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

Abstract

This invention relates to a negative electrode active material with improved carbon coating properties and a method for evaluating the coating properties. According to this invention, the uniformity of carbon coating in a negative electrode active material for lithium-ion batteries is assessed with high reliability, thereby preferentially selecting potentially agglomerated groups within the raw material unit (LOT), thus improving process efficiency.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0160801, filed on November 13, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0002] This invention relates to a negative electrode active material with improved carbon coating properties. This invention also relates to a method for evaluating the coating properties of the negative electrode active material. Background Technology

[0003] In the case of graphite anode active materials used in lithium-ion batteries, carbon coating is necessary to improve physical properties through enhanced conductivity and surface functional group substitution. During slurry preparation, which involves dispersing the active material as part of the electrode manufacturing process, the uniformity of the carbon coating and the control of functional groups are essential for forming a stable slurry. If the slurry preparation process is unstable, the likelihood of problems arising in subsequent electrode manufacturing processes due to agglomeration of the active materials is very high.

[0004] When preparing a slurry by dispersing active materials in water, it is important to assess the uniformity and extent of carbon coating on multiple particles at the raw material level before dispersion in order to confirm the agglomeration situation.

[0005] Traditionally, the D / G band ratio obtained from single-point Raman spectroscopy is analyzed to determine whether crystallinity is high or low, and is used as a simple indicator to determine whether a material is graphite. However, due to the high crystallinity of graphite, the main material, among carbon materials, and the fact that the D / G band ratio parameter of Raman spectroscopy cannot represent the actual surface properties of graphite, there are limitations in judging the coating uniformity and surface properties of carbon-coated graphite. Traditional Raman spectroscopy analysis suffers from low reliability in measuring the coating characteristics of negative electrode active materials due to its simple ratio calculations and limitations in small sample sizes.

[0006] Therefore, an analytical method is needed to identify the uniformity of carbon coating. Summary of the Invention

[0007] Technical issues

[0008] One object of the present invention is to provide a negative electrode active material for lithium secondary batteries with improved coating properties. A method for evaluating the coating properties of the negative electrode active material is also provided.

[0009] Solution to the problem

[0010] To address the aforementioned problems, this invention provides a negative electrode active material for lithium secondary batteries, wherein the ratio of the D-band peak area to the G-band peak area from the Raman spectrum is 0.5 or higher, the relative standard deviation is 18% or higher, and the Raman shift range of the D-band is 1250 to 1450 cm⁻¹. -1 The Raman shift of the G-band ranges from 1500 to 1700 cm. -1 .

[0011] According to one embodiment, the negative electrode active material may comprise graphite coated with amorphous carbon.

[0012] According to one embodiment, the Raman spectroscopy measurement can be performed on 200 to 1000 points.

[0013] According to another aspect of the present invention, a method for evaluating negative electrode active materials for lithium secondary batteries is provided, comprising: measuring the Raman spectrum of a negative electrode active material coated with amorphous carbon; performing two-dimensional mapping based on the measurement results; and obtaining the Raman shift D band from 1250 to 1450 cm⁻¹. -1 and G-band 1500 to 1700 cm -1 The average value and standard deviation of the ratio of D-band peak area to G-band peak area are used to predict the electrode's performance. If the ratio of D-band peak area to G-band peak area is greater than 0.5 and the relative standard deviation is greater than 18%, the electrode is considered to have good performance.

[0014] According to another aspect of the present invention, an electrode performance prediction method including the above-described method is provided.

[0015] According to another aspect of the present invention, a system comprising the above-described method is provided.

[0016] Specific details of other embodiments of the present invention are contained in the following detailed description.

[0017] Invention Effects

[0018] According to the present invention, the uniformity of carbon coating on the negative electrode active material for lithium secondary batteries can be reliably identified, thus allowing for the preferential selection of groups with agglomeration potential in the raw material unit (LOT unit), thereby improving process efficiency. Attached Figure Description

[0019] Figure 1 This displays the results of Raman spectroscopy measurements.

[0020] Figure 2 Display the results of the two-dimensional Raman mapping.

[0021] Figure 3 This shows the relationship between the D / G belt ratio and the presence or absence of slurry agglomeration.

[0022] Figure 4 This shows the relationship between the relative standard deviation of the D / G belt and the presence or absence of slurry agglomeration. Detailed Implementation

[0023] This invention can be modified in various ways and has many embodiments, which will be illustrated and described in detail. However, this is not intended to limit the invention to the specific embodiments, but should be understood to include all variations, equivalents and alternatives within the spirit and technical scope of the invention.

