Porous carbon-Ag composite, negative electrode including the same, and lithium ion secondary battery including the negative electrode

Abstract

The present invention provides a porous carbon-Ag composite including macroporous carbon particles and Ag particles inserted into the pores of the carbon, a negative electrode including the composite, and a lithium ion secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183018, filed December 23, 2022, and Korean Patent Application No. 10-2023-0189414, filed December 22, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

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

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

[0004] Known all-solid-state lithium-ion secondary batteries include, for example, anode-less lithium-ion secondary batteries that include a negative electrode active material layer that contains a metal that forms an alloy with lithium and a carbon material.

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

[0006] However, the above-described conventional techniques still have many areas to be improved due to problems such as the generation of dendrites as a deposition form of metallic lithium deposited between the negative electrode active material layer and the current collector during charging, and voids that are generated when the metallic lithium dissolves during discharging. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Yong-Gun Lee et al. High-energy long-cycling all-solid-state lithium metal batteries enabled by silver-carbon composite anodes, Nature Energy, 5, 299 (2020). Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a porous carbon-Ag composite that improves the dispersibility of Ag particles, prevents the aggregation of Ag particles, improves the application efficiency of Ag particles, and provides an excellent mechanical buffer function against thickness changes due to contraction / expansion during charge / discharge in a lithium deposition-type negative electrode.

[0009] Another object of the present invention is to provide a negative electrode containing the porous carbon-Ag composite, thereby improving the charge-discharge efficiency and life characteristics of the battery, and a lithium ion secondary battery including the same. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides A porous carbon-Ag composite is provided, which includes macroporous carbon particles and Ag particles inserted into the pores of the carbon.

[0011] The present invention also provides a current collector and a negative electrode active material layer, The negative electrode active material layer provides a negative electrode including the porous carbon-Ag composite.

[0012] The present invention also provides The present invention provides a lithium ion secondary battery including a positive electrode, the negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0013] In the porous carbon-Ag composite of the present invention, Ag particles are well fixed in the surface pores of the macroporous carbon, which improves the dispersibility of the Ag particles, prevents the aggregation of the Ag particles, and improves the application efficiency of the Ag particles.

[0014] In addition, in the case of a lithium deposition type anode, thickness changes significantly due to contraction / expansion during charge / discharge. However, in the porous carbon-Ag composite of the present invention, the pores of the macroporous carbon act as a mechanical buffer against such thickness changes, thereby improving the charge / discharge efficiency and life characteristics of the battery.

[0015] The negative electrode and lithium ion secondary battery of the present invention contain the porous carbon-Ag composite, thereby improving the charge-discharge efficiency and life characteristics of the battery. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram schematically illustrating the structure of a lithium ion secondary battery of the present invention in comparison with a conventional battery structure; [Figure 2] 1 is a SEM image showing the morphology of the macroporous carbon and the porous carbon-Ag composite used in the present invention; [Figure 3] 1 shows SEM images of microporous carbon (activated carbon) and non-porous carbon (carbon black) used in conventional technology. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will now be described in more detail to aid in understanding the invention.

[0018] The terms and words used in this specification and claims should not be interpreted limitedly to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention. Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expression includes the plural expression unless it has a clearly different meaning in the context.

[0019] When a component is referred to as being "connected to, equipped with, or mounted on" another component, it should be understood that the component may be directly connected to or mounted on the other component, but there may also be other components between them. Conversely, 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 between them. Meanwhile, other expressions describing the relationship between components, such as "on top of" and "directly on top of," or "between" and "immediately between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0020] As used herein, the term "combination" is inclusive of mixtures, alloys, reaction products, and the like, unless specifically stated to the contrary.

[0021] The porous carbon-Ag composite of the present invention is characterized by including macroporous carbon particles and Ag particles inserted into the pores of the carbon.

[0022] The porous carbon-Ag composite improves the dispersibility of Ag particles by effectively fixing them in the surface pores of the macroporous carbon, preventing their aggregation and improving the application efficiency of Ag particles. In particular, in the case of lithium deposition-type anodes, which experience significant thickness changes due to contraction / expansion during charge / discharge, the pores of the macroporous carbon act as a mechanical buffer against such thickness changes, improving the charge / discharge efficiency and life characteristics of the battery.

[0023] In one embodiment of the present invention, the macroporous carbon particles may include pores having a size of 60 nm to 0.5 μm on the surface thereof, The Ag particle size (D50) may be 20 nm to 100 nm.

