Positive electrode for secondary battery and secondary battery comprising same

Abstract

A positive electrode for a secondary battery of the present invention comprises: a first positive electrode layer; and second positive electrode layer, the first positive electrode layer including a first positive electrode active material and a first coating layer for coating the surface of the first positive electrode active material, and the second positive electrode layer including a second positive electrode active material and a second coating layer for coating the surface of the second positive electrode active material, wherein the content of the first coating layer is less than 1 wt% on the basis of the total weight of the first positive electrode active material, and the content of the second coating layer is 1 wt% or more on the basis of the total weight of the second positive electrode active material.

Description

Anode for secondary battery and secondary battery containing same

[0001] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2023-0106806, dated August 16, 2023, and Republic of Korea Patent Application No. 10-2024-0109247, dated August 14, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode for a secondary battery and a secondary battery including the same, and more particularly, to a positive electrode for a secondary battery including a first positive electrode layer and a second positive electrode layer.

[0003] Lithium all-solid-state batteries utilize sulfide, polymer, or oxide solid electrolytes and can directly convert chemical energy into electrical energy by oxidizing or reducing lithium ions via the solid-state material. In particular, their environmental friendliness, safety, and high-energy-density storage capacity have led to a growing demand for them as sustainable secondary batteries, potentially addressing the limitations of currently commercialized lithium secondary batteries, including low energy density, high cost, and toxicity.

[0004] However, all-solid-state batteries are facing issues such as reduced battery capacity due to irreversibility caused by interfacial side reactions between the solid electrolyte and electrode during charge / discharge reactions, interfacial resistance, and uneven distribution of electrode charge due to space-charge layer formation. Furthermore, the low ionic conductivity of the all-solid-state material itself is hindering the commercialization of next-generation lithium all-solid-state batteries.

[0005] To address these issues, electrode active material composites containing a protective layer between the solid electrolyte and the electrode active material have been developed. However, although the protective layer is thinly coated and reduces interfacial side reactions between the solid electrolyte and the electrode active material, the protective layer itself acts as a resistor, resulting in resistance deviation as the electrode loading increases.

[0006] Therefore, research is needed on a composite of positive electrode active materials that suppresses interfacial side reactions between solid electrolytes and electrode active materials, reduces resistance, improves charge / discharge performance, and enhances capacity retention.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] (Patent Document 1) Republic of Korea Publication No. 10-2022-0042726

[0010] Accordingly, the purpose of the present invention is to provide a positive electrode for an all-solid-state battery in which the resistance deviation that occurs as the loading in the positive electrode layer increases is reduced by controlling the content of the coating layer of the positive electrode active material, and the lifespan of the battery is improved by preventing side reactions between the solid electrolyte and the positive electrode active material.

[0011] To solve the above-mentioned problem,

[0012] In one embodiment of the present invention, a positive electrode for a secondary battery is provided, wherein the positive electrode includes a first positive electrode layer and a second positive electrode layer, the first positive electrode layer includes a first positive electrode active material and a first coating layer coating a surface of the first positive electrode active material, the second positive electrode layer includes a second positive electrode active material and a second coating layer coating a surface of the second positive electrode active material, and the content of the first coating layer is less than 1 wt% based on the total weight of the first positive electrode active material, and the content of the second coating layer is 1 wt% or more based on the total weight of the second positive electrode active material.

[0013] In one embodiment of the present invention, a cathode for a secondary battery is provided, which is disposed between the current collector and the solid electrolyte, wherein the first cathode layer is in contact with one surface of the current collector, and the second cathode layer is in contact with one surface of the solid electrolyte.

[0014] In one embodiment of the present invention, the first anode layer (T a ) and the second anode layer (T b ) provides a secondary battery positive electrode having a thickness ratio of 20~69:31~80.

[0015] In one embodiment of the present invention, the first anode layer (T a ) and the second anode layer (T b ) provides a secondary battery positive electrode having a thickness ratio of 20 to 50:50 to 80.

[0016] In one embodiment of the present invention, the first coating layer and the second coating layer provide a positive electrode for a secondary battery including lithium oxide.

[0017] In one embodiment of the present invention, the lithium oxide is Li4Ti5O 12 , LiNbO3, LiTaO3, LiCoO2, Li3BO3, Li2ZrO3, Li3PO4, Li4SiO4, and Li2WO4.

