Method for analyzing failed sodium-ion battery

Abstract

The invention provides a method for analyzing a failed sodium-ion battery, which comprises the following steps: a pretreatment step: contacting a negative pole piece of the failed sodium-ion battery with an alcohol solvent to obtain a pretreated negative pole piece; a testing step: testing the capacity of the pretreated negative pole piece to obtain a tested capacity; a comparison step: comparing the test capacity with the reference capacity to obtain a capacity difference value; and a judgment step: according to the capacity difference value, judging whether the failure reason of the failed sodium-ion battery is caused by the negative pole piece or not. Therefore, accurate analysis of the negative pole piece of the sodium-ion battery can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a method for analyzing a failed sodium-ion battery. BACKGROUND

[0002] With the increasing demand for renewable energy worldwide and the rapid development of electric vehicles, energy storage systems and other fields, sodium-ion batteries, as a new energy storage solution, have a growing market prospect. However, with the widespread application of sodium-ion batteries, the failure of sodium-ion batteries occurs from time to time, which seriously affects the performance and life of sodium-ion batteries. Therefore, one of the current research focuses is to analyze the failure of sodium-ion batteries to lock the failure mechanism in order to confirm the next optimization direction.

[0003] Due to the different energy storage mechanisms of sodium-ion batteries and lithium-ion batteries, the existing failure analysis methods of lithium-ion batteries cannot accurately measure the failure mechanism of the negative electrode of sodium-ion batteries. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a method for analyzing a failed sodium-ion battery. The method can accurately analyze whether the cause of the failure of the sodium-ion battery is caused by the negative electrode, and can provide guidance for the subsequent design, development and optimization of the negative electrode material.

[0005] In order to achieve the above-mentioned purpose, the present application provides a method for analyzing a failed sodium-ion battery, the method comprising: a pretreatment step of contacting a negative electrode tab of the failed sodium-ion battery with an alcohol solvent to obtain a pretreated negative electrode tab; a test step of testing the capacity of the pretreated negative electrode tab to obtain a test capacity; a comparison step of comparing the test capacity with a reference capacity to obtain a capacity difference; and a determination step of determining whether the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab according to the capacity difference.

[0006] The present application adopts the method of contacting the alcohol solvent with the negative electrode tab of the sodium-ion battery, which does not damage the negative electrode material of the sodium-ion battery, and at the same time, by introducing new chemical reactions, the surface accumulation products of the negative electrode tab are dissolved and / or reacted, the diffusion channels of the electrolyte and sodium ions in the button cell assembled by the negative electrode tab are improved, thereby the thermodynamic capacity of the negative electrode material can be truly played in the subsequent capacity test process, so as to accurately characterize whether the negative electrode of the sodium-ion battery fails, and further effectively guide the design and development and optimization of the negative electrode material.

[0007] In some embodiments, the alcohol solvent includes one or more of ethanol, propanol, isopropanol, and butanol.

[0008] In some embodiments, the alcohol solvent comprises ethanol.

[0009] The alcohol solvent can remove the residual stacking product on the negative electrode sheet of the sodium-ion battery without damaging the solid electrolyte interface film formed on the negative electrode sheet of the sodium-ion battery during the first charge-discharge cycle, so that the thermodynamic capacity of the negative electrode material can be truly exhibited during the subsequent capacity test, and whether the negative electrode of the sodium-ion battery is invalid can be accurately characterized.

[0010] In some embodiments, the reference capacity is the capacity of the negative electrode sheet of a normal sodium-ion battery measured using the same test method as the invalid sodium-ion battery, and the production conditions and use conditions of the normal sodium-ion battery are the same as those of the invalid sodium-ion battery.

[0011] In some embodiments, when the absolute value of the capacity difference is greater than a first preset capacity, it is determined that the cause of the failure of the invalid sodium-ion battery is the negative electrode sheet of the invalid sodium-ion battery; and when the absolute value of the capacity difference is less than or equal to the first preset capacity, it is determined that the cause of the failure of the invalid sodium-ion battery is not the negative electrode sheet of the invalid sodium-ion battery.

[0012] In some embodiments, the first preset capacity is less than or equal to 5 mAh / g.

[0013] In some embodiments, the reference capacity is the capacity of the negative electrode sheet of the invalid sodium-ion battery calculated according to the actual capacity of the invalid sodium-ion battery.

[0014] In some embodiments, when the absolute value of the capacity difference is less than or equal to a second preset capacity, it is determined that the cause of the failure of the invalid sodium-ion battery is the negative electrode sheet of the invalid sodium-ion battery; and when the absolute value of the capacity difference is greater than the second preset capacity, it is determined that the cause of the failure of the invalid sodium-ion battery is not the negative electrode sheet of the invalid sodium-ion battery.

[0015] In some embodiments, the second preset capacity is less than or equal to 10 mAh / g.

[0016] In some embodiments, in the pretreatment step, contacting the negative electrode sheet of the invalid sodium-ion battery with the alcohol solvent comprises soaking the negative electrode sheet of the invalid sodium-ion battery in the alcohol solvent.

[0017] In some embodiments, the duration of contacting the negative electrode sheet of the invalid sodium-ion battery with the alcohol solvent is 1.5 h to 5 h.

[0018] In some embodiments, the time length for contacting the negative electrode tab of the failed sodium-ion battery with the alcohol solvent is 1.5-3 hours. In this way, the accumulated product remaining on the negative electrode tab of the failed sodium-ion battery can be removed without damaging the tab, which is conducive to more accurate subsequent testing of the capacity of the negative electrode tab and determination of whether the failure of the failed sodium-ion battery is caused by the negative electrode tab.

[0019] In some embodiments, in the testing step, the pretreated negative electrode tab is made into a button cell for capacity testing.

[0020] In some embodiments, when the negative electrode tab of the failed sodium-ion battery is coated with a negative electrode film layer on both sides, the pretreatment step further comprises a removal sub-step of removing the negative electrode film layer on one side of the negative electrode tab of the failed sodium-ion battery. In this way, the influence on the accuracy of the test results when testing the capacity of the button cell can be eliminated.

[0021] In some embodiments, the capacity of the pretreated negative electrode tab is tested under a current of 0.01-0.1 C.

[0022] In some embodiments, the capacity of the pretreated negative electrode tab is tested under a current of 0.05 C. The use of the above-mentioned current for charging and discharging test of the button cell can eliminate the polarization of the button cell assembly and exert the intrinsic thermodynamic capacity of the negative electrode material.

