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

Abstract

The present invention relates to an electrode for a secondary battery, comprising: a current collector; a first active material layer formed on one surface or both surfaces of the current collector; and a second active material layer formed on the first active material layer, wherein a total active material layer including the first and second active material layers satisfies a Di value of 1.1 to 5 according to [equation 1] Di = (Di2nd = Di1st) / Di (in equation 1, Di1st represents an average particle diameter (D50) of the active material in the first layer, Di2nd represents an average particle diameter (D50) of the active material included in the second active material layer, and DiTotal represents an average particle diameter (D50) of the active material included in the total active material layer including the first and second active material layers).

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. 10-2024-0195409 dated December 24, 2024, and all contents disclosed in the document of said Korean patent application 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, the electrode comprises heterogeneous active materials with controlled particle sizes.

[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 an alternative, research is underway on the technology of applying iron phosphate as the cathode active material. However, iron phosphate-based active materials have issues such as low adhesion to the current collector and poor capacitance characteristics. Additionally, iron phosphate-based active materials are typically characterized by small particle sizes. Nevertheless, electrodes utilizing small-particle active materials suffer from increased side reactions and degraded lifespan performance due to the increased specific surface area (BET) resulting from the small particle size. Furthermore, there is a limitation in that energy release is suppressed at low temperatures as the movement of lithium ions within the electrode is restricted.

[0006] Accordingly, the development of new technologies is required to overcome the limitations associated with the application of iron phosphate-based active materials.

[0007] Accordingly, the present invention aims to provide an electrode with improved high-temperature life characteristics and low-temperature energy performance, and a secondary battery including the same.

[0008] In order 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 a second active material layer formed on the first active material layer. In addition, the entire active material layer including the first and second active material layers satisfies a Di value in the range of 1.1 to 5 according to Formula 1 below.

[0009] [Formula 1]

[0010]

[0011] In the above Formula 1,

[0012] Di 1st represents the average particle size (D50) of the active material contained in the first active material layer, and

[0013] Di 2nd represents the average particle size (D50) of the active material included in the second active material layer, and

[0014] Di Total represents the average particle size (D50) of the active material included in the entire active material layer, including the first and second active material layers.

[0015] Specifically, in the above Equation 1, Di Total It is in the range of 1 to 3 (㎛).

[0016] Specifically, the Di value according to the above Formula 1 is in the range of 1.1 to 2.5.

[0017] In one embodiment, the thickness of the first active material layer is in the range of an average of 40% to 80% based on the total thickness of the active material layer.

[0018] In another embodiment, the first and second active material layers each independently include, as active materials, one or more of the active material according to the following chemical formula 1 and the active material according to the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0021] In the above chemical formula 1,

[0022] 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

[0023] X includes any one or more elements selected from the group consisting of F, S and N, and

[0024] a, b, and c are in the ranges of -0.5≤a≤0.5, 0≤b≤0.9, and 0≤c≤0.8, respectively.

[0025] Specifically, in the above chemical formula 1, b is in the range of 0.3 to 0.9.

[0026] [Chemical Formula 2]

[0027] Li p Ni 1-q-r-s Co q Mn r M 2 s O2

[0028] In the above chemical formula 2,

[0029] 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.

[0030] Specifically, in the above chemical formula 2, 1-qrs is in the range of 0.3 to 0.7.

[0031] In one embodiment, based on an electrode for a secondary battery according to the present invention, the first active material layer comprises an active material according to Formula 1 as the active material. Additionally, the second active material layer comprises an active material according to Formula 2 as the active material, or comprises a mixture of an active material according to Formula 1 and an active material according to Formula 2. Specifically, the second active material layer comprises a mixture of an active material according to Formula 1 and an active material according to Formula 2 as the active material. For example, in the second active material layer, the mixing ratio of the active material according to Formula 1 is 40 weight% or less.

[0032] For example, the above electrode can be applied as an anode.

[0033]

[0034] In addition, the present invention provides a secondary battery comprising the electrode described above. Specifically, the electrode is applied as the positive electrode of the secondary battery.

