Method for detecting sodium deposition on negative electrode of sodium ion battery

Abstract

Abstract: The present disclosure provides a method for detecting sodium deposition on a negative electrode of a sodium ion battery. The method comprises: a reaction step: placing test paper containing an indicator solution on the surface of a negative electrode sheet to enable the indicator solution to react with sodium deposition on the negative electrode, wherein the indicator solution changes color upon reaction with an alkaline substance; and a determination step: determining that sodium deposition is present on the negative electrode if any part of the test paper containing the indicator solution changes color, and determining that no sodium deposition is present on the negative electrode if the test paper containing the indicator solution does not change color.

Description

Detection method for sodium precipitation in negative electrode of sodium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure is based on Chinese patent application numbered 202410020830.4, filed on January 5, 2024, and entitled “Detection Method for Sodium Emission from Negative Electrode of Sodium Ion Battery”, and claims the priority of the Chinese patent application. The entire contents of the Chinese patent application are hereby incorporated into the present disclosure by reference. Technical Field

[0003] The present disclosure relates to the technical field of sodium ion batteries, and in particular to a method for detecting sodium precipitation in a negative electrode of a sodium ion battery. Background Art

[0004] Due to the advantages of abundant resources, low cost and wide distribution, the research and development of sodium-ion batteries is expected to alleviate to a certain extent the problem of limited development of secondary batteries caused by the shortage of lithium resources.

[0005] Because sodium ions have a larger radius than lithium ions, they face greater resistance to embedding into the negative electrode. This makes sodium deposition more likely in the negative electrode of sodium-ion batteries, severely impacting battery performance. Currently, determining whether sodium deposition occurs in the negative electrode of sodium-ion batteries typically requires additional physical and chemical analysis instruments. This is expensive, time-consuming, and cannot be directly tested on production lines.

[0006] Summary of the Invention

[0007] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a method for detecting sodium precipitation in the negative electrode of a sodium ion battery. The method is low in cost and can quickly and easily detect whether sodium precipitation exists in the negative electrode of a sodium ion battery.

[0008] In order to achieve the above objectives, the present disclosure provides a method for detecting sodium precipitation in a negative electrode of a sodium ion battery, comprising:

[0009] a reaction step, placing a test paper containing an indicator solution on the surface of the negative electrode to allow the indicator solution to react with the sodium precipitated on the negative electrode, wherein the indicator solution reacts with the alkaline substance to change color; and

[0010] The determination step comprises the following steps: if any part of the test paper containing the indicator solution changes color, it is determined that sodium is precipitated at the negative electrode; if the test paper containing the indicator solution does not change color, it is determined that no sodium is precipitated at the negative electrode.

[0011] In the detection method disclosed herein, whether sodium precipitation occurs at the negative electrode of a sodium ion battery can be determined simply and quickly by the color change of the test paper.

[0012] In some embodiments, the indicator solution includes a phenolphthalein solution, which turns pink when exposed to alkali, and the color change is obvious, which is convenient for determination.

[0013] In some embodiments, the phenolphthalein solution includes a solvent, wherein the solvent includes a solvent having a hydroxyl group. The solvent can react with the metallic sodium on the surface of the negative electrode, causing the test paper containing the phenolphthalein solution to change color.

[0014] In some embodiments, the solvent includes at least one of propanol, isopropanol, and butanol. Propanol, isopropanol, and butanol have little effect on the human body and react at a moderate rate with metallic sodium.

[0015] In some embodiments, the phenolphthalein solution comprises a phenolphthalein isopropanol solution. Isopropanol has no pungent taste, evaporates slowly, and reacts mildly with sodium, thereby improving detection accuracy.

[0016] In some embodiments, the mass concentration of the phenolphthalein isopropanol solution is 0.1 g / L-0.3 g / L. By setting the mass concentration of the phenolphthalein isopropanol solution within the above range, color change is facilitated, making it easier for the human eye to recognize the color change, and improving detection accuracy.

