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

Abstract

A solid electrolyte for an all-solid-state lithium-ion secondary battery and an all-solid-state lithium-ion secondary battery including same are disclosed. The solid electrolyte of the all-solid-state battery includes two or more binders having different molecular weights, and thus the porosity of the solid electrolyte can be reduced to improve the moldability of the solid electrolyte and the performance of the battery. The solid electrolyte for an all-solid-state lithium-ion secondary battery includes two or more binders having different molecular weights (Mw).

Description

Solid electrolyte for all-solid-state lithium-ion secondary batteries and all-solid-state lithium-ion secondary batteries containing the same

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

[0002] The present invention relates to a solid electrolyte applicable to an all-solid-state lithium-ion secondary battery and an all-solid-state lithium-ion secondary battery including the same, and more particularly, to a solid electrolyte for an all-solid-state lithium-ion secondary battery and an all-solid-state lithium-ion secondary battery including the same, which can improve the formability of the solid electrolyte and the performance of the battery by lowering the porosity by including two or more binders having different molecular weights in the solid electrolyte of the all-solid-state battery.

[0003] From the perspectives of battery capacity, safety, output, large-scale development, and miniaturization, various batteries are being studied to overcome the limitations of lithium secondary batteries, which are currently widely commercialized. Representative examples include metal-air batteries, which have much larger theoretical capacities than lithium secondary batteries in terms of capacity; all-solid-state batteries, which have no risk of explosion compared to lithium secondary batteries in terms of safety; super capacitors for output; sodium-sulfur batteries (NaS batteries) or redox flow batteries (RFBs) for large-scale development; and thin film batteries for miniaturization. These are all being continuously studied in academia and industry.

[0004] Among these, all-solid-state batteries are batteries that replace the liquid electrolyte used in lithium secondary batteries with a solid one. Accordingly, since flammable solvents are not used, there is no risk of fire or explosion due to decomposition reactions of conventional electrolytes, so safety can be significantly improved. Furthermore, since all-solid-state batteries can use lithium metal or a lithium alloy as the anode active material, they have the advantage of being able to dramatically improve the energy density for the mass and volume of the battery. Furthermore, the capacity density (capacity per unit weight) of lithium is approximately 10 times that of graphite, which is generally used as an anode active material. Therefore, when lithium is used as the anode active material, it is possible to increase the output of all-solid-state batteries while making them thinner.

[0005] As such a conventional all-solid-state battery, a battery is known that includes a metal layer formed of a metal that forms an alloy with lithium as an anode active material layer, and has an interface layer made of amorphous carbon on the anode active material layer. In addition, in this type of all-solid-state battery, when charging, metallic lithium is deposited between the amorphous carbon interface layer and the anode active material layer, and when discharging, the deposited metallic lithium is ionized and moves toward the cathode. However, when the all-solid-state battery as described above is repeatedly charged and discharged, the metallic lithium deposited between the amorphous carbon interface layer and the anode active material layer is ionized and dissolved, which may cause a problem in that a void is created, making it impossible to use the battery.

[0006] To address these issues, the industry has developed an all-solid-state battery comprised of a carbon-containing anode (i.e., a lithium-free anode) excluding a lithium metal layer. The anode of this all-solid-state battery does not contain lithium in the initial state or after complete discharge, and when overcharged, lithium ions moved from the positive electrode form an alloy or compound between the negative electrode current collector and the solid electrolyte, which can function as a negative electrode active material (i.e., lithium metal is plated on the surface of the negative electrode current collector during charging).

[0007] All-solid-state batteries, as described above, are manufactured by interposing a solid electrolyte membrane between the positive and negative electrodes. Furthermore, since sulfide-based all-solid-state batteries require a high-temperature and high-pressure molding process (such as isostatic pressing) after interposing the solid electrolyte membrane between the positive and negative electrodes, the solid electrolyte must have particularly excellent moldability. However, previously known solid electrolytes for sulfide-based all-solid-state batteries have poor moldability, which negatively affects battery performance. Therefore, a method for improving the moldability of solid electrolytes for sulfide-based all-solid-state batteries is required.

[0008] Accordingly, the purpose of the present invention is to provide a solid electrolyte for an all-solid-state lithium-ion secondary battery, which can improve the formability of the solid electrolyte and the performance of the battery by including two or more binders having different molecular weights in the solid electrolyte of the all-solid-state battery to reduce the porosity, and an all-solid-state lithium-ion secondary battery including the same.

[0009] To achieve the above purpose, the present invention provides a solid electrolyte for an all-solid-state lithium-ion secondary battery comprising two or more binders having different molecular weights (Mw).

[0010] In addition, the present invention provides an all-solid-state lithium ion secondary battery comprising a positive electrode; a negative electrode; and a solid electrolyte layer including the above-described solid electrolyte interposed therebetween.

[0011] According to the solid electrolyte for an all-solid-state lithium-ion secondary battery and the all-solid-state lithium-ion secondary battery including the same according to the present invention, the solid electrolyte of the all-solid-state battery includes two or more binders having different molecular weights to reduce the porosity, thereby having the advantage of improving the formability of the solid electrolyte and the performance of the battery.

[0012] Figure 1 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0013] Figure 2 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0014] Figure 3 is a graph showing the capacity retention rate according to the charge / discharge cycle of a battery according to one embodiment and a comparative example of the present invention.

[0015] Hereinafter, the present invention will be described in detail.

[0016] A solid electrolyte for an all-solid-state lithium-ion secondary battery according to the present invention includes two or more types of binders having different molecular weights (Mw).

[0017] All-solid-state batteries replace the liquid electrolyte used in lithium secondary batteries with a solid one. Consequently, they eliminate the use of flammable solvents, eliminating the risk of fire or explosion caused by decomposition reactions in conventional electrolytes. This significantly improves safety. These all-solid-state batteries offer the potential to address the inherent issues of liquid electrolytes, such as the low stability, energy density, and long lifespan of lithium-ion batteries.

[0018] The solid electrolytes of these all-solid-state batteries can be broadly classified into organic (polymer) solid electrolytes and inorganic solid electrolytes, and among these, inorganic solid electrolytes can be divided into sulfide and oxide solid electrolytes. In addition, the solid electrolyte that has undergone the most technological development is the sulfide solid electrolyte, and its development has progressed to the point where its ionic conductivity is close to that of organic electrolytes. Thus, among solid electrolytes, the sulfide solid electrolyte is ranked 10th. -3 S / cm to 10 -2 Not only does it have high ionic conductivity (S / cm), but it also has excellent thermal stability and interfacial compatibility, which is advantageous in improving resistance by making good contact with the interface due to its ductility.

[0019] However, since sulfide-based all-solid-state batteries require a high-temperature and high-pressure molding process (such as isostatic pressing) after interposing a solid electrolyte membrane between the positive and negative electrodes, the solid electrolyte must have excellent moldability, but conventional solid electrolytes for sulfide-based all-solid-state batteries have a problem in that their moldability is poor, which adversely affects the performance of the battery. Accordingly, the present applicant has solved the existing problem by including two or more types of binders with different molecular weights in the sulfide-based solid electrolyte, and intends to present a specific and practical solution below.