[0024] If the macroporous carbon particles are composed only of pores on the surface that are less than 60 nm in size, the use of the macroporous carbon particles will be less effective in improving the dispersibility of Ag. If the particles contain pores that are too large, the Ag particles will be inserted into the internal pores of the macroporous carbon in large numbers, which may make it difficult for these Ag particles to perform their functions.

[0025] The macroporous carbon particles may contain pores of less than 60 nm in size, for example, pores of 10 nm to less than 60 nm in size, or may contain pores of 100 nm to 1 μm in size.

[0026] Furthermore, if the Ag particle size (D50) is less than 20 nm, it is undesirable because many Ag particles are inserted into the internal pores of the macroporous carbon, and if the Ag particle size exceeds 100 nm, it is undesirable because the lithium alloy formation, lithium ion intercalation induction, and lithium deposition energy reduction effects of the Ag particles may be reduced. The Ag particle size (D50) is preferably 30 nm to 60 nm, and more preferably 40 nm to 60 nm.

[0027] The pore size present on the surface of the macroporous carbon particles can be measured by BET measurement using nitrogen gas adsorption / desorption and statistical image analysis through SEM analysis, and the Ag particle size can be measured by statistical image analysis through SEM analysis.

[0028] In one embodiment of the present invention, the macroporous carbon particles having a size (D50) of 0.5 μm to 10 μm can be used, and those having a size of 0.7 μm to 5 μm can be more preferably used.

[0029] If the macroporous carbon particle size (D50) is less than 0.5 μm, the binder application content increases sharply, which is undesirable, and if it exceeds 10 μm, the application efficiency for Ag loading decreases, which is undesirable.

[0030] The particle size (D50) of the macroporous carbon can be measured by a particle size analysis method using laser diffraction.

[0031] In one embodiment of the present invention, the macroporous carbon particles have a BET specific surface area of ​​300 to 1000 m 2 / g, more preferably 400 to 600m 2 / g.

[0032] The BET specific surface area is 300m 2 If the amount is less than 1000m / g, the dispersion and support effect on Ag particles will be reduced, which is not preferable. 2 If the content exceeds 1 / g, the structure is easily destroyed during the pressure application process for constructing the all-solid-state battery, and it is difficult to maintain the macropore characteristics, which is undesirable.

[0033] In one embodiment of the present invention, the macroporous carbon particles may have a bulk density of 0.1 to 1 g / ml, preferably 0.1 to 0.5 g / ml, and more preferably 0.1 to 0.3 g / ml.

[0034] If the bulk density is less than 0.1 g / ml, the pore structure is highly developed, and the structure easily collapses during the pressure application process for constructing an all-solid-state battery, making it difficult to maintain macropore characteristics, which is undesirable. If the bulk density exceeds 1 g / ml, the pore structure is not properly developed, resulting in a high-density carbon structure, which significantly reduces the dispersion and support effects for Ag particles, which is undesirable.

[0035] In one embodiment of the present invention, the porous carbon-Ag composite may have a bulk density of 0.12 to 0.3 g / ml, 0.15 to 0.3 g / ml, 0.2 to 0.3 g / ml, 0.15 to 0.25 g / ml, or 0.2 to 0.25 g / ml. When the bulk density is within the above range, as shown in Figures 1 and 2, the amount of Ag particles inserted into the internal pores of the macroporous carbon particles is reduced, and a larger amount is fixed in the pores on the surface of the macroporous carbon particles, which is preferable because it improves the utilization efficiency of the Ag particles and maintains the porosity of the macroporous carbon particles.

[0036] Furthermore, if the bulk density of the porous carbon-Ag composite is less than 0.12 g / ml, the efficiency of application of Ag nanoparticles decreases, which is undesirable as it reduces the initial charge-discharge efficiency and battery efficiency, while if it exceeds 0.3 g / ml, the internal porosity of the macroporous carbon particles decreases, and the efficiency of the Ag particles contained inside the macroporous carbon particles also becomes very low. Therefore, as confirmed in Experimental Example 2, there is a drawback in that the initial charge-discharge efficiency and battery efficiency are reduced.

[0037] In one embodiment of the present invention, the porous carbon-Ag composite may contain 70 to 90 parts by weight of macroporous carbon particles and 10 to 30 parts by weight of Ag particles, based on the total weight, and more preferably 80 to 90 parts by weight of macroporous carbon particles and 10 to 20 parts by weight of Ag particles.

[0038] When the content ratio of the macroporous carbon particles to the Ag particles satisfies the above range, it is preferable because the charge / discharge efficiency and life characteristics are improved.