[0017] In some embodiments, the test paper is placed on the surface of the negative electrode for 5 seconds or less. By keeping the test paper on the surface of the negative electrode within the above range, the phenolphthalein solution can be better controlled to react only with sodium precipitated on the surface, reducing the possibility of reaction with sodium in the micropores of the negative electrode material, further improving the accuracy of the test.

[0018] In some embodiments, prior to the reaction step, a test paper pretreatment step is included: wetting the test paper with an indicator solution; placing the wetted test paper on the surface of a porous carrier until the indicator solution diffuses throughout the test paper and no indicator solution drips from the test paper. By placing the wetted test paper on the surface of the porous carrier, the phenolphthalein solution that easily drips from the test paper can enter the pore structure of the porous carrier, reducing the probability of the indicator solution dripping from the test paper and entering the interior of the negative electrode to react with the embedded sodium in the subsequent reaction step, thereby reducing the interference of the metallic sodium embedded in the negative electrode on the test results and improving the accuracy of the test results.

[0019] In some embodiments, the test paper is placed on the surface of the porous support for 15 to 30 seconds. This placement facilitates diffusion of the indicator solution throughout the test paper and allows excess indicator solution to drip off the test paper, reducing the risk of interaction with sodium embedded in the negative electrode material and improving detection accuracy.

[0020] In some embodiments, the test paper pretreatment step further includes the step of selecting white test paper. By selecting white test paper, the interference of the test paper color on the test results is reduced, thereby improving the accuracy of the test results.

[0021] In some embodiments, when the indicator solution includes a phenolphthalein solution, in the determination step, if any portion of the test paper turns pink, it is determined that sodium deposition has occurred at the negative electrode; if the test paper does not change color, it is determined that no sodium deposition has occurred at the negative electrode. This determination step can accurately determine whether sodium deposition has occurred on the surface of the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a photograph showing the results of testing sample 1 using the detection method of Example 1 of the present disclosure.

[0023] FIG2 is a photograph of the detection results of Sample 6 using the detection method of Example 1 of the present disclosure.

[0024] FIG3 is a photograph of the detection results of Sample 8 using the detection method of Example 1 of the present disclosure.

[0025] FIG4 is an XRD pattern obtained by testing sample 1 using the method of comparative example 1.

[0026] FIG5 is an XRD pattern obtained by testing sample 6 using the method of Comparative Example 1.

[0027] FIG6 is an XRD pattern obtained by testing sample 8 using the method of Comparative Example 1. DETAILED DESCRIPTION

[0028] Below, with appropriate reference to the accompanying drawings, an embodiment of the method for detecting sodium precipitation at the negative electrode of a sodium ion battery disclosed herein is described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0029] " scope " disclosed in the present disclosure is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special scope. The scope that is limited in this way can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0033] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various detection methods commonly used in the art, for example, they can be measured according to the detection methods given in the present disclosure.

[0034] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to sodium ions.

[0035] During the charge and discharge process of sodium-ion batteries, there is a situation where sodium ions cannot be embedded in the negative electrode and metallic sodium is deposited on the surface. The sodium deposition on the negative electrode surface will not only cause the loss of active sodium, but in severe cases, it will pierce the separator and cause battery safety problems. When metallic sodium is deposited on the negative electrode surface, the color will change slightly. However, the negative electrode surface is usually black, and the black color will mask the color change of the negative electrode surface. Therefore, it cannot be directly judged by the naked eye. There are reports that use additional physical and chemical analysis instruments to determine the sodium deposition of the negative electrode sheet, but this method is usually carried out in the laboratory, the detection cost is high, and the detection process is complicated and time-consuming, which is not suitable for the detection needs of industrial mass-produced batteries. Therefore, there is an urgent need for a detection method that can easily and quickly detect sodium deposition in the factory, issue an early warning, and prevent sodium deposition batteries from entering the market.

