Anode material for lithium secondary battery cell, precursor for same, lithium secondary battery cell, and method for manufacturing anode material

Abstract

The present invention relates to an anode material for a lithium secondary battery cell, a precursor for the anode material, a lithium secondary battery cell, and a method for manufacturing the anode material. A precursor of an anode material according to an aspect of the present invention is an anode material precursor comprising graphite, in which the graphite may have peaks in a particle size range of 2 [mu] m to 8 [mu] m and a particle size range of 10 [mu] m to 25 [mu] m, respectively, and have a particle size distribution having a D50 of 6 [mu] m to 23 [mu] m.

Description

Technical Field

[0001] The present disclosure relates to an anode material for a lithium secondary battery cell, a precursor of the anode material, a lithium secondary battery cell, and a method of manufacturing the anode material. Background Art

[0002] Lithium secondary battery cells, particularly lithium ion secondary batteries, typically use carbon-based materials including graphite as anode active materials.

[0003] Since the carbon-based active materials have a low discharge voltage of -0.2V compared to the discharge voltage of lithium, they offer many advantages in terms of the energy density of secondary batteries. Nevertheless, as the fields with demands for high-capacity lithium secondary battery cells such as electric transportation vehicles increase, the demand for improving the performance of secondary batteries is increasing day by day.

[0004] In particular, improving the high-temperature performance in lithium secondary battery cells, such as high-temperature storage characteristics and high-temperature cycle characteristics for rapid charging, is an important task to be solved. Summary of the Invention

[0005] Technical Problem

[0006] Aspects of the present disclosure are to provide an anode material and a precursor of the anode material having excellent high-temperature storage characteristics and high-temperature cycle characteristics.

[0007] Another aspect of the present disclosure is to provide a method for manufacturing the anode material and the precursor.

[0008] The subject matter of the present disclosure is not limited to the matters described above. Those skilled in the art to which the present disclosure pertains will have no difficulty in understanding additional subject matters of the present disclosure based on the overall content of this specification.

[0009] Solution to the Problem

[0010] According to an aspect of the present disclosure, the anode material precursor includes graphite, wherein the graphite may have peaks in particle size ranges of 2 μm to 8 μm and 10 μm to 25 μm, respectively, and may have a particle size distribution with a D50 of 6 μm to 23 μm.

[0011] According to another aspect of the present disclosure, the anode material may be characterized in that the anode material precursor according to the aspect of the present disclosure is bonded by a binder.

[0012] According to another aspect of the present disclosure, a lithium secondary battery cell includes: an anode including a current collector and an anode material coated on a surface of the current collector; an electrolyte; and a cathode, wherein the anode material may be the anode material according to the aspect of the present disclosure.

[0013] According to another aspect of the present disclosure, a method for manufacturing an anode material includes: an operation of preparing a precursor of the anode material according to an aspect of the present disclosure; an operation of coating a binder on the precursor of the anode material; and an operation of heat-treating the precursor of the anode material coated with the binder.

[0014] Advantages of the Invention

[0015] According to an embodiment of the present disclosure, by restricting the particle size distribution of graphite constituting the anode material, an anode material having a high packing density can be provided, and thus, a lithium secondary battery cell including the anode material can have excellent high-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram showing a graph of the particle size distribution of a provided precursor of the anode material according to an embodiment of the present disclosure, and

[0017] Figure 2 is a schematic diagram showing a form in which a provided precursor powder of the anode material is applied to a current collector according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0018] Embodiments of the present disclosure are not limited to the embodiments disclosed below. For example, those skilled in the art who understand the concept of the present disclosure will be able to easily propose other embodiments included within the scope of the concept of the present disclosure by adding, modifying, deleting components, etc., but this will also be regarded as being included within the scope of the concept of the present disclosure.

