Lithium secondary battery with excellent thermal stability, and manufacturing method therefor

Abstract

According to one embodiment of the present invention, a lithium secondary battery is provided, the battery comprising: a cathode including a cathode current collector, and a cathode active material layer formed on one surface or both surfaces of the cathode current collector; an anode including an anode current collector, and an anode active material layer formed on one surface or both surfaces of the anode current collector; and a separator including a substrate, and an oxide-based solid electrolyte layer which is formed on one surface or both surfaces of the substrate and which includes lithium aluminum titanium phosphate (LATP), wherein the anode active material layer and the oxide-based solid electrolyte coating layer face each other, an inorganic layer including a reduced product of the LATP and an SEI material is formed at the interface between the oxide-based solid electrolyte layer and the anode active material layer, and the amount of F in the inorganic layer is 7-15 atom% on the basis of the total amount of atoms present in the inorganic layer.

Description

Lithium secondary battery with excellent thermal safety and method for manufacturing the same

[0001] Cross-citation with related application(s)

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

[0003] The present invention relates to a lithium secondary battery having excellent thermal safety and a method for manufacturing the same.

[0004] Due to the rapid increase in fossil fuel use, the demand for alternative and clean energy is increasing, and as part of this, the most actively researched field is the field of power generation and storage using electrochemistry.

[0005] A representative example of an electrochemical device that currently utilizes this type of electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0006] Recently, with the increase in technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has been rapidly increasing. Among them, much research has been conducted on lithium secondary batteries that exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, and they have also been commercialized and widely used.

[0007] Furthermore, with growing concern about environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles as alternatives to fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution. While nickel-metal hydride secondary batteries are primarily used as power sources for these electric and hybrid electric vehicles, research into the use of lithium secondary batteries, which boast high energy density and discharge voltage, is actively underway, and some are nearing commercialization.

[0008] Typically, lithium secondary batteries are structured to have an electrode assembly comprising a positive electrode, a negative electrode, and a porous separator, each impregnated with a non-aqueous electrolyte. Furthermore, the positive electrode is typically manufactured by coating a positive electrode mixture containing a positive electrode active material onto aluminum foil, while the negative electrode is typically manufactured by coating a negative electrode mixture containing a negative electrode active material onto copper foil.

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

[0010] However, recently, with the growth of devices requiring high-capacity batteries, such as electric vehicles and hybrid electric vehicles, the energy density level required for lithium secondary batteries is continuously increasing, and attempts are being made to use anodes containing Si, which has a high theoretical capacity, as anode active material.

[0011] However, Si-based materials containing Si are attracting attention due to their very high energy density, but their Coulombic efficiency decreases due to the irreversible phase formation of lithium silicate, and their thermal stability is poor due to the explosive reaction that occurs during thermal runaway, making them materials that require improvement.

[0012] At this time, the above Coulomb efficiency can be resolved to some extent by compensating for the irreversible reaction through the prelithiation process of the Si-based material, but the SEI formed at this time must be of good quality to reduce the increase in resistance, so that the output characteristics can be improved, and thermal stability is still an issue.

[0013] Accordingly, the present invention aims to provide a lithium secondary battery having improved thermal safety along with constant Coulombic efficiency by controlling SEI formation pattern.

[0014] According to one embodiment of the present invention,

[0015] A cathode comprising a cathode current collector and a cathode active material layer formed on one or both sides of the cathode current collector,

[0016] A negative electrode comprising a negative current collector and a negative active material layer formed on one or both sides of the negative current collector,

[0017] A separator comprising a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and including lithium aluminum titanium phosphate (LATP);

[0018] The above negative active material layer and the oxide-based solid electrolyte coating layer face each other,

[0019] An inorganic layer containing a reduced product of the LATP and an SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer,

[0020] A lithium secondary battery is provided in which the atomic content of F in the above-mentioned inorganic layer is 7 to 15 atomic% based on all atoms present in the above-mentioned inorganic layer.

[0021] Here, the inorganic layer may be included in the form of filling part or all of the pores of the oxide-based solid electrolyte layer, forming a separate layer at the interface between the oxide-based solid electrolyte layer and the lithium metal layer, or in the form of all of these.

[0022] At this time, in detail, the inorganic layer may be formed to fill the pores of the oxide-based solid electrolyte layer by 10 to 100 volume% based on the total pore volume, and to form a separate layer having a thickness of 5 nm to 100 nm.

[0023] More specifically, the LATP reducing agent is formed in a form that fills the pores of the oxide-based solid electrolyte layer along the surface of the LATP particles by more than 50% by weight,

[0024] The SEI material may be formed in a form that fills the pores of the oxide-based solid electrolyte layer together with the LATP reducer or on the surface of the LATP reducer in a space charge region where the concentration of Li+ is locally high, or as a separate layer on the surface of the oxide-based solid electrolyte layer, or both.

[0025] The reduced product of the LATP, which is one component of the above-mentioned inorganic layer, may include lithiated-LATP formed by a spontaneous lithiation reaction represented by the following reaction formula 1.

[0026] [Reaction Formula 1]

[0027] Li 1.3 Al 0.3 Ti 1.7 (PO4)3-> Li3Al 0.3 Ti 1.7 (PO4)3

[0028] In addition, the SEI material, which is another component of the above-mentioned inorganic layer, may include LiF, and further may include one or more materials selected from the group consisting of Li2CO3 and Li2O.

[0029] Moreover, the above-mentioned inorganic layer may be composed of a LATP reduction product and an SEI material.

[0030] Meanwhile, the oxide-based solid electrolyte layer can be formed on both sides of the substrate.

[0031] The above substrate may be a polyolefin substrate, and the oxide-based solid electrolyte layer may be composed of an oxide-based solid electrolyte including lithium aluminum titanium phosphate (LATP) and a binder.

[0032] Here, the oxide-based solid electrolyte layer may be formed on one side of the substrate to a thickness of 0.1 µm to 20 µm.

[0033] Meanwhile, the positive electrode active material layer may include a lithium transition metal oxide represented by the following chemical formula 1 as a positive electrode active material.

[0034] [Chemical Formula 1]

[0035] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O2

[0036] In the above formula,

[0037] M is at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo,

[0038] 0≤x≤0.5, 0 <a<1, 0<b<1, 0<c<1이다.

[0039] In addition, the negative electrode active material layer may contain at least 80 wt% of prelithiated silicon oxide as the negative electrode active material based on the total weight of the negative electrode active material.

[0040] Furthermore, the lithium secondary battery may further include an electrolyte including LiFSI as a lithium salt and fluoroethylene carbonate (FEC) as an electrolyte solvent.

