Anode active material complex for lithium-sulfur battery, anode and lithium-sulfur battery including the same

Abstract

A negative electrode active material composite for a lithium-sulfur battery according to exemplary embodiments of the present invention comprises silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer may comprise graphite and carbon nanotubes. Additionally, a negative electrode and a lithium-sulfur battery comprising the negative electrode active material composite for a lithium-sulfur battery are provided.

Description

Technology Field

[0001] The present invention relates to a negative electrode active material composite for a lithium-sulfur battery, a negative electrode including the same, and a lithium-sulfur battery. Background Technology

[0002] Rechargeable batteries are batteries capable of repeated charging and discharging, and are widely used as power sources for portable electronic devices such as mobile phones and laptop PCs, as well as large electronic devices such as automobiles.

[0003] Lithium-ion batteries, in particular, are actively being researched and commercialized due to their high operating voltage, energy density per unit weight, and light weight. For example, metal oxides (LiCoO2, LiNiMnCoO) 2, LiFePO₄, etc. can be used as the positive electrode active material, and graphite or silicon can be used as the negative electrode active material.

[0004] However, lithium-ion batteries have limitations in meeting the energy density and power density required for large electronic devices or electric vehicles. Therefore, lithium-sulfur batteries, which possess high theoretical capacity, are receiving significant attention as a substitute for lithium-ion batteries.

[0005] A lithium-sulfur battery refers to an electrode system that uses a sulfur-based compound with a sulfur-sulfur bond as the cathode material and lithium metal as the anode material. Sulfur has high theoretical capacity and, based on abundant resources, can maximize manufacturing costs and performance, while also offering the advantages of being environmentally friendly.

[0006] However, lithium-sulfur batteries face difficulties in actual commercialization due to problems such as the shuttle phenomenon of lithium polysulfide, the formation of dendrites on the lithium metal anode, and the volume expansion of sulfur compounds. Therefore, various studies to solve these issues are actively underway.

[0007] For example, Korean Patent Publication No. 10-2023-0075579 discloses a lithium-sulfur battery with improved energy density and output by using sulfur as a cathode material and a lithium metal anode material. However, it does not provide sufficient battery life characteristics and battery efficiency. Prior art literature

[0008] Republic of Korea Published Patent Application No. 10-2023-0075579 The problem to be solved

[0009] One objective of the present invention is to provide a negative electrode active material composite for a lithium-sulfur battery having improved reliability and operational stability.

[0010] One objective of the present invention is to provide a negative electrode for a lithium-sulfur battery having improved reliability and operational stability.

[0011] One objective of the present invention is to provide a lithium-sulfur battery having improved reliability and operational stability. means of solving the problem

[0012] A negative electrode active material composite for a lithium-sulfur battery according to exemplary embodiments comprises silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer may include graphite and carbon nanotubes.

[0013] In one embodiment, the mass ratio of the carbon layer to the silicon-based particles may be 0.1 to 2.0.

[0014] In one embodiment, the mass ratio of the carbon nanotube to the silicon-based particle may be 0.05 to 1.5.

[0015] In one embodiment, the mass ratio of the graphite to the silicon-based particles may be 0.05 to 1.5.

[0016] In one embodiment, the mass ratio of the graphite to the silicon-based particles and the mass ratio of the carbon nanotubes to the silicon-based particles may be the same.

[0017] In one embodiment, the silicon-carbon composite may have an average size of 50 nm to 5 µm when measured during SEM surface analysis.

[0018] In one embodiment, the silicon-based particle is a single particle, and the average particle size (D50) of the single particle may be 50 nm to 5 μm.

[0019] In one embodiment, the silicon-based particles may have a crystalline, amorphous, or a composite structure in which crystalline and amorphous materials are mixed.

[0020] In one embodiment, the silicon-based particles are Si, SiO X (0 <x≤2) 및 Si 합금 중 하나 이상을 포함할 수 있다.

[0021] A negative electrode for a lithium-sulfur battery according to exemplary embodiments may include a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector and comprising a negative electrode active material composite according to claim 1.

[0022] In one embodiment, the negative electrode active material layer may contain 20 weight percent or more of the negative electrode active material.

[0023] In one embodiment, the negative electrode active material layer may further include at least one of a binder and a conductive material.

[0024] A lithium-sulfur battery according to exemplary embodiments may include the negative electrode; and a positive electrode facing the negative electrode. Effects of the invention

[0025] A negative electrode active material composite for a lithium-sulfur battery according to exemplary embodiments of the present invention comprises silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer may include graphite and carbon nanotubes. For example, the structural stability and electrical conductivity of the silicon-based particles can be improved by forming a carbon layer on the surface of the silicon-based particles.

