Positive active material for all solid secondary battery, and all solid secondary battery including the same

Abstract

A positive electrode active material for an all-solid-state secondary battery and an all-solid-state secondary battery including the same are disclosed. The positive electrode active material for an all-solid-state secondary battery comprises a secondary particle comprising a plurality of primary particles and a buffer layer disposed on the surface of the secondary particle, wherein the secondary particle comprises a nickel-based lithium transition metal oxide represented by the following chemical formula 1, and the buffer layer comprises a copper-based compound represented by the following chemical formula 2. LiaNibM1cO2-eAe In Chemical Formula 1, M1, A, a, b, c, and e are as defined in the detailed description. LixCuyXz In the above chemical formula 2, x, y, z, and X are as defined in the detailed description.

Description

Technology Field

[0001] This invention relates to a positive electrode active material for an all-solid-state secondary battery and an all-solid-state secondary battery containing the same. Background Technology

[0002] Conventional lithium-ion batteries have consistently raised safety concerns due to the use of liquid electrolytes, which can easily ignite when exposed to water in the air. This safety issue is becoming an even greater concern as electric vehicles become a reality. Consequently, active research is currently being conducted on all-solid-state secondary batteries utilizing solid electrolytes made of inorganic materials to enhance safety.

[0003] By not using flammable organic dispersion media, all-solid-state batteries can significantly reduce the likelihood of fire or explosion in the event of a short circuit. Therefore, these all-solid-state batteries can offer significantly higher safety compared to lithium-ion batteries that use liquid electrolytes.

[0004] Currently, much research is being conducted on solid electrolytes for all-solid-state batteries based on sulfide-based solid electrolytes, which have excellent lithium ion conductivity.

[0005] Generally, sulfide-based solid electrolytes have the disadvantage of causing irreversible lithium loss at the interface with the cathode active material due to their high reactivity, which drastically reduces long-life characteristics. The problem to be solved

[0006] One aspect is to provide a positive electrode active material for an all-solid-state secondary battery that can improve the lifespan characteristics of an all-solid-state secondary battery containing a sulfide-based solid electrolyte by suppressing the surface reaction between the sulfide-based solid electrolyte and the positive electrode active material.

[0007] Another aspect is to provide a positive electrode of an all-solid-state secondary battery comprising the above-mentioned positive electrode active material.

[0008] Another aspect is to provide an all-solid-state secondary battery including the above-mentioned anode. means of solving the problem

[0009] Depending on one aspect,

[0010] As a positive electrode active material for all-solid-state secondary batteries,

[0011] The above positive active material comprises a secondary particle including a plurality of primary particles and a buffer layer disposed on the surface of the secondary particle, and

[0012] A positive electrode active material for an all-solid-state secondary battery is provided, wherein the particles comprise a nickel-based lithium transition metal oxide represented by the following chemical formula 1, and the buffer layer comprises a copper-based compound represented by the following chemical formula 2.

[0013] <Chemical Formula 1>

[0014] Li a Ni b M 1 c O 2-e A e

[0015] In Chemical Formula 1, M 1 is one or more elements selected from elements of groups 4 to 14, and A is F, S, Cl, Br, or a combination thereof; 0.9≤a≤1.3, 0.5≤b<1, 0 <c<1, b+c=1이고, 0≤e<1이다.

[0016] <Chemical Formula 2>

[0017] Li x Cu y X z

[0018] In the above chemical formula 2, 0≤x≤3, 1≤y≤5, 1≤z≤5, and X is a halogen element.

[0019] According to another aspect, a positive electrode layer for an all-solid-state secondary battery comprising the positive electrode active material described above is provided.

[0020] According to another aspect, the all-solid-state secondary battery comprises: an anode layer; a cathode layer; and a solid electrolyte layer disposed between the anode layer and the cathode layer.

[0021] An all-solid-state secondary battery is provided in which the anode layer described above comprises the anode active material. Effects of the invention

[0022] A positive electrode active material for an all-solid-state secondary battery according to one embodiment can improve the lifespan characteristics of an all-solid-state secondary battery by suppressing the increase in resistance and irreversible lithium loss at the interface between the positive electrode active material and the sulfide-based solid electrolyte. Brief explanation of the drawing

[0023] Figure 1 shows the structure of an all-solid-state secondary battery according to one embodiment. Figure 2 shows the structure of an all-solid-state secondary battery according to another embodiment. Figure 3 shows the structure of an all-solid-state secondary battery according to another embodiment. Figure 4 shows the impedance measurement results of all-solid-state secondary batteries prepared according to Example 1 and Comparative Example 1. Figure 5 shows the impedance measurement results of all-solid-state secondary batteries manufactured according to Examples 1 to 3. Figure 6 shows the results of measuring the recovery capacity of all-solid-state secondary batteries prepared according to Examples 1 to 3 and Comparative Example 1. Figure 7 shows the results of the lifespan characteristics evaluation of all-solid-state secondary batteries fabricated according to Example 1 and Comparative Example 1. Figure 8 is the result of cyclic voltammetry analysis showing the irreversible characteristics of the anode according to Example 1 and Comparative Example 1. Figure 9 shows the high voltage stability evaluation results of all-solid-state secondary batteries fabricated according to Example 1 and Comparative Example 1. FIGS. 10a to 10c are HAADF STEM and EDS showing cross-sections of secondary particles of the cathode active material prepared in Preparation Example 1, and FIG. 10d shows the EDS spectrum of regions A, B, and C indicated in FIG. 10a. Figures 11a and 11b are HAADF STEM and EDS showing a cross-section of the secondary particles (region where multiple primary particles are observed) of the cathode active material prepared in Preparation Example 1, and Figure 11c is a graph showing the EDS line profile of Cu as the position changes with the arrow in Figure 11b. Figure 12a shows a high-resolution transmission electron microscope (HRTEM) image of the buffer layer of the positive electrode active material prepared in Example 1, and Figure 12b shows its Fast Fourier Transform (FFT) pattern. FIG. 13a is a HAADF STEM image of a cross-section of the anode layer prepared in Example 1, where (1) indicates the anode active material portion of the NCM bulk region, (2) indicates the buffer layer portion with a high Cu distribution, and (3) indicates the region coated with an analytical polymer. Figure 13b is the electron energy loss spectroscopy (EELS) analysis spectrum of regions (1), (2), and (3) of Figure 13a. Figure 14 is the result of XPS analysis of the Cu peak during X-ray photoelectron analysis (XPS) of the buffer layer of the positive electrode active material prepared in Preparation Example 6 and Comparative Preparation Example 1. Figure 15 is the result of XPS analysis of the Cl peak during X-ray photoelectron analysis (XPS) of the buffer layer of the positive electrode active material prepared in Preparation Example 6. Figure 16 shows the measurement results of the Cu content (ppm) contained in the buffer layer of the positive electrode active material prepared in Preparation Examples 4 to 6. Figure 17 shows the high voltage stability measurement results of a torque cell manufactured using the positive active materials of Manufacturing Examples 1 to 6 and Comparative Manufacturing Example 1. FIG. 18 is the result of evaluating the lifespan characteristics of all-solid-state secondary batteries fabricated according to Examples 1, 7 to 9. Figure 19 shows the impedance measurement results of all-solid-state secondary batteries fabricated according to Examples 7 to 9. Specific details for implementing the invention

[0024] Referring to the attached drawings, exemplary positive electrode active materials for all-solid-state secondary batteries, a positive electrode containing the same, and an all-solid-state secondary battery will be described in more detail below.

[0025] Sulfide-based solid electrolytes are used as solid electrolytes for all-solid-state batteries. However, the performance of the anode in these sulfide-based solid electrolytes deteriorates due to reactions, so improvements are required.

[0026] Accordingly, the inventors have completed the present invention to provide a cathode for an all-solid-state secondary battery capable of preventing irreversible lithium loss due to high reactivity between a sulfide-based electrolyte and a cathode active material and providing stable lifespan characteristics.

[0027] A positive electrode for an all-solid-state secondary battery according to one embodiment comprises a secondary particle comprising a plurality of primary particles and a buffer layer disposed on the surface of the secondary particle, and

[0028] The above secondary particle comprises a nickel-based lithium transition metal oxide represented by the following chemical formula 1, and the buffer layer comprises a copper-based compound represented by the following chemical formula 2.

[0029] <Chemical Formula 1>

[0030] Li a Ni b M 1 c O 2-e A e

[0031] In Chemical Formula 1, M 1is one or more elements selected from elements of groups 4 to 14, and A is F, S, Cl, Br, or a combination thereof; 0.9≤a≤1.3, 0.5≤b<1, 0 <c<1, b+c=1이고, 0≤e<1이다.

