Anode material for lithium-ion secondary batteries, lithium-ion secondary battery, and method for manufacturing the anode material for lithium-ion secondary batteries

Abstract

To provide a negative electrode material for a lithium ion secondary battery with excellent charge-discharge cycle characteristics, a lithium ion secondary battery, and a manufacturing method for the negative electrode material for the lithium ion secondary battery.SOLUTION: A negative electrode material 100 for a lithium ion secondary battery includes inorganic particles 10, a first layer 20, and a second layer 30. The inorganic particles 10 contain Si and are capable of intercalating and deintercalating lithium ions. The first layer 20 contains carbon and covers all or some of the inorganic particles 10. The second layer 30 contains silicon oxycarbide (SiOxCy) and covers all or some of the first layer 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a negative electrode material for lithium-ion secondary batteries, a lithium-ion secondary battery, and a method for manufacturing a negative electrode material for lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion batteries are widely used as high-power, high-capacity secondary batteries in portable devices such as mobile phones, personal computers, and PDAs (personal data assistants), as well as for backup power supplies and vehicle power supplies. Lithium-ion batteries typically use lithium-containing composite oxides such as LiCoO2 as the positive electrode material and carbon-based materials as the negative electrode active material. When carbon-based materials are used as the negative electrode, their theoretical capacity is only 372 mAh / g, about 1 / 10th the capacity of metallic lithium. Furthermore, their theoretical density is low at 2.2 g / cc, and the density decreases even further when used as a negative electrode sheet. Therefore, using a material with a higher capacity per unit volume as the negative electrode is desirable for increasing battery capacity. Metals or metalloids such as Al, Ge, Si, Sn, Zn, and Pb are known to alloy with lithium, and secondary batteries using inorganic materials composed of these metals or metalloids as the negative electrode active material are being investigated. These inorganic materials have high capacity and high energy density, and can intercept and deintercept more lithium ions than negative electrodes made of carbon-based materials. Therefore, it is believed that high-capacity, high-energy-density batteries can be made using these materials, but their cycle characteristics are inferior to those of carbon-based materials.

[0003] The reason why inorganic materials have inferior cycle characteristics compared to carbon-based materials is thought to be that their volume changes significantly with the insertion and removal of lithium ions during charging and discharging, leading to problems such as the miniaturization of inorganic material particles and the detachment of the active material containing inorganic material particles from the current collector, resulting in a decrease in cycle characteristics.

[0004] As a technology to solve the above-mentioned problems, Patent Document 1 discloses a non-aqueous electrolyte secondary battery characterized by using a material in which a composite particle is formed in which the entire surface or part of the surrounding area of ​​a core particle made of solid phase A is coated with solid phase B, and solid phase A contains at least one of silicon, tin, and zinc as constituent elements, and solid phase B is a solid solution or intermetallic compound of any of silicon, tin, or zinc which are constituent elements of solid phase A, and at least one element selected from the group consisting of group 2 elements, transition elements, group 12 and 13 elements of the periodic table, and group 14 elements excluding carbon, and at least one of solid phase A or solid phase B is amorphous. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-291512 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in the non-aqueous electrolyte secondary battery disclosed in Patent Document 1, with only two phases, solid phase A and solid phase B, stress and strain due to expansion and contraction accumulate at the interphase boundary. As a result, after approximately 300 charge-discharge cycles, cracks occur, eventually leading to particle disintegration and a rapid decrease in charge-discharge capacity with each charge-discharge cycle. Furthermore, during lithium insertion into silicon particles, mechanical pressure of up to 10 MPa is applied to the silicon particles. This results in the fracture of the silicon particles and the destruction of the active material layer. For this reason, the use of nano-sized silicon particles of 150 nm or less is recommended, but this presents challenges in terms of both cost and supply. Moreover, because nano-sized silicon has a very large surface area, a large amount of electrolyte is consumed for interfacial film formation. This leads to problems such as a decrease in Coulomb efficiency due to side reactions of such electrolyte and a decrease in battery durability due to electrolyte depletion.

[0007] The present invention was made to solve the above-mentioned problems, and aims to provide a negative electrode material for lithium-ion secondary batteries, a lithium-ion secondary battery, and a method for manufacturing a negative electrode material for lithium-ion secondary batteries that have excellent charge-discharge cycle characteristics. [Means for solving the problem]

[0008] To achieve the objectives of the present invention, one embodiment of the negative electrode material for lithium-ion secondary batteries according to the present invention is: Inorganic particles containing Si and capable of intercalating and deintercalating lithium ions, A first layer containing carbon and covering all or part of the inorganic particles, Silicon oxycarbide (SiO x C y A second layer comprising ) and covering all or part of the first layer, Equipped with 、 The second layer further contains carbon particles, It is characterized by the following:

[0009] To achieve the objectives of the present invention, one embodiment of the method for producing a negative electrode material for lithium-ion secondary batteries according to the present invention is: A first coating step involves forming a first layer containing carbon on all or part of inorganic particles containing Si and capable of intercalating and deintercalating lithium ions, A second coating step in which a layer containing a precursor for the second layer is formed on all or part of the inorganic particles on which the first layer was formed in the first coating step, The process comprises a heating step of heating the inorganic particles on which a layer containing the precursor of the second layer has been formed in the second coating step, The aforementioned second layer is silicon oxycarbide (SiO x C y ) including fruit, The precursor of the second layer contains a silane coupling agent. In the second coating step described above, carbon particles are further added. , It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a negative electrode material for a lithium-ion secondary battery having excellent charge-discharge cycle characteristics, a lithium-ion secondary battery, and a manufacturing process of the negative electrode material for a lithium-ion secondary battery.

