Positive electrode and secondary battery including same

Abstract

A positive electrode according to an embodiment of the present invention may comprise: a positive electrode current collector comprising a first surface and a second surface; the first positive electrode material is formed on the first surface of the positive electrode current collector; and a second positive electrode material formed on the second surface of the positive electrode current collector. The first positive electrode material and the second positive electrode material may each include a first positive electrode active material and a second positive electrode active material. The first positive electrode active material and the second positive electrode active material may have different operating voltage ranges from each other. The weight ratio of the first positive electrode active material and the second positive electrode active material included in the first positive electrode material and the weight ratio of the first positive electrode active material and the second positive electrode active material included in the second positive electrode material may be different from each other.

Description

Technical Field

[0001] The present invention relates to a positive electrode and a secondary battery comprising the positive electrode. Background Art

[0002] As the electric vehicle market grows, there is a need to manufacture batteries that can travel long distances on a single charge. In order to increase the driving distance of electric vehicles, batteries need to have high energy density. Lithium secondary batteries exhibit high energy density and are therefore most suitable for use as batteries for electric vehicles.

[0003] Positive electrode materials for lithium secondary batteries for electric vehicles are being studied and developed to replace the currently used LiCoO2. When LiCoO2 is used in high energy density applications, it becomes the main cause of battery explosion due to structural instability. In order to improve the stability of LiCoO2, lithium-manganese oxides such as layered LiMnO2 and spinel LiMn2O4 are being considered, and recently, research is being conducted on the use of layered Ni, Co, and Mn ternary metal oxides. Layered Ni, Co, and Mn ternary metal oxides exhibit high power in the high state of charge (SOC) range, but experience a sharp drop in power in the low SOC range (SOC below 30%).

[0004] Therefore, a method is needed to improve the stability of lithium secondary batteries, increase the power in a low SOC range, and minimize the sharp voltage drop. Summary of the invention

[0005] Technical issues to be solved

[0006] The present invention provides a positive electrode and a secondary battery including the positive electrode, wherein the positive electrode improves the resistance increase amplitude during voltage drop by minimizing a sharp voltage drop.

[0007] Technical Solution

[0008] A positive electrode according to an embodiment of the present invention may include: a positive electrode collector, the positive electrode collector including a first face and a second face; a first positive electrode material, the first positive electrode material being formed on the first face of the positive electrode collector; and a second positive electrode material, the second positive electrode material being formed on the second face of the positive electrode collector. The first positive electrode material and the second positive electrode material may each include a first positive electrode active material and a second positive electrode active material. The first positive electrode active material and the second positive electrode active material may have operating voltage ranges different from each other. The weight ratio of the first positive electrode active material to the second positive electrode active material contained in the first positive electrode material and the weight ratio of the first positive electrode active material to the second positive electrode active material contained in the second positive electrode material may be different from each other.

[0009] According to the embodiment, the first positive electrode active material may include a layered lithium transition metal oxide, and the second positive electrode active material may include an olivine-structured lithium phosphate compound.

[0010] According to the embodiment, the layered structured lithium transition metal oxide may be represented by Chemical Formula 1 below.

[0011] [Chemical formula 1]

[0012] Li 1+a Ni x Mn y Co 1-x-y O2

[0013] In the chemical formula 1, 0≤a<0.5, 0 <x<1,0<y<0.5。

[0014] According to the embodiment, the oxide represented by the chemical formula 1 may be LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0015] According to the embodiment, the olivine-structured lithium phosphate compound may be represented by Chemical Formula 2 below.

[0016] [Chemical formula 2]

[0017] LiMPO4

[0018] In the chemical formula 2, M is one or more elements selected from Fe, Mn, Ni, Co and V.

[0019] According to an embodiment, the compound represented by the Chemical Formula 2 may be LiFePO 4 .

[0020] According to the embodiment, the first positive electrode active material may include a spinel-structured lithium nickel manganese-based oxide, and the second positive electrode active material may include an olivine-structured lithium iron phosphate compound.

