Positive electrode active material, positive electrode and lithium secondary battery including the same, and method for manufacturing the positive electrode active material

Abstract

The positive electrode active material according to the present invention includes a perlithium manganese-based oxide represented by the following Chemical Formula 1; and a carbon material coating layer disposed on the surface of the perlithium manganese-based oxide, the carbon material coating layer having a BET specific surface area of ​​1.0 m 2 / g or 2.0m 2 / g. [Chemical Formula 1] Li a [Ni b Co c Mn d M e ]O2 (in the above chemical formula 1, 1.00

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0035482 dated March 17, 2023 and Korean Patent Application No. 10-2023-0188921 dated December 21, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a positive electrode and a lithium secondary battery including the same, and a method for manufacturing the positive electrode active material, and more particularly to a positive electrode active material having excellent capacity characteristics and rate characteristics, and a positive electrode and a lithium secondary battery including the same. [Background technology]

[0003] A lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Of these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high cost of the raw material cobalt and unstable supply make it difficult to commercially apply to large-capacity batteries. Lithium nickel oxide has poor structural stability and is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but suffers from the problem of poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to overcome the problems of lithium transition metal oxides containing only Ni, Co, or Mn. Among these, lithium nickel cobalt manganese oxides (hereinafter referred to as "perlithium manganese oxides"), which have a higher Mn content than the contents of other metals except for lithium, are known to be high-capacity active materials and can ensure high energy density per unit volume, and research into this is currently underway.

[0005] However, in the case of perlithium manganese oxides containing excess lithium, the layered structure (LiM'O2) and rock-salt structure (Li2MnO3) are mixed, and the rock-salt structure is activated during the initial activation process, generating excess lithium ions. Furthermore, an oxygen-redox reaction occurs during the activation process of the rock-salt structure, which generates a large amount of gas, causing cracks inside the active material and the collapse of the crystalline structure, resulting in severe deterioration of the positive electrode and reduced lifespan.

[0006] On the other hand, perlithium manganese oxides have the problem of reduced rate characteristics. This is because when the Mn content is increased while the Co content is decreased, the Ni 2+ The ratio of Li + Ni layer 2+It is presumed that the diffusion rate of lithium ions is slowed down by cation mixing in which substitution occurs, resulting in increased resistance.

[0007] Therefore, there is a demand for the development of a lithium-rich manganese-based oxide that can simultaneously improve capacity characteristics and rate characteristics.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention is for solving such problems, and aims to provide a positive electrode active material including a carbon material coating layer with a specific content on the surface of a lithium-rich manganese-based oxide.

[0009] Moreover, the present invention aims to provide a positive electrode and a lithium secondary battery with improved electrochemical characteristics by including the positive electrode active material.

Means for Solving the Problems

[0010] In one aspect of the present invention, a lithium-rich manganese-based oxide represented by the following Chemical Formula 1; and a carbon material coating layer located on the surface of the lithium-rich manganese-based oxide are included, and the BET specific surface area is 1.0 m 2 / g to 2.0 m 2 / g, and a positive electrode active material is provided.

[0011] [Chemical Formula 1] Li a [Ni b Co​​​​​​​​​​​In the chemical formula 1, 1.10 ≦ a ≦ 1.5, 0.10 ≦ b ≦ 0.40, 0 ≦ c ≦ 0.05, 0.47 ≦ d ≦ 0.80, and 0 ≦ e ≦ 0.10 may also be satisfied.

[0013] In the chemical formula 1, 1.12 < a < 1.18, 0.24 < b < 0.36, 0 < c < 0.10, 0.47 ≦ d < 0.63, and 0 < e < 0.05, and M may be one or more selected from the group consisting of Al, Mg, V, Ti, Zr, Nb, and W.

[0014] On the other hand, the over-lithiated manganese-based oxide may have a mixed Li2MnO3 phase with a rock-salt structure and a LiM'O2 phase with a layered structure, and may be represented, for example, by the following chemical formula 2.

[0015] [Chemical formula 2] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w O2 In the [Chemical formula 2], 0.2 ≦ X ≦ 0.5, 0.4 ≦ y < 1, 0 ≦ z ≦ 0.1, 0 ≦ w ≦ 0., and M is one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0016] The carbon material coating layer may be amorphous.

