Porous carbon-silver composite, negative electrode comprising same, and lithium ion secondary battery comprising negative electrode

Abstract

The present invention provides a porous carbon-silver composite comprising macroporous carbon (MPC) particles and silver particles inserted into pores of carbon; a negative electrode comprising the composite; and a lithium ion secondary battery comprising the negative electrode.

Description

Technical Field

[0001] This application claims the benefit of and priority to Korean Patent Application No. 10-2022-0183018, filed on December 23, 2022, and Korean Patent Application No. 10-2023-0189414, filed on December 22, 2023, the disclosures of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a porous carbon-silver composite, a negative electrode comprising the same, and a lithium ion secondary battery comprising the negative electrode. Background Art

[0003] Recently, all-solid-state secondary batteries using solid electrolytes as electrolytes have attracted much attention. In order to improve the energy density of these all-solid-state secondary batteries, lithium has been proposed as a 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, by using lithium as a negative electrode active material, the output power can be increased while making the all-solid-state secondary battery thinner.

[0004] All-solid-state lithium ion secondary batteries are known, for example, an anodeless lithium ion secondary battery comprising a negative electrode active material layer comprising a metal that forms an alloy with lithium and a carbon material.

[0005] The driving mechanism of the above-mentioned anode-free lithium-ion secondary battery is: during charging, metallic lithium is precipitated from the negative electrode active layer and between the negative electrode active layer and the current collector; during discharging, metallic lithium is ionized and moves to the positive electrode.

[0006] However, the above-mentioned prior art still has many problems that need to be improved, for example, during charging, the metallic lithium precipitates between the negative electrode active material layer and the current collector in the form of dendrites, and during discharging, voids are generated when the metallic lithium dissolves.

[0007] [Prior art literature]

[0008] [Non-patent literature]

[0009] Yong-Gun Lee et al., High-energy long-cycling all-solid-state lithium metalbatteries enabled by silver-carbon composite anodes, Nature Energy, 5, 299 (2020). Summary of the invention

[0010] [Technical issues]

[0011] The present invention aims to provide a porous carbon-silver composite, which improves the dispersibility of silver particles, prevents silver particles from agglomerating, thereby improving the application efficiency of silver particles, and plays an excellent mechanical buffering role on the thickness change of the lithium-ion negative electrode caused by shrinkage / expansion during the charge and discharge process.

[0012] The present invention also aims to provide a negative electrode comprising a porous carbon-silver composite, which improves the charge and discharge efficiency and life characteristics of a battery, and to provide a lithium ion secondary battery.

[0013] [Technical solution]

[0014] To achieve the above object, the present invention provides a porous carbon-silver composite comprising macroporous carbon particles and silver particles inserted into the pores of the carbon.

[0015] In addition, the present invention provides a negative electrode comprising a current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises the porous carbon-silver composite.

[0016] In addition, the present invention also provides a lithium ion secondary battery, which includes a positive electrode, a negative electrode and a solid electrolyte arranged between the positive electrode and the negative electrode.

[0017] [Beneficial Effects]

[0018] Since the silver particles of the porous carbon-silver composite of the present invention are well fixed in the surface pores of the macroporous carbon, the porous carbon-silver composite of the present invention improves the dispersibility of the silver particles, prevents the silver particles from agglomerating, and thus improves the application efficiency of the silver particles.

[0019] In addition, since the lithium-ion negative electrode will produce severe thickness changes due to shrinkage / expansion during the charge and discharge process, and the pores of the macroporous carbon act as a mechanical buffer for these thickness changes, the porous carbon-silver composite of the present invention improves the charge and discharge efficiency and life characteristics of the battery.

[0020] The negative electrode and the lithium ion secondary battery of the present invention include the porous carbon-silver composite, and thus have the effect of improving the charge and discharge efficiency and life characteristics of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the structure of the lithium ion secondary battery of the present invention compared with a conventional battery structure.

[0022] Figure 2 are SEM images depicting the forms of macroporous carbon and porous carbon-silver composites used in the present invention.

[0023] Figure 3 are SEM images of microporous carbon (activated carbon) and nonporous carbon (carbon black) used in the prior art. DETAILED DESCRIPTION

[0024] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

[0025] The terms and words used in this specification and claims should not be interpreted according to their conventional meanings or dictionary meanings, but should be interpreted in a sense and concept consistent with the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of terms to best describe his invention. In addition, the terms used in this specification are only used to describe exemplary embodiments and are not intended to limit the present invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0026] When a component is referred to as being "connected to, equipped with, or mounted on" another component, it should be understood that it can be directly connected to or mounted on the component, but there may be other components 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 there are no other components in between. Other expressions describing the relationship between components, such as "on top of" and "directly on top of", "between" and "directly between", or "adjacent to" and "directly adjacent to" should also be interpreted similarly.

