All-solid-state batteries containing binders having polar functional groups

Abstract

An all-solid-state battery containing a binder having a polar functional group is disclosed. Specifically, an all-solid-state battery includes a negative electrode current collector, a negative electrode layer disposed on the negative electrode current collector, a solid electrolyte layer disposed on the negative electrode layer, a positive electrode layer disposed on the solid electrolyte layer, a positive electrode current collector disposed on the positive electrode layer, and a binder having a polar functional group.

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery containing an adhesive having a polar functional group. Background Art

[0002] The importance of anode-based technologies for improving the energy density of all-solid-state batteries is being recognized. Active materials for silicon-based anodes and all-solid-state batteries containing silicon-based anode active materials are being actively studied. However, during charge and discharge, the volume of the silicon-based anode active material changes significantly. Therefore, there may be problems such as cracks in the anode layer or separation of the anode layer from the current collector, resulting in a loss of reversible capacity of the all-solid-state battery. Although silicon-based anode active materials and all-solid-state batteries containing silicon-based anode active materials have the advantage of high charge capacity, they also have disadvantages such as poor cycling characteristics and low capacity retention rate.

[0003] Therefore, research and development are being actively carried out to improve the bonding strength of the adhesive forming the anode layer to achieve charge and discharge stability of all-solid-state batteries containing silicon-based anode active materials. However, all-solid-state batteries containing sulfide-based solid electrolytes have the following limitations: a non-polar solvent compatible with the sulfide-based solid electrolyte must be used during the slurry preparation process. Therefore, rubber-based adhesives without polar functional groups are usually used, resulting in a very low bonding strength. In addition, when the amount of the adhesive is increased to improve the bonding strength, the resistance may increase, leading to a decrease in battery performance. Summary of the Invention

[0004] An object of the present invention is to provide an all-solid-state battery having a high bonding strength between the anode layer and the anode current collector.

[0005] Another object of the present invention is to provide an all-solid-state battery capable of reducing the resistance in the anode layer.

[0006] The object of the present invention is not limited to the above-mentioned objects. From the following description and the appended claims, the above and other objects of the present invention will become more apparent.

[0007] According to an embodiment of the present invention, a all-solid-state battery is provided. The all-solid-state battery includes a negative electrode current collector. The all-solid-state battery further includes a negative electrode layer disposed on the negative electrode current collector and a solid electrolyte layer disposed on the negative electrode layer. The all-solid-state battery further includes a positive electrode layer disposed on the solid electrolyte layer and a positive electrode current collector disposed on the positive electrode layer. The negative electrode layer includes a first layer disposed on the negative electrode current collector. The first layer contains a first negative electrode active material and a first binder. The negative electrode layer further includes a second layer disposed on the first layer. The second layer contains a second negative electrode active material and a second binder. Each of the first binder and the second binder has a non-polar main chain and a polar functional group bonded to the non-polar main chain. In the negative electrode layer of the all-solid-state battery, the content of the first binder is higher than the content of the second binder.

[0008] Each of the first negative electrode active material and the second negative electrode active material may include a silicon-based negative electrode active material.

[0009] The non-polar main chain may include at least one of butadiene rubber (BR), styrene-butadiene rubber (SBR), or any combination thereof.

[0010] The polar functional group may include at least one of a carboxyl group, an acrylic group, or any combination thereof.

[0011] Each of the first binder and the second binder may have a polar functional group of 1 weight percentage (wt%) to 10 weight percentage with respect to its total weight.

[0012] The thickness (T 1 ) of the first layer and the thickness (T 2 ) of the second layer ratio (T 1 : T 2 ) may be in the range of 1:2 to 1:3.

[0013] The thickness of the negative electrode layer may be in the range of 20 micrometers (μm) to 100 micrometers (μm).

[0014] In the negative electrode layer, the ratio (A 1 ) of the content of the first binder and the content (A 2 ) of the second binder (A 1 : A 2 ) may be in the range of 1:0.1 to 1:0.5.