[0041] According to another embodiment of the present invention,

[0042] A step of manufacturing a separator by forming an oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) on one or both sides of a substrate;

[0043] A step of manufacturing a positive electrode by forming a positive electrode active material layer on one side or both sides of a positive electrode current collector, and manufacturing a negative electrode by forming a negative electrode active material layer on one side or both sides of a negative electrode current collector;

[0044] A step of manufacturing an electrode assembly by interposing the separator between the positive electrode and the negative electrode so that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other;

[0045] A step of manufacturing a secondary battery by embedding the electrode assembly and electrolyte into a secondary battery case;

[0046] A step of applying pressure to the secondary battery by placing the secondary battery between a plurality of pressure plates; and

[0047] A method for manufacturing a lithium secondary battery is provided, including a step of activating the secondary battery while applying pressure.

[0048] Here, the plurality of pressurizing plates may be fastened with a plurality of pressurizing bolts to apply pressure, and specifically, the pressurizing bolts may be fastened to the secondary battery with a fastening strength of 6 kgf·cm or more, and in detail, may be fastened to the secondary battery with a fastening strength in the range of 10 to 20 kgf·cm.

[0049] Additionally, the activation step may be performed at a temperature of 40°C to 60°C.

[0050] Figure 1 is a schematic diagram showing the formation of an inorganic layer at the interface between a cathode and a separator according to one embodiment of the present invention.

[0051] FIG. 2 is a top view of a pressurizing device applied to an activation process in a method for manufacturing a lithium secondary battery according to another embodiment of the present invention.

[0052] Figure 3 is a cross-sectional view of the pressurizing device of Figure 2.

[0053] Figure 4 is an SEM photograph of the surface of a separator obtained by disassembling a lithium secondary battery manufactured according to Experimental Example 1.

[0054] Figure 5 is an XRD graph of a separator obtained by disassembling lithium secondary batteries manufactured according to Experimental Example 1.

[0055] Figure 6 is a graph showing the Si component analysis according to the depth of the coating layer of the negative electrode obtained by disassembling lithium secondary batteries manufactured according to Experimental Example 2.

[0056] Figure 7 is a graph showing the composition analysis according to the depth of the coating layer of the negative electrode obtained by disassembling lithium secondary batteries manufactured according to Experimental Example 2.

[0057] Figure 8 is a graph showing the composition analysis according to the depth of the coating layer of the separator obtained by disassembling lithium secondary batteries manufactured according to Experimental Example 3.

[0058] Figure 9 is a DSC evaluation graph of lithium secondary batteries manufactured according to Experimental Example 4.

[0059] Figure 10 is a calorimeter evaluation graph of lithium secondary batteries manufactured according to Experimental Example 5.

[0060] Figure 11 is a DC-IR evaluation graph of lithium secondary batteries manufactured according to Experimental Example 6.

[0061] Figure 12 is a comparative graph of discharge rate characteristics of lithium secondary batteries manufactured according to Experimental Example 6.

[0062] Figure 13 is a DC-IR evaluation graph of lithium secondary batteries manufactured according to Experimental Example 7.

[0063] Figure 14 is a graph comparing discharge rate characteristics of lithium secondary batteries manufactured according to Experimental Example 7.

[0064] Hereinafter, the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0065] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense to those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0066] The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise. As used herein, the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0067] Meanwhile, the terms “consists of” and / or “consisting of” used in the specification mean that other components are not included in amounts greater than trace amounts, i.e., impurities, other than the mentioned components.

[0068] Furthermore, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to the illustrated components. In the drawings, the thicknesses are enlarged to clearly represent various layers and regions. Furthermore, in the drawings, the thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0069] Furthermore, when we say that a layer, membrane, region, plate, or other part is "on" or "over" another part, this includes not only cases where it is "directly on" the other part, but also cases where there are other parts in between. Conversely, when we say that a part is "directly on" another part, it means that there are no other parts in between. Furthermore, saying that a part is "on" or "over" a reference part means that it is located above or below the reference part, and does not necessarily mean that it is located "above" or "over" the direction opposite to gravity.

[0070] Additionally, throughout the specification, when we say "in plan", we mean when the target portion is viewed from above, and when we say "in cross section", we mean when the target portion is viewed from the side in a cross-section cut vertically.

[0071]

[0072] lithium secondary battery

[0073] A lithium secondary battery according to one embodiment of the present invention,

[0074] A cathode comprising a cathode current collector and a cathode active material layer formed on one or both sides of the cathode current collector,

[0075] A negative electrode comprising a negative current collector and a negative active material layer formed on one or both sides of the negative current collector,

[0076] A separator comprising a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and including lithium aluminum titanium phosphate (LATP);

[0077] The above negative active material layer and the oxide-based solid electrolyte coating layer face each other,

[0078] An inorganic layer containing a reduced product of the LATP and an SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer,

[0079] The atomic content of F in the above-mentioned inorganic layer is characterized by being included at 7 to 15 atomic% based on all atoms present in the above-mentioned inorganic layer.

[0080]

[0081] anode

[0082] The positive electrode may have a structure 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.

[0083] Here, the positive electrode current collector may be any conductive material that does not induce chemical changes in the battery, and is not particularly limited. For example, the current collector may be made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like.

[0084] The above-mentioned positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase adhesion to the positive electrode active material layer. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0085] The above positive electrode active material layer includes a positive electrode active material and may include a conductive agent, a binder, and other additives as needed.

[0086] The above positive electrode active material is not limited to a compound capable of reversible intercalation and deintercalation of lithium, but specifically may include a lithium metal oxide containing lithium and one or more metals 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 aCo b Mn c M 1-(a+b+c) O2

[0089] In the above formula,

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

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

[0092] In addition, the positive electrode active material is a lithium metal oxide, such as a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., 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 oxides (e.g., Li 1+x’’’ Ni 1-Y1 Co Y1 O2(here, -0.5≤x'''≤0.5, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, Li 1+x’’’’ Co 1-Y2 Mn Y2 O2(here, -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 oxides (e.g., 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 (Nip1 Co q1 Mn r1 )O4 (wherein, -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) oxide (e.g., Li 1+a3 (Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and a3, p2, q2, r2 and s2 are atomic fractions of independent elements, respectively, -0.5≤a3≤0.5, 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc.), lithium iron phosphate (e.g., Li 1+a4 Fe 1-p3 M p3 (PO 4-b4 )X b4 (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, and -0.5≤a4≤0.5, 0≤p3≤0.5, 0≤b4≤0.1) and the like, and any one or two or more compounds thereof may be included.

[0093] Among these, the lithium metal oxides are LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni)) in that they can improve the capacity characteristics and stability of the battery. 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 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 oxide (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 )O2), lithium iron phosphate (e.g., LiFePO4), etc., and any one or a mixture of two or more of these may be used, and Li(Ni) which is a lithium transition metal oxide represented by the chemical formula 1 0.86 Co 0.05 Mn 0.07 Al 0.02 ) may contain O2.