[0018] In one embodiment of the present invention, a positive electrode for a secondary battery is provided, wherein the solid electrolyte is a sulfide-based, polymer-based, oxide-based or halide-based solid electrolyte.

[0019] In one embodiment of the present invention, the secondary battery provides a positive electrode for a secondary battery that is an all-solid-state battery.

[0020] In one embodiment of the present invention, an all-solid-state lithium secondary battery is provided, comprising: a positive electrode according to the present invention; a negative electrode; and a solid electrolyte disposed between the positive electrode and the negative electrode.

[0021] The present invention includes a first positive electrode layer and a second positive electrode layer having a thickness of a specific ratio, and includes a specific content of a coating layer of a positive electrode active material within the first positive electrode layer and the second positive electrode layer, thereby suppressing side reactions between a solid electrolyte and an electrode layer and reducing resistance within the positive electrode, thereby having the effect of improving the performance of a battery.

[0022] FIG. 1 is a schematic diagram showing an anode according to one embodiment of the present invention.

[0023] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0024] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0025] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0026]

[0027] All-solid-state batteries suffer from reduced battery capacity due to interfacial resistance caused by interfacial side reactions between the solid electrolyte and electrode during charge / discharge reactions. To address these issues, electrode active material composites containing a protective layer between the solid electrolyte and the electrode active material are being developed. However, the protective layer itself acts as a resistor, causing resistance deviation as the loading within the electrode increases.

[0028] Therefore, the electrode has no problem at low loading, but 5 mAh / cm 2In the above high-loading, the resistance deviation increases along the thickness direction within the electrode, so that the electrode active material with relatively low resistance participates in charging and discharging. In other words, the positive electrode active material in contact with one side of the solid electrolyte has a lower resistance than the positive electrode active material in contact with one side of the current collector, so only the positive electrode active material in contact with one side of the solid electrolyte mainly participates in charging and discharging. However, if only the positive electrode active material arranged in a portion of the positive electrode participates in the battery's charging and discharging, there is a problem that the battery performance deteriorates rapidly as the number of cycles progresses.

[0029] The inventors of the present invention have completed an invention in which the positive electrode active material disposed in the positive electrode is uniformly involved in charging and discharging as a whole by controlling the thickness of the positive electrode layer and the content of the positive electrode active material coating layer in order to improve battery performance.

[0030]

[0031] Hereinafter, the composition and effects of the present invention will be described in detail.

[0032]

[0033] In one embodiment of the present invention, a positive electrode for an all-solid-state battery includes a first positive electrode layer and a second positive electrode layer, wherein the first positive electrode layer includes a first positive electrode active material and a first coating layer coating a surface of the first positive electrode active material, and the second positive electrode layer includes a second positive electrode active material and a second coating layer coating a surface of the second positive electrode active material, and the content of the first coating layer may be less than 1 wt% based on the total weight of the first positive electrode active material, and the content of the second coating layer may be 1 wt% or more based on the total weight of the second positive electrode active material.

[0034] FIG. 1 is a schematic diagram showing an anode according to one embodiment of the present invention.

[0035] Referring to Fig. 1, the positive electrode (1) may include a first positive electrode layer (201) and a second positive electrode layer (202). In addition, the positive electrode (1) may be disposed between a current collector (100) and a solid electrolyte (300). Here, the first positive electrode layer (201) may be in contact with one surface of the current collector (100), and the second positive electrode layer (202) may be in contact with one surface of the solid electrolyte (300).

[0036] The first positive electrode layer may include a first positive electrode active material and a first coating layer coating a surface of the first positive electrode active material.

[0037] The second positive electrode layer may include a second positive electrode active material and a second coating layer that coats the surface of the second positive electrode active material.

[0038] Here, the first positive electrode active material and the second positive electrode active material may include a lithium metal oxide represented by the following chemical formula 1:

[0039] [Chemical Formula 1]

[0040] Li x [Ni y Co z Mn w M 1 v ]O u

[0041] In the above chemical formula 1,

[0042] M 1 is at least one element 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,

[0043] x, y, z, w, v, and u are 1.0≤x≤1.30, 0.1≤y<0.95, 0.01, respectively. <z≤0.5, 0.01<w≤0.5, 0≤v≤0.2, 1.5≤u≤4.5이다.

[0044] The lithium metal oxide represented by the above chemical formula 1 is an oxide containing a transition metal together with lithium, and may contain a high content of nickel among the transition metals. As an example, the lithium metal oxide may be 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 It may include at least one selected from the group consisting of O2. The lithium metal oxide has a high nickel content and is excellent in improving the charge / discharge capacity of the battery.

