Precursor for negative electrode material of lithium secondary battery 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; and a method for manufacturing same, wherein by controlling the molding density of a negative electrode material precursor of a lithium secondary battery, high capacity characteristics and excellent lifespan characteristics of a negative electrode material can be ensured.

Description

Precursor for negative electrode material of lithium secondary battery and method for manufacturing the same

[0001] The present invention relates to a precursor for an anode material of a lithium secondary battery and a cathode material manufactured therefrom.

[0002] Lithium secondary batteries typically consist of a positive electrode containing a positive electrode material, a negative electrode containing an anode 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]

[0004] Metal oxides such as LiCoO2, LiMnO2, LiMn2O4 or LiCrO2 are used as cathode materials constituting the cathode 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 anode materials constituting the anode.

[0005]

[0006] Various types of carbon-based anode materials are used, including crystalline carbon-based materials such as natural graphite and artificial graphite, and amorphous carbon-based materials such as hard carbon and soft carbon. Among these, graphite-based anode materials, which have excellent reversibility and are advantageous for the lifespan characteristics of lithium secondary batteries, are the most widely used.

[0007]

[0008] However, graphite-based anode materials have relatively low theoretical capacity values ​​(e.g., approximately 372 mAh / g for LiC6 anodes), which is still somewhat insufficient to satisfy the electrochemical characteristics required in the relevant market.

[0009]

[0010] Therefore, many researchers are interested in group IV elements (Si, Ge, Sn) in the periodic table, and among them, silicon in particular has a very high theoretical capacity (Li 15 Si4 (Si: 3600 mAh / g) and low operating voltage (~0.1 V vs. Li / Li+) have attracted much attention as a very attractive material. However, during charge / discharge, silicon undergoes significant volume expansion and contraction due to its reaction with lithium, which can result in fine particle size loss 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 silicon have the problem that their capacity can rapidly decrease as the charge / discharge cycle progresses.

[0011] One aspect of the present invention is to provide a precursor for a negative electrode material of a lithium secondary battery capable of securing high capacity characteristics and excellent lifespan characteristics, and a method for manufacturing the same.

[0012]

[0013] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0014] According to one aspect of the present invention, a precursor for a negative electrode material of a lithium secondary battery may include silicon nanoparticles; a conductive material; and a carbon-based material, and may have a molding density of more than 1.3 g / cc and less than or equal to 1.6 g / cc.

[0015] The above-described conductive material may be at least one of natural graphite and artificial graphite.

[0016] The above-described carbon-based material may be at least one of coal-based pitch, petroleum-based pitch, coal tar, PAA, and PVA.

[0017] The above-described coal-based pitch and the above-described petroleum-based pitch may have a fixed carbon ratio of 60% or more and a beta-resin value of 10% or more.

[0018] The carbon-based material described above may additionally include a caking additive.

[0019] The above-described tackifying additive may be an olefin-based oligomer or polymer having viscoelasticity, or an organic substance having a binder function.

[0020] According to another aspect of the present invention, a method for manufacturing a precursor for a negative electrode material of a lithium secondary battery may include the steps of preparing silicon nanoparticles, a conductive material, and a carbon-based material; preparing a mixture by mixing the silicon nanoparticles, the conductive material, and the carbon-based material; and pressurizing and molding the mixture, wherein the pressurizing and molding step is performed at a pressure of 6 tons / cm. 2 More than 20 tons / cm 2 It may be done by applying the following pressure.

[0021] The above-described conductive material may be at least one of natural graphite and artificial graphite.

[0022] The above-described carbon-based material may be at least one of coal-based pitch, petroleum-based pitch, coal tar, PAA, and PVA.

[0023] The above-described coal-based pitch and the above-described petroleum-based pitch may have a fixed carbon ratio of 60% or more and a beta-resin value of 10% or more.

[0024] In the step of manufacturing the above-described mixture, a tackifying additive may be additionally mixed.

[0025] The above-described tackifying additive may be an olefin-based oligomer or polymer having viscoelasticity, or an organic substance having a binder function.

[0026] When the above-described carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressure forming step may be performed at a temperature 10°C higher than the softening point of the pitch or 150°C higher than the softening point of the pitch.

[0027] The above-described pressure forming step may be performed at room temperature.

[0028] The molding density of the precursor for the negative electrode material of the manufactured lithium secondary battery may be greater than 1.3 g / cc and less than or equal to 1.6 g / cc.

