Negative active material comprising graphite and silicon, and method for preparing same

Abstract

The present invention relates to a negative active material comprising graphite and silicon, and a method for preparing same. The negative active material, according to one aspect of the present invention, comprises graphite and silicon, wherein the silicon content in the negative active material is 5 wt% to 80 wt%, and the silicon is uniformly distributed in the negative active material. A secondary battery, according to another aspect of the present invention, comprises: a negative electrode; a positive electrode; and a separator formed between the negative electrode and the positive electrode, wherein the negative electrode comprises the negative active material of the present invention. The method for preparing a negative active material, according to another aspect of the present invention, comprises the steps of: mixing graphite with silicon particles; and forming a negative active material comprising the graphite and the silicon particles by applying one or more forces selected from the group consisting of shear force, tensile force, and compressive force to the particles formed as a result of the mixing.

Description

Negative active material containing graphite and silicon and method for producing the same

[0001] The present invention relates to a negative electrode active material comprising graphite and silicon and a method for producing the same.

[0002] Demand for secondary batteries, particularly lithium secondary batteries, is rapidly increasing due to technological developments and increasing demand for mobile devices and electric vehicles.

[0003] Lithium secondary batteries have traditionally used lithium metal as the negative electrode, but as problems such as battery short-circuiting and the risk of explosion have been pointed out, the use of carbon-based active materials that allow reversible insertion and de-insertion of lithium ions and maintain structural and electrical properties is increasing.

[0004] As carbon-based active materials, various forms of carbon-based materials, including artificial graphite, natural graphite, and hard carbon, have been applied, and carbon-based compounds that allow reversible lithium ion intercalation and deintercalation while maintaining structural and electrical properties, especially graphite-based materials, are mainly used. Graphite-based materials are the most widely used because they can guarantee the life characteristics of lithium secondary batteries with excellent reversibility.

[0005] Since graphite-based active materials have a low discharge voltage of -0.2 V compared to lithium, batteries using graphite-based active materials can exhibit a high discharge voltage of 3.6 V, providing many advantages in terms of energy density of lithium batteries. However, these carbon-based compounds have problems such as limitations in theoretical maximum capacity, safety issues, and reduced battery productivity due to the hydrophobicity of carbon-based compounds. That is, when highly crystalline graphite is applied to lithium secondary battery negative electrodes, the exposure between the hexagonal networks where lithium can be inserted is small, so the insertion and de-insertion speed of lithium ions is slow, and the lattice spacing is very dense, so capacity deterioration occurs due to volume changes caused by lithium insertion and de-insertion.

[0006] The present invention provides an anode active material as an anode material used in a lithium secondary battery, and in particular, provides an anode active material for a lithium secondary battery that ensures stability by increasing electrostatic capacity and suppressing volume expansion of silicon.

[0007] In addition, the present invention seeks to provide a lithium secondary battery including a negative electrode composed of the negative electrode active material of the present invention.

[0008] Furthermore, the present invention seeks to provide a method for manufacturing a negative electrode active material in which the silicon particle content is controlled by controlling the force applied as a process control variable in the manufacturing method.

[0009] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person having ordinary skill in the relevant technical field from the description below.

[0010] According to one aspect of the present invention, a negative electrode active material is a negative electrode active material comprising graphite and silicon, wherein the silicon content is 5 wt% to 80 wt% of the negative electrode active material, and the silicon is uniformly distributed within the negative electrode active material.

[0011] Among the above negative active materials, the silicon content at the point where the silicon content is minimum may be 70% or more of the silicon content at the point where the silicon content is maximum.

[0012] The size of the above negative electrode active material may be 0.6 ㎛ to 30 ㎛.

[0013] The size of the negative electrode active material may be 0.6 ㎛ or more and 6 ㎛ or less, and the silicon content of the negative electrode active material may be 10 wt% to 45 wt%.

[0014] The size of the above negative electrode active material may be 2 ㎛ or more and 12 ㎛ or less, and the silicon content of the above negative electrode active material may be 30 wt% to 50 wt%.

[0015] The size of the above negative electrode active material may be 2 ㎛ or more and 30 ㎛ or less, and the silicon content of the above negative electrode active material may be 30 wt% to 80 wt%.

[0016] The particle size of the silicon may be 1:10 to 1:35.

[0017] The particle size of the silicon may be 1:25 to 1:70.

[0018] The particle size of the silicon may be 1:25 to 1:350.

[0019] The aspect ratio of the above negative electrode active material may be 0.8:1 to 1.2:1.

[0020] The above silicon particles may be in a form surrounded by the graphite.

[0021] According to another aspect of the present invention, a secondary battery comprises a negative electrode; a positive electrode; and a separator formed between the negative electrode and the positive electrode, wherein the negative electrode comprises the negative electrode active material of the present invention.

