Silicon negative electrode active material, negative electrode, and secondary battery comprising same

Abstract

Disclosed is a silicon negative electrode active material for improving the electrochemical performance of a secondary battery. According to an aspect of the present invention, provided is a silicon negative electrode active material comprising silicon particles and a carbon material on the silicon particles, wherein the carbon content ratio (C0) of the silicon negative electrode active material satisfies Expression 1 below. [Equation 1]: 20 wt%≤C0={B / (A+B)}x100≤60 wt% In Expression 1, A is the silicon content in the silicon negative electrode active material, and B is the carbon content in the silicon negative electrode active material.

Description

Silicon negative electrode active material, negative electrode, and secondary battery containing the same

[0001] The present disclosure relates to a silicon negative electrode active material, and more specifically, to a silicon negative electrode active material, a negative electrode, and a secondary battery including the same.

[0002] The rapid growth of the secondary battery market has led to a surge in demand for high-capacity batteries, which in turn has fueled a surge in demand for silicon anode materials, which theoretically offer high capacities. However, during charge / discharge cycles, the volume expansion of the silicon anode material can lead to physical cracking and side reactions, making it difficult to achieve the theoretical capacity. Furthermore, the detachment of the silicon anode material from the current collector can damage the anode, limiting its ability to achieve high cycle performance.

[0003] To prevent physical breakage due to volume expansion of silicon anode materials, a method was employed to control the size of silicon particles to less than 150 nm. However, synthesizing silicon particles at the nanoscale presented challenges for mass production. To address this, a technology was introduced to crush silicon minerals to achieve particle sizes below 150 nm. However, simply crushing the primary particles to less than 150 nm resulted in excessively high specific surface areas, resulting in reduced initial capacity and difficulty in adhesion to the electrode.

[0004] According to one aspect of the present invention, a silicon negative electrode active material is provided in which volume expansion due to insertion / de-insertion of lithium ions during the charging / discharging process of a secondary battery is effectively suppressed.

[0005] According to another aspect of the present invention, there is provided a silicon negative electrode active material capable of improving electrochemical performance, such as initial coulombic efficiency, specific capacity, and capacity retention rate, of a secondary battery.

[0006] According to another aspect of the present invention, a method for manufacturing a silicon negative electrode active material capable of effectively controlling carbon content is provided.

[0007] According to another aspect of the present invention, there is provided a cathode capable of effectively suppressing side reactions between an electrolyte and a cathode.

[0008] According to another aspect of the present invention, a secondary battery having excellent cycle performance is provided.

[0009] The purposes of the present invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the present invention can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof described in the specification.

[0010] According to a first aspect of the present invention, a silicon negative electrode active material is provided, which comprises silicon particles and a carbon material on the silicon particles, wherein the ratio (C0) of the carbon content of the silicon negative electrode active material satisfies the following equation 1.

[0011] [Formula 1]

[0012] 20 wt%≤C0={B / (A+B)}x100≤60 wt%

[0013] In the above formula 1, A is the silicon content of the silicon negative electrode active material, and B is the carbon content of the silicon negative electrode active material.

[0014] According to the second aspect of the present invention, in the first aspect, the ratio of the carbon content of the silicon negative electrode active material may be 30 wt% or more and 45 wt% or less.

[0015] According to a third aspect of the present invention, in the first or second aspect, the ratio of the carbon content of the silicon negative electrode active material may be 35 wt% or more and 45 wt% or less.

[0016] According to a fourth aspect of the present invention, in any one of the first to third aspects, a pore having a long side size of 300 nm or more may not exist in a cross-section of the silicon negative electrode active material.

[0017] According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the silicon negative electrode active material includes a first region having a radius of 0 or more and 1 / 3 or less, a second region having a radius of more than 1 / 3 and 2 / 3 or less, and a third region having a radius of more than 2 / 3 and 3 / 3 or less, based on a midpoint on a long axis of a cross-section from which the silicon negative electrode active material is cut, and the ratios of carbon contents of each of the first to third regions may be the same or different. Here, a radius of 0 may mean a midpoint on a long axis of a cross-section from which the silicon negative electrode active material is cut. Alternatively, the first region may be a region having a radius of more than 0 and 1 / 3 or less.

[0018] According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the silicon negative electrode active material includes a first region having a radius of 0 or more and 1 / 3 or less, a second region having a radius of more than 1 / 3 and 2 / 3 or less, and a third region having a radius of more than 2 / 3 and 3 / 3 or less, based on a midpoint on the long axis of a cross-section from which the silicon negative electrode active material is cut, and in each of the regions, a unit area of ​​100 nm 2 A silicon negative electrode active material can be provided in which the difference in each carbon content of any two points included in the negative electrode active material is 10% or less in absolute value (unit: weight%). Specifically, in each of the above regions, a unit area of ​​100 nm 2The difference in the carbon content of any two points included in may be 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0.1% or less in absolute value, and more specifically, in each of the above regions, a unit area of ​​100 nm 2 The difference in the carbon content of any two points included in can be 0%. That is, in each of the above regions, a unit area of ​​100 nm 2 The carbon contents of any two points contained in may be identical.

[0019] According to the seventh aspect of the present invention, the ratio of the carbon content in each of the first to third regions in the fifth or sixth aspect may be different from each other.

[0020] According to an eighth aspect of the present invention, in any one of the fifth to seventh aspects, the ratio of the carbon content of the first region may be lower than the ratio of the carbon content of the second region.

[0021] According to a ninth aspect of the present invention, in any one of the fifth to eighth aspects, the ratio of the carbon content of the first region may be lower than the ratio of the carbon content of the third region.

[0022] According to a tenth aspect of the present invention, in any one of the fifth to ninth aspects, the ratio of the carbon content of the second region may be lower than the ratio of the carbon content of the third region.

[0023] According to an eleventh aspect of the present invention, in any one of the first to tenth aspects, the ratio of the carbon content may decrease as it goes deeper toward the center from the surface of the silicon negative electrode active material.

[0024] According to the twelfth aspect of the present invention, in any one of the first to eleventh aspects, the BET specific surface area is 10 m 2 / g or less, a silicon negative electrode active material can be provided.

[0025] According to a thirteenth aspect of the present invention, a negative electrode is provided comprising a silicon negative electrode active material according to any one of the first to twelfth aspects.

[0026] According to a fourteenth aspect of the present invention, a secondary battery is provided, comprising: a negative electrode according to the thirteenth aspect; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0027] According to a fifteenth aspect of the present invention, in any one of the first to fourteenth aspects, the carbon content of the first region (R1) may be 6 to 47 wt%, 6 to 44 wt%, 7 to 40 wt%, 8 to 36 wt%, 9 to 35 wt%, 10 to 30 wt%, 11 to 29 wt%, 12 to 28 wt%, 13 to 27 wt%, 14 to 26 wt%, 15 to 25 wt%, 16 to 24 wt%, 17 to 23 wt%, 18 to 22 wt%, 19 to 21 wt% or 20 to 21 wt%, and specifically may be 20.06 to 21 wt%.

[0028] According to a sixteenth aspect of the present invention, in any one of the first to fifteenth aspects, the carbon content of the second region (R2) may be 9 to 50 wt%, 10 to 49 wt%, 11 to 48 wt%, 15 to 44 wt%, 17 to 40 wt%, 20 to 38 wt%, 21 to 36 wt%, 25 to 33 wt%, 26 to 32 wt%, 27 to 32 wt%, 28 to 32 wt%, 29 to 32 wt%, or 30 to 31.65 wt%.

[0029] According to a seventeenth aspect of the present invention, in any one of the first to sixteenth aspects, the carbon content of the third region (R3) may be 20 to 65 wt%, 22 to 65 wt%, 25 to 60 wt%, 30 to 59 wt%, 35 to 55 wt%, 40 to 54 wt%, 45 to 53 wt%, 46 to 52 wt%, 47 to 51 wt%, 49 to 51 wt%, or 50 to 50.03 wt%.

[0030] The solutions to the above problems do not enumerate all the features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the detailed description below.

