Anode for anode-free battery, and anode-free battery comprising same

Abstract

The present invention relates to an anode for a secondary battery. More specifically, the present invention relates to an anode comprising: an anode current collector; an ion-conductive coating layer disposed on the anode current collector; and a cathode coating layer disposed on the ion-conductive coating layer.

Description

Anode for a cathode-free battery and a cathode-free battery comprising the same

[0001] The present invention relates to a cathode for a non-anode battery and a secondary battery including the same.

[0002] To increase the energy density of secondary batteries, the use of lithium as an anode active material has been proposed. Two methods for using lithium as an anode active material include using lithium or a lithium alloy as the anode active material layer and not forming an anode active material layer on the anode current collector. In the latter case, the anode current collector initially has no anode active material layer, and lithium, which is deposited at the interface between the anode current collector and the solid electrolyte during charging, is used as the active material. The anode current collector is composed of a metal that does not form an alloy or compound with lithium.

[0003] However, when lithium is used as an anode active material, metallic lithium is precipitated on the anode side during charging. When lithium is used as an anode active material layer, lithium is precipitated on the lithium layer. If an anode active material layer is not formed, lithium is precipitated on the anode current collector. The lithium precipitated on the anode side grows lithium dendrites when the secondary battery is repeatedly charged and discharged. These grown lithium dendrites can cause short circuits or capacity reduction in the battery. This makes it difficult to commercialize technologies that use lithium as an anode active material. Although methods for suppressing lithium dendrite precipitation and growth have been proposed, they have not yet been sufficiently improved, and further improvements are required.

[0004] The problem to be solved by the present invention is to provide a negative electrode that prevents the formation of lithium dendrites by improving the lithium deposition density and uniformity.

[0005] The negative electrode according to the present invention may include a negative electrode current collector, an ion conductive coating layer disposed on the negative electrode current collector, and a negative electrode coating layer disposed on the ion conductive coating layer. The ion conductive coating layer may include Li2S. The negative electrode coating layer may include first particles comprising a carbon-based material, and second particles comprising at least one selected from a metal or metalloid material.

[0006] According to another concept of the present invention, a negative electrode may include a negative electrode current collector and a negative electrode coating layer disposed on the negative electrode current collector. The negative electrode coating layer may include first particles comprising a carbon-based material, second particles comprising at least one selected from a metal or metalloid material, and third particles comprising Li2S.

[0007] A secondary battery according to another concept of the present invention may include the negative electrode, the positive electrode disposed opposite the negative electrode, and an electrolyte layer disposed between the negative electrode and the positive electrode.

[0008] According to one embodiment, a negative electrode can improve the lithium deposition density and uniformity during charge / discharge of a secondary battery including the negative electrode, thereby inducing uniform lithium growth on a negative electrode current collector, thereby providing a secondary battery with long-life performance.

[0009] FIG. 1 is a cross-sectional view schematically illustrating a secondary battery including a negative electrode according to embodiments of the present invention.

[0010] FIG. 2 is a cross-sectional view of a secondary battery unit cell including a negative electrode according to one embodiment of the present invention.

[0011] FIG. 3 is a cross-sectional view of a secondary battery unit cell including a negative electrode according to one embodiment of the present invention.

[0012] Figure 4 is a cross-sectional view of a cathode according to one embodiment of the present invention.

[0013] Figure 5 is a cross-sectional view of a cathode according to one embodiment of the present invention.

[0014] FIG. 6 is a cross-sectional view of a cathode according to one embodiment of the present invention, and shows a cathode including a lithium metal layer compared to FIG. 3.

[0015] FIG. 7 is a cross-sectional view of a cathode according to one embodiment of the present invention, and shows a cathode including a lithium metal layer compared to FIG. 4.

[0016] Figure 8 is a cross-sectional view of a cathode according to a comparative example of the present invention, showing lithium dendrites formed on a lithium metal layer.

[0017] Figure 9 is an enlarged view of a cathode according to one embodiment of the present invention.

[0018] Figure 10 is an enlarged view of a cathode according to one embodiment of the present invention.

[0019] Figure 11 is an enlarged view of a cathode according to one embodiment of the present invention.

[0020] Figure 12 is an enlarged view of a cathode coating layer according to one embodiment of the present invention.

[0021]

[0022] To fully understand the structure and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and subject to various modifications. However, the description of these embodiments is provided solely to ensure a complete disclosure of the present invention and to fully inform those skilled in the art of the invention of the scope of the invention.

[0023] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thicknesses of the components are exaggerated for the sake of clarity. Parts designated by the same reference numerals throughout the specification represent the same components.

[0024] Embodiments described herein will be described with reference to cross-sectional and / or plan views, which are ideal illustrations of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents. Accordingly, the regions illustrated in the drawings have a schematic nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific shapes of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, and third are used to describe various components in various embodiments of the present specification, these components should not be limited by such terms. These terms are used only to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0025] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise. As used herein, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components.

[0026] Unless otherwise defined herein, the particle size may be the average particle size. In addition, the particle size refers to the average particle size (D50), which means the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured by a method well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. Alternatively, the average particle size (D50) value can be obtained by measuring with a measuring device that utilizes dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. Alternatively, the average particle size (D50) value can be obtained by measuring with a laser diffraction method. When measuring by laser diffraction, more specifically, after the particles to be measured are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0027] In this specification, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic state.

[0028] As used herein, “alloy” means a mixture of two or more metals.

[0029] In this specification, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation.

[0030] In this specification, “positive electrode active material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0031] In this specification, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0032] In this specification, “lithiation” and “lithiate” mean a process of adding lithium to an electrode active material.

[0033] In this specification, “delithiation” and “delithiate” refer to a process of removing lithium from an electrode active material.

[0034] In this specification, “charging” and “charging” mean the process of providing electrochemical energy to a battery.

[0035] In this specification, “discharge” and “discharge” mean the process of removing electrochemical energy from a battery.

[0036] In this specification, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during the discharge process.

[0037] In this specification, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0038]

[0039] Lithium secondary battery (10)

[0040] FIG. 1 is a cross-sectional view schematically illustrating a secondary battery according to one embodiment of the present invention. Referring to FIG. 1, the secondary battery according to one embodiment includes a positive electrode layer (100), a negative electrode layer (200) facing the positive electrode layer (100), and an electrolyte layer (300) disposed between the positive electrode layer (100) and the negative electrode layer (200). However, the present invention is not limited thereto, and the secondary battery may further include an additional functional layer, such as an adhesion enhancing layer, disposed between the positive electrode layer (100) and the electrolyte layer (300) or between the negative electrode layer (200) and the electrolyte layer (300).

[0041] The secondary battery according to the present invention will be described with reference to the following description. The secondary battery including the negative electrode layer (200) according to the present invention is not limited to a specific example, and may be applied to various types of secondary batteries by including or combining each of the secondary battery components described below.

[0042] In one embodiment, it can be applied to an all-solid-state secondary battery including a solid electrolyte layer. In one embodiment, it can be applied to a lithium-sulfur secondary battery including a sulfide-based positive electrode active material and a sulfide-based solid electrolyte. In one embodiment, it can be applied to a non-anode battery not including an initial lithium precipitation layer. In one embodiment, it can be applied to a lithium metal battery including a gel polymer electrolyte and using a lithium metal layer as an anode.

[0043] Below, each component of the secondary battery is described in more detail.

[0044] Bipolar (100)

[0045] The positive electrode layer (100) of one embodiment includes a positive electrode current collector (110) and a positive electrode active material layer (120) disposed on the positive electrode current collector (110). The positive electrode active material layer (120) may include a positive electrode active material, a solid electrolyte, a conductive material, and a binder (BND).

[0046] The positive electrode current collector (110) can provide a reference surface on which the positive electrode active material layer (120) is arranged. The positive electrode current collector (110) can include a plate or foil including, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0047] Meanwhile, although not shown, a cathode coating layer (CTL) provided between the cathode current collector (110) and the cathode active material layer (120) may be further included. The cathode coating layer (CTL) may be directly disposed on, for example, one side or both sides of the cathode current collector (110). The cathode coating layer (CTL) may be coated on one side or both sides of the cathode current collector (110). No other layer may be disposed between the cathode current collector (110) and the cathode coating layer (CTL).

[0048] By directly arranging the cathode coating layer (CTL) on one or both sides of the cathode current collector (110), the bonding force between the cathode current collector (110) and the cathode active material layer (120) can be further improved. By arranging the cathode coating layer (CTL) between the cathode current collector (110) and the cathode active material layer (120), side reactions between the filler (FIL), the solid electrolyte (SEP), or the cathode active material (CAC) and the cathode current collector (110) can be more effectively suppressed. For example, the cathode coating layer (CTL) can prevent corrosion of the sulfide-based cathode active material (e.g., Li2S) by the cathode current collector (110). As a result, the cathode coating layer (CTL) can suppress deterioration of the secondary battery (10) during the charge / discharge process and improve the cycle characteristics of the secondary battery (10).

[0049] The thickness of the cathode coating layer (CTL) is, for example, 0.01 to 20%, 0.1 to 20%, 0.5 to 20%, 1 to 20%, 1 to 15%, 1 to 10%, 2 to 8%, or 3 to 7% of the thickness of the cathode current collector (110). The thickness of the cathode coating layer (CTL) may be, for example, 10 nm to 5 ㎛, 50 nm to 5 ㎛, 200 nm to 4 ㎛, 500 nm to 3 ㎛, 500 nm to 2 ㎛, 500 nm to 1.5 ㎛, or 700 nm to 1.3 ㎛. When the cathode coating layer (CTL) has a thickness in this range, the bonding force between the cathode current collector (110) and the cathode active material layer (120) is further improved, and an increase in interfacial resistance can be suppressed. The thickness of the cathode coating layer (CTL) can be measured, for example, from a scanning electron microscope (SEM) image of a cross-section of the cathode coating layer (CTL).

