Positive electrode active material for lithium secondary battery, lithium secondary battery comprising same, and method for manufacturing positive electrode active material

Abstract

A positive electrode active material for a lithium secondary battery according to embodiments of the present disclosure comprises lithium metal oxide particles containing cobalt and aluminum. The lithium metal oxide particles have a secondary particle form, which is formed by aggregation of primary particles, and the weight ratio of aluminum to cobalt contained in the primary particles satisfies a predetermined relational expression. A positive electrode can be achieved that has improved structural stability and high-temperature stability as well as high energy density and high output characteristics.

Description

Cathode active material for lithium secondary batteries, lithium secondary batteries containing the same, and method for manufacturing the cathode active material

[0001] The present disclosure relates to a positive electrode active material for a lithium secondary battery, a lithium secondary battery including the same, and a method for manufacturing the positive electrode active material.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are being actively researched and developed due to their high operating voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0005] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may include an outer packaging material (e.g., in the form of a pouch) that accommodates the electrode assembly and the electrolyte.

[0006] Lithium metal oxide can be used as a cathode active material in lithium secondary batteries. As lithium metal oxide increases in size, its energy density increases, but capacity and output may decrease. As the application range of lithium secondary batteries expands, demands for longer life, higher capacity, and higher energy density are increasing.

[0007]

[0008] An object of the present disclosure is to provide a cathode active material for a lithium secondary battery having improved energy density and stability.

[0009] An object of the present disclosure is to provide a lithium secondary battery including a positive electrode active material for a lithium secondary battery having improved energy density and stability.

[0010] An object of the present disclosure is to provide a method for manufacturing a cathode active material having improved energy density and stability.

[0011]

[0012] According to exemplary embodiments, a cathode active material for a lithium secondary battery includes lithium metal oxide particles containing cobalt and aluminum. The lithium metal oxide particles may include secondary particles formed by agglomeration of a plurality of primary particles. The cathode active material may have a WR of 0.9 to 1.1, as expressed by the following Equation 1.

[0013] [Formula 1]

[0014] WR=A / B

[0015] In the above formula 1, A may be a ratio of the content of aluminum to the content of cobalt contained in the primary particles of the lithium metal oxide particles having a particle size of n ㎛.

[0016] B may be a ratio of the content of aluminum to the content of cobalt contained in the primary particles of the lithium metal oxide particles having a particle size of n+10 ㎛.

[0017] The above n ㎛ may be 1 ㎛ to 22 ㎛.

[0018] In some embodiments, the weight ratio of aluminum to the weight of cobalt may be a value measured using atomic probe tomography (APT) on a cross-section of the primary particle.

[0019] In some embodiments, the ratio of the aluminum content in the primary particles of the particles having a particle size of n+10 μm to the aluminum content in the primary particles of the particles having a particle size of n μm among the lithium metal oxide particles may be 0.85 to 1.1.

[0020] In some embodiments, the particle size of the lithium metal oxide particles may be 0.8 μm to 30 μm.

[0021] In some embodiments, the short axis of each of the primary particles may be between 100 nm and 500 nm.

[0022] In some embodiments, the content of aluminum contained within each primary particle of the lithium metal oxide particles may be less than the content of cobalt contained within each primary particle of the lithium metal oxide particles.

[0023] In some embodiments, the lithium metal oxide particles may further comprise nickel or manganese.

[0024] In some embodiments, each of the lithium metal oxide particles may comprise a compound represented by the following chemical formula 1.

[0025] [Chemical Formula 1]

[0026] Li a Co x Al y M 1-x-y O 2+b

[0027] In the above chemical formula 1, 0.9≤a≤1.2, 0 <x≤0.3, 0<y≤0.2, -0.2≤b≤0.2이고, M은 Ni, Mn, Ti, Zr, Ba, Tb, Nb, Y, W, B 및 Sr 중 적어도 하나일 수 있다.

[0028] A lithium secondary battery according to exemplary embodiments includes a positive electrode including a positive electrode active material for a lithium secondary battery according to the above-described embodiments, and a negative electrode opposite to the positive electrode.

[0029] In a method for manufacturing a cathode active material according to exemplary embodiments, a first precursor including cobalt and aluminum can be manufactured. The first precursor includes cobalt and aluminum, and has an average particle diameter (D 50) with an average particle diameter (D) of 9 to 11 μm larger than 50 ) can be prepared. A precursor blend can be prepared by mixing a lithium precursor, the first precursor, and the second precursor. Lithium metal oxide particles can be prepared by calcining the precursor blend.

[0030] In some embodiments, the ratio (A1 / B1) between the ratio of the aluminum content to the cobalt content included in the first precursor (A1) and the ratio of the aluminum content to the cobalt content included in the second precursor (B1) may be 0.9 to 1.1.

[0031] In a method for manufacturing a cathode active material according to exemplary embodiments, a first precursor including cobalt can be manufactured. The first precursor includes cobalt and has an average particle diameter (D 50 ) with an average particle diameter (D) of 9 to 11 μm larger than 50 ) can be prepared. The second precursor, the lithium precursor, and the aluminum precursor can be mixed to prepare a first blend. The first blend and the first precursor can be mixed to prepare a second blend. The second blend can be fired to prepare lithium metal oxide particles.

[0032] In some embodiments, the first precursor and the second precursor may not contain aluminum.

