Method for manufacturing negative electrode active material for lithium secondary battery, negative electrode active material for lithium secondary battery manufactured by this method, and lithium secondary battery including this negative electrode active material

Abstract

The present invention relates to a method for producing a negative electrode active material for a lithium secondary battery, a negative electrode active material for a lithium secondary battery produced by the method, and a lithium secondary battery including the same. The method for producing a negative electrode active material for a lithium secondary battery includes a step of coating a negative electrode active material precursor containing Si with crude tar or soft pitch, and a step of heat-treating the resulting coating product. The crude tar contains 20% by weight or less of low-molecular-weight components that can be removed by a distillation process.

Description

Technical Field

[0001] Provided are a method for manufacturing a negative electrode active material for a lithium secondary battery, a negative electrode active material for a lithium secondary battery manufactured by this method, and a lithium secondary battery including this negative electrode active material.

Background Art

[0002] Lithium ion secondary batteries (LIBs) have attracted great attention as next-generation energy storage devices in the context of environmental issues becoming a global concern. Compared with typical secondary battery systems such as nickel-cadmium batteries and nickel-metal hydride batteries, lithium ion secondary batteries have high operating voltages, high energy densities, and excellent characteristics in terms of the memory effect, and are widely applied in various fields. With the increasing demand for high-energy-density lithium secondary batteries such as Ni-Cd batteries and nickel-metal hydride batteries, the use of silicon-based or silicon oxide-based materials having an effective capacity more than 10 times that of carbon-based materials as negative electrode active materials has been increasing.

[0003] Lithium ion secondary batteries are composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the performance of the battery is closely related to all of the characteristics of the components. Among them, the negative electrode active material constituting the negative electrode has been a carbon material such as hard carbon / soft carbon or graphite-based material for nearly 30 years since the development of lithium ion secondary batteries in 1991. Currently, most commercial batteries mainly use graphite materials, and battery manufacturers apply various combinations of graphite compositions.

[0004] Currently, the graphite material most commonly used as the negative electrode active material for lithium-ion secondary batteries has advantages in terms of low working voltage, stable life characteristics, efficiency, price, and environmental friendliness, but it has the disadvantage that its theoretical capacity is limited to a maximum of 372 mAh / g. Due to such limitations in theoretical capacity, it is difficult to ensure the driving range of electric vehicles, and there is also the problem that it is difficult to apply to various application fields.

[0005] Therefore, next-generation materials considered to overcome the capacity of graphite include oxides of various elements and Group 4 elements represented by Si. Among these, Si is the most actively studied as a candidate for high-capacity active materials from the viewpoints of price and versatility.

[0006] Theoretically, silicon-based anode active materials have a capacity more than 10 times higher than that of commercialized graphite-based anode active materials. However, when the silicon-based anode active material is charged, the volume change reaches 400%. Due to the stress (strain) generated during discharge, there are problems of battery performance degradation caused by short circuits with the current collector and the collapse of the electrode itself, so there is a problem that it is difficult to commercialize. That is, in the silicon-based anode active material, the Si crystal structure changes electrochemically and repeatedly during charge and discharge. As a result, the expansion / contraction of the active material repeats, and due to the collapse and deformation of the active material particles caused by this, the conductive network is lost, and the local inactivity in the electrode expands, while the irreversible capacity and cycle characteristics deteriorate. Also, considering the formation of SEI, defects (fractures) or cracks occur on the SEI surface formed due to the contraction / expansion of the electrode. The occurrence of defects and cracks exposes a new surface, and the occurrence of defects and cracks is accelerated by charging and discharging, so that a new surface continues to be exposed, and the specific surface area further increases. The newly exposed surface comes into contact with the electrolyte again, and due to the repeated phenomenon of the formation and growth of a new SEI, the battery characteristics deteriorate significantly through an increase in the diffusion path of lithium ions, an increase in electrolyte consumption, a decrease in conductivity, a deterioration of the Coulomb efficiency, a consumption of the lithium source, and an increase in resistance. Eventually, the battery cannot be used.

[0007] Such problems also occur when using a composite active material of Si and carbon. Therefore, solutions for suppressing expansion and the continuous formation of SEI have been studied. As methods, basically, a method of minimizing the specific surface area in a high-pressure forming process and a method of forming an additional coating layer externally to suppress mechanical expansion and control the specific surface area have been proposed. That is, a method of structurally densifying and a method of introducing a mechanical auxiliary structure have been proposed.

