All-solid-state lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to an all-solid-state lithium secondary battery and a method for manufacturing the same, wherein the all-solid-state lithium secondary battery comprises a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material layer comprises graphitized platelet-shaped carbon nanofibers (GPCNF) and silver nanoparticles.

Description

Technical Field

[0001] This invention relates to all-solid-state lithium secondary batteries and their preparation methods. Background Technology

[0002] Secondary batteries are primarily used in small devices such as mobile devices and laptops, but their applications have recently expanded to medium and large devices, such as energy storage systems (ESS) and electric vehicles (EVs), which require high energy and high output.

[0003] Recently, there has been an increasing interest in all-solid-state lithium secondary batteries. All-solid-state lithium secondary batteries use a non-flammable inorganic solid electrolyte instead of a liquid electrolyte. They have attracted significant attention due to their higher thermal stability compared to lithium secondary batteries using liquid electrolytes, a very low risk of explosion due to leakage during overcharging, and the elimination of the need for additional explosion prevention devices.

[0004] However, because all-solid-state lithium-ion batteries use a fairly large solid electrolyte, there have been many attempts to improve the battery's energy density. To this end, a metal layer capable of forming an alloy with lithium (e.g., lithium metal) is used as the negative electrode active material layer. However, if a metal layer is used, the ionization and dissolution of lithium deposited on the metal layer creates porosity between the solid electrolyte and the metal layer, which adversely affects battery operation. Furthermore, because lithium metal precipitates in a dendritic form on the surface of the metal layer during discharge of the all-solid-state lithium-ion battery, the battery's lifespan and safety are reduced.

[0005] To address this issue, traditionally, a method of applying high external pressure by placing end plates on the positive or negative electrode to prevent porosity formation has been used. However, when using end plates with applied external pressure, the volume of the all-solid-state lithium secondary battery increases excessively, resulting in a reduction in the energy density of the all-solid-state lithium secondary battery.

[0006] Therefore, a new method is needed to improve the lifespan and safety of all-solid-state lithium secondary batteries. Summary of the Invention

[0007] [Technical Issues]

[0008] One aspect of the present invention provides an all-solid-state lithium secondary battery in which lithium metal can be effectively stored by reducing lithium ions during charging, thereby improving initial charge / discharge efficiency and lifespan characteristics.

[0009] Another aspect of the present invention provides an all-solid-state lithium secondary battery that is price-competitive by reducing the amount of silver nanoparticles used.

[0010] Another aspect of the present invention provides a method for preparing the above-mentioned all-solid-state lithium secondary battery.

[0011] [Technical Solution]

[0012] According to one aspect of the present invention, an all-solid-state lithium secondary battery is provided, comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material layer comprises graphitized sheet carbon nanofibers (GPCNF) and silver nanoparticles.

[0013] According to another aspect of the present invention, a method for preparing an all-solid-state lithium secondary battery is provided, comprising: a first step of reducing silver ions in a mixture of silver ions and graphitized sheet carbon nanofibers to form a dry-mixed powder comprising graphitized sheet carbon nanofibers and silver nanoparticles disposed on the graphitized sheet carbon nanofibers; and a second step of forming a negative electrode active material layer on a negative electrode current collector using a negative electrode mixture containing the dry-mixed powder.

[0014] [Beneficial Effects]

[0015] Regarding the all-solid-state lithium secondary battery of the present invention, since the negative electrode active material layer comprises graphitized sheet-like carbon nanofibers and silver nanoparticles, lithium ions are reduced and deposited by the negative electrode active material layer during charging, thus lithium ions can be effectively stored in the negative electrode. Furthermore, since the stored lithium can dissolve as lithium ions during discharge, the lithium ions can migrate to the positive electrode. Graphitized sheet-like carbon nanofibers can improve the initial charge / discharge efficiency and lifespan characteristics of the battery by increasing the mobility of lithium ions. Moreover, when graphitized sheet-like carbon nanofibers are used, the lithium ions can migrate effectively even with the use of a small amount of silver nanoparticles, thus improving the price competitiveness of the prepared all-solid-state lithium secondary battery. Attached Figure Description

[0016] Figure 1 This is a schematic diagram illustrating the graphitized sheet-like carbon nanofibers mentioned in this invention.

[0017] Figure 2 This is a schematic diagram illustrating the sheet-like carbon nanofibers mentioned in this invention.

[0018] Figure 3 This is a schematic diagram illustrating the graphitized sheet-like carbon nanofibers mentioned in this invention.

[0019] Figure 4 This is a schematic diagram illustrating one embodiment of the all-solid-state lithium secondary battery of the present invention.

[0020] Figure 5This is a schematic diagram illustrating one embodiment of the all-solid-state lithium secondary battery of the present invention.

[0021] Figure 6 This is a transmission electron microscope (TEM) image of the sheet-like carbon nanofibers mentioned in this invention.

[0022] Figure 7 This is a TEM image of the graphitized sheet-like carbon nanofibers mentioned in this invention.

[0023] Figure 8 This is a TEM image of graphitized sheet-like carbon nanofibers containing silver nanoparticles in an all-solid-state lithium secondary battery used in one embodiment of the present invention.

[0024] Figure 9 This is a TEM image of sheet-like carbon nanofibers containing silver nanoparticles in an all-solid-state lithium secondary battery used in another embodiment of the present invention. Detailed Implementation

[0025] It will be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it will be further understood that, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the related technology and the technical concept of the invention.

[0026] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. In the specification, singular terms may include plural forms unless otherwise stated.

[0027] It will be further understood that, when used in this specification, the terms “comprising,” “including,” or “having” specify the presence of the said features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0028] In this specification, the term "specific surface area" is stated to be measured by the Brunauer-Emmett-Teller (BET) method, wherein, specifically, the specific surface area can be calculated using a Bell Japan Inc. BELSORP-mini II based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0029] The term "graphitized sheet-like carbon nanofibers" in this specification can refer to carbon structures in which graphene sheets are stacked into a fiber shape. (Reference) Figure 1Graphitized sheet carbon nanofibers can refer to carbon nanofibers with the following structure: the hexagonal lattice planes of carbon are arranged perpendicularly to the fiber axis (L). The length of a graphitized sheet carbon nanofiber refers to the length of the line segment or curve that appears when one end of the graphitized sheet carbon nanofiber is connected along its length; for example, it can refer to the distance between one end and the other end along the fiber axis when the graphitized sheet carbon nanofiber is stretched into a straight line. Furthermore, the diameter of a graphitized sheet carbon nanofiber refers to its width along its minor axis (D), which is perpendicular to the fiber axis (L) and parallel to the plane of the graphene sheet or the hexagonal lattice plane of the carbon.

