Negative electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including a negative electrode produced using the same

Abstract

The present disclosure relates to a method for producing a negative electrode active material for a lithium secondary battery, the method including the steps of: coating a base material for a negative electrode active material with a coating material; and heat-treating the resulting coating product, the coating material being a graphitizable carbon having a softening point of 50°C or lower, and the coating material being contained in an amount such that an amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for the negative electrode active material; and the negative electrode active material produced therefrom, and a lithium secondary battery including the same in its negative electrode.

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode active material for a lithium secondary battery and a method for manufacturing the same. The present disclosure also relates to a lithium secondary battery including a negative electrode manufactured therefrom. [Background technology]

[0002] Lithium ion secondary batteries (LIBs) are attracting much attention as a next-generation energy storage device amid growing global environmental concerns. Compared to typical secondary battery systems such as nickel-cadmium batteries and nickel metal hydride batteries, lithium ion secondary batteries have superior characteristics in terms of high operating voltage, energy density, and memory effect, leading to their widespread use in a variety of fields. As demand for high-energy-density lithium secondary batteries, such as Ni-Cd and Ni-MH, is increasing, silicon-based or silicon oxide-based materials, which have an effective capacity 10 times greater than that of carbon-based materials, are increasingly being used as negative electrode active materials.

[0003] Lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the battery's performance is closely related to the characteristics of all of these components. For the 30 years since the development of lithium-ion secondary batteries in 1991, the negative electrode active material has been either hard carbon / soft carbon or graphite-based materials. Currently, most commercial batteries primarily use graphite materials, with battery manufacturers (or cell companies) applying a variety of graphite compositions.

[0004] Graphite, currently the most commonly used negative electrode active material for lithium-ion secondary batteries, offers advantages such as low operating voltage, stable lifespan, efficiency, cost, and environmental friendliness. However, it has the disadvantage of being limited to a maximum theoretical capacity of 372 mAh / g. This theoretical capacity limit makes it difficult to ensure the driving range of electric vehicles and hinders its application in various fields. In response, the secondary battery industry has recently begun to require the addition of functionality through surface treatments to negative electrode active materials in order to improve charging output and lifespan. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a negative electrode active material for a lithium secondary battery having improved high-rate charge / discharge characteristics, a method for producing the same, and a secondary battery including the same.

[0006] Specifically, the present invention provides a negative electrode active material for a lithium secondary battery, which has improved high-speed charge / discharge characteristics by coating a base material for the negative electrode active material, a method for manufacturing the same, and a secondary battery including the same. [Means for solving the problem]

[0007] A method for producing a negative electrode active material for a lithium secondary battery according to one embodiment of the present disclosure includes the steps of: coating a base material for a negative electrode active material with a coating material; and heat-treating a coating product coated with the coating material; wherein the coating material is a graphitizable carbon having a softening point of 50°C or less, and the coating material is contained in an amount such that the amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for a negative electrode active material.

[0008] The base material for the negative electrode active material may be a base material obtained by graphitizing coke.

[0009] The coke may contain 70 parts by weight or more of green coke, with the remainder being calcined coke, relative to 100 parts by weight of total coke.

[0010] The green coke may be coal-based green coke, petroleum-based green coke, or a combination thereof.

[0011] The coating step may be a dry coating step in which no additional solvent is added.

[0012] The coating material may have a viscosity of 3,000 cPs or less at room temperature and have viscoelastic properties at room temperature.

[0013] The coating material may be one or more selected from the group consisting of coal-based coal tar, petroleum-based residual oil, phenolic resin, and wood tar.

[0014] The petroleum-based residual oil may be one or more selected from the group consisting of pyrolyzed fuel oil (PFO), naphtha cracking bottom oil (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), de-asphalted oil (DAO), atmospheric residue (AR), FCC-DO (fluid catalytic cracking decant oil), RFCC-DO (residue fluid catalytic cracking decant oil), and heavy aromatic oil.

[0015] The coating material may have a residual carbon amount of 10 to 40 parts by weight relative to 100 parts by weight of the coating material.

[0016] A negative electrode active material for a lithium secondary battery according to one embodiment of the present disclosure includes a base material for a negative electrode active material; and a coating layer that coats the base material. The coating layer is made of easily graphitizable carbons and has a softening point of 50°C or less. The coating material of the coating layer is included so that the amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for a negative electrode active material.

[0017] The base material for the negative electrode active material may be graphitized coke.

