Solid electrolyte sheet, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention relates to a solid electrolyte sheet including a first solid electrolyte layer and a second solid electrolyte layer located on the first solid electrolyte layer, wherein the first solid electrolyte layer includes a first solid electrolyte, the second solid electrolyte layer includes a second solid electrolyte, and the density of the first solid electrolyte is greater than the density of the second solid electrolyte.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte sheet, a method for manufacturing the same, and a lithium secondary battery including the same, and more specifically to a solid electrolyte sheet using two different types of solid electrolytes, a method for manufacturing the same, and a lithium secondary battery including the same. [Background technology]

[0002] As research into the safety and energy density of high-capacity batteries has been gaining attention, all-solid-state batteries are gaining attention as the next generation of batteries. All-solid-state batteries replace liquid electrolytes, which can cause explosions, with solid electrolytes, eliminating the use of flammable solvents within the battery and eliminating the risk of fires or explosions caused by reactions such as the decomposition of conventional electrolytes, ensuring the safety of the battery.

[0003] In addition, since lithium metal or lithium alloys can be used as the negative electrode material, the energy density relative to the mass and volume of the battery can be improved.The solid electrolyte used in the all-solid-state battery is generally an inorganic solid electrolyte, and various studies have been conducted on sulfide-based solid electrolytes having compositions such as Li6PS5Cl, which has an argyrodite structure.

[0004] To put all-solid-state batteries into practical use, large-area batteries must be produced, but to produce large-area all-solid-state batteries, it is necessary to make the cathode, separator, and anode into sheets, just like existing lithium-ion batteries. In particular, the separator consists of a solid electrolyte and a binder, and its properties (ionic conductivity, electrochemical stability, chemical stability) vary depending on the manufacturing method and the solid electrolyte material selected.

[0005] In the case of all-solid-state batteries, the solid electrolyte for the positive electrode composite and the solid electrolyte for the negative electrode composite can be used separately. The solid electrolyte in the positive electrode composite needs to be small in size to increase the contact area with the positive electrode active material, and it needs to have low interfacial resistance with the positive electrode and be stable at high voltages. On the other hand, the negative electrode composite needs to have a large contact area with the negative electrode active material, form a stable interface with the negative electrode material (lithium, silicon, graphite), and use a solid electrolyte that has stable properties at low voltages.

[0006] Therefore, in an all-solid-state battery, the solid electrolyte membrane sheet that functions as a separator between the positive electrode and the negative electrode must be made of a solid electrolyte material that has low interfacial resistance between the positive electrode and the negative electrode. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a solid electrolyte sheet that has low interfacial resistance between a positive electrode active material and a negative electrode active material, allows for a large contact area, and has excellent voltage stability, thereby providing excellent ion conductivity and, when applied to a lithium secondary battery, provides excellent electrochemical properties of the battery.

[0008] Another object of the present invention is to provide a method for producing a solid electrolyte sheet that is simple, has excellent process efficiency, and has the above-mentioned advantages.

[0009] Another object of the present invention is to provide a lithium secondary battery including a solid electrolyte sheet having the above advantages. [Means for solving the problem]

[0010] One embodiment of the present invention provides a solid electrolyte sheet comprising a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer, wherein the first solid electrolyte layer comprises a first solid electrolyte and the second solid electrolyte layer comprises a second solid electrolyte, the density of the first solid electrolyte being higher than the density of the second solid electrolyte, and the density difference between the first and second solid electrolytes being 0.15 to 1.65 g / cc.

[0011] The density of the first solid electrolyte may be 1.4 to 3.4 g / cc.

[0012] The density of the second solid electrolyte may be 1.1 to 2.1 g / cc.

[0013] The weight ratio of the first solid electrolyte to the second solid electrolyte may be 3:7 to 7:3.

[0014] The first solid electrolyte may be a halide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination thereof.

[0015] The sulfide-based solid electrolyte may have an argyrodite-based crystal structure.

[0016] The halide-based solid electrolyte may be represented by the following Chemical Formula 1, and the sulfide-based solid electrolyte may have an argyrodite-based crystal structure and may be represented by the following Chemical Formula 2. [Chemical formula 1] Li x M y A z [Chemical formula 2] Li 6-x PS 5-x D 1+x In the above Chemical Formula 1, M is Sc, In, Zr, Lu, Er, Y, Ho, or a combination thereof; A is F, Cl, Br, I, or a combination thereof; 1.5≦x≦3.5, 0.5≦y≦1.5, and 5≦z≦7; In the above Chemical Formula 2, 0≦x≦1, and D is F, Cl, B, I, or a combination thereof.

[0017] The second solid electrolyte may be a sulfide-based solid electrolyte.

[0018] The sulfide-based solid electrolyte has an argyrodite-based crystal structure and may be represented by the following Chemical Formula 3: [Chemical formula 3] Li 6-x PS 5-x E 1+x In the above Chemical Formula 3, 0≦x≦1, and E is F, Cl, B, I, or a combination thereof.

