Positive electrode for secondary battery and secondary battery comprising same

Abstract

The present invention relates to a positive electrode for a secondary battery and a secondary battery comprising the same, and more particularly, to a positive electrode for a secondary battery comprising a first positive electrode layer and a second positive electrode layer.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0142389, filed on October 23, 2023, the contents of which are incorporated herein by reference as a part of this specification.

[0002] The present invention relates to a positive electrode for a secondary battery and a secondary battery comprising the positive electrode, and more specifically, to a positive electrode for a secondary battery comprising a first positive electrode layer and a second positive electrode layer. Background Technology

[0003] A secondary battery is a device that converts external electrical energy into chemical energy for storage and generates electricity when needed. Because it can be recharged multiple times, it is also called a rechargeable battery. Common secondary batteries include lead-acid batteries, nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, and lithium-ion batteries. Compared to primary batteries that are discarded after single use, secondary batteries offer economic and environmental advantages.

[0004] Meanwhile, with the continuous development of wireless communication technology, the demand for secondary batteries—requiring lightweight, slim, and compact designs for use in portable devices or automotive components—is increasing. In particular, with the commercialization of hybrid and electric vehicles to prevent environmental pollution, research is underway into using secondary batteries in next-generation automotive batteries to extend lifespan while reducing manufacturing costs and weight. Among various secondary batteries, lithium-ion batteries have recently attracted attention due to their light weight, high energy density, high operating voltage, and long lifespan.

[0005] Typically, lithium batteries are made by packing an electrode assembly consisting of a negative electrode, a positive electrode, and a separator into a cylindrical or prismatic metal can or a pouch-like casing made of aluminum laminate, and then injecting an electrolyte into the electrode assembly.

[0006] Traditionally, liquid electrolytes, which are lithium salts dissolved in non-aqueous organic solvents, have been primarily used as electrolytes for lithium-ion secondary batteries. However, these liquid electrolytes present challenges such as the high potential for electrode material degradation and organic solvent evaporation, the risk of combustion or explosion due to ambient temperature and battery temperature rise, and the risk of leakage, making it difficult to achieve highly safe lithium-ion secondary batteries.

[0007] Meanwhile, all-solid-state batteries using solid electrolytes have the advantage of being able to manufacture electrode components in a safe and simple manner, as there is no risk of leakage.

[0008] When manufacturing all-solid-state batteries, a solid electrolyte must be added to the electrodes, but this can lead to side reactions between the solid electrolyte and the positive electrode active material, or reduce ionic conductivity.

[0009] Therefore, there is a need to develop a cathode that can improve battery performance by reducing side reactions between the solid electrolyte and the cathode active material while improving ionic conductivity.

[0010] [Existing Technical Documents]

[0011] [Patent Literature]

[0012] (Patent Document 1) Japanese Patent Publication No. 7228816 (February 16, 2023) Summary of the Invention

[0013] Technical issues

[0014] In order to solve the above problems, the inventors conducted various studies and confirmed that by using a positive electrode comprising a first positive electrode layer and a second positive electrode layer each containing different solid electrolytes, side reactions between the solid electrolyte and the positive electrode active material are reduced and ionic conductivity is improved, a battery with improved high power and lifespan characteristics can be manufactured, thus completing the present invention.

[0015] Therefore, the object of the present invention is to provide a positive electrode for a secondary battery that has improved lifespan characteristics by suppressing side reactions between the positive electrode active material and the solid electrolyte, and a secondary battery comprising the positive electrode.

[0016] Solution to the problem

[0017] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, comprising: a positive electrode current collector; and a positive electrode composite layer stacked on one side of the positive electrode current collector, wherein the positive electrode composite layer comprises a first positive electrode layer and a second positive electrode layer, the first positive electrode layer comprising a positive electrode active material, a first solid electrolyte, a conductive material and a binder, the second positive electrode layer comprising a positive electrode active material, a second solid electrolyte, a conductive material and a binder, and the first solid electrolyte and the second solid electrolyte are different from each other.

[0018] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the first solid electrolyte comprises a halide-based solid electrolyte and the second solid electrolyte comprises a sulfide-based solid electrolyte.

