Positive electrode active material containing spinel complex solid solution oxide, method for producing the same, and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material containing a spinel complex solid solution oxide, a method for producing the same, and a lithium secondary battery containing the same. The spinel complex solid solution oxide is a lithium nickel oxide (Li z Ni 1-z O) is compounded with a low content, and a positive electrode active material containing the compound exhibits stable life characteristics and excellent output characteristics depending on the type and content of the doping element substituted for the transition metal, the synthesis temperature, and the amount of impurities generated.

Description

[Technical Field]

[0001] The present invention provides a positive electrode active material containing a high-voltage spinel complex solid solution oxide having a discharge voltage of 4.5 V or more, a method for producing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] Lithium secondary batteries have been used as power sources for numerous consumer devices since Sony first adopted them in 1991 as the power source for its camcorder cameras. Now, with the growing demand for new power sources, such as electric vehicles and power storage devices, the development of positive electrode active materials with higher energy density has become necessary.

[0003] The current development direction of high energy density cathode active materials being promoted in the battery industry can be divided into the development of nickel-rich (Ni-rich) high capacity cathode active materials (NCM622, NCM811) that contain more nickel, and the development of high voltage spinel cathode active materials that have a high discharge voltage of 4.5V or more.

[0004] Among the positive electrode materials known to date, the only high-voltage positive electrode materials that exhibit discharge characteristics of 4.5 V or higher are spinel structure compounds (LiM z Mn 2-x O4), an inverse spinel structure (LiNiVO4), and the polyanion material LiCoNiPO4. Although these high-voltage positive electrode materials have a smaller capacity than existing nickel-rich high-capacity positive electrode materials with a 4V rating, their high voltage not only enables high energy density to be achieved, but also allows for a reduction in the number of batteries connected in series when configuring power supplies requiring high voltage, such as electric vehicles and power storage devices, thereby dramatically reducing the production costs of battery packs.

[0005] Among these high-voltage positive electrode materials, research is focused on high-voltage spinel positive electrode active materials, which minimize plateau potential at 4V and exhibit high capacity at 5V. High-voltage spinel positive electrode active materials use manganese (Mn) as their primary component, and do not use cobalt (Co), which is sensitive in terms of cost and supply, while using nickel (Ni) in a limited amount. This makes them recognized as an environmentally friendly positive electrode material with low production costs. However, to commercialize this positive electrode material, it is necessary to address the lifespan degradation caused by the elution of Mn and Ni at high voltages of 4.5V and above. Furthermore, because the electrical conductivity of this positive electrode material is relatively lower than that of nickel-rich positive electrode materials, it is necessary to improve the material's structural stability and electrical conductivity by doping with other metals or optimizing the crystal structure.

[0006] High-voltage spinel cathode active materials have two types of crystal structures: an ordered primitive cubic close pack (P4332) structure in which all Mn ions are +4 valent and the transition metals nickel and manganese are located in octahedral sites in a regular 1:3 arrangement; and a disordered face-centered cubic (Fd-3m) structure in which Mn ions are mixed with +4 and +3 valent, Li occupies the 8a site, Ni and Mn are randomly located in the 16d site, and oxygen (O) occupies the 32e site. These two crystal structures appear with different occupancies due to differences in the manufacturing process of the spinel cathode active material or the doping process of different elements, and impurities (lithium nickel oxide, Li) generated during this process are also present. z Ni 1-z The concentration of 0 may change, and the full width at half maximum, lattice constant, and lattice volume may change. Such differences can have a significant impact on the life and output characteristics of the battery.

[0007] In general, the redox reaction potential of high-voltage spinel cathode active materials is +2 / N +4 The 4.7V discharge region caused by M +3 / M +4When the mole number of Ni is 0.5, theoretically only a 4.7V discharge region appears, but in reality, when oxygen deficiency occurs during the high-temperature firing process of this positive electrode material, the potential of some Mn changes from +4 to +3 in order to adjust the potential neutrality of the material, and in this process, an irregular reaction occurs, resulting in lithium nickel oxide (Li z Ni 1-z O) is produced and composited within the crystal (Reaction Scheme 1). It is also known that the solid solubility limit of nickel in high-voltage spinel positive electrode active materials is up to 0.5 moles, and if more nickel is added, the nickel exceeding the solid solubility limit is composited within the crystal in the form of lithium nickel oxide (Reaction Scheme 2).