[0008] Kim of KETI (ACS applied Materials and Interfaces 2016, 8, 2109 - 12117) has presented a scheme to form a pitch coating layer on the surface of the active material. By forming the pitch coating, the electrical conductivity of the entire active material is improved and it acts as an electron transfer network. The micropores present in the pitch-based carbon facilitate the diffusion of Li + ions and describe the advantage of improving the structural stability due to the elastic properties of the pitch-based carbon coating. Also, CNRS in France (RSC Adv., 2019, 9, 10546 - 10553) emphasizes introducing pitch as a carbon source (resource) for Si-carbon composite active materials, highlighting the low cost of pitch.

[0009] However, in the negative electrode active material market, competition over price has been heating up as time goes by, and there is a need to minimize the unit price in the dimension of the active material.

Summary of the Invention

Problems to be Solved by the Invention

[0010] One embodiment aims to provide a method for manufacturing a negative electrode active material for a lithium secondary battery with a relatively small specific surface area economically.

[0011] Another embodiment aims to provide a negative electrode active material for a lithium secondary battery manufactured by the above manufacturing method.

[0012] Still another embodiment aims to provide a lithium secondary battery including the negative electrode active material manufactured by the above method.

Means for Solving the Problems

[0013] According to one embodiment, there is provided a method for manufacturing a negative electrode active material for a lithium secondary battery, including the steps of coating a negative electrode active material precursor containing Si with crude tar or soft pitch; and heat-treating the obtained coated product, wherein the crude tar contains a low molecular weight component that can be removed in a distillation process at a content of 20% by weight or less.

[0014] The low molecular weight component may have a weight average molecular weight (Mw) of 78 to 128.

[0015] The step of coating with the crude tar or the soft pitch may be carried out by adding the crude tar or the soft pitch to a solvent to produce a coating solution having a concentration of 50% to 70% by weight. The solvent may be N-methylpyrrolidone, dimethylformaldehyde, dimethyl sulfoxide, tetrahydrofuran, acetone, or a combination thereof.

[0016] The step of coating with the crude tar or the soft pitch may be carried out by mixing the negative electrode active material precursor with the crude tar or the soft pitch and performing this mixture at a speed of 50 rpm to 100 rpm for 10 minutes to 60 minutes.

[0017] In one embodiment, the heat treatment step can be carried out at 800°C to 950°C for 0.5 hours to 2 hours. In another embodiment, the heat treatment step can be carried out by heating at a heating rate of 2°C / min to 10°C / min to a final temperature of 950°C or less. In yet another embodiment, after a first heating to 300°C to 400°C at a heating rate of 2°C / min to 10°C / min, maintaining at this temperature for 0.5 hours to 2 hours, and then performing a second heating at a heating rate of 2°C / min to 10°C / min to a final temperature of 950°C or less.

[0018] The weight ratio of the negative electrode active material precursor to the crude tar or the soft pitch may be 2% to 20% by weight based on 100% by weight of the negative electrode active material precursor.

[0019] The negative electrode active material precursor containing Si may be Si, an Si-C composite, a silicon oxide, or a combination thereof.

[0020] Another embodiment provides a negative electrode active material for a lithium secondary battery, which includes a core containing Si manufactured by the above method, and amorphous carbon located on the surface of the core, and has a specific surface area of 1 m 2 / g to 6 m 2 / g.

[0021] In one embodiment, the amorphous carbon can exist in a layer-type that continuously covers the surface of the core. In another embodiment, the amorphous carbon can also exist in an island-type that is discontinuously located on the surface of the core.

[0022] The amorphous carbon can be soft carbon.

[0023] According to still another embodiment, there is provided a negative electrode including the negative electrode active material, a positive electrode including a positive electrode active material, and a lithium secondary battery including a non-aqueous electrolyte.

Advantages of the Invention

[0024] The method for manufacturing a negative electrode active material for a lithium secondary battery according to one embodiment can produce an active material with a small specific surface area through an economical process.

Brief Description of the Drawings

[0025]

Figure 1

Modes for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby. The present invention is defined only by the scope of the claims described below.

[0027] A method for manufacturing a negative electrode active material for a lithium secondary battery according to an embodiment includes a step of coating a negative electrode active material precursor containing Si with crude tar or soft pitch, and a step of heat-treating the obtained coated product. The crude tar may contain 20% by weight or less of low molecular weight components that can be removed in a distillation process.

[0028] Hereinafter, each step will be described in detail.

[0029] First, a negative electrode active material precursor containing Si is coated with crude tar or soft pitch.

[0030] The crude tar means the coal tar in the state obtained in the pig iron making process of the iron making process, and as described above, it means tar having a low molecular weight component content of 20% by weight or less.

[0031] The low molecular weight component is a component that can be recovered by a distillation process and has a weight average molecular weight (Mw) of 78 to 128. The content of the low molecular weight component is 20% by weight or less, and may be 15% to 20% by weight.