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

[0095] The conductive agent is a component for further improving the conductivity of the positive electrode active material, and the conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

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

[0097] The above binder is a component that assists in bonding between the conductive material, the positive electrode active material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 wt%, specifically 0.5 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0099] In addition, the above-mentioned other additives may further include, for example, fillers as components that suppress expansion. The fillers are not particularly limited as long as they can suppress expansion of the electrode without causing chemical changes in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0100]

[0101] cathode

[0102] The above negative electrode has a structure in which a negative electrode active material layer is formed on one or both sides of the negative electrode current collector, similar to the above positive electrode.

[0103] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0104] The above-mentioned negative electrode collector may typically have a thickness of 3 μm to 500 μm, and like the positive electrode collector, it may be provided with fine irregularities on the surface of the negative electrode collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0105] The above negative active material may include a conductive material, a binder, and other additives as described above together with the negative active material.

[0106] In the present invention, the negative electrode active material may contain at least 80 wt% of a prelithiated silicon oxide capable of exhibiting high energy density, etc., based on the total weight of the negative electrode active material.

[0107] As described above, the silicon oxide is a material that has a problem of poor thermal stability due to an explosive reaction that occurs during thermal runaway and a decrease in coulombic efficiency due to irreversible phase formation of lithium silicate. Previously, it was only mixed and used with carbon-based materials in an amount of 10 wt% or less, specifically 5 wt% or less, based on the total weight of the negative electrode active material.

[0108] However, according to the present invention, the above Coulomb efficiency is resolved by compensating for the irreversible reaction through the prelithiation process of the Si-based material, and a thick inorganic excess SEI with a high F content can be formed through the reduction product of LATP described below, thereby improving thermal stability, and can be included at 80 wt% to 100 wt%, specifically 90 wt% to 100 wt%, and more specifically 100 wt%.

[0109] Meanwhile, the silicon oxide can be specifically represented by the following chemical formula 2.

[0110] [Chemical Formula 2]

[0111] SiOx

[0112] Here, x is 0 <x<2이다.

[0113] Specifically, the silicon oxide may be SiO2 or SiO, and more specifically, may be SiO.

[0114] Here, the SiO is the total composition of a mixture of Si and SiO2, and the x value is determined according to the mixing ratio of Si and SiO2.

[0115] Such silicon oxide can be included as a negative electrode active material in a pre-lithiated state, and the pre-lithiation can be performed by contacting Li with silicon oxide powder, for example, by a physical or electronic method.

[0116] Meanwhile, the negative active material may include, in addition to silicon oxide, one or more carbon-based materials selected from the group consisting of graphite, amorphous hard carbon, low-crystalline soft carbon, carbon black, acetylene black, Ketjen black, super P, graphene, and fibrous carbon, Si-based materials, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, elements of group 1, 2, and 3 of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO2, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 더 포함할 수 있지만, 당업계에 알려진 것이라면 이들만으로 한정되는 것은 아니다.

[0117]

[0118] membrane

[0119] The above separator has a structure including a substrate and an oxide-based solid electrolyte layer formed on one or both sides of the substrate and including lithium aluminum titanium phosphate (LATP).

[0120] Here, the above-mentioned material can be used without any special restrictions as long as it is commonly used as a separator material in a lithium secondary battery, and in particular, it is preferable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity.

[0121] For example, the substrate may be a polyolefin-based substrate such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, and a porous polymer film or a laminated structure of two or more layers thereof may be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., may be used as the separator, but more specifically, it may be a polyolefin substrate.

[0122] An oxide-based solid electrolyte layer is formed on one or both sides of the above-described substrate.

[0123] At this time, the oxide-based solid electrolyte layer may include an oxide-based solid electrolyte including lithium aluminum titanium phosphate (LATP) and a binder.

[0124] The above oxide-based solid electrolyte may further include, in addition to lithium aluminum titanium phosphate, one or more lithium metal oxides or lithium metal phosphates selected from Nasicon-type solid electrolytes, Lisicon-type solid electrolytes, Garnet-type solid electrolytes, Perovskite-type solid electrolytes, and LiPON-type solid electrolytes, and more specifically, may further include one or more selected from the group consisting of LAGP (lithium aluminum germanium phosphate)-based compounds, LLZO (lithium lanthanum zirconium oxide)-based compounds, LLZTO (lithium lanthanum zirconium tantalum oxide)-based compounds, LLTO (lithium lanthanum titanium oxide)-based compounds, LSTP (lithium silicon titanium phosphate)-based compounds, and LGPO (lithium germanium phosphate)-based compounds, but specifically, lithium It may be composed of aluminum titanium phosphate.

[0125] Such oxide-based solid electrolyte may be included in an amount of 70 wt% to 99 wt%, and specifically, 80 wt% to 99 wt%, based on the total weight of the oxide-based solid electrolyte layer.

[0126] If the content is too low outside the above range, sufficient reduction intended by the present invention cannot be obtained, and if the content is too high, the content of the binder connecting them is too low, which may result in a decrease in the mechanical properties due to weakened adhesive force between the particles, which is not desirable.

[0127] The average diameter (D50) of the above oxide-based solid electrolyte particles may be 50 nanometers to 10 micrometers, specifically 50 nanometers to 5 micrometers, and more specifically 50 nanometers to 1 micrometer.

[0128] If the particle size is too small outside the above range, agglomeration between particles may occur due to reduced dispersibility. Conversely, if the particle size is too large, large pores are formed by the oxide-based solid electrolyte, which is rather unfavorable in terms of resistance. In other words, if the particle size is within the above range, lithium ion conductivity can be increased, resistance can be reduced, and improved secondary battery performance can be achieved.

[0129] The average diameter (D50) described above refers to the particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The D50 can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0130] Meanwhile, the binder, which is another component of the oxide-based solid electrolyte layer, is not limited as long as it does not cause a side reaction with the electrolyte, but in particular, a glass transition temperature (Tg) as low as possible can be used, and is preferably in the range of -200 to 200°C.

[0131] In addition, the binder does not necessarily need to have ion conducting ability, but it is more preferable to use a polymer having ion conducting ability.

[0132] Therefore, it is preferable that the binder have a high dielectric constant as much as possible, and since the degree of salt dissociation in the electrolyte actually depends on the dielectric constant of the electrolyte solvent, the higher the dielectric constant of the polymer, the better the degree of salt dissociation in the electrolyte. The dielectric constant of the polymer is preferably 1 or more, specifically, a range of 1.0 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or more.

[0133] In addition to the aforementioned functions, the binder may have the characteristic of being gelled when impregnated with a liquid electrolyte, thereby exhibiting a high degree of swelling. In fact, if the binder is a polymer having an excellent electrolyte swelling rate, the electrolyte injected after battery assembly will permeate into the polymer, and the polymer containing the absorbed electrolyte will have electrolyte ion conducting ability. Therefore, if possible, the solubility index should be in the range of 15 to 45 MPa. 1 / 2 Polymers are preferred, with a viscosity of 15 to 25 MPa. 1 / 2 and 30 to 45 MPa 1 / 2 The range is more desirable. The solubility index is 15 MPa. 1 / 2 Less than and 45 MPa 1 / 2 If it exceeds , it becomes difficult to be impregnated (swelled) by a conventional battery liquid electrolyte.