[0030] Figure 2 and Figure 3 This is an explanation Figure 1 A schematic diagram of the side (S) of carbon nanofibers. (Reference) Figure 2 and 3 The difference between sheet-like carbon nanofibers and graphitized sheet-like carbon nanofibers can be seen. Sheet-like carbon nanofibers have the same shape as described in the above paragraphs. However, the sides of sheet-like carbon nanofibers are graphene sheets (…). Figure 2 and 3 The edge plane of the black line segment in the middle ( Figure 2 The exposed form of E) while the sides of the graphitized sheet-like carbon nanofibers are the basal plane (E) Figure 3 B) The form of exposure. Through Figure 6 sheet-like carbon nanofibers and Figure 7 The difference is also clearly seen in TEM images of graphitized sheet-like carbon nanofibers.

[0031] Specifically, the graphitized sheet carbon nanofibers have a configuration in which multiple graphene sheets are stacked along the growth direction of the graphitized sheet carbon nanofibers, and the graphitized sheet carbon nanofibers include curved portions protruding toward the sides of the graphitized sheet carbon nanofibers, wherein the curved portions correspond to the basal plane of the graphene sheets. The curved portions are formed by extending one graphene sheet to connect it to another graphene sheet, and as... Figure 3 and 7 As shown, the basal surface is exposed to the outside from the side of the graphitized sheet carbon nanofiber. More specifically, the basal surface has a closed-loop shape and can exist in a bent state on the side of the graphitized sheet carbon nanofiber. This loop shape can appear periodically along the growth direction of the graphitized sheet carbon nanofiber.

[0032] Graphitized sheet-like carbon nanofibers can be formed by heat-treating the sheet-like carbon nanofibers at high temperatures. Specifically, graphitized sheet-like carbon nanofibers can be formed by heat-treating the sheet-like carbon nanofibers at temperatures above 2000°C (e.g., 2000°C to 3500°C). The heat treatment time can range from 10 minutes to 24 hours.

[0033] In this specification, the XRD (X-ray diffraction) measurement method for graphitized sheet-like carbon nanofibers and sheet-like carbon nanofibers can be described as follows. A Bruker AXS D4 Endeavor XRD instrument (voltage: 40 kV, current: 40 mA) can be used, and the measurement can be performed by Cu Kα radiation (wavelength: ... XRD analysis was performed by measuring at a scan rate of 87.5 seconds per 0.02° from 2θ to 10° to 90°. The full width at half maximum (FWHM) of the (002) crystal peak appearing at approximately 20° to 30° of 2θ was measured, and the d(002) and Lc(002) values ​​were calculated using the Scherrer formula.

[0034] I of this instruction manual D / I G The ratio can be measured from the wavelength peak diagram during Raman spectroscopy measurements. Specifically, after fitting the graph by setting a baseline to distinguish the D and G peaks, the ratio I can be confirmed by dividing the D peak intensity by the G peak intensity. D / I G (Using built-in software, NRS-2000B, Jasco). In the Raman spectrum, at 1590 cm⁻¹ -1 The nearby G peak is composed of carbon sp. 2 E key 2g Caused by vibration mode, and at 1350cm -1 The nearby D peak is at the sp of carbon. 2 This occurs when there is a defect in the key.

[0035] The average diameter of the graphitized sheet carbon nanofibers (or sheet carbon nanofibers) in this specification corresponds to the average diameter of the first 50 graphitized sheet carbon nanofibers (or sheet carbon nanofibers) arranged in order of maximum diameter when the negative electrode active material layer is observed using a scanning electron microscope (SEM) at a magnification of ×20000.

[0036] The average length of the graphitized sheet carbon nanofibers (or sheet carbon nanofibers) in this specification corresponds to the average length of the first 50 graphitized sheet carbon nanofibers (or sheet carbon nanofibers) arranged in order of maximum length when the negative electrode active material layer is observed by SEM at a magnification of ×20000.

[0037] The average particle size of the silver nanoparticles in this specification corresponds to the average particle size of the top 50 largest silver nanoparticles and the bottom 50 largest silver nanoparticles when observed with a transmission electron microscope (TEM) at a magnification of ×1,000,000.

[0038] The present invention will be described in detail below.

[0039] All-solid-state lithium secondary battery

[0040] An embodiment of the present invention provides an all-solid-state lithium secondary battery comprising a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material layer may comprise graphitized sheet carbon nanofibers (GPCNF) and silver nanoparticles.

[0041] (1) Negative electrode active material layer

[0042] All-solid-state lithium secondary batteries may include a negative electrode active material layer. Specifically, an all-solid-state lithium secondary battery may include a negative electrode, and the negative electrode may include a negative electrode current collector and a negative electrode active material layer.

[0043] There are no particular restrictions on the negative electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel that has been surface-treated with one of carbon, nickel, titanium, or silver can be used as the negative electrode current collector. Specifically, transition metals that can absorb carbon well, such as nickel or stainless steel, can be used as the negative electrode current collector.

[0044] refer to Figure 4 The negative electrode active material layer 100 may be disposed on at least one surface of the negative electrode current collector 110. Specifically, the negative electrode active material layer 100 may be disposed on one surface of the negative electrode current collector 110, or alternatively, it may be disposed on both surfaces of the negative electrode current collector (not shown).

[0045] The negative electrode active material layer may include graphitized sheet-like carbon nanofibers and silver nanoparticles. Specifically, the negative electrode active material layer may be composed of graphitized sheet-like carbon nanofibers and silver nanoparticles.

[0046] 1) Graphitized sheet-like carbon nanofibers

[0047] Graphitized sheet-like carbon nanofibers can act as a migration path, making it easier for lithium ions transferred from the positive electrode active material layer to be deposited and stored on the negative electrode current collector.

[0048] The graphitized sheet-like carbon nanofibers include curved portions protruding towards the sides of the graphitized sheet-like carbon nanofibers, wherein the curved portions correspond to the basal surface of the graphene sheet. That is, the basal surface is exposed outward from the side of the graphitized sheet-like carbon nanofibers. More specifically, the basal surface has a closed-loop shape and can exist in a curved state on the side of the graphitized sheet-like carbon nanofibers. This loop shape can appear periodically along the growth direction of the graphitized sheet-like carbon nanofibers. Since the movement of lithium ions on the basal surface can occur rapidly, the graphitized sheet-like carbon nanofibers can induce rapid movement of lithium ions. Therefore, the irreversible capacity for initial lithium ion storage can be reduced.

