Methods for characterizing the carbon coating layer of carbon-coated cathode materials and their applications

Abstract

This application relates to the field of battery material characterization technology, and particularly to a method for characterizing the carbon coating layer of a carbon-coated cathode material and its application. The method includes: preparing a sample to be tested: processing the carbon-coated cathode material using a focused ion beam method to prepare a sample to be tested; the thickness of the sample to be tested is less than 50 nm; characterizing and analyzing the sample to be tested: performing characterization and analysis on the sample to be tested using a transmission electron microscope (TEM) to determine the thickness and uniformity of the carbon coating layer of the carbon-coated cathode material. This application employs FIB-TEM combined technology to achieve effective characterization of complex structural materials; by using a focused ion beam method to process the carbon-coated cathode material to prepare a sample to be tested with a thickness of less than 50 nm, the limitations of thickness and region selection in traditional TEM sample preparation are overcome while ensuring the integrity of the sample to be tested, providing a testing basis for subsequent characterization and analysis.

Description

Technical Field

[0001] This application relates to the field of battery material characterization technology, and in particular to a method for characterizing the carbon coating layer of a carbon-coated cathode material and its application. Background Technology

[0002] In the field of electrochemical energy storage, lithium-ion batteries, with their high energy density (>200 Wh / kg), long cycle life (>1000 cycles), high charge-discharge efficiency (>95%), and stable operating voltage platform (3.6-3.8 V), have become the core power source for portable electronic devices, electric vehicles, and large-scale grid energy storage systems. As a key material in lithium-ion batteries, the performance of the cathode material directly determines the battery's energy density and cycle stability. Among them, nickel-cobalt-manganese ternary materials (LiNi... x Co y Mn (1-x-y) O2 (NCM) is considered the preferred cathode material for power batteries and energy storage batteries due to its high specific capacity, high operating voltage, and good stability. However, NCM materials still suffer from poor stability during electrochemical cycling, such as volume changes caused by lattice phase transitions, crack propagation, and poor thermal stability, all of which affect the cycle performance and safety of the cathode material and the battery. To address these issues, existing technologies have proposed modification methods such as ion doping, grain boundary regulation, concentration gradient design, and surface coating. Among these, carbon coating technology has become a research hotspot for NCM material optimization due to its multiple functionalities, including improving electronic conductivity, inhibiting grain growth, enhancing cycle stability, and improving thermal stability to some extent.

[0003] Against this backdrop, high-precision characterization of carbon coating layers is of positive significance for exploring the coating effect, morphology optimization, and performance correlation of NCM materials. Summary of the Invention

[0004] Carbon-coated NCM materials are an effective means to improve their performance. During the coating modification process, the thickness and uniformity of the carbon coating layer have a significant impact on the material properties. Therefore, accurately characterizing its thickness and uniformity, and further exploring its mechanism of action, has become a major challenge in current research on carbon-coated NCM materials. This application uses carbon-coated nickel-cobalt-manganese ternary materials as the research object, employing a one-step hot sintering process to prepare carbon-coated cathode materials. The thickness and uniformity of the carbon coating layer are systematically characterized using FIB-TEM technology. The aim is to evaluate the reliability of this technology in characterizing complex structural materials, provide theoretical support for the morphology optimization design of nickel-cobalt-manganese ternary materials, and expand the application potential of electron microscopy technology in new energy materials research.

[0005] A first aspect of this application provides a method for characterizing the carbon coating layer of a carbon-coated cathode material, the method comprising:

[0006] Preparation of the test sample: The carbon-coated cathode material was processed using the focused ion beam (FIB) method to prepare the test sample; the thickness of the test sample was less than 50 nm.

[0007] Characterization analysis of the test samples: Transmission electron microscopy (TEM) was used to characterize and analyze the test samples, and the thickness and uniformity of the carbon coating layer of the carbon-coated cathode material were measured.

[0008] Optionally, the step of preparing the sample to be tested includes:

[0009] Provide carbon-coated cathode material and select the target particle sampling area;

[0010] A protective layer is deposited on the surface of the target particle sampling area;

[0011] High-energy ion beams are used to etch carbon-coated cathode materials to form at least two trapezoidal grooves inside the target particles, a thin sheet is formed between the trapezoidal grooves, and a carbon coating layer is present on the surface of the thin sheet.

