Positive electrode active material, method of preparing the same, and rechargeable lithium battery including the same

Abstract

Disclosed are a positive electrode active material, a method of preparing the same, and a rechargeable lithium battery including the same. The positive electrode active material includes a nickel-based composite metal oxide that is a secondary particle in which a plurality of primary particles are aggregated, wherein the positive electrode active material includes a core and a shell, the primary particles of the shell are coated with a manganese-containing nickel-based composite metal oxide, and the manganese-containing nickel-based composite metal oxide has a layered structure.

Description

Technical Field

[0001] A positive electrode active material for rechargeable lithium batteries, a method for preparing the material, and a rechargeable lithium battery including the material are disclosed. Background Technology

[0002] To meet the demands for miniaturization and high performance in various devices, rechargeable lithium-ion batteries are becoming increasingly important in terms of high energy density, miniaturization, and weight reduction. Furthermore, the high capacity, high-temperature stability, and safety at high voltages of rechargeable lithium-ion batteries are becoming crucial for applications such as electric vehicles.

[0003] Various positive electrode active materials have been studied to realize rechargeable lithium batteries for the aforementioned applications.

[0004] Compared to traditional LiCoO2, nickel-based lithium transition metal oxides, which also include nickel, cobalt, and manganese, offer higher discharge capacity per unit weight. However, due to their low assembly density, they exhibit relatively low capacity and discharge capacity per unit volume. Furthermore, the safety of nickel-based lithium transition metal oxides may deteriorate when driven at high voltages.

[0005] Therefore, a method is needed to improve the structural stability and cycle life of nickel-based lithium transition metal oxides. Summary of the Invention

[0006] One embodiment provides a positive electrode active material that has improved structural stability and effectively improves the cycle life of rechargeable lithium batteries.

[0007] Another embodiment provides a method for preparing a positive electrode active material.

[0008] Another embodiment provides a rechargeable lithium battery that has improved charge / discharge efficiency and cycle life characteristics by employing a positive electrode containing positive electrode active material.

[0009] One embodiment provides a positive electrode active material comprising a nickel-based composite metal oxide, the nickel-based composite metal oxide being secondary particles, a plurality of primary particles aggregated within the secondary particles, wherein the positive electrode active material (e.g., the nickel-based composite metal oxide) comprises a core and a shell, the primary particles of the shell being coated with a manganese-containing nickel-based composite metal oxide, and the manganese-containing nickel-based composite metal oxide having a layered structure.

[0010] The nucleus may not include manganese.

[0011] The manganese concentration can have a concentration gradient, where the manganese concentration increases from the interior to the surface of the primary particles in the shell.

[0012] The coating of manganese on the shell (e.g., on the primary particles of the shell) can be in the form of islands or fine nanoparticles.

[0013] For example, relative to the manganese-containing nickel-based composite metal oxide of the shell, the manganese content in the positive electrode active material can be less than about 1.5 mol%.

[0014] The thickness of the shell can be less than or equal to about 2 μm.

[0015] The positive electrode active material can have a particle size of about 8 μm to about 18 μm.

[0016] Manganese-containing nickel complex metal oxides can be represented by chemical formula 1:

[0017] [Chemical Formula 1]

[0018] LiNi 1-x-y-z Co x Mn y M z O2

[0019] In chemical formula 1,

[0020] 0≤x≤0.5, 0.001≤y<0.015, 0≤z≤0.3, and M is at least one metallic element selected from Ni, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba, and Ce.

[0021] LiMnO2 may be present on the surface of the primary particles of the shell.

[0022] In this embodiment, the positive electrode active material can be prepared by the following method:

[0023] A mixture was prepared by adding a water-soluble solvent to a nickel-based complex metal compound and manganese hydroxide.

[0024] The mixture is reacted at approximately 40°C to approximately 100°C for approximately 30 minutes to approximately 1 hour to produce primary particles with a manganese-coated shell, and

[0025] The coated material is mixed with a lithium source and then fired.

[0026] Nickel-based complex metal compounds can be nickel-based complex metal oxides or nickel-based complex metal hydroxides.

[0027] Water-soluble solvents may include any one of NaOH, KOH, and mixtures thereof.

[0028] After the mixture is reacted at about 40°C to about 100°C for about 30 minutes to about 1 hour, the mixture may be dried at about 100°C to about 200°C. For example, the method may further include a step of drying the mixture at about 100°C to about 200°C after the step of reacting the mixture.

[0029] The firing temperature can be from about 600°C to about 800°C and the firing time can be from about 8 hours to about 30 hours or from about 8 hours to about 24 hours.

[0030] Another embodiment provides a rechargeable lithium battery comprising: a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte.

[0031] Further details of the implementation methods are included in the following detailed description.

[0032] The positive electrode active material does not include nickel-based composite metal oxides with spinel structures, but only includes nickel-based composite metal oxides with layered structures, thus solving the problem of reduced specific capacity caused by the inclusion of spinel structures.

[0033] In addition, rechargeable lithium batteries including a positive electrode containing a positive electrode active material according to the embodiments exhibit improved charging and discharging efficiency and cycle life characteristics. Attached Figure Description

[0034] Figure 1 This is a portion of a schematic cross-sectional view illustrating the positive electrode active material according to an embodiment.

