Sulfide-based solid electrolyte compound

Abstract

The present specification relates to a sulfide-based solid electrolyte compound and a lithium secondary battery comprising same, and, more specifically, to a method for improving the atmospheric stability and electrochemical stability of a sulfide-based solid electrolyte having an argyrodite-type crystal structure.

Description

sulfide-based solid electrolytes

[0001] The present specification relates to sulfide-based solid electrolyte compounds, solid electrolyte membranes containing the same, and lithium secondary batteries. More specifically, the present specification relates to a method for improving the atmospheric stability and electrochemical stability of a sulfide-based solid electrolyte having an azirodite-type crystal structure, and relates to a sulfide-based solid electrolyte compound, a solid electrolyte membrane, and a lithium secondary battery containing the same, wherein stability can be improved by forming a LiX crystal phase on at least a portion of the surface of the sulfide-based solid electrolyte compound having an azirodite-type crystal structure to suppress the decomposition reaction of the solid electrolyte.

[0002]

[0003] A battery stores electrical power by using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example of such a battery is the lithium secondary battery, which stores electrical energy based on the difference in chemical potential when lithium ions intercalate or deintercalate at the positive and negative electrodes.

[0004] The above lithium secondary battery is manufactured by using materials capable of reversible intercalation / deintercalation of lithium ions as positive and negative active materials, and by filling an organic electrolyte or a polymer electrolyte between the positive and negative electrodes.

[0005] However, these organic or polymer electrolytes typically use flammable organic solvents. Therefore, if abnormally high temperatures occur due to internal or external factors of the lithium secondary battery, a fire or explosion may occur due to the electrolyte.

[0006] Due to these safety concerns, solid-state batteries utilizing solid electrolytes are attracting attention as a substitute for liquid batteries. Solid-state batteries are expected to be commercialized as next-generation batteries with high energy density due to their high stability. Furthermore, if the solid electrolyte is introduced in the form of a membrane structure, it can replace the separator that is essential for liquid batteries.

[0007] Sulfide-based solid electrolytes are known as solid electrolytes used in lithium secondary batteries. Various crystal structures of sulfide-based solid electrolytes are known, one of which is the argyrodite-type crystal structure.

[0008] However, solid electrolytes have the problem of lower ionic conductivity than liquid electrolytes and can easily degrade due to decomposition reactions inside the battery. In addition, sulfide-based solid electrolytes have the problem of potentially generating hydrogen sulfide by reacting with moisture and / or oxygen in the atmosphere.

[0009] Therefore, it is necessary to develop novel compounds that possess high ionic conductivity while improving the atmospheric and electrochemical stability of sulfide-based solid electrolyte compounds.

[0010]

[0011] According to the present specification, one objective is to provide a sulfide-based solid electrolyte compound having an azirodite-type crystal structure, wherein a LiX crystal phase is retained on at least a portion of the surface to suppress the reaction between the solid electrolyte and moisture and / or oxygen, and simultaneously improves ionic conductivity, thereby providing a sulfide-based solid electrolyte compound having excellent atmospheric stability and electrochemical stability.

[0012] In addition, the present specification aims to provide a solid electrolyte membrane and a lithium secondary battery using a sulfide-based solid electrolyte compound defined herein.

[0013] The purposes of the present invention are not limited to those mentioned above, and other purposes and advantages of the present invention not mentioned may be understood from the following description and will be more clearly understood from the embodiments of this specification. Furthermore, it will be readily apparent that the purposes and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0014]

[0015] According to one aspect of the present specification, a sulfide-based solid electrolyte compound for a lithium-ion battery is provided, comprising a crystalline phase having an argyrodite-type crystal structure and comprising a LiX crystalline phase on at least a portion of the surface, wherein X is at least one selected from the group consisting of F, Cl, Br, and I.

[0016] The peak intensity ratio I(200) / I(220) of the (220) plane represented by the crystal phase of the above azirodite-type crystal structure and the (200) plane represented by the above LiX crystal phase may be 0.30 or less.

[0017] Here, in the crystal phase of the azirodite-type crystal structure, the molar ratio of lithium (Li) element and phosphorus (P) element Li / P may be greater than 5.7 and less than 6.15.

[0018] In addition, the molar ratio S / P of sulfur (S) and phosphorus (P) elements in the crystal phase of the azirodite-type crystal structure may be 4.00 to 6.00.

[0019] Meanwhile, the crystal phase of the above-mentioned azirodite-type crystal structure may contain two or more halogen elements.

[0020] Here, the molar ratio X / P of the halogen (X) element and the phosphorus (P) element in the crystal phase of the azirodite-type crystal structure may be 1.00 to 2.00.

