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

Abstract

The present invention aims to provide a positive electrode active material and a manufacturing method thereof that have been developed to suppress the occurrence of microcracks in the positive electrode active material and decomposition of the electrolyte during charging and discharging by forming the average crystallite size of the core part of the high-nickel positive electrode active material smaller than the average crystallite size of the shell part.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0024668, filed February 24, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material with a core-shell structure, and more specifically to a positive electrode active material in which the average crystal grain size of the core portion of the positive electrode active material particles is made smaller than the average crystal grain size of the shell portion, thereby maintaining capacity characteristics and improving life characteristics, and a method for producing the same. [Background technology]

[0003] With the development of mobile device technology and the increase in demand, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, with the development of technologies such as electric vehicles, demand for high-capacity secondary batteries has increased. However, if the size of the crystal grains within the primary particles is increased to increase capacity, the structure of the crystal lattice is deformed during the process of lithium ion insertion and extraction during charging and discharging, which can easily cause microcracks. Furthermore, electrolyte can penetrate into the positive electrode active material through the microcracks, degrading the active material structure and accelerating the decomposition of the electrolyte in the transition metals contained in the positive electrode active material, resulting in a rapid decline in life characteristics. Furthermore, the formation of a coating due to the decomposition of the electrolyte can increase resistance and reduce output characteristics.

[0005] Therefore, there is a need for the development of a positive electrode active material that can achieve high capacity and has excellent life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a cathode active material and a manufacturing method thereof that have been developed to suppress the occurrence of microcracks in the cathode active material and decomposition of the electrolyte during charge and discharge by forming the average crystallite size of the core portion of the high-nickel cathode active material smaller than the average crystallite size of the shell portion. [Means for solving the problem]

[0007] In one aspect, the present invention provides a positive electrode active material for a secondary battery, comprising lithium transition metal oxide particles having a core-shell structure including a core portion and a shell portion located on the surface of the core portion, wherein the average crystallite size of the core portion is smaller than the average crystallite size of the shell portion, and a nickel content of the total transition metals contained in the core portion and the shell portion is 80 atm% or more.

[0008] In another aspect, the present invention provides a positive electrode including the positive electrode active material according to the present invention, and a secondary battery including the positive electrode. [Effects of the Invention]

[0009] The cathode active material according to the present invention has a structure in which the average crystal grain size of the core portion is smaller than that of the shell portion, thereby suppressing the occurrence of defects such as microcracks in the core portion and the formation of a coating due to electrolyte decomposition. Furthermore, the shell portion maintains a larger average crystal grain size than the core portion, thereby providing advantages in terms of capacity characteristics, and its small specific surface area reduces reaction with the electrolyte. As a result, the cathode active material according to the present invention has superior life characteristics compared to conventional cathode active materials, while maintaining comparable capacity characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described in more detail.

[0011] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0012] In the present invention, the "core portion" refers to a region including the center of the positive electrode active material, and having a small average crystal grain size of 100 to 180 nm.

[0013] In the present invention, the "shell portion" refers to a region including the surface of the positive electrode active material, which has an average crystal grain size of 180 to 250 nm and is larger than the average crystal grain size of the core portion.

[0014] In the present invention, the term "crystal grain" refers to a single crystal particle unit having a regular atomic arrangement. The size of the crystal grains can be measured, for example, using a high-resolution transmission electron microscope (HR-TEM) TITAN G2 by magnifying the surface of a sample by 800,000 to 2,000,000 times, and the average crystal grain size can be measured by calculating the arithmetic mean value of the measured crystal grain sizes.

[0015] In the present invention, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material precursor is observed with a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0016] In the present invention, the term "secondary particles" refers to secondary structures formed by aggregation of a plurality of primary particles. The average particle size of the secondary particles can be measured using a particle size analyzer. In the present invention, a Microtrac S3500 particle size analyzer was used.