[0021] According to the embodiment, the spinel-structured lithium nickel manganese-based oxide may be represented by the following Chemical Formula 3.

[0022] [Chemical formula 3]

[0023] Li x Ni y Mn 2-y O4

[0024] In the chemical formula 3, 0.95≤x<1.05, 0.30≤y≤1.00.

[0025] According to the embodiment, the oxide represented by the chemical formula 3 may be LiNi 0.5 Mn 1.5 O4.

[0026] According to an embodiment, the first positive electrode material and the second positive electrode material may each further include a positive electrode active material different from the first positive electrode active material and the second positive electrode active material.

[0027] According to an embodiment, a weight ratio of the first positive electrode active material to the second positive electrode active material included in the first positive electrode material and the second positive electrode material may be 9:1 to 1:9.

[0028] According to an embodiment, a weight ratio of the first positive electrode active material to the second positive electrode active material contained in the first positive electrode material may be 1:9 to 6:4, and a weight ratio of the first positive electrode active material to the second positive electrode active material contained in the second positive electrode material may be 1:9 to 6:4.

[0029] According to the embodiment, the first positive electrode material and the second positive electrode material may each further include a conductive material and a binder.

[0030] A secondary battery according to an embodiment of the present invention may include: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode.

[0031] Beneficial Effects

[0032] The positive electrode according to the embodiment of the present invention includes positive electrode active materials having operating voltage ranges different from each other, and thus has an effect of being able to improve the power of the secondary battery in a low SOC range.

[0033] In addition, the positive electrode according to the embodiment of the present invention contains positive electrode active materials having different operating voltage ranges from each other, and at the same time, the content ratio (for example, weight ratio, weight %) of the positive electrode active materials is changed on different surfaces of the positive electrode collector, thereby generating voltage drop intervals of the secondary battery in respectively different SOC intervals, and the entire voltage curve shows the voltage average value of different surfaces of the positive electrode collector, thereby having the effect of improving the resistance increase amplitude during voltage drop and improving the performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 1 is a diagram showing a change in voltage of the secondary battery according to the SOC in the first embodiment.

[0035] Figure 2 3 is a graph showing a change in voltage of a secondary battery according to SOC in Comparative Example 1. FIG.

[0036] Figure 3 1 is a graph showing a change in voltage of the secondary battery according to the charge capacity in Example 1.

[0037] Figure 4 Graph showing voltage change of the secondary battery in Comparative Example 1 according to the charge capacity. DETAILED DESCRIPTION

[0038] The description of the structure or function of the implementation scheme proposed in this specification or the present invention is merely exemplified for the purpose of illustrating the implementation scheme according to the technical idea of ​​the present invention. The implementation scheme according to the technical idea of ​​the present invention can be implemented in various forms other than the implementation scheme proposed in this specification or the present invention, and should not be interpreted as the technical idea of ​​the present invention being limited to the implementation scheme described in this specification or the present invention.

[0039] Hereinafter, a positive electrode according to an embodiment of the present invention and a secondary battery including the positive electrode are described.

[0040] The positive electrode current collector of the positive electrode according to the embodiment of the present invention may include a first face and a second face. According to the embodiment, the first face and the second face may be different faces of the positive electrode current collector. For example, the first face may be one face (or front face) of the positive electrode current collector, and the second face may be the other face (or back face) of the positive electrode current collector.

[0041] The positive electrode according to the embodiment of the present invention may include a first positive electrode material disposed on a first surface of the positive electrode collector and a second positive electrode material disposed on a second surface of the positive electrode collector. For example, the first positive electrode material and the second positive electrode material may be formed on different surfaces of the positive electrode collector, respectively.

[0042] According to the embodiment, the first positive electrode material and the second positive electrode material may each include two or more positive electrode active materials that are the same as each other. For example, the first positive electrode material and the second positive electrode material may each include a first positive electrode active material and a second positive electrode active material.