[0021] In addition, in the crystal phase of the azirodite-type crystal structure, the molar ratio of phosphorus (P) element to the total sum of lithium (Li) element and halogen (X) element (Li+X) / P may be greater than 7.00.

[0022] In one embodiment, the crystalline phase of the azirodite-type crystal structure can be represented by the following chemical formula 1:

[0023] [Chemical Formula 1]

[0024] Li 7-x+y PS 6-x Cl x Br y

[0025] In the above Chemical Formula 1, 1≤x≤1.6, 0 <y≤0.4이다.

[0026] In addition, the peak intensity ratio I(200) / I(220) of the (220) plane represented by the crystal phase of the azirodite-type crystal structure and the (200) plane represented by the LiCl crystal phase may be 0.30 or less.

[0027] In another embodiment, the lattice constant of the crystal phase of the azirodite-type crystal structure may be greater than 9.439 Å and less than 9.645 Å.

[0028] Meanwhile, the above sulfide-based solid electrolyte compound for a lithium-ion battery can be obtained by mixing lithium sulfide (Li2S) powder, phosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder, and calcining at 350 to 600°C under an inert atmosphere or at 350 to 650°C under an atmosphere containing hydrogen sulfide gas.

[0029] In addition, the content of the lithium chloride (LiCl) powder may be higher than the content of the lithium bromide (LiBr) powder.

[0030] According to another aspect, a solid electrolyte membrane comprising the above-described sulfide-based solid electrolyte compound is provided.

[0031] According to another aspect, a lithium secondary battery having the solid electrolyte membrane described above is provided.

[0032]

[0033] According to the present specification, at least a portion of the surface of an azirodite-type sulfide-based solid electrolyte compound is mixed with a LiX crystalline phase to improve atmospheric stability and electrochemical stability, and a lithium secondary battery containing the same can exhibit stable cycle behavior without an increase in overvoltage even during long-term use.

[0034] In addition to the effects described above, the specific effects of the present invention are described together with the specific details of the specification below.

[0035]

[0036] FIG. 1 is the XRD analysis result of a sulfide-based compound according to one example of the present specification;

[0037] FIG. 2 is the amount of hydrogen sulfide generated by a sulfide-based compound according to one example of the present specification;

[0038] FIG. 3 is the result of evaluating the electrochemical characteristics of a symmetric cell containing a sulfide-based compound according to one example of the present specification.

[0039]

[0040] For convenience, specific terms are defined herein to facilitate a better understanding of this specification. Unless otherwise defined herein, scientific and technical terms used in this invention shall have the meanings generally understood by those skilled in the art. Furthermore, unless specifically indicated in the context, terms in their singular form shall be understood to include their plural form, and terms in their plural form shall be understood to include their singular form.

[0041]

[0042] sulfide-based solid electrolytes

[0043] A sulfide-based solid electrolyte compound according to one aspect of the present specification comprises a crystalline phase having an argyrodite-type crystal structure and may comprise a LiX crystalline phase on at least a portion of its surface.

[0044] The above sulfide-based solid electrolyte compound has lithium ion conductivity and may have a mixed phase including a crystalline phase with an azirodite-type crystal structure and a LiX crystalline phase.

[0045] The term "azirodite-type crystal structure" refers to a structure identical to that of azirodite (Ag8GeS6), a silver-germanium-sulfur mineral. The azirodite-type crystal structure can possess orthorhombic (Pna21) and cubic (F-43m) phases, among which the cubic crystal structure exhibits high lithium ion conductivity. Typically, the azirodite-type crystal structure displays the cubic phase, which exhibits excellent lithium ion conductivity at high temperatures, and the orthorhombic phase at low temperatures.

[0046] For example, Li7PS6, Li6PS5X (where X is at least one of Cl, Br, and I) are known as lithium ion conductive solid electrolyte compounds having an azirodite-type crystal structure.

[0047] However, the azirodite crystal structure has the problem of easily degrading performance due to sensitivity to air and humidity. Additionally, compounds with an azirodite crystal structure can easily decompose when reacting with lithium due to their narrow potential window.

[0048] On the other hand, the sulfide-based solid electrolyte compound includes a LiX phase having a relatively wide and stable potential window, which can suppress the decomposition reaction of the compound at the interface. Therefore, a secondary battery using the sulfide-based solid electrolyte compound can exhibit stable cycle behavior.

[0049] The LiX phase can be formed by adding an excess amount of LiX (where X is at least one of Cl, Br, and I) during the preparation of the above-mentioned sulfide-based solid electrolyte compound to retain LiX. At this time, two or more compounds, rather than just one compound, may be used as LiX so that one of the two remains.