[0026] The lithium-sulfur battery according to exemplary embodiments of the present invention has excellent electrochemical properties. For example, it has excellent cycle characteristics and Coulomb efficiency.

[0027] In the lithium-sulfur battery according to exemplary embodiments of the present invention, a silicon-carbon composite can be used as the negative electrode active material instead of the conventional lithium-metal negative electrode. Accordingly, internal safety can be improved along with electrochemical efficiency. Brief explanation of the drawing

[0028] FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to exemplary embodiments. FIG. 2 schematically illustrates a lithium-sulfur battery system according to one embodiment. Figure 3 shows (a) XRD measurement results and (b) TGA analysis results of the cathode active material composite of Example 1, respectively. Figure 4 shows (a) XRD measurement results and (b) TGA analysis results of the cathode active material composites of Examples 2 and 3, respectively. Figures 5 (a) to (d) are SEM images of the surface of the cathode active material composite of Example 1. Figures 6 (e) to (h) show the SEM-EDX analysis results of the cathode active material composite of Example 1. Figures 7 (a) to (c) are TEM images of the surface of the cathode active material composite of Example 1. FIG. 8(a) and (b) show 50 of the coin half cells of Examples 1 to 3th This shows the cycle characteristics and the charge / discharge graphs according to the cycle, respectively. Figures 9 (a) and (b) respectively show the rate characteristics (C-rate) and charge / discharge graphs according to current of the coin pool cell of Example 1. FIG. 10 shows 100 of the coin pool cell of Example 1 th This is an image of the cathode active material complex after cycling. Specific details for implementing the invention

[0029] A negative electrode active material composite for a lithium-sulfur battery according to exemplary embodiments of the present invention (hereinafter, negative electrode active material composite) comprises silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer may comprise graphite and carbon nanotubes. Additionally, a negative electrode for a lithium-sulfur battery and a lithium-sulfur battery comprising the negative electrode active material composite are provided.

[0030] Conventional lithium-sulfur batteries contain lithium polysulfide (Li2S) formed during the charging and discharging process. X The shuttle phenomenon in which , X=4,6,8) dissolves in the electrolyte and repeatedly moves between the anode and cathode is a major problem.

[0031] Lithium polysulfide can react with the lithium metal anode to form an SEI layer, which can reduce the efficiency of the battery. In addition, lithium dendrites may form due to non-uniform lithium deposition. Consequently, this can increase the internal resistance of the cell and reduce the power density and efficiency of the battery (e.g., reduced Coulomb efficiency). Therefore, we aim to provide an anode that can replace the lithium metal anode used in lithium-sulfur batteries.

[0032] FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to exemplary embodiments. FIG. 2 is a schematic representation of a lithium-sulfur battery system according to exemplary embodiments.

[0033] Referring to FIGS. 1 and 2, a lithium-sulfur battery according to one embodiment may include a positive electrode (100) and a negative electrode (130) facing the positive electrode (100).

[0034] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed on the negative electrode current collector (125). For example, the negative electrode active material layer (120) may be formed on one side or both sides of the negative electrode current collector (125).

[0035] For example, the negative electrode active material layer (120) may include a material capable of reversibly intercalating lithium ions. For example, the negative electrode active material may include a negative electrode active material complex described later.

[0036] A cathode active material composite according to exemplary embodiments comprises silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer may include graphite and carbon nanotubes. By including silicon-based particles, electrical conductivity can be improved, and by including a carbon layer, volume expansion of the silicon-based particles can be mitigated, thereby improving the lifespan characteristics of the battery. In addition, the formation of an unnecessary SEI layer by lithium polysulfide can be suppressed, thereby improving Coulomb efficiency.

[0037] For example, the carbon layer may be a coating layer that uniformly covers the entire surface of the silicon-based particle. For example, the carbon layer may be a coating layer that partially covers the particle surface by being formed in the form of an island layer or a pattern on the surface of the silicon-based particle.

[0038] In one embodiment, the mass ratio of the carbon layer to the silicon-based particles may be 0.1 to 2.0.

[0039] For example, the mass ratio of the carbon layer to the silicon-based particles may be 0.1 to 2.0, 0.1 to 1.9, 0.1 to 1.8, 0.1 to 1.7, 0.1 to 1.6, 0.1 to 1.5, 0.1 to 1.4, 0.1 to 1.3, 0.1 to 1.2, 0.1 to 1.1, 0.1 to 1.0, 0.1 to 0.9, 0.1 to 0.8, 0.1 to 0.7, 0.1 to 0.6, 0.1 to 0.5, 0.1 to 0.4, 0.1 to 0.3, 0.1 to 0.25, or 0.1 to 0.2.

