All-solid-state lithium secondary battery, method for manufacturing the same, method for using the same, and method for charging the same

Abstract

The present invention relates to an all-solid-state lithium secondary battery, a method for manufacturing the same, a method for using the same, and a method for charging the same. The all-solid-state lithium secondary battery includes: a positive electrode including a positive electrode active material layer; a solid electrolyte; and a negative electrode including a negative electrode active material layer that forms an alloy or a compound with lithium, wherein the solid electrolyte is between the positive electrode and the negative electrode, and the negative electrode active material layer includes about 33 wt% - about 95 wt% of amorphous carbon, and the amorphous carbon has a nitrogen adsorption specific surface area of greater than 0 m² / g - about 100 m² / g, a dibutyl phthalate oil absorption value of about 150 mL / 100 g - about 400 mL / 100 g, or a combination thereof, relative to the total mass of the negative electrode active material in the negative electrode active material layer, and the ratio of the initial charge capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer satisfies 0.01 < b / a < 0.5, where a is the initial charge capacity of the positive electrode active material layer and b is the initial charge capacity of the negative electrode active material layer.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefits of Japanese Patent Application No. 2019 - 066886 filed with the Japan Patent Office on March 29, 2019, Japanese Patent Application No. 2020 - 013978 filed with the Japan Patent Office on January 30, 2020, Korean Patent Application No. 10 - 2019 - 0097639 filed with the Korean Intellectual Property Office on August 9, 2019, and Korean Patent Application No. 10 - 2020 - 0026308 filed with the Korean Intellectual Property Office on March 3, 2020, and incorporates their respective contents herein by reference in their entireties. Technical field

[0003] The present disclosure relates to all - solid - state (solid) lithium secondary batteries, methods for manufacturing them, methods for using them, and methods for charging them. Background art

[0004] All - solid - state secondary batteries including solid electrolytes have been developed. In order to increase the energy density of all - solid - state secondary batteries, the use of lithium as a negative electrode active material has been proposed.

[0005] The capacity density (capacity per unit volume) of lithium is about 10 times that of graphite, which is used as a negative electrode active material. Therefore, by using lithium as a negative electrode active material, it may be possible to make all - solid - state secondary batteries thinner and increase their output power.

[0006] However, there are disadvantages in using lithium as a negative electrode active material, and improvements in all - solid - state secondary batteries using lithium as a negative electrode active material are desired. Summary of the invention

[0007] Provided herein are all - solid - state secondary batteries and methods for charging them, the all - solid - state secondary batteries having excellent battery characteristics, particularly both excellent cycle characteristics and excellent discharge rate characteristics.

[0008] Additional aspects will be set forth in part in the following description, and in part will be apparent from the description, or may be learned by practice of the embodiments provided herein.

[0009] According to one aspect of the present disclosure, there is provided an all - solid - state lithium secondary battery including: a positive electrode including a positive electrode active material layer; a solid electrolyte; and a negative electrode including a negative electrode active material layer that forms an alloy or compound with lithium, wherein the solid electrolyte is between the positive electrode and the negative electrode, and wherein the negative electrode active material layer includes about 33 weight percent (wt%) - about 95 wt% of amorphous carbon, relative to the total mass of the negative electrode active material in the negative electrode active material layer, and wherein the amorphous carbon has

[0010] Greater than 0 square meters per gram (m 2 / g) - a nitrogen adsorption specific surface area of about 100 square meters per gram,

[0011] a dibutyl phthalate (DBP) oil absorption value of about 150 milliliters per 100 grams (mL / 100g) - about 400 milliliters per 100 grams,

[0012] or a combination thereof, and

[0013] wherein the ratio of the initial charge (charged) capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer satisfies Inequality 1,

[0014] Inequality 1

[0015] 0.01 < b / a < 0.5

[0016] wherein a is the initial charge capacity (milliampere-hour, mAh) of the positive electrode active material layer, and b is the initial charge capacity (mAh) of the negative electrode active material layer.

[0017] In an embodiment, in the all-solid-state secondary battery, the amorphous carbon may have about 20 m 2 / g - about 100 m 2 / g of nitrogen adsorption specific surface area.

[0018] In an embodiment, in the all-solid-state secondary battery, the amorphous carbon may have about 30 m 2 / g - about 100 m 2 / g of nitrogen adsorption specific surface area.

[0019] In an embodiment, in the all-solid-state secondary battery, the amorphous carbon may have a DBP oil absorption value of about 150 mL / 100g - about 400 mL / 100g.

[0020] In an embodiment, in the all-solid-state secondary battery, the amorphous carbon may have a DBP oil absorption value of about 200 mL / 100g.

[0021] In an embodiment, in the all-solid-state secondary battery, the negative electrode active material layer may further include gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof.

[0022] In an embodiment, in the all-solid-state secondary battery, the negative electrode active material layer may include about 45 wt% - about 95 wt% of amorphous carbon, relative to the total mass of the negative electrode active material.

[0023] In one or more embodiments, in the all-solid-state secondary battery, the amorphous carbon may be carbon black.

[0024] In an embodiment, in the all-solid-state secondary battery, the carbon black may be furnace black, acetylene black, Ketjen black, or a combination thereof.

[0025] According to one aspect of the present disclosure, there is provided a method of manufacturing the all-solid-state lithium secondary battery, the method including: providing a solid electrolyte between the positive electrode and the negative electrode; and pressing the positive electrode, the solid electrolyte, and the negative electrode to manufacture the all-solid-state lithium secondary battery.

[0026] According to one aspect of the present disclosure, there is provided a method of using the all-solid-state lithium secondary battery, the method including: charging and discharging the all-solid-state lithium secondary battery while applying pressure to the all-solid-state lithium secondary battery between two plates.

[0027] According to still another aspect of the present disclosure, there is provided a method of charging the all-solid-state lithium secondary battery, the method including: charging the all-solid-state lithium secondary battery such that the amount of charge of the all-solid-state lithium secondary battery exceeds the initial charge capacity of the negative electrode active material layer.

[0028] In an embodiment, in the method of charging the all-solid-state secondary battery, the amount of charge is about 2 times to about 100 times the initial charge capacity of the negative electrode active material layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other aspects, features, and advantages of some embodiments of the present disclosure will become more apparent from the following description when considered in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a schematic cross-sectional view illustrating the structure of an all-solid-state secondary battery according to an exemplary embodiment;

[0031] Figure 2 is a schematic cross-sectional view illustrating the structure of the all-solid-state secondary battery after overcharging of the negative electrode;

[0032] Figure 3 is a cross-sectional view of an all-solid-state secondary battery according to another exemplary embodiment; and

[0033] Figure 4 is a cross-sectional view of an all-solid-state secondary battery according to another exemplary embodiment. DETAILED DESCRIPTION

[0034] The present disclosure will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, and should be construed to include all variations, equivalents, and alternatives within the scope of the present disclosure; on the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the effects and features of the present disclosure and the manner of implementing the present disclosure to those skilled in the art.

[0035] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting of the present disclosure. As used herein, the indefinite articles “a,” “an,” the definite article “the,” and “at least one” do not denote a limitation of quantity and are intended to cover both the singular and the plural, unless the context clearly indicates otherwise. For example, “an element” has the same meaning as “at least one element” unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the slash “ / ” or the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0036] In the drawings, for better understanding or ease of description, the dimensions or thicknesses of the respective layers, regions, or elements are arbitrarily enlarged or reduced, and thus the present disclosure is not limited thereto. Throughout the written description and the drawings, the same reference numerals and symbols will be used to denote the same or similar elements (features). It will also be understood that when an element such as a layer, film, region, or component is referred to as being “on” another element, it can be “directly on” the other element, or there may also be an intermediate layer, region, or component. Although the terms “first,” “second,” etc. may be used herein to describe various elements, components, regions, and / or layers, these elements, components, regions, and / or layers should not be limited by these terms. These terms are only used to distinguish one component from another and are not for the purpose of limitation. In the following description and drawings, components having substantially the same functional configuration are assigned the same reference numerals, and overlapping descriptions will be omitted.

[0037] As used herein, “about” includes the stated value and means within an acceptable deviation range for a particular value as determined by one of ordinary skill in the art in view of the measurements discussed and the errors associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations of the stated value, or within ±30%, 20%, 10%, or 5%.

[0038] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted in an idealized or overly formal sense unless clearly so defined herein.

[0039] Exemplary embodiments are described herein with reference to cross-sectional views that are schematic illustrations of idealized embodiments. As such, deviations from the shape of the figures as a result of, for example, manufacturing techniques and / or tolerances are to be expected. Accordingly, the embodiments described herein should not be construed as limited to the specific shapes of regions as shown herein, but include deviations in shapes resulting from, for example, manufacturing. For example, regions illustrated or described as flat may typically have rough and / or non-linear features. Additionally, sharp corners shown may be rounded. Thus, the regions shown in the figures are schematic in nature, and their shapes are not intended to illustrate the exact shape of the regions and are not intended to limit the scope of the claims.

[0040] As used herein, the C-rate means the current at which a battery is discharged in one hour. For example, the C-rate of a battery having a discharge capacity of 1.6 ampere-hours will be 1.6 amperes.

[0041] As used herein, the term "metal" refers to a metal or metalloid element selected from Groups 1-17 as defined in the Periodic Table of the Elements, including the lanthanide and actinide series. As used herein, "metalloid" means B, Si, Ge, As, Sb, Te, or a combination thereof.

[0042] As used herein, the dibutyl phthalate (DBP) oil absorption value or oil absorption amount (OAN) refers to the value in cubic centimeters of DBP absorbed by 100 grams (g) of amorphous carbon under the defined conditions. The DBP oil absorption value is proportional to the degree of aggregation of the amorphous carbon structure. The test method for measuring the DBP oil absorption value may be, for example, ASTM D2414, the content of which is hereby incorporated by reference in its entirety.

[0043] In all-solid-state secondary batteries, the use of lithium as a negative electrode active material has been proposed. However, during charging, lithium metal deposits at the interface between the negative electrode current collector and the solid electrolyte, and as the charging and discharging cycles are repeated, the deposited lithium metal can grow to form dendrites, thereby filling the gaps in the solid electrolyte. Lithium metal grown in the form of dendrites can cause a short circuit and result in a reduction in the charge capacity of the secondary battery.

[0044] To solve these problems, Japanese Patent Publication No. 2011-086554 (the entire content of which is incorporated herein by reference) discloses using a metal layer composed of lithium or a metal capable of alloying with lithium as a negative electrode active material layer, and providing an interface layer composed of amorphous carbon on the negative electrode active material layer. This allows lithium ions to disperse in the interface layer, so that precipitation and growth of lithium metal can be suppressed. However, the all-solid-state secondary battery disclosed in Japanese Patent Publication No. 2011-086554 is considered insufficient to meet recent requirements.

