Electrode material, electrode slurry, method for manufacturing electrode material, electrode, and method for manufacturing 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 manufacturing the electrode material, an electrode, and a method for manufacturing the electrode.

Background Art

[0002] An electrode constituting a secondary battery such as a lithium-ion secondary battery is 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 it.

[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 does not dissolve in water, it is necessary to prepare a slurry in which PVDF is dissolved in an organic solvent such as N-methyl-pyrrolidone (NMP), and there is a problem that the environmental load increases with the use of the organic solvent. Therefore, in recent years, the development of an aqueous binder that can be dispersed in an aqueous solvent with a low environmental load has been demanded.

[0005] As aqueous binders used for negative electrodes, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) have been developed. However, when these aqueous binders are used for the positive electrode as they are, there is a problem that they deteriorate by oxidation 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 in an aqueous solvent as suspended particles to prepare a positive electrode slurry. When this positive electrode slurry is applied to a current collector and dried to produce 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] Japanese Patent Publication No. 2017-91789 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0009] Furthermore, 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 within the positive electrode. As a result, the bonding between the positive electrode active materials themselves, and between the positive electrode active materials and the current collector, weakens, leading to a problem of reduced cycle characteristics in the secondary battery. This problem can also occur when the aqueous binder is used in the negative electrode.

[0010] The present invention has been made in view of the above, and aims to provide an electrode material for secondary batteries that suppresses a decrease in electrode capacity and has excellent cycle characteristics, an electrode slurry, a method for manufacturing the electrode material, an electrode, and a method for manufacturing the electrode. [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 the active material is coated in a shell-like manner with a non-aqueous binder.

[0012] In one preferred embodiment, a portion of the surface of the electrode active material is coated with a metal oxide, and a non-aqueous binder coats the entire surface of the electrode active material in a shell-like manner, covering the metal oxide.

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

[0014] The present invention relates to a method for manufacturing an electrode material for a secondary battery, and comprises the steps of: dissolving a non-aqueous binder powder in a non-aqueous solvent and dispersing an electrode active material powder 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 manner.

[0015] The electrode according to the present invention is an electrode for a secondary battery comprising an electrode mixture formed on a current collector, wherein the electrode mixture comprises an electrode material in which the entire surface of the electrode active material is covered in a shell-like manner with a non-aqueous binder, and a conductive additive, wherein the electrode active material contained in the electrode material is dispersed in a state in which the entire surface is covered in a shell-like manner with a non-aqueous binder, and when V1 is the total volume of the non-aqueous binder covering the entire surface of the electrode active material, and V2 is the total volume of the non-aqueous binder present in the region surrounded by the electrode active material covered with the non-aqueous binder, 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, wherein the electrode mixture comprises an electrode material in which the entire surface of the electrode active material is covered in a shell-like manner with a non-aqueous binder, and a conductive additive, wherein the electrode active material contained in the electrode material is dispersed in a state in which the entire surface is covered in a shell-like manner with a non-aqueous binder, and when V3 is the total volume of the region surrounded by the electrode active material covered in the non-aqueous binder, and V2 is the total volume of the non-aqueous binder present in the region surrounded by the electrode active material covered in the non-aqueous binder, V3 > V2.

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

Advantages of the Invention

[0018] According to the present invention, it is possible to provide an electrode material for a secondary battery, an electrode slurry, a method for manufacturing an electrode material, an electrode, and a method for manufacturing an electrode that suppress a decrease in electrode capacity and have excellent cycle characteristics.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram schematically showing the structure of a positive electrode material in an embodiment of the present invention. [Figure 2] It is a diagram schematically showing the structure of a positive electrode plate manufactured using a positive electrode slurry containing the positive electrode material in this embodiment. [Figure 3] It is a diagram schematically showing the structure of a positive electrode plate manufactured using a positive electrode slurry containing the positive electrode material in this embodiment. [Figure 4] It is a diagram schematically showing the structure of a positive electrode plate manufactured using a positive electrode slurry containing the positive electrode material in another embodiment of the present invention. [Figure 5] It is a diagram schematically showing Modification Example 1 of the positive electrode material. [Figure 6] It is a diagram schematically showing Modification Example 2 of the positive electrode material. [Figure 7] It is a diagram schematically showing Modification Example 3 of the positive electrode material. [Figure 8A] It is a photograph taken by SEM of the cross-section of the positive electrode plate manufactured in Example 1. [Figure 8B] It is a photograph taken by SEM of the cross-section of the positive electrode plate after staining the fluorine component in the positive electrode plate. [Figure 9A] It is a photograph taken by SEM of the cross-section of the positive electrode plate manufactured in Comparative Example 1. [Figure 9B]This is a photograph of a cross-section of a positive electrode plate taken with a scanning electron microscope (SEM) after staining the fluorine component in the positive electrode plate. [Figure 10A] This is a SEM image of the cross-section of the positive electrode plate fabricated in Example 2. [Figure 10B] This is a photograph of a cross-section of a positive electrode plate taken with a scanning electron microscope (SEM) after staining the fluorine component in the positive electrode plate. [Figure 11A] This is a SEM image of the cross-section of the positive electrode plate fabricated in Comparative Example 2. [Figure 11B] This is a photograph of a cross-section of a positive electrode plate taken with a scanning electron microscope (SEM) after staining the fluorine component in the positive electrode plate. [Figure 12A] This is a SEM image of the cross-section of the resin-embedded positive electrode plate, which was fabricated in Example 1. [Figure 12B] This photograph shows a diagram illustrating the areas in contact with the positive electrode active material within a region where the fluorine component in the positive electrode plate has been stained. [Figure 13A] This is a SEM image of the cross-section of the resin-embedded positive electrode plate, compared to the positive electrode plate fabricated in Comparative Example 1. [Figure 13B] This photograph shows a diagram illustrating the areas in contact with the positive electrode active material within a region where the fluorine component in the positive electrode plate has been stained. [Figure 14] This graph shows the measured cycle characteristics of a lithium-ion battery fabricated using the cathode material prepared in Example 1. [Figure 15] This graph shows the measured cycle characteristics of a lithium-ion battery fabricated using the cathode material prepared in Example 3. [Modes for carrying out the invention]

