Negative electrode and lithium ion secondary battery comprising same

Abstract

The present invention provides a negative electrode and a lithium ion secondary battery comprising the same, the negative electrode comprising a current collector and an active material layer, in which the active material layer comprises carbon material particles and metal sulfide particles, the metal sulfide comprising at least one selected from the group consisting of Ag2S, MnS, and GeS.

Description

[Technical field]

[0001] This application claims priority from Korean Patent Application No. 10-2023-0118217, filed on September 6, 2023, and Korean Patent Application No. 10-2024-0120636, filed on September 5, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a negative electrode and a lithium ion secondary battery comprising the negative electrode. [Background Technology]

[0003] In recent years, all-solid-state secondary batteries using solid electrolytes as electrolytes have attracted attention. In order to improve the energy density of these all-solid-state secondary batteries, it has been proposed to use lithium as the negative electrode active material. The capacity density (capacity per unit weight) of lithium is about 10 times that of graphite, which is commonly used as a negative electrode active material. Therefore, when lithium is used as the negative electrode active material, it is possible to achieve a thinner all-solid-state secondary battery while increasing power output.

[0004] As an all-solid-state lithium ion secondary battery, for example, an anode-less 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 anode-less lithium-ion secondary battery is driven by the following mechanism: metallic lithium is deposited from the negative electrode active material layer and between the negative electrode active material layer and the current collector during charge, and is ionized and migrates to the positive electrode during discharge.

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

[0007] [Prior art literature]

[0008] [Patent Document]

[0009] Korean Patent Application No. 10-2020-0052707 [Summary of the invention]

[0010] [Technical Issues]

[0011] 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 negative electrode.

[0012] [Technical solution]

[0013] To achieve the above object, the present invention provides a negative electrode comprising a current collector and an active material layer.

[0014] Wherein, the active material layer comprises carbon material particles and metal sulfide particles,

[0015] The metal sulfide comprises at least one selected from the group consisting of Ag2S, MnS and GeS.

[0016] The present invention also provides a lithium ion secondary battery comprising the negative electrode, a positive electrode, and an electrolyte disposed between the negative electrode and the positive electrode.

[0017] [Beneficial Effects]

[0018] The negative electrode of the present invention includes a negative electrode active material layer in the form of a mixture of carbon material particles and metal sulfide particles, providing effects of improving driving characteristics and life characteristics of a battery.

[0019] Furthermore, by including the negative electrode active material layer, the lithium ion secondary battery of the present invention can provide excellent driving characteristics and life characteristics. [Brief Description of the Drawings]

[0020] Figure 1 and Figure 2 This is a schematic cross-sectional view of the structure of the lithium-ion secondary battery of the present invention. [Specific implementation method]

[0021] Hereinafter, the present invention will be described in more detail for better understanding of the present invention.

[0022] The terms and words used in this specification and claims should not be interpreted as their ordinary meanings or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical ideas of the present invention based on the principle that the inventor can define the concept of the term in a manner he deems appropriate in order to best illustrate his invention. Moreover, the terms used herein are only used to describe illustrative examples and are not intended to limit the present invention. Unless the context clearly indicates otherwise, expressions in the singular include plural forms.

[0023] When a component is referred to as being “connected to, contained within, or mounted on” another component, it should be understood that it can be directly connected or mounted on the other component, but other components may be present in between. On the other hand, when a component is referred to as being “directly connected to or mounted on” another component, it should be understood that no other components are present in between. Other expressions describing the relationship between components, such as “on” and “directly on,” or “between” and “directly between,” or “adjacent” and “directly adjacent,” should be interpreted similarly.

[0024] As used herein, the term "combination" is inclusive of mixtures, alloys, reaction products, and the like, unless specifically stated otherwise.

[0025] The negative electrode of the present invention comprises a current collector and an active material layer.

[0026] Wherein, the active material layer comprises carbon material particles and metal sulfide particles,

[0027] The metal sulfide comprises at least one selected from the group consisting of Ag2S, MnS and GeS.

[0028] In one embodiment of the present invention, the content of the metal sulfide particles may be 10 to 50 parts by weight, preferably 12 to 28 parts by weight, and more preferably 15 to 25 parts by weight, based on 100 parts by weight of the total weight of the carbon material particles and the metal sulfide particles.

[0029] If the content of the metal sulfide is less than 10 parts by weight, it is insufficient to form an alloy with lithium, and thus the benefit of reducing the activation energy of alloying by adding the metal sulfide cannot be achieved, while if the content of the metal sulfide exceeds 50 parts by weight, it is undesirable because it reduces the storage capacity of lithium, resulting in a decrease in total capacity and a decrease in high-rate discharge characteristics.