[0008] [Reaction Scheme 1] LiNi 0.5 Mn 1.5 O4⇔qLi z Ni 1-z O+rLiNi 0.5-w Mn 1.5+w O4+sO2(at high T)

[0009] [Reaction Scheme 2] [Li + ][Ni 2+ ] x [Mn 3+ ] 1-2x [Mn 4+ ] 1+x [O 2 ]4⇒[Li + ] 2x [Ni 2+ ] x [Mn 4+ ] 2-x [O 2 ]4+(1-2x)Li + +(1-2x)e(at 4.1 V plateau) [Li + ] 2x [Ni 2+ ] x [Mn 4+ ] 2-x [O 2 ]4⇒[Ni 4+ ] x [Mn4+ ] 2-x [O 2 ]4+2xLi + +2xe(at 4.7 V plateau)

[0010] A regular cubic structure in which nickel and manganese are regularly arranged results in a slower lithium ion diffusion rate and lower electrical conductivity than a face-centered cubic structure in which nickel and manganese are relatively randomly arranged, resulting in inferior battery chemical performance. Furthermore, lithium nickel oxide itself is a nonconductor and does not participate in battery chemical reactions, which affects battery capacity and life characteristics. Therefore, high-voltage spinel cathode active materials need to have their electrochemical performance further improved through manufacturing process and structural control. Summary of the Invention [Problem to be solved by the invention]

[0011] When the synthesis temperature of a spinel cathode active material is increased to improve the crystallinity, oxygen deficiency problems increase and the concentration of lithium nickel oxide impurities increases, which can result in lifespan problems and reduced output.

[0012] An object of the present invention is to provide a positive electrode active material in which the crystallinity is improved by increasing the synthesis temperature of a spinel complex solid solution oxide, while the proportion of impurities is reduced.

[0013] Another object of the present invention is to provide a method for producing a positive electrode active material.

[0014] It is still another object of the present invention to provide a lithium secondary battery having a stable life and excellent high-power characteristics. [Means for solving the problem]

[0015] According to one embodiment of the present invention, a spinel complex solid solution oxide represented by the following formula 1 is included, and the spinel complex solid solution oxide has a lithium nickel oxide (Li ) content of 0.01% by weight relative to the total weight of the spinel complex solid solution oxide when Rietveld analysis is performed using an XRD spectrum.z Ni 1-z Provide a positive electrode active material with a weight of O, 0 < z ≤ 0.2) of 0 wt% to 2 wt%. [Chemical formula 1] Li 1+a Ni 1 / 2-x / 2 Mn 3 / 2-x / 2 M x O4 (In Chemical formula 1, M is any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb and combinations thereof, 0 ≤ a ≤ 0.1, and 0 < x ≤ 0.1)

[0016] The weight of lithium nickel oxide can be 0.01 wt% to 2 wt% based on the total weight of the spinel composite solid solution oxide.

[0017] May include a spinel composite solid solution oxide represented by the following Chemical formula 2. [Chemical formula 2] Li 1+a Ni 1 / 2-x / 2 Mn 3 / 2-x / 2 Ti x O4 (In Chemical formula 2, 0 ≤ a ≤ 0.1, and 0 < x ≤ 0.1)

[0018] In Chemical formula 1, 0.025 ≤ x ≤ 0.05 may be applicable.

[0019] The tap density of the spinel composite solid solution oxide is 1.2 g / cc to 2.2 g / cc, and the specific surface area can be 0.5 m 2 / g to 2.5 m 2 / g.

[0020] When the spinel composite solid solution oxide is subjected to Rietveld analysis in the XRD spectrum, the occupancy of the cube (P4332) in the crystal calculated by the following formula 1 is 0 to 0.1, the occupancy of the face-centered cube (Fd-3m) in the crystal calculated by the following formula 2 is 0.9 to 1, and the impurities (lithium nickel oxide, Li z Ni 1-zO) may be 0 to 0.02.

[0021] [Formula 1] Occupancy rate of a regular cube (P4332) = A P4332 / (A P4332 +A Fd-3m +Li z Ni 1-z O)

[0022] [Formula 2] Occupancy rate of face-centered cube (Fd-3m) = A Fd-3m / (A P4332 +A Fd-3m +Li z Ni 1-z O)

[0023] [Formula 3] Impurities (Li z Ni 1-z O) occupancy rate = Li z Ni 1-z O / (A P4332 +A Fd-3m +Li z Ni 1-z O)

[0024] (In Formulas 1 to 3, A P4332 is the weight percent of the regular cube (P4332), and A Fd-3m is the weight percent of face-centered cubic (Fd-3m), and Li z Ni 1-z O is an impurity (Li z Ni 1-z O) is the weight percent of

[0025] When Rietveld analysis is performed on the XRD spectrum of spinel complex solid solution oxide, the lattice constant a (Å) of the spinel structure may be greater than 8.1640 and less than 8.1900.

[0026] When the spinel complex solid solution oxide is subjected to Rietveld analysis in an XRD spectrum, the full width at half maximum (FWHM) may satisfy the following Equation 4.

[0027] [Formula 4] 0.01≦FWHM(deg)≦0.20((hkl)=(111), 2θ=18-20), 0.01≦FWHM(deg)≦0.25((hkl)=(222), 2θ=43~45).

[0028] According to another embodiment of the present invention, there is provided a method for producing a cathode active material containing a spinel complex solid solution oxide represented by the following Chemical Formula 1, the method including: dry-mixing a manganese salt, a nickel salt, and a lithium salt to prepare a mixed salt; mixing the mixed salt and a compound containing a doping element with a solvent to prepare a slurry; wet-pulverizing the slurry until the D50 of solid-phase mixed particles in the slurry is 100 nm to 300 nm to prepare a powder; calcining the powder at 400 to 600 degrees Celsius for 4 to 12 hours to remove organic matter unnecessary for the reaction; and firing the particles formed in the calcination process at 700 to 950 degrees Celsius for 6 to 24 hours.

