Precursor for negative electrode material of lithium secondary battery, negative electrode material manufactured therefrom, and method for manufacturing same

Abstract

One aspect of the present invention provides: a precursor for a negative electrode material of a lithium secondary battery having high capacity characteristics, excellent processability, and excellent lifespan characteristics through a structure in which fine natural graphite is distributed in high-hardness artificial graphite; a negative electrode material manufactured therefrom; and a method for manufacturing same.

Description

Precursor for negative electrode material of lithium secondary battery, negative electrode material manufactured therefrom, and method for manufacturing same

[0001] The present invention relates to a precursor for an anode material for a lithium secondary battery and an anode material manufactured therefrom. More specifically, the present invention relates to a precursor for an anode material for a lithium secondary battery formed by processing a mixture of artificial graphite and natural graphite fine powder, and an anode material manufactured therefrom.

[0002] Lithium secondary batteries typically consist of a positive electrode containing positive active material, a negative electrode containing negative active material, a separator, and an electrolyte. Charging and discharging occur through the intercalation and deintercalation of lithium ions. Lithium secondary batteries boast high energy density, high electromotive force, and high capacity, making them widely used in various fields, including mobile devices, electric vehicles, and hybrid electric vehicles.

[0003] Metal oxides such as LiCoO2, LiMnO2, LiMn2O4 or LiCrO2 are used as positive electrode active materials constituting the positive electrode of a lithium secondary battery, and metal materials such as metal lithium, carbon-based materials such as graphite or activated carbon and silicon oxide (SiOx) are used as negative electrode active materials constituting the negative electrode.

[0004] Initially, metallic lithium was mainly used as the above-mentioned negative electrode active material, but as the charge / discharge cycle progressed, lithium atoms grew on the surface of the metallic lithium, damaging the separator and causing the battery to break down. Therefore, recently, carbon-based materials have been mainly used.

[0005] Carbon-based anode active materials used in the negative electrodes of lithium secondary batteries have a potential close to that of lithium metal, so their crystal structure undergoes minimal change during the insertion and deintercalation of ionic lithium. Therefore, these carbon-based anode active materials contribute to the high capacity and excellent cycle life of lithium secondary batteries by enabling continuous and repetitive redox reactions at the electrode.

[0006] The above carbon-based negative electrode active material can be of various types, including crystalline carbon-based materials such as natural graphite and artificial graphite, or amorphous carbon-based materials such as hard carbon and soft carbon. Among these, graphite-based active materials are the most widely used due to their excellent reversibility and advantageous lifespan characteristics of lithium secondary batteries. In particular, because graphite-based active materials have a low discharge voltage of -0.2 V compared to lithium, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6 V, and lithium secondary batteries containing them have many advantages in terms of energy density.

[0007] However, graphite-based active materials have relatively low theoretical capacity values ​​(e.g., approximately 372 mAh / g for LiC6 cathodes), which is still somewhat insufficient to satisfy the electrochemical characteristics required in the relevant market.

[0008] Therefore, many researchers are interested in group IV elements (Si, Ge, Sn) in the periodic table, and among them, Si in particular has a very high theoretical capacity (Li 15Si4: 3600 mAh / g) and low operating voltage (~0.1 V vs. Li / Li+) have attracted much attention as a very attractive material. However, Si undergoes significant volume expansion and contraction due to its reaction with lithium during charge and discharge, which can result in fine particle size of the silicon active material powder and poor electrical contact between the silicon active material powder and the current collector. Due to this phenomenon, lithium secondary batteries containing Si have the problem that their capacity can rapidly decrease as the charge and discharge cycles progress.

[0009] The present invention aims to provide a precursor for an anode material of a lithium secondary battery having high capacity characteristics, excellent processability and excellent life characteristics, an anode material manufactured therefrom and a method for manufacturing the same.

[0010] The subject matter of the present invention is not limited to the above-described contents.

[0011] One aspect of the present invention provides a precursor for an anode material of a lithium secondary battery, which comprises a core of artificial graphite and natural graphite fine powder distributed on the surface of the core, and wherein the sphericity of the artificial graphite is 0.9 or more.

[0012] The center particle size (D50) of the above natural graphite powder may be 8 μm or less.

[0013] The above natural graphite powder may be included in an amount of 2 wt% or more and 7 wt% or less based on the total weight of the artificial graphite and the above natural graphite powder.

[0014] The precursor for the negative electrode material of the lithium secondary battery according to the present invention may additionally include SiOx (0≤x≤2) of 5 wt% or less based on the total weight of the artificial graphite and the natural graphite powder.

