Methods for comparing the coating integrity of composite positive electrode active materials
By setting ion-blocking electrodes on both sides of the composite positive electrode active material and applying voltage, and observing the current change, the problem of difficulty in comparing coating integrity in the prior art is solved, and efficient and accurate coating integrity testing is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CONTEMPORARY AMPEREX TECHNOLOGY CO LTD
- Filing Date
- 2025-01-02
- Publication Date
- 2026-07-03
AI Technical Summary
The lack of a simple and efficient method to directly compare the coating integrity of different composite positive electrode active materials affects the manufacturing process and electrochemical properties of electrode materials.
By setting ion-blocking electrodes on both sides of the composite positive electrode active material and applying the same voltage to the surface of the ion-blocking electrodes, the change in current is observed, stable current values are read, and the magnitudes of the current values are compared to evaluate the integrity of the coating layer.
This paper presents a simple, easy-to-operate, time-saving, accurate, and low-cost method suitable for batch testing of the coating integrity of composite positive electrode active materials.
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Figure CN122330232A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and specifically to a method for comparing the coating integrity of composite positive electrode active materials. Background Technology
[0002] With the increasing demand for high-energy-density batteries in the power and energy storage markets, improving battery performance has become a top priority, and developing new materials is a key approach to achieving this goal. Among these, coating modification technology, as an effective means of optimizing the performance of active materials, plays a significant role. The integrity of the coating layer has a significant impact on the manufacturing process and electrochemical properties of electrode materials.
[0003] However, there is currently a lack of simple and efficient methods to directly compare the coating integrity of different composite positive electrode active materials, which is an urgent problem to be solved. Summary of the Invention
[0004] In view of the above problems, this application provides a method for comparing the coating integrity of composite positive electrode active materials. The method is simple and easy to operate, has a short testing time, high accuracy, low cost, and is convenient for batch testing of multiple groups of composite positive electrode active materials.
[0005] This application provides a method for comparing the coating integrity of composite positive electrode active materials, the method comprising the following steps:
[0006] (1) Take at least two sets of composite positive electrode active materials, wherein the composite positive electrode active materials include positive electrode active materials and a coating layer disposed on at least a portion of the surface of the positive electrode active materials;
[0007] The positive electrode active materials in each group of composite positive electrode active materials have the same general chemical structural formula;
[0008] (2) Each group of composite positive electrode active materials was pressed into tablets for sample preparation. Then, ion blocking electrodes were set on both sides of each sample and the same voltage was applied to the surface of the ion blocking electrodes. The change of current was observed, the stable current value was read, the current value was compared, and the coating integrity of each group of composite positive electrode active materials was evaluated.
[0009] In the technical solution of this application, the conductivity of the composite positive electrode active material is determined by both ionic conductivity and electronic conductivity. Ionic conductivity refers to the migration ability of active ions in the material, which mainly depends on the chemical composition of the positive electrode active material. Electronic conductivity refers to the migration ability of electrons in the material, which mainly depends on the coating layer, especially the integrity of the coating layer. Specifically, high integrity of the coating layer can construct a continuous conductive network, significantly improving the electron transport efficiency of the composite positive electrode active material. Conversely, defects or discontinuities in the coating layer will interrupt the electron transport path, increase resistance, and reduce electronic conductivity. Therefore, the integrity of the coating layer is related to the conductivity of the material.
[0010] In this application, the positive electrode active materials in each group of composite positive electrode active materials have the same general chemical structure formula; the conductivity of different positive electrode active materials may vary greatly. Therefore, selecting the same type of positive electrode active materials in each group can reduce the influence of different types of positive electrode active materials on the comparison results during the test.
[0011] In this application, after voltage is applied, the active ions in the material are driven by the electric field to move unidirectionally. Due to the use of ion-blocking electrodes, the moving active ions gradually decelerate at one end of the electrode and gather together. The change in current response is reflected in the following: as voltage is applied, the current response tends to a stable value. After the current value is basically stable, the active ions are basically gathered at the electrode. Therefore, the magnitude of the current value is less affected by ionic conductivity and depends mainly on electronic conductivity, that is, it depends mainly on the integrity of the coating layer. As can be seen from the current-voltage characteristic curve, under the same voltage, the larger the current, the smaller the resistance. Therefore, this application judges the integrity of the coating layer by comparing the current values of different materials. The larger the current value, the higher the integrity of the coating layer. The above comparison process is simple and easy to operate, with short testing time, high accuracy, and low cost, which facilitates batch testing of multiple sets of composite positive electrode active materials.
