Negative electrode material of lithium secondary battery, and manufacturing method therefor

Abstract

One aspect of the present invention provides a negative electrode material for a lithium secondary battery and a manufacturing method therefor, wherein the negative electrode material includes nano-sized first silicon particles and micro-sized second silicon particles surrounded by a carbon coating layer, thereby securing high capacity characteristics and excellent lifespan characteristics.

Description

Anode material for lithium secondary batteries and method for manufacturing the same

[0001] The present invention relates to a negative electrode material for a lithium secondary battery and a method for manufacturing the same.

[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 negative electrode material for 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 negative electrode material for a lithium secondary battery may include first silicon particles having a particle size of less than 1.00 μm; second silicon particles having a particle size of 1.00 μm or more; and a carbon coating layer surrounding the first silicon particles, wherein the D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0015]

[0016] The carbon coating layer described above may be soft carbon, and the soft carbon may be derived from at least one of coal-based pitch and petroleum-based pitch.

[0017]

[0018] The above-described coal-based pitch may have a fixed carbon ratio of 60% or more and a beta-resin value of 10% or more.

[0019]

[0020] The D90 particle size of the first silicon particle described above may be 30 nm or more and 500 nm or less.

[0021]

[0022] The weight ratio of the second silicon particles described above may be 10% by weight or more and 80% by weight or less with respect to the total weight of the first silicon particles and the second silicon particles.

[0023]

[0024] In addition, the negative electrode material for the lithium secondary battery described above may have a relative particle size ratio derived by Equation 1 below of 0.20 or more and 0.99 or less.

[0025]

[0026] (Formula 1) Relative particle size ratio = D90 particle size (μm) of the second silicon particle / D50 particle size (μm) of the negative electrode material for lithium secondary batteries

[0027]

[0028] The half width of the particle size distribution of the first silicon particles described above may be 0.2 or more.

[0029]

[0030] The above-described negative electrode material for a lithium secondary battery may additionally include a conductive material, and the conductive material may be at least one of natural graphite and artificial graphite.

[0031]

[0032] The center particle size (D50) of the negative electrode material for the lithium secondary battery described above may be 8.0 μm or more and 15.0 μm or less.

[0033]

[0034] According to another aspect of the present invention, a method for manufacturing an anode material for a lithium secondary battery may include the steps of: preparing first silicon particles having a particle size of less than 1.00 μm and second silicon particles having a particle size of 1.00 μm or more; mixing the first silicon particles, the second silicon particles, and pitch to obtain a precursor; pressurizing and molding the precursor; carbonizing the precursor after the pressurizing and molding to obtain a molded body; and crushing and classifying the molded body. The D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0035]

[0036] In addition, a method for manufacturing a negative electrode material for a lithium secondary battery according to another embodiment of the present invention may include a step of preparing first silicon particles having a particle size of less than 1.00 μm; a step of carbon-coating the first silicon particles; a step of adding second silicon particles having a particle size of 1.00 μm or more and a carbon-based material to the first silicon particles after the carbon coating and mixing them to obtain a mixture; a step of heat-treating the mixture after the mixing to obtain a molded body; and a step of pulverizing and classifying the molded body; wherein the D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0037]

[0038] In the above-described method for manufacturing a negative electrode material for a lithium secondary battery, the weight ratio of the second silicon particles may be 10 wt% or more and 80 wt% or less with respect to the total weight of the first silicon particles and the second silicon particles.

[0039]

[0040] In the above-described mixing, a conductive material may be additionally mixed, and the conductive material may be at least one of natural graphite and artificial graphite.

[0041]

[0042] The step of preparing the first silicon described above may include a step of obtaining the first silicon by crushing the silicon raw material through mechanical milling.

[0043]

[0044] The solvent in the mechanical milling described above may be ethanol or IPA.

[0045]

[0046] The above-described mixing can be carried out through a milling process via contact with a powder.

[0047]

[0048] The method for manufacturing the above-described negative electrode material for a lithium secondary battery may additionally include a step of coating carbon on the surface of the manufactured negative electrode material.