[0017] The carbon material coating layer may contain any one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

[0018] The content of the carbon material coating layer may be 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the over-lithiated manganese-based oxide. The D of the positive electrode active material 50It may be 1 μm to 20 μm.

[0019] The electric conductivity of the positive electrode active material is 2.0×10 -3 S / cm to 5.0×10 -3 S / cm and may be acceptable.

[0020] In another aspect of the present invention, a positive electrode including the positive electrode active material is provided.

[0021] In another aspect of the present invention, a lithium secondary battery including the positive electrode, negative electrode, separator, and electrolyte is provided, and the positive electrode includes a positive electrode active material layer including the positive electrode active material.

[0022] The ratio of the discharge capacity at 0.33C charge and discharge to the discharge capacity at 0.1C charge and discharge of the lithium secondary battery may be 94.0% to 99.0%.

[0023] In another aspect of the present invention, a method for manufacturing a positive electrode active material includes: (A) a step of preparing a lithium-rich manganese-based oxide represented by the following Chemical Formula 1; and (B) a step of mixing the lithium-rich manganese-based oxide and a carbon material to form a carbon material coating layer located on the surface of the lithium-rich manganese-based oxide, and the content of the carbon material coating layer is 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the lithium-rich manganese-based oxide.

[0024] [Chemical Formula 1] Li a [Ni b Co c Mn d M e O2 In Chemical Formula 1, 1.00 < a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and M is one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0025] In step (B), the carbon material coating layer may be formed on the surface of the perlithium manganese-based oxide by applying a shear force. [Effects of the Invention]

[0026] The present invention can simultaneously improve the electrical conductivity and rate characteristics of the positive electrode active material surface by including a specific amount of a carbon material coating layer on the surface of a perlithium manganese-based oxide. The rate characteristics of a positive electrode are affected by the electrical conductivity and ionic conductivity within the positive electrode, but improving the electrical conductivity of the positive electrode active material that constitutes the positive electrode can improve the electrical conductivity and rate characteristics of the positive electrode.

[0027] In addition, since the cathode active material according to the present invention includes a carbon coating layer having excellent conductivity on its surface, it can achieve excellent electrical conductivity with only a small amount of conductive material without adding a separate conductive material during electrode fabrication, thereby increasing the amount of cathode active material contained in the electrode and increasing energy density. DETAILED DESCRIPTION OF THE INVENTION

[0028] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be embodied in a variety of different forms. These embodiments are provided solely to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art. The present invention is defined solely by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0029] Unless otherwise defined, all terms (including technical and scientific terms) used herein are used in the sense that they can be commonly understood by a person of ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0030] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified in the context. The words "including," "having," and "comprising" used in this specification do not exclude the presence or addition of one or more other elements other than the elements mentioned.

[0031] In this specification, when a part is said to include certain elements, this does not mean that it excludes other elements, unless otherwise specified, and it means that it may further include other elements.

[0032] In the present invention, the "specific surface area" is measured by the BET method, and specifically, may be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0033] In the present invention, "D 50 " means the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material. 50 may be measured using a laser diffraction method. For example, the positive electrode active material powder may be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph may then be obtained, and the particle size corresponding to 50% of the volume cumulative amount may be determined.

[0034] The present invention will now be described in further detail.

[0035] Positive electrode active material The positive electrode active material according to the present invention includes a lithium-rich manganese-based oxide represented by the following chemical formula 1 and a carbon material coating layer located on the surface of the lithium-rich manganese-based oxide, and the BET specific surface area is 1.0 m 2 / g to 2.0 m 2 / g may be.

[0036] [Chemical formula 1] Li a [Ni b Co c Mn d M e O2 In the chemical formula 1, M may be one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr. Preferably, M may be one or more selected from the group consisting of Al, W, Mg, V, Ti, Zr, and Nb.

[0037] On the other hand, a is the molar ratio of Li in the lithium-rich manganese-based oxide, and 1.00 < a, 1.10 ≤ a ≤ 1.5, or 1.12 < a < 1.18 may be. When a satisfies the above range, high-capacity characteristics and high energy density per unit volume can be realized.