[0030] In one embodiment of the present invention, the negative electrode may contain metal sulfide particles even before being assembled into a battery. In other words, in the present invention, the negative electrode may contain metal sulfide particles from the time of preparing the negative electrode active material and / or from the time of preparing the composition for forming the negative electrode active material layer (e.g., slurry).

[0031] In one example of the present invention, the negative electrode may not include a metal in an alkali form other than the metal sulfide.

[0032] In one embodiment of the present invention, the carbon material particles may be, for example, amorphous carbon material particles. However, the carbon material particles are not limited to amorphous particles. Specific examples of amorphous carbon materials may include, but are not limited to, carbon black such as acetylene black, furnace black, and Ketjen black, graphene, or a combination thereof.

[0033] When the amorphous carbon material particles contain pores, the size of the pores may be 1 nm or less, preferably 0.5 nm or less. However, it may be more preferable that the amorphous carbon material particles contain no pores. This is because if the amorphous carbon material particles contain pores, lithium may precipitate within the pores, and such lithium may become deactivated. Furthermore, the amount of deactivated lithium may increase with repeated charging and discharging.

[0034] The pore size of the amorphous carbon material particles can be measured by, for example, a nitrogen adsorption experiment or a transmission electron microscope.

[0035] As the metal sulfide used in the present invention, at least one selected from the group consisting of Ag2S, MnS and GeS has excellent effects compared with conventionally used TiS2, CoS, NiS, FeS, MoS2, CuS, Cu2S or WS2.

[0036] In one example of the present invention, the carbon material particles and the metal sulfide particles may be included in a randomly mixed form.

[0037] In one example of the present invention, carbon material particles having a particle size (D50) of 10 nm to 150 nm, preferably 20 nm to 100 nm, more preferably 20 nm to 60 nm may be used.

[0038] In one example of the present invention, metal sulfide particles having a particle size (D50) of 5 nm to 100 nm, preferably 5 nm to 80 nm, more preferably 10 nm to 60 nm may be used.

[0039] In one embodiment of the present invention, the ratio of the carbon material particle size (D50) to the metal sulfide particle size (D50) can be 1:0.03 to 1.5, 1:0.1 to 0.7, or 1:0.2 to 0.7. If the particle size ratio of the metal sulfide particles exceeds 1.5, the dispersibility of the electrode slurry will be impaired, resulting in problems such as reduced coating properties and electrode uniformity. In addition, if the particle size ratio of the metal sulfide particles is less than 0.03, the specific surface area of ​​the carbon material and metal sulfide particles will increase significantly, and the amount of binder and solvent used will increase significantly, which may cause problems such as reduced capacity and increased resistance, which is undesirable.

[0040] In the present invention, the particle size can be measured using a particle size analyzer, for example, a Mastersizer 3000 (Malvern panalytical).

[0041] In one embodiment of the present invention, the carbon material particles may contain 3 to 10 atomic % of oxygen based on all elements contained in the carbon material particles. An oxygen content of less than 3 atomic % is undesirable because it reduces the surface roughness of the active material layer, while an oxygen content of more than 10 atomic % is undesirable because it reduces battery performance due to side reactions with the solid electrolyte.

[0042] The lower limit of the oxygen content may be 3.5 atomic % or more, 4 atomic % or more, or 4.5 atomic % or more. Furthermore, the upper limit of the oxygen content may be 9.5 atomic % or less, 9 atomic % or less, 8 atomic % or less, 7.5 atomic % or less, 7 atomic % or less, 6.5 atomic % or less, 6 atomic % or less, or 5.5 atomic % or less. The oxygen content may be within a range consisting of a combination of the lower limit and the upper limit. Specifically, the oxygen content may more preferably be 5 to 10 atomic %.

[0043] In one embodiment of the present invention, oxygen may exist in the form of functional groups bound to the carbon material particles. Furthermore, the functional groups may include one or more selected from the group consisting of carboxyl, hydroxyl, ether, ester, aldehyde, carbonyl, and amide groups.

[0044] Carbon material particles containing 3 to 10 atomic percent oxygen can be prepared, for example, by oxidizing a carbon material. Specifically, oxygen functional groups can be introduced onto the surface of the carbon material by treating the carbon material with an acid and stirring the reaction at a temperature of 25°C to 60°C. The type of acid is not particularly limited and can be any type capable of introducing oxygen functional groups onto the surface of the carbon material. The acid can be, for example, sulfuric acid, nitric acid, or a mixture thereof. Oxidizing agents such as potassium permanganate can also be used.

[0045] Oxygen-containing carbon materials can be synthesized directly or purchased.

[0046] The content of oxygen and other elements in the carbon material can be measured using XPS or ESCA, for example, a K-Alpha (Thermo Fisher Scientific) instrument.

