Solid electrolyte for all-solid-state lithium-ion secondary battery and all-solid-state lithium-ion secondary battery comprising the same

Abstract

Disclosed is a solid electrolyte for an all-solid lithium ion secondary battery and an all-solid lithium ion secondary battery including the same. The solid electrolyte for the all-solid battery includes two or more types of binders having different molecular weights, and thus can reduce the porosity of the solid electrolyte, thereby improving the formability of the solid electrolyte and the performance of the battery. The solid electrolyte for the all-solid lithium ion secondary battery includes two or more types of binders having different molecular weights (Mw).

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2024-0109429, filed on August 14, 2024, and Korean Patent Application No. 10-2025-0112275, filed on August 13, 2025, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a solid electrolyte for all-solid-state lithium-ion secondary batteries and an all-solid-state lithium-ion secondary battery containing the solid electrolyte. More specifically, it relates to a solid electrolyte for all-solid-state lithium-ion secondary batteries and an all-solid-state lithium-ion secondary battery containing the solid electrolyte, wherein the solid electrolyte improves the formability of the solid electrolyte and the performance of the battery by incorporating two or more types of binders with different molecular weights into the solid electrolyte of the all-solid-state battery to reduce porosity. Background Technology

[0003] From the perspectives of battery capacity, safety, output, scalability, and miniaturization, various batteries are being researched to overcome the limitations of currently widely commercialized lithium-ion batteries. Typically, academia and industry are continuously researching metal-air batteries with much larger theoretical capacities compared to lithium-ion batteries; all-solid-state batteries that do not pose an explosion hazard compared to lithium-ion batteries; supercapacitors with high output; large-size Na-S batteries or redox flow batteries (RFB); and miniaturized thin-film batteries.

[0004] Among these batteries, all-solid-state batteries use a solid electrolyte instead of the liquid electrolyte used in lithium-ion secondary batteries. This eliminates the use of flammable solvents, thus eliminating the risk of fire or explosion caused by decomposition reactions in conventional electrolyte solutions, and significantly improving safety. Furthermore, all-solid-state batteries can use lithium metal or lithium alloys as the negative electrode active material, offering the advantage of significantly higher energy density relative to battery mass and volume. In addition, lithium's capacity density (capacity per unit weight) is approximately 10 times that of graphite, which is commonly used as the negative electrode active material. Therefore, when lithium is used as the negative electrode active material, output can be increased while reducing the size of the all-solid-state battery.

[0005] As a conventional all-solid-state battery, known batteries include a metal layer formed of a metal alloyed with lithium as the negative electrode active material layer, and an amorphous carbon interface layer on the negative electrode active material layer. Furthermore, in the case of such all-solid-state batteries, during charging, metallic lithium is deposited between the amorphous carbon interface layer and the negative electrode active material layer, and during discharging, the deposited metallic lithium is ionized and migrates towards the positive electrode. However, when the all-solid-state battery described above is repeatedly charged and discharged, the following problem may occur: the metallic lithium deposited between the amorphous carbon interface layer and the negative electrode active material layer can be ionized and dissolved, thereby creating voids that render the battery unusable.

[0006] To address these issues, all-solid-state batteries have been developed in this field using a negative electrode containing carbon materials but without a lithium metal layer (i.e., lithium-free negative electrodes). The negative electrode of such an all-solid-state battery does not contain lithium in its initial or fully discharged state. During overcharging, lithium ions migrating from the positive electrode form an alloy or compound between the negative electrode current collector and the solid electrolyte, which can be used as the negative electrode active material (i.e., lithium metal is deposited on the surface of the negative electrode current collector during charging).

[0007] All-solid-state batteries, as described above, are manufactured by placing a solid electrolyte membrane between the positive and negative electrodes. Furthermore, since sulfide-based all-solid-state batteries require high-temperature and high-pressure molding processes (e.g., isostatic pressing) after placing the solid electrolyte membrane between the positive and negative electrodes, the solid electrolyte must possess excellent formability. However, a problem exists: currently known sulfide-based solid electrolytes for all-solid-state batteries have poor formability, which adversely affects battery performance. Therefore, there is a need to improve methods for improving the formability of sulfide-based solid electrolytes for all-solid-state batteries. Summary of the Invention

[0008] [Technical Issues]

[0009] Therefore, one object of the present invention is to provide a solid electrolyte for an all-solid-state lithium-ion secondary battery and an all-solid-state lithium-ion secondary battery containing the solid electrolyte, wherein the solid electrolyte can improve the formability of the solid electrolyte and the performance of the battery by incorporating two or more types of binders with different molecular weights into the solid electrolyte of the all-solid-state battery to reduce the porosity.

[0010] [Technical Solution]

[0011] To achieve the above objectives, the present invention provides a solid electrolyte for all-solid-state lithium-ion secondary batteries, which comprises two or more types of binders with different molecular weights (Mw).

[0012] Furthermore, the present invention provides an all-solid-state lithium-ion secondary battery, which includes a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer includes the aforementioned solid electrolyte disposed between the positive electrode and the negative electrode.

[0013] [Beneficial Effects]

[0014] The solid electrolyte for all-solid-state lithium-ion secondary batteries and the all-solid-state lithium-ion secondary batteries containing the solid electrolyte of the present invention incorporate two or more types of binders with different molecular weights into the solid electrolyte of the all-solid-state battery to reduce porosity, thereby having the advantages of improving the formability of the solid electrolyte and the performance of the battery. Attached Figure Description

[0015] Figure 1 This is a cross-sectional schematic diagram illustrating the structure of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0016] Figure 2 This is a cross-sectional schematic diagram illustrating the structure of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0017] Figure 3 This is a graph showing the capacity retention rate of batteries in embodiments and comparative examples of the present invention as a function of charge-discharge cycles. Detailed Implementation

[0018] The present invention will now be described in detail.

[0019] The solid electrolyte for all-solid-state lithium-ion secondary batteries of the present invention comprises two or more types of binders with different molecular weights.

[0020] All-solid-state batteries are batteries that use a solid electrolyte instead of the liquid electrolyte used in lithium-ion batteries. Therefore, since flammable solvents are not used, there is no risk of fire or explosion due to the decomposition reactions of conventional electrolyte solutions, significantly improving safety. These all-solid-state batteries offer significant advantages over the low stability, low energy density, and long lifespan issues associated with the liquid electrolytes used in lithium-ion batteries.

[0021] Solid electrolytes in all-solid-state batteries can be broadly categorized into organic (polymer-based) solid electrolytes and inorganic solid electrolytes. Inorganic solid electrolytes can be further divided into sulfide-based and oxide-based types. Furthermore, the most technologically advanced solid electrolytes currently are sulfide-based solid electrolytes, and their development has progressed to the point where their ionic conductivity is approaching that of organic electrolyte solutions. Thus, among various solid electrolytes, sulfide-based solid electrolytes not only possess 10... -3 S / cm to 10 -2With its high ionic conductivity of S / cm, as well as excellent thermal stability and ductility, it has the advantage of improving resistance through good contact with the interface (interface compatibility).

[0022] However, because sulfide-based all-solid-state batteries require high-temperature and high-pressure molding processes (e.g., isostatic pressing) after the solid electrolyte membrane is placed between the positive and negative electrodes, the formability of the solid electrolyte must be particularly excellent. However, conventional sulfide-based solid electrolytes used in all-solid-state batteries have poor formability, which negatively impacts battery performance. Therefore, the applicant has addressed this problem by incorporating two or more types of binders with different molecular weights into the sulfide-based solid electrolyte and aims to provide the following specific and practical solutions.