[0012] In some embodiments, in step (1), the composite positive electrode active material is of the same type.
[0013] In the technical solution of this application, the positive electrode active materials in each group of composite positive electrode active materials are of the same type. Selecting the same material can reduce the influence of different types of positive electrode active materials on the comparison results during the test.
[0014] In some embodiments, in step (1), the positive electrode active material includes lithium phosphate.
[0015] In the technical solution of this application, lithium phosphate has poor conductivity. On the one hand, it needs to improve conductivity by setting a coating layer. Therefore, the integrity of the coating layer is very important to it. On the other hand, its poor conductivity has little adverse effect on the accuracy of the test results.
[0016] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M y PO4, 0.8≤m≤1, 0≤x≤1, 0≤y≤1, M is selected from any one or at least two combinations of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb.
[0017] In the technical solution of this application, the chemical formula of the lithium phosphate material is selected as described above. The aforementioned material itself has unique advantages in terms of cost and safety, but it requires a coating layer to improve its conductivity in order to increase energy density; moreover, its poor electronic conductivity has a relatively small adverse impact on the accuracy of test results.
[0018] In some implementations, in step (1), at least two sets of composite positive electrode active materials have the same mass.
[0019] In the technical solution of this application, the composite positive electrode active materials of different groups have the same mass, which can reduce the impact of the mass difference of the composite positive electrode active materials on the comparison results and improve the accuracy of the comparison results.
[0020] In some embodiments, the coating layer includes a carbon coating layer.
[0021] In the technical solution of this application, the carbon coating layer can effectively improve the electronic conductivity of the positive electrode active material and improve the overall electrochemical performance of the material. In terms of testing, the internal resistance has a significant impact on the selection of electron transfer paths. Electron transfer paths tend to choose paths with low internal resistance. Since the carbon coating layer has low internal resistance, electrons tend to transfer through the carbon coating layer, which improves the accuracy of the comparison results.
[0022] In some embodiments, step (1) further includes drying each group of composite positive electrode active materials.
[0023] In the technical solution of this application, each group of composite positive electrode active materials is dried. The main purpose is to reduce the influence of moisture in the composite positive electrode active materials on the comparison results and improve the accuracy of the test.
[0024] In some embodiments, in step (2), the ion blocking electrode comprises a stainless steel electrode.
[0025] In the technical solution of this application, stainless steel electrodes are used as ion blocking electrodes because: stainless steel materials have low cost, which makes it easier to reduce the testing cost of multiple parallel experiments; moreover, stainless steel materials have ion insulating properties, which can serve as effective ion blocking electrodes; at the same time, their conductivity is good, and the change in current value generated by electron conductivity is significant, which can improve the accuracy of comparison results.
[0026] In some implementations, the voltage in step (2) is 0.05-0.1V.
[0027] In the technical solution of this application, the voltage adjustment range is within the aforementioned range. Within a suitable voltage range, during current conduction, the internal resistance has a significant impact on the selection of the electron transfer path. The electron transfer path tends to choose the path with low internal resistance; that is, after applying voltage, electron transfer chooses the path through the coating layer. This selection can improve the accuracy of the comparison results.
[0028] In some implementations, in step (2), the stable current value is the difference between the current values at any two moments within 10 seconds ≤ 0.02mA.
[0029] In the technical solution of this application, if the difference between the current values at any two moments within the above time period is within the above range, the current value is in a stable state. The magnitude of the current value is less affected by the ionic conductivity and mainly depends on the electronic conductivity of the coating layer. Therefore, based on this, a relatively clear judgment can be made on the stable current value, which improves the testing efficiency and accuracy.
[0030] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description
[0031] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:
[0032] Figure 1 This is a diagram of the electronic transfer path for some embodiments of this application;
[0033] Figure 2This is a diagram of the electronic transfer path for some embodiments of this application;
[0034] Figure 3 This is a graph showing the change of current values over time in some embodiments of this application;
[0035] The reference numerals in the detailed embodiments are as follows:
[0036] 1-Positive electrode active material; 2-Coating layer; 3-Ion blocking electrode; 4-Electron transfer path. Detailed Implementation
[0037] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0039] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
[0042] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.
