Composite anode active material including two layers and method of manufacturing same

Abstract

The present invention relates to a composite anode active material comprising two layers and a method for manufacturing the same. When the surface of the carbon-based particle is coated with a coating with high energy density, a buffer layer is formed between the carbon-based particle and the coating. Therefore, the charge / discharge efficiency of the all-solid-state battery including the anode active material is improved. The anode active material has an inner core comprising carbon-based particles, a buffer layer covering at least a portion of a surface of the inner core and comprising a carbide, and a coating layer covering at least a portion of a surface of the buffer layer and comprising a lithium-philic material.

Description

Technical Field

[0001] The present invention relates to a composite anode active material including a bilayer and a method for manufacturing the same. Specifically, when a coating layer having a high energy density is coated on the surface of carbon-based particles, a buffer layer is formed between the carbon-based particles and the coating layer. Background Art

[0002] Batteries are configured to store energy using water that can undergo an electrochemical reaction in a cathode and an anode. Representative examples of such batteries are lithium secondary batteries, which store electrical energy through the chemical potential difference during the insertion / extraction of lithium ions in the cathode and the anode.

[0003] Lithium secondary batteries are manufactured by using materials capable of reversibly inserting / extracting lithium ions as cathode active materials and anode active materials, and adding an organic electrolyte solution, a polymer electrolyte solution, or a solid electrolyte between the cathode and the anode.

[0004] Although the anode active material of most commercial lithium secondary batteries is graphite, the manufacturing of lithium secondary batteries with a high energy density is limited due to the low theoretical capacity of graphite (372 milliampere-hours per gram of mass (mAh / g)). As alternatives to graphite, silicon (3579 mAh / g) and lithium metal (3682 mAh / g) with higher theoretical capacities have attracted much attention. However, silicon has a volume change rate of up to 300% during battery charging and discharging, so it is recommended to use silicon in combination with graphite rather than alone.

[0005] In this regard, there is a known method of manufacturing a composite anode active material by coating silicon on the surface of graphite using chemical vapor deposition (CVD) or the like. However, in this case, the adhesion between graphite and silicon is poor, so separation may easily occur during charging and discharging. Therefore, when separation occurs between graphite and silicon, the battery performance deteriorates and the initial charge / discharge efficiency decreases. Summary of the Invention

[0006] In view of the problems encountered in the related art, the present invention has been developed, and the present invention aims to provide an anode active material that can improve the initial charge / discharge efficiency of a battery.

[0007] Specifically, the present invention aims to provide an anode active material that can enhance the adhesion between a carbon material (such as graphite) and a lithiumophilic material (such as silicon) when the lithiumophilic material is coated on the surface of the carbon material.

[0008] In addition, the present invention aims to solve the problem that an uneven coating layer is formed when a lithiumophilic material is directly coated on the surface of a carbon material using chemical vapor deposition.

[0009] In particular, silicon, as an example of a lithiophilic material, undergoes a large volume expansion when its structure changes from amorphous to crystalline. Therefore, the present invention aims to provide an anode active material capable of suppressing silicon crystallization during charging.

[0010] The object of the present invention is not limited to the above object. The object of the present invention should be more clearly understood from the following description and can be achieved by the technical concepts described in the claims and their combinations.

[0011] One aspect of the present invention can provide an anode active material. The anode active material may have a core containing carbon-based particles, a buffer layer covering at least a part of the surface of the core and containing a carbide, and a coating covering at least a part of the surface of the buffer layer and containing a lithiophilic material.

[0012] In one embodiment, the carbon-based particles may include at least one selected from natural graphite, artificial graphite, or any combination thereof.

[0013] In one embodiment, the carbide may contain silicon (Si) and carbon (C) according to SiC x (0 < x ≤ 1). The carbide may include silicon carbide SiC x (0 < x ≤ 1).

[0014] In one embodiment, the thickness of the buffer layer may be from 1 nanometer (nm) to 20 nm.

[0015] In one embodiment, the lithiophilic material may contain a metal or metalloid capable of forming an alloy with lithium. The metal or metalloid capable of forming an alloy with lithium may include at least one selected from silicon (Si), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), magnesium (Mg), bismuth (Bi), tin (Sn), zinc (Zn), or any combination thereof.

[0016] In one embodiment, the lithiophilic material may include amorphous silicon (Si).

[0017] In one embodiment, the grain size of the lithiophilic material may be from 2 nm to 11 nm.

[0018] In one embodiment, the thickness of the coating may be from 10 nm to 300 nm.

[0019] In one embodiment, the difference (d max ) between the maximum value (d min ) and the minimum value (d max ) of the thickness of the coating (d min ) may be 5 nm or less.

[0020] In one embodiment, the amount of the coating can be from 10 weight percent (wt%) to 60 wt% based on the total weight of the anode active material.

[0021] In one embodiment, a all-solid-state battery can be provided. The battery may include an anode current collector and an anode active material layer including the above-mentioned anode active material and disposed on the anode current collector. The battery may further have a solid electrolyte layer including a solid electrolyte and disposed on the anode active material layer. The battery may further have a cathode active material layer including a cathode active material and disposed on the solid electrolyte layer, and may have a cathode current collector disposed on the cathode active material layer.

[0022] In one embodiment, when a forming process is performed on the all-solid-state battery and the result is represented by a graph, with the x-axis being the capacity (mAh / g) and the y-axis being the voltage (V) in the graph, no plateau is observed in the range where the state of charge (SoC) of the all-solid-state battery is from 24% to 44%.

[0023] Furthermore, in the above-mentioned graph, the slope can be 1.7 or less but greater than 0.8.