[0033] In some embodiments, the ratio of the content of cobalt in the second precursor to the content of cobalt in the first precursor may be 0.85 to 1.1 by weight.

[0034] In some embodiments, the content of the second precursor in the second blend may be greater than or equal to the content of the first precursor.

[0035]

[0036] The cathode active material for a lithium secondary battery according to embodiments of the present disclosure may include lithium metal oxide particles containing cobalt and aluminum and having a secondary particle form. High energy density and improved structural stability of the cathode active material can be realized.

[0037] The weight ratio of aluminum to the weight of cobalt contained in the primary particles of small particles among lithium metal oxide particles and the weight ratio of aluminum to the weight of cobalt contained in the primary particles of large particles can satisfy a predetermined relationship. The output characteristics and capacity of a positive electrode active material for a lithium secondary battery can be improved, while the room temperature life and high temperature stability can be improved.

[0038]

[0039] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0040] Figures 3 to 5 are APT analysis photographs of lithium metal oxide particles according to Example 1, Example 2, and Comparative Example 1, respectively.

[0041]

[0042] Embodiments of the present disclosure provide a positive electrode active material including lithium metal oxide particles and a lithium secondary battery including the same.

[0043] Lithium secondary batteries according to embodiments of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, lithium secondary batteries according to embodiments of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0044] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0045] In exemplary embodiments, a positive electrode active material for a lithium secondary battery (hereinafter, abbreviated as “positive electrode active material”) may include lithium metal oxide particles containing cobalt and aluminum.

[0046] Lithium metal oxide particles containing cobalt (Co) can have high lithium ion conductivity and reduce intra-particle resistance. Therefore, the output characteristics of lithium secondary batteries can be improved.

[0047] The lithium metal oxide particles described above contain aluminum (Al), which can improve the mechanical and chemical stability of the particles and enhance their heat resistance. Therefore, cracking of the positive electrode active material can be suppressed even during repeated charge-discharge cycles, and the high-temperature lifespan characteristics of the secondary battery can be improved.

[0048] The lithium metal oxide particles may include secondary particle forms. The secondary particles may refer to particles in which a plurality of primary particles are aggregated and are substantially regarded or observed as a single particle.

[0049] For example, the boundaries of the primary particles can be observed in a cross-sectional image of the secondary particles measured using a scanning electron microscope (SEM). Each primary particle can be distinguished through the boundaries within the secondary particle.

[0050] In one embodiment, the secondary particles may be aggregates of more than 10, 30, 50, or 100 primary particles.

[0051] In lithium metal oxide particles with a structure composed of aggregated primary particles with small average particle diameters, energy density can be improved while maintaining a short lithium ion migration distance. For example, lithium ions can migrate through the boundaries between primary particles, improving the lithium ion migration distance and velocity. Consequently, energy density can be improved while suppressing degradation of capacity and output characteristics.

[0052] According to some embodiments, the short axis of the primary particle may be 100 nm to 500 nm. The short axis may refer to the shortest diameter of the primary particle as measured by shape analysis such as SEM. Within this range, the movement distance of lithium ions is sufficiently shortened, and the primary particles can smoothly aggregate into secondary particles. In addition, the structural stability of the lithium metal oxide particles is improved, so that cracking can be suppressed.

[0053] According to exemplary embodiments, the positive electrode active material may have a WR of 0.9 to 1.1, as represented by the following equation 1.

[0054] [Formula 1]

[0055] WR=A / B

[0056] In the above formula 1, A may be a weight-based ratio of the content of aluminum to the content of cobalt contained in the primary particles of the lithium metal oxide particles having a particle size of n μm (hereinafter, referred to as 'small particles').

[0057] B may be a weight-based ratio of the content of aluminum to the content of cobalt contained in the primary particles of particles having a particle size of n+10 μm among the lithium metal oxide particles (hereinafter, referred to as "antibody"). The particle size of the antibody may include cases where it has a value arithmetically equal to n+10 μm and cases where it has a value that has a predetermined error therefrom but can be recognized as substantially the same.

[0058] For example, if A is the ratio of the contents of cobalt and aluminum measured from primary particles of lithium metal oxide particles having a particle size of about 4 μm, B may be the ratio of the contents of cobalt and aluminum measured from primary particles of lithium metal oxide particles having a particle size of about 14 μm.

[0059] In the above formula 1, n ㎛ is the minimum particle diameter (D) of the lithium metal oxide particles. min ) and maximum particle diameter (D max ) - It can be any value selected within the range of 10㎛ or less. The minimum particle diameter (D min ) may be the minimum particle diameter in the cumulative particle size distribution curve of the lithium metal oxide particles. The maximum particle diameter (D max ) may be the maximum particle size in the cumulative particle size distribution curve of the lithium metal oxide particles.

[0060] For example, in the above formula 1, n ㎛ may be 1 ㎛ to 22 ㎛, 1.4 ㎛ to 22 ㎛, 1.4 ㎛ to 18 ㎛, or 4.2 ㎛ to 16.1 ㎛. As particles having particle diameters in the above-described ranges satisfy the above formula 1, the concentration of cobalt and aluminum contained within each of the lithium metal oxide particles may become uniform.

[0061] In the present application, the “content” or “concentration” of any metal may mean the weight ratio of the metal within the lithium metal oxide particles or primary particles.