[0039] In one embodiment of the present invention, the porous carbon-Ag composite may further include 3 to 10 parts by weight of a binder, based on the total weight. For example, when wet preparing the porous carbon-Ag composite, a binder dissolved in a solvent may be used together with macroporous carbon and Ag particles. In this case, the porous carbon-Ag composite may include a binder. When the binder is included, the content of the macroporous carbon particles described above may be reduced by the content of the binder.

[0040] In one embodiment of the present invention, the porous carbon-Ag composite may further contain, in addition to Ag, particles that form an alloy with lithium. The metal particles may be particles of one or more metals selected from gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, and zinc.

[0041] The present invention includes a current collector and a negative electrode active material layer, The negative electrode active material layer provides a negative electrode including the porous carbon-Ag composite.

[0042] In one embodiment of the present invention, the negative electrode active material layer may contain, based on the total weight, 80 to 99 wt % of the porous carbon-Ag composite and 1 to 20 wt % of a binder, preferably 85 to 99 wt % of the porous carbon-Ag composite and 1 to 15 wt % of a binder, and more preferably 90 to 99 wt % of the porous carbon-Ag composite and 1 to 10 wt % of a binder.

[0043] When the content ratio of the negative electrode active material layer satisfies the above range, charge / discharge efficiency and life characteristics are improved, which is preferable.

[0044] The present invention also provides a negative electrode active material layer, comprising: a current collector; and The negative electrode active material layer may contain, based on the total weight, 50 to 98 wt % of macroporous carbon, 1 to 30 wt % of Ag particles, and 1 to 20 wt % of a binder, or 70 to 98 wt % of macroporous carbon, 1 to 20 wt % of Ag particles, and 1 to 10 wt % of a binder.

[0045] When the content ratio of the negative electrode active material layer satisfies the above range, charge / discharge efficiency and life characteristics are improved, which is preferable.

[0046] The present invention provides There is provided a lithium ion secondary battery comprising a positive electrode, the negative electrode of the present invention, and a solid electrolyte interposed between the negative electrode and the positive electrode.

[0047] The lithium ion secondary battery includes the negative electrode active material layer of the present invention, thereby providing improved driving characteristics.

[0048] In one embodiment of the present invention, the solid electrolyte may be a sulfide-based solid electrolyte.

[0049] In one embodiment of the present invention, the lithium ion secondary battery may be an anodeless battery, which means a battery in which a lithium deposition layer is formed between the negative electrode active material layer and the current collector during initial charging.

[0050] The embodiments of the present invention will be illustrated more specifically below.

[0051] <Configuration of lithium-ion secondary battery> A lithium ion secondary battery according to one embodiment of the present invention is a so-called all-solid-state lithium ion secondary battery that is charged and discharged by the movement of lithium ions between a positive electrode and a negative electrode. Specifically, this all-solid-state lithium ion secondary battery is composed of a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0052] (1) Positive electrode In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer arranged in this order toward the negative electrode.

[0053] The positive electrode current collector may be in the form of a plate or foil. The positive electrode current collector may be made of one metal or an alloy of two or more metals selected from the group consisting of indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, and lithium. The positive electrode current collector may further include a primer layer coated on the surface of the positive electrode current collector, the primer layer including a carbon-based conductive material and a binder. In this case, the adhesive strength and electrical conductivity between the positive electrode active material layer and the current collector may be significantly improved.

[0054] The positive electrode active material layer may reversibly absorb and release lithium ions. The positive electrode active material layer may include a positive electrode active material and a solid electrolyte.

[0055] The positive electrode active material may be a compound capable of intercalating / deintercalating lithium. Examples of the compound capable of intercalating / deintercalating lithium include Li a A 1-b B' b D'2 (wherein 0.90≦a≦1.8 and 0≦b≦0.5); Li a E1- b B' b O 2-c D' c (wherein 0.90≦a≦1.8, 0≦b≦0.5, and 0≦c≦0.05); LiE 2-b B' b O 4-c D' c (wherein 0≦b≦0.5 and 0≦c≦0.05); Li a Ni 1-b-c Co b B' c D' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Co b B' c O2-α F' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni 1-b-c Mn b B' c D' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li a Ni 1-b-c Mn b B' c O 2-α F' α (wherein, 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li a Ni b E c G d O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d G e O2 (wherein 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li a NiG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a CoG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a MnG b O2 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn2G b O4 (wherein 0.90≦a≦1.8, 0.001≦b≦0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Examples include those represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2); LiFePO4.