[0049] In X-ray diffraction (XRD) measurements of graphitized sheet carbon nanofibers, the d(002) can range from 0.330 nm to 0.350 nm, specifically from 0.330 nm to 0.345 nm, and more specifically from 0.330 nm to 0.340 nm. Within this range, the high crystallinity of the graphitized sheet carbon nanofibers significantly improves electrical conductivity, which is beneficial for lithium-ion storage and movement.

[0050] In the XRD measurements of the aforementioned sheet-like carbon nanofibers, the Lc(002) of the sheet-like carbon nanofibers can be from 20 nm to 200 nm, specifically from 20 nm to 150 nm, more specifically from 20 nm to 100 nm, for example from 35 nm to 100 nm. When these ranges are met, the electrical conductivity is improved due to the excellent graphitization degree of the graphitized sheet-like carbon nanofibers, and the mechanical strength of the material itself can be excellent due to the small number of crystallization defects in the length direction of the graphitized sheet-like carbon nanofibers. Therefore, during the dispersion and use of graphitized sheet-like carbon nanofibers, the phenomenon of graphitized sheet-like carbon nanofibers being cut can be reduced, and the battery degradation caused by defects in the graphitized sheet-like carbon nanofibers during battery charging and discharging can be minimized.

[0051] During Raman spectroscopy measurements, the Ig of graphitized sheet-like carbon nanofibers... D / I GThe value can be from 0.1 to 1.0, specifically from 0.1 to 0.5, and more specifically from 0.1 to 0.3. When the above range is met, the conductivity is significantly improved due to the high crystallinity of the graphitized sheet-like carbon nanofibers, which is beneficial for the storage and movement of lithium ions.

[0052] The average length of the graphitized sheet-like carbon nanofibers can range from 0.1 μm to 5 μm, specifically from 0.1 μm to 2.5 μm, and more specifically from 0.1 μm to 1 μm. When these ranges are met, the efficiency of all-solid-state lithium secondary batteries can be improved because conductive pathways can be effectively formed in the negative electrode active material layer. Furthermore, even if the silver nanoparticles undergo an alloying reaction with lithium ions, altering their volume, the structural collapse of the negative electrode active material layer can be effectively suppressed.

[0053] The average diameter of graphitized sheet carbon nanofibers can range from 10 nm to 500 nm, specifically from 10 nm to 400 nm, and more specifically from 10 nm to 300 nm. When the above range is met, the mechanical structure of the graphitized sheet carbon nanofibers can be effectively maintained even if the storage and movement of lithium ions occur through them.

[0054] The specific surface area of ​​graphitized sheet-like carbon nanofibers can reach 5 m². 2 / g to 10m 2 / g, specifically 5m 2 / g to 80m 2 / g, more specifically 5m 2 / g to 60m 2 / g. Under the above-mentioned conditions, since silver nanoparticles can be stably disposed on the surface of graphitized sheet-like carbon nanofibers, lithium ions can be effectively stored and moved.

[0055] Graphitized sheet-like carbon nanofibers can be included in the negative electrode active material layer in amounts of 50 wt% to 98 wt%, specifically 60 wt% to 95 wt%, and more specifically 70 wt% to 90 wt%. When the above ranges are met, the initial charge / discharge efficiency and lifetime characteristics of the all-solid-state lithium secondary battery can be improved because the lithium-ion mobility can be effectively increased while minimizing the reduction in energy density.

[0056] 2) Silver nanoparticles

[0057] Because silver nanoparticles are lithium-loving, they can readily form alloys with lithium ions. Therefore, silver nanoparticles can form alloys with lithium ions transferred from the positive electrode active material layer to promote lithium ion storage and diffusion into the negative electrode active material layer.

[0058] Silver nanoparticles may include silver (Ag). Furthermore, silver nanoparticles may also include at least one selected from the group consisting of gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, and zinc. Alternatively, silver nanoparticles may be formed from silver. Silver nanoparticles may be a solid phase.

[0059] Silver nanoparticles can be deposited on the surface of graphitized sheet-like carbon nanofibers. Specifically, silver nanoparticles can be formed by reducing silver ions in a silver ion solution on the surface of graphitized sheet-like carbon nanofibers, and correspondingly, silver nanoparticles can be deposited on the surface of graphitized sheet-like carbon nanofibers. Alternatively, silver nanoparticles can be deposited on the surface of sheet-like carbon nanofibers by mixing silver nanoparticle powder with powdered sheet-like carbon nanofibers.

[0060] The average particle size of silver nanoparticles can range from 1 nm to 100 nm, specifically from 1 nm to 50 nm, and more specifically from 1 nm to 30 nm, for example, from 1 nm to 2 nm. When these ranges are met, silver nanoparticles can be effectively dispersed in the negative electrode active material layer, thus promoting lithium-ion storage and diffusion even at low concentrations. Furthermore, the initial efficiency and lifespan characteristics of the battery can be improved.

[0061] In the negative electrode active material layer, based on the total weight of graphitized sheet-like carbon nanofibers and silver nanoparticles, the content of silver nanoparticles can range from 1 wt% to 40 wt%, and specifically from 3 wt% to 30 wt%, more specifically from 5 wt% to 20 wt%, for example from 7 wt% to 10 wt%. When the above range is met, the electrochemical performance of the all-solid-state lithium secondary battery can be improved because lithium ions transferred from the positive electrode active material layer can be effectively alloyed with the silver nanoparticles. Furthermore, since silver nanoparticles are used with a relatively low silver content, the energy density and price competitiveness of the all-solid-state lithium secondary battery can be improved.

[0062] In particular, silver nanoparticles can be used in amounts of less than 10% by weight, specifically from 7% to 10% by weight, because the negative electrode active material layer comprises graphitized sheet-like carbon nanofibers. Lithium ions transferred from the positive electrode active material layer alloy with the lithium-philic silver nanoparticles, thereby promoting lithium ion storage and diffusion into the negative electrode. This storage and diffusion, as described above, is further promoted, particularly through the layered structure on the sheet-like carbon nanofibers as described in this invention. Therefore, the rate of lithium metal deposition and storage on the negative electrode active material layer and the negative electrode current collector can also be improved. Furthermore, since the graphitized sheet-like carbon nanofibers have regularly spaced closed-loop shapes on their sides, the silver nanoparticles can be effectively dispersed and arranged along curved surfaces, and the aggregation of silver nanoparticles can be effectively suppressed even during repeated charging and discharging of the battery. Therefore, even with the use of a small amount of silver nanoparticles, the capacity and initial charge / discharge efficiency of the all-solid-state lithium secondary battery can be sufficiently improved.

