A negative electrode and lithium-ion secondary battery including the negative electrode

Abstract

The present invention provides a lithium-ion secondary battery comprising a current collector and an active material layer, wherein the active material layer comprises a negative electrode containing carbon material particles and metal oxide particles, and the negative electrode.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0182949 filed on December 23, 2022 and Korean Patent Application No. 10-2023-0186046 filed on December 19, 2023, and includes all the contents disclosed in the documents of the Korean patent applications as part of this specification.

[0002] The present invention relates to a negative electrode and a lithium-ion secondary battery including the negative electrode.

Background Art

[0003] Recently, all-solid-state secondary batteries using a solid electrolyte as an electrolyte have been attracting attention. In order to improve the energy density of such all-solid-state secondary batteries, it has been proposed to use lithium as a negative electrode active material. The capacity density of lithium (capacity per unit weight) is about 10 times that of graphite generally used as a negative electrode active material. Therefore, when lithium is used as a negative electrode active material, the output can be increased while thinning the all-solid-state secondary battery.

[0004] As an all-solid-state lithium-ion secondary battery, for example, an anodeless lithium-ion secondary battery including a negative electrode active material layer containing a metal that forms an alloy with lithium and a carbon material is known.

[0005] The anodeless lithium-ion secondary battery as described above is driven by a mechanism in which metallic lithium is deposited between the negative electrode active material layer and the current collector during charging, and the metallic lithium is ionized and moves to the positive electrode side during discharging.

[0006] The negative electrode active material layer is formed of a carbon material and a metal material such as Ag, and the development of various materials is required to improve the driving characteristics, life characteristics, etc. of the battery.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Republic of Korea Patent Publication No. 10-2015-0064697 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] An object of the present invention is to provide a negative electrode capable of improving the driving characteristics and life characteristics of a battery and a lithium-ion secondary battery including the same. [Means for Solving the Problems]

[0009] To achieve the above object, the present invention provides a negative electrode including a current collector and an active material layer, the active material layer including carbon material particles and metal oxide particles.

[0010] The present invention also provides a lithium-ion secondary battery including the negative electrode; a positive electrode; and an electrolyte interposed between the negative electrode and the positive electrode. [Effects of the Invention]

[0011] The negative electrode of the present invention includes a negative electrode active material layer in a form in which carbon material particles and metal oxide particles are mixed, thereby providing an effect of improving the driving characteristics and life characteristics of the battery.

[0012] The lithium-ion secondary battery of the present invention includes the negative electrode active material layer, thereby providing excellent driving characteristics and life characteristics. [Brief Description of the Drawings]

[0013] [Figure 1] It is a cross-sectional view schematically showing the structure of the lithium-ion secondary battery of the present invention. [Figure 2] It is a cross-sectional view schematically showing the structure of the lithium-ion secondary battery of the present invention. [Modes for Carrying Out the Invention]

[0014] The present invention will be described in more detail below to aid in understanding the present invention.

[0015] The terms and words used herein and in the claims shall not be interpreted in a manner that is consistent with the technical spirit of the invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Furthermore, the terms used herein are used solely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0016] When one element of a crime is described as being "connected, provided with, or provided for" another element, it should be understood that it may be directly connected to or provided for the other element, but other elements may also exist in between. On the other hand, when one element of a crime is described as being "directly connected to or provided for" another element, it should be understood that no other elements exist in between. Similarly, other expressions describing the relationship between elements, such as "on top of" and "directly on top of," or "between" and "immediately between," or "adjacent to" and "directly adjacent to," should be interpreted in the same way.

[0017] In this specification, the term “combination” includes mixtures, alloys, reaction products, etc., unless otherwise specified.

[0018] The negative electrode of the present invention comprises a current collector and an active material layer, wherein the active material layer comprises carbon material particles and metal oxide particles.

[0019] In one embodiment of the present invention, the metal oxide particles may be included in an amount of 10 to 50 parts by weight, preferably 12 to 25 parts by weight, and more preferably 15 to 25 parts by weight, based on a total weight of 100 parts by weight of carbon material particles and metal oxide particles.

[0020] As mentioned above, if the amount of metal oxide is less than 10 parts by weight, it is not sufficient to form an alloy with lithium, and therefore the advantage of lowering the alloying activation energy by adding metal oxide cannot be realized. If it exceeds 50 parts by weight, the storage capacity of lithium decreases, leading to problems such as a general decrease in capacity and a deterioration in high-rate discharge characteristics, which is undesirable.

[0021] In one embodiment of the present invention, the ratio of the particle size of the carbon material particles (D50) to the particle size of the metal oxide particles (D50) may be 1:0.03 to 1.5, 1:0.1 to 0.7, or 1:0.2 to 0.7. If the ratio of the particle size of the metal oxide particles exceeds 1.5, it inhibits dispersibility in the electrode slurry, reduces coating properties, and causes problems with electrode uniformity. Furthermore, if the ratio of the particle size of the metal oxide particles is less than 0.03, the specific surface area of ​​the carbon material and metal oxide particles increases significantly, which can lead to a significant increase in the amount of binder and solvent used, potentially causing problems with reduced capacity and increased resistance, and is therefore undesirable.

