Method for evaluating active material for secondary battery

Abstract

An evaluation method of an active material for a secondary battery, comprising: polishing a current collector to obtain a polished current collector; wherein the roughness Ra of the surface of the polished current collector satisfies: Ra>Dv50, wherein Dv50 is the volume average particle size of the active material; spraying the active material on the surface of the polished current collector to obtain a pole piece; and evaluating the active material based on the pole piece. The technical scheme of the application can improve the accuracy of performance evaluation of the battery active material.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a method for evaluating active materials for secondary batteries. Background Technology

[0002] In recent years, with the increasingly wide range of applications, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant advancements in battery technology, higher requirements have been placed on its performance evaluation.

[0003] In the characterization and analysis of battery materials, non-electrochemically active substances such as binders and conductive agents are present. However, these materials may interact with the active substances, thereby affecting the accuracy of the active substances in electrochemical performance evaluation. Therefore, improving the accuracy of performance evaluation of battery active substances is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide an evaluation method for active materials for secondary batteries, so as to improve the accuracy of performance evaluation of battery active materials.

[0005] In a first aspect, a method for evaluating active materials for secondary batteries is provided, comprising: polishing a current collector to obtain a polished current collector; wherein the surface roughness Ra of the polished current collector and the volume average particle size Dv50 of the active material satisfy: Ra > Dv50; spraying the active material onto the surface of the polished current collector to obtain an electrode; and evaluating the active material based on the electrode.

[0006] In this embodiment, the preparation of the electrode reduces the use of non-electrochemical active materials, thereby reducing variable interference in experiments and improving the accuracy of active material performance evaluation. Furthermore, the polishing process increases the surface roughness of the current collector. Subsequently, by spraying the active material onto the polished current collector surface, close contact between the active material and the current collector is achieved. Specifically, by setting the Ra value of the polished current collector to be greater than the Dv50 of the active material, the active material can achieve physical adsorption on the current collector surface through intermolecular forces such as van der Waals forces and electrostatic forces. This adsorption enhances the adhesion sites and adsorption characteristics of the active material on the current collector surface, reducing the use of non-active materials during electrode preparation, thus reducing variable interference from non-active materials and more directly reflecting the actual performance of the active material, thereby improving the accuracy of performance evaluation.

[0007] In one possible implementation, the electrode does not contain binders or conductive agents.

[0008] In the embodiments of this application, in the evaluation of the electrochemical performance of active materials, the use of electrodes without binders and conductive agents can reduce experimental variables. This method can reduce side reactions and interactions between non-electrochemical substances and active materials, more directly reflect the actual performance of active materials, reduce interference from external factors, and thus improve the accuracy of the evaluation.

[0009] In one possible implementation, grinding the current collector includes: placing and fixing the current collector on a substrate to support it; determining the grinding head of the grinding machine according to the roughness; fixing the grinding head to the front end of the grinding machine so that the grinding head contacts the current collector; turning on the power of the grinding machine to grind the current collector.

[0010] In the embodiments of this application, during the preparation of battery electrode sheets, by selecting a grinding head adapted to the surface characteristics of the current collector and considering the required surface roughness value, the grinding efficiency can be improved, thereby achieving the required surface roughness requirements.

[0011] In one possible implementation, the grinding head includes at least one of abrasive pads, steel grit, abrasive paste, and polishing cloth.

[0012] In the embodiments of this application, selecting the above-mentioned grinding head during the grinding process can achieve different roughness requirements on the surface of the current collector.

[0013] In one possible implementation, the spraying includes at least one of pressure spraying, air atomization spraying, high-speed rotary spraying, vacuum suction spraying, airless spraying, and ultrasonic spraying.

[0014] In the embodiments of this application, the actual application requirements during the evaluation process can be considered to select a suitable spraying technology.

[0015] In one possible implementation, the method further includes drying the electrode to remove solvent from it.

[0016] In the embodiments of this application, appropriate drying technologies can be flexibly selected according to the specific needs of various types of electrodes to efficiently and accurately remove solvents and moisture from inside the electrodes. This improves the stability of the electrodes during processing and is beneficial to the performance of the battery cells.

[0017] In one possible implementation, the drying process includes at least one of blower drying, hot air drying, vacuum drying, freeze drying, constant temperature drying, and microwave drying.

[0018] In the embodiments of this application, by considering factors such as the material properties of the electrode, the coating thickness, the required drying efficiency, and the cost, a suitable drying method can be selected.

[0019] In one possible implementation, the method further includes: purging the electrode to obtain the active material having a single-particle arrangement structure.

[0020] In this embodiment, the purging technique disperses the originally agglomerated active material particles, thereby embedding the particles into the uneven surface structure of the current collector and adsorbing them onto the current collector. This reduces localized differences caused by particle agglomeration or inhomogeneity, thus improving the accuracy of active material performance evaluation.

[0021] In one possible implementation, the purging includes at least one of hot gas purging, inert gas purging, compressed air purging, vacuum purging, and ultrasonic purging.

[0022] In the embodiments of this application, a suitable purging technology can be selected according to the actual needs of the electrode to meet different usage scenarios.

[0023] In one possible implementation, the electrode includes a positive electrode and a negative electrode.

[0024] In this embodiment of the application, the required electrode can be selected for performance evaluation according to the actual evaluation needs.

[0025] In one possible implementation, the positive electrode includes a positive active material, which comprises at least one of lithium-containing transition metal phosphate and lithium-containing transition metal oxide, wherein the positive active material is a lithium-containing transition metal phosphate, and the roughness Ra of the polished current collector surface is between 1.5 μm and 2 μm; or the positive active material is a lithium-containing transition metal oxide, and the roughness Ra of the polished current collector surface is between 11 μm and 15 μm; and / or, the negative electrode includes a negative active material, which comprises at least one of graphite and hard carbon, wherein the negative active material is graphite, and the roughness Ra of the polished current collector surface is between 18 μm and 22 μm; or the negative active material is hard carbon, and the roughness Ra of the polished current collector surface is between 11 μm and 18 μm.

[0026] In the embodiments of this application, the active substances to be evaluated can be selected according to the actual needs in the evaluation.

[0027] In one possible implementation, the electrode is applied to at least one of a characterization device and a battery, wherein the characterization device includes at least one of an in-situ scanning electron microscope, an in-situ transmission electron microscope, an in-situ X-ray photoelectron spectroscopy, a nanoindenter, and an external charge-discharge apparatus for assembling a half-cell; and the battery includes at least one of a half-cell and a full-cell.

[0028] In the embodiments of this application, the required characterization equipment or battery can be selected for evaluation according to the actual performance requirements of the active material. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of an evaluation method according to an embodiment of this application;

[0031] Figure 2 This is a schematic diagram of another evaluation method according to one embodiment of this application;

[0032] Figure 3 This is a schematic diagram of the electrode material according to one embodiment of this application;

[0033] Figure 4 This is a schematic diagram of a single battery cell in one embodiment of this application;

[0034] Figure 5 This is a schematic diagram of a battery cell according to another embodiment of this application;

[0035] Figure 6 This is a schematic diagram of the structure of a battery cell according to another embodiment of this application;

[0036] Figure 7 This is a schematic diagram of a battery according to one embodiment of this application;

[0037] Figure 8 This is a schematic diagram of the structure of a battery according to one embodiment of this application;

[0038] Figure 9 This is a schematic diagram of the structure of an electrical device according to an embodiment of this application;

[0039] Figure 10 This is a SEM image of an electrode sheet according to one embodiment of this application;

[0040] Figure 11 This is a charge-discharge curve at a 0.1C rate according to one embodiment of this application;

[0041] Figure 12 The graphs show the cycle performance of Examples 1-1, 1-2 and Comparative Example 1-1 of this application. Detailed Implementation

[0042] Hereinafter, embodiments of the evaluation method for active materials for secondary batteries according to this application are described in detail with appropriate reference to the accompanying drawings; however, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] 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 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 "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" 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.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0046] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] In the characterization and analysis of battery materials, the composition of electrodes is usually not limited to electrochemical active materials, but also includes inactive components such as binders and conductive agents. While these inactive materials are crucial for electrode processing and structural stability, their presence can interact with the active materials, thus affecting the accuracy of performance evaluation. For example, polymers in binders may cause swelling of the active materials, increasing their volume and thus impacting performance assessment. Conversely, while conductive agents can improve the electron conductivity of electrodes, improper distribution and dosage can increase internal electrode resistance, affecting the battery's initial charge-discharge efficiency and energy density.