[0020] The solid electrolyte for the above-mentioned all-solid-state lithium-ion secondary battery is formed by drying an electrolyte slurry, and is typically interposed between the positive and negative electrodes, but may also be included in the electrode (particularly, the positive electrode) as needed. For example, when the solid electrolyte is also included in the positive electrode, the solid electrolyte may be applied to at least a portion of the surfaces of components constituting the positive electrode, such as the positive electrode active material.

[0021] The above solid electrolyte may be in an amorphous state, a crystalline state, or a mixed state of amorphous and crystalline.

[0022] In addition, the solid electrolyte may include at least one selected from a sulfide-based solid electrolyte, a polymer-based solid electrolyte, and an oxide-based solid electrolyte, but it is preferable to include only a sulfide-based solid electrolyte.

[0023] More specifically, the solid electrolyte basically includes a sulfide-based solid electrolyte and a binder.

[0024] The above sulfide-based solid electrolyte contains sulfur (S) and has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and may include Li-PS-based glass or Li-PS-based glass ceramic. Non-limiting examples of such sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (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, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(p and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga or In), or a combination thereof. However, the present invention is not limited thereto, and may be composed of those constituting a typical sulfide-based solid electrolyte. Meanwhile, when using one including Li2S-P2S5, the mixing molar ratio of Li2S and P2S5 may be selected in the range of, for example, Li2S:P2S5=50:50 to 90:10.

[0025] However, in order for the solid electrolyte to exhibit optimal performance, it is preferable that the sulfide-based solid electrolyte basically include a compound having an argyrodite-type crystal structure, for example, a LPSCl (lithium phosphorus sulfur chloride)-based compound such as Li6PS5Cl.

[0026] In addition, the above sulfide-based solid electrolyte may include a lithium salt, and the lithium salt is an ionizable lithium salt, such as Li + X - It can be expressed as . The anion of these lithium salts is not particularly limited, but 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 - Examples include:

[0027] The binder included in the solid electrolyte for the above-mentioned all-solid-state lithium-ion secondary battery plays a central role in or assists in the adhesion between the solid electrolyte and the electrode.

[0028] As described above, the solid electrolyte includes two or more types of binders having different molecular weights, and for example, the solid electrolyte may include two types of binders having different molecular weights, i.e., a first binder and a second binder (it is noted that the 'molecular weight' of the binder described below is all 'weight average molar mass (Mw)').

[0029] The ratio of the molecular weight (Mw) of the first binder to the molecular weight (Mw) of the second binder may be 1:30 to 70, preferably 1:40 to 60, and more preferably 1:45 to 55. If the ratio of the molecular weight (Mw) of the first binder to the molecular weight (Mw) of the second binder exceeds 1:30 to 70, it may be impossible to achieve the purpose of the present invention, or the effect may reach its maximum and there may be no further practical benefit.

[0030] More specifically, one of the two binders (i.e., the first binder) may have a molecular weight of 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 other binder (i.e., the second binder) may have a molecular weight of 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.

[0031] If either the first binder or the second binder does not satisfy the above-mentioned molecular weight, the formability of the solid electrolyte membrane may deteriorate. Furthermore, even if the above-mentioned molecular weight is satisfied, if only one type of binder is used instead of two types, the mechanical properties or formability of the solid electrolyte membrane may deteriorate.

[0032] More specifically, it is preferred that the first binder basically comprises a rubber-based 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.

[0033] In addition, the first binder may further include at least one selected from the group consisting of acrylonitrile copolymer, acrylonitrile-styrene-butadiene copolymer, polyethylene, polypropylene, chlorosulfonated polyethylene, polyvinylpyrrolidone, cellulose acetate, cellulose acetate butyrate, polyamide, polyimide, polycarboxylate, and compounds exhibiting similar properties to these, as needed.

[0034] Examples of rubber compounds included in the first binder include butadiene rubbers, acrylic rubbers, and fluorine rubbers, such as butadiene rubber (BR), styrene butadiene rubber (SBR), acrylic styrene butadiene rubber (ASBR), acrylonitrile-butadiene rubber (ABR), nitrile butadiene rubber (NBR), and hydrogenated nitrile butadiene rubber (HNBR), and one or more of these may be included.

[0035] It is preferable that the second binder basically includes a rubber-based compound having a molecular weight of 100,000 to 1,500,000 g / mol, preferably 250,000 to 900,000 g / mol, and more preferably 400,000 to 600,000 g / mol.

[0036] In addition, the second binder may further include one or more selected from the group consisting of acrylonitrile copolymer, acrylonitrile-styrene-butadiene copolymer, polyethylene, polypropylene, chlorosulfonated polyethylene, polyvinylpyrrolidone, cellulose acetate, cellulose acetate butyrate, polyamide, polyimide, polycarboxylate, and compounds exhibiting similar properties to these, as needed.

[0037] Examples of rubber compounds included in the second binder include butadiene rubbers, acrylic rubbers, and fluorine rubbers, such as butadiene rubber (BR), styrene butadiene rubber (SBR), acrylic styrene butadiene rubber (ASBR), acrylonitrile-butadiene rubber (ABR), nitrile butadiene rubber (NBR), and hydrogenated nitrile butadiene rubber (HNBR), and one or more of these may be included.

[0038] In addition, the rubber-based compound included in the first binder and the rubber-based compound included in the second binder may be independently selected from the group consisting of butadiene-based rubber, acrylic-based rubber, fluorine-based rubber, and combinations thereof. That is, the rubber-based compound included in the first binder and the rubber-based compound included in the second binder may be the same or different.

[0039] However, it may be more preferable that the first binder basically includes nitrile butadiene rubber 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.

[0040] In addition, it may be more preferable that the second binder basically includes nitrile butadiene rubber having a molecular weight of 100,000 to 1,500,000 g / mol, preferably 250,000 to 900,000 g / mol, and more preferably 400,000 to 600,000 g / mol.

[0041] In addition, the difference in molecular weight between the first binder and the second binder may be 200,000 to 1,000,000 g / mol, preferably 300,000 to 700,000 g / mol, and more preferably 400,000 to 600,000 g / mol. If the difference in molecular weight between the first binder and the second binder is less than 200,000 g / mol, a problem of reduced formability of the solid electrolyte membrane may occur. In addition, if the difference in molecular weight between the first binder and the second binder exceeds 1,000,000 g / mol, a problem of reduced solubility may occur due to an excessive increase in the molecular weight of one of the binders.