[0031] According to one aspect of the present invention, volume expansion of a silicon anode active material due to lithium ion insertion / de-insertion during the charge / discharge process of a secondary battery can be effectively suppressed. Accordingly, one aspect of the present invention can simultaneously improve the initial coulombic efficiency, specific capacity, and capacity retention rate of a secondary battery by improving the mechanical durability of the silicon anode active material.

[0032] In addition to the aforementioned effects, specific effects of the present invention are described below along with specific details for implementing the invention. Furthermore, the effects of the present invention are not limited to the effects described above and can be readily achieved using the means and combinations thereof described in the specification.

[0033] FIG. 1 is a cross-sectional view of a silicon negative electrode active material according to one embodiment of the present invention.

[0034] Figure 2a is a FIB (Focused ion beam)-SEM (Scanning electron microscope) photograph of a silicon negative electrode material before heat treatment in the method according to Comparative Example 2.

[0035] Figure 2b is a FIB-SEM photograph of a silicon negative electrode material after heat treatment according to the method of Comparative Example 2.

[0036] Figure 3a is a FIB-SEM photograph of a silicon negative electrode material before heat treatment in the method according to Example 8.

[0037] Figure 3b is a FIB-SEM photograph of a silicon negative electrode material after heat treatment according to the method of Example 8.

[0038] Figure 4a is a SEM photograph of the surface of a silicon negative electrode material before 100 cycles in the method according to Comparative Example 2.

[0039] Figure 4b is a SEM photograph of the surface of a silicon negative electrode material after 100 cycles in the method according to Comparative Example 2.

[0040] Figure 5a is a SEM photograph of the surface of a silicon negative electrode material before 100 cycles in the method according to Example 8.

[0041] Figure 5b is an SEM photograph of the surface of a silicon negative electrode material after 100 cycles in the method according to Example 8.

[0042] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0043] If a term expressed as a component in this specification includes a functional expression, it may be defined to encompass not only the function in question but also other functions that can be clearly understood by a person skilled in the art.

[0044] When multiple embodiments are described in this specification, the effects of the present invention may be defined to include not only the operational effects derived from each embodiment itself, but also the effects resulting from the organic combination of each embodiment. For example, even if Embodiments 1 and 2 are described independently in this specification, unless the context clearly indicates otherwise, the effects resulting from the organic combination of Embodiments 1 and 2 may also be included in the effects of the present invention.

[0045] The numerical range indicated by the term 'to' in this specification refers to a numerical range that includes the values ​​described before and after the term as the lower limit and the upper limit, respectively. When multiple numerical values ​​are disclosed as the upper and lower limits of an arbitrary numerical range, the numerical range disclosed in this specification can be understood as any numerical range that has any one of the multiple lower limit values ​​and any one of the multiple upper limit values ​​as the lower limit and the upper limit, respectively. For example, when the specification describes a to b, or c to d, it can be understood that a or more and b or less (a~b), a or more and d or less (a~d), c or more and d or less (c~d), or c or more and b or less (c~b) is described.

[0046] As used herein, terms such as "about" or "substantially" mean a reasonable amount of variation from the term that does not significantly alter the final result. These terms may be interpreted to include a variation of at least ±5% or at least ±10%, provided that such variation does not alter the meaning of the term and render it invalid.

[0047] In this specification, the term "layer" or film may include cases where it is formed not only over the entire area when observing the area where the layer or film exists, but also cases where it is formed over only a portion of the area. For example, the surface of the layer or film may be defined to include a flat shape, a non-flat shape, and a combination thereof; or a continuous shape, a discontinuous shape, and a combination thereof. For example, when another element is formed as a layer or film directly on top of one element, the coverage of the other element on the surface of the one element may be defined as 1% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 99% or more.

[0048] In this specification, the average particle diameter of the particles is the particle diameter (D) when the cumulative percentage in the volume-based particle size distribution curve is 50% when measured by a laser diffraction particle size distribution measuring device. 50 ) can be defined as

[0049] In this specification, "weight average molecular weight" or "number average molecular weight" refers to a standard polystyrene-converted molecular weight, which can be analyzed using a GPC (Gel permeation chromatography) device. Here, the GPC analysis method can use tetrahydrofuran as a developing solvent, and can be performed under the analysis conditions of a sample concentration of 5 mg / mL, a sample introduction amount of 100 μL, a temperature of 40°C, and a flow rate of 1 mL / min.

[0050] According to one aspect of the present invention, a silicon negative electrode active material is provided, which comprises silicon particles and a carbon material on the silicon particles, wherein the carbon content ratio (C0) of the silicon negative electrode active material satisfies the following equation 1.

[0051] [Formula 1]

[0052] 20 wt%≤C 0= {B / (A+B)}x100≤60 wt%

[0053] In the above formula 1, A is the silicon content (weight %) of the silicon negative electrode active material, and B is the carbon content (weight %) of the silicon negative electrode active material.

[0054] Conventional silicon anode materials have a problem in that cracks occur on the surface due to volume expansion of the silicon anode active material caused by the insertion / de-insertion of lithium ions during the charge / discharge process of secondary batteries. To further improve mechanical durability, a process of coating the silicon anode active material with carbon materials was introduced. However, simply introducing carbon materials has made it difficult to simultaneously improve the initial coulombic efficiency, specific capacity, and capacity retention of secondary batteries. On the other hand, simply crushing silicon particles and using them has a problem in that the specific surface area becomes too high, which reduces the initial efficiency and capacity, and reduces the adhesiveness. To solve this problem, a process of agglomerating primary particles into secondary particles using a spray dryer has been attempted. However, the high specific surface area still results in problems such as loss of initial efficiency and capacity. According to one aspect of the present invention, by controlling the carbon content of the silicon anode active material within the numerical range described in Equation 1 based on the total weight of the silicon anode active material, the volume expansion of the silicon anode active material due to insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be effectively suppressed. Accordingly, the present invention can implement the effect of simultaneously improving the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery by improving the mechanical durability of the silicon anode active material. According to another aspect of the present invention, the problem of initial efficiency and capacity loss occurring due to the high specific surface area of ​​the aforementioned secondary battery can be solved.

[0055] Below, the configuration of the present invention is described in more detail.

[0056] 1. Silicon negative electrode material

[0057] silicon particles

[0058] The silicon particles according to the present invention can improve the capacity performance of a secondary battery and, at the same time, prevent destruction of the particles even when the volume of the particles expands as lithium ions are inserted.

[0059] The silicon particles according to the present invention are silicon particles crushed into nano-sizes, and are composed of Si, SiOx(0 <x≤2), Si-C 복합체 및 Si-Y 합금(Y는 알칼리금속, 알칼리토금속, 전이금속, 13족 원소, 14족 원소 및 희토류 원소로 이루어진 군에서 선택된 어느 하나의 원소이다)으로 이루어진 군에서 선택되는 1종 이상을 포함할 수 있고, 구체적으로 실리콘(Si)을 포함할 수 있다. 본 발명의 일 실시형태에 따르면, 상기 실리콘 입자가 분쇄된 실리콘일 경우 이차전지의 용량 특성이 더욱 개선될 수 있다.

[0060] In some embodiments of the present invention, the average particle diameter of the silicon particles may be 800 nm or less, 700 nm or less, 600 nm or less, or 500 nm or less, specifically 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more; and 120 nm or less, 150 nm or less, 200 nm or less, 300 nm or less, 400 nm or less, or 500 nm or less, and more specifically 50 to 500 nm, 60 to 400 nm, 70 to 300 nm, 80 to 300 nm, 80 to 200 nm, 90 to 150 nm, or 100 to 120 nm. According to some embodiments of the present invention, the lifespan of the secondary battery can be further improved by having the average particle diameter of the silicon particles fall within the above numerical range.

[0061] In some embodiments of the present invention, the silicon particles may be pulverized silicon raw material powder. Specifically, the average particle diameter of the silicon raw material powder may be 10 to 100 μm, and more specifically, 30 to 50 μm. According to some embodiments of the present invention, since the average particle diameter of the silicon raw material powder satisfies the numerical range, the particle diameter of the silicon particles is controlled, thereby further improving the lifespan of the secondary battery.

