KR20240022268A - Anode active material for lithium secondary battery, secondary battery comprising same, and method of manufactureing thereof - Google Patents

Abstract

The present invention relates to a negative electrode active material for lithium secondary batteries, a secondary battery containing the same, and a method for manufacturing the same. The negative electrode active material for lithium secondary batteries includes a graphite-based base material and a coating layer coated on the surface of the graphite-based base material, and the coating layer is carbon. It includes a layer and at least one carbon bead, and the carbon layer and the carbon bead may contain sulfur.

Description

Negative active material for lithium secondary battery, secondary battery containing same, and manufacturing method thereof

The present invention relates to batteries, and more specifically, to a negative electrode material for lithium secondary batteries, a secondary battery containing the same, and a method for manufacturing the same.

Social interest in the depletion of fossil fuels and environmental pollution caused by the use of fossil fuels is increasing, and eco-friendly energy sources are attracting attention as a solution to this problem. Among the eco-friendly energy sources, interest in electric energy is increasing, and in particular, lithium secondary batteries are attracting attention.

Lithium secondary batteries are widely used in small-sized applications such as mobile phones and laptops, and medium-to-large applications such as electric vehicles and energy storage systems. As the scope of application of lithium secondary batteries expands, the development of new materials for high capacity and high output is becoming important. However, when considering ways to improve electrochemical properties such as expanding efficient use time in small applications and improving energy characteristics in medium to large applications such as electric vehicles, improvement in electrochemical properties must be addressed. There remain technical challenges to be accomplished. Specifically, among the components of the lithium secondary battery, the negative electrode material serves to store lithium ions and is an element related to the capacity and lifespan of the lithium secondary battery. Various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon that allow insertion/extraction of lithium have been used as the anode material. Graphite has a low discharge voltage of 0.2 V compared to lithium, and batteries using graphite as a negative electrode active material exhibit a high discharge voltage of 3.6 V, providing an advantage in terms of energy density of lithium secondary batteries. In addition, it is the most widely used as it guarantees the long life of lithium secondary batteries due to its excellent reversibility.

In the case of natural graphite, it has the advantage of excellent utility as a cathode material because it is inexpensive and exhibits electrochemical properties similar to artificial graphite. However, natural graphite has a plate-like shape, so it has a large surface area and its edges are exposed, which poses a problem of electrolyte penetration or decomposition reaction when applied as a negative electrode active material. For this reason, the edges are peeled off or destroyed, causing a large irreversible reaction, and when manufacturing this into an electrode plate, the graphite material is pressed and oriented flat on the current collector, making it difficult to impregnate the electrolyte, leading to a decrease in charge and discharge characteristics. do.

To solve this problem, efforts are being made to transform natural graphite into a smooth surface shape through post-processing such as spheronization to reduce irreversible reactions and improve electrode fairness.

Graphite commercialized as the anode material shows excellent lifespan characteristics and high theoretical capacity due to continuous oxidation and reduction reactions due to small changes in crystal structure during insertion and desorption of lithium ions. However, the graphite can only accommodate one lithium ion per six carbon atoms, so it can secure a limited theoretical capacity, for example, about 372 mAh/g, which limits the requirements for high output and high capacity. .

Research on new anode materials is continuing to overcome the limitations of graphite, and in order to solve the above-mentioned problems, efforts are needed to suppress side reactions of the anode material with the electrolyte and further improve conductivity.

The technical problem to be solved by the present invention is to provide a negative electrode material that suppresses side reactions with electrolyte and further improves conductivity.

Another technical problem to be solved by the present invention is to provide a lithium secondary battery including the anode material having the above-described advantages.

Another technical problem to be solved by the present invention is to provide a method of manufacturing a negative electrode material having the above-described advantages.

According to an embodiment of the present invention, a negative electrode active material for a lithium secondary battery includes a graphite-based base material; and a coating layer coated on the surface of the graphite-based base material, wherein the coating layer includes a carbon layer and at least one carbon bead, wherein the carbon layer and the carbon beads include sulfur, and the content of the coating material is The negative electrode active material may contain 1.00 to 5.00 wt% by weight.

In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy Equation 1 below.

<Equation 1>

30 ≤ Coating material content [wt%]/ Sulfur content [wt%] ≤ 125

In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy Equation 2 below.

<Equation 2>

1.0 ≤ Coating material content [wt%] × BET specific surface area [m ² /g] ≤ 13

In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy Equation 3 below.

<Equation 3>

0.7 ≤ Raman(I _d /I _g ) ratio × sulfur content [wt%] × 100 ≤ 1.5

(The I _d refers to the peak intensity of amorphous carbon around a wavelength of 1350 cm ^-1 , and I _g refers to the peak intensity of crystalline carbon around a wavelength of 1575 cm ^-1 )

In one embodiment, the D90 particle size - D10 particle size of the secondary particles may be 22.6 to 23.9 ㎛. In one embodiment, the D10 particle size of the secondary particles may be 7.3 to 14.1 ㎛.

In one embodiment, the Span value ((D90-D10)/D50) of the secondary particle may be 0.96 to 1.55. In one embodiment, the ratio of Raman (I _d /I _g ) may satisfy the range of 0.346 to 0.362.