[0049] The present invention provides a negative electrode material for a lithium secondary battery comprising first silicon particles and second silicon particles surrounded by a carbon coating layer, thereby ensuring high capacity characteristics and excellent lifespan characteristics.

[0050]

[0051] More specifically, the negative electrode material of the present invention can have excellent cycle characteristics by including nano-sized first silicon particles in a carbon coating layer, and can secure high-capacity characteristics by additionally including micro-sized second silicon particles.

[0052] Figure 1 is a schematic diagram briefly showing one embodiment of a negative electrode material for a lithium secondary battery of the present invention.

[0053] 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.

[0054]

[0055] 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.

[0056]

[0057] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0058]

[0059] 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.

[0060]

[0061] Since silicon undergoes significant volume expansion and contraction due to a reaction with lithium during charge and discharge, lithium secondary batteries containing silicon have the problem that their capacity may rapidly decrease as charge and discharge cycles progress.

[0062]

[0063] In order to solve the above-described problem, the inventors of the present invention found that when nano-sized first silicon particles are protected with a carbon coating layer, not only can side reactions between the first silicon particles and the electrolyte be prevented, but also contact between the first silicon particles and the conductive material can be maintained despite expansion and contraction of the silicon, thereby improving the life characteristics of the negative electrode material.

[0064]

[0065] However, when the negative electrode material is composed of only nano-sized silicon particles, the initial efficiency of the negative electrode material tends to decrease as the reversibility of lithium ions decreases during charge and discharge.

[0066]

[0067] Accordingly, the inventors of the present invention also discovered that it is possible to secure both high capacity characteristics and excellent life characteristics of the negative electrode material by simultaneously including the nano-sized first silicon particles and the micro-sized second silicon particles.

[0068]

[0069] From this point of view, a negative electrode material for a lithium secondary battery according to an example of the present invention may include first silicon particles having a particle size of less than 1.00 μm; second silicon particles having a particle size of 1.00 μm or more; and a carbon coating layer surrounding the first silicon particles, and the D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0070]

[0071] In this specification, D90 and D50 mean particle sizes corresponding to 90% and 50% of the volume accumulation of the particle size distribution, respectively.

[0072]

[0073] Below, each configuration is described in detail.

[0074]

[0075] First silicon particle

[0076] As described above, one embodiment of the present invention may include nano-sized first silicon particles in order to prevent the life characteristics of the negative electrode material from being deteriorated due to volume expansion of silicon caused by repeated charge and discharge. That is, the particle size of the first silicon particles may be less than 1.00 μm. More specifically, for the same purpose as described above, the D90 particle size of the first silicon particles may be 500 nm or less, and in another embodiment, 300 nm or less. On the other hand, in order to prevent the D90 particle size of the first silicon particles of the present invention from becoming too small and thus deteriorating the initial electrochemical efficiency characteristics, one embodiment of the present invention may set the lower limit of the D90 particle size of the first silicon particles to 30 nm. In another embodiment, the lower limit of the D90 particle size of the first silicon particles may be 200 nm.

[0077]

[0078] In addition, as an example of the present invention, the half width of the particle size distribution of the first silicon particles may be 0.2 or more. This allows for excellent life characteristics and expansion characteristics of the negative electrode material to be secured.

[0079]

[0080] carbon coating layer

[0081] In order to suppress the volume expansion of the first silicon particles, the negative electrode material for a lithium secondary battery according to one embodiment of the present invention may include a carbon coating layer surrounding the first silicon particles.

[0082]

[0083] As described above, one embodiment of the present invention can prevent unnecessary side reactions by minimizing the contact area between the first silicon particles and the electrolyte through the carbon coating layer. In addition, according to one embodiment of the present invention, when the negative electrode material additionally includes a conductive material such as graphite, contact between the silicon particles and the conductive material can be maintained despite expansion and contraction of the first silicon particles, thereby ensuring excellent conductivity of the negative electrode material.

[0084]

[0085] Additionally, as an example, the carbon coating layer may be soft carbon.

[0086]

[0087] Here, the above graphitized carbon refers to a carbonaceous material having a nearly graphitized layered crystal structure (graphene structure: a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers) and which changes into a graphite structure when heat-treated at a temperature of 2500℃ or higher. The above graphitized carbon is not particularly limited, but examples thereof may include petroleum coke, coal coke, and mesocarbon spherules.