Brief Description of Drawings

[0011] [Figure 1] It is a cross-sectional view showing a negative electrode material for a lithium-ion secondary battery according to an embodiment. [Figure 2] It is a flowchart showing a manufacturing process of a negative electrode material for a lithium-ion secondary battery according to an embodiment. [Figure 3] It is a diagram for explaining a manufacturing process of a negative electrode material for a lithium-ion secondary battery according to an embodiment. [Figure 4] It is a diagram for explaining a manufacturing process of a negative electrode material for a lithium-ion secondary battery according to an embodiment. [Figure 5] It is a cross-sectional view showing a negative electrode material for a lithium-ion secondary battery according to a modified example. [Figure 6] (a) to (c) are TEM images of a negative electrode material for a lithium-ion secondary battery according to an example, (d) is a HAADF-STEM image of a negative electrode material for a lithium-ion secondary battery according to an example, and (e) to (h) are elemental division images of a negative electrode material for a lithium-ion secondary battery according to an example. [Figure 7] (a) to (d) are TEM images of a negative electrode material for a lithium-ion secondary battery according to an example. [Figure 8] (a) is a bright-field image of a negative electrode material for a lithium-ion secondary battery according to an example, (b) to (e) are elemental division images of a negative electrode material for a lithium-ion secondary battery according to an example, and (f) is an image obtained by superimposing FIGS. 8(b) to 8(e). [Figure 9] It is a diagram showing XRD patterns of a negative electrode material for a lithium-ion secondary battery according to an example, inorganic particles made of Si, and inorganic particles having a first layer formed thereon. [Figure 10]This figure shows the thermogravimetric analysis in an oxygen environment of the negative electrode material for a lithium-ion secondary battery according to the example, and the inorganic particles forming the first layer. [Figure 11] This figure shows the XPS spectrum of a negative electrode material for a lithium-ion secondary battery according to the example. [Figure 12] This figure shows the deconvolved HRXPS spectrum of C 1s of the negative electrode material for lithium-ion secondary batteries according to the example. [Figure 13] This figure shows the deconvoluted HRXPS spectrum of Si 2p, a negative electrode material for lithium-ion secondary batteries according to the example. [Figure 14] This figure shows the deconvolved HRXPS spectrum of O 1s, a negative electrode material for lithium-ion secondary batteries according to the example. [Figure 15] This figure shows the deconvolved HRXPS spectrum of N 1s of the negative electrode material for lithium-ion secondary batteries according to the example. [Figure 16] This figure shows the charge and discharge characteristics of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries according to the embodiment. [Figure 17] This figure shows the voltage profile of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries according to the embodiment. [Figure 18] This figure shows the differential capacitance profile of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries according to the embodiment. [Figure 19] This figure shows the charge and discharge characteristics of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries related to the comparative example. [Figure 20] This figure shows the voltage profile of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries related to the comparative example. [Figure 21] This figure shows the differential capacitance profile of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries related to the comparative example. [Figure 22](a) to (c) are SEM images of the upper surface of an anode created using the lithium-ion secondary battery negative electrode material according to the example, (d) is an SEM image of the cross-section of an anode created using the lithium-ion secondary battery negative electrode material according to the example, and (e) to (f) are SEM images of the cross-section of an anode created using the lithium-ion secondary battery negative electrode material of the comparative example. [Figure 23] This figure shows the charge and discharge characteristics of a negative electrode half-cell prepared using the negative electrode material for lithium-ion secondary batteries according to the embodiment. [Figure 24] This figure shows the charge and discharge characteristics of a full cell assembled using an anode made of the lithium-ion secondary battery negative electrode material according to the embodiment. [Figure 25] This figure shows the voltage profile of a full cell assembled using an anode made of the lithium-ion secondary battery negative electrode material according to the embodiment. [Modes for carrying out the invention]

[0012] Hereinafter, a negative electrode material for lithium-ion secondary batteries and a method for manufacturing the negative electrode material for lithium-ion secondary batteries according to embodiments of the present invention will be described with reference to the drawings.

[0013] The negative electrode material 100 for lithium-ion secondary batteries according to this embodiment comprises inorganic particles 10, a first layer 20, and a second layer 30, as shown in Figure 1. The negative electrode material 100 for lithium-ion secondary batteries is used as a negative electrode active material in a lithium-ion secondary battery.