[0056] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D' is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0057] Specific examples of the positive electrode active material include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium salts such as lithium manganese oxide and lithium iron phosphate, and lithium sulfide, etc. The positive electrode active material layer may contain only one type selected from these compounds as the positive electrode active material, or may contain two or more types selected from these compounds.

[0058] The positive electrode active material may include, among the aforementioned lithium salts, a lithium salt of a transition metal oxide having a layered rock salt structure. Here, the "layered rock salt structure" refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the direction of a cubic rock salt structure, with each atomic layer forming a two-dimensional plane. Furthermore, the "cubic rock salt structure" refers to a sodium chloride structure, which is a type of crystal structure. For example, the "cubic rock salt structure" refers to a structure in which face-centered cubic lattices in which cations and anions are respectively formed are shifted from each other by half the angle of the unit cell.

[0059] Examples of lithium salts of transition metal oxides having such a layered rock salt structure include LiNix Co y Al z O2 (NCA) or LiNi x Co y Mn z It may be a ternary lithium transition metal oxide such as O2 (NCM) (where 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). The positive electrode active material layer (14) contains a lithium salt of such a layered rock salt type ternary transition metal oxide as the positive electrode active material, and can improve the energy density and thermal stability of the all-solid-state lithium ion secondary battery (100).

[0060] Here, examples of the shape of the positive electrode active material include particle shapes such as true spherical and elliptical spherical. Also, the particle size of the positive electrode active material is not particularly limited as long as it is within a range applicable to the positive electrode active material of a normal all-solid-state lithium ion secondary battery. Further, the content of the positive electrode active material in the positive electrode active material layer is also not particularly limited as long as it is within a range applicable to the positive electrode of a normal all-solid-state lithium ion secondary battery.

[0061] Of course, the compound may have a coating layer on its surface, or the compound may be mixed with a compound having a coating layer. The coating layer may include a coating element compound such as an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compounds constituting these coating layers may be amorphous or crystalline. Examples of the coating elements included in the coating layer 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 mixtures thereof. The coating layer formation process may use any coating method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material. Since this is easily understood by those skilled in the art, a detailed description will be omitted.

[0062] A specific example of the coating layer is Li2O-ZrO2.

[0063] 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 below.

[0064] The positive electrode active material layer may be formed by appropriately blending not only the positive electrode active material and the solid electrolyte described above, but also additives such as a conductive material, a binder, a filler, a dispersant, or an ion-conductive auxiliary agent.

[0065] Examples of the conductive material include graphite, carbon black, acetylene black, Ketjen black, single-walled / multi-walled carbon nanotubes, carbon fiber, carbon nanofiber, and metal powder. Examples of the binder include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Examples of the filler, dispersant, and ion-conducting additive can be known materials typically used in electrodes of all-solid-state lithium-ion secondary batteries.

[0066] (2) Negative electrode In the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer arranged in this order toward the positive electrode.

[0067] 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., does not form an alloy or compound with lithium. Examples of materials constituting the negative electrode current collector include copper, stainless steel, titanium, iron, cobalt, and nickel. The negative electrode current collector may be made of one of these metals, or an alloy or clad material of two or more metals.

[0068] The negative electrode active material layer may not contain lithium in the negative electrode current collector, the negative electrode active material layer, or between the negative electrode active material layer and the solid electrolyte layer in an initial state or after full discharge. As described below, when an all-solid-state lithium-ion secondary battery according to one embodiment is overcharged, the negative electrode active material contained in the negative electrode active material layer and lithium ions transferred from the positive electrode may form an alloy or compound, and a metal layer containing lithium as a primary component may be formed (deposited) on the negative electrode. The metal layer may be deposited and disposed between the negative electrode current collector and the negative electrode active material layer, within the negative electrode active material layer, or in all of these locations. Between the negative electrode current collector and the negative electrode active material layer, the metal layer containing lithium as a primary component may be disposed closer to the negative electrode current collector layer than to the negative electrode active material layer.

[0069] The negative electrode active material layer of the present invention contains Ag as the negative electrode active material. Therefore, the metal layer formed during overcharge can contain a Li(Ag) alloy containing a γ1 phase, a βLi phase, or a combination of these phases, in which Ag is dissolved in lithium. Therefore, during discharge, only Li dissolves from the Li(Ag) alloy constituting the metal layer, and the dissolved Ag remains, suppressing the generation of voids. In this case, the Ag content in the deposited Li-Ag solid solution can be 60 wt% or less. Within this range, the decrease in average discharge potential due to the influence of Ag can be effectively suppressed. On the other hand, if the Ag content in the deposited Li-Ag solid solution is too low, the amount of Ag remaining during discharge will be small, and the generation of voids may not be sufficiently suppressed. Therefore, the Ag content in the deposited Li-Ag solid solution can be 20 wt% or more, for example, 40 wt% or more.