[0047] In one embodiment of the present invention, the composition of the carbon material particles containing oxygen may include, for example, the following:

[0048] [Table 1]

[0049]

[0050] In one embodiment of the present invention, oxygen may exist on the surface of the carbon material particles. The surface refers not only to the outer surface of the carbon material particles, but also includes the surface of pores (if any).

[0051] In one embodiment of the present invention, the active material layer may comprise 60 to 80% by weight of carbon material particles, 10 to 30% by weight of metal sulfide particles, and 3 to 20% by weight of a binder. The binder may be, for example, a resin material such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The binder may comprise one or more selected from these resin materials.

[0052] The active material layer may further contain 5 to 20% by weight of a conductive material. This material may be any conductive material shown below for the positive electrode.

[0053] In one example of the present invention, the carbon material particles and the metal sulfide particles may be included in the form of a carbon material-metal sulfide composite.

[0054] In anodeless batteries, the negative electrode active material layer is formed into a very thin film with a thickness of micrometers. However, conventional active material composites have difficulty forming small particle sizes. In other words, if the particle size of the active material composite is too large for a micron-thin film, it is difficult to form a negative electrode active material layer with good surface roughness. This reduction in surface roughness can lead to a decrease in the battery's driving characteristics.

[0055] The present invention provides significant improvements over the aforementioned problems of the prior art. Specifically, the carbon material-metal sulfide composite of the present invention forms a carbon material-metal sulfide composite having a significantly smaller particle size than conventional carbon materials. The carbon material forming the composite contains at least 3 atomic percent oxygen, so it mixes well with the metal sulfide particles and is uniformly distributed along with the metal sulfide particles. This enables the production of a carbon material-metal sulfide composite with excellent compositional uniformity. For the same reasons as described above, this also enables the production of smaller, uniformly sized carbon material-metal sulfide composites.

[0056] In one embodiment of the present invention, the carbon material-metal sulfide composite can be formed by one or more combinations selected from chemical bonding, van der Waals bonding, and bonding via a binder between carbon material particles and metal sulfide particles. Chemical bonding can occur between the metal sulfide particles and oxygen contained in the carbon material.

[0057] In one example of the present invention, the carbon material-metal sulfide composite may include 60 to 80 wt % of the carbon material, 10 to 30 wt % of the metal sulfide, and 3 to 20 wt % of the binder based on the total weight.

[0058] The binder can be used in wet production of the carbon material-metal sulfide composite by dissolving it in a solvent together with the carbon material particles and the metal sulfide particles. In this case, the carbon material-metal sulfide composite may contain the binder.

[0059] In one embodiment of the present invention, the particle size (D50) of the carbon material-metal sulfide composite may be 0.1 μm to 0.5 μm, and the upper limit of the particle size may be 0.4 μm or 0.3 μm.

[0060] Furthermore, the maximum particle size of the carbon material-metal sulfide composite may be 3 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less.

[0061] If the particle size of the carbon material-metal sulfide composite is too large for a micron film, it is difficult to form a negative electrode active material layer with good surface roughness, and the driving characteristics of the battery are reduced, so it is very important to make the particle size of the carbon material-metal sulfide composite smaller.

[0062] The reason for the deterioration of the battery driving characteristics is that when the surface roughness of the negative electrode active material layer is large, the contact with the electrolyte layer on the electrolyte side is insufficient, which is not conducive to the uniform precipitation of lithium on the negative electrode collector side.

[0063] In an anode-free lithium-ion secondary battery, the thickness of the negative electrode active material layer can generally be formed to be 1 μm to 100 μm or 10 μm to 60 μm, specifically 10 μm, 20 μm, 30 μm, 40 μm or 50 μm.

[0064] For example, if a carbon material-metal sulfide composite having a particle size of 10 μm is used to form a negative electrode active material layer having a thickness of 20 μm, it is obviously difficult to form an ideal surface roughness.

[0065] If the maximum particle size of the carbon material-metal sulfide composite is 3 μm or less, it is preferred because the surface roughness improvement effect can be more reliably achieved. On the other hand, if the maximum particle size exceeds 3 μm, it may be difficult to obtain good surface roughness when forming a thin film.

[0066] The particle size of the carbon material-metal sulfide composite can be measured using a particle size analyzer, for example, a Mastersizer 3000 (Malvern Panalytical).

[0067] The present invention also provides a lithium ion secondary battery comprising the negative electrode, a positive electrode, and an electrolyte disposed between the negative electrode and the positive electrode.

[0068] By including the negative electrode active material layer of the present invention, the lithium ion secondary battery can provide improved driving characteristics and lifespan characteristics.

[0069] In one example of the present invention, the solid electrolyte may include a sulfide-based solid electrolyte.