(The I _d refers to the peak intensity of amorphous carbon around a wavelength of 1350 cm ^-1 , and I _g refers to the peak intensity of crystalline carbon around a wavelength of 1575 cm ^-1 )

In one embodiment, the degree of orientation (I ₀₀₄ /I ₁₁₀ ) may be 10.0 to 14.0.

(I ₀₀₄ is the orientation peak intensity of the (004) plane of the graphite crystal in the XRD pattern, and I ₁₁₀ means the orientation peak intensity of the (110) plane of the graphite crystal in the XRD pattern)

In one embodiment, the sulfur content, in weight percent, may be 0.026 to 0.04 weight percent. In one embodiment, the graphite-based base material may be natural graphite, artificial graphite, or a combination thereof. In one embodiment, the carbon layer may be an amorphous carbon layer.

In one embodiment, the carbon layer may have a thickness of 1 to 30 nm. In one embodiment, the at least one carbon bead may be composed of at least one cluster. In one embodiment, the at least one carbon bead may have at least one of a spherical shape and an oval shape.

In another embodiment of the present invention, the method for producing a negative electrode active material for a lithium secondary battery of the present invention includes forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, and the resulting coating layer is processed for 800 to 800 hours. It may include carbonizing by heat treatment in the range of 2,700°C. In one embodiment, in the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, the ratio of the coating material to the coating material may be 1/20 to 1/5.

In one embodiment, the graphite-based material to be coated may include natural graphite, artificial graphite, and combinations thereof. In one embodiment, in the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, the quinoline insoluble content (QI) of the coating material is 0.05% by weight based on the total weight of the coating material. It may be from 2.0% by weight.

In one embodiment, in the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, the amount of fixed carbon in the coating material may be 19.5 to 96.2% by weight based on the total weight of coal tar.

According to one embodiment, the negative electrode material includes a carbon layer containing sulfur and at least one nanocarbon bead as a coating layer, thereby providing a negative electrode active material that suppresses side reactions with the electrolyte solution and further improves conductivity.

According to another embodiment of the present invention, a method of providing a negative electrode active material having the above advantages is provided.

FIG. 1A is a SEM photograph of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, FIG. 1B is a component analysis graph of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, and FIG. 1C is a graph of the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention. A TEM photo of the carbon layer is shown, according to one embodiment of the present invention.
Figure 2 is an SEM photograph of a negative electrode active material for a lithium secondary battery according to a comparative example of the present invention.

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

The terminology used herein is only intended to refer to specific embodiments and is not intended to limit the invention. As used herein, singular forms include plural forms unless phrases clearly indicate the contrary. As used in the specification, “comprising” means specifying a particular characteristic, area, integer, step, operation, element and/or ingredient, and the presence or presence of another characteristic, area, integer, step, operation, element and/or ingredient. This does not exclude addition.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part or may be accompanied by another part in between. In contrast, when a part is said to be "directly on top" of another part, there is no intervening part between them.

In this specification, D1O means the particle size at 10% by volume in the cumulative size-distribution curve, D50 is the particle size at 50% by volume, and D90 is the particle size at 90% by volume. It means size.

Although not defined differently, all terms including technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

FIG. 1A is a SEM photograph of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, FIG. 1B is a component analysis graph of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, and FIG. 1C is a graph of the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention. A TEM image of the carbon layer is shown, according to one embodiment of the present invention.

Referring to FIG. 1A, a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention includes a graphite-based base material and a coating layer coated on the surface of the graphite-based base material, and the coating layer includes a carbon layer and at least one carbon bead. (Carbon Beads).

The graphite-based base material may be at least one of natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, petroleum coke, resin sintered body, carbon fiber, heat part Y carbon, and a material made of amorphous carbon. . Specifically, the graphite-based base material may be natural graphite or artificial graphite.

The coating layer may be at least partially coated on the surface of the silicon base material using a coating material. The coating layer may be coated on part or all of the surface of the silicon base material.

The coating layer may be a layer composed of an amorphous carbon layer, a soft carbon layer, or a combination thereof. Specifically, the coating layer may be a coal tar carbon coating layer, and an amorphous carbon layer may be formed at a carbonization temperature of 1,200°C or lower, and a soft carbon layer containing a mixture of crystalline and amorphous elements may be formed in the range of 1,250 to 2,700°C. Accordingly, the coating layer may be amorphous or crystalline.

In one embodiment, the coating layer may contain 1.00 to 5.00 wt% of a coating material in the negative electrode active material. Specifically, the content of the coating material may be 1.04 to 4.16 wt % in the negative electrode active material. More specifically, the content of the coating material may be 1.04 to 3.12 wt% in the negative electrode active material. The content of the coating material refers to the content of the coating material after going through a carbonization process at 900°C.

If the content of the coating material exceeds the upper limit, the coating layer is formed thickly, which inhibits the movement of lithium ions and causes irreversibility, leading to a decrease in initial efficiency and initial capacity, resulting in a deterioration of lifespan. If the content of the coating material exceeds the lower limit, the formation of the coating layer becomes insufficient, and the edge surface of the graphite cannot be sufficiently coated, resulting in a side reaction with the electrolyte solution and deteriorating the lifespan of the battery.

