Electrode evaluation method and electrode manufacturing method

Abstract

To improve the accuracy of measuring the overall coating state of coated active material particles including active material particles and a coating layer covering the surface of the active material particles.SOLUTION: There is provided a method for evaluating the coating state of coated active material particles including active material particles, and a coating layer that covers the surface of the active material particles. The method includes the steps of: obtaining a SEM image of the coated active material particles while applying negative voltage to the coated active material particles (retarding mode); and detecting the presence or absence of the coating layer on the surface of the active material particles on the basis of the contrast in the SEM image thereby evaluating the coating state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to methods for evaluating and producing coated active material particles, and methods for producing electrodes. [Background technology]

[0002] As an active material used in the production of batteries such as all-solid-state secondary batteries and liquid secondary batteries, coated active material particles formed by providing a coating layer on the surface of active material particles (positive electrode active material particles or negative electrode active material particles) are known.

[0003] There are known methods for measuring the surface coating state (coating rate) of such coated active material particles by image analysis of TEM (transmission electron microscope) images, XPS (X-ray photoelectric spectroscopy) analysis, and the like.

[0004] However, image analysis of TEM images is a localized observation (for example, an area smaller than 1 μm square), and therefore it is not possible to measure the coating state of coated active material particles in the entire electrode (electrode composite layer) composed of a large number of coated active material particles.

[0005] Furthermore, XPS analysis measures the average composition from the surface to a depth of 3 to 10 nm. Therefore, even if there are uncoated areas of the active material particles, if a thick coating layer is present in some areas, the active material particles as a whole are considered to be coated. This makes it difficult to accurately measure the coating state of the coated active material particles. For example, XPS analysis cannot distinguish between the coating states on the left and right sides of Figures 7(a) and (b).

[0006] As described above, conventionally, the coating state has been measured based on local information (TEM) or average information (XPS), and therefore the coating state of the active material particles has not been accurately understood.

[0007] Furthermore, Japanese Patent Laid-Open Publication No. 2018-206619 (Patent Document 1) discloses a method for measuring the coating state (coating rate) of coated active material particles using image analysis of low-acceleration SEM images. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-206619 Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method of Patent Document 1, by lowering the acceleration voltage of primary electrons during SEM observation, it becomes difficult for the primary electrons to penetrate into the interior of the coated active material particles, and therefore an SEM image that reflects detailed information about the surface of the coated active material particles can be obtained.

[0010] However, the present inventors have found that even when image analysis of low-acceleration SEM images is used as in Patent Document 1, it may be difficult to measure the coating state depending on the materials of the positive electrode active material and the coating layer, the thickness of the coating layer, etc. Specifically, for example, when the atomic numbers of the elements contained in the constituent materials of the positive electrode active material and the coating layer are relatively close, or when the thickness of the coating layer is extremely thin, it is difficult to accurately measure the coating state by image analysis of low-acceleration SEM images.

[0011] An object of the present disclosure is to improve the accuracy of measuring the overall coating state of coated active material particles that include active material particles and a coating layer that coats the surfaces of the active material particles. [Means for solving the problem]

[0012] (1) A method for evaluating a coating state of coated active material particles, the coated active material particles having active material particles and a coating layer covering the surfaces of the active material particles, comprising: An evaluation method comprising: obtaining an SEM image of the coated active material particle while applying a negative voltage to the coated active material particle (retarding mode); detecting the presence or absence of the coating layer on the surface of the active material particle based on the contrast in the SEM image; and evaluating the coating state.

[0013] According to the evaluation method (1) above, by performing SEM observation in retarding mode, it is not necessary to reduce the amount of primary electrons irradiated onto the coated active material particles in order to obtain precise information about the surfaces of the coated active material particles by lowering the voltage (irradiation voltage) of the primary electrons irradiated onto the coated active material particles (see FIG. 5). Therefore, precise information about the surfaces of the coated active material particles can be obtained with high sensitivity. Therefore, it is possible to improve the measurement accuracy of the overall coating state of coated active material particles, which include active material particles and a coating layer that coats the surfaces of the active material particles.

[0014] (2) The evaluation method according to (1), wherein the irradiation voltage of the primary electrons when acquiring the SEM image is 0.1 to 1.0 kV.

[0015] According to the evaluation method (2) above, the accuracy of measuring the overall coating state of the coated active material particles can be improved more reliably.