[0045] It has been advantageously found that an all-solid-state secondary battery having both excellent cycle characteristics and discharge rate characteristics can be obtained by limiting the ratio of the initial charge capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer to a predetermined range, and using a negative electrode active material layer including amorphous carbon having a large structure or large particle size as the negative electrode active material.

[0046] It has also been advantageously found that by including a certain amount of amorphous carbon in the negative electrode, the number of interfaces between carbon particles or aggregates of carbon particles can be reduced, thereby promoting diffusion of lithium in the negative electrode active material layer and providing an all-solid-state secondary battery having both excellent cycle characteristics and excellent discharge rate characteristics.

[0047] Hereinafter, the all-solid-state secondary battery will be described in more detail. The embodiments presented herein are intended to illustrate all-solid-state secondary batteries embodying the technical concept of the present application; however, the present application is not limited to the following embodiments.

[0048] 1. Structure of All-Solid-State Secondary Battery

[0049] The all-solid-state secondary battery 1 according to the embodiment is a lithium secondary battery that is charged and discharged by migration of lithium ions between a positive electrode and a negative electrode. In particular, as Figure 1 shown, the all-solid-state secondary battery 1 may include a positive electrode 10, a negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20. The positive electrode may also be referred to as a positive electrode layer herein, the negative electrode may also be referred to as a negative electrode layer herein, and the solid electrolyte between the negative electrode and the positive electrode may also be referred to as a solid electrolyte layer herein.

[0050] (1) Positive Electrode

[0051] The positive electrode 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12 that are sequentially provided opposite to the negative electrode 20.

[0052] The positive electrode current collector 11 may have a sheet form or a foil form. The positive electrode current collector 11 may include a metal such as indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, lithium, an alloy thereof, or a combination thereof.

[0053] The positive electrode active material layer 12 can reversibly absorb and desorb lithium ions. In particular, the positive electrode active material layer 12 may include a positive electrode active material and a solid electrolyte.

[0054] For example, the positive electrode active material may be a lithium salt such as lithium cobalt oxide (hereinafter, LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter, NCA), lithium nickel cobalt manganese oxide (hereinafter, NCM), lithium manganese oxide, lithium iron phosphate, lithium sulfide, or a combination thereof. In one aspect, the positive electrode active material layer 12 may include only one of the foregoing as the positive electrode active material, or a combination of at least two including the foregoing compounds may be used.

[0055] The positive electrode active material may be, for example, a compound represented by: Li a A 1-b B’ b D 2 (where 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.); Li a E 1-b B’ b O 2-c D c (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b B’ b O 4-c D c (where 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B’ c D α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-b-c Co b B’ c O 2-α F’ α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Co b B’ c O 2-α F’ 2 (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b- c Mn b B’ c D α(where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-b-c Mn b B’ c O 2-α F’ α (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b-c Mn b B’ c O 2-α F’ 2 (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni b E c G d O 2 (where 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 O 2 (where 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1); Li a NiG b O 2 (where 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a CoG b O 2 (where 0.90 ≤ a ≤ 1, and 0.001 ≤ b ≤ 0.1); Li a MnG b O 2 (where 0.90 ≤ a ≤ 1, 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (where 0.90 ≤ a ≤ 1, and 0.001 ≤ b ≤ 0.1); QO 2 ; QS 2 ; LiQS 2 ; V 2 O 5 ; LiV 2 O 5 ; LiI’O 2 ; LiNiVO 4 ; Li (3-f) J2 (PO 4 ) 3 (where 0 ≤ f ≤ 2); Li (3-f) Fe 2 (PO 4 ) 3 (where 0 ≤ f ≤ 2); LiFePO 4 ; or a combination thereof. In the above formula, A can be nickel (Ni), cobalt (Co), manganese (Mn), or a combination thereof; B' can be aluminum (Al), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), rare earth elements, or a combination thereof; D can be oxygen (O), fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; E can be cobalt (Co), manganese (Mn), or a combination thereof; F' can be fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; G can be aluminum (Al), chromium (Cr), manganese (Mn), iron (Fe), magnesium (Mg), lanthanum (La), cerium (Ce), strontium (Sr), vanadium (V), or a combination thereof; Q can be titanium (Ti), molybdenum (Mo), manganese (Mn), or a combination thereof; I' can be chromium (Cr), vanadium (V), iron (Fe), scandium (Sc), yttrium (Y), or a combination thereof; and J can be vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), or a combination thereof.

[0056] The compounds listed above as the positive electrode active material may have a surface coating layer (hereinafter, also referred to as "coating layer"). Alternatively, a mixture of a compound without a coating layer and a compound with a coating layer selected from the compounds listed above can be used. In an embodiment, the coating layer on the surface of such a compound may include a compound of a coating element such as an oxide, hydroxide, oxyhydroxide, carbonate, or hydroxycarbonate of the coating element. In an embodiment, the compound for the coating layer can be amorphous or crystalline. In an embodiment, the coating element for the coating layer can be magnesium (Mg), aluminum (Al), cobalt (Co), potassium (K), sodium (Na), calcium (Ca), silicon (Si), titanium (Ti), vanadium (V), tin (Sn), germanium (Ge), gallium (Ga), boron (B), arsenic (As), zirconium (Zr), or a combination thereof. In an embodiment, the coating layer can be formed on the positive electrode active material using any suitable method that does not adversely affect the physical properties of the positive electrode active material. For example, the coating layer can be formed using a spraying method, an impregnation method, etc. These coating methods are well understood by those of ordinary skill in the art, and thus their detailed description will be omitted.

[0057] The positive electrode active material may include, for example, a lithium transition metal oxide having a layered rock salt-type structure, and may be selected from among the lithium transition metal oxides listed above. The term "layered rock salt-type structure" as used herein refers to the following structure: wherein oxygen atom layers and metal atom layers are alternately and regularly arranged in the <111> direction, and each atom layer forms a two-dimensional (2D) plane. The "cubic rock salt-type structure" refers to the sodium chloride (NaCl)-type crystal structure, and in particular, a structure in which the face-centered cubic (fcc) lattice formed by the corresponding cations and anions is arranged such that the ridges of the unit lattice (unit cell) are offset by 1 / 2.

[0058] The lithium transition metal oxide having such a layered rock salt-type structure may be, for example, a lithium ternary transition metal oxide such as LiNi x Co y Al z O 2 (NCA) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1), or LiNi x Co y Mn z O 2 (NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). Since the positive electrode active material layer 12 contains a lithium ternary transition metal oxide having such a layered rock salt-type structure as the positive electrode active material, the energy density and thermal stability of the all-solid-state secondary battery 1 can be improved.

[0059] The positive electrode active material may be in the form of particles having, for example, a true spherical particle shape or an ellipsoidal particle shape. The particle size of the positive electrode active material is not limited and may be within the range suitable for the positive electrode active material layer of the all-solid-state secondary battery. The amount of the positive electrode active material in the positive electrode active material layer 12 is not particularly limited and may be within the range suitable for the positive electrode of the all-solid-state secondary battery.

[0060] The positive electrode active material may be coated with a coating layer. The coating layer may be any coating layer suitable for the positive electrode active material of the all-solid-state secondary battery. The material of the coating layer may be, for example, Li 2 O-ZrO 2 .

[0061] The solid electrolyte included in the positive electrode active material layer 12 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 30 to be described later.

[0062] In addition to the positive electrode active material and the solid electrolyte, the positive electrode active material layer 12 may further include, for example, a conductive agent, a binder, a filler, an auxiliary ion conductor, a coating agent, and a dispersant. The conductive agent may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, or a combination thereof. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, or a combination thereof. The coating agent, dispersant, and auxiliary ion conductor that may be further added to the positive electrode active material layer 12 may be any materials suitable for use in the electrodes of all-solid-state secondary batteries.

[0063] (2) Negative electrode

[0064] The negative electrode 20 opposite to the positive electrode layer 10 may include a negative electrode current collector 21 and a negative electrode active material layer 22 that are sequentially provided.

[0065] The negative electrode current collector 21 may have a sheet shape or a foil shape. The negative electrode current collector 21 may be substantially composed of a material that does not react with lithium, such as a material that does not form an alloy or a compound with lithium, or be composed of such a material. The material of the negative electrode current collector 21 may be, for example, copper, stainless steel, titanium, iron, cobalt, nickel, or a combination thereof. The negative electrode current collector 21 may include a single metal or may be an alloy or a clad metal including two or more of these metals.

[0066] The negative electrode active material layer 22 may include a negative electrode active material that forms an alloy or a compound with lithium. The negative electrode active material layer may include amorphous carbon as the negative electrode active material that forms an alloy or a compound with lithium. The amorphous carbon may be carbon black such as acetylene black, furnace black, Ketjen black, or a combination thereof, or graphene. The negative electrode active material layer 22 may include one of the aforementioned amorphous carbons or a combination of at least two of the aforementioned amorphous carbons.

[0067] In the all-solid-state secondary battery 1 according to an embodiment, the negative electrode active material layer 22 may include amorphous carbon as the negative electrode active material in an amount of about 33% by weight or more based on the total mass of the negative electrode active material. The amorphous carbon has at least one of the following properties (a) or (b).

[0068] (a) A nitrogen adsorption specific surface area greater than 0 square meters per gram (m 2 / g) to about 100 m 2 / g, and

[0069] (b) A DBP oil absorption value of 150 milliliters mL / 100 grams (g) or more.

[0070] By using, in the negative electrode active material, one having about 100 m 2Amorphous carbon with a nitrogen adsorption specific surface area of 1 m² / g or less. The particle size of the amorphous carbon can increase, and thus the number of times lithium conducts across the grain boundaries of the amorphous carbon particles can decrease. Therefore, the diffusion of lithium within the negative electrode active material layer can be promoted. As a result, it can be difficult for lithium to be isolated (trapped) within the negative electrode layer during discharge, and thus the all-solid-state secondary battery can have improved cycle characteristics and discharge rate characteristics.

