All-solid-state lithium-ion secondary battery

Abstract

The present invention provides an all-solid-state lithium ion secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer comprises a carbon material and Ag and includes two or more layers.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0144772 filed November 2, 2022 and Korean Patent Application No. 10-2023-0148468 filed October 31, 2023, and incorporates all contents disclosed in the documents of said Korean patent applications as part of this specification.

[0002] The present invention relates to an all-solid-state lithium-ion secondary battery. [Background technology]

[0003] Recently, all-solid-state secondary batteries using solid electrolytes have been attracting attention. To improve the energy density of such all-solid-state secondary batteries, it has been proposed to use lithium as the negative electrode active material. The capacity density (capacity per unit weight) of lithium is about 10 times that of graphite, which is commonly used as a negative electrode active material. Therefore, when lithium is used as the negative electrode active material, it is possible to increase the output power while reducing the thickness of the all-solid-state secondary battery.

[0004] Known all-solid-state lithium-ion secondary batteries include those that have a metal layer made of a metal that forms an alloy with lithium as an anode active material layer and an interface layer made of amorphous carbon on the anode active material layer. In this type of all-solid-state lithium-ion secondary battery, metallic lithium precipitates between the amorphous carbon interface layer and the anode active material layer during charging, and the metallic lithium ionizes and migrates to the positive electrode during discharging.

[0005] However, when such all-solid-state lithium-ion secondary batteries are repeatedly charged and discharged, metallic lithium deposited between the amorphous carbon interface layer and the negative electrode active material layer ionizes and dissolves, resulting in voids and making the battery unusable. Therefore, when actually using this type of all-solid-state lithium-ion secondary battery, it is necessary to sandwich the battery from both the positive electrode current collector side and the negative electrode current collector side with end plates or the like and apply high external pressure to prevent voids from forming during charging and discharging. However, the presence of end plates or the like that apply external pressure can be a barrier to thinning all-solid-state lithium-ion secondary batteries.

[0006] For this reason, all-solid-state lithium-ion secondary batteries that do not require the application of high external pressure and have excellent discharge capacity are being actively developed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2015-0064697 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been devised to solve the above-mentioned problems of the prior art, The object of the present invention is to provide an all-solid-state lithium ion secondary battery that does not require application of high external pressure, suppresses dendrite formation, and has excellent discharge capacity and life characteristics. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides The battery includes a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, The negative electrode active material layer includes a carbon material and Ag, and includes two or more layers. [Effects of the Invention]

[0010] The all-solid-state lithium-ion secondary battery of the present invention does not require application of high external pressure, suppresses dendrite formation, and provides excellent discharge capacity and life characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically showing the structure of an all-solid-state lithium-ion secondary battery of the present invention. [Figure 2] 1 is a cross-sectional view schematically showing the structure of an all-solid-state lithium-ion secondary battery of the present invention. [Figure 3] 1 is a cross-sectional view schematically showing the structure of an all-solid-state lithium-ion secondary battery of the present invention. [Figure 4] 1 is a cross-sectional view schematically showing the structure of an all-solid-state lithium-ion secondary battery of the present invention. [Figure 5] 1 is a graph showing the results of measuring the cycle characteristics of the all-solid-state lithium ion secondary batteries of Example 7 of the present invention and Comparative Example 2. [Figure 6] FIG. 10 is a view showing an SEM image of the negative electrode of Example 6 of the present invention. [Figure 7] 1 is a graph showing the particle size distribution of a carbon material-metal composite of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described in more detail to aid in its understanding.

[0013] The terms and words used in this specification and claims should not be interpreted limited to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his or her invention. Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless a clearly different meaning is present in the context.

[0014] When a component is said to be "connected to, provided with, or mounted on" another component, it should be understood that it may be directly connected to or mounted on the other component, but there may also be other components between them. On the other hand, when a component is said to be "directly connected to or mounted on" another component, it should be understood that there are no other components between them. Meanwhile, other expressions describing the relationship between components, such as "on top of" and "directly on top of," or "between" and "immediately between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0015] As used herein, the term "combination" is inclusive of mixtures, alloys, reaction products, and the like, unless specifically stated to the contrary. As used herein, the terms "first," "second," and the like do not denote order, quantity, or importance, but rather are used to distinguish one element from another.

[0016] As shown in FIG. 1, the all-solid-state lithium-ion secondary battery (100) of the present invention includes a positive electrode (10), a negative electrode (20), and a solid electrolyte (30) interposed between the positive electrode and the negative electrode. The negative electrode includes a current collector (22) and a negative electrode active material layer (24), The negative electrode active material layer (24) contains a carbon material and Ag, and is characterized by comprising two or more layers.

[0017] In one embodiment of the present invention, the two or more layers include two layers containing a carbon material and Ag, and the two layers have different Ag contents.

[0018] In one embodiment of the present invention, of the two layers containing the carbon material and Ag, the layer adjacent to the negative electrode current collector (22) (e.g., FIG. 1, 24a) may have a higher Ag content ratio than the layer adjacent to the solid electrolyte (30) (e.g., FIG. 1, 24b). An all-solid-state battery having such a structure may provide superior discharge capacity and life characteristics.

[0019] Specifically, the layer disposed adjacent to the negative electrode current collector may contain 1.5 to 10 times, preferably 2 to 8 times, 2 to 4 times, or 2 to 3 times as much Ag as the layer disposed adjacent to the solid electrolyte.

[0020] The layer disposed adjacent to the negative electrode current collector may contain 20 to 80 wt %, 20 to 60 wt %, or 25 to 55 wt % of Ag based on 100 wt % of the total negative electrode active material, and may contain 20 to 80 wt % or 40 to 80 wt % of a carbon material based on 100 wt % of the total negative electrode active material.

[0021] The negative electrode active material layer disposed adjacent to the negative electrode current collector may further contain a binder. In this case, the negative electrode active material layer may contain 20 to 75 wt % of Ag, 20 to 75 wt % of a carbon material, and 1 to 10 wt % of a binder, or may contain 25 to 55 wt % of Ag, 40 to 73 wt % of a carbon material, and 1 to 10 wt % of a binder.

[0022] The layer disposed adjacent to the solid electrolyte may contain 10 to 60 wt %, 15 to 40 wt %, or 15 to 30 wt % of Ag based on 100 wt % of the total negative electrode active material, and may contain 40 to 90 wt %, 60 to 85 wt %, or 70 to 85 wt % of a carbon material based on 100 wt % of the total negative electrode active material.

[0023] The negative electrode active material layer disposed adjacent to the solid electrolyte may further contain a binder. In this case, the negative electrode active material layer may contain 10 to 55 wt % of Ag, 40 to 85 wt % of a carbon material, and 1 to 10 wt % of a binder, or may contain 15 to 30 wt % of Ag, 65 to 83 wt % of a carbon material, and 1 to 10 wt % of a binder.

[0024] In one embodiment of the present invention, the two layers containing the carbon material and Ag may each independently have a thickness of 1 μm to 50 μm.