[0045] The first coating layer may be coated entirely or partially on the surface of the first positive electrode active material particle.

[0046] The content of the first coating layer may be less than 1 wt% based on the total weight of the first positive electrode active material. Specifically, the content of the first coating layer may be 0.9 wt% or less, 0.8 wt% or less, 0.7 wt% or less, 0.6 wt% or less, 0.5 wt% or less, 0.4 wt% or less, 0.3 wt% or less, 0.2 wt% or less, or 0.1 wt% or less based on the total weight of the first positive electrode active material, but is not limited to these examples.

[0047] The first coating layer is coated with a content of less than 1.0 wt% on the surface of the first positive electrode active material in contact with one side of the current collector, thereby reducing the resistance of the electrode and improving the performance of the battery.

[0048] When the content of the first coating layer is 1.0 wt% or more, 5 mAh / cm 2 There is a problem that the resistance deviation in the above high-loading electrode increases, which reduces the initial capacity and efficiency of the electrode, and also reduces the capacity retention rate.

[0049] The thickness of the first coating layer may be 10 nm to 40 nm. Specifically, when the content of the first coating layer is 0.5 wt% based on the total weight of the first positive electrode active material, the average thickness of the first coating layer may be 20 nm.

[0050] The second coating layer may be coated entirely or partially on the surface of the second positive electrode active material particles.

[0051] The content of the second coating layer may be 1 wt% or more based on the total weight of the second positive electrode active material. Specifically, the content of the second coating layer may be 1.0 wt% or more, 1.1 wt% or more, 1.2 wt% or more, 1.3 wt% or more, 1.4 wt% or more, 1.5 wt% or more, 1.6 wt% or more, 1.7 wt% or more, 1.8 wt% or more, 1.9 wt% or more, or 2.0 wt% or more based on the total weight of the second positive electrode active material, but is not limited to these examples.

[0052] The second coating layer is coated with a content of 1.0 wt% or more on the surface of the second positive electrode active material in contact with one side of the solid electrolyte, thereby suppressing side reactions between the solid electrolyte and the positive electrode, thereby improving the performance of the battery.

[0053] When the content of the second coating layer is less than 1.0 wt%, there is a problem in that a side reaction occurs between the solid electrolyte and the positive electrode layer, resulting in a deterioration in battery performance.

[0054] The thickness of the second coating layer may be 40 nm to 100 nm. Specifically, when the content of the second coating layer is 1.0 wt% based on the total weight of the second positive electrode active material, the average thickness of the second coating layer may be 40 nm, and when the content of the second coating layer is 1.5 wt% based on the total weight of the second positive electrode active material, the average thickness of the second coating layer may be 60 nm.

[0055] The thickness of the first anode layer (T) a ) and the thickness of the second anode layer (T b ) may be in the range of 20~69:31~80. More specifically, the thickness (T of the first anode layer a ) and the thickness of the second anode layer (T b ) can be 20:80, 25:75, 30:70, 35:75, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, but are not limited to these examples.

[0056] The thickness of the first anode layer (T) a ) and the thickness of the second anode layer (T b ) can be in the range of 20~50 : 50~80. The thickness (T) of the first anode layer a ) is the thickness of the second anode layer (T b ) or the thickness of the second anode layer (T b ) is smaller than that, the resistance deviation between the first positive electrode active material included in the first positive electrode layer in contact with one surface of the current collector and the second positive electrode active material included in the second positive electrode layer in contact with one surface of the solid electrolyte can be reduced. Through this, the positive electrode active material arranged in the positive electrode can be uniformly involved in charging and discharging as a whole.

[0057] The thickness of the first anode layer (T) a ) and the thickness of the second anode layer (T b ) is outside the above range, for example, the thickness (T) of the first anode layer a ) and the thickness of the second anode layer (Tb ) is 70:30 or 10:90, the initial capacity and efficiency of the electrode are reduced, and the capacity retention rate is rapidly reduced, resulting in a problem of reduced battery life.

[0058] The first coating layer and the second coating layer may have the same composition, but may have different contents. The first coating layer and the second coating layer may include lithium oxide. The lithium oxide may be Li4Ti5O 12 , LiNbO3, LiTaO3, LiCoO2, Li3BO3, Li2ZrO3, Li3PO4, Li4SiO4, and Li2WO4.

