Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

A positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes active material particles including lithium-transition metal oxide particles having a single particle form. In the volume-weighted particle size distribution of the active material particles, the particle size (D50) at a volume fraction of 50% when the particles having the smallest particle size begin to accumulate is 2 [mu] m to 5 [mu] m. When D50 of the active material particles is expressed as a, the volume fraction of particles having a particle diameter of 2a [mu] m or more among the active material particles is 4% to 15%.

Description

Technical Field

[0001] This invention relates to a positive electrode active material for lithium secondary batteries and a lithium secondary battery including the same. More specifically, it relates to a positive electrode active material for lithium secondary batteries comprising a lithium-transition metal oxide and a lithium secondary battery including the same. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, rechargeable batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptops. In addition, in recent years, battery packs including rechargeable batteries have been developed for use as power sources in environmentally friendly vehicles such as hybrid electric vehicles.

[0003] Secondary batteries can be categorized into, for example, lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, so they are being actively developed and applied.

[0004] For example, a lithium secondary battery may include: an electrode assembly comprising a positive electrode, a negative electrode, and a separator; and an electrolyte impregnating the electrode assembly. The lithium secondary battery may also include an outer packaging material housing the electrode assembly and the electrolyte, such as a pouch-type outer packaging material.

[0005] Lithium metal oxide is used as the positive electrode active material in the lithium secondary battery, and preferably has high capacity, high power, and long lifespan characteristics. However, when the lithium metal oxide is designed as a high-power component, its thermal and mechanical stability decreases, which may reduce the lifespan characteristics and operational stability of the lithium secondary battery. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] One technical problem of the present invention is to provide a positive electrode active material for lithium secondary batteries with improved working stability and lifespan characteristics.

[0008] One technical problem of the present invention is to provide a lithium secondary battery comprising a positive electrode active material having improved operating stability and lifespan characteristics.

[0009] (II) Technical Solution

[0010] The positive electrode active material for a lithium secondary battery according to an embodiment of the present invention comprises active material particles, said active material particles comprising lithium-transition metal oxide particles having a single particle form. In the volume-weighted particle size distribution of said active material particles, the particle size (D50) at which the volume fraction reaches 50% starting from the smallest particle is 2 μm to 10 μm. When the D50 of the active material particles is denoted as a, the volume fraction of particles with a diameter of 2a μm or larger is 4% to 15%.

[0011] In some embodiments, the D50 of the active substance particles can be from 2.5 μm to 5 μm.

[0012] In some embodiments, the volume fraction of particles with a diameter of 2 μm or larger in the active material particles may be 5% to 10%.

[0013] In some embodiments, the volume fraction of particles with a diameter of less than 1 μm in the active material particles may be less than 5%.

[0014] In some embodiments, the volume fraction of particles with a diameter of less than 1 μm in the active material particles can be from 0.1% to 4.5%.

[0015] In some embodiments, the span of the active substance particles, as defined by Formula 1, can be from 1.0 to 1.5.

[0016] [Formula 1]

[0017] Span = (D90 - D10) / D50

[0018] In Formula 1, D50 is the particle size at 50% of the volume fraction accumulated from the smallest particle in the volume-weighted particle size distribution of the active material particles. D90 is the particle size at 90% of the volume fraction accumulated from the smallest particle in the volume-weighted particle size distribution of the active material particles. D10 is the particle size at 10% of the volume fraction accumulated from the smallest particle in the volume-weighted particle size distribution of the active material particles.

[0019] In some embodiments, the span of the active substance particles can be 1.1 to 1.4.

[0020] In some embodiments, the D10 of the active material particles can be from 1.3 μm to 4 μm.

[0021] In some embodiments, the D90 of the active substance particles can be from 4 μm to 15 μm.

[0022] In some embodiments, the lithium-transition metal oxide particles may contain nickel, and the molar fraction of nickel in the lithium-transition metal oxide particles, in addition to lithium and oxygen, may be 0.6 or more.

[0023] In some embodiments, the lithium-transition metal oxide particles may further comprise at least one element selected from Na, Mg, Ca, Sr, Ba, La, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, and Sn.

[0024] In some embodiments, the lithium-transition metal oxide particles may contain lanthanum at a content of 500 ppm to 4000 ppm relative to the total weight of the lithium-transition metal oxide particles.

[0025] The lithium secondary battery according to the present invention includes: a positive electrode, the positive electrode including the above-described positive electrode active material for lithium secondary batteries; and a negative electrode disposed opposite to the positive electrode.

[0026] (III) Beneficial Effects

[0027] According to embodiments of the present invention, the active material particles may comprise lithium-transition metal oxide particles in the form of single particles. Therefore, the generation of cracks in the active material particles or side reactions with the electrolyte are suppressed, thereby improving surface stability. Thus, a lithium secondary battery with improved lifetime and cycle characteristics can be provided.

[0028] According to an exemplary embodiment, the volume fraction of coarse powder in the active material particles can be adjusted. Therefore, a lithium secondary battery with improved lifetime and capacity characteristics can be provided.

[0029] The lithium secondary battery according to embodiments of the present invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar power generation and wind power generation. Furthermore, the lithium secondary battery according to embodiments of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0030] Figure 1 and Figure 2 This is an SEM image of a positive electrode active material for a lithium secondary battery according to an exemplary embodiment.

