Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

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

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on 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, and all the contents disclosed in the literature of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a manganese - rich cathode active material that achieves a lifespan improvement effect by adjusting the content of S - based impurities present on the surface, a method for manufacturing the same, a cathode including the cathode active material, and a lithium secondary battery.

Background Art

[0003] Since the commercialization in 1991, lithium secondary batteries have been energy storage media applied in various fields. As the market for products equipped with lithium secondary batteries expands, research for increasing the energy density of lithium secondary batteries has been actively conducted. One of the most notable methods is to develop a cathode active material with a composition that can utilize a larger amount of lithium than before.

[0004] [[ID=2I]] As a cathode active material that can utilize more lithium, a lithium - rich transition metal oxide having a layered structure and a molar ratio of lithium to transition metal exceeding 1 has been developed. Such a lithium - rich transition metal oxide can achieve high capacity by utilizing not only the cation redox reaction of transition metals but also the anion redox reaction using oxygen in the cathode structure. Currently, as a representative lithium - rich transition metal oxide that is actively studied, there is a lithium - rich manganese - based oxide (hereinafter referred to as Mn - rich lithium - rich manganese - based oxide) in which the molar ratio of lithium to transition metal exceeds 1 and the content of manganese among all transition metals exceeds 50 mol%.

[0005] However, in the case of Mn-rich lithium-excess manganese-based oxides, due to their low rate characteristics, that is, high resistance characteristics, they are mainly manufactured in the form of secondary particles in which primary particles are aggregated in order to shorten the migration distance of lithium and reduce the diffusion resistance. However, when the firing temperature is increased to improve the structural stability, the size of the primary particles increases and the resistance cannot be improved. Therefore, there is a need for a technique to increase the degree of structural completion while preventing the size of the primary particles from exceeding a certain level.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention provides a positive electrode active material and a method for manufacturing the same, which regulate the residual amount of S-based impurities on the surface to be a certain level or more during the synthesis of the positive electrode active material, so as to increase the degree of structural completion while preventing the size of the primary particles from becoming excessively large.

Means for Solving the Problems

[0008] According to one embodiment, the present invention includes a lithium-excess manganese-based oxide represented by the following Chemical Formula 1, and provides a positive electrode active material in which the sulfur content is 4,000 ppm or more based on the total weight of the positive electrode active material.

[0009] [Chemical Formula 1] Li 1+a [Mn 1-(a+b+c) Ni b M c O2 In the above Chemical Formula 1, M is one or more elements selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. 0.1 ≤ a ≤ 0.5, 0 ≤ b < 0.5, 0 ≤ c ≤ 0.1, and 0 ≤ a + b + c ≤ 0.5.

[0010] According to other embodiments, the present invention is A manufacturing method for producing the aforementioned positive electrode active material, The process involves supplying a transition metal-containing solution containing nickel and manganese sulfates or sulfides, an ammonium cation complex-forming agent, and a basic compound to a reactor and causing a coprecipitation reaction to form precursor particles for the positive electrode active material. The steps include: washing the aforementioned cathode active material precursor particles with water to produce a cathode active material precursor; The present invention provides a manufacturing method comprising the steps of mixing the positive electrode active material precursor with a lithium raw material and firing it at 800°C to 950°C.

[0011] According to further embodiments, the present invention provides a positive electrode for a lithium secondary battery containing the aforementioned positive electrode active material.

[0012] In further embodiments, the present invention provides a lithium secondary battery comprising the aforementioned positive electrode, a negative electrode containing a negative electrode active material, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0013] The present invention provides a method for producing a cathode active material containing a Mn-rich perlithium manganese oxide with low rate characteristics, which allows for increased structural stability while suppressing excessive growth of primary particles by adjusting the content of sulfur-based impurities without any additional steps.

