Negative electrode and secondary battery comprising same

Abstract

The present invention relates to a negative electrode having a multilayered structure which is formed by sequentially stacking: a negative electrode current collector; and a first negative electrode active material layer and a second negative electrode active material layer each having a specific composition. The purpose of the present invention is to provide a secondary battery having improved ionic conductivity and life characteristics by using the negative electrode.

Description

Negative electrode and secondary battery including the same

[0001] The present invention relates to a negative electrode and a secondary battery including the same.

[0002] With the increasing technological development and demand for electronic devices, society's overall dependence on electrical energy is growing, leading to a rapid increase in the demand for secondary batteries capable of efficiently storing and utilizing electrical energy. Accordingly, there is a need for technological development in secondary batteries that offer improved safety alongside enhanced lifespan and charging capacity.

[0003] In conventional secondary batteries using graphite as the anode, the use of a liquid electrolyte facilitates the penetration of the electrolyte into the anode, thereby enabling relatively easy lithium ion transfer. However, when using a liquid electrolyte, safety issues such as short circuits arise as the charging and discharging of the secondary battery are repeated; consequently, secondary battery technologies utilizing solid electrolytes are currently being developed.

[0004] When using solid electrolytes, unlike liquid electrolytes, it is difficult to ensure ionic conductivity within the electrode, so improvements are needed in this regard. Additionally, although conductive materials are added to enhance electron conductivity within the cathode, there is a problem of capacity loss caused by side reactions between the conductive materials and the solid electrolyte.

[0005] Accordingly, even when using solid electrolytes in secondary batteries, a new structural design is required to improve lifespan characteristics by ensuring interface stability between the anode and electrolyte through the suppression of side reactions between the electrolyte and the anode, along with improving ion conductivity.

[0006] To solve the above-mentioned problems, the present invention provides a cathode with a multilayer structure comprising a first cathode active material layer and a second cathode active material layer having different compositions, thereby suppressing side reactions at the interface between the solid electrolyte layer and the cathode, and by including a solid electrolyte in each of the cathode active material layers, thereby improving ion conductivity. The purpose of the invention is to provide a secondary battery with improved capacity and / or lifespan characteristics.

[0007] The present invention relates to a cathode in which a cathode current collector; a first cathode active material layer comprising a first conductive material and a first solid electrolyte; and a second cathode active material layer comprising a second solid electrolyte are sequentially stacked.

[0008] In one embodiment, the first solid electrolyte may be included in an amount of 9% or more to 38% or less based on the total weight of the first negative electrode active material layer, and the second solid electrolyte may be included in an amount of 9% or more to 40% or less based on the total weight of the second negative electrode active material layer.

[0009] In one embodiment, the second solid electrolyte may be included in a larger amount than the first solid electrolyte.

[0010] In one embodiment, the second solid electrolyte may be included in an amount of 20 parts by weight or more to 500 parts by weight or less based on 100 parts by weight of the first solid electrolyte.

[0011] In one embodiment, the first solid electrolyte and the second solid electrolyte may each independently comprise one or more selected from a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer-based solid electrolyte, and a halide-based solid electrolyte.

[0012] In one embodiment, the first solid electrolyte and the second solid electrolyte may each independently comprise an azirodite-based sulfide-based solid electrolyte.

[0013] In one embodiment, the first conductive material may be included in an amount of more than 0.5 weight% to 10 weight% or less based on the total weight of the first negative electrode active material layer.

[0014] In one embodiment, the second negative active material layer may further include a second conductive material.

[0015] In one embodiment, the second conductive material may be included in an amount of more than 0 weight% to 0.5 weight% or less based on the total weight of the second negative electrode active material layer.

[0016] In one embodiment, the first conductive material and the second conductive material may each comprise one or more selected from graphite, carbon black, conductive fiber, carbon nanotube, fluorocarbon, metal powder, conductive whisker, conductive metal oxide, and polyphenylene derivative.

[0017] In one embodiment, the ratio of the weight of the second solid electrolyte to the weight of the second conductive material may be 15 or more to 800 or less.

[0018] In one embodiment, the ratio of the weight of the first solid electrolyte to the weight of the first conductive material may be 0.9 or more and less than 76.

[0019] In one embodiment, the first negative electrode active material layer comprises a first negative electrode active material, and the second negative electrode active material layer comprises a second negative electrode active material, and the first negative electrode active material and the second negative electrode active material may each independently comprise graphite.

[0020] In one embodiment, the second cathode active material layer may be included in an amount of 40 parts by weight or more to 240 parts by weight or less based on 100 parts by weight of the first cathode active material layer.

[0021] In one embodiment, the thickness of the first negative electrode active material layer may be 30 μm or more to 200 μm or less, and the thickness of the second negative electrode active material layer may be 30 μm or more to 200 μm or less.

[0022] The present invention relates to a secondary battery comprising the above-mentioned negative electrode.

[0023] In one embodiment, the secondary battery may be characterized as being an all-solid-state battery.

[0024] The present invention utilizes a cathode with a multilayer structure and controls the composition of the first cathode active material layer and the second cathode active material layer (particularly the conductive material and solid electrolyte) of the multilayer cathode to suppress side reactions between the electrolyte and the cathode, thereby promoting interfacial stability between the cathode and the electrolyte.

[0025] The present invention allows the above-described cathode to be used in an all-solid-state battery, and by using a cathode with a multilayer structure as described above, the reactivity between the conductive material inside the cathode and the solid electrolyte layer can be suppressed, thereby having the effect of securing interfacial stability between the cathode and the solid electrolyte layer.

[0026] In particular, by controlling the composition of the conductive material and solid electrolyte of the first negative electrode active material layer and the second negative electrode active material layer, the second negative electrode active material layer with a low conductive material content can improve the interface characteristics of the solid electrolyte layer to suppress capacity loss, and the conductivity of the first negative electrode active material layer inside can be improved, so that when a conventional graphite negative electrode is applied to an all-solid-state battery, the capacity and / or life characteristics of the battery are improved.

[0027] Figure 1 is a schematic diagram of the cathode prepared in Examples 1 to 3.

[0028] Figure 2 is a schematic diagram showing the cathodes prepared in Comparative Examples 1 to 5.

[0029] Figure 3 is a graph showing the capacity retention rate of the secondary battery of Example 1 according to Experimental Example 1.

[0030] Figure 4 is a graph showing the capacity retention rate of the secondary battery of Example 2 according to Experimental Example 1.

[0031] Figure 5 is a graph showing the capacity retention rate of the secondary battery of Example 3 according to Experimental Example 1.

