High-voltage positive electrode active material

Abstract

The present invention provides a positive electrode active material comprising a core in the form of a single particle and a coating layer formed on the surface of the core, wherein the coating layer includes: a first coating layer which is applied in the form of dots to a portion of the surface of the core and contains tungsten (W) and an element (M) having a higher ionic conductivity than W; and a second coating layer which is applied to an uncoated portion, not coated with the first coating layer, of the surface of the core and selectively applied to the first coating layer, and contains boron (B). The content of the elements contained in the coating layer satisfies the following relationship A. (A): 10 < [B content / (W content + M content)] Х 100 < 20

Description

High-voltage positive electrode active material

[0001] The present invention relates to a positive electrode active material for high voltage, and more specifically, to a positive electrode active material capable of setting a high voltage by comprising a first coating layer formed of a specific coating form and element combination and a second coating layer formed of a specific element and coating form that complements the first coating layer, wherein the content of said elements satisfies a predetermined condition.

[0002] Due to their high energy density, voltage, long cycle life, and low self-discharge rate, lithium-ion batteries are used in various fields such as mobile devices, energy storage systems, and electric vehicles.

[0003] The cathode active materials used in such lithium secondary batteries generally have a secondary particle structure of several micrometers in size, formed by the aggregation of submicron-sized primary particles. This cathode active material with such a secondary particle structure has a problem in that the battery performance deteriorates as the secondary particles break down as the aggregated primary particles separate during repeated charging and discharging. Since this problem is caused by the structural characteristics of the secondary particles and is difficult to resolve without changing the structure, a one-body particle with a novel structure has been developed.

[0004] Among the problems observed in these single particles, a representative one is oxygen desorption. The degree of oxygen desorption is proportional to the calcination temperature and Ni content; when the calcination temperature is low, the degree of oxygen desorption is very small even if the Ni content increases.

[0005] Generally, high-Ni active materials in the form of secondary particles (Ni 80 mol% or more) have very little oxygen desorption because the calcination temperature during manufacturing is low, around 700–800°C. In particular, as the Ni content increases, the calcination temperature drops further to around 700°C, so there is almost no oxygen desorption. For this reason, various studies are being conducted on secondary particle active materials to further improve capacity, output, and efficiency rather than addressing the oxygen desorption phenomenon.

[0006] In contrast, since single particles require a high calcination temperature of approximately 850–1000°C, significant oxygen delamination occurs. Furthermore, because it is impossible to manufacture single-particle structures at low calcination temperatures, it is difficult to significantly lower the calcination temperature even when the Ni content increases, presenting a problem in improving the oxygen delamination phenomenon. This oxygen delamination phenomenon mostly occurs on the surface of the single particles.

[0007] As such, for single particles requiring high calcination temperatures, it becomes more difficult to manufacture high-Ni cathode active materials if the problem of oxygen desorption is not resolved.

[0008] For example, when the Ni content of a single particle is less than 60%, the degree of oxygen desorption is not severe, but when it is 60% or more, the degree of oxygen desorption increases, and in high-Ni cathode active materials, it becomes very severe, but it is difficult to solve this problem because the calcination temperature is high.

[0009] Oxygen desorption causes an excess of NiO, which is a rock salt structure, to form within the layered structure of the cathode active material and increases Li byproducts. As NiO gradually increases due to repeated charging and discharging, resistance increases, and as Li byproducts increase, various side reactions occur, resulting in degradation of battery performance such as capacity reduction; therefore, oxygen desorption is a major hurdle to the commercialization of single-particle active materials.

[0010] Therefore, as the method of drastically increasing Ni content to achieve high capacity causes many problems, there is a high need in the industry to develop cathode active materials with excellent lifespan characteristics based on enhanced structural stability while suppressing capacity reduction.

[0011] The present invention aims to solve the problems of the prior art described above and technical challenges that have been requested over time.