[0022] In one embodiment of the present invention, the carbon material particles and metal oxide particles may be present in an irregularly mixed form. When the metal oxide particles coat the carbon material particles in a core-shell structure, it is undesirable because lithium is difficult to insert into the carbon material particles that form the core. In particular, when the surface of the carbon material particles that form the core is densely coated with the metal oxide that forms the shell, the carbon material in the core structure has difficulty coming into contact with lithium, resulting in a substantially insufficient content of carbon material particles. Consequently, there is a disadvantage in that the negative electrode does not perform well.

[0023] In one embodiment of the present invention, the carbon material particles may be, for example, amorphous carbon material particles. Specific examples of the amorphous carbon material include carbon black such as acetylene black, furnace black, and Ketjenblack, graphene, or a combination thereof.

[0024] When the carbon material particles have a high degree of crystallinity, it becomes difficult to insert and remove lithium, which has the disadvantage of increasing the resistance of the cell.

[0025] If the amorphous carbon material particles contain pores, the pore diameter may be 1 nm or less, preferably 0.5 nm or less. However, it may be more preferable that the amorphous carbon material particles do not contain pores. This is because, if the amorphous carbon material particles contain pores, lithium may precipitate inside the pores, and such lithium may be deactivated. The amount of lithium deactivated in this way may increase as charging and discharging are repeated.

[0026] The pore size of the amorphous carbon material particles can be measured, for example, through nitrogen adsorption experiments or through a transmission electron microscope.

[0027] In one embodiment of the present invention, the carbon material particles may be those having a particle size (D50) of 10 nm to 150 nm, preferably 20 nm to 100 nm.

[0028] In one embodiment of the present invention, the carbon material particles may be carbon material particles containing 3 to 10 at% oxygen. If the oxygen content is less than 3 at%, it is undesirable because it reduces the surface roughness of the active material layer, and if it exceeds 10 at%, it is undesirable because it causes a decrease in battery performance due to a side reaction with the solid electrolyte.

[0029] The lower limit of the oxygen content may be 3.5 at% or more, 4 at% or more, or 4.5 at% or more. The upper limit of the oxygen content may be 9.5 at% or less, 9 at% or less, 8 at% or less, 7.5 at% or less, 7 at% or less, 6.5 at% or less, 6 at% or less, or 5.5 at% or less. The oxygen content may be within a range formed by a combination of the lower and upper limits. Specifically, an oxygen content of 5 to 10 at% may be more preferable.

[0030] In one embodiment of the present invention, the oxygen may exist in a form contained within a functional group bonded to the carbon material particles. The functional group may also contain at least one selected from the group consisting of a carboxyl group, a hydroxyl group, an ether group, an ester group, an aldehyde group, a carbonyl group, and an amide group.

[0031] Carbon material particles containing 3 to 10 at% oxygen can be produced, for example, by oxidizing a carbon material. Specifically, the carbon material can be treated with an acid and reacted while stirring at a temperature of 25°C to 60°C to introduce oxygen functional groups to the surface of the carbon material. The type of acid is not particularly limited and can be any acid that can introduce oxygen functional groups to the surface of the carbon material. Examples of the acid include sulfuric acid, nitric acid, or mixtures thereof, and an oxidizing agent such as potassium permanganate may also be used.

[0032] The carbon material containing the aforementioned oxygen may be manufactured and used directly, or it may be purchased and used.

[0033] The oxygen content in the carbon material can be measured using a photoelectron spectrometer (XPS or ESCA). For example, it can be measured using a K-Alpha (Thermo Fisher Scientific) instrument.

[0034] In one embodiment of the present invention, the oxygen may be present on the surface of the carbon material particles. The surface does not mean only the outer surface of the carbon material particles, but also includes the surface of pores if pores are present.

[0035] In one embodiment of the present invention, the metal oxide may be one or more selected from Al2O3, TiO2, ZnO, and SiO2.

[0036] The metal oxide particles may be those with a particle size (D50) of 10 nm to 150 nm, preferably 20 nm to 100 nm.

[0037] In one embodiment of the present invention, the active material layer may contain 60-80% by weight of carbon material particles, 10-30% by weight of metal oxide particles, and 3-20% by weight of a binder. Alternatively, it may contain 65-75% by weight of carbon material particles, 20-30% by weight of metal oxide particles, and 4-8% by weight of a binder.

[0038] When the metal oxide particles are present in an amount of less than 10% by weight, the performance improvement is not significant compared to when carbon material particles are used alone, which is undesirable. When the amount exceeds 30% by weight, the amount of by-products generated by the reaction of the metal oxide and lithium increases, leading to an increase in the amount of irreversible lithium, which may result in a decrease in usable capacity.

[0039] Examples of the binder include resin materials such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder may consist of one or more of these resin materials.

[0040] In one embodiment of the present invention, the carbon material particles and metal oxide particles may be included in the form of a carbon material-metal oxide composite.