[0017] In the present invention, the "particle size Dn" of a positive electrode active material refers to the particle size at the n% point in the cumulative particle size volume distribution. That is, D50 is the particle size at the 50% point in the cumulative particle size volume distribution, D90 is the particle size at the 90% point in the cumulative particle size volume distribution, and D10 is the particle size at the 10% point in the cumulative particle size volume distribution. Dn can be measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through a laser beam. D10, D50, and D90 can be measured by calculating the particle diameters at the 10%, 50%, and 90% points in the cumulative particle size volume distribution measured by the analyzer.

[0018] positive electrode active material The positive electrode active material of the present invention can include lithium transition metal oxide particles having a core-shell structure including a core portion and a shell portion located on the surface of the core portion.

[0019] The positive electrode active material of the present invention may contain 80 atm% or more of nickel among all transition metals contained in the core and shell. If the nickel content is less than 80 atm%, the capacity of the positive electrode active material may be reduced, making it difficult to apply to electrochemical devices requiring high capacity.

[0020] Specifically, the average crystal grain size of the core portion can be 100 to 180 nm, preferably 110 to 170 nm, and more preferably 120 to 160 nm. When the average crystal grain size of the core portion of the positive electrode active material for a lithium secondary battery satisfies the above range, the capacity of the lithium secondary battery can be maintained high and excellent life characteristics can be obtained.

[0021] The core portion may have a composition represented by the following [Chemical Formula 1].

[0022] [Chemical formula 1] Li x1 Ni a1 Co b1 Mn c1 Al d1 M 1 e1 O2

[0023] In Chemical Formula 1 above, M 1 can be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and it is particularly preferable to contain Zr in terms of improving the structural stability of the lithium transition metal oxide.

[0024] Said x1 represents the molar ratio of lithium in the lithium transition metal oxide, and can be 0.90 ≦ x1 ≦ 1.2, preferably 0.95 ≦ x1 ≦ 1.08, and more preferably 1 ≦ x1 ≦ 1.08.

[0025] Said a1 represents the molar ratio of nickel among the metal elements other than lithium in the lithium transition metal oxide, and can be 0.80 ≦ a1 ≦ 0.95 or 0.83 ≦ a1 ≦ 0.93. When the nickel content satisfies the above range, high-capacity characteristics can be realized.

[0026] Said b1 represents the molar ratio of cobalt among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < b1 < 0.20, 0 < b1 ≦ 0.15, or 0.01 ≦ b1 ≦ 0.10. The content of cobalt can vary according to the contents of said nickel, manganese, aluminum, and M 1 . When the content of cobalt is excessively high, there is a problem that the cost of raw materials increases as a whole and the reversible capacity decreases. When the content of cobalt is excessively low, there is a problem that it is difficult to simultaneously achieve sufficient rate characteristics and a high powder density of the battery.

[0027] Said c1 represents the molar ratio of manganese among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < c1 < 0.20, 0 < c1 ≤ 0.15, or 0.01 ≤ c1 ≤ 0.10. When the content of manganese is excessively high, problems may occur in achieving high capacity, and when the content of manganese is excessively low, there is a problem of high production cost.

[0028] Said d1 represents the molar ratio of aluminum among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < d1 < 0.20, 0 < d1 ≤ 0.15, or 0.01 ≤ d1 ≤ 0.10. When the content of aluminum is excessively high, there is a problem of increased resistance, and when it is excessively low, there is a problem of high production cost.

[0029] Said e1 represents the molar ratio of M among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 ≤ e1 ≤ 0.10, or 0 ≤ e1 ≤ 0.05. 1

[0030] On the other hand, the average crystal grain size of the shell part can be 180 - 250 nm, preferably 190 - 230 nm, and more preferably 200 - 220 nm. When the average crystal grain size of the shell part of the positive electrode active material for the lithium secondary battery satisfies the above range, the capacity of the lithium secondary battery can be increased, and the effect of optimizing the reaction surface area between the positive electrode active material and the electrolyte can be obtained.

[0031] The shell part can have a composition represented by the following [Chemical Formula 2].