[0048] To address the aforementioned issues, the preparation of binder- and conductive agent-free electrodes has attracted increasing attention. This method effectively reduces experimental variables, allowing analysis to focus more intently on the performance of the active material. However, current electrode preparation processes primarily rely on complex chemical reactions, such as high-temperature calcination, in-situ growth, and electrospinning. These chemical processes are not only complex but may also introduce side reactions, and the uncertainties of these reactions can lead to fluctuations in the quality of the active material, thus affecting the accuracy of performance evaluation. Therefore, how to prepare binder-free electrodes in a more direct manner to improve the accuracy of performance evaluation of battery active materials is a pressing issue that needs to be addressed.

[0049] In view of this, this application provides a method for evaluating active materials for secondary batteries, comprising: polishing a current collector to obtain a polished current collector; wherein the surface roughness Ra of the polished current collector and the volume average particle size Dv50 of the active material satisfy: Ra > Dv50; spraying the active material onto the surface of the polished current collector to obtain an electrode; and evaluating the active material based on the electrode.

[0050] In the above technical solution, by reducing the use of non-electrochemical active materials, the materials used in the evaluation are effectively controlled, which improves the accuracy of performance evaluation. The grinding process in this evaluation method increases the surface roughness of the current collector. Based on this, spraying the active material onto the ground current collector surface facilitates a tighter adhesion between the active material and the current collector. By setting the Ra value of the ground current collector to be greater than the Dv50 of the active material, the active material can achieve effective physical adsorption on the current collector surface through intermolecular forces such as van der Waals forces and electrostatic forces. This adsorption enhances the adhesion sites and adsorption characteristics of the active material on the current collector surface, reducing the use of inactive materials during electrode preparation. This reduces the variable interference of inactive materials on the active material, more directly reflects the actual performance of the active material, and thus improves the accuracy of performance evaluation.

[0051] The evaluation method of this application is described below with reference to the accompanying drawings.

[0052] [Evaluation Methodology]

[0053] This application provides a method for evaluating active materials for secondary batteries, used to evaluate the performance of battery active materials.

[0054] Figure 1 This is a schematic diagram of an evaluation method according to an embodiment of this application. Figure 1 As shown, evaluation method 200 includes the following steps:

[0055] S210, the current collector is polished to obtain a polished current collector; wherein, the surface roughness Ra of the polished current collector and the volume average particle size Dv50 of the active material satisfy: Ra>Dv50.

[0056] S220: The active material is sprayed onto the polished surface of the current collector to obtain the electrode sheet;

[0057] S230, based on electrode plates, evaluates active substances.

[0058] The electrode 121 includes an active material 1211 and a current collector 1212.

[0059] In S210, through a polishing process, the surface of the current collector 1212 has an uneven structure corresponding to its arithmetic average roughness (Ra). The active material 1211 adheres to the surface of the current collector 1212, that is, it is embedded in this uneven structure. After polishing, the surface of the current collector 1212 can obtain the expected roughness Ra.

[0060] Ra is used to characterize the microscopic properties of a material surface. It accurately reflects the microscopic unevenness of a processed surface, thus measuring the smoothness or roughness of the surface. The roughness value is calculated as the arithmetic mean of the absolute values ​​of the perpendicular distances from each point on the surface profile to a baseline within a specified sampling length. In other words, a smaller Ra value indicates a smoother surface with lower roughness; a larger Ra value indicates a rougher surface with more uneven structures and higher roughness.

[0061] In the embodiments of this application, the magnitude of Ra depends on the volume average particle size Dv50 of the active material 1211. Specifically, the surface roughness Ra of the current collector 1212 and the volume average particle size Dv50 of the active material 1211 satisfy the condition: Ra > Dv50. It should be noted that in the above relationship between Ra and Dv50, Ra can be used to characterize the average distance between the uneven positions on the surface of the current collector 1212 and the baseline. By setting Ra > Dv50, it can be understood that in the active material 1211, the particle size of particles with a cumulative volume particle size distribution percentage of 50% is smaller than Ra, so that these 50% of particles can be adsorbed on the aforementioned uneven structure. That is to say, when Ra is greater than Dv50, it means that there are more uneven positions on the surface of the current collector, allowing at least half of the active material particles to be adsorbed on these uneven structures.

[0062] For example, for lithium iron phosphate materials in the positive electrode active material, if its volume average particle size Dv50 is 1.4 μm, its corresponding Ra can be between 1.5 μm and 2 μm. For example, Ra can be 1.5 μm, 1.55 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, or any value within the above range. For ternary lithium nickel cobalt manganese oxide materials in the positive electrode active material, if its volume average particle size Dv50 is 10.6 μm, its corresponding Ra can be between 11 μm and 15 μm. For example, Ra can be 11 μm, 11.5 μm, 12 μm, 12.3 μm, 13 μm, 14 μm, 15 μm, or any value within the above range. For graphite materials in the negative electrode active material, if its volume average particle size Dv50 is 17.4 μm, its corresponding Ra can be between 18 μm and 22 μm. For example, Ra can be 18 μm, 18.1 μm, 19 μm, 19.6 μm, 20 μm, 21 μm, 22 μm, or any value within the above range. For the hard carbon material in the negative electrode active material, if its volume average particle size Dv50 is 10.6 μm, its corresponding Ra can be between 11 μm and 18 μm. For example, Ra can be 11 μm, 11.5 μm, 12 μm, 12.3 μm, 14 μm, 16 μm, 18 μm, or any value within the above range. In other words, this design allows 50% of the active material 1211 particles to be adsorbed onto the uneven surface structure of the current collector 1212. Thus, the active material 1211 particles can be stably adsorbed onto the uneven surface structure of the current collector 1212 through intermolecular forces such as van der Waals forces and electrostatic forces. Therefore, this adsorption effect can enhance the adhesion and adhesion sites of the active material 1211 on the surface of the current collector 1212, thereby reducing the use of inactive materials during the electrode preparation process. This reduces the variable interference of inactive materials on the active material, more directly reflects the actual performance of the active material, and thus improves the accuracy of the performance evaluation of the active material 1211.

[0063] In S220, active material 1211 is sprayed onto the surface of the polished current collector 1212 to obtain electrode 121. This process facilitates good contact between active material 1211 and current collector 1212.

[0064] In some embodiments, spraying includes at least one of pressure spraying, air atomization spraying, high-speed rotary spraying, vacuum suction spraying, airless spraying, and ultrasonic spraying. Each method has its own characteristics and applicable scope. Specifically, pressure spraying is simple to operate, low in cost, and suitable for spraying large areas; air atomization spraying can produce very fine particles and a uniform coating; high-speed rotary spraying has a fast coating speed and good coating uniformity; vacuum suction spraying produces a uniform coating and is suitable for substrates with complex shapes; airless spraying has high coating pressure, a dense coating, and is less prone to bubble formation; ultrasonic spraying produces very fine particles and a uniform coating, making it suitable for precision spraying.

