Lithium secondary battery having excellent thermal safety and method for manufacturing same

Abstract

According to one embodiment of the present disclosure, there is provided a lithium secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on one or both sides of the positive electrode current collector; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on one side or two sides of the negative electrode current collector; and a separator including a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and containing lithium aluminum titanium phosphate (LATP), in which the negative electrode active material layer and the oxide-based solid electrolyte layer face each other, wherein an inorganic layer containing a reduction product of the LATP and an SEI material is formed at an interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, and wherein an atomic content of F in the inorganic layer is included at 7 atomic percent (%) to 15 atomic percent based on all atoms present in the inorganic layer.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2023-0174493 filed on December 5, 2023, Korean Patent Application No. 10-2023-0169616 filed on November 29, 2023, and Korean Patent Application No. 10-2024-0166418 filed on November 20, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This disclosure relates to lithium secondary batteries with excellent thermal safety and methods for manufacturing the same. Background Technology

[0004] Due to the rapid increase in the use of fossil fuels, the demand for alternative or clean energy sources is growing, and as part of this, the most active research area is in the field of power generation and energy storage using electrochemistry.

[0005] Currently, secondary batteries are a representative example of electrochemical devices that utilize such electrochemical energy, and their application is gradually expanding.

[0006] Recently, with technological advancements and the increasing demand for mobile devices such as laptops, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly. Among such secondary batteries, lithium-ion batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, and are already commercially available and widely used, have been extensively studied.

[0007] Furthermore, with growing concern for environmental issues, research is frequently conducted on electric vehicles and hybrid electric vehicles that can replace fossil fuel-powered vehicles (e.g., gasoline and diesel vehicles), which are among the main causes of air pollution. Although nickel-metal hydride secondary batteries are primarily used as power sources for electric and hybrid electric vehicles, much research has been actively undertaken to utilize lithium secondary batteries with high energy density and high discharge voltage, some of which are already in the commercialization stage.

[0008] Lithium-ion secondary batteries typically have a structure in which a non-aqueous electrolyte is impregnated into an electrode assembly including a positive electrode, a negative electrode, and a porous separator. Typically, the positive electrode is prepared by coating a positive electrode mixture containing a positive electrode active material onto an aluminum foil, and the negative electrode is prepared by coating a negative electrode mixture containing a negative electrode active material onto a copper foil.

[0009] Typically, the positive electrode active material is a lithium transition metal oxide, while the negative electrode active material is a carbon-based material.

[0010] However, recently, with the development of fields requiring high-capacity batteries (such as electric vehicles and hybrid electric vehicles), the energy density level required for lithium secondary batteries has been continuously increasing, and attempts are being made to use Si-containing anodes with high theoretical capacity as anode active materials.

[0011] However, Si-based materials containing Si have attracted much attention due to their very high energy density, but they are materials that need improvement due to the irreversible phase formation of lithium silicates, which reduces coulombic efficiency and results in poor thermal stability due to the explosive reactions that occur during thermal runaway.

[0012] Currently, coulombic efficiency can be improved to some extent by compensating for irreversible reactions through the pre-lithiation process of Si-based materials. However, the SEI formed so far must be of good quality to reduce the increase in resistance and thus improve output characteristics, but thermal safety remains an issue. Summary of the Invention

[0013] Technical issues

[0014] Therefore, one object of this disclosure is to provide a lithium secondary battery with improved thermal safety and improved coulombic efficiency by controlling the SEI formation mode.

[0015] Technical solution

[0016] According to one embodiment of this disclosure, a lithium secondary battery is provided, comprising:

[0017] The positive electrode includes a positive current collector and a layer of positive active material formed on one or both sides of the positive current collector.

[0018] The negative electrode includes a negative electrode current collector and a layer of negative electrode active material formed on one or both sides of the negative electrode current collector, and

[0019] The separator includes a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and comprising lithium aluminum titanium phosphate (LATP).

[0020] The negative electrode active material layer and the oxide-based solid electrolyte layer face each other.

[0021] An inorganic layer containing LATP reduction products and SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer.

[0022] Based on all atoms present in the inorganic layer, the atomic content of F in the inorganic layer is included in the range of 7 atomic percentages (%) to 15 atomic percentages.

[0023] Here, the inorganic layer fills some or all of the pores of the oxide-based solid electrolyte layer, or the inorganic layer forms a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, or the inorganic layer includes all of these forms.

[0024] In this case, specifically, the inorganic layer can be configured to fill the pores of the oxide-based solid electrolyte layer at 10% to 100% volume based on the total pore volume, and form a separate layer with a thickness of 5 nm to 100 nm.

[0025] More specifically, LATP reduction products are formed in the form of 50% by weight or more filling the pores of an oxide-based solid electrolyte layer along the surface of the LATP particles.

[0026] SEI materials can form together with LATP reduction products on Li + In regions of locally high space charge concentration, the SEI material can be formed in the form of pores filling the surface of the LATP reduction product of an oxide-based solid electrolyte layer, or the SEI material can be formed as a single layer on the surface of the oxide-based solid electrolyte layer, or it can be formed in a manner that includes all of these forms.

[0027] The reduction product of LATP (which is a component of the inorganic layer) may include lithiated LATP formed by the spontaneous lithiation of LATP as shown in the following reaction formula 1.

[0028] [Reaction Formula 1]

[0029] Li 1.3 Al 0.3 Ti 1.7 (PO4)3 → Li3Al 0.3 Ti 1.7 (PO4)3

[0030] In addition, the SEI material (which is another component of the inorganic layer) may contain LiF, and in particular, it may also contain at least one material selected from Li2CO3 and Li2O.

[0031] In addition, the inorganic layer can be composed of LATP reduction products and SEI material.

[0032] Meanwhile, oxide-based solid electrolyte layers can be formed on both sides of the substrate.

[0033] The substrate can be a polyolefin substrate, and the oxide-based solid electrolyte layer can be composed of an oxide-based solid electrolyte containing lithium aluminum titanium phosphate (LATP) and a binder.

[0034] Here, an oxide-based solid electrolyte layer can be formed on one side of the substrate with a thickness of 0.1 μm to 20 μm.

[0035] Meanwhile, the positive electrode active material layer may contain a lithium transition metal oxide represented by the following chemical formula 1 as the positive electrode active material.

[0036] [Chemical Formula 1]

[0037] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O2

[0038] in,

[0039] M is selected from at least one of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and

[0040] 0 ≤ x ≤ 0.5, 0 <a<1,0<b<1,0<c<1。

[0041] Furthermore, based on the total weight of the negative electrode active material, the negative electrode active material layer may contain 80% by weight or more of pre-lithiated silicon oxide as the negative electrode active material.

[0042] In addition, lithium secondary batteries may also include an electrolyte containing LiFSI as a lithium salt and fluoroethylene carbonate (FEC) as an electrolyte solvent.

[0043] According to another embodiment of this disclosure, a method for manufacturing a lithium secondary battery is provided, the method comprising the following steps:

[0044] An oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) is formed on one or both sides of a substrate to prepare a separator.

[0045] A positive electrode active material layer is formed on one or both sides of the positive electrode current collector to prepare a positive electrode, and a negative electrode active material layer is formed on one or both sides of the negative electrode current collector to prepare a negative electrode.

[0046] An electrode assembly is fabricated by inserting a separator between the positive and negative electrodes so that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other.

[0047] Electrode components and electrolyte are incorporated into a secondary battery box to manufacture a secondary battery;

[0048] The secondary battery is positioned between a plurality of pressure plates, and pressure is applied to the secondary battery; and

[0049] The secondary battery is activated by applying pressure to it.

