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

Abstract

The present invention relates to a positive electrode active material, a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the same, the positive electrode active material comprising: a lithium-rich manganese-based oxide represented by chemical formula 1 wherein a sulfur content is 4,000 ppm or more based on the total weight of the positive electrode active material.

Description

Technical Field

[0001] Cross-references to related applications This application claims priority to Korean Patent Application No. 10-2023-0050981, filed on April 18, 2023, and Korean Patent Application No. 10-2024-0051382, filed on April 17, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0002] This invention relates to a manganese-rich positive electrode active material that improves lifespan by adjusting the content of S-type impurities present on the surface, its preparation method, and a positive electrode and a lithium secondary battery containing the positive electrode active material. Background Technology

[0003] Lithium-ion batteries are energy storage media that have been applied in various fields since their commercial introduction in 1991. With the expansion of the market for products equipped with lithium-ion batteries, research into improving their energy density has been actively pursued. One of the most promising approaches is the development of positive electrode active materials with compositions capable of utilizing significantly larger amounts of lithium than before.

[0004] As cathode active materials capable of utilizing larger amounts of lithium, lithium-rich transition metal oxides with a layered structure and a lithium-to-transition metal molar ratio greater than 1 have been developed. These lithium-rich transition metal oxides achieve high capacity because they utilize both the cation redox reaction of the transition metal and the anion redox reaction using oxygen in the cathode structure. Typical lithium-rich transition metal oxides currently under active research include lithium-rich manganese oxides (hereinafter referred to as Mn-rich and lithium-rich manganese oxides) where the lithium-to-transition metal molar ratio is greater than 1 and the manganese content in the total transition metal is greater than 50 mol%.

[0005] However, Mn- and lithium-rich manganese oxides exhibit low rate-of-use characteristics, i.e., high resistivity. Therefore, they are primarily manufactured as secondary particles (with primary particles mainly agglomerated) to reduce lithium migration distance and thus lower diffusion resistance. However, increasing the calcination temperature to improve structural stability leads to an increase in primary particle size, which does not improve resistivity. Therefore, a technique is needed to increase the calcination temperature without allowing the primary particle size to grow beyond a certain level, thereby enhancing structural integrity.

[0006] Existing technical documents Patent documents Korean Unexamined Patent Publication No. 2019-0052103 A Summary of the Invention

[0007] Technical issues One object of the present invention is to provide a positive electrode active material and a method for preparing the same, wherein the positive electrode active material is adjusted such that during the synthesis of the positive electrode active material, S-type impurities are maintained above a certain level on the surface, thereby enhancing structural integrity while preventing the size of primary particles from growing above a certain level.

[0008] Technical solution According to one embodiment of the present invention, a positive electrode active material is provided, the positive electrode active material comprising: Lithium-rich manganese oxides represented by the following chemical formula 1, Based on the total weight of the positive electrode active material, the sulfur content is above 4,000 ppm. [Chemical Formula 1] Li 1+a [Mn 1-(a+b+c) Ni b M c O2 In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤a≤0.5, 0≤b<0.5, 0≤c≤0.1, 0≤a+b+c≤0.5.

[0009] According to another embodiment of the present invention, a method for preparing the above-mentioned positive electrode active material is provided, the method comprising the following steps: Precursor particles for positive electrode active materials are formed by co-precipitating a solution containing transition metals such as nickel and manganese sulfates or sulfides, an ammonium cation complex forming agent, and an alkaline compound into a reactor. Precursors for positive electrode active materials are prepared by washing precursor particles with water; and The positive electrode active material precursor is mixed with lithium raw material, and the mixture is calcined at 800°C to 950°C.

[0010] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery is provided, the positive electrode for a lithium secondary battery comprising the above-mentioned positive electrode active material.

[0011] According to another embodiment of the present invention, a lithium secondary battery is provided, the lithium secondary battery comprising: The aforementioned positive electrode; A negative electrode, wherein the negative electrode contains a negative electrode active material; A diaphragm, wherein the diaphragm is located between the positive and negative electrodes; and Electrolytes.

[0012] Beneficial effects This invention provides a method for preparing a positive electrode active material, the positive electrode active material comprising a Mn-rich and lithium-rich manganese oxide with low rate capability, wherein the method can adjust the content of sulfur impurities without requiring a separate additional process, thereby enhancing structural stability and suppressing excessive growth of primary particles.

