Lithium secondary battery

Abstract

Provided is a lithium secondary battery comprising: a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; and a negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the positive electrode active material layer includes a sacrificial positive electrode material, which is a compound of chemical formula 1, in a content of 0.01 wt% to 0.5 wt% based on the weight of the positive electrode active material layer. <Chemical formula 1> LiaFe1-xMxOy (where, 1<a≤5, 0≤x≤0.35, 2<y≤4, and M is Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, or a combination thereof)

Description

lithium secondary battery

[0001] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery having excellent charge / discharge performance and high-temperature capacity retention rate.

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0140341 ​​dated October 15, 2024 and Korean Patent Application No. 10-2025-0135250 dated September 19, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of the specification.

[0003] Rechargeable batteries are a representative example of electrochemical devices that utilize electrochemical energy, and their application areas are increasingly expanding. Recently, with the technological development and growing demand for portable devices such as portable computers, mobile phones, and cameras, the demand for rechargeable batteries as an energy source has been rapidly increasing. Among these rechargeable batteries, much research has been conducted on lithium-ion batteries, which possess high energy density—that is, high capacity—and they have been commercialized and are widely used. Furthermore, there is a demand for high-capacity electrode designs to manufacture lithium-ion batteries with high output and high discharge voltage.

[0004] Various studies are underway to improve the charge and discharge characteristics of secondary batteries, and there is still room for improvement.

[0005] The technical problem that the present invention aims to solve is to provide a lithium secondary battery having excellent charge / discharge performance and high-temperature capacity retention rate.

[0006] To achieve the above technical problem, the present invention provides a lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer disposed on the positive current collector; and a negative electrode including a negative current collector and a negative active material layer disposed on the negative current collector, wherein the positive active material layer comprises 0.01 weight% to 0.5 weight% of the sacrificial positive electrode material, which is a compound of Formula 1, based on the weight of the positive active material layer.

[0007] <Chemical Formula 1>

[0008] Li a Fe 1-x M x O y

[0009] (Here, 1 <a≤5, 0≤x≤0.35, 2<y≤4, M은 Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, 또는 그 조합임)

[0010] In some embodiments, the positive active material layer may further include LiFeO2.

[0011] In some embodiments, the content of LiFeO2 in the positive active material layer may be 0.3% to 5% by weight based on the total weight of the positive active material layer.

[0012] In some embodiments, the compound of Formula 1 may include Li5FeO4.

[0013] In some embodiments, the positive active material layer may further include a compound of Formula 2 below as a sacrificial positive material.

[0014] <Chemical Formula 2>

[0015] Li b Fe 1-x M x O y

[0016] (Here, 3≤b≤7, 0≤x≤0.35, 3≤y≤4, M is Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, or a combination thereof)

[0017] In some embodiments, the positive active material layer may contain 0.02 weight% to 2.3 weight% of LiFeO2, a compound of Formula 1, and a compound of Formula 2 based on the weight of the positive active material layer.

[0018] In some embodiments, the positive active material layer may contain 0.03% to 1.8% by weight of LiFeO2, a compound of Formula 1, and a compound of Formula 2 based on the weight of the positive active material layer.

[0019] In some embodiments, the positive active material layer may contain 0.5% to 1.7% by weight of LiFeO2, a compound of Formula 1, and a compound of Formula 2 based on the weight of the positive active material layer.

[0020] In some embodiments, a separator may be further included between the anode and the cathode.

[0021] In some embodiments, the positive active material layer comprises a first positive active material layer disposed on the positive current collector and comprising a first positive active material; and a second positive active material layer disposed on the first positive active material layer and comprising a second positive active material, wherein the first positive active material layer comprises the sacrificial positive material, and the second positive active material layer may not comprise the sacrificial positive material.

[0022] In some embodiments, the thickness of the first positive active material layer may be 0.01 to 2 times the thickness of the second positive active material layer.

[0023] In some embodiments, the thickness of the first positive active material layer may be 0.1 to 0.9 times the thickness of the second positive active material layer.

[0024] In some embodiments, at least one of the first positive active material layer and the second positive active material layer may include an iron phosphate compound-based positive active material.

[0025] In some embodiments, the negative electrode active material layer may include a Si-based negative electrode active material containing carbon.

[0026] In some embodiments, the total thickness of the positive active material layer may be 80 μm to 300 μm.

[0027] In some embodiments, the anode further comprises a primer layer between the anode current collector and the anode active material layer, and the primer layer may further comprise LiFeO2.

[0028] In some embodiments, the positive active material layer may further include a compound of the following formula 3A as a sacrificial positive material.

[0029] <Chemical Formula 3A>

[0030] Li c M 1 (1-p) M 2 p O4

[0031] (In the above chemical formula 3A,

[0032] M 1 is Fe, Co, Mn, Zn, Al, or Ga, and

[0033] M 2 is one or more metals selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, wherein M 1 and M 2 It includes different metals,

[0034] c and p are 4≤c≤7 and 0≤p≤0.5, respectively.

[0035] In some embodiments, the positive active material layer may further include a compound of the following chemical formula 3B.

[0036] <Chemical Formula 3B>

[0037] M 3 (1-x) M 4 x O y

[0038] (In the above chemical formula 3B,

[0039] M 3 and M 4 are respectively W, Mo, Ni, Co, Nb, Ge, Ti, Ta, or Ce, where M 3 and M 4 It contains different metals,

[0040] x and y are 0≤x≤0.5 and 1≤y≤6, respectively.

[0041]

[0042] Another aspect of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer disposed on the positive current collector; a negative electrode including a negative current collector and a negative active material layer disposed on the negative current collector; and an electrolyte, wherein the positive active material layer comprises LiFeO2 and a sacrificial cathode material which is a compound of Formula 1, and the content of LiFeO2 and the sacrificial cathode material is 0.02 wt% to 2.3 wt% based on the total weight of the positive active material layer, and the electrolyte comprises a coumarin-based additive.

[0043] <Chemical Formula 1>

[0044] Li a Fe 1-x M x O y

[0045] (Here, 1 <a≤5, 0≤x≤0.35, 2<y≤4, M은 Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, 또는 그 조합임)

[0046] In some embodiments, the coumarin-based additive may include a compound having the structure of Formula 5 or Formula 6.

[0047] <Chemical Formula 5>

[0048]

[0049] (Here, R1 to R5 are each independently selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and an alkoxy group having 1 to 10 carbon atoms, and R is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms, or -OR'(R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms))

[0050] <Chemical Formula 6>

[0051]

[0052] (Here, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, R and R' are each independently an alkylene group having 1 to 10 carbon atoms, and m is an integer from 0 to 5)

[0053] In some embodiments, the concentration of the sacrificial cathode material and LiFeO2 may increase as it gets closer to the cathode current collector.

[0054] In some embodiments, the content of LiFeO2 and the sacrificial cathode material in the positive active material layer may be 0.5 weight% to 1.7 weight% based on the total weight of the positive active material layer.

[0055] In some embodiments, the weight ratio of Li5FeO4 and LiFeO2 present in the positive active material layer may be 1:20 to 1:500.

[0056] The lithium secondary battery according to the embodiments of the present invention has excellent charge / discharge performance and high-temperature capacity retention rate.

[0057] The effects obtainable from the exemplary embodiments of the present invention are not limited to those mentioned above, and other unmentioned effects can be clearly derived and understood by those skilled in the art to which the exemplary embodiments of the present disclosure belong from the following description. That is, unintended effects resulting from the implementation of the exemplary embodiments of the present disclosure can also be derived by those skilled in the art from the exemplary embodiments of the present disclosure.

[0058] FIG. 1 is a front view showing a lithium secondary battery according to one embodiment of the present invention.

[0059] FIG. 2 is a cross-sectional view showing an electrode assembly according to one embodiment of the present invention.