[0038] The b is the molar ratio of Ni in the lithium-rich manganese-based oxide, and 0 ≤ b ≤ 0.53, 0.10 ≤ b ≤ 0.40, or 0.24 < b < 0.36 may be.

[0039] The c is the molar ratio of Co in the lithium-rich manganese-based oxide, and 0 ≤ c ≤ 0.10, 0 ≤ c ≤ 0.05, or 0 < c < 0.10 may be. When c exceeds 0.1, it is difficult to ensure high capacity, and gas generation and deterioration of the positive electrode active material may become severe, and the life characteristics may decrease.

[0040] Said d is the molar ratio of Mn in the over-lithiated manganese-based oxide, and may be 0.47≦d≦1.00, 0.47≦d≦0.80, or 0.47≦d<0.63. When d is less than 0.47, the ratio of the rock-salt type structure phase becomes excessively small and the effect of capacity improvement is negligible.

[0041] Said e is the molar ratio of the doping element M in the over-lithiated manganese-based oxide, and may be 0≦e≦0.20, 0≦e≦0.10, or 0<e<0.05. If the content of the doping element is excessively large, it may have an adverse effect on the active material capacity.

[0042] In the case of an over-lithiated manganese-based oxide containing excess lithium, it has a structure in which a layered structure phase (LiM’O2) and a rock-salt type structure phase (Li2MnO3) coexist. However, in the initial activation process, the rock-salt type structure phase is activated and excess lithium ions are generated. Also, an oxygen-redox reaction occurs during the activation process of the rock-salt type structure phase, resulting in the generation of a large amount of gas. There is a problem that the deterioration of the positive electrode due to crack generation and crystal structure collapse inside the active material becomes severe and the life characteristics decrease.

[0043] On the other hand, the over-lithiated manganese-based oxide has a problem that the rate performance deteriorates. This is because when the Co content of the over-lithiated manganese-based oxide is decreased while increasing the Mn content, 2+ the ratio of Ni + becomes high and Ni 2+ [[ID=IS]]is substituted in the Li layer, and it is presumed that this is because the diffusion rate of lithium ions becomes slow due to cation mixing, resulting in an increase in resistance. As a result of repeated research to solve such problems, the inventors of the present invention have found that by forming a coating layer containing a carbon material excellent in conductivity (hereinafter referred to as "carbon material coating layer") on the surface of the over-lithiated manganese-based oxide, the electrical conductivity can be improved, and by restricting the content of the carbon material coating layer within a certain range, the rate performance can be improved simultaneously, thereby completing the present invention.

[0045] In addition, since the cathode active material according to the present invention includes a carbon coating layer having excellent conductivity on its surface, it can achieve excellent electrical conductivity with only a small amount of conductive material without adding a separate conductive material during electrode fabrication, thereby increasing the amount of cathode active material contained in the electrode and increasing energy density.

[0046] The content of the carbon material coating layer according to the present invention may be 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 1 to 6 parts by weight, based on 100 parts by weight of the perlithium manganese-based oxide. As the content of the carbon material coating layer increases, electrical conductivity may increase, but rate performance may decrease. This is because lithium ions cannot pass directly through the carbon material coating layer but must move through the electrolyte solution contained in the carbon material coating layer. Therefore, as the content of the carbon material coating layer increases, the internal curvature increases, hindering the movement of lithium ions. This effect is thought to be reflected in the decrease in rate performance.

[0047] In addition, as the content of the carbon material coating layer increases, the ratio of the positive electrode active material in the electrode decreases, resulting in a decrease in energy density. It is preferable to apply only the minimum carbon material content that can provide optimal conditions for improving the electrical conductivity of the electrode.

[0048] Meanwhile, the perlithium manganese-based oxide may be represented by the following chemical formula 2:

[0049] [Chemical formula 2] X Li2MnO3·(1-X)Li[Ni 1-y-z-w Mn y Co z M w ]O2 In Formula 2, M is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0050] The X represents the ratio of the rock salt structure phase (Li2MnO3) in the perlithium manganese oxide, and may be 0.2≦X≦0.5, 0.25≦X≦0.5, or 0.25≦X≦0.4. When the ratio of the rock salt structure phase (Li2MnO3) in the perlithium manganese oxide satisfies this range, high capacity characteristics can be achieved.

