Positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode comprising: a positive electrode active material; a solid electrolyte; a linear conductive material; and a rubber-based binder, wherein the linear conductive material and the rubber-based binder are included in a weight ratio of 0.45:1 to 4:1.

Description

Anode and lithium secondary battery including the same

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

[0002] With the increasing technological development and demand for various electronic devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, those featuring high energy density and voltage, long cycle life, and low self-discharge rates have been commercialized and are widely used. Consequently, there is a growing demand from the industry to improve the performance of secondary batteries.

[0003] A battery in which the liquid electrolyte used in conventional secondary batteries is replaced with a solid electrolyte is called an all-solid-state battery. All-solid-state batteries have the advantage of significantly improving safety because they do not use flammable solvents, so there is absolutely no risk of ignition or explosion caused by decomposition reactions of conventional electrolytes.

[0004] In these all-solid-state batteries, lithium ion conduction occurs at the interface through a solid electrolyte in powder form. Therefore, to maximize lithium ion conduction between particles within the all-solid-state battery and to prevent contact loss between particles due to volume changes during charging and discharging, secondary batteries using solid electrolytes require a pressurization process during manufacturing and also during battery operation.

[0005] Pressurization methods using jigs are known to ensure the smooth operation of all-solid-state batteries. Recently, as a type of isostatic pressurization method, batteries are also manufactured by rolling the anode through high-pressure pressurization, such as WIP (Warm Isostatic Press). Furthermore, while all-solid-state batteries require maintaining high operating pressure for stable operation, maintaining this high pressure necessitates an external pressurization system for the secondary battery, which leads to problems such as reduced energy density and capacity.

[0006] Accordingly, methods such as modifying the electrode binder or coating the positive electrode active material to improve contact between interfaces have been studied, but there are still limitations in lowering the operating pressure of all-solid-state batteries.

[0007] The present invention is designed to solve the above problems and provides an anode that reduces battery driving pressure by enhancing electrode properties through the use of a linear conductive material instead of a conventional point-type conductive material and a rubber-based binder as the conductive material included in the anode.

[0008] In addition, by adjusting the weight ratio of the linear conductive material and the rubber-based binder, we aim to provide an electrode that maintains contact between the conductive material and the particles within the anode even at low driving pressure and exhibits excellent flexibility in response to volume changes, thereby providing a lithium secondary battery with excellent electrochemical performance.

[0009] The present invention relates to an anode comprising an anode active material; a solid electrolyte; a linear conductive material; and a rubber-based binder, wherein the linear conductive material and the rubber-based binder are included in a weight ratio of 0.45:1 or more to 4:1 or less.

[0010] In one embodiment, the linear conductive material may include a carbon material.

[0011] In one embodiment, the linear conductive material may comprise one or more selected from carbon nanofibers, carbon fibers, carbon nanotubes, and carbon nanowires.

[0012] In one embodiment, the linear conductive material may include carbon nanofibers (CNF).

[0013] In one embodiment, the linear conductive material may have an aspect ratio of 10 or more to 100 or less.

[0014] In one embodiment, the linear conductive material may have a length of 5 μm or more to 25 μm or less.

[0015] In one embodiment, the linear conductive material may have a length of 9 μm or more to 14 μm or less.

[0016] In one embodiment, the rubber-based binder may comprise one or more selected from butadiene rubber (BR), styrene butadiene rubber (SBR), solution styrene butadiene rubber (SSBR), styrene ethylene butylene styrene (SEBS), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), hydrogenated styrene butadiene rubber (HSBR), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM rubber, and fluororubber.

[0017] In one embodiment, the solid electrolyte may comprise one or more selected from sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, and halide-based solid electrolytes.

[0018] In one embodiment, the anode may have a minimum diameter of cylindrical mandrel at which cracking begins to occur, when evaluating whether cracking occurs using a plurality of cylindrical mandrels with varying diameters according to the standard method of JIS K5600-5-1, such that the minimum diameter of the cylindrical mandrel at which cracking begins to occur is 1 mm or more to 9 mm or less.

[0019] In addition, the present invention relates to a lithium secondary battery comprising a positive electrode active material, a solid electrolyte, a linear conductive material, and a rubber-based binder, wherein the positive electrode comprises the linear conductive material and the rubber-based binder in a weight ratio of 0.45:1 or more to 4:1 or less.

[0020] In one embodiment, the lithium secondary battery may have a driving pressure of 1 MPa or more and 30 MPa or less.

[0021] In one embodiment, the lithium secondary battery may have an absolute value of the rate of change of the discharge capacity retention rate according to the change in driving pressure represented by the following Equation 1, which is 1 or less.

[0022] [Equation 1]

[0023] │(1st discharge capacity retention rate - 2nd discharge capacity retention rate) / (1st driving pressure - 2nd driving pressure)│

[0024] In the above Equation 1,

[0025] The above first discharge capacity retention rate refers to the discharge capacity retention rate in n cycles of charging and discharging at 0.33 C at the first driving pressure, and

[0026] The above second discharge capacity retention rate refers to the discharge capacity retention rate in n cycles of charging and discharging at 0.33 C at the second driving pressure, and

[0027] The first discharge capacity retention rate is the discharge capacity (Q) in one charge and discharge cycle at 0.33 C at the first driving pressure. a1 Discharge capacity (Q) in n cycles relative to ) an It is a percentage of the ratio of ),

[0028] The above second discharge capacity retention rate is the discharge capacity (Q) in one charge and discharge cycle at 0.33 C at the above second driving pressure. b1 Discharge capacity at n cycles relative to ) Qbn It is a percentage of the ratio of ),

[0029] The above n is an integer selected from 10 or more to 100 or less, and

[0030] The first driving pressure and the second driving pressure are each independently selected values ​​ranging from 1 MPa or more to 30 MPa or less, and

[0031] The first driving pressure is greater than the second driving pressure.