[0023] In some embodiments, the tested capacity is the discharge capacity measured in the second cycle of charging and discharging of the button cell. The capacity measured in the second cycle of charging and discharging can better reflect the intrinsic thermodynamic capacity of the negative electrode material and more accurately evaluate whether the sodium-ion battery negative electrode active material is lost.

[0024] In some embodiments, the pretreatment step further comprises a selection step of selecting a target region of the negative electrode tab of the failed sodium-ion battery.

[0025] In some embodiments, the pretreatment step further comprises a disassembly step of disassembling the failed sodium-ion battery to obtain the negative electrode tab of the failed sodium-ion battery.

[0026] This application provides a method for analyzing failed sodium-ion batteries. The method includes: a pretreatment step: contacting the negative electrode of the failed sodium-ion battery with an alcohol solvent to obtain a pretreated negative electrode; a testing step: testing the capacity of the pretreated negative electrode to obtain a test capacity; a comparison step: comparing the test capacity with a reference capacity to obtain a capacity difference; and a determination step: determining whether the failure of the failed sodium-ion battery is caused by the negative electrode based on the capacity difference. By contacting the negative electrode of the failed sodium-ion battery with an alcohol solvent, residual deposits on the negative electrode can be removed. This allows for accurate analysis of the negative electrode, thereby determining whether the failure is caused by the negative electrode and providing guidance for the subsequent design, development, and optimization of negative electrode materials. Attached Figure Description

[0027] Figure 1 A flowchart illustrating a method for analyzing failed sodium-ion batteries according to an embodiment of this application;

[0028] Figure 2 This is a photograph of the negative electrode of the failed sodium-ion battery in Example 4 of this application;

[0029] Figure 3 for Figure 2 Photographs of the negative electrode plates soaked in ethanol;

[0030] Figure 4 To be Figure 3 A photograph of the negative electrode plate fixed on a glass plate;

[0031] Figure 5 To be Figure 4 A photograph of one side of the negative electrode plate after wiping it;

[0032] Figure 6 For the reason Figure 5 A photograph of the small round pieces cut from the negative electrode sheet in the image;

[0033] Figure 7 To be Figure 6 A photo of small and medium-sized discs assembled into a button cell. Detailed Implementation

[0034] Hereinafter, specific embodiments of the method for analyzing a failed sodium-ion battery according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed description will be omitted in some cases. For example, detailed description of matters known well, repeated description of substantially identical structures will be 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 accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0035] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be defined by a lower limit and an upper limit, and the lower and upper limits define the boundaries of the particular range. Ranges can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and a range of 80-110 are listed, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all of the real combinations between "a" and "b", where "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all of the real numbers between "0" and "5" have been listed herein, and "0-5" is just a shorthand way of describing these numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0038] If not otherwise specified, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0039] If not otherwise specified, the terms used in the present application have the common meanings generally understood by the person skilled in the art.

[0040] If not otherwise specified, the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, according to the test methods given in the present application.

[0041] If not otherwise specified, in the present application, the term "active ion" refers to an ion that can be reversibly intercalated and deintercalated between the positive electrode and the negative electrode of the battery, including but not limited to sodium ion.

[0042] With the development and application of sodium ion battery technology, the problem of battery failure often occurs, and it is necessary to analyze the failure of the failed sodium ion battery, lock the failure mechanism, and determine the optimization direction of the next negative electrode material.

[0043] In the related art, the means for failure analysis of the negative electrode of the lithium ion battery is: cleaning the negative electrode sheet of the failed lithium ion battery with dimethyl carbonate (DMC) solvent to clean the accumulated products on the negative electrode sheet of the lithium ion battery; then assembling the cleaned negative electrode sheet into a button cell for capacity test. However, due to the different action mechanisms between the active ions and the negative electrode materials in sodium ion batteries and lithium ion batteries, the compositions of the accumulated products remaining on the negative electrode sheets of the two types of batteries are different. Therefore, using the same method as the lithium ion battery cannot characterize the real active material loss of the negative electrode material of the sodium ion battery, and problems such as abnormal capacity of the negative electrode sheet and poor consistency of the tested capacity may occur. Therefore, the means for failure analysis of the negative electrode of the lithium ion battery cannot accurately measure the failure mechanism of the negative electrode of the sodium ion battery.

[0044] Based on this, the present application provides a method for analyzing a failed sodium-ion battery. The method comprises the following steps: a pretreatment step: contacting the negative electrode sheet of the failed sodium-ion battery with an alcohol solvent to obtain a pretreated negative electrode sheet; a test step: testing the capacity of the pretreated negative electrode sheet to obtain a test capacity; a comparison step: comparing the test capacity with a reference capacity to obtain a capacity difference value; and a determination step: determining whether the cause of failure of the failed sodium-ion battery is caused by the negative electrode sheet according to the capacity difference value. In the present application, by contacting the negative electrode sheet of the failed sodium-ion battery with the alcohol solvent, the accumulated product remaining on the negative electrode sheet of the sodium-ion battery can be removed, so that the negative electrode sheet of the sodium-ion battery can be accurately analyzed to determine whether the cause of failure of the sodium-ion battery is caused by the negative electrode, which can provide guidance for the subsequent design, development and optimization of the negative electrode material.

[0045] An embodiment of the present application provides a method for analyzing a failed sodium-ion battery. As shown in the method comprises the following steps: Figure 1

[0046] Step S101, a pretreatment step: contacting the negative electrode sheet of the failed sodium-ion battery with an alcohol solvent to obtain a pretreated negative electrode sheet;

[0047] Step S102, a test step: testing the capacity of the pretreated negative electrode sheet to obtain a test capacity;

[0048] Step S103, a comparison step: comparing the test capacity with a reference capacity to obtain a capacity difference value;

[0049] Step S104, a determination step: determining whether the cause of failure of the failed sodium-ion battery is caused by the negative electrode sheet according to the capacity difference value.