[0062] In some examples, the silicon particles may be pulverized metal silicon (Metallurgical Grade Silicon; MG-Si). Specifically, the purity of the metal silicon may be 97 wt% or greater.

[0063] carbon materials

[0064] The silicon anode active material according to the present invention comprises a carbon material on the silicon particles. Specifically, the carbon material is a carbon source converted through heat treatment and chemical vapor deposition, and can suppress side reactions between the silicon particles and the electrolyte while effectively preventing volume expansion of the silicon particles.

[0065] In some embodiments of the present invention, the carbon material may be partially or completely coated on the surface of the silicon particle. Specifically, the shape of the carbon material may not be particularly limited, and for example, the carbon material may be in the form of a layer partially or completely coated on the surface of the silicon particle. According to some embodiments of the present invention, since the carbon material is partially or completely coated on the surface of the silicon particle, volume expansion of the silicon particle can be more effectively suppressed.

[0066] In some embodiments of the present invention, when the carbon material is formed in the form of a carbon layer, the thickness of the carbon layer may be 1 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, or 40 nm or more; and 110 nm or less, 100 nm or less, 90 nm or less, or 80 nm or less, and specifically 1 to 110 nm, 20 to 80 nm, or 40 to 80 nm. Specifically, when the thickness of the carbon layer satisfies the above numerical range, volume expansion of silicon particles during a charge / discharge process can be effectively prevented.

[0067] In some embodiments of the present invention, the carbon material may include a crystalline region and an amorphous region. Here, the criterion for distinguishing the crystalline region and the amorphous region is the crystallite size (L) of the thickness of the crystals constituting the carbon material in the c-axis direction (height direction). c ) may be. In some examples, the crystallite size of the crystalline region may be 100 nm or more, 200 nm or more, 500 nm or more, or 1,000 nm or more, and the crystallite size of the amorphous region may be less than 100 nm, less than 200 nm, less than 500 nm, or less than 1,000 nm. In some examples, the crystalline region may be derived from something manufactured by heat treating pitch, etc., and the amorphous region may be derived from acetylene gas, etc. of a chemical vapor deposition process. For example, a transmission electron microscope (TEM) analysis device may be used as an analysis method for the crystallite size.

[0068] In some embodiments of the present invention, based on the entire area of ​​the carbon material, the crystalline area may be 1% or more, 5% or more, or 10% or more; and 30% or less, 40% or less, or 50% or less, and specifically 1 to 50%, 5 to 40%, or 10 to 30%.

[0069] In some embodiments of the present invention, based on the entire area of ​​the carbon material, the amorphous area may be 50% or more, 60% or more, or 70% or more; and 90% or less, 95% or less, or 99% or less, and specifically 50 to 99%, 60 to 95%, or 70 to 90%.

[0070] Here, the crystalline and amorphous regions can be randomly distributed within the silicon negative electrode active material. Specifically, when the contents of the crystalline and amorphous regions are within the above numerical range, volume expansion of the silicon particles during the charge / discharge process can be effectively prevented.

[0071] Parameters

[0072] The ratio (C0) of the carbon content of the silicon negative electrode active material according to the present invention satisfies the following equation 1.

[0073] [Formula 1]

[0074] 20 wt%≤C 0= {B / (A+B)}x100≤60 wt%

[0075] In the above Equation 1, A is the silicon content of the silicon anode active material, and B is the carbon content of the silicon anode active material. Specifically, by adjusting the carbon content ratio of the silicon anode active material to 20 to 60 wt%, the initial coulombic efficiency and the capacity retention ratio of the secondary battery can be significantly improved. If the carbon content ratio of the silicon anode active material is below the above numerical range, the specific capacity of the secondary battery may increase, but the initial coulombic efficiency and the capacity retention ratio may be significantly low. If the carbon content ratio of the silicon anode active material exceeds the above numerical range, the initial coulombic efficiency and the specific capacity of the secondary battery may be significantly low.

[0076] In some examples, the silicon content and carbon content of the above silicon negative electrode material can be analyzed using EDS (Energy-dispersive X-ray spectroscopy) analysis equipment.

[0077] In some embodiments of the present invention, the ratio of the carbon content of the silicon negative electrode active material is 20 wt% or more, 20.62 wt% or more, 25 wt% or more, 29.16 wt% or more, 30 wt% or more, 31.33 wt% or more, 34.89 wt% or more, 35 wt% or more, 35.27 wt% or more, 38 wt% or more, 39 wt% or more, 40 wt% or more, 41 wt% or more, 42 wt% or more, 43 wt% or more, or 44 wt% or more; And it may be 44.47 wt% or less, 44.51 wt% or less, 44.75 wt% or less, 44.94 wt% or less, 45 wt% or less, 47.54 wt% or less, 48 ​​wt% or less, 48.16 wt% or less, 50 wt% or less, 53 wt% or less, 55 wt% or less, 59.20 wt% or less, or 60 wt% or less, and specifically 30 to 45 wt%, 35 to 45 wt%, 38 to 45 wt%, 39 to 45 wt%, 40 to 45 wt%, 41 to 45 wt%, 42 to 45 wt%, 43 to 45 wt%, or 44 to 45 wt%. According to some embodiments of the present invention, when the ratio of the carbon content of the silicon anode active material satisfies the above numerical range, the mechanical durability of the silicon anode active material is further improved, so that volume expansion of the silicon anode active material due to insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be effectively suppressed. Accordingly, the effect of simultaneously improving the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be realized.

[0078] In some embodiments of the present invention, the ratio of carbon content (C0) in the cut cross-section of the silicon negative electrode active material may be continuous. Here, the ratio of carbon content being continuous may mean that there is no pore with a long side of 300 nm or more in the cut cross-section of the silicon negative electrode active material. On the other hand, the ratio of carbon content being discontinuous may mean that there is at least one pore with a long side of 300 nm or more in the cut cross-section of the silicon negative electrode active material. For example, a method of measuring the continuity of the ratio of carbon content may be used, which involves cutting an anode active material having an average particle size of 15 μm using a FIB (Focused Ion Beam) and then measuring it with a SEM. According to some embodiments of the present invention, since the ratio of carbon content is continuous, the effect of simultaneously improving the initial coulombic efficiency, specific capacity, and capacity retention rate of a secondary battery may be realized.

[0079] FIG. 1 is a cross-sectional view of a silicon negative electrode active material according to one embodiment of the present invention.

[0080] Referring to FIG. 1, based on the midpoint on the long axis of the cross-section of the cut silicon anode active material (100), the silicon anode active material (100) according to the present invention may include a first region (R1) having a radius of 0 or more and 1 / 3 or less, a second region (R2) having a radius of more than 1 / 3 and 2 / 3 or less, and a third region (R3) having a radius of more than 2 / 3 and 3 / 3 or less. Here, the ratio of the carbon content of each of the first to third regions (R1 to R3) may be the same or different, and may be specifically different. According to some embodiments of the present invention, by satisfying the above formula 1 and controlling the carbon content of each of the first to third regions differently, the volume expansion of the silicon anode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be more effectively suppressed. Accordingly, the cycle stability of the secondary battery can be further improved.

[0081] In some embodiments of the present invention, the silicon negative electrode active material includes a first region (R1) having a radius of 0 or more and 1 / 3 or less, a second region (R2) having a radius of more than 1 / 3 and 2 / 3 or less, and a third region (R3) having a radius of more than 2 / 3 and 3 / 3 or less, based on a midpoint on the long axis of a cross-section from which the silicon negative electrode active material is cut, and in each of the regions, a unit area of ​​100 nm 2 The difference in the carbon content of any two points included in may be an absolute value of 10% or less. Specifically, in each of the above regions, a unit area of ​​100 nm 2 The difference in the carbon content of any two points included in may be 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1% or less, or 0.1% or less in absolute value, and more specifically, in each of the above regions, a unit area of ​​100 nm 2The difference in the carbon content of any two points included in can be 0%. That is, in each of the above regions, a unit area of ​​100 nm 2 The carbon contents of any two points included in may be the same. According to some embodiments of the present invention, a unit area of ​​100 nm 2 By ensuring that the difference in the carbon content of any two points included in the silicon anode material satisfies the above numerical range, the volume expansion of the silicon anode active material due to the insertion / de-insertion of lithium ions during the charging / discharging process of the secondary battery can be more effectively suppressed. Accordingly, the cycle stability of the secondary battery can be further improved.