[0014] The positive electrode active material produced in this way has the advantage of excellent resistance and capacitance characteristics because lithium travels a short distance and has low diffusion resistance. [Brief explanation of the drawing]

[0015] [Figure 1] These are photographs of the positive electrode active material particles produced in Example 1 and Comparative Example 1, observed at a magnification of 50k using a scanning electron microscope (SEM). [Figure 2] These are photographs of the positive electrode active material particles produced in Example 1 and Comparative Example 1, observed at a magnification of 20k using a scanning electron microscope (SEM). [Figure 3] These are photographs of the positive electrode active material particles produced in Example 1 and Comparative Example 1, observed at a magnification of 5k using a scanning electron microscope (SEM). [Figure 4] These are photographs of the positive electrode active material particles produced in Comparative Example 2, observed using a scanning electron microscope (SEM) at magnifications of 5k, 20k, and 50k, respectively. [Modes for carrying out the invention]

[0016] The present invention will be described in more detail below.

[0017] Cathode active materials containing Mn-rich perlithium manganese oxides, which have a manganese content of over 50 mol% of all metals excluding lithium, have the advantage of not only having a higher energy density than currently commercially available lithium nickel cobalt manganese (NCM) active materials, but also being able to reduce the amount of expensive cobalt used, thus saving on manufacturing costs.

[0018] However, Mn-rich cathode materials have the disadvantage of high resistance and poor rate characteristics because the oxidation / reduction reactions of oxygen ions and Mn ions occur relatively slowly. Therefore, improvements to these characteristics are essential for the commercialization of lithium secondary batteries using Mn-rich cathode materials.

[0019] Therefore, the inventors confirmed that when manufacturing a positive electrode active material containing a Mn-rich perlithium manganese oxide, by performing water washing with only water that does not contain any other flux substances during the precursor washing process, the residual sulfur content can be adjusted to 4,000 ppm or more relative to the total weight of the positive electrode active material. This has allowed for an improvement in the structural completeness of the positive electrode active material while reducing its resistance characteristics.

[0020] Specifically, when manufacturing the positive electrode active material, increasing the heat treatment temperature during the mixing and heat treatment stages of the positive electrode active material precursor and lithium raw material can improve particle crystallinity and the degree of firing completion. However, in the case of perlithium manganese oxides, a problem arises where the size of the primary particles increases and resistance increases due to high heat treatment temperatures. At this time, if the sulfur content in the positive electrode active material is 4,000 ppm or more, it hinders the growth process of the primary particles, so excessive growth of primary particles can be prevented by heat treatment at high temperatures.

[0021] In other words, by increasing the firing temperature, the growth of primary particles can be prevented while ensuring a certain minimum crystal size. This maintains the morphology of secondary particles formed from aggregated primary particles, shortening the distance lithium ions travel and reducing diffusion resistance.

[0022] In the present invention, the sulfur can exist in the form of, for example, a metallic sulfite (MeSO4), and the sulfur content refers only to the content of element S.

[0023] In this invention, "sulfur content" refers to the sulfur element content in the positive electrode active material obtained by ICP (inductively coupled plasma) analysis. Specifically, it refers to the result of 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 it with 50 mL of ultrapure water, and then analyzing it using an ICP-OES (PERKIN-ELMER, Optima 7300DV) instrument.

[0024] In this invention, "primary particle" refers to a particle unit that, when observed with a scanning electron microscope at a field of view of 5,000x to 20,000x, does not appear to have a grain boundary, and "secondary particle" refers to a particle formed by the aggregation of multiple primary particles.

[0025] 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 from scanning electron microscope images. In this case, particle size refers to the diameter of the longest axis of the primary particle.

[0026] In the present invention, "D 50 "50% of the volume cumulative particle size distribution of the particle powder" refers to the particle size corresponding to 50% of the volume cumulative particle size distribution, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac's S-3500), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. The particle size at the point where the volume cumulative amount reaches 50% in the obtained volume cumulative particle size distribution graph can then be determined.

[0027] In this invention, "crystallite" refers to a particle unit having substantially the same crystal orientation, which can be confirmed by EBSD (Electron Backscatter Diffraction) analysis. Specifically, it refers to the smallest particle unit that is displayed in the same color in an IPF (Inverse Pole Figure) map obtained by EBSD analysis of a cross-section of a positive electrode active material cut by ion milling.