[0043] In secondary batteries, coating technology, by constructing a stable interfacial film, effectively inhibits electrolyte decomposition and prevents hydrofluoric acid corrosion, metal ion dissolution, gas generation, and structural problems, making it an indispensable part of the production process. The integrity of the coating layer has a significant impact on the manufacturing process and electrochemical characteristics of the battery's electrode materials. However, a simple and efficient method is currently lacking to directly compare the coating integrity of different composite cathode active materials.
[0044] This application assesses the coating integrity of different groups of composite positive electrode active materials by setting ion-blocking electrodes on both sides of the composite positive electrode active material, applying the same voltage to the surface of the ion-blocking electrodes, and observing the change in current. This application provides a method for comparing the coating integrity of composite positive electrode active materials.
[0045] [Methods for comparing the coating integrity of composite positive electrode active materials]
[0046] This application provides a method for comparing the coating integrity of composite positive electrode active materials, the method comprising the following steps:
[0047] (1) Take at least two groups (e.g., three groups, six groups, ten groups, twenty groups, etc.) of composite positive electrode active materials, wherein the composite positive electrode active materials include positive electrode active materials and a coating layer disposed on at least a portion of the surface of the positive electrode active materials;
[0048] The positive electrode active materials in each group of composite positive electrode active materials have the same general chemical structural formula;
[0049] (2) Each group of composite positive electrode active materials was pressed into tablets for sample preparation. Then, ion blocking electrodes were set on both sides of each sample and the same voltage was applied to the surface of the ion blocking electrodes. The change of current was observed, the stable current value was read, the current value was compared, and the coating integrity of each group of composite positive electrode active materials was evaluated.
[0050] In this application, a multi-channel electrochemical workstation of model Bio-Logic VMP-300 was used for testing, and the current value was read using the Ec-Lab software that comes with the device.
[0051] In the technical solution of this application embodiment, the conductivity of the composite positive electrode active material is determined by both ionic conductivity and electronic conductivity. Ionic conductivity refers to the migration ability of active ions in the material, which mainly depends on the chemical composition of the positive electrode active material. Electronic conductivity refers to the migration ability of electrons in the material, which mainly depends on the coating layer, especially the integrity of the coating layer. Specifically, high integrity of the coating layer can construct a continuous conductive network, significantly improving the electron transport efficiency of the composite positive electrode active material. Conversely, defects or discontinuities in the coating layer will interrupt the electron transport path, increase resistance, and reduce electronic conductivity. Therefore, the integrity of the coating layer is related to the conductivity of the material.
[0052] In this application, the positive electrode active materials in each group of composite positive electrode active materials have the same general chemical structure formula; the conductivity of different positive electrode active materials may vary greatly. Therefore, selecting the same type of positive electrode active materials in each group can reduce the influence of different types of positive electrode active materials on the comparison results during the test.
[0053] In this application, after voltage is applied, the active ions in the material are driven by the electric field to move unidirectionally. Due to the use of ion-blocking electrodes, the moving active ions gradually decelerate at one end of the electrode and gather together. The change in current response is reflected in the following: as voltage is applied, the current response tends to a stable value. After the current value is basically stable, the active ions are basically gathered at the electrode. Therefore, the magnitude of the current value is less affected by ionic conductivity and depends mainly on electronic conductivity, that is, it depends mainly on the integrity of the coating layer. As can be seen from the current-voltage characteristic curve, under the same voltage, the larger the current, the smaller the resistance. Therefore, this application judges the integrity of the coating layer by comparing the current values of different materials. The larger the current value, the higher the integrity of the coating layer. The above comparison process is simple and easy to operate, with short testing time, high accuracy, and low cost, which facilitates batch testing of multiple sets of composite positive electrode active materials.
[0054] by Figure 1 For example, Figure 1 The composite positive electrode active material includes a positive electrode active material 1 and a coating layer 2 disposed on at least part of the surface of the positive electrode active material. Ion blocking electrodes 3 are disposed on both sides of the composite positive electrode active material, and the electron transfer path 4 is selected from the coating layer with low internal resistance.
[0055] by Figure 2 For example, Figure 2 The composite positive electrode active material includes a positive electrode active material 1 and a coating layer 2 disposed on at least part of the surface of the positive electrode active material. Ion blocking electrodes 3 are disposed on both sides of the composite positive electrode active material, and the electron transfer path 4 is selected from the coating layer with low internal resistance.