[0019] Another embodiment of the present invention provides a method for manufacturing a solid electrolyte sheet, the method including: forming a composition including a first solid electrolyte, a second solid electrolyte, a solvent, and a binder; applying the composition to a substrate; and drying the applied composition to form a solid electrolyte sheet, wherein the density of the first solid electrolyte is higher than the density of the second solid electrolyte, and the density difference between the first and second solid electrolytes is 0.15 to 1.65 g / cc.

[0020] The density of the first solid electrolyte may be 1.4 to 3.4 g / cc.

[0021] The density of the second solid electrolyte may be 1.1 to 2.1 g / cc.

[0022] The weight ratio of the first solid electrolyte to the second solid electrolyte may be 3:7 to 7:3.

[0023] In the step of drying the applied composition to form a solid electrolyte sheet, the first solid electrolyte and the second solid electrolyte may be separated during the drying due to a difference in density, forming a first solid electrolyte layer including the first solid electrolyte and a second solid electrolyte layer disposed on the first solid electrolyte layer and including the second solid electrolyte.

[0024] Another embodiment of the present invention provides an electrochemical cell comprising: a positive electrode; a negative electrode; and a solid electrolyte sheet located between the positive electrode and the negative electrode, the solid electrolyte sheet comprising a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer, the first solid electrolyte layer comprising a first solid electrolyte, and the second solid electrolyte layer comprising a second solid electrolyte, the density of the first solid electrolyte being higher than the density of the second solid electrolyte, the density difference between the first and second solid electrolytes being 0.15 to 1.65 g / cc, the first solid electrolyte layer being located on the positive electrode side, and the second solid electrolyte layer being located on the negative electrode side.

[0025] Another embodiment of the present invention provides an electric vehicle including the electrochemical cell. [Effects of the Invention]

[0026] In the solid electrolyte sheet according to one embodiment of the present invention, by appropriately adjusting the density and composition of the first solid electrolyte and the second solid electrolyte, the interfacial resistance with the positive electrode active material and the negative electrode active material of the battery can be reduced, the contact area can be increased, and the voltage stability can be improved, resulting in excellent ion conductivity and excellent electrochemical properties of the battery using the same.

[0027] The method for manufacturing a solid electrolyte sheet according to another embodiment of the present invention has excellent process efficiency due to the difference in density between the first solid electrolyte and the second solid electrolyte. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic cross-sectional view of a solid electrolyte sheet according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram schematically illustrating a process of forming a solid electrolyte sheet by drying an applied composition in a method for producing a solid electrolyte sheet according to another embodiment of the present invention. [Figure 3]FIG. 1 is a schematic cross-sectional view of an electrochemical cell (lithium secondary battery) according to another embodiment of the present invention, in which a positive electrode (or positive electrode composite), a negative electrode (or negative electrode composite), and a solid electrolyte sheet form a laminated structure. [Figure 4] 1 is a SEM image of a cross section of a solid electrolyte sheet manufactured according to Example 1. [Figure 5] 1 is a SEM image of a cross section of a solid electrolyte sheet manufactured according to Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0029] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0030] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the phrase clearly indicates otherwise. As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0031] Also, when one part is "on" or "above" another, this does not only mean that it is "directly on top" of the other, but also when there are other parts in between. Conversely, when one part is "directly above" another, there are no other parts in between.

[0032] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. Terms defined in commonly used dictionaries are further interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not to be interpreted in an ideal or very formal sense unless defined.

[0033] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0034] As used herein, "combinations thereof" expressed in Markush form means a mixture or combination of one or more components selected from the group consisting of components expressed in Markush form, and means that at least one component selected from the group consisting of the components is included.

[0035] The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the exemplary embodiments set forth herein.

[0036] <1. Solid electrolyte sheet> One embodiment of the present invention provides a solid electrolyte sheet comprising a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer, wherein the first solid electrolyte layer comprises a first solid electrolyte and the second solid electrolyte layer comprises a second solid electrolyte, the density of the first solid electrolyte being higher than the density of the second solid electrolyte, and the density difference between the first and second solid electrolytes being 0.15 to 1.65 g / cc.

[0037] FIG. 1 is a schematic cross-sectional view of a solid electrolyte sheet according to one embodiment of the present invention.

[0038] Referring to FIG. 1, a solid electrolyte sheet 100 according to one embodiment of the present invention includes a first solid electrolyte layer 10 and a second solid electrolyte layer 20 disposed on the first solid electrolyte layer.

[0039] The first solid electrolyte layer 10 includes a first solid electrolyte, and the second solid electrolyte layer 20 includes a second solid electrolyte.

[0040] In the present invention, when mounted in a lithium secondary battery, the first solid electrolyte layer can be located on the positive electrode side, and the second solid electrolyte layer can be located on the negative electrode side.

[0041] The first solid electrolyte contained in the first solid electrolyte layer is in contact with the positive electrode active material, and therefore must have good electrochemical stability with the positive electrode active material. More specifically, the particles must be small to increase the contact area with the positive electrode active material, and the interfacial resistance with the positive electrode active material must be small and stable at high voltages.