[0032] Figure 6 is a graph showing the capacity retention rate of the secondary battery of Comparative Example 1 according to Experimental Example 1.

[0033] Figure 7 is a graph showing the capacity retention rate of the secondary battery of Comparative Example 2 according to Experimental Example 1.

[0034] Figure 8 is a graph showing the capacity retention rate of the secondary battery of Comparative Example 3 according to Experimental Example 1.

[0035] Figure 9 is a graph showing the capacity retention rate of the secondary battery of Comparative Example 4 according to Experimental Example 1.

[0036] Figure 10 is a graph showing the capacity retention rate of the secondary battery of Comparative Example 5 according to Experimental Example 1.

[0037] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0038] Therefore, the configurations of the embodiments described in this specification are merely one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application. In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0039] In this specification, when a part is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Thus, for example, a composition comprising compound A may include compounds other than A. However, the term “comprising” also encompasses, in a more restrictive sense as a specific embodiment thereof, “essentially / essentially composed of” and “composed of,” so, for example, a “composition comprising compound A” may also be (essentially / essentially) composed of compound A.

[0040] In connection with this, terms such as “comprising” or “having,” as described in this specification, are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0041] In this specification, when any layer is described as being located “on” or “between” another arbitrary layer, this includes not only cases where any layer is in contact with another arbitrary layer, but also cases where another layer or material, etc., exists between the two layers.

[0042] Where in this specification a quantity, concentration, or other value or parameter is given as an enumeration of a range, a preferred range, a preferred upper limit, and a preferred lower limit, it should be understood that any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the range is disclosed separately, specifically discloses all ranges that may be formed. Where a range of numerical values ​​is mentioned in this specification, unless otherwise stated, for example, without limiting terms such as greater than or less than, the range is intended to include its endpoint value and all integers and fractions within that range. The scope of the invention is not intended to be limited to the specific value mentioned when defining the range.

[0043] Among the physical properties mentioned in this specification, if the measured temperature affects the property, the property is measured at room temperature unless specifically otherwise specified. The term "room temperature" refers to a natural temperature that has not been heated or cooled, and may mean, for example, any temperature within the range of about 10°C to 30°C, about 23°C, or about 25°C. Furthermore, unless specifically otherwise specified, the unit of temperature in this specification is °C.

[0044] In addition, among the physical properties mentioned in this specification, if the measured pressure affects the physical property, unless otherwise specifically defined, the physical property is measured at atmospheric pressure, that is, at about 1 atmosphere.

[0045] One aspect of the present invention provides a cathode having a cathode current collector; a first cathode active material layer comprising a first conductive material and a first solid electrolyte; and a second cathode active material layer comprising a second solid electrolyte, sequentially stacked.

[0046] The above-mentioned negative current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used.

[0047] The above-mentioned cathode current collector is generally made with a thickness of 3 μm or more to 500 μm or less.

[0048] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0049] The first negative active material layer is disposed on the negative current collector. Specifically, the first negative active material layer may be disposed on at least one surface of the negative current collector, and more specifically, may be disposed on one or both surfaces of the negative current collector.

[0050] The first cathode active material layer may include a first conductive material and a first solid electrolyte, and may additionally include a first binder.

[0051] The first solid electrolyte may include, but is not limited to, sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, and / or halide-based solid electrolytes.

[0052] The above sulfide-based solid electrolyte contains sulfur atoms (S), has ionic conductivity of metals belonging to Group 1 or Group 2 of the periodic table, and may have electronic insulation properties. The above sulfide-based solid electrolyte preferably contains at least Li, S, and P as elements and has lithium ion conductivity, but may include other elements other than Li, S, and P depending on the purpose or case. As the above-mentioned sulfide-based solid electrolyte, for example, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2OP2S5, Li2S-LiBr-P2S5, Li2SLi2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, Li2S-GeS2, Li2S-GeS2-ZnS, Li2SGa2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2SSiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2SSiS2-Li3PO4, or Li 10 GeP2S 12The above may include the above. The above sulfide-based solid electrolyte may include an azirodite-based solid electrolyte comprising one or more selected from Li6PS5F, Li6PS5Cl, Li6PS5Br, Li6PS5I, or Li6PS5X (where X is two or more selected from F, Cl, Br, and I). Alternatively, the above sulfide-based solid electrolyte may include an amorphous sulfide glass manufactured using Li2S, P2S5, etc. as a raw material, or may include a glass ceramic obtained by heat treating the sulfide glass, but is not limited thereto.

[0053] The above oxide-based solid electrolyte is, for example, LiPON, Li 3x La(2 / 3-x)(1 / 3-2x)TiO3(0.04 <x<0.16), Li 1+x Al x Ti 2-x (PO4)3(0 <x<2), Li 1+x Al x Ge 2-x (PO4)3(0 <x<2), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr, Ti)O3, Pb 1-x La x Zr 1-y Ti y O3(0≤x<1, 0≤y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3, HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y(Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M is Te, Nb, or Zr, 1≤x≤10), Li7La3Zr2O 12 , Li 3+x La3Zr 2-a M a O 12 (M is Ga, W, Nb, Ta, or Al, 0 <a<2, 1≤x≤10) 또는 이들의 조합을 포함할 수 있다. 또한 산화물계 고체 전해질은 Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M-doped LLZO, M=Ga, W, Nb, Ta, or Al, 0 <a<2, 1≤x≤10) 중에서 선택된 가넷계(Garnet-type) 고체 전해질, 또는 리튬-알루미늄-티타늄 인산염계(LATP, Li 1+x Al x Ti 2-x (PO4)3), lithium-aluminum-germanium phosphate system (LAGP, Li 1.5 Al 0.5 Ge 1.5 It may include, but is not limited to, a NASICON-based solid electrolyte selected from (PO4)3-based, lithium-silicon-titanium phosphate-based (LSTP, LiSiO2TiO2(PO4)3), or a combination thereof.

[0054] The above oxide-based solid electrolyte may be crystalline, amorphous, glassy, ​​or glass-ceramic, and may have various crystalline states depending on the manufacturing method and composition.

[0055] The above-mentioned polymer-based solid electrolyte is not particularly limited to any polymer material that is an ion-conducting material and is commonly used as a solid electrolyte material for all-solid-state batteries. The above-mentioned polymer-based solid electrolyte may include, for example, polyether-based polymers, polycarbonate-based polymers, acrylate-based polymers, polysiloxane-based polymers, phosphazene-based polymers, polyethylene oxide (PEO), polyethylene derivatives, alkylene oxide derivatives, phosphate ester polymers, polyaisation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, or polymers containing ionic dissociators. Alternatively, the above-mentioned polymer-based solid electrolyte may include, as a polymer resin, a branched copolymer, a comb-like polymer, and a cross-linked polymer resin, etc., in which an amorphous polymer such as polymethyl methacrylate (PMMA), polycarbonate, polysiloxane, and / or phosphazene is copolymerized as a comonomer to a polyethylene oxide (PEO) main chain.

