Positive electrode active material, method for preparing same, positive electrode, and rechargeable lithium battery

Abstract

The invention relates to a positive electrode active material, a method for preparing the same, a positive electrode, and a rechargeable lithium battery. The positive electrode active material includes particles having a core of a lithium nickel-based composite oxide, and a nickel reduction layer disposed on a surface of the core and containing nickel having an oxidation number of less than 3 +. The thickness of the nickel reduction layer from the surface of the particle to the center of the particle is less than or equal to 10 nanometers.

Description

Technical Field

[0001] According to one or more embodiments, the present disclosure relates to a positive electrode active material, a preparation method thereof, a positive electrode including the positive electrode active material, and a rechargeable lithium battery including the positive electrode. Background Art

[0002] Portable information devices (such as cellular phones, laptop computers, smart phones, etc.) and / or electric vehicles can use rechargeable lithium batteries with relatively high energy density and relatively high portability (e.g., easy portability) as driving power sources. Recently, research has been actively conducted to use rechargeable lithium batteries with relatively high energy density as driving power sources for hybrid vehicles and / or electric vehicles, or as power storage power sources for residential power storage (e.g., power walls).

[0003] One or more suitable positive electrode active materials have been studied to obtain or realize rechargeable lithium batteries for these purposes. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides and lithium cobalt oxides are mainly used as positive electrode active materials. In recent years, high nickel positive electrode active materials with a nickel content (e.g., amount) greater than or equal to about 80 mol% have been actively developed because they can achieve relatively high energy density. However, due to structural degradation caused by charging and discharging, surface side reactions with the electrolyte and / or degradation caused by particle fracture, the use of these positive electrode active materials may be limited. Accordingly, it is desirable or necessary to develop positive electrode active materials that achieve relatively high energy density and long cycle life characteristics. Summary of the invention

[0004] One or more aspects relate to a positive electrode active material including a lithium nickel-based composite oxide, a positive electrode, and a rechargeable lithium battery, which can achieve high capacity, inhibit or reduce structural degradation and crack generation due to charging and discharging, and obtain or achieve long cycle life characteristics.

[0005] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the presented embodiments of the disclosure.

[0006] According to one or more embodiments, the positive electrode active material includes a particle (e.g., in the form of a particle) (e.g., the positive electrode active material includes a plurality of particles or is in the form of a plurality of particles), the particle including a core of a lithium nickel composite oxide, and a nickel reduction layer disposed on the surface of the core and including nickel having an oxidation number less than about 3+. The thickness of the nickel reduction layer may be less than or equal to about 10 nanometers (nm) as measured from the particle surface (i.e., the surface of the particle) to the center of the particle (i.e., the center of the particle).

[0007] According to one or more embodiments, a method for preparing a positive electrode active material includes mixing a nickel-based composite hydroxide and a lithium raw material, followed by a first firing, crushing the first fired product, and washing with washing water to provide a washed first fired product, drying the washed first fired product, and then performing a second firing, wherein a weight ratio of the crushed first fired product to the washing water is about 1:0.5 to about 1:0.9.

[0008] One or more embodiments provide a positive electrode for a rechargeable lithium battery including the aforementioned positive electrode active material.

[0009] One or more embodiments provide a rechargeable lithium battery including the aforementioned positive electrode, a negative electrode, and an electrolyte.

[0010] The positive electrode active material according to one or more embodiments may obtain or achieve high capacity and long cycle life characteristics by suppressing or reducing structural degradation (eg, due to repeated charging and discharging), crack generation, and / or side reactions with an electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 to Figure 4 Each is a diagram schematically illustrating a lithium rechargeable battery according to one or more embodiments.

[0012] Figure 5 Annular dark field transmission electron microscope (ADF-TEM) image of a cross section of the first positive electrode active material prepared in Comparative Example 1 cut using a focused ion beam (FIB).

[0013] Figure 6 To magnify Figure 5 Scanning transmission electron microscope (STEM) image of the portion shown in the box.

[0014] Figure 7 For along Figure 6 The results of electron energy loss spectroscopy (EELS) in the direction indicated by the arrow.

[0015] Figure 8 The TEM image of the cross section of the positive electrode active material of Comparative Example 1 shows Figure 7 An image of the analysis results.

[0016] Fig. 9 1 is an ADF-TEM image of a cross section of the first positive electrode active material prepared in Example 1 cut by FIB.

[0017] Fig.10 By enlarging Fig. 9 STEM image taken of the section marked by the arrow.

[0018] Fig.11 Shown along Fig.10 The EELS results were performed in the direction indicated by the arrow.

[0019] Fig.12 The TEM image of the cross section of the positive electrode active material of Example 1 shows Fig.11 An image of the analysis results.

[0020] Fig.13 The results of differential scanning calorimetry (DSC) analysis of the positive electrode active materials prepared in Example 1 and Comparative Example 1 are shown.

[0021] Fig.14 Graph showing evaluation of cycle-life characteristics of the rechargeable lithium batteries of Example 1 and Comparative Example 1.

[0022] Fig.15 This is a SEM image of a cross section of the positive electrode active material of Comparative Example 1 taken after 75 cycles.

[0023] Fig.16 for Fig.15 An enlarged image of the first positive electrode active material is shown in FIG.

[0024] Fig.17 for Fig.15 An enlarged image of the second positive electrode active material is shown in FIG.

[0025] Fig.18 This is a SEM image of a cross section of the positive electrode active material of Example 1 taken after 75 cycles.

[0026] Description of Reference Numerals

[0027] 100: Rechargeable lithium battery 10: Positive electrode

[0028] 11: Positive electrode lead lug 12: Positive electrode terminal

[0029] 20: Negative electrode 21: Negative electrode lead lug

[0030] 22: Negative electrode terminal 30: Separator

[0031] 40: electrode assembly 50: shell

[0032] 60: Sealing member 70: Electrode terminal piece

[0033] 71: Positive electrode terminal tab 72: Negative electrode terminal tab DETAILED DESCRIPTION

[0034] Hereinafter, specific embodiments will be described in more detail so that those of ordinary skill in the art can easily implement them. Examples thereof are illustrated in the accompanying drawings, wherein the same reference numerals refer to the same elements throughout, and a repeated description thereof may not be provided. Accordingly, embodiments are only described with reference to the accompanying drawings to explain aspects of the present description. However, the present disclosure may be implemented in many different forms and should not be construed as being limited to the example embodiments set forth herein, but rather the present disclosure is limited by the scope of the claims.

[0035] The terms used herein are for describing the embodiments only and are not intended to limit the present disclosure.The singular expressions "a," "an," and "the" include plural expressions, including "at least one," unless the context clearly indicates otherwise.

[0036] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like, of the components.

[0037] In this document, it should be understood that the use of terms such as “comprises,” “comprise,” “comprising,” “includes,” “including,” “include,” “having,” “has,” and / or “have” are intended to specify the presence of implemented aspects, quantities, steps (e.g., actions or tasks), elements, and / or their (e.g., any appropriate) combinations, but do not exclude the possibility of the presence or addition of one or more other features, quantities, steps (e.g., actions or tasks), elements, and / or their (e.g., any appropriate) combinations.