[0088]

[0089] In particular, according to one embodiment of the present invention, the graphitized carbon may be derived from at least one of coal-based pitch and petroleum-based pitch. Derived from at least one of coal-based pitch and petroleum-based pitch may mean that at least one of the coal-based pitch and the petroleum-based pitch is carbonized.

[0090]

[0091] The above-mentioned coal-based pitch and petroleum-based pitch can also function as binders that stably support the structure of the negative electrode material. That is, the coal-based pitch and petroleum-based pitch are dispersed and positioned between the pores of the porous silicon-carbon composite, so that when the negative electrode material according to the present embodiment is applied to a battery, the porous structure of the silicon-carbon composite can be prevented from collapsing even with repeated charge and discharge cycles.

[0092]

[0093] Meanwhile, as an example, the coal-based pitch may have a fixed carbon ratio of 60% or more. More specifically, the fixed carbon ratio may be 70% or more.

[0094]

[0095] As the fixed carbon value of the coal-based pitch increases, 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 anode material of the present embodiment can be reduced. Consequently, side reactions with the electrolyte can also be reduced, contributing to increased initial battery efficiency.

[0096]

[0097] The beta resin value of the above coal-based pitch may be, for example, 10% or more, and more specifically, the beta resin value may be 25% or more.

[0098]

[0099] 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. In the present embodiment, since the carbon-based pitch having a β-resin value satisfying the above range is included, the porous structure of the silicon-carbon composite can be more stably maintained. Accordingly, when the negative electrode material according to the present embodiment is employed, a lithium secondary battery having excellent life characteristics and electrode plate expansion characteristics can be realized.

[0100]

[0101] Second silicon particle

[0102] As described above, one embodiment of the present invention may include, together with the first silicon particles, second silicon particles having a particle size of 1.00 μm or more.

[0103]

[0104] Additionally, as a non-limiting example, the D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0105]

[0106] Specifically, the second silicon particles having a micron size can improve the reversibility of lithium ions during charge and discharge, thereby increasing the capacity of the negative electrode material. For example, the D90 particle size of the second silicon particles may be 5.00 μm or more. In another embodiment, the D90 particle size of the second silicon particles may be 7.00 μm or more. The reason why one embodiment of the present invention limits the D90 particle size to the above-described range, rather than the D50 particle size, is that by limiting the D90 particle size of the second silicon particles, the second silicon particles can be stably assembled into the negative electrode precursor. In order to achieve the above-described purpose, one embodiment of the present invention may set the D90 particle size of the second silicon particles to 15.0 μm or less. In another embodiment, the D90 particle size of the second silicon particles may be 14.0 μm or less, and in another embodiment, it may be 13.5 μm or less.

[0107]

[0108] In addition, the second silicon particles may be a product having a half width of particle size distribution of less than 0.2 degrees, and this is to secure high capacity characteristics of the negative electrode material by including the second silicon particles having a half width of less than a certain level.

[0109]

[0110] Meanwhile, as an example, the weight ratio of the second silicon particles may be 10 wt% or more and 80 wt% or less with respect to the total weight of the first silicon particles and the second silicon particles.

[0111]

[0112] That is, in order to secure high-capacity characteristics as described above, the negative electrode material according to one embodiment of the present invention may contain the second silicon particles in an amount of 10 wt% or more based on the total weight of the first silicon particles and the second silicon particles. More specifically, it may contain 25 wt% or more or 50 wt% or more. However, if the amount of the second silicon particles in the negative electrode material is excessively large, the relative amount of the first silicon particles described above may decrease, which may deteriorate the life characteristics of the negative electrode material. To prevent this, one embodiment of the present invention may set the weight ratio of the second silicon to the total weight of the first silicon particles and the second silicon particles to 80 wt% or less. More specifically, it may contain 78 wt% or less or 60 wt% or less.

[0113]

[0114] In addition, according to one embodiment of the present invention, the relative particle size ratio derived by the following equation 1 can be set to 0.20 or more and 0.99 or less.