[0029] The precursor for the anode material of the lithium secondary battery of the present invention can provide an anode material formed with a high-density carbon layer that is physically and chemically robust by controlling the molding density. As a result, the anode material obtained from the precursor for the anode material of the present invention can secure high-capacity characteristics and excellent cycle life characteristics.

[0030] Figure 1 is an image photograph of a molded body obtained by carbonizing a precursor for a negative electrode material of a lithium secondary battery of Invention Example 1.

[0031] Figure 2 is an SEM image of a cross-section of a cathode coated with the cathode material of Comparative Example 1 on a collector.

[0032] Figure 3 is an SEM image of a cross-section of a cathode coated with the cathode material of Invention Example 1 on a collector.

[0033] Figure 4 is an SEM image of a cross-section of a cathode coated with the cathode material of Comparative Example 2 on a collector.

[0034] Figure 5 is an SEM image of a cross-section of a cathode coated with the cathode material of Comparative Example 3 on the entire body.

[0035] Figure 6 is a graph showing the expansion rate (%) by cycle number of Invention Examples 1 and 2 and Comparative Examples 1 to 3.

[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]

[0038] 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.

[0039]

[0040] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0041]

[0042] Although not essential, it should be noted that the technical solutions according to each aspect of the present invention can also be usefully applied to other aspects of the present invention. Furthermore, the compositions and various useful parameters according to each aspect of the present invention can be appropriately combined with other aspects to achieve beneficial effects.

[0043]

[0044] In the case of a negative electrode material containing silicon nanoparticles, irreversible products such as an SEI layer, carbon monoxide (CO), or carbon dioxide (CO2) may be generated by reaction with lithium during charge and discharge, and large volume expansion and contraction of the silicon nanoparticles may occur.

[0045]

[0046] In this case, some of the silicon nanoparticles may be partially exposed on the surface and react with the electrolyte, resulting in the formation of a new SEI and the subsequent depletion of lithium. As a result, conventional anode materials containing silicon nanoparticles have suffered from poor cycle life.

[0047]

[0048] To solve the above-described problems, the inventors of the present invention found that when a high-density carbon layer that is physically and chemically strong is formed inside the negative electrode material, not only can the contact path between the silicon nanoparticles and the conductive material be strengthened, but also the expansion of the silicon nanoparticles can be controlled.

[0049]

[0050] In addition, the inventors of the present invention have found that the high-density carbon layer has low conductivity (10) of silicon raw material. -4 It was found that by supplementing the S / cm) it is possible to induce a reversible reaction with lithium, and as a result, the capacity of the negative electrode material can be increased while simultaneously improving the life characteristics.

[0051]

[0052] In addition, the inventors realized that in order to provide the high-density carbon layer described above, it was necessary to control the molding density of a precursor for a negative electrode material of a lithium secondary battery to a certain level, and thus derived the present invention.

[0053]

[0054] From this perspective, a precursor for a negative electrode material for a lithium secondary battery according to an example of the present invention may include silicon nanoparticles; a conductive material; and a carbon-based material, and may have a molding density of more than 1.3 g / cc and less than or equal to 1.6 g / cc. Each component is described in detail below.

[0055]

[0056] silicon nanoparticles

[0057] One example of the present invention may include silicon nanoparticles for the purpose of providing a cathode material having high capacity characteristics.

[0058]

[0059] As a non-limiting example, the D50 particle size of the silicon nanoparticles may be 50 nm or more and 250 nm or less. This is to secure high capacity while preventing expansion of the silicon nanoparticles due to repeated charge / discharge. Here, D50 refers to a particle size corresponding to 50% of the volume accumulation of the particle size distribution. As another example, the D50 particle size of the silicon nanoparticles may be 50 nm or more and 150 nm or less, and as another example, may be 100 nm or more and 150 nm or less.

[0060]

[0061] In addition, the weight ratio of silicon nanoparticles included in the negative electrode precursor for a lithium secondary battery according to one embodiment of the present invention may be 40 wt% or more and 70 wt% or less based on the total weight of the negative electrode precursor.

[0062]

[0063] According to one embodiment of the present invention, the negative electrode material for a lithium secondary battery can secure high capacity characteristics of the negative electrode material by containing 40 wt% or more of the silicon nanoparticles. On the other hand, if the silicon nanoparticles are excessively included in the negative electrode material precursor, the silicon nanoparticles and the conductive material, either individually or as a whole, cannot be completely surrounded by the carbon coating layer, and in this case, the structure of the negative electrode material, which is a silicon-carbon composite, may result in collapse. For this reason, one embodiment of the present invention can contain the silicon nanoparticles in an amount of 70 wt% or less based on the total weight of the negative electrode material precursor for a lithium secondary battery.