[0016] (3) The evaluation method according to (1) or (2), wherein the coating layer contains a conductive material.

[0017] According to the evaluation method (3) above, the accuracy of measuring the overall coating state of the coated active material particles can be improved more reliably.

[0018] (4) A method for producing coated active material particles having active material particles and a coating layer that coats at least a portion of the surface of the active material particles, the method comprising: a coating step of forming a coating layer on the surface of the active material particles to obtain the coated active material particles; an evaluation step of evaluating the coating state of the coated active material particles obtained in the coating step using the evaluation method according to any one of (1) to (3); A method for producing coated active material particles, comprising:

[0019] According to the manufacturing method of coated active material particles described above in (4), the measurement accuracy of the overall coating state of the coated active material particles can be improved, and therefore, coated active material particles with a good coating state can be obtained by using the information on the evaluation results of the coating state.

[0020] (5) A method for producing an electrode having an electrode mixture layer containing coated active material particles having active material particles and a coating layer that coats at least a portion of the surface of the active material particles, the method comprising: forming the electrode mixture layer containing the coated active material particles; an evaluation step of evaluating the coating state of the coated active material particles contained in the electrode mixture layer using the evaluation method according to any one of (1) to (3); A method for manufacturing an electrode, comprising:

[0021] According to the electrode manufacturing method (5) above, the accuracy of measuring the overall coating state of the coated active material particles can be improved, and therefore, by using the information on the evaluation results of the coating state, it is possible to obtain an electrode with a good coating state of the coated active material particles. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a diagram showing an SEM image obtained in Example 1. [Figure 2] FIG. 2 is a partially enlarged view of an SEM image obtained in Example 1. [Figure 3] FIG. 1 is a diagram showing an SEM image obtained in Comparative Example 1. [Figure 4] FIG. 3 is a diagram showing EDS qualitative analysis charts for the active material particles (B) with a high coverage and the active material particles (A) with a low coverage shown in FIG. 2. [Figure 5] FIG. 2 is a schematic diagram for explaining an evaluation method (method using a retarding mode low-acceleration SEM image) according to an embodiment. [Figure 6] FIG. 1 is a schematic diagram for explaining a conventional evaluation method (a method using a low-acceleration SEM image in normal mode). [Figure 7] FIG. 1 is a schematic diagram for explaining the problems of the conventional evaluation method (XPS). DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present disclosure will be described. However, the present disclosure is not limited thereto. In this specification, the "positive electrode" and the "negative electrode" will be collectively referred to as "electrodes."

[0024] <Method for evaluating coated active material particles> In the method for evaluating coated active material particles of this embodiment, a SEM (scanning electron microscope) image of the coated active material particles is obtained while a negative voltage (retarding voltage) is applied to the coated active material particles (retarding mode), and the presence or absence of a coating layer on the surface of the active material particles is detected based on the contrast in the SEM image, and the coating state is evaluated.

[0025] The coated active material particles include active material particles and a coating layer that coats the surfaces of the active material particles. The active material particles are, for example, positive electrode active material particles or negative electrode active material particles for a battery.

[0026] When the active material particles are positive electrode active material particles, the positive electrode active material particles are, for example, lithium cobalt oxide, lithium nickel oxide (NCA), lithium manganate, lithium nickel cobalt manganate, etc. (e.g., Li 1.15 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc.), lithium nickel cobalt aluminate, and lithium iron phosphate.

[0027] The coating layer preferably contains a conductive material. In this case, the measurement accuracy of the overall coating state of the coated active material particles can be more reliably improved. This is because the inclusion of a conductive material (i.e., a material that can use a potential difference as an indicator) makes it possible to evaluate the coating state based on the contrast difference in an SEM image caused by the potential difference. The conductive material is not particularly limited, but examples thereof include Nb.

[0028] The coating layer may contain, for example, a Li-ion conductive oxide such as lithium niobate (LiNbO). The coating layer may also function as a buffer layer in an electrode of an all-solid-state battery to mitigate volume changes due to expansion and contraction of the active material particles and solid electrolyte particles.

[0029] The coated active material particles can be prepared by coating active material particles with a coating layer by any of various known coating methods.

[0030] The SEM used in this embodiment is not particularly limited, and may be, for example, an SEM using a thermionic electron emission electron gun or an SEM using a field emission electron gun (FE-SEM: field emission scanning electron microscope). When an FE-SEM is used, the coating state of the active material particles can be evaluated more precisely.