[0082] In some embodiments of the present invention, the ratio of the carbon content of the first region (R1) may be lower than the carbon content of the second region (R2). According to some embodiments of the present invention, by adjusting the ratio of the carbon content of the first region (R1) to be lower than the ratio of the carbon content of the second region (R2), the volume expansion of the silicon negative electrode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0083] In some examples, the difference (R2-R1) between the ratio of the carbon content of the second region (R2) and the ratio of the carbon content of the first region (R1) may be 0.1 wt% or more, 5 wt% or more, 10 wt% or more, or 11 wt% or more; and 12 wt% or less, 13 wt% or less, 15 wt% or less, 17 wt% or less, 20 wt% or less, or 21 wt% or less, and specifically 0.1 to 21 wt%, 5 to 15 wt%, or 10 to 13 wt%, specifically 10 to 12 wt%, and more specifically 11 to 12 wt%. Specifically, when the difference (R2-R1) between the carbon content ratio of the second region (R2) and the carbon content ratio of the first region (R1) satisfies the above numerical range, the electrochemical performance of the secondary battery can be further improved.

[0084] In some embodiments of the present invention, the ratio of the carbon content of the first region (R1) may be lower than the ratio of the carbon content of the third region (R3). According to some embodiments of the present invention, by adjusting the ratio of the carbon content of the first region (R1) to be lower than the ratio of the carbon content of the third region (R3), the volume expansion of the silicon negative electrode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0085] In some examples, the difference (R3-R1) between the ratio of the carbon content of the third region (R3) and the ratio of the carbon content of the first region (R1) may be 0.1 wt% or more, 5 wt% or more, 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, or 28 wt% or more; and 31 wt% or less, 32 wt% or less, 33 wt% or less, 35 wt% or less, or 40 wt% or less, and specifically 0.1 to 40 wt%, 10 to 35 wt%, 15 to 33 wt%, 25 to 32 wt%, or 28 to 31 wt%. Specifically, when the difference (R3-R1) between the ratio of the carbon content of the third region (R3) and the ratio of the carbon content of the first region (R1) satisfies the numerical range, the electrochemical performance of the secondary battery can be further improved.

[0086] In some embodiments of the present invention, the ratio of the carbon content of the second region (R2) may be lower than the ratio of the carbon content of the third region (R3). According to some embodiments of the present invention, by adjusting the ratio of the carbon content of the second region (R2) to be lower than the ratio of the carbon content of the third region (R3), the volume expansion of the silicon negative electrode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0087] In some examples, the difference (R3-R2) in the ratio of the carbon content of the third region (R3) to the carbon content of the second region (R2) may be 0.1 wt% or more, 5 wt% or more, 10 wt% or more, 16 wt% or more, 17 wt% or more, or 18 wt% or more; and 19 wt% or less, 20 wt% or less, 25 wt% or less, 30 wt% or less, 33 wt% or less, or 34 wt% or less, and specifically 0.1 to 34 wt%, 5 to 20 wt%, 16 to 20 wt%, 17 to 20 wt%, 18 to 20 wt%, or 18 to 19 wt%. Specifically, when the difference (R3-R2) between the carbon content ratio of the third region (R3) and the carbon content ratio of the second region (R2) satisfies the numerical range, the electrochemical performance of the secondary battery can be further improved.

[0088] In some embodiments of the present invention, the carbon content may decrease as it goes deeper from the surface toward the center of the silicon negative electrode active material. According to some embodiments of the present invention, since the carbon content decreases as it goes deeper from the surface toward the center of the silicon negative electrode active material, the volume expansion of the silicon negative electrode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery may be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery may be further improved.

[0089] In some embodiments of the present invention, the carbon content of the first region (R1) is 6 wt% or more, 7 wt% or more, 8 wt% or more, 9 wt% or more, 10 wt% or more, 10.61 wt% or more, 11 wt% or more, 12 wt% or more, 13 wt% or more, 15 wt% or more, 15.03 wt% or more, 15.21 wt% or more, 16 wt% or more, 16.55 wt% or more, 17 wt% or more, 17.81 wt% or more, 18.97 wt% or more, or 20.06 wt% or more; And it may be 21 wt% or less, 22 wt% or less, 23 wt% or less, 24 wt% or less, 25 wt% or less, 25.38 wt% or less, 26 wt% or less, 27 wt% or less, 28 wt% or less, 29 wt% or less, 30 wt% or less, 31.86 wt% or less, 33 wt% or less, 34.33 wt% or less, 35 wt% or less, 35.22 wt% or less, 36 wt% or less, 38 wt% or less, 40 wt% or less, 41 wt% or less, 42 wt% or less, 43.64 wt% or less, 44 wt% or less, 45 wt% or less, 46 wt% or less, 46.34 wt% or less, or 47 wt% or less, and specifically 6 to 44 wt%, 7 to 40 wt%, 8 to 36 wt%, 9 to It may be 35 wt%, 10 to 30 wt%, 11 to 29 wt%, 12 to 28 wt%, 13 to 27 wt%, 14 to 26 wt%, 15 to 25 wt%, 16 to 24 wt%, 17 to 23 wt%, 18 to 22 wt%, 19 to 21 wt% or 20 to 21 wt%, and specifically 20.06 to 21 wt%.According to some embodiments of the present invention, by controlling the carbon content of the first region (R1) within the above numerical range, volume expansion of the silicon negative electrode active material due to insertion / de-insertion of lithium ions during the charging / discharging process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0090] In some embodiments of the present invention, the carbon content of the second region (R2) is 9 wt% or more, 10 wt% or more, 11 wt% or more, 13 wt% or more, 14 wt% or more, 15.96 wt% or more, 17 wt% or more, 19 wt% or more, 20 wt% or more, 21 wt% or more, 23 wt% or more, 25 wt% or more, 26 wt% or more, 27 wt% or more, 28 wt% or more, 29 wt% or more, or 30 wt% or more; And it may be 31.65 wt% or less, 32 wt% or less, 33 wt% or less, 34.54 wt% or less, 35 wt% or less, 35.58 wt% or less, 36 wt% or less, 37 wt% or less, 38 wt% or less, 39.91 wt% or less, 40 wt% or less, 43.75 wt% or less, 44 wt% or less, 46.55 wt% or less, 48 ​​wt% or less, 49 wt% or less, 49.02 wt% or less or 50 wt% or less, and specifically 9 to 50 wt%, 10 to 49 wt%, 11 to 48 wt%, 15 to 44 wt%, 17 to 40 wt%, 20 to 38 wt%, 21 to 36 wt%, 25 to 33 wt%, 26 to 32 wt%, It may be 27 to 32 wt%, 28 to 32 wt%, 29 to 32 wt%, or 30 to 31.65 wt%. According to some embodiments of the present invention, by controlling the carbon content of the second region (R2) within the above numerical range, the volume expansion of the silicon negative electrode active material due to the insertion / de-insertion of lithium ions during the charge / discharge process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0091] In some embodiments of the present invention, the carbon content of the third region (R3) is 20 wt% or more, 22 wt% or more, 22.37 wt% or more, 25 wt% or more, 30 wt% or more, 31.92 wt% or more, 34.05 wt% or more, 34.84 wt% or more, 35 wt% or more, 39.02 wt% or more, 40 wt% or more, 43.94 wt% or more, 46 wt% or more, 46.70 wt% or more, 47 wt% or more, 47.81 wt% or more, 49 wt% or more, or 50 wt% or more; And it may be 50.03 wt% or less, 50.46 wt% or less, 51 wt% or less, 52 wt% or less, 53 wt% or less, 54 wt% or less, 55 wt% or less, 56 wt% or less, 56.08 wt% or less, 59 wt% or less, 60 wt% or less, 64.86 wt% or less, or 65 wt% or less, and specifically 20 to 65 wt%, 22 to 65 wt%, 25 to 60 wt%, 30 to 59 wt%, 35 to 55 wt%, 40 to 54 wt%, 45 to 53 wt%, 46 to 52 wt%, 47 to 51 wt%, 49 to 51 wt%, or 50 to 50.03 wt%. According to some embodiments of the present invention, by controlling the carbon content of the third region (R3) within the above numerical range, the volume expansion of the silicon negative electrode active material due to insertion / de-insertion of lithium ions during the charging / discharging process of the secondary battery can be more effectively suppressed, and thus the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0092] physical properties