[0041] In anodeless batteries, the negative electrode active material layer is formed as an extremely thin film with a micro-thickness. However, conventional active material composites have the problem of being very difficult to form with a small particle size. In other words, if the particle size of the active material composite is too large for a micro-thick film, it is difficult to form a negative electrode active material layer with excellent surface roughness, and such a decrease in surface roughness acts as a cause of reduced battery driving characteristics.

[0042] The present invention offers a significant improvement over the aforementioned problems of the prior art. Specifically, the carbon material-metal oxide composite of the present invention forms a carbon material-metal oxide composite with significantly smaller particle size compared to the use of conventional carbon materials. The carbon material forming the composite contains 3 at% or more of oxygen, is well mixed with the metal oxide particles, and has the characteristic of being uniformly distributed with the metal oxide particles. Therefore, it is possible to manufacture a carbon material-metal oxide composite with excellent component uniformity. Furthermore, for the reasons mentioned above, it is possible to manufacture a carbon material-metal oxide composite with small and uniform particle size.

[0043] In one embodiment of the present invention, the carbon material-metal oxide composite may be composed of at least one bond selected from chemical bonds between carbon material particles and metal oxide particles, van der Waals bonds between carbon material particles and metal oxide particles, and binder bonds between carbon material particles and metal oxide particles. The chemical bond may be a bond between the metal oxide particles and oxygen contained in the carbon material.

[0044] In one embodiment of the present invention, the carbon material-metal oxide composite may contain, based on total weight, 60-80% by weight of carbon material particles, 10-30% by weight of metal oxide particles, and 3-20% by weight of binder. Alternatively, it may contain 65-75% by weight of carbon material particles, 20-30% by weight of metal oxide particles, and 4-8% by weight of binder. The binder may be dissolved in a solvent together with the carbon material particles and metal oxide particles during the wet manufacturing of the carbon material-metal oxide composite, in which case the binder may be included in the carbon material-metal oxide composite.

[0045] In one embodiment of the present invention, the particle size (D50) of the carbon material-metal oxide composite may be 0.1 μm to 0.5 μm. The upper limit of the particle size may be 0.4 μm or 0.3 μm.

[0046] Furthermore, the maximum particle size of the carbon material-metal oxide composite may be 3 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0047] If the particle size of the carbon material-metal oxide composite is too large for a micro-thick thin film, it becomes difficult to form a negative electrode active material layer with excellent surface roughness, which also degrades the battery's driving characteristics. Therefore, it is extremely important to manufacture the carbon material-metal oxide composite with a small particle size.

[0048] The reason why the driving characteristics of the aforementioned battery deteriorate is that when the surface roughness of the negative electrode active material layer is large, sufficient contact with the electrolyte layer does not occur in the direction of the electrolyte, and it does not help in the uniform deposition of lithium in the direction of the negative electrode current collector.

[0049] In an anodeless lithium-ion secondary battery, the thickness of the negative electrode active material layer may typically be in the range of 1 μm to 100 μm, or 10 μm to 60 μm. Specifically, it may be formed with thicknesses such as 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm.

[0050] For example, when forming a negative electrode active material layer with a thickness of 20 μm, it is obvious that using a carbon material-metal oxide composite with a particle size of 10 μm will make it difficult to form a desirable surface roughness.

[0051] When the maximum particle size of the carbon material-metal oxide composite is 3 μm or less, it is preferable because the effect of improving surface roughness can be obtained more reliably. On the other hand, when it exceeds 3 μm, it may be difficult to obtain excellent surface roughness when forming a thin film.

[0052] The particle size of the carbon material-metal oxide composite can be measured using a particle size analyzer. For example, it can be measured using a Mastersizer 3000 (Malvem panalytical) instrument.

[0053] The present invention provides a negative electrode active material layer containing the carbon material-metal oxide composite.

[0054] The negative electrode active material layer has a uniform distribution of carbon material and metal oxide, and exhibits excellent surface roughness, thus providing the effect of improving the driving characteristics of a lithium-ion secondary battery containing it.

[0055] Furthermore, the present invention provides a lithium-ion secondary battery comprising a negative electrode; a positive electrode; and an electrolyte interposed between the negative electrode and the positive electrode.

[0056] The lithium-ion secondary battery may be an anodeless battery.

[0057] The lithium-ion secondary battery, by including the negative electrode active material layer of the present invention, provides improved driving characteristics and lifespan characteristics.

[0058] In one embodiment of the present invention, the solid electrolyte may be a sulfide-based solid electrolyte.

[0059] In one embodiment of the present invention, the lithium-ion secondary battery may be an anodeless battery.

[0060] The embodiments of the present invention will be illustrated more specifically below.

[0061] <Configuration of an all-solid-state lithium-ion secondary battery> Figure 1 is a cross-sectional view showing a schematic configuration of an all-solid-state lithium-ion secondary battery according to one embodiment of the present invention.

[0062] An all-solid-state lithium-ion secondary battery (100) according to one embodiment of the present invention is a so-called lithium-ion secondary battery that performs charging and discharging by the movement of lithium ions between a positive electrode (10) and a negative electrode (20). Specifically, as shown in Figure 1, this all-solid-state lithium-ion secondary battery (100) is composed of a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20).