[0065] During the preparation of battery electrode 121, a suitable spraying method can be selected based on actual application requirements. For example, the selection should consider the particle size, morphology, and electrochemical properties of the active material 1211 particles, as well as the type of substrate, such as copper foil or aluminum foil. Simultaneously, coating quality, such as uniformity, adhesion, and conductivity, must also be considered. By considering these factors, the most suitable spraying technology can be determined, which is beneficial for the electrode 121 to achieve the expected performance standards.

[0066] In S230, the performance of the active material 121 in the electrode 121 prepared in the above process can be evaluated. Specifically, the electrode 121 prepared in the embodiments of this application can eliminate the oxidation caused by conductive agents and binders, thus allowing for a more accurate evaluation of the electrochemical performance of the active material 1211. For example, the electrode 121 can be used to prepare half-cells or full-cells to compare the first-cycle charge-discharge efficiency of lithium iron phosphate materials with different carbon coating amounts. It can also be used to observe the volume expansion and contraction process of individual particles in the active material 1211 due to lithium insertion / extraction during charge-discharge.

[0067] Furthermore, the electrode 121 prepared in this embodiment can also be used to prepare characterization equipment. For example, the electrode 121 can be used to prepare in-situ scanning electron microscopes, in-situ transmission electron microscopes, in-situ X-ray photoelectron spectroscopy, and nanoindentation instruments, or to assemble half-cell external charge-discharge instruments, etc. For the evaluation process of the characterization equipment, the volume of the crystal lattice can be evaluated in-situ using transmission electron microscopy, or the chemical valence state of elements can be measured in-situ using X-ray photoelectron spectroscopy, and the mechanical properties of single particles can be tested using nanoindentation. Therefore, the required characterization equipment or battery can be selected for evaluation according to the actual performance requirements of the active material 1211.

[0068] In some embodiments, electrode 121 does not contain binders or conductive agents. For performance evaluation of battery active material 1211, electrode 121 without binders and conductive agents can reduce experimental variables, thereby improving the accuracy of performance evaluation. Specifically, this not only reduces side reactions between non-electrochemical materials and active material 1211, but also reduces interactions between them. For example, in the synthesis of lithium iron phosphate (LFP) cathode active material, in order to evaluate the performance comparison before and after material modification, it may be necessary to adjust the carbon coating amount of LFP material to study the effect of carbon coating on gas production in LFP cells. However, in this process, binders and conductive agents usually undergo side reactions such as oxidative decomposition with the cathode active material, resulting in the generation of additional gas, and the amount of gas produced by this side reaction is relatively large. Therefore, binders and conductive agents will affect the actual gas production of the cell, and thus affect the performance evaluation results.

[0069] Therefore, by using the electrode 121 in this embodiment, which contains no binder or conductive agent, side reactions during the synthesis process are reduced, making the carbon coating more accurate for the gas production of the lithium iron phosphate cell, thereby improving the accuracy of the performance evaluation of the active material 1211. For example, the polymer in the binder may swell with the active material 1211, resulting in larger particles and affecting the performance evaluation results. Therefore, this method can reduce interference from external factors, thereby improving the accuracy of the performance evaluation of the active material 1211.

[0070] In some embodiments, electrode 121 includes a positive electrode and a negative electrode. The electrode 121 to be evaluated can be selected according to the actual needs of the evaluation, and this application does not limit this selection. For example, for the evaluation of lithium iron phosphate materials, the required volume average particle size Dv50 of the lithium iron phosphate particles in the positive electrode is set.

[0071] In some embodiments, the positive electrode sheet includes a positive electrode active material, which includes at least one of lithium-containing transition metal phosphate and lithium-containing transition metal oxide. Wherein, the positive electrode active material is a lithium-containing transition metal phosphate, and the surface roughness Ra of the polished current collector 1212 is between 1.5 μm and 2 μm. For example, the lithium-containing transition metal phosphate includes lithium iron phosphate. Ra can be 1.5 μm, 1.55 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, or any value within the above range. When the positive electrode active material is a lithium-containing transition metal oxide, the surface roughness Ra of the polished current collector 1212 is between 11 μm and 15 μm. For example, the lithium-containing transition metal oxide includes lithium nickel cobalt manganese oxide. Ra can be 11 μm, 11.5 μm, 12 μm, 12.3 μm, 13 μm, 14 μm, 15 μm, or any value within the above range.

[0072] In some embodiments, the negative electrode sheet includes a negative electrode active material, which includes at least one of graphite and hard carbon. The negative electrode active material is graphite, and the surface roughness Ra of the polished current collector 1212 is between 18 μm and 22 μm. For example, Ra is 18 μm, 18.1 μm, 19 μm, 19.6 μm, 20 μm, 21 μm, 22 μm, or any value within the above range. Alternatively, if the negative electrode active material is hard carbon, the surface roughness Ra of the polished current collector 1212 is between 11 μm and 18 μm. For example, Ra is 11 μm, 11.5 μm, 12 μm, 12.3 μm, 14 μm, 16 μm, 18 μm, or any value within the above range.

[0073] Figure 2 This is a schematic diagram illustrating another evaluation method according to an embodiment of this application. For example... Figure 2 As shown, step S210 above may specifically include:

[0074] S211, The current collector 1212 is placed and fixed on the substrate to support the current collector 1212;

[0075] S212, Determine the grinding head of the grinding machine based on the surface roughness;

[0076] S213, fix the grinding head to the front end of the grinder so that the grinding head contacts the collector 1212;

[0077] S214, turn on the power of the grinder and grind the current collector 1212.

[0078] Specifically, in S211, by placing and fixing the current collector 1212 on the substrate, it is beneficial to provide a support base for the subsequent polishing process, thereby improving the smoothness of the processing.

[0079] It should be noted that the substrate used in the current collector 1212 in this application is not particularly limited in terms of material, such as glass, plastic, metal, ceramic, etc., and this application does not impose any restrictions on it. In practical applications, the choice of substrate depends on factors such as the mechanical strength, heat resistance, insulation required during the polishing process, and compatibility with the material of the current collector 1212.

[0080] It should be noted that the substrate surface should be as smooth as possible, as this contributes to the uniformity and stability of the current collector 1212 grinding process. During grinding, the smoothness of the substrate surface can affect the movement trajectory of the grinding head and the grinding effect. Therefore, a smooth substrate helps the grinding head move smoothly, resulting in a more uniform grinding effect.

[0081] In S212, during the finishing process of the current collector 1212 on the material surface, the grinding machine is an important surface treatment tool. The grinding machine can grind and polish the material surface using different grinding heads to meet these different roughness requirements.

[0082] In some embodiments, the grinding head includes at least one of a scouring pad, steel grit, polishing paste, and polishing cloth. The scouring pad grinding head has a coarser grit size, is suitable for surfaces with a high Ra value, and can conform to workpiece surfaces of various shapes to achieve uniform grinding; the steel grit grinding head has different grit sizes, with the grinding ability gradually decreasing from coarse to fine, and this grinding head can effectively remove the hard layer from the metal surface; the polishing paste can adapt to various materials and roughness requirements; the polishing cloth grinding head is used to achieve a very smooth surface, can perform fine polishing, thereby providing a low roughness, and is suitable for various materials.

[0083] Alternatively, you can choose grinding heads with different grit sizes for polishing. For example, polishing paste with a grit size of 200-400 typically corresponds to an Ra value between 0.8μm and 1.6μm; polishing paste with a grit size of 600-800 typically corresponds to an Ra value between 0.4 and 0.8μm; and polishing paste with a grit size of 1000-1500 typically corresponds to an Ra value between 0.1μm and 0.4μm. For steel grit of different mesh sizes, the Ra value corresponding to 400 mesh is generally between 0.1μm and 0.2μm, the Ra value corresponding to 350 mesh is generally between 0.2μm and 0.3μm, the Ra value corresponding to 300 mesh is generally between 0.3μm and 0.4μm, the Ra value corresponding to 250 mesh is generally between 0.4μm and 0.6μm, the Ra value corresponding to 200 mesh is generally between 0.6μm and 0.8μm, the Ra value corresponding to 150 mesh is generally between 0.8μm and 1.6μm, and the Ra value corresponding to 100 mesh is generally between 1.6μm and 3.2μm.