[0134] Examples of such binders include polyvinylidene fluorideco-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, It may be at least one selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and polyvinylalcohol.

[0135] Specifically, the oxide-based solid electrolyte layer of the present invention is intended to form a reduced product of LATP at the interface between the LATP included in the oxide-based solid electrolyte layer and the negative electrode active material layer of the negative electrode, and therefore is preferably composed of an oxide-based solid electrolyte including the LATP and a binder, and it is preferable that no other materials are included as they may interfere with the reduction of LATP.

[0136] Accordingly, the binder may be included in an amount of 1 wt% to 30 wt%, specifically 1 wt% to 20 wt%, based on the total weight of the oxide-based solid electrolyte layer.

[0137] The above-described oxide-based solid electrolyte layer may be formed on one or both sides of the substrate, but since it exhibits better overvoltage reduction when formed on both sides, it is more preferable to form it on both sides. Of course, when the oxide-based solid electrolyte layer is formed on only one side, the electrode assembly must be manufactured so that the oxide-based solid electrolyte layer faces the negative electrode active material layer of the negative electrode in order to form the LATP reduction product intended by the present invention.

[0138] At this time, the oxide-based solid electrolyte layer can be formed on one side of the substrate to a thickness of 0.1 µm to 20 µm, and more specifically, can be formed to a thickness of 1 µm to 10 µm.

[0139] If it is too thin beyond the above range, the effect of generating LATP reduction intended by the original cannot be sufficiently obtained, and if it is too thick, the resistance may rather increase, which is not desirable.

[0140] Meanwhile, the total thickness of the separator including the substrate and the oxide-based solid electrolyte layer may be 5 micrometers to 50 micrometers, specifically 5 micrometers to 40 micrometers, and more specifically 10 micrometers to 30 micrometers. When the thickness of the separator satisfies the above range, the resistance value of the lithium secondary battery can be minimized while effectively preventing a short circuit between the positive and negative electrodes. As a result, the reduction in energy density of the lithium secondary battery can be prevented and the life characteristics can be improved.

[0141] Meanwhile, whether the oxide-based solid electrolyte layer is formed on one side or both sides, the oxide-based solid electrolyte layer faces the negative electrode active material layer of the negative electrode, and accordingly, the LATP reduction product is formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer. Specifically, it is formed as lithium ions move during charge / discharge of the lithium secondary battery, particularly during the activation process.

[0142] Here, the reduced product of the LATP may include lithiated-LATP formed by a spontaneous lithiation reaction represented by the following reaction scheme 1.

[0143] [Reaction Formula 1]

[0144] Li 1.3 Al 0.3 Ti 1.7 (PO4)3-> Li3Al 0.3 Ti 1.7 (PO4)3

[0145] In addition, at the interface between the cathode and the separator, lithium ions reacting with the electrolyte during the charging / discharging, particularly the activation, process of the lithium secondary battery form an SEI material.

[0146] Accordingly, an inorganic layer including a reduced product of LATP and an SEI material is formed at the interface between the oxide-based solid electrolyte layer and the negative active material layer, and more specifically, the inorganic layer may be composed of the reduced product of LATP and the SEI material.

[0147] At this time, the SEI material may include LiF, and further, may include one or more materials selected from the group consisting of Li2CO3 and Li2O. In other words, the inorganic layer may include lithiated-LATP and LiF, and in addition, one or more materials selected from the group consisting of Li2CO3 and Li2O.

[0148] Since this inorganic layer is formed by the combination of LATP of the oxide-based solid electrolyte layer and lithium ions and the reaction of the electrolyte and lithium ions, it can be formed mainly on the surface of the oxide-based solid electrolyte layer.

[0149] At this time, since the oxide-based solid electrolyte layer includes pores therein, the inorganic layer may be formed in a form that fills part or all of the pores of the oxide-based solid electrolyte layer, or may be formed as a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, or may be formed in a form of both of these, that is, may be formed while being included in the pores or forming a layer.

[0150] When the above-mentioned inorganic layer fills the pores of the above-mentioned oxide-based solid electrolyte layer, it can be filled at 10% to 100% by volume based on the total volume of the pores, specifically at 30% to 100% by volume, and more specifically at 50% to 80% by volume.

[0151] In addition, 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 this layer may be 5 nm to 100 nm, specifically 5 nm to 50 nm, and even more specifically 10 nm to 50 nm.

[0152] More specifically, since the LATP of the oxide-based solid electrolyte layer begins to form a reduced product when it meets the prelithiated silicon oxide, the LATP reduced product is formed in a form that fills the pores of the oxide-based solid electrolyte layer along the surface of the LATP particles by more than 50% by weight based on the weight, and when the surface of the separator has a space charge region with a locally high concentration of Li+ due to charging, such as an activation process of the lithium secondary battery, an SEI material is formed by a side reaction between Li ions and the electrolyte in the space charge region.

[0153] Accordingly, the SEI material may be formed in the form of filling the pores of the oxide-based solid electrolyte layer together with the LATP reducer or on the surface of the LATP reducer in the above region, or may be formed as a separate layer on the surface of the oxide-based solid electrolyte layer, or may be formed in the form of all of these.

[0154] To more easily explain the formation of this inorganic layer, Fig. 1 shows a schematic diagram of the interface where the separator of the present invention and the cathode come into contact.

[0155] Referring to Fig. 1, the separator (110) is composed of a structure including a substrate (111) and an oxide-based solid electrolyte layer (112) including LATP formed on one surface of the substrate (111). This oxide-based solid electrolyte layer (112) is in direct contact with the negative active material layer (121) formed on the negative electrode current collector (122) of the negative electrode (120), and when LATP and Li ions meet at the interface, a reduced substance (131) including lithiated-LATP, in which LATP is reduced, is formed by a spontaneous reaction. At this time, more than 50 wt% of the reduced substance is formed along the surface of the LATP particles and fills the pores of the oxide-based solid electrolyte layer (112). Afterwards, the pores of the oxide solid electrolyte layer and the surface thereof have a space charge region (132) with a locally high concentration of Li+, and through a side reaction of the electrolyte in this region (132), an SEI material is formed, which fills the remaining pores of the oxide solid electrolyte layer together with or separately from the LATP reduction product, and is also formed as a separate layer having a thickness (t), and an additional inorganic layer (132) is formed on the surface of the oxide solid electrolyte layer (112).

[0156] Meanwhile, in order to achieve the intended effect of the present invention, the inorganic layer may include F atoms in an amount of 7 to 15 atomic%, specifically 8 to 15 atomic%, and more specifically 10 to 13 atomic%, based on all atoms present in the inorganic layer.