[0014] The inorganic particles 10 contain Si and are capable of intercalating and deintercalating lithium ions. The inorganic particles 10 only need to contain Si and be capable of intercalating and deintercalating lithium ions, and may include particles such as Si, metal silicide, B-doped Si, and P-doped Si. Preferably, the inorganic particles 10 consist of Si particles. The inorganic particles 10 are, for example, particles with an average particle size of 0.02 μm to 20 μm. If the average particle size of the inorganic particles is less than 0.02 μm, they tend to aggregate and become difficult to handle, and if it exceeds 20 μm, the volume change of the inorganic particles is significant during charging and discharging, causing distortion and resulting in the particle becoming finely powdered. The average particle size of the inorganic particles is preferably in the range of 0.05 μm to 10 μm.

[0015] The first layer 20 contains carbon and covers all or part of the inorganic particles 10. The first layer 20 is obtained by coating the inorganic particles 10 with polydopamine and heating the polydopamine-coated inorganic particles 10, as described later. The thickness of the first layer 20 is preferably 5 nm to 100 nm.

[0016] The second layer 30 is silicon oxycarbide (SiO x C yThe first layer 20 contains a silane coupling agent, which is a precursor of silicon oxycarbide, and covers all or part of the first layer 20. Also, X = 0.5 to 3.5 and Y = 0.3 to 3.5. The second layer 30 is formed by coating the inorganic particles 10 on which the first layer 20 is formed with a silane coupling agent, which is a precursor of silicon oxycarbide, and then heat-treating the inorganic particles 10 on which the first layer 20 coated with the silane coupling agent is formed. The second layer 30 preferably contains silicon oxycarbide black glass. The second layer 30 also preferably further contains carbon particles 31. The carbon particles 31 include carbon black, acetylene black, fullerene, heteroatom-doped carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene. The carbon black includes Ketjenblack and Super p(registered trademark). Because silicon oxycarbide has inherent limitations in its electronic conductivity, the inclusion of carbon particles 31 in the second layer 30 ensures the overall electronic conductivity of the negative electrode material 100 for lithium-ion secondary batteries. Furthermore, the second layer 30 may contain nitrogen derived from the silane coupling agent. The inclusion of nitrogen is considered beneficial to the overall electronic conductivity of the negative electrode material 100 for lithium-ion secondary batteries.

[0017] Next, a method for manufacturing the negative electrode material 100 for lithium-ion secondary batteries having the above configuration will be described.

[0018] As shown in Figure 2, the method for manufacturing a negative electrode material for lithium-ion secondary batteries comprises a first coating step (step S101), a second coating step (step S102), and a heating step (step S103).

[0019] In the first coating step (step S101), as shown in Figure 3, a first layer 20 containing carbon is formed on all or part of the inorganic particles 10 containing Si and capable of intercalating and deintercalating lithium ions. Specifically, the inorganic particles 10 are dispersed in a solution of ultrapure water and methanol. This solution is sonicated and then stirred. Next, Tris buffer solution at 8.5 pH is added, the solution is sonicated, and then stirred. Next, dopamine powder is added to this solution and stirred. The mass ratio of dopamine powder to inorganic particles 10 can be 1:4 to 4:1, preferably 1:1. Preferably, 3-hydroxytyramine hydrochloride is used as the dopamine powder. The overall color of the solution changes from yellowish-brown to black over time, indicating polymerization from dopamine to polydopamine. Due to the excellent adhesion of polydopamine, this process yields inorganic particles 10 coated with polydopamine. A solution containing polydopamine-coated inorganic particles 10 is further freeze-dried. The resulting polydopamine-coated inorganic particles 10 are then heat-treated at 600°C to 1000°C for 1 to 3 hours in an inert atmosphere (e.g., N2 or Ar atmosphere). This yields inorganic particles 10 with a first layer 20 containing carbon.

[0020] In the second coating step (step S102), as shown in Figure 4, a precursor 40 for the second layer 30 is formed on all or part of the inorganic particles 10 on which the first layer 20 was formed in the first coating step (step S101). Specifically, the inorganic particles 10 on which the first layer 20 was formed are placed in an aqueous solution containing a silane coupling agent and ultrapure water. Next, this aqueous solution is stirred and then ultrasonically treated. Subsequently, a solution in which carbon particles 31 are dispersed in a methanol and ultrapure water solution is mixed with the aqueous solution containing the inorganic particles 10 on which the first layer 20 was formed, a silane coupling agent, and ultrapure water, and stirred. Finally, this solution is freeze-dried to remove the solvent. As the carbon particles 31, carbon black, acetylene black, fullerene, heteroatom-doped carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene can be used. Preferably, 2 gm to 20 gm of inorganic particles 10 with the first layer 20 formed is added to an aqueous solution containing 25 ml to 100 ml of silane coupling agent and ultrapure water. Preferably, 12 gm of inorganic particles 10 with the first layer 20 formed is added to an aqueous solution containing 50 ml of silane coupling agent containing 1 gm of carbon particles 31 and ultrapure water.

