Positive electrode active material for lithium secondary battery, method for preparing same, 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 comprises lithium-transition metal oxide particles which comprise a lithium-sulfur-metal-containing moiety and which have a minimum particle diameter (Dminimum) of more than 1 [mu] m, the lithium-transition metal oxide particles have a relative standard deviation of 10.5% or less in sulfur signal values as measured repeatedly 10 times by X-ray photoelectron spectroscopy (XPS) analysis.

Description

Technical Field

[0001] This invention relates to a positive electrode active material for lithium secondary batteries, its preparation method, and a lithium secondary battery containing the positive electrode active material. 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 that include rechargeable batteries have been developed for use as power sources for environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Examples of rechargeable batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium-ion batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and lightweight design, thus they are being actively developed and applied.

[0004] As the application scope of lithium-ion batteries expands, there is a growing demand for longer lifespan, higher capacity, and greater operational stability. For example, the power and lifespan characteristics of lithium-ion batteries may be reduced due to side reactions in the positive electrode active material and electrolyte. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] According to one aspect of the present invention, a positive electrode active material for lithium secondary batteries with improved power characteristics and lifetime characteristics can be provided.

[0007] According to one aspect of the present invention, a method for preparing a positive electrode active material for lithium secondary batteries with improved power characteristics and lifetime characteristics can be provided.

[0008] According to one aspect of the present invention, a lithium secondary battery having improved power characteristics and lifespan characteristics can be provided.

[0009] (II) Technical Solution

[0010] According to an exemplary embodiment of the present invention, the positive electrode active material for a lithium secondary battery comprises lithium-transition metal oxide particles, wherein the lithium-transition metal oxide particles contain a lithium-sulfur-metal portion and have a minimum particle size (D) 最小 For particles larger than 1 μm, the relative standard deviation of the sulfur signal value of the lithium-transition metal oxide particles measured repeatedly 10 times by X-ray photoelectron spectroscopy (XPS) was less than 10.5%.

[0011] In some embodiments, the positive electrode active material may comprise a plurality of the lithium-transition metal oxide particles, and the X-ray photoelectron spectroscopy (XPS) analysis may be performed on a square region with a width of 0.9 mm and a length of 0.9 mm filled with the plurality of lithium-transition metal oxide particles.

[0012] In some implementations, the relative standard deviation can be from 4.5% to 9.0%.

[0013] In some embodiments, the lithium-sulfur-metal portion may contain at least one selected from Al, Ti, Zr, W, Sr, Ba, Ta, Nb, Mo, K, B, and Na.

[0014] In some embodiments, the lithium-transition metal oxide particles may comprise secondary particles formed by the aggregation of multiple primary particles, and the portion containing lithium-sulfur-metal may be located between the primary particles or on the surface of the secondary particles.

[0015] In some embodiments, the sulfur content of the lithium-transition metal oxide particles may be from 3,000 ppm to 6,000 ppm relative to the total weight of the lithium-transition metal oxide particles.

[0016] In some embodiments, the minimum particle size (D) of the lithium-transition metal oxide particles is... 最小 The thickness can range from 2.1 μm to 2.7 μm.

[0017] A lithium secondary battery according to an exemplary embodiment of the present invention includes: a positive electrode comprising the above-described positive electrode active material for lithium secondary batteries; and a negative electrode disposed opposite to the positive electrode.

[0018] According to an exemplary embodiment of the present invention, a method for preparing a positive electrode active material for a lithium secondary battery involves preparing first primary lithium-transition metal oxide particles. The first primary lithium-transition metal oxide particles, a metal oxide, and a sulfur compound are dry-mixed to form a mixture. A solvent is added to the mixture and the mixture is dried to prepare second primary lithium-transition metal oxide particles. The second primary lithium-transition metal oxide particles are calcined at a temperature higher than the drying temperature to prepare lithium-transition metal oxide particles, wherein the lithium-transition metal oxide particles contain a lithium-sulfur-metal fraction and have a minimum particle size (D...). 最小 The size exceeds 1 μm. The relative standard deviation of the sulfur signal value of the lithium-transition metal oxide particles after 10 repeated measurements by X-ray photoelectron spectroscopy (XPS) was less than 10.5%.

[0019] In some embodiments, the metal oxide may comprise a composition selected from Al₂O₃, TiO₂, Ti₂O₃, ZrO₂, H₃BO₃, B₂O₃, SrO₂, SrAl₂O₄, SrTiO₃, SrWO₄, BaO, WO₃, and (NH₄). 10 H2(W2O7)6, MgO, Ta2O5, Nb2O5, MoO3, H4[W 12 SiO 40 At least one of H4SiO4·12MoO3 and (NH4)2MoO4.

[0020] In some embodiments, the sulfur compound may contain at least one selected from (NH4)2SO4, HSO3NH2, NH4SO3NH2, Al2(SO4)3, AlK(SO4)2, Al(NH4)(SO4)2, Ti(SO4)2, TiOSO4, and SrSO4.

[0021] In some embodiments, the sulfur content of the sulfur compound may be from 2,000 ppm to 4,000 ppm relative to the total weight of the mixture.

[0022] In some embodiments, the solvent content may be from 2% by weight to 11% by weight relative to the total weight of the mixture.

[0023] In some embodiments, the drying temperature can be from 110°C to 240°C.

[0024] In some embodiments, the calcination can be carried out at 300°C to 500°C.

[0025] In some embodiments, the preparation method may further include a step of pulverizing the mixture after drying and before calcination.

[0026] (III) Beneficial Effects

[0027] According to one embodiment of the present invention, impurities on the surface of the positive electrode active material can be reduced, and the capacity and lifespan characteristics of the lithium secondary battery can be improved.

[0028] According to one embodiment of the present invention, the high-temperature storage characteristics of lithium secondary batteries can be improved. Furthermore, the amount of gas generated by lithium secondary batteries can be reduced.

[0029] The positive electrode active material for lithium secondary batteries and the lithium secondary battery containing the positive electrode active material 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. The positive electrode active material for lithium secondary batteries and the lithium secondary battery containing the positive electrode active material of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles, which prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0030] Figure 1 This is a process flow diagram illustrating a method for preparing a positive electrode active material according to an exemplary embodiment.

[0031] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views of a lithium secondary battery according to an exemplary embodiment.

[0032] Figure 4 This is a graph showing the sulfur signal values ​​of the lithium-transition metal oxide particles of Example 1 obtained by X-ray photoelectron spectroscopy (XPS) analysis.

[0033] Figures 5 to 9 The images are scanning electron microscope (SEM) images of the positive electrode active materials of Examples 1, 2, 8, 10 and Comparative Example 8, respectively.

[0034] Figures 10 to 12 The images are quantitative maps (Q-maps) of the positive electrode active materials of Example 2, Comparative Example 3, and Comparative Example 6, obtained by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Detailed Implementation

[0035] According to an embodiment of the present invention, a positive electrode active material for a lithium secondary battery comprising a coating element (hereinafter, simply referred to as "positive electrode active material") is provided. Furthermore, a method for preparing the positive electrode active material and a lithium secondary battery comprising the positive electrode active material (hereinafter, simply referred to as "secondary battery") are provided.