[0157] Beyond the above range, when the F atom content is low, a thick layer of organic components with low interatomic binding energy and low lithium ion conductivity is formed instead of an inorganic excess, i.e. an inorganic rich SEI layer, and thus an SEI layer that is easily decomposed is formed, and thus thermal stability becomes unstable and resistance increases, which is not desirable. On the other hand, when the F atom content is too high, since an excessive amount of a material containing such F element must be added to the electrolyte, side reactions easily occur within the electrolyte, and the viscosity of the electrolyte increases, which is not desirable because there is a problem that the ionic conductivity for lithium ions to move through the electrolyte decreases.

[0158] In addition, since the inorganic layer grows on the pores of the oxide-based solid electrolyte layer and the interface between the oxide and the cathode as described above, it can be formed to a thickness thicker than a general SEI layer, and is therefore more effective in improving thermal safety.

[0159]

[0160] electrolyte

[0161] Meanwhile, the lithium secondary battery may further include an electrolyte.

[0162] Here, the electrolyte is a lithium non-aqueous electrolyte, and may include a lithium salt and a non-aqueous organic solvent.

[0163] The above lithium salt is used as a medium for transferring ions in a lithium secondary battery. Lithium salt is, for example, Li as a cation. + , and the anion is 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 - It may include at least one selected from the group consisting of .

[0164] Specifically, the lithium salt is 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 specifically, it may essentially include Li[N(SO2F)2], i.e., LiFSI, thereby increasing the content of F atoms in the inorganic layer, thereby reducing thermal decomposition and enhancing thermal safety.

[0165] In addition to these, lithium salts commonly used in the electrolyte of lithium secondary batteries can be used without limitation.

[0166] The lithium salt may be appropriately changed within a generally usable range, but in order to obtain an optimal effect of forming a film for preventing corrosion on the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, specifically, at a concentration of 1 M to 2.5 M, and more specifically, at a concentration of 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics during high-temperature storage of a lithium secondary battery is sufficient, and the viscosity of the electrolyte is appropriate, so that the electrolyte impregnation property can be improved.

[0167] The above non-aqueous organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charge / discharge process of a lithium secondary battery and can exhibit the desired properties together with additives. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used alone or in combination of two or more, and specifically, carbonate-based organic solvents can be used.

[0168] Among the organic solvents, the carbonate-based organic solvent may include at least one of a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC), and specifically, by including fluoroethylene carbonate (FEC), the content of F atoms in the inorganic layer may be increased, thereby exhibiting the intended effect of the present invention.

[0169] In addition, the linear carbonate-based organic solvent is a solvent having low viscosity and low dielectric constant, and may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, and more specifically, may include diethyl carbonate.

[0170] The above ether organic solvent may be any one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more thereof, but is not limited thereto.

[0171] The above ester organic solvent may include at least one selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0172] Specific examples of the linear ester organic solvent include, but are not limited to, one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or a mixture of two or more thereof.

[0173] The above cyclic ester organic solvent may be, as a specific example, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more thereof, but is not limited thereto.

[0174] Among the above ester solvents, cyclic carbonate compounds are preferably used as high-viscosity organic solvents with high dielectric constants, which facilitate the dissociation of lithium salts in the electrolyte. When low-viscosity, low-dielectric constant linear carbonate compounds such as dimethyl carbonate and diethyl carbonate, and linear ester compounds are mixed and used in an appropriate ratio with these cyclic carbonate compounds, a gel-type electrolyte with high electrical conductivity can be produced, and thus, the compounds can be used more preferably.

[0175] Furthermore, the lithium non-aqueous electrolyte further includes a functional additive, and the functional additive may be included to prevent cathode collapse from occurring in a high-power environment, or to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0176] Specifically, the functional additive may include at least one functional additive selected from the group consisting of, as representative examples, sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0177] The above sultone-based compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone, and may be included in an amount of 0.3 wt% to 5 wt%, specifically 1 wt% to 5 wt%, based on the total weight of the gel electrolyte. When the content of the sultone-based compound in the gel electrolyte exceeds 5 wt%, an excessively thick film may be formed on the electrode surface, which may cause an increase in resistance and a deterioration in output, and the resistance may also increase due to an excessive amount of additive, which may deteriorate the output characteristics.

[0178] The above sulfite compound may include at least one compound selected from the group consisting of 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-butylene glycol sulfite, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0179] The above sulfone compound may include at least one compound selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, and methylvinyl sulfone, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0180] The above sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS), and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0181] In addition, the halogen-substituted carbonate compound may include fluoroethylene carbonate (FEC) and may be included in an amount of 5 wt% or less based on the total weight of the gel electrolyte. If the content of the halogen-substituted carbonate compound in the gel electrolyte exceeds 5 wt%, cell swelling performance may deteriorate.

[0182] In addition, the nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0183] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte. If the content of the cyclic carbonate compound in the gel electrolyte exceeds 3 wt%, the cell swelling suppression performance may deteriorate.

[0184] The above phosphate compound may include at least one compound selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphite, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0185] The above borate compound may include lithium oxalyldifluoroborate, and may be included in an amount of 3 wt% or less based on the total weight of the gel electrolyte.

[0186] The lithium salt-based compound is a compound different from the lithium salt included in the lithium non-aqueous electrolyte, and may include at least one compound selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and may be included in an amount of 3 wt% or less based on the total weight of the gel-type electrolyte.

[0187] The functional additives may be mixed in an amount of two or more, and may be included in an amount of 20 wt% or less, specifically 0.1 wt% to 10 wt%, based on the total weight of the lithium non-aqueous electrolyte. If the content of the functional additive exceeds 20 wt%, there is a possibility that excessive side reactions may occur within the lithium non-aqueous electrolyte during charging and discharging of the battery. In particular, since they may not be sufficiently decomposed at high temperatures, they may exist as unreacted substances or precipitated substances within the lithium non-aqueous electrolyte at room temperature. Accordingly, side reactions that reduce the lifespan or resistance characteristics of the lithium metal battery may occur.

[0188]

[0189] Manufacturing method of lithium secondary battery

[0190] Meanwhile, a method for manufacturing a lithium secondary battery according to another embodiment of the present invention is provided.

[0191] Specifically, the manufacturing method of the lithium secondary battery is as follows:

[0192] A step of manufacturing a separator by forming an oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) on one or both sides of a substrate;

[0193] A step of manufacturing a positive electrode by forming a positive electrode active material layer on one side or both sides of a positive electrode current collector, and manufacturing a negative electrode by forming a negative electrode active material layer on one side or both sides of a negative electrode current collector;

[0194] A step of manufacturing an electrode assembly by interposing the separator between the positive electrode and the negative electrode so that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other;

[0195] A step of manufacturing a secondary battery by embedding the electrode assembly and electrolyte into a secondary battery case;

[0196] A step of applying pressure to the secondary battery by placing the secondary battery between a plurality of pressure plates; and

[0197] It is characterized by including a step of activating the secondary battery while applying pressure.