[0035] Figure 2 It is a perspective view that schematically illustrates the typical structure of a rechargeable lithium battery.

[0036] Figure 3 The evaluation results of the cycle life (100 cycles) of the coin batteries of Example 1 and Comparative Examples 1 to 4 are shown.

[0037] <Symbol Description>

[0038] 1: Secondary particles

[0039] 3: Primary particles

[0040] 5a: Shell

[0041] 5b: Core

[0042] 7: Grain boundaries

[0043] 31: Rechargeable lithium battery

[0044] 32: Negative electrode

[0045] 33: Positive electrode

[0046] 34: partition

[0047] 35: Battery casing

[0048] 36: Capping assembly Detailed Implementation

[0049] The embodiments are described in detail below. However, this is provided by way of example, and the present disclosure is not limited thereto, and is limited only by the scope of the claims.

[0050] As used herein, unless otherwise specifically defined, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it may be directly on the other element or there may be an intermediate element present.

[0051] In this disclosure, "particle size" or "particle diameter" can be defined as the average particle diameter (D50) based on approximately 50% of the volumetric accumulation in a particle size distribution curve. Particle diameter can be measured, for example, by electron microscopy using a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), or by laser diffraction methods. Laser diffraction can be used to measure the particle size. The particles to be measured are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT 3000) to irradiate ultrasonic waves at an output of approximately 60 W at approximately 28 kHz. The average particle diameter (D50) in the 50% reference of the particle size distribution in the measurement device can be calculated.

[0052] In this specification, "center" refers to the point that bisects the longest axis of the particle.

[0053] "Primary particles" can be crystalline particles or grains. Multiple primary particles form grain boundaries and aggregate together to form secondary particles. Primary particles can have various shapes, such as spherical or near-spherical (plate-like, etc.).

[0054] "Secondary particles" refer to particles that contain multiple primary particles but are not aggregates of other particles, or particles that no longer aggregate, and may be spherical or pseudo-spherical.

[0055] The following text refers to Figure 1 Describes the positive electrode active material used in rechargeable lithium batteries. Figure 1 This is a schematic cross-sectional view showing a positive electrode active material according to an embodiment, the positive electrode active material comprising primary particles coated at grain boundaries.

[0056] refer to Figure 1 According to the embodiments, the positive electrode active material includes a nickel-based composite metal oxide, which includes secondary particles 1, in which a plurality of primary particles 3 are aggregated.

[0057] The secondary particle 1 includes a core 5b and a shell 5a, and the shell 5a includes a nickel-based composite metal oxide, which includes manganese (hereinafter also referred to as manganese-containing nickel-based composite metal oxide) coated at the grain boundaries 7 of the plurality of primary particles 3. That is, the positive electrode active material may include manganese-containing nickel-based composite metal oxide coated at the grain boundaries 7 between the primary particles 3 corresponding to a predetermined depth of the shell 5a. Here, the core 5b of the secondary particle 1 may not include the manganese-containing nickel-based composite metal oxide. In other words, the core 5b may not include manganese. That is, the manganese-containing nickel-based composite metal oxide may only be coated at the grain boundaries 7 of the primary particles 3 in the shell 5a of the secondary particle 1, while manganese may not be coated in the core 5b.

[0058] The core 5b of the secondary particle 1 may refer to: a region that is less than or equal to about 50% to about 80% of the total distance (100% of length) from the center of the secondary particle 1 to the outermost surface, for example, a region that is less than or equal to about 75% of the total distance from the center, less than or equal to about 70% of the total distance, less than or equal to about 65% of the total distance, less than or equal to about 60% of the total distance, less than or equal to about 55% of the total distance, or less than or equal to about 50% of the total distance, or a region excluding the region within about 2 μm from the outermost surface of the secondary particle 1.

[0059] The shell 5a is the portion excluding the core 5b, and the region that is less than or equal to about 20% to less than or equal to about 50% of the distance from the outermost surface relative to the total distance (100% of length) from the center of the secondary particle 1 to the outermost surface, for example, a region that is less than or equal to about 25%, less than or equal to about 30%, less than or equal to about 20%, less than or equal to about 40%, less than or equal to about 45%, or less than or equal to about 50% of the distance from the outermost surface.

[0060] That is, the thickness of shell 5a may be less than or equal to about 2 μm, and specifically, the thickness of shell 5a may be less than or equal to about 2 μm, less than or equal to about 1.5 μm, less than or equal to about 1.0 μm, or less than or equal to about 0.5 μm.

