Anode active material and lithium secondary battery comprising the same

Abstract

An anode active material for a lithium secondary battery includes a core portion including a solid electrolyte, and a shell portion enclosing the core portion and including a silicon-based active material. A lithium secondary battery includes a case and an electrode assembly accommodated in the case, the electrode assembly including an anode including the anode active material and a cathode facing the anode. By using the anode active material for a lithium secondary battery of the present invention, the lithium secondary battery can maintain long-term life characteristics without sudden capacity reduction.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0122147, filed on September 14, 2021, with the Korean Intellectual Property Office (KIPO), the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to an anode active material and a lithium secondary battery containing the anode active material. Background Technology

[0004] With the development of information and display technologies, rechargeable and dischargeable secondary batteries have been widely used as power sources for mobile electronic devices such as cameras, mobile phones, and laptops. Furthermore, battery packs incorporating secondary batteries have recently been developed and are being used as power sources for environmentally friendly vehicles such as electric vehicles.

[0005] Secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Due to their high operating voltage and energy density per unit weight, advantages such as high charging rates and lightweight design, secondary batteries are actively being developed and applied.

[0006] For example, a lithium secondary battery may include an electrode assembly and an electrolyte immersed in the electrode assembly, the electrode assembly including a cathode, an anode, and a separator (membrane). The lithium secondary battery may also include a housing, for example having a bag shape for housing the electrode assembly and the electrolyte.

[0007] With the expanding applications of lithium-ion batteries, higher capacity and power are being developed. In particular, high-capacity silicon-based active materials are being used as anode active materials. While silicon-based active materials have large theoretical capacities, they can experience significant volume expansion during charging. This can lead to cracks in the active material and potentially cause electrolyte side reactions on the crack surfaces. Summary of the Invention

[0008] According to one aspect of the present invention, an anodic active material with improved lifetime characteristics is provided.

[0009] According to one aspect of the present invention, a lithium secondary battery is provided, comprising an anode active material having improved lifetime characteristics.

[0010] The anode active material includes: a core containing a solid electrolyte; and a shell encapsulating the core and containing a silicon-based active material.

[0011] In some implementations, the shell portion may completely surround the surface of the core portion.

[0012] In some embodiments, the solid electrolyte may comprise an oxide-based solid electrolyte or a sulfide-based solid electrolyte.

[0013] In some embodiments, the oxide-based solid electrolyte may include at least one selected from the group consisting of LIPON compounds, perovskite compounds, NASICON compounds, garnet compounds, glass, phosphoric acid-based compounds, and crystalline oxides.

[0014] In some embodiments, the sulfide-based solid electrolyte may include at least one selected from the group consisting of: thio-LISICON type compounds, LGPS type compounds, LPS type compounds, 30Li2S•26B2S3•44LiI, 63Li2S•36SiS2•1Li3PO4, 57Li2S•38SiS2•5Li4SiO4, 70Li2S•30P2S5, 50Li2S•50GeS2, Li2S-P2S5, Li2S-SiS2, LiI-Li2S -SiS2, LiI-Si2S-P2S5, LiI-LiBr-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2O-Li2SP2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P 2S5, Li2S-P2S5-GeS2, Li2S-P2S5-LiCl, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2 and LiPO4-Li2S-SiS.

[0015] In some embodiments, the ionic conductivity of the solid electrolyte is 1 × 10⁻⁶. -4 S / cm or higher.

[0016] In some embodiments, the solid electrolyte may have an average particle diameter (D) in the range of 1 μm to 10 μm. 50 ).

[0017] In some embodiments, the silicon-based active material may include silicon particles, silicon-carbon composites, silicon oxides, and / or silicon alloys.

[0018] In some embodiments, the thickness of the shell can be in the range of 0.5 μm to 10 μm.

[0019] In some embodiments, the shell may also include a carbon-based active material.

[0020] In some embodiments, based on 100 parts by weight of the shell portion, the content of the carbon-based active material contained in the shell portion may be in the range of 2 parts by weight to 20 parts by weight.

[0021] In some embodiments, carbon-based active materials may include activated carbon, carbon nanotubes (CNTs), carbon nanowires, graphene, carbon fibers, carbon black, graphite, hard carbon, soft carbon, and / or porous carbon.