[0043] According to the embodiment, the first positive electrode active material and the second positive electrode active material may have different operating voltage ranges from each other. According to the embodiment, the content ratio (e.g., weight ratio) of the first positive electrode active material to the second positive electrode active material contained in the first positive electrode material and the content ratio (e.g., weight ratio) of the first positive electrode active material to the second positive electrode active material contained in the second positive electrode material may be different from each other.

[0044] According to the embodiment, the positive electrode according to the embodiment of the present invention includes a positive electrode collector. The positive electrode collector may include a known conductive material within the range of not causing a chemical reaction in the secondary battery. For example, the current collector may include any one of stainless steel, nickel (Ni), aluminum (Al), titanium (Ti), copper (Cu) and their alloys, and may be provided in various forms such as a film, a sheet, and a foil.

[0045] According to the embodiment, the first positive electrode material and the second positive electrode material may each contain a first positive electrode active material and a second positive electrode active material having operating voltage ranges different from each other, so that in a higher state of charge (SOC) range, due to the positive electrode active material having a high operating voltage range, high power can be exhibited, and in a lower SOC range, due to the positive electrode active material having a relatively low operating voltage range, an effect that can compensate for the sharp drop in power due to increased resistance can occur.

[0046] According to the embodiment, the weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material and the weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be different from each other. Experimentally, when positive active materials having different operating voltage ranges are mixed, due to the difference in the operating voltages of the two materials, a sharp voltage drop occurs in the transient region, resulting in an increase in resistance, and therefore there may be a risk of reduced power of the secondary battery. In this regard, the content ratio (e.g., weight ratio) of the first and second surfaces of the positive current collector is defined differently in the present invention, so that a voltage drop interval can be generated in different SOC intervals, and the entire voltage curve of the secondary battery shows the voltage average of different surfaces of the positive current collector, so that the resistance increase amplitude during the voltage drop can be improved, and therefore the effect of improving the performance of the secondary battery can be provided.

[0047] According to the embodiment, the first positive electrode active material and the second positive electrode active material may form structures different from each other. For example, the first positive electrode active material may include a lithium transition metal oxide of a layered structure, and the second positive electrode active material may include a lithium phosphate compound of an olivine structure. In the lithium transition metal oxide of a layered structure, the constituent elements of the positive electrode active material are located in the layered structure, and lithium ions can be stored between the lattice layers when the secondary battery is charged. For example, the lithium transition metal oxide of the layered structure may be a ternary transition metal oxide. However, the present invention is not necessarily limited thereto. In another embodiment, in addition to the above examples, the positive electrode active material may further include additional active materials. For example, the positive electrode active material may also be a transition metal oxide containing four or more elements.

[0048] In addition, the olivine-structured lithium phosphate compound has a hexahedral shape, and is characterized by having a higher structural stability than a layered structure. For example, the olivine-structured lithium phosphate compound may be lithium iron phosphate (LFP).

[0049] According to the embodiment, the first positive active material may include one or more selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium cobalt-nickel oxide, lithium cobalt-manganese oxide, lithium manganese-nickel oxide, and lithium cobalt-nickel-manganese oxide having a layered structure.

[0050] According to the embodiment, the layered structured lithium transition metal oxide may be represented by Chemical Formula 1 below.

[0051] [Chemical formula 1]

[0052] Li 1+a Ni x Mn y Co 1-x-y O2

[0053] In the chemical formula 1, 0≤a<0.5, 0 <x<1,0<y<0.5。

[0054] For example, the oxide represented by Chemical Formula 1 may be LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0055] According to the embodiment, the second positive active material may be a Fe-based olivine-structured lithium oxide in which a portion of Fe is substituted with other elements.

[0056] According to the embodiment, the olivine-structured lithium phosphate compound may be represented by Chemical Formula 2 below.

[0057] [Chemical formula 2]

[0058] LiMPO4

[0059] In the chemical formula 2, M is one or more elements selected from Fe, Mn, Ni, Co and V.

