Composite positive active material, preparation method thereof, positive electrode comprising same, and all-solid-state rechargeable batteries

Abstract

The present invention relates to a composite positive active material, a preparation method thereof, a positive electrode comprising same, and all-solid-state rechargeable batteries, the composite positive active material comprising: a core particle including a lithium transition metal-based composite oxide; and a first coating layer positioned on the surface of the core particle and including a composite solid electrolyte, wherein the composite solid electrolyte includes a first particle and a second coating layer positioned on the surface of the first particle and including a second particle, the first particle including a first solid electrolyte having an elastic modulus of less than 20 GPa, and the second particle including a second solid electrolyte having an elastic modulus of greater than or equal to 20 GPa.

Description

Composite cathode active material and its manufacturing method, cathode and all-solid-state secondary battery containing the same

[0001] The present invention relates to a composite cathode active material and a method for producing the same, and to a cathode and an all-solid-state secondary battery including the same.

[0002] Lithium secondary batteries, which offer high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] Commercially available lithium secondary batteries use electrolytes containing flammable organic solvents, posing safety concerns that can lead to explosions or fires in the event of collisions, penetrations, or other problems. Therefore, all-solid-state secondary batteries, which utilize solid electrolytes instead of the electrolyte, are being proposed. All-solid-state secondary batteries are comprised entirely of solid materials, offering the advantage of safety by eliminating the risk of electrolyte leakage and explosion.

[0004] A composite cathode active material according to one embodiment and a cathode including the same can increase the movement of lithium ions by improving the interfacial contact between components in a cathode active material layer, thereby implementing an all-solid-state secondary battery with improved initial charge / discharge characteristics and life characteristics.

[0005] In one embodiment, a composite cathode active material is provided, comprising: a core particle comprising a lithium transition metal-based composite oxide; and a first coating layer located on a surface of the core particle and comprising a composite solid electrolyte, wherein the composite solid electrolyte comprises the first particle; and a second coating layer located on a surface of the first particle and comprising second particles; wherein the first particle comprises a first solid electrolyte having an elastic modulus of less than 20 GPa, and the second particle comprises a second solid electrolyte having an elastic modulus of 20 GPa or greater.

[0006] In another embodiment, a method for producing a composite cathode active material is provided, including mixing first particles and second particles, performing a first heat treatment, mixing the resultant of the first heat treatment with a lithium transition metal composite oxide, and performing a second heat treatment, wherein the first particles include a first solid electrolyte having an elastic modulus of less than 20 GPa, and the second particles include a second solid electrolyte having an elastic modulus of 20 GPa or more.

[0007] In another embodiment, a positive electrode is provided, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector and including the composite positive electrode active material described above.

[0008] In another embodiment, an all-solid-state secondary battery is provided, comprising the above-described positive electrode; a negative electrode; and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0009] A composite cathode active material according to one embodiment and a cathode including the same can increase the movement of lithium ions by improving the interfacial contact between components in a cathode active material layer, thereby improving the initial charge / discharge characteristics and life characteristics of an all-solid-state secondary battery.

[0010] Figures 1 and 2 are cross-sectional views schematically showing an all-solid-state secondary battery according to one embodiment.

[0011] Figure 3 is a schematic diagram schematically showing the structure of a composite positive electrode active material according to one embodiment.

[0012] Figure 4 is a graph measuring the change in current according to voltage for an all-solid-state secondary battery manufactured using 75Li2S-25P2S5.

[0013] Figure 5 is a graph measuring the change in current according to voltage for an all-solid-state secondary battery manufactured using Li5PS5Cl.

[0014] Figure 6 is a graph measuring the voltage change according to the specific capacity during the initial charge / discharge of the first cycle for all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1.

[0015] Figure 7 is a graph measuring the voltage change according to the specific capacity during the second cycle for all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1.

[0016] Figure 8 is a graph measuring the voltage change according to the specific capacity at the third cycle for all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1.

[0017] Figure 9 is a graph showing the voltage change according to the specific capacity after the initial charge / discharge in Evaluation Example 3 and 20 cycles for the all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1.

[0018] Figure 10 is a graph showing the change in specific capacity according to the number of cycles after the initial charge / discharge in Evaluation Example 3 and 40 cycles for all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1.

[0019] Below, specific implementation examples are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0020] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0021] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0022] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0023] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0024] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0025] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0026] The average thickness can be measured using methods well known to those skilled in the art, such as transmission electron microscope images or scanning electron microscope images. For example, the average thickness can be calculated by calculating the arithmetic mean of the thicknesses measured at five equally spaced points.

[0027] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0028] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0029] composite cathode active material

[0030] In one embodiment, a composite cathode active material is provided, comprising: a core particle comprising a lithium transition metal-based composite oxide; and a first coating layer located on a surface of the core particle and comprising a composite solid electrolyte, wherein the composite solid electrolyte comprises the first particle; and a second coating layer located on a surface of the first particle and comprising second particles; wherein the first particle comprises a first solid electrolyte having an elastic modulus of less than 20 GPa, and the second particle comprises a second solid electrolyte having an elastic modulus of 20 GPa or greater.

[0031] All-solid-state secondary batteries utilize solid electrolytes instead of the liquid electrolytes found in commercially available lithium secondary batteries. Because the electrolyte is solid, it is structurally robust, reducing the risk of fire or explosion due to external impacts. Furthermore, the battery can be designed in any shape, allowing for flexible design and deployment in a variety of fields, including electric vehicle platforms.

[0032] However, compared to lithium secondary batteries that use a flexible liquid electrolyte, the use of a fixed-form solid electrolyte has the disadvantage of poor interfacial contact between the active material and the solid electrolyte, or between the solid electrolyte and the solid electrolyte. Therefore, the non-contact areas between the active material and the solid electrolyte, or between the solid electrolyte and the solid electrolyte, cannot conduct lithium, which can lead to isolation of lithium ions during charge and discharge, or the uneven distribution of current can cause lithium metal to easily precipitate and grow in specific areas. If this phenomenon worsens, there is a concern that the performance of the battery may deteriorate or a short circuit may occur, so the development of an all-solid-state secondary battery with excellent interfacial contact of the electrode materials is necessary.

[0033] In one embodiment, a composite cathode active material is proposed that can solve the problem of poor interfacial contact between components within a cathode active material layer and the problem of reduced battery performance due to difficulty in moving lithium ions caused by electrochemical side reactions.

[0034] According to one embodiment, a composite cathode active material can be implemented as a cathode and an all-solid-state secondary battery capable of improving battery performance by introducing a combination of solid electrolyte particles having a low elastic modulus and solid electrolyte particles having a high elastic modulus as a coating layer on the surface of a core particle containing a lithium transition metal-based composite oxide, thereby improving interfacial contact between components within the cathode active material layer.

[0035] core particle

[0036] The core particle comprises a lithium transition metal composite oxide. The lithium transition metal composite oxide is a composite oxide comprising lithium and a transition metal, and any material commonly used as a positive electrode active material in an all-solid-state secondary battery can be applied without limitation.

[0037] For example, the lithium transition metal-based composite oxide may use a lithium transition metal-based compound capable of reversible intercalation and deintercalation of lithium, and may include a compound represented by any one of the following chemical formulas.

[0038] Li a A 1-b X b D2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li a A 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a E 1-b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a E 2-b X b O 4-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Cob X c D α (0.90 ≤ a ≤1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 <α ≤ 2); Li a Ni 1-b-c Co b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mr b X c D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mr b X c O 2-α T α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mr b X c O 2-α T2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b HAVE BEEN c G d O2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mr d G eO2(0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4(0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4(0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); Li a FePO4(0.90 ≤ a ≤ 1.8).