[0036] 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.

[0037] In an exemplary embodiment, the positive electrode active material may comprise lithium (Li)-transition metal oxide particles. The lithium-transition metal oxide particles may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al). For example, the positive electrode active material may comprise a plurality of the lithium-transition metal oxide particles.

[0038] In some embodiments, the positive electrode active material or the lithium-transition metal oxide particles may comprise a layered structure or a crystal structure represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] Li x Ni a M b O 2+z

[0041] In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, or -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0042] 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 indicate the bonding relationships of the main active elements, and it should be understood that Formula 1 includes the introduction and substitution of additional elements.

[0043] 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 include the chemical structures represented by Formula 1.

[0044] The auxiliary element may include at least one selected from, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may function as an auxiliary active element, working together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.

[0045] For example, the positive electrode active material or the lithium-transition metal oxide particles may contain a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0046] [Chemical Formula 1-1]

[0047] Li x Ni a M1 b1 M2 b2 O 2+z

[0048] In chemical formula 1-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the values ​​can be 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, and -0.5≤z≤0.1.

[0049] The positive electrode active material may further contain doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as doping elements. For example, one of the elements described above or a combination of two or more of the elements described above can be used as doping elements.

[0050] The dopant element may exist on the surface of the lithium-transition metal oxide particles or permeate through the surface of the lithium-transition metal oxide particles and be contained in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0051] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0052] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (high-Ni) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0053] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may decrease relatively, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.

[0054] In the NCM-based lithium oxide, the Ni content (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 0.95 or more. In some embodiments, the Ni content can be 0.8 to 0.98, 0.82 to 0.98, 0.83 to 0.98, 0.84 to 0.98, 0.85 to 0.98, 0.88 to 0.98, or 0.9 to 0.98.

[0055] In an exemplary embodiment, the lithium-transition metal oxide particles may contain a portion containing lithium-sulfur-metal.

[0056] In some embodiments, the lithium-transition metal oxide particles may comprise secondary particles formed by the aggregation of multiple primary particles, and the portion containing lithium-sulfur-metal may be located between the primary particles or on the surface of the secondary particles.

[0057] For example, the lithium-sulfur-metal portion can be formed by the combination of residual lithium, sulfur, and metal elements present between primary particles or on the surface of secondary particles of lithium-transition metal oxide particles. The lithium-sulfur-metal portion can have relatively high structural stability compared to impurities (e.g., residual lithium). Therefore, impurities on the surface of lithium-transition metal oxide particles can be reduced, thereby improving the capacity and lifespan characteristics of the secondary battery. For example, the residual lithium can include lithium hydroxide (LiOH), lithium carbonate (Li₂CO₃), etc.

[0058] In some embodiments, the primary particles present on the surface of the lithium-transition metal oxide particles can have a hexagonal close-packed structure. Therefore, even in a small space, a large amount of lithium and transition metal elements can be contained in a stable layered structure, thus improving the capacity and lifetime characteristics of the secondary battery.

[0059] In one embodiment, the lithium-sulfur-metal portion may comprise a compound of Li2SO4 and a metal element.

[0060] In one embodiment, the lithium-sulfur-metal portion may contain at least one metal element selected from Al, Ti, Zr, W, Sr, Ba, Ta, Nb, Mo, K, B, and Na. For example, the lithium-sulfur-metal portion may contain a mixture of the metal element and a lithium-sulfur compound.

[0061] In one embodiment, the lithium-sulfur-metal portion may contain at least one selected from Li2SO4, Li(NH4)SO4, Li(N2H5)SO4, LiNaSO4, LiKSO4, Li2NaK(SO4)2, Li2S2O6, Li2Mg2(SO4)3, LiB(SO4)2, LiB(S2O7)2 and Li5B(SO4)4.

[0062] In some embodiments, the lithium-sulfur-metal portion may contain a monoclinic crystal structure. Therefore, the specific surface area of ​​the lithium-transition metal oxide particles can be reduced, and the surfaces of the primary and / or secondary particles can be protected by the lithium-sulfur-metal portion, thereby improving the lifespan characteristics and driving stability of the secondary battery.

[0063] The lithium-sulfur-metal portion of a monoclinic crystal structure can diffuse lithium via a paddle-wheel mechanism. Therefore, the ionic conductivity of the positive electrode active material can be improved, and the resistance can be reduced, thereby enhancing power characteristics.

[0064] For example, the propeller mechanism could be a phenomenon in which elements, including oxygen, rotate around sulfur ions that form anions, thereby reducing the activation energy required for lithium ion migration.

[0065] For example, the crystal structure of the lithium-sulfur-metal portion can be confirmed by selected area electron diffraction (TEM-SAED) analysis.

[0066] In an exemplary embodiment, the relative standard deviation of the sulfur signal value of lithium-transition metal oxide particles measured repeatedly 10 times by X-ray photoelectron spectroscopy (XPS) can be less than 10.5%, and in some embodiments, the relative standard deviation can be from 4.5% to 9.0%. Within the above range, the lithium-sulfur-metal portion can be uniformly disposed on the surface of the lithium-transition metal oxide particles. Therefore, the lifespan and high-temperature storage characteristics of lithium secondary batteries can be improved, and gas generation can be reduced.

[0067] The X-ray photoelectron spectroscopy (XPS) analysis can be performed on a square region with a width of 0.9 mm and a length of 0.9 mm filled with multiple lithium-transition metal oxide particles.

[0068] For example, lithium-transition metal oxide particles can be completely filled into a square container with a width of 0.9 mm and a length of 0.9 mm, and the square container can be subjected to the XPS analysis 10 times.

[0069] For example, the XPS analysis can measure a region less than 10 nm from the surface of the lithium-transition metal oxide particle towards its center. Therefore, the elemental composition of the surface portion of the lithium-transition metal oxide particle can be obtained.

[0070] For example, in a graph obtained through XPS analysis, the horizontal axis can be the binding energy in eV, and the vertical axis can be the sulfur signal value in cps. The relative standard deviation can be calculated after repeatedly measuring the sulfur signal value 10 times.

[0071] The relative standard deviation can be defined as the value obtained by dividing the standard deviation of the sulfur signal value obtained by repeated measurement of lithium-transition metal oxide particles by XPS 10 times by the average value of the sulfur signal value and multiplying it by 100.

[0072] According to one implementation scheme, the positive electrode active material that becomes the object of the above measurement method can be a positive electrode active material prepared by the following preparation method.

[0073] According to one implementation scheme, the positive electrode active material that becomes the object of the above measurement method can be a positive electrode active material recovered from a lithium secondary battery or a positive electrode.

[0074] For example, a lithium secondary battery can be disassembled to obtain the positive electrode. The positive electrode can be placed in an organic solvent (e.g., N-methyl-2-pyrrolidone, NMP) and kept for about 5 minutes to dissolve the binder and remove the positive electrode current collector, and then the organic solvent can be removed by drying.

[0075] The remaining positive electrode active material and conductive material after drying can be added to a container along with distilled water and stirred for about 1 hour, and then left to stand for about 10 minutes to separate the conductive material and positive electrode active material.