[0050] Here, excess may mean that (Li+X) / P, which is the sum of the molar ratio of lithium (Li) element and phosphorus (P) element Li / P and the molar ratio of halogen (X) element and phosphorus (P) element X / P, is greater than 7.

[0051] The peak intensity ratio I(200) / I(220) of the (220) plane represented by the crystalline phase of the azirodite-type crystal structure and the (200) plane represented by the LiX crystalline phase is 0.30 or less, for example, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, or two of these. It may be a range of values, but is not limited to this.

[0052] In XRD analysis using a Cu target, the (220) plane may appear at approximately 2θ=25.2, and the (200) plane may appear at approximately 2θ=34.9. If the peak intensity ratio of the azirodite-type crystal phase and the LiX crystal phase satisfies the above-mentioned range, problems such as a decrease in the ionic conductivity of the solid electrolyte or a decrease in atmospheric stability can be prevented.

[0053] Here, in the crystalline phase of the azirodite-type crystal structure, the molar ratio Li / P of lithium (Li) and phosphorus (P) elements is greater than 5.7 and less than 6.15, for example, 5.71, 5.72, 5.73, 5.74, 5.75, 5.76, 5.77, 5.78, 5.79, 5.80, 5.81, 5.82, 5.83, 5.84, 5.85, 5.86, 5.87, 5.88, 5.89, 5.90, 5.91, 5.92, 5.93, 5.94, 5.95, 5.96, 5.97, 5.98, 5.99, 6.00, 6.01, 6.02, 6.03, 6.04, 6.05, 6.06, 6.07, 6.08, 6.09, 6.10, 6.11, 6.12, 6.13, 6.14, 6.15, or a range between two of these values, but is not limited thereto.

[0054] If the Li / P value falls outside the above range, the arrangement and distribution ratio of lithium ions within the compound change, which may lead to a decrease in ionic conductivity.

[0055] In addition, in the crystal phase of the azirodite-type crystal structure, the molar ratio S / P of sulfur (S) and phosphorus (P) elements is 4.00 to 6.00, for example, 4.00, 4.05, 4.10, 4.15, 4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60, 4.65, 4.70, 4.75, 4.80, 4.85, 4.90, 4.95, 5.00, 5.05, 5.10, 5.15, 5.20, 5.25, 5.30, 5.35, 5.40, 5.45, 5.50, 5.55, 5.60, It may be 5.65, 5.70, 5.75, 5.80, 5.85, 5.90, 5.95, 6.00, or a range between two of these values, but is not limited thereto.

[0056] If the S / P value satisfies the above range, the chemical stability and high ionic conductivity of the compound can be secured in balance.

[0057] In an azyrodite-type crystal structure, replacing sulfur with a halogen anion stabilizes the cubic phase, allowing the structure to be maintained even at room temperature.

[0058] Substituted halogen elements can form vacancies at Li sites within the azirodite unit cell, thereby reducing activation energy and forming new lithium ion conduction pathways, which can consequently improve lithium ion conductivity.

[0059] Meanwhile, the crystal phase of the above-mentioned azyrodite-type crystal structure may contain two or more halogen elements. Halogen elements include F, Cl, Br, I, etc., but Cl, Br, I, etc. can typically be used in compounds having an azyrodite-type crystal structure.

[0060] Here, in the crystal phase of the azyrodite-type crystal structure, the molar ratio X / P of the halogen (X) element and the phosphorus (P) element is 1.00 to 2.00, for example, 1.00, 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.14, 1.16, 1.18, 1.20, 1.22, 1.24, 1.26, 1.28, 1.30, 1.32, 1.34, 1.36, 1.38, 1.40, 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60, 1.62, 1.64, 1.66, 1.68, 1.70, 1.72, 1.74, 1.76, 1.78, 1.80, 1.82, 1.84, 1.86, 1.88, 1.90, 1.92, 1.94, 1.96, 1.98, 2.00, or a range between two of these values, but is not limited thereto.

[0061] In one example, in the crystal phase of the azyrodite-type crystal structure, the molar ratio of phosphorus (P) element to the total sum of lithium (Li) element and halogen (X) element (Li+X) / P is greater than 7.00, e.g., 7.01, 7.02, 7.03, 7.04, 7.05, 7.06, 7.07, 7.08, 7.09, 7.10, 7.11, 7.12, 7.13, 7.14, 7.15, 7.16, 7.17, 7.18, 7.19, 7.20, 7.21, 7.22, 7.23, 7.24, 7.25, 7.26, 7.27, 7.28, 7.29, 7.30, 7.31, 7.32, 7.33, 7.34, 7.35, 7.36, 7.37, 7.38, 7.39, 7.40, 7.41, 7.42, 7.43, 7.44, 7.45, 7.46, 7.47, 7.48, 7.49, 7.50, or a range between two of these values, but is not limited thereto.