[0019] In addition, throughout the specification, unless otherwise specifically stated, the term "comprising" a certain component does not exclude other components, but means that other components can be included. In addition, the difference between "above and below (top and bottom)", "forward and backward (front and rear)", or "left and right (left and right)" in this specification does not mean an absolute physical positional relationship, and it should be noted that even if it is above, it can be implemented as having a shape below, unless it is contrary to natural phenomena or clearly impossible to achieve.

[0020] In addition, it should be noted that, unless otherwise specified in the present disclosure, the mixing ratio or composition is based on weight.

[0021] In addition, each implementation example described below is only one example of implementing the technical concept of the present disclosure, and the scope of rights of the present disclosure is not limited to each implementation example.

[0022] Hereinafter, the present disclosure will be described in detail.

[0023] If the total internal pore volume is large after applying the anode active material to the current collector and rolling the current collector, the high-temperature performance of the anode is likely to deteriorate. Therefore, when minimizing the change in the structure of the electrode and the change in the total internal pore volume during electrode rolling, the high-temperature characteristics of the lithium-ion battery can be improved.

[0024] The inventors of the present disclosure have conducted in-depth research to improve this, and have found that if the particle size distribution of graphite is controlled, the bulk density of the anode material can be significantly increased compared to the related art, and thus the high-temperature performance can be improved, resulting in the present disclosure.

[0025] That is, according to an embodiment of the present disclosure, the anode material precursor includes graphite, and the particle size distribution of the graphite has the form as Figure 1 shown. As can be seen in the drawings, the particle size distribution of the graphite can have two peaks, one of the two peaks (fine particle peak) is formed in the particle size range of 2 μm to 8 μm, and the other peak (macro particle peak) can be formed in the particle size range of 10 μm to 25 μm. The particle size of the powder generally follows a normal distribution, and in the case where the powder follows such a normal distribution, it is known that particles with a small particle size penetrate into the gaps between particles with a large particle size, thereby increasing the density of the powder. However, according to the research results of the inventors of the present disclosure, rather than such a situation, in the case of being clearly divided into two peaks, not only can the density of the powder be further increased, but also the bulk density of the anode material finally forming the anode can be increased. Therefore, the present disclosure limits the particle size of the anode material precursor powder such that the anode material precursor powder has peaks in the fine particle region and the macro particle region, respectively. Figure 2 Shows the form in which the anode material precursor powder of the present disclosure is formed on the surface of the current collector. As can be seen in the drawings, the density can be increased by the presence of fine particles between the macro particles. In particular, since the gap between the macro particles and the fine particle size can be well coordinated by having peaks in two particle size ranges, the density can be further increased.

[0026] At this time, as described above, the fine particle peak is formed in the region where the particle size is 2 μm to 8 μm, and the macro particle peak can be formed in the region where the particle size is 10 μm to 25 μm. By adjusting the particle size in this way, the density can be maximized. According to another embodiment of the present disclosure, the region where the fine particle peak is formed can be in the range of 3 μm to 7 μm, and the region where the macro particle peak is formed can be in the range of 12 μm to 22 μm.

[0027] In an embodiment of the present disclosure, the full width at half maximum (A) of the fine particle peak may have a value of 0.5 times to 0.9 times (=A / B) compared to the full width at half maximum (B) of the macroscopic particle peak (meaning the width when the intensity is half at the corresponding peak in the graph). This means that the fine particle peak should be formed sharper compared to the macroscopic particle peak, and if the full width at half maximum of the fine particle peak is further restricted in this way, the fine particles can effectively penetrate between the macroscopic particle peaks to increase the density of the powder. In an embodiment of the present disclosure, if the fine particle peak and the macroscopic particle peak have an overlapping form, the full width at half maximum of each peak can be calculated by extracting individual peaks using the maximum likelihood deconvolution method.

[0028] In addition, in an embodiment of the present disclosure, the median (D50) of the particle size of the entire anode material precursor graphite powder may have a value between 6 μm and 23 μm.

[0029] Although not necessarily limited thereto, the particle size distribution of graphite can be obtained by mixing two or more kinds of graphite powders having different particle size distributions at an appropriate ratio.