[0035] In one embodiment, the secondary battery comprises a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. Here, the positive electrode is the electrode described above.

[0036] The above-mentioned cathode comprises 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 active material comprises a carbon-based active material.

[0037] In one embodiment, the negative electrode active material further comprises a silicon-based active material. Specifically, the silicon-based active material comprises silicon (Si), silicon carbide (SiC), a carbon-silicon composite (Si / C), and silicon oxide (SiO₂). q ..., provided that it includes one or more of 0.8≤q≤2.5). For example, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt% based on the total weight of the active material in the negative electrode active material layer.

[0038] For example, the above secondary battery is applied as a battery for automobiles or an Energy Storage System (ESS).

[0039] The electrode for a secondary battery according to the present invention can simultaneously achieve excellent high-temperature life characteristics and low-temperature energy performance.

[0040] Figure 1 is a schematic diagram illustrating the cross-sectional structure of an anode according to Example 4.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045]

[0046] The present invention will be described in more detail below.

[0047]

[0048] 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 a second active material layer formed on the first active material layer. Specifically, the entire active material layer comprising the first and second active material layers has a Di value in the range of 1.1 to 3.5 according to Formula 1 below.

[0049] [Formula 1]

[0050]

[0051] In the above Formula 1,

[0052] Di 1st represents the average particle size (D50) of the active material contained in the first active material layer, and

[0053] Di 2nd represents the average particle size (D50) of the active material included in the second active material layer, and

[0054] Di Total represents the average particle size (D50) of the active material included in the entire active material layer, including the first and second active material layers.

[0055] In the present invention, Equation 1 controls the particle size distribution of the active material contained in the first and second active material layers. The layer-by-layer average particle size (D50) is calculated based on the average particle size (D50), specifically based on the volume-based average (Dv50). The active material having the average particle size (D50) can be calculated, for example, through dynamic light scattering. Alternatively, it is also possible to obtain the active material having the corresponding average particle size (D50) commercially.

[0056] Specifically, in the above Equation 1, Di TotalIt is in the range of 1 to 3 (㎛). More specifically, Di Total The range is 1.1 to 3 (㎛), 1.5 to 3 (㎛), 1 to 2.2 (㎛), 1.5 to 2 (㎛), 2 to 2.5 (㎛), or 1.5 to 2.2 (㎛).

[0057] In addition, the Di value according to the above formula 1 is in the range of 1.1 to 5, 1.1 to 3.5, 1.1 to 2.5, 1.1 to 2, 1.5 to 2, 2 to 2.5, or 1.1 to 1.5.

[0058] In the present invention, Formula 1 represents the control of the particle size distribution of the active material included in the first and second active material layers. In the present invention, by controlling the range related to Formula 1 as described above, the high-temperature life and low-temperature energy performance of the secondary battery can be improved. In particular, it was confirmed that the low-temperature energy performance is improved when the particle size distribution (Di) specified in Formula 1 has a small value within the above range.

[0059] In one embodiment, the thickness of the first active material layer is in the range of an average of 40% to 80% based on the total thickness of the active material layer. Specifically, the thickness of the first active material layer is in the range of an average of 40% to 80%, 45% to 80%, 40% to 75%, 55% to 80%, or 40% to 55%. The first active material layer comprises an active material having a relatively small average particle size. For example, the active material included in the first active material layer may be a lithium iron phosphate active material, and the average particle size may be in the range of 0.5 μm to 1.1 μm. In the present invention, maintaining the thickness of the first active material layer above a certain level is advantageous for improving high-temperature lifespan and low-temperature energy performance.

[0060] In one embodiment, the first active material layer comprises, respectively, one or more of the active materials according to the following chemical formula 1 and the active material according to the following chemical formula 1.

[0061] [Chemical Formula 1]

[0062] Li 1+a Fe 1-b M 1 b (PO 4-c )X c

[0063] In the above chemical formula 1,

[0064] 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

[0065] X includes any one or more elements selected from the group consisting of F, S and N, and

[0066] a, b, and c are in the ranges of -0.5≤a≤0.5, 0≤b≤0.9, and 0≤c≤0.8, respectively.