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

[0021] The positive electrode material in this embodiment is a positive electrode material for a secondary battery, and as shown in the schematic diagram of Figure 1, the positive electrode material 1 includes a positive electrode active material 10, and the entire surface of the positive electrode active material 10 is covered in a shell-like coating with a non-aqueous binder 20. Here, the non-aqueous binder 20 is made of a fluororesin that does not dissolve in aqueous solvents such as water, but is soluble in non-aqueous solvents such as organic solvents, and typically includes polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, etc.

[0022] The secondary batteries to which the positive electrode material in this embodiment is applied include lithium-ion secondary batteries and lithium-sulfur secondary batteries. Furthermore, the positive electrode active material is, for example, LiCoO2, LiNiO2, LiNi in the case of a lithium-ion secondary battery. 0.8 Co 0.2 This includes lithium-containing composite oxides such as O2, LiMn2O4, LiFePO4, and LiNiCoMnO2. Furthermore, it is preferable that the positive electrode active material consists of two or more positive electrode active materials with different particle sizes. The positive electrode active material with a small particle size can be formed, for example, using a flux method.

[0023] The positive electrode material 1 in this embodiment can be manufactured by the steps of dissolving the powder of a non-aqueous binder 20 in a non-aqueous solvent, dispersing the 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 with the non-aqueous binder 20 in a shell-like manner. Note that the drying of the non-aqueous solvent may be done by vacuum drying at room temperature without heating.

[0024] Here, the non-aqueous solvent consists of a material in which the powder of the non-aqueous binder 20 can be dissolved, and includes organic solvents such as N-methyl-2-pyrrolidone (NMP).

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

[0026] In this embodiment, the positive electrode slurry contains a positive electrode mixture comprising the positive electrode material 1 and a conductive additive, and the positive electrode mixture is dispersed in an aqueous solvent. The non-aqueous binder 20 coating the surface of the positive electrode active material 10 is not dissolved in the aqueous solvent.

[0027] Here, the aqueous solvent consists 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 additive is not particularly limited, but it is preferable to include cellulose nanofibers. Since the aqueous solvent has low viscosity, a positive electrode slurry of appropriate viscosity can be obtained by using cellulose nanofibers, which have high viscosity-enhancing properties, as a conductive additive.

[0028] Furthermore, the positive electrode plate in this embodiment can be manufactured by applying the above-mentioned positive electrode slurry onto a current collector and then drying the coating film. Alternatively, the coating film may be dried by heat-pressing the positive electrode slurry and the current collector using a roll press or the like.

[0029] In this embodiment, the entire surface of the positive electrode active material 10 is coated with a non-aqueous binder 20. Therefore, even when a positive electrode slurry is prepared by dispersing the positive electrode mixture containing the positive electrode material 1 and a conductive additive in an aqueous solvent, the lithium of the positive electrode active material 10 does not dissolve into the aqueous solvent. As a result, the decrease in positive electrode capacity caused by lithium dissolving into the aqueous solvent can be suppressed.

[0030] Furthermore, when a positive electrode plate is manufactured using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the non-aqueous binder 20 does not dissolve in the aqueous solvent. As shown in the schematic diagram of Figure 2, the positive electrode active material 10 is uniformly dispersed with the non-aqueous binder 20 covering its entire surface in a shell-like manner. Therefore, the non-aqueous binder 20 is also uniformly dispersed, and the positive electrode active material 10 particles themselves, as well as the positive electrode active material 10 particles and the current collector, can be uniformly bonded together with the non-aqueous binder 20 throughout the entire positive electrode. This makes it possible to realize 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 with different particle sizes, the positive electrode active material 10 is dispersed more uniformly, and the bonding between the positive electrode active material 10 and the current collector via the non-aqueous binder 20 is improved, resulting in a greater improvement in cycle characteristics.