[0115]

[0116] (Formula 1) Relative particle size ratio = D90 particle size (μm) of the second silicon particle / D50 particle size (μm) of the negative electrode material for lithium secondary batteries

[0117]

[0118] That is, in one example of the present invention, in order to facilitate particle size control of an anode material for a lithium secondary battery and to improve cycle characteristics of the anode material, the relative particle size ratio value derived by Equation 1 may be set to 0.99 or less. When the relative particle size ratio exceeds 0.99, the reason why the cycle characteristics of the anode material are reduced is believed to be that when the second silicon particles and the first silicon particles are mixed to obtain a precursor and then spray-dried, the second silicon particles are not normally assembled within the precursor.

[0119]

[0120] conductive material

[0121] Although not a material that must be added, one embodiment of the present invention may additionally include a conductive material to secure a conductive path with the first silicon particles and improve the reversibility of lithium ions, thereby increasing the capacity and efficiency of the negative electrode material.

[0122]

[0123] 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 material 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 material. However, if the amount becomes excessive, capturing by the carbon coating layer may become difficult, so 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 material.

[0124]

[0125] More specifically, an example of the above-mentioned challenging material may be at least one of natural graphite and artificial graphite.

[0126]

[0127] Hereinafter, a negative electrode material for a lithium secondary battery according to one embodiment of the present invention including all or part of the above-described configurations is described.

[0128]

[0129] The above-mentioned negative electrode material for a lithium secondary battery may have a center particle size (D50) of 8.0 μm or more and 15.0 μm or less.

[0130]

[0131] Specifically, the negative electrode material for a lithium secondary battery, which is an example of the present invention, can secure uniform thickness quality of the electrode plate by setting the center particle size (D50) to 8.0 μm or more. More specifically, the center particle size of the negative electrode material may be 9.0 μm or more or 10.0 μm or more. On the other hand, if the center particle size is excessively large, exceeding 15.0 μm, a problem may occur in the uniform thickness quality of the electrode plate, resulting in a problem that the performance of the battery may vary depending on the part. Therefore, in one embodiment of the present invention, the upper limit may be 15.0 μm. More specifically, the center particle size of the negative electrode material may be 12.0 μm or less.

[0132]

[0133] Additionally, the silicon content of the negative electrode material for a lithium secondary battery according to one embodiment of the present invention may be 30 wt% or more and 70 wt% or less.

[0134]

[0135] According to one embodiment of the present invention, a negative electrode material for a lithium secondary battery can secure high capacity characteristics of the negative electrode material by containing 30 wt% or more of the silicon. More specifically, the silicon content may be 40 wt% or more. On the other hand, if the silicon is excessively included in the negative electrode material, the silicon particles 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 may contain the silicon in an amount of 70 wt% or less based on the total weight of the negative electrode material for a lithium secondary battery. More specifically, the silicon content may be 60 wt% or less.

[0136]

[0137] As described above, the negative electrode material for a lithium secondary battery according to the present invention can secure high capacity characteristics and excellent lifespan characteristics by including nano-sized first silicon particles and micro-sized second silicon particles surrounded by a carbon coating layer.

[0138]

[0139] Specifically, the negative electrode material according to an embodiment of the present invention may have a discharge capacity of 1250 mAh / g or more, an initial efficiency of 84.0% or more, and a 50-cycle lifespan of 60.0% or more. In another embodiment, the negative electrode material may have a discharge capacity of 1500 mAh / g or more, an initial efficiency of 87.0% or more, and a 50-cycle lifespan of 65.0% or more.

[0140]

[0141] Hereinafter, a method for manufacturing an anode material for a lithium secondary battery of the present invention will be described. However, the following method for manufacturing an anode material for a lithium secondary battery is merely an example, and it is not necessary for the anode material for 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.

[0142]

[0143] A method for manufacturing an anode material for a lithium secondary battery according to one embodiment of the present invention may include the steps of: preparing first silicon particles having a particle size of less than 1.00 μm and second silicon particles having a particle size of 1.00 μm or more; mixing the first silicon particles, the second silicon particles, and pitch to obtain a precursor; pressurizing and molding the precursor; carbonizing the precursor after the pressurizing and molding to obtain a molded body; and crushing and classifying the molded body. The D90 particle size of the second silicon particles may be 5.00 μm or more and 15.0 μm or less.