[0024] Another aspect of the present invention provides a method for manufacturing an anode active material. The method may include: preparing carbon-based particles, a carbide precursor, and a lithiophilic material precursor. The method may further include forming a buffer layer disposed to cover at least a part of the surface of a core including the carbon-based particles. The method may further include forming a coating disposed to cover at least a part of the surface of the buffer layer. The buffer layer may include a carbide derived from the carbide precursor, and the coating may include a lithiophilic material derived from the lithiophilic material precursor.

[0025] In one embodiment, forming the buffer layer and forming the coating can be performed using chemical vapor deposition (CVD).

[0026] Thus, the carbide can include SiC x (0 < x ≤ 1).

[0027] In one embodiment, the carbide precursor may include silane gas and hydrocarbon gas.

[0028] In one embodiment, the lithiophilic material may include amorphous silicon (Si).

[0029] Furthermore, the lithiophilic material precursor may include at least one selected from SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, SiH3Cl, or any combination thereof, where H is hydrogen and Cl is chlorine.

[0030] In addition, the coating can be formed by chemical vapor deposition at a temperature of 700 °C or lower, or 475 °C or lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other features of the present invention will be described in detail with reference to certain embodiments shown in the accompanying drawings, which are given by way of illustration only and thus do not limit the present invention. In the drawings:

[0032] Figure 1 The general structure of a all-solid-state battery is shown;

[0033] Figure 2 The structure of the anode active material according to the present invention is shown;

[0034] Figure 3 An enlarged view of the surface structure of the anode active material according to the present invention is shown;

[0035] Figure 4 The results of X-ray diffraction (XRD) on Preparation Example 1 are shown;

[0036] Figure 5 The results of XRD on Comparative Preparation Example 1 are shown;

[0037] Figure 6 The results of X-ray photoelectron spectroscopy (XPS) on Preparation Example 1 are shown;

[0038] Figure 7 The results of XPS on Comparative Preparation Example 1 are shown;

[0039] Figure 8A The energy-dispersive X-ray spectroscopy (EDS) image of elemental carbon (C) in Preparation Example 1 is shown;

[0040] Figure 8B The EDS images of elemental carbon (C) and elemental silicon (Si) in Preparation Example 1 are shown;

[0041] Figure 9A The EDS image of elemental carbon (C) in Comparative Preparation Example 1 is shown;

[0042] Figure 9B The EDS images of elemental carbon (C) and elemental silicon (Si) in Comparative Preparation Example 1 are shown;

[0043] Figure 10A The EDS image of elemental carbon (C) in Comparative Preparation Example 2 is shown;

[0044] Figure 10B The EDS images of elemental carbon (C) and elemental silicon (Si) in Comparative Preparation Example 2 are shown;

[0045] Figure 11 Shows the charge / discharge graphs of Example 1 and Comparative Example 1;

[0046] Figure 12 Shows a partial enlarged view of the charge / discharge graph according to Figure 11 ;

[0047] Figure 13 Shows the charge / discharge graphs of the respective embodiments; and

[0048] Figure 14 Shows the charge / discharge graphs of the respective comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0049] The above and other objects, features, and advantages of the present invention will be more clearly understood from the following embodiments presented in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed herein but may be changed into different forms. These embodiments are provided to fully illustrate the present invention and to fully convey the spirit of the present invention to those skilled in the art.

[0050] In these drawings, the same reference numerals refer to the same or similar elements. For the sake of clarity of the present disclosure, the dimensions of the structures are depicted as larger than the actual size. It should be understood that although terms such as "first", "second", etc. may be used herein to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the present invention, the "first" element discussed below may be referred to as the "second" element. Similarly, the "second" element may also be referred to as the "first" element. As used herein, the singular form is intended to also include the plural form unless the context clearly dictates otherwise.

[0051] It should be further understood that when terms such as "comprising", "including", or "having" are used in this specification, it means that the stated features, integers, steps, operations, elements, components, or combinations thereof exist. However, these terms do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Additionally, it should be understood that when an element such as a layer, film, region, or sheet is referred to as being "on" another element, the element can be directly on the other element or there can be intervening elements between them. Similarly, when an element such as a layer, film, region, or sheet is referred to as being "under" another element, the element can be directly under the other element or there can be intervening elements between them.

[0052] Unless otherwise specified, all numbers, values, and / or expressions representing amounts of components, reaction conditions, polymer compositions, and mixtures used herein are to be considered approximations that include, among other things, various uncertainties (such uncertainties that inherently occur in obtaining these values and that affect the measured values), and thus should be understood to be modified in all instances by the term "about". In addition, when a numerical range is disclosed in this specification, the range is continuous and includes all values from the minimum value to the maximum value of the range, unless otherwise specified. Further, when such a range refers to integer values, all integers from the minimum value to the maximum value are included, unless otherwise specified.

[0053] In this specification, when describing a range of a variable, the variable is intended to include all values, including the endpoints described within the range. For example, the range "5 to 10" should be understood to include any sub-ranges (such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc.) as well as the individual values of 5, 6, 7, 8, 9, and 10, and should also be understood to include any values between the valid integers within the range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. Additionally, for example, the range "10% to 30%" should be understood to include sub-ranges (such as 10% to 15%, 12% to 18%, 20% to 30%, etc.) as well as all integers (including values from 10% to 30% such as 10%, 11%, 12%, 13%, etc.), and should also be understood to include any values between the valid integers within the range, such as 10.5%, 15.5%, 25.5%, etc.

[0054] Figure 1 A all-solid-state battery according to the present invention is shown. Referring to Figure 1 , the all-solid-state battery may include: an anode current collector 10, an anode active material layer 20, a solid electrolyte layer 30, a cathode active material layer 40, and a cathode current collector 50. The anode active material layer 20 contains an anode active material according to the present invention and is disposed on the anode current collector 10. The solid electrolyte layer 30 contains a solid electrolyte and is disposed on the anode active material layer 20. The cathode active material layer 40 contains a cathode active material and is disposed on the solid electrolyte layer 30. The cathode current collector 50 is disposed on the cathode active material layer 40.