[0023] Solid electrolytes for all-solid-state lithium-ion secondary batteries are formed by drying an electrolyte slurry and are typically disposed between the positive and negative electrodes, but can also be included in the electrodes (especially the positive electrode) if desired. For example, when the positive electrode also contains a solid electrolyte, the solid electrolyte can be applied to at least a portion of the surface of the components constituting the positive electrode (e.g., the positive electrode active material).

[0024] Solid electrolytes can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0025] In addition, the solid electrolyte may include at least one selected from sulfide solid electrolytes, polymer solid electrolytes and oxide solid electrolytes, but preferably only sulfide solid electrolytes.

[0026] More specifically, the solid electrolyte essentially comprises a sulfide-based solid electrolyte and a binder.

[0027] Sulfide-based solid electrolytes contain sulfur (S) and possess the ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glasses or Li-PS-based glass ceramics. Non-limiting examples of such sulfide-based solid electrolytes may include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where X is a halogen element), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n(where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In), or a combination thereof. However, it is not limited to this and can be composed of substances that constitute typical sulfide solid electrolytes. Meanwhile, when using substances containing Li₂S-P₂S₅, the molar ratio of Li₂S to P₂S₅ can be selected, for example, in the range of Li₂S:P₂S₅ = 50:50 to 90:10.

[0028] However, in order for the solid electrolyte to exhibit optimal performance, it is preferable that the sulfide solid electrolyte essentially contains a compound having a sulfogermanium sulfide crystal structure, such as a compound based on LPSCl (lithium phosphorus sulfide), for example, Li6PS5Cl.

[0029] Furthermore, sulfide solid electrolytes can contain lithium salts, and lithium salts can be represented as Li. + X - It is an ionizable lithium salt. The anion of this lithium salt is not particularly limited, and examples may include 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.

[0030] The adhesive contained in the solid electrolyte for all-solid-state lithium-ion secondary batteries plays an important role in the adhesion between the solid electrolyte and the electrode, or assists in the adhesion between the solid electrolyte and the electrode.

[0031] As described above, solid electrolytes contain two or more types of binders with different molecular weights. For example, a solid electrolyte may contain two types of binders with different molecular weights, namely a first binder and a second binder (note that the “molecular weight” of the binders mentioned below refers to “weight-average molecular weight (Mw)”).

[0032] The ratio of the molecular weight (Mw) of the first adhesive to the molecular weight (Mw) of the second adhesive can be from 1:30 to 70, preferably from 1:40 to 60, and more preferably from 1:45 to 55. If the ratio of the molecular weight (Mw) of the first adhesive to the molecular weight (Mw) of the second adhesive is outside the range of 1:30 to 70, the objective of the invention may not be achieved, or the effect may have reached its maximum and there may be no further benefit.

[0033] More specifically, the molecular weight of one of the two types of adhesives (i.e., the first adhesive) may be 3,000 to 50,000 g / mol, preferably 5,000 to 30,000 g / mol, more preferably 7,000 to 15,000 g / mol, and the molecular weight of the other type of adhesive (i.e., the second adhesive) may be 100,000 to 1,500,000 g / mol, preferably 250,000 to 900,000 g / mol, more preferably 400,000 to 600,000 g / mol.

[0034] If the first or second adhesive does not meet the aforementioned molecular weight, the formability of the solid electrolyte membrane may be reduced. Furthermore, even if the aforementioned molecular weight is met, using only one type of adhesive instead of two types may result in problems such as deterioration of the mechanical properties or formability of the solid electrolyte membrane.

[0035] More specifically, preferably, the first adhesive comprises a rubber-like compound having a molecular weight of 3,000 to 50,000 g / mol, preferably 5,000 to 30,000 g / mol, and more preferably 7,000 to 15,000 g / mol.

[0036] In addition, as needed, the first adhesive may also comprise one or more compounds selected from the group consisting of acrylonitrile copolymers, acrylonitrile-styrene-butadiene copolymers, polyethylene, polypropylene, chlorosulfonated polyethylene, polyvinylpyrrolidone, cellulose acetate, cellulose acetate butyrate, polyamides, polyimides, polycarboxylate esters, and compounds exhibiting properties similar to those thereof.

[0037] Examples of rubber compounds included in the first adhesive may include butadiene rubbers (e.g., butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylic styrene-butadiene rubber (ASBR), acrylonitrile-butadiene rubber (ABR), nitrile rubber (NBR) and hydrogenated nitrile rubber (HNBR)), acrylic rubbers and fluororubbers, and may include one or more of them.

[0038] Preferably, the second adhesive comprises a rubber compound having a molecular weight of 100,000 to 1,500,000 g / mol, more preferably 250,000 to 900,000 g / mol, and even more preferably 400,000 to 600,000 g / mol.

[0039] In addition, as needed, the second adhesive may also comprise one or more compounds selected from the group consisting of acrylonitrile copolymers, acrylonitrile-styrene-butadiene copolymers, polyethylene, polypropylene, chlorosulfonated polyethylene, polyvinylpyrrolidone, cellulose acetate, cellulose acetate butyrate, polyamides, polyimides, polycarboxylate esters, and compounds exhibiting properties similar to those thereof.

[0040] Examples of rubber compounds included in the second adhesive may include butadiene rubbers (e.g., butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylic styrene-butadiene rubber (ASBR), acrylonitrile-butadiene rubber (ABR), nitrile rubber (NBR) and hydrogenated nitrile rubber (HNBR)), acrylic rubbers and fluororubbers, and may include one or more of them.

[0041] Furthermore, the rubber compounds contained in the first adhesive and the rubber compounds contained in the second adhesive can be independently selected from the group consisting of butadiene rubbers, acrylic rubbers, fluororubbers, and combinations thereof. That is, the rubber compounds contained in the first adhesive and the rubber compounds contained in the second adhesive can be the same or different.

[0042] However, more preferably, the first adhesive comprises nitrile rubber with a molecular weight of 3,000 to 50,000 g / mol, preferably 5,000 to 30,000 g / mol, and more preferably 7,000 to 15,000 g / mol.

[0043] Furthermore, more preferably, the second adhesive comprises nitrile rubber with a molecular weight of 100,000 g / mol to 1,500,000 g / mol, preferably 250,000 g / mol to 900,000 g / mol, and more preferably 400,000 g / mol to 600,000 g / mol.

[0044] Furthermore, the molecular weight difference between the first and second binders can be from 200,000 to 1,000,000 g / mol, preferably from 300,000 to 700,000 g / mol, and more preferably from 400,000 to 600,000 g / mol. If the molecular weight difference between the first and second binders is less than 200,000 g / mol, the formability of the solid electrolyte membrane may be reduced. Furthermore, if the molecular weight difference between the first and second binders exceeds 1,000,000 g / mol, the molecular weight of one type of binder may be excessively increased, leading to reduced solubility.

[0045] Meanwhile, by weight, the content ratio of the first binder and the second binder can be from 5:95 to 30:70, preferably from 10:90 to 20:80, and more preferably from 10:90 to 15:85. If the content of the first binder is less than 5% by weight based on the total weight of the first and second binders, the effect of improving formability may be reduced. Furthermore, if the content of the first binder exceeds 30% by weight based on the total weight of the first and second binders, the excessive input of the low molecular weight binder (i.e., the first binder) may prevent the contact between binder particles from being maintained, which could negatively impact the battery's lifespan performance. The low molecular weight binder and the high molecular weight binder must be in uniform contact because if an excessive amount of low molecular weight binder is added, a large number of low molecular weight binder particles that cannot contact the high molecular weight binder particles will be generated. That is, if the low molecular weight binder is used alone, the pressure-formed solid electrolyte membrane lacks the strength to maintain its structure, resulting in a springback phenomenon, causing the membrane to slightly return to its pre-pressure state. Similarly, even if a large number of low molecular weight binder particles that do not contact the high molecular weight binder particles are formed, springback will still occur in the solid electrolyte membrane. Furthermore, if the content of the first adhesive exceeds 30% by weight based on the total weight of the first and second adhesives, the ionic conductivity of the solid electrolyte membrane increases, potentially leading to an increase in the resistance of the battery.