[0012] After conducting in-depth research and various experiments, the inventors of this application have developed a cathode active material having a new type of coating layer that enables operation under high voltage to maximize capacity, while maintaining excellent structural stability and minimizing electrolyte decomposition reactions even under such conditions, in a cathode active material that contains Ni as a main component but does not have a high Ni level. Based on this, the present invention has been completed.

[0013] Accordingly, the positive electrode active material of the present invention is a positive electrode active material comprising a single-particle core and a coating layer formed on the surface of the core,

[0014] The above coating layer is,

[0015] A first coating layer applied in the form of dots on a portion of the core surface and comprising tungsten (W) and an element (metal M, hereinafter M) having a relatively higher ionic conductivity than said W; and

[0016] A second coating layer comprising boron (B) applied to an uncoated portion of the core surface where the first coating layer is not applied and optionally applied on the first coating layer;

[0017] It includes, and is characterized by the content of elements included in the coating layer satisfying the following relationship A.

[0018] 10 < [B content / (W content + M content)] Х 100 < 20 (A).

[0019]

[0020] The cathode active material of the present invention may preferably be a mid-Ni cathode active material having a Ni content of 40 to 80%, preferably 40 to 70%, and more preferably 40 to 65% based on the total amount of transition metal in the core. Such a mid-Ni cathode active material can minimize the structural instability of a high-Ni cathode active material having a Ni content exceeding 80%, while providing a higher capacity than conventional Co-based LCO cathode active materials.

[0021] In one specific example, the core may be composed of a composition of the following chemical formula 1.

[0022] Li a Ni b Co c Mn d D e O 2-z Q z (1)

[0023] In the above formula,

[0024] 0.7≤a≤1.3, 0.4≤b≤0.8, 0.1≤c≤0.3, 0.1≤d≤0.4, 0≤e≤0.1, 0≤a≤0.2, b+c+d+e=1;

[0025] D is one or more elements selected from alkaline earth metals, transition metals, post-transition metals, metalloids, and nonmetals as a dopant;

[0026] Q is an anion containing one or more elements among F, S, and P.

[0027] The above alkaline earth metals may be, for example, Be, Mg, Ca, Sr, Ba, Ra, etc., and the transition metals may be, for example, Sc, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc., and the post-transition metals and metalloids may be, for example, Al, Ga, In, Sn, Tl, Pb, Bi, Po, B, Si, Ge, As, Sb, Te, At, etc., and the nonmetals may be, for example, C, P, S, Se, etc.

[0028]

[0029] The cathode active material of the present invention has a lower Ni content than high-Ni cathode active materials, and consequently has a lower total capacity, but such capacity reduction can be substantially eliminated by setting it to high voltage charging conditions. Specifically, the cathode active material of the present invention can have a full charge voltage ("charge upper limit voltage") set to a high voltage of 4.35 to 4.5 V. The setting of such a high voltage is possible because a coating layer with specific requirements as defined above is formed on the surface of the core.

[0030]

[0031] Specifically, the positive electrode active material according to the present invention is characterized in that the coating layer comprises a first coating layer composed of a specific coating form and an element combination (W, M) and a second coating layer composed of a specific element (B) and a coating form that complements the first coating layer, and that the content of the elements (W, M, B) in the coating layer has a mutual relationship satisfying a predetermined condition.

[0032] These structural features are essential for a single-particle core that exhibits high particle strength and consequently excellent lifespan characteristics, in order to resolve structural instability such as the aforementioned oxygen depletion phenomenon and to achieve stable output characteristics under high voltage.

[0033]

[0034] First, the term "one-body particle" used in this specification is used to distinguish it from the cathode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which were commonly used in the past. It is a concept that includes a single particle consisting of one primary particle and a semi-one-body particle consisting of 30 or fewer primary particles aggregated. The "primary particle" refers to the smallest particle unit that is distinguished as a single unit when the cross-section of the cathode active material is observed through a scanning electron microscope (SEM), and may consist of a single grain or multiple grains.

[0035] Accordingly, in the present invention, the single particle form of the core may be a form consisting of a single particle, a quasi-single particle, or a combination thereof.