[0040] When forming a silicon-carbon composite within the above range, direct contact between silicon-based particles and the electrolyte can be prevented to create a stable SEI layer. By improving the electrical conductivity and structural stability of the cathode active material composite, cycle characteristics and battery efficiency can be enhanced.

[0041] In one embodiment, the carbon layer may include carbon nanotubes and graphite. When the carbon layer includes graphite and carbon nanotubes among carbon materials, the silicon-based particles and the carbon material can form a composite well, and the formation of a nano-scale structure is also easy.

[0042] For example, carbon nanotubes may include single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanocones, etc.

[0043] For example, graphite may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0044] In one embodiment, the mass ratio of the carbon nanotube to the silicon-based particle may be 0.05 to 1.5. For example, the mass ratio of the carbon nanotube to the silicon-based particle may be 0.05 to 1.5, 0.1 to 1.5, 0.1 to 1.4, 0.1 to 1.3, 0.1 to 1.2, 0.1 to 1.1, or 0.1 to 1.

[0045] In one embodiment, the mass ratio of the graphite to the silicon-based particles may be 0.05 to 1.5. For example, the mass ratio of the graphite to the silicon-based particles may be 0.05 to 1.5, 0.1 to 1.5, 0.1 to 1.4, 0.1 to 1.3, 0.1 to 1.2, 0.1 to 1.1, or 0.1 to 1.

[0046] In one embodiment, the mass ratio of the graphite to the silicon-based particles and the mass ratio of the carbon nanotubes to the silicon-based particles may be the same. Within this range, the structural stability and electrical conductivity of the silicon-based particles can be improved, and a stable SEI layer can be formed. When applied to a lithium-sulfur battery, cycle characteristics and Coulomb efficiency can be improved.

[0047] In one embodiment, the average size of the cathode active material composite measured during Scanning Electron Microscope (SEM) surface analysis may be 50 nm to 5 μm.

[0048] For example, the average size measured during SEM surface analysis may be 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more. For example, the average size measured during SEM surface analysis may be 5 µm or less, 4.5 µm or less, 4 µm or less, 3.5 µm or less, 3 µm or less, or 2 µm or less. Within the above ranges, the volume change of the active material due to charging and discharging of the battery can be minimized, thereby improving the structural stability of the electrode and the electrical conductivity of the active material particles.

[0049] In one embodiment, the silicon-based particle is a single particle, and the average particle size (D50) of the single particle may be 50 nm to 5 μm. For example, the average particle size of the single particle may be 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more. For example, it may be 5 μm or less, 4.5 μm or less, 4 μm or less, 3.5 μm or less, 3 μm or less, or 2 μm or less.

[0050] "Average particle size (D50)" refers to the value of the particle size corresponding to 50% of the smallest particle when the total number of particles is set to 100% in a distribution curve in which particle sizes are accumulated from the smallest particle to the largest particle. For example, it may refer to the particle size when the volume accumulation percentage is 50%.

[0051] The average particle size (D50) can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer (PSA) or by measuring from TEM or SEM images. In addition, it can be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from therein.

[0052] For example, "single particle" may refer to a non-aggregated particle (monolith). On the other hand, "secondary particle" may refer to a particle in which multiple primary particles aggregate to be considered or observed as substantially one particle. For example, in the case of a secondary particle, the boundary of the primary particles may be observed in an SEM cross-sectional image. For example, a secondary particle may consist of more than 10, 30 or more, 50 or more, or 100 or more primary particles aggregated together.

[0053] The above secondary particles and the above single particles can be distinguished by the morphology of the particles. For example, the above secondary particles and the above single particles can be distinguished based on cross-sectional images of the particles measured by a scanning electron microscope (SEM). For example, in the case of the above single particles, unlike the secondary particles, the boundaries of the primary particles may not be observed in the SEM cross-sectional image.

[0054] Meanwhile, fine particles (e.g., particles having a volume of 1 / 100 or less relative to the volume of the single particle) may be attached to the surface of the single particle, and such form is not excluded from the concept of the single particle. For example, the single particles may exist in contact. For example, 2 to 10, 2 to 5, or 2 to 3 single particles may exist in contact.

[0055] The above particles are not crystallographically distinct. Therefore, the above secondary particles and the above single particles may be crystallographically single crystals or polycrystalline.

[0056] In one embodiment, the silicon-based particles may have a crystalline, amorphous, or a composite structure in which crystalline and amorphous materials are mixed. Preferably, they may have a crystalline structure. When they have a crystalline structure, they can store more lithium ions or increase mobility. Additionally, they have superior electrical conductivity and mechanical strength.

[0057] In one embodiment, the silicon-based particles are, for example, Si, SiO X (0 <x≤2), Si 합금 등일 수 있다.