In one embodiment, the coating layer may include the amorphous or crystalline carbon layer described above and at least one carbon bead. The carbon layer and the carbon beads may be coated with a coating material, for example, a coating material derived from coal tar. The carbon layer may be a layered coating layer with a high carbon content. The carbon beads may be in the shape of grains with a high carbon content.

In one embodiment, the carbon layer and carbon beads may contain sulfur. Since the carbon layer and the carbon beads contain sulfur, the sulfur doped into the carbon lattice provides extra electrons, thereby increasing the electron concentration and improving electrical conductivity.

Referring to FIG. 1B, in the negative electrode active material for a lithium secondary battery according to an embodiment of the present invention, the carbon layer and the carbon beads contain 0.026 to 0.040% by weight of sulfur based on 100% by weight of the total negative electrode active material composition. can do. Specifically, the sulfur content may include 0.030 to 0.036% by weight. If the sulfur content exceeds the upper limit, the coating layer containing sulfur is formed thickly, which reduces the movement of lithium ions and deteriorates the lifespan of the battery. If the sulfur content exceeds the lower limit, the formation of the coating layer becomes insufficient and the edge surface of the graphite cannot be sufficiently coated, resulting in a side reaction with the electrolyte solution, resulting in a problem of deterioration of battery life.

According to an embodiment of the present invention, the coating layer of the negative electrode active material for a lithium secondary battery may be a carbon layer in which at least one of amorphous and crystalline layers coexists. In one embodiment, the carbon layer may have a thickness ranging from 1 to 30 nm. Specifically, the thickness of the carbon layer may range from 3 to 30 nm. If the thickness of the carbon layer exceeds the upper limit, the coating layer acts as a resistance, inhibiting the movement of lithium ions, causing irreversibility, which reduces initial efficiency and initial capacity, leading to a problem that battery life is deteriorated. If the thickness of the carbon layer exceeds the lower limit, the formation of the carbon layer is insufficient and the edge surface of the graphite cannot be sufficiently coated, resulting in a side reaction with the electrolyte solution, which reduces the lifespan of the battery.

In one embodiment, the carbon beads may be composed of at least one cluster. The cluster refers to a group of grains, and the carbon beads may have the shape of not only a single grain, but also a group of grains. Since the carbon beads are composed of at least one cluster, there is an advantage in securing excellent electrical conductivity by forming a conductive chain.

In one embodiment, the at least one carbon bead may be disposed on at least one of the graphite-based base material and the carbon layer. Specifically, the carbon beads may be disposed on the graphite-based base material, may be placed on the carbon layer, may be partially disposed on the graphite-based base material, and may be partially disposed on the carbon layer. .

In one embodiment, the negative electrode active material of the present invention may be composed of at least one secondary particle, and the D10 of the secondary particle may be 7.3 to 14.1 ㎛. Specifically, D10 may be 8.52 to 12.1 ㎛. More specifically, D10 may be 2.3 to 4.0 ㎛. If the range of D10 is outside the lower limit, the content of fine powder increases, causing contact problems and deterioration of electrochemical properties.

In one embodiment, the average particle diameter (D50) of the secondary particles may be 13.9 to 23.7 ㎛. Specifically, the D50 may be 15.5 to 20.6 ㎛. More specifically, the D50 may be 15.5 to 18.4 ㎛.

If the range of D50 is outside the upper limit, dispersion occurs and adverse effects occur on electrode quality such as electrode rolling characteristics, resulting in deterioration of electrochemical properties. If the range of D50 is outside the lower limit, there is a problem that the yield is reduced during the pulverizing process, causing problems in the process.

In one embodiment, the D90 of the secondary particle may be 31.3 to 36.0 ㎛. Specifically, the D90 may be 31.8 to 35.2 ㎛.

If the range of D90 is outside the upper limit, dispersion occurs and adverse effects occur on electrode quality such as electrode rolling characteristics, resulting in deterioration of electrochemical properties. If the range of D90 is outside the lower limit, there is a problem of lowering the yield in the pulverizing process or sieving process.

In one embodiment, D90 - D10 of the secondary particles may be 22.6 to 23.9 ㎛. If the value of D90 - D10 is outside the upper limit, there is a problem in controlling the dispersion to be uniform if the difference in particle size between the coarse powder and the fine particles is excessively large. If the value of D90 - D10 exceeds the lower limit, the difference in particle size between the coarse powder and the fine particles becomes excessively small, causing a problem in maintaining uniform contact between the particles.

In one embodiment, the Span value ((D90-D10)/D50) of the secondary particle may range from 0.96 to 1.55. Specifically, the Span value may range from 1.12 to 1.50.

If the Span value exceeds the upper limit, the particle size distribution becomes wide, making uniform dispersion difficult. If the Span value exceeds the lower limit, the particle size distribution becomes narrow, making it difficult to maintain uniform contact between particles.

In one embodiment, the negative electrode active material may have a Raman (I _d /I _g ) ratio of 0.303 to 0.382. The Raman (I _d /I _g ) ratio refers to the peak intensity of amorphous carbon compared to the peak intensity of crystalline carbon. Specifically, the Raman (I _d /I _g ) ratio may be 0.346 to 0.362.