[0062] The cobalt content and aluminum content contained in the primary particles can be measured by atom probe tomography (APT) on a cross-section of the primary particles. For example, the lithium metal oxide particles can be cut to expose the cross-section of the primary particles, and then APT analysis can be performed on the cross-section of the primary particles.

[0063] In one embodiment, APT analysis of a primary particle cross-section can be performed by cutting the primary particle with the cross-section exposed into a needle structure having a tip radius of about 40 nm and loading it into a chamber.

[0064] For example, the lithium metal oxide particles may be cut, and the internal composition of the primary particles having a short axis of 100 nm to 500 nm may be measured using the method described above. In one embodiment, the internal composition may be the arithmetic mean of values ​​measured twice.

[0065] As the concentrations of aluminum and cobalt inside the primary particles of the lithium metal oxide particles satisfy the above-described Equation 1, an increase in the internal resistance of the lithium metal oxide can be prevented, and the stability of the internal structure can be further improved.

[0066] For example, when doping / coating a cathode active material containing particles of different sizes with aluminum (Al), the surface area and diffusion rate may differ depending on the size of the particles, and thus the doping or coating content may vary. For example, the aluminum (Al) content may be relatively high in relatively small particles (e.g., small particles), and the internal doping or coating amount of aluminum (Al) may be low in relatively large particles (e.g., large particles). In this case, the concentration ratio of aluminum to cobalt in the small particles may become relatively large. Therefore, the output of a lithium secondary battery may be reduced by small particles with a high aluminum content.

[0067] Furthermore, the relatively low aluminum content of the opposing particles may degrade high-temperature life and structural stability. Furthermore, differences in aluminum content between particles may cause stress (e.g., stress, oxidation) to be concentrated on particles with relatively low aluminum content, accelerating deterioration.

[0068] According to exemplary embodiments, the aluminum content within the primary particles of the opposing particles and the aluminum content within the primary particles of the small particles may be substantially identical. Accordingly, variations in the content or concentration of aluminum and cobalt depending on particle size may be reduced.

[0069] In some embodiments, WR in Equation 1 may be greater than 0.90, for example, 0.91 or greater, 0.93 or greater, 0.95 or greater, or 0.98 or greater. In some embodiments, WR in Equation 1 may be less than 1.10, for example, 1.09 or less, or 1.08 or less.

[0070] In one embodiment, WR may be from 0.93 to 1.09, for example from 0.95 to 1.08, from 0.95 to 1.08, or from 0.98 to 1.08.

[0071] Within the above range, the stability of the positive electrode active material can be further improved, and the local deviation of the aluminum concentration according to the difference in particle size can be reduced, thereby improving the output characteristics and cycle characteristics.

[0072] For example, when the weight ratio of aluminum to the weight of cobalt contained in the primary particle of any one randomly selected particle among the lithium metal oxide particles is C, the weight ratio of aluminum to the weight of cobalt contained in the primary particle of each of the lithium metal oxide particles may be 0.9C to 1.1C.

[0073] If the concentrations of aluminum and cobalt differ depending on the particle size, the energy density and stability of the positive electrode active material may be reduced, and the stress and oxidation due to charge and discharge may be concentrated on some particles, increasing the rate of deterioration.

[0074] According to exemplary embodiments, the lithium metal oxide particles may have a uniform aluminum concentration throughout, thereby improving the lifespan and stability of the cathode active material. Furthermore, the overall weight ratio of aluminum to cobalt in the lithium metal oxide particles may be uniform, thereby improving capacity and output characteristics.

[0075] In one embodiment, the ratio of the aluminum content (concentration) in the primary particles of the particles having a particle size of n+10 μm to the aluminum content (concentration) in the primary particles of the particles having a particle size of n μm among the lithium metal oxide particles may be 0.85 to 1.125, 0.85 to 1.1, 0.9 to 1.05, or 0.95 to 1.05.

[0076] In some embodiments, the content of aluminum contained within each primary particle of the lithium metal oxide particles may be less than the content of cobalt contained within each primary particle of the lithium metal oxide particles. For example, in Equation 1, A and B may each be less than 1.

[0077] For example, when A and B exceed 1, the concentration of aluminum within the lithium metal oxide particles may become excessively high. Consequently, the internal resistance of the lithium metal oxide particles may increase, and the conductivity of the particles may decrease. Consequently, the output and capacity of the lithium secondary battery may decrease.

[0078] Since the concentration of cobalt contained within the primary particles of the lithium metal oxide particles is greater than that of aluminum, the heat resistance and structural stability of the positive electrode active material can be improved while preventing a decrease in energy density and lithium ion conductivity. Accordingly, the output of the secondary battery can be improved while preventing deterioration and defects of the positive electrode active material even under harsh conditions of repeated charge / discharge and high temperature / high humidity.

[0079] In some embodiments, A and B in Equation 1 may each be 0.7 or less, for example, 0.6 or less, 0.5 or less, 0.2 or less, or 0.189 or less. In one embodiment, A and B may each be 0.001 or more, 0.01 or more, 0.03 or more, or 0.0653.

[0080] Within the above range, the mechanical properties and chemical stability of the positive electrode active material can be improved, and an increase in resistance can be prevented. Accordingly, the output characteristics and room-temperature / high-temperature cycling characteristics of the lithium secondary battery can be improved simultaneously.

