Cathode active material and method for manufacturing same

Abstract

A method for manufacturing a cathode active material according to the present invention may comprise the steps of: preparing a preliminary cathode active material precursor containing nickel and manganese; preparing a doping source containing cobalt; providing the preliminary precursor into the doping source, followed by refluxing reaction, thereby preparing a cathode active material precursor; and mixing the cathode active material precursor and a lithium precursor, followed by firing, thereby manufacturing the cathode active material.

Description

Cathode active material and method for producing the same

[0001] The present invention relates to a cathode active material and a method for producing the same, and more particularly, to a cathode active material comprising lithium metal, nickel metal, manganese metal, and a dopant, and a method for producing the same.

[0002] A cathode active material refers to an active material that exists in the cathode material of a secondary battery and electrochemically produces electrical energy.

[0003] The positive electrode active material present in the positive electrode initially contains lithium ions and provides lithium ions to the negative electrode during the charging process of the secondary battery.

[0004] Accordingly, cathode active materials are being used in various industries, such as lithium metal batteries, lithium air batteries, and lithium ion polymer batteries.

[0005] As the field of application increases, various cathode active materials are being studied. For example, Korean Patent Registration No. 10-0815583 discloses a method for producing a cathode active material for a lithium secondary battery, the method comprising the steps of: mixing a first metal including nickel, cobalt, and manganese, and an aqueous metal salt solution optionally containing a second metal, a chelating agent, and an aqueous basic solution to produce a coprecipitated compound; drying or heat-treating the coprecipitated compound to produce an active material precursor; and mixing the active material precursor and a lithium salt and calcining the mixture to produce a lithium composite metal oxide, wherein the lithium composite metal oxide is characterized in that it has a layered structure.

[0006] The technical problem to be solved by the present invention is to provide a cathode active material having improved rate characteristics under high-speed charge / discharge conditions.

[0007] Another technical problem to be solved by the present invention is to provide a cathode active material having improved stability for charge / discharge cycles under high-speed charge / discharge conditions.

[0008] Another technical problem that the present invention seeks to solve is to provide a method for manufacturing a cathode active material with reduced manufacturing process costs.

[0009] Another technical problem that the present invention seeks to solve is to provide a method for manufacturing a cathode active material with a shortened manufacturing time.

[0010] Another technical problem that the present invention seeks to solve is to provide a method for manufacturing a cathode active material that is easy to mass-produce.

[0011] The technical problems to be solved by the present invention are not limited to those described above.

[0012] To solve the above technical problem, the present invention provides a method for manufacturing a cathode active material.

[0013] According to one embodiment, the method for producing the positive electrode active material may include a step of preparing a preliminary positive electrode active material precursor including nickel and manganese, a step of preparing a doping source including cobalt, a step of providing the preliminary positive electrode active material precursor to the doping source and subjecting it to a refluxing reaction to produce the positive electrode active material precursor, and a step of mixing and firing the positive electrode active material precursor and a lithium precursor to produce the positive electrode active material.

[0014] According to one embodiment, the step of manufacturing the positive electrode active material precursor may include controlling the crystal structure of the surface and the crystal structure of the internal primary particles of the positive electrode active material differently.

[0015] According to one embodiment, in the step of manufacturing the positive electrode active material precursor, the refluxing reaction temperature may be controlled to 84°C or lower, and the refluxing reaction time may be controlled to 8 hours or lower.

[0016] According to one embodiment, the preliminary cathode active material may include a transition metal hydroxide containing nickel and manganese, and the doping source may include a cobalt nitrate solution.

[0017] According to one embodiment, in the method for producing the positive electrode active material, which comprises doping cobalt on the surface of the transition metal hydroxide containing nickel and manganese to produce the positive electrode active material precursor and then firing it together with the lithium precursor, the positive electrode active material precursor may be subjected to a first heat treatment at a first temperature, the positive electrode active material precursor subjected to the first heat treatment may be subjected to a second heat treatment at a second temperature higher than the first temperature, and depending on the second temperature, the crystal structure of the surface and the interior of the primary particle of the positive electrode active material may be controlled differently or identically.

[0018] According to one embodiment, the second temperature may include being controlled to be 700°C or more and less than 800°C, the internal crystal structure of the primary particles of the positive electrode active material may include being controlled to be a layered structure, and the surface crystal structure may include being controlled to be a spinel structure by cobalt.

[0019] According to one embodiment, the rate characteristics and stability for charge / discharge cycles under 5C conditions may be improved by different crystal structures of the interior and surface of the primary particles of the positive electrode active material.

[0020] In order to solve the above technical problem, the present invention provides a cathode active material manufactured by the above-described manufacturing method.

[0021] According to one embodiment, the cathode active material doped with cobalt on the surface of a composite metal oxide including lithium, nickel, and manganese may include a primary particle of the cathode active material having different crystal structures at the interior and the surface, the interior of the primary particle may include a layered structure, and the surface of the primary particle may include a spinel structure.

[0022] According to one embodiment, when performing a charge / discharge cycle on the positive electrode active material, the crystal structure of the surface of the positive electrode active material may be converted into a rock salt structure.

[0023] According to one embodiment, when the positive electrode active material is subjected to 100 charge / discharge cycles under 5C conditions, the spinel structure present at a distance of 9.4 nm or less from the surface of the positive electrode active material may be converted to the rock salt structure.