[0050] The anode coating layer (CTL) may include, for example, a carbon-based conductive material. The carbon-based conductive material included in the anode coating layer (CTL) may be selected from among the carbon-based conductive materials used in the anode active material layer (120). The anode coating layer (CTL) may include the same carbon-based conductive material as the carbon-based conductive material used in the anode active material layer (120). Since the anode coating layer (CTL) includes a carbon-based conductive material, the anode coating layer (CTL) may be, for example, a conductive layer.

[0051] The cathode coating layer (CTL) may additionally include, for example, a binder. By additionally including a binder in the cathode coating layer (CTL), the bonding strength between the cathode current collector (110) and the cathode active material layer (120) may be further improved. The binder included in the cathode coating layer (CTL) may be, for example, a conductive binder or a non-conductive binder. The conductive binder may be, for example, an ion-conductive binder and / or an electron-conductive binder. A binder having both ion-conductivity and electron-conductivity may belong to both an ion-conductive binder and an electron-conductive binder.

[0052] The binder included in the positive electrode coating layer (CTL) may be selected from among the binders used in the positive electrode active material layer (120). The positive electrode coating layer (CTL) may include the same binder as the binder used in the positive electrode active material layer (120). The binder included in the positive electrode coating layer (CTL) is, for example, a fluorinated binder. The fluorinated binder included in the positive electrode coating layer (CTL) is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a combination thereof. The positive electrode coating layer (CTL) may be, for example, a binding layer including a binder. The positive electrode coating layer (CTL) may be, for example, a conductive layer including a binder and a carbon-based conductive material.

[0053] The cathode coating layer (CTL) can be disposed on the cathode current collector (110) in a dry or wet manner, for example. The cathode coating layer (CTL) can be disposed on the cathode current collector (110) in a dry manner, for example, by deposition such as CVD or PVD. The cathode coating layer (CTL) can be disposed on the cathode current collector (110) in a wet manner, for example, by spin coating, dip coating, or the like. The cathode coating layer (CTL) can be disposed on the cathode current collector (110) in a wet manner, for example, by deposition of a carbon-based conductive material on a substrate by deposition. A dry-coated cathode coating layer (CTL) is made of a carbon-based conductive material and may not include a binder. The cathode coating layer (CTL) can be disposed on the cathode current collector (110) in a dry manner, for example, by coating a composition including a carbon-based conductive material, a binder, and a solvent on the surface of the electrode current collector and drying it. The cathode coating layer (CTL) can have a single-layer structure or a multi-layer structure including a plurality of layers. Multi-layer structures can be two-layer, three-layer, four-layer, etc.

[0054] In another embodiment of the present invention, the positive electrode collector (110) may be omitted. The thickness of the positive electrode collector (110) may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 5 μm to 25 μm, or 10 μm to 20 μm.

[0055] The cathode current collector (110) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof.

[0056] The base film may be, for example, an insulator. If the base film includes an insulating thermoplastic polymer, the base film may soften or liquefy when a short circuit occurs, thereby preventing battery operation and suppressing a rapid increase in current.

[0057] The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or an alloy thereof. The metal layer may act as an electrochemical fuse to prevent short circuits by being cut off in the event of overcurrent. The limit current and maximum current can be controlled by controlling the thickness of the metal layer. The metal layer may be plated or deposited on the base film. When the thickness of the metal layer is reduced, the limit current and / or maximum current of the positive electrode current collector (110) decrease, thereby improving the stability of the lithium battery in the event of a short circuit.

[0058] A lead tab may be added to the metal layer for external connection. The lead tab may be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer may melt, electrically connecting the metal layer to the lead tab.

[0059] In order to make the welding between the metal layer and the lead tab more solid, a metal chip may be added between the metal layer and the lead tab. The metal chip may be a thin piece of the same material as the metal of the metal layer. The metal chip may be, for example, a metal foil, a metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. By placing the metal chip on the metal layer and then welding it with the lead tab, the lead tab may be welded to the metal chip / metal layer laminate or the metal chip / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal chip may melt, so that the metal layer or the metal layer / metal chip laminate may be electrically connected to the lead tab. The metal chip and / or the lead tab may be added to a portion of the metal layer.

[0060] The thickness of the base film may be, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C or less, or 100 to 200 °C. When the base film has a melting point in this range, the base film can be melted during the process of welding the lead tab and easily bonded to the lead tab. In order to improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film.

[0061] The thickness of the metal layer may be, for example, 0.01 to 3 ㎛, 0.1 to 3 ㎛, 0.1 to 2 ㎛, or 0.1 to ㎛. By having a thickness in this range of the metal layer, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 ㎛, 2 to 7 ㎛, or 4 to 6 ㎛. By having a thickness in this range of the metal piece, the connection between the metal layer and the lead tab can be performed more easily. By having the laminated structure of the base film and the metal layer as described above, the positive electrode current collector (110) can reduce the weight of the positive electrode layer (100), and consequently, the energy density of the secondary battery can be improved.

[0062] In one embodiment of the present invention, the content of the positive electrode active material in the positive electrode active material layer (120) may be 10 wt% to 99 wt%, 30 wt% to 80 wt%, 40 wt% to 70 wt%, or 40 wt% to 50 wt% of the total weight of the positive electrode active material layer (120). If the content of the positive electrode active material is excessively reduced, the energy density of the all-solid-state battery (10) may be reduced. If the content of the positive electrode active material is excessively increased, the deterioration of the secondary battery (10) may be accelerated due to a change in the volume of the positive electrode during charge and discharge.

[0063] The positive electrode active material within the positive electrode active material layer (120) can reversibly absorb and desorb lithium ions. The positive electrode active material may include a plurality of particles. The positive electrode active material according to the present invention may include an oxide-based positive electrode active material, a sulfide-based positive electrode active material, or a combination thereof.

[0064] (oxide-based cathode active material)

[0065] The oxide-based cathode active material may include, for example, a lithium transition metal oxide, a metal oxide, or a combination thereof. The lithium transition metal oxide may include, for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt mangense oxide, lithium manganate, lithium iron phosphate, or a combination thereof. The lithium oxide may include, for example, iron oxide, vanadium oxide, or a combination thereof.

[0066] The sulfide-based cathode active material may include, for example, nickel sulfide, copper sulfide, Li2S, a Li2S-containing complex, or a combination thereof. A more specific description of the sulfide-based cathode active material according to an embodiment of the present invention will be provided below.

[0067] The oxide-based cathode active material may be, for example, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. The lithium-containing oxide-based cathode active material may be, for example, Li. a A 1-b B' b D2 (in the above formula, 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li a E 1-b B' b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B' b O4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B' c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B' c O 2-α F' α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B' c O 2-α F' α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B' c D α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (In the above equation, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c Gd O2 (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O2 (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (in the above formula, 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); may include a compound represented by any one of the chemical formulas of LiFePO4.

[0068] In the chemical formula representing the compound described above, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0069] The oxide-based cathode active material may include, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in a direction, and thereby each atomic layer forms a two-dimensional plane. The "cubic rock salt structure" refers to the sodium chloride type (NaCl type) structure, which is a type of crystal structure, and specifically refers to a structure in which the face-centered cubic lattice (fcc) formed by each cation and anion is arranged with a displacement of half of the ridge of the unit lattice. Lithium transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn zO2(NCM) (0 <x<1,0<y<1, 0<z<1, x+y+z=1) 등의 삼원계 리튬전이금속산화물일 수 있다. 양극 활물질이 층상암염형 구조를 갖는 삼원계 리튬전이금속산화물을 포함하는 경우, 이차 전지(10)의 에너지 밀도가 커지고 열안정성이 향상될 수 있다.

[0070] The oxide-based positive electrode active material may be covered by a coating layer (not shown). The oxide-based positive electrode active material may also be a mixture of the above-described compound and a compound to which a coating layer is added. Meanwhile, the coating layer added to the surface of the positive electrode active material may include, for example, an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of the coating elements below. The compound forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer may include, for example, Li2O-ZrO2 (LZO). The method of forming the coating layer may be selected within a range that does not adversely affect the physical properties of the positive electrode active material. The method of forming the coating layer may include, for example, spray coating, dipping, etc.

[0071] When the oxide-based cathode active material is a ternary lithium transition metal oxide such as NCA or NCM and contains nickel (Ni), it is possible to increase the capacity density of the secondary battery (10) and reduce metal dissolution of the cathode active material in a charged state. As a result, the cycle characteristics of the secondary battery (10) in a charged state are improved. Meanwhile, the "cycle characteristics" are characteristics indicating the degree to which the secondary battery (10) is deteriorated by charge / discharge of the all-solid-state battery (10). A secondary battery (10) having high cycle characteristics may have a small degree of deterioration of the secondary battery (10) due to charge / discharge, and a secondary battery (10) having low cycle characteristics may have a large degree of deterioration of the secondary battery (10) due to charge / discharge.

[0072] The oxide-based cathode active material may have a particle shape such as a sphere or an ellipsoid, for example. The particle size and content of the oxide-based cathode active material are not particularly limited. The size of the oxide-based cathode active material may be, for example, 0.1 to 30 μm, 0.5 to 20 μm, or 1 to 15 μm. The oxide-based cathode active material may be, for example, a single-crystal particle or a polycrystalline particle.