[0015] The precursor for the negative electrode material of the lithium secondary battery according to the present invention may have a coverage value of 0.3 or more and 0.7 or less according to the following [Relational Formula 1].

[0016] [Relationship 1]

[0017] Coverage =

[0018] When the center of the particle of the above precursor is cut, the porosity of the artificial graphite may be 30 area% or less with respect to the total area of ​​the fracture surface.

[0019] The precursor for the negative electrode material of the lithium secondary battery according to the present invention has a specific surface area of ​​3 m 2 / g can be less.

[0020] Another aspect of the present invention provides a method for producing a precursor for an anode material of a lithium secondary battery, comprising the steps of: preparing artificial graphite and natural graphite powder; a spheroidizing step of spheroidizing the artificial graphite using equipment utilizing high-speed centrifugal force at a linear speed of 55 m / s to 70 m / s for 3 to 7 minutes; a step of mixing natural graphite powder into the spheroidized artificial graphite to produce a mixture; and an assembly spheroidizing step of spheroidizing and assembling the mixture using equipment utilizing high-speed centrifugal force at a linear speed of 55 m / s to 70 m / s for 1 to 5 minutes.

[0021] After the above spheroidization step, the spheroidization degree of the artificial graphite may be 0.9 or more.

[0022] In the step of manufacturing the above mixture, the natural graphite powder may be mixed in an amount of 2 wt% or more and 7 wt% or less based on the total weight of the artificial graphite and the natural graphite powder.

[0023] In the step of manufacturing the above mixture, 5 wt% or less of SiOx (0≤x≤2) can be additionally mixed with respect to the total weight of the artificial graphite and the natural graphite powder.

[0024] The above sphericalization step and the assembly sphericalization step may be performed using equipment that utilizes horizontal or vertical centrifugal force.

[0025] Another aspect of the present invention provides a method for manufacturing an anode material for a lithium secondary battery, comprising the steps of: manufacturing a precursor for an anode material for a lithium secondary battery according to the method for manufacturing a precursor for an anode material for a lithium secondary battery described above; adding a binder to the precursor; and carbonizing the precursor to which the binder has been added at 800°C or higher.

[0026] The negative electrode material of a lithium secondary battery manufactured by the above-described method for manufacturing a negative electrode material may include a core of artificial graphite and natural graphite fine powder distributed on the surface of the core, wherein the artificial graphite and the natural graphite fine powder may be bonded via amorphous carbon. In addition, the negative electrode material of a lithium secondary battery according to the present invention may be characterized by having a sphericity of 0.83 or more.

[0027] The negative electrode material of the lithium secondary battery according to the present invention may include artificial graphite having a sphericity of 0.9 or more, and may additionally include SiOx (0≤x≤2) of 5 wt% or less based on the total weight of the artificial graphite and the natural graphite powder.

[0028] The negative electrode material of the lithium secondary battery according to the present invention may have a coverage value of 0.3 or more and 0.7 or less according to the following [Relational Expression 1].

[0029] [Relationship 1]

[0030] Coverage =

[0031] The precursor for a negative electrode material of a lithium secondary battery according to the present invention and the negative electrode material manufactured therefrom can secure high capacity characteristics and excellent processability through an island structure in which finely divided natural graphite is distributed like islands on the surface of high-hardness artificial graphite.

[0032] In addition, the precursor for the negative electrode material of the lithium secondary battery according to the present invention and the negative electrode material manufactured therefrom can secure excellent life characteristics by protecting artificial graphite, which is advantageous in life characteristics, with natural graphite through the structure described above.

[0033] Figure 1 is a schematic diagram of a precursor for a negative electrode material of a lithium secondary battery according to the present invention.

[0034] Figure 2 is a schematic diagram of a precursor for a negative electrode material of a lithium secondary battery according to the present invention into which SiOx is inserted.

[0035] Figure 3 is a schematic diagram of a negative electrode material of a lithium secondary battery according to the present invention into which SiOx is inserted.

[0036] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0037] In this specification, the term "including" is used to indicate that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0038] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0039] Artificial graphite, a crystalline carbon material, is formed by applying high thermal energy of over 2,700°C to form a graphite crystal structure, which makes it more crystallographically stable than natural graphite. Therefore, artificial graphite exhibits minimal change in crystal structure even after repeated lithium-ion charging and discharging, resulting in a relatively longer lifespan than natural graphite. Typically, artificial graphite-based negative electrode active materials have a lifespan that is two to three times longer than that of natural graphite.