[0038] In the accompanying drawings, the thickness of layers, films, panels, regions, etc. are exaggerated for clarity, wherein the same reference numerals denote the same elements throughout, and a repeated description thereof may not be provided in the specification. It will be understood that if (for example, when) an element (such as a layer, film, region, or substrate) is referred to as being "on" another element, it may be directly on the other element, or there may also be intervening elements. In contrast, if (for example, when) an element is referred to as being "directly on" another element, there are no intervening elements.

[0039] In one or more embodiments, the term “layer” herein includes not only a shape formed on the entire surface when viewed from a plan view but also a shape formed on a partial surface.

[0040] It will be understood that although the terms "first", "second", "third", etc. may be used herein to describe one or more appropriate elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings stated herein, a first element, component, region, layer or part described herein may be referred to as a second element, component, region, layer or part.

[0041] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one of," "one of," and "selected from," if (e.g., when) preceding or following a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, the expressions "at least one of a to c," "at least one of a, b, and c," and "at least one selected from a, b, and c" may indicate only a, only b, only c, both a and b (e.g., simultaneously), both a and c (e.g., simultaneously), both b and c (e.g., simultaneously), all of a, b, and c, or variations thereof.

[0042] Spatially relative terms (such as "below," "below," "below," "above," "on," etc.) may be used herein to easily describe the relationship of one element or feature to another element or feature. It will be understood that the spatially relative terms are intended to cover different orientations of the device in use or operation in addition to the orientations illustrated in the drawings. For example, if (e.g., when) the device in the drawings is turned over, an element described as "below" or "below" other elements or features will be oriented "above" the other elements or features. Thus, the example term "below" may cover both (e.g., simultaneously) orientations of above and below. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative terms used herein may be interpreted accordingly.

[0043] The terms used in this article are used for the purpose of describing only specific embodiments, and are not intended to limit the present disclosure. Unless otherwise defined, all terms used in this article (including chemical terms, technical terms and scientific terms) have the same meaning as the meaning generally understood by those of ordinary skill in the field to which the present disclosure belongs. It will be further understood that terms (such as those defined in common dictionaries) should be interpreted as having the same meaning as their meanings in the context of the relevant field and the present disclosure, and will not be interpreted in an ideal or overly formal sense, unless explicitly defined in this article.

[0044] Example embodiments are described herein with reference to cross-sectional views of schematic diagrams as ideal embodiments. As such, it is expected that the shapes illustrated will be different due to, for example, manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as being limited to the specific shapes of the zones illustrated herein, but should include deviations in shape, for example, caused by manufacturing. For example, a zone illustrated or described as flat may typically have rough and / or nonlinear features. Moreover, the illustrated sharp corners may be rounded. Therefore, the zones illustrated in the accompanying drawings are schematic in nature, and their shapes are not intended to illustrate the precise shape of the zones, and are not intended to limit the scope of the claims.

[0045] The term "may" will be understood to refer to "one or more embodiments of the present disclosure", some of which include the described elements, and some of which do not include the elements and / or include alternative elements. Similarly, alternative language such as "or" means that "one or more embodiments of the present disclosure" each include the corresponding listed items.

[0046] In this context, "consisting essentially of" indicates that any additional components do not substantially affect the chemical, physical, optical, or electrical properties of the target moiety.

[0047] Further, in this specification, the phrase “on a plane” or “plan view” indicates that a target portion is observed from the top, and the phrase “on a cross section” indicates that a cross section formed by vertically cutting the target portion is observed from the side.

[0048] The term "particle size" as used herein refers to the average diameter of the particles when the particles are spherical, and refers to the average major axis length of the particles when the particles are non-spherical. For example, the average particle size can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer or by a transmission electron micrograph or a scanning electron micrograph. The average particle size value can be obtained by measuring using a dynamic light scattering method, performing data analysis, counting the number of particles in each particle size range, and calculating therefrom. Unless otherwise specified, the average particle size (D 50 ) may refer to the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. If (for example, when) the measurement is performed by laser diffraction, more specifically, the particles to be measured are dispersed in a dispersion medium, and then an ultrasonic wave of about 28 kHz is introduced into a laser diffraction particle size measuring device of the related art (for example, MT 3000 available from Microtrac, Ltd.), and after irradiation with an output power of 60 W, the average particle diameter (D ) based on 50% of the particle size distribution in the measuring device may be calculated. 50 When no other definition is provided, the average particle size (D) as used herein is 50)The diameter of the particle at which the cumulative volume is 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in a scanning electron microscope image.

[0049] In this document, the term "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0050] In this document, the term "metal" is construed to include the concepts of ordinary metals, transition metals, and metalloids (semi-metals).

[0051] Positive electrode active material

[0052] In one or more embodiments, the positive electrode active material may be provided as particles (e.g., each as multiple particles) including a core of a lithium nickel-based composite oxide (e.g., in the form of particles including a core of a lithium nickel-based composite oxide), and may further include a nickel reduction layer disposed on the surface of the core. The nickel reduction layer may include nickel with an oxidation number less than 3+. For example, as measured from the particle surface (i.e., the surface of the particle) to (e.g., toward) the particle center (i.e., the center of the particle), the nickel reduction layer is present with a thickness of less than or equal to about 10 nanometers (nm).

[0053] Based on the total amount of metals other than lithium in 100 mol% of the lithium nickel-based composite oxide, the nickel content (e.g., amount) may be greater than or equal to about 80 mol%, for example, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, greater than or equal to about 94 mol%; and less than or equal to about 99 mol%.

[0054] For example, the lithium nickel-based composite oxide may be represented by Chemical Formula 1.

[0055] Chemical Formula 1

[0056] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0057] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.2, 0.8 ≤ x1 < 1, 0 < y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 and M 2Each of them can be independently at least one (e.g., one or more) element selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X can be at least one (e.g., one or more) element selected from F, P, and S.

[0058] In Chemical Formula 1, 0.85 ≤ x1 < 1, 0 < y1 ≤ 0.15, and 0 ≤ z1 ≤ 0.15, or 0.9 ≤ x1 < 1, 0 < y1 ≤ 0.1, and 0 ≤ z1 ≤ 0.1.

[0059] For example, the lithium nickel-based composite oxide can be represented by Chemical Formula 2 or Chemical Formula 3.

[0060] Chemical Formula 2

[0061] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0062] In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.2, 0.8 ≤ x2 < 1, 0 < y2 ≤ 0.2, 0 ≤ z2 ≤ 0.2, 0.9 ≤ x2 + y2 + z2 ≤ 1.1, and 0 ≤ b2 ≤ 0.1, M 3 can be at least one (e.g., one or more) element selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X can be F, P, S, and / or its (e.g., any appropriate) combination.