[0067] 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, 0.5 to 0.9, or 0.3 to 0.7. 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.

[0068] 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 0.3PO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 It is at least one type of PO4.

[0069] 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.

[0070]

[0071] [Chemical Formula 2]

[0072] Li p Ni 1-q-r-s Co q Mn r M 2 s O2

[0073] In the above chemical formula 2,

[0074] 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.

[0075] 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 내지 0.7 범위 또는 0.5 내지 0.7 범위이다.

[0076]

[0077] In one example, the first active material layer comprises an active material according to Chemical Formula 1 as the active material. The first active material layer may comprise a lithium iron phosphate series active material represented by Chemical Formula 1. For example, the first active material layer comprises, alone, a lithium iron phosphate series active material represented by Chemical Formula 1 as the active material.

[0078] Additionally, the second active material layer comprises an active material according to Formula 2 as an active material, or comprises a mixture of an active material according to Formula 1 and an active material according to Formula 2. For example, the second active material layer comprises an active material according to Formula 2 alone as an active material. As another example, the second active material layer comprises a mixture of an active material according to Formula 1 and an active material according to Formula 2 as an active material.

[0079] In another example, the second active material layer comprises a mixture of an active material according to Formula 1 and an active material according to Formula 2 as active materials. Here, the mixing ratio of the active material according to Formula 1 is 40 weight% or less. Specifically, the mixing ratio of the active material according to Formula 1 is in the range of 0.1 to 40 weight%, 0.1 to 35 weight%, 10 to 40 weight%, 20 to 40 weight%, 0.1 to 15 weight%, or 25 to 35 weight%. The mixing ratio of the active material according to Formula 1 is based on the combined content of the active material according to Formula 1 and the active material according to Formula 2 in the second active material layer.

[0080] For example, in the present invention, the first active material layer comprises, as the active material, a lithium iron phosphate-based active material (e.g., LFP or LMFP) having a relatively small particle size, alone. Additionally, the second active material layer comprises, as the active material, a lithium nickel-cobalt-based active material (e.g., NCM) having a relatively large particle size, alone, or comprises a mixture of a lithium iron phosphate-based active material and a lithium nickel-cobalt-based active material. Through such combinations, the present invention can improve high-temperature life and low-temperature energy performance while ensuring the safety of the secondary battery.

[0081] For example, the active material according to the above chemical formula 1 has an average particle size (D50) in the range of 0.1㎛ to 2㎛, 0.3㎛ to 1.5㎛, 0.5㎛ to 1.1㎛, 0.4㎛ to 0.8㎛, or 0.8㎛ to 1.1㎛. In addition, the active material according to the above chemical formula 2 has an average particle size (D50) in the range of 3㎛ to 15㎛, 3㎛ to 10㎛, 3㎛ to 5㎛, or 4㎛ to 5㎛.

[0082] 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.

[0083] In one embodiment, the electrode can be applied as a positive electrode. Specifically, the electrode is a positive electrode for a secondary battery. The positive electrode for a secondary battery 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.

[0084] 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.

[0085] 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).

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Meanwhile, the positive electrode for a 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.

[0090]

[0091] secondary battery

[0092] In addition, the present invention provides, in one embodiment, a secondary battery comprising the electrode for a secondary battery described above. The secondary battery may include a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode. Furthermore, the electrode described above can be applied as a positive electrode.

[0093] Specifically, the secondary battery may be a battery for automobiles or for an Energy Storage System (ESS). For example, the secondary battery is a lithium secondary battery or a pouch-type lithium secondary battery.

[0094] 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.

[0095] 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 applying, drying, and pressing a cathode active material onto the cathode current collector, and, if necessary, a conductive material, an organic binder polymer, a filler, etc. as described above may be optionally further included.