[0093] In some embodiments of the present invention, the BET specific surface area of ​​the silicon negative electrode active material is 10.0 m 2 / g or less, 6.0 m 2 / g or less, 4.0 m 2 / g or less, or 2.0 m 2 / g or less, specifically 1.0 m 2 / g or less, 0.9 m 2 / g or less, 0.8 m 2 / g or less, 0.79m 2 / g or less, 0.69 m 2 / g or less, 0.60 m 2 / g or less, or 0.58 m 2 / g or less, and more specifically 0.01 m 2 / g or more and any one of the above multiple numerical values ​​may be less than or equal to one or more of the above numerical values. According to some embodiments of the present invention, since the BET specific surface area of ​​the silicon negative electrode active material satisfies the numerical range, side reactions between the electrolyte and the negative electrode can be effectively suppressed.

[0094] Manufacturing method

[0095] A method for producing a silicon anode active material according to the present invention may include: (S1) preparing a mixture including a silicon nanoparticle dispersion and a carbon precursor solution; (S2) spray drying the mixture to produce a preliminary silicon anode active material; and (S3) producing a silicon anode active material from the preliminary silicon anode active material using a heat treatment method and a chemical vapor deposition method.

[0096] In some examples, the silicon nanoparticle dispersion may be a dispersion in which silicon nanoparticles are dispersed in a dispersion medium. Specifically, the average particle diameter of the silicon nanoparticles may be 150 nm or less. Furthermore, the dispersion medium is not particularly limited, and any compound capable of dispersing silicon nanoparticles may be selected, such as ethanol.

[0097] In some examples, the carbon precursor solution is not particularly limited and may be a solution of various carbon sources dissolved in a solvent. Specifically, the carbon source may be pitch such as petroleum pitch or coal tar pitch, aromatic carbon materials such as sugars, lignin, and cellulose, polyacrylonitrile, etc.

[0098] In some examples, various stirrers commonly used in the art can be used to mix the silicon nanoparticle dispersion and the carbon precursor solution. For example, the mixture can be stirred at 1,000 to 3,000 rpm for 60 to 120 minutes.

[0099] The preliminary silicon anode active material according to the present invention may be a composite in which silicon and carbon sources are granulated. Specifically, the aforementioned dispersion medium and solvent can be removed through the spray drying method, thereby allowing the silicon and carbon to be granulated in the form of a composite.

[0100] In some examples, the spray drying method is not particularly limited and may be a method performed with hot air at 50 to 150°C.

[0101] In some examples, the heat treatment method is not particularly limited and may be a method of heat treating the preliminary silicon negative electrode active material at 600 to 1200°C for 1 to 10 hours. Through the heat treatment method, empty regions randomly distributed within the interior of the preliminary silicon negative electrode active material may be formed.

[0102] In some examples, the chemical vapor deposition method is not particularly limited and may include a step of introducing carbon gas at a rate of 500 to 3000 sccm for 1 to 10 hours. Through the chemical vapor deposition method, carbon derived from the carbon gas can fill the empty space. Specifically, the carbon gas is not particularly limited and may include acetylene gas, ethylene, toluene, methane, and the like.

[0103] In some examples, the heat treatment method and the chemical vapor deposition method can be performed simultaneously without being separated in time.

[0104] 2. Cathode

[0105] According to another aspect of the present invention, a negative electrode comprising the silicon negative electrode active material is provided.

[0106] A method for manufacturing a negative electrode according to the present invention may include the steps of preparing a negative electrode slurry including a silicon negative electrode active material, an electrode conductive material, and a negative electrode binder according to some embodiments; coating and drying the negative electrode slurry on at least one surface of a negative electrode current collector to form a negative electrode active material layer; and rolling the current collector on which the negative electrode active material layer is formed.

[0107] In some examples, the negative electrode current collector may serve as a passage to transfer electrons from the outside to cause an electrochemical reaction in the negative electrode active material or to receive electrons from the negative electrode active material and send them to the outside. For example, the negative electrode current collector may be made of copper, stainless steel, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. For example, the thickness of the negative electrode current collector may be 6 μm to 55 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0108] In some examples, the step of rolling the current collector having the negative electrode active material layer formed thereon may be performed under conditions of a composite density of 1.0 g / cc or more. When using a silicon negative electrode active material according to some embodiments of the present invention, even if the rolling process is performed under the above conditions, the particles are not destroyed, thereby further improving the compression resistance. Here, the composite density refers to the degree to which the composite material is pressed well, and may vary depending on the pressure and thickness of the roll press.

[0109] In some embodiments of the present invention, the negative electrode slurry may further include a graphite-based active material in addition to the silicon negative electrode active material. For example, the graphite-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fibers, and graphitized mesocarbon microbeads.

[0110] The above-mentioned negative electrode binder can suppress separation between negative electrode active material (silicon negative electrode active material) particles, or between the negative electrode active material layer and the current collector. A polymer commonly used in electrodes in the relevant technical field can be used as the above-mentioned negative electrode binder. These negative electrode binders include, but are not limited to, poly(vinylidene fluoride co-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), polyacrylate, cellulose acetate, cellulose acetate butyrate. Examples of such polymers include, but are not limited to, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyano ethylsucrose, pullulan, and carboxyl methyl cellulose.

[0111] The conductive material for an electrode according to the present invention is not particularly limited and may be one selected from the group consisting of graphite, carbon black, carbon fibers or metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, or a mixture of two or more conductive materials thereof, and more specifically, may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials thereof.

[0112] 3. Secondary batteries

[0113] According to another aspect of the present invention, a secondary battery is provided, comprising: a cathode according to some embodiments; a cathode; a separator interposed between the cathode and the anode; and an electrolyte. The above-described parts and repeated descriptions are briefly described or omitted.

[0114] anode

[0115] The positive electrode according to the present invention may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a conductive material, and a positive electrode binder.

[0116] In some examples, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of copper, stainless steel, aluminum, titanium, calcined carbon, stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The positive electrode current collector may typically have a thickness of 6 to 20 μm.

[0117] In some examples, the cathode active material may include a lithium transition metal oxide. The lithium transition metal oxide may be, for example, Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Li x3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0≤y2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, O≤y3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Ni z1 O4(0.5 <x10<1.3, 0<z1<2), Li x11 Mn 2-z2 Co z2 O4(0.5 <x11<1.3, 0<z2<2), Li x12 CoPO4(0.5 <x12<1.3) 및 Li x13 FePO4(0.5 <x13<1.3)로 이루어진 군에서 선택되는 하나 이상을 포함할 수 있다.

[0118] In some examples, the conductive material used in the anode may be the same as or different from the conductive material used in the cathode.

[0119] In some examples, the positive electrode binder may be the same as or different from the negative electrode binder.

[0120] membrane

[0121] The separation membrane according to the present invention may be composed of a porous substrate or may include a porous substrate and a coating layer.

[0122] The porous substrate according to the present invention can be a porous structure having high resistance to electrolyte and fine pore diameters, capable of providing a path for lithium ions to move while electrically insulating the negative electrode and the positive electrode to prevent short circuits.

[0123] In some examples, any organic or inorganic material having electrical insulation properties may be used as a constituent material of the porous substrate without particular limitation. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulphone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, and may specifically include polyolefin. Polyolefin not only has excellent coating properties, but also allows for thinning the separator, increasing the ratio of the electrode active material layer in the battery, and thus increasing the capacity per volume.

[0124] In some examples, the weight average molecular weight (Mw) of the polyolefin may be 100,000 to 500,000 g / mol. If the weight average molecular weight of the polyolefin is less than the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may become difficult. The shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the secondary battery increases.