[0029] [Chemical formula 1] Li 1+a Ni 1 / 2-x / 2 Mn 3 / 2-x / 2 M x O4 (In Chemical Formula 1, M is any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof; 0≦a≦0.1, and 0 <x≦0.1である)

[0030] The lithium salt may be any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing lithium.

[0031] The manganese salt may be any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing manganese.

[0032] The nickel salt may be any one compound selected from the group consisting of nickel-containing oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof.

[0033] The compound containing a doping element may be any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof, containing any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof.

[0034] The positive electrode active material may contain secondary particles having an average particle size of 5 micrometers to 30 micrometers, which are formed by aggregating primary particles having an average particle size of 100 nm to 500 nm.

[0035] According to another embodiment of the present invention, there is provided a lithium secondary battery including: a positive electrode including the positive electrode active material; a negative electrode including the negative electrode active material; and an electrolyte disposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0036] The positive electrode active material containing the spinel complex solid solution oxide of the present invention provides stable life and excellent high-power characteristics by increasing the synthesis temperature to improve crystallinity and reducing the impurity occupancy rate. [Brief explanation of the drawings]

[0037] [Figure 1] 1 is a graph showing the content of impurities (lithium nickel oxide) depending on the firing temperature of spinel complex solid solution oxides produced in Examples and Comparative Examples. [Figure 2] 1 is a graph showing the full width at half maximum as a function of the firing temperature of a spinel complex solid solution oxide prepared in a comparative example. [Figure 3] 1 is a graph showing the full width at half maximum of the spinel complex solid solution oxides prepared in the examples as a function of the firing temperature. [Figure 4]1 is a graph showing the lattice constant of spinel complex solid solution oxides prepared in Examples and Comparative Examples as a function of firing temperature. [Figure 5] 1 is a graph showing the lattice volume of spinel complex solid solution oxides prepared in Examples and Comparative Examples as a function of firing temperature. [Figure 6] 1 is a graph showing charge and discharge curves at 0.1 C of a battery including a spinel composite solid solution oxide prepared in a comparative example. [Figure 7] 1 is a graph showing the life characteristics of a battery including a spinel composite solid solution oxide prepared in a comparative example. [Figure 8] 1 is a graph showing the rate characteristics of a battery including a spinel composite solid solution oxide prepared in a comparative example. [Figure 9] 1 is a graph showing the charge and discharge curves at 0.1 C of a battery containing a spinel composite solid solution oxide prepared in an example. [Figure 10] 1 is a graph showing the life characteristics of a battery containing a spinel composite solid solution oxide prepared in an example. [Figure 11] 1 is a graph showing the rate characteristics of a battery containing a spinel composite solid solution oxide prepared in an example. BEST MODE FOR CARRYING OUT THE INVENTION

[0038] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is given by way of example only, and the present invention is not limited thereto, but is defined only by the scope of the claims that follow.

[0039] A positive electrode active material according to an embodiment of the present invention includes a spinel complex solid solution oxide represented by Chemical Formula 1. [Chemical formula 1] Li 1+a Ni 1 / 2-x / 2 Mn 3 / 2-x / 2 M x O4

[0040] In Chemical Formula 1, a is the molar ratio of lithium (Li), and the Li content can vary depending on the range of a. a can be 0 ≦ a ≦ 0.1, and specifically, it can be 0 ≦ a ≦ 0.05. If the Li content is insufficient, the crystallinity decreases, leading to a capacity reduction. When the Li content is excessive, a large amount of unreacted water-soluble base remains on the surface of the cathode active material, making it difficult to adjust the viscosity during slurry production, and excessive carbon dioxide gas may be generated, resulting in a decline in battery performance.

[0041] The spinel composite solid-solution oxide represented by Chemical Formula 1 has an improved crystallinity with an increase in the synthesis temperature. However, due to the selection of the type and content of the doping element and the changes in the doping process, the occupancy rate of impurities is low.

[0042] Therefore, the spinel composite solid-solution oxide can be doped with any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof. Specifically, it can be doped with any one selected from the group consisting of Co, Al, Fe, Ti, and combinations thereof. More specifically, it can be doped with Ti.

[0043] In particular, when Ti is selected as the doping element, the spinel composite solid-solution oxide is represented by Chemical Formula 2. [Chemical Formula 2] Li 1+a Ni 1 / 2-x / 2 Mn 3 / 2-x / 2 Ti x O4

[0044] As in Chemical Formula 2, when Ti is selected as the doping element, the weight of lithium nickel oxide (Li z Ni 1-z O, 0 < z ≦ 0.2), which is an impurity, can be made lower.