[0059] The first positive electrode layer and the second positive electrode layer include the same composition of positive electrode active material, solid electrolyte, conductive material, and binder, and the contents of the first coating layer and the second coating layer may be different.

[0060] The above solid electrolyte may include at least one selected from the group consisting of a sulfide-based solid electrolyte, a polymer-based solid electrolyte, an oxide-based solid electrolyte, and a halide-based solid electrolyte, and preferably includes a sulfide-based solid electrolyte. The above solid electrolyte may be in the form of particles.

[0061] 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.

[0062] Specifically, the sulfide-based solid electrolyte may include at least one 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 may include at least one selected from the group consisting of Li6PS5Cl, Li6PS5Br, and Li6PS5I. The above Li6PS5Cl, Li6PS5Br, and Li6PS5I may be argyrodite type solid electrolytes. In addition, the sulfide-based solid electrolyte may be in a form doped with trace elements, for example, Li6PS5Cl may be additionally doped with bromine (Br).

[0063] The above polymer-based solid electrolyte is a polymer electrolyte material formed by adding a polymer resin to a composite of a lithium salt and a polymer resin, that is, a solvated lithium salt, and is about 1x10 -7 S / cm or more, preferably about 1x10 -5 It can exhibit ionic conductivity of S / cm or more.

[0064] Non-limiting examples of the polymer resin include polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives such as polyethylene oxide, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, etc., and may include one or more of these. In addition, the polymer electrolyte may include, as a polymer resin, a branched copolymer in which an amorphous polymer such as PMMA, polycarbonate, polysiloxane (PDMS) and / or phosphazene is copolymerized as a comonomer in a polyethylene oxide (PEO) main chain, a comb-like polymer, and a cross-linked polymer resin, and may include one or more of these.

[0065] In the electrolyte of the present invention, the lithium salt mentioned above is an ionizable lithium salt and is Li + X - It can be expressed as . There is no particular limitation on the anion of these lithium salts, 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 - , (CF3CF2SO2)2N - Examples include:

[0066] The above oxide-based solid electrolyte may contain oxygen (O) and have the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table. For example, an LLTO-based compound, Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li1 +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 (wherein, 0≤x≤1, 0≤y≤1), may include at least one selected from among LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and LLZO compounds.

[0067] The above halide-based solid electrolyte (Li-MX) contains a halogen element (X) and a metal element (M), and as the metal element (M), a metal or semimetal having an oxidation number of divalent, trivalent, or tetravalent is mainly used. For example, M is a metal element and may be 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 and may be F, Cl, or Br. Specifically, the halide-based solid electrolyte may be Li3YCl6, Li3YBr6, etc., but is not limited thereto.

[0068] The lithium secondary battery according to the present invention can exhibit excellent battery performance by including the positive electrode of the present invention described above, suppressing side reactions occurring at the interface between the positive electrode active material and the solid electrolyte, and reducing resistance within the positive electrode.

[0069] At this time, the positive electrode may have a structure in which a positive electrode composite layer containing the positive electrode active material of the present invention described above is formed on the positive electrode current collector.

[0070] The above-mentioned positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0071] In addition, the positive electrode composite layer contains a positive electrode active material, a conductive material, a binder, and a solid electrolyte, and may further contain additives in some cases.

[0072] In addition, the conductive material is not particularly limited as long as it is conductive without causing a chemical change in the battery, and specifically, graphite, a carbon-based material, a metal powder or metal fiber, a needle-shaped or branch-shaped conductive whisker, a conductive metal oxide, a conductive polymer, and any one of these or a mixture thereof may be used. More specifically, graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; Examples of conductive whiskers include needle- or branch-shaped whiskers such as zinc oxide whiskers, calcium carbonate whiskers, titanium dioxide whiskers, silicon oxide 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; and any one of these or a mixture of two or more thereof may be used.

[0073] In addition, the binder for the positive electrode is one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), or a mixture of two or more thereof, N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), acrylonitrile-based styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), and the like, conjugated diene rubber latex, It may be any one selected from the group consisting of carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluoroelastomer, various copolymers, etc., or a mixture of two or more thereof.

[0074] In addition, the negative electrode may have a structure in which a negative electrode composite layer containing a negative electrode active material is formed on a negative electrode current collector.

[0075] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may include, for example, stainless steel, copper, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

[0076] In addition, the negative electrode composite layer contains a negative electrode active material, a conductive material, a binder, and a solid electrolyte, and may further contain additives in some cases.