[0025] In one embodiment of the present invention, as shown in Figure 2 or 3, the all-solid-state lithium-ion secondary battery of the present invention may further include a layer (24c) containing 0-5 wt% or 0-2 wt% Ag, based on 100 wt% of the total negative electrode active material, in addition to the two layers (24a, 24b) containing the carbonaceous material and Ag. The layer may further contain 95-100 wt% or 98-100 wt% of the carbonaceous material. Furthermore, when the layer further contains a binder, it may contain 0-5 wt% Ag, 90-99 wt% carbonaceous material, and 1-10 wt% binder, or it may contain 0-2 wt% Ag, 90-99 wt% carbonaceous material, and 1-10 wt% binder.

[0026] In one embodiment of the present invention, the layer containing 0 to 5 wt % of Ag and a carbon material may preferably be formed as a layer containing no Ag. The layer may further contain a binder, and in this case, the layer may contain 90 to 99 wt % of the carbon material and 1 to 10 wt % of the binder.

[0027] In one embodiment of the present invention, the layer (24c) containing 0 to 5 wt % of Ag and a carbon material may be disposed between two layers (24a, 24b) containing the carbon material and Ag, as shown in FIG. 3, or may be disposed between the solid electrolyte adjacent layer (24b) and the solid electrolyte (30) of the two layers, as shown in FIG. 2.

[0028] In one embodiment of the present invention, the layer (24c) containing 0 to 5 wt % of Ag and a carbon material may be preferably disposed between the solid electrolyte adjacent layer (24b) and the solid electrolyte (30) of the two layers, as shown in FIG. 2.

[0029] In one embodiment of the present invention, the layer (24c) containing 0 to 5 wt % of Ag and a carbon material may have a thickness of 1 μm to 30 μm.

[0030] In one embodiment of the present invention, the negative electrode active material layer of the present invention may further include a layer containing 80 to 100 wt%, 90 to 100 wt%, or 95 to 100 wt%, based on 100 wt% of the total negative electrode active material, in addition to the two layers containing the carbonaceous material and Ag. The layer may further contain 0 to 20 wt%, 0 to 10 wt%, or 0 to 5 wt% of the carbonaceous material. The layer may further contain a binder. In this case, the layer may contain 80 to 99 wt% Ag, 0 to 19 wt% carbonaceous material, and 1 to 10 wt% binder, or 90 to 99 wt% Ag, 0 to 9 wt% carbonaceous material, and 1 to 10 wt% binder, or 95 to 99 wt% Ag, 0 to 4 wt% carbonaceous material, and 1 to 10 wt% binder.

[0031] In one embodiment of the present invention, the layer containing 80 to 100% by weight of Ag may be disposed between the negative electrode current collector and the layer adjacent to the negative electrode current collector, of the two layers.

[0032] In one embodiment of the present invention, the layer containing 80 to 100 wt % of Ag may have a thickness of 1 μm to 30 μm.

[0033] In one embodiment of the present invention, the two or more layers may include one layer containing a carbon material and Ag, and one layer containing 0 to 5 wt % of Ag and a carbon material.

[0034] In this case, one layer containing the carbonaceous material and Ag may be located relatively closer to the current collector, and one layer containing 0-5 wt % Ag and the carbonaceous material may be located relatively closer to the solid electrolyte, where the one layer containing 0-5 wt % Ag and the carbonaceous material is as described above.

[0035] In one embodiment of the present invention, the carbon particles contained in one or more layers of the negative electrode active material layer may be, for example, amorphous carbon particles. However, the carbon particles are not limited to amorphous particles. Specific examples of the amorphous carbon material include carbon black such as acetylene black, furnace black, and ketjen black, graphene, or a combination thereof.

[0036] When the amorphous carbon particles contain pores, the pore diameter may be 1 nm or less, preferably 0.5 nm or less. However, it may be more preferable that the amorphous carbon particles do not contain pores. This is because, when the amorphous carbon particles contain pores, lithium may be precipitated inside the pores and the lithium may be deactivated. The amount of deactivated lithium may increase with repeated charge and discharge.

[0037] The pore size of the amorphous carbon particles can be measured, for example, through a nitrogen adsorption experiment or through a transmission electron microscope.

[0038] The carbonaceous particles may contain 3 to 10 at% oxygen. When the oxygen content is within the above range, the surface roughness of the negative electrode active material layer is significantly improved, which is preferable, as it also improves the driving characteristics of the battery. In particular, in the case of a layer containing Ag, it is preferable that the carbonaceous particles contain 3 to 10 at% oxygen.

[0039] In one embodiment of the present invention, the oxygen may be present in a form contained in a functional group bound to the carbon material particle, and the functional group may include one or more selected from the group consisting of a carboxy group, a hydroxy group, an ether group, an ester group, an aldehyde group, a carbonyl group, and an amide group.

[0040] The carbonaceous particles containing 3 to 10 at% oxygen may be produced, for example, by oxidizing a carbonaceous material. Specifically, the carbonaceous material may be treated with an acid and reacted with stirring at a temperature of 25 to 60°C to introduce oxygen functional groups onto the surface of the carbonaceous material. The type of acid is not particularly limited, and any acid may be used as long as it can introduce oxygen functional groups onto the surface of the carbonaceous material. Examples of the acid include sulfuric acid, nitric acid, and a mixture thereof, and an oxidizing agent such as potassium permanganate may also be used.

[0041] The oxygen content of the carbon material may be measured using a photoelectron spectrometer (XPS or ESCA), for example, a K-Alpha (Thermo Fisher Scientific) device.

[0042] In one embodiment of the present invention, the oxygen may be present on the surface of the carbonaceous particles. The surface does not mean only the outer surface of the carbonaceous particles, but also includes the surfaces of pores, if any.

[0043] In one embodiment of the present invention, each of the negative electrode active material layers may further contain, in addition to Ag particles, particles of one or more types selected from gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, and zinc.

[0044] In one embodiment of the present invention, the carbon particles may have a particle size (D50) of 10 nm to 100 nm or 20 nm to 60 nm, and the Ag particles and other metal particles may have a particle size (D50) of 20 nm to 100 nm, 20 nm to 60 nm, or 30 nm to 60 nm.

[0045] In one embodiment of the present invention, any one or more layers included in the negative electrode active material layer may contain oxygen in an amount of 2 to 10 at %. When the oxygen content is within the above range, the surface roughness of the layer is significantly improved, which is preferable because it improves the driving characteristics of the battery.

[0046] Among the layers included in the negative electrode active material layer, at least one layer containing a carbon material and Ag may further contain 65 to 85 at % of carbon and 0.5 to 5 at % of Ag together with the oxygen, and more preferably may further contain 74 to 85 at % of carbon and 0.5 to 3 at % of Ag.

[0047] Any one or more of the layers may further contain 5 to 25 at % of fluorine (F), and more preferably 10 to 20 at % of fluorine (F).

[0048] Any one or more of the layers may further contain 0.01 to 1 at % of sulfur (S), and more preferably 0.01 to 0.5 at % of sulfur (S).

[0049] In one embodiment of the present invention, any one or more of the layers may contain 2 to 10 at % of oxygen, 65 to 85 at % of carbon, 0.5 to 5 at % of Ag, and 5 to 25 at % of fluorine (F).

[0050] More preferably, it may contain 2.5 to 5 at % of oxygen, 74 to 85 at % of carbon, 0.5 to 3 at % of Ag, and 10 to 20 at % of fluorine (F).

[0051] In addition to the above components, the composition may further contain sulfur (S).