[0032] The low molecular weight component may include naphthalene, low boiling point components having a boiling point lower than the boiling point of naphthalene, and high boiling point components having a boiling point higher than the boiling point of naphthalene.

[0033] The low boiling point components having a boiling point lower than that of naphthalene may be, for example, pyridine, trimethylbenzene, cresol, or a combination thereof, and may further include other components having a low boiling point. The content of the low boiling point component may be 13% to 16% by weight.

[0034] The higher-boiling components than naphthalene can be, for example, 9H-fluorene, isoquinoline, methylnaphthalene, 2-methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, or a combination thereof, and can further contain other components having a high boiling point. The content of the higher-boiling components can be 2% to 7% by weight.

[0035] In particular, the crude tar, different from the commonly used tar, among the higher-boiling components, contains methylnaphthalene, 2-methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, or a combination thereof in a content of 1.5% to 3% by weight.

[0036] The crude tar according to one embodiment can further contain pitch in the remaining content. That is, the crude tar contains low molecular weight components and soft pitch, and generally, if the low molecular weight components are distilled off, this is called soft pitch. Therefore, the soft pitch used in the coating step means the components remaining after distilling off the low molecular weight components from the crude tar.

[0037] The Si-containing negative electrode active material precursor generally means an Si-based material used as a negative electrode active material for a lithium secondary battery, and examples thereof can be Si, an Si-C composite, an Si oxide, or a combination thereof. At this time, the Si oxide can be SiO x (where 0 < x < 2). The Si-C composite can contain silicon particles and crystalline carbon, and can also contain silicon particles, amorphous carbon, and crystalline carbon.

[0038] Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke. Examples of the crystalline carbon include natural graphite, artificial graphite, or a combination thereof.

[0039] In one embodiment, as the negative electrode active material precursor containing Si, an Si-C composite can be appropriately used, and an Si-C composite containing silicon particles, amorphous carbon, and crystalline carbon can be used to SiO x It can be more appropriately used for reasons of higher initial efficiency and high design capacity. At this time, based on 100% by weight of the negative electrode active material precursor, silicon can be 30% to 50% by weight, amorphous carbon can be 20% to 35% by weight, and crystalline carbon can be 20% to 35% by weight. The Si-C composite containing silicon particles, amorphous carbon, and crystalline carbon can be formed by mixing Si and crystalline carbon, adding an amorphous carbon precursor to this mixture, shaping it, and then carbonizing the obtained shaped body. Examples of the amorphous carbon precursor include coal-based pitch, coal-based binder pitch, petroleum-based pitch, mesophase pitch, tar, low-molecular-weight heavy oil, furan resin, and the like. Further, the shaping step can be carried out by applying a pressure of 100 ton / cm 2 to 300 ton / cm 2 and the carbonization step can be carried out by heat treatment at 800°C to 950°C.

[0040] In the step of coating with the crude tar or the soft pitch, the weight ratio of the negative electrode active material precursor to the crude tar or the soft pitch can be 2% to 20% based on 100% by weight of the negative electrode active material precursor. When the amount of the crude tar or the soft pitch used is within the above range, the specific surface area of the produced negative electrode active material can be significantly reduced to suppress the formation of SEI, and thus it may be advantageous for improving the life characteristics.

[0041] In the step of coating with the crude tar or the soft pitch, the crude tar can be used in a solid phase or a liquid phase. That is, the coating step can be carried out by adding the crude tar or the soft pitch to a solvent and using a coating solution with a concentration of 50 wt% to 70 wt% in a liquid phase method. When the crude tar or the soft pitch is added to the solvent in this way, the viscosity of the crude tar or the soft pitch can be controlled, so that the coating process can be carried out more easily. In one embodiment, the coating solution concentration can be 50 wt% to 70 wt%. When the concentration of the coating solution is within the above range, it has a sufficient specific surface area reduction effect. However, at lower concentrations, due to the effect of the volatilized solvent, the improvement of the specific surface area may not be sufficiently achieved.

[0042] The solvent can be N-methylpyrrolidone, dimethylformaldehyde, dimethyl sulfoxide, tetrahydrofuran, acetone or a combination thereof.

[0043] In the step of coating with the crude tar or the soft pitch, the negative electrode active material precursor and the crude tar or the soft pitch can be mixed, and this mixture can be carried out at a speed of 50 rpm to 100 rpm for 10 minutes to 60 minutes. Also, the mixing step can be carried out for 20 minutes to 40 minutes. When the mixing step is carried out at the above speed, it can have the advantage of improving the specific surface area due to the formation of a sufficient coating layer. When it is carried out during the above time, the specific surface area has a tendency to gradually decrease due to the change in time. When outside the mixing speed and time range, a sufficient reduction effect of the specific surface area cannot be achieved, and rather, there may be a reverse result of increase.