[0050] ​As mentioned above, the interaction mechanism between active ions and negative electrode materials in sodium-ion batteries is different from that in lithium-ion batteries. Therefore, the means for failure analysis of lithium-ion battery negative electrodes cannot be used to characterize the real active material loss of sodium-ion battery negative electrode materials. The lithium storage mechanism of lithium-ion battery negative electrode materials (such as graphite) is mainly the reaction of lithium with negative electrode materials (such as graphite) to form lithium-carbon compounds. The failure analysis of lithium-ion battery negative electrodes is usually to disassemble the lithium-ion battery negative electrode sheet and soak it in DMC. The purpose of soaking is to clean the residual electrolyte and electrolyte by-products on the lithium-ion battery negative electrode sheet, so that the capacity of the negative electrode material can be truly exerted in the subsequent test process. However, the sodium storage mechanism of sodium-ion battery negative electrode materials (such as hard carbon) is mainly the adsorption or intercalation of sodium ions or sodium elements into the negative electrode materials. The sodium ions or sodium elements in the sodium-ion battery negative electrode materials (such as hard carbon) are easily oxidized to generate by-products when exposed to air. The commonly used cleaning solvent DMC for lithium-ion batteries cannot remove the sodium elements and their oxidation by-products on the negative electrode sheet of the sodium-ion battery, resulting in that the capacity of the negative electrode material cannot be truly exerted after the disassembled negative electrode sheet of the sodium-ion battery is assembled into a button cell, and the consistency of the exerted capacity is poor. Therefore, the present application is mainly aimed at the particularity of the negative electrode sheet of the sodium-ion battery. By contacting the negative electrode sheet of the sodium-ion battery with an alcohol solvent, the accumulated products on the negative electrode sheet can be dissolved and / or reacted without damaging the negative electrode material of the sodium-ion battery, thereby improving the diffusion channel of the electrolyte and sodium ions in the button cell assembled from the negative electrode sheet. Thus, the thermodynamic capacity of the negative electrode material can be truly exerted in the subsequent capacity test process, so as to accurately determine whether the failure of the sodium-ion battery is caused by the negative electrode, thereby effectively guiding the design, development and optimization of the negative electrode material.

[0051] It should be noted that in the present application, determining whether the cause of the failure of the failed sodium-ion battery is caused by the negative electrode sheet of the failed sodium-ion battery specifically refers to determining whether the cause of the failure of the failed sodium-ion battery is caused by the negative electrode material of the failed sodium-ion battery.

[0052] The failed sodium-ion battery in the present application can include a low-capacity sodium-ion battery. By contacting the negative electrode sheet of the failed sodium-ion battery with an alcohol solvent, the accumulated products on the negative electrode sheet of the sodium-ion battery can be removed. In this way, the negative electrode sheet of the sodium-ion battery can be accurately analyzed to determine whether the cause of the failure of the failed sodium-ion battery (such as a low-capacity sodium-ion battery) is caused by the negative electrode, thereby providing guidance for the subsequent design, development and optimization of the negative electrode material.

[0053] In some embodiments, the low-capacity sodium-ion battery refers to a battery in which the actual exerted capacity of the sodium-ion battery is abnormally low compared to the designed capacity during the test process. For example, when the actual exerted capacity of the sodium-ion battery is 10% lower than the designed capacity, the sodium-ion battery is considered to have low capacity.

[0054] In some embodiments, the method further comprises, before the pretreatment step, a disassembling step of disassembling the failed sodium-ion battery to obtain the anode tab of the failed sodium-ion battery. Illustratively, the disassembling can be performed in a battery disassembling house (or dry house), which is safer.

[0055] In some embodiments, the disassembling of the failed sodium-ion battery can be performed when the failed sodium-ion battery is at 0% SOC ~ 100% SOC. Alternatively, the disassembling is performed when the failed sodium-ion battery is at 0% SOC. The disassembling performed when the failed sodium-ion battery is at 0% SOC can result in less residue (e.g. residual active ions) in the anode tab, which is beneficial for the subsequent pretreatment of the anode tab and for the true capacity of the anode tab to be exhibited. In addition, the disassembling performed when the failed sodium-ion battery is at 0% SOC makes the disassembling process safer.

[0056] In some embodiments, the method further comprises, before the pretreatment step, a selecting step of selecting a target region of the anode tab of the failed sodium-ion battery. The target region can illustratively include one or more of a large area region, a corner region, a black spot region, or a dark mark region, etc. Alternatively, the target region can include a more representative region such as a large area region.

[0057] In some embodiments, the method further comprises cutting the selected target region of the anode tab of the failed sodium-ion battery, and contacting the cut target region of the anode tab with the alcohol solvent.

[0058] In some embodiments, the contacting, in the pretreatment step, of the anode tab of the failed sodium-ion battery with the alcohol solvent comprises soaking the anode tab of the failed sodium-ion battery in the alcohol solvent.

[0059] In some embodiments, the contacting, in the pretreatment step, of the anode tab of the failed sodium-ion battery with the alcohol solvent can further comprise spraying the alcohol solvent onto the anode tab of the failed sodium-ion battery.

[0060] In some embodiments, the alcohol solvent comprises one or more of ethanol, propanol, isopropanol, butanol. Alternatively, the alcohol solvent comprises ethanol.

[0061] In the present application, alcohol solvents such as ethanol, propanol, isopropanol, butanol, etc. can remove the residual accumulation product on the negative electrode sheet of the sodium-ion battery, but will not damage the solid electrolyte interface membrane (SEI) film formed on the negative electrode sheet of the sodium-ion battery in the first charge-discharge cycle, so that the thermodynamic capacity of the negative electrode material can be truly played in the subsequent capacity test process, thereby accurately characterizing whether the negative electrode of the sodium-ion battery is invalid. In addition, these solvents are low in cost and easy to operate. Therefore, using ethanol, propanol, isopropanol, butanol as the cleaning medium of the negative electrode sheet of the sodium-ion battery can also reduce the cost and be suitable for practical application.

[0062] In some embodiments, after the negative electrode sheet is contacted with the alcohol solvent, the method further comprises a drying step of drying the negative electrode sheet. Optionally, the above drying is performed at 100°C for 20 minutes.

[0063] In some embodiments, in the test step, the pretreated negative electrode sheet is made into a button cell for capacity test.

[0064] In some embodiments, when the negative electrode sheet of the invalid sodium-ion battery is coated with a negative electrode film layer on both sides, the pretreatment step further comprises a removal sub-step of removing the negative electrode film layer on one side of the negative electrode sheet of the invalid sodium-ion battery. Illustratively, first, the pretreated negative electrode sheet is fixed on a substrate. For example, the substrate can include a glass plate. By fixing, the oxidation of the negative electrode sheet can be reduced and the test interface can be prevented from being damaged, affecting the test results. Secondly, the fixed negative electrode sheet is wiped with a solvent to wipe the double-sided negative electrode sheet into a single-sided negative electrode sheet, eliminating the influence on the accuracy of the test results when testing the capacity of the button cell. The solvent used for wiping includes one or more of N-methyl pyrrolidone (NMP), ethanol, deionized water, but is not limited thereto.