[0051] The y is the molar ratio of Mn in the layered structure phase (LiM'O2), and may be 0.4≦y<1, 0.4≦y≦0.8, or 0.4≦y≦0.7.

[0052] The z is the molar ratio of Co in the layered structure phase (LiM'O2) and may be 0≦z≦0.1, 0≦z≦0.08, or 0≦z≦0.05. If z exceeds 0.1, gas generation and deterioration of the positive electrode active material may become severe, possibly resulting in reduced life characteristics.

[0053] The w is the molar ratio of the doping element M in the layered structure phase (LiM'O2), and may be 0≦w≦0.2, 0≦w≦0.1, or 0≦w≦0.05.

[0054] Meanwhile, according to one embodiment of the present invention, the carbon material coating layer may be amorphous. When driven at high voltage, there is a problem of gas generation due to a side reaction of carbon, but when the carbon material coating layer is amorphous, the amount of gas generation can be reduced.

[0055] The carbon material coating layer may include at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.The positive electrode active material according to the present invention includes a conductive carbon material to improve the electrical conductivity of the positive electrode active material surface and facilitate the diffusion path of lithium ions, thereby improving rate characteristics.

[0056] On the other hand, the positive electrode active material according to one embodiment of the present invention has a BET specific surface area of ​​0.5 m 2 / g or 10.0m 2 / g, preferably 0.5m 2 / g or 8.0m 2 / g, more preferably 0.5m 2 / g or 5.0m 2 / g, more preferably 1.0m 2 / g or 2.0m 2 / g. The BET specific surface area of ​​the positive electrode active material may be 1 m 2 If the surface area is less than 2.0 m / g, the reaction area with the electrolyte is insufficient, making it difficult to achieve sufficient capacity. 2 If the content exceeds 1 / g, moisture absorption is rapid, resulting in a decrease in adhesive strength during electrode manufacturing, or side reactions with the electrolyte are accelerated during electrode operation, making it difficult to ensure life characteristics.

[0057] In addition, the cathode active material according to an embodiment of the present invention may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter D 50 The thickness of the positive electrode active material may be 1 μm to 20 μm, preferably 3 μm to 15 μm, and more preferably 5 μm to 12 μm. 50 When the above range is satisfied, excellent electrode density can be achieved and the deterioration of capacity characteristics and rate characteristics can be minimized.

[0058] Method for producing positive electrode active material The positive electrode active material according to an embodiment of the present invention may be manufactured by the following method. However, it is not limited thereto.

[0059] Specifically, the method for manufacturing the positive electrode active material according to the present invention includes (A) a step of preparing a lithium-rich manganese-based oxide represented by the following Chemical Formula 1, and (B) a step of mixing the lithium-rich manganese-based oxide and a carbon material to form a carbon material coating layer located on the surface of the lithium-rich manganese-based oxide. The content of the carbon material coating layer may be 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the lithium-rich manganese-based oxide.

[0060] [Chemical Formula 1] Li a [Ni b Co c Mn d M e O2 In Chemical Formula 1, 1.00 < a, 0 ≤ b ≤ 0.53, 0 ≤ c ≤ 0.10, 0.47 ≤ d ≤ 1.00, 0 ≤ e ≤ 0.20, and M is one or more selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

[0061] The method for manufacturing the positive electrode active material will be further described step by step.

[0062] (A) Step of preparing a lithium-rich manganese-based oxide First, the lithium-rich manganese-based oxide may be purchased and used as a commercially available lithium-rich manganese-based oxide, or may be manufactured by a method for manufacturing a lithium-rich manganese-based oxide known in the art.

[0063] For example, the lithium-rich manganese-based oxide may be manufactured by mixing a transition metal precursor and a lithium raw material substance and then firing them.

[0064] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). One of these may be used alone, or a mixture of two or more of them may be used.

[0065] Meanwhile, the transition metal precursor may be in the form of a hydroxide, oxide, or carbonate. When a precursor in the form of a carbonate is used, it is more preferable in that a cathode active material having a relatively large specific surface area can be prepared.