[0044] Also, before the mixing step, a pre-mixing step can be further carried out.

[0045] Next, the obtained coating product is heat-treated. The heat treatment step can be carried out at 800°C to 950°C for 0.5 hours to 2 hours. In another embodiment, the heat treatment step can also be carried out by heating at a heating rate of 2°C / min to 10°C / min to a final temperature of 950°C or less, for example, 800°C to 950°C. In yet another embodiment, the heat treatment step is first heated to 300°C to 400°C at a heating rate of 2°C / min to 10°C / min, maintained at this temperature for 0.5 hours to 2 hours, and then secondarily heated at a heating rate of 2°C / min to 10°C / min from the temperature after the first heating to a final temperature of 950°C or less, for example, 800°C to 950°C.

[0046] By the heat treatment step, crude tar or soft pitch can be converted into amorphous carbon and located on the core surface.

[0047] The negative electrode active material produced by such a process includes a core containing Si and amorphous carbon located on the surface of this core, and the BET specific surface area can be 1 m 2 / g to 6 m 2 / g. When the BET specific surface area of the negative electrode active material is within the above range, SEI formation on the surface can be suppressed, and as a result, the cycle life characteristics can be improved, which is appropriate.

[0048] The core can be Si, a Si-C composite, a silicon oxide, or a combination thereof. At this time, the silicon oxide can be SiO x (0 < x < 2). The Si-C composite can contain silicon particles and crystalline carbon, and can also contain silicon particles, amorphous carbon, and crystalline carbon.

[0049] The amorphous carbon located on the core surface can be soft carbon converted from crude tar or soft pitch.

[0050] The amorphous carbon can exist in a layer-type that continuously covers the core surface, or can also exist in an island-type that is discontinuously located on the core surface.

[0051] The content of the amorphous carbon can be 2% to 20% by weight based on 100% by weight of the negative electrode active material. When the content of the amorphous carbon is within the above range, sufficient capacity can be exhibited, and it can have the advantage of excellent cycle life characteristics. Since the soft carbon embodied in the above process has a very low capacity compared to Si and crystalline carbon contained in the core, it is appropriate to control the specific surface area using a small amount within the above range for performance improvement.

[0052] According to one embodiment, a lithium secondary battery including a negative electrode, a positive electrode, and an electrolyte is provided.

[0053] The negative electrode can include a current collector and a negative electrode active material layer formed on the current collector and including the negative electrode active material according to one embodiment.

[0054] In the negative electrode active material layer, the content of the negative electrode active material can be 80% to 98% by weight based on the total weight of the negative electrode active material layer.

[0055] The negative electrode active material layer includes a binder and can optionally further include a conductive agent. The content of the binder in the negative electrode active material layer can be 1% to 5% by weight based on the total weight of the negative electrode active material layer. When further including a conductive agent, 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive agent can be used.

[0056] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, or a combination thereof can be used.

[0057] Examples of the non-aqueous binder include ethylene-propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0058] Examples of the aqueous binder may include styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0059] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used can be 0.1 to 3 parts by weight with respect to 100 parts by weight of the negative electrode active material.

[0060] The conductive agent is used to impart conductivity to the electrode, and in the battery to be constructed, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive agent include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing a mixture thereof.

[0061] As the current collector, those selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0062] The negative electrode is formed by mixing a negative electrode active material, a binder, and optionally a conductive agent in a solvent to produce an active material composition, and applying this active material composition to a current collector. As the solvent, water can be used.

[0063] Since such a method for forming a negative electrode is well-known in the art, detailed description thereof is omitted in this specification.

[0064] The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector and containing a positive electrode active material.

[0065] The positive electrode active material can include a compound (lithiated insertion compound) capable of reversible insertion and desorption of lithium. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium can be used. As a more specific example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b D2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5); Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a E 1-b X b O 2-c D c (0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a E 2-b X b O 4-c D c(0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α ≤ 2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li aCoG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); Li a FePO4(0.90 ≤ a ≤ 1.8)

[0066] In the above chemical formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0067] Of course, those having a coating layer on the surface of this compound can also be used, or the compound and the compound having a coating layer can be mixed and used. This coating layer can contain at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers can be amorphous or crystalline. As the coating elements contained in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof can be used. The coating layer formation process can use any coating method as long as such an element is used for the compound and the physical properties of the positive electrode active material are not adversely affected (for example, spray coating, dipping method, etc.). Since this is well understood by those skilled in the art, detailed description thereof is omitted.

[0068] In the positive electrode, the content of the positive electrode active material can be 90% to 98% by weight based on the total weight of the positive electrode active material layer.