[0050] Here, multiple pressure plates can be fastened with multiple pressure bolts to apply pressure. Specifically, the pressure bolts can press the secondary battery with a fastening strength of 6 kgf·cm or greater, and more specifically, the pressure bolts can press the secondary battery with a fastening strength in the range of 10 kgf·cm to 20 kgf·cm.

[0051] In addition, the activation step can be carried out at a temperature of 40°C to 60°C. Attached Figure Description

[0052] Figure 1 This is a schematic diagram illustrating the state in which an inorganic layer is formed at the interface between the negative electrode and the separator according to one embodiment of the present disclosure.

[0053] Figure 2 A top view of a pressurizing apparatus used in the activation process of a method for manufacturing a lithium secondary battery according to another embodiment of this disclosure.

[0054] Figure 3 for Figure 2 A cross-sectional view of the pressurization device.

[0055] Figure 4 This is a SEM image of the surface of the separator obtained by disassembling a lithium secondary battery manufactured according to Experimental Example 1.

[0056] Figure 5 The image shows the XRD pattern of the separator obtained by disassembling the lithium secondary battery manufactured according to Experimental Example 1.

[0057] Figure 6 A graph showing the Si composition analysis of the negative electrode obtained by disassembling the lithium secondary battery manufactured according to Experimental Example 2, based on the coating depth.

[0058] Figure 7 A graph showing the compositional analysis of the negative electrode obtained by disassembling the lithium secondary battery manufactured according to Experimental Example 2, based on the coating depth.

[0059] Figure 8 A diagram showing the compositional analysis of the separator obtained by disassembling a lithium secondary battery manufactured according to Experimental Example 3, based on the coating depth.

[0060] Figure 9 A graph showing the DSC evaluation of the lithium secondary battery manufactured according to Experimental Example 4.

[0061] Figure 10 A graph showing the thermal evaluation of the lithium secondary battery manufactured according to Experimental Example 5.

[0062] Figure 11 A graph showing the DC-IR evaluation of the lithium secondary battery manufactured according to Experimental Example 6.

[0063] Figure 12 A graph showing a comparison of the discharge rate characteristics of the lithium secondary batteries manufactured according to Experimental Example 6.

[0064] Figure 13 A graph showing the DC-IR evaluation of the lithium secondary battery manufactured according to Experimental Example 7.

[0065] Figure 14 A graph showing a comparison of the discharge rate characteristics of the lithium secondary batteries manufactured according to Experimental Example 7. Detailed Implementation

[0066] In the following description and claims, the terms or words used should not be construed as limited to their ordinary or dictionary meanings, and this disclosure should be interpreted with meanings and concepts consistent with the technical concept of this disclosure, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their own inventions.

[0067] Unless otherwise defined, all terms used herein (including technical and scientific terms) are to be understood in the sense that would be commonly understood by one of ordinary skill in the art to which this disclosure pertains. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless specifically and explicitly limited.

[0068] The terminology used herein is provided to describe embodiments and not to limit the inventive concept. In this specification, the singular forms include the plural forms unless the context clearly indicates otherwise. The terms “comprising” and / or “including” as used herein do not exclude the presence or addition of one or more elements in addition to those mentioned.

[0069] At the same time, the term “composed of” as used herein means that, in addition to the listed components, it does not contain any other components at levels greater than the impurity level (i.e., trace amounts).

[0070] Because the dimensions and thicknesses of the components are arbitrarily shown in the accompanying drawings for ease of description, this disclosure is not necessarily limited to the dimensions and thicknesses shown. Thicknesses are depicted at an enlarged scale in the drawings to clearly show different layers and regions. Furthermore, the thickness of a particular layer or region is exaggerated in the drawings for ease of description.

[0071] When layers, films, regions, plates, etc., are disposed "on" a specific component, this description includes not only cases where layers, films, regions, plates, etc., are "directly disposed on" a specific component, but also cases where layers, films, regions, plates, etc., are disposed on a specific component via another component. When a component is "directly disposed on another component," this means that there is no new assembly between the two components. Furthermore, when an assembly is disposed "on" a reference component, this means that the assembly exists on top of or below the reference component, and does not necessarily mean that the assembly is disposed only on the top of the reference component opposite to the direction of gravity.

[0072] Furthermore, throughout this description, the term "in a plan view" refers to an object viewed from above, and the term "in a cross-sectional view" refers to a vertical cross-section of an object viewed from the side.

[0073] Lithium secondary batteries

[0074] One embodiment of the lithium secondary battery according to this disclosure includes:

[0075] The positive electrode includes a positive current collector and a layer of positive active material formed on one or both sides of the positive current collector.

[0076] The negative electrode includes a negative electrode current collector and a layer of negative electrode active material formed on one or both sides of the negative electrode current collector, and

[0077] The separator includes a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and comprising lithium aluminum titanium phosphate (LATP).

[0078] The negative electrode active material layer and the oxide-based solid electrolyte layer face each other.

[0079] An inorganic layer containing LATP reduction products and SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer.

[0080] Based on all atoms present in the inorganic layer, the atomic content of F in the inorganic layer is included in the range of 7 atomic percentages (%) to 15 atomic percentages.

[0081] positive electrode

[0082] The positive electrode has a structure including a positive electrode current collector and a layer of positive electrode active material formed on one or both sides of the positive electrode current collector.

[0083] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause any chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., can be used as the current collector.

[0084] The positive electrode current collector may have a thickness of 3 μm to 500 μm and may have fine protrusions and depressions formed on its surface to enhance the adhesion of the positive electrode active material layer. For example, the positive electrode current collector may be used in various forms (such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric structures).

[0085] The positive electrode active material layer may contain a positive electrode active material and may optionally contain a conductive material, a binder, and other additives.

[0086] There is no limitation on the positive electrode active material as long as it is a compound capable of reversibly intercalating and deintercalating lithium, where the positive electrode active material may specifically include a lithium metal oxide containing lithium and at least one metal (such as cobalt, manganese, nickel, or aluminum). More specifically, the positive electrode active material may include a lithium transition metal oxide represented by the following Chemical Formula 1:

[0087] [Chemical Formula 1]

[0088] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O2

[0089] Wherein,

[0090] M is at least one selected from Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and

[0091] 0 ≤ x ≤ 0.5, 0 < a < 1, 0 < b < 1, 0 < c < 1.

[0092] In addition, the positive electrode active material may include lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as Li 1+x' Ni 1-Y Mn Y O2 (where -0.5 ≤ x' ≤ 0.5, 0 < Y < 1), Li 1+x'' Mn 2-Z Ni Z O4 (where, -0.5 ≤ x'' ≤ 0.5, 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (such as Li 1+x''' Ni 1-Y1 Co Y1 O2 (where, -0.5 ≤ x''' ≤ 0.5, 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (such as Li 1+x'''' Co1-Y2 Mn Y2 O2 (where, -0.5 ≤ x'''' ≤ 0.5, 0 < Y2 < 1), Li 1+x''''' Mn 2-Z1 Co Z1 O4 (where, -0.5 ≤ x''''' ≤ 0.5, 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (such as Li 1+a1 (Ni p Co q Mn r )O2 (where, -0.5 ≤ a1 ≤ 0.5, 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li 1+a2 (Ni p1 Co q1 Mn r1 )O4 (where, -0.5 ≤ a2 ≤ 0.5, 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (such as Li 1+a3 (Ni p2 Co<00000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 )O2 and Li(Ni 0.8 Mn 0.1 Co 0.1 O2, etc.), lithium nickel cobalt aluminum oxides (e.g., Li(Ni) 0.8 Co 0.15 Al 0.05 (O2, etc.) or lithium nickel manganese cobalt aluminum oxide (e.g., Li(Ni) 0.86 Co 0.05 Mn 0.07 Al 0.02 Lithium iron phosphate (e.g., LiFePO4), etc., and mixtures of two or more thereof can be used, and may include lithium transition metal oxides Li(Ni) represented by chemical formula 1. 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2.