[0096] In addition, the cathode comprises a cathode current collector; and a cathode active material layer located on the cathode current collector and containing a cathode active material. In addition, the cathode active material comprises a carbon-based active material. For example, the carbon-based active material may be 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 portions, 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. 예를 들어, 상기 탄소계 활물질로는 흑연을 포함할 수 있다. 상기 흑연은 천연 흑연 및 인조 흑연 중 어느 하나 이상을 포함할 수 있다. 예컨대, 상기 탄소계 활물질은 천연 흑연을 단독으로 포함할 수 있으며, 경우에 따라서는 천연 흑연과 인조 흑연을 혼합한 형태로 포함할 수 있다.

[0097] In one embodiment, the cathode further comprises a silicon-based active material as an active material. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt% based on the total weight of the active material in the cathode active material layer. Specifically, the content of the silicon-based active material is in the range of 0.1 wt% to 30 wt%, 1 wt% to 30 wt%, 1 wt% to 10 wt%, 0.1 wt% to 5 wt%, 5 wt% to 30 wt%, or 6 wt% to 20 wt% based on the total weight of the active material contained in the cathode active material layer. The silicon-based active material has the advantage of increasing the cathode capacity compared to carbon-based active materials. On the other hand, the silicon-based active material has the problem of causing volume changes during the charging and discharging process. Therefore, it is desirable to control the content of the silicon-based active material by considering the application field or form of the secondary battery.

[0098] Specifically, the silicon-based active material is silicon (Si), silicon carbide (SiC), a carbon-silicon composite (Si / C), and silicon oxide (SiO₂). q ..., provided that it includes one or more of the following: , provided that 0.8≤q≤2.5). As one example, the 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. The silicon (Si)-containing particles may include silicon (Si) particles as a main component as a metal component, silicon (Si) particles, silicon oxide (SiO, SiO2) particles, or a mixture of silicon (Si) particles and silicon oxide (SiO, SiO2) particles.

[0099] In addition, the silicon-based active material may be doped with Li, Mg, Al, Ca, or Ti, or form an alloy. Furthermore, the silicon-based active material may be surface-treated with a carbon coating layer or the like for the purpose of suppressing volume expansion during charging or improving electrical conductivity.

[0100] The above conductive material may include one or more types of carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and thermal black; graphene; carbon nanotubes and carbon fibers, but is not limited thereto.

[0101] As an example, the above-mentioned cathode active material layer may contain carbon black, carbon nanotubes, carbon fibers, etc., as a conductive material, either alone or in combination.

[0102] At this time, the content of the conductive material may be 0.1 to 5 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the conductive material may be 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the conductive material within the above range, the present invention can prevent the decrease in charging capacity caused by an increase in the resistance of the negative electrode due to a low content of the conductive material. Furthermore, the present invention can prevent problems such as a decrease in charging capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of conductive material exceeding the above range, or an increase in electrical resistance due to an increase in the loading amount of the negative electrode active material layer.

[0103] In addition, the binder is a component that assists in the bonding of the cathode active material and the conductive material, as well as the bonding to the current collector, and can be appropriately applied within a range that does not degrade the electrical properties of the cathode. For example, the binder may include one or more of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber. For example, the binder is styrene butadiene rubber (SBR) or fluororubber.

[0104] The content of the binder may be 0.1 to 5 parts by weight per 100 parts by weight of the entire negative electrode active material layer. Specifically, the binder may be 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight per 100 parts by weight of the entire negative electrode active material layer. By controlling the content of the binder contained in the negative electrode active material layer to the above range, the present invention can prevent the adhesion of the active material layer from being reduced due to a low content of binder or the electrical properties of the negative electrode from being reduced due to an excessive amount of binder.

[0105] In addition, the above-mentioned negative electrode active material layer may further include the previously described thickener.

[0106] In addition, the cathode active material layer may have an average thickness of 100㎛ to 800㎛, and specifically, may have an average thickness of 100㎛ to 780㎛; 100㎛ to 550㎛; 120㎛ to 500㎛; 140㎛ to 200㎛ or 140㎛ to 160㎛.

[0107] 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.

[0108] 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.

