Silicon nanoparticles for secondary battery negative electrode active material and method for producing same

Abstract

The present invention relates to an efficient method for producing silicon nanoparticles with controlled particle size while minimizing the content of impurities such as metals and oxygen. Specifically, the present invention relates to a method for producing silicon nanoparticles with a particle size of 80 nm or less by using fine polysilicon powder as a raw material. <D 50 <150nm and 100nm <D 90 A method for producing silicon nanoparticles having a particle size of <250 nm, a total metal impurity content of 200 ppm or less, and a total oxygen content of 10.0% or less can be provided.

Description

[Technical Field]

[0001] The present invention relates to silicon nanoparticles for use as an anode active material in secondary batteries, which can improve the initial discharge capacity (IDC), initial efficiency (ICE) and life characteristics of secondary batteries, and a method for manufacturing the same. [Background technology]

[0002] The improvement in the performance of secondary batteries is based on the components of the positive electrode material, negative electrode material, and electrolyte.

[0003] Among the above components, graphite-based materials, which are mainly used as the negative electrode active material of negative electrode materials, have excellent electrochemical performance and are commonly used commercially due to their low price. However, their theoretical capacity is limited to 370 mAh / g, which limits their application to high-capacity secondary batteries.

[0004] To overcome these limitations, non-graphite anode materials such as silicon, tin, and germanium have emerged as alternatives, with silicon attracting attention as a potential graphite replacement due to its theoretical capacity of 4000-4200mAh / g, more than 10 times that of graphite. However, despite its high theoretical capacity, silicon experiences a large volume expansion of approximately 400% during the charge and discharge process, which can lead to structural damage and a shorter lifespan.

[0005] As a method for alleviating the volume expansion of silicon, a method has been developed in which a carbon material is mixed to produce a composite material, and it is known to use silicon nanoparticles as the silicon material.

[0006] In order to exhibit excellent quality as a negative electrode active material so as to improve battery performance when applied to secondary batteries, silicon nanoparticles need to have low impurity contents such as metals and oxygen, and their particle size needs to be controlled.

[0007] For this reason, silicon nanoparticles have been produced using various silicon raw materials, but problems still exist, such as the low purity of the silicon raw materials themselves, high raw material and processing costs, and the tendency for impurities to flow in during processing.

[0008] Specifically, when metal silicon (MG-Si) is used as the silicon raw material, it has a high impurity content, and it is difficult to significantly reduce the impurity content even through the pulverization process. Therefore, when metal silicon is made into nanoparticles and used in secondary batteries, side reactions can occur during the charge and discharge of the battery, which ultimately has a negative impact on the battery's performance.

[0009] In addition, when silicon kerf, which is produced when cutting silicon ingots, is used as a raw material, the raw material itself may be highly pure, but it has the disadvantage of being easily contaminated by the lubricating oil and water used during the cutting process. Silicon oxidizes when it comes into contact with water, so when this is used as a raw material, the oxygen and impurity content increases, which can lead to a decrease in battery performance when used in secondary batteries.

[0010] In addition, when using polysilicon chunks or chips, the initial particle size is too large, which increases the number of grinding steps, increasing grinding time and costs.In addition, they are more expensive than other raw materials, making them inefficient and unsuitable for mass production.

[0011] Therefore, it is necessary to develop a method that can solve the above problems, minimize the content of impurities such as metals and oxygen, and efficiently manufacture and produce silicon nanoparticles with controlled particle size. Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION An object of the present invention is to provide an efficient method for producing silicon nanoparticles with controlled particle size while minimizing the content of impurities such as metals and oxygen.

[0013] Another object of the present invention is to provide an anode active material for a secondary battery prepared by the above method, which can improve the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery, and an anode material for a secondary battery and a secondary battery including the same.

[0014] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, the objects and advantages of the present invention can be realized and understood by the means and combinations thereof as set forth in the claims. [Means for solving the problem]

[0015] According to one aspect of the present invention, a method for manufacturing a polysilicon powder by dry grinding the polysilicon powder is provided. crushing Wet grinding of polysilicon fine powder to obtain silicon nanoparticles wherein the polysilicon powder is 0.2 mm <D 50 <0.4mm and 0.5mm <D 90 The silicon nanoparticles have a particle size of <1 mm and a total metal impurity content of 500 ppm or less, and <D 50 <150nm and 100nm <D 90 A method for producing silicon nanoparticles having a particle size of <250 nm and a total metal impurity content of 200 ppm or less can be provided.

[0016] According to another aspect of the present invention, 80 nm <D 50 <150nm and 100nm <D 90 Silicon nanoparticles can be provided having a particle size of <250 nm, a total metal impurity content of 200 ppm or less, and a total oxygen content of 10.0% or less.