[0094] Based on the total weight of the positive electrode active material layer, the positive electrode active material may be included in an amount of 60% to 98% by weight, preferably 80% to 98% by weight, and more preferably 90% to 98% by weight.

[0095] The conductive material is a component used to further improve the conductivity of the positive electrode active material. There are no particular limitations on such conductive materials, as long as they are conductive without causing any chemical changes in the battery, and examples include: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked black; graphite powder, such as natural graphite, artificial graphite, or graphite with a well-formed crystal structure; conductive fibers, such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0096] Based on the total weight of the positive electrode active material layer, the conductive material may be included in an amount of 0.1 wt% to 20 wt%, specifically 0.5 wt% to 10 wt%, and more specifically 0.5 wt% to 5 wt%.

[0097] A binder is a component that facilitates the bonding between conductive materials, positive electrode active materials, and positive electrode current collectors. Examples of binders may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0098] Typically, the binder may be included in an amount of 0.5% to 20% by weight, specifically 0.5% to 10% by weight, and more specifically 0.5% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0099] In addition, other additives may include, for example, fillers as components used to suppress expansion. There are no particular limitations on fillers, as long as they can suppress electrode expansion without causing any chemical changes in the battery, and examples may include: olefinic polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber.

[0100] negative electrode

[0101] Similar to the positive electrode, the negative electrode has a structure in which a layer of negative electrode active material is formed on one or both sides of the negative electrode current collector.

[0102] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause any chemical changes in the battery. Examples of negative electrode current collectors can include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, and so on.

[0103] The thickness of the negative electrode current collector can typically range from 3 μm to 500 μm. Similar to the positive electrode current collector, the negative electrode current collector can have fine protrusions and depressions formed on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in a wide variety of forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven structures.

[0104] The negative electrode active material layer may contain the aforementioned conductive material, binder, and other additives together with the negative electrode active material.

[0105] In this disclosure, based on the total weight of the negative electrode active material, the negative electrode active material may contain 80% by weight or more of pre-lithiated silicon oxide that can exhibit high energy density, etc.

[0106] As mentioned above, silicon oxide is a material with problems such as reduced coulombic efficiency due to the formation of an irreversible phase of lithium silicate and poor thermal safety due to explosive reactions that occur during thermal runaway, and it was previously used only in mixtures with carbon-based materials at 10% by weight or less of the total weight of the negative electrode active material, and more specifically 5% by weight or less.

[0107] However, according to this disclosure, since the coulombic efficiency is improved by compensating for the irreversible reaction through the pre-lithiation process of Si-based materials, an inorganic-rich SEI with a high F content can be thickly formed by the reduction product of LATP as described below, thereby improving thermal safety, and thus it can be included in an amount of 80% to 100% by weight, specifically 90% to 100% by weight, and more specifically 100% by weight.

[0108] Meanwhile, silicon oxide can be specifically represented by the following chemical formula 2.

[0109] [Chemical Formula 2]

[0110] SiOx

[0111] Where x is 0 <x<2。

[0112] Specifically, the silicon oxide can be SiO2 or SiO, and more specifically, SiO.

[0113] Here, SiO is the total composition of the mixture of Si and SiO2, and the x value is determined based on the mixing ratio of Si and SiO2.

[0114] Silicon oxide can be included as a negative electrode active material in a pre-lithiated state, and pre-lithiation can be carried out, for example, by a physicoelectronic method of contacting Li with silicon oxide powder.

[0115] In addition to silicon oxides, negative electrode active materials may also include: at least one carbon-based material selected from graphite, amorphous hard carbon, low-crystallinity soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, and fibrous carbon; Si-based materials; and metal composite oxides, such as Li. x Fe2O3 (0≤x≤1), Li x WO2 (0≤x≤1), Sn x Me 1- x Me' y O zwhere Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SiO, SiO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides; and the like, without limitation, as long as they are known in the art.

[0116] Separator

[0117] The separator has a structure including a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and containing lithium aluminum titanium phosphate (LATP).

[0118] Here, the substrate can be used without particular limitation as long as it is commonly used as a substrate for a separator in a lithium secondary battery, and those having excellent electrolyte moisture retention ability while having low resistance to ion migration of the electrolyte are particularly preferred.

[0119] For example, the substrate is a polyolefin-based substrate such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, and a porous polymer film or a laminated structure of two or more layers thereof can be used. In addition, a typical porous non-woven fabric (e.g., a non-woven fabric made of glass fibers with a high melting point, polyethylene terephthalate fibers, etc.) can be used as the separator, but specifically, it can be a polyolefin substrate.

[0120] An oxide-based solid electrolyte layer is formed on one or both sides of the substrate.

[0121] In this case, the oxide-based solid electrolyte layer can contain an oxide-based solid electrolyte containing lithium aluminum titanium phosphate (LATP) and a binder.

[0122] In addition to lithium aluminum titanium phosphate, the oxide-based solid electrolyte layer may also include at least one lithium metal oxide or lithium metal phosphate selected from Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, garnet-type solid electrolytes, perovskite-type solid electrolytes, and LiPON-type solid electrolytes as other oxide-based solid electrolytes. More specific examples may include compounds selected from at least one of: LAGP (lithium aluminum germanium phosphate), LLZO (lithium lanthanum zirconium oxide), LLZTO (lithium lanthanum zirconium tantalum oxide), LLTO (lithium lanthanum titanium oxide), LSTP (lithium silicon titanium phosphate), and LGPO (lithium germanium phosphate). Specifically, it may be composed of lithium aluminum titanium phosphate.

[0123] Based on the total weight of the oxide-based solid electrolyte layer, the oxide-based solid electrolyte may be included in an amount of 70% to 99% by weight, and specifically 80% to 99% by weight.

[0124] If the content is too low and outside the above range, it may be impossible to obtain sufficient reduction product as desired in this application. If the content is too high, the content of the binder that connects them is too low, which weakens the bond strength between the particles and may therefore deteriorate the mechanical properties, which is not preferred.

[0125] The average diameter (D50) of oxide-based solid electrolyte particles can be from 50 nanometers to 10 micrometers, specifically from 50 nanometers to 5 micrometers, and more specifically from 50 nanometers to 1 micrometer.

[0126] If the average diameter is too small and falls outside the above range, particle aggregation may occur due to reduced dispersibility. Conversely, if the average diameter is too large, the pores formed due to the oxide-based solid electrolyte are too large, which is not preferable in terms of resistance. That is, when the average diameter meets the above range, lithium-ion conductivity can be improved, thereby reducing resistance and exhibiting improved secondary battery performance.

[0127] As used herein, the average diameter D50 refers to the particle size at which the cumulative volume of the particles reaches 50% in the particle size distribution curve. D50 can be measured, for example, using laser diffraction. Laser diffraction can typically measure particle sizes in the submicron range to several millimeters and can obtain results with high reproducibility and high resolution.

