Positive electrode active material for lithium secondary battery, preparation method thereof and lithium secondary battery comprising the same

Abstract

The present invention relates to a positive electrode active material, a preparation method thereof, and a lithium secondary battery comprising the positive electrode active material. The positive electrode active material includes a plurality of primary particles, at least one secondary particle including an agglomerate of the plurality of primary particles, or a combination thereof. The primary particles have an α-NaFeO2 crystal structure and include a lithium transition metal oxide containing at least one of Ni, Co, Mn, and Al. Part of the transition metal positions in the crystal lattice of the crystal structure are replaced by a doping element M, and part of the oxygen element positions in the crystal lattice are replaced by a sulfur element S. The M includes Mg, Ti, Zr, W, Si, Ca, B, V, or a combination thereof. The content of M in the lithium transition metal oxide is 1,000 ppm to 4,000 ppm, and the content of S in the lithium transition metal oxide is less than or equal to 1,000 ppm.

Description

Technical Field

[0001] The invention relates to a positive electrode active material for a lithium secondary battery with a new composition, a preparation method thereof and a lithium secondary battery comprising the positive electrode active material. Background Art

[0002] Since Sony commercialized lithium secondary batteries in 1991, demand has been increasing across a wide range of applications, from small home appliances like mobile information technology products to large and medium-sized electric vehicles and energy storage systems. In particular, these systems require inexpensive, high-energy cathode materials. However, cobalt, the primary raw material for single-crystal LiCoO2 (LCO), the currently commercialized cathode active material, is expensive.

[0003] Therefore, in recent years, LiNi, in which a portion of Co is replaced by other transition metals, has been used as a positive electrode active material for medium and large secondary batteries. x Co y Mn z O2(NCM, x+y+z=1) and LiNi x Co y Al z O2 (NCA, x + y + z = 1) is used to replace LCO, and the advantage is that as a raw material for such NCM and NCA-based positive active materials, nickel is cheap and has a high reversible capacity. In particular, in terms of high capacity, NCM and NCA with a molar ratio of Ni greater than or equal to 50 mol% are of interest. Generally, such Ni-based positive active materials are prepared by mixing a transition metal compound precursor synthesized by a coprecipitation method with a lithium source and then synthesizing it in a solid phase. However, the Ni-based positive electrode material synthesized in this way exists in the form of secondary particles agglomerated by small primary particles, so the problem is that microcracks occur inside the secondary particles during a long charge / discharge process. Microcracks lead to side reactions between the new interface of the positive active material and the electrolyte, resulting in degradation of battery performance, such as decreased safety caused by gas generation, and decreased battery performance caused by depletion of the electrolyte. Furthermore, the need to increase electrode density (>3.3 g / cc) to achieve high energy density leads to the collapse of secondary particles, resulting in electrolyte depletion caused by side reactions with the electrolyte, which in turn leads to a sharp drop in initial life. Consequently, this means that Ni-based positive active materials in the form of secondary particles synthesized by existing coprecipitation methods cannot achieve high energy density.

[0004] In order to solve the above-mentioned problems of Ni-based positive active materials in the form of secondary particles, single-particle Ni-based positive active materials have been studied in recent years. When the electrode density is increased (>3.3g / cc) to achieve high energy density, single-crystal Ni-based positive active materials do not experience particle collapse, and thus can achieve excellent electrochemical performance. However, when conducting electrochemical evaluations of such single-crystal Ni-based positive active materials, it has been proposed that due to the unstable Ni 3+ and Ni 4+ Therefore, in order to develop high-energy lithium secondary batteries, there is still a need for technologies to stabilize the unstable Ni ions in single-crystal Ni-based positive electrode active materials. Summary of the Invention

[0005] Technical issues

[0006] According to one aspect, a positive electrode active material is provided which does not crack at a high electrode density while achieving a high energy density and improving long life characteristics.

[0007] Technical Solution

[0008] According to one aspect, a positive electrode active material is provided, comprising: a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof, wherein:

[0009] The primary particles have an α-NaFeO2 type crystal structure and include a lithium transition metal oxide containing at least one of Ni, Co, Mn and Al, and part of the transition metal positions in the crystal lattice of the crystal structure are replaced by a doping element M, and part of the oxygen element positions in the crystal lattice are replaced by a sulfur (S) element, wherein,

[0010] The M includes Mg, Ti, Zr, W, Si, Ca, B, V or a combination thereof, wherein,

[0011] In the lithium transition metal oxide, the content of M is 1,000 ppm to 4,000 ppm,

[0012] In the lithium transition metal oxide, a content of S is less than or equal to 1,000 ppm.

[0013] According to another aspect, a method for preparing a positive electrode active material is provided, comprising the steps of mixing a compound containing a Li element, a transition metal compound, a compound containing a sulfur (S) element, and a compound containing an M element to obtain a precursor of a lithium transition metal oxide;

[0014] The step of heat-treating the precursor to obtain the positive electrode active material comprising a plurality of primary particles, at least one secondary particle comprising an aggregate of a plurality of primary particles, or a combination thereof.

[0015] According to yet another aspect, a positive electrode is provided, comprising the positive electrode active material.

[0016] According to another aspect, a lithium secondary battery is provided, which includes the positive electrode, the negative electrode, and an electrolyte.

[0017] Beneficial effects

[0018] According to one aspect of the present invention, a positive electrode active material including a lithium transition metal oxide includes a single crystal, a single particle, an agglomerate of these single particles, or a combination thereof, and a portion of the transition metal is replaced by a doping element M, and a portion of the oxygen is replaced by sulfur (S), wherein the content of M is 1,000 ppm to 4,000 ppm, and the content of S is less than or equal to 1,000 ppm, thereby stabilizing the unstable Ni ions present in the high-Ni-based lithium transition metal oxide and preventing degradation between charge and discharge, thereby increasing the capacity per volume and improving the life stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The following are scanning electron microscope (SEM) images of the positive electrode active materials of Preparation Examples 6 to 9.

[0020] Figure 2 Graph showing the S2p XPS analysis results of Preparation Example 1.

[0021] Figure 3 Graph showing capacity retention according to cycles of Examples 1 to 3 and Comparative Examples 2, 5, 6, 9, and 11.

[0022] Figure 4 It is a graph showing the capacity retention rate according to cycles of Examples 4 and 5 and Comparative Examples 12 to 14.

[0023] Figure 5 is a schematic diagram of a lithium battery according to an exemplary embodiment.

[0024] <Description of the main parts of the drawings>

[0025] 1: Lithium battery 2: Negative electrode

[0026] 3: positive electrode 4: separator

[0027] 5: Battery case 6: Cover assembly DETAILED DESCRIPTION

[0028] The present inventive concept described below is susceptible to various modifications and embodiments. Therefore, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present inventive concept to the specific embodiments. Instead, it should be understood that all modifications, equivalents, or alternatives within the technical scope of the present inventive concept are included in the present inventive concept.