[0032] Since the anode of the present invention uses a linear conductive material, the electrode properties are enhanced compared to an anode using a point conductive material, which can increase the flexibility of the electrode and reduce the battery driving pressure.

[0033] In particular, by using a linear conductive material of a specific length to solve the dispersion problem within the electrode, and by adjusting the mixing weight ratio of the linear conductive material and the rubber-based binder, contact between the conductive material and the particles within the anode can be maintained even at low driving pressure, and a lithium secondary battery with excellent electrochemical performance can be provided that is flexible to volume changes due to charging and discharging.

[0034] Figure 1 is an image showing the results of testing the anode flexibility of Example 1 according to Experimental Example 3.

[0035] Figure 2 is an image showing the results of testing the anode flexibility of Comparative Example 1 according to Experimental Example 3.

[0036] Figure 3 is an image showing the evaluation results for the anode slurry of Comparative Example 4 according to Experimental Example 4.

[0037] Figure 4 is an image showing the evaluation results for the anode slurry of Comparative Example 5 according to Experimental Example 4.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 any range 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.

[0044] 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.

[0045] 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 normal pressure, that is, atmospheric pressure (about 1 atmosphere).

[0046] One aspect of the present invention relates to an anode.

[0047] The above anode is an anode comprising an anode active material; a solid electrolyte; a linear conductive material; and a rubber-based binder; wherein the linear conductive material and the rubber-based binder may be included in a weight ratio of 0.45:1 or more to 4:1 or less.

[0048] The above anode may include an anode current collector. The above anode may include an anode current collector and an anode active material layer formed on one or both sides of the anode current collector. In this case, the anode active material layer may include an anode active material, a solid electrolyte, a linear conductive material, and a rubber-based binder.

[0049] The above-mentioned positive active material is a material that serves as a source of lithium ions during charging and discharging, and may include a material capable of absorbing and releasing lithium ions. 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 c2Ni-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 c3 A 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.

[0050] The above-mentioned positive active material may further include a lithium ion conductive coating layer on its surface. The lithium ion conductive coating layer may include an oxide or a solid electrolyte. For example, the oxide may be LiNbO3, Li2ZrO3, or Li4Ti5O. 12 , LiBO 2, Alternatively, it may include Li3PO4, but is not limited thereto. The solid electrolyte may include the solid electrolyte described below, but is not limited thereto. The lithium ion conductive coating layer may be crystalline and may include amorphous.

[0051] The above positive active material may have a capacity per weight of 160 mAh / g or more. Specifically, it may be 165 mAh / g or more, 170 mAh / g or more, 175 mAh / g or more, or 180 mAh / g or more. In addition, the redox potential of the above positive active material may be 4.5 V or less.

[0052] The above positive active material may preferably include a compound with a layered structure, but is not limited thereto.

[0053] The above positive active material may be a primary particle, a secondary particle formed by the aggregation of primary particles, or a single particle in the form of a single crystal, but is not limited thereto.

[0054] Average particle size (D of the above positive active material) 50 ) may be 2 μm or more to 10 μm or less, specifically 3 μm or more to 8 μm or less, but is not limited thereto.

[0055] The above positive active material may be included in an amount of 50% by weight or more to 99% by weight or less, 50% by weight or more to 90% by weight or less, or 60% by weight or more to 80% by weight or less, based on the total weight of the above positive active material layer. When the content of the above positive active material satisfies the above range, the energy density of the lithium secondary battery can be increased even at low driving pressure, or the lifespan characteristics can be improved.

[0056] The above solid electrolyte may include oxide-based solid electrolytes, sulfide-based solid electrolytes, polymer-based solid electrolytes, halide-based solid electrolytes, or combinations thereof, but is not limited thereto, and any solid electrolyte other than a conventional liquid electrolyte may be used without limitation.

[0057] As the above oxide-based solid electrolyte, for example, Li xa La yaTiO3 [xa=0.3~0.7, ya=0.3~0.7](LLTO), Li xb La yb Zr zb Mbb mb O nb (Mbb is at least one element among Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, xb satisfies 5≤xb≤10, yb satisfies 1≤yb≤4, zb satisfies 1≤zb≤4, mb satisfies 0≤mb≤2, and nb satisfies 5≤nb≤20), Li xc B yc Mcc zc O nc (Mcc is at least one element among C, S, Al, Si, Ga, Ge, In, and Sn, xc satisfies 0≤xc≤5, yc satisfies 0≤yc≤1, zc satisfies 0≤zc≤1, and nc satisfies 0≤nc≤6), Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd (However, 1≤xd≤3, 0≤yd≤1, 0≤zd≤2, 0≤ad≤1, 1≤md≤7, 3≤nd≤13), Li (3-2xe) Mee xe DeeO(xe represents a number between 0 and 0.1, and Mee represents a divalent metal atom. Dee represents a halogen atom or a combination of two or more halogen atoms), Li xf Si yf O zf (1≤xf≤5, 0 <yf≤3, 1≤zf≤10), Li xg S yg O zg (1≤xg≤3, 0 <yg≤2, 1≤zg≤10), Li3BO3-Li2SO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li6BaLa2Ta2O 12 , Li3PO (4-3 / 2w) N w(w is w<1), Li having a LISICON (Lithium superionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La having a perovskite-type crystal structure 0.55 Li 0.35 LiTi2P3O having a TiO3, NASICON (Sodium(Na) superionic conductor) type crystal structure 12 , Li 1+xh+yh (Al, Ga) xh (Ti, Ge) 2-xh Si yh P3- yh O 12 (where 0≤xh≤1, 0≤yh≤1), Li7La3Zr2O having a garnet-type crystal structure 12 Examples include (LLZO). Alternatively, phosphorus compounds containing Li, P, and O may also be used. Examples include lithium phosphate (Li3PO4), LiPON in which some of the oxygen in lithium phosphate is substituted with nitrogen, LiPOD1 (where D1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au, etc.). Alternatively, LiA1ON (where A1 is at least one selected from Si, B, Ge, Al, C, and Ga, etc.) may also be used.