[0031] Figure 3 and Figure 4 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment.

[0032] Figures 5 to 7 The images are SEM images of the positive electrode active materials for lithium secondary batteries according to Example 1, Example 4 and Comparative Example 1, respectively. Detailed Implementation

[0033] The present invention provides a positive electrode active material for lithium secondary batteries (hereinafter referred to as positive electrode active material) comprising lithium-transition metal oxide particles and a lithium secondary battery comprising the same.

[0034] The embodiments of the present invention will now be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0035] The positive electrode active material according to an exemplary embodiment comprises active material particles, said active material particles comprising lithium-transition metal oxide particles in the form of single particles.

[0036] The term "single-particle form" as used in this invention can be used to, for example, exclude secondary particles formed by the aggregation of multiple primary particles. For example, the lithium-transition metal oxide particles can substantially consist of particles in single-particle form, and can exclude secondary particle structures formed by the assembly or aggregation of primary particles (e.g., more than 10, 20, 30, 40, 50, etc.).

[0037] The term "single-particle form" as used in this invention does not exclude, for example, two to ten individual particles that are bonded or adhered to each other to have a monomeric form.

[0038] In some implementations, the lithium-transition metal oxide particles may include a structure in which multiple primary particles are merged together to substantially transform into a single particle.

[0039] For example, the lithium-transition metal oxide particles may be in the form of granular or spherical single particles.

[0040] For example, the lithium-transition metal oxide particles may contain nickel (Ni) and may further contain at least one of cobalt (Co) or manganese (Mn).

[0041] For example, the lithium-transition metal oxide particles can be represented by the following chemical formula 1.

[0042] [Chemical Formula 1]

[0043] Li x Ni yM z O 2+w

[0044] In the aforementioned chemical formula 1, the elements can be 0.9≤x≤1.5, 0.6≤y≤0.99, 0.01≤z≤0.4, and -0.1≤w≤0.1. M can be one or more elements selected from Na, Mg, Ca, Sr, Ba, La, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, and Sn.

[0045] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material or lithium-transition metal oxide particles, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood to include the introduction and substitution of additional elements.

[0046] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure to form a bond, and this should be understood to also apply to crystal structures represented by Formula 1.

[0047] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Sr, Ba, La, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, and Sn. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0048] The positive electrode active material may further include dopant elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as dopant elements. For example, two or more of the auxiliary elements described above can be used as dopant elements, either alone or in combination.

[0049] In some embodiments, among the elements other than lithium and oxygen, the molar fraction of nickel in the lithium-transition metal oxide particles may be 0.6 or more. For example, in the chemical formula 1, the molar ratio or concentration y of Ni may be 0.6 or more, 0.7 or more, or 0.8 or more. For example, y may be 0.6 to 0.99, 0.7 to 0.98, or 0.8 to 0.95.

[0050] Ni can be provided as a transition metal relevant to the power and capacity of lithium secondary batteries. Therefore, high-power cathodes and high-power lithium secondary batteries comprising lithium-transition metal oxide particles with a high-Ni composition, as described above, can be provided.

[0051] For example, when using a high-nickel content (high Ni) composition with a nickel mole fraction (y) of 0.8 or higher, the calcination of lithium-transition metal oxide particles can be carried out at a relatively low temperature. Therefore, lithium-transition metal oxide particles in single-particle form can be formed at a relatively low temperature.

[0052] In one embodiment, the lithium-transition metal oxide particles may comprise nickel, cobalt, and manganese. For example, the lithium-transition metal oxide particles may comprise nickel-cobalt-manganese (NCM)-based lithium oxides. In this case, NCM-based lithium oxides with increased nickel content can be used.

[0053] In one embodiment, the lithium-transition metal oxide particles may further comprise at least one element selected from Mg, Ca, Sr, Ba, La, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, and Sn. For example, the lithium-transition metal oxide particles may comprise nickel, cobalt, manganese, and lanthanum. For example, the lanthanum contained in the lithium-transition metal oxide particles may be derived from lanthanum-containing compounds provided as a flux, as described later.

[0054] In one embodiment, the lanthanum content relative to the total weight of the lithium-transition metal oxide particles can be 500 ppm to 4000 ppm, 1000 ppm to 3000 ppm, or 1500 ppm to 2500 ppm. Within these ranges, single particles with a more uniform morphology can be formed at relatively low temperatures.

[0055] For example, when the lanthanum content relative to the total weight of the lithium-transition metal oxide particles is excessively increased, large, non-uniform particles may form. Furthermore, lanthanum doping into the crystal structure of the lithium-transition metal oxide may reduce power and capacity characteristics. Conversely, when the lanthanum content relative to the total weight of the lithium-transition metal oxide particles is excessively reduced, sufficient formation of single particles may not be achieved. Within the aforementioned ranges, excessive formation of coarse powder can be prevented while forming the single particles. Therefore, the initial efficiency of the secondary battery can be increased, and lifetime characteristics can be further improved while achieving high capacity characteristics.

[0056] For example, nickel can be provided as a metal related to the capacity of lithium-ion batteries. Higher nickel content generally improves the capacity and power characteristics of lithium-ion batteries, but excessive nickel content can reduce lifespan and decrease mechanical and electrical stability. For instance, increased nickel content may increase the volume change of oxide particles during repeated charge-discharge cycles. Therefore, increased cracking in the oxide particles or increased side reactions with the electrolyte can reduce structural stability. Consequently, adequate capacity retention may not be guaranteed during repeated charge-discharge cycles at high temperatures (e.g., above 60°C).