[0060] FIG. 3 is a cross-sectional view showing an anode according to one embodiment of the present invention.

[0061] FIG. 4 is a cross-sectional view showing a cathode according to one embodiment of the present invention.

[0062] Hereinafter, preferred embodiments of the concept of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the concept of the present invention may be modified in various different forms, and the scope of the concept of the present invention should not be interpreted as being limited by the embodiments described below. It is preferable to interpret the embodiments of the concept of the present invention as being provided to more completely explain the concept of the present invention to those with average knowledge in the art. Identical reference numerals denote identical elements throughout. Furthermore, various elements and areas in the drawings are depicted schematically. Accordingly, the concept of the present invention is not limited by the relative sizes or spacing depicted in the accompanying drawings.

[0063] Terms such as first, second, etc. may be used to describe various components, but said components are not limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the concept of the present invention, the first component may be named the second component, and conversely, the second component may be named the first component.

[0064] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the concept of the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, expressions such as “comprising” or “having” are intended to indicate the existence of the features, number, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, actions, components, parts, or combinations thereof.

[0065] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by those skilled in the art to which the concept of the present invention pertains. Furthermore, it will be understood that commonly used terms, such as those defined in advance, should be interpreted as having meanings consistent with their intent in the context of the relevant technology, and should not be interpreted in an overly formal sense unless explicitly defined herein.

[0066] Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described in succession may be performed substantially simultaneously or in the reverse order of the description.

[0067] In the accompanying drawings, variations of the depicted shapes may be anticipated, for example, depending on manufacturing techniques and / or tolerances. Accordingly, embodiments of the present invention should not be interpreted as being limited to specific shapes of the areas depicted herein, but should include, for example, variations in shape resulting from the manufacturing process. All terms "and / or" used herein include each of the mentioned components and all combinations of one or more of them.

[0068]

[0069] FIG. 1 is a front view showing a lithium secondary battery (1) according to one embodiment of the present invention.

[0070] Referring to FIG. 1, a lithium secondary battery (1) according to one embodiment of the present invention comprises a positive electrode, a negative electrode, and a battery case (150) in which the electrode assembly is mounted. In some embodiments, the lithium secondary battery (1) may further comprise an electrolyte together with an electrode assembly (not shown) inside the battery case (150). In some embodiments, the lithium secondary battery (1) may further comprise a solid electrolyte between the positive electrode and the negative electrode.

[0071] For example, the above electrolyte or solid electrolyte allows ions to move between the positive and negative electrodes, and through this ion exchange between the positive and negative electrodes, the lithium secondary battery (1) can perform charging and discharging. Examples of the electrolyte or solid electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used when manufacturing a lithium secondary battery, but are not limited to these.

[0072] Additionally, the battery case (150) includes a sealing portion (155) of a structure sealed by heat fusion along the outer circumference. The battery case (150) may be a laminate sheet comprising a resin layer and a metal layer. In some embodiments, the battery case (150) is made of a laminate sheet and may consist of an outer resin layer forming the outermost layer, a barrier metal layer that prevents the penetration of material, and an inner resin layer for sealing. However, the embodiments of the present invention are not limited to the structure described above and may be replaced with a battery case of a secondary battery of another general structure.

[0073] Additionally, the electrode assembly (not shown) may be formed in a jelly-roll type (wound type), stack type (laminated type), or composite type (stack and folding type) structure. In some embodiments, the electrode assembly (not shown) may include an anode, a cathode, and a separator disposed between them.

[0074] In addition, in this embodiment, the battery case (150) may be structured such that an electrode lead (140), which is electrically connected to a plurality of electrode tabs (not shown) extending from an electrode assembly (not shown), is exposed to the outside. More specifically, the electrode lead (140) may protrude outwardly from the battery case (150) through the sealing portion (155). In addition, in this embodiment, a lead film (160) may be positioned between the electrode lead (140) and the sealing portion (155).

[0075] The lead film (160) can not only prevent a short circuit from occurring between the electrode lead (140) and the blocking metal layer of the battery case (150), but also improve the sealing performance of the battery case (150). When the lead film (160) is provided, the phenomenon of reduced adhesion during thermal fusion between the metal electrode lead (140) and the polymer battery case (150) can be prevented. In addition, it is preferable that the lead film (160) be an insulating material capable of blocking the application of current from the electrode lead (140) to the battery case (150). The lead film (160) is made of a film having insulating and thermal fusion properties. The lead film (160) may include one or more layers of material selected from, for example, polyimide (PI), polypropylene, polyethylene, and polyethylene terephthalate (PET). In some embodiments, the length of the lead film (160) may be increased to also serve the function of preventing a short circuit in the portion of the electrode lead (140) exposed outside the battery case (150).

[0076] In some embodiments, the electrode lead (140) includes an anode lead (141) electrically connected to an anode tab included in the electrode assembly and a cathode lead (145) electrically connected to a cathode tab included in the electrode assembly.

[0077] In some embodiments, the lithium secondary battery (1) may be a bidirectional pouch battery cell in which a positive lead (141) and a negative lead (145) protrude from each side of the battery case (150). However, not limited thereto, the lithium secondary battery (1) may be a unidirectional pouch battery cell in which a positive lead (141) and a negative lead (145) are arranged together on the same side of the battery case (150). In other embodiments, the lithium secondary battery (1) may be a secondary battery in which an electrode assembly is housed within a prismatic or cylindrical battery case.

[0078] Although the following description is based on bidirectional pouch battery cells, it may be described in the same or similar manner for unidirectional pouch battery cells. A person skilled in the art will understand that the following description is applicable to unidirectional pouch battery cells, prismatic secondary batteries, and cylindrical battery cases.

[0079]

[0080] FIG. 2 is a cross-sectional view showing an electrode assembly (40) according to one embodiment of the present invention.

[0081] Referring to FIG. 2, the electrode assembly (40) is formed by alternately stacking a positive electrode (10) and a negative electrode (20) with a separator (30) in between. At this time, the electrode assembly (40) may be provided with electrode tabs, and the electrode tabs are connected to the positive electrode (10) and the negative electrode (20) of the electrode assembly (40), respectively, and may protrude outward from the electrode assembly (40). A plurality of electrode tabs connected to the positive electrode (10) and a plurality of electrode tabs connected to the negative electrode (20) may protrude from the electrode assembly (40) in different directions and / or the same direction. The manufactured electrode assembly (40) may be housed in a battery case (150). As previously described, the lithium secondary battery (1) including the electrode assembly (40) may be manufactured in a pouch type, a prismatic type, or a cylindrical type.

[0082]

[0083] FIG. 3 is a cross-sectional view showing an anode (10) according to one embodiment of the present invention.

[0084] Referring to FIG. 3, the anode (10) is formed by coating a primer layer (12) and anode active material layers (13, 14) on both sides of an anode current collector (11). In some embodiments, the primer layer (12) may be applied to the surface of the anode current collector (11). In some embodiments, the primer layer (12) may have a patterned structure and may be provided on the surface of the anode current collector (11). In some embodiments, the entire surface of the anode current collector (11) may be coated with a dot pattern primer layer (12).

[0085] In FIG. 3, a positive active material layer is shown provided on both surfaces of the positive current collector (11), but a positive active material layer may be provided on only one surface.

[0086] The above positive current collector (11) is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. The above positive current collector (11) may include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.

[0087] In some embodiments, the positive current collector (11) may form fine irregularities on its surface to increase adhesion with the active material described later. In some embodiments, the positive current collector (11) may have various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0088] In some embodiments, the positive current collector (11) may have a thickness of about 10 μm to about 25 μm, but the present invention is not limited thereto.