[0039] In the above chemical formulas, A is selected from Ni, Co, Mn, or a combination thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is selected from O, F, S, P, or a combination thereof; E is selected from Co, Mn, or a combination thereof; T is selected from F, S, P, or a combination thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is selected from Ti, Mo, Mn, or a combination thereof; Z is selected from Cr, V, Fe, Sc, Y, or a combination thereof; J is selected from V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0040] For example, the lithium transition metal composite oxide may include, for example, lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), lithium iron phosphate compound (LFP), or a combination thereof.

[0041] The core particles may include, for example, a lithium nickel-based oxide represented by the following chemical formula 11, a lithium cobalt-based oxide represented by the following chemical formula 12, a lithium iron phosphate-based compound represented by the following chemical formula 13, a cobalt-free lithium nickel-manganese-based oxide represented by the following chemical formula 14, or a combination thereof.

[0042] [Chemical Formula 11]

[0043] Li a11 Ni x1 M 5 y1 M 6 z1 O 2-b11 X b11

[0044] In the above chemical formula 11, 0.9≤a11≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b11≤0.1, and M 5 and M 6 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0045] In the above chemical formula 11, 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2.

[0046] [Chemical Formula 12]

[0047] Li a12 Co x2 M 7 y2 O 2-b12 X b12

[0048] In the above chemical formula 12, 0.9≤a12≤1.8, 0.7≤x2≤1, 0≤y2≤0.3, 0.9≤x2+y2≤1.1, and 0≤b12≤0.1, and M 7 is Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0049] [Chemical Formula 13]

[0050] Li a13 Fe x3 M 8 y3 PO 4-b13 X b13

[0051] In the above chemical formula 13, 0.9≤a13≤1.8, 0.6≤x3≤1, 0≤y3≤0.4, and 0≤b13≤0.1, and M 8 is Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0052] [Chemical Formula 14]

[0053] Li a14 Ni x4 Mn y4 M 9 z4 O 2-b14 X b14

[0054] In the above chemical formula 14, 0.9≤a14≤1.8, 0.8≤x4<1, 0 <y4≤0.2, 0≤z4≤0.2, 0.9≤x4+y4+z4≤1.1, 및 0≤b14≤0.1이고 M 9 is Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zr, or a combination thereof, and X is F, P, S, or a combination thereof.

[0055] In one embodiment, the average particle diameter (D) of the core particles 50 ) may be 1 ㎛ to 25 ㎛, for example, 3 ㎛ to 25 ㎛, 1 ㎛ to 20 ㎛, 1 ㎛ to 18 ㎛, 3 ㎛ to 15 ㎛, or 5 ㎛ to 15 ㎛. In this range, the composite cathode active material can be harmoniously mixed with other components in the cathode active material layer, and high capacity and high energy density can be implemented. Here, the average particle diameter is obtained by selecting 20 or so random particles from a scanning electron microscope image for core particles, measuring their particle diameters (diameter, or major axis, or major axis length), and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0056] The core particle may be in the form of a secondary particle formed by agglomeration of a plurality of primary particles, or may be in the form of a single particle. In addition, the core particle may be spherical or nearly spherical in shape, or may be polyhedral or irregular in shape.

[0057] For example, in the composite cathode active material, the core particles may be included in an amount of 70 wt% to 90 wt%, for example, 82 wt% to 88 wt%, based on 100 wt% of the composite cathode active material. When this is satisfied, the composite cathode active material can be harmoniously mixed with other components within the cathode active material layer, and high capacity and high energy density can be realized.

[0058] First coating layer

[0059] The composite cathode active material is positioned on the surface of the aforementioned core particle and includes a first coating layer including a composite solid electrolyte.

[0060] A schematic diagram showing the structure of a composite cathode active material according to one embodiment is illustrated in FIG. 3. The composite cathode active material (50) includes a first coating layer (11) positioned on the surface of a core particle (1), and the first coating layer (11) includes a composite solid electrolyte (2). Here, the first coating layer (11) may be a layer including a plurality (two or more) of composite solid electrolytes (2) positioned to surround the surface of the core particle (1), and may be, for example, a layer composed of a plurality of composite solid electrolytes (2). In this way, by introducing the first coating layer (11) including the composite solid electrolyte (2) onto the surface of the core particle (1), the interfacial contact between components in the composite cathode active material layer can be improved, thereby improving the movement of lithium ions. In addition, it can contribute to securing the performance of the battery by maintaining the contact between components despite the change in the volume of the battery during charge and discharge.

[0061] composite solid electrolyte

[0062] The composite solid electrolyte (2) includes, as illustrated in FIG. 3, a first particle (10); and a second coating layer (21) positioned on the surface of the first particle (10) and including second particles (20). Here, the second coating layer (21) may be a layer including a plurality (two or more) of second particles (20) positioned to surround the surface of one of the first particles (10), and may be, for example, a layer composed of a plurality of second particles (20).

[0063] A first particle (10) is used as a core constituting a composite solid electrolyte, which is a component of a first coating layer (11), and the first particle (10) includes a first solid electrolyte having an elastic modulus of less than 20 GPa. By utilizing the first solid electrolyte having such a low elastic modulus as the core of the composite solid electrolyte and introducing it as a component of the first coating layer (11), the interfacial contact between the composite positive electrode active material and the solid electrolyte in the positive electrode active material layer can be improved, thereby increasing the movement of lithium ions.

[0064] For example, the first solid electrolyte may have an elastic modulus of less than 20 GPa, for example, greater than or equal to 10 GPa and less than 20 GPa, from 12 GPa to 19 GPa, or from 13 GPa to 18.5 GPa.

[0065] A representative example of the first solid electrolyte is a sulfide-based solid electrolyte, and may be a sulfide-based solid electrolyte that does not contain a halogen element.

[0066] For example, the first solid electrolyte may be represented by the following chemical formula 1. When this is satisfied, the interfacial contact between the composite positive electrode active material and the solid electrolyte in the positive electrode active material layer can be improved, thereby increasing the movement of lithium ions.

[0067] [Chemical Formula 1]

[0068] A(Li2S)-B(P2S5)

[0069] In the above chemical formula 1, A represents the mol% content of Li2S with respect to 100 mol% of the total of Li2S and P2S5, and B represents the mol% content of P2S5 with respect to 100 mol% of the total of Li2S and P2S5, and 50≤A≤99 and 1≤B≤50.

[0070] For example, in the above chemical formula 1, 50≤A≤98, 50≤A≤95, 50≤A≤90, 50≤A≤85, 50≤A≤80, or 50≤A≤75 may be present, and 2≤B≤50, 5≤B≤50, 10≤B≤50, 15≤B≤50, 20≤B≤50, or 25≤B≤50 may be present.

[0071] In one embodiment, the sulfide-based solid electrolyte may include Li2S-P2S5, 75Li2S-25P2S5, or a combination thereof.

[0072] The average particle diameter (D) of the first particle (10) 50 ) may be, for example, 0.1 ㎛ to 30 ㎛, for example, 0.1 ㎛ to 8 ㎛, 0.1 ㎛ to 5.0 ㎛, 0.1 ㎛ to 3.0 ㎛, or 0.7 ㎛ to 3 ㎛, 1 ㎛ to 3 ㎛, and may be small particles of 0.1 ㎛ to 1.9 ㎛, or large particles of 2.0 ㎛ to 5.0 ㎛. The first particle (10) may have an average particle diameter (D 50 ) may be a mixture of small particles having a diameter of 0.1 ㎛ to 1.9 ㎛ and large particles having an average particle diameter of 2.0 ㎛ to 5.0 ㎛. When using such first particles (10), not only can the contact and connectivity with the core particles (1) and the second particles (20) be improved, but also the interfacial contact between the composite positive electrode active material and the solid electrolyte in the positive electrode active material layer can be improved to maximize the movement of lithium ions. At this time, the average particle diameter of the first particles may be measured by a scanning electron microscope image, and for example, the particle size distribution is obtained by measuring the size (diameter or long axis length) of about 20 particles in the scanning electron microscope image, and here, D 50 It may have been calculated.