[0022] According to another aspect of the present invention, a method for producing a negative electrode active material comprises: a step of mixing graphite and silicon particles; and a step of applying at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force to the particles formed by the mixing, thereby forming a negative electrode active material comprising the graphite and the silicon particles.

[0023] The above force may include two or more forces selected from the group consisting of shear force, tensile force and compressive force.

[0024] The sum of one or more forces selected from the group consisting of shear force, tensile force and compressive force may be from 0.003 kW / g to 4 kW / g.

[0025] The size of the negative electrode active material may be controlled by controlling the size of the sum of one or more forces selected from the group consisting of the shear force, tensile force, and compressive force.

[0026] The silicon particles may be penetrated by the above force.

[0027] The above mixing step; and the step of forming a negative electrode active material including the graphite and the silicon particles; may be performed simultaneously.

[0028] In the step of forming a negative electrode active material including the graphite and the silicon particles by applying a force to the particles formed by the above mixture, the force may include at least one selected from the group consisting of a shear force, a tensile force, and a compressive force, and in the step of forming a negative electrode active material including the graphite and the silicon particles, the force may be applied in stages.

[0029] The stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force, and compressive force may be performed by dividing the sum of one or more forces selected from the group consisting of the above shear force, tensile force, and compressive force into five or more steps in which the sum of one or more forces selected from the group consisting of the above shear force, tensile force, and compressive force sequentially increases, and applying one or more forces selected from the group consisting of the above shear force, tensile force, and compressive force.

[0030] The stepwise application of the tensile and compressive forces may be such that the sum of one or more forces selected from the group consisting of the shear force, tensile force and compressive force starts from 0.002 to 0.004 kW / g.

[0031] The stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force may be such that the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at each step is greater than 100% and less than 660% of the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at the previous step.

[0032] The stepwise application of one or more forces selected from the group consisting of shear force, tensile force and compressive force may be such that the final step maintains the sum of one or more forces selected from the group consisting of shear force, tensile force and compressive force for 90 to 200 minutes.

[0033] According to one aspect of the present invention, an anode active material is provided as an anode material used in a lithium secondary battery, and in particular, an anode active material for a lithium secondary battery is provided that is advanced in both increasing electrostatic capacity and ensuring stability by suppressing volume expansion of silicon.

[0034] According to another aspect of the present invention, a lithium secondary battery including a negative electrode composed of the negative electrode active material of the present invention can be provided.

[0035] According to another aspect of the present invention, a method for manufacturing a negative electrode active material can be provided in which the silicon particle content is controlled by controlling the force applied as a process control variable in the manufacturing method.

[0036] FIG. 1 is a conceptual diagram showing the direction in which one or more forces selected from the group consisting of shear force, tensile force, and compressive force are applied in a method for manufacturing a negative electrode active material according to the present invention, and the resulting penetration of silicon into graphite.

[0037] Figure 2 is a conceptual diagram showing the process of silicon and graphite being pulverized and then recombined during the manufacturing process of graphite and silicon as a negative electrode active material according to the present invention.

[0038] Figure 3 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 1-1 and 1-2 of the present invention.

[0039] Figure 4 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 2-1 and 2-2 of the present invention.

[0040] Figure 5 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 3-1 and 3-2 of the present invention.

[0041] Figure 6 is a FIB-SEM image (silicon content by location) of a negative electrode material according to a comparative example.

[0042] Figure 7 is a graph of the discharge capacity of a battery including a negative electrode including a negative electrode active material of an embodiment of the present invention.

[0043] Hereinafter, embodiments are described in detail with reference to the attached drawings. However, the embodiments may be modified in various ways, and the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, or alternatives to the embodiments are included within the scope of the patent application.

[0044] The terms used in the examples are for illustrative purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood to not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0045] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which the embodiments pertain. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0046] In addition, when describing with reference to the attached drawings, the same components will be given the same reference numerals regardless of the drawing numbers, and redundant descriptions thereof will be omitted. When describing an embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted. In addition, when describing a component of an embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only to distinguish the component from other components, and the nature, order, or sequence of the component is not limited by the terms. When a component is described as being "connected," "coupled," or "connected" to another component, it should be understood that the component may be directly connected or connected to the other component, but another component may also be "connected," "coupled," or "connected" between each component.

[0047] Components included in one embodiment and components with common functions will be described using the same names in other embodiments. Unless otherwise stated, the descriptions given in one embodiment can be applied to other embodiments, and detailed descriptions will be omitted to the extent of overlap.

[0048] According to one aspect of the present invention, a negative electrode active material comprises graphite and silicon, wherein the silicon content is 5 wt% to 80 wt% of the negative electrode active material, and the silicon is uniformly distributed within the negative electrode active material. The silicon content in the negative electrode active material may be measured as a silicon content (ratio) measured at each point during a cross-sectional analysis of the negative electrode active material.