[0030] In an embodiment of the present disclosure, the graphite may be natural graphite. As in an embodiment of the present disclosure, when the particle size is controlled such that two peaks appear, natural graphite may exhibit excellent electrode processability and electrochemical properties compared to the electrode processability and electrochemical properties of artificial graphite. In an embodiment of the present disclosure, the graphite may be flake graphite, amorphous graphite, or a combination thereof.

[0031] To obtain a high density, it is advantageous for the graphite to be as spherical as possible. Therefore, in the case of graphite powder corresponding to the fine particle region with a particle size of 2 μm to 8 μm, the sphericity may be 95% or more, and in the case of graphite powder corresponding to the macroscopic particle region with a particle size of 10 μm to 25 μm, the sphericity may be 85% or more. In addition, the sphericity of the entire graphite powder may be 90% or more. In the present disclosure, the sphericity means the degree of approaching a spherical shape, and the closer it is to 1, the closer the shape is to a spherical shape. In an embodiment of the present disclosure, the sphericity can be obtained by dispersing the sample powder in an ethanol solvent using FlowCAM PV, then obtaining an optical image through a flow cell and an objective lens, and analyzing the shape using a dedicated algorithm.

[0032] In addition, according to an embodiment of the present disclosure, the intensity of the macro particle peak can be 2 to 5 times the intensity of the fine particle peak. When the intensity of the macro particle peak is 2 to 5 times the intensity of the fine particle peak, the adhesion strength of the anode material of the electrode to the electrode can be increased. The intensity of each peak means the frequency of the powder corresponding to the particle size of the corresponding peak, and can be determined by the count measured by a particle size measuring device. Although not necessarily limited thereto, an example of the particle size measuring device can be a Cilas-1090 particle size analyzer.

[0033] In an embodiment of the present disclosure, the anode material can be a precursor of the anode material bonded by a binder. The binder is obtained by coating the precursor with a binder material and then carbonizing the precursor, and through this process, the anode materials can be bonded to each other and / or to the current collector with sufficient strength.

[0034] The binder material can be obtained by carbonizing hard carbon, soft carbon, or a combination thereof. The binder based on hard carbon can be one or two or more selected from the group consisting of sucrose, phenolic resin, furan resin, furfuryl alcohol, polyacrylonitrile, polyimide, epoxy resin, cellulose, and styrene. In addition, the soft carbon can be a tar or asphalt composition derived from coal or petroleum.

[0035] A method for manufacturing the anode material described above is as follows. However, the following manufacturing method is only an illustrative method for manufacturing the precursor or anode material of the present disclosure, and does not necessarily mean that the precursor or anode material of the present disclosure should be manufactured by the following manufacturing method.

[0036] First, an operation of preparing a precursor provided by an embodiment of the present disclosure can be performed.

[0037] Thereafter, an operation of mixing the obtained precursor with the binder material can be performed. To mix the precursor and the binder material, a method of applying a shear force by high-speed rotation after adding each material can be used, and thus, a material in the form of the binder material coated on the graphite particles forming the precursor can be obtained. At this time, the binder material can be added at a ratio of 8% to 15% by weight based on the weight of natural graphite.

[0038] An operation of performing heat treatment on the precursor coated with the binder material is performed. The binder material can be carbonized by heat treatment to become a carbon-based material. In an embodiment of the present disclosure, the carbonization yield of the binder material after heat treatment can be in the range of 30% to 70%.

[0039] The heat treatment can be carried out at a temperature of about 800 °C to 1300 °C for 30 minutes to 120 minutes. If the temperature is low or the time is short, sufficient carbonization effect cannot be obtained, and if the temperature is too high or the time is long, the device may be overloaded or may not be economically advantageous.

[0040] The anode material including graphite and a binder (carbon-based material) can be obtained by the process described above.