[0028] On the other hand, in this invention, the "average crystallite size" can be quantitatively analyzed using X-ray diffraction analysis (XRD) with CuKα X-rays. Specifically, the average crystal size of the crystal grains can be quantitatively analyzed by placing the particles to be measured in a holder, irradiating the particles with X-rays, and analyzing the resulting diffraction pattern. For sampling, a powder sample of the particles to be measured is placed in the central groove of a general powder holder, the surface is made uniform using a glass slide, and the height of the sample is made equal to the periphery of the holder. Then, using a Bruker D8 Endeavor (light source: CuKα, λ=1.54Å) equipped with a LynxEye XE-T position-sensitive detector, X-ray diffraction analysis is performed in the region of FDS 0.5°, 2θ=15°~90°, with a step size of 0.02 degrees and a total scan time of approximately 20 minutes. Rietveld refinement is performed on the measured data, taking into account the charge at each site (metal ions at transition metal sites are +3, and Ni ions at Li sites are +2) and cation mixing. When analyzing grain size, instrumental brodadening is considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and all peaks within the measurement range are used during fitting. For peak shape fitting, only the Lorenzian contribution to the First Principal (FP) peak type available in TOPAS is used, and strain is not considered at this time.

[0029] In this invention, the "BET specific surface area" is calculated using the BET (Brunauer-Emmett-Teller) multipoint method from nitrogen adsorption isotherms obtained under a 77K liquid nitrogen atmosphere using BELSORP-MAX (MicrotracBEL corp.).

[0030] positive electrode active material The positive electrode active material according to the present invention contains a lithium-rich manganese-based oxide represented by the following chemical formula 1, and the sulfur content is 4,000 ppm or more, preferably 4,000 ppm to 8,000 ppm, more preferably 5,000 ppm to 7,000 ppm based on the total weight of the positive electrode active material.

[0031] [Chemical formula 1] Li 1+a [Mn 1-(a+b+c) Ni b M c O2 In the above chemical formula 1, M is any one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, 0.1 ≦ a ≦ 0.5, 0 ≦ b < 0.5, 0 ≦ c ≦ 0.1, 0 ≦ a + b + c ≦ 0.5.

[0032] As described above, however, when the sulfur content in the positive electrode active material is 4,000 ppm or more, excessive growth of primary particles can be prevented even by heat treatment at a high temperature. However, when the sulfur content becomes excessively high, the problem of capacity reduction due to an increase in the ratio of impurities may become serious. Therefore, it is necessary to adjust the sulfur content in consideration of this point.

[0033] On the other hand, in the above chemical formula 1, a is the molar ratio of Li in the lithium-rich manganese-based oxide, and 0.1 ≦ a ≦ 0.5, 0.1 ≦ a ≦ 0.4, or 0.12 ≦ a ≦ 1.17 may also be satisfied. When a satisfies the above range, high capacity can be realized.

[0034] b is the molar ratio of Ni in the lithium-rich manganese-based oxide, and 0 ≦ b < 0.5, 0.1 ≦ b ≦ 0.4, or 0.25 ≦ b ≦ 0.35 may also be satisfied.

[0035] The aforementioned c is the molar ratio of the doping element M in the perlithium manganese oxide, and may be 0 ≤ c ≤ 0.1, 0 ≤ c ≤ 0.05, or 0 ≤ c ≤ 0.01. The doping element M is preferably Co, and if the doping element content is excessively high, it may not only adversely affect the capacity of the active material, but also worsen gas generation and degradation of the positive electrode active material due to increased oxygen-oxidation-reduction reactions, potentially leading to a decrease in lifetime characteristics.

[0036] The above 1-(a+b+c) is the molar ratio of Mn in the perlithium manganese oxide, and may be 0≦a+b+c≦0.5, 0≦a+b+c<0.5, or 0.35≦a+b+c≦0.45. When a+b+c is greater than 0.5, that is, when 1-(a+b+c) is less than 0.5, the proportion of the rock salt structural phase becomes excessively small, and the improvement effect on structural stability is minimal.

[0037] Preferably, in the above chemical formula 1, 0.1≦a≦0.4, 0.1≦b≦0.4, 0≦c≦0.05, and 0≦a+b+c<0.5 may also be true, and more preferably, 0.12≦a≦0.17, 0.25≦b≦0.35, 0≦c≦0.01, and 0.35≦a+b+c≦0.45 may also be true.