[0066] The transition metal precursor may be prepared through a co-precipitation process. For example, the transition metal precursor may be prepared by dissolving each transition metal-containing raw material in a solvent to prepare a metal solution, and then mixing the metal solution, an ammonium cation complexing agent, and a basic compound, followed by co-precipitation. If necessary, an oxidizing agent or oxygen gas may be added during the co-precipitation reaction.

[0067] In this case, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal. Specifically, the transition metal-containing raw material may be NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4H2O, manganese acetate, manganese halide, cobalt oxide, cobalt sulfate, cobalt nitrate, cobalt acetate, cobalt halide, etc.

[0068] The ammonium cation complexing agent may be one or more selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0069] The basic compound may be one or more selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Furthermore, when a basic compound is used together with an oxidizing agent, an oxide-form precursor can be obtained.

[0070] On the other hand, the transition metal precursor and the lithium source material can be mixed in amounts such that the molar ratio of total transition metals (Ni+Co+Mn):Li is 1:1.1 to 1:1.5, preferably 1:1.15 to 1:1.4, and more preferably 1:1.25 to 1:1.4.

[0071] The firing may be performed at a temperature of 600°C to 1000°C or 700°C to 950°C for a time of 5 to 30 hours or 5 to 20 hours. The firing atmosphere may be air or oxygen, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0072] (B) Step of forming a carbon coating layer on the surface of the perlithium manganese oxide Next, the perlithium manganese-based oxide and a carbon material are mixed to form a carbon material coating layer located on the surface of the perlithium manganese-based oxide, and the content of the carbon material coating layer may be 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 1 to 6 parts by weight, based on 100 parts by weight of the perlithium manganese-based oxide.

[0073] According to an embodiment of the present invention, the carbonaceous material coating layer may be formed on the surface of the perlithium manganese-based oxide by applying a shear force during the formation of the carbonaceous material coating layer. The carbonaceous material coating layer may be formed by a physical method such as mechanofusion, mixing, or milling.

[0074] The step of forming the carbon material coating layer does not require a separate heat treatment process. By eliminating the heat treatment process, the cathode active material according to one aspect of the present invention can be manufactured through a simple process. Furthermore, by eliminating the heat treatment process, the oxidation number or structure of the transition metal compound is not changed. This allows the cathode active material to be manufactured with fewer side reactions.

[0075] positive electrode Next, the positive electrode according to the present invention will be described.

[0076] The positive electrode according to the present invention includes a perlithium manganese-based oxide represented by Chemical Formula 1 as a positive electrode active material. Specifically, the positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to the present invention. Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0077] The positive electrode current collector may contain a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0078] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material, as required.

[0079] In this case, the positive electrode active material may be included in an amount of 80 wt % to 99 wt %, more specifically, 90 wt % to 98 wt %, based on the total weight of the positive electrode active material layer.

[0080] The conductive material is used to impart conductivity to the electrode. Any material that exhibits electronic conductivity without causing chemical changes in the resulting battery can be used without any particular limitations. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material may be present in an amount of 0.01 to 10 wt %, preferably 0.1 to 9 wt %, and more preferably 0.1 to 5 wt %, based on the total weight of the positive electrode active material layer.

[0081] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0082] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0083] The lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

[0084] Meanwhile, the positive electrode according to the present invention may have an electrode density of about 2.5 g / cc to 3.8 g / cc, 2.5 g / cc to 3.5 g / cc, or 2.8 g / cc to 3.2 g / cc. When the electrode density of the positive electrode satisfies the above range, a high energy density can be achieved.

[0085] As described above, the lithium secondary battery of the present invention, which uses the perlithium manganese-based oxide represented by Chemical Formula 1 as a positive electrode active material, can stably operate the cell even when the end-of-charge voltage is set as high as 4.3 V to 4.6 V during battery operation, and can achieve high capacity characteristics.

[0086] Other than the above, the positive electrode is the same as that described above, so a detailed description will be omitted and only the remaining components will be described below.

[0087] Meanwhile, the negative electrode according to the present invention includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0088] The negative electrode current collector may be made of any material that does not induce chemical changes in the battery and has high conductivity. Examples of such materials include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be made in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0089] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0090] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of one or more of these can be used. A thin film of metallic lithium can also be used as the negative electrode active material. The carbon material can be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch-derived cokes.