[0128] Meanwhile, there are no restrictions on the binder for other components of the oxide-based solid electrolyte layer, as long as it does not cause side reactions with the electrolyte. However, in particular, binders with the lowest possible glass transition temperature (Tg) can be used, preferably in the range of -200°C to 200°C.

[0129] Furthermore, the adhesive does not necessarily need to have ion conductivity, but it is more preferable to use a polymer with ion conductivity.

[0130] Therefore, if possible, the binder preferably has a high dielectric constant. In fact, since the degree of dissociation of salts in the electrolyte depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the greater the improvement in the degree of salt dissociation in the electrolyte. The dielectric constant of the polymer can be 1 or greater, specifically in the range of 1.0 to 100 (measurement frequency = 1 kHz), and particularly preferably 10 or greater.

[0131] In addition to the aforementioned functions, the binder can also exhibit a high electrolyte impregnation rate (swelling degree) upon gelation when impregnated in a liquid electrolyte. When the binder has a practically excellent electrolyte impregnation rate, the electrolyte injected after battery assembly can permeate into the polymer, and the polymer containing the absorbed electrolyte possesses electrolyte ion conductivity. Therefore, if possible, a solubility parameter of 15 MPa is preferred. 1 / 2 up to 45 MPa 1 / 2 The polymer, and more preferably 15 MPa 1 / 2 Up to 25 MPa 1 / 2 and 30 MPa 1 / 2 up to 45 MPa 1 / 2 The range. When the solubility parameter is less than 15 MPa. 1 / 2 or greater than 45 MPa 1 / 2 At that time, it will become difficult to be swollen by the typical liquid electrolyte used in batteries.

[0132] Examples of adhesives include those selected from at least one of the following: polyvinylidene fluoride-copoly-hexafluoropropylene, polyvinylidene fluoride-copoly-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-copoly-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, and polyvinyl alcohol.

[0133] In detail, the oxide-based solid electrolyte layer of this application is intended to make the LATP contained in such an oxide-based solid electrolyte layer face the negative electrode active material layer of the negative electrode, thereby forming a reduction product of LATP at the interface between them. Therefore, the oxide-based solid electrolyte layer of this application is preferably composed of an oxide-based solid electrolyte containing LATP and a binder, and preferably does not contain other materials, as they may interfere with the reduction of LATP.

[0134] Therefore, based on the total weight of the oxide-based solid electrolyte layer, the binder can be included in an amount of 1% to 30% by weight, specifically 1% to 20% by weight.

[0135] Such an oxide-based solid electrolyte layer can be formed on one or both sides of the substrate, but it is preferred to form it on both sides because it exhibits better overvoltage reduction when formed on both sides. Of course, when the oxide-based solid electrolyte layer is formed on only one side, the electrode assembly must be manufactured such that the oxide-based solid electrolyte layer faces the negative electrode active material layer of the negative electrode to form the LATP reduction product desired in this application.

[0136] In this case, the oxide-based solid electrolyte layer can be formed on one side of the substrate with a thickness of 0.1 μm to 20 μm, and specifically, with a thickness of 1 μm to 10 μm.

[0137] If the thickness is too thin and outside the above range, the desired effect of generating LATP reduction products may not be achieved, while if the thickness is too thick, the resistance may increase, which is not preferred.

[0138] Meanwhile, the total thickness of the separator, including the substrate and the oxide-based solid electrolyte layer, can be from 5 micrometers to 50 micrometers, specifically from 5 micrometers to 40 micrometers, and more specifically from 10 micrometers to 30 micrometers. If the thickness of the separator meets the above range, short circuits between the positive and negative electrodes can be effectively prevented while minimizing the resistance of the lithium secondary battery. Therefore, the energy density of the lithium secondary battery can be prevented from decreasing and its lifespan characteristics can be improved.

[0139] Simultaneously, if the oxide-based solid electrolyte layer is formed on one or both sides, the oxide-based solid electrolyte layer faces the negative electrode active material layer, thereby forming LATP reduction products at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer. Specifically, lithium ions move during the charging / discharging (especially the activation process) of the lithium secondary battery, thereby forming reduction products.

[0140] Here, the reduction product of LATP may include lithiated LATP formed by the spontaneous lithiation reaction of LATP as shown in the following reaction formula 1.

[0141] [Reaction Formula 1]

[0142] Li 1.3 Al 0.3 Ti 1.7 (PO4)3 → Li3Al 0.3 Ti 1.7 (PO4)3

[0143] Furthermore, at the interface between the negative electrode and the separator, lithium ions react with the electrolyte during the charging / discharging (especially the activation process) of the lithium secondary battery to form SEI material.

[0144] Therefore, an inorganic layer containing LATP reduction products and SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, and specifically, the inorganic layer can be composed of LATP reduction products and SEI material.

[0145] In this case, the SEI material may contain LiF, and more particularly, may also contain at least one material selected from Li₂CO₃ and Li₂O. In other words, the inorganic layer may contain lithiated LATP and LiF, and in addition, may contain at least one material selected from Li₂CO₃ and Li₂O.

[0146] Such inorganic layers are formed through the bonding between LATP in the oxide-based solid electrolyte layer and lithium ions, as well as the reaction between the electrolyte and lithium ions, and thus can be formed primarily on the surface of the oxide-based solid electrolyte layer.

[0147] In this case, since the oxide-based solid electrolyte layer includes pores, the inorganic layer can be formed in the form of filling some or all of the pores of the oxide-based solid electrolyte layer, or it can be formed as a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, or it can include all of these forms, i.e., it can be included in the pores or it can be formed at the same time as forming the layer.

[0148] When the inorganic layer fills the pores of the oxide-based solid electrolyte layer, it can fill 10% to 100% of the total pore volume, specifically 30% to 100% of the total pore volume, and more specifically 50% to 80% of the total pore volume.

[0149] Furthermore, when the inorganic layer is formed as a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, the thickness of the layer can be from 5 nm to 100 nm, specifically from 5 nm to 50 nm, and more specifically from 10 nm to 50 nm.

[0150] More specifically, since the LATP-based oxide solid electrolyte layer begins to form reduction products upon encountering pre-lithiated silicon oxide, the LATP reduction products are formed in the form of filling the pores of the oxide-based solid electrolyte layer along the surface of the LATP particles in a manner greater than 50% by weight, when the surface of the separator becomes Li-containing due to the charging (e.g., activation process) of the lithium secondary battery. + When the concentration of Li ions in a locally high space charge region is high, SEI material is formed through side reactions between Li ions in the space charge region and the electrolyte.

[0151] Therefore, the SEI material can be formed together with the LATP reduction products in the above regions, or it can be formed in the form of pores in an oxide-based solid electrolyte layer filling the surface of the LATP reduction products, or it can be formed as a separate layer on the surface of the oxide-based solid electrolyte layer, or it can be formed in all of these forms.

[0152] To more easily explain the formation of such inorganic layers Figure 1 A schematic diagram of the interface between the separator and the negative electrode of this disclosure is shown.

[0153] Reference Figure 1 The separator 110 has a structure including a substrate 111 and an oxide-based solid electrolyte layer 112 containing LATP formed on one side of the substrate 111. This oxide-based solid electrolyte layer 112 is in direct contact with a negative electrode active material layer 121 formed on a negative electrode current collector 122 of the negative electrode 120. When LATP and Li ions meet at their interface, a reduction product 131 is formed, containing lithium-ionized LATP that has been spontaneously reduced therein. At this time, 50% by weight or more of the reduction product forms along the surface of the LATP particles and fills the pores of the oxide-based solid electrolyte layer 112. Then, the pores of the oxide-based solid electrolyte layer and its surface have a space charge region 132 with locally high Li+ concentration, and an SEI material is formed in this region 132 by a side reaction of the electrolyte. This SEI material, together with or alone, fills the remaining pores of the oxide-based solid electrolyte layer, also forming a separate layer with a thickness t. An additional inorganic layer 132 is formed on the surface of the oxide-based solid electrolyte layer 112.