[0077] At this time, the negative electrode active material may be one selected from the group consisting of lithium metal, lithium alloy, lithium metal composite oxide, lithium-containing titanium composite oxide (LTO), and combinations thereof. Here, the lithium alloy may be an alloy composed 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 is an oxide (MeOx) of any one metal (Me) selected from the group consisting of lithium and Si, Sn, Zn, Mg, Cd, Ce, Ni, and Fe, and for example, Li x Fe2O3(0 <x≤1) 또는 Li x WO2(0 <x≤1)일 수 있다.

[0078] In addition, the negative electrode active material is Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 산화물 등을 사용할 수 있고, 결정질 탄소, 비정질 탄소 또는 탄소 복합체와 같은 탄소계 음극활물질이 단독으로 또는 2종 이상이 혼용되어 사용될 수 있다.

[0079] In addition, examples of the conductive material include nickel powder, cobalt oxide, titanium oxide, carbon, etc. As for the carbon, any one or more selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene may be mentioned.

[0080] In addition, the binder for the negative electrode is one selected from the group consisting of N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) or a mixture of two or more thereof, N,N-bis[3-(triethoxysilyl)propyl]urea, polyethylene oxide (PEO), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), conjugated diene rubber latex such as styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), butadiene rubber (BR), carboxymethyl cellulose (CMC), It may be one selected from the group consisting of starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc., or a mixture of two or more thereof.

[0081] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0082] However, the following examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0083]

[0084] Example 1

[0085] (1) Manufacturing of positive electrode active material

[0086] Li2CO3 and Ni 0.8 Co 0.1 Mn 0.1(OH)2 was mixed in a weight ratio of 1.1:1 to form a reaction mixture, and the reaction mixture was placed in a stainless steel crucible and subjected to a primary heat treatment at 600°C in an air atmosphere for 5 hours to form a plastic mixture, which was then cooled. Thereafter, the mixture was crushed and sieved, and the crushed plastic mixture was placed in an aluminum crucible and subjected to a secondary heat treatment at 800°C in an air atmosphere for 10 hours to produce a positive electrode active material matrix having a particle size (D50) of 5 μm.

[0087] Next, to form a protective layer, titanium (IV) isopropoxide and lithium ethoxide as precursors of lithium titanium oxide are added in a stoichiometric ratio and dissolved in ethanol to form Li4Ti5O 12 Prepare a solution, and the prepared positive electrode active material is Li4Ti5O 12 A mixed solution was prepared by adding it to a solution. The mixed solution was mixed for 24 hours using a lab blender (Waring), vacuum-dried to remove the solvent ethanol, and placed in a tube furnace with an inner diameter of 50 mm and a length of 1,000 mm, followed by heat treatment at 400°C for 4 hours to obtain Li4Ti5O 12 A first active material composite containing 0.3 parts by weight of the total weight of the positive electrode active material was manufactured.

[0088] Also, Li4Ti5O 12 A second active material composite was manufactured using the same method as the first active material composite manufacturing method, except that the positive electrode active material was included in an amount of 1.2 parts by weight relative to the total weight of the positive electrode active material.

[0089] (2) Manufacturing of electrodes

[0090] 81.9 wt% of the first active material composite manufactured in (1) above, 15.6 wt% of the solid electrolyte LPS, 1.5 wt% of the carbon black powder, and 1 wt% of the PTFE as a binder were mixed at 5000 rpm for 1 minute without a solvent using a lab blender (Waring) (first mixing). Thereafter, a high-shear mixing (PBV-0.1 L, Irie Shokai) was performed by applying a shear force of 100 N to the mixture (second mixing) to prepare a dough. Next, the dough was used to manufacture a first positive electrode layer having a free-standing structure using a two-roll mill (MR-3, Inoue).

[0091] A second positive electrode layer was manufactured in the same manner as the manufacture of the electrode layer A, except that it included the second active material composite manufactured in (1) above.

[0092] A free-standing film was placed on one side of an aluminum current collector having a thickness of 15 μm so that the thickness ratio of the first positive electrode layer and the second positive electrode layer was 30:70, and pressure was applied to manufacture a positive electrode.

[0093] Example 2

[0094] An anode was manufactured using the same method as described in Example 1, except that the thickness ratio of the first anode layer and the second anode layer was 50:50.