[0019] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the first solid electrolyte is represented by the following chemical formula 1:

[0020] [Chemical Formula 1]

[0021] Li-MX

[0022] In chemical formula 1,

[0023] M is a metallic element selected from the group consisting of Y, Sc, Cr, Mn, Fe, Co, Ni, Al, Ga, As, Sb, Bi, Mg, Ca, Zn, Cd, Tb, Dy, Ho, Er, Tm, and Yb, and X is a halogen element, which is F, Cl, or Br.

[0024] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the second solid electrolyte comprises one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS.

[0025] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the positive electrode composite layer is disposed between the positive electrode current collector and the solid electrolyte layer, and a second positive electrode layer is disposed on one side of the solid electrolyte layer.

[0026] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the mass ratio of a first positive electrode layer to a second positive electrode layer is 20:80 to 80:20.

[0027] In one aspect of the invention, a positive electrode for a lithium secondary battery is provided, wherein the loading level of the positive electrode is 5 mAh / cm². 2 above.

[0028] In one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, wherein the secondary battery is an all-solid-state battery.

[0029] In one aspect of the present invention, an all-solid-state lithium secondary battery is provided, comprising: a positive electrode as described in any of the preceding aspects; a negative electrode; and a solid electrolyte disposed between the positive electrode and the negative electrode.

[0030] Beneficial effects

[0031] The present invention can provide a battery with improved high power and lifespan characteristics by suppressing side reactions between the positive electrode active material and the solid electrolyte to reduce the resistance of the battery during operation and to achieve improved ionic conductivity of the secondary battery. Attached Figure Description

[0032] Figure 1This is a schematic diagram of a secondary battery according to an embodiment of the present invention. Detailed Implementation

[0033] The invention will be described in more detail below.

[0034] The terms or words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings, but should be understood as being consistent with the ideas and concepts of the invention, based on the principle that the inventors can appropriately define the terms in order to best describe the invention.

[0035] The terminology used in this specification is for illustrative purposes only and is not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions. In this invention, the terms "comprising" or "having" are intended to specify the presence of the features, numbers, steps, ingredients, or combinations thereof described in this specification, and do not exclude the possibility of the presence or addition of one or more other features, numbers, steps, ingredients, or combinations thereof.

[0036] When manufacturing all-solid-state batteries, a solid electrolyte must be added to the electrodes to ensure ion conduction, but this can lead to side reactions between the solid electrolyte and the positive electrode active material, or reduce ion conductivity.

[0037] Therefore, the object of the present invention is to provide a positive electrode for secondary batteries that can improve high power and lifespan characteristics by reducing side reactions between the solid electrolyte and the positive electrode active material and improving ionic conductivity.

[0038] Below, in reference Figure 1 Before providing a detailed description of the positive electrode of the secondary battery according to the embodiments of the present invention, the structure of the secondary battery including the positive electrode will be briefly described first.

[0039] Figure 1 This is a schematic diagram of a lithium secondary battery according to an embodiment of the present invention.

[0040] See Figure 1 The lithium secondary battery 1 may include a positive electrode current collector 100, a positive electrode composite layer 200 and a solid electrolyte layer 300, and the positive electrode composite layer 200 may include a first positive electrode layer 201 and a second positive electrode layer 202.

[0041] The positive electrode composite layer 200 can be disposed between the positive electrode current collector 100 and the solid electrolyte layer 300.

[0042] The first positive electrode layer 201 can be disposed on one side of the positive electrode current collector 100, and the second positive electrode layer 202 can be disposed on one side of the solid electrolyte layer 300.

[0043] The positive electrode of the embodiments of the present invention will be described in more detail below.

[0044] According to one embodiment of the present invention, the positive electrode for a lithium secondary battery may include a positive current collector and a positive electrode composite layer stacked on one side of the positive current collector, wherein the positive electrode composite layer 200 includes a first positive electrode layer 201 and a second positive electrode layer 202, the first positive electrode layer 201 includes a positive electrode active material, a first solid electrolyte, a conductive material and a binder, the second positive electrode layer 202 includes a positive electrode active material, a second solid electrolyte, a conductive material and a binder, and the first solid electrolyte and the second solid electrolyte are different from each other.