[0032] In this embodiment, the positive electrode material 1 has a structure in which the entire surface of the positive electrode active material 10 is covered in a shell-like structure with a non-aqueous binder 20, 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 cathode slurry is prepared by dispersing a cathode mixture containing a non-aqueous binder 20 such as PVDF in an organic solvent, conductive additives such as carbon black contained in the cathode mixture do not dissolve in the organic solvent, and furthermore, the small nanometer-level pores absorb the organic solvent, resulting in a large amount of organic solvent being used.

[0034] On the other hand, although an organic solvent (non-aqueous solvent) is also used to prepare the positive electrode material 1 in this embodiment, the organic solvent only contains the positive electrode active material 10 and a non-aqueous binder 20 that dissolves in the organic solvent. Therefore, the amount of non-aqueous solvent used can be significantly reduced compared to the conventional method of preparing a positive electrode slurry by dispersing a positive electrode mixture containing a non-aqueous binder 20 such as PVDF in an organic solvent. 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 additive is dispersed in an aqueous solvent, the amount of non-aqueous solvent used when manufacturing a secondary battery can be significantly reduced.

[0035] Furthermore, in this embodiment, the positive electrode material 1 has a shell-like coating over the entire surface of the positive electrode active material 10 with a non-aqueous binder 20, which helps to suppress the decrease in positive electrode capacity and improve cycle characteristics. Therefore, in order to obtain such effects, the amount of non-aqueous binder 20 used in the manufacturing process of the positive electrode material 1 should be within a range that can coat the entire surface of the positive electrode active material 10 in a shell-like manner, depending on the amount of positive electrode active material 10. Normally, considering variations in the size of the positive electrode active material 10 and variations in the manufacturing process of the positive electrode material 1, it is sufficient to use the minimum amount of non-aqueous binder 20, including any excess.

[0036] As described above, when a positive electrode plate is manufactured using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the non-aqueous binder 20 is uniformly dispersed on the entire surface of the positive electrode active material 10, as shown in the schematic diagram of Figure 3, with the non-aqueous binder 20 covering it in a shell-like manner. In this case, since only a minimal amount of the non-aqueous binder 20 is used, the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20 contains only an excess amount of the non-aqueous binder 40, and most of the region 50 is in a void state.

[0037] Therefore, when V1 is the total volume of the non-aqueous binder 20 covering the entire surface of the positive electrode active material 10, and V2 is the total volume of the non-aqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, the relationship V1 > V2 holds true. Also, when V3 is the total volume of the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, the relationship V3 > V2 holds true.

[0038] Furthermore, the above relationship holds true when the positive electrode mixture formed on the current collector is viewed in a cross-section perpendicular to the film thickness direction. If A1 is the total area of ​​the non-aqueous binder 20 covering the entire surface of the positive electrode active material 10, and A2 is the total area of ​​the non-aqueous binder 40 in the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then A1 > A2. Also, if A3 is the total area of ​​the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then A3 > A2.

[0039] In this embodiment, the positive electrode material 1 has its entire surface of the positive electrode active material 10 coated with a non-aqueous binder 20 in a shell-like manner. This prevents the lithium of the positive electrode active material 10 from dissolving into the aqueous solvent when 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, thereby suppressing a decrease in positive electrode capacity.

[0040] Furthermore, when a positive electrode plate is manufactured using the positive electrode slurry containing the positive electrode material 1 in this embodiment, the non-aqueous binder 20 does not dissolve in the aqueous solvent. Therefore, the positive electrode active material 10 is uniformly dispersed on its entire surface, covered in a shell-like layer of the non-aqueous binder 20. As a result, the non-aqueous binder 20 is also uniformly dispersed, and the positive electrode active material 10 particles themselves, as well as the positive electrode active material 10 particles and the current collector, can be uniformly bonded together by the non-aqueous binder 20 throughout the entire positive electrode. This makes it possible to realize a secondary battery with excellent cycle characteristics.

[0041] Since this effect is obtained by coating the surface of the positive electrode active material 10 with a non-aqueous binder 20 in a shell-like manner, it is not necessarily required that the entire surface of the positive electrode active material 10 be completely coated with the non-aqueous binder 20 in a shell-like manner. This effect can also be obtained when only a part of the surface of the positive electrode active material 10 is coated with the non-aqueous binder 20 in a shell-like manner.

[0042] For example, when comparing a case in this embodiment where a positive electrode plate is made using a positive electrode slurry in which a positive electrode mixture containing a positive electrode material 1, in which a portion of the surface of the positive electrode active material 10 is coated in a shell-like manner with the non-aqueous binder 20, is dispersed in an aqueous solvent, with a case in the conventional method where a positive electrode plate is made using a positive electrode slurry in which a positive electrode mixture containing a non-aqueous binder 20 is dispersed in an organic solvent, using the same amount of non-aqueous binder 20, it was confirmed that the secondary battery made by this embodiment has superior characteristics in terms of positive electrode capacity and cycle characteristics compared to the secondary battery made by the conventional method.