[0084] During the fabrication of the battery electrode 121, a matching grinding head needs to be selected based on the material characteristics of the current collector 1212 surface and its required Ra value standard. This selection not only improves the efficiency of the grinding operation but also helps the surface of the current collector 1212 to accurately meet the required surface roughness requirements, thereby improving the overall performance and reliability of the battery.

[0085] In S213, the grinding head is in close contact with the surface of the current collector 1212. This step ensures that the grinding head fits tightly against the surface to be processed, which is beneficial for the subsequent grinding process.

[0086] In S214, after the power of the grinder is turned on, its high-speed rotating grinding head grinds the surface of the current collector 1212 to achieve the required surface roughness Ra and smoothness.

[0087] In some embodiments, method 200 further includes: designing the dimensions of the current collector 1212 according to the actual requirements of the electrode 121. Based on these dimensions, the polished current collector 1212 is cut, and the cut current collector 1212 is weighed and its mass data is recorded. Therefore, in the electrode 121 preparation process of this application, using the data from the polished substrate can improve the accuracy and reliability of subsequent tests.

[0088] In some embodiments, method 200 further includes drying the electrode 121 to remove solvent from the electrode 121.

[0089] In some embodiments, the drying process includes at least one of blower drying, hot air drying, vacuum drying, freeze drying, constant temperature drying, and microwave drying. Different drying methods are suitable for different production needs and material properties. Specifically, blower drying uses a circulating fan to blow hot air, which helps to balance the temperature inside the chamber and thus achieve the drying effect; hot air drying uses heated airflow to improve drying efficiency and accelerate solvent evaporation; vacuum drying is suitable for drying heat-sensitive electrodes and can reduce material degradation caused by high temperatures; freeze drying is suitable for electrodes 121 that are extremely sensitive to temperature and can maintain the structure and activity of electrodes 121; constant temperature drying is suitable for electrodes 121 that require precise control of drying conditions and maintains the consistency of electrode quality; microwave drying has a fast drying speed and high efficiency, can penetrate materials, and is suitable for electrodes 121 that need to be dried uniformly.

[0090] In the preparation of electrode 121, selecting a suitable drying method is beneficial to the quality and performance of the final product. Specifically, when choosing a drying method, factors such as the material properties of electrode 121, coating thickness, required drying efficiency, and cost need to be considered. For example, for electrode 121 made of heat-sensitive materials or requiring the preservation of the activity of active material 1211, vacuum drying or freeze-drying may be preferred to reduce heat damage and improve drying quality. For situations requiring rapid mass production, hot air drying or forced-air drying may be chosen to improve production efficiency. Through reasonable drying treatment, the uniformity and consistency of battery electrode 121 can be improved, thereby enhancing the overall performance and lifespan of the battery.

[0091] In some embodiments, method 200 further includes: purging the electrode 121 to obtain an active material 1211 with a single-particle arrangement structure. During the preparation of the electrode 121, the active material 1211 is treated with a purging technique to obtain an electrode 121 with a single-particle arrangement structure, which is beneficial for battery performance evaluation. Specifically, the purging technique disperses the originally agglomerated active material 1211 particles, enabling the particles to embed into the uneven structure of the current collector 1212, thereby adsorbing onto the current collector 1212. This facilitates the achievement of a single-particle arrangement structure, reducing local differences caused by particle agglomeration or inhomogeneity, thus improving the accuracy of battery performance evaluation.

[0092] In some embodiments, purging includes at least one of hot gas purging, inert gas purging, compressed air purging, vacuum purging, and ultrasonic purging. The choice of purging method for electrode 121 depends on factors such as the material of electrode 121, coating thickness, required level of cleanliness, and production efficiency. For example, inert gas purging may be preferred for electrode materials sensitive to moisture and oxygen, while compressed air purging may be chosen for cost-sensitive applications. Proper purging treatment can improve the surface quality of battery electrode 121 and the final performance of the battery.

[0093] Next, with appropriate reference to the accompanying drawings, the battery cell, battery, and power-consuming device prepared by the electrode 121 in the evaluation method of this application will be described.

[0094] [Battery cell]

[0095] This application provides a battery cell for evaluating the performance of active material 1211.

[0096] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0097] Next, the electrode 121 of this application will be described with appropriate reference to the accompanying drawings.

[0098] Figure 3 This is a schematic diagram of the electrode 121 material according to an embodiment of this application. Figure 3 As shown, the electrode 121 includes an active material 1211 and a current collector 1212.

[0099] In the embodiments of this application, see Figure 3The surface of the current collector 1212 has an uneven structure corresponding to its Ra, and the active material 1211 is attached to the surface of the current collector 1212, that is, embedded in the uneven structure.

[0100] In some embodiments, the active material 1211 is arranged in the form of single particles on the uneven structure of the current collector 1212. For the battery, the single-particle arrangement enables a more uniform particle distribution and reduces local differences caused by particle agglomeration or unevenness, thereby facilitating the evaluation of the performance of the active material 1211.

[0101] Furthermore, single-particle arrangement offers unique advantages in constructing single-particle models. Specifically, single-particle models allow for detailed analysis of each individual particle, focusing on the characteristics of a single particle and thus revealing electrochemical reaction mechanisms at the microscopic level. Therefore, this single-particle arrangement approach facilitates the research and analysis of single-particle models.

[0102] In the embodiments of this application, electrode 121 contains no binder or conductive agent. Using an electrode 121 without binder and conductive agent during the evaluation of its electrochemical performance reduces variables in the experiment, thereby minimizing the impact of binder and conductive agent on the performance of the active material 1211. A system without binder and conductive agent can more directly reflect the true performance of the active material 1211 itself, reducing interference from external factors. Simultaneously, this approach also reduces the interaction between binder and conductive agent and the active material 1211, not only reducing swelling of the active material but also minimizing potential side reactions and interface problems, thus improving the accuracy of the evaluation.

[0103] Some properties of electrode 121 in this application have been mentioned in the preceding text. A more detailed description of electrode 121 will follow.

[0104] [Positive electrode plate]

[0105] The positive electrode may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0106] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0107] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode active material can be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following: lithium-containing transition metal oxides, lithium phosphates with an olivine structure, or materials with a spinel structure. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNiO2). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0109] As mentioned earlier, the positive electrode active material is embedded in the uneven structure on the surface of the current collector 1212 to form a positive electrode sheet.

[0110] [Negative electrode plate]

[0111] The negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0112] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0113] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0115] As mentioned earlier, the negative electrode active material is embedded in the uneven structure on the surface of the current collector 1212 to form a negative electrode sheet.

[0116] [Electrolytes]

[0117] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0118] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0119] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0120] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0121] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0122] [Isolation membrane]

[0123] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0124] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0125] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0126] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0127] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] This application does not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0129] Furthermore, the technical solution of this application can be applied to various batteries, such as lithium-ion batteries, lithium metal batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, magnesium batteries, calcium batteries, zinc batteries, aluminum batteries, etc., and this application does not limit them.

[0130] Figure 4 This is a schematic diagram of a single battery cell according to one embodiment of this application. Figure 4 As shown, the battery cell 100 can be a coin cell, including an electrode 121, a lithium sheet 122, and a separator 123. The electrode 121 includes an active material 1211 and a current collector 1212, with the active material 1211 embedded in the uneven structure of the current collector 1212 surface. Specifically, the x-direction is the height direction of the battery cell 100. By sequentially arranging the current collector 1212, active material 1211, separator 123, and lithium sheet 122 along the x-direction, a coin cell is obtained.