[0073] With respect to the first solid electrolyte, the description of the solid electrolyte described below in the positive electrode active material layer may be applied, except for the above-described contents.

[0074] The second coating layer (21) located on the surface of the first particle (10) described above includes a second particle (20), and the second particle (20) includes a second solid electrolyte having an elastic modulus of 20 GPa or more. In this way, by applying the second solid electrolyte having a higher elastic modulus than the first solid electrolyte as a component of the second coating layer, it is possible to secure the effect of improving electrochemical stability by the second particle (2) while maintaining the effect of improving interfacial contact by the first particle (1). Through this, it is possible to secure excellent charge / discharge characteristics and capacity characteristics of the battery.

[0075] For example, the second solid electrolyte may have an elastic modulus of greater than or equal to 20 GPa, for example, from 20 GPa to 50 GPa, from 20 GPa to 40 GPa, from 20 GPa to 30 GPa, or from 20 GPa to 25 GPa.

[0076] A representative example of the second solid electrolyte is a halogen-containing sulfide-based solid electrolyte, and the halogen-containing sulfide-based solid electrolyte may be a solid electrolyte containing a halogen element and sulfur.

[0077] For example, the second solid electrolyte can be represented by the following chemical formula 2.

[0078] [Chemical Formula 2]

[0079] (Li a1 M 1 b1 M 2 c1 )(P d1 M 3 e1 )(S f1 M 4 g1 )X h1

[0080] In the above chemical formula 2, 4≤a1≤8, and M 1 is Mg, Cu, Ag, or a combination thereof, and 0≤b1<0.5, and M 2is Na, K, or a combination thereof, 0≤c1<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d1<4, 0≤e1<1 이고, M 4 is O, SO n , or a combination thereof, and 1.5≤n≤5, 3≤f1≤12, 0≤g1<2, and X is F, Cl, Br, I, or a combination thereof, and 0

[0081] In one embodiment, in the chemical formula 2, a halogen element (X) is essential, and for example, 1≤h1≤2 may be satisfied. In another example, in the chemical formula 2, M 1 If the element is required, 0 <b1<0.5로 표시될 수 있다. 화학식 2에서 M 3 can be understood as an element substituted in place of P, for example, 0 <e1<1일 수 있다. 화학식 2에서 M 4 is substituted in the S position, for example, 0 <g1<2일 수 있고, S의 비율인 f는 예를 들어 3≤f1≤7일 수 있다. M 4 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0082] In one embodiment, the sulfide-based solid electrolyte is Li5PS5Cl, Li5PS5Br, Li5PS5Cl 0.5 Br 0.5 , or a combination thereof.

[0083] For example, the average particle diameter (D) of the second particle (20) 50 ) is the average particle diameter (D) of the first particle (10). 50 ) may be smaller than, for example, the average particle diameter (D) of the second particle (20) 50 ​) may be 0.01 ㎛ to 5 ㎛, for example, 0.01 ㎛ to 4.5 ㎛, 0.01 ㎛ to 4.0 ㎛, 0.01 ㎛ to 3.5 ㎛, 0.01 ㎛ to 3.0 ㎛, 0.01 ㎛ to 2.5 ㎛, 0.01 ㎛ to 2 ㎛, 0.01 ㎛ to 1 ㎛, or 0.05 ㎛ to 0.6 ㎛. When such second particles (20) are used, excellent contact and connectivity with the first particles (10) can be secured, while the effect of improving the interface contact by the first particles (10) can be achieved in harmony with the effect of improving the electrochemical stability. At this time, the average particle size of the second particle may be measured by a scanning electron microscope image, for example, the particle size distribution is obtained by measuring the size (diameter or length of the major axis) of about 20 particles in a scanning electron microscope image, and here D 50 It may have been calculated.

[0084] With respect to the second solid electrolyte, the description of the solid electrolyte described below in the positive electrode active material layer may be applied, except for the above-described contents.

[0085] In one implementation example, the average particle diameter (D) of the first particle (10) 50 ) is the average particle diameter (D) of the second particle (20). 50 ) may be larger than the average particle diameter (D) of the first particle (10). For example, the average particle diameter (D) of the first particle (10) 50 ) is the average particle diameter (D) of the second particle (20). 50 ) may be 2 to 20 times greater than the first particle (10), for example, 2 to 10 times greater, 3 to 8 times greater, or 4 to 6 times greater. When this is satisfied, the effect of improving electrochemical stability by the second particle (20) can be harmoniously secured without hindering the effect of improving interfacial contact by the first particle (10).

[0086] In one embodiment, the average particle diameter (D) of the core particles (1) 50 ) is the average particle diameter (D) of the first particle (10). 50) may be 2 to 18 times greater than that of the core particle (1), for example, 2 to 10 times greater, 2 to 6 times greater, or 3 to 5 times greater. The effect of securing high capacity and high energy density by the core particle (1) and the effect of improving interface contact between components in the positive electrode active material layer by the first particle (10) can be harmoniously improved.

[0087] For example, the average particle diameter of the core particles (1) may be 2 to 30 times larger than the average particle diameter of the second particles (20), for example, 5 to 25 times larger, 10 to 25 times larger, or 20 to 25 times larger. The effect of securing high capacity and high energy density by the core particles (1) and the effect of securing cell performance by improving electrochemical stability by the second particles (20) can be harmoniously improved.

[0088] In one embodiment, the average thickness of the first coating layer may be from 0.5 μm to 20 μm, for example, from 0.5 μm to 15 μm, from 0.5 μm to 10 μm, from 0.5 μm to 5 μm, or from 1 μm to 4.5 μm. In this range, the effects of improving interfacial contact and improving lithium ion movement by the first particles (10) can be maximized.

[0089] For example, the average thickness of the second coating layer may be 0.01 μm to 15 μm, for example, 0.05 μm to 10 μm, 0.1 μm to 8 μm, 0.5 μm to 5 μm, or 0.5 μm to 1.5 μm. In this range, the effect of improving cell performance by improving electrochemical stability by the second particles (20) can be maximized.

[0090] According to one embodiment, the first solid electrolyte may be included in an amount of 90 wt% to 99 wt%, for example, 93 wt% to 99 wt%, or 94 wt% to 98 wt%, based on 100 wt% of the total of the first solid electrolyte and the second solid electrolyte. Within this range, it may be advantageous to secure excellent charge / discharge characteristics and capacity characteristics of the battery.

[0091] According to one embodiment, the second solid electrolyte may be included in an amount of 1 wt% to 10 wt%, for example, 1 wt% to 7 wt%, or 2 wt% to 6 wt%, based on 100 wt% of the total of the first solid electrolyte and the second solid electrolyte. Within this range, it may be advantageous to secure excellent charge / discharge characteristics and safety of the battery.

[0092] For example, in the composite cathode active material, the first particles may be included in an amount of 9.5 wt% to 20 wt%, for example, 11 wt% to 15 wt%, based on 100 wt% of the composite cathode active material. Within this range, it may be advantageous to secure excellent charge / discharge characteristics and safety of the battery.