[0040] However, since the above artificial graphite has poor electrode processability compared to natural graphite, it is desirable to use it by mixing it with a certain ratio of natural graphite.

[0041] Therefore, considering the use and purpose of lithium secondary batteries, it is necessary to secure the desired level of electrochemical characteristics by mixing artificial graphite and natural graphite in an appropriate ratio.

[0042] The inventors of the present invention have found that by positioning artificial graphite having relatively high hardness in an inner core and distributing natural graphite fine powder having relatively excellent electrode processability on the surface of the inner core like an island structure, insertion and de-insertion of lithium particles in the anode material can be facilitated, thereby providing an anode material for a lithium secondary battery having high capacity characteristics and excellent processability.

[0043] In addition, the inventors of the present invention also discovered that artificial graphite, which has advantageous life-cycle characteristics, can be protected by natural graphite through the island structure, thereby providing a negative electrode material for a lithium secondary battery with excellent life-cycle characteristics.

[0044] From this point of view, a precursor for a negative electrode material of a lithium secondary battery according to one embodiment of the present invention may include a core of artificial graphite and natural graphite fine powder distributed on the surface of the core.

[0045] Figure 1 is a schematic diagram of a precursor for a negative electrode material of a lithium secondary battery according to one embodiment of the present invention. Examining this, it can be seen that natural graphite fine powder (1) is distributed like an island on the surface of the core of artificial graphite (2).

[0046] In addition, the precursor for the negative electrode material of the lithium secondary battery according to one embodiment of the present invention may have a sphericity of the artificial graphite of 0.9 or more. When the sphericity of the artificial graphite is less than 0.9, the side reaction sites between the artificial graphite and the electrolyte increase, which may cause unnecessary chemical reactions. As a result, as described below, the coverage value of [Relational Expression 1] regarding the ratio of the surface area of ​​the natural graphite fine powder in contact with the artificial graphite to the total surface area of ​​the artificial graphite may decrease below a certain level, which may result in a decrease in electrode adhesion. Since the higher the sphericity of the artificial graphite is, the better, the present invention does not specifically limit the upper limit thereof.

[0047] Specifically, the precursor for the negative electrode material of a lithium secondary battery according to an example of the present invention may have a coverage value of 0.3 or more and 0.7 or less by the following [Relational Formula 1]. When the coverage value is less than 0.3, the surface area of ​​the natural graphite fine powder, which contributes to improving the electrode processability, may not be sufficient in the surface area of ​​the entire core, which may reduce the adhesive strength of the electrode. In addition, since the coverage value of [Relational Formula 1] of 0.3 or more means that most of the natural graphite fine powder exists on the surface of the artificial graphite, the present invention can prevent the phenomenon of the natural graphite fine powder excessively flowing into the core and causing the structure of the precursor to collapse by setting the coverage value to 0.3 or more. More preferably, the coverage value may be 0.4 or more.

[0048] [Relationship 1]

[0049] Coverage =

[0050] On the other hand, if the coverage value exceeds 0.7, the problem may arise that if some of the natural graphite is exfoliated due to the increased natural graphite in contact with the artificial graphite, the entire natural graphite may be exfoliated. This problem arises from the relatively good adhesive properties of natural graphite compared to artificial graphite. Furthermore, it is more preferable that the coverage value be 0.6 or less.

[0051] In order to secure the above coverage value at an appropriate level, the present invention may include natural graphite fine powder in an amount of 2 wt% or more and 7 wt% or less based on the total weight of artificial graphite and natural graphite fine powder, which is the weight of the entire graphite.

[0052] As an example of the present invention, when the center of the particle of the precursor is cut, the porosity of the artificial graphite may be 30 area% or less with respect to the total area of ​​the fracture surface.

[0053] When the porosity exceeds 30 area% of the total area of ​​the fracture surface, natural graphite fine powder may be mixed into the artificial graphite core, which may cause an excessive increase in the specific surface area. In addition, when natural graphite fine powder is mixed in this way, the span of the particles in the negative electrode precursor may widen, which may cause particle collapse. At this time, the span may be derived by the following equation, and in the equation below, D90, D50, and D10 represent particle sizes corresponding to 90%, 50%, and 10% of the volume accumulation of the particle size distribution, respectively. Since electrode life characteristics may be deteriorated when particles collapse, the negative electrode material of the present invention may have a porosity of 30 area% or less of the total area of ​​the fracture surface. More preferably, the porosity of the artificial graphite may be 25 area% or less of the total area of ​​the fracture surface, and even more preferably, it may be 20 area% or less. Since the porosity of the artificial graphite is better the smaller it is, the present invention does not specifically limit the lower limit of the porosity, but as an example, the porosity of the artificial graphite may be 10 area% or more.