[0055] The anode current collector 10 can be configured to transfer electrons to or receive electrons from the anode active material during charging and discharging. The anode current collector 10 can be a plate-shaped substrate having conductivity. Specifically, the anode current collector 10 can be in the form of a sheet, a thin film, or a foil.

[0056] The anode current collector 10 can contain a material that does not react with lithium. Specifically, the anode current collector 10 can contain at least one selected from nickel (Ni), copper (Cu), stainless steel, or any combination thereof.

[0057] The thickness of the anode current collector 10 is not particularly limited and may be, for example, from 1 micrometer (μm) to 500 μm.

[0058] The solid electrolyte layer 30 may be provided between the cathode active material layer 40 and the anode active material layer 20 and may contain a solid electrolyte having lithium ion conductivity.

[0059] The solid electrolyte may include an oxide-based solid electrolyte, a sulfide-based solid electrolyte, etc. Here, a sulfide-based solid electrolyte having high lithium ion conductivity can be used. The sulfide-based solid electrolyte is not particularly limited, but examples thereof may include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers and Z is any one selected from Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers and M is any one selected from P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S 12 etc.

[0060] Examples of the oxide-based solid electrolyte may include perovskite-type LLTO (Li 3x La 2 / 3-x TiO3), phosphate-based NASICON-type LATP (Li 1+x Al x Ti 2-x (PO4)3), etc.

[0061] The cathode active material layer 40 may contain a cathode active material, a solid electrolyte, a conductive material, and a binder. The cathode active material can store and release lithium ions. Examples of the cathode active material may include rock salt layer-type active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, or Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3O2, etc.; spinel-type active materials such as LiMn2O4 or Li(Ni 0.5 Mn 1.5 )O4, etc.; inverse spinel-type active materials such as LiNiVO4 or LiCoVO4, etc.; olivine-type active materials such as LiFePO4, LiMnPO4, LiCoPO4 or LiNiPO4, etc.; silicon-containing active materials such as Li2FeSiO4 or Li2MnSiO4, etc.; rock salt layer-type active materials in which a part of transition metals are replaced by different metals, such as LiNi 0.8 Co (0.2-x) Al x O2(0 < x < 0.2), spinel-type active materials in which a part of transition metals are replaced by different metals, such as Li 1+x Mn 2-x-y M y O4 (where M is at least one selected from Al, Mg, Co, Fe, Ni and Zn, 0 < x + y < 2); lithium titanate such as Li4Ti5O 12 etc. In addition, the cathode active material can also be configured to be coated with a lithium metal oxide on its surface.

[0062] The conductive material can be configured to impart conductivity to the cathode active material layer 40. Examples of the conductive material can include carbon black, conductive graphite, acetylene black, carbon fiber, graphene, etc.

[0063] The binder can be configured to physically bond various components included in the cathode active material layer 40. Examples of the binder can include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc.

[0064] The solid electrolyte included in the cathode active material layer 40 can be used to improve the lithium ion conductivity of the cathode active material layer 40 and is substantially the same as the solid electrolyte of the solid electrolyte layer 30. Therefore, a detailed description thereof is omitted. Here, "substantially the same" means that the same type of solid electrolyte can be used, not necessarily meaning that the same solid electrolyte must be used.

[0065] The cathode current collector 50 can include a plate-shaped substrate having conductivity. The cathode current collector 50 can include aluminum foil. The thickness of the cathode current collector 50 is not particularly limited and can be, for example, 1 μm to 500 μm.

[0066] The anode active material layer 20 may include an anode active material and may further include a solid electrolyte, a binder, and a conductive material. Here, the solid electrolyte, the binder, and the conductive material included in the anode active material layer 20 are substantially the same as the solid electrolyte included in the solid electrolyte layer 30 and the binder and the conductive material included in the cathode active material layer 40. Accordingly, a detailed description thereof is omitted. Here, "substantially the same" means that the same types of solid electrolyte, binder, and conductive material may be used, and does not necessarily mean that the same solid electrolyte, binder, and conductive material must be used.

[0067] The following is a detailed description of the anode active material.

[0068] Anode active material

[0069] Figure 2 An anode active material 200 according to the present invention is shown. Referring to Figure 2 , the anode active material 200 according to the present invention may include a core 210 having carbon-based particles, a buffer layer 220 covering at least a part of the surface of the core 210 and including a carbide, and a coating layer 230 covering at least a part of the surface of the buffer layer 220 and including a lithiumophilic material. The anode active material 200 according to the present invention may have a core-shell structure having the carbon-based particles as the core and the buffer layer 220 and the coating layer 230 as the shell, as Figure 2 shown.

[0070] Here, the shape of the carbon-based particles is not particularly limited, but in one embodiment, it may be spherical.

[0071] In one embodiment, the carbon-based particles may be those capable of reversibly inserting and extracting lithium and may include, for example, at least one selected from natural graphite, artificial graphite, or any combination thereof.

[0072] The buffer layer 220 may be inserted between the core 210 and the coating layer 230 to enhance the adhesion between the core 210 and the coating layer 230. Specifically, the carbide and the lithiumophilic material may be mixed at the interface between the buffer layer 220 and the coating layer 230. Here, the carbon included in the carbide may serve to inhibit the crystallization and volume expansion of the lithiumophilic material. Accordingly, it is possible to prevent separation from occurring at the interface between the coating layer 230 and the buffer layer 220 due to the repeated volume expansion and contraction of the coating layer 230 during charging and discharging of the all-solid-state battery.