[0062] Here, if the halogen (X) element contains Cl and Br, the content of Cl may be higher than the content of Br.

[0063] In addition, the content of the above Br is 0.05 to 0.4 moles based on 1 mole of the above phosphorus (P) element, for example, 0.05 mole, 0.06 mole, 0.07 mole, 0.08 mole, 0.09 mole, 0.1 mole, 0.11 mole, 0.12 mole, 0.13 mole, 0.14 mole, 0.15 mole, 0.16 mole, 0.17 mole, 0.18 mole, 0.19 mole, 0.2 mole, 0.21 mole, 0.22 mole, 0.23 mole, 0.24 mole, 0.25 mole, 0.26 mole, 0.27 mole, 0.28 mole, 0.29 mole, 0.3 mole, 0.31 mole, 0.32 mole, 0.33 mole, 0.34 mole, It may be 0.35 moles, 0.36 moles, 0.37 moles, 0.38 moles, 0.39 moles, 0.4 moles, or a range between two of these values, but is not limited thereto.

[0064] In one embodiment, the crystalline phase of the azirodite-type crystal structure can be represented by the following chemical formula 1:

[0065] [Chemical Formula 1]

[0066] Li 7-x+y PS 6-x Cl x Br y

[0067] In the above Chemical Formula 1, 1≤x≤1.6, 0 <y≤0.4이다. 예를 들어, 상기 x는 1, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26, 1.28, 1.3, 1.32, 1.34, 1.36, 1.38, 1.4, 1.42, 1.44, 1.46, 1.48, 1.5, 1.52, 1.54, 1.56, 1.58, 1.6 또는 이들 중 두 값의 사이 값일 수 있고, 상기 y는 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4 또는 이들 중 두 값의 사이 값일 수 있으나, 이에 한정되는 것은 아니다.

[0068] In addition, the peak intensity ratio I(200) / I(220) of the (200) plane represented by the crystalline phase of the azirodite-type crystal structure, which contains Cl and Br but has a higher Cl content than Br, and the (200) plane represented by the LiCl crystal phase is 0.30 or less, for example, 0.30, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, It may be 0.03, 0.02, 0.01, or a range between two of these values, but is not limited thereto.

[0069] As such, if the molar ratio of Cl and Br and the value of I (200) / I (220) satisfy the range described above, LiCl remains on at least a portion of the surface of the compound, thereby suppressing the decomposition reaction of the solid electrolyte at the interface and reducing the generation of hydrogen sulfide caused by substances present in the atmosphere. In addition, it can have high ionic conductivity even after contact with the atmosphere.

[0070] In another embodiment, the lattice constant of the crystal phase of the azirodite-type crystal structure is greater than 9.439 Å and less than 9.645 Å, for example, 9.440 Å, 9.445 Å, 9.450 Å, 9.455 Å, 9.460 Å, 9.465 Å, 9.470 Å, 9.475 Å, 9.480 Å, 9.485 Å, 9.490 Å, 9.495 Å, 9.500 Å, 9.505 Å, 9.510 Å, 9.515 Å, 9.520 Å, 9.525 Å, 9.530 Å, 9.535 Å, 9.540 Å, 9.545 Å, 9.550 Å, 9.555 Å, 9.560 Å, 9.565 Å, 9.570 Å, 9.575 Å, 9.580 Å, 9.585 Å, 9.590 Å, 9.595 Å, 9.600 Å, 9.605 Å, 9.610 Å, 9.615 Å, 9.620 Å, 9.625 Å, 9.630 Å, 9.635 Å, 9.640 Å, 9.644 Å, or a range between two of these values, but is not limited thereto.

[0071] A compound containing an azirodite-type crystal phase satisfying the range of lattice constants described above may have a lithium conduction pathway formed by substituting a halogen anion at the position of a sulfur anion.

