Dry electrode mixture, electrode plate, and power storage device

Abstract

A dry electrode mixture 38 contains an electrode active material 40, a conductive material 42, and a binder 44, and has a structure in which a composite 46 of the conductive material 42 and the binder 44 covers the surface of the electrode active material 40 in a net shape. With respect to a first phase that is composed of an element derived from the electrode active material 40, an element derived from the conductive material 42, and elemental oxygen, a second phase that is composed of an element derived from the electrode active material 40, an element derived from the conductive material 42, an element derived from the binder 44, and elemental oxygen, and a third phase that is composed of an element derived from the conductive material 42, an element derived from the binder 44, and elemental oxygen, which are obtained by SEM-EDX analysis of the dry electrode mixture 38, if A is the area ratio of the third phase to the total area of the first phase, the second phase, and the third phase and B is the amount of the element derived from the binder 44 in the third phase, A × B is more than 0.25 wt%.

Description

Dry electrode mixture, electrode plate, and power storage device

[0001] The present disclosure relates to a dry electrode mixture, an electrode plate, and a power storage device.

[0002] Conventionally, a battery in which a positive electrode plate and a negative electrode plate are laminated with a separator interposed therebetween and housed in an exterior can is known (see, for example, Patent Document 1). Each electrode plate has a structure in which an electrode mixture layer is laminated on a current collector. The electrode mixture layer is composed of an electrode mixture in which an electrode active material, a conductive material, a binder, and a solvent as required are mixed.

[0003] Japanese Patent Application Laid-Open No. 2008-166030

[0004] Power storage devices including batteries are constantly required to reduce costs and increase capacity. In response to such demands, it is conceivable to replace a single-particle system electrode active material in which the particle size of the active material particles is substantially only one size with a multi-particle system electrode active material in which the particle size is two or more sizes. However, when a multi-particle system electrode active material is used, it tends to be difficult to form a conductive path composed of a conductive material and a binder on the surface of the active material particles having a small particle size. If a conductive path is not formed on the surface of the active material particles, the active material particles cannot contribute to the charge and discharge of the power storage device, which may cause a deterioration in the quality of the power storage device. Particularly in a dry electrode mixture having an extremely low solvent content, it is more difficult to form a conductive path because the binder is difficult to diffuse. Therefore, a deterioration in the quality of the power storage device is likely to occur.

[0005] The present disclosure has been made in view of such circumstances, and one of its objects is to provide a technique for suppressing a deterioration in the performance of a power storage device.

[0006] One aspect of this disclosure is a dry electrode mixture. This dry electrode mixture contains an electrode active material, a conductive material, and a binder, and has a structure in which a composite of the conductive material and the binder covers the surface of the electrode active material in a mesh-like manner. The dry electrode mixture is obtained by elemental mapping of the mixture surface by SEM-EDX analysis, and consists of a first phase composed of elements derived from the electrode active material, elements derived from the conductive material, and oxygen; a second phase composed of elements derived from the electrode active material, elements derived from the conductive material, elements derived from the binder, and oxygen; and a third phase composed of elements derived from the conductive material, elements derived from the binder, and oxygen. When the area ratio of the third phase to the total area of ​​the first, second, and third phases is A, and the amount of elements derived from the binder contained in the third phase is B, then A × B is greater than 0.25 wt%.

[0007] Another aspect of the present disclosure is an electrode plate. This electrode plate comprises a current collector and an electrode mixture layer provided on the current collector and containing the dry electrode mixture of the above aspect.

[0008] Another aspect of the present disclosure is an energy storage device, which comprises electrode plates according to the above aspect.

[0009] Any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure.

[0010] According to this disclosure, it is possible to suppress the performance degradation of energy storage devices.

[0011] This is a cross-sectional view of an energy storage device according to an embodiment. This is a perspective view of the electrode group. This is a cross-sectional view of a part of the electrode plate. This figure shows the conductive path network ratio and charge / discharge cycle maintenance rate for each embodiment and comparative example.

[0012] The present disclosure will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the present disclosure. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. Furthermore, where terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. In addition, some components that are not important for explaining the embodiments are omitted in each drawing.

