Silicon-based negative electrode material, method for manufacturing same, and lithium secondary battery comprising same

Abstract

The present invention relates to a negative electrode material to be used in a lithium-ion battery and the like and, more specifically, to a manufacturing method for coating conductive polymer polyaniline on an active material containing silicon and pure silicon, and to a lithium-ion battery using a highly stable silicon-based negative electrode material. To this end, provided is a method for manufacturing a silicon-based negative electrode material, the method being characterized by comprising the steps of: preparing a silicon-based active material (S100) and synthesizing and preparing conductive polymer polyaniline (S200); coating the surface of the silicon-based active material with the conductive polymer polyaniline having a layered structure to form a coating layer (S300); and forming a stable solid electrolyte interface after the formation step of a silicon-based active material electrode coated with a conductive polymer (S400).

Description

Silicon-based negative electrode material, method for producing the same, and lithium secondary battery including the same

[0001] The present invention relates to an anode material used in a lithium secondary battery, and more particularly, to a manufacturing method for coating a conductive polymer polyaniline on an active material containing pure silicon and silicon, and to a lithium secondary battery utilizing a high-stability silicon-based anode material.

[0002] With the recent advancement of portable electronic devices and the popularization of electric vehicles (EVs), there is a growing demand for lithium-ion batteries featuring high energy density and dramatically improved charge / discharge cycle life. To achieve this goal, significant research and development efforts are being conducted on raw materials such as anodes, cathodes, electrolytes, and separators. Among these raw materials, a particular focus is on the development of electrode materials, and currently commercialized anode materials are primarily graphite-based. Graphite-based anode materials are currently commercialized due to their economic feasibility and superior stability.

[0003] Graphite anode materials have a relatively low theoretical capacity (372 mAh / g) compared to other next-generation anode materials. This limitation in theoretical capacity is insufficient to meet the market demand for batteries with high energy and power densities. Silicon anodes have a high theoretical capacity (Li 4.4 4200 mAh / g on Si) and low operating voltage (<0.4 V vs. Li / Li). + ), and is attracting attention as one of the most promising anode materials for achieving high energy density in lithium-ion batteries due to its abundant resources.

[0004] However, despite these advantageous properties, silicon has the property of undergoing excessive volume changes of up to 300% during the alloying reaction with lithium ions, which causes various problems as the active material particles break and lose contact, making it difficult to replace graphite-based anode materials.

[0005] Recently, the application of conductive polymer coatings to silicon surfaces has been emphasized to form a stable solid-electrolyte interface (SEI) by forming electronic pathways and to withstand stress. However, most reported polymer coatings are easily dissolved in organic electrolyte solvents after cycling, have difficulty controlling the properties of the SEI, and fail to improve uniform interfacial charge flow in response to isotropic volume changes at the silicon surface. Consequently, volume expansion of silicon remains an unresolved issue.

[0006] Prior art literature

[0007] Patent documents

[0008] 1. Republic of Korea Patent Publication No. 10-2013-0139555 (Metal-doped silicon oxide, negative electrode material for secondary battery containing the same, and manufacturing method thereof)

[0009] 2. Republic of Korea Patent Publication No. 10-2019-0143661 (Carbon composite material encapsulated with silicon for secondary battery negative electrode material and manufacturing method thereof),

[0010] 3. Republic of Korea Patent Publication No. 10-2023-0063474 (Method for producing silicon nanopowder for lithium secondary battery negative electrode material using recycled waste silicon material and silicon nanopowder).

[0011] Accordingly, the present invention has been devised to solve the above problems, and the problem to be solved by the present invention is to provide a silicon-based negative electrode material capable of simultaneously improving the high-speed stability and stable charge / discharge cycle life of a high-capacity silicon negative electrode material of a lithium ion battery, a method for producing the same, and a lithium secondary battery including the same.