[0076] The conductive material separated on the surface of distilled water can be removed, and the positive electrode active material that has settled to the bottom of the container can be obtained. This positive electrode active material can be dried in a chamber at approximately 100°C for about 2 hours and used as the positive electrode active material for XPS analysis.

[0077] In an exemplary embodiment, the minimum particle size (D) of the lithium-transition metal oxide particles is... 最小 The minimum particle size (D) of the lithium-transition metal oxide particles can exceed 1 μm. In some embodiments, the minimum particle size (D) of the lithium-transition metal oxide particles is... 最小The particle size can range from 2.1 μm to 2.7 μm. Within this range, cracks can be prevented during the crushing or rolling process due to the aggregation of sulfur compounds and small-diameter particles. Therefore, the lifespan and high-temperature storage characteristics of lithium secondary batteries can be improved, and gas generation can be reduced.

[0078] The minimum particle size (D) 最小 () can refer to the smallest particle size in the particle size distribution obtained from particle volume.

[0079] By simultaneously controlling the relative standard deviation and the minimum particle size (D) 最小 This technology can suppress the aggregation of small-diameter particles, sulfur compounds, and metal elements, and can also make the lithium-sulfur-metal components uniformly distributed, thereby improving the life characteristics of secondary batteries.

[0080] In some embodiments, the sulfur content of the lithium-transition metal oxide particles can be from 3000 ppm to 6000 ppm relative to the total weight of the lithium-transition metal oxide particles. Within this range, a lithium-sulfur-metal fraction can be sufficiently formed while maintaining or improving capacity characteristics.

[0081] The preparation method of the above-mentioned positive electrode active material for lithium secondary batteries is described in detail below.

[0082] Figure 1 This is a process flow diagram illustrating a method for preparing a positive electrode active material according to an exemplary embodiment.

[0083] Reference Figure 1 First primary lithium-transition metal oxide particles can be prepared (e.g., step S10).

[0084] For example, first primary lithium-transition metal oxide particles can be prepared by reacting a nickel-containing transition metal precursor with a lithium precursor. The transition metal precursor (e.g., a Ni-Co-Mn precursor) can be prepared by a co-precipitation reaction.

[0085] For example, the transition metal precursor can be prepared by a co-precipitation reaction of a metal salt. The metal salt may include nickel salt, manganese salt, and / or cobalt salt.

[0086] The nickel salt may include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, and their hydrates. Examples of the manganese salt may include manganese sulfate, manganese acetate, and their hydrates. Examples of the cobalt salt may include cobalt sulfate, cobalt nitrate, cobalt carbonate, and their hydrates. These may be used alone or in combination of two or more.

[0087] An aqueous solution can be prepared by mixing the metal salt with a precipitant and / or a chelating agent in the proportions or concentration ratios of the metals as described with reference to Chemical Formula 1. Transition metal precursors can be prepared by co-precipitating the aqueous solution in a reactor.

[0088] The precipitant may contain alkaline compounds such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). The chelating agent may contain ammonia (e.g., NH3·H2O) and ammonium carbonate (e.g., NH4HCO3).

[0089] For example, the coprecipitation reaction can be carried out at a temperature of about 40°C to 60°C for about 24 to 72 hours.

[0090] The lithium precursor compound 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.

[0091] In an exemplary embodiment, the first primary lithium-transition metal oxide particles, the metal oxide, and the sulfur compound may be dry-mixed to form a mixture (e.g., step S20).

[0092] The dry mixing refers to mixing first primary lithium-transition metal oxide particles, metal oxide powder, and sulfur compound powder without solvent.

[0093] For example, the metal oxide can be provided as a metal source containing a lithium-sulfur-metal fraction, and the sulfur compound can be provided as a sulfur source containing a lithium-sulfur-metal fraction.

[0094] In some embodiments, the metal oxide may comprise a composition selected from Al₂O₃, TiO₂, Ti₂O₃, ZrO₂, B₂O₃, H₃BO₃, SrO₂, SrAl₂O₄, SrTiO₃, SrWO₄, BaO, WO₃, and (NH₄). 10 H2(W2O7)6, MgO, Ta2O5, Nb2O5, MoO3, H4[W 12 SiO 40 At least one of H4SiO4·12MoO3 and (NH4)2MoO4.

[0095] In some embodiments, the amount of the metal oxide added may be from 0.1 mol% to 1.0 mol% relative to the total number of moles of the first primary lithium-transition metal oxide particles. Within this range, the power and capacity characteristics of the positive electrode active material can be improved.

[0096] In some embodiments, the sulfur compound may comprise a sulfonyl group compound.

[0097] For example, the sulfur compound may contain at least one selected from (NH4)2SO4, HSO3NH2, NH4SO3NH2, Al2(SO4)3, AlK(SO4)2, Al(NH4)(SO4)2, Ti(SO4)2, TiOSO4 and SrSO4.

[0098] In some embodiments, the sulfur content of the sulfur compound relative to the total weight of the mixture can be from 2000 ppm to 4000 ppm. Within this range, a lithium-sulfur-metal moiety can be sufficiently formed while maintaining or improving capacity characteristics.

[0099] In an exemplary embodiment, a solvent may be added to the mixture and dried to prepare second primary lithium-transition metal oxide particles (e.g., step S30).

[0100] For example, the mixture can be added to a dryer along with a solvent and then vacuum dried to form a primary lithium-sulfur-metal fraction. For instance, the addition of the solvent and the vacuum drying can be performed simultaneously.

[0101] For example, the primary lithium-sulfur-metal portion may contain substantially the same substance as the lithium-sulfur-metal portion. The primary lithium-sulfur-metal portion may exhibit a relatively unstable state of being bound between primary particles or on secondary particles of the second primary lithium-transition metal oxide particles before calcination.

[0102] For example, the solvent can be added by pouring, dropping, spraying, or misting.

[0103] For example, the addition of the solvent and the drying can be carried out in a vertical conical dryer (helical type conical dryer), a horizontal conical dryer (shovel type conical dryer), a vertical cylindrical dryer (helical type cylindrical dryer), etc.

[0104] In one embodiment, the drying and stirring can be performed simultaneously. For example, the mixture and the solvent can be dried while being stirred at a low speed (e.g., below 100 rpm). This prevents cracking of the first primary lithium-transition metal oxide particles while uniformly forming the primary lithium-sulfur-metal content.

[0105] After forming a mixture by dry mixing, a solvent can be added to the mixture and then dried. This suppresses the aggregation of the first primary lithium-transition metal oxide particles and sulfur compounds, allowing the lithium-sulfur-metal portion to be uniformly formed between the primary particles or on the surface of the secondary particles of the lithium-transition metal oxide.

[0106] According to some implementation schemes, a water washing process involving the addition of substantially the same or similar amount of water as the first primary lithium-transition metal oxide particles can be omitted. Therefore, damage or collapse of the layered structure of the primary particles can be prevented.

[0107] In some embodiments, the solvent content may be from 2% to 11% by weight relative to the total weight of the mixture. Within this range, impurities in the first primary lithium-transition metal oxide particles can be sufficiently removed while preventing damage or collapse of the layered structure of the primary particles, as is the case with water washing.

[0108] For example, the solvent may be pure water or ultrapure water.