[0054] Span = (D90-D10) / D50

[0055] The artificial graphite may be graphitized needle coke or pitch coke, high-temperature heat-treated waste coke, or a combination thereof. The waste coke may be coke used as a packing material in an Acheson graphitization furnace or a LWG (Lengthwise Graphitization) graphitization furnace.

[0056] In addition, the center particle size (D50) of the natural graphite fine powder included in the negative electrode precursor of the present invention may be 8 μm or less. Such natural graphite fine powder can contribute to forming a dense precursor structure by increasing the affinity between artificial graphite and the binder. In addition, since natural graphite has a relatively high affinity with the electrode current collector, it can improve the electrode adhesion with the current collector and perform an anchoring function within the precursor structure. Meanwhile, if the center particle size of the natural graphite fine powder becomes excessively small, the electrode processability may deteriorate. As an example, the center particle size (D50) of the natural graphite fine powder may be 3 μm or more.

[0057] As described above, the present invention can utilize waste coke used as a packing material as a cathode material, and natural graphite fines can be utilized as a cathode material, so it has the advantage of being environmentally friendly in that it can be recycled.

[0058] Meanwhile, a precursor for a negative electrode material of a lithium secondary battery according to another embodiment of the present invention may additionally include SiOx (0 ≤ x ≤ 2) of 5 wt% or less based on the total weight of the artificial graphite and the natural graphite powder.

[0059] That is, the present invention can increase the capacity of the electrode by introducing Si, which has a higher theoretical capacity than graphite-based active materials, in the form of an oxide at the precursor stage. However, when SiOx is added in excess of 5 wt%, problems such as particle cracking or loss of electrical contact may occur due to expansion of SiOx caused by continuous charge and discharge, thereby reducing the discharge capacity. Therefore, in a non-limiting embodiment of the present invention, the weight range of SiOx may be 5 wt% or less based on the total weight of the artificial graphite and the natural graphite.

[0060] Additionally, it is preferable that the SiOx is in contact with the artificial graphite. This is to suppress structural expansion resulting from SiOx expansion through the high-hardness artificial graphite.

[0061] Looking at Fig. 2, which is a schematic diagram of a precursor for a negative electrode material of a lithium secondary battery according to an embodiment of the present invention in which SiOx is inserted, it can be seen that SiOx (3) (0 ≤ x ≤ 2) is additionally bonded to the artificial graphite (2) in an island structure in which natural graphite fine powder (1) is distributed on the surface of the artificial graphite (2).

[0062] The precursor for the negative electrode material of the lithium secondary battery of the present invention has a specific surface area of ​​3 m as measured by the BET method. 2 / g or less. The specific surface area is 3m 2 If it exceeds / g, voids may be created inside the precursor, exposing some of the artificial graphite to the outside, causing the artificial graphite and the electrolyte to come into contact, which may result in a decrease in capacity.

[0063] As described above, the precursor for the negative electrode material of the lithium secondary battery according to the present invention can secure high capacity characteristics, excellent processability, and excellent life characteristics through a structure in which artificial graphite is used as an inner core and natural graphite fine powder is positioned on the surface thereof.

[0064] Hereinafter, the negative electrode material of the lithium secondary battery according to the present invention will be described in detail.

[0065] The negative electrode material of a lithium secondary battery manufactured by adding a binder to the above-described precursor for the negative electrode material and carbonizing it may include a core of artificial graphite and natural graphite fine powder distributed on the surface of the core, and may be characterized in that the artificial graphite and the natural graphite fine powder are bonded via amorphous carbon. In this case, the amorphous carbon may be formed by carbonizing the added binder.

[0066] Figure 3 is a schematic diagram of a cathode material according to one embodiment of the present invention. Through the schematic diagram, it can be confirmed that natural graphite powder (1) and artificial graphite (2) are bonded via amorphous carbon (4).

[0067] In addition, the negative electrode material of the lithium secondary battery according to the present invention may have a sphericity of 0.83 or higher. If the sphericity of the manufactured negative electrode material is less than 0.83, the specific surface area increases, which may lead to an increase in side reaction sites, thereby causing unnecessary side reactions. A more preferable lower limit is 0.85, and an even more preferable lower limit is 0.90.

[0068] Meanwhile, the negative electrode material of a lithium secondary battery according to another embodiment of the present invention may additionally include SiOx (0 ≤ x ≤ 2) of 5 wt% or less based on the total weight of the artificial graphite and the natural graphite powder, and it is preferable that the SiOx is in contact with the artificial graphite.