[0042] On the other hand, the second solid electrolyte contained in the second solid electrolyte layer is in contact with the negative electrode active material, and therefore must have good electrochemical stability with the negative electrode active material. More specifically, it must have a large contact area with the negative electrode active material, large particles to facilitate ion migration, small interfacial resistance with the negative electrode active material, and be stable at low voltage.

[0043] In particular, the density of the first solid electrolyte is higher than the density of the second solid electrolyte, and the density difference between the first solid electrolyte and the second solid electrolyte is 0.15 to 1.65 g / cc.

[0044] The first solid electrolyte is a halide-based solid electrolyte or a sulfide-based solid electrolyte that has a halogen-rich composition, high ionic conductivity, and is electrochemically stable as a positive electrode active material, while the second solid electrolyte is a sulfide-based solid electrolyte that is stable as a negative electrode, but has a halogen-less composition, low ionic conductivity, and is stable as a negative electrode active material.

[0045] Since the density of the first solid electrolyte is greater than that of the second solid electrolyte, the battery can have excellent capacity, initial efficiency, and life characteristics. Furthermore, as will be described later, there is an advantage in that the manufacturing process of the solid electrolyte sheet according to the present invention is efficient. Details will be described later.

[0046] In particular, the density difference between the first solid electrolyte and the second solid electrolyte may be 0.15 to 1.65 g / cc, more specifically, 1.0 to 1.65 g / cc or 1.0 to 1.5 g / cc. By adjusting the density difference in this manner, the above-mentioned effects can be maximized. More specifically, if the density difference is too large, the ionic conductivity of the solid electrolyte sheet may be degraded, while if the density difference is too small, the capacity, initial efficiency, and life characteristics of the battery may be degraded.

[0047] In this specification, the solid electrolyte density can be measured by applying a pressure of 20 MPa to the produced solid electrolyte powder, pelletizing it, and then measuring the volume and weight under room temperature and atmospheric pressure conditions.

[0048] If the density of the first solid electrolyte is too high, there is no problem of layer separation from the second solid electrolyte during the manufacturing process, as described in the manufacturing method below, but there is a risk of problems such as a decrease in the energy density of the cell due to an increase in the solid electrolyte density and a decrease in the ionic conductivity of the solid electrolyte sheet due to an excessively large density difference between the first solid electrolyte and the second solid electrolyte.On the other hand, if the density of the first solid electrolyte is too low, there is a risk of problems such as difficulty in layer separation from the second solid electrolyte during the manufacturing process, as described below, and a decrease in the capacity, initial efficiency, and life characteristics of the battery due to an excessively small density difference between the second solid electrolyte and the first solid electrolyte.

[0049] More specifically, the density of the second solid electrolyte may be 1.1 to 2.1 g / cc. If the density of the second solid electrolyte is too high, it may be difficult to separate the second solid electrolyte from the first solid electrolyte, and the density difference between the second solid electrolyte and the first solid electrolyte may be too small, resulting in deterioration of the battery's capacity, initial efficiency, and life characteristics. On the other hand, if the density of the second solid electrolyte is too low, it may float to the solvent surface, and the density difference between the second solid electrolyte and the first solid electrolyte may be too large, resulting in deterioration of the ionic conductivity of the solid electrolyte sheet.

[0050] The first solid electrolyte may be a halide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination thereof. The first solid electrolyte may be a halide-based solid electrolyte or a sulfide-based solid electrolyte, thereby satisfying the aforementioned required characteristics of the first solid electrolyte. Specifically, the interfacial resistance with the positive electrode active material is low, and the first solid electrolyte is stable at high voltages, resulting in excellent ionic conductivity of the solid electrolyte sheet and excellent electrochemical properties of the battery.

[0051] More specifically, the halide-based solid electrolyte can be represented by the following Chemical Formula 1:

[0052] [Chemical formula 1] Li x M y A z In Chemical Formula 1, M is Sc, In, Zr, Lu, Er, Y, Ho, or a combination thereof; A is F, Cl, Br, I, or a combination thereof; and 1.5≦x≦3.5, 0.5≦y≦1.5, and 5≦z≦7.

[0053] For example, the halide-based solid electrolyte may be, but is not limited to, Li3InCl6, Li2ZrCl6, Li3ScCl6, Li2ErCl6, Li2LuCl6, Li2HoCl6, and the like.

[0054] The sulfide-based solid electrolyte may have an argyrodite-based crystal structure. Among sulfide-based solid electrolytes, the argyrodite-based crystal structure may be particularly advantageous in terms of ionic conductivity.

[0055] More specifically, the sulfide-based solid electrolyte can be represented by the following Chemical Formula 2.

[0056] [Chemical formula 2] Li 6-x PS 5-x D 1+x In the above Chemical Formula 2, 0≦x≦1, and D is F, Cl, B, I, or a combination thereof.

[0057] For example, the sulfide-based solid electrolyte may be Li6PS5Cl, Li 5.7 PS 4.7 Cl 1.3 , Li 5.5 PS 4.5 Cl 1.5 It may be, but is not limited to, the above.