[0064]

[0065] conductive material

[0066] One embodiment of the present invention may additionally include a conductive material to secure a conductive path with the above-described silicon nanoparticles and improve the reversibility of lithium ions, thereby increasing the capacity and efficiency of the negative electrode material.

[0067]

[0068] For the above-described purpose, one example of the present invention may include the conductive material in an amount of 10 wt% or more based on the total weight of the negative electrode precursor for a lithium secondary battery. More specifically, the conductive material may be included in an amount of 20 wt% or more based on the total weight of the negative electrode precursor. However, if the amount is excessive, capturing by a carbon coating layer may become difficult, and therefore, one embodiment of the present invention may set the weight ratio of the conductive material to 30 wt% or less based on the total weight of the negative electrode precursor.

[0069]

[0070] More specifically, an example of the above-mentioned challenging material may be at least one of natural graphite and artificial graphite.

[0071]

[0072] carbon-based materials

[0073] As described above, one embodiment of the present invention can secure high capacity characteristics and excellent life characteristics of the negative electrode material by forming a high-density carbon layer that is physically and chemically strong.

[0074]

[0075] In this way, the precursor for the negative electrode material of a lithium secondary battery according to an example of the present invention may include a carbon-based material for the purpose of forming the carbon layer.

[0076]

[0077] According to one embodiment of the present invention, the carbonaceous material may be at least one of coal pitch, petroleum pitch, coal tar, PAA, and PVA. These carbonaceous materials can be carbonized into amorphous carbon and also function as a binder that stably supports the structure of the negative electrode material later. That is, the carbonaceous materials are dispersed and positioned between the pores of the porous silicon-carbon composite, so that when the negative electrode material precursor according to the present embodiment is applied to a battery, the porous structure of the silicon-carbon composite can be prevented from collapsing even when charge and discharge cycles are repeated.

[0078]

[0079] Meanwhile, as an example, the coal-based pitch and the petroleum-based pitch may have a fixed carbon ratio of 60% or more. More specifically, the fixed carbon ratio may be 70% or more.

[0080]

[0081] As the fixed carbon values ​​of the above-described coal-based pitch and the above-described petroleum-based pitch increase, silicon particles with low intrinsic conductivity and conductive paths can be created, leading to increased capacity and efficiency. Furthermore, when the fixed carbon value satisfies the above range, the internal pores of the negative electrode material of the present embodiment can be reduced. Accordingly, side reactions with the electrolyte can also be reduced, contributing to increased initial efficiency of the battery.

[0082]

[0083] The beta resin value of the above coal-based pitch and the above petroleum-based pitch may be, for example, 10% or more, and more specifically, the beta resin value may be 25% or more.

[0084]

[0085] Specifically, the β-resin value refers to the value obtained by subtracting the quinoline capacity (benzeneinsoluble) from the benzene-insoluble value. This β-resin value is proportional to the cohesion. According to an embodiment of the present invention, when coal-based pitch or petroleum-based pitch having a β-resin value satisfying the above range is used, the porous structure of the silicon-carbon composite can be more stably maintained. Accordingly, an embodiment of the present invention can implement a lithium secondary battery having excellent life characteristics and electrode expansion characteristics.

[0086]

[0087] Meanwhile, the carbon-based material according to an example of the present invention may additionally include a caking additive. This caking additive may help maintain the shape of the molded body. The caking additive is not particularly limited within the scope that can achieve the above-described purpose, but as an example, the caking additive may be an olefin-based oligomer or polymer having viscoelasticity, or an organic material having a binder function, such as PVDF, SBR, CMC, or PAA.

[0088]

[0089] Hereinafter, a precursor for a negative electrode material of a lithium secondary battery according to one embodiment of the present invention will be described in detail.

[0090]

[0091] As described above, one example of the present invention can increase the capacity of the negative electrode material and improve its lifespan characteristics by forming a high-density carbon layer that is physically and chemically strong inside the negative electrode material.

[0092]

[0093] In order to provide such a high-density carbon layer, the negative electrode precursor according to an example of the present invention may have a molding density of more than 1.3 g / cc and less than or equal to 1.6 g / cc.