[0069] Since this is the same as the above-mentioned content regarding the precursor for the negative electrode material of a lithium secondary battery, it will be omitted.

[0070] Below, a method for manufacturing a precursor for a negative electrode material of a lithium secondary battery of the present invention is described.

[0071] A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery according to the present invention may include the steps of preparing artificial graphite and natural graphite powder; spheroidizing the artificial graphite using equipment utilizing high-speed centrifugal force at a linear speed of 55 m / s or more and 70 m / s or less for 3 to 7 minutes; mixing natural graphite powder into the artificial graphite to manufacture a mixture; and assembling and spheroidizing the mixture using equipment utilizing high-speed centrifugal force at a linear speed of 55 m / s or more and 70 m / s or less for 1 to 5 minutes.

[0072] In the step of manufacturing the above mixture, natural graphite fine powder may be mixed in an amount of 2 wt% or more and 7 wt% or less based on the total weight of the artificial graphite and the natural graphite fine powder, in order to manufacture a negative electrode precursor having an appropriate level of coverage value as described above.

[0073] Meanwhile, as described above, the method for manufacturing a precursor for a negative electrode material of a lithium secondary battery according to an embodiment of the present invention can spheroidize artificial graphite using equipment utilizing high-speed centrifugal force at a linear speed of 55 m / s or more and 70 m / s or less for a time of 3 minutes or more and 7 minutes or less. If the linear speed is less than 55 m / s or the duration is less than 3 minutes, the centrifugal force required for spheroidization may not be sufficient, which may cause a problem in that most of the artificial graphite particles cannot be secured in a spheroidized state. More preferably, the linear speed during spheroidization may be 60 m / s or more, and the duration may be 5 minutes or more.

[0074] On the other hand, if the linear velocity exceeds 70 m / s or the duration exceeds 7 minutes, the spheroidized artificial graphite particles may be pulverized, widening the span of the particle size distribution. In particular, as the content of finely divided artificial graphite increases, the capacity characteristics of the electrode may deteriorate. More preferably, the linear velocity during spheroidization may be 65 m / s or less, and even more preferably, 60 m / s or less, and even more preferably, the spheroidization duration may be 5 minutes or less.

[0075] After the above spheroidization step, the spheroidization degree of the artificial graphite may be 0.9 or more, and since this is the same as the above-described content of the negative electrode precursor of the present invention, it will be omitted.

[0076] Finally, the above spheroidization step and the above assembly spheroidization step can be performed using equipment utilizing horizontal or vertical centrifugal force, examples of which include Nara Machinery's NHS series or Hosokawa Micron's Mechanofusion or Faculty.

[0077] Meanwhile, according to a method for manufacturing a precursor for a negative electrode material of a lithium secondary battery according to another embodiment of the present invention, in the step of manufacturing a mixture by mixing natural graphite powder into spherical artificial graphite, 5 wt% or less of SiOx (0 ≤ x ≤ 2) can be additionally mixed together with respect to the total weight of the artificial graphite and the natural graphite powder.

[0078] This is because, as described above, by including SiOx at 5 wt% or less, the capacity of the electrode can be increased while suppressing expansion of Si particles resulting from continuous charge and discharge.

[0079] According to an example of the present invention, a method for manufacturing an anode material for a lithium secondary battery can be manufactured by adding a binder to the above-described anode material precursor and carbonizing the same at 800°C or higher. The present invention not only evaporates volatile components existing within the precursor by carbonizing the anode material precursor at 800°C or higher, but also solidifies the binder to secure the internal structure of the desired anode material.

[0080] At this time, the binder is not necessarily limited to this, but may be an amorphous carbon material, such as soft carbon or hard carbon.

[0081] Specifically, soft carbon binders may include coal tar, petroleum residues, and pitches derived from them, and hard carbon binders may include PVC, phenol resin, and PET.

[0082] Hereinafter, a method for manufacturing a negative electrode of a lithium secondary battery of the present invention will be described in detail.

[0083] The above negative electrode can be manufactured by mixing a negative electrode material manufactured according to one embodiment of the present invention, a binder, and optionally a conductive material to manufacture a composition for forming a negative electrode active material layer, and then applying the composition to a negative electrode current collector.

[0084] The negative electrode current collector may be, for example, copper foil, nickel foil, stainless steel, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0085] Examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene. The binder may be mixed in an amount of 1 wt% to 30 wt% based on the total amount of the composition for forming the negative electrode active material layer.