[0070] In one example of the present invention, the secondary battery may include a metal sulfide having an increased sulfur content due to a reaction between sulfur contained in the sulfide-based solid electrolyte and the metal sulfide contained in the negative electrode.

[0071] In one embodiment of the present invention, the lithium-ion secondary battery may be an anode-free battery.

[0072] Hereinafter, examples of the present invention will be described in more detail.

[0073] <Composition of All-Solid-State Lithium-Ion Secondary Battery>

[0074] Figure 1 1 is a cross-sectional view showing a schematic configuration of an all-solid-state lithium-ion secondary battery according to one example of the present invention.

[0075] The all-solid-state lithium-ion secondary battery (100) according to one embodiment of the present invention is a so-called lithium-ion secondary battery that is charged and discharged by the movement of lithium ions between the positive electrode (10) and the negative electrode (20). Specifically, Figure 1 As shown, the all-solid-state lithium-ion secondary battery (100) comprises 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).

[0076] (1) Positive electrode

[0077] like Figure 1 As shown, the positive electrode (10) includes a positive electrode current collector (12) and a positive electrode active material layer (14) which are sequentially arranged toward the negative electrode (20).

[0078] The positive electrode current collector (12) may be a plate or foil. The positive electrode current collector (12) may be, for example, a metal selected from indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium, or an alloy of two or more metals.

[0079] The positive electrode active material layer (14) can reversibly absorb and release lithium ions. The positive electrode active material layer (14) can include a positive electrode active material and a solid electrolyte.

[0080] The positive electrode active material may be a compound capable of inserting / removing lithium. Examples of compounds capable of inserting or removing lithium include: Li a A 1-b B' b D'2 (where 0.90≤a≤1.8, 0≤b≤0.5); Li a E 1-b B' b O 2-c D' c (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE 2-b B' b O 4-c D' c (where 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b- c Co b B'c D' α (where 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 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni 1-b-c Mn b B' c D' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li a Ni b E c G d O2 (where 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 (where 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 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Li a MnG b O2 (where 0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (where 0.90≤a≤1.8, 0.001≤b≤0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(where 0≤f≤2);Li (3-f)Fe2(PO4)3 (where 0 ≤ f ≤ 2); LiFePO4; Li4Ti5O 12 (LTO); and any one represented by one of the above formulas.

[0081] In the above formulas, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D' is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or any combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or any combination thereof; Q is Ti, Mo, Mn, or any combination thereof; I' is Cr, V, Fe, Sc, Y, or any combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or any combination thereof.

[0082] Specific examples of the positive electrode active material may include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganate (hereinafter referred to as NCM), lithium manganate, lithium iron phosphate, and other lithium salts, as well as lithium sulfide. The positive electrode active material layer (14) may contain only one selected from these compounds as the positive electrode active material, or may contain two or more of them.

[0083] The positive electrode active material may contain a lithium salt of a transition metal oxide having a layered rock salt structure among the above lithium salts. Here, the "layered rock salt structure" is a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged along the direction of the cubic rock salt structure, such that each atomic layer forms a two-dimensional plane. In addition, the "cubic rock salt structure" refers to the sodium chloride structure, which is a type of crystal structure. For example, the "cubic rock salt structure" refers to a structure in which face-centered cubic lattices formed by cations and anions respectively are offset by 1 / 2 of the edge of the unit cell.

[0084] The lithium salt of the transition metal oxide having this layered rock salt structure may include, for example, LiNi x Co y Al z O2 (NCA) or LiNi x Co y Mn z O2 (NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), and other ternary lithium transition metal oxides. The positive electrode active material layer (14) may contain a lithium salt of a ternary transition metal oxide having this layered rock salt structure as the positive electrode active material to improve the energy density and thermal stability of the all-solid-state lithium ion secondary battery (100).

[0085] Here, the shape of the positive electrode active material can have a particle shape such as a sphere or an ellipsoid. In addition, the particle size of the positive electrode active material is not particularly limited and can be within the range of positive electrode active materials suitable for conventional all-solid-state lithium-ion secondary batteries. In addition, the content of the positive electrode active material in the positive electrode active material layer (14) is not particularly limited and can be within the range of positive electrodes suitable for conventional all-solid-state lithium-ion secondary batteries.

[0086] Of course, a compound having a coating on the surface of the compound can also be used, or a mixture of the compound and a compound having a coating can be used. The coating can contain a coating element compound, such as an oxide, hydroxide, oxyhydroxide, oxycarbonate or hydroxycarbonate of the coating element. The compounds constituting these coatings can be amorphous or crystalline. The coating element contained in the coating can be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating formation process can be carried out using any coating method (such as spraying, dipping, etc.), as long as the compound can be coated in a manner that does not adversely affect the properties of the positive electrode active material, which is fully understood by those skilled in the art and will not be described in detail.