[0045] x is the molar ratio of the doping element. x can be 0 < x ≦ 0.1, specifically, it can be 0.025 ≦ x ≦ 0.05. When the molar ratio of the doping element is 0, the effect of reducing the weight of the impurity lithium nickel oxide cannot be obtained. When it exceeds 0.1, the capacity and voltage decrease according to the decrease of Ni and Mn, and impurities may occur.

[0046] Also, after removing the same amount (x / 2) at the nickel and manganese positions, the doping element can be replaced by the amount (x) removed by nickel and manganese. In this case, the positive electrode active material can have a high tap density and specific surface area. When a lithium secondary battery is manufactured using this, improved battery life characteristics and high rate characteristics can be obtained.

[0047] Specifically, the tap density of the spinel composite solid solution oxide is 1.2 g / cc to 2.5 g / cc, and the specific surface area can be 0.5 m 2 / g to 2.5 m 2 / g. When the tap density of the spinel composite solid solution oxide is less than 1.2 g / cc, the electrode thickness becomes thick, the resistance increases, and the cell capacity may decrease. When the tap density exceeds 2.5 g / cc, the diffusion distance of lithium in the oxide becomes long, and it becomes difficult to form a high-power electrode. When the specific surface area of the spinel composite solid solution oxide is less than 0.5 m 2 / g, there are few sites for Li to enter and exit, and the high-rate charging characteristics and output characteristics deteriorate. When the specific surface area exceeds 2.5 m 2 / g, the activity of the active material with respect to the electrolyte becomes excessive, and the initial irreversible capacity becomes large, making it difficult to manufacture a high-capacity battery.

[0048] As the impurity occupancy rate of the spinel composite solid solution oxide decreases, during Rietveld analysis of the spinel composite solid solution oxide in the XRD spectrum, lithium nickel oxide (Li z Ni[[ID=When the weight of O, 0 < z ≤ 0.2) is 0 wt% to 2 wt%, specifically it can be 0.01 wt% to 2.0 wt%, specifically it can be 0.01 wt% to 1.2 wt%, and specifically it can be 0.01 wt% to 1.0 wt%. When the weight of lithium nickel oxide as an impurity exceeds 2 wt%, lifespan problems and output reduction may occur.

[0049] In the XRD spectrum, the Rietveld analysis method specifically uses the XRD cell parameter, which is the value of the lattice constant obtained by analyzing the XRD measurement data of the spinel composite solid solution oxide represented by Chemical Formula 1 by applying a reference substance to the JADE Software ICDD (Internaional Centre for Diffraction Data) card, to perform Rietveld analysis, thereby analyzing each crystal structure and the occupancy rate of lithium nickel oxide.

[0050] Also, when performing Rietveld analysis on the spinel composite solid solution oxide in the XRD spectrum, the occupancy of the cube (P4332) in the crystal calculated by the following Mathematical Formula 1 is 0 to 0.1, the occupancy of the face-centered cube (Fd-3m) in the crystal calculated by the following Mathematical Formula 2 is 0.9 to 1, and the occupancy of the impurity (lithium nickel oxide, Li z Ni 1-z O) in the crystal is 0 to -0.02. [Mathematical Formula 1]<o:p>Occupancy of cube (P4332) = A P4332 / (A P4332 + A Fd-3m + Li z Ni 1-z O) [Mathematical Formula 2] Occupancy of face-centered cube (Fd-3m) = A Fd-3m / (A P4332 + A<00001I3>+ Li z Ni 1-z O)<00003 + 9>[Mathematical Formula 3] Impurity (Li z Ni 1-z O) occupancy = Liz Ni 1-z O / (A P4332 +A Fd-3m +Li z Ni 1-z O)

[0051] In formulas 1 to 3, A P4332 is the weight percent of the regular cube (P4332), and A Fd-3m is the weight percent of face-centered cubic (Fd-3m), and Li z Ni 1-z O is an impurity (Li z Ni 1-z 0) by weight. P4332 and A Fd-3m The XRD measurement data of the spinel complex solid solution oxide represented by chemical formula 1 can be analyzed by Rietveld analysis using the XRD cell parameters, which are the lattice constant values ​​analyzed by applying the reference material to the JADE Software ICDD (International Centre for Diffraction Data) card, to obtain each crystal structure.

[0052] The occupancy rate of regular cubes (P4332) in the spinel complex solid solution oxide crystal is more than 0.1, or the occupancy rate of face-centered cubes (Fd-3m) in the crystal is less than 0.9, or there are impurities (Li z Ni 1-z If the occupancy rate of O) exceeds 0.02, the rate characteristics deteriorate and the life becomes shorter.

[0053] Furthermore, the spinel complex solid solution oxide may have a lattice constant a (Å) of the spinel structure that is greater than 8.1640 and less than 8.1900. Specifically, the lattice constant a (Å) of the spinel structure may be 8.1810 to 8.1900. If the lattice constant a (Å) of the spinel structure is less than 8.1640, Li ion migration is difficult, and if it exceeds 8.1900, structural stability may be lacked, resulting in reduced life characteristics.