[0049] In order to increase the battery capacity of a lithium secondary battery, it is desirable to use silicon together with graphite as an anode active material, but silicon undergoes volume expansion during long-term operation, which shortens the battery life. According to the present invention, silicon particles are surrounded by graphite, or silicon is inserted (or positioned) into the pores of graphite or into the paths in which the pores expand internally, thereby acting as a frame and suppressing the volume expansion of the silicon. For example, when silicon expands into the free space within the pores or paths, or expands beyond the free space of the pores or paths, the graphite may act as a frame, resulting in a volume expansion suppression effect.

[0050] According to the present invention, by adding silicon particles, the electric capacity is increased while the volume expansion caused by the addition is suppressed.

[0051] The graphite of the present invention may be natural graphite, artificial graphite, soft carbon, hard carbon, expanded graphite, etc.

[0052] If the content of the silicon in the negative electrode active material is less than 5 wt%, the effect of increasing the regular capacity by adding silicon cannot be sufficiently obtained, and there may be a problem of a decrease in capacity. If the content of the silicon in the negative electrode active material exceeds 80 wt%, there may be a problem of a decrease in the battery capacity retention rate due to electrode destruction caused by volume expansion.

[0053] The content of the silicon in the negative electrode active material may be 5 wt% to 80 wt%; 10 wt% to 80 wt%; 20 wt% to 80 wt%; 25 wt% to 70 wt%; 30 wt% to 70 wt%; 30 wt% to 60 wt%; 10 wt% to 70 wt%; 10 wt% to 60 wt%; 10 wt% to 50 wt%; 20 wt% to 60 wt%; 30 wt% to 50 wt%; 40 wt% to 50 wt%.

[0054] Among the above negative active materials, the silicon content at the point where the silicon content is minimum may be 70% or more of the silicon content at the point where the silicon content is maximum. The silicon content is measured by the unit area (1 ㎛) on the FIB-SEM image. 2 ) can be measured by the silicon ratio, but is not limited thereto. The silicon content at the point where the silicon content is minimum is 70% or more of the silicon content at the point where the silicon content is maximum, which means that the minimum and maximum values ​​do not show a large difference and show a difference of within 30%, that is, it means that the silicon is uniformly distributed in the negative active material.

[0055] Preferably, the silicon content at the point where the silicon content is minimum among the negative active materials may be 80% or more, 90% or more, or 95% or more of the silicon content at the point where the silicon content is maximum.

[0056] The size of the above negative electrode active material may be 0.6 μm to 30 μm. The size of the above negative electrode active material is the particle diameter in the case of spherical particles, and the length corresponding to the longest length in the case of non-spherical particles. That is, in the case of a crushed ball with an elliptical cross-section, the size corresponds to the major diameter.

[0057] If the size of the above-mentioned negative electrode active material is smaller than 0.6 ㎛, there may be a problem of reduced initial efficiency, and if the size of the above-mentioned negative electrode active material is larger than 30 ㎛, there may be a problem of difficulty in producing it as a high-density electrode material.

[0058] The size of the negative electrode active material may vary depending on the intended use, and as shown in the examples below, it is possible to control the size, and a wide range of negative electrode active materials are included as follows.

[0059] Although not limited thereto, by way of example, the negative electrode active material can be manufactured by controlling the (average) size of the negative electrode active material within the range of Examples 1 to 3 below.

[0060] The size of the negative electrode active material is 0.6 ㎛ to 30 ㎛; 0.6 ㎛ to 20 ㎛; 0.6 ㎛ to 15 ㎛; 0.6 ㎛ to 12 ㎛; 1 ㎛ to 25 ㎛; 5 ㎛ to 25 ㎛; 5 ㎛ to 20 ㎛; 10 ㎛ to 20 ㎛; 10 ㎛ to 15 ㎛; 1 ㎛ to 25 ㎛; 1 ㎛ to 20 ㎛; 1 ㎛ to 15 ㎛; 1 ㎛ to 10 ㎛; 2 ㎛ to 30 ㎛; 2 ㎛ to 20 ㎛; 2 ㎛ to 15 ㎛; 2 ㎛ to 12 ㎛; 5 ㎛ to 30 ㎛; 10 ㎛ to 30 ㎛; 15 ㎛ to 30 ㎛; 20 ㎛ to 30 ㎛; or 25 ㎛ to 30 ㎛.

[0061] Meanwhile, the negative electrode active material of the present invention may have a silicon content within the negative electrode active material (a single particle) that varies depending on its size. That is, by adjusting the size and amount of applied force, the size of the negative electrode active material particle can be adjusted, thereby controlling the silicon content within the particle.

[0062] Although the present invention is not limited thereto, the size of the negative electrode active material may be 0.6 ㎛ or more and 6 ㎛ or less, and the silicon content in the negative electrode active material may be 10 wt% to 45 wt%.

[0063] Also, although the present invention is not limited thereto, the size of the negative electrode active material may be 2 ㎛ or more and 12 ㎛ or less, and the silicon content in the negative electrode active material may be 30 wt% to 50 wt%.