[0042] Meanwhile, the content ratio of the first binder and the second binder may be 5:95 to 30:70, preferably 10:90 to 20:80, and more preferably 10:90 to 15:85 in terms of weight ratio. If the content of the first binder is less than 5 wt% based on the total weight of the first binder and the second binder, the effect of improving the formability may be reduced. In addition, if the content of the first binder exceeds 30 wt% based on the total weight of the first binder and the second binder, contact between binder particles may not be maintained due to excessive input of the low molecular weight binder (i.e., the first binder), which may adversely affect the life performance of the battery. The low molecular weight binder and the high molecular weight binder must be in uniform contact, but if the low molecular weight binder is added in excessive amounts, a problem occurs in which a large number of low molecular weight binder particles are generated that cannot come into contact with the high molecular weight binder particles. That is, if the low molecular weight binder is used alone, the force to maintain the structure of the pressurized solid electrolyte membrane is insufficient, resulting in a springback phenomenon in which the membrane slightly returns to its pre-pressurization state. In the case where a large number of low molecular weight binder particles that cannot come into contact with the high molecular weight binder particles are generated as described above, the springback phenomenon of the solid electrolyte membrane also occurs. In addition, if the content of the first binder exceeds 30 wt% based on the total weight of the first binder and the second binder, the ionic conductivity of the solid electrolyte membrane may increase, which may cause an increase in battery resistance.

[0043] In this way, when two or more types of binders with different molecular weights are included in a solid electrolyte, the voids 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 includes two or more types of binders with different molecular weights, binders with relatively small molecular weights are positioned between binders with relatively large molecular weights, which presents advantages such as improving the density of the solid electrolyte. Furthermore, when isotropic pressurization is performed in this state, the void ratio of the solid electrolyte can be reduced to an excellent level, thereby maximizing not only the formability of the solid electrolyte but also the increase in the contact area with the electrode. Accordingly, the formability of the solid electrolyte and the performance of the battery can be improved compared to conventional cases.

[0044] In addition, among the solid electrolytes, only a binder with a relatively small molecular weight (i.e., the first binder) is positioned alone on the interface side that comes into contact with the electrode, thereby increasing the interfacial bonding between the electrode and the solid electrolyte membrane. Therefore, the solid electrolyte in this case may include a first binder layer including the first binder; and a second binder layer including the first binder and the second binder in a mixed state. Accordingly, when the solid electrolyte is interposed between the positive electrode and the negative electrode, the solid electrolyte may be composed of a 1a binder layer that comes into contact with the positive electrode, a 1b binder layer that comes into contact with the negative electrode, and a second binder layer that is interposed between the 1a binder layer and the 1b binder layer.

[0045] Meanwhile, during the manufacture of the solid electrolyte, a solvent may be included in the electrolyte slurry. The solvent serves to dissolve the first binder and the second binder, and includes a solvent having a dielectric constant of more than 0 and less than 20, preferably 0.1 to 10, and more preferably 0.3 to 5. In particular, since the sulfide-based solid electrolyte has a characteristic of its structure collapsing when reacted with a polar organic solvent, the dielectric constant of the first solvent must be less than 20.

[0046] More specifically, the electrolyte slurry may include one or more of the following solvents having a dielectric constant greater than 0 and less than 20.

[0047] These solvents include butyrate compounds such as n-butyl butyrate, iso-butyl butyrate, pentyl butyrate, hexyl butyrate, and heptyl butyrate; sulfone compounds such as ethylmethyl sulfone and tetramethylene sulfone; nitrile compounds such as acetonitrile; carbonate compounds such as propylene carbonate; gamma-butyrolactone; toluene compounds; xylene compounds; anisole compounds; benzene compounds; Examples thereof include methane hydrocarbon compounds having 6 or more carbon atoms, such as hexane, heptane, nonane, and decane; methane hydrocarbon compounds containing a halogen element, such as dibromomethane and dichloromethane; chloroform compounds; and acetate compounds, such as benzyl acetate and octyl acetate.

[0048] The solvent may preferably include at least one of a butyrate compound, a toluene compound, a xylene compound, an anisole compound, and an acetate compound, and may more preferably include a butyrate compound as a base.

[0049] The content ratio of the sulfide-based solid electrolyte and the binder (including the first binder and the second binder) included in the above solid electrolyte may be 90:10 to 98:2, preferably 91:9 to 97:3, and more preferably 93:7 to 95:5 in weight ratio.

[0050] If the content of the binder is less than 2 wt%, problems such as the electrolyte slurry not being dispersed due to insufficient binder content may occur.

[0051] In addition, if the content of the binder exceeds 10 wt%, problems such as gelation of the electrolyte slurry may occur due to excessive binder content.

[0052] In addition, the solid electrolyte may further include one or more of a crosslinking monomer and an inorganic particle, if necessary.

[0053] The above crosslinking monomer is capable of forming a polymer matrix by crosslinking the positive electrode and the electrolyte through a photopolymerization or thermal polymerization reaction, and may be exemplified by at least one selected from among trimethylolpropane ethoxylate triacrylate, polyethyleneglycol diacrylate, triethyleneglycol diacrylate, trimethylopropaneethoxylate triacrylate, bisphenol A ethoxylate dimethacrylate, derivatives thereof, and mixtures thereof.

[0054] The above inorganic particles can be evenly dispersed in the solid electrolyte to improve the mechanical strength of the solid electrolyte, and include 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), selenium oxide (CeO2), magnesium oxide (MgO), nickel oxide (NiO), calcium oxide (CaO), zinc oxide (ZnO), zirconium dioxide (ZrO2), silicon carbide (SiC), and derivatives thereof. and one or more selected from mixtures thereof.

[0055] Here, a method for manufacturing a solid electrolyte for an all-solid-state lithium-ion secondary battery will be briefly described. A solid electrolyte for an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention can be manufactured through the steps of (a) preparing a binder solution by mixing two or more binders having different molecular weights, (b) preparing an electrolyte slurry by mixing the prepared binder solution with a sulfide-based solid electrolyte and a solvent, and (c) drying the prepared electrolyte slurry. In addition, according to one embodiment of the present invention, the prepared electrolyte slurry can be formed by applying, coating, and drying it on a release film. In addition, according to another embodiment of the present invention, the prepared electrolyte slurry can be formed by applying, coating, and drying it on an electrode.

[0056] Meanwhile, the solid electrolyte for the all-solid-state lithium-ion secondary battery described above may be composed of multiple layers, and preferably may be composed of two layers.

[0057] That is, the solid electrolyte at this time becomes an electrolyte complex, and therefore, the electrolyte complex may include two types of phase-separated solid electrolytes, a first solid electrolyte disposed on the positive electrode side; and a second solid electrolyte disposed on the negative electrode side; forming a layered structure.

[0058] The first solid electrolyte and the second solid electrolyte each basically include a sulfide-based solid electrolyte and two or more types of binders having different molecular weights (Mw).

[0059] The sulfide-based solid electrolyte included in the first solid electrolyte and the sulfide-based solid electrolyte included in the second solid electrolyte each separately include the sulfide-based solid electrolyte described above, and their specific compositions may be the same or different within the relevant range.

[0060] Each of the binder included in the first solid electrolyte and the binder included in the second solid electrolyte includes the binder described above, that is, two or more types of binders having different molecular weights (Mw), and the specific composition may be the same or different within the relevant range.

[0061] In addition, among the two or more types of binders having different molecular weights, it is preferable that the binder having a relatively small molecular weight is in a liquid state at room temperature, and the binder having a relatively large molecular weight is in a solid state at room temperature (however, when the two types of binders are dissolved in an organic solvent, a liquid binder solution is produced).