[0058] Preferably, the size of the first solid electrolyte particles may be 3 μm or less. Such a sufficiently small size of the first solid electrolyte particles can increase the contact area with the positive electrode active material.

[0059] In this specification, the term "particle size" refers to the average particle size when the particles of the solid electrolyte or positive electrode active material are spherical, and refers to the length of the major axis when the particles are non-spherical.

[0060] On the other hand, the second solid electrolyte may be a sulfide-based solid electrolyte. The sulfide-based solid electrolyte can satisfy the aforementioned required characteristics of the second solid electrolyte. That is, the interfacial resistance with the negative electrode active material is low, and the solid electrolyte sheet is stable at low voltage, resulting in excellent ionic conductivity and excellent electrochemical properties of the battery.

[0061] The sulfide-based solid electrolyte may have an argyrodite-based crystal structure.

[0062] The sulfide-based solid electrolyte can be represented by the following Chemical Formula 3.

[0063] [Chemical formula 3] Li 6-x PS 5-x E 1+x In the above Chemical Formula 3, 0≦x≦1, and E is F, Cl, B, I, or a combination thereof.

[0064] Preferably, the size of the second solid electrolyte particles may be 3 μm to 10 μm. Such a sufficiently large size of the second solid electrolyte particles can increase the contact area with the negative electrode active material, making ion migration easier.

[0065] Meanwhile, the weight ratio of the first solid electrolyte to the second solid electrolyte may be 3:7 to 7:3. If the content of the first solid electrolyte is too small, the first solid electrolyte layer may not cover the entire second solid electrolyte layer, which may result in a problem that the second solid electrolyte layer comes into contact with the positive electrode. If the content of the second solid electrolyte is too large, the second solid electrolyte layer may not cover the entire first solid electrolyte layer, which may result in a problem that the first solid electrolyte layer comes into contact with the negative electrode. If the second solid electrolyte layer comes into contact with the positive electrode or the first solid electrolyte layer comes into contact with the negative electrode, an electrochemical side reaction may occur, which may result in a deterioration of the battery characteristics.

[0066] 2. Manufacturing method of solid electrolyte sheet FIG. 2 is a flowchart of a method for manufacturing a solid electrolyte sheet according to another embodiment of the present invention.

[0067] Referring to FIG. 2 , another embodiment of the present invention provides a method for manufacturing a solid electrolyte sheet, including: forming a composition including a first solid electrolyte, a second solid electrolyte, a solvent, and a binder; applying the composition to a substrate; and drying the applied composition to form a solid electrolyte sheet, wherein the density of the first solid electrolyte is higher than the density of the second solid electrolyte, and the density difference between the first and second solid electrolytes is 0.15 to 1.65 g / cc.

[0068] Hereinafter, each step of a method for manufacturing a solid electrolyte sheet according to another embodiment of the present invention will be described in detail.

[0069] First, a composition containing a first solid electrolyte, a second solid electrolyte, a solvent, and a binder is formed.

[0070] In this case, the density of the first solid electrolyte is higher than that of the second solid electrolyte, and the density difference between the first solid electrolyte and the second solid electrolyte is 0.15 to 1.65 g / cc. The advantages of this will be described in more detail in the drying step below.

[0071] The first solid electrolyte may be a halide-based solid electrolyte or a sulfide-based solid electrolyte.

[0072] More specifically, the halide-based solid electrolyte can be represented by the following Chemical Formula 1:

[0073] [Chemical formula 1] Li x M y A z In Chemical Formula 1, M is Sc, In, Zr, Lu, Er, Y, Ho, or a combination thereof; A is F, Cl, Br, I, or a combination thereof; and 1.5≦x≦3.5, 0.5≦y≦1.5, and 5≦z≦7.

[0074] For example, the halide-based solid electrolyte may be, but is not limited to, Li3InCl6, Li2ZrCl6, Li3ScCl6, Li2ErCl6, Li2LuCl6, Li2HoCl6, and the like.

[0075] The sulfide-based solid electrolyte may have an argyrodite-based crystal structure.

[0076] More specifically, the sulfide-based solid electrolyte can be represented by the following Chemical Formula 2.

[0077] [Chemical formula 2] Li 6-x PS 5-x D 1+x In the above Chemical Formula 2, 0≦x≦1, and D is F, Cl, B, I, or a combination thereof.

[0078] For example, the sulfide-based solid electrolyte may be Li6PS5Cl, Li 5.7 PS 4.7 Cl 1.3 , Li 5.5 PS 4.5 Cl 1.5 It may be, but is not limited to, the above.

[0079] Preferably, the size of the first solid electrolyte particles may be 3 μm or less. The advantages associated with this are the same as those described above, and therefore will not be described here.

[0080] The second solid electrolyte may be a sulfide-based solid electrolyte.

[0081] The sulfide-based solid electrolyte may have an argyrodite-based crystal structure.

[0082] The sulfide-based solid electrolyte can be represented by the following Chemical Formula 3.