[0086] The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and specifically, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or summer black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. The conductive material can be mixed in an amount of 0.1 wt% to 30 wt% based on the total amount of the composition for forming the negative electrode active material layer.

[0087] (Example)

[0088] (Example 1)

[0089] (1) Manufacturing of cathode material

[0090] First, natural graphite fine powder and artificial graphite, which is packing waste coke graphitized in an Acheson graphitization furnace, were prepared. Thereafter, the natural graphite and the artificial graphite were pulverized using an ACM (Air Classifier Mill). After pulverization, the center particle size (D50) of the artificial graphite was 10 μm, and the span ((D90-D10) / D50) value was 1.29. In addition, the center particle size (D50) of the natural graphite fine powder manufactured after pulverization was 5 μm, and the D100 was 9 μm. After the pulverization, the artificial graphite was spheroidized at a linear speed of 60 m / s for 5 minutes using a Nara kikai-Hybridizer facility, and the spheroidization degree of the artificial graphite was measured, respectively, and is shown in Table 1. Next, spheroidized artificial graphite and natural graphite fines were added at 95 wt% and 5 wt%, respectively, based on the total graphite weight, to prepare a mixture. The resulting mixture was then granulated and spheroidized for 3 minutes at a linear speed of 60 m / s using a Nara kikai-Hybridizer facility. The coverage values ​​of the cathode precursors produced through this process were calculated and are shown in Table 1.

[0091] The coverage value, which is the ratio of the surface area of ​​natural graphite in contact with the artificial graphite to the total surface area of ​​the artificial graphite, was measured using a Jeol SEM (Scanning Electron Microscope). At this time, after obtaining an SEM image of the negative electrode precursor at a magnification of 3000x using the equipment, the ratio of the surface area of ​​natural graphite in contact with the artificial graphite to the total surface area of ​​the artificial graphite was measured from the image. This operation was repeated 50 times, and the average value of the measured values ​​was calculated, which was then used as the coverage value in [Equation 1].

[0092] Next, 3 wt% of pitch binder relative to the total weight of graphite was added to the above-mentioned negative electrode precursor. A Nara Kikai-Hybridizer was used to further mix the binder into the mixture. Mixing was performed at a linear speed of 60 m / s for 5 minutes. The precursor was then carbonized at 1200°C for 30 minutes to produce a negative electrode material for a lithium secondary battery.

[0093] During the process, a negative electrode material composed only of spherical artificial graphite is shown in Table 1 as a conventional example, and in the case of Comparative Examples 1 and 2 and Invention Examples 1 and 2, it was confirmed that a structure was formed in which natural graphite fine powder was distributed in the core of the artificial graphite.

[0094] (2) Physical properties evaluation

[0095] Afterwards, 97 wt% of the manufactured negative electrode material, 2 wt% of a binder including carboxymethyl cellulose and styrene butadiene rubber, and 1 wt% of a Super P conductive material, which is a carbon black conductive material, were mixed in a distilled water solvent to prepare a negative electrode active material slurry.

[0096] The above-mentioned negative active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and pressed using a roll press. Thereafter, it was vacuum-dried in a vacuum oven at 100°C for 12 hours. At this time, the time point at which the negative active material separated from the copper (Cu) current collector occurred was measured. The corresponding time point is shown in Table 1 as electrode adhesion (time). In addition, the adhesion (gf) between the manufactured negative active material and the copper (Cu) current collector was measured and is also shown in Table 1.

[0097] Sample graphite molding degree Coverage value Electrode adhesion (h) Adhesion (gf) Conventional example 10.88-3120 Comparative example 10.840.189540 Comparative example 20.890.2710770 Invention example 10.910.3212970 Invention example 20.930.38121020

[0098] As a result of the above experiment, invention examples 1 and 2 showed excellent electrode adhesion by forming an island structure in which natural graphite powder is distributed on the artificial graphite core and satisfying the range of coverage values ​​presented in the present invention.

[0099] On the other hand, the conventional example was a structure composed only of artificial graphite, and due to the absence of natural graphite fine powder that can improve electrode processability, it was not possible to secure the desired level of electrode adhesion.

[0100] In addition, Comparative Examples 1 and 2 formed an island structure in which natural graphite fine powder was distributed in an artificial graphite core, but since the degree of sphericity of the artificial graphite was less than 0.9, the number of side reaction sites between the artificial graphite and the electrolyte increased, resulting in an unnecessary chemical reaction, and as a result, the natural graphite fine powder could not sufficiently wrap the artificial graphite core, resulting in a decrease in electrode adhesion.