[0022] In some embodiments, the shell may also include a carbon coating.

[0023] The lithium secondary battery includes a case and an electrode assembly housed within the case. The electrode assembly includes an anode containing an anode active material for a lithium secondary battery according to the above embodiments, and a cathode facing the anode.

[0024] In some embodiments, the lithium secondary battery may also include a liquid electrolyte injected into the casing.

[0025] In the anolytical active material according to an exemplary embodiment of the present invention, the core comprising a solid electrolyte can be completely contained within a shell comprising a silicon-based active material, and may not be exposed to the outside during the initial stage of its lifespan. As the lifespan progresses, cracks appear in the shell comprising the silicon-based active material, allowing the solid electrolyte in the core to re-engage in the reaction. Therefore, the consumed electrolyte can be replenished to improve the lifespan characteristics of the lithium secondary battery. Attached Figure Description

[0026] Figure 1 A schematic cross-sectional view is provided to illustrate an anodic active material according to an exemplary embodiment.

[0027] Figure 2 and Figure 3 These are schematic top views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment, respectively.

[0028] Figure 4 A scanning electron microscopy (SEM) image showing a cross-section of an anodic active material particle according to an exemplary embodiment.

[0029] Figure 5 SEM images showing the cross-section of the anodic active material particles according to an exemplary embodiment after 400 charge and discharge cycles.

[0030] Figure 6 A graph illustrating the capacity retention of the lithium secondary batteries in the examples and comparative examples under repeated charge / discharge conditions. Detailed Implementation

[0031] According to an exemplary embodiment of the present invention, an anode active material is provided, comprising a core containing a solid electrolyte and a shell, the shell encapsulating the core and containing a silicon-based active material. Furthermore, an anode for a lithium secondary battery and a lithium secondary battery comprising the aforementioned anode active material are provided.

[0032] The present invention will be described in detail below with reference to embodiments and accompanying drawings. However, those skilled in the art will understand that the provided drawings and the described embodiments are intended to further understand the spirit of the invention and not to limit the subject matter to be protected as disclosed in the detailed description and appended claims.

[0033] Compared to graphite-based active materials, silicon-based active materials used in lithium-ion batteries can have significantly larger theoretical capacities. However, silicon-based active materials may exhibit a large volume expansion rate during charging, which can lead to cracking due to repeated expansion and contraction during the charging / discharging process.

[0034] Therefore, the surface area of ​​the anode active material increases, and the electrolyte contained in the battery can react with the increased surface area and be rapidly consumed. Furthermore, side reactions such as gas generation may occur during the reaction process, thereby reducing the battery's lifespan characteristics.

[0035] According to embodiments of the present invention, the anode active material may include a core containing a solid electrolyte, and the surface of the core may be encapsulated by a silicon-based active material to form a shell. In some embodiments, the shell may be formed to completely surround the surface of the core.

[0036] Figure 1 A schematic cross-sectional view is provided to illustrate an anodic active material according to an exemplary embodiment.

[0037] refer to Figure 1 In the initial stage of its lifespan, the core 10, including the solid electrolyte, can be completely contained within the shell 20, which includes silicon-based active material, so as not to be exposed to the outside (see [link]). Figure 1 (a)). As charging / discharging occurs via a battery reaction, when a crack 30 is generated in the casing 20, the solid electrolyte in the core 10, which exists within the anode active material particles, can newly participate in the reaction (see [reference]). Figure 1 (b) Therefore, the electrolyte consumed during charging / discharging can be replenished to improve the lifespan characteristics of lithium secondary batteries.

[0038] In exemplary embodiments, the solid electrolyte may include an oxide-based solid electrolyte and / or a sulfide-based solid electrolyte. In a preferred embodiment, a sulfide-based solid electrolyte may be used.

[0039] Non-limiting embodiments of oxide-based solid electrolytes may include LIPON compounds (e.g., Li...). 2.9 PO 3.3 N 0.46 (etc.), perovskite-type compounds (e.g., La) 0.51 Li 0.34 TiO 2.94 (LLTO, etc.), NASICON compounds (such as Li) 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP, etc.), garnet-type compounds (e.g., Li7La3Zr2O) 12 (LLZO) etc.), glasses (e.g., 50Li4SiO4·50Li3BO3, etc.), phosphoric acid-based compounds (e.g., Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) and crystalline oxides (e.g., Li) 3.6 Si 0.6 P 0.4 O4). These can be used alone or in combination.