[0063] positive electrode As shown in FIG. 1, the positive electrode (10) includes a positive electrode current collector (12) and a positive electrode active material layer (14) arranged in order toward the negative electrode (20).

[0064] The positive electrode current collector (12) may be plate-shaped or foil-shaped. The positive electrode current collector (12) may be, for example, an alloy of one metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, lithium or two or more metals.

[0065] The positive electrode active material layer (14) can reversibly occlude and release lithium ions. The positive electrode active material layer (14) may contain a positive electrode active material and a solid electrolyte.

[0066] The positive electrode active material may be a compound capable of inserting / desorbing lithium. Examples of the compound capable of inserting / desorbing lithium include Li a A 1-b B’ b D’2 (in the above formula, 0.90 ≦ a ≦ 1.8 and 0 ≦ b ≦ 0.5); Li a E 1-b B’ b O 2-c D’ c (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE 2-b B’ b O 4-c D’ c (in the above formula, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b B’ c D’ α (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α ≦ 2); Li a Ni 1-b-c Co b B’ c O 2-α F’ α (in the above formula, 0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Lia Ni 1-b-c Mn b B' c D' α (In the above formula, 0.90 ≤ a ≤ 1.8, 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 (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni b E c G d O2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1);Li a Ni b Co c Mn d G e O2(In the above formula, 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1);Li a NiG b O2 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(In the above formula, 0≦f≦2);Li (3-f) Examples include those represented by the formulas Fe2(PO4)3 (where 0≦f≦2 in the above formula) or LiFePO4.

[0067] In the above chemical formulas, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D' is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0068] Specific examples of the positive electrode active material include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminate (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium salts such as lithium manganese oxide and lithium iron phosphate, and lithium sulfide. The positive electrode active material layer (14) may contain only one compound selected from these compounds as the positive electrode active material, or it may contain two or more compounds.

[0069] The positive electrode active material may include lithium salts of transition metal oxides having a layered rock salt structure, among the lithium salts mentioned above. Here, "layered rock salt structure" refers to a structure in which oxygen atomic layers and metal atomic layers are regularly arranged alternately in the direction of a cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. Furthermore, "cubic rock salt structure" means a sodium chloride type structure, which is a type of crystal structure. For example, a "cubic rock salt structure" shows a structure in which face-centered cubic lattices, on which cations and anions are formed, are arranged offset from each other by half a unit cell corner.

[0070] Examples of lithium salts of transition metal oxides having such a layered rock salt-type structure include LiNi x Co y Al z O2(NCA) or LiNix Co y Mn z It may also be a ternary lithium transition metal oxide such as O2(NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). The positive electrode active material layer (14) contains a lithium salt of such a layered rock salt type ternary transition metal oxide as the positive electrode active material, and can improve the energy density and thermal stability of the all-solid-state lithium ion secondary battery (100).

[0071] Here, examples of the shape of the positive electrode active material include particulate shapes such as true spherical and ellipsoidal. Further, the particle size of the positive electrode active material is not particularly limited, and may be within a range applicable to the positive electrode active material of a normal all-solid-state lithium ion secondary battery. Also, the content of the positive electrode active material in the positive electrode active material layer (14) is not particularly limited, and is possible as long as it is within a range applicable to the positive electrode of a normal all-solid-state lithium ion secondary battery.

[0072] Of course, those having a coating layer on the surface of the compound may also be used, or the compound and the compound having a coating layer may be mixed and used. This coating layer may contain a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds constituting these coating layers may be amorphous or crystalline. Examples of the coating element contained in the coating layer include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer formation process may use any coating method as long as these elements are used for the compound and the coating is performed by a method that does not adversely affect the physical properties of the positive electrode active material (for example, spray coating, dipping method, etc.). Since this is well understood by those skilled in the art, a detailed description is omitted.

[0073] Specific examples of the coating layer include Li2O-ZrO2 and the like.

[0074] The solid electrolyte contained in the positive electrode active material layer (14) may be the same type as the solid electrolyte contained in the solid electrolyte layer (30) described later, or it may be different.

[0075] Furthermore, the positive electrode active material layer (14) may contain not only the positive electrode active material and solid electrolyte mentioned above, but also appropriately blended additives such as conductive agents, binders, fillers, dispersants, or ion conductivity enhancers.

[0076] Examples of the conductive agent include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or metal powder. Examples of the binder include styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. As the filler, dispersant, or ion conductivity enhancer, known materials commonly used in electrodes for all-solid-state lithium-ion secondary batteries may be used.

[0077] (2) Negative electrode The negative electrode (20) may include a negative electrode current collector (22) and a negative electrode active material layer (24) arranged sequentially toward the positive electrode (10).

[0078] The negative electrode current collector (22) may be in the form of a plate or foil. The negative electrode current collector (22) may contain a material that does not react with lithium, that is, a material that does not form any alloys or compounds with lithium. Examples of materials that make up the negative electrode current collector (22) include copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector (22) may be composed of one of these metals, or it may be composed of an alloy or clad material of two or more metals.