[0052] The atomic ratio may be measured using a photoelectron spectrometer (XPS or ESCA). For example, the atomic ratio may be measured using a Nexsa4 (Thermo Fisher Scientific) device.

[0053] In one embodiment of the present invention, any one or more layers included in the negative electrode active material layer may have the following surface roughness characteristics: 0.01μm≦Sa≦0.3μm 0.5μm≦Sz≦5μm 500mm -1 ≦Spc≦1500mm -1 0.005≦Sdr≦0.15.

[0054] When the surface roughness satisfies the above range, the overall battery characteristics, particularly the life characteristics, can be improved. Specifically, when the surface roughness of the negative electrode active material layer exceeds the above range, sufficient contact with the electrolyte layer is not achieved toward the electrolyte side, and uniform deposition of lithium is not facilitated toward the negative electrode current collector side, which may result in a deterioration of the battery characteristics.

[0055] The surface roughness of the negative electrode active material layer may be measured using a microscope, for example, a 3D laser confocal microscope (manufactured by KEYENCE Corporation).

[0056] The Sa (arithmetic mean height of the profile) may be a maximum of 0.3 μm or less, 0.2 μm or less, 0.1 μm or less, 0.08 μm or less, or 0.075 μm or less, and may be a minimum of 0.01 μm or more, 0.02 μm or more, 0.03 μm or more, 0.04 μm or more, 0.05 μm or more, 0.06 μm or more, or 0.07 μm or more. Furthermore, while it may be more preferable for Sa to be in the range of 0.01 μm≦Sa≦0.1 μm, it is not limited to these ranges and may be set to a range that combines the maximum and minimum values. The Sa represents the average absolute value of the height difference between each point relative to the mean plane of the surface.

[0057] The Sz (maximum height roughness of the profile) may be a maximum of 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1.5 μm or less, and may be a minimum of 0.5 μm or more, 0.8 μm or more, 1 μm or more, 1.1 μm or more, 1.2 μm or more, or 1.3 μm or more. Furthermore, the Sz may more preferably be in the range of 0.5 μm≦Sz≦1.6 μm, but is not limited to these ranges and may be set to a range that combines the maximum and minimum values. The Sz is the maximum height roughness within a single surface and indicates the distance between the highest and lowest points within a single surface.

[0058] The maximum Spc (roughness by peak number) is 1500 mm -1 Below, 1400mm -1 Below, 1300mm -1 Below, 1200mm -1 Below, 1100mm -1 or less than 1000mm -1 May be less than 500mm -1 Over 600mm -1 Over 700mm -1 Over 800mm -1 or more, or 900mm -1 It may be more than 500mm. -1 ≦Spc≦1100mm -1 However, the range of the maximum value and the minimum value may be set to any combination of these ranges. The Spc is a roughness based on the number of peaks, and is a measure of the steepness of the peaks.

[0059] The Sdr (interfacial area increase) may be a maximum of 0.15 or less, 0.1 or less, 0.05 or less, 0.03 or less, or 0.02 or less, and may be a minimum of 0.005 or more, 0.01 or more, or 0.015 or more. While a range of 0.005≦Sdr≦0.03 may be more preferable, the Sdr is not limited to this range and may be set to a range combining the maximum and minimum values. The Sdr is the increase in the interfacial area and refers to the ratio of the expanded area (the surface area of ​​the measured shape) to the area when the measurement region is viewed perpendicularly.

[0060] The meanings of Sa, Sz, Spc, and Sdr are described above, but these are used in the same meaning as commonly used in this field.

[0061] In one embodiment of the present invention, the carbon particles and Ag particles contained in one or more of the negative electrode active material layers may be contained in the form of a carbon-metal composite.

[0062] In the present invention, the negative electrode active material layer may be formed as a very thin film having a micron thickness and may include a carbonaceous-Ag composite in which carbonaceous particles and Ag particles are bonded together. However, the conventional carbonaceous-Ag composite has a problem in that the carbonaceous particles and Ag particles are difficult to distribute uniformly.

[0063] Furthermore, conventional carbonaceous material-Ag composites have the problem that it is very difficult to form them with small particle sizes. That is, if the particle size of the carbonaceous material-Ag composite is too large for a micro-thick thin film, it is difficult to form a negative electrode active material layer with good surface roughness, which also deteriorates the driving characteristics of the battery. Therefore, it is very important to form the carbonaceous material-Ag composite with small particle sizes.

[0064] The present invention provides an effect of dramatically improving the above-mentioned problems of the prior art.

[0065] That is, the carbonaceous material-Ag composite has a significantly smaller particle size than when conventional carbonaceous materials are used. The carbonaceous material forming the composite contains 3 at% or more of oxygen, which is well mixed with metal particles and uniformly distributed with Ag particles. This makes it possible to produce a carbonaceous material-Ag composite with excellent component uniformity. Furthermore, for the above reasons, it is possible to produce a carbonaceous material-Ag composite with a small and uniform particle size.

[0066] In one embodiment of the present invention, the carbonaceous material-Ag composite may be formed by one or more bonds selected from the group consisting of chemical bonds between carbonaceous material particles and Ag particles, van der Waals bonds between carbonaceous material particles and Ag particles, and bonds between carbonaceous material particles and Ag particles via a binder. The chemical bonds may be Ag-O bonds between Ag particles and oxygen contained in the carbonaceous material.

[0067] In one embodiment of the present invention, the carbon particles may have a particle size (D50) of 10 nm to 100 nm or 20 nm to 60 nm, and the Ag particles may have a particle size (D50) of 20 nm to 100 nm, 20 nm to 60 nm, or 30 nm to 60 nm.

[0068] In one embodiment of the present invention, the particle size (D50) of the carbon material-Ag composite may be 0.1 μm to 0.5 μm, and the upper limit of the particle size may be 0.4 μm or 0.3 μm.

[0069] The maximum particle size of the carbon material-Ag composite may be 3 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0070] If the particle size of the carbonaceous material-Ag composite is too large for a micro-thick thin film, it is difficult to form a negative electrode active material layer with excellent surface roughness, which deteriorates the driving characteristics of the battery. Therefore, it is very important to produce the carbonaceous material-Ag composite with a small particle size.

[0071] The reason why the driving characteristics of the battery deteriorate is that when the surface roughness of the negative electrode active material layer is large, it does not come into sufficient contact with the electrolyte layer, which does not contribute to uniform deposition of lithium on the negative electrode current collector.

[0072] In an anodeless lithium ion secondary battery, the thickness of the negative electrode active material layer may be formed in the range of usually 1 μm to 100 μm, or 10 μm to 60 μm, and specifically, may be formed to a thickness of 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc.

[0073] For example, when forming a negative electrode active material layer having a thickness of 20 μm, if a carbon material-Ag composite having a particle size of 10 μm is used, it is obvious that it is difficult to form a desirable surface roughness.

[0074] When the maximum particle size of the carbon material-metal composite is 3 μm or less, the effect of improving the surface roughness can be more reliably obtained, which is preferable. On the other hand, when it exceeds 3 μm, it may be difficult to obtain an excellent surface roughness when forming a thin film. Therefore, the maximum particle size of the carbon material-Ag composite may be 3 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0075] The particle size of the carbon material-Ag composite may be measured using a particle size analyzer, for example, a Mastersizer 3000 (Malvem Panalytical) instrument.