[0144]

[0145] Each step is explained in detail below.

[0146]

[0147] Step of preparing first silicon particles and second silicon particles

[0148] According to one embodiment of the present invention, first silicon particles having a particle size of less than 1.00 μm and second silicon particles having a particle size of 1.00 μm or more can be prepared. At this time, as described above, the D90 particle size of the second silicon particles can be 5.00 μm or more and 15.0 μm or less.

[0149]

[0150] In order to obtain the first silicon having a particle size of less than 1.00 μm, a non-limiting embodiment of the present invention may pulverize the silicon raw material through mechanical milling.

[0151]

[0152] As an example, the mechanical milling can be performed using stabilized zirconia. Furthermore, to improve nano-processing efficiency, suppress the generation of fine particles, and prevent oxidation of silicon particles, 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 are available in various sizes and can be utilized in process design, and are therefore not limited thereto.

[0153]

[0154] 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.

[0155]

[0156] 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.

[0157]

[0158] Meanwhile, with respect to the second silicon particles, the relative particle size ratio derived by Equation 1 below may be 0.20 or more and 0.99 or less. Since this has been described above with respect to the negative electrode material of the present invention, specific details will be omitted.

[0159]

[0160] (Formula 1) Relative particle size ratio = D90 particle size (μm) of the second silicon particle / D50 particle size (μm) of the negative electrode material for lithium secondary batteries

[0161]

[0162] Step of obtaining a precursor by mixing

[0163] After preparing the first silicon particles and the second silicon particles, they can be mixed with pitch to obtain a cathode precursor.

[0164]

[0165] The mixing of the first silicon particles, the second silicon particles and the pitch described above may be performed simultaneously, but it is also possible that at least two of the three are mixed first and then the remaining one is mixed.

[0166]

[0167] If, according to one embodiment of the present invention, the first silicon particles and the second silicon particles are mixed first and then the pitch is added, the mixture of the first silicon particles and the second silicon particles can be spray-dried to remove the solvent, and the pitch can be added to the spray-dried body obtained thereby and then mixed to obtain a precursor.

[0168]

[0169] As described above with respect to the negative electrode material, as a non-limiting example, the weight ratio of the second silicon particles added in the mixture may be 10 wt% or more and 80 wt% or less with respect to the total weight of the first silicon particles and the second silicon particles.

[0170]

[0171] Additionally, the above mixing can be performed through a milling process via contact with a powder, and non-limiting examples thereof include mechanofusion or a ball mill. When performing a milling process via contact with a powder, the independent flow of the first silicon particles can be reduced when mixed with a solvent.

[0172]

[0173] And, according to another embodiment of the present invention, a conductive material may be additionally mixed to improve the conductivity of the negative electrode material, and as described above, the conductive material may be at least one of natural graphite and artificial graphite.

[0174]

[0175] Additionally, as a non-limiting example, the center particle size (D50) of the conductive material may be smaller than the center particle size of the precursor so that the conductive material can be completely captured within the precursor, and as a non-limiting example of the present invention, the center particle size of the conductive material may be 8 μm to 10 μm.

[0176]

[0177] Step of pressurizing and molding the precursor

[0178] According to one example of the present invention, a specific pressure can be applied to the precursor for a specified time range to minimize the pores present within the precursor. Specifically, when pressurizing is performed in this manner, the pitch can fill the micropores within the precursor, thereby reducing the specific surface area of ​​the negative electrode material and improving the electrochemical properties. As a non-limiting example, the pressurizing can be performed by filling a self-manufactured mold with the precursor powder and using a pressurizing device, and the resulting semi-finished product can be specified in the form of a block.

[0179]

[0180] A step of carbonizing a precursor to obtain a molded body

[0181] The present invention not only evaporates volatile components existing within the existing precursor by carbonizing the precursor at 800°C or higher, but also solidifies 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 reduce capacity and efficiency. Therefore, the carbonization may be performed at a temperature range of 1000°C or lower. In particular, the carbonization may be performed in an inert atmosphere to suppress oxidation of silicon particles.