[0079] In the initial state or after complete discharge, lithium may not be present in the negative electrode active material layer (24), the negative electrode current collector (22), the negative electrode active material layer (24), or between the negative electrode active material layer (24) and the solid electrolyte layer (30). As will be described later, when an all-solid-state lithium-ion secondary battery (100) according to one embodiment is overcharged, the active material contained in the negative electrode active material layer (24) and lithium ions that have moved from the positive electrode (10) form an alloy or compound, and a metal layer (26) mainly composed of lithium may be formed (deposited) on the negative electrode (20) as shown in Figure 2. The metal layer (26) may be deposited and arranged between the negative electrode current collector (22) and the negative electrode active material layer (24), inside the negative electrode active material layer (24), or in all of these locations. The lithium-based metal layer (26) may be positioned between the negative electrode current collector (22) and the negative electrode active material layer (24) closer to the negative electrode current collector layer (22) than to the negative electrode active material layer (24).

[0080] The negative electrode active material layer (24) may contain carbon material particles, metal oxide particles, and a binder. By including the binder (adhesive), the negative electrode active material layer (24) can be stabilized on the negative electrode current collector (22). Examples of materials constituting the binder (adhesive) include resin materials such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder (adhesive) may consist of one or more of these resin materials.

[0081] Furthermore, the negative electrode active material layer (24) may contain additives commonly used in all-solid-state lithium-ion secondary batteries, such as fillers, dispersants, and ion conductive agents. Specific examples of these additives are the same as those described above for the positive electrode.

[0082] The total thickness of the negative electrode active material layer (24) is not particularly limited, but may be 1 μm to 100 μm, or 10 μm to 60 μm. If the thickness of the negative electrode active material layer (24) is less than 1 μm, the performance of the all-solid-state secondary battery may not be sufficiently improved. If the thickness of the negative electrode active material layer (24) exceeds 100 μm, the resistance of the negative electrode active material layer (24) becomes high, and as a result, the performance of the all-solid-state secondary battery may not be sufficiently improved. By using the binder described above, the thickness of the negative electrode active material layer (24) can be easily ensured at an appropriate level.

[0083] On the other hand, the negative electrode current collector (22) may further include a film containing a material capable of forming an alloy or compound with lithium, wherein the film is disposed between the negative electrode current collector (22) and the negative electrode active material layer.

[0084] The negative electrode current collector (22) does not react with lithium metal, but this may make it difficult to deposit a smooth lithium metal layer on top of it. The film may be used as a wetting layer to allow the lithium metal to be deposited flatly on top of the negative electrode current collector (22).

[0085] The materials capable of forming alloys with the lithium metal used in the film may include silicon, magnesium, aluminum, lead, silver, tin, or combinations thereof. The materials capable of forming compounds with the lithium metal used in the film may include carbon, titanium sulfide, iron sulfide, or combinations thereof. The content of the material used in the film may be small, within a range that does not affect the electrochemical properties and / or the oxidation-reduction potential of the electrode. The film can be applied flatly onto the negative electrode current collector (22) to prevent cracking during the charging cycle of the all-solid-state lithium-ion secondary battery (100). The film may be applied using methods such as physical deposition such as evaporation or sputtering, chemical deposition or plating.

[0086] The thickness of the film may be 1 nm to 500 nm. The thickness of the film may be, for example, 2 nm to 400 nm. The thickness of the film may be, for example, 3 nm to 300 nm. The thickness of the film may be, for example, 4 nm to 200 nm. The thickness of the film may be, for example, 5 nm to 100 nm.

[0087] (3) Solid electrolyte layer The solid electrolyte layer (30) is located between the positive electrode (10) and the negative electrode (20) (for example, between the positive electrode active material layer (14) and the negative electrode active material layer (24)). The solid electrolyte layer (30) contains a solid electrolyte that can move ions. The solid electrolyte layer (30) may also contain a sulfide-based solid electrolyte.

[0088] The sulfide-based solid electrolytes are Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (m and n are positive numbers, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In), or a combination thereof. The solid electrolyte may consist of one material selected from these sulfide-based solid electrolyte materials, or it may consist of two or more materials.

[0089] The aforementioned sulfide-based solid electrolyte may include a solid electrolyte represented by the following chemical formula 1: [C1] Li x M' y PS z A w In the above chemical formula 1, x, y, z, and w are independently between 0 and 6; M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and A is at least one of F, Cl, Br, or I.

[0090] As the solid electrolyte, one of the sulfide solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements may be used. For example, one containing Li2S-P2S5 may be used. When using a sulfide-based solid electrolyte material containing Li2S-P2S5, the molar ratio of Li2S to P2S5 may be selected in the range of, for example, Li2S:P2S5 = 50:50 to 90:10.

[0091] Furthermore, the solid electrolyte may be in an amorphous state or a crystalline state. It may also be in a state where amorphous and crystalline materials are mixed.