If the Raman (I _d /I _g ) ratio exceeds the upper limit, the coating layer is formed thickly, causing adverse effects on battery performance such as initial capacity, initial efficiency, and battery life. If the Raman (I _d /I _g ) ratio exceeds the lower limit, the formation of the coating layer is not sufficient, and the edge surface of the graphite cannot be sufficiently coated, resulting in a side reaction with the electrolyte solution, shortening the battery life. It may cause deterioration.

In one embodiment, the degree of orientation (I ₀₀₄ /I ₁₁₀ ) of the negative electrode active material may be 10.0 to 14.0. The degree of orientation refers to the ratio of the peak intensity of the (110) plane of the graphite crystal to the peak intensity of the orientation of the (004) plane in the XRD pattern obtained from X-ray diffraction measurement.

Specifically, the degree of orientation may be 11.0 to 13.0. More specifically, the degree of orientation may be 12.1 to 12.8. If the degree of orientation is outside the upper limit of the above-mentioned range, smooth impregnation of the electrolyte may be prevented, mobility may be increased, and smooth insertion and desorption of lithium ions may be hindered, resulting in a decrease in battery life. If the degree of orientation is outside the lower limit of the above-mentioned range, the non-orientation of the negative electrode active material increases when forming the electrode, which may interfere with the smooth insertion and desorption process of lithium ions, resulting in a decrease in battery life.

In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy Equation 1 below.

<Equation 1>

30 ≤ Coating material content [wt%]/Sulfur content [wt%] ≤ 125

The formula 1 above means that the content of the coating material relative to the sulfur is the content of the coating material remaining in the negative electrode active material that has undergone the carbonization process divided by the content of sulfur. Equation 1 above can satisfy 30.0 to 125.0. Specifically, Equation 1 above may satisfy 34.0 to 115.0. By satisfying Equation 1 above, there is an advantage that the initial capacity, initial efficiency, and mixing life of the battery are improved when the sulfur inside the coating material has an appropriate content.

If it exceeds the upper limit of Equation 1, the coating layer becomes thick, inhibiting the movement of lithium ions and causing irreversibility, which reduces initial efficiency and initial capacity and deteriorates the life of the battery. The lower limit of Equation 1 If it deviates from this, the edge surface of the graphite cannot be sufficiently coated due to insufficient coating layer, resulting in a side reaction with the electrolyte solution, leading to a problem of deterioration of lifespan.

In one embodiment, the negative electrode active material of the present invention may satisfy Equation 2 below.

<Equation 2>

1.0 ≤ Coating material content [wt%] × BET specific surface area [m ² /g] ≤ 13

Equation 2 refers to the relationship between the BET specific surface area and the coating material content. Equation 2 above can satisfy 1.0 to 13.0. Specifically, Equation 1 above may satisfy 2.0 to 10.0. By satisfying Equation 2 above, it is possible to have a correlation in an appropriate range that derives the optimal BET specific surface area when coated with an appropriate coating amount.

If it exceeds the upper limit of Equation 2, the coating layer becomes thick, inhibiting the movement of lithium ions and causing irreversibility, which reduces initial efficiency and initial capacity and causes deterioration of lifespan. The lower limit of Equation 1 is If it deviates, there is a problem that the edge surface of the graphite cannot be sufficiently coated due to insufficient coating layer, resulting in a side reaction with the electrolyte solution and deterioration of battery life.

In one embodiment, the negative electrode active material may satisfy Equation 3 below.

<Equation 3>

0.7 ≤ Raman(I _d /I _g ) ratio × sulfur content [wt%] × 100 ≤ 1.5

Equation 3 above means the percentage of the Raman (I _d /I _g ) ratio of the surface carbon layer remaining in the negative electrode active material that has gone through the carbonization process multiplied by the value of the sulfur content. Equation 3 above can satisfy 0.7 to 1.5. Specifically, Equation 2 may satisfy 0.9 to 1.35. By satisfying the above formula, an appropriate amount of sulfur is contained in the coating layer of the amorphous or soft carbon layer, thereby providing the advantage of excellent battery characteristics.

If it exceeds the upper limit of Equation 2, the coating layer becomes thick, which inhibits the movement of lithium ions and causes irreversibility, which reduces the initial efficiency and initial capacity of the battery and deteriorates the lifespan of the battery. If it exceeds the lower limit of Equation 2 above, there is a problem that the coating layer is insufficient, causing deterioration of the initial efficiency and lifespan of the battery.

According to an embodiment of the present invention, a method of manufacturing a negative electrode active material for a lithium secondary battery includes uniformly mixing a graphite-based coating material and a sulfur-containing coating material and carbonizing the mixed resultant by heat treatment. The graphite-based coating material is the same as the graphite-based base material described above to the extent that it is not inconsistent with the above-described graphite-based base material.

The sulfur-containing coating material may be a sulfur-containing material, for example, coal tar. The sulfur-containing coating material may be in powder, liquid, or gaseous form. Specifically, it may be a liquid material containing sulfur.