[0012] However, the technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0013] In order to achieve the above technical task, a method for manufacturing a silicon-based negative electrode material is provided, characterized by including the steps of preparing a silicon-based active material (S100), synthesizing and preparing a conductive polymer polyaniline (S200); forming a coating layer by coating a layered conductive polymer polyaniline on the surface of the silicon-based active material (S300); and forming a stable solid electrolyte interface by going through a chemical reaction step of a silicon-based active material electrode coated with a conductive polymer (S400).

[0014] Additionally, silicon is a composite of silicon and carbon or silicon and graphite, and graphite is either natural graphite or artificial graphite. Furthermore, silicon and graphite are in a 5:1 weight ratio.

[0015] Additionally, the particle size of the silicon is 0.1 μm to 100 μm.

[0016] Additionally, it includes 60 to 90 parts by mass of a silicon-based active material, 0 to 20 parts by mass of a conductive material not containing 0, and 0 to 20 parts by mass of a binder not containing 0, per 100 parts by mass of a slurry-type negative electrode material.

[0017] Additionally, the binder may be an aqueous binder that mixes a conductive material with polyacrylic acid and its derivatives, or carboxymethyl cellulose and its derivatives, and styrene butadiene and its derivatives.

[0018] In addition, polyaniline is polyaniline doped with p-toluenesulfonic acid, and polyaniline with high conductivity can be manufactured.

[0019] Additionally, the molar ratio of p-toluenesulfonic acid and aniline is 1:1.

[0020] In addition, the solvent for dispersing the conductive polymer and the silicon-based active material is a mixed solvent of 50 to 100 mass% of dimethylformamide and 0 to 50 mass% of ethanol.

[0021] In addition, the temperature during the process of mixing silicon-based active materials and conductive polymers to proceed with the coating process and evaporating the solvent is 40 to 80°C and the stirring speed is 100 to 500 rpm.

[0022] Additionally, in the formation step of the coating layer (S300), the surface of the silicon-based active material and the conductive polymer polyaniline are coated by uniform hydrogen bonding.

[0023] In addition, in the solid electrolyte interface formation step (S400), a solid electrolyte interface is formed that includes a phase containing lithium fluoride uniformly in each layer by the layered structure of polyaniline.

[0024] Additionally, the conductive polymer polyaniline coating layer does not readily dissolve in organic electrolyte solvents.

[0025] The above-described object of the present invention can also be achieved by a silicon-based negative electrode material characterized by being manufactured by the above-described method for manufacturing a negative electrode material as another embodiment.

[0026] In addition, the above-described object of the present invention can also be achieved by a lithium secondary battery characterized by including a silicon-based negative electrode material manufactured by the above-described method for manufacturing a negative electrode material as another embodiment.

[0027] According to one embodiment of the present invention, there is an effect of improving the electrical conductivity of a silicon-based negative electrode active material by uniformly coating the surface through a direct film formation method using a conductive polymer.

[0028] In addition, according to the present invention, a uniform and stable solid electrolyte interface is formed by polyaniline having a layered structure, and the problem of volume expansion / contraction due to charge / discharge is effectively suppressed, thereby preventing particle destruction of the negative active material and thickening of the solid electrolyte interface.

[0029] In addition, the silicon-based negative electrode active material protected by the direct film formation method used in the present invention has improved capacity and lifespan characteristics in a high-speed charge / discharge environment, and thus has the advantage of being usable in high-performance secondary batteries.

[0030] In addition, the manufacturing method of the present invention is simple and effective and is easy to industrialize.

[0031] However, the effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0032] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0033] Figure 1 is a schematic diagram of a silicon substrate including a conductive polymer coating layer.

[0034] Figure 2 is an HRTEM image of the conductive polymer coating layer of Example 2.

[0035] Figure 3 is an XPS depth graph of the solid electrolyte interface after charge and discharge in Example 2.

[0036] Figure 4 is a graph of charging capacity according to the C-rate of Example 1-4.

[0037] Figure 5 is a graph of charging capacity according to C-rate of Comparative Example 1 and Example 2.

[0038] Figure 6 is a capacity maintenance comparison graph of Comparative Example 1 and Example 2.