[0060] For example, the compound represented by Chemical Formula 2 may be LiFePO 4 .

[0061] According to the embodiment, the first positive active material may include a spinel structured lithium nickel manganese-based oxide, and the second positive active material may include an olivine structured lithium iron phosphate compound. The spinel structured lithium nickel manganese-based oxide has a three-dimensional lattice structure and thus has excellent stability.

[0062] According to the embodiment, the spinel-structured lithium nickel manganese-based oxide may be represented by Chemical Formula 3 below.

[0063] [Chemical formula 3]

[0064] Li x Ni y Mn 2-y O4

[0065] In the chemical formula 3, 0.95≤x<1.05, 0.30≤y≤1.00.

[0066] For example, the oxide represented by Chemical Formula 3 may be LiNi 0.5 Mn 1.5 O4.

[0067] As described above, a positive electrode active material having a low operating voltage range and a positive electrode active material having a relatively high operating voltage range are mixed, and at the same time, the content ratios (for example, weight ratios) of the positive electrode active materials having different operating voltage ranges on different sides (for example, the first side and the second side) of the positive electrode collector are defined differently, so that the sharp drop in power due to the increase in resistance can be compensated in the low SOC range, and the entire voltage curve of the secondary battery shows the average value of the voltages of the different sides of the positive electrode collector, so that the increase in resistance during voltage drop can be improved, thereby providing a technical effect of improving the performance of the secondary battery.

[0068] According to the embodiment, the first positive electrode material and the second positive electrode material may each further include a positive electrode active material different from the first positive electrode active material and the second positive electrode active material. The positive electrode active material different from the first positive electrode active material and the second positive electrode active material may include one or more selected from a lithium transition metal oxide of a layered structure, a lithium nickel manganese-based oxide of a spinel structure, and a lithium phosphate compound of an olivine structure. The operating voltage range of the secondary battery is increased or decreased by the added positive electrode active material, so that the final operating voltage range can be adjusted to the desired level.

[0069] According to the embodiment, the content ratio (for example, weight ratio) of the first positive electrode active material to the second positive electrode active material contained in each of the first positive electrode material and the second positive electrode material can satisfy a numerical range, thereby achieving all the technical effects of improving the stability of the lithium secondary battery and improving the power in the low SOC range.

[0070] For example, the content ratio of the first positive electrode active material to the second positive electrode active material contained in each of the first positive electrode material and the second positive electrode material may be 9: 1 to 1: 9. According to the embodiment, the content ratio may be based on the weight of the first positive electrode active material to the second positive electrode active material contained in each of the first positive electrode material and the second positive electrode material.

[0071] According to the embodiment, when the weight ratio of the first positive active material to the second positive active material in the first positive electrode material is 5:5, the weight ratio of the first positive active material to the second positive active material in the second positive electrode material may range from 9:1 to 1:9, excluding 5:5.

[0072] According to the embodiment, when the weight ratio of the first positive active material to the second positive active material in the first positive electrode material is 7:3, the weight ratio of the first positive active material to the second positive active material in the second positive electrode material may range from 9:1 to 1:9 excluding 7:3.

[0073] According to the embodiment, a weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material may be 1:9 to 6:4, and a weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be 1:9 to 6:4.

[0074] According to the embodiment, a weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material may be 1:9 to 5:5, and a weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be 2:8 to 6:4.

[0075] According to the embodiment, a weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material may be 1:9 to 4:6, and a weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be 3:7 to 6:4.

[0076] According to the embodiment, a weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material may be 1:9 to 3:7, and a weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be 4:6 to 6:4.

[0077] According to the embodiment, a weight ratio of the first positive active material to the second positive active material contained in the first positive electrode material may be 1:9 to 2:8, and a weight ratio of the first positive active material to the second positive active material contained in the second positive electrode material may be 5:5 to 6:4.