[0063] In the negative electrode active material layer, the weight ratio of graphitized sheet-like carbon nanofibers to silver nanoparticles can be from 99:1 to 60:40, specifically from 97:3 to 70:30, and more specifically from 95:5 to 80:20, for example from 95:5 to 88:12. When the above range is met, the capacity and initial charge / discharge efficiency of the all-solid-state lithium secondary battery can be improved more effectively.

[0064] The loading of the negative electrode active material layer can be 0.1 mg / cm³. 2 Up to 2.0 mg / cm 2 Specifically, it is 0.3 mg / cm³. 2 Up to 1.8 mg / cm 2 More specifically, 0.5 mg / cm³ 2 Up to 1.6 mg / cm 2 When the above range is met, the effect of improving the initial efficiency and lifespan of the battery can be maximized without reducing the energy density due to the increase in negative electrode thickness.

[0065] The thickness of the negative electrode active material layer can range from 1 μm to 100 μm, specifically from 1 μm to 50 μm, and more specifically from 1 μm to 20 μm. When the above range is met, the effect of improving the initial efficiency and lifespan of the battery can be maximized without reducing the energy density due to the increase in the thickness of the negative electrode.

[0066] 3) Negative electrode adhesive

[0067] The negative electrode active material layer may also include a negative electrode binder. The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0068] The negative electrode binder can be included in the negative electrode active material layer in an amount of 1% to 20% by weight, specifically 1% to 15% by weight, and more specifically 1% to 10% by weight. When the above ranges are met, the mechanical properties of the negative electrode can be improved while maintaining its resistance at a low level, and lithium-ion storage and diffusion can be further promoted.

[0069] In some cases, the negative electrode active material layer may also include at least one of lithium ions, lithium, and an alloy of lithium and silver nanoparticles. Specifically, if the all-solid-state lithium secondary battery is operating, at least one of lithium ions, lithium, and an alloy of lithium and silver nanoparticles may be present in the negative electrode active material layer due to lithium ions transferred from the positive electrode active material layer.

[0070] (2) Positive electrode active material layer

[0071] All-solid-state lithium secondary batteries may include a positive electrode active material layer. Specifically, an all-solid-state lithium secondary battery may include a positive electrode, and the positive electrode may include or be composed of a positive electrode active material layer.

[0072] The positive electrode may include a positive electrode current collector. There are no particular limitations on the positive electrode current collector, as long as it has high conductivity without causing adverse chemical changes in the positive electrode or the battery. The positive electrode current collector may, for example, include at least one selected from the group consisting of stainless steel, copper, aluminum, nickel, titanium, and calcined carbon, and may specifically include aluminum. The positive electrode includes a carbon-based conductive agent and a binder, and may also include a base coating applied to the surface of the positive electrode current collector. Therefore, the conductivity and adhesion between the positive electrode active material layer and the current collector can be significantly improved.

[0073] The positive electrode active material layer can be disposed on at least one surface of the positive electrode current collector. Specifically, the positive electrode active material layer can be disposed on one or both surfaces of the positive electrode current collector.

[0074] The positive electrode active material layer may include a positive electrode active material.

[0075] The positive electrode active material may include a layered compound, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium manganese oxide, including Li 1+x Mn 2-x O4 (where x is from 0 to 0.33), LiMnO3, LiMn2O3, LiMn2O4, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; nickel (Ni)-site lithium nickel oxide represented by the chemical formula LiNi 1-x M x O2 (where M = cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), phosphorus (P), magnesium (Mg), calcium (Ca), zirconium (Zr), titanium (Ti), ruthenium (Ru), niobium (Nb), tungsten (W), boron (B), silicon (Si), sodium (Na), potassium (K), molybdenum (Mo), vanadium (V), or gallium (Ga), and x = 0.01 to 0.3); lithium manganese composite oxide represented by the chemical formula LiMn 1-x M x O2 (where M = Co, nickel (Ni), Fe, chromium (Cr), zinc (Zn), or tantalum (Ta), and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); spinel-structured lithium manganese composite oxide represented by LiNi x Mn 2-x O4; LiMn2O4 in which a part of lithium (Li) is substituted with an alkaline earth metal ion; disulfide; LiMn x Fe 1-x PO4 (0 ≤ x ≤ 0.9); or Fe2(MoO4)3. However, the positive electrode active material is not limited thereto.

[0076] The positive electrode active material may include Li 1+x M y O 2+z , where M may be at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, 0 ≤ x ≤ 5, 0 < y ≤ 2, and 0 ≤ z ≤ 2. Specifically, Li 1+x M y O 2+z may include those selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, Li[Ni 0.5 Co 0.3 Mn 0.2 O2, Li[Ni 0.6 Co 0.2 Mn0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2, LiMn2O4, LiFePO4 and 0.5Li2MnO3·0.5Li[Mn 0.4 Ni 0.3 Co 0.3 At least one of the group consisting of O2. Preferably, Li 1+x M y O 2+z It can include Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2 and Li[Ni 0.9 Co 0.05 Mn 0.05 Any of O2. Because the positive electrode active material includes Li 1+x M y O 2+z Lithium can be fully supplied to the negative electrode, and because of Li 1+x M y O 2+z It exhibits electrochemical activity after the first cycle without causing degradation in overall battery performance, thus preventing battery capacity loss due to irreversible capacity loss at the negative electrode. 1+x M y O 2+z It can be in the form of secondary particles formed by combining or assembling primary particles, or alternatively, it can be in the form of a single particle.

[0077] The positive electrode active material may be included in the positive electrode active material layer in an amount of 50% to 95% by weight, specifically 60% to 90% by weight.

[0078] The positive electrode active material layer may also include a solid electrolyte.

[0079] Solid electrolytes may specifically include at least one selected from the group consisting of polymer solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes.

[0080] Polymer solid electrolytes can be composites of lithium salts and polymer resins. Specifically, polymer solid electrolytes can be formed by adding a polymer resin to a solvated lithium salt. Specifically, the ionic conductivity of the polymer solid electrolyte can be approximately 1 × 10⁻⁶. -7 S / cm or higher, preferably about 1×10 -3 S / cm or higher.

[0081] Polymer resins include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives (e.g., polyethylene oxide), phosphate polymers, polylyzed lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, or polymers containing ionic dissociation groups, and may include more than one of these. Furthermore, polymeric solid electrolytes are polymer resins, examples of which may be branched copolymers, comb-like polymer resins, and crosslinked polymer resins obtained by copolymerizing amorphous polymers (e.g., PMMA, polycarbonate, polysiloxane (PDMS), and / or phosphazene) as comonomers into the PEO (polyethylene oxide) backbone, and may include at least one of these.