[0073] (Sulphide-based positive electrode active material)

[0074] The cathode active material layer (120) according to embodiments of the present invention may include a sulfide-based cathode active material. More specifically, the sulfide-based cathode active material may include a Li2S-containing cathode active material (CAC). The Li2S-containing cathode active material (CAC) may include, for example, a complex of Li2S and carbon, a complex of Li2S, carbon, and a solid electrolyte, a complex of Li2S and a solid electrolyte, a complex of Li2S and a lithium salt, a complex of Li2S, a lithium salt, and carbon, a complex of Li2S, a lithium salt, a metal halide, and carbon, a complex of Li2S and a metal carbide, a complex of Li2S, carbon, and a metal carbide, a complex of Li2S and a metal nitride, a complex of Li2S, carbon, and a metal nitride, or a combination thereof.

[0075] The cathode active material (CAC) may include a sulfide-based composite (CAM) and a conductive material (CMA). In one embodiment, the sulfide-based composite (CAM) may have a particle shape such as a spherical shape or an elliptical shape. The particle size of the sulfide-based composite (CAM) is not particularly limited and may be within a range applicable to general cathode active materials. The size of the sulfide-based composite (CAM) may be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm. The conductive material (CMA) may cover the surface of the sulfide-based composite (CAM).

[0076] The conductive material (CMA) may include carbon. The conductive material (CMA) may include, without limitation, any material containing carbon atoms used as a conductive material in the art. For example, the conductive material (CMA) may include crystalline carbon, amorphous carbon, or a combination thereof. The conductive material (CMA) may include, for example, a sintered product of a carbon precursor. The conductive material (CMA) may include, for example, carbon nanostructures.

[0077] The conductive material (CMA) may include, for example, porous carbon or non-porous carbon. The porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon may be, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, etc.; graphite, activated carbon, or a combination thereof. The form of the carbon in the conductive material (CMA) may be, but is not limited to, particle form, sheet form, fiber form, etc., and any form used as carbon in the art may be used.

[0078] In one embodiment of the present invention, the conductive material (CMA) may include a fibrous carbon-based material. Since the conductive material (CMA) includes a fibrous carbon-based material, the electronic conductivity of the cathode active material (CAC) may be further enhanced. Since the conductive material (CMA) includes a fibrous carbon-based material, electronic conduction may be facilitated from the surface to the interior of the cathode active material (CAC). The internal resistance of the sulfide-based composite (CAM) may be reduced by the conductive material (CMA), and the cycle characteristics of the secondary battery may be further improved.

[0079] The aspect ratio of the fibrous carbon-based material can be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. When the fibrous carbon-based material has an aspect ratio in this range, the overall electronic conductivity of the cathode active material (CAC) is improved, and local electronic conductivity imbalance within the cathode active material (CAC) can be further alleviated.

[0080] The fibrous carbon-based material may include, for example, carbon nanostructures. The carbon nanostructures may include, for example, carbon nanofibers (CNFs), carbon nanotubes (CNTs), carbon nanobelts, carbon nanorods, or combinations thereof. The carbon nanostructures may form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure composed of multiple carbon nanostructures aggregated together.

[0081] The diameter of the primary carbon nanostructure can be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 20 nm. The length of the primary carbon nanostructure can be, for example, 10 nm to 2 μm, 10 nm to 1.5 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 200 nm, or 10 nm to 100 nm. The diameter and length of the primary carbon nanostructure can be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Alternatively, the diameter and / or length of the primary carbon nanostructure can be measured by laser diffraction.

[0082] The secondary carbon nanostructure may be, for example, a structure formed by assembling primary carbon nanostructures in whole or in part to form a bundle or bunch shape. The secondary carbon nanostructure may include, for example, a bundle-type carbon nanostructure, a rope-type carbon nanostructure, or a combination thereof. The diameter of the secondary carbon nanostructure may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructure can be measured by laser diffraction. The secondary carbon nanostructure can be converted into the primary carbon nanostructure by, for example, dispersing it in a solvent or the like and then used in the manufacture of a cathode active material (CAC).

[0083] The method for manufacturing the cathode active material (CAC) according to the present embodiments may be, but is not limited to, a dry method, a wet method, or a combination thereof. In the art, methods for manufacturing the cathode active material (CAC) include, but are not necessarily limited to, milling, heat treatment, or deposition, and any method used in the art may be used.

[0084] In one embodiment of the present invention, the sulfide-based composite (CAM) in the cathode active material (CAC) may include a composite of Li2S and a solid electrolyte. The solid electrolyte may be, for example, an amorphous solid electrolyte, and any ion-conducting material used in the art may be used. The solid electrolyte may be, for example, an inorganic solid electrolyte. The solid electrolyte may be, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte includes, for example, Li, S, and P, and may optionally further include a halogen element. The sulfide-based solid electrolyte may be selected from among sulfide-based solid electrolytes used in the electrolyte layer. The sulfide-based solid electrolyte may have, for example, a molecular weight of 1×10 at room temperature. -5 It can have an ionic conductivity of S / cm or more. Sulfide-based solid electrolytes include, for example, Li3PO4-Li2SO4, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0*?*x*2, Li 7-x PS 6-x Br x , 0*x*2, and Li 7-x PS6-x I x , may contain one or more selected from 0*x*2.

[0085] The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may optionally contain other elements. The oxide-based solid electrolyte has, for example, a 1×10 -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from oxide-based solid electrolytes used in the solid electrolyte layer. The solid electrolyte may be, for example, a mixture of a sulfide-based solid electrolyte and a lithium salt. For example, it may be a mixture of Li3PO4-Li2SO4 and a binary lithium salt, or a mixture of Li3PO4-Li2SO4 and a ternary lithium salt.

[0086] In one embodiment of the present invention, the sulfide-based composite (CAM) within the cathode active material (CAC) may include a composite of Li2S and a lithium salt. In other words, the composite (CAM) may include Li2S and a lithium salt compound. The lithium salt compound may not include, for example, sulfur (S) atoms.

[0087] The lithium salt compound may be, for example, a binary compound composed of lithium and one element selected from groups 13 to 17 of the periodic table. The binary compound may include, for example, one or more selected from LiF, LiCl, LiBr, LiI, LiH, Li2S, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, LiI3, and LiB3. The lithium salt compound may be, for example, a ternary compound composed of lithium and two elements selected from groups 13 to 17 of the periodic table. The ternary compound may include, for example, one or more selected from Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, and Li3BN2. For example, the lithium salt compound may be one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI.

[0088] In one embodiment of the present invention, the sulfide-based composite (CAM) may include a composite of Li2S and a metal carbide. The metal carbide may be, for example, a two-dimensional metal carbide. The two-dimensional metal carbide may be, for example, MXene. The two-dimensional metal carbide may be, for example, M n+1 C n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) can be expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb 0.5 )2CT x , Nb2CT x , V2CT x , Ti3C2T x , (V 0.5 , Cr 0.5)3C2T x , Ti3CNT x , Ta4C3T x , Nb4C3T x or a combination thereof. The surface of the two-dimensional metal carbide may be terminated with O, OH and / or F.

[0089] In one embodiment of the present invention, the sulfide-based composite (CAM) may include a composite of Li2S and a metal nitride. The metal nitride may be, for example, a two-dimensional metal nitride. The two-dimensional metal nitride may be, for example, M n+1 N n T x (M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups) can be expressed as The surface of the two-dimensional metal nitride can be terminated with O, OH and / or F.

[0090] A composite (CAM) containing a cathode active material (CAC) and Li2S according to one embodiment of the present invention will be described in more detail. The cathode active material (CAC) may include a composite of Li2S, a lithium salt, and carbon. More specifically, the cathode active material (CAC) may include a composite of Li2S, a lithium halide, and carbon.

[0091] The composite (CAM) according to the present embodiments may have ductility. The composite (CAM) may function as a buffer material within the positive electrode active material layer (120). The composite (CAM) may prevent the occurrence of defects due to volume changes in the positive electrode active material layer (120).

[0092] In one embodiment, the composite (CAM) comprises Li2S-Li a X b(1≤a≤5, 1≤b≤5) may include a compound represented by X. The X may be I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2 or a combination thereof. a may be, for example, 1, 2, 3, 4 or 5. b may be, for example, 1, 2, 3, 4 or 5.

[0093] In one embodiment, the composite (CAM) may include a solid solution of Li2S and a lithium salt. The ionic conductivity of the composite (CAM) may be improved by the composite (CAM) including the solid solution of Li2S and a lithium salt. For example, since the solid solution of Li2S and a lithium salt includes lithium ions arranged within Li2S crystallites, the ionic conductivity of the solid solution of Li2S and a lithium salt may be improved compared to the ionic conductivity of Li2S. Consequently, the composite (CAM) according to the present invention may have high ionic conductivity and low internal resistance. The cycle characteristics of an all-solid-state secondary battery including the composite (CAM) of the present invention may be improved.

[0094] The size of the Li2S crystallites of the complex (CAM) obtained from the XRD spectrum may be, for example, 20 nm or less, 15 nm or less, or 10 nm or less. The size of the Li2S crystallites of the complex (CAM) obtained from the XRD spectrum may be, for example, 1 to 20 nm, 1 to 15 nm, or 3 to 10 nm. As the size of the Li2S crystallites decreases, the contact area between Li2S and the lithium salt may increase. As the contact area between Li2S and the lithium salt increases, the ionic conductivity of the complex of Li2S and the lithium salt may be improved.

[0095] The complex (CAM) according to one embodiment may further comprise a metal halide. In other words, the complex (CAM) may comprise a complex of Li2S, a lithium salt, and a metal halide. The metal halide may contain a metal other than lithium.