[0093] For example, in the composite cathode active material, the second particles may be included in an amount of 0.5 wt% to 10 wt%, for example, 1 wt% to 3 wt%, based on 100 wt% of the composite cathode active material. Within this range, it may be advantageous to secure excellent charge / discharge characteristics and safety of the battery.

[0094] Method for manufacturing composite cathode active material

[0095] In one embodiment, a method for producing a composite cathode active material is provided, including mixing first particles and second particles, performing a first heat treatment, mixing the resultant of the first heat treatment with a lithium transition metal composite oxide, and performing a second heat treatment, wherein the first particles include a first solid electrolyte having an elastic modulus of less than 20 GPa, and the second particles include a second solid electrolyte having an elastic modulus of 20 GPa or more.

[0096] The above description is about a method for manufacturing a composite cathode active material, which is an example of an embodiment. In the following, descriptions that overlap with the content of the composite cathode active material are omitted, and a process for manufacturing the composite cathode active material, which is an example of an embodiment, is described in detail.

[0097] First, the first and second particles described above are prepared, mixed, and then subjected to a first heat treatment. The above-described description can be applied equally to the first and second particles.

[0098] For example, the first heat treatment may be performed at 30° C. to 200° C., 50° C. to 180° C., 70° C. to 150° C., or 100° C. to 140° C. In addition, the first heat treatment may be performed in the temperature range for 0.5 to 5 hours, for example, 1 to 3 hours. When this is satisfied, a second coating layer including second particles can be uniformly formed on the surface of the first particles, and excellent adhesion between the first particles and the second particles can be secured, thereby effectively producing a composite solid electrolyte.

[0099] Next, the result of the first heat treatment is mixed with a lithium transition metal composite oxide, and then a second heat treatment is performed. At this time, the above-described explanation can be equally applied to the lithium transition metal composite oxide.

[0100] For example, the second heat treatment can be performed at 50° C. to 300° C., for example, 70° C. to 250° C., 90° C. to 200° C., 100° C. to 150° C., or 110° C. to 130° C. In addition, the second heat treatment can be performed in the temperature range for 0.5 to 5 hours, for example, 1 to 3 hours. When this is satisfied, excellent adhesion between the core particles and the composite solid electrolyte can be secured to uniformly form the first coating layer, and the effect of improving the interface contact between the components in the positive electrode active material layer and improving the battery performance due to the introduction of the core particles and the first coating layer can be maximized.

[0101] In one embodiment, the mixing ratio of the first particles and the second particles can be designed to be 90 wt% to 99 wt% of the first solid electrolyte relative to 100 wt% of the total of the first solid electrolyte and the second solid electrolyte in the composite positive electrode active material to be finally obtained, for example, 93 wt% to 99 wt%, or 94 wt% to 98 wt%. By designing the mixing ratio within this range, the coating layer formed by the first particles and the second particles can be uniformly formed, and the effects resulting from the use of the first particles and the second particles can be harmonized with each other.

[0102] In one embodiment, the mixing ratio of the first particles and the second particles can be designed to be 1 wt% to 10 wt% of the second solid electrolyte relative to 100 wt% of the total of the first solid electrolyte and the second solid electrolyte in the composite positive electrode active material to be finally obtained, for example, 1 wt% to 7 wt%, or 2 wt% to 6 wt%. By designing the mixing ratio within this range, the coating layer formed by the first particles and the second particles can be uniformly formed, and the effects resulting from the use of the first particles and the second particles can be harmonized with each other.

[0103] anode

[0104] In one embodiment, a positive electrode is provided, comprising: a positive electrode current collector; and a positive electrode active material layer positioned on the positive electrode current collector and including the composite positive electrode active material described above.

[0105] In addition to the composite cathode active material described above, the above cathode active material layer may optionally include an additional cathode active material, or may further include a solid electrolyte, a binder, and / or a conductive material.

[0106] The above additional positive electrode active material may further include a positive electrode active material in which the first coating layer is not formed in the above-described composite positive electrode active material.

[0107] In one embodiment, the additional positive electrode active material may include a buffer layer on the particle surface. The buffer layer may be expressed as a coating layer, a protective layer, etc., and may serve to lower the interfacial resistance between the additional positive electrode active material and the solid electrolyte. For example, the buffer layer may include a lithium-metal-oxide, wherein the metal may be, for example, Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, Zr, or a combination thereof. The lithium-metal-oxide is excellent in lowering the interfacial resistance between the additional positive electrode active material and the solid electrolyte particles by facilitating the movement of lithium ions and electron conduction, thereby improving the performance of the positive electrode active material.

[0108] solid electrolyte

[0109] The positive electrode active material layer is a solid electrolyte, and may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or a combination thereof.

[0110] In order to secure excellent ionic conductivity, the positive electrode active material layer includes a sulfide-based solid electrolyte as a solid electrolyte. The sulfide-based solid electrolyte includes, for example, Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I or Cl), 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 integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0111] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or 50:50 to 80:20, and optionally heat-treating them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0112] Methods for mixing sulfur-containing raw materials for manufacturing sulfide-based solid electrolytes include mechanical milling or solution milling. Mechanical milling involves placing starting materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. The heat treatment can be performed at a temperature ranging from 400°C to 600°C, for example, from 450°C to 500°C, or from 460°C to 490°C, for 5 to 30 hours, 10 to 24 hours, or 15 to 20 hours. Heat treatment under the above conditions can maximize ionic conductivity. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them twice or more, in which case a sulfide-based solid electrolyte with high ionic conductivity and strength can be manufactured.

[0113] According to one embodiment, sulfide-based solid electrolyte particles can be manufactured through heat treatment A, for example, mixing sulfur-containing raw materials and calcining at 120°C to 350°C, and heat treatment B, for example, mixing the results of heat treatment A and calcining at 350°C to 800°C. Heat treatments A and B can each be performed in an inert gas or nitrogen atmosphere. Heat treatment A can be performed for 1 to 10 hours, and heat treatment B can be performed for 5 to 20 hours. Heat treatment A can have the effect of milling small raw materials, and heat treatment A can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and durability can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of heat treatment A may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of heat treatment B may be, for example, 380°C to 700°C, or 400°C to 600°C.

[0114] For example, the sulfide-based solid electrolyte may be in the form of particles and may include argyrodite-type sulfides. These argyrodite-type sulfide-based solid electrolyte particles have an ionic conductivity of 10, which is the ionic conductivity of a typical liquid electrolyte at room temperature. -4 10 inland -2 It possesses high ionic conductivity approaching the S / cm range. Furthermore, it can form a close bond between the positive electrode active material and the solid electrolyte without causing a decrease in ionic conductivity, and can form a close interface between the electrode and the solid electrolyte layer. An all-solid-state secondary battery including this can exhibit improved battery performance, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

[0115] The above argyrodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the following chemical formula 21.

[0116] [Chemical Formula 21]

[0117] (Li a21 M 21 b21 M 22 c21 )(P d21 M 23 e21 )(S f21 M 24 g21 )X h21

[0118] In the above chemical formula 21, 4≤a21≤8, and M 21 is Mg, Cu, Ag, or a combination thereof, and 0≤b21<0.5, and M 22 is Na, K, or a combination thereof, 0≤c21<0.5, and M 23 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d21<4, 0≤e21<1 이고, M 24 is O, SO n21 , or a combination thereof, and 1.5≤n21≤5, 3≤f21≤12, 0≤g21<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h21≤2.

