Positive electrode active material and lithium secondary battery including the same

Abstract

The present specification relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, the present specification relates to a positive electrode active material and a lithium secondary battery including the same, the positive electrode active material being a positive electrode active material including a lithium complex oxide, the lithium complex oxide including at least lithium and a transition metal, the lithium complex oxide including at least one of unit particles and secondary particles in which the unit particles are agglomerated, a coating layer including lithium and tungsten being formed on at least a portion of the surface of one or more of the unit particles, thereby improving capacity and resistance characteristics.

Description

Technical Field

[0001] This specification relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a positive electrode active material and a lithium secondary battery including the same, wherein the positive electrode active material is a positive electrode active material comprising a lithium composite oxide, wherein the lithium composite oxide comprises at least lithium and a transition metal, wherein the lithium composite oxide comprises at least one of unit particles and secondary particles formed by agglomerating the unit particles, and wherein a thin coating comprising lithium and tungsten is formed on at least a portion of the surface of one or more of the unit particles to improve capacity and resistance characteristics. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. As a representative example of such batteries, there are lithium secondary batteries that store electrical energy through the difference in chemical potential during the insertion / extraction of lithium ions at the positive and negative electrodes.

[0003] The aforementioned lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative electrode active materials, and filling the space between the positive and negative electrodes with organic or polymer electrolytes.

[0004] Lithium composite oxides are used as positive electrode active materials for lithium secondary batteries. For example, composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2 are currently under research.

[0005] Among the above-mentioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifetime characteristics and charge / discharge efficiency. However, due to the high price of cobalt used as a raw material, it has the disadvantage of limited price competitiveness.

[0006] Lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they suffer from small capacity and poor high-temperature performance. In addition, LiNiO2-based cathode active materials have the advantage of high discharge capacity, but due to the active cation mixing of lithium and nickel, they are not only difficult to synthesize, but also have the problem of very low rate performance and lifetime characteristics of the synthesized cathode active materials.

[0007] Accordingly, in order to improve low-rate performance and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, ternary lithium composite oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al) or quaternary lithium composite oxides such as NCMA (Ni-Co-Mn-Al) have been developed, in which a portion of the nickel is replaced by cobalt, manganese, and / or aluminum. Since the lower the nickel content in the ternary or quaternary lithium composite oxides mentioned above, the lower the reversible capacity, research on increasing the nickel content in lithium composite oxides is currently underway.

[0008] However, with the increase of nickel content in lithium composite oxides, the stability decreases due to increased cation mixing within the crystal structure, or there is an increase in the content of unreacted lithium impurities such as LiOH and Li2CO3 on the surface. As the content of lithium impurities remaining on the surface of the aforementioned lithium composite oxides increases, gas generation and bulging phenomena in lithium secondary batteries using these lithium composite oxides as the positive electrode active material may be exacerbated. Furthermore, with the increase of lithium impurities remaining on the surface of the aforementioned lithium composite oxides, when preparing pastes for forming the positive electrode active material layer using these lithium composite oxides, there is a problem of gelation of the paste composition due to lithium impurities.

[0009] On the other hand, existing polycrystalline cathode active materials suffer from problems such as cracking or structural collapse at grain boundaries and side reactions with the electrolyte during charging and discharging, leading to increased gas generation. To address these stability and gas generation issues, single-crystal cathode active materials are being developed.

[0010] However, in single-crystal positive electrode active materials with relatively large particle sizes, there is a problem of increased resistance and reduced capacity due to the longer lithium migration path. Summary of the Invention

[0011] Technical issues In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles plays a leading role in the market, the demand for positive electrode active materials used in lithium secondary batteries is also increasing.

[0012] For example, in the prior art, from the point of view of ensuring safety, lithium secondary batteries using lithium iron phosphate (LFP) are mainly used. However, recently, the use of nickel-based lithium composite oxides with a larger energy capacity per unit weight than LFP has been expanding (of course, at present, the relatively cheaper LFP is still used to reduce costs).

[0013] Therefore, the positive electrode active materials used in higher-specification lithium secondary batteries need to simultaneously meet the expected stability and reliability even under more severe operating conditions.

[0014] Considering these various environments, one object of this specification is to provide a positive electrode active material comprising a lithium composite oxide containing at least lithium and a transition metal, and which exhibits excellent electrochemical performance by forming a thin coating containing lithium and tungsten on at least a portion of the surface of more than one unit particle, thereby increasing charge and discharge capacity while reducing resistance.

[0015] In addition, another object of this specification is to provide a lithium secondary battery using the positive electrode active material as defined herein.

[0016] The purpose of this specification is not limited to those stated above. Other purposes and advantages not mentioned herein will be understood through the following description and through the embodiments described herein. Furthermore, it will be readily understood that the purposes and advantages of this invention can be achieved by the means and combinations thereof described in the claims.

[0017] Technical solution According to one aspect of this specification, a positive electrode active material is provided, comprising a lithium composite oxide capable of lithium intercalation / deintercalation, wherein the lithium composite oxide comprises at least lithium and a transition metal, and the lithium composite oxide comprises at least one of unit particles and secondary particles formed by agglomerating the unit particles. A first coating comprising lithium and tungsten and having an average thickness of 3 nm to 10 nm is formed on at least a portion of the surface of one or more of the unit particles. For example, the thickness of the first coating may be 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, or a range between two such values, but is not limited thereto.

[0018] In addition, the average particle size (D) of the above-mentioned unit particles 50 The value is 0.2 Up to 5 For example, it could be 0.2. 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 Or the range between two of their values.

[0019] In one example, the lithium composite oxide described above may contain tungsten in a doped state within the unit particle.

[0020] On the other hand, the tungsten element contained in one or more of the aforementioned unit particles can exhibit a concentration gradient that decreases toward the center of the aforementioned unit particles.

[0021] Furthermore, the aforementioned tungsten concentration gradient may exist only from the surface of the unit particle to a predetermined depth. For example, the predetermined depth, when the diameter of the unit particle is d, may be 0.001d, 0.002d, 0.003d, 0.004d, 0.005d, 0.006d, 0.007d, 0.008d, 0.009d, 0.01d, or a range between two of these values, but is not limited thereto.