[0039] Figure 7 is a flow chart briefly showing a method for manufacturing a silicon-based negative electrode material according to one embodiment of the present invention.

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily practice the present invention. However, the description of the present invention is merely an embodiment for structural and functional explanation, and therefore the scope of the present invention should not be construed as being limited by the embodiments described in the text. In other words, since the embodiments can be modified in various ways and can have various forms, the scope of the present invention should be understood to include equivalents that can realize the technical idea. In addition, the purposes or effects presented in the present invention do not mean that a specific embodiment must include all of them or only such effects, and therefore the scope of the present invention should not be construed as being limited thereby.

[0041] The meanings of terms described in the present invention should be understood as follows.

[0042] Terms such as "first" and "second" are intended to distinguish one component from another, and the scope of the rights should not be limited by these terms. For example, a first component could be referred to as a second component, and similarly, a second component could also be referred to as a first component. When a component is referred to as being "connected" to another component, it should be understood that it may be directly connected to that other component, but there may also be other components in between. Conversely, when a component is referred to as being "directly connected" to another component, it should be understood that there are no other components in between. Meanwhile, other expressions describing the relationship between components, such as "between" and "immediately between" or "adjacent to" and "directly adjacent to", should be interpreted similarly.

[0043] Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "comprises" or "has" should be understood to specify the presence of stated features, numbers, steps, operations, components, parts, or combinations thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0044] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted to be consistent with their meaning within the context of the relevant technology, and should not be interpreted as having ideal or overly formal meanings unless explicitly defined herein.

[0045] Figure 7 is a flowchart briefly illustrating a method for manufacturing a silicon-based anode material according to one embodiment of the present invention. As illustrated in Figure 7, a silicon-based raw material is first prepared, and a conductive polymer layered film is formed on the surface of the prepared silicon-based material, thereby manufacturing the material. Subsequently, a stable solid electrolyte interface is formed during the formation step, thereby manufacturing the material. Each process is described in detail below.

[0046] In order to uniformly treat the surface of a silicon-based negative electrode active material, a method of uniformly coating a conductive polymer in a layered structure on the surface of a silicon-based material through strong hydrogen bonding is included. The silicon-based negative electrode material coated with the conductive polymer of the present invention does not readily dissolve in an organic electrolyte solvent, and, as shown in Fig. 1, forms a uniform and abundant LiF phase by controlling the components of the solid electrolyte interface formed during cycling, thereby providing an negative electrode material with excellent electrochemical cycling and expansion suppression performance, thereby providing a high-capacity, high-speed charging, and high-stability lithium-ion battery.

[0047] Preparation of silicon-based active materials (S100)

[0048] The silicon-based active material of the present invention is basically silicon-only nanoparticles, and may include silicon / carbon or silicon / graphite composites. These silicon nanoparticles have a diameter of about 100 nm and can exhibit high-capacity characteristics due to a large surface area. In addition, the particle size of silicon in the silicon-based negative electrode material is 0.1 μm to 100 μm, and in the case of silicon / carbon or silicon / graphite composites, the silicon and graphite may have a weight ratio of about 3:1 to 6:1, and preferably a weight ratio of 5:1. In addition, the graphite is natural graphite or artificial graphite. In addition, the slurry-type negative electrode material includes 60 to 90 parts by mass of the silicon-based active material, 0 to 20 parts by mass of a conductive material not including 0, and 0 to 20 parts by mass of a binder not including 0, per 100 parts by mass of the slurry-type negative electrode material.

[0049] Synthesis of conductive polymer polyaniline (S200)

[0050] A conductive polyaniline doped with p-toluenesulfonic acid is synthesized. The polyaniline is polyaniline doped with p-toluenesulfonic acid. The molar ratio of p-toluenesulfonic acid to aniline is 1:1.

[0051] Direct coating layer formation (S300)

[0052] A coating layer of a conductive polymer layer structure synthesized on the surface of a silicon-based active material is formed. The dispersion is evaporated at a medium temperature, and a uniform conductive polymer coating layer is formed through strong hydrogen bonding between the polyaniline doped with p-toluenesulfonic acid and the silicon surface. The temperature during the solvent evaporation process for forming the coating layer is 40°C to 80°C, and the stirring speed is 100 to 500 rpm.