[0038] On the other hand, in the perlithium manganese oxide represented by chemical formula 1, the ratio of moles of Li to moles of all metal elements excluding Li (Li / Me) may 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 satisfies the above range, the rate characteristics and capacity characteristics are excellent. If the Li / Me ratio is excessively high, the electrical conductivity decreases, the rock salt structure phase (Li2MnO3) increases, and the degeneration rate accelerates; if it is excessively low, the effect of improving energy density is slight.

[0039] On the other hand, in the case of perlithium manganese oxides containing an excess of lithium, the structure is a mixture of a layered phase (LiM'O2) and a rock salt phase (Li2MnO3), and the composition of the perlithium manganese oxide may be represented by the following chemical formula 2.

[0040] [Chemical formula 2] XLi2MnO3·(1-X)Li[Ni 1-y-z Mn y M z ]O2 In the aforementioned chemical formula 2, M is one or more elements selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. 0.1 ≤ X ≤ 0.5, 0.4 ≤ y < 1, and 0 ≤ z ≤ 0.2.

[0041] The above X represents the ratio of the Li2MnO3 phase in the perlithium manganese oxide, and the above y and z represent the molar ratios of Mn and doping element M on the LiM'O2 layer, respectively.

[0042] On the other hand, the positive electrode active material according to the present invention may further include a coating layer on the surface of the perlithium manganese oxide, if necessary. When the positive electrode active material includes a coating layer, the coating layer suppresses contact between the perlithium manganese oxide and the electrolyte, reducing side reactions of the electrolyte, thereby improving the lifespan characteristics.

[0043] The aforementioned coating layer contains coating element M 1 It may include the coating element M 1 For example, the coating element M may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Nb, Sn, Sr, and Zr, preferably Al, Co, Nb, W, and combinations thereof, and more preferably Al, Co, and combinations thereof. 1 It may contain two or more types, for example, Al and Co.

[0044] The aforementioned coating element exists in the coating layer in oxide form, i.e., M 1 It can exist within Oz (1 ≤ z ≤ 4).

[0045] The coating layer 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, atomic layer deposition is preferred because it allows for the formation of a large coating layer area.

[0046] The area of ​​the coating layer may be 10% to 100%, preferably 30% to 100%, and more preferably 50% to 100%, based on the total surface area of ​​the perlithium manganese oxide particles. When the area of ​​the coating layer satisfies the above range, it exhibits excellent improvement in lifespan characteristics.

[0047] On the other hand, the positive electrode active material according to the present invention may be in the form of secondary particles formed by the aggregation of multiple primary particles, and the average particle size of the primary particles may be 0.01 μm to 5 μm, preferably 0.01 μm to 2 μm, and more preferably 0.01 μm to 0.1 μm. In order to improve structural stability, firing at a certain temperature or higher is performed to increase the average particle size of the primary particles, but when the average particle size of the primary particles exceeds 5 μm, the diffusion resistance increases as the distance lithium travels increases, which is undesirable.

[0048] Furthermore, the D of the positive electrode active material 50 , in other words, the D of the secondary particle 50 The diameter may be 2 μm to 15 μm, preferably 2 μm to 13 μm, and more preferably 5 μm to 12 μm. D of the positive electrode active material 50 When the above range is satisfied, an excellent electrode density can be achieved, and the degradation of capacity and rate characteristics can be minimized.

[0049] Furthermore, the average crystallite size of the positive electrode active material may be 20 nm to 150 nm, preferably 20 nm to 100 nm, and more preferably 60 nm to 100 nm. From the standpoint of enhancing crystallinity, a larger average crystallite size is preferable, but when considering the resulting increase in resistance, it is preferable that it does not exceed 150 nm.

[0050] Furthermore, the BET specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g~10m 2 / g, specifically 1m 2 / g~6m 2 / g, more specifically 1.2m 2 / g~3m 2 It may also be / g. If the BET specific surface area of ​​the positive electrode active material is excessively low, the reaction area with the electrolyte will be insufficient, making it difficult to achieve sufficient capacity. If the specific surface area is excessively high, moisture absorption will be rapid, accelerating side reactions with the electrolyte and making it difficult to ensure lifespan characteristics.