[0056] The above-mentioned halide-based solid electrolyte may, for example, contain a halogen element as the main component of anion. Containing a halogen element as the main component of anion may mean that the proportion (molar ratio) of the halogen element is the highest among all anions constituting the halide-based solid electrolyte. The ratio of the halogen (X) element to all anions constituting the above-mentioned halide-based solid electrolyte may, for example, be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. The halogen element may be one or more types. The above-mentioned halide-based solid electrolyte may, for example, not contain a sulfur element (S element). The above-mentioned halide-based solid electrolyte may, for example, contain a Li element, an M element (M is a metal other than Li), and an X element. X may, for example, be F, Cl, Br, I, or a combination thereof. The above halide-based solid electrolyte may include, for example, Br or Cl as X. The above halide-based solid electrolyte may include, for example, a metal element such as Sc, Y, B, Al, Ga, or In as M. The composition of the above halide-based solid electrolyte is, for example, Li 6-3a M a Br b Cl c (M is a metal other than Li, and 0 <a<2, 0≤b≤6, 0≤c≤6, b+c=6)일 수 있다. 상기 할라이드계 고체 전해질은 예를 들어 Li3YBr6, Li3YCl6, 또는 Li3YBr2Cl4등일 수 있다.

[0057] For example, the first solid electrolyte may include a sulfide-based solid electrolyte. Specifically, the first solid electrolyte may include an azirodite-based sulfide solid electrolyte, but is not limited thereto.

[0058] The first solid electrolyte may be included in the first negative electrode active material layer in an amount of 9% by weight or more to 38% by weight or less based on the total weight of the first negative electrode active material layer, but is not limited thereto. For example, the first solid electrolyte may satisfy a range of content consisting of one lower limit selected from 9% by weight or more, 12% by weight or more, 15% by weight or more, 18% by weight or more, 20% by weight or more, 25% by weight or more, and 27% by weight or more, and one upper limit selected from 38% by weight or less, 36% by weight or less, 34% by weight or less, 32% by weight or less, and 30% by weight or less, based on the total weight of the first negative electrode active material layer. If the content of the first solid electrolyte is less than 9% by weight, the ion conductivity inside the electrode may decrease, causing problems in performance development, and if it exceeds 38% by weight, the electrode thickness may increase, causing problems in resistance.

[0059] The first conductive material may be used to improve the conductivity of the first cathode active material layer, and may be used without special limitations as long as it is conductive without causing chemical changes. Examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjenblack, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and may include one of these alone or a mixture of two or more. As an example, the first conductive material may include carbon-based materials such as carbon black, acetylene black, ketjenblack, channel black, furnace black, lamp black, thermal black, and carbon fibers. For example, Super C65 may be used as the first conductive material, but is not limited thereto.

[0060] The first conductive material may be included in the first negative electrode active material layer in an amount of more than 0.5 wt% to 10 wt% or less based on the total weight of the first negative electrode active material layer, but is not limited thereto. For example, the first conductive material may satisfy a content within a range consisting of one lower limit selected from more than 0.5 wt%, 1.0 wt% or more, 1.5 wt% or more, 2.0 wt% or more, 2.5 wt% or more, and 3.0 wt% or more based on the total weight of the first negative electrode active material layer, and one upper limit selected from 10 wt% or less, 9.0 wt% or less, 8.0 wt% or less, 7.0 wt% or less, 6.5 wt% or less, 6.0 wt% or less, 5.5 wt% or less, and 5.0 wt% or less. If the content of the first conductive material is 0.5 weight% or less, a problem may occur in which the electrical conductivity inside the electrode decreases, and if it exceeds 10 weight%, a problem may occur in which the reactivity between the conductive material and the solid electrolyte increases.

[0061] The ratio of the weight of the first solid electrolyte to the weight of the first conductive material in the first cathode active material layer may be 0.9 or more and less than 76, but is not limited thereto. For example, the ratio of the weight of the first solid electrolyte to the weight of the first conductive material may be 1 or more and 70 or less, 1.5 or more and 60 or less, 2 or more and 50 or less, 2.5 or more and 40 or less, 3 or more and 30 or less, 3.5 or more and 20 or less, 4 or more and 15 or less, or 5 or more and 10 or more, but is not limited thereto.

[0062] The first negative electrode active material layer may include a first negative electrode active material. The first negative electrode active material may be a negative electrode active material commonly used in secondary batteries. Examples include carbonaceous materials such as graphite, artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Ag, Au, Si alloy, Sn alloy, or Al alloy; SiO βExamples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, or lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. For example, the artificial graphite and natural graphite may be mixed in a weight ratio range of 1:1 or more to 10:1 or less, 2:1 or more to 9:1 or less, or 3:1 or more to 8:1 or less, but are not limited thereto. As an example, the artificial graphite and natural graphite may be mixed in a weight ratio of 4:1 and included as a negative electrode active material. A metallic lithium thin film may also be used as the negative electrode active material. The carbonaceous material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, or high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. Additionally, the above-mentioned cathode active material layer may be omitted depending on the case, in which case the cathode may include a cathode current collector or may include a cathode current collector and a protective layer formed on the cathode current collector, but is not limited thereto.

[0063] The first cathode active material may preferably include graphite.

[0064] Average particle size (D) of the first negative electrode active material 50 ) may be 5 μm or more to 50 μm or less, specifically 10 μm or more to 20 μm or less, but is not limited thereto.

[0065] The above "average particle size (D 50 "" refers to the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size, and the said particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to calculate the particle size distribution by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam. By calculating the particle diameter at the point where the cumulative distribution of particle numbers according to particle size in the measuring device reaches 50%, D 50 Particle size can be measured.

[0066] The first negative active material in the first negative active material layer may satisfy a content selected from any one range based on the total weight of the first negative active material layer, such as 52 wt% or more to less than 90.9 wt%, 53 wt% or more to 90 wt% or less, 54 wt% or more to 85 wt% or less, 55 wt% or more to 80 wt% or less, 56 wt% or more to 75 wt% or less, 57 wt% or more to 70 wt% or less, 58 wt% or more to 69 wt% or less, 59 wt% or more to 68 wt% or less, and 63 wt% or more to 67 wt% or less, but is not limited thereto.