[0013] The advantage of positive electrode active materials prepared in this way is that they have excellent resistance and capacity characteristics, due to the short lithium migration distance and low diffusion resistance. Attached Figure Description

[0014] Figure 1 These are photographs of the positive electrode active material particles prepared in Example 1 and Comparative Example 1, observed by scanning electron microscopy (SEM) at a magnification of 50 k.

[0015] Figure 2 These are photographs of the positive electrode active material particles prepared in Example 1 and Comparative Example 1, observed by scanning electron microscopy (SEM) at a magnification of 20 k.

[0016] Figure 3 These are photographs of the positive electrode active material particles prepared in Example 1 and Comparative Example 1, observed by scanning electron microscopy (SEM) at a magnification of 5 k.

[0017] Figure 4 These are photographs of the positive electrode active material particles prepared in Comparative Example 2, observed by scanning electron microscopy (SEM) at magnifications of 5 k, 20 k, and 50 k, respectively. Detailed Implementation

[0018] The embodiments of the present invention will be described in detail below.

[0019] Compared with currently commercialized lithium nickel cobalt manganese (NCM) active materials, the advantages of positive electrode active materials containing Mn-rich and lithium-rich manganese oxides with a manganese content of more than 50 mol% in all metals except lithium are that they not only have high energy density, but also reduce the amount of expensive cobalt used, thereby reducing the preparation cost.

[0020] However, Mn-rich cathode materials suffer from high resistance and low rate capability because the oxidation / reduction reactions of oxygen and Mn ions proceed relatively slowly. Therefore, improvements are absolutely necessary to commercialize lithium-ion batteries using Mn-rich cathode materials.

[0021] In this regard, the inventors have confirmed that during the preparation of a positive electrode active material containing a manganese oxide rich in Mn and lithium, the precursor is washed with water that does not contain a separate co-solvent during the precursor washing process. This allows the residual sulfur content based on the total weight of the positive electrode active material to be adjusted to more than 4,000 ppm, thereby enhancing the structural integrity of the positive electrode active material while reducing its resistivity.

[0022] Specifically, during the preparation of cathode active materials, increasing the heat treatment temperature in the steps of mixing the precursor and lithium raw material leads to superior particle crystallinity and a higher degree of calcination completion. However, in the case of lithium-rich manganese oxides, a problem arises because the high heat treatment temperature increases the size of the primary particles, resulting in increased electrical resistance. In this case, if the sulfur content in the cathode active material is above 4,000 ppm, the growth process of the primary particles is hindered, thus preventing excessive growth of primary particles due to heat treatment at high temperatures.

[0023] In other words, by increasing the calcination temperature, the growth of primary particles can be prevented while ensuring that the crystal size is above a certain level. Therefore, while maintaining the secondary particle form of the aggregated primary particles, the migration distance of lithium ions is shortened, and diffusion resistance can be reduced.

[0024] In this invention, sulfur may exist, for example, in the form of metal sulfate (MeSO4), and the sulfur content refers only to the content of S element therein.

[0025] In this invention, "sulfur content" refers to the sulfur content in the positive electrode active material obtained by ICP analysis. Specifically, it means mixing 0.1 g of the positive electrode active material to be analyzed with 2 mL of distilled water and 1 mL of concentrated nitric acid, diluting with 50 mL of deionized water, and then analyzing it using an ICP-OES instrument (PerkinElmer, Optima 7300DV).

[0026] In this invention, "primary particles" refer to particles in which grain boundaries are not clearly present when observed using a scanning electron microscope in a field of view with a magnification of 5,000 to 20,000. "Secondary particles" are particles formed by the aggregation of multiple primary particles.

[0027] In this invention, "average particle size of primary particles" refers to the arithmetic mean calculated after measuring the particle sizes of at least 20 primary particles observed in a scanning electron microscope image. Here, particle size refers to the diameter of the longest axis of the primary particle.

[0028] In this invention, "D" 50"" refers to the particle size corresponding to 50% of the cumulative volume in the volumetric particle size distribution of the powder being measured, and can be measured using laser diffraction. For example, D 50 The following steps can be used to determine the particle size distribution: disperse the positive electrode active material powder in a dispersion medium, introduce the resulting dispersion into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), irradiate it with ultrasound at an output of 60 W at approximately 28 kHz to obtain a volumetric cumulative particle size distribution map, and then determine the particle size corresponding to 50% of the cumulative volume.