[0036] Based on this, the present disclosure proposes a method for detecting sodium precipitation in the negative electrode of a sodium ion battery, which includes a reaction step and a determination step.

[0037] In the reaction step, a test paper containing an indicator solution is placed on the surface of the negative electrode to allow the indicator solution to react with the sodium precipitated at the negative electrode. The indicator solution reacts with an alkaline substance to change color, such as a m-cresol violet solution, a Nile blue solution, or a phenolphthalein solution. In the determination step, if any portion of the test paper containing the indicator solution changes color, it is determined that sodium precipitated at the negative electrode; if the test paper containing the indicator solution does not change color, it is determined that no sodium precipitated at the negative electrode.

[0038] In the detection method disclosed in the present invention, the indicator solution reacts with the alkaline substance to change color, causing the test paper to change color, thereby being able to simply and quickly determine whether the negative electrode of the sodium ion battery is precipitating sodium. If the negative electrode of the sodium ion battery precipitates sodium, the indicator solution can react with the precipitated sodium to form an alkaline substance, causing the test paper to change color. Even if the sodium precipitated at the negative electrode is oxidized to sodium oxide during detection, sodium oxide in the air can easily react with water to generate sodium hydroxide, causing the indicator solution to change color. Therefore, it does not affect the determination of sodium precipitation at the negative electrode. In addition, the position of sodium precipitation on the surface of the electrode and the degree of sodium precipitation can be accurately determined by the color change position and color depth of the test paper. In addition, the existing detection method uses XRD to test whether the battery is precipitating sodium. This solution can only test whether a certain position of the negative electrode is precipitating sodium, while the detection method disclosed in the present invention can quickly test the position of sodium precipitation and the degree of sodium precipitation of the entire negative electrode.

[0039] In some embodiments, the indicator solution is preferably a phenolphthalein solution, which turns pink when exposed to alkali, and the color change is obvious, which is conducive to judgment. In this disclosure, the term "phenolphthalein solution" refers to a solution with phenolphthalein as a solute.

[0040] In the detection method disclosed herein, a test paper containing a phenolphthalein solution is placed on the surface of the negative electrode. If sodium precipitates on the surface of the negative electrode, the solvent of the phenolphthalein solution can react with the metallic sodium on the surface of the negative electrode, so that the pH is between 8.2 and 10.0, and the test paper containing the phenolphthalein solution turns pink (as the alkalinity increases, the color becomes darker and can become pink, red, or purple).

[0041] For the solvent of the above-mentioned phenolphthalein solution, as long as it can react with sodium and the resulting product is alkaline. In some embodiments, the solvent of the above-mentioned phenolphthalein solution includes a solvent (R-OH) with a hydroxyl group. Alternatively, the solvent with a hydroxyl group is selected from at least one of an alcohol solvent and a phenolic solvent, including but not limited to ethanol, propanol, isopropanol, butanol, phenol, etc. From the perspective of environmental protection, little impact on the human body, and reaction speed, at least one of propanol, isopropanol, and butanol is preferred.

[0042] In addition, during the charge and discharge process of the sodium ion battery, sodium ions are normally embedded in the micropores inside the negative electrode material. However, due to the limitations of the negative electrode material, some sodium ions may precipitate on the surface of the negative electrode material. The metallic sodium in the micropores does not affect the safety performance of the battery. However, if the above-mentioned phenolphthalein solution comes into contact with the metallic sodium in the micropores, it will also cause the test paper to change color. In view of this, in some embodiments, it is more preferred that the above-mentioned phenolphthalein solution include phenolphthalein isopropanol solution. Isopropanol has no irritating taste, evaporates slowly, and reacts mildly with sodium. It can reduce the possibility of reaction with sodium embedded in the micropores of the negative electrode material due to an uncontrollable reaction speed, thereby further improving the detection accuracy.