[0018] The coke may contain 70 parts by weight or more of green coke, with the remainder being calcined coke, relative to 100 parts by weight of total coke.

[0019] The green coke may be coal-based green coke, petroleum-based green coke, or a combination thereof.

[0020] The coating material may be a carbon material having room temperature viscoelasticity with a viscosity of 3,000 cPs or less at room temperature.

[0021] The coating material may have a residual carbon amount of 10 to 40 parts by weight relative to 100 parts by weight of the coating material.

[0022] The negative electrode active material for a lithium secondary battery may have a Raman spectrum measurement value Id / Ig of 0.300 to 0.450, where Id is at a wavelength of 1350 cm -1 The peak intensity measured at 1575 cm -1 is the peak intensity measured at

[0023] A lithium secondary battery according to one embodiment of the present disclosure includes a positive electrode; a negative electrode; and an electrolyte, and the negative electrode may include a negative electrode active material for a lithium secondary battery produced by the disclosed method. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a negative electrode active material that has high-speed charge / discharge characteristics without being significantly inferior in initial efficiency, and a method for producing the same.

[0025] Furthermore, according to the present invention, by coating the base material with a coating material having a controlled carbon content, it is possible to provide a negative electrode active material that is prevented from cracking. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a diagram showing TEM observation of the surface of a negative electrode material according to an embodiment of the present disclosure before and after coating. [Figure 2] FIG. 2 is a view of a coated negative electrode material according to one embodiment of the present disclosure, observed by SEM. [Figure 3] FIG. 1 illustrates Raman spectrum measurements of one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0028] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0029] When an element is referred to as being "on" another element, it may be directly on top of the other element, or there may be other elements between them. In contrast, when an element is referred to as being "directly on top of" another element, there are no other elements between them.

[0030] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0031] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and unless otherwise defined, are not interpreted in an ideal or very formal sense.

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily implement and practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0033] Each stage will be explained in detail below.

[0034] The negative electrode material of a lithium secondary battery repeatedly expands and contracts during use, which can cause cracks on its surface, increasing its specific surface area and resulting in poor battery performance. Therefore, the present invention devised a method for coating the surface of the negative electrode material to prevent cracks caused by charge and discharge.

[0035] A method for manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment of the present disclosure may include: coating a base material for a negative electrode active material with a coating material; and heat-treating the coating product coated with the coating material.

[0036] The coating material may be graphitizable carbons and have a softening point of 50°C or less. The coating material may have a viscosity of 3,000 cPs or less at room temperature, specifically, a viscosity of 1 to 3,000 cPs, and more specifically, a viscosity of 1 to 2,000 cPs. In other words, the coating material of one embodiment of the present disclosure can have viscoelastic properties at room temperature. Specifically, the softening point of the coating material may be above 0 to 50°C or less, above 0 to 41°C or less, above 0 to 30°C or less, or 20 to 30°C or less.

[0037] Specifically, the coating material may be one or more selected from the group consisting of coal-based coal tar, petroleum-based residual oil, phenolic resin, and wood tar. Here, the petroleum-based residual oil may be one or more selected from the group consisting of pyrolyzed fuel oil (PFO), naphtha cracking bottom oil (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), deasphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking decant oil (FCC-DO), residue fluid catalytic cracking decant oil (RFCC-DO), and heavy aromatic oil.

[0038] Even if the coating material is included in the group consisting of coal-based coal tar, petroleum-based residual oil, phenolic resin, and wood tar, the coating material must have a softening point of 50°C or less and exhibit viscoelastic properties at room temperature.

[0039] This is also related to the coating method.

[0040] Methods for coating a negative electrode active material include wet coating and dry coating. Wet coating is a method in which a base material for the negative electrode active material to be coated is immersed in a solution containing a coating material, while dry coating is a method in which the base material and the coating material are immediately and uniformly mixed using a mixer (including a mixer that applies shearing force) without adding a separate solvent. In the present disclosure, the coating material is applied using a dry coating method.

[0041] The room-temperature viscoelastic coating material according to an embodiment of the present disclosure has fluidity, which is characteristic of a liquid, and therefore provides better coverage of the surface of the anode material than typical solid coating materials, which have little fluidity. In other words, the room-temperature viscoelastic coating material adheres uniformly to the surface of the anode material and is carbonized by heat treatment to form an amorphous carbon coating layer on the surface of the anode material. For example, if the coating material is coal tar, it undergoes a phase change from coal tar to coal tar pitch and then from coal tar pitch to soft carbon, while if the coating material is phenol, it undergoes a phase change to hard carbon.