[0013] Figure 1 is a cross-sectional view of the energy storage device 1 according to an embodiment. Figure 2 is a perspective view of the electrode group 2. Note that in Figures 1 and 2, the distinction between the current collector 34 and the electrode mixture layer 36 is omitted. The energy storage device 1 is, for example, a rechargeable secondary battery such as a lithium-ion battery, nickel-metal hydride battery, or nickel-cadmium battery, or a capacitor such as an electric double-layer capacitor. The energy storage device 1 comprises the electrode group 2, a first insulating plate 4, a second insulating plate 6, and an outer casing 8.

[0014] Electrode group 2 is, for example, cylindrical, and has a wound structure in which a strip-shaped first electrode plate 10 and a strip-shaped second electrode plate 12 are stacked with a strip-shaped separator 14 in between, and wound in a spiral shape. Therefore, the first electrode plate 10, the second electrode plate 12 and the separator 14 are stacked alternately in the radial direction Y of electrode group 2. In electrode group 2, the longitudinal direction of each electrode plate and separator 14 is the winding direction Z, and the short direction of each electrode plate and separator 14, in other words, the width direction, is the axial direction X. In this embodiment, the first electrode plate 10 is the positive electrode plate and the second electrode plate 12 is the negative electrode plate. However, the first electrode plate 10 may be the negative electrode plate and the second electrode plate 12 may be the positive electrode plate. Furthermore, in the following, when the polarity of the electrode plates is not distinguished, the first electrode plate 10 and the second electrode plate 12 will be collectively referred to as electrode plate 11. The separator 14 is composed of a microporous film having ion permeability and insulating properties, such as polypropylene or polyethylene.

[0015] A first lead 16 is attached to the first electrode plate 10. A second lead 18 is attached to the second electrode plate 12. Each lead is attached to the current collector 34 (see Figure 3, etc.) of each electrode plate 11 by welding or the like. The first lead 16 protrudes from one end of the electrode group 2 in the axial direction X. The second lead 18 protrudes from the other end of the electrode group 2 in the axial direction X. In this embodiment, one lead is attached to each electrode plate, but multiple leads may be attached to each electrode plate. Furthermore, the attachment positions of the leads on each electrode plate are not limited to those illustrated in Figure 2.

[0016] The first insulating plate 4 and the second insulating plate 6 are arranged so as to sandwich the electrode group 2 in the axial direction X. The electrode group 2, the first insulating plate 4, and the second insulating plate 6 are housed together with the electrolyte (not shown) in an outer container 8. The outer container 8 is a bottomed cylindrical metal container. The first insulating plate 4 is positioned on the opening side of the outer container 8. The second insulating plate 6 is positioned on the bottom side of the outer container 8. A sealing body 20 is fitted into the opening of the outer container 8. A gasket 22 is provided between the outer container 8 and the sealing body 20. This seals the electrode group 2, the first insulating plate 4, the second insulating plate 6, and the electrolyte inside the outer container 8.

[0017] The sealing body 20 includes a filter 24, a lower valve body 26, an upper valve body 28, an insulating member 30, and a cap 32. Each component of the sealing body 20 has, for example, a disc shape or a ring shape. In addition, each component except the insulating member 30 is electrically connected to one another. The filter 24 has an opening 24a and covers the opening of the outer can 8. The lower valve body 26 and the upper valve body 28 cover the opening of the outer can 8 and close the opening 24a. The lower valve body 26 and the upper valve body 28 are connected at their respective central portions, with the insulating member 30 interposed between their respective peripheral portions. When the internal pressure of the outer can 8 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 26 may rupture. As a result, the upper valve body 28 bulges towards the cap 32 and separates from the lower valve body 26. Consequently, the electrical connection between the lower valve body 26 and the upper valve body 28 is interrupted. A cap 32 is placed over the outside of the upper valve body 28.

[0018] The first lead 16 extends towards the sealing body 20 through a through hole in the first insulating plate 4. The second lead 18 extends towards the bottom of the outer can 8, passing outside the second insulating plate 6. The first lead 16 is connected to the filter 24 by welding or the like. The cap 32 is electrically connected to the filter 24 to form the first electrode terminal. The second lead 18 is connected to the bottom of the outer can 8 by welding or the like. Therefore, the outer can 8 forms the second electrode terminal.