[0119] For example, in chemical formula 21, a halogen element (X) may be included as an essential element, in which case 0 <h21≤2로 표시될 수 있다. 일 예로 화학식 21에 M 21 Elements may be required, in which case 0 <b21<0.5로 표시될 수 있다. 화학식 21에서 M 23 can be understood as an element substituted in the P position, and 0 <e21<1일 수 있다. 화학식 21에서 M 24 is substituted in the S position, for example, 0 <g21<2일 수 있으며, S의 비율인 f21는 예를 들어 3≤f21≤7일 수 있다. M 24 Go SO n If SO n21It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0120] For example, in chemical formula 21, a21+b21+c21+h21=7, d21+e21=1, and f21+g21+h21=6.

[0121] As a specific example, argyrodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S. 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25, or combinations thereof, but are not limited thereto.

[0122] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0123] The average particle size (D50) of the sulfide-based solid electrolyte particles may be, for example, 0.1 ㎛ to 5.0 ㎛ or 0.1 ㎛ to 3.0 ㎛, and may be small particles of 0.1 ㎛ to 1.9 ㎛ or large particles of 2.0 ㎛ to 5.0 ㎛. The sulfide-based solid electrolyte particles may be a mixture of small particles having an average particle size of 0.1 ㎛ to 1.9 ㎛ and large particles having an average particle size of 2.0 ㎛ to 5.0 ㎛. When such a sulfide-based solid electrolyte is used, it can effectively penetrate between positive electrode active materials, and the contactability with the positive electrode active material and the connectivity between the solid electrolyte particles can be excellent. At this time, the average particle diameter of the sulfide-based solid electrolyte particles may be measured from an electron microscope image, and for example, the particle size distribution may be obtained by measuring the size (diameter or length of the major axis) of about 20 particles in a scanning electron microscope image, and D50 may be calculated from this.

[0124] The above oxide-based solid electrolyte is, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12(0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof.

[0125] The above halide-based solid electrolyte contains a halogen element as a main component, and may mean that the ratio of the halide element to all elements constituting the solid electrolyte is 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. For example, the halide-based solid electrolyte may not contain a sulfur element.

[0126] The halide-based solid electrolyte may contain lithium element, a metal element other than lithium, and a halogen element. The metal element other than lithium may be Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof. The halogen element may be F, Cl, Br, I, or a combination thereof, and may be Cl, Br, or a combination thereof. The halide-based solid electrolyte may contain, for example, Li a M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3) can be represented. The halide-based solid electrolyte is, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6 Hf 0.4 Yb 0.6 Cl6, or combinations thereof, but is not limited thereto.

[0127] The above oxide-based or halide-based solid electrolyte is in the form of particles, and the average particle diameter (D50) may be 5.0 ㎛ or less, for example, 0.1 ㎛ to 5.0 ㎛, 0.5 ㎛ to 5.0 ㎛, 0.5 ㎛ to 4.0 ㎛, 0.5 ㎛ to 3.0 ㎛, 0.5 ㎛ to 2.0 ㎛, or 0.5 ㎛ to 1.0 ㎛.

[0128] The positive electrode active material including the composite positive electrode active material and the additional positive electrode active material (the sum of the composite positive electrode active material and the additional positive electrode active material) may be included in an amount of 55 wt% to 99 wt% with respect to 100 wt% of the positive electrode active material layer, for example, 65 wt% to 95 wt%, or 75 wt% to 91 wt%. In this range, it may be advantageous to secure performance including charge / discharge characteristics and life characteristics of the battery.

[0129] Excluding the composite solid electrolyte included in the composite positive electrode active material, the solid electrolyte (particularly, the sulfide-based solid electrolyte) may be included in an amount of 0.1 wt% to 35 wt%, for example, 0.5 wt% to 35 wt%, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%, based on the total weight of the positive electrode active material layer. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state battery can be improved without reducing the capacity.

[0130] Challenge

[0131] The above-described positive electrode active material layer further includes a conductive material, and the conductive material is used to provide conductivity to the electrode. In the battery to be formed, any material that does not cause chemical changes and is electronically conductive can be used. For example, the conductive material may include a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, or carbon nanotube; a metal-based material containing copper, nickel, aluminum, or silver in the form of metal powder or metal fiber; a conductive polymer such as a polyphenylene derivative; or a conductive material including a mixture thereof. As a representative example, the conductive material may include carbon black, acetylene black, carbon nanofiber, carbon nanotube, or a combination thereof.

[0132] The positive electrode active material layer may include the conductive material in an amount of 0.01 wt% to 3 wt%, 0.05 wt% to 2 wt%, or 0.1 wt% to 1 wt% based on 100 wt% of the positive electrode active material layer.

[0133] In addition to the components described above, the positive electrode active material layer may optionally further include a binder and / or other additives.

[0134] bookbinder

[0135] The above binder serves to adhere the positive electrode active material particles well to each other and to adhere the positive electrode active material well to the positive electrode current collector (201). Representative examples of the binder include, but are not limited to, one or more selected from among polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, polyacrylonitrile, polymethyl methacrylate, vinylidene fluoride / hexafluoropropylene copolymer, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0136] The content of the binder in the positive electrode active material layer may be about 0.1 wt% to 5 wt% with respect to 100 wt% of the positive electrode active material layer, for example, 0.1 wt% to 3 wt%, 0.1 wt% to 2 wt%, or 0.1 wt% to 1 wt%.

[0137] Other additives

[0138] In addition to the aforementioned positive electrode active material, binder, and conductive agent, the positive electrode active material layer may further include other additives, such as fillers, coating agents, dispersants, and ion-conducting aids. The fillers, coating agents, dispersants, and ion-conducting aids that may be included in the positive electrode may be any known material commonly used in the positive electrode of an all-solid-state secondary battery.

[0139] All-solid-state secondary battery

[0140] In one embodiment, an all-solid-state secondary battery is provided, comprising the above-described positive electrode; a negative electrode; and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0141] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 1, the all-solid-state secondary battery (100) may have a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode collector (201) are laminated is housed in a battery case. The all-solid-state secondary battery (100) may further include an elastic layer (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). Although FIG. 1 illustrates one electrode assembly including a negative electrode (400), a solid electrolyte layer (300), and a positive electrode (200), an all-solid-state secondary battery may be manufactured by laminating two or more electrode assemblies.

[0142] cathode

[0143] The negative electrode includes a negative current collector; and a negative active material layer positioned on the negative current collector. The negative active material layer includes a negative active material and may further include a binder and / or a conductive material.

[0144] The above negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0145] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0146] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0147] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used, and the Si-based negative electrode active material may be silicon, a silicon-carbon composite, or SiO. x(0 <x≤2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn-R 합금(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Q 및 R로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택되는 것을 사용할 수 있다.

[0148] For example, the negative active material may include silicon-carbon composite particles. The average particle diameter (D) of the silicon-carbon composite particles 50 ) may be, for example, 0.5 ㎛ to 20 ㎛. The average particle diameter (D 50 ) is measured by a particle size analyzer and means the diameter of particles having a cumulative volume of 50% by volume in the particle size distribution. With respect to 100 wt% of the silicon-carbon composite particles, silicon may be included in an amount of 10 wt% to 60 wt% and carbon may be included in an amount of 40 wt% to 90 wt%. The silicon-carbon composite particles may include, for example, a core including silicon particles, and a carbon coating layer located on the surface of the core. The average particle diameter (D) of the silicon particles in the core 50) may be 10 nm to 1 ㎛, or 10 nm to 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 <x≤2)로 표시될 수 있다. 또한, 상기 탄소 코팅층의 두께는 약 5 nm 내지 100 nm일 수 있다.