[0154] In addition, in order to achieve the desired effect of this disclosure, the inorganic layer may contain F atoms in an amount of 7 atomic percentage (%) to 15 atomic%, specifically 8 atomic percentage (%) to 15 atomic%, and more specifically 10 atomic percentage (%) to 13 atomic%.

[0155] If the F atom content is low and outside the above range, a thick organic component layer with low interatomic binding energy and low lithium-ion conductivity is formed instead of an inorganic-rich (i.e., inorganic-rich) SEI layer. This results in an easily decomposed SEI layer, leading to unstable thermal stability and increased electrical resistance, which is not preferred. On the other hand, if the F atom content is too high, an excessive amount of material containing such F must be added to the electrolyte. This easily leads to side reactions within the electrolyte, increases the electrolyte viscosity, and reduces the ionic conductivity for lithium-ion movement through the electrolyte, which is also not preferred.

[0156] Furthermore, as mentioned above, the inorganic layers are grown in the pores of the oxide-based solid electrolyte layer and at their interface with the negative electrode, allowing them to be formed to be thicker than typical SEI layers, which is more effective in improving thermal safety.

[0157] electrolyte

[0158] In addition, lithium secondary batteries may also include an electrolyte.

[0159] Here, the electrolyte is a non-aqueous lithium electrolyte and may contain lithium salts and non-aqueous organic solvents.

[0160] Lithium salts are used as a medium for transferring ions within lithium secondary batteries. For example, lithium salts can contain Li. + It is a cation, and may contain at least one of the following as an anion: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3- (CF3CF2SO2)2N - (CF3SO2)2N - (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2)2CH - CF3(CF2)7SO3 - and SCN - .

[0161] Specifically, lithium salts may include a single substance or a mixture of two or more of the following: LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2), and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), but more specifically, lithium salts can essentially include Li[N(SO2F)2], i.e., LiFSI, thereby increasing the F atom content in the inorganic layer and reducing thermal decomposition to improve thermal safety.

[0162] Apart from these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without particular restrictions.

[0163] The concentration of lithium salt can be appropriately varied within the generally available range, but lithium salt can be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically 1 M to 2.5 M, and even more specifically 1 M to 2 M, to achieve the best effect of forming a film on the electrode surface to prevent corrosion. When the concentration of lithium salt meets the above range, the effect of improving the cycle characteristics of lithium secondary batteries during high-temperature storage is sufficient, and the viscosity of the electrolyte is appropriate to improve electrolyte impregnation.

[0164] There are no restrictions on non-aqueous organic solvents, as long as they minimize decomposition caused by oxidation reactions, etc., during the charging and discharging of lithium secondary batteries, and exhibit the desired properties with the additives. For example, carbonate-based organic solvents, ether-based organic solvents, ester-based organic solvents, etc., or mixtures of both or more thereof, can be used alone, and specifically, carbonate-based organic solvents can be used.

[0165] The carbonate-based organic solvents in the organic solvents can include at least one selected from organic solvents based on cyclic carbonates and organic solvents based on linear carbonates. Specifically, the cyclic carbonate-based organic solvents can include at least one selected from: ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, vinylene carbonate, vinyl ethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, the organic solvent can include fluoroethylene carbonate (FEC) to increase the F atom content in the inorganic layer, thereby achieving the desired effect of this application.

[0166] Furthermore, the organic solvent based on linear carbonates is a solvent with low viscosity and low dielectric constant, and may include at least one of the following: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl ethyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and more specifically, it may include diethyl carbonate.

[0167] Ether-based organic solvents may include, but are not limited to, any of the following: ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or mixtures of two or more thereof.

[0168] Ester-based organic solvents may include at least one selected from linear ester-based organic solvents and cyclic ester-based organic solvents.

[0169] Specific examples of organic solvents based on linear esters may include, but are not limited to, any of the following: methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, or mixtures of two or more thereof.

[0170] Specific examples of organic solvents based on cyclic esters may include, but are not limited to, any of the following: γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone, or mixtures of two or more thereof.

[0171] In ester-based solvents, cyclic carbonate-based compounds are preferred because they are high-viscosity organic solvents that effectively dissociate lithium salts in the electrolyte due to their high dielectric constant. When the above-mentioned cyclic carbonate-based compounds are mixed with low-viscosity, low-dielectric-constant linear carbonate-based compounds (e.g., dimethyl carbonate and diethyl carbonate) in appropriate ratios, a gel-type electrolyte with high conductivity can be prepared, which is even more preferable.

[0172] In addition, non-aqueous lithium electrolytes also contain functional additives, which may be used to prevent negative electrode collapse in high-power environments, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharging prevention, and swelling reduction during high-temperature storage.

[0173] Specifically, as a representative example, functional additives may include at least one functional additive selected from the following: compounds based on sulfonyl lactones, compounds based on sulfites, compounds based on sulfones, compounds based on sulfates, compounds based on halogen-substituted carbonates, compounds based on nitriles, compounds based on cyclic carbonates, compounds based on phosphate esters / salts, compounds based on borate esters / salts, and compounds based on lithium salts.

[0174] The sulfonyl-based compound may include at least one compound selected from the group consisting of 1,3-propanesulfonyl (PS), 1,4-butanesulfonyl, ethanesulfonyl, 1,3-propenesulfonyl (PRS), 1,4-butenesulfonyl, and 1-methyl-1,3-propenesulfonyl, and may be included in an amount of 0.3% to 5% by weight, particularly 1% to 5% by weight, based on the total weight of the gel electrolyte. When the amount of the sulfonyl-based compound in the gel electrolyte exceeds 5% by weight, an excessively thick layer may form on the electrode surface, leading to increased resistance and output degradation, and the increased resistance due to excessive additives may further degrade the output characteristics.

[0175] The sulfite-based compound may include at least one compound selected from the following: ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, and 1,3-butanediol sulfite, and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0176] The sulfone-based compound may include at least one compound selected from the following: divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0177] The sulfate-based compounds may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS), and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0178] Furthermore, compounds based on halogen-substituted carbonates may include fluoroethylene carbonate (FEC) and may be included in an amount of 5% by weight or less based on the total weight of the gel electrolyte. When the amount of halogen-substituted carbonate compounds in the gel electrolyte exceeds 5% by weight, the battery swelling performance may deteriorate.

[0179] In addition, nitrile-based compounds may include at least one compound selected from the following: succinate, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanoic acid, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzyl nitrile, 4-fluorobenzyl nitrile, difluorobenzyl nitrile, trifluorobenzyl nitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0180] The cyclic carbonate-based compound may include vinylene carbonate (VC) or ethylene ethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte. If the content of the cyclic carbonate-based compound in the gel electrolyte is greater than 3% by weight, the battery swelling suppression performance may deteriorate.

[0181] The phosphate ester / salt-based compound may include at least one compound selected from the following: lithium difluoro(bis(oxalato)phosphate), lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite, and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0182] Borate-based compounds may include lithium oxaloyl difluoroborate and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0183] The lithium salt-based compound is a compound that is different from the lithium salt contained in the lithium non-aqueous electrolyte. The lithium salt-based compound may include at least one compound selected from the following: LiPO2F2, LiODFB, LiBOB (lithium bis(oxalato)borate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3% by weight or less based on the total weight of the gel electrolyte.