[0058] For example, Si can be pure silicon. SiO X (0 <x≤2)는 실리콘 산화물일 수 있다. Si 합금은 예를 들어, Si-Z' 합금 (상기 Z'는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 희토류 원소 및 이들의 조합으로부터 선택된 1종 이상의 원소이며, Si는 아님)일 수 있다.

[0059] In some embodiments, the sphericity of the silicon-based particles may be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.9 or higher. Within this range, the aggregation of the silicon-based particles is suppressed, the capacity and lifespan characteristics of the battery are improved, and the rate of change in electrode thickness can be reduced.

[0060] For example, the sphericity of the silicon-based particles can be measured using a particle shape analyzer (QICPIC-LIXELL, Sympatec GmbH). For example, after deriving the cumulative distribution of the sphericity of the silicon-based particles through the particle shape analyzer, the sphericity corresponding to 50% of the distribution from particles with high sphericity can be determined as the sphericity of the silicon-based particles.

[0061] In an exemplary embodiment, the negative electrode active material can be manufactured as follows.

[0062] First, silicon particles can be prepared (e.g., S-10). The size, diameter, and other specific details of the silicon particles can be applied in the same manner as described above.

[0063] Next, silicon-based particles, multi-walled carbon nanotubes, and graphite can be mixed and milled to form a negative electrode active material mixture (S-20).

[0064] The mixing ratio may be applied in the same manner as described above. For example, mixing and / or milling may be performed in a milling machine. If necessary, solvents, binders, etc., may also be mixed. For example, the milling may be performed at 20 to 50 vibration sec -1 The process can be carried out at a speed of 0.5 to 1 hour. For example, the milling can be carried out for 10 minutes or more. For example, the milling can be carried out for 2 hours or less, or 1 hour or less. Within the above range, silicon-based particles, carbon nanotubes, and graphite can be sufficiently uniformly mixed.

[0065] Next, the formed cathode active material mixture can be annealed at 200 to 700°C (e.g., S-30).

[0066] For example, annealing can be performed in a furnace under inert gas conditions, and the annealing temperature can be 200°C or higher, 300°C or higher, or 400°C or higher. For example, the annealing temperature can be 900°C or lower, 800°C or lower, or 700°C or lower. Within the above range, carbon-based particles can be sufficiently firmly contacted or coated on silicon-based particles. If the temperature is lower than the above range, the annealing effect is negligible, and if the temperature is higher than the above range, carbon loss may occur, which may alter the structure and electrochemical properties of the cathode active material composite.

[0067] For example, the annealing may be carried out for 0.5 to 4 hours. For example, the annealing may be carried out for 30 minutes or more, 1 hour or more, or 2 hours or more. For example, the annealing may be carried out for 6 hours or less, 5 hours or less, 4 hours or less, or 3 hours or less. Within the above range, carbon-based particles can be sufficiently firmly contacted or coated on the surface of silicon-based particles.

[0068] Next, the annealed cathode active material mixture can be left at room temperature to obtain a cathode active material composite (e.g., S-40). The specific details of the finally obtained cathode active material composite are the same as those described above.

[0069] Referring again to FIGS. 1 and 2, the negative active material layer (120) may include a negative active material. For example, the negative active material may include the aforementioned negative active material composite. In some embodiments, the negative active material layer (120) may further include a binder and a conductive material as needed.

[0070] In some embodiments, the content of the cathode active material in the total weight of the cathode active material layer (120) may be 20 wt% or more, 30 wt% or more, 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, or 80 wt% or more.

[0071] In some embodiments, the content of the cathode active material in the total weight of the cathode active material layer (120) may be 99% by weight or less, 98% by weight or less, 97% by weight or less, 96% by weight or less, or 95% by weight or less.

[0072] For example, the binder may include organic binders such as polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, and polymethylmethacrylate; and water-based binders such as styrene-butadiene rubber (SBR). Additionally, the binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0073] In some embodiments, the content of the binder may be 1 weight% or more, 2 weight% or more, 3 weight% or more, 4 weight% or more, or 5 weight% or more of the total weight of the negative electrode active material layer (120). The content of the binder may be 40 weight% or less, 35 weight% or less, 30 weight% or less, 25 weight% or less, or 20 weight% or less of the total weight of the negative electrode active material layer (120).

[0074] In some embodiments, the negative active material layer (120) may or may not include a conductive material as needed. The conductive material may include, for example, carbon-based conductive materials such as graphite, carbon black, graphene, carbon nanotubes; metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3.

[0075] In some embodiments, the content of the conductive material may be 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt% or more, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, or 5 wt% or more of the total weight of the negative electrode active material layer (120). The content of the binder may be 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, or 10 wt% or less of the total weight of the negative electrode active material layer (120).