[0058] 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.

[0059] Specific sulfide-based solid electrolytes include, 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, Li 10 GeP2S 12 , or a azirodite-based sulfide solid electrolytes represented by Li6PS5X (where X is one or more halogen elements) may be used.

[0060] The above polymer-based solid electrolyte includes polymer materials that are ion-conducting materials and are typically used as solid electrolyte materials for all-solid-state batteries, but is not specifically limited thereto. The above 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 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.

[0061] The above polymer-based solid electrolyte may include a gel-type polymer electrolyte. The above gel-type polymer electrolyte comprises an organic electrolyte containing a lithium salt and a polymer resin, wherein the organic electrolyte comprises 60 to 400 parts by weight per 100 parts by weight of the polymer resin. The polymer resin applied to the above gel-type polymer electrolyte is not limited to specific components, but may include, for example, polyvinyl chloride (PVC), poly(Methyl methacrylate) (PMMA), polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), or poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP).

[0062] 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.

[0063] The above solid electrolyte may include a sulfide-based solid electrolyte, specifically an azirodite-based sulfide solid electrolyte, but is not limited thereto.

[0064] The solid electrolyte may be included in an amount of 0.1% to 40% by weight, 1% to 30% by weight, or 10% to 30% by weight, based on the total weight of the positive electrode active material layer. When the content of the solid electrolyte satisfies the above range, contact between the positive electrode active material and the solid electrolyte can be maintained, and ion conductivity can be improved to achieve excellent electrochemical performance.

[0065] The above-mentioned linear conductive material is used to impart conductivity to the electrode and may be used without special restrictions as long as it possesses electronic conductivity without causing chemical changes. The above-mentioned linear conductive material may include carbon materials. For example, the above-mentioned linear conductive material may refer to a conductive material containing carbon, or a conductive material having carbon as its main component. The above-mentioned linear conductive material is not limited thereto, provided it includes carbon materials.

[0066] The above linear conductive material may comprise, for example, one or more selected from carbon nanofibers (CNF), carbon fibers (CF), carbon nanotubes (CNT), and carbon nanowires.

[0067] The above linear conductive material may refer to a conductive material having an aspect ratio of 10 or more. The aspect ratio of the above conductive material is a value obtained by dividing the length of the major axis by the length of the minor axis, and may refer to the ratio of the length to the diameter of the cross-section.

[0068] The aspect ratio of the linear conductive material may have a range consisting of one lower limit selected from 10 or more, 12 or more, 14 or more, 15 or more, 16 or more, 18 or more, 20 or more, 22 or more, 24 or more, 25 or more, 26 or more, 28 or more, 30 or more, 35 or more, 40 or more, 45 or more, and 50 or more, and one upper limit selected from 100 or less, 95 or less, 90 or less, 85 or less, 80 or less, 75 or less, 70 or less, 65 or less, 60 or less, 55 or less, and 50 or less. Specifically, the aspect ratio of the linear conductive material may be 10 or more to 100 or less, 20 or more to 90 or less, 30 or more to 80 or less, 40 or more to 70 or less, or 40 or more to 60 or less. By using a linear conductive material having an aspect ratio within the range described above in the anode, a long conductive path can be secured in the anode, and compared to the case where a point-type conductive material such as conventional carbon black is used, contact with the solid electrolyte can be increased, and physical properties such as electrode flexibility can be enhanced, thereby reducing the driving pressure of the lithium secondary battery.

[0069] The above linear conductive material may include carbon nanofibers (CNF).

[0070] The above linear conductive material may include a length of 5 μm or more to 25 μm or less. For example, the above linear conductive material may have a range consisting of one lower limit selected from a length of 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, and 10 μm or more, and one upper limit selected from 25 μm or less, 24 μm or less, 23 μm or less, 22 μm or less, 21 μm or less, 20 μm or less, 19 μm or less, 18 μm or less, 17 μm or less, 16 μm or less, 15 μm or less, and 14 μm or less. Specifically, the above linear conductive material may have a length of 7 μm or more to 20 μm or less, 8 μm or more to 16 μm or less, or 9 μm or more to 14 μm or less. If the length of the linear conductive material is less than 5 μm, it is difficult to secure a sufficient conductive path within the anode, and if the length of the linear conductive material is greater than 25 μm, entanglement may occur between the conductive materials, which may cause problems with dispersibility within the electrode.

[0071] The above linear conductive material is 1 m 2 / g or more to 20 m 2 It can have a BET specific surface area of ​​less than 1 / g. The above BET specific surface area is a specific surface area measured by the BET method, and can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using, for example, BELSORP-mini II or mini X from BEL Japan.

[0072] The linear conductive material may be included in an amount of 0.01 wt% or more to 10 wt% or less based on the total weight of the positive electrode active material layer. Specifically, the linear conductive material may be included in an amount of 0.1 wt% or more to 10 wt% or less, or 0.1 wt% or more to 5 wt% or less based on the total weight of the positive electrode active material layer. When the content of the linear conductive material satisfies the above range, it has the effect of maintaining contact between the conductive material and the particles within the positive electrode even at low driving pressures, and improving electrochemical performance and / or lifespan characteristics.