[0092] The solid electrolyte layer (30) may further contain a binder. Examples of the binder material include resins such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polyacrylic acid. The binder material may be the same as or different from the material constituting the binder in the positive electrode active material layer (14) and the negative electrode active material layer (24).

[0093] (4) Configuration of an all-solid-state lithium-ion secondary battery The all-solid-state lithium-ion secondary battery (100) of the present invention may be an all-solid-state lithium-ion secondary battery (100) comprising a positive electrode (10), a solid electrolyte layer (30), and a negative electrode (20) in that order, as shown in Figure 1. The negative electrode (20) comprises a negative electrode current collector (22) and a negative electrode active material layer (24).

[0094] The negative electrode current collector (22) may include Ni foil, Ni-coated Cu foil, stainless steel foil, or a combination thereof. Such a negative electrode current collector (22) can further improve the discharge capacity.

[0095] <Manufacturing method for all-solid-state lithium-ion secondary batteries> Next, a method for manufacturing the all-solid-state lithium-ion secondary battery (100) will be described. In one embodiment, the all-solid-state lithium-ion secondary battery (100) is obtained by first manufacturing a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30), and then stacking these layers.

[0096] (1) Process for manufacturing the positive electrode The process for manufacturing a positive electrode can be explained as follows. First, the materials constituting the positive electrode active material layer (14) (positive electrode active material, binder (binding agent), etc.) are added to a nonpolar solvent to prepare a slurry (or paste). Next, the obtained slurry is applied onto the prepared positive electrode current collector (12). This is dried to obtain a laminate. Then, the obtained laminate is pressurized, for example, using hydrostatic pressure to obtain the positive electrode (10). In this case, the pressurization step is omitted.

[0097] (2) Process for manufacturing the negative electrode The process for manufacturing a negative electrode can be explained as follows: First, the materials constituting the negative electrode active material layer (24) (carbon material particles, metal oxide particles, binder, etc.) are added to a polar or nonpolar solvent to produce a slurry (a paste may also be used). Next, the obtained slurry is applied onto the prepared negative electrode current collector (22) to form the negative electrode active material layer.

[0098] If the negative electrode active material layer further includes one or more layers, additional layers may be laminated in the manner described above.

[0099] Next, the laminate obtained by the above method is pressurized, for example, using hydrostatic pressure to produce a negative electrode (20). The pressurization step may be omitted. Furthermore, the method of applying the slurry to the negative electrode current collector (22) is not particularly limited and includes, for example, screen printing, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade method, gravure coating, etc.

[0100] Although a method for forming the negative electrode active material layer with two layers was described above, when additional layers are to be formed, the slurry for each layer is manufactured, and the negative electrode is manufactured by sequentially stacking each layer according to the stacking order using the method described above.

[0101] (3) Process for preparing the solid electrolyte layer The solid electrolyte layer (30) can be made from a solid electrolyte containing, for example, a sulfide-based solid electrolyte material.

[0102] First, a sulfide-based solid electrolyte material is obtained by processing the starting materials (e.g., Li2S, P2S5, etc.) using a melt-quenching method or a mechanical milling method. For example, when using the melt-quenching method, a predetermined amount of the starting materials is mixed, formed into pellets, reacted in a vacuum at a predetermined reaction temperature, and then quenched to produce the sulfide-based solid electrolyte material. The reaction temperature of the Li2S and P2S5 mixture may be 400°C to 1000°C, for example, 800°C to 900°C. The reaction time may be 0.1 hours to 12 hours, for example, 1 hour to 12 hours. The quenching temperature of the reactants may be 10°C or lower, for example, 0°C or lower, and the quenching rate may usually be 1°C / sec to 10000°C / sec, for example, 1°C / sec to 1000°C / sec.

[0103] Furthermore, when using the mechanical milling method, sulfide-based solid electrolyte materials can be produced by stirring and reacting the starting materials using a ball mill or the like. The stirring speed and stirring time of the mechanical milling method are not particularly limited, but a faster stirring speed can increase the rate of production of sulfide-based solid electrolyte materials, and a longer stirring time can increase the conversion rate of the raw materials to sulfide-based solid electrolyte materials.

[0104] Subsequently, the resulting mixed raw material (sulfide-based solid electrolyte material) can be heat-treated at a predetermined temperature and then pulverized to produce particulate solid electrolyte. If the solid electrolyte has a glass transition temperature, it may change from amorphous to crystalline upon heat treatment.

[0105] Next, the solid electrolyte obtained by the above method can be used to produce a solid electrolyte layer (30) by forming a film using a known film formation method such as aerosol deposition, cold spray, or sputtering. Alternatively, the solid electrolyte layer (30) can be produced by pressurizing solid electrolyte particles. Furthermore, the solid electrolyte layer (30) can be produced by mixing a solid electrolyte with a solvent and a binder, then coating, drying, and pressurizing the mixture.

[0106] (4) Lamination process By placing a solid electrolyte layer (30) between a positive electrode (10) and a negative electrode (20) and pressurizing it using, for example, hydrostatic pressure, an all-solid-state lithium-ion secondary battery (100) according to one embodiment can be obtained.