[0027] As used herein, a "combination" is inclusive of mixtures, alloys, and reaction products unless otherwise specified.

[0028] The porous carbon-silver composite of the present invention is characterized in that it comprises macroporous carbon particles and silver particles inserted into the pores of the carbon.

[0029] Since the silver particles are well fixed in the surface pores of the macroporous carbon, the porous carbon-silver composite improves the dispersion of the silver particles and prevents the agglomeration of the silver particles, thereby improving the application efficiency of the silver particles. Especially in the case of lithium-ion anodes, the thickness changes caused by shrinkage / expansion during charge and discharge are very serious, and the pores of the macroporous carbon act as a mechanical buffer for these thickness changes, thereby improving the charge and discharge efficiency and life characteristics of the battery.

[0030] In one embodiment of the present invention, the surface of the macroporous carbon particles may include pores with a size of 60 nm to 0.5 μm, and the particle size (D50) of the silver particles may be 20 nm to 100 nm.

[0031] If the pores on the surface of the macroporous carbon particles are composed only of pores with a size less than 60 nm, it is difficult to achieve the effect of improving the silver dispersion by using the macroporous carbon particles. If the macroporous carbon particles contain pores that are too large, these silver particles may have difficulty in functioning due to the large amount of silver particles inserted into the internal pores of the macroporous carbon.

[0032] The macroporous carbon particles may also include pores with a size less than 60 nm, such as pores with a size from less than 10 nm to 60 nm, and may also include pores with a size from 100 nm to 1 μm.

[0033] In addition, when the particle size (D50) of silver is less than 20nm, it is not desirable because a large amount of silver particles are inserted into the internal pores of the macroporous carbon; when the particle size of the silver particles exceeds 100nm, it is not desirable because the silver particles may reduce the effect of forming lithium alloys, inducing lithium ion insertion and reducing lithium precipitation energy. The particle size (D50) of the silver particles is preferably 30nm to 60nm, and even more preferably 40nm to 60nm.

[0034] The pore size of the surface of the macroporous carbon particles can be measured using a BET measurement method using nitrogen absorption / desorption and a statistical image analysis method using a scanning electron microscope analysis, and the particle size of silver can be measured by a statistical image analysis method using a SEM analysis.

[0035] In one embodiment of the present invention, macroporous carbon particles having a particle size (D50) of 0.5 μm to 10 μm, more preferably 0.7 μm to 5 μm may be used.

[0036] When the particle size (D50) of the macroporous carbon is less than 0.5 μm, the amount of binder used increases rapidly, which is undesirable because it increases electrode resistance; when the particle size exceeds 10 μm, it is undesirable because it reduces the application efficiency of the Ag carrier.

[0037] The particle size (D50) of the macroporous carbon can be measured by laser diffraction particle size analysis.

[0038] In one embodiment of the present invention, the BET specific surface area of ​​the macroporous carbon particles can be 300 m 2 / g to 1000m 2 / g, more preferably 400m 2 / g to 600m 2 / g.

[0039] If the BET specific surface area is less than 300 m 2 / g, it will reduce the dispersion effect of silver particles and is therefore undesirable; if the BET specific surface area exceeds 1000m 2 / g, the structure is likely to collapse during the pressurization process of manufacturing all-solid-state batteries, and it is difficult to maintain the porous macroporous characteristics, which is not desirable.

[0040] In one embodiment of the present invention, the bulk density of the macroporous carbon particles may be 0.1 g / ml to 1 g / ml, preferably 0.1 g / ml to 0.5 g / ml, and more preferably 0.1 g / ml to 0.3 g / ml.

[0041] When the stacking density is less than 0.1 g / ml, the pore structure is highly developed, the structure is prone to collapse during the pressurization process of manufacturing all-solid-state batteries, and it is difficult to maintain the porous macroporous characteristics, so it is not desirable; when the stacking density exceeds 1 g / ml, it is a dense carbon structure, the pore structure is not well developed, and the dispersion effect on silver particles is significantly reduced, so it is not desirable.

[0042] In one embodiment of the present invention, the bulk density of the macroporous carbon-silver composite may be 0.12 g / ml to 0.3 g / ml, 0.15 g / ml to 0.3 g / ml, 0.2 g / ml to 0.3 g / ml, 0.15 g / ml to 0.25 g / ml, or 0.2 g / ml to 0.25 g / ml. Figure 1 and Figure 2 As shown, when the packing density is within the above range, the amount of silver particles inserted into the pores inside the macroporous carbon particles is reduced, and a large amount of silver particles are fixed in the surface pores of the macroporous carbon particles, thereby improving the utilization efficiency of the silver particles and maintaining the porosity of the macroporous carbon particles, which is preferred.