[0045] According to an embodiment of the present invention, the first solid electrolyte may comprise a halide-based solid electrolyte.

[0046] Halogenated solid electrolytes (Li-MX) consist of halogen elements (X) and metal elements (M), in which metals or metalloids with oxidation states of 2, 3 or 4 are mainly used as the metal element (M).

[0047] The first solid electrolyte can be represented by the following chemical formula 1:

[0048] [Chemical Formula 1]

[0049] Li-MX

[0050] In chemical formula 1, M is a metallic element selected from the group consisting of Y, Sc, Cr, Mn, Fe, Co, Ni, Al, Ga, As, Sb, Bi, Mg, Ca, Zn, Cd, Tb, Dy, Ho, Er, Tm, and Yb.

[0051] X is a halogen element, which can be F, Cl, or Br.

[0052] Specifically, the halide-based solid electrolyte can be Li3YCl6, Li3YBr6, Li3YCl3Br3, etc., but is not limited to these examples.

[0053] According to an embodiment of the present invention, the second solid electrolyte may comprise a sulfide-based solid electrolyte.

[0054] The 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. It may include Li-PS glass or Li-PS glass ceramic.

[0055] Specifically, the sulfide solid electrolyte may include one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS, and preferably includes one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, and Li6PS5I. The Li6PS5Cl, Li6PS5Br, and Li6PS5I may be silver sulfide-germanium ore type solid electrolytes. In addition, sulfide solid electrolytes can be in the form of being doped with trace elements; for example, Li6PS5Cl can also be doped with bromine (Br).

[0056] Generally, halide solid electrolytes have relatively good oxidation stability, but their ionic conductivity is lower compared to sulfide solid electrolytes. Furthermore, the lower oxidation stability of sulfide solid electrolytes can cause side reactions with cathode materials such as NCM, leading to increased resistance during battery operation.

[0057] Therefore, the present invention can provide a positive electrode for secondary batteries that has improved high power and lifespan characteristics by including a halide-based solid electrolyte with excellent oxidation stability in the positive electrode composite layer in contact with the positive electrode current collector and a sulfide-based solid electrolyte with excellent ionic conductivity in the positive electrode composite layer in contact with the solid electrolyte.

[0058] According to one embodiment of the present invention, the positive electrode composite layer may include a positive electrode active material, a solid electrolyte, a conductive material, and a binder.

[0059] The positive electrode active material may include lithium metal oxide represented by the following chemical formula 2:

[0060] [Chemical Formula 2]

[0061] Li x [Ni y Co z Mn w M 1 v O u

[0062] In chemical formula 2, M 1It is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are respectively 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 <z≤0.5,0.01<w≤0.5,0≤v≤0.2,1.5≤u≤4.5。

[0063] The lithium metal oxide represented by chemical formula 2 is an oxide containing lithium and a transition metal, and may contain a high content of nickel among the transition metals. As an example, the lithium metal oxide may include lithium selected from LiNi. 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 and LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 This lithium metal oxide comprises one or more of the group consisting of O2. It contains a high nickel content, which has an excellent effect on improving the charge and discharge capacity of the battery.

[0064] The solid electrolyte may include one or more selected from the group consisting of sulfide solid electrolytes, polymer solid electrolytes, oxide solid electrolytes, and halide solid electrolytes, and preferably may include sulfide solid electrolytes. The solid electrolyte may be in particulate form.

[0065] Sulfide solid electrolytes and halide solid electrolytes are as described above.

[0066] Polymer-based solid electrolytes are polymer electrolyte materials formed by adding polymer resins to solvated lithium salts; that is, composites of lithium salts and polymer resins, which can exhibit approximately 1×10⁻⁶. -7 S / cm or higher, preferably about 1×10 -5Ionic conductivity above S / cm.

[0067] Non-limiting examples of the polymer resin include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, polyphosphazene polymers, polyethylene derivatives, olefin oxide derivatives (such as polyethylene oxide), phosphate polymers, polyaziridinium, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, etc., and may include one or more of these. Furthermore, as a polymer resin, the polymer electrolyte may include one or more of the following: branched copolymers copolymerized on the PEO (ethylene oxide) backbone as comonomers of amorphous polymers (such as PMMA, polycarbonate, polysiloxane (PDMS), and / or polyphosphazene), comb-like polymer resins, and crosslinked polymer resins.