[0042] Finally, an amorphous carbon coating layer is formed on the surface of the anode material. This amorphous carbon coating layer prevents direct contact between the electrochemically active graphite edge and the electrolyte, while also suppressing the simultaneous intercalation reaction of Li ions and the solvent into the graphite layer, thereby reducing irreversible reactions.

[0043] The use of room temperature viscoelastic materials as coating materials combines the advantages of both wet and dry coating: the uniform coating layer achieved by wet coating is achieved by room temperature viscoelasticity, while the cost efficiency and mass productivity of dry coating are achieved.

[0044] The coating material may contain 20% by weight or less of low molecular weight components (weight average molecular weight (Mw) of 60 to 150) that can be removed by a distillation process.

[0045] In one embodiment of the present disclosure, the content of the coating material is defined by the amount of residual carbon. That is, the coating material of one embodiment of the present disclosure is contained so that the amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for the negative electrode active material. Specifically, the coating material is contained so that the amount of residual carbon is 2 to 4 parts by weight per 100 parts by weight of the base material for the negative electrode active material, and more specifically, the coating material is contained so that the amount of residual carbon is 3 to 4 parts by weight per 100 parts by weight of the base material for the negative electrode active material.

[0046] If the amount of residual carbon in the coating material exceeds this range, the carbon layer formed after carbonization may act as a resistance to Li-ion movement and adversely affect charging characteristics.On the other hand, if the amount of residual carbon is too low, the amount of coating material is insufficient, and the surface of the base material is exposed without coating, resulting in little technical advantage.

[0047] The coating material is contained in an amount of 2.5 to 50 parts by weight relative to 100 parts by weight of the base material. Specifically, the coating material is contained in an amount of 5 to 25 parts by weight, more specifically 15 to 20 parts by weight relative to 100 parts by weight of the base material.

[0048] The coating material may have a residual carbon amount of 10 to 40 parts by weight relative to 100 parts by weight of the coating material. Specifically, the coating material may have a residual carbon amount of 10 to 30 parts by weight relative to 100 parts by weight of the coating material, and more specifically, the coating material may have a residual carbon amount of 15 to 25 parts by weight relative to 100 parts by weight of the coating material.

[0049] The base material for a negative electrode active material according to an embodiment of the present disclosure is graphitized coke. Hereinafter, coke that can be used as the base material will be specifically described.

[0050] The coke of one embodiment of the present disclosure may contain 70 parts by weight or more of green coke and the remainder being calcined coke, relative to 100 parts by weight of whole coke. Specifically, the coke may contain 80 parts by weight or more of green coke and the remainder being calcined coke, relative to 100 parts by weight of whole coke. More specifically, the coke may contain 90 parts by weight or more of green coke and the remainder being calcined coke, relative to 100 parts by weight of whole coke. Even more specifically, the coke may contain 100 parts by weight of green coke and the remainder being calcined coke, relative to 100 parts by weight of whole coke.

[0051] Compared to calcined coke, graphitization of green coke allows for greater ordering (La) and stacking (Lc) of graphene layers in the graphite structure, which further reduces the micro (up to 2 nm) and meso (2 to 50 nm) pore regions in the pore distribution. As a result, the higher the green coke content, the better the quality of the artificial graphite formed after graphitization, improving long-term charge / discharge characteristics.

[0052] The green coke may be a coal-based green coke, a petroleum-based green coke, or a combination thereof.

[0053] In addition, the graphitized coke of the present disclosure may be any coke that falls within the above-mentioned range, and the graphitization conditions are in accordance with the graphitization conditions of general coke.

[0054] The coated product is then heat-treated to obtain a negative electrode active material for a lithium secondary battery. The coated product is then heat-treated to carbonize the coating material.

[0055] The temperature range of the heat treatment step may be 1000-1400° C., specifically 1100-1300° C., more specifically 1200-1300° C. The time range of the heat treatment step may be 1 hour to 4 hours, specifically 1 hour to 3 hours, preferably about 2 hours.

[0056] A negative electrode active material for a lithium secondary battery according to one embodiment of the present disclosure includes a base material for a negative electrode active material; and a coating layer coating the base material, the coating layer being made of graphitizable carbons and having a softening point of 50°C or less, and the coating material being included so that the amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for a negative electrode active material. The coating material and the base material have been described in detail in the description of the manufacturing method, and will not be described further below.

[0057] The base material for the negative electrode active material may be graphitized coke.