[0081] In some embodiments, the particle size of the lithium metal oxide particles may be from 0.8 μm to 32 μm. In one embodiment, the particle size may be from 1.0 μm to 32 μm, from 1.4 μm to 30 μm, from 1.4 μm to 26.2 μm, from 1.4 μm to 22 μm, or from 4.2 μm to 16.1 μm.

[0082] For example, when the particle size of lithium metal oxide particles is 32㎛ or less, the mechanical properties and structural stability of the particles can be improved, thereby improving the cycle characteristics of lithium secondary batteries. For example, when the particle size of lithium metal oxide particles is 0.8㎛ or more, the movement distance of lithium ions can be shortened, and the capacity characteristics and output characteristics of lithium secondary batteries can be improved.

[0083] In one embodiment, the average particle diameter (D) of the positive electrode active material 50 ) may be 4 ㎛ to 20 ㎛, 4 ㎛ to 15 ㎛, or 5 ㎛ to 12 ㎛.

[0084] In one embodiment, the positive active material may have a bimodal particle size distribution. The volume particle size distribution curve of the positive active material may have two different modes. For example, the volume particle size distribution curve of the positive active material may have modes at n μm and n+10 μm. The tap density of the positive active material and the packing density of the electrode may be improved.

[0085] In some embodiments, each of the lithium metal oxide particles may comprise a compound represented by the following chemical formula 1.

[0086] [Chemical Formula 1]

[0087] Li a Co x Al y M 1-x-y O 2+b

[0088] In the above chemical formula 1, 0.9≤a≤1.2, 0 <x≤0.3, 0<y≤0.2, -0.2≤b≤0.2이고, M은 Ni, Mn, Ti, Zr, Ba, Tb, Nb, Y, W, B 및 Sr 중 적어도 하나일 수 있다.

[0089] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained within the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M may serve as the main active element of the positive electrode active material. Chemical Formula 1 is provided to express the bonding relationship of the main active element and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0090] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0091] The auxiliary element may include, for example, at least one selected from the group consisting of Na, Mg, Ca, Hf, V, Nb, Ta, Cr, Mo, Fe, Cu, Ag, Zn, Ga, C, Si, Sn, Ra, P, and S. The auxiliary element may also act as an auxiliary active element contributing to the capacity / output activity of the positive electrode active material, for example, together with Al, Co, Ni, or Mn.

[0092] According to embodiments of the present disclosure, a cathode active material can be manufactured using heterogeneous precursors having different average particle diameters.

[0093] According to exemplary embodiments, the average particle diameter (D 50 ) can produce different first and second precursors. For example, the average particle diameter (D) of the second precursor 50 ) is the average particle diameter (D) of the first precursor 50 ) may be 9 μm to 11 μm larger than the average particle size of the first precursor and the second precursor. In one embodiment, the average particle size of the first precursor and the second precursor may be controlled by the co-precipitation time, co-precipitation temperature, etc.

[0094] The first precursor and the second precursor may comprise a complex metal salt compound. For example, a transition metal solution may be prepared by mixing active material metal precursors with a precipitant and / or chelating agent in a solvent. The first precursor and the second precursor may be prepared by co-precipitating the transition metal solution in a reactor.

[0095] The above active material metal precursor may include a salt of an active material metal (e.g., nickel, cobalt, manganese, aluminum, etc.). For example, examples of the nickel salt include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, and hydrates thereof. Examples of the manganese salt include manganese sulfate, manganese acetate, and hydrates thereof. Examples of the cobalt salt include cobalt sulfate, cobalt nitrate, cobalt carbonate, and hydrates thereof. Examples of the aluminum salt include aluminum sulfate, aluminum nitrate, aluminum hydroxide, and hydrates thereof.

[0096] The precipitant may include an alkaline compound such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), etc. The chelating agent may include, for example, ammonia water, ammonium carbonate, etc.

[0097] According to exemplary embodiments, the first precursor and the second precursor may each contain cobalt and aluminum.

[0098] In one embodiment, the ratio of the aluminum content to the cobalt content included in the first precursor and the ratio of the aluminum content to the cobalt content included in the second precursor may be substantially the same.

[0099] For example, the ratio (A1 / B1) between the weight-based ratio (A1) of the aluminum content to the cobalt content included in the first precursor and the weight-based ratio (B1) of the aluminum content to the cobalt content included in the second precursor may be 0.9 to 1.1, 0.93 to 1.09, 0.95 to 1.08, or 0.95 to 1.05.

[0100] According to exemplary embodiments, a precursor blend may be prepared by mixing the first precursor and the second precursor together with a lithium precursor.

[0101] The above lithium precursor may include lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, etc. These may be used alone or in combination of two or more.

[0102] According to exemplary embodiments, the precursor blend may be introduced into a reactor and calcined to produce lithium metal oxide particles. The lithium metal oxide particles may have a secondary particle form formed by agglomeration of a plurality of primary particles. For example, the primary particles may be derived from the first precursor and the second precursor.

[0103] By controlling the content ratio of aluminum and cobalt in heterogeneous precursors having different particle sizes to be substantially identical, the concentrations of aluminum and cobalt in the primary particles can be controlled to be substantially identical. Accordingly, the cobalt and aluminum contents can be uniform throughout the entire region of the lithium metal oxide particles, thereby improving life characteristics, structural stability, and output characteristics.