[0024] A method for producing a cathode active material according to the present invention may include a step of preparing a preliminary cathode active material precursor containing nickel and manganese, a step of preparing a doping source containing cobalt, a step of providing the preliminary cathode active material precursor to the doping source and subjecting it to a refluxing reaction to produce a cathode active material precursor, and a step of mixing and firing the cathode active material precursor and a lithium precursor to produce the cathode active material.

[0025] In the step of manufacturing the positive electrode active material precursor, cobalt is doped on the surface of the preliminary positive electrode active material precursor, and in the step of manufacturing the positive electrode active material, the second temperature at which the positive electrode active material precursor and the lithium precursor are subjected to a second heat treatment is controlled to be 700°C or more and less than 800°C, so that the positive electrode active material having a spinel structure on the surface of the primary particle and a layered structure on the inside of the primary particle can be provided.

[0026] The cathode active material manufactured by the above-described manufacturing method may be one in which cobalt is doped along the surface of a composite metal oxide including lithium, nickel, and manganese.

[0027] And, as described above, the interior of the primary particle of the positive electrode active material may have a layered structure, and the surface of the primary particle of the positive electrode active material may have a spinel structure.

[0028] Accordingly, when a lithium secondary battery to which the positive electrode active material is applied is subjected to a charge / discharge cycle under high-speed charge / discharge conditions (e.g., 5C), the discharge capacity and energy density of the lithium secondary battery are improved due to the layered structure inside the positive electrode active material, and the spinel structure on the surface of the positive electrode active material not only acts as a passivation layer, but also has a three-dimensional channel shape for lithium ion diffusion, so that the rate characteristics and long-term stability for the charge / discharge cycle can be significantly improved.

[0029] Figure 1 is a flowchart illustrating a method for manufacturing a cathode active material according to an embodiment of the present invention.

[0030] FIG. 2 is a drawing for explaining a preliminary cathode active material and a doping source according to an embodiment of the present invention.

[0031] FIG. 3 is a drawing for explaining a method for manufacturing a positive electrode active material precursor according to an embodiment of the present invention.

[0032] FIG. 4 is a drawing for explaining a method for manufacturing a cathode active material according to an embodiment of the present invention.

[0033] FIG. 5 is a drawing for explaining a cathode active material according to an embodiment of the present invention.

[0034] FIGS. 6 to 8 are photographs and graphs for comparing the surface and interior of the positive electrode active material according to Experimental Example 1, Comparative Example 1, and Experimental Example 2 of the present invention.

[0035] Figure 9 is a graph for comparing the rate characteristics of half cells according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0036] FIG. 10 is a graph for comparing the stability of charge / discharge cycles of half cells according to Experimental Example 1, Comparative Example 2, and Comparative Example 2 of the present invention.

[0037] Figure 11 is a graph for comparing the stability of charge / discharge cycles of full cells according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0038] Figure 12 is a graph for comparing the stability of the crystal structure during the charge / discharge process of the half cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0039] FIG. 13 and FIG. 14 are TEM photographs for comparing the crystal structure of the positive electrode active material after charge / discharge of the half-cell according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0040] FIG. 15 and FIG. 16 are graphs for comparing resistance values ​​for charge / discharge after performing charge / discharge of a half cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0041] Figures 17 and 18 are graphs for comparing the amount of organic and inorganic layers on the surface of a positive electrode active material after charging / discharging of a half-cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0042] FIG. 19 and FIG. 20 are TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) analysis results for the positive and negative electrodes after charge / discharge of the full cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0043] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical concept of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art.

[0044] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. In addition, in the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents.

[0045] Also, although terms such as first, second, and third have been used to describe various components in various embodiments of this specification, these components should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiments. Also, the term "and / or" has been used herein to mean including at least one of the components listed before and after.

[0046] In the specification, singular expressions include plural expressions unless the context clearly dictates otherwise. In addition, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, component, or combination thereof described in the specification, and should not be construed as excluding the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In addition, the term "connection" is used in the present specification to mean both indirectly connecting multiple components and directly connecting them.

[0047] In addition, when describing the present invention below, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0048]

[0049] FIG. 1 is a flowchart for explaining a method for manufacturing a cathode active material according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a preliminary cathode active material and a doping source according to an embodiment of the present invention, FIG. 3 is a diagram for explaining a method for manufacturing a cathode active material precursor according to an embodiment of the present invention, FIG. 4 is a diagram for explaining a method for manufacturing a cathode active material according to an embodiment of the present invention, and FIG. 5 is a diagram for explaining a cathode active material according to an embodiment of the present invention.

[0050] Referring to FIGS. 1 and 2, a preliminary cathode active material precursor (110) containing nickel and manganese is prepared (S100), and a doping source (120) containing cobalt is prepared (S120).

[0051] The preliminary cathode active material precursor (110) may be a transition metal hydroxide containing nickel and manganese. For example, the preliminary cathode active material precursor (110) may be manufactured by a method of co-precipitation reaction of a nickel source and a manganese source. For example, the chemical composition of the preliminary cathode active material precursor (110) may be Ni 0.94 Mn 0.06 It could be (OH)2.

[0052] And, the doping source (120) may be, for example, a cobalt nitrate solution. For example, the doping source (120) may be Co(NO3). 2ㆍ It could be 6H2O.

[0053] Referring to FIGS. 1 and 3, the preliminary cathode active material precursor (110) is provided to the doping source (120) and a refluxing reaction is performed to manufacture the cathode active material precursor (100) (S300).