[0182]

[0183] Step of crushing and classifying the molded body

[0184] According to a method for manufacturing an anode material for a lithium secondary battery according to one embodiment of the present invention, the molded body can be pulverized and classified. Through this, an anode material of a desired size can be obtained. As a non-limiting example, the pulverization can be performed by dry pulverization, and the dry pulverization can be performed using a jet mill or a pin mill.

[0185]

[0186] Step of coating carbon on the cathode material

[0187] As described above, after obtaining the negative electrode material by crushing and classifying, one example of the present invention may additionally include a step of coating the surface of the negative electrode material with carbon.

[0188]

[0189] 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.

[0190]

[0191] Meanwhile, according to a method for manufacturing a negative electrode material for a lithium secondary battery according to another embodiment of the present invention, a step of coating carbon on the surface of the first silicon particle before the mixing described above may be included.

[0192]

[0193] More specifically, the method for manufacturing the negative electrode material may include a step of preparing first silicon particles having a particle size of less than 1.00 μm; a step of carbon-coating the first silicon particles; a step of adding second silicon particles having a particle size of 1.00 μm or more and a carbon-based material to the first silicon particles after the carbon coating and mixing them to obtain a mixture; a step of heat-treating the mixture after the mixing to obtain a molded body; and a step of pulverizing and classifying the molded body.

[0194]

[0195] At this time, the carbon coating step can be performed by adding pitch to the first silicon particles and then carbonizing them, and the carbon-based material can be at least one of petroleum-based pitch, coal tar, PAA, and PVA having a softening point of less than 250°C as described above.

[0196]

[0197] In this way, when carbon coating is directly performed on the first silicon particles before mixing, unlike the case where a carbon precursor such as pitch is indirectly coated as described above, conductivity in the primary particle state can be secured preferentially, so there is an advantage in that the capacity and efficiency characteristics of the entire negative electrode material can be further increased.

[0198]

[0199] In addition, if the contents described for each step in this specification are contents that can be easily adopted by a person skilled in the art, the same can be applied even in a case where carbon coating is directly performed on the first silicon particle and then the second silicon particle and pitch are mixed according to another embodiment of the present invention.

[0200]

[0201] For example, the weight ratio of the second silicon particles may be 10 wt% or more and 80 wt% or less based on the total weight of the first silicon particles and the second silicon particles. In addition, a conductive material may be additionally mixed during the mixing, and the conductive material may be at least one of natural graphite and artificial graphite. In addition, when preparing the first silicon, the silicon raw material may be pulverized through mechanical milling, and the solvent in the mechanical milling may be ethanol or IPA. In addition, the mixing may be performed through a milling process through contact with a powder, and the method for manufacturing the negative electrode material may additionally include a step of coating carbon on the surface of the manufactured negative electrode material.

[0202]

[0203] Hereinafter, a method for manufacturing a negative electrode of a lithium secondary battery of the present invention will be described in detail.

[0204]

[0205] 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.

[0206]

[0207] 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.

[0208]

[0209] 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.

[0210]

[0211] 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.

[0212] (Example)

[0213] (1) Manufacturing of cathode material

[0214] First, a silicon raw material (Poly-Si) having a half width at half maximum of a particle size distribution of 0.2 degrees or more was prepared. Next, the silicon raw material was pulverized using stabilized zirconia having a size of 0.1 mm, thereby obtaining a slurry of first silicon particles having a particle size of less than 1.00 μm and a D90 particle size of 200 nm. In addition, the pulverization was performed in an ethanol solvent having a purity of 99%, and the solid content ratio was 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, flake graphite having a center particle size (D50) of 8.00 μm and second silicon particles having a half width at half maximum of a particle size distribution of less than 0.2 degrees and a particle size of 1.00 μm or more were added to the slurry of the first silicon particles obtained by the above-described process. At this time, the weight ratio of the added first silicon particles and the second silicon particles with respect to the total weight of the negative electrode material is shown in Table 1 below. In addition, the D90 particle size of the second silicon particles, along with the weight ratio, is also shown in Table 1. This was then spray-dried to obtain a powder state. Thereafter, petroleum pitch was added, and mixing using mechanofusion was performed to manufacture a negative electrode precursor. The pitch had a fixed carbon ratio of 70% or more and a β-resin value of 25%. Thereafter, the precursor was pressurized to obtain a block-shaped semi-finished product. Next, the semi-finished product was carbonized at a temperature of 900°C in an inert atmosphere. Afterwards, after going through a pulverization process using a JET mill, a carbon raw material such as petroleum pitch or coal tar, PAA, or PVA having a softening point of less than 250°C 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 in an inert atmosphere at a temperature of 900°C, and the negative electrode material was obtained through sieving.