[0062] In addition, each of the first solid electrolyte and the second solid electrolyte may further include, if necessary, one or more of the crosslinking monomer and inorganic particles described above.

[0063] Continuing, an all-solid-state lithium-ion secondary battery including the solid electrolyte for the all-solid-state lithium-ion secondary battery described above is described.

[0064] The above-mentioned all-solid-state lithium-ion secondary battery includes a positive electrode, a negative electrode, and a solid electrolyte layer including the above-mentioned solid electrolyte interposed between them, and is preferably a sulfide-based all-solid-state lithium-ion secondary battery.

[0065] FIG. 1 is a cross-sectional schematic diagram showing the configuration 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 by lithium ions moving between a positive electrode (100) and a negative electrode (200). Specifically, as illustrated in FIG. 1, 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 the solid electrolyte. Hereinafter, each of these will be described.

[0066] anode

[0067] As illustrated in Fig. 1, the positive electrode (100) includes a positive electrode active material layer (140) and a positive electrode current collector (120) sequentially arranged in the direction of the negative electrode (200). The positive electrode current collector (120) may have a plate shape or a foil shape. The positive electrode current collector (120) may be, for example, one type of metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more types of metals.

[0068] The positive electrode active material layer (140) can reversibly absorb and release lithium ions. In addition, the positive electrode active material layer (140) includes a positive electrode active material and may further include a solid electrolyte. The positive electrode active material may be a compound capable of insertion / de-insertion of lithium. Examples of the compound capable of insertion / de-insertion of lithium include Li a A 1-b B' bD'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); LEE 2-b B' b O 4-c D' c (0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b B' c D' α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 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 Ni 1-b-c Mr b B' c D' α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mr 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 Ni b HAVE BEEN c G d O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤ 0.1); Li a Ni b Co c Mr 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); Lia 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; LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2); Li (3-f) It can be expressed as one of Fe2(PO4)3(0≤f≤2); LiFePO4.

[0069] In the above chemical formula, A is Ni, Co, Mn or a combination thereof, B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element 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.

[0070] Specific examples of the positive electrode active material include lithium salts such as lithium cobaltate (LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminumate (NCA), lithium nickel cobalt manganese (NCM), lithium manganese acid, and lithium iron phosphate, and lithium sulfide. The positive electrode active material layer (140) may include only one selected from these compounds as the positive electrode active material, or may include two or more.

[0071] The above-described positive electrode active material may include a lithium salt of a transition metal oxide having a layered rock salt structure among the lithium salts described above. Here, the layered rock salt structure refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the direction of the cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. In addition, the cubic rock salt structure refers to a sodium chloride 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 in which cations and anions are respectively formed are arranged with a displacement of half of the edges of the unit cell.

[0072] Lithium salts of transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z It may be a ternary lithium transition metal oxide such as O2(NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1). The positive electrode active material layer (140) may include a lithium salt of a ternary transition metal oxide having such a layered rock salt structure as a positive electrode active material, thereby improving the energy density and thermal stability of an all-solid-state lithium ion secondary battery (1000).

[0073] Examples of the shape of the positive electrode active material include spherical, elliptical, and other particle shapes. In addition, the particle size of the positive electrode active material is not particularly limited and may be within a range applicable to positive electrode active materials of a typical all-solid-state lithium-ion secondary battery. In addition, the content of the positive electrode active material in the positive electrode active material layer (140) is also not particularly limited and may be within a range applicable to positive electrodes of a typical all-solid-state lithium-ion secondary battery.

[0074] In addition, the compound having a coating layer on the surface can be used, and the compound and the compound having the coating layer can be mixed and used. The coating layer can include a coating element compound of an oxide, a hydroxide, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The compounds forming these coating layers can be amorphous or crystalline. Examples of the coating elements included in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof, and a specific example of the coating layer includes Li2O-ZrO2, etc. The coating layer forming process can use any coating method as long as it can coat the compound with these elements in a method that does not adversely affect the properties of the positive electrode active material (for example, spray coating, dipping, etc.), and since this is well understood by those working in this field, a detailed description thereof will be omitted.

[0075] 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. In addition, the positive electrode active material layer (140) may be a mixture of not only the positive electrode active material and the solid electrolyte described above, but also additives such as a conductive agent, a binder, a filler, a dispersant, or an ion conductive assistant. Examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder. In addition, the binder is mixed with the active material and the conductive agent to bind each component and help particle growth, and examples thereof include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. In addition, the filler, dispersant, or ion conductive auxiliary agent may be exemplified by known materials commonly used in electrodes of all-solid-state lithium-ion secondary batteries. In addition, the positive electrode active material layer (140) may include the positive electrode active material, conductive agent, and binder in granular form.

[0076] cathode

[0077] Next, the negative electrode (200) includes a negative electrode active material layer (240) positioned closer to the positive electrode (100) side and in contact with the solid electrolyte layer (300), and a negative electrode current collector (220) positioned on the outermost side or the like based on the stacking direction, facing the opposite side of the negative electrode active material layer (240) that does not contact the solid electrolyte layer (300). In addition, the negative electrode may not include a separate lithium metal except for lithium metal formed during charging (i.e., corresponding to a non-anode all-solid-state battery).

[0078] Negative active material layer

[0079] The above-mentioned negative electrode active material layer (240) may include one or more types of negative electrode active materials capable of forming an alloy or compound with lithium. In the initial state or after complete discharge, lithium may not be included between the negative electrode current collector (220), the negative electrode active material layer (240), or the negative electrode active material layer (240) and the solid electrolyte layer (300). Fig. 2 is a cross-sectional schematic diagram showing the configuration of an all-solid-state lithium ion secondary battery according to one embodiment of the present invention.

[0080] As described below, when the all-solid-state lithium ion secondary battery (1000) according to one embodiment is overcharged, the negative active material included in the negative active material layer (240) and the lithium ions that have moved from the positive electrode (100) form an alloy or compound, so that, for example, as illustrated in FIG. 2, a metal layer (260) containing lithium as a main component may be formed (deposited) on the negative electrode (200). The metal layer (260) may be formed by being deposited between the negative current collector (220) and the negative active material layer (240), inside the negative active material layer (240), or both. When the metal layer (260) is positioned between the negative electrode current collector (220) and the negative electrode active material layer (240), the metal layer (260) may be formed closer to the negative electrode current collector layer (220) than to the negative electrode active material layer (240).

[0081] The negative electrode active material layer (240) according to one embodiment of the present invention may include at least one lithium-friendly material 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), alumina (Al2O3), zinc peroxide (ZnO2), and lithium fluoride (LiF) as the negative electrode active material. In addition, it may be more preferable to apply silver (Ag) as the lithium-friendly material among these. However, the present invention is not limited thereto, and any lithium-friendly material having similar physical properties or characteristics to these may be applied without any special limitation.