[0054] Specifically, the doping source (120) in the reactor may be stirred while being maintained at a specific temperature. For example, the temperature may be maintained at 84°C or lower. For example, the temperature may be a refluxing reaction temperature. For example, the stirring speed may be controlled at 200 rpm.

[0055] Thereafter, the preliminary cathode active material precursor (110) is provided to the reactor, and the doping source (120) and the preliminary cathode active material precursor (110) can be subjected to a refluxing reaction for a specific period of time. Accordingly, nickel on the surface of the preliminary cathode active material precursor (110) can be replaced with cobalt in the doping source (120). In other words, cobalt can be doped in the doping source (120) along the surface of the preliminary cathode active material precursor (110). Accordingly, the cathode active material precursor (100) doped with cobalt on the surface can be easily manufactured. For example, the refluxing reaction temperature can be maintained at 84° C. or lower. For example, the refluxing reaction time can be controlled to 8 hours or lower. For example, the chemical composition of the cathode active material precursor (100) is, the chemical composition is, Ni 0.88 Co 0.06 Mn 0.06 It could be (OH)2.

[0056] Accordingly, in the step of manufacturing the positive electrode active material (200) described later, the crystal structure of the surface and the interior of the primary particle of the positive electrode active material (200) described later can be controlled differently by cobalt doped on the surface of the positive electrode active material precursor (100).

[0057] In contrast, if cobalt is not doped on the surface of the positive electrode active material precursor (100), even if the positive electrode active material precursor (100) and the lithium precursor (210) described below are mixed and fired under the same conditions in the step of manufacturing the positive electrode active material (200) described below, the crystal structure of the surface and the interior of the primary particles of the positive electrode active material (200) described below cannot be controlled differently. In other words, the crystal structure of the surface and the interior of the primary particles of the positive electrode active material (200) described below can be controlled identically.

[0058] In addition, compared to a conventional manufacturing process of doping a doping metal into a cathode active material precursor by a solution process before calcining the cathode active material precursor and the lithium precursor, the heat treatment temperature (e.g., 84°C or less) is reduced and the heat treatment time (e.g., 8 hours or less) is significantly shortened, so not only is the manufacturing process time for the doping process shortened, but the manufacturing process cost can also be reduced.

[0059] Referring to FIG. 1 and FIG. 4, the positive electrode active material precursor (100) and the lithium precursor (210) described above are mixed and calcined to produce the positive electrode active material (200) described above (S400).

[0060] Specifically, the positive electrode active material precursor (100) and the lithium precursor (210) can be physically mixed. For example, the lithium precursor (210) may be LiOH ㆍ It may be H2O. For example, the positive electrode active material precursor (100) and the lithium precursor (210) may be mixed using a mixing device so that the molar ratio of the transition metal of the positive electrode active material precursor (100) and the molar ratio of the lithium of the lithium precursor (210) are 1:1.03.

[0061] Thereafter, a mixture of the positive electrode active material precursor (100) and the lithium precursor (210) may be provided to a reactor for heat treatment, subjected to a first heat treatment at a first temperature, and then subjected to a second heat treatment at a second temperature higher than the first temperature. For example, the first temperature may be controlled to 500°C. For example, the first heat treatment time may be 5 hours. For example, the second heat treatment time may be 10 hours. At this time, depending on the second temperature, the crystal structure of the surface and the interior of the primary particles of the positive electrode active material (200) may be controlled differently or identically.

[0062] According to an example, the second temperature can be controlled to be 700°C or more and less than 800°C. Accordingly, the surface of the primary particle of the positive electrode active material (200) may have a spinel structure, and the interior of the primary particle of the positive electrode active material (200) may have a layered structure. Due to this, the rate characteristics of the lithium secondary battery and the long-term stability for the charge / discharge cycle can be improved under high-speed charge / discharge rate (e.g., 5C) conditions.

[0063] In contrast, when the second temperature is controlled to be 800°C or higher, the surface and interior of the primary particles of the positive electrode active material (200) may have a layered structure. As a result, under high-speed charge / discharge conditions (e.g., 5C), the rate characteristics of the lithium secondary battery and long-term stability for charge / discharge cycles may deteriorate.

[0064] In addition, when the second temperature is controlled to be less than 700°C, the crystallinity of the positive electrode active material (200) and the ordering of the layered structure may be significantly reduced. As a result, under high-speed charge / discharge conditions (e.g., 5C), the initial capacity, rate characteristics, and long-term stability for charge / discharge cycles of the lithium secondary battery may be degraded. In this case, for example, the second temperature may be 650°C.

[0065] Therefore, in the method for manufacturing the positive electrode active material (200) according to the embodiment of the present application, the second temperature at which the positive electrode active material precursor (100) and the lithium precursor (210) are subjected to a second heat treatment may be controlled to be 700°C or more and less than 800°C. Accordingly, the surface of the primary particle of the positive electrode active material (200) may have a spinel structure, and the interior of the primary particle of the positive electrode active material (200) may have a layered structure. As a result, a lithium secondary battery with improved rate characteristics and long-term stability for charge / discharge cycles under high-speed charge / discharge conditions (e.g., 5C) may be provided.

[0066] In general, in the step of manufacturing the positive electrode active material precursor (100), cobalt is doped on the surface of the preliminary positive electrode active material precursor (110), and in the step of manufacturing the positive electrode active material (200), the second temperature at which the positive electrode active material precursor (100) and the lithium precursor (210) are subjected to a second heat treatment must be controlled to be 700°C or more and less than 800°C, so that the surface of the primary particle of the positive electrode active material (200) may have a spinel structure, and the interior of the primary particle of the positive electrode active material (200) may have a layered structure.