[0043] In some embodiments, the mass concentration of the phenolphthalein isopropanol solution is 0.1 g / L-0.3 g / L. For example, the mass concentration of the phenolphthalein isopropanol solution is 0.1 g / L, 0.15 g / L, 0.16 g / L, 0.17 g / L, 0.18 g / L, 0.19 g / L, 0.20 g / L, 0.25 g / L, 0.26 g / L, 0.27 g / L, 0.28 g / L, 0.29 g / L, 0.3 g / L, or a value between any two ranges. Preferably, the mass concentration of the phenolphthalein isopropanol solution is 0.15 g / L-0.2 g / L. By making the mass concentration of the phenolphthalein isopropanol solution within the above range, it is conducive to color change, making it easier for the human eye to recognize the color change, and improving the detection accuracy.

[0044] It should be noted that isopropanol is consumed during the above reaction steps and diffusion process, so the mass concentration of the phenolphthalein isopropanol solution is different at different stages. The mass concentration of the phenolphthalein isopropanol solution listed in the embodiments of the present disclosure is the mass concentration of the phenolphthalein isopropanol solution in the initial state.

[0045] In some embodiments, the test paper is placed on the surface of the negative electrode sheet for a time of less than or equal to 5 seconds, for example, the placement time is 0.5 seconds, 1 second, 1.5 seconds, 2 seconds, 2.1 seconds, 2.2 seconds, 2.3 seconds, 2.4 seconds, 2.5 seconds, 2.6 seconds, 2.7 seconds, 2.8 seconds, 2.9 seconds, 3 seconds, 3.1 seconds, 3.2 seconds, 3.3 seconds, 3.4 seconds, 3.5 seconds, 3.6 seconds, 3.7 seconds, 3.8 seconds, 3.9 seconds, 4 seconds, 4.5 seconds, 5 seconds, or a value between two ranges. Preferably, the placement time is 2 seconds to 4 seconds. By making the placement time of the test paper on the surface of the negative electrode sheet within the above range, the indicator solution can be better controlled to react only with the sodium precipitated on the surface, reducing the possibility of its reaction with the sodium in the micropores of the negative electrode material, and further improving the accuracy of the detection.

[0046] In some embodiments, during the reaction step, a cover plate may be placed on the test paper to ensure sufficient contact between the test paper and the surface of the negative electrode, thereby reducing the impact of curling of the test paper on the determination result. The cover plate used is not particularly limited and any well-known cover plate with good flatness may be selected, for example, a glass plate.

[0047] In some embodiments, before the above-mentioned reaction step, a test paper pretreatment step is further included, and the test paper pretreatment step includes the following steps (a) and (b).

[0048] Step (a): Wet the test paper with the indicator solution.

[0049] In the present disclosure, the so-called wetting means that the indicator solution soaks the surface of the test paper and then spreads and penetrates the entire test paper.

[0050] The method for wetting the test paper is not particularly limited, as long as the entire test paper is wetted with the indicator solution. Common methods for wetting test paper in the art can be used. For example, the indicator solution can be sprayed onto the surface of the test paper. In some embodiments, the test paper can be grasped with tweezers, and then the indicator solution can be sprayed onto the surface of the test paper from both sides.

[0051] The test paper used is not particularly limited; any known test paper with good adsorption properties and mechanical stability can be used. For example, filter paper can be used. In some embodiments, the test paper pretreatment step further includes the step of using white test paper. By using white test paper, the interference of the test paper color on the test results is reduced, thereby improving the accuracy of the test results.

[0052] Step (b): placing the wetted test paper on the surface of the porous carrier until the indicator solution diffuses throughout the test paper and no solution drips from the test paper.

[0053] In the present disclosure, "porous carrier" refers to a carrier with a microporous structure on the surface and inside. The porous carrier is not particularly limited, and commonly used porous carriers in the art can be used. For example, the porous carrier can be: foam. By placing the wetted test paper on the surface of the porous carrier, the indicator solution that easily drips from the inside of the test paper can enter the pore structure of the porous carrier, reducing the probability of the indicator solution dripping from the test paper and entering the inside of the negative electrode to react with the embedded sodium in the subsequent reaction step, reducing the interference of the metallic sodium embedded in the negative electrode on the test results, and improving the accuracy of the test results.