[0065] In some embodiments, the capacity tested in the test step can be gram capacity.

[0066] In some embodiments, the pretreatment step further comprises a punching step of punching the negative electrode sheet of the invalid sodium-ion battery. Illustratively, the single-sided negative electrode sheet after wiping in the above step is punched into small round pieces as the positive electrode sheet of the button cell.

[0067] In some embodiments, the negative electrode sheet of the button cell can include a pure sodium sheet. In some embodiments, the electrolyte of the button cell can include anhydrous sodium perchlorate solution. In some embodiments, the separator film of the button cell can be glass fiber.

[0068] In some embodiments, the pre-processed negative electrode sheet is tested for capacity after being assembled into a button cell.

[0069] In some embodiments, the capacity of the pre-processed negative electrode sheet is tested at a current of 0.01C-0.1C.

[0070] In some embodiments, the capacity of the pre-processed negative electrode sheet is tested at a current of 0.05C.

[0071] In the present application, the use of a current range of 0.01C-0.1C, optionally 0.05C, for the charge-discharge test of the button cell can eliminate the polarization of the button cell assembly and exert the intrinsic thermodynamic capacity of the negative electrode material. If the capacity measured at a current range of 0.01C-0.1C, optionally 0.05C, shows that the capacity of the negative electrode material is low (i.e. failure), it indicates that there is active material loss in the negative electrode material, resulting in abnormal capacity of the negative electrode material in the sodium-ion battery, because the polarization of the button cell assembly has been eliminated at this current.

[0072] In some embodiments, the test capacity can be the discharge capacity measured in the second cycle of charge-discharge cycling of the button cell. The newly assembled button cell undergoes an activation process during the first cycle of charge-discharge cycling, during which the positive electrode sheet, negative electrode sheet, and electrolyte adapt to each other, so the capacity measured in the second cycle of charge-discharge cycling more accurately reflects the intrinsic thermodynamic capacity of the negative electrode material and can more accurately evaluate whether the sodium-ion battery negative active material is lost.

[0073] In some embodiments, for the same pre-processed negative electrode sheet, the sheet can be cut at the same location (e.g. large area) to assemble multiple button cells, for example, 5-10, and the capacity of each button cell is tested, and the average of the capacities of the multiple button cells is taken as the test capacity of the pre-processed negative electrode sheet.

[0074] In some embodiments, the reference capacity is the capacity of the negative electrode sheet of a normal sodium-ion battery measured using the same test method as the failed sodium-ion battery, wherein the production conditions and use conditions of the normal sodium-ion battery are the same as those of the failed sodium-ion battery.

[0075] In some embodiments, the reference capacity can be a reference gram capacity.

[0076] In some embodiments, in a case where the absolute value of the capacity difference value is less than or equal to a first preset capacity, it is determined that the cause of failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery; in a case where the absolute value of the capacity difference value is greater than the first preset capacity, it is determined that the cause of failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery. In sodium-ion batteries produced and tested in the same batch, the impact of the production process on the sodium-ion batteries is the same. When the cause of failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery, the capacities of the negative electrode of the failed sodium-ion battery and the normal sodium-ion battery measured under the same treatment and the same test conditions should be close, i.e., the test capacity and the reference capacity should be close. Therefore, when the cause of failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery, the absolute value of the capacity difference value between the test capacity and the reference capacity is less than or equal to the first preset capacity. When the cause of failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery, the capacities of the negative electrode of the failed sodium-ion battery and the normal sodium-ion battery measured under the same treatment and the same test conditions should be different, i.e., the test capacity of the failed sodium-ion battery is low. Therefore, when the cause of failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery, the absolute value of the capacity difference value between the test capacity and the reference capacity is greater than the first preset capacity.

[0077] In some embodiments, if there is a part of the sodium-ion batteries failed (e.g. low capacity) in the same batch of production and testing, the cause of the failure of the failed sodium-ion battery can be determined by comparing the capacity of the negative electrode tab of the failed sodium-ion battery with the capacity of the negative electrode tab of the normal sodium-ion battery. For example, the method of the present application can comprise: disassembling the normal sodium-ion battery and the failed sodium-ion battery to obtain the negative electrode tab of the normal sodium-ion battery and the negative electrode tab of the failed sodium-ion battery; pretreating the negative electrode tab of the normal sodium-ion battery and the negative electrode tab of the failed sodium-ion battery, which at least comprises contacting the negative electrode tab of the normal sodium-ion battery and the negative electrode tab of the failed sodium-ion battery with an alcohol solvent respectively; assembling the pretreated negative electrode tab of the normal sodium-ion battery and the pretreated negative electrode tab of the failed sodium-ion battery into button cells respectively; testing the discharge capacity of the button cells in the second cycle of charge and discharge, wherein the test result of the discharge capacity of the button cell corresponding to the negative electrode tab of the failed sodium-ion battery is used as the test capacity, and the test result of the discharge capacity of the button cell corresponding to the negative electrode tab of the normal sodium-ion battery is used as the reference capacity; comparing the test capacity with the reference capacity to obtain a capacity difference; in the case that the absolute value of the capacity difference is less than or equal to a first preset capacity, it is determined that the cause of the failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery; in the case that the absolute value of the capacity difference is greater than the first preset capacity, it is determined that the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery.

[0078] In some embodiments, the first preset capacity is less than or equal to 5 mAh / g.

[0079] In some embodiments, the reference capacity can also be the capacity of the negative electrode tab of the failed sodium-ion battery calculated according to the actual capacity of the failed sodium-ion battery.

[0080] For example, the capacity of the negative electrode tab of the failed sodium-ion battery can be determined according to the actual capacity of the failed sodium-ion battery and the excess ratio of the negative electrode capacity to the positive electrode capacity (CB value) per unit area of the positive electrode. For example, when the actual capacity of the failed sodium-ion battery is 26 Ah, the CB value of the failed sodium-ion battery is 1.2, the total weight of the negative electrode film layer is 108 g, and the mass fraction of the negative electrode active material in the negative electrode film layer is 96.2%, then the capacity of the negative electrode tab of the failed sodium-ion battery is 1.2 x 26 Ah x 1000 / (108 g x 96.2%) = 300 mAh / g.