[0073] The above binder serves to improve adhesion between particles within the anode and / or adhesion between the anode active material and the anode current collector. Specifically, the binder may include a rubber-based binder, and the rubber-based binder is, for example, butadiene rubber (BR), styrene butadiene rubber (SBR), solution styrene butadiene rubber (SSBR), styrene ethylene butylene styrene (SEBS), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), hydrogenated styrene butadiene rubber (HSBR), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM rubber, or fluororubber. It may include one or more of the following.

[0074] The rubber-based binder may be included in an amount of 0.1% by weight or more to 30% by weight or less based on the total weight of the positive electrode active material layer, specifically in an amount of 0.1% by weight or more to 10% by weight or less, or 0.1% by weight or more to 5% by weight or less. When the content of the rubber-based binder satisfies the above range, the physical properties of the positive electrode are controlled so that the driving pressure can be lowered, and the electrochemical performance and / or life characteristics of the lithium secondary battery are improved even at low driving pressure.

[0075] The above-mentioned anode may comprise the linear conductive material and the rubber-based binder in a weight ratio of 0.45:1 or more to 4:1 or less. Specifically, the weight ratio of the linear conductive material and the rubber-based binder may be 0.45:1 or more to 3.5:1 or less, 0.5:1 or more to 3:1 or less, 1:1 or more to 3:1 or less, or greater than 1:1 to 4:1 or less. When the weight ratio of the linear conductive material and the rubber-based binder satisfies the above range, the lithium secondary battery maintains contact between the conductive material and the particles within the anode even at low driving pressure and is flexible to volume changes, thereby having the effect of excellent electrochemical performance.

[0076] The above anode or anode active material layer may further include additives, and the additives may include, for example, fillers, coating agents, dispersants, thickeners, or ion conductivity aids, but any known material generally used in electrodes may be used without limitation.

[0077] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and may be made of, for example, copper (Cu), nickel (Ni), aluminum (Al), vanadium (V), gold (Au), platinum (Pt), chromium (Cr), iron (Fe), zinc (Zn), indium (In), germanium (Ge), lithium (Li), magnesium (Mg), stainless steel (e.g., SUS), titanium (Ti), cobalt (Co), or an alloy thereof.

[0078] The anode current collector may have a thickness of 3 μm or more to 500 μm or less, and fine irregularities may be formed on the surface of the anode current collector to increase the adhesion of the anode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. The anode current collector may be omitted depending on the case.

[0079] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method. Specifically, it can be manufactured by applying a composition for forming an anode active material layer, comprising the anode active material, solid electrolyte, linear conductive material, and rubber-based binder, onto the anode current collector, followed by drying and rolling. At this time, the composition for forming the anode active material layer may further include a solvent, and the types and contents of the anode active material, solid electrolyte, linear conductive material, and rubber-based binder are as described above.

[0080] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, anisole, xylene, butyl butyrate, heptyl butyrate, octyl butyrate, butyl acetate, heptyl acetate, octyl acetate, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient to dissolve or disperse the above-mentioned cathode active material, linear conductive material, rubber-based binder, etc., considering the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0081] The above anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector, but is not limited thereto.

[0082] When evaluating whether cracks occur in the anode using a plurality of cylindrical mandrels with varying diameters according to the standard method of JIS K5600-5-1, the minimum diameter of the cylindrical mandrel at which cracks begin to occur may be 9 mm or less. Specifically, the minimum diameter of the cylindrical mandrel at which cracks begin to occur may be selected from a combination consisting of one upper limit selected from 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, 5 mm or less, and 4 mm or less, and one lower limit selected from 1 mm or more, 2 mm or more, 3 mm or more, and 4 mm or more. When the flexibility of the anode satisfies the above range, contact between interfaces can be maximized even at low driving pressure, and it is flexible to volume changes occurring during the charging and discharging process, which is effective in improving the performance and / or life characteristics of the secondary battery.

[0083] Another aspect of the present invention relates to a lithium secondary battery.

[0084] The above lithium secondary battery may include a positive electrode comprising a positive electrode active material, a solid electrolyte, a linear conductive material, and a rubber-based binder, and the positive electrode may include the linear conductive material and the rubber-based binder in a weight ratio of 0.45:1 or more to 4:1 or less.

[0085] The above description can be applied in the same way to the positive active material, solid electrolyte, linear conductive material, and rubber-based binder.

[0086] Typically, all-solid-state batteries require high pressures reaching tens of MPa for stable operation, and consequently, there was a problem where performance characteristics such as energy density or capacity were reduced due to external devices required to maintain this pressure.

[0087] However, the lithium secondary battery of the present invention can secure a long conductive path by including the linear conductive material in the positive electrode, and has the effect of reducing the driving pressure of the lithium secondary battery by strengthening the physical properties of the positive electrode compared to conventional point-type conductive materials.

[0088] In addition, by including the linear conductive material and the rubber-based binder in the anode in a weight ratio of 0.45:1 or more to 4:1 or less, contact between the conductive material and the particles within the anode can be maintained even at low driving pressure, and flexibility in volume change during the charging and discharging process is achieved, thereby improving the performance and / or life characteristics of the lithium secondary battery even at driving pressures of 1 MPa or more to 30 MPa or less.

[0089] For stable operation, the above lithium secondary battery may have an operating pressure of 1 MPa or more to 30 MPa or less. Specifically, the operating pressure of the above lithium secondary battery may be a range consisting of one lower limit selected from 1 MPa or more, 2 MPa or more, 3 MPa or more, 4 MPa or more, and 5 MPa or more, and one upper limit selected from 30 MPa or less, 25 MPa or less, 20 MPa or less, 15 MPa or less, 10 MPa or less, less than 10 MPa, 9 MPa or less, 8 MPa or less, 7 MPa or less, 6 MPa or less, and 5 MPa or less.