[0198] Figures 2 and 3 schematically illustrate a top view and a cross-sectional view, respectively, of a pressurizing device applied to the method for manufacturing such a lithium secondary battery.

[0199] A lithium secondary battery according to the present invention is manufactured by manufacturing a positive electrode, a negative electrode, and a separator as described above, respectively, and laminating the oxide-based solid electrolyte layer of the separator so that it faces the negative electrode active material layer of the negative electrode to manufacture an electrode assembly, and then embedding these together with the electrolyte in a secondary battery case.

[0200] Hereafter, referring to FIGS. 2 and 3, pressure is applied to the lithium secondary battery (200) from above and below or from the left and right while a plate-shaped pressure plate (210) is positioned on the upper and lower or left and right sides of the lithium secondary battery (200). In the case of FIGS. 2 and 3, a predetermined pressure (F) is applied simultaneously to the upper and lower portions of the lithium secondary battery (200) using the pressure plate (210) as an intermediate medium, so that the pressure can be applied much more uniformly than when pressure is applied directly to the lithium secondary battery (200) without an intermediate medium or when pressure is applied to only one of the upper and lower surfaces.

[0201] Meanwhile, it is also possible to fix one side of the lithium secondary battery (200) to the support and apply pressure only to the opposite side. For example, in a state where a movable pressure plate (210) continuously applies pressure to an immovable support (i.e., the support and the pressure plate are in a completely close state), an external force is applied to the pressure plate (210) to temporarily create a predetermined space, the lithium secondary battery (200) is interposed, and then the external force applied to the pressure plate (210) is removed again. In this case, a uniform pressure (F) can be applied to both sides of the lithium secondary battery (100) in a very easy manner.

[0202] Here, a plurality of pressure plates (210) can be fastened with a plurality of pressure bolts (220) to apply pressure to the lithium secondary battery (200). When pressure (F) is applied by fastening with the pressure bolts (220) in this way, there may be an advantage in that the pressure can be applied to an accurate location.

[0203] For example, the above-mentioned applied pressure (F) can be expressed as a fastening torque strength of the pressurizing jig (120), and the pressurizing bolt (120) can be pressed with a fastening strength of 6 kgf·cm or more, and in detail, can be pressed with a fastening strength of 10 to 20 kgf·cm.

[0204] When pressure is applied with a bonding strength of less than 6 kgf·cm, effective SEI formation may be difficult.

[0205] Meanwhile, when two or more lithium secondary batteries are stacked and pressure is applied simultaneously from the top and bottom using a pressure plate as an intermediate medium, pressure can be applied uniformly to multiple lithium secondary batteries. In addition, a multilayer pressure application method in which lithium secondary batteries are individually sandwiched between multiple pressure plates and then pressure is applied is also possible.

[0206] Next, the lithium secondary battery can be activated while applying pressure.

[0207] Here, the activation may include a charge-discharge process and may be performed at a temperature of 25°C to 60°C, and more specifically, may be performed at a temperature of 40°C to 60°C.

[0208] Specifically, during the manufacturing process of a lithium secondary battery, an inorganic layer including a reduced product of LATP and an SEI material can be formed at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer by an activation process, and by applying a specific range of pressure to the lithium secondary battery in the activation step, the formation aspect of the inorganic layer including a reduced product of LATP and an SEI material can be controlled with good quality.

[0209]

[0210] Hereinafter, examples will be described to demonstrate that a lithium secondary battery according to one embodiment of the present invention exhibits improved effects.

[0211]

[0212] <Example 1>(LATP)

[0213] A separator was manufactured by forming an oxide-based solid electrolyte layer (thickness: 2 μm) on both sides of a polyolefin material substrate (polyethylene, thickness: 9 μm).

[0214] Here, the oxide-based solid electrolyte layer is Li 1.3 Al 0.3 Ti 1.7 (PO4)3: An electrolyte slurry was prepared by mixing an acrylic copolymer (CSB130, Toyoink) in a weight ratio of 95:5 and dispersing it in acetone, and coating one side of the polyolefin material substrate and drying it.

[0215]

[0216] <Comparative Example 1>(CCS)

[0217] A separation membrane was manufactured by forming an organic-inorganic mixed layer (thickness: 20 μm) on both sides of a polyolefin material substrate (polyethylene, thickness: 9 μm).

[0218] Here, the organic / inorganic mixed layer was manufactured by mixing Al2O3:CSB130 in a weight ratio of 95:5 and dispersing it in NMP, coating the organic / inorganic slurry on one surface of the polyolefin material substrate, and drying it.

[0219]

[0220] Experimental Example 1

[0221] First, a surface SEM photograph of the membrane manufactured in Example 1 was taken and shown in Fig. 4, and an XRD analysis was performed and the graph was shown in Fig. 5.

[0222] Afterwards, a 15 micrometer thick aluminum (Al) metal film was prepared as a positive electrode collector, and Li(Ni) was applied as a positive electrode active material on one surface of the aluminum metal film. 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2: A cathode slurry was prepared by dispersing carbon nanotubes as a conductive material and PVDF as a binder in a weight ratio of 96 1:3 in NMP solvent, and coating, drying, and rolling to a thickness of 60 micrometers to prepare a cathode.

[0223] An 8 micrometer thick copper (Cu) metal film was prepared as a negative electrode current collector, and on one surface of the copper metal film, prelithiated SiO as a negative electrode active material, carbon black as a conductive material, and SBR and CMC as binders were dispersed in an NMP solvent at a weight ratio of 80:10:9.5:0.5, and the resulting negative electrode slurry was coated, dried, and rolled to a thickness of 100 micrometers to manufacture a negative electrode.

[0224] Between the positive electrode and the negative electrode, the separators manufactured in Example 1 were interposed, and the oxide-based solid electrolyte layer or the organic-inorganic mixed layer was placed so as to face the negative electrode, thereby manufacturing an electrode assembly, and an electrolyte was injected therein in which LIFSI was dissolved to a concentration of 1.0 M and LiPF6 to a concentration of 0.5 M in a non-aqueous organic solvent having a composition of fluoroethylene carbonate (FEC): diethyl carbonate (DEC) = 10:90 (volume ratio), thereby manufacturing a 100 mA pouch-type bi-cell.

[0225] For the above-mentioned bicelles, the pressurized jig was pressed at 25°C with a clamping strength of 12 kgf·cm, and the process was performed three times: charging at a constant current of 0.1C until the voltage reached 4.20V, aging at 25°C for 24 hours, aging at 60°C for 20 hours, and then completely discharging at a constant current of 0.33C.

[0226] After disassembling the above-mentioned bicelles that completed charge and discharge, SEM photographs of the surface of the separator were taken and shown in Fig. 4 along with the SEM photographs of the separator before charge and discharge. XRD analysis was performed by comparing the diffraction patterns obtained by irradiating the surface of the separator with X-rays at an angle of 0 to 50 degrees with the peak positions of LATP and lithiated LATP of ICDD, and the results are shown in Fig. 5.