[0043] A positive electrode material 1 in which a portion of the surface of the positive electrode active material 10 is covered in a shell-like manner with a non-aqueous binder 20 can be manufactured by setting the amount of non-aqueous binder 20 used in the manufacturing process of the positive electrode material 1 to a range that can cover a portion of the surface of the positive electrode active material 10 in a shell-like manner.

[0044] Furthermore, in cases where a portion of the surface of the positive electrode active material 10 is covered in a shell-like manner with a non-aqueous binder 20, 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 covered with the non-aqueous binder 20, and more preferably that 70% or more of the surface of the positive electrode active material 10 is covered with the non-aqueous binder 20.

[0045] When a positive electrode plate is fabricated using a positive electrode slurry containing such positive electrode material 1, the positive electrode active material 10 is uniformly dispersed on a portion of its surface, with a non-aqueous binder 20 covering it in a shell-like manner, as shown in the schematic diagram of Figure 4. In this case, since less non-aqueous binder 20 is used compared to when the entire surface of the positive electrode active material 10 is covered in a shell-like manner, there is almost no non-aqueous binder 40 in the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, resulting in a void state.

[0046] Therefore, similar to the case where the entire surface of the positive electrode active material 10 is covered in a shell-like manner, if V1 is the total volume of the non-aqueous binder 20 covering a portion of the surface of the positive electrode active material 10, and V2 is the total volume of the non-aqueous binder 40 present in the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then the relationship V1 > V2 holds. Also, if V3 is the total volume of the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then the relationship V3 > V2 holds.

[0047] Furthermore, the above relationship holds true when the positive electrode mixture formed on the current collector is viewed in a cross-section perpendicular to the film thickness direction. If A1 is the total area of ​​the non-aqueous binder 20 covering a portion of the surface of the positive electrode active material 10, and A2 is the total area of ​​the non-aqueous binder 40 in the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then A1 > A2. Also, if A3 is the total area of ​​the region 50 surrounded by the positive electrode active material 10 covered with the non-aqueous binder 20, then A3 > A2.

[0048] <Example of variation> In the above embodiment, the positive electrode material 1 has a structure in which the entire surface or a part of the surface of the positive electrode active material 10 is covered with a non-aqueous binder 20 in a shell-like manner. However, if the thickness of the non-aqueous binder 20 covering is too thick, the electrical resistance on the surface of the positive electrode active material 10 will increase, which may lead to a decrease in battery capacity. This modified example shows a structure of the positive electrode material 1 that can suppress the decrease in battery capacity caused by an increase in the thickness of the non-aqueous binder 20.

[0049] Figure 5 schematically shows an example of modification of the positive electrode material 1, where a portion of the surface of the positive electrode active material 10 is coated with metal oxide 30, and the non-aqueous binder 20 forms a shell-like structure that covers the entire surface of the positive electrode active material 10, overlaying the metal oxide 30. This structure suppresses the increase in electrical resistance on the surface of the positive electrode active material 10, thereby maintaining the binding effect of the non-aqueous binder 20 (improvement of cycle characteristics) while suppressing a decrease in battery capacity.

[0050] The positive electrode material 1 in this modification example 1 can be manufactured by performing a step of attaching a metal oxide 30 to a part of the surface of the positive electrode active material 10 before the step of coating the entire surface of the positive electrode active material 10 with a non-aqueous binder 20 in a shell-like manner. This makes it possible to coat the entire surface of the positive electrode active material 10 with the non-aqueous binder 20 in a shell-like manner so as to cover the metal oxide 30.

[0051] The metal oxide 30 coating 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. can be used. Furthermore, the coating of the metal oxide 30 on the surface of the positive electrode active material 10 can be carried out, for example, by mixing the positive electrode active material 10 and the metal oxide 30 and sintering or firing them.

[0052] Figure 6 schematically shows an example of deformation of the positive electrode material 1, in which the entire surface of the positive electrode active material 10 is covered in a shell-like structure with either a non-aqueous binder 20 or a metal oxide 30.

[0053] Figure 7 schematically shows an example of deformation of the positive electrode material 1, in which the entire surface of the positive electrode active material 10 is covered in a shell-like structure with 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 with the structure shown in Figures 6 and 7, although the entire surface of the positive electrode active material 10 is not coated with a non-aqueous binder 20, part or all of the surface of the positive electrode active material 10 is coated with a metal oxide 30. Therefore, it is possible to suppress the decrease in battery capacity while maintaining the binding effect of the non-aqueous binder 20.