[0061] Shell 5a may be the region in which the coating of primary particles 3 is formed at the grain boundaries. In an embodiment, the size of the primary particles 3 may be from about 50 nm to about 800 nm or from about 100 nm to about 800 nm. The size of the primary particles 3 may be greater than or equal to about 50 nm, greater than or equal to about 100 nm, greater than or equal to about 150 nm, greater than or equal to about 200 nm, greater than or equal to about 250 nm, greater than or equal to about 300 nm, greater than or equal to about 350 nm, greater than or equal to about 400 nm, greater than or equal to about 450 nm, greater than or equal to about 500 nm, greater than or equal to about 550 nm, greater than or equal to about 600 nm, greater than or equal to about 650 nm, greater than or equal to about 700 nm, or greater than or equal to about 750 nm. In another embodiment, the size of the primary particle 3 may be less than or equal to about 800 nm, less than or equal to about 750 nm, less than or equal to about 700 nm, less than or equal to about 650 nm, less than or equal to about 600 nm, less than or equal to about 550 nm, less than or equal to about 500 nm, less than or equal to about 450 nm, less than or equal to about 400 nm, less than or equal to about 350 nm, less than or equal to about 300 nm, less than or equal to about 250 nm, less than or equal to about 200 nm, or less than or equal to about 150 nm.

[0062] Manganese-containing nickel-based composite metal oxides can have a layered structure. When the nickel-based composite metal oxide of the positive electrode active material has a spinel structure, it has the effect of increasing stability. However, since the spinel structure of the nickel-based composite metal oxide occupies a larger capacity in the positive electrode active material than the layered structure, the specific capacity of the positive electrode active material may deteriorate due to the presence of more spinel structure nickel-based composite metal oxides.

[0063] Therefore, the present invention provides a positive electrode active material for rechargeable lithium batteries by including layered nickel composite metal oxides instead of spinel-structured nickel composite metal oxides, so that the layered nickel composite metal oxides can be contained between the primary particles contained in the shell of a core-shell structured positive electrode active material. This positive electrode active material has excellent stability and high specific capacity.

[0064] In other words, secondary particles 1 may consist only of layered manganese-containing nickel composite metal oxides, but may completely exclude compounds with spinel or rock salt structures. When secondary particles 1 do not contain compounds with spinel structures, the problem of specific capacity degradation caused by the presence of spinel structures in the positive electrode active material can be solved.

[0065] The shell 5a comprises a layered structure of manganese-containing nickel-based composite metal oxide between primary particles 3 (i.e., grain boundaries), and the manganese content present at the grain boundaries 7 of the multiple primary particles 3 in the shell 5a can be greater than the manganese coated inside the primary particles 3. In other words, the manganese-containing nickel-based composite metal oxide included in the shell 5a can have a manganese concentration gradient that increases from the interior to the surface of the primary particles 3.

[0066] "Grain boundary" refers to the interface between two adjacent primary particles 3. In an embodiment, based on the total distance from the center of the primary particle 3 to the outermost surface (the interface between adjacent primary particles 3), the grain boundary can represent a region from about 20% of the length to about 40% of the length from the outermost surface, for example, a region from about 25% of the length, a region from about 30% of the length, or a region from about 35% of the length. The interior of the primary particle 3 excludes the portion of the grain boundary. In an implementation, based on the total distance from the center of the primary particle 3 to the outermost surface (the interface between adjacent primary particles 3), the interior of the primary particle 3 can represent a region from the center of the primary particle 3 less than or equal to about 60% of the length to less than or equal to about 80% of the length. For example, less than or equal to about 40% of the length from the center of the primary particle 3, less than or equal to about 45% of the length from the center of the primary particle 3, less than or equal to about 50% of the length from the center of the primary particle 3, less than or equal to about 55% of the length from the center of the primary particle 3, less than or equal to about 60% of the length from the center of the primary particle 3, less than or equal to about 65% of the length from the center of the primary particle 3, less than or equal to about 70% of the length from the center of the primary particle 3, less than or equal to about 75% of the length from the center of the primary particle 3, or less than or equal to about 80% of the length from the center of the primary particle 3.

[0067] The manganese-containing nickel composite metal oxide coated on the primary particles 3 of shell 5a can be coated in the form of islands or fine nanoparticles. The "fine nanoparticles" can be spherical, rod-shaped, needle-shaped or plate-shaped particles with a particle size of about 10 nm to about 100 nm.

[0068] In this embodiment, the total amount (mol%) of the metals (excluding lithium) in the nickel-based composite metal oxide may include manganese in an amount greater than or equal to about 0.1 mol% and less than about 1.5 mol%. When the total amount (mol%) of the metals (excluding lithium) in the nickel-based composite metal oxide includes manganese in an amount greater than or equal to about 0.1 mol% and less than about 1.5 mol%, the structural stability and cycle characteristics of the positive electrode active material can be improved.

[0069] In embodiments, based on the total amount (mol%) of metals (excluding lithium) in manganese-containing nickel-based composite metal oxides, the manganese content may be greater than or equal to about 0.1 mol%, greater than or equal to about 0.2 mol%, greater than or equal to about 0.3 mol%, greater than or equal to about 0.4 mol%, greater than or equal to about 0.5 mol%, greater than or equal to about 0.6 mol%, greater than or equal to about 0.7 mol%, greater than or equal to about 0.8 mol%, greater than or equal to about 0.9 mol%, greater than or equal to about 1.0 mol%, greater than or equal to about 1.1 mol%, greater than or equal to about 1.2 mol%, greater than or equal to... Of about 1.3 mol%, or greater than or equal to about 1.4 mol%, and less than about 1.5 mol%, less than or equal to about 1.4 mol%, less than or equal to about 1.3 mol%, less than or equal to about 1.2 mol%, less than or equal to about 1.1 mol%, less than or equal to about 1.0 mol%, less than or equal to about 0.9 mol%, less than or equal to about 0.8 mol%, less than or equal to about 0.7 mol%, less than or equal to about 0.6 mol%, less than or equal to about 0.5 mol%, less than or equal to about 0.4 mol%, less than or equal to about 0.3 mol%, or less than or equal to about 0.2 mol%.