[0227] Referring to FIGS. 4 and 5, it can be confirmed that after charging and discharging, a Li reduction product is formed on the surface of the separator according to the present invention, thereby filling the pores of the oxide-based solid electrolyte layer.

[0228]

[0229] Experimental Example 2

[0230] In the same manner as in Experimental Example 1, bicelles were manufactured using the separator of Example 1 and the separator of Comparative Example 1, and charge / discharge were performed.

[0231] Afterwards, after disassembling the above-mentioned bicelles, a quantitative element analysis was performed in the depth direction while etching the separator sample with a sputtering gun of XPS equipment on the cathode surface (spot size: 200 μm, sputtering gun energy: 1000 eV, etching rate: 1.08 nm / sec), and the content of elements was analyzed through this to examine the SEI material composition analysis and its thickness, and the results are shown in Figs. 6 and 7 below. In addition, the atomic content of F is shown in Table 1.

[0232] Specifically, Fig. 6 shows the results of analyzing the Si element content on the cathode surface, and from these, the thickness of the inorganic layer was examined, and Fig. 7 shows the results of analyzing the element contents of Li, F, C, and O.

[0233] Referring to FIG. 6, the cathode of the bicell using the separator of Comparative Example 1 shows that the Si content increases quickly, indicating that the inorganic layer is relatively thin, whereas the cathode of the bicell using the separator of Example 1 of the present application shows that the Si exposure appears late, indicating that a thicker inorganic layer is formed.

[0234] Meanwhile, referring to FIG. 7 and Table 1 below, it can be seen that the contents of Li, F, and O are high and the content of C is low on the cathode surface of the bicelle using the separator of Example 1, indicating that a large amount of SEI material, such as LiF and Li2O, is formed.

[0235] Example 1 Comparative Example 1 F atomic ratio max(%)8.95.9

[0236] Experimental Example 3

[0237] The XPS profile analysis was performed on the membrane of Example 1 as in Experimental Example 2 to analyze the content of elements, and the results are shown in Fig. 8.

[0238] Afterwards, using the same method as in Experimental Example 1, a bicell was manufactured using the separator of Example 1 and charge / discharge was performed.

[0239] After charge and discharge, the above-mentioned bicelles were disassembled and the content of elements was analyzed through XPS profile analysis on the surface of the separator. The results are shown in Figure 8 below along with the analysis data of the separator before charge and discharge. In addition, the atomic content of F is shown in Table 2.

[0240] Referring to Fig. 8 and Table 2, it can be seen that the content of F on the surface of the separator increases rapidly after charge and discharge, indicating that F corresponding to the SEI component increases with charge and discharge, and thus, an inorganic layer with an excess of inorganic matter is formed.

[0241] Example 1F atomic ratio max(%)12.2

[0242]

[0243] Experimental Example 4

[0244] In the same manner as in Experimental Example 1, bicelles were manufactured using the separator of Example 1 and the separator of Comparative Example 1, and charge / discharge were performed. The completely discharged bicelles were disassembled, the electrolyte was washed from the negative electrode, and then DSC evaluation was performed.

[0245] The above DSC evaluation measured the heat flow at which an exothermic or endothermic reaction occurred when a completely discharged electrode was heated at a heating rate of 10°C / min in the range of 25 to 250°C.

[0246] In addition, in the same manner as in Experimental Example 1, bi-cells were manufactured using the separator of Example 1 and the separator of Comparative Example 1, and charge-discharge was performed. After being fully charged again under the conditions of 0.1 C and 4.35 V through CC-CV, the cells were disassembled and the DSC evaluation was performed on the cathode.

[0247] The results are shown in Figure 9 below.

[0248] Referring to FIG. 9, it can be confirmed that the main peak is broadened and a split is observed in the negative electrode of the bicell including the separator according to Example 1 of the present invention under fully charged and electrolyte containing conditions, compared to the case including the separator of Comparative Example 1. In addition, it can be confirmed that a high temperature shift in the onset temperature is observed in the negative electrode of the bicell including the separator of Example 1 of the present invention under the conditions of complete discharge and electrolyte washing, and from this, it can be seen that the thermal safety is superior when the separator according to the present invention is used.

[0249]

[0250] Experimental Example 5

[0251] Calorimeter evaluation was performed to measure the total calorific value (water temperature) of the exothermic reaction when a spark was applied to the material in an autoclave pressurized with an O2 atmosphere of 30 bar for the cathode under the same conditions as in Experimental Example 4 above to cause forced ignition, and the results are shown in Fig. 10.

[0252] Referring to FIG. 10, it can be confirmed that under fully charged, electrolyte-containing conditions, the calorific value of the cathode of the bicell including the separator of Example 1 is reduced by approximately 5.7% (4224->3985 Cal / g) compared to the cathode of the bicell including the separator of Comparative Example 1, and under fully discharged, electrolyte-washed conditions, it can be confirmed that the calorific value is reduced by approximately 8.6% (3075->2812 cal / g).

[0253] From this, it can also be seen that when the separation membrane according to the present invention is used, thermal safety is superior.

[0254]

[0255] Experimental Example 6

[0256] In the same manner as in Experimental Example 1, bicelles were manufactured using the separator of Example 1 and the separator of Comparative Example 1.

[0257] The manufactured bicelles were charged at 45°C with a constant current of 0.1C until the voltage reached 4.20V while the pressurized jig was applied with a clamping strength of 6 kgf·cm ('LATP6'), 12 kgf·cm ('LATP12'), and 18 kgf·cm ('LATP18') at a pressure of 45°C, aged at 25°C for 24 hours, aged at 60°C for 20 hours, and then completely discharged at a constant current of 0.33C, which was performed three times.

[0258] Afterwards, the charging state of SOC 50 was set, and when a 2.5C discharge current was applied for 0.1, 10, and 30 seconds, respectively, the DCIR was measured, and the results are shown in Figure 11 below.

[0259] In addition, the discharge rate characteristics were evaluated and the results are shown in Figure 12 below.

[0260] The above discharge rate characteristics were obtained by performing CC / CV (cut when CV current reaches 0.05C) on the bi-cells at 0.2C, discharging them three times at 0.2C, 0.33C, 0.5C, 1C, 2C, and 3C, and reporting the capacity at each third time to confirm the maintenance rate of the discharge capacity at high rates compared to the discharge capacity at 0.2C.

[0261] Referring to Figures 11 and 12, it can be confirmed that resistance is reduced when a separator according to the present invention is used, and the rate of reduction is greater when the applied pressure is increased. Meanwhile, it can be confirmed that there is little or no significant difference in performance in terms of capacity, or that it is superior.

[0262]

[0263] Experimental Example 7

[0264] The positive electrode was prepared as in Experimental Example 1, and the negative electrode was manufactured in the same manner as in Experimental Example 1, except that graphite and SiO were mixed in a weight ratio of 94.5:5.5 as the negative electrode active material.