[0032] <Chemical Formula 2>

[0033] Li x Cu y X z

[0034] In the above chemical formula 2, 0≤x≤3, 1≤y≤5, 1≤z≤5, and X is a halogen element.

[0035] Generally, sulfide-based electrolytes have the disadvantage of causing irreversible lithium loss at the interface of the positive electrode active material due to high reactivity with the positive electrode active material, and rapidly reducing long-life characteristics. A positive electrode active material for an all-solid-state secondary battery according to one embodiment can control such disadvantages by forming a buffer layer containing a copper-based compound represented by Chemical Formula 2 as a surface protection layer, thereby improving the chemical resistance of the battery by reducing degradation at the interface and reactivity with the sulfide-based electrolyte, and providing a relatively low charge-transfer resistance so that Li ions can be smoothly charged and discharged.

[0036] The above buffer layer is a lithiophilic buffer layer that minimizes side reactions with the electrolyte on the surface of a high-nickel-based lithium transition metal oxide and allows Li ions to be effectively transferred into the active material.

[0037] The above buffer layer can provide an all-solid-state secondary battery having high lithium conductivity, chemical resistance, voltage resistance, and long lifespan performance by applying a copper-based catalyst (e.g., CuCl2) and placing a copper-based compound of Li-Cu-X composition on the surface of active material particles.

[0038] The above buffer layer includes a copper-based compound represented by the following chemical formula 2.

[0039] <Chemical Formula 2>

[0040] Li x Cu y X z

[0041] In the above chemical formula 2, 0≤x≤3, 1≤y≤5, 1≤z≤5, and X is a halogen element.

[0042] In the above chemical formula 2, X may be F, Cl, Br, I, or a combination thereof.

[0043] According to one embodiment, the copper-based compound may include a compound represented by the following chemical formula 2a, a compound represented by the chemical formula 2b, or a combination thereof.

[0044] <Chemical Formula 2a>

[0045] Cu y Cl z

[0046] In the above chemical formula 2a, 1≤y≤5 and 1≤z≤5.

[0047] <Chemical Formula 2b>

[0048] Li x Cu y Cl z

[0049] In the above chemical formula 2b, 0 <x≤3, 1≤y≤5, 1≤z≤5이고, X는 할로겐족 원소이다.

[0050] Compared to a bare High Ni cathode active material without such a surface protection layer, the above-described buffer layer can control side reactions with sulfide-based solid electrolytes and improve room temperature / high temperature lifespan and interfacial resistance characteristics. The above-described buffer layer possesses lithium-friendly properties with simultaneously improved chemical resistance and Li ion transport capabilities.

[0051] According to one embodiment, the content of the copper-based compound may be in the range of 0.0005 mol% to 0.2 mol% based on 100 mol% of the nickel-based lithium transition metal oxide. For example, the content of the copper-based compound may be in the range of 0.005 mol% to 0.1 mol% based on 100 mol% of the nickel-based lithium transition metal oxide. The content of the copper-based compound is not limited to the above range, but when it is in the above range, it can effectively reduce the interfacial resistance of the positive electrode active material and bring about a capacity improvement effect.

[0052] The above buffer layer is not only disposed on the surface of a secondary particle comprising a plurality of primary particles, but a copper-based compound may also be present at the interface between the plurality of primary particles. In other words, a buffer layer can be formed by penetrating not only the surface of the secondary particle but also the interface of the primary particle.

[0053] According to one embodiment, the buffer layer may exist in a crystalline phase. The buffer layer may have a Li-Cu-Cl-based nanocrystalline grain shape.

[0054] According to one embodiment, the buffer layer may exist in an amorphous phase, or may exist in a mixed phase of crystalline and amorphous phases.

[0055] The thickness of the buffer layer may be, for example, 5 to 100 nm, or for example, 10 to 80 nm. Within the above range, the interfacial resistance of the positive active material can be effectively reduced.

[0056] The buffer layer may be composed of particles or thin films containing a copper-based compound represented by the above chemical formula 2.

[0057] As the core of the positive electrode active material in which such a buffer layer is formed, a nickel-based lithium transition metal oxide containing 50 mol% or more of nickel (Ni) based on the total molar of the transition metal is used. By including a nickel content within the above range, a high-capacity positive electrode active material can be provided. For example, the nickel-based lithium transition metal oxide may contain 55 mol% or more, 60 mol% or more, 65 mol% or more, 70 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, or 90 mol% or more of nickel (Ni) based on the total molar of the transition metal. For example, the nickel-based lithium transition metal oxide may have a nickel content of 80 to 98 mol% based on the total molar of the transition metal.

[0058] The above nickel-based lithium transition metal oxide can be represented by the following chemical formula 1.

[0059] <Chemical Formula 1>

[0060] Li a Ni b M 1 c O 2-e A e

[0061] In Chemical Formula 1, M 1 is one or more elements selected from elements of groups 4 to 14, and A is F, S, Cl, Br, or a combination thereof; 0.9≤a≤1.3, 0.5≤b<1, 0 <c<1, b+c=1이고, 0≤e<1이다.

[0062] According to one embodiment, the nickel-based lithium transition metal oxide can be represented by the following chemical formula 1a.

[0063] <Chemical Formula 1a>

[0064] Li a Ni b M 2 c M 3 d O 2-e A e

[0065] In chemical formula 1a, M 2is Co, Mn, Al, or a combination thereof; M 3 is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), aluminum (Al), phosphorus (P), zinc (Zn), silicon (Si), niobium (Nb), cobalt (Co) or a combination thereof; A is F, S, Cl, Br or a combination thereof; 0.8≤a≤1.2, 0.7≤b<1, 0 <c<1, 0<d<1, b+c+d=1이고, 0≤e<1이다.

[0066] According to one embodiment, the nickel-based lithium transition metal oxide can be represented by the following chemical formula 1b.

[0067] <Chemical Formula 1b>

[0068] Li a Ni b Co c M 4 d O2

[0069] In the above chemical formula 1b, M 4 is Al, Mn, Zr, Mg or a combination thereof; 0.9≤a≤1.1, 0.7≤b<1, 0 <c≤0.3, 0<d≤0.3, b+c+d=1이다.

[0070] In this way, by using a nickel-based lithium transition metal oxide with a high nickel content, a cathode with excellent capacity characteristics can be obtained. In Chemical Formula 1b, the cobalt content may be 0.5 to 30 mol%, for example 1 to 25 mol%, or 3 to 20 mol%.

[0071] In chemical formula 1b, M 4 If α is manganese, the manganese content may be 0.2 to 5 mol%, for example, 0.3 to 4 mol%, or 0.4 to 3 mol%. And in Chemical Formula 1b, M 4 In the case where it is aluminum, the aluminum content may be 0.2 to 5 mol%, for example, 0.3 to 4 mol% or 0.5 to 3 mol%.

[0072] The above nickel-based lithium transition metal oxide may be, for example, a compound represented by Chemical Formula 3 or a compound represented by Chemical Formula 4 below.

[0073] <Chemical Formula 3>

[0074] LiNi 1-x-y Co x Al y O2

[0075] In Chemical Formula 3, 0.005≤x≤0.3 and 0.002≤y≤0.05.

[0076] <Chemical Formula 4>

[0077] LiNi 1-x-y Co x Mn y O2

[0078] In Chemical Formula 4, 0.005≤x≤0.3 and 0.002≤y≤0.05.

[0079] According to one embodiment, the compound of Formula 3 may have, for example, a nickel content of 80 to 98 mol%, a cobalt content of 0.5 to 30 mol%, and an aluminum content of 0.2 to 5 mol%.

[0080] According to one embodiment, the compound of Formula 4 may have, for example, a nickel content of 80 to 98 mol%, a cobalt content of 0.5 to 30 mol%, and a manganese content of 0.2 to 5 mol%.

[0081] According to one embodiment, the nickel-based lithium transition metal oxide is, for example, LiNi 0.896 Co 0.072 Mn 0.031 O 2, LiNi 0.917 Co 0.069 Al 0.014 O 2, LiNi 0.88 Co 0.105 Al 0.015 O 2, LiNi 0.88 Co 0.105 Mn 0.015 O 2, LiNi 0.845 Co0.105 Mn 0.05 It could be O2.

[0082] The above positive active material can be manufactured, for example, by the following manufacturing method.