[0082] Lithium salts are ionizable and can be represented as Li + X - There are no particular restrictions on the anion of lithium salts, but examples can be 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 - .

[0083] Oxide-based solid electrolytes may include oxygen (O) and may have ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. As non-limiting examples, they may include compounds selected from LLTO compounds, Li6La2CaTa2O, etc. 12 Li6La2ANb2O 12 (A is Ca or Sr) , Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (where 0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO4)3 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1), LiTi x Zr 2-x (PO4)3 (where 0≤x≤1, 0≤y≤1), and at least one of the following: LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds. However, oxide solid electrolytes are not particularly limited to these.

[0084] Sulfide solid electrolytes contain sulfur (S) and have the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. These sulfide solid electrolytes may include Li-PS glass or Li-PS glass-ceramics. Non-limiting examples of sulfide solid electrolytes include Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and the sulfide solid electrolyte may include at least one of these. However, sulfide solid electrolytes are not particularly limited to this.

[0085] Halogenated solid electrolytes may include at least one of Li3YCl6 and Li3YBr6, but are not particularly limited thereto.

[0086] The solid electrolyte may be included in the positive electrode active material layer in an amount of 5% to 50% by weight, specifically 10% to 30% by weight.

[0087] The positive electrode active material layer may also include a positive electrode conductive agent.

[0088] There are no particular limitations on the positive electrode conductive agent, as long as it is conductive and does not cause adverse chemical changes in the positive electrode or battery. For example, the positive electrode conductive agent may include one selected from, for example, conductive materials such as: graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal cracking carbon black; graphene; conductive fibers, such as carbon nanofibers and carbon nanotubes; fluorocarbon compounds; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, or mixtures of two or more of them.

[0089] The positive electrode conductive agent can be included in the positive electrode active material layer in an amount of 1% to 30% by weight.

[0090] The positive electrode active material layer may also include a positive electrode binder.

[0091] There are no particular limitations on the positive electrode binder, as long as it is a component that facilitates the bonding between the positive electrode active material and the conductive agent, as well as the bonding with the current collector. Specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), and fluororubber.

[0092] The positive electrode binder may be included in the positive electrode active material layer in an amount of 1% to 30% by weight.

[0093] If necessary, the positive electrode active material layer may include at least one additive, such as an oxidation stabilizer, a reduction stabilizer, a flame retardant, a heat stabilizer, and an antifogging agent.

[0094] (3) Solid electrolyte layer

[0095] All-solid-state lithium secondary batteries may include a solid electrolyte layer.

[0096] In all-solid-state lithium secondary batteries, the solid electrolyte layer can serve as an insulating layer and can also be used as an ion conduction channel.

[0097] refer to Figure 4 The solid electrolyte layer 300 can be disposed between the negative electrode active material layer 100 and the positive electrode active material layer 200.

[0098] The solid electrolyte layer 300 includes a solid electrolyte. The solid electrolyte may specifically include at least one selected from the group consisting of polymer solid electrolytes, oxide solid electrolytes, and sulfide solid electrolytes.

[0099] Polymer solid electrolytes can be composites of lithium salts and polymer resins. Specifically, polymer solid electrolytes can be formed by adding a polymer resin to a solvated lithium salt. Specifically, the ionic conductivity of the polymer solid electrolyte can be approximately 1 × 10⁻⁶. -7 S / cm or higher, preferably about 1×10 -3 S / cm or higher.

[0100] Polymer resins include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives (e.g., polyethylene oxide), phosphate polymers, polylyzed lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, or polymers containing ionic dissociative groups, and may include more than one of these. Furthermore, polymeric solid electrolytes are polymer resins, examples of which may be branched copolymers, comb-like polymer resins, and crosslinked polymer resins obtained by copolymerizing amorphous polymers (e.g., PMMA, polycarbonate, polysiloxane (PDMS), and / or phosphazene) as comonomers into the PEO (polyethylene oxide) backbone, and may include at least one of these.

[0101] Lithium salts are ionizable and can be represented as Li + X - There are no particular restrictions on the anion of lithium salts, but examples can be 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 - .

[0102] Oxide-based solid electrolytes may include oxygen (O) and may have ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. As non-limiting examples, they may include compounds selected from LLTO compounds, Li6La2CaTa2O, etc. 12 Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (where 0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO4)3 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1), LiTi x Zr 2-x (PO4)3 (where 0≤x≤1, 0≤y≤1), and at least one of the following: LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds. However, oxide solid electrolytes are not particularly limited to these.

[0103] Sulfide solid electrolytes contain sulfur (S) and have the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table. These sulfide solid electrolytes may include Li-PS glass or Li-PS glass-ceramics. Non-limiting examples of sulfide solid electrolytes include Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and the sulfide solid electrolyte may include at least one of these. However, sulfide solid electrolytes are not particularly limited to this.

[0104] The solid electrolyte layer may also include an adhesive for the solid electrolyte layer. An adhesive for the solid electrolyte layer can be introduced to achieve bonding between solid electrolytes and bonding between the solid electrolyte layer and battery elements (e.g., positive electrode, negative electrode, etc.) stacked on its two surfaces.

[0105] There are no particular limitations on the materials used for the solid electrolyte layer adhesive, and it can be appropriately selected from the range of compositions used in solid electrolyte adhesives for all-solid-state lithium secondary batteries. Specifically, the solid electrolyte layer adhesive may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymer (SBS), nitrile rubber (NBR), fluororubber, and acrylic adhesives.

[0106] Considering the ionic conductivity, physical strength, and energy density of batteries using solid electrolyte layers, the thickness of the solid electrolyte layer can range from 10 μm to 90 μm, specifically from 20 μm to 80 μm. Furthermore, the tensile strength of the solid electrolyte layer can be 500 kgf / cm². 2 Up to 2000 kgf / cm 2 Furthermore, the porosity of the solid electrolyte layer 300 can be less than 15% or less than about 10%.

[0107] All-solid-state lithium secondary batteries may also include a metal layer. (Reference) Figure 5The all-solid-state lithium secondary battery 10 also includes a negative electrode current collector 110, and may further include a metal layer 120 disposed between the negative electrode active material layer 100 and the negative electrode current collector 110 in the charged state. The metal layer 120 may contain lithium, and may specifically be formed of lithium.

[0108] The metal layer can refer to the layer formed when lithium ions transferred from the positive electrode active material layer are stored on the negative electrode current collector and the negative electrode active material layer through the negative electrode active material layer during charging of an all-solid-state lithium secondary battery. Therefore, the metal layer is clearly visible during charging.