[0104] According to exemplary embodiments, the first precursor and the second precursor may each contain cobalt and may not contain aluminum.

[0105] The content (concentration) of cobalt included in the first precursor and the content (concentration) of cobalt included in the second precursor may be substantially the same. For example, the ratio of the content of cobalt in the second precursor to the content of cobalt in the first precursor may be 0.85 to 1.1, 0.9 to 1.05, or 0.95 to 1.05 by weight.

[0106] According to exemplary embodiments, the second precursor may be uniformly mixed with a lithium precursor and an aluminum precursor to produce a first blend. For example, the mixing may be performed using a dry high-speed mixer.

[0107] According to exemplary embodiments, the first precursor may be added to the first blend and uniformly mixed to produce a second blend. The second blend may be added to a reactor and calcined to produce lithium metal oxide particles having a secondary particle form.

[0108] The second precursor may be mixed with the aluminum precursor before the first precursor, so that the first precursor, the second precursor, and the aluminum precursor may be more uniformly mixed within the second blend. Accordingly, the concentration of cobalt relative to aluminum within the lithium metal oxide particles may be uniform throughout.

[0109] For example, when the first precursor, the second precursor, and the aluminum precursor are simultaneously mixed and fired, the aluminum doping amount and / or coating amount for the second precursor, which has a relatively large size, may decrease. Accordingly, the aluminum concentration within the primary particles derived from the first precursor may relatively increase.

[0110] In one embodiment, the content of the second precursor in the second blend may be greater than or equal to the content of the first precursor. For example, the content ratio of the first precursor and the second precursor in the second blend may be 1:9 to 5:5, 2:8 to 4:6, or 3:7 to 4:6 by weight. The second precursor having a relatively large size may be first mixed with the aluminum precursor in a high content to make the cobalt and aluminum content ratio in the secondary particles more uniform.

[0111] In one embodiment, the firing of the precursor blend or the second blend may be performed in an oxygen-containing atmosphere at a temperature of about 600° C. to 900° C. for about 10 to 15 hours.

[0112] Hereinafter, a lithium secondary battery including a positive electrode including the positive electrode active material for a lithium secondary battery described above is described with reference to FIGS. 1 and 2.

[0113] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, FIG. 2 is a cross-sectional view taken along line Ⅰ-Ⅰ' of FIG. 1 in the thickness direction.

[0114] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) including a positive electrode active material including the lithium metal oxide particles described above, and a negative electrode (130) facing the positive electrode (100).

[0115] The positive electrode (100) may include a positive electrode active material layer (110) formed by applying a positive electrode active material including the lithium metal oxide particles described above to a positive electrode current collector (105).

[0116] For example, a positive electrode slurry can be prepared by mixing and stirring a positive electrode active material with a binder, a conductive agent, and / or a dispersing agent in a solvent. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector (105), and then dried and rolled to prepare a positive electrode (100).

[0117] The positive electrode current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (105) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0118] The binder may include, for example, an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0119] For example, a PVDF series binder may be used as a binder for forming a positive electrode. In this case, the amount of binder for forming a positive electrode active material layer (110) may be reduced and the amount of positive electrode active material may be relatively increased, thereby improving the output and capacity of the secondary battery.

[0120] The conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0121] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed by coating a negative electrode active material on at least one surface of the negative electrode current collector (125).

[0122] The above-mentioned negative active material can be any material known in the art capable of absorbing and desorbing lithium ions without particular limitation. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium alloys; silicon, or tin; etc. can be used.

[0123] Examples of the above amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500°C or lower, and mesophase pitch-based carbon fibers (MPCF).

[0124] Examples of the above crystalline carbon include graphitic carbons such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0125] Elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0126] The negative electrode current collector (125) may include gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, for example, copper or a copper alloy.

[0127] In some embodiments, the negative electrode active material may be mixed and stirred with a binder, a conductive agent, and / or a dispersing agent in a solvent to produce a slurry. After coating the slurry on the negative electrode current collector, the slurry may be dried and compressed to produce a negative electrode (130).

[0128] Materials substantially identical to or similar to the above-described binder and conductive agent may be used. In some embodiments, the binder for forming the negative electrode may include, for example, an aqueous binder such as styrene-butadiene rubber (SBR) for compatibility with the carbon-based active material, and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0129] In some embodiments, a separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). The separator (140) may include a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0130] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of the electrode cells may be stacked to form an electrode assembly (150) in the form of, for example, a jelly roll. For example, the electrode assembly (150) may be formed by winding, stacking, folding, or the like of the separator (140).

[0131] The above electrode assembly may be housed together with an electrolyte within a case (160) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0132] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF -, (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0133] Examples of the organic solvent that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0134] As illustrated in FIG. 1, electrode tabs (positive electrode tabs and negative electrode tabs) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form electrode leads (positive electrode leads (107) and negative electrode leads (127)) that extend or are exposed to the outside of the case (160).

[0135] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0136]

[0137] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0138]

[0139] Example 1

[0140] Preparation of positive electrode active material

[0141] NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water to a composition of 90:5:3:2. The distilled water was bubbled with N2 for 24 hours to remove internal dissolved oxygen before use.