[0094]

[0095] More specifically, the precursor for a negative electrode material of a lithium secondary battery according to an example of the present invention can provide a high-density internal carbon layer by setting the molding density to exceed 1.3 g / cc. As a result, an example of the present invention can not only eliminate pores in the negative electrode material, but also increase the surface coverage of the silicon nanoparticles as the internal carbon layer sufficiently wraps the silicon nanoparticles. In addition, an embodiment of the present invention can increase the number of silicon nanoparticles per unit volume by narrowing the distance between the silicon nanoparticles through the above-described molding density, thereby increasing the electrochemical capacity. According to another example, the lower limit of the molding density may be 1.4 g / cc. On the other hand, if the molding density is excessively high, the strength of the negative electrode material increases, which may increase the generation of fine powder during subsequent pulverization. Therefore, an example of the present invention may set the upper limit of the molding density to 1.6 g / cc. In another example, the upper limit of the molding density may be 1.55 g / cc, and in another example, it may be 1.5 g / cc.

[0096]

[0097] Meanwhile, when the above-described precursor for the negative electrode material is carbonized at a certain temperature or higher and then pulverized and classified, the negative electrode material of the present invention can be obtained, and the negative electrode material of the present invention is described in detail below.

[0098]

[0099] As described above, the precursor for a negative electrode material according to an example of the present invention can control the molding density within a certain range, and as a result, the negative electrode material obtained from the precursor for a negative electrode material can have an appropriate level of tap density and specific surface area and exhibit excellent electrochemical performance.

[0100]

[0101] More specifically, the tap density of the negative electrode material according to one embodiment of the present invention may be 0.50 g / cc or more and 0.72 g / cc or less, and the specific surface area may be 2 m 2 / g or more than 7.3m 2 / g can be less.

[0102]

[0103] Meanwhile, the D50 particle size of the negative electrode material of the lithium secondary battery according to one embodiment of the present invention may be 8.0 μm or more and 15.0 μm or less.

[0104]

[0105] Specifically, in order to prevent the problem of battery performance varying from section to section by ensuring uniform thickness quality of the electrode plate, the negative electrode material of a lithium secondary battery, which is an example of the present invention, may have a center particle size (D50) of 8.0 μm or more and 15.0 μm or less. More specifically, the center particle size of the negative electrode material may be 9.0 μm or more and 12.0 μm or less, or 10.0 μm or more and 11.0 μm or less.

[0106]

[0107] Hereinafter, a method for manufacturing a precursor for an anode material of a lithium secondary battery of the present invention will be described. However, the method for manufacturing a precursor for an anode material of a lithium secondary battery described below is merely an example, and it is not necessary for the precursor for an anode material of a lithium secondary battery of the present invention to be manufactured by this manufacturing method. It should be noted that any manufacturing method that satisfies the claims of the present invention will not cause any problems in implementing and using each embodiment of the present invention.

[0108]

[0109] A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery according to an example of the present invention may include the steps of preparing silicon nanoparticles, a conductive material, and a carbon-based material; the step of mixing the silicon nanoparticles, the conductive material, and the carbon-based material to manufacture a mixture; and the step of pressurizing and molding the mixture, wherein the pressurizing and molding step may be performed at a pressure of 6 tons / cm. 2 More than 20 tons / cm 2 This can be done by applying the following pressure. Each step is described in detail below.

[0110]

[0111] First, one embodiment of the present invention can prepare silicon nanoparticles, a conductive material, and a carbon-based material.

[0112]

[0113] To obtain the above silicon nanoparticles, a non-limiting embodiment of the present invention may pulverize silicon raw materials through mechanical milling. As a result, the D50 particle size of the pulverized silicon nanoparticles may be 50 nm or more and 250 nm or less, as described above.

[0114]

[0115] Furthermore, as an example, the mechanical milling may be performed using stabilized zirconia. Furthermore, to improve nano-processing efficiency, suppress the generation of fine particles, and prevent silicon particles from oxidizing, the size of the zirconia beads may be less than twice the D99 of the silicon raw material being introduced. However, the zirconia beads used may be of various sizes and can be utilized in process design, and are therefore not limited thereto.

[0116]

[0117] Other detailed conditions for mechanical milling are not specifically limited, as they can be sufficiently designed by a skilled technician according to the purpose. However, as an example, the BPR (Ball Per Ratio) of the silicon raw material to the stabilized zirconia balls may be set to 5:1, and the rotation speed of the rotor inside the grinder may be maintained at 2,500 rpm.

[0118]

[0119] And, according to one example of the present invention, the solvent in the mechanical milling may be an organic solvent such as ethanol or IPA to prevent oxidation of the silicon raw material.