[0024] Typically, battery manufacturing processes involve preparing a negative electrode active material, such as carbon-coated graphite, in an aqueous slurry and then coating it onto a current collector. Here, because agglomeration occurs when only crystalline graphite is used to prepare the slurry, the process includes coating the graphite with amorphous carbon. This coating step increases the number of functional groups on the surface of the negative electrode active material, promoting its reaction with the solvent.

[0025] Traditionally, the D / G band ratio obtained from Raman spectroscopy is analyzed to determine whether crystallinity is high or low, and is used as a simple indicator to determine whether a material is graphite. However, traditional methods have limitations in determining the coating uniformity and surface properties of carbon-coated graphite.

[0026] In fact, when carbon coating is applied to graphite, the crystallinity of the carbon coating is lower than that of the graphite itself. Furthermore, the D / G band ratio tends to increase compared to uncoated graphite (bare graphite), and the deviation of the coated graphite also tends to increase. In this invention, the aim is to evaluate the crystallinity and uniformity of coated graphite particles based on the D / G band ratio and its average value and deviation. Furthermore, the aim is to establish standards for identifying the characteristics of the coated surface based on analytical information and for evaluating the degree of agglomeration of active materials at the raw material level during slurry preparation.

[0027] The following will describe in more detail the negative electrode active material for lithium secondary batteries and its evaluation method according to embodiments of the present invention.

[0028] This invention provides a negative electrode active material for lithium secondary batteries, wherein the ratio of the D-band peak area to the G-band peak area (D / G band ratio) from the Raman spectrum is 0.5 or higher, the relative standard deviation is 18% or higher, and the Raman shift range of the D band is 1250 to 1450 cm⁻¹. -1 The Raman shift of the G-band ranges from 1500 to 1700 cm. -1 .

[0029] The negative electrode active material of the present invention may contain graphite coated with amorphous carbon.

[0030] Different crystal planes of graphite transform or rotate around a symmetry axis, and at 1580 cm⁻¹ -1A Raman peak appears in the nearby G-band region. This peak indicates the monocrystalline nature of high-order pyrolytic graphite (HOPG), and the peak height in the G-band is proportional to the monocrystalline nature.

[0031] Carbon with an amorphous structure (such as carbon black) at 1350 cm⁻¹ -1 The nearby D-band region shows peaks. The D-band is associated with structural disorder near the edges of irregular crystallites. Therefore, the D-band is proportional to the degree of disorder in the sample and has the opposite properties to the G-band.

[0032] Therefore, the degree of disorder in graphite can be determined by analyzing the D / G band area ratio based on the Raman peak intensity. When crystalline graphite is coated with amorphous carbon, crystallinity decreases, and the D / G band area ratio increases accordingly. Furthermore, uniformity deteriorates, and the deviation of the D / G band area ratio increases. In particular, when the D / G band area ratio is 0.5 or higher (e.g., 0.5 to 0.7 or 0.5 to 0.6) and the relative standard deviation is 18% or higher (e.g., 18 to 22, 18 to 21, or 18 to 20), the coating properties of the negative electrode active material are excellent, thereby preventing agglomeration during slurry preparation.

[0033] According to one implementation, Raman spectroscopy measurements can be performed on 200 to 1000 points (e.g., 200 to 800, 300 to 600, 350 to 550 points). There is no particular limitation on the number of measurements or the number of measurement points, as long as it is 400 or more, and it can be appropriately selected from 400 or more.

[0034] According to the present invention, reliability can be ensured by increasing the number of measurement points, and the average and standard deviation can be calculated from the measurements of multiple points.

[0035] According to another aspect of the present invention, a method for evaluating negative electrode active materials for lithium secondary batteries is provided, comprising: measuring the Raman spectrum of a negative electrode active material coated with amorphous carbon; performing two-dimensional mapping based on the measurement results; and obtaining the Raman shift D band from 1250 to 1450 cm⁻¹. -1 and G-band 1500 to 1700 cm -1 The mean and standard deviation of the ratio of D-band peak area to G-band peak area are used to predict the electrode's performance. If the ratio of D-band peak area to G-band peak area is greater than 0.5 (e.g., 0.5 to 0.7 or 0.5 to 0.6) and the relative standard deviation is greater than 18% (e.g., 18 to 22, 18 to 21, or 18 to 20), the electrode is predicted to have good performance.

[0036] According to another aspect of the present invention, an electrode performance prediction method including the above-described method is provided.

[0037] According to another aspect of the present invention, a system comprising the above-described method is provided.

[0038] Embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0039] Example

[0040] Samples 1 to 4 were prepared by spreading graphite (QCG-N2, manufactured by ShanShan) coated with bitumen on a glass slide. The bitumen used for coating is a carbonaceous material manufactured by heat-treating the residue obtained from petroleum distillation.