[0067] In conclusion, the method for manufacturing the cathode active material (200) according to an embodiment of the present application may include a step of preparing the preliminary cathode active material precursor (110) containing nickel and manganese, a step of preparing the doping source (120) containing cobalt, a step of providing the preliminary cathode active material precursor (110) to the doping source and performing a refluxing reaction to manufacture the cathode active material precursor (100), and a step of mixing and firing the cathode active material precursor (100) and the lithium precursor (210) to manufacture the cathode active material (200).

[0068] In the step of manufacturing the positive electrode active material precursor (100), cobalt is doped on the surface of the preliminary positive electrode active material precursor (110), and in the step of manufacturing the positive electrode active material (200), the second temperature at which the positive electrode active material precursor (100) and the lithium precursor (210) are subjected to a secondary heat treatment is controlled to be 700°C or more and less than 800°C, so that the positive electrode active material (200) having a spinel structure on the surface of the primary particle and a layered structure inside the primary particle can be provided. Accordingly, under high-speed charge / discharge conditions (e.g., 5C), a lithium secondary battery having improved rate characteristics and long-term stability for charge / discharge cycles can be provided.

[0069] Referring to FIGS. 1 to 5, the positive electrode active material (200) manufactured by the above-described manufacturing method is described.

[0070] The above cathode active material (200) may include cobalt doped along the surface of a composite metal oxide including lithium, nickel, and manganese. For example, the chemical composition of the above cathode active material (200) is Li 1.03 Ni 0.88 Co 0.06 Mn 0.06 It could be O2.

[0071] And, as described above, the interior (201) of the primary particle of the positive electrode active material (200) may have a layered structure, and the surface (202) of the primary particle of the positive electrode active material (200) may have a spinel structure.

[0072] Accordingly, when a lithium secondary battery to which the positive electrode active material (200) is applied is subjected to a charge / discharge cycle under high-speed charge / discharge conditions (e.g., 5C), the discharge capacity and energy density of the lithium secondary battery are improved due to the layered structure of the interior (201) of the positive electrode active material (200), and the spinel structure of the surface (202) of the positive electrode active material not only acts as a passivation layer, but also has a three-dimensional channel shape for lithium ion diffusion, so that the rate characteristics and long-term stability for the charge / discharge cycle can be significantly improved.

[0073] For example, as described below with reference to FIGS. 13 and 14, when a lithium secondary battery to which the positive electrode active material (200) is applied is subjected to 100 charge / discharge cycles under 5C conditions, the inherent structure (inside: layered structure, outside: spinel structure) of the positive electrode active material (200) can be maintained, except that the spinel structure existing at a distance of 9.4 nm or less from the surface (202) of the positive electrode active material (200) is converted to a rock salt structure. This means that side reactions at the interface between the positive electrode active material (200) and the electrolyte are effectively suppressed during the charge / discharge cycle under 5C conditions.

[0074] In conclusion, the cathode active material (200) according to the embodiment of the present application may be one in which cobalt is doped along the surface of a composite metal oxide including lithium, nickel, and manganese.

[0075] In addition, the interior (201) of the primary particle of the positive electrode active material (200) may have a layered structure, and the surface (202) of the primary particle of the positive electrode active material (200) may have a spinel structure.

[0076] Accordingly, when a lithium secondary battery to which the positive electrode active material (200) is applied is subjected to a charge / discharge cycle under high-speed charge / discharge conditions (e.g., 5C), the discharge capacity and energy density of the lithium secondary battery are improved due to the layered structure of the interior (201) of the positive electrode active material (200), and the spinel structure of the surface (202) of the positive electrode active material not only acts as a passivation layer, but also has a three-dimensional channel shape for lithium ion diffusion, so that the rate characteristics and long-term stability for the charge / discharge cycle can be significantly improved.

[0077]

[0078] Hereinafter, specific experimental examples and characteristic evaluation results of positive electrode active materials according to embodiments of the present invention are described.

[0079]

[0080] Positive electrode active material according to Experimental Example 1

[0081] Transition metal hydroxide (Ni) as a preliminary cathode active material precursor 0.94 Mn 0.06 (OH)2, 2g) was prepared by precipitation reaction and cobalt nitrate solution (Co(NO3)) was used as a doping source. 2ㆍ 6H2O, 3M, 100mL) was prepared.

[0082] And, while stirring the doping source at 84°C and 200 rpm, the preliminary cathode active material precursor is provided and refluxed for 8 hours to form a cathode active material precursor (Ni) doped with cobalt on the surface. 0.88 Co 0.06 Mn 0.06 (OH)2) was prepared.

[0083] And, the above cathode active material precursor and lithium precursor (LiOH ㆍAfter physically mixing the transition metal and lithium in a molar ratio of 1:1.03, the mixture was provided to a reactor of a tube heat treatment furnace, and the temperature of the reactor was increased (2°C / min) from room temperature to the first temperature (500°C) and then subjected to a first heat treatment for 5 hours. Afterwards, the temperature of the reactor was increased (2°C / min) from the first temperature (500°C) to the second temperature (700°C) and then subjected to a second heat treatment for 10 hours, thereby obtaining a cathode active material (Li 1.03 Ni 0.88 Co 0.06 Mn 0.06 O2) was manufactured.