[0054] In some embodiments, the porous carrier is used to place the test paper with a supporting surface parallel to the horizontal direction, so that the test paper is parallel to the horizontal direction, thereby reducing the influence of gravity on the diffusion process of the indicator solution, so that the indicator solution is evenly distributed inside the test paper, and reducing the interference of the uneven distribution of the indicator solution in the test paper on the test results.

[0055] In some embodiments, the test paper is placed on the surface of the porous carrier for 15 seconds to 30 seconds, for example, the placement time is 15 seconds, 16 seconds, 17 seconds, 18 seconds, 19 seconds, 20 seconds, 21 seconds, 22 seconds, 23 seconds, 24 seconds, 25 seconds, 26 seconds, 27 seconds, 28 seconds, 29 seconds, 30 seconds or a value between the ranges consisting of any two values. Preferably, the placement time is 20 seconds to 25 seconds. By placing the test paper on the surface of the porous carrier for the above-mentioned time, it is beneficial for the indicator solution to diffuse into the entire test paper, and it is possible to cause excessive indicator solution to drip from the test paper, reducing the risk of it interacting with sodium embedded in the negative electrode material, and improving the detection accuracy.

[0056] In the present disclosure, when the indicator solution is a phenolphthalein solution, if any part of the test paper turns pink, it is determined to be sodium precipitation. Furthermore, the degree of sodium precipitation can be further specifically determined based on the depth of the color change and the size of the color change area.

[0057] Specifically, in this disclosure, "pink" can be divided into pink, red, and purple-red according to the color depth. The darker the color of the test paper, the more serious the sodium precipitation of the negative electrode. Based on this, the following judgment can be made:

[0058] If any part of the test paper turns purple-red, and / or the discolored area of ​​the test paper is larger than 1 / 3 of the test paper area, it is determined that the negative electrode has serious sodium precipitation;

[0059] If any part of the test paper turns red, and / or the discolored area of ​​the test paper is 1 / 6 to 1 / 3 of the test paper area, it is determined that there is a slightly serious sodium precipitation on the negative electrode;

[0060] If the test paper turns pink, and / or the discolored area of ​​the test paper is less than 1 / 6 of the test paper surface, it is determined that there is slight sodium precipitation in the negative electrode.

[0061] Example

[0062] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0063] Example 1

[0064] Ten cells were randomly selected from the completed sodium-ion battery production line and numbered as samples 1 to 10. Samples 1 to 10 were disassembled as follows: first, the clamps of the battery samples were removed, then the battery packaging was cut to expose the negative electrode, and finally, the negative electrode was removed.

[0065] The negative electrode sheets disassembled from samples 1 to 10 were tested using the following methods.

[0066] Step (a): Spray a phenolphthalein solution with a mass concentration (C) of 0.2 g / L and isopropyl alcohol evenly onto the surface of the white test paper to wet the paper. This step takes about 2 seconds.

[0067] Step (b): Place the wetted test paper on the surface of the foam and leave it there for 25 seconds (T1), until the phenolphthalein solution diffuses throughout the test paper and no phenolphthalein solution drips from the test paper.

[0068] Reaction step: Place the test paper treated in step (b) on the surface of the negative electrode and press it with a glass plate for 4 seconds (T2).

[0069] Determination Step: After placement, take a photo of the test strips for samples 1-10. Then, based on the color of the test strips, determine the sodium deposition status of the sodium-ion battery according to the following criteria. This step takes approximately 3 seconds.