[0125] In some examples, the thickness of the porous substrate may be, for example, 3 to 50 μm or 4 to 30 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may increase excessively.

[0126] In some examples, the average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure that is interconnected with each other, so that gas or liquid can pass from one side of the porous substrate to the other side.

[0127] A separator according to another embodiment of the present invention may include a coating layer disposed on at least one surface of the porous substrate, which can improve the mechanical strength and heat resistance of a separator for a secondary battery and increase ion conductivity within the secondary battery.

[0128] The coating layer according to the present invention may include a binder polymer and inorganic particles.

[0129] The binder polymer according to the present invention can connect inorganic particles and stably fix them. The binder polymer may be, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used in combination.

[0130] According to another embodiment of the present invention, the weight ratio of the inorganic particles and the binder polymer (inorganic particles: binder polymer) may be 50:50 to 99:1, specifically 70:30 to 95:5. If the content ratio of the inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer may increase, thereby deteriorating the thermal stability improvement performance of the separator, and the pore size and porosity may decrease due to a decrease in the empty space formed between the inorganic particles, thereby causing a deterioration in the performance of the final battery, and if the content of the binder polymer is exceeded, the content of the binder polymer may be too small, thereby weakening the peeling resistance of the coating layer.

[0131] The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the secondary battery to which they are applied (e.g., Li / Li). + There are no particular restrictions as long as no oxidation and / or reduction reaction occurs at a reference voltage of 0 to 5 V. For example, when using inorganic particles with a high dielectric constant, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of the electrolyte salt, such as a lithium salt, in the liquid electrolyte.

[0132] For the reasons described above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport capability, or a mixture thereof.

[0133] In some examples, the inorganic particles having a dielectric constant of 5 or greater include Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-yTi y O3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x It may be a mixture of one or more selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0134] In some examples, the inorganic particles having the lithium ion transport capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0< x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x <4, 0 < y < 2), SiS2 series glass(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 series glass(Li x P y S z, 0 < x < 3, 0 < y < 3, 0 < z < 7) may be a mixture of one or more selected from the group consisting of:

[0135] In some examples, the average particle diameter (D) of the above inorganic particles 50 ) may be 1 nm to 10 μm, specifically 10 nm to 2 μm, and more specifically 50 nm to 1 μm, for forming a coating layer of uniform thickness and an appropriate porosity. The "average particle diameter (D50)" refers to the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter. The average particle diameter can be measured using a laser diffraction method. Specifically, after dispersing the target powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction pattern according to particle size when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0136] In some examples, the thickness of the coating layer may be 0.1 to 10 μm, specifically 1 to 3 μm, and more specifically 1.4 to 1.6 μm. When the thickness of the coating layer satisfies the above numerical range, the insulation and thermal stability of the separator can be increased, while the energy density of the battery can be improved.

[0137] electrolyte

[0138] The electrolyte according to the present invention may include a solvent and a lithium salt.

[0139] The solvent according to the present invention is, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl methyl carbonate (EMC), gamma-buturolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, propionic acid. It may be one or a mixture of two or more selected from the group consisting of ethyl, ethyl propionate and butyl propionate.

[0140] Lithium salt according to the present invention is, for example, NO3 - , F - , Cl - , Br - , I - , PF6 - It may contain anions such as:

[0141] The secondary battery according to the present invention may be a cylindrical, square, or pouch-shaped secondary battery, but is not particularly limited as long as it corresponds to a charging / discharging device.

[0142] In this specification, a process is performed by charging in a constant current (CC) / constant voltage (CV) manner until the voltage reaches 0.05 V (vs. Li) at a charge rate of 0.5 C, and discharging with a cut-off of 1.5 V at a discharge rate of 0.5 C to perform a formation process, and then charging in a CC / CV manner at 0.5 C until the voltage reaches 0.05 V, and discharging to 1.5 V at 0.5 C are repeated to perform a 100-cycle test, whereby the initial coulombic efficiency, specific capacity, and capacity retention of the half-cell can be measured.

[0143] In some embodiments of the present invention, the initial coulombic efficiency of the half-cell may be 80% or more, 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, or 92% or more, and any one or more of the plurality of lower limits may be 100% or less.

[0144] In some embodiments of the present invention, the specific capacity of the half-cell may be 380 mAh / g or more, 400 mAh / g or more, 408 mAh / g or more, or 430 mAh / g or more.

[0145] In some embodiments of the present invention, the capacity retention rate of the half-cell may be 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more, 99% or more, or 100%.

[0146] Another embodiment of the present invention can provide a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery pack can be used as a power source for one or more medium- to large-sized devices selected from the group consisting of, for example, power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0147] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited by the following contents.

[0148] [Manufacturing Example 1: Manufacturing of Silicon Negative Electrode Material]

[0149] <Examples 1 to 13: Silicon negative electrode active material with controlled carbon content>

[0150] Steps for preparing a silicon nanoparticle dispersion:

[0151] Average particle diameter (D 50 ) was added to a dispersion medium (ethanol) to prepare a silicon nanoparticle dispersion having a silicon nanoparticle content of 10 wt%.

[0152] Steps to prepare the first mixture:

[0153] Average particle diameter (D 50 ) was prepared by mixing pitch powder of 5 μm and solvent (Tetrahydrofuran, THF) in a weight ratio of 2:8.

[0154] A step of stirring the above silicon nanoparticle dispersion and the above first mixture and then spray drying:

[0155] A third mixture was prepared by stirring a second mixture containing the above silicon nanoparticle dispersion and the above first mixture at 3,000 rpm for 120 minutes. The third mixture was spray-dried with hot air at 85°C to prepare a preliminary silicon negative electrode active material in which silicon particles and pitch were granulated.

[0156] A step of manufacturing a silicon negative electrode active material by performing a heat treatment process and a chemical vapor deposition method on the above-mentioned preliminary silicon negative electrode active material:

[0157] The above-mentioned preliminary silicon anode active material particles were heat-treated under an inert atmosphere and a chamber at 800°C at the heat-treatment temperatures listed in Table 1 below for the heat-treatment times listed in Table 1 below to induce carbonization of the pitch. Simultaneously with the heat-treatment method, a chemical vapor deposition method was performed in which acetylene gas was injected for the heat-treatment times listed in Table 1 below to finally manufacture the silicon anode active material.

[0158] <Comparative Example: Silicon negative electrode material with uncontrolled carbon content>

[0159] <Comparative Examples 1 to 3: When the carbon content of the silicon negative electrode material is less than 20 wt%>

[0160] Comparative examples 1 and 2:

[0161] A silicon anode active material was manufactured using the same method as in Example 1, but the heat treatment times of the heat treatment process and the chemical vapor deposition process were changed to 100 minutes (Comparative Example 1) and 120 minutes (Comparative Example 2), respectively, to manufacture silicon anode active materials according to Comparative Examples 1 and 2.

[0162] Comparative Example 3:

[0163] A silicon anode active material was manufactured using the same method as Example 1, but the heat treatment temperature of the heat treatment process and the chemical vapor deposition process was changed to 830°C and the heat treatment time to 120 minutes, thereby manufacturing a silicon anode active material of Comparative Example 3.

[0164] <Comparative Examples 4 and 5: When the carbon content of the silicon negative electrode material exceeds 60 wt%>

[0165] A silicon anode active material was manufactured using the same method as Example 1, but the heat treatment times of the heat treatment process and the chemical vapor deposition process were changed to 500 minutes (Comparative Example 4) and 600 minutes (Comparative Example 5), respectively, to manufacture silicon anode active materials according to Comparative Examples 4 and 5.

[0166] [Experimental Example 1: Parameter Measurement Method for Silicon Negative Electrode Materials]

[0167] Referring to FIG. 1, based on the midpoint on the major axis of the cross-section of the silicon negative electrode active material (100) manufactured by the method according to Manufacturing Example 1, the silicon negative electrode active material (100) may include a first region (R1) having a radius of 0 or more and 1 / 3 or less, a second region (R2) having a radius of more than 1 / 3 and 2 / 3 or less, and a third region (R3) having a radius of more than 2 / 3 and 3 / 3 or less. Here, the midpoint on the major axis (L) may be the center point when the silicon negative electrode active material is assumed to be spherical.