[0022] Here, the tungsten element contained in one or more of the aforementioned unit particles may be present at a depth of 0.1 nm to 10 nm, for example, 50 mol%, 52.5 mol%, 55 mol%, 57.5 mol%, 60 mol%, 62.5 mol%, 65 mol%, 67.5 mol%, 70 mol%, 72.5 mol%, 75 mol%, 77.5 mol%, 80 mol%, 82.5 mol%, 85 mol%, 87.5 mol%, 90 mol%, or a range between two of these values, in a direction from the surface of the aforementioned unit particle toward the center of the aforementioned unit particle. For example, 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, or a range between two of these values.

[0023] Furthermore, in one or more of the aforementioned unit particles, at least one of the aforementioned transition metal elements, excluding tungsten, may exhibit a concentration gradient that increases toward the center of the aforementioned unit particle.

[0024] On the other hand, the concentration gradient of the aforementioned transition metal elements may exist only from the surface of the aforementioned unit particle to a predetermined depth. For example, the predetermined depth, when the diameter of the aforementioned unit particle is d, may be 0.001d, 0.002d, 0.003d, 0.004d, 0.005d, 0.006d, 0.007d, 0.008d, 0.009d, 0.01d, or a range between two of these values, but is not limited thereto.

[0025] In one example, the above-mentioned lithium composite oxide can be represented by the following chemical formula 1: [Chemical Formula 1] Li w Ni 1-(x+y+z) W x M1 y M2 z O2 In the above chemical formula 1, M1 is at least one selected from Co, Mn and Al, and M2 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, P, Sr, Ge, Nd, Gd and Cu, with 0.5≤w≤1.5, 0≤x≤0.20, 0≤y≤0.60, 0≤z≤0.20, and 0.40≤1-(x+y+z) ≤0.70. Here, w can be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50 or a range between two of these values, and x can be 0.01, 0.02, or 0. The values ​​are 0.3, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or a range between two of these values. The value y can be 0, 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0. The range of values ​​for z is 22, 0.25, 0.28, 0.31, 0.34, 0.37, 0.40, 0.43, 0.46, 0.49, 0.52, 0.55, 0.58, 0.60, or a range between two of these values. The z values ​​can be 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or 0.1. 1, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 or a range between two of these values, where 1-(x+y+z) can be 0.40, 0.42, 0.45, 0.48, 0.51, 0.54, 0.57, 0.60, 0.63, 0.66, 0.69, 0.70 or a range between two of these values.

[0026] Here, the first coating may comprise a tungsten oxide represented by the following chemical formula 2: [Chemical Formula 2] Li a W b M3 c O d In the above Chemical Formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, W, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd, 0 ≤ a ≤ 10, 0 < b ≤ 8, 0 ≤ c ≤ 8, 2 ≤ d ≤ 13. Herein, the above a can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range between two of these values, the above b can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between two of these values, the above c can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between two of these values, and the above d can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or a range between two of these values.

[0027] In addition, the above first coating may contain a Li6W2O9 phase.

[0028] On the other hand, on at least a part of the surfaces of one or more of the above unit particles, a second coating containing tungsten oxide particles with an average particle diameter of 1 nm to 415 nm may be formed.

[0029] Herein, the average particle diameter of the above tungsten oxide particles is 1 nm to 415 nm or less. For example, it can be 1 nm, 10 nm, 25 nm, 40 nm, 55 nm, 70 nm, 85 nm, 100 nm, 115 nm, 130 nm, 145 nm, 160 nm, 175 nm, 190 nm, 205 nm, 220 nm, 235 nm, 250 nm, 265 nm, 280 nm, 295 nm, 310 nm, 325 nm, 340 nm, 355 nm, 370 nm, 385 nm, 400 nm, 415 nm, or a range between two of these values.

[0030] The above tungsten oxide particles can be represented by the above Chemical Formula 2.

[0031] In addition, the above second coating may contain a Li6W2O9 phase.

[0032] According to another aspect of this specification, a positive electrode containing the above positive electrode active material is provided.

[0033] According to another aspect of this specification, a lithium secondary battery using the above-described positive electrode is provided.

[0034] Beneficial effects According to this specification, a tungsten concentration gradient of thin thickness is formed in the near-surface region of the unit particles constituting lithium composite oxide, and a coating containing tungsten oxide is formed on the surface of the unit particles, thereby improving capacity and resistance characteristics.

[0035] In addition to the effects described above, the specific effects of the present invention will be described below while explaining the specific matters for carrying out the invention. Attached Figure Description

[0036] Figure 1 The results are XRD analysis of the lithium metal oxide prepared in Example 1; Figure 2 The EDS analysis results and surface images of Examples 1-2, Examples 1-5 and Comparative Examples 1-5 prepared in Preparation Example 1 are shown. Figure 3 and Figure 4 These are the TEM analysis results of Examples 1-2 prepared in Preparation Example 1; Figure 5 The results are EIS analysis of the lithium secondary battery prepared in Example 2. Detailed Implementation

[0037] To facilitate understanding of this specification, specific terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used in this specification shall have the meanings commonly understood by one of ordinary skill in the art. Furthermore, unless the context specifically indicates otherwise, the singular form of a term shall also include its plural form, and the plural form of a term shall also be understood to include its singular form.

[0038] Positive electrode active material According to one aspect of this specification, the positive electrode active material is capable of reversible lithium ion insertion / extraction and comprises a lithium composite oxide.

[0039] The aforementioned lithium composite oxide is a composite metal oxide capable of lithium ion insertion / extraction, comprising a layered crystal structure belonging to the R-3m space group. In the diffraction pattern obtained by XRD analysis, the aforementioned lithium composite oxide containing the layered crystal structure exhibits characteristic peaks in the region of 2θ ranging from 18° to 20°.

[0040] In one embodiment, the lithium composite oxide comprises at least lithium and a transition metal. The transition metal may comprise at least one, at least two, at least three, or all of nickel, cobalt, manganese, and aluminum.

[0041] In a non-limiting example, the aforementioned lithium composite oxide may be a lithium-nickel composite oxide containing nickel. Furthermore, the aforementioned lithium composite oxide may be a lithium-nickel composite oxide containing both nickel and cobalt.