[0021] The silane coupling agent includes at least one of the following: vinyl-based silane coupling agents, epoxy-based silane coupling agents, styryl-based silane coupling agents, methacrylic-based silane coupling agents, acrylic-based silane coupling agents, amino-based silane coupling agents, isocyanurate-based silane coupling agents, ureido-based silane coupling agents, mercapto-based silane coupling agents, isocyanate-based silane coupling agents, and acid anhydride-based silane coupling agents.

[0022] Vinyl silane coupling agents include vinyltrimethoxysilane and vinyltriethoxysilane. Epoxy silane coupling agents include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. Styryl silane coupling agents include p-styryltrimethoxysilane. Methacrylic silane coupling agents include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane. Acrylic silane coupling agents include 3-acryloxypropyltrimethoxysilane. Amino-based silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and hydrochloride salts of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane. Isocyanurate-based silane coupling agents include tris-(trimethoxysilylpropyl)isocyanurate, ureido-based silane coupling agents include 3-ureidopropyltrialkoxysilane, mercapto-based silane coupling agents include 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane. Isocyanate-based silane coupling agents include 3-isocyanatepropyltriethoxysilane. The acid anhydride-based silane coupling agent contains 3-trimethoxysilylpropyl succinic anhydride.

[0023] The silane coupling agent preferably comprises an amino-based silane coupling agent, and more preferably comprises 3-(aminopropyl)triethoxysilane.

[0024] In the heating step (step S103), the inorganic particles 10 on which the precursor 40 of the second layer 30 was formed in the second coating step (step S102) are heated. Specifically, the powder obtained after freeze-drying in the second coating step (step S102) is pulverized with a mortar and pestle and heat-treated at 800°C to 1250°C for 2 to 12 hours under a nitrogen or argon atmosphere. As a result, the precursor 40 of the second layer 30 is converted to silicon oxycarbide, the second layer 30 is formed, and the negative electrode material 100 for lithium-ion secondary batteries shown in Figure 1 is obtained. The second layer 30 also contains carbon particles 31.

[0025] As described above, according to the lithium-ion secondary battery anode material 100 and the method for manufacturing the lithium-ion secondary battery anode material 100 of this embodiment, coating the inorganic particles 10 with the first layer 20 and the second layer 30 not only improves the durability of the lithium-ion secondary battery anode material 100, but also prevents the lithium insertion / removal reaction from being inhibited by the appropriate structural defects of the second layer 30. Therefore, the inclusion of carbon particles 31 in the second layer 30 ensures the overall electronic conductivity of the lithium-ion secondary battery anode material 100. Thus, it is possible to provide a lithium-ion secondary battery anode material 100 with excellent charge-discharge cycle characteristics.

[0026] (modified version) In the above-described embodiment, an example was described in which a first layer 20 containing carbon is formed by coating the entire surface or part of the inorganic particles 10 with dopamine in the first coating step (step S101) and then heat-treating it. However, in the first coating step (step S101), it is sufficient to form a first layer 20 containing carbon, and the first layer 20 containing carbon may be formed by other methods. Melamine, aniline, catechol / diethylenetriamine, or pyrrole may be used instead of 3-hydroxytyramine hydrochloride. Furthermore, the first layer 20 containing carbon may be formed using thiophene, styrene, resorcinol / formaldehyde, benzoxazine, etc., by other methods.

[0027] In the above-described embodiment of the lithium-ion secondary battery anode material 100, an example in which the second layer 30 contains carbon particles 31 was explained. However, as shown in Figure 5, the second layer 30 only needs to contain silicon oxycarbide and does not need to contain carbon particles 31. By including silicon oxycarbide in the second layer 30, not only is the durability of the lithium-ion secondary battery anode material 100 improved, similar to the case in which carbon particles 31 are included, but the lithium insertion and removal reaction is not inhibited by appropriate structural defects in the second layer 30, making it possible to obtain a lithium-ion secondary battery anode material 100 with excellent charge-discharge cycle characteristics. In addition, a component having electronic conductivity may be included instead of, or together with, the carbon particles 31. [Examples]

[0028] The effects of the lithium-ion secondary battery negative electrode material 100 are demonstrated below by examples. These examples illustrate one embodiment of the present disclosure, and the present disclosure is not limited thereto.

[0029] First, we will describe the manufacturing method of the lithium-ion secondary battery negative electrode material 100 of Example 1.

[0030] In the first coating step (step S101), as shown in Figure 3, a first layer 20 containing carbon was formed on all or part of the inorganic particles 10 made of Si, which are capable of intercalating and deintercalating lithium ions. Specifically, 8 gm of inorganic particles 10 with a particle size of 1 μm to 5 μm was dispersed in 800 ml of a solution of ultrapure water and methanol. This solution was sonicated for 1 hour and then stirred overnight. Next, 100 ml of Tris buffer solution at 8.5 pH was added, the solution was sonicated for 30 minutes, and then stirred for 30 minutes. Next, 3-hydroxytyramine hydrochloride was added to the solution as dopamine powder and stirred for 48 hours. The overall color of the solution changed from yellowish-brown to black over time, indicating polymerization from dopamine to polydopamine. Due to the excellent adhesion of polydopamine, this process yielded inorganic particles 10 coated with polydopamine. The solution containing the polydopamine-coated inorganic particles 10 was further freeze-dried. The obtained inorganic particles 10 coated with polydopamine were freeze-dried and then heat-treated at 800°C for 2 hours in an inert atmosphere (N2 atmosphere). This resulted in inorganic particles 10 with a first layer 20 containing carbon. The thickness of the first layer 20 was approximately 50 nm.