[0072] Meanwhile, the sulfide-based solid electrolyte compound for the lithium-ion battery is prepared by mixing lithium sulfide (Li2S) powder, phosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder, and subjecting the mixture to an inert atmosphere at 350–600°C, for example, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C, 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C, 450°C, 455°C, 460°C, 465°C, 470°C, 475°C, 480°C. Calcining at 485℃, 490℃, 495℃, 500℃, 505℃, 510℃, 515℃, 520℃, 525℃, 530℃, 535℃, 540℃, 545℃, 550℃, 555℃, 560℃, 565℃, 570℃, 575℃, 580℃, 585℃, 590℃, 595℃, 600℃, or a temperature within a range between two of these values, or calcining at 350 to 650℃ in an atmosphere containing hydrogen sulfide gas, e.g., 350℃, 355℃, 360℃, 365℃, 370℃, 375℃, 380℃, 385℃, 390℃, 395℃, 400℃, 405℃, 410℃, 415℃, 420℃, 425℃, 430℃, 435℃, 440℃, 445℃, 450℃, 455℃, 460℃, 465℃, 470℃, 475℃, 480℃, 485℃, 490℃, 495℃, 500℃, 505℃, 510℃, 515℃, 520℃, 525℃, 530℃, 535℃, 540℃, 545℃, 550℃, 555℃, 560℃, 565℃, 570℃, 575℃, 580℃, 585℃, 590℃, 595℃, 600℃, 605℃, It can be obtained by firing at a temperature of 610℃, 615℃, 620℃, 625℃, 630℃, 635℃, 640℃, 645℃, 650℃, or a range between two of these values.

[0073] Here, each component can be stoichiometrically calculated and mixed to have the composition of Chemical Formula 1 described above.

[0074] In addition, the firing temperature and atmosphere can be applied differently depending on the desired composition.

[0075] In addition, the content of the lithium chloride (LiCl) powder may be higher than the content of the lithium bromide (LiBr) powder. Compounds of this type may have high ionic conductivity and excellent stability.

[0076] Meanwhile, the excess lithium bromide powder can be added to leave the lithium chloride (LiCl) phase on the surface of the sulfide-based solid electrolyte compound. For example, the lithium bromide powder can be added such that the value obtained by dividing the total number of moles of lithium (Li), chlorine (Cl), and bromine (Br) elements by the number of moles of phosphorus (P) element is greater than 7.

[0077]

[0078] solid electrolyte membrane

[0079] According to another aspect, a solid electrolyte membrane comprising the above-described sulfide-based solid electrolyte compound is provided.

[0080] Here, the solid electrolyte membrane may refer to a sulfide-based solid electrolyte compound, which is a type of solid-phase material capable of ion conduction, formed in a membrane-like structure.

[0081] A solid electrolyte membrane can be manufactured according to conventional methods known in the art, for example, by press-molding a powder of a sulfide-based solid electrolyte compound and then processing it into the required shape.

[0082] However, since it is difficult to maintain a membrane-like structure with sulfide-based compounds alone, solid electrolyte membranes can be manufactured by mixing a binder.

[0083] Here, the binder should preferably have excellent binding strength to the sulfide-based compound, excellent flexibility without reducing ion conductivity, and be easily peelable from the release film typically used in the manufacture of solid electrolyte membranes.

[0084] Examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), 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.

[0085] This type of solid electrolyte membrane can be manufactured by applying a slurry containing a sulfide-based compound, a binder, and a solvent onto a release film, and then removing the solvent.

[0086] In addition, the above solid electrolyte membrane may further include a conductive material, an auxiliary binder, etc., as needed.

[0087] Conductive materials are used to impart conductivity so that electron movement accompanying ion movement is possible, and their types are not limited as long as they possess electronic conductivity without unnecessary chemical reactions. Examples include graphite, carbon black, acetylene black, Ketjen black, furnace black, lamp black, thermo black, carbon fiber, carbon nanotube, graphene, copper, aluminum, nickel, gold, silver, conductive polymers, etc.

[0088] The content of the sulfide-based solid electrolyte compound in the above solid electrolyte membrane is 80 to 99.9 wt%, for example, 80 wt%, 80.5 wt%, 81 wt%, 81.5 wt%, 82 wt%, 82.5 wt%, 83 wt%, 83.5 wt%, 84 wt%, 84.5 wt%, 85 wt%, 85.5 wt%, 86 wt%, 86.5 wt%, 87 wt%, 87.5 wt%, 88 wt%, 88.5 wt%, 89 wt%, 89.5 wt%, 90 wt%, 90.5 wt%, 91 wt%, 91.5 wt%, 92 wt%, 92.5 wt%, 93 wt%, 93.5 wt%, 94 wt%, 94.5 wt%, 95 wt%, 95.5 wt%, 96 wt%, 96.5 wt%, 97 wt%, 97.5 wt%, 98 wt%, 98.5 wt%, 99 wt%, 99.5 wt%, 99.9 wt%, or a range between two of these values, but is not limited thereto.