[0149] For example, the silicon-carbon composite particle may include a core including silicon particles and crystalline carbon, and a carbon coating layer located on the surface of the core and including amorphous carbon. For example, in the silicon-carbon composite particle, the amorphous carbon may not be present in the core but may be present only in the carbon coating layer. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon may be formed from coal pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin (phenol resin, furan resin, polyimide resin, etc.). At this time, the content of the crystalline carbon may be 10 wt% to 70 wt%, and the content of the amorphous carbon may be 20 wt% to 40 wt% with respect to 100 wt% of the silicon-carbon composite particle.

[0150] In the above silicon-carbon composite particle, the core may include a void in the central portion. The radius of the void may be 30% to 50% of the radius of the silicon-carbon composite particle.

[0151] The silicon-carbon composite particles described above can effectively suppress problems such as volume expansion, structural collapse, or particle crushing due to charge and discharge, thereby preventing the phenomenon of conductive path disconnection, realizing high capacity and high efficiency, and are advantageous for use under high voltage or fast charging conditions.

[0152] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight.

[0153] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

[0154] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0155] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0156] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0157] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0158] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0159] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof. The amount of such thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0160] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0161] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0162] As another example, the negative electrode may be a precipitation-type negative electrode. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0163] Fig. 2 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to Fig. 2, the precipitation-type negative electrode (400') may include a negative electrode current collector (401) and a negative electrode coating layer (405) positioned on the negative electrode current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or deposited between the negative electrode current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a negative electrode current collector (401), a lithium metal layer (404) positioned on the negative electrode current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0164] The above cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a metal, a carbon material, or a combination thereof.

[0165] The metal may be a lithium-philic metal, and may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one of these or may be composed of several types of alloys. When the metal is present in the form of particles, the average particle diameter (D 50 ) may be less than about 4 μm, for example, 10 nm to 4 μm.

[0166] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof. For example, the carbon material may refer to amorphous carbon.

[0167] When the cathode coating layer (405) includes both the metal and the carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The cathode coating layer (405) may include, for example, a carbon material supported with a catalytic metal, or may include a mixture of metal particles and carbon material particles.

[0168] The cathode coating layer (405) may include, for example, the above-described lithium-philic metal and amorphous carbon, in which case the precipitation of the lithium metal can be effectively promoted. As a specific example, the cathode coating layer (405) may include a composite in which a lithium-philic metal is supported on amorphous carbon.

[0169] The cathode coating layer (405) may further include a binder, which may be, for example, a conductive binder. In addition, the cathode coating layer (405) may further include general additives such as fillers, dispersants, and ionic conductive agents.

[0170] The thickness of the cathode coating layer (405) may be, for example, 100 nm to 20 μm, or 500 nm to 10 μm, or 1 μm to 5 μm.

[0171] The precipitation-type negative electrode (400') may further include, for example, a thin film on the surface of the negative electrode current collector, that is, between the negative electrode current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one type thereof or may be composed of multiple types of alloys. The thin film may further planarize the precipitation form of the lithium metal layer (404) and further improve the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0172] The lithium metal layer (404) may include lithium metal or a lithium alloy. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0173] The thickness of the lithium metal layer (404) may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the lithium metal layer (404) is too thin, it may be difficult to perform the role of a lithium storage, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0174] When such a precipitation-type cathode is applied, the cathode coating layer (405) can play a role in protecting the lithium metal layer (404) and suppressing the precipitation growth of lithium deadlight. Accordingly, short-circuiting and capacity reduction of the all-solid-state battery can be suppressed, and the life characteristics can be improved.

[0175] solid electrolyte layer

[0176] The solid electrolyte layer (300) includes a solid electrolyte. The solid electrolyte included in the solid electrolyte layer may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or a combination thereof. Since the details of these solid electrolytes are as described above, their description is omitted.

[0177] Meanwhile, the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle diameter (D) of the solid electrolyte contained in the positive electrode (200). 50 ) may be larger than the average particle size of the solid electrolyte (200). In this case, the overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state secondary battery. For example, the average particle size (D) of the solid electrolyte included in the positive electrode (200) 50 ) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing the resistance and improving the overall performance of the all-solid-state secondary battery. Here, the average particle diameter (D of the solid electrolyte 50 ) may be measured using a particle size analyzer using laser diffraction.

[0178] The solid electrolyte may be included in an amount of 70 wt% to 99.9 wt% based on 100 wt% of the solid electrolyte layer, for example, 75 wt% to 99.9 wt%, 80 wt% to 99.9 wt%, 85 wt% to 99.9 wt%, 90 wt% to 99.9 wt%, or 95 wt% to 99.9 wt%.

[0179] Alternatively, according to one embodiment, the solid electrolyte layer may use the composite solid electrolyte (2) described above as the solid electrolyte. That is, the solid electrolyte layer (300) may include the composite solid electrolyte (2) as the solid electrolyte, and may use only the composite solid electrolyte (2) described above as the solid electrolyte, or may use the composite solid electrolyte (2) mixed with a solid electrolyte that is commonly used.

[0180] In one embodiment, the composite solid electrolyte may be included in an amount of 70 wt% to 99.9 wt% relative to 100 wt% of the solid electrolyte layer, for example, 75 wt% to 99.9 wt%, 80 wt% to 99.9 wt%, 85 wt% to 99.9 wt%, 90 wt% to 99.9 wt%, or 95 wt% to 99.9 wt%.

[0181] The above solid electrolyte layer may further include a binder in addition to the solid electrolyte. At this time, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate polymer, or a combination thereof, but is not limited thereto, and any binder used in the relevant technical field may be used. The acrylate polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0182] The binder may be included in an amount of 0.1 wt% to 3 wt% based on 100 wt% of the solid electrolyte layer, for example, 0.5 wt% to 2 wt%, or 0.5 wt% to 1.5 wt%. When the binder is included in the above range, the components within the solid electrolyte layer can be well combined without lowering the ionic conductivity of the solid electrolyte, thereby improving the durability and reliability of the battery.

[0183] The above solid electrolyte layer can be formed by adding a solid electrolyte to a binder solution, coating the same on a base film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0184] The thickness of the solid electrolyte layer may be, for example, 100 μm to 3000 μm, for example, 100 μm to 2000 μm, 100 μm to 1000 μm, 100 μm to 800 μm, 100 μm to 400 μm, or 100 μm to 300 μm.

[0185] The solid electrolyte layer may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0186] The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0187] The lithium salt may be applied without limitation on type, and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0188] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0189] Ionic liquids are salts or molten salts that are composed only of ions and are liquid at room temperature, with a melting point below room temperature.

[0190] The ionic liquid comprises a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, trizolium, and mixtures thereof, and b) BF4. - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4- , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may be a compound containing one or more anions selected from among.

[0191] The ionic liquid may be at least one selected from the group consisting of, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0192] In the solid electrolyte layer, the weight ratio of the solid electrolyte to the ionic liquid may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by improving the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0193] The above-mentioned all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0194] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0195] Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0196] Example 1

[0197] 1. Manufacturing of composite cathode active materials

[0198] 97 wt% of the first solid electrolyte 75Li2S-25P2S5(D 50 =3 μm) and 3 wt% of the second solid electrolyte Li5PS5Cl(D 50 =0.6 ㎛) was added to a xylene solvent and stirred. At this time, the mixing ratio of the first solid electrolyte and the second solid electrolyte was designed so that the second solid electrolyte was 3 wt% with respect to the total 100 wt% of the first solid electrolyte and the second solid electrolyte in the final obtained composite cathode active material. Thereafter, the result of the stirring was subjected to a first heat treatment at 120°C for 2 hours to obtain a composite solid electrolyte in which the surface of the 75Li2S-25P2S5 particles was coated with Li5PS5Cl particles.

