Negative electrode active material for lithium secondary battery and evaluation method thereof

Abstract

The present invention relates to a negative electrode active material having improved carbon coating properties and a method for evaluating coating properties thereof. According to the present invention, the carbon coating uniformity of a negative electrode active material for a lithium secondary battery is identified with high reliability, thereby preferentially selecting groups that are likely to undergo aggregation, among raw material units (LOT), leading to improved process efficiency.

Description

Negative active material for lithium secondary batteries and method for evaluating the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0160801 filed November 13, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0002] The present invention relates to a negative electrode active material with improved carbon coating characteristics. It also relates to a method for evaluating the coating characteristics of a negative electrode active material.

[0003] In the case of graphite negative electrode active materials used in lithium secondary batteries, carbon coating is essential to enhance conductivity and improve physical properties through the substitution of surface functional groups. In the slurry preparation step involving the dispersion of active materials, which is one of the electrode manufacturing processes, the uniformity of the carbon coating and the control of functional groups are essential factors for the stable formation of the slurry. If the slurry preparation is not stable, there is a very high possibility that problems will occur in subsequent electrode manufacturing steps due to aggregation of active materials.

[0004] When preparing a slurry by dispersing an active material in water, it is important to determine the uniformity and extent of the carbon coating on various particles at the raw material level before dispersion in order to check for aggregation.

[0005] Conventionally, the D / G band ratio obtained from a single-point Raman spectrum was analyzed to determine the level of crystallinity and applied as a simple indicator to identify only the presence of graphite material. However, since graphite, a key material, is characterized by high crystallinity among carbon materials, and the D / G band ratio parameter of the Raman spectrum does not represent the actual surface characteristics of graphite, there are limitations in assessing coating uniformity and surface characteristics of carbon-coated graphite. Furthermore, conventional Raman spectrum analysis suffers from the drawbacks of simple ratio calculations and low sample size, which leads to a problem where the reliability of measurement results regarding the coating characteristics of cathode active materials is reduced.

[0006] Therefore, an analytical method is required to determine the uniformity of the carbon coating.

[0007] The objective of the present invention is to provide a negative electrode active material for a lithium secondary battery with improved coating characteristics. It is also to provide a method for evaluating the coating characteristics of the negative electrode active material.

[0008] To solve the above problem, the present invention provides a Raman spectrum in which the ratio of the D-band peak area to the G-band peak area is 0.5 or greater, the relative standard deviation is 18% or greater, and the Raman shift range is D-band 1250–1450 cm⁻¹ -1 and G band 1500~1700cm -1 Phosphorus provides a negative electrode active material for lithium secondary batteries.

[0009] According to one embodiment, the negative electrode active material may include graphite coated with amorphous carbon.

[0010] According to one embodiment, the Raman spectrum measurement can be performed for 200 to 1000 points.

[0011] According to another embodiment of the present invention, the method comprises the steps of: measuring a Raman spectrum for a negative electrode active material coated with amorphous carbon; performing two-dimensional mapping from the measurement results; and Raman shift D band 1250–1450 cm⁻¹ -1 and G band 1500~1700cm -1 A method for evaluating a negative electrode active material for a lithium secondary battery is provided, comprising the step of calculating the mean and standard deviation of the D-band peak area / G-band peak area ratio, and predicting that the performance of the electrode is good when the D-band peak area / G-band peak area ratio is 0.5 or higher and the relative standard deviation is 18% or higher.

[0012] According to another embodiment of the present invention, a method for predicting electrode performance is provided, comprising the method described above.

[0013] In addition, according to another embodiment of the present invention, a system comprising the method as described above is provided.

[0014] Specific details of other embodiments of the present invention are included in the following detailed description.

[0015] According to the present invention, process efficiency can be improved by reliably identifying the uniformity of carbon coating characteristics for a negative electrode active material for a lithium secondary battery and preferentially selecting groups within a raw material lot that are likely to undergo aggregation.

[0016] Figure 1 shows the results of Raman spectrum measurements.

[0017] Figure 2 shows the 2D Raman mapping results.

[0018] Figure 3 shows the relationship between the D / G band ratio and the presence or absence of slurry clumping.

[0019] Figure 4 shows the relationship between the relative standard deviation of the D / G band and the presence or absence of slurry clumping.

[0020] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0021] Generally, the battery manufacturing process includes a step of preparing a negative electrode active material, such as carbon-coated graphite, as an aqueous slurry and coating it onto a current collector. At this time, since there is a problem of aggregation occurring when the slurry is prepared solely with crystalline graphite, a step of coating the graphite with amorphous carbon is included. By including this coating step, the surface of the negative electrode active material becomes more functional with respect to functional groups and reacts more easily with the solvent.