[0089] Here, the thickness of the solid electrolyte membrane is not limited and ranges from 5 to 300 µm, for example, 5 µm, 10 µm, 15 µm, 20 µm, 25 µm, 30 µm, 35 µm, 40 µm, 45 µm, 50 µm, 55 µm, 60 µm, 65 µm, 70 µm, 75 µm, 80 µm, 85 µm, 90 µm, 95 µm, 100 µm, 105 µm, 110 µm, 115 µm, 120 µm, 125 µm, 130 µm, 135 µm, 140 µm, 145 µm, 150 µm, 155 µm, 160 µm, 165 µm, 170 µm, 175 It may have a range between two of these values, such as µm, 180 µm, 185 µm, 190 µm, 195 µm, 200 µm, 205 µm, 210 µm, 215 µm, 220 µm, 225 µm, 230 µm, 235 µm, 240 µm, 245 µm, 250 µm, 255 µm, 260 µm, 265 µm, 270 µm, 275 µm, 280 µm, 285 µm, 290 µm, 295 µm, 300 µm.

[0090] Meanwhile, the above-mentioned solid electrolyte membrane may have free-standing characteristics that allow it to be used without a separate support, but is not limited thereto.

[0091]

[0092] lithium secondary battery

[0093] According to another aspect of the present specification, a lithium secondary battery having the solid electrolyte membrane described above may be provided.

[0094] The above-described solid electrolyte membrane may be disposed as a separate layer (solid electrolyte layer) between the anode and the cathode. Additionally, the solid electrolyte may be partially included within the anode active material layer of the anode independently of the solid electrolyte layer, or the solid electrolyte may be partially included within the cathode active material layer of the cathode independently of the solid electrolyte layer.

[0095] That is, the above lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite to the positive electrode, and a solid electrolyte membrane interposed between the positive electrode and the negative electrode. Here, since the solid electrolyte membrane is the same as previously described, a detailed description is omitted for convenience, and only the remaining components not described below will be described in detail.

[0096] The above lithium secondary battery may optionally further include a battery container housing the electrode assembly of the positive electrode, the negative electrode, and the solid electrolyte membrane, and a sealing member sealing the battery container.

[0097] The above positive electrode may include a positive current collector and a positive active material layer located on the positive current collector.

[0098] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0099] The above-mentioned cathode active material may use a compound capable of reversible intercalation / deintercalation of lithium. Examples include, but are not limited to, cobalt oxide-based (LCO), nickel oxide-based (LNO), manganese oxide-based (LMO), nickel-cobalt-manganese oxide-based (NCM), nickel-cobalt-aluminum oxide-based (NCA), iron phosphate-based (LFP), and those doped with and / or coated therefrom.

[0100] The above positive active material layer can be manufactured by applying a positive slurry composition, which includes a conductive material and optionally a binder together with the positive active material, to the positive current collector.

[0101] At this time, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer. Excellent capacity characteristics may be exhibited when included within the above-mentioned content range, but it is not necessarily limited thereto.

[0102] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses 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 whiskey 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 conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0103] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), 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 binder may be included in an amount of 0.1% to 15% by weight based on the total weight of the positive active material layer.

[0104] The above anode can be manufactured according to a conventional anode manufacturing method. Specifically, it can be manufactured by applying an anode slurry composition, prepared by dissolving or dispersing an anode active material, a binder, and a conductive material in a solvent, onto an anode current collector, and then drying and rolling.

[0105] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, 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 if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0106] In addition, in another embodiment, the anode may be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0107] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0108] 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, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0109] The above-mentioned cathode active material layer can be manufactured by applying a cathode slurry composition, which includes a conductive material and optionally a binder together with the above-mentioned cathode active material, to the above-mentioned cathode current collector.

[0110] 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, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and 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. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include 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, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0111] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0112] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer.

[0113] Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0114] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0115] In one embodiment, the negative active material layer may be manufactured by applying a negative slurry composition, prepared by dissolving or dispersing a negative active material and optionally a binder and a conductive material in a solvent, onto a negative current collector and drying it, or by casting the negative slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a negative current collector.

[0116] As described above, a lithium secondary battery including a solid electrolyte membrane according to the present specification exhibits stable cycle characteristics without increasing overvoltage, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicle fields such as hybrid electric vehicles (HEV).

[0117] The external shape of the lithium secondary battery according to the present specification is not subject to any particular limitations, but may be cylindrical, prismatic, pouch, or coin-shaped using a can. In addition, the lithium secondary battery may not only be used as a battery cell for powering small devices, but may also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0118] According to another aspect of the present specification, a battery module comprising the lithium secondary battery as a unit cell and / or a battery pack comprising the same may be provided.