[0029] The terms used below are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. Hereinafter, terms such as "including" or "having" are intended to indicate the presence of features, numbers, steps, operations, constituent elements, parts, ingredients, materials, or combinations thereof described in the specification, but it should be understood that this does not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, constituent elements, parts, ingredients, materials, or combinations thereof. The " / " used below can be interpreted as "and" or "or" as the case may be.

[0030] To clearly represent the various layers and regions, the thicknesses in the figures are exaggerated or reduced. Throughout this specification, similar parts are given the same reference numerals. Throughout this specification, when a part of a layer, film, region, plate, etc. is located "on" or "above" another part, this includes not only the case where it is directly on the other part, but also the case where there are other parts between them. Throughout this specification, terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are only used to distinguish one component from another.

[0031] Hereinafter, a positive active material, a preparation method thereof, and a lithium secondary battery having a positive electrode including the positive active material according to an exemplary embodiment will be described in more detail.

[0032] According to one embodiment, a positive electrode active material includes a plurality of primary particles, an agglomerate of a plurality of primary particles, or a combination thereof, wherein the primary particles have an α-NaFeO2 type crystal structure and include a lithium transition metal oxide containing at least one of Ni, Co, Mn, and Al, and part of the transition metal positions in the crystal lattice of the crystal structure are substituted by a doping element M, and part of the oxygen element positions in the crystal lattice are substituted by a sulfur (S) element, wherein the M includes Mg, Ti, Zr, W, Si, Ca, B, V, or a combination thereof, wherein the content of the M in the lithium transition metal oxide is 1,000 ppm to 4,000 ppm, and the content of the S in the lithium transition metal oxide is less than or equal to 1,000 ppm.

[0033] Here, the term "aggregate of primary particles" refers to a situation in which the surfaces of one or more primary particles are brought into contact with one another during the heat treatment of the primary particles. Furthermore, the term "aggregate of primary particles" refers to a situation in which the surfaces of a plurality of primary particles are brought into contact with one another when a coating is present on the surfaces of the primary particles. This concept is different from secondary particles, as the aforementioned secondary particles are formed by forming a coating on the outer surface of an aggregate of a plurality of primary particles, thereby forming a form in which the plurality of primary particles are nested within the coating.

[0034] In the positive electrode active material according to one embodiment of the present invention, a portion of the transition metal is replaced by a doping element M, and a portion of the O is replaced by S, wherein the content of M is 1,000 ppm to 4,000 ppm and the content of S is less than or equal to 1,000 ppm, thereby having high capacity and long life characteristics. When the S content exceeds 1,000 ppm, the initial discharge capacity decreases, and when the total amount of the doping element does not meet the above range, the life characteristics deteriorate. Therefore, when the content ratio of the doping element and the content ratio of the S element are met, high capacity and long life characteristics can be achieved simultaneously.

[0035] According to one embodiment, the lithium transition metal oxide includes Ni, and the content of nickel in the lithium transition metal oxide may be greater than or equal to 80 mol %.

[0036] For example, in the lithium transition metal oxide, the nickel content may be greater than or equal to 81 mol%, greater than or equal to 82 mol%, greater than or equal to 83 mol%, greater than or equal to 84 mol%, greater than or equal to 85 mol%, greater than or equal to 86 mol%, or greater than or equal to 87 mol%.

[0037] According to one embodiment, in the lithium transition metal oxide, the content of M may be 1,200 ppm to 4,000 ppm. For example, the content of M may be 1,200 ppm to 3,800 ppm.

[0038] According to one embodiment, the lithium transition metal oxide includes W, and the content of W may be 900 ppm to 2,500 ppm.

[0039] According to one embodiment, the doping element may include Mg, Ti, W, Si, Ca, V, or a combination thereof. For example, the doping element may include Mg, Ti, and W.

[0040] According to one embodiment, in the crystal lattice of the lithium transition metal oxide, some of the lithium element positions may be substituted by one or more alkali metal elements.

[0041] For example, the alkali metal element may include Na, K, or a combination thereof.

[0042] According to one embodiment, the content of the alkali metal element in the lithium transition metal oxide may be 100 ppm to 250 ppm. For example, the content of the alkali metal element may be 120 ppm to 230 ppm, 130 ppm to 220 ppm, or 140 ppm to 210 ppm.

[0043] According to one embodiment, in the lithium transition metal oxide, the molar ratio of Li / molar ratio of transition metal may be less than 1. This is different from lithium-rich positive electrode active materials having a molar ratio of Li exceeding 1. Although the molar ratio of Li is less than 1, it has high capacity and long life characteristics due to the introduction of alkali metal elements, doping elements and S elements.

[0044] According to one embodiment, the lithium transition metal oxide may be represented by the following Chemical Formula 1:

[0045] <Chemical Formula 1>

[0046] Li 1-x A x M1 1-y M2 y O 2-z S z

[0047] In the chemical formula 1,

[0048] A is sodium (Na) or potassium (K),

[0049] M1 includes Ni, Co, Mn, Al or a combination thereof,

[0050] M2 includes Mg, Ti, Zr, W, Si, Ca, B, V or a combination thereof, and

[0051] 0 <x≤0.05、0<y<0.05、0<z<0.01。

[0052] For example, the A may be Na. For example, the y may be 0 <y<0.02。

[0053] According to one embodiment, the lithium transition metal oxide may be represented by the following Chemical Formula 2:

[0054] <Chemical Formula 2>

[0055] Li 1-x Na x M1 1-α-β W α M3 β O 2-z S z

[0056] In the chemical formula 2,

[0057] M1 includes Ni, Co, Mn, Al, or a combination thereof,

[0058] M3 includes Mg, Ti, Zr, Si, Ca, B, V, or a combination thereof, and

[0059] 0 < x ≤ 0.05, 0 < α ≤ 0.01, 0 < β ≤ 0.02, 0 < z < 0.01.

[0060] For example, it can be 0 < β ≤ 0.01.

[0061] Since the content of W is 0 < α ≤ 0.01, the structural stability of the lithium transition metal oxide is improved. When the substitution molar ratio of W exceeds 0.01, the structural stability decreases due to the distortion of the crystal structure, and WO3 is formed as an impurity, so the electrochemical properties may be reduced.

[0062] According to one embodiment, the lithium transition metal oxide can be represented by the following Chemical Formula 3:

[0063] <Chemical Formula 3>

[0064] Li 1-x Na x M1 1-α-γ-δ W α Mg γ Ti δ O 2-z S z

[0065] M1 includes Ni, Co, Mn, Al, or a combination thereof, and

[0066] is 0 < x ≤ 0.05, 0 < α ≤ 0.01, 0 < γ ≤ 0.01, 0 < δ ≤ 0.01, 0 < z < 0.01.