[0096] The complex (CAM) is Li2S-Li a X1 b -MX2 c A compound represented by may include a compound represented by . a may be an integer from 1 to 5, b may be an integer from 1 to 5, and c may be an integer from 1 to 5. M may be selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). Each of X1 and X2 may be selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0097] The composite (CAM) may include a solid solution of Li2S, a lithium salt, and a metal halide. For example, the composite (CAM) may include a compound (or solid solution) represented by Li2S-LiI-AlI3. As described above, the composite (CAM) and a conductive material (CMA, e.g., carbon nanostructure) may constitute a cathode active material (CAC) according to the present invention.

[0098] The Mohs hardness of the composite (CAM) may be lower than that of the lithium salt. The composite (CAM) may have improved ductility compared to the lithium salt. The improved ductility of the composite (CAM) effectively prevents internal defects due to volume changes in the positive electrode active material layer (120).

[0099] The Mohs hardness of Li2S is, for example, 0.6. The Mohs hardness of the composite (CAM) may be, for example, less than 2, less than 1.5, less than 1, or less than 0.7. If the Mohs hardness of the composite (CAM) increases excessively, it may be difficult to provide ductility.

[0100] The Mohs hardness of the lithium salt may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, or 2.0 or more. For example, the Mohs hardness of LiI is 2.0. Since the lithium salt has a Mohs hardness within this range, the pulverization of Li2S can be performed more easily during the milling process, and a solid solution of Li2S and the lithium salt can be formed more easily.

[0101] Since Li2S has relatively low ionic conductivity, a complex of Li2S and a lithium salt can be formed to improve ionic conductivity. The complex (CAM), which is a complex of Li2S and a lithium salt, can have improved ionic conductivity compared to Li2S alone. The content of Li2S in the complex (CAM) can be 50 wt% to 95 wt%, 50 wt% to 90 wt%, 50 wt% to 80 wt%, or 50 wt% to 70 wt% of the total weight of the complex (CAM). When the complex (CAM) has a Li2S content in this range, the complex (CAM) can have both improved ionic conductivity and excellent ductility.

[0102] The content of the lithium salt in the composite (CAM) can be 5 wt% to 50 wt%, 10 wt% to 50 wt%, 20 wt% to 50 wt%, or 30 wt% to 50 wt% of the total weight of the composite (CAM). By having the lithium salt content in this range, the composite (CAM) can have both improved ionic conductivity and excellent ductility.

[0103] The content of the metal halide in the composite (CAM) may be 5 wt% to 30 wt%, or 5 wt% to 20 wt%, of the total weight of the composite (CAM). By having the metal halide content in this range, the composite (CAM) can simultaneously have improved ionic conductivity and excellent ductility.

[0104] In one embodiment, the content of Li2S in the composite (CAM) may be greater than the content of the lithium salt. The content of Li2S in the composite (CAM) may be greater than the content of the metal halide. For example, the molar ratio of Li2S to the lithium salt in the composite (CAM) may be 51:49 to 95:5, 55:45 to 90:10, 60:40 to 90:10, or 70:30 to 90:10. By having such a molar ratio, the composite (CAM) may have both enhanced ionic conductivity and excellent ductility.

[0105] The ionic conductivity of the complex (CAM) according to embodiments of the present invention is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. For example, the ionic conductivity can be measured using an electrochemical impedance spectroscopy, a direct current polarization method, etc. Since the composite (CAM) has an ionic conductivity in this range, the internal resistance of the positive electrode active material layer (120) including the composite (CAM) can be further reduced.

[0106] The average particle diameter (D50) of the composite (CAM) may be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The average particle diameter of the composite (CAM) may be, for example, 0.1 μm to 2 μm, 0.1 μm to 1.5 μm, or 0.1 μm to 1 μm.

[0107] The size of the Li2S particles in the composite (CAM) can be, for example, 2 μm or less, 1.5 μm or less, or 1 μm or less. The size of the Li2S particles can be, for example, 0.1 μm to 2 μm, 0.1 μm to 1.5 μm, or 0.1 μm to 1 μm.

[0108] The cathode active material layer (120) may further include a solid electrolyte (SEP) in addition to the Li2S-containing cathode active material (CAC). The solid electrolyte (SEP) in the cathode active material layer (120) may be the same as or different from the solid electrolyte in the electrolyte layer (300) described below.

[0109] The solid electrolyte (SEP) in the positive electrode active material layer (120) may have a smaller average particle diameter (D50) than the solid electrolyte in the electrolyte layer (300). For example, the average particle diameter of the solid electrolyte (SEP) in the positive electrode active material layer (120) may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average particle diameter of the solid electrolyte in the electrolyte layer (300).

[0110] In one embodiment, the content of the cathode active material (CAC) in the cathode active material layer (120) may be 40 wt% to 90 wt%, 50 wt% to 90 wt%, or 60 wt% to 90 wt% of the total weight of the cathode active material layer (120). Among the components in the cathode active material layer (120), the cathode active material (CAC) may have the largest content. The content of the solid electrolyte (SEP) in the cathode active material layer (120) may be 10 wt% to 70 wt%, 10 wt% to 60 wt%, or 10 wt% to 40 wt% of the total weight of the cathode active material layer (120).

[0111] The solid electrolyte (SEP) may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z. m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In, Li 7-x PS 6-x Cl x , 0*x*2, Li 7-x PS 6-x Br x , 0*x*2, and Li 7-x PS 6-x I x, may be one or more selected from 0*x*2. The sulfide-based solid electrolyte is manufactured by treating starting materials such as Li2S and P2S5 by a melting rapid cooling method or a mechanical milling method. In addition, heat treatment may be performed after the treatment. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may be, for example, one containing sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form a solid electrolyte, the mixing molar ratio of Li2S and P2S5 is, for example, in the range of Li2S:P2S5=20:80 to 90:10, 25:75 to 90:10, 30:70 to 70:30, 40:60 to 60:40.

[0112] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1:

[0113] <Chemical Formula 1>

[0114] Li + 12-n-x A n+ X 2- 6-x Y - x

[0115] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, X is S, Se or Te, Y is Cl, Br, I, F, CN, OCN, SCN or N3, and 1*n*5, 0*x*2. The sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may be an argyrodite-type compound including at least one selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound including at least one selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0116] Alternatively, the sulfide-based solid electrolyte is Li 7-a M a PS 6-c X c It may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)), where X may be F, Br, Cl, or a combination thereof. M is candium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof. Can be.

[0117] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed.

[0118] (filler)

[0119] The positive electrode active material layer (120) may further include a filler (FIL). In one embodiment, the content of the filler (FIL) in the positive electrode active material layer (120) may be 0.1 to 20 wt%, 0.1 to 10 wt%, or 0.1 to 5 wt% of the total weight of the positive electrode active material layer (120).

[0120] According to embodiments of the present invention, the filler (FIL) may be an inorganic filler, an organic filler, or a combination thereof. In one embodiment, the filler (FIL) may include an amorphous inorganic filler. The inorganic filler may be, for example, an amorphous lithium metal oxyhalide. In one embodiment, after preparing a crystalline lithium metal oxyhalide, the crystalline lithium metal oxyhalide may be melted to prepare a molten salt, which may then be cooled to prepare an amorphous lithium metal oxyhalide. In another embodiment, the composition of the lithium metal oxyhalide may be controlled to directly prepare the amorphous lithium metal oxyhalide. The amorphous inorganic filler may have, for example, ductility. Since the amorphous inorganic filler has ductility, it can more effectively accommodate volume changes during charge and discharge of the all-solid-state battery (10). In contrast, the crystalline lithium metal oxyhalide may be relatively brittle compared to the amorphous lithium metal halide. Whether or not the inorganic filler is amorphous can be confirmed using an XRD spectrum.

[0121] The inorganic filler may be, for example, glassy. The inorganic filler may include, for example, a glassy lithium metal oxyhalide having a glass transition temperature (Tg). The glassy lithium metal oxyhalide may have ductility. Since the inorganic filler has ductility, the volume change of the all-solid-state secondary battery (10) can be effectively accommodated during charge and discharge or can be easily deformed according to the volume change of the all-solid-state secondary battery (10).

[0122] The glass transition temperature of the inorganic filler may be, for example, 20°C or lower, 10°C or lower, 0°C or lower, or -10°C or lower. Because the inorganic filler has such a low glass transition temperature, it can easily transition from a brittle, crystalline metal salt state to a ductile, glassy state. For example, the inorganic filler can be easily transitioned from a crystalline, molten salt state to a glassy state by melting and then cooling it. Alternatively, the glassy state can be obtained during the manufacturing process of the inorganic filler. The glass transition temperature can be measured, for example, using a differential scanning calorimeter (DSC). The glass transition temperature can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0123] The melting point of the inorganic filler may be, for example, 100°C or higher, 105°C or higher, 110°C or higher, 115°C or higher, 120°C or higher, 125°C or higher, 130°C or higher, 135°C or higher, 140°C or higher, or 145°C or higher. The melting point of the inorganic filler may be, for example, 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, 160°C or lower, or 150°C or lower. Since the inorganic filler has a melting point within this range, the inorganic filler can be melted to form a molten salt state and then cooled to easily produce an amorphous inorganic filler. The melting point of the inorganic filler can be measured, for example, using differential scanning calorimetry (DSC).