[0067] The first negative electrode active material layer may include a first binder. The first binder may serve to improve adhesion between negative electrode active materials and / or adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0068] The first binder in the first negative active material layer may satisfy a content within a range consisting of one lower limit selected from 0.1 wt% or more, 0.5 wt% or more, 1.0 wt% or more, 1.5 wt% or more, 2.0 wt% or more, and 2.5 wt% or more, and one upper limit selected from 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, and 5 wt% or less, based on the total weight of the first negative active material layer.

[0069] The thickness of the first cathode active material layer is 30 μm or more to 200 μm or less, preferably 35 μm or more to 100 μm or less, 40 μm or more to 60 μm or less, or 45 μm or more to 50 μm or less, but is not limited thereto.

[0070] The weight per unit area of ​​the first negative electrode active material layer is 5 g / cm² 3 From 35 g / cm² or more 3It may be less than or equal to, preferably 10 g / cm³ 3 From 30 g / cm³ or more 3 Below, more preferably 15 g / cm² 3 From 20 g / cm² or more 3 It may be less than, but is not limited to.

[0071] The loading amount of the first negative electrode active material layer is 1.0 mAh / cm 2 From 0 to 5.0 mAh / cm² 2 It may be less than or equal to, preferably 1.5 mAh / cm² 2 From 4.5 mAh / cm² 2 It may be less than or equal to, and more preferably 2.0 mAh / cm² 2 From 4.0 mAh / cm² or higher 2 It may be less than, but is not limited to.

[0072] The second negative active material layer is disposed on the first negative active material layer. If the first negative active material layer is disposed on one or both sides of the negative current collector, the second negative active material layer may also be disposed on the first negative active material layer disposed on one or both sides of the negative current collector.

[0073] The second negative electrode active material layer may include a second solid electrolyte.

[0074] The second solid electrolyte mentioned above may include, but is not limited to, sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, and / or halide-based solid electrolytes. The above description may be applied in the same way to the sulfide-based solid electrolyte, oxide-based solid electrolyte, polymer-based solid electrolyte, and halide-based solid electrolyte.

[0075] The second solid electrolyte may comprise a material identical to or different from the first solid electrolyte. For example, the second solid electrolyte may comprise a sulfide-based solid electrolyte. Specifically, the second solid electrolyte may comprise an azirodite-based sulfide solid electrolyte, but is not limited thereto.

[0076] The second solid electrolyte included in the second negative electrode active material layer may be included in an amount of 9 weight% or more to 40 weight% or less based on the total weight of the second negative electrode active material layer, but is not limited thereto. For example, the second solid electrolyte included in the second negative electrode active material layer may satisfy a content within a range consisting of one lower limit selected from 9 weight% or more, 12 weight% or more, 15 weight% or more, 18 weight% or more, 20 weight% or more, 22 weight% or more, 25 weight% or more, 27 weight% or more, and 28 weight% or more based on the total weight of the second negative electrode active material layer, and one upper limit selected from 40 weight% or less, 38 weight% or less, 36 weight% or less, 34 weight% or less, 32 weight% or less, and 30 weight% or less. If the content of the second solid electrolyte is less than 9 weight%, the ion conductivity inside the electrode may decrease, causing problems with performance, and if it exceeds 40 weight%, the electrode thickness may increase, causing problems with increased resistance.

[0077] The above cathode may contain the second solid electrolyte in a greater amount than the first solid electrolyte.

[0078] The second negative active material layer may additionally include a second conductive material.

[0079] The second conductive material may be used to improve the conductivity of the second cathode active material layer, and may be used without special limitations as long as it is conductive without causing chemical changes. Examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjenblack, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and may include one of these alone or a mixture of two or more. As an example, the second conductive material may include carbon-based materials such as carbon black, acetylene black, ketjenblack, channel black, furnace black, lamp black, thermal black, and carbon fibers. For example, Super C65 may be used as the second conductive material, but is not limited thereto.

[0080] The first conductive material may be the same as the second conductive material, or they may be different from each other.

[0081] The second conductive material may be included in the second negative active material layer in an amount greater than 0 weight% to 0.5 weight% or less based on the total weight of the second negative active material layer, but is not limited thereto. For example, the second conductive material may be in an amount of 0.1 weight% or more to 0.5 weight% or less, preferably 0.2 weight% or more to 0.5 weight% or less, and more preferably 0.3 weight% or more to 0.5 weight% or less based on the total weight of the second negative active material layer. When the content of the second conductive material is controlled as described above, the occurrence of side reactions between the solid electrolyte and the second conductive material can be suppressed while ensuring electrical conductivity.

[0082] The conductive material included in the above-mentioned cathode may be included only in the first cathode active material layer, or the first conductive material included in the first cathode active material layer may be included in a larger amount than the second conductive material included in the second cathode active material layer. By forming the second cathode active material layer with a low conductive material content on the solid electrolyte layer interface side, capacity loss due to side reactions between carbon and the solid electrolyte can be suppressed, and the first cathode active material layer formed on the cathode current collector interface side has a relatively high conductive material content, thereby improving conductivity and thereby improving the capacity and / or lifespan performance of the secondary battery.

[0083] The ratio of the weight of the second solid electrolyte to the weight of the second conductive material in the second cathode active material layer may be 15 or more to 800 or less, but is not limited thereto. For example, the ratio of the weight of the second solid electrolyte to the weight of the second conductive material may satisfy any one weight ratio selected from 15 or more to 800 or less, 20 or more to 700 or less, 30 or more to 600 or less, 40 or more to 500 or less, 50 or more to 400 or less, 55 or more to 300 or less, and 58 or more to 200 or less.