[0142] After this, the above mixed solution was put into a reactor at 60°C, and NH3H2O ​​was added so that the pH became 10.5, and stirred at a constant speed to prepare a transition metal solution. NH3H2O ​​was added in an amount more than 4 times the molar ratio of the transition metal being added. NaOH was added into the reactor at a constant speed so that the molar ratio of the transition metal and NaOH in the prepared transition metal solution became 1:2. After that, a coprecipitation reaction was performed for 38 hours to obtain an average particle diameter (D 50 ) was prepared as a preliminary active material precursor having an average particle diameter of 4.5 μm. The preliminary active material precursor was heat-treated in an oven at 120°C for 10 hours to obtain a first precursor having an average particle diameter of 4.5 μm. The "average particle diameter (D 50)" was measured as the particle size at a volume fraction of 50% among the volume particle size distribution obtained by accumulating particles in order of smallest particle size.

[0143] After this, a second precursor having an average particle size of 14.5 μm was manufactured using the same method as above, except that the total precipitation reaction time was changed from 38 hours to 78 hours in the precursor manufacturing method.

[0144] Lithium hydroxide, the first precursor, and the second precursor were added to a dry high-speed mixer in a ratio of 1.05:0.6:0.4, and then uniformly mixed for about 5 minutes to prepare a mixture.

[0145] The above mixture was placed in a sintering furnace and heated to 750°C at a heating rate of 2°C / min, and maintained at 750°C for 10 hours. During the heating and maintenance, oxygen was continuously passed at a flow rate of 10 mL / min. After the sintering was completed, natural cooling was performed to room temperature, and the cathode active material LiNi was obtained through pulverization and classification. 0.9 Co 0.05 Mn 0.03 Al 0.02 O2 was manufactured.

[0146] Manufacturing of lithium secondary batteries

[0147] A secondary battery was manufactured using the prepared positive electrode active material. Specifically, a positive electrode slurry was prepared by mixing the positive electrode active material, a conductive agent (Denka Black), and a binder (PVDF) in a mass ratio of 93:5:2. The positive electrode slurry was coated on an aluminum current collector, followed by drying and pressing to produce a positive electrode. After pressing, the target electrode density of the positive electrode was adjusted to 3.3 g / cc.

[0148] Lithium metal was used as the negative active material.

[0149] The positive and negative electrodes manufactured as described above were notched into circular shapes having diameters of Φ14 and Φ16, respectively, and laminated, and a separator (polyethylene, thickness 13 ㎛) notched into Φ19 was interposed between the positive and negative electrodes to form an electrode cell. The electrode cell was placed in a coin cell outer case having a diameter of 20 mm and a height of 1.6 mm, and an electrolyte was injected to assemble the cell, and the electrode was aged for more than 12 hours so that the electrolyte could be impregnated into the inside of the electrode.

[0150] The electrolyte used was 1M LiPF6 dissolved in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0151] Example 2

[0152] The positive electrode active material (LiNi) was mixed in the same manner as in Example 1, except that NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water to have a composition of 90:5:4:1. 0.9 Co 0.05 Mn 0.04 Al 0.01 O2) and secondary batteries were manufactured.

[0153] Example 3

[0154] The first precursor and the second precursor were prepared in the same manner as in Example 2, except that Al2(SO4)3 was not added during the co-precipitation of the first precursor and the second precursor.

[0155] Lithium hydroxide, second precursor (D 50 : 14.5㎛) and Al(OH)2 were mixed in a dry high-speed mixer at a ratio of 1.05:0.6:0.01 for about 2 minutes. After that, the first precursor (D 50 : 4.5㎛) was added to a dry high-speed mixer at a ratio of 0.4 and mixed uniformly for about 5 minutes.

[0156] The above mixture was placed in a sintering furnace and heated to 750°C at a heating rate of 2°C / min, and maintained at 750°C for 10 hours. During the heating and maintenance, oxygen was continuously passed at a flow rate of 10 mL / min. After the sintering was completed, the mixture was naturally cooled to room temperature, and the cathode active material (LiNi) was crushed and classified. 0.9 Co 0.05 Mn 0.04 Al 0.01 O2) and secondary batteries were manufactured.

[0157] Example 4

[0158] The positive electrode active material (LiNi) was prepared in the same manner as in Example 1, except that the co-precipitation time was changed during the preparation of the first precursor and the second precursor, so that the average particle diameter of the first precursor was adjusted to 16.2 μm and the average particle diameter of the second precursor was adjusted to 25.1 μm. 0.9 Co 0.05 Mn 0.03 Al 0.02 O2) and secondary batteries were manufactured.

[0159] Comparative Example 1

[0160] The first precursor and the second precursor were prepared in the same manner as in Example 1, except that Al2(SO4)3 was not added during the co-precipitation of the first precursor and the second precursor.

[0161] Lithium hydroxide, the first precursor, the second precursor, and Al(OH)2 were placed in a dry high-speed mixer at a ratio of 1.05:0.6:0.4:0.1, and then uniformly mixed for about 5 minutes to prepare a mixture.

[0162] The above mixture was placed in a sintering furnace and heated to 750°C at a heating rate of 2°C / min, and maintained at 750°C for 10 hours. During the heating and maintenance, oxygen was continuously passed at a flow rate of 10 mL / min. After the sintering was completed, the mixture was naturally cooled to room temperature, and the cathode active material (LiNi) was crushed and classified. 0.9 Co 0.05 Mn 0.04 Al 0.01 O2) and secondary batteries were manufactured.