[0071] The amorphous carbon included as the negative electrode active material can have, for example, a nitrogen adsorption specific surface area of about 1 square meter per gram (m² / g) or more, about 5 m² / g or more, about 10 m² / g or more, about 20 m² / g or more, about 30 m² / g or more, about 40 m² / g or more, about 50 m² / g or more, or about 60 m² / g or more. By having a lower limit of the nitrogen adsorption specific surface area of the amorphous carbon within these ranges, the discharge rate characteristics of the all-solid-state secondary battery can be further improved. The amorphous carbon included as the negative electrode active material can have, for example, a nitrogen adsorption specific surface area of about 1 m² / g - about 100 m² / g, about 5 m² / g - about 100 m² / g, about 10 m² / g - about 100 m² / g, about 20 m² / g - about 100 m² / g, about 30 m² / g - about 100 m² / g, about 40 m² / g - about 100 m² / g, about 50 m² / g - about 100 m² / g, or about 60 m² / g - about 100 m² / g. 2 / g) or more, about 5 m² 2 / g or more, about 10 m² 2 / g or more, about 20 m² 2 / g or more, about 30 m² 2 / g or more, about 40 m² 2 / g or more, about 50 m² 2 / g or more, or about 60 m² 2 / g or more. By having a lower limit of the nitrogen adsorption specific surface area of the amorphous carbon within these ranges, the discharge rate characteristics of the all-solid-state secondary battery can be further improved. The amorphous carbon included as the negative electrode active material can have, for example, a nitrogen adsorption specific surface area of about 1 m² / g - about 100 m² / g, about 5 m² / g - about 100 m² / g, about 10 m² / g - about 100 m² / g, about 20 m² / g - about 100 m² / g, about 30 m² / g - about 100 m² / g, about 40 m² / g - about 100 m² / g, about 50 m² / g - about 100 m² / g, or about 60 m² / g - about 100 m² / g. 2 / g - about 100 m² 2 / g, about 5 m² 2 / g - about 100 m² 2 / g, about 10 m² 2 / g - about 100 m² 2 / g, about 20 m² 2 / g - about 100 m² 2 / g, about 30 m² 2 / g - about 100 m² 2 / g, about 40 m² 2 / g - about 100 m² 2 / g, about 50 m² 2 / g - about 100 m² 2 / g, or about 60 m² 2 / g - about 100 m² 2 / g.

[0072] As used herein, when the negative electrode active material layer includes a single type of amorphous carbon, the nitrogen adsorption specific surface area of the amorphous carbon included as the negative electrode active material in the negative electrode active material layer refers to the nitrogen adsorption specific surface area of the single type of amorphous carbon. When the negative electrode active material layer includes multiple types of amorphous carbon, the nitrogen adsorption specific surface area refers to the nitrogen adsorption specific surface areas of the multiple types of amorphous carbon respectively.

[0073] The nitrogen adsorption specific surface area of the amorphous carbon included in the negative electrode active material layer 22 can be measured by a nitrogen adsorption method (for example, as described in JIS K6217-2:2001, the content of which is incorporated herein by reference in its entirety). Briefly, amorphous carbon such as carbon black is degassed once at a high temperature of about 300 °C and then cooled to the liquid nitrogen temperature in a nitrogen atmosphere. Then, once the equilibrium state is reached, the mass increase (nitrogen adsorption amount) of the carbon sample under the nitrogen atmosphere pressure can be measured and applied to the Brunauer-Emmett-Teller (BET) equation to thereby calculate the value of the nitrogen adsorption specific surface area.

[0074] DBP oil absorption value

[0075] Since the amorphous carbon included as the negative electrode active material and having a DBP oil absorption value of 150 mL / 100 g or more, the size of the aggregates (primary aggregates) of carbon particles can be large, so that the diffusion of lithium through the aggregates can be promoted. As a result, the diffusion of lithium in the negative electrode active material layer can be promoted, and it can be difficult for lithium to deposit in the negative electrode layer during charging, and thus the all-solid-state secondary battery can have improved cycle characteristics and discharge rate characteristics.

[0076] The amorphous carbon included as the negative electrode active material can have, for example, a DBP oil absorption value of about 400 mL / 100 g or less, about 350 mL / 100 g or less, about 300 mL / 100 g or less, about 250 mL / 100 g or less, or about 200 mL / 100 g or less. By having the upper limit of the DBP oil absorption value of the amorphous carbon within these ranges, the discharge rate characteristics can be further improved. The amorphous carbon included as the negative electrode active material can have, for example, a DBP oil absorption value of about 150 mL / 100 g - about 400 mL / 100 g, about 150 mL / 100 g - about 350 mL / 100 g, about 150 mL / 100 g - about 300 mL / 100 g, about 150 mL / 100 g - about 250 mL / 100 g, or about 150 mL / 100 g - about 200 mL / 100 g.

[0077] As used herein, when the negative electrode active material layer includes one type of amorphous carbon as the negative electrode active material in the negative electrode active material layer, the "DBP oil absorption value" can correspond to the DBP oil absorption value of the one type of amorphous carbon. When the negative electrode active material layer includes multiple types of amorphous carbon as the negative electrode active material in the negative electrode active material layer, the "DBP oil absorption value" can correspond to the DBP oil absorption values of the multiple types of amorphous carbon respectively.

[0078] The DBP oil absorption value of the amorphous carbon included in the negative electrode active material layer can be measured by a DBP oil absorption value measurement method, such as the method defined in JIS K6217-4:2008, and the content of JIS K6217-4:2008 is hereby incorporated by reference in its entirety. Specifically, dibutyl phthalate (DBP) from a burette can be titrated at a constant rate into a sample being stirred with a rotor. As DBP is added, the mixture can change from a free-flowing powder to a slightly viscous substance. When the torque generated by the change in viscosity reaches a set value or a certain proportion of the maximum torque obtained from the torque curve, the measurement end point is reached. The volume (mL) of DBP at the end point can be divided by the mass (g) of the sample and then multiplied by 100 to thereby calculate the DBP oil absorption value (mL / 100g).

[0079] The negative electrode active material layer can include amorphous carbon as the only negative electrode active material capable of forming an alloy or compound with lithium, or can further include a metal or a metalloid in addition to amorphous carbon. For example, the metal or metalloid can be gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof.

[0080] When a metal or a metalloid is further included as the negative electrode active material, the metal or metalloid negative electrode active material can have a particle size of, for example, about 4 micrometers (μm) or less, or about 100 nanometers (nm) or less. For example, the particle size of the metal or metalloid negative electrode active material refers to the median diameter (D50) measured using a laser particle size distribution analyzer. The lower limit of the particle size is not particularly limited, but can be, for example, about 10 nm. The negative electrode active material can have a particle size of, for example, about 4 μm or less, about 3 μm or less, about 2 μm or less, about 1 μm or less, or about 900 nm or less. For example, the negative electrode active material can have a particle size of about 10 nm - about 4 μm, about 10 nm - about 3 μm, about 10 nm - about 2 μm, about 10 nm - about 1 μm, or about 10 nm - about 900 nm. A all-solid-state secondary battery including a metal or metalloid negative electrode active material having a particle size within these ranges can have further improved output characteristics and cycle characteristics. When the negative electrode active material layer includes a metal or a metalloid such as gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof that can form a compound or alloy with lithium in an amount of about 5% by weight or more based on the total mass of the negative electrode active material, this effect can be achieved. For example, nickel (Ni) that does not form an alloy with lithium is not the negative electrode active material.

[0081] The total amount of amorphous carbon

[0082] When the negative electrode active material layer includes less than 33% by weight of (a) greater than 0m 2 / g to 100m 2When the amorphous carbon has a nitrogen adsorption specific surface area of 10 m² / g or less, (b) a DBP oil absorption value of 150 mL / 100 g or more, or a combination of (a) and (b), the cycle characteristics and discharge rate characteristics of the all-solid-state secondary battery may not be sufficiently improved. Therefore, the amount of amorphous carbon having the property of (a) and / or (b) (for example, satisfying the conditions of (a) and / or (b)) in the negative electrode active material layer is 33% by weight or more, based on the total weight of the negative electrode active material.

[0083] The upper limit of the amount of amorphous carbon satisfying the conditions of (a) and / or (b) is not particularly limited, but may be, for example, 95% by weight or less.

[0084] As used herein, the amount of amorphous carbon in the negative electrode active material layer refers to the total weight of one type or more types of amorphous carbon that satisfy the conditions of (a) and / or (b) with respect to (i.e., relative to) the total weight of the negative electrode active material included in the negative electrode active material layer, which is regarded as 100% by weight. For example, the negative electrode active material layer may include a mixture of amorphous carbon and a metal or metalloid such as gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof. The amount of amorphous carbon may be, for example, about 33% to 95% by weight, about 40% to 95% by weight, about 45% to 95% by weight, about 50% to 95% by weight, about 55% to 95% by weight, about 60% to 95% by weight, about 65% to 95% by weight, or about 70% to 95% by weight, relative to the total weight of the mixture. The amount of amorphous carbon may be, for example, about 33% to 92.5% by weight, about 33% to 90% by weight, or about 33% to 87.5% by weight, relative to the total weight of the mixture. The amount and / or type of amorphous carbon that satisfy the conditions of (a) and / or (b) in the negative electrode active material layer can be measured, for example, using the following methods. First, the amount of carbon in the negative electrode active material layer can be measured using a combustion method. Specifically, the amount of carbon in the negative electrode active material layer can be measured by heating a sample of the negative electrode active material layer at a high temperature in an atmosphere of helium mixed with oxygen to quantify the amount of carbon dioxide generated therefrom. Second, the number of different types of amorphous carbon included in the negative electrode active material layer can be determined by evaluating the particle size distribution using a laser scattering method. The particle size and structure of the amorphous carbon can be observed using a transmission electron microscope (TEM). By combining the results of the combustion method and the particle size observation, information about the type of amorphous carbon included in the negative electrode active material layer, the amount of each type of amorphous carbon, and the particle size and structure of each type of amorphous carbon can be obtained, such that the amount of amorphous carbon that satisfies the conditions of (a) and / or (b) in the negative electrode active material layer can be measured. The amount of amorphous carbon that satisfies the conditions of (a) and / or (b) in the negative electrode active material layer of the all-solid-state secondary battery 1 as a final product can also be evaluated from the preparation conditions of the negative electrode active material layer (such as the nitrogen adsorption specific surface area, DBP oil absorption value, the amount of each type of amorphous carbon, and the amount of other negative electrode active materials).

[0085] The negative electrode active material layer may further include a binder. By including a binder, the negative electrode active material layer can be stabilized on the negative electrode current collector. The material of the binder may be, for example, a resin material such as styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), or a combination thereof.