[0067] The x can be 0 < x ≤ 0.05. Here, x refers to the substitution molar ratio of Na to Li in the lithium transition metal oxide represented by Chemical Formula 3. Part of Li in the lithium transition metal oxide represented by Chemical Formula 3 is replaced by Na, thereby improving the structural stability. When Na is substituted in the lattice space where Li is located, during charging, when lithium is deintercalated due to the intervention of Na with a larger ionic radius than lithium, the expansion of the crystal structure is suppressed by the repulsive force between oxygen atoms in the lithium transition metal oxide. As a result, the structural stability of the lithium transition metal oxide can also be achieved during repeated charging.

[0068] According to one embodiment, γ can be 0 < γ ≤ 0.005. Here, γ refers to the substitution molar ratio of Mg to the M1 element in the lithium transition metal oxide represented by Chemical Formula 3. When the substitution molar ratio of Mg satisfies the above range, the structural expansion of the lithium transition metal oxide in the charged state can be suppressed.

[0069] According to one embodiment, δ can be 0 < δ ≤ 0.005. Here, δ refers to the substitution molar ratio of Ti to the M1 element in the lithium transition metal oxide represented by Chemical Formula 3. When the substitution molar ratio of Ti satisfies the above range, the structural expansion of the lithium transition metal oxide in the charged state can be suppressed.

[0070] When W, Mg, and Ti are substituted for the lithium transition metal oxide at the above molar ratios, during the insertion and extraction of lithium in the charged state, due to the interaction between oxygen in the lithium transition metal oxide, the structural expansion of the crystal is suppressed, so the structural stability is improved, thereby improving the life characteristics.

[0071] According to one embodiment, when α, γ, and δ satisfy the above ranges, the structural stability of the lithium transition metal oxide is guaranteed. When any one of α, γ, and δ exceeds the above range, an impurity phase is formed, which may not only act as an impedance during the insertion and extraction of lithium, but may also cause the collapse of the crystal structure during repeated charging.

[0072] According to one embodiment, in Chemical Formula 3, γ and δ can be 0 < β ≤ 0.003 and 0 < γ ≤ 0.003, respectively.

[0073] For example, in Chemical Formula 3, it can be γ = δ. When γ = δ, for example, when the molar ratios of Mg and Ti are the same, due to the charge balance in the lithium transition metal oxide during charging and discharging, the collapse of the crystal structure is suppressed, so the structural stability is improved. As a result, the life characteristics are improved.

[0074] According to one embodiment, z can be 0 < z ≤ 0.01. Here, z refers to the substitution molar ratio of S to the O element in the lithium transition metal oxide represented by Chemical Formula 3.

[0075] Since part of the oxygen element is substituted by S, the binding force with the transition metal increases accordingly, so the transition of the crystal structure of the lithium transition metal oxide is suppressed. As a result, the structural stability of the lithium transition metal oxide is improved.

[0076] On the other hand, when the substitution molar ratio of S exceeds 0.01, the crystal structure becomes unstable due to the repulsive force of S anions, so the life characteristics are reduced, and an impedance layer for the insertion and extraction of lithium is formed during charging, so the initial discharge capacity also decreases.

[0077] According to one embodiment, the lithium transition metal oxide may be a single particle. The concept of a single particle is distinguished from a secondary particle formed by the agglomeration of multiple particles or a particle formed by the agglomeration of multiple particles and the coating of the periphery of the agglomerate. Since the lithium transition metal oxide has a single particle form, particle breakage can be prevented even at a high electrode density. Therefore, a high energy density of the positive electrode active material including the lithium transition metal oxide can be achieved. In addition, compared with secondary particles formed by the agglomeration of multiple single particles, breakage during rolling is suppressed, so that a high energy density can be achieved and degradation of life due to particle breakage can be prevented.

[0078] According to one embodiment, the lithium transition metal oxide may comprise a single crystal. A single crystal is distinct from a single particle. A single particle refers to a particle formed as a single particle, regardless of the type and number of crystals within it, and a single crystal refers to a particle having only one crystal within it. These single-crystal lithium transition metal oxides have very high structural stability and are more conductive to lithium ion conduction than polycrystalline materials, resulting in superior high-speed charging characteristics compared to polycrystalline active materials.

[0079] According to one embodiment, the positive electrode active material is a single crystal or single particle. Since it is formed into a single crystal or single particle, its structure is stable and a high-density electrode can be realized. Therefore, a lithium secondary battery including the positive electrode active material can have both improved life characteristics and high energy density.

[0080] According to one embodiment, the lithium transition metal oxide may be represented by any one of the following Chemical Formulas 4-1 to 4-3.

[0081] <Chemical Formula 4-1>

[0082] Li 1-x1 Na x1 Ni a1 Co b1 Mn c1 W d1 Mg e1 Ti f1 O 2-z1 S z1

[0083] <Chemical Formula 4-2>

[0084] Li 1-x2 Na x2 Ni a2 Co b2 Al c2 W d2 Mg e2 Ti f2 O 2-z2 S z2

[0085] <Chemical Formula 4-3>

[0086] Li 1-x3 Na x3 Ni a3 Co b3 W d3 Mg e3 Ti f3 O 2-z3 S z3

[0087] In the said Chemical Formula 4-1,

[0088] 0 < x1 ≤ 0.05, 0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, 0 < d1 ≤ 0.01, 0 < d1 ≤ 0.005, 0 < e1 ≤ 0.005, 0 < (1 - x1) / (a1 + b1 + c1 + d1 + e1 + f1) < 1, 0.7 < a1 / (b1 + c1 + d1 + e1 + f1) < 1, 0 < (b1 + c1) / (a1 + b1 + c1 + d1 + e1 + f1) < 0.2, and 0 < z1 < 0.01,

[0089] In the said Chemical Formula 4-2,

[0090] When x2 is greater than 0 and less than or equal to 0.05, a2 is greater than 0 and less than 1, b2 is greater than 0 and less than 1, c2 is greater than 0 and less than 1, d2 is greater than 0 and less than or equal to 0.01, d2 is greater than 0 and less than or equal to 0.005, e2 is greater than 0 and less than or equal to 0.005, (1−x2) / (a2 + b2 + c2 + d2 + e2 + f2) is greater than 0 and less than 1, a2 / (b2 + c2 + d2 + e2 + f2) is greater than 0.7 and less than 1, (b2 + c2) / (a2 + b2 + c2 + d2 + e2 + f2) is greater than 0 and less than 0.2, and z2 is greater than 0 and less than 0.01,

[0091] In the said Chemical Formula 4-3,

[0092] 0 < x3 ≤ 0.05, 0 < a3 < 1, 0 < b3 < 1, 0 < d3 ≤ 0.01, 0 < d3 ≤ 0.005, 0 < e3 ≤ 0.005, 0 < (1 - x3) / (a3 + b3 + d3 + e3 + f3) < 1, 0.7 < a3 / (b3 + d3 + e3 + f3) < 1, 0 < b3 / (a3 + b3 + d3 + e3 + f3) < 0.2, and 0 < z3 < 0.01. [[ID=4i]]

[0093] The lithium transition metal oxide satisfying the said composition can stabilize the unstable Ni ions inside and can have a high energy density and long - life stability.