In one embodiment, the coating material may have 25 to 45 dyne/cm, specifically, 30 to 40 dyne/cm at room temperature. The graphite base material to be coated may have a higher surface tension than the coating material. Accordingly, due to the difference in surface tension between the coating material and the material to be coated, the coating material can be uniformly coated on the surface of the material to be coated, and the remaining coating material remaining after being coated on the surface is spherical to lower the surface energy in the carbonization process. Alternatively, carbon beads are formed by forming an oval shape. Thereafter, after going through a carbonization process, it can be converted to carbon.

In one embodiment, the step of uniformly mixing the graphite-based coating material and the sulfur-containing coating material may include mixing the graphite-based coating material in the range of 1 to 24 parts by weight based on 100 parts by weight of the coating material. Specifically, the coating material can be mixed in the range of 5 to 20 parts by weight. Specifically, the range of the graphite-based coating material relative to the coating material may be in the range of 5 to 15 parts by weight.

When the range of the coating material exceeds the upper limit, agglomeration or assembly between particles is caused, causing an increase in particle size, the coating layer is formed thick, and the coating layer acts as a resistance, thereby inhibiting the movement of lithium ions. There is a problem that the initial efficiency and initial capacity are reduced and the battery life is deteriorated due to irreversibility. If the range of the coating material exceeds the lower limit, the coating layer becomes insufficient and the edge surface of the graphite cannot be sufficiently coated, which may cause side reactions with the electrolyte solution and result in deterioration of lifespan.

In one embodiment, uniformly mixing the graphite-based coating material and the sulfur-containing coating material may be performed by a dry mixing step. The dry mixing step may be a mechanical mixing process, and the mechanical mixing process may include ball milling, mechanofusion milling, shaker milling, planetary milling, or attrition. attritor milling, disk milling, shape milling, nauta milling, nobilta milling, Planetary, 3D-mixer, V-mixer, Mechano-Fusion, It can be performed by selecting any one method among Hybridizer, Pate Mixer, or a combination thereof.

In the step of heat treating and carbonizing the mixed result, the coating material may be carbonized on the surface of the coated material while heat treating the mixed result of the coating material and the coated material.

In one embodiment, the step of carbonizing the mixed resultant by heat treatment may be performed in the range of 800 to 2,700 °C. Specifically, the above range may be carried out in the range of 1,000 to 2,500°C.

If heat treatment is performed outside the upper limit of the above range, there is a problem in that the amorphous layer is converted to a crystalline layer and output. If heat treatment is performed outside the lower limit of the above range, there is a problem in that uniform amorphization or soft carbonization of the coating material cannot be achieved.

In one embodiment, in the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, the ratio of the coating material to the coating material may be 1/20 to 1/5. Specifically, the ratio of the coating material to the coating material may be 2/25 to 17/100.

If it exceeds the upper limit of the ratio, it causes agglomeration or assembly between particles, causing an increase in particle size, and the thick coating layer acts as a resistance, causing inhibition and irreversibility of lithium movement, resulting in a decrease in initial efficiency and initial capacity, There is a problem that causes deterioration of battery life. If the ratio exceeds the lower limit, the formation of the coating layer is insufficient, and the edge surface of the graphite cannot be sufficiently coated, resulting in a side reaction with the electrolyte solution, thereby deteriorating the lifespan of the battery.

In one embodiment, in forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material. The quinoline insoluble component (QI) of the material to be coated may be included in an amount of 0.05 to 2.0% by weight based on the total weight of the material to be coated. Specifically, the quinoline insoluble content (QI) may be 0.07% by weight to 0.7% by weight based on the total weight of the coating material. If the quinoline insoluble content is outside the upper limit of the above range, which means that the coating amount is large, the amorphous or soft carbon layer acts as a resistance, inhibiting lithium movement and causing irreversibility, resulting in a decrease in initial efficiency and initial capacity and the life of the battery. There is a problem that causes deterioration. If the quinoline insoluble content is outside the lower limit of the above range, this means that the coating amount is small, and the edge surface of the graphite cannot be sufficiently coated due to insufficient amorphous or soft carbon layer, resulting in a side reaction with the electrolyte solution, resulting in battery failure. There is a problem that causes lifespan to deteriorate.

In one embodiment, in the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material, the amount of fixed carbon in the coating material may be 19.5 to 96.2% by weight based on the total weight of coal tar.

According to another embodiment of the present invention, a lithium secondary battery may include a negative electrode containing the above-described negative electrode active material, a positive electrode containing the positive electrode active material, a separator positioned between the negative electrode and the positive electrode, and an electrolyte solution. The description of the negative electrode active material is the same as the negative electrode active material for lithium secondary batteries described above to the extent that it does not contradict.

_The anode is LiCoO ₂ , LiNiO ₂ , LiNi _{x Mn y O 2 , Li 1+z} Ni _x Mn _{y Co 1-xy O 2 ,} LiNi , LiMnO ₂ , LiCrO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , LiFePO ₄ , and combinations thereof, where x is 0.3 to 0.8, y is 0.1 to 0.45, and z is independently It may be 0 to 0.2. More specifically, the anode may be LiFePO ₄ , LiCoO ₂ , NCM811, and NCM622. The negative electrode may use the above-described active material for lithium secondary batteries, or a negative electrode active material manufactured through the precursor manufacturing method of the negative electrode active material.