[0082] Accordingly, the metal layer (260) formed during overcharge may include a Li (lithium affinity material) alloy including a γ1 phase, a βLi phase, or a combination thereof in which the lithium affinity material is dissolved in lithium. Therefore, during discharge, only Li is dissolved in the Li (lithium affinity material) alloy constituting the metal layer (260), and the dissolved lithium affinity material remains, thereby suppressing the occurrence of pores. In this case, the content of the lithium affinity material in the precipitated Li-lithium affinity material solid solution may be 60 wt% or less. Within this range, the decrease in the average discharge potential due to the influence of the lithium affinity material can be effectively suppressed. On the other hand, if the content of the lithium affinity material in the precipitated Li-lithium affinity material solid solution is too low, the amount of lithium affinity material remaining during discharge becomes small, and it may be difficult to sufficiently suppress the occurrence of pores. For this reason, the content of the lithium-affinity material in the precipitated Li-lithium-affinity material solid solution may be 20 wt% or more, for example, 40 wt% or more.

[0083] In one embodiment of the present invention, the lithium-affinity material does not necessarily need to be uniformly present in the negative electrode active material layer (240), and may be distributed in the negative electrode current collector (220) side of the negative electrode active material layer (240). In this case, lithium ions may react with the lithium-affinity material distribution layer in the negative electrode active material layer (240) that has reached the vicinity of the negative electrode current collector (220), thereby forming a Li (lithium-affinity material) alloy as a metal layer (260).

[0084] If the content of the lithium-affinity material included in the negative electrode active material layer (240) is excessively low, it may be difficult to suppress the occurrence of pores because the lithium-affinity material remaining during discharge also decreases. Therefore, the negative electrode active material layer (240) may include 10 wt% or more, preferably 20 wt% or more, of the lithium-affinity material based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer (240) in the initial state before charge / discharge is performed. Meanwhile, in the relationship between the reaction potential of the lithium-affinity material and Li, if the lithium-affinity material increases, the average discharge potential may decrease, which may lower the energy density of the battery. Therefore, from the viewpoint of high energy density, the upper limit of the content of the lithium-affinity material may be preferably 50 wt% or less based on 100 wt% of the total negative electrode active material included in the negative electrode active material layer (240).

[0085] In addition, in the negative electrode active material layer (240), if the content of the lithium-affinity material per unit area is excessively low when viewed in the stacking direction of the negative electrode (200), it may be difficult to suppress the occurrence of pores because the lithium-affinity material remaining during discharge also decreases. Therefore, the content of the lithium-affinity material per unit area in the negative electrode active material layer (240) is 0.05 mg / cm 2 Ideally, 0.10 mg / cm 2On the other hand, if the content of lithium-affinity material per unit area is too high, the average discharge potential may decrease, which may lower the energy density of the battery. Therefore, the upper limit of the content of lithium-affinity material per unit area is 5 mg / cm. 2 Less than or equal to 2 mg / cm 2 It could be as follows:

[0086] In addition, in the initial state before charge / discharge, the lithium-affinity material included in the negative electrode active material layer (240) may be in the form of particles or a film. When the lithium-affinity material exists in the form of particles, the average particle diameter (d50, diameter length or average diameter) of the lithium-affinity material may be, but is not limited to, 20 nm to 1 μm.

[0087] Meanwhile, the negative electrode active material layer (240) may include a carbon material as a negative electrode active material in addition to a lithium-friendly material. Amorphous carbon may be preferably used as the carbon material included in the negative electrode active material layer (240). Specific examples of the amorphous carbon include amorphous carbon black (amorphous acetylene black, amorphous furnace black, amorphous Ketjen black), amorphous activated carbon, amorphous graphene, and combinations thereof. However, among the negative electrode active material layers (240), by positioning a carbon material having a relatively small particle size on the interface side that comes into contact with the solid electrolyte layer (300), the interface of the negative electrode active material layer (240) that comes into contact with the solid electrolyte layer (300) can be made flatter. Based on 100 wt% of the total negative active material included in the negative active material layer (240), the negative active material other than the lithium-compatible material may be combined to be 50 wt% or more, for example, 70 wt% or more. The content of the negative active material other than the lithium-compatible material may be measured using the same method as the method for measuring the content of the lithium-compatible material.

[0088] And, the carbon material included 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% of oxygen. When the oxygen is included 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 may be further improved. In one embodiment of the present invention, the oxygen may exist in a form included in a functional group bonded to the carbon material particles. In addition, the functional group may include at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an ether group, an ester group, an aldehyde group, a carbonyl group, and an amide group.

[0089] The carbon material particles containing 2 to 10 at% of oxygen can be produced, for example, by a method of oxidizing the carbon material. For example, 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. The type of the acid is not particularly limited, and any acid that can introduce oxygen functional groups to the surface of the carbon material can be used. Examples of the acid include sulfuric acid, nitric acid, or mixtures thereof, and an oxidizing agent such as potassium permanganate can also be used.

[0090] The content of oxygen contained in the above carbon material particles can be measured using a photoelectron spectroscopy (XPS or ESCA). For example, it can be measured using a K-Alpha (Thermo Fisher Scientific) device. In one embodiment of the present invention, the oxygen may be present on the surface of the carbon material particles. The surface does not mean only the outer surface of the carbon material particles, but also includes, for example, the inner surface of the pores if pores exist.

[0091] And, when the carbon material contains oxygen as described above, the negative electrode active material layer (240) may contain 2 to 10 at% of oxygen, 65 to 85 at% of carbon, and 0.5 to 5 at% of silver, and preferably may contain 2.5 to 5 at% of oxygen, 74 to 85 at% of carbon, and 0.5 to 3 at% of silver. In addition, the negative electrode active material layer (240) may further contain 5 to 25 at% of fluorine (F), and preferably 10 to 20 at% of fluorine (F). In addition, the negative electrode active material layer (240) may further contain 0.01 to 1 at% of sulfur (S), and preferably 0.01 to 0.5 at% of sulfur (S). In one embodiment of the present invention, the negative active material layer (240) may include 2 to 10 at% of oxygen, 65 to 85 at% of carbon, 0.5 to 5 at% of silver, and 5 to 25 at% of fluorine, preferably 2.5 to 5 at% of oxygen, 74 to 85 at% of carbon, 0.5 to 3 at% of silver, and 10 to 20 at% of fluorine, and may further include sulfur. The above atomic composition ratios may be measured using a photoelectron spectroscopy (XPS or ESCA). For example, the composition ratios may be measured using a Nexsa4 (Thermo Fisher Scientific) device.

[0092] Meanwhile, the negative electrode active material layer (240) may further include a binder for the purpose of stabilizing the negative electrode active material layer (240) on the negative electrode current collector (220). The binder may be, for example, a resin such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. In addition, the negative electrode active material layer (240) may appropriately contain additives used in conventional all-solid-state batteries, such as fillers, dispersants, and ion conductive additives. Specific examples of the additives are the same as those described in the positive electrode section described above.