[0109] In addition, the separator interposed between the positive and negative electrodes of the lithium secondary battery is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is one commonly used in the industry. Specifically, the separator may be one comprising one or more polymers selected from chemically resistant and hydrophobic polypropylene; polyethylene; and polyethylene-propylene copolymer. The separator may have the form of a porous polymer substrate, such as a sheet or nonwoven fabric, containing the aforementioned polymer, and in some cases, may have the form of a composite separator in which organic or inorganic particles are coated on the porous polymer substrate by an organic binder. Furthermore, the separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0110] Meanwhile, the secondary battery according to the present invention is not particularly limited, but may be a secondary battery of a form that includes a stack type; a zigzag type; or a zigzag-stack type electrode assembly.

[0111] In addition, the secondary battery according to the present invention may include a lithium salt-containing electrolyte. The lithium salt-containing electrolyte 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] The above lithium salt is a substance that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0116] 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.

[0117] Meanwhile, in one embodiment, the present invention provides a module including the secondary battery described above to a battery pack including the module.

[0118] 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.

[0119] 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 secondary battery according to the present invention may be a pouch-type battery.

[0120] As described above, the secondary battery according to the present invention can be used in a battery module or battery pack comprising a plurality of 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).

[0121] Meanwhile, in one embodiment, the present invention provides a module including the secondary battery described above to a battery pack including the module.

[0122] 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.

[0123] 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.

[0124] 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).

[0125] The present invention will be explained in more detail below through examples and experimental examples.

[0126] 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.

[0127]

[0128] Examples 1 to 4, Comparative Example 1: Anode preparation

[0129] LiMn 0.6 Fe 0.4 A first electrode slurry was prepared by mixing a PO4 positive electrode active material (hereinafter referred to as 'LMFP'), a conductive material mixed with carbon nanotubes (CNT) and carbon black, and a PVDF binder in a weight ratio of 95:2:3 in an N-methylpyrrolidone solvent. As the positive electrode active material (LMFP), an active material with an average particle size (D50) of 0.6 (μm) was used.

[0130] A second electrode slurry was prepared by mixing two types of cathode active materials, a conductive material mixed with carbon nanotubes (CNT) and carbon black, and a PVDF binder in an N-methylpyrrolidone solvent at a weight ratio of 95:2:3. The two types of cathode active materials were LiMn 0.6 Fe 0.4 PO4(LMFP) and LiNi 0.65 Co 0.15 Mn 0.2 O2 (hereinafter referred to as 'NCM') was used in combination.

[0131] First and second electrode slurries were sequentially applied onto an aluminum current collector (15 μm Al A grade) using a dual slot die. Then, a two-layer cathode structure containing first and second active material layers was manufactured by drying and rolling. The first electrode slurry was formed as the lower layer, the first active material layer, and the second electrode slurry was formed as the upper layer, the second active material layer. The composition of the active materials included in the first and second electrode slurries is listed in Table 1 below. The layer-by-layer loading amount was controlled during the discharge of the first and second electrode slurries to satisfy the composition in Table 1 below and the Di in Table 3. In Table 1 below, the content was calculated based on weight%.

[0132] Classification First Electrode Slurry Second Electrode Slurry LMFP Content D50 (㎛) NCM Content D50 (㎛) LMFP Content D50 (㎛) Example 1 100% 0.6 100% 4.50% - Example 2 100% 0.6 90% 4.5 10% 0.6 Example 3 100% 0.6 70% 4.5 30% 0.6 Example 4 100% 0.6 70% 4.5 30% 1.0 Comparative Example 1 100% 0.6 40% 4.5 60% 0.6

[0133] FIG. 1 is a schematic diagram illustrating the cross-sectional structure of an anode according to Example 4. Referring to FIG. 4, the anode (100) has a structure in which a first active material layer (110) and a second active material layer (120) are sequentially formed on an aluminum (Al) current collector (101). The first active material layer (110) includes LMFP as an active material, and the second active material layer (120) includes LMFP and NCM in a ratio of 70:30 as active materials. Additionally, the anode (100) is manufactured such that the first active material layer (110) has a loading amount approximately twice as high as that of the second active material layer (120).