[0032] [Chemical Formula 2] Li x2 Ni a2 Co b2 Mn c2 Al d2 M 2 e2 O2

[0033] In the above Chemical Formula 2, M 2It can be at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and it is particularly preferable to contain Zr in terms of improving the structural stability of the lithium transition metal oxide.

[0034] Said x2 represents the molar ratio of lithium in the lithium transition metal oxide, and can be 0.90 ≦ x2 ≦ 1.2, preferably 0.95 ≦ x2 ≦ 1.08, and more preferably 1 ≦ x2 ≦ 1.08.

[0035] Said a2 represents the molar ratio of nickel among the metal elements other than lithium in the lithium transition metal oxide, and can be 0.83 ≦ a2 < 1.0 or 0.85 ≦ a2 ≦ 0.99. When the nickel content satisfies the above range, high capacity characteristics can be realized.

[0036] Said b2 represents the molar ratio of cobalt among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < b2 < 0.20, 0 < b2 ≦ 0.15, or 0.01 ≦ b2 ≦ 0.10. The content of cobalt can vary according to the contents of said nickel, manganese, aluminum, and M 1 When the content of cobalt is excessively high, there is a problem that the cost of raw materials increases as a whole and the reversible capacity decreases. When the content of cobalt is excessively low, it is difficult to simultaneously achieve sufficient rate characteristics and a high powder density of the battery.

[0037] Said c2 represents the molar ratio of manganese among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < c2 < 0.20, 0 < c2 ≦ 0.15, or 0.01 ≦ c2 ≦ 0.10. When the content of manganese is excessively high, problems may occur in expressing high capacity. When the content of manganese is excessively low, there is a problem that the production cost increases.

[0038] Said d2 represents the molar ratio of aluminum among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < d2 < 0.20, 0 < d2 ≤ 0.15, or 0.01 ≤ d2 ≤ 0.10. When the aluminum content is excessively high, there is a problem that the resistance increases, and when it is excessively low, there is a problem that the production cost increases.

[0039] Said e2 represents the molar ratio of M among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 ≤ e2 ≤ 0.10, or 0 ≤ e2 ≤ 0.05. 2

[0040] In one embodiment of the present invention, a1 described in Chemical Formula 1 of the core part can be smaller than a2 described in Chemical Formula 2 of the shell part.

[0041] The positive electrode active material according to the present invention can have the average crystallite size of the core part smaller than that of the shell part. By making the average crystallite size of the core part smaller than that of the shell part in the high-nickel lithium transition metal oxide, the generation of defects such as micro cracks in the core part and the formation of a film due to the decomposition of the electrolytic solution can be suppressed. Note that the shell part can maintain a larger average crystallite size than the core part, has the advantage of capacity characteristics, and can reduce the reactivity with the electrolytic solution due to its small specific surface area. Thereby, the positive electrode active material of the present invention can maintain the initial capacity characteristics and output characteristics and improve the life characteristics when applied to a battery.

[0042] Specifically, for the positive electrode active material for a lithium secondary battery according to the present invention, the difference between the average crystallite size of the core part and the average crystallite size of the shell part can be 20 to 150 nm, preferably 30 to 100 nm, more preferably 40 to 80 nm. When the difference between the average crystallite size of the core part and the average crystallite size of the shell part of the positive electrode active material for a lithium secondary battery satisfies the above range, the positive electrode active material of the present invention can maintain the initial capacity characteristics and output characteristics and improve the life characteristics when applied to a battery.

[0043] The positive electrode active material may further include a coating layer formed on a surface thereof, and the coating layer may include one or more metals selected from the group consisting of B, Al, Hf, Nb, Ta, Mo, Si, Zn, and Zr.

[0044] The coating layer prevents contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery, thereby suppressing the occurrence of side reactions, thereby improving the life characteristics and increasing the packing density of the positive electrode active material.

[0045] The coating layer may be formed on the entire surface of the positive electrode active material or may be formed partially. Specifically, when the coating layer is formed partially on the surface of the positive electrode active material, it may be formed on 20% or more of the total area of ​​the positive electrode active material. If the area of ​​the coating layer is less than 20%, the effects of improving the life characteristics and packing density due to the formation of the coating layer may be minimal.