[0063] In Chemical Formula 2, 0.9 ≤ x2 ≤ 0.99, 0.01 ≤ y2 ≤ 0.1, and 0 ≤ z2 ≤ 0.1.

[0064] [Chemical Formula 3]

[0065] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0066] In Chemical Formula 3, 0.9≤a3≤1.2, 0.8≤x3≤0.98, 0.01≤y3≤0.19, 0.01≤z3≤0.19, 0≤w3≤0.19, 0.9≤x3+y3+z3+w3≤1.1, and 0≤b3≤0.1, M 4 It may be Al, Mn and / or any suitable combination thereof, M 5 It may be at least one (e.g., one or more) element selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X may be F, P, S, and / or (e.g., any appropriate) combination thereof.

[0067] In Chemical Formula 3, 0.9≤x3≤0.98, 0.01≤y3≤0.09, 0.01≤z3≤0.09, and 0≤w3≤0.09.

[0068] It will be understood that high nickel positive electrode active materials require a water washing process because residual lithium is excessively produced on the particle surface during the synthesis process. In the washing process, ideally only lithium compounds (such as Li2CO3, LiOH, etc.) on the surface of the positive electrode active material particles should be removed. However, depending on the degree, conditions, etc. of the washing process, even the active lithium inside the positive electrode active material may be removed therewith. In this way, if (for example, when) the lithium inside the structure of the positive electrode active material is removed, not only the reversible capacity will be reduced, but also the crystal structure will change or phase change will occur, thereby degrading the performance. For example, if (for example, when) lithium is dissolved, lithium nickel oxide, etc. may become nickel oxide, etc., for example, forming NiO, resulting in a reduction in which the oxidation number of Ni is reduced from 3+ to 2+. Because Ni (II) compounds (such as NiO, etc.) will not be converted back into lithium-containing compounds, the result will not only reduce the reversible capacity, but also promote the side reactions of the surface of the positive electrode active material particles and the electrolyte, thereby causing the degradation of the overall battery performance. Thus, on the surface of the positive electrode active material particle, the portion where the oxidation number of nickel becomes lower than 3+ may be referred to as a "nickel reduction layer", for example, a "low oxidation layer" or a "disordering layer".

[0069] In one or more embodiments, by appropriately or suitably adjusting the washing process to reduce the thickness of the nickel reduction layer to about 10 nanometers (nm) or less, a positive electrode active material can be provided that can inhibit or reduce degradation of the positive electrode active material (e.g., due to charging and discharging) and improve the cycle life characteristics of a rechargeable lithium battery.

[0070] The thickness of the nickel reduction layer may be, for example, less than or equal to about 7 nm, for example, about 1 nm to about 7 nm, about 1 nm to about 5 nm, or about 2 nm to about 4 nm. The thickness of the nickel reduction layer can be measured by performing TEM-EELS analysis on a cross section of the positive electrode active material particle. For example, in a TEM image of a cross section of a positive electrode active material particle, EELS analysis is performed from the surface of the particle toward the inside, and in the EELS analysis graph, the portion where the peak near 855 eV moves to the left can be identified as a portion where the oxidation number of nickel has become less than 3+, and the portion can be defined as a nickel reduction layer. The nickel reduction layer according to one or more embodiments is observed to have a thickness range of 10 nm or less from the surface of the particle toward the inside.

[0071] The nickel reduction layer may include NiO, and the composition inside the particle (i.e., excluding the nickel reduction layer) may be, for example, a mixture of the composition of Chemical Formula 1 and a compound such as NiO. Accordingly, the oxidation number of nickel in the nickel reduction layer may be greater than or equal to about 2+ and less than about 3+, for example, greater than or equal to about 2+ and / or less than or equal to about 2.5+.

[0072] In one or more embodiments, the oxidation number of nickel in the particles excluding the nickel reduction layer (eg, each particle excluding the nickel reduction layer) may be about 3+.

[0073] The particles may be in the form of secondary particles (e.g., particles having a core of a secondary particle), which may be (e.g., may each be) provided or made by aggregating a plurality of primary particles (i.e., a plurality of aggregated primary particles), or may be single particles (e.g., in the form of single particles) (e.g., the single particles are each a monolithic core).

[0074] The average particle size (D 50 ) may be about 0.5 micrometers (μm) to about 20 μm or about 1 μm to about 18 μm. For example, if (for example, when) the particles are in the form of secondary particles, the average particle size (D 50 ) may be about 3 μm to about 20 μm, about 5 μm to about 18 μm, or about 8 μm to about 15 μm. If (for example, when) the particles are in the form of single particles, the average particle size (D 50 ) may be about 0.5 μm to about 8 μm or about 1 μm to about 5 μm. The average particle size (D 50 ) refers to the diameter of particles accounting for 50% by volume of the cumulative volume in a particle size distribution obtained by randomly measuring the sizes (particle diameters or major axis lengths) of about 20 particles in a scanning electron microscope image.

[0075] Herein, a single particle may exist alone without a grain boundary within the particle, and each particle may be composed of one particle, for example, the particle may be selected from a single particle (e.g., having a single particle core), a monolithic structure (e.g., having a monolithic core), a one-piece structure (e.g., having an one-piece core), and / or a non-aggregated particle (e.g., having a non-aggregated core) (wherein the particles are not aggregated with each other, but exist as independent phases in morphology). In some embodiments, the particle may be represented as a single particle (one-piece particle, single crystal grain), for example, a single crystal. A single particle may exist alone, or the single particles may be aggregated together. For example, about 2 to about 10 single particles may be aggregated with each other and in contact with each other.

[0076] In one or more embodiments, if (for example, when) the particles are in the form of secondary particles (cores), at least a portion of the primary particles constituting each secondary particle (core) may be arranged in a radial array structure. Hereinafter, the radial array structure will be explained in more detail.

[0077] At least a portion of the primary particles constituting the secondary particles may have a plate shape (e.g., in the form of a plate). In the plate structure, the maximum length of the widest side may be referred to as the major axis length (a), and the maximum length of the side approximately orthogonal to it (e.g., perpendicular) may be referred to as the thickness (t), wherein the thickness (t) may be shorter than the major axis length (a). The direction of the major axis length (a) may be referred to as the face direction, and the direction in which the thickness is defined may be referred to as the thickness direction. In one or more embodiments, the radial array structure refers to that the primary particles are arranged in the thickness direction, and the thickness direction is orthogonal to (e.g., perpendicular to) the direction from the center of the secondary particle toward the surface of the secondary particle, or forms an angle of ±5° with the orthogonal direction.