[0076] In one embodiment, the thickness of the negative active material layer (120) may be 20 to 50 μm, or 30 to 40 μm.

[0077] A lithium-sulfur battery may include a positive electrode (100) facing the negative electrode (130) described above.

[0078] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed on the positive electrode current collector (105). For example, the positive electrode active material layer (110) may be formed on one side or both sides of the positive electrode current collector (105).

[0079] For example, the anode active material, anode binder, conductive material, etc. can be dispersed in a solvent (or dispersion medium) to prepare an anode slurry. The anode slurry can be applied, dried, and rolled onto an anode current collector (105) to form an anode active material layer (110).

[0080] For example, the positive current collector (105) may include stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof.

[0081] For example, the positive active material layer (110) may include a positive active material capable of providing capacity through an electrochemical reaction. In some embodiments, the positive active material layer (110) may further include a binder and a conductive material.

[0082] The above positive active material is, for example, sulfur (S8), Li2S n (n≥1), organic sulfur compounds and carbon-sulfur polymers ((C2S x )n: x=2.5 to 50, n≥2) can be.

[0083] The anode binder may include organic binders such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate; water-based binders such as styrene-butadiene rubber (SBR). For example, the anode binder may be used together with a cellulose-based thickener.

[0084] The above conductive material may include, for example, carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes; and metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0085] In some embodiments, the area of ​​the negative electrode (130) may be larger than the area of ​​the positive electrode (100). In this case, lithium ions generated from the positive electrode (100) can move smoothly to the negative electrode (130) without precipitating in the middle.

[0086] In some embodiments, a separator (140) may be interposed between the anode (100) and the cathode (130). For example, an electrode assembly may be formed by winding, stacking, zigzag-folding, etc. of the separator (140).

[0087] For example, the separator (140) may include a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. Additionally, for example, the separator (140) may include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0088] A lithium-sulfur battery according to one embodiment may include a positive lead (not shown) connected to a positive electrode and protruding outside of a case (160); and a negative lead (not shown) connected to a negative electrode and protruding outside of a case (160).

[0089] For example, the positive lead can be electrically connected to the positive electrode. Similarly, the negative lead can be electrically connected to the negative electrode.

[0090] For example, the positive lead can be electrically connected to the positive current collector. Additionally, the negative lead can be electrically connected to the negative current collector.

[0091] For example, the positive current collector may include a positive tab protruding from one side of the positive current collector.

[0092] For example, the anode tab may be integral with the anode current collector or connected to the anode current collector by welding or the like. An anode active material layer may not be formed on the anode tab. The anode current collector and the anode lead may be electrically connected through the anode tab.

[0093] For example, the negative current collector may include a negative tab protruding from one side of the negative current collector.

[0094] For example, the above-mentioned cathode tab may be integral with the cathode current collector or connected to the cathode current collector by welding or the like. A cathode active material layer may not be formed on the above-mentioned cathode tab. The cathode current collector and the cathode lead may be electrically connected through the above-mentioned cathode tab.

[0095] For example, the electrode assembly and the above-described electrolyte can be housed together in a case (160) to form a lithium secondary battery.

[0096] The above lithium secondary battery can be manufactured in, for example, cylindrical, prismatic, pouch, or coin types.

[0097] In one embodiment, the electrolyte may include a lithium salt, an organic solvent, and, if necessary, an additive.

[0098] For example, the above lithium salt is Li + X - It can be expressed as.

[0099] In one embodiment, the X - is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It could be any one of them.

[0100] In some embodiments, the lithium salt may include LITFSI, LiBF4, LiPF6, etc.

[0101] As the above organic solvent, those known in the art may be used. For example, the above organic solvent may include ether-based solvents, carbonate-based solvents, ketone-based solvents, alcohol-based solvents, ester-based solvents, aprotic solvents, etc.

[0102] As the above additive, those known in the art may be used. For example, the above additive may include fluorine-containing carbonate compounds, vinylidene carbonate compounds, fluorine-containing lithium phosphate compounds, sulfone compounds, sulfate compounds, borate compounds, nitrile compounds, amine compounds, silane compounds, benzene compounds, etc.

[0103] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0104] Example 1

[0105] (1) Preparation of cathode active material composite

[0106] Si nanoparticles (≤50 nm, Alfa Aesar), MWCNT (Hanwha Nanotech Corp. CM-100, diameter: 10 nm–14 nm), and graphite (TIMCAL TIMREX® SFG6, TIMCAL Ltd.) are placed in a mini ball mill in a mass ratio of 6:2:2 and mixed for 30 minutes at 35 vibrations / min to prepare a cathode active material mixture. The cathode active material mixture is transferred to an alumina crucible and heated for 2 hours at 500°C under inert (Ar) conditions for 3°C min -1 The furnace was annealed at a heating rate. Afterward, the furnace was naturally cooled until it reached room temperature, at which point a cathode active material composite was obtained.