[0031] In the second coating step (step S102), as shown in Figure 4, a precursor 40 for the second layer 30 was formed on all or part of the inorganic particles 10 on which the first layer 20 was formed in the first coating step (step S101). Specifically, the inorganic particles 10 on which the first layer 20 was formed were placed in an aqueous solution containing 3-(aminopropyl)triethoxysilane and ultrapure water. Next, this aqueous solution was stirred for 6 hours, and then sonicated for 1 hour. Subsequently, a solution in which acetylene black was dispersed as carbon particles 31 in a solution of methanol and ultrapure water was mixed with the inorganic particles 10 on which the first layer 20 was formed, and the aqueous solution containing 3-(aminopropyl)triethoxysilane and ultrapure water, and stirred overnight. Finally, this solution was freeze-dried to remove the solvent.

[0032] In the heating step (step S103), the inorganic particles 10 on which the second layer 30 was formed in the second coating step (step S102) are heated. Specifically, the powder obtained after freeze-drying in the second coating step (step S102) is pulverized with a mortar and pestle and heat-treated at 1000°C for 10 hours under a nitrogen atmosphere. As a result, the precursor 40 of the second layer 30 is converted to silicon oxycarbide (SiC x O y The material changes to black glass BG, forming a second layer 30, and the negative electrode material 100 for lithium-ion secondary batteries of Example 1 is obtained. The second layer 30 also contains carbon particles 31.

[0033] Next, TEM (Transmission Electron Microscope) images, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images using EDS (Energy dispersive X-ray spectroscopy) mapping, and elemental separation images were taken of the lithium-ion secondary battery anode material 100 of Example 1. TEM images of the lithium-ion secondary battery anode material 100 of Example 1 are shown in Figures 6(a) to 6(c). Furthermore, HAADF-STEM images using EDS mapping of the lithium-ion secondary battery anode material 100 of Example 1 are shown in Figure 6(d), elemental separation images of C are shown in Figure 6(e), elemental separation images of N are shown in Figure 6(f), elemental separation images of O are shown in Figure 6(g), and elemental separation images of Si are shown in Figure 6(h). Additionally, TEM images of the lithium-ion secondary battery anode material 100 of Example 1 are shown in Figures 7(a) to 7(d).

[0034] The negative electrode material 100 for lithium-ion secondary batteries in Example 1 clearly showed micron-sized characteristics in Figure 6(a). The inset in Figure 6(a) shows a magnified portion near the edge, further clarifying the presence of carbon C and silicon oxycarbide black glass BG layers surrounding the inorganic particles 10, which are Si. Furthermore, as shown in Figures 6(a) to 6(c) and 7(a) to 7(d), acetylene black AB nanoparticles were embedded in the silicon oxycarbide black glass BG layer. Since silicon oxycarbide black glass BG, which is a suboxide of silicon carbide (SiC), has inherent limitations in electronic conductivity, it is thought that the embedding of acetylene black AB nanoparticles ensures the overall electronic conductivity of the negative electrode material 100 for lithium-ion secondary batteries in Example 1. In addition, strong interfacial interactions between the SiC portion and the carbon nanostructure are assumed to promote the diffusion rate of lithium.

[0035] Next, as shown in Figure 8(a), a bright-field image of one particle of the lithium-ion secondary battery negative electrode material 100 of Example 1 was acquired. The spot in the bright-field image was due to acetylene black AB nanoparticles embedded in the silicon oxycarbide black glass BG layer, which was further evident from the elemental separation images, as shown in Figures 8(b) to 8(e). Figure 8(b) shows the elemental separation image of C, Figure 8(c) shows the elemental separation image of N, Figure 8(d) shows the elemental separation image of O, and Figure 8(e) shows the elemental separation image of Si. The acetylene black AB nanoparticles are indicated by the arrow shown in Figure 8(b). Figure 8(f) is an image obtained by superimposing Figures 8(b) to 8(e).

[0036] Next, as shown in Figure 9, the X-ray diffraction (XRD) patterns of inorganic particles 10 made of Si, inorganic particles 10 with the first layer 20 formed on them, and the lithium-ion secondary battery anode material 100 of Example 1 were measured. In Figure 9, Si um is inorganic particles 10, Si / C is inorganic particles 10 with the first layer 20 formed on them, and Si / C / ABG is the lithium-ion secondary battery anode material 100 of Example 1. The peaks at 28.4°(111), 47.3°(220), 56.1°(311), 69.2°(400), and 74.4°(331) suggest that the crystallinity of the inorganic particles 10 is also present in the lithium-ion secondary battery anode material 100 of Example 1.