[0073] In addition, the buffer layer 220 may be uniformly formed on the surface of the core 210. Since the buffer layer 220 is uniformly formed on the surface of the core 210, the buffer layer 220 may be used as a buffer to uniformly form the coating layer 230.

[0074] When the buffer layer 220 and the coating layer 230 are uniformly formed on the inner core 210, even if volume expansion occurs due to charging, the coating layer 230 will expand locally. This alleviates the phenomenon that stress is concentrated on a specific part, and ultimately improves the charge / discharge efficiency of the all-solid-state battery and extends its lifespan.

[0075] The carbide contained in the buffer layer 220 may be a compound of carbon (C) and one or more positive elements, particularly silicon carbide represented by SiC x (0 < x ≤ 1).

[0076] In one embodiment, the thickness of the buffer layer 220 can be from 1 nm to 20 nm. If the thickness of the buffer layer 220 is less than 1 nm, the buffering function of the buffer layer 220 may be reduced. On the other hand, if the thickness of the buffer layer 220 exceeds 20 nm, the energy density of the all-solid-state battery may be reduced.

[0077] In one embodiment, the coating layer 230 covering at least a part of the surface of the buffer layer 220 may contain a material with a high theoretical capacity. In particular, it may contain a lithiophilic material, which is a metal or metalloid capable of forming an alloy with lithium.

[0078] In the detailed description, the lithiophilic material may refer to a material that forms and induces lithium metal in a uniform form by minimizing the nucleation resistance during the reduction of lithium ions to lithium metal.

[0079] In one embodiment, the metal or metalloid capable of forming an alloy with lithium may include at least one selected from silicon (Si), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), magnesium (Mg), bismuth (Bi), tin (Sn), zinc (Zn), or any combination thereof. In particular, the lithiophilic material may include amorphous silicon (Si).

[0080] The charging of the all-solid-state battery is generally as follows. When a voltage is applied to the all-solid-state battery, lithium ions are released from the cathode active material. The lithium ions can move through the solid electrolyte layer 30 with lithium ion conductivity to the anode active material layer 20. The lithium ions are stored by being embedded in the anode active material (such as graphite) of the anode active material layer 20.

[0081] Thus, when a lithiophilic material as in the present invention (i.e., a metal or metalloid capable of forming an alloy with lithium) is included, the lithium ions are stored in the form of a lithium alloy with a high energy density, thereby increasing the capacity of the all-solid-state battery.

[0082] In one embodiment, the grain size of the lithiumophilic material can be from 2 nm to 11 nm, and in one example, it can be from 2 nm to 3 nm. Here, the grain size can be measured by performing X-ray diffraction (XRD) on the anode active material 200 including the coating 230.

[0083] In addition, the grain size can also be calculated using the following formula.

[0084] [Grain size formula]

[0085] D = 0.9·λ / β·cosθ

[0086] (where D is the grain size (nm), λ is the X-ray wavelength (nm), β is the half-width of the XRD peak (rad), and θ is the half-value of 2θ of the XRD peak).

[0087] When the grain size of the lithiumophilic material is from 2 nm to 11 nm, the crystallization phenomenon in which the amorphous lithiumophilic material transforms into a crystal during charging can be suppressed. In particular, when the grain size of the lithiumophilic material is from 2 nm to 3 nm, an excellent effect of suppressing crystallization can be presented.

[0088] In one embodiment, the thickness of the coating 230 can be from 10 nm to 300 nm. In particular, the thickness of the coating 230 can be from 20 nm to 300 nm. If the thickness of the coating 230 is less than 10 nm, the capacity of the all-solid-state battery may decrease. On the other hand, if the thickness of the coating 230 exceeds 300 nm, the degree of volume expansion of the coating 230 during charging may increase, which may accelerate the deterioration of the anode active material 200.

[0089] Figure 3 The surface of the anode active material 200 according to the present invention is shown. Here, the coating 230 is shown in a somewhat exaggerated manner to explain the difference between the maximum and minimum values of the thickness, which will be described later.

[0090] In one embodiment, the difference (d max ) between the maximum value (d min ) and the minimum value (d max ) of the thickness of the coating 230 can be 10 nm or less. In one example, the difference (d min ) between the maximum value (d max ) and the minimum value (d min ) of the thickness of the coating 230 can be 5 nm or less. In another example, the difference (d max ) between the maximum value (d min ) and the minimum value (d max)The difference (d min ) between the minimum value of the thickness of the coating 230 and max -d min ) can be 1.5 nm or less.

[0091] In the anode active material 200 according to the present invention, by forming a buffer layer 220 between the core 210 and the coating 230, the coating 230 can be applied more uniformly. The difference (d max ) between the maximum value (d min ) and the minimum value (d max -d min ) of the thickness of the coating 230 represents the uniformity of the coating 230.

[0092] Here, the difference (d max ) between the maximum value (d min ) and the minimum value (d max -d min ) of the thickness of the coating 230 can be measured and calculated by performing energy-dispersive X-ray spectroscopy (EDS) on the surface of the anode active material 200. In addition, during the EDS imaging process, when the magnification is increased to the extreme and the imaging range is limited to a very narrow range, regardless of the actual coating uniformity of the coating, the difference (d max ) between the maximum value (d min ) and the minimum value (d max -d min ) of the thickness of the coating 230 will approach 0 nm. In one embodiment, the magnification can be set from 20,000 times to 100,000 times.

[0093] If the difference (d max ) between the maximum value (d min ) and the minimum value (d max -d min ) of the thickness of the coating 230 exceeds 10 nm, it can be determined that the application of the coating 230 is uneven. In this case, when the all-solid-state battery containing the anode active material 200 is charged, local volume expansion will occur, accelerating the interfacial separation between the core 210 and the buffer layer 220 or between the buffer layer 220 and the coating 230.

