Electrode comprising active material layer having double-layered structure and secondary battery comprising same

Abstract

The present invention relates to an electrode for a secondary battery and a secondary battery comprising same. The electrode for a secondary battery comprises: a current collector; a first active material layer which is formed on one side or both sides of the current collector and includes a first lithium iron phosphate (F1) as an active material; and a second active material layer formed on the first active material layer and including lithium nickel oxide (N) or lithium nickel oxide (N) and a second lithium iron phosphate (F2) as active materials. In the second active material layer, the content of lithium nickel oxide (N) is 70 wt %, based on the weight of the active materials included in the second active material layer, and the density of the total active material layer comprising the first and second active material layers is on average 2.8 g / cc or more.

Description

Electrode comprising an active material layer with a double-layer structure and a secondary battery comprising the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0191491 dated December 19, 2024, and all contents disclosed in the literature of said Korean patent applications are incorporated herein as part of this specification.

[0002] The present invention relates to an electrode having a double-layer structure and a secondary battery including the same, and more specifically, said electrode comprises heterogeneous active materials.

[0003] Lithium-ion batteries are used as energy sources for various electronic devices, and as technology advances, there is a growing need for batteries that can deliver significantly higher capacity than existing ones within the same space or design.

[0004] Lithium transition metal composite oxides are used as the cathode active materials for these lithium secondary batteries. Conventionally, research on lithium nickel oxide-based active materials, which exhibit high operating voltage and excellent capacity characteristics, has been actively conducted. However, lithium nickel oxide-based active materials have a limitation in that they have low thermal stability.

[0005] As one alternative, research is underway on technology that applies lithium iron phosphate as the cathode active material. However, lithium iron phosphate-based active materials have problems such as low adhesion to the current collector and poor capacity characteristics.

[0006] Accordingly, the development of new technologies capable of overcoming the limitations associated with the application of specific active materials is required.

[0007] Accordingly, the present invention aims to provide an electrode for a secondary battery with improved high energy density and rapid charging performance, and a secondary battery to which the same is applied.

[0008] To solve the problem described above, in one embodiment, an electrode for a secondary battery according to the present invention comprises: a current collector; a first active material layer formed on one or both sides of the current collector and comprising a first lithium iron phosphate (F1) as an active material; and a second active material layer formed on the first active material layer and comprising lithium nickel oxide (N) or lithium nickel oxide (N) and a second lithium iron phosphate (F2) as active materials. In one example, in the second active material layer, the content of lithium nickel oxide (N) is 70 weight% or more based on the weight of the active material included in the second active material layer. In addition, the density of the active material layer, including the first and second active material layers, is an average of 2.8 g / cc or more.

[0009] Specifically, the electrode for the secondary battery has a weight ratio of the content of the first and second lithium iron phosphate (F1+F2) and the content of lithium nickel oxide (N) based on the sum of the first and second active material layers, ranging from 50:50 to 80:20.

[0010] In one example, in the second active material layer, the ratio of the second lithium iron phosphate (F2) content to the lithium nickel oxide (N) content is in the weight ratio range of 2:98 to 30:70.

[0011] In another example, the second active material layer comprises lithium nickel oxide (N) alone as the active material.

[0012] For example, the above lithium nickel oxide (N) has a single-particle structure.

[0013] The above first and second lithium iron phosphates (F1, F2) can each be independently represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0016] In the above chemical formula 1,

[0017] M 1 It comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and

[0018] X includes any one or more elements selected from the group consisting of F, S and N, and

[0019] a, b, and c are in the ranges of -0.5≤a≤0.5, 0≤b≤0.9, and 0≤c≤0.8, respectively.

[0020] Specifically, in the above chemical formula 1, b is in the range of 0.5 to 0.9.

[0021] The above lithium nickel oxide active material (N) can be represented by the following chemical formula 2.

[0022] [Chemical Formula 2]

[0023] Li p Ni 1-q-r-s Co q Mn r M 2 s O2

[0024] In the above chemical formula 2,

[0025] M 2 is one or more elements selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 0.9≤p≤1.5, 0≤q≤1, 0≤r≤0.5, 0≤s≤0.1, 0≤q+r+s≤1.

[0026] Specifically, in the above chemical formula 2, 1-qrs is in the range of 0.3 to 0.7.

[0027] In another example, the combined loading amount of the first and second active material layers is an average of 400 to 800 (mg / 25cm²). 2 ) is a range. The loading amount of the first active material layer and the loading amount of the second active material layer are in a weight ratio range of 5:5 to 8:2.

