), C １ represents the perimeter of the electrode active material, and C ２ represents the total length of the contact portion of the non-aqueous binder that is in contact with the periphery of the electrode active material.)

34. A method for producing an electrode for a secondary battery, comprising the steps of: A step of forming an electrode material in which a part of the surface of an electrode active material is covered with a non-aqueous binder in a shell shape by the method according to claim 28; A step of dispersing an electrode mixture containing the electrode material and a conductive assistant in an aqueous solvent to form an electrode slurry; a step of applying the electrode slurry onto a current collector and then drying the applied film; A method for manufacturing an electrode, comprising:

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