[0036]

[0037] In terms used herein such as "dot-shaped coating" and "dot-shaped coating part," "dot shape" or "dot shape" indicates that the area where the material is applied forms an independent or overlapping coating part of a small area. This type of coating is distinguished from a form in which a large area is coated entirely or partially; although its size is not specified, it can be said to be close to the shape of a somewhat small dot when the applied area is viewed in a planar view.

[0038] The above dot-shaped coating improves output characteristics by expanding the reaction surface area with lithium ions through the provision of a large BET specific surface area, thereby enabling the provision of high-output cathode active materials and suppressing electrolyte decomposition reactions by preventing direct reaction of the electrolyte with the core surface. In other words, to increase the upper charging voltage limit, the oxidation state increases, and the highly reactive transition metal ions (Ni 4+ Physical contact between the body and the electrolyte can be suppressed by the dot-shaped coating.

[0039]

[0040] The tungsten (W) contained in the first coating layer in the form of dots can maintain a stable structure (WO bond: 653 kJ / mol) at high temperatures, thereby minimizing structural instability caused by oxygen desorption, which is a problem of single-particle cores, and can provide improved power density due to high electrical conductivity.

[0041] On the other hand, W has a limitation in that it may act as a resistive layer when forming a coating layer alone, as its low ionic conductivity restricts charge movement.

[0042] Accordingly, an element (M) with relatively higher ionic conductivity than W is included in the first coating layer, thereby improving the mobility of lithium ions and providing high output characteristics required for high-voltage cathode active materials.

[0043] Examples of such an element (M) include one element selected from Al, Fe, Nb, Ge, P, and Si, among which Al is particularly preferred.

[0044] The above M not only improves the ion conductivity of the first coating layer but also assists in forming a coating layer by mixing it with W in an appropriate ratio, thereby helping W to have a more uniform dot-shaped coating distribution. That is, the distribution of the dot-shaped coating part containing W when M is used together is more uniform than the distribution of the dot-shaped coating part formed when W is used alone, which can be confirmed in the experimental details described below.

[0045]

[0046] The second coating layer covers the uncoated area due to its relatively high wettability and low viscosity compared to the first coating layer, and in some cases, it can also be applied on the first coating layer.

[0047] The boron (B) included in this second coating layer is an element that satisfies the above characteristics.

[0048] B tends to form an amorphous LBO layer when the heat treatment temperature for coating is in the range of approximately 300 to 400°C, and a LiBO2-B2O3 layer at a lower heat treatment temperature, which can lead to an increase in initial resistance, so a heat treatment temperature of 430 to 500°C may be desirable.

[0049]

[0050] Based on the particle size of the positive electrode active material, the size or volume of the first coating layer and the second coating layer can be said to be substantially determined by the content of the elements forming each coating layer, and since the relationship between the content of these elements is defined in the above-mentioned relationship A, and the ratio of the B content to the sum of the W content and the M content is in the range of more than 10% to less than 20%, the relative size of the first coating layer and the second coating layer can also be said to have such a relationship.

[0051] If the calculated value in equation A is 10% or less, it may be insufficient to form a second coating layer to exhibit the desired characteristics, and conversely, if it is 20% or more, the second coating layer may become enlarged and impair the high-voltage output characteristics due to the increase in resistance, so it is undesirable.

[0052] It may be desirable for the mutual relationship between the W content and M content in the first coating layer to satisfy the condition of the following relationship B.

[0053] 1 < (W content / M content) < 2 (B)

[0054] As mentioned above, when W and M are used together, the distribution of the dot-shaped coating portion based on W becomes uniform and the size tends to decrease, which is desirable. However, if the M content is greater than the W content, the Li reduction effect decreases and the BET specific surface area may decrease, so it may be desirable to satisfy the content conditions within the above range.

[0055] For example, based on the total amount of cathode active material, the W content may be 2 to 4 wt% and the M content may be 1 to 3 wt%. When M is Al, the preferred M content may be 1 to 2.5 wt%. The ranges of W content and M content can be said to be substantially the same as those described above.