[0109] In some embodiments, the drying temperature can be between 110°C and 240°C. The drying temperature may refer to the internal temperature of the dryer rather than the temperature of the dryer's heat source. Within this range, solvent drying and the formation of the primary lithium-sulfur-metal fraction can be performed simultaneously, further improving the lifespan and power characteristics of the secondary battery.

[0110] For example, the sulfur compound and / or the metal oxide can react with residual lithium present on the surface of the first primary lithium-transition metal oxide particles to convert it into a primary lithium-sulfur-metal fraction. Therefore, residual lithium on the surface of the lithium-transition metal oxide particles can be reduced, and the lifespan and power characteristics of the secondary battery can be improved.

[0111] In some embodiments, the mixture can be pulverized after drying and before calcination (e.g., step S35). This allows for the pulverization of the first primary lithium-transition metal oxide particles and the aggregates of sulfur compounds, and can further improve the lifespan characteristics of the secondary battery.

[0112] For example, the pulverization can be carried out by a high-speed mixer, an air classifier mill (ACM), a disc mill, etc.

[0113] In an exemplary embodiment, the second primary lithium-transition metal oxide particles may be calcined at a temperature above the drying temperature to prepare lithium-transition metal oxide particles containing a lithium-sulfur-metal fraction (e.g., step S40).

[0114] The calcination can be carried out at 300°C to 500°C. Within this range, the primary lithium-sulfur-metal portion can be converted into a lithium-sulfur-metal portion between the primary particles or on the surface of the secondary particles of the lithium-transition metal oxide particles, and can be stably disposed between the primary particles or on the secondary particles. Therefore, the lifespan characteristics of the secondary battery can be further improved.

[0115] According to one embodiment, the calcination can be carried out in an oxygen atmosphere.

[0116] The minimum particle size (D) of lithium-transition metal oxide particles prepared according to the above preparation method 最小 The particle size can be adjusted to more than 1 μm by crushing and / or grading.

[0117] The relative standard deviation of the sulfur signal value of the lithium-transition metal oxide particles prepared by the above preparation method, after repeated measurements by XPS analysis for 10 times, can be less than 10.5%.

[0118] Figure 2 and Figure 3 These are schematic plan views and schematic cross-sectional views illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 3 It is along Figure 2 A cross-sectional view taken along the thickness direction of the I-I' line.

[0119] Figure 2 and Figure 3 The structure shown is an example for illustrative purposes, and the structure of the lithium secondary battery according to the embodiments of the present invention is not limited thereto.

[0120] Reference Figure 2 and Figure 3 The lithium secondary battery may include a positive electrode 100 and a negative electrode 130, wherein the positive electrode 100 contains the aforementioned positive electrode active material, and the negative electrode 130 is disposed opposite to the positive electrode 100.

[0121] The positive electrode 100 may include a positive electrode active material layer 110, which is formed by coating the positive electrode active material onto at least one side of the positive electrode current collector 105.

[0122] The positive current collector 105 may comprise stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector 105 may also comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive current collector 105 may be from 10 μm to 50 μm.

[0123] The positive electrode active material layer 110 may contain the aforementioned positive electrode active material.

[0124] The positive electrode active material may comprise a plurality of the lithium-transition metal oxide particles. For example, the total content of the lithium-transition metal oxide particles in the total weight of the positive electrode active material may be 50% by weight or more. In some embodiments, the total content of the lithium-transition metal oxide particles in the total weight of the positive electrode active material may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0125] In one embodiment, the positive electrode active material may substantially consist of the lithium-transition metal oxide particles.

[0126] The positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated onto at least one side of the positive electrode current collector 105, then dried and calendered to produce a positive electrode active material layer 110. The coating process can include gravure coating, slot die coating, multilayer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, and other methods. The positive electrode active material layer 110 may further contain a binder and optionally further contain conductive materials, thickeners, etc.

[0127] The solvent can be N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0128] The adhesive may contain polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These can be used alone or in combination of two or more.

[0129] In one embodiment, a PVDF-based binder can be used as the positive electrode binder. 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. Therefore, the power characteristics and capacity characteristics of the secondary battery can be improved.

[0130] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode active material layer 110. For example, the conductive material may also comprise carbon-based conductive materials such as graphite, carbon black (e.g., Denka Black), acetylene black, Ketjen black, graphene, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs), and carbon fibers, and / or metal-based conductive materials comprising perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These can be used alone or in combination of two or more.

[0131] The cathode slurry may further contain thickeners and / or dispersants. In one embodiment, the cathode slurry may contain thickeners such as carboxymethyl cellulose (CMC).

[0132] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one side of the negative electrode current collector 125.

[0133] For example, the negative electrode current collector 125 may comprise copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, polymer substrate coated with conductive metal, etc. These can be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 125 can be from 10 μm to 50 μm.

[0134] The negative electrode active material layer 120 may include a negative electrode active material. The negative electrode active material may be a material that allows lithium ions to be intercalated and deintercalated. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, etc.; lithium metal; lithium alloy; silicon (Si)-containing material or tin (Sn)-containing material, etc. These may be used alone or in combination of two or more.

[0135] The amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0136] The crystalline carbon may include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0137] The lithium metal may include pure lithium metal and / or lithium metal formed with a protective layer for inhibiting dendrite growth, etc. In one embodiment, the lithium metal-containing layer deposited or coated on the negative electrode current collector 125 may be used as the negative electrode active material layer 120. In one embodiment, the lithium thin film layer may be used as the negative electrode active material layer 120.

[0138] As the elements included in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. may be cited. These may be used alone or in combination of two or more.

[0139] The silicon-containing material may provide further increased capacity characteristics. The silicon-containing material may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composite, etc.

[0140] The metal may include lithium and / or magnesium, and the metal-doped SiO x (0 < x < 2) may include metal silicate.

[0141] The negative electrode active material may be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry may be coated / deposited on the negative electrode current collector 125 and then dried and calendered to prepare the negative electrode active material layer 120. The coating may include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, knife coating, dip coating, rod coating, casting, etc. The negative electrode active material layer 120 may further include an adhesive, and may optionally further include a conductive material, a thickener, etc.

[0142] The solvents contained in the negative electrode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc. These can be used alone or in combination of two or more.

[0143] As the adhesive, conductive material and thickener, the aforementioned substances that can be used in the manufacture of the positive electrode 100 can be used.

[0144] In some implementations, the negative electrode binder can be a styrene-butadiene rubber (SBR) based binder, a carboxymethyl cellulose (CMC) based binder, a polyacrylic acid based binder, or a poly(3,4-ethylenedioxythiophene) (PEDOT) based binder. These can be used alone or in combination of two or more.

[0145] In an exemplary embodiment, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may be configured to prevent short circuits between the positive electrode 100 and the negative electrode 130 and to allow ion flow. For example, the thickness of the separator may be from 10 μm to 20 μm.

[0146] For example, diaphragm 140 may comprise a porous polymer membrane or a porous nonwoven fabric.

[0147] The porous polymer membrane may contain polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. These may be used alone or in combination of two or more.