[0058] The coke contains 70 parts by weight or more of green coke with respect to 100 parts by weight of the total coke, and the remainder being calcined coke.

[0059] The green coke may be coal-based green coke, petroleum-based green coke, or a combination thereof.

[0060] The coating material may be a carbon material having room temperature viscoelasticity with a viscosity of 3,000 cPs or less at room temperature.

[0061] The coating material may have a residual carbon amount of 10 to 40 parts by weight relative to 100 parts by weight of the coating material.

[0062] The negative electrode active material for a lithium secondary battery may have a Raman spectrum measurement value of Id / Ig of 0.300 to 0.450, specifically 0.340 to 0.400, more specifically 0.350 to 0.390. Here, Id is the Raman spectrum measured at a wavelength of 1350 cm -1 The peak intensity measured at 1575 cm -1 is the peak intensity measured at

[0063] The negative electrode active material for a lithium secondary battery according to one embodiment of the present disclosure has a specific surface area of ​​0.9 to 2.7 m 2 / g, capacity of 350 to 380 mAh / g, initial efficiency of 90 to 93%, 3C rate (CC), -0.1 V cut off charge characteristics of 160 to 250 mAh / g. Specifically, the specific surface area may be 1.1 to 2.6 m 2 / g, capacity may be 350 to 355mAh / g, initial efficiency may be 91 to 93%, and 3C rate (CC), -0.1V cut off charge characteristics may be 160 to 200mAh / g.

[0064] A lithium secondary battery according to one embodiment of the present disclosure includes a positive electrode; a negative electrode; and an electrolyte, wherein the negative electrode is produced by the disclosed method.

[0065] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention. [Example]

[0066] Coke and coating materials were prepared with the compositions shown in the tables below. Table 1 shows the composition of the coke, and Table 2 shows the composition of the coating material.

[0067] The coal tar used in this experimental example had a residual carbon content of 20 parts by weight per 100 parts by weight of coal tar, a softening point of 25-30°C, and 21.94% by weight of fixed carbon, while the phenolic resin used had a residual carbon content of 40 parts by weight per 100 parts by weight of phenolic resin, a softening point of 37-50°C, and 40.05% by weight of fixed carbon.

[0068] [Table 1]

[0069] [Table 2]

[0070] The base materials and coating materials were prepared as shown in Tables 1 and 2. The base materials were dry-coated with the coating materials. The combinations are shown in Table 3 below.

[0071] The dry coating method was performed by mixing the mixture at 25 rpm for 5 minutes using a planetary mixer and then at 100 rpm for 30 minutes. The coating layer was carbonized at 1250°C for 2 hours to obtain a negative electrode active material.

[0072] The particle size, specific surface area, tap density, initial capacity, initial efficiency, Id / Ig ratio, and rapid charge / discharge of the prepared negative active material were evaluated and are shown in Table 3 below.

[0073] The respective measurement methods are as follows.

[0074] - Particle size: Laser diffraction method, particle size span = (D90-D10) / D50

[0075] -Raman: Microscope magnification: x20, range: 20 x 20 μm, 532 nm laser, power: 2.31 mW, mode: XY 2D-mapping, exp. time: 1 sec, accumulation: 1 time, ND filter: 172. After measurement, the Id / Ig ratio was calculated. Here, Id is the wavelength of 1350 cm -1 The peak intensity of amorphous carbon in the region, Ig, is at a wavelength of 1575 cm -1 This means the peak intensity of crystalline carbon in the region of

[0076] -Specific surface area: The specific surface area was measured using the BET method (Surface area and Porosity analyzer) (Micromeritics, ASAP2020).

[0077] -Initial capacity: Charge CC-CV0.1C&5mV (0.005C cutoff), discharge capacity (mAh / g) after measuring 3 times of discharge 0.1C1.5V cut-off

[0078] - Initial efficiency: Charge CC-CV 0.1C & 5mV (0.005C cutoff), discharge 0.1C 1.5V cut-off, (discharge capacity / charge capacity) x 100 after one measurement

[0079] - Fast charging characteristics: Charge CC-CV 0.1C & 5mV (0.005C cutoff), discharge 0.1C 1.5V cutoff 3 times, then measure the time (sec) & capacity (mAh / g) when it reaches -0.1V during 3C-rate CC charging

[0080] [Table 3]

[0081] As a result of the above, compared to the anode active material made of uncoated coke, the anode active material coated with graphitizable carbons, i.e., coal tar, had superior initial capacity, specific surface area, and charging characteristics, and the Raman Id / Ig ratio was increased, confirming the amorphization of the surface.