[0029] In this invention, "microcrystal" refers to particle units having substantially the same crystal orientation, which can be confirmed by EBSD (electron backscatter diffraction) analysis. Specifically, it is the smallest particle unit exhibiting the same color in the IPF pattern obtained by EBSD analysis of a cross-section of a positive electrode active material cut by ion milling.

[0030] On the other hand, in this invention, the "average crystallite size" can be quantitatively analyzed using X-ray diffraction (XRD) analysis with Cu Kα X-rays. Specifically, the average crystallite size can be quantitatively analyzed through the following steps: the particle to be measured is placed in a holder, the particle is irradiated with X-rays, and the resulting diffraction grating is analyzed. Sampling is performed through the following steps: a powder sample of the particle to be measured is placed in the central groove of a universal powder holder, the surface is smoothed using a glass slide, and the sample height is set to be equal to the edge of the holder. Then, X-ray diffraction analysis is performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54Å) equipped with a LynxEye XE-T position-sensitive detector at an FDS of 0.5°, a step size of 0.02° in the range of 2θ=15° to 90°, and a total scan time of approximately 20 minutes. The measurement data are Rietveld refined to take into account the charge at each site (metal +3 at transition metal sites, Ni +2 at Li sites) and cation mixing. In crystallite size analysis, the fundamental parameter method (FPA) implemented in the Bruker TOPAS program is used to account for instrument broadening, and all peaks within the measurement range are used in the fitting. Among the peak types available in TOPAS, only the Lorentz contribution to first-principles (FP) is used for peak shape fitting, in which case strain is not considered.

[0031] In this invention, the “BET specific surface area” is calculated using the BET (Brunauer-Emmett-Teller) multipoint method based on nitrogen adsorption isotherms obtained using BELSORP-MAX (MicrotracBEL Corp.) at 77 K in a liquid nitrogen atmosphere.

[0032] Positive electrode active material The positive electrode active material according to the present invention comprises: Lithium-rich manganese oxides represented by the following chemical formula 1, Based on the total weight of the positive electrode active material, the sulfur content can be 4,000 ppm or more, preferably 4,000 ppm to 8,000 ppm, and more preferably 5,000 ppm to 7,000 ppm. [Chemical Formula 1] Li 1+a [Mn 1-(a+b+c) Ni b M c O2 In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤a≤0.5, 0≤b<0.5, 0≤c≤0.1, 0≤a+b+c≤0.5.

[0033] As mentioned above, if the sulfur content in the positive electrode active material is above 4,000 ppm, excessive growth of primary particles can be prevented even during high-temperature heat treatment. However, if the sulfur content becomes too high, the capacity reduction problem due to the increased impurity ratio may become more severe, so this must be taken into account when adjusting the sulfur content.

[0034] On the other hand, in chemical formula 1, 'a' represents the molar ratio of Li in the lithium-rich manganese oxide, which can be 0.1 ≤ a ≤ 0.5, 0.1 ≤ a ≤ 0.4, or 0.12 ≤ a ≤ 1.17. When 'a' meets the above range, high capacity can be achieved.

[0035] b is the molar ratio of Ni in lithium-rich manganese oxides, which can be 0≤b<0.5, 0.1≤b≤0.4, or 0.25≤b≤0.35.

[0036] c is the molar ratio of dopant element M in lithium-rich manganese oxides, which can be 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.05, or 0 ≤ c ≤ 0.01. Dopant element M is preferably Co. If the content of the dopant element is too high, it may not only adversely affect the capacity of the active material, but may also increase the oxygen-oxidation-reduction reaction, which may exacerbate gas generation and degradation of the positive electrode active material, thereby reducing lifetime characteristics.

[0037] 1-(a+b+c) is the molar ratio of Mn in lithium-rich manganese oxides, which can be 0≤a+b+c≤0.5, 0≤a+b+c<0.5, or 0.35≤a+b+c≤0.45. If a+b+c is greater than 0.5, that is, 1-(a+b+c) is less than 0.5, the proportion of rock salt phase becomes too small, so the effect of improving structural stability is slight.

[0038] Preferably, in chemical formula 1, 0.1≤a≤0.4, 0.1≤b≤0.4, 0≤c≤0.05, 0≤a+b+c<0.5; more preferably, 0.12≤a≤0.17, 0.25≤b≤0.35, 0≤c≤0.01, 0.35≤a+b+c≤0.45.