[0043] In addition, when the packing density of the porous carbon-Ag composite is less than 0.12 g / ml, the application efficiency of the silver nanoparticles is reduced, which is undesirable because both the initial charge and discharge efficiency and the battery efficiency are reduced; when the packing density exceeds 0.3 g / ml, the internal porosity of the macroporous carbon particles is reduced, and the efficiency of the silver particles contained in the macroporous carbon particles is also low. Therefore, the disadvantage is that both the initial charge and discharge efficiency and the battery efficiency are reduced, which has been confirmed in Experimental Example 2.

[0044] In one embodiment of the present invention, the porous carbon-silver composite may contain 70 to 90 parts by weight of macroporous carbon particles and 10 to 30 parts by weight of silver particles, more preferably 80 to 90 parts by weight of macroporous carbon particles and 10 to 20 parts by weight of silver particles, based on the total weight.

[0045] When the content ratio of the macroporous carbon particles to the silver particles satisfies the above range, both the charge / discharge efficiency and the lifespan characteristics are improved, thus being desirable.

[0046] In one embodiment of the present invention, the porous carbon-silver composite may further contain 3 to 10 parts by weight of a binder based on the total weight. For example, when the porous carbon-silver composite is prepared by a wet method, a binder dissolved in a solvent together with macroporous carbon and silver particles may be used, in which case the porous carbon-silver composite may contain a binder. When the binder is contained, the content of the above-mentioned macroporous carbon particles may be reduced due to the content of the binder.

[0047] In one embodiment of the present invention, the porous carbon-silver composite may further contain particles that form an alloy with lithium in addition to silver. The metal particles may be one or more particles selected from gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium and zinc.

[0048] The present invention provides a negative electrode comprising a current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises the porous carbon-silver composite.

[0049] In one embodiment of the present invention, the negative electrode active material layer may contain 80 wt % to 99 wt % of the porous carbon-silver composite and 1 wt % to 20 wt % of the binder, preferably 85 wt % to 99 wt % of the porous carbon-silver composite and 1 wt % to 15 wt % of the binder, and more preferably 90 wt % to 99 wt % of the porous carbon-silver composite and 1 wt % to 10 wt % of the binder, based on the total weight.

[0050] When the content ratio of the negative electrode active material layer satisfies the above range, charge and discharge efficiency and life characteristics may be improved, thus being desirable.

[0051] In addition, the present invention further comprises a current collector and a negative electrode active material layer, wherein the negative electrode active material layer may comprise 50 wt % to 98 wt % of macroporous carbon, 1 wt % to 30 wt % of silver particles, and 1 wt % to 20 wt % of a binder based on the total weight. In addition, the negative electrode active material layer may comprise 70 wt % to 98 wt % of macroporous carbon, 1 wt % to 20 wt % of Ag particles, and 1 wt % to 10 wt % of a binder based on the total weight.

[0052] When the content ratio of the negative electrode active material layer satisfies the above range, charge and discharge efficiency and life characteristics may be improved, thus being desirable.

[0053] The present invention provides a lithium ion secondary battery, which comprises a positive electrode, a negative electrode of the present invention and a solid electrolyte arranged between the negative electrode and the positive electrode.

[0054] A lithium ion secondary battery provides improved driving characteristics by including the negative electrode active material layer of the present invention.

[0055] In one embodiment of the present invention, the solid electrolyte may be a sulfide-based solid electrolyte.

[0056] In one embodiment of the present invention, the lithium ion secondary battery may be an anode-less battery. An anode-less battery is a battery that forms a lithium precipitation layer between the negative electrode active material layer and the current collector during initial charging.

[0057] Hereinafter, embodiments of the present invention will be described in more detail.

[0058] <Composition of lithium-ion secondary battery>

[0059] The lithium ion rechargeable battery of one embodiment of the present invention is a so-called all-solid-state lithium ion rechargeable battery, which is charged and discharged by transferring lithium ions between a positive electrode and a negative electrode. Specifically, this all-solid-state lithium ion secondary battery includes a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0060] (1) Positive electrode

[0061] In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer which are sequentially disposed toward the negative electrode.

[0062] The positive electrode current collector may be in the form of a plate or foil. The positive electrode current collector may be a metal selected from, for example, indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium and lithium, or an alloy of two or more of these metals. In addition, the positive electrode current collector may include a carbon-based conductive material and a binder, and may also include a primer layer coated on the surface of the positive electrode current collector. In this case, the adhesion and conductivity between the positive electrode active material layer and the current collector may be significantly improved.

[0063] The positive electrode active material layer can reversibly absorb and release lithium ions. The positive electrode active material layer may include a positive electrode active material and a solid electrolyte.

[0064] 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 NeG 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 Mn 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); and LiFePO4.