[0056] contrast Figure 1 and Figure 2 It can be seen that, Figure 1 The coating layer of the composite positive electrode active material has high integrity, and its corresponding electron transfer path is basically composed of the coating layer. It has low internal resistance and large current value. Figure 2 The coating integrity of the composite positive electrode active material is relatively low. Its corresponding electron transfer path is basically composed of two parts: the coating layer and the positive electrode active material. It has a large internal resistance and a small current value. Therefore, by comparing the current values, the coating integrity of the two groups of composite positive electrode active materials can be evaluated.
[0057] In the technical solution of this application embodiment, each group of composite positive electrode active materials is compressed into tablets to form uniform thin sheets, which facilitates conduction using ion-blocking electrodes. In this application, a tablet press is used to compress each group of composite positive electrode active materials into tablets. For example, a tablet press of model SPY-12B can be selected. The parameters for tablet compression can be designed according to the mass of the composite positive electrode active materials, etc. The tablet compression conditions for each group of composite positive electrode active materials are the same. For example, the compression pressure is 0.5-5T, such as 1T, 2T, 3T, 4T, etc.; the compression temperature is 10-50℃, such as 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, etc.
[0058] This application does not limit the thickness and size of the sheets obtained after compression. Different groups of composite positive electrode active materials will produce sheets with the same thickness and shape after compression, which helps improve the accuracy of comparison results. For example, the thickness of the obtained sheets is 0.05-0.25 mm, such as 0.1 mm, 0.15 mm, 0.2 mm, etc., and the shape can be a circular sheet with an area of 0.5-1.5 cm². 2 For example, 0.6cm 2 0.785cm 2 0.8cm 2 0.9cm 2 1cm 2 1.2cm 2 1.4cm 2 wait.
[0059] In some embodiments, the voltage is a DC voltage.
[0060] In some embodiments, in step (1), the types of positive electrode active materials in the composite positive electrode active material are the same.
[0061] In the technical solution of this application embodiment, the positive electrode active materials in each group of composite positive electrode active materials are of the same type. Selecting the same material can reduce the impact of different types of positive electrode active materials on the comparison results during the test.
[0062] In some embodiments, in step (1), the positive electrode active material includes lithium phosphate.
[0063] In the technical solution of this application embodiment, lithium phosphate has poor conductivity. On the one hand, it needs to improve conductivity by setting a coating layer. Therefore, the integrity of the coating layer is very important to it. On the other hand, its poor conductivity has little adverse effect on the accuracy of the test results.
[0064] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-yMn x M y PO4, 0.8≤m≤1 (e.g. 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, etc.), 0≤x≤1 (e.g. 0.2, 0.4, 0.6, 0.8, etc.), 0≤y≤1 (e.g. 0.2, 0.4, 0.6, 0.8, etc.), M is selected from any one or at least two combinations of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb.
[0065] In the technical solution of this application embodiment, the chemical formula of the lithium phosphate material is selected as described above. The above material itself has unique advantages in terms of cost and safety, but it needs to improve its conductivity by setting a coating layer to increase energy density; moreover, its poor electronic conductivity has a relatively small adverse impact on the accuracy of test results.
[0066] In some embodiments, in step (1), at least two sets of composite positive electrode active materials have the same mass.
[0067] In the technical solution of this application embodiment, the composite positive electrode active materials of different groups have the same mass, which can reduce the impact of the mass difference of the composite positive electrode active materials on the comparison results and improve the accuracy of the comparison results.
[0068] This application does not impose specific numerical values on the mass of different groups of composite positive electrode active materials, as long as they meet the requirements for tableting. As an example, the mass of the at least two groups of composite positive electrode active materials is 0.1-0.5g, such as 0.2g, 0.3g, 0.4g, etc.
[0069] In some embodiments, based on the mass of the composite positive electrode active material as 100%, the mass content of the coating layer is 0.8%-2.4%, for example 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, etc.
[0070] In some embodiments, the coating layer includes a carbon coating layer.
[0071] In the technical solution of this application embodiment, the carbon coating layer can effectively improve the electronic conductivity of the positive electrode active material and improve the overall electrochemical performance of the material. In terms of testing, the internal resistance has a significant impact on the selection of electron transfer paths. Electron transfer paths tend to choose paths with low internal resistance. Since the carbon coating layer has low internal resistance, electrons tend to transfer through the carbon coating layer, which improves the accuracy of the comparison results.
[0072] In this application, the carbon content of the carbon coating layer can be designed as needed. For example, based on the total mass of the carbon coating layer being 100%, the mass content of the carbon element is greater than or equal to 90%, such as 92%, 94%, 96%, 98%, etc.