[0109] The metal layer can be observed during discharge, but theoretically it may not be observable during full discharge.

[0110] This invention is meaningful for all-solid-state lithium secondary batteries, but may not be very meaningful for lithium secondary batteries using liquid electrolytes. For example, if a liquid electrolyte is used, it may be difficult to store lithium completely in the negative electrode because the lithium stored in the negative electrode (e.g., in the form of a metal layer) may be continuously exposed to the liquid electrolyte.

[0111] Method for producing all-solid-state lithium secondary battery

[0112] Another embodiment of the present invention provides a method for preparing an all-solid-state lithium secondary battery, which may include: a first step of reducing silver ions in a mixture of silver ions and graphitized sheet carbon nanofibers to form a dry-mixed powder comprising graphitized sheet carbon nanofibers and silver nanoparticles disposed on the graphitized sheet carbon nanofibers; and a second step of forming a negative electrode active material layer on a negative electrode current collector using a negative electrode slurry comprising the dry-mixed powder. Here, the all-solid-state lithium secondary battery may be the same as the all-solid-state lithium secondary battery of the above embodiment. Furthermore, the negative electrode active material layer may be the same as the negative electrode active material layer of the above embodiment.

[0113] (1) First step

[0114] In the first step, a dry-mixed powder comprising graphitized sheet-like carbon nanofibers and silver nanoparticles disposed on the graphitized sheet-like carbon nanofibers is formed. The dry-mixed powder can be prepared by mixing powdered silver nanoparticles and powdered graphitized sheet-like carbon nanofibers. Alternatively, the dry-mixed powder can also be prepared by incorporating graphitized sheet-like carbon nanofibers into a silver ion solution and then reducing the silver nanoparticles. Various methods exist for reducing silver nanoparticles, such as chemical reduction, electrochemical reduction, photochemical reduction, laser reduction, ultrasonic reduction, and sputtering; however, preferably, a chemical reduction method utilizing a polyol process or a microwave-assisted polyol method utilizing microwaves can be used.

[0115] In the polyol process, the silver ion solution may include a solvent and a stabilizer in addition to silver ions. Ethylene glycol can be used as the solvent, and polyvinylpyrrolidone can be used as the stabilizer. However, the invention is not necessarily limited to these.

[0116] The molar concentration of silver ions in the silver ion solution can range from 1 mM to 1,000 mM, specifically from 1 mM to 500 mM, and more specifically from 1 mM to 300 mM. When the above molar concentration range is met, the amount and size of the formed silver nanoparticles can be adjusted to an appropriate level, thus effectively controlling the capacity, initial charge / discharge efficiency, and lifetime characteristics of the all-solid-state lithium secondary battery.

[0117] In the first step, the reduction of silver ions may include reacting the mixed solution at a temperature of 100°C to 500°C, and may specifically include reacting at a temperature of 100°C to 300°C. That is, the mixed solution can be reacted by heat treatment at the above temperatures. Therefore, silver ions can be appropriately reduced to obtain silver nanoparticles with a desired size. Furthermore, in the above process, the silver nanoparticles can be disposed on the surface of graphitized sheet-like carbon nanofibers.

[0118] The reduction of silver ions may involve adjusting the pH of the mixed solution. Specifically, the mixed solution can be adjusted to have an acidity of pH 8 to pH 14, more specifically pH 9 to pH 13. Therefore, silver ions can be appropriately reduced to obtain silver nanoparticles with the desired size.

[0119] Subsequently, a dry-mixed powder can be obtained by washing and then drying the solid components of the mixed solution.

[0120] In the dry-mixed powder, the weight ratio of graphitized sheet-like carbon nanofibers to silver nanoparticles can be from 99:1 to 60:40, specifically from 97:3 to 70:30, and more specifically from 95:5 to 80:20. When the above range is met, the capacity and initial charge / discharge efficiency of the all-solid-state lithium secondary battery can be improved more effectively.

[0121] (2) Second step

[0122] In the second step, a negative electrode active material layer can be formed on the negative electrode current collector using a negative electrode slurry containing the dry-mixed powder. The negative electrode slurry may contain the dry-mixed powder and a solvent for the negative electrode slurry.

[0123] The solvent for the negative electrode slurry can be selected from the group consisting of free water and N-methylpyrrolidone, but is not necessarily limited to this.

[0124] The negative electrode slurry may also include a negative electrode binder. The negative electrode binder may be the same as the negative electrode binder in the above embodiments.

[0125] In the second step, a negative electrode active material layer can be formed by coating and drying the negative electrode slurry onto the negative electrode current collector. In some cases, a pressurization process can be added in addition to the coating and drying process.

[0126] Furthermore, the present invention provides a battery module including the all-solid-state lithium secondary battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of this device may include power tools driven by an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheelers, including electric bicycles (E-bicycles) and electric scooters (E-scooters); electric golf carts; urban air mobility (UAM); and energy storage systems, but the device is not limited to these.

[0127] The invention will be described in more detail below with reference to embodiments, but the embodiments are merely illustrative and the scope of the invention is not limited thereto.

[0128] Examples and comparative examples

[0129] Example 1: Preparation of an all-solid-state lithium secondary battery

[0130] (1) Negative electrode preparation

[0131] Graphitized sheet carbon nanofibers were prepared by heat-treating sheet carbon nanofibers at 2,800 °C for 6 hours in an argon (Ar) atmosphere.

[0132] The mixed solution was prepared by mixing graphitized sheet carbon nanofibers, AgNO3, and polyvinylpyrrolidone in ethylene glycol solvent, adjusting the pH to a range of 8 to 14 using NaOH particles, and then stirring for 24 hours. The mixed solution, which had been ultrasonically bubbled with Ar, was then treated with a microwave reactor (LG Electronics) in continuous wave mode (2.45 GHz, 500 W) at time units of 10 seconds, 20 seconds, 30 seconds, 1 minute, 2 minutes, and 5 minutes, with repeated heating and cooling. Silver ions were thus reduced, resulting in silver nanoparticles affixed to the graphitized sheet carbon nanofibers. Subsequently, the mixture was filtered and washed with acetone solution and dried in a vacuum oven at 100°C for 24 hours to obtain a dry-mixed powder comprising graphitized sheet carbon nanofibers and silver nanoparticles affixed to them (see [link to product description]). Figure 8 The amount of silver nanoparticles was 10% by weight (based on the total weight of graphitized sheet carbon nanofibers and silver nanoparticles), and the average particle size of the silver nanoparticles was 2 nm.