[0037] Next, to estimate the free carbon content of the inorganic particles 10 forming the first layer 20 and the lithium-ion secondary battery anode material 100 of Example 1, thermogravimetric analysis (TAG) in an oxygen environment was performed as shown in Figure 10. In the inorganic particles 10 forming the first layer 20, the first layer 20 was oxidized and removed, so the mass decreased to about 45% at 600°C. In the lithium-ion secondary battery anode material 100 of Example 1, since it has a second layer 30, the first layer 20 was not oxidized and removed, so about 85% of the mass remained even at 900°C.

[0038] Figure 11 shows the XPS (X-ray photoelectron spectroscopy) spectrum of the lithium-ion secondary battery anode material 100 of Example 1. Figures 12 to 15 show the deconvoluted HRXPS (High-Resolution XPS) spectra of C 1s, Si 2p, O 1s, and N 1s of the lithium-ion secondary battery anode material 100 of Example 1, respectively.

[0039] It is important to understand that silicon oxycarbide black glass BG is composed of mixed structural units of SiC4, SiC3O, SiC2O2, SiCO3, and SiO4 arranged in an amorphous manner.

[0040] To further study the chemical environment of the elements present in the negative electrode material 100 for a lithium-ion secondary battery of Example 1, XPS spectra were measured. The broad XPS spectrum of the negative electrode material 100 for a lithium-ion secondary battery of Example 1 shown in FIG. 11 showed the presence of characteristic Si 2p (~100 eV), Si 2s (~156 eV), C 1s (~285 eV), N 1s (~400 eV), and O 1s (534 eV) peaks.

[0041] The deconvoluted HRXPS spectra of C 1s shown in FIG. 12, Si 2p shown in FIG. 13, and O 1s shown in FIG. 14 clearly showed the presence of various carbon, Si, and oxygen functional groups that may be attributed to the SiC4, SiC3O, SiC2O2, SiCO3, and SiO4 moieties. These SiC x O 4-x moieties were components of silicon oxycarbide black glass and had an amorphous network.

[0042] Analysis by XPS also showed that nitrogen doping was present in the silicon oxycarbide black glass BG as shown in FIG. 15. This nitrogen doping was uniform as apparent from the TEM elemental mappings shown in FIGS. 6(f) and 8(c). The presence of nitrogen is considered beneficial for the overall electron conductivity of the negative electrode material 100 for a lithium-ion secondary battery of Example 1.

[0043] Next, the charge-discharge characteristics and the like of the negative electrode material 100 for a lithium-ion secondary battery of Example 1 were measured. Also, for comparison, the charge-discharge characteristics and the like of the negative electrode material for a lithium-ion secondary battery of Comparative Example 1 were measured. The negative electrode material for a lithium-ion secondary battery of Comparative Example 1 used inorganic particles 10 made of Si. The inorganic particles 10 are the raw materials for the negative electrode material 100 for a lithium-ion secondary battery of Example 1.

[0044] First, a slurry of lithium-ion secondary battery negative electrode material 100 of Example 1 was prepared using a binder of carboxymethylcellulose (CMC) and polyacrylic acid (PAA) in mass, as shown in Table 1. CMC and PAY were used in equal proportions. Acetylene black was used as a conductive support. Ultrapure water was used as the solvent. The slurry prepared above was cast onto battery-grade copper foil, dried at 80°C, and then subjected to appropriate roll pressing at 80°C. Studies of half-cells and whole-cells were conducted using CR2025 coin batteries. A slurry of lithium-ion secondary battery negative electrode material for Comparative Example 1 was prepared in the same manner as for lithium-ion secondary battery negative electrode material 100 of Example 1.

[0045] [Table 1]

[0046] Next, a 1.0M LiPF6 negative electrode half-cell was prepared using the slurry of the lithium-ion secondary battery negative electrode material 100 from Example 1, with EC:DED as the electrolyte. Lithium foil was used as the counter and reference electrode. Negative electrode half-cell screening was performed within a potential window of 0.010V to 1.200V. A negative electrode half-cell was also prepared for the lithium-ion secondary battery negative electrode material of Comparative Example 1 in the same manner as in Example 1.

[0047] Next, the charge-discharge characteristics of the negative electrode half-cell prepared using the lithium-ion secondary battery negative electrode material 100 of Example 1 prepared above were measured, and the measurement results are shown in Figure 16. Also, as shown in Figure 16, 1 st , 5 th , 8 th , 58 th , 63 rd The voltage profiles for several selected cycles shown are measured and are presented in Figure 17. The differential capacitance profile estimated from the voltage profiles shown in Figure 17 is also measured and is presented in Figure 18.