[0078] According to the embodiment, a weight ratio of the first positive electrode active material to the second positive electrode active material contained in the first positive electrode material may be 2:8, and a weight ratio of the first positive electrode active material to the second positive electrode active material contained in the second positive electrode material may be 6:4.

[0079] According to the embodiment, based on the total weight of the first positive electrode material, the content of the first positive electrode active material in the first positive electrode material may be 10 wt % or more, or may be 60 wt % or less, 50 wt % or less, 40 wt % or less, 30 wt % or less, or 20 wt % or less. The content of the first positive electrode active material included may be within the range formed by appropriately selecting the above upper and lower limits.

[0080] According to the embodiment, based on the total weight of the first positive electrode material, the content of the second positive electrode active material in the first positive electrode material can be 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, or 90% by weight or less. The content of the second positive electrode active material included can be within the range formed by appropriately selecting the above upper and lower limits.

[0081] According to the embodiment, based on the total weight of the second positive electrode material, the content of the first positive electrode active material in the second positive electrode material can be 10% by weight or more, 20% by weight or more, 30% by weight or more, 40% by weight or more, or 60% by weight or less. The content of the first positive electrode active material included can be within the range formed by appropriately selecting the above upper and lower limits.

[0082] According to the embodiment, based on the total weight of the second positive electrode material, the content of the second positive electrode active material in the second positive electrode material may be 40 wt % or more, or may be 90 wt % or less, 80 wt % or less, 70 wt % or less, 60 wt % or less, or 50 wt % or less. The content of the second positive electrode active material included may be within the range formed by appropriately selecting the above upper and lower limits.

[0083] In an implementation that satisfies the above range, high capacity and high energy of the secondary battery can be achieved, and voltage drop intervals can be generated in different SOC intervals, thereby improving the resistance increase during voltage drop, thereby providing an effect of improving the performance of the secondary battery.

[0084] According to the embodiment, the first positive electrode material and the second positive electrode material may each further include a conductive material and a binder. The binder can improve mechanical stability by mediating the combination between the positive electrode current collector and the positive electrode material. For example, the binder can be an organic binder or a water-based binder. For example, the organic binder can be any one of poly (vinylidene fluoride -co-hexafluoropropylene) copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile (Polyacrylonitrile) and polymethyl methacrylate (Polymethylmethacrylate), and the water-based binder can be styrene-butadiene rubber (SBR), but is not limited thereto.

[0085] The conductive material can improve the conductivity of the secondary battery. The conductive material can include a metal-based substance. The conductive material can include a conventional carbon-based conductive material. For example, the conductive material can include any one of graphite, carbon black, graphene and carbon nanotubes. According to an embodiment, the conductive material can include carbon nanotubes.

[0086] A secondary battery according to an embodiment of the present invention may include a positive electrode that may improve the performance of the secondary battery as described above, and may further include a negative electrode and a separator disposed between the positive electrode and the negative electrode.

[0087] According to the embodiment, the secondary battery can be manufactured by a known method. For example, it can be manufactured by placing a porous separator between a positive electrode and a negative electrode and adding an electrolyte.

[0088] According to the embodiment, the positive electrode is the same as the positive electrode as described above, and the negative electrode may include a negative electrode current collector and a negative electrode material. The negative electrode current collector may include any one of stainless steel, nickel (Ni), aluminum (Al), titanium (Ti), copper (Cu) and their alloys, and may be provided in various forms such as films, sheets, foils, etc. The negative electrode material may include a negative electrode active material. The negative electrode active material may be a material that can be embedded and deintercalated with lithium ions. For example, the negative electrode active material may be any one of carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, lithium alloys, silicon (Si) and tin (Sn). According to the embodiment, the negative electrode active material may be natural graphite or artificial graphite, but is not limited thereto. In addition, according to the embodiment, the negative electrode material may further include a binder and a conductive material, and the types of applicable binders and conductive materials are the same as those described in the above-mentioned positive electrode materials.