[0046] In this way, when two or more types of binders with different molecular weights are incorporated into a solid electrolyte, the porosity within the solid electrolyte can be reduced, thereby increasing the formability of the solid electrolyte and the contact area with the electrode. In other words, when the solid electrolyte contains two or more types of binders with different molecular weights, the binder with the relatively smaller molecular weight is positioned between the binders with the relatively larger molecular weight, which exhibits advantages such as increased density of the solid electrolyte. Furthermore, if isostatic pressure is applied under these conditions, the formability of the solid electrolyte and the contact area with the electrode can be maximized by reducing the porosity of the solid electrolyte to an excellent level. Therefore, compared to conventional methods, the formability of the solid electrolyte and the performance of the battery can be improved.

[0047] Furthermore, in the solid electrolyte, only the binder with a relatively small molecular weight (i.e., the first binder) is located alone on the interface side in contact with the electrode, thereby increasing the interfacial adhesion between the electrode and the solid electrolyte membrane. Therefore, in this case, the solid electrolyte may comprise: a first binder layer containing the first binder; and a second binder layer containing the first binder and the second binder in a mixed state. Thus, when the solid electrolyte is placed between the positive and negative electrodes, the solid electrolyte may consist of a 1a binder layer in contact with the positive electrode, a 1b binder layer in contact with the negative electrode, and a second binder layer disposed between the 1a binder layer and the 1b binder layer.

[0048] Simultaneously, during the manufacturing process of the solid electrolyte, a solvent can be added to the electrolyte slurry. The solvent serves to dissolve the first and second binders, and includes solvents with a dielectric constant greater than 0 and less than 20, preferably 0.1 to 10, and more preferably 0.3 to 5. In particular, since sulfide-based solid electrolytes exhibit structural collapse upon reaction with polar organic solvents, the dielectric constant of the solvent must be less than 20.

[0049] More specifically, the electrolyte slurry may contain one or more solvents with a dielectric constant greater than 0 and less than 20.

[0050] Examples of such solvents may include: butyrate compounds, such as n-butyl butyrate, isobutyl butyrate, pentyl butyrate, hexyl butyrate, and heptyl butyrate; sulfone compounds, such as ethyl methyl sulfone and sulfolane; nitrile compounds, such as acetonitrile; carbonate compounds, such as propylene carbonate; γ-butyrolactone; toluene compounds; xylene compounds; anisole compounds; benzene compounds; methane-based hydrocarbon compounds having six or more carbon atoms, such as hexane, heptane, nonane, and decane; methane-based hydrocarbon compounds containing halogen elements, such as dibromomethane and dichloromethane; chloroform compounds; and acetate compounds, such as benzyl acetate and octyl acetate.

[0051] The solvent may preferably contain at least one of butyrate compounds, toluene compounds, xylene compounds, anisole compounds and acetate compounds, and more preferably substantially contain butyrate compounds.

[0052] By weight, the ratio of sulfide-based solid electrolyte to binder (including first binder and second binder) in the above-mentioned solid electrolyte can be 90:10 to 98:2, preferably 91:9 to 97:3, and more preferably 93:7 to 95:5.

[0053] If the binder content is less than 2% by weight, problems such as the electrolyte slurry not being dispersed may occur due to insufficient binder content.

[0054] Furthermore, if the adhesive content exceeds 10% by weight, problems such as gelation of the electrolyte slurry may occur due to the excessive adhesive content.

[0055] Additionally, if desired, the solid electrolyte may further include one or more of cross-linked monomers and inorganic particles.

[0056] Crosslinking monomers can crosslink the cathode and electrolyte through photopolymerization or thermal polymerization to form a polymer matrix, and examples of such crosslinking monomers can be at least one selected from ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylated bisphenol A dimethacrylate, derivatives thereof, and mixtures thereof.

[0057] Inorganic particles can be uniformly dispersed within a solid electrolyte and used to improve the mechanical strength of the solid electrolyte. Examples of such particles may be at least one selected from alumina (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), barium titanate (BaTiO3), lithium oxide (Li2O), lithium fluoride (LiF), lithium hydroxide (LiOH), lithium nitride (Li3N), barium oxide (BaO), sodium oxide (Na2O), lithium carbonate (Li2CO3), calcium carbonate (CaCO3), lithium aluminate (LiAlO2), strontium titanate (SrTiO3), tin oxide (SnO2), cerium oxide (CeO2), magnesium oxide (MgO), nickel oxide (NiO), calcium oxide (CaO), zinc oxide (ZnO), zirconium dioxide (ZrO2), silicon carbide (SiC), their derivatives, and mixtures thereof.

[0058] Here, a method for manufacturing a solid electrolyte for an all-solid-state lithium-ion secondary battery is briefly described. One embodiment of the solid electrolyte for an all-solid-state lithium-ion secondary battery according to the present invention can be prepared by the following steps: (a) mixing two or more types of binders with different molecular weights to prepare a binder solution; (b) mixing the prepared binder solution with a sulfide-based solid electrolyte and a solvent to prepare an electrolyte slurry; and (c) drying the prepared electrolyte slurry. Alternatively, according to one embodiment of the present invention, the solid electrolyte can be formed by applying, coating, and drying the prepared electrolyte slurry onto a release film. Furthermore, according to another embodiment of the present invention, the solid electrolyte can be formed by applying, coating, and drying the prepared electrolyte slurry onto an electrode.

[0059] Meanwhile, the solid electrolyte for all-solid-state lithium-ion secondary batteries, as described above, can be composed of multiple layers, and preferably two layers.

[0060] That is, in this case, the solid electrolyte becomes an electrolyte complex. Therefore, the electrolyte complex can contain two phase-separated solid electrolytes and can have a layered structure formed by a first solid electrolyte placed on the positive electrode side and a second solid electrolyte placed on the negative electrode side.

[0061] The first and second solid electrolytes each essentially comprise sulfide-based solid electrolytes and two or more types of binders with different molecular weights (Mw).

[0062] The sulfide-based solid electrolyte contained in the first solid electrolyte and the sulfide-based solid electrolyte contained in the second solid electrolyte each independently contain the aforementioned sulfide-based solid electrolyte, and their specific compositions may be the same or different within the relevant range.

[0063] The adhesive contained in the first solid electrolyte and the adhesive contained in the second solid electrolyte each contain the aforementioned adhesives, that is, two or more types of adhesives with different molecular weights (Mw), and the specific compositions may be the same or different within the relevant range.

[0064] In addition, among two or more types of adhesives with different molecular weights, it is preferred that the adhesive with the relatively smaller molecular weight is a liquid at room temperature, while the adhesive with the relatively larger molecular weight is a solid at room temperature (however, when both types of adhesives are dissolved in an organic solvent, a liquid adhesive solution is produced).

[0065] Furthermore, if necessary, the first solid electrolyte and the second solid electrolyte may each further contain one or more of the aforementioned crosslinked monomers and inorganic particles.

[0066] The following section describes an all-solid-state lithium-ion secondary battery that includes the solid electrolyte for all-solid-state lithium-ion secondary batteries described above.