[0017] According to yet another aspect of the present invention, it is possible to provide a secondary battery negative electrode material and a secondary battery, which contain the negative electrode active material for a secondary battery, which contains the silicon nanoparticles of the present invention. [Effects of the Invention]

[0018] According to the method for producing silicon nanoparticles of the present invention, since polysilicon fine powder, which has a relatively low raw material cost and a low content of metal impurities, is used as a raw material, the process cost can be reduced and silicon nanoparticles can be produced efficiently.

[0019] According to the method for producing silicon nanoparticles of the present invention, 80 nm <D 50 <150nm and 100nm <D 90 High purity and high quality silicon nanoparticles can be produced with particle sizes of <250 nm, total metal impurity contents of 200 ppm or less, and total oxygen contents of 10.0% or less.

[0020] By using silicon nanoparticles produced by the method for producing silicon nanoparticles according to the present invention as a negative electrode active material for a secondary battery, the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery can be improved.

[0021] The above-mentioned effects and specific effects of the present invention will be described in conjunction with the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a graph showing floating initial coulombic efficiency (ICE; discharge amount relative to initial charge amount) and initial discharge capacity (IDC; initial discharge capacity) in a half-cell test using silicon nanoparticles according to Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. [Figure 2]1 is a graph showing a capacity maintenance rate in a half-cell test in which silicon nanoparticles according to Example 1 of the present invention, Comparative Example 1, and Comparative Example 2 are applied. DETAILED DESCRIPTION OF THE INVENTION

[0023] The above-mentioned objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the technical concept of the present invention. In describing the present invention, if a detailed description of known technologies relating to the present invention is deemed to obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0024] Of the contents not described in this specification, explanations of those that can be sufficiently inferred from a technical standpoint by a person of ordinary skill in this technical field will be omitted.

[0025] In this specification, the term "metals of metal impurities" refers to metal elements that affect the quality when silicon nanoparticles are used as a negative electrode active material in a secondary battery, and typically refers to the 24 metal elements Al to Zn listed in Tables 2 and 3 of this specification, but is not necessarily limited to these.

[0026] In the following, when an arbitrary structure is arranged "on top (or bottom)" of a component or "above (or below)" a component, it means that the arbitrary structure is not only arranged in contact with the upper surface (or lower surface) of the component, but also that other structures may be interposed between the component and the arbitrary structure arranged above (or below) the component.

[0027] Also, when a certain component is described as being "connected", "coupled" or "joined" to another component, it should be understood that the above components may be directly connected or joined to each other, but other components may "intervene" between the components, or each component may be "connected", "coupled" or "joined" through other components.

[0028] In this specification, "<X" and "≦X" respectively mean less than X and less than or equal to X, and ">X" and "≧X" respectively mean greater than X and greater than or equal to X.

[0029] In this specification, the sizes of balls and beads mean "diameter".

[0030] Hereinafter, the method for manufacturing silicon nanoparticles according to the present invention will be described in detail.

[0031] The present invention uses polysilicon fine powder as a raw material for silicon nanoparticles. However, since polysilicon fine powder is a raw material with relatively low demand, its price is low, the impurity content is very low, and when used as an active material of a secondary battery, the performance of the secondary battery can be improved.

[0032] Specifically, the present invention selects polysilicon fine powder having a particle size of 0.2 mm < D 50 < 0.4 mm and 0.5 mm < D 90 < 1 mm and a total metal impurity content of 500 ppm or less as a raw material. By pulverizing these raw materials of polysilicon fine powder, preferably, 80 nm < D 50 < 150 nm and 100 nm < D 90 < 250 nm, more preferably, 100 nm < D 50 < 120 nm and 120 nm < D 90 < 200 nm and a total metal impurity content of 200 ppm or less, silicon nanoparticles can be produced.

[0033] The pulverization of the polysilicon powder can be carried out by either dry pulverization or wet pulverization. The size of the silicon particles should be gradually reduced by the pulverization. The pulverization apparatus is not particularly limited, and any apparatus commonly used in the art can be used.

[0034] For example, dry milling can be carried out using one type of apparatus selected from the group consisting of a ball mill apparatus, a jet mill apparatus, and a disk mill apparatus, and is preferably carried out using a ball mill apparatus.

[0035] When dry grinding is carried out using a ball mill, the balls selected for the ball mill may be approximately 10 to 50 mm in size, more preferably 10 to 30 mm in size, and even more preferably 20 to 25 mm in size.

[0036] Furthermore, when selecting a ball mill for dry milling, the material of the balls to be used may be a ceramic material, a metal material, a ceramic-metal composite material, etc., and is not particularly limited, but it is preferable not to use a material containing as a main component the metal impurities listed in Tables 2 and 3 of this specification. Furthermore, it is more preferable to select a material for the balls that has properties such as hardness and density that can exhibit excellent milling performance in the milling process, and as a specific example, zirconia balls containing zirconium (Zr) can be used.