[0057] For example, the conductivity or resistance of lithium secondary batteries can be improved by cobalt (Co), and the mechanical and electrical stability of lithium secondary batteries can be improved by manganese (Mn).

[0058] In an exemplary embodiment, when the lithium-transition metal oxide particles are in the form of single particles, the formation of particle cracks can be reduced during the crushing process. Therefore, suppressing the increase in the specific surface area of ​​the lithium-transition metal oxide particles in the form of single particles reduces side reactions with the electrolyte. Thus, a secondary battery with improved lifetime characteristics and capacity retention during repeated charge-discharge cycles can be provided.

[0059] According to an exemplary embodiment, in the volume-weighted particle size distribution of the active material particles containing the lithium-transition metal oxide particles, the particle size (D50) at the point where the volume fraction is 50% when accumulated from the smallest particle is 2 μm to 10 μm.

[0060] For example, in the volume-weighted particle size distribution, the particle size or D50 at the 50% volume fraction accumulated from the smallest particle can be measured using a particle size analyzer (PSA). "Particle size" can refer to the longest diameter of the particle.

[0061] For example, when the D50 of the lithium-transition metal oxide particles exceeds 10 μm, the diffusion path of lithium ions within the particles may increase. Therefore, the resistance of the positive electrode active material will increase, potentially reducing the capacity characteristics and efficiency of the secondary battery.

[0062] For example, when the D50 of the lithium-transition metal oxide particles is less than 2 μm, the excessive grinding conditions significantly increase the proportion of micro powder, which may reduce the lifetime characteristics of the positive electrode active material.

[0063] According to some implementation schemes, by satisfying the above-mentioned range, the D50 of the active material particles can improve lifetime characteristics while ensuring high capacity and high power characteristics.

[0064] For example, the D50 of the active material particles containing the lithium-transition metal oxide particles can be 2.5 μm to 5 μm, 3 μm to 4.5 μm, or 3.3 μm to 4 μm. Within the above ranges, the uniformity of the active material particles can be further increased, and the capacity characteristics and charge / discharge efficiency of the positive electrode active material can be further improved.

[0065] For example, the D50 of the active substance particles can be represented by a.

[0066] According to an exemplary embodiment, the volume fraction of particles with a diameter of 2 μm or larger in the active material particles in the volume-weighted particle size distribution can be 4% to 15%.

[0067] For example, in this invention, particles with a diameter of 2 μm or larger can be defined as "coarse powder".

[0068] According to one embodiment, the coarse powder may refer to the form of an aggregate of two or more lithium-transition metal oxide primary particles having the single particle form described above.

[0069] Figure 1 These are SEM images of the positive electrode active material according to an exemplary embodiment. For example, Figure 1 It can be an SEM image of the active substance particles containing the coarse powder.

[0070] Reference Figure 1 This may include particles with a diameter of 2 μm or larger, i.e., coarse powder, in the active material particles comprising the single-particle lithium-transition metal oxide particles. For example, the single-particle lithium-transition metal oxide particles may remain as aggregates of multiple single particles during calcination and crushing. Therefore, the volume fraction of coarse powder in the active material particles increases, which may reduce the uniformity of the positive electrode active material during washing or coating.

[0071] For example, when the volume fraction (%) of the coarse powder in the active material particles is less than 4%, excessive crushing during the calcination and crushing process may increase the generation of cracks in the active material particles.

[0072] For example, when the volume fraction (%) of the coarse powder in the active material particles exceeds 15%, it may provide an uneven particle size distribution of the active material particles. Therefore, it may excessively reduce the uniformity during the washing or coating process of the positive electrode active material.

[0073] According to some embodiments, the volume fraction (%) of the coarse powder can be 4.5% or more, 5% or more, or 6% or more. For example, the volume fraction (%) of the coarse powder can be less than 13%, less than 10%, or less than 9%. For example, the volume fraction (%) of the coarse powder in the active material particles can be 5% to 10% or 6% to 9%. Within the above ranges, the generation of cracks within the positive electrode active material particles can be suppressed. Furthermore, the crushing can be performed more uniformly, and the uniformity of the lithium-transition metal oxide particles in single-particle form can be improved. Therefore, the uniformity of the positive electrode active material in the washing or coating process can be improved, and the life characteristics of the lithium secondary battery can be further improved.

[0074] In one embodiment, the active substance particles may contain particles with a diameter of less than 1 μm.

[0075] For example, in this invention, particles with a diameter of less than 1 μm can be defined as "micro powder".

[0076] Figure 2 These are SEM images of the positive electrode active material according to an exemplary embodiment. For example, Figure 2 It can be an SEM image of the active substance particles containing the micropowder.

[0077] Reference Figure 2 The active material particles may contain particles with a diameter of less than 1 μm, i.e., micro powder. For example, during the calcination and crushing process, excessive increase in crushing pressure may produce micro powder (e.g., Figure 2 (a) or may produce particle cracks (e.g., Figure 2 (b) Therefore, it may reduce the lifespan characteristics of the secondary battery.