[0015] According to an embodiment of the present invention, a all-solid-state battery is provided, which has a high adhesion strength between the negative electrode layer and the negative electrode current collector, and at the same time has a low resistance in the negative electrode layer.

[0016] According to an embodiment of the present invention, a all-solid-state battery with a high energy density is provided.

[0017] The effects of the present invention are not limited to the above effects. It should be understood that the effects of the present invention include all effects that can be derived from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Shows a all-solid-state battery according to an embodiment of the present invention;

[0019] Figure 2 Shows a scanning electron microscope (SEM) analysis of the negative electrode layer according to Example 1;

[0020] Figure 3 Shows an energy dispersive X-ray spectroscopy (EDS) analysis of the negative electrode layer according to Example 1;

[0021] Figure 4 Shows the capacity retention rates of all-solid-state batteries according to Example 1 and 2 and Comparative Examples 1 and 2;

[0022] Figure 5 Shows the rate of the negative electrodes of all-solid-state batteries according to Example 1 and Comparative Examples 1 and 2, and the results were obtained when each negative electrode was lithiated;

[0023] Figure 6 Shows the rate of the negative electrodes of all-solid-state batteries according to Example 1 and Comparative Examples 1 and 2, and the results were obtained when each negative electrode was delithiated; and

[0024] Figure 7 Shows the capacity retention rates for each rate of all-solid-state batteries according to Example 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0025] The above objects, other objects, features, and advantages of the present invention will be more easily understood from the embodiments and the drawings described below. However, the present invention is not limited to the embodiments described herein and can be implemented in other forms. The embodiments described herein are provided to make the disclosure complete and comprehensive and to fully convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. Throughout the drawings, the same elements are denoted by the same reference numerals. In the drawings, the dimensions of the structures are larger than the actual dimensions to make the present invention clear. Terms such as "first", "second", etc. used herein may be used to describe various components, but these components should not be construed as being limited to these terms. These terms are only used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and the second component may also be referred to as the first component.

[0026] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It should be further understood that the terms "comprising", "including" or "having" as used herein specify the presence of the stated features, regions, integers, steps, operations, elements, and / or components. These terms do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or combinations thereof. It should also be understood that when an element such as a layer, film, region, or sheet is referred to as being "on" another element, it can be directly on the other element, or there can be one or more intervening elements therebetween. Similarly, when an element such as a layer, film, region, or sheet is referred to as being "under" another element, it can be directly under the other element, or there can be intervening elements therebetween.

[0027] Unless otherwise specified, all numbers, values, and / or expressions representing amounts of components, reaction conditions, polymer compositions, and mixtures used herein should be considered approximations that inherently contain various uncertainties (especially those that are inherent in obtaining such values and affect measured values), and should thus be understood to be modified in all instances by the term "about". In addition, when a numerical range is disclosed in this specification, the range is continuous and includes all values from the minimum value of the range to its maximum value, unless otherwise specified. Further, when such a range relates to integer values, all integers from the minimum value to the maximum value are included, unless otherwise specified.

[0028] Figure 1 A all-solid-state battery according to an embodiment of the present invention is shown. The all-solid-state battery may include a negative electrode current collector 10 and a negative electrode layer 20 disposed on the negative electrode current collector 10. The all-solid-state battery may further include a solid electrolyte layer 30 disposed on the negative electrode layer 20 and a positive electrode layer 40 disposed on the solid electrolyte layer 30. The all-solid-state battery may additionally include a positive electrode current collector 50 disposed on the positive electrode layer 40.

[0029] The negative electrode current collector 10 may be a conductive substrate having a plate-like form. For example, the negative electrode current collector 10 may have the form of a sheet, film, or foil.

[0030] There is no particular limitation on the thickness of the negative electrode current collector 10, but it may be, for example, in the range of 1 μm to 500 μm.

[0031] The negative electrode current collector 10 may contain copper (Cu), nickel (Ni), stainless steel, etc.