[0070] Severe sodium precipitation: Any part of the test paper turns purple-red, and / or the discolored area of ​​the test paper is larger than 1 / 3 of the test paper area;

[0071] Slightly severe sodium precipitation: any part of the test paper turns red, and / or the discolored area of ​​the test paper is 1 / 6 to 1 / 3 of the test paper area;

[0072] Slight sodium precipitation: the test paper turns pink, and / or the discolored area of ​​the test paper is less than 1 / 6 of the test paper area;

[0073] No sodium precipitation: the test paper does not change color.

[0074] The detection time for each sample (including step (a), step (b), reaction step, and determination step) is approximately 34 seconds. The specific detection results are shown in Table 1-1 below.

[0075] Table 1-1

[0076] Among them, the photos of sample 1, sample 6 and sample 8 are shown in Figures 1 to 3 respectively.

[0077] Comparative Example 1

[0078] For battery samples 1 to 10 in Example 1, the disassembled negative electrode sheets were cut into negative electrode samples of appropriate sizes and tested as follows.

[0079] Equipment analysis steps: A high-precision wide-angle XRD device (Bruker discover D8) was used to analyze the above-mentioned negative electrode samples under vacuum conditions with a scanning range of 5° to 80° and a scanning speed of 3° / min. This step took about 3 hours.

[0080] Determination Steps: Compare the sodium metal spectrum (COD 9008545) from the Bruker Element Standard Card Library and determine the sodium deposition status of the sodium-ion battery according to the following criteria. This step takes about half an hour.

[0081] Severe sodium precipitation: A diffraction peak with an intensity greater than or equal to 10,000 appears at the 110 peak position of metallic sodium (2θ diffraction angle is between 25 degrees and 30 degrees).

[0082] Slightly severe sodium precipitation: A diffraction peak with an intensity greater than or equal to 2000 and less than 10000 appears at the 110 peak position of metallic sodium (2θ diffraction angle is between 25 degrees and 30 degrees).

[0083] Slight sodium precipitation: A diffraction peak with an intensity greater than or equal to 50 and less than 2000 appears at the 110 peak position of metallic sodium (2θ diffraction angle is between 25 degrees and 30 degrees).

[0084] No sodium precipitation: a diffraction peak intensity less than 50 appears at the metallic sodium 110 peak position (2θ diffraction angle is between 25 degrees and 30 degrees), or the metallic sodium 110 peak is not detected.

[0085] The testing time for each sample (including the equipment analysis step and the judgment step) was approximately 3.5 hours. The specific test results are shown in Table 1-2 below.

[0086] Table 1-2

[0087] Among them, the XRD patterns of sample 1, sample 6 and sample 8 are shown in Figures 4 to 6 respectively.

[0088] As shown in Tables 1-1 and 1-2 above, compared with existing detection methods, the detection method disclosed herein can easily and quickly detect sodium precipitation on the negative electrode surface. Moreover, the detection results are basically consistent with those of existing methods.

[0089] Example 2

[0090] In the battery production line, 10 batteries were randomly selected from the prepared sodium-ion battery products and numbered as samples 11 to 20.

[0091] The same procedures as in Example 1 were used, except that a phenolphthalein solution with a mass concentration (C) of 0.1 g / L and isopropyl alcohol was used as the solvent. The test paper was placed on the foam surface for 20 seconds (T1) and on the negative electrode sheet for 3 seconds (T2). The test time for each sample was approximately 28 seconds, and the test results are shown in Table 2.

[0092] Table 2

[0093] Comparative Example 2

[0094] The above samples 11 to 20 were tested using the same method as in Comparative Example 1, and the results were consistent with those in Example 2.

[0095] Example 3

[0096] In the battery production line, 10 batteries were randomly selected from the prepared sodium-ion battery products and numbered as samples 21 to 30.

[0097] The same procedures as in Example 1 were used, except that a phenolphthalein solution with a mass concentration (C) of 0.2 g / L and isopropyl alcohol was used as the solvent. The test paper was placed on the foam surface for 20 seconds (T1) and on the negative electrode sheet for 3 seconds (T2). The test time for each sample was approximately 28 seconds, and the results are shown in Table 3.