[0084]

[0085] Positive electrode active material according to Experimental Example 2

[0086] In the sintering process of the cathode active material precursor and the lithium precursor, the cathode active material (Li) according to Experimental Example 2 was prepared in the same manner as Experimental Example 1, except that the secondary heat treatment temperature was controlled to 800°C. 1.03 Ni 0.88 Co 0.06 Mn 0.06 O2) was manufactured.

[0087]

[0088] Positive electrode active material according to comparative example 1

[0089] Nickel sulfate solution (NiSO4·6H2O), cobalt sulfate solution (CoSO 4ㆍ 6H2O), manganese sulfate solution (MnSO4·6H2O), chelating agent (NH4OH), and pH adjuster (NaOH) were used to prepare a cathode active material precursor (Ni) by a co-precipitation method (nitrogen atmosphere, 45.5°C, 900 rpm, pH 11~11.1, 24 hours). 0.88 Co 0.06 Mn 0.06 (OH)2) was prepared.

[0090] Afterwards, the calcination process of the positive electrode active material precursor and the lithium precursor was performed in the same manner as the positive electrode active material according to Experimental Example 1, and the positive electrode active material (Li) according to Comparative Example 1 1.03 Ni0.88 Co 0.06 Mn 0.06 O2) was manufactured.

[0091]

[0092] Positive electrode active material according to comparative example 2

[0093] The cathode active material (Li) that is commercially available and sold as a cathode active material 1.03 Ni 0.88 Co 0.06 Mn 0.06 O2) was prepared.

[0094]

[0095] Half cell according to Experimental Example 1

[0096] Aluminum foil was prepared as a positive electrode current collector, the positive electrode active material according to Experimental Example 1 was prepared as a positive electrode active material, a mixed powder of Super-P and KS-6 was prepared as a conductive material, and PVDF (Polyvinylidene Fluoride, with NMP (N-Methyl-2-Pyrrolidone)) was prepared as a binder. Then, the positive electrode active material, the conductive material, and the binder were mixed in a weight ratio of 85:7.5:7.5 to prepare a positive electrode slurry.

[0097] And, the positive electrode slurry is applied on the positive electrode current collector at 3 mg to 4 mg / cm -2 The positive electrode was manufactured by loading.

[0098] Then, a separator (PP, polypropylene, celgard 2400 model) was placed between the positive electrode and the graphite electrode, and an electrolyte (1.13 M LiPF6 in EC / DMC / DEC (3:4:3 volume ratio)) was provided to assemble a half cell.

[0099]

[0100] Half cell according to Experimental Example 2

[0101] A half-cell according to Experimental Example 2 was assembled in the same manner as the half-cell according to Experimental Example 1, except that the positive electrode active material according to Experimental Example 2 was prepared as the positive electrode active material.

[0102]

[0103] Half cell according to comparative example 1

[0104] A half-cell according to Comparative Example 1 was assembled in the same manner as the half-cell according to Experimental Example 1, except that the positive electrode active material according to Comparative Example 1 was prepared as the positive electrode active material.

[0105]

[0106] Half cell according to comparative example 2

[0107] A half-cell according to Comparative Example 2 was assembled in the same manner as the half-cell according to Experimental Example 1, except that the positive electrode active material according to Comparative Example 2 was prepared as the positive electrode active material.

[0108]

[0109] Full cell according to Experimental Example 1

[0110] A positive electrode of a half-cell according to Experimental Example 1 was prepared, and a negative electrode was prepared in which a negative electrode slurry (containing graphite) was loaded on a negative electrode current collector (copper foil). Specifically, the N / P ratio of the negative electrode and the positive electrode was controlled to 1.2.

[0111] Then, a separator (PP, polypropylene, celgard 2400 model) was placed between the positive electrode and the negative electrode, and an electrolyte (1.0 M LiPF6in EC / EMC (3:7 volume ratio with VC (2 wt%)) was provided to assemble a full cell.

[0112]

[0113] Full cell according to comparative example 1

[0114] A full cell according to Comparative Example 1 was assembled in the same manner as the full cell according to Experimental Example 1, except that the positive electrode of the half cell according to Comparative Example 1 was prepared as the positive electrode.

[0115]

[0116] FIGS. 6 to 8 are photographs and graphs for comparing the surface and interior of the positive electrode active material according to Experimental Example 1, Comparative Example 1, and Experimental Example 2 of the present invention.

[0117] Referring to Fig. 6, the cathode active material (CE-NCM) according to Experimental Example 1 was photographed using TEM, and the distribution of transition metal elements (Ni, Co, Mn) on the surface and inside of the cathode active material (CE-NCM) according to Experimental Example 1 was subjected to mapping analysis using EDS. Referring to Fig. 7, the cathode active material (TR-NCM) according to Comparative Example 1 was photographed using TEM, and the distribution of transition metal elements (Ni, Co, Mn) on the surface and inside of the cathode active material (TR-NCM) according to Comparative Example 1 was subjected to mapping analysis using EDS. Referring to Fig. 8, the cathode active material (CE-NCM 800) according to Experimental Example 2 was photographed using TEM, and the distribution of transition metal elements (Ni, Co, Mn) on the surface and inside of the cathode active material (CE-NCM 800) according to Experimental Example 2 was subjected to mapping analysis using EDS.