[0028] In addition, the present invention provides a secondary battery comprising the electrode described above. Specifically, the electrode described above is applied as a positive electrode. For example, the secondary battery is a battery for automobiles or for an Energy Storage System (ESS).

[0029] The electrode for a secondary battery according to the present invention has excellent rapid charging performance while maintaining high energy density characteristics.

[0030] Figure 1 is a graph showing the results of evaluating the rolling density (g / cc) for each electrode according to the embodiments and comparative examples of the present invention.

[0031] FIG. 2 is a graph showing the results of the SOC (%) reached during rapid charging for secondary batteries according to the embodiments and comparative examples of the present invention.

[0032] Figure 3 is a graph showing the results of measuring the resistance (mΩ) according to SOC during discharge for electrodes according to the embodiments and comparative examples of the present invention.

[0033] Figure 4 is a graph showing the results of measuring the resistance (mΩ) according to SOC during charging for electrodes according to the embodiments and comparative examples of the present invention.

[0034] FIG. 5 is a graph showing the results of evaluating the capacity retention rate (%) at a high temperature (45℃) for secondary batteries according to the embodiments and comparative examples of the present invention.

[0035] FIG. 6 is a graph showing the results of evaluating the capacity retention rate (%) at room temperature (25℃) for secondary batteries according to the embodiments and comparative examples of the present invention.

[0036] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0037] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0038] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0039] Furthermore, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "immediately below" the other part, but also cases where there is another part in between. Additionally, in the present application, being "placed on" may include cases where it is placed on the lower part as well as on the upper part.

[0040]

[0041] The present invention will be described in more detail below.

[0042]

[0043] In one embodiment, an electrode for a secondary battery according to the present invention comprises: a current collector; a first active material layer formed on one or both sides of the current collector and comprising a first lithium iron phosphate (F1) as an active material; and a second active material layer formed on the first active material layer and comprising a second lithium iron phosphate (F2) and lithium nickel oxide (N) or lithium nickel oxide (N) as active materials. The electrode for a secondary battery according to the present invention has a structure in which a double layer of active material is formed on the current collector. The electrode for a secondary battery applies both a lithium iron phosphate active material and a lithium nickel oxide active material. By using a mixture of the two types of active materials, the present invention can achieve high energy density, excellent rapid charging performance, and high thermal safety.

[0044] In the present invention, the "first active material layer" refers to an active material layer formed to be in contact with a current collector, and may be classified, for example, as a lower active material layer. Additionally, the "second active material layer" refers to an active material layer formed on the first active material layer, and may be classified, for example, as an upper active material layer.

[0045] In the second active material layer above, the content of lithium nickel oxide (N) is 70 wt% or more based on the weight of the active material included in the second active material layer. The content of lithium nickel oxide (N) in the second active material layer is controlled to be relatively high. For example, in the second active material layer above, the content of lithium nickel oxide (N) is 70 wt% or more, in the range of 75 wt% to 99 wt%, in the range of 80 wt% to 99 wt%, in the range of 70 wt% to 98 wt%, in the range of 75 wt% to 98 wt%, in the range of 80 wt% to 95 wt%, in the range of 75 wt% to 85 wt%, in the range of 85 wt% to 95 wt%, or in the range of 90 wt% to 95 wt%. As another example, lithium nickel oxide (N) may be used alone as the active material in the second active material layer. In the present invention, the second active material layer corresponds to the upper layer of an electrode with a double-layer structure. The above second active material layer can achieve excellent output characteristics by controlling the content of lithium nickel oxide (N) to a high level.

[0046] The density of the active material layer, which is the sum of the first and second active material layers, is an average of 2.8 g / cc or higher. Specifically, the density of the active material layer, which is the sum of the first and second active material layers, is an average of 2.8 g / cc or higher, in the range of 2.8 g / cc to 5 g / cc, in the range of 2.8 g / cc to 3 g / cc, in the range of 2.85 g / cc to 3 g / cc, in the range of 2.6 g / cc to 3 g / cc, or in the range of 2.87 g / cc to 3 g / cc. In the present invention, lithium iron phosphate (F1) is applied as an active material in the first active material layer, and lithium nickel oxide (N) alone or lithium nickel oxide (N) and second lithium iron phosphate (F2) are applied as active materials in the second active material layer. In particular, the present invention achieves a high rolling density by controlling the ratio of active materials applied to the second active material layer.