[0012] The thin sheet was thinned using a low-energy ion beam to prepare a sheet-like sample with a thickness of less than 50 nm.

[0013] In some embodiments, a nanomanipulator is used to remove the prepared sheet and weld it to a copper mesh, and then a low-energy ion beam is used to thin the sheet.

[0014] In some embodiments, scanning electron microscopy (SEM) is used to observe the carbon-coated cathode material. Since carbon-coated cathode materials are mostly spherical particles, particles with regular morphology and no defects are preferentially selected as target particles. To avoid the influence of arc surface deformation on the characterization results during sampling, relatively flat local areas of the particles are preferentially selected as sampling areas.

[0015] In some embodiments, the material of the protective layer may include tungsten, copper, platinum, titanium, nickel, etc.; in order to improve the protective effect and avoid damage to the sample surface during the cutting process, the material of the protective layer may be tungsten.

[0016] The deposition method of the protective layer is not particularly limited, as long as it can achieve the deposition purpose; for example, electrochemical deposition, chemical vapor deposition, magnetron sputtering, etc.

[0017] In some embodiments, both the high-energy ion beam and the low-energy ion beam are gallium ion beams.

[0018] Optionally, the processing conditions for the high-energy ion beam are: voltage 16kV-30kV, current 10nA-30nA; and the processing conditions for the low-energy ion beam are: voltage 2kV-10kV, current 20pA-80pA.

[0019] Further optionally, the processing conditions for the high-energy ion beam are: voltage 30kV, current 21nA; and the processing conditions for the low-energy ion beam are: voltage 5kV, current 40pA.

[0020] Traditional TEM typically employs mechanical sample preparation for thickness control, such as sanding and ion thinning. However, precise control of the thinning rate and final thickness is difficult during this process. Furthermore, samples with complex structures require even higher precision in sample preparation. Slight differences in hardness across different parts of the material, or uneven application of force, can easily lead to inconsistent sample thickness, and in severe cases, even cracks or breakage. These issues make traditional methods unsuitable for testing and characterizing complex samples (such as carbon-coated cathode materials). This application utilizes a high-energy ion beam to etch trapezoidal grooves in two regions above and below the protective layer. The high energy of the ion beam bombards the material surface, causing localized sputtering removal to initially form a thin sheet. The trapezoidal groove design effectively reduces stress concentration and ensures the structural integrity of the sample. Subsequently, the thin sheet is separated from the particle substrate using a rotating sample stage and U-shaped cutting technology. A nanorobot (Easylift) is used to extract the separated thin sheet and weld it onto a copper mesh for subsequent observation under a transmission electron microscope. To further ensure the high resolution requirements of transmission electron microscopy (TEM) observations, a low-energy ion beam was used to further thin and polish the sheet, reducing the sample thickness to the tens of nanometers level. Through multiple thinning and polishing operations, gallium ion implantation damage introduced by the ion beam during sample preparation can be minimized, thus ensuring the accuracy of TEM analysis results. This application leverages the high precision and flexibility of FIB technology to achieve the preparation of high-precision material samples, laying a solid foundation for subsequent TEM and other analyses.

[0021] In some embodiments, this application employs transmission electron microscopy to characterize and analyze the sample under test, focusing on the thickness and uniformity of the carbon coating layer; observes the overall morphology of the particle sample (including the target particle and the sample under test) using low-magnification TEM imaging mode, and determines the thickness of the carbon coating layer using high-resolution imaging mode.

[0022] In some embodiments, the step of characterizing and analyzing the sample to be tested further includes: using X-ray energy dispersive spectroscopy (EDS) to determine and analyze the elemental composition and spatial distribution of the sample to be tested, and combining the results of carbon coating thickness and coating uniformity measured by transmission electron microscopy to jointly evaluate the bonding state between the carbon coating and the nickel-cobalt-manganese ternary material.

[0023] In some implementations, a one-step hot sintering process is used to prepare carbon-coated cathode materials.