[0086] Since the negative electrode active material layer includes such a binder, the negative electrode active material layer can be stably held on the negative electrode current collector. Additionally, cracking of the negative electrode active material layer can be suppressed despite volume changes and / or relative position changes of the negative electrode active material layer during charging and discharging. For example, when the negative electrode active material layer does not include a binder, the negative electrode active material layer can be easily separated from the negative electrode current collector. The region of the negative electrode current collector from which the negative electrode active material layer is separated can be exposed and thus can come into contact with the solid electrolyte layer, making a short circuit more likely to occur. The negative electrode active material layer can be formed, for example, by applying a slurry in which materials for forming the negative electrode active material layer are dispersed onto the negative electrode current collector and then drying the applied slurry. By including a binder in the negative electrode active material layer, the negative electrode active material can be stably dispersed in the slurry. For example, when the slurry is applied to the negative electrode current collector using a screen printing method, clogging of the screen (e.g., clogging caused by aggregates of the negative electrode active material) can be suppressed.

[0087] The negative electrode active material layer can have a thickness, for example, of 50% or less, about 40% or less, about 30% or less, about 20% or less, about 10% or less, or about 5% or less of the thickness of the positive electrode active material layer. For example, the negative electrode active material layer can have a thickness of about 0.1 μm - about 20 μm, about 0.5 μm - about 20 μm, about 0.5 μm - about 15 μm, about 0.5 μm - about 10 μm, about 1 μm - about 10 μm, or about 1 μm - about 7 μm. When the thickness of the negative electrode active material layer is too small, the negative electrode active material layer can collapse due to lithium dendrites formed between the negative electrode active material layer and the negative electrode current collector, such that the cycle characteristics of the all-solid-state lithium secondary battery may not be improved. When the thickness of the negative electrode active material layer is too large, the all-solid-state lithium secondary battery can have a reduced energy density and can have an increased internal resistance due to the negative electrode active material layer and thus may not have improved cycle characteristics.

[0088] The negative electrode active material layer can further include additives suitable for use in an all-solid-state secondary battery, such as fillers, dispersants, ion conductors, or combinations thereof, the respective amounts of which can be determined by those skilled in the art without undue experimentation.

[0089] The all-solid-state lithium secondary battery 1 may further include a thin film (not shown) on the negative electrode current collector 21, and the thin film includes an element capable of alloying with lithium. The thin film may be provided, for example, between the negative electrode current collector 21 and the negative electrode active material layer 22. For example, the thin film may include an element capable of alloying with lithium. The element capable of alloying with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, or a combination thereof, but is not limited thereto. Any element capable of alloying with lithium may be used. The thin film may be composed of one of these metals or an alloy of these metals. By providing the thin film on the negative electrode current collector 21, for example, the layer of metal deposited between the thin film and the negative electrode active material layer may be flattened, further improving the cycle characteristics of the all-solid-state lithium secondary battery 1.

[0090] For example, the thin film may have a thickness of about 1 nm - about 800 nm, about 10 nm - about 700 nm, about 50 nm - about 600 nm, or about 100 nm - about 500 nm. When the thickness of the thin film is less than 1 nm, the thin film may not function properly. When the thickness of the thin film is too thick, the thin film may absorb lithium, such that the amount of lithium deposition on the negative electrode may be reduced, resulting in deterioration of the energy density and cycle characteristics of the all-solid-state lithium secondary battery. The thin film may be provided on the negative electrode current collector, for example, by lithium deposition, sputtering, or plating. However, the embodiments are not limited to these methods, and any suitable thin film forming method may be used.

[0091] Referring to Figures 2 to 4 , the all-solid-state lithium secondary battery 1 may further include a metal layer 23 provided, for example, between the negative electrode current collector 21 and the solid electrolyte layer 30 by charging. Referring to Figures 2 to 4 , the all-solid-state lithium secondary battery may further include a metal layer 23 provided, for example, between the negative electrode current collector 21 and the negative electrode active material layer 22 by charging. Referring to Figure 3 and 4, the all-solid-state lithium secondary battery 1 may further include a metal layer 23 provided, for example, within the negative electrode active material layer 22 by charging. The metal layer 23 may be composed of or substantially composed of lithium metal or a lithium alloy. Thus, the metal layer 23 may act as, for example, a lithium reservoir. The lithium alloy may be, for example, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, or a combination thereof. However, the embodiments are not limited thereto. Any lithium alloy may be used. The thickness of the metal layer 23 is not particularly limited. For example, the metal layer may have a thickness of about 1 μm - about 1000 μm, about 1 μm - about 500 μm, about 1 μm - about 200 μm, about 1 μm - about 150 μm, about 1 μm - about 100 μm, or about 1 μm - about 50 μm. When the thickness of the metal layer is too small, the metal layer may not be properly used as a lithium reservoir. When the thickness of the metal layer is too large, the mass and volume of the all-solid-state lithium secondary battery may increase disadvantageously, and it is possible that its cycling characteristics may deteriorate.

[0092] In another embodiment, the metal layer may be, for example, a metal foil having a thickness within the above range. In the all-solid-state lithium secondary battery 1, for example, before the assembly of the all-solid-state lithium secondary battery 1, the metal layer 23 may be provided between the negative electrode current collector 21 and the negative electrode active material layer 22. When a lithium metal foil as the metal layer 23 is provided between the negative electrode current collector 21 and the negative electrode active material layer 22 before the assembly of the all-solid-state lithium secondary battery 1, the lithium metal foil may be used as a lithium reservoir.

[0093] (3) Solid electrolyte layer

[0094] The solid electrolyte layer 30 may be provided between the positive electrode 10 and the negative electrode 20, and in particular, between the positive electrode active material layer 12 and the negative electrode active material layer 22. The solid electrolyte layer may include a solid electrolyte capable of transporting ions.

[0095] The solid electrolyte may be composed of or substantially composed of, for example, a solid electrolyte material including sulfides (hereinafter, referred to as a sulfide-based solid electrolyte material). The sulfide-based solid electrolyte material may be, for example, Li 2 S-P 2 S 5 , Li 2 S-P 2 S 5 -LiX (where X is a halogen such as I or Cl), Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3 , Li 2 S-P 2 S 5 -Z m S n (where m and n are each independently positive numbers, and Z is Ge, Zn or Ga), Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li p MO q (where p and q are each independently positive numbers, and M is P, Si, Ge, B, Al, Ga or In). Combinations of at least two of the aforementioned sulfide-based solid electrolyte materials can also be used.

[0096] Among the above sulfide-based solid electrolyte materials, the material composed of sulfur (S), phosphorus (P) and lithium (Li) can be used as a solid electrolyte. For example, a sulfide-based solid electrolyte material including Li 2 S-P 2 S 5 can be used. When using a material including Li 2 S-P 2 S 5 as the sulfide-based solid electrolyte material, the mixed molar ratio of Li 2 S to P 2 S 5 (Li 2 S:P 2 S 5)It can be, for example, in the range of about 50:50 to about 90:10.

[0097] The solid electrolyte can be in an amorphous state or can be in a crystalline state. The solid electrolyte can be in a mixed state of amorphous and crystalline forms.

[0098] Sulfide-based solid electrolyte materials can include, for example, Li 7 P 3 S 11 , Li 7 PS 6 , Li 4 P 2 S 6 , Li 3 PS 6 , Li 3 PS 4 , Li 2 P 2 S 6 , or a combination thereof.

[0099] Sulfide-based solid electrolyte materials can include, for example, argyrodite-type solid electrolytes represented by Formula 1.

[0100] Formula 1

[0101] Li + 12-n-x A n+ X 2- 6-x Y’ - x

[0102] In Formula 1, A can be P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X can be S, Se, or Te; Y can be Cl, Br, I, F, CN, OCN, SCN, or N 3 , 0 ≤ x ≤ 2, and n is the valence of A. In an embodiment, n can be 3, 4, or 5.

[0103] Argyrodite-type solid electrolytes can include, for example, Li 7-x PS 6-x Cl x (where 0 ≤ x ≤ 2), Li 7-x PS 6-x Br x (where 0 ≤ x ≤ 2), Li 7-x PS 6-x I x (where 0 ≤ x ≤ 2), or a combination thereof. For example, argyrodite-type solid electrolytes can include Li 6 PS 5 Cl, Li 6PS 5 Br, Li 6 PS 5 I, or a combination thereof.

[0104] The solid electrolyte may have an elastic modulus, i.e., Young's modulus, of, for example, about 35 GigaPascals (GPa) or less, about 30 GPa or less, about 27 GPa or less, about 25 GPa or less, or about 23 GPa or less. For example, the solid electrolyte may have an elastic modulus, i.e., Young's modulus, of, for example, about 10 - about 35 GPa, about 15 - about 35 GPa, about 15 - about 30 GPa, or about 15 - about 25 GPa. Since the solid electrolyte has an elastic modulus within these ranges, pressing and / or sintering of the solid electrolyte can be more easily performed.

[0105] The solid electrolyte layer may further include a binder. The material of the binder may be, for example, a resin such as styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polyacrylic acid (PAA), or a combination thereof. The material of the binder may be the same as or different from the material of the binder in the positive electrode active material layer 12 and the negative electrode active material layer 22.

[0106] (4) Initial charge capacity ratio

[0107] According to one or more embodiments, the all-solid-state secondary battery 1 according to the embodiment may be configured such that the initial charge capacity of the positive electrode active material layer 12 is greater than the initial charge capacity of the negative electrode active material layer 22. As will be described later, the all-solid-state secondary battery 1 according to the embodiment is charged (i.e., overcharged) until it exceeds the initial charge capacity of the negative electrode active material layer 22. In the initial charging stage, lithium is absorbed into the negative electrode active material layer 22. That is, the negative electrode active material may form an alloy or compound with the lithium ions that have migrated from the positive electrode layer 10. When the all-solid-state secondary battery 1 is charged (i.e., overcharged) beyond the initial charge capacity of the negative electrode active material layer 22, lithium may be deposited on the rear surface of the negative electrode active material layer 22, i.e., between the negative electrode current collector 21 and the negative electrode active material layer 22, thereby forming a metal layer 23, as Figure 2As shown. The metal layer 23 may be composed of lithium (i.e., metallic lithium). Without being limited by theory, it is understood that the formation of the lithium metal layer is attributed to the negative electrode active material composed of a certain material, i.e., a material capable of forming an alloy or compound with lithium. During discharge, lithium in the negative electrode active material layer 22 and the metal layer 23 can be ionized and move toward the positive electrode layer 10. Therefore, in the all-solid-state secondary battery 1, lithium can be used as the negative electrode active material. Since the negative electrode active material layer 22 is provided on the metal layer 23 (e.g., covering the metal layer 23), the negative electrode active material layer 22 can act as a protective layer for the metal layer 23 and at the same time inhibit the deposition and growth of dendritic metallic lithium. This can inhibit short circuits and capacity reduction in the all-solid-state secondary battery 1 and thus further improve the characteristics of the all-solid-state secondary battery. In the case where the metal layer 23 is provided by charging the all-solid-state lithium secondary battery after assembly, for example, in the initial state or fully discharged state of the all-solid-state secondary battery, the negative electrode current collector 21, the negative electrode active material layer 22, and the region therebetween may be regions free of Li, e.g., regions not including Li metal or Li alloy.