[0067] The all-solid-state lithium-ion secondary battery includes a positive electrode, a negative electrode, and a solid electrolyte layer containing the aforementioned solid electrolyte disposed therebetween, and is preferably a sulfide-based all-solid-state lithium-ion secondary battery.

[0068] Figure 1 This is a cross-sectional schematic diagram illustrating the structure of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention. The all-solid-state lithium-ion secondary battery 1000 according to one embodiment of the present invention is a so-called lithium-ion secondary battery that performs charging and discharging via lithium ions moving between a positive electrode 100 and a negative electrode 200. Specifically, as... Figure 1 As shown, the all-solid-state lithium-ion secondary battery 1000 includes a positive electrode 100, a negative electrode 200, and a solid electrolyte layer 300 disposed between the positive electrode 100 and the negative electrode 200 and including a solid electrolyte. These will be described one by one below.

[0069] positive electrode

[0070] like Figure 1 As shown, the positive electrode 100 includes a positive electrode active material layer 140 and a positive electrode current collector 120 arranged sequentially in the direction of the negative electrode 200. The positive electrode current collector 120 may be plate-shaped or foil-shaped. The positive electrode current collector 120 may be, for example, a metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium and lithium, or an alloy of two or more of these metals.

[0071] The positive electrode active material layer 140 is capable of reversibly inserting and deintercalating lithium ions. Furthermore, the positive electrode active material layer 140 includes a positive electrode active material and may also include a solid electrolyte. The positive electrode active material can be a compound capable of lithium insertion / deintercalation. Examples of compounds capable of lithium insertion / deintercalation include compounds represented by any of the following: Li a A 1-b B' b D'2(0.90≤a≤1.8, 0≤b≤0.5); Li a E1- b B' b O 2-c D' c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B' b O 4-c D' c (0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co bB' c D’ α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05\0<α≤2);Li a Nor 1-b-c Co b B' c O 2-α F’ α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05\0<α<2);Li a Nor 1-b-c Mn b B' c D’ α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05\0<α≤2);Li a Nor 1-b-c Mn b B' c O 2-α F’ α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05\0<α<2);Li a Nor b E c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Nor b Co c Mn d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);Li a NiG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a MnG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn2G b O4(0.90≤a≤1.8,0.001≤b≤0.1);QO2;QS2;LiQS2;V2O5;LiV2O5;LiI'O2;LiVO4;Li (3-f) J2(PO4)3(0≤f≤2);Li (3-f) Fe2(PO4)3(0≤f≤2);LiFePO4。

[0072] In the above formula, A is Ni, Co, Mn or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D' is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; F' is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I' is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0073] Specific examples of the positive electrode active material may include lithium salts such as lithium cobaltate (LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminate (NCA), lithium nickel cobalt manganate (NCM), lithium manganate, lithium iron phosphate, and lithium sulfide. The positive electrode active material layer 140 may include only one or two or more selected from these compounds as the positive electrode active material.

[0074] The positive electrode active material may include the transition metal oxide lithium salt having a layered rock salt structure among the above lithium salts. Here, the layered rock salt structure is a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged in the direction of the cubic rock salt structure, and as a result, each atom layer forms a two-dimensional plane. In addition, the cubic rock salt structure refers to a sodium chloride-type structure which is a type of crystal structure. For example, the cubic rock salt structure refers to a structure in which face-centered cubic lattices respectively formed by positive ions and negative ions are displaced from each other by 1 / 2 of the side length of the unit lattice.

[0075] The transition metal oxide lithium salt having such a layered rock salt structure may be, for example, a ternary lithium transition metal oxide, such as LiNi x Co y Al z O₂(NCA) or LiNi x Co y Mn z O₂(NCM) (wherein 0<x<1, 0<y<1, 0<z<1, x+y+z=1). By including the ternary transition metal oxide lithium salt having such a layered rock salt structure as the positive electrode active material, the positive electrode active material layer 140 can improve the energy density and thermal stability of the all-solid-state lithium-ion secondary battery 1000.

[0076] The shape of the positive electrode active material can be, for example, particulate, such as spherical or ellipsoidal. Furthermore, there are no particular limitations on the particle size of the positive electrode active material, and it is feasible as long as it falls within the range suitable for positive electrode active materials in common all-solid-state lithium-ion secondary batteries. Moreover, there are no particular limitations on the content of the positive electrode active material in the positive electrode active material layer 140, and it is feasible as long as it falls within the range suitable for positive electrodes in common all-solid-state lithium-ion secondary batteries.

[0077] Alternatively, compounds having a coating on the surface of the aforementioned compounds can be used, or mixtures of the aforementioned compounds and compounds having a coating can be used. The coating may comprise oxides or hydroxides of coating elements, hydroxyoxides of coating elements, oxycarbonates of coating elements, or hydroxycarbonates of coating elements, etc., of coating element compounds. The compounds constituting these coatings may be amorphous or crystalline. The coating elements included in the coating may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof, and specific examples of the aforementioned coatings may include Li2O-ZrO2, etc. The coating formation process may use any coating method (e.g., spraying, dipping, etc.) as long as it can coat the material in a manner that does not adversely affect the properties of the positive electrode active material due to the use of these elements in the compound, and a detailed description thereof will be omitted, as it will be well understood by those skilled in the art.

[0078] The solid electrolyte that may be further included in the positive electrode active material layer 140 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 300 described below. Furthermore, the positive electrode active material layer 140 may be a positive electrode active material layer obtained by mixing additives (e.g., conductive agents, binders, fillers, dispersants, or ion-conducting agents) with the aforementioned positive electrode active material and solid electrolyte. The conductive agent may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder. Additionally, the binder is mixed with the active material and conductive material to bind the components and aid particle growth, and may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. Furthermore, the filler, dispersant, ion-conducting agent, etc., may be known materials commonly used in all-solid-state lithium-ion secondary battery electrodes. Furthermore, the positive electrode active material layer 140 may include the positive electrode active material, conductive material, and binder in particulate form as described above.

[0079] negative electrode

[0080] Next, the negative electrode 200 includes: a negative electrode active material layer 240, which is positioned closer to the positive electrode 100 and in contact with the solid electrolyte layer 300; and a negative electrode current collector 220, which is positioned at the outermost position based on the stacking direction, facing the opposite side of the negative electrode active material layer 240 that is not in contact with the solid electrolyte layer 300. Furthermore, apart from the lithium metal formed during charging, the negative electrode may not contain any separate lithium metal (i.e., an anode-less all-solid-state battery).

[0081] Negative electrode active material layer

[0082] The negative electrode active material layer 240 may include one or more types of negative electrode active materials capable of forming alloys or compounds with lithium. In the initial state or after full discharge, lithium may not be present between the negative electrode current collector 220 and the negative electrode active material layer 240 or between the negative electrode active material layer 240 and the solid electrolyte layer 300. Figure 2 This is a cross-sectional schematic diagram illustrating the structure of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0083] As will be described later, if the all-solid-state lithium-ion secondary battery 1000 of the embodiment is overcharged, the negative electrode active material contained in the negative electrode active material layer 240 and the lithium ions that have moved from the positive electrode 100 will form an alloy or compound, and a metal layer 260 containing lithium as the main component can be formed (deposited) on the negative electrode 200, as... Figure 2 As shown. The metal layer 260 can be deposited and formed between the negative electrode current collector 220 and the negative electrode active material layer 240, and / or deposited and formed in the negative electrode active material layer 240. If the metal layer 260 is disposed between the negative electrode current collector 220 and the negative electrode active material layer 240, the metal layer 260 can be disposed closer to the negative electrode current collector layer 220 than the negative electrode active material layer 240.