[0199] The above composite solid electrolyte is LiNi 0.8 Co 0.1 Al 0.1 O2(D50 =15 ㎛) was added to the xylene solvent and stirred. At this time, with respect to 100 wt% of the composite cathode active material finally obtained, LiNi 0.8 Co 0.1 Al 0.1 The composition was designed to be 85 wt% of O2, 14.7 wt% of the first solid electrolyte, and 0.3 wt% of the second solid electrolyte. Subsequently, the composite solid electrolyte was added to the xylene solvent, stirred, and the resultant was subjected to a second heat treatment at 100°C for 1 hour. Through this, LiNi 0.8 Co 0.1 Al 0.1 A composite cathode active material coated on the surface of O2 particles with the above composite solid electrolytes was obtained. In the composite cathode active material thus obtained, the average thickness of the first coating layer was 4.5 μm, and the average thickness of the second coating layer was 0.7 μm, which were measured using a scanning electron microscope and in the same manner as described above.

[0200] 2. Manufacturing of the anode

[0201] A solid electrolyte of Li6PS5Cl containing 13.5 wt% argyrodite-type crystals (D 50 =1㎛), 85 wt% of the aforementioned composite cathode active material, 1.0 wt% of PVDF binder, and 0.5 wt% of carbon nanotube conductive material were mixed to prepare a cathode slurry. The cathode slurry was applied onto one side of an aluminum foil cathode current collector using a bar coater, and then dried in a convection oven at 80°C for 10 minutes and rolled to prepare a cathode in which a cathode active material layer was formed on the cathode current collector.

[0202] 3. Manufacturing of solid electrolyte layer

[0203] An argyrodite-type solid electrolyte Li6PS5Cl(D) was added to a binder solution in which an acrylic binder (SX-A334, Zeon) was dissolved in an isobutylyl isobutylate (IBIB) solvent. 50=3㎛) was added and stirred to prepare a solid electrolyte layer slurry. The solid electrolyte layer slurry contained 98.5 wt% of solid electrolyte and 1.5 wt% of binder. The solid electrolyte layer slurry was applied onto a release PET film using a bar coater and dried at room temperature to prepare a solid electrolyte layer.

[0204] 4. Manufacturing of the cathode

[0205] Primary entry (D 50 ) carbon black with an average particle diameter (D) of about 30 nm 50 ) is prepared by mixing silver (Ag) having a diameter of about 60 nm in a weight ratio of 3:1, and adding 0.25 g of the above complex to 2 g of an NMP solution containing 7 wt% of polyvinylidene fluoride binder (# 9300 from Kureha) and mixing them to prepare a negative electrode slurry. The prepared negative electrode slurry is applied to a nickel foil current collector using a bar coater and dried in a convection oven at 80°C for 10 minutes to obtain a laminate. The obtained laminate is vacuum-dried at 100°C for 10 hours to prepare a deposition-type negative electrode in which a negative electrode coating layer is formed on the negative electrode current collector.

[0206] 5. Manufacturing of all-solid-state secondary batteries

[0207] The prepared positive electrode, negative electrode, and solid electrolyte layer were cut, and the solid electrolyte layer was laminated on the positive electrode, followed by the negative electrode. This was sealed in a pouch shape and subjected to warm isostatic pressing (WIP) at 85°C and 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0208] Example 2

[0209] In the manufacture of the solid electrolyte layer, the argyrodite-type solid electrolyte Li6PS5Cl(D 50 =3㎛) was used instead of the composite solid electrolyte, and a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0210] Comparative Example 1

[0211] In the manufacture of the positive electrode, LiNi is used instead of the composite positive electrode active material. 0.8 Co 0.1 Al 0.1 O2(D 50 =5 ㎛) was used as the positive electrode active material, and a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0212] Evaluation Example 1: Evaluation of Elastic Modulus of Solid Electrolyte

[0213] In order to evaluate the elastic modulus of the solid electrolyte, the elastic modulus (E) by the Young's module was measured using the impulse excitation technique (IET), and the measurement results are shown in Table 1 below.

[0214] Solid electrolyte typeElastic modulus (E)75Li2S-25P2S518 GPaLi5PS5Cl22.1 GPa

[0215] Referring to Table 1, it can be confirmed that 75Li2S-25P2S5 has an elastic modulus of less than 20 GPa, and Li5PS5Cl has an elastic modulus of more than 22.1 GPa.

[0216] Evaluation Example 2: Evaluation of the electrochemical stability of solid electrolytes

[0217] In order to evaluate the electrochemical stability of the solid electrolyte, cyclic voltammetry was performed using the solid electrolytes 75Li2S-25P2S5 and Li5PS5Cl used in Table 1 above. The solid electrolyte powder was placed in a mold and pressed with a hydraulic press of 4 tons to produce a pellet shape, and a cell for evaluating the electrochemical stability was manufactured using a lithium counter electrode.

[0218] For the above cells, cyclic voltammetry (CV) evaluation was performed. A constant voltage was scanned per unit time over a voltage range of 2.25–4.45 V. When the voltage limit was reached, the scan direction was reversed and the voltage was continuously scanned, thereby measuring the current according to the voltage change. For each cell, the change in current according to voltage was measured, and the results are shown in Figs. 4 and 5, respectively.

[0219] Referring to FIGS. 4 and 5, it can be confirmed that the all-solid-state secondary battery manufactured using Li5PS5Cl has superior electrochemical stability compared to the all-solid-state secondary battery manufactured using 75Li2S-25P2S5.

[0220] Evaluation Example 3: Initial Charge-Discharge Performance Evaluation

[0221] For the all-solid-state secondary batteries manufactured in Example 1, Example 2, and Comparative Example 1, in order to evaluate the initial charge / discharge performance, the voltage change according to the specific capacity (mAh / g) at the time of the initial charge / discharge performance was measured and the results are shown in FIGS. 6 to 8.

[0222] For each battery, the initial charge / discharge (first cycle) was performed by charging to an upper limit voltage of 4.25 V at a constant current of 0.1 C at 45°C and then discharging to an end voltage of 2.5 V at 0.1 C, as shown in Fig. 6. The second cycle was then performed under the same voltage range conditions of 0.1 C charge and 0.33 C discharge, as shown in Fig. 7. The third cycle was then performed under the same voltage range conditions of 0.1 C charge and 1.0 C discharge, as shown in Fig. 8.

[0223] In addition, the charge capacity in the first to third cycles, the charge / discharge efficiency (the ratio of the former to the latter discharge capacity), and the rate capability were measured and shown in Table 2 below.

[0224] 1st cycle 2nd cycle 3rd cycle Rate capability CH (mAh / g) DCH (mAh / g) ICE (%) CH (mAh / g) DCH (mAh / g) CE (%) CH (mAh / g) DCH (mAh / g) CE (%) 1C / 0.33C (%) Example 1 236.2 205.487.0 205.6 191.8 93.3 192.4 178.0 92.5 92.8 Example 2 248.5 214.486.3 212.5 197.9 93.1 200.2 184.5 92.2 93.2 Comparative example 1 244.2 204.5 83.7 196.9 176.3 89.5 178.5 155.6 87.2 88.3

[0225] Referring to FIGS. 6 to 8, in all of the first to third cycles, in the case of Examples 1 and 2 in which a composite positive electrode active material was applied to the positive electrode active material layer, the resistance was lower than in Comparative Example 1 in which a composite positive electrode active material was not applied.

[0226] In addition, referring to Table 2, Example 1 and Example 2 have high charge capacity and discharge capacity, excellent charge / discharge efficiency, and excellent rate performance in all of the first to third cycles compared to Comparative Example 1, and thus, it is understood that the cell performance is improved when a composite cathode active material is applied to the cathode active material layer.