[0055] The positive electrode material 1 with the structure shown in Figures 6 and 7 can be manufactured by the steps of: attaching a metal oxide 30 to a part or the entire surface of the positive electrode active material 10; dissolving a non-aqueous binder 20 powder in a non-aqueous solvent; dispersing the powder of the positive electrode active material 10 with the metal oxide 30 attached 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 manufacturing the positive electrode material 1 can be appropriately determined according to the amount of positive electrode active material 10, within a range that can cover part or all of the 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] <Fabrication of positive electrode material> 0.05 g of non-aqueous binder (PVDF) powder was dissolved in 0.45 g of non-aqueous solvent (NMP solvent), and 0.95 g of positive electrode active material (lithium iron phosphate (LiFePO4)) powder was dispersed in the non-aqueous solvent. Then, the non-aqueous solvent was 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 coated with a shell-like layer of non-aqueous binder.

[0059] <Fabrication of the positive electrode plate> A cathode slurry was prepared by mixing the cathode material 1 prepared by the above method, a conductive additive (containing cellulose nanofibers), and a dispersant in an aqueous solvent (pure water) in a mass ratio of 95:4:1.

[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 fabricated in the same manner as in Example 1, except that a ternary (LiNiCoMnO2) material was used for the positive electrode active material.

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

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

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

[0065] The cross-sectional images obtained by SEM were acquired by first creating a cross-section of the fabricated positive electrode plate sample using a focused ion beam (FIB), then treating the cross-section with conductivity, and finally imaging it under conditions of an acceleration voltage of 15 kV and a magnification of 2000x.

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

[0067] Specifically, when V1 is the total volume of the binder (PVDF) 20 covering the surface of the positive electrode active material 10, and V2 is the total volume of the binder (PVDF) 20 in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that V1 > V2. Furthermore, when V3 is the total volume of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that V3 > V2.

[0068] Furthermore, in the cross-section of the positive electrode mixture, when A1 is the total area of ​​the binder (PVDF) 20 covering the surface of the positive electrode active material 10, and A2 is the total area of ​​the binder (PVDF) 20 in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that A1 > A2. Also, when A3 is the total area of ​​the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that A3 > A2.

[0069] On the other hand, Figure 9A is a SEM image of the cross-section of the positive electrode plate fabricated in Comparative Example 1, and Figure 9B is an image of the cross-section of the positive electrode plate at the same position, taken using EDS (energy-dispersive X-ray spectroscopy), with the region where the fluorine component (PVDF) was detected by EDS stained and highlighted. The SEM cross-sectional images were obtained under the same conditions as in Example 1.

[0070] As shown in Figure 9B, in the positive electrode plate fabricated in Comparative Example 1, it was confirmed that the binder (PVDF) 20 was dispersed between the positive electrode active materials 10, but there were almost no areas on the surface of the positive electrode active materials 10 that were covered in a shell-like manner by the binder (PVDF). In other words, in the positive electrode plate fabricated in Comparative Example 1, it was confirmed that the binder (PVDF) was compressed into the gaps formed between the positive electrode active materials 10. That is, as in Example 1, the binder (PVDF) did not exist around the positive electrode active materials 10 in a shell-like manner with a thin film, but rather the binder (PVDF) was found to be present in a way that filled the gaps formed between the positive electrode active materials 10.

[0071] Figure 10A is a SEM image of a cross-section of the positive electrode plate fabricated in Example 2. 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. Figure 10B is an image of the cross-section of the positive electrode plate at the same location, taken using EDS (energy-dispersive X-ray spectroscopy). The region where the fluorine component (PVDF) was detected by EDS is stained and highlighted. The SEM cross-sectional image was obtained under the same conditions as in Example 1.

[0072] As shown in Figure 10B, in the positive electrode plate fabricated in Example 2, similar to Example 1, it was confirmed that many areas on the surface of the positive electrode active material 10 were covered in a shell-like structure with a non-aqueous binder (PVDF) 20. Furthermore, it was confirmed that the amount of binder (PVDF) 20 present in the gaps formed between the positive electrode active materials 10 was small.

[0073] Specifically, when V1 is the total volume of the binder (PVDF) 20 covering the surface of the positive electrode active material 10, and V2 is the total volume of the binder (PVDF) in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF), it was confirmed that V1 > V2. Furthermore, when V3 is the total volume of the region surrounded by the positive electrode active material 10 covered with the binder (PVDF), it was confirmed that V3 > V2.

[0074] Furthermore, in the cross-section of the positive electrode mixture, when A1 is the total area of ​​the binder (PVDF) 20 covering the surface of the positive electrode active material 10, and A2 is the total area of ​​the binder (PVDF) 20 in the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that A1 > A2. Also, when A3 is the total area of ​​the region surrounded by the positive electrode active material 10 covered with the binder (PVDF) 20, it was confirmed that A3 > A2.

[0075] On the other hand, Figure 11A is a SEM image of the cross-section of the positive electrode plate fabricated in Comparative Example 2, and Figure 11B is an image of the cross-section of the positive electrode plate at the same position, taken using EDS (energy-dispersive X-ray spectroscopy), with the region where the fluorine component (PVDF) was detected by EDS stained and highlighted. The SEM cross-sectional images were obtained under the same conditions as in Example 1.