[0184] Two or more functional additives may be mixed, and may be included in an amount of 20% by weight or less, particularly from 0.1% to 10% by weight, based on the total weight of the lithium non-aqueous electrolyte. If the content of the functional additives is greater than 20% by weight, there is a possibility that excessive side reactions may occur in the lithium non-aqueous electrolyte during battery charging and discharging. In particular, it may not decompose sufficiently at high temperatures and may exist in the lithium non-aqueous electrolyte as unreacted material or in a precipitated state at room temperature. As a result, side reactions that reduce the lifespan or resistivity characteristics of the lithium metal battery may occur.

[0185] Manufacturing method of lithium secondary batteries

[0186] Additionally, according to another embodiment of this disclosure, a method for manufacturing lithium secondary batteries is provided.

[0187] Specifically, the method for manufacturing lithium secondary batteries includes the following steps:

[0188] An oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) is formed on one or both sides of a substrate to prepare a separator.

[0189] A positive electrode active material layer is formed on one or both sides of the positive electrode current collector to prepare a positive electrode, and a negative electrode active material layer is formed on one or both sides of the negative electrode current collector to prepare a negative electrode.

[0190] An electrode assembly is fabricated by inserting a separator between the positive and negative electrodes, so that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other.

[0191] Electrode components and electrolyte are incorporated into a secondary battery box to manufacture a secondary battery;

[0192] Positioning the secondary battery between a plurality of pressure plates and applying pressure to the secondary battery; and

[0193] The secondary battery is activated by applying pressure to it.

[0194] Figure 2 and Figure 3 Top view and cross-sectional view of a pressurizing device used in a method for manufacturing lithium secondary batteries are shown schematically, respectively.

[0195] The lithium secondary battery according to this disclosure is manufactured as follows: a positive electrode, a negative electrode and a separator as described above are prepared respectively, and the electrode assembly is prepared by laminating the oxide-based solid electrolyte layer of the separator and the negative electrode active material layer of the negative electrode to each other in such a way that they are facing each other, and then the assembly is incorporated into a secondary battery case together with the electrolyte.

[0196] Then, refer to Figure 2 and Figure 3 With the plate-shaped pressure plate 210 positioned above or below or to the left or right of the lithium secondary battery 200, pressure is applied to the lithium secondary battery 200 above or below or to the left or right. Figure 2 and Figure 3 In this process, since the pressure plate 210 is used as an intermediate medium to apply a predetermined pressure F to both the upper and lower parts of the lithium secondary battery 200 at the same time, the pressure can be applied more evenly compared to the case where pressure is applied directly to the lithium secondary battery 200 without an intermediate medium or only to one side of the upper and lower sides.

[0197] Alternatively, one side of the lithium secondary battery 200 can be fixed to the support, while pressure is applied only to the opposite side. For example, while the movable pressure plate 210 continuously applies pressure to the stationary support (i.e., the support and pressure plate are completely and tightly fitted), an external force is applied to the pressure plate 210 to temporarily create a predetermined space for inserting the lithium secondary battery 200, and then the external force applied to the pressure plate 210 is removed. At this time, a uniform pressure F can be applied to both sides of the lithium secondary battery 100 very easily.

[0198] Here, multiple pressure plates 210 can be fastened with multiple pressure bolts 220 to apply pressure to the lithium secondary battery 200. As described above, when pressure F is applied by fastening with pressure bolts 220, it has the advantage of applying pressure to the correct position.

[0199] For example, the applied pressure F can be represented by the tightening torque strength of the pressure clamp 120, which can press with a tightening strength of 6 kgf·cm or greater, specifically, with a tightening strength of 10 kgf·cm to 20 kgf·cm.

[0200] When pressure is applied with a fastening strength of less than 6 kgf·cm, it may be difficult to form an effective SEI.

[0201] Meanwhile, when two or more lithium secondary batteries are stacked and pressure is applied simultaneously to the top and bottom using a pressure plate as an intermediate medium, pressure can be applied evenly to the plurality of lithium secondary batteries. Furthermore, a multi-layered pressure application method is also feasible, i.e., inserting the lithium secondary batteries one by one between the plurality of pressure plates and then applying pressure.

[0202] Then, activation can be performed under pressure applied to the lithium secondary battery.

[0203] Here, activation may include a charge-discharge process and may be carried out at 25°C to 60°C, more specifically, at a temperature of 40°C to 60°C.

[0204] Specifically, through the activation process in the manufacturing process of lithium secondary batteries as described above, an inorganic layer containing LATP reduction products and SEI material can be formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer. Furthermore, by applying a specific range of pressure to the lithium secondary battery during the activation step, the formation mode of the inorganic layer containing LATP reduction products and SEI material can be controlled with high quality.

[0205] In the following description, a lithium secondary battery according to one embodiment of the present disclosure will be shown with reference to examples to demonstrate its improved performance.

[0206] Example 1 (LATP)

[0207] An oxide-based solid electrolyte layer (thickness: 2 μm) is formed on both sides of a polyolefin substrate (polyethylene, thickness: 9 μm) to prepare a separator.

[0208] Here, an oxide-based solid electrolyte layer is prepared by: applying Li 1.3 Al 0.3 Ti 1.7 (PO4)3: Acrylic copolymer (CSB130, Toyoink) was mixed in a weight ratio of 95:5, the mixture was dispersed in acetone to prepare an electrolyte slurry, the electrolyte slurry was coated on one side of a polyolefin substrate and dried.

[0209] Comparative Example 1 (CCS)

[0210] An organic / inorganic hybrid layer (thickness: 20 μm) is formed on both sides of a polyolefin substrate (polyethylene, thickness: 9 μm) to prepare a separator.

[0211] Here, the organic / inorganic hybrid layer is prepared by mixing Al2O3 and CSB130 at a weight ratio of 95:5 and dispersing the mixture in NMP to prepare an organic / inorganic slurry. The organic / inorganic slurry is then coated onto one side of a polyolefin substrate and dried.

[0212] <Experimental Example 1>

[0213] First, surface SEM images of the separator prepared in Example 1 were taken and shown. Figure 4 In the middle, XRD analysis was performed and presented. Figure 5 In the diagram.

[0214] Then, a 15-micrometer-thick aluminum (Al) metal film was prepared as the positive electrode current collector. Li(Ni) was then used as the positive electrode active material. 0.86 Co 0.05 Mn 0.07 Al 0.02 O2, carbon nanotubes as conductive materials, and PVDF as a binder were added to NMP solvent in a weight ratio of 96:1:3 and dispersed to prepare a positive electrode slurry. The positive electrode slurry was coated onto one side of an aluminum metal film to a thickness of 60 micrometers, followed by drying and rolling to prepare the positive electrode.

[0215] An 8-micrometer-thick copper (Cu) metal film was prepared as the negative electrode current collector. Pre-lithiated SiO (as the negative electrode active material), carbon black (as the conductive material), and SBR and CMC (as binders) were added to NMP solvent in a weight ratio of 80:10:9.5:0.5 and dispersed to prepare a negative electrode slurry. The negative electrode slurry was coated onto one side of the copper metal film to a thickness of 100 micrometers, followed by drying and rolling to prepare the negative electrode.