[0041] According to an embodiment of the present disclosure, a secondary battery including the anode material described above can be provided. The secondary battery according to an embodiment of the present disclosure is provided as a lithium secondary battery cell, and may include an anode, a cathode, and an electrolyte including the anode material described above. In an embodiment of the present disclosure, a separator between the cathode and the anode may also be included.

[0042] In an embodiment of the present disclosure, the anode can be manufactured by applying a slurry including the anode material (anode active material) manufactured according to an embodiment of the present disclosure to a current collector and drying the current collector.

[0043] The slurry can be obtained by mixing the anode material, a binder material, and a solvent.

[0044] Any substance used in a lithium secondary battery cell can be used as the electrolyte, and its type is not limited.

[0045] Distilled water can be used as the solvent.

[0046] As needed, the slurry may further include a conductive agent. The conductive agent is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity, and specifically, the following can be used: graphite (e.g., natural graphite, artificial graphite, etc.); carbon black (e.g., acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.); conductive fibers (e.g., carbon fibers, metal fibers, etc.); metal powders (e.g., fluorocarbons, aluminum, nickel powders, etc.); conductive whiskers (e.g., zinc oxide, potassium titanate, etc.); conductive metal oxides (e.g., titanium oxide, etc.); conductive materials (e.g., polyphenylene derivatives, etc.). The conductive material can be mixed at a ratio of 0.1% by weight to 30% by weight based on the total weight of the composition (e.g., slurry) used to form the anode active material layer.

[0047] In addition, the current collector to which the slurry including the anode material is applied can be any material used in the technical field of lithium secondary battery cells, and its type is not limited, but some examples thereof can be copper foil, nickel foil, stainless steel, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0048] Embodiments of the present invention

[0049] (Example)

[0050] Hereinafter, the present disclosure will be described in more detail by way of examples. However, it should be noted that the following examples are only intended to illustrate and embody the present disclosure, and are not intended to limit the scope of rights of the present disclosure. This is because the scope of rights of the present disclosure is determined by the matters described in the patent claims and the matters reasonably inferred therefrom.

[0051] Preparation of Anode Material Precursors and Anode Materials

[0052] Prepare natural graphite powder having the particle size distribution described in Table 1 below as a precursor of the anode material. In Table 1 below, the intensity ratio means the intensity ratio of the macro particle peak to the intensity of the fine particle peak, and indicates how many times the intensity of the macro particle peak is greater than the intensity of the fine particle peak. In all examples, the sphericity of the powder in the particle size range of 2 μm to 8 μm is 97% or more, and the sphericity of the powder in the particle size range of 10 μm to 25 μm is confirmed to be 85% or more. In addition, it is confirmed that the sphericity of the entire powder is 86% or more. Further, for all examples, the full width at half maximum of the fine particle peak is 0.5 to 0.9 times that of the macro particle peak.

[0053] [Table 1]

[0054]

[0055]

[0056] In the anode material precursor obtained under the conditions described in Table 1 above, as the binder material, pitch derived from coal tar having a softening point of 110 °C (residual carbon content of 40% or more) and phenolic resin are mixed at a weight ratio of 6:4 to obtain a mixture, and the mixture is mixed at a ratio of 3 parts by weight with respect to 100 parts by weight of the total precursor, and shear force is applied by high-speed rotation to coat the particles. The coated particles are carbonized by heat treatment at a temperature of 1100 °C for 30 minutes to obtain the anode material. In all of the above examples, the weight of the binder material is adjusted to fall within the range of 8% to 15% with respect to the weight of natural graphite. In addition, it is confirmed that the carbonization yield of the binder material also satisfies 30% to 70% in all examples.

[0057] Manufacture of Anodes and Half-Cell Units

[0058] 97 wt% of the anode material obtained through the process described above was mixed with 2 wt% of a binder containing carboxymethyl cellulose and styrene-butadiene rubber and 1 wt% of Super P conductive agent in a distilled water solvent to prepare an anode active material slurry. The slurry was applied to a copper current collector, dried at 100 °C for 10 minutes, and then pressed in a roll press. After that, an anode was fabricated by vacuum drying in a vacuum oven maintained at 100 °C for 12 hours. For each example, the electrode density of the fabricated anode ranged from 1.35 g / cc to 1.82 g / cc (see Table 2).