[0064] Also, although the present invention is not limited thereto, the size of the negative electrode active material may be 2 μm or more and 30 μm or less, and the silicon content in the negative electrode active material may be 30 wt% to 80 wt%.

[0065] That is, the silicon content is controlled according to the size of the negative electrode active material (particle), and this means that the size of the negative electrode active material can be controlled while simultaneously controlling the silicon content by controlling one or more forces selected from the group consisting of shear force, tensile force, and compressive force applied in a manufacturing process such as milling.

[0066] The particle size of the silicon may be 1:10 to 1:35 of the graphite, the particle size of the silicon may be 1:25 to 1:70 of the graphite, and the particle size of the silicon may be 1:25 to 1:350 of the graphite.

[0067] When the size of the silicon is within the above range relative to the size of the graphite, the graphite can act as a frame as a core to suppress the volume expansion of the silicon inserted inside.

[0068] If the particle size of the silicon: particle size of the graphite is smaller than 1:10 (i.e., if the particle size of the graphite is relatively small beyond a certain level), there may be a problem in that the silicon cannot effectively penetrate into the graphite, and thus exists as pure silicon independent particles that are not inserted into the graphite, and thus the graphite cannot exert its function of suppressing the volume expansion of the silicon. In addition, if the particle size of the silicon: particle size of the graphite is larger than 1:350 (i.e., if the particle size of the graphite is relatively large beyond a certain level), there may be a problem in that the graphite as a core becomes excessively large and cannot be used as a high-density electrode material.

[0069] The aspect ratio of the above negative electrode active material may be 0.8:1 to 1.2:1. The negative electrode active material may be a spherical shape with an aspect ratio of 1:1, but may be in the shape of a ball that is distorted in a certain direction. The negative electrode active material may be a perfect spherical shape, but since at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force is applied in a certain direction during the manufacturing process, it may be a shape that is not a perfect spherical shape but has a certain degree of spherical shape.

[0070] If the aspect ratio of the above-mentioned negative electrode active material exceeds the range of 0.8:1 to 1.2:1, i.e., if it is a rod- or needle-shaped particle that is too long in a certain direction, i.e., if the ellipticity becomes severe, there may be a problem of the SEI (Solid-Electrolyte-Interphase) layer being formed unevenly, thereby reducing the initial efficiency.

[0071] The silicon particles may be surrounded by the graphite. That is, the graphite may be wrapped around the silicon particles. The negative active material according to one embodiment of the present invention may be formed in a form in which graphite wraps around the silicon particles within the bulk particles. In this way, the graphite wraps around the silicon particles, thereby exhibiting the effect of suppressing volume expansion of the silicon particles as a frame.

[0072] According to another aspect of the present invention, a negative electrode comprises the negative electrode active material of the present invention.

[0073] According to another aspect of the present invention, a secondary battery comprises: a negative electrode; a positive electrode; and a separator formed between the negative electrode and the positive electrode, wherein the negative electrode comprises the negative electrode active material of the present invention. The secondary battery of the present invention may be a lithium secondary battery.

[0074] Below, a lithium secondary battery is described along with a negative electrode including the negative electrode active material of the present invention.

[0075] The secondary battery according to the present invention is a lithium secondary battery, in which silicon particles are uniformly dispersed from the surface of the negative electrode active material to the inside, and graphite surrounds the silicon particles, thereby suppressing volume expansion of the negative electrode active material during charging and discharging.

[0076] A lithium secondary battery comprises a negative electrode, a separator, and a positive electrode. Typically, the negative electrode, separator, and positive electrode of a lithium secondary battery are wound or folded and housed in a battery container. For example, the lithium secondary battery may be a large-scale thin-film battery. The lithium secondary battery may be, for example, a lithium ion secondary battery. Meanwhile, a separator is placed between the positive and negative electrodes to form a battery structure. For example, the battery structures are laminated in a bi-cell structure, then impregnated with an organic electrolyte, and the resulting product is housed in a pouch and sealed, thereby forming a lithium ion polymer secondary battery. Multiple battery structures are laminated to form a battery pack, and such a battery pack can be used in all devices requiring high capacity and high output. For example, it can be used in laptops, smartphones, power tools, electric vehicles, etc.

[0077] According to another aspect of the present invention, a method for producing a negative electrode active material comprises: a step of mixing graphite and silicon particles; and a step of applying at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force to the particles formed by the mixing, thereby forming a negative electrode active material comprising the graphite and the silicon particles.

[0078] FIG. 1 is a conceptual diagram showing the direction in which one or more forces selected from the group consisting of shear force, tensile force, and compressive force are applied in a method for manufacturing a negative electrode active material according to the present invention, and the resulting penetration of silicon into graphite, and FIG. 2 is a conceptual diagram showing the process in which silicon and graphite are pulverized and recombined during the manufacturing process of graphite and silicon of a negative electrode active material according to the present invention.