[0163] Comparative Example 2

[0164] The positive electrode active material (LiNi) was mixed in the same manner as in Comparative Example 1, except that NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water to have a composition of 90:3:3:4. 0.9 Co 0.03 Mn 0.03 Al 0.04 O2) and secondary batteries were manufactured.

[0165] Comparative Example 3

[0166] The positive electrode active material (LiNi) was mixed in the same manner as in Comparative Example 1, except that NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water to have a composition of 90:5:4:1. 0.9 Co 0.05 Mn 0.04 Al 0.01 O2) and secondary batteries were manufactured.

[0167]

[0168] Experimental example

[0169] (1) Measurement of Al / Co weight ratio in primary particles

[0170] Among the positive electrode active materials prepared according to the above-described examples and comparative examples, particles having a particle size of n μm were cut so that the cross-section of the primary particles was exposed. Thereafter, the primary particles were processed into a needle structure having a tip radius of approximately 40 nm to prepare a sample. The sample was loaded into the chamber of an atomic probe tomography analyzer (LEAP4000X HR, CAMECA) to measure the internal composition of the primary particles.

[0171] Specifically, measurements were made under the conditions of a mass resolving power of 1,100, a lateral resolution of 0.4 nm, and a depth resolution of 0.2 nm, and the analytical sensitivity was less than 10 ppm.

[0172] Afterwards, the concentrations of aluminum and cobalt inside the primary particles were measured using the same method for particles having a particle size of about n+10㎛ among the positive electrode active materials.

[0173] WR(A / B) was calculated by taking the Al / Co weight ratio measured in particles having a particle size of n ㎛ as A and the Al / Co weight ratio measured in particles having a particle size of n+10 ㎛ as B.

[0174] In Comparative Examples 1-1 and 1-2, measurements were made with different target particle sizes (n ㎛) of the positive electrode active material prepared according to Comparative Example 1. Referring to Comparative Examples 1-1 and 1-2, the positive electrode active material of Comparative Example 1 had a WR outside the range of the examples at any target particle size (n ㎛).

[0175] n ㎛, n+10㎛, measured Al / Co weight ratio and WR are as shown in Table 1 below.

[0176] n ㎛ particle n+10 ㎛ particle WR(A / B) particle size(㎛) Al(wt%) Co(wt%) A(Al / Co) particle size(㎛) Al(wt%) Co(wt%) B(Al / Co) Example 14.30.432.270.18914.50.412.340.1751.08 Example 24.20.072.300.03014.80.072.260.0310.98 Example 34.30.252.830.088314.80.242.450.09790.90 Example 416.10.182.540.070826.20.162.4 50.06531.09Comparative Example 14.50.652.440.26614.20.072.680.02610.2Comparative Example 1-11.71.802.010.89611.60.142.570.05416.44Comparative Example 1-211.00.132.540.05121.00.042.700.01483.45Comparative Example 24.50.951.830.51914.50.981.620.6050.86Comparative Example 34.50.422.100.2014.20.312.090.1481.35

[0177] Figures 3 to 5 are APT analysis photographs of lithium metal oxide particles prepared sequentially according to Example 1, Example 2, and Comparative Example 1.

[0178] In FIGS. 3 to 5, “N” is an APT analysis image for a particle having a particle size of n ㎛, and “N+10” is an APT analysis image for a particle having a particle size of n+10 ㎛.

[0179] Referring to FIGS. 3 and 4, in the positive electrode active materials prepared in Examples 1 and 2, the degree of distribution of aluminum and cobalt within the primary particles of particles having a particle size of n ㎛ was similar to the degree of distribution of aluminum and cobalt within the primary particles of particles having a particle size of n+10 ㎛.

[0180] However, referring to Fig. 5, it can be confirmed that in the positive electrode active material prepared in Comparative Example 1, the aluminum concentration in the primary particles of particles having a particle size of n ㎛ is greater than the aluminum concentration in the primary particles of particles having a particle size of n+10 ㎛. In the case of Comparative Example 1, the aluminum doping was concentrated in particles having relatively small particle sizes.

[0181]

[0182] (2) Initial discharge capacity evaluation

[0183] Lithium secondary batteries manufactured according to the examples and comparative examples were placed in a 25°C chamber, charged (CC / CV 0.1C 4.3V 0.05C CUT-OFF) and discharged (CC 0.1C 3.0V CUT-OFF), and then the battery capacity (initial discharge capacity) was measured.

[0184]

[0185] (3) Capacity maintenance rate evaluation

[0186] Lithium secondary batteries manufactured according to Examples and Comparative Examples were placed in a 25°C chamber, and then charged (CC / CV 0.1C 4.3V 0.05C CUT-OFF) and discharged (CC 0.1C 3.0V CUT-OFF) once, and then charged (CC / CV 0.1C 4.3V 0.05C CUT-OFF) and discharged (CC 4.0C 3.0V CUT-OFF) once again. The capacity retention rate was evaluated by converting the value obtained by dividing the 4.0C discharge capacity by the 0.1C discharge capacity into a percentage (%).

[0187]

[0188] (4) Evaluation of high temperature life characteristics

[0189] Lithium secondary batteries manufactured according to the examples and comparative examples were placed in a 45°C chamber, and then charging (CC / CV 1.0C 4.3V 0.05C CUT-OFF) and discharging (CC 1.0C 3.0V CUT-OFF) were repeated 300 times. The high-temperature life characteristics were evaluated as a percentage of the discharge capacity at 300 times divided by the discharge capacity at 1 time.