[0047] The electrode for a secondary battery according to the present invention has a structure in which a two-layer active material layer is formed on a current collector. In one example, the electrode for the secondary battery has a structure in which the first active material layer comprises a first lithium iron phosphate (F1) as an active material, and the second active material layer comprises a second lithium iron phosphate (F2) and a lithium nickel oxide (N) as active materials. In another example, the electrode for the secondary battery has a structure in which the first active material layer comprises a first lithium iron phosphate (F1) as an active material, and the second active material layer comprises a lithium nickel oxide (N) as an active material.

[0048] Specifically, the ratio of the combined content (F1+F2) of the first and second lithium iron phosphate active materials to the content of lithium nickel oxide (N) is in the range of a weight ratio of 50:50 to 80:20. The present invention is characterized by having a relatively low ratio of lithium nickel oxide active material (N) based on the total active material applied to the electrode. For example, the ratio of the combined content (F1+F2) of the first and second lithium iron phosphate active materials to the content of lithium nickel oxide (N) is in the range of a weight ratio of 65:35 to 80:20 or a range of a weight ratio of 70:30 to 80:20.

[0049] The present invention controls the ratio of the lithium iron phosphate active material (F1+F2) to be relatively high based on the entire active material layer, which is the sum of the first and second active material layers. Through this, the present invention can achieve excellent thermal stability. In addition, the present invention controls the ratio of the lithium nickel oxide active material (N) within the second active material layer to be high. Through this, excellent charge / discharge characteristics and high energy density are achieved.

[0050] In one example, the second active material layer has a structure comprising a second lithium iron phosphate (F2) and a lithium nickel oxide (N) as active materials. If the two types of active materials are formed into a single layer, there is a problem of increased resistance due to interference effects between the two types of active materials. By forming a double-layer structure, the present invention can suppress the increase in resistance between the two types of active materials and improve overvoltage performance. In the second active material layer, the ratio of the content of the second lithium iron phosphate (F2) to the content of the lithium nickel oxide (N) is in the weight ratio range of 2:98 to 30:70, or in the weight ratio range of 5:95 to 20:80.

[0051] In the present invention, the second active material layer has a structure in which a first lithium iron phosphate (F1) oxide is dispersed within a lithium nickel oxide (N) matrix. Through this, the second active material layer exhibits the characteristics of lithium nickel oxide (N) more strongly. In the electrode for a secondary battery according to the present invention, the first active material layer exhibits the characteristics of a lithium iron phosphate active material, and the second active material layer exhibits the characteristics of a lithium nickel oxide active material. The second active material layer contributes to increasing the capacity of the electrode, and the first active material layer contributes to increasing the thermal stability of the electrode.

[0052] In addition, in the present invention, lithium iron phosphate (F1) is placed in the lower layer, which is the first active material layer, and lithium nickel oxide (N) and lithium iron phosphate (F2) or lithium nickel oxide (N) are placed in the upper layer, which is the second active material layer, in order to realize an active material layer with high loading. Lithium iron phosphate (F1) has properties that make it difficult to roll, whereas lithium nickel oxide (N) has properties that make it easier to roll compared to lithium iron phosphate (F1). Therefore, when lithium nickel oxide (N) and lithium iron phosphate (F2) or lithium nickel oxide (N) are placed in the upper layer and lithium iron phosphate (F1) is placed in the lower layer and rolling is performed, the lithium nickel oxide (N) is directly rolled by the rolling roller, and the lithium iron phosphate (F1) in the lower layer is indirectly rolled by the rolling roller, thereby achieving a higher rolling rate and being advantageous for realizing high loading.

[0053] In another example, in the electrode for the secondary battery, the second active material layer has a structure that includes lithium nickel oxide (N) as an active material. When lithium nickel oxide (N) is applied alone as an active material to the second active material layer, a high energy density can be achieved due to an increase in the loading amount of lithium nickel oxide (N).

[0054] In one embodiment, the first and second lithium iron phosphate active materials (F1, F2) are each independently represented by the following chemical formula 1.

[0055] [Chemical Formula 1]

[0056] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0057] In the above chemical formula 1,

[0058] M 1 It comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and

[0059] X includes any one or more elements selected from the group consisting of F, S and N, and

[0060] a, b, and c are in the ranges of -0.5≤a≤0.5, 0≤b≤0.9, and 0≤c≤0.8, respectively.

[0061] In the above formula 1, for example, b is in the range of 0 to 0.7, 0.1 to 0.9, 0.3 to 0.9, 0.3 to 0.7, or 0.5 to 0.9. In one example, in the above formula 1, b is in the range of 0.61 to 0.85, thereby increasing the operating voltage range of the electrode.