[0134]

[0135] Comparative Examples 2 and 3: Anode Manufacturing

[0136] A second electrode slurry was prepared by mixing two types of cathode active materials, a conductive material mixed with carbon nanotubes (CNT) and carbon black, and a PVDF binder in an N-methylpyrrolidone solvent at a weight ratio of 95:2:3. The two types of cathode active materials were LiMn 0.6 Fe 0.4 PO4(LMFP) and LiNi 0.65 Co 0.15 Mn 0.2 O2 (hereinafter referred to as 'NCM') was used in combination.

[0137] An electrode slurry was applied onto an aluminum current collector (15 μm Al A grade) using a slot die. Then, a single-layer anode was manufactured by drying and rolling. The composition of the active material contained in the electrode slurry is listed in Table 2 below. In Table 2, the content was calculated based on weight%.

[0138] Separating electrode slurry NCM content D50 (㎛) LMFP content D50 (㎛) Comparative Example 230% 4.5 70% 0.6 Comparative Example 340% 4.5 60% 0.6

[0139]

[0140] Experimental Example 1: Calculation of Particle Size Distribution Di Value

[0141] For the cathodes prepared in Examples 1 to 4 and Comparative Examples 1 to 3, the Di value according to Formula 1 was calculated using the average particle size of the active material contained in the active material layer.

[0142] [Formula 1]

[0143]

[0144] In the above Formula 1,

[0145] Di 1st represents the average particle size (D50) of the active material contained in the first active material layer, and

[0146] Di 2nd represents the average particle size (D50) of the active material included in the second active material layer, and

[0147] Di Total represents the average particle size (D50) of the active material included in the entire active material layer, including the first and second active material layers.

[0148] The anodes according to Examples 1 to 4 and Comparative Example 1 were controlled such that the content of the active material per layer and the loading amount per layer were satisfied with the Di value according to Formula 1 in Table 3 below.

[0149] Distinction 1st (㎛)Di 2nd (㎛)Di Total (㎛)Di Example 10.6 4.5 1.7 6 2.22 Example 20.6 4.1 1.7 6 1.99 Example 30.6 3.3 3.7 6 1.55 Example 40.6 3.4 5 2.0 7 1.38 Comparative Example 10.6 2.1 6 1.7 6 0.89 Comparative Example 2 2.0 7 2.0 7 1.00 Comparative Example 3 2.9 4 2.9 4 1.00

[0150] In Table 3 above, considering that Comparative Examples 2 and 3 have a structure formed of a single layer, the average particle size (D50) of the active material in the active material layer is Di 2nd It was written in, and the value of Di according to Formula 1 was calculated as 1.

[0151]

[0152] Experimental Example 2: High-temperature life and low-temperature energy measurement

[0153] Secondary battery manufacturing

[0154] Secondary batteries were manufactured using the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 2. Specifically, specimens prepared in Examples 1 to 4 and Comparative Examples 1 to 2, respectively, were used as the positive electrodes.

[0155] A cathode slurry was prepared by mixing a natural graphite active material, a carbon black conductive material, and an SBR (Styrene-Butadiene Rubber) binder in a water solvent at a weight ratio of 96:1.4:3. 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.

[0156] An electrode assembly was manufactured by placing a separator between the manufactured positive and negative electrodes. The number of stacks 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.

[0157] 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.

[0158]

[0159] High-temperature cycle performance evaluation

[0160] The manufactured secondary battery was subjected to 200 charge-discharge cycles at 45°C, 0.33C charge, and 0.5C discharge conditions. The capacity retention rate (%) was evaluated at the point of 200 charge-discharge cycles. The evaluation results are shown in Table 4 below.

[0161]

[0162] Low-temperature energy performance evaluation

[0163] The manufactured secondary batteries were repeatedly charged at 25°C and 0.33°C and discharged at -10°C and 0.33°C. For each secondary battery, the discharge energy (Wh) was evaluated after 200 charge-discharge cycles. The evaluation results are shown in Table 4 below.