[0051] Method for manufacturing positive electrode active material The method for producing a positive electrode active material according to the present invention includes the steps of: supplying a transition metal-containing solution containing nickel and manganese sulfate or sulfide, an ammonium cation complex-forming agent, and a basic compound to a reactor and causing a coprecipitation reaction to form precursor particles for the positive electrode active material; washing the precursor particles with water to produce a precursor for the positive electrode active material; and mixing the precursor for the positive electrode active material with a lithium raw material and calcining at 800°C to 950°C.

[0052] The step of forming the precursor particles for the positive electrode active material can be carried out, for example, by dissolving each transition metal-containing raw material in a solvent to produce a transition metal-containing solution, then mixing the transition metal-containing solution, an ammonium cation complex-forming agent, and a basic compound, and then proceeding with a coprecipitation reaction. Furthermore, if necessary, an oxidizing agent or oxygen gas can be added during the coprecipitation reaction.

[0053] On the other hand, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halide, or sulfide of each transition metal. However, the transition metal-containing solution of the present invention contains sulfates or sulfides of nickel and manganese. Specifically, the transition metal-containing raw material may 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., and the transition metal-containing solution contains at least one selected from the group consisting of NiSO4, NiSO4·6H2O, nickel sulfide, MnSO4·H2O, and manganese sulfide.

[0054] The ammonium cation complex-forming agent may be at least one selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3.

[0055] The basic compound may be at least one selected from the group consisting of NaOH, Na2CO3, KOH, and Ca(OH)2. The form of the precursor may change depending on the type of basic compound used. For example, when NaOH is used as the basic compound, a hydroxide-form precursor can be obtained, and when Na2CO3 is used as the basic compound, a carbonate-form precursor can be obtained. Also, when a basic compound and an oxidizing agent are used together, an oxide-form precursor can be obtained.

[0056] On the other hand, the precursor for the positive electrode active material may be in the form of a hydroxide, oxide, or carbonate.

[0057] In one embodiment of the present invention, the step of washing the cathode active material precursor particles with water may be carried out using ultrapure water (deionized water), and it is preferable that no substances other than water are added during washing. In a typical precursor washing step, a flux substance such as NaOH is used, but in this case, it is difficult for the sulfur content to remain above 4,000 ppm.

[0058] Specifically, the washing is preferably carried out by stirring the precursor particles at a temperature of 20°C to 30°C, with a weight ratio of precursor to water of 2:1 to 10:1, for 10 minutes at 1,000 rpm to 3,000 rpm. After washing, the particles may be filtered and dried by exposing them to a temperature of 100°C to 150°C for 5 to 15 hours.

[0059] On the other hand, examples of lithium raw materials include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), chlorides (e.g., lithium chloride (LiCl)), etc.), and one of these alone or a mixture of two or more can be used.

[0060] On the other hand, the cathode active material precursor and the lithium raw material may be mixed in an amount such that the molar ratio of all transition metals (Ni+Co+Mn):Li is 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.

[0061] On the other hand, the firing may 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 firing temperature is 800°C or higher, the structural completeness can be improved, but it is preferable not to exceed 950°C in order to prevent excessive growth of primary particles. The firing time may be 5 hours to 20 hours, preferably 10 hours to 15 hours. The firing atmosphere may be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing 20 to 100% by volume of oxygen.

[0062] Generally, when manufacturing a positive electrode active material containing a Mn-rich perlithium manganese oxide, raising the calcination temperature to 800°C or higher can lead to a problem where the primary particle size becomes excessively large, resulting in increased resistance. However, as in the present invention, this problem can be prevented if 4,000 ppm or more of sulfur remains on the surface.

[0063] Positive electrode and lithium secondary battery The positive electrode according to the present invention includes the positive electrode active material, and the lithium secondary battery according to the present invention includes the positive electrode, a negative electrode containing the negative electrode active material, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte.

[0064] The positive electrode and lithium secondary battery containing the same according to the present invention can be manufactured by conventional methods for manufacturing positive electrodes and lithium secondary batteries in the industry, except that the positive electrode active material described above is used.