[0227] In particular, in the case of Example 2, which uses a composite solid electrolyte in the solid electrolyte layer, it can be confirmed that the charge capacity and discharge capacity are higher than in Example 1, and the rate performance is also excellent.

[0228] Evaluation Example 4: Capacity evaluation after 20 cycles

[0229] For the all-solid-state secondary batteries manufactured in Examples 1, 2, and Comparative Example 1, initial charging and discharging were performed as in Evaluation Example 3, and then charging at 0.33 C and discharging at 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C were repeated 20 times, and a graph of voltage according to specific capacity (mAh / g) is shown in Fig. 9.

[0230] Referring to Figure 9, in the case of Examples 1 and 2 in which a composite positive electrode active material was applied to the positive electrode active material layer, the resistance was lower than that of Comparative Example 1 when the cycle was repeated 20 times compared to Comparative Example 1 in which a composite positive electrode active material was not applied. In addition, in the case of Example 2 in which a composite solid electrolyte was also applied to the solid electrolyte layer in addition to applying a composite positive electrode active material to the positive electrode active material layer, the resistance was lower than that of Example 1, confirming that the cell performance was superior.

[0231] Evaluation Example 5: Evaluation of life characteristics after 40 cycles

[0232] For the all-solid-state secondary batteries manufactured in Examples 1, 2, and Comparative Example 1, initial charge and discharge were performed as in Evaluation Example 3, and then charging at 0.33 C and discharging at 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C were repeated 40 or more times to evaluate the life characteristics, and the specific capacity (mAh / g) according to the number of cycles was measured and shown in Fig. 10.

[0233] Referring to Fig. 10, in the case of Examples 1 and 2 in which a composite positive electrode active material was applied to the positive electrode active material layer, it can be confirmed that the efficiency (ratio of the specific capacity at 40 cycles to the specific capacity at 0 cycles) is higher than that of Comparative Example 1 in which a composite positive electrode active material was not applied when the cycle was repeated 40 or more times. In particular, in the case of Example 2 in which a composite solid electrolyte was also applied to the solid electrolyte layer in addition to applying a composite positive electrode active material to the positive electrode active material layer, it can be confirmed that the efficiency is higher than that of Example 1.

[0234] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0235] [Explanation of symbols]

[0236] 50: Composite cathode active material 1: Core particle

[0237] 2: Composite solid electrolyte 10: First particle

[0238] 20: Second particle 11: First coating layer

[0239] 21: Second coating layer

[0240] 100: All-solid-state battery 200: Cathode

[0241] 201: Cathode current collector 203: Cathode active material layer

[0242] 300: solid electrolyte layer 400: cathode

[0243] 401: Negative current collector 403: Negative active material layer

[0244] 400': Precipitation type cathode 404: Lithium metal layer

[0245] 405: Cathode coating layer 500: Elastic layer

Claims

1. Core particles comprising a lithium transition metal composite oxide; and A first coating layer located on the surface of the core particle and including a composite solid electrolyte, The composite solid electrolyte comprises a first particle; and a second coating layer located on the surface of the first particle and including a second particle; The first particle comprises a first solid electrolyte having an elastic modulus of less than 20 GPa, The second particle is a composite positive electrode active material including a second solid electrolyte having an elastic modulus of 20 GPa or more.

2. In paragraph 1, The above lithium transition metal composite oxide is a composite cathode active material including lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium manganese oxide, lithium iron phosphate compound, or a combination thereof.

3. In paragraph 1, A composite cathode active material having an average particle diameter of the core particles of 1 ㎛ to 25 ㎛.

4. In paragraph 1, The first solid electrolyte is a composite positive electrode active material that is a sulfide-based solid electrolyte.

5. In paragraph 1, The second solid electrolyte is a composite positive electrode active material that is a halide-based solid electrolyte.

6. In paragraph 1, The first solid electrolyte is a composite positive electrode active material represented by the following chemical formula 1. [Chemical Formula 1] A(Li2S)-B(P2S5) In the above chemical formula 1, A represents the mol% content of Li2S with respect to 100 mol% of the total of Li2S and P2S5, and B represents the mol% content of P2S5 with respect to 100 mol% of the total of Li2S and P2S5, and 50≤A≤99 and 1≤B≤50.

7. In paragraph 5, The above halide-based solid electrolyte is a composite positive electrode active material represented by the following chemical formula 2. [Chemical Formula 2] (Li a1 M 1 b1 M 2 c1 (P) d1 M 3 e1 )(S f1 M 4 g1 )X h1 In the above chemical formula 2, 4≤a1≤8, and M 1 is Mg, Cu, Ag, or a combination thereof, and 0≤b1<0.5, and M 2 is Na, K, or a combination thereof, 0≤c1<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d1<4, 0≤e1<1 이고, M 4 is O, SO n , or a combination thereof, and 1.5≤n≤5, 3≤f1≤12, 0≤g1<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h1≤2이다.

8. In paragraph 1, A composite positive electrode active material having an average particle diameter of the first particle of 0.1 ㎛ to 30 ㎛.

9. In paragraph 1, A composite positive electrode active material having an average particle diameter of the second particles of 0.01 ㎛ to 5 ㎛.

10. In paragraph 1, A composite positive electrode active material having an average thickness of the first coating layer of 0.5 ㎛ to 20 ㎛.

11. In paragraph 1, A composite positive electrode active material having an average thickness of the second coating layer of 0.01 ㎛ to 15 ㎛.

12. In paragraph 1, A composite cathode active material in which the average particle diameter of the first particle is 2 to 20 times greater than the average particle diameter of the second particle.

13. In paragraph 1, A composite cathode active material comprising 1 to 10 wt% of a second solid electrolyte relative to 100 wt% of the total of the first solid electrolyte and the second solid electrolyte.

14. After mixing the first and second particles, perform the first heat treatment, It includes mixing the result of the first heat treatment with a lithium transition metal composite oxide and then performing a second heat treatment. The first particle comprises a first solid electrolyte having an elastic modulus of less than 20 GPa, A method for producing a composite positive electrode active material comprising a second solid electrolyte having an elastic modulus of 20 GPa or more.

15. In paragraph 14, The first heat treatment is performed at 30°C to 200°C for 0.5 to 5 hours, A method for producing a composite cathode active material, wherein the second heat treatment is performed at 50°C to 300°C for 0.5 to 5 hours.

16. Anode current collector; and A positive electrode comprising a positive electrode active material layer positioned on the positive electrode current collector and comprising a composite positive electrode active material according to any one of claims 1 to 13.

17. In paragraph 16, The above positive electrode active material layer includes a sulfide-based solid electrolyte, A positive electrode in which the above sulfide-based solid electrolyte is included in an amount of 0.1 wt% to 35 wt% based on the total weight of the positive electrode active material layer.

18. The anode according to Article 16; cathode; and An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive electrode and the negative electrode.

19. In paragraph 18, The solid electrolyte layer comprises a composite solid electrolyte comprising a first particle; and a second coating layer positioned on the surface of the first particle and including second particles, The first particle comprises a first solid electrolyte having an elastic modulus of less than 20 GPa, An all-solid-state secondary battery comprising a second solid electrolyte having an elastic modulus of 20 GPa or more.

20. In paragraph 18, The negative electrode comprises a negative electrode current collector; and a negative electrode coating layer positioned on the negative electrode current collector and including a lithium-philic metal, a carbon material, or a combination thereof; An all-solid-state secondary battery comprising a lithium metal layer formed by charging between the negative electrode current collector and the negative electrode coating layer.

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