[0073] In some embodiments, step (1) further includes drying each group of composite positive electrode active materials.
[0074] In the technical solution of this application embodiment, drying each group of composite positive electrode active materials is mainly to reduce the influence of moisture in the composite positive electrode active materials on the comparison results and improve the accuracy of the test.
[0075] This application does not limit the drying method; any method known in the art may be used. As an example, the drying method includes drying in an oven.
[0076] This application does not impose restrictions on the drying temperature and time, as long as the drying requirements are met. For example, the drying temperature is 80-150℃, such as 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc. For example, the drying time is 0.1-3h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, etc.
[0077] In some embodiments, in step (2), the ion blocking electrode comprises a stainless steel electrode.
[0078] In the technical solution of this application embodiment, stainless steel electrodes are used as ion blocking electrodes because: stainless steel materials have low cost, which makes it easier to reduce the testing cost of multiple parallel experiments; moreover, stainless steel materials have ion insulating properties, which can serve as effective ion blocking electrodes; at the same time, their conductivity is good, and the change in current value generated by electron conductivity is significant, which can improve the accuracy of comparison results.
[0079] In some embodiments, in step (2), the voltage is 0.05-0.1V, such as 0.06V, 0.07V, 0.08V, 0.09V, etc.
[0080] In the technical solution of this application, the voltage adjustment range is within the aforementioned range. Within a suitable voltage range, during current conduction, the internal resistance has a significant impact on the selection of the electron transfer path. The electron transfer path tends to choose the path with low internal resistance; that is, after applying voltage, electron transfer chooses the path through the coating layer. This selection can improve the accuracy of the comparison results.
[0081] In some embodiments, in step (2), the stable current value is within 10s (e.g., 2s, 4s, 6s, 8s, etc.), and the difference between the current values at any two moments is ≤0.02mA, such as 0.005mA, 0.01mA, 0.015mA, etc.
[0082] In the technical solution of this application embodiment, if the difference between the current values at any two moments within the above time period is within the above range, the current value is in a stable state. The magnitude of the current value is less affected by the ionic conductivity and mainly depends on the electronic conductivity of the coating layer. Therefore, based on this, a relatively clear judgment can be made on the stable current value, which improves the testing efficiency and accuracy.
[0083] In some embodiments, the method for comparing the coating integrity of the composite positive electrode active material includes the following steps:
[0084] (1) Take at least two sets of composite positive electrode active materials, wherein the composite positive electrode active materials include positive electrode active materials and a coating layer disposed on at least a portion of the surface of the positive electrode active materials;
[0085] Among them, the mass of any two groups of composite positive electrode active materials is the same, ranging from 0.1 to 0.5 g; the chemical structure formula of any two groups of positive electrode active materials is the same;
[0086] (2) After drying each group of composite positive electrode active materials, press them into tablets. Set ion blocking electrodes on both sides of each group of composite positive electrode active materials and apply the same voltage to the surface of the ion blocking electrodes. The voltage value is 0.05-0.1V. Observe the change of current, read the stable current value, compare the current value, and evaluate the coating integrity of each group of composite positive electrode active materials.
[0087] [Example]
[0088] Example 1
[0089] (1) Take two sets of composite positive electrode active materials, wherein the composite positive electrode active materials include positive electrode active materials and a carbon coating layer disposed on at least part of the surface of the positive electrode active materials;
[0090] The two groups of composite positive electrode active materials have the same mass, 0.3g; the two groups of positive electrode active materials are of the same type, with the chemical formula LiFePO4, namely material 1 and material 2. Material 1 was used to prepare sample 1, and the carbon coating layer accounts for 2.4% of the mass of the composite positive electrode active material. Material 2 was used to prepare sample 2, and the carbon coating layer accounts for 1.6% of the mass of the composite positive electrode active material. It is known that the coating integrity of material 1 is better than that of material 2.
[0091] (2) After drying the two sets of composite positive electrode active materials at 120℃ for 1 hour, pour them into a mold and disperse them evenly inside the mold. Then, use a tablet press (model SPY-12B) at 25℃ and a pressure of 2T to press them into uniform thin sheets with a thickness of 0.15mm, a circular shape, and an area of 0.785cm². 2 The samples were designated as Sample 1 and Sample 2, respectively. Stainless steel electrodes were placed on both sides of the two groups of composite positive electrode active materials. The same DC voltage of 0.05V was applied to the surface of the stainless steel electrodes by an electrochemical workstation. The change in current was observed and a stable current value was read (the test instrument was a Bio-Logic VMP-300). The magnitude of the current values was compared to evaluate the coating integrity of each group of composite positive electrode active materials and compared with known results.