[0070] If the negative electrode active material layer contains too little Ag, the amount of Ag remaining during discharge will also decrease, which may make it difficult to prevent the formation of voids. Therefore, the negative electrode active material layer may contain 10 wt % or more, for example, 20 wt % or more, of Ag based on 100 wt % of the total negative electrode active material contained in the negative electrode active material layer in an initial state when no charge or discharge is performed.

[0071] The negative electrode active material layer may further contain macroporous carbon as a negative electrode active material other than Ag, and may further contain one or more elements selected from Au, Pt, Pd, Si, Al, Bi, Sn, In, and Zn.

[0072] The negative electrode active material layer may further contain a binder. By including the binder, the negative electrode active material layer can be stabilized on the negative electrode current collector. Examples of materials constituting the binder include resin materials such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder may be made of one or more resin materials selected from these resin materials.

[0073] The negative electrode active material layer may also contain an additive used in a typical all-solid-state lithium ion secondary battery, such as a filler, a dispersant, an ion conductive material, etc. Specific examples of the additive are the same as those described above for the positive electrode.

[0074] The total 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 as a result, the performance of the all-solid-state secondary battery may not be sufficiently improved. By using the above-mentioned binder, the thickness of the negative electrode active material layer can be easily ensured at an appropriate level.

[0075] Meanwhile, the negative electrode may further include a film containing a material capable of forming an alloy or compound with lithium on the negative electrode current collector, and the film may be disposed between the negative electrode current collector and the negative electrode active material layer.

[0076] The negative electrode current collector does not react with lithium metal, but it can make it difficult to deposit a smooth lithium metal layer on top of it. The film can also be used as a wetting layer to deposit lithium metal evenly on top of the negative electrode current collector.

[0077] The material capable of forming an alloy with lithium metal used in the film may include silicon, magnesium, aluminum, lead, silver, tin, or a combination thereof. The material capable of forming a compound with lithium metal used in the film may include carbon, titanium sulfide, iron sulfide, or a combination thereof. The content of the material used in the film may be small enough to not affect the electrochemical properties and / or redox potential of the electrode. The film may be applied evenly on the negative electrode current collector to prevent cracking during charging cycles of the all-solid-state lithium-ion secondary battery. The film may be applied by physical vapor deposition (e.g., evaporation or sputtering), chemical vapor deposition, plating, or other methods.

[0078] 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.

[0079] (3) Solid electrolyte layer In the present invention, the solid electrolyte layer is disposed between a positive electrode and a negative electrode (for example, between a positive electrode active material layer and a negative electrode active material layer). The solid electrolyte layer includes a solid electrolyte capable of transferring ions. The solid electrolyte layer may include a sulfide-based solid electrolyte.

[0080] The sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In), or a combination thereof. The solid electrolyte may be made of one material selected from these sulfide-based solid electrolyte materials, or may be made of two or more materials.

[0081] The sulfide-based solid electrolyte may include a solid electrolyte represented by the following Chemical Formula 1:

[0082] [C1] Li x M' y PS z A w In the above Chemical Formula 1, x, y, z, and w are, independently of one another, between 0 and 6; M' is any one or more of As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; A is one or more of F, Cl, Br, or I.

[0083] The solid electrolyte may be any of the sulfide solid electrolyte materials containing sulfur (S), phosphorus (P), and lithium (Li) as constituent elements. For example, a material containing Li2S-P2S5 may be used. When a sulfide solid electrolyte material containing Li2S-P2S5 is used, the molar ratio of Li2S to P2S5 may be selected within the range of Li2S:P2S5=50:50 to 90:10.

[0084] The solid electrolyte may be in an amorphous state, a crystalline state, or a mixture of amorphous and crystalline states.

[0085] The solid electrolyte layer may further contain a binder. Examples of the binder include styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymer (SBS), nitrile-butadiene rubber (NBR), fluororubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polyacrylic acid, and other resins and acrylic binders. The binder may be the same as or different from the binders in the positive electrode active material layer and the negative electrode active material layer.