[0094] Conventional positive electrode active materials, including high-nickel-based lithium nickel cobalt manganese oxides, must stabilize unstable Ni ions. However, by introducing W, Mg, and Ti into some of the transition metal positions in the crystal, the positive electrode active material can achieve overall charge balance, thereby suppressing the oxidation of Ni(II) ions to unstable Ni(III) or Ni(IV) ions, and allowing the unstable Ni(III) or Ni(IV) to be reduced to Ni(II). On the other hand, the loss of conductivity caused by the substitution of some transition metal elements, such as W, Mg, and Ti, is compensated by the substitution of some O for S, and the reduction of Li conductivity due to structural deformation during charge and discharge is suppressed by the substitution of some Li for Na, thereby obtaining a positive electrode active material with a stable single crystal structure, high capacity, and long life.

[0095] According to one embodiment, the average particle size (D 50 ) can be 0.1 μm to 20 μm. For example, the average particle size (D 50 ) can be 0.1 μm to 15 μm, 0.1 μm to 10 μm, 1 μm to 20 μm, 5 μm to 20 μm, 1 μm to 15 μm, 1 μm to 10 μm, 5 μm to 15 μm or 5 μm to 10 μm. When the average particle size of the lithium transition metal oxide is within the range, the required energy density per volume can be achieved. When the average particle size of the lithium transition metal oxide exceeds 20 μm, it will cause a sudden drop in charge and discharge capacity. When the average particle size of the lithium transition metal oxide is less than or equal to 0.1 μm, it is difficult to obtain the required energy density per volume.

[0096] Hereinafter, a method for preparing a positive active material according to one aspect will be described in detail.

[0097] The method for preparing a positive active material according to one embodiment includes the steps of mixing a compound containing a Li element, a transition metal compound, a compound containing a sulfur (S) element, and a compound containing an M element to obtain a precursor of a lithium transition metal oxide; and

[0098] The step of heat-treating the precursor to obtain the above-mentioned positive electrode active material comprising a plurality of primary particles, at least one secondary particle comprising an agglomerate of a plurality of primary particles, or a combination thereof, wherein the primary particles have an α-NaFeO2 type crystal structure and include a lithium transition metal compound comprising at least one of Ni, Co, Mn and Al, and part of the transition metal positions in the crystal lattice of the crystal structure are replaced by a doping element M, and part of the oxygen element positions in the crystal lattice are replaced by a sulfur (S) element, wherein,

[0099] The M includes Mg, Ti, Zr, W, Si, Ca, B, V or a combination thereof, wherein,

[0100] In the lithium transition metal compound, the content of M is 1,000 ppm to 4,000 ppm,

[0101] In the lithium transition metal compound, the content of S is less than or equal to 1,000 ppm.

[0102] Generally speaking, in order to synthesize single-particle materials, transition metal precursors / lithium precursors are synthesized by dry mixing and heat treatment at high temperatures (>1,000°C), but due to structural changes in the positive electrode active material caused by the reduction of nickel ions during high-temperature calcination, it is difficult to achieve high reversible capacity, and the presence of excessive residual lithium on the surface of the active material causes stability problems.

[0103] On the other hand, the inventors induced crystal growth at a low temperature of less than 1,000°C after mixing a crystal growth aid with the synthetic raw material to synthesize a single particle material capable of achieving a high reversible capacity. At this time, the crystal growth aid has a melting point that can melt at the sintering temperature of the positive electrode active material. Compared with the synthesis method of high-temperature heat treatment of transition metal precursors / lithium precursors by dry methods, this synthesis method has a lower heat treatment temperature, so the structural change of the positive electrode active material is small, thereby achieving a high reversible capacity and synthesizing a material with less residual lithium on the surface.

[0104] In addition, since the crystal growth aid melts at the sintering temperature of the positive electrode active material to promote uniform mixing and crystal growth of the synthetic raw material materials, the entire process time can be shortened, thereby reducing the preparation cost.

[0105] According to one embodiment, the crystal growth aid may include an alkali metal salt containing an S element, such as a lithium salt. Since the crystal growth aid includes the S element, the S element penetrates into the positive electrode active material crystal during firing, thereby enabling some of the oxygen lattice positions in the crystal to be replaced by the S element. At this time, relative to the entire positive electrode active material, the S element is preferably replaced with less than or equal to 1,000 ppm, and when it exceeds 1,000 ppm, its capacity decreases. This is believed to be because, during the charging and discharging process of the lithium secondary battery, the excess S element acts as a resistance layer that prevents the movement of lithium ions.

[0106] The mixing step includes mechanically mixing the compound containing the specific element. The mechanical mixing is performed by a dry method. The mechanical mixing refers to the process of forming a uniform mixture by applying mechanical force to crush and mix the substances to be mixed. The mechanical mixing can be performed by a mixing device, for example, a ball mill using chemically inert beads, a planetary mill, a stirred ball mill, a vibrating mill, etc. At this time, a small amount of alcohol such as ethanol and a higher fatty acid such as stearic acid can be selectively added to maximize the mixing effect.

[0107] The mechanical mixing is performed in an oxidizing environment in order to prevent the reduction of the transition metal in the transition metal supply source (eg, Ni compound), thereby achieving structural stability of the active material.

[0108] The lithium-containing compound may include lithium hydroxide, oxide, nitride, carbonate, or a combination thereof, but is not limited thereto. For example, the lithium precursor may be LiOH or Li2CO3.

[0109] The transition metal compound may include a hydroxide, oxide, nitride, carbonate or a combination thereof of at least one transition metal selected from Ni, Co, Mn and Al, but is not limited thereto. For example, Ni 0.88 Co 0.09 Al 0.03 (OH)2、Ni 0.80 Co 0.10 Mn 0.10 (OH)2, etc.

[0110] The sulfur (S)-containing compound is a crystal growth aid and can be, for example, lithium sulfate. For example, it can be Li2SO4. The crystal growth aid helps form single crystals and single particles. If the crystal growth aid is not included, the positive electrode active material is synthesized in the form of secondary particles. However, when the crystal growth aid is used in a specific content ratio, single crystals, single particles, and aggregates formed by the aggregation of single particles can be formed.