[0070] As described above, the positive electrode active material according to the embodiment includes a nickel-based composite metal oxide containing a high concentration of manganese between the primary particles present in the shell 5a at a certain depth from the outermost surface of the secondary particles 1. This embodiment may differ from the conventional configuration of coating the surface of the secondary particles or deeply doping to the core of the secondary particles, and improves the specific capacity of the positive electrode active material by coating manganese only at the grain boundaries of the primary particles down to a predetermined depth from the outermost surface.

[0071] Furthermore, because the grain boundaries of the primary particle 3 include a manganese-containing nickel-based composite metal oxide 7 (nickel-based lithium metal oxide), lithium can diffuse smoothly from the core 5b of the secondary particle 1, while the elution of nickel ions from the core 5b of the secondary particle 1 can be suppressed. In addition, side reactions between the primary particles of the core 5b of the secondary particle 1 and the electrolyte solution can be suppressed. Therefore, the cycle characteristics of a rechargeable lithium battery including a positive electrode active material having the above-described structure can be improved.

[0072] Furthermore, the manganese-containing nickel-based composite metal oxide 7 disposed at the grain boundaries of adjacent primary particles 3 can adapt to the volume changes of the primary particles according to charging and discharging, and suppress cracks between primary particles, thereby suppressing the mechanical strength degradation of the positive electrode active material after long-term charging and discharging, and thus preventing the degradation of the rechargeable lithium battery. In addition, manganese is coated on the primary particles 3, thus stabilizing the crystal structure of the nickel-based composite metal oxide and greatly improving the cycle characteristics of the rechargeable lithium battery including the positive electrode active material.

[0073] Manganese-containing nickel complex metal oxides can be represented by chemical formula 1:

[0074] [Chemical Formula 1]

[0075] LiNi 1-x-y-z Co x Mn y M z O2

[0076] In chemical formula 1,

[0077] 0≤x≤0.5, 0.001≤y<0.015, 0≤z≤0.3, and M is at least one metallic element selected from Ni, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba, and Ce.

[0078] In the implementation method, the compound of chemical formula 1 may be LiNi. 1-x-y Co x Mn y O2 or LiNi 1-x-y-z Co x Mn y Al z O2.

[0079] Because manganese-containing nickel-based composite metal oxides contain a high nickel content, their capacity can be maximized. While a high nickel content can result in high capacity, it may also lead to a low cycle life. However, this low cycle life issue can be resolved by including manganese at a predetermined content.

[0080] In this embodiment, y in chemical formula 1 can be in the range of 0.001 ≤ y < 0.015. In this embodiment, the manganese-containing nickel-based composite metal oxide 7 can be Li[(NiCoAl)]. 0.995 Mn 0.005 O2, Li[(NiCoAl)] 0.99 Mn 0.01 O2, Li[(NiCoAl)] 0.986 Mn 0.014 O2 or combinations thereof (wherein these formulas, the molar amounts of Ni, Co and Al are not necessarily equal, but are described concisely to focus on the amount of manganese).

[0081] In an embodiment, the grain boundaries 7 of the primary particles 3 of the shell 5a may further include lithium manganese oxide, and the lithium manganese oxide may be LiMnO2.

[0082] The particle size (D50) of the positive electrode active material can be from about 8 μm to about 18 μm. Specifically, the particle size of the positive electrode active material can be greater than or equal to about 8 μm, greater than or equal to about 9 μm, greater than or equal to about 10 μm, greater than or equal to about 11 μm, greater than or equal to about 12 μm, greater than or equal to about 13 μm, greater than or equal to about 14 μm, greater than or equal to about 15 μm, greater than or equal to about 16 μm, or greater than or equal to about 17 μm and less than or equal to about 18 μm, less than or equal to about 17 μm, less than or equal to about 16 μm, less than or equal to about 15 μm, less than or equal to about 14 μm, less than or equal to about 13 μm, less than or equal to about 12 μm, less than or equal to about 11 μm, less than or equal to about 10 μm, or less than or equal to about 9 μm.

[0083] The positive electrode active material can be prepared according to the following preparation method.

[0084] First, a manganese compound is mixed with a nickel-based composite metal compound that forms secondary particles, and multiple primary particles aggregate within the secondary particles.

[0085] The nickel-based complex metal compound may be a nickel-based complex metal oxide or a nickel-based complex metal hydroxide, and in the embodiments, the nickel-based complex metal compound may be a compound represented by chemical formula 2 or chemical formula 3:

[0086] [Chemical Formula 2]

[0087] Ni 1-x-y Co x M y (OH)2

[0088] In chemical formula 2,

[0089] 0≤x≤0.5, 0≤y≤0.3, and M is at least one metallic element selected from Ni, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba, and Ce.