[0087] A specific example of the coating layer may include Li2O-ZrO2.

[0088] The solid electrolyte contained in the positive electrode active material layer (14) may be the same as or different from the solid electrolyte contained in the solid electrolyte layer (30) described later.

[0089] The positive electrode active material layer (14) may also be a suitable formulation of additives such as conductive materials, binders, fillers, dispersants or ion conductivity aids in addition to the above-mentioned positive electrode active materials and solid electrolytes.

[0090] The conductive material can be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber or metal powder. The binder can also include, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride or polyethylene. In addition, any known material commonly used in the electrode of all-solid-state lithium ion secondary battery can be used as filler, dispersant or ion conductivity auxiliary agent.

[0091] (2) Negative electrode

[0092] The negative electrode (20) may include a negative electrode current collector (22) and a negative electrode active material layer (24) sequentially disposed toward the positive electrode (10).

[0093] The negative electrode current collector (22) may be a plate or foil. The negative electrode current collector (22) may include a material that does not react with lithium, that is, a material that does not form any alloy or compound with lithium. Materials constituting the negative electrode current collector (22) may include, for example, copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector (22) may be composed of one of these metals, or may be composed of an alloy or composite material of two or more metals.

[0094] The negative electrode active material layer (24) may not contain lithium in the negative electrode current collector (22), in the negative electrode active material layer (24), or between the negative electrode active material layer (24) and the solid electrolyte layer (30) in the initial state or in the fully discharged state. As described later, when the all-solid-state lithium-ion secondary battery (100) according to one embodiment of the present invention is overcharged, the active material contained in the negative electrode active material layer (24) and the lithium ions migrated from the positive electrode (10) may form an alloy or a compound, such as Figure 2 As shown, a metal layer (26) containing lithium as a main component can be formed (precipitated) on the negative electrode (20). The metal layer (26) can be precipitated and arranged between the negative electrode collector (22) and the negative electrode active material layer (24) and / or within the negative electrode active material layer (24). Between the negative electrode collector layer (22) and the negative electrode active material layer (24), the metal layer (26) containing lithium as a main component can be arranged closer to the negative electrode collector layer (22) than the negative electrode active material layer (24).

[0095] The negative electrode active material layer (24) may include carbon material particles, metal sulfide particles, and a binder. By including the binder, the negative electrode active material layer (24) can be stabilized on the negative electrode current collector (22). The material constituting the binder may be, for example, a resin material such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The binder may include one or more selected from these resin materials.

[0096] The negative electrode active material layer (24) may also be appropriately provided with additives used in conventional all-solid-state lithium ion secondary batteries, such as fillers, dispersants, conductive materials, etc. Specific examples of the additives are the same as those described above for the positive electrode.

[0097] The total thickness of the negative electrode active material layer (24) is not particularly limited and may be 1 μm to 100 μm, or 10 μm to 60 μm. If the thickness of the negative electrode active material layer (24) becomes 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) may be high, and as a result, the performance of the all-solid-state secondary battery may not be sufficiently improved. Using the above-mentioned binder, a negative electrode active material layer (24) of appropriate thickness can be easily achieved.

[0098] Meanwhile, the negative electrode current collector (22) may further include a film containing a material capable of forming an alloy or a compound with lithium, wherein the film may be provided between the negative electrode current collector (22) and the negative electrode active material layer.

[0099] The negative electrode current collector (22) does not react with lithium metal, but may make it difficult to deposit a smooth lithium metal layer on it. The film can also serve as a wetting layer, allowing lithium metal to be deposited evenly on the upper part of the negative electrode current collector (22).

[0100] The material used in the membrane that can form an alloy with lithium metal may include silicon, magnesium, aluminum, lead, silver, tin or a combination thereof. The material used in the membrane that can form a compound with lithium metal may include carbon, titanium sulfide, iron sulfide or a combination thereof. The content of the material used in the membrane can be a small amount, within a range that does not affect the electrochemical properties and / or redox potential of the electrode. The membrane can be evenly coated on the negative electrode collector (22) to prevent cracking of the all-solid-state lithium ion secondary battery (100) during the charging cycle. The coating of the membrane can be carried out by physical deposition (such as evaporation or sputtering), chemical deposition or plating.

[0101] 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.

[0102] (3) Solid electrolyte layer

[0103] A solid electrolyte layer (30) is provided between the positive electrode (10) and the negative electrode (20) (e.g., between the positive electrode active material layer (14) and the negative electrode active material layer (24)). The solid electrolyte layer (30) includes a solid electrolyte capable of transferring ions. The solid electrolyte layer (30) may include a sulfide-based solid electrolyte.

[0104] Sulfide solid electrolytes can be Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n(where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (wherein p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In) or any combination thereof. The solid electrolyte may include one material selected from these sulfide-based solid electrolyte materials, or may include two or more materials selected therefrom.