[0076] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer.

[0077] In one embodiment of the present invention, the solid electrolyte may be a sulfide-based solid electrolyte.

[0078] Hereinafter, the embodiments of the present invention will be described in more detail.

[0079] <Configuration of all-solid-state lithium-ion secondary battery> FIG. 1 is a cross-sectional view showing a schematic configuration of an all-solid-state lithium-ion secondary battery according to an embodiment of the present invention.

[0080] An all-solid-state lithium-ion secondary battery (100) according to one embodiment of the present invention is a so-called lithium-ion secondary battery that is charged and discharged by the movement of lithium ions between a positive electrode (10) and a negative electrode (20). Specifically, as shown in Figure 1, this all-solid-state lithium-ion secondary battery (100) is composed of a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20).

[0081] (1) Positive electrode As shown in FIG. 1, the positive electrode (10) includes a positive electrode current collector (12) and a positive electrode active material layer (14) arranged in this order toward the negative electrode (20).

[0082] The positive electrode current collector (12) may be in the form of a plate or foil and may be made of, for example, one metal selected from the group consisting of indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more metals.

[0083] The positive electrode active material layer 14 can reversibly absorb and release lithium ions and may include a positive electrode active material and a solid electrolyte.

[0084] The positive electrode active material may be a compound capable of inserting / extracting lithium. Examples of the compound capable of inserting / extracting lithium include Li a A 1-b B' b D'2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E1- b B' b O 2-c D' c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B' b O 4-c D' c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B' c D' α (wherein, 0.90≦a≦1.8, 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(wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni 1-b-c Mn b B' c D' α (wherein, 0.90≦a≦1.8, 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 (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d G e O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Examples include those represented by the formula Fe2(PO4)3 (0≦f≦2); LiFePO4.

[0085] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D' is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; and J is typically V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0086] Specific examples of the positive electrode active material include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium salts such as lithium manganese oxide and lithium iron phosphate, and lithium sulfide. The positive electrode active material layer (14) may contain only one type selected from these compounds as the positive electrode active material, or may contain two or more types selected from these compounds.

[0087] The positive electrode active material may include, among the lithium salts described above, a lithium salt of a transition metal oxide having a layered rock salt structure. Here, the "layered rock salt structure" refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the direction of a cubic rock salt structure, resulting in each atomic layer forming a two-dimensional plane. Furthermore, the "cubic rock salt structure" refers to a sodium chloride structure, which is a type of crystal structure. For example, the "cubic rock salt structure" refers to a structure in which face-centered cubic lattices in which cations and anions are respectively formed are shifted from each other by half the angle of the unit cell.

[0088] Examples of lithium salts of transition metal oxides having such a layered rock salt structure include LiNi x Co y Al z O2(NCA) or LiNix Co y Mn z It may also be a ternary lithium transition metal oxide such as O2(NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). The positive electrode active material layer (14) contains a lithium salt of such a layered rock salt type ternary transition metal oxide as the positive electrode active material, and can improve the energy density and thermal stability of the all-solid-state lithium ion secondary battery (100).

[0089] Here, examples of the shape of the positive electrode active material include particulate shapes such as true spherical and ellipsoidal. Also, the particle size of the positive electrode active material is not particularly limited, and may be within a range applicable to the positive electrode active material of a normal all-solid-state lithium ion secondary battery. Further, the content of the positive electrode active material in the positive electrode active material layer (14) is not particularly limited, and may be within a range applicable to the positive electrode of a normal all-solid-state lithium ion secondary battery.

[0090] Of course, those having a coating layer on the surface of the compound may also be used, or the compound and the compound having a coating layer may be mixed and used. This coating layer may contain a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds constituting these coating layers may be amorphous or crystalline. Examples of the coating element contained in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer formation process may use any coating method as long as these elements are used for the compound and the physical properties of the positive electrode active material are not adversely affected (for example, spray coating, dipping method, etc.). Since this is well understood by those skilled in this field, detailed description thereof is omitted.

[0091] Specific examples of the coating layer include Li2O-ZrO2 and the like.

[0092] The solid electrolyte contained in the positive electrode active material layer (14) may be the same as or different from the solid electrolyte contained in the solid electrolyte layer (30) described below.

[0093] The positive electrode active material layer (14) may contain not only the above-described positive electrode active material and solid electrolyte, but also an appropriate blend of additives such as a conductive agent, a binder, a filler, a dispersant, or an ion-conductive auxiliary agent.

[0094] Examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Examples of the binder include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Examples of the filler, dispersant, and ion-conducting additive may include known materials typically used in electrodes of all-solid-state lithium-ion secondary batteries.

[0095] (2) Negative electrode The negative electrode (20) may include a negative electrode current collector (22) and a negative electrode active material layer (24) arranged in this order toward the positive electrode (10).

[0096] The negative electrode current collector 22 may be in the form of a plate or foil. The negative electrode current collector 22 may include a material that does not react with lithium, i.e., does not form an alloy or compound with lithium. Examples of materials that can be used for the negative electrode current collector 22 include copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector 22 may be made of one of these metals, or may be made of an alloy or clad material of two or more metals.

[0097] The anode active material layer (24) may contain one or more anode active materials capable of forming an alloy or compound with lithium. In the initial state or after full discharge, lithium may not be present in the anode current collector (22), the anode active material layer (24), or between the anode active material layer (24) and the solid electrolyte layer (30). As described below, when an all-solid-state lithium-ion secondary battery (100) according to one embodiment is overcharged, the anode active material contained in the anode active material layer (24) and lithium ions transferred from the cathode (10) may form an alloy or compound, resulting in the formation (precipitation) of a lithium-based metal layer (26) on the anode (20), as shown in FIG. 4. The metal layer (26) may be deposited between the anode current collector (22) and the anode active material layer (24), within the anode active material layer (24), or in all of these locations. The metal layer (26) containing lithium as a main component may be disposed between the negative electrode current collector (22) and the negative electrode active material layer (24) closer to the negative electrode current collector layer (22) than to the negative electrode active material layer (24).

[0098] According to one embodiment, the negative electrode active material layer (24) may contain Ag as an essential negative electrode active material. Accordingly, the metal layer (26) formed during overcharge may contain a Li(Ag) alloy containing a γ1 phase, a βLi phase, or a combination thereof, in which Ag is dissolved in lithium. Therefore, during discharge, only Li dissolves from the Li(Ag) alloy constituting the metal layer (26), and the dissolved Ag remains, suppressing the generation of voids. In this case, the Ag content in the deposited Li-Ag solid solution may be 60% by weight or less. This range effectively suppresses the decrease in average discharge potential due to the influence of Ag. On the other hand, if the Ag content in the deposited Li-Ag solid solution is too low, the amount of Ag remaining during discharge may be small, and the generation of voids may not be sufficiently suppressed. Therefore, the Ag content in the deposited Li-Ag solid solution may be 20% by weight or more, for example, 40% by weight or more.