[0031] "Retarding mode" is a mode in which a negative voltage (retarding voltage) is applied to the sample (coated active material particles) to be observed, thereby decelerating the primary electron beam just before the sample. The method of acquiring SEM images in "retarding mode" is also called the retarding method (deceleration method). In the retarding method, the electron beam (primary electrons) accelerated by the electron gun is decelerated by an electrostatic solution (deceleration electrolysis) just before the sample (for example, between the sample and the beam column) (see Figure 5).

[0032] When performing SEM observations in normal mode using a low acceleration voltage, lowering the acceleration voltage of the primary electrons (i.e., the irradiation voltage) reduces the amount of primary electrons, resulting in a decrease in sensitivity (see Figure 6). In contrast, the retarding method decelerates the primary electron beam just before the sample to lower the irradiation voltage, eliminating the need to lower the acceleration voltage of the primary electrons and allowing the amount of primary electron irradiation to be maintained (see Figure 5). As a result, the retarding method makes it possible to detect precise information about the surface of the sample (coated active material particles) without reducing sensitivity.

[0033] The coating layer provided on active material particles (such as positive electrode active material particles) for batteries is required to be thin (for example, 10 nm in average thickness). In the case of liquid-based batteries, a coating layer of relatively uniform thickness is created by adding an additive to the electrolyte solution during charging and discharging. However, in the case of all-solid-state batteries, the coating is applied directly to the active material particles, making it difficult to maintain a uniform coating state. For this reason, it is desirable to evaluate (inspect) the coating state, especially for coated active material particles for all-solid-state batteries.

[0034] In order to obtain accurate information about the coating state of such a thin coating layer, even low-acceleration SEM observation under normal SEM observation conditions would result in picking up too much information about the active material particles inside the coated active material particles, making it impossible to obtain accurate information about the coating state. Therefore, the evaluation method of this embodiment is particularly useful for obtaining accurate information about the coating state of such a thin coating layer.

[0035] Furthermore, in SEM images obtained using the retarding method, a negative voltage is applied to the sample stage, resulting in a larger contrast difference due to the potential difference of the target sample compared to the normal mode. Therefore, even if the atomic numbers of the elements constituting the coating layer of the coated active material particles are relatively close to the atomic numbers of the elements constituting the positive electrode active material particles, the contrast difference between the coated and uncoated portions can be distinguished based on the potential difference between the coating layer and the positive electrode active material particles. Thus, in this embodiment, it is preferable to evaluate the coating state of the coated active material particles based on the contrast difference resulting from the potential difference.

[0036] In addition, the evaluation method of the present disclosure has the advantage that, since it is possible to obtain information relating to differences in potential (conductivity) in this way, it is also possible to obtain information relating to battery performance relating to conductivity, such as battery resistance.

[0037] In the evaluation method of this embodiment, for example, the coating state of each coated active material particle can be evaluated based on an evaluation criterion in which a measured coating rate equal to or greater than a predetermined threshold is deemed "good coating," and a measured coating rate less than the threshold is deemed "poor coating."

[0038] Furthermore, for example, whether an electrode is good or not can be determined based on the proportion of active material particles with a high coverage (good coverage) in the electrode mixture layer that constitutes the electrode.

[0039] The irradiation voltage (accelerating voltage and retarding voltage) of the primary electrons when obtaining an SEM image is preferably adjusted so that the contrast difference between the active material particles and the coating layer is sufficiently large. Although this varies depending on the type of active material particles and coating layer, the irradiation voltage is preferably 0.1 to 1.0 kV, and more preferably 0.2 to 0.5 kV. If the irradiation voltage is higher than this, not only surface information but also internal information of the coated active material particles will be picked up, reducing the contrast difference between the coated and uncoated portions and making it difficult to accurately measure the coating state. If the irradiation voltage is lower than this, the number of primary electrons irradiated onto the coated active material particles will decrease, and the number of detected secondary electrons will also decrease, resulting in a decrease in measurement sensitivity.

[0040] The irradiation voltage is basically "(primary electron acceleration voltage) - (retarding voltage)", and the irradiation voltage can be adjusted by controlling the primary electron acceleration voltage and retarding voltage.

[0041] The acceleration voltage is not particularly limited, but is preferably 2 kV or less in order to prevent damage to the sample (coated active material particles).