[0090] In addition, the above lithium secondary battery may have an absolute value of the rate of change of discharge capacity retention rate according to the change in driving pressure represented by the following Equation 1 that is 1 or less.

[0091] [Equation 1]

[0092] │(1st discharge capacity retention rate - 2nd discharge capacity retention rate) / (1st driving pressure - 2nd driving pressure)│

[0093] In the above Equation 1, the first discharge capacity retention rate refers to the discharge capacity retention rate during n charge and discharge cycles at 0.33 C at the first driving pressure, and the second discharge capacity retention rate refers to the discharge capacity retention rate during n charge and discharge cycles at 0.33 C at the second driving pressure, and the first discharge capacity retention rate is the discharge capacity (Q) during one charge and discharge cycle at 0.33 C at the first driving pressure. a1 Discharge capacity (Q) in n cycles relative to ) an The percentage of the ratio of ) (=Q an / Q a1 X 100), and the second discharge capacity retention rate is the discharge capacity (Q) in one charge and discharge cycle at 0.33 C at the second driving pressure. b1 Discharge capacity at n cycles relative to ) Qbn The percentage of the ratio of ) (=Q bn / Q b1 X 100), where n is an integer selected from 10 or more to 100 or less, and the first driving pressure and the second driving pressure are each independently selected from a value of 1 MPa or more to 30 MPa or less, and the first driving pressure is greater than the second driving pressure.

[0094] Equation 1 above represents the ratio of the difference in discharge capacity retention rate to the difference in driving pressure. The meaning of the value (absolute value) of Equation 1 being 1 or less is that even if the lithium secondary battery is driven under different driving pressures, the difference in the discharge capacity retention rate of the lithium secondary battery is significantly small. In other words, even if the driving pressure of the lithium secondary battery of the present invention is lowered compared to the conventional method, the difference in the discharge capacity retention rate at any given point in time is significantly small, meaning that the performance characteristics and / or life characteristics of the lithium secondary battery are excellent even at low driving pressures. The value (absolute value) of Equation 1 above may be less than 1, and specifically, it may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0 or more, 0.001 or more, 0.002 or more, or 0.005 or more.

[0095] The first discharge capacity retention rate refers to the discharge capacity retention rate during n charge and discharge cycles at 0.33 C at the first driving pressure, and specifically, the first discharge capacity retention rate refers to the discharge capacity (Q) during one charge and discharge cycle at 0.33 C at the first driving pressure. a1 Discharge capacity (Q) in n cycles relative to ) an Percentage of the ratio of ) (Q an / Q a1 It may mean a value calculated as X 100).

[0096] The above second discharge capacity retention rate refers to the discharge capacity retention rate during n charge and discharge cycles at 0.33 C at the above second driving pressure, and specifically, the above second discharge capacity retention rate refers to the discharge capacity (Q) during one charge and discharge cycle at 0.33 C at the above second driving pressure. b1 Discharge capacity (Q) in n cycles relative to ) bn Percentage of the ratio of ) (Q bn / Q b1 It may mean a value calculated as X 100).

[0097] The above discharge capacity (Q a1, Q an, Q b1, Q bn ) may refer to the discharge capacity measured after charging to an arbitrarily set terminal voltage of the lithium secondary battery. Here, "terminal voltage" may refer to the upper limit voltage of charging or the end voltage of charging when charging / discharging the lithium secondary battery. In lithium secondary batteries, CC (Constant Current) charging refers to a method of charging at a specified constant A (ampere) by continuously flowing a constant current, and CV (Constant Voltage) charging refers to a charging mode that maintains a constant voltage and charges at a specified V (volt). Generally, when charging a secondary battery, it can be charged using the CC / CV method. In this CC / CV charging method, charging begins in CC mode, and as the voltage rises and reaches a constant voltage, the charging switches to CV mode, gradually reducing the current amount while charging at a constant voltage until the current (I) reaches a set value, at which point charging is terminated. The above-mentioned terminal voltage may refer to the voltage at which the charging mode switches from CC charging mode to CV charging mode. Alternatively, for example, it may refer to a voltage arbitrarily set by the user to terminate charging in CC charging mode, or an arbitrary constant voltage set during charging in CV charging mode.

[0098] At this time, the above-mentioned terminal voltage may be any value selected from a range of, for example, 4 V or more to 4.3 V or less, and the above-mentioned current (I) may be 0.01 C or more to 0.1 C or less, but is not limited thereto.

[0099] Meanwhile, the discharge capacity can be measured by discharging the lithium secondary battery in a CC manner after charging it to the terminal voltage, and the discharge may include, for example, CC discharging to a selected voltage within a range of 1.5 V or more to 3.5 V or less. The discharge voltage of 1.5 V or more to 3.5 V or less is a concept that includes a discharge termination voltage and / or a discharge end voltage, and may refer to the minimum voltage for discharge during the charging and discharging of the lithium secondary battery. That is, it may refer to the voltage at the point where the discharge ends when discharging the lithium secondary battery after charging it. For example, it may mean that the discharge ends at the moment the selected voltage within the range is reached while CC discharging the lithium secondary battery after CC / CV charging. The voltage selected in the range of 1.5 V or more to 3.5 V or less may preferably be a value selected in the range of 1.8 V or more to 3.0 V or less, more preferably a value selected in the range of 2.0 V or more to 2.6 V or less, or a value selected in the range of 2.0 V or more to 3.5 V or less.

[0100] The first driving pressure and the second driving pressure are each independently selected values ​​from 1 MPa or more to 30 MPa or less, for example, the first driving pressure may be 10 MPa or more to 30 MPa or less, the second driving pressure may be 1 MPa or more to 10 MPa or less, and the first driving pressure may be a value greater than the second driving pressure.