[0164] Classification 45℃, Capacity Retention Rate (%) Low Temperature Energy (Wh) Example 186.877.3 Example 287.577.9 Example 388.182.0 Example 492.385.0 Comparative Example 185.574.2 Comparative Example 275.671.5 Comparative Example 379.569.2

[0165] Referring to Table 4, it can be seen that Examples 1 to 4 have a capacity retention rate of 86% or higher during high-temperature (45°C) charging and discharging, and a low-temperature energy exceeding 77 (Wh). In particular, it was confirmed that Example 4 simultaneously achieves excellent high-temperature and low-temperature characteristics. In contrast, Comparative Example 1 is a case where the LMFP content of the second active material layer is 60%. Comparative Example 1 showed a high-temperature capacity retention rate of 85.5%, but it was confirmed that the low-temperature energy had a low value of 74.2 (Wh). Furthermore, Comparative Examples 2 and 3 are cases where a single-layer cathode is formed by mixing LMFP and NCM active materials, respectively. It can be seen that Comparative Examples 2 and 3 have lower high-temperature and low-temperature characteristics compared to Examples 1 to 4.

[0166]

[0167] 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 present invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0168] 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.

[0169]

[0170] [Explanation of the symbol]

[0171] 100: Anode

[0172] 101: Entire house

[0173] 110: First active material layer

[0174] 120: Second active material layer

Claims

The whole house; A first active material layer formed on one or both sides of the above-mentioned current collector; and It includes a second active material layer formed on the first active material layer, The entire active material layer including the first and second active material layers above is an electrode for a secondary battery having a Di value in the range of 1.1 to 5 according to Formula 1 below: [Formula 1] In the above Formula 1, Di 1st represents the average particle size (D50) of the active material contained in the first active material layer, and Di 2nd represents the average particle size (D50) of the active material included in the second active material layer, and Di Total represents the average particle size (D50) of the active material included in the entire active material layer, including the first and second active material layers. In Article 1, In the above Formula 1, Di Total The electrode for a secondary battery is in the range of 1 to 3 (㎛). In Article 1, An electrode for a secondary battery in which the Di value according to the above Formula 1 is in the range of 1.1 to 2.

5. In Article 1, An electrode for a secondary battery in which the thickness of the first active material layer is in the range of an average of 40% to 80% based on the total active material layer thickness. In Article 1, The first and second active material layers each independently comprise, as active materials, an electrode for a secondary battery comprising an active material according to the following chemical formula 1 and one or more of the active materials according to 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, and [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. In Article 5, In Chemical Formula 1, b is an electrode for a secondary battery in the range of 0.3 to 0.

9. In Article 5, In Chemical Formula 2, 1-qrs is an electrode for a secondary battery in the range of 0.3 to 0.

7. In Article 5, The first active material layer comprises an active material according to the above chemical formula 1 as an active material, and The second active material layer comprises an active material according to Chemical Formula 2 as the active material, or a mixture of an active material according to Chemical Formula 1 and an active material according to Chemical Formula 2, for an electrode for a secondary battery. In Article 5, The second active material layer comprises a mixture of an active material according to Chemical Formula 1 and an active material according to Chemical Formula 2 as active materials, wherein An electrode for a secondary battery in which the mixing ratio of the active material according to Chemical Formula 1 is 40 weight% or less. In Article 1, An electrode for a secondary battery characterized in that the above electrode is a positive electrode. A secondary battery comprising an electrode according to claim 1. In Article 11, The above secondary battery comprises a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode, wherein The above positive electrode is a secondary battery comprising an electrode according to claim 1. In Article 12, The above cathode comprises a cathode current collector; and a cathode active material layer located on the cathode current collector and containing a cathode active material, and The above negative electrode active material is a secondary battery comprising a carbon-based active material. In Article 12, The above negative electrode active material further includes a silicon-based active material, and The above silicon-based active materials are silicon (Si), silicon carbide (SiC), a carbon-silicon composite (Si / C), and silicon oxide (SiO₂). q ..., provided that it includes at least one of 0.8≤q≤2.5), A secondary battery in which the above silicon-based active material has a content ranging from 0.1% to 30% by weight based on the total weight of the active material in the negative electrode active material layer. In Article 13, The above secondary battery is characterized by being a battery for automobiles or an Energy Storage System (ESS).

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