[0083] [Chemical formula 3] Li6-x PS 5-x E 1+x In the above Chemical Formula 3, 0≦x≦1, and E is F, Cl, B, I, or a combination thereof.

[0084] Preferably, the size of the second solid electrolyte particles may be 3 μm to 10 μm. The advantages associated with this are the same as those described above, and therefore will not be described here.

[0085] The density of the first solid electrolyte may be 1.4 to 3.4 g / cc. The advantages associated with this are the same as those described above, and therefore will not be described here.

[0086] The density of the second solid electrolyte may be 1.1 to 2.1 g / cc. The advantages associated with this are the same as those described above, and therefore will not be described here.

[0087] Meanwhile, the weight ratio of the first solid electrolyte to the second solid electrolyte may be 3:7 to 7:3. The advantages associated with this are the same as those described above, and therefore will not be described here.

[0088] The solvent is not particularly limited as long as it is used as a solvent for solid electrolytes in the art. For example, one or more selected from xylene, toluene, and isobutyl isobutyrate may be used, but is not limited thereto.

[0089] The binder is not particularly limited as long as it is used as a binder in the art, and may be, for example, one or more selected from nitrile butadiene rubber (NBR), PTFE, styrene-butadiene-styrene copolymer, acrylic resin, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate, but is not limited thereto.

[0090] Of course, it goes without saying that the composition may further contain other additives to improve other properties as needed.

[0091] The composition is then applied onto a substrate.

[0092] The material of the substrate is not particularly limited as long as it is chemically stable to the slurry.

[0093] For example, the substrate may include one or more selected from PET (Polyethyleneterephthalate), PEN (Polyethylenenaphthalate), PES (Polyethersulfone), PC (Polycarbonate), PP (Polypropylene), and porous nonwoven fabric, but is not limited thereto.

[0094] The applied composition is then dried to form a solid electrolyte sheet.

[0095] FIG. 2 is a diagram schematically illustrating the process of forming a solid electrolyte sheet by drying the applied composition.

[0096] 2, as described above, the density of the first solid electrolyte is higher than the density of the second solid electrolyte. The first and second solid electrolytes, which were uniformly dispersed and mixed in the slurry formation step, naturally separate and form layers during the drying process due to the difference in density. As a result, a first solid electrolyte layer including the first solid electrolyte and a second solid electrolyte layer disposed on the first solid electrolyte layer and including the second solid electrolyte can be formed.

[0097] In the prior art, when forming a solid electrolyte sheet or laminate using two types of solid electrolytes, a sequential lamination method was used in which a first layer was formed and then a second layer was formed on the first layer. This sequential lamination method had the problem of poor process efficiency. In contrast, the method for manufacturing a solid electrolyte according to the present invention forms a composition containing both the first and second solid electrolytes, and then undergoes a natural separation process due to the difference in density between the first and second solid electrolytes, thereby forming a laminate of the first and second solid electrolyte layers in one step. Therefore, it has the advantage of excellent process efficiency.

[0098] In particular, when the density difference between the first solid electrolyte and the second solid electrolyte is 0.15 to 1.65 g / cc, the formation of the laminate through the separation process can be carried out efficiently. More specifically, if the density difference is too small, the first solid electrolyte and the second solid electrolyte may be mixed together without being separated into layers, whereas if the density difference is too large, the first solid electrolyte layer and the second solid electrolyte layer may be separated after drying.

[0099] The method for such a coating step is not particularly limited as long as it is a method commonly used in the art, and for example, blade coating can be used.

[0100] 3. Electrochemical Cell Another embodiment of the present invention provides an electrochemical cell comprising: a positive electrode; a negative electrode; and a solid electrolyte sheet located between the positive electrode and the negative electrode, the solid electrolyte sheet comprising a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer, the first solid electrolyte layer comprising a first solid electrolyte, and the second solid electrolyte layer comprising a second solid electrolyte, the density of the first solid electrolyte being higher than the density of the second solid electrolyte, the density difference between the first and second solid electrolytes being 0.15 to 1.65 g / cc, the first solid electrolyte layer being located on the positive electrode side, and the second solid electrolyte layer being located on the negative electrode side.

[0101] The electrochemical cell is not particularly limited, and may be, for example, a lithium secondary battery.

[0102] FIG. 3 is a schematic cross-sectional view of an electrochemical cell (lithium secondary battery) according to another embodiment of the present invention, in which a positive electrode (or positive electrode composite), a negative electrode (or negative electrode composite), and a solid electrolyte sheet form a laminated structure.

[0103] Referring to FIG. 3, a first solid electrolyte layer including a first solid electrolyte may be located on the positive electrode side (positive electrode composite), and a second solid electrolyte layer may be located on the negative electrode side (negative electrode composite).

[0104] As described above, the first solid electrolyte layer, which has excellent interfacial characteristics with the positive electrode, is located on the positive electrode side, and the second solid electrolyte layer, which has excellent interfacial characteristics with the negative electrode, is located on the negative electrode side, thereby achieving excellent electrochemical characteristics of the secondary battery. [Example]

[0105] Hereinafter, the present invention will be described in more detail with reference to the following examples, which are merely preferred examples of the present invention and are not intended to limit the scope of the present invention.