[0120]

[0121] The conductive material may be at least one of natural graphite and artificial graphite, and the carbonaceous material may be at least one of coal pitch, petroleum pitch, coal tar, PAA, and PVA. In addition, the coal pitch and the petroleum pitch may have a fixed carbon ratio of 60% or more and a beta resin value of 10% or more. Since this is the same as the content described above with respect to the precursor for the negative electrode material, a detailed description thereof is omitted.

[0122]

[0123] In this way, after preparing silicon nanoparticles, a conductive material, and a carbon-based material, the materials can be mixed to obtain a mixture. In addition, according to another embodiment of the present invention, a tackifying additive can be additionally mixed during the above-described mixing. As a non-limiting example, the tackifying additive can be an olefin-based oligomer or polymer having viscoelasticity, and an organic material having a binder function such as PVDF, SBR, CMC, or PAA.

[0124]

[0125] The above mixing may be performed simultaneously, and at least two of the above-described materials may be mixed first, followed by the remaining materials. For example, the silicon nanoparticles and the conductive material may be mixed first, then spray-dried to obtain a spray-dried product, after which the carbon-based material may be added, and then the spray-dried product and the carbon-based material may be mixed. In addition, when the carbon-based material is added, the tackifying additive may be optionally added. However, this is also merely an example and is not necessarily limited thereto.

[0126]

[0127] Additionally, the above mixing can be performed through a milling process via contact with the powder, and non-limiting examples thereof include mechanofusion or a ball mill. When performing a milling process via contact with the powder, the independent flow of silicon nanoparticles can be reduced when mixed with a solvent.

[0128]

[0129] A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery according to one embodiment of the present invention may include a step of pressurizing and molding the mixture.

[0130]

[0131] That is, according to one example of the present invention, in order to obtain a precursor for a negative electrode material having the above-described molding density, a specific pressure can be applied to the mixture for a specified time range. More specifically, when pressurizing is performed in this way, the carbon-based material in the above-described negative electrode material precursor can fill the micropores inside the precursor, thereby reducing the specific surface area of ​​the negative electrode material and improving the electrochemical performance of the negative electrode material. As a non-limiting example, the pressurizing can be performed by filling the precursor powder into a self-manufactured mold and using a pressurizing device, and the semi-finished product obtained thereby can be specified in the form of a block.

[0132]

[0133] In particular, according to a non-limiting embodiment of the present invention, the pressure forming step is 6 tons / cm 2 More than 20 tons / cm 2 It can be done by applying the following pressure.

[0134]

[0135] The above pressure forming step is 6 tons / cm 2 More than 20 tons / cm 2 By applying the pressure below, the molding density of the precursor for the negative electrode material can be controlled to an appropriate level. More specifically, in one embodiment of the present invention, by setting the pressure during pressurizing molding within the above-described range, the molding density of the precursor for the negative electrode material can be maintained at more than 1.3 g / cc and less than 1.6 g / cc. As another example, the pressurizing molding step is 6 tons / cm. 2 More than 15 tons / cm 2 This can be done by applying a pressure below, as another example, 10 tons / cm 2 More than 11 tons / cm 2 This can be done by applying the following pressure:

[0136]

[0137] Meanwhile, in an example of the present invention, when the carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressure forming step may be performed at a temperature 10°C higher than the softening point of the pitch or 150°C higher than the softening point of the pitch.

[0138]

[0139] One example of the present invention is that by performing press molding at a temperature range of 10°C higher than the softening point of the pitch, the viscosity of the pitch can be increased, thereby removing pores inside the negative electrode precursor, and the surface coverage of the silicon nanoparticles can be maintained high. However, if the temperature in the press molding step is higher than 150°C higher than the softening point of the pitch, a problem may arise in which the structure and shape of the molded body change due to gas generation or deformation of some components. As another example, the temperature range in the press molding step may be 10°C higher than the softening point of the pitch to 100°C higher than the softening point of the pitch, or 50°C higher than the softening point of the pitch to 100°C higher than the softening point of the pitch.

[0140]

[0141] However, according to another embodiment of the present invention, the pressurizing step can be performed even at room temperature.

[0142]

[0143] In general, as described above, heat treatment must be accompanied in order for the press molding step to be smoothly performed. However, according to a non-limiting example of the present invention, when a high-coating pitch having a β-resin value of a certain level or higher is used or a caking additive is additionally added, a precursor for a negative electrode material having a molding density suggested by the present invention can be obtained even by press molding without a separate heat treatment. In this case, since a separate heat treatment process is not required, there is an advantage in that time and cost can be saved in that the energy input thereto can be reduced.