[0083] A method for manufacturing a positive electrode active material of an all-solid-state secondary battery according to one embodiment is,

[0084] A nickel-based lithium transition metal oxide represented by the following chemical formula 1 is Cu n X m A step of coating with a coating solution containing a catalyst (wherein 1≤n≤5, 1≤m≤5, and X is a halogen element) and LiOH; and

[0085] It may include the step of drying and heat-treating the above-mentioned coated nickel-based lithium transition metal oxide.

[0086] Cu n X m The positive electrode active material of an all-solid-state secondary battery synthesized via a sol-gel method using a catalyst and LiOH is, as described above, Li on the surface of a nickel-based lithium transition metal oxide x -Cu y -X z A protective layer of the structure can be introduced.

[0087] A positive electrode for an all-solid-state secondary battery according to one embodiment includes the positive electrode active material described above.

[0088] According to one embodiment, the anode may further include a solid electrolyte together with the anode active material.

[0089] The solid electrolyte is a sulfide-based solid electrolyte, for example, Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be one or more selected from , 0≤x≤2. The solid electrolyte included in the positive electrode may be included with the same or different composition as that included in the solid electrolyte layer of the all-solid-state secondary battery.

[0090] In the anode, the solid electrolyte may be 5 to 15 parts by weight based on 100 parts by weight of the total weight of the anode, the total content of the anode active material may be 80 to 90 parts by weight, the conductive agent may be 0.5 to 1 part by weight, and the binder may be 1 to 2 parts by weight.

[0091] In another aspect, an all-solid-state secondary battery is provided comprising the anode layer, the cathode layer, and a sulfide-based solid electrolyte layer interposed between them as described above.

[0092] A solid-state secondary battery according to exemplary embodiments is described in more detail below.

[0093] A solid-state secondary battery according to one embodiment comprises a positive electrode layer; a negative electrode layer; and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a positive current collector and a positive active material layer disposed on the positive current collector, and the negative electrode layer comprises a negative current collector and a negative active material layer disposed on the negative current collector.

[0094] The above anode layer includes an anode according to one embodiment.

[0095] [All-solid-state secondary battery]

[0096] Referring to FIG. 1, the all-solid-state secondary battery (1) comprises a positive electrode layer (10); a negative electrode layer (20); and a solid electrolyte layer (30) disposed between the positive electrode layer (10) and the negative electrode layer (20). The positive electrode layer (10) comprises a positive current collector (11) and a positive active material layer (12) disposed on the positive current collector (11), and the negative electrode layer (20) comprises a negative current collector (21) and a first negative active material layer (22) disposed on the negative current collector.

[0097] [Bipolar layer: Bipolar current collector]

[0098] The positive current collector (11) is made of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, such as a plate or foil. The positive current collector (11) can be omitted.

[0099] [Anode layer: Anode active material]

[0100] The positive active material layer (12) includes, for example, a positive active material and a solid electrolyte. The solid electrolyte included in the positive layer (10) is similar to or different from the solid electrolyte included in the solid electrolyte layer (30). For details regarding the solid electrolyte, refer to the solid electrolyte layer (30).

[0101] The cathode active material is a cathode active material capable of reversibly absorbing and desorbing lithium ions. The cathode active material may be, for example, lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, and lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these; any material used as a cathode active material in the relevant technical field is acceptable. The cathode active material may be a single material or a mixture of two or more materials.

[0102] Lithium transition metal oxides are, for example, Li a A 1-b B b D2(wherein 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above equation, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α F α(In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α F2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α F α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α F2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2(wherein 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d GeO2(wherein the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoGb O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a MnG b O2(in the above equation, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(wherein 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f)Fe2(PO4)3(0 ≤ f ≤ 2); a compound represented by any one of the chemical formulas of LiFePO4. In such a compound, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. A compound having a coating layer added to the surface of such a compound may also be used, and a mixture of the compound described above and a compound having a coating layer added may also be used. The coating layer applied to the surface of such a compound comprises, for example, a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element. The compound forming this coating layer is amorphous or crystalline. The coating elements included in the coating layer are Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The method for forming the coating layer is selected within a range that does not adversely affect the physical properties of the cathode active material. The coating method is, for example, spray coating or immersion. Since the specific coating method is well understood by those skilled in the art, a detailed explanation will be omitted.

[0103] The cathode active material includes, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen and metal atomic layers are alternately and regularly arranged in a specific direction, thereby forming a two-dimensional plane for each layer. The "cubic rock salt type structure" represents a sodium chloride (NaCl type) structure, which is a type of crystal structure; specifically, it exhibits a structure in which the face-centered cubic lattices (fcc) formed by cations and anions, respectively, are offset from each other by half the ridge of the unit lattice. Lithium transition metal oxides having such a layered rock salt type structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z It is a ternary lithium transition metal oxide such as O2(NCM) (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1). When the positive electrode active material includes a ternary lithium transition metal oxide having a layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery (1) are further improved.

[0104] As described above, the positive electrode active material may be covered by a coating layer. The coating layer may be any material known as a coating layer for the positive electrode active material of an all-solid-state secondary battery. For example, the coating layer is Li2O-ZrO2 (LZO), etc.

[0105] When the positive electrode active material contains nickel (Ni) as a ternary lithium transition metal oxide such as NCA or NCM, for example, the capacity density of the all-solid-state secondary battery (1) is increased, and the metal leaching of the positive electrode active material in the charged state can be reduced. As a result, the cycle characteristics of the all-solid-state secondary battery (1) in the charged state are improved.

[0106] The shape of the positive active material is, for example, a particle shape such as a sphere, an elliptical sphere, etc. The particle size of the positive active material is not particularly limited and is within a range applicable to the positive active material of a conventional all-solid-state secondary battery. The content of the positive active material of the positive layer (10) is also not particularly limited and is within a range applicable to the positive of a conventional all-solid-state secondary battery.

[0107] [Anode layer: Solid electrolyte]

[0108] The positive electrode active material layer (12) may include, for example, a solid electrolyte. The solid electrolyte included in the positive electrode layer (10) may be the same as or different from the solid electrolyte included in the solid electrolyte layer (30). For details regarding the solid electrolyte, refer to the solid electrolyte layer (30).

[0109] The solid electrolyte included in the positive electrode active material layer (12) may have an average particle size (D50) smaller than that of the solid electrolyte included in the solid electrolyte layer (30). For example, the average particle size of the solid electrolyte included in the positive electrode active material layer (12) may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average particle size of the solid electrolyte included in the solid electrolyte layer (30).

[0110] [Bipolar layer: Binder]

[0111] The positive active material layer (12) may include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose, etc., but is not necessarily limited to these and any binder used in the relevant technical field is possible. The binder may be composed of a single binder or a plurality of different binders.

[0112] [Bipolar Layer: Challenge Material]

[0113] The positive active material layer (12) may include a conductive material. The conductive material is, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc.

[0114] [Anode Layer: Other Additives]

[0115] The anode layer (10) may further include additives such as fillers, coating agents, dispersants, and ion conductivity aids in addition to the anode active material, solid electrolyte, binder, and conductive material described above.

[0116] The filler, coating agent, dispersant, ion-conducting auxiliary agent, etc. that the anode layer (10) may include can be any known material generally used in the electrodes of all-solid-state secondary batteries.

[0117] In the anode, the content of the anode active material is 80-93 parts by weight, the content of the solid electrolyte is 5 to 10 parts by weight, the content of the conductive agent is 0.5 to 5 parts by weight, for example, 0.5 to 1 part by weight, and the content of the binder is 0.1 to 5 parts by weight, for example, 0.1 to 2 parts by weight. Here, the respective contents of the anode active material, solid electrolyte, binder, and conductive agent are based on 100 parts by weight of the total weight of the anode.

[0118] The thickness of the anode is, for example, 70 to 150 μm.

[0119] [Solid Electrolyte Layer]

[0120] [Solid Electrolyte Layer: Sulfide-based Solid Electrolyte]

[0121] Referring to FIGS. 1 to 3, the solid electrolyte layer (30) includes a sulfide-based solid electrolyte disposed between the anode layer (10) and the cathode layer (20).

[0122] Sulfide-based solid electrolytes are, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, and solid electrolytes are, for example, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , 0≤x≤2, and one or more selected from. Sulfide-based solid electrolytes are produced by processing starting materials such as Li2S, P2S5, etc., by melt quenching or mechanical milling.

[0123] Li2S-P2S5-LiX includes, for example, Li2S-P2S5-LiCl, or Li2S-P2S5-LiCl-LiBr.

[0124] In addition, heat treatment may be performed after such treatment. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above, for example. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form the solid electrolyte, the molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 50 : 50 to 90 : 10.