[0054] In addition, the full width at half maximum (FWHM) of the spinel complex solid solution oxide satisfies the following formula 4. [Formula 4] 0.01≦FWHM(deg)≦0.20((hkl)=(111), 2θ=18-20), 0.01≦FWHM(deg)≦0.25((hkl)=(222), 2θ=43~45).

[0055] When the full width at half maximum of a spinel complex solid solution oxide is less than 0.01 when ((hkl)=(111), 2θ=18~20) or less than 0.01 when ((hkl)=(222), 2θ=43~45), the crystallinity becomes too good, which can restrict Li-ion movement and degrade performance. When the full width at half maximum is more than 0.20 when ((hkl)=(111), 2θ=18~20) or more than 0.25 when ((hkl)=(222), 2θ=43~45), the crystallinity of the structure decreases, which can degrade life and rate characteristics.

[0056] In this way, the spinel complex solid solution oxide is occupied by a regular cube (P4332) and a face-centered cube (Fd-3m) in an optimized solid solution ratio within the crystal, and lithium nickel oxide (Li z Ni 1-z O) is compounded with a low content, and a cathode active material containing the compound exhibits stable life characteristics and excellent output characteristics depending on the type and content of the doping element substituted for the transition metal, the synthesis temperature, and the amount of impurities generated.

[0057] A method for manufacturing a positive electrode active material according to another embodiment of the present invention provides a method for manufacturing a positive electrode active material including such a spinel complex solid solution oxide.

[0058] Specifically, the method for producing the positive electrode active material includes the steps of dry-mixing manganese salt, nickel salt, and lithium salt to produce a mixed salt; mixing the mixed salt and a compound containing a doping element with a solvent to produce a slurry, and wet-pulverizing the slurry until the D50 of the solid-phase mixture particles in the slurry is 100 nm to 300 nm to produce a powder; calcining the powder at 400 to 600 degrees Celsius for 4 to 12 hours to remove organic matter unnecessary for the reaction; and firing the particles formed in the calcination step at 700 to 950 degrees Celsius for 6 to 24 hours.

[0059] In the process of preparing the mixed salt, the manganese salt, the nickel salt, the lithium salt, and the compound containing the doping element may be mixed in an equivalent ratio.

[0060] The lithium salt is any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing lithium, the manganese salt is any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing manganese, and the nickel salt can be any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing nickel, but is not limited thereto.

[0061] For example, the lithium salt may be any one compound selected from the group consisting of Li(OH), Li2O, LiCO3, LiNO3, Li2SO4, LiNO3, CHClO1, and mixtures thereof; the manganese salt may be any one compound selected from the group consisting of Mn(OH)2, Mn3O4, Mn2O3, MnO2, MnOOH, MnCO3, Mn(NO3)2, MnSO4, Mn(NO3)2, and Mn(CO2CH3)2, and mixtures thereof; and the nickel salt may be any one compound selected from the group consisting of Ni(OH)2, NiO, NiOOH, NiCO3, Ni(NO3)2, NiSO4, NiC2O4, Ni(NO3)2, Ni(CO2CH3)2, and mixtures thereof.

[0062] The compound containing a doping element may be any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof, containing any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof, but is not limited thereto.

[0063] As an example, the compound containing the doping element may be any one compound selected from the group consisting of Al2O3, TiO2, Co3O4, BaO, ZrO2, and mixtures thereof.

[0064] In the process of producing the powder, the mixed salt and the compound containing the doping element are dispersed in a solvent, and then mechanically wet-milled using a media mill such as a bead mill while applying energy.

[0065] Wet milling can uniformly mill particles to nano-sized sizes, which can prevent the inclusion of foreign matter that can occur during dry milling. In addition, the reaction during firing can proceed uniformly, suppressing unreacted areas throughout the material.

[0066] The wet grinding can be carried out using a bead mill, which can be of the vertical, horizontal or basket type.

[0067] The solvent used in the wet grinding can be various organic solvents and aqueous solvents, for example, water. The total weight of the various metal salts can be 50% by weight to 60% by weight of the total weight of the slurry.

[0068] Wet milling is performed until the D50 of the solid-phase mixture particles in the slurry is 100 nm to 500 nm, specifically, until the D50 is 300 nm to 400 nm. If the D50 of the solid-phase mixture particles during wet milling is less than 100 nm, the particles of the synthesized material will be too small, which may result in reduced lifespan. If the D50 exceeds 500 nm, heterogeneous reactions are likely to occur, making it difficult to obtain a uniform phase and reducing crystallinity during synthesis.

[0069] The liquid mixture produced by wet milling can be powdered by heat drying, hot air drying, spray drying or freeze drying.

[0070] The produced powder is sintered by placing the metal powder in an electric furnace and heat treating it in air, nitrogen (N2) gas, or oxygen (O2) gas. Specifically, a calcination process is first carried out at 400-600°C for 4-12 hours to remove organic matter not required for the reaction, and then the main calcination is carried out at 700-950°C for 6-24 hours.