[0133] The dry-mixed powder and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) as a solvent and stirred to form a negative electrode slurry. In the negative electrode slurry, the weight ratio of the dry-mixed powder to PVDF was 93:7.

[0134] The negative electrode slurry was coated onto a stainless steel current collector (thickness: 15 μm), dried in a vacuum oven at 100°C for 12 hours, and then rolled using a roller press to prepare a negative electrode comprising a stainless steel current collector and a negative electrode active material layer disposed on the stainless steel current collector. The thickness of the negative electrode active material layer was 10 μm, and the loading of the negative electrode active material layer was 1 mg / cm³. 2 .

[0135] (2) Preparation of positive electrode

[0136] Li[Ni] will be used as the positive electrode active material 0.82 Co 0.14 Mn 0.04 O2, Li6PS6Cl as a solid electrolyte, carbon nanofibers (VGCF, Showa Denko) as a conductive agent, and polytetrafluoroethylene as a binder were added sequentially to a container in a weight ratio of 77:20:1:2. Each time a component was added, the mixture was stirred 10 times at 10,000 RPM for 30 seconds each time using a laboratory mixer to prepare the positive electrode mixture. The mixture was then subjected to high-shear mixing for 5 minutes at 100°C and 100 rpm using a twin-screw kneader (LG Electronics) to prepare the positive electrode mixture. A 200 μm thick self-standing membrane was prepared from the positive electrode mixture at 100°C using a twin-roll mill (Inoue Mfg., Inc.). This membrane was then placed on one side of an aluminum current collector (thickness: 20 μm) coated with a primer, and bonded to the current collector using a laminating roller maintained at 120°C to prepare the positive electrode.

[0137] (3) Preparation of all-solid-state lithium secondary batteries

[0138] A solid electrolyte slurry was prepared by mixing Li6PS6Cl solid electrolyte and nitrile rubber (NBR) with xylene as a solvent, and then mixing the mixture with zirconia balls at 2,000 RPM for 10 cycles, 1 minute each, using a ThinkyMixer. The solid electrolyte slurry was then coated onto a PET film as a release liner and dried in a vacuum oven at 45°C for 6 hours to prepare a solid electrolyte layer. In this case, the weight ratio of Li6PS6Cl solid electrolyte to nitrile rubber (NBR) was 95:5 (wt%), and the thickness of the prepared solid electrolyte layer was 100 μm.

[0139] A solid electrolyte layer was placed between the negative and positive electrodes to prepare the assembly, which was then placed in a bag and sealed. The bag was then fixed to an Al plate, and the bag was pressurized at 500 MPa for 30 minutes using an isostatic press (warm isostatic pressing) to prepare the all-solid-state lithium secondary battery of Example 1.

[0140] Examples 2 to 5: Preparation of all-solid-state lithium secondary batteries

[0141] All-solid-state lithium secondary batteries were prepared in the same manner as in Example 1, except that the weight ratio of graphitized sheet carbon nanofibers, AgNO3 and polyvinylpyrrolidone, pH value and reaction conditions in the microwave reactor were controlled to adjust the amount and average particle size of silver nanoparticles, as shown in Table 2.

[0142] Comparative Examples 1 and 2: Fabrication of All-Solid-State Lithium Secondary Batteries

[0143] (1) Negative electrode preparation

[0144] All-solid-state lithium secondary batteries were prepared in the same manner as in Example 1, except that carbon black (PRINTEX, Orion Engineered Carbons) was used instead of the graphitized sheet carbon nanofibers in Example 1, and the weight ratio of carbon black, AgNO3 and polyvinylpyrrolidone, pH value and reaction conditions in the microwave reactor were controlled to adjust the amount and average particle size of silver nanoparticles, as shown in Table 2.

[0145] Comparative Example 3: Preparation of Lithium Secondary Batteries

[0146] (1) Preparation of negative and positive electrodes

[0147] The negative and positive electrodes were prepared in the same manner as in Example 1.

[0148] (3) Preparation of lithium secondary batteries

[0149] Subsequently, a 15 μm thick polyethylene separator was placed between the prepared negative and positive electrodes to prepare a single cell. Then, an electrolyte solution (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio), lithium hexafluorophosphate (LiPF6 1mol)) was injected into the single cell to prepare a lithium secondary battery.

[0150] Comparative Example 4: Preparation of Lithium Secondary Batteries

[0151] Lithium secondary batteries were prepared in the same manner as in Comparative Example 3, except that the weight ratio of graphitized sheet carbon nanofibers, AgNO3 and polyvinylpyrrolidone, pH value and reaction conditions in the microwave reactor were controlled to adjust the amount and average particle size of silver nanoparticles, as shown in Table 2.

[0152] Comparative Example 5: Preparation of Lithium Secondary Batteries

[0153] All-solid-state lithium secondary batteries were prepared in the same manner as in Example 1, except that non-graphitized sheet carbon nanofibers were used instead of graphitized sheet carbon nanofibers. Figure 9 This is a TEM image of a dry-mixed powder containing silver nanoparticles disposed on the sheet-like carbon nanofibers.

[0154] As a result of observing the prepared negative electrodes, the d(002) of the graphitized sheet carbon nanofibers in Examples 1 to 5 and Comparative Examples 3 and 4 was 0.335 nm, and the Lc(002) was 41 nm. For XRD analysis of the graphitized sheet carbon nanofibers, a Bruker AXS D4 Endeavor XRD (voltage: 40 kV, current: 40 mA) was used. XRD analysis was performed by Cu Kα radiation (wavelength: Measurements were performed at a scan rate of 0.02° every 87.5 seconds, from 2θ of 10° to 90°. In the measurement results, the full width at half maximum (FWHM) of the (002) crystal peak appearing at approximately 20° to 30° of 2θ was measured, and the d(002) and Lc(002) values ​​were calculated using the Scherrer formula. The I of graphitized sheet-like carbon nanofibers... D / I G The ratio is 0.24. D / I G The ratio is measured from the wavelength peak diagram during Raman spectroscopy measurements.

[0155] Sheet-like carbon nanofibers were evaluated in the same manner.

[0156] [Table 1]

[0157] d(002) (nm) Lc(002) (nm) I D / I G ]]> Graphitized sheet-shaped carbon nanofiber 0.335 41 0.24 Sheet-shaped carbon nanofiber 0.336 28 1.33

[0158] The average length of the sheet-like carbon nanofibers and graphitized sheet-like carbon nanofibers is 1 μm, and the average diameter is 200 nm. The average diameter corresponds to the average diameter of the first 50 graphitized sheet-like carbon nanofibers (or sheet-like carbon nanofibers) arranged in order of maximum average diameter when observed using a scanning electron microscope (SEM) at ×20,000 magnification. The average length corresponds to the average length of the first 50 graphitized sheet-like carbon nanofibers (or sheet-like carbon nanofibers) arranged in order of maximum average length when observed using a SEM at ×20,000 magnification.