[0076] As shown in Figure 11B, in the positive electrode plate fabricated in Comparative Example 2, it was confirmed that the binder (PVDF) 20 was dispersed between the positive electrode active materials 10, similar to Comparative Example 1. However, almost no areas on the surface of the positive electrode active materials 10 were found to be covered in a shell-like manner by the binder (PVDF). In other words, the comparative example 2 In the positive electrode plate fabricated using this method, it was confirmed that the binder (PVDF) was compressed into the gaps formed between the positive electrode active materials 10. In other words, unlike in Example 1, the binder (PVDF) did not exist around the positive electrode active materials 10 in a thin, shell-like manner, but rather it was confirmed that the binder (PVDF) was present in a way that filled the gaps formed between the positive electrode active materials 10.

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

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

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

[0080] Incidentally, when observing the cross-section of a positive electrode plate with an SEM, there is a risk that the binder (PVDF) located on the far side of the cross-section may also be imaged as being on the same plane as the cross-section. Therefore, to avoid such effects, after embedding the positive electrode plates prepared in Example 1 and Comparative Example 1 in resin, a cross-section of the resin-embedded positive electrode plate was prepared using the BIB (Broad Ion Beam) method, and then the conductively treated cross-section was photographed under conditions of an acceleration voltage of 15kV and a magnification of 3000x to obtain an SEM cross-sectional image.

[0081] Figure 12A is a SEM image of the cross-section of the resin-embedded positive electrode plate fabricated in Example 1, and Figure 12B is an image of the cross-section of the positive electrode plate at the same position taken with EDS (energy-dispersive X-ray spectroscopy) to detect the fluorine component (PVDF) in the positive electrode plate. The region where the fluorine component was detected by EDS was stained, and the portion 20 in contact with the positive electrode active material 10 in the stained region is shown as a line diagram.

[0082] Similarly, Figure 13A is a SEM image of a cross-section of the resin-embedded positive electrode plate fabricated in Comparative Example 1, and Figure 13B is an image of the fluorine component (PVDF) in the positive electrode plate, obtained by EDS (energy-dispersive X-ray spectroscopy) on the same cross-section of the positive electrode plate, staining the area where the fluorine component was detected by EDS, and plotting the area 20 in contact with the positive electrode active material 10 within the stained area.

[0083] Based on the SEM images of Figure 12B (Example 1) and Figure 13B (Comparative Example 1), the coverage rate 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 rate of the positive electrode plate made in Example 1 was 37%, while the coverage rate of the positive electrode plate made in Comparative Example 1 was 10%.

[0084] Furthermore, the reason why the coverage rate C of the resin-embedded positive electrode plate is smaller than that of the non-resin-embedded positive electrode plate is thought to be that when the positive electrode plate is resin-embedded, after embedding the positive electrode plate in the resin, when the resin is hardened by heating, some of the binder (PVDF), which is particularly thinly coated, peels off from the surface of the positive electrode active material 10 due to the difference in expansion rates between the positive electrode active material and the resin.

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

[0086] <Evaluation of the cycle characteristics of lithium-ion secondary batteries> An electrode body was fabricated by winding the positive electrode plate and negative electrode plate (lithium metal foil) prepared in Example 1 with a separator in between. This electrode body was then placed 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, and the change in discharge capacity [mAh / g] was measured to determine its cycle characteristics.

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

[0089] As shown in Figure 14, the cycle characteristics of the lithium-ion secondary battery made using the positive electrode material of Example 1 show that the number of cycles required for the discharge capacity to decrease to 1 / 3 of the initial capacity is approximately twice as high as that of the lithium-ion secondary battery made using the positive electrode material of Comparative Example 1. This is thought to be because the positive electrode active material 10 is uniformly dispersed with the entire surface covered in a shell-like layer of non-aqueous binder 20, resulting in uniform dispersion of the non-aqueous binder 20. Consequently, the positive electrode active material 10 particles themselves, and the positive electrode active material 10 particles and the current collector, are uniformly bonded together by the non-aqueous binder 20 throughout the entire positive electrode.

[0090] As shown in Figure 14, the initial capacity of the lithium-ion secondary battery made using the positive electrode material of Example 1 is slightly lower than the initial capacity of the lithium-ion secondary battery made using the positive electrode material of Comparative Example 1. This is thought to be because the entire surface of the positive electrode active material 10 is covered in a shell-like layer with the non-aqueous binder 20, which increases the electrical resistance on the surface of the positive electrode active material 10.

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

[0092] Subsequently, using the same method 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-like manner, covering the metal oxide, to produce a positive electrode material 1 with the structure shown in Figure 5.