[0039] On the other hand, in lithium-rich manganese oxides represented by Formula 1, the ratio of the molar number of Li to the molar number of all metal elements other than Li (Li / Me) can be 1.1 to 1.5, preferably 1.1 to 1.4, and more preferably 1.12 to 1.17. When the Li / Me ratio meets the above range, excellent rate performance and capacity characteristics can be exhibited. When the Li / Me ratio is too high, the conductivity may decrease, and the rock salt phase (Li₂MnO₃) may increase, which may increase the degradation rate. When the Li / Me ratio is too low, the effect on improving energy density is slight.

[0040] However, in the case of lithium-rich manganese oxides containing excessive lithium, it has a structure in which layered phases (LiM'O2) and rock salt phases (Li2MnO3) are mixed. The composition of lithium-rich manganese oxides can be represented by the following chemical formula 2.

[0041] [Chemical Formula 2] X Li2MnO3·(1-X)Li[Ni 1-y-z Mn y M z O2 In chemical formula 2, M can be at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤X≤0.5, 0.4≤y<1, 0≤z≤0.2.

[0042] X refers to the proportion of the Li2MnO3 phase in lithium-rich manganese oxides, while y and z refer to the molar ratio of Mn to dopant M in the LiM'O2 layer.

[0043] On the other hand, if desired, the positive electrode active material according to the invention may also include a coating on the surface of the lithium-rich manganese oxide. When the positive electrode active material includes a coating, the contact between the lithium-rich manganese oxide and the electrolyte is suppressed by the coating, and side reactions of the electrolyte are reduced, thereby achieving the effect of improved lifespan characteristics.

[0044] The coating may include coating element M 1 Coating element M 1 It can be, for example, at least one selected from Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, preferably Al, Co, Nb, W, and combinations thereof, more preferably Al, Co, and combinations thereof. Coating element M 1 It can contain more than two types, such as Al and Co.

[0045] The coating element can be in oxide form (i.e., M) 1 Oz (1≤z≤4) exists in the coating.

[0046] The coating can be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, forming the coating by atomic layer deposition is preferred because the coating can be formed with a wider area.

[0047] Based on the total surface area of ​​the lithium-rich manganese oxide particles, the coating formation area can be 10% to 100%, preferably 30% to 100%, and more preferably 50% to 100%. When the coating formation area meets the above range, the effect of improving lifetime characteristics is excellent.

[0048] On the other hand, the positive electrode active material according to the present invention can be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle size of the primary particles can be from 0.01 μm to 5 μm, preferably from 0.01 μm to 2 μm, and more preferably from 0.01 μm to 0.1 μm. In order to improve structural stability, the average particle size of the primary particles is increased while calcining at a certain temperature, but if the average particle size of the primary particles is greater than 5 μm, the diffusion resistance increases with the length of the lithium migration distance, which is not preferred.

[0049] In addition, the D of the positive electrode active material 50 That is, the D of secondary particles 50 The diameter can be from 2 μm to 15 μm, preferably from 2 μm to 13 μm, and more preferably from 5 μm to 12 μm. When the D of the positive electrode active material... 50 When the above range is met, excellent electrode density can be achieved, and the reduction in capacity and rate performance can be minimized.

[0050] Furthermore, the average crystallite size of the positive electrode active material can be from 20 nm to 150 nm, preferably from 20 nm to 100 nm, and more preferably from 60 nm to 100 nm. From the viewpoint of enhancing crystallinity, a large average crystallite size is preferred, but considering the resulting increase in resistance, an average crystallite size of no more than 150 nm is preferred.

[0051] Furthermore, the BET specific surface area of ​​the positive electrode active material can be 0.1 m². 2 / g to 10 m 2 / g, specifically 1 m 2 / g to 6m 2 / g, more specifically 1.2 m 2 / g to 3 m 2 / g. If the BET specific surface area of ​​the positive electrode active material is too low, the reaction area with the electrolyte is insufficient, making it difficult to achieve sufficient capacity. If the specific surface area is too high, rapid moisture absorption and accelerated side reactions with the electrolyte make it difficult to ensure lifetime characteristics.

[0052] Methods for preparing positive electrode active materials The method for preparing positive electrode active materials according to the present invention includes the following steps: Precursor particles for positive electrode active materials are formed by co-precipitating a solution containing transition metals such as nickel and manganese sulfates or sulfides, an ammonium cation complex forming agent, and an alkaline compound into a reactor. Precursors for positive electrode active materials are prepared by washing precursor particles with water; and The positive electrode active material precursor is mixed with lithium raw material, and the mixture is calcined at 800°C to 950°C.