[0111] The M-containing element compound may include, but is not limited to, hydroxides, oxides, nitrides, carbonates, or combinations thereof of elements including Mg, Ti, Zr, W, Si, Ca, B, V, or combinations thereof, such as W(OH)6, WO3, Mg(OH)2, MgCO3, Ti(OH)2, and TiO2.

[0112] According to one embodiment, the Li-containing compound includes a lithium hydroxide, oxide, nitride, carbonate, or a combination thereof, and the S-containing compound includes lithium sulfate. For example, the Li-containing compound includes a lithium hydroxide, and the S-containing compound includes lithium sulfate. Therefore, the S element can replace oxygen positions in the crystal during the heat treatment process.

[0113] According to one embodiment, the Li-containing compound and the S-containing element compound may be mixed in a molar ratio of 99:1 to 99.9:0.1.

[0114] When the ratio of the Li-containing compound to the S-containing compound exceeds 99:1, for example, when the ratio is 98:2, initial discharge capacity decreases due to an increase in impedance caused by excessive introduction of the S element.

[0115] In addition, the lithium transition metal oxide precursor may further include a compound containing a Na element.

[0116] The Na-containing compound may include, but is not limited to, a hydroxide, an oxide, a nitride, a carbonate, or a combination thereof of Na, for example, NaOH, Na2CO3, or a combination thereof.

[0117] After the mixing step, a heat treatment step may be included. The heat treatment step may include a first heat treatment step and a second heat treatment step. The first heat treatment step and the second heat treatment step may be performed continuously, or have a rest period after the first heat treatment step. In addition, the first heat treatment step and the second heat treatment step may be performed in the same or different chambers.

[0118] The heat treatment temperature in the first heat treatment step may be higher than the heat treatment temperature in the second heat treatment step.

[0119] The first heat treatment step may be performed at a heat treatment temperature of 800° C. to 1200° C. The heat treatment temperature may be, for example, 850° C. to 1200° C., 860° C. to 1200° C., 870° C. to 1200° C., 880° C. to 1200° C., 890° C. to 1200° C., or 900° C. to 1200° C., but is not limited thereto, and includes all ranges formed by selecting any two points within the ranges.

[0120] The second heat treatment step may be performed at a heat treatment temperature of 700° C. to 800° C. The heat treatment temperature may be 710° C. to 800° C., 720° C. to 800° C., 730° C. to 800° C., 740° C. to 800° C., 750° C. to 800° C., 700° C. to 780° C., 700° C. to 760° C., 700° C. to 750° C., or 700° C. to 730° C., but is not limited thereto, and includes all ranges formed by selecting any two points within the ranges.

[0121] According to one embodiment, the heat treatment time in the first heat treatment step may be shorter than the heat treatment time in the second heat treatment step.

[0122] For example, the heat treatment time in the first heat treatment step may be 3 hours to 5 hours, 4 hours to 5 hours, or 3 hours to 4 hours, but is not limited thereto, and includes all ranges formed by selecting any two points within the ranges.

[0123] For example, the heat treatment time in the second heat treatment step may be 10 hours to 20 hours or 10 hours to 15 hours, but is not limited thereto, and includes all ranges consisting of selecting any two points within the ranges.

[0124] The first heat treatment step may include a step of heat treatment at a heat treatment temperature of 800° C. to 1200° C. for 3 hours to 5 hours.

[0125] The second heat treatment step may include a step of heat treatment at a heat treatment temperature of 700° C. to 800° C. for 10 hours to 20 hours.

[0126] The first heat treatment step causes the lithium transition metal oxide to form a positive electrode active material with a layered structure, while causing particle growth to achieve a single crystal shape. In the first heat treatment step, it is believed that each primary particle in the lithium transition metal oxide in the secondary particle shape grows rapidly, and therefore cannot withstand the stress between the particles and exposes the interior of the primary particles and condenses with each other, thereby forming a single crystal positive electrode active material for a secondary battery. In the second heat treatment step, heat treatment is performed for a long time at a lower temperature than the first heat treatment step, thereby improving the crystallinity of the layered structure generated in the first heat treatment step. A single-phase, single-crystal and single-particle high-nickel-based positive electrode active material can be obtained by the first and second heat treatment steps.

[0127] According to one embodiment, the lithium transition metal oxide prepared by the preparation method is a single crystal or a single particle, and the single crystal may have a layered structure. In addition, the average particle size of the lithium transition metal oxide may be 0.1 μm to 20 μm.

[0128] In addition, regarding the content of the lithium transition metal oxide, refer to the above description.

[0129] In addition, in the lithium transition metal oxide prepared by the preparation method of the positive electrode active material, the existing Ni 2+ oxidation, and lead to the existing unstable Ni 3+ ions are reduced to Ni 2+ ions, thereby obtaining a lithium transition metal oxide with a stable structure and high density. In addition, due to the reduced Ni 2+ ions and Li + The similar ionic radius of the ions promotes Li / Ni disordering. During the process of Li insertion and extraction, Ni ions fill the empty lattice, thereby achieving structural stability of the crystal.

[0130] According to another aspect, a positive electrode is provided, comprising the positive electrode active material.

[0131] According to another aspect, a lithium secondary battery is provided, which includes the positive electrode, the negative electrode, and an electrolyte.

[0132] Since the lithium secondary battery includes the positive electrode active material comprising the lithium transition metal oxide, the capacity retention rate after 50 charge and discharge cycles is greater than or equal to 89%.

[0133] The initial discharge capacity of the lithium secondary battery is greater than or equal to 204 mAh / g.

[0134] The positive electrode and the lithium secondary battery including the same may be prepared by the following method.

[0135] First, prepare the positive electrode.

[0136] For example, a positive electrode active material composition comprising the above-mentioned positive electrode active material, a conductive material, a binder, and a solvent is prepared. The positive electrode active material composition is directly coated on a metal current collector to prepare a positive electrode plate. Alternatively, the positive electrode active material composition can be cast on a separate support, and then a film peeled from the support can be laminated on a metal current collector to prepare a positive electrode plate. The positive electrode is not limited to the forms listed above and can also be in forms other than those listed.

[0137] As the conductive material, graphite such as natural graphite and artificial graphite; carbon black; conductive tubes such as carbon nanotubes; conductive whiskers such as fluorocarbons, zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide, etc. can be used, but it is not limited to these, and all materials that can be used as conductive materials in the relevant technical field can be used.

[0138] As the binder, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, mixtures thereof, metal salts, or styrene-butadiene rubber-based polymers can be used, but are not limited thereto. All materials that can be used as a binder in the relevant technical field can be used. As another example of the binder, lithium salts, sodium salts, calcium salts, or Na salts of the above polymers can be used.

[0139] As the solvent, N-methylpyrrolidone, acetone, water, or the like may be used, but is not limited thereto, and all materials that can be used as a solvent in the relevant technical field may be used.