[0215]

[0216] (2) Manufacturing of cathode

[0217] 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.

[0218]

[0219] 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.

[0220]

[0221] (3) Electrochemical evaluation

[0222] 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.

[0223]

[0224] The discharge capacity, initial efficiency, and 50-cycle life of the above battery were measured and are shown in Table 2 below.

[0225]

[0226] 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.

[0227] Classification 2 Silicon Particles 1st Silicon Particles (Wt%) 2nd Silicon Particles Weight Ratio to Total Silicon Particles (Wt%) Anode Material Center Particle Size (D50) (μm) Relative Particle Size Ratio Weight % D90 Particle Size (μm) Comparative Example 105.050010.5-Invention Example 1155.03033.310.20.49 Invention Example 2255.02055.59.90.51 Invention Example 3355.01077.710.80.46 Comparative Example 2505.0010010.90.46 Comparative Example 309.050010.5-Invention Example 4159.03033.310.80 .93Invention Example 5259.02055.511.20.89Invention Example 6359.01077.712.50.80Comparative Example 4509.0010012.80.78Comparative Example 5013.050010.5-Comparative Example 61513.03033.311.21.34Comparative Example 72513.02055.512.31.22Comparative Example 85013.0010016.80.89

[0228] Discharge capacity (mAh / g) Initial efficiency (%) Lifespan (%@50 cycle) Comparative example 1121383.578.5 Invention example 1129584.575.8 Invention example 2158885.676.4 Invention example 3169287.668.5 Comparative example 2174287.839.8 Comparative example 3121383.578. 5 Invention Example 4141686.575.3 Invention Example 5174587.575.4 Invention Example 6178588.469.4 Comparative Example 4185289.235.6 Comparative Example 5121383.578.5 Comparative Example 6152586.554.5 Comparative Example 7171487.248.5 Comparative Example 8198089.218.9

[0229] The electrodes including the negative electrode materials of Comparative Examples 1, 3, and 5, in which the weight ratio of the second silicon particles is less than 10 wt% with respect to the total weight of the first silicon particles and the second silicon particles, could not secure high-capacity characteristics.

[0230]

[0231] In addition, Comparative Examples 2, 4 and 8, in which the weight ratio of the second silicon particles was more than 80 wt%, had poor 50-cycle lifespans.

[0232]

[0233] In Comparative Examples 5 to 7, where the relative particle size ratio was outside the range proposed by the present invention, the D90 of the second silicon particle became excessively large compared to the central particle size of the negative electrode material, so that the structure of the negative electrode material collapsed and excellent electrochemical properties could not be secured.

[0234]

[0235] On the other hand, invention examples 1 to 6, which satisfy all the conditions proposed by the present invention, were excellent in discharge capacity, initial efficiency, and 50 cycle characteristics. Fig. 1 is a schematic diagram briefly showing the negative electrode material for a lithium secondary battery obtained by the above-described manufacturing method. As can be seen from the drawing, the negative electrode material includes a conductive material (3) together with the first silicon particle (1) and the second silicon particle (2) within the carbon coating layer (4).

Claims

1. First silicon particles having a particle size of less than 1.00 μm; Second silicon particles having a particle size of 1.00 μm or more; and A carbon coating layer surrounding the first silicon particle is included, The D90 particle size of the above second silicon particles is 5.00 μm or more and 15.0 μm or less, An anode material for a lithium secondary battery, having a relative particle size ratio of 0.20 or more and 0.99 or less, as derived by Equation 1 below. (Formula 1) Relative particle size ratio = D90 particle size of second silicon particle (μm) / D50 particle size of negative electrode material for lithium secondary battery (μm) 2. In paragraph 1, The above carbon coating layer is a negative electrode material for a lithium secondary battery made of soft carbon.