[0118] As can be seen in FIGS. 6 to 8, cobalt (Co) is distributed along the surface of the positive electrode active material according to Experimental Example 1, and nickel (Ni) and manganese (Mn) are distributed relatively more than cobalt (Co) inside the positive electrode active material. In addition, it can be seen that the crystal structure of the surface of the positive electrode active material according to Experimental Example 1 is a spinel structure, and the crystal structure of the inside of the positive electrode active material is a layered structure. In other words, it can be seen that the crystal structures of the surface and the inside of the positive electrode active material according to Experimental Example 1 are different. This factor is due to the preliminary positive electrode active material precursor (Ni0.94 Mn 0.06 It is interpreted that this is due to the doping of cobalt (Co) on the surface of (OH)2).

[0119] And, it can be seen that nickel, manganese, and cobalt are uniformly distributed on the surface and inside of the positive electrode active material according to Comparative Example 1. In addition, it can be seen that the crystal structure on the surface and inside of the positive electrode active material according to Comparative Example 1 is a layered structure. This factor is interpreted to be due to the fact that cobalt is not doped on the surface of the positive electrode active material precursor according to Comparative Example 1.

[0120] In addition, it can be seen that nickel, manganese, and cobalt are uniformly distributed on the surface and inside of the positive electrode active material according to Experimental Example 2. In addition, it can be seen that the surface and inside of the positive electrode active material according to Experimental Example 2 have a layered structure. This factor is interpreted to be due to the fact that the secondary heat treatment temperature of the positive electrode active material precursor and lithium was controlled to 800°C.

[0121] Therefore, in the method for manufacturing a cathode active material according to an embodiment of the present application, it can be seen that the method of manufacturing a cathode active material precursor by doping cobalt on the surface of a preliminary cathode active material and controlling the secondary heat treatment temperature of the cathode active material precursor to be 700°C or more and less than 800°C is a method for controlling the crystal structure of the surface and the interior of the primary particle of the cathode active material differently.

[0122]

[0123] Figure 9 is a graph for comparing the rate characteristics of half cells according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0124] Referring to Fig. 9, the capacity of the half-cell according to Experimental Example 1 (CE-NCM) and Comparative Example 1 (TR-NCM) was measured according to the charge / discharge rate (0.1C, 0.2C, 0.3C, 0.5C, 1C, 2C, 3C, 5C, 0.5C).

[0125] As can be seen in Fig. 9, the half cell according to Experimental Example 1 has better rate characteristics than the half cell according to Experimental Example 2 under charge / discharge conditions (0.5C to 5C).

[0126]

[0127] FIG. 10 is a graph for comparing the stability of charge / discharge cycles of half cells according to Experimental Example 1, Comparative Example 2, and Comparative Example 2 of the present invention.

[0128] Referring to Fig. 10, the capacity of the half cells according to Experimental Example 1 (CE-NCM), Comparative Example 1 (TR-NCM), and Comparative Example 2 (Commercial-NCM) was measured while performing 100 charge / discharge cycles (charge / discharge cycle conditions: 0.1C (formation cycle), 0.5C (2 cycles), 1C (2 cycles), 3C (2 cycles), 5C (100 cycles)) in the range of 2.7 V to 4.3 V.

[0129] As can be seen in Fig. 10, under 5C conditions, the capacity retention rate of the half cell according to Experimental Example 1 is 89%, which is significantly superior to the capacity retention rates of the half cells according to Comparative Examples 1 and 2.

[0130]

[0131] Figure 11 is a graph for comparing the stability of charge / discharge cycles of full cells according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0132] Referring to Fig. 11, the capacity was measured while performing 1,000 charge / discharge cycles (charge / discharge cycle conditions: 0.1C (formation cycle), 0.5C (2 cycles), 1C (2 cycles), 3C (2 cycles), 5C (1,000 cycles)) on the full cells according to Experimental Example 1 (CE-NCM) and Comparative Example 1 (TR-NCM) in the range of 3.0 V to 4.2 V.

[0133] As can be seen in Fig. 11, under 5C conditions, the capacity retention rate of the full cell according to Experimental Example 1 is 90%, which is significantly better than that of the full cell according to Comparative Example 1.

[0134]

[0135] Figure 12 is a graph for comparing the stability of the crystal structure during the charge / discharge process of the half cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0136] Referring to Fig. 12, the half-cells according to Comparative Example 1 (TR-NCM) and Experimental Example 1 (CE-NCM) were subjected to 100 charge / discharge cycles under the conditions described above in Fig. 10, and the results were expressed as dq / dv curves.

[0137] As can be seen in Fig. 12, under 5C conditions, for charge / discharge cycles (1 cycle to 100 cycles), the cathode active material of the half-cell according to Experimental Example 1 shows significantly less change in crystal structure than the cathode active material of the half-cell according to Comparative Example 1.

[0138] In summary, referring to FIGS. 9 to 12, it can be seen that the rate characteristics and long-term stability for charge / discharge cycles of the half-cell and full-cell to which the positive electrode material according to Experimental Example 1 was applied are superior to those of the comparative examples. This is interpreted as being due to the fact that the surface of the positive electrode material according to Experimental Example 1 has a spinel structure and the interior has a layered structure. Accordingly, during the charge / discharge process, the discharge capacity and energy density are improved due to the layered structure of the interior of the positive electrode material according to Experimental Example 1, and the spinel structure on the surface of the positive electrode material according to Experimental Example 1 not only acts as a passivation layer, but also has a three-dimensional channel shape for lithium ion diffusion, so it can be seen that the rate characteristics for high-speed charge / discharge rates and long-term stability for charge / discharge cycles are significantly improved.