[0089] In some embodiments, the positive active material layer (13, 14) may include a first positive active material layer (13) and a second positive active material layer (14). The first positive active material layer (13) may be disposed on the primer layer (12). In some embodiments, the second positive active material layer (14) may be disposed on the first positive active material layer (13).

[0090] The first positive active material layer (13) comprises a first positive active material, and the second positive active material layer (14) may comprise a second positive active material. The first positive active material and the second positive active material may each independently comprise a positive active material as described below.

[0091] The above-mentioned positive electrode active material may comprise, for example, lithium transition metal oxide; lithium metal iron phosphate; lithium nickel-manganese-cobalt oxide; an oxide in which a portion of lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these, but is not limited thereto. Specifically, the above-mentioned positive electrode active material may comprise, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; and a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x Ni-site type lithium nickel oxide represented by MxO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); Li in which part of the Li of the chemical formula is substituted with aluminum ions. 1+x (Ni a Co b Mn c Al d ) 1-x Examples include O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a+b+c+d=1); lithium metal phosphate LiMPO4 (where M is M = Fe, Co, Ni, or Mn), disulfide compounds; Fe2(MoO4)3, etc., but are not limited to these.

[0092] In some embodiments, the first positive active material and the second positive active material may be of the same type. In some embodiments, both the first positive active material and the second positive active material may comprise a lithium metal phosphate material. In some embodiments, when the first positive active material and the second positive active material are of the same type, an interface may not be observed between the first positive active material layer (13) and the second positive active material layer (14). In some embodiments, the first positive active material layer (13) and the second positive active material layer (14) may be formed integrally.

[0093] In some embodiments, the first positive electrode active material and the second positive electrode active material may be different materials. In some embodiments, one of the first positive electrode active material and the second positive electrode active material may include a lithium metal phosphate material and the other may include a lithium nickel-manganese-cobalt oxide material.

[0094] The above positive active materials can be connected and fixed to each other by a positive binder.

[0095] The above-mentioned anode binder is adhesive, stable in electrochemical reactions, and capable of maintaining a stable form by binding electrode materials such as the anode active material and the anode conductive material, and is not limited to specific components.Non-limiting examples of such anode binders include styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block polymer (SBS), styrene ethylene butadiene block polymer (SEB), styrene-(styrene butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene terpolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene) polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, and polyvinylidene fluoride-co-hexafluoropropylene. It may be polyvinylidene fluoride-co-trichloroethylene, polymethyl(meth)acrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, polypropylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, or may contain two or more of these.Specifically, the binder may include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), polymethyl methacrylate, polyethylhexyl acrylate, and polybutyl acrylate. In a specific embodiment, the anode binder may include one or more selected from these.

[0096] The above positive active material may further include a positive conductive material to reduce electrical resistance.

[0097] The above-mentioned positive electrode conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery. Non-limiting examples include graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskey such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. In a specific embodiment, the above-mentioned positive electrode conductive material may include one or more selected from these.

[0098] In some embodiments, at least one of the first positive active material layer (13) and the second positive active material layer (14) may include a positive active material based on an iron phosphate compound.

[0099] In some embodiments, the content of the iron phosphate compound-based positive active material in the first positive active material layer (13) may be about 50 wt% or more based on the total weight of the first positive active material layer (13). In some embodiments, the first positive active material layer (13) may contain about 55 wt% or more, about 60 wt% or more, about 65 wt% or more, about 70 wt% or more, about 75 wt% or more, about 80 wt% or more, or about 85 wt% or more based on the total weight of the first positive active material layer (13).

[0100] In some embodiments, the content of the iron phosphate compound-based positive active material in the second positive active material layer (14) may be about 50 wt% or more based on the total weight of the second positive active material layer (14). In some embodiments, the second positive active material layer (14) may contain about 55 wt% or more, about 60 wt% or more, about 65 wt% or more, about 70 wt% or more, about 75 wt% or more, about 80 wt% or more, or about 85 wt% or more based on the total weight of the second positive active material layer (14).

[0101] The above positive active material layer (13, 14) may include a sacrificial positive material comprising a compound of the following chemical formula 1.

[0102] <Chemical Formula 1>

[0103] Li a Fe 1-x M x O y

[0104] (Here, 1 <a≤5, 0≤x≤0.35, 2<y≤4, M은 Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, 또는 그 조합임)

[0105] In some embodiments, the compound of Formula 1 may include Li5FeO4. In some embodiments, the compound of Formula 1 may include Li3FeO 3.5 It may include.

[0106] The above positive active material layer (13, 14) may contain about 0.01 weight% to about 0.5 weight% of the sacrificial positive material, which is a compound of Formula 1, based on the weight of the above positive active material layer (13, 14). In some embodiments, the electrode active material layer (13, 14) comprises the sacrificial cathode material, which is a compound of Formula 1, in an amount of about 0.01 wt% to about 0.5 wt%, about 0.02 wt% to about 0.48 wt%, about 0.05 wt% to about 0.45 wt%, about 0.07 wt% to about 0.43 wt%, about 0.1 wt% to about 0.4 wt%, about 0.12 wt% to about 0.38 wt%, about 0.15 wt% to about 0.35 wt%, about 0.17 wt% to about 0.33 wt%, about 0.2 wt% to about 0.3 wt%, about 0.22 wt% to about 0.28 wt%, about 0.24 wt% to about 0.26 wt%, or any of the above values, based on the weight of the cathode active material layer (13, 14). It can have a value between two numbers.

[0107] If the content of the sacrificial cathode material, which is a compound of Formula 1, in the positive active material layer (13, 14) is too low, the charging capacity of the lithium secondary battery (1) may decrease. If the content of the sacrificial cathode material, which is a compound of Formula 1, in the positive active material layer (13, 14) is too high, the electrical resistance of the positive (10) may increase excessively.

[0108] When the compound represented by Chemical Formula 1 above is Li5FeO4, the Li5FeO4 may remain in the positive active material layer (13, 14) in the form of a decomposition product remaining after releasing an excess amount of lithium ions and oxygen (O2) gas following the initial charging of the secondary battery. At this time, when the secondary battery is charged at a charging voltage of 3.5V to 4.0V, the decomposition product of the Li5FeO4 becomes LiFeO2, Li3FeO 3.5 It may include etc., and when the secondary battery is charged at a charging voltage of 4.0V or higher, it may include Li3FeO4, etc. Since the above LiFeO2 has a structure capable of lithium ion intercalation and deintercalation, it can participate in electrochemical reactions in the above positive active material layer (13, 14) during the charging and discharging of the secondary battery. In addition, the above Li3FeO 3.5 Li3FeO4, etc., possess spare lithium ions, so they can contribute to the charge / discharge capacity of the anode after initial charge / discharge / activation.

[0109] In some embodiments, the positive active material layer (13, 14) may include a sacrificial positive material comprising a compound of the following chemical formula 2.

[0110] <Chemical Formula 2>

[0111] Li b Fe 1-x M x O y

[0112] (Here, 3≤b≤7, 0≤x≤0.35, 3≤y≤4, M is Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, or a combination thereof)

[0113]

[0114] In some embodiments, the positive active material layer (13, 14) may include a sacrificial positive material comprising a compound of the following chemical formula 3A.

[0115]

[0116] <Chemical Formula 3A>

[0117] Li c M 1 (1-p) M 2 p O4

[0118] In the above chemical formula 3A,

[0119] M 1 is Fe, Co, Mn, Zn, Al, or Ga, and

[0120] M 2 is one or more metals selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, wherein M 1 and M 2 It includes different metals,

[0121] c and p are 4≤c≤7 and 0≤p≤0.5, respectively.