[0089] According to the embodiment, the electrolyte can be a non-aqueous electrolyte. The electrolyte can include a lithium salt and an organic solvent. For example, the organic solvent can include one or more selected from propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), vinylene carbonate (VC), dimethyl sulfoxide (Dimethyl sulfoxide), acetonitrile (Acetonitrile), dimethoxyethane (Dimethoxyethane), diethoxyethane (Diethoxyethane), cyclopentane (Sulfolane), gamma-butyrolactone (Gamma-butyrolactone), propylene sulfide (Propylene sulfide) and tetrahydrofuran (Tetrahydrofuran).

[0090] According to the embodiment, the separator may be provided between the positive electrode and the negative electrode. The separator may be provided to prevent a short circuit between the positive electrode and the negative electrode and to generate a flow of ions.

[0091] For example, the separator may include a porous polymer film or a porous nonwoven fabric. The porous polymer film may be composed of a single layer or multiple layers of polyolefin-based polymers including ethylene (Ethylene) polymers, propylene (Propylene) polymers, ethylene / butylene (Ethylene / Butene) copolymers, ethylene / hexene (Ethylene / Hexene) copolymers, and ethylene / methacrylate (Ethylene / Methacrylate) copolymers. The porous nonwoven fabric may include high melting point glass fiber, polyethylene terephthalate (Polyethylene terephthalate) fiber. However, it is not limited thereto, and according to the embodiment, the separator may be a high heat-resistant separator (ceramic coated separator (Ceramic coated separator)) including ceramic (Ceramic).

[0092] According to the embodiment, a plurality of secondary batteries are provided, which may be formed by winding, lamination, folding, or zigzag stacking in a housing. In addition, a module may include a secondary battery as a single cell, and a device may include the module as a power source.

[0093] The present invention will be further described below based on examples and comparative examples. However, the following examples and comparative examples are merely illustrative examples for describing the embodiments of the present invention in more detail, and the present invention is not limited to the following examples and comparative examples.

[0094] <Manufacturing Example>-Manufacturing of Positive Electrode

[0095] Production Example 1

[0096] 97 wt % of the first positive electrode active material and the mixture of the second positive electrode active material (20 wt % of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 80 wt% LiFePO4), 1 wt% carbon nanotubes and 2 wt% polyvinylidene fluoride are mixed with methyl pyrrolidone (N-methyl-2-pyrrolidone) to produce the first positive electrode material. While producing the first positive electrode material, 97 wt% of the first positive electrode active material and the mixture of the second positive electrode active material (60 wt% LiNi 0.8 Co 0.1 Mn 0.1 O2 and 40 wt% LiFePO4), 1 wt% carbon nanotubes and 2 wt% polyvinylidene fluoride were mixed with methylpyrrolidone (N-methyl-2-pyrrolidone) to produce a second positive electrode material.

[0097] The first positive electrode material and the second positive electrode material were coated on different surfaces of an aluminum current collector having a thickness of 12 μm and then dried. The dried first positive electrode material and the second positive electrode material were rolled to manufacture a positive electrode.

[0098] Production Example 2

[0099] The positive electrode was manufactured by the same process as in Manufacturing Example 1, except that 10 wt % of LiNi 0.8 Co 0.1 Mn 0.1 O2 and 90 wt% LiFePO4 were used as the first positive electrode material instead of the mixture of 20 wt% LiNi in Manufacturing Example 1. 0.8 Co 0.1 Mn 0.1 O2 and 80 wt% LiFePO4 as the first positive electrode material, and mixed with 50 wt% LiNi 0.8 Co 0.1 Mn 0.1 O2 and 50 wt% LiFePO4 were used as the second positive electrode material instead of the mixed 60 wt% LiNi 0.8 Co 0.1 Mn 0.1 O2 and 40 wt% LiFePO4 were used as the second positive electrode material.