[0081] In some embodiments, when the absolute value of the capacity difference is less than or equal to the second preset capacity, it is determined that the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery; when the absolute value of the capacity difference is greater than the second preset capacity, it is determined that the cause of the failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery. When the cause of the failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery, the test capacity measured by processing the negative electrode tab of the failed sodium-ion battery and assembling it into a button cell is a normal negative electrode capacity value. When the reference capacity is the capacity of the negative electrode tab of the failed sodium-ion battery calculated according to the actual capacity of the failed sodium-ion battery, the reference capacity is an abnormally low negative electrode capacity value. In this case, the capacity difference between the reference capacity and the test capacity will be larger. Therefore, when the cause of the failure of the failed sodium-ion battery is not caused by the negative electrode tab of the failed sodium-ion battery, the absolute value of the capacity difference between the reference capacity and the test capacity is greater than the second preset capacity. When the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery, the test capacity measured by processing the negative electrode tab of the failed sodium-ion battery and assembling it into a button cell is an abnormally low negative electrode capacity value. When the reference capacity is the capacity of the negative electrode tab of the failed sodium-ion battery calculated according to the actual capacity of the failed sodium-ion battery, the reference capacity is also an abnormally low negative electrode capacity value. In this case, the reference capacity and the test capacity will be closer. Therefore, when the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery, the absolute value of the capacity difference between the reference capacity and the test capacity is less than or equal to the second preset capacity.

[0082] In some embodiments, when all sodium-ion batteries produced and tested in the same batch are all failed (e.g., low capacity), whether the cause of the failure of the failed sodium-ion battery is caused by the negative electrode tab of the failed sodium-ion battery can be determined by comparing the capacity of the negative electrode tab of the failed sodium-ion battery calculated according to the actual capacity of the failed sodium-ion battery.

[0083] For example, the method of the present application can comprise: determining the capacity of the negative electrode tab of the failed sodium-ion battery as a reference capacity by the actual capacity of the failed sodium-ion battery and the excess ratio (CB value) of the negative electrode capacity to the positive electrode capacity per unit area of the positive electrode face; obtaining the test capacity of the negative electrode tab of the failed sodium-ion battery in the manner described above; comparing the test capacity with the reference capacity to obtain a capacity difference; determining that the cause of failure of the failed sodium-ion battery is the negative electrode tab of the failed sodium-ion battery if the absolute value of the capacity difference between the test capacity and the reference capacity is less than or equal to a second preset capacity; and determining that the cause of failure of the failed sodium-ion battery is not the negative electrode tab of the failed sodium-ion battery if the absolute value of the capacity difference between the test capacity and the reference capacity is greater than the second preset capacity.

[0084] In some embodiments, if there are some failed sodium-ion batteries in the same batch of sodium-ion batteries produced and tested, the cause of failure of the failed sodium-ion battery can also be determined by comparing the capacity of the negative electrode tab of the failed sodium-ion battery calculated from the actual capacity of the failed sodium-ion battery.

[0085] It should be noted that the second preset capacity can be the test capacity error of the sodium-ion battery negative electrode material (for example, hard carbon) in the full cell and the button cell.

[0086] In some embodiments, the second preset capacity is less than or equal to 10 mAh / g.

[0087] In some embodiments, the second preset capacity is less than or equal to 8 mAh / g.

[0088] In some embodiments, the negative electrode tab is contacted with the alcohol solvent for 1.5 h to 5 h. For example, the negative electrode tab can be contacted with the alcohol solvent for 1.5 h, 2 h, 3 h, 4 h or 5 h, but is not limited thereto.

[0089] In the present application, the negative electrode tab is contacted with the alcohol solvent for a time within the above range, which can remove the accumulated product remaining on the negative electrode tab of the failed sodium-ion battery without damaging the tab, and is conducive to more accurately testing the capacity of the negative electrode tab and determining whether the cause of failure of the failed sodium-ion battery is the negative electrode tab.

[0090] In some embodiments, the negative electrode tab is contacted with the alcohol solvent for 1.5 h to 3 h, and optionally 2 h.

[0091] In the present application, the negative electrode tab is contacted with the alcohol solvent for a time within the above range, which can remove the accumulated product remaining on the negative electrode tab of the failed sodium-ion battery without damaging the tab, and can also improve the analysis efficiency.

[0092] Examples

[0093] Hereinafter, the examples of the present application will be described. The examples described below are exemplary and are for the purpose of explanation of the present application only and are not to be understood as a limitation of the present application. In the examples, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0094] Example 1

[0095] In this example, ethanol is taken as an example to demonstrate that alcohol solvents can remove the accumulated reactants on the negative electrode sheet of the sodium ion battery, thereby achieving the purpose of accurately determining whether the negative electrode sheet of the sodium ion battery is failed. As a comparison, the same experiment is carried out by replacing ethanol with dimethyl carbonate DMC.

[0096] Normal sodium ion batteries with different state of charge (SOC) are selected as the analysis objects, and the selected normal sodium ion batteries are prepared by the following method:

[0097] Positive electrode sheet: sodium ferricyanide (Na4Fe(CN)6), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are dissolved in an appropriate amount of N-methyl pyrrolidone (NMP) according to a weight ratio of 97:2:1, and the mixture is uniformly prepared into a positive electrode slurry; then the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained;

[0098] Negative electrode sheet: hard carbon, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickening agent sodium hydroxymethyl cellulose (CMC-Na) are dissolved in deionized water according to a weight ratio of 96.2:0.8:1.8:1.2, and the mixture is uniformly prepared into a negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained;

[0099] Electrolyte: dimethyl carbonate, methyl ethyl carbonate, and ethylene carbonate are mixed as solvents according to a volume ratio of 1:1:1 to obtain an organic solvent, and then sodium hexafluorophosphate is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L;

[0100] Separator: glass fiber membrane is used as the separator;

[0101] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then the bare battery is obtained by winding, the bare battery is welded with the tab, the bare battery is put into the aluminum shell, and the bare battery is baked at 80°C to remove water, then the battery without electricity is obtained by injecting electrolyte and sealing. The battery without electricity is sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity test, and the like, to obtain the sodium ion battery.

[0102] Two sodium ion batteries are prepared by using the above method. First, the two sodium ion batteries are charged at a current of 0.33C for 3h to 4V, so that the state of charge of the two sodium ion batteries is 100% SOC, then one of the sodium ion batteries is discharged at a current of 0.33C for 1.5h to 3.2V, so that the state of charge of the sodium ion battery is 50% SOC; the other sodium ion battery is discharged at a current of 0.33C for 3h to 2.5V, so that the state of charge of the sodium ion battery is 0% SOC.