[0107] The all-solid-state lithium-ion secondary battery (100) of the present invention does not require the application of high external pressure using an end plate or the like, and can provide improved discharge capacity even when the external pressure applied to the positive electrode (10), negative electrode (20), and solid electrolyte layer (30) during use is 1 MPa or less.

[0108] <Charging method for all-solid-state lithium-ion rechargeable batteries> Next, we will explain how to charge the all-solid-state lithium-ion secondary battery (100).

[0109] One embodiment of a method for charging an all-solid-state lithium-ion secondary battery (100) involves charging the all-solid-state lithium-ion secondary battery (100) beyond the charging capacity of the negative electrode active material layer (24) (i.e., overcharging).

[0110] In the initial stages of charging, lithium may be absorbed into the negative electrode active material layer (24). When charging exceeds the charging capacity of the negative electrode active material layer (24), lithium may be deposited on the back surface of the negative electrode active material layer (24), that is, between the negative electrode current collector (22) and the negative electrode active material layer (24), as shown in Figure 2. This lithium may form a metal layer (26) that was not present at the time of manufacture. During discharge, the lithium in the negative electrode active material layer (24) and the metal layer (26) can be ionized and move to the positive electrode (10) side. Therefore, in the all-solid-state lithium-ion secondary battery (100) of the present invention, lithium may be used as the negative electrode active material. Furthermore, since the negative electrode active material layer (24) coats the metal layer (26), it functions as a protective layer for the metal layer (26) and at the same time can suppress the deposition and growth of dendritic metallic lithium. This suppresses short circuits and capacity degradation in the all-solid-state lithium-ion secondary battery (100), and further improves the characteristics of the all-solid-state lithium-ion secondary battery (100). In addition, according to one embodiment, since the metal layer (26) is not formed in advance, the manufacturing cost of the all-solid-state lithium-ion secondary battery (100) can be reduced.

[0111] Furthermore, the metal layer (26) is not limited to being formed between the negative electrode current collector (22) and the negative electrode active material layer (24) as shown in Figure 2, but may also be formed inside the negative electrode active material layer (24). Alternatively, the metal layer (26) may be formed entirely between the negative electrode current collector (22) and the negative electrode active material layer (24) and inside the negative electrode active material layer (24).

[0112] The all-solid-state lithium-ion secondary battery (100) of the present invention may be manufactured as a unit battery having a positive electrode / separator / negative electrode structure, a bicell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked battery structure in which the unit battery structure is repeated.

[0113] The shape of the all-solid-state lithium-ion secondary battery (100) of the present invention is not particularly limited, and examples include coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, and rectangular shapes. It can also be applied to large batteries used in electric vehicles and the like. For example, the all-solid-state lithium-ion secondary battery (100) may be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). It may also be used in fields where large amounts of power storage are required. For example, it may be used in electric bicycles or power tools.

[0114] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0115] Manufacturing Example 1: Selection of carbon material samples into which oxygen functional groups have been introduced. Various types of commercially available carbon materials were purchased, and the oxygen content contained in each carbon material was analyzed using the method described below. Based on these analysis, carbon black with an oxygen content of 5.2 at% (Sample 1), carbon black with an oxygen content of 2.6 at% (Sample 2), and carbon black with an oxygen content of 1.3 at% (Sample 3) were selected and used.

[0116] <Analysis method> (1) Analytical equipment We used a K-Alpha (Thermo Fisher Scientific) photoelectron spectrometer (XPS or ESCA).

[0117] (2) Analysis method First, survey scan spectra and narrow scan spectra were obtained for each sample. For the narrow scan spectra, four points were measured for each position, and the average and deviation were calculated.

[0118] (3) Common experimental conditions for ESCA X-ray source:Monochromated Al Ka(1486.6 eV) X-ray spot size: 400μm Operation mode: CAE (Constant Analyzer Energy) mode Survey scan: pass energy 200 eV, energy step 1 eV Narrow scan:scanned mode, pass energy 50 eV, energy step 0.1 eV Charge compensation: flood gun off SF:Al THERMO1, ECF:TPP-2M, BG subtraction:Smart

[0119] [Table 1]

[0120] Example 1-1: Preparation of negative electrode active material slurry 6 g of carbon black with a particle size (D50) of 41 nm (containing 5.2 at% oxygen), 32 g of Al2O with a particle size (D50) of 10 nm to 20 nm, 9.33 g of PVdF binder (6% solids), and 6 g of NMP solution were placed in a Thinky mixer container and mixed 12 times for 3 minutes each at 1800 rpm. Then, another 6 g of NMP solution was added and mixed 5 times for 3 minutes each at 1800 rpm to produce the negative electrode active material slurry of Example 1.

[0121] Examples 1-2: Preparation of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that TiO2 with a particle size (D50) of 10 nm to 20 nm was used instead of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0122] Examples 1-3: Production of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that SiO2 with a particle size (D50) of 10 nm to 20 nm was used instead of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0123] Examples 1-4: Preparation of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that carbon black with a particle size (D50) of 50 nm (containing an oxygen concentration of 2.6 at%) was used instead of carbon black (containing an oxygen concentration of 5.2 at%) as in Example 1.