[0216] The separator prepared in Example 1 was inserted between the positive and negative electrodes, and the oxide-based solid electrolyte layer or organic-inorganic hybrid layer was positioned facing the negative electrode to prepare an electrode assembly. An electrolyte obtained by dissolving 1.0 M LIFSI and 0.5 M LiPF6 in a non-aqueous organic solvent with a composition of fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 10:90 (volume ratio) was injected into the electrode assembly to fabricate a 100 mA pouch cell.

[0217] With the pressure clamps tightened to a strength of 12 kgf·cm, the dual batteries were charged at 25°C with a constant current of 0.1 C until the voltage reached 4.20 V. They were then aged at 25°C for 24 hours, then at 60°C for 20 hours, and finally completely discharged at a constant current of 0.33 C. This cycle was repeated three times.

[0218] After disassembling the dual-battery system after charging and discharging, SEM images of the separator surface were taken and presented together with SEM images of the separator before charging and discharging. Figure 4 XRD analysis was performed by irradiating the surface of the separator with X-rays at angles from 0 to 50 degrees and comparing the resulting diffraction patterns with the peak positions of LATP from ICDD and lithium-ionized LATP. The results are shown in [Figure / Table / Illustration]. Figure 5 middle.

[0219] Reference Figure 4 and Figure 5 It can be determined that after charging and discharging, Li reduction products are formed on the surface of the separator according to this disclosure, thereby filling the pores of the oxide-based solid electrolyte layer.

[0220] <Experimental Example 2>

[0221] A dual battery was manufactured using the separator of Example 1 and the separator of Comparative Example 1 in the same manner as in Experimental Example 1, and then subjected to charging and discharging.

[0222] The dual-cell assembly was then disassembled, and a separator sample was etched onto the negative electrode surface using a sputtering torch on an XPS instrument. Elemental quantitative analysis was performed along the depth direction (spot size: 200 μm, sputtering torch energy: 1000 eV, etching rate: 1.08 nm / s) to examine the composition and thickness of the SEI material through the analysis of elemental content. The results are shown below. Figure 6 and Figure 7 In addition, the atomic content of F is shown in Table 1 below.

[0223] Specifically, Figure 6 The results of analyzing the Si content on the negative electrode surface are shown, and the thickness of the inorganic layer is examined accordingly. Figure 7 The content analysis of other elements Li, F, C and O is shown.

[0224] Reference Figure 6 As can be seen, in the negative electrode of the dual cell using the separator of Comparative Example 1, the Si content increases in a short period of time, indicating that the inorganic layer is relatively thin. In contrast, in the negative electrode of the dual cell using the separator of Example 1 of this disclosure, Si exposure occurs later, indicating that a thicker inorganic layer is formed.

[0225] On the other hand, refer to the following Figure 7 As can be seen from Table 1, on the negative electrode surface of the dual cell using the separator of Example 1, the contents of Li, F and O are high, while the contents of C are low, indicating that a large amount of SEI materials such as LiF and Li2O are formed.

[0226] [Table 1]

[0227]

[0228] <Experimental Example 3>

[0229] As in Experimental Example 2, the separator from Example 1 underwent XPS profile analysis, and the elemental composition was analyzed. The results are shown in... Figure 8 middle.

[0230] Then, the dual batteries were manufactured using the separator of Example 1 in the same manner as in Experimental Example 1, and subjected to charging and discharging.

[0231] After charging and discharging, the dual-cell system was disassembled, and the elemental composition on the separator surface was analyzed using XPS profiling. The results are presented together with analytical data of the separator prior to charging and discharging. Figure 8 In addition, the atomic content of F is shown in Table 2.

[0232] Reference Figure 8 As shown in Table 2, the F content on the surface of the separator increases rapidly after charging and discharging, thus corresponding to the increase of F in the SEI component with charging and discharging, and the formation of an inorganic layer with excess inorganic matter.

[0233] [Table 2]

[0234]

[0235] <Experimental Example 4>

[0236] A dual-cell battery was manufactured using the separators of Example 1 and Comparative Example 1 in the same manner as in Experimental Example 1, and underwent charging and discharging. The fully discharged dual-cell battery was disassembled, the negative electrode was cleaned with electrolyte, and then DSC evaluation was performed.

[0237] For DSC evaluation, the heat flow during exothermic or endothermic reactions is measured when the fully discharged electrode is heated at a heating rate of 10°C / min in the range of 25°C to 250°C.

[0238] Furthermore, a dual-cell battery was fabricated using the separators of Example 1 and Comparative Example 1 in the same manner as in Experimental Example 1, and subjected to charging and discharging. The dual-cell battery was then fully charged again using CC-CV at 0.1 C and 4.35 V, and then disassembled for DSC evaluation of the negative electrode.

[0239] The results are shown below. Figure 9 middle.

[0240] Reference Figure 9It can be determined that, in the negative electrode of the dual battery including the separator of Embodiment 1 according to the present disclosure under fully charged and electrolyte-containing conditions, the main peak is wider than that in the case including the separator of Comparative Example 1, and splitting is observed. Furthermore, it can be determined that, under fully discharged and electrolyte-cleaning conditions, a high-temperature shift in the initial temperature is observed in the negative electrode of the dual battery including the separator of Embodiment 1 according to the present disclosure. Thus, it can be seen that thermal safety is excellent when using the separator according to the present disclosure.

[0241] <Experimental Example 5>

[0242] Under the same conditions as in Experimental Example 4, the negative electrode was then forcibly ignited by applying a spark to the material in a high-pressure reactor pressurized at 30 bar in an O2 atmosphere. The total heat of the exothermic reaction (water temperature) was measured by calorimetry. The results are shown in... Figure 10 middle.

[0243] Reference Figure 10 It can be determined that, under fully charged and electrolyte-containing conditions, the calorific value of the negative electrode in the dual cell including the separator of Example 1 is reduced by about 5.7% (4224 Cal / g -> 3985 Cal / g) compared to the negative electrode in the dual cell including the separator of Comparative Example 1, and the calorific value is reduced by about 8.6% (3075 Cal / g -> 2812 Cal / g) under fully discharged and electrolyte-cleaned conditions.

[0244] It can also be seen that thermal safety is excellent when the separator according to this disclosure is used.

[0245] <Experimental Example 6>

[0246] The dual cells were manufactured using the separators of Example 1 and Comparative Example 1 in the same manner as in Experimental Example 1.

[0247] With the pressure fixtures pressed at fastening strengths of 6 kgf·cm (“LATP6”), 12 kgf·cm (“LATP12”), and 18 kgf·cm (“LATP18”), the manufactured dual-cell batteries were charged at 45°C with a constant current of 0.1 C until the voltage reached 4.20 V. They were then aged at 25°C for 24 hours, aged at 60°C for 20 hours, and finally completely discharged at a constant current of 0.33 C. This cycle was repeated three times.

[0248] Then, with the state of charge set to SOC 50 and a 2.5 C discharge current applied for 0.1 seconds, 10 seconds, and 30 seconds, the DCIR was measured, and the results are shown below. Figure 11 middle.

[0249] The discharge rate characteristics were also evaluated, and the results are shown below. Figure 12 middle.

[0250] To evaluate the discharge rate characteristics, the dual-cell battery was charged at 0.2 C using CC / CV (with the CV current cut off when it reached 0.05 C), and then discharged three times at 0.2 C, 0.33 C, 0.5 C, 1 C, 2 C, and 3 C, respectively. Based on the capacity of each third discharge, the retention rate of the discharge capacity at high rates relative to the discharge capacity at 0.2 C was determined.