[0040] Non-limiting embodiments of sulfide-based solid electrolytes may include thio-LISICON type compounds (e.g., Li...). 3.25 Ge 0.25 P 0.75 S4, etc.), LGPS type compounds (e.g., Li) 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), LPS-type compounds (e.g., Li7P3S) 11 Li 3.25 P 0.95S4, Li3PS4, etc.), 30Li2S•26B2S3•44LiI, 63Li2S•36SiS2•1Li3PO4, 57Li2S•38SiS2•5Li4SiO4, 70Li2 S•30P2S5, 50Li2S•50GeS2, Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li LiI-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2O-Li2SP2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5-GeS2, Li2S-P2S5-LiCl, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, etc. These can be used individually or in combination.

[0041] In some embodiments, the ionic conductivity of the solid electrolyte can be 1 × 10⁻⁶. -4 S / cm or higher. Preferably, the ionic conductivity of the solid electrolyte can be 5 × 10⁻⁶. -4 S / cm or higher, more preferably 1×10 -3 S / cm or higher. Within the above-mentioned range of ionic conductivity, ion transfer between the anode and cathode can be promoted, thereby reducing the internal resistance between the anode and cathode. Therefore, the power characteristics of lithium secondary batteries can be improved.

[0042] Ionic conductivity can be measured at room temperature (e.g., about 25°C) using the DC polarization method, or it can be measured using the complex impedance method.

[0043] In some embodiments, the average particle diameter (D) of the solid electrolyte is... 50 The particle size can be in the range of 1 μm to 10 μm, preferably 3 μm to 7 μm. Within this particle size range, a suitable amount of solid electrolyte can be obtained, thereby improving the lifespan characteristics and energy density of the secondary battery.

[0044] Average particle diameter (D) 50 "" refers to the value corresponding to 50% of the particle diameter from the smallest particle on the cumulative distribution curve of particle size, based on 100% of the total number of particles. Average particle diameter (D) 50 It can be measured by methods known to those skilled in the art.

[0045] For example, the average particle size can be measured using a particle size analyzer, or the average particle size can be measured from TEM (Transmission Electron Microscope) images or SEM (Scanning Electron Microscope) images. The average particle size can also be measured using a measuring device employing dynamic light scattering method, or can be calculated after counting the number of particles in each particle size range through data analysis.

[0046] In some embodiments, the silicon-based active material can include silicon particles, silicon-carbon composites, silicon oxides, silicon alloys, etc. These can be used alone or in combination.

[0047] The silicon particles can exist in the form of primary particles, or in the form of secondary particles aggregated from primary particles. The silicon-carbon composite can include silicon particles dispersed in a carbon matrix and / or carbon-silicon composite particles.

[0048] The silicon oxide can be represented as, for example, SiO x (0 < x < 2). The silicon alloy can include, for example, Si-Z' alloy (where Z' is at least one element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, or combinations thereof, excluding Si).

[0049] In some embodiments, the thickness of the shell portion can be in the range from 0.5 μm to 10 μm, preferably from 0.7 μm to 7 μm, more preferably from 1 μm to 5 μm. For example, if the thickness of the shell portion is less than 0.5 μm, cracks may occur in the shell portion during the pressing process for manufacturing the electrode, and thus the solid electrolyte in the core portion may be exposed.

[0050] For example, if the thickness of the shell portion exceeds 10 μm, the volume expansion rate of the anode active material may increase excessively, and thus cracks are likely to occur with repeated charge / discharge. In this case, the electrical contact performance between the anode active materials may deteriorate, or the electrolyte consumption may be accelerated through the cracks. In addition, the amount of the silicon-based active material may increase excessively, so the electrolyte consumption may be greater than the amount of the solid electrolyte replenishment.

[0051] In an exemplary embodiment, the shell portion can further include a carbon-based active material. Therefore, the conductivity and durability of the anode active material can be improved, thereby improving the power and life characteristics of the lithium secondary battery.

[0052] Non-limiting embodiments of carbon-based active materials may include graphite particles with artificially formed pores, or carbon bodies (pyrolytic carbon) made by sintering a carbon precursor such as pitch to form pores therein.