[0095] Example 3

[0096] Li4Ti5O 12 A positive electrode was manufactured using the same method as described in Example 1, except that a first active material composite containing 0.9 parts by weight of the positive electrode active material was manufactured.

[0097] Example 4

[0098] Li4Ti5O 12 A positive electrode was manufactured using the same method as described in Example 1, except that a second active material composite containing 0.9 parts by weight of the total weight of the positive electrode active material was manufactured.

[0099] Example 5

[0100] A positive electrode was manufactured in the same manner as described in Example 1, except that niobium (V) ethoxide was used as a precursor of lithium niobium oxide instead of lithium titanium oxide.

[0101] Example 6

[0102] A positive electrode was manufactured in the same manner as described in Example 1, except that tantalum (V) ethoxide was used as a precursor of lithium tantalum oxide instead of lithium titanium oxide.

[0103]

[0104] Comparative Example 1

[0105] An anode was manufactured using the same method as described in Example 1, except that the thickness ratio of the first anode layer and the second anode layer was 70:30.

[0106] Comparative Example 2

[0107] An anode was manufactured using the same method as described in Example 1, except that the thickness ratio of the first anode layer and the second anode layer was 10:90.

[0108] Comparative Example 3

[0109] Li4Ti5O 12 A positive electrode was manufactured using the same method as described in Example 1, except that a first active material composite containing 1.2 parts by weight of the positive electrode active material was manufactured.

[0110] Comparative Example 4

[0111] Li4Ti5O 12 A positive electrode was manufactured using the same method as described in Example 1, except that a second active material composite containing 0.3 parts by weight of the total weight of the positive electrode active material was manufactured.

[0112] Comparative Example 5

[0113] Li4Ti5O 12 A first active material composite comprising 0.7 parts by weight of the total weight of the positive electrode active material and Li4Ti5O 12 A positive electrode was manufactured using the same method as described in Example 1, except that a second active material composite containing 0.7 parts by weight of the total weight of the positive electrode active material was manufactured.

[0114] Table 1 below shows the materials, contents, and thickness ratios of the positive electrode layers of the active material composites manufactured in Examples 1 to 6 and Comparative Examples 1 to 5.

[0115] Coating layer material First anode layer Second anode layer First anode layer: Second anode layer thickness ratio First coating layer content (weight %) Second coating layer content (weight %) Example 1 Li4Ti5O 12 0.31.230:70 Example 2Li4Ti5O 12 0.31.250:50Example 3Li4Ti5O 12 0.91.230:70 Example 4Li4Ti5O 12 0.31.030:70Example 5LiNbO30.31.230:70Example 6LiTaO30.31.230:70Comparative example 1Li4Ti5O 12 0.31.270:30Comparative example 2Li4Ti5O 12 0.31.210:90 Comparative example 3Li4Ti5O 12 1.21.230:70 Comparative example 4Li4Ti5O 12 0.30.330:70 Comparative example 5Li4Ti5O 12 0.70.730:70

[0116]

[0117] Experimental Example 1: Initial Discharge Capacity and Efficiency Evaluation

[0118] Lithium metal having a thickness of 40 μm was used as the negative electrode, and a Li6PS5Cl solid electrolyte membrane having a thickness of 50 μm was interposed between the positive electrode and the negative electrode manufactured in Examples 1 to 6 and Comparative Examples 1 to 5, and then pressurized at a pressure of 500 MPa, and this was manufactured in the form of a jig cell having a driving pressure of 3 MPa and a capacity of 5 mAh / cm2, and cell evaluation was performed.

[0119] The battery was charged at a rate (C-rate) of 0.1 C until the voltage reached 4.25 V (vs. Li), and then cut-off was performed at a rate of 0.05 C while maintaining 4.25 V (vs. Li). Subsequently, the battery was discharged at a rate (C-rate) of 0.1 C until the voltage reached 3.0 V (vs. Li) (1 st Cycle). The initial efficiency was calculated using the discharge capacity / charge capacity x 100 (%).

[0120] Table 2 below shows the results of initial capacity and initial efficiency.