[0024] Optionally, the preparation method of the carbon-coated cathode material includes: mixing powdered nickel-cobalt-manganese ternary cathode material with a carbon source precursor solution and stirring evenly to obtain a suspension; heating to remove water from the suspension to obtain a gel-like material; and calcining the gel-like material to obtain the carbon-coated cathode material.

[0025] The nickel-cobalt-manganese ternary cathode material can include NCM811, NCM111, NCM442, NCM523, NCM613, NCM622, etc.; NCM811 can be selected as the alternative.

[0026] Optionally, the carbon source precursor solution is an aqueous solution of PVA (polyvinyl alcohol), and the concentration of the aqueous PVA solution is 0.1-2 mol / L; the polyvinyl alcohol can be commercially available, such as the Shanghai Test Polyvinyl Alcohol 1750±50 product.

[0027] Further optionally, the concentration of the PVA aqueous solution is 1 mol / L.

[0028] Optionally, the weight ratio of the powdered nickel-cobalt-manganese ternary cathode material to the carbon source precursor solution is (8-12):1; examples include 8:1, 9:1, 10:1, 11:1, 12:1; and further optionally 10:1.

[0029] Optionally, the heating temperature is 80-110°C; examples include 80°C, 85°C, 90°C, 95°C, 100°C, and 110°C; further, 100°C is optional.

[0030] Optionally, the calcination temperature is 350℃-500℃, and the calcination time is 20min-60min.

[0031] In some embodiments, the preparation method of the carbon-coated cathode material includes: mixing powdered nickel-cobalt-manganese ternary cathode material (NCM811) with a carbon source precursor solution at a weight ratio of 10:1, and stirring evenly to obtain a suspension; heating the suspension at 100°C to evaporate the water in the suspension to obtain a black, viscous, gel-like material; and calcining the gel-like material at 400°C for 30 minutes in an air atmosphere to obtain the carbon-coated cathode material.

[0032] The second aspect of this application provides an application of a method for characterizing the carbon coating layer of a carbon-coated cathode material, the method being applied in the field of battery material research and development.

[0033] The characterization method provided in this application can not only be used to characterize the microstructure and thickness of carbon-coated nickel-cobalt-manganese cathode materials, but can also be extended to the research of other new energy materials, and has great application potential.

[0034] Beneficial effects:

[0035] This application provides a method for characterizing the carbon coating layer of a carbon-coated cathode material and its application, which has the following advantages:

[0036] (1) This application uses FIB-TEM combined technology to achieve effective characterization of complex structure materials; the carbon-coated cathode material is processed by focused ion beam method to prepare a sample with a thickness of less than 50 nm. While ensuring the integrity of the sample, it solves the limitations of thickness and region selection in traditional transmission electron microscopy sample preparation, which facilitates subsequent characterization operations and provides a new analytical approach for revealing the relationship between the microstructure and composition of materials.

[0037] (2) This application uses a specific FIB processing method to process carbon-coated cathode material to form at least two trapezoidal grooves, with a thin sheet formed between the grooves, in order to meet the strict requirements of transmission electron microscopy analysis for sample thickness and coating uniformity; through precise ion beam cutting and thinning process, the limitations of traditional sample preparation methods in processing complex microstructure materials are overcome, providing a test basis for subsequent characterization and analysis.

[0038] (3) The FIB-TEM combined technology of this application can effectively characterize the thickness and uniformity of the carbon coating layer of the carbon-coated nickel-cobalt-manganese ternary cathode material, providing strong support for in-depth exploration of the correlation between the carbon coating layer and the material performance.

[0039] (4) The characterization method of this application is simple to operate, easy to implement, and the characterization results are accurate and reliable. It can be widely promoted in the field of battery materials and has broad application prospects. Attached Figure Description

[0040] Figure 1 Scanning electron microscope (SEM) images of carbon-coated cathode materials from the examples; Figure 1 (a) shows the overall distribution of the nickel-cobalt-manganese ternary particles, and (b) shows the low-magnification morphology of individual nickel-cobalt-manganese ternary particles.

[0041] Figure 2 Scanning electron microscope (SEM) images of each step in the preparation of the test sample in the example; Figure 2 (a) shows the selection of target particles; (b) shows the deposition of a protective layer; (c) shows the cutting of grooves to form a thin sheet; (d) shows the extraction of the sample by a nanorobot; (e) shows the welding of the sample to a copper mesh; and (f) shows the thinning process.