[0144]

[0145] The cathode material precursor obtained through the above-described steps can be obtained as a cathode material through carbonization, pulverization, and classification steps, and a method for manufacturing a cathode material from the cathode material precursor is described in detail below.

[0146]

[0147] A non-limiting example of the present invention is that a molded body can be obtained by carbonizing a precursor obtained by the above-described method.

[0148]

[0149] More specifically, the carbonization can be performed at a temperature range of 800°C or higher and 1000°C or lower. In one embodiment of the present invention, by carbonizing the precursor at 800°C or higher, not only can evaporate volatile components existing inside the existing precursor, but also harden the pitch to secure the internal structure of the negative electrode material. In addition, if the temperature during carbonization becomes too high, silicon carbide and silicon nitride without electrochemical performance may be generated, which may lower the capacity and efficiency, so the carbonization can be performed at a temperature range of 1000°C or lower. In particular, the carbonization can be performed in an inert atmosphere to suppress oxidation of silicon particles.

[0150]

[0151] The formed body thus obtained can be obtained as a negative electrode material of a desired size by crushing and classifying. As a non-limiting example, the crushing can be performed by dry crushing, and the dry crushing can be performed using a jet mill or a pin mill.

[0152]

[0153] According to a non-limiting embodiment of the present invention, the obtained negative electrode material may additionally include a step of carbon coating on the surface of the negative electrode material.

[0154]

[0155] The above carbon coating step can be performed by adding a carbon-based material and performing a heat treatment, and the carbon-based material can be at least one of petroleum pitch, coal tar, PAA, and PVA having a softening point of less than 250°C. In addition, but not limited thereto, the coating can be performed using a twisted blade mixer. At this time, process variables such as time and rotation speed, but considering that these can be appropriately designed by a person skilled in the art according to the purpose, they are not described in the present invention.

[0156]

[0157] Hereinafter, a method for manufacturing a negative electrode of a lithium secondary battery of the present invention will be described in detail.

[0158]

[0159] 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 material layer, and then applying the composition to a negative electrode current collector.

[0160]

[0161] 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.

[0162]

[0163] Examples of the binder include, but are not limited to, polyacrylic acid, 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 material layer.

[0164]

[0165] The conductive material is not particularly limited as long as it has conductivity without causing chemical changes 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 material layer.

[0166] (1) Manufacturing of cathode precursor

[0167] First, a silicon raw material (Poly-Si) was prepared. Next, the silicon raw material was pulverized using stabilized zirconia having a size of 0.1 mm, thereby obtaining a slurry of silicon nanoparticles with a D50 particle size of 150 nm. In addition, the pulverization was performed in an ethanol solvent having a purity of 99%, and the solid content ratio corresponded to 10%. In addition, the BPR of the stabilized zirconia during the pulverization was 5:1, and the rotation speed of the rotor inside the pulverizer was maintained at 2500 rpm. Next, 20 wt% of flake graphite having a center particle size (D50) of 8.00 μm was added to the slurry of silicon nanoparticles obtained by the above-described process based on the total weight of the precursor, and this was spray-dried to obtain a powder. Thereafter, 40 wt% of petroleum pitch based on the total weight of the precursor was added to the obtained powder, and mixing was performed using mechanofusion to manufacture a cathode precursor. The above petroleum-based pitch had a fixed carbon ratio of 70% or more and a β-resin value of 25%. Thereafter, the precursor was press-molded to obtain a block-shaped negative electrode precursor. The press-molding was performed at the temperature and pressure shown in Table 1 below. At this time, the pressure was applied using a pressurizing device to a cylindrical mold having a radius of 1 cm and a height of 5 cm. Thereafter, the molding density of the manufactured negative electrode precursor was measured and is shown in Table 1 below. At this time, the molding density was measured by dividing the weight (g) of the molded body by the volume (cc).