[0107] (2) Preparation of the cathode

[0108] A cathode slurry was prepared by mixing the cathode active material composite prepared in (1), a conductive material (Super-P), and a water-based binder (CMC / SBR 1:1) in a mini ball for 30 minutes in a weight ratio of 70:15:15.

[0109] The above cathode slurry was applied (20 μm) to a copper foil, dried at 80°C for 3 hours to evaporate the solvent, heat-treated in a vacuum oven at 80°C for 3 hours, and then rolled to produce a cathode.

[0110] (3) Manufacturing of a coin half-cell

[0111] The above negative electrode was cut into a disk (diameter 14 mm) and used, and a lithium metal thin film (MTI KOREA, thickness 0.17 mm, diameter 16 mm) was used as the counter electrode. A battery was assembled by interposing a polypropylene separator between the negative electrode and the counter electrode, and a coin half cell (2032R) was manufactured by injecting 1 M LiTFSI (Aldrich, 99.95%) and 0.25 M LiNO3 (Aesar, 99.98%, anhydrous) into a mixed solvent (1:1 v / v) of 1,2-dimethoxyethane (DME, Sigma Aldrich, 99.5%, anhydrous) and 1,3-dioxolane (DOL, Sigma Aldrich, 99.8%, anhydrous) as the electrolyte.

[0112] (4) Manufacturing of coin full-cell

[0113] A positive electrode slurry was prepared by dispersing positive electrode active material sulfur (Sulfur powder, Sigma-Aldrich), conductive material (Super-P), and binder (PVDF) in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 65:25:10.

[0114] The above anode slurry was applied (15 μm) to an aluminum foil, dried at 60°C for 1 hour to evaporate the solvent, heat-treated at 70°C for 10 hours in a vacuum oven, and then rolled to produce an anode.

[0115] The anode was prelithiated. The prelithiated anode was cut into a disc (14 mm in diameter) and a battery was assembled by interposing a polypropylene separator between the cathodes prepared in (2). A coin pool cell was prepared by injecting 1 M LiTFSI and 0.25 M LiNO3 into a mixed solvent (1:1 v / v) of DME / DOL as the electrolyte into the assembled battery.

[0116] Examples 2-4 and Comparative Examples 1-6

[0117] Example 2 was carried out in the same manner as Example 1, except that the mass ratio of Si, MWCNT, and graphite was 8:1:1 when (1) preparing the cathode active material composite.

[0118] Example 3 was carried out in the same manner as Example 1, except that (1) the mass ratio of Si, MWCNT, and graphite in the preparation of the cathode active material composite was 4:2:4.

[0119] Example 4 was carried out in the same manner as Example 1, except that (1) the mass ratio of Si, MWCNT, and graphite in the preparation of the cathode active material composite was 3:3:3.

[0120] Comparative Example 1 was carried out in the same manner as Example 1, except that graphene was used instead of MWCNT when manufacturing the (1) cathode active material composite.

[0121] Comparative Example 2 was carried out in the same manner as Example 1, except that the mass ratio of Si to MWCNT was 6:4 when manufacturing the (1) cathode active material composite.

[0122] Comparative Example 3 was carried out in the same manner as Example 1, except that the mass ratio of Si to graphite was 6:4 when manufacturing the (1) cathode active material composite.

[0123] Comparative Example 4 was carried out in the same manner as Example 1, except that (1) the mass ratio of Si, MWCNT, and graphite in the preparation of the cathode active material composite was 2:4:4.

[0124] Comparative Example 5 was carried out in the same manner as Example 1, except that the mixture was annealed at 1,000°C instead of 500°C when preparing the (1) cathode active material composite.

[0125] Comparative Example 6 used lithium metal as the negative electrode instead of the negative electrode of (2) when manufacturing (4) coin pool cell.

[0127] Experimental Example 1: XRD Analysis of Cathode Active Material Composite

[0128] X-ray diffraction (XRD) was performed to analyze the internal crystal structure of the cathode active material composites of Examples 1 to 3 (Rigaku D / MAX-2200). The results are shown in Figures 3(a) and 4(a).

[0129] Referring to Figures 3(a) and 4(a), Si peaks were observed at 2θ=28.4°, 47.2°, 56.1°, 69.2°, and 76.3° inside the cathode active material composite, and carbon nanotube and graphite peaks were observed at 26.5°. In addition, it was confirmed that no other impurities were included.