[0078] If (for example, when) at least a portion of the primary particles have a radial array structure, there may be relatively more lithium diffusion channels between the primary particles around the surface of the secondary particles. As a result, more crystal planes capable of transferring lithium to the outside may be exposed (for example, to improve lithium diffusion), thereby providing or ensuring high initial efficiency and capacity. In one or more embodiments, the openings exposed to the surface point to the center of the secondary particles, which can promote lithium diffusion. In one or more embodiments, the radially arranged primary particles can cause the secondary particles to shrink and expand substantially uniformly during the deintercalation and / or intercalation of lithium. Such openings may exist in the (001) direction (for example, in the direction of particle expansion during the deintercalation of lithium), thereby providing or acting as a buffer against shrinkage and expansion. In one or more embodiments, due to the size of the primary particles and the radial array structure, the possibility of cracks occurring during the contraction and expansion of the secondary particles is small. For example, the pores inside the secondary particles can further slow down the volume change, thereby reducing the cracks between the primary particles during charging and discharging, thereby improving the cycle life characteristics of the rechargeable lithium battery and / or reducing the resistance increase of the rechargeable lithium battery.

[0079] For example, secondary particles can include an inner portion comprising an irregular porous structure and an outer portion comprising a radial array structure as a zone around the inner portion (e.g., around the inner portion). For example, unlike the primary particles placed in the outer portion, the primary particles placed in the inner portion can be arranged irregularly. The radial array structure refers to that at least a portion of the primary particles are arranged radially. Compared with the pore size and porosity of the outer portion, the pore size and porosity of the inner portion may be larger and irregular.

[0080] If (for example, when) the secondary particles have an irregular porous structure in the inner part, there may be an aspect of reducing the diffusion distance of lithium ions to the inner part, and in the outer part, lithium ions can be easily inserted into the radially arranged surface of the primary particles. In one or more embodiments, because the primary particles have a small size, it is easy to establish and maintain (for example, ensure) lithium transfer paths between particles. In addition, the primary particles having holes and small sizes between them can slow down the volume change during charging and discharging, and as a result, the stress caused by the volume change during charging and discharging is minimized or reduced. This positive electrode active material can reduce the resistance increase of the rechargeable lithium battery and improve the capacity characteristics and cycle life characteristics.

[0081] In differential scanning calorimetry (DSC) analysis, the positive electrode active material according to one or more embodiments may have a ratio of peak intensity at about 250° C. to peak intensity at about 220° C. of less than 20, for example, less than or equal to about 19, or less than or equal to about 15.

[0082] In one or more embodiments, in the DSC analysis, the positive electrode active material according to one or more embodiments may have no peak in the range of about 170°C to about 210°C (e.g., around about 190°C). In addition, in the DSC analysis, in the range of about 170°C to about 210°C (e.g., at about 190°C), the exothermic range of the positive electrode active material according to one or more embodiments may be less than or equal to about 30 joules per gram (J / g) or about 1J / g to about 20J / g. If (e.g., when) the positive electrode active material satisfies the DSC analysis results described herein, structural degradation and crack generation due to charging and discharging may be suppressed or reduced to obtain or achieve excellent or appropriate cycle life characteristics.

[0083] Method for preparing positive electrode active material

[0084] In one or more embodiments, a method for preparing a positive electrode active material includes: (i) mixing a nickel-based composite hydroxide and at least one lithium raw material, followed by a first firing (e.g., to provide a first fired product), (ii) pulverizing the first fired product and washing it with washing water (e.g., the pulverized first fired product) to provide a washed first fired product, and (iii) drying the washed first fired product, followed by a second firing. Herein, for example, in the washing step (e.g., an action or task), the weight ratio of the pulverized first fired product to the washing water may be from about 1:0.5 to about 1:0.9. For example, the weight ratio may be from about 1:0.6 to about 1:0.8 or from about 1:0.7 to about 1:0.9.

[0085] Since a high-nickel positive electrode active material may produce an excessive (or large amount of) residual lithium on the surface, washing is performed during the synthesis process. In this case, generally, based on about 1 part by weight of the positive electrode active material, about 1 part by weight or more of washing water can be used for washing. In one or more embodiments, based on about 1 part by weight of the positive electrode active material, an attempt may be made to reduce or slow down the washing (e.g., the amount of washing) by adjusting the washing water to about 0.9 part by weight or less. For example, suppressing the additional use of washing water can prevent the thickness of the nickel reduction layer on the surface of the positive electrode active material particles (e.g., the surface of the particles of the positive electrode active material) from further increasing, and / or can suppress or reduce the structural deterioration of the positive electrode active material caused by repeated charging and discharging, thereby improving the cycle life characteristics of the rechargeable lithium battery.

[0086] Based on the total amount of metals in the nickel-based composite hydroxide of 100 mol%, the nickel content (e.g., amount) may be greater than or equal to about 80 mol%, for example, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, greater than or equal to about 94 mol%; and less than or equal to about 99 mol%.

[0087] In one or more embodiments, the nickel-based composite hydroxide may be represented by Chemical Formula 11.

[0088] Chemical Formula 11

[0089] Ni x11 M 11 y11 M 12 z11 (OH)2

[0090] In Chemical Formula 11, 0.8 ≤ x11 < 1, 0 < y11 ≤ 0.2, 0 ≤ z11 ≤ 0.2, 0.9 ≤ x11 + y11 + z11 ≤ 1.1, and M 11 and M 12It may be at least one (e.g., one or more) element selected independently from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0091] In Chemical Formula 11, 0.85 ≤ x11 < 1, 0 < y11 ≤ 0.15, and 0 ≤ z11 ≤ 0.15, or 0.9 ≤ x11 < 1, 0 < y11 ≤ 0.1, and 0 ≤ z11 ≤ 0.1.

[0092] The molar ratio of lithium in the lithium raw material to the total metal of the nickel-based composite hydroxide may be, for example, about 1:0.9 to about 1:1.2.

[0093] The first firing may be carried out in an oxygen atmosphere, for example, in a temperature range of about 700 °C to about 950 °C or about 730 °C to about 900 °C or about 750 °C to about 890 °C for about 2 hours to about 20 hours or about 4 hours to about 18 hours.

[0094] The second firing may be carried out in an oxygen atmosphere, for example, in a temperature range of about 600 °C to about 820 °C or about 650 °C to about 800 °C or about 670 °C to about 750 °C for about 2 hours to about 20 hours or about 3 hours to about 17 hours. Additionally, the second firing (i.e., heat treatment) temperature may be lower than the first firing (i.e., heat treatment) temperature, and the second firing (i.e., heat treatment) time may be substantially the same as or shorter than the first firing (i.e., heat treatment) time.

[0095] Positive electrode

[0096] Some embodiments provide a positive electrode for a rechargeable lithium battery including the aforementioned positive electrode active material. For example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, where the positive electrode active material layer may include the aforementioned positive electrode active material. In addition to the aforementioned positive electrode active material described herein, the positive electrode active material layer may further include other types (kinds) of positive electrode active materials and may optionally further include a binder, a conductive material, and / or a combination thereof (e.g., any suitable combination).

[0097] Binder

[0098] The binder can improve the bonding properties between the positive electrode active material particles and / or the bonding properties between the positive electrode active material particles and the positive electrode current collector. Examples of the binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth) acrylated styrene-butadiene rubber, epoxy resin, (meth) acrylic resin, polyester resin or nylon, but are not limited thereto.