[0093] The total thickness of the negative electrode active material layer (240) is not particularly limited and may be, for example, 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 not be sufficient. In addition, 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, resulting in insufficient performance of the all-solid-state battery. For reference, by using the binder mentioned above, the thickness of the negative electrode active material layer (240) can be easily secured at an appropriate level.

[0094] negative current collector

[0095] The negative electrode current collector (220) may be positioned at the outermost side in the stacking direction, facing the opposite side of the negative electrode active material layer (240) that does not contact the solid electrolyte layer (300), as illustrated in FIG. 1. However, if the battery includes a structure of more than a bi-cell, it may be positioned at a location other than the outermost side in the stacking direction.

[0096] The negative electrode current collector (220) may be plate-shaped or foil-shaped. The negative electrode current collector (220) may include a material that does not react with lithium, i.e., does not form any alloy or compound with lithium. Examples of materials constituting the negative electrode current collector (220) include copper, aluminum, stainless steel, titanium, iron, cobalt, and nickel. In addition, the negative electrode current collector (220) may be composed of one type of these metals, or may be composed of an alloy of two or more types of metals or a clad material.

[0097] Initial charge capacity ratio

[0098] Meanwhile, in an all-solid-state lithium ion secondary battery (1000) according to one embodiment, the initial charge capacity of the positive electrode active material layer (140) may be configured to be excessively large compared to the initial charge capacity of the negative electrode active material layer (240). As described below, the all-solid-state lithium ion secondary battery (1000) according to one embodiment can be used by charging (i.e., overcharging) exceeding the initial charge capacity of the negative electrode active material layer (240). In the initial stage of charging, lithium may be absorbed into the negative electrode active material layer (240). That is, the negative electrode active material may form an alloy or compound with lithium ions that have moved from the positive electrode (100). When charging is performed exceeding the initial charge capacity of the negative electrode active material layer (240), as illustrated in FIG. 2, lithium may be precipitated on the back surface of the negative electrode active material layer (240), i.e., between the negative electrode current collector (220) and the negative electrode active material layer (240), and a metal layer (260) may be formed by this lithium. The metal layer (260) may be mainly composed of lithium in which a lithium-affinity material is dissolved (i.e., lithium-affinity material-Li solid solution). This phenomenon may be caused by a material that forms an alloy or compound with the lithium-affinity material included in the negative electrode, for example. During discharge, lithium in the negative electrode active material layer (240) and the metal layer (260) may be ionized and move toward the positive electrode (100) while leaving the dissolved lithium-affinity material. Therefore, lithium may be used as the negative electrode active material in an all-solid-state lithium ion secondary battery (1000). In addition, since the lithium-affinity layer (230) and the negative electrode active material layer (240) coat the metal layer (260) at the same time, they function as a protective layer for the metal layer (260) and can suppress the precipitation and growth of dendritic metallic lithium. In this way, short-circuiting and capacity reduction of 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. In addition, according to one embodiment, since the metal layer (260) is not formed in advance, there is also an advantage of being able to reduce the manufacturing cost of the all-solid-state lithium ion secondary battery (1000).

[0099] In an all-solid-state lithium-ion secondary battery (1000) according to one embodiment, it is preferable that the ratio (b+c / a) of the initial charge capacity of the positive electrode active material layer (140) to the initial charge capacity of the negative electrode active material layer (240) and the lithium affinity layer (230) satisfies the following equation.

[0100] [Formula 1]

[0101] 0.01< b+c / a < 0.5

[0102] In the above equation 1, a is the initial charge capacity (mAh) of the positive electrode active material layer (140), b is the initial charge capacity (mAh) of the negative electrode active material layer (240), and c is the initial charge capacity (mAh) of the lithium affinity layer (230).

[0103] At this time, if the initial charge capacity ratio is 0.01 or less, the lithium affinity layer (230) and the negative electrode active material layer (240) may not function sufficiently as a protective layer, which may deteriorate the characteristics of the all-solid-state lithium ion secondary battery (1000). For example, if the thickness of the lithium affinity layer (230) and the negative electrode active material layer (240) is very thin, the capacity ratio may become 0.01 or less. In this case, there is a concern that the lithium affinity layer (230) and the negative electrode active material layer (240) may collapse due to repeated charge and discharge, and dendritic metallic lithium may precipitate and grow. As a result, the characteristics of the all-solid-state lithium ion secondary battery (1000) may deteriorate. On the other hand, if the initial charge capacity ratio is 0.5 or more, the battery capacity may decrease because the amount of lithium precipitated from the negative electrode decreases.

[0104] Manufacturing method of all-solid-state lithium-ion secondary battery

[0105] Next, a method for manufacturing the all-solid-state lithium ion secondary battery (1000) will be described. The all-solid-state lithium ion secondary battery (1000) according to one embodiment may be manufactured by manufacturing a positive electrode (100), a negative electrode (200), and a solid electrolyte layer (300) separately and then laminating them. In addition, the all-solid-state lithium ion secondary battery (1000) according to another embodiment may be manufactured by forming a solid electrolyte on one surface of the positive electrode (100) or the negative electrode (200) and then laminating the remaining electrodes. In addition, the all-solid-state lithium ion secondary battery (1000) according to another embodiment may be manufactured by forming a first solid electrolyte on one surface of the positive electrode (100), separately forming a second solid electrolyte on one surface of the negative electrode (200), and then laminating the first solid electrolyte and the second solid electrolyte so that they face each other.

[0106] The above-described positive electrode manufacturing process first adds materials (positive electrode active material, binder, etc.) constituting the positive electrode active material layer (140) to a non-polar solvent to prepare a slurry (or paste), and then applies the prepared slurry onto a positive electrode current collector (120) and dries it to obtain a laminate. Then, the laminate can be pressed, for example, with hydrostatic pressure, etc., to manufacture a positive electrode (100). At this time, the pressing process can be omitted.

[0107] Next, the negative electrode manufacturing process adds materials (negative electrode active material including carbon material and lithium-friendly material, binder, etc.) constituting the negative electrode active material layer (240) to a polar solvent or a non-polar solvent to manufacture a slurry (or paste), and then applies the manufactured slurry onto a negative electrode current collector (220) surface-treated with a lithium-friendly material and then dries to obtain a laminate (however, it may be composed of only the negative electrode current collector surface-treated with a lithium-friendly material without the negative electrode active material layer). At this time, the process of surface-treating the negative electrode current collector with the lithium-friendly material may be by a method selected from the group consisting of an atomic layer deposition method, a sputtering method, and a plasma method. Subsequently, the negative electrode (200) may be manufactured by pressurizing the laminate, for example, by hydrostatic pressure. At this time, the pressurizing process may be omitted. In addition, the method of applying the slurry to the negative electrode collector (220) is not particularly limited, and for example, screen printing, metal mask printing, electrostatic painting, dip coating, spray coating, roll coating, doctor blade, gravure coating, etc. can be used.

[0108] In a state where a solid electrolyte layer (300) is interposed between the positive electrode (100) and negative electrode (200) manufactured in this manner, an all-solid-state lithium ion secondary battery (1000) according to one embodiment can be manufactured by applying pressure, for example, using hydrostatic pressure.