[0125] Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be an argyrodite-type compound containing one or more selected from 0≤x≤2. In particular, the sulfide-based solid electrolyte may be an argyrodite-type compound containing one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0126] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0127] The elastic modulus of the above solid electrolyte is, for example, 15 to 35 GPa.

[0128] [Solid Electrolyte Layer: Binder]

[0129] The solid electrolyte layer (30) may include, for example, a binder. The binder included in the solid electrolyte layer (30) may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these, and any binder used in the relevant technical field is possible. The binder of the solid electrolyte layer (30) may be the same as or different from the binder included in the positive electrode active material layer (12) and the negative electrode active material layer (22).

[0130] The solid electrolyte layer has a thickness of, for example, 30 to 60 μm.

[0131] [Cathode layer]

[0132] [Cathode layer: Cathode active material]

[0133] The first negative electrode active material layer (22) includes, for example, a negative electrode active material and a binder.

[0134] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle shape. The average particle size of the negative electrode active material having a particle shape is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, or 900 nm or less. The average particle size of the negative electrode active material having a particle shape is, for example, 10 nm to 4 μm or less, 10 nm to 3 μm or less, 10 nm to 2 μm or less, 10 nm to 1 μm or less, or 10 nm to 900 nm or less. By having the negative electrode active material with an average particle size within this range, the reversible absorption and / or desorption of lithium during charging and discharging may be more facilitated. The average particle size of the negative electrode active material is, for example, a median diameter (D50) measured using a laser particle size distribution meter.

[0135] The cathode active material included in the first cathode active material layer (22) comprises, for example, one or more selected from carbon-based cathode active materials and metal or metalloid cathode active materials.

[0136] The carbon-based cathode active material is, in particular, amorphous carbon. Amorphous carbon is, for example, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, etc., but is not necessarily limited to these, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0137] The metal or metalloid cathode active material comprises one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but is not necessarily limited to these; any metal cathode active material or metalloid cathode active material that forms an alloy or compound with lithium in the relevant technical field is acceptable. For example, nickel (Ni) is not a metal cathode active material because it does not form an alloy with lithium.

[0138] The first negative electrode active material layer (22) may include a type of negative electrode active material among these negative electrode active materials, or may include a mixture of multiple different negative electrode active materials. For example, the first negative electrode active material layer (22) may include only amorphous carbon, or one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer (22) may include a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of a mixture of amorphous carbon and gold, etc., is, for example, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1 by weight ratio, but is not necessarily limited to these ranges and is selected according to the required characteristics of the all-solid-state secondary battery (1). By having the negative electrode active material have this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0139] The negative electrode active material included in the first negative electrode active material layer (22) comprises a mixture of first particles made of amorphous carbon, for example, and second particles made of a metal or metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the metalloid is a semiconductor. The content of the second particles is 8 to 60 weight%, 10 to 50 weight%, 15 to 40 weight%, or 20 to 30 weight% based on the total weight of the mixture. By having the second particles in this range, the cycle characteristics of, for example, the all-solid-state secondary battery (1) are further improved.

[0140] [Cathode layer: Binder]

[0141] The binder included in the first negative electrode active material layer (22) is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose, etc., but is not necessarily limited to these and any binder used in the relevant technical field is possible. The binder may be composed of a single binder or a plurality of different binders.

[0142] The first negative active material layer (22) is stabilized on the negative current collector (21) by including a binder. Additionally, cracking of the first negative active material layer (22) is suppressed despite changes in volume and / or relative position of the first negative active material layer (22) during the charging and discharging process. For example, if the first negative active material layer (22) does not include a binder, it is possible for the first negative active material layer (22) to be easily separated from the negative current collector (21). The portion where the first negative active material layer (22) is separated from the negative current collector (21) is exposed and comes into contact with the solid electrolyte layer (30), thereby increasing the likelihood of a short circuit. The first negative active material layer (22) is manufactured, for example, by applying a slurry in which the material constituting the first negative active material layer (22) is dispersed onto the negative current collector (21) and drying it. By including a binder in the first cathode active material layer (22), stable dispersion of the cathode active material in the slurry is possible. For example, when the slurry is applied to the cathode current collector (21) by a screen printing method, it is possible to suppress clogging of the screen (e.g., clogging by aggregates of the cathode active material).

[0143] [Cathode layer: Other additives]

[0144] The first negative electrode active material layer (22) may further include additives used in conventional all-solid-state secondary batteries (1), such as fillers, coating agents, dispersants, ion-conducting aids, etc.

[0145] [Cathode layer: First cathode active material layer]

[0146] The thickness of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (d12). The thickness of the first negative electrode active material layer (22) is, for example, 1 μm to 20 μm, 2 μm to 10 μm, or 3 μm to 7 μm. If the thickness of the first negative electrode active material layer (22) is excessively thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) cause the first negative electrode active material layer (22) to collapse, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0147] If the thickness of the first negative electrode active material layer (22) decreases, for example, the charging capacity of the first negative electrode active material layer (22) also decreases. The charging capacity of the first negative electrode active material layer (22) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 2% or less compared to the charging capacity of the positive electrode active material layer (12). The charging capacity of the first negative electrode active material layer (22) is, for example, 0.1% to 50%, 0.1% to 40%, 0.1% to 30%, 0.1% to 20%, 0.1% to 10%, 0.1% to 5%, or 0.1% to 2% compared to the charging capacity of the positive electrode active material layer (12). If the charge capacity of the first negative electrode active material layer (22) is excessively small, the thickness of the first negative electrode active material layer (22) becomes very thin, and thus, during repeated charge and discharge processes, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) cause the first negative electrode active material layer (22) to collapse, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases, and the internal resistance of the all-solid-state secondary battery (1) caused by the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0148] The charge capacity of the positive active material layer (12) is obtained by multiplying the charge capacity density (mAh / g) of the positive active material by the mass of the positive active material in the positive active material layer (12). When multiple types of positive active materials are used, the charge capacity density × mass value is calculated for each positive active material, and the sum of these values ​​is the charge capacity of the positive active material layer (12). The charge capacity of the first negative active material layer (22) is also calculated in the same way. That is, the charge capacity of the first negative active material layer (22) is obtained by multiplying the charge capacity density (mAh / g) of the negative active material by the mass of the negative active material in the first negative active material layer (22). When multiple types of negative active materials are used, the charge capacity density × mass value is calculated for each negative active material, and the sum of these values ​​is the capacity of the first negative active material layer (22). Here, the charge capacity density of the positive active material and the negative active material is a capacity estimated using an all-solid-state half-cell using lithium metal as the counter electrode. The charge capacity of the positive active material layer (12) and the first negative active material layer (22) is directly measured by measuring the charge capacity using an all-solid-state half-cell. By dividing the measured charge capacity by the mass of each active material, the charge capacity density is obtained. Alternatively, the charge capacity of the positive active material layer (12) and the first negative active material layer (22) may be the initial charge capacity measured during the first cycle of charging.

[0149] [Cathode layer: Second cathode active material layer (23) (precipitation layer)]

[0150] Referring to FIG. 2, the all-solid-state secondary battery (1) may further include a second negative electrode active material layer (23) disposed between, for example, a negative electrode current collector (21) and a first negative electrode active material layer (22) by charging. The all-solid-state secondary battery (1) may further include a second negative electrode active material layer (23) disposed between a solid electrolyte layer (30) and a first negative electrode active material layer (22) by charging. The all-solid-state secondary battery (1) may further include a second negative electrode active material layer (23) disposed between, for example, a negative electrode current collector (21) and a first negative electrode active material layer (22) and between a solid electrolyte layer (30) and a first negative electrode active material layer (22) by charging. The second negative electrode active material layer (23) is a metal layer comprising lithium or a lithium alloy. The metal layer comprises lithium or a lithium alloy. Accordingly, the second negative electrode active material layer (23) is a metal layer containing lithium, so it acts as, for example, a lithium reservoir. The lithium alloy is, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these, and any alloy used as a lithium alloy in the relevant technical field is possible. The second negative electrode active material layer (23) may be made of one of these alloys or lithium, or may be made of various types of alloys.

[0151] The thickness of the second negative electrode active material layer (23) is not particularly limited, but, for example, 1 μm to 1000 μm, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the second negative electrode active material layer (23) is excessively thin, it is difficult for the second negative electrode active material layer (23) to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer (23) is excessively thick, the mass and volume of the all-solid-state secondary battery (1) increase, and there is a possibility that the cycle characteristics may deteriorate. The second negative electrode active material layer (23) may, for example, be a metal foil having a thickness within this range.