[0103] The 50% SOC sodium ion battery and the 0% SOC sodium ion battery are respectively disassembled in a dry room, and the negative electrode sheets are obtained. The obtained negative electrode sheets are respectively cleaned with DMC and ethanol for 2 hours, dried at 100°C, wiped to be single-sided, then parallel sampling is performed to obtain 14mm diameter analyzed electrode sheets, and the analyzed electrode sheets are assembled into multiple CR2430 button batteries for capacity test. The working electrode of the button battery is the analyzed electrode sheet, the reference electrode is a pure metal sodium disc, the separator is a glass fiber disc, and the electrolyte is a 1mol / L sodium hexafluorophosphate solution, and the solvent used for the electrolyte is an organic solvent obtained by mixing dimethyl carbonate, methyl ethyl carbonate, and ethylene carbonate in a volume ratio of 1:1:1.

[0104] The button battery is subjected to two charge and discharge tests, and the test steps are as follows:

[0105] ①0.05C constant current discharge to 0.005V, record the discharge gram capacity D1;

[0106] ②stand for 5 minutes;

[0107] ③0.05C constant current charge to 2V, record the charge gram capacity C1;

[0108] ④stand for 5 minutes;

[0109] ⑤0.05C constant current discharge to 0.005V, record the discharge gram capacity D2;

[0110] ⑥stand for 5 minutes;

[0111] ⑦0.05C constant current charge to 2V, record the charge gram capacity C2.

[0112] The discharge gram capacity D1 and the charge gram capacity C1 are the discharge gram capacity and the charge gram capacity in the first cycle process; the discharge gram capacity D2 and the charge gram capacity C2 are the discharge gram capacity and the charge gram capacity in the second cycle process.

[0113] The following Table 1 shows the capacity test results of the negative pole piece of the sodium ion battery with different SOC after being cleaned with different cleaning media.

[0114] Table 1

[0115]

[0116] In Table 1, " / " represents the absence.

[0117] As can be seen from Table 1, the test capacity data of the sodium ion battery negative pole piece cleaned with DMC is abnormal and the polarization is large. Specifically, the consistency of the charge gram capacity and the discharge gram capacity of the pole piece corresponding to the 1#-3# samples at 0% SOC and the 1#-4# samples at 50% SOC after the first cycle is poor, and in the second cycle, some samples cannot be desodiated. Therefore, the method of soaking the sodium ion battery negative pole piece in DMC cannot evaluate the true capacity of the negative pole material. The test capacity of the pole piece cleaned with ethanol has good capacity consistency at both 0% SOC and 50% SOC.

[0118] In addition, since there are fewer residual accumulation products in the 0% SOC sodium ion battery negative pole piece, the residual amount of sodium oxidized in the negative pole material is also small. Therefore, the capacity test results of the 0% SOC negative pole piece cleaned with DMC and cleaned with ethanol are relatively small. For the 50% SOC sodium ion battery negative pole piece, since there are more residual accumulation products in the negative pole piece, the capacity test results of the pole piece cleaned with DMC and cleaned with ethanol also have large differences. This further verifies that ethanol can remove the residual accumulation products on the sodium ion battery negative pole piece.

[0119] Example 2

[0120] In this example, the fresh activated full discharge pole piece cleaned with ethanol and the fresh cold-pressed pole piece not cleaned with ethanol are respectively assembled into button cells for capacity test.

[0121] First, the sodium ion battery is prepared in the same way as in Example 1, then the normal sodium ion battery is charged to 4.3V with a current of 0.02C, and then discharged to 2V with a current of 0.02C for activation. After that, the activated sodium ion battery is disassembled to obtain its negative pole piece as a fresh activated full discharge pole piece. The obtained fresh activated full discharge pole piece is cleaned with ethanol for 2h, dried at 100°C, wiped to be single-sided, and then sampled in parallel to obtain a diameter of 14mm to-be-analyzed pole piece.

[0122] The fresh cold-pressed electrode was prepared in the same manner as in Example 1. The fresh cold-pressed electrode was sampled in parallel to obtain a 14 mm diameter electrode to be analyzed.

[0123] The electrode to be analyzed was assembled into a CR2430 button cell in the same manner as in Example 1, and two charge-discharge tests were performed on the button cell in the same manner as in Example 1.

[0124] Table 2 below shows the capacity test results of the fresh activated full-discharge electrode and the fresh cold-pressed electrode.

[0125] Table 2

[0126]

[0127] In Table 2, " / " represents the absence.

[0128] As can be seen from Table 2, the fresh cold-pressed electrode has similar sodium extraction capacity (i.e., charge gram capacity) and significantly different sodium intercalation capacity (i.e., discharge gram capacity) compared to the fresh activated full-discharge electrode and the fresh activated full-discharge electrode washed with ethanol during the first cycle. The reason is that the fresh cold-pressed electrode does not form an SEI film, and a large amount of sodium intercalation is used to form the SEI film during the first sodium intercalation. The capacity of the fresh cold-pressed electrode and the fresh activated full-discharge electrode washed with ethanol is basically the same during the second cycle. This can indicate that the washing method using ethanol does not damage the state of the electrode, such as the SEI film, and can ensure the true capacity of the material.

[0129] The test data of Example 1 and Example 2 can prove that the capacity consistency is good when the capacity of the sodium ion battery negative electrode is tested by the method of washing the sodium ion battery negative electrode with an alcohol solvent, and the alcohol solvent does not damage the state of the electrode. Therefore, the method of the present application can be used to accurately determine whether the sodium ion battery negative electrode is invalid.

[0130] Example 3

[0131] In this example, the effect of the contact time of the sodium ion battery negative electrode with an alcohol solvent on the capacity test results of the button cell made of the sodium ion battery negative electrode is illustrated by the following experimental process.

[0132] A normally fully charged sodium ion battery was disassembled in a battery disassembly room, i.e., a dry room, and the disassembled negative electrode was selected and cut to obtain an electrode to be analyzed. The selected sodium ion battery was prepared in the same manner as the normal sodium ion battery in Example 1.

[0133] The above-obtained to-be-analyzed electrode sheet was soaked in ethanol for different durations, and was assembled into a CR2430 button cell in the same manner as in Example 1, and the above button cell was subjected to two charge-discharge tests in the same manner as in Example 1.