[0053] In the step of forming precursor particles for the positive electrode active material, the precursor particles can be prepared, for example, by a method comprising: dissolving each transition metal-containing raw material in a solvent to prepare a transition metal-containing solution; mixing the transition metal-containing solution, an ammonium cation complexing agent, and a basic compound; and then subjecting the mixture to a co-precipitation reaction. Furthermore, if desired, an oxidant or oxygen can be added during the co-precipitation reaction.

[0054] On the other hand, the raw materials containing transition metals can be acetates, carbonates, nitrates, sulfates, halides, sulfides, etc., of various transition metals. However, the solution containing transition metals in this invention includes sulfates or sulfides of nickel and manganese. Specifically, the raw materials containing transition metals can be: NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel sulfide, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, manganese sulfide, etc. The solution containing transition metals includes at least one selected from NiSO4, NiSO4·6H2O, nickel sulfide, MnSO4·H2O, and manganese sulfide.

[0055] The ammonium cation complex forming agent can be at least one selected from NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4 and (NH4)2CO3.

[0056] The basic compound can be at least one selected from NaOH, Na₂CO₃, KOH, and Ca(OH)₂. The form of the precursor can vary depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a precursor in the form of a hydroxide can be obtained; when Na₂CO₃ is used as the basic compound, a precursor in the form of a carbonate can be obtained. Furthermore, when the basic compound is used in conjunction with an oxidizing agent, a precursor in the form of an oxide can be obtained.

[0057] On the other hand, the precursors for positive electrode active materials can be in the form of hydroxides, oxides, or carbonates.

[0058] In one embodiment of the invention, the step of washing the precursor particles of the positive electrode active material with water can be carried out using deionized water, and preferably no substances other than water are added during washing. In typical precursor washing steps, a co-solvent material such as NaOH is used, but in this case, the sulfur content is unlikely to remain above 4,000 ppm.

[0059] Specifically, the precursor particles are preferably washed at a temperature of 20°C to 30°C and stirred at 1,000 rpm to 3,000 rpm for 10 minutes to adjust the weight ratio of precursor to water to 2:1 to 10:1. After washing, the precursor particles can be dried by filtration and exposure to a temperature of 100°C to 150°C for 5 to 15 hours.

[0060] On the other hand, lithium raw materials can be mentioned, for example, lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH∙H2O) etc.), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3) etc.), chlorides (e.g., lithium chloride (LiCl) etc.), etc., wherein one type or a mixture of two or more types can be used alone.

[0061] On the other hand, the amount of precursor for positive electrode active material and lithium raw material can make the molar ratio of all transition metals (Ni+Co+Mn):Li 1:1.1 to 1:1.5, preferably 1:1.1 to 1:1.4, and more preferably 1:1.12 to 1:1.17.

[0062] On the other hand, calcination can be carried out at a temperature of 800°C to 950°C, preferably 850°C to 950°C, and more preferably 870°C to 920°C. When the calcination temperature is above 800°C, structural integrity can be improved, but it is preferable not to exceed 950°C, thereby preventing excessive growth of primary particles. The calcination time can be 5 to 20 hours, preferably 10 to 15 hours. Furthermore, the calcination atmosphere can be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100% by volume oxygen.

[0063] Typically, during the preparation of positive electrode active materials containing Mn-rich and lithium-rich manganese oxides, there is a problem of excessive increase in primary particle size and resistance when the calcination temperature is increased to above 800°C. However, as in this invention, this problem can be prevented when more than 4,000 ppm of sulfur is retained on the surface.

[0064] Positive electrode and lithium secondary battery The positive electrode according to the present invention comprises a positive electrode active material, and the lithium secondary battery according to the present invention comprises: positive electrode; A negative electrode, wherein the negative electrode contains a negative electrode active material; A diaphragm, wherein the diaphragm is located between the positive and negative electrodes; and Electrolytes.

[0065] In addition to using the aforementioned positive electrode active material, the positive electrode and the lithium secondary battery containing the present invention can be manufactured by conventional methods in the art for manufacturing positive electrodes and lithium secondary batteries.

[0066] For example, a lithium secondary battery can be manufactured by the following steps: inserting a separator between a positive electrode containing positive electrode active material and a negative electrode containing negative electrode active material; stacking and drying them sequentially to prepare an electrode assembly; inserting the electrode assembly into a casing; injecting electrolyte; and sealing the casing. Lithium secondary batteries can be cylindrical, prismatic, coin-shaped, or pouch-shaped.