[0042] The retarding voltage is, for example, 1.9 kV or less.

[0043] FIG. 4 shows EDS qualitative analysis charts for the high-coverage active material particles (B) and the low-coverage active material particles (A) shown in FIG. 2. In FIG. 4, the chart for the low-coverage active material particles (A) (white active material particles) shows a peak derived from NCA (Ni, Co), the active material particle material. On the other hand, the chart for the high-coverage active material particles (B) (black active material particles) shows a peak derived from Nb contained in the coating layer. This shows that, in this embodiment, the evaluation results of the coating state of the active material particles based on the contrast of the SEM image are consistent with the results of elemental analysis by EDS.

[0044] In principle, it is also possible to evaluate the coating state of coated active material particles by combining SEM observation with energy dispersive X-ray spectroscopy (EDS, EDX, XEDS, etc.). This method utilizes elemental analysis results obtained using EDS or other methods. However, obtaining information on the outermost surface of coated active material particles using EDS or other methods to obtain an elemental mapping image typically takes more than an hour for just one field of view. Furthermore, obtaining comprehensive information on raw material powders or electrodes made of coated active material particles requires measuring multiple fields of view, which requires an extremely long measurement time. Therefore, it is not realistic to evaluate the coating state of coated active material particles using this method. While it is possible to analyze only one specific point per particle, obtaining comprehensive information on electrodes, etc. requires measuring a large number of particles, which also requires an extremely long measurement time.

[0045] In contrast, the evaluation method of the coated active material particles of the present embodiment is simple and requires a short observation time, and therefore the coating state of the active material particles can be quickly evaluated. Therefore, by using the evaluation method of the present embodiment, it is possible to easily evaluate (inspect) the quality of the coating state of the active material particles, for example, for coated active material particles used as a raw material for an electrode or for an electrode (electrode mixture layer) manufactured using the coated active material particles.

[0046] <Method of manufacturing coated active material particles>

[0047] In the method for producing coated active material particles of this embodiment, coated active material particles are produced that have active material particles and a coating layer that covers at least a portion of the surface of the active material particles.

[0048] The method for producing coated active material particles of the present embodiment includes at least a coating step of forming a coating layer on the surface of the active material particles to obtain coated active material particles; and an evaluation step of evaluating the coating state of the coated active material particles obtained in the coating step using the above evaluation method.

[0049] According to the method for manufacturing coated active material particles of this embodiment, the above-mentioned evaluation method can improve the measurement accuracy of the overall coating state of the coated active material particles, and therefore, using the information from the evaluation results of the coating state, it is possible to obtain coated active material particles with a good coating state.

[0050] The method for producing coated active material particles of this embodiment may include, for example, a sorting step of excluding powder raw material composed of coated active material particles, powder raw material having a ratio of coated active material particles evaluated as having a poor coating state by the above-mentioned evaluation method that is higher than a predetermined threshold value. By such a step, it is possible to provide a powder raw material having a good coating state of coated active material particles.

[0051] Furthermore, for example, the evaluation results may be fed back to adjust the manufacturing conditions for the coated active material particles so as to reduce the proportion of coated active material particles that are evaluated as having a poor coating state, thereby obtaining raw material powder in which the coated active material particles have a good coating state.

[0052] <Electrode manufacturing method> The electrode manufacturing method of this embodiment produces an electrode having an electrode mixture layer containing coated active material particles. The coated active material particles have active material particles and a coating layer that coats at least a portion of the surface of the active material particles, as described above.

[0053] The method for manufacturing an electrode according to the present embodiment includes at least: forming an electrode mixture layer containing coated active material particles; and an evaluation step of evaluating the coating state of the coated active material particles contained in the electrode mixture layer using the above evaluation method.

[0054] According to the electrode manufacturing method of this embodiment, the above-mentioned evaluation method can improve the measurement accuracy of the overall coating state of the coated active material particles, and therefore, by using the information from the evaluation results of the coating state, it is possible to obtain an electrode with a good coating state of the coated active material particles.

[0055] In the evaluation step, the coating state of the coated active material particles contained in the electrode mixture layer is evaluated, for example, by performing image analysis of an SEM image of the surface of the electrode mixture layer.