[0140] The contents of the positive electrode active material, conductive material, binder, and solvent are at levels commonly used in lithium batteries. Depending on the application and composition of the lithium battery, one or more of the conductive material, binder, and solvent may be omitted.

[0141] Then, prepare the negative electrode.

[0142] For example, a negative electrode active material composition comprising a mixture of a negative electrode active material, a conductive material, a binder, and a solvent is prepared. This negative electrode active material composition is directly coated on a metal current collector having a thickness of 3 to 500 μm and dried to produce a negative electrode plate. Alternatively, the negative electrode active material composition can be cast onto a separate support, and the film peeled from the support is then laminated onto a metal current collector to produce a negative electrode plate.

[0143] The negative electrode current collector is not particularly limited as long as it is a conductive material that does not cause chemical changes in the battery in the relevant technical field. For example, copper, nickel, and copper surface treated with carbon can be used.

[0144] As the negative electrode active material, any material that can be used as a negative electrode active material for lithium batteries in the relevant technical field can be used. For example, it can include at least one selected from the group consisting of lithium metal, metals that can be alloyed with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

[0145] For example, the metal that can be alloyed with lithium can be Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element or a combined element thereof, but not Si), Sn-Y alloy (where Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth element or a combined element thereof, but not Sn), etc. The element Y can be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se or Te.

[0146] For example, the transition metal oxide can be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, etc.

[0147] For example, the non-transition metal oxide can be SnO2, SiO x (0 < x < 2), etc.

[0148] The carbon-based material can be crystalline carbon, amorphous carbon or a mixture thereof. The crystalline carbon can be amorphous, plate-like, flaky, spherical or fibrous graphite, such as natural graphite or artificial graphite, etc., and the amorphous carbon can be soft carbon (soft carbon: low-temperature fired carbon), hard carbon, mesophase pitch carbide, and fired coke, etc.

[0149] As the conductive material, binder and solvent in the negative electrode active material composition, the same materials as those in the case of the positive electrode active material composition can be used.

[0150] The contents of the negative electrode active material, conductive material, binder and solvent are at levels commonly used in lithium batteries. Depending on the use and composition of the lithium battery, one or more of the conductive material, binder and solvent can be omitted.

[0151] Then, a separator inserted between the positive electrode and the negative electrode is prepared.

[0152] As the diaphragm, all materials commonly used in lithium batteries can be used. A material with low impedance to the movement of electrolyte ions and excellent electrolyte permeability can be used. The diaphragm can be a single-layer film or a multilayer film, for example, it can be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene (PTFE) or a combination thereof, and can be in the form of a non-woven fabric or a woven fabric. In addition, a mixed multilayer film such as a polyethylene / polypropylene 2-layer diaphragm, a polyethylene / polypropylene / polyethylene 3-layer diaphragm, a polypropylene / polyethylene / polypropylene 3-layer diaphragm, etc. can be used. For example, in lithium ion batteries, a windable diaphragm such as polyethylene, polypropylene, etc. can be used, and in lithium ion polymer batteries, a diaphragm with excellent organic electrolyte permeability can be used. For example, the diaphragm can be prepared by the following method.

[0153] A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition can be directly applied to an electrode and dried to form a separator. Alternatively, the separator composition can be cast onto a support and dried, and then a separator film peeled from the support can be laminated onto the electrode to form a separator.

[0154] The polymer resin used to prepare the separator is not particularly limited, and any material used as an electrode plate binder can be used, for example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or a mixture thereof.

[0155] Then, prepare the electrolyte.

[0156] For example, the electrolyte may be an organic electrolyte. Alternatively, the electrolyte may be a solid. For example, it may be boron oxide or lithium oxynitride, but is not limited thereto. Any material known in the art that can be used as a solid electrolyte may be used. The solid electrolyte may be formed on the negative electrode by sputtering or other methods.

[0157] For example, the organic electrolyte can be prepared by dissolving a lithium salt in an organic solvent.

[0158] As the organic solvent, all materials that can be used as organic solvents in the technical field can be used. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, and dibutyl carbonate; esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, and 2-methyltetrahydrofuran; nitriles such as acetonitrile; and amides such as dimethylformamide. The organic solvent can be used alone or in combination. For example, a solvent containing a mixed cyclic carbonate and a chain carbonate can be used.

[0159] Alternatively, a gel polymer electrolyte such as polyethylene oxide or polyacrylonitrile impregnated with an electrolyte solution, or LiI, Li3N, Li x Ge y P z S α 、Li x Ge y P z S α X δ (X=F, Cl, Br) and other inorganic solid electrolytes.

[0160] As the lithium salt, all materials that can be used as lithium salts in the relevant technical field can be used. For example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (however, x and y are natural numbers), LiCl, LiI or a mixture thereof, etc.

[0161] like Figure 5 As shown, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, negative electrode 2, and separator 4 are contained in a battery case 5 by winding or folding. Then, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6, thereby completing the lithium battery 1. The battery case 5 can be cylindrical, square, pouch-shaped, coin-shaped, or film-shaped. For example, the lithium battery 1 can be a film-shaped battery. The lithium battery 1 can be a lithium-ion battery.

[0162] A separator may be provided between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked into a bi-battery structure, it is immersed in an organic electrolyte, and the resultant is housed in a bag and sealed to complete a lithium ion polymer battery.

[0163] Furthermore, multiple battery structures are stacked to form battery packs, which can be used in all devices requiring high capacity and high power, such as laptop computers, smartphones, and electric vehicles.

[0164] Furthermore, due to the excellent lifespan and high-speed characteristics of the lithium battery, it can be used in electric vehicles (EVs). For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Furthermore, it can be used in fields that require large amounts of electricity storage, such as electric bicycles, power tools, and power storage systems.

[0165] The present invention is described in more detail by the following Preparation Examples, Examples and Comparative Examples. However, the Examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0166] (Preparation of Positive Electrode Active Material)

[0167] Preparation Examples 1 to 19

[0168] The materials in specific contents shown in Tables 1 and 2 below were mechanically mixed for about 15 minutes, and the mixed powder was then fired at 960° C. for 4 hours and at 700° C. for 10 hours to synthesize a positive electrode active material.

[0169]

Table 1

[0170]

[0171]

Table 2

[0172]

[0173] (Half-cell preparation)

[0174] Example 1

[0175] The positive electrode active material synthesized in Preparation Example 1, the conductive material, and the binder were mixed at a weight ratio of 96:2:2 to prepare a slurry. Here, carbon black (Super-P) was used as the conductive material, and polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone was used as the binder.

[0176] The slurry was evenly coated on an Al current collector and dried at 110°C for 2 hours to prepare a positive electrode. The loading level of the plate was 11.0 mg / cm 2 , the electrode density is 3.6g / cc.