[0065] In the above formula, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D' is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F’ is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0066] Specific examples of the positive electrode active material include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium 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 may contain only one or more than two selected from these compounds as the positive electrode active material.

[0067] 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" means that oxygen atom layers and metal atom layers are regularly arranged alternately in the direction of the cubic rock salt structure, so that each atomic layer forms a two-dimensional plane. In addition, the "cubic rock salt structure" means a sodium chloride-type structure, which is a crystal structure. For example, the "cubic rock salt structure" means the following structure: a face-centered cubic lattice formed by cations and anions is arranged so as to错开 1 / 2 of the unit lattice angle.

[0068] For example, the lithium salt of a transition metal oxide having such a layered rock salt type structure may be a ternary lithium transition metal oxide, such as 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). The positive electrode active material layer (14) may contain a ternary transition metal oxide lithium salt having such a layered rock salt type 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).

[0069] For example, the shape of the positive electrode active material may be a particulate shape such as spherical or elliptical. In addition, the particle size of the positive electrode active material is not particularly limited and may be within the range applicable to the positive electrode active material of a conventional all-solid-state lithium ion secondary battery. In addition, the content of the positive electrode active material in the positive electrode active material layer is not particularly limited and may be within the range applicable to the positive electrode of a conventional all-solid-state lithium ion secondary battery.

[0070] Of course, the surface of the compound may also have a coating, or a mixture of a compound and a compound having a coating. The coating may include coating element compounds such as oxides or hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, or hydroxycarbonates of coating elements. The compound forming the coating may be amorphous or crystalline. The coating elements contained in the coating may include Mg, Al, Co, Mn, Ni, Cu, Fe, P, K, Na, Ca, Si, Ti, Ru, Nb, W, V, Mo, Sn, Zn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating formation process may be performed by any coating method (e.g., spraying, impregnation, etc.), as long as these elements can be coated on the compound in a manner that does not adversely affect the performance of the positive electrode active material. This process is well known to those skilled in the art and is therefore omitted here.

[0071] Specific examples of the above coating include Li2O-ZrO2.

[0072] The solid electrolyte contained in the positive electrode active material layer may be the same as or different from the solid electrolyte contained in the solid electrolyte layer described later.

[0073] Furthermore, in addition to the above-mentioned positive electrode active material and solid electrolyte, the positive electrode active material layer may further contain any suitable combination of additives, such as a conductive agent, a binder (adhesive), a filler, a dispersant, or an ion conductive aid.

[0074] Conductive agent can include, for example, graphite, carbon black, acetylene black, Ketjen black, single-walled or multi-walled carbon nanotubes, carbon fiber, carbon nanofiber, or metal powder. Adhesive (binder) can also include, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride or polyethylene, etc. In addition, filler, dispersant or ionic conductive additive can be any material commonly used in the electrode of all-solid-state lithium ion secondary battery.

[0075] (2) Negative electrode

[0076] In the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer sequentially disposed toward the positive electrode.

[0077] The negative electrode current collector may be in the form of a plate or foil. The negative electrode current collector may include a material that does not react with lithium, i.e., a material that does not form any alloy or compound with lithium. Materials constituting the negative electrode current collector include, for example, copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector may be composed of one of these metals, or may be composed of an alloy or coating material of two or more metals.

[0078] In the initial state or in the state after full discharge, the negative electrode active layer may not contain lithium in the negative electrode current collector, in the negative electrode active layer, or between the negative electrode active layer and the solid electrolyte layer. As described below, overcharging of an all-solid-state lithium-ion secondary battery of one embodiment may cause the negative electrode active material contained in the negative electrode active material layer and the lithium ions migrated from the positive electrode to form an alloy or compound, and a metal layer with lithium as the main component may be formed (precipitated) on the negative electrode. The metal layer may be precipitated and arranged between the negative electrode current collector and the negative electrode active material layer, inside the negative electrode active material layer, or both. Between the negative electrode current collector and the negative electrode active material layer, the lithium-based metal layer may be arranged closer to the negative electrode current collector layer than to the negative electrode active material layer.

[0079] The negative electrode active material layer of the present invention contains Ag as a negative electrode active material. Therefore, the metal layer formed during overcharging may include a Li(Ag) alloy containing a γ1 phase, a βLi phase or a combination thereof, wherein Ag is used in the lithium. Therefore, during the discharge process, only Li is dissolved in the Li(Ag) alloy constituting the metal layer, and the Ag used is retained to suppress the formation of voids. In this case, the silver content in the precipitated Li-Ag solid solution may be less than 60 wt%. Within this range, the decrease in the average discharge potential due to the influence of silver can be effectively suppressed. On the other hand, if the silver content in the precipitated Li-Ag solid solution is too low, the amount of silver remaining during discharge will be less, and the appearance of voids may not be fully suppressed. Therefore, the silver content in the precipitated Li-Ag solid solution may be greater than 20 wt%, for example, greater than 40 wt%.