[0053] In some embodiments, the carbon-based active material may include an amorphous structure or a crystalline structure. Preferably, the carbon-based active material may have an amorphous structure.

[0054] In some embodiments, carbon-based active materials may include activated carbon, carbon nanotubes (CNTs), carbon nanowires, graphene, carbon fibers, carbon black, graphite, hard carbon, soft carbon, porous carbon (microporous carbon / mesoporous carbon / macroporous carbon), etc. These can be used alone or in combination.

[0055] In an exemplary embodiment, the casing may further include a carbon coating. In this case, direct exposure of the silicon in the silicon-based coating to the electrolyte solution can be prevented, thus reducing side reactions with the electrolyte solution. Therefore, volume expansion of the secondary battery during charging and discharging can be suppressed, and the lifespan characteristics of the lithium secondary battery can be further improved.

[0056] In some embodiments, the carbon coating content can be in the range of 2 to 20 parts by weight, based on 100 parts by weight of the total weight of the shell.

[0057] For example, the thickness of the carbon coating can be in the range of 0.001 μm to 10 μm, preferably 0.01 μm to 5 μm, and more preferably 0.01 μm to 1 μm. Within the above thickness range, direct contact between the shell containing the silicon-based active material and the electrolyte can be prevented.

[0058] Figure 2 and 3 These are schematic top views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment, respectively.

[0059] A lithium secondary battery may include an anode containing the anode active material as described above.

[0060] refer to Figure 2 and Figure 3 The lithium secondary battery may include an electrode assembly comprising a cathode 100, an anode 130, and an insulating layer 140 between the cathode and the anode. The electrodes may be housed in a housing 160 and impregnated with an electrolyte.

[0061] The cathode 100 may include a cathode active material layer 110, which is formed by coating a mixture containing cathode active materials onto the cathode current collector 105.

[0062] The cathode current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper or alloys thereof, and may preferably include aluminum or aluminum alloys.

[0063] The cathode active material may include compounds capable of reversibly inserting and deintercalating lithium ions. In some embodiments, the cathode active material may include a lithium-transition metal oxide. For example, the lithium-transition metal oxide may include nickel (Ni), and may also include at least one of cobalt (Co) and manganese (Mn).

[0064] For example, lithium-transition metal oxides can be represented by the following chemical formula 1.

[0065] 【Chemical Formula 1】

[0066] Li x Ni 1-y M y O 2+z

[0067] In chemical formula 1, 0.9 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7, and -0.1 ≤ z ≤ 0.1. M can be at least one element selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0068] In some embodiments, the molar ratio or concentration of Ni(1-y) in Formula 1 may be 0.8 or greater, and in preferred embodiments may exceed 0.8.

[0069] The mixture can be prepared by mixing and stirring the cathode active material with a binder, conductive material and / or dispersant in a solvent. The mixture can be applied to the cathode current collector 105, then dried and pressed to form the cathode 100.

[0070] Solvents may include, for example, non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0071] Adhesives may include organic-based adhesives, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based adhesives, such as styrene-butadiene rubber (SBR), which can be used with thickeners such as carboxymethyl cellulose (CMC).

[0072] For example, PVDF-based binders can be used as cathode binders. In this case, the amount of binder used to form the cathode active material layer can be reduced, and the amount of cathode active material can be relatively increased. Therefore, the capacity and power of lithium secondary batteries can be further improved.

[0073] To promote electron mobility between active material particles, conductive materials may be included. For example, conductive materials may include carbon-based conductive materials (such as graphite, carbon black, graphene, carbon nanotubes, etc.), and / or metal-based materials (such as tin, tin oxide, titanium oxide), as well as perovskite materials (such as LaSrCoO3, LaSrMnO3, etc.).

[0074] In an exemplary embodiment, the above-described anodic active material can be used to prepare an anodic slurry. For example, the anodic active material can be mixed with an anodic binder, a conductive material, and a thickener in a solvent to form an anodic slurry.

[0075] For example, anodizing adhesives may include polymeric materials such as styrene-butadiene rubber (SBR). Thickeners may include carboxymethyl cellulose (CMC).

[0076] For example, the conductive material may include a material that is substantially the same as or similar to the material used in the cathode active material layer described above.