[0065] For example, a lithium secondary battery can be manufactured by sequentially stacking and drying an electrode assembly with a separator membrane interposed between a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, inserting this assembly into a case, and then injecting an electrolyte and sealing it. The lithium secondary battery may be cylindrical, prismatic, coin-type, or pouch-type battery.

[0066] The positive electrode and the negative electrode can each be manufactured by applying an active material layer-forming composition containing electrode active material onto a current collector, and then drying it.

[0067] The composition for forming the positive electrode active material layer may optionally further contain, in addition to the positive electrode active material, a binder, a conductive material, a filler, and the like. The composition for forming the negative electrode active material layer may optionally further contain, in addition to the negative electrode active material, a binder, a conductive material, a filler, and the like.

[0068] The current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, the current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0069] In addition to the above-described positive electrode active material, the positive electrode can further contain a normal positive electrode active material. For example, 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). It can further contain any one or more positive electrode active materials selected from the group consisting of), but preferably, only the above positive electrode active material can be used alone.

[0070] The positive electrode active material may be contained in an amount of 80% to 99% by weight based on the total weight of the positive electrode active material layer.

[0071] In one embodiment of the present invention, the negative electrode can contain, as a negative electrode active material, any one or more selected from the group consisting of carbon-based materials; silicon-based materials; metals, or alloys of these metals and lithium; metal composite oxides; materials capable of doping and de-doping lithium; lithium metal; and transition metal oxides. Preferably, it can contain a carbon-based material, a silicon-based material, or a mixture thereof.

[0072] As the carbonaceous material, any carbonaceous negative electrode active material generally used in a lithium secondary battery can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0073] The silicon-based material is Si, SiO x (0 < x < 2) and Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si). It is preferably SiO. The silicon-based negative electrode active material has a capacity nearly about 10 times higher than that of graphite and can reduce the mass loading (mg·cm -2 ) to improve the rapid charging performance of the battery.

[0074] As the metal or an alloy of these metals and lithium, a metal selected from the group consisting of 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 these metals and lithium can be used.

[0075] Examples of the metal composite oxide include 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(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), one or more selected from the group consisting thereof can be used.

[0076] Examples of the substance capable of doping and undoping lithium include Sn, SnO2, Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. Also, at least one of these and SiO2 may be mixed and used.

[0077] In the Si - Y and Sn - Y, the element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, 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.

[0078] Examples of the transition metal oxide include lithium - containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0079] The negative electrode active material may be contained in an amount of 80% to 99% by weight based on the total weight of the solid content in the negative electrode slurry.

[0080] The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1% to 10% by weight based on the total weight of the active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0081] The conductive material is a component for further improving the conductivity of the active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, based on the total weight of the active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0082] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any membrane used as a separation membrane in a lithium secondary battery can be used without special limitations, and it is particularly preferable that it has low resistance to ion movement in the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and they can be selectively used in single-layer or multi-layer structures.

[0083] Furthermore, the electrolytes mentioned above include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0084] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0085] The organic solvent can be any solvent that serves as a medium through which ions involved in the electrochemical reaction of the battery can move, without any special restrictions. Specifically, the organic solvents include 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0086] The lithium salt can be used without any special restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, as the anion of the lithium salt, 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 - The lithium salt may be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0087] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0088] The present invention will be described in more detail below through specific examples.

[0089] [Example: Production of positive electrode active 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. Then, 100 mL of a 28 wt% aqueous ammonia solution was added. Subsequently, a transition metal solution (NiSO4 and MnSO4 mixed in a nickel:manganese molar ratio of 35:65), aqueous ammonia solution, and sodium hydroxide solution were added to the coprecipitation reactor, and a coprecipitation reaction was carried out to form a precursor. The precursor particles were separated and washed with water at 25°C with a weight ratio of precursor to ultrapure water of 5:1, stirring at 2,000 rpm for 10 minutes. The precursor was then dried in an oven at 130°C to produce the final precursor.

[0090] The precursor synthesized by the coprecipitation reaction and LiOH are mixed so that the transition metal:Li molar ratio is 1:1.3, and the mixture is heat-treated at 900°C for 15 hours under an oxygen atmosphere, and Li 1.13 Ni 0.31 Mn 0.56 A positive electrode active material having an O2 composition was manufactured. The manufactured positive electrode active material had an average primary particle size of 0.05 μm and secondary particles of D 50The surface area is 10 μm, the average crystallite size is 80 nm, and the BET specific surface area is 1.5 m². 2 It was / g.