[0101] The terminal voltage and discharge voltage for measuring the first discharge capacity retention rate and the second discharge capacity retention rate may be the same.

[0102] In addition, the measurement of the discharge capacity may be performed after the step of activating the lithium secondary battery. At this time, the step of activating the lithium secondary battery may be performed according to a generally known activation process for secondary batteries, and, for example, may be performed in a CC / CV charging mode by setting the terminal voltage as the charging end voltage and in a CC discharge mode by setting any voltage selected in the range of 1.5 V or more to 3.5 V or less as the discharge end voltage, but is not limited thereto.

[0103] The lithium secondary battery of the present invention may include the positive electrode, the electrolyte, and the negative electrode.

[0104] The above-mentioned cathode may include a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector. In another example, the above-mentioned cathode may be an anode-less cathode that does not include a cathode active material layer immediately after battery manufacturing, but includes only a cathode current collector or includes a lithium-affinity material layer on the cathode current collector, and forms a cathode active material layer such as a lithium metal layer through battery charging.

[0105] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel (e.g., SUS), aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated or coated with carbon, nickel, titanium, or silver, or aluminum-cadmium alloy may be used.

[0106] The above-mentioned negative current collector can typically have a thickness of 3 μm or more to 500 μm or less, and fine irregularities can be formed on the surface of the negative current collector to strengthen the bonding force of the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0107] The above-mentioned cathode active material layer may optionally include a cathode binder, a cathode conductive material, and / or a cathode additive, together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, for example, by applying a composition for forming a cathode active material layer containing the cathode active material onto a cathode current collector and drying it, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector. The composition for forming a cathode active material layer may further include a solvent, and the solvent may be selected from examples of solvents included in the aforementioned composition for forming an anode active material layer.

[0108] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as 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 alloys, Sn alloys, or Al alloys; and SiO₂ 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 복합체와 같이 상기 금속질 화합물과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다. 또한, 상기 음극 활물질로서 금속 리튬 또는 금속 리튬 박막이 사용될 수도 있다. 또, 탄소재료는 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.

[0109] In addition, the above-mentioned cathode binder serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), 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. The above-mentioned cathode binder may be included in an amount of 0.1% by weight or more to 30% by weight or less with respect to the total weight of the cathode active material layer.

[0110] The above-mentioned conductive material for the cathode is used to impart conductivity to the cathode, and can be used without special restrictions as long as it has electronic conductivity without causing chemical changes. Specific examples include 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, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above-mentioned conductive material for the cathode may be included in an amount of 0.1% by weight or more to 30% by weight or less with respect to the total weight of the cathode active material layer.

[0111] Examples of the above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0112] The above electrolyte may include, for example, an organic solvent and / or a lithium salt.

[0113] 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 or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol or isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures 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.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can simultaneously satisfy high dielectric constant and low viscosity characteristics, and excellent ionic conductivity characteristics can be achieved, so the performance of the electrolyte can be excellent.

[0114] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte. The above lithium salt may be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries.

[0115] For example, the above lithium salt is Li as a cation + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , BF6 - , SF6 - , B 10 Cl 10 - , BF2C2O4 - , BC4O8 - , PF4C2O4- , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , F3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CH3SO3 - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may include at least one selected from a group consisting of

[0116] Specifically, the lithium salts mentioned above are LiCl, LiBr, LiI, LiBF4, LiClO4, LiAlO4, LiAlCl4, LiPF6, LiSbF6, LiAsF6, LiB 10 Cl 10 Examples include at least one selected from the group consisting of LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), LiCH3SO3, LiCF3CO2, LiCH3CO2, and LiBETI (LiN(SO2CF2CF3)2). Specifically, the lithium salt may include a single substance or a mixture of two or more selected from the group consisting of LiBF4, LiClO4, LiPF6, LiBOB (LiB(C2O4)2), LiCF3SO3, LiTFSI (LiN(SO2CF3)2), LiFSI (LiN(SO2F)2), and LiBETI (LiN(SO2CF2CF3)2).

[0117] The lithium salt may be included in the electrolyte at a concentration of 0.1 M or more to 4 M or more, specifically in a range of 0.1 M or more to 2 M or less, and more specifically in a range of 0.8 M or more to 1.6 M or less. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance, and lithium ions can move effectively, thereby improving the output characteristics of the lithium secondary battery.

[0118] In addition, the lithium secondary battery may optionally further include a separator. The separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It may be used without special limitations as long as it is generally used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of ions in the electrolyte and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and 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 fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure. The separator may be omitted depending on the case.

[0119] The above electrolyte may include a solid electrolyte, and if the solid electrolyte is included, the solid electrolyte can take the place of a separator, so the lithium secondary battery may not include a separator.

[0120] The above-mentioned solid electrolyte may include, for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, polymer-based solid electrolytes, or halide-based solid electrolytes, but is not limited thereto. The same description of the solid electrolyte described above may be applied to the oxide-based solid electrolyte, sulfide-based solid electrolyte, polymer-based solid electrolyte, or halide-based solid electrolyte.

[0121] The above lithium secondary battery may be pouch-type, prismatic-type, or cylindrical, and its shape and size can be applied without restriction as long as it is a commonly used lithium secondary battery.

[0122] Additionally, the lithium 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.

[0123] 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.

[0124]

[0125] <Example 1>

[0126] NCM 811 was prepared as the positive active material, an azirodite-based sulfide solid electrolyte (Li6PS5Cl) as the solid electrolyte, 14 μm carbon nanofiber (CNF) as the linear conductive material, and butadiene rubber (BR) as the binder. Then, these materials were mixed in a butyl butyrate solvent in a weight ratio of positive active material : solid electrolyte : linear conductive material : binder = 80 : 16 : 2 : 2, and a positive slurry was prepared using a thin mixer. The prepared positive slurry was then coated onto an aluminum current collector and dried at 100°C for 12 hours to produce a positive electrode.