[0148] The porous nonwoven fabric may contain high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0149] The diaphragm 140 may also contain a ceramic-based material. For example, coating or dispersing inorganic particles on or within the polymer membrane can improve heat resistance.

[0150] The diaphragm 140 may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric.

[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 battery cells. For example, the electrode assembly 150 can be formed by winding, stacking, z-folding, stack-folding, etc. of the separator 140.

[0152] The electrode assembly 150, together with the electrolyte, is housed in the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can be a non-aqueous electrolyte.

[0153] Non-aqueous electrolytes may contain a lithium salt as the electrolyte and an organic solvent. For example, the lithium salt may be made from Li... + X - This is represented, for example, by the anion (X) of the lithium salt. - ), 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 - (CF3CF2SO2)2N - wait.

[0154] The organic solvent may be, for example, propylene carbonate (PC), ethylene carbonate (EC), butene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), and diethylene glycol dimethyl ether. These include ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0155] The non-aqueous electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These may be used alone or in combination of two or more.

[0156] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0157] The fluorinated carbonate-based compound may include fluoroethylene carbonate (FEC), etc.

[0158] The sulcinolone compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0159] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0160] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, etc.

[0161] The phosphate-based compound may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.

[0162] The borate-based compound may include lithium bis(oxalate) borate, etc.

[0163] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery can be made into an all-solid-state battery. Furthermore, a solid electrolyte layer can be disposed between the positive electrode 100 and the negative electrode 130 instead of the separator 140.

[0164] The solid electrolyte may comprise a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may comprise Li₂S-P₂S₅, Li₂S-P₂S₅-LiCl, Li₂S-P₂S₅-LiBr, Li₂S-P₂S₅-LiCl-LiBr, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, Li₂S-P₂S₅-Z m Sn (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2), etc. These can be used individually or in combination of two or more.

[0165] In one embodiment, the solid electrolyte may further comprise oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, and Li2O-B2O3-ZnO.

[0166] like Figure 2 and 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 outside the housing 160.

[0167] The lithium secondary battery can be made in shapes such as cylindrical, prismatic, pouch, or coin, for example, using a can.

[0168] The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples 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 and technical concept of the present invention, which is obvious to those skilled in the art, and such modifications and variations naturally fall within the scope of the claims.

[0169] Example 1

[0170] (1) Preparation of lithium-transition metal oxide particles

[0171] 1) Preparation of the first primary lithium-transition metal oxide particles (S10)

[0172] NiSO4, CoSO4, and MnSO4 were added and mixed in a molar ratio of 88:9:3 to prepare a mixture in distilled water that had undergone internal dissolved oxygen removal by bubbling with N2 for 24 hours. This mixture was then added to a reactor at 50°C, and a co-precipitation reaction was carried out for 48 hours using NaOH and NH3·H2O 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.

[0173] Lithium hydroxide and the transition metal precursor were added to a dry high-speed mixer at a ratio of 1.01:1 and mixed uniformly for 5 minutes. The mixture was then placed in a calcination furnace and heated to 700-720°C at a rate of 2°C / min, and maintained at 700-720°C for 10 hours. Oxygen was continuously introduced at a flow rate of 20 L / min during the heating and calcination process. After calcination, the mixture was allowed to cool naturally to room temperature and then pulverized and graded to obtain a LiNi composition. 0.88 Co 0.09 Mn 0.03 O2 in the form of primary lithium-transition metal oxide particles (average particle size (D50): 10 μm).

[0174] 2) Formation of the mixture (S20)

[0175] The first primary lithium-transition metal oxide particles, Al2O3 powder and WO3 powder as metal oxides, and (NH4)2SO4 powder as a sulfur compound are dry-mixed to form a mixture.

[0176] The contents of Al2O3 and WO3 are 0.20 mol% (total content of metal oxides: 0.40 mol%) relative to the total molar number of the first primary lithium-transition metal oxide particles. The amount of (NH4)2SO4 added is adjusted so that the sulfur content of the sulfur compound is 3000 ppm relative to the total weight of the mixture.

[0177] 3) Solvent addition and drying (S30)

[0178] The mixture was added to a vertical conical dryer (OKAWARA MFG, model name: RM-25VD-SR) using a heat transfer fluid heating method. 5% by weight of pure water relative to the total weight of the mixture was added to the dryer, and vacuum drying was performed to prepare second primary lithium-transition metal oxide particles containing a primary lithium-sulfur-metal fraction. The internal temperature (drying temperature) of the dryer was adjusted to 170°C. The internal temperature of the dryer was measured by a thermometer installed inside the dryer.

[0179] During the vacuum drying process, the mixture and pure water are stirred at a low speed of less than 100 rpm.

[0180] The vacuum drying is carried out under the following conditions.

[0181] Heat transfer fluid (heat source) set temperature: 200℃

[0182] Dryer internal temperature: 170℃

[0183] Drying time: 6 hours

[0184] Reactor size: 25L

[0185] The amount of the mixture added: 30 kg

[0186] Stirring speed: 80 rpm

[0187] Solvent addition rate: 0.5 L / min

[0188] Solvent temperature: -25℃ to 45℃

[0189] 4) Crushing (S35)

[0190] The second primary lithium-transition metal oxide particles were added to a high-speed mixer (Nippon Coke & Engineering, model name: FM20C / I) and pulverized.

[0191] The pulverization is carried out under the following conditions.

[0192] Mixer reactor size: 20L

[0193] Amount of the second primary lithium-transition metal oxide particles added: 15 kg

[0194] Mixer reactor temperature: maintained at ambient temperature using cooling water.

[0195] Lower blade: Standard type blade

[0196] Upper blade: Grinding blade

[0197] Grinding speed: 700 rpm

[0198] Grinding time: 20 minutes

[0199] 5) Calcination (S40)

[0200] The second primary lithium-transition metal oxide particles were placed in a calcining furnace, oxygen was supplied at a flow rate of 20 L / min, and the temperature was increased to 400°C at a rate of 2°C / min, and maintained at 400°C for 10 hours. The calcined material was classified using a 325-mesh sieve to obtain lithium-transition metal oxide particles.

[0201] (2) Manufacturing of lithium half-cells

[0202] A lithium half-cell is manufactured by using the lithium-transition metal oxide particles as the positive electrode active material.

[0203] 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 slurry. The positive electrode slurry is then coated onto an aluminum current collector and dried and calendered to manufacture the positive electrode. After calendering, the density of the positive electrode is adjusted to 3.3 g / cm³. 3 .

[0204] Lithium metal is used as the negative electrode.

[0205] The positive and negative electrodes manufactured as described above are cut (notched) into circles with diameters of Φ14 and Φ16 respectively and stacked. A separator (polyethylene, 13μm thick) cut to Φ19 is placed between the positive and negative electrodes to form a battery cell. ΦN (N is a positive number) can represent a circle with a diameter of N mm.

[0206] The battery cell is assembled by placing it into a coin battery casing material with a diameter of 20 mm and a height of 3.2 mm (CR2032) and injecting electrolyte, and then aging it for more than 12 hours to allow the electrolyte to penetrate into the electrode.

[0207] The electrolyte is a 1M LiPF6 solution formed using a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0208] The 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 3.0V cut-off).