[0190]

[0191] The evaluation results are shown in Table 2 below.

[0192] Classification Initial discharge capacity (mAh / g) Capacity retention rate (%) High temperature life characteristics (%) Example 1 21 280.47 5.3 Example 2 21 683.76 9.1 Example 3 21 482.56 9.3 Example 4 21 180.67 8.2 Comparative example 1 21 885.95 6.9 Comparative example 2 19 250.28 4.7 Comparative example 3 21 885.95 6.9

[0193] Referring to Tables 1 and 2, in the examples, the ratio of Al / Co of particles having a particle size of n+10 ㎛ to Al / Co of particles having a particle size of n ㎛ was 0.9 to 1.1, and the initial discharge capacity, capacity retention rate, and high-temperature life characteristics were improved.

[0194] In comparative examples, the ratio of Al / Co of particles having a particle size of n+10 ㎛ to Al / Co of particles having a particle size of n ㎛ was less than 0.9 or more than 1.1, and the initial discharge capacity, capacity retention rate, and / or high-temperature life characteristics of the secondary battery were deteriorated.

[0195] In the case of Comparative Example 2, the Al / Co weight ratio inside the primary particle was relatively high, so the initial discharge capacity and capacity retention rate of the secondary battery rapidly decreased.

Claims

1. Contains lithium metal oxide particles having a secondary particle form in which a plurality of primary particles are aggregated, and contains cobalt and aluminum. A positive electrode active material for a lithium secondary battery, having a WR of 0.9 to 1.1, as expressed by the following formula 1: [Formula 1] WR=A / B (In the above formula 1, A is the ratio of the content of aluminum to the content of cobalt contained in the primary particles of the lithium metal oxide particles having a particle size of n ㎛, B is the ratio of the content of aluminum to the content of cobalt contained in the primary particles of the lithium metal oxide particles having a particle size of n+10㎛, The above n ㎛ is 1 ㎛ to 22 ㎛).

2. A positive electrode active material for a lithium secondary battery, wherein the ratio of the content of aluminum to the content of cobalt in claim 1 is a value measured using atomic probe tomography (APT) on a cross-section of the primary particle.

3. A positive electrode active material for a lithium secondary battery, wherein, in claim 1 or 2, the ratio of the aluminum content in the primary particles of the particles having a particle diameter of n+10 ㎛ to the aluminum content in the primary particles of the particles having a particle diameter of n ㎛ among the lithium metal oxide particles is 0.85 to 1.

1.

4. A positive electrode active material for a lithium secondary battery, according to any one of claims 1 to 3, wherein the particle size of the lithium metal oxide particles is 0.8 μm to 32 μm.

5. A positive electrode active material for a lithium secondary battery, wherein each of the primary particles has a short axis of 100 nm to 500 nm, according to any one of claims 1 to 4.

6. A positive electrode active material for a lithium secondary battery, wherein the content of aluminum contained in each primary particle of the lithium metal oxide particles is smaller than the content of cobalt contained in each primary particle of the lithium metal oxide particles, according to any one of claims 1 to 5.

7. A positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6, wherein the lithium metal oxide particles further comprise nickel or manganese.

8. In any one of claims 1 to 7, each of the lithium metal oxide particles is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a Co x Al y M 1-x-y O 2+b (In the above chemical formula 1, 0.9≤a≤1.2, 0 <x≤0.3, 0<y≤0.2, -0.2≤b≤0.2이고, M은 Ni, Mn, Ti, Zr, Ba, Tb, Nb, Y, W, B 및 Sr 중 적어도 하나임).

9. A positive electrode comprising a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 8; and A lithium secondary battery comprising a cathode opposite to the positive electrode.

10. A step of preparing a first precursor containing cobalt and aluminum; Contains cobalt and aluminum, and the average particle diameter (D) of the first precursor 50 ) with an average particle diameter (D) of 9 to 11 μm larger than 50 ) for preparing a second precursor; A step of preparing a precursor blend by mixing a lithium precursor, the first precursor, and the second precursor; and A method for producing a positive electrode active material, comprising a step of calcining the above precursor blend.

11. A method for manufacturing a positive electrode active material according to claim 10, wherein the ratio (A1 / B1) of the aluminum content to the cobalt content included in the first precursor and the aluminum content to the cobalt content included in the second precursor is 0.9 to 1.

1.

12. A step of preparing a first precursor containing cobalt; Contains cobalt, and the average particle diameter (D) of the first precursor 50 ) with an average particle diameter (D) of 9 to 11 μm larger than 50 ) for preparing a second precursor; A step of preparing a first blend by mixing the second precursor, lithium precursor, and aluminum precursor; A step of preparing a second blend by mixing the first blend and the first precursor; and A method for producing a positive electrode active material, comprising a step of sintering the second blend.

13. A method for producing a positive electrode active material according to claim 12, wherein the first precursor and the second precursor do not contain aluminum.

14. A method for producing a positive electrode active material according to claim 12 or 13, wherein the ratio of the content of cobalt in the second precursor to the content of cobalt in the first precursor is 0.85 to 1.1 by weight.

15. A method for producing a positive electrode active material according to any one of claims 12 to 14, wherein the content of the second precursor in the second blend is greater than or equal to the content of the first precursor.

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