[0099] The presence of at least one Li-Ag solid solution in the γ1 phase or βLi phase in the metal layer (26) can be confirmed, for example, by analyzing the peak position and peak intensity ratio in XRD measurement. The Ag content in the precipitated Li-Ag solid solution can also be measured, for example, by XRD measurement. In this case, the diffraction peak positions of pure metallic lithium and metallic lithium containing Ag as a solid solution (Li-Ag solid solution) differ. The diffraction peak position of metallic lithium containing Ag as a solid solution approaches that of pure metallic lithium as the concentration of Ag in the solid solution decreases. For example, in XRD measurement using a Cu target, the diffraction peak shifts from around 2θ = 37.0° to around 36.5° as the concentration of Ag in the solid solution decreases. The amount of Ag in the solid solution can be estimated from this peak position. Alternatively, the amount of Ag in the solid solution can be measured using ICP or other methods.

[0100] In one embodiment, Ag does not necessarily have to be uniformly present in the negative electrode active material layer (24), and may be unevenly distributed in the negative electrode active material layer (24) on the side of the negative electrode current collector (22). In this case, lithium ions may react with the Ag unevenly distributed layer in the negative electrode active material layer (24) that has reached the vicinity of the negative electrode current collector (22), thereby forming a Li(Ag) alloy as the metal layer (26).

[0101] If the Ag content in the negative electrode active material layer (24) is too low, the amount of Ag remaining during discharge will also decrease, which may make it impossible to prevent the formation of voids. Therefore, the negative electrode active material layer (24) may contain 10 wt % or more of Ag, for example, 20 wt % or more, based on 100 wt % of the total negative electrode active material contained in the negative electrode active material layer, in an initial state when no charge or discharge is performed.

[0102] On the other hand, the upper limit of the Ag content in the negative electrode active material contained in the negative electrode active material layer (24) may be 100 wt %. However, due to the relationship between the reaction potential of Ag and Li, an increase in Ag may lower the average discharge potential and may also reduce the energy density of the battery. Therefore, from the viewpoint of increasing the energy density, the Ag content may be 80 wt % or less, for example, 50 wt % or less.

[0103] The Ag content (wt %) in the negative electrode active material layer (24) can be measured, for example, as follows. That is, the all-solid-state lithium-ion secondary battery (100) is discharged and then disassembled, and the negative electrode active material layer (24) is recovered from the surface of the negative electrode (20). The Ag content in the recovered material can then be determined using EDX, XRF, ICP, or the like. Alternatively, the Ag content can be confirmed, for example, by SEM-EDS analysis from a cross-sectional direction.

[0104] Furthermore, if the content of Ag per unit area of ​​the negative electrode active material layer (24) is too low when viewed from the stacking direction of the negative electrode (20), the amount of Ag remaining during discharge will also be small, which may make it impossible to suppress the generation of voids. Therefore, the content of Ag per unit area of ​​the negative electrode active material layer (24) is set to 0.05 mg / cm. 2 or more, for example, 0.10 mg / cm 2 It may be more than that.

[0105] On the other hand, if the content of Ag per unit area is too high, the average discharge potential may decrease, and the energy density of the battery may decrease. Therefore, the content of Ag per unit area is set to 5.0 mg / cm. 2 For example, 2.0 mg / cm 2 It may be the following:

[0106] The Ag content per unit area of ​​the negative electrode active material layer (24) can be measured, for example, as follows. That is, the all-solid-state lithium ion secondary battery (100) is disassembled after discharge, and the Ag content can be determined by SEM-EDS composition analysis of the surface or cross-section of the negative electrode (20). Alternatively, the Ag content can be determined by XPS, ICP, or other methods.

[0107] Furthermore, the Ag contained in the negative electrode active material layer (24) in the initial state before charging and discharging may be in the form of particles or a film. When present in the form of particles, the average particle diameter (d50) of Ag (diameter length or average diameter) may be, but is not limited to, 20 nm to 1 μm.

[0108] The negative electrode active material layer (24) may further contain, as an optional negative electrode active material other than Ag, for example, one or more selected from amorphous carbon, Au, Pt, Pd, Si, Al, Bi, Sn, In, and Zn.

[0109] Amorphous carbon may be preferably used as the carbon material contained in the negative electrode active material layer 24. Specific examples of the amorphous carbon include carbon black such as acetylene black, furnace black, and ketjen black, graphene, or a combination thereof.

[0110] Based on 100% by weight of the total negative electrode active material contained in the negative electrode active material layer 24, the total amount of the negative electrode active material other than Ag may be 50% by weight or more, for example, 70% by weight or more. The content of the negative electrode active material other than Ag may be measured in the same manner as the Ag content.

[0111] The negative electrode active material layer (24) may further contain a binder. The binder can stabilize the negative electrode active material layer (24) on the negative electrode current collector (22). Examples of materials constituting the binder include resin materials such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder may be composed of one or more resin materials selected from these resin materials.

[0112] The negative electrode active material layer (24) may also contain additives used in conventional all-solid-state lithium-ion secondary batteries, such as fillers, dispersants, ion conductive agents, etc. Specific examples of the additives are the same as those described above for the positive electrode.

[0113] The total thickness of the negative electrode active material layer (24) is not particularly limited, but may be 1 μm to 100 μm, or 10 μm to 60 μm. If the thickness of the negative electrode active material layer (24) is less than 1 μm, the performance of the all-solid-state secondary battery may not be sufficiently improved. If the thickness of the negative electrode active material layer (24) is more than 100 μm, the resistance of the negative electrode active material layer (24) increases, and as a result, the performance of the all-solid-state secondary battery may not be sufficiently improved. By using the above-mentioned binder, the thickness of the negative electrode active material layer (24) can be easily ensured at an appropriate level.

[0114] Meanwhile, the negative electrode current collector (22) may further include a film containing a material capable of forming an alloy or compound with lithium, and the film may be disposed between the negative electrode current collector (22) and the negative electrode active material layer.

[0115] The negative electrode current collector (22) does not react with lithium metal, but may make it difficult to deposit a smooth lithium metal layer on top. The film may be used as a wetting layer to allow lithium metal to deposit evenly on top of the negative electrode current collector (22).

[0116] The material capable of forming an alloy with lithium metal used in the film may include silicon, magnesium, aluminum, lead, silver, tin, or a combination thereof. The material capable of forming a compound with lithium metal used in the film may include carbon, titanium sulfide, iron sulfide, or a combination thereof. The content of the material used in the film may be small as long as it does not affect the electrochemical properties and / or redox potential of the electrode. The film may be applied evenly on the negative electrode current collector (22) to prevent cracking during charging cycles of the all-solid-state lithium-ion secondary battery (100). The film may be applied using a method such as physical vapor deposition (e.g., evaporation or sputtering), chemical vapor deposition, or plating.

[0117] The thickness of the film may be 1 nm to 500 nm. The thickness of the film may be, for example, 2 nm to 400 nm. The thickness of the film may be, for example, 3 nm to 300 nm. The thickness of the film may be, for example, 4 nm to 200 nm. The thickness of the film may be, for example, 5 nm to 100 nm.

[0118] (3) Solid electrolyte layer The solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20) (for example, between the positive electrode active material layer (14) and the negative electrode active material layer (24)). The solid electrolyte layer (30) contains a solid electrolyte capable of transferring ions. The solid electrolyte layer (30) may contain a sulfide-based solid electrolyte.

[0119] The sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (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, and Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In), or a combination thereof. The solid electrolyte may be made of one material selected from these sulfide-based solid electrolyte materials, or may be made of two or more materials.