[0022] Conventionally, the D / G band ratio obtained from Raman spectra was analyzed to determine high or low crystallinity and applied as a simple indicator to identify only the presence of graphite material. However, conventional methods have limitations in assessing coating uniformity and surface characteristics of carbon-coated graphite.

[0023] When actual graphite material is treated with a carbon coating, the crystallinity of the carbon coating is lower than that of the graphite. In addition, compared to bare graphite, the D / G band ratio of the coated graphite tends to be higher, and the deviation also tends to increase. In this invention, the crystallinity and uniformity of coated graphite particles are evaluated based on the D / G band ratio and its mean and deviation. Furthermore, the characteristics of the coating surface are identified from the analyzed information, and a standard is established to evaluate the degree of aggregation of the active material at the raw material level during slurry preparation.

[0024] Hereinafter, a negative electrode active material for a lithium secondary battery and a method for evaluating the same according to an embodiment of the present invention will be described in more detail.

[0025] The present invention relates to a Raman spectrum in which the ratio of the D-band peak area to the G-band peak area (D / G band peak area, D / G band ratio) is 0.5 or greater, the relative standard deviation is 18% or greater, and the Raman shift range is D-band 1250–1450 cm⁻¹. -1 and G band 1500~1700cm -1 Phosphorus provides a negative electrode active material for lithium secondary batteries.

[0026] The negative electrode active material of the present invention may include graphite coated with amorphous carbon.

[0027] Different planes of graphite transform or rotate around the axis of symmetry, 1580 cm -1 A Raman peak appears in the nearby G band region. This peak indicates the single crystallinity of highly ordered pyrolytic graphite (HOPG), and the height of the peak in the G band is proportional to this single crystallinity.

[0028] In the case of carbon with an amorphous structure, for example, carbon black, 1350 cm -1 It exhibits a peak in the nearby D-band region. The D-band is associated with structural disturbances near irregular microcrystalline edges. Therefore, the D-band is proportional to the disorder of the sample and is opposite to the nature of the G-band.

[0029] Therefore, the degree of disorder of graphite can be determined by checking the D / G band peak area ratio according to Raman peak intensity. When crystalline graphite is coated with amorphous carbon, the D / G band peak area ratio value increases as crystallinity decreases. In addition, uniformity decreases and the deviation of the D / G band peak area ratio value increases. In particular, when the ratio of the D / G band peak area is 0.5 or higher, for example, 0.5 to 0.7 or 0.5 to 0.6, and the relative standard deviation is 18% or higher, for example, 18 to 22, 18 to 21, or 18 to 20, the coating properties of the cathode active material are excellent, and aggregation phenomena can be prevented during slurry preparation.

[0030] According to one embodiment, the Raman spectrum measurement may be performed for 200 to 1000 points, for example, 200 to 800, 300 to 600, or 350 to 550 points. The number of measurements or points is not particularly limited as long as it is 400 or more, and can be appropriately selected to be 400 or more.

[0031] The present invention ensures reliability by increasing the number of measurement points and can calculate the average and standard deviation from the measurement values ​​of multiple points.

[0032] According to another embodiment of the present invention, the method comprises the steps of: measuring a Raman spectrum for a negative electrode active material coated with amorphous carbon; performing two-dimensional mapping from the measurement results; and Raman shift D band 1250–1450 cm⁻¹ -1 and G band 1500~1700cm -1A method for evaluating a negative electrode active material for a lithium secondary battery is provided, comprising the step of calculating the mean and standard deviation of the ratio of the D-band peak area to the G-band peak area, wherein the ratio of the D-band peak area to the G-band peak area is 0.5 or higher, for example, 0.5 to 0.7 or 0.5 to 0.6, and the relative standard deviation is 18%, for example, 18 to 22, 18 to 21 or 18 to 20, and the performance of the electrode is predicted to be good.

[0033] According to another embodiment of the present invention, a method for predicting electrode performance is provided, comprising the method described above.

[0034] In addition, according to another embodiment of the present invention, a system comprising the method as described above is provided.

[0035] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0036] Examples

[0037] Samples 1 to 4 were prepared by spreading graphite (QCG-N2, ShanShan) with a pitch-coated surface onto a slide glass. The pitch used for the coating is a carbon material produced by heat-treating the residue obtained from the distillation of petroleum.