[0084] In one embodiment of the present invention, the negative electrode active material layer 240 may include one or more lithiophilic materials selected from the group consisting of silver (Ag), gold (Au), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO), manganese monoxide (MnO), silicon dioxide (SiO2), titanium dioxide (TiO2), aluminum oxide (Al2O3), zinc peroxide (ZnO2), and lithium fluoride (LiF). Furthermore, silver (Ag) may be more preferably used as the lithiophilic material among these materials. However, it is not limited thereto, and any lithiophilic material with similar properties or characteristics may be used without particular limitation.

[0085] Therefore, the metal layer (260) formed during overcharging may contain a Li (lithophile material) alloy containing a γ1 phase, a βLi phase, or a combination thereof, wherein the lithiophile material is dissolved in lithium. Thus, during discharge, only Li dissolves in the Li (lithophile material) alloy constituting the metal layer 260, and the dissolved lithiophile material remains, thereby suppressing the appearance of voids. In this case, the content of the lithiophile material in the deposited Li-lithophile material solid solution can be 60% by weight or less. If this content is within this range, the decrease in average discharge potential due to the influence of the lithiophile material can be effectively suppressed. On the other hand, if the content of the lithiophile material in the deposited Li-lithophile material solid solution is too small, the amount of lithiophile material remaining during discharge is reduced, and the appearance of voids may not be sufficiently suppressed. Therefore, the content of the lithiophile material in the deposited Li-lithophile material solid solution can be 20% by weight or more, for example, 40% by weight or more.

[0086] In one embodiment of the invention, the lithiophilic material does not necessarily need to be uniformly present in the negative electrode active material layer 240, and can be locally present within the negative electrode active material layer 240 toward the negative electrode current collector 220. In this case, lithium ions can react with the localized lithiophilic material layer within the negative electrode active material layer 240 that has reached the vicinity of the negative electrode current collector 220, thereby forming a Li (lithiophilic material) alloy as the metal layer 260.

[0087] If the content of the lithiophilic material contained in the negative electrode active material layer 240 is too low, it may be difficult to suppress the formation of porosity because the amount of lithiophilic material remaining during discharge is also reduced. Therefore, based on a total of 100% by weight of negative electrode active material contained in the negative electrode active material layer 240, the negative electrode active material layer 240 may contain 10% by weight or more, preferably 20% by weight or more of lithiophilic material in its initial state before charging / discharging. Meanwhile, regarding the relationship between the reaction potential of the lithiophilic material and Li, an increase in the lithiophilic material content can reduce the average discharge potential, thereby reducing the energy density of the battery. Therefore, from the perspective of high energy density, based on a total of 100% by weight of negative electrode active material contained in the negative electrode active material layer 240, the upper limit of the lithiophilic material content can preferably be 50% by weight or less.

[0088] Furthermore, in the negative electrode active material layer 240, if the content of lithiophilic material per unit area is too low when viewed in the stacking direction of the negative electrode 200, the residual lithiophilic material during discharge may also be reduced, making it difficult to suppress the formation of porosity. Therefore, the content of lithiophilic material per unit area in the negative electrode active material layer 240 can be 0.05 mg / cm². 2 Above, preferably 0.10 mg / cm 2That's all. However, if the content of lithiophilic material per unit area is too high, the average discharge potential may decrease, thereby reducing the battery's energy density. Therefore, the upper limit for the content of lithiophilic material per unit area can be 5 mg / cm². 2 The following is preferred: 2 mg / cm 2 the following.

[0089] Furthermore, in the initial state without charging or discharging, the lithiophilic material contained in the negative electrode active material layer 240 can be a particulate phase or a film phase. When the lithiophilic material exists as a particulate phase, the average particle size (d50, diameter length or average diameter) of the lithiophilic material can be from 20 nm to 1 μm, but is not limited thereto.

[0090] In addition to the lithiophilic material, the negative electrode active material layer 240 may also contain carbon material as the negative electrode active material. Amorphous carbon is preferably used as the carbon material contained in the negative electrode active material layer 240. Specific examples of amorphous carbon include amorphous carbon black (amorphous acetylene black, amorphous furnace black, amorphous Ketjen black), amorphous activated carbon, amorphous graphene, and combinations thereof. However, on the interface side of the negative electrode active material layer 240 in contact with the solid electrolyte layer 300, the interface can be further planarized by placing carbon material with relatively small particle sizes. Based on the total 100% by weight of negative electrode active material contained in the negative electrode active material layer 240, the negative electrode active material other than the lithiophilic material can be 50% by weight or more, for example, 70% by weight or more. The content of the negative electrode active material other than the lithiophilic material can be measured using the same method as that used to measure the content of the lithiophilic material.

[0091] Furthermore, the carbon material contained in the negative electrode active material layer 240 may contain oxygen. More specifically, the carbon material particles constituting the carbon material may contain 2 to 10 at% oxygen. When the oxygen content is in the range of 2 to 10 at%, the surface roughness of the negative electrode active material layer and the operating characteristics of the battery can be further improved. In one embodiment of the invention, oxygen may be present in the form of functional groups bonded to the carbon material particles. Additionally, the functional groups may contain at least one selected from the group consisting of carboxyl, hydroxyl, ether, ester, aldehyde, carbonyl, and amide groups.

[0092] Carbon material particles containing 2 to 10 at% oxygen can be manufactured, for example, by oxidizing the carbon material. For instance, the carbon material can be treated with an acid, stirred and reacted at a temperature of 25 to 60°C to introduce oxygen functional groups to the surface of the carbon material. There are no particular limitations on the type of acid, and any acid capable of introducing oxygen functional groups to the surface of the carbon material can be used. Examples of acids include sulfuric acid, nitric acid, or mixtures thereof, and oxidizing agents such as potassium permanganate can also be used.

[0093] The oxygen content contained in carbon material particles can be measured using photoelectron spectroscopy (XPS or ESCA). For example, a K-α (Thermo Fisher Scientific) device can be used for measurement. In one embodiment of the invention, oxygen may be present on the surface of the carbon material particles. This surface refers not only to the outer surface of the carbon material particles but also, for example, the inner surface of pores (if pores are present).

[0094] Furthermore, when the carbon material contains oxygen as described above, the negative electrode active material layer 240 may contain 2 to 10 at% oxygen, 65 to 85 at% carbon, and 0.5 to 5 at% silver (Ag), preferably 2.5 to 5 at% oxygen, 74 to 85 at% carbon, and 0.5 to 3 at% silver. Additionally, the negative electrode active material layer 240 may further contain 5 to 25 at% and preferably 10 to 20 at% fluorine (F). Furthermore, the negative electrode active material layer 240 may further contain 0.01 to 1 at% and preferably 0.01 to 0.5 at% sulfur (S). In one embodiment of the invention, the negative electrode active material layer 240 may comprise 2 to 10 at% oxygen, 65 to 85 at% carbon, 0.5 to 5 at% silver, and 5 to 25 at% fluorine, preferably 2.5 to 5 at% oxygen, 74 to 85 at% carbon, 0.5 to 3 at% silver, and 10 to 20 at% fluorine, and may further comprise sulfur. The atomic composition ratio can be measured using photoelectron spectroscopy (XPS or ESCA). For example, a Nexsa4 (Thermo Fisher Scientific) device can be used to measure the composition ratio.

[0095] Simultaneously, the negative electrode active material layer 240 may also include an adhesive for stabilizing the negative electrode active material layer 240 on the negative electrode current collector 220. The adhesive may be, for example, a resin, such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. Additionally, the negative electrode active material layer 240 may be suitably blended with additives commonly used in all-solid-state batteries (e.g., fillers, dispersants, and ion-conducting agents). Specific examples of these additives are the same as those described in the positive electrode section above.