The separation membrane is a conventional porous polymer film used as a separator, such as ethylene homopolymer, propylene homopolymer, ethylene/propylene copolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Porous polymer films made of polyolefin-based polymers, such as polymers, can be used alone or by laminating them, or conventional porous non-woven fabrics, such as high-melting point glass fibers, polyethylene terephthalate fibers, etc., can be used. , this is a non-limiting example.

In the electrolyte solution, the lithium salt that can be included as the electrolyte may be those commonly used in electrolyte solutions for lithium secondary batteries without limitation. For example, the anions of the lithium salt include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , It may be any one selected from the group consisting of CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

In the electrolyte solution, organic solvents commonly used in electrolytes for lithium secondary batteries can be used without limitation, and representative examples include propylene carbonate (PC), ethylene carbonate (EC), and Ethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene Any one selected from the group consisting of carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more of these, can be typically used.

The lithium secondary battery may be placed in a battery case. The battery case is a non-limiting example and may be any one of a cylindrical shape using a can, a rectangular shape, a pouch type, and a coin type.

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

<Ingredient characteristics>

The coating material of the present invention is liquid coal tar generated during the drying of raw coal in a steel mill and has fluidity at room temperature, so ASTM D3104 (softening point measurement method 1, softening point above 50 ℃), ASTM D36 (softening point measurement) Method 2, softening point above 30 ℃), the specific gravity is 1.1 to 1.3 g/cc, and when carbonized at 900 ℃, it may be a liquid material containing sulfur with a fixed carbon amount of 19 to 22%.

When the liquid material is coated on a base material to be coated, a carbon layer containing sulfur and carbon beads (CB) are formed on the surface of the base material due to the characteristics of the liquid.

<Manufacturing process>

As a process for manufacturing the anode material of the present invention, the coating process includes uniform dry mixing between the silicon-based coating material and the coating material to form the carbon beads and a coating layer including an amorphous or soft carbon layer of the anode material. and a carbonization process of heat treatment at a temperature of 800 to 3,200°C after the dry dispersion process. The mixing and dispersion method is performed through methods such as Planetary, 3D-mixer, V-mixer, Mechano-fusion, Hybridizer, and Paste Mixer.

<Example 1>

Artificial graphite was used as the graphite-based coating material, and liquid coal tar was used as the coating material. Specifically, the liquid coal tar is coated on the artificial graphite to manufacture a negative electrode active material containing a material carbonized at 900°C.

<Example 2>

The liquid coal tar was coated on the artificial graphite and carbonized at 1,200° C., in the same manner as in Example 1.

<Example 3>

The liquid coal tar was coated on the artificial graphite and carbonized at 1,500°C, in the same manner as in Example 1.

<Example 4>

The liquid coal tar was coated on the artificial graphite and carbonized at 1,600° C., in the same manner as in Example 1.

<Example 5>

The liquid coal tar was coated on the artificial graphite and carbonized at 2,500° C., in the same manner as in Example 1.

<Comparative Example 1>

A negative electrode active material was prepared without the artificial graphite of Example 1 coated with a coating material.

<Comparative Example 2>

The same procedure as Example 1 was carried out except that artificial graphite, which was a coating material, was coated at 900° C. using a vapor phase CVD method.

<Comparative Example 3>

The same procedure as Example 1 was carried out except that artificial graphite, which was a coating material, was coated with solid pitch and carbonized at 900°C.

<Comparative Example 4>

The same procedure as in Example 1 was carried out except that artificial graphite, which was a coating material, was coated with solid pitch and carbonized at 1,200°C.

<Manufacture of graphite-based electrode>

The negative electrode active material, binder (SBR-CMC), and conductive material (Super P) prepared in the Examples and Comparative Examples were prepared so that the weight ratio of the negative electrode active material: binder: conductive material was 96.1:2.9:1, respectively, and then added to distilled water to uniformly A slurry is prepared by mixing thoroughly. The slurry is uniformly applied to a copper (Cu, approximately 10 ㎛ thick) current collector, compressed in a roll press, and then dried to produce a negative electrode. Specifically, the electrode is manufactured to have a loading amount of 7 to 8 mg/cm ² and an electrode density of 1.55 to 1.60 g/cc.

Lithium metal (Li-Metal) was used as the counter electrode, and the electrolyte was 1 mole of LiPF ₆ solution in a mixed solvent with a volume ratio of 3:7 of ethylene carbonate (EC) and dimethyl carbonate (DMC). Use the dissolved product.

A CR 2032 half coin cell is manufactured according to a conventional manufacturing method using the negative electrode, lithium metal, and electrolyte solution.

Table 1 below shows the initial capacity, initial efficiency, and lifespan for Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention. The initial efficiency is calculated as (discharge capacity/charge capacity) × 100 after measuring charging CC-CV 0.1 C & 5 mV (0.005 C cutoff) and discharging 0.1 C 1.5 V cut-off once. In addition, the initial capacity is measured three times for charging CC-CV 0.1 C & 5 mV (0.005 C cutoff) and discharging 0.1 C 1.5 V cut-off, and the specific capacity (mAh/g) of 3 ^rd cycle when discharging. Calculate .