[0108] In particular, in the all-solid-state secondary battery 1 according to the embodiment, the ratio of the initial charge capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer, i.e., the initial charge capacity ratio, may satisfy Inequality 1.

[0109] Inequality 1

[0110] 0.01 < b / a < 0.5

[0111] In Inequality 1, a is the initial charge capacity (milliampere-hour, mAh) of the positive electrode active material layer 12, and b is the initial charge capacity (mAh) of the negative electrode active material layer 22.

[0112] The initial charge capacity ratio may be, for example, 0.01 < b / a ≤ 0.45, 0.01 < b / a ≤ 0.4, 0.02 ≤ b / a ≤ 0.3, 0.03 ≤ b / a ≤ 0.2, or 0.05 ≤ b / a ≤ 0.1.

[0113] When the initial charge capacity ratio is 0.01 or less, the characteristics of the all-solid-state secondary battery may deteriorate. Without being limited by theory, it is considered that the deterioration of the battery properties may be caused by the negative electrode active material layer not sufficiently acting as a protective layer. For example, when the thickness of the negative electrode active material layer is too small, the initial charge capacity ratio may be 0.01 or less. In this case, the negative electrode active material layer may collapse through repeated charging and discharging, making it possible for dendritic metallic lithium to deposit and grow. Therefore, the characteristics of the all-solid-state secondary battery may deteriorate. For this reason, the initial charge capacity ratio is limited to be greater than 0.01.

[0114] When the initial charge capacity ratio is 0.5 or greater, the amount of lithium deposition on the negative electrode can be reduced, so that the battery capacity can be decreased. For this reason, the initial charge capacity ratio is limited to less than 0.5.

[0115] Measurement of Initial Charge Capacity

[0116] The initial charge capacity of each of the positive electrode active material layer 12 and the negative electrode active material layer 22 can be calculated using the following method.

[0117] The initial charge capacity of the positive electrode active material layer can be obtained, for example, by multiplying the charge capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode active material layer. When multiple types of positive electrode active materials are used, the initial charge capacity of the positive electrode active material layer can be determined as follows: multiplying the charge capacity density of each positive electrode active material by its mass and calculating the sum of the multiplication values of the positive electrode active materials as the initial charge capacity of the positive electrode active material layer.

[0118] The initial charge capacity of the negative electrode active material layer can be calculated using the same method. That is, the initial charge capacity of the negative electrode active material layer can be obtained, for example, by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the negative electrode active material layer. When multiple types of negative electrode active materials are used, the initial charge capacity of the negative electrode active material layer can be determined as follows: multiplying the charge capacity density of each negative electrode active material by its mass and calculating the sum of the multiplication values of the negative electrode active materials as the initial charge capacity of the negative electrode active material layer.

[0119] The charge capacity density of the positive electrode active material and the negative electrode active material is the capacity evaluated using an all-solid-state half-cell with a lithium metal as the counter electrode.

[0120] The initial charge capacity of the positive electrode active material layer and the negative electrode active material layer can be directly measured using an all-solid-state half-cell. As a specific method for directly measuring the initial charge capacity, the following method can be used.

[0121] First, after manufacturing an all-solid-state half-cell using the positive electrode active material layer as the working electrode and Li as the counter electrode, it is charged by constant current-constant voltage (CC-CV) from the open circuit voltage (OCV) to the upper limit charging voltage to thereby measure the initial charge capacity of the positive electrode active material layer. The upper limit charging voltage defined in the standard of JIS C 8712:2015 is 4.25 V for the positive electrode based on lithium cobalt oxide, and for other positive electrodes, it may refer to the voltage that can be obtained by applying the safety requirements specified in A.3.2.3 of JIS C 8712:2015 (for applying other upper limit charging voltages). The initial charge capacity of the negative electrode active material layer can be measured as follows: an all-solid-state half-cell manufactured using the negative electrode active material layer as the working electrode and Li as the counter electrode is charged by constant current-constant voltage (CC-CV) from the open circuit voltage (OCV) to 0.01 V.

[0122] The above all-solid-state half-cell can be manufactured, for example, using the following method. The positive electrode active material layer or the negative electrode active material layer whose initial charge capacity is to be measured can be punched into a disk form having a diameter of about 13 millimeters (mm). 200 milligrams (mg) of solid electrolyte powder used in an all-solid-state secondary battery can be hardened under a pressure of about 40 megapascals (MPa) to form a disk having a diameter of about 13 mm and a thickness of about 1.5 mm. After placing this disk in a tube having an inner diameter of about 13 mm, the positive electrode active material layer or the negative electrode active material layer punched in the form of a disk can be placed in the tube from one side of the tube, and then a lithium foil having a diameter of about 13 mm and a thickness of 0.03 mm can be inserted into the tube from the opposite side of the tube. In addition, stainless steel disks can be placed in the tube on each side, and then the tube can be pressurized in the axial direction of the tube at a pressure of about 300 MPa or more to 1000 MPa or less for about 1 minute to integrate the components in the tube. When integrating the components, a pressure of about 300 MPa or more can be applied to easily bring the components into close contact. When the applied pressure is 1000 MPa or more, the resulting effect is stagnant. Therefore, the pressure can be about 1000 MPa or less. Then the obtained structure can be sealed in a case where a pressure of 22 MPa is constantly applied, thereby manufacturing an all-solid-state half-cell.

[0123] (5) Structure of all-solid-state secondary battery

[0124] According to one or more embodiments, as Figures 1 to 4As shown, the all-solid-state secondary battery 1 may include 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. The positive electrode 10 may include a positive electrode active material layer 12 and a positive electrode current collector 11, and the negative electrode 20 may include a negative electrode active material layer 22 and a negative electrode current collector 21.

[0125] Referring to Figure 1 , the all-solid-state secondary battery 1 may include, for example, a positive electrode current collector 11, a positive electrode active material layer 12, a solid electrolyte layer 30, a negative electrode active material layer 22 that forms an alloy or compound with lithium, and a negative electrode current collector 21 in the order stated below. The negative electrode active material layer 22 may include amorphous carbon and metal or metalloid negative electrode active material particles. The negative electrode current collector 21 may include, for example, nickel, stainless steel, titanium, iron, cobalt, copper, or a combination thereof.

[0126] Referring to Figure 2 , the all-solid-state secondary battery 1 may include, for example, a positive electrode current collector 11, a positive electrode active material layer 12, a solid electrolyte layer 30, a negative electrode active material layer 22 that forms an alloy or compound with lithium, a metal layer 23, and a negative electrode current collector 21 in the order stated below. The negative electrode active material layer 22 may include amorphous carbon and metal or metalloid negative electrode active material particles. The negative electrode current collector 21 may include, for example, nickel, stainless steel, titanium, iron, cobalt, copper, or a combination thereof.

[0127] Referring to Figures 1 to 2 , the all-solid-state secondary battery 1 may further include a negative electrode current collector 21 stacked on the side of the negative electrode active material layer 22 opposite to the solid electrolyte layer 30, and the negative electrode current collector 21 may be a thin film formed of stainless steel.

[0128] Referring to Figures 1 to 2 , in the all-solid-state secondary battery 1, the positive electrode active material layer 12, the solid electrolyte layer 30, and the negative electrode active material layer 22 may be sealed with a laminated film (not shown).

[0129] 2. Method for manufacturing an all-solid-state secondary battery

[0130] Next, a method for manufacturing the all-solid-state secondary battery 1 according to the above-described embodiment will be described. The all-solid-state secondary battery 1 according to one or more embodiments may be obtained by independently forming the positive electrode 10, the negative electrode 20, and the solid electrolyte layer 30 and then laminating them.

[0131] (1) Formation of the positive electrode layer

[0132] First, starting materials for the positive electrode active material layer, such as a positive electrode active material and a binder, can be added to a non-polar solvent to prepare a slurry (e.g., paste). Next, the prepared slurry can be coated on a previously prepared positive electrode current collector, and then dried to obtain a laminate. Subsequently, the obtained laminate can be pressed using, for example, isostatic pressing to thereby obtain a positive electrode. The pressing can be omitted.

[0133] (2) Formation of the negative electrode layer

[0134] First, starting materials for the negative electrode active material layer, such as a negative electrode active material and a binder, can be added to a polar solvent or a non-polar solvent to prepare a slurry (e.g., paste). Next, the prepared slurry can be coated on a negative electrode current collector, and then dried to obtain a laminate. Subsequently, the obtained laminate can be pressed using, for example, isostatic pressing to thereby form a negative electrode. The pressing can be omitted.

[0135] (3) Formation of the solid electrolyte layer

[0136] The solid electrolyte layer 30 can be formed from a solid electrolyte material prepared from a sulfide-based solid electrolyte material.

[0137] First, starting raw materials (e.g., Li 2 S or P 2 S 5 ) can be subjected to a melt quenching or mechanical milling process to thereby obtain a sulfide-based solid electrolyte material.

[0138] For example, in the case of melt quenching, after mixing a predetermined amount of starting raw materials together and then forming a pellet, the pellet can be subjected to a reaction under vacuum at a predetermined reaction temperature, and then quenched to prepare a sulfide-based solid electrolyte material. Additionally, the reaction temperature of a mixture of Li 2 S and P 2 S 5 can be, for example, about 400 °C - about 1000 °C, or about 800 °C - about 900 °C. The reaction time can be, for example, about 0.1 - 12 hours, or about 1 - 12 hours. Additionally, the quenching temperature of the reaction product can generally be, for example, about 10 °C or lower, or about 0 °C or lower, and the quenching rate can generally be, for example, about 1 degree Celsius per second (°C / s) - about 10,000 °C / s, or about 1 °C / s - about 1000 °C / s.

[0139] In the case of using mechanical grinding, the starting raw materials can react while being stirred using, for example, a ball mill, thereby preparing a sulfide-based solid electrolyte material. There are no particular limitations on the stirring rate and stirring time during mechanical grinding. However, the higher the stirring rate, the faster the production rate of the sulfide-based solid electrolyte material can become. The longer the stirring time, the greater the conversion rate of the raw materials into the sulfide-based solid electrolyte material.