[0078] According to some embodiments, the active material particles may not contain particles with a diameter of less than 1 μm. For example, in the crushing process of the lithium-transition metal oxide particles, over-crushing can be suppressed by adjusting the calcination temperature or crushing pressure to a predetermined range. Therefore, the active material particles may not contain microparticles. This improves the capacity characteristics of the positive electrode active material and increases efficiency while enhancing lifetime characteristics during repeated charge-discharge cycles.

[0079] According to some implementation schemes, the volume fraction of particles with a diameter of less than 1 μm in the active substance particles in the volume-weighted particle size distribution can be less than 5%.

[0080] For example, when the volume fraction of particles with a diameter of less than 1 μm (i.e., micropowder) in the active material particles increases excessively, the positive electrode active material may be over-pulverized. This may reduce the structural stability of the positive electrode active material particles and may promote side reactions with the electrolyte. Consequently, the positive electrode active material may degrade during repeated charge-discharge cycles, potentially reducing the lifespan characteristics of the secondary battery.

[0081] According to some embodiments, the volume fraction of particles with a diameter of less than 1 μm in the active material particles can be 0.1% to 4.5%, 0.2% to 3%, 0.25% to 2%, or 0.3% to 1%. Within these ranges, excessive grinding of the positive electrode active material particles can be reduced, thereby reducing cracks in the active material particles. Since the degradation of the active material particles is suppressed, the capacity retention rate of the lithium secondary battery during repeated charge and discharge can be further improved.

[0082] According to embodiments of the present invention, by controlling the D50 of the active material particles and the volume fraction of the coarse powder within a predetermined range, a positive electrode active material with an improved particle size distribution can be provided. Therefore, the lithium secondary battery can have improved lifetime and capacity characteristics.

[0083] According to some implementation schemes, the span of the active substance particles, as defined by Formula 1, can be from 1.0 to 1.5.

[0084] [Formula 1]

[0085] Span = (D90 - D10) / D50

[0086] In Equation 1, D50 is the particle size at 50% of the volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution. D90 is the particle size at 90% of the volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution of the active material particles. D10 is the particle size at 10% of the volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution of the active material particles.

[0087] For example, span can represent the particle size deviation of the active material particles. As the span decreases, a more uniform particle size distribution of the active material particles can be provided.

[0088] For example, when the span of the active material particles is reduced excessively, the active material particles may be excessively fragmented. Therefore, during repeated charge and discharge, the excessive generation of cracks in the positive electrode active material particles may excessively reduce structural stability.

[0089] For example, when the span of the active material particles increases excessively, the uniformity of the particle size distribution decreases, which may increase the proportion of micro or coarse powder in the positive electrode active material. Therefore, the uniformity may decrease during the washing or coating process of the positive electrode active material.

[0090] In one embodiment, the span of the active material particles can be 1.1 to 1.4 or 1.15 to 1.19. Within these ranges, the uniformity of the particle size distribution of the active material particles can be improved. Therefore, the capacity characteristics and efficiency of the secondary battery can be improved, and the capacity retention rate during repeated charge and discharge can be further improved.

[0091] In some embodiments, the D10 of the active substance particles can be 1.3 μm to 4 μm, 1.4 μm to 3 μm, 1.5 μm to 2.5 μm, or 1.6 μm to 2 μm.

[0092] In one embodiment, the D10 of the active substance particles can be greater than a / 2μm.

[0093] In some embodiments, the D90 of the active substance particles can be 4 μm to 15 μm, 5 μm to 10 μm, or 5.6 μm to 6 μm.

[0094] According to some implementation schemes, the positive electrode active material can have improved stability and energy density by including active material particles with D10 and D90 adjusted to the above range.

[0095] For example, the particle size distribution of the active material particles can be changed by the particle size and element content ratio of the precursor (e.g., NCM precursor) used in the preparation of the active material particles, whether a flux is used, the heat treatment temperature, heat treatment time and heating rate in the heat treatment or calcination process, the pressure and time in the crushing process, and the screen size and pressure in the screening or grading process.

[0096] In some embodiments, the active material particles may include a coating formed on the surface of the lithium-transition metal oxide particles, and the coating contains a lanthanum (La)-containing compound. Therefore, the ionic conductivity of the surface of the lithium-transition metal oxide particles can be increased.

[0097] In one embodiment, the lanthanum-containing compound may include La(OH)3, La2O3, LaPO4·xH2O, or La2(SO4)3.

[0098] In one embodiment, the coating comprising the lanthanum-containing compound may be doped or coated with a metal compound or an inorganic compound. For example, the metal compound or inorganic compound may contain an element of Formula 1 (e.g., M in Formula 1). Therefore, the layered structure of the lanthanum-containing compound is doped with a highly conductive metal, thereby improving the power characteristics of the active material particles. Thus, even if the positive electrode active material with a high nickel content is manufactured as a single particle, the power characteristics of the secondary battery can be maintained.

[0099] According to some implementation schemes, the positive electrode active material can be prepared by mixing lithium precursors and transition metal precursors with a flux.

[0100] For example, lithium precursors and transition metal precursors can be prepared.

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

[0102] For example, the transition metal precursor can be prepared by a co-precipitation reaction of a metal salt. The metal salt may include nickel salts, manganese salts, and cobalt salts.