[0067] The positive electrode and the negative electrode can be manufactured by the following steps: coating a composition for forming an active material layer containing an electrode active material onto a current collector, and then drying the coating.

[0068] If necessary, in addition to the positive electrode active material, the composition for forming the positive electrode active material layer may optionally further contain a binder, a conductive material, a filler, etc. If necessary, in addition to the negative electrode active material, the composition for forming the negative electrode active material layer may optionally further contain a binder, a conductive material, a filler, etc.

[0069] The current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the current collector usually has a thickness of 3 μm to 500 μm. In addition, the current collector may have fine concavities and convexities formed on its surface to enhance the adhesion of the active material. For example, the current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric structure.

[0070] In addition to the above positive electrode active material, the positive electrode may further contain typical positive electrode active materials. For example, it may also contain any one or more positive electrode active materials selected from LCO (LiCoO2), LNO (LiNiO2), LFP (LiFePO4), and NCM (Li[Ni p Co q Mn r1 O2, 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1), but preferably, only the above positive electrode active material can be used alone.

[0071] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80% by weight to 99% by weight.

[0072] In one embodiment of the present invention, the negative electrode may contain at least one of the following substances as the negative electrode active material: carbon-based materials; silicone-based materials; metals or alloys of lithium and metals; metal composite oxides; materials that can be doped with lithium and de-doped with lithium; lithium metal; and transition metal oxides. Preferably, it may contain carbon-based materials, silicon-based materials, or a mixture thereof.

[0073] As the carbonaceous material, any carbonaceous negative electrode active material commonly used in lithium secondary batteries can be used without particular limitation, and as typical examples, crystalline carbon, amorphous carbon, or both thereof can be used. Examples of crystalline carbon can include: graphite, such as irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include: soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0074] The silicon-based material is at least one selected from Si, SiO x (0 < x < 2) and Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), and SiO is preferred. The capacity of the silicon-based negative electrode active material is almost 10 times higher than that of graphite, and the mass loading (mg-cm -2 ) can be reduced, thereby improving the rapid charging performance of the battery.

[0075] As the metal or an alloy of lithium and a metal, a metal selected from Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or an alloy of lithium and a metal can be used.

[0076] As the metal composite oxide, one selected from PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0 ≤ x ≤ 1), Li x WO2(0 ≤ x ≤ 1), and Sn x Me 1-x Me’ y O z (where Me is Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group I, Group II, and Group III of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) can be used.

[0077] The material that can be doped with lithium and de-doped with lithium can include: Sn, SnO2, Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc., and at least one of these can be mixed and used with SiO2.

[0078] In Si-Y and Sn-Y, element Y can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db(𬭊), Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0079] Examples of transition metal oxides may include lithium-containing titanium oxide (LTO), vanadium oxides, lithium vanadium oxides, etc.

[0080] Based on the total weight of solids in the negative electrode slurry, the content of the negative electrode active material can be from 80% to 99% by weight.

[0081] The adhesive is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is added in an amount from 0.1% to 10% by weight based on the total weight of the active material layer. Examples of adhesives may include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0082] Conductive materials are components used to further improve the conductivity of active materials, and the amount added based on the total weight of the active material layers can be less than 10% by weight, specifically less than 5% by weight. Such conductive materials are not particularly limited, as long as they are conductive and do not cause chemical changes in the battery, and for example, the following can be used: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; conductive materials, such as polyphenylene derivatives, etc.

[0083] On the other hand, in lithium secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer are preferred. Specifically, porous polymer membranes can be used as separators, such as porous polymer membranes prepared from polyolefin polymers, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0084] In addition, the electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used to manufacture lithium secondary batteries.

[0085] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0086] Any organic solvent can be used without particular restriction, as long as it can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; sulfolane, etc. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity are even more preferred.

[0087] Lithium salts can be used without particular restrictions, as long as they can provide the lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F...- Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of the following can be used as a lithium salt: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Lithium salts can be used in concentrations ranging from 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent electrolyte performance, and lithium ions can move efficiently.

[0088] In addition to the electrolyte component, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte may also contain one or more additives, such as alkylene carbonate halide compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc. In this case, based on the total weight of the electrolyte, the content of the additives can be from 0.1 to 5% by weight.

[0089] The invention will be described in more detail below with reference to specific embodiments.