[0019] Next, the structure of the electrode plate 11 will be described in detail. Figure 3 is a cross-sectional view of a part of the electrode plate 11. The electrode plate 11 comprises a current collector 34 and an electrode mixture layer 36. The current collector 34 is made of a strip-shaped metal foil. In the case of a typical lithium-ion secondary battery, the current collector 34 is made of aluminum foil or the like if it is the positive electrode, and copper foil or the like if it is the negative electrode.

[0020] The electrode mixture layer 36 is provided on the current collector 34. For example, the electrode mixture layer 36 is laminated on both main surfaces of the current collector 34. The electrode mixture layer 36 contains a dry electrode mixture 38. For example, the electrode mixture layer 36 is formed by pressing an electrode mixture sheet, in which the dry electrode mixture 38 is molded into a sheet, onto the surface of the current collector 34.

[0021] The dry electrode mixture 38 contains an electrode active material 40, a conductive material 42, and a binder 44. The dry electrode mixture 38 also has a structure in which a composite 46 of the conductive material 42 and binder 44 covers the surface of the electrode active material 40 in a mesh-like manner. At least a portion of the binder 44 is fibrous, and the conductive material 42 is bonded to the fibrous binder 44. As a result, a conductive fiber network, i.e., a conductive path network, composed of the composite 46 is formed on the surface of the electrode active material 40. As an example, the solvent content of the dry electrode mixture 38 is less than 5% by mass, less than 3% by mass, less than 0.1% by mass, or substantially 0% of the total mass of the dry electrode mixture 38. In other words, the solid content of the dry electrode mixture 38 is 95% or more, 97% or more, 99.9% or more, or substantially 100% of the total mass of the dry electrode mixture 38.

[0022] In the case of a typical lithium-ion secondary battery, the electrode active material is lithium nickel cobalt manganese composite oxide (NCM), lithium nickel cobalt aluminum composite oxide (NCA), lithium iron phosphate (LFP), etc. for the positive electrode, and graphite, etc. for the negative electrode. The electrode active material 40 is preferably a complex particle system such as a two-particle system, but it may also be a single-particle system. For example, the electrode active material 40 includes a first particle with a median diameter D50 of 5 μm or more and 30 μm or less, and a particle with a median diameter D50 of 1 μm or more and 8 μm or less and a different median diameter D50 from the first particle.

[0023] The conductive material 42 is carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphite, etc. The median diameter D50 of the conductive material is, for example, 10 nm to 1 μm. The binder 44 preferably contains at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber. The fluororubber is not particularly limited as long as it is a rubber containing fluorine, but examples include fluororubber such as vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), tetrafluoroethylene-purple orovinyl ether rubber (FFKM), or copolymers thereof. The median diameter D50 of the binder 44 is 100 μm to 500 μm.

[0024] The dry electrode mixture 38 is obtained by elemental mapping of the mixture surface by SEM-EDX analysis (scanning electron microscope-energy dispersive X-ray analysis) and consists of a first phase composed of elements derived from the electrode active material 40, elements derived from the conductive material 42, and oxygen; a second phase composed of elements derived from the electrode active material 40, elements derived from the conductive material 42, elements derived from the binder 44, and oxygen; and a third phase composed of elements derived from the conductive material 42, elements derived from the binder 44, and oxygen. When A is the area ratio of the third phase to the total area of ​​the first, second, and third phases, and B is the amount of elements derived from the binder 44 contained in the third phase, A × B is greater than 0.25 wt%, preferably 0.26 wt% or more. A × B represents the area ratio of the conductive path network on the surface of the dry electrode mixture 38, i.e., the conductive path network ratio.

[0025] The conductive path network ratio can be calculated using SEM-EDX (JSM7900F: manufactured by JEOL Ltd.) and the calculation software AZtec6.1 SP1 (manufactured by Oxford Corporation) installed on SEM-EDX, as follows. In the following explanation, we will use as an example the case in which the dry electrode mixture 38 contains NCM as the electrode active material 40, AB as the conductive material 42, and PTFE as the binder 44.

[0026] Specifically, elemental mapping is first performed on the dry electrode mixture 38. Maps are then created for elements derived from the electrode active material 40, elements derived from the conductive material 42, elements derived from the binder 44, and oxygen. For example, maps are created for nickel (Ni) as an element derived from the electrode active material 40, carbon (C) as an element derived from the conductive material 42 or binder 44, and fluorine (F) and oxygen (O) as elements derived from the binder 44. The EDX magnification is also adjusted to create an elemental map image with dimensions of 300 μm x 400 μm.