[0032] The negative electrode layer 20 may include a first layer 21 disposed on the negative electrode current collector 10 and a second layer 22 disposed on the first layer 21. The negative electrode layer 20 may contain a negative electrode active material, a solid electrolyte, a binder, etc. Hereinafter, the negative electrode active material, the solid electrolyte, and the binder contained in the first layer 21 are respectively referred to as the first negative electrode active material, the first solid electrolyte, and the first binder. In addition, the negative electrode active material, the solid electrolyte, and the binder contained in the second layer 22 are respectively referred to as the second negative electrode active material, the second solid electrolyte, and the second binder. However, the meanings of the negative electrode active material, the solid electrolyte, and the binder used when describing the negative electrode layer 20 should be obvious from the context.

[0033] The first layer 21 may have a layered structure in physical contact with the negative electrode current collector 10. The first layer 21 has a high binder content, thereby enhancing the adhesion strength between the negative electrode layer 20 and the negative electrode current collector 10.

[0034] The first layer 21 may contain a first negative electrode active material, a first solid electrolyte, and a first binder.

[0035] The first negative electrode active material may include at least one selected from a silicon-based negative electrode active material, a carbon-based negative electrode active material, or any combination thereof.

[0036] The silicon-based negative electrode active material may include at least one selected from silicon (Si), silicon oxide (SiO x )(0 < x < 2), Si-containing alloy, or any combination thereof. The Si-containing alloy may include an alloy of Si and at least one element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, or any combination thereof.

[0037] The carbon-based negative electrode active material may be graphite (such as mesocarbon microbeads (MCMB) and highly oriented pyrolytic graphite (HOPG)) or amorphous carbon (such as hard carbon and soft carbon).

[0038] The negative electrode active material may be a composite material of a silicon-based negative electrode active material and a carbon-based negative electrode active material. For example, the surface of the carbon-based negative electrode active material may be coated with a silicon-based negative electrode active material. As another example, the surface of the silicon-based negative electrode active material may be coated with a carbon-based negative electrode active material.

[0039] The first solid electrolyte may include at least one selected from an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or any combination thereof. In addition, the solid electrolyte may be in a crystalline, amorphous, or combined form.

[0040] Examples of the oxide-based solid electrolyte may include perovskite-type LLTO (Li 3x La 2 / 3-x TiO 3) Phosphate-based NASICON-type LATP (Li 1+x Al x Ti 2-x (PO 4 ) 3 ) etc.

[0041] Examples of sulfide-based solid electrolytes can include Li 2 S-P 2 S 5 、Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiCl, Li 2 S-P 2 S 5 -LiBr, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 、Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3 、Li 2 S-P 2 S 5 -Z m S n (where m and n are each independently positive numbers, and Z is one of germanium (Ge), zinc (Zn), or gallium (Ga)), Li 2 S-GeS 2 、Li 2 S-SiS 2 -Li 3 PO4 , Li 2 S - SiS 2 -Li x MO y (wherein x and y are each independently positive numbers, and M is one of phosphorus (P), Si, Ge, boron (B), aluminum (Al), Ga, and indium (In)), Li 10 GeP 2 S 12 etc.

[0042] The first solid electrolyte may include a sulfide - based solid electrolyte having a thiogermanate crystal structure. The sulfide - based solid electrolyte having a thiogermanate crystal structure may include Li 7-y PS 6-y Ha y (wherein Ha includes chlorine (Cl), bromine (Br), or iodine (I), and 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (wherein Ha1 and Ha2 are different from each other and each independently includes Cl, Br, or I, 0 < b < 1, and 0 < z ≤ 2) or at least one of any combination thereof.

[0043] The first binder may have a non - polar main chain and polar functional groups bonded to the main chain. Using a polymer having polar functional groups as the first binder can enhance the adhesion strength between components such as the first negative electrode active material, the first solid electrolyte, etc., and the adhesion strength between the first layer 21 and the negative electrode current collector 10.

[0044] The non - polar main chain may include at least one selected from butadiene rubber (BR), styrene - butadiene rubber (SBR), or any combination thereof.

[0045] The polar functional groups may include at least one selected from carboxyl group, acrylate group, or any combination thereof. The acrylate group may contain a “-C=O” group and a “-C=C - ” group. For example, the acrylate group may refer to the moiety represented by Formula 1.