[0105] The sulfide-based solid electrolyte may include a solid electrolyte represented by the following Chemical Formula 1:

[0106] <Chemical Formula 1>

[0107] Li x M' y PS z A w

[0108] wherein x, y, z and w are independently 0 to 6;

[0109] M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; and

[0110] A is at least one of F, Cl, Br or I.

[0111] As a solid electrolyte, a sulfide-based solid electrolyte material containing sulfur (S), phosphorus (P), and lithium (Li) can be used as components. For example, a material containing Li2S-P2S5 can be used. When using a material containing Li2S-P2S5 as a sulfide-based solid electrolyte material, the mixing molar ratio of Li2S and P2S5 can be selected within the range of 50:50 to 90:10, for example.

[0112] In addition, the solid electrolyte can be amorphous or crystalline. It can also be a mixture of amorphous and crystalline.

[0113] The solid electrolyte layer (30) may further include a binder. Examples of binder materials include resins such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polyacrylic acid. The binder may be the same as or different from the binder material constituting the positive electrode active material layer (14) and the negative electrode active material layer (24).

[0114] (4) Composition of all-solid-state lithium-ion secondary batteries

[0115] The all-solid-state lithium-ion secondary battery (100) of the present invention can be as follows Figure 1The all-solid-state lithium-ion secondary battery (100) shown includes a positive electrode (10), a solid electrolyte layer (30) and a negative electrode (20) in sequence.

[0116] <Method for Manufacturing All-Solid-State Lithium-Ion Secondary Battery>

[0117] Next, a method for manufacturing an all-solid-state lithium-ion secondary battery (100) is described. According to one embodiment, the all-solid-state lithium-ion secondary battery (100) can be obtained by separately manufacturing a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30), and then laminating the above layers.

[0118] (1) Manufacturing process of positive electrode

[0119] An example of a manufacturing process for a positive electrode is as follows. First, the materials constituting the positive electrode active material layer (14) (positive electrode active material, binder, etc.) are added to a non-polar solvent to form a slurry (or paste). The resulting slurry is then applied to a prepared positive electrode current collector (12). This is dried to obtain a laminate. The resulting laminate is then pressurized, for example, using hydrostatic pressure to obtain a positive electrode (10). In this case, the pressurization process can be omitted.

[0120] (2) Negative electrode manufacturing process

[0121] An example of a negative electrode manufacturing process is as follows. First, the materials constituting the negative electrode active material layer (24) (carbon material particles, metal sulfide particles, binder, etc.) are added to a polar solvent or a non-polar solvent to prepare a slurry (preferably a paste). The resulting slurry is then applied to a prepared negative electrode current collector (22) to form the negative electrode active material layer.

[0122] If the negative electrode active material layer further includes one or more layers, the other layers may be stacked in the same manner as described above.

[0123] The laminate obtained by the above method is then pressurized, for example, using hydrostatic pressure, to produce the negative electrode (20). The pressurization process may also be omitted. In addition, the method of applying the slurry to the negative electrode collector (22) is not particularly limited and may include, for example, screen printing, metal mask printing, electrostatic coating, dip coating, spray coating, roller coating, doctor blade, gravure coating, etc.

[0124] The above description is about the method of forming two negative electrode active material layers. However, even when forming other layers, the negative electrode can be manufactured by preparing slurries for forming each layer and sequentially stacking each layer in the stacking order using the above method.

[0125] (3) Manufacturing process of solid electrolyte layer

[0126] The solid electrolyte layer (30) may be made of a solid electrolyte containing, for example, a sulfide-based solid electrolyte material.

[0127] First, the starting material (e.g., Li2S, P2S5, etc.) is treated by melt quenching or mechanical grinding to obtain a sulfide solid electrolyte material. For example, when the melt quenching method is adopted, the sulfide solid electrolyte material can be prepared by mixing a predetermined amount of starting raw materials, granulating them, reacting them at a predetermined reaction temperature in a vacuum and quenching them. In addition, the reaction temperature of the mixture of Li2S and P2S5 can be 400°C to 1000°C, for example, 800°C to 900°C. In addition, the reaction time can be 0.1 to 12 hours, for example, 1 to 12 hours. Moreover, the quenching temperature of the reactant can be below 10°C, for example, below 0°C, and the quenching rate can generally be 1°C / sec to 10000°C / sec, for example, 1°C / sec to 1000°C / sec.

[0128] In addition, when mechanical milling is used, the sulfide-based solid electrolyte material can be prepared by stirring and reacting the starting materials using a ball mill, etc. There are no particular restrictions on the stirring speed and stirring time of the mechanical milling method, but the faster the stirring speed, the faster the sulfide-based solid electrolyte material is produced, and the longer the stirring time, the higher the conversion rate of the raw materials into the sulfide-based solid electrolyte material.