[0131] It should be noted that the lithium sheet 122 described above serves as the counter electrode in this embodiment. Furthermore, the counter electrode of the coin cell in this application may also include other counter electrodes such as platinum electrodes, gold electrodes, and graphite electrodes; this application does not impose any limitations on this. For ease of description, this application uses the lithium sheet 122 as an example for illustration.

[0132] Figure 5 This is a schematic diagram of a battery cell according to another embodiment of this application.

[0133] Figure 6 This is a schematic diagram of the structure of a battery cell according to another embodiment of this application. Figure 6 As shown, the outer packaging of the battery cell 100 includes a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator 123 can be formed into an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The battery cell 100 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to specific practical needs.

[0134] In some embodiments, the battery cells 100 can also be assembled into a battery module. The number of battery cells 100 contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0135] [Battery]

[0136] This application provides a battery, including the battery cell described in the above embodiments.

[0137] Figure 7 This is a schematic diagram of a battery according to one embodiment of this application. Figure 8 This is a schematic diagram of the battery structure according to one embodiment of this application. (Refer to...) Figure 7 and Figure 8 The battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box 401 and a lower box 402, the upper box 401 covering the lower box 402 to form a closed space for accommodating the battery cells 100. The plurality of battery cells 100 may be arranged in any manner within the battery box.

[0138] [Electrical appliances]

[0139] This application also provides an electrical device that includes the battery described in the foregoing embodiments. The electrical device includes at least one of the battery cell 100 or battery 400 provided in this application. The battery cell 100 or battery 400 can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0140] For example, Figure 9 This is a schematic diagram of the structure of an electrical device according to one embodiment of this application. Figure 9As shown, the electrical device is vehicle 1, which can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A motor 500, a controller 600, and a battery 400 can be installed inside vehicle 1. The controller 600 controls the battery 400 to supply power to the motor 500. For example, the battery 400 can be installed at the bottom, front, or rear of vehicle 1. The battery 400 can be used to power vehicle 1; for example, it can serve as the operating power source for vehicle 1's electrical system, such as for the power requirements of starting, navigation, and operation. In another embodiment of this application, the battery 400 can not only serve as the operating power source for vehicle 1 but also as the driving power source, replacing or partially replacing gasoline or natural gas to provide driving power to vehicle 1.

[0141] As the electrical device, either battery cell 100 or battery 400 can be selected according to its usage requirements.

[0142] The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery for this electrical device, a 100-cell battery or a 400-cell battery can be used.

[0143] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell (100) as their power source.

[0144] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0145] [Examples and Comparative Examples]

[0146] [Example 1-1]

[0147] (1) Preparation of current collector:

[0148] Aluminum foil with a thickness of 60 μm is used as the current collector.

[0149] Polishing process: Lay the aluminum foil flat and fix it on a smooth glass plate. Use a 200-400 grit polishing compound on the polishing head of the polishing machine, ensuring the compound contacts the aluminum foil. Then, turn on the power of the polishing machine and set the polishing speed to 20-100 rpm. First, polish horizontally back and forth for 10 revolutions, then polish vertically back and forth for 10 revolutions. Repeat this process 4 times to obtain the polished aluminum foil with a surface roughness Ra of 1.5 μm.

[0150] Punching process: A punching machine with a diameter of 14mm is used. First, the polished aluminum foil is wrapped with weighing paper, and then the aluminum foil is punched to obtain small round pieces. Then, the small round pieces are weighed using a four-digit balance, and the mass of the punched aluminum foil is recorded.

[0151] (2) Preparation of the positive electrode sheet:

[0152] Preparation of lithium iron phosphate suspension: First, place the assembled grinding jars on the worktable of the ball mill, ensuring the jars are properly connected to the transmission device—neither too loose nor too tight. To maintain stable operation of the planetary ball mill, reduce noise and vibration, and extend equipment life, the total weight of the four grinding jars on the main wheel (including the grinding jars, grinding balls, sample, and additives) should be consistent. If the sample volume is small, two grinding jars can be used for symmetrical grinding.

[0153] During grinding, first set the grinding parameters. This planetary ball mill is usually controlled by a microcomputer program, allowing settings such as a rotation speed of 500 rpm, a total grinding time of 6 hours, a 5-minute pause every 30 minutes, and three alternating forward and reverse operations. After setting, start the ball mill. After grinding for 6 hours, the equipment will automatically stop. Then, remove the grinding jar from the ball mill and turn off the mill. Next, filter the product by pouring it through a 1000-mesh sieve into a clean petri dish. After sieving out the zirconium balls, return them to the grinding jar. After the slurry in the petri dish has settled for 2-3 minutes, remove the supernatant and return it to the grinding jar. Repeat this process until all four grinding jars have been filtered. The lithium iron phosphate nanoparticles have a Dv50 of 1.41 μm. The solvent for the lithium iron phosphate suspension should be a chemically stable solvent to minimize chemical reactions with the positive electrode active material, such as water, ethanol, or methanol.

[0154] Spraying: The suspension of lithium iron phosphate nanoparticles is loaded into a spray gun, with the lithium iron phosphate nanoparticles accounting for 1% of the total mass of the suspension. 0.5 mL of the suspension is sprayed onto the punched current collector to obtain the positive electrode sheet.

[0155] Drying: Place the coated positive electrode sheet into a forced-air drying oven and set it to 85°C to remove the solvent from the electrode sheet.

[0156] Purging: Hot gas is used to purge the lithium iron phosphate nanoparticles so that they are arranged in single particles on the surface of the aluminum foil, while removing some of the lithium iron phosphate nanoparticles that have not been firmly adsorbed.

[0157] Weighing: The current collector is weighed using a high-precision balance (accuracy 0.1mg) before and after spraying. The difference between the two is the weight of the adsorbed active substance, i.e. the amount of adsorption.

[0158] (3) Preparation of negative electrode sheet:

[0159] Lithium foil is used as the negative electrode.

[0160] (4) Separating membrane:

[0161] A conventional polypropylene diaphragm is used.

[0162] (5) Preparation of electrolyte:

[0163] The electrolyte is a solution of ethylene carbonate (EC) / 1,3-dioxolane (DOL) / ethyl methyl carbonate (EMC) (volume ratio 1:1:1) in which 1.0 mol / L lithium hexafluorophosphate and 1.0% lithium nitrate are dissolved.

[0164] (6) Preparation of button half-cells:

[0165] After purging, transfer the positive electrode sheet into the glove box for assembly. First, place the negative electrode shell on a lint-free sheet, then place the nickel mesh inside the negative electrode shell with the convex side of the mesh facing upwards. Next, prepare a clean lithium sheet and remove the oxide film from its surface. Then, add 35 μl of electrolyte and place a flat separator membrane in the center; the electrolyte will naturally diffuse during this process. Add another 35 μl of electrolyte, and then place the positive electrode sheet. After that, cover the positive electrode shell with the positive active material facing down and centered, and use ceramic tweezers to smooth the electrode sheet flat. Finally, place the negative electrode shell upwards on the sealing machine, set the sealing parameters to 500 psi, and seal the battery.

[0166] [Examples 1-2]

[0167] The difference between Examples 1-2 and Examples 1-1 is that the grinding heads used in the polishing process of the aluminum foil are different, resulting in different surface roughness Ra and different adsorption amounts.

[0168] [Examples 1-3]

[0169] The difference between Examples 1-3 and Examples 1-1 is that the active material is different. Ternary lithium nickel cobalt manganese oxide material (where the molar ratio of nickel, cobalt and manganese is 8:1:1) is used, with a volume average particle size Dv50 of 10.6 μm, a surface roughness Ra of 11 μm on the aluminum foil, and an adsorption capacity of 25 mg.