[0124] Examples 1-5: Preparation of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that carbon black with a particle size (D50) of 50 nm (containing an oxygen concentration of 2.6 at%) was used instead of carbon black (containing an oxygen concentration of 5.2 at%), and ZnO with a particle size (D50) of 35 nm to 45 nm was used instead of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0125] Examples 1-6: Preparation of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that carbon black with a particle size (D50) of 40 nm (containing an oxygen concentration of 1.3 at%) was used instead of carbon black (containing an oxygen concentration of 5.2 at%), and TiO2 with a particle size (D50) of 10 nm to 20 nm was used instead of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0126] Examples 1-7: Preparation of negative electrode active material slurry The negative electrode active material slurry was prepared in the same manner as in Example 1, except that carbon black with a particle size (D50) of 40 nm (containing an oxygen concentration of 1.3 at%) was used instead of carbon black (containing an oxygen concentration of 5.2 at%), and ZnO with a particle size (D50) of 35 nm to 45 nm was used instead of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0127] Comparative Example 1-1: Production of anode active material slurry The negative electrode active material slurry for Comparative Example 1 was prepared in the same manner as in Example 1, except that 2 g of Ag with a particle size (D50) of 40 nm to 60 nm was used instead of 2 g of Al2O3 with a particle size (D50) of 10 nm to 20 nm.

[0128] Examples 2-1 to 2-7 and Comparative Example 2-1: Manufacturing of the negative electrode Each negative electrode active material slurry produced in Examples 1-1 to 1-7 and Comparative Example 1-1 was blade-coated onto SUS foil to a thickness of 10 μm, dried, and then used to produce the negative electrodes (1.2 mAh / cm²) of Examples 2-1 to 2-7 and Comparative Example 2-1. 2 They manufactured ).

[0129] Manufacturing of all-solid-state lithium-ion secondary batteries in Examples 3-1 to 3-7 and Comparative Example 3-1 As for the positive electrode, the positive electrode active material has a current collector flow rate of 5 mAh / cm². 2 Using the positive electrode loaded with the above method, the negative electrodes produced in Examples 2-1 to 2-7 and Comparative Example 2-1 were used as the negative electrodes, and a sulfide-based all-solid electrolyte (LPSCl composition) was used as the electrolyte to produce the pouch-shaped monocells of Examples 3-1 to 3-7 and Comparative Example 3-1.

[0130] Experimental Example 1: Evaluation of Battery Characteristics The pouch-shaped monocells of Examples 3-1 to 3-7 and Comparative Example 3-1 were driven in an operating voltage range of 4.25V-3.0V and an operating temperature of 60°C to evaluate their cycle characteristics, and the results are shown in Table 2 below.

[0131] [Table 2] [Explanation of Symbols]

[0132] 100: All-solid-state lithium-ion secondary battery 10: Positive electrode 12: Positive electrode current collector 14: Positive electrode active material layer 20: Negative electrode 22: Negative electrode current collector 24: Negative electrode active material layer 26: Metal layer 30: Solid electrolyte layer

Claims

1. Including a current collector and an active material layer, The active material layer is a negative electrode containing carbon material particles and metal oxide particles.

2. The negative electrode according to claim 1, characterized in that the metal oxide particles are included in an amount of 10 to 50 parts by weight based on 100 parts by weight of the total weight of the carbon material particles and the metal oxide particles.

3. The negative electrode according to claim 1, characterized in that the ratio of the particle size (D50) of the carbon material particles to the particle size (D50) of the metal oxide particles is 1:0.03 to 1.

5.

4. The negative electrode according to claim 1, characterized in that the carbon material particles are amorphous carbon material particles.

5. The aforementioned metal oxide is Al ２ O ３ , TiO ２ ZnO, and SiO ２ The negative electrode according to claim 4, characterized in that it is one or more selected from the following.

6. The negative electrode according to claim 1, characterized in that the active material layer contains 60 to 80% by weight of carbon material particles, 10 to 30% by weight of metal oxide particles, and 3 to 20% by weight of a binder.

7. The negative electrode according to claim 1, characterized in that the carbon material particles contain 3 to 10 at% oxygen.

8. The negative electrode according to claim 7, characterized in that the oxygen exists in a form contained in a functional group bonded to carbon material particles.

9. The negative electrode according to claim 8, characterized in that the functional group comprises one or more selected from the group consisting of a carboxyl group, a hydroxyl group, an ether group, an ester group, an aldehyde group, a carbonyl group, and an amide group.

10. A lithium-ion secondary battery comprising a negative electrode; a positive electrode; and an electrolyte interposed between the negative electrode and the positive electrode, as described in any one of claims 1 to 9.

11. The lithium-ion secondary battery according to claim 10, characterized in that the electrolyte includes a sulfide-based solid electrolyte.

12. The lithium-ion secondary battery according to claim 11, characterized in that the lithium-ion secondary battery is an anodeless battery.

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