[0042] On the other hand, in order to improve low-rate performance and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the aforementioned lithium-nickel composite oxides can be ternary types such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary types such as NCMA (Ni-Co-Mn-Al), where a portion of the nickel is replaced by cobalt, manganese, and / or aluminum. These ternary or quaternary lithium composite oxides may further contain dopants other than nickel, cobalt, manganese, and aluminum. In another embodiment, the aforementioned lithium-nickel composite oxides can be cobalt-free lithium composite oxides, where cobalt is not present in the bulk particles. These cobalt-free lithium composite oxides may further contain dopants other than nickel, cobalt, manganese, and aluminum.

[0043] On the other hand, the aforementioned lithium composite oxide can exist solely as unit particles, or contain secondary particles formed by the aggregation of unit particles, or contain secondary particles formed by the aggregation of unit particles. Here, the aforementioned unit particles can be referred to as primary particles. Furthermore, the aforementioned unit particles can be in single-crystal form, but are not limited thereto.

[0044] Unless otherwise defined, the term “surface portion of a particle” as used herein refers to the region relatively close to the “outermost surface” of the particle, and “center portion of a particle” refers to the region relatively closer to the “center” of the particle than the aforementioned “surface portion”.

[0045] Accordingly, "the surface portion of a unit particle (primary particle)" refers to the area relatively close to the "outermost surface" of the unit particle (primary particle), and "the center portion of a unit particle (primary particle)" refers to the area relatively closer to the "center" of the unit particle (primary particle) than the aforementioned "surface portion".

[0046] Similarly, "the surface part of the secondary particle" refers to the area relatively close to the "outermost surface" of the secondary particle, while "the center part of the secondary particle" refers to the area relatively closer to the "center" of the secondary particle than the "surface part".

[0047] At this point, the region within any particle other than the "surface portion of the particle" can be defined as the "center portion of the particle".

[0048] The aforementioned unit particles can have round, rod-shaped, elliptical, and / or amorphous shapes. Furthermore, unless intentionally done during the manufacturing process, unit particles of various shapes can exist within the same positive electrode active material. Additionally, the aforementioned single particle or unit particle refers to a particle unit that does not exhibit grain boundaries when observed using a scanning electron microscope at a magnification of 5,000 to 20,000x.

[0049] On the other hand, in one example, the average particle size (D) of the aforementioned unit particles 50 The value can be 0.2. Up to 5 For example, it could be 0.2. 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 Or the range between two of their values.

[0050] The average particle size (D) of the above unit particles 50 The average particle size can be the average of the length of the major axis and the length of the minor axis of the aforementioned unit particle ([major axis length + minor axis length] / 2). The average particle size of the aforementioned unit particle can be calculated as the average particle size of all unit particles observed from the surface SEM image and / or cross-sectional SEM image of the aforementioned lithium composite oxide.

[0051] When the average particle size of the aforementioned unit particles is too small, the specific surface area of ​​the positive electrode active material will increase excessively, which may lead to a decrease in stability due to side reactions with the electrolyte. On the other hand, when the average particle size of the aforementioned unit particles is too large, it may actually lead to a decrease in the diffusivity of lithium ions.

[0052] Furthermore, the particle size distribution of the lithium composite oxide in the aforementioned positive electrode active material can be determined using a laser diffraction method. For example, after dispersing the particles in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000) and irradiated with approximately 28 kHz ultrasound at a 60 W output to obtain a volumetric particle size distribution curve. The particle size corresponding to 50% of the volumetric accumulation can then be defined as the average particle size (D). 50 ).

[0053] In this article, “particle size” and “particle diameter” or “particle size” are used to mean the same thing, unless otherwise defined. All “average particle size” refers to the particle size corresponding to 50% of the volume accumulation as determined by the aforementioned laser diffraction method.

[0054] In the presence of secondary particles formed by the aggregation of the aforementioned unit particles, the aforementioned secondary particles may be formed by the aggregation of 2 to 10 of the aforementioned unit particles, for example, by the aggregation of 2, 3, 4, 5, 6, 7, 8, 9 or 10 of the aforementioned unit particles, but are not limited thereto.

[0055] The unit particles constituting the secondary particles may have voids and / or grain boundaries between them. The unit particles may be spaced apart from adjacent unit particles within the secondary particle, forming internal voids. Alternatively, the unit particles may not contact adjacent unit particles to form grain boundaries, but instead contact internal voids, thereby forming a surface existing within the secondary particle. On the other hand, the surface of the unit particles at the outermost surface of the secondary particle exposed to external air (outer atmosphere) forms the surface of the secondary particle.

[0056] The average particle size of the secondary particles formed by the aggregation of the aforementioned unit particles can vary depending on the number of unit particles aggregated, but is typically between 1 and 10. For example, it can be 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 Or the range between two of their values.

[0057] In one example, the lithium composite oxide described above may contain tungsten in a doped state within the unit particle.

[0058] The crystal structure of lithium composite oxides doped with tungsten is stable, which can reduce the generation of structural stress or cracks that may occur during charging and discharging. Furthermore, these tungsten-doped lithium composite oxides exhibit superior discharge capacity and high-rate performance. On the other hand, tungsten doping expands the diffusion path of lithium ions in the lithium composite oxide, thereby reducing interfacial resistance. In other words, tungsten doping can improve the high-output characteristics of the positive electrode active material.

[0059] However, doped tungsten may, depending on its doping state, hinder lithium-ion diffusion or act as a resistor, reducing the conductivity of lithium composite oxides. Furthermore, some tungsten may act as an impurity, thus reducing structural stability. While not always the case, the greater the amount of doped tungsten, the higher the likelihood of such side effects.

[0060] Furthermore, the tungsten element within the aforementioned lithium composite oxide can exist within one or more of the aforementioned unit particles in the form of a concentration gradient that gradually decreases towards the center of the unit particle. That is, the concentration gradient of the tungsten element formed within the aforementioned unit particle can be in the direction from the surface of the unit particle towards the center of the unit particle.

[0061] In this specification, simply doping within a unit particle, forming a concentration gradient within a unit particle, and existing on the surface of a unit particle can be distinguished from each other.

[0062] The characteristics of this tungsten element can be determined using various methods. For example, it can be confirmed through STEM-EDS analysis.

[0063] Thus, when the tungsten element exhibits a concentration gradient that decreases towards the center of the unit particle, the side effects can be minimized while enjoying the advantages of tungsten doping mentioned above.

[0064] This concentration gradient can be formed by dry mixing lithium composite oxide with tungsten compounds followed by a predetermined low-temperature heat treatment process. In particular, by introducing tungsten in this way in a thin layer, the aforementioned lithium composite oxide can exhibit excellent capacitance and resistivity characteristics.