[0084] The second negative electrode active material layer may include a second negative electrode active material. The second negative electrode active material may be a negative electrode active material commonly used in secondary batteries. Examples include carbonaceous materials such as graphite, artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Ag, Au, Si alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, 바나듐 산화물, 또는 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 예를들어 상기 인조 흑연과 천연 흑연을 1 : 1 이상 내지 10 : 1 이하, 2 : 1 이상 내지 9 : 1 이하, 또는 3 : 1 이상 내지 8 : 1 이하의 중량비 범위로 혼합할 수 있으나 이에 제한되지 않는다. 일예로 상기 인조 흑연 및 천연 흑연은 4 : 1의 중량비로 혼합되어 음극 활물질로 포함될 수 있다. 상기 음극 활물질로서 금속 리튬 박막이 사용될 수도 있다. 상기 탄소질 재료는 저결정 탄소 및 고결정성 탄소 등이 모두 사용될 수 있다. 저결정성 탄소로는 연화탄소 (soft carbon) 및 경화탄소 (hard carbon)가 대표적이며, 고결정성 탄소로는 무정형, 판상, 인편상, 구형 또는 섬유형의 천연 흑연 또는 인조 흑연, 키시흑연 (Kish graphite), 열분해 탄소 (pyrolytic carbon), 메조페이스 피치계 탄소섬유 (mesophase pitch based carbon fiber), 탄소 미소구체 (meso-carbon microbeads), 메조페이스 피치 (Mesophase pitches), 또는 석유와 석탄계 코크스 (petroleum or coal tar pitch derived cokes) 등의 고온 소성탄소가 대표적이다. 또한 경우에 따라 상기 음극 활물질 층은 생략될 수 있고, 이 경우 상기 음극은 음극 집전체를 포함하는 것이거나, 또는 상기 음극 집전체 및 상기 음극 집전체 상에 형성된 보호층을 포함하는 것일 수 있으나, 이에 한정되는 것은 아니다.

[0085] The description of the material that may be included as the first cathode active material can be applied in the same way to the second cathode active material. The second cathode active material may include a material that is identical to or different from the first cathode active material. The second cathode active material may preferably include graphite.

[0086] The second negative active material in the second negative active material layer may satisfy a content selected from any one range of 59.5 wt% or more to less than 91 wt%, 60 wt% or more to 90 wt% or less, 61 wt% or more to 85 wt% or less, 62 wt% or more to 80 wt% or less, 63 wt% or more to 75 wt% or less, 64 wt% or more to 70 wt% or less, and 65 wt% or more to 70 wt% or less, based on the total weight of the second negative active material layer, but is not limited thereto.

[0087] Average particle size (D) of the second negative electrode active material above 50 ) may be 5 μm or more to 50 μm or less, specifically 10 μm or more to 20 μm or less, but is not limited thereto.

[0088] The second negative active material layer may include a second binder, and the second binder may be described in the same way as the first binder. The second binder may include a material that is the same as or different from the first binder.

[0089] The second binder in the second negative active material layer may satisfy a content within a range consisting of one lower limit selected from 0.1 wt% or more, 0.5 wt% or more, 1.0 wt% or more, 1.5 wt% or more, 2.0 wt% or more, and 2.5 wt% or more, and one upper limit selected from 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, 10 wt% or less, and 5 wt% or less, based on the total weight of the second negative active material layer.

[0090] The thickness of the second cathode active material layer is 30 μm or more to 200 μm or less, preferably 35 μm or more to 100 μm or less, more preferably 45 μm or more to 50 μm or less, but is not limited thereto.

[0091] The weight per unit area of ​​the second cathode active material layer is 5 g / cm² 3 From 35 g / cm² or more 3 It may be less than or equal to, preferably 10 g / cm³ 3 From 30 g / cm³ or more 3 Below, more preferably 15 g / cm² 3 From 20 g / cm² or more 3 It may be less than, but is not limited to.

[0092] The loading amount of the second negative electrode active material layer is 1.0 mAh / cm 2 From 0 to 5.0 mAh / cm² 2 It may be less than or equal to, preferably 1.5 mAh / cm² 2 From 4.5 mAh / cm² 2 It may be less than or equal to, and more preferably 2.0 mAh / cm² 2 From 4.0 mAh / cm² or higher 2 It may be less than, but is not limited to.

[0093] Based on 100 parts by weight of the first solid electrolyte, the second solid electrolyte may be included in an amount of 20 parts by weight or more to 500 parts by weight or less, but is not limited thereto. For example, based on 100 parts by weight of the first solid electrolyte, the second solid electrolyte may be 20 parts by weight or more to 500 parts by weight or less, 60 parts by weight or more to 400 parts by weight or less, 70 parts by weight or more to 300 parts by weight or less, 80 parts by weight or more to 200 parts by weight or less, 90 parts by weight or more to 150 parts by weight or less, 100 parts by weight or more to 140 parts by weight or less, or 100 parts by weight or more to 130 parts by weight or less. In addition, based on 100 parts by weight of the first solid electrolyte, the second solid electrolyte may be 100 parts by weight or more to 500 parts by weight or less, 100 parts by weight or more to 450 parts by weight or less, 100 parts by weight or more to 400 parts by weight or less, or 100 parts by weight or more to 350 parts by weight or less. When the content of the second solid electrolyte relative to 100 parts by weight of the first solid electrolyte satisfies the above range, interfacial stability between the negative electrode and the electrolyte can be improved, or there is an effect of improving the capacity and / or life characteristics of the battery.

[0094] The ratio of the weight of the first conductive material to the weight of the second conductive material may satisfy any one of the following ranges, for example: greater than 1 to 200 or less, greater than 1 to 150 or less, greater than 1 to 100 or less, greater than 1 to 50 or less, greater than 1 to 40 or less, greater than 2 to 30 or less, greater than 4 to 20 or less, and greater than 5 to 10 or less. When the weight ratio of the first conductive material to the second conductive material satisfies the above range, interface stability between the negative electrode and the electrolyte can be improved, or there is an effect of improving the capacity and / or life characteristics of the battery.

[0095] Based on 100 parts by weight of the first negative electrode active material layer, the second negative electrode active material layer may be included in an amount of 40 parts by weight or more to 240 parts by weight or less, but is not limited thereto. For example, based on 100 parts by weight of the first negative electrode active material layer, the second negative electrode active material layer may be included in an amount of 42 parts by weight or more to 235 parts by weight or less, 50 parts by weight or more to 200 parts by weight or less, 53 parts by weight or more to 186 parts by weight or less, 60 parts by weight or more to 180 parts by weight or less, or 66 parts by weight or more to 150 parts by weight or less. When the content of the second negative electrode active material layer based on 100 parts by weight of the first negative electrode active material layer satisfies the above range, interfacial stability between the negative electrode and the electrolyte can be improved, or there is an effect of improving the capacity and / or lifespan characteristics of the battery.

[0096] The above cathode may additionally include cathode additives. For example, it may further include additives such as fillers, coating agents, dispersants, thickeners, and ion conductivity aids, and any known material generally used for electrodes may be used without limitation.

[0097] In another example, the above-mentioned negative electrode may be a negative electrode for an anodeless battery that does not include a negative electrode active material layer immediately after battery manufacturing, and forms a negative electrode active material layer such as a lithium metal layer through battery charging.

[0098] As another aspect of the present invention, a method for manufacturing the cathode can be provided.