[0119] The battery module or the battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0120]

[0121] The present invention will be described in more detail below through examples. However, these examples are intended solely to illustrate the present invention and should not be interpreted as limiting the scope of the present invention.

[0122]

[0123] Preparation Example 1. Preparation of sulfide-based compounds

[0124] Comparative Example 1

[0125] In a drying chamber (DP-60℃), lithium precursor Li2S, phosphorus precursor P2S5, and chlorine precursor LiCl are prepared to form the desired composition Li. 5.7 PS 4.7 Cl 1.3 Weighed and mixed in stoichiometric ratios to obtain [the desired result].

[0126] The mixture was placed in a crucible containing Al2O3 and calcined. To suppress the reaction with the gas present inside the calcination furnace, N2 gas was flowed as an inert gas, and the mixture was calcined by raising the temperature to a maximum of 570 ℃ to produce the sulfide-based compound of Comparative Example 1.

[0127]

[0128] Comparative Example 2

[0129] In a drying chamber (DP-60℃), lithium precursor Li2S, phosphorus precursor P2S5, chlorine precursor LiCl, and bromine precursor LiBr are prepared as Li of the desired composition. 6.15 PS 4.7 Cl 1.3 Br 0.45 A sulfide-based compound was prepared in the same manner as Comparative Example 1, except that it was weighed in stoichiometric ratios to obtain [the desired result].

[0130]

[0131] Example 1

[0132] In a drying chamber (DP-60℃), lithium precursor Li2S, phosphorus precursor P2S5, chlorine precursor LiCl, and bromine precursor LiBr are prepared to form Li of the desired composition. 5.775 PS 4.7 Cl 1.3 Br 0.075 A sulfide-based compound was prepared in the same manner as Comparative Example 1, except that it was weighed to obtain [the desired result].

[0133]

[0134] Example 2

[0135] In a drying chamber (DP-60℃), lithium precursor Li2S, phosphorus precursor P2S5, chlorine precursor LiCl, and bromine precursor LiBr are prepared to form Li of the desired composition. 5.85 PS 4.7 Cl 1.3 Br 0.15 A sulfide-based compound was prepared in the same manner as Comparative Example 1, except that it was weighed to obtain [the desired result].

[0136]

[0137] Experimental Example 1. Characterization of Sulfide Compounds

[0138] The composition of the sulfide-based compound prepared according to Preparation Example 1, the ionic conductivity before and after exposure to the atmosphere, the lattice parameter, and the intensity ratio I(200) / I(220) of the peak intensity of the (200) plane of the LiCl crystal phase and the (220) plane of the azirodite-type crystal phase were measured and are shown in Table 1 below.

[0139] XRD analysis was performed using a Bruker D8 Advance diffractometer with Cu-Kα radiation (1.540598 Å), and the results are shown in Figure 1.

[0140] To evaluate atmospheric stability, air with a controlled dew point (DP-40℃) at room temperature was flowed through a sulfide-based compound, and the amount of hydrogen sulfide generated was measured using a hydrogen sulfide sensor and is shown in Figure 2. The ionic conductivity of the sulfide-based compound was measured before and after the evaluation, respectively.

[0141] Classification Comparative Example 1 Comparative Example 2 Example 1 Example 2 Composition Limol 5.7 6.15 5.7 75 5.85 P1 1 1 1 S 4.7 4.7 4.7 4.7 Cl 1.3 1.3 1.3 1.3 Br - 0.4 5 0.0 75 0.15 Ionic Conductivity (Before Exposure) mS / cm 3.7 8 2.5 4 3.8 6 4.15 Ionic Conductivity (After Exposure) mS / cm 0.9 5 0.6 5 1.5 4 1.79 Lattice Constant Å 9.4 39 9.6 45 9.4 6 9.5 01 I(200) / I(220) - 0.00 0.3 1 0.0 5 0.09

[0142] Referring to Table 1, Comparative Example 1, which lacks bromine, and Comparative Example 2, which has an excessively high bromine ratio, actually exhibited lower ionic conductivity than the Examples. In particular, this difference became even more evident after the atmospheric stability evaluation. Specifically, Comparative Example 2 showed a sharp decrease in ionic conductivity after exposure to the atmosphere, despite containing residual LiCl. Referring to Figure 1 and Table 1, it can be confirmed that residual LiCl remained in the sulfide compounds of Comparative Example 2, Example 1, and Example 2 due to the excess amount of LiBr.

[0143] Referring to Figure 2, the amount of hydrogen sulfide generated in Example 1 was reduced compared to Comparative Example 1 due to the influence of residual LiCl.