[0037] Wet pulverization can be performed in two stages: primary wet pulverization and secondary wet pulverization. For example, wet pulverization can be performed using a bead mill. After the primary wet pulverization, the particle size of the silicon nanoparticles can be reduced to 80 nm by secondary wet pulverization. <D 50 <150nm and 100nm <D 90 It can be adjusted to meet <250nm.

[0038] For example, both the primary wet-pulverization and the secondary wet-pulverization can be carried out in a bead mill device, and in this case, it is preferable to select beads, which are the second beads used in the secondary wet-pulverization, having an average size smaller than that of the first beads used in the primary wet-pulverization.

[0039] Specifically, the average size of the first beads may be, for example, 0.2 to 5 mm, for example, 0.3 to 1 mm, or 0.3 to 0.5 mm, and the average size of the second beads may be, for example, 0.05 to 0.5 mm, 0.1 to 0.3 mm, or 0.1 to 0.2 mm, but are not limited to these, and the average size of the first beads must be larger than the average size of the second beads.

[0040] Furthermore, when selecting a bead mill for wet milling, the material of the beads used is not particularly limited and may be a ceramic material, a metal material, a ceramic-metal mixed material, or the like, but it is preferable not to use a material containing as a main component the metal impurities listed in Tables 2 and 3 of this specification. Furthermore, it is more preferable to select a material for the beads that has properties such as hardness and density that can exhibit excellent milling performance in the milling process, and as a specific example, zirconia beads containing zirconium (Zr) can be used.

[0041] Thus, a solvent is used when wet grinding is carried out, and an alcohol-based solvent can be used at this time, such as ethanol, propanol, or methanol.

[0042] Furthermore, in order to increase the degree of dispersion of silicon and prevent oxidation of silicon, an additive can be used together with a solvent when wet-milling, and for example, stearic acid can be used as the additive. Preferably, the stearic acid additive is dissolved in a solvent before starting wet-milling, and then stirred with silicon to increase the degree of dispersion while mixing.

[0043] By carrying out wet or dry milling, the impurity content can be even higher, as it is common for the material to be contaminated by substances such as lubricants used in cutting equipment and solvents such as water used in wet milling, and in particular the oxygen content can increase due to silicon oxidation.

[0044] If the oxygen content of silicon nanoparticles increases, their performance may be reduced when used as a negative electrode active material for a secondary battery. Therefore, it is important to control the total oxygen content of silicon nanoparticles to a low level. This is a separate characteristic from the impurity metal content and is a requirement for high-quality, high-purity silicon nanoparticles that must be met independently of the particle size control of the silicon nanoparticles. Therefore, the total oxygen content of the final silicon nanoparticles is preferably 10.0% or less.

[0045] Thus, the silicon nanoparticles produced according to the method for producing silicon nanoparticles of the present invention may have high purity and precisely controlled particle size, and therefore may have the effect of improving initial discharge capacity, initial efficiency, and life characteristics when applied to secondary batteries. [Example]

[0046] The structure and operation of the present invention will be described in more detail below with reference to preferred embodiments of the present invention, which are presented as preferred examples of the present invention and are not to be construed as limiting the present invention in any sense.

[0047] 1. Silicon Nanoparticle Production Polysilicon fine powder (OCI, ST900) was used as the raw material in Example 1, metal silicon (MG-Si) was used as the raw material in Comparative Example 1, and silicon kerf was used as the raw material in Comparative Example 2. Dry milling was performed in a ball mill using zirconia balls, and wet milling was performed in a bead mill using zirconia beads to produce silicon nanoparticles.

[0048] The initial particle sizes and final particle sizes of the raw materials in Example 1, Comparative Example 1, and Comparative Example 2, and the grinding conditions (size of balls or beads and grinding time) are as shown in Table 1 below.

[0049] [Table 1]

[0050] As shown in Table 1 above, for the sake of comparison between the experiments, the final particle sizes after grinding were adjusted to be as similar as possible, and since the initial particle sizes of the raw materials were different, the grinding processes were different.

[0051] In the wet grinding step, 100 parts by weight (600 g) of the raw material was mixed with 400 parts by weight (2400 g) of ethanol and 20 parts by weight (120 g) of stearic acid.

[0052] The metal contents of the silicon raw materials (before pulverization) in Example 1 and Comparative Examples 1 and 2 are shown in Table 2 below, and the metal impurity contents and oxygen contents of the silicon nanoparticles (after pulverization; in a slurry state) are shown in Table 3 below. The metal impurity contents were measured using Thermo Fisher's "iCAP 7600" equipment, and the oxygen contents were measured using LECO's "ONH836" equipment.

[0053] [Table 2]

[0054] [Table 3]

[0055] As can be seen from Tables 2 and 3 above, the silicon nanoparticles of Example 1 had a significantly lower content of impurity metal elements than the silicon nanoparticles of Comparative Examples 1 and 2.