[0094] On the other hand, when the difference (d max ) between the maximum value (d min ) and the minimum value (d max -d min) is 5 nm or less, it can be determined that the coating 230 is applied uniformly. In one embodiment, when the maximum value (d max ) and the minimum value of the thickness of the coating 230 (d min ) max -d min ) is 1.5 nm or less, it can be determined that the application of coating 230 is very uniform.

[0095] As such, uniform volume expansion may occur during charging of the all-solid-state battery including the anode active material 200. Therefore, interface separation between the core 210 and the buffer layer 220 or between the buffer layer 220 and the coating layer 230 may be prevented.

[0096] The amount of the coating layer 230 may be 10 weight percent (wt%) to 60 wt% based on the total weight of the anode active material 200. If the amount of the coating layer 230 is less than 10 wt%, the theoretical capacity of the anode active material 200 may be reduced based on the total weight of the anode active material 200. On the other hand, if the amount of the coating layer 230 exceeds 60 wt%, the volume expansion of the coating layer 230 may be aggravated, which may increase the interface separation.

[0097] The state of charge of a battery refers to how much energy is currently remaining. The percentage of the available storage (remaining) capacity at the current state of charge relative to the maximum capacity that can be stored when the battery is fully charged (the maximum storage capacity of the battery) can be defined as "SoC (%)". In this specification, SoC is referred to as "state of charge".

[0098] In this regard, when a formation process is performed on an all-solid-state battery comprising an anode active material 200 according to the present invention and the results are represented in a graph, with the x-axis being the capacity in milliampere hours per gram mass (mAh / g) and the y-axis being the voltage (V), no platform is observed within the range of 24% to 44% of the state of charge (SoC) of the all-solid-state battery.

[0099] Here, a platform refers to a flat voltage on a graph, which may be due to crystallization of a lithiophilic material. For example, when amorphous silicon (Si) is used as a lithiophilic material, and during the formation of an all-solid-state battery including amorphous silicon, the structure of the amorphous silicon is transformed into a crystal, a platform can be observed. On the contrary, if no platform is observed, it is understood that such crystallization does not occur.

[0100] The all-solid-state battery including the anode active material 200 according to the present invention does not show a plateau in the range of 24% to 44% of the state of charge (SoC) of the all-solid-state battery, which means that the lithiophilic material does not crystallize. Therefore, during the initial charge and discharge, irreversible capacity reduction can be suppressed. In addition, volume expansion of the layer 20 of the anode active material 200 can be suppressed.

[0101] In addition, in the above figure, the slope can be 1.7 or less, but greater than 0.8, and can be 1.3 to 1.5 in one embodiment. If the slope of the figure is 0.8 or less, the lithiophilic material may crystallize to some extent. On the other hand, if the slope of the figure exceeds 1.7, the lithiophilic material may not fully function as the anode active material due to an increase in the resistance of the material.

[0102] A method for manufacturing the anode active material 200 is described below.

[0103] Method for manufacturing anode active material

[0104] The method for manufacturing the anode active material 200 according to the present invention includes: preparing carbon-based particles, a carbide precursor, and a lithiophilic material precursor; forming a buffer layer 220 that is provided to cover at least a part of the surface of a core 210 including the carbon-based particles; and forming a coating 230 that is provided to cover at least a part of the surface of the buffer layer 220.

[0105] Here, the carbon-based particles can reversibly intercalate and deintercalate lithium and are substantially the same as those carbon-based particles described for the anode active material 200. Therefore, a detailed description thereof is omitted.

[0106] The buffer layer 220 may include a carbide derived from the carbide precursor. The carbide precursor may be a material that is converted into a carbide by a predetermined deposition process. Specifically, the carbide precursor may include a carbon (C)-containing precursor and a precursor containing a positive element that combines with carbon (C) to form a carbide. In addition, a precursor containing both carbon (C) and a positive element may also be used. Here, the carbide precursor may be provided in the form of a gas.

[0107] In addition, the coating 230 may include a lithiophilic material derived from the lithiophilic material precursor. The lithiophilic material precursor may be a material that is converted into a lithiophilic material by a predetermined deposition process. Here, the lithiophilic material precursor may be provided in the form of a gas.

[0108] After preparing the carbon-based particles, the carbide precursor, and the lithiophilic material precursor in this manner, a buffer layer 220 can be formed by coating the carbide on the surface of the carbon-based particles. Chemical vapor deposition (CVD) can be used to form the buffer layer 220. Through chemical vapor deposition, the carbide precursor can be converted into carbide, and the lithiophilic material precursor can be converted into lithiophilic material.

[0109] Chemical vapor deposition is a process of forming a coating 230 on a material to be coated by using a chemical reaction between a solid-gas or liquid-gas with different properties. CVD can be distinguished from chemical vapor reaction (CVR).

[0110] Forming the buffer layer 220 using chemical vapor deposition can be carried out under milder conditions than those typically used in the related art field to coat the carbide on the surface of the carbon-based particles. It is known that the process of applying carbon (C) using chemical vapor deposition generally can be carried out at a high temperature of 900 °C to 1300 °C. The process of applying the buffer layer 220 according to the present invention can be carried out under conditions lower than the above temperature. For example, chemical vapor deposition can be carried out at 400 °C to 500 °C.

[0111] In addition, the thickness of the buffer layer 220 formed using chemical vapor deposition can be 1 nm to 20 nm.

[0112] The carbide in the buffer layer 220 can include SiC x (0 < x ≤ 1). Therefore, the carbide precursor for forming the carbide expressed as SiC x (0 < x ≤ 1) using chemical vapor deposition can include silane gas and hydrocarbon gas.

[0113] Silane gas acts as a precursor containing positive elements and can include, for example, at least one selected from SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, SiH3Cl, or any combination thereof, where H is hydrogen and Cl is chlorine. In one embodiment, SiH4 can be used.