[0168] The ratio (C0) of the carbon content of the silicon negative electrode active material described in Table 1 below can be calculated using Equation 1 below, the ratio (C1) of the carbon content of the first region (R1) can be calculated using Equation 2 below, the ratio (C2) of the carbon content of the second region (R2) can be calculated using Equation 3 below, and the ratio (C3) of the carbon content of the third region (R3) can be calculated using Equation 4 below. At this time, each of the silicon content (unit: weight %) and carbon content (unit: weight %) in Equations 1 to 4 below can be measured using an EDS (Energy-dispersive X-ray spectroscopy) analysis device from AMETECH.

[0169] [Formula 1]

[0170] C0={B / (A+B)}x100

[0171] In the above formula 1, A is the silicon content of the silicon negative electrode active material, and B is the carbon content of the silicon negative electrode active material.

[0172] [Formula 2]

[0173] C1={B1 / (A1+B1)}x100

[0174] In the above formula 2, A1 is the silicon content of the first region and B1 is the carbon content of the first region.

[0175] [Formula 3]

[0176] C2={B2 / (A2+B2)}x100

[0177] In the above formula 3, A2 is the silicon content of the second region and B2 is the carbon content of the second region.

[0178] [Formula 4]

[0179] C3={B3 / (A3+B3)}x100

[0180] In the above formula 4, A3 is the silicon content of the third region and B3 is the carbon content of the third region.

[0181] Heat treatment temperature (℃) Heat treatment time (min) Carbon content ratio of silicon negative electrode active material (C0, wt%) First region (C1, wt%) Second region (C2, wt%) Third region (C3, wt%) Example 1 800 150 20.62 10.61 15.96 22.37 Example 2 800 180 29.16 15.03 25.06 31.92 Example 3 800 240 31.33 18.97 27.24 34.05 Example 4 800 300 34.89 34.33 34.54 34.84 Example 5 830 300 35 .2716.5525.0139.02Example 680036043.8243.6443.7543.94Example 783036044.4735.2239.9146.70Example 885036044.5120.0631.6550.03Example 993036044.7517.8122.9456.8 0Example 1090036044.9415.2135.5850.46Example 1180044047.5446.3446.5547.81Example 1283044048.1625.3838.9153.09Example 1380048059.2031.8649.0264.86Comparative Example 18001001 0.515.168.6811.76Comparative Example 280012018.4317.7515.4019.50Comparative Example 383012018.9612.3018.9222.11Comparative Example 480050061.3333.7351.4466.04Comparative Example 580060070.7945.6755.8774.03

[0182] In the above Table 1, it can be confirmed that as the heat treatment time increases, the carbon content of the silicon anode active material increases as the content of carbon material penetrating into the pores of the silicon anode active material particles through heat treatment and chemical vapor deposition increases.

[0183] In addition, the carbon content inside the silicon negative electrode active material can be controlled by controlling the heat treatment temperature. It can be confirmed that as the heat treatment temperature increases, the carbon content in the outer region increases compared to the carbon content in the inner region. Specifically, in Examples 6 to 10, it can be confirmed that as the heat treatment temperature increases, the difference (R3-R2) between the carbon content in the third region (R3) and the carbon content in the second region (R2) and the difference (R2-R1) between the carbon content in the second region (R2) and the carbon content in the first region (R1) increase.

[0184] [Experimental Example 2: Measurement of the Specific Surface Area of ​​Silicon Anode Materials]

[0185] Nitrogen gas was adsorbed onto each silicon negative electrode active material manufactured by the method according to Manufacturing Example 1 above, and the amount of adsorbed nitrogen gas was measured to analyze the BET specific surface area of ​​the silicon negative electrode active material.

[0186] Heat treatment temperature (℃) Heat treatment time (min) Carbon content ratio of silicon negative electrode active material (C0, wt%) 1st region (C1, wt%) 2nd region (C2, wt%) 3rd region (C3, wt%) BET (m 2 / g)Example 180015020.6210.6115.9622.379.92Example 280018029.1615.0325.0631.928.84Example 380024031.3318.9727.2434.054.69Example 480030034.8934.3334.5434.841.95Example 583030035.271 6.5525.0139.021.73Example 680036043.8243.6443.7543.940.79Example 783036044.4735.2239.9146.700.66Example 885036044.5120.0631.6550.030.58Example 993036044.7517.8122.9456.800.66 Example 1090036044.9415.2135.5850.460.83Example 1180044047.5446.3446.5547.810.69Example 1283044048.1625.3838.9153.090.67Example 1380048059.2031.8649.0264.860.64Comparative Example 180010010.515 .168.6811.7615.88Comparative Example 280012018.4317.7515.4019.5013.64Comparative Example 383012018.9612.3018.9222.1111.96Comparative Example 480050061.3333.7351.4466.040.59Comparative Example 580060070.7945.6755.8774.030.54

[0187] In Table 2 above, it can be confirmed that as the heat treatment time increases, the carbon content of the silicon anode active material increases and the specific surface area decreases. This means that as the heat treatment time increases, the specific surface area of ​​the silicon anode active material decreases as the carbon material is layered in the pores of the silicon anode active material particles through heat treatment and chemical vapor deposition.

[0188] Furthermore, when the total carbon content is similar, it can be confirmed that the silicon anode active material manufactured to have a concentration gradient with a lower carbon content toward the center has a similar carbon content but a reduced specific surface area. This can be inferred from the fact that as the heat treatment temperature increases, a relatively greater amount of carbon is deposited on the surface, resulting in a lower specific surface area compared to anode active materials with similar carbon content.

[0189] [Experimental Example 3: Morphological Analysis of Pores in Silicon Anode Materials]

[0190] Fig. 2a is a FIB (Focused ion beam)-SEM (Scanning electron microscope) image of a silicon anode active material before heat treatment in a method according to Comparative Example 2. Fig. 2b is a FIB-SEM image of a silicon anode active material after heat treatment in a method according to Comparative Example 2. Fig. 3a is a FIB-SEM image of a silicon anode active material before heat treatment in a method according to Example 8. Fig. 3b is a FIB-SEM image of a silicon anode active material after heat treatment in a method according to Example 8.

[0191] Referring to FIGS. 2a, 2b, 3a, and 3b, it can be confirmed that the silicon negative electrode active material manufactured by the method according to Example 8 has no pores compared to Comparative Example 2.

[0192] [Experimental Example 4: Electrochemical Performance Evaluation of Half-Cells]

[0193] Preparation of half-cell samples:

[0194] Graphite: The negative electrode active material manufactured in the above Manufacturing Example 1: CMC (carboxy methyl cellulose): SBR (styrene-butadiene rubber) was mixed in a weight ratio of 87:10:1.5:1.5, and a solvent (H2O) was added to adjust the viscosity to manufacture a negative electrode slurry with a total solid content of 50 wt%. The manufactured negative electrode slurry was coated on a current collector (copper foil) with a thickness of 18 μm, dried at 90 ° C. for 60 minutes, and then adjusted to a composite density of 1.0 g / cc using a roll press, and then dried in a vacuum oven at 90 ° C. for 24 hours to manufacture a negative electrode (thickness: 40 μm). Li metal was used as the counter electrode, and a polyethylene material separator (thickness: 80 μm) was used as the separator, and an electrolyte was injected to manufacture a half-cell. At this time, an electrolyte was used in which 10 wt% of fluoroethylene carbonate (FEC) as an additive and 1M LiPF6 were dissolved in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1.

[0195] Evaluation method:

[0196] For the fabricated half-cells, the initial coulombic efficiency was measured at a current of 0.1 C, and the capacity retention was evaluated at a current of 0.5 C. Specifically, the formation process was performed by charging at a charge rate of 0.5 C in a constant current (CC) / constant voltage (CV) manner until the voltage reached 0.05 V (vs. Li), and then performing a cycle of discharging at a discharge rate of 0.5 C with a cut-off of 1.5 V. Subsequently, charging at 0.5 C in a CC / CV manner until the voltage reached 0.05 V, and discharging at 0.5 C to 1.5 V were repeated, and the specific capacity, initial coulombic efficiency, and capacity retention were measured for up to 100 cycles.