[0090] <Example: Preparation of Cathode Material> Example 1 Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and the temperature was maintained at 50 °C. 100 mL of a 28% by weight ammonia solution was added. Then, a transition metal solution containing NiSO4 and MnSO4 in a nickel:manganese molar ratio of 35:65, the ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor, and a coprecipitation reaction was carried out to form precursor particles. The precursor particles were separated, stirred at 2000 rpm for 10 minutes at 25 °C to adjust the precursor to deionized water weight ratio to 5:1, washed with water, and then dried in an oven at 130 °C to prepare the precursor.

[0091] The precursor synthesized via co-precipitation was mixed with LiOH to achieve a transition metal:Li molar ratio of 1:1.3, and the mixture was heat-treated at 900°C for 15 hours under an oxygen atmosphere to prepare a Li-based product. 1.13 Ni 0.31 Mn 0.56 The positive electrode active material for O2. The prepared positive electrode active material has an average particle size of 0.05 μm for primary particles and a D0.05 of 10 μm for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 1.5 m². 2 / g.

[0092] Comparative Example 1 The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, a 1 M NaOH aqueous solution was used instead of deionized water when washing the precursor particles. The positive electrode active material prepared in Comparative Example 1 had an average particle size of 0.2 μm for primary particles and a D0 of 10 μm for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 1.0 m². 2 / g.

[0093] Comparative Example 2 The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, a 0.5 M NaOH aqueous solution was used instead of deionized water when washing the precursor particles. The positive electrode active material prepared in Comparative Example 2 had an average particle size of 0.1 μm for primary particles and a D0.1 for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 1.2 m². 2 / g.

[0094] Example 2 The positive electrode active material was prepared in the same manner as in Example 1, except that, in Example 1, the level of the precursor co-precipitation reaction time was controlled to ensure that the D of the precipitated precursor was...50 The value was set at the 3 μm level, and the weight ratio of precursor to deionized water during washing of precursor particles was changed from 5:1 to 2:1. The positive electrode active material prepared in Example 2 had an average particle size of 0.05 μm for primary particles and a D0.05 for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 2.5 m². 2 / g.

[0095] Comparative Example 3 The positive electrode active material was prepared in the same manner as in Example 2, except that in Example 2, a 0.5 M NaOH aqueous solution was used instead of deionized water when washing the precursor particles. The positive electrode active material prepared in Comparative Example 3 had an average particle size of 0.1 μm for primary particles and a D0.05 of 3 μm for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 1.7 m². 2 / g.

[0096] Comparative Example 4 The positive electrode active material was prepared in the same manner as in Example 2, except that in Example 2, a 1 M NaOH aqueous solution was used instead of deionized water when washing the precursor particles. The positive electrode active material prepared in Comparative Example 4 had an average particle size of 0.2 μm for primary particles and a D0.05 of 3 μm for secondary particles. 50 The average crystallite size is 80 nm, and the BET specific surface area is 1.4 m². 2 / g.

[0097] [Experimental Example] Experimental Example 1. Measurement of S content in positive electrode active materials 0.1 g of the positive electrode active material powder prepared in Examples 1 to 2 and Comparative Examples 1 to 4 was mixed with 2 mL of distilled water and 1 mL of concentrated nitric acid, then diluted with 50 mL of deionized water, and the sulfur content was measured using an ICP-OES instrument (PerkinElmer, Optima 7300DV). The results are listed in Table 1 below.

[0098] [Table 1]

[0099] Experimental Example 2. SEM Analysis exist Figures 1 to 3 The image shows photographs of the positive electrode active materials prepared in Examples 1 and Comparative Examples 1 to 2, observed by scanning electron microscopy (SEM) at magnifications of 50 k, 20 k, and 5 k.

[0100] As can be seen from the photographs, the positive electrode active materials of Comparative Examples 1 and 2 are composed of larger primary particles compared to the positive electrode active material of Example 1.

[0101] Experiment Example 3: Evaluation of Coin Cell Performance 1) Manufacturing of the positive electrode The positive electrode active material, conductive material (carbon black), and binder (polyvinylidene fluoride) from Example 1 were added to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 94:3:3 to prepare a positive electrode slurry with a solid content of 60% by weight. The positive electrode slurry was coated onto a 15 μm thick aluminum (Al) film serving as the positive electrode current collector until a thickness of 45 μm was achieved. After drying, the film was calendered to produce a loading capacity of 2.8 mAh / cm². 2 The positive electrode was also fabricated using the positive electrode active materials of Examples 2 and Comparative Examples 1 to 4, respectively.