[0209] (3) Manufacturing of lithium secondary batteries

[0210] Lithium secondary batteries are manufactured by using the lithium-transition metal oxide particles as the positive electrode active material.

[0211] Specifically, the positive electrode active material, acetylene black and carbon nanotubes (CNTs) as conductive materials, and PVDF as a binder are mixed in a mass ratio of 97.7:0.4:0.6:1.3 to prepare a positive electrode slurry. The positive electrode slurry is then coated onto an aluminum current collector and dried and calendered to manufacture the positive electrode. After calendering, the density of the positive electrode is adjusted to 3.69 g / cm³. 3 .

[0212] A negative electrode slurry is prepared, comprising a mixture of 47.25 wt% natural graphite and 47.25 wt% artificial graphite as the negative electrode active material, 3 wt% flake-type conductive material graphite (KS6) as the conductive material, 1.2 wt% styrene-butadiene rubber (SBR) as the binder, and 1.3 wt% carboxymethyl cellulose (CMC) as the thickener. The negative electrode slurry is coated onto a copper substrate and then dried and calendered to manufacture the negative electrode.

[0213] Fourteen positive electrodes and fifteen negative electrodes are cut to specified sizes and stacked. A separator (polyethylene, 25 μm thick) is placed between the positive and negative electrodes to form a battery cell. The tab portions of the positive and negative electrodes are then welded together. The welded positive / separator / negative electrode assembly is placed in a soft package, and the three sides except for the electrolyte injection surface are sealed. At this point, the portion with the tabs is included in the sealed portion. Electrolyte is injected through the electrolyte injection surface, and the electrolyte injection surface is sealed, then immersed for at least 12 hours.

[0214] The electrolyte is prepared by adding 1% by weight of vinylene carbonate (VC) and 0.5% by weight of 1,3-propenyl sulphol (PRS) relative to the total weight of the solution to a 1M LiPF6 solution prepared using a mixed solvent of EC / EMC (25 / 75; volume ratio).

[0215] Examples 2 to 25, and Comparative Examples 7 and 8

[0216] The positive electrode active material, lithium half-cell, and lithium secondary battery were manufactured using the same method as in Example 1, except that the types of metal oxides, sulfur compounds, sulfur content (addition amount) relative to the total weight of the mixture, pure water content (addition amount) relative to the total weight of the mixture, drying temperature (dryer internal temperature), calcination temperature, and minimum particle size after fractionation (D) were changed / adjusted as shown in Tables 1 and 2. 最小 And whether to crush (S35).

[0217] Even if the types of metal oxides and sulfur compounds are changed, the content remains the same as in Example 1.

[0218] Comparative Example 1

[0219] Lithium half-cells and lithium secondary cells were manufactured using the same method as in Example 1, except that the first primary lithium-transition metal oxide particles were used as the positive electrode active material.

[0220] Comparative Example 2

[0221] An aqueous solution of the sulfur compound is prepared by adding (NH4)2SO4 as a sulfur compound to pure water at 5% by weight relative to the weight of the first primary lithium-transition metal oxide particles and stirring.

[0222] The first primary lithium-transition metal oxide particles and the aqueous solution of the sulfur compound are mixed to prepare a mixture (without the addition of metal oxides).

[0223] The amount of (NH4)2SO4 added is adjusted so that the sulfur content of the sulfur compound is 3000 ppm relative to the total weight of the first primary lithium-transition metal oxide particles and the sulfur compound.

[0224] The mixture was vacuum dried in a dryer with the same equipment and conditions as in Example 1 to prepare second primary lithium-transition metal oxide particles. The internal temperature (drying temperature) of the dryer was adjusted to 170°C.

[0225] Except for the above-mentioned contents and the absence of pulverization (S35), the positive electrode active material, lithium half-cell and lithium secondary cell are manufactured by the same method as in Example 1.

[0226] Comparative Example 3

[0227] The first primary lithium-transition metal oxide particles, along with Al2O3 powder and WO3 powder (which are metal oxides), are dry-mixed to form a first mixture. The contents of Al2O3 and WO3 are 0.2 mol% (total metal oxide content: 0.4 mol%) relative to the total moles of the first primary lithium-transition metal oxide particles.

[0228] The first mixture was mixed with the aqueous solution of the sulfur compound from Comparative Example 2 to prepare a second mixture.

[0229] The second mixture was vacuum dried in a dryer with the same equipment and conditions as in Example 1 to prepare second primary lithium-transition metal oxide particles. The internal temperature (drying temperature) of the dryer was adjusted to 170°C.

[0230] Except for the above-mentioned contents and the absence of pulverization (S35), the positive electrode active material, lithium half-cell and lithium secondary cell are manufactured by the same method as in Example 1.

[0231] Comparative Example 4 and Comparative Example 5

[0232] The positive electrode active material, lithium half-cell and lithium secondary cell were manufactured by the same method as in Comparative Example 3, except that the types of sulfur compounds were changed as shown in Table 1.

[0233] Comparative Example 6

[0234] The positive electrode active material, lithium half-cell and lithium secondary cell were manufactured by the same method as in Example 1, except that pure water was not added during the drying (S30) process and no pulverization was performed (S35).

[0235] Experimental Example

[0236] (1) XPS Analysis

[0237] The positive electrode active material particles prepared according to the above embodiments and comparative examples were completely filled into a square container with a width of 0.9 mm and a length of 0.9 mm to prepare a sample.

[0238] The sample was analyzed using an ESCALAB 250Xi device from Thermo Fisher Scientific.

[0239] [XPS Analysis Conditions]

[0240] i) X-ray type: Al kα, 1486.68 eV, beam size 900 μm

[0241] ii) Analyzer: Constant analyzer energy (CAE) mode

[0242] iii) Number of scans: 20 to 50

[0243] iv) Pass energy: 20 eV

[0244] v) Dwell time: 50ms to 100ms

[0245] vi) Energy step: 0.1 eV

[0246] vii) Etching depth: 10nm

[0247] Specifically, the sulfur signal value is measured by integrating the area of ​​the S2p3 / 2 peak region (168 eV to 172 eV) of the sample.

[0248] Repeat the above measurement 10 times, divide the standard deviation of the 10 measured sulfur signal values ​​by the average value of the sulfur signal values ​​and multiply by 100 to calculate the relative standard deviation of the sulfur signal values.

[0249] Figure 4 This is a graph showing the sulfur signal values ​​of the lithium-transition metal oxide particles of Example 1 obtained by XPS analysis.

[0250] The presence of lithium-sulfur-metal fractions was confirmed by measuring the relative standard deviations of tungsten and aluminum signal values ​​using the same method as the relative standard deviations of sulfur signal values.

[0251] (2) Minimum particle size (D) 最小 Measurement of )

[0252] The minimum particle size (D) of the positive electrode active material particles prepared according to the above examples and comparative examples was measured using a particle size analyzer (Microstatic S3500). 最小 ).

[0253] Specifically, positive electrode active material particles are dispersed in a dispersion medium and added to the particle size analyzer. A laser beam is passed through the positive electrode active material particles to measure the differences in diffraction patterns based on particle size. The particle size distribution is obtained from the differences in the diffraction patterns.