[0077] In some embodiments, the above-mentioned anode slurry may be applied to at least one surface of the anode current collector 125, and then dried and pressed to form an anode active material layer 120.

[0078] For example, the anode current collector 125 may comprise a metallic material that provides improved conductivity and adhesion and is non-reactive within the voltage range of the battery. For example, the anode current collector 125 may comprise gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and may preferably comprise copper or copper alloys.

[0079] An isolation layer 140 may be inserted between the cathode 100 and the anode 130. The isolation layer 140 may comprise a porous polymer film prepared from, for example, a polyolefin-based polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc.). The isolation layer 140 may also comprise a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0080] In some embodiments, the area and / or volume of the anode 130 (e.g., the contact area with the separator 140) can be larger than the area and / or volume of the cathode 100. Therefore, lithium ions generated from the cathode 100 can be readily transferred to the anode 130 without loss due to precipitation or sedimentation, further improving the power and capacity of the secondary battery.

[0081] In an exemplary embodiment, an electrode cell may be defined by a cathode 100, an anode 130, and an insulating layer 140, and multiple electrode cells may be stacked to form an electrode assembly 150, which may have, for example, a jelly roll shape. For example, the electrode assembly 150 may be formed by winding, laminating, or folding the insulating layer 140.

[0082] The electrode assembly 150 may be housed together with the electrolyte in a housing 160 to define a lithium secondary battery. In an exemplary embodiment, the electrolyte may include a liquid electrolyte, a solid electrolyte, a gel electrolyte, and / or a polymeric ionic liquid.

[0083] In an exemplary embodiment, the liquid electrolyte may include an organic solvent, an ionic liquid, an alkali metal salt, and / or an alkaline earth metal salt.

[0084] In an exemplary embodiment, a non-aqueous electrolyte solution can be used as a liquid electrolyte. The non-aqueous electrolyte solution may include a lithium salt and an organic solvent. The lithium salt can be Li... + X - This indicates that the lithium salt anion X - It can include, for example, 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 - (CF3CF2SO2)2N - wait.

[0085] Organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These can be used alone or in combination.

[0086] like Figure 2 As shown, electrode tabs (cathode tabs and anode tabs) can protrude from the cathode current collector 105 and anode current collector 125 included in each electrode unit to one side of the housing 160. The electrode tabs can be welded to one side of the housing 160 to connect to electrode leads (cathode leads 107 and anode leads 127), which can extend or be exposed to the outside of the housing 160.

[0087] Lithium secondary batteries can be manufactured in various shapes, such as cylindrical, square, pouch-shaped, or coin-shaped containers.

[0088] Preferred embodiments are presented below to describe the invention in more detail. However, the following examples are merely illustrative, and those skilled in the art will readily understand that various changes and modifications can be made within the scope and spirit of the invention. Such changes and modifications are appropriately included within the scope of the technical solutions claimed in this application.

[0089] Example 1

[0090] Preparation of anode active materials

[0091] The average particle diameter (D) 50 A solid electrolyte with a particle size of 5 μm (Li₂S-P₂S₅), silicon powder with a particle size of 500 nm or smaller, and pitch were placed in a grinder and ground at 100 rpm for 2 hours to form a 2.5 μm thick (D) layer on the surface of the solid electrolyte. 50 A silicon material layer of 10 μm.

[0092] Subsequently, a heat treatment at 600°C was performed to prepare a core-shell structured anode active material completely surrounded by silicon active material, without exposing the solid electrolyte to the outside. Furthermore, 3 wt% carbon based on the residual carbon content was coated onto it via chemical vapor deposition (CVD).

[0093] Anode fabrication

[0094] A slurry of 95.5 wt% prepared anolyte, 1 wt% CNT as conductive material, 2 wt% styrene-butadiene rubber (SBR) as binder and 1.5 wt% carboxymethyl cellulose (CMC) as thickener was prepared by mixing.

[0095] The anode active material slurry is coated onto a copper substrate, dried, and pressed to prepare the anode.

[0096] Manufacturing of lithium-ion batteries

[0097] The preparation of a lithium secondary battery includes an anode prepared as described above and uses LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the counter electrode (cathode).

[0098] Lithium-ion cells are constructed by inserting a separator (polyethylene, thickness: 20 μm) between the anode and cathode.