[0071] In this case, the firing is performed at a temperature between 700 and 950°C, more specifically between 800 and 950°C, and more specifically between 900 and 950°C. If the firing temperature is below 700°C, the thermal energy required for the reaction is insufficient, resulting in insufficient crystal growth, resulting in small crystal size and an excessively large specific surface area. If the firing temperature exceeds 950°C, the primary particles grow excessively, causing excessive oxygen deficiency, which can lead to irregular reactions and partial or total amorphization, resulting in a decrease in electrochemical performance.

[0072] After the firing, an annealing process at 400 to 700 degrees Celsius may be further included. When annealing is performed, oxygen deficiency that occurs during high-temperature firing can be reduced, and the crystals can be stabilized, improving the electrochemical properties.

[0073] The fired powder is subjected to classification and sieving processes, and the size of the filter used in the classification process can be 250 mesh to 350 mesh. The produced powder also contains secondary particles that are formed by aggregating primary particles with an average particle size of 100 nm to 500 nm.

[0074] The average particle size of the secondary particles can be adjusted to 1 to 30 micrometers, specifically 5 to 20 micrometers, more specifically 5 to 15 micrometers, and even more specifically 5 to 10 micrometers. When the average particle size of the secondary particles of the positive electrode active material is 1 to 30 micrometers, stability during electrode application is increased and the generation of fine particles can be minimized, which has the effect of improving the safety and output characteristics of the battery.

[0075] As described above, the method for manufacturing a positive electrode active material according to one embodiment of the present invention is for manufacturing a high-voltage spinel composite solid solution oxide, and various metal salts are dry-mixed in a solid phase at an equivalent ratio, followed by wet pulverization. Through the drying and firing processes, the solid solution ratio of the crystalline structure and the mixing ratio of lithium nickel oxide can be relatively easily controlled.

[0076] Another embodiment of the present invention provides a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode including the negative electrode active material, and an electrolyte disposed between the positive electrode and the negative electrode.

[0077] The lithium secondary battery may have any of the configurations of a conventional lithium secondary battery except that it includes a positive electrode active material according to an embodiment of the present invention as a positive electrode active material, and therefore, detailed description thereof will be omitted. DETAILED DESCRIPTION OF THE INVENTION

[0078] Examples of the present invention and comparative examples will be described below. However, the examples are merely examples of the present invention, and the present invention is not limited to these examples.

[0079] [Production Example 1: Production of spinel complex solid solution oxide] Examples 1 to 6 Mn2O3 as manganese salt, Ni(OH)2 as nickel salt, and Li2CO3 as lithium salt were mixed in an equivalent ratio, and then the doping elements were added to these mixtures in an equivalent ratio to obtain dry mixtures. These mixtures were then wet-pulverized in an aqueous solution using a bead mill until the D50 reached 100-300 nm. After drying with hot air, the resulting powder was placed in an electric furnace and fired at various temperatures to produce the spinel complex solid solution oxides shown in Table 1.

[0080] [Table 1]

[0081] (Comparative Examples 1 to 6) As an example for comparison with the examples, a known spinel complex solid solution oxide equivalent ratio was selected and manufactured as a comparative example.

[0082] Mn2O3 as manganese salt, Ni(OH)2 as nickel salt, and Li2CO3 as lithium salt were mixed in an equivalent ratio. At this time, none of the salts except Ni and Mn were doped. Wet milling was carried out using a bead mill until the D50 was 100-300 nm. After drying with hot air, the resulting powder was placed in an electric furnace and fired at various temperatures to produce the spinel complex solid solution oxides shown in Table 2.

[0083] [Table 2]

[0084] [Experimental Example 1: XRD Measurement] The X-ray diffraction patterns of the spinel complex solid solution oxides prepared in the examples and comparative examples were measured using an X-ray diffraction analyzer (trade name: Rint-2000, company: Rigaku, Japan). The 2θ value of the peak showing the maximum intensity and the corresponding intensity value were calculated as the analysis results. These were then applied to the JADE Software ICDD (International Centre for Diffraction Data) card to measure the lattice constant on the XRD and the lithium nickel oxide content, full width at half maximum, and lattice constant by Rietveld analysis. The results are shown in Tables 3 and 4 and Figures 1 to 5.

[0085] [Table 3]

[0086] [Table 4]

[0087] Table 3 shows the numerical values ​​of the XRD results for the experiments in which the comparative examples were fired at different temperatures, and FIGS. 1, 2, 4 and 5 are diagrams of these.

[0088] Referring to Table 3, Figures 1, 2, 4, and 5, it can be seen that as the firing temperature increases, the FWHM decreases, contributing to improved crystallinity. It can also be seen that the oxygen deficiency problem increases, resulting in an increase in the amount of lithium nickel oxide impurities.

[0089] Table 4 shows the numerical values ​​of the XRD results for the experiments in which Ti was doped at the Ni and Mn positions and sintered at different temperatures, and Figures 1, 3, 4, and 5 are diagrams of these.