[0127] <Example 2>

[0128] In Example 1, a cathode was prepared in the same manner as in Example 1, except that 9 μm carbon nanofibers (CNF) were used instead of 14 μm carbon nanofibers (CNF).

[0129] <Example 3>

[0130] In Example 1, the cathode was prepared in the same manner as in Example 1, except that the cathode active material : solid electrolyte : linear conductive material : binder was mixed in a weight ratio of 80 : 18.45 : 0.55 : 1 instead of a weight ratio of 80 : 16 : 2 : 2.

[0131] <Comparative Example 1>

[0132] In Example 1, instead of 14 µm carbon nanofibers (CNF), a particle size of 150 nm and a BET specific surface area of ​​63 m² were used. 2 The anode was prepared in the same manner as in Example 1, except that Super C65 (carbon black particles) of 1 / g was used.

[0133] <Comparative Example 2>

[0134] In Example 1, the anode was prepared in the same manner as in Example 1, except that the anode active material : solid electrolyte : linear conductive material : binder were mixed in a solvent in a weight ratio of 80 : 16 : 0.6 : 1.4.

[0135] <Comparative Example 3>

[0136] In Example 1, the anode was prepared in the same manner as in Example 1, except that the anode active material : solid electrolyte : linear conductive material : binder were mixed in a solvent in a weight ratio of 80 : 16 : 1.7 : 0.3.

[0137] <Comparative Example 4>

[0138] In Example 1, an anode was prepared in the same manner as in Example 1, except that polytetrafluoroethylene (PTFE) was used instead of butadiene rubber (BR) as the binder.

[0139] <Comparative Example 5>

[0140] In Example 1, an anode was prepared in the same manner as in Example 1, except that polyvinylidene fluoride (PVDF) was used instead of butadiene rubber (BR) as the binder.

[0141] <Comparative Example 6>

[0142] NCM 811 was prepared as the positive active material, an azirodite-based sulfide solid electrolyte (Li6PS5Cl) as the solid electrolyte, 14 μm carbon nanofiber (CNF) as the linear conductive material, and polytetrafluoroethylene (PTFE) as the binder. Then, these materials were mixed in a mortar in a weight ratio of positive active material : solid electrolyte : linear conductive material : binder = 80 : 14.45 : 0.55 : 2 to produce a positive sheet, and the positive sheet was pressed onto an aluminum current collector sheet to produce a positive electrode through a dry process.

[0143]

[0144] <Experimental Example 1>

[0145] (anode)

[0146] The anodes of Examples 1 and 2 were used.

[0147] (cathode)

[0148] For the cathode, a cathode was used in which a non-cathode coating layer slurry, prepared with a weight ratio of amorphous carbon to silver nanoparticles = 3 to 1 and mixed with a PVdF binder and NMP solvent, was applied to a SUS foil.

[0149] (Solid electrolyte layer)

[0150] The solid electrolyte layer used contained Li6PS5Cl solid electrolyte.

[0151] (Lithium secondary battery)

[0152] A lithium secondary battery was fabricated by stacking a positive electrode, a solid electrolyte, and a negative electrode and sealing them in a pouch under vacuum. Here, parts of the positive current collector and the negative current collector were protruded outward from the pouch to maintain the vacuum of the battery. These protrusions served as the positive and negative terminals. Additionally, this lithium secondary battery was subjected to hydrostatic pressure treatment at 500 MPa for 30 minutes.

[0153]

[0154] The manufactured lithium secondary battery was operated under the following charge-discharge conditions at an operating voltage range of 4.25 V and an operating temperature of 60°C under a driving pressure of 10 MPa and 5 MPa, and the ratio of the capacity charged and discharged at 1C to the capacity charged and discharged at 0.1C (1C-rate (relative to 0.1C)) was evaluated and is shown in Table 1 below. The 1C-rate (relative to 0.1C) is a value representing the discharge capacity at a high rate (1C) relative to the cell capacity and indicates the output characteristics of the lithium secondary battery.

[0155] Charge / Discharge Conditions

[0156] 0.1 C, 4.25V CC / CV charging, 0.05C cut-off / 0.1 C, 3V CC discharging

[0157] 1 C, 4.25V CC / CV charging, 0.05C cut-off / 1 C, 3V CC discharging

[0158] Classification Example 1 Example 2 Cell Driving Pressure 10 MPa 5 MPa 10 MPa 5 MPa 1C-rate (relative to 0.1C) 92.6% 91.6% 92.3% 91.9%

[0159]

[0160] <Experimental Example 2>

[0161] A lithium secondary battery was manufactured as in Experimental Example 1 using the cathodes of Examples 1 and 2 and Comparative Examples 1 to 3. The capacity retention rate of the manufactured lithium secondary battery at 20, 50, and 100 cycles was evaluated under the following charge-discharge conditions at driving pressures of 10 MPa and 5 MPa, and the results are shown in Table 2 below.

[0162] Charge / Discharge Conditions

[0163] Charging: 0.33C 4.25V CC / CV, 0.05C cut-off

[0164] Discharge: 0.33C, 3.0V, CC

[0165] Classification Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cell Driving Pressure 10 MPa 5 MPa 10 MPa 5 MPa 5 MPa 10 MPa 5 MPa 10 MPa 5 MPa Capacity Retention Rate (%) 20 Cycles 97.8% 97.9% 98.2% 97.9% 93.8% 94.1% 87.5% 95.3% 88.1% 50 Cycles 95.0% 95.1% 95.6% 95.0% 84.5% 87.4% 71.2% 90.2% 77.7% 100 Cycles 91.0% 91.0% 91.6% 90.9% 68.7% 77.1% 45.0% 82.4% 59.1%

[0166]

[0167] <Experimental Example 3>

[0168] For the anodes prepared in Examples 1 and 2 and Comparative Examples 1 to 3, a flexibility test was conducted by evaluating whether cracks occurred using a plurality of cylindrical mandrels with varying diameters according to the standard method of JIS K5600-5-1, and evaluating the minimum diameter of the cylindrical mandrel at which cracks began to occur, and the results are shown in Table 3 below. The test results of Example 1 are shown in Fig. 1, and the test results of Comparative Example 1 are shown in Fig. 2.