[0140] Then, the obtained mixed raw materials (sulfide-based solid electrolyte material) can be heat-treated at a predetermined temperature and then subjected to milling to thereby prepare a solid electrolyte in the form of particles. When the solid electrolyte has a glass transition temperature, the solid electrolyte can be transformed from an amorphous phase to a crystalline phase by heat treatment.

[0141] Subsequently, the solid electrolyte material obtained by the above method can be subjected to film formation using an existing film formation method such as aerosol deposition, cold spraying, or sputtering, thereby forming a solid electrolyte layer 30. The solid electrolyte layer 30 can be formed by pressing only the solid electrolyte material particles. The solid electrolyte layer 30 can be formed by mixing the solid electrolyte material, a solvent, and a binder together to obtain a mixture, coating the mixture, and drying and pressing the resulting product.

[0142] (4) Lamination

[0143] The solid electrolyte layer 30 can be disposed between the positive electrode 10 and the negative electrode 20 and then pressed using, for example, isostatic pressing, thereby obtaining the all-solid-state secondary battery 1 according to the embodiment.

[0144] For example, the method of manufacturing an all-solid-state secondary battery can further include pressing a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer stacked in the order described below by isostatic pressing.

[0145] The pressing can be carried out, for example, at a temperature from room temperature (about 20 - 22 °C) to 90 °C or less, or at a temperature from about 20 °C to about 90 °C. In another embodiment, the pressing can be carried out at a high temperature of 100 °C or more. The pressing time can be, for example, about 30 minutes or shorter, about 20 minutes or shorter, about 15 minutes or shorter, or about 10 minutes or shorter. The pressing time can be, for example, about 1 millisecond (ms) - about 30 minutes, about 1 ms - about 20 minutes, about 1 ms - about 15 minutes, or about 1 ms - about 10 minutes. The pressing can be carried out using, for example, isostatic pressing, roll pressing, or flat pressing. However, the embodiments are not limited thereto. Any suitable pressing method can be used. The pressure applied during pressing can be, for example, about 300 MPa or more, about 350 MPa or more, about 400 MPa or more, about 450 MPa or more, about 500 MPa or more, or about 550 MPa or more. For example, the pressure applied during pressing can be about 300 MPa - about 1000 MPa, about 350 MPa - about 950 MPa, about 400 MPa - about 900 MPa, about 450 MPa - about 850 MPa, about 500 MPa - about 800 MPa, or about 550 MPa - about 750 MPa. By pressing under such conditions, for example, the solid electrolyte particles can be sintered to thereby form a solid electrolyte layer.

[0146] When charging and / or discharging the all-solid-state secondary battery manufactured using the above method, the all-solid-state secondary battery can operate under pressure. The pressure can be about 0.5 MPa or more, about 5 MPa or more, or about 10 MPa or more. The pressure can be applied by, for example, a method including: placing the all-solid-state lithium secondary battery between two rigid plates, and then fixing the all-solid-state lithium secondary battery between the two plates with screws.

[0147] The two plates can be high-hardness plates having a Mohs hardness scale of, for example, 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, or 5.0 or more. For example, the Mohs hardness scale of stainless steel is 5.5 - 6.3, the Mohs hardness scale of aluminum is 2 - 2.4, the Mohs hardness scale of brass is 3.0, and the Mohs hardness scale of glass is 5.5. For example, the plates can have a Mohs hardness of about 1.5 - about 6.3. For example, the rigid plates can be formed of materials such as stainless steel, brass, aluminum, glass, or a combination thereof.

[0148] In a all-solid-state lithium secondary battery according to one or more embodiments, as the charging and discharging of the all-solid-state lithium secondary battery are repeated, for example, due to the dissolution by ionization of the precipitated metallic lithium, pores may be formed at the interface between the metal layer and the negative electrode active material layer. In order to suppress the formation of the pores and the corresponding reduction in battery output, the pressure may be maintained at, for example, about 0.5 MPa or greater. When the pressure is too high, short circuit of the battery may occur. Therefore, the pressure may be, for example, 10 MPa or less.

[0149] 3. Method for charging an all-solid-state secondary battery

[0150] Now, a method for charging the all-solid-state secondary battery 1 will be described.

[0151] In one or more embodiments, the method for charging the all-solid-state secondary battery 1 is characterized in that the all-solid-state secondary battery 1 can be charged (i.e., overcharged) until it exceeds the initial charge capacity of the negative electrode active material layer 22.

[0152] In the initial charging stage, lithium can be absorbed into the negative electrode active material layer 22. When the all-solid-state secondary battery 1 is charged beyond the initial charge capacity of the negative electrode active material layer 22, as Figure 2 shown, lithium can be deposited on the rear surface of the negative electrode active material layer 22, that is, between the negative electrode current collector 21 and the negative electrode active material layer 22, thereby forming a lithium metal layer 23 that did not exist during the assembly of the all-solid-state lithium secondary battery 1. During discharging, the lithium in the negative electrode active material layer 22 and the metal layer 23 can be ionized and move toward the positive electrode layer 10. Therefore, in the all-solid-state secondary battery 1, lithium can be used as the negative electrode active material. In addition, since the negative electrode active material layer 22 covers the metal layer 23, the negative electrode active material layer 22 can function as a protective layer for the metal layer 23 and at the same time suppress the deposition and growth of lithium metal dendrites. Therefore, short circuit and capacity reduction of the all-solid-state secondary battery can be suppressed, and in addition, the characteristics of the all-solid-state secondary battery can be improved. Further, according to such an embodiment, since the metal layer is not pre-formed before the initial charging, the manufacturing cost of the all-solid-state secondary battery can be reduced.

[0153] When the charged amount of the all-solid-state secondary battery is less than twice the initial charge capacity of the negative electrode active material layer, the amount of lithium deposited on the negative electrode layer can be reduced, and the battery capacity can be reduced. For this reason, the charged amount of the all-solid-state secondary battery may be at least twice the initial charge capacity of the negative electrode active material layer.

[0154] When the charge amount of the all-solid-state secondary battery exceeds 100 times the initial charge capacity of the negative electrode active material layer 22, the thickness of the negative electrode layer 20 may become insufficient, and the negative electrode layer 20 may collapse through repeated charge and discharge cycles, thereby causing dendrite deposition and growth. For this reason, the charge amount of the all-solid-state secondary battery may be about 100 times or less the initial charge capacity of the negative electrode active material layer.

[0155] As Figure 2 shown, the metal layer 23 may be provided between the negative electrode current collector 21 and the negative electrode active material layer 22. However, the embodiment is not limited thereto. For example, as Figure 3 shown, the metal layer 23 may be formed within the negative electrode active material layer 22. For example, as Figure 4 shown, the metal layer 23 may be formed both between the negative electrode current collector 21 and the negative electrode active material layer 22 and within the negative electrode active material layer 22.

[0156] By charging the all-solid-state secondary battery, lithium can be deposited between the negative electrode current collector and the negative electrode active material layer or in a layer formed within the negative electrode active material layer, thereby suppressing the formation of voids in the all-solid-state secondary battery caused by charging and discharging. This can suppress an increase in pressure in the all-solid-state secondary battery caused by charging and discharging compared to when the deposition of lithium in the form of a layer does not occur.

[0157] As described above, since the negative electrode active material layer includes a negative electrode active material containing amorphous carbon and a metal or metalloid such as gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof, when the all-solid-state secondary battery is overcharged, the deposition of lithium on the surface of the negative electrode active material layer adjacent to the solid electrolyte layer can be suppressed. As a result, the deposition and growth of dendritic metallic lithium can be suppressed. Therefore, the short circuit and capacity reduction of the all-solid-state secondary battery can be suppressed, and thus the characteristics of the all-solid-state secondary battery can be improved.

[0158] Examples

[0159] One or more embodiments of the present disclosure will now be described in detail with reference to the following examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of one or more embodiments of the present disclosure.

[0160] Example 1

[0161] 1. Fabrication of Samples

[0162] First, all-solid-state secondary battery samples (Numbers 1-12) including amorphous carbon as the negative electrode active material were fabricated according to the following procedure. The all-solid-state secondary battery samples were fabricated to have the same structure except for using different types of amorphous carbon in the negative electrode active material layer.

[0163] (1) Formation of the positive electrode layer

[0164] Prepare LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) as the positive electrode active material. The prepared positive electrode active material is used in the method disclosed in Non-Patent Document 1 indicated above (i.e., Naoki Suzuku et al., Synthesis and Electrochemical Properties of Li 1+2x Zn 1–x PS 4 Solid Electrolyte”, Chemistry of Materials, No. 30, 2236 - 2244, 2018) and coated with Li 2 O-ZrO 2 and incorporated herein by reference. Prepare the argyrodite-type crystal Li 6 PS 5 Cl as the solid electrolyte. Prepare polytetrafluoroethylene (PTFE) binder (Teflon TM binder, available from DuPont). Prepare carbon nanofibers (CNF) as the conductive agent. Then, the prepared positive electrode active material, solid electrolyte, conductive agent, and binder are mixed together at a weight ratio of approximately 88:12:2:1 to obtain a mixture. The mixture is elongated into a sheet form to thereby form a positive electrode active material sheet. The positive electrode active material sheet is formed into a size of approximately 1.7 cm 2 and then pressed onto a positive electrode current collector made of aluminum foil having a thickness of approximately 18 μm to thereby fabricate the positive electrode layer.

[0165] (2) Formation of the negative electrode layer

[0166] The negative electrode layer including silver (Ag) particles and amorphous carbon as the negative electrode active material is formed using the following method.

[0167] First, 2 g of amorphous carbon (carbon black) and 2 g of silver (Ag) particles with an average particle size of about 60 nm (denoted as "Ag" in Table 1) were placed in a container, and 5.1 g of an N-methylpyrrolidone (NMP) solution containing 7.8 wt% of a binder (#9300, available from KUREHA) was added thereto. Then, the mixed solution was stirred while gradually adding NMP to prepare a slurry. The prepared slurry was coated on a negative electrode current collector formed of a SUS304 thin film with a thickness of about 10 μm using a doctor blade coater, and then dried in air at about 80 °C for about 20 minutes, and further dried in vacuo at about 100 °C for about 12 hours to thereby form a laminate. The formed laminate was punched into a size (area) of about 2 square centimeters (cm 2 ), to thereby fabricate a negative electrode layer. The negative electrode layer has protrusions that serve as terminals of the negative electrode. This will be described later. By using such a method, a negative electrode layer for use in Samples 1-12 was fabricated.