[0099] Conductive Materials

[0100] A conductive material (e.g., an electrical conductor) is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material may include: carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); and / or (e.g., any appropriate) mixtures thereof.

[0101] The respective contents (eg, amounts) of the binder and the conductive material may be about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer.

[0102] The positive electrode current collector may include an Al foil, but the present disclosure is not limited thereto.

[0103] Rechargeable lithium battery

[0104] Some embodiments provide a rechargeable lithium battery including the aforementioned positive electrode, negative electrode, and electrolyte. As an example, the rechargeable lithium battery may include a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte.

[0105] For example, rechargeable lithium batteries may be classified into cylindrical batteries, prismatic batteries, pouch batteries, coin batteries, etc., according to shapes. Figure 1 to Figure 4 is a schematic diagram showing a rechargeable lithium battery according to one or more embodiments, wherein Figure 1 For cylindrical batteries, Figure 2 is a prismatic cell, and Figure 3-4 Each is a pouch-shaped battery. Figure 1 to Figure 4 , the rechargeable lithium battery 100 includes: an electrode assembly 40 having a separator 30 interposed between a positive electrode 10 and a negative electrode 20, wherein a case 50 is housed in the electrode assembly 40. The positive electrode 10, the negative electrode 20 and the separator 30 may be impregnated with an electrolyte solution. Figure 1As shown in , the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Figure 2 In the embodiment, the rechargeable lithium battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. Figure 3 As shown in FIG. 1 , the rechargeable lithium battery 100 includes electrode tabs, for example, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for introducing current formed in the electrode assembly 40 to the outside. Figure 4 As shown in FIG. 1 , the rechargeable lithium battery 100 includes an electrode tab 70 serving as an electrical path for introducing current formed in the electrode assembly 40 to the outside.

[0106] Negative electrode

[0107] The negative electrode may include a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material and may further include a binder, a conductive material and / or (eg, any appropriate) combination thereof.

[0108] Negative electrode active material

[0109] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, or a transition metal oxide.

[0110] Examples of materials that can reversibly intercalate / deintercalate lithium ions may include crystalline carbon, amorphous carbon, and / or (e.g., any suitable) combinations thereof as carbonaceous negative electrode active materials. Crystalline carbon may be natural graphite or artificial graphite in an amorphous or flaky, flake-like, spherical, or fibrous (e.g., in the form of fibers). Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0111] The lithium metal alloy may include an alloy of lithium and at least one metal of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn (e.g., selected from one or more of the foregoing).

[0112] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, silicon-carbon composites, SiO x(0 < x ≤ 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and their (e.g., any suitable) combinations, such as 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, Te, Po, and / or their (e.g., any suitable) combinations) or their (e.g., any suitable) combinations. The Sn-based negative electrode active material can be Sn, SnO x (0 < x ≤ 2), Sn alloy, and / or their (e.g., any suitable) combinations.

[0113] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) can be, for example, about 0.5 μm to about 20 μm. According to one or more embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it can include secondary particles (cores) in which silicon primary particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the silicon primary particles. For example, the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed (present) in the amorphous carbon matrix.

[0114] The silicon-carbon composite can further include crystalline carbon. For example, the silicon-carbon composite can include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, and / or their (e.g., any suitable) combinations. The amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbonized products, and calcined coke.

[0115] If (e.g., when) the silicon-carbon composite includes silicon and amorphous carbon, then based on 100 wt% of the silicon-carbon composite, the content (e.g., amount) of silicon can be about 10 wt% to about 50 wt% and the content (e.g., amount) of amorphous carbon can be about 50 wt% to about 90 wt%. In one or more embodiments, if (e.g., when) the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, then based on 100 wt% of the silicon-carbon composite, the content (e.g., amount) of silicon can be about 10 wt% to about 50 wt%, the content (e.g., amount) of crystalline carbon can be about 10 wt% to about 70 wt%, and the content (e.g., amount) of amorphous carbon can be about 20 wt% to about 40 wt%.

[0116] In addition, the thickness of the amorphous carbon coating may be from about 5 nanometers (nm) to about 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) may be from about 10 nm to about 1 μm or from about 10 nm to about 200 nm. The silicon particles may exist as silicon alone, in the form of a silicon alloy, or in the oxidized form of silicon. The oxidized form of silicon may be represented by SiO x (0 < x ≤ 2). In some embodiments, the atomic content (e.g., amount) ratio of Si:O indicating the degree of oxidation may be from about 99:1 to about 33:67. If (e.g., when) no other definition is provided otherwise, the average particle size (D 50 ) as used herein indicates the diameter of the particles with a cumulative volume of about 50% by volume in the particle size distribution.

[0117] The Si-based negative electrode active material or the Sn-based negative electrode active material may be mixed with the carbon-based negative electrode active material. If (e.g., when) the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed and used with the carbon-based negative electrode active material, the mixing ratio may be a weight ratio of from about 1:99 to about 90:10.

[0118] Binder

[0119] The binder is used to bond the negative electrode active material particles well to each other and is also used to bond the negative electrode active material to the negative electrode current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, and / or a combination thereof (e.g., any suitable combination).

[0120] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and / or a combination thereof (e.g., any suitable combination).

[0121] The aqueous binder may include styrene-butadiene rubber, (meth)acrylate esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, poly(ethylene oxide), polyvinylpyrrolidone, poly(epichlorohydrin), polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and / or a combination thereof (e.g., any suitable combination).

[0122] If (for example, when) an aqueous binder is used as a binder in the negative electrode active material layer, a cellulose compound capable of imparting viscosity may be further included. As the cellulose compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and an alkali metal salt thereof may be mixed and used. The alkali metal may be Na, K or Li.

[0123] The dry binder may be a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and / or (eg, any appropriate) combinations thereof.

[0124] Conductive Materials

[0125] A conductive material (e.g., an electrical conductor) is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.); metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers (such as polyphenylene derivatives); and / or (e.g., any appropriate) mixtures thereof.

[0126] Based on 100wt% of the negative electrode active material layer, the content (e.g., amount) of the negative electrode active material may be about 95wt% to about 99.5wt%, and based on 100wt% of the negative electrode active material layer, the content (e.g., amount) of the binder may be about 0.5wt% to about 5wt%. For example, the negative electrode active material layer may include about 90wt% to about 99wt% of the negative electrode active material, about 0.5wt% to about 5wt% of the binder, and about 0wt% to about 5wt% of the conductive material.

[0127] Negative electrode current collector

[0128] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof, and may be in the form of foil, sheet or foam. The thickness of the negative electrode current collector may be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm or about 7 μm to about 10 μm.

[0129] Electrolyte

[0130] For example, the electrolyte for a rechargeable lithium battery may be an electrolyte that may include a non-aqueous organic solvent and a lithium salt.

[0131] The non-aqueous organic solvent is used as a medium for transmitting ions participating in the electrochemical reaction of the battery. The non-aqueous organic solvent may include carbonate solvents, ester solvents, ether solvents, ketone solvents or alcohol solvents, aprotic solvents and / or (for example, any appropriate) combinations thereof.