[0152] In the all-solid-state secondary battery (1), the second negative electrode active material layer (23) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) for example before assembly of the all-solid-state secondary battery (1), or is deposited between the negative electrode current collector (21) and the first negative electrode active material layer (22) by charging after assembly of the all-solid-state secondary battery (1). When the second negative electrode active material layer (23) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembly of the all-solid-state secondary battery (1), the second negative electrode active material layer (23) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembly of the all-solid-state secondary battery (1). Accordingly, the cycle characteristics of the all-solid-state secondary battery (1) including the second negative electrode active material layer (23) are further improved. When the second negative electrode active material layer (23) is precipitated by charging after assembly of the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer (23) is not included during assembly of the all-solid-state secondary battery (1). For example, when charging the all-solid-state secondary battery (1), it is charged in excess of the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the beginning of charging, lithium is absorbed in the first negative electrode active material layer (22). The negative electrode active material included in the first negative electrode active material layer (22) forms an alloy or compound with lithium ions that have moved from the positive electrode layer (10). When charging is performed beyond the capacity of the first negative electrode active material layer (22), lithium is deposited, for example, on the back surface of the first negative electrode active material layer (22), that is, between the negative current collector (21) and the first negative electrode active material layer (22), and a metal layer corresponding to the second negative electrode active material layer (23) is formed by the deposited lithium. The second negative electrode active material layer (23) is a metal layer composed mainly of lithium (i.e., metallic lithium). This result is obtained, for example, by the negative electrode active material included in the first negative electrode active material layer (22) being composed of a material that forms an alloy or compound with lithium.During discharge, lithium in the first negative electrode active material layer (22) and the second negative electrode active material layer (23), i.e., the metal layer, is ionized and moves toward the positive electrode layer (10). Therefore, it is possible to use lithium as a negative electrode active material in the all-solid-state secondary battery (1). In addition, since the first negative electrode active material layer (22) covers the second negative electrode active material layer (23), it acts as a protective layer for the second negative electrode active material layer (23), i.e., the metal layer, while simultaneously suppressing the precipitation growth of lithium dendrites. Thus, short circuits and capacity degradation of the all-solid-state secondary battery (1) are suppressed, and consequently, the cycle characteristics of the all-solid-state secondary battery (1) are improved. Additionally, when the second negative electrode active material layer (23) is formed by charging after assembly of the all-solid-state secondary battery (1), the negative electrode current collector (21), the first negative electrode active material layer (22), and the region between them are, for example, Li-free regions that do not contain lithium (Li) in the initial state or after discharge state of the all-solid-state secondary battery.

[0153] [Cathode layer: Third cathode active material layer]

[0154] Referring to FIG. 3, the all-solid-state secondary battery (1) may include a third negative electrode active material layer (24). The third negative electrode active material layer (24) is a metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the third negative electrode active material layer (24) is a metal layer containing lithium, it acts as, for example, a lithium reservoir. The lithium alloy is, for example, Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these; any alloy used as a lithium alloy in the relevant technical field is possible. The third negative electrode active material layer (24) may be composed of one of these alloys or lithium, or may be composed of various types of alloys.

[0155] The thickness of the third negative electrode active material layer (24) is not particularly limited, but is, for example, 1 μm to 100 μm, for example 10 to 100 μm, 1 μm to 50 μm, 1 μm to 40 μm, 1 μm to 30 μm, 1 μm to 20 μm, 1 μm to 15 μm, 1 μm to 10 μm, or 1 μm to 5 μm. If the thickness of the third negative electrode active material layer (24) is excessively thin, it is difficult for the third negative electrode active material layer (24) to perform the role of a lithium reservoir. If the thickness of the third negative electrode active material layer (24) is excessively thick, the mass and volume of the all-solid-state secondary battery (1) increase, and there is a possibility that the cycle characteristics may deteriorate. The third negative electrode active material layer (24) may be, for example, a metal deposition layer or a metal foil having a thickness within this range.

[0156] A lithium halide layer may be additionally disposed on the third negative electrode active material layer (24). The lithium halide layer may act as a passivation layer to prevent deterioration of the third negative electrode active material layer (24). Since the lithium halide layer is a high-strength and high-hardness layer, it may serve as a protecting layer that protects the third negative electrode active material layer (24). The lithium halide layer may include one or more selected from LiF, LiCl, LiBr, and LiI. The lithium halide layer may be a LiF layer. The lithium halide layer may be disposed on the third negative electrode active material layer (24) by deposition. The thickness of the lithium halide layer is not particularly limited, but, for example, 10㎛ to 300㎛, 10㎛ to 200㎛, 10㎛ to 150㎛, 10㎛ to 100㎛, 10㎛ to 90㎛, 10㎛ to 80㎛, 10㎛ to 60㎛, or 20㎛ to 50㎛. If the thickness of the lithium halide layer is excessively thin, it is difficult for the lithium halide layer to prevent deterioration of the third negative electrode active material layer (24). If the thickness of the lithium halide layer is excessively thick, the energy density of the all-solid-state secondary battery (1) may decrease.

[0157] A carbon layer may be additionally disposed on the lithium halide layer. By additionally disposing of a carbon layer on the lithium halide layer, the interfacial resistance between the lithium halide layer and the solid electrolyte layer (30) may be reduced. The thickness of the carbon layer may be, for example, 1 μm to 10 μm, 2 μm to 10 μm, or 1 μm to 5 μm. If the thickness of the carbon layer is excessively thin, it may be difficult to effectively reduce the interfacial resistance between the lithium halide layer and the solid electrolyte layer (30). If the thickness of the carbon layer is excessively thick, the energy density of the all-solid-state secondary battery (1) may be reduced. The carbon layer may include a binder and a carbon-based material. The carbon-based material may include amorphous carbon, crystalline carbon, etc. The binder may include the binder used in the anode layer described above. The carbon layer may include both amorphous carbon and crystalline carbon. The weight ratio of amorphous carbon and crystalline carbon included in the carbon layer may be, for example, 4:6 to 6:4.

[0158] [Cathode layer: Cathode current collector]

[0159] The negative electrode current collector (21) is composed of a material that does not react with, for example, lithium, that is, does not form any alloys or compounds. The material constituting the negative electrode current collector (21) may be, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited to these; any material used as an electrode current collector in the relevant technical field is acceptable. The negative electrode current collector (21) may be composed of one of the metals described above, or may be composed of an alloy or coating material of two or more metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0160] The all-solid-state secondary battery (1) may further include a thin film containing an element capable of forming an alloy with lithium, for example, on a negative electrode current collector (21). The thin film is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22). The thin film contains, for example, an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium is, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but is not necessarily limited to these, and any element capable of forming an alloy with lithium in the relevant technical field is possible. The thin film is composed of one of these metals or is composed of an alloy of various types of metals. By placing the thin film on the negative electrode current collector (21), the deposition pattern of the second negative electrode active material layer (23) deposited between, for example, the thin film (24) and the first negative electrode active material layer (22) is further flattened, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0161] The thickness of the thin film is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film is less than 1 nm, it may be difficult to perform the function provided by the thin film. If the thickness of the thin film is excessively thick, the thin film itself absorbs lithium, and the amount of lithium precipitated at the negative electrode decreases, which lowers the energy density of the all-solid-state battery and may degrade the cycle characteristics of the all-solid-state secondary battery (1). The thin film may be placed on the negative electrode current collector (21) by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods, and any method capable of forming a thin film in the relevant technical field is possible.

[0162] An all-solid-state secondary battery according to one embodiment can be applied to medium-to-large batteries or energy storage systems (ESS). An all-solid-state secondary battery according to one embodiment can be used, for example, in automobile batteries.

[0163] Next, we will examine a method for manufacturing an all-solid-state secondary battery employing a cathode containing the aforementioned cathode active material.

[0164] First, a composition for forming an anode active material layer is prepared by mixing the aforementioned anode active material, binder, solid electrolyte, conductive material, and solvent.

[0165] An anode layer is provided by coating the composition for forming the anode active material layer onto an anode current collector and drying it to form an anode active material layer.

[0166] The above drying is carried out at 40 to 60°C.

[0167] Separately, the method includes the step of providing a cathode layer comprising a cathode current collector and a first cathode active material layer; the step of preparing a laminate by providing a solid electrolyte layer between the cathode layer and the anode layer; and the step of pressing the laminate.

[0168] Pressurization is performed in the range of 25 to 90°C, and the pressure is applied at 550 MPa or less, for example, 500 MPa or less, for example, in the range of 400 to 500 MPa to complete the all-solid-state secondary battery. The pressurization time may vary depending on the temperature and pressure, for example, less than 30 minutes. In addition, the pressurization may be, for example, isostatic press, roll press, or plate press.