[0122]

[0123] Here, the compound represented by the above chemical formula 3A is a superlithium compound containing an excess amount of lithium element, which can compensate for irreversible lithium loss by releasing the excess lithium element during initial charging:

[0124] In this case, the compound represented by the above chemical formula 3A is Li6CoO4, Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 O4, Li6Co 0.7 Zn 0.2 Al 0.1 O4, Li5FeO4, Li6MnO4, Li6ZnO4, Li5AlO4, Li5GaO4, etc. may be included alone or in two or more types. For example, the compound represented by the above chemical formula 3A is M 1 This is Li6CoO4, Li6Co where Fe, Co, or Mn is Fe, Co, or Mn 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3O4, Li6Co 0.7 Zn 0.2 Al 0.1 It may include one or more types among O4, Li5FeO4, and Li6MnO4.

[0125] The above compounds have the advantage of being easy to apply to lithium secondary batteries because the amount of lithium ions released during charging of the secondary battery is significantly large, allowing for the compensation of lithium ion loss with a small amount, and the potential required for the compounds to release lithium exists within the charging potential range of the lithium secondary battery. In particular, Li5FeO4 has excellent compatibility with the cathode active material in secondary batteries using LiFePO4 as the cathode active material, and since the operating voltage range matches that of LiFePO4, it has the characteristic of high charge / discharge performance. In addition, the above Li5FeO4 has the advantage of excellent economic efficiency as it has a relatively low price compared to other over-lithium compounds.

[0126] In some embodiments, the positive active material layer (13, 14) may further include a compound of the following formula 3B.

[0127]

[0128] <Chemical Formula 3B>

[0129] M 3 (1-x) M 4 x O y

[0130] In the above chemical formula 3B,

[0131] M 3 and M 4 are respectively W, Mo, Ni, Co, Nb, Ge, Ti, Ta, or Ce, where M 3 and M 4 It contains different metals,

[0132] x and y are 0≤x≤0.5 and 1≤y≤6, respectively.

[0133]

[0134] The sacrificial cathode material of Formula 3A releases an excess amount of lithium during the charging of a secondary battery, generating a significant amount of oxygen (O2) gas in the process. The generated oxygen (O2) gas increases the internal pressure of the battery cell, which can deform and / or damage the battery case during use, thereby reducing the safety of the battery. Furthermore, the oxygen gas can form gas traps at the interface between the positive and / or negative electrodes, interfering with the electrochemical reaction of the electrodes or damaging the active layer of each electrode, which can act as a factor reducing the cycle characteristics and lifespan characteristics of the secondary battery; consequently, the commercialization of Li5FeO4 is being delayed. These problems can be resolved by adding the compound of Formula 3B.

[0135] Compounds of Formula 3B include oxides comprising a single metal and / or a heterometal having an oxidation number of +2 to +6. In compounds of Formula 3B, the transition of a metal element can be performed due to the activation of an oxidation-reduction reaction during the charging and discharging of a secondary battery under voltage conditions of 2.0 to 4.0 V, and in this process, said metal element can react with oxygen ions. That is, said metal element can be oxidized by reacting with oxygen ions, thereby removing oxygen (O2) generated inside the anode and / or battery. Exemplary compounds of Formula 3B include WO, WO2, WO3, MoO, MoO2, MoO3, NiO, NiO2, CoO, CoO2, NbO, NbO2, Nb2O5, GeO, GeO2, TiO, TiO2, TaO, Ta2O5, CeO2, NbTiO2, NbTiO5, NbTaO2, NbTaO5, or combinations thereof.

[0136] In some embodiments, the positive active material layer (13, 14) may further include LiFeO2. The content of LiFeO2 in the positive active material layer (13, 14) may be about 0.3 weight% to about 5 weight% based on the total weight of the positive active material layer (13, 14). In some embodiments, the content of LiFeO2 in the positive active material layer (13, 14) is about 0.3 wt% to about 5 wt%, about 0.5 wt% to about 5.8 wt%, about 0.7 wt% to about 5.6 wt%, about 1 wt% to about 5.4 wt%, about 1.3 wt% to about 5.2 wt%, about 1.5 wt% to about 5 wt%, about 1.7 wt% to about 4.8 wt%, about 2 wt% to about 4.6 wt%, about 2.3 wt% to about 4.4 wt%, about 2.5 wt% to about 4.2 wt%, about 2.7 wt% to about 4 wt%, about 3 wt% to about 3.8 wt%, about 3.3 wt% to about 3.6 wt%, or any two of these values. It can have a range between the values.

[0137] If the content of LiFeO2 in the positive active material layer (13, 14) is too low, the charging capacity of the lithium secondary battery (1) may decrease. If the content of LiFeO2 in the positive active material layer (13, 14) is too high, the electrical resistance of the positive (10) may increase excessively.

[0138] In some embodiments, the positive active material layer (13, 14) may comprise LiFeO2 and a sacrificial cathode material of Formula 1 or Formula 2. In some embodiments, the sacrificial cathode material of Formula 1 or Formula 2 is Li5FeO4 and / or Li3FeO 3.5 It may include.

[0139] In some embodiments, the weight ratio of the compound of Formula 1 and LiFeO2 present in the positive active material layer (13, 14), for example, the weight ratio of Li5FeO4 to LiFeO2, may be about 1:20 to about 1:500.

[0140] In some embodiments, the weight ratio of the compound of Formula 1 and LiFeO2 of the anode active material layer (13, 14) may be about 1:20 to about 1:500, about 1:30 to about 1:450, about 1:50 to about 1:400, about 1:80 to about 1:350, about 1:100 to about 1:300, about 1:120 to about 1:250, about 1:150 to about 1:200, or a range between any two of these ratios.

[0141] If the weight ratio of the compound of Formula 1 and LiFeO2 in the positive active material layer (13, 14) deviates from the above range, the charging capacity of the lithium secondary battery (1) may decrease or the electrical resistance of the positive electrode (10) may increase excessively.

[0142] In some embodiments, the weight ratio of Li5FeO4 to LiFeO2 of the positive active material layer (13, 14) may be about 1:20 to about 1:500, about 1:30 to about 1:450, about 1:50 to about 1:400, about 1:80 to about 1:350, about 1:100 to about 1:300, about 1:120 to about 1:250, about 1:150 to about 1:200, or a range between any two of these ratios.

[0143] If the weight ratio of Li5FeO4 and LiFeO2 in the positive active material layers (13, 14) deviates from the above range, the charging capacity of the lithium secondary battery (1) may decrease or the electrical resistance of the positive electrode (10) may increase excessively.

[0144] In some embodiments, the weight of the sacrificial cathode material (i.e., compounds of Formulas 1 to 3A) and LiFeO2 of the positive active material layer (13, 14) may be about 0.02 weight% to about 2.3 weight% based on the weight of the positive active material layer (13, 14). In some embodiments, the weight of the sacrificial cathode material (i.e., compounds of Formulas 1 to 3A) and LiFeO2 of the cathode active material layer (13, 14) is about 0.02 wt% to about 2.3 wt%, about 0.03 wt% to about 2.2 wt%, about 0.05 wt% to about 2.1 wt%, about 0.07 wt% to about 2 wt%, about 0.1 wt% to about 1.9 wt%, about 0.2 wt% to about 1.8 wt%, about 0.3 wt% to about 1.7 wt%, about 0.4 wt% to about 1.6 wt%, about 0.5 wt% to about 1.5 wt%, about 0.6 wt% to about 1.4 wt%, about 0.7 wt% to about 1.3 wt%, and about 0.8 wt% based on the weight of the cathode active material layer (13, 14). It may have a range of up to about 1.2 weight%, about 0.9 weight% to about 1.1 weight%, or between any two of these figures.