[0027] Next, from the obtained elemental map image, images of the first, second, and third phases are created using the calculation software AZtec6.1 SP1. In creating these images, the boundary tolerance range is set to 6 and the grouping level is set to 0 as parameter settings. The first phase is a NiCO phase composed of Ni, C, and O. Therefore, the first phase mainly corresponds to the electrode active material 40 and the conductive material 42. The second phase is a NiCFO phase composed of Ni, C, F, and O. Therefore, the second phase mainly corresponds to the conductive material 42 and binder 44 in contact with the surface of the electrode active material 40. The third phase is a CFO phase composed of C, F, and O. Therefore, the third phase mainly corresponds to the binder 44 in contact with the surface of the electrode active material 40 and the conductive material 42 in contact with the binder 44. The source of the C included in the second phase is mainly the conductive material 42 on the surface of the electrode active material 40. The carbon (C) contained in the third phase mainly comes from the conductive material 42 that is intertwined with the binder 44.

[0028] Next, the images of the three phases obtained are stacked to create a stacked image. Then, the area ratio of each phase is calculated from the number of pixels in each phase in the stacked image. This allows us to obtain the area ratio A of the third phase to the total area of ​​the first, second, and third phases.

[0029] Next, the amount B (wt%) of elements derived from the binder 44 contained in the third phase is calculated from the peak height in the EDX spectrum. For example, the amount B of element F, which is derived solely from the binder 44, is calculated. Then, the area ratio A of the third phase and the amount B of F are added together to calculate the conductive path network ratio. Preferably, the conductive path network ratio is calculated at 10 or more locations on the dry electrode mixture 38, and the average value is taken as the conductive path network ratio of the dry electrode mixture 38.

[0030] By setting the conductive path network ratio to over 0.25 wt%, conductive paths can be easily formed not only on the surface of the electrode active material 40 with large particle size, but also on the surface of the electrode active material 40 with small particle size. This improves the charge-discharge cycle characteristics of the energy storage device 1. Therefore, it is possible to suppress the performance degradation of the energy storage device 1 that may occur when a complex particle dry electrode mixture 38 is used. It is preferable that the dry electrode mixture 38 for the positive electrode satisfies the above-mentioned conductive path network ratio condition, but the dry electrode mixture 38 for the negative electrode may also satisfy this condition. Furthermore, even if the dry electrode mixture 38 is a single-particle system, the performance of the energy storage device 1 can be improved by setting the conductive path network ratio to over 0.25 wt%.

[0031] The dry electrode mixture 38 preferably contains 0.1 parts by weight or more and less than 4 parts by weight of binder 44 per 100 parts by weight of electrode active material 40. By having a binder content of 0.1 parts by weight or more, the charge and discharge performance of the energy storage device 1 can be maintained more reliably. Furthermore, by having a binder content of less than 4 parts by weight, it is possible to suppress an excessive decrease in the energy density of the energy storage device 1 due to an excess of binder 44 that does not contribute to the discharge capacity of the energy storage device 1. It is more preferable that the binder content 44 is 2 parts by weight or less per 100 parts by weight of electrode active material 40. The content of the conductive material 42 is, for example, 0.1 parts by weight or more and 4 parts by weight per 100 parts by weight of electrode active material 40.

[0032] The embodiments of this disclosure have been described in detail above. The embodiments described above are merely examples of how to implement this disclosure. The content of the embodiments does not limit the technical scope of this disclosure, and many design changes, such as changes, additions, and deletions of components, are possible as long as they do not depart from the spirit of the invention as defined in the claims. A new embodiment with design changes will have the combined effects of both the embodiment and the variation. In the embodiments described above, the content in which such design changes are possible is emphasized with notations such as "of this embodiment" or "in this embodiment," but design changes are also permitted even if there are no such notations. Furthermore, any combination of components included in each embodiment is also valid as an embodiment of this disclosure. The hatching applied to the cross-section in the drawings does not limit the material of the object to which the hatching is applied.