[0169] This will be explained in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not limited thereto.

[0170] (Manufacture of positive electrode active material)

[0171] Preparation Example 1

[0172] First, a Ni-rich NCM active material was prepared by the following method.

[0173] nickel-based active material precursor (Ni) through the coprecipitation method described below 0.90Co 0.07 Mn 0.03 (OH)2) was synthesized. In the following manufacturing process, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were used as metal raw materials to form the nickel-based active material precursor. Ammonia water with a concentration of 0.35 mol / L was added to the reactor, and the reaction was started at a stirring speed of 250 rpm and a reaction temperature of 50°C. Metal raw materials and ammonia water were simultaneously added at a rate of 6.00 L / hr and 0.6 L / hr, respectively, and NaOH was added to adjust the pH. At this time, the pH inside the reactor was adjusted to 11.3–11.4. After carrying out the reaction for 33 hours, the reaction product was collected. After washing the product, it was hot-air dried at 150°C for 24 hours to obtain the nickel-based active material precursor (Ni 0.90 Co 0.07 Mn 0.03 (OH)2) was prepared. The active material was then mixed with lithium in a 1:1 molar ratio and heat-treated at approximately 750°C for 10 hours to produce Li 1.0 Ni 0.90 Co 0.07 Mn 0.03 O2 (Ni-rich NCM) active material was obtained.

[0174] Separately, a coating solution was prepared by adding CuCl2 and LiOH·H2O to ethanol and stirring and mixing at room temperature for 30 minutes. Here, based on 1 mole of Ni-rich NCM active material, the content of CuCl2 was set to 0.005 mol% and the content of LiOH·H2O was set to 1.0 mol%.

[0175] The above coating solution is the Li 1.0 Ni 0.90 Co 0.07 Mn 0.03O2 (Ni-rich NCM) active material fine powder was mixed in equal weight, and the mixed solution was heated at 150°C for more than 2 hours while stirring to evaporate and dry the alcohol solvent. By carrying out the above process, residual lithium such as LiCuCl2, lithium carbonate, and lithium hydroxide could be supported on the particle surface of the cathode active material fine powder.

[0176] Subsequently, the above-mentioned cathode active material was heat-treated at approximately 300°C for 4 hours under an oxygen atmosphere. Through this heat treatment process, the LiCuCl2 and residual lithium present on the upper surface of the cathode active material were Li x -Cu y -Cl z (0≤x≤3, 1≤y≤5, 1≤z≤5) and converted into a buffer layer with Li2O as the main component, finally obtaining a positive electrode active material coated with lithium Cu halide on the surface of Ni-rich NCM particles.

[0177] Preparation Example 2

[0178] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.01 mol% based on 1 mol of Ni-rich NCM active material.

[0179] Preparation Example 3

[0180] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.025 mol% based on 1 mol of Ni-rich NCM active material.

[0181] Preparation Example 4

[0182] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.05 mol% based on 1 mol of Ni-rich NCM active material.

[0183] Preparation Example 5

[0184] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.1 mol% based on 1 mol of Ni-rich NCM active material.

[0185] Preparation Example 6

[0186] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.2 mol% based on 1 mol of Ni-rich NCM active material.

[0187] Preparation Example 7

[0188] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.0005 mol% based on 1 mol of Ni-rich NCM active material.

[0189] Preparation Example 8

[0190] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.001 mol% based on 1 mol of Ni-rich NCM active material.

[0191] Preparation Example 9

[0192] A positive electrode active material was obtained by carrying out the same process as in Preparation Example 1, except that the content of CuCl2 was changed to 0.003 mol% based on 1 mol of Ni-rich NCM active material.

[0193] Comparative Manufacturing Example 1

[0194] As a positive electrode active material, Li x -Cu y -Cl z Li in a state where a buffer layer is not formed 1.00 Ni 0.90 Co 0.07 Mn 0.03 O2 (Ni-rich NCM) active material was used.

[0195] (Manufacturing of all-solid-state secondary batteries)

[0196] Example 1

[0197] As the positive active material, the positive active material obtained according to Preparation Example 1 was used, as the solid electrolyte, an azirodite-based solid electrolyte (Li6PS5Cl) (D50=1㎛, crystalline) was used, and as the conductive agent, carbon nanofiber (CNF) was used. These materials were mixed to form a positive active material composition in a weight ratio of positive active material: conductive agent: solid electrolyte = 60:5:35%.

[0198] The cathode used Li metal with a thickness of 40㎛.

[0199] A composition comprising the above-mentioned positive active material, solid electrolyte, and carbon nanofiber in a weight ratio of 60:35:5% was prepared by uniformly distributing it over a solid electrolyte filled in a torque cell with a diameter of 13 mm. The solid electrolyte was first filled by applying pressure using hand pressing, and after introducing the prepared positive mixture onto the solid electrolyte layer, a torque cell with a negative electrode / solid electrolyte / positive electrode structure was prepared by plate pressing at a pressure of 4 tons per unit area for 2 minutes. The pressure applied to the torque cell was set to a torque pressure of 4 N·m.

[0200] Examples 2 to 9

[0201] An all-solid-state secondary battery was manufactured in the same manner as Example 1, except that the positive active materials of Examples 2 to 9 were used instead of the positive active material of Example 1 when manufacturing the positive layer.

[0202] Comparative Example 1

[0203] An all-solid-state secondary battery was manufactured in the same manner as Example 1, except that the positive active material of Comparative Example 1 was used instead of the positive active material of Manufacturing Example 1 when manufacturing the positive layer.

[0204] Evaluation Example 1: Impedance Measurement

[0205] For the all-solid-state secondary batteries prepared according to Examples 1 to 3 and Comparative Example 1, resistance was measured at 45°C using the 2-probe method with an impedance analyzer (Solartron 1260A Impedance / Gain-Phase Analyzer). The amplitude was ±10 mV, and the frequency range was 10 mHz to 1 MHz.

[0206] The all-solid-state secondary battery prepared according to Example 1 and Comparative Example 1 was charged to a site of charge (SOC) of 100 at a rate of 0.1 C-rate under 4.25 V CCCV / CC conditions, and a Nyquist plot for the impedance measurement results after a stabilization time of 1 hour is shown in FIG. 4. In FIG. 4, the interfacial resistance of the electrode is determined by the position and size of the semicircles. Multiple semicircles are fitted to the measured profile, and the interfacial resistance at the electrode is measured after calculating the difference between the left x-axis intercept and the right x-axis intercept of the semicircles.

[0207] As shown in FIG. 4, it can be seen that the interfacial resistance of the all-solid-state secondary battery prepared according to Examples 1 to 3 is significantly reduced due to the formation of a buffer layer compared to the all-solid-state secondary battery prepared according to Comparative Example 1.

[0208] The impedance measurement results of the all-solid-state secondary batteries of Examples 1 to 3 are shown in FIG. 5. As shown in FIG. 5, R according to the content of CuCl2 ct When comparing (interfacial resistance), the lower the content, the higher the R of the formed buffer layer. ct It was found to be excellent.

[0209] R of Examples 1 to 3 and Comparative Example 1 ct The (interface resistance) values ​​are shown in Table 1 below.

[0210] Type R ct . Comparative Example 1 332.1 Example 1 31.4 Example 2 35.1 Example 3 34.6

[0211] Evaluation Example 2: Measurement of Discharge Rate Characteristics and Recovery Capacity

[0212] For the all-solid-state secondary batteries prepared according to Examples 1 to 3 and Comparative Example 1, charging was performed at a 0.1 C-rate under 4.25 V CCCV / CC conditions, and discharging was performed at rates by discharging at 0.1 C, 0.33 C-rate, and 1.0 C-rate, respectively.

[0213] Figure 6 is a graph showing the characteristics according to high-rate discharge, and it can be seen that the all-solid-state secondary batteries of Examples 1 to 3 exhibit superior discharge rate characteristics compared to Comparative Example 1, which has no buffer layer. Subsequently, charging and discharging were performed at a low rate of 0.1 C-rate, and the discharge recovery capacity obtained in each case was measured, and the results are shown in Table 2.

[0214] Type Recovery capacity (mAh / g) Comparative Example 1 180.0 Example 1 195.5 Example 2 192.4 Example 3 189.8

[0215] As shown in Table 2, it can be seen that the all-solid-state secondary batteries of Examples 1 to 3, in which a buffer layer is formed after high-rate (1.0C) discharge, exhibit superior recovery capacity characteristics compared to Comparative Example 1, which does not have a buffer layer.