[0046] [Formula 1]

[0047]

[0048] Alternatively, the acrylate group may refer to the moiety represented by Formula 2.

[0049] [Formula 2]

[0050]

[0051] In Formulas 1 and 2, * may refer to a site connected to a nonpolar main chain. In addition, when at least one * is connected to the nonpolar main chain, the rest may contain hydrogen or an alkyl group having 1 to 3 carbon atoms.

[0052] The first binder may contain 1 weight percent (wt%) to 10 weight percent of polar functional groups relative to its total weight. When the content of the polar functional groups is less than 1 wt%, the effect of enhancing the adhesion strength may be negligible. On the contrary, when the content of the polar functional groups exceeds 10 wt%, side reactions may occur with the sulfide-based solid electrolyte.

[0053] The second layer 22 may be a layered structure provided on the first layer 21. The second layer 22 has a low binder content. Therefore, the resistance caused by the binder in the negative electrode layer 20 can be reduced.

[0054] The second layer 22 may include a second negative electrode active material, a second solid electrolyte, and a second binder.

[0055] The second negative electrode active material may be the same as or different from the first negative electrode active material. The second negative electrode active material may include at least one selected from a silicon-based negative electrode active material, a carbon-based negative electrode active material, or any combination thereof. The silicon-based negative electrode active material, the carbon-based negative electrode active material, and their composite materials may be the same as those described above.

[0056] The second solid electrolyte may be the same as or different from the first solid electrolyte. The second solid electrolyte may include at least one selected from an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or any combination thereof. In addition, the solid electrolyte may be in a crystalline, amorphous, or combined form. The oxide-based solid electrolyte and the sulfide-based solid electrolyte are as described above.

[0057] The second binder may have a nonpolar main chain and polar functional groups bonded to the main chain. The second binder may be the same as or different from the first binder. The nonpolar main chain and the polar functional groups are as described above.

[0058] The second binder may contain 1 weight percent to 10 weight percent of polar functional groups relative to its total weight. When the content of the polar functional groups is less than 1 wt%, the effect of enhancing the adhesion strength may be negligible. On the contrary, when the content of the polar functional groups exceeds 10 wt%, side reactions may occur with the sulfide-based solid electrolyte.

[0059] Embodiments of the present invention can enhance the adhesion strength between the negative electrode layer 20 and the negative electrode current collector 10 while reducing the resistance in the negative electrode layer 20. To this end, the ratio of the content (A 1 ) of the first binder in the negative electrode layer 20 to the content (A 2 ) of the second binder (A 1 : A 2)Adjusted to be in the range of 1:0.1 to 1:0.5. While enhancing the adhesion strength between the negative electrode layer 20 and the negative electrode current collector 10 by increasing the content of the first binder contained in the first layer 21 in direct contact with the negative electrode current collector 10, the resistance in the negative electrode layer 20 can be reduced by decreasing the content of the second binder contained in the second layer 22.

[0060] On the other hand, in order to minimize the resistance in the negative electrode layer 20, the ratio of the thickness (T 1 ) of the first layer 21 to the thickness (T 2 ) of the second layer 22 (T 1 :T 2 ) can be adjusted to be in the range of 1:2 to 1:3. The resistance in the negative electrode layer 20 can be reduced by making the thickness of the second layer 22 with a low binder content larger.

[0061] The thickness of the negative electrode layer 20 can be in the range of 20 micrometers (μm) to 100 μm. When the thickness of the negative electrode layer 20 exceeds 100 μm, the energy density of the all-solid-state battery may decrease.

[0062] The negative electrode layer 20 may contain 60% to 80% by weight of a negative electrode active material, 10% to 35% by weight of a solid electrolyte, and 1% to 10% by weight of a binder. However, the content of each component is not limited to the above numerical range and can be appropriately adjusted according to the desired capacity and performance of the all-solid-state battery. The content of the negative electrode active material may refer to the total content of the first negative electrode active material and the second negative electrode active material, the content of the solid electrolyte may refer to the total content of the first solid electrolyte and the second solid electrolyte, and the content of the binder may refer to the total content of the first binder and the second binder.