[0139]

[0140] FIG. 13 and FIG. 14 are TEM photographs for comparing the crystal structure of the positive electrode active material after charge / discharge of the half-cell according to Experimental Example 1 and Comparative Example 1 of the present invention.

[0141] Referring to Fig. 13, after the half-cell according to Experimental Example 1 (CE-NCM) was subjected to 100 charge / discharge cycles under the conditions described above in Fig. 10, a TEM photograph was taken of the positive electrode material of the half-cell according to Experimental Example 1 (CE-NCM). Referring to Fig. 14, after the half-cell according to Comparative Example 1 (TR-NCM) was subjected to 100 charge / discharge cycles under the conditions described above in Fig. 10, a TEM photograph was taken of the positive electrode material of the half-cell according to Comparative Example 1 (TR-NCM).

[0142] As can be seen in FIGS. 13 and 14, during the charge / discharge cycle, it can be seen that the spinel structure existing at a distance of 9.4 nm or less from the surface of the positive electrode active material of the half-cell according to Experimental Example 1 is converted to a rock salt structure. In addition, it can be seen that the crystal structure of the positive electrode active material of the half-cell according to Experimental Example 1 is maintained, except that some of the crystal structure is converted to a rock salt structure (inside: layered structure, surface: spinel structure).

[0143] And, during the charge / discharge process, it can be seen that the layered structure existing at a distance of 16.1 nm or less from the surface of the positive electrode active material of the half-cell according to Comparative Example 1 is converted into a rock salt structure.

[0144] Accordingly, it can be seen that the positive electrode active material of the half cell according to Experimental Example 1 effectively suppresses the side reaction occurring at the interface between the positive electrode active material and the electrolyte more effectively than the positive electrode active material of the half cell according to Comparative Example 1.

[0145]

[0146] FIG. 15 and FIG. 16 are graphs for comparing resistance values ​​for charge / discharge after performing charge / discharge of a half cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0147] Referring to FIG. 15, after performing 100 charge / discharge cycles on the half-cell (TR-NCM) according to Comparative Example 1 under the conditions described above in FIG. 10, the half-cell (TR-NCM) according to Comparative Example 1 was subjected to EIS (Electrochemical Impedance Spectroscopy) analysis while performing charge / discharge, and the frequency was Fourier transformed into time to represent a DRT (Distribution of Relaxation Times) graph. Referring to FIG. 16, after performing 100 charge / discharge cycles on the half-cell (CE-NCM) according to Experimental Example 1 under the conditions described above in FIG. 10, the half-cell (CE-NCM) according to Experimental Example 1 was subjected to EIS analysis while performing charge / discharge, and the frequency was Fourier transformed into time to represent a DRT graph.

[0148] As can be seen in FIGS. 15 and 16, the half-cell according to Experimental Example 1 has a higher R for charge / discharge under voltage conditions (3.6 V to 4.3 V) than the half-cell according to Comparative Example 1. ct (Charge transfer resistance) It can be seen that the value is significantly low.

[0149] This factor is interpreted to be due to the fact that, due to the instability of the interface between the positive electrode active material and the electrolyte of the half-cell according to Comparative Example 1, the electrolyte was decomposed during the 100-cycle charge / discharge process, forming more organic layers than inorganic layers at the interface, whereas, due to the stability of the interface between the positive electrode active material and the electrolyte of the half-cell according to Experimental Example 1, the inorganic layers were formed more at the interface than organic layers at the interface during the 100-cycle charge / discharge process.

[0150]

[0151] Figures 17 and 18 are graphs for comparing the amount of organic and inorganic layers on the surface of a positive electrode active material after charging / discharging of a half-cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0152] Referring to Fig. 17, after the half-cell (TR-NCM) according to Comparative Example 1 was subjected to 100 charge / discharge cycles under the conditions described above in Fig. 10, XPS analysis was performed on the positive electrode active material of the half-cell (TR-NCM) according to Comparative Example 1 for the C 1s spectrum (Fig. 17a), F 1s spectrum (Fig. 17b), and P 2p spectrum (Fig. 17c). Referring to Fig. 18, after the half-cell (CE-NCM) according to Experimental Example 1 was subjected to 100 charge / discharge cycles under the conditions described above in Fig. 10, XPS analysis was performed on the positive electrode active material of the half-cell (CE-NCM) according to Experimental Example 1 for the C 1s spectrum (Fig. 18a), F 1s spectrum (Fig. 18b), and P 2p spectrum (Fig. 18c).

[0153] As can be seen in FIGS. 17 and 18, the inorganic layer on the surface of the positive electrode active material of the half-cell according to Experimental Example 1 is larger than the inorganic layer on the surface of the positive electrode active material of the half-cell according to Comparative Example 1.

[0154] The organic layer (Li2CO3, C=O) on the surface of the cathode active material increases the interfacial resistance of the interface between the cathode active material and the electrolyte, but the inorganic layer (Li) on the surface of the cathode active material increases the interfacial resistance of the interface between the cathode active material and the electrolyte. x PF y , LiF) not only has higher ionic conductivity than the organic layer, but can also function as a passivation layer.

[0155] Accordingly, it can be seen that the interface between the positive electrode active material and the electrolyte of the half cell according to Experimental Example 1 has superior interface stability than the interface between the positive electrode active material and the electrolyte of the half cell according to Comparative Example 1.