[0103] Examples of nickel salts include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, and their hydrates. Examples of manganese salts include manganese sulfate, manganese acetate, and their hydrates. Examples of cobalt salts include cobalt sulfate, cobalt nitrate, cobalt carbonate, and their hydrates.

[0104] The metal salt can be mixed with a precipitant and / or chelating agent to prepare an aqueous solution, satisfying the content or concentration ratio of each metal as described with reference to Chemical Formula 1. The aqueous solution can be co-precipitated in a reactor to prepare a transition metal precursor.

[0105] The precipitant may include alkaline compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The chelating agent may include, for example, ammonia (e.g., NH4OH) and ammonium carbonate (e.g., NH3HCO3).

[0106] The temperature of the coprecipitation reaction can be adjusted, for example, from about 40°C to 60°C. The reaction time can be adjusted from about 24 hours to 72 hours.

[0107] According to some implementation schemes, the lithium precursor and the lithium transition metal precursor can be mixed with a flux and then calcined.

[0108] For example, when lithium precursors and transition metal precursors are mixed and calcined without the addition of a flux, the calcination temperature can be increased to single-particle form of the transition metal precursor, which is in the form of secondary particles. However, when the calcination temperature is excessively increased, the residual lithium present on the surface of the active material particles may increase. In this case, gas may be generated due to particle cracking caused by repeated charging and discharging. Therefore, the capacity retention of the secondary battery may be reduced.

[0109] When the flux is added and mixed, the flux and the lithium precursor react to form a liquid intermediate. In this case, the intermediate can react with the transition metal precursor, and rearrangement may occur to reduce surface tension.

[0110] The flux can induce solution reprecipitation after the aforementioned rearrangement. This rearrangement results in solution reprecipitation, which reduces the pores within the lithium-transition metal oxide particles.

[0111] For example, the reprecipitated lithium-transition metal oxide particles can be densified to have a single-particle form. In this case, particle cracking and gas generation caused by repeated charge-discharge cycles of the secondary battery can be reduced, thereby improving the battery's lifespan characteristics.

[0112] For example, the flux can be La(OH)3. In this case, a coating containing lanthanum compounds can be formed on the surface of the lithium-transition metal oxide particles during the calcination process.

[0113] In some embodiments, the flux (e.g., La(OH)3) can be pulverized prior to calcination. In this case, the particle size can be sufficiently reduced, thereby improving reactivity with the lithium precursor and transition metal precursor. Therefore, the lithium-transition metal oxide particles and coating can be readily formed in single-particle form.

[0114] For example, the flux powder can be pulverized to an average particle size of less than 1 μm. In this case, lithium-transition metal oxide particles with a uniform single-particle form can be formed. Therefore, the reduction in capacity and lifespan characteristics of the secondary battery caused by non-uniform single-particle form can be prevented.

[0115] In some embodiments, when La(OH)3 is used as the flux, the lanthanum content in the flux can be from 1000 ppm to 3000 ppm or from 1500 ppm to 2500 ppm relative to the total weight of the lithium-transition metal oxide particles. Within these ranges, the flux can form single particles while preventing the formation of non-uniform microparticles (e.g., the aforementioned micro powder) and large particles (e.g., the aforementioned coarse powder). Therefore, the lifespan and power characteristics of the secondary battery can be improved.

[0116] For example, excessive addition of lanthanum can lead to the formation of large, non-uniform particles. Furthermore, lanthanum doping into the crystal structure of lithium-transition metal oxides can potentially reduce power and capacity characteristics.

[0117] For example, if the amount of lanthanum added is reduced excessively, it may be impossible to achieve sufficient formation of individual particles. Within the aforementioned range, it is possible to prevent the excessive generation of coarse powder while forming the individual particles. Therefore, the initial efficiency of the secondary battery can be increased, and the lifetime characteristics can be further improved while achieving high capacity characteristics.

[0118] The mixture of lithium precursor, lithium transition metal precursor and flux is calcined to form lithium-transition metal oxide particles with a coating containing lanthanum compounds on the surface.

[0119] For example, the metal cations in compounds used as fluxes can have ionic radii larger than those of nickel, cobalt, and manganese. For instance, La(OH)3 contains La... 3+ The ionic radius of Li can be 103.2 pm. + The ionic radius of Ni can be 76 pm. 3+ The ionic radius can be 56 pm, Co 3+ The ionic radius of Mn can be 68.5 pm. 4+ The ionic radius can be 67 pm. In this case, due to the large ionic radius of La ions, they can remain on the surface in compound form, rather than being included in the layered structure. The flux remaining on the surface can promote the rearrangement, solution redeposition, and densification of the aforementioned lithium-transition metal oxide particles. Therefore, the formation of the single-particle form of lithium-transition metal oxide particles can be promoted at a lower calcination temperature.

[0120] For example, the flux remaining on the surface can form the lanthanum-containing coating on the surface of the lithium-transition metal oxide particles. The lanthanum-containing coating can have high lithium-ion conductivity. Therefore, the high capacity and high power characteristics of the secondary battery can be achieved while simultaneously improving its lifetime characteristics.

[0121] In some embodiments, a metal compound or inorganic compound may be further added during the above-described step of adding a flux for mixing. For example, a metal compound or inorganic compound may be added together with La(OH)3 to a mixture of lithium precursor and transition metal precursor.