[0216] Evaluation Example 3: Life Characteristics

[0217] In the all-solid-state secondary battery prepared according to Example 1 and Comparative Example 1, the charge and discharge characteristics were evaluated using a charge / discharger (Manufacturer: TOYO, Model: TOYO-3100).

[0218] The first charge / discharge was performed by charging with a constant current of 0.1C until it reached 4.25 V, followed by charging with a constant voltage of 0.05C until it reached 0.05 V. After the charging was complete, the cell was rested for about 10 minutes, and then discharged with a constant current of 0.1C until the voltage reached 2.5 V.

[0219] For the life evaluation, constant current charging was performed at 1C until the voltage reached 4.25 V, followed by constant voltage charging until the voltage reached 0.05C. After the charging was complete, the cell was given a rest period of about 10 minutes, and then evaluated by repeating a cycle of constant current discharge at 1C until the voltage reached 2.5 V 50 times.

[0220] The capacity retention ratio (CRR) was calculated from Equation 1 below, and the results of the capacity retention ratio evaluation are shown in Figure 7.

[0221] [Equation 1]

[0222] Capacity Retention Rate (Lifetime) [%] = [Discharge Capacity of Each Cycle / 1 st [Discharge capacity per cycle] × 100

[0223] As shown in Fig. 7, it can be seen that the capacity retention rate of the all-solid-state secondary battery manufactured according to Example 1 is significantly improved compared to Comparative Example 1.

[0224] Evaluation Example 4: Cyclic voltammetry analysis

[0225] To confirm the irreversible characteristics of the anode according to Example 1 and Comparative Example 1, cyclic voltammetry analysis was performed from 2.5V to 4.25V at a rate of 0.05 mV / s at 45°C using lithium metal as the reference electrode and counter electrode, and the results are shown in Fig. 8.

[0226] In FIG. 8, the graph of Comparative Example 1 shows a suppressed area compared to the graph of Example 1, and a suppressed area indicates greater irreversibility. As seen in FIG. 8, the anode of Example 1 showed a higher voltage onset voltage shift depending on the Cu content, and it can be seen that the irreversibility is suppressed compared to Comparative Example 1, indicating a higher number of reversible lithium ions.

[0227] Evaluation Example 5: High Voltage Stability Evaluation

[0228] In order to evaluate the high voltage stability of the cathode active materials of Preparation Example 1 and Comparative Preparation Example 1, an electrochemical evaluation was performed at 45°C on all-solid-state secondary batteries prepared according to Example 1 and Comparative Example 1 using each cathode active material as follows.

[0229] First, the cell was charged to a maximum Li cathode voltage of 4.25 V with a constant current of 0.1 C rate relative to the theoretical capacity. Then, while maintaining a constant voltage of 4.25 V, the cell was cut off at a current of 0.05 C rate and left idle for 1 hour. Subsequently, resistance was measured at 45°C using an impedance analyzer according to the 2-probe method under the equilibrium voltage state. The amplitude was ±10 mV, and the frequency range was 10 mHz to 1 MHz. Using the same method as above, the cell was charged again to 4.25 V with a constant current of 0.1 C rate, maintained in a constant voltage state for 12 hours, and left idle for 1 hour. Resistance measurements were repeated at 12-hour intervals for up to 60 hours using the same method, and the interfacial resistance values ​​were calculated from the measured Nyquist plots. The results are shown in Fig. 9.

[0230] As shown in Fig. 9, the all-solid-state secondary battery of Example 1 exhibits excellent interfacial resistance characteristics, with a gradual increase in interfacial resistance compared to Comparative Example 1, which lacks a buffer layer, due to the formation of the buffer layer, and also exhibits excellent high-voltage stability compared to Comparative Example 1.

[0231] Evaluation Example 6: Evaluation of Surface Cu Distribution

[0232] HAADF (High-Angle Annular Dark Field) STEM and EDS (Energy Dispersive X-ray Spectroscopy) analysis were performed on the cross-section of the cathode active material prepared in Preparation Example 1.

[0233] FIGS. 10a to 10c are HAADF STEM and EDS showing cross-sections of secondary particles of the cathode active material prepared in Preparation Example 1, and FIG. 10d shows the EDS spectrum of regions A, B, and C indicated in FIG. 10a.

[0234] As seen in FIGS. 10a to 10d, the positive active material of Preparation Example 1 has a buffer layer containing a copper-based compound coated in an island type on the surface or near-surface of the active material secondary particle, and the coating width is about 200 nm.

[0235] Figures 11a and 11b are HAADF STEM and EDS showing a cross-section of the secondary particles (region where multiple primary particles are observed) of the cathode active material prepared in Preparation Example 1, and Figure 11c is a graph showing the EDS line profile of Cu as the position changes with the arrow in Figure 11b.

[0236] As shown in FIGS. 11a to 11c, the cathode active material prepared in Preparation Example 1 showed a Cu distribution up to the interface region of the primary particles forming the secondary particles, and it was found that the buffer layer was formed not only on the surface of the secondary particles of the active material but also on the interface of the primary particles.

[0237] Evaluation Example 7: Phase evaluation of the buffer layer

[0238] Figure 12a shows a high-resolution transmission electron microscope (HRTEM) image of the buffer layer of the positive electrode active material prepared in Preparation Example 1, and Figure 12b shows its Fast Fourier Transform (FFT) pattern.

[0239] As shown in FIGS. 12a and 12b, it can be seen that the buffer layer formed on the positive electrode active material prepared in Preparation Example 1 has a Li-Cu-Cl-based nanocrystalline grain shape.

[0240] Evaluation Example 8: EELS Spectrum Evaluation

[0241] FIG. 13a is a HAADF STEM image of a cross-section of the anode layer prepared in Example 1, where (1) indicates the anode active material portion of the NCM bulk region, (2) indicates the buffer layer portion with a high Cu distribution, and (3) indicates the polymer-coated region.

[0242] Figure 13b shows the electron energy loss spectroscopy (EELS) analysis spectra of regions (1), (2), and (3).

[0243] As seen in FIGS. 13a and 13b, trace amounts of Li are detected in the buffer layer region with high Cu distribution, indicating that a Cu-based buffer layer containing Li covers the surface of the active material.

[0244] Evaluation Example 9: XPS Analysis

[0245] X-ray photoelectron analysis (XPS) was performed on the buffer layer of the cathode active material prepared in Preparation Example 6 and Comparative Example 1, and the XPS analysis results for the Cu peak are shown in FIG. 14, and the XPS analysis results for the Cl peak are shown in FIG. 15.

[0246] As shown in Fig. 14, Cu2p 1 / 2 Characteristic peaks appear at 951.8 eV and 954.0 eV, and Cu2p 3 / 2 Characteristic peaks appear at 932.5 eV and 934.0 eV, which means that most of the Cu in the buffer layer exists in the form of a Cu complex or a lithium-Cu complex with oxidation states of +1 and +2.

[0247] As shown in Fig. 15, Cl2p 1 / 2 and Cl2p 3 / 2 Characteristic peaks appear at 199.9 eV and 198.1 eV, respectively, which means that they exist in the buffer layer in the form of Cu halide or lithium Cu halide.

[0248] Evaluation Example 10: ICP Analysis

[0249] To determine the content of elements included in the buffer layer of the cathode active materials prepared in Preparation Examples 4 to 6, analysis was performed according to the following method using the Inductively Coupled Plasma Spectroscopy (ICP) method. An ICP-AES (ICP 5300DV, Perkinelemer) was used as the ICP analyzer.

[0250] 0.1 g each of the positive electrode active material was taken, 2 ml of distilled water and 3 ml of concentrated nitric acid were added to it, the lid was closed, and the sample was dissolved. Afterward, once the sample was completely dissolved, 50 ml of ultrapure water was added to dilute it. Then, the diluted solution was diluted 10-fold again and analyzed by ICP. The ICP was operated under the following conditions: Forward Power 1300 W; Torch Height 15 mm; Plasma Gas Flow 15.00 L / min; Sample Gas Flow 0.8 L / min; Auxiliary Gas Flow 0.20 L / min; and Pump Speed ​​1.5 ml / min. As a result, the content of elements contained in the buffer layer of the positive electrode active material is shown in Table 3 below.

[0251] In addition, the Cu content (ppm) contained in the buffer layer of the cathode active material prepared in Preparation Examples 4 to 6 is shown in FIG. 16.