[0156]

[0157] FIG. 19 and FIG. 20 are TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) analysis results for the positive and negative electrodes after charge / discharge of the full cell according to Comparative Example 1 and Experimental Example 1 of the present invention.

[0158] Referring to FIG. 19, after performing 1,000 charge / discharge cycles on the full cells according to Comparative Example 1 (TR-NCM) and Experimental Example 1 (CE-NMC) under the conditions described above in FIG. 11, TOF-SIMS analysis was performed on the byproducts formed on the surface of the positive electrode active material of the full cells according to Comparative Example 1 (TR-NCM) and Experimental Example 1 (CE-NMC). Referring to FIG. 20, after performing 1,000 charge / discharge cycles on the full cells according to Comparative Example 1 (TR-NCM) and Experimental Example 1 (CE-NMC) under the conditions described above in FIG. 11, TOF-SIMS analysis was performed on the byproducts formed on the surface of the negative electrode active material (graphite) of the full cells according to Comparative Example 1 (TR-NCM) and Experimental Example 1 (CE-NMC).

[0159] As can be seen in FIGS. 19 and 20, the full cell according to Experimental Example 1 has a smaller amount of byproducts formed on the surface of the positive electrode active material than the full cell according to Comparative Example 1. This is interpreted as being due to the fact that nickel is exposed on the surface of the positive electrode active material of the full cell according to Comparative Example 1, but cobalt is doped on the surface of the positive electrode active material of the full cell according to Experimental Example 1, thereby preventing nickel from being exposed.

[0160] And, it can be seen that the full cell according to Experimental Example 1 has a smaller amount of by-products formed on the surface of the negative electrode active material than the full cell according to Comparative Example 1, and the formation of lithium dendrites is effectively suppressed.

[0161] Therefore, it can be seen that the stability of the interface between the positive electrode active material and the electrolyte is improved during the charge / discharge process by doping cobalt on the particle surface of the positive electrode active material according to the embodiment of the present application, so that the formation of by-products on the surface of the positive and negative electrodes of the full cell is suppressed, and the formation of lithium dendrites on the surface of the negative electrode is effectively suppressed.

[0162]

[0163] While the present invention has been described in detail using preferred embodiments, the scope of the present invention is not limited to the specific embodiments described above, and should be interpreted in accordance with the appended claims. Furthermore, those skilled in the art will appreciate that numerous modifications and variations are possible without departing from the scope of the present invention.

[0164] The cathode active material according to an embodiment of the present invention can be used in various devices such as lithium secondary batteries, electric vehicles, mobile devices, and ESS.

Claims

1. A step of preparing a preliminary cathode active material precursor containing nickel and manganese; A step of preparing a doping source containing cobalt; A step of providing the preliminary cathode active material precursor to the above doping source and causing a refluxing reaction to produce a cathode active material precursor; and A method for producing a cathode active material, comprising the step of mixing and calcining the cathode active material precursor and the lithium precursor to produce a cathode active material.

2. In paragraph 1, A method for manufacturing a cathode active material, comprising controlling the crystal structure of the surface and the crystal structure of the primary particle of the cathode active material differently by the step of manufacturing the cathode active material precursor.

3. In paragraph 2, A method for producing a cathode active material, comprising: in the step of producing the cathode active material precursor, the refluxing reaction temperature is controlled to 84°C or lower, and the refluxing reaction time is controlled to 8 hours or lower.

4. In paragraph 1, The above-mentioned preliminary cathode active material comprises a transition metal hydroxide containing nickel and manganese, A method for producing a cathode active material, wherein the above doping source comprises a cobalt nitrate solution.

5. A method for manufacturing a cathode active material, comprising: manufacturing a cathode active material precursor by doping cobalt on the surface of a transition metal hydroxide containing nickel and manganese, and then firing the cathode active material precursor together with a lithium precursor; The above cathode active material precursor includes being subjected to a first heat treatment at a first temperature, and the first heat-treated cathode active material precursor includes being subjected to a second heat treatment at a second temperature higher than the first temperature. A method for manufacturing a cathode active material, including controlling the crystal structure of the surface and interior of the primary particles of the cathode active material differently or identically depending on the second temperature.

6. In paragraph 5, The second temperature is controlled to be 700°C or more and less than 800°C, A method for manufacturing a cathode active material, wherein the internal crystal structure of the primary particles of the cathode active material is controlled to a layered structure, and the surface crystal structure is controlled to a spinel structure by cobalt.

7. In paragraph 6, A method for manufacturing a cathode active material, which includes improving rate characteristics and stability for charge / discharge cycles under 5C conditions by different internal and surface crystal structures of the primary particles of the cathode active material.

8. In a cathode active material in which cobalt is doped on the surface of a composite metal oxide containing lithium, nickel, and manganese, Including that the crystal structures of the interior and surface of the primary particles of the above-mentioned positive electrode active material are different, The interior of the above primary particle includes a layered structure, A cathode active material comprising the surface of the primary particle having a spinel structure.

9. In paragraph 8, A cathode active material, wherein when a charge / discharge cycle is performed on the cathode active material, the crystal structure of the surface of the cathode active material is converted into a rock salt structure.

10. In paragraph 9, A cathode active material, wherein when 100 charge / discharge cycles are performed under 5C conditions for the cathode active material, the spinel structure existing at a distance of 9.4 nm or less from the surface of the cathode active material is converted into the rock salt structure.

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