[0132] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valerolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. In one or more embodiments, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles (such as R-CN (wherein R is a C2-C20 straight chain, branched or cyclic hydrocarbon group, and may include a double bond, an aromatic ring or an ether bond, etc.); amides (such as dimethylformamide); dioxolanes (such as 1,3-dioxolane, 1,4-dioxolane, etc.); sulfolane, etc.

[0133] The non-aqueous organic solvent may be used alone or as a mixture of two or more types (or species), and if (for example, when) used as a mixture of two or more types (species), the mixing ratio may be suitably or appropriately adjusted according to the desired or appropriate battery performance, which is widely understood by those skilled in the art.

[0134] If (for example, when) a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be used in mixture, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0135] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon organic solvent may be mixed and used in a volume ratio of about 1:1 to about 30:1.

[0136] The electrolyte may further include vinyl ethylene carbonate, vinylene carbonate or ethylene carbonate-based compounds to improve the battery cycle life.

[0137] Examples of the ethylene carbonate-based compound may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, or cyanoethylene carbonate.

[0138] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, ensures the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts may include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are integers of 1 to 20), at least one of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFBOP) and lithium bis(oxalato)borate (LiBOB).

[0139] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. If (e.g., when) the concentration of the lithium salt is within the described range, the electrolyte may have suitable or appropriate ionic conductivity and viscosity, and thus excellent or appropriate performance may be achieved, and lithium ions may be efficiently moved.

[0140] Diaphragm

[0141] According to the type (or kind) of the rechargeable lithium battery, the separator may be present between the positive electrode and the negative electrode. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, a polytetrafluoroethylene separator, or a multilayer film of two or more layers thereof (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0142] The separator may include a porous substrate and a coating on one or both surfaces (eg, opposite surfaces) of the porous substrate, the coating including an organic material, an inorganic material, and / or (eg, any suitable) combination thereof.

[0143] The porous substrate can be a polymer film formed by any one polymer selected from the following or a copolymer or mixture of two or more thereof: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, polytetrafluoroethylene (e.g., Teflon).

[0144] The porous substrate may have a thickness of about 1 micrometer (μm) to about 40 μm, for example, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 10 μm to about 15 μm.

[0145] The organic material may include a (meth)acryl-based copolymer, which includes: a first structural unit derived from (meth)acrylamide, and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0146] The inorganic material may include inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and (e.g., any suitable) combinations thereof, but the present disclosure is not limited thereto. The average particle size (D 50 ) may be from about 1 nm to about 2000 nm, for example, from about 100 nm to about 1000 nm or from about 100 nm to about 700 nm.

[0147] The organic material and the inorganic material may be mixed in one coating layer, or may exist in a form in which a coating layer including an organic material and a coating layer including an inorganic material are stackable.

[0148] The coating layer may have a thickness of about 0.5 μm to about 20 μm, for example, about 1 μm to about 10 μm or about 1 μm to about 5 μm.

[0149] Terms such as "substantially", "about" and "approximately" are used as relative terms and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values ​​that would be recognized by one of ordinary skill in the art. They include the stated value and an acceptable range of deviation determined by one of ordinary skill in the art taking into account the limitations and errors associated with the measurement of that quantity. For example, "about" may refer to one or more standard deviations, or ±30%, ±20%, ±10%, ±5% of the stated value.

[0150] The numerical ranges disclosed herein include and are intended to disclose all sub-ranges of the same numerical precision. For example, the range of "1.0 to 10.0" includes all sub-ranges (such as 2.4 to 7.6, for example) having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0. Therefore, the applicant reserves the right to amend this specification (including the claims) to explicitly set forth any sub-ranges contained within the range explicitly set forth herein.

[0151] Examples and comparative examples of the present disclosure are described in more detail herein.However, the following examples are merely examples of one or more embodiments, and the present disclosure is not limited to the following examples.

[0152] Example

[0153] Example 1

[0154] 1. Preparation of positive electrode active material

[0155] Preparation of the first lithium nickel composite oxide

[0156] First, a nickel composite hydroxide (Ni ) as a precursor of the first positive electrode active material was synthesized by a coprecipitation method described in more detail elsewhere herein. 0.945 Co 0.04 Al 0.015 (OH)2). For example, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O) and sodium aluminum sulfate (NaAl(SO4)2·12H2O) are dissolved in a solvent of distilled water at a molar ratio of 94.5:4:1.5 to prepare a mixed solution of metal raw materials. In order to form a complex compound, ammonia water (NH4OH) and sodium hydroxide (NaOH) as a precipitant are prepared.

[0157] Step 1 (e.g., action or task): 2.5 kW / m 3 , NH 4 OH 0.40 M, pH 10.5 ~ 11.5, reaction time 6 hours hour

[0158] First, ammonia water was added to the reactor at a concentration of 0.40 M. Then, the reactor was heated at 2.5 kW / m 3 ) and a reaction temperature of 50° C., and the reaction is started, while the metal raw material mixed solution and the complexing agent (NH4OH) are added thereto at 85 mL / min and 10 mL / min, respectively. The reaction is carried out for 6 hours, while NaOH is added thereto to maintain the pH. After checking, if (for example, when) the average particle size of the core particles obtained as a result of the reaction is about 6.5 micrometers (μm) to 7.5 μm, the second step (for example, action or task) is performed as described herein.

[0159] Step 2 (e.g., action or task): 2.0 kW / m 3 , NH4 OH0.45M, pH10.5~11.5, reaction Response time 18 hours hour

[0160] The reaction temperature was maintained at 50°C, while the metal raw material mixed solution and the complexing agent were added at 85 mL / min and 12 mL / min, respectively, and the concentration of the complexing agent was set to 0.45 M. While adding NaOH thereto to maintain the pH, the reaction was carried out for 18 hours. In this article, the stirring power was reduced to 2.0 kW / m 3 , which is less than the stirring power in step 1 (e.g., action or task). After checking, if (e.g., when) the average particle size of the particles including the core and the intermediate layer obtained is within the range of 13.5 μm to 14 μm, step 3 (e.g., action or task) is performed as described herein.

[0161] Step 3 (e.g., action or task): 1.5 kW / m 3 , NH4 OH 0.45M, pH 10.5~11.5, reaction Time 14 Hour

[0162] The reaction temperature was maintained at 50°C, but the metal raw material mixed solution and the complexing agent were added at the same rate as in step 2 (e.g., action or task), and the concentration of the complexing agent was also set to the same concentration of the complexing agent as in step 2 (e.g., action or task). The reaction was carried out for 14 hours while adding NaOH to maintain the pH. In this article, the stirring power was reduced to 1.5 kW / m 3 , which is less than the stirring power in step 2 (e.g., action or task).

[0163] Post-processing

[0164] The obtained material was washed and dried with hot air at about 150° C. for 24 hours to obtain a first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2).