[0090] Referring to Table 4, FIGS. 1, 3, 4, and 5, it can be seen that in the Examples, unlike the Comparative Examples, as the temperature increases, not only the crystallinity improves but also the amount of lithium nickel oxide impurities decreases.

[0091] [Production Example 2: Production of Lithium Secondary Battery] 10.68 g (89 wt % of the initial composition) of the spinel composite solid solution oxide prepared in the examples and comparative examples, 0.84 g (7 wt % of the total composition), and 8 g (4 wt % of the total composition) of HSV900 as a binder were mixed uniformly, and 15 g of NMP as a solvent was mixed uniformly. The mixture was then applied to an aluminum foil and dried to prepare a cathode.

[0092] Using the fabricated cathode and lithium metal as the counter electrode, a porous polyethylene film as the separator, and a liquid electrolyte of 1.2M LiPF6 solute in a mixed solvent of EC (ethylene carbonate) and DEC (diethyl carbonate), a 2016 standard coin cell was fabricated according to the standard manufacturing process for lithium secondary batteries.

[0093] [Experimental Example 2: Battery characteristic evaluation] To evaluate the characteristics of the lithium secondary battery produced in Production Example 2, an electrochemical analyzer (WBCS3999K 32, manufactured by Woori Engineering) was used. Battery capacity was confirmed at room temperature by charging and discharging at 0.1 C for three cycles in a voltage range of 3.0 V to 4.9 V, battery life was confirmed by charging and discharging at 1 C for 250 cycles in a voltage range of 3.0 V to 4.9 V, and battery output characteristics (rate) were confirmed by checking the discharge capacity from 0.1 C to 10 C in a voltage range of 3.0 V to 4.9 V. The results are shown in Table 5, Table 6, and FIGS. 6 to 11.

[0094] [Table 5]

[0095] [Table 6]

[0096] Table 5 shows the numerical results of electrochemical analysis of the coin-type battery manufactured using the spinel complex solid solution oxide manufactured in the comparative example, and FIGS. 6 to 8 show the results diagrammatically.

[0097] Referring to Table 5 and Figures 6 to 8, it can be seen that the 1C cycle efficiency (1C retention cycle) increases as the firing temperature increases. This is because, based on Table 3 and Figure 2, as the crystallinity increases, the structure is stabilized, improving the lifespan.

[0098] It can be seen that the high output rate characteristics also improve, but at 10C it is not possible to achieve more than 70% of the performance at 0.1C.

[0099] It can also be seen that the capacity drops sharply at 0.1C discharge capacity when the firing temperature reaches 900 degrees Celsius. This is presumed to be because as the firing temperature increases, impurities (lithium nickel oxide) increase, preventing the output limit from being exceeded.

[0100] Table 6 shows the numerical results of electrochemical analysis of the coin-type battery manufactured using the spinel composite solid solution oxide manufactured in the examples, and FIGS. 9 to 11 show the results diagrammatically.

[0101] 9 to 11, it can be seen that as the firing temperature increases, the 1C cycle efficiency (1C retention cycle) increases, as in the comparative example. This is because, as can be seen from Table 3 and Figure 3, as the crystallinity increases, the structure becomes more stable, improving the lifespan.

[0102] It was also confirmed that the high-rate output characteristics were improved, and that the high-rate output characteristics were 10% to 15% better than those of the comparative example. Unlike the comparative example, the example maintains high crystallinity (full width at half maximum) even at firing temperatures of 900 degrees Celsius or higher by doping with Ti, as can be seen from Table 4 and Figure 2, and the life does not deteriorate. In addition, the lattice constant and cell volume increase, increasing the diffusion rate of lithium (Li), which is thought to enable the maintenance of excellent high-rate characteristics and good life characteristics.

[0103] In the examples, it can be seen that the 0.1C discharge capacity is also about 5% higher even when the firing temperature is above 900°C. This is believed to be because, unlike the comparative examples, impurities (lithium nickel oxide) are reduced as the firing temperature increases.

[0104] Therefore, it can be confirmed that the positive electrode active material in which the lattice constant and full width at half maximum of lithium nickel oxide are controlled within the ranges of the present invention exhibits the best capacity and output characteristics and good life characteristics.

[0105] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention. [Industrial Applicability]

[0106] The present invention relates to a cathode active material containing a high-voltage spinel complex solid solution oxide having a discharge voltage of 4.5 V or more, a method for producing the same, and a lithium secondary battery containing the same. The cathode active material containing the spinel complex solid solution oxide can provide stable life and excellent high-power characteristics by increasing the synthesis temperature to improve crystallinity while reducing the impurity concentration.