[0038] The manufactured samples were analyzed using 2D Raman mapping (LamRam HR Evolution, Horiba). Three scans were performed for 1 second per point, and signals were collected using an x50 objective lens by irradiating the sample with a 532 nm laser.

[0039] Using software (Horiba), the baseline and area, as well as the integral values ​​of the D-band and G-band for each point, were calculated, and the mean and standard deviation of the D / G band ratio for each active material were determined. The baseline and Raman shift range were determined by specifying them regardless of the characteristics of the sample.

[0040] The analysis conditions are as follows:

[0041] Excitation laser wavelength: 532nm

[0042] Laser Power: 0.8mW

[0043] Detector exposure time (exposure time per unit analysis area): Measured 3 times at 1 second intervals for a total of 1 second.

[0044] Grating: 600 groove / mm

[0045] Pixel resolution: 1cm -1

[0046] Mapping size: 40μm x 40μm

[0047] Mapping pixel size 2μm x 2μm

[0048] Measurement points: 400

[0049] D / G band ratio = D band peak area / G band peak area

[0050] Raman shift area range

[0051] D-band: 1250~1450cm -1

[0052] G Band: 1500~1700cm -1

[0053]

[0054] The mean, standard deviation, and relative standard deviation (RSD) were calculated from the measurements for a total of 400 points.

[0055] The graph of the Raman spectrum measurement results for Sample 1 is shown in Fig. 1. In addition, the 2D mapping results are shown in Fig. 2.

[0056] The D / G band ratio, standard deviation, relative standard deviation, and results regarding the presence or absence of aggregation for samples 1 to 4 are listed in Table 1.

[0057] D / G Band Ratio Standard Deviation Relative Standard Deviation (%) Residual Amount After Coagulation Filter (g) Sample 10.5 10.0 9 7 19.1 X 0.9 Sample 20.5 20.1 19.1 X 2.1 Sample 30.4 9 0.0 7 114.6 O 7.0 Sample 40.4 8 0.0 8 4 17.3 O 10.4

[0058] The relationship between the D / G band ratio and the presence or absence of slurry clumping according to the example is graphed in FIG. 3. The graph of clumping X corresponds to sample 1, and the graph of clumping O corresponds to sample 3. In addition, the relationship between the relative standard deviation of the D / G band and the presence or absence of slurry clumping according to the example is graphed in FIG. 4.

[0059] As described above, it was confirmed that the relationship between the D / G band ratio, relative standard deviation, and the presence or absence of slurry aggregation is consistent based on a specific value. Specifically, for an active material analyzed according to the present invention, if the criteria of a D / G band peak area ratio of 0.5 or higher and a relative standard deviation of 18% or higher are satisfied, it can be determined that the carbon coating uniformity is excellent. It can be predicted that an active material satisfying the above criteria will not exhibit aggregation during slurry preparation, and accordingly, coating characteristics can be predicted for the active material in powder form prior to slurry preparation. Furthermore, by selecting an active material that satisfies specific criteria, an active material with improved coating characteristics can be provided.

[0060] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and variations within the scope of the essential characteristics of the present invention. Furthermore, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. From the Raman spectrum, the ratio of D-band peak area to G-band peak area is 0.5 or greater, and the relative standard deviation is 18% or greater, and The Raman shift range is D band 1250–1450 cm -1 and G band 1500~1700cm -1 Phosphorus, negative electrode active material for lithium secondary batteries.

2. In Paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the negative electrode active material comprises graphite coated with amorphous carbon.

3. In Paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the above Raman spectrum measurement is performed for 200 to 1000 points.

4. A step of measuring the Raman spectrum of the cathode active material; Step of two-dimensional mapping from measurement results; and Raman shift D band 1250~1450cm -1 and G band 1500~1700cm -1 It includes the step of calculating the mean and standard deviation of the D-band peak area / G-band peak area ratio, A method for evaluating a negative electrode active material for a lithium secondary battery, wherein the electrode performance is predicted to be good when the ratio of the D-band peak area to the G-band peak area is 0.5 or higher and the relative standard deviation is 18% or higher.

5. In Paragraph 4, A method for evaluating a negative electrode active material for a lithium secondary battery, wherein the negative electrode active material comprises graphite coated with amorphous carbon.

6. In Paragraph 4, A method for evaluating a negative electrode active material for a lithium secondary battery, wherein the above Raman spectrum measurement is performed on 200 to 1000 points or more.

7. A method for predicting electrode performance including the method according to paragraph 4.

8. A system including the method according to paragraph 4.

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