[0053] Formation of a stable solid electrolyte interface (S400)

[0054] The ignition step of a silicon electrode coated with a layered conductive polymer is performed. During this process, the layered structure of polyaniline reacts with an electrolyte containing fluoroethylene carbonate (FEC), forming a solid electrolyte interface uniformly containing a lithium fluoride-rich phase in each layer.

[0055] Silicon-based negative electrode active material coated with conductive polyaniline in a layered structure

[0056] Silicon-based anode materials coated with polyaniline doped with p-toluenesulfonic acid exhibit superior performance under fast charging conditions of 10 A / g compared to unmodified silicon-based anode materials. These characteristics make them suitable for the high-speed charging currently required.

[0057] Example 1: Direct formation of a coating layer

[0058] A silicon-based active material is added at a concentration of 0.02 g / mL to a solvent containing ethanol and distilled water in a volume ratio of 9:1, and the surface is activated through ultrasonic treatment, after which the powder is separated through centrifugation. Optionally, the solvent for dispersing the conductive polymer and the silicon-based active material is a mixed solvent of 50 to 100 mass% dimethylformamide and 0 to 50 mass% ethanol.

[0059] Next, the recovered silicon powder is added to a solvent containing dimethylformamide / ethanol in a volume ratio of 9:1 at a concentration of 0.02 g / mL and ultrasonic dispersion is performed.

[0060] Next, polyaniline doped with toluenesulfonic acid is added to a dimethylformamide solvent at a concentration of 0.05 g / mL and ultrasonic dispersion is performed. At this time, the mass ratio of silicon to polyaniline is 1:1.

[0061] A solution containing a silicon-based active material dispersed in a solution containing polyaniline is slowly added at a rate of 2 mL / min while stirring at 300 rpm, and the solvent is evaporated at 65°C. Once the solvent has completely evaporated, the recovered powder is removed from the residual solvent and moisture under vacuum at 30°C for 12 hours.

[0062] Example 2: Direct film formation

[0063] There are no changes other than adjusting the amount of polyaniline powder so that the mass ratio of silicon and polyaniline in Example 1 is 2:1.

[0064] Example 3: Direct film formation

[0065] There are no changes other than adjusting the amount of polyaniline powder so that the mass ratio of silicon and polyaniline in Example 1 is 3:1.

[0066] Example 4: Direct film formation

[0067] There are no changes other than adjusting the amount of polyaniline powder so that the mass ratio of silicon and polyaniline in Example 1 is 4:1.

[0068] Comparative Example 1: Silicon-based negative electrode active material

[0069] It uses a silicon-based active material that has not been treated with a conductive polymer on the surface.

[0070] Figure 2 is a high-resolution transmission electron microscopy (HRTEM) image of the conductive polymer coating layer of Example 2. As shown in Figure 2, it was confirmed through HRTEM that a uniform and thin conductive polymer layer was formed due to strong hydrogen bonding between the silicon-based active material surface and polyaniline doped with p-toluenesulfonic acid.

[0071] Figure 3 is an XPS (X-ray photoelectron spectroscopy) depth graph of a solid electrolyte interface formed on a conductive polymer coating layer on the surface of a silicon-based active material of Example 2. As shown in Figure 3, it was confirmed that a phase rich in lithium fluoride was uniformly distributed at each depth of the solid electrolyte interface.

[0072] Figure 4 is a graph of the charge capacity according to the C (Current)-rate of Examples 1-4. Through Examples 1-4, electrochemical performance was evaluated according to the C-rate according to the mass ratio of silicon and polyaniline. In Example 2, it can be seen that high charge capacity is observed under high-speed current density conditions, reversible capacity, and subsequent cycles. In Example 1, where the amount of polyaniline was small, the volume expansion of silicon was not effectively suppressed, and in Examples 3 and 4, it was confirmed that the amount of polyaniline was too large, leading to unevenness of the coating and consequently to a decrease in performance.