[0062] In a specific example, the active material according to the above chemical formula 1 is Li 1+a FePO4 (-0.3≤a≤0.3) and Li 1+a Fe 1-b Mn b It is one or more of PO4 (-0.3≤a≤0.3, 0.3≤b≤0.9). For example, the active material according to Chemical Formula 1 above is LiFePO4, LiFe 0.7 Mn 0.3 PO4, LiFe 0.6 Mn 0.4 PO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.4 Mn 0.6 PO4 and LiFe 0.3 Mn 0.7 It is at least one type of PO4.

[0063] In another example, the active material according to the above chemical formula 1 may have a carbon (C) coated structure. Through the carbon coating, the electrical conductivity of the active material according to the chemical formula 1 can be increased.

[0064] In another embodiment, the lithium nickel oxide active material (N) is represented by the following chemical formula 2.

[0065] [Chemical Formula 2]

[0066] Li p Ni 1-q-r-s Coq Mn r M 2 s O2

[0067] In the above chemical formula 2,

[0068] M 2 is one or more elements selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 0.9≤p≤1.5, 0≤q≤1, 0≤r≤0.5, 0≤s≤0.1, 0≤q+r+s≤1.

[0069] Specifically, the active material according to the above chemical formula 2 is Li p (Ni 1-q-r Co q Mn r )O4(0.5 <p<1.3, 0<q<1, 0<r<1)로 표시될 수 있다. 예를 들어, 상기 화학식 2에서 q 및 r은 각각 독립적으로 0.05 내지 0.9 범위, 0.1 내지 0.8 범위, 또는 0.1 내지 0.3 범위이다. 보다 구체적으로, 상기 화학식 2에서, 1-q-r-s는 0.3~0.7 범위 또는 0.5~0.7 범위이다.

[0070] In one embodiment, the combined loading amount of the first and second active material layers is an average of 400 to 1,000 (mg / 25cm²). 2 ) is in the range. Specifically, the combined loading amount of the first and second active material layers is an average of 500 to 1,000 (mg / 25cm²). 2 ) range, average 600 to 1,000 (mg / 25cm) 2 ) range, average 500 to 800 (mg / 25cm) 2 ) Range or average 400 to 700 (mg / 25cm) 2 The electrode for a secondary battery according to the present invention is formed by simultaneously coating lower and upper active material layers on a current collector by applying Double Layer Slot Die Coating (DLD) technology. Through this, the electrode has excellent electrode manufacturing efficiency and enables the realization of a high loading amount.

[0071] In one example, the loading ratio of the first active material layer and the second active material layer is in the range of a weight ratio of 5:5 to 8:2. Specifically, the loading ratio of the first active material layer and the second active material layer is in the range of a weight ratio of 6:4 to 8:2, 7:3 to 8:2, 5:5 to 7:3, or 6.5:3.5 to 7.5:2.5. In the present invention, the loading amount of the first active material layer is controlled to be equal to or higher than the loading amount of the second active material layer. By controlling the loading amount of the first active material layer to a high level, sufficient thermal safety can be ensured.

[0072] As another example, in order to obtain the advantages of increasing the loading amount of the active material layer and rapid charge / discharge characteristics, the ratio of the loading amount of the first active material layer to the second active material layer may be in the weight ratio range of 4:6 to 2:8. That is, the loading amount of the upper layer can be increased, and the loading amount of the entire active material layer can be increased by increasing the content of lithium nickel oxide (N), which has a relatively higher rolling rate compared to lithium iron phosphate (F2) in the upper layer.

[0073] Specifically, the loading ratio of the first active material layer and the second active material layer may be in the weight ratio range of 4:6 to 2:8, 3:7 to 2:8, 5:5 to 3:7, or 3.5:6.5 to 2.5:7.5.

[0074] Meanwhile, in the present invention, the lithium nickel oxide (N) may be in the form of a single particle. The lithium nickel oxide (N) may be in the form of a secondary particle or a single particle, but the single particle has higher rolling strength, which is advantageous for increasing the rolling rate.

[0075] Here, a single particle refers to a particle form in which approximately 1 to 10 primary particles, appearing as a single particle in electron microscopy, are aggregated. The primary particles within the single particle exhibit larger particle sizes and larger crystal sizes compared to the primary particles within the secondary particle. As a result, the single particle has a greater ability to withstand rolling than the secondary particle.