[0109] The all-solid-state lithium ion secondary battery (1000) of the present invention can be manufactured in the form of a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of positive electrode / solid electrolyte layer / negative electrode / solid electrolyte layer / positive electrode, or a laminated battery having a structure of repeated unit cells. In addition, the all-solid-state lithium ion secondary battery according to the present invention can be utilized as a semi-solid battery including a liquid electrolyte if necessary, and in this case, a separate polymer separator can be further included.

[0110] The shape of the all-solid-state lithium ion secondary battery (1000) of the present invention is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, and cone-shaped batteries. Furthermore, the all-solid-state lithium ion secondary battery (1000) can be applied to large-scale batteries used in electric vehicles, etc. For example, the all-solid-state lithium ion secondary battery (1000) can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Furthermore, it can be used in fields requiring large amounts of power storage, such as electric bicycles or power tools.

[0111] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0112] [Example 1] Manufacture of an all-solid-state lithium-ion secondary battery

[0113] First, 80 g of lithium transition metal oxide, 6.5 g of carbon black, 9.83 g of nitrile butadiene rubber (binder), 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 to prepare a cathode slurry. Next, using a spray coating method, the prepared cathode slurry was applied to the surface of a cathode current collector (aluminum foil), vacuum-dried at 100°C for 10 hours, and then pressurized with hydrostatic pressure to prepare a cathode.

[0114] Then, 6.5 g of carbon black, 9.83 g of PVdF binder (solid content 6%), 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 to prepare a negative active material slurry. Then, using a spray coating method, the prepared negative active material slurry was applied to the surface of a negative electrode current collector (SUS foil), vacuum dried at 100°C for 10 hours, and then pressurized with hydrostatic pressure to prepare a negative electrode.

[0115] Separately, a binder solution was prepared by mixing and dissolving butadiene rubber (liquid at room temperature) having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber (solid at room temperature) having a molecular weight (Mw) of 500,000 g / mol in an organic solvent (n-butyl butyrate) at a weight ratio of 10:90. Then, 0.3 g of the binder solution prepared above, 10 g of a sulfide-based solid electrolyte (Li6PS5Cl), and 10.3 g of butyl butyrate (solvent) were mixed so that the solid content became 35 to 55 wt%, and then placed in a Thinky mixer container and mixed 12 times at 2,000 rpm for 3 minutes each to prepare an electrolyte slurry. Next, the prepared electrolyte slurry was applied onto the release film using a bar coater and then vacuum dried at 70°C for 5 hours.

[0116] Finally, the above-mentioned dried and manufactured solid electrolyte was separated from the release film and interposed between the manufactured negative electrode and positive electrode, and this laminate was covered with a pouch made of polypropylene material, sealed, and isostatically pressed for 30 minutes to manufacture an all-solid-state battery laminated in the order of negative electrode / solid electrolyte / positive electrode.

[0117] [Example 2] Manufacture of an all-solid-state lithium-ion secondary battery

[0118] An all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber having 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.

[0119] [Example 3] Manufacture of an all-solid-state lithium-ion secondary battery

[0120] An all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber having 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.

[0121] [Comparative Example 1] Manufacturing of an All-Solid-State Lithium-Ion Secondary Battery

[0122] An all-solid-state battery was manufactured in the same manner as in Example 1, except that only butadiene rubber having a molecular weight (Mw) of 500,000 g / mol was included as a binder in the binder solution used to manufacture the electrolyte slurry.

[0123] [Comparative Example 2] Manufacturing of an All-Solid-State Lithium-Ion Secondary Battery

[0124] An all-solid-state battery was manufactured in the same manner as in Example 1, except that the binder solution used to manufacture the electrolyte slurry contained butadiene rubber (solid at room temperature) having a molecular weight (Mw) of 190,000 g / mol and butadiene rubber (solid at room temperature) having a molecular weight (Mw) of 340,000 g / mol in a weight ratio of 10:90 instead of butadiene rubber having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber having a molecular weight (Mw) of 500,000 g / mol.

[0125] [Comparative Example 3] Manufacturing of an All-Solid-State Lithium-Ion Secondary Battery

[0126] An all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber having 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.

[0127] [Comparative Example 4] Manufacturing of an All-Solid-State Lithium-Ion Secondary Battery

[0128] An all-solid-state battery was manufactured in the same manner as in Example 1, except that the mixing ratio of butadiene rubber having a molecular weight (Mw) of 10,000 g / mol and butadiene rubber having 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.

[0129] [Experimental Example 1] Measurement and Evaluation of Porosity of Solid Electrolyte

[0130] The porosity of each of the solid electrolytes manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was measured before and after isotropic pressing, and the results are shown in Table 1 below.

[0131] Meanwhile, the porosity was measured by measuring the mass and thickness of the solid electrolyte, and then sequentially calculating the volume and density (d1) using these values, and then using the following equation 2.

[0132] [Formula 2]

[0133] Porosity (%) = [1-(d1 / d2)] × 100

[0134] In the above equation 2, d1 is the actual density (mass / actual volume, True Density) calculated above, and d2 is the theoretical density (mass / theoretical volume, Theoretical Density).

[0135] In addition, the thickness increase / decrease rate in Table 1 below was measured using a precision thickness measuring device (model name: TESA mu HITE, manufacturer: TESA) and Equation 3 below. In addition, when the electrolyte slurry is applied and dried to manufacture a solid electrolyte, all parts of the solid electrolyte are formed with a very uniform thickness, so there is no specific part that must be measured. However, since the deviation is the smallest, the measurement was made about the center, which is generally measured.

[0136] [Formula 3]

[0137] Thickness increase / decrease rate (%) = [(T2-T1) / T1] × 100

[0138] In the above equation 3, T1 is the thickness of the solid electrolyte before isotropic pressing, and T2 is the thickness of the isotropically pressed solid electrolyte.

[0139] Porosity (Porosity, %)Porosity reduction rate (%)Thickness increase rate (%)Before pressurizationAfter pressurizationExample 150.310.379.6-45.6Example 250.410.679.0-44.6Example 350.811.178.2-44.6Comparative example 151.212.875.0-43.7Comparative example 250.512.774.9-43.3Comparative example 349.011.975.8-42.1Comparative example 448.911.277.1-42.4

[0140] As can be seen from Table 1 above, the solid electrolytes of Examples 1 to 3 containing two types of binders having different molecular weights had excellent formability, and the degree of reduction in porosity (i.e., porosity reduction rate) after pressurization was greater than that of Comparative Examples 1 to 4. In addition, through comparison and contrast of Examples 1 to 3, it was confirmed that as the ratio of low-molecular-weight binders was lowered, the extent of reduction in porosity also increased.

[0141] On the other hand, in the case of Comparative Example 1, since a low molecular weight binder was not used, the formability was bound to be inferior, and accordingly, the degree of reduction in the void ratio after pressurization was small.

[0142] That is, as in Examples 1 to 3, binders with relatively small molecular weights must be positioned between binders with relatively large molecular weights in order to increase the reduction in porosity and improve the density of the solid electrolyte. However, Comparative Example 1 did not use a binder with a low molecular weight, so the formability of the solid electrolyte was inferior to that of Examples 1 to 3.