[0063] The solid electrolyte layer 30 may have a sheet form with at least two main surfaces facing each other. Each of the two main surfaces may be mathematically flat, and a part of it may also include a uniform curved surface. Alternatively, protrusions and depressions formed during the formation of the solid electrolyte layer 30 may be included. In this regard, the sheet form is not limited to a relatively thin rectangular parallelepiped form.

[0064] In the sheet-form solid electrolyte layer 30, the distance between the two main surfaces facing each other may be the thickness of the solid electrolyte layer 30. The length in the first direction (e.g., the width direction) perpendicular to the thickness direction of the solid electrolyte layer 30 is greater than its thickness. Additionally, the length in the second direction (e.g., the length direction) perpendicular to both the thickness direction and the first direction of the solid electrolyte layer 30 is greater than its thickness.

[0065] There is no particular limitation on the thickness of the solid electrolyte layer 30, but it can be in the range of 1 μm to 100 μm. The thickness of the solid electrolyte layer 30 may refer to the average value obtained by measuring the measurement target at five points.

[0066] The solid electrolyte layer 30 may contain a solid electrolyte having lithium ion conductivity, a binder, and the like.

[0067] The solid electrolyte may be the same as or different from the solid electrolyte contained in the negative electrode layer 20. The solid electrolyte may include at least one selected from oxide-based solid electrolytes, sulfide-based solid electrolytes, or any combination thereof. In addition, the solid electrolyte may be crystalline, amorphous, or a combination thereof.

[0068] Examples of the oxide-based solid electrolyte may include perovskite-type LLTO (Li 3x La 2 / 3-x TiO 3 ), phosphate-based NASICON-type LATP (Li 1+x Al x Ti 2-x (PO 4 ) 3 ), etc.

[0069] Examples of the sulfide-based solid electrolyte may include Li 2 S-P 2 S 5 , Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiCl, Li 2 S-P 2 S 5 , Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 , Li 2 S-SiS 2 -B2 S 3 -LiI, Li 2 S - SiS 2 -P 2 S 5 -LiI, Li 2 S - B 2 S 3 , Li 2 S - P 2 S 5 -Z m S n (wherein, m and n are each independently a positive number, and Z is one of Ge, Zn, and Ga), Li 2 S - GeS 2 , Li 2 S - SiS 2 -Li 3 PO 4 , Li 2 S - SiS 2 -Li x MO y (wherein, x and y are each independently a positive number, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP 2 S 12 etc.

[0070] The solid electrolyte may include a sulfide - based solid electrolyte having a thiogalena crystal structure. The sulfide - based solid electrolyte having a thiogalena crystal structure may include those selected from Li 7-y PS 6-y Ha y (wherein, Ha includes Cl, Br, or I, and 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (wherein, Ha1 and Ha2 are different from each other and each independently includes Cl, Br, or I, 0 < b < 1, and 0 < z ≤ 2) or at least one of any combination thereof.

[0071] Examples of the binder may include butadiene rubber (BR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. The binder in the solid electrolyte layer 30 may exist in a granular form, a linear form, etc.

[0072] The positive electrode layer 40 may contain a positive electrode active material, a solid electrolyte, a conductive additive, a binder, etc.

[0073] The positive electrode active material may include a lithium transition metal oxide that stores and releases lithium.

[0074] The lithium transition metal oxide may include any material commonly known in the art to which the present invention pertains. For example, the lithium transition metal oxide may include LiNi x1 Co x2 Mn x3 O 2 (0.65 ≤ x1 ≤ 0.85, 0.05 < x2 < 0.25, 0.03 < x3 < 0.2, and x + x2 + x3 = 1).

[0075] Regarding the average particle size D of the positive electrode active material 50 there is no particular limitation, but it may be, for example, in the range of 1 μm to 20 μm. The average particle size (D 50 ) of the positive electrode active material can be measured using currently available laser diffraction scattering type particle size distribution analyzers (for example, particle size distribution measurement devices purchased from Microtrac). Additionally, the average particle size can be calculated by randomly extracting 200 particles from an electron micrograph.