[0096] The total thickness of the negative electrode active material layer 240 is not particularly limited and can be, for example, from 1 to 100 μm. If the thickness of the negative electrode active material layer 240 is less than 1 μm, the performance of the all-solid-state battery may be insufficient. Furthermore, if the thickness of the negative electrode active material layer 240 exceeds 100 μm, the resistance of the negative electrode active material layer 240 increases, leading to insufficient performance of the all-solid-state battery. For reference, by using the aforementioned adhesive, the thickness of the negative electrode active material layer 240 can be easily ensured to be at an appropriate level.

[0097] Negative current collector

[0098] like Figure 1 As shown, based on the stacking orientation, the negative electrode current collector 220 can be located on the outermost side, opposite to the non-contact solid electrolyte layer 300 facing the negative electrode active material layer 240. However, if the battery includes a structure with more than one dual cell, it can also be located in a position other than the outermost side, depending on the stacking orientation.

[0099] The negative electrode current collector 220 can be in the form of a plate or a foil. The negative electrode current collector 220 may contain a material that does not react with lithium, i.e., a material that does not form any alloy or compound with lithium. Examples of materials constituting the negative electrode current collector 220 may include copper, aluminum, stainless steel, titanium, iron, cobalt, and nickel. Furthermore, the negative electrode current collector 220 may be composed of one of these metals, an alloy of two or more of these metals, or a coating material.

[0100] Initial charging capacity ratio

[0101] Meanwhile, in one embodiment of the all-solid-state lithium-ion secondary battery 1000, the initial charging capacity of the positive electrode active material layer 140 can be configured to be excessively large relative to the initial charging capacity of the negative electrode active material layer 240. As described below, one embodiment of the all-solid-state lithium-ion secondary battery 1000 can be charged (i.e., overcharged) to exceed the initial charging capacity of the negative electrode active material layer 240 and used. At the start of charging, lithium can be intercalated into the negative electrode active material layer 240. That is, the negative electrode active material can form an alloy or compound with the lithium ions that have moved from the positive electrode 100. When charging is performed until the initial charging capacity of the negative electrode active material layer 240 is exceeded, as... Figure 2As shown, lithium can be deposited on the back side of the negative electrode active material layer 240, that is, between the negative electrode current collector 220 and the negative electrode active material layer 240, and a metal layer 260 can be formed through this lithium. The metal layer 260 can be mainly composed of lithium dissolved with a lithiophilic material (i.e., a lithiophilic material-Li solid solution). This phenomenon can be caused by materials that form alloys or compounds with the lithiophilic material (e.g., lithium) contained in the negative electrode. During discharge, the lithium in the negative electrode active material layer 240 and the metal layer 260 can be ionized and move towards the positive electrode 100, while leaving behind the solid solution of the lithiophilic material. Therefore, lithium can be used as the negative electrode active material in the all-solid-state lithium-ion secondary battery 1000. Furthermore, since the lithiophilic layer 230 and the negative electrode active material layer 240 simultaneously coat the metal layer 260, they can serve as a protective layer for the metal layer 260 and simultaneously suppress the deposition and growth of lithium dendrites. As a result, short circuits and capacity degradation in the all-solid-state lithium-ion secondary battery 1000 can be suppressed, and further, the characteristics of the all-solid-state lithium-ion secondary battery 1000 can be improved. Additionally, according to one embodiment, since the metal layer 260 is not pre-formed, it also has the advantage of reducing the manufacturing cost of the all-solid-state lithium-ion secondary battery 1000.

[0102] In one embodiment of the all-solid-state lithium-ion secondary battery 1000, it is preferable that the ratio of the initial charging capacity of the positive electrode active material layer 140 to the initial charging capacity of the negative electrode active material layer 240 and the lithiophilic layer 230 ((b+c) / a) satisfies the following relationship.

[0103] [Relation 1]

[0104] 0.01 < (b + c) / a < 0.5

[0105] Where a is the initial charging capacity (mAh) of the positive electrode active material layer 140, b is the initial charging capacity (mAh) of the negative electrode active material layer 240, and c is the initial charging capacity (mAh) of the lithiophilic layer 230.

[0106] In this scenario, if the initial charge-to-capacity ratio is below 0.01, the lithiophilic layer 230 and the negative electrode active material layer 240 may not adequately function as protective layers, potentially degrading the characteristics of the all-solid-state lithium-ion secondary battery 1000. For example, when the thickness of the lithiophilic layer 230 and the negative electrode active material layer 240 is very thin, the capacity ratio can fall below 0.01. In this case, there are concerns that the lithiophilic layer 230 and the negative electrode active material layer 240 may collapse due to repeated charging and discharging, and that lithium dendrites may deposit and grow. Consequently, the characteristics of the all-solid-state lithium-ion secondary battery 1000 may degrade. Simultaneously, if the initial charge-to-capacity ratio is above 0.5, the battery capacity may decrease due to the reduced lithium deposition at the negative electrode.

[0107] Manufacturing method of all-solid-state lithium-ion secondary batteries

[0108] Next, a method for manufacturing an all-solid-state lithium-ion secondary battery 1000 will be described. One embodiment of the all-solid-state lithium-ion secondary battery 1000 can be obtained by separately manufacturing a positive electrode 100, a negative electrode 200, and a solid electrolyte layer 300, and then stacking these layers. Alternatively, another embodiment of the all-solid-state lithium-ion secondary battery 1000 can be manufactured by forming a solid electrolyte on one surface of the positive electrode 100 or the negative electrode 200, and then stacking the remaining electrodes. Another embodiment of the all-solid-state lithium-ion secondary battery 1000 can also be manufactured by forming a first solid electrolyte on one surface of the positive electrode 100, forming a second solid electrolyte separately on one surface of the negative electrode 200, and then stacking the first and second solid electrolytes so that they face each other.

[0109] In the positive electrode manufacturing process, firstly, materials constituting the positive electrode active material layer 140 (positive electrode active material, binder, etc.) are added to a non-polar solvent to prepare a slurry (or paste), and the prepared slurry is applied to the positive electrode current collector 120 and then dried to obtain a laminate. Next, the laminate is pressurized using, for example, hydrostatic pressure to manufacture the positive electrode 100. In this case, the pressing process can be omitted.

[0110] Next, in the negative electrode manufacturing process, materials constituting the negative electrode active material layer 240 (carbon materials, negative electrode active materials including lithium-philic materials, binders, etc.) are added to a polar or non-polar solvent to prepare a slurry (or paste), and the prepared slurry is applied to the negative electrode current collector 220 whose surface has been treated with a lithium-philic material, and then dried to obtain a laminate (however, it is also acceptable to construct only the negative electrode current collector whose surface has been treated with a lithium-philic material without constructing the negative electrode active material layer). In this case, the process of surface treating the negative electrode current collector with a lithium-philic material can be carried out by a method selected from the group consisting of atomic layer deposition, sputtering, and plasma methods. Subsequently, the laminate can be pressurized using, for example, hydrostatic pressure to manufacture the negative electrode 200. In this case, the pressing process can be omitted. Furthermore, the method of applying the slurry to the negative electrode current collector 220 is not particularly limited, and methods such as screen printing, metal mask printing, electrostatic spraying, dip coating, spraying, roll coating, doctor blade coating, gravure coating, etc., can be used.

[0111] With the solid electrolyte layer 300 positioned between the positive electrode 100 and the negative electrode 200 manufactured in this manner, an all-solid-state lithium-ion secondary battery 1000 of one embodiment can be manufactured by pressurizing it, for example, using hydrostatic pressure.