[0122] Therefore, the coating can be doped or coated with a metal compound or an inorganic compound. For example, the metal compound or inorganic compound can contain an element of Formula 1 (e.g., M in Formula 1). Thus, the layered structure of the lanthanum-containing compound is doped with a highly conductive metal, thereby improving the power characteristics of the active material particles. Therefore, even if the positive electrode active material with a high nickel content is prepared as a single particle, the power characteristics of the secondary battery can be maintained.

[0123] In some embodiments, the calcination temperature can be from 700°C to 1200°C or from 800°C to 1050°C. Within these ranges, lithium-transition metal oxide particles in single-particle form with the aforementioned uniform particle size distribution can be formed.

[0124] In some implementations, the calcination temperature described above can satisfy Equations 2 and 3.

[0125] [Equation 2]

[0126] t1-50≤T1(℃)≤t1+50

[0127] In Equation 2, t1 can be the temperature according to Equation 3, and T1 can be the temperature at which the calcination is performed.

[0128] [Formula 3]

[0129] t1(℃) = (-520) × y + 1300

[0130] In Formula 3, y can be the y in the above chemical formula 1.

[0131] For example, when the molar fraction (y) of nickel in the lithium-transition metal oxide particles, excluding lithium and oxygen, is 0.6 to 0.99, the calcination temperature can be from about 735°C to 1038°C. For example, when the molar fraction (y) of nickel is 0.6, the calcination temperature can be from 938°C to 1038°C.

[0132] In one embodiment, when the mole fraction (y) of nickel is 0.8 to 0.99, the calcination temperature can be from about 735°C to 934°C.

[0133] According to some implementation schemes, a jet mill can be used to break down the calcined lithium-transition metal oxide particles. Therefore, the lithium-transition metal oxide particles aggregated during the calcination process can be in single-particle form.

[0134] According to some embodiments, the crushing pressure of the jet mill can be from 1 bar to 5 bar. For example, when the crushing pressure exceeds 5 bar, the fine powder in the lithium-transition metal oxide particles in single-particle form may increase, and particle cracking may occur. For example, when the crushing pressure is below 1 bar, particles that agglomerate during the calcination process may not be crushed and remain. Therefore, the uniformity and lifetime characteristics of the positive electrode active material may be reduced.

[0135] According to one embodiment, the crushing pressure can be greater than 1 bar or more than 1.3 bar, for example, less than 4.5 bar, less than 3.5 bar, less than 2.5 bar, or less than 2 bar. Within the above range, lithium-transition metal oxide particles with the volume fraction of the fine powder and coarse powder adjusted to the above range can be formed.

[0136] Figure 3 and Figure 4 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment.

[0137] The following is for reference Figure 3 and Figure 4 A lithium secondary battery is provided, comprising a positive electrode containing the above-mentioned positive electrode active material for lithium secondary batteries.

[0138] Reference Figure 3 and Figure 4 A lithium secondary battery may include a positive electrode 100 containing positive electrode active material, a negative electrode 130, and a separator 140.

[0139] The positive electrode 100 may include a positive electrode active material layer 110, which is formed by coating the positive electrode active material containing the above-mentioned lithium-transition metal oxide particles onto the positive electrode current collector 105.

[0140] For example, the lithium-transition metal oxide particles can be mixed and stirred with binders, conductive materials, and / or dispersing materials in a solvent to prepare a slurry. The slurry can be coated onto the positive electrode current collector 105 and then dried and calendered to manufacture the positive electrode.

[0141] The positive current collector 105 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, such as aluminum or aluminum alloys.

[0142] The adhesive may include, for example, organic-based adhesives such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate, or water-based adhesives such as styrene-butadiene rubber (SBR), and may be used with thickeners such as carboxymethyl cellulose (CMC).

[0143] For example, a PVDF-based binder can be used as the binder for forming the positive electrode. In this case, the amount of binder used to form the positive electrode active material layer 110 can be reduced and the amount of positive electrode active material can be relatively increased, thus improving the power and capacity of the secondary battery.

[0144] The conductive material may be included to facilitate electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials containing perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0145] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, which is formed by coating the negative electrode active material onto the negative electrode current collector 125.

[0146] The negative electrode active material can be any material known in the art that enables lithium ion insertion and extraction, without particular restriction. 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. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. Elements included in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc.

[0147] The negative current collector 125 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, such as copper or copper alloys.

[0148] In some embodiments, the negative electrode active material can be mixed and stirred in a solvent with a binder, conductive material, and / or dispersant to prepare a slurry. The slurry can then be coated onto the negative electrode current collector and subsequently dried and calendered to manufacture the negative electrode 130.

[0149] The adhesive and the conductive material may be made of substances substantially the same as or similar to those described above. In some embodiments, for compatibility with carbon-based active materials, the adhesive used to form the negative electrode may contain a water-based adhesive such as styrene-butadiene rubber (SBR) and may be used with a thickener such as carboxymethyl cellulose (CMC).

[0150] The separator 140 can be located between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer membrane prepared from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The separator 140 may also include a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0151] According to an exemplary embodiment, the battery cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and an electrode assembly 150 can be formed, for example, in the form of a jelly roll, by stacking multiple said battery cells. For example, the electrode assembly 150 can be formed by winding, lamination, folding, etc., of the separator 140.

[0152] The electrode assembly, together with the electrolyte, is housed in a casing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte can be used.