[0080] If the silver content in the negative electrode active layer is too small, the occurrence of voids may not be suppressed because the amount of silver remaining after discharge is also reduced. Therefore, in an initial state where no charge and discharge are performed, the negative electrode active layer may contain at least 10 wt % of Ag, for example at least 20 wt % of Ag, based on 100 wt % of the total negative electrode active material contained in the negative electrode active layer.

[0081] The negative electrode active material layer contains macroporous carbon as a negative electrode active material in addition to Ag. In addition, in addition to Ag, it may contain at least one selected from Au, Pt, Pd, Si, Al, Bi, Sn, In and Zn.

[0082] The negative electrode active layer may further include a binder. By adding a binder, the negative electrode active layer can be stabilized on the negative electrode current collector. The material constituting the binder includes, for example, a resin such as styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder may include one or more selected from these resin materials.

[0083] The negative electrode active material layer may also be appropriately added with additives used in conventional all-solid-state lithium ion secondary batteries, such as fillers, dispersants, or ion conductors, etc. Specific examples of these additives are the same as those of the positive electrode additives described above.

[0084] The overall thickness of the negative electrode active material layer 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 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 exceeds 100 μm, the resistance of the negative electrode active material layer may be high, and thus the performance of the all-solid-state secondary battery may not be sufficiently improved. By using the above-mentioned binder, the thickness of the negative electrode active material layer can be easily controlled at a suitable level.

[0085] Meanwhile, the negative electrode current collector may further include a film including a material capable of forming an alloy or a compound with lithium, wherein the film may be disposed between the negative electrode current collector and the negative electrode active material layer.

[0086] The negative electrode current collector does not react with metallic lithium, but can make it difficult to form a smooth lithium metal layer on top. The film can also act as a wetting layer, allowing lithium metal to be smoothly deposited on the negative electrode current collector.

[0087] The material used in the film 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 film 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 film can be less and will not affect the electrochemical properties of the electrode and / or the redox potential of the electrode. The film can be laid flat on the negative electrode current collector to prevent cracks from occurring during the charging cycle of the all-solid-state lithium-ion secondary battery. The film can be coated by physical deposition (e.g., evaporation or sputtering), chemical deposition or plating.

[0088] 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. For example, the thickness of the film may be 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.

[0089] (3) Solid electrolyte layer

[0090] In the present invention, the solid electrolyte layer is disposed between the positive electrode and the negative electrode (eg, between the positive electrode active material layer and the negative electrode active material layer). The solid electrolyte layer includes a solid electrolyte capable of moving ions. The solid electrolyte layer may include a sulfide-based solid electrolyte.

[0091] Sulfide solid electrolytes may include Li2S-P2S5, Li2S-P2S5-LiX (wherein X is a halogen atom), 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 any one selected from Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (wherein p and q are positive numbers, and M is any one selected from P, Si, Ge, B, Al, Ga, and In) or a combination thereof. The solid electrolyte may include one or two or more materials selected from these sulfide-based solid electrolyte materials.

[0092] The sulfide-based solid electrolyte may include a solid electrolyte represented by the following Formula 1:

[0093] <Formula 1>

[0094] Li x M' y PS z A w ,

[0095] wherein x, y, z and w are independently greater than or equal to 0 and less than or equal to 6;

[0096] M' is at least one of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb and Ta;

[0097] A is at least one of F, Cl, Br and I.

[0098] As a solid electrolyte, a sulfide solid electrolyte material containing sulfur (S), phosphorus (P) and lithium (Li) as components can be used. For example, a material containing Li2S-P2S5 can be used. When a material containing Li2S-P2S5 is used as a sulfide solid electrolyte material, the mixing molar ratio of Li2S to P2S5 can be selected in the range of, for example, Li2S:P2S5=50:50 to 90:10.

[0099] Solid electrolytes can be amorphous or crystalline, or a mixture of amorphous and crystalline.

[0100] The solid electrolyte layer may further include an adhesive (binder). For example, such adhesive (binder) materials include resins and acrylic adhesives, such as styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymer (SBS), nitrile rubber (NBR), fluororubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polyacrylic acid. The adhesive (binder) material may be the same or different from the material constituting the adhesive (binder) in the positive active layer and the negative active layer.

[0101] (4) Composition of all-solid-state lithium-ion secondary batteries

[0102] The all-solid-state lithium-ion secondary battery of the present invention may be an all-solid-state lithium-ion secondary battery including the above-mentioned positive electrode, solid electrolyte layer, and negative electrode in sequence.