[0086] (4) Structure of all-solid-state lithium-ion secondary battery 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-described positive electrode, solid electrolyte layer, and negative electrode in this order.

[0087] <Manufacturing method for all-solid-state lithium-ion secondary batteries> Next, a method for producing the all-solid-state lithium-ion secondary battery will be described. The all-solid-state lithium-ion secondary battery according to one embodiment can be obtained by first preparing a positive electrode, a negative electrode, and a solid electrolyte layer, and then laminating the layers.

[0088] (1) Positive electrode manufacturing process The positive electrode fabrication process is described as follows: First, materials constituting the positive electrode active material layer (positive electrode active material, binder, etc.) are added to a non-polar solvent to prepare a slurry (or paste). Next, the obtained slurry is applied to a prepared positive electrode current collector. This is dried to obtain a laminate. Next, the obtained laminate is pressed, for example, using hydrostatic pressure, to obtain a positive electrode. Also, the pressing step is omitted.

[0089] (2) Negative electrode manufacturing process The negative electrode fabrication process is described as follows: First, materials constituting the negative electrode active material layer (macroporous carbon, Ag particles (or a porous carbon-Ag composite made of these materials), a binder, etc.) are added to a polar or nonpolar solvent to prepare a slurry (which may be a paste). Next, the obtained slurry is applied to a prepared negative electrode current collector to form the negative electrode active material layer.

[0090] When the negative electrode active material layer includes one or more additional layers, the additional layers may be stacked in the same manner as above.

[0091] Subsequently, the laminate obtained by the above method is pressed, for example, using hydrostatic pressure, to produce a negative electrode. The pressing step may be omitted. The method for applying the slurry to the negative electrode current collector is not particularly limited, and examples thereof include screen printing, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, and gravure coating.

[0092] Although the method for forming a two-layer negative electrode active material layer has been described above, when an additional layer is to be formed, a slurry for forming each layer may be prepared, and the layers may be sequentially stacked in the stacking order according to the method described above to manufacture a negative electrode.

[0093] (3) Solid electrolyte layer fabrication process The solid electrolyte layer can be made of, for example, a solid electrolyte containing a sulfide-based solid electrolyte material.

[0094] First, starting materials (e.g., Li2S, P2S5, etc.) are processed by melt quenching or mechanical milling to obtain a sulfide-based solid electrolyte material. For example, when using the melt quenching method, predetermined amounts of starting materials are mixed and formed into pellets, which are reacted in a vacuum at a predetermined reaction temperature and then quenched to produce a sulfide-based solid electrolyte material. The reaction temperature for the mixture of Li2S and P2S5 may be 400°C to 1000°C, for example, 800°C to 900°C. The reaction time may be 0.1 hours to 12 hours, for example, 1 hour to 12 hours. The quenching temperature of the reaction product may be 10°C or lower, for example, 0°C or lower, and the quenching rate may be typically 1°C / second to 10,000°C / second, for example, 1°C / second to 1000°C / second.

[0095] Furthermore, when a mechanical milling method is used, a sulfide-based solid electrolyte material can be produced by stirring and reacting the starting materials using a ball mill, etc. Furthermore, the stirring speed and stirring time in the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the rate at which the sulfide-based solid electrolyte material is produced, and the longer the stirring time, the higher the conversion rate of the raw materials to the sulfide-based solid electrolyte material.

[0096] The resulting mixed raw material (sulfide-based solid electrolyte material) is then heat-treated at a predetermined temperature and pulverized to produce a particulate solid electrolyte. If the solid electrolyte has a glass transition point, the heat treatment may cause it to change from amorphous to crystalline.

[0097] Subsequently, the solid electrolyte obtained by the above method can be formed into a film using a known film formation method such as an aerosol positioning method, a cold spray method, or a sputtering method, thereby producing a solid electrolyte layer. The solid electrolyte layer can also be produced by compressing solid electrolyte particles. The solid electrolyte layer can also be produced by mixing the solid electrolyte with a solvent and a binder, applying the mixture, drying it, and pressurizing it.

[0098] (4)Lamination process A solid electrolyte layer is disposed between the positive electrode and the negative electrode, and this is pressurized using, for example, hydrostatic pressure, to obtain an all-solid-state lithium ion secondary battery according to one embodiment.

[0099] The all-solid-state lithium-ion secondary battery of the present invention does not require application of high external pressure using end plates or the like, and can provide improved discharge capacity even when the external pressure applied to the positive electrode, negative electrode, and solid electrolyte layer during use is 1 MPa or less.