[0112] The all-solid-state lithium-ion secondary battery 1000 of the present invention can be manufactured as a single cell having a positive electrode / solid electrolyte layer / negative electrode structure, a dual cell having a positive electrode / solid electrolyte layer / negative electrode / solid electrolyte layer / positive electrode structure, or a stacked battery structure with repeated single cell structures. Furthermore, if desired, the all-solid-state lithium-ion secondary battery of the present invention can be used as a semi-solid-state battery, even including a liquid electrolyte, and in this case, a separate polymer separator may be further included.

[0113] The shape of the all-solid-state lithium-ion secondary battery 1000 of the present invention is not particularly limited, and can be exemplified, for example, as a coin type, button type, sheet type, stacked type, cylindrical type, flat type, horn type, etc. Furthermore, it can be applied to large batteries used in electric vehicles, etc. For example, the all-solid-state lithium-ion secondary battery 1000 can also be used in hybrid electric vehicles, such as plug-in hybrid electric vehicles (PHEVs). Additionally, it can be used in fields requiring large amounts of energy storage. For example, it can be used in electric bicycles or power tools.

[0114] Preferred embodiments are given below to aid in understanding the invention. However, the embodiments below are merely illustrative of the invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the invention, and it is equally natural that such changes and modifications fall within the scope of the appended claims.

[0115] [Example 1] Manufacturing of an all-solid-state lithium-ion secondary battery

[0116] First, 80 g of lithium transition metal oxide, 6.5 g of carbon black, 9.83 g of nitrile rubber (adhesive), and 8.17 g of butyl butyrate (solvent) were placed in a Thinky mixer container and mixed 12 times at 2,000 rpm for 3 minutes each time to prepare a positive electrode slurry. Then, the prepared positive electrode slurry was applied to the surface of a positive electrode current collector (aluminum foil) using a spraying method, vacuum dried at 100°C for 10 hours, and then pressurized using hydrostatic pressure to prepare the positive electrode.

[0117] In addition, 6.5 g of carbon black, 9.83 g of PVdF binder (6% solids content) and 8.17 g of NMP solution were placed in a Thinky mixer container and mixed 12 times at 2,000 rpm for 3 minutes each time to prepare a negative electrode active material slurry. Subsequently, the prepared negative electrode active material slurry was applied to the surface of the negative electrode current collector (SUS foil) by spraying, vacuum dried at 100°C for 10 hours, and then pressurized using hydrostatic pressure to prepare the negative electrode.

[0118] Separately, butadiene rubber with a molecular weight (Mw) of 10,000 g / mol (liquid at room temperature) and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol (solid at room temperature) were mixed in a weight ratio of 10:90 and dissolved in an organic solvent (n-butyl butyrate) to prepare an adhesive solution. Then, more than 0.3 g of the prepared adhesive solution, 10 g of a sulfide-based solid electrolyte (Li6PS5Cl), and 10.3 g of butyl butyrate (solvent) were mixed to achieve a solid content of 35 to 55% by weight. This mixture was placed in a Thinky mixer container and mixed 12 times at 2,000 rpm for 3 minutes each time to prepare an electrolyte slurry. The prepared electrolyte slurry was then applied to a release film using a bar coater and subsequently vacuum dried at 70°C for 5 hours.

[0119] Finally, the dried solid electrolyte is separated from the stripping membrane and placed between the prepared negative and positive electrodes. The laminate is covered with a bag made of polypropylene, sealed, and isostatically pressurized for 30 minutes to produce an all-solid-state battery with the negative electrode / solid electrolyte / positive electrode sequentially stacked.

[0120] [Example 2] Manufacturing of an all-solid-state lithium-ion secondary battery

[0121] The all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber with a molecular weight (Mw) of 10,000 g / mol and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol was changed from a weight ratio of 10:90 to a weight ratio of 20:80.

[0122] [Example 3] Manufacturing of an all-solid-state lithium-ion secondary battery

[0123] The all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber with a molecular weight (Mw) of 10,000 g / mol and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol was changed from a weight ratio of 10:90 to a weight ratio of 30:70.

[0124] [Comparative Example 1] Manufacturing of all-solid-state lithium-ion secondary batteries

[0125] The all-solid-state battery was manufactured in the same manner as in Example 1, except that the binder solution used to prepare the electrolyte slurry contained only butadiene rubber with a molecular weight (Mw) of 500,000 g / mol as a binder.

[0126] [Comparative Example 2] Manufacturing of All-Solid-State Lithium-ion Secondary Batteries

[0127] The all-solid-state battery was manufactured in the same manner as in Example 1, except that instead of using butadiene rubber with a molecular weight (Mw) of 10,000 g / mol and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol, butadiene rubber with a molecular weight (Mw) of 190,000 g / mol (solid at room temperature) and butadiene rubber with a molecular weight (Mw) of 340,000 g / mol (solid at room temperature) were added to the binder solution used to prepare the electrolyte slurry in a weight ratio of 10:90.

[0128] [Comparative Example 3] Manufacturing of All-Solid-State Lithium-ion Secondary Batteries

[0129] The all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber with a molecular weight (Mw) of 10,000 g / mol and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol was changed from a weight ratio of 10:90 to a weight ratio of 50:50.

[0130] [Comparative Example 4] Manufacturing of all-solid-state lithium-ion secondary batteries

[0131] The all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber with a molecular weight (Mw) of 10,000 g / mol and butadiene rubber with a molecular weight (Mw) of 500,000 g / mol was changed from a weight ratio of 10:90 to a weight ratio of 40:60.

[0132] [Experimental Example 1] Measurement and Evaluation of Porosity of Solid Electrolytes

[0133] The porosity of each solid electrolyte prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was measured before and after the application of isostatic pressure, and the results are shown in Table 1 below.

[0134] Simultaneously, the mass and thickness of the solid electrolyte are measured, and then the volume and density (d1) are calculated sequentially using these values. The porosity is then measured using Equation 2 below.

[0135] [Equation 2]

[0136] Porosity (%) = [1 - (d1 / d2)] × 100

[0137] Where d1 is the true density (mass / actual volume) calculated above, and d2 is the theoretical density (mass / theoretical volume).

[0138] Additionally, the increase / decrease rate of thickness in Table 1 below was measured using a precision thickness measuring device (model name: TESA mu HITE, manufacturer: TESA) and Equation 3 below. Furthermore, when the electrolyte slurry is applied and dried to manufacture a solid electrolyte, since all parts of the solid electrolyte are formed with a very uniform thickness, there is no specific part to be measured; instead, the measurement is performed at the center, which is usually because the deviation is minimal.

[0139] [Equation 3]

[0140] Thickness increase / decrease rate (%) = [(T2-T1) / T1] × 100

[0141] Where T1 is the thickness of the solid electrolyte before isostatic pressure is applied, and T2 is the thickness of the solid electrolyte after isostatic pressure is applied.

[0142] [Table 1]

[0143] As shown in Table 1 above, the solid electrolytes of Examples 1 to 3 (which contain two types of binders with different molecular weights) exhibited excellent formability, resulting in a greater reduction in porosity under pressure (i.e., the rate of reduction in porosity) compared to Comparative Examples 1 to 4. Furthermore, comparisons and contrasts between Examples 1 to 3 confirmed that the reduction in porosity increased with decreasing proportions of low molecular weight binders.

[0144] On the other hand, Comparative Example 1 does not use a low molecular weight adhesive, and therefore its formability is inherently poor. Consequently, the reduction in porosity after pressurization is smaller.