[0033] The structure of the energy storage device 1 can be modified as appropriate. For example, the energy storage device 1 is not limited to a cylindrical battery, but may be a rectangular battery with a rectangular metal case, a laminated battery with a resin casing, etc. Alternatively, two current collector plates may be provided instead of the first insulating plate 4 and the second insulating plate 6, with the current collector 34 of the first electrode plate 10 joined to one current collector plate and the current collector 34 of the second electrode plate 12 joined to the other current collector plate.

[0034] The embodiments may be specified by the items described below. [Item 1] The mixture contains an electrode active material (40), a conductive material (42), and a binder (44), and has a structure in which a composite (46) of the conductive material (42) and binder (44) covers the surface of the electrode active material (40) in a mesh-like manner, and the first phase, obtained by elemental mapping of the surface of the mixture by SEM-EDX analysis, consists of elements derived from the electrode active material (40), elements derived from the conductive material (42), and oxygen; the second phase consists of elements derived from the electrode active material (40), elements derived from the conductive material (42), elements derived from the binder (44), and oxygen; and the third phase consists of elements derived from the conductive material (42), elements derived from the binder (44), and oxygen. When the area ratio of the third phase to the total area of ​​the first, second, and third phases is A, and the amount of elements derived from the binder (44) contained in the third phase is B, then A × B is greater than 0.25 wt%. Dry electrode mixture (38). [Item 2] The dry electrode mixture (38) of Item 1, containing 0.1 parts by weight or more and less than 4 parts by weight of binder (44) per 100 parts by weight of electrode active material (40). [Item 3] The dry electrode mixture (38) of Item 1 or Item 2, wherein the binder (44) comprises at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and fluororubber. [Item 4] Electrode plate (11) comprising a current collector (34) and an electrode mixture layer (36) provided on the current collector (34) and containing any of the dry electrode mixtures (38) of Items 1 to 3. [Item 5] Energy storage device (1) comprising the electrode plate (11) of Item 4.

[0035] The following describes embodiments of the present invention, but these embodiments are merely illustrative examples for suitably illustrating the present invention and do not limit the present invention in any way.

[0036] (Example 1) Using a pulverizer (NOB300 - Novilta®: manufactured by Hosokawa Micron Corporation), NCM as an electrode active material, AB as a conductive material (manufactured by Denka Corporation), and PTFE powder (TE5448: manufactured by Mitsui Chemours Fluoroproducts Corporation) as a binder were mixed for 5 minutes. The amounts of conductive material and binder added were 0.6 parts by weight and 1 part by weight, respectively, per 100 parts by weight of electrode active material. The obtained mixture was put into a roll kneader (heating stretcher: manufactured by Imoto Seisakusho Co., Ltd.) and passed through the roll kneader once to obtain the dry cathode mixture according to Example 1. The obtained dry cathode mixture had a solid content concentration of 100%.

[0037] The obtained dry positive electrode mixture was passed between a pair of forming rolls and rolled to produce a positive electrode mixture sheet. The thickness of the positive electrode mixture sheet was approximately 100 μm. The obtained positive electrode mixture sheet was laminated onto an aluminum alloy foil to be used as a positive electrode current collector, and the positive electrode mixture sheet and the positive electrode current collector were pressed together by passing them between a pair of rolling rolls. This resulted in a positive electrode plate in which a positive electrode mixture layer was laminated onto the current collector. A negative electrode active material mixture electrode was also prepared as a negative electrode plate. Aluminum leads were attached to the positive electrode plate, and nickel leads were attached to the negative electrode plate.

[0038] An electrode body was fabricated by sandwiching a polyolefin separator between a positive electrode plate and a negative electrode plate, and then winding this laminate in a spiral shape. After housing this electrode body and a non-aqueous electrolyte inside an outer casing, the opening of the outer casing was sealed to obtain the test cell according to Example 1. The non-aqueous electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:3 as a non-aqueous solvent, and adding LiPF as the electrolyte salt. ６ A solution prepared by dissolving the substance in 1.0 mol / L was used.