[0056] Furthermore, although Example 1 underwent wet pulverization twice, the oxygen content was lower than that of Comparative Examples 1 and 2, in which wet pulverization was performed once or twice, and the total oxygen content of Example 1 satisfied the requirement of 10% or less.

[0057] 2. Half-Cell Test (1) Manufacturing of silicon-carbon composite materials Silicon-carbon composites were prepared using the silicon nanoparticle slurries prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively, and pitch (HSPP with a softening point of 240°C; OCI Co.), and the specific method is as follows.

[0058] After completely dissolving 4.5 g of pitch in 200 ml of THF (tetrahydrofuran), 40 g of crushed silicon nanoparticle slurry was added and stirred for over 1 hour. After drying using an evaporator, the dried powder was placed in a muffle furnace and heat-treated at 1000°C under a nitrogen gas atmosphere to produce a silicon-carbon composite.

[0059] (2) Manufacturing of half cells To analyze the electrochemical properties of the negative electrode material for secondary batteries, a negative electrode plate was fabricated using a powder mixture of 10% by weight of silicon-carbon composite and 90% by weight of artificial graphite as the negative electrode active material. The negative electrode plate was fabricated by casting a slurry containing the active material, conductive material (Super-P, Imerys Graphite & Carbon), and binder in a weight ratio of 94:1:5 onto copper foil. The binder was a mixture of CMC and SBR in a weight ratio of 3:7. The fabricated negative electrode plate was fabricated into a coin cell using Li metal as the counter electrode, and its electrochemical properties were confirmed.

[0060] (3) Measurement method and conditions for half-cell test The charge and discharge conditions were charge CC / CV: 0.01V / 0.01C, discharge CC 1.5V, and the rate limiting was 0.2C.

[0061] Using a half-cell TOSCAT-3100 device, the initial charge efficiency (ICE; discharge capacity relative to initial charge), initial charge capacity (ICC; initial charge capacity), and initial discharge capacity (IDC; initial discharge capacity) were measured and are shown in Table 4 below. A graph of the floating ICE and IDC is shown in Figure 1. Furthermore, the lifespan after 40 cycles was measured, and the capacity retention is shown in Figure 2 (horizontal axis: number of cycles, vertical axis: specific discharge capacity).

[0062] [Table 4]

[0063] As can be seen from Table 4, Figures 1 and 2 above, when the silicon nanoparticles of Example 1 were used, it was found that the initial charge capacity (ICC), initial discharge capacity (IDC), initial efficiency (ICE), etc. were superior in all aspects compared to Comparative Examples 1 and 2, which used other raw materials (MG-Si, Si kerf), and the capacity retention rate was also improved.

[0064] Although the present invention has been described above with reference to illustrative drawings, the present invention is not limited to the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention are not explicitly described and explained while the embodiments of the present invention are described above, it is natural that the effects that can be predicted by the configuration should also be recognized.

Claims

1. dry-milling the polysilicon fine powder; and wet-milling the dry-milled pulverized polysilicon fine powder to obtain silicon nanoparticles; Including, The polysilicon fine powder has a diameter of 0.2 mm<D ５０ <0.4 mm and 0.5 mm < D ９０ having a particle size of <1 mm and a total metal impurity content of 500 ppm or less; The silicon nanoparticles are 80 nm < D ５０ < 150 nm and 100 nm < D ９０ having a particle size of <250 nm and a total metal impurity content of 200 ppm or less; Method for producing silicon nanoparticles.

2. The total oxygen content of the silicon nanoparticles is 10.0% or less. The method for producing silicon nanoparticles according to claim 1 .

3. The dry milling is carried out in one type of apparatus selected from the group consisting of a ball mill apparatus, a jet mill apparatus, and a disk mill apparatus. The method for producing silicon nanoparticles according to claim 1 .

4. The wet pulverization is divided into primary wet pulverization and secondary wet pulverization, and is carried out in a bead mill. The primary wet pulverization and the secondary wet pulverization are performed using first beads and second beads having different sizes, and the average size of the second beads is smaller than the average size of the first beads. The method for producing silicon nanoparticles according to claim 1 .

5. The wet grinding is carried out by adding an alcohol-based solvent. The method for producing silicon nanoparticles according to claim 1 .

6. Add stearic acid to the alcohol-based solvent; The method for producing silicon nanoparticles according to claim 5 .

7. The silicon nanoparticles are used as a negative electrode active material for a secondary battery. The method for producing silicon nanoparticles according to claim 1 .

8. The silicon nanoparticles are used as a negative electrode material for a secondary battery. The method for producing silicon nanoparticles according to claim 1 .

9. The silicon nanoparticles are used as a secondary battery. The method for producing silicon nanoparticles according to claim 1 .

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