[0120] The sulfide-based solid electrolyte may include a solid electrolyte represented by the following Chemical Formula 1: [Chemical formula 1] Li x M' y PS z A w In the above Chemical Formula 1, x, y, z, and w are, independently of one another, between 0 and 6; M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; A is at least one of F, Cl, Br, or I.

[0121] The solid electrolyte may be any of the sulfide solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements. For example, a material containing Li2S-P2S5 may be used. When a sulfide solid electrolyte material containing Li2S-P2S5 is used, the molar ratio of Li2S to P2S5 may be selected within the range of, for example, Li2S:P2S5=50:50 to 90:10.

[0122] The solid electrolyte may be in an amorphous state, a crystalline state, or a mixture of amorphous and crystalline states.

[0123] The solid electrolyte layer (30) may further contain a binder. Examples of the binder include resins such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polyacrylic acid. The binder may be the same as or different from the binders in the positive electrode active material layer (14) and the negative electrode active material layer (24).

[0124] (4) Initial charge capacity ratio In one embodiment of the all-solid-state lithium-ion secondary battery (100), the initial charge capacity of the positive electrode active material layer (14) is configured to be excessive relative to the initial charge capacity of the negative electrode active material layer (24). As described below, the all-solid-state lithium-ion secondary battery (100) according to one embodiment may be used after being charged beyond the initial charge capacity of the negative electrode active material layer (24) (i.e., overcharged). At the initial stage of charging, lithium may be absorbed into the negative electrode active material layer (24). That is, the negative electrode active material may form an alloy or compound with lithium ions migrated from the positive electrode (10). When the negative electrode active material layer (24) is charged beyond its initial charge capacity, lithium may precipitate on the back surface of the negative electrode active material layer (24), i.e., between the negative electrode current collector (22) and the negative electrode active material layer (24), as shown in FIG. 4 , and this lithium may form a metal layer (26). The metal layer (26) may be composed mainly of lithium with Ag dissolved therein (i.e., an Ag-Li solid solution). This phenomenon may occur in the case of a negative electrode active material, such as a material that forms an alloy or compound with lithium. During discharge, the lithium in the negative electrode active material layer (24) and the metal layer (26) can ionize and migrate to the positive electrode (10), leaving behind dissolved Ag. Therefore, lithium may be used as the negative electrode active material in the all-solid-state lithium-ion secondary battery (100). Furthermore, the negative electrode active material layer (24) coats the metal layer (26), thereby functioning as a protective layer for the metal layer (26) and suppressing the deposition and growth of lithium dendrites.

[0125] In an all-solid-state lithium-ion secondary battery (100) according to one embodiment, the ratio of the initial charge capacity of the positive electrode active material layer (14) to the initial charge capacity of the negative electrode active material layer (24), i.e., the initial charge capacity ratio b / a, preferably satisfies the following formula (100):

[0126] 0.01 (where a is the initial charge capacity (mAh) of the positive electrode active material layer (14), and b is the initial charge capacity (mAh) of the negative electrode active material layer (24).)

[0127] ​If the initial charge capacity ratio is 0.01 or less, the characteristics of the all-solid-state lithium-ion secondary battery (100) may be degraded. This may be because the negative electrode active material layer (24) does not function adequately as a protective layer. For example, if the thickness of the negative electrode active material layer (24) is very thin, the capacity ratio may be 0.01 or less. In this case, repeated charge and discharge may cause the negative electrode active material layer (24) to collapse, leading to the precipitation and growth of lithium metal dendrites. As a result, the characteristics of the all-solid-state lithium-ion secondary battery (100) may be degraded. Therefore, the initial charge capacity ratio may be 0.01 or more. On the other hand, if the initial charge capacity ratio is 0.5 or more, the amount of lithium precipitation in the negative electrode may decrease, resulting in a decrease in battery capacity. Therefore, the initial charge capacity ratio may be less than 0.5.

[0128] (5) Structure of all-solid-state lithium-ion secondary battery The all-solid-state lithium-ion secondary battery (100) of the present invention is an all-solid-state lithium-ion secondary battery (100) including, in this order, a positive electrode (10), a solid electrolyte layer (30), and a negative electrode (20). The negative electrode (20) includes a negative electrode current collector (22) and a negative electrode active material layer (24), and the negative electrode active material layer (24) includes a carbon material and Ag and includes two or more layers.

[0129] The negative electrode current collector 22 may include Ni foil, Ni-coated Cu foil, stainless steel foil, or a combination thereof, which can further improve the discharge capacity.

[0130] <Manufacturing method for all-solid-state lithium-ion secondary batteries> Next, we will explain the method for manufacturing the all-solid-state lithium-ion secondary battery 100. In one embodiment, the all-solid-state lithium-ion secondary battery 100 is obtained by first fabricating the positive electrode 10, the negative electrode 20, and the solid electrolyte layer 30, and then laminating these layers together.

[0131] (1) Positive electrode manufacturing process The process for producing a positive electrode is described below as an example. First, materials constituting the positive electrode active material layer (14) (positive electrode active material, binder, etc.) are added to a non-polar solvent to prepare a slurry (or paste). Next, the obtained slurry is applied to a prepared positive electrode current collector (12). This is dried to obtain a laminate. Next, the obtained laminate is pressed using, for example, hydrostatic pressure to obtain a positive electrode (10). The pressing step is omitted.

[0132] (2) Negative electrode manufacturing process The manufacturing process of the negative electrode is described below as an example. First, materials constituting the negative electrode active material layer (24) (e.g., negative electrode active material containing Ag, binder) are added to a polar or non-polar solvent to prepare a slurry (which may be a paste). The obtained slurry is then applied to a prepared negative electrode current collector (22) to form a first layer of negative electrode active material. Next, a slurry (which may be a paste) is prepared by mixing the first layer with a different Ag content. The obtained slurry is then applied to the top surface of the second layer and dried to obtain a laminate.

[0133] When the negative electrode active material layer further includes one or more layers, the additional layers may be laminated in the same manner as above.

[0134] The resulting laminate is then pressed, for example, using hydrostatic pressure, to produce the negative electrode (20). The pressing step may be omitted. The method for applying the slurry to the negative electrode current collector (22) is not particularly limited, and examples thereof include screen printing, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, and gravure coating.

[0135] Although the method for forming the negative electrode active material layer in two layers has been described above, when an additional layer is to be formed, a slurry for forming each layer may be prepared, and the layers may be sequentially stacked in the stacking order according to the above-described method to manufacture a negative electrode.

[0136] (3) Solid electrolyte layer fabrication process The solid electrolyte layer (30) can be made of a solid electrolyte containing, for example, a sulfide-based solid electrolyte material.

[0137] First, starting materials (e.g., Li2S, P2S5, etc.) are processed by melt quenching or mechanical milling to obtain a sulfide-based solid electrolyte material. For example, when using the melt quenching method, predetermined amounts of starting materials are mixed and formed into pellets, which are reacted in a vacuum at a predetermined reaction temperature and then quenched to produce a sulfide-based solid electrolyte material. The reaction temperature for the mixture of Li2S and P2S5 may be 400°C to 1000°C, for example, 800°C to 900°C. The reaction time may be 0.1 hours to 12 hours, for example, 1 hour to 12 hours. The quenching temperature of the reaction product may be 10°C or lower, for example, 0°C or lower, and the quenching rate may be typically 1°C / sec to 10,000°C / sec, for example, 1°C / sec to 1000°C / sec.