[0124] The inorganic filler may be an ionic conductive inorganic filler. The inorganic filler may have, for example, an ionic conductivity of 0.01 mS / cm or more, 0.05 mS / cm or more, 0.1 mS / cm or more, 0.3 mS / cm or more, 0.5 mS / cm or more, 0.7 mS / cm or more, or 1.0 mS / cm or more at 25°C1 atm. The ionic conductivity may be measured by AC impedance analysis. The voltage amplitude used in the AC impedance analysis may be 5 to 10 mV, and the frequency may be 1 MHz to 1 Hz. Since the inorganic filler has ionic conductivity, an increase in the interfacial resistance between the positive active material (CAC) particles, between the solid electrolyte (SEP) particles, and / or between the positive active material (CAC) and the solid electrolyte (SEP) within the positive active material layer (120) may be effectively suppressed.

[0125] The elastic modulus (elastic modulus or Young's modulus) of the inorganic filler at 30° C. may be 10 GPa or less, 5 GPa or less, 3 GPa or less, or 2 GP a or less. Since the inorganic filler has an elastic modulus in this low range, the positive electrode active material layer (120) can effectively accommodate the volume change of the secondary battery (10). Accordingly, the cycle characteristics of the secondary battery (10) according to the present invention can be improved. The elastic modulus of the inorganic filler can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0126] The elastic modulus of the inorganic filler may be, for example, lower than the elastic modulus of the solid electrolyte (SEP). The elastic modulus of the solid electrolyte (SEP) at 30° C. may be, for example, 22 GPa to 30 GPa. The elastic modulus of the inorganic filler may be, for example, 90% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the elastic modulus of the solid electrolyte (SEP).

[0127] An inorganic filler, i.e., a filler (FIL), can be uniformly provided within the positive electrode active material layer (120). In the secondary battery (10) of the present invention, since the inorganic filler has a lower elastic modulus than the solid electrolyte (SEP), the inorganic filler can easily fill the pores between the solid electrolytes (SEP) and / or the pores between the solid electrolyte (SEP) and the positive electrode active material (CAC), thereby reducing the internal resistance of the positive electrode active material layer (120) and easily accommodating a volume change of the positive electrode active material layer (120) during charge and discharge. As a result, the cycle characteristics of the secondary battery (10) can be further improved. The elastic modulus of the solid electrolyte (SEP) can be measured, for example, using a dynamic mechanical analyzer (DMA).

[0128] The inorganic filler may have, for example, viscoelasticity. The inorganic filler may have, for example, viscoelastic creep. The viscoelastic creep rate of the inorganic filler may be, for example, 1×10-4 % / s or more, 2×10-4 % / s or more, or 4×10-4 % / s or more. % / s is the ratio of the deformed size to the initial size per unit time (second). Since the inorganic filler has viscoelasticity, the volume change during charge and discharge of the all-solid-state battery (10) can be easily accommodated, and the shape can be continuously deformed without defects. The creep rate is the change rate over time of the inorganic filler under stress at a constant temperature, i.e., the strain rate. The creep rate can be measured using, for example, a universal testing machine.

[0129] Weapon filler is Li a Al b M c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e, M은 원소주기율표 3족 내지 15족에서 선택되는 금속) 표시되는 리튬금속옥시할라이드(lithium metal oxyhalide)를 포함할 수 있다. 리튬금속옥시할라이드의 금속 M은 예를 들어 Fe, Ga, In, As, Sb, Mo, Bi, B 또는 이들의 조합을 포함할 수 있다.

[0130] Lithium metal oxyhalides are, for example, Li a Al b O d Cl e (0 <a≤3; 0<b≤3; 0<d≤2; 1<e≤4; d<e), Li a Al b Fe c O d Cl e(0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Ga c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b In c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b As c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Sb c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b Mo c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), ), Li a Al b Bi c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e), Li a Al b B c O d Cl e (0 <a≤3; 0<b≤3; 0≤c<2; 0<d≤2; 1<e≤4; d<e) 또는 이들의 조합을 포함할 수 있다.

[0131] Lithium metal oxyhalides are, for example, LiAl x O z Cl w(0 <x≤2; 0<z≤1; 2<w<4; z<w), LiAlxFeyOzClw (0<x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Yes y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x In y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x I y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Sat y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Mo y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x Bi y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w), LiAl x B y Oh z Cl w (0 <x≤2; 0≤y<1; 0<z≤1; 2<w<4; z<w) 또는 이들의 조합을 포함할 수 있다.

[0132] The content of the inorganic filler in the positive electrode active material layer (120) may be smaller than the content of the solid electrolyte (SEP). The weight ratio of the solid electrolyte (SEP) and the inorganic filler in the positive electrode active material layer (120) may be 99:1 to 50:50, 99:1 to 60:40, 99:1 to 70:30, 99:1 to 80:20, or 99:1 to 90:10. Since the solid electrolyte (SEP) and the inorganic filler have a weight ratio in this range, the volume change during charge and discharge of the positive electrode active material layer (120) can be more easily accommodated. As a result, the cycle characteristics of the secondary battery (10) can be further improved.

[0133] In another embodiment, the filler (FIL) may include an organic filler. The organic filler may include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene (PP), cycloolefin polymers, and combinations thereof.

[0134] (Challenge)

[0135] The positive electrode active material layer (120) may further include a conductive material. The conductive material may be, for example, a carbon-based material, a metal-based material, or a combination thereof. In one embodiment of the present invention, as shown in FIG. 3, the conductive material (CMA) within the positive electrode active material layer (120) may form a positive electrode active material (CAC) together with a composite material (CAM).

[0136] The conductive material content in the positive electrode active material layer (120) may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer (120).

[0137] The metal-based material may be, but is not limited to, metal powder, metal fiber, or a combination thereof, and any metal-based material used as a conductive material in the relevant technical field may be used.

[0138] The carbon-based material may include, for example, amorphous carbon. By including amorphous carbon in the carbon-based material, side reactions between the carbon-based material and the solid electrolyte (SEP) can be suppressed. Therefore, the cycle characteristics of the all-solid-state battery (10) including the carbon-based material can be further improved. The specific description of the carbon-based material may be the same as or similar to that described above regarding the conductive agent (CMA).

[0139] (bookbinder)

[0140] The positive electrode active material layer (120) may further include a binder (BND). The binder may be, but is not limited to, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, etc., and any binder used in the relevant technical field may be used. The content of the binder (BND) in the positive electrode active material layer (120) may be, for example, 0.1 wt% to 10 wt%, 0.5 to 5 wt%, or 0.5 to 2 wt% of the total weight of the positive electrode active material layer (120). The binder (BND) may be omitted.

[0141] The positive electrode active material layer (120) may further include additives such as a coating agent, a dispersant, an ion-conducting aid, etc., in addition to the above-described positive electrode active material (e.g., CAM), solid electrolyte (SEP), binder (BND), conductive material (CMA), and filler (FIL). The coating agent, dispersant, ion-conducting aid, etc. that may be included in the positive electrode active material layer (120) may be any known material generally used in electrodes of secondary batteries.

[0142] Cathode (200)

[0143] The negative electrode according to the present invention may include a negative electrode current collector (210) and a negative electrode coating layer on the negative electrode current collector (210). The negative electrode may be expressed as a negative electrode layer.

[0144] In one embodiment, the cathode layer (200) may include a cathode current collector (210) and a cathode coating layer (220) disposed on the cathode current collector (210).

[0145] In one embodiment, the negative electrode layer (200) may include a negative electrode current collector (210), an ion conductive coating layer (Icl) disposed on the negative electrode current collector (210), and a negative electrode coating layer (220) disposed on the ion conductive coating layer (ICL).

[0146] (negative current collector)

[0147] The negative electrode current collector (210) can provide a reference surface on which the negative electrode coating layer (220) is disposed. The negative electrode current collector (210) can include, for example, a material that does not react with lithium, i.e., does not form an alloy or compound with lithium. For example, the negative electrode current collector (210) can include at least one metal selected from the group consisting of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The thickness of the negative electrode current collector (210) can be 1 μm to 20 μm, more specifically 5 μm to 15 μm, and more specifically 7 μm to 10 μm.

[0148] The negative electrode current collector (210) may be composed of one of the above-described metals, or may include an alloy or coating material of two or more metals. The negative electrode current collector (210) may have, for example, a plate shape or a foil shape. Meanwhile, in one embodiment, the negative electrode current collector (210) may be omitted.

[0149] Although not shown, an anode current collector (210) according to one embodiment may include a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The polymer may be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The anode current collector (210) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode current collector (210), refer to the positive electrode current collector (110) described above. Since the negative electrode current collector (210) has this structure, the weight of the negative electrode layer (200) can be reduced, and as a result, the energy density of the secondary battery (10) can be improved.

[0150] (Cathode coating layer)

[0151] The negative electrode coating layer (220) may be configured to allow lithium metal to grow between the negative electrode current collector (210) and the secondary battery (10) when charging. The negative electrode coating layer (220) may serve as a protective layer for the lithium metal and at the same time suppress the precipitation and growth of lithium dendrites. The negative electrode coating layer (220) may include first particles (PTC1) including a carbon-based material, second particles (PTC2) including at least one selected from a metal or metalloid material, and third particles (PTC3) including Li2S.

[0152] For example, the first particle (PTC1) may include at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene. The second particle (PTC2) may include at least one metal selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn).

[0153] In one embodiment, the cathode coating layer (220) may include a mixture of carbon black and silver (Ag). In one embodiment, the content of the first particles (PTC1) in the cathode coating layer (220) may be 70 wt% to 90 wt%, 70 wt% to 80 wt%, 80 wt% to 90 wt%, or 85 wt% to 90 wt% based on the total weight of the cathode coating layer.