[0042] Figure 3Characterization results of carbon-coated cathode material and the sample under test; Figure 3 (a) is the overall HAADF image (high-angle annular dark field image) of the sample to be tested; (b) is the high-magnification HAADF image of the particle edge of the sample to be tested; (c) is the overall EDS mapping image of the sample to be tested. Detailed Implementation

[0043] This application provides a method for characterizing the carbon coating layer of carbon-coated cathode materials. Examples verify the efficiency and reliability of FIB-TEM in characterizing complex structural materials (carbon-coated nickel-cobalt-manganese ternary cathode materials). The ultrathin samples prepared by the focused ion beam method can accurately meet the requirements of TEM analysis. Combined with high-resolution imaging and energy dispersive spectroscopy, the compositional consistency and thickness distribution characteristics of the carbon coating layer are revealed, providing strong support for further research on the relationship between the carbon coating layer and material properties.

[0044] In some embodiments, the carbon-coated cathode material in the embodiments of this application is prepared using a one-step hot sintering process.

[0045] The method for preparing the carbon-coated cathode material provided in this application includes: mixing powdered nickel-cobalt-manganese ternary cathode material (NCM811) with a carbon source precursor solution at a weight ratio of 10:1 and stirring evenly to obtain a suspension; heating the suspension at 100°C to evaporate the water in the suspension to obtain a black, viscous, gel-like material; and calcining the gel-like material at 400°C for 30 minutes in an air atmosphere to obtain the carbon-coated cathode material.

[0046] The carbon source precursor solution is an aqueous solution of PVA (polyvinyl alcohol), and the concentration of the PVA aqueous solution is 1 mol / L; the polyvinyl alcohol has the product number 30153160 (named polyvinyl alcohol 1750±50) and is sourced from Shanghai Testing.

[0047] The scanning electron microscope image of the obtained carbon-coated cathode material is shown below. Figure 1 .like Figure 1 As shown, the microstructure of the carbon-coated cathode material prepared by the above method consists of secondary particles, with particle sizes concentrated in the range of 3μm-20μm. The particle surfaces are rough and the shapes are mostly approximately spherical. Furthermore, the secondary particles exhibit a loose packing characteristic in terms of distribution, with a certain degree of voids between most of the secondary particles.

[0048] Furthermore, all raw materials, equipment, and other consumables used in this application are commercially available.

[0049] Example 1

[0050] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material, the method comprising:

[0051] S1. Preparation of the test sample: The carbon-coated cathode material was processed using a focused ion beam method to prepare a test sample with a thickness of 50 nm; the specific preparation steps include:

[0052] S1.1, Provide carbon-coated cathode material and select the target particle sampling area ( Figure 2 (Figure (a))

[0053] S1.2, Deposit a protective layer on the surface of the target particle sampling area ( Figure 2 (Figure b)

[0054] S1.3. High-energy ion beams are used to etch the carbon-coated cathode material to form two trapezoidal grooves inside the target particle, with a thin sheet formed between the trapezoidal grooves. A carbon coating layer exists on the surface of the thin sheet. Figure 2 (Figure (c)); the thin film is separated from the particle substrate by a rotating sample stage and U-shaped cutting technique; the high-energy ion beam is a gallium ion beam; the processing conditions of the high-energy ion beam are: voltage 30kV, current 21nA.

[0055] S1.4. The prepared thin film is removed using a nanorobot (Easylift). Figure 2 (Figure d)

[0056] S1.5, Weld the thin sheet to the surface of the copper mesh ( Figure 2 (Figure e)

[0057] S1.6. The thin sheet is thinned and polished using a low-energy ion beam to prepare a sheet-like sample to be tested with a thickness of less than 50 nm. Figure 2 (See Figure (f)). The low-energy ion beam is a gallium ion beam; the processing conditions for the low-energy ion beam are: voltage 5kV, current 40pA.