[0091] Comparative Example 1. In Example 1, the positive electrode active material was produced in the same manner as in Example 1, except that a 1 M NaOH aqueous solution was used instead of ultrapure water during the washing of the precursor particles. The positive electrode active material produced in Comparative Example 1 had an average particle size of 0.2 μm for primary particles and a D for secondary particles. 50 The surface area is 10 μm, the average crystallite size is 80 nm, and the BET specific surface area is 1.0 m². 2 It was / g.

[0092] Comparative Example 2. In Example 1, the positive electrode active material was produced in the same manner as in Example 1, except that a 0.5 M NaOH aqueous solution was used instead of ultrapure water when washing the precursor particles. The positive electrode active material produced in Comparative Example 2 had an average particle size of 0.1 μm for primary particles and a D for secondary particles. 50 The surface area is 10 μm, the average crystallite size is 80 nm, and the BET specific surface area is 1.2 m². 2 It was / g.

[0093] Example 2. In Example 1, the coprecipitation reaction time of the precursor was determined by the time of the precipitated precursor. 50 The cathode active material was manufactured in the same manner as in Example 1, except that the value was controlled to a level of 3 μm, and the weight ratio of the precursor to ultrapure water during the washing of the precursor particles was changed from 5:1 to 2:1. The cathode active material manufactured in Example 2 had an average particle size of 0.05 μm for the primary particles and a secondary particle size of D 50 The surface area is 3 μm, the average crystallite size is 80 nm, and the BET specific surface area is 2.5 m². 2 It was / g.

[0094] Comparative Example 3. In Example 2, the positive electrode active material was produced in the same manner as in Example 2, except that a 0.5 M NaOH aqueous solution was used instead of ultrapure water when washing the precursor particles. The positive electrode active material produced in Comparative Example 3 had an average particle size of 0.1 μm for primary particles and a D for secondary particles. 50The surface area is 3 μm, the average crystallite size is 80 nm, and the BET specific surface area is 1.7 m². 2 It was / g.

[0095] Comparative Example 4. In Example 2, the positive electrode active material was produced in the same manner as in Example 2, except that a 1 M NaOH aqueous solution was used instead of ultrapure water when washing the precursor particles. The positive electrode active material produced in Comparative Example 4 had an average primary particle size of 0.2 μm and a secondary particle size of D 50 The surface area is 3 μm, the average crystallite size is 80 nm, and the BET specific surface area is 1.4 m². 2 It was / g.

[0096] [Example of experiment] Experimental Example 1. Measurement of S content in positive electrode active material 0.1 g of the positive electrode active material powder produced in Examples 1-2 and Comparative Examples 1-4 was mixed with 2 mL of distilled water and 1 mL of concentrated nitric acid, then diluted with 50 mL of ultrapure water. The sulfur element content was then measured using an ICP-OES (PERKIN-ELMER, Optima 7300DV) instrument, and the results are shown in Table 1 below.

[0097] [Table 1]

[0098] Experimental Example 2. SEM Analysis Figures 1 to 3 show photographs of the positive electrode active materials produced in Example 1 and Comparative Examples 1-2, observed at magnifications of 50k, 20k, and 5k using a scanning electron microscope (SEM).

[0099] Through the photographs, it can be confirmed that the positive electrode active material of Comparative Examples 1-2 consists of larger primary particles compared to the positive electrode active material of Example 1.

[0100] Experimental Example 3. Performance Evaluation of Coin Cells 1) Manufacturing of the positive electrode A positive electrode slurry with a solid content of 60% by weight was prepared by adding the positive electrode active material, conductive material (carbon black), and binder (polyvinylidene fluoride) from Example 1 to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 94:3:3. The positive electrode slurry was then applied to a 15 μm thick aluminum (Al) thin film, which served as the positive electrode current collector, to a thickness of 45 μm and dried. After this, a roll press was performed, resulting in a loading amount of 2.8 mAh / cm². 2 A positive electrode was manufactured. Using the same method, positive electrodes using the positive electrode active materials of Example 2 and Comparative Examples 1-4 were also manufactured, respectively.