[0065] The concentration gradient of tungsten within a unit particle can reduce the resistivity at the particle surface.

[0066] That is, the concentration gradient of tungsten can exist only from the surface of the unit particle to a predetermined depth. Regions without a concentration gradient include areas where tungsten is absent or where the concentration difference with location is not significant.

[0067] For example, the content of tungsten element contained in one or more of the above-mentioned unit particles at a depth of 0.1 nm to 10 nm, such as 50 mol%, 52.5 mol%, 55 mol%, 57.5 mol%, 60 mol%, 62.5 mol%, 65 mol%, 67.5 mol%, 70 mol%, 72.5 mol%, 75 mol%, 77.5 mol%, 80 mol%, 82.5 mol%, 85 mol%, 87.5 mol%, 90 mol%, or a range between two of these values, may exist, but is not limited thereto.

[0068] In particular, most of the tungsten elements contained in the aforementioned unit particles can be located in the aforementioned concentration gradient layer.

[0069] On the other hand, through the concentration gradient formed by tungsten, at least one of the transition metal elements constituting the lithium composite oxide can exhibit a concentration gradient that increases from the surface toward the center.

[0070] Therefore, the concentration gradient of the aforementioned transition metal elements can exist only from the surface of the aforementioned unit particle to a predetermined depth.

[0071] In one embodiment, the above-mentioned lithium composite oxide can be represented by the following chemical formula 1: [Chemical Formula 1] Li w Ni 1-(x+y+z) W x M1 y M2 z O2 In the above chemical formula 1, M1 is at least one selected from Co, Mn and Al, and M2 is at least one selected from Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, P, Sr, Ge, Nd, Gd and Cu, with 0.5≤w≤1.5, 0≤x≤0.20, 0≤y≤0.60, 0≤z≤0.20, and 0.40≤1-(x+y+z) ≤0.70.

[0072] Here, w, representing the ratio of lithium to all other elements in the aforementioned lithium composite oxide, can be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or a range between two of these values.

[0073] The value x, representing the ratio of tungsten to all elements other than lithium in the aforementioned lithium composite oxide, can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or a range between two of these values.

[0074] In the above chemical formula 1, M1 refers to Co, Mn, and / or Al present in the above lithium composite oxide. The value y, representing the ratio of M1 to all elements other than lithium in the above lithium composite oxide, can be 0, 0.01, 0.04, 0.07, 0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, 0.31, 0.34, 0.37, 0.40, 0.43, 0.46, 0.49, 0.52, 0.55, 0.58, 0.6, or a range between two of these values.

[0075] In the above chemical formula 1, M2 refers to a dopant other than tungsten doped into the lithium composite oxide. The dopant may exist in a doped state within the crystal lattice of the lithium composite oxide (at least one of the lithium layer and / or transition metal layer). The value z, representing the ratio of M2 to all elements other than lithium in the lithium composite oxide, can be 0.00, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or a range between two of these values.

[0076] In the case where the lithium composite oxide contains a dopant, z is greater than 0 in the above chemical formula 1; in the case where the lithium composite oxide does not contain a dopant, z is 0 in the above chemical formula 1.

[0077] The upper and lower limits of the contents of nickel, tungsten, M1 and dopant M2 as defined in the above chemical formula 1 can be appropriately selected within the range that satisfies the above definitions.

[0078] In one example, 1-(x+y+z), representing the ratio of nickel to all elements other than lithium in the above lithium composite oxide, can be 0.40, 0.42, 0.45, 0.48, 0.51, 0.54, 0.57, 0.60, 0.63, 0.66, 0.69, 0.70, or a range between two of these values.

[0079] That is, the aforementioned lithium composite oxide can be a medium-nickel compound. Compared with high-nickel compounds, the lattice oxygen release and surface phase transition tendency of medium-nickel cathode active materials are mitigated, thereby suppressing heat generation and thermal runaway caused by overcharging, short circuits, thermal shock, etc.

[0080] In addition, nickel-based cathode active materials generate relatively few microcracks or metal ion dissolutions during repeated charge and discharge, thus exhibiting excellent lifespan characteristics.

[0081] However, typical medium-nickel cathode active materials have the disadvantage of lower capacity compared to high-nickel cathode active materials.

[0082] The aforementioned lithium composite oxides are medium-nickel lithium composite oxides formed by the agglomeration of single crystals or a small number of single crystal particles, thus exhibiting excellent lifetime and stability. Furthermore, tungsten doping and / or coating through low-temperature heat treatment can result in high capacity and low resistivity. In addition, the aforementioned lithium composite oxides exhibit excellent high-rate capacity.

[0083] Furthermore, when the aforementioned lithium composite oxide contains secondary particles formed by the aggregation of unit particles, the aforementioned concentration gradient layer can also be formed on at least a portion of the interface where there is contact between the unit particles and no direct contact with the external environment, but is not limited thereto.

[0084] On the other hand, a coating may be formed on at least a portion of the surface of one or more of the aforementioned unit particles.

[0085] The tungsten in the above coating can exist in the form of tungsten oxide or lithium tungsten oxide.

[0086] The above coating can be defined as a region containing tungsten oxide and / or lithium tungsten oxide.

[0087] That is, a first coating comprising lithium and tungsten can be formed on at least a portion of the surface of one or more of the aforementioned unit particles. Specifically, tungsten oxide can be present on at least a portion of the surface of one or more of the aforementioned unit particles. For example, the thickness of the first coating can be 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, or a range between two such values, but is not limited thereto.

[0088] Here, the first coating mentioned above refers to the thin coating observed on the surface of the aforementioned unit particle by TEM analysis.

[0089] In this specification, the tungsten concentration gradient and the first coating are distinct concepts. Here, the first coating refers to the tungsten oxide existing independently of the lithium composite oxide.

[0090] The aforementioned tungsten oxide can form a first coating on at least a portion of the surface of the aforementioned unit particles, thereby improving capacitance and resistance characteristics.

[0091] This first coating can be formed by dry mixing lithium composite oxide with tungsten compounds and then applying a predetermined low-temperature heat treatment process.

[0092] In one example, the aforementioned tungsten concentration gradient layer and the aforementioned first coating layer may coexist. In this case, in order to combine their thicknesses to form a thin layer, a specific process as described above is required.