[0131] Experimental Example 2: TGA Analysis of Cathode Active Material Complex

[0132] The weight change of the samples of the cathode active material composites of Examples 1 to 3 was confirmed using a thermogravimetric analyzer (TGA, SHIMADZU DTG-60H) in the temperature range from 25°C to 800°C. The results are shown in Figures 3(b) and 4(b).

[0133] Referring to Figures 3(b) and 4(b), it can be seen that the weight decreases with the proportion of carbon material in the cathode active material composite.

[0135] Experimental Example 3: SEM-EDX Analysis of Cathode Active Material Composite

[0136] The surface of the cathode active material composite of Example 1 was observed using a scanning electron microscope (SEM, JSM7000F). The results are shown in Figures 5(a) to (d).

[0137] The SEM-EDX mapping results are shown in Figures 6(f) to (g).

[0138] The SEM-EDX scan results are shown in Fig. 6(h).

[0139] In FIGS. 5(a) to (d), it can be seen that the cathode active material composite according to the embodiment has a coating layer formed by Si particles (black arrows) surrounded by graphite flakes (yellow arrows) and carbon nanotubes (red arrows).

[0140] Figures 6(f) to (g) also show that in the cathode active material composite according to the embodiment, graphite and carbon nanotubes cover the Si particles well.

[0141] In the SEM-EDX-spaecta of Fig. 6(h), both Si and carbon (graphite and carbon nanotube) peaks were confirmed, and it can be expected that the cathode active material composite is structurally stable even when repeated charging and discharging.

[0143] Experimental Example 4: TEM and HR-TEM analysis of cathode active material composite

[0144] The surface of the cathode active material composite of Example 1 was observed using a transmission electron microscope (TEM, JEM-2100F) and HRTEM (High-resolution TEM). The TEM observation results are shown in Figures 7 (a) and (b), and the HR-TEM observation results are shown in Figure 7 (c).

[0145] Referring to Figures 7(a) and (b), it can be seen that Si particles are well surrounded and coated on graphite and carbon nanotubes. Figure 7(c) shows the lattice planes of silicon, carbon nanotubes, and graphite, as well as the interplanar spacing.

[0147] Experimental Example 5: Electrochemical Characteristics of a Coin Half Cell

[0148] 50 coin half cells of Examples (1 to 4) and Comparative Examples (1 to 5) thThe charge / discharge characteristics (specific capacity, Coulombic efficiencies) according to the cycle were measured at room temperature. The tests were conducted at a current of 0.1C up to 5 cycles, and at a current of 0.2C from 6 cycles onwards. The results are shown in Table 1.

[0149] Additionally, the results of Examples (1 to 3) are illustrated in FIG. 8(a). 1 st , 2 nd , 50 th The charge / discharge graph in the cycle is also shown in Fig. 8(b).

[0150] specific capacity (mAh·g -1 ) charge / discharge capacity Coulombic efficiencies (%) 1 st 50 th 1 st 50 th Example 1 2480 / 1263 737 / 713 51 96.7 Example 2 2804 / 2084 142 / 137 74 96.4 Example 3 1321 / 363 398 / 373 27 93.7 Example 4 1450 / 491 452 / 427 33 94.4 Comparative Example 1 2781 / 1540 622 / 561 55 90.2 Comparative Example 2 2070 / 1223 497 / 437 59 88.0 Comparative Example 3 2547 / 1670 569 / 511 66 90.0 Comparative Example 4 987 / 754 458 / 410 76 90.0 Comparative Example 5 2344 / 1164 510 / 465 50 91.1

[0151] In Comparative Example 1, when graphene is used instead of graphite as the carbon material, the capacity loss is large and the Coulomb efficiency is low when the cycle is repeated.

[0152] In Comparative Example 2, it was confirmed that when only carbon nanotubes were used as the carbon material, an unstable SEI layer was formed, resulting in lower lifespan characteristics and Coulomb efficiency.

[0153] In Comparative Example 3, it was confirmed that when only graphite is used as the carbon material, the initial capacity increases compared to Example 1, but there are limitations in improving the lifespan characteristics.

[0154] Comparative Example 4 confirmed that when the silicon content in the cathode active material composite is low, the capacity characteristics are inferior and the Coulomb efficiency decreases.

[0155] In Comparative Example 5, it can be seen that if the annealing temperature is too high when manufacturing the cathode active material composite, the lifespan characteristics and Coulomb efficiency are reduced.

[0156] On the other hand, Example 1 is excellent overall in terms of cycle characteristics, Coulomb efficiency, and capacity retention rate. Example 2 is excellent in high capacity and Coulomb efficiency, while Examples 3 and 4 are excellent in Coulomb efficiency and capacity retention rate.