[0101] 2) Coin cell manufacturing A negative electrode slurry with a solid content of 60% by weight was prepared by adding a negative electrode active material (graphite), a binder (SBR (styrene-butadiene rubber)-CMC (carboxymethylcellulose)), 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 then coated to a thickness of 67 μm onto a 10 μm thick copper (Cu) thin film, which served as a negative electrode current collector, and dried. After that, a roll press was performed to obtain a loading amount of 3.0 mAh / cm². 2 We manufactured the negative electrode.

[0102] For the positive electrodes of Examples 1-2 and Comparative Examples 1-4 manufactured in 1) above, an electrode assembly was fabricated by interposing a 15 μm thick polyethylene-based separation membrane between the positive and negative electrodes. This assembly was then placed inside a coin-type (2032 type) secondary battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. In this case, the electrolyte was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2, in which 1 M of LiPF6 was dissolved, and this electrolyte was injected to manufacture the lithium secondary battery.

[0103] 3) Lifespan evaluation Coin cells to which the positive electrode active materials of Examples 1-2 and Comparative Examples 1-4 were applied were formed at 45°C, and then charged at 25°C in CCCV (constant current constant voltage) mode at a rate of 0.5C until the voltage reached 4.4V. After this, discharge was performed at a constant current of 0.5C until the voltage reached 2.5V, and the initial discharge capacity and initial resistance were measured. The discharge capacity retention rate and resistance increase rate were measured while performing this charge-discharge cycle 50 times, and the results are shown in Table 2 below.

[0104] [Table 2]

[0105] As can be seen from the results in Table 2 above, the coin cell using the positive electrode active material of Example 1-2, which has a sulfur content of 4,000 ppm or more, shows improved values ​​in terms of initial capacity and initial resistance compared to the coin cell using the positive electrode active material of Comparative Example 1-4, which has a sulfur content of less than 4,000 ppm. This result demonstrates that even when the same firing temperature is applied, adjusting the sulfur content in the positive electrode active material improves crystallinity, suppresses the growth of primary particles, and prevents an increase in resistance. Furthermore, in terms of capacity retention rate and resistance increase rate after 50 cycles, the coin cell using the positive electrode active material of Example 1-2 shows superior performance compared to the coin cell using the positive electrode active material of Comparative Example 1-4. This is because the control of primary particles reduces stress during the repeated charge-discharge process, resulting in improved capacity and resistance changes as the cycle progresses.

Claims

1. A positive electrode active material containing a perlithium manganese oxide represented by the following chemical formula 1, The sulfur content of the positive electrode active material is 4,000 ppm or more based on the total weight of the positive electrode active material. [Chemical formula 1] Li １＋ａ [Mn １－（ａ＋ｂ＋ｃ） Ni ｂ M ｃ ]O ２ In the aforementioned chemical formula 1, M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr. A positive electrode active material such that 0.1 ≤ a ≤ 0.5, 0 ≤ b < 0.5, 0 ≤ c ≤ 0.1, and 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 of the positive electrode active material 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 of the positive electrode active material is 0.01 μm to 0.1 μm.

4. The D of the positive electrode active material ５０ The positive electrode active material according to claim 1, wherein the diameter is 2 μm to 15 μm.

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

6. The positive electrode active material according to claim 1, wherein in the 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 of the positive electrode active material is 4,000 ppm to 8,000 ppm based on the total weight of the positive electrode active material.

8. A method for producing the positive electrode active material described in claim 1, The process involves supplying a transition metal-containing solution containing nickel and manganese sulfates or sulfides, an ammonium cation complex-forming agent, and a basic compound to a reactor and causing a coprecipitation reaction to form precursor particles for the positive electrode active material. The steps include: washing the aforementioned cathode active material precursor particles with water to produce a cathode active material precursor; A manufacturing method comprising the steps of mixing the positive electrode active material precursor with a lithium raw material and firing at 800°C to 950°C.

9. The manufacturing method according to claim 8, wherein no substances other than water are added during the aforementioned washing.

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

11. The positive electrode described in claim 10, A negative electrode containing a negative electrode active material, A separation membrane interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

Images