[0056] The content of B forming the second coating layer may be 0.2 to 0.7 wt% based on the total amount of the positive active material.

[0057] If the B content is too low, it may be difficult to form a second coating layer to exhibit the desired characteristics, and conversely, if it is too high, the coating layer becomes thicker, the BET specific surface area decreases, and the ionic conductivity decreases, which is undesirable.

[0058]

[0059] The first coating layer and the second coating layer formed on such a core may differ in the type of compound depending on the elements constituting them.

[0060] For example, the above W and M may exist in the form of oxides, lithium compounds, or mixtures thereof. Likewise, B may also exist in the form of oxides, lithium compounds, or mixtures thereof.

[0061] Here, to distinguish between oxides and lithium compounds, compounds containing lithium are excluded from oxides, and compounds containing lithium that are in the form of oxides are classified as lithium compounds. When the raw material for forming the coating layer is an oxide, the oxide in its original form or in a form with a changed oxidation state may form the coating layer, or a lithium compound generated through the reaction of the oxide with lithium remaining on the core surface may form the coating layer, or a mixture thereof may form the coating layer.

[0062] Accordingly, the first coating layer may include a dot-shaped coating part made of an oxide, a dot-shaped coating part made of a lithium compound, and a dot-shaped coating part made of an oxide and a lithium compound.

[0063] On the other hand, the second coating layer forms a single coating layer and may have a uniform composition overall, but it is obvious that there may be localized regions where oxide is the main component and regions where lithium compounds are the main component. However, it may be desirable for the second coating layer to have more amorphous phases than crystalline phases to provide a wide coating surface.

[0064]

[0065] In one specific example, the oxide of the first coating layer may comprise one or more compositions selected from the following chemical formulas 2 to 3, and the lithium compound may comprise one or more compositions selected from the following chemical formulas 4 to 6.

[0066] W x O y (2)

[0067] M x1 O y1 (3)

[0068] Li e W f O g (4)

[0069] Li h M i O j (5)

[0070] Li k W m M n O p (6)

[0071] In the above formulas,

[0072] 0.95≤x≤3.1, 2.95≤y≤6.1;

[0073] 0.95≤x1≤3.1, 2.95≤y1≤6.1;

[0074] 0.95≤e≤3.1, 0.95≤f≤2.1, 2.9≤g≤6.1;

[0075] 0.95≤h≤2.1, 0.95≤i≤2.1, 2.9≤j≤6.1;

[0076] It satisfies the conditions 0.95≤k≤5.1, 0.95≤m≤5.1, 0.95≤n≤5.1, and 0.95≤p≤7.1.

[0077] Li of Chemical Formula 4, a W-based lithium compound e W f O g For example, it can be Li2WO4, which is produced at a heat treatment temperature of 400 to 600°C and has excellent rate characteristics and lifespan characteristics at high voltage.

[0078] Li of Formula 5, an M-based lithium compound h M i O jAs previously mentioned, when M is Al, Fe, Nb, Ge, P, or Si, the ionic conductivity compared to W has the following magnitude relationship: Al>Fe>Nb>Ge>P>Si>W(Li2WO4).

[0079] For example, LiAl2O3 has an ionic conductivity of approximately 3×10 -3 Approximately ~10 of Li2WO4 as of S / cm -7 It is much higher than S / cm.

[0080]

[0081] In another specific example, the oxide of the second coating layer may comprise the composition of Formula 7 below, and the lithium compound may comprise the composition of Formula 8 below.

[0082] B x2 O y2 (7)

[0083] Li s B t O u (8)

[0084] In the above formulas,

[0085] 0.95≤x2≤3.1, 2.95≤y2≤6.1;

[0086] It satisfies the conditions 0.95≤s≤2.1, 0.95≤t≤2.1, and 2.9≤u≤6.1.

[0087]

[0088] In one preferred example, the positive active material of the present invention has a tap density (TD) of 1.90 to 2.15 g / cm³ 3 It may be in the range, and the BET specific surface area is 0.80 to 0.95 m² 2 It can be in the range of / g.