[0056] The electrode manufacturing method of the present embodiment may include, for example, a selection step of excluding electrodes in which the ratio of coated active material particles evaluated as having a poor coating state by the above-mentioned evaluation method is greater than a predetermined threshold value. By such a step, an electrode in which the coated active material particles have a good coating state can be obtained.

[0057] Furthermore, for example, an electrode having a good coating state of coated active material particles may be obtained by feeding back the evaluation results and adjusting the manufacturing conditions of the coated active material particles so as to reduce the proportion of coated active material particles evaluated as having a poor coating state.

[0058] According to the above-described methods for manufacturing coated active material particles and electrodes, it is possible to easily obtain good electrodes (electrodes with good coating conditions of coated active material particles) based on the evaluation results of the state of the coated active material particles and electrodes, without conducting evaluation tests on the final battery produced.

[0059] In this embodiment, the electrode may be a positive electrode or a negative electrode.

[0060] The electrode is, for example, a positive electrode including a positive electrode current collector foil and a positive electrode mixture layer. The positive electrode current collector foil may be, for example, an aluminum (Al) foil.

[0061] The positive electrode mixture layer includes at least a positive electrode active material. For example, the positive electrode mixture layer may consist essentially of the positive electrode active material. In addition to the positive electrode active material, the positive electrode mixture layer may also include, for example, a conductive material, a binder, and the like.

[0062] The positive electrode active material contains the coated active material particles described above.

[0063] The conductive material may include, for example, a conductive carbon material (eg, vapor grown carbon fiber (VGCF)). The binder may include, for example, polyvinylidene fluoride (PVdF).

[0064] The electrode is, for example, a negative electrode including a negative electrode current collector foil and a negative electrode mixture layer. The negative electrode current collector foil may be, for example, a copper (Cu) foil, a nickel (Ni) foil, or the like.

[0065] The negative electrode mixture layer includes at least a negative electrode active material. For example, the negative electrode mixture layer may consist essentially of the negative electrode active material. In addition to the negative electrode active material, the negative electrode mixture layer may also include, for example, a conductive material, a binder, and the like.

[0066] Examples of the negative electrode active material include graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloys, tin, tin oxide, tin-based alloys, and lithium titanate (Li4Ti5O 12 ) may contain at least one selected from the group consisting of

[0067] The coated active material particles and electrodes obtained by the manufacturing method of the present disclosure can be used in secondary batteries such as lithium ion secondary batteries (nonaqueous electrolyte secondary batteries) and all-solid-state secondary batteries. Secondary batteries can be used as power sources for electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like. However, the coated active material particles and electrodes obtained by the manufacturing method of the present disclosure are not limited to such in-vehicle applications and can be used in a variety of applications. [Example]

[0068] Hereinafter, the present embodiment will be described using examples, but the present embodiment is not limited thereto.

[0069] <Preparation of Coated Active Material Particles> Coated active material particles were prepared by coating cathode active material particles composed of an NCA (lithium nickelate) - based cathode active material with a coating layer containing Nb (a coating layer composed of LiNbO₃). The target value for the thickness of the coating layer was 10 nm. Note that for the coating layer of the coated active material particles used in all - solid - state batteries, it is better for the thickness to be thinner and the coating rate to be closer to 100%.

[0070] <Fabrication of Cathode> A cathode slurry was prepared by stirring a cathode active material coated with LiNbO₃, a sulfide - based solid electrolyte, carbon fibers by vapor - phase growth method, a PVdF (polyvinylidene fluoride) - based binder, and a cathode mixture containing butyl butyrate using an ultrasonic disperser. Here, the weight ratio of the NCA - based cathode active material:sulfide - based solid electrolyte:carbon fibers by vapor - phase growth method:PVdF - based binder was 88.2:9.8:1.3:0.7.

[0071] This cathode slurry was applied onto a cathode current collector foil (Al foil) by the blade method, and the applied cathode slurry was dried on a hot plate at 100 °C for 30 minutes. Thereby, a cathode in which a cathode mixture layer was formed on the cathode current collector foil was obtained.

[0072] <SEM Observation> (Example 1) Regarding the cathode (cathode mixture layer with cathode current collector foil) obtained above, from the side opposite to the cathode current collector foil, an SEM image of the cathode mixture layer was acquired using FE - SEM (manufactured by Hitachi High - Tech Corporation: SU8000) under the following observation conditions.