[0092] Examples 2-3 and Comparative Example 1
[0093] Except for the parameters in Table 1, the comparisons were made according to the method described in Example 1.
[0094] Table 1
[0095]
[0096] In the table, "—" indicates that no data is involved.
[0097] Comparative Example 1
[0098] The integrity of the coating layer of the two groups of composite positive electrode active materials in Example 1 was analyzed using the iron leaching method. The specific process is as follows:
[0099] Take the same mass and type of powder sample from Example 1, mix them with the same concentration, volume and type of acidic solution, and react them at the same temperature and time. The acidic solution is a 0.1M sulfuric acid solution.
[0100] Solid-liquid separation was performed on the mixtures after each reaction to obtain filtrate and insoluble matter;
[0101] The concentration of Fe in each group of filtrates was measured, and the coating integrity of the two groups of positive electrode active materials was evaluated based on the concentration of Fe.
[0102] Specifically, 0.5g of disodium ethylenediaminetetraacetate complexing agent was added to an acidic solution, and then 1g of material 1 and material 2 were mixed with 50mL of 0.1M sulfuric acid solution. The acid dissolution reaction was carried out at 25℃ for 60min.
[0103] Performance testing
[0104] In Examples 1-3, stable current values were recorded using a Bio-Logic VMP-300 electrochemical workstation to evaluate the coating integrity of different groups of composite positive electrode active materials. The tests were repeated 10 times, and the accuracy of the results was statistically analyzed.
[0105] In Comparative Example 1, Sample 1 and Sample 2 were tested three times. After 60 minutes, the average iron leaching amounts were 105250 ppm and 106650 ppm, respectively. The iron leaching concentration of Sample 1 was lower than that of Sample 2, meaning that the coating integrity of Sample 1 was higher than that of Sample 2.
[0106] The test results are summarized in Table 2.
[0107] Table 2
[0108]
[0109] Figure 3 The graph shows the change of current value over time for Examples 1 and 2 of this application. The graph shows that in Examples 1 and 2, the stable current value of Sample 1 is higher than that of Sample 2. Combined with the results of Comparative Example 1, it can be seen that the method described in this application is simple and easy to operate, has a short testing time, high accuracy, low cost, and is convenient for batch testing of multiple groups of composite positive electrode active materials.
[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.
Claims
1. A method of comparing the coating integrity of composite cathode active materials, characterized by, The method includes the following steps: (1) Take at least two sets of composite positive electrode active materials, wherein the composite positive electrode active materials include positive electrode active materials and a coating layer disposed on at least a portion of the surface of the positive electrode active materials; The positive electrode active materials in each group of composite positive electrode active materials have the same general chemical structural formula; (2) Each group of composite positive electrode active materials was pressed into tablets for sample preparation. Then, ion blocking electrodes were set on both sides of each sample and the same voltage was applied to the surface of the ion blocking electrodes. The change of current was observed, the stable current value was read, the current value was compared, and the coating integrity of each group of composite positive electrode active materials was evaluated.
2. The method of claim 1, wherein, In step (1), the types of positive electrode active materials in the composite positive electrode active material are the same.
3. The method according to claim 1 or 2, characterized in that, In step (1), the positive electrode active material includes lithium phosphate.
4. The method according to claim 3, characterized in that, The lithium-containing phosphate material has a chemical formula of Li m Fe 1-x- y Mn x M y PO4, 0.8≤m≤1, 0≤x≤1, 0≤y≤1, M is selected from any one or a combination of at least two of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb.
5. The method according to any one of claims 1-4, characterized in that, In step (1), at least two sets of composite positive electrode active materials have the same mass.
6. The method according to any one of claims 1-5, characterized in that, The coating layer includes a carbon coating layer.
7. The method according to any one of claims 1-6, characterized in that, Step (1) also includes drying each group of composite positive electrode active materials.
8. The method according to any one of claims 1-7, characterized in that, In step (2), the ion blocking electrode includes a stainless steel electrode.
9. The method according to any one of claims 1-8, characterized in that, In step (2), the voltage is 0.05-0.1V.
10. The method according to any one of claims 1-9, characterized in that, In step (2), the stable current value is that the difference between the current values at any two moments within 10s is ≤0.02mA.