[0114] Hydrocarbon gas acts as a precursor containing carbon (C) and can include, for example, at least one selected from methane (CH4), acetylene (C2H2), ethylene (C2H4), or any combination thereof.

[0115] Thus, a buffer layer 220 can be obtained in which the carbide is uniformly applied on the surface of the inner core 210.

[0116] According to the present invention, after forming the buffer layer 220 on the inner core 210 using chemical vapor deposition, a coating 230 can be formed by coating a lithiophilic material. Here, chemical vapor deposition (CVD) can be used to form the coating 230.

[0117] The coating 230 is not directly applied to the surface of the core 210, but is formed after a buffer layer 220 is uniformly formed on the core 210. Therefore, the coating 230 can also be uniformly formed on the buffer layer 220.

[0118] In addition, when the coating 230 is formed on the buffer layer 220, carbides and lithiophilic materials can be mixed at the interface between the buffer layer 220 and the coating 230. Carbon in the carbides can inhibit the growth of lithiophilic materials at the interface, achieving a smaller grain size.

[0119] In one embodiment, the lithiophilic material is a material with a high theoretical capacity and can include lithiophilic materials in the form of metals or metalloids capable of alloying with lithium. Metals or metalloids capable of alloying with lithium can include at least one selected from silicon (Si), gold (Au), platinum (Pt), magnesium (Mg), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or any combination thereof. In one example, the lithiophilic material can include amorphous silicon (Si).

[0120] In addition, when amorphous silicon (Si) is used as the lithiophilic material, the lithiophilic material precursor can be silane gas. For example, the silane gas can include at least one selected from SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, SiH3Cl, or any combination thereof.

[0121] In addition, the anode active material 200 obtained by the method for manufacturing the anode active material 200 is substantially the same as the above-described anode active material 200. Therefore, redundant description thereof is omitted.

[0122] The present invention can be better understood through the following examples and comparative examples. However, these examples are not to be construed as limiting the technical spirit of the present invention.

[0123] Preparation Example 1

[0124] In step (a), spherical natural graphite is prepared as the carbon-based particles, and silane gas and ethylene (C2H4) are prepared as carbide precursors. In addition, silane gas is also used as the lithiophilic material precursor.

[0125] In step (b), the reactor of the equipment for chemical vapor deposition is heated to about 475 °C in an argon (Ar) atmosphere. Then, 50 grams (g) of the prepared spherical natural graphite is placed into the reactor, and the prepared silane (SiH4) gas and ethylene (C2H4) are injected at flow rates of 100 standard cubic centimeters per minute (sccm) and 32 sccm, respectively, to coat the surface of the natural graphite with silicon carbide, thereby forming a buffer layer. The formation of the buffer layer is carried out for about 70 minutes.

[0126] In step (c), after setting the temperature of the reactor to about 475 °C, silane gas is injected at a flow rate of 100 sccm for about 10 minutes to coat the surface of the buffer layer with silicon (Si), thereby forming a coating.

[0127] Thereby, an anode active material is obtained, in which a buffer layer containing silicon carbide and a coating containing silicon (Si) are formed on the core containing carbon-based particles.

[0128] Comparative Preparation Example 1

[0129] In step (a), spherical natural graphite is prepared as the carbon-based particles, and silane gas and ethylene (C2H4) are prepared as carbide precursors. In addition, silane gas is also used as a prelithiation material precursor.

[0130] In step (b), the reactor of the equipment for chemical vapor deposition is heated to about 475 °C in an argon (Ar) atmosphere. Then, 50 g of the prepared spherical natural graphite is placed into the reactor, and the prepared silane (SiH4) gas is injected at a flow rate of 100 sccm to directly coat the surface of the spherical natural graphite with silicon (Si), thereby forming a coating. Herein, chemical vapor deposition is carried out for about 73 minutes.

[0131] Thereby, an anode active material is obtained, in which a coating containing silicon (Si) is formed on the core containing carbon-based particles.

[0132] Comparative Preparation Example 2

[0133] Except for not performing step (c), the anode active material is manufactured in the same manner as in Preparation Example 1. Thereby, an anode active material is obtained, in which a buffer layer containing silicon carbide is formed on the core containing carbon-based particles.

[0134] Test Example 1 - Analysis of grain size

[0135] To determine the grain size of the anode active material manufactured according to the present invention, the anode active materials according to Preparation Example 1 and Comparative Preparation Example 1 were analyzed by XRD. The measurement range was θ = 20° to 70°, and the measurement results are shown in Figure 4 and Figure 5 in.

[0136] Referring to Figure 4 , no distinct peaks were observed at 2θ = 28°, 47°, and 56° which are representative of silicon crystallization. Additionally, using the above grain size formula (Formula 1), the grain size of silicon contained in the coating was calculated to be 2.34 nm.

[0137] Referring to Figure 5 , compared with Figure 4 , distinct peaks were observed at 2θ = 28°, 47°, and 56° which are representative of silicon crystallization. Additionally, using the above grain size formula (Formula 1), the grain size of silicon contained in the coating was calculated to be 11.89 nm.

[0138] Based on the above results, it was confirmed that in the anode active material (including the core, buffer layer, and coating) manufactured according to the present invention, the effect of suppressing silicon crystallization is significant.

[0139] Test Example 2 - Analysis of chemical bond form

[0140] To analyze the composition of the anode active material manufactured according to the present invention, the anode active materials according to Preparation Example 1 and Comparative Preparation Example 1 were analyzed by XPS. The results are shown in Figure 6 and Figure 7 .