[0170] [Examples 1-4]

[0171] The difference between Examples 1-4 and Examples 1-1 is that: the positive electrode uses a lithium sheet, and the negative electrode uses the same preparation method as the positive electrode in Example 1, using graphite as the negative electrode active material. A graphite suspension is prepared by grinding, wherein the volume average particle size Dv50 of the graphite particles is 17.4 μm; the current collector uses a copper sheet with a thickness of 100 μm. The surface roughness Ra of the copper sheet is 18 μm and the adsorption capacity is 22 mg due to the different grinding heads used in the grinding process.

[0172] [Examples 1-5]

[0173] The difference between Examples 1-5 and Examples 1-1 is that: the positive electrode uses a lithium sheet, and the negative electrode uses the same preparation method as the positive electrode in Example 1, using hard carbon as the negative electrode active material. A hard carbon suspension is prepared by grinding, wherein the volume average particle size Dv50 of the hard carbon particles is 10.6 μm; the current collector uses copper foil, and the surface roughness Ra of the copper foil is 18 μm and the adsorption capacity is 22 mg due to the different grinding head used in the grinding process.

[0174] [Comparative Example 1-1]

[0175] The difference between Comparative Example 1 and Example 1-1 is that the aluminum foil was not polished, resulting in a different adsorption capacity.

[0176] [Comparative Examples 1-2]

[0177] The difference between Comparative Examples 1-2 and Examples 1-3 is that the aluminum foil was not polished, resulting in different adsorption amounts.

[0178] [Comparative Examples 1-3]

[0179] The difference between Comparative Examples 1-3 and Examples 1-4 is that the copper sheets were not polished, resulting in different adsorption amounts.

[0180] [Comparative Examples 1-4]

[0181] The difference between Comparative Examples 1-4 and Examples 1-5 is that the copper foil was not polished, resulting in different adsorption amounts.

[0182] Table 1 shows the specific parameters of the electrodes of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-4 during the preparation of the electrodes, and Table 2 shows the relevant test results of the coin cells.

[0183] Table 1. Specific parameters of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-4.

[0184]

[0185] In Table 1, "Dv50" refers to the particle size corresponding to the particles whose cumulative volumetric particle size distribution percentage reaches 50% in the active material, and "Ra" refers to the surface roughness of the current collector.

[0186] [Physical Characterization of Electrodes]

[0187] (1) Surface morphology characterization

[0188] Surface morphology was characterized using scanning electron microscopy (SEM).

[0189] (2) Roughness measurement

[0190] The surface roughness Ra of the current collector was measured using a 3D profile measuring instrument.

[0191] (3) Test of volumetric particle size distribution

[0192] Volume average particle size can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions. As an example, take an appropriate amount of composite material and test the volume average particle size of the material using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Specifically, take an appropriate amount of the sample to be tested (sample concentration of 8-12% opacity is sufficient), add 20 ml of deionized water, and simultaneously perform external ultrasonic treatment for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to the standard GB / T19077-2016 / ISO 13320:2009.

[0193] (4) Test of adsorption capacity

[0194] The adsorption capacity is used to characterize the mass of active substances; the greater the adsorption capacity, the greater the mass of active substances.

[0195] Specifically, a high-precision balance is used to weigh the current collector before and after spraying the active material, and the mass difference is taken as the amount of active material adsorbed.

[0196] [Battery Performance Characterization]

[0197] (1) Cyclic performance test

[0198] The test temperature was 25℃. The coin cells prepared in the above embodiments and comparative examples were charged at a constant current of 0.33C to 3.65V, then charged at a constant voltage of 0.05C, and after resting for 10 minutes, discharged at 0.33C to 2.0V. The capacity obtained in this step was used as the initial capacity. Cyclic tests were performed using a constant current of 0.33C to 3.65V, a constant voltage of 3.65V to 0.05C, and a discharge of 0.33C to 2.0V. The capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The upper and lower voltage limits depend on the type of active material. For example, the upper voltage limit for lithium iron phosphate is 3.65V, and the lower voltage limit is 2.0V; the upper voltage limit for ternary nickel-cobalt-manganese lithium oxide is 4.25V, and the lower voltage limit is 2.5V; the upper voltage limit for graphite is 2V, and the lower voltage limit is 0.005V; and the upper voltage limit for hard carbon is 2V, and the lower voltage limit is 0V.

[0199] Then, calculate the number of cycles required for the battery to retain 90% of its capacity. The capacity retention rate (%) after n cycles is calculated as follows: (Discharge capacity of the nth cycle / Discharge capacity of the first cycle) × 100%.

[0200] (2) Gram capacity test

[0201] Coin cells were fabricated using active materials and then tested. Specifically, a positive electrode was fabricated using a positive active material and a lithium sheet was used as the negative electrode to fabricate a coin cell; or, a negative electrode was fabricated using a negative active material and a lithium sheet was used as the positive electrode to fabricate a coin cell.

[0202] The button cell was placed in a 25°C oven and left to stand for 2 hours before being charged and discharged.

[0203] The 0.1C charge-discharge process is as follows: charge with a constant current of 0.1C to 3.65V, continue constant voltage charging until the charging current is less than 0.05C and then stop; pause for 5 minutes; discharge with a constant current of 0.1C to 2.0V. The discharge capacity of this step is the discharge capacity of the active material.

[0204] (3) Battery cycle charge and discharge test

[0205] At 25℃, the coin cell was charged at a constant current rate of 1C to 4.2V, then charged at the upper voltage limit to a constant voltage until the current cutoff was 0.05C. After resting for 15 minutes, the coin cell was discharged at a constant current rate of 1C to 2.5V. This constitutes one charge-discharge cycle. This charge-discharge cycle was repeated for 3 cycles.

[0206] Table 2 Test results of Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-4

[0207] Number of cycles with a capacity retention rate of 90% Capacity (mAh / g) Example 1-1 85 140 Examples 1-2 89 169 Examples 1-3 95 175 Examples 1-4 105 354 Examples 1-5 100 475 Comparative Example 1-1 37 115 Comparative Examples 1-2 74 124 Comparative Examples 1-3 100 305 Comparative Examples 1-4 94 345

[0208] In this application, capacity retention rate is used to characterize the cycle performance of a battery. The higher the capacity retention rate, the higher the capacity is retained after the battery has cycled to a specific number of times, which means the battery has better cycle performance.

[0209] Figure 10 This is a SEM image of an electrode sheet according to one embodiment of this application. Specifically, it is a SEM image of the positive electrode sheet represented by Examples 1-1. From Figure 10 It can be seen that the lithium iron phosphate nanoparticles are uniformly attached to the surface of the aluminum foil, achieving a physical adsorption effect. The particle size distribution of these lithium iron phosphate nanoparticles ranges from 50 nm to 150 nm.

[0210] Figure 11 This is a charge-discharge curve diagram at a 0.1C rate according to an embodiment of this application. Specifically, it shows the charge-discharge curve of the coin cell represented by Example 1-1. During testing, three identical coin cells were prepared according to the operating steps in Example 1-1, and then the first charge-discharge curves of these cells at a 0.1C rate were measured, and the results were obtained respectively. Figure 11 (a), (b), and (c) in the example. From... Figure 11 As can be seen from (a), (b) and (c) in the figure, the test results of the three batteries prepared according to Example 1-1 are consistent, which shows that the batteries are reliable and stable during the charging and discharging process.

[0211] As can be seen from Examples 1-1 to 1-5, the technical solution of this application can not only use lithium sheets as half-cells in the positive electrode active material, but also in the negative electrode active material, thus adapting to different battery testing requirements.