[0138] Furthermore, when mechanical milling is used, the sulfide-based solid electrolyte material can be produced by stirring and reacting the starting materials using a ball mill, etc. Furthermore, the stirring speed and stirring time in the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the production rate of the sulfide-based solid electrolyte material can be, and the longer the stirring time, the higher the conversion rate of the raw materials to the sulfide-based solid electrolyte material can be.

[0139] The resulting mixed raw material (sulfide-based solid electrolyte material) is then heat-treated at a predetermined temperature and pulverized to produce a particulate solid electrolyte. If the solid electrolyte has a glass transition point, the heat treatment may cause it to change from amorphous to crystalline.

[0140] The solid electrolyte obtained by the above method can then be formed into a film using a known film formation method, such as aerosol deposition, cold spray, or sputtering, to produce a solid electrolyte layer 30. Alternatively, the solid electrolyte layer 30 can be produced by compressing solid electrolyte particles. Alternatively, the solid electrolyte layer 30 can be produced by mixing the solid electrolyte with a solvent and a binder, applying the mixture, drying, and pressurizing the mixture.

[0141] (4) Lamination process An all-solid-state lithium-ion secondary battery (100) according to one embodiment can be obtained by disposing a solid electrolyte layer (30) between a positive electrode (10) and a negative electrode (20) and pressurizing them using, for example, hydrostatic pressure.

[0142] The all-solid-state lithium-ion secondary battery (100) of the present invention does not require application of high external pressure using end plates or the like, and can provide improved discharge capacity even when the external pressure applied to the positive electrode (10), the negative electrode (20), and the solid electrolyte layer (30) during use is 1 MPa or less.

[0143] <Charging method for all-solid-state lithium-ion secondary batteries> Next, a method for charging the all-solid-state lithium-ion secondary battery (100) will be described.

[0144] In one embodiment, a method for charging an all-solid-state lithium-ion secondary battery (100) is to charge the all-solid-state lithium-ion secondary battery (100) beyond the charge capacity of the negative electrode active material layer (24) (i.e., overcharge).

[0145] At the beginning of charging, lithium may be absorbed into the negative electrode active material layer (24). If charging exceeds the charge capacity of the negative electrode active material layer (24), as shown in FIG. 4, lithium may precipitate on the back surface of the negative electrode active material layer (24), i.e., between the negative electrode current collector (22) and the negative electrode active material layer (24). This lithium may form a metal layer (26) that was not present at the time of manufacturing. During discharge, lithium in the negative electrode active material layer (24) and the metal layer (26) may ionize and migrate to the positive electrode (10). Therefore, lithium may be used as the negative electrode active material in the all-solid-state lithium-ion secondary battery (100) of the present invention. Furthermore, the negative electrode active material layer (24) coats the metal layer (26), thereby functioning as a protective layer for the metal layer (26) and simultaneously suppressing the deposition and growth of dendritic metallic lithium. This suppresses short circuits and capacity reduction in the all-solid-state lithium-ion secondary battery 100, and further improves the characteristics of the all-solid-state lithium-ion secondary battery 100. Furthermore, according to one embodiment, the metal layer 26 is not pre-formed, which reduces the manufacturing cost of the all-solid-state lithium-ion secondary battery 100.

[0146] 4, the metal layer 26 is not limited to being formed between the negative electrode current collector 22 and the negative electrode active material layer 24, but may be formed inside the negative electrode active material layer 24. The metal layer 26 may be formed both between the negative electrode current collector 22 and the negative electrode active material layer 24 and inside the negative electrode active material layer 24.

[0147] The all-solid-state lithium ion secondary battery (100) of the present invention may be fabricated in the form of a unit cell having a positive electrode / separator / negative electrode structure, a bi-cell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked battery structure in which the unit cell structure is repeated.

[0148] The shape of the all-solid-state lithium-ion secondary battery (100) of the present invention is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. It can also be applied to large-scale batteries used in electric vehicles. For example, the all-solid-state lithium-ion secondary battery (100) may be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). It may also be used in fields requiring large-scale power storage. For example, it may be used in electric bicycles or power tools.

[0149] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0150] Comparative Example 1: Production of negative electrode 6 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 2 g of Ag with a particle size (D50) of 40 nm to 60 nm, 9.33 g of PVdF binder (solid content 6%), and 7.67 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a negative electrode active material slurry.

[0151] Then, the slurry was coated on a SUS foil to a thickness of 60 μm and dried to prepare a negative electrode.

[0152] Example 1: Preparation of negative electrode 3 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 1.33 g of Ag with a particle size (D50) of 40 nm to 60 nm, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a first negative electrode active material slurry.

[0153] 3 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 0.66 g of Ag with a particle size (D50) of 40 nm to 60 nm, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a second negative electrode active material slurry.

[0154] Thereafter, the first negative electrode active material slurry was coated on a SUS foil to a thickness of 30 μm and dried. Then, the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 30 μm and dried to prepare a negative electrode.

[0155] Example 2: Preparation of negative electrode 3 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 2 g of Ag with a particle size (D50) of 40 nm to 60 nm, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a first negative electrode active material slurry.

[0156] 3 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a second negative electrode active material slurry.

[0157] Thereafter, the first negative electrode active material slurry was coated on a SUS foil to a thickness of 30 μm and dried. Then, the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 30 μm and dried to prepare a negative electrode.

[0158] Example 3: Preparation of negative electrode 2 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 1.33 g of Ag with a particle size (D50) of 40 nm to 60 nm, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a first negative electrode active material slurry.

[0159] 2 g of amorphous carbon black with a particle size (D50) of 40-60 nm and an oxygen content of 5.2 at%, 0.66 g of Ag with a particle size (D50) of 40-60 nm, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a second negative electrode active material slurry.

[0160] 2 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a third negative electrode active material slurry.

[0161] Then, the first negative electrode active material slurry was coated on a SUS foil to a thickness of 20 μm and dried. Then, the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 20 μm and dried.

[0162] Next, the third negative electrode active material slurry was coated on the upper surface of the second negative electrode active material layer formed by the coating to a thickness of 20 μm and dried to prepare a negative electrode.

[0163] Example 4: Preparation of negative electrode A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode active material slurry was coated on a SUS foil to a thickness of 40 μm (Example 1: 30 μm) and dried, and then the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 20 μm (Example 1: 30 μm) and dried.

[0164] Example 5: Preparation of negative electrode 2 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 1.33 g of Ag with a particle size (D50) of 40 nm to 60 nm, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a first negative electrode active material slurry.

[0165] 2 g of amorphous carbon black with a particle size (D50) of 40-60 nm and an oxygen content of 5.2 at%, 0.66 g of Ag with a particle size (D50) of 40-60 nm, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a second negative electrode active material slurry.

[0166] 2 to 5 g of Ag with a particle size (D50) of 40 to 60 nm, 3.11 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a third negative electrode active material slurry.

[0167] Thereafter, the third negative electrode active material slurry was coated on a SUS foil to a thickness of 10 μm and dried. Then, the first negative electrode active material slurry was coated on the upper surface of the third coating layer to a thickness of 20 μm and dried. Finally, the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 20 μm and dried to prepare a negative electrode.