[0089] As can be confirmed from the experimental details described below, the cathode active material of the present invention, due to the composition of a unique coating layer, provides a high tap density and BET specific surface area compared to conventional cathode active materials, which enables the expression of high energy density, excellent output characteristics, etc.

[0090]

[0091] The present invention also provides a secondary battery comprising the above-mentioned positive active material. Since the composition and manufacturing method of the secondary battery are known in the art, a detailed description thereof is omitted in this specification.

[0092] As explained above, the positive electrode active material according to the present invention comprises a first coating layer composed of a specific coating form and an element combination (W, M) and a second coating layer composed of a specific element (B) and a coating form that complements the first coating layer, and the content of the elements (W, M, B) in the coating layer has a mutual relationship that satisfies a predetermined condition, thereby minimizing structural instability caused by oxygen depletion phenomena, etc., and enabling use at high voltage, so that even when the Ni content is reduced, the full charge voltage can be increased to exhibit improved capacity and lifespan characteristics.

[0093] Figure 1 is an SEM image of a positive electrode active material using W alone during the formation of the first coating layer in Experimental Example 1;

[0094] Figure 2 is an SEM image of a positive electrode active material using W+Al when forming the first coating layer in Experimental Example 1.

[0095] The present invention will be described further below with reference to embodiments thereof, but the scope of the invention is not limited by them.

[0096]

[0097] [Example 1]

[0098] A nickel-cobalt-manganese hydroxide precursor aqueous solution was prepared by adding NiSO4 as a nickel precursor, CoSO4 as a cobalt precursor, and MnSO4 as a manganese precursor to water in a molar ratio of 0.62:0.06:0.32.

[0099] By slowly adding an aqueous sodium hydroxide solution dropwise while stirring the above aqueous solution and stirring the reaction mixture for 5 hours, the above precursor aqueous solution is neutralized to obtain a nickel-cobalt-manganese hydroxide, Ni 0.62 Co 0.06 Mn 0.32 (OH)2 was precipitated.

[0100] To the precursor (nickel-cobalt-manganese hydroxide) obtained in this way, Li2CO3 and Y2O3 and ZrO2 were mixed as dopants at concentrations of 1.5 wt% and 3 wt%, respectively, and calcined at 960°C for 10 hours to obtain LiNi 0.62 Co 0.06 Mn 0.32 O2 was manufactured.

[0101] LiNi prepared above 0.62 Co 0.06 Mn 0.32 Al2O3, B2O3, and WO3 were mixed in O2 such that the content of the active material was Al 1.5 wt%, B 0.5 wt%, and W 3 wt%, and heat-treated at 430°C for 7 hours to prepare a positive electrode active material with a coating layer formed.

[0102]

[0103] [Example 2]

[0104] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that Al2O3 and WO3 were mixed so that the content in the active material was 1.5 wt% Al and 3 wt% W and subjected to a first heat treatment at 430°C for 7 hours, and then B2O3 was mixed so that the content in the active material was 0.5 wt% B and subjected to a second heat treatment at 430°C for 7 hours.

[0105]

[0106] [Example 3]

[0107] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that B2O3 was mixed so that the content of B in the active material was 0.6 wt%.

[0108]

[0109] [Example 4]

[0110] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that B2O3 was mixed so that the content of B in the active material was 0.7 wt%.

[0111]

[0112] [Example 5]

[0113] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that it was heat-treated at 500°C for 7 hours.

[0114]

[0115] [Example 6]

[0116] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that Al2O3, B2O3, and WO3 were mixed so that the content in the active material was Al 2.5 wt%, B 0.5 wt%, and W 2 wt%.

[0117]

[0118] [Comparative Example 1]

[0119] A nickel-cobalt-manganese hydroxide precursor aqueous solution was prepared by adding NiSO4 as a nickel precursor, CoSO4 as a cobalt precursor, and MnSO4 as a manganese precursor to water in a molar ratio of 0.62:0.06:0.32.