[0100] Production Example 3

[0101] The positive electrode was manufactured by the same process as in Manufacturing Example 1, except that, instead of coating the first positive electrode material and the second positive electrode material on different surfaces of an aluminum current collector with a thickness of 12 μm and then drying them in Manufacturing Example 1, the first positive electrode material was coated on different surfaces of an aluminum current collector with a thickness of 12 μm and then dried, and the second positive electrode material was not manufactured.

[0102] Production Example 4

[0103] The positive electrode was manufactured by the same process as in Manufacturing Example 2, except that, instead of coating the first positive electrode material and the second positive electrode material on different surfaces of an aluminum current collector with a thickness of 12 μm and then drying them in Manufacturing Example 2, the first positive electrode material was coated on different surfaces of an aluminum current collector with a thickness of 12 μm and then dried, and the second positive electrode material was not manufactured.

[0104] <Example> - Manufacturing of secondary battery

[0105] Example 1

[0106] Negative electrode manufacturing

[0107] 25 wt% natural graphite, 70 wt% artificial graphite, 4 wt% styrene butadiene rubber and 1 wt% carbon nanotubes were mixed with distilled water to produce a negative electrode material. The negative electrode material was coated on a copper current collector having a thickness of 8 μm and then dried. The dried negative electrode material was rolled to produce a negative electrode.

[0108] Manufacturing of secondary batteries

[0109] A polyethylene separator having a thickness of 13 μm was placed between the negative electrode prepared as described above and the positive electrode of Manufacturing Example 1. Then, an electrolyte solution in which 1M LiPF6 was dissolved in a solvent mixed with 25 volume % of ethylene carbonate and 75 volume % of diethyl carbonate was injected to prepare a secondary battery.

[0110] Example 2

[0111] A secondary battery was manufactured by the same process as in Example 1, except that the positive electrode of Manufacturing Example 2 was used instead of the positive electrode of Manufacturing Example 1 in Example 1.

[0112] Comparative Example 1

[0113] A secondary battery was manufactured by the same process as in Example 1, except that the positive electrode of Manufacturing Example 3 was used instead of the positive electrode of Manufacturing Example 1 in Example 1.

[0114] Comparative Example 2

[0115] A secondary battery was manufactured by the same process as in Example 1, except that the positive electrode of Manufacturing Example 4 was used instead of the positive electrode of Manufacturing Example 1 in Example 1.

[0116] <Experimental example>

[0117] Experimental Example 1 - Measurement of voltage drop according to SOC

[0118] The voltage drop according to the SOC was measured for the secondary batteries manufactured in Example 1 and Comparative Example 1 in the voltage range of 4.5 to 2.5 V based on the positive electrode potential. Figure 1 The measurement results of Example 1 are shown in FIG. Figure 2 The measurement results of Comparative Example 1 are shown in FIG.

[0119] Experimental Example 2 - Measurement of voltage drop according to charging capacity

[0120] The secondary batteries manufactured in Example 1 and Comparative Example 1 were charged under constant current (CC) conditions in a voltage range of 4.5 to 2.5 V based on the positive electrode potential, and a voltage drop according to the charge capacity was measured. Figure 3 The measurement results of Example 1 are shown in FIG. Figure 4 The measurement results of Comparative Example 1 are shown in FIG.

[0121] exist Figure 3 and Figure 4 In FIG. 1 , the dotted curve represents the intensity of the voltage drop of the secondary battery when charged under a 1 / 3C constant current condition, and the solid curve represents the intensity of the voltage drop of the secondary battery when charged under a 2.0C constant current condition.

[0122] Analysis of experimental examples

[0123] See also Figures 1 to 4 It can be confirmed that, in the case of Example 1, the voltage drop interval is divided into two parts, the intensity of the voltage drop becomes 1 / 2, and the slope of the voltage drop becomes gentler, compared with Comparative Example 1. 0.8 Co 0.1 Mn 0.1 O2 and LiFePO4 are used as positive electrode active materials, but as in Example 1, by changing the LiNi 0.8 Co 0.1 Mn 0.1The content ratio (e.g., weight ratio) of O2 and LiFePO4 can divide the interval where the voltage drop occurs. Therefore, the entire voltage profile shows the average value of the voltage on both sides of the positive electrode collector, thereby improving the resistance increase during the voltage drop, and thus it can be confirmed that the performance of the secondary battery can be improved.