[0079] Referring to FIGS. 1 and 2, a method for manufacturing a negative electrode active material of the present invention is described. First, silicon and graphite particles are mixed, and then at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force is applied. At this time, the shear stress and at least one force selected from the group consisting of the shear stress and the shear force, the tensile force, and the compressive force are applied to the graphite particles with a time difference or simultaneously. Due to the shear stress, a gap is formed on the surface or inside of the graphite, or the graphite is pulverized into a smaller size. Due to the pressure, the gap on the surface or inside of the graphite is expanded into a path, or silicon (nanopowder) particles surround the pulverized graphite particles (including graphite with silicon penetrated (inserted) therein), and through this, graphite-silicon units may clump together to form a spherical complex.

[0080] Simultaneously, the silicon particles are also crushed into smaller sizes by one or more forces selected from the group consisting of shear (stress), tensile and compressive forces, and penetrate from the surface to the center through paths formed in the graphite or penetrate the crushed graphite and agglomerate outward. Furthermore, the completed composite can be transformed into a spherical shape by one or more forces selected from the group consisting of shear (stress), tensile and compressive forces.

[0081] The sum of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force may be from 0.003 kW / g to 4 kW / g. If the sum of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force is less than 0.003 kW / g, there may be a problem that silicon does not penetrate into the graphite or the composite does not become spherical, and if the sum of the tensile force and the compressive force is greater than 4 kW / g, there may be a problem that the graphite does not have a desired particle size and is pulverized.

[0082] The size of the negative electrode active material may be controlled by controlling the magnitude of the sum of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force. The size of the negative electrode active material is controlled by controlling the magnitude of the sum of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force, and thereby the content of silicon particles in the negative electrode active material can also be controlled.

[0083] The above mixing step; and the step of forming a negative electrode active material including the graphite and the silicon particles; may be performed simultaneously. After the mixing step, the step of forming a negative electrode active material including graphite and silicon particles by applying at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force may be performed sequentially, or the mixing step and the step of forming a negative electrode active material including graphite and silicon particles by applying at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force may be performed simultaneously without temporal distinction.

[0084] In the step of forming a negative electrode active material including the graphite and the silicon particles by applying at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force to the particles formed by the above mixture, the step may be to apply at least one force selected from the group consisting of a shear force, a tensile force, and a compressive force in stages.

[0085] As described as an example in the examples below, rather than applying one or more forces selected from the group consisting of shear force, tensile force, and compressive force to the mixed particles at the same level all at once, the force may be applied sequentially in stages while increasing the sum of one or more forces selected from the group consisting of shear force, tensile force, and compressive force. As can be confirmed through the examples and comparative examples below, it can be seen that the discharge capacity retention rate of the battery including the negative electrode including the negative electrode active material of the examples manufactured by applying one or more forces selected from the group consisting of shear force, tensile force, and compressive force sequentially and in stages is high.

[0086] As an example, the stepwise application of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force may be divided into five or more steps in which the sum of one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force sequentially increases, and the one or more forces selected from the group consisting of the shear force, the tensile force, and the compressive force are applied.

[0087] The stepwise application of one or more forces selected from the group consisting of the shear force, the tensile force and the compressive force may be such that the sum of the one or more forces selected from the group consisting of the shear force, the tensile force and the compressive force starts from 0.002 to 0.004 kW / g.

[0088] The stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force may be such that the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at each step is greater than 100% and less than 660% of the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at the previous step.

[0089] The stepwise application of one or more forces selected from the group consisting of shear force, tensile force and compressive force may be such that the final step maintains the sum of one or more forces selected from the group consisting of shear force, tensile force and compressive force for 90 to 200 minutes.

[0090] Hereinafter, the present invention will be described in more detail by way of examples and comparative examples.

[0091] However, the following examples are only intended to illustrate the present invention, and the content of the present invention is not limited to the following examples.

[0092] The particle sizes of graphite and silicon particles in the examples and comparative examples were measured using a MALVERN MASTERSIZER 3000 measuring device.

[0093] 1) 126 g of graphite particles with a D50 size of 6 ㎛ and 174 g of silicon particles with a D50 size of 75 nm were prepared and mixed.

[0094] 2) The above mixture was placed in a mixing device, and a negative electrode active material was manufactured by gradually increasing one or more forces selected from the group consisting of shear force, tensile force, and compressive force applied as shown below.

[0095] - under -

[0096] 1) An average force of 0.04 kW / g was applied for 20 minutes.

[0097] 2) An average force of 0.13 kW / g was applied for 5 minutes.

[0098] 3) An average force of 0.30 kW / g was applied for 7 minutes.

[0099] 4) An average force of 0.60 kW / g was applied for 12 minutes.

[0100] 5) An average force of 0.87 kW / g was applied for 15 minutes.