[0090] [Chemical Formula 3]

[0091] Ni 1-x-y Co x M y O2

[0092] In chemical formula 3,

[0093] 0≤x≤0.5, 0≤y≤0.3, and M is at least one metallic element selected from Ni, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba, and Ce.

[0094] The compound represented by chemical formula 2 can be Ni. 1-x Co x (OH)2 or Ni 1-x-y Co x Al y (OH)2, and the compound represented by chemical formula 3 can be Ni. 1-x Co x O2 or Ni 1-x-y Co x Al y O2.

[0095] Manganese compounds can be manganese hydroxide (Mn(OH)2).

[0096] When mixing nickel-based composite metal compounds and manganese compounds, a water-soluble solvent can be added and the mixture can be mixed using a wet mixing method. This is because during dry mixing, the manganese compound is more likely to be present on the surface of the shell rather than at the grain boundaries of the primary particles of the nickel-based composite metal compound shell.

[0097] Water-soluble solvents may include any one of NaOH, KOH, and mixtures thereof.

[0098] After mixing a nickel-based composite metal compound and a manganese compound, the mixture is reacted in a coating reactor to uniformly distribute manganese at the grain boundaries of the primary particles of the nickel-based composite metal compound shell, i.e., to coat the primary particles of the shell with manganese.

[0099] The temperature range of the coating reactor can be from about 40°C to about 100°C, specifically, greater than or equal to about 40°C, greater than or equal to about 50°C, greater than or equal to about 60°C, greater than or equal to about 70°C, greater than or equal to about 80°C, or greater than or equal to about 90°C and less than or equal to about 100°C, less than or equal to about 90°C, less than or equal to about 80°C, less than or equal to about 70°C, less than or equal to about 60°C, or less than or equal to about 50°C. In embodiments, the temperature of the coating reactor can be kept uniform during the reaction process.

[0100] The reaction time can be from approximately 30 minutes to approximately 1 hour.

[0101] The method may further include drying the reaction mixture to produce a nickel-based complex metal compound with a core-shell structure, wherein a manganese-containing nickel-based complex metal compound shell is formed on a nickel-based complex metal compound core.

[0102] The drying temperature can be from about 100°C to about 200°C, from about 120°C to about 180°C, or from about 140°C to about 160°C.

[0103] Subsequently, the lithium source is mixed with the coated material and calcined to obtain the positive electrode active material, which is a nickel-based composite metal oxide. The lithium source can be LiOH, Li2CO3, or their hydrates.

[0104] The firing temperature can be in the range of about 600°C to about 800°C, or specifically greater than or equal to about 600°C, greater than or equal to about 620°C, greater than or equal to about 640°C, greater than or equal to about 660°C, greater than or equal to about 680°C, greater than or equal to about 700°C, greater than or equal to about 720°C, greater than or equal to about 740°C, greater than or equal to about 760°C, or greater than or equal to about 780°C and less than or equal to about 800°C, less than or equal to about 780°C, less than or equal to about 760°C, less than or equal to about 740°C, less than or equal to about 720°C, less than or equal to about 700°C, less than or equal to about 680°C, less than or equal to about 660°C, less than or equal to about 640°C, or less than or equal to about 620°C.

[0105] The firing time can be from about 8 hours to about 30 hours, from about 8 hours to about 24 hours, or from about 10 hours to about 24 hours.

[0106] In this case, apart from the firing process, nickel-based composite metal compounds can be fired at temperatures of approximately 500°C to approximately 800°C.

[0107] In another embodiment, the rechargeable lithium battery includes: a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and an electrolyte.

[0108] The following describes a rechargeable lithium battery according to an embodiment, with reference to the accompanying drawings. Figure 2 This is a perspective view that schematically illustrates a typical structure of a rechargeable lithium battery according to an embodiment.

[0109] refer to Figure 2 The rechargeable lithium battery 31 includes a positive electrode 33, a negative electrode 32, and a separator 34 containing positive electrode active material according to an embodiment. The aforementioned positive electrode 33, negative electrode 32, and separator 34 containing positive electrode active material are wound or folded and housed in a battery casing 35. Then, an organic electrolyte is injected into the battery casing 35 and sealed using a capping assembly 36 to complete the rechargeable lithium battery 31. The battery casing 35 may be cylindrical, square, thin-film, etc.

[0110] Rechargeable lithium batteries can be lithium-ion batteries.

[0111] The positive and negative electrodes are manufactured by applying a composition for forming a positive active material layer and a composition for forming a negative active material layer onto a current collector, respectively, and then drying them.

[0112] The composition for forming the positive electrode active material is prepared by mixing the positive electrode active material, a conductive agent, a binder, and a solvent, wherein the positive electrode active material is as described above.

[0113] The binder facilitates the bonding between the positive electrode active material and / or conductive agents, and the adhesion of these materials to the current collector. Non-limiting examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and / or various copolymers. Based on the total weight of 100 parts by weight of the positive electrode active material, the binder may be included in an amount of about 1 to 5 parts by weight. When the amount of binder is within this range, the adhesion of the positive electrode active material layer to the current collector can be suitable or good.