[0046] In addition, the coating layer may be formed at a thickness ratio of 1 / 10,000 to 1 / 100 of the average particle diameter of the positive electrode active material particles. If the thickness ratio of the coating layer to the positive electrode active material particles is less than 1 / 10,000, the effects of improving the life characteristics and packing density due to the formation of the coating layer may be minimal, and if the thickness ratio exceeds 1 / 100, the battery characteristics may be degraded.

[0047] Method for producing positive electrode active material A method for producing a cathode active material according to the present invention includes the steps of: preparing a first transition metal-containing solution containing nickel, cobalt, manganese, and aluminum; introducing the first transition metal-containing solution, a basic aqueous solution, and an ammonium cation complex-forming agent into a reactor and causing a co-precipitation reaction to form core particles; introducing a second transition metal-containing solution, a basic aqueous solution, and an ammonium cation complex-forming agent into the reaction solution containing the core particles and causing a co-precipitation reaction to form shells on the core particles, thereby forming cathode active material precursor particles; and mixing the cathode active material precursor with a lithium-containing raw material and firing the mixture.

[0048] All of the above-described positive electrode active material methods may be applied to the manufacturing method of the positive electrode active material.

[0049] The method for producing the cathode active material precursor of the present invention will be specifically described step by step.

[0050] First, a first transition metal-containing solution and a second transition metal-containing solution containing nickel, cobalt, manganese, and aluminum are prepared.

[0051] The first transition metal-containing solution and the second transition metal-containing solution can contain, for example, a nickel (Ni)-containing source material, a cobalt (Co)-containing source material, a manganese (Mn)-containing source material, and an aluminum (Al)-containing source material.

[0052] The nickel (Ni)-containing raw material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a fatty acid nickel salt, a nickel halide, or a combination thereof.

[0053] The cobalt (Co)-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0054] The manganese (Mn)-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, the manganese (Mn)-containing raw material may be, but is not limited to, a manganese oxide such as MnO, MnO, or MnO; a manganese salt such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, or manganese fatty acid; a manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0055] The aluminum (Al)-containing raw material may be, for example, an aluminum-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically may be, but is not limited to, Al(OH), AlO, Al(OCOCH), Al(NO,), Al(SO).

[0056] The first transition metal-containing solution and the second transition metal-containing solution may be prepared by adding a nickel (Ni)-containing raw material, a cobalt (Co)-containing raw material, a manganese (Mn)-containing raw material, and an aluminum (Al)-containing raw material to a solvent, specifically, water or a mixed solvent of an organic solvent (e.g., alcohol) that can be uniformly mixed with water, or by mixing an aqueous solution of a nickel (Ni)-containing raw material, an aqueous solution of a cobalt (Co)-containing raw material, an aqueous solution of a manganese (Mn)-containing raw material, and an aqueous solution of an aluminum (Al)-containing raw material.

[0057] According to the present invention, the first transition metal-containing solution and the second transition metal-containing solution can contain 80 atm % or more of nickel relative to the total number of moles of the transition metals.

[0058] The crystal grain size of the core and shell parts of the positive electrode active material can be adjusted by, for example, varying the transition metal composition, for example, by varying the nickel content of the first transition metal-containing solution and the second transition metal-containing solution, by varying whether or not a doping element is added to the core and shell parts, or by varying the amount of doping element added to the core and shell parts.

[0059] In one embodiment of the present invention, the transition metal-containing solution may be prepared in the form of a first transition metal-containing solution containing nickel, cobalt, manganese, and aluminum, and a second transition metal-containing solution containing nickel, cobalt, manganese, and aluminum, and having a higher mole fraction of nickel relative to the total transition metals than the first transition metal-containing solution.

[0060] In yet another embodiment of the present invention, the transition metal-containing solution may be prepared in the form of a first transition metal-containing solution and a second transition metal-containing solution, each of which differs in the type or content of a doping element.