[0165] First firing

[0166] First, the first nickel-based composite hydroxide obtained from the post-treatment and LiOH were mixed at a molar ratio of Li / (Ni+Co+Al)=1.01, and then preliminarily fired at 820°C for 8 hours in an oxygen atmosphere in a furnace to produce a composite oxide (a first fired product). Subsequently, the composite oxide was pulverized to an average particle size (D) of about 13 micrometers (μm) by using an airflow impact mill. 50 ). Then, a secondary particle having L is produced. 1.01 i 0.945 Co 0.04 Al 0.015The first lithium nickel composite oxide composed of O2 is radially arranged in at least a portion of the primary particles in the secondary particles.

[0167] 2. Preparation of the Second Lithium-Nickel Composite Oxide

[0168] The second nickel composite hydroxide (Ni) as the precursor of the second positive electrode active material was synthesized by a coprecipitation method. 0.94 Co 0.04 Al 0.01 Mn 0.01 (OH)2). For example, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), sodium aluminum sulfate (NaAl(SO4)2·12H2O) and manganese sulfate (MnSO4·H2O) as metal raw materials are dissolved in a solvent of distilled water at a molar ratio of 94:4:1:1 to prepare a mixed solution. The subsequent synthesis is the same as described for the first nickel composite hydroxide.

[0169] The obtained second nickel-based composite hydroxide was mixed with lithium hydroxide at a molar ratio of 1:1, and then heat-treated at 870° C. in an oxygen atmosphere. Subsequently, the obtained product was ground using an airflow impact grinder to obtain a granular product having an average particle size (D 50 ) is a second lithium nickel composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 O2).

[0170] 3. Preparation of the final positive electrode active material

[0171] The first lithium nickel composite oxide and the second lithium nickel composite oxide were mixed at a weight ratio of 8:2, and the mixture was mixed with washing water (distilled water) at a weight ratio of 1:0.9 for washing. Subsequently, after separating the washing water, the obtained product was dried at 180°C and secondary fired at 750°C for 8 hours to prepare a final positive electrode active material in which the first positive electrode active material and the second positive electrode active material were mixed.

[0172] 4. Manufacturing of rechargeable lithium battery cells

[0173] 98.5 wt % of the final positive electrode active material, 1.0 wt % of the polyvinylidene fluoride binder and 0.5 wt % of the carbon nanotube conductive material were mixed to prepare a positive electrode active material layer slurry, and the positive electrode active material layer slurry was coated on an aluminum foil current collector, and then dried and pressed to manufacture a positive electrode.

[0174] 97.5 wt% of graphite negative electrode active material, 1.5 wt% of carboxymethyl cellulose and 1 wt% of styrene-butadiene rubber were mixed in an aqueous solvent to prepare a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector, then dried and pressed to make a negative electrode.

[0175] A rechargeable lithium battery cell was manufactured in a conventional method using a polytetrafluoroethylene separator and using an electrolyte prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0176] Comparative Example 1

[0177] In the washing step (e.g., action or task) of the positive electrode active material, after the crushed first fired product (i.e., the first lithium nickel composite oxide and the second lithium nickel composite oxide) and washing water are mixed at a weight ratio of 1:0.9, 0.6 parts by weight of washing water are further added thereto to wash under the condition that the weight ratio of the crushed first fired product and the washing water is 1:1.5. Except for this difference, the positive electrode active material and the rechargeable lithium battery cell are manufactured in substantially the same manner as in Example 1.

[0178] Evaluation Example 1: STEM and EELS Analysis

[0179] The thickness of the nickel reduction layer can be specifically measured by the following method: (i) obtaining a TEM image of a cross section of a positive electrode active material particle cut by FIB; (ii) magnifying an area near the particle surface in the cross-sectional TEM image to obtain a STEM image; (iii) performing EELS analysis from the surface to the inside of the particle in the STEM image to obtain EELS data at each depth; and (iv) finding curves in the EELS data where the peak near 855 eV moves to the left, and determining at what depth from the particle surface these curves appear, and defining this depth as the thickness of the nickel reduction layer. Figure 5 is an annular dark field transmission electron microscope (ADF-TEM) image of a cross section of the first positive electrode active material in the form of secondary particles cut using a focused ion beam (FIB) in the positive electrode active material according to Comparative Example 1. Figure 6 To magnify Figure 5 Scanning transmission electron microscopy (STEM) image of the area marked by the box. Figure 6 Electron energy loss spectroscopy (EELS) analysis was performed in the direction marked by the arrow, and the results were Figure 7 In Figure 7 In the figure, the portion where the peak near 855 electron volts (eV) moves to the left may be (for example, it can be said to be) a position where the oxidation number of nickel becomes less than 3+. Figure 8 This condition is shown by reflecting the thickness in the TEM image of the cross section of the positive electrode active material of Comparative Example 1. Figure 8 , the thickness of the nickel reduction layer where the oxidation number of nickel becomes less than 3+ is about 25 nanometers (nm).

[0180] Fig. 9 This is an ADF-TEM image of a cross section of the first positive electrode active material in the form of secondary particles cut by FIB in the positive electrode active material particles of Example 1. Fig. 9 The numbers 1 and 4 in refer to the locations of the analysis targets. Fig.10 is through amplification by Fig. 9 The STEM image of the part marked by the arrow is obtained. Fig.10 In the depth direction, EELS analysis was performed and the results were Fig.11 Similarly, Fig.11 The portion where the peak near 855 eV moves to the left is where the oxidation number of nickel becomes less than 3+. Fig.12 This condition is shown by reflecting the thickness in the TEM image of the cross section of the positive electrode active material of Example 1. Fig.12 In Example 1, the thickness of the nickel reduction layer where the oxidation number of nickel becomes less than 3+ is about 3 nanometers (nm).

[0181] Comparative Example 1 showed a nickel reduction layer thickness of 25 nanometers (nm), but Example 1 showed a thickness of less than or equal to 7 nanometers (nm), which was thinner than the thickness of Comparative Example 1 (eg, thinner than the thickness of Comparative Example 1).

[0182] Evaluation Example 2: DSC Analysis

[0183] The positive electrode active materials prepared in Example 1 and Comparative Example 1 were subjected to differential scanning calorimetry (DSC) analysis, and the results were Fig.13 DSC analysis was performed using a differential scanning calorimeter (SENSYS Evo; SETARAM Instrumentation). Specifically, 15 mg of samples charged to 4.45 V (vs. Li / Li + ) positive electrode, add 20 μl of electrolyte to make an evaluation battery cell, and heat up to 400° C. at a rate of 10° C. / min, and measure the heat flow according to the temperature. The three curves of Example 1 correspond to the three experimental results of the positive electrode active material of Example 1. Reference Fig.13 , Comparative Example 1 shows the first peak at around 190°C, but Example 1 shows no peak at the corresponding temperature.

[0184] In one or more embodiments, the exothermic amount was calculated at the first peak near 190° C. by DSC analysis, and the results are shown in Table 1. Table 1 shows two analysis results of Comparative Example 1 and three analysis results of Example 1.