[0041] The prepared samples were analyzed using 2D Raman mapping (LamRam HR Evolution, manufactured by Horiba). Each point was scanned three times per 1 second, and a 532 nm laser was applied to the sample, with signals collected using an x50 objective lens.

[0042] The baseline and area, as well as the integral values ​​of the D-band and G-band at each point, were calculated using software (Horiba). The mean and standard deviation of the D / G band ratio for each active material were also calculated. The choice of baseline and Raman shift range was independent of sample characteristics.

[0043] The analysis conditions are as follows: Excitation laser wavelength: 532 nm Laser power: 0.8 mW Detector exposure time (exposure time per unit analysis area): 3 repeated measurements, 1 second each, total 1 second. Grating: 600 grooves / mm Pixel resolution: 1 cm -1 Mapping size: 40 μm × 40 μm Mapped pixel size 2 μm × 2 μm Measurement points: 400 D / G band ratio = D band peak area / G band peak area Raman displacement region range D-band: 1250~1450 cm -1 G-band: 1500–1700 cm -1 The mean, standard deviation, and relative standard deviation (RSD) are calculated from all 400 measurements.

[0044] The Raman spectral measurement results of sample 1 are illustrated in the figure. Figure 1 Additionally, the 2D mapping results are shown in... Figure 2 .

[0045] The results of D / G band ratio, standard deviation, relative standard deviation, and presence or absence of aggregation for samples 1 to 4 are shown in Table 1.

[0046] [Table 1]

[0047] According to the embodiment, the relationship between the D / G belt ratio and the presence or absence of slurry agglomeration is... Figure 3 The figures are illustrated graphically. The graph for agglomeration X is for sample 1, and the graph for agglomeration O is for sample 3. Furthermore, the relationship between the relative standard deviation of the D / G bands and the presence or absence of slurry agglomeration according to the embodiments is shown in... Figure 4 As shown in the image.

[0048] As described above, it was confirmed that, based on specific values, the relationship between the D / G band ratio and relative standard deviation and the presence or absence of slurry agglomeration is consistent. Specifically, it can be determined that when the active material analyzed according to the present invention meets the criteria of a D / G band peak area ratio of 0.5 or higher and a relative standard deviation of 18% or higher, the carbon coating uniformity is excellent. It can be predicted that the active material meeting the above criteria will not undergo agglomeration during slurry manufacturing, and therefore the coating characteristics of the active material in powder form can be predicted before slurry manufacturing. Furthermore, by selecting active materials that meet specific criteria, active materials with improved coating characteristics can be provided.

[0049] The above description is merely an example of the technical concept of the present invention. Those skilled in the art can make various modifications and variations without departing from the essential characteristics of the present invention. Furthermore, the embodiments disclosed in this invention are not intended to limit the technical concept of the invention, but rather to explain it; the scope of the technical concept of the invention is not limited by these embodiments. The scope of protection of this invention should be interpreted through the claims, and all technical concepts within their equivalents should be interpreted as being included within the scope of the claims of this invention.

Claims

1. A negative electrode active material for lithium secondary batteries, wherein, The ratio of the D-band peak area to the G-band peak area from the Raman spectrum is greater than 0.5, the relative standard deviation is greater than 18%, and the Raman shift range of the D-band is 1250 to 1450 cm⁻¹. -1 The Raman shift of the G-band ranges from 1500 to 1700 cm. -1 .

2. The negative electrode active material for lithium secondary batteries as described in claim 1, wherein, The negative electrode active material comprises graphite coated with amorphous carbon.

3. The negative electrode active material for lithium secondary batteries as described in claim 1, wherein, The Raman spectroscopy measurements were performed at 200 to 1000 points.

4. An evaluation method for negative electrode active materials for lithium secondary batteries, comprising the following steps: Measure the Raman spectrum of the negative electrode active material; Perform two-dimensional mapping based on the measurement results; as well as Raman displacement D zone was obtained from 1250 to 1450 cm. -1 and G-band 1500 to 1700 cm -1 The mean and standard deviation of the ratio of the peak area of ​​the D band to the peak area of ​​the G band. Specifically, if the ratio of the D-band peak area to the G-band peak area is greater than 0.5 and the relative standard deviation is greater than 18%, the predicted electrode performance is good.

5. The evaluation method for negative electrode active materials for lithium secondary batteries as described in claim 4, wherein, The negative electrode active material comprises graphite coated with amorphous carbon.

6. The evaluation method for negative electrode active materials for lithium secondary batteries as described in claim 4, wherein, The Raman spectroscopy measurements were performed at 200 to 1000 points.

7. A method for predicting electrode performance, comprising the method of claim 4.

8. A system comprising the method of claim 4.

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