[0091] The negative electrode active material may be included in an amount of 80 wt % to 99 wt %, 82 wt % to 99 wt %, or 84 wt % to 99 wt %, based on the total weight of the negative electrode active material layer.

[0092] The binder is a component that helps bind the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0093] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be included in an amount of 1 wt % to 30 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0094] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0095] The separator according to the present invention separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, a separator coated with a ceramic component or a polymer material to ensure heat resistance or mechanical strength can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0096] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0097] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0098] The organic solvent can be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; dibutyl ether; ether-based solvents such as ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylenecarbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0099] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitation. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be one or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is in the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0100] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphate, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additives may be included in an amount of 0.1 to 10.0 wt % based on the total weight of the electrolyte.

[0101] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0102] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0103] The battery module or battery pack can be used as a power source for medium to large devices, such as one or more of: power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0104] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0105] Examples and Comparative Examples Example 1 Ni 0.33 Mn 0.67 (OH)2 and Li2CO3 were mixed so that the molar ratio of Li / transition metal was 1.3:1, and the mixture was calcined at 900°C for 10 hours to obtain D 50 The perlithium manganese oxide (Li 1.13 Ni 0.31 Mn 0.56 O2) was produced.

[0106] The prepared perlithium manganese oxide was added to water at 25°C in a ratio of 1:5 and stirred at room temperature for 20 minutes, and then the perlithium manganese oxide was filtered and dried at 120°C.

[0107] Thereafter, the perlithium manganese-based oxide and Ketjen black were mixed in a weight ratio of 96:4, and then placed in a Nobilta mixer and milled at a rotation speed of 2000 rpm for 10 minutes to prepare a cathode active material in which the surface of the perlithium manganese-based oxide was coated with Ketjen black carbon material.

[0108] Example 2 A positive electrode active material in which the surface of the perlithium manganese oxide was coated with Ketjen black carbon material was prepared in the same manner as in Example 1, except that the perlithium manganese oxide and Ketjen black were mixed in a weight ratio of 92:8.

[0109] Comparative Example 1 A positive electrode active material was prepared by coating the surface of the perlithium manganese-based oxide prepared in Example 1 with no Ketjen black carbon material.

[0110] Comparative Example 2 A positive electrode active material in which the surface of the perlithium manganese oxide was coated with Ketjen black carbon material was prepared in the same manner as in Example 1, except that the perlithium manganese oxide and Ketjen black were mixed in a weight ratio of 99.8:0.2.

[0111] Comparative Example 3 A positive electrode active material in which the surface of the perlithium manganese oxide was coated with Ketjen black carbon material was prepared in the same manner as in Example 1, except that the perlithium manganese oxide and Ketjen black were mixed in a weight ratio of 88:12.

[0112] Experimental Example 1: Measurement of the specific surface area of ​​the positive electrode active material The specific surface areas of the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 were measured.

[0113] Specifically, it may be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a specific surface area measuring device (model name: BELSORP-mino II, manufacturer: BEL Japan Inc.) The results obtained at this time are shown in Table 1 below.

[0114] [Table 1]

[0115] As shown in Table 1 above, the positive electrode active materials of Examples 1 and 2 contain a specific content of the carbon material coating layer, and it can be confirmed that they have a larger specific surface area than the positive electrode active materials in which no carbon material coating layer is formed (Comparative Example 1) and the positive electrode active materials in which the content of the carbon material coating layer is less than 0.5 parts by weight based on 100 parts by weight of the perlithium manganese-based oxide (Comparative Example 2).

[0116] Specifically, the positive electrode active materials of Examples 1 and 2 have a BET specific surface area of ​​1.0 m 2 / g or 2.0m 2This ensures that the reaction area with the electrolyte is sufficient, making it possible to achieve sufficient capacity, and since side reactions with the electrolyte are not accelerated when the electrode is driven, it is possible to ensure life characteristics.