[0101] 6) An average force of 1.47 kW / g was applied for 55 minutes.

[0102] 7) An average force of 1.80 kW / g was applied for 20 minutes.

[0103] 8) An average force of 3.36 kW / g was applied for 150 minutes.

[0104] 9) Finally, the applied power was increased to 4 kW / g and maintained for 120 minutes, after which mixing was terminated.

[0105] The negative active material was manufactured twice under the same conditions (Example 1-1 and Example 1-2).

[0106] Example 2

[0107] 1) 126 g of graphite particles with a D50 size of 10 ㎛ and 174 g of silicon particles with a D50 size of 75 nm were prepared and mixed.

[0108] 2) The above mixture was placed in a mixing device, and a negative electrode active material was manufactured by gradually increasing one or more forces selected from the group consisting of shear force, tensile force, and compressive force applied as shown below.

[0109] - under -

[0110] 1) An average force of 0.04 kW / g was applied for 20 minutes.

[0111] 2) An average force of 0.13 kW / g was applied for 5 minutes.

[0112] 3) An average force of 0.30 kW / g was applied for 7 minutes.

[0113] 4) An average force of 0.60 kW / g was applied for 12 minutes.

[0114] 5) An average force of 0.87 kW / g was applied for 15 minutes.

[0115] 6) An average force of 1.47 kW / g was applied for 55 minutes.

[0116] 7) An average force of 1.80 kW / g was applied for 20 minutes.

[0117] 8) An average force of 3.36 kW / g was applied for 150 minutes.

[0118] 9) Finally, the applied power was increased to 4 kW / g and maintained for 120 minutes before mixing was terminated.

[0119] The negative active material was manufactured twice under the same conditions (Example 2-1 and Example 2-2).

[0120] Example 3

[0121] 1) 126 g of graphite particles with a D50 size of 20 ㎛ and 174 g of silicon particles with a D50 size of 75 nm were prepared and mixed.

[0122] 2) The above mixture was placed in a mixing device, and a negative electrode active material was manufactured by gradually increasing one or more forces selected from the group consisting of shear force, tensile force, and compressive force applied as shown below.

[0123] - under -

[0124] 1) An average force of 0.04 kW / g was applied for 20 minutes.

[0125] 2) An average force of 0.13 kW / g was applied for 5 minutes.

[0126] 3) An average force of 0.30 kW / g was applied for 7 minutes.

[0127] 4) An average force of 0.60 kW / g was applied for 12 minutes.

[0128] 5) An average force of 0.87 kW / g was applied for 15 minutes.

[0129] 6) An average force of 1.47 kW / g was applied for 55 minutes.

[0130] 7) An average force of 1.80 kW / g was applied for 20 minutes.

[0131] 8) An average force of 3.36 kW / g was applied for 150 minutes.

[0132] 9) Finally, the applied power was increased to 4 kW / g and maintained for 120 minutes before mixing was terminated.

[0133] The negative active material was manufactured twice under the same conditions (Example 3-1 and Example 3-2).

[0134] Comparative Example 1

[0135] 126 g of graphite particles with a D50 size of 10 ㎛ and 174 g of silicon particles with a D50 size of 75 nm were prepared and placed in a mechanical mixing device and mixed at a power of 4 kW / g to manufacture a negative electrode active material. That is, in the comparative example, the negative electrode active material was manufactured under the same conditions as Example 2, except that one or more forces selected from the group consisting of shear force, tensile force, and compressive force applied stepwise were not increased.

[0136] Experimental example

[0137] The properties of the negative electrode active materials manufactured in Examples 1 to 3 (Examples 1-1 to 3-2) and Comparative Examples were measured and are shown in the table below.

[0138] The method for measuring the particle size and silicon content of the negative electrode active material in the table below is as follows.

[0139] 1) After sampling the negative electrode material using Ag Paste, Pt (platinum) coating was performed.

[0140] 2) Place the above Pt-coated negative electrode material into a scanning electron microscope (SEM) chamber and 1 -6 After creating an environment of less than 10 mbar, Pt plating was performed, and then approximately 50% of the particles were cut using an ion beam to observe cross-sectional images.

[0141] 3) Through EDS (Energy Dispersive Spectroscopy) mapping of the cut particle cross-section, the area where the Pt content exceeded 50 wt% among the entire particle cross-section was defined as the Pt area, and the area excluding the Pt area was defined as the composite area.

[0142] 4) The particle size of the negative active material was measured based on the long axis of the composite region.

[0143] 5) The silicon content in the negative electrode material was measured in wt% by randomly designating at least two points including the center in the complex region using EDS.