[0144]

[0145] Preparation Example 2. Preparation of a solid electrolyte membrane and a lithium secondary battery (symmetric cell)

[0146] A pressure cell was prepared by applying a uniaxial pressure of 200 MPa to 200 mg of the sulfide-based compounds of the comparative example and the example. At this time, Li metal was inserted at both ends of the solid electrolyte to prepare a symmetric lithium secondary battery cell with a Li / sulfide-based compound / Li electrode structure.

[0147]

[0148] Experimental Example 2. Evaluation of Electrochemical Characteristics of a Lithium Secondary Battery (Symmetric Cell)

[0149] The lithium secondary battery (symmetric cell) prepared in Preparation Example 2 was evaluated using a TOSCAT-3100 instrument from Toyo. At this time, a current of 0.25 mA per unit area was applied, and 300 cycles of evaluation were performed. The electrochemical stability of the solid electrolyte was evaluated by repeating stripping / plating (1 hr each) per cycle, and the results are shown in Fig. 3.

[0150] Typically, due to the narrow potential window of the solid electrolyte, a decomposition reaction of the solid electrolyte occurs at the interface between the lithium electrode and the solid electrolyte. However, referring to Figure 3, in the symmetric cell of Example 1 in which LiCl, which has a wide and stable potential window compared to the solid electrolyte, remains, the interfacial decomposition reaction is suppressed, and stable cycle behavior is exhibited without an increase in the overpotential on the y-axis.

[0151]

[0152] Although embodiments of the present invention have been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be included within the scope of the rights of the present invention.

Claims

1. Contains a crystal phase of an argyrodite-type crystal structure, and It includes a LiX crystalline phase on at least a portion of the surface, and The above X is at least one selected from the group consisting of F, Cl, Br, and I, Sulfide-based solid electrolyte compound.

2. In Paragraph 1, A peak intensity ratio I(200) / I(220) of the (220) plane represented by the crystalline phase of the above azirodite-type crystal structure and the (200) plane represented by the above LiX crystal phase is 0.30 or less, Sulfide-based solid electrolyte compound.

3. In Paragraph 1, In the crystal phase of the above azirodite-type crystal structure, the molar ratio of lithium (Li) elements to phosphorus (P) elements Li / P is greater than 5.7 and less than 6.15, Sulfide-based solid electrolyte compound.

4. In Paragraph 1, In the crystal phase of the above azirodite-type crystal structure, the molar ratio S / P of sulfur (S) and phosphorus (P) elements is 4.00 to 6.00, Sulfide-based solid electrolyte compound.

5. In Paragraph 1, The crystal phase of the above-mentioned azirodite-type crystal structure comprises two or more halogen elements, Sulfide-based solid electrolyte compound.

6. In Paragraph 1, In the crystal phase of the above agrodite-type crystal structure, the molar ratio X / P of the halogen (X) element and the phosphorus (P) element is 1.00 to 2.00, Sulfide-based solid electrolyte compound.

7. In Paragraph 6, In the crystal phase of the above azyrodite-type crystal structure, the molar ratio of phosphorus (P) element to the total sum of lithium (Li) element and halogen (X) element (Li+X) / P is greater than 7.00, Sulfide-based solid electrolyte compound.

8. In Paragraph 1, The crystalline phase of the above azirodite-type crystal structure is represented by the following chemical formula 1, Sulfide-based solid electrolyte compounds for lithium-ion batteries: [Chemical Formula 1] Li 7-x+y PS 6-x Cl x Br y In the above chemical formula 1, 1≤x≤1.6, 0 <y≤0.4이다.

9. In Paragraph 8, A peak intensity ratio I(200) / I(220) of the (220) plane represented by the crystalline phase of the above azirodite-type crystal structure and the (200) plane represented by the above LiCl crystal phase is 0.30 or less, Sulfide-based solid electrolyte compound.

10. In Paragraph 1, The lattice constant of the crystal phase of the above azirodite-type crystal structure is greater than 9.439 Å and less than 9.645 Å, Sulfide-based solid electrolyte compound.

11. In Paragraph 1, A mixture of lithium sulfide (Li2S) powder, phosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder, and lithium bromide (LiBr) powder, and calcined at 350–600°C under an inert atmosphere or at 350–650°C under an atmosphere containing hydrogen sulfide gas, obtained Sulfide-based solid electrolyte compound.

12. In Paragraph 11, The content of the lithium chloride (LiCl) powder is higher than the content of the lithium bromide (LiBr) powder. Sulfide-based solid electrolyte compound.

13. A sulfide-based solid electrolyte compound according to any one of claims 1 to 12, Solid electrolyte membrane.

14. A solid electrolyte membrane according to paragraph 13, Lithium secondary battery.

Images