[0251] Reference Figure 11 and Figure 12 It can be determined that when the separator according to this disclosure is used, the resistance decreases, and the rate of decrease is even greater when the applied pressure increases. On the other hand, it can be determined that, in terms of capacity, there is almost no significant difference in performance, or the performance is excellent.

[0252] <Experimental Example 7>

[0253] The positive electrode was prepared in the same manner as in Experimental Example 1, and the negative electrode was prepared in the same manner, except that a mixture of graphite and SiO with a weight ratio of 94.5:5.5 was used as the negative electrode active material.

[0254] Furthermore, using the separators prepared in Example 1 and Comparative Example 1, and with the oxide-based solid electrolyte layer or organic-inorganic hybrid layer facing the negative electrode, an electrode assembly was fabricated. An electrolyte in which 1 M LiPF6 was dissolved in a carbonate solvent of EC:EMC = 3:7 (volume%) was used, and in the fabrication of the stacked battery, the positive and negative electrodes were stacked three times each to fabricate an 840 mA pouch cell.

[0255] With the pressure fixtures tightened to a strength of 12 kgf·cm, the manufactured dual-cell batteries were charged at 45°C with a constant current of 0.1 C until the voltage reached 4.20 V. They were then aged at 25°C for 24 hours, aged at 60°C for 20 hours, and finally discharged completely with a constant current of 0.33 C. This cycle was repeated three times.

[0256] The state of charge was set to SOC 50, and the DCIR was measured by discharging at 2.5 C. The results are shown below. Figure 13 middle.

[0257] The discharge rate characteristics were also evaluated, and the results are shown below. Figure 14 middle.

[0258] The method for evaluating discharge rate characteristics is as described in Experimental Example 6.

[0259] Reference Figure 13 and Figure 14 It can be determined that when the separator according to this application is used, the resistance decreases, and the rate of decrease is even greater when the applied pressure increases. On the other hand, it can be determined that, in terms of capacity, there is almost no significant difference in performance, or the performance is excellent.

[0260] Based on the above disclosure, those skilled in the art can make various applications and modifications without departing from the spirit and scope of this disclosure.

[0261] Industrial applicability

[0262] According to this disclosure, a lithium secondary battery forms an oxide-based solid electrolyte layer containing LATP on a separator substrate and contacts it with a negative electrode active material layer, such that LATP reduction products are formed together with the SEI material at the interface between them, thereby forming a thick, inorganic-rich SEI with a high F atom content, which is effective in improving the thermal safety of the lithium secondary battery.

[0263] Furthermore, the formation mode of this inorganic SEI with high F atom content can be controlled to improve battery performance.

Claims

1. A lithium secondary battery, comprising: The positive electrode includes a positive current collector and a positive active material layer formed on one or both sides of the positive current collector. The negative electrode includes a negative electrode current collector and a layer of negative electrode active material formed on one or both sides of the negative electrode current collector, and The separator includes a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and comprising lithium aluminum titanium phosphate (LATP). The negative electrode active material layer and the oxide-based solid electrolyte layer face each other. An inorganic layer containing the reduction product of LATP and SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer. The atomic content of F in the inorganic layer is included in the range of 7 atomic percentages (%) to 15 atomic percentages, based on all atoms present in the inorganic layer.

2. The lithium secondary battery according to claim 1, The inorganic layer fills some or all of the pores of the oxide-based solid electrolyte layer, or the inorganic layer forms a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, or the inorganic layer includes all of these forms.

3. The lithium secondary battery according to claim 2, The inorganic layer is configured to fill the pores with a total volume of 10% to 100% based on the total volume of the oxide-based solid electrolyte layer, and to form a separate layer with a thickness of 5 nm to 100 nm.

4. The lithium secondary battery according to claim 5, The LATP reduction product is formed in the form of 50% by weight or more filling the pores of the oxide-based solid electrolyte layer along the surface of the LATP particles. The SEI material is formed together with the LATP reduction product in a space charge region where the Li+ concentration is locally high, or the SEI material is formed in the form of filling pores in the surface of the LATP reduction product of the oxide-based solid electrolyte layer, or the SEI material is formed as a separate layer on the surface of the oxide-based solid electrolyte layer, or the SEI material is formed in a manner that includes all of these forms.

5. The lithium secondary battery according to claim 1, The reduction product of said LATP comprises lithiated LATP formed by the spontaneous lithiation reaction of said LATP as shown in the following reaction formula 1. [Reaction Formula 1] Yes 1.3 Al 0.3 Of 1.7 (PO4)3 → Li3Al 0.3 Of 1.7 (PO4)3.

6. The lithium secondary battery according to claim 1, The SEI material mentioned above contains LiF.

7. The lithium secondary battery according to claim 5, The SEI material further comprises at least one material selected from Li2CO3 and Li2O.

8. The lithium secondary battery according to claim 1, The inorganic layer is composed of LATP reduction products and SEI material.

9. The lithium secondary battery according to claim 1, The oxide-based solid electrolyte layer is formed on both sides of the substrate.

10. The lithium secondary battery according to claim 1, The substrate is a polyolefin substrate.

11. The lithium secondary battery according to claim 1, The oxide-based solid electrolyte layer is composed of an oxide-based solid electrolyte containing lithium aluminum titanium phosphate (LATP) and a binder.

12. The lithium secondary battery according to claim 1, The oxide-based solid electrolyte layer is formed on one side of the substrate with a thickness of 0.1 μm to 20 μm.

13. The lithium secondary battery according to claim 1, The positive electrode active material layer comprises a lithium transition metal oxide represented by the following chemical formula 1 as the positive electrode active material: [Chemical Formula 1] Li 1+x Ni a Co b Mr c M 1-(a+b+c) O2 in, M is selected from at least one of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and 0≤x≤0.5,0 <a<1,0<b<1,0<c<1。 14. The lithium secondary battery according to claim 1, Based on the total weight of the negative electrode active material, the negative electrode active material layer contains 80% by weight or more of pre-lithiated silicon oxide as the negative electrode active material.

15. The lithium secondary battery according to claim 1, The lithium secondary battery further includes an electrolyte containing LiFSI as a lithium salt and fluoroethylene carbonate (FEC) as an electrolyte solvent.

16. A method for manufacturing a lithium secondary battery according to claim 1, the method comprising the following steps: An oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) is formed on one or both sides of a substrate to prepare a separator. A positive electrode active material layer is formed on one or both sides of the positive electrode current collector to prepare a positive electrode, and a negative electrode active material layer is formed on one or both sides of the negative electrode current collector to prepare a negative electrode. The separator is inserted between the positive electrode and the negative electrode such that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other, thereby fabricating an electrode assembly; The electrode assembly and electrolyte are incorporated into a secondary battery box to manufacture a secondary battery; The secondary battery is positioned between a plurality of pressure plates and pressure is applied to the secondary battery; as well as The secondary battery is activated under pressure.

17. The method for manufacturing a lithium secondary battery according to claim 16, The plurality of pressure plates are fastened with a plurality of pressure bolts to apply pressure.

18. The method for manufacturing a lithium secondary battery according to claim 17, The pressure bolts thereon press the secondary battery with a fastening strength of 6 kgf·cm or greater.

19. The method for manufacturing a lithium secondary battery according to claim 17, The pressure bolts press the secondary battery with a tightening strength in the range of 10 kgf·cm to 20 kgf·cm.

20. The method for manufacturing a lithium secondary battery according to claim 17, The activation step is carried out at a temperature of 40°C to 60°C.

Images