[0068] In the electrolyte of the present invention, the aforementioned lithium salt can be represented as Li + X - It is an ionizable lithium salt. There are no specific restrictions on the anion of this lithium salt, but it 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.

[0069] The oxide-based solid electrolyte may contain oxygen (O) and possess the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. For example, it may include one or more of the following: LLTO compounds, Li6La2CaTa2O 12 Li6La2ANb2O 12 (where A is Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4) 3-y (where 0≤x≤1, 0≤y≤1), LiAl x Zr 2-x (PO4)3 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1), LiTi x Zr 2-x (PO4)3 (where 0≤x≤1, 0≤y≤1), LISICON-type compounds, LIPON-type compounds, perovskite-type compounds, NASICON-type compounds, and LLZO-type compounds.

[0070] Furthermore, there are no particular limitations on the conductive materials, as long as they are conductive and do not cause chemical changes in the battery. Specifically, they can include graphite, carbon-based materials, metal powders or metal fibers, needle-like or dendritic conductive whiskers, conductive metal oxides, conductive polymers, and any one or mixtures thereof. More specifically, the following can be used: natural or artificial graphite as graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; needle-like or dendritic conductive whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon dioxide whiskers, silicon carbide whiskers, aluminum borate whiskers, magnesium borate whiskers, potassium titanate whiskers, silicon nitride whiskers, silicon carbide whiskers, and alumina whiskers; conductive metal oxides such as titanium oxide or conductive polymers such as polyphenylene derivatives, etc. Any one or a mixture of two or more of these can be used.

[0071] Furthermore, the positive electrode binder can be selected from any one or a mixture of two or more of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), or selected from N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP). Any one or a mixture of two or more of the following: conjugated diene rubber latexes (such as acrylonitrile styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), etc.), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0072] According to one embodiment of the present invention, the mass ratio of the first positive electrode layer to the second positive electrode layer can be from 20:80 to 80:20. More specifically, the mass ratio of the first positive electrode layer to the second positive electrode layer can be 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25 or 80:20, but is not limited to these ranges.

[0073] If the mass ratio of the first positive electrode layer to the second positive electrode layer exceeds the above range, there will be a problem of significant deterioration in the battery's lifespan characteristics.

[0074] According to one embodiment of the present invention, the loading level of the positive electrode can be 5 mAh / cm². 2 above.

[0075] According to one embodiment of this disclosure, the lithium secondary battery can be an all-solid-state battery.

[0076] The lithium secondary battery may include a positive electrode, a negative electrode, and a solid electrolyte between the positive and negative electrodes according to any embodiment of the present invention.

[0077] Lithium secondary batteries can be all-solid-state lithium secondary batteries.

[0078] The lithium secondary battery of the present invention includes the positive electrode of the present invention as described above, and can exhibit excellent battery performance, with reduced side reactions between the positive electrode active material and the solid electrolyte and lower resistance within the positive electrode.

[0079] In this case, the positive electrode may have a structure in which a positive electrode composite layer including the first positive electrode layer and the second positive electrode layer of the present invention is formed on the positive electrode current collector.

[0080] The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it may include stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0081] In addition, the negative electrode may have a structure in which a negative electrode composite layer including a negative electrode active material is formed on the negative electrode current collector.

[0082] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, it may include stainless steel, copper, nickel, titanium, fired carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0083] In addition, the negative electrode composite layer may contain a negative electrode active material, a conductive material, a binder, and a solid electrolyte, and may sometimes also contain additives.

[0084] In this case, the negative electrode active material may be any one selected from the group consisting of lithium metal, lithium alloy, lithium metal composite oxide, lithium titanium composite oxide (LTO), and combinations thereof. Here, the lithium alloy may be an alloy of lithium and at least one metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn. In addition, the lithium metal composite oxide may be an oxide (MeOx) of lithium and a metal (Me) selected from the group consisting of Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe. For example, it may be Li x Fe2O3 (0 < x ≤ 1) or Li x WO2 (0 < x ≤ 1).