[0145] In some embodiments, the weight of the sacrificial cathode material (i.e., compounds of Formulas 1 to 3A) and LiFeO2 of the positive active material layer (13, 14) may be about 0.03 weight% to about 1.8 weight% based on the weight of the positive active material layer (13, 14). The weight of the sacrificial cathode material (i.e., compounds of Formulas 1 to 3A) and LiFeO2 of the positive active material layer (13, 14) may be about 0.5 weight% to about 1.7 weight% based on the weight of the positive active material layer (13, 14).

[0146] If the weight of the sacrificial cathode material and LiFeO2 in the first positive active material layer (13) is too small, the charging capacity of the lithium secondary battery (1) may decrease. Conversely, if the weight of the sacrificial cathode material and LiFeO2 in the first positive active material layer (13) is too large, the electrical resistance of the first positive active material layer (13) may increase excessively.

[0147] In some embodiments, the concentration of the sacrificial cathode material may increase as it gets closer to the anode current collector (11). In some embodiments, the concentration of LiFeO2 may increase as it gets closer to the anode current collector (11). In some embodiments, the concentrations of the sacrificial cathode material and LiFeO2 may increase as they get closer to the anode current collector (11). In some embodiments, the sum of the concentrations of the sacrificial cathode material and LiFeO2 may increase as it gets closer to the anode current collector (11).

[0148] In some embodiments, the second positive active material layer (14) may not contain a sacrificial positive material (i.e., a compound of Formula 1 to Formula 3A). In some embodiments, the second positive active material layer (14) may contain a sacrificial positive material (i.e., a compound of Formula 1 to Formula 3A), but the content thereof may differ from that of the first positive active material layer (13). In some embodiments, the content of the sacrificial positive material in the second positive active material layer (14) may be less than the content of the sacrificial positive material in the first positive active material layer (13). In some embodiments, the content of the sacrificial positive material in the second positive active material layer (14) may be about 0.01 times to about 0.5 times the content of the sacrificial positive material in the first positive active material layer (13).

[0149] In some embodiments, the total thickness of the positive active material layer (13, 14) may be about 80 μm to about 300 μm. In some embodiments, the total thickness of the positive active material layer (13, 14) may be about 80 µm to about 300 µm, about 90 µm to about 290 µm, about 100 µm to about 280 µm, about 110 µm to about 270 µm, about 120 µm to about 260 µm, about 130 µm to about 250 µm, about 140 µm to about 240 µm, about 150 µm to about 230 µm, about 160 µm to about 220 µm, about 170 µm to about 210 µm, about 180 µm to about 200 µm, or a range between any two of these values. However, the present invention is not limited thereto. The method of measuring thickness is not limited to this, but may be a value measured using, for example, a thickness gauge (Mitutoyo, VL-50S-B).

[0150] If the total thickness of the positive active material layer (13, 14) is too small, the capacity of the secondary battery may be insufficient. If the total thickness of the positive active material layer (13, 14) is too large, the internal resistance increases and there is a risk of delamination from the current collector.

[0151] The thickness of the first positive active material layer (13) may be about 0.01 times to about 2 times the thickness of the second positive active material layer (14). In some embodiments, the thickness of the first positive active material layer (13) may be about 0.1 times to about 0.9 times the thickness of the second positive active material layer (14).

[0152] In some embodiments, the thickness of the first positive active material layer (13) may be about 0.01 to about 2 times, about 0.02 to about 1.9 times, about 0.05 to about 1.8 times, about 0.1 to about 1.7 times, about 0.2 to about 1.6 times, about 0.3 to about 1.5 times, about 0.4 to about 1.4 times, about 0.5 to about 1.3 times, about 0.6 to about 1.2 times, about 0.7 to about 1.1 times, about 0.8 to about 1.0 times, or a range between any two of these values.

[0153] If the thickness of the first positive active material layer (13) is too thin compared to the thickness of the second positive active material layer (14), it is difficult to increase the loading amount of the active material, and the charge / discharge performance may also be reduced. If the thickness of the first positive active material layer (13) is too thick compared to the thickness of the second positive active material layer (14), the electrical resistance may increase.

[0154]

[0155] In some embodiments, the first positive electrode active material and the second positive electrode active material are electrochemically reactive materials, and at least one of the first positive electrode active material and the second positive electrode active material may comprise a lithium iron phosphate compound represented by the following chemical formula 4, which is capable of reversibly intercalating and deintercalating lithium ions:

[0156] <Chemical Formula 4>

[0157] LiFe r M 5 (1-r) XO4

[0158] In the above chemical formula 4,

[0159] M 5It is one or more elements selected from W, Cu, Fe, V, Cr, CO, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0160] X is one or more of P, Si, S, As, and Sb, and

[0161] 0≤r≤0.5.

[0162] The lithium iron phosphate compound represented by Chemical Formula 4 above is a promising active material that possesses excellent lifespan characteristics and superior advantages in all aspects of safety, including overcharging and over-discharging, because it has the best structural stability due to having an olivin structure. In particular, the lithium iron phosphate compound is PO4 - Due to its strong bonding strength, it has excellent high-temperature stability, and because it contains iron, which is resource-abundant and inexpensive, it is cheaper than LiCoO2, LiNiO2, or LiMn2O4, and because it has low toxicity, it has less impact on the environment.

[0163] The lithium iron phosphate compound represented by the above chemical formula 4 is a lithium phosphate containing iron, and in some cases, another transition metal (M 5 It may have a doped form. For example, the lithium iron phosphate compound is LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 It may include PO4, etc.

[0164] In some embodiments, the anode (10) may further include a primer layer (12). In some embodiments, the primer layer (12) may include a conductive material and a binder.

[0165] In some embodiments, the conductive material of the primer layer (12) is intended to impart conductivity to the primer layer (12) to lower electrical resistance, and is not particularly limited as long as it is conductive without causing chemical changes in the lithium secondary battery (1). In some embodiments, the conductive material may be graphite such as natural graphite or artificial graphite; carbon black-based carbon compounds such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, 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; or combinations thereof.

[0166] In some embodiments, the binder of the primer layer (12) is, for example, styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile butadiene rubber (NBR), styrene butadiene styrene block copolymer (SBS), styrene ethylene butadiene block copolymer (SEB), styrene-(styrene butadiene)-styrene block copolymer, natural rubber (NR), isoprene rubber (IR), ethylene-propylene-diene terpolymer (EPDM), poly(ethylene-co-propylene-co-5-methylene-2-norbornene) (poly(ethylene-co-propylene-co-5-methylene-2-norbornene)), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl chloride, polyvinylidene fluoride-hexafluoropropylene (polyvinylidene It may include fluoride-co-hexafluoropropylene), polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene, polypropylene, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, polypropylene oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, or a combination thereof.Specifically, the binder may include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), polymethyl(meth)acrylate, polyethylhexyl acrylate, polybutyl acrylate, or two or more of these, but is not limited thereto.

[0167] In some embodiments, the primer layer (12) may further include a sacrificial cathode material. In some embodiments, the sacrificial cathode material may include a compound of Formula 1. For example, the primer layer (12) may further include Li5FeO4.

[0168] In some embodiments, the primer layer (12) may further include a compound of Formula 2 as a sacrificial cathode material.

[0169] In some embodiments, the thickness of the primer layer (12) may have a range of, for example, about 100 nm to about 20 µm, about 200 nm to about 18 µm, about 500 nm to about 16 µm, about 700 nm to about 14 µm, about 1 µm to about 12 µm, about 2 µm to about 10 µm, about 5 µm to about 8 µm, or between any two of these values. However, the present invention is not limited thereto. The thickness of the primer layer (12) may represent a value measured by a known method of measuring thickness. The method of measuring thickness may be, for example, a value measured using a thickness gauge (Mitutoyo, VL-50S-B), although it is not limited thereto.

[0170] If the thickness of the primer layer (12) is too small, the adhesion effect may be insufficient. If the thickness of the primer layer (12) is too large, the resistance may increase.