[0168] Example 6: Preparation of negative electrode 6 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 6 g of Ag with a particle size (D50) of 40 nm to 60 nm, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a first negative electrode active material slurry.

[0169] 6 g of amorphous carbon black with a particle size (D50) of 40 nm to 60 nm and an oxygen content of 5.2 at%, 4.67 g of PVdF binder (solid content 6%), and 1.5 g of NMP solution were placed in a Thinky mixer container and mixed at 2000 rpm for 3 minutes each 12 times. Then, 5 g of NMP solution was added and mixed at 2000 rpm for 3 minutes each 5 times to prepare a second negative electrode active material slurry.

[0170] Thereafter, the first negative electrode active material slurry was coated on a SUS foil to a thickness of 20 μm and dried. Then, the second negative electrode active material slurry was coated on the upper surface of the first negative electrode active material layer formed by the coating to a thickness of 40 μm and dried to prepare a negative electrode.

[0171] Manufacture of all-solid-state lithium-ion secondary batteries in Example 7 and Comparative Example 2 The positive electrode active material is placed on the current collector at 5mAh / cm 2 The positive electrode prepared in Example 7 and Comparative Example 2 was used as the positive electrode, the negative electrode prepared in Example 6 and Comparative Example 1 was used as the negative electrode, and a sulfide-based all-solid electrolyte was used as the electrolyte to prepare pouch-shaped mono-cells in Example 7 and Comparative Example 2.

[0172] Experimental Example 1: Evaluation of battery characteristics The pouch-shaped mono-cells of Example 7 and Comparative Example 2 were operated in the operating voltage range of 4.25 V to 3.0 V and at a driving temperature of 60° C. under the following charge-discharge conditions to evaluate the cycle characteristics. The results are shown in FIG.

[0173] Charging conditions: 0.33C, 4.25V CC / CV, 0.1C cut-off Discharge conditions: 0.33C, 3.0V, CC

[0174] It can be seen from FIG. 5 that the battery of Example 7, compared to the battery of Comparative Example 2, can be driven without a significant decrease in cell capacity as the cycles progress.

[0175] Fig. 6 shows an SEM image of the negative electrode of Example 6. As can be seen from Fig. 6, it can be seen that the negative electrode of Example 6 has many Ag particles arranged in the active material layer close to the current collector, and it is believed that the battery of Example 7 has improved cycle characteristics due to the inclusion of a negative electrode having such a structure.

[0176] Experimental Example 2: Measurement of particle size of carbon material-Ag composite (1) Separation of carbon-metal composite samples A portion of the carbon material-metal composite contained in the negative electrode active material slurry of Comparative Example 3, which was prepared in the same manner as the first negative electrode active material slurry of Example 1 and the first negative electrode active material slurry of Comparative Example 3, except that carbon black having an oxygen content of 2.6 at% was used instead of carbon black having an oxygen content of 5.2 at%, was extracted and diluted in an NMP solution to prepare an analysis sample.

[0177] (2) Analytical equipment Particle size analysis was performed using a particle size analyzer, model name Mastersizer 3000 (Malvem Panalytical). Specifically, the carbon material-metal composite analysis sample 1 (Example 1, containing carbon black with an oxygen content of 5.2 at%) and the carbon material-metal composite analysis sample 2 (Comparative Example 3, containing carbon black with an oxygen content of 2.6 at%) prepared in (1) above were placed in the sample inlet of the analyzer so that the laser absorbance was 10-15% of the laser obscuration, and measurement was performed.

[0178] The analyzer can analyze particle sizes ranging from 0.01 μm to 3500 μm and is a particle size analyzer suitable for wet and dry dispersion types using laser diffraction.

[0179] (3) Analysis results The particle size analysis results of the carbon material-metal composite analysis samples 1 and 2 are shown in Table 1 below and FIG.

[0180] [Table 1]

[0181] From the results in Table 1, it can be seen that the particle size of the carbon material-metal composite containing carbon black with an oxygen content of 5.2 at% is significantly smaller than the particle size of the carbon material-metal composite containing carbon black with an oxygen content of 2.6 at%. Furthermore, from the analysis results shown in Figure 7, it can be seen that the maximum particle size of the carbon material-metal composite containing carbon black with an oxygen content of 5.2 at% is 1 μm or less, which is significantly smaller than the particle size of the carbon material-metal composite containing carbon black with an oxygen content of 2.6 at%.

Claims

1. The battery includes a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a carbon material and Ag, and includes two or more layers.

2. the two or more layers include two layers containing a carbon material and Ag; The all-solid-state lithium-ion secondary battery according to claim 1 , wherein the two layers have different Ag contents.

3. 3. The all-solid-state lithium ion secondary battery according to claim 2, wherein, of the two layers containing the carbon material and Ag, the layer adjacent to the negative electrode current collector has a higher Ag content ratio than the layer adjacent to the solid electrolyte.

4. 4. The all-solid-state lithium-ion secondary battery according to claim 3, wherein the layer disposed adjacent to the negative electrode current collector contains 1.5 to 10 times more Ag than the layer disposed adjacent to the solid electrolyte.

5. 4. The all-solid-state lithium-ion secondary battery according to claim 3, wherein the two layers containing the carbon material and Ag each independently have a thickness of 1 μm to 50 μm.

6. 4. The all-solid-state lithium-ion secondary battery of claim 3, further comprising a layer containing 0 to 5 wt % of Ag and a carbon material, based on 100 wt % of the total negative electrode active material, in addition to the two layers containing the carbon material and Ag.

7. 7. The all-solid-state lithium-ion secondary battery according to claim 6, wherein the layer containing 0 to 5 wt % of Ag and a carbon material is a layer containing no Ag.

8. 7. The all-solid-state lithium-ion secondary battery according to claim 6, wherein the layer containing 0 to 5 wt % of Ag and the carbon material is disposed between two layers containing the carbon material and Ag, or between the layer of the two layers that is disposed adjacent to the solid electrolyte and the solid electrolyte.

9. 9. The all-solid-state lithium ion secondary battery according to claim 8, wherein the layer containing 0 to 5 wt % of Ag and a carbon material is disposed between the layer adjacent to the solid electrolyte and the solid electrolyte, of the two layers.

10. 7. The all-solid-state lithium-ion secondary battery according to claim 6, wherein the layer containing 0 to 5 wt % of Ag and a carbon material has a thickness of 1 μm to 30 μm.

11. 4. The all-solid-state lithium-ion secondary battery of claim 3, further comprising a layer containing 80 to 100 wt % of Ag based on 100 wt % of the total negative electrode active material, in addition to the two layers containing the carbon material and Ag.

12. 12. The all-solid-state lithium-ion secondary battery of claim 11, wherein the layer containing 80 to 100 wt % of Ag, based on 100 wt % of the total negative electrode active material, is disposed between the layer adjacent to the negative electrode current collector and the negative electrode current collector.

13. 2. The all-solid-state lithium-ion secondary battery of claim 1, wherein the two or more layers include one layer containing a carbon material and Ag and one layer containing 0 to 5 wt % of Ag and a carbon material.

14. The all-solid-state lithium-ion secondary battery according to claim 1 , wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer.

15. 2. The all-solid-state lithium ion secondary battery according to claim 1, wherein the solid electrolyte is a sulfide-based solid electrolyte.

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