[0141] Comparing Figure 6 and Figure 7 , Si - Si, Si - C, and O - Si - O bonds were formed. However, in the anode active material according to Preparation Example 1 (where a coating was formed on the buffer layer), Si - O - C and C - Si - C bonds were formed.

[0142] These bonds are presumably due to the formation of a buffer layer containing silicon carbide between the carbon - based particles and the coating.

[0143] Test Example 3 - Analysis of coating uniformity

[0144] To determine the coating uniformity of the anode active material manufactured according to the present invention, the surfaces of the anode active materials according to Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2 were analyzed by EDS.

[0145] Figure 8A shows the detection of the element carbon (C) in Preparation Example 1, Figure 8B shows the detection of the element carbon (C) and the element silicon (Si). Figure 9A shows the detection of the element carbon (C) in Comparative Preparation Example 1, Figure 9B shows the detection of the element carbon (C) and the element silicon (Si). Figure 10A shows the detection of the element carbon (C) in Comparative Preparation Example 2, Figure 10BDetection of elemental carbon (C) and elemental silicon (Si) is shown.

[0146] As Figure 8B , 9B and 10B, the maximum thickness of the buffer layer, the minimum thickness of the buffer layer, the difference between the two, the maximum thickness of the coating, the minimum thickness of the coating, and the difference between the two in the anode active material are listed in Table 1 below.

[0147] [Table 1]

[0148]

[0149] Referring to Table 1, the thickness difference of the buffer layer in Preparation Example 1 was measured to be 0.97 nm, confirming that the buffer layer was uniformly formed on the carbon-based particles. In addition, the thickness difference of the coating in Preparation Example 1 was measured to be 1.04 nm, confirming that the coating was uniformly formed on the buffer layer.

[0150] In contrast, in Comparative Preparation Example 1 (where silicon (Si) was directly applied to the surface of the carbon-based particles), the thickness difference of the coating was measured to be 5.97 nm, confirming that the coating was not uniformly applied to the carbon-based particles.

[0151] In addition, in Comparative Preparation Example 2, a buffer layer containing silicon carbide was uniformly applied, but a coating containing silicon was not formed.

[0152] Manufacture of all-solid-state battery

[0153] To evaluate the electrochemical performance of the all-solid-state battery using the anode active material according to the present invention, an all-solid-state battery was manufactured by the following method.

[0154] Example 1

[0155] An anode slurry was prepared by mixing the anode active material according to Preparation Example 1, a solid electrolyte, a binder, and a conductive material in a weight ratio of 58:39:2:1. Here, the solid electrolyte was a argyrodite sulfide-based electrolyte with a particle size of 500 nm to 1 μm, the conductive material was vapor-grown carbon fiber (VGCF), and the binder was a solution obtained by dissolving butadiene rubber (BR) in hexyl butyrate as a solvent in a weight ratio of 6.3:93.7.

[0156] The anode slurry was applied to a nickel foil (Ni foil) as an anode current collector, and then dried in an oven at 80 °C in an argon atmosphere for 10 minutes and in a vacuum at 100 °C for 2 hours or longer to form an anode plate.

[0157] A sulfide-based solid electrolyte of argyrodite with a particle size of 3 μm - 5 μm and a lithium metal with a thickness of 1 T (1 mm) are stacked on an anode plate, and then a pressure of 58000 N is applied thereto, thereby manufacturing a compressed all-solid-state battery. Accordingly, the designed capacity of the compressed all-solid-state battery is approximately 700 mAh / g.

[0158] Comparative Example 1

[0159] A compressed all-solid-state battery is manufactured in the same manner as in Example 1, except that the anode active material according to Comparative Preparation Example 1 is used.

[0160] Test Example 4 - Formation process

[0161] The compressed batteries according to Example 1 and Comparative Example 1 are subjected to a formation process under the following conditions. Here, the formation process is a process of activating the compressed battery to endow it with electrical characteristics, and can be understood as the first charge and discharge of the all-solid-state battery. The conditions are as follows:

[0162] - Cut-off voltage (V): 0.005 V - 1.5 V (formation), 0.005 V - 1.0 V (cycle)

[0163] - Formation C-rate (C): 0.1 C lithiation, 0.1 C delithiation

[0164] - Cycle C-rate (C): 0.3 C lithiation, 0.13 delithiation

[0165] The results of the formation processes of Example 1 and Comparative Example 1 are shown in Figure 11 , and the range of the state of charge (SoC) from 24% to 44% is magnified and shown in Figure 11 . In addition, the relevant specific values are listed in Tables 2 and 3 below. Figure 12

[0166] [Table 2]

[0167]

[0168]

[0169] [Table 3]

[0170]

[0171] Referring to Figure 11 and Figure 12 , no plateau is observed in the compressed battery according to Example 1. In contrast, a plateau is observed in the compressed battery according to Comparative Example 1.

[0172] These results indicate that in Comparative Example 1, crystalline silicon grows near a state of charge (SoC) of 44% (about 0.43 V) and gradually crystallizes. However, in Example 1, it was understood that since the growth of crystalline silicon was suppressed, no plateau was observed. Thus, it was confirmed that crystallization was suppressed when forming the coating on the buffer layer.

[0173] Test Example 5 - Formation processes of various examples and comparative examples

[0174] To improve the reliability of Test Example 4, four all-solid-state battery compression cells were fabricated in the same manner as in Example 1. They were named Si / SiC / G-700(1); Si / SiC / G-700(2); Si / SiC / G-700(3) and Si / SiC / G-700(4). In addition, three all-solid-state battery compression cells were fabricated in the same manner as in Comparative Example 1. They were named Si / G-700(1); Si / G-700(2) and Si / G-700(3).

[0175] After all seven all-solid-state battery compression cells had undergone the forming process, the results are shown in Figure 13 and Figure 14 . In addition, the relevant specific values are listed in Table 4 below. The specific test conditions were the same as those in Test Example 4.