[0061] Specifically, the doping element may be, for example, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, or S, and in terms of improving the structural stability of the lithium transition metal oxide, it is particularly preferable to include Zr.

[0062] When Zr is used as a doping element, the average crystal grain size of the core portion can be adjusted to be smaller than the average crystal grain size of the shell portion by increasing the content of Zr in the first transition metal-containing solution compared to the second transition metal-containing solution.

[0063] Next, the transition metal-containing solution is introduced into a reactor, and a coprecipitation reaction is carried out while an ammonium cation complexing agent and a basic aqueous solution are introduced to produce transition metal hydroxide in the form of secondary particles formed by aggregation of primary particles.

[0064] The ammonium cation complexing agent may be NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, or NH4CO3, or a mixture of one or more of these. The ammonium cation-containing complexing agent may also be used in the form of an aqueous solution, in which the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0065] The basic aqueous solution may contain at least one selected from the group consisting of NaOH, KOH, and Ca(OH)2, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water. The concentration of the basic aqueous solution may be 2 to 5 M, preferably 3 to 4 M. When the concentration of the basic aqueous solution satisfies the above range, precursor particles of uniform size can be formed, the precursor particle formation time can be rapid, and the yield can be excellent. The basic aqueous solution is added to adjust the pH of the reaction solution, and the amount of the basic aqueous solution can be adjusted to maintain a pH of 9 to 12 during the coprecipitation reaction, preferably a pH of 10.5 to 11.5.

[0066] According to the present invention, the temperature during the coprecipitation reaction can be 30 to 60°C, preferably 30 to 50°C. Producing a transition metal hydroxide within the above temperature range facilitates control of the coprecipitation reaction and improves productivity. If the coprecipitation reaction is carried out at a temperature below 30°C, which is outside the above temperature range, productivity may decrease due to loss of transition metal ions. If the coprecipitation reaction is carried out at a temperature above 60°C, crystal grains may grow excessively, making it difficult to control the size of primary particles, and rapid evaporation of ammonia may occur, making it difficult to control the coprecipitation reaction.

[0067] The pH during the coprecipitation reaction can be 9 to 12, preferably 10.5 to 11.5. By carrying out the coprecipitation reaction at a pH within this range, transition metal hydroxide particles with appropriate particle size distribution and density can be produced. On the other hand, if the mixture is coprecipitation reaction at a pH below 9, there is a problem of reduced productivity due to loss of transition metal ions, and if the coprecipitation reaction is carried out at a pH above 12, there is a problem of secondary particles not growing.

[0068] In one embodiment of the present invention, the first transition metal-containing solution is introduced into a reactor, and then a basic aqueous solution and an ammonium cation complexing agent are introduced to carry out a co-precipitation reaction to grow a core portion in the form of a secondary particle formed by aggregation of primary particles. When the average particle size D50 of the cathode active material precursor particles in the reaction solution reaches 85% or more, preferably 90% or more, of the total particle size, the second transition metal-containing solution is introduced into the reactor, and then a basic aqueous solution and an ammonium cation complexing agent are introduced to carry out a co-precipitation reaction. In this manner, a shell portion is grown around the core portion, thereby producing a cathode active material precursor.

[0069] The positive electrode active material according to the present invention may be prepared by mixing the above-described positive electrode active material precursor with a lithium-containing raw material and calcining the mixture.

[0070] Here, the lithium-containing raw material is not particularly limited as long as it is a compound containing a lithium source, but preferably, at least one selected from the group consisting of lithium carbonate (Li2CO3), lithium hydroxide (LiOH), LiNO3, CH3COOLi, and Li2(COO)2 can be used.

[0071] Preferably, the positive electrode active material according to the present invention can be prepared by mixing the positive electrode active material precursor and the lithium-containing raw material in a molar ratio of 1.0 to 1.1, preferably 1.03 to 1.1, and firing the mixture at 600 to 850° C. for 3 to 30 hours.

[0072] If the lithium-containing raw material is mixed in an amount less than the above range, the capacity of the resulting positive electrode active material may be reduced. If the lithium-containing raw material is mixed in an amount exceeding the above range, the particles may be sintered during the firing process, making it difficult to produce the positive electrode active material, resulting in a reduction in capacity and separation of the positive electrode active material particles after firing.