[0106] Comparative Example 1: Type 1 Li6PS5Cl solid electrolyte sheet (1) Manufacturing of solid electrolytes Li6PS5Cl was synthesized by dry milling. Specifically, the dry milling process involved weighing out Li2S, P2S5, and LiCl according to the composition, mixing them at 300 rpm for 8 hours using a planetary mill, and then forming pellets at 300 MPa. The pellets were then heat-treated at 550°C in an argon (Ar) atmosphere to synthesize Li6PS5Cl argyrodite-based solid electrolyte. The volume and mass of the pellets were measured to determine the density. The density of the solid electrolyte was 1.4 g / cc under atmospheric pressure and room temperature conditions.

[0107] (2) Manufacturing of solid electrolyte sheets The synthesized solid electrolyte was mixed with 3 wt % NBR binder dissolved in xylene to form a slurry (composition).

[0108] Then, the slurry (composition) was applied onto a PET substrate by blade coating.

[0109] Thereafter, the applied slurry (composition) was dried at 50° C. to form a solid electrolyte sheet.

[0110] (3) Manufacture of lithium secondary batteries The solid electrolyte sheet was subjected to electrochemical evaluation using a powder cell. 2 The solid electrolyte sheet is then removed from the PET carrier film and placed in a pressed cell. The composite electrode is then loaded onto the sheet. The composite electrode is made of a positive electrode, solid electrolyte, and conductive agent (Denka Black) in a ratio of 70:29:1 wt%, with an area of ​​0.785 cm. 2 The electrodes were fabricated with a 20.0 mg load at an area of ​​1000 mW and densified at 300 MPa. They were then bonded with an In-Li counter electrode at 50 MPa and the cell was clamped at the same pressure.

[0111] Comparative example 2: Type 1 Li 5.7 PS 4.7 Cl 1.3 Solid Electrolyte Sheet Li2S, P2S5, and LiCl were used to change the composition. 5.7 PS 4.7 Cl 1.3 Except for the synthesis of the solid electrolyte, a solid electrolyte, a solid electrolyte sheet, and a lithium secondary battery were manufactured in the same manner as in Comparative Example 1. The density of the manufactured solid electrolyte was 1.6 g / cc under atmospheric pressure and room temperature conditions.

[0112] Comparative example 3: Type 1 Li 5.5 PS 4.5 Cl 1.5 Solid Electrolyte Sheet Li2S, P2S5, and LiCl were used to change the composition. 5.5 PS 4.5 Cl 1.5 Except for the synthesis of the solid electrolyte, a solid electrolyte, a solid electrolyte sheet, and a lithium secondary battery were manufactured in the same manner as in Comparative Example 1. The density of the manufactured solid electrolyte was 1.8 g / cc under atmospheric pressure and room temperature conditions.

[0113] Comparative Example 4: Type 1 Li3InCl6 solid electrolyte sheet (1) Manufacturing of solid electrolytes Li3InCl6, a halide-based solid electrolyte, was synthesized by dry milling and mixing LiCl and InCl3 according to the composition, vacuum drying, and then heat treatment at 270°C. The ionic conductivity of the Li3InCl6 powder was 0.63 mS / cm, and the electronic conductivity was 1.52 × 10 -9 The density of the produced solid electrolyte was 3 g / cc under atmospheric pressure and room temperature conditions.

[0114] (2) Manufacturing of solid electrolyte sheets and lithium secondary batteries A solid electrolyte sheet and a lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that the synthesized Li3InCl6 solid electrolyte was used.

[0115] Example 1: Li3InCl6 and Li6PS5Cl50: 50 wt% two-type solid electrolyte sheet (1) Manufacturing of solid electrolytes The same procedures as in Comparative Examples 1 and 4 were carried out to produce Li6PS5Cl solid electrolyte and Li3InCl6 solid electrolyte.

[0116] (2) Manufacturing of solid electrolyte sheets A composition (slurry) was formed by mixing 50:50 parts by weight of Li3InCl6 solid electrolyte as the first solid electrolyte and Li6PS5Cl solid electrolyte as the second solid electrolyte with 3 wt% NBR binder dissolved in xylene.

[0117] Then, the composition (slurry) was applied onto a polyethylene terephthalate (PET) substrate using a PET carrier film by blade coating.

[0118] The applied composition (slurry) was then dried at 50°C to produce a solid electrolyte sheet including a first solid electrolyte layer containing the first solid electrolyte and a second solid electrolyte layer containing the second solid electrolyte.