[0073] Fig. 5 is a graph of the charge capacity according to the C-rate of Comparative Example 1 and Example 2. As shown in Fig. 5, Example 2 is an optimized condition through an electrochemical performance evaluation according to the C-rate depending on the mass ratio of silicon and polyaniline. It was found that the electrochemical performance evaluation according to the C-rate of Comparative Example 1 under the conditions of Example 2 showed excellent fast-charge performance, reversibility, and excellent charge capacity in subsequent cycles. Through this, it was confirmed that a stable solid electrolyte interface of silicon was formed to suppress effective volume expansion and increase uniform electron conductivity, thereby securing fast-charge capability.

[0074] Figure 6 is a capacity retention comparison graph of Comparative Example 1 and Example 2. As shown in Figure 6, life stability evaluation according to long-term cycles at a high-speed current density of 1 A / g was performed for Comparative Example 1 and Example 2. It was confirmed that Comparative Example 1 showed a rapid performance decline after about 20 cycles, whereas Example 2, a silicone coated with a conductive polymer according to the present invention, showed excellent life stability.

[0075] Experimental conditions

[0076] Electrochemical performance tests were conducted by fabricating half cells using 2032 standard coin cells using lithium metal as a reference electrode.

[0077] - The active material of the electrode used silicon nanopowder with a diameter of approximately 100 nm.

[0078] - The challenge material used was super P, and the binder used was PAA (Polyacrylic Acid).

[0079] - The weight ratio of the active material, conductive material, and binder is 7:1:2, and the areal density of the electrode is 1 mg / cm 2 The electrode was manufactured based on this.

[0080] - Capacity loading area density of the electrode 1 g / cm 2 The electrode was manufactured based on this.

[0081] - The electrolyte used was 1M LiPF6in EC(Ethylene Carbonate)) / EMC(Ethyl Methyl Carbonate)(3 / 7 v / v) + VC(Vinylene Carbonate) 1.0 wt% + FEC(fluoroethylene carbonate) 10 wt%.

[0082] - The C-rate of the Martian stage was calculated based on the theoretical capacity of 3600 mAh / g of the active material. The Martian charge stage was charged to 10 mV at a constant current of 0.05 C and then charged from 10 mV to 0.005 C at a constant voltage. The Martian discharge stage was discharged to 1.5 V at a constant current of 0.05 C. The Martian charge and discharge were repeated three times.

[0083] - After the Mars stage, charge and discharge were repeated five times each at rates of 0.2, 0.5, 1, 2, 5, 7, and 10 A / g to perform high-speed performance tests. The charge and discharge cycle stages were charged to 10 mV at the constant current of the corresponding stage. The discharge stage was discharged to 1.5 V at the constant current of the corresponding stage. Afterwards, reversibility was evaluated by charging and discharging five times at a current density of 0.2 A / g.

[0084] - Initial charge capacity refers to the charge capacity in the first cycle in the charge / discharge cycle test.

[0085] - The 10 A / g fast charge capacity retention rate was calculated as the percentage of the first charge capacity of 10 A / g compared to the first cycle charge capacity in the charge / discharge cycle test.

[0086] - Electrochemical charge / discharge cycles for long-life evaluation were performed 150 times under a current density of 1 A / g.

[0087] Examples and Comparative Examples Initial Charge Capacity (mAh / g) 1 A / g Charge Capacity Retention Rate (%) 10 A / g Fast Charge Capacity Retention Rate (%) Example 13820.549.70.1 Example 23467.162.816.9 Example 33527.467.00.1 Example 43477.570.50.2 Comparative Example 13389.062.60.1

[0088]

[0089] The detailed description of the preferred embodiments of the present invention disclosed above has been provided to enable those skilled in the art to implement and practice the present invention. While the above description has been made with reference to preferred embodiments of the present invention, those skilled in the art will appreciate that various modifications and variations can be made to the present invention without departing from the scope of the present invention. For example, those skilled in the art can utilize the individual components described in the above-described embodiments in combination with each other. Accordingly, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0090] The present invention may be embodied in other specific forms without departing from the spirit and essential characteristics thereof. Therefore, the above detailed description should not be construed in any way as limiting but rather as illustrative. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all changes coming within the equivalent scope of the claims are intended to be included therein. The present invention is not intended to be limited to the embodiments set forth herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Furthermore, claims that are not explicitly cited in the claims may be combined to form an embodiment or incorporated into a new claim by post-application amendment.