[0177] The prepared positive electrode was used as a working electrode, a lithium foil was used as a counter electrode, and a liquid electrolyte was used, wherein LiPF6 was added as a lithium salt to a mixed solvent of EC / EMC / DEC in a volume ratio of 3 / 4 / 3 to achieve a LiPF6 concentration of 1.3 M, and a CR2032 half-cell was prepared according to a generally known process.

[0178] Examples 2 to 5

[0179] A CR2032 half-cell was prepared in the same manner as in Example 1, except that the positive electrode active materials synthesized in Preparation Examples 2 to 5 were used instead of the positive electrode active material synthesized in Preparation Example 1.

[0180] Comparative Examples 1 to 14

[0181] CR2032 half cells were prepared in the same manner as in Example 1, except that the positive electrode active materials synthesized in Preparation Examples 6 to 19 were used instead of the positive electrode active material synthesized in Preparation Example 1.

[0182] Evaluation Example 1: SEM and XPS Analysis

[0183] The positive electrode active materials synthesized in Preparation Examples 6 to 9 were subjected to SEM analysis, and the SEM photos are as follows: Figure 1 Preparation Example 6 in which lithium sulfate was not added was confirmed to have a secondary particle shape, but it was confirmed that all positive electrode active materials in the form of single particles or aggregates of single particles were synthesized in Preparation Examples 7 to 9 in which lithium sulfate was added.

[0184] In addition, XPS analysis was performed on the positive electrode active material prepared in Preparation Example 1 to confirm whether the S element replaced the oxygen position in the crystal. The results are as follows: Figure 2 As shown. Figure 2 As a result of XPS analysis, raw data including noise was obtained (indicated by a dark solid line), and two main peaks at about 164 eV and 170 eV were observed from a graph (indicated by two dotted lines) fitted by removing noise from these data. These peaks refer to the presence of an SO bond in the structure of the positive electrode active material, and this proves that S in the active material replaces the oxygen position.

[0185] Evaluation Example 2: Analysis based on the S element ratio

[0186] The initial discharge capacity and initial efficiency were measured for the positive electrode active materials synthesized in Preparation Examples 1, 8, and 9. The results are shown in Table 3 below.

[0187]

Table 3

[0188] S (ppm) D50(μm) Initial discharge capacity (mAh / g) Initial efficiency (%) Preparation Example 1 970 5.1 205 89 Preparation Example 8 1980 5.3 202 88 Preparation Example 9 9150 5.7 195 84

[0189] It can be seen that as the ratio of lithium sulfate increases, the average size of the particles (D50) increases, while the reversible capacity decreases. As a result, it can be seen that excessive S substitution leads to a decrease in reversible capacity.

[0190] Evaluation Example 3: Element Ratio Analysis

[0191] For the positive electrode active materials synthesized in Preparation Examples 1 to 3 and Preparation Examples 10 to 16, the content ratios of Na, doping elements (W, Mg, Ti) and S element were analyzed, as shown in Table 4 below.

[0192]

Table 4

[0193] Na (ppm) W(ppm) Mg (ppm) Ti (ppm) S (ppm) Preparation Example 1 200 1,000 200 200 970 Preparation Example 2 200 2,400 700 700 970 Preparation Example 3 200 1,500 300 300 970 Preparation Example 10 200 - 200 200 970 Preparation Example 11 200 - 700 700 970 Preparation Example 12 200 2,800 700 700 970 Preparation Example 13 200 2,600 200 200 970 Preparation Example 14 200 800 200 200 970 Preparation Example 15 200 2,400 900 900 970 Preparation Example 16 200 920 30 30 970

[0194] As shown in Table 4, it can be confirmed that the S content in the positive electrode active materials synthesized in Preparation Examples 1 to 3 is less than or equal to 1000 ppm, and the total content of the doping elements W, Mg, and Ti is 1000 ppm to 4000 ppm. In addition, in Preparation Examples 10 to 16, it was confirmed that the total content of the doping elements exceeded the range of 1000 ppm to 4000 ppm.

[0195] Evaluation Example 4: Normal Temperature Life Evaluation (1)

[0196] The half-cells prepared in Examples 1 to 3 and Comparative Examples 2, 5 to 11 were left to rest for 10 hours, then charged to 4.25 V at 0.2 C in constant current (CC) mode, and then charged to a current corresponding to 0.05 C in constant voltage (CV) mode. Subsequently, they were discharged to 3.0 V at 0.2 C in CC mode, completing the formation process.

[0197] Then, at room temperature (25°C), the battery was charged to 4.25 V at 0.5 C in CC mode, and then charged to a current corresponding to 0.05 C in CV mode. Then, the battery was discharged to 3.0 V at 1 C in CC mode, and this process was repeated 50 times. The capacity retention rate of the cycle was calculated as follows: Figure 3 and as shown in Table 6. In addition, the initial discharge capacity and initial efficiency were calculated, and the results are shown in Table 5 below.

[0198]

Table 5

[0199]

[0200]

Table 6

[0201] Capacity retention after 50 cycles (%) Comparative Example 2 23.4 Comparative Example 5 38.3 Comparative Example 6 48.4 Comparative Example 9 83.5 Comparative Example 11 75.3 Example 1 89.8 Example 2 91.4 Example 3 90.0

[0202] It can be seen from Table 5 that in Comparative Examples 7 and 8 using the positive electrode active materials of Preparation Examples 12 and 13 having a W content exceeding 2500 ppm, and Comparative Example 10 using the positive electrode active material of Preparation Example 15 having a doping element content exceeding 4000 ppm, the initial reversible capacity and efficiency were reduced compared to Examples 1 to 3. Therefore, room temperature life evaluation was performed on Comparative Examples 2, 5, 6, 9, and 11, which had initial discharge capacity and initial efficiency similar to those of Examples 1 to 3.

[0203] Refer to Table 6 and Figure 3 Comparative Examples 2, 5, 6, 9, and 11 had similar initial discharge capacities and initial efficiencies as Examples 1 to 3, but experienced a sudden capacity drop as the charge and discharge cycles progressed. After 50 cycles, Examples 1 to 3 showed a maximum capacity retention difference of approximately 68%.

[0204] This is considered to be a result that, in Examples 1 to 3, the total content of the doping elements was 1000 ppm to 4000 ppm, but the total content of the doping elements included in Comparative Examples 2, 5, 6, 9, and 11 exceeded the range.

[0205] Evaluation Example 5: Normal Temperature Life Evaluation (2)

[0206] The half-cells prepared in Examples 4 and 5 and Comparative Examples 12 to 14 were left to stand for 10 hours, then charged to 4.25 V at 0.2 C in CC mode, and then charged to a current corresponding to 0.05 C in CV mode. Subsequently, they were discharged to 3.0 V at 0.2 C in CC mode, thereby completing the formation process.