[0119] (3) Lithium secondary battery manufacturing The solid electrolyte sheet was subjected to electrochemical evaluation using a powder cell. 2 The solid electrolyte sheet is then removed from the PET carrier film and placed in a pressed cell. The composite electrode is then loaded onto the sheet. The composite electrode is made of a positive electrode active material, solid electrolyte, and conductive agent (denka black) in a ratio of 70:29:1 wt%, with an area of ​​0.785 cm. 2 The electrodes were fabricated with a 20.0 mg load on an area of ​​100 μm and densified at 300 MPa. They were then bonded at 50 MPa using an In-Li counter electrode, and the cell was clamped at the same pressure. The first solid electrolyte layer was positioned on the composite electrode side, and the second solid electrolyte layer was positioned on the In-Li counter electrode side.

[0120] Example 2: Li3InCl6 and Li 5.7 PS 4.7 Cl 1.3 50:50wt% Type 2 solid electrolyte sheet The first solid electrolyte was the Li3InCl6 solid electrolyte prepared in Comparative Example 4, and the second solid electrolyte was the LiInCl6 solid electrolyte prepared in Comparative Example 2. 5.7 PS 4.7 Cl 1.3 A solid electrolyte sheet and a lithium secondary battery were produced in the same manner as in Example 1, except that a solid electrolyte was used.

[0121] Example 3: Li3InCl6 and Li 5.5 PS 4.5 Cl 1.5 50:50wt% Type 2 solid electrolyte sheet The first solid electrolyte was the Li3InCl6 solid electrolyte prepared in Comparative Example 4, and the second solid electrolyte was the LiInCl6 solid electrolyte prepared in Comparative Example 3. 5.5 PS 4.5 Cl 1.5 A solid electrolyte sheet and a lithium secondary battery were produced in the same manner as in Example 1, except that a solid electrolyte was used.

[0122] Example 4: Li 5.5 PS 4.5 Cl 1.5 and Li6PS5Cl50:50wt%2 solid electrolyte sheet The first solid electrolyte was Li produced in accordance with Comparative Example 3. 5.5 PS 4.5 Cl 1.5 A solid electrolyte sheet and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the Li6PS5Cl solid electrolyte manufactured in Comparative Example 1 was used as the solid electrolyte and the second solid electrolyte.

[0123] Example 5: Li 5.5 PS 4.5 Cl 1.5 and Li 5.7 PS 4.7 Cl 1.3 50:50wt% Type 2 solid electrolyte sheet The first solid electrolyte was Li produced in accordance with Comparative Example 3. 5.5 PS 4.5 Cl 1.5 The solid electrolyte and the second solid electrolyte were prepared according to Comparative Example 2. 5.7PS 4.7 Cl 1.3 A solid electrolyte sheet and a lithium secondary battery were produced in the same manner as in Example 1, except that a solid electrolyte was used.

[0124] Comparative Example 5 A solid electrolyte sheet and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the lithium secondary battery was manufactured so that the Li6PS5Cl solid electrolyte was located on the In-Li counter electrode side and the Li3InCl6 solid electrolyte was located on the composite electrode side of the manufactured solid electrolyte sheet.

[0125] <Experimental Example 1: Solid electrolyte sheet SEM image analysis> The cross sections of the solid electrolyte sheets manufactured in Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM), and the results are shown in FIG. 4 (Example 1) and FIG. 5 (Comparative Example 1).

[0126] 4 and 5, it was confirmed that the solid electrolyte sheet according to Example 1 has a laminate structure in which the first solid electrolyte layer and the second solid electrolyte layer are formed separately, whereas the solid electrolyte sheet according to Comparative Example 1 is in a simple mixed state without distinction of the solid electrolytes.

[0127] <Experimental Example 2: Evaluation of ionic conductivity of solid electrolyte sheet> An experiment to evaluate the ionic conductivity of the solid electrolyte sheets produced in Examples 1 to 5 and Comparative Examples 1 to 4 was carried out, and the results are shown in Table 1 below.

[0128] Specifically, the synthesized solid electrolyte was crushed and then pelletized under a pressure of 300 MPa. Then, a cell was fabricated using SUS as the working electrode under a pressure of 70 MPa. Then, a voltage of 10 mV was applied at 30°C to measure the impedance.

[0129] [Table 1]

[0130] Referring to Table 1, it was confirmed that the ionic conductivity of the solid electrolyte sheets manufactured in Examples 1 to 5 was generally excellent, but in the cases of Comparative Examples 1 and 4, the ionic conductivity was significantly reduced.

[0131] <Experimental Example 3: Evaluation of electrochemical characteristics of lithium secondary batteries> The lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 4 were subjected to an electrochemical property evaluation experiment using compressed powder cells, and the results are shown in Table 2 below. The specific experimental method is as follows.

[0132] (1) Initial charge capacity, discharge capacity and initial efficiency evaluation After the battery was manufactured, it was aged at room temperature for 2 hours and then subjected to a charge-discharge test. The capacity evaluation was performed with a reference capacity of 180 mAh / g, and the charge-discharge conditions were CC / CV 1.9 to 3.60 V with a 1 / 20 C cut-off. The initial capacity was measured under 0.1 C charge / 0.1 C discharge conditions.

[0133] (2) Lifespan characteristics evaluation The life characteristics were evaluated by calculating the percentage of the discharge capacity after 30 charge / discharge cycles relative to the initial discharge capacity.