[0154] In one embodiment, the content of the second particles (PTC2) in the cathode coating layer (220) may be 10 wt% to 30 wt%, 20 wt% to 30 wt%, 10 wt% to 20 wt%, or 10 wt% to 15 wt% with respect to the total weight of the cathode coating layer.

[0155] In one embodiment, the weight ratio of the first particle (PTC1) to the weight ratio of the second particle (PTC2) in the cathode coating layer (220) may be 2 to 10.

[0156] In one embodiment, the average particle diameter (D50) of the first particle (PTC1) may be 30 nm to 90 nm, 50 nm to 100 nm, 10 nm to 500 nm, 200 nm to 500 nm, or 10 nm to 200 nm.

[0157] In one embodiment, the average particle diameter (D50) of the second particles (PTC2) may be 10 nm to 60 nm, 30 nm to 90 nm, 50 nm to 150 nm, or 100 nm to 5 μm.

[0158] The negative electrode coating layer (220) may include a third particle (PTC3). The third particle (PTC3) may include Li2S. The negative electrode coating layer (220) may have a form in which the first particle (ptc1), the second particle (ptc2), and the third particle (ptc3) are randomly mixed without any specific rule. By including the third particle (PTC3) in the negative electrode coating layer (220), the ionic conductivity of the negative electrode may be improved. In addition, uniform lithium deposition on the negative electrode current collector may be induced, thereby preventing lithium dendrite formation and improving the life characteristics.

[0159] In one embodiment, the content of the third particle (PTC3) in the cathode coating layer (220) may be 0.0001 wt% to 2 wt% with respect to the total weight of the cathode coating layer.

[0160] In one embodiment, the average particle diameter (D50) of the third particle (PTC3) may be 1 nm to 200 nm.

[0161] Fig. 12 is an enlarged cross-sectional view of the negative electrode coating layer (220). The negative electrode coating layer may have a first thickness (TK1). The negative electrode coating layer (220) may be thinner than the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer (120). The thickness of the negative electrode coating layer (220) may be, for example, 1 μm to 20 μm, 2 μm to 10 μm, 10 μm to 20 μm, 7 μm to 15 μm, 7 μm to 10 μm, or 3 μm to 7 μm. If the thickness of the negative electrode coating layer (220) is too thin, lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210) may collapse the negative electrode coating layer (220), thereby deteriorating the cycle characteristics of the secondary battery (10). If the thickness of the negative electrode coating layer (220) is excessively increased, the energy density of the secondary battery (10) may decrease and the internal resistance of the secondary battery (10) due to the negative electrode coating layer (220) may increase, thereby deteriorating the cycle characteristics of the cell.

[0162] Meanwhile, although not shown, a carbon layer may be further included to improve adhesion between the cathode coating layer (220) and the electrolyte layer (300).

[0163] Referring to Fig. 12, the negative electrode coating layer (220) may include a first surface (SF1) in contact with the negative electrode current collector (210) and a second surface (SF2) in contact with the electrolyte layer (300). When an ion conductive coating layer (ICL) is further included as in Fig. 4, the first surface (SF1) of the negative electrode coating layer (220) may be in contact with the ion conductive coating layer (ICL).

[0164] The content of the third particle (PTC3) in the negative electrode coating layer (220) may decrease from the first side (SF1) to the second side (SF2) in the Y direction. The content of the third particle (PTC3) in the negative electrode coating layer (220) may increase as it approaches the negative electrode current collector (210).

[0165] The first surface (SF1) of the negative electrode coating layer (220) may be a part of the negative electrode coating layer (220) that contacts the negative electrode current collector (210), and the first surface (SF1) may have a predetermined thickness. The second surface (SF2) of the negative electrode coating layer (220) may be a part of the negative electrode coating layer (220) that contacts the electrolyte layer (300), and the second surface (sf2) may have a predetermined thickness. In one embodiment, the content of the third particles (PTC3) of the first surface (SF1) may be greater than the content of the third particles (PTC3) of the second surface (SF2). In one embodiment, the content of the third particles (PTC3) present in the range from the center of the negative electrode coating layer to the first surface (SF1) may be greater than the content of the third particles (PTC3) present in the range from the center of the negative electrode coating layer to the second surface (SF2).

[0166] The cathode coating layer (220) may further include additives other than metal and carbon. The cathode coating layer (220) may further include, for example, at least one additive selected from the group consisting of a binder (BND), a filler, a coating agent, a dispersant, and an ion conductive additive.

[0167] (Ion conductive coating layer)

[0168] Referring to FIG. 4, the negative electrode may include an ion conductive coating layer (ICL) on the negative electrode current collector (210). The ion conductive coating layer (ICL) may be disposed between the negative electrode current collector (210) and the negative electrode coating layer (220).

[0169] By disposing the ion conductive coating layer (ICL) on one surface of the negative electrode current collector (210), for example, the deposition shape of the lithium metal layer (230) deposited between the ion conductive coating layer (ICL) and the negative electrode current collector (210) becomes flatter, and the cycle characteristics of the secondary battery can be improved. The ion conductive coating layer (ICL) may have a low energy barrier and thus high ionic conductivity. The ion conductive coating layer (ICL) may improve the ionic conductivity of the negative electrode. In addition, uniform lithium deposition on the negative electrode current collector (210) may be induced, thereby preventing the formation of lithium dendrites and improving the life characteristics. The ion conductive coating layer (ICL) may include a third particle (PTC3). The third particle (PTC3) may include Li2S. In one embodiment, the ionic conductivity of the ion conductive coating layer may be 10 -7 S / m to 10 -6 It could be S / m.

[0170] The ion conductive coating layer (ICL) may have a second thickness (TK2). In one embodiment, the second thickness (TK2) may be 100 nm to 10 μm.

[0171] The ion conductive coating layer (ICL) may further include other additives. For example, the ion conductive coating layer (ICL) may further include at least one additive selected from the group consisting of a binder (BND), a filler, a coating agent, a dispersant, and an ion conductive additive.

[0172] The ion conductive coating layer (ICL) can be formed on the negative electrode current collector (210) by, for example, a vacuum deposition method, a sputtering method, a plating method, etc., but is not necessarily limited to these methods, and any method capable of forming a coating layer in the relevant technical field can be used.

[0173] (lithium metal layer)

[0174] Figures 6 and 7 are for explaining a secondary battery according to one embodiment of the present invention. As an example, referring to Figure 6, the secondary battery in a charged state may further include a lithium metal layer (230) provided between the negative electrode current collector (210) and the ion conductive coating layer (icl). Referring to Figure 7, the secondary battery in a charged state may further include a lithium metal layer (230) provided between the negative electrode current collector (210) and the negative electrode coating layer (220). The negative electrode layer (200) according to the present embodiment may include a negative electrode current collector (210), a lithium metal layer (230), an ion conductive coating layer (ICL), and a negative electrode coating layer (220).

[0175] The lithium metal layer (230) may include lithium or a lithium alloy. Since the lithium metal layer (230) is a metal layer containing lithium, it may function as a lithium reservoir, for example. The lithium alloy may include, but is not limited to, 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, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The lithium metal layer (230) may be formed of one of these alloys or lithium, or may be formed of several types of alloys. The lithium metal layer (230) may be, for example, a plated layer. The lithium metal layer (230) may be deposited between the negative electrode coating layer (220) and the negative electrode current collector (210), for example, during the charging process of a secondary battery. When including an ion conductive coating layer (ICL), a lithium metal layer (230) can be precipitated between the ion conductive coating layer (ICL) and the negative electrode current collector (210).

[0176] Referring to FIGS. 6 and 7, the lithium metal layer (230) may have a third thickness (TK3). The third thickness (TK3) is not particularly limited, but may be, for example, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the third thickness (TK3) of the lithium metal layer (230) is too thin, it may be difficult for the lithium metal layer (230) to perform the role of a lithium reservoir. If the third thickness (TK3) of the lithium metal layer (230) is too thick, the mass and volume of the secondary battery may increase, and the cycle characteristics of the secondary battery may rather deteriorate.

[0177] In another embodiment of the present invention, the lithium metal layer (230) in the negative electrode layer (200) may be provided between the negative electrode current collector (210) and the negative electrode coating layer (220), for example, before assembling the secondary battery. Alternatively, it may be provided between the negative electrode current collector (210) and the ion conductive coating layer (ICL) before assembling the secondary battery. When the lithium metal layer (230) is disposed before assembling the secondary battery, the lithium metal layer (230) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (210) and the negative electrode coating layer (220) before assembling the secondary battery.

[0178] When the lithium metal layer (230) is precipitated by charging after assembling the secondary battery, the energy density of the secondary battery can increase because the lithium metal layer (230) is not included when assembling the secondary battery. When charging the secondary battery, the charging can exceed the charging capacity of the negative electrode coating layer (220). That is, the negative electrode coating layer (220) is overcharged. At the initial stage of charging, lithium can be absorbed into the negative electrode coating layer (220). When charging exceeds the capacity of the negative electrode coating layer (220), lithium can be precipitated, for example, between the negative electrode coating layer (220) and the negative electrode current collector (210). The precipitated lithium can form a lithium metal layer (230).

[0179] The lithium metal layer (230) may be mainly composed of lithium (i.e., metallic lithium). During discharge, lithium in the lithium metal layer (230) may be ionized and move to the positive electrode layer (100). In other words, lithium may be used as an anode active material in a secondary battery. In addition, since the anode coating layer (220) covers the lithium metal layer (230), the anode coating layer (220) may protect the lithium metal layer (230) while simultaneously suppressing the precipitation and growth of lithium dendrites. Therefore, the anode coating layer (220) may suppress short-circuiting and capacity reduction of the secondary battery and improve the cycle characteristics of the secondary battery. In addition, the ion conductive coating layer (ICL) may protect the lithium metal layer (230) while simultaneously improving the lithium deposition density and ensuring that the lithium deposition layer is uniformly deposited.