[0099] The method for manufacturing the above cathode may include the steps of: preparing a composition for forming a first cathode active material layer comprising a first conductive material and a first solid electrolyte; preparing a composition for forming a second cathode active material layer comprising a second solid electrolyte; forming a first cathode active material layer on a cathode current collector using the composition for forming a first cathode active material layer; and forming a second cathode active material layer on the first cathode active material layer using the composition for forming a second cathode active material layer.

[0100] The composition for forming the first negative electrode active material layer may further include a first negative electrode active material. Additionally, the composition for forming the first negative electrode active material layer may further include a first binder.

[0101] The step of preparing the composition for forming the first cathode active material layer may include, for example, the step of preparing the composition for forming the first cathode active material layer by mixing the first cathode active material, the first conductive material, the first solid electrolyte, and the first binder.

[0102] The description of the first cathode active material, the first conductive material, the first solid electrolyte, and the first binder above can be applied in the same way as the description above.

[0103] The composition for forming the second negative electrode active material layer may additionally include a second negative electrode active material. Additionally, the composition for forming the second negative electrode active material layer may additionally include a second conductive material. Additionally, the composition for forming the second negative electrode active material layer may additionally include a second binder.

[0104] The step of preparing the composition for forming the second cathode active material layer may include, for example, a step of preparing the composition for forming the second cathode active material layer by mixing the second cathode active material, the second solid electrolyte, and the second binder, or a step of preparing the composition for forming the second cathode active material layer by mixing the second cathode active material, the second conductive material, the second solid electrolyte, and the second binder.

[0105] The description of the second negative electrode active material, the second conductive material, the second solid electrolyte, and the second binder can be applied in the same way as the description above.

[0106] The step of forming a first cathode active material layer on the cathode current collector using the composition for forming the first cathode active material layer can specifically use a slurry coating process.

[0107] The description of the above-mentioned negative current collector and the above-mentioned first negative active material layer can be applied in the same way as the description above.

[0108] Specifically, the step of forming a second cathode active material layer on the first cathode active material layer using the composition for forming the second cathode active material layer may utilize a slurry coating process.

[0109] The description of the second negative electrode active material layer above can be applied in the same way as the description above.

[0110] For example, the step of forming the negative electrode active material layer comprises mixing the composition for forming the first negative electrode active material layer and the slurry solvent for the first negative electrode active material layer to produce a slurry for forming the first negative electrode active material layer, and mixing the composition for forming the second negative electrode active material layer and the slurry solvent for the second negative electrode active material layer to produce a slurry for forming the second negative electrode active material layer. Subsequently, the negative electrode may be manufactured by including the step of applying the slurry for forming the first negative electrode active material layer onto a negative electrode current collector and drying the applied first negative electrode active material layer, and then applying and rolling the slurry for forming the second negative electrode active material layer and drying it. Alternatively, the negative electrode may be manufactured by including the step of applying the slurry for forming the first negative electrode active material layer onto a negative electrode current collector and, before drying the applied first negative electrode active material layer, applying and rolling the slurry for forming the second negative electrode active material layer and drying it. At this time, the drying may be performed for 10 hours in a vacuum oven at 130°C, for example, but is not limited thereto.

[0111] One aspect of the present invention is to provide a secondary battery comprising the negative electrode.

[0112] The secondary battery of the present invention may include a positive electrode, an electrolyte, and a negative electrode.

[0113] In the above secondary battery, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0114] The above positive current collector may be subject to the same provisions as the above negative current collector. The above positive current collector may include a material identical to or different from the above negative current collector.

[0115] The above positive active material layer may optionally include a binder, a conductive material, an electrolyte and / or additives together with the positive active material.

[0116] The above-mentioned positive active material may be a positive active material commonly used in lithium secondary batteries. Specifically, the above-mentioned positive active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a material with the chemical formula Li (1-b) (Ni x M 1 (1-x) )M 2 y O2(here M 1 is at least one selected from Co and Mn, and M 2 is at least one selected from Al, Zr, B, W, Mo, Cr, Ta, Nb, Mg, Ce, Hf, La, Ti, Sr, Ba, F, P, S, Na, Si, and Y, and 0 <b<0.1, 0.3≤x≤1, 0≤y≤0.1)의 층상구조 화합물; LiFe3O4등의 리튬 철 산화물; 화학식 Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3A lithium manganese complex oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; a lithium iron phosphate compound (LFP) having the chemical formula LiFePO4, for example; LiFe x M1 (1-x) P y M2 (1-y) O4(wherein, M1 = 1 or more of Mn, Co, Ni, Al, V, B, Cd, Cu, Mg, Zn, Ti, Nb, Zr and Cr, and 0 <x≤1, M2 = Si, N, S, Cl, Br, 및 F 중 1 이상이며, 0<y≤1)의 화학식을 갖는 리튬 철 금속 인산화물(LMFP); 등을 들 수 있지만, 이들만으로 한정되는 것은 아니다. 상기 양극은 Li-metal일 수도 있다.

[0117] Average particle size (D of the above positive active material) 50 ) may be 1 μm or more to 50 μm or less, specifically 5 μm or more to 20 μm or less, but is not limited thereto.

[0118] The content of the above positive active material may be 50% by weight or more to 90% by weight or less, preferably 70% by weight or more to 85% by weight or less, based on the total weight of the above positive active material layer, but is not limited thereto.

[0119] The conductive material and binder that may be included in the positive active material layer may include materials that are the same as or different from the binder and conductive material used in the negative active material layer.

[0120] The conductive material of the positive active material layer may be included in an amount of 0.1% by weight or more to 5% by weight or less, preferably 0.1% by weight or more to 2% by weight or less, based on the total weight of the positive active material layer, but is not limited thereto.

[0121] The binder of the positive active material layer may be included in an amount of 0.5% by weight or more to 1.5% by weight or less, preferably 0.7% by weight or more to 1.4% by weight or less, and more preferably 0.9% by weight or more to 1.3% by weight or less, based on the total weight of the positive active material layer, but is not limited thereto.

[0122] The thickness of the above positive active material layer is 50 μm or more to 200 μm or less, preferably 70 μm or more to 150 μm or less, more preferably 90 μm or more to 120 μm or less, but is not limited thereto.

[0123] The loading amount of the above positive active material layer is 1.0 mAh / cm² 2 From 6.0 mAh / cm² or higher 2 It may be less than or equal to, preferably 2.5 mAh / cm² 2 From 0 to 5.0 mAh / cm² 2 It may be less than or equal to, and more preferably 3.5 mAh / cm² 2 From 4.5 mAh / cm² 2 It may be less than, but is not limited to.