[0093] Furthermore, when the aforementioned lithium composite oxide contains secondary particles formed by the aggregation of unit particles, the aforementioned first coating may also be formed on at least a portion of the interface that is not in direct contact with the external environment through contact between the unit particles, but is not limited thereto.

[0094] On the other hand, when the aforementioned tungsten oxide forms particles on the surface of the aforementioned lithium composite oxide, the average particle size is from 1 nm to 415 nm. For example, it can be 1 nm, 10 nm, 25 nm, 40 nm, 55 nm, 70 nm, 85 nm, 100 nm, 115 nm, 130 nm, 145 nm, 160 nm, 175 nm, 190 nm, 205 nm, 220 nm, 235 nm, 250 nm, 265 nm, 280 nm, 295 nm, 310 nm, 325 nm, 340 nm, 355 nm, 370 nm, 385 nm, 400 nm, 415 nm, or a range between two of these values, but is not limited thereto.

[0095] That is, the aforementioned tungsten oxide particles can form a discontinuous island-like second coating on at least a portion of the surface of one or more of the aforementioned unit particles. The thickness of the aforementioned second coating can be from 1 nm to 415 nm, for example, it can be 1 nm, 10 nm, 25 nm, 40 nm, 55 nm, 70 nm, 85 nm, 100 nm, 115 nm, 130 nm, 145 nm, 160 nm, 175 nm, 190 nm, 205 nm, 220 nm, 235 nm, 250 nm, 265 nm, 280 nm, 295 nm, 310 nm, 325 nm, 340 nm, 355 nm, 370 nm, 385 nm, 400 nm, 415 nm or a range between two of these values, but is not limited thereto.

[0096] When the tungsten oxide particles in the second coating grow excessively, the proportion of the material that can act as a resistor increases, which may reduce the performance of the positive electrode active material.

[0097] Here, the first coating and the second coating existing on the surface of the aforementioned lithium composite oxide can be distinguished based on whether or not particles are formed.

[0098] Depending on the temperature at which the first and second coatings are formed, the coatings may contain various phases, including lithium, tungsten, and oxygen. For example, they may contain phases such as WO3, Li6W2O9, and Li4WO5, but are not limited to these.

[0099] Here, the performance can vary depending on the type of phase contained in the coating. If the coating contains the Li6W2O9 phase, the resistance is low and the capacity reduction caused by the reaction of tungsten and lithium can be minimized.

[0100] The WO3 phase, due to its low conductivity, can reduce capacity and increase resistance. However, during the complete conversion of WO3 to the Li6W2O9 phase, the lithium within the aforementioned lithium composite oxide reacts, potentially further reducing capacity. Therefore, besides precisely converting the WO3 phase to the Li6W2O9 phase, depending on the conditions, the coexistence of the WO3 and Li6W2O9 phases can minimize capacity reduction while simultaneously reducing resistance.

[0101] Here, the tungsten oxide of the first coating and / or the second coating can be represented by the following chemical formula 2: [Chemical Formula 2] Li a W b M3 c O d In the above chemical formula 2, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd, where 0 ≤ a ≤ 10, 0 <b≤8、0≤c≤8、2≤d≤13。

[0102] Here, the aforementioned tungsten oxide can react with lithium impurities, and the ratio 'a' can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range between two of these values. Here, when lithium impurities are not introduced into the coating, 'a' can be 0.

[0103] The value of b, which represents the tungsten ratio in the coating, can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range between two of these values.

[0104] The M3 mentioned above can refer to any component other than tungsten oxide introduced during coating formation, and the c representing its ratio can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or a range of two such values. If no component other than tungsten oxide is introduced, the c can be 0.

[0105] The above d can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13 or a range between two of these values, and can be determined based on the above stoichiometric ratios of Li, W, and M3.

[0106] The upper and lower limits of the content of lithium, tungsten and M3 as defined in the above chemical formula 2 can be appropriately selected within the range that satisfies the above definitions.

[0107] As the above-mentioned positive electrode active material, it can be prepared by various methods as long as it meets the above characteristics. However, based on one aspect, the following method can be considered.

[0108] One method for preparing a positive electrode active material may include a step of mixing lithium transition metal oxide and tungsten oxide and then subjecting the mixture to heat treatment.

[0109] Here, the above heat treatment can be carried out at the highest temperature in the range of 300°C to 500°C, such as 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, 335°C, 340°C, 345°C, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C, 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C, 450°C, 455°C, 460°C, 465°C, 470°C, 475°C, 480°C, 485°C, 490°C, 495°C, 500°C, or any two of these values, but is not limited thereto.

[0110] As mentioned above, the performance of the prepared positive electrode active material can be superior when heat treatment is performed at low temperatures. In one example, to obtain a better phase equilibrium of the tungsten compound, the above heat treatment can be performed at 325°C to 375°C, but is not limited to this.

[0111] The temperature can be maintained at the above maximum temperature for 1 hour to 24 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, 15.5 hours, 16 hours, 16.5 hours, 17 hours, 17.5 hours, 18 hours, 18.5 hours, 19 hours, 19.5 hours, 20 hours, 20.5 hours, 21 hours, 21.5 hours, 22 hours, 22.5 hours, 23 hours, 23.5 hours, 24 hours, or a range of two of these values, but is not limited thereto.

[0112] The heat treatment described above can be performed at a rate from 0.1°C / min to 10°C / min, for example, 0.1°C / min, 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min, 10°C / min, or any two of these values, up to the highest temperature mentioned above, but is not limited thereto.

[0113] Lithium secondary batteries According to another aspect of this specification, a positive electrode comprising a positive current collector and a positive active material layer formed on the positive current collector can be provided. Here, the positive active material layer may comprise positive active materials according to various embodiments of this specification. Therefore, the positive active material is the same as described above, and for convenience, detailed descriptions are omitted; only the remaining components not previously described will be described below.

[0114] The aforementioned positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, it can be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or materials with surface treatments of carbon, nickel, titanium, silver, etc., on aluminum or stainless steel surfaces. Furthermore, the aforementioned positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0115] The aforementioned positive electrode active material layer can be prepared by coating the aforementioned positive electrode current collector with a positive electrode slurry composition that includes a conductive material together with the aforementioned positive electrode active material and, if necessary, a binder.