[0180] When a lithium metal layer (230) is formed by charging after assembling a secondary battery, the negative electrode layer (200), that is, the negative electrode collector (210) and the negative electrode coating layer (220) and the region therebetween may be a Li-free region that does not contain lithium (Li) in the initial state of the secondary battery or in the state after complete discharge. An anode that does not contain lithium in the initial state may be referred to as a non-cathode structure, and a secondary battery including the same may be referred to as a non-cathode battery or a Li-free battery. A non-cathode battery is a secondary battery that uses only a negative electrode collector, and the battery can be operated through a process in which lithium ions transferred from the positive electrode during charging are deposited on the surface of the negative electrode collector, and the lithium deposited on the negative electrode collector is eluted again and inserted into the positive electrode during discharge.

[0181] Electrolyte layer (300)

[0182] An electrolyte layer (300) may be provided between the anode layer (100) and the cathode layer (200). In one embodiment, the electrolyte layer (300) may include a solid electrolyte layer. In one embodiment, the electrolyte layer (300) may include a gel polymer electrolyte layer or a semi-solid electrolyte layer.

[0183] The solid electrolyte layer may include a sulfide-based solid electrolyte having excellent lithium ion conductivity characteristics. The solid electrolyte layer may be the same as or different from any of the materials included in the solid electrolyte in the aforementioned positive electrode active material layer (120).

[0184] The gel polymer electrolyte layer may include a liquid electrolyte and a gel polymer electrolyte containing a cross-linked polymer in the pores of a porous substrate constituting the separator. In this structure, the liquid electrolyte may be contained in a cross-linked polymer network having a cross-linked structure, thereby preventing leakage to the outside.

[0185] (solid electrolyte)

[0186] The electrolyte layer (300) may include a solid electrolyte. The solid electrolyte may have a particle shape such as a sphere or an ellipsoid. The solid electrolyte may include a sulfide-based solid electrolyte. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may include, for example, at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material including Li2S-P2S5. When using a sulfide-based solid electrolyte material including Li2S-P2S5 to form the solid electrolyte, the mixing molar ratio of Li2S and P2S5 may be, for example, in the range of Li2S:P2S5=50:50 to 90:10.

[0187] In one embodiment, the solid electrolyte is Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x The solid electrolyte may include an argyrodite-type compound including at least one selected from (0≤x≤2). The solid electrolyte may include an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0188] In another embodiment, the solid electrolyte is Li 7-a M a PS 6-c X cArgyrodite-type compounds may include, wherein X may be Cl, Br, or a combination thereof. M may be Na, K, Fe, Mg, Ca, Ag, Cu, Zr, Zn, or a combination thereof. Each of a and c may be a real number between 0 and 2.

[0189] The density of the argyrodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. When the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state battery is reduced, and the defect of the solid electrolyte membrane being penetrated and short-circuited due to the formation of lithium dendrites can be prevented. The elastic modulus of the solid electrolyte is, for example, 15 GPa to 35 GPa.

[0190] The solid electrolyte can be in direct contact with the negative electrode coating layer (220). As a result, the second solid electrolyte can suppress lithium dendrites formed between the negative electrode coating layer (220) and the negative electrode current collector (210). The solid electrolyte can effectively suppress negative electrode side reactions. As a result, the cell performance of the secondary battery (10) according to the present invention can be improved.

[0191] The solid electrolyte may further include a silver binder (BND). The binder (BND) in the electrolyte layer (300) may be, for example, but is not limited to, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. The binder in the electrolyte layer (300) may be the same as or different from the binder (BND) in the positive active material layer (120) or the binder (BND) in the negative electrode coating layer (220).

[0192] The content of the binder (BND) in the electrolyte layer (300) may be 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 1 wt%, 0 to 0.5 wt%, or 0 to 0.1 wt% with respect to the total weight of the electrolyte layer (300).

[0193] (gel polymer electrolyte)

[0194] The electrolyte layer (300) may include a gel polymer electrolyte. Gel polymer electrolyte may be used interchangeably with gel polymer electrolyte or semi-solid electrolyte.

[0195] The gel polymer electrolyte layer may include a gel polymer electrolyte containing a liquid electrolyte and a crosslinked polymer in the pores of a separator containing a porous substrate. In this structure, the liquid electrolyte may be impregnated into the crosslinked polymer network having a crosslinked structure, thereby preventing leakage to the outside.

[0196] The pore diameter of the separator is generally 0.01 μm to 10 μm, and the thickness can be generally 5 μm to 20 μm. Examples of such separators include olefin-based polymers such as polypropylene; sheets or nonwoven fabrics made of glass fiber or polyethylene; and the like. When a solid polymer electrolyte is used as the electrolyte, the solid polymer electrolyte can also function as the separator.

[0197] Specific examples of olefin polymers include polyethylene, polypropylene, or a multilayer membrane of two or more layers thereof, and mixed multilayer membranes such as a polyethylene / polypropylene two-layer membrane, a polyethylene / polypropylene / polyethylene three-layer membrane, and a polypropylene / polyethylene / polypropylene three-layer membrane may be used.

[0198] Additional coating layers can be formed on both sides of the porous substrate that constitutes the separator. This coating layer can improve cell performance by suppressing lithium dendrite formation through its rigidity without significantly increasing cell resistance.

[0199] As an example, in a secondary battery using lithium metal as a negative electrode, a liquid electrolyte is impregnated within a polymer matrix of a gel polymer electrolyte, so that there is no leakage and electrochemical side reactions and electrolyte decomposition reactions occurring at the positive and negative electrodes are suppressed, thereby ensuring stability.

[0200] A liquid electrolyte is contained in a gel polymer electrolyte, and the liquid electrolyte contains a lithium salt and an organic solvent.

[0201] As the organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used. Carbonate solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl carbonate can be used.

[0202] The above lithium salts can be all those commonly used in secondary batteries, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0203] The concentration of the lithium salt may be, for example, 1 M to 5 M, for example, 1 M to 2.5 M, in the liquid electrolyte. In the above range, a sufficient amount of lithium ions required for charging and discharging a secondary battery can be generated.

[0204] The presence of a gel polymer electrolyte can minimize the interfacial resistance between the positive and negative electrodes and facilitate lithium movement.

[0205] A secondary battery according to one embodiment of the present invention can be applied to various types of electric devices such as automobiles, mobile phones, and / or energy storage devices, and the present invention is not limited thereto.

[0206] The following examples and comparative examples will further illustrate the present invention. However, these examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0207]

[0208] Manufacturing examples for each component for manufacturing a secondary battery are described below.

[0209] Manufacturing Example 1: Manufacturing of anode

[0210] A Li2S-LiI-CNF composite was prepared as a cathode active material. PVDF-HFP was prepared as a binder. LiAlCl was used as an inorganic filler. 2.5 O 0.75 (LACO75) was prepared. These materials were mixed in a weight ratio of positive electrode active material: LACO75: solid electrolyte: binder = 60:20:19:1 to prepare a composition for forming a positive electrode active material layer.

[0211] The composition for forming the above positive electrode active material layer was milled, then dry-coated on one side of a positive electrode current collector made of aluminum foil coated with carbon on one side, and pressed at 1 MPa, (>130)°C for (10) minutes to manufacture a positive electrode.

[0212] The thickness of the positive electrode was approximately 120 μm, and the loading level of the positive electrode mixture was approximately 8 mg / cm2. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm. The areas of the positive electrode active material layer and the positive electrode current collector were identical.

[0213] Manufacturing Example 2: Manufacturing of a solid electrolyte layer

[0214] Li6PS5Cl solid electrolyte in the form of argyrodite crystals (D 50 =3.0 um, crystalline), a mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of the solid electrolyte. Octyl acetate was added to the prepared mixture and stirred to prepare a slurry. The prepared slurry was applied using a bar coater onto a 15 ㎛ thick nonwoven fabric placed on a 75 ㎛ thick PET substrate, and dried in air at 80 ℃ for 10 minutes to prepare a laminate. The prepared laminate was vacuum-dried at 80 ℃ for 2 hours to prepare a solid electrolyte layer.

[0215] Manufacturing Example 3-1: Cathode Manufacturing

[0216] A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. Li2S was prepared as a third particle (PTC3) to form an ion conductive coating layer (ICL). A coating layer mixture composition including Li2S was prepared, applied onto the negative electrode current collector, and dried to prepare an ion conductive coating layer.

[0217] To form a cathode coating layer, carbon black (CB) was prepared as the first particle (PTC1) and silver (Ag) particles were prepared as the second particle (PTC2). 4 g of a mixed powder of carbon black (CB) and silver (Ag) particles in a weight ratio of 85:15 was placed in a container, and 4 g of an NMP solution containing 7 wt% PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby producing a cathode having a structure of anode current collector / ion conductive coating layer / cathode coating layer. The thickness of the cathode coating layer was approximately 15 μm. The areas of the cathode current collector, ion-conductive coating layer, and cathode coating layer were the same.

[0218] Manufacturing Example 3-2: Cathode Manufacturing

[0219] To form a cathode coating layer, carbon black (CB) particles were prepared as the first particle (PTC1) and silver (Ag) particles as the second particle (PTC2). Unlike Manufacturing Example 3-1, Li2S particles were additionally prepared as the third particle (PTC3) to form a cathode coating layer.