[0168]

[0169] (2) Manufacturing of cathode material

[0170] Next, the above-mentioned negative electrode material was carbonized at a temperature of 900℃ in an inert atmosphere. Afterwards, after going through a pulverization process using a JET mill, petroleum pitch with a softening point of less than 250℃ was evenly dispersed on the surface of the pulverized particles to perform additional coating. At this time, the additional coating was performed using a twisted blade mixer. Afterwards, heat treatment was performed at a temperature of 900℃ in an inert atmosphere, and the negative electrode material was obtained through sieving. The D01, D50, and D90 particle sizes of the obtained negative electrode material were measured using a laser diffraction-type particle size analyzer, and the measured values ​​are shown in Table 1 below. The D01, D50, and D90 particle sizes refer to particle sizes corresponding to 1%, 50%, and 90% of the volume accumulation of the particle size distribution, respectively.

[0171]

[0172] In addition, the tap density and BET specific surface area of ​​the obtained negative electrode material were measured and shown in Table 1 below.

[0173]

[0174] (3) Manufacturing of cathode

[0175] A slurry of negative active material was prepared by mixing 75 wt% of the manufactured negative electrode material, 24 wt% of a binder containing polyacrylic acid (PAA), and 1 wt% of a Super P conductive material in a distilled water solvent.

[0176]

[0177] The above-mentioned negative active material slurry was applied to a copper (Cu) current collector, dried, and pressed in a roll press at a rolling density of 1.0 g / cc. Thereafter, the negative electrode was manufactured by vacuum drying in a vacuum oven.

[0178]

[0179] (4) Electrochemical evaluation

[0180] To evaluate the electrochemical characteristics, a lithium secondary battery was manufactured. Specifically, a half coin cell of the 2032 coin cell type was manufactured using the 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 having a volume ratio of 3:7 of ethylene carbonate (EC): ethyl methyl carbonate (EMC), according to a conventional manufacturing method. 10 wt% of FEC additive was added to the electrolyte.

[0181]

[0182] The discharge capacity, initial efficiency, and 50-cycle life of the above battery were measured and are shown in Table 2 below.

[0183]

[0184] The current during charge and discharge was measured at 0.1 C in the initial cycle. Furthermore, a current of 0.5 C was applied during charge and discharge based on the first 1 C capacity, and the 50-cycle life was measured. The charge cut-off current was set to 0.005 C.

[0185] ClassificationPressure molding stageMolding body density (g / cc)Cathode material particle sizeTemperature (℃)Pressure (ton / cm) 2 )D01D50D90Comparative example 127041.012.1210.0219.24Invention example 127061.411.729.8919.25Comparative example 2270211.631.059.8219.02Comparative example 3270211.750.899.7519.35Invention example 2Room temperature201.521.659.7419.68

[0186] ClassificationTap Density (g / cc) Specific surface area (m 2 / g)Discharge capacity (mAh / g)Initial efficiency (%)Lifespan (%, @50cycle)Comparative example 10.3212.56135782.530.2Invention example 10.556.51133585.158.2Comparative example 20.549.45133084.548.5Comparative example 30.57.98128781.832Invention example 20.527.25133884.849.8

[0187] In the case of comparative example 1, the pressure in the pressurizing molding step was 6 tons / cm 2 As a result, the density of the molded body was only 1.01 g / cc. As a result, the pores in the negative electrode material were not eliminated, and the coverage of the silicon nanoparticles was low, resulting in poor initial efficiency and lifespan characteristics of the battery.

[0188]

[0189] For comparative examples 2 and 3, the pressure in the pressurizing step was 20 tons / cm 2 As the density of the molded body was excessively high, the strength of the molded body increased, and the generation of fine particles (D10) of the negative electrode material increased during crushing. As a result, it can be confirmed that the specific surface area values ​​were measured to be large in the cases of Comparative Examples 2 and 3.

[0190]

[0191] On the other hand, in the case of Invention Example 1, since all the conditions proposed by the present invention were satisfied, the discharge capacity, initial efficiency, and 50-cycle characteristics were all excellent. At this time, an image photograph of a molded body obtained by carbonizing the precursor for the negative electrode material of the lithium secondary battery of Invention Example 1 is shown in Fig. 1 below.

[0192]

[0193] In particular, looking at Invention Example 2, it can be seen that the present invention can obtain a precursor for a negative electrode material having excellent electrochemical properties even when pressurized molding is performed at room temperature.

[0194]

[0195] FIGS. 2 to 5 show SEM images of cross-sections of negative electrodes coated with negative electrode materials of Comparative Example 1, Inventive Example 1, Comparative Example 2, and Comparative Example 3, respectively, on current collectors. Looking at FIGS. 2 to 5, it can be seen that, in the case of Inventive Example 1, pores are relatively removed compared to Comparative Example 1. In addition, looking at FIGS. 4 and 5, in the case of Comparative Examples 2 and 3, the density of the molded body increased, but the pulverized shape was not uniform, and it can be seen that sharp parts existed after pulverization. As a result, it is presumed that a large amount of fine powder was generated during pulverization in Comparative Examples 2 and 3.