[0048] The negative electrode half-cell prepared using the lithium-ion secondary battery negative electrode material 100 of Example 1 initially showed a reversible capacity of approximately 1803 mAh / g (8th cycle) at a charge / discharge current of 100 mA / g, as shown in Figure 16. The attractive charge / discharge characteristics were demonstrated by the advantage of retaining approximately 55% of the reversible capacity (i.e., 994 mAh / g, 55th cycle) even when the charge / discharge current was increased 40-fold (i.e., 4000 mA / g). Furthermore, when the charge current was returned to 100 mAh / g, a reversible capacity of 2149 mAh / g was obtained (58th cycle). This demonstrates that the lithium-ion secondary battery negative electrode material 100 of Example 1 possesses excellent charge / discharge characteristics. Also, as shown in Figure 17, st , 5 th , 8 th , 58 th , 63 rd From the measurement results of the voltage profiles of several selected cycles shown, the differential capacitance profile shown in Figure 18 was estimated. The advantages of the lithium-ion secondary battery anode material 100 of Example 1 were further understood by this differential capacitance profile. In detail, the uniform presence of a characteristic delithiation peak of Si centered at approximately 0.45 V clearly indicated that the delithiation capability of the lithium-ion secondary battery anode material 100 of Example 1 was not impaired throughout the cycle. Importantly, the peak potential and peak intensity remained constant throughout the cycles (cycles 5, 8, 58, and 63), indicating the structural integrity of the lithium-ion secondary battery anode material 100 of Example 1 during charging and discharging.

[0049] In contrast, the charge-discharge characteristics of the negative electrode half-cell of the lithium-ion secondary battery negative electrode material of Comparative Example 1 were measured, and the measurement results are shown in Figure 19. Also, as shown in Figure 19, st , 5 th , 8 th , 58 th , 63 rd The voltage profiles for several selected cycles shown are measured and are shown in Figure 20. The differential capacitance profile estimated from the voltage profiles shown in Figure 20 is also measured and is shown in Figure 21.

[0050] Similar measurements were performed using the lithium-ion secondary battery anode material of Comparative Example 1. The charge-discharge characteristics of the anode half-cell of the lithium-ion secondary battery anode material of Comparative Example 1 are shown in Figure 19. The initial reversible capacity measured was approximately 1550 mAh / g, but decreased to approximately 680 mAh / g over an 8-cycle span, indicating a rapid capacity degradation. At the end of the charge-discharge characteristic measurement, the reversible capacity was found to be 121 mAh / g (63rd cycle). This was less than 10% of the initial reversible capacity. This loss is thought to be due to the structural collapse of the lithium-ion secondary battery anode material of Comparative Example 1 due to mechanical fragmentation and pulverization caused by aggressive and uncontrolled volume expansion. The loss of lithiation-delithiation capability could be further observed in the voltage profiles of several selected cycles, shown in Figure 20, and clearly shown in the differential capacity profile, shown in Figure 21. Unlike the measurement results for the lithium-ion secondary battery anode material 100 of Example 1, shown in Figure 18, in the case of the lithium-ion secondary battery anode material of Comparative Example 1, as shown in Figure 21, the delithiation peak disappeared from the 5th cycle to the 63rd cycle. The disappearance of the characteristic delithiation peak during charging and discharging is thought to be due to mechanical damage to the lithium-ion secondary battery anode material of Comparative Example 1. This suggests that the methodology devised to design the lithium-ion secondary battery anode material 100 of Example 1 is more effective in withstanding lithium storage in a reversible manner.

[0051] Next, in order to understand the better and more stable charge-discharge characteristics of the anode of the lithium-ion secondary battery anode material 100 of Example 1 compared to the lithium-ion secondary battery anode material of Comparative Example 1, SEM images of each anode were taken. SEM (Scanning Electron Microscope) images of the upper surface of the anode created using the lithium-ion secondary battery anode material 100 of Example 1 are shown in Figures 22(a) to 22(c). SEM image of the cross-section of the anode created using the lithium-ion secondary battery anode material 100 of Example 1 is shown in Figure 22(d). SEM images of the cross-section of the anode created using the lithium-ion secondary battery anode material of Comparative Example 1 are shown in Figures 22(e) to 22(f).

[0052] SEM images of the anode of the lithium-ion secondary battery negative electrode material 100 of Example 1, specifically the top view shown in Figures 22(a) to 22(c) and the cross-section shown in Figure 22(d), clearly demonstrated the excellent structural integrity of the anode film even after charge-discharge characteristic testing. The structural integrity of the anode of the lithium-ion secondary battery negative electrode material 100 of Example 1, as seen in the SEM images, was consistent with the differential capacitance profile, where a constant delithiation peak intensity at a constant potential (~0.450V) supported the structural durability of the lithium-ion secondary battery negative electrode material 100 of Example 1 in reversible lithium storage. No cracks from the current collector or pilling of the anode film occurred despite the use of commercially available conventional CMC and PAA binders. This demonstrates the dual beneficial features of the proposed design, where silicon oxycarbide black glass can efficiently handle the enormous pressure caused by silicon lithiation, thus preventing pulverization and loss of lithiation-delithiation capability. In addition, it was found that the reduced volume expansion of the anode material helps maintain the function of the CMC-PAA binder, thus helping to maintain good adhesion to the current collector.