[0117] On the other hand, when the content of the carbon material coating layer exceeds 10 parts by weight based on 100 parts by weight of perlithium manganese oxide (Comparative Example 3), the specific surface area is larger than that of the examples, but as will be discussed in the following Experimental Example 3, there is a possibility that the rate characteristics will deteriorate.

[0118] Experimental Example 2: Measurement of electrical conductivity The electric conductivity of the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 was measured after rolling under a 2 ton condition. The measurement results are shown in Table 2 below.

[0119] The electrical conductivity was measured using a powder resistance measuring device. Specifically, 5 g of each of the positive electrode active materials of the examples and comparative examples was placed in a cylindrical 4-pin probe mold, and the mold containing the positive electrode active material was pressed at 2 tons to measure the powder resistance, and then the electrical conductivity was calculated.

[0120] [Table 2]

[0121] As shown in Table 2 above, it can be seen that the electrical conductivity of Example 1 is 1.35 times higher and the electrical conductivity of Example 2 is 2.06 times higher than when no carbon material coating layer is formed (Comparative Example 1).

[0122] Specifically, the electrical conductivity of Examples 1 and 2 is 2.0 × 10 -3 S / cm or 5.0 x 10 -3 Meets S / cm.

[0123] On the other hand, when the content of the carbon material coating layer exceeds 10 parts by weight based on 100 parts by weight of perlithium manganese oxide (Comparative Example 3), the electrical conductivity is higher than that of the examples, but as will be discussed in Experimental Example 3, there is a possibility that the rate characteristics will decrease.

[0124] Experimental Example 3: Evaluation of capacity and rate characteristics The capacity characteristics and rate characteristics of lithium secondary half-cells prepared as follows using the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated by the following methods. The measurement results are shown in Table 3 below.

[0125] Specifically, the lithium secondary battery half cell was manufactured as follows.

[0126] Positive electrode slurries were prepared by mixing each of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3, a conductive material (Super-C), and a PVDF binder in N-methylpyrrolidone in the weight ratios shown in Table 3. The positive electrode slurries were then applied to an aluminum current collector sheet, dried, and rolled to prepare positive electrodes.

[0127] Using the cathode and a lithium metal thin film as the anode, half-cells of Examples 1-1, 2-1, and Comparative Examples 1-1 to 3-1 were fabricated. Each half-cell was then charged at 45° C. with a constant current of 0.1 C to 4.65 V, and then discharged at a constant current of 0.1 C to 2.0 V, thereby performing an activation process.

[0128] After the activation process, the half-cell was charged at a constant current of 0.1 C at 25°C to 4.4 V, and then discharged at a constant current of 0.1 C to 2.5 V, and the charge capacity and discharge capacity were measured. At the same temperature, the half-cell was charged at a constant current of 0.33 C to 4.4 V, and then discharged at a constant current of 0.33 C to 2.5 V, and the charge capacity and discharge capacity were measured.

[0129] The rate characteristics were measured as the ratio of the discharge capacity measured above at 0.1 C charge / discharge to the discharge capacity measured above at 0.33 C charge / discharge.

[0130] [Table 3]

[0131] As can be seen from Table 3, the half-cells of Examples 1-1 and 2-1, which employ a positive electrode active material having a carbon material coating layer, exhibit higher rate performance than the half-cells of Comparative Examples 1-1 and 1-2, which employ a positive electrode active material without a carbon material coating layer. Specifically, the half-cells of Examples 1-1 and 2-1 exhibited a ratio of the discharge capacity at 0.33 C charge / discharge to the discharge capacity at 0.1 C charge / discharge of 94.0% to 99.0%. This is believed to be because the carbon material coating layer improves the electrical conductivity of the positive electrode active material, reducing electrode resistance and improving rate performance.

[0132] However, the half-cell of Comparative Example 3-1, which used a cathode active material with a carbonaceous coating layer content outside the range of the present invention, exhibited poor rate performance. This is because, although electrical conductivity increases as the carbonaceous coating layer content increases (see Table 2), lithium ions cannot pass directly through the carbonaceous coating layer but must move through the electrolyte solution that fills the carbonaceous coating layer. Therefore, the higher the carbonaceous coating layer content, the higher the internal curvature becomes, hindering the movement of lithium ions. This effect is believed to be reflected in the poor rate performance.