[0073] Furthermore, if the calcination temperature is below 600°C, the raw materials may remain in the particles due to insufficient reaction, reducing the high-temperature stability of the battery, and the volume density and crystallinity may decrease, resulting in reduced structural stability. On the other hand, if the calcination temperature exceeds 850°C, uneven particle growth may occur, resulting in excessively large particle diameters, reducing the amount of particles that can be contained per unit area, and thus reducing the volumetric capacity of the battery. On the other hand, in consideration of particle size control, capacity, stability, and reduction of lithium-containing by-products in the produced positive electrode active material, the calcination temperature is more preferably 700 to 750°C.

[0074] Furthermore, if the calcination time is less than 3 hours, the reaction time may be too short, making it difficult to obtain a highly crystalline positive electrode active material. If the calcination time exceeds 30 hours, the particle size may become too large, reducing production efficiency.

[0075] In one embodiment of the present invention, the average crystal grain size of the core portion can be adjusted to be smaller than the average crystal grain size of the shell portion by adding a doping element during the firing step to increase the content of the doping element in the shell portion compared to the core portion.

[0076] Specifically, the doping element may be, for example, Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, or S, and in terms of improving the structural stability of the lithium transition metal oxide, it is particularly preferable to include Zr.

[0077] The doping elements can be each independently 0.1 to 2 mol %, preferably 0.2 to 1 mol %, based on the total moles of metal elements other than lithium contained in the core and shell parts. For example, if the doping elements are each independently contained in the core and shell parts at less than 0.1 mol %, the effect of improving structural stability and output characteristics due to the addition of the doping elements may be minimal, while if they exceed 2 mol %, the capacity may decrease and lithium by-products may increase.

[0078] positive electrode A positive electrode according to the present invention includes the above-described positive electrode active material of the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material of the present invention. Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0079] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the voltage range of the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0080] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material, as required.

[0081] In this case, the positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics can be exhibited when contained in this range.

[0082] The conductive material is used to impart conductivity to the electrode. Any material that does not cause chemical changes in the resulting battery and has electronic conductivity can be used without particular limitations. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0083] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0084] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer onto a positive electrode current collector, the composition being prepared by dissolving or dispersing the positive electrode active material described above and, if necessary, selectively a binder, a conductive material, and a dispersant in a solvent, followed by drying and rolling.

[0085] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for manufacturing a positive electrode.

[0086] Alternatively, the positive electrode can be produced by casting the composition for forming a positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0087] Electrochemical elements The electrochemical device according to the present invention will be described below. The electrochemical device according to the present invention includes the above-described positive electrode of the present invention. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0088] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is as described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0089] The lithium secondary battery may further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0090] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0091] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0092] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0093] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. These may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0094] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0095] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0096] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be added in an amount of 10 wt % or less, specifically 5 wt % or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; 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.

[0097] The negative electrode active material layer can be produced by applying a composition for forming a negative electrode active material layer, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, onto a negative electrode current collector and drying the composition. Alternatively, the negative electrode active material layer can be produced by casting the composition for forming a negative electrode active material layer onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector.

[0098] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion movement in the electrolyte and excellent humidification ability for the electrolyte solution is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0099] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0100] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0101] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0102] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be 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 at least one 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. The concentration of the lithium salt is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0103] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0104] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0105] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0106] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0107] The shape of the lithium secondary battery is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0108] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0109] Examples of the medium to large size devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0110] Example 1 NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 83:5:10:2 to prepare a 2M aqueous solution of first transition metals.

[0111] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of second transition metals.

[0112] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0113] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0114] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0115] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0116] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0117] Example 2 NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2M aqueous solution of first transition metals.

[0118] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of second transition metals.

[0119] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0120] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0121] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0122] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0123] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0124] Example 3 NiSO4, CoSO4, MnSO4 and Al2(SO4) 3- Zr(SO4)2 was mixed in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese:aluminum:zirconium was 85:6.5:6.5:1.5:0.5 to prepare a 2M first transition metal aqueous solution.