[0220] A mixed powder of 4 g of carbon black (CB), silver (Ag), and Li2S particles in a weight ratio of 85:14:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a negative electrode collector / negative electrode coating layer structure. The thickness of the negative electrode coating layer was approximately 15 μm. The areas of the negative electrode collector and the negative electrode coating layer were the same.

[0221] Manufacturing Example 3-3: Cathode Manufacturing

[0222] A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. To form an ion-conductive coating layer (ICL), a third particle (PTC3) Li2S was prepared. A coating layer mixture composition including Li2S was prepared, applied onto the negative electrode current collector, and dried to prepare an ion-conductive coating layer.

[0223] To form a cathode coating layer, carbon black (CB) particles were prepared as the first particle (PTC1) and silver (Ag) particles as the second particle (PTC2). Additionally, Li2S particles were prepared as the third particle (PTC3).

[0224] A mixed powder of 4 g of carbon black (CB), silver (Ag), and Li2S particles in a weight ratio of 85:14:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a structure of negative electrode current collector / ion conductive coating layer / negative electrode coating layer. The thickness of the negative electrode coating layer was approximately 15 μm. The areas of the negative electrode current collector and the negative electrode coating layer were the same.

[0225] Manufacturing Example 3-4: Cathode Manufacturing

[0226] A 10 ㎛ thick SUS foil was prepared as a negative electrode current collector. To form a negative electrode coating layer, carbon black (CB) particles were prepared as the first particle (PTC1) and silver (Ag) particles were prepared as the second particle (PTC2). 4 g of a mixed powder of carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80 °C for 10 minutes, and then vacuum-dried at 40 °C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby manufacturing a negative electrode having a negative electrode collector / negative electrode coating layer structure. The thickness of the negative electrode coating layer was approximately 15 μm.

[0227] Manufacturing Example 3-5: Cathode Manufacturing

[0228] A 10 ㎛ thick SUS foil was prepared as a negative electrode collector, and a negative electrode without an additional coating layer was manufactured.

[0229] Example 1: Preparation of an all-solid-state battery

[0230] An all-solid-state secondary battery was manufactured by sequentially stacking the positive electrode of Manufacturing Example 1, the solid electrolyte layer of Manufacturing Example 2, and the negative electrode of Manufacturing Example 3-1. A secondary battery having an ion conductive coating layer (ICL) and a negative electrode coating layer including first and second particles was manufactured.

[0231] Example 2: Fabrication of an all-solid-state battery

[0232] An all-solid-state secondary battery was manufactured by sequentially laminating the positive electrode of Manufacturing Example 1, the solid electrolyte layer of Manufacturing Example 2, and the negative electrode of Manufacturing Example 3-2. A secondary battery having a negative electrode coating layer including all of the first particles, the second particles, and the third particles was manufactured.

[0233] Example 3: Preparation of an all-solid-state battery

[0234] An all-solid-state secondary battery was manufactured by sequentially stacking the positive electrode of Manufacturing Example 1, the solid electrolyte layer of Manufacturing Example 2, and the negative electrode of Manufacturing Example 3-3. A secondary battery having an ion conductive coating layer (ICL) and a negative electrode coating layer including first particles, second particles, and third particles was manufactured.

[0235] Comparative Example 1: Manufacturing of an All-Solid-State Battery

[0236] An all-solid-state secondary battery was manufactured by sequentially stacking the positive electrode of Manufacturing Example 1, the solid electrolyte layer of Manufacturing Example 2, and the negative electrode of Manufacturing Examples 3-4. A secondary battery was manufactured having a negative electrode coating layer containing only first particles and second particles and not having an ion-conductive coating layer.

[0237] Comparative Example 2: Manufacturing of an All-Solid-State Battery

[0238] An all-solid-state secondary battery was manufactured by sequentially stacking the positive electrode of Manufacturing Example 1, the solid electrolyte layer of Manufacturing Example 2, and the negative electrode of Manufacturing Examples 3-5. A secondary battery was manufactured that did not have a negative electrode coating layer and used only a current collector as the negative electrode.

[0239] The above examples and comparative examples are summarized and shown in Table 1 below.

[0240] Ion conductive coating layer Cathode coating layer 1st particle 2nd particle 3rd particle Example 1 OOOX Example 2 XOOO Example 3 OOOO Comparative example 1 XOOX Comparative example 2 XXXX

[0241] Evaluation Example 1: Battery Performance Evaluation

[0242] Battery performance was evaluated using the batteries manufactured in the above examples and comparative examples. The secondary batteries were initially charged to 4.25 V under constant current (0.1 C) conditions, rested for 10 minutes, and then discharged to 3.0 V under constant current (0.1 C) conditions to measure the initial charge / discharge capacity and efficiency. The results are shown in Table 2 below.

[0243] Charging capacity (mAh)Discharging capacity (mAh)Charging / discharging efficiency (%)Example 1236mAh202mAh85.6%Example 2232mAh203mAh87.5%Example 3235mAh205mAh87.2%Comparative example 1230mAh200mAh86.9%Comparative example 2231mAh / g173mAh74.9%

[0244] Referring to Table 2 above, the charge / discharge efficiencies of the secondary batteries manufactured in the examples and comparative examples were confirmed to be at similar levels. However, in the case of comparative example 2, since only the negative electrode current collector was used as the negative electrode without any coating layer, it can be seen that the charge / discharge efficiency was very low.

[0245] Evaluation Example 2: Life Characteristics Evaluation

[0246] The batteries manufactured in the above examples and comparative examples were used to evaluate their lifespan characteristics. Charge and discharge were performed at a 0.1C charge / 0.1C discharge rate over a voltage range of 4.2 V to 3.7 V. Charge and discharge were performed until a short circuit occurred, and if the number of cycles exceeded 400, the cycles were stopped without further measurement. Table 3 below presents the experimental results for the number of cycles and capacity retention rate.

[0247] Number of cycles until short circuit occurs Capacity retention rate (%) Example 1 400 84% Example 2 400 83% Example 3 400 85% Comparative example 1 294 81.2% Comparative example 2 1964.7%

[0248] Referring to the results in Table 3 above, in Examples 1 to 3 of the present invention, no short circuit occurred until 400 charge / discharge cycles. In contrast, in Comparative Example 1, a short circuit occurred after approximately 300 cycles, and in Comparative Example 2, a short circuit occurred after approximately 20 cycles. It can be seen that Comparative Example 2, which consists only of a negative electrode collector, has very poor battery stability and lifespan characteristics. Even considering the excellent lifespan characteristics of Comparative Example 1, it can be seen that the lifespan characteristics of the battery according to the examples of the present invention are further improved.

[0249] 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 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.

Claims

1. Negative current collector; An ion conductive coating layer disposed on the negative electrode current collector; and Including a cathode coating layer disposed on the above ion conductive coating layer, The cathode coating layer comprises first particles comprising a carbon-based material, and second particles comprising at least one selected from a metal or metalloid material, The above ion conductive coating layer comprises a third particle containing Li2S, cathode.

2. In paragraph 1, The first particle comprises at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene, The second particle comprises one or a combination of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). cathode.

3. In paragraph 1, The above cathode coating layer further comprises Li2S, cathode.

4. In paragraph 1, The thickness of the above cathode coating layer is 10 μm to 20 μm, cathode.

5. In paragraph 1, The thickness of the above ion conductive coating layer is 100 nm to 10 μm, cathode.

6. In paragraph 1, The weight ratio of the first particle to the second particle in the cathode coating layer is 2 to 10, cathode.

7. In paragraph 1, The average particle diameter (d50) of the first particle is 10 nm to 200 nm, The average particle diameter (d50) of the above second particles is 100 nm to 5 μm. cathode.

8. In paragraph 1, The ionic conductivity of the above ion conductive coating layer is 10 -7 S / cm to 10 -6 S / cm, cathode.

9. In paragraph 1, The above first particle is carbon black, The second particle is silver (Ag). cathode.

10. Negative current collector; and Including a cathode coating layer disposed on the above cathode current collector, The cathode coating layer comprises first particles comprising a carbon-based material, second particles comprising at least one selected from a metal or metalloid material, and third particles comprising Li2S. cathode.

11. In paragraph 10, The content of the above Li2S is 0.0001 wt% to 2 wt% with respect to the entire cathode coating layer, cathode.

12. In paragraph 10, The negative electrode coating layer includes a first surface adjacent to the negative electrode current collector and a second surface opposite to the first surface, A cathode in which the content of Li2S included in the first surface is greater than the content of Li2S included in the second surface.

13. In paragraph 10, The first particle comprises at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene, The second particle comprises one or a combination of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). cathode.

14. In paragraph 10, The average particle diameter (d50) of the first particle is 10 nm to 200 nm, The average particle diameter (d50) of the above second particles is 100 nm to 5 μm. cathode.

15. In paragraph 10, The thickness of the above cathode coating layer is 10 μm to 20 μm, cathode.

16. In paragraph 10, The weight ratio of the first particle to the second particle in the cathode coating layer is 2 to 10, cathode.

17. A cathode according to any one of paragraphs 1 to 16; an anode positioned opposite the cathode; and Comprising an electrolyte layer disposed between the cathode and the anode, Secondary battery.

18. In paragraph 17, The above electrolyte layer comprises a solid electrolyte, Secondary battery.

19. In paragraph 17, The above electrolyte layer comprises a gel polymer electrolyte, Secondary battery.

20. In paragraph 17, The above positive electrode contains a sulfide-based positive electrode active material, The above electrolyte layer comprises a sulfide-based solid electrolyte, Secondary battery.

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