[0076] The electrode for a secondary battery described above has a structure in which an active material layer is formed on a current collector. In the present invention, the active material layer comprises a first and a second active material layer. In the first and second active material layers, the content of the active material may be 85 to 98 parts by weight per 100 parts by weight of each active material layer, and specifically, may be 90 to 98 parts by weight or 95 to 98 parts by weight.

[0077] In addition, the first and second active material layers may each include a conductive material, a binder and / or a dispersant, etc., in addition to the active material.

[0078] At this time, the conductive material may be used to improve performance such as the electrical conductivity of the anode, and one or more selected from the group consisting of carbon black, acetylene black, ketjenblack, carbon fiber, and carbon nanofiber (CNT) may be used. For example, the conductive material may include carbon black or carbon nanofiber (CNT).

[0079] In addition, the content of the conductive material may be in the range of 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, 0.3 to 1.5 parts by weight, or 0.5 to 1.2 parts by weight per 100 parts by weight of the active material layer. By applying carbon nanofibers (CNT) as the conductive material, the content of the conductive material can be reduced while maintaining electrical conductivity.

[0080] In addition, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As one example, the binder may include polyvinylidene fluoride.

[0081] In addition, the binder may be included in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the total active material layer, specifically 2 to 8 parts by weight; or 2 to 5 parts by weight.

[0082] Meanwhile, the positive electrode for a lithium secondary battery according to the present invention may use a current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, a surface-treated material such as carbon, nickel, titanium, silver, etc. may be used. In addition, the current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. Furthermore, the average thickness of the current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0083]

[0084] secondary battery

[0085] In addition, the present invention provides, in one embodiment, a secondary battery comprising the electrode for a secondary battery described above. Specifically, the secondary battery may be a battery for an automobile or for an Energy Storage System (ESS). For example, the secondary battery is a lithium secondary battery or a pouch-type lithium secondary battery.

[0086] A secondary battery according to the present invention may include a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode.

[0087] The above-mentioned cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector and containing a cathode active material. Specifically, the cathode is manufactured by coating, drying, and pressing a cathode active material onto a cathode current collector, and, if necessary, a conductive material, an organic binder polymer, a filler, etc. as described above may be optionally further included.

[0088] In addition, the above-mentioned cathode active material is, for example, carbon and graphite materials such as graphite having a completely formed layered crystal structure like natural graphite, soft carbon having a low-crystallinity layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), hard carbon in which such structures are mixed with amorphous parts, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerene, activated carbon, etc.; 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, Group 1, 2, and 3 elements 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; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni계 재료; 티타늄 산화물; 리튬 티타늄 산화물 등을 사용할 수 있다.

[0089] As an example, the cathode active material may include graphite and silicon (Si)-containing particles together, and the graphite may include one or more of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure, and the silicon (Si)-containing particles may include silicon (Si) particles, silicon oxide (SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO2) particles, as particles containing silicon (Si) as a main component as a metal component.

[0090] In this case, the negative electrode active material may comprise 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si) containing particles, based on 100 parts by weight of the total. By controlling the content of graphite and silicon (Si) containing particles included in the negative electrode active material to the above range, the present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery.

[0091] In addition, the cathode active material layer may have an average thickness of 100㎛ to 200㎛, and specifically, may have an average thickness of 100㎛ to 180㎛; 100㎛ to 150㎛; 120㎛ to 200㎛; 140㎛ to 200㎛ or 140㎛ to 160㎛.

[0092] In addition, the above-mentioned negative 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, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used.

[0093] In addition, the above-mentioned negative current collector, like the positive current collector, may form fine irregularities on its surface to strengthen the bonding force with the negative active material, and can take various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics. Furthermore, the average thickness of the above-mentioned negative current collector can be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0094] In addition, the separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the industry, but specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated by an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. Furthermore, the pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0095] Meanwhile, the above positive and negative electrodes may be wound into a jelly roll form and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form, but are not limited thereto.

[0096] In addition, the lithium salt-containing electrolyte according to the present invention may consist of an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0097] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0098] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0099] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0100] The above lithium salt is a substance that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0101] In addition, for the purpose of improving charge / discharge characteristics and flame retardancy, the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further enriched, carbon dioxide gas may be further enriched to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc.

[0102] Meanwhile, in one embodiment, the present invention provides a module including the secondary battery described above to a battery pack including the module.