[0053] In contrast, in the case of the anode fabricated with the lithium-ion secondary battery negative electrode material of Comparative Example 1, mechanical damage due to inherently uncontrolled aggressive volume expansion and contraction significantly impaired the lithiumization-de-lithiation capability during charge-discharge cycles. This further compromised the structural stability of the anode, leading to battery failure, as is evident from the cross-sectional images of the anode of the lithium-ion secondary battery negative electrode material of Comparative Example 1 shown in Figures 22(e) to 22(f). This explains why, in the case of the negative electrode half-cell fabricated with the lithium-ion secondary battery negative electrode material of Comparative Example 1, the reversible capacity loss accelerated (~53%) in the first few cycles (the first eighth cycle).

[0054] Next, to investigate the stable reversible lithiation behavior of the lithium-ion secondary battery negative electrode material 100 of Example 1, charge-discharge characteristics were measured.

[0055] As shown in Figure 23, the charge-discharge characteristics of a negative electrode half-cell using the lithium-ion secondary battery negative electrode material 100 of Example 1 were measured at a charge-discharge current of 1000 mA / g in a potential window of 0.010 V to 1.200 V. This shows the change in lithiumization-delithiation capacity and the accompanying Coulomb efficiency during charge-discharge at a charge-discharge current of 1000 mA / g. This negative electrode half-cell was pre-charged and discharged several times at a charge-discharge current of 100 mA / g before being subjected to the relatively high charge-discharge current of 1000 mA / g. This measurement of charge-discharge characteristics showed remarkable reversible capacity retention behavior of the anode using the lithium-ion secondary battery negative electrode material 100 of Example 1 for more than 300 cycles. Furthermore, it showed a reversible capacity of approximately 1700 mAh / g after 305 charge-discharge cycles.

[0056] Next, in order to investigate the feasibility of the practical application of the lithium-ion secondary battery anode material 100 of Example 1 as an anode for a lithium-ion battery, a full cell was manufactured by combining an anode using the lithium-ion secondary battery anode material 100 of Example 1 with a commercially available lithium-nickel-cobalt-aluminum oxide (NCA) cathode. The charge and discharge characteristics of this full cell are shown in Figure 24.

[0057] Figure 24 shows the charge-discharge characteristics of a full cell at various charge-discharge currents with respect to the Si content of the anode. Figure 25 shows the voltage profiles for several selected cycles, as indicated by the arrows in Figure 24. The capacity obtained at the end of the charge-discharge characteristic measurement (rightmost arrow in Figure 24) was approximately 83% of the first discharge capacity. This measurement indicates that the anode using lithium-ion secondary battery negative electrode material 100 of Example 1 has the potential to be used in commercially available lithium-ion batteries with conventionally available binders.

[0058] As described above, the lithium-ion secondary battery anode material 100 of Example 1 showed a reversible capacity of approximately 1700 mAh / g after 305 charge-discharge cycles by coating the inorganic particles 10 with the first layer 20 and the second layer 30. Furthermore, TEM imaging of the lithium-ion secondary battery anode material 100 of Example 1 clearly showed the presence of carbon C and silicon oxycarbide black glass BG layers surrounding the inorganic particles 10, which are Si. In addition, acetylene black AB nanoparticles were embedded in the silicon oxycarbide black glass BG layer. Since oxycarbide black glass, which is a suboxide of silicon carbide (SiC), has inherent limitations in electronic conductivity, it is thought that the embedding of acetylene black AB nanoparticles ensures the overall electronic conductivity of the lithium-ion secondary battery anode material 100 of Example 1. Furthermore, although inorganic particles 10 made of Si were used in Example 1 described above, it is believed that similar results can be obtained by using particles such as metal silicide, B-doped Si, or P-doped Si as the inorganic particles 10.

[0059] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention. [Explanation of Symbols]

[0060] 10...Inorganic particles 20…1st layer 30…Second layer 31…Carbon particles 40… Precursor AB...Acetylene Black C…Carbon BG...Silicon oxycarbide black glass 100... Negative electrode material for lithium-ion secondary batteries

Claims

1. Inorganic particles containing Si and capable of intercalating and deintercalating lithium ions, A first layer containing carbon and covering all or part of the inorganic particles, Silicon oxycarbide (SiO ｘ C ｙ A second layer comprising ) and covering all or part of the first layer, Equipped with, The second layer further contains carbon particles, A negative electrode material for lithium-ion secondary batteries characterized by the following features.

2. The carbon particles include carbon black, acetylene black, fullerene, heteroatom-doped carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene. The negative electrode material for lithium-ion secondary batteries according to feature 1.

3. The negative electrode material for a lithium-ion secondary battery according to claim 1 or 2 is included in the negative electrode active material. Lithium-ion rechargeable battery.

4. A first coating step involves forming a first layer containing carbon on all or part of inorganic particles containing Si and capable of intercalating and deintercalating lithium ions, A second coating step in which a layer containing a precursor for the second layer is formed on all or part of the inorganic particles on which the first layer was formed in the first coating step, The process comprises a heating step of heating the inorganic particles on which a layer containing the precursor of the second layer has been formed in the second coating step, The aforementioned second layer is silicon oxycarbide (SiO ｘ C ｙ ) including, The precursor of the second layer contains a silane coupling agent. In the second coating step described above, carbon particles are further added. A method for manufacturing a negative electrode material for lithium-ion secondary batteries, characterized by the above.

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