[0196]

[0197] Fig. 6 is a graph showing the expansion ratio (%) by cycle number of Inventive Examples 1 and 2 and Comparative Examples 1 to 3. Referring to Fig. 6, it can be confirmed that Inventive Examples 1 and 2 and Comparative Example 2, in which the molding density exceeds 1.3 g / cc, have low expansion ratios because the high-density carbon layer controls the expansion of the silicon nanoparticles. However, in the case of Comparative Example 1, in which the molding density is less than 1.3 g / cc, the high-density carbon layer is not formed, so the expansion of the silicon nanoparticles is not suppressed, resulting in a high expansion ratio. In Comparative Example 3, in which the molding density is excessively high, the hardness of the molded body increases, so that the fine powder content increases during pulverization, resulting in the independent existence of silicon nanoparticles, resulting in a high expansion ratio.

Claims

1. Silicon nanoparticles; challenging material; and Contains carbon-based materials, A precursor for an anode material of a lithium secondary battery having a molding density of more than 1.3 g / cc and less than or equal to 1.6 g / cc.

2. In paragraph 1, The above-mentioned challenging material is a precursor for an anode material of a lithium secondary battery, wherein the precursor is at least one of natural graphite and artificial graphite.

3. In paragraph 1, The above carbon-based material is a precursor for an anode material of a lithium secondary battery, wherein the carbon-based material is at least one of coal pitch, petroleum pitch, coal tar, PAA, and PVA.

4. In paragraph 3, The above-mentioned coal-based pitch and the above-mentioned petroleum-based pitch are precursors for negative electrode materials of lithium secondary batteries having a fixed carbon ratio of 60% or more and a beta-resin value of 10% or more.

5. In paragraph 1, The above carbon-based material is a precursor for an anode material of a lithium secondary battery, additionally containing a tackifying additive.

6. In paragraph 5, The above-mentioned viscous additive is a precursor for an anode material of a lithium secondary battery, which is an olefin-based oligomer or polymer having viscoelasticity, or an organic substance having a binder function.

7. Step of preparing silicon nanoparticles, conductive material and carbon-based material; A step of preparing a mixture by mixing the silicon nanoparticles, the conductive material, and the carbon-based material; Comprising a step of pressurizing and molding the above mixture, The above pressurizing step is 6 tons / cm 2 More than 20 tons / cm 2 A method for manufacturing a precursor for a negative electrode material of a lithium secondary battery, the method comprising applying the following pressure:

8. In paragraph 7, A method for producing a precursor for an anode material of a lithium secondary battery, wherein the above-mentioned challenging material is at least one of natural graphite and artificial graphite.

9. In paragraph 7, A method for producing a precursor for an anode material of a lithium secondary battery, wherein the carbon-based material is at least one of coal pitch, petroleum pitch, coal tar, PAA, and PVA.

10. In paragraph 9, A method for manufacturing a precursor for an anode material of a lithium secondary battery, wherein the above-mentioned coal-based pitch and the above-mentioned petroleum-based pitch have a fixed carbon ratio of 60% or more and a beta-resin value of 10% or more.

11. In paragraph 7, A method for manufacturing a precursor for an anode material of a lithium secondary battery, wherein a caking additive is additionally mixed in the step of manufacturing the above mixture.

12. In paragraph 11, A method for producing a precursor for an anode material of a lithium secondary battery, wherein the above-mentioned viscoelastic additive is an olefin-based oligomer or polymer having viscoelasticity, or an organic substance having a binder function.

13. In paragraph 9, A method for manufacturing a precursor for an anode material of a lithium secondary battery, wherein when the carbon-based material is the coal-based pitch or the petroleum-based pitch, the pressurizing and molding step is performed at a temperature of 10°C higher than the softening point of the pitch to a temperature of 150°C higher than the softening point of the pitch.

14. In clause 10 or 11, A method for manufacturing a precursor for an anode material of a lithium secondary battery, wherein the above-mentioned pressurizing forming step is performed at room temperature.

15. In paragraph 8, A method for manufacturing a precursor for an anode material of a lithium secondary battery, wherein the molding density of the precursor for an anode material of the manufactured lithium secondary battery is more than 1.3 g / cc and less than or equal to 1.6 g / cc.

Images