[0143] In the case of Comparative Example 2, although the solid electrolyte contains two types of binders with different molecular weights, the difference in molecular weights is not large, so the formability is bound to be poor, and accordingly, the degree of reduction in porosity after pressurization was small.

[0144] That is, through comparison and contrast between Examples 1 to 3 and Comparative Example 2, it can be confirmed that even if the solid electrolyte includes two types of binders having different molecular weights, if the difference in molecular weights is outside the scope of the present invention, the degree of reduction in porosity is bound to be small, as in Comparative Example 1. In addition, the degree of reduction in porosity is large only when binders having relatively small molecular weights are positioned between binders having relatively large molecular weights, but since the difference in molecular weight between the two types of binders is not large, the effect is insufficient.

[0145] In Comparative Examples 3 and 4, although the solid electrolyte contained two types of binders having different molecular weights, and the difference in molecular weight was set to be the same as in Example 1, the degree of decrease in porosity after pressurization was small. This is because the mixing ratio of the low-molecular-weight binder and the high-molecular-weight binder was outside the scope of the present invention, and this is because contact between binder particles was not maintained due to the excessive addition of the low-molecular-weight binder, i.e., butadiene rubber (liquid) having a molecular weight (Mw) of 10,000 g / mol. In other words, the low-molecular-weight binder and the high-molecular-weight binder must be in uniform contact, but if the low-molecular-weight binder is added in excessive amount, a problem occurs in which a large number of low-molecular-weight binder particles are generated that do not come into contact with the high-molecular-weight binder particles. In addition, when a low molecular weight binder is used alone, the force to maintain the structure of the pressurized solid electrolyte membrane is insufficient, resulting in a springback phenomenon in which the membrane slightly returns to its pre-pressurization state. In the case where a large number of low molecular weight binder particles are generated that do not come into contact with the high molecular weight binder particles as described above, the springback phenomenon of the solid electrolyte membrane is also caused.

[0146] In addition, the rate of increase or decrease in the thickness of the solid electrolyte due to isotropic pressing is also affected by the degree of reduction in porosity, and as shown in Table 1 above, as the rate of reduction in porosity increases, the degree of reduction in the thickness of the solid electrolyte also tends to increase.

[0147] [Experimental Example 2] Performance Evaluation of All-Solid-State Battery

[0148] For each of the all-solid-state batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4, a driving pressure of 10 MPa was applied using a jig, and charging and discharging were performed under the following conditions while a constant driving pressure was applied to evaluate the capacity retention rate according to the charge and discharge cycle, and the results are shown in Fig. 3.

[0149] - Charge / discharge conditions: Charge to 4.25 V in CC / CV mode at an operating temperature of 60°C and 0.33 C, discharge to 3.0 V with a constant current, and repeat charge / discharge 100 times.

[0150] 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, and as a result, the batteries of Examples 1 to 3, which included two types of binders with different molecular weights in the solid electrolyte, showed a high capacity retention rate exceeding 95% even after 100 charge / discharge cycles, as shown in FIG. 3. On the other hand, it was confirmed that the battery of Comparative Example 1, which did not include a low-molecular-weight binder in the solid electrolyte, and the battery of Comparative Example 2, which included two types of binders with different molecular weights in the solid electrolyte but the difference in molecular weight was not large, showed a rapid decrease in capacity retention rate from the initial charge / discharge time.

[0151] In addition, it was confirmed that the battery of Comparative Example 3, which included two types of binders with different molecular weights with an appropriate difference in the solid electrolyte, but in which the mixing ratio of the low molecular weight binder and the high molecular weight binder was outside the scope of the present invention, showed the most rapid decrease in capacity retention rate from the initial charge / discharge time.

[0152] And, the battery of Comparative Example 4, which included two types of binders with different molecular weights with an appropriate difference in the solid electrolyte, but in which the mixing ratio of the low molecular weight binder and the high molecular weight binder was outside the scope of the present invention, showed better performance than the other Comparative Examples, but showed significantly lower performance than the batteries of Examples 1 to 3.

[0153] Therefore, it can be seen that there is a limit to improving the rapid charging performance if the solid electrolyte contains only one type of binder, or if the solid electrolyte contains two types of binders having different molecular weights but the molecular weights between the binders are not large, or if the solid electrolyte contains two types of binders having different molecular weights with an appropriate difference but the mixing ratio between the binders is outside the scope of the present invention.

[0154] [Explanation of symbols]

[0155] 100: Bipolar

[0156] 120: Positive current collector

[0157] 140: Positive electrode active material layer

[0158] 200: Cathode

[0159] 220: Negative current collector

[0160] 240: Negative active material layer

[0161] 260: Metal layer

[0162] 300: Solid electrolyte layer

[0163] 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 binders having different molecular weights (Mw).

2. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that in claim 1, the solid electrolyte comprises a first binder and a second binder having different molecular weights (Mw), and a 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. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that, in claim 2, the molecular weight (Mw) of the first binder is 3,000 to 50,000 g / mol, and the molecular weight (Mw) of the second binder is 100,000 to 1,500,000 g / mol.

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

5. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that in claim 2, the first binder comprises a rubber-based compound having a molecular weight (Mw) of 3,000 to 50,000 g / mol, and the second binder comprises a rubber-based compound having a molecular weight (Mw) of 100,000 to 1,500,000 g / mol.

6. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that in claim 5, the rubber-based compound included in the first binder and the rubber-based compound included in the second binder are independently selected from the group consisting of butadiene-based rubber, acrylic-based rubber, fluorine-based rubber, and combinations thereof.

7. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that the content ratio of the first binder and the second binder in claim 2 is 5:95 to 30:70 in weight ratio.

8. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that in claim 2, the solid electrolyte comprises a first binder layer including a first binder; and a second binder layer including the first binder and the second binder in a mixed state.

9. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that the solid electrolyte comprises a sulfide-based solid electrolyte and two or more types of binders having different molecular weights (Mw) according to claim 1.

10. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that the content ratio of the sulfide-based solid electrolyte and the binder in claim 9 is 90:10 to 98:2 in weight ratio.

11. In claim 1, the solid electrolyte comprises two types of phase-separated solid electrolytes, a first solid electrolyte disposed on the positive electrode side; and a second solid electrolyte disposed on the negative electrode side; which form a layered structure. A solid electrolyte for an all-solid-state lithium-ion secondary battery, characterized in that each of the binder included in the first solid electrolyte and the binder included in the second solid electrolyte includes two or more types of binders having 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 comprising the solid electrolyte of claim 1 interposed therebetween.

13. An all-solid-state lithium-ion secondary battery according to claim 12, characterized in that the negative electrode does not contain a separate lithium metal other than lithium metal formed when the battery is charged.

14. An all-solid-state lithium-ion secondary battery according to claim 12, characterized in that the all-solid-state lithium-ion secondary battery is a sulfide-based all-solid-state lithium-ion secondary battery.

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