[0144] Size of negative electrode active material Ratio of the content at the point where the silicon content inside the negative electrode material is maximum to the content at the point where the silicon content is minimum Example 1 [Example 1-1] 0.6~3 ㎛ 1:0.9 (43.45 : 40.78) [Example 1-2] 3~6 ㎛ 1:1 (47.26 : 46.46) Example 2 [Example 2-1] 2~6 ㎛ 1:1 (38.41 : 36.80) [Example 2-2] 6~12 ㎛ 1:1 (49.16 : 46.76) Example 3 [Example 3-1] 2~13 ㎛ 1: 0.7 (67.97 : 49.29) [Example 3-2] 13~30 ㎛ 1:0.9 (78.16 : 72.19) Comparative Example 1 [Comparative Example 1] 6~12 ㎛1: 4.2 (8.20: 35.07)

[0145] *Unit: wt%

[0146] Referring to Table 1, it can be confirmed that the negative electrode active materials of Examples 1-1 to 3-2 according to the present invention have silicon uniformly distributed and inserted into the graphite, compared to the negative electrode active materials of the comparative examples.

[0147] Meanwhile, FIG. 3 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 1-1 and 1-2 of the present invention, FIG. 4 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 2-1 and 2-2 of the present invention, FIG. 5 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to Examples 3-1 and 3-2 of the present invention, and FIG. 6 is a FIB-SEM image (silicon content by location) of a negative electrode active material according to a comparative example.

[0148] Fig. 3 is a FIB-SEM image of a negative electrode active material according to the present invention. Through Figs. 3 to 5, it can be confirmed that the silicon:carbon content ratio at each location is controlled according to the negative electrode particle size of the negative electrode active material of the present invention.

[0149] A battery including a negative electrode including the negative electrode active material manufactured in this manner was manufactured, and the battery performance (discharge capacity) was measured, which is shown in Table 2 below.

[0150] Batteries containing the negative electrode materials of Examples 1-1 to 3-2 and Comparative Examples were manufactured, and a half-cell test was conducted according to the number of charge / discharge cycles. The negative electrode materials of Examples 1-1 to 3-2 and Comparative Examples were each mixed with a conductive agent and a binder to form a slurry, and the slurry was coated on copper foil, dried, and standardized to a certain size (12 pi) to form a negative electrode material.

[0151] After manufacturing a coin cell battery based on the above-mentioned negative active material, the discharge capacity (mAh / g) was measured through a half-cell test in which charging and discharging were performed 10 times at a 0.1 C-rate, and the results are shown in Table 2 below.

[0152] Discharge capacity according to number of charge / discharge cycles Number of charge / discharge cycles Example 1-1 Example 1-2 Example 2-1 Example 2-2 Example 3-1 Example 3-2 Comparative example 1 1 46 9.95 1 49 3.87 1 44 8.66 1 55 8.66 1 5 15 15 63 1 42 1.94 1 49 0.47 2 1 47 9.23 1 50 5.68 1 46 0.27 1 57 7.26 1 5 2 3.05 1 43 1.311345.6831492.711512.861470.301583.481535.391441.461233.9241499.721517.141477.251587.861541.131449.431147.2251502.311520.641478.50158 6.481545.321458.781076.6861503.111520.421479.911584.021544.431466.111018.4671499.341516.931477.111581.111544.901471.28970.9681501.071518 .491483.061580.621546.911476.05925.9291497.241514.271481.961575.081544.891479.74891.59101488.321504.341476.871561.641536.761482.19859.04

[0153] *Unit: mAh / g

[0154] In addition, using a battery including a negative electrode including the negative electrode active material of Examples 1-1 to 3-2 and a comparative example, the discharge capacity maintenance rate by repeating charge and discharge several times compared to the initial discharge capacity is shown in Table 3 below.

[0155] Capacity retention rate according to the number of charge / discharge cycles Number of charge / discharge cycles Example 1-1 Example 1-2 Example 2-1 Example 2-2 Example 3-1 Example 3-2 Comparative Example 1 100.00 100.00 100.00 100.00 100.00 100.00 100.00 2100.63 100.79 100.80 101.19 100.49 100.66 90.29 3101.55 101.27 101.49 101.59 101.30 101.37 82.79 4102.03 101.56 101.97 101.87 101.68 101.93 76.97 5102.20 101.79 102.0 6101.78101.96102.5972.246102.26101.78102.16101.63101.90103.1168.337102.00101.54101.96101.44101.93103.4765.148102.12101.65102.37101.41102.06103.8162.129101.86101.37102.30101.05101.93104.0659.8210101.25100.70101.95100.19101.39104.2457.64

[0156] *unit: %

[0157] Figure 7 is a graph of the discharge capacity of a battery including a negative electrode including a negative electrode active material of an embodiment of the present invention.