[0099] The cathode / diaphragm / anode assembly was placed in a bag and sealed after electrolyte injection. A 1M LiPF6 solution was used as the electrolyte, which was a mixed solvent of EC / FEC / EMC / DEC (volume ratio: 20 / 10 / 20 / 50). After sealing and immersion for at least 12 hours, three charge / discharge cycles were performed at 0.1C (charge condition CC-CV 0.1C 4.2V 0.01C cut-off point, discharge condition CC 0.1C 2.5V cut-off point).

[0100] Example 2

[0101] The average particle diameter (D) 50A solid electrolyte (Li₂S-P₂S₅) with a particle size of 5 μm and silicon powder with a particle size of 500 nm or smaller were placed in a mill and milled at 100 rpm for 5 hours to form a 11 μm thick (D) layer on the surface of the solid electrolyte. 50 A silicon material layer of 27 μm.

[0102] Subsequently, a heat treatment at 600°C was performed to prepare a core-shell structured anode active material completely surrounded by silicon active material, without exposing the solid electrolyte to the outside. Furthermore, 3 wt% carbon based on the residual carbon content was coated onto it via chemical vapor deposition (CVD).

[0103] In addition to using the anode active material prepared above, a lithium secondary battery was manufactured using the same method as in Example 1.

[0104] Comparative Example 1

[0105] Si powder with a particle size of 500 nm or smaller and pitch were placed in a grinding mill and ground at 100 rpm for 2 hours to prepare D. 50 The particles are 10 μm in size, and then the anode active material is prepared by heat treatment at 600 °C.

[0106] In addition to using the anode active material prepared above, a lithium secondary battery was manufactured using the same method as in Example 1.

[0107] Comparative Example 2

[0108] The average particle diameter (D) 50 A solid electrolyte (Li2S-P2S5) with a size of 5 μm and silicon powder with a size of 500 nm or smaller are placed in a mill and milled at 100 rpm for 1 hour to form an anode active material in which only a portion of the surface of the solid electrolyte is covered by silicon particles.

[0109] In addition to using the anode active material prepared above, a lithium secondary battery was manufactured using the same method as in Example 1.

[0110] Experimental Example

[0111] (1) SEM image analysis

[0112] Figure 4 A scanning electron microscopy (SEM) image showing the cross-section of the anodic active material particles according to Example 1. Figure 5 SEM images showing the cross-section of the anodic active material particles according to Example 1 after 400 charge and discharge cycles.

[0113] refer to Figure 4 In the early stages of a lithium-ion battery's lifespan, the solid electrolyte is completely surrounded by silicon particles. Referring to Figure 5, after 400 cycles, cracks appear in the shell formed by the silicon-based active material, exposing the solid electrolyte.

[0114] In an exemplary embodiment, the battery may be powered by a liquid electrolyte injected into the pouch during the initial phase of the lithium secondary battery's lifespan. As charge / discharge cycles are repeated, the silicon-based active material in the casing may repeatedly shrink and expand, and cracks may appear in the anode active material. Therefore, the solid electrolyte present inside the casing can be exposed to the outside to participate in the battery reaction as an electrolyte.

[0115] Therefore, solid electrolytes can replenish the consumed liquid electrolytes to participate in the reaction, thereby continuously maintaining the lifespan of lithium secondary batteries.

[0116] (2) Determination of capacity retention (lifetime characteristics) during repeated charge / discharge cycles

[0117] The lithium secondary batteries according to the examples and comparative examples were subjected to 800 cycles of charging (CC / CV 0.5C 4.2V 0.05C cutoff point) and discharging (CC 0.3C 2.5V cutoff point). Capacity retention was evaluated by the percentage of discharge capacity in each cycle relative to the discharge capacity in the first cycle. The evaluation results are shown in… Figure 6 .

[0118] refer to Figure 6 The capacity retention of the lithium secondary battery using the anode active material of Comparative Example 1, which does not include a solid electrolyte, deteriorates rapidly around the 400th cycle.

[0119] In the battery of Comparative Example 1, cracks formed in the anode active material during repeated charging / discharging, and the initial electrolyte was rapidly consumed due to side reactions with the electrolyte on the crack surface. Therefore, the capacity decreased rapidly due to the depletion of electrolyte.