[0103] The above battery pack can be used as a power source for medium-to-large devices requiring high temperature stability, long cycle characteristics, and high rate characteristics. Specific examples of such medium-to-large devices include power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems. More specifically, hybrid electric vehicles (HEVs) can be cited, but are not limited thereto.

[0104] Furthermore, the above-mentioned positive and negative electrodes may be wound into a jelly roll shape and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form. For example, the lithium secondary battery according to the present invention may be a pouch-type battery.

[0105] As described above, a lithium secondary battery comprising a positive electrode active material according to the present invention can be used in a battery module or battery pack comprising multiple unit cells. Specifically, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0106] The present invention will be explained in more detail below through examples and experimental examples.

[0107] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0108]

[0109] Example 1

[0110] LiMn 0.6 Fe 0.4 A bottom electrode slurry was prepared by mixing PO4 positive electrode active material (active material F1(S20)), carbon nanotube (CNT) conductive material (LB.CNT), H-NBR dispersant (HPD-1), and PVDF binder (KF7200) in an N-methylpyrrolidone solvent in a weight ratio of 95.98:1.2:0.32:2.5.

[0111] An upper electrode slurry was prepared by mixing two types of cathode active materials (active materials F2 (S20) and N (PN6A08)), a carbon nanotube (CNT) conductive material (LB.CNT), an H-NBR dispersant (HPD-1), and a PVDF binder (KF7200) in an N-methylpyrrolidone solvent at a weight ratio of 95.98:1.2:0.32:2.5. The two types of cathode active materials were LiMn 0.6 Fe 0.4 PO4 (active material F2, S20) and LiNi 0.65 Co 0.15 Mn 0.2 O2 (active material N, PN6A08) was mixed and used in a weight ratio of 30:70 (F2:N). In particular, the active material N was applied in a single particle state.

[0112] A two-layer cathode comprising first and second active material layers was manufactured by applying lower and upper electrode slurries onto an aluminum current collector (15 μm Al A grade) using a dual slot die, followed by drying and rolling. The loading amount of the first active material layer was 420 mg / 25 cm². 2 ) and the loading amount of the second active material layer is 180 (mg / 25cm 2 It was controlled by ).

[0113] The detailed composition of the electrode slurry layer by layer is disclosed in Table 1 below. In Table 1, the composition was calculated based on weight%.

[0114] Content (wt%) 2nd Active Layer Active Material (F2+N) 95.96 Conductive Agent 0.8 Dispersant 0.24 Binder 3 1st Active Layer Active Material F1 95.96 Conductive Agent 0.8 Dispersant 0.24 Binder 3

[0115]

[0116] Examples 2 to 5

[0117] When preparing the top electrode slurry, LiMn is used as the active material 0.6 Fe 0.4 PO4 (active material F2, S20) and LiNi 0.65 Co 0.15 Mn 0.2 A cathode was prepared using the same process as in Example 1, except that O2 (active material N, PN6A08) was mixed in the ratio shown in Table 2 below.

[0118] Classification Active material F2 content (weight ratio) Active material N content (weight ratio) Example 2 2080 Example 3 1090 Example 4 595 Example 5 0100

[0119]

[0120] Comparative Examples 1 and 2

[0121] When preparing the top electrode slurry, LiMn is used as the active material 0.6 Fe 0.4 PO4 (active material F2, S20) and LiNi 0.65 Co 0.15 Mn 0.2 A cathode was prepared using the same process as in Example 1, except that O2 (active material N, PN6A08) was mixed in the ratio shown in Table 3 below.

[0122] Classification Active material F2 content (weight ratio) Active material N content (weight ratio) Comparative Example 1 40 60 Comparative Example 2 50 50

[0123]

[0124] Comparative Example 3

[0125] An electrode slurry was prepared by mixing two types of cathode active materials (active materials F2 (S20) and N (PN6A08)), a carbon nanotube (CNT) conductive material (LB.CNT), an H-NBR dispersant (HPD-1), and a PVDF binder (KF7200) in an N-methylpyrrolidone solvent at a weight ratio of 95.98:1.2:0.32:2.5. The two types of cathode active materials were LiMn 0.6 Fe 0.4 PO4 (active material F2, S20) and LiNi 0.65 Co 0.15 Mn 0.2 O2 (active material N, PN6A08) was mixed and used in a weight ratio of 30:70 (F2:N).

[0126] An anode containing a single-layer active material layer was prepared by applying an electrode slurry onto an aluminum current collector (15 μm Al A grade) using a slot die, followed by drying and rolling. The loading amount of the anode active material layer was 600 mg / 25 cm². 2 It was controlled by ).