[0039] The positive electrode mixture layer of the test cell according to Example 1 was subjected to the SEM-EDX analysis described in the embodiment, and the conductive path network ratio was calculated. The test cell was then charged at a constant current of 0.5C at a temperature of 25°C until the cell voltage reached 4.2V, and then charged again at a constant voltage until the current was 1 / 50C at 4.2V. Afterward, it was discharged at a constant current of 0.5C until the cell voltage reached 2.5V. The discharge capacity at this time was defined as the initial discharge capacity. This charge-discharge cycle was repeated 100 times, and the discharge capacity was measured again. The ratio of the discharge capacity after 100 cycles to the initial discharge capacity was calculated as the charge-discharge cycle maintenance rate. The results are shown in Figure 4.

[0040] (Example 2) A test cell was prepared in the same manner as in Example 1, except that the amount of binder added was 0.75 parts by weight and the number of times it was passed through the roll kneader was 3. The conductive path network ratio and charge / discharge cycle maintenance rate were then calculated. The results are shown in Figure 4.

[0041] (Example 3) A test cell was prepared in the same manner as in Example 1, except that PTFE powder (F106: manufactured by Daikin Industries, Ltd.) was used as the binder and the amount of binder added was 0.75 parts by weight. The conductive path network ratio and charge / discharge cycle maintenance rate were calculated. The results are shown in Figure 4.

[0042] (Comparative Example 1) A test cell was prepared in the same manner as in Example 1, except that the amount of binder added was 0.75 parts by weight and the mixture was not kneaded in a roll kneader. The conductive path network ratio and charge / discharge cycle maintenance rate were then calculated. The results are shown in Figure 4.

[0043] FIG. 4 is a diagram showing the conductive path network ratio and the charge-discharge cycle maintenance rate of each example and comparative example. As shown in FIG. 4, in Examples 1 to 3 where the conductive path network ratio is more than 0.25 wt%, the charge-discharge cycle maintenance rate was higher than that of Comparative Example 1 where the conductive path network ratio is 0.25 wt%. From this, it was confirmed that by setting the conductive path network ratio to more than 0.25 wt%, preferably 0.26 wt% or more, the charge-discharge cycle maintenance rate can be increased, and thus the performance degradation of the power storage device 1 can be suppressed. Also, it was confirmed that by setting the conductive path network ratio to more than 0.31 wt%, and further 0.45 wt% or more, the charge-discharge cycle maintenance rate can be further increased.

[0044] From the comparison between Example 1 and Comparative Example 1, it can be seen that if the difference in the addition amount of the conductive material is about 0.15 parts by weight, the presence or absence of roll kneading has a greater impact on the conductive path network ratio and the charge-discharge cycle maintenance rate than the difference in the addition amount. Also, from the comparison between Example 3 and Comparative Example 1, it can be seen that even when the types of binders are different, the conductive path network ratio and the charge-discharge cycle maintenance rate can be increased by performing roll kneading.

[0045] The present disclosure can be used for dry electrode binders, electrode plates, and power storage devices.

[0046] 1 Power storage device, 11 Electrode plate, 34 Current collector, 36 Electrode binder layer, 38 Dry electrode binder, 40 Electrode active material, 42 Conductive material, 44 Binder, 46 Composite.

Claims

1. A dry electrode mixture comprising an electrode active material, a conductive material, and a binder, wherein the surface of the electrode active material is covered in a mesh-like structure by a composite of the conductive material and the binder, and elemental mapping of the mixture surface by SEM-EDX analysis reveals a first phase composed of elements derived from the electrode active material, elements derived from the conductive material, and oxygen; a second phase composed of elements derived from the electrode active material, elements derived from the conductive material, elements derived from the binder, and oxygen; and a third phase composed of elements derived from the conductive material, elements derived from the binder, and oxygen, wherein when the area ratio of the third phase to the total area of ​​the first, second, and third phases is A, and the amount of elements derived from the binder contained in the third phase is B, then A × B is greater than 0.25 wt%.

2. The dry electrode mixture according to claim 1, wherein the binder is contained in an amount of 0.1 parts by weight or more and less than 4 parts by weight per 100 parts by weight of the electrode active material.

3. The dry electrode mixture according to claim 1 or 2, wherein the binder comprises at least one selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and fluorinated rubber.

4. An electrode plate comprising a current collector and an electrode mixture layer provided on the current collector and containing the dry electrode mixture described in claim 1 or 2.

5. An energy storage device comprising the electrode plate described in claim 4.

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