[0153] The non-aqueous electrolyte comprises a lithium salt as the electrolyte and an organic solvent. The lithium salt can be, for example, made from Li... + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by 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 - wait.

[0154] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0155] like Figure 3 As shown, the tabs (positive tab and negative tab) can protrude from the positive current collector 105 and negative current collector 125 belonging to each cell and extend to one side of the housing 160. The tabs can be fused to said side of the housing 160 to form electrode leads (positive lead 107 and negative lead 127) extending to or exposed to the outside of the housing 160.

[0156] The lithium secondary battery can be made in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0157] The following preferred embodiments are presented to help understand the present invention. However, these embodiments are only for illustrating the present invention and are not intended to limit the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept, which will be obvious to those skilled in the art. Such modifications and variations are naturally within the scope of the claims.

[0158] Examples and Comparative Examples

[0159] (1) Preparation of transition metal precursors

[0160] NiSO4, CoSO4, and MnSO4 were mixed in a ratio of 0.88:0.09:0.03 using distilled water that had been bubbled with N2 for 24 hours to remove dissolved oxygen. The solution was added to a reactor at 50°C, and a co-precipitation reaction was carried out for 48 hours using NaOH and NH4OH as precipitating and chelating agents, respectively, to obtain Ni as a transition metal precursor. 0.88 Co 0.09 Mn 0.03 (OH)2. The obtained precursor was dried at 80°C for 12 hours, and then dried again at 110°C for 12 hours.

[0161] (2) Preparation of positive electrode active material

[0162] The transition metal precursor, LiOH·H2O as a lithium precursor, and La(OH)3 as a flux are added to a dry high-speed mixer for mixing. At this time, the above substances are added to make the molar ratio of transition metal (Ni, Co, Mn) to Li 1:1.03.

[0163] The mixed powder was then added to a calcination furnace, and oxygen was supplied at a flow rate of 100 mL / min to maintain an oxygen concentration above 95%. The temperature was then increased to approximately 840°C to 900°C at a rate of 2°C / min. This temperature was maintained for 10 hours. After calcination, the powder was finely pulverized using a jet mill (Sturtevant Corporation) to obtain the positive electrode active material.

[0164] In the examples and comparative examples, the calcination temperature (°C), the lanthanum content (ppm) relative to the total weight of the lithium-transition metal oxide particles, and the crushing pressure (bar) of the jet mill were adjusted as shown in Table 1 below.

[0165] (3) Manufacturing of lithium secondary batteries

[0166] A secondary battery is manufactured using the aforementioned positive electrode active material. Specifically, the positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder are mixed in a mass ratio of 93:5:2 to prepare a positive electrode mixture, which is then coated onto an aluminum current collector, and the positive electrode is manufactured by drying and calendering. The target electrode density of the calendered positive electrode is adjusted to 3.6 g / cm³ to 3.7 g / cm³.

[0167] Lithium metal is used as the negative electrode active material.

[0168] The positive and negative electrodes, manufactured as described above, are notched into circular shapes with diameters of Φ14 and Φ16, respectively, and then stacked. A separator (polyethylene, 13μm thick), cut with a diameter of Φ19, is placed between the positive and negative electrodes to form a battery cell. The battery cell is then placed inside a coin cell casing material with a diameter of 20mm and a height of 1.6mm, and electrolyte is injected for assembly. The cells are aged for at least 12 hours to allow the electrolyte to penetrate the electrodes.

[0169] The electrolyte used is a 1M LiPF6 electrolyte dissolved in a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0170] The secondary battery manufactured as described above was subjected to formation charging and discharging (charging conditions: CC-CV 0.1C 4.3V 0.005C cut-off, discharging conditions: CC 0.1C 3V cut-off).

[0171] [Table 1]

[0172]

[0173] Experimental Example

[0174] (1) Measurement of particle size distribution

[0175] The volume-weighted particle size distribution of the positive electrode active materials of the examples and comparative examples was measured using a laser diffraction particle size analyzer (Microtrac S3500 Extended).

[0176] When accumulating particles in ascending order of size, D10 is the particle size at 10% volume fraction, D50 is the particle size at 50% volume fraction, and D90 is the particle size at 90% volume fraction.

[0177] Particles with a diameter of less than 1 μm are classified as micro powder, while particles with a diameter more than twice that of D50 are classified as coarse powder.

[0178] The span (dimensionless) is calculated using (D90-D10) / D50.

[0179] In addition, the cross-sections of the positive electrode active materials of Example 1, Comparative Example 1 and Comparative Example 2 were observed using a scanning electron microscope (SEM).

[0180] The measurement results are shown in Table 2 below.

[0181] [Table 2]

[0182]

[0183] Referring to Table 2 above, in the case of the positive electrode active material according to the embodiment, D50 is adjusted to 2 μm to 5 μm, and the cumulative relative particle size (%) of coarse powder is adjusted to the range of 4% to 15%.

[0184] In the embodiment where the calcination temperature and crushing pressure are adjusted to an appropriate range, the positive electrode active material has a uniform particle size distribution overall.

[0185] In comparative examples where the calcination temperature or crushing pressure was adjusted to be higher or lower, an uneven particle size distribution was observed overall compared to the examples.

[0186] For example, in Comparative Example 1 where no flux was used and in Comparative Example 2 where the crushing pressure was adjusted too high, an uneven particle size distribution was observed.