[0185] Table 1

[0186]

[0187]

[0188] Referring to Table 1, Example 1 showed a heat release of 19 joules per gram (J / g) or less at about 190° C., which was lower than that of Comparative Example 1.

[0189] Evaluation Example 3: Evaluation of cycle life characteristics

[0190] At 25° C., the rechargeable lithium battery cells of Example 1 and Comparative Example 1 were initially charged and discharged by charging to 4.45 V at a constant current of 0.2 C, charging to 0.05 C at a constant voltage, and then discharging to 3.0 V at 0.2 C. Subsequently, the rechargeable lithium battery cells were charged and discharged at 1.0 C in a voltage range of 3.0 V to 4.45 V for 75 cycles at 45° C. Fig.14 The capacity retention rate according to the number of cycles is shown. Fig.14 , compared with Comparative Example 1, Example 1 shows that the cycle life characteristics are greatly improved.

[0191] Fig.15 An SEM image showing a cross section of the positive electrode active material of Comparative Example 1 after 75 cycles is shown. Fig.16 To magnify Fig.15 Images obtained of large particles in the form of secondary particles. Fig.17 To magnify Fig.15 An image of a small particle in single particle form. Figure 15 to Figure 17 , Comparative Example 1 showed cracks and microvoids in both large and small particles (eg, simultaneously) after 75 cycles, confirming that structural degradation had advanced.

[0192] Fig.18 : is a SEM image showing a cross section of the positive electrode active material of Example 1 after 75 cycles. Fig.18 , unlike Comparative Example 1, Example 1 shows relatively few (e.g., almost no) cracks and (e.g., no) micropores in both large particles and small particles (e.g., simultaneously), which confirms that structural degradation is effectively suppressed or reduced, and accordingly, it can be understood that the cycle life characteristics of Example 1 are improved.

[0193] The battery management system (BMS) device and / or any other related device or component according to the embodiment of the present disclosure described herein may be implemented using any appropriate hardware, firmware (e.g., a dedicated integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of the device may be formed on an integrated circuit (IC) chip or on a separate IC chip. In addition, the components of the device may be implemented on a flexible printed circuit film, a tape carrier package (TCP), or a printed circuit board (PCB), or formed on a substrate. In addition, the components of the device may be processes or threads running on one or more processors in one or more computing devices, executing computer program instructions and interacting with other system components to perform the functions described herein. The computer program instructions are stored in a memory, which may be implemented in a computing device using a standard memory device (such as, for example, a random access memory (RAM)). The computer program instructions may also be stored in other non-temporary computer-readable media (such as, for example, a CD-ROM, a flash drive, etc.). Moreover, those skilled in the art should recognize that, without departing from the scope of the present disclosure, the functions of various computing devices may be combined or integrated into a single computing device, or the functions of a particular computing device may be distributed on one or more other computing devices.

[0194] Although the present disclosure has been described in conjunction with what are presently considered to be practical example embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments. Instead, the present disclosure is intended to cover one or more suitable modifications and equivalent arrangements included within the spirit and scope of the claims and their equivalents.

Claims

1. A positive electrode active material, comprising: Particles, the particles comprising A core of a lithium nickel composite oxide; and a nickel reduction layer on the surface of the core and comprising nickel having an oxidation number less than 3+, The thickness of the nickel reduction layer from the surface of the particle toward the center of the particle is less than or equal to 10 nanometers.

2. The positive electrode active material according to claim 1, wherein The amount of nickel is greater than or equal to 80 mol % based on 100 mol % of the total amount of metals other than lithium in the lithium nickel-based composite oxide.

3. The positive electrode active material according to claim 1, wherein The lithium nickel composite oxide is represented by Chemical Formula 1: Chemical formula 1 Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In Chemical Formula 1, 0.9≤a1≤1.2， 0.8≤x1<1， 0<y1≤0.2， 0≤z1≤0.2， 0.9≤x1+y1+z1≤1.1, 0≤b1≤0.1， M 1 and M 2 Each is independently at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is at least one element selected from F, P and S.

4. The positive electrode active material according to claim 1, wherein The thickness of the nickel reduction layer is 1 nanometer to 7 nanometers.

5. The positive electrode active material according to claim 1, wherein The oxidation number of the nickel in the nickel reduction layer is greater than or equal to 2+ and less than 2.5+.

6. The positive electrode active material according to claim 1, wherein The oxidation number of the nickel of the particles excluding the nickel reduction layer is 3+.

7. The positive electrode active material according to claim 1, wherein The nickel reduction layer includes NiO.

8. The positive electrode active material according to claim 1, wherein The particle is in the form of a single particle or a secondary particle which is an aggregation of a plurality of primary particles.

9. The positive electrode active material according to claim 1, wherein the average particle size D of the particles is 50 0.5 micron to 20 microns.

10. The positive electrode active material according to claim 1, wherein The positive electrode active material has a ratio of a peak intensity at 250° C. to a peak intensity at 220° C. of less than 20 in differential scanning calorimetry analysis.

11. The positive electrode active material according to claim 1, wherein The positive electrode active material does not include a peak within a range of 170° C. to 210° C. in differential scanning calorimetry analysis.

12. The positive electrode active material according to claim 1, wherein In differential scanning calorimetry analysis, the positive electrode active material has a heat release amount less than or equal to 30 joules per gram in the range of 170° C. to 210° C.

13. A method for preparing a positive electrode active material, the method comprising: Mixing the nickel composite hydroxide and the lithium raw material, followed by first firing; pulverizing the first fired product and washing it with wash water to provide a washed first fired product; as well as drying the washed first fired product, followed by a second firing, The weight ratio of the crushed first fired product to the washing water is 1:0.5 to 1:0.

9.

14. The method of claim 13, wherein The weight ratio is 1:0.7 to 1:0.

9.

15. The method of claim 13, wherein The amount of nickel is 80 mol% to 99 mol% based on 100 mol% of the total amount of metals in the nickel-based composite hydroxide.

16. The method of claim 13, wherein The nickel composite hydroxide is represented by Chemical Formula 11: Chemical formula 11 No x11 M 11 y11 M 12 z11 (OH)2 In Chemical Formula 11, 0.8≤x11<1， 0<y11≤0.2， 0≤z11≤0.2， 0.9≤x11+y11+z11≤1.1, and M 11 and M 12 Each is independently at least one element selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr.

17. The method of claim 13, wherein The molar ratio of lithium in the lithium raw material to the total metal of the nickel composite hydroxide is 1:0.9 to 1:1.

2.

18. The method of claim 13, wherein The first firing is performed at a temperature of 700°C to 950°C, and The second calcination is performed at a temperature of 600°C to 820°C.

19. A positive electrode for a rechargeable lithium battery, comprising the positive electrode active material according to any one of claims 1 to 12 or a positive electrode active material prepared by the method according to any one of claims 13 to 18.

20. A rechargeable lithium battery comprising The positive electrode according to claim 19, negative electrode, and Electrolyte.

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