[0069] In one embodiment, the positive electrode active material layer can further contain a binder and a conductive agent. At this time, the contents of the binder and the conductive agent can be 1% to 5% by weight respectively based on the total weight of the positive electrode active material layer.

[0070] The binder plays a role in enabling the positive electrode active material particles to adhere well to each other and also enabling the positive electrode active material to adhere well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0071] The conductive agent is used to impart conductivity to the electrode, and in the battery being configured, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive agent include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber; metal-based substances such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0072] As the current collector, aluminum foil, nickel foil, or a combination thereof can be used, but is not limited thereto.

[0073] The positive electrode active material layer is formed by mixing a positive electrode active material, a binder, and a conductive agent in a solvent to produce an active material composition, and applying this active material composition to a current collector. Since such a method for forming the active material layer is well-known in the art, detailed description thereof is omitted herein. As the solvent, N-methylpyrrolidone, etc. can be used, but is not limited thereto.

[0074] The electrolyte contains a non-aqueous organic solvent and a lithium salt.

[0075] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0076] As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used.

[0077] As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolide, mevalonolactone, caprolactone, etc. can be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone-based solvent, cyclohexanone, etc. can be used. Also, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms and can contain a double bond, ring, or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane-based solvents, etc. can be used.

[0078] The non-aqueous organic solvent can be used alone or in combination of one or more. When used in combination of one or more, the mixing ratio can be appropriately adjusted according to the target battery performance, which can be widely understood by those skilled in the art.

[0079] In addition, in the case of the carbonate solvent, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed and used, the performance of the electrolytic solution can be excellent when they are mixed and used at a volume ratio of 1:1 to 1:9.

[0080] When the non-aqueous organic solvents are used in combination, a mixed solvent of cyclic carbonate and chain carbonate, a mixed solvent of cyclic carbonate and propionate solvent, or a mixed solvent of cyclic carbonate, chain carbonate and propionate solvent can be used. As the propionate solvent, methyl propionate, ethyl propionate, propyl propionate or a combination thereof can be used.

[0081] At this time, when the cyclic carbonate and the chain carbonate or the cyclic carbonate and the propionate solvent are used in combination, the performance of the electrolytic solution can be excellent when they are mixed and used at a volume ratio of 1:1 to 1:9. Also, when the cyclic carbonate, the chain carbonate and the propionate solvent are mixed and used, they can be mixed and used at a volume ratio of 1:1:1 to 3:3:4. Of course, the mixing ratio of the solvents can also be appropriately adjusted according to the desired physical properties.

[0082] The non-aqueous organic solvent can further contain an aromatic hydrocarbon organic solvent in the carbonate solvent. At this time, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed at a volume ratio of 1:1 to 30:1.

[0083] As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by the following Chemical Formula 1 can be used.

[0084]

Chem.

[0085] (In the above chemical formula 1, R1 to R6 are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group, and combinations thereof.)

[0086] Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and those selected from the group consisting of combinations thereof.)

[0087] The electrolyte may further contain vinylene carbonate or an ethylene carbonate compound of the following chemical formula 2 as a life improvement additive in order to improve the battery life.)

[0088]

Chem.

[0089] (In Chemical Formula 2, R7 and R8 are the same as or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, and at least one of R7 and R8 is selected from the group consisting of a halogen group, a cyano group (CN), a nitro group (NO2), and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R7 and R8 are not hydrogen at the same time.)

[0090] Typical examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When such a life-improving additive is further used, its usage amount can be appropriately adjusted.

[0091] The electrolyte can further contain vinyl ethylene carbonate, propane sultone, succinonitrile, or a combination thereof, and at this time, the usage amount can be appropriately adjusted.

[0092] The lithium salt is dissolved in an organic solvent and acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of such lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB), and includes one or more selected from the group as a supporting electrolyte salt. The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0093] Depending on the type of lithium secondary battery, a separator can also be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used. Of course, it is possible to use a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene.

[0094] Fig. 1 shows an exploded perspective view of a lithium secondary battery according to an embodiment of the present invention. The lithium secondary battery according to an embodiment will be described by taking a rectangular one as an example, but the present invention is not limited thereto and can be applied to batteries in various forms such as cylindrical and pouch types.

[0095] Referring to Fig. 1, a lithium secondary battery 100 according to an embodiment can include an electrode assembly 40 wound with a separator 30 interposed therebetween between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown).

Examples

[0096] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0097] (Comparative Example 1) Poly-Si was pulverized using a wet mill with isopropyl alcohol solvent so that D50 was 200 nm or less to produce an Si solution.

[0098] The produced Si solution and high-purity natural graphite with D50 of 3 μm or less were added and mixed, and a spray drying process was carried out to produce composite spheres having a size with D90 of 30 μm or less.