[0082] In contrast, when non-graphitizable carbons were coated with phenolic resin, the rapid charging characteristics were improved compared to the uncoated negative electrode material, depending on the degree of control of the amount of residual carbon.

[0083] Furthermore, even when coated with coal tar, the initial capacity, initial efficiency, specific surface area, and charging characteristics differ depending on the ratio of green coke to the coke matrix, but the Raman Id / Ig ratio showed that the amorphization of the surface does not change significantly depending on the coating material. This indicates that the charging characteristics tend to improve by adjusting the appropriate content of green coke and coating material.

[0084] The present invention is not limited to the examples, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the above-described examples are illustrative in all respects and not limiting.

Claims

1. Coating the base material for the negative electrode active material with a coating material; and heat treating the product coated with the coating material; A method for producing a negative electrode active material for a lithium secondary battery, comprising: The coating material is a graphitizable carbon having a softening point of 50°C or less, The coating material is contained in an amount of residual carbon of 1 to 5 parts by weight per 100 parts by weight of the base material for a negative electrode active material, The Id / Ig of the Raman spectrum measurement value of the negative electrode active material is 0.354 to 0.383, The wavelength of Id is 1350 cm －１ The peak intensity measured at 1575 cm －１ is the peak intensity measured at The method for producing a negative electrode active material for a lithium secondary battery, wherein the specific surface area of ​​the negative electrode active material is 0.9 to 2.7 m 2 / g.

2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1 , wherein the base material for the negative electrode active material is a base material obtained by graphitizing coke.

3. 3. The method of claim 2, wherein the coke comprises 70 parts by weight or more of green coke and the remainder of calcined coke, based on 100 parts by weight of the total coke.

4. The method for producing a negative electrode active material for a lithium secondary battery according to claim 3 , wherein the green coke is a coal-based green coke, a petroleum-based green coke, or a combination thereof.

5. 10. The method of claim 1, wherein the coating step is a dry coating step in which no additional solvent is added.

6. 2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the coating material has a viscosity of 3,000 cPs or less at room temperature and has viscoelastic properties at room temperature.

7. 2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the coating material is at least one selected from the group consisting of coal-based coal tar, petroleum-based residual oil, and wood tar.

8. The petroleum residue oils include pyrolyzed fuel oil (PFO), naphtha cracking bottom oil (NCB), and ethylene cracker bottom oil. oil, EBO), vacuum residue (VR), de-asphalted oil (DAO), atmospheric residue (AR), FCC-DO (fluid catalytic cracking decant oil), RFCC-DO (residue fluid catalytic 8. The method for producing a negative electrode active material for a lithium secondary battery according to claim 7, wherein the active material is at least one selected from the group consisting of cracking decant oil, and heavy aromatic oil.

9. 2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the coating material has a residual carbon amount of 10 to 40 parts by weight per 100 parts by weight of the coating material.

10. a base material for a negative electrode active material; and a coating layer that coats the base material; The coating layer is made of graphitizable carbon and has a softening point of 50°C or less, The coating material of the coating layer is contained so that the amount of residual carbon is 1 to 5 parts by weight per 100 parts by weight of the base material for a negative electrode active material, The Id / Ig of the Raman spectrum measurement value of the negative electrode active material is 0.354 to 0.383, The wavelength of Id is 1350 cm －１ The peak intensity measured at 1575 cm －１ is the peak intensity measured at The negative electrode active material for a lithium secondary battery has a specific surface area of ​​0.9 to 2.7 m 2 / g.

11. The negative electrode active material for a lithium secondary battery according to claim 10 , wherein the base material for the negative electrode active material is graphitized coke.

12. The negative electrode active material for a lithium secondary battery according to claim 11, wherein the coke comprises 70 parts by weight or more of green coke and the remainder of calcined coke, based on 100 parts by weight of total coke.

13. The negative electrode active material for a lithium secondary battery according to claim 12 , wherein the green coke is a coal-based green coke, a petroleum-based green coke, or a combination thereof.

14. The negative electrode active material for a lithium secondary battery according to claim 10, wherein the coating material is a carbon having a viscosity of 3,000 cPs or less at room temperature and viscoelastic properties at room temperature.

15. 11. The negative electrode active material for a lithium secondary battery according to claim 10, wherein the coating material has a residual carbon amount of 10 to 40 parts by weight per 100 parts by weight of the coating material.

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