[0076] The positive electrode active material may be coated with an alkali metal oxide.

[0077] The alkali metal oxide may contain an alkali metal element, a transition metal element, and / or a substitution element.

[0078] The alkali metal element may include at least one selected from lithium (Li), sodium (Na), potassium (K), or any combination thereof. In an embodiment, the alkali metal element includes lithium (Li).

[0079] The transition metal element may include any alkali metal oxide commonly used in the art to which the present invention pertains. For example, the transition metal element may include at least one selected from niobium (Nb), tantalum (Ta), zirconium (Zr), or any combination thereof.

[0080] The solid electrolyte may be responsible for the movement of lithium ions in the positive electrode layer 40. The solid electrolyte may be the same as or different from the solid electrolytes of the negative electrode layer 20 and the solid electrolyte layer 30.

[0081] The solid electrolyte may include at least one selected from oxide-based solid electrolytes, sulfide-based solid electrolytes, or any combination thereof. Additionally, the solid electrolyte may be in crystalline, amorphous, or a combined form.

[0082] Examples of the oxide-based solid electrolyte may include perovskite-type LLTO (Li 3x La 2 / 3-x TiO 3 ), phosphate-based NASICON-type LATP (Li 1+x Alx Ti 2-x (PO 4 ) 3 ) etc.

[0083] Examples of sulfide-based solid electrolytes can include Li 2 S-P 2 S 5 、Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiCl, Li 2 S-P 2 S 5 -LiBr, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 、Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3 、Li 2 S-P 2 S 5 -Z m S n (where m and n are each independently positive numbers, and Z is one of Ge, Zn, and Ga), Li 2 S-GeS 2 、Li 2 S-SiS 2 -Li 3 PO 4 、Li 2 S-SiS 2 -Lix MO y (wherein x and y are each independently a positive number, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP 2 S 12 etc.

[0084] The solid electrolyte may include a sulfide-based solid electrolyte having a thiogermanate crystal structure. The sulfide-based solid electrolyte having a thiogermanate crystal structure may include at least one selected from the group consisting of Li 7-y PS 6-y Ha y (wherein Ha includes Cl, Br, or I, and 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (wherein Ha1 and Ha2 are different from each other and each independently includes Cl, Br, or I, 0 < b < 1, and 0 < z ≤ 2) or any combination thereof.

[0085] Examples of the conductive additive may include carbon black, conductive graphite, acetylene black, graphene, carbon nanotubes, carbon nanofibers, vapor-grown carbon fibers, etc.

[0086] Examples of the binder may include butadiene rubber (BR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. The binder in the positive electrode layer 40 may exist in a particulate form, a linear form, etc.

[0087] The positive electrode layer 40 may contain 70% to 90% by weight of the positive electrode active material, 10% to 15% by weight of the solid electrolyte, 1% to 5% by weight of the conductive additive, and 1% to 5% by weight of the binder. However, the content of each component can be appropriately adjusted in consideration of the capacity and efficiency of the desired all-solid-state battery.

[0088] There is no particular limitation on the thickness of the positive electrode layer 40, but it may be in the range of 1 μm to 100 μm. The thickness of the positive electrode layer 40 may refer to the average value obtained by measuring at five points on the measurement target. In addition, the thickness of the positive electrode layer 40 may refer to the thickness of the all-solid-state battery in the discharged state.

[0089] The positive electrode current collector 50 may include a conductive substrate having a plate-like form. For example, the positive electrode current collector 50 may have the form of a sheet, a thin film, or a foil.

[0090] The positive electrode current collector 50 may include aluminum foil.

[0091] There is no particular limitation on the thickness of the positive electrode current collector 50, but it can be, for example, in the range of 1 μm to 500 μm.

[0092] Another embodiment of the present invention will be described in more detail by the following examples. The following examples are only examples for enhancing the understanding of the present invention. The scope of the present invention is not limited thereto.

[0093] Example 1

[0094] A all-solid-state battery having the same structure as Figure 1 shown was fabricated.