[0171] In some embodiments, the primer layer (12) may further include LiFeO2. The content of LiFeO2 in the primer layer (12) may be about 0.3 weight% to about 8 weight% based on the total weight of the primer layer. In some embodiments, the content of LiFeO2 in the primer layer (12) is about 0.3 wt% to about 8 wt%, about 0.5 wt% to about 7.8 wt%, about 0.7 wt% to about 7.5 wt%, about 1 wt% to about 7.3 wt%, about 1.3 wt% to about 7 wt%, about 1.5 wt% to about 6.8 wt%, about 1.7 wt% to about 6.5 wt%, about 2 wt% to about 6.3 wt%, about 2.3 wt% to about 6 wt%, about 2.5 wt% to about 5.8 wt%, about 2.7 wt% to about 5.5 wt%, about 3 wt% to about 5.3 wt%, about 3.3 wt% to about 5 wt%, about 3.5 wt% to about 4.8 wt%, about 3.7 wt% to about It may have a range of 4.5 wt%, about 4 wt% to about 4.3 wt%, or between any two of these figures.

[0172] If the content of LiFeO2 in the primer layer (12) is too low, the charging capacity of the lithium secondary battery (1) may decrease. If the content of LiFeO2 in the primer layer (12) is too high, the electrical resistance of the primer layer (12) may increase excessively.

[0173] In some embodiments, the thickness ratio of the positive active material layer (13, 14) and the primer layer (12) may be about 5:1 to about 50:1. In some embodiments, the thickness ratio of the positive active material layer (13, 14) and the primer layer (12) may be about 5:1 to about 50:1, about 10:1 to about 40:1, about 20:1 to about 30:1, or a value between any two of the above ratios.

[0174] If the thickness of the positive active material layer (13, 14) is too thick compared to the thickness of the primer layer (12), there is a risk that the positive active material layer (13, 14) will peel off. If the thickness of the positive active material layer (13, 14) is too thin compared to the thickness of the primer layer (12), the internal resistance of the secondary battery may increase and the electrical capacity may decrease.

[0175]

[0176] FIG. 4 is a cross-sectional view showing a cathode (20) according to one embodiment of the present invention.

[0177] Referring to FIG. 4, the cathode (20) is formed by coating cathode active material layers (22, 23) on both sides of a cathode current collector (21).

[0178] In FIG. 4, the negative active material layer provided on one surface of the negative current collector (21) is shown as being provided in two layers, but it may be provided in one layer. Also, in FIG. 4, the negative active material layer is shown as being provided on both surfaces of the negative current collector (21), but the negative active material layer may be provided on only one surface.

[0179] The above negative current collector (21) is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. The above negative current collector (21) may be, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy.

[0180] In some embodiments, the negative current collector (21) may form fine irregularities on its surface to increase the bonding strength with the negative active material described later. In some embodiments, the negative current collector (21) may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0181] In some embodiments, the negative current collector (21) may have a thickness of about 1 μm to about 100 μm, but the present invention is not limited thereto.

[0182] In some embodiments, the negative active material layer (22, 23) may include a first negative active material layer (22) and a second negative active material layer (23).

[0183] The first cathode active material layer (22) and the second cathode active material layer (23) may each independently include a cathode active material as described below.

[0184] The above-mentioned cathode active material is carbon, for example, graphite-based carbon such as non-graphitized carbon, natural graphite, or artificial graphite; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z(wherein Me is one or more of Mn, Fe, Pb, and Ge, and Me' is one or more of Al, B, P, Si, elements of Group 1, Group 2, and Group 3 of the periodic table, and halogens, and 0 <x≤1, 1≤y≤3, 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있으나, 이들만으로 한정되는 것은 아니다.

[0185] In some embodiments, the negative electrode active material may be a Si-based negative electrode active material and may include one or more of, for example, Li2SiO3, Li2Si2O5, Li3SiO3, and Li4SiO4.

[0186] In some embodiments, the negative electrode active material may include a Si-based negative electrode active material containing carbon. Specifically, the negative electrode active material may further include a carbon coating layer on the particle surface. In this case, the amount of the carbon coating may be 20% by weight or less, preferably about 1% to about 20% by weight, based on the total weight of the silicon-based negative electrode active material.

[0187] Referring again to FIG. 2, the electrode assembly (40) may include a separator (30) between the positive electrode (10) and the negative electrode (20).

[0188] In some embodiments, the separator (30) separates the positive electrode (10) and the negative electrode (20) and provides a passage for the movement of lithium ions, and can be used without special limitations as long as it is a separator typically used in lithium-ion secondary batteries. In particular, it is desirable that the separator (30) has low resistance to the movement of ions of the electrolyte and excellent electrolyte retention capacity.

[0189] Specifically, a porous polymer film, such as a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used as the separator (30). Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used as the separator (30). Additionally, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and the separator (30) may have a single-layer or multi-layer structure. In some embodiments, the separator (30) may include a safety reinforced separator (SRS) with a thin coating of a ceramic material on its surface.

[0190] In addition, conventional porous nonwoven fabrics, such as high-melting-point glass fibers, polyethylene terephthalate fibers, etc., may be used as the separation membrane (30), but are not limited thereto.

[0191] However, if the lithium secondary battery (1) described with reference to FIG. 1 is a solid-state secondary battery, the separator (30) may be omitted.

[0192] Referring again to FIG. 1, the lithium secondary battery (1) may further include an electrolyte.

[0193] The above electrolyte may be one or more mixed organic solvents selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, and butyl propionate.

[0194] In some embodiments, the electrolyte may further comprise a lithium salt, and the anion of the lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , F3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -It may be one or more selected from a group consisting of

[0195] In some embodiments, the electrolyte may comprise a lithium salt, an organic solvent, and a coumarin-based additive. The electrolyte comprising the coumarin-based additive can effectively remove oxygen gas generated from the sacrificial cathode material.

[0196] In some embodiments, the coumarin-based additive may include a compound having the structure of Formula 5 or Formula 6 below.

[0197] <Chemical Formula 5>

[0198]

[0199] (Here, R1 to R5 are each independently selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and an alkoxy group having 1 to 10 carbon atoms, and R is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms, or -OR'(R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms))

[0200] <Chemical Formula 6>

[0201]

[0202] (Here, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, R and R' are each independently an alkylene group having 1 to 10 carbon atoms, and m is an integer from 0 to 5)

[0203] In some embodiments, the coumarin-based additive may be contained in the electrolyte in an amount of about 0.01 weight% to about 5 weight% based on the total weight of the electrolyte. In some embodiments,

[0204] The above coumarin-based additive may be included in the electrolyte in an amount of about 0.01 wt% to about 5 wt%, about 0.02 wt% to about 4.5 wt%, about 0.05 wt% to about 4 wt%, about 0.07 wt% to about 3.7 wt%, about 0.1 wt% to about 3.5 wt%, about 0.15 wt% to about 3.3 wt%, about 0.2 wt% to about 3 wt%, about 0.3 wt% to about 2.7 wt%, about 0.4 wt% to about 2.5 wt%, about 0.5 wt% to about 2.2 wt%, about 0.6 wt% to about 2 wt%, about 0.7 wt% to about 1.8 wt%, about 0.8 wt% to about 1.5 wt%, or a range between any two of these figures, based on the total weight of the electrolyte.

[0205] If the content of the above coumarin-based additive is too low, the effect of removing O2 may be insufficient. If the content of the above coumarin-based additive is too high, battery performance may be degraded due to increased resistance.

[0206]

[0207] The structure and effects of the present invention will be explained in more detail below with specific examples and comparative examples, but these examples are intended only to provide a clearer understanding of the present invention and are not intended to limit the scope of the present invention.