Claims

1. It includes a spinel complex solid solution oxide represented by the following chemical formula 1: The spinel complex solid solution oxide is found to contain lithium nickel oxide (Li) in a Rietveld analysis of an XRD spectrum based on the total weight of the spinel complex solid solution oxide. ｚ Ni １－ｚ O, 0 < z ≦ 0.2) is 0 wt.% to 2 wt.%, The spinel complex solid solution oxide has a tap density of 1.2 g / cc to 2.2 g / cc and a specific surface area of ​​0.5 m 2 / g to 2.5 m 2 / g. Cathode active material. [Chemical formula 1] Li １＋ａ Ni １／２－ｘ／２ Mn ３／２－ｘ／２ M ｘ O ４ (In the above Chemical Formula 1, M is any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof; 0≦a≦0.1 and 0<x≦0.1)

2. The weight of the lithium nickel oxide is 0.01 wt % to 2 wt % based on the total weight of the spinel complex solid solution oxide. The positive electrode active material according to claim 1 .

3. The spinel composite solid solution oxide is represented by the following chemical formula 2: The positive electrode active material according to claim 1 . [Chemical formula 2] From １＋ａ Yes １／２－ｘ／２ MỎ ３／２－ｘ／２ Till ｘ Oh ４ (In the above Chemical Formula 2, 0≦a≦0.1 and 0<x≦0.1)

4. In the above formula 1, 0.025≦x≦0.05; The positive electrode active material according to claim 1 .

5. The spinel complex solid solution oxide has a regular cube (P4 ３ 32) is 0 to 0.1, the occupancy rate of the face-centered cubic (Fd-3m) in the crystal calculated by the following formula 2 is 0.9 to 1, and the occupancy rate of the impurities in the crystal (lithium nickel oxide, Li ｚ Ni １－ｚ O) is 0 to 0.02; The positive electrode active material according to claim 1 . [Formula 1] Regular cube (P4 ３ 32) Occupancy rate = A Ｐ４３３２ / (A Ｐ４３３２ +A Ｆｄ－３ｍ +Li ｚ Ni １－ｚ O) [Formula 2] Occupancy rate of face-centered cube (Fd-3m) = A Ｆｄ－３ｍ / (A Ｐ４３３２ +A Ｆｄ－３ｍ +Li ｚ Ni １－ｚ O) [Formula 3] Impurities (Li ｚ Ni １－ｚ Occupancy rate of Li ｚ Ni １－ｚ O / (A Ｐ４３３２ +A Ｆｄ－３ｍ +Li ｚ Ni １－ｚ O) (In the above formulas 1 to 3, A Ｐ４３３２ is a regular cube (P4 ３ 32) by weight of A Ｆｄ－３ｍ is the weight percent of face-centered cubic (Fd-3m), and Li ｚ Ni １－ｚ O is an impurity (Li ｚ Ni １－ｚ O) is the weight percent of

6. The spinel complex solid solution oxide has a lattice constant a (Å) of a spinel structure in a Rietveld analysis of an XRD spectrum of more than 8.1640 to less than 8.1900. The positive electrode active material according to claim 1 .

7. The spinel complex solid solution oxide has a full width at half maximum (FWHM) that satisfies the following Equation 4 when Rietveld analyzed in an XRD spectrum: The positive electrode active material according to claim 1 . [Formula 4] 0.01≦FWHM (deg)≦0.20 ((hkl)=(111), 2θ=18 to 20), 0.01≦FWHM (deg)≦0.25 ((hkl)=(222), 2θ=43 to 45).

8. A method for producing the positive electrode active material according to claim 1, comprising: dry-mixing a manganese salt, a nickel salt, and a lithium salt to produce a mixed salt; a step of preparing a slurry by mixing the mixed salt and a compound containing a doping element with a solvent, and wet-pulverizing the slurry until the D50 of the solid-phase mixture particles in the slurry is 100 nm to 300 nm to prepare a powder; a calcination step of calcining the powder at 400 to 600 degrees Celsius for 4 to 12 hours to remove organic substances not necessary for the reaction; and calcining the particles formed in the calcination step at 700 to 950 degrees Celsius for 6 to 24 hours. A method for producing a positive electrode active material comprising a spinel complex solid solution oxide represented by the following chemical formula 1: [Chemical formula 1] Li １＋ａ Ni １／２－ｘ／２ Mn ３／２－ｘ／２ M ｘ O ４ (In the above Chemical Formula 1, M is any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof; 0≦a≦0.1 and 0<x≦0.1)

9. the lithium salt is any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing lithium; the manganese salt is any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof containing manganese; The nickel salt is any one compound selected from the group consisting of nickel-containing oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof. The method for producing a positive electrode active material according to claim 8 .

10. The compound containing a doping element is any one compound selected from the group consisting of oxides, hydroxides, nitrates, carbonates, acetates, and mixtures thereof, containing any one doping element selected from the group consisting of Co, Mg, Ti, Al, Ba, Cr, Fe, Mo, W, Zr, Y, Nb, and combinations thereof; The method for producing a positive electrode active material according to claim 8 .

11. The positive electrode active material includes secondary particles having an average particle size of 5 micrometers to 30 micrometers, which are formed by assembling primary particles having an average particle size of 100 nm to 500 nm, The method for producing a positive electrode active material according to claim 8 .

12. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 7; a negative electrode including a negative electrode active material; and an electrolyte located between the positive electrode and the negative electrode; Lithium secondary battery.

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