[0103] <Method for manufacturing all-solid-state lithium-ion secondary battery>

[0104] Next, a method for manufacturing the above-mentioned all-solid-state lithium ion secondary battery will be described. The all-solid-state lithium ion secondary battery of one embodiment can be obtained by separately manufacturing a positive electrode, a negative electrode, and a solid electrolyte layer and then stacking the layers.

[0105] (1) Manufacturing process of positive electrode

[0106] The positive electrode manufacturing process is as follows. First, the materials constituting the positive electrode active layer (positive electrode active material, binder (adhesive), etc.) are added to a non-polar solvent to form a slurry (or paste). The obtained slurry is then coated on the prepared positive electrode current collector. It is dried to obtain a laminate. The laminate is then pressurized using, for example, hydrostatic pressure to obtain a positive electrode. In this case, the pressurization process can be omitted.

[0107] (2) Negative electrode manufacturing process

[0108] The negative electrode manufacturing process is as follows. First, the materials constituting the negative electrode active material layer (macroporous carbon, silver particles (or porous carbon-silver composites made of these materials) and a binder) are added to a polar or non-polar solvent to prepare a slurry (or paste). The obtained slurry is then coated on the prepared negative electrode current collector to form a negative electrode active material layer.

[0109] If the negative electrode active material layer further includes one or more additional layers, the additional layers may be stacked in the same manner as described above.

[0110] The laminate obtained by the above method is then pressurized using, for example, hydrostatic pressure to produce a negative electrode. The pressurization process may be preferably omitted. In addition, the method of applying the slurry to the negative electrode current collector is not particularly limited, and may include, for example, screen printing, metal mask printing, electrostatic coating, dip coating, spray coating, roller coating, doctor blade coating, gravure coating, etc.

[0111] The method of forming a two-layer negative electrode active material layer is described above, but even if an additional layer is to be formed, the negative electrode can be manufactured by preparing a slurry for forming each layer and sequentially stacking each layer according to the stacking order according to the above method.

[0112] (3) Solid Electrolyte Layer Manufacturing Process

[0113] The solid electrolyte layer can be made using a solid electrolyte including, for example, a sulfide-based solid electrolyte material.

[0114] First, the starting material (such as Li2S, P2S5, etc.) is processed by melt quenching or mechanical grinding to obtain a sulfide solid electrolyte material. For example, when using the melt quenching method, the starting material is mixed in a predetermined amount, granulated, reacted at a predetermined reaction temperature in a vacuum, and then quenched to generate a sulfide solid electrolyte material. In addition, the reaction temperature of the Li2S and P2S5 mixture may be 400°C to 1000°C, for example, 800°C to 900°C. In addition, the reaction time may be 0.1 hours to 12 hours, for example, 1 hour to 12 hours. In addition, the quenching temperature of the reactant may be below 10°C, for example, below 0°C, and the quenching rate may generally be 1°C / second to 10000°C / second, for example, 1°C / second to 1000°C / second.

[0115] In addition, when the mechanical grinding method is used, the starting materials can be stirred and reacted using a ball mill, etc. to prepare the sulfide-based solid electrolyte material. In addition, there is no particular restriction on the stirring speed and stirring time of the mechanical grinding method, but the faster the stirring speed, the faster the sulfide-based solid electrolyte material can be produced, and the longer the stirring time, the higher the conversion rate of the raw material to the sulfide-based solid electrolyte material.

[0116] The obtained mixed raw material (sulfide-based solid electrolyte material) is then heat-treated at a predetermined temperature and 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.

[0117] The solid electrolyte obtained by the above method can be used to prepare a solid electrolyte layer by coating, and the coating uses a known coating method, such as an aerosol positioning method, a cold spray method, a sputtering method, etc. The solid electrolyte layer can also be prepared by pressurizing the solid electrolyte particles. The solid electrolyte layer can also be prepared by mixing the solid electrolyte with a solvent and a binder, and then drying and pressurizing.

[0118] (4) Lamination process

[0119] The all-solid-state lithium ion secondary battery of one embodiment can be obtained by providing a solid electrolyte layer between the positive electrode and the negative electrode and pressurizing the solid electrolyte layer using, for example, hydrostatic pressure.

[0120] The all-solid-state lithium-ion secondary battery of the present invention does not require the use of end plates to apply a high external pressure, and can provide improved discharge capacity even when the external pressure applied to the positive electrode, the negative electrode and the solid electrolyte layer during use is less than 1 MPa.

[0121] <Method for Charging All-Solid-State Lithium-Ion Secondary Battery>

[0122] Next, a charging method of the all-solid-state lithium-ion secondary battery is provided as follows.

[0123] According to one embodiment, a method of charging an all-solid-state lithium ion secondary battery may include charging the all-solid-state lithium ion secondary battery to exceed a charge capacity of a negative active material layer (ie, overcharging).