[0120] In Comparative Example 2, silicon particles were coated on a portion of the surface of the solid electrolyte. Compared with Comparative Example 1, the lifetime characteristics were improved, but the capacity retention was significantly reduced around the 500th cycle.

[0121] In Comparative Example 2, the solid electrolyte was exposed to the outside from the early stages of the battery life and participated in the battery reaction. Compared with Comparative Example 1, the addition of a solid electrolyte improved the battery life characteristics, but both the liquid and solid electrolytes were consumed from the early stages of the reaction, and the capacity retention deteriorated rapidly around the 500th cycle.

[0122] In Example 2, a thicker shell containing silicon-based active material was formed. During repeated charge / discharge cycles, the increased content of silicon active material led to faster consumption of the liquid electrolyte. Therefore, even with the addition of a solid electrolyte through cracking, the capacity retention rate was relatively lower after 550 cycles compared to Example 1.

[0123] In Example 1, a silicon-based anode active material including a solid electrolyte was used, and the lifetime characteristics were maintained without rapid degradation before 800 cycles.

[0124] As described above, according to an exemplary embodiment, the solid electrolyte can be encapsulated within the active material and may not participate in the reaction during the initial stage of its lifespan. Due to repeated charging / discharging, the shell, including the silicon-based active material, may crack, potentially exposing the solid electrolyte to participate in the reaction.

[0125] Therefore, even when the liquid electrolyte is depleted while the battery life is being consumed, a solid electrolyte located inside the anode active material can be added to maintain ion mobility. Thus, lithium-ion secondary batteries can maintain long-term lifespan characteristics without a sudden decrease in capacity.

Claims

1. An anode active material, wherein, include: The core, which includes a solid electrolyte; and The shell portion encapsulates the core portion and includes a silicon-based active material and a carbon coating. The thickness of the shell portion is in the range of 0.5 μm to 10 μm. The shell portion completely surrounds the surface of the core portion. The silicon-based active material is covered by the carbon coating.

2. The anode active material according to claim 1, wherein, The solid electrolyte includes oxide-based solid electrolytes or sulfide-based solid electrolytes.

3. The anode active material according to claim 2, wherein, The oxide-based solid electrolyte includes at least one selected from the group consisting of LIPON compounds, perovskite compounds, NASICON compounds, and garnet compounds.

4. The anode active material according to claim 2, wherein, The sulfide-based solid electrolyte comprises at least one selected from the group consisting of: thio-LISICON type compounds, LGPS type compounds, LPS type compounds, 30Li2S•26B2S3•44LiI, 63Li2S•36SiS2•1Li3PO4, 57Li2S•38SiS2•5Li4SiO4, 70Li2S•30P2S5, 50Li2S•50GeS2, Li2S-P2S5, Li2S-SiS2, and LiI-Li2S-SiS2. , LiI-Si2S-P2S5, LiI-LiBr-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2O-Li2SP2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S 5. Li2S-P2S5-GeS2, Li2S-P2S5-LiCl, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2 and LiPO4-Li2S-SiS.

5. The anode active material according to claim 1, wherein, The ionic conductivity of the solid electrolyte is 1×10⁻⁶. - 4 S / cm or greater.

6. The anode active material according to claim 1, wherein, The average particle diameter (D) of the solid electrolyte 50 The range is from 1 μm to 10 μm.

7. The anode active material according to claim 1, wherein, The silicon-based active material includes at least one selected from the group consisting of silicon particles, silicon-carbon composites, silicon oxides, and silicon alloys.

8. The anodic active material according to claim 1, wherein, The shell also includes carbon-based active materials.

9. The anodic active material according to claim 8, wherein, Based on 100 parts by weight of the shell portion, the content of the carbon-based active material contained in the shell portion is in the range of 2 parts by weight to 20 parts by weight.

10. The anodic active material according to claim 8, wherein, The carbon-based active material includes at least one selected from the group consisting of activated carbon, carbon nanotubes (CNTs), graphene, carbon fibers, carbon black, graphite, hard carbon, and soft carbon.

11. A lithium secondary battery, wherein, include: shell; and An electrode assembly housed within the housing, wherein the electrode assembly comprises: An anode, comprising the anode active material according to claim 1; and The cathode facing the anode.

12. The lithium secondary battery according to claim 11, wherein, The lithium secondary battery also includes a liquid electrolyte injected into the casing.

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