[0099] The produced composite spheres and a coal-based binder pitch with D50 of 3 μm or less were put into a mechano fusion equipment to produce a composite. At this time, the usage amounts of Si, pitch, and natural graphite were used so that in the produced composite, Si was 37.9 wt%, pitch was 35.2 wt%, and natural graphite was 26.9 wt%.

[0100] The produced composite was formed into a molded body using a pressure molding equipment at a pressure of 1.8 ton / cm 2 A carbonization process of heat-treating the produced molded body at 950 °C was carried out. In this carbonization process, internal low-molecular organic substances were removed, and the pitch was converted into soft carbon. The produced carbonized body was pulverized to a D50 level of about 15 μm using a jet mill and sieved. The classified product was used as a negative electrode active material. The BET specific surface area of this negative electrode active material was 12.2 m 2 / g.

[0101] (Example 1) The classified product produced in Comparative Example 1 was used as a negative electrode active material precursor.

[0102] 100% by weight of the negative electrode active material precursor and 20% by weight of crude tar were mixed, and this mixture was added and pre-mixed for 5 minutes using a planetary mixer, and then a coating process of mixing at 80 rpm for 30 minutes was carried out.

[0103] The crude tar used contains 20% by weight of low molecular weight components that can be removed in the distillation process. The low molecular weight components include pyridine, trimethylbenzene, cresol, naphthalene, methylnaphthalene, 2-methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, and 9H-fluorene. Among them, those in which the total of methylnaphthalene, 2-methylnaphthalene, dimethylnaphthalene, and trimethylnaphthalene is 1.74% by weight were used.

[0104] The obtained coating product was heated to 950 °C at a heating rate of 10 °C / min, and then heat treatment was carried out at 950 °C for 1 hour to produce a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in a layered manner on the surface of this core. At this time, the content of amorphous carbon was 10% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the produced negative electrode active material was 2.69 m 2 / g.

[0105] (Example 2) The crude tar used in Example 1 was added to an N-methylpyrrolidone solvent to produce a crude tar solution with a concentration of 89% by weight.

[0106] Based on 100% by weight of the negative electrode active material precursor produced in Example 1, so that the crude tar was 10% by weight, the negative electrode active material precursor and the crude tar solution were pre-mixed for 5 minutes using a planetary mixer, and then a coating process of mixing at 80 rpm for 30 minutes was carried out.

[0107] The obtained coating product was heated to 950°C at a heating rate of 10°C / min, and then heat-treated at 950°C for 1 hour to produce a negative electrode active material including a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and soft carbon amorphous carbon located in layers on the surface of this core. At this time, the ratio of amorphous carbon derived from crude tar was 1.8% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 4.64 m 2 / g.

[0108] (Example 3) The negative electrode active material precursor 100% by weight and 20% by weight of crude tar were mixed, and after adding this mixture and performing preliminary mixing for 5 minutes using a planetary mixer, a coating step of mixing at 80 rpm for 60 minutes was performed. Except for this, it was carried out in the same manner as in Example 1 to produce a negative electrode active material including a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and soft carbon amorphous carbon located in layers on the surface of this core. At this time, the content of amorphous carbon was 2.2% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 2.91 m 2 / g.

[0109] (Example 4) Using a planetary mixer, preliminary mixing was performed for 5 minutes on the negative electrode active material precursor and the crude tar liquid so that the crude tar was 20% by weight with respect to 100% by weight of the negative electrode active material precursor produced in Example 1. After that, except for performing a coating step of mixing at 80 rpm for 60 minutes, it was carried out in the same manner as in Example 2 to produce a negative electrode active material including a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and soft carbon amorphous carbon located in layers on the surface of this core. At this time, the content of amorphous carbon was 2.2% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 3.12 m 2 / g.

[0110] (Example 5) 100% by weight of the negative electrode active material precursor and 20% by weight of crude tar were mixed, and after adding this mixture and performing preliminary mixing for 5 minutes using a planetary mixer, a coating step of mixing at 120 rpm for 60 minutes was carried out, except for this, the same procedure as in Example 1 was carried out to produce a core containing Si, soft carbon and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in a layer on the surface of this core. At this time, the content of amorphous carbon was 2.2% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 3.48 m 2 / g.

[0111] (Example 6) The crude tar used in Example 1 was added to an N-methylpyrrolidone solvent to produce a crude tar solution with a concentration of 12.5% by weight.

[0112] Using a planetary mixer, the negative electrode active material precursor and the crude tar solution were preliminarily mixed for 5 minutes so that the crude tar was 10% by weight based on 100% by weight of the negative electrode active material precursor produced in Example 1, and then a coating step of mixing at 80 rpm for 30 minutes was carried out.