[0058] S2. Characterization analysis of the test samples: Transmission electron microscopy and X-ray energy dispersive spectroscopy were used to characterize and analyze the test samples, determining the thickness and uniformity of the carbon coating layer of the carbon-coated cathode material; specifically:

[0059] S2.1 Observe the overall morphology of the target particles and the sample under test through low-magnification TEM imaging mode. Figure 3 (a) Figure Figure 3 (Figure b)

[0060] S2.2 The thickness of the carbon coating layer was measured to be 8nm-15nm using high-resolution imaging mode, with an average thickness of 10nm (since the distribution of the carbon coating layer is not completely uniform, the thickness measurement result is within the range of 8nm-15nm).

[0061] S2.3. X-ray energy dispersive spectroscopy was used to determine and analyze the elemental composition and spatial distribution of the sample. The results are shown in [Figure 1]. Figure 3 Figure (c) shows the bonding state between the carbon coating layer and the nickel-cobalt-manganese ternary material, which is evaluated by combining the results of carbon coating layer thickness and coating uniformity measured by transmission electron microscopy.

[0062] like Figure 3 As shown in Figure (a), the carbon-coated nickel-cobalt-manganese cathode material is used as secondary particles. Its cross-sectional morphology reveals that the secondary particles consist of primary particles ranging from tens to hundreds of nanometers in size, and these primary particles are loosely arranged rather than densely packed. Further details are provided below. Figure 3 As shown in Figure (b), high-resolution imaging revealed that the carbon coating layer was mainly distributed at the particle edges, exhibiting good continuity. Its thickness was approximately tens of nanometers, and the thickness distribution was relatively uniform. Furthermore, X-ray energy dispersive spectroscopy analysis showed that the presence of carbon (C) was clearly visible at the particle edges of the nickel-cobalt-manganese ternary cathode material, while O, Ni, Co, and Mn elements were uniformly distributed within the particles. In summary, the test results indicate that the carbon coating layer of the sample is complete and uniform, demonstrating good adhesion between the carbon coating layer and the nickel-cobalt-manganese ternary cathode material.

[0063] Example 2

[0064] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material, the method comprising:

[0065] S1. Preparation of the test sample: The carbon-coated cathode material was processed using a focused ion beam method to prepare a test sample with a thickness of 40 nm; the specific preparation steps include:

[0066] S1.1 Provide carbon-coated cathode material and select the target particle sampling area;

[0067] S1.2 Deposit a protective layer on the surface of the target particle sampling area;

[0068] S1.3. High-energy ion beams are used to etch the carbon-coated cathode material to form two trapezoidal grooves inside the target particle, with a thin sheet formed between the trapezoidal grooves. A carbon coating layer exists on the surface of the thin sheet. Figure 2 (Figure (c)); the thin film is separated from the particle substrate by a rotating sample stage and U-shaped cutting technique; the high-energy ion beam is a gallium ion beam; the processing conditions of the high-energy ion beam are: voltage 30kV, current 21nA.

[0069] S1.4. The prepared thin film is removed using a nanorobot (Easylift);

[0070] S1.5. Weld the thin sheet to the surface of the copper mesh;

[0071] S1.6. The thin sheet is thinned and polished using a low-energy ion beam to prepare a sheet-like sample with a thickness of less than 50 nm. The low-energy ion beam is a gallium ion beam; the processing conditions of the low-energy ion beam are: voltage 5 kV, current 40 pA.

[0072] S2. Characterization analysis of the test samples: Transmission electron microscopy and X-ray energy dispersive spectroscopy were used to characterize and analyze the test samples, determining the thickness and uniformity of the carbon coating layer of the carbon-coated cathode material; specifically:

[0073] S2.1 Observe the overall morphology of the target particles and the sample under test through low-magnification TEM imaging mode;

[0074] S2.2 The thickness of the carbon coating layer was measured to be 8nm-15nm using high-resolution imaging mode, with an average thickness of 10nm (since the distribution of the carbon coating layer is not completely uniform, the thickness measurement result is within the range of 8nm-15nm).

[0075] S2.3. X-ray energy dispersive spectroscopy was used to determine and analyze the elemental composition and spatial distribution of the sample. The results are shown in [Figure 1]. Figure 3 Figure (c) shows the bonding state between the carbon coating layer and the nickel-cobalt-manganese ternary material, which is evaluated by combining the results of carbon coating layer thickness and coating uniformity measured by transmission electron microscopy.