[0124] In the early stage of charging, lithium may be absorbed into the negative electrode active material layer. If the charge exceeds the charge capacity of the negative electrode active layer, lithium will be precipitated on the back of the negative electrode active layer, that is, between the negative electrode current collector and the negative electrode active layer, and lithium may form a metal layer that does not exist during manufacturing. During the discharge process, the lithium in the negative electrode active material layer and the metal layer can be ionized and migrated to the positive electrode side. Therefore, in the all-solid-state lithium ion secondary battery of the present invention, lithium can be used as the negative electrode active material. In addition, since the negative electrode active material layer is coated with the metal layer, it can serve as a protective layer for the metal layer, while suppressing the precipitation and growth of dendritic metal lithium. In this way, the short circuit and capacity reduction of the all-solid-state lithium ion secondary battery can be suppressed, and the characteristics of the all-solid-state lithium ion secondary battery can be further improved. In addition, according to one embodiment, since the metal layer is not preformed, the manufacturing cost of the all-solid-state lithium ion secondary battery can be reduced.

[0125] In addition, the metal layer is not limited to being formed between the negative electrode current collector and the negative electrode active material layer, but can also be formed inside the negative electrode active material layer. In addition, the metal layer can be formed both between the negative electrode current collector and the negative electrode active material layer and inside the negative electrode active material layer.

[0126] The all-solid-state lithium-ion secondary battery of the present invention can be manufactured as a unit cell having a positive electrode / separator / negative electrode structure, a dual cell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked cell having a repeated unit cell structure.

[0127] The shape of the all-solid-state lithium ion secondary battery of the present invention is not particularly limited, for example, it can be coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, trumpet-shaped, etc. The present invention can also be applied to large batteries used in electric vehicles. For example, all-solid-state lithium ion secondary batteries can be used in hybrid vehicles, such as plug-in hybrid electric vehicles (PHEV). They can also be used in applications requiring a large amount of power storage. For example, they can be used in electric bicycles or electric tools.

[0128] Hereinafter, examples are provided to describe the present invention in detail. However, embodiments of the present invention may be modified in many other ways, and the scope of the present invention should not be construed as being limited only to the examples described below. Examples of the present invention are provided to more fully illustrate the present invention to those of ordinary skill in the art.

[0129] Examples 1 to 3 and Comparative Examples 1 to 5: Preparation of Negative Electrode

[0130] A negative active material slurry composition was prepared using the carbon material, silver nanoparticles, and a binder listed in Table 1 below.

[0131] Specifically, a mixture of the carbon material listed in Table 1 below, silver nanoparticles, and a PVdF binder was placed in a Thinky mixer container with an NMP solvent and mixed at 2000 rpm to prepare a negative active material slurry containing a porous carbon-silver composite.

[0132] Each of the negative electrode active material slurries prepared by the above method was coated on a SUS foil to a thickness of 10 μm and dried, thereby preparing negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 5.

[0133] [Table 1]

[0134]

[0135] Experimental Example 1: Measurement of Apparent Density of Carbon-Silver Composite

[0136] The bulk density of the porous carbon-silver composites prepared in Example 2 and Comparative Example 5 was measured by the JIS K 1469 method. Specifically, the porous carbon-silver composites were prepared and used for measuring the bulk density using the same method as in Example 2 and Comparative Example 5 above, except that the PVdF binder was not used. That is, the carbon material and the silver nanoparticles were placed in a Thinky mixer container with an NMP solvent, mixed at 2000 rpm to prepare a slurry, and then dried to prepare a carbon-silver composite in a powder phase, and the bulk density was measured by the JIS K 1469 method.

[0137] According to the above measurement results, it can be determined that the bulk density of the porous carbon-silver composite prepared in Example 2 is 0.22 g / ml, and the apparent density of the porous carbon-silver composite prepared in Comparative Example 5 is 0.32 g / ml.

[0138] It can be seen from these results that in the porous carbon-silver composite prepared in Comparative Example 5, many silver particles are inserted into the internal pores of the macroporous carbon, resulting in an increase in the packing density, while in the porous carbon-silver composite prepared in Example 2, most of the silver particles are located in the surface pores of the macroporous carbon, resulting in a relatively low density.

[0139] Preparation of All-Solid-State Lithium Ion Secondary Batteries of Examples 4 to 6 and Comparative Examples 6 to 10

[0140] As the positive electrode, Li[Ni 0.82 Co 0.14 Mn 0.04 ]O2, Li6PS6Cl as a solid electrolyte, carbon nanofiber (VGCF, manufactured by Showa Denko) as a conductive material, and polytetrafluoroethylene as a binder were sequentially added to the container in a weight ratio of 77:20:1:2. After each addition of each component, mixing was repeated 10 times at 10000 rpm using a Lab Blender for 30 seconds each time, thereby preparing a positive electrode mixture.