[0120] By slowly adding an aqueous sodium hydroxide solution dropwise while stirring the above aqueous solution and stirring the reaction mixture for 5 hours, the above precursor aqueous solution is neutralized to obtain a nickel-cobalt-manganese hydroxide, Ni 0.62 Co 0.06 Mn 0.32 (OH)2 was precipitated.

[0121] To the precursor (nickel-cobalt-manganese hydroxide) obtained in this way, Li2CO3 and Y2O3 and ZrO2 were mixed as dopants at concentrations of 1.5 wt% and 3 wt%, respectively, and calcined at 960°C for 10 hours to obtain LiNi 0.62 Co 0.06 Mn 0.32 O2 was manufactured.

[0122] Then, the positive electrode active material was prepared by heat treatment at 430℃ for 7 hours.

[0123]

[0124] [Comparative Example 2]

[0125] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that B2O3 was mixed so that the B content in the active material was 0.5 wt% without Al and W, and heat-treated at 430°C for 7 hours.

[0126]

[0127] [Comparative Example 3]

[0128] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that Al2O3 and WO3 were mixed without B so that the content in the active material was Al 1.5 wt% and W 3 wt%, and heat-treated at 430°C for 7 hours.

[0129]

[0130] [Comparative Example 4]

[0131] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as Comparative Example 3, except that it was heat-treated at 500℃ for 7 hours.

[0132]

[0133] [Comparative Example 5]

[0134] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that Al2O3 and B2O3 were mixed without W so that the content in the active material was Al 1.5 wt% and B 0.5 wt%, and heat-treated at 430°C for 7 hours.

[0135]

[0136] [Comparative Example 6]

[0137] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that WO2 and B2O3 were mixed so that the content in the active material was 3 wt% and B was 0.5 wt% without Al, and heat-treated at 430°C for 7 hours.

[0138]

[0139] [Comparative Example 7]

[0140] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that it was heat-treated at 600°C for 7 hours.

[0141]

[0142] [Comparative Example 8]

[0143] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that B2O3 was mixed so that the B content in the active material was 0.3 wt%.

[0144]

[0145] [Comparative Example 9]

[0146] A positive electrode active material with a coating layer formed thereon was prepared in the same manner as in Example 1, except that WO3 and Al2O3 were mixed so that the content in the active material was W 1.5 wt% and Al 3 wt%.

[0147]

[0148] [Experimental Example 1]

[0149] For the cathode active materials prepared in the above examples and comparative examples, particle size, residual lithium, BET specific surface area, and tap density were measured based on XRD, and the results are shown in Table 1 below.

[0150]

[0151] <XRD 측정>

[0152] Power Source: CuKα (Linear Focus), Wavelength: 1.541836 Å, Control Axis: 2θ / θ,

[0153] Measurement method: Continuous, Counting unit: cps, Starting angle: 10.0°,

[0154] Termination angle: 80.0°, Accumulation count: 1, Sampling width: 0.01°,

[0155] Scan speed: 1.3° / min, Voltage: 40kV, Current: 40mA,

[0156] Divergence slit: 0.2 mm, divergence species limiting slit: 10 mm,

[0157] Scattering slit: Open, Receiving slit: Open, Offset angle: 0°,

[0158] Goniometer radius: 285 mm, optical system: focusing method, attachment: ASC-48,

[0159] Slit: Slit detector for D / teX, Ultra: D / teX Ultra,

[0160] Filter: None, Rotation Speed: 30 rpm, Incident Monochrome: CBO Ni-Kβ

[0161]

[0162] Measurement of Residual Lithium

[0163] ① Sample Pretreatment

[0164] - Place 5±0.01g of sample and 100g of distilled water into a conical beaker containing a magnetic bar and stir for 5 minutes.

[0165] - Natural filtration of the sample stirred on filter paper

[0166] - Place the filtered liquid in a beaker and titrate

[0167] ② Inspection Method

[0168] - After filling the titrator with the titrant (0.1N HCl), remove air bubbles from the cylinder.