The above lifespan is based on charging CC-CV 0.1 C & 5 mV (0.005 C cutoff), discharging 0.1 C 1.5 V cut-off after 3 activations and initial capacity confirmation, charging CC-CV 0.5 C & 5 mV (0.005C cutoff) discharge. 0.5 C 1.5 V cut-off After measuring the life cycle 50 times, calculate the (discharge capacity at last life time/initial capacity) value.

coating material carbonization temperature
(℃) Initial capacity
(mAh/g) initial efficiency
(%) mixed life
(%) Example 1 coal tar 900 352.8 92.6 92.0 Example 2 coal tar 1,200 355.2 93.0 93.5 Example 3 coal tar 1,500 355.3 93.1 93.7 Example 4 coal tar 1,600 356.2 93.5 94.8 Example 5 coal tar 2,500 356.8 93.7 95.7 Comparative Example 1 X X 355.0 93.7 78.1 Comparative example 2 methane gas 900 349.6 91.1 81.2 Comparative example 3 pitch 900 348.7 90.7 79.5 Comparative example 4 pitch 1,200 351.1 90.6 81.1

Accordingly, looking at Table 1 above, it can be seen that the initial capacity, initial efficiency, and mixed life of the lithium secondary battery are excellent when liquid coal tar is used as the coating material and the carbonization temperature is 900 ℃ or higher, specifically, 1,600 ℃ or higher. Looking at Table 2 below, you can check the characteristics according to the ratio of the coated material to the coating material.

Coating material coating
matter coating material
content After carbonization
coating material
content Carbon
Biz
existence and nonexistence Carbon
Biz
size sulfur
content Equation 1 Early
Volume Early
efficiency mix
life span (wt%) (wt%) (wt%) - (mAh/g) (%) (%) Example 1 synthetic
black smoke coal tar 5 1.04 O <10 0.03 34.6 353.2 92.6 92.0 Example 2 Artificial graphite coal tar 15 3.12 O <10 0.034 91.7 352.5 92.4 91.8 Example 3 Artificial graphite coal tar 20 4.16 O <10 0.036 115.0 351.2 92.5 91.5 Comparative Example 1 synthetic
black smoke coal tar 0 0 X - 0 0 354.5 89.1 78.8 Comparative example 2 synthetic
black smoke coal tar 25 5.2 O <10 0.041 126.0 348.8 88.5 76.6 Comparative Example 5 synthetic
black smoke pitch 5 3.5 X - 0.025 140.0 352.2 87.2 75.9 Comparative Example 6 synthetic
black smoke methane
gas gas 3.5 X - 0 0 345.5 88.2 73.5 Comparative Example 7 Artificial graphite phenol
Resin 7.5 3 X - 0 0 349.1 87.7 73.9

Looking at Table 2, it can be seen that with respect to 100 parts by weight of the coating material, the content of the coating material satisfies the range of the present invention, and the initial capacity, initial efficiency, and mixing life are superior to those outside the above range.

Table 3 below shows the D10, D50, and D90 values, Span value, BET specific surface area, d002, orientation (I004/I110), initial capacity, expansion rate, and initial efficiency of secondary particles according to the examples and comparative examples of the present invention. , and represents the mixing life.

The particle size distribution of secondary particles D10, D50, and D90 was measured by laser diffraction.

The expansion rate is the percentage of (thickness of electrode after ^50th cycle - thickness of Cu current collector) - (thickness of fresh electrode - thickness of Cu current collector) divided by (thickness of fresh electrode - thickness of Cu current collector). it means.

The BET specific surface area was measured using the BET method (Surface area and Porosity Analyzer) ASAP2020 from Micromeritics.

Raman values are: microscope ratio of x20, 20 × 20 ㎛, laser of 532 ㎚, power of 2.31 mW, After measurement, the I _d /I _g value was calculated. I _d refers to the peak intensity of amorphous carbon around a wavelength of 1350 cm ^-1 , and I _g refers to the peak intensity of crystalline carbon around a wavelength of 1575 cm ^-1 .

The degree of orientation was converted into a value divided by measuring the peak intensity of the (004) plane by measuring the peak intensity of the (110) plane using the XRD diffraction method.

Sulfur content secondary particle
D50 secondary particle
D10 secondary particle
D90 D90-D10 Span value
(D90-D10/D50) BET
specific surface area Raman(Id/Ig) Orientation
(I004/I110) Early
Volume expansion rate Early
efficiency mix
life span Equation 2 Equation 3 (wt%) (㎛) (㎛) (㎛) (㎛) m ² /g (mAh/g) (%) (%) (%) (%) Example 1 0.03 15.5 8.52 31.8 23.3 1.50 1.98 0.346 12.6 353.2 29.5 92.6 92 2.1 1.04 Example 2 0.034 18.4 10.5 33.1 22.6 1.23 2.03 0.354 12.8 352.5 27.7 92.4 91.8 6.3 1.20 Example 3 0.036 20.6 12.1 35.2 23.1 1.12 2.15 0.362 12.1 351.2 25.5 92.5 91.5 8.9 1.30 Comparative Example 1 0 13.2 7.2 31.2 24.0 1.82 1.56 0.233 14.2 354.5 32.8 93.2 88.8 0 0 Comparative example 2 0.041 23.8 14.9 36.8 21.9 0.95 2.54 0.383 9.8 348.8 30.1 91.1 89.8 13.2 1.57 Comparative Example 5 0.025 18.5 9.9 38.8 28.9 1.56 4.85 0.249 18.2 346.5 32.2 90.2 79.8 17.0 0.62 Comparative Example 6 0 13.8 8.2 33.2 25 1.81 5.64 0.302 14.8 347.7 34.5 88.8 81.1 19.7 0 Comparative example 7 0 19.1 9.8 34.8 25 1.31 8.94 0.28 14.3 348.2 32.8 90.4 87 26.8 0