[0176] [Table 4]

[0177]

[0178]

[0179] Referring to Figure 13 , in any of the four all-solid-state battery compression cells fabricated in the same manner as in Example 1, no plateau was observed. In addition, referring to Figure 14 , in the three all-solid-state battery compression cells fabricated in the same manner as in Comparative Example 1, a plateau was observed.

[0180] In addition, as shown in Table 3, the slopes of the four all-solid-state battery compression cells fabricated in the same manner as in Example 1 were from 1.393 to 1.467. In addition, the slopes of the three all-solid-state battery compression cells fabricated in the same manner as in Comparative Example 1 were from 0.267 to 0.282.

[0181] According to the present invention, the adhesion between the core and the coating can be enhanced by sequentially coating a buffer layer containing carbide and a coating containing a lithiophilic material on a core containing carbon-based particles.

[0182] In addition, by applying the lithiophilic material on the buffer layer instead of directly on the carbon-based particles, a uniform coating can be obtained.

[0183] In addition, by growing the coating at a relatively low temperature (700 °C or lower, 450 °C or lower), the growth of crystalline silicon can be suppressed, and the volume expansion of the anode active material layer can be reduced.

[0184] The effects of the present invention are not limited to the above effects. It should be understood that the effects of the present invention include all effects that can be inferred from the description of the present invention.

[0185] The embodiments of the present invention have been described above. Those skilled in the art will understand that various modifications and changes can be made by changing, deleting, or adding components without departing from the scope and spirit of the present invention disclosed in the appended claims, and these will also be considered to be included within the scope of the rights of the present invention.

Claims

1. An anode active material comprising: an inner core comprising carbon-based particles; a buffer layer covering at least a portion of the surface of the core and comprising carbide; and A coating layer covers at least a portion of the surface of the buffer layer and comprises a lithium-philic material.

2. The anode active material according to claim 1, wherein The carbon-based particles include at least one selected from natural graphite, artificial graphite or any combination thereof.

3. The anode active material according to claim 1, wherein The carbide is based on SiC x And contains silicon and carbon, of which 0 <x≤1。 4. The anode active material according to claim 1, wherein The buffer layer has a thickness of 1 nm to 20 nm.

5. The anode active material according to claim 1, wherein The lithium-philic material comprises a metal or a metalloid capable of forming an alloy with lithium, and the metal or the metalloid capable of forming an alloy with lithium comprises at least one selected from silicon, gold, platinum, palladium, silver, aluminum, bismuth, tin, zinc or any combination thereof.

6. The anode active material according to claim 1, wherein The lithium-philic material includes amorphous silicon.

7. The anode active material according to claim 1, wherein The grain size of the lithium-philic material is 2 nm to 11 nm.

8. The anode active material according to claim 1, wherein The coating has a thickness of 10 nm to 300 nm.

9. The anode active material according to claim 1, wherein The maximum value d of the coating thickness max The minimum value d of the coating thickness min The difference between max -d min 5nm or less.

10. The anode active material according to claim 1, wherein The amount of the coating layer is 10 wt % to 60 wt % based on the total weight of the anode active material.

11. An all-solid-state battery, comprising: Anode current collector; an anode active material layer, the anode active material layer being disposed on the anode current collector, wherein the anode active material comprises: i) an inner core comprising carbon-based particles, ii) a buffer layer covering at least a portion of the surface of the inner core and comprising carbide; and iii) a coating layer, which covers at least a portion of the surface of the buffer layer and comprises a lithium-philic material; a solid electrolyte layer comprising a solid electrolyte and disposed on the anode active material layer; a cathode active material layer comprising a cathode active material and disposed on the solid electrolyte layer; and A cathode current collector is disposed on the cathode active material layer.

12. The all-solid-state battery according to claim 11, wherein: When the formation process was performed on an all-solid-state battery and the results were plotted with capacity in milliampere-hours per gram mass on the x-axis and voltage on the y-axis, no plateau was observed in the range of 24% to 44% state of charge of the all-solid-state battery.

13. The all-solid-state battery according to claim 11, wherein: When the formation process is performed on an all-solid-state battery and the results are graphed, with capacity on the x-axis and voltage on the y-axis, the slope of the graph is 1.7 or less but greater than 0.8 over a range of 24% to 44% state of charge of the all-solid-state battery.

14. A method for producing an anode active material, the method comprising: preparing carbon-based particles, carbide precursors and lithium-philic material precursors; forming a buffer layer disposed to cover at least a portion of a surface of an inner core comprising carbon-based particles; as well as forming a coating layer, the coating layer being arranged to cover at least a portion of the surface of the buffer layer, wherein the buffer layer comprises a carbide derived from a carbide precursor, and The coating comprises a lithiophilic material derived from a lithiophilic material precursor.

15. The method for producing an anode active material according to claim 14, wherein: The formation of the buffer layer and the formation of the coating layer are performed using chemical vapor deposition.

16. The method for producing an anode active material according to claim 14, wherein: The carbide is based on SiC x And contains silicon and carbon, of which 0 <x≤1。 17. The method for producing an anode active material according to claim 14, wherein: The carbide precursor includes silane gas and hydrocarbon gas.

18. The method for producing an anode active material according to claim 15, wherein: The lithium-philic material includes amorphous silicon.

19. The method for producing an anode active material according to claim 14, wherein: The lithium-philic material precursor includes at least one selected from SiH4, Si2H6, Si3H8, SiCl4, SiHCl3, Si2Cl6, SiH2Cl2, SiH3Cl or any combination thereof, wherein H is hydrogen and Cl is chlorine.

20. The method for producing an anode active material according to claim 15, wherein: The coating formation using chemical vapor deposition is carried out at a temperature of 475°C or less.

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