[0252] Sample Buffer layer coating amount Li Ni Co Mn Cu Li / Me mol % Preparation Example 4 Ni90 NCM positive electrode active material Cu 0.05mol% 1.05 90.41 6.89 2.66 0.05 Preparation Example 5 Cu 0.10mol% 1.05 90.38 6.87 2.65 0.10 Preparation Example 6 Cu 0.20mol% 1.04 90.25 6.91 2.63 0.20

[0253] As shown in Table 3 and Figure 16, in all Manufacturing Examples 4 to 6, the Cu mol% ratio of the Input / output of CuCl2 added during the synthesis of the Cu-based buffer layer was 1, which confirmed that the Cu-based buffer layer was coated on the active material without loss of the CuCl2 raw material during the manufacturing process.

[0254] Evaluation Example 11: Comparison of interfacial resistance by content

[0255] As in Evaluation Example 5, torque cells were manufactured using the cathode active materials of Manufacturing Examples 1 to 6 and Comparative Manufacturing Example 1, and electrochemical evaluations were performed. The interfacial resistance values ​​of each torque cell are shown in FIG. 17.

[0256] As shown in Fig. 17, it can be seen that even when the CuCl2 content of the buffer layer is increased to 0.2 mol%, the interfacial resistance is significantly lowered compared to Comparative Example 1, thereby maintaining a stable interfacial state. Meanwhile, lower interfacial resistance was induced as the CuCl2 content in the buffer layer decreased.

[0257] Evaluation Example 12: Life Evaluation

[0258] For all-solid-state secondary batteries prepared according to Examples 1, 7 to 9, lifespan characteristics were evaluated as in Evaluation Example 3, and the results are shown in FIG. 18.

[0259] As shown in FIG. 18, it can be seen that the all-solid-state secondary batteries produced according to Examples 1, 7 to 9 have better lifespan characteristics than Comparative Example 1, even if the coating amount of the buffer layer is small.

[0260] Evaluation Example 13: Impedance Measurement

[0261] For all-solid-state secondary batteries prepared according to Examples 7 to 9, the impedance was measured as in Evaluation Example 1, and the results are shown in FIG. 19 and Table 4 below.

[0262] Type R ct . Comparative Example 1 332.1 Example 7 22.3 Example 8 25.9 Example 9 31.6

[0263] As shown in FIG. 19 and Table 4, R of Examples 7 to 9 ct The (interface resistance) value was found to be significantly reduced compared to Comparative Example 1.

[0264] Although one embodiment has been described above with reference to the drawings and examples, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the scope of protection of the present invention should be determined by the appended claims. Explanation of the symbols

[0265] 1 : All-solid-state secondary battery 10 : Cathode 11: Positive current collector 12: Positive active material 20: Cathode layer 21: Cathode current collector 22 : Cathode active material layer 23 : Second cathode active material layer (precipitation layer) 24: Third cathode active material layer (metal layer) 30: Solid electrolyte

Claims

Claim 1 A positive electrode active material for an all-solid-state secondary battery, wherein the positive electrode active material comprises a secondary particle comprising a plurality of primary particles and a buffer layer disposed on the surface of the secondary particle, wherein the secondary particle comprises a nickel-based lithium transition metal oxide represented by the following Chemical Formula 1, and the buffer layer comprises a copper-based compound represented by the following Chemical Formula 2. a Ni b M 1 c O 2-e A e In Chemical Formula 1, M 1 is one or more elements selected from elements of groups 4 to 14, and A is F, S, Cl, Br, or a combination thereof; 0.9≤a≤1.3, 0.5≤b<1, 0 <c<1, b+c=1이고, 0≤e<1이다.<화학식 2> Li x Cu y X z In the above chemical formula 2, 1≤x≤3, 1≤y≤5, 1≤z≤5, and X is a halogen element. Claim 2 A positive electrode active material for an all-solid-state secondary battery, wherein X in Chemical Formula 2 is F, Cl, Br, I, or a combination thereof. Claim 3 In claim 1, the positive electrode active material for an all-solid-state secondary battery comprising the copper-based compound being a compound represented by the following chemical formula 2b or a combination thereof: <Chemical Formula 2b>Li x Cu y Cl z In the above chemical formula 2b, 1 <x≤3, 1≤y≤5, 1≤z≤5이고, X는 할로겐족 원소이다. Claim 4 A positive electrode active material for an all-solid-state secondary battery according to claim 1, wherein the content of the copper-based compound is in the range of 0.0005 mol% to 0.2 mol% based on 1 mol of the nickel-based lithium transition metal oxide. Claim 5 A positive electrode active material for an all-solid-state secondary battery according to claim 1, wherein the content of the copper-based compound is in the range of 0.005 mol% to 0.1 mol% based on 1 mol of the nickel-based lithium transition metal oxide. Claim 6 In claim 1, the copper-based compound is a positive active material for an all-solid-state secondary battery further included at the interface between the plurality of primary particles. Claim 7 In claim 1, the buffer layer is a positive active material for an all-solid-state secondary battery existing in a crystalline state. Claim 8 In claim 1, the buffer layer is a positive active material for an all-solid-state secondary battery existing in a mixed phase of crystalline and amorphous phases. Claim 9 In claim 1, the nickel-based lithium transition metal oxide is a positive electrode active material for an all-solid-state secondary battery represented by the following chemical formula 1a: <Chemical Formula 1a>Li a Ni b M 2 c M 3 d O 2-e A e In chemical formula 1a, M 2 is Co, Mn, Al, or a combination thereof; M 3 is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), aluminum (Al), phosphorus (P), zinc (Zn), silicon (Si), niobium (Nb), cobalt (Co) or a combination thereof; A is F, S, Cl, Br or a combination thereof; 0.8≤a≤1.2, 0.7≤b<1, 0 <c<1, 0<d<1, b+c+d=1이고, 0≤e<1이다. Claim 10 In claim 1, the nickel-based lithium transition metal oxide is a positive electrode active material for an all-solid-state secondary battery represented by the following chemical formula 1b: <Chemical Formula 1b>Li a Ni b Co c M 4 d In the above chemical formula 1b, O2, M 4 is Al, Mn, Zr, Mg or a combination thereof; 0.9≤a≤1.1, 0.7≤b<1, 0 <c≤0.3, 0<d≤0.3, b+c+d=1이다. Claim 11 A positive electrode active material for an all-solid-state secondary battery according to claim 1, wherein the nickel content in the nickel-based lithium transition metal oxide is 80 to 98 mol% based on the total molar of the transition metal. Claim 12 In claim 1, the positive electrode active material is a positive electrode active material for an all-solid-state secondary battery having a residual lithium content of 100 ppm or more. Claim 13 A positive electrode for an all-solid-state secondary battery comprising a positive electrode active material for an all-solid-state secondary battery according to any one of claims 1 to 12. Claim 14 In paragraph 13, the anode is a cathode for an all-solid-state secondary battery further comprising a solid electrolyte. Claim 15 In claim 14, the solid electrolyte is a sulfide-based solid electrolyte, and the sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x One or more positive electrodes for an all-solid-state secondary battery selected from , 0≤x≤2. Claim 16 In claim 14, the solid electrolyte is a positive electrode for an all-solid-state secondary battery in an amount of 5 to 10 parts by weight based on 100 parts by weight of the total weight of the positive electrode. Claim 17 A solid-state secondary battery comprising: a positive electrode layer; a negative electrode layer; and a sulfide-based solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; wherein the positive electrode layer comprises a positive electrode according to claim 13. Claim 18 In claim 17, the sulfide-based solid electrolyte layer comprises Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x An all-solid-state secondary battery comprising one or more sulfide-based solid electrolytes selected from , 0≤x≤2. Claim 19 In claim 17, the negative electrode layer comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and a binder, wherein the negative electrode active material has a particle form and the average particle size of the negative electrode active material is 4 μm or less. Claim 20 In claim 19, the negative electrode active material comprises one or more selected from a carbon-based negative electrode active material and a metal or metalloid negative electrode active material, and the carbon-based negative electrode active material comprises one or more selected from amorphous carbon and crystalline carbon, in a solid-state secondary battery. Claim 21 A nickel-based lithium transition metal oxide represented by the following chemical formula 1 is Cu n X m A method for manufacturing a positive electrode active material for an all-solid-state secondary battery according to claim 1, comprising: a step of coating with a coating solution comprising LiOH and a catalyst comprising (wherein 1≤n≤5, 1≤m≤5, and X is a halogen element); and a step of drying and heat-treating the coated nickel-based lithium transition metal oxide: <Chemical Formula 1>Li a Ni b M 1 c O 2-e A e In Chemical Formula 1, M 1 is one or more elements selected from elements of groups 4 to 14, and A is F, S, Cl, Br, or a combination thereof; 0.9≤a≤1.3, 0.5≤b<1, 0 <c<1, b+c=1이고, 0≤e<1이다.

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