[0169] - Titrate: 0.1N HCl

[0170] - Titrate dispensing method: DET

[0171] - Automatic titration completion condition: pH 2.5

[0172] - Calculation: FP(1)=4.5, EP(1)

[0173] - Titration rate: Greatest.

[0174]

[0175] <BET 비표면적 측정>

[0176] Measurements were taken using Micromeritics’ Tristar II 3020, and Vacprep061 was used as the pretreatment device.

[0177] The specific surface area value was measured by pre-treating with a pre-treatment device at 100°C for 60 minutes and at 300°C for 120 minutes, and measuring the adsorption amount using a BET measuring device at liquid nitrogen temperatures (-77K, -195.8°C) and relative pressure (P / P0) in the range of 0.05-0.3.

[0178]

[0179] The following facts were confirmed through experiments.

[0180]

[0181] First, the positive active material of Comparative Example 2, which lacks a first coating layer, has a low BET specific surface area, and the positive active materials of Comparative Examples 3 and 4, which lack a second coating layer, have a high residual lithium content. Furthermore, the positive active materials of Comparative Examples 5 to 7, which possess both a first coating layer and a second coating layer but have an elemental composition different from the examples, do not have excellent electrochemical properties as described below.

[0182]

[0183] Second, Comparative Examples 8 and 9, which have a first coating layer and a second coating layer, wherein the first coating layer contains W and Al and the second coating layer contains B, have different content conditions from the Examples, and as described below, their electrochemical properties are not excellent.

[0184]

[0185] Third, separately from the above experiment, SEM images were obtained for cases where W was used alone and cases where W+Al was used when forming the first coating layer, respectively, and are disclosed in FIGS. 1 and 2. When compared to FIG. 1, it can be seen that in the case of FIG. 2, the dot-shaped coating portions are more uniformly distributed and their size is reduced due to the combined use of Al.

[0186]

[0187] [Experimental Example 2]

[0188] After manufacturing a 2032 coin-type half cell using the positive active materials prepared in each of the above examples and comparative examples, an electrochemical evaluation was performed, and the results are shown in Table 2 below.

[0189] Specifically, a positive electrode active material, a polyvinylidene fluoride binder (KF1100), and a Super-P conductive material were mixed in a weight ratio of 96:2:2, and this mixture was added to an N-methyl-2-pyrrolidone solvent to prepare a positive electrode active material slurry. Then, the slurry was coated onto an aluminum foil (thickness: 20 μm) serving as a positive electrode current collector, dried at 120°C, and subjected to a compression process to manufacture a positive electrode plate. The loading level of the rolled positive electrode was 17 mg / cm². 2 and the rolled density is 3.3 g / cm³ 3 The above electrode plate was stamped to 14Φ, and a 2032 coin-type half cell was manufactured using lithium metal as the negative electrode and an electrolyte (EC / DMC / EMC 3:4:3 + LiPF6 1 mol). After aging the coin-type half cell manufactured above at room temperature for 12 hours, a charge-discharge test was performed.

[0190] Specifically, charging and discharging were performed on the lithium secondary battery under conditions of 0.1C, 4.45V (charging) and 0.1C, 2.5V (discharging). In addition, the resistance was calculated by dividing the applied current by the voltage change between 0 and 65 seconds from the start of discharge, and the lifespan and resistance increase rate were verified by repeating the process 50 times at 45℃. The results are shown in Table 2 below.

[0191]

[0192] As shown in Table 2 above, it can be seen that the lithium secondary batteries of the examples have larger charge and discharge capacities, superior cycle characteristics, and lower resistance compared to the lithium secondary batteries of the comparative examples.

[0193]

[0194] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A positive active material comprising a single-particle core and a coating layer formed on the surface of the core, The above coating layer is, A first coating layer applied in the form of dots on a portion of the core surface and comprising tungsten (W) and an element (M) having a relatively higher ionic conductivity than said W; and A second coating layer comprising boron (B) applied to an uncoated portion of the core surface where the first coating layer is not applied and optionally applied on the first coating layer; A positive electrode active material characterized by including, and having the content of elements included in the coating layer satisfying the following relationship A: 10 < [B content / (W content + M content)] Х 100 < 20 (A) 2. The positive electrode active material according to claim 1, characterized in that the core has a Ni content of 40 to 80% based on the total amount of transition metal.