[0134] The following Table 3 shows the capacity test results of the electrode sheets corresponding to different soaking times.

[0135] Table 3

[0136]

[0137]

[0138] In Table 3, " / " represents the absence.

[0139] The standard deviation σ in Table 2 can be calculated by the following formula (1) and formula (2):

[0140]

[0141]

[0142] wherein S is the variance of the test capacities between the parallel samples, n is the number of parallel samples, i takes 1, 2, … n; X i is the test capacity corresponding to the ith sample; X0 is the average value of the test capacities between the parallel samples.

[0143] As can be seen from Table 3, for the negative electrode sheet of a sodium-ion battery fully charged, by setting the contact time of the negative electrode sheet with the alcohol solvent within 1.5h-5h, the standard deviation σ of the test capacities between the parallel samples is small, that is, by setting the contact time of the negative electrode sheet with the alcohol solvent within 1.5h-5h, the negative electrode sheet can be thoroughly cleaned, and the consistency of the test capacity of the negative electrode sheet is good.

[0144] Example 4

[0145] Take A batch of negative electrode materials and B batch of negative electrode materials to prepare 15 sodium-ion batteries A and 15 sodium-ion batteries B in the same batch according to the same preparation method as in Example 1, to obtain a total of 30 sodium-ion batteries prepared in the same batch.

[0146] The following cycle test steps were performed on the above 30 sodium-ion batteries:

[0147] ①0.33C constant current charging to 4.3V, and then constant voltage charging to 0.05C;

[0148] ②Rest for 5 minutes;

[0149] ③0.33C constant current discharging to 2V;

[0150] ④ Let it stand for 5 minutes;

[0151] ⑤ Repeat steps ① to ④ 100 times.

[0152] The test results showed that the test capacity of 15 sodium-ion batteries A from cycle 50 to 100 was generally lower than that of sodium-ion batteries B from cycle 50 to 100. The average test capacity of 15 sodium-ion batteries A from cycle 50 was 17 Ah, while the average test capacity of 15 sodium-ion batteries B from cycle 50 was 26 Ah. The average test capacity of sodium-ion batteries A was 34.6% lower than that of sodium-ion batteries B, indicating that all sodium-ion batteries A experienced low capacity.

[0153] To analyze the cause of the low capacity of battery A, two sodium-ion batteries, one with low capacity (A) and one with normal capacity (B), were analyzed at 50% SOC. The specific process included the following:

[0154] 1) The low-capacity sodium-ion battery A and the normal sodium-ion battery B were disassembled in the battery disassembly room, i.e., the drying room. The large area of ​​the negative electrode sheet disassembled from each battery was selected as the area to be analyzed and cut off. Figure 2 The image shows a photograph of the negative electrode of a disassembled low-capacity sodium-ion battery.

[0155] 2) Soak the cut-off negative electrode sheet in ethanol for 2.5 hours (e.g.) Figure 3 (As shown), and then dried at 100°C. Here, the purpose of soaking in ethanol is to clean the residual electrolyte and electrolyte by-products on the negative electrode sheet, as well as the elemental sodium and its oxides in the hard carbon material of sodium-ion batteries, so that the capacity of the negative electrode active material can be truly utilized;

[0156] 3) Secure the soaked negative electrode sheet to the glass plate with tape (e.g., Figure 4 (As shown), this reduces the oxidation of the negative electrode and prevents damage to the test interface, which could affect the test results;

[0157] 4) Wipe the fixed negative electrode sheet with a lint-free paper dampened with water, turning the double-sided negative electrode sheet into a single-sided negative electrode sheet (e.g., Figure 5 (as shown);

[0158] 5) The single-sided negative electrode sheet obtained in 4) is punched into a small circular sheet with a diameter of 14 mm (e.g. Figure 6 As shown), the small discs were assembled into CR2430 button cells according to the method of Example 1 for capacity testing; in step 5), two types of button cells were assembled, one being a button cell A' assembled from the negative electrode of a low-capacity sodium-ion battery A, and the other being a button cell B' assembled from the negative electrode of a normal sodium-ion battery B.

[0159] 6) Perform two charge-discharge tests on the assembled button cell A' and button cell B' in step 5) according to the following test procedure:

[0160] ① 0.05C constant current discharge to 0.005V, record the discharge gram capacity D1;

[0161] ② Stand for 5 minutes;

[0162] ③ 0.05C constant current charge to 2V, record the charge gram capacity C1;

[0163] ④ Stand for 5 minutes;

[0164] ⑤ 0.05C constant current discharge to 0.005V, record the discharge gram capacity D2;

[0165] ⑥ Stand for 5 minutes;

[0166] ⑦ 0.05C constant current charge to 2V, record the charge gram capacity C2.

[0167] The charge gram capacity C2 at step ⑦ in the test process of button cell A' is the test capacity of the negative electrode sheet of the low-capacity sodium-ion battery A.

[0168] The charge gram capacity C2 at step ⑦ in the test process of button cell B' is the test capacity of the negative electrode sheet of the normal sodium-ion battery B, i.e. the reference capacity.

[0169] The following Table 4 shows the capacity test results in Example 4 and the analysis results of the low-capacity reason.

[0170] Table 4

[0171]

[0172] As can be seen from Table 4, after the same ethanol treatment and test, the negative electrode sheet of the low-capacity sodium-ion battery A and the negative electrode sheet of the normal sodium-ion battery B respectively obtain the test capacity corresponding to the negative electrode sheet of the low-capacity sodium-ion battery A and the reference capacity corresponding to the negative electrode sheet of the normal sodium-ion battery B. The measured test capacity and reference capacity are close, and the absolute value of the capacity difference is less than 5mAh / g. This shows that the capacity of the negative electrode sheet of the low-capacity sodium-ion battery A and the capacity of the negative electrode sheet of the normal sodium-ion battery B are not much different, and the capacity of the negative electrode sheet of the low-capacity sodium-ion battery A can be normally played. Therefore, the reason for the low capacity of the sodium-ion battery prepared by the negative electrode material of batch A is not caused by the negative electrode material of batch A. After excluding this reason, the experimenters will perform other analysis tests to continue analyzing the reason for the low capacity of the sodium-ion battery A. This is not described in detail herein.

[0173] Example 5

[0174] The 15 sodium ion batteries C were prepared according to the same preparation method as in Example 1.