[0093] <Evaluation of the cycle characteristics of lithium-ion secondary batteries> A lithium-ion secondary battery was fabricated using the cathode material 1 prepared in Example 3, in the same manner as in Example 1, and its cycle characteristics were measured.

[0094] Figure 15 is a graph showing the measurement results of the cycle characteristics. The graph indicated by arrow A shows the cycle characteristics of the lithium-ion secondary battery made using the cathode material of Example 1, the graph indicated by arrow B shows the cycle characteristics of the lithium-ion secondary battery made using the cathode material of Comparative Example 1, and the graph indicated by arrow C shows the cycle characteristics of the lithium-ion secondary battery made using the cathode material of Example 3.

[0095] As shown in Figure 15, the initial capacity of the lithium-ion secondary battery made using the positive electrode material of Example 3 is improved compared to the initial capacity of the lithium-ion secondary battery made using the positive electrode material of Example 1. This is thought to be because the increase in electrical resistance on the surface of the positive electrode active material 10 was suppressed by attaching a metal oxide 30 with low electrical resistance to the surface of the positive electrode active material 10. Furthermore, the improvement in cycle characteristics due to the shell-like coating of the non-aqueous binder 20 over the entire surface of the positive electrode active material 10 is maintained.

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

[0097] For example, in the above embodiment, a method for manufacturing the positive electrode material 1 was 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-like manner with the non-aqueous binder 20. However, the invention is not limited to this, and 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 with the powder of the finely ground 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] Furthermore, in the above embodiment, the positive electrode was described as an example of an electrode in a secondary battery, but the negative electrode could be lithium titanate (Li4Ti5O 12Even when using lithium-containing negative electrode active materials such as ) the lithium in the negative electrode active material does not dissolve into the aqueous solvent, thus suppressing a decrease in negative electrode capacity. Furthermore, even when using negative electrode active materials such as graphite or silicon in the negative electrode, the negative electrode active materials themselves, and the negative electrode active materials and the current collector, are bound together by a uniformly dispersed non-aqueous binder, thus enabling the realization of a secondary battery with excellent cycle characteristics. [Explanation of symbols]

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

Claims

1. Electrode material for secondary batteries, Contains electrode active material, A portion of the surface of the electrode active material is coated with a metal oxide. An electrode material in which the entire surface of the electrode active material is covered with a non-aqueous binder in a shell-like manner so as to cover the metal oxide.

2. Electrode material for secondary batteries, Contains electrode active material, The electrode material is characterized in that the entire surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder and a metal oxide.

3. Electrode material for secondary batteries, Contains electrode active material, The entire surface of the electrode active material is coated with a metal oxide in a shell-like manner. An electrode material in which a portion of the surface of the aforementioned metal oxide is coated with a non-aqueous binder.

4. The electrode material according to any one of claims 1 to 3, wherein the non-aqueous binder comprises a fluororesin.

5. The electrode material according to any one of claims 1 to 3, wherein the electrode active material comprises a positive electrode active material.

6. The electrode material according to any one of claims 1 to 3, wherein the electrode active material is a lithium-containing composite oxide.

7. An electrode slurry comprising an electrode mixture, The electrode mixture comprises an electrode material and a conductive additive. The electrode material contains an electrode active material, and the entire surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode mixture is an electrode slurry dispersed in an aqueous solvent.

8. An electrode slurry containing an electrode mixture, The electrode mixture comprises the electrode material according to any one of claims 1 to 3 and a conductive additive. The electrode mixture is an electrode slurry dispersed in an aqueous solvent.

9. The electrode slurry according to claim 7 or 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 7 or 8, wherein the conductive additive comprises cellulose nanofibers.

11. A method for manufacturing electrode materials for secondary batteries, A process of attaching a metal oxide to a part of the surface of the electrode active material, A step of dissolving the powder of a non-aqueous binder in a non-aqueous solvent, and dispersing the powder of the electrode active material in the non-aqueous solvent, The process involves evaporating the non-aqueous solvent to coat the entire surface of the electrode active material with the non-aqueous binder in a shell-like manner. Includes, A method for manufacturing an electrode material, wherein the entire surface of the electrode active material is coated in a shell-like manner with the non-aqueous binder so as to cover the metal oxide.

12. A method for manufacturing electrode materials for secondary batteries, A process of attaching a metal oxide to a part of the surface of the electrode active material, A step of dissolving the 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 its surface in the non-aqueous solvent, The step of evaporating the non-aqueous solvent and Includes, A method for manufacturing an electrode material, wherein, in the step of evaporating the non-aqueous solvent, the entire surface of the electrode active material is coated in a shell-like manner with the non-aqueous binder and the metal oxide.

13. A method for manufacturing electrode materials for secondary batteries, A process of depositing a metal oxide in a shell-like manner onto the entire surface of the electrode active material, A step of dissolving the powder of a non-aqueous binder in a non-aqueous solvent, and dispersing the powder of the electrode active material, on which the metal oxide is attached to the entire surface, in the non-aqueous solvent, The step of evaporating the non-aqueous solvent and Includes, A method for manufacturing an electrode material, wherein, in the step of evaporating the non-aqueous solvent, a portion of the surface of the metal oxide is coated with the non-aqueous binder.

14. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material according to any one of claims 1 to 3 and a conductive additive. The electrode active material contained in the electrode material is dispersed in a state in which its entire surface is covered in a shell-like coating of a non-aqueous binder. The total volume of the non-aqueous binder covering the entire surface of the electrode active material is V. １ V is the total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, V １ >V ２ The electrode.

15. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material according to any one of claims 1 to 3 and a conductive additive. The electrode active material contained in the electrode material is dispersed in a state in which its entire surface is coated in a shell-like manner with a non-aqueous binder. In the cross-section of the electrode mixture, the total area of ​​the non-aqueous binder covering the entire surface of the electrode active material is A. １ A is the sum of the areas of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, A １ > A ２ The electrode.

16. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material according to any one of claims 1 to 3 and a conductive additive. The electrode active material contained in the electrode material is uniformly dispersed with its entire surface covered in a shell-like coating of a non-aqueous binder. Let the total volume of the regions surrounded by the electrode active material coated with the non-aqueous binder be V ３ and let the total volume of the non-aqueous binder present in the regions surrounded by the electrode active material coated with the non-aqueous binder be V ２ When this is the case, V ３ > V ２ That is, an electrode

17. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material according to any one of claims 1 to 3 and a conductive additive. The electrode active material contained in the electrode material is uniformly dispersed with its entire surface covered in a shell-like coating of a non-aqueous binder. In the cross-section of the electrode mixture, the sum of the areas of the regions surrounded by the electrode active material coated with the non-aqueous binder is A. ３ A is the sum of the areas of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, A ３ > A ２ The electrode.

18. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material contains an electrode active material, and the entire surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which its entire surface is coated in a shell-like manner with a non-aqueous binder. An electrode in which, when V1 is the total volume of the non-aqueous binder covering the entire surface of the electrode active material, and V2 is the total volume of the non-aqueous binder in the region surrounded by the electrode active material covered with the non-aqueous binder, V1 > V2.

19. A method for manufacturing electrodes for secondary batteries, A step of forming an electrode material in which the entire surface of the electrode active material is covered in a shell-like manner with a non-aqueous binder by any one of claims 11 to 13, The process involves dispersing the electrode mixture containing the electrode material and a conductive additive in an aqueous solvent to form an electrode slurry. The process involves applying the electrode slurry onto the current collector and then drying the coating film. A method for manufacturing electrodes, including

20. An electrode slurry containing an electrode mixture, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode mixture is an electrode slurry dispersed in an aqueous solvent.

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

22. The electrode slurry according to claim 20, wherein the non-aqueous binder comprises a fluororesin.

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

24. The electrode slurry according to claim 20, wherein the non-aqueous binder coating the surface of the electrode active material is not dissolved in the aqueous solvent.

25. The electrode slurry according to claim 20, wherein the conductive additive comprises cellulose nanofibers.

26. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which a portion of its surface is covered in a shell-like structure with a non-aqueous binder. The total volume of the non-aqueous binder covering a portion of the surface of the electrode active material is V. １ V is the total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, V １ >V ２ The electrode.

27. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which a portion of its surface is covered in a shell-like structure with a non-aqueous binder. In the cross-section of the electrode mixture, the total area of ​​the non-aqueous binder covering a portion of the surface of the electrode active material is A. １ A is the sum of the areas of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, A １ > A ２ The electrode.

28. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which a portion of its surface is covered in a shell-like structure with a non-aqueous binder. The sum of the volumes of the regions surrounded by the electrode active material coated with the non-aqueous binder is V. ３ V is the total volume of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, V ３ >V ２ The electrode.

29. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which a portion of its surface is covered in a shell-like structure with a non-aqueous binder. In the cross-section of the electrode mixture, the sum of the areas of the regions surrounded by the electrode active material coated with the non-aqueous binder is A. ３ A is the sum of the areas of the non-aqueous binder present in the region surrounded by the electrode active material coated with the non-aqueous binder. ２ In that case, A ３ > A ２ The electrode.

30. An electrode for a secondary battery comprising an electrode mixture formed on a current collector, The electrode mixture comprises an electrode material and a conductive additive. The electrode material includes an electrode active material, and a portion of the surface of the electrode active material is coated in a shell-like manner with a non-aqueous binder. The electrode active material contained in the electrode material is dispersed in a state in which a portion of its surface is covered in a shell-like structure with a non-aqueous binder. An electrode in which the coverage C, defined by the following formula (1), is 30% or more in the cross-section of the electrode mixture. C=(C ２ ÷C １ )×100・・・・(1) (In equation (1), C １ This represents the circumference of the electrode active material, C ２ This represents the total length of the contact area of ​​the non-aqueous binder in contact with the surrounding electrode active material.

Images