[0254] The smallest particle size in the particle size distribution is evaluated as the smallest particle size (D). 最小 ).

[0255] (3) Measurement of sulfur content

[0256] The sulfur content relative to the total weight of the lithium-transition metal oxide particles prepared according to the above examples and comparative examples was measured using a C / S analyzer (carbon / sulfur analyzer, CS844, LECO).

[0257] Specifically, the positive electrode active material particles are divided into 0.02g to 0.04g portions and added to a ceramic crucible. In the ceramic crucible, a combustion aid (LECOCEL II) and iron chips are added in a 1:1 mass ratio.

[0258] The ceramic crucible is placed in a high-frequency induction device, oxygen is supplied at a flow rate of 3 L / min, and combustion is carried out at 2600°C to 2700°C.

[0259] The sulfur-containing inorganic compound gas (e.g., SO2 gas) generated during the combustion process is passed through an infrared detection cell, and the change in infrared absorption relative to a blank is measured to determine the sulfur content of the lithium-transition metal oxide particles relative to the total weight.

[0260] (4) Measurement of residual lithium (Li2CO3) content

[0261] The content of Li2CO3 relative to the total weight of the lithium-transition metal oxide particles prepared according to the above examples and comparative examples was measured using a C / S analyzer (carbon / sulfur analyzer, CS844, Lico).

[0262] Specifically, the carbon content in the sample is measured by detecting the CO2 produced by burning 1g of positive electrode active material sample, and the content of Li2CO3 is calculated by taking into account the atomic weights of lithium, carbon and oxygen.

[0263] (5) Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS)

[0264] For the lithium-transition metal oxide particles of Examples 2, 3, and 6, quantitative maps (Q-maps) were obtained using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The SEM equipment used was an Apreo 2S from Thermo Fisher Scientific, and the SEM-EDS equipment used was a FlatQuad from Bruker.

[0265] The SEM-EDS measurement conditions are as follows.

[0266] i) Accelerating voltage: 10kV

[0267] ii) Beam current: 0.8nA

[0268] iii) Detectors: Everhart-Thornley Detector (ETD), FlatQuad EDS (FQ-EDS)

[0269] iv) Use case: Standard

[0270] v) Laboratory temperature: 20±5℃

[0271] vi) Laboratory relative humidity: below 65%

[0272] Specifically, the sample of lithium-transition metal oxide particles was tightly adhered to carbon tape and thoroughly blown with an air gun.

[0273] The sample was then mounted in an SEM.

[0274] Insert the FQ-EDS detector, then adjust the working distance (WD) to 11mm, and adjust the focus and alignment.

[0275] The magnification was set to 1000x, and EDS mapping was performed for 300 seconds to obtain a quantitative image.

[0276] (6) Evaluation of graded loss rate

[0277] The total weight of the lithium-transition metal oxide particles after grading (weight before grading) is measured relative to the total weight of the lithium-transition metal oxide particles before grading. The grading loss rate is evaluated by subtracting the weight after grading from the weight before grading, dividing by the weight before grading, and then multiplying by 100.

[0278] (7) Evaluation of initial discharge capacity

[0279] The lithium half-cells manufactured according to the above embodiments and comparative examples were charged in a chamber at 25°C (CC-CV 0.1C 4.3V 0.005C cut-off), and then discharged (CC 0.1C 3.0V cut-off) before measuring the battery capacity (initial discharge capacity).

[0280] (8) Evaluation of high-temperature capacity retention (41°C, 800 cycles)

[0281] The lithium secondary batteries according to the examples and comparative examples were placed in a chamber maintained at 41°C and charged (CC-CV 0.66C 4.2V 0.1C cutoff) and discharged (CC 0.66C 2.5V cutoff), and the discharge capacity was measured.

[0282] A cut-off voltage is specified at a cut-off current of 0.1C to achieve a state of charge (SOC) of 97% based on the measured discharge capacity. The cut-off voltage is specified to be between 4.155V and 4.175V.

[0283] The lithium secondary battery was repeatedly charged (CC-CV 0.66C 4.155-4.175V 0.1C cutoff) and discharged (CC 0.66C 2.5V cutoff) 800 times. The high-temperature capacity retention rate was evaluated by dividing the discharge capacity of the 800th discharge by the discharge capacity of the 1st discharge and multiplying by 100.

[0284] (9) Evaluation of high-temperature storage characteristics (60℃, 16 weeks)

[0285] The lithium secondary batteries according to the examples and comparative examples were charged (CC-CV 0.1C 4.2V 0.05C cutoff) and discharged (CC 0.1C 2.5V cutoff), and the initial discharge capacity was measured.

[0286] The lithium secondary battery is recharged (CC-CV 0.1C 4.2V 0.05C cutoff) and discharged to a depth of discharge (DOD) of 3%, thereby preparing a battery with a state of charge (SOC) of 97%.

[0287] The battery was placed in a chamber maintained at 60°C and left for 16 weeks.

[0288] After 16 weeks, the battery was charged (CC-CV 0.1C 4.2V 0.05C cutoff) and discharged (CC 0.1C 2.5V cutoff), and the discharge capacity was measured.

[0289] The high-temperature storage characteristics are evaluated by dividing the discharge capacity by the initial discharge capacity and multiplying by 100.

[0290] (10) Measurement of the amount of high-temperature gas generated

[0291] The SOC 97% battery prepared in Experimental Example (9) was placed in a chamber maintained at 60°C and left for 16 weeks, and the amount of gas produced was measured.

[0292] Specifically, the battery is placed in a jig designed according to the battery size and pierced with a needle. The pressure change inside the jig is then measured and converted into the amount of gas generated.

[0293] The measurement and evaluation results are shown in Tables 3 and 4.

[0294] Table 1 shows the types of metal oxides, sulfur compounds, sulfur content (addition amount) relative to the total weight of the mixture, pure water content (addition amount) relative to the total weight of the mixture, and whether or not the mixture was pulverized in the examples and comparative examples. For whether or not the mixture was pulverized, ○ indicates that it was pulverized, and Ⅹ indicates that it was not pulverized.

[0295] Table 2 shows the drying temperature (dryer internal temperature), calcination temperature, and minimum particle size (D) for the examples and comparative examples. 最小 ).

[0296] [Table 1]

[0297]

[0298] [Table 2]

[0299]

[0300] Table 3 shows the relative standard deviation of the sulfur (S) signal value / tungsten (W) signal value / aluminum (Al) signal value of lithium-transition metal oxide particles measured repeatedly by XPS 10 times in the examples and comparative examples, the sulfur content relative to the total weight of lithium-transition metal oxide particles, the residual lithium (Li2CO3) content relative to the total weight of lithium-transition metal oxide particles, and the fractionation loss rate.

[0301] Table 4 shows the initial discharge capacity, high-temperature capacity retention, high-temperature storage characteristics, and high-temperature gas generation of the examples and comparative examples.

[0302] [Table 3]

[0303]

[0304] [Table 4]

[0305]

[0306] Refer to Tables 1 to 4 for the minimum particle size (D) of lithium-transition metal oxide particles. 最小 In the examples where the diameter exceeds 1 μm and the relative standard deviation is less than 10.5%, the initial discharge capacity, high-temperature capacity retention rate and high-temperature storage characteristics are improved compared with the comparative example, and the amount of high-temperature gas generated is reduced.