[0125] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of second transition metals.

[0126] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0127] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0128] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0129] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0130] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al+Zr) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0131] Example 4 NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2M aqueous solution of first transition metals.

[0132] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of second transition metals.

[0133] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0134] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0135] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0136] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0137] LiOH, the obtained cathode active material precursor, and ZrO2 were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al):Zr was 1.05:1:0.005, and this was calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15 μm.

[0138] Example 5 NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2M aqueous solution of first transition metals.

[0139] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 1.5M aqueous solution of second transition metals.

[0140] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0141] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0142] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0143] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0144] LiOH, the obtained cathode active material precursor, and ZrO2 were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al):Zr was 1.05:1:0.005, and this was calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15 μm.

[0145] Example 6 NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2.5M aqueous solution of first transition metals.

[0146] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of second transition metals.

[0147] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0148] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0149] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0150] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0151] LiOH, the obtained cathode active material precursor, and ZrO2 were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al):Zr was 1.05:1:0.005, and this was calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15 μm.

[0152] Comparative Example 1 NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of transition metals.

[0153] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0154] Next, the transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a coprecipitation reaction was carried out for 15 hours to produce precursor particles.

[0155] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0156] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0157] Comparative Example 2 NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2M aqueous solution of transition metals.

[0158] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0159] Next, the transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a coprecipitation reaction was carried out for 15 hours to produce precursor particles.

[0160] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0161] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0162] Comparative Example 3 NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 83:5:10:2 to prepare a 2M aqueous solution of transition metals.

[0163] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0164] Next, the transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a coprecipitation reaction was carried out for 15 hours to produce precursor particles.

[0165] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0166] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0167] Comparative Example 4 NiSO4, CoSO4, MnSO4 and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 90:4:4:2 to prepare a 2M aqueous solution of first transition metals.

[0168] In addition, NiSO4, CoSO4, MnSO4, and Al2(SO4)3 were mixed in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese:aluminum was 85:6.5:6.5:2 to prepare a 2M aqueous solution of second transition metals.

[0169] Next, deionized water was added to a reactor set at 45°C, and nitrogen gas was purged into the reactor to remove dissolved oxygen in the water and create a non-oxidizing atmosphere inside the reactor. Next, 4M NaOH was added to maintain the pH inside the reactor at 11.

[0170] Next, the first transition metal aqueous solution, sodium hydroxide aqueous solution, and ammonium aqueous solution were added to the reactor at a rate of 4 mL / min, 4 mL / min, and 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH was set to 11, and a co-precipitation reaction was carried out for 15 hours to produce the core of the precursor particle.

[0171] After that, when the average particle size D50 of the precursor particles in the reaction solution reached 14 μm, a secondary transition metal aqueous solution was added to the reactor at a rate of 4 mL / min, a sodium hydroxide aqueous solution at 4 mL / min, and an ammonium aqueous solution at 1 mL / min, respectively, and the reaction temperature was set to 45°C, the pH to 11, and an additional coprecipitation reaction was carried out for 1 hour to grow the shell of the precursor particles.

[0172] When the average particle size of the precursor particles reached 15 μm, the reaction was terminated, and the precursor particles were separated from the reaction solution by filtering and dried to obtain a positive electrode active material precursor.

[0173] LiOH and the obtained cathode active material precursor were mixed so that the molar ratio of Li:(Ni+Co+Mn+Al) was 1.05:1, and then calcined at 730°C for 15 hours to produce a lithium transition metal oxide with an average particle size D50 of 15μm.

[0174] Experimental Example 1 The average crystal grain sizes in the core and shell of the lithium transition metal oxide particles produced in Examples 1 to 6 and Comparative Examples 1 to 4 were measured using a TITAN G2 HR-TEM by the following method. The measurement results are shown in Table 1.