[0197] Carbon content ratio of silicon anode active material (C0, wt%) 1st region (C1, wt%) 2nd region (C2, wt%) 3rd region (C3, wt%) ICE (%) Specific capacity (mAh / g) Capacity retention rate (%) (@100 cycle) Example 1 20.6 2 10.6 1 15.9 6 22.3 7 8 2.2 5 10 8 7 Example 2 29.1 6 15.0 3 25.0 6 3 1.9 2 8 3.7 4 9 18 8 9 Example 3 31.3 3 18.9 27.2 4 34.0 5 8 5.5 4 8 4 9 1.1 Example 4 34.8 9 34.3 33 34.5 4 34.8 4 8 6.5 4 7 0 9 3.3 Example 5 35.27 1 6.5525.0139.028747694.7Example 643.8243.6443.7543.9490.944396.9Example 744.4735.2239.9146.7090.244798.8Example 844.5120.0631.6550.0392.1452100Example 944.7517.8122.9456.8090.24449 7.9 Example 1044.9415.2135.5850.4689.744598.1 Example 1147.5446.3446.5547.8185.843593.5 Example 1248.1625.3838.9153.0986.344293.8 Example 1359.2031.8649.0264.8684.340892.3 Comparative Example 110.515.1 68.6811.7674.353082Comparative Example 218.4317.7515.4019.5075.551184.5Comparative Example 318.9612.3018.9222.1178.551984.8Comparative Example 461.3333.7351.4466.0479.237687.1Comparative Example 570.7945.6755.8774.0376.433482.4

[0198] Referring to Table 3 above, when Examples 1 to 13 and Comparative Examples 1 to 5 are compared with each other in terms of simultaneously improving the initial Coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery according to the carbon content of the silicon anode active material, the initial Coulombic efficiency and the capacity retention rate of the secondary battery can be significantly improved when the carbon content of the silicon anode active material satisfies 20 to 60 wt%. If the carbon content of the silicon anode active material is below the above numerical range, the specific capacity of the secondary battery may increase, but the initial Coulombic efficiency and the capacity retention rate may be significantly low. If the carbon content of the silicon anode active material exceeds the above numerical range, the initial Coulombic efficiency and the specific capacity of the secondary battery may be significantly low.

[0199] Referring to Table 3 above, when Examples 1 to 13 are compared with each other from the viewpoint of simultaneously improving the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery according to the carbon content of the silicon anode active material, it can be confirmed that the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery are further increased by satisfying the carbon content of the silicon anode active material of 30 to 45 wt%.

[0200] In addition, in cases where there is no carbon around the silicon, as in Comparative Example 2, asymmetry in expansion may occur, which may cause asymmetric stress to continue to occur during continuous cycling, resulting in secondary particle breakage. However, if the carbon content in the silicon negative electrode active material is continuous, this phenomenon can be effectively prevented.

[0201] In addition, as in Examples 1 to 13, the carbon content decreases as it goes deeper from the surface toward the center of the silicon anode active material, so that the volume expansion rate of the surface is greater than that of the inside when the volume of the silicon anode active material is expanded due to the insertion / desorption of lithium ions during the charging / discharging process of the secondary battery, and accordingly, the initial coulombic efficiency, specific capacity, and capacity retention rate of the secondary battery can be further improved.

[0202] [Experimental Example 5: Morphology of silicon anode material after 100 cycles]

[0203] Fig. 4a is an SEM photograph of the surface of a silicon anode active material before 100 cycles in the method according to Comparative Example 2. Fig. 4b is an SEM photograph of the surface of a silicon anode active material after 100 cycles in the method according to Comparative Example 2. Fig. 5a is an SEM photograph of the surface of a silicon anode active material before 100 cycles in the method according to Example 8. Fig. 5b is an SEM photograph of the surface of a silicon anode active material after 100 cycles in the method according to Example 8.

[0204] Referring to FIGS. 4a, 4b, 5a, and 5b, the silicon anode active material manufactured by the method according to Example 8 exhibited the effect of no cracks on the surface, as compared to Comparative Example 2, by controlling the carbon content in the anode active material. On the other hand, cracks were observed on the surface of the silicon anode active material of Comparative Example 2 after 100 cycles.

[0205] [Experimental Example 6: Continuity Analysis of Carbon Content Ratios]

[0206] In order to confirm the uniform mixed phase of carbon, the negative electrode active material of Example 8 was used as a sample. Specifically, a cross-section of the silicon negative electrode active material of Example 8 with an average particle diameter of 15 μm was cut using a FIB (focused ion beam) and measured using a SEM. In the same way, the negative electrode active material of Comparative Example 2 with an average particle diameter of 15 μm was measured using the sample. As a result of the measurement, more than 10 pores with a long side of 300 nm were observed in the sample of Comparative Example 2, while no pores with a long side of 300 nm were observed in the sample of Example 8.

[0207] Ratio of carbon content (C0) 300 nm pore observation presence or absence Example 8 Continuity observed X Comparative example 2 Discontinuity 10 observed

[0208] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

[0209] [Explanation of symbols]

[0210] R1: Area 1

[0211] R2: Area 2

[0212] R3: Third Area

[0213] 100: Silicon negative electrode material

Claims

1. Silicon particles; and As a silicon negative electrode active material including a carbon material on the silicon particle, The ratio of carbon content of the above silicon negative electrode material (C 0 ) satisfies the following equation 1. Silicon cathode active material: [Formula 1] 20 wt%≤C 0 ={B / (A+B)}x100≤60 wt% In the above equation 1, A is the silicon content of the above silicon negative electrode active material, B is the carbon content of the above silicon negative electrode active material.

2. In paragraph 1, The carbon content ratio of the above silicon negative electrode active material is 30 wt% or more and 45 wt% or less, Silicon negative electrode active material.

3. In paragraph 1, The carbon content ratio of the above silicon negative electrode active material is 35 wt% or more and 45 wt% or less, Silicon negative electrode active material.

4. In paragraph 1, In the cross-section of the above silicon negative electrode active material, there is no pore having a size of 300 nm or more along the long side. Silicon negative electrode active material.

5. In paragraph 1, The above silicon negative electrode active material is, Based on the midpoint on the long axis of the cross-section where the above silicon negative electrode material is cut, A first region with a radius greater than or equal to 0 and less than or equal to 1 / 3, A second area with a radius greater than 1 / 3 and less than 2 / 3, and Includes a third area with a radius greater than 2 / 3 and less than or equal to 3 / 3, The ratio of the carbon content of each of the first to third regions is the same or different from each other, Silicon negative electrode active material.

6. In paragraph 1, The above silicon negative electrode active material is, Based on the midpoint on the long axis of the cross-section where the above silicon negative electrode material is cut, A first region with a radius greater than or equal to 0 and less than or equal to 1 / 3, A second area with a radius greater than 1 / 3 and less than 2 / 3, and Includes a third area with a radius greater than 2 / 3 and less than or equal to 3 / 3, In each of the above areas, unit area is 100 nm 2 The difference in the carbon content of any two points included in is less than 10% in absolute value. Silicon negative electrode active material.

7. In paragraph 5, The ratio of carbon content in each of the first to third regions is different from each other. Silicon negative electrode active material.

8. In paragraph 5, The ratio of the carbon content of the first region is lower than the ratio of the carbon content of the second region, Silicon negative electrode active material.

9. In paragraph 5, The ratio of the carbon content of the first region is lower than the ratio of the carbon content of the third region. Silicon negative electrode active material.

10. In paragraph 5, The ratio of the carbon content of the second region is lower than the ratio of the carbon content of the third region. Silicon negative electrode active material.

11. In paragraph 1, As the depth increases from the surface of the silicon negative electrode material toward the center, the proportion of carbon content decreases. Silicon negative electrode active material.

12. In paragraph 1, BET surface area is 10m 2 / g or less, silicon negative electrode active material.

13. A negative electrode comprising a silicon negative electrode active material according to Article 1.

14. Cathode according to Article 13; anode; A separator interposed between the cathode and the anode; and containing an electrolyte; Secondary battery.

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