[0114] There are no particular limitations on the conductive agent, as long as it does not cause chemical changes in the battery and is conductive. Non-limiting examples of conductive agents may include graphite, such as natural and / or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, and / or charcoal black; conductive fibers such as carbon fibers and / or metal fibers; fluorides; metal powders such as aluminum powder and / or nickel powder; zinc oxide; conductive whiskers such as potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Based on the total weight of 100 parts by weight of the positive electrode active material, the amount of conductive agent can be from about 1 part by weight to about 5 parts by weight. When the amount of conductive agent is within this range, the conductivity characteristics of the resulting electrode can be improved.

[0115] Non-limiting examples of solvents include N-methylpyrrolidone. Based on the total weight of 100 parts by weight of the positive electrode active material, the amount of solvent can be from about 1 part by weight to about 10 parts by weight. When the amount of solvent is within this range, the active material layer can be readily formed.

[0116] The positive current collector can have a thickness of approximately 3 μm to approximately 500 μm. There are no particular limitations on the materials used for the positive current collector, as long as they do not cause chemical changes in the battery and have high conductivity, and can be, for example, stainless steel; aluminum; nickel; titanium; heat-treated carbon; and / or aluminum or stainless steel surface-treated with carbon, nickel, titanium, and / or silver. The current collector can have fine irregularities formed on its surface to increase adhesion to the positive electrode active material, and can be provided in any suitable form, such as a film, sheet, foil, mesh, porous body, foam, and / or nonwoven fabric.

[0117] Additionally, the negative electrode active material, binder, conductive agent, CMC (carboxymethyl cellulose), and solvent can be mixed to prepare a composition for forming the negative electrode active material layer. The negative electrode active material can be or includes materials capable of intercalating and deintercalating lithium ions. Non-limiting examples of negative electrode active materials include carbon-based materials such as graphite and / or carbon, lithium metal, alloys thereof, and / or silicon oxide-based materials. In some embodiments, silicon oxide may be used.

[0118] The binder and solvent can be substantially the same as those used for the positive electrode. CMC can be used as a thickener to aid adhesion and control viscosity during the coating process. Based on the total weight of 100 parts by weight of the negative electrode active material, the amount of binder added can be from about 1 part by weight to about 5 parts by weight. Based on the total weight of 100 parts by weight of the negative electrode active material, the amount of CMC used is from about 1 part by weight to about 5 parts by weight. When the amount of CMC is within the above range, adhesion and coating performance can be improved. Based on the total weight of 100 parts by weight of the negative electrode active material, the amount of solvent used can be from about 10 parts by weight to about 200 parts by weight. When the amount of solvent is within this range, a layer of negative electrode active material can be easily formed.

[0119] The negative current collector can have a thickness of approximately 3 μm to approximately 500 μm. There are no particular limitations on the material of the negative current collector, as long as it does not cause chemical changes in the battery and has high conductivity. Non-limiting examples may include copper; stainless steel; aluminum; nickel; titanium; heat-treated carbon; copper and / or stainless steel surface-treated with carbon, nickel, titanium, and / or silver; and / or aluminum-cadmium alloys, etc. The negative current collector may have fine irregularities formed on its surface to increase adhesion to the negative electrode active material and can be provided in any suitable form (e.g., film, sheet, foil, mesh, porous body, foam, and / or nonwoven fabric), similar to the positive current collector.

[0120] A separator can be disposed between the positive and negative electrodes to be wound or laminated to form an electrode assembly. The separator can have a pore size of about 0.01 μm to about 10 μm and a thickness of about 5 μm to about 300 μm. Specific examples may include olefin polymers, such as polypropylene and polyethylene; or sheets or nonwoven fabrics formed from glass fibers. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also be used as the separator.

[0121] When the electrode assembly is housed in the casing, an electrolyte is injected, and the resulting product is sealed, completing the rechargeable lithium battery. The electrolyte can be a non-aqueous electrolyte including non-aqueous solvents and lithium salts, an organic solid electrolyte, or an inorganic solid electrolyte. Non-aqueous solvents can be, or include, for example, proton-inert organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate. Lithium salts can be materials that are readily soluble in non-aqueous solvents, and non-limiting examples may be selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, such as integers in the range of 1 to 20), lithium difluoro(bis(oxalate)phosphate), LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalate)borate, LiBOB) and lithium difluoro(oxalate)borate (LiDFOB).

[0122] Non-limiting examples of organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfides, polyvinyl alcohol, and polyvinylidene fluoride.

[0123] Non-limiting examples of inorganic solid electrolytes include Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2, etc.

[0124] Furthermore, rechargeable lithium batteries can be assembled from circuits to form battery packs, and single or multiple battery packs can be used in all devices requiring high capacity and high power, as needed. For example, they can be used in laptops, smartphones, and electric vehicles. In addition, rechargeable lithium batteries possess excellent storage stability, cycle life characteristics, and high-rate characteristics at high temperatures, making them suitable for electric vehicles (EVs). For example, they can be used in hybrid vehicles, such as plug-in hybrid electric vehicles (PHEVs).

[0125] This disclosure is explained in more detail in the following embodiments and comparative examples. However, it should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting this disclosure.