[0102] 2) Manufacturing of coin batteries A negative electrode slurry with a solid content of 60 wt% was prepared by adding a negative electrode active material (graphite), a binder (SBR-CMC), and a conductive material (carbon black) to water as a solvent in a weight ratio of 95:3.5:1.5. The negative electrode slurry was coated onto a 10 μm thick copper (Cu) film serving as the negative electrode current collector until a thickness of 67 μm was achieved. After drying, the film was calendered to produce a loading capacity of 3.0 mAh / cm². 2 The negative electrode.

[0103] For each of the positive electrodes of Examples 1 to 2 and Comparative Examples 1 to 4 manufactured in 1) above, a 15 μm thick polyethylene separator was inserted between the positive and negative electrodes to prepare an electrode assembly. The electrode assembly was then placed inside a coin-shaped (2032 type) secondary battery casing, and an electrolyte was injected into the casing to manufacture a lithium secondary battery. In this case, as the electrolyte, an electrolyte prepared by dissolving 1 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) at a volume ratio of 1:2 was injected to manufacture the lithium secondary battery.

[0104] 3) Life assessment A coin cell was formed at 45°C using the positive electrode active materials of Examples 1 to 2 and Comparative Examples 1 to 4. The coin cell was then charged to 4.4 V at 25°C in CCCV mode at a rate of 0.5 C. The coin cell was then discharged to 2.5 V at a constant current of 0.5 C to measure the initial discharge capacity and initial resistance. The discharge capacity retention rate and resistance increase rate were measured during 50 charge-discharge cycles, and the results are shown in Table 2 below.

[0105] [Table 2]

[0106] The results in Table 2 confirm that, compared to the coin batteries using the positive electrode active materials of Comparative Examples 1 to 4, where the sulfur content is less than 4,000 ppm, the coin batteries using the positive electrode active materials of Examples 1 to 2, where the sulfur content is 4,000 ppm or more, exhibit improved values ​​in terms of initial capacity and initial resistance. This result indicates that even when the same calcination temperature is applied, adjusting the sulfur content in the positive electrode active material improves crystallinity, suppresses primary particle growth, and prevents resistance increase. Furthermore, in terms of capacity retention and resistance increase rate after 50 cycles, the coin batteries using the positive electrode active materials of Examples 1 to 4 exhibit superior performance. This result indicates that as the primary particle size is controlled, stress during repeated charge-discharge processes is reduced, and the changes in capacity and resistance with cycling progress are improved.

Claims

1. A positive electrode active material, said positive electrode active material comprising: Lithium-rich manganese oxides represented by the following chemical formula 1, Based on the total weight of the positive electrode active material, the sulfur content is above 4,000 ppm. [Chemical Formula 1] Li 1+a [Mr 1-(a+b+c) Ni b M c ]O2 In chemical formula 1, M is selected from at least one of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.1≤a≤0.5, 0≤b<0.5, 0≤c≤0.1, 0≤a+b+c≤0.

5.

2. The positive electrode active material according to claim 1, wherein the average particle size of the primary particles is 0.01 μm to 5 μm.

3. The positive electrode active material according to claim 2, wherein the average particle size of the primary particles is 0.01 μm to 0.1 μm.

4. The positive electrode active material according to claim 1, wherein D 50 The range is from 2 μm to 15 μm.

5. The positive electrode active material according to claim 1, wherein the average crystallite size is from 20 nm to 150 nm.

6. The positive electrode active material according to claim 1, wherein in chemical formula 1, 0.1≤a≤0.4, 0.1≤b≤0.4, 0≤c≤0.05, and 0≤a+b+c<0.

5.

7. The positive electrode active material according to claim 1, wherein the sulfur content is from 4,000 ppm to 8,000 ppm based on the total weight of the positive electrode active material.

8. A method for preparing the positive electrode active material according to claim 1, the method comprising the following steps: Precursor particles for positive electrode active materials are formed by co-precipitating a solution containing transition metals such as nickel and manganese sulfates or sulfides, an ammonium cation complex forming agent, and an alkaline compound into a reactor. The precursor for the positive electrode active material is prepared by washing the precursor particles with water. and The positive electrode active material is mixed with a lithium raw material using a precursor, and the mixture is calcined at 800°C to 950°C.

9. The method for preparing a positive electrode active material according to claim 8, wherein no substances other than water are added during the washing process.

10. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 7.

11. A lithium secondary battery, the lithium secondary battery comprising: The positive electrode as described in claim 9; A negative electrode, wherein the negative electrode contains a negative electrode active material; A separator, the separator being located between the positive electrode and the negative electrode; and Electrolytes.

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