[0116] At this point, the aforementioned positive electrode active material can be contained in an amount of 80% to 99% by weight, and more specifically 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer. Excellent capacity characteristics can be exhibited when contained within the above-mentioned content range, but it is not necessarily limited thereto.

[0117] The aforementioned conductive materials are used to impart conductivity to the electrodes. In the constructed battery, any material that exhibits electronic conductivity without causing a chemical change can be used without particular restriction. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these materials can be used alone or in combination of two or more. The aforementioned conductive materials can be included in an amount from 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0118] The aforementioned binder enhances the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these binders may be used alone or in combination of two or more. The binder may be included in an amount from 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0119] In addition to using the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition, which is prepared by dissolving or dispersing the aforementioned positive electrode active material and selectively dissolving or dispersing a binder and conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0120] The solvents mentioned above can be solvents commonly used in this technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, etc., and one of them can be used alone or in combination of two or more. The amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and preparation yield of the slurry, and to achieve a viscosity that exhibits excellent thickness uniformity when coated subsequently for the preparation of the positive electrode.

[0121] In another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then pressing the film layer obtained by peeling it off from the support onto the positive electrode current collector.

[0122] Furthermore, according to another aspect of the present invention, an electrochemical element comprising the aforementioned positive electrode can be provided. Specifically, the aforementioned electrochemical element can be a battery, a capacitor, or more specifically, a lithium secondary battery.

[0123] The aforementioned lithium secondary battery may specifically include a positive electrode, a negative electrode opposite to the positive electrode, and a separator and electrolyte between the positive electrode and the negative electrode. Here, the positive electrode is the same as that described above, and for convenience, a detailed description is omitted. Only the remaining components not described above will be specifically described below.

[0124] The aforementioned lithium secondary battery may optionally further include a battery container housing an electrode assembly comprising the aforementioned positive electrode, the aforementioned negative electrode, and the aforementioned separator, as well as a sealing component for sealing the aforementioned battery container.

[0125] The aforementioned negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the aforementioned negative electrode current collector.

[0126] The aforementioned negative electrode current collector is not particularly limited as long as it possesses high conductivity without causing chemical changes in the battery. For example, it can be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, materials with surface treatments of copper or stainless steel using carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys. Furthermore, the aforementioned negative electrode current collector typically has a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities can be formed on its surface to enhance the adhesion of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0127] The aforementioned negative electrode active material layer can be prepared by coating the aforementioned negative electrode current collector with a negative electrode slurry composition that includes a conductive material together with the aforementioned negative electrode active material and, if necessary, a binder.

[0128] As the aforementioned negative electrode active material, compounds capable of reversible lithium insertion and extraction can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂. β Metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, may be used. Furthermore, lithium metal films may also be used as the aforementioned negative electrode active material. Additionally, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, may be used. Soft carbon and hard carbon are representative examples of low-crystallinity carbon. High-crystallinity carbon includes amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature sintered carbon from petroleum or coal tar pitchdered cokes.

[0129] The aforementioned negative electrode active material may be contained in 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0130] The aforementioned binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added at a rate of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0131] The aforementioned conductive material is a component used to further improve the conductivity of the negative electrode active material, and can be added at a rate of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. This conductive material is not particularly limited as long as it is conductive without causing a chemical change in the battery. For example, graphite such as natural or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0132] In one embodiment, the aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing the negative electrode active material and the binder and conductive material in a solvent, onto the negative electrode current collector and then drying it; or it can be prepared by casting the aforementioned negative electrode slurry composition onto a separate support and then pressing the film layer obtained by peeling it off from the support onto the negative electrode current collector.

[0133] On the other hand, in the aforementioned lithium secondary battery, the separator separates the negative electrode from the positive electrode and provides a channel for lithium ion movement. Any separator commonly used in lithium secondary batteries can be used without particular restrictions, but those with low resistance to electrolyte ion movement and excellent electrolyte wetting ability are particularly preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more of these. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymeric substances can be used, and they can be selectively used in single-layer or multi-layer structures.

[0134] Furthermore, examples of electrolytes used in this invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries.

[0135] Specifically, the electrolyte may include organic solvents and lithium salts.

[0136] As for the aforementioned organic solvents, any solvent that can act as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without particular restrictions. Specifically, as the aforementioned organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (EPC) can be used. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane solvents. Among these, carbonate solvents are preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge-discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte performance can be excellent.

[0137] The lithium salts mentioned above can be used without particular restriction as long as they are compounds capable of providing lithium ions used in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 are all acceptable lithium salts. The concentration of the lithium salts is preferably in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within this range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0138] When the electrolyte used in this document is a solid electrolyte, for example, solid inorganic electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, and halide-based solid electrolytes can be used, and sulfide-based solid electrolytes are preferred.

[0139] As materials for sulfide-based solid electrolytes, solid electrolytes containing Li, X (here, X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S can be used. Examples of such sulfide-based solid electrolyte materials include Li₂S-P₂S₅, Li₂S-P₂S-LiX (here, X is a halogen element such as I or Cl), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (Here, m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Here, p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.)

[0140] Solid electrolytes, preferably sulfide-based solid electrolytes, can be amorphous or crystalline, or a mixture of amorphous and crystalline substances.

[0141] Li7La3Zr2O is a material used as an oxide-based solid electrolyte. 12 Li 7-xLa3Zr 1-x Nb x O 12 Li 7- 3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0142] The aforementioned solid electrolyte can be disposed as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Furthermore, the aforementioned solid electrolyte can be partially contained within the positive electrode active material layer of the positive electrode, independent of the aforementioned solid electrolyte layer, or the aforementioned solid electrolyte can be partially contained within the negative electrode active material layer of the negative electrode, independent of the aforementioned solid electrolyte layer.

[0143] In addition to the aforementioned electrolyte components, the electrolyte may further contain additives such as difluoroethylene carbonate or other halogenated alkylene carbonate compounds, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride, etc., to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity. In this case, the aforementioned additives may be included in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0144] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent discharge capacity, output characteristics and lifespan characteristics, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0145] The shape of the lithium secondary battery according to the present invention is not particularly limited, but it can be cylindrical, square, pouch-shaped, or coin-shaped, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also preferably as a unit battery in medium to large-sized battery modules containing multiple battery cells.

[0146] According to another aspect of the present invention, a battery module comprising the above-mentioned lithium secondary battery as a unit and / or a battery pack comprising the same can be provided.