The present invention is not limited to the above embodiments and/or examples, but can be manufactured in various different forms, and those skilled in the art may change the technical idea or essential features of the present invention. You will be able to understand that it can be implemented in other specific forms without doing so. Therefore, the implementation examples and/or embodiments described above should be understood in all respects as illustrative and not restrictive.

Claims (20)

Graphite base material; and
It includes a coating layer coated on the surface of the graphite-based base material,
The coating layer includes a carbon layer and at least one carbon bead,
The carbon layer and the carbon beads contain sulfur,
A negative electrode active material for a lithium secondary battery containing a coating material content of 1.00 to 5.00 wt% in weight percent of the negative electrode active material.
According to claim 1,
A negative electrode active material for a lithium secondary battery that satisfies the following formula 1.
<Equation 1>
30 ≤ Coating material content [wt%]/ Sulfur content [wt%] ≤ 125
According to claim 1,
A negative electrode active material for a lithium secondary battery that satisfies the following formula 2.
<Equation 2>
1.0 ≤ Coating material content [wt%] × BET specific surface area [m ² /g] ≤ 13
According to claim 1,
A negative electrode active material for a lithium secondary battery that satisfies the following formula 3.
<Equation 3>
0.7 ≤ Raman(I _d /I _g ) ratio × sulfur content [wt%] × 100 ≤ 1.5
(The I _d refers to the peak intensity of amorphous carbon around a wavelength of 1350 cm ^-1 , and I _g refers to the peak intensity of crystalline carbon around a wavelength of 1575 cm ^-1 )
According to claim 1,
A negative electrode active material for a lithium secondary battery having a D90 particle size of the secondary particle - D10 particle size of 22.6 to 23.9 ㎛.
According to claim 1,
A negative electrode active material for a lithium secondary battery in which the D10 particle size of the secondary particles is 7.3 to 14.1 ㎛.
According to claim 1,
A negative electrode active material for a lithium secondary battery whose span value ((D90-D10)/D50) of the secondary particles is 0.96 to 1.55.
According to claim 1,
A negative electrode active material for a lithium secondary battery whose Raman (I _d /I _g ) ratio satisfies the range of 0.346 to 0.362.
(The I _d refers to the peak intensity of amorphous carbon around a wavelength of 1350 cm ^-1 , and I _g refers to the peak intensity of crystalline carbon around a wavelength of 1575 cm ^-1 )
According to claim 1,
A negative electrode active material for a lithium secondary battery having an orientation degree (I ₀₀₄ /I ₁₁₀ ) of 10.0 to 14.0.
(I ₀₀₄ is the orientation peak intensity of the (004) plane of the graphite crystal in the XRD pattern, and I ₁₁₀ means the orientation peak intensity of the (110) plane of the graphite crystal in the XRD pattern)
According to claim 1,
The anode active material for a lithium secondary battery has a sulfur content of 0.026 to 0.04 wt% in weight %.
According to claim 1,
The graphite-based base material is a negative electrode active material for lithium secondary batteries that is natural graphite, artificial graphite, and a combination thereof.
According to claim 1,
The carbon layer is an amorphous carbon layer, a negative electrode active material for a lithium secondary battery.
According to claim 1,
A negative electrode active material for a lithium secondary battery wherein the carbon layer has a thickness of 1 to 30 nm.
According to claim 1,
The at least one carbon bead is a negative electrode active material for a lithium secondary battery consisting of at least one cluster.
According to claim 1,
The at least one carbon bead is at least one of spherical and oval shapes.
Forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material; and
A method of producing a negative electrode active material for a lithium secondary battery, comprising the step of carbonizing the resulting coating layer by heat treatment in the range of 800 to 2,700 ° C.
According to claim 16,
In the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material,
A method for producing a negative electrode active material for a lithium secondary battery, wherein the ratio of the coated material to the coating material is 1/20 to 1/5.

According to claim 16,
The graphite-based coating material is a method of producing a negative electrode active material for a lithium secondary battery including natural graphite, artificial graphite, and a combination thereof.
According to claim 16,
In the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material,
A method for producing a negative active material for a lithium secondary battery, wherein the quinoline insoluble content (QI) of the material to be coated is 0.05% to 2.0% by weight based on the total weight of the material to be coated.
In clause 16
In the step of forming a coating layer by mixing a graphite-based coating material and a sulfur-containing coating material,
A method for producing a negative electrode active material for a lithium secondary battery, wherein the fixed carbon amount of the coating material is 19.5 to 96.2% by weight based on the total weight of coal tar.