[0207] Then, at room temperature (25°C), the battery was charged to 4.25 V at 0.5 C in CC mode, and then charged to a current corresponding to 0.05 C in CV mode. Then, the battery was discharged to 3.0 V at 1 C in CC mode, and this process was repeated 50 times. The capacity retention rate of the cycle was calculated as follows: Figure 4 and as shown in Table 7.

[0208]

Table 7

[0209] Capacity retention after 50 cycles (%) Comparative Example 12 82.6 Comparative Example 13 88.3 Comparative Example 14 85.4 Example 4 92.2 Example 5 91.0

[0210] Reference Figure 4As shown in Table 7, compared with Comparative Example 13 and Comparative Example 14 using a total content of doping elements of less than 1000 ppm (Comparative Example 14 using the positive active material of Preparation Example 19) and more than 4000 ppm (Comparative Example 13 using the positive active material of Preparation Example 18), Examples 4 and 5 of the positive active materials of Preparation Examples 4 and 5 having a total content of doping elements of 1000 ppm to 4000 ppm and a S content of less than or equal to 1000 ppm show improved capacity retention after 50 cycles. In addition, compared with Comparative Example 2 of the positive active material of Preparation Example 17 not containing W, Examples 4 and 5 also show improved capacity retention. Therefore, it can be seen that the NCM-based positive active material includes W, the total content of doping elements is 1000 ppm to 4000 ppm, and when the S content is less than or equal to 1000 ppm, it shows high capacity and long life characteristics. Although preferred embodiments of the present invention have been described above with reference to the accompanying drawings and examples, these are merely exemplary and those skilled in the art will appreciate that various modifications and equivalent embodiments may be made therefrom. Therefore, the scope of protection of the present invention shall depend solely on the appended claims.

Claims

1. A positive electrode active material comprising: A plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof, wherein The primary particles have an α-NaFeO2 type crystal structure and include a lithium transition metal oxide containing at least one of Ni, Co, Mn and Al, and part of the transition metal positions in the crystal lattice of the crystal structure are replaced by a doping element M, and part of the oxygen element positions in the crystal lattice are replaced by a sulfur element S, wherein, The M includes Mg, Ti, W or a combination thereof, wherein, In the lithium transition metal oxide, the content of M is 1,000 ppm to 4,000 ppm, In the lithium transition metal oxide, the content of S is less than or equal to 1,000 ppm, The lithium transition metal oxide is represented by the following chemical formula 1: <Chemical Formula 1> The 1-x A x M1 1-y M2 y O 2-z S z In the chemical formula 1, A is Na, M1 includes Ni, Co, Mn, Al or a combination thereof, M2 includes Mg, Ti, W or a combination thereof, and 0 <x≤0.05、0<y<0.05、0<z<0.01。 2. The positive electrode active material according to claim 1, wherein The lithium transition metal oxide includes W, In the lithium transition metal oxide, the content of W is 1,000 ppm to 4,000 ppm.

3. The positive electrode active material according to claim 1, wherein In the lithium transition metal oxide, the content of Na is 100 ppm to 250 ppm.

4. The positive electrode active material according to claim 1, wherein In the lithium transition metal oxide, the content of M is 1,200 ppm to 4,000 ppm.

5. The positive electrode active material according to claim 1, wherein In the lithium transition metal oxide, the content of nickel is greater than or equal to 80 mol %.

6. The positive electrode active material according to claim 1, wherein The lithium transition metal oxide is represented by the following chemical formula 2: <Chemical Formula 2> Li 1-x So x M1 1-α-β W α M3 β O 2-z S z In the chemical formula 2, M1 includes Ni, Co, Mn, Al or a combination thereof, M3 includes Mg, Ti or a combination thereof, and 0 <x≤0.05、0<α≤0.01、0<β≤0.02、0<z<0.01。 7. The positive electrode active material according to claim 1, wherein The lithium transition metal oxide is represented by the following chemical formula 3: <Chemical Formula 3> Li 1-x So x M1 1-α-γ-δ W α Mg γ Tea δ O 2-z S z M1 includes Ni, Co, Mn, Al or a combination thereof, and 0 <x≤0.05、0<α≤0.01、0<γ≤0.01、0<δ≤0.01、0<z<0.01。 8. The positive electrode active material according to claim 7, wherein In the chemical formula 3, 0<γ≤0.005, and 0<δ≤0.

005.

9. The positive electrode active material according to claim 7, wherein In the chemical formula 3, γ=δ.

10. The positive electrode active material according to claim 1, wherein In the lithium transition metal oxide, a molar ratio of Li / a molar ratio of a transition metal is less than 1.

11. The positive electrode active material according to claim 1, wherein The average particle size of the primary particles is 1 μm to 20 μm.

12. A method for preparing a positive electrode active material, comprising: a step of mixing a compound containing a Li element, a transition metal compound, a compound containing an S element, and a compound containing an M element to obtain a precursor of a lithium transition metal oxide; The step of heat-treating the precursor to obtain a positive electrode active material comprising a plurality of primary particles, an aggregate of a plurality of primary particles, or a combination thereof, wherein: The primary particles have an α-NaFeO2 type crystal structure and include a lithium transition metal compound containing at least one of Ni, Co, Mn and Al, and part of the transition metal positions in the crystal lattice of the crystal structure are replaced by the doping element M, and part of the oxygen element positions in the crystal lattice are replaced by the S element, wherein, The M includes Mg, Ti, W or a combination thereof, In the lithium transition metal oxide, the content of M is 1,000 ppm to 4,000 ppm, In the lithium transition metal oxide, the content of S is less than or equal to 1,000 ppm, The lithium transition metal oxide is represented by the following chemical formula 1: <Chemical Formula 1> The 1-x A x M1 1-y M2 y O 2-z S z In the chemical formula 1, A is Na, M1 includes Ni, Co, Mn, Al or a combination thereof, M2 includes Mg, Ti, W or a combination thereof, and 0 <x≤0.05、0<y<0.05、0<z<0.01。 13. The method for preparing a positive electrode active material according to claim 12, wherein: The Li-containing compound includes lithium hydroxide, oxide, nitride, carbonate or a combination thereof, The sulfur-containing compound includes lithium sulfate.

14. The method for preparing a positive electrode active material according to claim 12, wherein: The Li element-containing compound and the S element-containing compound are mixed in a molar ratio of 99:1 to 99.9:0.

1.

15. The method for preparing a positive electrode active material according to claim 12, wherein: The heat treatment includes a first heat treatment step and a second heat treatment step, wherein: The heat treatment temperature in the first heat treatment step is higher than the heat treatment temperature in the second heat treatment step. 16 . A positive electrode comprising the positive electrode active material according to claim 1 .

17. A lithium secondary battery comprising: A positive electrode comprising a positive electrode active material according to any one of claims 1 to 11; negative electrode; as well as electrolytes.

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