[0124] On the other hand, even if LiNi is mixed as in Comparative Example 1 0.8 Co 0.1 Mn 0.1 O2 and LiFePO4 are used as positive electrode active materials. If LiNi 0.8 Co 0.1 Mn 0.1 When the content ratio (eg, weight ratio) of O2 and LiFePO4 is the same, a sharp voltage drop occurs in the range of about SOC 30% or the range of about 60% to about 70% of the charge capacity, and the resistance increases, thus confirming the problem of reduced performance of the secondary battery.

Claims

1. A positive electrode, comprising: A positive electrode current collector, the positive electrode current collector comprising a first surface and a second surface; A first positive electrode material, wherein the first positive electrode material is formed on the first surface of the positive electrode current collector; as well as a second positive electrode material, wherein the second positive electrode material is formed on the second surface of the positive electrode current collector, The first positive electrode material and the second positive electrode material each contain a first positive electrode active material and a second positive electrode active material. The first positive electrode active material and the second positive electrode active material have different operating voltage ranges from each other. A weight ratio of the first positive electrode active material to the second positive electrode active material contained in the first positive electrode material and a weight ratio of the first positive electrode active material to the second positive electrode active material contained in the second positive electrode material are different from each other.

2. The positive electrode according to claim 1, wherein The first positive electrode active material includes a layered lithium transition metal oxide, and the second positive electrode active material includes an olivine-structured lithium phosphate compound.

3. The positive electrode according to claim 2, wherein The layered lithium transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li 1+a Ni x Mr y Co 1-x-y O2 In the chemical formula 1, 0≤a<0.5, 0 <x<1,0<y<0.5。 4. The positive electrode according to claim 3, wherein The oxide represented by the chemical formula 1 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

5. The positive electrode according to claim 2, wherein The olivine-structured lithium phosphate compound is represented by the following chemical formula 2: [Chemical formula 2] LiMPO4 In the chemical formula 2, M is one or more elements selected from Fe, Mn, Ni, Co and V.

6. The positive electrode according to claim 5, wherein The compound represented by the chemical formula 2 is LiFePO 4 .

7. The positive electrode according to claim 1, wherein The first positive electrode active material includes a lithium nickel manganese-based oxide with a spinel structure, and the second positive electrode active material includes a lithium iron phosphate compound with an olivine structure.

8. The positive electrode according to claim 7, wherein The spinel-structured lithium nickel manganese-based oxide is represented by the following chemical formula 3: [Chemical formula 3] Li x Ni y Mr 2-y O4 In the chemical formula 3, 0.95≤x<1.05, 0.30≤y≤1.

00.

9. The positive electrode according to claim 8, wherein The oxide represented by the chemical formula 3 is LiNi 0.5 Mn 1.5 O4.

10. The positive electrode according to claim 1, wherein Each of the first positive electrode material and the second positive electrode material further includes a positive electrode active material different from the first positive electrode active material and the second positive electrode active material.

11. The positive electrode according to claim 1, wherein A weight ratio of the first positive electrode active material to the second positive electrode active material included in the first positive electrode material and the second positive electrode material is 9:1 to 1:

9.

12. The positive electrode according to claim 1, wherein The weight ratio of the first positive electrode active material to the second positive electrode active material in the first positive electrode material is 1:9 to 6:4, and the weight ratio of the first positive electrode active material to the second positive electrode active material in the second positive electrode material is 1:9 to 6:

4.

13. The positive electrode according to claim 1, wherein The first positive electrode material and the second positive electrode material each further include a conductive material and a binder.

14. A secondary battery comprising: The positive electrode according to claim 1; negative electrode; as well as A separator is disposed between the positive electrode and the negative electrode.

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