[0076] Example 3

[0077] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material. The specific implementation method is the same as in Embodiment 1; the difference is that the processing conditions of the high-energy ion beam are: voltage 16kV and current 10nA.

[0078] Example 4

[0079] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material. The specific implementation method is the same as in Embodiment 1; the difference is that the high-energy ion beam processing conditions are: voltage 30kV and current 30nA.

[0080] Example 5

[0081] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material. The specific implementation method is the same as in Embodiment 1; the difference is that the processing conditions of the low-energy ion beam are: voltage 2kV and current 20pA.

[0082] Example 6

[0083] This embodiment provides a method for characterizing the carbon coating layer of a carbon-coated cathode material. The specific implementation method is the same as in Embodiment 1; the difference is that the processing conditions of the low-energy ion beam are: voltage 10kV and current 80pA.

[0084] The combined schemes of Examples 1-6 demonstrate that the use of FIB-TEM in this application for sample processing and detection of carbon-coated nickel-cobalt-manganese ternary cathode materials enables efficient and reliable characterization of fine and complex structural materials. The ultrathin samples prepared by the specific FIB method can accurately meet the requirements of TEM analysis. Combined with high-resolution imaging and energy dispersive spectroscopy, the compositional consistency and thickness distribution characteristics of the carbon coating layer are revealed, providing strong support for further research on the relationship between the carbon coating layer and material properties.

[0085] It should be noted that the detailed descriptions listed in this application are merely specific descriptions of feasible implementations of the technology, and are not intended to limit the scope of protection of this application. All equivalent implementations or modifications made without departing from the spirit of the technology of this application should be included within the scope of protection of this application.

Claims

1. A method of characterizing a carbon coating layer of a carbon-coated cathode material, characterized by, The method comprises the following steps: Preparation of the sample to be tested: a carbon-coated positive electrode material is treated by a focused ion beam method to obtain a sample to be tested; the preparation method of the carbon-coated positive electrode material comprises: mixing a powdery nickel-cobalt-manganese ternary positive electrode material with a carbon source precursor solution, stirring uniformly to obtain a suspension; removing water in the suspension by heating to obtain a gel material; calcining the gel material to obtain the carbon-coated positive electrode material; the thickness of the sample to be tested is less than 50 nm; Characterization analysis of the sample to be tested: the sample to be tested is characterized and analyzed by a transmission electron microscope to measure the thickness and uniformity of the carbon-coated layer of the carbon-coated positive electrode material; the overall morphology of the particle sample is observed by a low-magnification TEM imaging mode, the thickness of the carbon-coated layer is measured by a high-resolution imaging mode, the element composition and element spatial distribution of the sample to be tested are measured and analyzed by X-ray energy dispersive spectroscopy, and the combination state of the carbon-coated layer and the nickel-cobalt-manganese ternary material is evaluated together based on the thickness and uniformity of the carbon-coated layer measured by the transmission electron microscope; The step of preparing the sample to be tested comprises: Providing a carbon-coated positive electrode material and selecting a target particle sampling area; Depositing a protective layer on the surface of the target particle sampling area; Using a high-energy ion beam to etch the carbon-coated positive electrode material to form at least two trapezoidal grooves in the target particle, wherein a thin sheet is formed between the trapezoidal grooves, and the surface of the thin sheet has a carbon-coated layer; Using a low-energy ion beam to thin the thin sheet to obtain a thin sheet-shaped sample to be tested with a thickness of less than 50 nm; The processing conditions of the high-energy ion beam are: voltage 30 kV, current 21 nA; the processing conditions of the low-energy ion beam are: voltage 5 kV, current 40 pA.

2. The method of characterizing a carbon coating of a carbon-coated cathode material of claim 1, wherein, The material of the protective layer comprises tungsten.

3. The method of characterizing a carbon coating of a carbon-coated cathode material of claim 2, wherein, Both the high-energy ion beam and the low-energy ion beam are gallium ion beams.

4. Use of a method of characterizing a carbon coating layer of a carbon-coated positive electrode material according to claim 1, characterized in that The method is applied to the field of battery material research and development.

Images