[0121] 0.1 C Initial Capacity (mAh) 0.1 C Initial Efficiency (%) Example 15.09 4.0 Example 25.09 4.2 Example 35.09 3.9 Example 45.19 3.7 Example 55.09 4.1 Example 65.09 3.7 Comparative Example 14.58 8.1 Comparative Example 24.79 3.4 Comparative Example 34.29 2.8 Comparative Example 44.38 5.2 Comparative Example 54.59 0.1

[0122]

[0123] Experimental Example 2: Evaluation of Battery Life Characteristics

[0124] After charging at a rate (C-rate) of 0.33 C until the voltage reached 4.25 V (vs. Li), the battery was cut off at a rate of 0.1 C while maintaining 4.25 V (vs. Li). Subsequently, the battery was discharged at a rate (C-rate) of 0.33 C until the voltage reached 3.0 V (vs. Li) (1 stCycle). The above charge / discharge test was repeated 50 cycles, and the capacity retention rate of the discharge capacity was measured. Table 3 below shows the measured capacity retention rate.

[0125] Capacity retention rate (%) Example 190.2 Example 288.4 Example 394.8 Example 487.9 Example 590.9 Example 689.0 Comparative example 154.0 Comparative example 268.2 Comparative example 372.9 Comparative example 442.1 Comparative example 558.3

[0126] As shown in Tables 2 and 3 above, the batteries according to Examples 1 to 6 include a cathode active material composite in which the content of the first coating layer is less than 1 wt% based on the total weight of the first cathode active material, the content of the second coating layer is 1 wt% or more based on the total weight of the second cathode active material, and the thickness ratio of the first cathode layer and the second cathode layer is 20 to 69:31 to 80, and thus it was confirmed that the initial capacity and efficiency of the battery were excellent, and the life characteristics were also remarkably excellent. On the other hand, the batteries according to Comparative Examples 1 and 2 had a thickness ratio between the first cathode layer and the second cathode layer exceeding the range of 20 to 69:31 to 80, and thus it was confirmed that the capacity retention rate was remarkably low.

[0127] In addition, it was confirmed that the batteries according to Comparative Examples 3 to 5 include a cathode active material composite in which the content of the first coating layer exceeds 1 wt% based on the total weight of the first cathode active material or the content of the second coating layer is less than 1 wt% based on the total weight of the second cathode active material, and the initial capacity and efficiency of the battery are reduced, and the life characteristics are also significantly deteriorated.

[0128] [Explanation of symbols]

[0129] 1: Bipolar

[0130] 100: Positive current collector

[0131] 201: First bipolar layer

[0132] 202: Second bipolar layer

[0133] 300: Solid electrolyte

Claims

1. In the case of a cathode for a secondary battery, The above anode comprises a first anode layer and a second anode layer, The first positive electrode layer includes a first positive electrode active material and a first coating layer that coats the surface of the first positive electrode active material, The second positive electrode layer includes a second positive electrode active material and a second coating layer that coats the surface of the second positive electrode active material, The content of the first coating layer is less than 1 wt% based on the total weight of the first positive electrode active material, A positive electrode for a secondary battery, wherein the content of the second coating layer is 1 wt% or more based on the total weight of the second positive electrode active material.

2. In paragraph 1, The above positive electrode is placed between the current collector and the solid electrolyte, A cathode for a secondary battery, wherein the first cathode layer is in contact with one surface of the current collector, and the second cathode layer is in contact with one surface of the solid electrolyte.

3. In paragraph 1, The above first anode layer (T a ) and the second bipolar layer (T b ) A secondary battery cathode having a thickness ratio of 20 to 69:31 to 80.

4. In paragraph 3, The above first anode layer (T a ) and the second bipolar layer (T b ) A secondary battery cathode having a thickness ratio of 20 to 50:50 to 80.

5. In paragraph 1, A positive electrode for a secondary battery, wherein the first coating layer and the second coating layer contain lithium oxide.

6. In paragraph 5, The above lithium oxide is Li 4 Ti 5 O 12 , LiNbO 3 , LiTaO 3 , LiCoO 2 , Li 3 BO 3 , Li 2 ZrO 3 , Li 3 PO 4 , Li 4 SiO 4 and Li 2 WO 4 A cathode for a secondary battery, wherein the cathode is one selected from the group consisting of:

7. In paragraph 2, A cathode for a secondary battery, wherein the solid electrolyte is a sulfide-based, polymer-based, oxide-based or halide-based solid electrolyte.

8. In paragraph 1, A cathode for a secondary battery, wherein the secondary battery is an all-solid-state battery.

9. An anode according to any one of clauses 1 to 8; cathode; and An all-solid-state lithium secondary battery comprising a solid electrolyte disposed between the positive electrode and the negative electrode.

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