[0212] As shown in Table 2, based on Examples 1-1 and 1-2, the volume average particle size Dv50 of the positive electrode active material lithium iron phosphate is the same, but the Ra value of the current collector surface is different. When Ra > Dv50, as the Ra value increases, more active material is adsorbed on the current collector surface, which helps to improve the specific capacity of the battery and make the cycle more stable. Therefore, this design is beneficial to the specific capacity and cycle performance of the battery.

[0213] As shown in Table 2, and based on Examples 1-1 and 1-1, it is evident that polishing the surface of the aluminum foil to form a current collector with a corresponding roughness, and then spraying the positive electrode active material lithium iron phosphate onto the surface of this current collector, can increase the adsorption capacity of the active material on the current collector surface. This is beneficial for maximizing the battery's specific capacity, improving cycle performance, and thus enabling the active material to perform its specific capacity normally and achieve stable cycling.

[0214] As shown in Table 2, and based on Examples 1-3 and Comparative Examples 1-2, polishing the surface of the aluminum foil to form a current collector with a corresponding roughness, and then spraying the positive electrode active material, ternary nickel-cobalt-manganese oxide, onto the surface of this current collector, can increase the adsorption capacity of the active material on the current collector surface. This is beneficial for improving the battery's specific capacity and cycle performance, thereby enabling the active material to perform its specific capacity normally and achieve stable cycling.

[0215] As shown in Table 2, and based on Examples 1-4 and Comparative Examples 1-3, grinding the surface of the copper sheet to form a current collector with a corresponding roughness, and then spraying the negative electrode active material graphite onto the surface of the current collector, can increase the adsorption capacity of the active material on the current collector surface. This is beneficial for improving the battery's specific capacity and cycle performance, thereby enabling the active material to perform its specific capacity normally and achieve stable cycling.

[0216] As shown in Table 2, and based on Examples 1-5 and Comparative Examples 1-4, polishing the surface of the copper foil to form a current collector with a corresponding roughness, and then spraying the negative electrode active material hard carbon onto the surface of the current collector, can increase the adsorption capacity of the active material on the current collector surface. This is beneficial for improving the battery's specific capacity and cycle performance, thereby facilitating the normal operation of the active material within its specific capacity and enabling stable cycling.

[0217] Figure 12 The figures shown are the cycle performance curves of Examples 1-1, 1-2, and Comparative Example 1-1 of this application. Specifically, they are the charge-discharge curves of the coin cell half-cells represented by Examples 1-1, 1-2, and Comparative Example 1-1. Figure 12 It is known that for lithium iron phosphate with different particle sizes Dv50, the roughness Ra of the current collector aluminum foil satisfies Ra > Dv50, which is beneficial for the current collector to adsorb more positive electrode active material, thereby enabling the specific capacity to approach the theoretical specific capacity of lithium iron phosphate. Simultaneously, it can also increase the battery's cycle performance, thus facilitating material evaluation.

[0218] [Example 2-1]

[0219] (1) Preparation of current collector:

[0220] Aluminum foil with a thickness of 60 μm is used as the current collector.

[0221] Polishing process: Lay the aluminum foil flat and fix it on a smooth glass plate. Use a 200-400 grit polishing compound on the polishing head of the polishing machine, ensuring the compound contacts the aluminum foil. Then, turn on the power of the polishing machine and set the polishing speed to 20-100 rpm. First, polish horizontally back and forth for 10 revolutions, then polish vertically back and forth for 10 revolutions. Repeat this process 4 times to obtain the polished aluminum foil with a surface roughness Ra of 1.5 μm.

[0222] Punching process: A punching machine with a diameter of 14mm is used. First, the polished aluminum foil is wrapped with weighing paper, and then the aluminum foil is punched to obtain small round pieces. Then, the small round pieces are weighed using a four-digit balance, and the mass of the punched aluminum foil is recorded.

[0223] (2) Preparation of the positive electrode sheet:

[0224] Preparation of lithium iron phosphate suspension: First, place the assembled grinding jars on the worktable of the ball mill, ensuring the jars are properly connected to the transmission device—neither too loose nor too tight. To maintain stable operation of the planetary ball mill, reduce noise and vibration, and extend equipment life, the total weight of the four grinding jars on the main wheel (including the grinding jars, grinding balls, sample, and additives) should be consistent. If the sample volume is small, two grinding jars can be used for symmetrical grinding.

[0225] During grinding, first set the grinding parameters. This planetary ball mill is usually controlled by a microcomputer program, allowing settings such as a rotation speed of 500 rpm, a total grinding time of 6 hours, a 5-minute pause every 30 minutes, and three alternating forward and reverse operations. After setting, start the ball mill. After grinding for 6 hours, the equipment will automatically stop. Then, remove the grinding jar from the ball mill and turn off the mill. Next, filter the product by pouring it through a 1000-mesh sieve into a clean petri dish. After sieving out the zirconium balls, return them to the grinding jar. After the slurry in the petri dish has settled for 2-3 minutes, remove the supernatant and return it to the grinding jar. Repeat this process until all four grinding jars have been filtered. The lithium iron phosphate nanoparticles have a Dv50 of 1.41 μm. The solvent for the lithium iron phosphate suspension should be a chemically stable solvent to minimize chemical reactions with the positive electrode active material, such as water, ethanol, or methanol.

[0226] Spraying: A suspension of lithium iron phosphate nanoparticles, comprising 1% of the total mass of the suspension, is loaded into a spray gun. 0.5 mL of the suspension is sprayed onto the punched current collector to obtain the positive electrode sheet. The sprayed surface density of the lithium iron phosphate material is 150 mg / 1540.25 mm. 2 .

[0227] Drying: Place the coated positive electrode sheet into a forced-air drying oven and set it to 85°C to remove the solvent from the electrode sheet.

[0228] Purging: Hot gas is used to purge the lithium iron phosphate nanoparticles so that they are arranged in single particles on the surface of the aluminum foil, while removing some of the lithium iron phosphate nanoparticles that have not been firmly adsorbed.

[0229] Weighing: The current collector was weighed using a high-precision balance (accuracy 0.1mg) before and after spraying. The difference between the two weighings represents the weight of the adsorbed active material, i.e., the adsorption capacity. Specifically, the adsorption capacity of the lithium iron phosphate material was 15mg / 153.86mm². 2 .

[0230] (3) Preparation of negative electrode sheet:

[0231] Lithium foil is used as the negative electrode.

[0232] (4) Separating membrane:

[0233] A conventional polypropylene diaphragm is used.

[0234] (5) Preparation of electrolyte:

[0235] The electrolyte is a solution of ethylene carbonate (EC) / 1,3-dioxolane (DOL) / ethyl methyl carbonate (EMC) (volume ratio 1:1:1) in which 1.0 mol / L lithium hexafluorophosphate and 1.0% lithium nitrate are dissolved.

[0236] (6) Fabrication of pouch cells:

[0237] The positive electrode, separator, and negative electrode are stacked in sequence to obtain a soft-pack stacked cell; the cell is placed in a pre-cut aluminum-plastic bag, electrolyte is added, and it is sealed. After high-temperature standing, formation, aging, capacity measurement, and k-value measurement, a single battery cell is obtained.

[0238] [Comparative Example 2-1]

[0239] The difference between Comparative Example 2-1 and Example 2-1 is that the aluminum foil was not polished, resulting in different adsorption amounts, and the positive electrode contains a binder and a conductive agent. The preparation of the positive electrode is as follows:

[0240] Lithium iron phosphate powder, conductive carbon, and polyvinylidene fluoride were mixed uniformly in a mass ratio of 90%:5%:5%. NMP was then added and the mixture was thoroughly stirred to prepare a positive electrode slurry. This slurry was then coated on both sides of a positive electrode current collector. After drying, cold pressing, and die-cutting, the positive electrode active layer was obtained to prepare the positive electrode sheet. The lithium iron phosphate material loading was 20 mg / 153.86 mm². 2 The coating surface density of the lithium iron phosphate material is 203.65 mg / 1540.25 mm. 2 .