[0158] As shown in Tables 2 and 3 and FIG. 7, the battery including the negative electrode active material of the present invention suppressed silicon expansion as a result of 10 charge / discharge experiments, so that even when charge / discharge was repeated, the change in the total volume of the negative electrode material was very small, and thus, the discharge capacity was maintained even after several charge / discharge cycles. Through the evaluation of the capacity retention rate in the charge / discharge experiments of Examples 1-1 to 3-2 and the Comparative Example, it was confirmed that the volume expansion of the negative electrode active material was suppressed compared to the negative electrode active material of the Comparative Example with a lower capacity retention rate, as the negative electrode active materials of Examples 1-1 to 3-2 maintained a constant capacity retention rate, and through this, it was confirmed that the volume expansion of silicon inside the negative electrode active material was also suppressed.

[0159] That is, the negative electrode active material of the present invention has silicon uniformly distributed inside, and the graphite core acts as a frame to suppress expansion of the silicon, and as a result, internal changes due to repeated volume expansion of the negative electrode active material are suppressed, so that the capacity retention rate does not decrease.

[0160] Although the embodiments have been described above, those skilled in the art will appreciate that various technical modifications and variations can be applied based on the above. For example, appropriate results can still be achieved even if the described techniques are performed in a different order than described, and / or components of the described systems, structures, devices, circuits, etc. are combined or combined in a different manner than described, or are replaced or substituted with other components or equivalents.

[0161] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims described below.

Claims

1. As a negative electrode active material containing graphite and silicon, The silicon content is 5 wt% to 80 wt% of the negative electrode active material, The above silicon is uniformly distributed within the negative electrode active material, Negative active material.

2. In paragraph 1, Among the above negative active materials, the silicon content at the point where the silicon content is minimum is 70% or more of the silicon content at the point where the silicon content is maximum. Negative active material.

3. In paragraph 1, The size of the above negative active material is 0.6 ㎛ to 30 ㎛, Negative active material.

4. In paragraph 1, The size of the negative electrode active material is 0.6 ㎛ or more and 6 ㎛ or less, and the silicon content of the negative electrode active material is 10 wt% to 45 wt%. Negative active material.

5. In paragraph 1, The size of the negative electrode active material is 2 ㎛ or more and 12 ㎛ or less, and the silicon content of the negative electrode active material is 30 wt% to 50 wt%. Negative active material.

6. In paragraph 1, The size of the negative electrode active material is 2 ㎛ or more and 30 ㎛ or less, and the silicon content of the negative electrode active material is 30 wt% to 80 wt%. Negative active material.

7. In paragraph 1, The particle size of the silicon above: the particle size of the graphite above is 1:10 to 1:35, Negative active material.

8. In paragraph 1, The particle size of the silicon above: the particle size of the graphite above is 1:25 to 1:70, Negative active material.

9. In paragraph 1, The particle size of the silicon above: the particle size of the graphite above is 1:25 to 1:350, Negative active material.

10. In paragraph 1, The aspect ratio of the above negative active material is 0.8:1 to 1.2:1, Negative active material.

11. In paragraph 1, The above silicon particles are in a form surrounded by the graphite, Negative active material.

12. Including a cathode; an anode; and a separator formed between the cathode and the anode, The above negative electrode comprises the negative electrode active material of the first clause. Secondary battery.

13. A step of mixing graphite and silicon particles; and A step of forming a negative electrode active material including the graphite and the silicon particles by applying at least one force selected from the group consisting of shear force, tensile force, and compressive force to the particles formed by the above mixture; including, Method for manufacturing negative electrode active material.

14. In paragraph 13, The sum of one or more forces selected from the group consisting of shear force, tensile force and compressive force is from 0.003 kW / g to 4 kW / g, Method for manufacturing negative electrode active material.

15. In paragraph 13, By controlling the magnitude of the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force, Controlling the size of the above negative electrode active material, Method for manufacturing negative electrode active material.

16. In paragraph 13, The above mixing step; and the step of forming a negative electrode active material including the graphite and the silicon particles; are performed simultaneously. Method for manufacturing negative electrode active material.

17. In paragraph 13, In the step of forming a negative electrode active material including the graphite and the silicon particles by applying at least one force selected from the group consisting of shear force, tensile force and compressive force to the particles formed by the above mixture; Stepwise application of one or more forces selected from the group consisting of shear force, tensile force and compressive force, Method for manufacturing negative electrode active material.

18. In paragraph 17, The stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force means applying one or more forces selected from the group consisting of the above shear force, tensile force and compressive force in five or more steps in which the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force sequentially increases. Method for manufacturing negative electrode active material.

19. In paragraph 18, Stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force, wherein the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force starts from 0.002 to 0.004 kW / g. Method for manufacturing negative electrode active material.

20. In paragraph 18, Stepwise application of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force, wherein the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at each step is greater than 100% and less than 660% of the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force at the previous step. Method for manufacturing negative electrode active material.

21. In paragraph 18, Stepwise applying one or more forces selected from the group consisting of the above shear force, tensile force and compressive force, wherein the final step is to maintain the sum of one or more forces selected from the group consisting of the above shear force, tensile force and compressive force for 90 to 200 minutes. Method for manufacturing negative electrode active material.

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