[0158] Experimental Example 6: Electrochemical Characteristics of a Coin Pool Cell 2

[0159] The coin pool cell of Example 1 at 0.1C for 75 th Charge and discharge characteristics according to the cycle were measured at room temperature. 100 th The energy density was also checked after the cycle.

[0160] 100 coin pool cells of Example 1 at 0.5C th The charge / discharge characteristics and energy density according to the cycle were measured at room temperature.

[0161] 100 coin pool cells of Comparative Example 6 at 0.2C th The charge / discharge characteristics and energy density according to the cycle were measured at room temperature. The results are shown in Table 2.

[0162] Specific capacity (mAh·g -1 )charge / discharge capacity Coulombic efficiencies (%) Energy density(Whkg -1 ) beginning After cycling beginning After cycling Example 1 0.1C 720 / 610 328 / 324 84 98.7 542 0.5C 710 / 668 243 / 235 94 96.5 437 Comparative Example 6 950 / 927 400 / 390 97.5 97.5 350

[0163] Referring to Table 2, Example 1 exhibits similar capacity characteristics and Coulomb efficiency after cycling compared to Comparative Example 6. It also demonstrates excellent cycle characteristics and battery efficiency even at higher currents. Therefore, it can replace conventional lithium metal anodes. For example, it can prevent issues such as lithium dendrites or internal short circuits, which were previously problematic, thereby ensuring battery stability. Example 1 also exhibits excellent energy density even at relatively high currents.

[0165] Experimental Example 7: Electrochemical Characteristics of a Coin Pool Cell 3

[0166] The rate characteristics (C-rate) and charge / discharge graphs according to current of the coin pool cell of Example 1 are shown in FIG. 9(a) and (b), respectively.

[0167] Referring to FIG. 9, Example 1 has excellent cycle stability even at a high C-rate, and also has excellent capacity retention rate and Coulomb efficiency.

[0169] Experimental Example 8: 100 th SEM-EDS analysis of active material particles after charge-discharge cycles

[0170] The coin pool cell of Example 1 is cycled 100 times at room temperature thAfter cycle charge-discharge, the cathode was decomposed to separate the cathode active material composite. The surface of the separated cathode active material composite was washed with DOL:DME (1:1, v / v), the SEI layer was removed, and the composite was dried. Subsequently, the cathode active material composite was analyzed using SEM and EDS mapping. The results are shown in Figure 10.

[0171] Referring to Fig. 10, it can be seen in the SEM image that the silicon-based particles of the cathode active material composite are well coated by a carbon layer.

[0172] Both silicon-based particles and carbon (graphite and carbon nanotubes) were identified in SEM-EDX mapping and EDX spectra, confirming that the cathode active material composite is structurally stable even with repeated charging and discharging of the cathode.

Claims

Claim 1 A negative electrode active material composite for a lithium-sulfur battery, comprising silicon-based particles and a carbon layer covering at least a portion of the surface of the silicon-based particles, wherein the carbon layer comprises graphite and carbon nanotubes, the mass ratio of the graphite to the silicon-based particles is 0.1 to 1.5, the mass ratio of the carbon nanotubes to the silicon-based particles is 0.1 to 1.5, and the mass ratio of the graphite to the silicon-based particles and the mass ratio of the carbon nanotubes to the silicon-based particles are the same. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 Claim 1, wherein the negative electrode active material composite is a negative electrode active material composite for a lithium-sulfur battery having an average size of 50 nm to 5 µm as measured by SEM surface analysis. Claim 7 A negative electrode active material composite for a lithium-sulfur battery according to claim 1, wherein the silicon-based particle is a single particle and the average particle size (D50) of the single particle is 50 nm to 5 μm. Claim 8 A negative electrode active material composite for a lithium-sulfur battery according to claim 1, wherein the silicon-based particles have a crystalline, amorphous, or a composite structure in which crystalline and amorphous are mixed. Claim 9 In claim 1, the silicon-based particles are Si, SiO X (0 <x≤2) 및 Si 합금 중 하나 이상을 포함하는, 리튬-황 전지용 음극 활물질 복합체. Claim 10 A negative electrode for a lithium-sulfur battery comprising: a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector and comprising a negative electrode active material composite according to claim 1. Claim 11 A negative electrode for a lithium-sulfur battery according to claim 10, wherein the negative electrode active material layer comprises 20 weight% or more of the negative electrode active material. Claim 12 A negative electrode for a lithium-sulfur battery according to claim 10, wherein the negative electrode active material layer further comprises at least one of a binder and a conductive material. Claim 13 A lithium-sulfur battery comprising a cathode according to claim 10; and a positive electrode facing the cathode.

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