3. The positive active material according to claim 2, wherein the core comprises a composition of the following chemical formula 1: Li a Ni b Co c Mr d D e O 2-z Q z (1) In the above formula, 0.7≤a≤1.3, 0.4≤b≤0.8, 0.1≤c≤0.3, 0.1≤d≤0.4, 0≤e≤0.1, 0≤a≤0.2, b+c+d+e=1; D is one or more elements selected from alkaline earth metals, transition metals, post-transition metals, metalloids, and nonmetals as a dopant; Q is an anion containing one or more elements among F, S, and P.

4. The positive active material according to claim 1, characterized in that the full charge voltage is a high voltage of 4.35 to 4.5V.

5. The positive electrode active material according to claim 1, wherein the single particle form of the core is a single particle consisting of one primary particle, a semi-one-body particle formed by aggregating 30 or fewer primary particles, or a combination thereof.

6. A positive active material according to claim 1, characterized in that M is one element selected from Al, Fe, Nb, Ge, P, and Si.

7. A positive active material according to claim 6, characterized in that M is Al 8. A positive active material according to claim 1, characterized in that the contents of W and M satisfy the following relationship B: 1 < (W content / M content) < 2 (B) 9. The positive electrode active material according to claim 1, characterized in that, based on the total amount of the positive electrode active material, the W content is 2 to 4 wt% and the M content is 1 to 3 wt%.

10. The positive electrode active material according to claim 1, characterized in that the B content is 0.2 to 0.7 wt% based on the total amount of the positive electrode active material.

11. A positive electrode active material according to claim 1, wherein W and M exist in the form of an oxide, a lithium compound, or a mixture thereof.

12. The positive active material according to claim 1, wherein B exists in the form of an oxide, a lithium compound, or a mixture thereof.

13. The positive electrode active material according to claim 1, wherein the first coating layer comprises a dot-shaped coating part made of an oxide, a dot-shaped coating part made of a lithium compound, and a dot-shaped coating part made of an oxide and a lithium compound.

14. The positive active material according to claim 1, wherein the second coating layer is characterized in that the amorphous phase is more abundant than the crystalline phase.

15. In Paragraph 11, The above oxide comprises one or more compositions selected from the following chemical formulas 2 to 3; A positive electrode active material characterized by comprising one or more compositions selected from the following chemical formulas 4 to 6, wherein the lithium compound: W x O y (2) M x1 O y1 (3) Li e W f O g (4) Li h Al i O j (5) Li k W m Al n O p (6) In the above formulas, 0.95≤x≤3.1, 2.95≤y≤6.1; 0.95≤x1≤3.1, 2.95≤y1≤6.1; 0.95≤e≤3.1, 0.95≤f≤2.1, 2.9≤g≤6.1; 0.95≤h≤2.1, 0.95≤i≤2.1, 2.9≤j≤6.1; It satisfies the conditions 0.95≤k≤5.1, 0.95≤m≤5.1, 0.95≤n≤5.1, and 0.95≤p≤7.

1.

16. A positive electrode active material according to claim 12, wherein the oxide comprises a composition of the following chemical formula 7 and the lithium compound comprises a composition of the following chemical formula 8: B x2 O y2 (7) Li s B t O u (8) In the above formulas, 0.95≤x2≤3.1, 2.95≤y2≤6.1; It satisfies the conditions 0.95≤s≤2.1, 0.95≤t≤2.1, and 2.9≤u≤6.

1.

17. In claim 1, the BET specific surface area is 0.80 to 0.95 m² 2 A positive active material characterized by being in the range of / g.

18. In claim 1, the tap density (TD) is 1.90 to 2.15 g / cm³ 3 A positive electrode active material characterized by being within the range of 19. A secondary battery characterized by including a positive electrode active material according to claim 1.

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