[0126] Example 1

[0127] (Preparation of positive electrode active material)

[0128] Add nickel-based complex metal hydroxide (Ni) to it 0.94 Co 0.04 Al 0.02 In a reactor containing (OH)₂ and distilled water, after supplying N₂ gas at 4000 sccm, the aqueous solution in the reactor is stirred at 300 to 600 rpm while maintaining at 45°C. Subsequently, a 2M solution of manganese hydroxide and a 5.5M solution of NaOH are continuously added to the reactor for 30 minutes to 1 hour. While maintaining the temperature in the reactor at 50°C to 80°C, the mixture is stirred for 30 minutes to coat a nickel-based composite metal hydroxide with 1 mol% manganese. The coated product is then dried in a vacuum dryer at 150°C to obtain a nickel-based composite metal hydroxide with a core-shell structure, comprising a nickel-based composite metal hydroxide core and a manganese-containing nickel-based composite metal hydroxide shell thereon. Here, the manganese content is 1 mol%, based on the total amount of metals other than lithium in the shell.

[0129] Subsequently, a core-shell structured nickel-based composite metal hydroxide and lithium hydroxide were mixed in a 1:1 molar ratio, and then calcined at 720°C for 12 hours to obtain a mixture containing Li[Ni]. 0.94 Co 0.04 Al 0.02 O2 core and Li[Ni 0.93 Co 0.04 Al 0.02 Mn 0.01 O2 shell positive electrode active material powder.

[0130] (Manufacturing of the positive electrode)

[0131] A positive electrode active material slurry was prepared by mixing 94 wt% of positive electrode active material, 3 wt% of Ketjen black, and 3 wt% of polyvinylidene fluoride in N-methylpyrrolidone solvent. The positive electrode active material slurry was coated onto an Al film, and then dried and compressed to manufacture the positive electrode.

[0132] (Manufacturing of coin cells)

[0133] A coin battery is manufactured using a solution of a positive electrode, lithium metal as a counter electrode, a PTFE separator, and 1.15 M of LiPF6 as an electrolyte dissolved in a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate) (volume ratio 3:4:3).

[0134] Example 2

[0135] (Preparation of positive electrode active material)

[0136] Adding nickel-based composite metal oxides (Ni) 0.94 Co 0.04 Al 0.02 In a reactor containing O2 and distilled water, N2 gas was supplied at 4000 sccm, and the aqueous solution in the reactor was stirred at 300 to 600 rpm while maintaining 45°C. Subsequently, a 2M manganese hydroxide and a 5.5M NaOH aqueous solution were continuously added to the reactor for 30 minutes to 1 hour. While the reactor was maintained at 50°C to 70°C, the resulting mixture was stirred for 30 minutes to coat a nickel-based composite metal oxide with 1 mol% manganese. The coated product was then dried in a vacuum dryer at 150°C to obtain a nickel-based composite metal oxide with a core-shell structure, having a nickel-based composite metal oxide core and a manganese-containing nickel-based composite metal oxide shell formed thereon. Here, the manganese content is 1 mol%, based on the total amount of metals other than lithium in the shell.

[0137] Subsequently, a core-shell structured nickel composite metal oxide and lithium hydroxide were mixed in a 1:1 molar ratio and calcined at 720°C for 12 hours to obtain a mixture containing Li[Ni]. 0.94 Co 0.04 Al 0.02 O2 core and Li[Ni 0.93 Co 0.04 Al 0.02 Mn 0.01 O2 shell positive electrode active material powder.

[0138] (Manufacturing of the positive electrode)

[0139] A positive electrode active material slurry was prepared by mixing 94 wt% of positive electrode active material, 3 wt% of Ketjen black, and 3 wt% of polyvinylidene fluoride in N-methylpyrrolidone solvent. The positive electrode active material slurry was coated onto an Al film, and then dried and compressed to manufacture the positive electrode.

[0140] (Manufacturing of coin cells)

[0141] A coin battery is manufactured using a solution of a positive electrode, lithium metal as a counter electrode, a PTFE separator, and 1.15 M of LiPF6 as an electrolyte dissolved in a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate) (volume ratio 3:4:3).

[0142] Comparative Example 1

[0143] The positive electrode active material was prepared according to the same method as in Example 1, except that no aqueous manganese hydroxide solution was added, and then the positive electrode and coin cell were manufactured using it.

[0144] Comparative Example 2

[0145] The positive electrode active material was prepared using the same method as in Example 1, except that it was dried and mixed with a nickel-based composite metal hydroxide (Ni 0.94 Co 0.04 Al 0.02 (OH)2) and manganese hydroxide, and then, by using them, positive electrodes and coin cells are manufactured.

[0146] Comparative Example 3

[0147] The positive electrode active material was prepared according to the same method as in Example 1, except that when coating with 1 mol% Mn, the coating was carried out by stirring in a reactor for 1 hour and 30 minutes, the resulting product was dried, and then mixed with lithium hydroxide at a 1:1 molar ratio. The mixture was calcined at 720°C for 24 hours to dope manganese into the core, and then the positive electrode and coin cell were manufactured using it.