[0085] In addition, metal composite oxides such as Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, 2, 3 elements in the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5, and carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon, or carbon composites may be used alone or in combination of two or more.

[0086] In addition, conductive materials may include nickel powder, cobalt oxide, titanium oxide, carbon, etc. As carbon, any one or more selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene can be used.

[0087] Furthermore, the negative electrode binder can be selected from any one or a mixture of two or more of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), or selected from N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP). Any one or a mixture of two or more of the following groups: o-HFP), conjugated diene rubber latexes (such as styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), etc.), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0088] Example

[0089] Preferred embodiments will be presented below to aid in understanding the present invention. However, the following embodiments are only for illustrative purposes. Various modifications and variations can be made within the scope and technical concept of the present invention, which will be apparent to those skilled in the art, and such modifications and variations are included within the appended claims.

[0090] Example 1: Manufacturing of the positive electrode

[0091] Using a laboratory mixer at 5000 rpm, mix LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li3YCl6 were mixed at a mass ratio of 85:15 for 30 minutes, then CNTs and PTFE were added at a 1:1 ratio to 2% of the total weight, and mixed for another 5 minutes. Subsequently, a self-standing first cathode composite layer was fabricated using a two-roll mill (MR-3, Inoue Co.).

[0092] Using a laboratory mixer at 5000 rpm, mix LiNi 0.8 Co 0.1 Mn 0.1O2 and Li6PS5Cl (LPSCl) were mixed at a mass ratio of 85:15 for 30 minutes, then CNTs and PTFE were added at a 1:1 ratio to 2% of the total weight, and mixed for another 5 minutes. Subsequently, a self-standing second cathode composite layer was fabricated using a two-roll mill (MR-3, Inoue Co.).

[0093] The first positive electrode composite layer is stacked on one side of the aluminum current collector, and the second positive electrode composite layer is then stacked sequentially on one side of the first positive electrode composite layer. Pressure is then applied to manufacture the positive electrode. At this point, the mass ratio of the first positive electrode composite layer to the second positive electrode composite layer is 50:50.

[0094] Example 2

[0095] The positive electrode was manufactured in the same manner as described in Example 1, except that Li3YCl3Br3 was used as the first solid electrolyte and Li6PS5Cl was used as the second solid electrolyte.

[0096] Example 3

[0097] Except that the mass ratio of the first positive electrode composite layer to the second positive electrode composite layer is 30:70, the positive electrode is manufactured in the same manner as described in Example 1.

[0098] Example 4

[0099] Except that the mass ratio of the first positive electrode composite layer to the second positive electrode composite layer is 70:30, the positive electrode is manufactured in the same manner as described in Example 1.

[0100] Comparative Example 1

[0101] The positive electrode is manufactured in the same manner as described in Example 1, except that only the first positive electrode composite layer is used and the second positive electrode composite layer is not used.

[0102] Comparative Example 2

[0103] The positive electrode is manufactured in the same manner as described in Example 1, except that the first positive electrode composite layer is not used and only the second positive electrode composite layer is used.

[0104] Comparative Example 3

[0105] Except that the first positive electrode composite layer contains Li6PS5Cl (LPSCl) powder and the second positive electrode composite layer contains Li3YCl6 powder, the positive electrode is manufactured in the same manner as described in Example 1.

[0106] Comparative Example 4

[0107] Except that the mass ratio of the first positive electrode composite layer to the second positive electrode composite layer is 10:90, the positive electrode is manufactured in the same manner as described in Example 1.

[0108] Table 1

[0109]

[0110] Experimental Example 1: Evaluation of Initial Discharge Capacity and Efficiency

[0111] Using a 40 μm thick lithium metal as the negative electrode, a 50 μm thick Li6PS5Cl solid electrolyte membrane was inserted between the positive electrode manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 and the aforementioned negative electrode. Then, a pressure of 500 MPa was applied, with a driving pressure of 10 MPa and a designed capacity of 6 mAh / cm³. 2 The form of the clamped battery cell was evaluated.

[0112] The battery cell is charged at a rate of 0.1 C until the voltage reaches 4.3 V, then held at 4.3 V and cut off at a rate of 0.05 C. It is then discharged at a rate of 0.1 C until the voltage reaches 3.0 V during discharge. The initial efficiency is calculated as initial discharge capacity / initial charge capacity × 100 (%).