[0127]

[0128] Experimental Example 1: Evaluation of Rolled Density

[0129] Rolling was performed on the cathodes prepared in Examples 1 to 5 and Comparative Examples 1 to 2 to achieve a porosity of 26 (v / v)%. After rolling, with the applied pressure removed, the density (rolled density) of each sample was measured at 25°C for 1 hour. The measurement results are shown in Table 6 and Figure 1 below. In Table 4 and Figure 1 below, the active material N content in the second active material layer is, based on the second active material layer, the active material N (LiNi 0.65 Co 0.15 Mn 0.2 This represents the ratio of O2, PN6A08).

[0130] No. Active material N content (weight ratio) in the second active material layer Rolled density (g / cc) Example 1 70 2.85 Example 2 80 2.88 Example 3 90 2.88 Example 4 95 2.89 Example 5 100 2.86 Comparative Example 160 2.65 Comparative Example 250 2.67

[0131] Referring to Table 4 and Figure 1, Examples 1 to 5, in which the N content of the active material in the second active material layer is in the range of 65 weight ratio or higher, are confirmed to have a rolled density of 2.85 (g / cc) or higher. In particular, when the N content of the active material in the second active material layer is 80 weight ratio or higher (Examples 2 to 5), it was found that the rolled density did not show a significant change. However, in the case of Example 5, in which the N content of the active material in the second active material layer is 100, it was confirmed that the rolled density actually decreased slightly despite the increase in the ratio of N of the active material. In the case of Examples 2 to 4, it can be seen that the rolled density is very high, in the range of 2.88 to 2.89 (g / cc).

[0132] In contrast, in the case of Comparative Examples 1 and 2, it can be seen that the rolling density is at the level of 2.65 to 2.67 (g / cc).

[0133]

[0134] Active material N in a single-particle state has relatively excellent rolling characteristics. In the present invention, excellent rolling density was achieved by applying active material N to the upper second active material layer. In particular, it was confirmed that even better rolling density can be achieved when active material N and active material F2 are mixed in the second active material layer (Examples 2 to 4).

[0135]

[0136] Experimental Example 2: Evaluation of Achieved SOC (%) via Rapid Charging

[0137] A secondary battery was manufactured using the anodes of Example 2 and Comparative Example 3. Specifically, specimens prepared in Example 2 and Comparative Example 3, respectively, were used as the anodes.

[0138] A cathode slurry was prepared by mixing natural graphite, a conductive material, a binder, and a dispersant in a water solvent in a weight ratio of 95.86:0.8:2.3:1.03. The cathode was manufactured by applying the cathode slurry onto a copper current collector, followed by drying and rolling. The porosity was controlled to 29% (v / v) by adjusting the degree of rolling. The detailed composition of the cathode slurry is disclosed in Table 5 below.

[0139] Classification Raw Material Content (wt%) Cathode Active Material Layer Active Material Natural Graphite (AML-412) 95.86% Conductive Material 1 Super-C65 (98.13wt%) 0.8% Conductive Material 2 SWNT (1.88wt%) Binder SBR (AX-B096) 2.3% Dispersant 1 Daiciel 2200 1.01% Dispersant 2 PVP+TA 0.02% Current Collector 8 um Cu B grade - Porosity (%) 29% -

[0140] An electrode assembly was manufactured by interposing a separator between the manufactured positive and negative electrodes. The stack number of the electrode assembly was set to 33+1. The manufactured electrode assembly was placed inside an aluminum pouch case, and then an electrolyte was injected into the case to manufacture a secondary battery. The manufactured secondary battery is a medium-to-large lithium secondary battery with a total width of 111.1 mm and a total length of 301.5 mm. The electrolyte was prepared by dissolving 1.0 M concentration lithium hexafluorophosphate (LiPF6) in an organic solvent mixed with ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate (EC / EMC / DEC) in a volume ratio of 30 / 40 / 30.

[0141]

[0142] For each manufactured secondary battery, the SOC (%) reached during rapid charging was evaluated. For each sample, the evaluation was performed twice under conditions of 25℃, and the average value is shown in Fig. 2.

[0143] Referring to FIG. 2, it can be seen that the secondary battery with the cathode of Example 2 has an excellent SOC attainment rate under rapid charging conditions of 2C or higher. Specifically, when rapidly charging under 3C conditions, the secondary battery with the cathode of Example 2 achieves an SOC of 47%, whereas the secondary battery with the cathode of Comparative Example 3 achieves an SOC of 30%.