[0134] [Table 2]

[0135] Referring to Table 2, it was confirmed that the lithium secondary batteries according to Examples 1 to 5 were generally superior in charge capacity, discharge capacity, initial efficiency, and life characteristics compared to the lithium secondary batteries according to Comparative Examples 1 to 5. In particular, it was confirmed that the lithium secondary batteries according to Examples 1 to 3 were very superior in charge capacity, discharge capacity, initial efficiency, and life characteristics. It was also confirmed that the lithium secondary battery according to Comparative Example 5 had significantly reduced charge capacity, discharge capacity, initial efficiency, and life characteristics because the density of the first solid electrolyte was lower than the density of the second solid electrolyte.

[0136] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention.

[0137] Therefore, the true scope of the invention will be defined by the appended claims and their equivalents. [Explanation of symbols]

[0138] 10: First solid electrolyte layer 20:Second solid electrolyte layer 100: Solid electrolyte sheet

Claims

1. a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer; the first solid electrolyte layer includes a first solid electrolyte, and the second solid electrolyte layer includes a second solid electrolyte; a density of the first solid electrolyte being higher than a density of the second solid electrolyte, and a density difference between the first solid electrolyte and the second solid electrolyte being 0.15 to 1.65 g / cc;

2. 2. The solid electrolyte sheet according to claim 1, wherein the density of the first solid electrolyte is 1.4 to 3.4 g / cc.

3. 2. The solid electrolyte sheet according to claim 1, wherein the density of the second solid electrolyte is 1.1 to 2.1 g / cc.

4. 2. The solid electrolyte sheet according to claim 1, wherein a weight ratio of the first solid electrolyte to the second solid electrolyte is 3:7 to 7:

3.

5. 2. The solid electrolyte sheet according to claim 1, wherein the first solid electrolyte is a halide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination thereof.

6. The halide-based solid electrolyte is represented by the following chemical formula 1: The sulfide-based solid electrolyte has an argyrodite-based crystal structure and is a solid electrolyte sheet represented by the following chemical formula 2: [Chemical formula 1] Li ｘ M ｙ A ｚ [Chemical formula 2] Li ６－ｘ PS ５－ｘ D １＋ｘ In Formula 1, M is Sc, In, Zr, Lu, Er, Y, Ho, or a combination thereof; A is F, Cl, Br, I, or a combination thereof; 1.5≦x≦3.5, 0.5≦y≦1.5, and 5≦z≦7; In Formula 2, 0≦x≦1, and D is F, Cl, B, I, or a combination thereof.

7. The solid electrolyte sheet according to claim 1 , wherein the second solid electrolyte is a sulfide-based solid electrolyte.

8. The solid electrolyte sheet according to claim 7, wherein the sulfide-based solid electrolyte has an argyrodite-based crystal structure and is represented by the following chemical formula 3: [Chemical formula 3] Li ６－ｘ PS ５－ｘ E １＋ｘ In Formula 3, 0≦x≦1, and E is F, Cl, B, I, or a combination thereof.

9. forming a composition comprising a first solid electrolyte, a second solid electrolyte, a solvent, and a binder; applying the composition onto a substrate; and drying the applied composition to form a solid electrolyte sheet; a density of the first solid electrolyte being higher than a density of the second solid electrolyte, and a density difference between the first solid electrolyte and the second solid electrolyte being 0.15 to 1.65 g / cc.

10. 10. The method for manufacturing a solid electrolyte sheet according to claim 9, wherein the density of the first solid electrolyte is 1.4 to 3.4 g / cc.

11. 10. The method for manufacturing a solid electrolyte sheet according to claim 9, wherein the density of the second solid electrolyte is 1.1 to 2.1 g / cc.

12. 10. The method for manufacturing a solid electrolyte sheet according to claim 9, wherein a weight ratio of the first solid electrolyte to the second solid electrolyte is 3:7 to 7:

3.

13. drying the applied composition to form a solid electrolyte sheet, 10. The method for manufacturing a solid electrolyte sheet according to claim 9, wherein during the drying, the first solid electrolyte and the second solid electrolyte are separated due to a difference in density, thereby forming a first solid electrolyte layer including the first solid electrolyte and a second solid electrolyte layer disposed on the first solid electrolyte layer and including the second solid electrolyte.

14. a positive electrode; a negative electrode; and a solid electrolyte sheet located between the positive electrode and the negative electrode; the solid electrolyte sheet includes a first solid electrolyte layer and a second solid electrolyte layer disposed on the first solid electrolyte layer, the first solid electrolyte layer includes a first solid electrolyte, and the second solid electrolyte layer includes a second solid electrolyte; the density of the first solid electrolyte is higher than the density of the second solid electrolyte, and the density difference between the first solid electrolyte and the second solid electrolyte is 0.15 to 1.65 g / cc; An electrochemical cell, wherein the first solid electrolyte layer is located on the positive electrode side, and the second solid electrolyte layer is located on the negative electrode side.

15. An electric vehicle comprising the electrochemical cell of claim 14.

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