[0169] Classification Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Mandrel Diameter 3 mm 4 mm 10 mm 10 mm 14 mm

[0170]

[0171] <Experimental Example 4>

[0172] The results of evaluating the state of the anode slurry after mixing with a butyl butyrate solvent for Comparative Examples 4 and 5 are shown in Figures 3 and 4, respectively.

[0173] According to Fig. 3, the PTFE binder of Comparative Example 4 was not dissolved, so it was impossible to manufacture an anode using an anode slurry, and according to Fig. 4, it was confirmed that the PVDF binder of Comparative Example 5 had undissolved gel in the solvent, so it was impossible to manufacture an anode using an anode slurry.

[0174]

[0175] <Experimental Example 5>

[0176] A lithium secondary battery was manufactured as in Experimental Example 1 using the cathodes of Example 3 and Comparative Example 6. The manufactured lithium secondary battery was operated under the following charge-discharge conditions at an operating pressure of 5 MPa, an operating voltage range of 4.25 V, and an operating temperature of 60°C, and the ratio of the capacity charged and discharged at 1C to the capacity charged and discharged at 0.1C (1C-rate (relative to 0.1C)) was evaluated, and the results are shown in Table 4 below.

[0177] Charge / Discharge Conditions

[0178] 0.1 C, 4.25V CC / CV charging, 0.05C cut-off / 0.1 C, 3V CC discharging

[0179] 1 C, 4.25V CC / CV charging, 0.05C cut-off / 1 C, 3V CC discharging

[0180] Classification Example 3 Comparative Example 6 Driving Pressure 5 MPa 5 MPa 1C-rate (relative to 0.1C) 94.1% 90.4%

Claims

Positive active material; Solid electrolyte; Linear conductive material; and As an anode comprising a rubber-based binder, An anode comprising the above linear conductive material and a rubber-based binder in a weight ratio of 0.45:1 or more to 4:1 or less. In paragraph 1, The above linear conductive material is an anode comprising a carbon material. In paragraph 1, The above linear conductive material comprises one or more selected from carbon nanofibers, carbon fibers, carbon nanotubes, and carbon nanowires, forming an anode. In paragraph 1, The above linear conductive material is an anode comprising carbon nanofibers (CNF). In paragraph 1, The above linear conductive material is an anode having an aspect ratio of 10 or more to 100 or less. In paragraph 1, The above linear conductive material is an anode having a length of 5 μm or more to 25 μm or less. In paragraph 1, The above linear conductive material is an anode having a length of 9 μm or more to 14 μm or less. In paragraph 1, The above rubber-based binder comprises one or more selected from butadiene rubber (BR), styrene butadiene rubber (SBR), solution styrene butadiene rubber (SSBR), styrene ethylene butylene styrene (SEBS), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), hydrogenated styrene butadiene rubber (HSBR), ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM rubber, and fluororubber, forming an anode. In paragraph 1, The above-mentioned solid electrolyte comprises one or more selected from sulfide-based solid electrolytes, oxide-based solid electrolytes, polymer-based solid electrolytes, and halide-based solid electrolytes, forming an anode. In paragraph 1, The above anode is an anode in which, when the occurrence of cracking is evaluated using a plurality of cylindrical mandrels with varying diameters according to the standard method of JIS K5600-5-1, the minimum diameter of the cylindrical mandrel at which cracking begins to occur is 1 mm or more and 9 mm or less. A lithium secondary battery comprising a positive electrode including a positive electrode active material, a solid electrolyte, a linear conductive material, and a rubber-based binder, The above positive electrode is a lithium secondary battery comprising the above linear conductive material and the above rubber-based binder in a weight ratio of 0.45:1 or more to 4:1 or less. In Paragraph 11, The above lithium secondary battery is a lithium secondary battery having an operating pressure of 1 MPa or more and 30 MPa or less. In Paragraph 11, The above lithium secondary battery is a lithium secondary battery in which the absolute value of the rate of change of the discharge capacity retention rate according to the change in driving pressure represented by the following Equation 1 is 1 or less: [Equation 1] │(1st discharge capacity retention rate - 2nd discharge capacity retention rate) / (1st driving pressure - 2nd driving pressure)│ In the above Equation 1, The above first discharge capacity retention rate refers to the discharge capacity retention rate in n cycles of charging and discharging at 0.33 C at the first driving pressure, and The above second discharge capacity retention rate refers to the discharge capacity retention rate in n cycles of charging and discharging at 0.33 C at the second driving pressure, and The first discharge capacity retention rate is the discharge capacity (Q) in one charge and discharge cycle at 0.33 C at the first driving pressure. a1 Discharge capacity (Q) in n cycles relative to ) an It is a percentage of the ratio of ), The above second discharge capacity retention rate is the discharge capacity (Q) in one charge and discharge cycle at 0.33 C at the above second driving pressure. b1 Discharge capacity at n cycles relative to ) Qbn It is a percentage of the ratio of ), The above n is an integer selected from 10 or more to 100 or less, and The first driving pressure and the second driving pressure are each independently selected values ​​ranging from 1 MPa or more to 30 MPa or less, and The first driving pressure is greater than the second driving pressure.

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