[0124] In the above secondary battery, the negative electrode is as described above.

[0125] The above secondary battery includes a lithium secondary battery and may include a structure comprising a positive electrode, a negative electrode, an electrolyte, and / or a separator as a conventional secondary battery, but preferably, as an all-solid-state battery, when a solid electrolyte is used as the electrolyte, the separator may be omitted because the solid electrolyte acts as the separator. In addition, the above secondary battery may be a semi-solid-state battery, in which case it may include a separate polymer separator.

[0126] In the case where the electrolyte included in the above secondary battery includes a solid electrolyte, the above secondary battery may be characterized as being an all-solid-state battery.

[0127] In the case of the above-mentioned conventional secondary battery, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery, but is not limited to these.

[0128] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0129] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0130] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, as the anion of the above lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may be at least one selected from the group consisting of, and the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2.

[0131] The above-mentioned solid inorganic electrolyte may include oxide-based solid electrolytes, sulfide-based solid electrolytes, or halide-based solid electrolytes. The above-mentioned description may apply equally to the oxide-based solid electrolytes, sulfide-based solid electrolytes, or halide-based solid electrolytes.

[0132] In addition, the separator separates the negative and positive electrodes and provides a pathway for the movement of lithium ions; generally, if it is used as a separator in a secondary battery, it can be used without any special restrictions. Furthermore, if the electrolyte includes a solid electrolyte, the separator may include a solid electrolyte, and the solid electrolyte may perform the role of a separator.

[0133] Specifically, a porous polymer film made of a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. A coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0134] The above secondary battery may be pouch-type, prismatic-type, or cylindrical, and its shape and size may be applied without restriction as long as it is a commonly used secondary battery.

[0135] Additionally, the secondary battery may further include a case capable of sealing the electrode assembly, such as a container, pouch, pack, or module, for housing the electrode assembly comprising the positive electrode, electrolyte, and negative electrode. The case may optionally further include a sealing member.

[0136] In the following, the present invention is described in detail with reference to examples to specifically explain the disclosure of the present invention as described above and the intended functions and effects of the present invention. However, the examples may be modified in various different forms, and the scope of this specification is not to be interpreted as being limited only to these examples. It is emphasized that the examples are provided to represent the present invention and to explain it more specifically to those skilled in the art.

[0137]

[0138] Examples and Comparative Examples

[0139] Example 1.

[0140] A composition for forming a first negative electrode active material layer was prepared, comprising 66.15 wt% of graphite as the first negative electrode active material, 28.35 wt% of LPSCl as the first solid electrolyte, 3.0 wt% of Super C65 as the first conductive material, and 2.5 wt% of SBR rubber binder as the first binder.

[0141] A composition for forming a second negative electrode active material layer was prepared, comprising 67.9 wt% of graphite as the second negative electrode active material, 29.1 wt% of LPSCl as the second solid electrolyte, 0.5 wt% of Super C65 as the second conductive material, and 2.5 wt% of SBR rubber binder as the second binder.

[0142] A stainless steel (SUS) with a thickness of 10 μm was prepared as a negative electrode current collector. The composition for forming the first negative electrode active material layer was applied onto the current collector, and the first negative electrode active material layer was formed by rolling and drying.

[0143] A cathode was manufactured by applying a composition for forming a cathode active material layer onto a first cathode active material layer formed on the above current collector, rolling it, and drying it to form a second cathode active material layer.

[0144] A composition for forming an anode active material layer was prepared comprising 83 wt% of NCM811 as an anode active material, 15 wt% of LPSCl as a solid electrolyte, 1 wt% of carbon nanofiber (CNF) as an anode conductive material, and 1 wt% of SBR rubber binder as an anode binder.

[0145] Aluminum with a thickness of 14 μm was prepared as a positive current collector. A positive active material layer forming composition prepared above was applied onto the current collector, and a positive active material layer was formed by rolling and drying the composition to manufacture a positive electrode.

[0146] A secondary battery was manufactured by interposing a solid electrolyte layer containing LPSCl, a solid electrolyte, between the cathode and anode manufactured above.

[0147] Example 2.

[0148] A composition for forming a first negative electrode active material layer was prepared, comprising 66.15 wt% of graphite as the first negative electrode active material, 28.35 wt% of LPSCl as the first solid electrolyte, 3.0 wt% of Super C65 as the first conductive material, and 2.5 wt% of SBR rubber binder as the first binder.

[0149] A composition for forming a second negative electrode active material layer was prepared, comprising 68.25 wt% of graphite as the second negative electrode active material, 29.25 wt% of LPSCl as the second solid electrolyte, and 2.5 wt% of SBR rubber binder as the second binder.

[0150] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0151] Example 3.

[0152] A composition for forming a first negative electrode active material layer was prepared, comprising 64.75 wt% of graphite as the first negative electrode active material, 27.75 wt% of LPSCl as the first solid electrolyte, 5.0 wt% of Super C65 as the first conductive material, and 2.5 wt% of SBR rubber binder as the first binder.

[0153] A composition for forming a second negative electrode active material layer was prepared, comprising 67.9 wt% of graphite as the second negative electrode active material, 29.1 wt% of LPSCl as the second solid electrolyte, 0.5 wt% of Super C65 as the second conductive material, and 2.5 wt% of SBR rubber binder as the second binder.

[0154] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0155] Comparative Example 1.

[0156] A composition for forming a negative electrode active material layer was prepared comprising 67.9 wt% of graphite as a negative electrode active material, 29.1 wt% of LPSCl as a solid electrolyte, 0.5 wt% of Super C65 as a conductive material, and 2.5 wt% of SBR rubber binder as a binder.

[0157] A stainless steel (SUS) with a thickness of 10 μm was prepared as a negative electrode current collector. A negative electrode was manufactured by applying a composition for forming a negative electrode active material layer onto the current collector, rolling it, and drying it to form a negative electrode active material layer.

[0158] A secondary battery was manufactured in the same manner as in Example 1, except for using the above-mentioned negative electrode.

[0159] Comparative Example 2.

[0160] A composition for forming a first negative electrode active material layer was prepared comprising 94.5 wt% of graphite as the first negative electrode active material, 3.0 wt% of Super C65 as the first conductive material, and 2.5 wt% of an SBR rubber binder as the first binder. The first negative electrode active material layer did not contain a solid electrolyte.