[0147] The aforementioned battery module or battery pack can be used as a power tool; an electric vehicle including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or a power source for medium to large-sized equipment in an energy storage system.

[0148] The above-described matters will be described in more detail below through examples. However, these examples are for illustrative purposes only, and the scope of this specification should not be construed as being limited to these examples.

[0149] Preparation Example 1. Preparation of Positive Electrode Active Material (1) Example 1 Ni synthesized via coprecipitation reaction 0.60 Co 0.08 Mn 0.32 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) and heat-treated in air at 950°C for 4 hours to obtain an intermediate product (lithium transition metal oxide).

[0150] Next, the above intermediate product and WO3 (weighed such that the content of tungsten in the above intermediate product relative to the total transition metal is 0.1 mol%, 0.3 mol%, or 0.5 mol%) are mixed and heat-treated in an air-atmosphere furnace at 350°C or 470°C for 4 hours to obtain a final product with a tungsten-containing coating formed on the surface of the above lithium transition metal oxide.

[0151] The results of ICP analysis on the final product confirmed that the tungsten content in the final product was consistent with the design composition.

[0152] (2) Example 2 Ni synthesized via coprecipitation reaction 0.60 Co 0.08 Mn 0.32The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) and heat-treated at 950°C for 4 hours in air atmosphere to obtain the intermediate product (lithium transition metal oxide).

[0153] Next, the above intermediate product and WO3 (weighed to make the content of tungsten in the above intermediate product relative to the total transition metals 0.3 mol%) are mixed and heat-treated in an air-atmosphere calcination furnace at 300°C to 400°C for 4 hours to obtain a final product with a tungsten-containing coating formed on the surface of the above lithium transition metal oxide.

[0154] The results of ICP analysis on the final product confirmed that the tungsten content in the final product was consistent with the design composition.

[0155] (3) Comparative Example 1 Ni synthesized via coprecipitation reaction 0.60 Co 0.08 Mn 0.32 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) and heat-treated at 950°C for 4 hours in air atmosphere to obtain the intermediate product (lithium transition metal oxide).

[0156] Next, the intermediate product is heat-treated in an air-atmosphere calcination furnace at 350°C, 470°C, or 700°C for 4 hours to obtain the final product.

[0157] In addition, except for heat treatment at 700°C for 4 hours, the final product was obtained in the same manner as in Example 1 and used as Comparative Examples 1-4 to 1-6.

[0158] (4) Comparative Example 2 Ni synthesized via coprecipitation reaction 0.60 Co 0.08 Mn 0.32 The (OH)2 hydroxide precursor was mixed with LiOH (Li / (Ni+Co+Mn) molar ratio = 1.03) and heat-treated in air at 950°C for 4 hours to obtain the final product.

[0159] Preparation Example 2. Preparation of Lithium Secondary Battery (Half-Cell) A positive electrode slurry was prepared by dispersing 94% by weight of each positive electrode active material, 3% by weight of carbon black, and 3% by weight of PVDF binder prepared according to Preparation Example 1 in 30g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was then uniformly coated onto an aluminum film with a thickness of 15μm and vacuum dried at 135°C to prepare a positive electrode for lithium secondary batteries.

[0160] For the above positive electrode, lithium foil was used as the counter electrode, a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separator, and an electrolyte containing LiPF6 at a concentration of 1.15 M was used in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7.

[0161] Experimental Example 1. Crystallographic Analysis of Positive Electrode Active Material Since the distribution of the coating formed in each of the positive electrode active materials prepared according to Preparation Example 1 is different, X-ray diffraction (XRD) analysis was performed to analyze the crystallographic properties of the lithium transition metal oxide contained in the positive electrode active materials.

[0162] Specifically, the XRD analysis described above was performed using a Bruker D8E Endeavor diffractometer employing Cu-Kα radiation (1.540598 Å). From the diffraction patterns obtained by X-ray diffraction (XRD) analysis of the aforementioned positive electrode active material using Cu-kα lines, each tungsten phase was defined with reference to the ICDD XRD standard data card.

[0163] The XRD analysis results are shown in Table 1 below. Figure 1 middle.

[0164] [Table 1]

[0165] Referring to the results in Table 1 above, it can be confirmed that the phase of tungsten (W) formed according to the heat treatment temperature changes.

[0166] Further analysis confirmed that when the heat treatment temperature after adding tungsten raw materials was 300°C to 350°C, although Li6W2O9 was formed, some WO3 remained. On the other hand, at temperatures above 375°C, all WO3 reacted to become the Li6W2O9 phase, and at temperatures above 700°C, the Li4WO5 phase was formed.

[0167] Since WO3 acts as a resistor that cannot participate in the charge-discharge reaction, its resistance is reduced and its performance is improved when WO3 reacts with lithium during tungsten coating. However, if heat treatment is performed at excessively high temperatures, the lithium inside the cathode material will react with tungsten, resulting in a reduction in capacity and a decrease in performance.

[0168] Experimental Example 2. Surface Characteristic Analysis of Positive Electrode Active Material EDS analysis was performed on the samples prepared in Preparation Example 1, including Examples 1-2, Examples 1-5, and Comparative Examples 1-5. The results are shown below. Figure 2 .

[0169] Reference Figure 2 It was confirmed that the surfaces of Examples 1-2, Examples 1-5 and Comparative Examples 1-5, which underwent surface modification, had coatings formed in an island-like pattern.

[0170] In Examples 1-2, tungsten oxide particles with a minimum diameter of 21.1 nm and a maximum diameter of 210.8 nm were found, and the average particle size was confirmed to be 86.7 nm.

[0171] In Examples 1-5, tungsten oxide particles with a minimum diameter of 28.1 nm and a maximum diameter of 657.9 nm were found, and the average particle size was confirmed to be 218.0 nm.

[0172] In Comparative Examples 1-5, there were tungsten oxide particles with a minimum size of 135 nm and a maximum size of 1,257 nm, and the average particle size was confirmed to be 416.1 nm.

[0173] That is, in Examples 1-2 and Examples 1-5, tungsten oxide coatings with relatively small particle sizes compared to lithium composite oxide particles were formed, but in Comparative Examples 1-5, tungsten oxide coatings with relatively large particle sizes were formed.