[0129] The resulting mixed raw material (sulfide-based solid electrolyte material) is then heat-treated at a predetermined temperature and then pulverized to produce a granular solid electrolyte. If the solid electrolyte has a glass transition point, it can be transformed from amorphous to crystalline by heat treatment.

[0130] The solid electrolyte obtained by the above method can then be used to prepare a solid electrolyte layer (30) by thin film deposition using a known thin film deposition method, such as an aerosol deposition method, a cold spray method, or a sputtering method. Alternatively, the solid electrolyte layer (30) can be prepared by pressurizing solid electrolyte particles. Alternatively, the solid electrolyte layer (30) can be prepared by mixing the solid electrolyte with a solvent and a binder, followed by coating, drying, and pressurizing.

[0131] (4) Layering process

[0132] An all-solid-state lithium-ion secondary battery (100) according to one embodiment can be obtained by providing a solid electrolyte layer (30) between a positive electrode (10) and a negative electrode (20) and pressurizing the solid electrolyte layer (30) using, for example, hydrostatic pressure.

[0133] The all-solid-state lithium-ion secondary battery (100) of the present invention does not require high external pressure to be applied by end plates, and can provide improved discharge capacity even when the external pressure applied to the positive electrode (10), the negative electrode (20) and the solid electrolyte layer (30) during use is less than 1 MPa.

[0134] <Method for Charging All-Solid-State Lithium-Ion Secondary Batteries>

[0135] Next, a method for charging the all-solid-state lithium-ion secondary battery (100) is described.

[0136] According to one example, a method for charging the all-solid-state lithium-ion secondary battery (100) may be to charge the all-solid-state lithium-ion secondary battery (100) to a value exceeding the charge capacity of the negative electrode active material layer (24) (ie, overcharging).

[0137] In the initial stage of charging, lithium may be absorbed in the negative electrode active material layer (24). Figure 2 As shown, charging beyond the charge capacity of the negative electrode active material layer (24) can cause lithium to precipitate on the back side 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), and the lithium can form a metal layer (26) that does not exist during manufacturing. During the discharge process, the lithium in the negative electrode active material layer (24) and the metal layer (26) can be ionized and migrate to the positive electrode (10) side. Therefore, in the all-solid-state lithium ion secondary battery (100) of the present invention, lithium can be used as the negative electrode active material. In addition, since the negative electrode active material layer (24) covers the metal layer (26), it can serve as a protective layer for the metal layer (26), inhibiting the precipitation and growth of dendritic metal lithium. In this way, short circuit and capacity degradation of the all-solid-state lithium ion secondary battery (100) can be suppressed, and the characteristics of the all-solid-state lithium ion secondary battery (100) can be improved. Furthermore, according to one embodiment, the metal layer (26) is not preformed, which can reduce the manufacturing cost of the all-solid-state lithium-ion secondary battery (100).

[0138] In addition, the metal layer (26) is not limited to Figure 2 The metal layer (26) is shown as being formed between the negative electrode current collector (22) and the negative electrode active material layer (24), but may also be formed inside the negative electrode active material layer (24). In addition, the metal layer (26) may be formed simultaneously between the negative electrode current collector (22) and the negative electrode active material layer (24) and inside the negative electrode active material layer (24).

[0139] The all-solid-state lithium-ion secondary battery (100) of the present invention can be manufactured into a unit cell having a positive electrode / separator / negative electrode structure, a double cell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked core having the unit cell structure repeated.

[0140] The shape of the all-solid-state lithium ion secondary battery (100) of the present invention is not particularly limited, and can be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, angular, etc. It can also be applied to large batteries used in electric vehicles. For example, the all-solid-state lithium ion secondary battery (100) can also be used in hybrid vehicles, such as plug-in hybrid electric vehicles (PHEVs). It can also be used in applications that require large amounts of power storage. For example, it can be used in electric bicycles or electric tools.

[0141] [Example]

[0142] Hereinafter, the present invention will be described with reference to the embodiments to explain the present invention in detail. However, the embodiments of the present invention can be modified into many other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. The embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

[0143] Example 1: Preparation of negative electrode active material slurry

[0144] 6 g of carbon black with a particle size (D50) of 41 nm, 2 g of Ag2S with a particle size (D50) of 10 nm to 60 nm, 9.33 g of PVdF binder (6% solids), and 6 g of NMP solvent were placed in a Thinky mixer container and mixed at 1800 rpm for 12 times, each for 3 minutes. Then, an additional 6 g of NMP solvent was added, and mixing was performed at 1800 rpm for five times, each for 3 minutes, to prepare the negative electrode active material slurry of Example 1.