[0161] A composition for forming a second negative electrode active material layer was prepared comprising 97.0 wt% of graphite as the second negative electrode active material, 0.5 wt% of Super C65 as the second conductive material, and 2.5 wt% of SBR rubber binder as the second binder. The second negative electrode active material layer did not contain a solid electrolyte.

[0162] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0163] Comparative Example 3.

[0164] A composition for forming a first negative electrode active material layer was prepared, comprising 68.25 wt% of graphite as the first negative electrode active material, 29.25 wt% of LPSCl as the first solid electrolyte, and 2.5 wt% of SBR rubber binder as the first binder.

[0165] A composition for forming a second negative electrode active material layer was prepared, comprising 78 wt% of graphite as the second negative electrode active material, 19.5 wt% of LPSCl as the second solid electrolyte, and 2.5 wt% of SBR rubber binder as the second binder.

[0166] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0167] Comparative Example 4.

[0168] A composition for forming a first negative electrode active material layer was prepared, comprising 66.15 wt% of graphite as the first negative electrode active material, 28.35 wt% of LPSCl as the first solid electrolyte, 3.0 wt% of Super C65 as the first conductive material, and 2.5 wt% of SBR rubber binder as the first binder.

[0169] A composition for forming a second negative electrode active material layer was prepared, comprising 97 wt% of graphite as the second negative electrode active material, 0.5 wt% of Super C65 as the second conductive material, and 2.5 wt% of SBR rubber binder as the second binder.

[0170] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0171] Comparative Example 5.

[0172] A composition for forming a first negative electrode active material layer was prepared, comprising 68.25 wt% of graphite as the first negative electrode active material, 29.25 wt% of LPSCl as the first solid electrolyte, and 2.5 wt% of SBR rubber binder as the first binder.

[0173] A composition for forming a second negative electrode active material layer was prepared, comprising 97.5 wt% of graphite as the second negative electrode active material and 2.5 wt% of SBR rubber binder as the second binder.

[0174] A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the composition for forming the first negative electrode active material layer and the composition for forming the second negative electrode active material layer were prepared as described above.

[0175]

[0176] Experimental Example

[0177] Experimental Example 1. Evaluation of lifespan characteristics of a secondary battery

[0178] A schematic diagram of the cathodes prepared in Examples 1 to 3 is shown in FIG. 1, and a schematic diagram of the cathodes prepared in Comparative Examples 1 to 5 is shown in FIG. 2.

[0179] To evaluate the lifespan characteristics of the secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5, the capacity retention rate for each secondary battery was measured at the following operating voltage range and an operating temperature of 60°C. The specific charge and discharge conditions are as follows.

[0180] (Charging / Discharging Conditions)

[0181] Charging: 0.33C, 4.2V, CC / CV, 0.1C cut-off

[0182] Discharge: 0.33C, 3.0V, CC

[0183] Under the conditions described above, 20 charge-discharge cycles were repeated, and the capacity retention rate of each secondary battery was measured by comparing the discharge capacity of the first cycle with the discharge capacity of the 20th cycle. The capacity changes over 20 cycles of Examples 1 to 3 are shown in FIGS. 3 to 5, and the capacity changes over 20 cycles of Comparative Examples 1 to 5 are shown in FIGS. 6 to 10. The measured capacity retention rates of each secondary battery are shown in Table 1 below.

[0184] Classification Capacity Retention Rate (%) (0.33C, 20 cycles) Example 198.8 Example 298.6 Example 398.4 Comparative Example 194.3 Comparative Example 284.1 Comparative Example 391.3 Comparative Example 488.2 Comparative Example 585.6

[0185]

[0186] As can be seen from the results above, it was confirmed that Examples 1 to 3, which include the configuration of the present invention, showed a high capacity retention rate of 98.4% to 98.8%.

Claims

1. Cathode current collector; A first negative active material layer comprising a first conductive material and a first solid electrolyte; and A second negative active material layer comprising a second solid electrolyte; This sequentially stacked cathode.

2. In Paragraph 1, The first solid electrolyte is included in an amount of 9% by weight or more to 38% by weight or less based on the total weight of the first negative electrode active material layer, and The cathode, wherein the second solid electrolyte is included in an amount of 9% or more to 40% or less based on the total weight of the second cathode active material layer.

3. In Paragraph 1, A cathode in which the second solid electrolyte is contained in a greater amount than the first solid electrolyte.

4. In Paragraph 1, A cathode comprising, based on 100 parts by weight of the first solid electrolyte, 20 parts by weight or more and 500 parts by weight or less of the second solid electrolyte.

5. In Paragraph 1, A cathode wherein the first solid electrolyte and the second solid electrolyte each independently comprise one or more selected from sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, and halide-based solid electrolytes.

6. In Paragraph 1, A cathode wherein the first solid electrolyte and the second solid electrolyte each independently comprise an azirodite-based sulfide-based solid electrolyte.

7. In Paragraph 1, A cathode comprising the first conductive material in an amount of more than 0.5 weight% to 10 weight% or less based on the total weight of the first cathode active material layer.

8. In Paragraph 1, The cathode, wherein the second cathode active material layer further comprises a second conductive material.

9. In Paragraph 8, The cathode, wherein the second conductive material is included in an amount of more than 0 weight% to 0.5 weight% or less based on the total weight of the second cathode active material layer.

10. In Paragraph 8, A cathode wherein the first conductive material and the second conductive material each comprise one or more selected from graphite, carbon black, conductive fiber, carbon nanotube, fluorocarbon, metal powder, conductive whisker, conductive metal oxide, and polyphenylene derivative.

11. In Paragraph 8, A cathode having a ratio of the weight of the second solid electrolyte to the weight of the second conductive material of 15 or more to 800 or less.

12. In Paragraph 1, A cathode in which the ratio of the weight of the first solid electrolyte to the weight of the first conductive material is 0.9 or more and less than 76.

13. In Paragraph 1, The first negative electrode active material layer comprises the first negative electrode active material, and The second negative electrode active material layer comprises a second negative electrode active material, A cathode in which the first cathode active material and the second cathode active material each independently comprise graphite.

14. In Paragraph 1, A cathode comprising, based on 100 parts by weight of the first cathode active material layer, 40 parts by weight or more and 240 parts by weight or less of the second cathode active material layer.

15. In Paragraph 1, The thickness of the first negative electrode active material layer is 30 μm or more to 200 μm or less, and A cathode having a thickness of 30 μm or more to 200 μm or less of the second cathode active material layer.

16. A secondary battery comprising a negative electrode according to any one of claims 1 to 15.

17. In Paragraph 16, A secondary battery characterized in that the above secondary battery is a solid-state battery.

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