[0113] After heating the obtained coating product to 950 °C at a heating rate of 10 °C / min, a heat treatment of maintaining at 950 °C for 1 hour was carried out to produce a core containing Si, soft carbon and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in a layer on the surface of this core. At this time, the content of amorphous carbon was 4.4% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 5.72 m 2 / g.

[0114] (Example 7) After performing pre-mixing for 5 minutes, a coating process of mixing at 80 rpm for 60 minutes was carried out. Except for this, it was carried out in the same manner as in Example 6 to produce a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in layers on the surface of this core. At this time, the content of amorphous carbon was 4.4% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 5.38 m 2 / g.

[0115] (Example 8) After performing pre-mixing for 5 minutes, a coating process of mixing at 80 rpm for 90 minutes was carried out. Except for this, it was carried out in the same manner as in Example 6 to produce a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in layers on the surface of this core. At this time, the content of amorphous carbon was 4.4% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 5.45 m 2 / g.

[0116] (Example 9) After performing pre-mixing for 5 minutes, a coating process of mixing at 80 rpm for 120 minutes was carried out. Except for this, it was carried out in the same manner as in Example 6 to produce a core containing Si, soft carbon, and graphite in a weight ratio of 37.9:35.2:26.9, and a negative electrode active material containing soft carbon amorphous carbon located in layers on the surface of this core. At this time, the content of amorphous carbon was 4.4% by weight based on 100% by weight of the entire negative electrode active material. The BET specific surface area of the negative electrode active material was 4.95 m 2 / g.

[0117] *Particle size distribution measurement The Comparative Example 1 and the Example 1For the negative electrode active materials of ~5, the particle sizes D1, D10, D50, and D90 were measured with a particle size analyzer (product name: Cilas1090, manufacturer: Cilas), and the results are shown in Table 1 below. At this time, D1 means the diameter of the particles with a cumulative volume of 1% in the particle size distribution, D10 means the diameter of the particles with a cumulative volume of 10% in the particle size distribution, D50 means the diameter of the particles with a cumulative volume of 50% in the particle size distribution, and D90 means the diameter of the particles with a cumulative volume of 90% in the particle size distribution.

[0118] Also, the Span value was calculated from the measured D90, D10, and D50 values according to Equation 1 below, and the results are shown in Table 1 below. [Equation 1] Span = (D90 - D10) / D50

[0119] The particle sizes D1, D10, D50, and D90 of the negative electrode active materials of Comparative Example 2 and Examples 6 - 9 were measured with a particle size analyzer (product name: Cilas1090, manufacturer: Cilas), and the results are shown in Table 2 below.

[0120] Also, the Span value was calculated, and the results are shown in Table 2 below.

[0121] *BET measurement After degassing the negative electrode active materials produced in Comparative Example 1 and Examples 1 - 5 at 300°C for 3 hours, the BET specific surface area was measured by the nitrogen gas adsorption BET method using a 3Flex device from Micromeritics, and the results are shown in Table 1 below. When the BET value for the active material of Comparative Example 1 was set to 100%, the ratio of the BET values for the active materials of Examples 1 - 5 was calculated in %, that is, the BET of the active material in the example / BET of the active material in Comparative Example 1, and the results are shown in Table 1 below as the BET conversion rate.

[0122] Also, the BET specific surface areas of the negative electrode active materials produced in Comparative Example 2 and Examples 6 - 9 were measured, and the results are shown in Table 2 below. When the BET value for the active material of Comparative Example 1 was set to 100%, the examples 6 ~ 9The BET value ratio to the active material is obtained in %, that is, the BET of the active material in the example / the BET of the active material in Comparative Example 1, and the results are shown in the following table 2 as shown below.

[0123] *Tap density measurement The said Comparative Example 1 and the tap density of the negative electrode active materials of the said Examples 6 to 9 were measured by the ISO3953 method, and the results are shown in the following table 2 as shown below.

[0124]

Table 1

[0125]

Table 2

[0126] As shown in Table 1 above, the span values of Examples 1 to 5 coated with crude tar are smaller than those of Comparative Example 1 without coating, and a significant improvement in BET can be seen, indicating that the particle size of the active material particles is uniformly controlled. In particular, the span values and BET conversion rates of Examples 1, 3 and 5 coated with tar by dry coating are smaller than those of Examples 2 and 4 coated with tar by wet coating, indicating that the effect is more excellent.

[0127] Also, in Examples 1 3 and 5 carried out by dry coating, it can be seen that the BET value of Example 1 in which the mixed coating process was carried out for 30 minutes is shown to be the smallest.