[0144]

[0145] Experimental Example 3: Evaluation of Resistance by SOC During Charging and Discharging

[0146] The secondary batteries to which the positive electrodes of Example 2 and Comparative Example 3 were applied were discharged under 2C conditions while in a charged state, and the resistance evaluation for each SOC was performed twice. In addition, each discharged secondary battery was charged under 2C conditions, and the resistance evaluation for each SOC was performed twice. The resistance for each SOC during discharge is shown in Fig. 3, and the resistance for each SOC during charging is shown in Fig. 4.

[0147] Referring to FIGS. 3 and 4, it can be seen that the secondary battery with the positive electrode of Example 2 exhibits relatively low resistance under conditions of SOC 30% or higher. In addition, it was confirmed that the change in resistance according to the SOC state of the secondary battery is not significant.

[0148]

[0149] Experimental Example 4: Evaluation of lifespan characteristics at high temperature and room temperature

[0150] For secondary batteries using the positive electrodes of Example 2 and Comparative Example 3, charge and discharge were repeated under 1C conditions at high temperature (45°C) and room temperature (25°C). The capacity retention rate (%) according to the number of cycles (N) was evaluated. The capacity retention rate at high temperature (45°C) is shown in FIG. 5, and the capacity retention rate at room temperature (25°C) is shown in FIG. 6.

[0151] Referring to FIGS. 5 and FIGS. 6, it can be seen that the secondary battery with the positive electrode of Example 2 has a relatively excellent capacity retention rate at both high temperature and room temperature.

[0152]

[0153] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0154] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. Entire house; A first active material layer formed on one or both sides of the above-mentioned current collector and comprising a first lithium iron phosphate (F1) as an active material; and A second active material layer formed on the first active material layer and comprising lithium nickel oxide (N) and a second lithium iron phosphate (F2) or lithium nickel oxide (N) as active materials, In the second active material layer above, Based on the weight of the active material included in the second active material layer, the content of lithium nickel oxide (N) is 65 weight% or more, and An electrode for a secondary battery having an average density of 2.8 g / cc or more of the combined density of the first and second active material layers.

2. In Paragraph 1, Based on the sum of the first and second active material layers, An electrode for a secondary battery in which the ratio of the combined content of the first and second lithium iron phosphates (F1+F2) to the content of lithium nickel oxide (N) is in the range of a weight ratio of 50:50 to 80:

20.

3. In Paragraph 1, In the second active material layer above, An electrode for a secondary battery in which the ratio of the content of second lithium iron phosphate (F2) to the content of lithium nickel oxide (N) is in the range of a weight ratio of 2:98 to 30:

70.

4. In Paragraph 1, In the second active material layer above, An electrode for a secondary battery containing lithium nickel oxide (N) alone as the active material.

5. In Paragraph 1, The above lithium nickel oxide (N) is an electrode for a secondary battery having a single-particle structure.

6. In Paragraph 1, The first and second lithium iron phosphates (F1, F2) are each independently electrodes for a secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a Fe 1-b M 1 b (PO 4-c )X c In the above chemical formula 1, M 1 It comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and X includes any one or more elements selected from the group consisting of F, S and N, and a, b, and c are in the ranges of -0.5≤a≤0.5, 0≤b≤0.9, and 0≤c≤0.8, respectively.

7. In Paragraph 6, In Chemical Formula 1, b is an electrode for a secondary battery in the range of 0.5 to 0.

9.

8. In Paragraph 1, The lithium nickel oxide active material (N) is an electrode for a secondary battery represented by the following chemical formula 2: [Chemical Formula 2] Li p Ni 1-q-r-s Co q Mr r M 2 s O2 In the above chemical formula 2, M 2 is one or more elements selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 0.9≤p≤1.5, 0≤q≤1, 0≤r≤0.5, 0≤s≤0.1, 0≤q+r+s≤1.

9. In Paragraph 8, In Chemical Formula 2, 1-qrs is an electrode for a secondary battery in the range of 0.3 to 0.

7.

10. In Paragraph 1, The combined loading amount of the first and second active material layers is an average of 400 to 800 (mg / 25cm²). 2 ) is a range, and An electrode for a secondary battery in which the loading ratio of the first active material layer and the second active material layer is in the range of a weight ratio of 5:5 to 8:

2.

11. A secondary battery comprising an electrode according to claim 1.

12. In Paragraph 10, The above secondary battery is characterized by being a battery for automobiles or an Energy Storage System (ESS).

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