[0101] (Example 2)

[0102] (1) Manufacturing of cathode material

[0103] (Invention Example 1) Flaky natural graphite powder having the same particle size distribution as that of the synthetic graphite, which is waste coke packing material graphitized in an Acheson graphitizer, was prepared. The synthetic graphite was spheroidized using a Nara kikai-Hybridizer facility at the linear speed and spheroidization time shown in Table 2. Thereafter, the spheroidization degree of the synthetic graphite was measured and shown in Table 2. Next, the spheroidized synthetic graphite and natural graphite powder were added in the weight ranges shown in Table 2 based on the total graphite weight to prepare a mixture. When SiOx was added, SiOx was additionally added at the corresponding stage in the weight range shown in Table 2 based on the total graphite weight. Thereafter, the prepared mixture was granulated and spheroidized using a Nara kikai-Hybridizer facility at a linear speed of 60 m / s for 3 minutes. The porosity of the prepared negative electrode precursor was measured and shown in Table 2.

[0104] The porosity of the cathode precursor was measured using a surface area analyzer. Specifically, particles with a particle size between D40 and D60 were extracted, and their centers were cut using a Focused Ion Beam (FIB). The area fraction occupied by pores relative to the total area of ​​the crack fracture surface was then measured. This process was repeated 20 times, and the average values ​​were calculated and presented in Table 2.

[0105] Next, 3 wt% of pitch binder was added to the manufactured negative electrode precursor based on the total weight of graphite. A Nara kikai-Hybridizer facility was used to ensure good mixing of the negative electrode precursor and the binder. The mixing was performed at a linear speed of 60 m / s for 5 minutes. Thereafter, the precursor was carbonized at 1200°C for 30 minutes to manufacture a negative electrode material for a lithium secondary battery. The sphericity of the manufactured negative electrode material was measured and is shown in Table 2.

[0106] The sphericity of artificial graphite and cathode materials was analyzed using FlowCAM PV. Specifically, cathode powder was dispersed in ethanol, and optical images were obtained through an objective lens. The sphericity was measured using an algorithm built into the system.

[0107] (2) Manufacturing of cathode

[0108] A slurry of negative active material was prepared by mixing 97 wt% of the manufactured negative electrode material, 2 wt% of a binder including carboxymethyl cellulose and styrene butadiene rubber, and 1 wt% of a Super P conductive material in a distilled water solvent.

[0109] The above-mentioned negative active material slurry was applied to a copper (Cu) current collector, dried at 100°C for 10 minutes, and pressed using a roll press. Thereafter, the negative electrode was manufactured by vacuum drying in a 100°C vacuum oven for 12 hours. After vacuum drying, the electrode density of the negative electrode was set to 1.5 to 1.7 g / cc.

[0110] (3) Electrochemical evaluation

[0111] To evaluate electrochemical characteristics, a lithium secondary battery was manufactured. Specifically, a half coin cell of the 2032 coin cell type was manufactured using a negative electrode manufactured by the above method, a counter electrode of lithium metal (Li-metal), and an electrolyte solution containing 1 mol of LiPF6 solution dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:1, according to a conventional manufacturing method.

[0112] The third discharge capacity and initial efficiency of the above battery were measured and are shown in Table 2 below.

[0113] Classification Artificial graphite content (wt%) Natural graphite content (wt%) SiOx content (wt%) Spheroidization stage Artificial graphite spheroidization degree Porosity (area%) Negative electrode material spheroidization degree 3rd discharge capacity (mAh / g) Initial efficiency (%) Linear velocity (m / s) Spheroidization time (min) Invention example 397306050.92230.8934792 Comparative example 397305050.86350.7233787 Invention example 497307050.92280.8535193 Invention example 597356050.92190.83101588 Comparative example 497376050.92320.7595379 Comparative example 597308050.88330.7788477

[0114] In the case of Comparative Example 3, the linear velocity in the spheroidization stage of the artificial graphite was only 50 m / s, so the spheroidization of the artificial graphite was not properly achieved, and the porosity of the artificial graphite also exceeded 30 area%. As a result, Comparative Example 3 could not secure high-capacity characteristics.

[0115] Comparative Example 4 showed that the sphericity of the negative electrode material was less than 0.83, and the electrode exhibited a third discharge capacity of less than 1000 mAh and an initial efficiency of less than 85%, showing a deterioration in electrochemical characteristics.

[0116] In the case of Comparative Example 5, the linear velocity in the spheroidization stage of artificial graphite exceeded 70 m / s, and the electrochemical characteristics deteriorated.