[0098] Table 3

[0099] Comparative Example 3

[0100] The above samples 21 to 30 were tested using the same method as in Comparative Example 1, and the results were consistent with those in Example 3.

[0101] Example 4

[0102] In the battery production line, 10 batteries were randomly selected from the prepared sodium-ion battery products and numbered as samples 31 to 40.

[0103] The same procedures as in Example 1 were used, except that a phenolphthalein solution with a mass concentration (C) of 0.2 g / L and isopropyl alcohol was used as the solvent. The test paper was placed on the foam surface for 20 seconds (T1) and on the negative electrode sheet for 5 seconds (T2). The test time for each sample was approximately 30 seconds, and the results are shown in Table 4.

[0104] Table 4

[0105] Comparative Example 4

[0106] The above samples 31 to 40 were tested using the same method as in Comparative Example 1, and the results were consistent with those in Example 4.

[0107] Example 5

[0108] In the battery production line, 10 batteries were randomly selected from the prepared sodium-ion battery products and numbered as samples 41 to 50.

[0109] The same procedures as in Example 1 were used, except that a phenolphthalein solution with a mass concentration (C) of 0.2 g / L and a solvent of amyl alcohol was used. The test paper was placed on the foam surface for 20 seconds (T1) and on the negative electrode sheet for 60 seconds (T2). The test time for each sample was approximately 1 minute 25 seconds, and the results are shown in Table 5.

[0110] Table 5

[0111] Comparative Example 5

[0112] The above samples 41 to 50 were tested using the same method as in Comparative Example 1, and the results were consistent with those in Example 5.

[0113] From the comparison of the above embodiments and comparative examples, it can be seen that, compared with the existing detection method, the detection method disclosed in the present invention can simply and quickly detect the sodium precipitation on the negative electrode surface, and the detection results are basically consistent with those of the existing method.

[0114] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A method for detecting sodium precipitation in a negative electrode of a sodium ion battery, comprising: a reaction step, placing a test paper containing an indicator solution on the surface of the negative electrode plate to allow the indicator solution to react with the sodium precipitated on the negative electrode, wherein the indicator solution reacts with the alkaline substance to change color; as well as The determination step is as follows: if any part of the test paper containing the indicator solution changes color, it is determined that sodium precipitation exists at the negative electrode; if the test paper containing the indicator solution does not change color, it is determined that no sodium precipitation exists at the negative electrode.

2. The detection method according to claim 1, wherein The indicator solution includes a phenolphthalein solution.

3. The detection method according to claim 2, wherein The phenolphthalein solution includes a solvent including hydroxyl groups.

4. The detection method according to claim 3, wherein The solvent includes at least one of propanol, isopropanol, and butanol.

5. The detection method according to any one of claims 2 to 4, wherein The phenolphthalein solution includes a phenolphthalein isopropanol solution.

6. The detection method according to claim 5, wherein The mass concentration of the phenolphthalein isopropanol solution is 0.1 g / L to 0.3 g / L.

7. The detection method according to any one of claims 1 to 6, wherein The test paper is placed on the surface of the negative electrode plate for less than or equal to 5 seconds.

8. The detection method according to any one of claims 1 to 7, wherein Before the reaction step, the method further includes a test paper pretreatment step: Wetting the test paper with the indicator solution; The wetted test paper is placed on the surface of the porous carrier until the indicator solution diffuses to the entire test paper and no indicator solution drips from the test paper.

9. The detection method according to claim 8, wherein The test paper is placed on the surface of the porous carrier for 15 to 30 seconds.

10. The detection method according to claim 8 or 9, wherein The test paper pretreatment step also includes the step of selecting white test paper.

11. The detection method according to any one of claims 2 to 10, wherein In the determination step, When any part of the test paper turns pink, it is determined that sodium precipitation occurs at the negative electrode; When the test paper does not change color, it is determined that there is no sodium precipitation at the negative electrode.

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