[0113] Table 2 below shows the results for initial discharge capacity and initial efficiency.

[0114] Table 2

[0115]

[0116] Experimental Example 2: Evaluation of Battery Life Characteristics

[0117] The battery cell was charged at a rate of 0.5 C until the voltage reached 4.3 V, then held at 4.3 V and cut off at a rate of 0.1 C. It was then discharged at a rate of 0.5 C until the voltage reached 3.0 V during discharge. This charge-discharge test was repeated 50 times, and the discharge capacity after 50 cycles was measured as the capacity retention rate compared to the initial discharge capacity (0.1 C). Table 3 below shows the measured capacity retention rates.

[0118] Table 3

[0119]

[0120] As shown in Table 3 above, it can be confirmed that, compared with the positive electrodes for secondary batteries of Comparative Examples 1 and 2 which are composed of a single-component monolayer, the positive electrode for secondary batteries of Comparative Example 3 which contains a sulfide-based solid electrolyte in the first positive electrode composite layer and a halide-based solid electrolyte in the second positive electrode composite layer, or the positive electrode for secondary batteries of Comparative Example 4 which has a mass ratio of the first positive electrode composite layer to the second positive electrode composite layer outside the range of 20:80 to 80:20, the positive electrodes for secondary batteries of Examples 1 to 4 which contain a halide-based solid electrolyte in the first positive electrode composite layer and a sulfide-based solid electrolyte in the second positive electrode composite layer exhibit superior capacity retention.

[0121] [Explanation of reference numerals in the attached figures]

[0122] 1: Positive electrode

[0123] 100: Positive current collector

[0124] 200: Positive electrode composite layer

[0125] 201: First positive electrode layer

[0126] 202: Second positive electrode layer

[0127] 300: Solid electrolyte layer

Claims

1. A positive electrode for a lithium secondary battery, comprising: Positive current collector; and A positive electrode composite layer is stacked on one side of the positive electrode current collector; in, The positive electrode composite layer includes a first positive electrode layer and a second positive electrode layer. The first positive electrode layer comprises a positive electrode active material, a first solid electrolyte, a conductive material, and a binder. The second positive electrode layer comprises a positive electrode active material, a second solid electrolyte, a conductive material, and a binder, and The first solid electrolyte and the second solid electrolyte are different from each other.

2. The positive electrode for a lithium secondary battery as described in claim 1, in, The first solid electrolyte includes halide solid electrolytes, and The second type of solid electrolyte includes sulfide solid electrolytes.

3. The positive electrode for a lithium secondary battery as described in claim 2, in, The first solid electrolyte is represented by the following chemical formula 1: [Chemical Formula 1] Li-MX In chemical formula 1, M is a metallic element selected from the group consisting of Y, Sc, Cr, Mn, Fe, Co, Ni, Al, Ga, As, Sb, Bi, Mg, Ca, Zn, Cd, Tb, Dy, Ho, Er, Tm, and Yb; X is a halogen element, which is F, Cl, or Br.

4. The positive electrode for a lithium secondary battery as described in claim 2, in, The second solid electrolyte comprises one or more selected from the group consisting of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li2S-P2S5, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2S5, Li2S-P2S5-SiS2, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, and Li2S-GeS2-ZnS.

5. The positive electrode for a lithium secondary battery as described in claim 1, in, The positive electrode composite layer is disposed between the positive electrode current collector and the solid electrolyte layer, and The second positive electrode layer is disposed on one side of the solid electrolyte layer.

6. The positive electrode for a lithium secondary battery as described in claim 1, in, The mass ratio of the first cathode layer to the second cathode layer is 20:80 to 80:

20.

7. The positive electrode for a lithium secondary battery as described in claim 1, in, The positive electrode has a load level of 5 mAh / cm². 2 above.

8. The positive electrode for a lithium secondary battery as described in claim 1, in, The secondary battery is an all-solid-state battery.

9. An all-solid-state lithium secondary battery, comprising: The positive electrode according to any one of claims 1 to 8; Negative electrode; and A solid electrolyte disposed between the positive electrode and the negative electrode.

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