[0073] (Observation Conditions) Irradiation voltage: 0.2 kV (retarding mode) Acceleration voltage: 1.7kV Retarding voltage: 1.5 kV

[0074] (Image analysis of SEM images) Of the 256 gradations in a particle image at a 2500x magnification (0.2 μm × 0.2 μm), the presence or absence of a coating layer was determined by gradation numbers 160 to 255 being white (no coating layer) and gradation numbers less than 160 being black (coating layer present).

[0075] 1 shows an SEM image obtained in Example 1. FIG. 2 shows a partially enlarged view of the SEM image obtained in Example 1.

[0076] From the SEM images shown in Figures 1 and 2, it can be seen that there is a large difference in contrast between the coated portion (coating layer) and the uncoated portion (active material particles), and that the two can be distinguished by image analysis of the SEM images.

[0077] In the 2500x magnification field shown in Figure 1, the total number of active material particles was 43, and the number of low-coverage active material particles (white active material particles) was 3. From this, the proportion of high-coverage active material particles (black active material particles) to the total number of active material particles was calculated to be 93%.

[0078] By calculating the proportion of active material particles with a high coverage in this way, it is possible to evaluate the quality of the coating state of the active material particles, for example, for a raw material powder of coated active material particles or an electrode (electrode mixture layer) made using the same, based on that proportion. Note that when determining the proportion of active material particles with such a high coverage, it is preferable to calculate the proportion from the average value of five or more fields of view, for example.

[0079] (Comparative Example 1) SEM observation was performed in normal mode (backscattered electron image) (without using retarding mode). Except for this, SEM observation was performed on the positive electrode obtained above in the same manner as in Example 1. The SEM image obtained in Comparative Example 1 is shown in FIG.

[0080] The SEM image shown in FIG. 3 shows that the difference in contrast between the coated portion (coating layer) and the uncoated portion (active material particles) is small, making it difficult to distinguish between the two by image analysis of the SEM image.

[0081] In the coated active material particles observed by SEM, the atomic number of Nb contained in the coating layer is relatively close to the atomic number of the elements constituting the positive electrode active material particles made of an NCA-based positive electrode active material. In SEM images obtained in normal mode, the difference in atomic numbers of the elements constituting the target sample has a significant effect on the contrast, and this is thought to be why the difference in contrast between the coated and uncoated portions is small in the SEM image of Comparative Example 1.

[0082] In contrast, when SEM observation is performed in retarding mode as in Example 1, the difference in potential of the target sample has a significant effect on the contrast. In the coated active material particles described above, the atomic numbers of the elements constituting the coating layer and the elements constituting the positive electrode active material particles are relatively close, but the difference in potential between the coating layer and the positive electrode active material particles is relatively large. This is thought to be why the difference in contrast between the coated and uncoated portions in the SEM image of Example 1 is relatively large.

[0083] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is not limited to the above description, but is defined by the claims. It is therefore intended to include all modifications that come within the meaning and scope of equivalency of the appended claims.

Claims

1. A method for evaluating an electrode, comprising: the electrode includes an electrode mixture layer; the electrode mixture layer contains coated active material particles, the coated active material particles include active material particles and a coating layer that coats the surfaces of the active material particles, the active material particles are made of an NCA-based positive electrode active material, the coating layer is made of LiNbO 3 ; The evaluation method includes: obtaining an SEM image of the electrode mixture layer containing the coated active material particles by a retarding method; distinguishing the coated active material particles into coated active material particles with a high coverage rate and coated active material particles with a low coverage rate based on the contrast of the coated active material particles in the SEM image; and determining whether the electrode is good or bad based on the proportion of the coated active material particles with a high coverage in the electrode mixture layer; Including, Electrode evaluation methods.

2. 2. The evaluation method according to claim 1, wherein the irradiation voltage of the primary electrons when acquiring the SEM image is 0.1 to 1.0 kV.

3. The evaluation method according to claim 1 , wherein the coating layer includes a conductive material.

4. A method for manufacturing an electrode including an electrode mixture layer containing coated active material particles having active material particles and a coating layer that coats at least a portion of the surfaces of the active material particles, the method comprising: the active material particles are made of an NCA-based positive electrode active material, the coating layer is made of LiNbO 3 ; forming the electrode mixture layer containing the coated active material particles; an evaluation step of determining whether the electrode is good or bad using the evaluation method according to claim 1; A method for manufacturing an electrode, comprising:

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