[0100] <Charging method for all-solid-state lithium-ion secondary batteries> Next, a method for charging the all-solid-state lithium-ion secondary battery will be described.

[0101] A method for charging an all-solid-state lithium-ion secondary battery according to an embodiment may involve charging the all-solid-state lithium-ion secondary battery beyond the charge capacity of the negative electrode active material layer (i.e., overcharging).

[0102] During the initial charging period, lithium may be absorbed within the negative electrode active material layer. When the negative electrode active material layer is charged beyond its charge capacity, lithium may be deposited on the back surface of the negative electrode active material layer, i.e., between the negative electrode current collector and the negative electrode active material layer, forming a metal layer that was not present at the time of manufacture. During discharge, lithium in the negative electrode active material layer and the metal layer may ionize and migrate to the positive electrode. Therefore, in the all-solid-state lithium-ion secondary battery of the present invention, lithium can be used as the negative electrode active material. Furthermore, the negative electrode active material layer coats the metal layer, thereby functioning as a protective layer for the metal layer and simultaneously suppressing the deposition and growth of resinous metallic lithium. This suppresses short-circuiting and capacity loss in the all-solid-state lithium-ion secondary battery and further improves its characteristics. Furthermore, according to one embodiment, the metal layer is not pre-formed, thereby reducing the manufacturing cost of the all-solid-state lithium-ion secondary battery.

[0103] 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 may be formed inside the negative electrode active material layer, or may be formed both between the negative electrode current collector and the negative electrode active material layer and inside the negative electrode active material layer.

[0104] The all-solid-state lithium ion secondary battery of the present invention can be fabricated in the form of a unit cell having a positive electrode / separator / negative electrode structure, a bi-cell having a positive electrode / separator / negative electrode / separator / positive electrode structure, or a stacked battery structure in which the unit cell structure is repeated.

[0105] The shape of the all-solid-state lithium ion secondary battery of the present invention is not particularly limited, and examples thereof include coin type, button type, sheet type, laminate type, cylindrical type, flat type, and prismatic type. It can also be applied to large batteries used in electric vehicles and the like. For example, the all-solid-state lithium ion secondary battery can also be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). It can also be used in fields requiring large-scale power storage. For example, it can be used in electric bicycles, power tools, and the like.

[0106] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0107] Examples 1 to 3 and Comparative Examples 1 to 5: Production of negative electrodes A negative electrode active material slurry composition was prepared using the carbon material, Ag nanoparticles, and binder listed in Table 1 below.

[0108] Specifically, a mixture of the carbon material, Ag nanoparticles, and PVdF binder listed in Table 1 below was placed in a Thinky mixer container together with NMP solvent and mixed at 2000 rpm to prepare a negative electrode active material slurry containing a porous carbon-Ag composite.

[0109] Each of the negative electrode active material slurries prepared above was coated on a SUS foil to a thickness of 10 μm and dried to prepare negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 5.

[0110] [Table 1]

[0111] Experimental Example 1: Measurement of apparent density of carbon-Ag composite The bulk density of the porous carbon-Ag composites prepared in Example 2 and Comparative Example 5 was measured according to the method of JIS K 1469. Specifically, porous carbon-Ag composites were prepared and used for bulk density measurement in the same manner as in Example 2 and Comparative Example 5, except that a PVdF binder was not used. That is, the carbon material and Ag nanoparticles were placed in a Thinky mixer container together with an NMP solvent and mixed at 2000 rpm to prepare a slurry. This was then dried to prepare a powdered carbon-Ag composite, and the bulk density was measured according to the method of JIS K 1469.

[0112] From the measurement results, it was confirmed that the bulk density of the porous carbon-Ag composite prepared in Example 2 was 0.22 g / ml, and the apparent density of the porous carbon-Ag composite prepared in Comparative Example 5 was 0.32 g / ml.

[0113] These results show that in the porous carbon-Ag composite prepared in Comparative Example 5, Ag particles were inserted into the internal pores of the macroporous carbon, resulting in an increased bulk density, whereas in the porous carbon-Ag composite prepared in Example 2, most of the Ag particles were located in the surface pores of the macroporous carbon, resulting in a relatively low density.

[0114] Manufacture of all-solid-state lithium-ion secondary batteries of Examples 4 to 6 and Comparative Examples 6 to 10 The positive electrode active material is 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 a container in a weight ratio of 77:20:1:2. After each addition, the mixture was mixed at 10,000 rpm for 30 seconds using a lab blender 10 times to prepare the positive electrode mixture.