[0159] Experimental Example 1: Initial charge / discharge efficiency evaluation

[0160] Each battery from the examples and comparative examples was mounted on a pressure clamp, and the bolts / nuts located at the corners were tightened with the same pressure of 1 N·m to prepare a single cell. The initial charge / discharge efficiency was evaluated by the ratio of the capacity of one charge to the capacity of one discharge when the single cell was charged once and discharged once at 60°C under the following conditions (see Table 2).

[0161] Charging conditions: Charge at 0.1C CC to 4.25V, then charge at 4.25V CV, with a 0.05C cutoff. Discharge conditions: Discharge at 0.1C CC to 3.0V.

[0162] Experimental Example 2: Capacity retention rate evaluation

[0163] Each battery from the Examples and Comparative Examples was charged and discharged at 60°C under the following conditions, and the capacity retention (%) at the 50th cycle was then evaluated. The discharge capacity at the first charge / discharge cycle was set as 100%.

[0164] Charging conditions: Charge at 0.5C CC to 4.25V, then stop at 0.5C.

[0165] Discharge conditions: Discharge at 0.33C CC to 3.0V.

[0166] [Table 2]

[0167]

[0168] The average particle size of the silver nanoparticles corresponds to the average particle size of the top 50 largest silver nanoparticles and the bottom 50 largest silver nanoparticles when observed with TEM at a magnification of ×1,000,000. GPCNF is graphitized sheet carbon nanofiber, PCNF is non-graphitized sheet carbon nanofiber, and CB is carbon black.

[0169] The amount of silver nanoparticles refers to the total weight of sheet-like carbon nanofibers and silver nanoparticles in the negative electrode active material layer.

Claims

1. An all-solid-state lithium secondary battery, comprising: A positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer comprises graphitized sheet-like carbon nanofibers and silver nanoparticles. The graphitized sheet-like carbon nanofibers have multiple graphene sheets stacked along the growth direction of the graphitized sheet-like carbon nanofibers, and The graphitized sheet-like carbon nanofibers include curved portions protruding toward the sides of the graphitized sheet-like carbon nanofibers, wherein the curved portions correspond to the base surface of the graphene sheet; and In this process, the hexagonal grid planes of carbon in the graphitized sheet-like carbon nanofibers are arranged at right angles to the fiber axis.

2. The all-solid-state lithium secondary battery as described in claim 1, wherein, The graphitized sheet carbon nanofibers are formed by heat-treating sheet carbon nanofibers at temperatures above 2000°C.

3. The all-solid-state lithium secondary battery as described in claim 1, wherein, The curved portion is formed by extending one graphene sheet to connect it to another graphene sheet, and The base surface has a closed-loop shape and exists in a curved state on the side of the graphitized sheet carbon nanofibers. The ring shape appears periodically along the growth direction of the graphitized sheet carbon nanofibers.

4. The all-solid-state lithium secondary battery as described in claim 1, wherein, The silver nanoparticles are disposed on the surface of the graphitized sheet-like carbon nanofibers.

5. The all-solid-state lithium secondary battery as described in claim 1, wherein, In the X-ray diffraction (XRD) measurements of the graphitized sheet-like carbon nanofibers, The d(002) of the graphitized sheet carbon nanofibers is 0.330 nm to 0.350 nm.

6. The all-solid-state lithium secondary battery as described in claim 1, wherein, In the XRD measurements of the graphitized sheet-like carbon nanofibers, The Lc(002) of the graphitized sheet carbon nanofibers is 20 nm to 200 nm.

7. The all-solid-state lithium secondary battery as described in claim 1, wherein, The graphitized sheet-like carbon nanofibers I D / I G The value ranges from 0.1 to 1.

0.

8. The all-solid-state lithium secondary battery as described in claim 1, wherein, The graphitized sheet-like carbon nanofibers have an average diameter of 10 nm to 500 nm.

9. The all-solid-state lithium secondary battery as described in claim 1, wherein, The graphitized sheet-like carbon nanofibers have an average length of 0.1 μm to 5 μm.

10. The all-solid-state lithium secondary battery as described in claim 1, wherein, The specific surface area of ​​the graphitized sheet-like carbon nanofibers is 5 m². 2 / g to 100m 2 / g.

11. The all-solid-state lithium secondary battery as described in claim 1, wherein, The graphitized sheet-like carbon nanofibers are included in the negative electrode active material layer in an amount of 50% to 98% by weight.

12. The all-solid-state lithium secondary battery as described in claim 1, wherein, The average particle size of the silver nanoparticles is 1 nm to 100 nm.

13. The all-solid-state lithium secondary battery as described in claim 1, wherein, In the negative electrode active material layer Based on the total weight of the graphitized sheet-like carbon nanofibers and the silver nanoparticles, the content of the silver nanoparticles is from 1% to 40% by weight.

14. The all-solid-state lithium secondary battery as described in claim 1, wherein, The weight ratio of the graphitized sheet-like carbon nanofibers to the silver nanoparticles is 99:1 to 60:

40.

15. The all-solid-state lithium secondary battery as described in claim 1, wherein, The negative electrode active material layer also includes a negative electrode binder.

16. The all-solid-state lithium secondary battery as described in claim 1, wherein, The thickness of the negative electrode active material layer is from 1 μm to 100 μm.

17. The all-solid-state lithium secondary battery of claim 1, further comprising a negative electrode current collector, and A metal layer disposed between the negative electrode active material layer and the negative electrode current collector in the charging state. in, The metal layer contains lithium.

18. The all-solid-state lithium secondary battery as described in claim 1, wherein, In the negative electrode active material layer, based on the total weight of the graphitized sheet carbon nanofibers and the silver nanoparticles, the content of the silver nanoparticles is 7% to 10% by weight.

19. A method for preparing the all-solid-state lithium secondary battery according to claim 1, the method comprising: The first step involves reducing silver ions in a mixture of silver ions and graphitized sheet carbon nanofibers to form a dry-mixed powder containing graphitized sheet carbon nanofibers and silver nanoparticles disposed on the graphitized sheet carbon nanofibers; and The second step involves forming a layer of negative electrode active material on the negative electrode current collector using the negative electrode mixture containing the dry-mixed powder.

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