Claims

1. A step of preparing a silicon-based active material (S100) and synthesizing and preparing a conductive polymer polyaniline (S200); A step (S300) of forming a coating layer by coating the conductive polymer polyaniline in a layered structure on the surface of the silicon-based active material; and A method for manufacturing a silicon-based negative electrode material, characterized by comprising a step (S400) of forming a stable solid electrolyte interface through a chemical reaction step of a silicon-based active material electrode coated with the conductive polymer.

2. In paragraph 1, A method for manufacturing a silicon-based negative electrode material, characterized in that the silicon is a composite of silicon and carbon or silicon and graphite.

3. In paragraph 2, A method for manufacturing a silicon-based negative electrode material, characterized in that the graphite is natural graphite or artificial graphite.

4. In paragraph 2, A method for manufacturing a silicon-based negative electrode material, characterized in that the silicon and the graphite are in a weight ratio of 5:

1.

5. In paragraph 1, A method for manufacturing a silicon-based negative electrode material, characterized in that the particle size of the silicon is 0.1 μm to 100 μm.

6. In paragraph 1, For 100 parts by mass of the above negative electrode material in slurry form 60 to 90 mass parts of the above silicon-based active material, A conductive material having a mass of 0 to 20 parts by weight, not including 0, and A method for manufacturing a silicon-based negative electrode material, characterized in that it contains 0 to 20 parts by mass of a binder not including 0.

7. In paragraph 6, A method for manufacturing a silicon-based negative electrode material, characterized in that the binder is an aqueous binder that mixes a conductive material, polyacrylic acid and its derivatives, or carboxymethyl cellulose and its derivatives, and styrene butadiene and its derivatives.

8. In paragraph 1, A method for manufacturing a silicon-based negative electrode material, characterized in that the above polyaniline is polyaniline doped with p-toluenesulfonic acid.

9. In paragraph 8, A method for manufacturing a silicon-based negative electrode material, characterized in that the molar ratio of the above p-toluenesulfonic acid and the above aniline is 1:

1.

10. In paragraph 1, The solvent for dispersing the conductive polymer and the silicon-based active material is 50 to 100 mass% dimethylformamide; and A method for manufacturing a silicon-based negative electrode material, characterized in that the mixture solvent is 0 to 50 mass% ethanol.

11. In paragraph 1, A method for manufacturing a silicon-based negative electrode material, characterized in that the temperature during the process of mixing the silicon-based active material and the conductive polymer to perform a coating process and evaporating the solvent is 40 to 80°C and the stirring speed is 100 to 500 rpm.

12. In paragraph 1, A method for manufacturing a silicon-based negative electrode material, characterized in that in the step of forming the coating layer (S300), the surface of the silicon-based active material and the conductive polymer polyaniline are uniformly coated by hydrogen bonding.

13. In paragraph 1, A silicon-based negative electrode material, characterized in that the solid electrolyte interface forming step (S400) includes a phase uniformly containing lithium fluoride in each layer due to the layered structure of the polyaniline.

14. In paragraph 1, A silicon-based negative electrode material characterized in that the conductive polymer polyaniline coating layer does not readily dissolve in an organic electrolyte solvent.

15. A silicon-based negative electrode material characterized by being manufactured by a method for manufacturing a negative electrode material according to any one of claims 1 to 14.

16. A lithium secondary battery characterized by including a silicon-based negative electrode material manufactured by a method for manufacturing a negative electrode material according to any one of claims 1 to 14.

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