[0145] Example 2: Preparation of negative electrode active material slurry

[0146] A negative active material slurry was prepared in the same manner as in Example 1, except that 2 g of GeS having a particle size of 10 nm to 60 nm was used instead of 2 g of Ag 2 S.

[0147] Example 3: Preparation of negative electrode active material slurry

[0148] A negative active material slurry was prepared in the same manner as in Example 1, except that 2 g of MnS having a particle size of 10 nm to 60 nm was used instead of 2 g of Ag 2 S.

[0149] Comparative Example 1: Preparation of negative electrode active material slurry

[0150] A negative active material slurry was prepared in the same manner as in Example 1, except that 2 g of Ag having a particle size of 40 nm to 100 nm was used instead of 2 g of Ag 2 S.

[0151] Examples 4 to 6 and Comparative Example 2: Preparation of Negative Electrode

[0152] The negative electrodes (0.9 mAh / cm2) of Examples 4 to 6 and Comparative Example 2 were prepared by applying the negative electrode slurries prepared in Examples 1 to 3 and Comparative Example 1 on SUS foil with a thickness of 10 μm by a doctor blade and drying. 2 ).

[0153] Preparation of All-Solid-State Lithium-Ion Secondary Batteries of Examples 7 to 9 and Comparative Example 3

[0154] By using NCM and argyrodite electrolyte mixed at a weight ratio of 5.7:1 as the positive electrode active material, the current collector was charged at 6 mAh / cm 2 The loaded positive electrode, the negative electrode prepared in Examples 4 to 6 and Comparative Example 2 as the negative electrode, and the sulfide-based all-solid-state electrolyte (LPSCl composition) as the electrolyte were used to manufacture the pouch-type single cells of Examples 7 to 9 and Comparative Example 3.

[0155] Experimental Example 1: Battery Characteristics Evaluation

[0156] The following experiments were conducted on the pouch-type single cells prepared in Examples 7 to 8 and Comparative Example 3, and the results are shown in Table 2 below.

[0157] (1) Initial efficiency evaluation

[0158] The pouch cell was charged at a C-rate of 0.1C until the voltage reached 4.25V (vs. Li), and then cut off at a rate of 0.05C while maintaining 4.25V (vs. Li). It was then discharged at a C-rate of 0.1C until the voltage reached 3.0V (vs. Li) (first cycle). The initial efficiency was calculated as discharge capacity / charge capacity × 100 (%).

[0159] (2) Discharge capacity evaluation

[0160] The pouch-type single cell was operated in an operating voltage range of 4.25V-3.0V and an operating temperature of 60°C to evaluate its cycle characteristics.

[0161] (3) Life performance evaluation

[0162] The pouch-type single cell was charged at a rate of 0.33C (C rate) at an operating temperature of 60°C until the voltage reached 4.25V (vs. Li), and then cut off at a rate of 0.1C while maintaining 4.25V (vs. Li). It was then discharged at a rate of 0.33C (C rate) until the voltage at discharge reached 3.0V (vs. Li) (first cycle). This charge and discharge test was repeated 20 cycles to measure the capacity retention rate of the discharge capacity.

[0163] [Table 2]

[0164]

Claims

1. A negative electrode comprising a current collector and an active material layer, in, The active material layer comprises carbon material particles and metal sulfide particles, The metal sulfide comprises at least one selected from the group consisting of Ag2S, MnS and GeS.

2. The negative electrode according to claim 1, in, The metal sulfide particles may be 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 sulfide particles.

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

5.

4. The negative electrode according to claim 1, in, The negative electrode comprises metal sulfide particles even before being assembled into a battery.

5. The negative electrode according to claim 1, in, The carbon material particles are amorphous carbon material particles.

6. The negative electrode according to claim 1, in, The active material layer includes 60 to 80 wt % of carbon material particles, 10 to 30 wt % of metal sulfide particles, and 3 to 20 wt % of a binder.

7. The negative electrode according to claim 1, in, The carbon material particles contain 3 to 10 atomic % of oxygen.

8. The negative electrode according to claim 7, in, The oxygen exists in the form of functional groups bonded to the carbon material particles. 9 . A lithium ion secondary battery comprising: the negative electrode according to claim 1 ; a positive electrode; and an electrolyte disposed between the negative electrode and the positive electrode.

10. The lithium ion secondary battery according to claim 9, in, The electrolyte includes a sulfide-based solid electrolyte.

11. The lithium ion secondary battery according to claim 10, in, The secondary battery includes a metal sulfide whose sulfur content is increased due to a reaction between sulfur contained in the sulfide-based solid electrolyte and the metal sulfide contained in the negative electrode.

12. The lithium ion secondary battery according to claim 10, in, The lithium-ion secondary battery is an anode-free battery.

Images