[0141] To the above mixture, a shear force of 100 was applied at 100° C. using a twin-screw kneader (manufactured by LG Electronics), thereby performing high shear mixing for 5 minutes, and a positive electrode mixture was prepared.

[0142] A 200 μm thick self-standing film was prepared from the positive electrode mixture using a double roll mill (manufactured by Inoue) at 100° C. The film was then placed on one side of an aluminum current collector (thickness μm) coated with a primer layer, and the film was adhered to the current collector using a laminating roller at 120° C., thereby preparing a positive electrode.

[0143] The negative electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was used as the negative electrode, a liquid electrolyte of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio of 1:2) with 1 mole of lithium hexafluorophosphate (LiPF6) was used for the battery of Comparative Example 1, and a sulfide-based all-solid-state electrolyte (Li6PS6Cl) was used for the remaining batteries to produce pouch-type single cells of Examples 4 to 6 and Comparative Examples 6 to 10.

[0144] The sulfide-based all-solid electrolyte was prepared by mixing Li6PS6Cl solid electrolyte and nitrile rubber (NBR) in xylene as a solvent, and then mixing 10 times at 2000 rpm for 1 minute each time in a Thinky mixer with zirconium oxide balls to prepare a solid electrolyte slurry, which was coated on a PET film as a release paper, and dried in a vacuum oven at 45°C for 6 hours to form a film. The weight ratio of Li6PS6Cl to NBR was 95:5, and the thickness of the film was 100 μm.

[0145] A solid electrolyte is placed between the negative electrode and the positive electrode to prepare an assembly, which is then placed in a bag and sealed. The bag is then fixed on an Al plate and pressurized at 500 MPa for 30 minutes using an isostatic press to make an all-solid-state lithium secondary battery.

[0146] Experimental Example 2: Evaluation of Battery Characteristics

[0147] The pouch-type cells of Examples 4 to 6 and Comparative Examples 6 to 10 were operated under the following charge / discharge conditions at an operating voltage of 4.25 V to 3.0 V and an operating temperature of 60°C to evaluate their initial charge / discharge efficiency and cycle characteristics. The results are shown in Table 2 below.

[0148] For reference, each of the batteries in the examples and comparative examples was mounted on a press jig, and the bolts / nuts located on the square corners were tightened with the same pressure of 1 N.m to prepare a single battery.

[0149] (1) Initial charge / discharge efficiency (%) refers to the ratio of the charge capacity to the discharge capacity when a battery is charged once and discharged once at 60° C. under the following conditions.

[0150] Charging conditions: 0.1C CC charge to 4.25V, then CV charge to 4.25V, 0.05C cut-off

[0151] Discharge condition: 0.1C CC discharge to 3.0V

[0152] (2) Cycle characteristics refer to the ratio of the capacity at one discharge to the capacity at 50 discharges when charge and discharge are repeated 50 times at 60°C under the following conditions.

[0153] Charging conditions 0.5C, 4.25V CC / CV, 0.1C cut-off

[0154] Discharge conditions: 0.5C, 3.0V, CC [Table 2]

[0155]

Claims

1. A porous carbon-silver composite comprising macroporous carbon particles and silver particles inserted into the pores of the carbon.

2. The porous carbon-silver composite according to claim 1, wherein The macroporous carbon particles contain pores with a size of 60 nm to 0.5 μm on their surface, wherein the particle size D of the silver particles is 50 20nm to 100nm.

3. The porous carbon-silver composite according to claim 2, wherein The particle size D of the macroporous carbon particles 50 0.5μm to 10μm.

4. The porous carbon-silver composite according to claim 3, wherein The BET specific surface area of ​​the macroporous carbon particles is 300 m 2 / g to 1000m 2 / g.

5. The porous carbon-silver composite according to claim 3, wherein The bulk density of the macroporous carbon particles is 0.1 g / ml to 1 g / ml.

6. The porous carbon-silver composite according to claim 1, wherein The porous carbon-silver composite includes 70 to 90 parts by weight of macroporous carbon particles and 10 to 30 parts by weight of silver particles based on the total weight.

7. A negative electrode comprising a current collector and a negative electrode active material layer, wherein: The negative electrode active material layer comprises the porous carbon-silver composite according to claim 1 .

8. The negative electrode according to claim 7, wherein The negative active material layer includes 80 wt % to 99 wt % of the porous carbon-silver composite and 1 wt % to 20 wt % of a binder based on the total weight. 9 . A lithium ion secondary battery comprising a positive electrode, the negative electrode according to claim 7 , and a solid electrolyte disposed between the positive electrode and the negative electrode.

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

11. The lithium ion secondary battery according to claim 10, wherein: The lithium ion secondary battery is an anode-free battery.

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