[0133] Meanwhile, when considering the carbon coating layer and the content of the conductive material, it was determined that the carbon coating layer can act as an additional conductive material under the same electrode composition. Therefore, a half-cell of Comparative Example 1-2, which was manufactured by increasing the content of the conductive material in the electrode, was compared with Example 1. As a result, it was determined that the increase in the content of the conductive material improved the electrode's electrical conductivity compared to before the electrode composition change (Comparative Example 1-1), thereby contributing to improved rate performance. However, it was confirmed that the half-cells still exhibited lower rate performance than those of Examples 1-1 and 2-1. Therefore, it was determined that applying a carbon coating directly to the surface is more effective for improving rate performance than increasing the content of the conductive material in the electrode composition.

Claims

1. a perlithium manganese oxide represented by the following chemical formula 1; a carbon material coating layer located on a surface of the perlithium manganese-based oxide, The BET specific surface area of ​​the positive electrode active material is 1.0 m ２ / g to 2.0m ２ / g, [Chemical formula 1] Li ａ [Ni ｂ Co ｃ Mn ｄ M ｅ ]O ２ In Chemical Formula 1, 1.00<a, 0≦b≦0.53, 0≦c≦0.10, 0.47≦d≦1.00, and 0≦e≦0.20, and M is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

2. 2. The positive electrode active material of claim 1, wherein, in Formula 1, 1.10≦a≦1.5, 0.10≦b≦0.40, 0≦c≦0.05, 0.47≦d≦0.80, and 0≦e≦0.

10.

3. 2. The positive electrode active material of claim 1, wherein, in Formula 1, 1.12<a<1.18, 0.24<b<0.36, 0<c<0.10, 0.47≦d<0.63, and 0<e<0.05; and M is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, Nb, and W.

4. The perlithium manganese-based oxide is represented by the following chemical formula 2: [Chemical formula 2] X Li ２ MnO ３ ・(1-^)L[Ni １－ｙ－ｚ－ｗ Mn ｙ Co ｚ M ｗ ]O ２ 2. The positive electrode active material of claim 1, wherein, in Chemical Formula 2, 0.2≦x≦0.5, 0.4≦y<1, 0≦z≦0.1, and 0≦w≦0.2, and M is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

5. The positive electrode active material according to claim 1 , wherein the carbon material coating layer is amorphous.

6. 2. The positive electrode active material of claim 1, wherein the carbon material coating layer comprises at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

7. 2. The positive electrode active material of claim 1, wherein the carbon coating layer is present in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the perlithium manganese-based oxide.

8. D of the positive electrode active material ５０ The positive electrode active material according to claim 1 , wherein the thickness of the first and second electrodes is 1 μm to 20 μm.

9. The electrical conductivity of the positive electrode active material is 2.0×10 －３ S / cm to 5.0 x 10 －３ 2. The positive electrode active material according to claim 1, wherein the conductivity is 0.5 S / cm.

10. A positive electrode comprising the positive electrode active material according to claim 1 .

11. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, A lithium secondary battery, wherein the positive electrode comprises a positive electrode active material layer containing the positive electrode active material according to claim 1 .

12. 12. The lithium secondary battery of claim 11, wherein a ratio of a discharge capacity at 0.33C charge / discharge to a discharge capacity at 0.1C charge / discharge of the lithium secondary battery is 94.0% to 99.0%.

13. (A) preparing a perlithium manganese-based oxide represented by the following chemical formula 1; (B) mixing the perlithium manganese-based oxide with a carbon material to form a carbon material coating layer located on the surface of the perlithium manganese-based oxide; The content of the carbon material coating layer is 0.5 to 10 parts by weight based on 100 parts by weight of the perlithium manganese-based oxide, [Chemical formula 1] Li ａ [Ni ｂ Co ｃ Mn ｄ M ｅ ]O ２ wherein, in Formula 1, 1.00<a, 0≦b≦0.53, 0≦c≦0.10, 0.47≦d≦1.00, and 0≦e≦0.20; and M is at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr.

14. The method for producing a positive electrode active material according to claim 13 , wherein in step (B), the carbon material coating layer is formed on the surface of the perlithium manganese-based oxide by applying a shear force.

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