[0117] On the other hand, since invention examples 3 to 5 satisfy both the structure and manufacturing method proposed by the present invention, the electrodes including the corresponding negative electrode materials exhibited high capacity characteristics, excellent processability, and excellent life characteristics.

[0118] In particular, through Invention Example 5, it was confirmed that when 5 wt% or less of SiOx is included in the negative electrode material, the capacity of the electrode can be increased without structural collapse.

Claims

1. Artificial graphite core and Contains natural graphite powder distributed on the surface of the above core, A precursor for a negative electrode material of a lithium secondary battery, wherein the sphericity of the artificial graphite above is 0.9 or higher.

2. In paragraph 1, A precursor for a negative electrode material of a lithium secondary battery, wherein the center particle size (D50) of the above natural graphite powder is 8 μm or less.

3. In paragraph 1, A precursor for a negative electrode material of a lithium secondary battery, wherein the natural graphite powder is included in an amount of 2% by weight or more and 7% by weight or less based on the total weight of the artificial graphite and the natural graphite powder.

4. In paragraph 1, A precursor for a negative electrode material of a lithium secondary battery, additionally comprising 5 wt% or less of SiOx (0≤x≤2) relative to the total weight of the artificial graphite and the natural graphite powder.

5. In paragraph 1, A precursor for a negative electrode material of a lithium secondary battery having a coverage value of 0.3 or more and 0.7 or less according to the following [Relationship Formula 1]. [Relationship 1] Coverage = 6. In paragraph 1, A precursor for a negative electrode material of a lithium secondary battery, wherein when the center of the particle of the precursor is cut, the porosity of the artificial graphite is 30% or less with respect to the total area of ​​the fracture surface.

7. In paragraph 1, Specific surface area is 3m 2 / g or less. Precursor for negative electrode material of lithium secondary battery.

8. Step for preparing artificial graphite and natural graphite powder; A step of spherizing the above artificial graphite using equipment utilizing high-speed centrifugal force; A step of preparing a mixture by mixing the natural graphite powder into the artificial graphite; and A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, comprising a step of assembling and spheroidizing the above mixture using equipment utilizing high-speed centrifugal force.

9. In paragraph 8, A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, wherein after the above assembling and spheroidizing steps, the spheroidization degree of the artificial graphite is 0.9 or more.

10. In paragraph 8, A method for producing a precursor for a negative electrode material of a lithium secondary battery, wherein in the step of producing the mixture, the natural graphite fine powder is mixed in an amount of 2% by weight or more and 7% by weight or less based on the total weight of the artificial graphite and the natural graphite fine powder.

11. In paragraph 8, A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, wherein, in the step of manufacturing the mixture, 5 wt% or less of SiOx (0≤x≤2) is additionally mixed with respect to the total weight of the artificial graphite and the natural graphite powder.

12. In paragraph 8, A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, wherein the above-mentioned spheroidizing step and the above-mentioned assembling and spheroidizing step are performed using equipment utilizing horizontal or vertical centrifugal force.

13. In paragraph 8, A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, wherein the above spheroidizing step is performed at a linear speed of 55 m / s or more and 70 m / s or less for a time of 3 minutes or more and 7 minutes or less.

14. In paragraph 8, A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, wherein the above-mentioned assembling and spheroidizing step is performed at a linear speed of 55 m / s or more and 70 m / s or less for a time of 1 minute or more and 5 minutes or less.

15. A step of manufacturing a precursor for a negative electrode material of a lithium secondary battery according to at least one of claims 8 to 14; A step of adding a binder to the above precursor; and A method for manufacturing a negative electrode material for a lithium secondary battery, comprising a step of carbonizing the precursor to which a binder is added at 800°C or higher.

16. Artificial graphite core and Contains natural graphite powder distributed on the surface of the core, The above artificial graphite and the above natural graphite powder are combined through amorphous carbon, A negative electrode material for a lithium secondary battery with a sphericity of 0.83 or higher.

17. In paragraph 16, A negative electrode material for a lithium secondary battery, wherein the sphericity of the artificial graphite above is 0.9 or higher.

18. In paragraph 16, A negative electrode material for a lithium secondary battery, further comprising SiOx (0≤x≤2) in an amount of 5 wt% or less relative to the total weight of the artificial graphite and the natural graphite powder.

19. In paragraph 16, A negative electrode material for a lithium secondary battery having a coverage value of 0.3 or more and 0.7 or less according to the following [Relationship Formula 1]. [Relationship 1] Coverage =

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