[0148] Comparative Example 4

[0149] The positive electrode active material was prepared according to the same method as in Example 1, except that it was coated with 1.5 mol% Mn, and then used to manufacture the positive electrode and the coin cell.

[0150] Assessment 1: Evaluation of initial charge / discharge capacity and charge / discharge efficiency.

[0151] The coin batteries according to Examples 1 and 2 and Comparative Examples 1 to 4 were charged and discharged once at 0.2C, and then the charging capacity, discharging capacity, and charging and discharging efficiency were measured. The results are shown in Table 1.

[0152] (Table 1)

[0153]

[0154]

[0155] As shown in Table 1, compared with the coin batteries of Comparative Examples 1 to 4, the coin battery of Example 1 exhibits excellent charging and discharging capacity and excellent charging and discharging efficiency.

[0156] Evaluation 2: Evaluation of Cycle Life Characteristics

[0157] The coin cell batteries according to Example 1 and Comparative Examples 1 to 4 were charged at a constant current rate of 1.0C to a voltage of 4.30V (for lithium), and then cut off at a current rate of 0.05C in constant voltage mode while maintaining 4.30V at 45°C. Subsequently, the coin cell batteries were discharged at a constant current rate of 1.0C to a voltage of 3.0V (for lithium), which was considered one cycle, and this was repeated until the 50th cycle. A 10-minute pause was set after each charge / discharge cycle in all charge and discharge cycles. The cycle life (capacity retention) of the coin cell batteries at the 100th cycle was measured, and the results are shown in Table 2 and... Figure 3 middle.

[0158] Calculate the capacity retention rate according to Equation 1:

[0159] [Equation 1]

[0160] Capacity retention rate at the 100th cycle [%] = [Discharge capacity at the 100th cycle / Discharge capacity at the 1st cycle] × 100 [%]

[0161] (Table 2)

[0162]

[0163] As shown in Table 2 and Figure 3 As shown, compared with the coin batteries according to Comparative Examples 1 to 4, the coin battery according to the embodiment exhibits excellent cycle life.

[0164] Although this disclosure has been described in conjunction with exemplary embodiments now regarded as practical, it should be understood that this disclosure is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A positive electrode active material, comprising: Nickel-based composite metal oxides are secondary particles, with multiple primary particles aggregated within these secondary particles. The secondary particles comprise a core and a shell, wherein the core does not include manganese. The surface of the primary particles of the shell is coated with a manganese-containing nickel-based composite metal oxide. The manganese-containing nickel-based composite metal oxide has a layered structure. The manganese content in the positive electrode active material is less than 1.5 mol%, and The manganese-containing nickel-based composite metal oxide mentioned above is represented by chemical formula 1: [Chemical Formula 1] LiNi 1-x-y-z Co x Mn y M z O2 In chemical formula 1, 0≤x≤0.5, 0.001≤y<0.015, 0≤z≤0.3, and M is at least one metallic element selected from Ni, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba, and Ce.

2. The positive electrode active material of claim 1, wherein the manganese concentration has a concentration gradient, wherein the manganese concentration increases from the interior to the surface of the primary particles of the shell.

3. The positive electrode active material according to claim 1, wherein the manganese-containing nickel composite metal oxide is in the form of islands or fine nanoparticles on the surface of the primary particles of the shell.

4. The positive electrode active material according to claim 1, wherein the thickness of the shell is less than or equal to 2 μm.

5. The positive electrode active material according to claim 1, wherein the positive electrode active material has a particle size of 8 μm to 18 μm.

6. The positive electrode active material according to claim 1, wherein the positive electrode active material further comprises LiMnO2 on the surface of the primary particles of the shell.

7. A method for preparing a positive electrode active material as described in any one of claims 1-6, comprising: A mixture is prepared by adding a water-soluble solvent to a nickel-based complex metal compound and manganese hydroxide, wherein the nickel-based complex metal compound is a secondary particle, multiple primary particles are aggregated within the secondary particles, and the secondary particles comprise a core and a shell. The mixture is reacted at 40°C to 100°C for 30 minutes to 1 hour to coat the grain boundaries between the primary particles of the shell of the nickel-based composite metal compound with a manganese-containing nickel-based composite metal oxide. The coated material is mixed with a lithium source and then fired. Wherein, based on the total number of moles of metals other than lithium in the manganese-containing nickel composite metal oxide, the manganese content in the manganese-containing nickel composite metal oxide is less than 1.5 mol.

8. The method of claim 7, wherein the nickel-based composite metal compound is one of nickel-based composite metal oxide and nickel-based composite metal hydroxide.

9. The method of claim 7, wherein the water-soluble solvent comprises any one of NaOH, KOH, and mixtures thereof.

10. The method of claim 7, wherein after reacting the mixture at 40°C to 100°C for 30 minutes to 1 hour, the mixture is dried at 100°C to 200°C.

11. The method of claim 7, wherein the firing temperature is 600 °C to 800 °C and the firing time is 8 hours to 30 hours or 8 hours to 24 hours.

12. A rechargeable lithium battery comprising: a positive electrode comprising the positive active material of any one of claims 1-6 or the positive active material prepared by the method of any one of claims 7-11; a negative electrode comprising a negative active material; and an electrolyte.

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