[0128] Also, as shown in the said table 1 it can be seen that the span values of Examples 1 to 5 coated with crude tar are smaller than those of Comparative Example 1 without coating, and the BET has decreased.

[0129] Note that, as shown in Table 2 above, since the span values of the active materials in Examples 6 to 9 are smaller than those in Comparative Example 2, it can be seen that a uniform active material was produced. As a result, when a negative electrode is manufactured using this active material, it is possible to improve the packing density, and thus it can be predicted that a higher-capacity negative electrode can be manufactured. However, the table with the crude tar input increased to 20% 1 of the examples 3 ~ 5 The results show that, compared with the 10% crude tar input presented in Table 2 , the improvement in the BET value is insufficient and the particle size uniformity is somewhat inferior. This is presumably the result obtained by the residual soft carbon derived from the crude tar input.

[0130] The present invention is not limited to the above-described examples, and can be manufactured in various different forms. Those having ordinary knowledge in the technical field to which the present invention pertains should be able to understand that it can be implemented in other specific forms without changing the technical idea and essential features of the present invention. Therefore, it must be understood that the examples described above are illustrative in all respects and not restrictive.

Claims

1. Coating a negative electrode active material precursor containing Si with solid-phase or liquid-phase crude tar; and A method for producing a negative electrode active material for a lithium secondary battery, comprising the step of heat-treating the obtained coated product, wherein the crude tar contains 20% by weight or less of low molecular weight components that can be removed in a distillation process, and the crude tar contains 1.5% to 3% by weight of methylnaphthalene, 2-methylnaphthalene, dimethylnaphthalene, trimethylnaphthalene, or a combination thereof among the high-boiling components. A method for producing a negative electrode active material for a lithium secondary battery.

2. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the low molecular weight component has a weight average molecular weight (Mw) of 78 to 128.

3. The method for producing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the step of coating with the crude tar is carried out with a coating liquid having a concentration of 50% to 70% by weight by adding the crude tar to a solvent.

4. The method for producing a negative electrode active material for a lithium secondary battery according to claim 3, wherein the solvent is N-methylpyrrolidone, dimethylformaldehyde, dimethyl sulfoxide, tetrahydrofuran, acetone, or a combination thereof.

5. Coating a negative electrode active material precursor containing Si with solid-phase or liquid-phase crude tar or solid-phase or liquid-phase soft pitch obtained by distilling and removing low molecular weight components from the crude tar; and A method for producing a negative electrode active material for a lithium secondary battery, comprising the step of heat-treating the obtained coated product, wherein the crude tar contains 20% by weight or less of low molecular weight components that can be removed in a distillation process, and the step of coating with the crude tar or the soft pitch is carried out by mixing the negative electrode active material precursor with the crude tar or the soft pitch and performing this mixture at a speed of 50 rpm to 100 rpm for 10 minutes to 60 minutes. A method for producing a negative electrode active material for a lithium secondary battery.

6. Coating a negative electrode active material precursor containing Si with solid-phase or liquid-phase crude tar or solid-phase or liquid-phase soft pitch obtained by distilling and removing low molecular weight components from the crude tar; and A method for producing a negative electrode active material for a lithium secondary battery, comprising the step of heat-treating the obtained coated product, wherein the crude tar contains 20% by weight or less of low molecular weight components that can be removed in a distillation process, The method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the heat treatment step is carried out at 800 ° C to 950 ° C for 0.5 hour to 2 hours.

7. The method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the heat treatment step is carried out by heating at a heating rate of 2 ° C / min to 10 ° C / min to a final temperature of 950 ° C or lower.

8. Coating a negative electrode active material precursor containing Si with a solid-phase or liquid-phase crude tar or a solid-phase or liquid-phase soft pitch obtained by distilling and removing low-molecular-weight components with the crude tar; and A method for manufacturing a negative electrode active material for a lithium secondary battery, comprising a step of heat-treating the obtained coated product, wherein the crude tar contains low-molecular-weight components that can be removed in a distillation step in a content of 20% by weight or less, The method for manufacturing a negative electrode active material for a lithium secondary battery, wherein the heat treatment step is carried out by first heating to 300 ° C to 400 ° C at a heating rate of 2 ° C / min to 10 ° C / min, maintaining at this temperature for 0.5 hour to 2 hours, and then secondarily heating at a heating rate of 2 ° C / min to 10 ° C / min to a final temperature of 950 ° C or lower.

9. The method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the weight ratio of the negative electrode active material precursor to the crude tar is 2% by weight to 20% by weight based on 100% by weight of the negative electrode active material precursor.

10. The method for manufacturing a negative electrode active material for a lithium secondary battery according to claim 1, wherein the negative electrode active material precursor containing Si is Si, an Si—C composite, a silicon oxide, or a combination thereof.

Images