[0307] In Example 4, where the sulfur content exceeds 6000 ppm relative to the total weight of lithium-transition metal oxide particles, the initial discharge capacity is relatively reduced and the high-temperature capacity retention is relatively lower compared to other examples.

[0308] In Example 6, where the sulfur content relative to the total weight of lithium-transition metal oxide particles is less than 3000 ppm, the residual lithium content and high-temperature gas generation are relatively increased, while the high-temperature capacity retention and high-temperature storage characteristics are relatively reduced compared to other examples.

[0309] In Example 8, where the amount of pure water added exceeds 11% by weight relative to the total weight of the mixture, aggregates of small-diameter particles and sulfur compounds are formed, resulting in an increase in the relative standard deviation. Consequently, compared to other examples, the residual lithium content and the amount of high-temperature gas generated are relatively increased, while the initial discharge capacity, high-temperature capacity retention, and high-temperature storage characteristics are relatively decreased.

[0310] In Example 10, where the amount of pure water added relative to the total weight of the mixture was less than 2% by weight, the fractionation loss rate and the amount of high-temperature gas generated were relatively increased compared to other examples, while the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics were relatively decreased.

[0311] In Examples 20 and 21, where the drying temperature (internal temperature of the dryer) is not in the range of 110°C to 240°C, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics are relatively reduced compared to other examples, while the graded loss rate and high-temperature gas generation are relatively increased.

[0312] In Examples 24 and 25, where the calcination temperature is not in the range of 300°C to 500°C, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics are relatively reduced compared to other examples, while the amount of high-temperature gas generated is relatively increased.

[0313] In Comparative Example 1, where no metal oxides and sulfur compounds were added, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics decreased compared to the Examples, while the amount of high-temperature gas generated increased.

[0314] In Comparative Examples 2 to 5, where an aqueous solution of sulfur compound and first primary lithium-transition metal oxide particles were wet-mixed without the addition of solvent / drying after dry mixing of the sulfur compound, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics decreased, and the amount of high-temperature gas generated increased, compared to the examples.

[0315] In Comparative Example 6, where no solvent was added and only dry mixing was performed, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics decreased compared to the Examples, while the amount of high-temperature gas generated increased.

[0316] Figures 5 to 9These are scanning electron microscope (SEM) images of the positive electrode active materials of Examples 1, 2, 8, 10 and Comparative Example 8.

[0317] See Tables 1 to 4 and Figure 5 , Figure 6 and Figure 9 Within a relative standard deviation of less than 10.5% but with a minimum particle size (D) 最小 In Comparative Examples 7 and 8, where the particle size was less than 1 μm, the initial discharge capacity, high-temperature capacity retention rate, and high-temperature storage characteristics decreased compared to Example 1, which was pulverized in the same manner, and the amount of high-temperature gas generated increased.

[0318] See Tables 1 to 4 and Figure 7 and Figure 8 Depending on the amount of solvent added, the formation of small-diameter particles and sulfur compound aggregates can be suppressed, while a lithium-sulfur-metal portion can be formed uniformly.

[0319] Figures 10 to 12 The images are quantitative maps of the positive electrode active materials of Example 2, Comparative Example 3, and Comparative Example 6, obtained by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS).

[0320] See Tables 1 to 4 and Figures 10 to 12 In Comparative Example 3, which used an aqueous solution of sulfur compound instead of sulfur compound powder, and in Comparative Example 6, which did not add solvent, an uneven lithium-sulfur-metal content was formed compared to Example 2.

Claims

1. A positive electrode active material for lithium secondary batteries, said positive electrode active material comprising lithium-transition metal oxide particles, said lithium-transition metal oxide particles comprising a lithium-sulfur-metal portion and having a minimum particle size D 最小 More than 1μm The relative standard deviation of the sulfur signal value of the lithium-transition metal oxide particles measured repeatedly 10 times by X-ray photoelectron spectroscopy (XPS) was less than 10.5%.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The positive electrode active material comprises a plurality of the lithium-transition metal oxide particles, and the X-ray photoelectron spectroscopy (XPS) analysis is performed on a square region with a width of 0.9 mm and a length of 0.9 mm filled with the plurality of lithium-transition metal oxide particles.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The relative standard deviation is 4.5% to 9.0%.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-sulfur-metal portion comprises at least one selected from Al, Ti, Zr, W, Sr, Ba, Ta, Nb, Mo, K, B, and Na.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The lithium-transition metal oxide particles comprise secondary particles formed by the aggregation of multiple primary particles, with the lithium-sulfur-metal portion located between the primary particles or on the surface of the secondary particles.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The sulfur content of the lithium-transition metal oxide particles is between 3,000 ppm and 6,000 ppm relative to the total weight of the lithium-transition metal oxide particles.

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The minimum particle size D of the lithium-transition metal oxide particles 最小 The range is from 2.1 μm to 2.7 μm.

8. A lithium secondary battery, comprising: The positive electrode comprises the positive electrode active material for lithium secondary batteries as described in claim 1; as well as The negative electrode is positioned opposite to the positive electrode.

9. A method for preparing a positive electrode active material for lithium secondary batteries, comprising the following steps: Prepare the first primary lithium-transition metal oxide particles; The first primary lithium-transition metal oxide particles, metal oxides, and sulfur compounds are dry-mixed to form a mixture; A solvent was added to the mixture and dried to prepare second primary lithium-transition metal oxide particles; as well as The second primary lithium-transition metal oxide particles are calcined at a temperature higher than the stated drying temperature to prepare lithium-transition metal oxide particles, the lithium-transition metal oxide particles comprising a lithium-sulfur-metal fraction and having a minimum particle size D. 最小 More than 1μm The relative standard deviation of the sulfur signal value of the lithium-transition metal oxide particles measured repeatedly 10 times by X-ray photoelectron spectroscopy (XPS) was less than 10.5%.

10. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The metal oxide comprises a subset selected from Al₂O₃, TiO₂, Ti₂O₃, ZrO₂, H₃BO₃, B₂O₃, SrO₂, SrAl₂O₄, SrTiO₃, SrWO₄, BaO, WO₃, and (NH₄). 10 H2(W2O7)6, MgO, Ta2O5, Nb2O5, MoO3, H4[W 12 SiO 40 At least one of H4SiO4·12MoO3 and (NH4)2MoO4.

11. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The sulfur compound comprises at least one selected from (NH4)2SO4, HSO3NH2, NH4SO3NH2, Al2(SO4)3, AlK(SO4)2, Al(NH4)(SO4)2, Ti(SO4)2, TiOSO4 and SrSO4.

12. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The sulfur content of the sulfur compound is between 2000 ppm and 4000 ppm relative to the total weight of the mixture.

13. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The solvent content is from 2% to 11% by weight relative to the total weight of the mixture.

14. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The drying temperature is between 110°C and 240°C.

15. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The calcination is carried out at 300°C to 500°C.

16. The method for preparing the positive electrode active material for lithium secondary batteries according to claim 9, wherein, The preparation method further includes a step of pulverizing the mixture after drying and before calcination.

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