[0095] A slurry containing a silicon-based negative electrode active material, a sulfide-based solid electrolyte, and a first binder was applied onto a negative electrode current collector and dried to form a first layer. A slurry containing a silicon-based negative electrode active material, a sulfide-based solid electrolyte, and a second binder was applied onto the first layer and dried to form a second layer. As the first binder and the second binder, styrene-butadiene rubber (SBR) having a substituted acrylic group as a polar functional group was used. Table 1 shows the thickness and thickness ratio of the first layer and the second layer, and the ratio of the binder in the negative electrode layer.

[0096] A solid electrolyte layer containing a sulfide-based solid electrolyte, a positive electrode layer, and a positive electrode current collector were sequentially stacked on the thus-formed negative electrode layer to complete the fabrication of the all-solid-state battery.

[0097] Example 2

[0098] An all-solid-state battery was fabricated in the same manner as in Example 1, except that the thickness and thickness ratio of the first layer and the second layer were changed as shown in Table 1.

[0099] Comparative Example 1

[0100] A slurry containing a silicon-based negative electrode active material, a sulfide-based solid electrolyte, and a binder was applied onto a negative electrode current collector and dried to form a negative electrode layer in a single-layer form. The silicon-based negative electrode active material and the sulfide-based solid electrolyte used were the same as those used in Example 1. Butadiene rubber was used as the binder. Table 1 shows the thickness of the negative electrode layer and the content of the binder.

[0101] In the same manner as in Example 1 and using the same materials, a solid electrolyte layer, a positive electrode layer, and a positive electrode current collector were stacked on the thus-formed negative electrode to complete the fabrication of the all-solid-state battery.

[0102] Comparative Example 2

[0103] An all-solid-state battery was fabricated in the same manner as in Comparative Example 1 and using the same materials, except that styrene-butadiene rubber (SBR) having a substituted acrylic group was used as the binder in the same manner as in Example 1.

[0104] The adhesion strength between the negative electrode layer and the negative electrode current collector according to Examples 1 and 2 and Comparative Examples 1 and 2 was measured as follows. The negative electrode layer and the negative electrode current collector were inserted between polyethylene terephthalate (PET) films with a thickness of about 100 μm, and then compressed for about 1 second using a flat press under the following conditions: the temperature was about 60 °C (degrees Celsius), and the pressure was 6.5 megapascals (Mpa). The resulting product was attached to a glass slide and then mounted on the holder of a UTM device. The force required to separate the negative electrode layer and the negative electrode current collector was measured by applying a force at a measurement speed of 300 mm / min. The results are shown in Table 2.

[0105] The resistance in the negative electrode layer according to Examples 1 and 2 and Comparative Examples 1 and 2 was measured by the DC Load measurement method. Specifically, after discharging the all-solid-state battery for several seconds, the open-circuit voltage (OCV) level was measured using a voltmeter. A load was connected to the all-solid-state battery, and then the voltage level was measured. The resistance value of the negative electrode layer was calculated using the voltage level difference that occurred at this time. The results are shown in Table 2.

[0106] [Table 1]

[0107]

[0108] 1) The thickness ratio in the negative electrode layer refers to the ratio of the thickness of the first layer to the thickness of the second layer.

[0109] 2) The content ratio of the binder refers to the ratio of the content of the first binder to the content of the second binder in the negative electrode layer.

[0110] [Table 2]

[0111]

[0112] As can be seen from Table 2, in the cases of Examples 1 and 2 and Comparative Example 2 in which a binder having a polar functional group was used, the adhesion strength between the negative electrode layer and the negative electrode current collector was significantly better than that of Comparative Example 1. On the other hand, it can be seen that in the cases of Examples 1 and 2 in which the content ratio of the binder was adjusted by dividing the negative electrode layer into a double layer composed of a first layer and a second layer, the resistance in the negative electrode layer was significantly lower than that of Comparative Example 2.