[0168] Amorphous carbon having a nitrogen adsorption specific surface area and DBP oil absorption value as shown in Table 1 was used to form the negative electrode layers for Samples 1-12. The amorphous carbon used to form the negative electrode layers for Samples 1-10 was furnace black ("FB" in Table 1). The amorphous carbons used to form the negative electrode layers for Samples 11 and 12 were acetylene black ("AB" in Table 1) and Ketjen black ("KB" in Table 1), respectively. Each negative electrode layer was fabricated such that the amorphous carbon in the negative electrode active material layer had a nitrogen adsorption specific surface area, DBP oil absorption value, and amorphous carbon content as shown in Table 1. In the fabricated all-solid-state secondary battery samples, it was confirmed that the nitrogen adsorption specific surface area and DBP oil absorption value of the amorphous carbon in each negative electrode active material layer had the values shown in Table 1. Each negative electrode layer for Samples 1-12 was fabricated such that the amorphous carbon content in each negative electrode active material layer reached the value shown in Table 1.

[0169] (3) Formation of the solid electrolyte layer

[0170] To the above Li 6 PS 5 Cl solid electrolyte, 1 wt% of a rubber-based binder (A334, available from ZEON) relative to the mass of the solid electrolyte was added. Then, xylene and diethylbenzene were added to the mixture while stirring to thereby prepare a slurry. The prepared slurry was coated on a nonwoven fabric using a doctor blade coater, and then dried in air at about 40 °C. The obtained laminate was vacuum dried at about 40 °C for about 12 hours. The dried laminate was punched to reach an area of about 2.2 cm 2 , to thereby fabricate a solid electrolyte layer.

[0171] (4) Fabrication of All-Solid-State Secondary Batteries

[0172] Stack the positive electrode layer, solid electrolyte layer, and negative electrode layer formed as described above on top of each other in the stated order, and then seal them with a laminate film under vacuum to thereby fabricate all-solid-state secondary batteries. Fabricate all-solid-state secondary battery samples numbered 1 - 12 in this manner. Let portions of the positive electrode current collector and negative electrode current collector protrude from the laminate film without breaking the vacuum of the battery. The protruding portions serve as terminals for the positive electrode layer and negative electrode layer. Then, subject each all-solid-state secondary battery to isostatic pressing at about 490 MPa for 30 minutes. Then, place the all-solid-state secondary battery between two stainless steel plates (sheets), the two stainless steel plates (sheets) being placed on opposite sides of the all-solid-state secondary battery in the stacking direction, each having a thickness of about 1 centimeter (cm). Specifically, the two stainless steel plates each have four holes at the same positions, and place the all-solid-state secondary battery within the rectangular space defined by the four holes in each plate. In this state, pass four bolts through the four holes in each of the two stainless steel plates from the outside of the two stainless steel plates. Subsequently, fasten the four bolts with nuts respectively, as if pressing the two stainless steel plates from the outside, such that a pressure of about 4 MPa is applied to the all-solid-state secondary battery.

[0173] 2. Initial Charge Capacity

[0174] Measure the initial charge capacity (mAh) of the positive electrode active material layer and the initial charge capacity (mAh) of the negative electrode active material layer of each of the all-solid-state secondary battery samples numbered 1 - 12 by the following method.

[0175] Specifically, fabricate all-solid-state half-cell batteries using the method described above. Then, use the positive electrode active material layer of each cell battery as the working electrode and Li as the counter electrode for CC-CV charging, from the open circuit voltage (OCV) to the upper limit charging voltage (specifically, 4.25 V), to thereby measure the initial charge capacity of the positive electrode active material layer. Fabricate all-solid-state half-cell batteries using the negative electrode active material layer as the working electrode and Li as the counter electrode, and then subject them to CC-CV charging from the open circuit voltage (OCV) to 0.01 V, to thereby measure the initial charge capacity of the negative electrode active material layer. The initial charge capacities of the positive electrode active material layer and negative electrode active material layer in each of the measured samples, and their initial charge capacity ratios are shown in Table 1.

[0176] 3. Characteristic Evaluation

[0177] Conduct charge-discharge cycle tests on each of the all-solid-state secondary battery samples numbered 1 - 12 to evaluate their characteristics.

[0178] (1) Charge-Discharge Cycle Test

[0179] The charge-discharge cycle tests of each all-solid-state secondary battery were carried out in a constant temperature bath at 60 °C. In the first cycle, each all-solid-state secondary battery was charged with a constant current of 0.5 mA / cm 2 until the battery voltage reached 4.25 V, and then charged with a constant voltage of 4.25 V until the current reached 0.2 mA. Thereafter, the all-solid-state secondary battery was discharged with a constant current of 0.5 milliamperes per square centimeter (mA / cm 2 ) until the battery voltage reached 2.5 V. In the second and third cycles, each all-solid-state secondary battery was charged under the same conditions as in the first cycle, and then discharged with a constant current of 1.67 mA / cm 2 and 5.0 mA / cm 2 until the battery voltage reached 2.5 V. After the fourth cycle, charging and discharging were carried out at a constant current of 0.5 mA / cm 2 , and this was repeated for 105 cycles or more to thereby evaluate the battery characteristics of each sample.

[0180] (2) Cycle characteristics

[0181] The cycle characteristics of each all-solid-state secondary battery were evaluated using the capacity retention obtained through the charge-discharge cycle test. Specifically, the ratio of the discharge capacity (mAh) at the 105th cycle in the charge-discharge cycle test to the discharge capacity (mAh) at the fifth cycle was defined as the "capacity retention (%)" of the all-solid-state secondary battery. Samples with a capacity retention of 88% or more were evaluated as having "excellent cycle characteristics". The evaluation results of the capacity retention of the samples are shown in Table 1.

[0182] (3) Discharge rate characteristics

[0183] The discharge rate characteristics of each all-solid-state secondary battery were evaluated by the discharge capacity ratio obtained from the charge-discharge cycle test. Specifically, the ratio of the discharge capacity (mAh) at the third cycle in the charge-discharge cycle test to the discharge capacity at the second cycle was defined as the "discharge capacity ratio (%)" of the all-solid-state secondary battery. Samples with a discharge capacity ratio of 92% or more were evaluated as having "excellent discharge rate characteristics". The evaluation results of the discharge capacity ratio of the samples are shown in Table 1.

[0184]

[0185] 4. Evaluation

[0186] As shown in Table 1, Samples No. 1, 2, 4 - 7, and 10 - 12 meet the requirements of the present invention, that is, they contain 33% by weight or more of the total mass of the negative electrode active material that satisfies (a) greater than 0 m2 / g and 100 m 2 / g or less nitrogen adsorption specific surface area, and / or (b) an all-solid-state secondary battery according to an embodiment of amorphous carbon having a DBP oil absorption value of 150 mL / 100 g or more. It was found that all of the all-solid-state secondary battery samples had a capacity retention of 88% or more, a discharge capacity ratio of 92% or more, and excellent cycle characteristics and discharge rate characteristics. It was found that compared with Sample No. 10 having a nitrogen adsorption specific surface area of less than 30 m 2 / g, each of Samples No. 1, 4, 5, 7, and 11 including 33 wt% or more of amorphous carbon having a nitrogen adsorption specific surface area of 30 m 2 / g or more and 100 m 2 / g or less had a higher discharge capacity ratio and improved discharge rate characteristics. Compared with Sample No. 4 having a DBP oil absorption value of more than 200 mL / 100 g, Samples No. 1, 2, and 6 having a DBP oil absorption value of 150 mL / 100 g or more and 200 mL / 100 g or less had both a greater capacity retention and a discharge capacity ratio. These results indicate that when including the same type of amorphous carbon, by including amorphous carbon having a DBP oil absorption value of 200 mL / 100 g or less, the cycle characteristics and discharge rate characteristics can be further improved.

[0187] Samples No. 3, 8, and 9 were all-solid-state secondary batteries as comparative examples and did not satisfy some requirements (nitrogen adsorption specific surface area and DBP oil absorption value) defined by the inventive concept. It was found that these samples were poor in at least one of the cycle characteristics or discharge rate characteristics.

[0188] Samples No. 3, 8, and 9 each had a nitrogen adsorption specific surface area of more than 100 m 2 / g and at the same time had a DBP oil absorption value of less than 150 mL / 100 g and had poor cycle characteristics. Without being limited by theory, it is considered that the reason for such poor cycle characteristics may be that due to small particle size and small aggregates, lithium needs to diffuse into the negative electrode layer through multiple (multiple) grain boundaries and interfaces of aggregates. In other words, it is considered that during discharge, it is difficult for lithium to reach the interface between the active material and the solid electrolyte, and thus the amount of lithium isolated in the negative electrode layer increases.

[0189] Example 2

[0190] In Example 2, all-solid-state secondary battery samples Nos. 13 - 18 in which the amount of amorphous carbon in the negative electrode active material layer was changed were manufactured according to the following procedure.

[0191] Specifically, an amorphous carbon (furnace black, FB) and silver (Ag) particles (having an average particle size of about 60 nm) presenting a nitrogen adsorption specific surface area and DBP oil absorption value as shown in Table 2 are prepared as the negative electrode active material. The amorphous carbon and Ag particles are mixed such that the amount of the amorphous carbon relative to the total mass of the negative electrode active material in the negative electrode active material layer is as shown in Table 2, and the negative electrode layer is manufactured in the same manner as in Example 1.

[0192] In the same manner as in Example 1, a positive electrode layer and a solid electrolyte layer are manufactured, and then stacked with the negative electrode layer to thereby manufacture all-solid-state secondary battery samples Nos. 13 - 18. The various battery characteristics of the manufactured samples are evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0193]

[0194] As shown in Table 2, samples Nos. 13 - 18 satisfy the requirements for the present invention, that is, an all-solid-state secondary battery according to an embodiment containing an amorphous carbon having a nitrogen adsorption specific surface area satisfying (a) greater than 0 m 2 / g and 100 m 2 / g or less and a DBP oil absorption value of 150 mL / 100 g or more in an amount of 33% by weight or more relative to the total mass of the negative electrode active material. It is found that all-solid-state secondary battery samples Nos. 14 - 18 all have a capacity retention of 88% or more, a discharge capacity ratio of 92% or more, and excellent cycle characteristics and discharge rate characteristics. Considering the results of samples Nos. 13 - 18, the amount of the amorphous carbon can be about 33% by weight or more to 95% by weight or less relative to the total mass of the negative electrode active material, and for example, can be about 33% by weight or more to 87.5% by weight or less relative to the total mass of the negative electrode active material.

[0195] Example 3

[0196] In Example 3, all-solid-state secondary battery samples Nos. 19 and 20 including an amorphous carbon as the negative electrode active material layer are manufactured according to the following procedure.