[0174] The cross-sectional TEM images obtained after cross-sectional processing of the positive electrode active materials prepared in Preparation Example 1 according to Examples 1-2 using a focused ion beam (FIB) were analyzed, and the STEM-EDS line scan results are shown below. Figure 3 and Figure 4 .

[0175] Reference Figure 3 and Figure 4 Based on the EDS analysis results, it can be confirmed that the tungsten concentration decreases from the surface of the unit particle towards the center of the particle.

[0176] More specifically, a thin first coating with a thickness ranging from 3 nm to 10 nm is formed on the positive electrode active material, and a portion of the tungsten is doped into the lithium composite oxide through diffusion.

[0177] Experimental Example 3. Evaluation of the electrochemical characteristics of lithium secondary batteries (half-cells) For the lithium secondary battery (half-cell) prepared in Preparation Example 2, charge / discharge experiments were conducted using an electrochemical analysis apparatus (TOYO SYSTEM CO., LTD., Toscat-3100) at 25°C, a voltage range of 3.0V to 4.45V, and a discharge rate of 2.0C / 0.1C. The initial charge capacity, initial discharge capacity, initial efficiency, and 2.0C / 0.1C rate performance were measured.

[0178] On the other hand, the initial resistance (R) of the lithium secondary battery prepared according to Preparation Example 2 ct The measurements were performed using electrochemical impedance spectroscopy (EIS) in the frequency range of 10 kHz to 0.01 Hz.

[0179] The above measurement results are shown in Tables 2 and 3 below. Figure 5 middle.

[0180] [Table 2]

[0181] [Table 3]

[0182] Referring to the results in Tables 2 and 3 above, it can be confirmed that the tungsten-coated Examples 2 all showed significant improvements in C-rate (2C), initial efficiency, and charging capacity compared to the uncoated Comparative Examples 1-1. Furthermore, it can be confirmed that Examples 2-3 to 2-5, which underwent heat treatment at 350°C to 400°C, were more suitable in terms of overall capacity, C-rate, and resistance. This is believed to be due to the decrease in capacity and increase in resistance caused by the residual WO3 phase at relatively lower temperatures.

[0183] Reference Figure 5 Considering the lower resistance in the examples compared to Comparative Example 2, it can be confirmed that the resistance characteristics were improved by tungsten coating. Furthermore, as examined above, particularly in Examples 2-4 and 2-5, the resistance characteristics were further improved as the proportion of WO3 acting as resistance due to the heat treatment temperature decreased.

[0184] The embodiments of the present invention have been described above. However, those skilled in the art can make various modifications and alterations to the present invention by adding, changing, deleting, or supplementing constituent elements without departing from the spirit of the present invention as described in the claims, and these modifications and alterations should also be considered to be included within the scope of the present invention.

Claims

1. A positive electrode active material, characterized in that, This includes lithium composite oxides capable of lithium intercalation / deintercalation. The aforementioned lithium composite oxides contain at least lithium and transition metals. The aforementioned lithium composite oxide comprises at least one of unit particles and secondary particles formed by agglomerating the aforementioned unit particles. A first coating comprising lithium and tungsten and having an average thickness of 3 nm to 10 nm is formed on at least a portion of the surface of one or more of the aforementioned unit particles.

2. The positive electrode active material according to claim 1, characterized in that, The average particle size (D) of the above unit particles 50 The value is 0.2 Up to 5 .

3. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium composite oxide contains tungsten in a doped state within the aforementioned unit particles.

4. The positive electrode active material according to claim 3, characterized in that, The tungsten element contained in one or more of the aforementioned unit particles exhibits a concentration gradient that decreases toward the center of the aforementioned unit particles.

5. The positive electrode active material according to claim 4, characterized in that, The concentration gradient of tungsten exists only from the surface of the aforementioned unit particle to a predetermined depth.

6. The positive electrode active material according to claim 5, characterized in that, More than 50 mol% of the tungsten element contained in one or more of the aforementioned unit particles are present at a depth of 0.1 nm to 10 nm in the direction from the surface of the aforementioned unit particles toward the center of the aforementioned unit particles.

7. The positive electrode active material according to claim 4, characterized in that, In one or more of the aforementioned unit particles, at least one of the aforementioned transition metal elements, excluding tungsten, exhibits a concentration gradient that increases toward the center of the aforementioned unit particle.

8. The positive electrode active material according to claim 7, characterized in that, The concentration gradient of the aforementioned transition metal elements exists only from the surface of the aforementioned unit particle to a predetermined depth.

9. The positive electrode active material according to claim 1, characterized in that, The above-mentioned lithium composite oxide is represented by the following chemical formula 1: [Chemical Formula 1] The w Nor 1-(x+y+z) W x M1 y M2 z O2 In the above chemical formula 1, M1 is at least one selected from Co, Mn, and Al. M2 is selected from at least one of Na, K, Mg, Ba, B, Ce, Hf, Ta, Cr, F, Al, V, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, P, Sr, Ge, Nd, Gd, and Cu. 0.5≤w≤1.5, 0≤x≤0.20, 0≤y≤0.60, 0≤z≤0.20, 0.40≤1-(x+y+z) ≤0.

70.

10. The positive electrode active material according to claim 1, characterized in that, The first coating described above comprises a tungsten oxide represented by the following chemical formula 2: [Chemical Formula 2] Li a W b M3 c O d In the above chemical formula 2, M3 is selected from at least one of Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd. 0≤a≤10、0 <b≤8、0≤c≤8、2≤d≤13。 11. The positive electrode active material according to claim 1, characterized in that, The first coating described above contains the Li6W2O9 phase.

12. The positive electrode active material according to claim 1, characterized in that, A second coating comprising tungsten oxide particles with an average particle size of 1 nm to 415 nm is formed on at least a portion of the surface of one or more of the aforementioned unit particles.

13. The positive electrode active material according to claim 12, characterized in that, The above-mentioned tungsten oxide particles are represented by the following chemical formula 2: [Chemical Formula 2] Li a W b M3 c O d In the above chemical formula 2, M3 is selected from at least one of Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd. 0≤a≤10、0 <b≤8、0≤c≤8、2≤d≤13。 14. The positive electrode active material according to claim 12, characterized in that, The second coating described above contains the Li6W2O9 phase.

15. A positive electrode, characterized in that, It includes the positive electrode active material according to any one of claims 1 to 14.

16. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 15.

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