[0115] The mixture was subjected to high shear mixing for 5 minutes at 100° C. using a Twin Screw Kneader (manufactured by LG Electronics) by applying a shear force of 100 to prepare a positive electrode mixture.

[0116] The positive electrode mixture was prepared into a 200 μm-thick freestanding film using a two-roll mill (manufactured by Inoue) at 100° C. The film was then placed on one side of a primer-coated aluminum current collector (thickness 1 μm), and the film was bonded to the current collector using a lamination roll maintained at 120° C. to prepare a positive electrode.

[0117] The negative electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 5 were used as the negative electrodes, and the electrolyte used in the battery of Comparative Example 1 was a liquid electrolyte prepared by injecting lithium hexafluorophosphate (LiPF6 1 mol) into ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 1:2), while the remaining batteries used a sulfide-based all-solid electrolyte (Li6PS6Cl). Pouch-type mono-cells were produced in Examples 4 to 6 and Comparative Examples 6 to 10.

[0118] The sulfide-based all-solid-state electrolyte was prepared by mixing Li6PS6Cl solid electrolyte and nitrile butadiene rubber (NBR) in xylene as a solvent, and then mixing with zirconia balls in a Thinky Mixer at 2,000 rpm for 1 minute 10 times to prepare a solid electrolyte slurry, which was then coated onto a PET film as release paper and dried in a vacuum oven at 45°C for 6 hours to prepare a membrane. The weight ratio of Li6PS6Cl to NBR was 95:5, and the membrane thickness was 100 μm.

[0119] After preparing an assembly by disposing a solid electrolyte between the negative electrode and the positive electrode, the assembly was placed in a pouch and sealed. The pouch was then fixed on an Al plate and subjected to a pressure treatment at 500 MPa for 30 minutes using an isostatic press to prepare an all-solid-state lithium secondary battery.

[0120] Experimental example 2: Battery characteristic evaluation The pouch-type mono-cells of Examples 4 to 6 and Comparative Examples 6 to 10 were operated under the following charge / discharge conditions at an operating voltage range of 4.25 V to 3.0 V and an operating temperature of 60° C., and the initial charge / discharge efficiency and cycle characteristics were evaluated. The results are shown in Table 2 below.

[0121] For reference, each of the batteries of the example and comparative example was mounted on a pressure jig, and the bolts / nuts located at the four corners were tightened with the same pressure of 1 N.m to prepare a monocell.

[0122] (1) The initial charge / discharge efficiency (%) was evaluated as the ratio of the single discharge capacity to the single charge capacity when the battery was charged and discharged once at 60°C under the following conditions:

[0123] Charging conditions: 0.1C CC charge up to 4.25V, then CV charge to 4.25V. 0.05C cut-off Discharge conditions: 0.1C CC discharge to 3.0V (2) The cycle characteristics were evaluated by repeating charge and discharge 50 times at 60°C under the following conditions, and calculating the ratio of the discharge capacity for 50 times to the discharge capacity for one time.

[0124] Charging conditions: 0.5C, 4.25V CC / CV, 0.1C cut-off Discharge conditions: 0.5C, 3.0V, CC

[0125]

Table 2

Claims

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

2. the macroporous carbon particles have pores on their surfaces with a size of 60 nm or more and 0.5 μm or less; 2. The porous carbon-Ag composite according to claim 1, wherein the Ag particle size (D50) is 20 nm or more and 100 nm or less.

3. The porous carbon-Ag composite according to claim 2, wherein the size (D50) of the macroporous carbon particles is 0.5 μm or more and 10 μm or less.

4. The BET specific surface area of ​​the macroporous carbon particles is 300 m ２ / g or more, 1000m ２ The porous carbon-Ag composite according to claim 3, wherein the Ag content is 0.1 / g or less.

5. 4. The porous carbon-Ag composite according to claim 3, wherein the macroporous carbon particles have a bulk density of 0.1 g / ml or more and 1 g / ml or less.

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

7. a current collector and a negative electrode active material layer, The negative electrode active material layer comprises the porous carbon-Ag composite according to any one of claims 1 to 6.

8. 8. The negative electrode of claim 7, wherein the negative electrode active material layer comprises, based on the total weight, 80 wt % to 99 wt % of the porous carbon-Ag composite and 1 wt % to 20 wt % of a binder.

9. A lithium ion secondary battery comprising: a positive electrode; the negative electrode according to claim 7; and a solid electrolyte interposed between the positive electrode and the negative electrode.

10. 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 anodeless battery.

Images