[0113] Figure 2 The analysis results of the negative electrode layer according to Example 1 are shown, and analysis was performed using a scanning electron microscope (SEM). Figure 3 The analysis results of the negative electrode layer according to Example 1 are shown, and analysis was performed using energy-dispersive X-ray spectroscopy (EDS). From Figure 2 and Figure 3It can be seen that the first layer and the second layer according to Embodiment 1 are well formed and do not cause interface separation.

[0114] Figure 4 The measurement results of the capacity retention rate of all-solid-state batteries according to Embodiment 1 and 2 and Comparative Examples 1 and 2 are shown. The measurement temperature was adjusted to about 30°C. The capacity retention rate of the all-solid-state batteries according to Embodiment 1 and 2 is higher than that of the all-solid-state batteries according to Comparative Examples 1 and 2.

[0115] Figure 5 The evaluation results of the negative electrodes of all-solid-state batteries according to Embodiment 1 and Comparative Examples 1 and 2 for various rates are shown, where the results were obtained when each negative electrode was lithiated. Figure 6 The evaluation results of the negative electrodes of all-solid-state batteries according to Embodiment 1 and Comparative Examples 1 and 2 for various rates are shown, where the results were obtained when each negative electrode was delithiated. It can be seen that the rate performance is favorable in the case of Embodiment 1 compared to the cases of Comparative Examples 1 and 2. This indicates that the content of the binder that acts as a resistor for ion conduction is minimized when forming the double layer, thereby reducing the resistance and improving the battery output performance. This is also consistent with the result of the reduced resistance shown in Table 2.

[0116] Figure 7 The measurement results of the capacity retention rate of all-solid-state batteries according to Embodiment 1 and 2 and Comparative Examples 1 and 2 for each rate are shown. From Figure 7 It can be seen that in the cases of Embodiment 1 and 2, the output characteristics for each rate are superior to those of Comparative Examples 1 and 2. In particular, there is a trend that the output performance in Embodiment 2 is slightly improved, which means that the energy density is increased by optimizing the thickness of the first layer and the second layer.

[0117] Such results may be attributed to the high adhesion strength and low resistance confirmed in Table 2 above.

[0118] Although the present invention has been particularly shown and described with reference to the embodiments, it should be understood that the scope of the present invention is not limited to the described embodiments. Modified forms are also included within the scope of the present invention.

Claims

1. An all-solid-state battery, comprising: A negative electrode current collector; A negative electrode layer disposed on the negative electrode current collector; a solid electrolyte layer disposed on the negative electrode layer; a positive electrode layer disposed on the solid electrolyte layer; as well as a positive electrode current collector disposed on the positive electrode layer, Wherein, the negative electrode layer comprises: a first layer disposed on the negative electrode current collector, the first layer comprising a first negative electrode active material and a first binder, and a second layer disposed on the first layer, the second layer comprising a second negative electrode active material and a second binder, Each of the first binder and the second binder includes a non-polar main chain and a polar functional group bonded to the non-polar main chain, and in the negative electrode layer, the content of the first binder is higher than that of the second binder.

2. The all-solid-state battery according to claim 1, wherein: Each of the first negative electrode active material and the second negative electrode active material includes a silicon-based negative electrode active material.

3. The all-solid-state battery according to claim 1, wherein: The non-polar main chain includes at least one of butadiene rubber, styrene butadiene rubber or any combination thereof.

4. The all-solid-state battery according to claim 1, wherein: The polar functional group includes at least one of a carboxyl group, an acrylic group or any combination thereof.

5. The all-solid-state battery according to claim 1, wherein: Each of the first binder and the second binder includes 1 wt % to 10 wt % of a polar functional group relative to the total weight thereof.

6. The all-solid-state battery according to claim 1, wherein: A ratio T1:T2 of a thickness T1 of the first layer to a thickness T2 of the second layer is in a range of 1:2 to 1:

3.

7. The all-solid-state battery according to claim 1, wherein: The thickness of the negative electrode layer is in the range of 20 micrometers to 100 micrometers.

8. The all-solid-state battery according to claim 1, wherein: In the negative electrode layer, a ratio A1:A2 of a content A1 of the first binder to a content A2 of the second binder is in a range of 1:0.1 to 1:0.5.

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