[0197] Specifically, an amorphous carbon (Ketjen black, KB) and platinum (Pt) particles (having an average particle size of about 1 μm) presenting a nitrogen adsorption specific surface area and DBP oil absorption value as shown in Table 3 are prepared as the negative electrode active material. The amorphous carbon and Pt particles are mixed such that the amount of the amorphous carbon relative to the total mass of the negative electrode active material in the negative electrode active material layer is as shown in Table 3, and the negative electrode layer is manufactured in the same manner as in Example 1.

[0198] In the same manner as in Example 1, a positive electrode layer and a solid electrolyte layer were fabricated and then stacked with the negative electrode layer to thereby fabricate all-solid-state secondary battery samples Nos. 19 and 20. The fabricated samples were evaluated for various battery characteristics in the same manner as in Example 1. The results are shown in Table 3.

[0199]

[0200] As shown in Table 3, samples Nos. 19 and 20 satisfy the requirements for the present invention, that is, an all-solid-state secondary battery according to an embodiment containing amorphous carbon having at least one of (a) a nitrogen adsorption specific surface area greater than 0 m 2 / g and 100 m 2 / g or less and (b) a DBP oil absorption value of 150 mL / 100 g or more, based on the total mass of the negative electrode active material. It was found that all of the all-solid-state secondary battery samples had a capacity retention of 88% or more, a discharge capacity ratio of 92% or more, and excellent cycle characteristics and discharge rate characteristics. From these results, it was confirmed that the advantages of the inventive concept can be obtained by using a mixture of amorphous carbon and platinum as the negative electrode active material.

[0201] As described above, according to one or more embodiments, there are provided an all-solid-state secondary battery excellent in both cycle characteristics and discharge rate characteristics and a method of charging the all-solid-state secondary battery.

Claims

1. All-solid-state lithium secondary battery, comprising: a positive electrode including a positive electrode active material layer; a solid electrolyte; and a negative electrode including a negative electrode active material layer that forms an alloy or compound with lithium, wherein the solid electrolyte is between the positive electrode and the negative electrode, wherein the negative electrode active material layer comprises 33% to 95% by weight of amorphous carbon, relative to the total mass of the negative electrode active materials in the negative electrode active material layer, wherein the amorphous carbon has a dibutyl phthalate oil absorption value of 150 mL / 100 g - 200 mL / 100 g, or a combination of a nitrogen adsorption specific surface area of 20 m² / g - 100 m² / g and a dibutyl phthalate oil absorption value of 150 mL / 100 g - 200 mL / 100 g, and wherein the ratio of the initial charge capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer satisfies Inequality 1, Inequality 1 0.01 < b / a < 0.5 wherein a is the initial charge capacity of the positive electrode active material layer and b is the initial charge capacity of the negative electrode active material layer.

2. The all-solid-state lithium secondary battery according to claim 1, wherein the amorphous carbon has a nitrogen adsorption specific surface area of 30 m² / g - 100 m² / g.

3. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode active material layer further comprises gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof.

4. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode active material layer comprises 33% to 87.5% by weight of the amorphous carbon, relative to the total mass of the negative electrode active material.

5. The all-solid-state lithium secondary battery according to claim 1, wherein the amorphous carbon is carbon black.

6. The all-solid-state lithium secondary battery according to claim 5, wherein the carbon black is furnace black, acetylene black, Ketjen black, or a combination thereof.

7. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode further comprises a binder.

8. The all-solid-state lithium secondary battery according to claim 1, wherein the thickness of the negative electrode active material layer is 50% or less of the thickness of the positive electrode active material layer, and wherein the thickness of the negative electrode active material layer is 0.1 µm - 20 µm.

9. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode further comprises a negative electrode current collector and a film on the negative electrode current collector, wherein the film comprises an element capable of alloying with lithium, and the film is disposed between the negative electrode current collector and the negative electrode active material layer.

10. The all-solid-state lithium secondary battery according to claim 9, wherein the film has a thickness of 1 nm - 800 nm.

11. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode further comprises a negative electrode current collector and a metal layer, wherein the metal layer is disposed between the negative electrode current collector and the solid electrolyte, and wherein the metal layer comprises lithium metal.

12. The all-solid-state lithium secondary battery according to claim 11, wherein the metal layer is disposed between the negative electrode current collector and the negative electrode active material layer, or is disposed within the negative electrode active material layer.

13. The all-solid-state lithium secondary battery according to claim 1, wherein the negative electrode further includes a negative electrode current collector, and in the initial state or fully discharged state of the all-solid-state lithium secondary battery, the negative electrode current collector, the negative electrode active material layer, and the region between the negative electrode current collector and the solid electrolyte do not include lithium metal or lithium alloy.

14. The all-solid-state lithium secondary battery according to claim 1, wherein the solid electrolyte includes a sulfide solid electrolyte.

15. The all-solid-state lithium secondary battery according to claim 14, wherein the sulfide solid electrolyte comprises Li 2 S-P 2 S 5 , where X is a halogen, Li 2 S-P 2 S 5 -LiX, Li 2 S-P 2 S 5 -Li 2 O, Li 2 S-P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3 , where m and n are each independently positive numbers and Z is Ge, Zn or Ga, Li 2 S-P 2 S 5 -Z m S n , Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , where p and q are each independently positive numbers and M is P, Si, Ge, B, Al, Ga or In, Li 2 S-SiS 2 -Li p MO q , or a combination thereof.

16. The all-solid-state lithium secondary battery according to claim 14, wherein the sulfide solid electrolyte comprises Li 7 P 3 S 11 、Li 7 PS 6 、Li 4 P 2 S 6 、Li 3 PS 6 、Li 3 PS 4 、Li 2 P 2 S 6 、or a combination thereof.

17. The all-solid-state lithium secondary battery according to claim 14, wherein the sulfide solid electrolyte includes a thiogermanate-type solid electrolyte represented by Formula 1: Formula 1 Li + 12-n-x A n+ X 2- 6-x Y’ - x wherein, in Formula 1, 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 N 3 , n is the valence of A, and 0≤x≤2。 18. The all-solid-state lithium secondary battery according to claim 17, wherein the argyrodite-type solid electrolyte comprises Li where 0 ≤ x ≤ 2 7-x PS 6-x Cl x , Li where 0 ≤ x ≤ 2 7-x PS 6-x Br x , Li where 0 ≤ x ≤ 2 7-x PS 6-x I x , or a combination thereof.

19. The all-solid-state lithium secondary battery according to claim 1, wherein the solid electrolyte has an elastic modulus of 15 GPa - 35 GPa.

20. The all-solid-state lithium secondary battery according to claim 1, wherein the positive electrode further includes a positive electrode current collector and the negative electrode further includes a negative electrode current collector, wherein the positive electrode current collector, the positive electrode active material layer, the solid electrolyte, the negative electrode active material layer, and the negative electrode current collector are arranged in the stated order, and the negative electrode active material layer includes a metal, a metalloid, or a combination thereof and the amorphous carbon.

21. The all-solid-state lithium secondary battery according to claim 20, wherein the negative electrode current collector includes nickel, stainless steel, titanium, iron, cobalt, copper, or a combination thereof.

22. The all-solid-state lithium secondary battery according to claim 1, which further includes a negative electrode current collector disposed on the side of the negative electrode active material layer opposite to the solid electrolyte, wherein the negative electrode current collector is a film including stainless steel.

23. The all-solid-state lithium secondary battery according to claim 1, which further includes a positive electrode current collector, a negative electrode current collector, and a metal layer, wherein the positive electrode current collector, the positive electrode active material layer, the solid electrolyte, the negative electrode active material layer, the metal layer, and the negative electrode current collector are arranged in the stated order, wherein the negative electrode active material layer includes a metal, a metalloid, or a combination thereof and the amorphous carbon as the negative electrode active material, and the metal layer includes lithium metal.

24. The all-solid-state lithium secondary battery according to claim 1, wherein the positive electrode, the solid electrolyte, and the negative electrode are sealed in a laminated film.

25. A method for manufacturing the all-solid-state lithium secondary battery according to any one of claims 1 - 24, the method comprising: providing a solid electrolyte between a positive electrode and a negative electrode; and pressing the positive electrode, the solid electrolyte, and the negative electrode to manufacture the all-solid-state lithium secondary battery.

26. The method according to claim 25, wherein the pressing is isostatic pressing under a pressure of 300 MPa - 1000 MPa.

27. A method of using a all-solid-state lithium secondary battery according to any one of claims 1-24, the method comprising: while applying pressure to the all-solid-state lithium secondary battery between two plates, charging and discharging the all-solid-state lithium secondary battery.

28. The method according to claim 27, wherein the applying pressure includes applying a pressure of 0.5 MPa - 10 MPa.

29. A method of charging an all-solid-state lithium secondary battery, the method comprising: charging an all-solid-state lithium secondary battery according to any one of claims 1-24 such that the charge amount of the all-solid-state secondary battery exceeds the initial charge capacity of the negative electrode active material layer.

30. The method according to claim 29, wherein the charge amount is two to 100 times the initial charge capacity of the negative electrode active material layer.

31. An all-solid-state lithium secondary battery, comprising: a positive electrode including a positive electrode active material layer; a negative electrode including a negative electrode active material layer, a solid electrolyte between the positive electrode and the negative electrode and including a argyrodite-type solid electrolyte represented by Formula 1, Formula 1 Li + 12-n-x A n+ X 2- 6-x Y’ - x wherein, in Formula 1, 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 N 3 , n is the valence of A, 0≤x≤2, and wherein the negative electrode active material layer includes a negative electrode active material, the negative electrode active material including a metal, a metalloid, or a combination thereof and amorphous carbon, wherein the amorphous carbon is present in an amount of 33 wt% - 95 wt% based on the total mass of the negative electrode active material in the negative electrode active material layer, wherein the metal, the metalloid, or the combination thereof is gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, indium, zinc, or a combination thereof, wherein the amorphous carbon has a dibutyl phthalate oil absorption value of 150 ml / 100 g - 200 ml / 100 g, or a combination of a nitrogen adsorption specific surface area of 20 m² / g - 100 m² / g and a dibutyl phthalate oil absorption value of 150 ml / 100 g - 200 ml / 100 g, and wherein the ratio of the initial charge capacity of the positive electrode active material layer to the initial charge capacity of the negative electrode active material layer satisfies Inequality 1 Inequality 1 0.01 < b / a < 0.5 wherein a is the initial charge capacity of the positive electrode active material layer and b is the initial charge capacity of the negative electrode active material layer.

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