[0145] That is, as in Examples 1 to 3, the relatively low molecular weight adhesives must be positioned between the relatively high molecular weight adhesives to significantly reduce porosity and increase the density of the solid electrolyte. However, Comparative Example 1 exhibits worse formability compared to Examples 1 to 3 because it did not use a low molecular weight adhesive.

[0146] In Comparative Example 2, although the solid electrolyte contained two types of binders with different molecular weights, the difference in molecular weight was not significant, resulting in poor formability. Therefore, the reduction in porosity after pressurization was relatively small.

[0147] That is, by comparing and contrasting Examples 1 to 3 with Comparative Example 2, it can be confirmed that even if the solid electrolyte contains two types of binders with different molecular weights, the degree of reduction in porosity is inevitably smaller, as in Comparative Example 1, if the molecular weight difference is outside the scope of the present invention. This is because, although the reduction in porosity can only occur when the relatively low molecular weight binder is located between the relatively high molecular weight binders, the insignificant molecular weight difference between the two binders results in minimal effect.

[0148] For Comparative Examples 3 and 4, although the solid electrolyte contained two types of binders with different molecular weights, and the difference in molecular weight was set to be the same as in Example 1, the decrease in porosity after pressurization was smaller. This is because the mixing ratio of the low molecular weight binder and the high molecular weight binder is outside the scope of this invention, and because the excessive addition of the low molecular weight binder (i.e., butadiene rubber (liquid) with a molecular weight (Mw) of 10,000 g / mol) results in insufficient contact between the binder particles. That is, the low molecular weight binder and the high molecular weight binder must be in uniform contact. However, if the low molecular weight binder is added in excess, there is a problem of generating a large number of low molecular weight binder particles that do not contact the high molecular weight binder particles. In addition, when the low molecular weight binder is used alone, the force used to maintain the structure of the pressurized solid electrolyte membrane is insufficient, resulting in springback, in which the membrane slightly returns to its state before pressurization. Springback of the solid electrolyte membrane also occurs when a large number of low molecular weight binder particles do not contact the high molecular weight binder particles, as described above.

[0149] Furthermore, the rate of increase or decrease in the thickness of the solid electrolyte due to the application of isostatic pressure is also affected by the degree of porosity reduction, and as shown in Table 1 above, the degree of reduction in the thickness of the solid electrolyte tends to increase as the porosity reduction rate increases.

[0150] [Experimental Example 2] Performance Evaluation of All-Solid-State Batteries

[0151] A driving pressure of 10 MPa was applied using a clamp to each all-solid-state battery manufactured in Examples 1 to 3 and Comparative Examples 1 to 4, and charging and discharging were performed under the following conditions while a constant driving pressure was applied to evaluate the capacity retention with charge-discharge cycles, and the results are shown in... Figure 3 middle.

[0152] - Charge / discharge conditions: At an operating temperature of 60°C, charge to 4.25 V in CC / CV mode and at 0.33C, discharge to 3.0 V at a constant current, and repeat the charge / discharge cycle 100 times.

[0153] As described above, the performance of the all-solid-state batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated. The results showed that the batteries of Examples 1 to 3, which contained two types of binders with different molecular weights in the solid electrolyte, exhibited a high capacity retention of over 95% even after 100 charge / discharge cycles. Figure 3 As shown. On the other hand, it can be confirmed that the battery of Comparative Example 1, which does not contain low molecular weight binders in the solid electrolyte, and the battery of Comparative Example 2, which contains two types of binders with different molecular weights but with small molecular weight differences in the solid electrolyte, show a rapid decrease in capacity retention from the initial charging / discharging.

[0154] Furthermore, it can be confirmed that the battery of Comparative Example 3 contains two types of binders with different molecular weights and appropriate molecular weight differences in the solid electrolyte, but the mixing ratio of the low molecular weight binder and the high molecular weight binder is outside the scope of the present invention, which shows the fastest decrease in capacity retention from the initial charge / discharge.

[0155] Furthermore, the battery of Comparative Example 4 contains two types of binders with different molecular weights and appropriate molecular weight differences in the solid electrolyte, but the mixing ratio of the low molecular weight binder and the high molecular weight binder is outside the scope of the present invention. It shows better performance than the other comparative examples, but shows significantly lower performance than the batteries of Examples 1 to 3.

[0156] Therefore, it can be seen that if the solid electrolyte contains only one type of binder, or if the solid electrolyte contains two types of binders with different molecular weights but the molecular weight difference between the binders is not significant, or if the solid electrolyte contains two types of binders with different molecular weights and appropriate molecular weight differences, but the mixing ratio between the binders is outside the scope of this invention, there are limitations to improving fast charging performance.

[0157] [Figure Labels]

[0158] 100: Positive electrode

[0159] 120: Positive current collector

[0160] 140: Positive electrode active material layer

[0161] 200: Negative electrode

[0162] 220: Negative electrode current collector

[0163] 240: Negative electrode active material layer

[0164] 260: Metal layer

[0165] 300: Solid electrolyte layer

[0166] 1000: All-solid-state lithium-ion secondary battery

Claims

1. A solid electrolyte for an all-solid-state lithium-ion secondary battery, comprising two or more types of binders with different molecular weights.

2. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 1, wherein, The solid electrolyte comprises a first binder and a second binder with different molecular weights (Mw), and the ratio of the molecular weight (Mw) of the first binder to the molecular weight (Mw) of the second binder is 1:30 to 70.

3. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 2, wherein, The first adhesive has a molecular weight (Mw) of 3,000 to 50,000 g / mol, and the second adhesive has a molecular weight (Mw) of 100,000 to 1,500,000 g / mol.

4. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 2, wherein, The molecular weight (Mw) difference between the first and second adhesives is 200,000 to 1,000,000 g / mol.

5. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 2, wherein, The first adhesive comprises a rubber compound with a molecular weight (Mw) of 3,000 to 50,000 g / mol, and the second adhesive comprises a rubber compound with a molecular weight (Mw) of 100,000 to 1,500,000 g / mol.

6. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 5, wherein, The rubber compounds contained in the first adhesive and the rubber compounds contained in the second adhesive are independently selected from the group consisting of butadiene rubbers, acrylic rubbers, fluororubbers, and combinations thereof.

7. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 2, wherein, The content ratio of the first adhesive and the second adhesive, by weight, is 5:95 to 30:

70.

8. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 2, wherein, The solid electrolyte comprises: a first adhesive layer containing a first adhesive; and a second adhesive layer containing a first adhesive and a second adhesive in a mixed state.

9. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 1, wherein, The solid electrolyte comprises a sulfide solid electrolyte and two or more types of binders with different molecular weights (Mw).

10. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 9, wherein, The ratio of the sulfide-based solid electrolyte to the two or more types of binders is 90:10 to 98:2 by weight.

11. The solid electrolyte for an all-solid-state lithium-ion secondary battery as described in claim 1, wherein, The solid electrolyte comprises two phase-separated solid electrolytes, namely a first solid electrolyte disposed on the positive electrode side and a second solid electrolyte disposed on the negative electrode side. The first and second solid electrolytes form a layered structure. The binders contained in the first solid electrolyte and the second solid electrolyte each contain two or more types of binders with different molecular weights (Mw).

12. An all-solid-state lithium-ion secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the solid electrolyte layer comprises the solid electrolyte of claim 1.

13. The all-solid-state lithium-ion secondary battery as described in claim 12, wherein, Apart from the lithium metal formed during battery charging, the negative electrode does not contain any other lithium metal.

14. The all-solid-state lithium-ion secondary battery as described in claim 12, wherein, The all-solid-state lithium-ion secondary battery is a sulfide-based all-solid-state lithium-ion secondary battery.

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