[0187] Figures 5 to 7 The images are SEM images of the positive electrode active materials for lithium secondary batteries according to Example 1, Example 4 and Comparative Example 1, respectively.

[0188] Reference Figure 5 The positive electrode active material prepared according to Example 1, by adjusting the calcination temperature to 840°C and the crushing pressure to 1.5 bar, has a uniform single-particle form. Almost no particle cracks or micropowder are produced, and a suitable amount of coarse powder composed of aggregates of two or more particles is formed.

[0189] Reference Figure 6 In Example 4, where the crushing pressure is adjusted to be lower, although the amount of coarse powder formed by the aggregation of more than two particles increases, the amount of fine powder remains low.

[0190] Reference Figure 7 The positive electrode active material according to Comparative Example 1, without the addition of flux, has a relatively small D50. Furthermore, due to insufficient single-particle formation, it exhibits a morphology of multiple small particles aggregated rather than a uniform single-particle form.

[0191] (2) Measurement of capacity retention (lifetime characteristics) during repeated charge and discharge cycles

[0192] The lithium secondary batteries of the examples and comparative examples were charged (CC / CV 0.5C 4.3V 0.05C cutoff) and discharged (CC 1.0C 3.0V cutoff) in a chamber at 45°C, and the cycle was repeated 200 times. The lifetime retention rate was evaluated as a percentage of the discharge capacity of the 200th cycle divided by the discharge capacity of the 1st cycle.

[0193] The evaluation results are shown in Table 3 below.

[0194] [Table 3]

[0195]

[0196] Referring to Table 3, in the case of an example containing a positive electrode active material in which the cumulative relative particle size (%) of coarse powder is adjusted to 4% to 15%, improved lifetime characteristics are achieved.

[0197] In Example 4, where the crushing pressure was adjusted to be lower, single particles were uniformly formed and the amount of micronized powder was reduced. Therefore, side reactions with the electrolyte were reduced, thereby improving lifespan characteristics.

[0198] In Example 7, where the calcination temperature was adjusted to a lower level, particle growth was not sufficiently achieved compared to the other examples. Consequently, the lifespan characteristics of the secondary battery were reduced.

[0199] In Comparative Example 1, the calcination temperature was lower and no flux was included, resulting in insufficient formation of single particles and inadequate particle fragmentation. Consequently, the particle size distribution was uneven, leading to reduced lifespan characteristics.

[0200] In Comparative Example 2, which included a positive electrode active material in which the pulverizing pressure was adjusted to be higher, resulting in the cumulative relative particle amount of coarse powder being adjusted to less than 4%, the capacity retention rate was further deteriorated due to the increase in particle cracks compared to the Examples and other comparative examples.

[0201] In Comparative Example 2, although the calcination temperature was adjusted to 860°C, excessive crushing led to an increase in microparticles. Consequently, the capacity retention rate was further reduced.

Claims

1. A positive electrode active material for lithium secondary batteries, comprising active material particles, said active material particles comprising lithium-transition metal oxide particles in the form of single particles. In the volume-weighted particle size distribution of the active material particles, the particle size D50 at the point where the volume fraction reaches 50% starting from the smallest particle is 2 μm to 10 μm. When the D50 of the active material particles is denoted as a, the volume fraction of particles with a diameter of 2aμm or larger in the active material particles is 4% to 15%.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The D50 of the active substance particles is 2.5 μm to 5 μm.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The volume fraction of particles with a diameter of 2 μm or larger in the active material particles is 5% to 10%.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The volume fraction of particles with a diameter of less than 1 μm in the active substance particles is less than 5%.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The volume fraction of particles with a diameter of less than 1 μm in the active material particles is 0.1% to 4.5%.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The active substance particles have a span of 1.0 to 1.5, as defined by Formula 1: [Formula 1] Span = (D90 - D10) / D50 In Formula 1, D50 is the particle size at 50% volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution of the active material particles; D90 is the particle size at 90% volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution of the active material particles; and D10 is the particle size at 10% volume fraction when accumulating from the smallest particle in the volume-weighted particle size distribution of the active material particles.

7. The positive electrode active material for lithium secondary batteries according to claim 6, wherein, The span of the active substance particles is 1.1 to 1.

4.

8. The positive electrode active material for lithium secondary batteries according to claim 6, wherein, The D10 of the active substance particles is 1.3 μm to 4 μm.

9. The positive electrode active material for lithium secondary batteries according to claim 6, wherein, The active substance particles have a D90 of 4 μm to 15 μm.

10. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal oxide particles contain nickel, and in the lithium-transition metal oxide particles, the molar fraction of nickel, excluding lithium and oxygen, is 0.6 or more.

11. The positive electrode active material for lithium secondary batteries according to claim 10, wherein, The lithium-transition metal oxide particles further comprise at least one element selected from Na, Mg, Ca, Sr, Ba, La, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, and Sn.

12. The positive electrode active material for lithium secondary batteries according to claim 11, wherein, The lithium-transition metal oxide particles contain lanthanum at a content of 500 ppm to 4000 ppm relative to the total weight of the lithium-transition metal oxide particles.

13. A lithium secondary battery, comprising: A positive electrode, comprising the positive electrode active material for a lithium secondary battery as described in claim 1; and a negative electrode, disposed opposite to the positive electrode.

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