[0175] [Table 1]

[0176] Experimental Example 2: Evaluation of initial discharge capacity The lithium transition metal oxides prepared in the examples and comparative examples were used as the positive electrode active material, carbon black as the conductive material, and polyvinylidene fluoride as the binder, and the positive electrode slurry was prepared by mixing them in N-methylpyrrolidone solvent to a weight ratio of positive electrode active material:conductive material:binder of 96:2:2. The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode.

[0177] Next, a negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (polyvinylidene fluoride, PVDF) were mixed in a weight ratio of 95:2:3 in N-methylpyrrolidone solvent to prepare a negative electrode slurry. The negative electrode slurry composition was applied to a copper current collector, dried, and then rolled to prepare a negative electrode.

[0178] A porous polyethylene separator was interposed between the cathode and anode to prepare electrode granules, which were then placed inside a battery case. An electrolyte solution was then injected into the case to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving 1M LiPF6 in an organic solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of 3:4:3, to which 2 wt% vinyl carbonate (VC) was added.

[0179] Each of the lithium secondary batteries prepared as described above was charged at 25° C. at a constant current of 0.1 C up to 4.25 V, and then discharged at a constant current of 0.1 C down to 2.5 V to measure the initial discharge capacity.

[0180] [Table 2]

[0181] As shown in Table 2, it was confirmed that the secondary batteries containing the lithium transition metal oxide particles prepared in Examples 1 to 6 and Comparative Examples 1 to 4 had similar initial discharge capacities.

[0182] Experimental example 3 - Evaluation of life characteristics Each of the lithium secondary batteries prepared in Experimental Example 2 was charged at 45°C at a constant current of 0.3 C up to 4.25 V and discharged at a constant current of 0.3 C down to 2.5 V, which constitutes one cycle. After 100 charge-discharge cycles, the capacity retention rate after 100 cycles was measured.

[0183] [Table 3]

[0184] As shown in Table 3, the secondary batteries containing the lithium transition metal oxide particles prepared in Examples 1 to 6 were measured to have a higher capacity retention rate after 100 cycles than the secondary batteries containing the lithium transition metal oxide particles prepared in Comparative Examples 1 to 4, confirming that they have excellent cycle characteristics.

Claims

1. The lithium transition metal oxide particles have a core-shell structure including a core and a shell located on the surface of the core, The average crystallite size of the core portion is smaller than the average crystallite size of the shell portion, The nickel content of the total transition metals contained in the core and shell is 80 atm % or more, The core part is a positive electrode active material for a lithium secondary battery having a composition represented by the following [Chemical Formula 1]: [Chemical formula 1] Li x1 Ni a1 Co b1 Mn c1 Al d1 M 1 e1 O 2 In the formula 1, M 1 is at least one selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.90≦x1≦1.1, 0.80≦a1≦0.95, 0<b1<0.20, 0<c1<0.20, 0<d1≦0.10, 0≦e1<0.

10.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the difference between the average crystal grain size of the core portion and the average crystal grain size of the shell portion is 20 to 150 nm.

3. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the difference between the average crystal grain size of the core portion and the average crystal grain size of the shell portion is 30 to 100 nm.

4. 4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average crystal grain size of the core portion is 100 to 180 nm.

5. 5. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the shell portion has an average crystal grain size of 180 to 250 nm.

6. 6. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium transition metal oxide has a core portion having a smaller molar fraction of nickel among all transition metals than a shell portion having a molar fraction of nickel among all transition metals.

7. The positive electrode active material for a lithium secondary battery according to claim 6, wherein the shell portion has a composition represented by the following [Chemical Formula 2]: [Chemical formula 2] Li ｘ２ Ni ａ２ Co ｂ２ Mn ｃ２ Al ｄ２ M ２ ｅ２ O ２ In the above chemical formula 2, M ２ is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.90≦x2≦1.1, 0.83≦a2<1.0, 0<b2<0.17, 0<c2<0.17, 0<d2≦0.10, 0≦e2<0.

10.

8. A positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 1 .

9. A lithium secondary battery comprising: the positive electrode according to claim 8; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

Images