[0265] In addition, using the separator manufactured in Example 1 and Comparative Example 1, an electrode assembly was manufactured by placing the oxide-based solid electrolyte layer or the organic-inorganic mixed layer facing the negative electrode, and an electrolyte in which 1M LiPF6 was dissolved in a carbonate solvent of EC:EMC = 3:7 (vol%) was used, and in manufacturing a stack cell, the positive electrode / negative electrode was stacked three times to manufacture an 840 mA pouch-type battery cell.

[0266] The manufactured bicell was charged at 45°C with a constant current of 0.1C until the voltage reached 4.20V while the pressurized jig was pressurized with a clamping strength of 12 kgf·cm, aged at 25°C for 24 hours, aged at 60°C for 20 hours, and then completely discharged at a constant current of 0.33C, and this process was performed three times.

[0267] DCIR was measured by setting the state of charge to SOC 50 and discharging under 2.5C conditions, and the results are shown in Figure 13 below.

[0268] In addition, the discharge rate characteristics were evaluated and the results are shown in Figure 14 below.

[0269] The above discharge rate characteristic evaluation method is as described in Experimental Example 6 above.

[0270] Referring to FIGS. 13 and 14, it can be confirmed that resistance is reduced when a separator according to the present invention is used, and that the rate of reduction is greater when the applied pressure is increased. Meanwhile, it can be confirmed that there is little or no significant difference in performance in terms of capacity, or that it is superior.

[0271]

[0272] Anyone with ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

[0273] The lithium secondary battery according to the present invention forms an oxide-based solid electrolyte layer containing LATP on a separator substrate and contacts it with a negative electrode active material layer, thereby forming a thick SEI with an excess of inorganic substances having a high F atom content by forming a LATP reduction product together with an SEI material at the interface between the two, thereby having the effect of improving the thermal safety of the lithium secondary battery.

[0274] In addition, the formation pattern of the SEI with a high inorganic content of these F atoms can be controlled to improve battery performance.

Claims

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

2. In paragraph 1, A lithium secondary battery, wherein the inorganic layer fills part or all of the pores of the oxide-based solid electrolyte layer, forms a separate layer at the interface between the oxide-based solid electrolyte layer and the negative electrode active material layer, or is included in the form of all of these.

3. In paragraph 2, A lithium secondary battery, wherein the above-mentioned inorganic layer fills the pores of the above-mentioned oxide-based solid electrolyte layer by 10 to 100 volume% based on the total pore volume and forms a separate layer having a thickness of 5 to 100 nm.

4. In paragraph 5, The above LATP reduction product is formed in a form in which more than 50% by weight of the LATP particles fills the pores of the oxide-based solid electrolyte layer along the surface of the LATP particles, A lithium secondary battery, wherein the SEI material is formed in a form that fills the pores of the oxide-based solid electrolyte layer together with the LATP reducer, or on the surface of the LATP reducer, in a space charge region where the concentration of Li+ is locally high, or as a separate layer on the surface of the oxide-based solid electrolyte layer, or both.

5. In paragraph 1, A lithium secondary battery, wherein the reduced product of the above LATP comprises lithiated-LATP formed by a spontaneous lithiation reaction represented by the following reaction scheme 1. [Reaction Formula 1] Li 1.3 Al 0.3 You 1.7 (PO 4 ) 3 -> Li 3 Al 0.3 You 1.7 (PO 4 ) 3 6. In paragraph 1, The above SEI material is a lithium secondary battery containing LiF.

7. In paragraph 5, The above SEI material is Li 2 CO 3 , and Li 2 A lithium secondary battery further comprising at least one material selected from the group consisting of O.

8. In paragraph 1, The above-mentioned inorganic layer is a lithium secondary battery composed of a LATP reduction product and an SEI material.

9. In paragraph 1, A lithium secondary battery in which the above oxide-based solid electrolyte layers are formed on both sides of the substrate.

10. In paragraph 1, The above description is a lithium secondary battery using a polyolefin substrate.

11. In paragraph 1, A lithium secondary battery, wherein the oxide-based solid electrolyte layer is composed of an oxide-based solid electrolyte including lithium aluminum titanium phosphate (LATP) and a binder.

12. In paragraph 1, A lithium secondary battery, wherein the above oxide-based solid electrolyte layers are formed on one side of the substrate to a thickness of 0.1 ㎛ to 20 ㎛.

13. In paragraph 1, The above cathode active material layer comprises a lithium transition metal oxide represented by the following chemical formula 1 as a cathode active material, a lithium secondary battery: [Chemical Formula 1] Li 1+x Ni a Co b Mr c M 1-(a+b+c) O 2 In the above formula, M is at least one selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, 0≤x≤0.5, 0 <a<1, 0<b<1, 0<c<1이다.

14. In paragraph 1, A lithium secondary battery, wherein the negative electrode active material layer contains lithium-ion silicon oxide as a negative electrode active material in an amount of 80 wt% or more based on the total weight of the negative electrode active material.

15. In paragraph 1, The lithium secondary battery further comprises an electrolyte comprising LiFSI as a lithium salt and fluoroethylene carbonate (FEC) as an electrolyte solvent.

16. A method for manufacturing a lithium secondary battery according to Article 1, A step of manufacturing a separator by forming an oxide-based solid electrolyte layer containing lithium aluminum titanium phosphate (LATP) on one or both sides of a substrate; A step of manufacturing a positive electrode by forming a positive electrode active material layer on one side or both sides of a positive electrode current collector, and manufacturing a negative electrode by forming a negative electrode active material layer on one side or both sides of a negative electrode current collector; A step of manufacturing an electrode assembly by interposing the separator between the positive electrode and the negative electrode so that the oxide-based solid electrolyte layer and the negative electrode active material layer face each other; A step of manufacturing a secondary battery by embedding the above electrode assembly and electrolyte into a secondary battery case; A step of applying pressure to the secondary battery by positioning the secondary battery between a plurality of pressurizing plates; and A method for manufacturing a lithium secondary battery, comprising: a step of activating the secondary battery while applying pressure to the secondary battery.

17. In paragraph 16, A method for manufacturing a lithium secondary battery, wherein the plurality of pressurizing plates are connected by a plurality of pressurizing bolts to apply pressure.

18. In paragraph 17, A method for manufacturing a lithium secondary battery, wherein the above-mentioned pressurizing bolt pressurizes the secondary battery with a fastening strength of 6 kgf·cm or more.

19. In Article 17, A method for manufacturing a lithium secondary battery, wherein the above-mentioned pressurizing bolt pressurizes the secondary battery with a fastening strength in the range of 10 to 20 kgf·cm.

20. In paragraph 17, A method for manufacturing a lithium secondary battery, wherein the above activation step is performed at a temperature of 40°C to 60°C.

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