[0241] Table 3 shows the specific parameters of the electrodes in Example 2-1 and Comparative Example 2-1 during the electrode preparation process, and Table 4 shows the relevant test results of the pouch-pack stacked battery.

[0242] Table 3 Specific parameters of Example 2-1 and Comparative Example 2-1

[0243] Materials for active substances Dv50(μm) Current collector materials Ra(μm) Example 2-1 Lithium iron phosphate 1.41 Aluminum foil 1.5 Comparative Example 2-1 Lithium iron phosphate 1.41 Aluminum foil 0.09

[0244] In Table 3, "Dv50" refers to the particle size corresponding to the particles whose cumulative volumetric particle size distribution percentage reaches 50% in the active material, and "Ra" refers to the surface roughness of the current collector.

[0245] [Physical Characterization of Electrodes]

[0246] (1) Surface morphology characterization

[0247] Surface morphology was characterized using scanning electron microscopy (SEM).

[0248] (2) Roughness measurement

[0249] The surface roughness Ra of the current collector was measured using a 3D profile measuring instrument.

[0250] (3) Test of volumetric particle size distribution

[0251] Volume average particle size can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and measure according to the manufacturer's instructions. As an example, take an appropriate amount of composite material and test the volume average particle size of the material using a Malvern 2000 (MasterSizer 2000) laser particle size analyzer. Specifically, take an appropriate amount of the sample to be tested (sample concentration of 8-12% opacity is sufficient), add 20 ml of deionized water, and simultaneously perform external ultrasonic treatment for 5 min (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to the standard GB / T19077-2016 / ISO 13320:2009.

[0252] (4) Test of adsorption capacity / loading

[0253] The adsorption capacity or loading capacity is used to characterize the mass of active substances. The greater the adsorption capacity or loading capacity, the greater the mass of active substances.

[0254] Adsorption capacity: The adsorption capacity of the active material was measured in Example 2-1. Specifically, a high-precision balance was used to weigh the current collector before and after spraying the active material, and the difference in mass was taken as the adsorption capacity of the active material.

[0255] Loading amount: The loading amount of active material was measured in Comparative Example 2-1. Specifically, the mass of the current collector before coating, m1 = current collector area × current collector surface density, was first calculated. Then, the mass of the prepared electrode, m2, was weighed. At this time, the loading amount of active material = (m2-m1) × the mass ratio of active material to slurry.

[0256] [Battery Performance Characterization]

[0257] (1) Difference in gas production

[0258] Specifically, the gas production of the batteries in Example 2-1 and Comparative Example 2-1 was tested using the equal volume method. First, the battery to be tested was placed in a sealed container system, nitrogen gas was introduced to purge the air from the container, the vent valve was closed, and the internal pressure P1 and temperature T1 of the container were recorded. At this time, the amount of gas in the system was n1 = P1V / RT1. Then, the battery was heated, and the internal pressure P2 and temperature T2 of the container were recorded. At this time, the gas production was n2 = P2V / RT2 - n1.

[0259] In Example 2-1 and Comparative Example 2-1, the gas production difference was measured using a lithium iron phosphate battery with Maclean CAS number 15365-14-7. First, the gas production n2, i.e., the gas production before modification, was obtained according to the gas production test method described above. Then, the active material was modified. Specifically, the active material was immersed in a glucose solution, dried at 105°C, and then calcined in a muffle furnace at 650°C for 6 hours. Subsequently, annealing was performed to obtain an active material containing carbon coating, i.e., the modified active material. At this point, the gas production n2' of the modified material was measured again according to the gas production test method described above.

[0260] At this point, the gas production difference is |n2'-n2|, which means the gas production difference is the absolute value of the gas production difference before and after the modification.

[0261] Table 4 Test results of Example 2-1 and Comparative Example 2-1

[0262] Difference in gas production (μL) Example 2-1 9 Comparative Example 2-1 1

[0263] This application uses the gas production difference to characterize the accuracy of active material evaluation. Specifically, since the binder and conductive agent in the electrode usually undergo side reactions such as oxidative decomposition with the active material, additional gas is generated. This side reaction produces a large amount of gas, which affects the actual gas production difference result, making the gas production difference smaller. A larger gas production difference indicates a more accurate test result, meaning a higher accuracy in active material evaluation.

[0264] As shown in Table 3, based on Examples 2-1 and 2-1, the electrode of Example 2-1 does not contain binders or conductive agents, which can reduce side reactions caused by binders and conductive agents with the active material during the synthesis of the active material. Therefore, the gas production difference of Comparative Example 2-1 is smaller, meaning that its gas production difference test result is inaccurate; the gas production difference of Example 2-1 is larger, meaning that the gas production difference test result is more accurate. Therefore, using the electrode in the embodiments of this application can improve the accuracy of performance evaluation of battery active materials.

[0265] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for evaluating active materials for secondary batteries, characterized in that, include: The current collector is polished to obtain a polished current collector; wherein the surface roughness Ra of the polished current collector and the volume average particle size Dv50 of the active material satisfy: Ra>Dv50. The active material is sprayed onto the polished current collector surface to obtain an electrode sheet; The active material is evaluated based on the electrode.

2. The method according to claim 1, characterized in that, The electrode does not contain binders or conductive agents.

3. The method according to claim 1 or 2, characterized in that, The polishing of the current collector includes: The current collector is placed and fixed on the substrate to support it; The grinding head of the grinding machine is determined based on the roughness. The grinding head is fixed to the front end of the grinder so that it comes into contact with the current collector; Turn on the power of the grinder and grind the current collector.

4. The method according to claim 3, characterized in that, The grinding head includes at least one of scouring pad, steel grit, polishing paste, and polishing cloth.

5. The method according to any one of claims 1 to 4, characterized in that, The spraying includes at least one of pressure spraying, air atomization spraying, high-speed rotary spraying, vacuum suction spraying, airless spraying, and ultrasonic spraying.

6. The method according to any one of claims 1 to 5, characterized in that, The method further includes: The electrode is dried to remove the solvent from it.

7. The method according to claim 6, characterized in that, The drying process includes at least one of the following: forced air drying, hot air drying, vacuum drying, freeze drying, constant temperature drying, and microwave drying.

8. The method according to any one of claims 1 to 7, characterized in that, The method further includes: The electrode is purged to obtain the active material having a single-particle arrangement structure.

9. The method according to claim 8, characterized in that, The purging includes at least one of hot gas purging, inert gas purging, compressed air purging, vacuum purging, and ultrasonic purging.

10. The method according to any one of claims 1 to 9, characterized in that, The electrode includes a positive electrode and a negative electrode.

11. The method according to claim 10, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes at least one of lithium-containing transition metal phosphate and lithium-containing transition metal oxide, wherein... The positive electrode active material is a lithium-containing transition metal phosphate, and the surface roughness Ra of the polished current collector is between 1.5 μm and 2 μm. The positive electrode active material is a lithium-containing transition metal oxide, and the surface roughness Ra of the polished current collector is between 11 μm and 15 μm; and / or, The negative electrode sheet includes a negative electrode active material, which includes at least one of graphite and hard carbon. The negative electrode active material is graphite, and the surface roughness Ra of the polished current collector is between 18 μm and 22 μm. The negative electrode active material is hard carbon, and the surface roughness Ra of the polished current collector is between 11 μm and 18 μm.

12. The method according to any one of claims 1 to 11, characterized in that, The electrode is used in at least one of the characterization device and the battery, wherein... The characterization equipment includes at least one of the following: in-situ scanning electron microscope, in-situ transmission electron microscope, in-situ X-ray photoelectron spectroscopy, nanoindentation instrument, and external charge-discharge instrument for assembled half-cells. The battery includes at least one of a half-cell and a full-cell battery.

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