[0059] In addition to the anodes fabricated by the above method, lithium metal was used as the counter electrode, and a 2032 coin cell type half-cell was fabricated using LiPF6 dissolved in a solvent containing ethylene carbonate and dimethyl carbonate mixed in a volume ratio of 1:1 as the electrolyte.

[0060] The initial efficiency (%), capacity (mAh / g), and capacity retention rate after 50 full cycles of the fabricated half-cells were measured, and the results are shown in Table 2.

[0061] [Table 2]

[0062]

[0063]

[0064] As can be seen in Table 2 above, when an anode was fabricated using an anode material that meets the conditions provided by the embodiments of the present disclosure and is used for secondary batteries, not only was an equivalent capacity level shown compared to the prior art examples using natural graphite as the anode (which is mainly used in the related art), but also an equivalent or higher capacity retention rate was shown compared to the capacity retention rates of the prior art examples.

[0065] Therefore, the excellent effects of the present disclosure can be confirmed.

Claims

1. A precursor of an anode material comprising graphite, Among them, the graphite has peaks in the particle size ranges of 2 μm to 8 μm and 10 μm to 25 μm respectively, and has a particle size distribution with a D50 of 6 μm to 23 μm.

2. The anode material precursor according to claim 1, wherein, In the particle size distribution, the intensity of the peak present in the particle size range of 10 μm to 25 μm is 2 to 5 times the intensity of the peak present in the particle size range of 2 μm to 8 μm.

3. The anode material precursor according to claim 1, wherein The full width at half maximum (A) of the peak present in the particle size range of 2 μm to 8 μm is 0.5 to 0.9 times the full width at half maximum (B) of the peak present in the particle size range of 10 μm to 25 μm.

4. The anode material precursor according to claim 1, wherein, The sphericity of the graphite with a particle size of 2 μm to 8 μm is 95% or greater, and the sphericity of the graphite with a particle size of 10 μm to 25 μm is 85% or greater.

5. The anode material precursor according to claim 4, wherein, The overall sphericity of the graphite is 90% or greater.

6. The anode material precursor according to claim 1, wherein, The graphite is natural graphite.

7. The anode material precursor according to claim 6, wherein, The natural graphite is flake graphite, amorphous graphite or a combination thereof.

8. An anode material, characterized in that, The precursor of the anode material according to any one of claims 1 to 7 is bonded by a binder.

9. The anode material according to claim 8, wherein, The binder is formed by carbonizing hard carbon, soft carbon or a combination thereof.

10. The anode material according to claim 9, wherein, The material of the binder is added at a ratio of 8% to 15% by weight relative to the natural graphite, and the material of the binder has a carbonization yield in the range of 30% to 70%.

11. The anode material according to claim 9, wherein, The hard carbon is one or two or more selected from the group consisting of sucrose, phenolic resin, furan resin, furfuryl alcohol, polyacrylonitrile, polyimide, epoxy resin, cellulose and styrene.

12. The anode material according to claim 9, wherein, The soft carbon is a tar or pitch composition derived from coal or petroleum.

13. A lithium secondary battery cell, comprising: an anode including a current collector and an anode material coated on the surface of the current collector; an electrolyte; and a cathode, wherein the anode material is the anode material according to claim 8.

14. A method for manufacturing an anode material, comprising: an operation of preparing a precursor of the anode material according to any one of claims 1 to 7; an operation of coating a binder material on the precursor of the anode material; and an operation of heat-treating the precursor of the anode material coated with the binder.

15. The method for manufacturing an anode material according to claim 14, wherein, The binder material is added at a ratio of 8% to 15% by weight of the natural graphite, and after the heat treatment, the carbonization yield of the binder is in the range of 30% to 70%.

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