[0208]

[0209] Example 1

[0210] Carbon black as a conductive material (specific surface area 58 m²) 2A primer layer slurry was prepared by mixing water as a dispersion medium with styrene-butadiene rubber (SBR) as a binder and carboxymethylcellulose (CMC daicel2200 1.5% aqueous solution) as a dispersant. At this time, the content ratios of the conductive material, binder, and dispersant in the slurry were 29.5 wt%, 69 wt%, and 1.5 wt%, respectively. The solid content ratio in the primer layer slurry was 7 wt%.

[0211] A prepared slurry for a primer layer was applied to one side of an aluminum current collector (thickness 10 μm) and dried at 130°C to form a primer layer on the entire surface of the aluminum current collector.

[0212] Lithium iron phosphate particles (LiFePO4, D) as a positive electrode active material 50 : 1 μm), carbon nanotubes as a conductive material, and polyvinylidene fluoride as a binder were added to N-methyl-2-pyrrolidone (NMP), a solvent, in a weight ratio of 96:1:3. Subsequently, 0.5 wt% of Li5FeO4 was added based on the total weight of the solids to prepare an anode slurry (solid content 65 wt%).

[0213] The above anode slurry is applied to an aluminum current collector at 3.7 mAh / cm 2 After coating and drying with a loading amount, a positive electrode was manufactured by performing a roll press (thickness of the positive electrode active material layer: 220㎛).

[0214] A cathode slurry (solid content: 50 wt%) was prepared by adding graphite and Si / C-based active materials as cathode active materials, SBR-CMC as a binder, and carbon black as a conductive agent to water, a solvent, in a weight ratio of 90:5.5:4.0:0.5. The above cathode slurry was applied to an 8 μm thick copper (Cu) thin film cathode current collector at a rate of 3.9 mAh / cm² 2 After coating and drying with a loading amount, a cathode was manufactured by performing a roll press (thickness of cathode active material: 160㎛).

[0215] An electrode assembly was manufactured by sequentially stacking the above anode, a polyolefin-based porous separator, and a cathode.

[0216] A lithium secondary battery was manufactured by housing the assembled electrode assembly inside a battery case and then injecting a non-aqueous electrolyte.

[0217] The above-mentioned non-aqueous electrolyte was prepared by mixing ethylene carbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:55:15 to prepare an organic solvent, and dissolving LiPF6 as a lithium salt in the organic solvent to a molar concentration of 1.0 M.

[0218] After charging the fabricated battery to 4.2 V at 3 A (50 mA cut), a formation process was performed to discharge it to 2 V at 0.2 C, 10 A, 20 A, and 30 A, respectively, or with an 80°C cut, and the charge / discharge characteristics of the battery were measured.

[0219] Subsequently, the components were analyzed by analyzing the positive active material layer of the battery whose charge / discharge characteristics were measured.

[0220]

[0221] Examples 2 to 7

[0222] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of Li5FeO4 added as a sacrificial cathode material when manufacturing the cathode slurry was varied as shown in Table 1, and the charge / discharge characteristics were measured in the same manner as in Example 1.

[0223] In addition, the components were analyzed by analyzing the positive active material layer of the battery whose charge / discharge characteristics were measured.

[0224]

[0225] Comparative Example 1

[0226] A lithium secondary battery was manufactured in the same manner as in Example 1, except that no sacrificial cathode material was added when manufacturing the cathode slurry, and charge / discharge characteristics were measured in the same manner as in Example 1.

[0227] In addition, the components were analyzed by analyzing the positive active material layer of the battery whose charge / discharge characteristics were measured.

[0228]

[0229] Comparative Example 2 and Comparative Example 3

[0230] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the content of Li5FeO4 added as a sacrificial cathode material when manufacturing the cathode slurry was varied as shown in Table 1, and the charge / discharge characteristics were measured in the same manner as in Example 1.

[0231] In addition, the components were analyzed by analyzing the positive active material layer of the battery whose charge / discharge characteristics were measured.

[0232]

[0233]

[0234]

[0235]

[0236] Referring to Table 1, it can be seen that all or part of the Li5FeO4 added to the cathode active material layer is converted to LiFeO2 after the activation process, and that in some examples, Li5FeO4 partially remains. Additionally, in the examples, a portion of the Li5FeO4 is Li3FeO 3.5 You can see that it is being converted to.

[0237] Table 2 shows the results measured in Examples 1 to 7 and Comparative Examples 1 to 3. Relative values ​​are shown with the measurement result of Comparative Example 1 set to 100.

[0238]

[0239] Table 2

[0240]

[0241]

[0242] Referring to Table 2, it can be seen that the lithium secondary batteries of Examples 1 to 7 show improved charging capacity compared to the lithium secondary batteries of Comparative Examples 1 to 3.

[0243]

[0244] Example 8

[0245] A lithium secondary battery was manufactured in the same manner as in Example 1, except that when preparing the electrolyte, a coumarin-based additive of the following chemical formula 7 was added in a ratio of 0.1 parts by weight to 99.9 parts by weight of an organic solvent.

[0246] <Chemical Formula 7>

[0247]

[0248]

[0249] Example 9

[0250] A lithium secondary battery was manufactured in the same manner as in Example 1, except that when preparing the electrolyte, a coumarin-based additive of Formula 8 was added at a ratio of 0.1 parts by weight to 99.9 parts by weight of an organic solvent.

[0251] <Chemical Formula 8>

[0252]

[0253]

[0254] High-temperature cycle characteristics evaluation

[0255] Cycle characteristics were evaluated for each of the lithium secondary batteries prepared in Example 1, Example 8, Example 9, and Comparative Example 1.

[0256] Specifically, each of the lithium secondary batteries prepared in Example 1, Example 8, Example 9, and Comparative Example 1 was charged to 4.2V at 45°C with a constant current of 0.33C and discharged to 3.0V with a constant current of 0.33C as one cycle, and after performing 100 cycles of charge and discharge, the capacity retention rate relative to the initial capacity after 100 cycles was measured. The results are shown in Table 3 below.

[0257] Table 3

[0258]

[0259]

[0260] Referring to Table 3, it can be seen that the capacity retention rate of the lithium secondary battery manufactured by including a sacrificial cathode material in the cathode active material layer is relatively higher. In particular, it can be seen that the capacity retention rate of the lithium secondary batteries of Examples 8 and 9, in which a coumarin-based additive was added to the electrolyte, is significantly superior.

[0261]

[0262] Example 10

[0263] A lithium secondary battery was manufactured in the same manner as in Example 4, except that a sacrificial cathode material was added to the primer layer. Li5FeO4 was added as a sacrificial cathode material to the slurry for the primer layer, and the content of the sacrificial cathode material added to the slurry for the primer layer was 1.5 wt%.

[0264] In addition, charge and discharge characteristics were measured in the same way as in Example 4.

[0265]

[0266] Example 11

[0267] A lithium secondary battery was manufactured and charge / discharge characteristics were measured in the same manner as in Example 10, except that the content of the sacrificial cathode material in the primer layer slurry was 3 wt%.

[0268]

[0269] Example 12

[0270] A lithium secondary battery was manufactured and charge / discharge characteristics were measured in the same manner as in Example 10, except that the content of the sacrificial cathode material in the primer layer slurry was 4 wt%.

[0271]

[0272] Table 4 shows the measured charge / discharge capacities for the lithium secondary batteries according to Examples 10 to 12. The listed charge / discharge capacities are relative values ​​with the charge / discharge capacity of the lithium secondary battery according to Comparative Example 1 set to 100.

[0273]

[0274] Table 4

[0275]

[0276]

[0277] Referring to Table 4, it can be seen that the lithium secondary batteries of Examples 10 to 12 have slightly better charge / discharge performance compared to lithium secondary batteries in which a sacrificial cathode material is added only to the positive active material layer.