[0175] The following cycle test steps were performed on the 15 sodium ion batteries C:

[0176] ① 0.33C constant current charging to 4.3V, and then constant voltage charging to 0.05C;

[0177] ② resting for 5 minutes;

[0178] ③ 0.33C constant current discharging to 2V;

[0179] ④ resting for 5 minutes;

[0180] ⑤ cycles 1-4 for 5 times.

[0181] The test results showed that the test capacities of the 15 sodium ion batteries C in the 2nd-5th cycles were generally lower than the designed capacity, and the average value of the test capacities of the 15 sodium ion batteries C in the 2nd cycle was 18 Ah, which was 33% lower than the designed capacity, indicating that all the sodium ion batteries C were low in capacity.

[0182] In order to analyze the reason for the low capacity of the sodium ion battery C, one low-capacity sodium ion battery C was taken for analysis under the state of charge of 50% SOC. Specifically, the low-capacity sodium ion battery C was processed in the same manner as in Example 4, and a CR2430 button cell was assembled and subjected to the same capacity test to obtain the test capacity.

[0183] The difference lies in that the reference capacity is calculated by the following method:

[0184] The reference capacity is the capacity of the negative electrode sheet calculated according to the actual capacity of the taken low-capacity sodium ion battery C. Specifically, the actual capacity of the taken low-capacity sodium ion battery C is 18 Ah, the design CB value of the sodium ion battery C is 1.2, the total mass of the negative electrode film layer in the low-capacity sodium ion battery C is 108 g, and the proportion of the negative electrode material in the total mass of the negative electrode film layer is 96.2%. Therefore, the capacity of the negative electrode sheet of the taken low-capacity sodium ion battery C can be determined as 1.2x18 Ahx1000 / (108g x 96.2%) = 208 mAh / g.

[0185] Table 5 below shows the capacity test results of Example 5 and the analysis results of the low capacity reason.

[0186] Table 5

[0187]

[0188] As can be seen from Table 5, the test capacity of the negative electrode sheet of the low-capacity sodium-ion battery C after being treated with ethanol and assembled and discharged is close to the reference capacity calculated according to the actual capacity of the low-capacity sodium-ion battery C, and the absolute value of the capacity difference is less than 10 mAh / g. This indicates that the negative electrode sheet of the low-capacity sodium-ion battery C is abnormal. Therefore, the reason why the sodium-ion battery C prepared from the negative electrode material of the C batch has low capacity is that the capacity of the negative electrode material of the C batch cannot be normally exerted.

[0189] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the configuration elements of the embodiments are also included in the scope of the present application.

Claims

1. A method for analyzing failed sodium-ion batteries, characterized in that, The method includes: Pretreatment step: The negative electrode of the failed sodium-ion battery is contacted with an alcohol solvent to obtain a pretreated negative electrode. Test steps: Test the capacity of the pretreated negative electrode sheet to obtain the test capacity; Comparison step: Compare the test capacity with the reference capacity to obtain the capacity difference; Determination Steps: Based on the capacity difference, determine whether the failure of the sodium-ion battery is caused by the negative electrode.

2. The method according to claim 1, characterized in that, The alcohol solvents include one or more of ethanol, propanol, isopropanol, and butanol.

3. The method according to claim 1 or 2, characterized in that, The alcohol solvents include ethanol.

4. The method according to any one of claims 1 to 3, characterized in that, The reference capacity is the capacity of the negative electrode of a normal sodium-ion battery, measured using the same test method as the failed sodium-ion battery, and the normal sodium-ion battery is manufactured and used under the same conditions as the failed sodium-ion battery.

5. The method according to claim 4, characterized in that, If the absolute value of the capacity difference is greater than the first preset capacity, it is determined that the failure of the sodium-ion battery is caused by the negative electrode of the sodium-ion battery. If the absolute value of the capacity difference is less than or equal to the first preset capacity, it is determined that the failure of the sodium-ion battery is not caused by the negative electrode of the sodium-ion battery.

6. The method according to claim 5, characterized in that, The first preset capacity is less than or equal to 5 mAh / g.

7. The method according to any one of claims 1 to 3, characterized in that, The reference capacity is the capacity of the negative electrode of the failed sodium-ion battery calculated based on the actual capacity of the failed sodium-ion battery.

8. The method according to claim 7, characterized in that, If the absolute value of the capacity difference is less than or equal to the second preset capacity, it is determined that the failure of the sodium-ion battery is caused by the negative electrode of the sodium-ion battery. If the absolute value of the capacity difference is greater than the second preset capacity, it is determined that the failure of the sodium-ion battery is not caused by the negative electrode of the sodium-ion battery.

9. The method according to claim 8, characterized in that, The second preset capacity is less than or equal to 10mAh / g.

10. The method according to any one of claims 1 to 9, characterized in that, In the pretreatment step, contacting the negative electrode of the failed sodium-ion battery with an alcohol solvent includes immersing the negative electrode of the failed sodium-ion battery in the alcohol solvent.

11. The method according to any one of claims 1 to 10, characterized in that, The negative electrode of the failed sodium-ion battery is contacted with an alcohol solvent for 1.5 to 5 hours.

12. The method according to any one of claims 1 to 11, characterized in that, The negative electrode of the failed sodium-ion battery is contacted with an alcohol solvent for 1.5 to 3 hours.

13. The method according to any one of claims 1 to 12, characterized in that, In the testing step, the pretreated negative electrode sheet is made into a button cell and its capacity is tested.

14. The method according to claim 13, characterized in that, When the negative electrode of the failed sodium-ion battery is coated with a negative electrode film on both sides, the pretreatment step further includes a removal sub-step of removing the negative electrode film on one side of the negative electrode of the failed sodium-ion battery.

15. The method according to claim 13 or 14, characterized in that, The capacity of the pretreated negative electrode was tested under a current of 0.01C to 0.1C.

16. The method according to claim 15, characterized in that, The capacity of the pretreated negative electrode was tested under a current of 0.05C.

17. The method according to any one of claims 13 to 16, characterized in that, The test capacity is the discharge capacity of the coin cell measured during the second charge-discharge cycle.

18. The method according to any one of claims 1 to 17, characterized in that, Prior to the pretreatment step, a step of selecting a target area for the negative electrode sheet of the failed sodium-ion battery is also included.

19. The method according to any one of claims 1 to 18, characterized in that, Prior to the pretreatment step, a disassembly step is included to disassemble the failed sodium-ion battery to obtain the negative electrode sheet of the failed sodium-ion battery.

Images