3. In paragraph 2, The above graphitized carbon is an anode material for a lithium secondary battery derived from at least one of coal-based pitch and petroleum-based pitch.

4. In paragraph 3, The above-mentioned coal-based pitch is an anode material for a lithium secondary battery having a fixed carbon ratio of 60% or more and a beta resin value of 10% or more.

5. In paragraph 1, A negative electrode material for a lithium secondary battery, wherein the D90 particle size of the first silicon particle is 30 nm or more and 500 nm or less.

6. In paragraph 1, A negative electrode material for a lithium secondary battery, wherein the weight ratio of the second silicon particles is 10 wt% or more and 80 wt% or less with respect to the total weight of the first silicon particles and the second silicon particles.

7. In paragraph 1, A negative electrode material for a lithium secondary battery, wherein the half width of the particle size distribution of the first silicon particle is 0.2 or more.

8. In paragraph 1, A negative electrode material for a lithium secondary battery additionally containing a challenging material.

9. In paragraph 8, The above-mentioned challenging material is a negative electrode material for a lithium secondary battery, which is at least one of natural graphite and artificial graphite.

10. In paragraph 1, A negative electrode material for a lithium secondary battery having a center particle size (D50) of 8.0 μm or more and 15.0 μm or less.

11. A step of preparing first silicon particles having a particle size of less than 1.00 μm and second silicon particles having a particle size of 1.00 μm or more; A step of obtaining a precursor by mixing the first silicon particles, the second silicon particles, and pitch; A step of pressurizing and molding the above precursor; A step of carbonizing the precursor after the above pressurized forming to obtain a molded body; and A step of crushing and classifying the above-mentioned molded body; A method for manufacturing an anode material for a lithium secondary battery, wherein the D90 particle size of the second silicon particles is 5.00 μm or more and 15.0 μm or less.

12. A step of preparing first silicon particles having a particle size of less than 1.00 μm; A step of coating the first silicon particle with carbon; After the carbon coating, a step of adding second silicon particles having a particle size of 1.00 μm or more and a carbon-based material to the first silicon particles and mixing them to obtain a mixture; A step including a step of heat-treating the mixture after the above mixing to obtain a molded body; and A step of crushing and classifying the above-mentioned molded body; A method for manufacturing an anode material for a lithium secondary battery, wherein the D90 particle size of the second silicon particles is 5.00 μm or more and 15.0 μm or less.

13. In paragraph 12, A method for manufacturing an anode material for a lithium secondary battery, wherein the carbon-based material is at least one of petroleum pitch, coal tar, PAA, and PVA having a softening point of less than 250°C.

14. In paragraph 11 or 12, A method for manufacturing an anode material for a lithium secondary battery, wherein the weight ratio of the second silicon particles is 10 wt% or more and 80 wt% or less with respect to the total weight of the first silicon particles and the second silicon particles.

15. In paragraph 11 or 12, A method for manufacturing a negative electrode material for a lithium secondary battery, wherein a conductive material is additionally mixed during the above mixing.

16. In paragraph 15, A method for manufacturing an anode material for a lithium secondary battery, wherein the above-mentioned challenging material is at least one of natural graphite and artificial graphite.

17. In paragraph 11 or 12, A method for manufacturing an anode material for a lithium secondary battery, comprising the step of obtaining the first silicon by pulverizing a silicon raw material through mechanical milling when preparing the first silicon.

18. In paragraph 17, A method for manufacturing an anode material for a lithium secondary battery, wherein the solvent in the mechanical milling is ethanol or IPA.

19. In paragraph 11 or 12, The above mixing is a method for manufacturing a negative electrode material for a lithium secondary battery, which is performed through a milling process via contact mediation with powder.

20. In paragraph 11 or 12, A method for manufacturing an anode material for a lithium secondary battery, further comprising a step of coating the surface of the manufactured anode material with carbon.

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