[0278] As described above, although embodiments of the present invention have been described in detail, a person skilled in the art to which the present invention pertains will be able to modify and implement the present invention in various ways without departing from the spirit and scope of the present invention as defined in the appended claims. Therefore, future modifications to the embodiments of the present invention will not depart from the technology of the present invention.

[0279]

[0280] [Explanation of the symbol]

[0281] 1: Lithium secondary battery

[0282] 10: Anode

[0283] 11: Positive current collector

[0284] 12: Primer layer

[0285] 13: First positive active material layer

[0286] 14: Second positive electrode active material layer

[0287] 20: Cathode

[0288] 21: Cathode current collector

[0289] 22: First cathode active material layer

[0290] 23: Second negative electrode active material layer

[0291] 30: Separator

[0292] 40: Electrode assembly

[0293] 140: Electrode Lead

[0294] 141: Positive lead

[0295] 145: Cathode lead

[0296] 150: Battery Case

[0297] 155: Sealing part

[0298] 160: Lead film

Claims

1. A positive electrode comprising a positive current collector and a positive active material layer disposed on the positive current collector; and A cathode comprising a cathode current collector and a cathode active material layer disposed on the cathode current collector; Includes, A lithium secondary battery comprising a positive active material layer containing 0.01% to 0.5% by weight of the sacrificial cathode material, which is a compound of Chemical Formula 1, based on the weight of the positive active material layer. <Chemical Formula 1> Li a Feb 1-x M x O y (Here, 1 <a≤5, 0≤x≤0.35, 2<y≤4, M은 Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, 또는 그 조합임) 2. In Paragraph 1, A lithium secondary battery characterized in that the positive active material layer further comprises LiFeO2.

3. In Paragraph 2, A lithium secondary battery characterized in that the content of LiFeO2 in the positive active material layer is 0.3% to 5% by weight based on the total weight of the positive active material layer.

4. In Paragraph 1, A lithium secondary battery characterized by the compound of the above chemical formula 1 comprising Li5FeO4.

5. In Paragraph 1, A lithium secondary battery characterized in that the above-mentioned positive active material layer further comprises a compound of the following chemical formula 2 as a sacrificial positive material. <Chemical Formula 2> Li b Feb 1-x M x O y (Here, 3≤b≤7, 0≤x≤0.35, 3≤y≤4, M is Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, or a combination thereof) 6. In Paragraph 5, A lithium secondary battery characterized in that the positive electrode active material layer comprises 0.02% to 2.3% by weight of LiFeO2, a compound of Formula 1, and a compound of Formula 2 based on the weight of the positive electrode active material layer.

7. In Paragraph 5, A lithium secondary battery characterized in that the positive electrode active material layer comprises LiFeO2, a compound of Formula 1, and a compound of Formula 2 in an amount of 0.03% to 1.8% by weight based on the weight of the positive electrode active material layer.

8. In Paragraph 5, A lithium secondary battery characterized in that the positive electrode active material layer comprises 0.5% by weight to 1.7% by weight of LiFeO2, a compound of Formula 1, and a compound of Formula 2 based on the weight of the positive electrode active material layer.

9. In Paragraph 1, A lithium secondary battery characterized by further including a separator between the anode and the cathode.

10. In Paragraph 1, The above positive active material layer is: A first positive active material layer disposed on the above positive current collector and comprising a first positive active material; and A second positive active material layer disposed on the first positive active material layer and comprising a second positive active material; Includes, A lithium secondary battery characterized in that the first positive active material layer comprises the sacrificial positive material, and the second positive active material layer does not comprise the sacrificial positive material.

11. In Paragraph 10, A lithium secondary battery characterized in that the thickness of the first positive active material layer is 0.01 to 2 times the thickness of the second positive active material layer.

12. In Paragraph 10, A lithium secondary battery characterized in that the thickness of the first positive active material layer is 0.1 to 0.9 times the thickness of the second positive active material layer.

13. In Paragraph 10, A lithium secondary battery characterized in that at least one of the first positive active material layer and the second positive active material layer comprises an iron phosphate compound-based positive active material.

14. In Paragraph 1, A lithium secondary battery characterized in that the above-mentioned negative electrode active material layer comprises a Si-based negative electrode active material containing carbon.

15. In Paragraph 1, A lithium secondary battery characterized in that the total thickness of the positive active material layer is 80 μm to 300 μm.

16. In Paragraph 1, A lithium secondary battery characterized in that the above positive electrode further comprises a primer layer between the above positive electrode current collector and the above positive electrode active material layer, and the primer layer further comprises LiFeO2.

17. In Paragraph 1, A lithium secondary battery characterized in that the above-mentioned positive active material layer further comprises a compound of the following chemical formula 3A as a sacrificial positive material. <Chemical Formula 3A> Li c M 1 (1-p) M 2 p O4 (In the above chemical formula 3A, M 1 is Fe, Co, Mn, Zn, Al, or Ga, and M 2 is one or more metals selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Co, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, wherein M 1 and M 2 It includes different metals, c and p are 4≤c≤7 and 0≤p≤0.5, respectively.

18. In Paragraph 17, A lithium secondary battery characterized in that the positive electrode active material layer further comprises a compound of the following chemical formula 3B. <Chemical Formula 3B> M 3 (1-x) M 4 x O y (In the above chemical formula 3B, M 3 and M 4 are respectively W, Mo, Ni, Co, Nb, Ge, Ti, Ta, or Ce, where M 3 and M 4 It contains different metals, x and y are 0≤x≤0.5 and 1≤y≤6, respectively.

19. A positive electrode comprising a positive current collector and a positive active material layer disposed on the positive current collector; A cathode comprising a cathode current collector and a cathode active material layer disposed on the cathode current collector; and Electrolytes; Includes, The above positive active material layer comprises LiFeO2 and a sacrificial cathode material which is a compound of Formula 1, and the content of LiFeO2 and the sacrificial cathode material is 0.02 wt% to 2.3 wt% based on the total weight of the above positive active material layer, and The above electrolyte is a lithium secondary battery containing a coumarin-based additive. <Chemical Formula 1> Li a Feb 1-x M x O y (Here, 1 <a≤5, 0≤x≤0.35, 2<y≤4, M은 Ga, Zr, Ti, Mg, Ca, Ba, Sc, Mn, Zn, Cu, V, Cr, Sr, In, Al, 또는 그 조합임) 20. In Paragraph 19, A lithium secondary battery characterized in that the above-mentioned coumarin-based additive comprises a compound having the structure of Chemical Formula 5 or Chemical Formula 6. <Chemical Formula 5> (Here, R1 to R5 are each independently selected from the group consisting of H, an alkyl group having 1 to 10 carbon atoms, and an alkoxy group having 1 to 10 carbon atoms, and R is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms, or -OR'(R' is an aliphatic unsaturated hydrocarbon group having 2 to 10 carbon atoms)) <Chemical Formula 6> (Here, R1 is an alkyl group having 1 to 10 carbon atoms, R2 is an alkylene group having 1 to 10 carbon atoms, L is a direct bond, -O-, -COO-, -RO-, or -R'COO-, R and R' are each independently an alkylene group having 1 to 10 carbon atoms, and m is an integer from 0 to 5) 21. In Paragraph 19, A lithium secondary battery characterized in that the concentration of the sacrificial cathode material and LiFeO2 increases as it gets closer to the cathode current collector.

22. In Paragraph 19, A lithium secondary battery characterized in that the positive active material layer comprises 0.5% to 1.7% by weight of LiFeO2 and the sacrificial cathode material based on the total weight of the positive active material layer.

23. In Paragraph 19, A lithium secondary battery characterized by a weight ratio of Li5FeO4 and LiFeO2 present in the positive electrode active material layer being 1:20 to 1:500.

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